Patent Application
20080069588
(Image Forming Apparatus and Image Forming Process)
An image forming apparatus of the present invention includes a latent electrostatic image-bearing member (possibly referred to as photoconductor), a charging unit, a writing unit, a developing unit, a transfer unit and a fixing unit, wherein the time spent by an arbitrary point on the latent electrostatic image-bearing member in moving from a position in which to face the writing unit to a position in which to face the developing unit (referred to as exposing-to-developing time length) is shorter than 50 ms and longer than the transit time of a photoconductor; further, it includes other units suitably selected according to need, such as a cleaning unit, a charge-eliminating unit, a developer recycling unit and a control unit.
An image forming process of the present invention includes a charging step, a writing step, a developing step, a transfer step and a fixing step, wherein the time spent by an arbitrary point on a latent electrostatic image-bearing member in moving from a position in which to face a writing unit to a position in which to face a developing unit (referred to as exposing-to-developing time length) is shorter than 50 ms and longer than the transit time of a photoconductor; further, it includes other steps suitably selected according to necessity, such as a cleaning step, a charge-eliminating step, a recycling step and a control step.
The image forming process of the present invention can be suitably carried out by an image forming apparatus of the present invention; the charging step can be conducted by the charging unit, the writing step can be conducted by the writing unit, the developing step can be conducted by the developing unit, the transfer step can be conducted by the transfer unit, the charge-eliminating step can be conducted by the charge-eliminating unit, the fixing step can be conducted by the fixing unit, and the other steps can be conducted by the other units.
—Formation of Latent Electrostatic Image—
A latent electrostatic image can be formed, for example, by uniformly charging the surface of a latent electrostatic image-bearing member and then imagewisely exposing the latent electrostatic image-bearing member by means of a latent electrostatic image forming unit.
The latent electrostatic image forming unit includes at least a charger which uniformly charges the surface of a latent electrostatic image-bearing member, and an exposer which exposes the surface of the latent electrostatic image-bearing member imagewisely, for example.
—Charging Unit—
The charger is not particularly limited and may be suitably selected according to the purpose. Examples thereof include a contact charger known in the art which is provided with a conductive/semiconductive roller, a brush, a film, a rubber blade and the like; a noncontact charger utilizing corona discharge such as a corotron or scorotron; and a roller-shaped closely-placed charger (including a close-type noncontact charger in which there is a gap of 100 μm or less between a photoconductor surface and the charger, as described in Japanese Patent Application Laid-Open (JP-A) No. 2002-148904 or Japanese Patent Application Laid-Open (JP-A) No. 2002-148905, for example).
A photoconductor of the present invention is charged normally to the range of −300V to −150V, preferably to the range of −500V to −1,000V, by the charging unit. This is what charging a photoconductor to a desired potential in the present invention means.
It is desirable that the electric field intensity applied to a latent electrostatic image-bearing member by the charger be in the range of 20 to 60V/μm, more desirably in the range of 30 to 50V/μm. The higher the electric field intensity applied to a photoconductor is, the better dot reproducibility is; however, when the electric field intensity is too high, there could be breakdown of the photoconductor, carrier attachment at the time of developing and the like, which are problematic.
Note that the electric field intensity is represented by Equation (A) below.
Electric field intensity (V/μm)=SV/G (A)
It should be noted that in Equation (A), SV denotes the surface potential (V) at an unexposed portion of a latent electrostatic image-bearing member in a developing position. G denotes the film thickness (μm) of a photosensitive layer including at least a photosensitive layer (charge generating layer and charge transporting layer).
—Writing Unit—
The writing can be carried out, for example, by imagewisely exposing the surface of the latent electrostatic image-bearing member, with the use of the exposer. For the exposer, a light source with a resolution of 1,200 dpi or more is used, and a suitable one can be selected according to the purpose; examples thereof include copying optical systems, rod lens array systems, laser optical systems and liquid crystal shutter optical systems. Additionally, in the present invention, a back-exposure system, in which exposure is imagewisely conducted from the back surface side of the latent electrostatic image-bearing member, may be employed.
As the light source, light sources capable of retaining high luminance, such as light-emitting diodes (LEDs), laser diodes (LDs) or electroluminescences (ELs) are used. Amongst them, one in which multi-beam exposure is conducted using a plurality of laser beams, one in which a light source used as a multi-beam light source is composed of three surface-emitting lasers or more, and one in which surface-emitting lasers are constructed in a two-dimensional manner are desirable; a multichannel laser diode array (LDA) in which an LD is placed in the form of an array described in Japanese Patent (JP-B) No. 3227226, and a surface-emitting laser in which an emitting point can be placed in a two-dimensional manner described in Japanese Patent Application Laid-Open (JP-A) No. 2004-287085 are very advantageous in carrying out high-density writing.
The resolution of the light source (writing light) used determines the resolution of a latent electrostatic image to be formed, and further, of a toner image to be formed, and a clearer image can be obtained as the resolution increases. However, when writing is carried out with the resolution high, greater time is thereby spent on the writing; thus, when there is only one writing light source, writing becomes a rate-limiting factor in a drum linear velocity (process speed). Therefore, when there is only one writing light source, a resolution of 2,400 dpi or so is the maximum. When there is a plurality of writing light sources, “2,400 dpi×number of writing light sources” is, in effect, the maximum because a writing region can be shared by the writing light sources. Amongst these light sources, a light-emitting diode and a laser diode are favorably used because of their high irradiation energy.
In the present invention, although dependent upon an initial charge potential, the surface potential when a photoconductor has moved to a developing site after being exposed is normally in the range of −0V to −200V, preferably in the range of −0V to −100V, and more preferably in the range of −0V to −50V.
—Developing Unit—
The developing can be carried out by developing the latent electrostatic image with the use of a toner, and so forming a toner image (visible image). For the toner, a toner having the same polarity as the charge polarity of a photoconductor is used, and a latent electrostatic image is developed by means of reversal developing (negative-positive developing). There are the following two developing methods: a one-component process in which an image is developed using only toner, and a two-component process in which a two-component developer composed of a toner and a carrier is used.
Also, when a plurality of color toner images are sequentially superimposed on a photoconductor, the use of a contact developing unit may disturb toner images previously developed. Therefore, when a plurality of color toner images are formed, it is desirable to use a noncontact developing unit allowing for jumping developing.
As to an image forming process used in the present invention, there is such a required condition that the time spent by a point on a photoconductor surface in passing between the writing unit and developing unit (exposing-to-developing time length) is 50 ms or less.
—Transfer Unit—
The transfer unit is a unit for transferring the visible image to a transfer material (recording medium such as paper; hereinafter possibly referred to as “transfer paper”), which can be divided into a method of directly transferring a visible image from a conductor surface to a recording medium, and a method in which an intermediate transfer member is used, and a visible image is primarily transferred onto the intermediate transfer member, then the visible image is secondarily transferred onto the recording medium. The transfer unit can be favorably used in both aspects, but when there is a great negative effect as high image quality is achieved, the former (direct transfer) method that is smaller in the number of transfers is more favorable.
The transfer can be carried out, for example, by transferring the visible image in such a manner that the latent electrostatic image-bearing member (photoconductor) is charged using a transfer charger, and it can be carried out by the transfer unit. The transfer unit is not particularly limited and may be suitably selected from those known in the art according to the purpose; preferred examples thereof include a transfer conveyance belt capable of conveying a recording medium as well at the same time.
It is desirable that each of the transfer units (primary and secondary transfer units) have at least a transfer charger which peels off and charges the visible image formed on the latent electrostatic image-bearing member, toward the side of the recording medium. As to the transfer unit, whether there is one, two or more than two does not matter. Examples of the transfer charger include corona transfer devices by means of corona discharge, transfer belts, transfer rollers, pressure transfer rollers and adhesive transfer devices. Note that for the recording medium, a suitable one can be selected from conventional recording media (recording papers), without any restrictions in particular.
It is possible to use a transfer belt or transfer roller for a transfer charger, in which case it is desirable that a contact type of a transfer belt, transfer roller, etc. generating less ozone be used. Note that although both a constant-voltage system and a constant-current system are applicable to a voltage/current applying system at the time of transfer, a constant-current system that is able to keep the transfer charge amount constant and that is superior in stability is more desirable. For the transfer member, any conventional transfer member can be used as long as it can satisfy the structure of the present invention.
The photoconductor passage charge amount per cycle of image formation greatly varies according to the photoconductor surface potential after transfer (surface potential on the occasion of entry into a charge-eliminating portion). The larger this is, the greater impact there will be on electrostatic fatigue of a photoconductor when repeatedly used.
This passage charge amount is equivalent to a charge amount flowing in the film thickness direction of a photoconductor. As operations in an image forming apparatus of a photoconductor, the apparatus is charged (negatively charged in most cases) to a desired charge potential by a main charger, and light writing is carried out based upon an input signal corresponding to a manuscript. On this occasion, photocarriers are generated at the part where writing has been conducted, thereby neutralizing surface charge (decaying in potential). At this time, a charge amount dependent upon a photocarrier generation amount flows in the photoconductor film thickness direction. Meanwhile, after passing a developing step and a transfer step, the region where light writing is not conducted (unwritten portion) moves to a charge-eliminating step (if necessary, a cleaning step is carried out before the charge-eliminating step). Here, when the surface potential of the photoconductor is close to a potential given by main charging (except for dark-decay elements), a charge amount which is approximately the same as that at the region where light writing has been conducted is to flow in the photoconductor film thickness direction. Typically, since present-day manuscripts are low in writing percentage, in this system a current which flows in the charge-eliminating step occupies most of the passage charge amount of the photoconductor when repeatedly used (assuming that the writing percentage is 10%, a current which flows in the charge-eliminating step occupies 90% of the total).
This passage charge has a great impact on photoconductor electrostatic properties, for example causing deterioration of a material forming a photoconductor. As a result of it, depending upon the passage charge amount, the residual potential of a photoconductor, in particular, is made to increase. If the residual potential of a photoconductor increases, the image density decreases in negative-positive developing used in the present invention, hence a great problem. Therefore, in order to aim for achievement of a long lifetime (high durability) of a photoconductor in an image forming apparatus, there is a problem in working out how to reduce the passage charge amount of the photoconductor.
In contrast to the foregoing, it may be thought reasonable to exclude a light elimination process; however, unless the charger ability of a main charger is great, charging cannot be stabilized, thus possibly leading to a problem with afterimages. Passage charge of a photoconductor is generated, as light irradiation is conducted according to the potential with respect to the charging of the photoconductor surface (electric field produced thereby) and thus photocarriers which have been generated move. Therefore, if the photoconductor surface potential can be decayed by a means other than light, it is possible to lower the passage charge amount per rotation of a photoconductor (cycle of image formation).
To achieve the foregoing, adjustment of the photoconductor passage charge amount by adjusting a transfer bias in a transfer step is effective. Specifically, an unwritten portion, which is charged by main charging and in which writing is not conducted, enters a transfer step, with its potential close to the potential thereof when charged, except for an dark-decay amount. On this occasion, by lowering the absolute value on the polarity side charged by a main charging deice to 100V or less, photocarriers are hardly generated and passage charge is not generated, when the unwritten portion enters a charge-eliminating step subsequent to the transfer step. It is desirable that this value be close to 0V as much as possible.
Further, with adjustment of a transfer bias, by applying a transfer bias such that a photoconductor is charged to have the opposite polarity in photoconductor surface potential to a charge polarity given by main charging, photocarriers will never arise, which makes this idea even more desirable. However, in a transfer condition in which a photoconductor is charged to an opposite polarity, in some cases a great deal of transfer dust could be generated, or main charging for a next image forming process (cycle) could be delayed. In that case, since a trouble such as afterimages could be caused, it is desirable that the absolute value of an opposite polarity be 100V or less.
Addition of the controls makes it possible to utilize the effect in the present invention conspicuously and usefully.
—Fixing Unit—
In the fixing, a visible image transferred onto a recording medium is fixed using a fixing device, and the image may be fixed for each of color toners every time each color toner is transferred onto the recording medium, or images for each of color toners may be fixed at one time with the images superimposed on the recording medium.
The fixing device is not particularly limited and may be suitably selected according to the purpose, but a heating/pressurizing unit is suitably used. Examples of the heating/pressurizing unit include a combination of a heating roller and a pressuring roller and a combination of a heating roller, a pressurizing roller and an endless belt. Typically, it is desirable that heating in the heating/pressurizing unit take place in the temperature range of 80° C. to 200° C. It should be noted that in the present invention, an optical fixing device in the art, for example, may be used along with or in place of the fixing unit in the fixing step, according to the purpose.
—Others—
The charge-eliminating unit is not particularly limited and may be suitably selected from charge eliminators known in the art. Examples thereof include laser diodes (LDs), light-emitting diodes (LEDs) and electroluminescences (ELs).
In addition, a combination of a fluorescent lamp, tungsten lamp, halogen lamp, mercury-vapor lamp, sodium-vapor lamp, xenon lamp, etc. and a certain optical filter, or the like can be used. Filters such as a sharp-cut filter, a band-pass filter, a near-infrared cut filter, a dichroic filter, an interference filter and a color temperature conversion filter can also be used.
The cleaning unit is not particularly limited and may be suitably selected from cleaning units known in the art as long as it can remove the electrophotographic toner remaining on the latent electrostatic image-bearing member; examples thereof include magnetic brush cleaners, electrostatic brush cleaners, magnetic roller cleaners, blade cleaners, brush cleaners and web cleaners.
The recycling unit is used for recycling and conveying the electrophotographic color toner removed by the cleaning unit to the developing unit; conventional conveying units are exemplified.
The control unit is used for controlling the above-mentioned steps, and this can be suitably conducted by a control unit.
The control unit is not particularly limited and may be suitably selected from control units known in the art as long as it can control the movements of the units; examples thereof include an apparatus such as a sequencer or computer.
Here, one aspect of an image forming apparatus of the present invention is explained with reference to
The image forming apparatus shown in the figure is provided with a full-color image forming unit which forms full-color images, including a drum-shaped image-bearing member (hereinafter referred to as “image-bearing member”).
Note that hereinafter “color” will denote colors except black, and “full-color” will denote colors including black. In compliance with this, “color toner” will denote toners of colors except black.
In the vicinity of an image-bearing member (1) for full-color image formation, a charger (2), an exposer (3), a developing unit (full-color developing unit) (4), an intermediate transfer bearing member (5), a primary transfer roller (10), a secondary transfer roller (6), a cleaning device (8), an intermediate transfer bearing member cleaning device (9) and the like are disposed roughly in this order with respect to the rotational direction (direction of the arrow (R1)) of the image-bearing member (1).
In
A wire charger, a roller charger or the like is used for the charger (2). When high-speed charging is required and the charging nip can be kept wide, a scorotron charger is favorably used, whereas in an attempt to achieve compactness and in an after-mentioned image forming apparatus, a roller charger that generates a smaller amount of acid gas (NOx, SOx, etc.) or ozone is effectively used. An image-bearing member is charged by this charger; the higher the electric field intensity applied to a photoconductor is, the more preferable dot reproducibility can be obtained; therefore, it is desirable that an electric field intensity of 2V/μm or more be applied. However, in light of a possibility of causing breakdown of the image-bearing member and carrier attachment at the time of developing, which are problematic, the maximum value is generally 60V/μm or less, more desirably 50V/μm or less.
A light source capable of retaining high luminance, such as a light-emitting diode (LED), laser diode (LD) or electroluminescence (EL), is used for the exposer (3). The resolution of the light source (writing light) determines the resolution of a latent electrostatic image to be formed, and further, of a toner image to be formed, and a clearer image can be obtained as the resolution increases. However, when writing is carried out with the resolution high, greater time is thereby spent on the writing; thus, when there is only one writing light source, writing becomes a rate-limiting factor in a drum linear velocity (process speed). Therefore, when there is only one writing light source, a resolution of 1,200 dpi or so is the maximum. When there is a plurality of writing light sources, “1,200 dpi×number of writing light sources” is, in effect, the maximum because a writing region can be shared by the writing light sources. Amongst these light sources, a light-emitting diode and a laser diode are favorably used because of their high irradiation energy.
Having a large number of emitting points and thus making it possible to increase the number of dots simultaneously written, a surface-emitting laser, in particular, is very advantageous in an apparatus utilizing high-density writing as in the present invention.
The developing unit (4), which is a developing unit, has four developing sleeves. The developing unit (4) is composed of a rotary (40) which rotates in the direction of the arrow (R2), and four full-color developing devices (4Y), (4M), (4C) and (4K) mounted thereupon.
As for the developing unit (4), a developing device for a color used in developing a latent electrostatic image formed on the image-bearing member (1) is to be placed in a developing position opposed to the image-bearing member (1) surface by the rotation of the rotary (40) in the direction of the arrow (R2). Latent electrostatic images for the colors of yellow, magenta, cyan and black formed on the image-bearing member (1) are given toners of each color and developed as toner images of each color, as developing biases are applied to the developing devices (4Y), (4M), (4C) and (4K) by a developing bias applying power supply (not shown in the figure).
In the developing unit (4), toners with the same polarity as the charge polarity of a photoconductor are used, and latent electrostatic images are developed by means of reversal developing (negative-positive developing). A digital light source is generally used for images that are low in image area ratio, and it is advantageous to consider the lifetime of the light source in a reversal developing system in which written parts are developed using toner. There are two methods, i.e. a one-component process in which an image is developed using only toner, and a two-component process in which a two-component developer composed of a toner and a carrier is used; the developing unit (4) can be favorably used in both cases.
For example, when a two-component developer is used, the developing device of yellow (4Y) includes a nonmagnetic yellow toner and a magnetic carrier. The developing device of magenta (4M) includes a nonmagnetic magenta toner and a magnetic carrier. The developing device of cyan (4C) includes a nonmagnetic cyan toner and a magnetic carrier. The developing device of black (4K) includes a nonmagnetic black toner and a magnetic carrier.
By being transferred to transfer paper, a toner image formed on an image-bearing member becomes an image on the transfer paper; on this occasion, there are two methods. One is a method of directly transferring a toner image developed on an image-bearing member surface onto transfer paper, and the other is a method of temporarily transferring a toner image from an image-bearing member onto an intermediate transfer member, and then transferring this onto transfer paper. Both cases are applicable to the present invention.
Here, an intermediate transfer bearing member temporarily bears the toner images of each color developed, and forms an image in which a plurality of colors are sequentially superimposed, by retransferring these toner images onto the transfer bearing member. It is possible to use a transfer belt or transfer roller for a transfer bearing member, but it is desirable that a contact type of a transfer belt, transfer roller, etc. generating less ozone be used. The intermediate transfer bearing member (5) is rotationally driven in the direction of the arrow (R3), set on a plurality of rollers. Provided on the inside of the intermediate transfer bearing member (5), the primary transfer roller (10) presses the intermediate transfer bearing member(5) against the image-bearing member (1) surface. A primary transfer bias is applied to the primary transfer roller (10) from a primary transfer bias applying power supply (not shown in the figure), and thus toner images of each color on the image-bearing member (1) are transferred onto the intermediate transfer bearing member (5) and sequentially superimposed.
The secondary transfer roller (6) is for transferring a full-color toner image on the intermediate transfer bearing member (5) to a transfer material (11) such as paper, and rotates in the direction of the arrow (R4). The transfer material (11) is stored in a paper feed cassette (12), and provided to a first transfer portion (transfer nip portion) (13) situated between the intermediate transfer bearing member (5) and the secondary transfer roller (6) at a predetermined timing by a feeding conveyance unit (not shown in the figure). On this occasion, a secondary transfer bias is applied to the secondary transfer roller (6) from a secondary transfer bias applying power supply (not shown in the figure), and thus a full-color toner image of the four colors on the intermediate transfer bearing member (5) is secondarily transferred onto the transfer material (11) at one time.
When toner images are directly transferred from an image-bearing member to a transfer material without using an intermediate transfer member like the one described above, toner images of a plurality of colors are formed on the image-bearing member, and the toner images are transferred to the transfer material at one time.
Note that although both a constant-voltage system and a constant-current system are applicable to a voltage/current applying system at the time of transfer, a constant-current system that is able to keep the transfer charge amount constant and that is superior in stability is more desirable. What is particularly suitable is a method of controlling a current value to an image-bearing member, by deducting currents which flow through parts relating to a transfer member and which do not flow into the image-bearing member, from currents which have been output from a power supply member (high-voltage power supply) supplying charge to the transfer member.
A transfer current is a current based upon a required charge amount given to peel off a toner electrostatically attached to a photoconductor and move it to a transfer receiving member (transfer paper, intermediate transfer member or the like). In order to avoid transfer defects such as a transfer residue, it is advisable to increase a transfer current; however, when negative-positive developing is used, charging with the opposite polarity to the charge polarity of an image-bearing member is given, and electrostatic fatigue of the image-bearing member will therefore be conspicuous. A large transfer current is advantageous in that it is possible to give a charge amount which is greater than the electrostatic adhesion between a photoconductor and a toner; however, a discharge phenomenon arises between a transfer member and an image-bearing member when the current value is greater than a certain threshold value, and toner images minutely developed are disturbed as a result. Thus, a maximum value is in such a range as can prevent this discharge phenomenon from arising. This threshold value varies depending upon the gap (distance) between a transfer member and an image-bearing member, upon the materials forming them, and upon the like; it is possible to avoid a discharge phenomenon when the current value is roughly 200 μA or less. Therefore, the maximum value of a transfer current is 200 μA or so.
A conventional transfer member can be used for the transfer member as long as it can satisfy the structure of the present invention.
Also, decreasing the image-bearing member surface potential (part not exposed with writing light) after transfer by controlling a transfer current as described above makes it possible to lower the image-bearing member passage charge amount per cycle of image formation, which is effective in the present invention.
The cleaning device (8) removes a toner (residual toner) which has not been transferred to the intermediate transfer bearing member (5) or the transfer material (11) but remains on the image-bearing member (1), when a full-color toner image on the image-bearing member (1) is transferred to the intermediate transfer bearing member (5) or the transfer material (11). When there is a toner remaining on the image-bearing member (1), it is removed from the image-bearing member (1) by a fur brush or blade. Cleaning is sometimes carried out only with a cleaning brush. For the cleaning brush, a conventional one typified by fur brush and magnetic fur brush can be used.
The intermediate transfer bearing member cleaning device (9) removes a toner (residual toner) which has not been transferred to the transfer material (11) but remains on the intermediate transfer bearing member (5), when a toner image on the intermediate transfer bearing member (5) is transferred to the transfer material (11).
The transfer material (11) to which a full-color toner image of the four colors has been thus transferred is conveyed by a transfer conveyance belt (7) to a fixing device (14), where the transfer material (11) is heated and pressurized and the full-color toner image of the four colors is fixed on the surface thereof. Accordingly, a full-color image of the four colors is formed on the transfer material (11).
Although not shown in the figure, a light source for a charge-eliminating lamp or the like may be suitably selected from conventional charge eliminators as long as it can remove a charge remaining on the image-bearing member (1); examples thereof include a laser diode (LD) and an electroluminescence (EL). Alternatively, a combination of a fluorescent lamp, tungsten lamp, halogen lamp, mercury-vapor lamp, sodium-vapor lamp, xenon lamp, etc. and a certain optical filter, or the like can be used. Filters such as a sharp-cut filter, a band-pass filter, a near-infrared cut filter, a dichroic filter, an interference filter and a color temperature conversion filter are applicable to the optical filter.
Next,
In
This photoconductor (15) is able to rotate in the direction of the arrow (R5) in
A secondary transfer roller (24) is for transferring a full-color toner image on the intermediate transfer bearing member (22) onto a transfer material (25) such as paper, and conveys the transfer material (25) in the direction of the arrow (R7). The transfer material (25) is stored in a paper feed cassette (26), and provided to a first transfer portion (transfer nip portion) (27) situated between the intermediate transfer bearing member (22) and the secondary transfer roller (24) by a feeding conveyance unit (not shown in the figure) at a predetermined timing. On this occasion, a secondary transfer bias is applied to the secondary transfer roller (24) from a secondary transfer bias applying power supply (not shown in the figure), and thus a full-color toner image of the four colors on the intermediate transfer bearing member (22) is secondarily transferred onto the transfer material (25) at one time.
Also, toner images formed on a photoconductor are made to become images on transfer paper, by being transferred to the transfer paper; as well as a method in which an intermediate transfer member is used as described above, there is a method of directly transferring toner images to a transfer material without using an intermediate transfer member. Both cases are applicable to the present invention.
In the full-color image forming apparatus shown in
Next, writing is carried out with a resolution of 1,200 dpi or more (preferably 2,400 dpi or more), by means of laser light from the exposing members (16Y), (16M), (16C) and (16K) placed on the outside of a photoconductor, and latent electrostatic images corresponding to images of each color to be produced are formed. As the writing light sources, light sources suitable for an arbitrary photoconductor are used as described earlier. In this case also, with respect to the resolution of writing, 2,400 dpi is an approximate maximum value per writing light source.
Next, toner images are formed, as latent images are developed by the developing units (17Y), (17M), (17C) and (17K). The developing units (17Y), (17M), (17C) and (17K) are developing units which conduct developing with toners of Y (yellow), M (magenta), C (cyan) and K (black), and toner images of each color produced on the photoconductor (15) are sequentially superimposed on the intermediate transfer bearing member (22).
The transfer material (25) is conveyed from a tray by a paper feed roller (not shown in the figure), then made to stop once by a pair of resist rollers (not shown in the figure), and subsequently sent to the transfer conveyance belt (27) at a timing corresponding with an image formation on the intermediate transfer bearing member (22). As the transfer paper (25) held on the transfer conveyance belt (27) is conveyed, toner images of each color are transferred in the position (transfer position) (26) where the transfer paper (25) makes contact with the intermediate transfer bearing member (22).
Toner images on a photoconductor are transferred onto the transfer material (25) by means of an electric field created according to the potential difference between a transfer bias applied to the secondary transfer roller (24) and the intermediate transfer bearing member (22). The recording material (25) which has passed a transfer portion and on which toner images of the four colors are sequentially superimposed is conveyed to a fixing device (28), where the toners are fixed, and then sent to a paper ejecting portion not shown in the figure.
Also, a residual toner which has not been transferred by the first transfer roller (23) but remains on the photoconductor (15) is collected by the cleaner (19).
Subsequently, an unnecessary residual charge on the photoconductor is removed by the charge eliminating member (20). After that, charging is evenly given by a charger again, and a next image is formed.
It should be noted that although the image forming elements are disposed in the order of the colors Y (yellow), M (magenta), C (cyan) and K (black) as seen from the charge eliminator toward the primary transfer roller in the example of
Also, as described earlier, it is desirable that a photoconductor surface after transfer be charged to 100V or less on the same polarity as the polarity of charging by a main charger, more desirably charged on the opposite polarity thereto, even more desirably charged to 100V or less on the opposite polarity thereto. This makes it possible to reduce the residual potential of a photoconductor when repeatedly used.
The image forming unit described above may be installed in a copier, facsimile or printer in a fixed manner, and also installed as a process cartridge in those apparatuses. A process cartridge is an apparatus (component) housing a photoconductor, and also including a latent electrostatic image forming unit, a developing unit, a transfer unit, a cleaning unit, a charge eliminating unit and the like.
The following explains embodiments in the present invention, with reference to the drawings.
In
The image forming apparatus in the figure is provided with a color image forming unit which forms color images (images of colors except black), and a black image forming unit which forms black images, including drum-shaped electrophotographic photoconductors (hereinafter referred to as “photoconductors”) (301) and (310) respectively. Amongst these photoconductors, the photoconductor (301) (first photoconductor) is for forming color images, and the photoconductor (310) (second photoconductor) is for forming black images. Note that hereinafter “color” will denote colors except black, and “full-color” will denote colors including black. In compliance with this, “color toner” will denote toners of colors except black.
In the vicinity of the photoconductor (301) for color image formation, a charger (302), an exposer (303), a developing unit (color developing unit) (304), an intermediate transfer member (305a), a transfer roller (transfer device) (305b), a secondary transfer roller (306), a cleaning device (307a), an intermediate transfer member cleaning device (307b) and the like are disposed roughly in this order with respect to the rotational direction (direction of the arrow R1) of the photoconductor (301).
In
A wire-system charger, a roller-shaped charger or the like is used for the charger (302). When high-speed charging is required and the charging nip can be kept wide, a charger of the scorotron system is favorably used, whereas in an attempt to achieve compactness and in an after-mentioned image forming apparatus, a roller-shaped charger that generates a smaller amount of acid gas (NOx, SOx, etc.) or ozone is effectively used. A photoconductor is charged by this charger; the higher the electric field intensity applied to a photoconductor is, the better dot reproducibility is; therefore, it is desirable that an electric field intensity of 20V/μm or more be applied. However, in light of a possibility of causing breakdown of the photoconductor and carrier attachment at the time of developing, which are problematic, the maximum value is generally 60V/μm or less, more desirably 50V/μm or less.
A light source capable of retaining high luminance, such as a light-emitting diode (LED), laser diode (LD) or electroluminescence (EL), is used for the exposer (303). The resolution of the light source (writing light) determines the resolution of a latent electrostatic image to be formed, and further, of a toner image to be formed, and a clearer image can be obtained as the resolution increases. However, when writing is carried out with the resolution high, greater time is thereby spent on the writing; thus, when there is only one writing light source, writing becomes a rate-limiting factor in a drum linear velocity (processing speed). Therefore, when there is only one writing light source, a resolution of 1,200 dpi or so is the maximum. When there is a plurality of writing light sources, “1,200 dpi×number of writing light sources” is, in effect, the maximum because a writing region can be shared by the writing light sources. Amongst these light sources, a light-emitting diode and a laser diode are favorably used because of their high irradiation energy. Having a large number of emitting points and thus making it possible to increase the number of dots simultaneously written, a surface-emitting laser, in particular, is very advantageous in an apparatus utilizing high-density writing as in the present invention.
The developing unit (304), which is a developing unit, has three developing sleeves. The developing unit (304) is composed of a rotary (304a) which rotates in the direction of the arrow (R4), and three color developing devices (304Y), (304M) and (304C) mounted thereupon.
As for the developing unit (304), a developing device for a color used in developing a latent electrostatic image formed on the photoconductor (301) is to be placed in a developing position opposed to the photoconductor (301) surface by the rotation of the rotary (304a) in the direction of the arrow (R4). Latent electrostatic images for the colors of yellow, magenta and cyan formed on the photoconductor (301) are given toners of each color and developed as toner images of each color, as developing biases are applied to the developing devices (304Y), (304M) and (304C) by a developing bias applying power supply (not shown in the figure).
In the developing unit (304), toners with the same polarity as the charge polarity of a photoconductor are used, and latent electrostatic images are developed by means of reversal developing (negative-positive developing). In the case of a digital light source today, although it varies according to the light source used in the exposer, the image area ratio is generally low; in response, it is advantageous if a reversal developing system, in which toner developing is carried out on a written part, allows for the lifetime of a light source or the like. There are two methods, i.e. a one-component system in which developing is only carried out by toner, and a two-component system in which a two-component developer composed of toner and carriers is used; the developing unit (304) can be favorably used in both cases. For example, when a two-component developer is used, the developing device of yellow (304Y) includes a nonmagnetic yellow toner and magnetic carriers. The developing device of magenta (304M) includes a nonmagnetic magenta toner and magnetic carriers. The developing device of cyan (304C) includes a nonmagnetic cyan toner and magnetic carriers. Meanwhile, as to an after-mentioned developing unit (313) for black, a developing device of black (313K) includes a nonmagnetic black toner and magnetic carriers.
By being transferred to transfer paper, a toner image formed on a photoconductor becomes an image on the transfer paper; on this occasion, there are two methods. One is a method of directly transferring a toner image developed on a photoconductor surface to transfer paper, and the other is a method of temporarily transferring a toner image from a photoconductor to an intermediate transfer member, and then transferring this to transfer paper. Both cases are applicable to the present invention. Here, an intermediate transfer member temporarily supports the toner images of each color developed, and forms an image in which a plurality of colors are sequentially superimposed, by retransferring these toner images onto the transfer member. It is possible to use a transfer belt or transfer roller for a transfer bearing member, but it is desirable that a contact type of a transfer belt, transfer roller, etc. generating less ozone be used. The intermediate transfer member (305a) is rotationally driven in the direction of the arrow (R5), set on a plurality of rollers. Provided on the inside of the intermediate transfer member (305a), the primary transfer roller (305b) presses the intermediate transfer member (305a) against the photoconductor (301) surface. A primary transfer bias is applied to the primary transfer roller (5b) from a primary transfer bias applying power supply (not shown in the figure), and thus toner images of each color on the photoconductor (301) are transferred onto the intermediate transfer member (305a) and sequentially superimposed. 10 The secondary transfer roller (306) transfers a color toner image on the intermediate transfer member (305a) to a transfer material (P) such as paper, and rotates in the direction of the arrow (R6). The transfer material (P) is stored in a paper feed cassette (330), and provided to a first transfer portion (transfer nip portion) (N1) situated between the intermediate transfer member (305a) and the secondary transfer roller (306) at a predetermined timing by a feeding conveyance unit (not shown in the figure). On this occasion, a secondary transfer bias is applied to the secondary transfer roller (306) from a secondary transfer bias applying power supply (not shown in the figure), and thus a color toner image of the three colors on the intermediate transfer member (305a) is secondarily transferred onto the transfer material (P) at one time.
When toner images are directly transferred from a photoconductor to a transfer material without using an intermediate transfer member like the one described above, toner images of a plurality of colors are formed on a photoconductor, and the toner images are transferred onto the transfer material at one time.
Note that although both a constant-voltage system and a constant-current system are applicable to a voltage/current applying system at the time of transfer, a constant-current system that is able to keep the transfer charge amount constant and that is superior in stability is more desirable. What is particularly suitable is a method of controlling a current value to a photoconductor, by deducting currents which flow through parts relating to a transfer member and which do not flow into the photoconductor, from currents which have been output from a power supply member (high-voltage power supply) supplying charge to the transfer member.
A transfer current is a current based upon a required charge amount given to peel off a toner electrostatically attached to a photoconductor and move it to a transfer receiving member (transfer paper, intermediate transfer member or the like). In order to avoid transfer defects such as a transfer residue, it is advisable to increase a transfer current; however, when negative-positive developing is used, charging with the opposite polarity to the charge polarity of a photoconductor is given, and electrostatic fatigue of the photoconductor will therefore be conspicuous. A large transfer current is advantageous in that it is possible to give a charge amount which is greater than the electrostatic adhesion between a photoconductor and a toner; however, a discharge phenomenon arises between a transfer member and a photoconductor when the current value is greater than a certain threshold value, and toner images minutely developed are disturbed as a result. Thus, a maximum value is in such a range as can prevent this discharge phenomenon from arising. This threshold value varies depending upon the gap (distance) between a transfer member and a photoconductor, upon the materials forming them, and upon the like. A conventional transfer member can be used for the transfer member as long as it can satisfy the structure of the present invention.
Also, decreasing the photoconductor surface potential (part not exposed with writing light) after transfer by controlling a transfer current as described earlier makes it possible to lower the photoconductor passage charge amount per cycle of image formation, which is effective in the present invention.
The cleaning device (7a) removes a color toner (residual toner) which has not been transferred to the intermediate transfer member (5a) or the recording material (P) but remains on the photoconductor (1), when a color toner image on the photoconductor (1) is transferred to the intermediate transfer member (5a) or the recording material (P). When there is a toner remaining on the photoconductor (1), it is removed from the photoconductor (1) by a fur brush or blade. Cleaning is sometimes carried out only with a cleaning brush, and a conventional one, exemplified primarily by a fur brush or magnetic fur brush, is used for a cleaning brush.
The intermediate transfer member cleaning device (7b) removes a color toner (residual toner) which has not been transferred onto the recording material (P) but remains on the intermediate transfer member (5a), when a color toner image on the intermediate transfer member (5a) is transferred onto the recording material (P).
In the vicinity of the photoconductor (10) for black image formation, a charger (11), an exposer (12), a developing unit (black developing unit) (13), a transfer roller (transfer device) (14), a cleaning device (15) and the like are disposed roughly in this order with respect to the rotational direction (direction of the arrow R10) of the photoconductor (10).
The charger (11) evenly charges the photoconductor (10) surface to a predetermined polarity and potential. The exposer (12) forms a latent electrostatic image for black, by irradiating the photoconductor (10) surface with laser light after the photoconductor (10) has been charged, in accordance with image information. The developing unit (13) develops a latent electrostatic image as a black toner image, by attaching a black toner to the latent electrostatic image. The transfer roller (14) touches the photoconductor (10) surface to form a second transfer nip portion (N2) between itself and the photoconductor (10), and rotates in the arrow (R14) direction. In this second transfer portion (N2), a black toner image on the photoconductor (10) is transferred by the transfer roller (14) to the recording material (P), to whose surface color toner images of yellow, magenta and cyan have been transferred in the first transfer portion (N1).
The recording material (P) to which a full-color toner image of the four colors has been thus transferred is conveyed to a fixing device (20), where the recording material (P) is heated and pressurized and the full-color toner image of the four colors is fixed on the surface thereof. Accordingly, a full-color image of the four colors is formed on the recording material (P). Meanwhile, a black toner (residual toner) which has not been transferred onto the recording material (P) but remains on the photoconductor (10) is removed by the cleaning device (15).
Although not shown in the figure, a light source for a charge-eliminating lamp or the like may be suitably selected from conventional charge eliminators as long as it can remove a charge remaining on the photoconductors (1) and (10); examples thereof include a laser diode (LD) and an electroluminescence (EL). Alternatively, a combination of a fluorescent lamp, tungsten lamp, halogen lamp, mercury-vapor lamp, sodium-vapor lamp, xenon lamp, etc. and a certain optical filter, or the like can be used. Filters such as a sharp-cut filter, a band-pass filter, a near-infrared cut filter, a dichroic filter, an interference filter and a color temperature conversion filter are applicable to the optical filter.
Next, another example of an image forming apparatus of the present invention is shown in
The image forming apparatus in the figure is provided with an image forming section (first image forming section) which forms toner images for black and yellow, and an image forming section (second image forming section) which forms toner images for magenta and cyan. In the first image forming section, a yellow toner is mentioned as a color toner accompanying a black toner, but this is not always the case, and a color toner for magenta or cyan may be used in place of the yellow toner. For color toners supplied to the second image forming section, anything but color toners supplied to the first image forming section is acceptable, and there is no limitation in particular.
In the vicinity of the photoconductor (50), a charger (51), an exposer (52), a developing device (53), a transfer device (54), a cleaning device (55), an intermediate transfer member cleaning device (56) and the like are disposed roughly in this order with respect to the rotational direction (direction of the arrow R50) of the photoconductor (50).
The developing device (53), which is a developing unit, has two developing sleeves. The developing unit (53) is composed of a rotary (53a) which rotates in the direction of the arrow (R53), and two color developing devices (53Y) and (53K) mounted thereupon.
As for the developing device (53), a developing device for a color used in developing a latent electrostatic image formed on the photoconductor (50) is to be placed in a developing position opposed to the photoconductor (50) surface by the rotation of the rotary (53a) in the direction of the arrow (R53). Latent electrostatic images for the colors of yellow and black formed on the photoconductor (50) are given toners of each color and developed as toner images of each color, as developing biases are applied to the developing devices (53Y) and (53K) by a developing bias applying power supply (not shown in the figure).
Meanwhile, in the vicinity of the other photoconductor (60) for image formation, a charger (61), an exposer (62), a developing unit (63), a transfer device (64), a cleaning device (65) and the like are disposed roughly in this order with respect to the rotational direction (direction of the arrow R60) of the photoconductor (60).
The exposer (62) forms latent electrostatic images for magenta and cyan, by irradiating the photoconductor (60) surface with laser light after the photoconductor (60) has been charged, in accordance with image information. As for the developing unit (63), a developing device for a color used in developing a latent electrostatic image formed on the photoconductor (60) is to be placed in a developing position opposed to the photoconductor (60) surface by the rotation of a rotary (63a) in the direction of the arrow (R63). Latent electrostatic images for the colors of magenta and cyan formed on the photoconductor (60) are given toners of each color and developed as toner images of each color, as developing biases are applied to the developing devices (63M) and (63C) by a developing bias applying power supply (not shown in the figure).
In the transfer device (64), toner images of magenta and cyan formed on the photoconductor (60) are transferred to an intermediate transfer member (66), to whose surface toner images of black and yellow have been transferred in the transfer device (54). By being transferred onto transfer paper, a toner image formed on the photoconductor becomes an image on the transfer paper; on this occasion, there are two methods. One is a method of directly transferring a toner image developed on a photoconductor surface to transfer paper, and the other is a method of temporarily transferring a toner image from a photoconductor to an intermediate transfer member, and then transferring this to transfer paper. Both cases are applicable to the present invention.
Here, an intermediate transfer member temporarily bears each developed color image, and forms an image with a plurality of colors sequentially superimposed, by retransferring these toner images onto the transfer paper. It is possible to use a transfer belt or transfer roller for a transfer bearing member, but it is desirable that a contact type of a transfer belt, transfer roller, etc. generating less ozone be used. The intermediate transfer member (66) is rotationally driven in the direction of the arrow in the figure, set on a plurality of rollers. On the inside of the intermediate transfer member (66) are placed the corona transfer devices (54) and (64) by means of corona discharge. Primary transfer biases are applied to the corona transfer devices (54) and (64) from a primary transfer bias applying power supply (not shown in the figure), and thus toner images of each color on the photoconductors (50) and (60) are transferred onto the intermediate transfer member (66) and sequentially superimposed.
A secondary transfer bias is applied to a secondary transfer roller (70) from a secondary transfer bias applying power supply (not shown in the figure), and thus a full-color toner image on the intermediate transfer member (66) is secondarily transferred onto the recording material (P) at one time.
When toner images are directly transferred from a photoconductor to a recording material without using an intermediate transfer member like the one described above, a plurality of color toner images are formed on the photoconductor, and the toner images are transferred onto a transfer material at one time.
The recording material (P) to which a full-color toner image of the four colors has been thus transferred is conveyed to a fixing device (80), where the recording material (P) is heated and pressurized and the full-color toner image of the four colors is fixed on the surface thereof Meanwhile, a toner (residual toner) which has not been transferred onto the recording material (P) but remains on the intermediate transfer member (66) is removed by the intermediate transfer member cleaning device (56).
The image forming unit described above may be installed in a copier, facsimile or printer in a fixed manner, or may be incorporated in form of a process cartridge into those apparatuses. A process cartridge is a device (component) housing a photoconductor, and also including a latent electrostatic image forming unit, a developing unit, a transfer unit, a cleaning unit, a charge eliminating unit and the like.
—Latent Electrostatic Image-bearing Member—
The latent electrostatic image-bearing member preferably expresses a transit time shorter than the exposing-to-developing time length in an image forming apparatus used; it is desirable that the latent electrostatic image-bearing member have on a support a photosensitive layer which is formed of a charge generating layer and a charge transporting layer in a multi-layered structure; and the latent electrostatic image-bearing member may be suitably selected from latent electrostatic image-bearing members known in the art as long as it does not prevent generation of a sufficient amount photocarriers or hinder the mobility of a hole.
Next, an electrophotographic photoconductor used in the present invention will be explained in detail, with reference to drawings.
As the conductive support (31), what can be used is a conductive support showing such conductivity that the volume resistance is 1010Ω·cm or less; for example, a support formed by coating a film-like or cylindrical piece of plastic or paper with a metal such as aluminum, nickel, chrome, nichrome, copper, gold, silver or platinum or a metal oxide such as tin oxide or indium oxide by vapor deposition or sputtering; the support may be a plate of aluminum, aluminum alloy, nickel, stainless, etc., or a plate formed into a tube by extrusion or drawing and surface treating by cut, superfinishing and polishing can be used. Also, an endless nickel belt or an endless stainless belt can be used as a conductive support.
The support may be prepared by dispersing a conductive fine particle into a suitable binder resin and coating onto a support material. Examples of the conductive powder include carbon black, acethylene black, a metal powder of aluminum, nickel, iron, nichrome, copper, zinc, silver, etc., or a metal oxide powder of conductive tin oxide and ITO. Examples of the binder resin used together with the conductive powder include thermoplastic resins, thermosetting resins or photocurable resins, such as polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethylcellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyltoluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenol resin or alkyd resin. Such a conductive layer can be provided by dispersing the conductive powder and binder resin in a certain solvent, for example tetrahydrofuran, dichloromethane, methyl ethyl ketone or toluene, and then applying them.
Further, the support which is prepared by forming a conductive layer on the suitable cylindrical base with a thermal contraction inner tube made of a suitable material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber or teflon (registered trademark) can also be favorably used as the conductive support in the present invention.
Of these, an aluminum cylindrical support easily capable of undergoing an anode oxide coating treatment can be most favorably used. The aluminum mentioned here includes both pure aluminum and aluminum alloy. Specifically, aluminums and aluminum alloys according to No. 1000 to No. 1999, No. 3000 to No. 3999 and No. 6000 to No. 6999 of JIS are most suitable. Anode oxide coat films are produced by subjecting various metals and alloys to an anodizing treatment in electrolyte solution; amongst those anode oxide coat films, a coat film called alumite, produced by subjecting aluminum or aluminum alloy to an anodizing treatment in electrolyte solution, is most suitable for a photoconductor used in the present invention. In particular, alumite is superior in preventing point defects (black spots and background smear) caused when used in reversal developing (negative-positive developing).
An anodizing treatment is carried out in an acid bath of chromic acid, sulfuric acid, oxalic acid, phosphoric acid, boric acid, sulfamic acid, etc. Of these, a treatment by means of a sulfate bath is most suitable. As one example, the treatment is carried out under the following conditions: 10% to 20% in sulfuric acid concentration, 5° C. to 25° C. in bath temperature, 1A/dm2 to 4A/dm2 in current density, 5V to 30V in electrolysis voltage, and 5 min to 60 min in treating time; however, note that the treatment is not necessarily carried out under these conditions. Since an anode oxide coat film thus produced is porous and highly insulative, its surface is very unstable. Accordingly, there is a temporal change after production, and property values of the anode oxide coat film are liable to change. In order to avoid this, it is desirable that the anode oxide coat film be also given a sealing treatment. For sealing treatments, there are some methods including a method of immersing an anode oxide coat film in a solution containing nickel fluoride or nickel acetate, a method of immersing an anode oxide coat film in boiling water, a method of treating an anode oxide coat film by means of pressurized steam, and the like. Amongst these methods, a method of immersing an anode oxide coat film in a solution containing nickel acetate is most favorable. Subsequent to the sealing treatment, a washing treatment is carried out on the anode oxide coat film. The main purpose of this treatment is to remove an excessive amount of materials, such as metallic salt, attached owing to the sealing treatment. When materials such as metallic salt remain excessively on the support (anode oxide coat film) surface, not only will the quality of a coat film formed thereupon be negatively affected, but also a low resistance component will generally remain, hence ironically a cause of occurrence of background smear. Washing may take place only once with the use of demineralized water, but normally washing takes place in many steps. On this occasion, it is desirable that a last washing liquid be as clean (deionized) as possible. Also, in one step of a multistep washing process, it is desirable that physical scrubbing be conducted by a contact member. It is desirable that the film thickness of an anode oxide coat film thusly formed be in the range of 5 μm to 15 μm or so. When the film thickness is far smaller than the foregoing, there will be an insufficient effect with respect to barrier properties as an anode oxide coat film, whereas when the film thickness is far greater than the foregoing, there will be a very great rise in time constant as an electrode, and so generation of a residual potential and a decrease in the response of a photoconductor are probable.
In light of the compactness of an image forming apparatus, it is desirable that a support be shaped like a cylinder (drum) whose external diameter is 40 mm or less.
Next, the intermediate layer (39) will be examined. An intermediate layer is, in general, formed mainly of resin; it is desirable that this resin be highly resistant to typical organic solvents, in consideration that it is coated with a solvent serving as a photosensitive layer. Examples of the resin include water-soluble resins such as polyvinyl alcohol, casein and sodium polyacrylate; alcohol-soluble resins such as copolymerized nylon and methoxymethylated nylon; and curable resins forming three-dimensional networks, such as polyurethane, melamine resin, phenol resin, alkyd-melamine resin and epoxy resin.
It is possible that an intermediate layer contains metal oxides for reduction of residual potential or the like, which simultaneously has such an effect as moire prevention. Examples of metal oxides include titanium oxide, silica, alumina, zirconium oxide, tin oxide and indium oxide. Amongst these, titanium oxide and tin oxide, in particular, are effectively used. Also, metal oxides used may be given surface treatment if necessary.
These intermediate layers can be formed by using a certain solvent and a certain coating method as in the case of the photosensitive layer. It is appropriate that the thickness of an intermediate layer be 0 μm to 5 μm.
The intermediate layer (39) has at least two functions, i.e. a function of preventing a charge of an opposite polarity, induced to the electrode side when a photoconductor is charged, from being injected into a photosensitive layer, and another function of preventing moire caused at the time of writing by coherent light similar to laser light. A functionally-divided intermediate layer, in which these functions are assigned to two layers or more in a divided manner, is an effective means for a photoconductor used in the present invention. The following explains a functionally-divided intermediate layer composed of a charge blocking layer (43) and a moire prevention layer (45).
The charge blocking layer (43) is a layer having the function of preventing a charge of an opposite polarity, induced to the electrode (conductive support (31)) when a photoconductor is charged, from being injected into a photosensitive layer from the support. It has the function of preventing hole injection in the case of negative charge, and the function of preventing electron injection in the case of positive charge. Examples of the charge blocking layer include an anode oxide coating typified by an aluminum oxide layer; an inorganic-type insulating layer typified by SiO; a layer formed by a glassy network of a metal oxide; a layer formed of polyphosphazene; a layer formed of an aminosilane reaction product; a layer formed of an insulative binder resin; and a layer formed of a curable binder resin. Amongst these layers, a layer formed of an insulative binder resin and a layer formed of a curable binder resin, able to be formed in accordance with a wet coating method, can be favorably used. A charge blocking layer is used with a moire prevention layer and a photosensitive layer formed thereupon in a multi-layered structure; therefore, when these layers are provided by a wet coating method, it is important that the charge blocking layer be formed of such a material or have such a structure as prevents the coat film from being corroded by coating solvents for the moire prevention layer and the photosensitive layer.
Examples of usable binder resins include thermoplastic resins and thermosetting resins such as polyamide, polyester and vinyl chloride-vinyl acetate copolymer; for example, it is also possible to use a thermosetting resin in which a compound containing a plurality of active hydrogen atoms (hydrogen atoms in —OH groups, —NH2 groups, —NH groups, etc.) and a compound containing a plurality of isocyanate groups and/or a compound containing a plurality of epoxy groups are thermally polymerized. In this case, examples of a compound having a plurality of active hydrogen atoms include an acrylic-type resin containing active hydrogen, such as polyvinylbutyral, phenoxy resin, phenol resin, polyamide, polyester, polyethyleneglycol, polypropylene glycol, polybutylene glycol or hydroxyethyl methacrylate. Examples of a compound containing a plurality of isocyanate groups include tolylenediisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, etc. or a prepolymer thereof Examples of a compound containing a plurality of epoxy groups include bisphenol A type epoxy resin. In particular, polyamide can be most favorably used, in terms of film forming properties, environmental stability and solvent resistance. Amongst polyamides, N-methoxymethylated nylon is most suitable. N-methoxymethylated nylon can be obtained by modifying a polyamide which contains polyamide 6 as a component, for example in accordance with the method proposed by T. L. Cairns (J. Am. Chem. Soc. 71. P651 (1949)). N-methoxymethylated nylon is produced by substituting a methoxymethyl group for a hydrogen atom in an amide bond of an original polyamide. The substitution ratio can be selected in a wide range, depending upon a modifying condition; however, it is desirable in terms of environmental stability that the substitution ratio be in the range of 10 mol % to 85 mol %, because the hygroscopicity of an intermediate layer is curbed to some extent and N-methoxymethylated nylon is superior in alcohol affinity. It is more desirable that the substitution ratio be in the range of 20 mol % to 50 mol %. Also, it is desirable that the substitution ratio be 85mol % or less; as the amide substitution degree (degree of N-N-methoxymethyl) increases, alcoholic solvent affinity increases; however, since a relaxation condition of main chains, a coordinated state between main chains, or the like possibly changes, strongly affected by bulk side chain groups around the main chains, hygroscopicity also increases and crystallizability decreases, which causes the melting point to decrease, and mechanical strength and elasticity decrease. It is more desirable that the substitution ratio be 70 mol% or less. Further, according to a result of study, as a nylon, nylon 6 is most favorable, and nylon 66 is second most favorable; conversely, a copolymerized nylon such as nylon 6/66/610 is not much favorable, as opposed to the disclosure in Japanese Patent Application Laid-Open (JP-A) No. 9-265202.
Thermosetting resins produced by thermally polymerizing oil-free alkyd resins and amino resins, such as butylated melamine resins, and further, photocurable resins produced for example by combining resins having unsaturated bonds, such as polyurethanes having unsaturated bonds and unsaturated polyesters, and photopolymerization initiators, such as thioxanthone-based compounds and methylbenzyl formate, can also be used as binder resins.
Additionally, a binder resin may have a rectifiable conductive polymer or have a function such as the controlling of charge injection from a base by adding a resin/compound with an acceptor (donor) property according to a charge polarity.
Also, it is desirable that the film thickness of a charge blocking layer be approximately in the range of 0.1 μm to 2.0 μm or so, more desirably in the range of 0.3 μm to 2.0 μm. As a charge blocking layer becomes thick, an increase in residual potential becomes conspicuous especially at low temperature and low humidity, due to the repetition of charging and exposure; whereas, as it becomes very thin, an effect with respect to blocking properties decreases. An agent, a solvent, an additive, a hardening accelerator and the like necessary for hardening (crosslinkage) are added to the charge blocking layer (43) if need be, and the charge blocking layer (43) is formed on a base by blade coating, an immersion coating method, spray coating, beat coating, a nozzle coating method, etc. according to an ordinary procedure. After applied, the charge blocking layer (43) is dried or hardened by drying, heating, or hardening with the use of light or the like.
The moire prevention layer (45) has the function of preventing a moire image caused by light interference inside a photosensitive layer, when writing is carried out by means of coherent light similar to laser light. When an intermediate layer is functionally divided, a metal oxide is contained in a moire prevention layer such that this moire prevention layer has a photocarrier generating function at the time of writing. Basically, the moire prevention layer has the function of dispersing the writing light. Having a material of a great refractive index is effective for a moire prevention layer to express such a function.
Since, in a photoconductor having a functionally-divided intermediate layer, charge injection from the support (31) is prevented by a charge blocking layer, it is desirable in terms of prevention of residual potential that at least a charge of the same polarity as a charge on the charged photoconductor surface be able to be moved in a moire prevention layer. Thus, in the case of a negatively-charged photoconductor, for example, it is desirable that a moire prevention layer be given electron conductivity, and so it is desirable that a moire prevention layer having a metal oxide with electron conductivity or a conductive moire prevention layer be used. Alternatively, the use of an electronically conductive material (for example accepter), etc. for a moire prevention layer makes the effect of the present invention even more remarkable.
For a binder resin, a material similar to that of a charge blocking layer can be used, but in light of the fact that a photosensitive layer (charge generating layer (35) and charge transporting layer (37)) is formed on a moire prevention layer, it is important that the material of the binder resin not be corroded by a coating solvent for the photosensitive layer (charge generating layer and charge transporting layer).
For a binder resin, a thermosetting resin is favorably used. In particular, a mixture of alkyd resin and melamine resin is most favorably used. On this occasion, the mixing ratio between an alkyd resin and a melamine resin is an important factor in determining the structure and properties of a moire prevention layer. When the ratio (weight ratio) of an alkyd resin to a melamine resin is in the range of 5:5 to 8:2, it can be said as a favorable mixing ratio. If more melamine resin is contained than in the case of 5:5, volume contraction becomes greater at the time of thermal hardening, easily causing coating defects, and the residual potential of a photoconductor is made greater, which is not favorable. Meanwhile, if more alkyd resin is contained than in the case of 8:2, the residual potential of a photoconductor can be effectively reduced, but the bulk resistance becomes very low, further causing background smear, which is not favorable either.
As to a moire prevention layer, the volume ratio between a metal oxide and a binder resin determines important properties thereof. Accordingly, it is important that the volume ratio of an metal oxide to a binder resin be in the range of 1:1 to 3:1. When the volume ratio of a metal oxide to a binder resin is less than 1:1, not only could moire preventing ability lower, but also the residual potential could rise greatly when repeatedly used. Meanwhile, when the volume ratio is in a greater range than 3:1, not only could adhesion of a binder resin be poor, but also surface properties of a coating could worsen and film forming properties of a photosensitive layer above could be negatively affected. This negative effect can become a serious problem, when a photosensitive layer is formed in a multi-layered structure, and a thin layer such as a charge generating layer is formed. And again, when the volume ratio is greater than 3:1, it is possible that a metal oxide surface cannot be covered with binder resin, and so the metal oxide surface directly makes contact with a charge generating material, thus making the incidence of photocarriers high, and negatively affecting background smear.
Further, by using two types of metal oxides of different average particle diameters for a moire prevention layer, it is possible to improve opacifying power over a conductive base and thus prevent moire; also, it is possible to remove a pinhole, which can be a cause of abnormal images. In order to do so, it is important that the ratio of the average particle diameter of the two types of metal oxides used be in a certain range (0.2<D2/D1≦0.5). When the particle diameter ratio is outside a range prescribed by the present invention, in other words when the ratio of the average particle diameter of a metal oxide (T2) to the average particle diameter of a metal oxide (T1) that is larger in average particle diameter is very small (0.2≧D2/D1), activity on metal oxide surfaces increases, and electrostatic stability in an electrophotographic photoconductor is greatly impaired. Also, when the ratio of the average particle diameter of the other metal oxide (T2) to the average particle diameter of one metal oxide (T1) is very large (D2/D1>0.5), opacifying power over a conductive base lowers, and preventing power over moire and abnormal images lowers. The average particle diameter mentioned here is calculated from a particle size distribution measurement obtained when strong dispersion is conducted in an aqueous system.
Also, how large is the average particle diameter (D2) of the metal oxide (T2) that is smaller in particle diameter is an important factor, and 0.05 μm<D2<0.20 μm is important. When the average particle diameter (D2) is 0.05 μm or less, opacifying power lowers, and moire could be generated. Meanwhile, when the average particle diameter (D2) is 0.20 μm or more, the filling percentage of metal oxides on a moire prevention layer is lowered, and thus effect of preventing background smear cannot be sufficiently exerted.
Also, the mixing ratio (weight ratio) between the two types of metal oxides is also an important factor. When T2/(T1+T2) is less than 0.2, the filling percentage of the metal oxides is not much great, and thus effect of preventing background smear cannot be sufficiently exerted. Meanwhile, when T2/(T1+T2) is greater than 0.8, opacifying power lowers, and moire could be caused. Therefore, 0.2≦T2/(T1+T2)≦0.8 is important.
Also, it is appropriate that the thickness of the moire prevention layer be in the range of 1 μm to 10 μm, preferably 2 μm to 5 μm. When the layer thickness is less than 1 μm, expression of the prevention effect is poor, whereas when the layer thickness is more than 10 μm, residual potential accumulates, which is not desirable.
Metal oxides are dispersed along with a solvent and a binder resin by means of a ball mill, a sand mill, an attritor, etc. according to an ordinary procedure, with the addition of an agent, a solvent, an additive, a hardening accelerator and the like necessary for hardening (crosslinkage) if need be, and then formed on a base by means of blade coating, an immersion coating method, spray coating, beat coating, a nozzle coating method, etc. according to an ordinary procedure. After applied, the moire prevention layer is dried or hardened by drying, heating, or hardening with the use of light or the like.
Next, a photosensitive layer will be explained. A photosensitive layer is composed of the charge generating layer (35) which contains an organic charge generating material as a charge generating material, and the charge transporting layer (37) including a charge transporting material as a main component.
The charge generating layer (35) is a layer including an organic charge generating material as a charge generating material, as a main component. The charge generating layer (35) is formed, as an organic charge generating material is dispersed in a certain solvent, along with a binder resin if necessary, with the use of a ball mill, an attritor, a sand mill, a supersonic wave, etc., and this mixture is applied on a conductive support and dried.
Examples of the binder resin used in a charge generating layer if necessary include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinylbutyral, polyvinyl formal, polyvinylketone, polystyrene, polysulfone, poly-N-vinylcarbazole, polyacrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinylpyridine, cellulosic resin, casein, polyvinyl alcohol and polyvinylpyrrolidone. To 100 parts by weight of charge generating material, it is appropriate that the amount of binder resin be 0 part by weight to 500 parts by weight, preferably 10 parts by weight to 300 parts by weight.
Examples of the solvent used here include isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellusolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene, xylene and ligroin. Examples of a coating method of a coating solution include an immersion coating method, spray coating, beat coating, nozzle coating, spinner coating and ring coating. It is appropriate that the film thickness of a charge generating layer be in the range of 0.01 μm to 5 μm, preferably in the range of 0.1 μm to 2 μm.
For a charge generating material, an organic charge generating material can be used.
For organic charge generating materials, conventional materials can be used, preferably disazo pigments or trisazo pigments and phthalocyanine series pigments. Examples thereof include phthalocyanine series pigments such as metal phthalocyanine and metal-free phthalocyanine; azlenium salt pigments; squaric acid methine pigments; azo pigments having carbazole skeletons; azo pigments having triphenylamine skeletons; azo pigments having diphenylamine skeletons; azo pigments having dibenzothiophene skeletons; azo pigements having fluorenone skeletons; azo pigments having oxadiazole skeletons; azo pigments having bisstilbene skeletons; azo pigments having distyryl oxadiazole skeletons; azo pigments having distyryl carbazole skeletons; perylene series pigments; anthraquinone series or polycyclic quinone series pigments; quinonimine series pigments; diphenylmethane and triphenylmethane series pigments; benzoquinone and naphthoquinone series pigments; cyanine and azomethine series pigments; indigoid series pigments; and bisbenzimidazole series pigments. These charge generating materials can be used independently or as mixtures each including two types or more.
Amongst them, the azo pigment represented by Structural Formula (1) below is effectively used. In particular, an asymmetric azo pigment, in which Cp1 and Cp2 are different from each other in an azo pigment, is great in carrier generating efficiency, and can therefore be effectively used as a charge generating material in the present invention.
In Structural Formula (1), both Cp1 and Cp2 denote coupler residues; R201 and R202 each denote a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group or a cyano group, and whether R201 and R202 are the same or different does not matter. Cp1 and Cp2 are represented by Structural Formula (2) bellow.
In Structural formula (2), R203 denotes a hydrogen atom, an alkyl group such as a methyl group or ethyl group, or an aryl group such as a phenyl group. R204, R205, R206, R207 and R208 each denote a hydrogen atom, a nitro group, a cyano group, a halogen atom such as fluorine, chlorine, bromine or iodine, an alkyl halide group such as a trifluoromethyl group, an alkyl group such as a methyl group or ethyl group, an alkoxy group such as a methoxy group or ethoxy group, a dialkylamino group, or a hydroxyl group; and Z denotes an atom group necessary to form a substituted/unsubstituted aromatic carbocycle or a substituted/unsubstituted aromatic heterocycle.
Also, titanyl phthalocyanine can be effectively used for a charge generating material in the present invention. In particular, a titanylphthalocyanine crystal that has a maximum diffraction peak of at least 27.2° of Bragg angle (20±0.2°), especially a titanylphthalocyanine crystal that has a maximum diffraction peak of at least 27.2°, has major peaks at 9.4°, 9.6° and 24.0°, has a minimum-angle diffraction peak at 7.3°, does not have a diffraction peak between the peaks at 7.3° and 9.4°, and does not have a diffraction peak at 26.3°, in an X-ray diffraction spectrum using a CuKα X-ray (1.542 Å), is great in carrier generating efficiency, and can therefore be effectively used as a charge generating material in the present invention.
As to an organic charge generating material contained in an electrophotographic photoconductor in the present invention, the effect can be expressed by reducing the particle size of a charge generating material as much as possible; it is desirable that the average particle size be 0.25 μm or less, more desirably 0.2 μm or less. A production method thereof is described below. A method for controlling the particle size of a charge generating material contained in a photosensitive layer is a method in which after a charge generating material is dispersed, coarse particles greater than 0.25 μm in size are removed.
Here, the average particle size denotes the volume average particle diameter, which can be determined by an ultracentrifugal automatic particle size distribution measuring apparatus CAPA-700 (produced by Horiba, Ltd.). On this occasion, the average particle size is calculated as a particle diameter (median diameter) equivalent to 50% of a cumulative distribution. However, there is a possibility that coarse particles existing in small amounts can not be detected by this method; accordingly, in order to calculate the average particle size in further detail, it is important to observe a charge generating material powder or a dispersion liquid thereof under an electron microscope, and thusly calculate the size thereof.
Next, a method in which after an organic charge generating material is dispersed, coarse particles are removed will be described.
The foregoing method is a method in which after preparing a dispersion liquid containing particles that have been made as fine as possible, the dispersion liquid is filtered with a certain filter. As for the preparation of the dispersion liquid, a typical method is used; a dispersion liquid is obtained, as an organic charge generating material is dispersed in a certain solvent, along with a binder resin if necessary, with the use of a ball mill, an attritor, a sand mill, a bead mill, a supersonic wave, etc. On this occasion, it is advisable to select a binder resin according to the electrostatic properties of a photoconductor or the like, and to select a solvent according to its wettability to a pigment, the dispersibility of a pigment, or the like.
This method is very effective in that it is even possible to remove coarse particles remaining in small amounts which are invisible to the naked eye (or which cannot be detected by means of particle diameter measurement), and also in that a particle size distribution is tightly controlled. Specifically, a dispersion liquid prepared in that manner is filtered with a filter of 5 μm or less in effective hole diameter, more preferably 3 μm or less, and a dispersion liquid is thus completed. According to this method as well, it is possible to prepare a dispersion liquid only including an organic charge generating material which is small in particle size (0.25 μm or less, preferably 0.2 μm or less), and by installing in an image forming apparatus a photoconductor utilizing this dispersion liquid, the effects of the present invention are made even more remarkable.
On this occasion, when the particle size of the dispersion liquid filtered is very large, or the particle size distribution is very wide, it is possible that loss caused by filtration may become great, or filtration may be made impossible because of clogging caused. Therefore, in a dispersion liquid before filtered, it is desirable that dispersion be continued until the average particle size attains 0.3 μm or less and the standard deviation thereof attains 0.2 μm or less. When the average particle size is 0.3 μm or more, loss caused by filtration becomes great, and when the standard deviation is 0.2 μm or more, there could be such a trouble that filtering time may lengthen greatly.
As to a charge generating material used in the present invention, intermolecular hydrogen bonding force, which is characteristic of a charge generating material showing a high-sensitive property, is very strong. Thus, interaction between particles in pigment particles dispersed is also very strong. As a result, there is a very strong possibility that charge generating material particles dispersed by a dispersing device or the like will flocculate again because of dilution or the like; by conducting filtration with a filter whose size is smaller than a particular size after dispersion as described above, it is possible to remove such a flocculation product. On this occasion, since a dispersion liquid is in a state of thixotropy, even particles which are smaller in size than the effective hole diameter of a filter used are removed. Alternatively, it is possible to change a liquid with structural viscosity into a state close to newtonian character by means of filtration. Thus, by removing coarse particles of a charge generating material, the effect of the present invention is improved remarkably.
A filter with which the dispersion liquid is filtered varies according to the size of coarse particles to be removed; according to a study by the present inventors, with respect to a photoconductor used in an electrophotographic apparatus which requires a resolution of 600 dpi or so, the existence of coarse particles of 3 μm or more in size, at least, has an impact on images. Therefore, a filter with an effective hole diameter of 5 μm or less should be used. It is more desirable that a filter with an effective hole diameter of 3 μm or less be used. As this effective hole diameter becomes smaller, there will be a greater effect on removal of coarse particles, but if the effective hole diameter is very small, necessary pigment particles themselves will be filtered out, and so there has to be an appropriate size. Moreover, if it is very small, there will be problems arising in which filtration takes a great deal of time, a filter is clogged, an enormous load is put when a liquid is sent using a pump or the like, and so forth. Here, it goes without saying that a material which is resistant to a solvent used in the dispersion liquid to be filtered is used for the filter.
The charge transporting layer (37), a layer including a charge transporting material as a main component, can be formed, as a charge transporting material and a binder resin are dissolved or dispersed in a certain solvent, and this mixture is applied on a charge generating layer and dried. Additionally, it is possible to add a plasticizer, a leveling agent, an antioxidant and the like if necessary.
Charge transporting materials can be divided into hole transporting materials and electron transport materials. Examples of hole transporting materials include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethylglutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, polyvinyl phenanthrene, polysilane, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazoline derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, and other conventional materials. Each of these charge transporting materials may be used alone or in combination with two or more.
Examples of electron transport materials include electron accepting materials such as chloranil, bromanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno[1,2-b]thiophene-4-on, 1,3,7-trinitrodibenzothiophene-5,5-dioxide and benzoquinone derivatives.
Examples of binder resins include thermoplastic and thermosetting resins such as polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy resin, polycarbonate, cellulose acetate resin, ethylcellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyltoluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, phenol resin and alkyd resin.
To 100 parts by weight of binder resin, it is appropriate that the amount of charge transporting material be 20 parts by weight to 300 parts by weight, preferably 40 parts by weight to 150 parts by weight. It is desirable that the thickness of a charge transporting layer be in the range of 5 μm to 100 μm or so.
For the solvent used here, tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, acetone or the like can be used. The use of a non-halogenated solvent is desirable, due to the intention of reducing damage to the environment and so forth. Specifically, cyclic ethers such as tetrahydrofuran, dioxolan and dioxane, aromatic series hydrocarbons such as toluene and xylene, and derivatives thereof can be favorably used.
In the present invention, a plasticizer and a leveling agent may be added to the charge transporting layer. For the plasticizer, a typical resinous plasticizer, such as dibutyl phthalate or dioctyl phthalate, can be used as it is, and it is appropriate that the amount thereof used be in the range of 0% by weight to 30% by weight or to the content of the binder resin. For the leveling agent, a silicone oil such as dimethyl silicone oil or methylphenyl silicone oil, a polymer having a perfluoroalkyl group for a side chain, or an oligomer can be used, and it is appropriate that the amount thereof used be in the range of 0% by weight to 1% by weight to the content of the binder resin.
The transit time of a photoconductor is, in general, determined by the carrier transporting ability of this charge transporting layer as described above. A control method of the transit time will be described.
The transit time depends upon the time during which photocarriers generated in a charge generating layer are injected into a charge transporting layer, cross the charge transporting layer and erase a surface charge. Within the foregoing time, the time during which carriers are injected and erase a surface charge can be ignored because it is sufficiently short in comparison with the time during which carriers cross the charge transporting layer. Therefore, the transit time roughly denotes the time during which carriers cross the charge transporting layer.
To control the transit time means to control the transfer velocity of carriers and the moving distance of the carriers. The former depends upon the composition, material, etc. of a charge transporting layer, and the latter depends upon the thickness of the charge transporting layer.
The composition of the charge transporting layer is determined by the type of a charge transporting material, the type of a binder resin, the charge transporting material density, and the presence/absence and type of additives. Amongst them, the type of a charge transporting material, the charge transporting material density, and the type of a binder resin greatly affect the composition of a charge transporting layer. As for the type of a charge transporting material, generally by using a material of great mobility for a charge transporting material, it is possible to shorten the transit time. As for the type of a binder resin, by using a binder resin of small polarity or a high-molecular charge transporting material, it is possible to shorten the transit time. As for the charge transporting material density, the higher the density is, the shorter the transit time can be made. As for the film thickness of a charge transporting layer, the smaller the film thickness is, the shorter the transit time can be made.
However, when the charge transporting layer is placed on a surface, it is hardly possible to design the charge transporting layer merely for shortening the transit time. For example, when the charge transporting material density is made high to a maximum degree, the transit time is shortened, to be sure, but abrasion resistance is extremely lowered, and the lifetime of the photoconductor is shortened. Also, when a charge transporting layer is made extremely thin, the transit time is shortened, but it is highly likely that side effects such as breakdown and background smear will be caused, and therefore a charge transporting layer cannot be easily made thin.
Therefore, a charge transporting layer is composed of the material, and the transit time is measured; optimization is achieved according to the relation between the transit time and the lifetime of a photoconductor.
Also, forming a protective layer on a surface layer, as the carrier transport velocity in a charge transporting layer is given top priority, is an effective means in the present invention. In this case, since it is possible to design the charge transporting layer only focusing attention on the carrier transfer velocity, with the abrasion resistance of the charge transporting layer ignored to some extent, the above-mentioned method can be employed.
As to an electrophotographic photoconductor of the present invention, a protective layer may be placed on a photosensitive layer, with the intention of protecting the photosensitive layer. In recent years, as computers have been used on a day-to-day basis, compactness of apparatuses, as well as high-speed output by printers, has been hoped for. Accordingly, by providing a protective layer and thusly improving durability, a photoconductor of the present invention, which is highly sensitive and free of abnormal defects, can be effectively used.
In this case, since the protective layer is placed as a photoconductor surface layer, lack of consideration of carrier transporting ability will affect the transit time. For this reason, layer structure and layer thickness are important to a protective layer. As to layer structure, after-mentioned two types can be effectively used. As to film thickness, it is important in whatever case not to make a protective layer thicker than necessary.
Effective protective layers used in the present invention are broadly divided into two types. One is a structure in which a filler is added to the inside of a binder resin. The other is a structure in which a crosslinkable binder is used.
First, the structure in which a filler is added to a protective layer will be explained.
Examples of materials used for protective layers include resins such as ABS resin, ACS resin, olefin-vinyl monomer copolymer, chlorinated polyether, allyl resin, phenol resin, polyacetal, polyamide, polyamide imide, polyacrylate, polyallyl sulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyarylate, polyether sulfone, polyethylene, polyethylene terephthalate, polyimide, acrylic resin, polymethylpentene, polypropylene, polyphenylene oxide, polysulfone, polystyrene, AS resin, butadiene-styrene copolymer, polyurethane, polyvinyl chloride, polyvinylidene chloride and epoxy resin. Amongst them, polycarbonate and polyarylate can be most favorably used.
In addition, the following can be added to protective layers, with the intention of improving abrasion resistance: fluorine resins such as polytetrafluoroethylene; silicone resins; these resins having inorganic fillers such as titanium oxide, tin oxide, potassium titanate and silica, or organic fillers dispersed; and the like. Examples of filler materials used for protective layers of photoconductors are as follows: as organic filler materials, there are fluorine resin powders such as polytetrafluoroethylene, silicone resin powders, a-carbon powders, and the like; as inorganic filler materials, there are metal powders such as copper, tin, aluminum and indium, metal oxides such as silica, tin oxide, zinc oxide, titanium oxide, indium oxide, antimony oxide, bismuth oxide, antimony-doped tin oxide and tin-doped indium oxide, and inorganic materials such as potassium titanate. In particular, inorganic pigments and metal oxides are favorable, and silica, titanium oxide and alumina are effective.
The filler density in a protective layer varies according to the type of filler used or the electrophotographic process condition in which a photoconductor is used; however, it is desirable that the ratio of a filler in a total solid content on the top surface side of the protective layer be approximately 5% by weight or more, preferably 10% by weight or more and 50% by weight or less, more preferably 30% by weight or less. It is desirable that the volume average particle diameter of a filler used be in the range of 0.1 μm to 2 μm, more desirably 0.3 μm to 1 μm. In this case, when the average particle diameter is very small, abrasion resistance of the protective layer cannot be sufficiently exerted; in contrast, when it is very large, surface properties of a coating may be degraded, or a coat film itself cannot be formed.
The average particle diameter of a filler in the present invention denotes a volume average particle diameter, unless there is a specific mention to state otherwise; it is calculated by an ultracentrifugal automatic particle size distribution measuring apparatus CAPA-700 (produced by Horiba, Ltd.). Here, the average particle diameter of a filler is calculated as a particle diameter (median diameter) equivalent to 50% of a cumulative distribution. Also, it is important that the standard deviation of particles measured at the same time be 1 μm or less. When the standard deviation is greater than this value, the particle size distribution may be so wide that the effect of the present invention cannot be remarkably obtained.
Also, the pH of a filler used in the present invention greatly affects resolution and the dispersibility of the filler. One reason for that is thought to be that a filler, particularly a metal oxide, leaves hydrochloric acid, etc. when produced. When the residual amount of hydrochloric acid, etc. is large, occurrence of image blur is inevitable, and hydrochloric acid, etc. may affect the dispersibility of a filler depending upon the residual amount thereof.
Another reason for that is a difference in charging properties on the surface of a filler, particularly on the surface of a metal oxide. Normally, particles dispersed in a liquid are positively or negatively charged, and ions having the opposite charge gather to keep the particles electrically neutral; here, the dispersed state of the particles is stabilized as an electric double layer is formed. The potential (zeta potential) of a place in the liquid gradually lowers as measured away from the particles, and the potential of an electrically neutral region which is sufficiently away from the particles stands at zero. Therefore, stability is improved as an increase in the absolute value of the zeta potential heightens the repulsion of particles, and stability is lowered as the absolute value of the zeta potential nears zero. Meanwhile, the zeta potential greatly varies according to the pH value of a system; at a certain pH value, the potential stands at zero and an isoelectric point is created. Accordingly, a dispersion system can be stabilized by raising the absolute value of the zeta potential, away from an isoelectric point of a system as much as possible.
In a structure of the present invention, it has been confirmed that a filler whose pH at the isoelectric point is 5 or more is favorable in preventing image blur, and that the more basic a filler is, the more greater effect it tends to have on the preventing of image blur. As to a basic filler of a high pH at an isoelectric point, the zeta potential becomes even higher when a system is acid, and dispersibility and the stability of dispersibility are thus improved.
Here, as the pH value of a filler in the present invention, the pH value from a zeta potential to an isoelectric point is written. On this occasion, the zeta potential was measured by a laser zeta electrometer produced by Otsuka Electronics Co., Ltd.
Further, for fillers which prevent image blur from easily arising, fillers of high electrical insulation quality (1010Ω·cm or more in resistivity) are favorable, particularly fillers whose pH is 5 or more and fillers whose dielectric constant is 5 or more. Also, not to mention the fact that fillers whose pH is 5 or more or fillers whose dielectric constant is 5 or more can be used independently, it is also possible to combine fillers whose ph is 5 or less and fillers whose ph is 5 or more as mixtures each including two types or more and to combine fillers whose dielectric constant is 5 or less and fillers whose dielectric constant is 5 or more as mixtures each including two types or more. Amongst these fillers, α-alumina that is highly insulative and highly thermostable and has a hexagonal close packing structure with high abrasion resistance is particularly effective in that image blur can be prevented and abrasion resistance can be improved.
The resistivity of a filler used in the present invention is defined as follows. Since the resistivity value of a powder such as a filler varies according to a filling percentage, it needs to be measured under certain conditions. In the present invention, the resistivity value of a filler was measured using a similar apparatus to the measuring apparatus disclosed in Japanese Patent Application Laid-Open (JP-A) No. 5-113688 (
The dielectric constant of a filler was measured as follows. Such a cell as used in the measurement of resistivity was used, the capacitance was measured after a load was applied, and the dielectric constant was thusly calculated. For the measurement of the capacitance, a DIELECTRIC LOSS MEASURING APPARATUS (Ando Electric Co., Ltd.) was used.
Further, these fillers can be surface-treated by at least one type of surface-treating agent, and this is favorable in that further dispersibility of fillers is possible. Since reduction in the dispersibility of fillers not only causes rise in residual potential but also causes reduction in the transperency of coat films, generation of coating defects and reduction in abrasion resistance, a serious problem in which achievement of high durability or high image quality is hampered may be caused. For surface-treating agents, all conventionally-used surface-treating agents are acceptable; however, surface-treating agents which make it possible to retain the insulating properties of fillers are favorable. For example, the following are more favorable in that further dispersibility of fillers and prevention of image blurring are possible: titanate-based coupling agents, aluminum-based coupling agents, zircoaluminate-based coupling agents, higher fatty acids, etc. or mixtures of the foregoing and silane coupling agents, and Al2O3, TiO2, ZrO2, silicone, aluminum stearate, etc. or mixtures thereof. Although treatment by silane coupling agents increases effects of image blurring, it is possible that the effects may be curbed by mixing the surface-treating agents and silane coupling agents. The surface-treating amount varies according to the average primary particle diameter of the filler used; however, it is appropriate that the surface-treating amount be in the range of 3% by weight to 30% by weight, more preferably in the range of 5% by weight to 20% by weight. When the surface-treating amount is smaller than this, dispersibility of a filler cannot be effectively obtained, and when the surface-treating amount is far greater than this, a sharp rise in residual potential is caused. Each of these filler materials is used alone or in combination with two or more. The surface-treating amount of a filler is defined as the weight ratio of a surface-treating agent used to a filler amount, as described above.
These filler materials can be dispersed by using a certain dispersing device. Also, a filler used is dispersed to a primary particle level due to the transmittance of the protective layer, and a filler with fewer aggregates is therefore favorable.
Also, a charge transporting material is contained in a protective layer to reduce residual potential and improve responsiveness. For charge transporting materials, the materials mentioned in the explanation of a charge transporting layer, and conventional charge transporting materials can be used. When a low-molecular charge transporting material is used as a charge transporting material, a density gradient in the protective layer may be provided. Reducing the surface side of the protective layer in density to improve abrasion resistance is an effective means. Here, the density denotes the ratio of the weight of a low-molecular charge transporting material to the gross weight of all materials constituting a protective layer, and a density gradient denotes such a gradient that the density lowers on the surface side with respect to the weight ratio. Also, the use of a high-molecular charge transporting material is very advantageous in improving the durability of a photoconductor. According to a result of study by the present inventors, in the case of a protective layer with such structure, a filler dispersed in the protective layer does not affect the transit time much, and the transit time is determined by the carrier transport velocity at the portion composed of [binder resin+ charge transporting material] constituting a binder matrix. Therefore, in this case also, it is reasonable to apply such ideas as described for a charge transporting layer.
In addition, it is possible to use a conventional high-molecular charge transporting material for a binder resin in the protective layer. As an effect which is created when this is used, improvement in abrasion resistance and high-speed charge transport can be achieved.
As a formation method of the protective layer, an ordinary coating method is employed. Additionally, it is appropriate that the thickness of the protective layer be in the range of 0.1 μm to 10 μm or so.
Next, as to a binder structure of the protective layer, a protective layer with crosslinked structure will be explained (hereinafter referred to as crosslinked type protective layer).
As for the formation of a crosslinked structure, a reactive monomer having a plurality of crosslinkable functional groups in one molecule is used, crosslinking reaction is brought about by using light or thermal energy, and a three-dimensional network is formed. This network functions as a binder resin and expresses high abrasion resistance.
For the reactive monomer, a monomer having charge transporting ability wholly or partially is used. By using such a monomer, a charge transport site is formed in a network, and functions required for a protective layer can be sufficiently expressed. For the monomer having charge transporting ability, a reactive monomer with triarylamine structure can be effectively used. Such structure makes it possible to secure a sufficient carrier transport velocity and shorten the transit time.
A protective layer having such a network is, on the one hand, high in abrasion resistance, but on the other hand great in volume contraction at the time of crosslinking reaction, thereby possibly causing a crack when made very thick. In such a case, a protective layer may be formed into a multi-layered structure in which a protective layer of a low-molecular dispersed polymer is used for an under layer (photosensitive layer side) and a protective layer having a crosslinked structure is formed as an upper layer (surface side).
Amongst crosslinked type protective layers, a protective layer with a specific structure mentioned below can be used in a particularly effective manner.
The specific crosslinked type protective layer is a protective layer formed by hardening at least a trifunctional or more radical polymerizable monomer having no charge transporting structure and a monofunctional radical polymerizable compound having a charge transporting structure. Due to a crosslinked structure formed by hardening a trifunctional or more radical polymerizable monomer, a three-dimensional network is developed, a surface layer which is very high in crosslink density, very hard and highly elastic can be obtained, and the surface layer is even and very smooth; thus, high abrasion resistance and scratch resistance can be achieved. As just described, it is important to increase the crosslink density of a photoconductor surface, in other words the number of crosslinking bonds per unit volume; however, since a large number of bonds are formed in an instant in hardening reaction, internal stress arises owing to volume contraction. Since this internal stress increases as the film thickness of a crosslinked type protective layer becomes greater, it is likely that cracks and film peeling will arise when all layers in a protective layer are hardened. Even when this phenomenon does not appear in a primary stage, it may become liable to arise with time, affected by hazards and thermal variations of charging, developing, transfer and cleaning as a protective layer is repeatedly used in an electrophotographic process.
Methods for solving this problem are oriented toward softening a cured resin layer, for example (1) introducing a high-molecular component into a crosslinked layer and a crosslinked structure, (2) using monofunctional and difunctional radical polymerizable monomers in large amounts and (3) using polyfunctional monomers which have pliable groups; however, in any of the methods, the crosslink density of a crosslinked layer lowers, and so a dramatic increase in abrasion resistance cannot be achieved. In contrast to this, as for the photoconductor of the present invention, a crosslinked type protective layer high in crosslink density, in which a three-dimensional network is developed on a charge transporting layer, is provided, preferably with its film thickness set in the range of 1 μm to 10 μm; thus, the cracks and film peeling are prevented from arising, and also very high abrasion resistance can be achieved. By adjusting the thickness of the crosslinked type protective layer to the range of 2 μm to 8 μm, the problem can be solved even more easily, and also it is possible to select a material with high crosslink density leading to further improvement in abrasion resistance.
A photoconductor of the present invention can prevent cracks and film peeling for the reasons that internal stress does not increase as the crosslinked type protective layer can be made thin, internal stress in the crosslinked type protective layer serving as a surface can be moderated as there is a photosensitive layer or charge transporting layer placed thereunder, and so forth. Accordingly, it is not necessary for the crosslinked type protective layer to contain a large amount of high-molecular material; and scratches and toner filming resulting from incompatibility with a hardened material produced by a reaction between a high-molecular material and a radical polymerizable component (radical polymerizable monomer and radical polymerizable compound having a charge transporting structure), brought about when the crosslinked type protective layer contains the high-molecular material, are unlikely to arise. Further, when a thick film equivalent to all layers in the protective layer is hardened by irradiation of light energy, light transmission to the inside is restricted due to absorption by a charge transporting structure, thereby possibly preventing hardening reaction from progressing sufficiently. Since the crosslinked type protective layer of the present invention is made to be a thin layer of preferably 10 μm or less, hardening reaction progresses evenly to the inside, and high abrasion resistance can be maintained on the inside as well as on the surface. Also, in forming a crosslinked type protective layer of the present invention, a monofunctional radical polymerizable compound having a charge transporting structure is contained in addition to the trifunctional radical polymerizable monomer, and this radical polymerizable compound is taken into a crosslinking bond when the trifunctional or more radical polymerizable monomer is hardened. In contrast to the foregoing, when a low-molecular charge transporting material with no functional groups is contained in a crosslinked surface layer, their incompatibility causes deposition of the low-molecular charge transporting material or white turbidity, and the mechanical strength of the crosslinked surface layer decreases. Meanwhile, when a difunctional or more charge transport compound is used as a main component, it is fixed in a crosslinked structure by a plurality of bonds, and the crosslink density increases further; however, since a charge transporting structure is very large in volume, distortion of a cured resin structure becomes very great, which causes internal stress in a crosslinked type protective layer to increase.
Further, the photoconductor of the present invention has excellent electrical properties, and thus the photoconductor is excellent in repetitive stability, thereby making it possible to produce a highly durable and highly stabilized photoconductor. This is attributable to the fact that as a component material of the crosslinked type protective layer, a radical polymerizable compound having a monofunctional charge transporting structure is used and radical polymerizable compound is fixed as pendants between the crosslinked bonds. A charge transporting material having no functional group causes deposition and white turbidity as described above, resulting in conspicuous degradation of electrical properties such as reduction in sensitivity and increase in residual potential in repetitive use. When a difunctional or more charge transporting compound is mainly used, the compound is fixed by a plurality of bonds in the crosslinked structure; thus, an intermediate structure (cation radical) cannot be stably maintained at the time of charge transport, and a decrease in sensitivity and a rise in residual potential due to charge trapping are liable to arise. These deteriorations in electrical properties lead to a decrease in image density, and images having narrowing of letters and characters, etc. Further, in a photoconductor of the present invention, designing allowing for high mobility with little charge trapping, which is for conventional photoconductors, can be applied to a charge transporting layer provided as an under layer of the crosslinked type protective layer, and electrical side effects caused by the crosslinked type protective layer can be reduced to a minimum level.
Further, in the crosslinked type protective layer formation according to the present invention, in particular, the abrasion resistance can be remarkably exerted, by making the crosslinked type protective layer insoluble in organic solvent. A crosslinked type protective layer of the present invention is formed by hardening a trifunctional or more radical polymerizable monomer having no charge transporting structure and a monofunctional radical polymerizable compound having a charge transporting structure, and the whole layer has a high crosslink density with a three-dimensional network developed; however, it is possible that the crosslink density may locally lower and the crosslinked type protective layer may be formed as an aggregate of minute hardened materials which are crosslinked highly densely, depending upon contained materials other than the components (for example, additives such as a monofunctional or difunctional monomer, a high-molecular binder, an antioxidant, a leveling agent and a plasticizer, and dissolved mixture components from an under layer) and hardening conditions. The crosslinked type protective layer is weak in bonding force between hardened materials and soluble in organic solvent and also makes it easier for local abrasion and desorption to the extent of minute hardened materials to arise while repeatedly used in an electrophotographic process. By making a crosslinked type protective layer insoluble in organic solvent as in the present invention, a high degree of crosslinkage is obtained as an original three-dimensional network is developed, and also hardened materials are made high in molecular weight as a chain reaction progresses in a wide range; therefore, a dramatic improvement in abrasion resistance can be achieved.
Next, constituent materials for the crosslinked type protective layer coating solution of the present invention will be explained.
A trifunctional or more radical polymerizable monomer having no charge transporting structure in the present invention does not, for example, have a hole transport structure such as triarylamine, hydrazone, pyrazoline, carbazole, etc. or an electron transport structure such as an electron-withdrawing aromatic ring having a condensed polycyclic quinone, diphenoquinone, cyano group, nitro group, etc., and also the radical polymerizable monomer denotes a monomer having three radical polymerizable functional groups or more. For these radical polymerizable functional groups, any groups are suitable as long as they have carbon-carbon double bonds and are capable of radical polymerization. Examples of these radical polymerizable functional groups include the 1-substituted ethylene functional group, the 1,1-substituted ethylene functional group and both shown below.
(1) Examples of the 1-substituted ethylene functional group include the functional group represented by the following Structural Formula 10.
CH2═CH—X1— Structural Formula 10
(In Structural Formula 10, X1 denotes a phenylene group that may have a substituent group, an arylene group such as a naphthylene group, an alkenylene group that may have a substituent group, a —CO— group, a —COO— group, a —CON(R10)— group (R10 denotes hydrogen, an alkyl group such as a methyl group or ethyl group, an aralkyl group such as a benzyl group, naphthylmethyl group or phenethyl group, or an aryl group such as a phenyl group or naphthyl group), or an —S— group.)
Specific examples of these functional groups include a vinyl group, a styryl group, a 2-methyl-1,3-butadienyl group, a vinylcarbonyl group, an acryloyloxy group, an acryloylamide group and a vinyl thioether group.
(2) Examples of the 1,1-substituted ethylene functional group include the functional group represented by the following Structural Formula 11.
CH2═C(Y)—X2— Structural Formula 11
(In Structural Formula 11, Y denotes an alkyl group that may have a substituent group, an aralkyl group that may have a substituent group, an aryl group that may have a substituent group such as a phenyl group or naphthyl group, a halogen atom, a cyano group, a nitro group, an alkoxy group such as a methoxy group or ethoxy group, a —COOR11 group (R11 denotes a hydrogen atom, an alkyl group that may have a substituent group such as a methyl group or ethyl group, an aralkyl group that may have a substituent group such as a benzyl group or phenethyl group, or an aryl group that may have a substituent group such as a phenyl group or naphthyl group), or a —CONR12R13 group (R12 and R13 each denote a hydrogen atom, an alkyl group that may have a substituent group such as a methyl group or ethyl group, an aralkyl group that may have a substituent group such as a benzyl group, naphthylmethyl group or phenethyl group, or an aryl group that may have a substituent group such as a phenyl group or naphthyl group, and R12 and R13 may be the same or different from each other.); meanwhile, X2 denotes the same substituent group, single bond or alkylene group as X1 in Structural Formula 10 above. Here, note that at least either Y or X2 denotes an oxycarbonyl group, a cyano group, an alkenylene group or an aromatic ring.) Specific examples of these functional groups include an α-acryloyloxy chloride group, a methacryloyloxy group, an α-cyanoethylene group, an α-cyanoacryloyloxy group, an α-cyano phenylene group and an methacryloyl amino group.
Examples of substituent groups replacing these substituent groups for X1, X2 and Y include a halogen atom, a nitro group, a cyano group, an alkyl group such as a methyl group or ethyl group, an alkoxy group such as a methoxy group or ethoxy group, an aryloxy group such as a phenoxy group, an aryl group such as a phenyl group or naphthyl group, and an aralkyl group such as a benzyl group or phenethyl group.
Amongst these radical polymerizable functional groups, an acryloyloxy group and a methacryloyloxy group, in particular, are useful, and a compound with three acryloyloxy groups or more can be obtained, for example, by using a compound with three or more hydroxyl groups in a molecule thereof and acrylic acid (salt), acrylic acid halide or acrylic acid ester, and bringing them into ester reaction or ester exchange reaction. Also, a compound with three or more methacryloyloxy groups can be obtained in a similar manner. Additionally, radical polymerizable functional groups in a monomer having three or more radical polymerizable functional groups may be the same or different from each other.
For specific trifunctional or more radical polymerizable monomers having no charge transporting structure, the following compounds are mentioned as examples; however, these compounds do not include all such radical polymerizable monomers.
Examples of the radical polymerizable monomers used in the present invention include trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, trimethylolpropane alkylene-modified triacrylate, trimethylolpropane ethyleneoxy-modified (hereinafter EO-modified)triacrylate, trimethylolpropane propyleneoxy-modified (hereinafter PO-modified)triacrylate, trimethylolpropane caprolactone-modified triacrylate, trimethylolpropane alkylene-modified trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate (PETTA), glycerol triacrylate, glycerol epichlorohydrin-modified (hereinafter ECH-modified) triacrylate, glycerol EO-modified triacrylate, glycerol PO-modified triacrylate, tris (acryloxyethyl)isocyanurate, dipentaerythritol hexaacrylate (DPHA), dipentaerythritol caprolactone-modified hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkylated dipentaerythritol pentaacrylate, alkylated dipentaerythritol tetraacrylate, alkylated dipentaerythritol triacrylate, dimethylolpropane tetraacrylate (DTMPTA), pentaerythritolethoxy tetraacrylate, phosphoric acid EO-modified triacrylate, 2,2,5,5,-tetrahydroxymethylcyclopentanone tetraacrylate. These can be used independently, or two or more types amongst these can be used together.
As to a trifunctional or more radical polymerizable monomer having no charge transporting structure in the present invention, since intricate crosslinking bonds are formed in a crosslinked type protective layer, it is desirable that the proportion of the molecular weight to the number of functional groups in the monomer (molecular weight/the number of functional groups) be 250 or less. Also, when this proportion is 250 or greater, the crosslinked type protective layer is soft and tends to lower in abrasion resistance somewhat; therefore, as to monomers with modified groups such as EO, PO and caprolactone amongst the monomers and the like mentioned above as examples, it is not desirable to use monomers with extremely long modified groups independently. The content of the trifunctional or more radical polymerizable monomer having no charge transporting structure for a crosslinked type protective layer in the total weight of the crosslinked type protective layer is 20% by weight to 80% by weight, preferably 30% by weight to 70% by weight. When the monomer component is less than 20% by weight, the three-dimensional crosslinking bond density in the crosslinked type protective layer is small, and therefore a dramatic improvement in abrasion resistance tends to be difficult to achieve in comparison with related art in which a thermoplastic binder resin is used. When the monomer component is greater than 80% by weight, the contained amount of a charge transport compound decreases, and therefore deterioration in electrical properties tends to arise. Since electrical properties and abrasion resistance required vary depending upon the process used, and thus the film thickness of a crosslinked type protective layer in the present photoconductor varies, the monomer component cannot be unequivocally defined; however, in light of a balance between both electrical properties and abrasion resistance, it is most desirable that the monomer component be in the range of 30% by weight to 70% by weight.
A monofunctional radical polymerizable compound having a charge transporting structure used in a crosslinked type protective layer of the present invention has, for example, a hole transport structure such as triarylamine, hydrazone, pyrazoline, carbazole, etc. or an electron transport structure such as an electron-withdrawing aromatic ring having a condensed polycyclic quinone, diphenoquinone, cyano group, nitro group, etc., and also the radical polymerizable compound denotes a compound having one radical polymerizable functional group. Examples of this radical polymerizable functional group include any of the radical polymerizable monomers, and an acryloyloxy group and a methacryloyloxy group are particularly useful. As a charge transporting structure, a triarylamine structure is highly effective, and particularly when the compound represented by General Structural Formula (1) or (2) is used, electrical properties such as sensitivity and residual potential can be favorably sustained.
{In the general structural formulae, R1 denotes a hydrogen atom, a halogen atom, an alkyl group that may have a substituent group, an aralkyl group that may have a substituent group, an aryl group that may have a substituent group, a cyano group, a nitro group, an alkoxy group, a —COOR7 group (R7 denotes a hydrogen atom, an alkyl group that may have a substituent group, an aralkyl group that may have a substituent group, or an aryl group that may have a substituent group), a carbonyl halide group, or a CONR8R9 group (R8 and R9 each denote a hydrogen atom, a halogen atom, an alkyl group that may have a substituent group, an aralkyl group that may have a substituent group, or an aryl group that may have a substituent group, and R8 and R9 may be the same or different from each other); Ar1 and Ar2 each denote a substituted/unsubstituted arylene group, and Ar1 and Ar2 may be the same or different from each other. Ar3 and Ar4 each denote a substituted/unsubstituted aryl group, and Ar3 and Ar4 may be the same or different from each other. X denotes a single bond, a substituted/unsubstituted alkylene group, a substituted/unsubstituted cycloalkylene group, a substituted/unsubstituted alkylene ether group, an oxygen atom, a sulfur atom or a vinylene group. Z denotes a substituted/unsubstituted alkylene group, a substituted/unsubstituted alkylene ether divalent group or an alkyleneoxycarbonyl divalent group. “m” and “n” respectively denote an integer of 0 to 3.}
Specific examples represented by General Structural Formulae (1) and (2) are shown below.
In General Structural Formulae (1) and (2), it is possible to mention that amongst substituent groups for R1, an alkyl group can be a methyl group, ethyl group, propyl group, butyl group, etc.; an aryl group can be a phenyl group, naphthyl group, etc.; an aralkyl group can be a benzyl group, phenethyl group, naphthylmethyl group, etc.; and an alkoxy group can be a methoxy group, ethoxy group, propoxy group, etc. These groups may be replaced by a halogen atom, a nitro group, a cyano group, an alkyl group such as a methyl group or ethyl group, an alkoxy group such as a methoxy group or ethoxy group, an aryloxy group such as a phenoxy group, an aryl group such as a phenyl group or naphthyl group, and an aralkyl group such as a benzyl group or phenethyl group.
Amongst the substituent groups for R1, a hydrogen atom and a methyl group are particularly favorable.
Ar3 and Ar4 respectively denote a substituted/unsubstituted aryl group; in the present invention, examples of the substituted/unsubstituted aryl group include condensed polycyclic hydrocarbon groups, non-condensed cyclic hydrocarbon groups and heterocyclic groups, and specific examples thereof include the following groups.
Examples of the condensed polycyclic hydrocarbon groups forming a ring and having 18 or less carbon atoms include a pentanyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, a biphenylenyl group, an as-indacenyl group, an s-indacenyl group, a fluorenyl group, an acenaphthylenyl group, a pleiadenyl group, an acenaphthenyl group, a phenalenyl group, a phenanthryl group, an anthryl group, a fluoranthenyl group, an acephenanthrylenyl group, an aceanthrylenyl group, a triphenylel group, a pyrenyl group, a crycenyl group and a naphthacenyl group.
Examples of the non-condensed cyclic hydrocarbon groups include monovalent groups of monocyclic hydrocarbon compounds such as benzene, diphenyl ether, polyethylene diphenyl ether, diphenyl thioether and diphenyl sulfone; monovalent groups of non-condensed polycyclic hydrocarbon compounds such as biphenyl, polyphenyl, diphenylalkane, diphenylalkene, diphenylalkyne, triphenylmethane, distyrylbenzene, 1,1-diphenyl cycloalkane, polyphenylalkane and polyphenylalkene; and monovalent groups of cyclic assembly hydrocarbon compounds such as 9,9-diphenylfluorene.
Examples of the heterocyclic groups include monovalent groups of carbazole, dibenzofuran, dibenzothiophene, oxadiazole and thiadiazole.
The aryl groups denoted by Ar3 and Ar4 may respectively have such a substituent group as shown below.
(In the structural formula, R3 and R4 each denote independently a hydrogen atom, and any of the alkyl groups or aryl groups defined in (2). Examples of the aryl group include phenyl group, biphenyl group and naphthyl group. These groups may contain an alkoxy group having C1 to C4, an alkyl group having C1 to C4 or a halogen atom as a substituent group. R3 and R4 may together form a ring.) Specific examples thereof include amino group, diethylamino group, N-methyl-N-phenylamino group, N,N-diphenylamino group, N,N-di(tolyl)amino group, dibenzyl amino group, piperidino group, morpholino group and pyrrolidino group.
The arylene groups denoted by Ar1 and Ar2 are divalent groups derived from the aryl groups denoted by Ar3 and Ar4.
“X” in Structural Formulae 10 and 11 denotes a single bond, a substituted/unsubstituted alkylene group, a substituted/unsubstituted cycloalkylene group, a substituted/unsubstituted alkylene ether group, an oxgen atom, a sulfur atom or a vinylene group.
For the substituted/unsubstituted alkylene group, the following are suitable: straight-chain/branched-chain alkylene groups having C1 to C12, preferably C1 to C8, more preferably C1 to C4. These alkylene groups may have a phenyl group substituted with a fluorine atom, a hydroxyl group, a cyano group, an alkoxy group having C1 to C4, a phenyl group or a halogen atom, and an alkyl group having C1 to C4 or an alkoxy group having C1 to C4. Specific examples thereof include methylene groups, ethylene groups, n-butylene groups, i-propylene groups, t-butylene groups, s-butylene groups, n-propylene groups, trifluoromethylene groups, 2-hydroxyethylene groups, 2-ethoxyethylene groups, 2-cyanoethylene groups, 2-methoxyethylene groups, benzylidene groups, phenylethylene groups, 4-chlorophenylethylene groups, 4-methylphenylethylene groups and 4-biphenylethylene groups.
The substituted/unsubstituted cycloalkylene group is a cyclic alkylene group having C5 to C7. These cyclic alkylene groups may have a fluorine atom, a hydroxyl group, an alkyl group having C1 to C4 and an alkoxy group having C1 to C4. Specific examples thereof include cyclohexylidene group, cyclohexylene group and 3,3-dimethylcyclohexylidene group.
For the substituted/unsubstituted alkylene ether group, the following are suitable: ethyleneoxy, propyleneoxy, ethyleneglycol, propylenglycol, diethyleneglycol, tetraethyleneglycol, and tripropyleneglycol. The alkylene ether groups and the alkylene groups may have a substituent group such as hydroxyl group, methyl group and ethyl group.
Vinylene group are represented by
“Z” in Structural Formulae 10 and 11 denotes a substituted/unsubstituted alkylene group, a substituted/unsubstituted alkylene ether divalent group or an alkyleneoxycarbonyl divalent group.
Examples of the substituted/unsubstituted alkylene group include one similar to the alkylene group denoted by X.
Examples of the substituted/unsubstituted alkylene ether divalent group include the alkylene ether divalent group denoted by X.
Examples of the alkyleneoxycarbonyl divalent group include a caprolactone divalent modified group.
Also, examples of a monofunctional radical polymerizable compound having a charge transporting structure in the present invention include a compound having the structure shown in General Structural Formula (3).
(In Formula (3), “o”, “p” and “q” respectively denote an integer of 0 or 1; Ra denotes a hydrogen atom or a methyl group; Rb and Rc, which are substituent groups other than hydrogen atoms, denote alkyl groups of 1 to 6 in carbon number and may be different from each other in carbon number when their carbon numbers are 2 or more. “s” and “t” respectively denote an integer of 0 to 3. Za denotes a single bond, a methylene group or an ethylene group.)
For the compound represented by the general structural formula, a compound in which the substituent groups of Rb and Rc are methyl groups or ethyl groups is particularly favorable.
As to the monofunctional radical polymerizable compounds having charge transporting structures represented by General Structural Formulae (1) to (3), particularly the one represented by General Structural Formula (3), used in the present invention, since the monofunctional radical polymerizable compound is polymerized with double bonds between carbon atoms being open at both sides, they do not have a terminate structure and they are incorporated into chain polymers; when in polymers formed by crosslinking polymerization between the monofunctional radical polymerizable compounds and trifunctional or more radical polymerizable monomers, the monofunctional radical polymerizable compound exists in high-molecular main chains and also in crosslinked chains between main chains (a crosslinked chain is classified into an intermolecular crosslinked chain formed between one high molecule and another, and an intramolecular crosslinked chain in which a site where there is a folded main chain and a monomer-derived site polymerized in a position away from the foregoing site in the main chain are crosslinked in one high molecule); whether the monofunctional radical polymerizable compound exists in main chains or in crosslinked chains, triarylamine structures, which hang down from chain parts, each have at least three aryl groups disposed in radial directions from a nitrogen atom; although bulky, it is not that the triarylamine structures are directly combined to the chain parts, but the triarylamine structures are hanging down from the chain parts via carbonyl groups or the like, and so the triarylamine structures are fixed in such a manner as to allow for flexible steric positioning; thus, since these triarylamine structures can be spatially positioned in such a manner as to be suitably adjacent to each other in polymers, there is little structural distortion in molecules; also, when used as surface layers of electrophotographic photoconductors, it is inferred that intramolecular structures which are relatively free of severance of charge transport paths can be employed.
Specific examples of monofunctional radical polymerizable compounds having charge transporting structures in the present invention will be shown below; however, it should be noted that the monofunctional radical polymerizable compounds are not confined to the following compounds.
A monofunctional radical polymerizable compound having a charge transporting structure in the present invention plays an important role in adding to charge transporting performance of a crosslinked type protective layer, and the content of this monofunctional radical polymerizable compound in the crosslinked type protective layer is in the range of 20% by weight to 80% by weight, preferably in the range of 30% by weight to 70% by weight. When this monofunctional radical polymerizable compound contained is less than 20% by weight, charge transporting performance of a crosslinked type protective layer cannot be sufficiently retained, and deteriorations in electrical properties such as decrease in sensitivity and increase in residual potential tend to arise through repetitive use. When it is greater than 80% by weight, the contained amount of a trifunctional monomer having no charge transporting structure decreases, which causes the crosslinking bond density to decrease, and so high abrasion resistance tends to be difficult to perform. Since electrical properties and abrasion resistance required vary depending upon the process used, and thus the thickness of a crosslinked type protective layer in a photoconductor of the present invention varies, the amount of the monofunctional radical polymerizable compound cannot be unequivocally determined; however, in light of a balance between both electrical properties and abrasion resistance, it is most desirable that the monofunctional radical polymerizable compound contained be in the range of 30% by weight to 70% by weight.
A crosslinked type protective layer that is a component of an electrophotographic photoconductor of the present invention is formed by hardening at least a trifunctional or more radical polymerizable monomer having no charge transporting structure and a monofunctional radical polymerizable compound having a charge transporting structure; besides, monofunctional and difunctional radical polymerizable monomers, a functional monomer and a radical polymerizable oligomer can be additionally used for the purpose of adding functions, for example adjustment of viscosity at the time of coating, moderation of stress in the crosslinked type protective layer, reduction in surface energy and reduction in friction coefficient. For the radical polymerizable monomers and the radical polymerizable oligomer, conventional ones can be used.
Examples of monofunctional radical monomers include 2-ethylhexylacrylate, 2-hydroxyethylacrylate, 2-hydroxypropylacrylate, tetrahydrofurfrylacrylate, 2-ethylhexylcarbitolacrylate, 3-methoxybutylacrylate, benzylacrylate, cyclohexylacrylate, isoamylacrylate, isobutylacrylate, methoxytriethyleneglycolacrylate, phenoxytetraethyleneglycolacrylate, cetylacrylate, isostearylacrylate, stearylacrylate and styrene monomer.
Examples of difunctional radical polymerizable monomers include 1,3-butane dioldiacrylate, 1,4-butanedioldiacrylate, 1,4-butane dioldimethacrylate, 1,6-hexanedioldiacrylate, 1,6-hexanedioldimethacrylate, diethyleneglycoldiacrylate, neopentylglycoldiacrylatebisphenol B-EO-modified diacrylate, bisphenol F-EO-modified diacrylate and neopentylglocoldiacrylate.
Examples of functional monmers include fluorinated monomers such as octafluoropentylacrylate, 2-perfluorooctylethylacrylate, 2-perfluorooctylethylmethacrylate and 2-perfluoroisononylethylacrylate; monomers having polysiloxane groups such as acryloylpolydimethylsiloxaneethyl, methacryloylpolydimethylsiloxaneethyl, acryloylpolydimethylsiloxanepropyl, acryloylpolydimethylsiloxanebutyl and diacryloylpolydimethylsiloxanediethyl, which are between 20 and 70 in siloxane repeating unit as described in Japanese Patent Application Publication (JP-B) Nos. 05-60503 and 06-45770.
Examples of radical polymerizable oligomers include epoxyacrylate oligomers, urethaneacrylate oligomers and polyesteracrylate oligomers.
It should be noted that when monofunctional and difunctional radical polymerizable monomers and radical polymerizable oligomers are contained in large amounts, the three-dimensional crosslinking bond density in a crosslinked type protective layer, in effect, decreases and a decrease in abrasion resistance is brought about. Thus, it is desirable that the contained amount of these monomers and oligomers be 50 parts by weight or less, more desirably 30 parts by weight or less, in relation to 100 parts by weight of trifunctional or more radical polymerizable monomers.
Also, a crosslinked type protective layer of the present invention is formed by hardening at least a trifunctional or more radical polymerizable monomer having no charge transporting structure and a monofunctional radical polymerizable compound having a charge transporting structure; if necessary, a polymerization initiator may be contained in a crosslinked type protective layer coating solution to make this hardening reaction progress efficiently.
Examples of thermal polymerization initiators include peroxide -based initiators such as 2,5-dimethylhexane-2,5-dihydropar oxide, dicumylparoxide, benzoylparoxide, t-butylcumylpar oxide, 2,5-dimethyl-2,5-di(par oxybenzoyl)hexyne-3, di-t-butylbelloxide, t-butylhydronaliumbell oxide, cumene hydronalium belloxide, lauroylpar oxide and 2,2-bis (4,4-di-t-butyl par clohexy)propane; and azo based initiators, such as azobisisobutylnitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, azobisisobutylamidine hydrochloride and 4,4′-azobis-4-cyanovaleric acid.
Examples of photopolymerization initiators include acetophenone or ketal based photopolymerization initiators such as diethoxyacetophenone, 2,2-dimethoxy-, 2-diphenylethane-1-one, 1-hydroxy-cyclohexyl phenyl ketone, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 2-benzyl-2-dimethylamino-1-(4-morpholino phenyl)butanone-1, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 2-methyl-2-morpholino(4-methylthio phenyl)propan-1-one and 1-phenyl-1,2-propanedione-2-(o-carboethoxy)oxime; benzoin ether based photopolymerization initiators such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether and benzoin isopropyl ether; benzophenone based photopolymerization initiators such as benzophenone, 4-hydroxybenzophenone, methyl o-benzoylbenzoate, 2-benzoylnaphthalene, 4-benzoylbiphenyl, 4-benzoyl phenyl ether, acrylicized benzophenone and 1,4-benzoylbenzene; thio xanthone based photopolymerization initiators such as 2-isopropyl thioxanthone, 2-chloro thioxanthone, 2,4-dimethyl thioxanthone, 2,4-diethyl thioxanthone and 2,4-dichloro thioxanthone; and other photopolymerization initiators such as ethylanthraquinone, 2,4,6-trymethyl benzoic diphenyl phosphine acid, 4,6-trimethyl benzoic phenyl ethoxy phosphine oxide, bis(2,4,6-trimethyl benzoyl)phenylphosphine oxide, bis(2, 4-dimethoxybenzoyl)-2,4,4-trimethyl pentylphosphine oxide, methylphenyl glyoxylate ester, 9,10-phenanthrene, acridine compounds, triazine compound and imidazole compounds. Also, compounds having photopolymerization promoting effect may be used independently or together with the photopolymerization initiators. Examples thereof include triethanolamine, methyldiethanolamine, 4-dimethylamino ethyl benzoate, 4-dimethylamino isoamyl benzoate, ethyl benzoate(2-dimethylamino) and 4,4′-dimethylamino benzophenone.
Two or more types amongst these polymerization initiators may be mixed together. In relation to 100 parts by weight of a total contained material having radical polymerizability, the contained amount of a polymerization initiator is in the range of 0.5 parts by weight to 40 parts by weight, preferably in the range of 1 part by weight to 20 parts by weight.
Further, it is possible for a crosslinked type protective layer forming coating solution of the present invention to contain additives such as various types of plasticizers (for the purpose of moderating stress, improving adhesion, etc.), a leveling agent and a low-molecular charge transporting material without radical reactivity if necessary. Conventional ones can be used for these additives; for plasticizers, ones used in typical resins, such as dibutyl phthalate and dioctyl phthalate, can be utilized, and the amount of each plasticizer used is reduced to 20% by weight or less, preferably 10% by weight or less, in relation to a total solid content in the coating solution. For leveling agents, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having perfluoroalkyl groups for side chains can be used, and it is appropriate that the amount of each leveling agent used be 3% by weight or less in relation to a total solid content in the coating solution.
A crosslinked type protective layer of the present invention is formed, as a coating solution containing at least the trifunctional or more radical polymerizable monomer having no charge transporting structure and the monofunctional radical polymerizable compound having a charge transporting structure is applied onto the charge transporting layer and hardened. When the radical polymerizable monomer is a liquid, the coating solution can be applied, with another component dissolved in the radical polymerizable monomer; if necessary, a solvent is used to dilute the coating solution. Examples of a solvent used on this occasion include alcohols such as methanol, ethanol, propanol and butanol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as tetrahydrofuran, dioxane and propyl ether, halogens such as dichloromethane, dichloroethane, trichloroethane and chlorobenzene, aromatics such as benzene, toluene and xylene; and cellosolves such as methylcellosolve, ethylcellosolve and cellosolve acetate. These solvents may be used alone or in combination with two or more. The dilution ratio of a coating solution by a solvent varies according to the solubility of a component, the coating method employed and the desired layer thickness, and can be arbitrarily decided. Coating can be carried out by means of an immersion coating method, spray coating, beat coating, ring coating or the like.
In the present invention, after the crosslinked type protective layer coating solution is applied, it is hardened with energy from outside given to it, and a crosslinked type protective layer is thus formed; examples of the external energy used on this occasion include heat, steam and radiant rays. As a method for applying thermal energy, the crosslinked type protective layer coating solution is heated from the coating surface side or the support side, using a gas such as air or nitrogen, steam, a thermal medium selected from various types, infrared rays or electromagnetic waves. It is desirable that the heating temperature be in the range of 100° C. to 170° C.; when it is less than 100° C., the reaction rate is low, and hardening reaction tends to be incomplete. When it stands at a high temperature greater than 170° C., hardening reaction progresses unevenly, and a great distortion, a large number of unreacted residues and unreactive termini arise in the crosslinked type protective layer. To make hardening reaction progress evenly, a method in which after heating takes place at a relatively low temperature of less than 100° C., heating takes place at 100° C. or more, and reaction is thus completed is also effective. For light energy, a UV irradiation light source such as a high-pressure mercury-vapor lamp or metal halide lamp having an emission wavelength in an ultraviolet region can be used mainly; also, a visible light source can be selected according to the absorption wavelength of a radical polymerizable contained material or a photopolymerization initiator. It is desirable that the amount of irradiating light be in the range of 50 mW/cm2 to 1,000 mW/cm2; when it is less than 50 mW/cm2, hardening reaction takes more time. When it is 1,000 mW/cm2 or greater, reaction progresses unevenly, causing local creases to arise on the crosslinked type protective layer surface, and also causing a large number of unreacted residues and unreactive termini to arise. Also, the abrupt crosslinkage makes internal stress greater, which is a cause of cracks and film peeling. Examples of radiant energy include a thing using electron rays. Amongst these types of energy, thermal energy and light energy are useful in that the reaction rate can be controlled with ease and an apparatus can be simplified.
It is desirable that the thickness of a crosslinked type protective layer of the present invention be 1 μm to 10 μm, more desirably 2 μm to 8 μm. When it is greater than 10 μm, cracks and film peeling are liable to arise as described above; when it is 8 μm or less, improvement in a margin makes it possible to increase the crosslink density, and further, to select a material which enhances abrasion resistance and set hardening conditions. Meanwhile, radical polymerization reaction is easily hindered by oxygen; specifically, on a surface contiguous to the air, crosslinkage is liable to stop progressing or become uneven, affected by a radical trap which is due to oxygen. This effect becomes conspicuous when the surface layer is less than 1 μm, and the crosslinked type protective layer of this thickness or smaller is liable to cause a decrease in abrasion resistance and uneven abrasion. Also, when the crosslinked type protective layer coating solution is applied, the components of the charge transporting layer, which is the under layer of the crosslinked type protective layer, are mixed therein, in particular, the mixed components spread throughout the crosslinked type protective layer, thereby hindering hardening reaction and decreasing the crosslink density. For these reasons, the crosslinked type protective layer used in the present invention has favorable abrasion resistance and scratch resistance when it is 1 μm or more in thickness; however, when the crosslinked type protective layer is locally peeled off as far as the charge transporting layer that is an under layer through repetitive use, abrasion at the locally peeled portions increases, and so the density of halftone images is liable to become uneven owing to variations in charging properties and sensitivity. Therefore, to achieve a long lifetime and high image quality, it is desirable that the film thickness of a crosslinked type protective layer be 2 μm or more.
A structure in which a charge blocking layer, a moire prevention layer, a photosensitive layer (charge generating layer and charge transporting layer) and a crosslinked type protective layer of an electrophotographic photoconductor of the present invention are formed in this order in a multi-layered structure is characterized in that when the crosslinked type protective layer, which is a top surface, is insoluble in organic solvent, a dramatic improvement in abrasion resistance and scratch resistance can be achieved. As for a method of testing the solubility in the organic solvent, one droplet of an organic solvent which greatly dissolves high-molecular materials, such as tetrahydrofuran or dichloromethane, is applied onto the photoconductor surface layer, and a deformation of the photoconductor surface is observed under a stereomicroscope after the droplet has been naturally dried, thereby making it possible to measure the solubility. A highly soluble photoconductor experiences changes, including a phenomenon in which the central part of the liquid droplet becomes concave and its vicinity protrudes upward, a phenomenon in which the charge transporting material is deposited and white turbidity or loss of transparency is caused by the crystallization, and a phenomenon in which creases arise as a surface swells and later contracts. Conversely, not experiencing the phenomena, an insoluble photoconductor stays exactly the same as it was before a droplet has been applied.
In order to make the crosslinked type protective layer insoluble in organic solvent in the present invention, it is important to control the following: (1) adjustment of contents of composition components for the crosslinked type protective layer coating solution; (2) adjustment of the solid content concentration of a diluent solvent for the crosslinked type protective layer coating solution; (3) selection of a coating method for the crosslinked type protective layer; (4) control of hardening conditions for the crosslinked type protective layer; (5) achievement of low solubility of a charge transporting layer that is the under layer. However, it is not that the insolubility of the crosslinked type protective layer in organic solvent is achieved by one factor alone.
As to the composition components of the crosslinked type protective layer coating solution, when additives such as a binder resin having no radical polymerizable functional group, an antioxidant and a plasticizer are contained in large amounts besides the trifunctional or more radical polymerizable monomer having no charge transporting structure and the monofunctional radical polymerizable compound having a charge transporting structure, the crosslink density decreases and a phase separation between hardened materials created as a result of a reaction and the additive materials arises; thus, the crosslinked type protective layer coating solution tends to be soluble in organic solvent. Specifically, it is important that the total content of the additive materials be reduced to 20% by weight or less in relation to a total solid content in the coating solution. Also, in order to prevent the crosslink density from lowering, it is desirable that the total content of a difunctional radical polymerizable monomer, a reactive oligomer and a reactive polymer be 20% by weight or less to a trifunctional radical polymerizable monomer. Further, when a difunctional or more radical polymerizable compound having a charge transporting structure is contained in large amounts, the structural body that is large in volume is fixed in a crosslinked structure by a plurality of bonds, which causes distortion to arise easily, and the crosslinked type protective layer coating solution tends to be an aggregate of minute hardened materials. It is possible that the crosslinked type protective layer coating solution may become soluble in organic solvent as a result of this. Although it depends upon the compound structure, it is desirable that the content of a difunctional or more radical polymerizable compound having a charge transporting structure be 10% by weight or less to the monofunctional radical polymerizable compound having a charge transporting structure.
As to the diluent solvent for the crosslinked type protective layer coating solution, when a solvent low in evaporation rate is used, it is possible that a residual solvent may hamper hardening and may increase the mixed amount of the layer components, and therefore uneven hardening and a decrease in hardening density may be brought about. Thus, the crosslinked type protective layer coating solution tends to be soluble in organic solvent. Specifically, tetrahydrofuran, a mixed solvent of tetrahydrofuran and methanol, ethyl acetate, methyl ethyl ketone, ethylcellosolve or the like is useful; however, a diluent solvent is selected according to the coating method. As for the density of the solid content, when it is very low for a similar reason, the crosslinked type protective layer coating solution tends to be soluble in organic solvent. Due to restrictions on the layer thickness and the coating solution viscosity, there are limitations on a maximum density. Specifically, it is desirable that a diluting solvent be contained by the range of 10% by weight to 50% by weight. As a coating method for a crosslinked type protective layer, a method of reducing the content of a solvent when a coating film is formed and reducing the time during which to be contiguous with the solvent is suitable for a similar reason; specifically, a spray coating method, and a ring coating method whereby the amount of a coating solution is restricted are suitable. Also, use of a high-molecular charge transporting material as a charge transporting layer and formation of an intermediate layer insoluble in the coating solvent for the crosslinked type protective layer between a photosensitive layer (or the charge transporting layer) and the crosslinked type protective layer are effective means of preventing the mixed amount of the components of the under layer.
As for hardening conditions for the crosslinked type protective layer, when the energy of heating or light irradiation is low, hardening is not completed and solubility in organic solvent increases. Conversely, when the crosslinked type protective layer is hardened with very high energy, hardening reaction becomes uneven, the number of uncrosslinked parts and radical stoppage portions increases and the crosslinked type protective layer is liable to be an aggregate of minute hardened materials. For this reason, it is possible that the crosslinked type protective layer may be soluble in organic solvent. To make it insoluble in organic solvent, such thermal hardening conditions as 100° C. to 170° C. and 10 min to 3 hr are favorable, and such hardening conditions by means of UV light irradiation as 50 W/cm2 to 1,000 mW/cm2, 5 sec to 5 min and limitation of a temperature rise to 50° C. or less for preventing uneven hardening reaction are favorable.
A method for making a crosslinked type protective layer constituting the electrophotographic photoconductor of the present invention, insoluble in organic solvent is mentioned as follows. For example, when an acrylate monomer having three acryloyloxy groups and a triarylamine compound having one acryloyloxy group are used for the coating solution, the content ratio is in the range of 7:3 to 3:7, a polymerization initiator is added by 3% by weight to 20% by weight in relation to the total amount of these acrylate compounds, and a solvent is added to prepare the coating solution. For example, in a charge transporting layer that is an under layer of the crosslinked type protective layer, when a triarylamine-based donor is used for a charge transporting material, polycarbonate is used for the binder resin and the surface layer is formed by means of spray coating, it is desirable that a solvent for the coating solution be tetrahydrofuran, 2-butanone, ethyl acetate or the like, and the amount of it used is 3 times to 10 times the total amount of the acrylate compounds.
Subsequently, for example, by means of spraying or the like, the coating solution prepared is applied onto a photoconductor in which an intermediate layer, a charge generating layer and the charge transporting layer are formed in this order in a multi-layered structure on a support such as an aluminum cylinder. After that, the coating solution is dried naturally or dried at a relatively low temperature for a short period of time (25° C. to 80° C., 1 min to 10 min), and then hardened by UV irradiation or heating.
In the case of UV irradiation, a metal halide lamp or the like is used; it is desirable that the illuminance be in the range of 50 W/cm2 to 1,000 mW/cm2 and that the time be in the range of 5 sec to 5 min or so, and the drum temperature is controlled in such a manner as not to be greater than 50° C.
In the case of thermal hardening, it is desirable that the heating temperature be in the range of 100° C. to 170° C.; for example, when an air blasting type oven is used as a heating unit and the heating temperature is set at 150° C., the heating time will be in the range of 20 min to 3 hr.
After the hardening is finished, the coating solution is further heated at a temperature of 100° C. to 150° C. for 10 min to 30 min to reduce residual solvent, and a photoconductor of the present invention is thus obtained.
Also, besides the protective layer containing a filler and the crosslinked type protective layer, it is possible to use for a protective layer a conventional material such as a-C or a-SiC formed by a vacuum thin film forming method.
As described above, when a protective layer is formed on a photoconductor, charge eliminating light may not sufficiently reach a photosensitive layer and so charge elimination may not definitely function, unless an appropriate protective layer is selected. Also, since the protective layer absorbs charge eliminating light, the photosensitive layer may deteriorate and a rise in residual potential may be caused. Therefore, in any of the protective layers, it is desirable that the transmittance thereof be 30% or more, more desirably 50% or more, even more desirably 85% or more to a charge eliminating light used.
As described above, forming a protective layer on the surface of a photoconductor not only enhances the durability (abrasion resistance) of the photoconductor, but also produces a novel effect which monochrome image forming apparatuses do not have, when used in an after-mentioned tandem-type full-color image forming apparatus.
In the present invention, in an attempt to improve environment resistance, it is possible to add an antioxidant to respective layers of the protective layer, the charge transporting layer, the charge generating layer, the charge blocking layer, the moire prevention layer, etc., especially for the purpose of preventing a decrease in sensitivity and an increase in residual potential.
2,6-di-t-butyl-p-cresol, butylated hydroxyanisole, 2,6-di-t-butyl-4-ethylphenol, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2″-methylene-bis-(4-methyl-6-t-butylphenol), 2,2″-methylene-bis-(4-ethyl-6-t-butylphenol), 4,4″-thiobis-(3-methyl-6-t-butylphenol), 4,4″-butylidenebis-(3-methyl-6-t-butylphenol), 1,1,3-tris-(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis-[methylene-3-(3″,5″-di-t-butyl-4″-hydroxyphenyl)propionate]methane, and bis[3,3″-bis(4″-hydroxy-3″-t-butylphenyl)butylic acid]glycol ester, tocopherols and the like.
(P-phenylenediamines)
N-phenyl-N′-isopropyl-p-phenylenediamine, N,N′-di-sec-butyl-p-phenylenediamine, N-phenyl-N-sec-butyl-p-phenylenediamine, N,N′-di-isopropyl-p-phenylenediamine, N,N′-dimethyl-N,N′-di-t-butyl-p-phenylenediamine and the like.
(Hydroquinones)
2,5-di-t-octylhydroquinone, 2,6-didodecylhydroquinone, 2-dodecylhydroquinone, 2-dodecyl-5-chlorohydroquinone, 2-t-octyl-5-methylhydroquinone, 2-(2-octadecenyl)-5-methylhydroquinone and the like.
(Organic Sulfur Compounds)
lauryl-3,3′-thiodipropionate, “distearyl-3,3′-thiodipropionate, “ditetradecyl-3,3′-thiodipropionate and the like.
(Organic Phosphorus Compound)
triphenylphosphine, tri(nonylphenyl)phosphine, tri(dinonylphenyl)phosphine, tricresylphosphine, tri(2,4-dibutylphenoxy)phosphine and the like.
The compounds are known as antioxidants of rubbers, plastics, oils and fats, etc., and commercially-supplied antioxidants can be obtained with ease. The additive amount of antioxidants in the present invention is in the range of 0.01% by weight to 10% by weight to the gross weight of the layers to which the antioxidants are added.
In the case of full-color images, images of a variety of forms are input; conversely, images of fixed forms may also be input. For example, there are stamps of approval seen in Japanese documents and the like. Things like stamps of approval are normally positioned in the vicinity of ends of an image area, and colors used for them are limited. Image writing, developing and transfer are performed on a photoconductor in image forming elements on an average basis when images are always written in a random manner; conversely, when a large number of image formations are repeated in particular parts or particular image forming elements are exclusively used as described above, there will be lack of a balance with respect to the durability of the photoconductor. When a photoconductor which is (physically/chemically/mechanically) small in surficial durability is used under these conditions, lack of durability becomes conspicuous, leading to problems on images. Meanwhile, when a photoconductor is made highly durable, local variations of this type are small, thereby being unlikely to result in defects on images; therefore, the photoconductor is very effective in that high durability can be achieved and also output images can be made more stable.
Hereinafter, the present invention will be further described referring to specific Examples, however, the present invention is not limited to the following Examples. Note that the following unit term of “part” or “parts” respectively means “part by mass” or “parts by mass”.
First, the method of synthesizing an azo pigment and a titanylphthalocyanine crystal will be described. The azo pigments used in the following Examples were prepared according to the method described in Japanese Patent Application Laid-Open (JP-A) No. 60-29109 and Japanese Patent (JP-B) No. 3026645. The titanylphthalocyanine crystal used in the following Examples was prepared according to the method described in Japanese Patent (JP-B) No. 2004-83859.
A pigment was produced according to the Example 1 described in Japanese Patent Application Laid-Open (JP-A) No. 2004-83859.
Specifically, 292 g of 1,3-diiminoisoindline and 1,800 parts of sulfolane were mixed, and 20.4 g of titanium tetrabutoxide was delivered by drops into the mixture in a nitrogen gas stream. Upon completion of the dropping, the temperature of the mixture was gradually increased to 180° C. and then stirred and reacted for 5 hours while keeping the reaction temperature from 170° C. to 180° C. After completion of the reaction, the reactant was naturally cooled, and the precipitate was filtered and the filtrated precipitate was washed until the powder of the precipitate turned into blue by chloroform. Next, the powder was washed with methanol several times and further washed with 80° C. hot water several times and then dried to obtain a coarse titanylphthalocyanine. The coarse titanylphthalocyanine was dissolved in 20 times its volume of a sulfuric acid, and the titanylphthalocyanine solution was delivered by drops into 100 times its volume of ice water with stirring to obtain a precipitate of crystal. The precipitated crystal was filtered and then repeatedly washed with ion exchange water (pH: 7.0; relative conductivity: 1.0 μS/cm) until the wash solution became neutral (the pH value of the ion exchange water after washing was 6.8 and the relative conductivity was 2.6 μS/cm), thereby obtaining a titanylphthalocyanine pigment wet cake (water paste).
Forty grams of the obtained wet cake (water paste) was put in 200 g of tetrahydrofuran and the mixture was strongly stirred in a homomixer (MARKII f-Model, manufactured by KENIS, Ltd. at 2,000 rpm at room temperature. When the navy blue color of the paste turned into light blue (20 minutes later from the start of stirring), the stirring was stopped. Immediately after that, the mixture was filtered under reduced pressure. A crystal obtained in the filtration equipment was washed with tetrahydrofuran to thereby obtain a pigment wet cake. The pigment wet cake was dried at 70° C. under reduced pressure (5 mmHg) for two days to obtain 8.5 parts by mass of a titanylphthalocyanine crystal. This was termed as Pigment A-1. The solid content of the wet cake was 15% by mass. A crystal conversion solvent of 33 times the volume of the wet cake based on mass ratio was used. Note that no halogen-containing compound was used in raw materials of Synthesis Example A-1. The obtained titanylphthalocyanine powder was measured by an X-ray diffractometer under the following conditions, and it was found that a titanylphthalocyanine powder having a maximum peak at 27.2±0.2° of Bragg angle 2θ with respect to Cu—Kα line (wavelength: 1.542 angstrom), a peak at 7.3±0.2° of the minimum angle and further having primary peaks at 9.4±0.2°, 9.6±0.2°, 24.0±0.2° and having no peak in between the peak of 7.3° and the peak of 9.4°, further having no peak at 26.3° was obtained.
Apart of the water paste obtained in Synthesis Example A-1 was dried at 80° C. under reduced pressure (5 mmHg) for 2 days to thereby obtain a low-crystalline titanylphthalocyanine powder.
X-ray tube: Cu
Power voltage: 50 kV
Power current: 30 mA
Scanning rate: 2°/min
Scanning range: 30 to 400
Time constant: 2 seconds
A part of the titanylphthalocyanine (water paste) before the crystal conversion prepared in Synthesis Example A-1 was diluted with ion exchange water so as to be about 1% by mass and the surface of the diluted suspension was skimmed with a copper skimmer subjected to a conductive treatment. Then, the titanylphthalocyanine was observed to determine the particle diameter with a transmission electron microscope (TEM, H-9000 NAR, manufactured by Hitachi, Ltd.) at 75,000-fold magnification. The average particle diameter was determined as follows.
The TEM image observed as above was printed on a film as a TEM photograph. From the projected titanylphthalocyanine particles, 30 particles having a needle-like shape were arbitrarily selected and the longest diameter of the respective particles was measured. The total measurement value of the longest diameters of the 30 particles was averaged out and the average value was regarded as the average particle diameter of the titanylphthalocyanine particles.
The average particle diameter of titanylphthalocyanine in the water paste (wet cake) in Synthesis Example A-1 determined by the above-noted method was 0.06 μm.
Further, the crystal-converted titanylphthalocyanine crystal immediately before the filtration in Synthesis Example A-1 was diluted with tetrahydrofuran so as to be about 1% by mass and the surface of the diluted suspension was observed in the same manner as described above. The average particle diameter determined by the same method as described above was shown in Table A-1. Note that in the titanylphthalocyanine crystal prepared in Synthesis Example A-1, all the crystal particles did not necessarily have the same shape, i.e., there were crystal particles having an approximately triangular or quadrangular shape, however, the crystal particles were similar in size. For this reason, the average particle diameter was calculated assuming the length of the longest diagonal line of the crystal particle was the longest diameter. As a result, the average particle diameter was 0.12 μm.
The pigment A-1 prepared in Synthesis Example A-1 was dispersed in the following composition under the following conditions to prepare a dispersion as a charge-generating layer coating solution.
In a commercially available bead mill, the 2-butanone with the polyvinylbutyral dissolved therein and the titanylphthalocyanine pigment (Pigment A-1) were put and the components were dispersed using a PSZ ball having a diameter of 0.5 mm at a rotor speed of 1,200 rpm for 30 minutes to thereby prepare a dispersion. This was named as Dispersion A-1.
The following composition was dispersed under the following conditions to prepare a dispersion as a charge generating coating solution.
In a bead mill, a solvent (2-butanone) with the polyvinylbutyral dissolved therein and the azo pigment were put and the components were dispersed using a PSZ ball having a diameter of 10 mm at a rotor speed of 85 rpm for 7 days to thereby prepare a dispersion. This was named as Dispersion A-2.
A dispersion (Dispersion A-3) was prepared in the same manner as in Dispersion Preparation Example A-2, except that the azo pigment used in Dispersion Preparation Example A-2 was changed to a pigment represented by the following structural formula.
The particle size distribution of the pigment particle in the dispersion prepared as above was measured by a particle size distribution analyzer (CAPA-700, manufactured by HORIBA Instruments Inc.). Table A-1 shows the result.
Over the surface of an aluminum drum (JIS 1050) having an external diameter of 60 mm, an intermediate coating solution, a charge generating layer coating solution and a charge transporting coating solution each having the following composition were applied sequentially, the applied coating solutions were sequentially dried to form an intermediate layer having a thickness of 3.5 μm, a charge generating layer having a thickness of 0.5 μm and a charge transporting layer having a thickness of 17 μm, thereby preparing a multi-layered photoconductor (electrophotographic photoconductor 1a).
The Dispersion A-2 prepared as above was used.
A photoconductor (photoconductor 2a) was prepared in the same manner as in Photoconductor Preparation Example A-1, except that the layer thickness of the charge transporting layer formed in Photoconductor Preparation Example A-1 was changed to 27 μm.
A photoconductor (photoconductor 3a) was prepared in the same manner as in Photoconductor Preparation Example A-1, except that the layer thickness of the charge transporting layer was changed to 37 μm.
A photoconductor (photoconductor 4a) was prepared in the same manner as in Photoconductor Preparation Example A-1, except that the layer thickness of the charge transporting layer was changed to 15 μm and a protective layer having the following composition and a thickness of 1 μm was formed on the charge transporting layer.
A photoconductor (photoconductor 5a) was prepared in the same manner as in Photoconductor Preparation Example A-4, except that the layer thickness of the protective layer was changed to 7 μm.
A photoconductor (photoconductor 6a) was prepared in the same manner as in Photoconductor Preparation Example A-1, except that the layer thickness of the charge transporting layer was changed to 15 μm and a protective layer having the following composition and a thickness of 1 μm was formed on the charge transporting layer.
The protective layer was formed as follows. The charge transporting layer surface was spray-coated with the protective layer coating solution, the applied protective layer coating solution was naturally dried for 20 minutes, and the coated layer was photo-irradiated under the conditions of metal halide lamp: 160 W/cm, irradiation intensity: 500 mW/cm2 and irradiation time: 60 seconds.
A photoconductor (photoconductor 7a) was prepared in the same manner as in Photoconductor Preparation Example A-6, except that the layer thickness of the protective layer was changed to 8 μm.
A photoconductor (photoconductor 8a) was prepared in the same manner as in Photoconductor Preparation Example A-1, except that the intermediate layer formed in Photoconductor Preparation Example A-1 was changed so as to have a multi-layered structure composed of a charge blocking layer and a moire prevention layer, a charge blocking layer coating solution and a moire prevention layer coating solution each having the following composition were sequentially applied over the surface of an aluminum drum and the respectively applied coating solutions were dried to form a charge blocking layer having a thickness of 1.0 μm and a moire prevention layer having a thickness of 3.5 μm.
A photoconductor (photoconductor 9a) was prepared in the same manner as in Photoconductor Preparation Example A-1, except that the Dispersion A-3 was used instead of the charge generating coating solution used in Photoconductor Preparation Example A-1.
The transit time of the prepared photoconductors 1a and 9a was determined as described below.
The potential at an exposed region of the respective photoconductors was determined under the following conditions using the equipment described in Japanese Patent Application Laid-Open (JP-A) No. 2000-275872 (shown in
Linear velocity of photoconductor: 262 mm/sec
Resolution in the sub-scanning direction: 400 dpi
Static power in image surface: 0.3 mW (exposure dose: 0.4 μJ/cm2)
Wavelength of writing light: 655 nm
Charge elimination device: activated
Charging condition: the charged amount of the photoconductor surface was controlled such that the surface potential before writing was set to −800V.
Under the above-mentioned conditions, a surface electrometer set to the developing position, as shown in
The thus obtained potential values in the exposed region of the respective photoconductors were individually plotted with respect to the exposing-to-developing time lengths as shown in
The photoconductor “1a” prepared in Photoconductor Preparation Example A-1 was mounted in an image forming apparatus as shown in
Since the image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°, and the linear velocity of the photoconductor was 480 mm/sec, the LDs were arranged so that the time length the arbitrarily determined point on the photoconductor irradiated with the writing light reaching the center of the developing sleeve (exposing-to-developing time length) was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias)
Surface potential of exposed region: −120 V (potential used in solid part of image)
The potential at an exposed region in each of the prepared photoconductors was measured by the following method. Specifically, a surface potential meter was mounted to a position of the developing unit as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table A-3 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table A-3 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
The electrophotographic photoconductors 2a to 9a prepared in Photoconductor Preparation Examples A-2 to A-9 were evaluated in the same conditions as in Example A-1. Table A-3 shows the evaluation results. Table A-3 also shows the electrophotographic photoconductor numbers used in Examples A-2 to A-6 and Comparative Examples A-1 to A-3.
In Examples A-2 to A-6 and Comparative Examples A-1 to A-3, to obtain the above-noted exposing-to-developing time lengths, the angle of the electrometer was set to the following degrees.
The results shown in Table A-3 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples A-1 to A-6), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-1 to A-3), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples A-1 to A-6), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-1 to A-3), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Further, from the evaluation results using a blank image, the evaluation rank of background smear could be elevated and the improvement effect could be kept up even after repetitive use by making an intermediate layer have a multi-layered structure composed of a charge blocking layer and a moire prevention layer (Example A-5).
Furthermore, in a comparison between Example A-1 and Example A-6, the surface potential at the exposed region in the photoconductor 1a used in A-1 was lower than that of the photoconductor 9a used in Example A-6. This shows that the asymmetrical azo pigment used in the photoconductor 1a contributed to the high-photosensitivity.
Photoconductors were respectively prepared in the same manner as in Photoconductor Preparation Examples A-1 to A-8, except that the respective charge generating layer coating solutions used in Photoconductor Preparation Examples A-1 to A-8 were changed to Dispersion A-1 (the prepared photoconductors were named as photoconductors 10a to 17a in this order).
The transit time length of the prepared photoconductors 10a to 17a was determined as described below.
The potential at an exposed region of the respective photoconductors was determined under the following conditions using the equipment described in Japanese Patent Application Laid-Open (JP-A) No. 2000-275872 (shown in
Linear velocity of photoconductor: 262 mm/sec
Resolution in the sub-scanning direction: 400 dpi
Static power in image surface: 0.3 mW (exposure dose: 0.4 μJ/cm2)
Wavelength of writing light: 780 nm
Charge elimination device: activated
Charging condition: the charged amount of the photoconductor surface was controlled such that the surface potential before writing was set to −800V.
Under the above-mentioned conditions, a surface electrometer set to the developing position, as shown in
The thus obtained potential values in the exposed region of the respective photoconductors were individually plotted with respect to the exposing-to-developing time lengths as shown in
The prepared electrophotographic photoconductor 10a was attached to a process cartridge and the process cartridge was placed in an image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias)
Surface potential of exposed region: −150 V
The potential at an exposed region in each of the prepared photoconductors was measured by the following method. Specifically, a surface potential meter was mounted to a position of a developing unit of magenta station as shown in
After negatively charging each of the photoconductors to −800 V, 10,000 sheets in total of the image were printed out in succession using the image forming apparatus. An image printed out in the initial stage and an image printed out after outputting the 10,000 sheets were evaluated. The level of image density was ranked according to the following four grades. A photoconductor provided extremely favorable image density was ranked A, a photoconductor provided favorable image density was ranked B, a photoconductor provided slightly poor image density was ranked C and a photoconductor provided extremely poor image density was ranked D. Table A-5 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (1) to (3) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Electrophotographic photoconductors 11a to 17a prepared as described above under the same conditions as in Example A-7 were evaluated. Table A-5 shows the result. Table A-5 also shows the electrophotographic photoconductor numbers used in Examples A-8 to A-11 and Comparative Examples A-4 to A-6.
The results shown in Table A-5 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples A-7 to A-11), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-4 to A-6), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples A-7 to A-11), the image density was high, and even after repetitive use of the photoconductors, excellent color images could be formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-4 to A-6), the image density was lowered after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples A-7 to A-11), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-4 to A-6), the residual image level was degraded after repetitive use of the photoconductors.
Photoconductors were prepared in the same manner as in Photoconductor Preparation Examples A-10 to A-17, except that the conductive support used in Photoconductor Preparation Examples A-10 to A-17 was changed to a nickel (Ni) belt having an external diameter of 168 mm (the prepared photoconductors were named as photoconductors 18a to 25a in this order).
The transit time length of the prepared photoconductors 18a to 25a was determined as described below.
The potential at an exposed region of the respective photoconductors was determined under the following conditions using the equipment described in Japanese Patent Application Laid-Open (JP-A) No. 2000-275872 (shown in
Linear velocity of photoconductor: 262 mm/sec
Resolution in the sub-scanning direction: 400 dpi
Static power in image surface: 0.3 mW (exposure dose: 0.4 μJ/cm2)
Wavelength of writing light: 780 nm
Charge elimination device: activated
Charging condition: the charged amount of the photoconductor surface was controlled such that the surface potential before writing was set to −800V.
Under the above-mentioned conditions, a surface electrometer set to the developing position, as shown in
The thus obtained potential values in the exposed region of the respective photoconductors were individually plotted with respect to the exposing-to-developing time lengths as shown in
The thus prepared photoconductor A-18 was placed in an image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias)
Surface potential of exposed region: −80 V (potential at solid part of image)
The potential at an exposed region in each of the prepared photoconductors was measured by the following method. Specifically, a surface potential meter was mounted to a position of the developing unit as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table A-7 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table A-7 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Electrophotographic photoconductors 19a to 25a prepared as described above under the same conditions as in Example A-12 were evaluated. Table A-7 shows the result. Table A-7 also shows the electrophotographic photoconductor numbers used in Examples A-13 to A-16 and Comparative Examples A-7 to A-9.
The results shown in Table A-7 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples A-12 to A-16), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-7 to A-9), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples A-12 to A-16), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-7 to A-9), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Further, from the evaluation results using a blank image, the evaluation rank of background smear could be elevated and the improvement effect could be kept up even after repetitive use by making an intermediate layer have a multi-layered structure composed of a charge blocking layer and a moire prevention layer
The prepared electrophotographic photoconductor 18a was attached to a process cartridge, and the process cartridge was placed in an image forming apparatus having a structure as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias) Surface potential of exposed region: −150 V (potential at solid part of image)
The potential at an exposed region in each of the prepared photoconductors was measured by the following method. Specifically, a surface potential meter was mounted to a position of a developing unit of magenta station as shown in
Using the image forming apparatus, 10,000 sheets of an ISO/JIS-SCID image N1 (portrait) were output, and the color reproductivity of the image print was visually checked and evaluated. The level of color reproductivity was ranked according to the following four grades. A photoconductor provided extremely favorable color reproductivity was ranked A, a photoconductor provided favorable color reproductivity was ranked B, a photoconductor provided slightly poor color reproductivity was ranked C and a photoconductor provided extremely poor color reproductivity was ranked D. Table A-8 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (1) to (3) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Electrophotographic photoconductors 19a to 25a prepared as described above under the same conditions as in Example A-17 were evaluated. Table A-8 shows the result. Table A-8 also shows the electrophotographic photoconductor numbers used in Examples A-18 to A-21 and Comparative Examples A-10 to A-12.
The results shown in Table A-8 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples A-17 to A-21), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-10 to A-12), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples A-17 to A-21), the color reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent color image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-10 to A-12), the color reproductivity was degraded after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples A-17 to A-21), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples A-10 to A-12), the residual image level was degraded after repetitive use of the photoconductors.
A pigment was produced according to the Example 1 described in Japanese Patent Application Laid-Open (JP-A) No. 2004-83859.
Specifically, 292 g of 1,3-diiminoisoindline and 1,800 parts of sulfolane were mixed, and 20.4 g of titanium tetrabutoxide was delivered by drops into the mixture in a nitrogen gas stream. Upon completion of the dropping, the temperature of the mixture was gradually increased to 180° C. and then stirred and reacted for 5 hours while keeping the reaction temperature from 170° C. to 180° C. After completion of the reaction, the reactant was naturally cooled, and the precipitate was filtered and the filtrated precipitate was washed until the powder of the precipitate turned into blue by chloroform. Next, the powder was washed with methanol several times and further washed with 80° C. hot water several times and then dried to obtain a coarse titanylphthalocyanine. The coarse titanylphthalocyanine was dissolved in 20 times its volume of a sulfuric acid, and the titanylphthalocyanine solution was delivered by drops into 100 times its volume of ice water with stirring to obtain a precipitate of crystal. The precipitated crystal was filtered and then repeatedly washed with ion exchange water (pH: 7.0; relative conductivity: 1.0 μS/cm) until the wash solution became neutral (the pH value of the ion exchange water after washing was 6.8 and the relative conductivity was 2.6 μS/cm), thereby obtaining a titanylphthalocyanine pigment wet cake (water paste).
Forty grams of the obtained wet cake (water paste) was put in 200 g of tetrahydrofuran and the mixture was strongly stirred in a homomixer (MARKII f-Model, manufactured by KENIS, Ltd. at 2,000 rpm at room temperature. When the navy blue color of the paste turned into light blue (20 minutes later from the start of stirring), the stirring was stopped. Immediately after that, the mixture was filtered under reduced pressure. A crystal obtained in the filtration equipment was washed with tetrahydrofuran to thereby obtain a pigment wet cake. The pigment wet cake was dried at 70° C. under reduced pressure (5 mmHg) for two days to obtain 8.5 parts by mass of a titanylphthalocyanine crystal. This was termed as Pigment B-1. The solid content of the wet cake was 15% by mass. A crystal conversion solvent of 33 times the volume of the wet cake based on mass ratio was used. Note that no halogen-containing compound was used in raw materials of Synthesis Example B-1. The obtained titanylphthalocyanine powder was measured by an X-ray diffractometer under the following conditions, and it was found that a titanylphthalocyanine powder having a maximum peak at 27.2±0.2° of Bragg angle 2θ with respect to Cu—Kα line (wavelength: 1.542 angstrom), a peak at 7.3±0.2° of the minimum angle and further having primary peaks at 9.4±0.2°, 9.6±0.2°, 24.0±0.2° and having no peak in between the peak of 7.3° and the peak of 9.4°, further having no peak at 26.3° was obtained.
A part of the water paste obtained in Synthesis Example B-1 was dried at 80° C. under reduced pressure (5 mmHg) for 2 days to thereby obtain a low-crystalline titanylphthalocyanine powder.
X-ray tube: Cu
Power voltage: 50 kV
Power current: 30 mA
Scanning rate: 2°/min
Scanning range: 3° to 40°
Time constant: 2 seconds
A part of the titanylphthalocyanine (water paste) before the crystal conversion prepared in Synthesis Example B-1 was diluted with ion exchange water so as to be about 1% by mass and the surface of the diluted suspension was skimmed with a copper skimmer subjected to a conductive treatment. Then, the titanylphthalocyanine was observed to determine the particle diameter with a transmission electron microscope (TEM, H-9000 NAR, manufactured by Hitachi, Ltd.) at 75,000-fold magnification. The average particle diameter was determined as follows.
The TEM image observed as above was printed on a film as a TEM photograph. From the projected titanylphthalocyanine particles, 30 particles having a needle-like shape were arbitrarily selected and the longest diameter of the respective particles was measured. The total measurement value of the longest diameters of the 30 particles was averaged out and the average value was regarded as the average particle diameter of the titanylphthalocyanine particles. The average particle diameter of titanylphthalocyanine in the water paste (wet cake) in Synthesis Example B-1 determined by the above-noted method was 0.06 μm.
Further, the crystal-converted titanylphthalocyanine crystal immediately before the filtration in Synthesis Example B-1 was diluted with tetrahydrofuran so as to be about 1% by mass and the surface of the diluted suspension was observed in the same manner as described above. The average particle diameter determined by the same method as described above was shown in Table B-1. Note that in the titanylphthalocyanine crystal prepared in Synthesis Example B-1, all the crystal particles did not necessarily have the same shape, i.e., there were crystal particles having an approximately triangular or quadrangular shape, however, the crystal particles were similar in size. For this reason, the average particle diameter was calculated assuming the length of the longest diagonal line of the crystal particle was the longest diameter. As a result, the average particle diameter was 0.12 μm.
The pigment B-1 prepared in Synthesis Example B-1 was dispersed in the following composition under the following conditions to prepare a dispersion as a charge-generating layer coating solution.
In a commercially available bead mill, the 2-butanone with the polyvinylbutyral dissolved therein and the titanylphthalocyanine pigment (Pigment B-1) were put and the components were dispersed using a PSZ ball having a diameter of 0.5 mm at a rotor speed of 1,200 rpm for 30 minutes to thereby prepare a dispersion. This was named as Dispersion B-1.
The following composition was dispersed under the following conditions to prepare a dispersion as a charge generating coating solution.
In a bead mill, a solvent (2-butanone) with the polyvinylbutyral dissolved therein and the azo pigment were put and the components were dispersed using a PSZ ball having a diameter of 10 mm at a rotor speed of 85 rpm for 7 days to thereby prepare a dispersion. This was named as Dispersion B-2.
A dispersion (Dispersion B-3) was prepared in the same manner as in Dispersion Preparation Example B-2, except that the azo pigment used in Dispersion Preparation Example B-2 was changed to a pigment represented by the following structural formula.
The particle size distribution of the pigment particle in the dispersion prepared as above was measured by a particle size distribution analyzer (CAPB-700, manufactured by HORIBA Instruments Inc.). Table B-1 shows the result.
Over the surface of an aluminum drum (JIS 1050) having an external diameter of 60 mm, an intermediate coating solution, a charge generating layer coating solution and a charge transporting coating solution each having the following composition were applied sequentially, the applied coating solutions were sequentially dried to form an intermediate layer having a thickness of 3.5 μm, a charge generating layer having a thickness of 0.5 μm and a charge transporting layer having a thickness of 17 μm, thereby preparing a multi-layered photoconductor (photoconductor 1b).
The Dispersion B-2 prepared as above was used.
A photoconductor (photoconductor 2b) was prepared in the same manner as in Photoconductor Preparation Example B-1, except that the layer thickness of the charge transporting layer formed in Photoconductor Preparation Example B-1 was changed to 27 μm.
A photoconductor (photoconductor 3b) was prepared in the same manner as in Photoconductor Preparation Example B-1, except that the layer thickness of the charge transporting layer was changed to 37 μm.
A photoconductor (photoconductor 4b) was prepared in the same manner as in Photoconductor Preparation Example B-1, except that the layer thickness of the charge transporting layer was changed to 15 μm and a protective layer having the following composition and a thickness of 1 μm was formed on the charge transporting layer.
A photoconductor (photoconductor 6b) was prepared in the same manner as in Photoconductor Preparation Example B-4, except that the layer thickness of the protective layer was changed to 7 μm.
A photoconductor (photoconductor 6b) was prepared in the same manner as in Photoconductor Preparation Example B-1, except that the layer thickness of the charge transporting layer was changed to 15 μm and a protective layer having the following composition and a thickness of 1 μm was formed on the charge transporting layer.
The protective layer was formed as follows. The charge transporting layer surface was spray-coated with the protective layer coating solution, the applied protective layer coating solution was naturally dried for 20 minutes, and the coated layer was photo-irradiated under the conditions of metal halide lamp: 160 W/cm, irradiation intensity: 500 mW/cm2 and irradiation time: 60 seconds.
A photoconductor (photoconductor 7b) was prepared in the same manner as in Photoconductor Preparation Example B-6, except that the layer thickness of the protective layer was changed to 8 μm.
A photoconductor (photoconductor 8b) was prepared in the same manner as in Photoconductor Preparation Example B-1, except that the intermediate layer formed in Photoconductor Preparation Example B-1 was changed so as to have a multi-layered structure composed of a charge blocking layer and a moire prevention layer, a charge blocking layer coating solution and a moire prevention layer coating solution each having the following composition were sequentially applied over the surface of an aluminum drum and the respectively applied coating solutions were dried to form a charge blocking layer having a thickness of 1.0 μm and a moire prevention layer having a thickness of 3.5 μm.
A photoconductor (photoconductor 9b) was prepared in the same manner as in Photoconductor Preparation Example B-1, except that the Dispersion B-3 was used instead of the charge generating coating solution used in Photoconductor Preparation Example B-1.
The transit time of the prepared photoconductors 1b to 9b was determined as described below.
The potential at an exposed region of the respective photoconductors was determined under the following conditions using the equipment described in Japanese Patent Application Laid-Open (JP-A) No. 2000-275872 (shown in
Linear velocity of photoconductor: 262 mm/sec
Resolution in the sub-scanning direction: 400 dpi
Static power in image surface: 0.3 mW (exposure dose: 0.4 μJ/cm2)
Wavelength of writing light: 655 nm
Charge elimination device: activated
Charging condition: the charged amount of the photoconductor surface was controlled such that the surface potential before writing was set to −800V.
Under the above-mentioned conditions, a surface electrometer set to the developing position, as shown in
The thus obtained potential values in the exposed region of the respective photoconductors were individually plotted with respect to the exposing-to-developing time lengths as shown in
The photoconductor 1b prepared as above was mounted (in a black image forming section) in a two-drum image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
Another photoconductor 1b which was different from the above-noted photoconductor 1b was mounted (in a color image forming section) in the image forming apparatus. A scorotoron charger (corona charge system) was used as a charging member to charge the photoconductor surface. An image was written at a resolution of 1,200 dpi using a semiconductor laser having a wavelength of 655 nm as the image exposing light source (four-channel LDAs in which four LDs are arranged in an array (1×4)—a semiconductor laser having a structure as described in Japanese Patent (JP-B) No. 3227226, although the arrangement differs from that of the semiconductor laser described therein, and an image is written by the use of a polygon mirror), the image was developed by two-component developing process using a color toner having an average particle diameter of 6.8 μm. The developed image was transferred onto a transfer sheet using a primary transfer belt and a secondary transfer belt as transfer members, the photoconductor surface was cleaned by blade cleaning method and a charge remaining on the photoconductor surface was eliminated using an LED having a wavelength of 660 nm as the charge elimination light source.
Since the image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°, and the linear velocity of the photoconductor was 480 mm/sec, the LDs were arranged so that the time length the arbitrarily determined point on the photoconductor irradiated with the writing light reaching the center of the developing sleeve (exposing-to-developing time length) was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias) Surface potential of exposed region: −120 V (potential used in solid part of image)
Photoconductor 1b was mounted to the black image forming section, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a position of the developing unit in the black image forming section as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table B-3-1 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table B-3-1 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Other photoconductors 1b which were different from the above-noted photoconductors 1b for evaluation in the black image forming section were respectively mounted in the black image forming section and the color image forming section, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a position of the developing unit in the color image forming section as shown in
After negatively charging each of the photoconductors to −800 V, 10,000 sheets in total of the image were printed out in succession using the image forming apparatus. An image printed out in the initial stage and an image printed out after outputting the 10,000 sheets were evaluated. The level of image density was ranked according to the following four grades. A photoconductor provided extremely favorable image density was ranked A, a photoconductor provided favorable image density was ranked B, a photoconductor provided slightly poor image density was ranked C and a photoconductor provided extremely poor image density was ranked D. Table B-3-2 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (4) to (6) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (4) to (6) were carried out again.
Photoconductors 2b to 9b prepared as above in the same conditions as in Example B-1 were evaluated. Tables B-3-1 and B-3-2 show the evaluation results. Tables B-3-1 and B-3-2 also show the electrophotographic photoconductor numbers used in Examples B-2 to B-6 and Comparative Examples B-1 to B-3. Note that in the image forming apparatus in which the photoconductor 7b was mounted, the resolution was set to 600 dpi.
The results shown in Table B-3-1 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-1 to B-6), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-1 to B-3), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-1 to B-6), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-1 to B-3), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Further, from the evaluation results using a blank image, the evaluation rank of background smear could be elevated and the improvement effect could be kept up even after repetitive use by making an intermediate layer have a multi-layered structure composed of a charge blocking layer and a moire prevention layer (Example B-5).
Furthermore, in a comparison between Example B-1 and Example B-6, the surface potential at the exposed region in the photoconductor 1b used in B-1 was lower than that of the photoconductor 9b used in Example B-6. This shows that the asymmetrical azo pigment used in the photoconductor 1b contributed to the high-photosensitivity.
The results shown in Table B-3-2 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-1 to B-6), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-1 to B-3), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-1 to B-6), the image density was high, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-1 to B-3), the image density was lowered after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples B-1 to B-6), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-1 to B-3), the residual image level was degraded after repetitive use of the photoconductors.
Photoconductors were respectively prepared in the same manner as in Photoconductor Preparation Examples B-1 to B-8, except that the respective charge generating layer coating solutions used in Photoconductor Preparation Examples B-1 to B-8 were changed to Dispersion B-1 (the prepared photoconductors were named as photoconductors 10b to 17b in this order).
The transit time length of the prepared photoconductors 10b to 17b was determined as described below.
The potential at an exposed region of the respective photoconductors was determined under the following conditions using the equipment described in Japanese Patent Application Laid-Open (JP-A) No. 2000-275872 (shown in
Linear velocity of photoconductor: 262 mm/sec
Resolution in the sub-scanning direction: 400 dpi
Static power in image surface: 0.3 mW (exposure dose: 0.4 μJ/cm2)
Wavelength of writing light: 780 nm
Charge elimination device: activated
Charging condition: the charged amount of the photoconductor surface was controlled such that the surface potential before writing was set to −800V.
Under the above-mentioned conditions, a surface electrometer set to the developing position, as shown in
The thus obtained potential values in the exposed region of the respective photoconductors were individually plotted with respect to the exposing-to-developing time lengths as shown in
The prepared electrophotographic photoconductor 10b was attached to a process cartridge and the process cartridge was placed (in a black image forming section) in an image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
Another photoconductor 10b which was different from the above-noted photoconductor 10b was attached to a process cartridge and the process cartridge was placed (in a color image forming section) in the image forming apparatus. The photoconductor was charged using a scorotoron charger (corona charge system) as a charging member. An image was written at a resolution of 2,400 dpi using a light source according to the surface-emitting laser array described in Japanese Patent Application Laid-Open (JP-A) No. 2004-287085 (light emitting points are dimensionally arrayed in 8×4; the number of laser beams: 32, wavelength: 780 nm) as an image exposure light source. The image was developed by two-component developing process using toners each having an average particle diameter of 6.2 μm (a yellow toner, a magenta toner, a cyan toner and a black toner were individually used for each station). The developed image was transferred onto a transfer sheet using a primary transfer belt and a secondary transfer belt as transfer members, the photoconductor surface was cleaned by blade cleaning method and a charge remaining on the photoconductor surface was eliminated using an LED having a wavelength of 655 nm as the charge elimination light source.
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias)
Surface potential of exposed region: −150 V
The photoconductor 10b was attached to a process cartridge the process cartridge was placed in the black image forming section, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a position of a developing unit of in the black image forming section as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table B-5-1 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table B-5-1 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Other photoconductors 10b which were different from the above-noted photoconductors 10b were respectively mounted in the black image forming section and the color image forming section, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion in the color image forming section as shown in
After negatively charging each of the photoconductors to −800 V, 10,000 sheets in total of the image were printed out in succession using the image forming apparatus. An image printed out in the initial stage and an image printed out after outputting the 10,000 sheets were evaluated. The level of image density was ranked according to the following four grades. A photoconductor provided extremely favorable image density was ranked A, a photoconductor provided favorable image density was ranked B, a photoconductor provided slightly poor image density was ranked C and a photoconductor provided extremely poor image density was ranked D. Table B-5-2 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (4) to (6) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (4) to (6) were carried out again.
Photoconductors 11b to 17b prepared as described above under the same conditions as in Example B-7 were evaluated. Tables B-5-1 and B-5-2 show the result. Tables B-5-1 and B-5-2 also show the electrophotographic photoconductor numbers used in Examples B-8 to B-11 and Comparative Examples B-4 to B-6. Note that in the image forming apparatus in which the photoconductor 16b was mounted, the resolution was set to 600 dpi.
The results shown in Table B-5-1 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-7 to B-11), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-4 to B-6), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-7 to B-11), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-4 to B-6), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Further, from the evaluation results using a blank image, the evaluation rank of background smear could be elevated and the improvement effect could be kept up even after repetitive use by making an intermediate layer have a multi-layered structure composed of a charge blocking layer and a moire prevention layer (Example B-1).
The results shown in Table B-5-2 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-7 to B-11), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-4 to B-6), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-7 to B-11), the image density was high, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-4 to B-6), the image density was lowered after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples B-7 to B-11), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-4 to B-6), the residual image level was degraded after repetitive use of the photoconductors.
The thus prepared photoconductor 10b was placed in an image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
Another photoconductor 10b which was different from the above-noted photoconductor 10b was mounted (in an image forming section S2) in the image forming apparatus. For the charging member, a charge roller was closely situated in a distance of 50 μm from the photoconductor surface, and the photoconductor was charged. The surface of the charge roller was wound round with a gap-forming tape having a thickness of 50 μm such that only in image-non-formed surface areas at both ends of the photoconductor, the photoconductor surface could make contact with the charge roller. An image was written at a resolution of 1,200 dpi using a semiconductor laser having a wavelength of 780 nm as the image exposing light source (four-channel LDs in which four LDs are arranged in an array (1×4)—a semiconductor laser having a structure as described in Japanese Patent (JP-B) No. 3227226, although the arrangement differs from that of the semiconductor laser described therein, and an image is written by the use of a polygon mirror), the image was developed by two-component developing process using a color toner having an average particle diameter of 6.8 μm. The developed image was transferred onto a transfer sheet using a primary transfer belt and a secondary transfer belt as transfer members, the photoconductor surface was cleaned by blade cleaning method and a charge remaining on the photoconductor surface was eliminated using an LED having a wavelength of 660 nm as the charge elimination light source.
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias)
Surface potential of exposed region: −80 V (potential at solid part of image)
Photoconductor 10b was mounted to the image forming section S1, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table B-6-1 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table B-6-1 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Other photoconductors 10b which were different from the above-noted photoconductors 10b for evaluation in the image forming section S1 were respectively mounted in the image forming section S1 and an image forming section S2, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion in the image forming section S2 as shown in
After negatively charging each of the photoconductors to −800 V, 10,000 sheets in total of the image were printed out in succession using the image forming apparatus. An image printed out in the initial stage and an image printed out after outputting the 10,000 sheets were evaluated. The level of image density was ranked according to the following four grades. A photoconductor provided extremely favorable image density was ranked A, a photoconductor provided favorable image density was ranked B, a photoconductor provided slightly poor image density was ranked C and a photoconductor provided extremely poor image density was ranked D.
Table B-6-2 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (4) to (6) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (4) to (6) were carried out again.
Photoconductors 11b to 17b prepared as above under the same conditions as used in Example B-12 were evaluated. Tables B-6-1 and B-6-2 show the evaluation results. Tables B-6-1 and B-6-2 also show the electrophotographic photoconductor numbers used in Examples B-13 to B-16 and Comparative Examples B-7 to B-9. Note that in the image forming apparatus in which the photoconductor 16b was mounted, the resolution was set to 600 dpi.
The results shown in Table B-6-1 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-12 to B-16), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-7 to B-9), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-12 to B-16), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-7 to B-9), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Further, from the evaluation results using a blank image, the evaluation rank of background smear could be elevated and the improvement effect could be kept up even after repetitive use by making an intermediate layer have a multi-layered structure composed of a charge blocking layer and a moire prevention layer (Example B-16).
Further, the results shown in Table B-6-2 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-12 to B-16), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-7 to B-9), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-12 to B-16), the image density was high, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-7 to B-9), the image density was lowered after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples B-12 to B-16), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-7 to B-9), the residual image level was degraded after repetitive use of the photoconductors.
The thus prepared photoconductor 10b was attached to a process cartridge and the process cartridge was placed (in an image forming section S1) in an image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
Another photoconductor 10b which was different from the above-noted photoconductor 10b was mounted (in an image forming section S2) in the image forming apparatus. For the charging member, a charge roller was closely situated in a distance of 50 μm from the photoconductor surface, and the photoconductor was charged. The surface of the charge roller was wound round with a gap-forming tape having a thickness of 50 μm such that only in image-non-formed surface areas at both ends of the photoconductor, the photoconductor surface could make contact with the charge roller. An image was written at a resolution of 2,400 dpi using a light source according to the surface-emitting laser array described in Japanese Patent Application Laid-Open (JP-A) No. 2004-287085 (light emitting points are dimensionally arrayed in 8×4; the number of laser beams: 32, wavelength: 780 nm) as an image exposure light source. The image was developed by two-component developing process using a color toner having an average particle diameter of 6.2 μm . The developed image was transferred onto a transfer sheet using a transfer belt as a transfer member, the photoconductor surface was cleaned by blade cleaning method and a charge remaining on the photoconductor surface was eliminated using an LED having a wavelength of 655 nm as the charge elimination light source and a charge remaining on the photoconductor surface was eliminated using an LED having a wavelength of 660 nm as the charge elimination light source.
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
The process conditions were set so that the following conditions could be obtained at the initial operation.
Charge potential of photoconductor (potential of unexposed region): −800 V
Developing bias: −550V (negative/positive developing bias)
Surface potential of exposed region: −80 V (potential at solid part of image)
Photoconductor 10b was attached to a process cartridge and the process cartridge was mounted to the image forming section S1, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion in the image forming section S1 as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table B-7-1 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table B-7-1 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Other photoconductors 10b which were different from the above-noted photoconductors 10b for evaluation in the image forming section S1 were respectively mounted in the image forming section S1 and an image forming section S2, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion in the image forming section S2 as shown in
Using the image forming apparatus, 10,000 sheets of an ISO/JIS-SCID image N1 (portrait) were output, and the color reproductivity of the image print was visually checked and evaluated. The level of color reproductivity was ranked according to the following four grades. A photoconductor provided extremely favorable color reproductivity was ranked A, a photoconductor provided favorable color reproductivity was ranked B, a photoconductor provided slightly poor color reproductivity was ranked C and a photoconductor provided extremely poor color reproductivity was ranked D. Table B-7-2 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (4) to (6) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (4) to (6) were carried out again.
Photoconductors 11b to 17b prepared as above under the same conditions as used in Example B-17 were evaluated. Tables B-7-1 and B-7-2 show the evaluation results. Tables B7-1 and B-7-2 also show the electrophotographic photoconductor numbers used in Examples B-18 to B-21 and Comparative Examples B-10 to B-12. Note that in the image forming apparatus in which the photoconductor 16b was mounted, the resolution was set to 600 dpi.
The results shown in Table B7-1 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-17 to B-21), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-10 to B-12), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-17 to B-21), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-10 to B-12), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Further, from the evaluation results using a blank image, the evaluation rank of background smear could be elevated and the improvement effect could be kept up even after repetitive use by making an intermediate layer have a multi-layered structure composed of a charge blocking layer and a moire prevention layer
Further, the results shown in Table B-7-2 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-17 to B-21), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-10 to B-12), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-17 to B-21), the color reproductivity was excellent, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-10 to B-12), the color reproductivity was degraded after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples B-17 to B-21), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-10 to B-12), the residual image level was degraded after repetitive use of the photoconductors.
Other photoconductor 1b which were different from the photoconductor 1b prepared as above were respectively mounted (in a black image forming section and a color image forming section) in a two-drum image forming apparatus as shown in
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
Still another photoconductor 1b which was different from the above-noted photoconductors 1b was mounted (in the color image forming section) in the same image forming apparatus.
The image exposure light source was placed such that an angle formed with a straight line drawn from the irradiating part (the center in which an image was written on the photoconductor) of the image exposure light source to the core of the photoconductor and another straight line drawn from the core of the developing sleeve to the core of the photoconductor was 45°. The photoconductor was activated at a linear velocity of 480 mm/sec, and thus the exposing-to-developing time length was 49 ms.
Photoconductor 1b was mounted to the black image forming section, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion in the black image forming section as shown in
A blank image print was output using the image forming apparatus to evaluate background smear under the conditions of 22° C. and a relative humidity of 50%. The level of background smear was evaluated based on the number of black points and the size of the black points occurred in the background of the output print. The state of background smear was ranked according to the following four grades. A photoconductor provided an extremely favorable result was ranked A, a photoconductor provided a favorable result was ranked B, a photoconductor provided a slightly poor result was ranked C and a photoconductor provided an extremely poor result was ranked D. Table B-8-1 shows the evaluation results.
Using the image forming apparatus, an isolated one-dot image was output to evaluate the dot reproductivity. The one-dot image print was observed by an optical microscope, and the definitude of the dot outline was ranked according to the following four grades. A photoconductor provided extremely favorable dot reproductivity was ranked A, a photoconductor provided favorable dot reproductivity was ranked B, a photoconductor provided slightly poor dot reproductivity was ranked C and a photoconductor provided extremely poor dot reproductivity was ranked D. Table B-8-1 shows the evaluation results.
After the evaluations (1) to (3) were carried out, 10,000 sheets of a chart with an image area of 6% (characters having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (1) to (3) were carried out again.
Other photoconductors 1b which were different from the above-noted photoconductor 1b for evaluation in the black image forming section were respectively mounted in the black image forming section and the color image forming section, and the following evaluations were carried out.
The potential at an exposed region in the prepared photoconductor was measured by the following method. Specifically, a surface potential meter was mounted to a developed portion in a color image forming section as shown in
After negatively charging each of the photoconductors to −800 V, 10,000 sheets in total of the image were printed out in succession using the image forming apparatus. An image printed out in the initial stage and an image printed out after outputting the 10,000 sheets were evaluated. The level of image density was ranked according to the following four grades. A photoconductor provided extremely favorable image density was ranked A, a photoconductor provided favorable image density was ranked B, a photoconductor provided slightly poor image density was ranked C and a photoconductor provided extremely poor image density was ranked D. Table B-8-2 shows the evaluation results.
An A4 size chart as shown in
After the evaluations (4) to (6) were carried out, 10,000 sheets of a full-color chart with an image area of 6% (oblique lines having an image area ratio equivalent to 6% to the entire area of the A4 sheet were averagely written) were printed out in succession under the above-noted process conditions. After outputting 10,000 sheets in succession, the evaluations (4) to (6) were carried out again.
Photoconductors 2b, 3b, 9b, 10b and 11b prepared as above under the same conditions as used in Example B-22 were evaluated. Tables B-8-1 and B-8-2 show the evaluation results. Tables B-8-1 and B-8-2 also show the electrophotographic photoconductor numbers used in Examples B-23 to B-24 and Comparative Examples B-13 to B-15. Note that in the image forming apparatus in which the photoconductor 8b was mounted, the resolution was set to 600 dpi.
The results shown in Table B-8-1 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-22 to B-24), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-13 to B-15), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-22 to B-24), the dot reproductivity was excellent, and even after repetitive use of the photoconductors, images having excellent dot image quality were formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-13 to B-15), the dot reproductivity was degraded after the repetitive use of the photoconductors.
Furthermore, in a comparison between Example B-22 and Example B-23, the surface potential at the exposed region in the photoconductor 1b used in B-22 was lower than that of the photoconductor 9b used in Example B-23. This shows that the asymmetrical azo pigment used in the photoconductor 1b contributed to the high-photosensitivity.
The results shown in Table B-8-2 verified that when the transit time length was shorter than the exposing-to-developing time length (Examples B-22 to B-24), the light decay property was favorably exhibited in the initial stage of the use of the photoconductors and even after repetitive use of the photoconductors. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-13 to B-15), a rise in surface potential was observed, and after repetitive use of the photoconductors, the phenomenon was conspicuous.
It was also found that the transit time length was shorter than the exposing-to-developing time length (Examples B-22 to B-24), the image density was high, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, it was found that when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-13 to B-15), the image density was lowered after the repetitive use of the photoconductors.
Further, when the transit time length was shorter than the exposing-to-developing time length (Examples B-22 to B-24), a favorable residual image level was obtained, and even after repetitive use of the photoconductors, excellent full-color images could be formed. In contrast, when the transit time length was longer than the exposing-to-developing time length (Comparative Examples B-13 to B-15), the residual image level was degraded after repetitive use of the photoconductors.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-250503 | Sep 2006 | JP | national |
| 2006-250648 | Sep 2006 | JP | national |
| 2007-181536 | Jul 2007 | JP | national |
| 2007-181538 | Jul 2007 | JP | national |
