Patent Grant
7593682
1. Field of the Invention
The present application relates to an image forming apparatus, an image forming method and a process cartridge for use in facsimile machines, photocopiers and printers.
2. Discussion of the Background
Unexamined published Japanese patent application No. (hereinafter referred to as JOP) 2001-054571 describes an image forming apparatus developed to restrain the occurrence of image blur to provide a long-life image bearing member. Image blur is caused by accumulation of nitrogen oxides ascribable to a lubricant supplied to the surface of an image bearing member. The image forming apparatus has a structure in which a lubricant supplying device supplies a lubricant to a photoreceptor functioning as an image bearing member to make the friction coefficient of the surface of the photoreceptor low. A process of reducing the surface friction coefficient of the photoreceptor and a process of increasing the surface friction coefficient of the photoreceptor are described. In the process of increasing the surface friction coefficient of the photoreceptor, nitrogen oxides produced during charging are removed. In the process of increasing the friction coefficient of the surface of the photoreceptor, for example, the contact pressure of the cleaning blade to the photoreceptor is greater than in the process of decreasing the surface friction coefficient.
In the technology described above, the surface friction coefficient of the photoreceptor is altered by changing, for example the contact pressure of the cleaning blade, to remove nitrogen oxides produced during charging. However, it was found recently that it is difficult to prevent deterioration of image quality such as image blur simply by removing the nitrogen oxides. In addition, in the technology described above, there is no mention that the lubricant protects a photoreceptor. Also there is no mention that the lubricant may be deteriorated by charging.
Further, JOP 2001-228668 describes an image forming apparatus in which a plurality of image bearing members are arranged along the transfer direction of a transfer material. Toner images formed on the surface of each image bearing member are transferred to the transfer material and the remaining toner attached to the surface of each image bearing member after the toner image is transferred to the transfer material is removed by a cleaning device. Further, a toner retrieving device is provided in the image forming apparatus to return the remaining toner removed by the cleaning device to the cleaning device and to prevent deterioration of image quality by paper dust contained in the remaining toner. That is, JOP 2001-228668 describes an image forming apparatus in which the toner retrieving devices are provided to the image bearing members except for the image bearing member disposed on the uppermost stream side from the transfer material. The toner retrieving devices are disposed between the cleaning devices to remove the remaining toner from the image bearing members and the developing devices. However, the technology described above does not refer to removal of the lubricant on the surface of the image bearing member.
In addition, JOP 2002-6689 describes an image forming apparatus in which a lubricant is supplied to the image bearing member on which toner images are formed to elongate the life of the image bearing member and to improve the image quality. Therein, the number of rotations n of the image bearing member is preset for the surface friction coefficient of the image. During image formation, when the number of the rotation of the image bearing member has reached a number n+A (A is an integer), the transfer current at the transfer portion is increased without performing image formation to increase the amount of the lubricant retrieved from the surface of the image bearing member. Thereby, the friction coefficient of the surface of the image bearing member is temporarily raised so that the product produced resulting from charging can be removed. After removing the product produced from the charging, the transfer current is returned to a level suitable for image formation and the image bearing member is rotated without forming images to apply the lubricant to the surface thereof up to a suitable amount. Thereby, the surface friction coefficient of the image bearing member is reduced. Thereafter, images are formed while applying the lubricant.
To raise the friction coefficient of the image bearing member, the technology described above describes a technology for removing nitrogen oxides together with the lubricant by changing the polarity of the transfer bias. It was recently found that it is difficult to prevent deterioration of image quality such as image blur simply by removing the nitrogen oxides. In addition, in the technology described above, there is no mention or concept that the lubricant protects a photoreceptor. Also there is no mention about deterioration of the lubricant by charging.
Further, JOP 2002-357983 describes a lubricant supplying device and an image forming device wherein the lubricant is used. In the device, the lubricant is sufficiently supplied without causing the increasing cost due to the increases of the mounting space of a member to supply the lubricant and the number of parts. The lubricant supply device is provided to supply the lubricant to the surface of a photoreceptor. The lubricant supply device has a blade-shaped member in which a lubricant is inclinationally dispersed in a rubber-like elastic member to make the lubricant present in a large quantity on one surface side than the other. In addition, the lubricant supply device supplies the lubricant to the surface of a photoreceptive drum by bringing the side of the blade-shaped member having the lubricant in a large amount into press-contact with the surface of the photoreceptor.
However, the technology does not refer to the method of supplying a lubricant to the photoreceptor in which the lubricant is contained in parts to dispense with the space for a solid or powder lubricant. In addition, there is no mention about removing the lubricant on the surface of the photoreceptor.
Applying a lubricant to a photoreceptor is also a means by which a protective layer may be added, such as of an image bearing member of an image forming apparatus to provide, for example, a long life of the image bearing member and quality images. The objects of the application of a lubricant are to prevent the occurrence of toner filming (fusion attachment), improve transfer efficiency by reducing the friction coefficient and prevent poor cleaning performance. JOPs 2002-244516, 2002-156877, 2002-55580, and 2002-244487 describe technologies related thereto.
JOP2002-229227 describes a technology to improve anti-abrasion property by applying a lubricant containing zinc stearate to a photoreceptor using a non-contact charging device to obtain a long-life charging member and photoreceptor. In the technology, organic particulates are dispersed in the photoreceptive layer of the photoreceptor. JOP H10-142897 describes an image forming apparatus having a blade form supplementary member. The blade form supplementary member is provided to even out the lubricant applied at the portion between the charging portion and the developing portion and to stem lubricants having a large particle diameter.
The widely-used known cleaning method for an image forming apparatus in typical electrophotography is a method in which a cleaning blade is used. There are a number of image forming apparatuses having only a blade as a cleaning device. In addition, in the case of a high speed electrophotographic machine, to avoid a state in which a large amount of toner is locally attached, an image forming apparatus is proposed in which a brush is provided on the upstream from the blade. However, such technologies have a drawback in that it is impossible to sufficiently remove the recently developed (polymerized) toner having a circularity of 0.96 to less than 1.00. In spite of this, there are short life image forming apparatuses which can remove such toner by giving some devise to toner and a blade. In addition, spherical (polymerized) toner has a high transfer ratio, meaning that the amount of the remaining toner is small. Therefore, there is proposed an image forming apparatus in which the developing device performs cleaning without a dedicated cleaning device.
In addition, a polarity control device provided on the upstream side from the cleaning device was used in an old-type image forming apparatus but few of them are now seen. One of the reasons is that such a polarity control device is no longer required due to improvements in cleaning technology and a desire for cost reduction. Among the cleaning devices having a brush on the upstream side from the blade, some cleaning devices also function as a polarity control device to which a voltage is applied but they are not popular. However, there are many image forming apparatuses having a polarity control device when the cleaning device mentioned above is not provided thereto.
As a charging device to charge the image bearing member of an image forming apparatus, the charging device using corona discharging used to be popular. However, this charging device using corona discharging has a drawback in that such a charging device produces ozone in a large amount. In addition, since a high power source is required to apply a voltage as high as 5 to 10 kV to perform corona discharging it is difficult to reduce cost of an image forming apparatus.
Therefore, contact type charging devices, in which a charging member contacts an image bearing member, have been adopted in many cases instead of a corona discharging device. This contact-type charging device can solve most of the drawbacks involved in the charging devices using the corona discharging mentioned above. On the other hand, the contact-type charging device invites problems such as abnormal images referred to as image deletion and increased abrasion of the image bearing member. In addition, when AC is used as an application voltage, noises occur, which also becomes a problem. In addition, the charging device rubs toner, paper dust, etc., with an image bearing member (photoreceptor), which accelerates contamination. Work-up in printing stemming from this contamination creates another printing problem. To solve these kinds of problems, JOP H10-312098 describes a technology in which the contamination due to toner and paper dust caused by a charging device mentioned above is prevented by controlling an applied voltage using a supplementary charging member and a charging member. In addition, by this technology, the occurrence of abnormal images referred to as positive-ghost in a cleaner-less system can be prevented.
As mentioned above, applying a lubricant to the image bearing member of an image forming apparatus is widely performed to improve transferability and/or cleanability. However, when an image bearing member is charged by a charging device having a charging member disposed in the vicinity of or contacting with the image bearing member, the lubricant on the image bearing member deteriorates due to the charging and the amount of the lubricant on the image bearing member decreases. As a result, it is difficult for the lubricant to carry out its function. Moreover, if the degraded lubricant is left on the image bearing member and not removed, the lubricant gradually accumulates. Thereby, the image quality deteriorates and abnormal images occur. There is a problem that typically used cleaning blades or cleaning brushes cannot sufficiently remove the degraded lubricant on the surface of the image bearing member by a charging device.
Because of these reasons, the present applicants recognize that a need exists for an image forming apparatus, an image forming method and a process cartridge in which degraded lubricants are adequately removed to thereby improve the quality of images.
Accordingly, one object of the invention to provide an image forming apparatus which can prevent deterioration of the image quality and occurrence of abnormal images by eliminating degraded lubricant and remaining on the image bearing member by discharging the charging device thereto. Another object of the present invention is to provide an image forming apparatus which operates a controlling device to remove a lubricant on the surface of an image bearing member. A further object is to provide a process cartridge and an image forming method using the image forming apparatus.
These objects and the details of the present invention as hereinafter described will become more readily apparent and can be attained, either individually or in combination, by an image forming apparatus including an image bearing member to bear a latent image, a charging device to charge the image bearing member which includes a charging member disposed in the vicinity of, in contact with, or both in the vicinity of and in contact with the image bearing member, a transfer device to transfer the image to a transfer body, a lubricant supplying device to supply a lubricant to the surface of the image bearing member, disposed on the downstream side from the transfer device relative to the rotation direction of the image bearing member and on the upstream side from the charging member relative thereto, a developing device to develop the latent image with a developer, disposed on the downstream side from the charging member relative to the rotation direction of the image bearing member and on the upstream side from the transfer device relative thereto, a discharging device to discharge the image bearing member, a cleaning device to clean the surface of the image bearing member, and a controlling device to control a lubricant supplying mode and a lubricant removing mode in which the lubricant is removed from the surface of the image bearing member.
It is preferred that, in the image forming apparatus mentioned above, the cleaning device and the controlling device are provided to remove the lubricant applied to the surface of the image bearing member with the developer supplied from the developing device.
It is still further preferred that, in the image forming apparatus mentioned above, the lubricant removing mode of the controlling device is triggered based on an operation period of time or a number of printed images.
It is still further preferred that, in the image forming apparatus mentioned above, the image bearing member includes a protective layer as the surface layer.
It is still further preferred that, in the image forming apparatus mentioned above, the binder resin includes a binder resin which includes a cross-linkage structure.
It is still further preferred that, in the image forming apparatus mentioned above, the binder resin including a cross-linkage structure includes one or more charge transfer portions.
It is still further preferred that, in the image forming apparatus mentioned above, the cleaning device is provided to remove a degraded lubricant from the surface of the image bearing member.
As another aspect of the present application, an image forming method is provided which includes charging the surface of an image bearing member with a charging device, irradiating a portion of the image bearing member other than an image portion with light by an irradiating device to form a latent electrostatic image, developing an image by supplying a developer to the latent electrostatic image with a developing device, transferring the developed image to a transfer body by a transfer device, fixing the transferred image on the transfer body by a fixing device, discharging the image bearing member with a discharging device, supplying a lubricant to the surface of the image bearing member, removing the developer remaining on the surface of the image bearing member with a cleaning device, and controlling at least one of a lubricant supply mode and a lubricant removing mode to remove the lubricant on the image bearing member.
It is preferred that the image forming method mentioned above includes controlling the lubricant removing mode, discharging the the surface of the image bearing member with the discharging device such that a voltage of the image bearing member is close to 0 V in absolute value, and supplying the developer for removing the lubricant with the developing device to the surface of the image bearing member by applying a bias smaller in absolute value than a development bias applied thereto during image formation.
It is still further preferred that the image forming method mentioned above includes controlling the lubricant removing mode, supplying the developer to the image bearing member with the developing device with the same bias as the bias during the irradiating. In addition, a voltage (Vch) applied to the charging device is formed of only DC component while satisfying the following relationship (1):
|Vth|≦|Vch|≦|Vth|+|Vdev| (1),
wherein, Vth represents a voltage when discharging starts, and Vdev represents a development bias, which is the applied voltage of the DC component to the developing device.
It is still further preferred that the image forming method mentioned above includes controlling the lubricant removing mode. In addition, the surface voltage of the image bearing member is the same as the surface voltage thereof during the irradiating, an applied voltage to the charging device contains only a DC component without an AC component, and the developing device supplies the developer to the image bearing member with a bias greater in absolute value than the bias during image formation.
It is still further preferred that the image forming method mentioned above includes controlling the lubricant removing mode, which is triggered based on an operation period of time or a number of printed images.
It is still further preferred that the supplying in the image forming method mentioned above includes applying the lubricant immediately after the lubricant is removed.
It is still further preferred that, in the image forming method, the lubricant removed from the surface of the image bearing member is a degraded lubricant.
As another aspect of the present application, a process cartridge is provided which includes an image bearing member to bear a latent electrostatic image, a developing device to develop the latent electrostatic image with a developer, a lubricant supplying device to supply a lubricant to the surface of the image bearing member, a discharging device to discharge the surface of the image bearing member, a cleaning device to clean the surface of the image bearing member, and optionally a charging device to charge the image bearing member. In addition, the discharging device and the cleaning device are provided to remove the lubricant with the developer supplied from the developing device, and the cleaning device is provided in a lubricant removing mode controlled by a controlling device in an image forming apparatus to which the process cartridge is detachably attached.
It is preferred that, in the process cartridge, the controlling device which controls the lubricant removing mode is based on an operation period of time or a number of printed images.
It is still further preferred that, in the process cartridge mentioned above, the lubricant removed with the developer supplied from the developing device is a degraded lubricant.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the detailed description when considered in connection with the accompanying drawings in which like reference characters designate like corresponding parts throughout and wherein:
Embodiments of the present invention will be described in detail below with reference to the drawing attached thereto.
General Description Of Photocopier
In
The behavior of the image forming apparatus having such a structure is described below with reference to
A transfer material, e.g., transfer (recording) paper, is fed at a suitable timing from the paper feeding device 18 to between the image bearing member 2 and the transfer device 6 disposed opposing the image bearing member 2. Then, the toner image formed on the image bearing member 2 is electrostatically transferred to the transfer material. The transfer material on which the toner image is transferred passes through the fixing device 10, where the toner image is fixed on the transfer material upon application of heat and pressure. The transfer material which has passed through the fixing device 10 is discharged to a paper discharging portion. The toner which has not been transferred to the transfer material and remains on the surface of the image bearing member 2 is removed by the cleaning device 7. The fixing device 10 can be structured by, for example, two rollers, but can also have another structure formed by, for example, a belt and roller.
The developing device 5 illustrated in
In addition, the transfer device 6 illustrated in
Furthermore, the cleaning device 7 illustrated in
The cleaning blade 7 functioning as a cleaning device can be formed of a material selected from known material such as polyurethane rubber, silicone rubber, nitrile rubber, and chloroprene rubber. The elasticity, thickness and pressure-contact angle to the image bearing member 2 of the material is suitably set for use. A discharging device can be used as illustrated in
A lubricant supplying device is described below with reference to
The lubricant of a lubrication member 102 is suitably supplied to the image bearing member 2 by the fur brush 7-1. Typically, the lubricant is continuously supplied but can be intermittently supplied by using a typical cam or electromagnetic clutch by which the lubrication member 102 can be attached to and detached from the fur brush 7-1. In addition, it is also possible to control the supply of the lubricant on a necessity basis by monitoring, for example, the torque of the image bearing member, the electric current of the driving motor, and the reflectivity of the image bearing member 2.
Further, it is also possible to have a structure as illustrated in
The lubricant uniforming device 103 preferably supplies a lubricant to the image bearing member 2 in such a manner that the lubricant is supplied via, for example, a rotation brush or a rotation roller which is in contact with a solid lubricant and the image bearing member. However, in terms of size reduction of a device and cost reduction, it is also possible to directly contact a lubricant with the image bearing member 2.
In this embodiment, a rotation brush is used as the lubricant supplying device. However, there is no specific limit to the lubricant supplying device. Therefore, using other members such as a rotation roller and a belt having an endless form does not cause any problem.
In addition, it is possible to use a metal salt of a fatty acid as a lubricant in a form of powder or solid depending on the supplying manner to an image bearing member. A solid form is preferred to a powder form considering the problems such as scattering. Specific examples of the metal elements forming such metal salts of a fatty acid include zinc, lithium, sodium, calcium, magnesium, aluminum, lead, and nickel. Specific examples of the fatty acids forming such metal salts of a fatty acid include stearic acid, lauric acid, and palmitic acid. Among them, when a solid lubricant is used in a form of a rectangular column, zinc stearate is preferred and when a powder lubricant having a sphere form is used, calcium stearate is preferred.
The lubricant removing mode and the lubricant supplying mode are described below. In the structure illustrated in
Therefore, once a thin layer of a lubricant is formed when an image forming apparatus is used for the first time or when an image bearing member is exchanged, the thin layer can be maintained for a certain period of time when the structure mentioned above including the fur brush 7-1 and the cleaning blade 7 is used. The thickness of such a thin layer is little affected by the cleaning blade 7, which is constantly in contact with the image bearing member 2. However, since the lubricant is attached to the other devices in contact with the image bearing member 2, it is known that the variance of the layer thickness caused by direct charging by the charging device is large. Therefore, when a charging roller is used to charge the image bearing member 2, it is preferred to constantly apply the lubricant even after a protective layer is formed in the lubricant supplying mode mentioned above. In this case, when the transfer device 6 has a mechanism which can attach and detach the transfer device 6 to and from the image bearing member 2, it is preferred to detach the transfer device 6 from the image bearing member 2. Similarly, when the developing device 5 also has a mechanism which can attach and detach the developing device 5 to and from the image bearing member 2, it is preferred to detach the developing device 6 from the image bearing member 2 as well.
Description Of Experiment Results
The results of the experiments on the mechanism forming a thin layer on the photoreceptor serving as the image bearing member 2 are shown in Table 1,
According to the results of this experiment, it is not easy to form a thin layer. In addition, it is found that once a thin layer is formed it is not easy to remove or peel off the thin layer. Therefore, when an image forming apparatus is used for the first time or when the image bearing member 2 is exchanged, it is possible to form a suitable thin layer by passing through a layer uniforming member (including an application brush and a uniforming blade) at least three times. The thus formed thin layer is found to have a good cleanability and the ability of preventing an adverse effect caused by charging. Especially, considering shortening the control time in the method of present application, sufficient application number of times of a lubricant to the image bearing member 2 are three to ten times.
The description will be made with reference to the experiments and the measuring results. As seen in Table 1, the average layer thickness is 4.9 nm after a lubricant is applied once. This my be insufficient because the layer is typically preferred to be formed of a two-molecular layer, which has a thickness of about 10 nm. On the other hand, when a lubricant is applied ten times, the layer thickness is considered to be sufficient.
Therefore, considering shortening the controlling time, the suitable number T of application times is represented by the following relationship (2):
3<T≦10 (2),
in the relationship, T represents an integer. The number of application times can be substituted with the number of rotation times of the photoreceptor (image bearing member).
The relationship between a lubricant and abrasion is shown in Table 2.
This experiment was performed in such a manner that a polycarbonate (PC) substrate was abraded using an abrasion wheel to which a toner was attached.
From No. 4 in Table 2, it is found that the polycarbonate (PC) substrate to which the lubricant (ZnST) is applied is abraded little when the polycarbonate substrate is abraded with an abrasion wheel to which a toner having a lubricant thereon beforehand is attached. In addition, from No. 2 in Table 2, it is found that the polycarbonate (PC) substrate to which the lubricant (ZnST) is applied is abraded when the polycarbonate substrate is abraded with an abrasion wheel to which a toner not having a lubricant thereon is attached.
Further,
Description Of Flow Charts
Flowcharts of the lubricant removing mode and the lubricant supplying mode are described below with reference to
The flowchart illustrated in
The flowchart illustrated in
The flowchart illustrated in
The flowchart illustrated in
The difference between the flowcharts illustrated in
In this embodiment, the preparatory rotation is, for example, to raise the temperature of the fixing device, to determine an applied potential to the charging device, to determine an applied potential to the developing device, and to adjust the toner concentration. In addition, when a color image forming apparatus is used, color and positioning of images may be adjusted. Further, in the post image formation rotation, for example, toner remaining on the image bearing member after image formation is removed and the image bearing member is discharged.
Description Of Lubricant Removing Mode
To remove the lubricant on the surface of an image bearing member, it is effective to pressure-contact with the lubricant a member on which a lubricant is not attached. For example, the lubricant can be removed by pressure-contacting a transfer material (e.g., recording paper), an intermediate transfer belt, a transfer belt or a combination thereof with the image bearing member when lubricant is not attached to the transfer material, the intermediate transfer belt or the transfer belt. However, once a lubricant is attached to the members and devices mentioned above, the members mentioned above become less effective from the next time use forward because the amount of the lubricant removed decreases.
In one embodiment, a toner functioning as a developer is used to remove the lubricant remaining on an image bearing member. Since a lubricant is normally not attached to a toner, the toner is effective as a member for removing lubricant. In addition, it is from a developing device that such a toner is supplied to the image bearing member. The toner remaining on the image bearing member can be retrieved by a cleaning device or a transfer device.
However, there is a range of suitable amount of a toner attached to an image bearing member to remove a lubricant thereon. Therefore, it is preferred to control the amount of toner. When the developing bias applied during image formation is applied to control the amount of toner, the surface potential of an image bearing member is controlled by controlling the charging bias. In addition, when the charging bias applied during image formation is used, the developing bias is controlled. Further, it is possible to control both developing bias and charging bias. Furthermore, it is possible to control the amount of toner attached to the image bearing member by controlling the charge amount of toner. However, this method is not preferred because the control is complicated.
In embodiment, the suitable amount of toner for use in removing a lubricant is described. Preferably, the amount of a toner attached to the image bearing member is not less than 0.01 mg/cm2. When the amount of a toner attached to the image bearing member is not less than 0.6 mg/cm2, drawbacks may arise such that the amount of toner consumption increases, the toner scatters, cleaning at the cleaning portion becomes insufficient, and the toner clogs at toner transfer portion including the cleaning case. When the amount of a toner attached to the image bearing member is too small, the lubricant is not sufficiently removed. Therefore, the amount of a toner attached to the image bearing member is preferably from about 0.1 to about 0.6 mg/cm2. Further, to restrain the amount of a toner consumed, the amount of a toner attached to the image bearing member is more preferably about 0.1 to about 0.3 mg/cm2. When an image bearing member is rotated a predetermined number of times, a toner is attached to the image bearing member irrespective of the intention of an operator (the present application). But the amount of such a toner attached thereto is extremely small, which is 0.05 mg/cm2 at maximum.
In addition, when a roller charging device is used, there are two charging bias types. One is DC overlapped with AC and the other is DC only. When a lubricant is removed or applied, DC only is preferred. One reason is that the number of discharging times is large when DC overlapped with AC is used. Therefore, the lubricant is degraded by the discharging. Therefore, even when DC overlapped with AC is used during image formation, DC only is preferred to be used when a lubricant is removed or applied.
In addition, with regard to the developing bias, there are two cases, which are also DC overlapped with AC and DC only. DC overlapped with AC is not preferred. This is because a stress to attract the toner attached to the image bearing member back to the developing device is produced. The toner attracted back to the developing device has a lubricant thereon. The lubricant attached to the toner attaches to a carrier, a developing roller, etc., in the developing device, thereby hindering charging of a toner.
When the toner retrieved at the cleaning portion is reused in the developing device, the lubricant attached to toner is removed by the cleaning device or at a retrieval transfer path. Therefore, when the toner is attracted back to the developing device, the amount of the lubricant attached thereto is small. Thus, the influence on the toner charging mentioned above is limited.
The values of the surface potential of an image bearing member and the developing bias to control the amount of the toner attached as mentioned above are described in detail. The voltage difference between the surface potential of the image bearing member and the developing bias is referred to as a developing potential. This developing potential is preferred to be from about 50 to about 400 V.
A case is described in which the developing bias (applied voltage to the image bearing member: Vdev) is the same as that during image formation and is not changed in the lubricant removing mode.
The developing potential mentioned above is suitable to limit the amount of a toner attached to an image bearing member within the value mentioned above. More specifically, this is achieved when the surface potential of an image bearing member is made to be smaller in absolute value than the developing bias and larger in absolute value than the irradiation voltage during image formation. However, the suitable surface potential set for an image bearing member depends on whether a toner used is a single-component developer or a two-component developer, the amount of the charge of a toner, etc.
Below is a case in which the developing bias is the same as that in image formation and a two-component developer is used. In this case, only the surface potential (Vh) of an image bearing member is changed. The surface potential of an image bearing member is controlled by a voltage (charging bias: Vch) applied to a charging device. In addition, when instead of a corona charger such as a charging roller or a charging blade, but a charging device contacting or disposed in the vicinity of an image bearing member is used, the charging bias is preferably set to satisfy the following relationship (1):
|Vth|≦|Vch|≦|Vth|+|Vdev| (1
Further, it is preferred to set the charging bias based on the following relationship (3) to restrain the amount of toner attached in a suitable range.
|Vth|+150≦|Vch|<|Vth|+|vdev|−50 (3)
In addition, when a coroner charger is used, it is preferred to control the voltage applied to the grid to obtain the developing potential mentioned above.
Below is a case in which the surface potential of an image bearing is the same as that during image formation and the developing bias is changed in the lubricant removing mode.
The developing bias can be changed by providing a power supply which can change the voltage applied to an image bearing member. The developing bias applied during image formation is changed in the lubricant removing mode by controlling the power supply mentioned above by a controller. As mentioned above, when the developing bias is DC overlapped with AC, it is preferred not to apply AC.
When the developing bias is changed, the charging bias is preferred to be DC only. Attention should be paid to the fact that when only DC in DC overlapped with AC is simply applied to an image bearing member, the surface potential thereof is not the same as that in image formation.
Below is an example of when an image bearing member is charged at 700 V.
DC overlapped with AC
DC: Vdc=700 V
AC: Vpp=2.2 kV, f=1 kHz
DC only
DC: Vdc=1400 V
Vth is assumed to be 700 V.
Description of set voltage in lubricant supplying mode
Below is the description of the value of the applied voltage set in the lubricant supplying mode in the flowcharts in
Especially, a case is described below in which a detachment-attachment mechanism is not provided to a developing device, and a charging device having a charging member contacting with or disposed in the vicinity of an image bearing member is used.
For example, when the charging voltage (Vh) of an image bearing member during image formation is set to be −800 V, the voltage at an irradiated printed portion is −150 V, the voltage applied to a developing device is −450 V, the toner is negatively charged, and the voltage applied to the developing device is applied in the lubricant supplying mode, the voltage (Vch) applied to the charging device is preferred to be without overlapping AC and set in the range in which the charging voltage (Vh) of the image bearing member satisfies the following relationship (4). That is, it is preferred to set the charging voltage (Vh) of the image bearing member lower than the voltage applied to the developing device. Further, it is preferred to set Vh to be a voltage about 100 V lower than the voltage (−450 V in the case mentioned above) applied to the developing device. That is, Vh is preferred to be set about −550 V.
−450V>Vh>−800V (4)
However, with regard to −800 V, which is the lower limit thereof, when the developing device has a sufficient ability to further charge an image bearing member, the range of Vh can be extended to the limit. For example, with a developing device having an ability for −1,200V, Vh can be −1,200 V as well. With such a value, toner attachment to an image bearing member can be prevented and easily form a thin layer of lubricant.
The voltage (Vch) applied to a developing device satisfying the relationship (1) varies depending on the layer thickness of the photoreceptor of an image bearing member. The value obtained from the image bearing member used in the experiment roughly satisfies the following relationship (5).
−1150V>Vch>−1500V (5)
Next, when the developing device is grounded in the lubricant supplying mode instead of being applying the voltage during image formation thereto, it is preferred to apply the voltage (Vch) to a developing device without overlapping AC and set the voltage (Vch) in the range in which the charging voltage (Vh) of the image bearing member satisfies the following relationship (6). Further, it is preferred to set Vh to a value about 100 V lower than the voltage (i.e., 0 V in the case mentioned above) applied to the developing device. That is, Vh is preferred to be not greater than −100 V.
0V>Vh>−800V (6)
However, with regard to −800 V, which is the lower limit thereof, when the developing device has a sufficient ability to further charge an image bearing member, the range of Vh can be extended to the limit. For example, with a developing device having an ability for −1,200V, Vh can be −1,200 V as well. With such a value, toner attachment to an image bearing member can be prevented and easily form a thin layer of lubricant.
The voltage (Vch) applied to a developing device satisfying the relationship (3) varies depending on the layer thickness of the photoreceptor of an image bearing member. The value obtained from the image bearing member used in the experiment roughly satisfies the following relationship (7).
0V≧Vch>−1500V (7)
However, in the relationships (5) and (7), there is a possibility that discharging occurs between the charging device and the image bearing member. When such discharging occurs, a thin layer of lubricant is difficult to form on the image forming apparatus. Therefore, to prevent discharging between the charging device and the image bearing member, there is a method in which only discharging to the image bearing member is performed and charging thereto by the charging device is not performed.
In the case described above, negative charging is adopted. When positive charging is performed, the inequality sign is reversed. Description of cross-linkage type protective layer of image bearing member
As the binder structure of the protective layer of an image bearing member, a protective layer having a cross-linkage structure is effectively used. Cross linkage structure is formed in such a manner that a cross linkage reaction is performed with light and thermal energy using a reactive monomer having multiple cross-linkage functional groups in one molecule to form a three-dimensional mesh structure. This mesh structure functions as a binder resin and exercises a high anti-abrasion property. In terms of electric stability, anti-abrasion, and life, it is extremely effective to use a monomer partially or entirely having a charge transport ability as the reactive monomer mentioned above. By using such a monomer, charge transport portions are formed in the mesh structure so that the function as a protective layer can be fully exercised.
Specific examples of such reactive monomers include compounds having at least one charge transport component and at least one silicon atom having a hydrolytic substituent group in the same molecule, compounds having a charge transport component and a hydroxyl group in the same molecule, compounds having a charge transport component and a carboxylic group in the same molecule, compounds having a charge transport component and an epoxy group in the same molecule, and compounds having a charge transport component and an isocyanate group in the same molecule. These charge transport materials having a reactive group can be used alone or in combination.
It is further preferred to use a reactive monomer having a triaryl amine structure because, as a monomer having a charge transport ability, such a reactive monomer is electrically and chemically stable, the transfer speed of carrier is high, etc.
Other than these, a polymeric monomer or a polymeric oligomer having one or two functional groups can be used in combination with the reactive monomer mentioned above to impart functions of adjusting viscosity during application, relaxing the stress in cross-linkage type charge transport layer, reducing the surface energy, decreasing the friction index, etc. Known polymeric monomers and oligomers can be used.
In this embodiment, compounds in which positive holes are transferred are polymerized or cross-linked using light or thermal energy. When polymerization is performed using heat, there are two cases, which are polymerization with only thermal energy and with thermal energy together with a polymerization initiator. To perform the polymerization at a low temperature, it is preferred to add a polymerization initiator.
When polymerization is performed using light, it is preferred to use ultraviolet rays as the light. However, it is rare that polymerization proceeds with only light. Therefore, in general, an optical polymerization initiator is used in combination with light. The optical polymerization initiator is a compound that initiates polymerization by absorbing ultraviolet rays having a wavelength of not greater than 400 nm to form active species such as radicals and ions. In this embodiment, it is possible to use the thermal and optical polymerization initiators mentioned above in combination.
The charge transport layer having the mesh structure formed as mentioned above has a good anti-abrasion property. However, such a layer significantly contracts in size during cross-linkage reaction so that cracking and so on may occur when too thick a layer is formed. In such a case, it is possible to have a layered protective layer. In such a layered protective layer, its bottom (photosensitive layer side) layer is formed of a polymer in which low molecular weight molecules are dispersed, and its upper (surface side) layer has a cross linkage structure.
Below are examples of the photoreceptors (image bearing member) using the cross-linkage type protective layer mentioned above. In the descriptions in the following examples, the numbers represent weight ratios in parts, unless otherwise specified.
Electrophotographic Photoreceptor A
Electrophotographic photoreceptor A was manufactured in the same manner as illustrated in the electrophotographic photoreceptor mentioned above except that the liquid for application for a protective layer, the layer thickness and manufacturing conditions were changed as follows.
The following components were mixed to prepare a liquid for application for a protective layer. This liquid for application was applied to the charge transport layer and dried. The resultant was cured and dried with heat at 110° C. for one hour and a protective layer having a thickness of 3 μm was formed.
Electrophotographic Photoreceptor B
Electrophotographic photoreceptor B was manufactured in the same manner as illustrated in the electrophotographic photoreceptor mentioned above except that the liquid for application for the protective layer, the layer thickness and manufacturing conditions were changed as follows.
Thirty parts of a positive hole transport compound having the following chemical formula (I), 0.6 parts of acrylic monomer having the following chemical formula (II) and 0.6 parts of an optical polymerization initiator (1-hydroxy-cyclohexyl-phenyl-ketone) were dissolved in a mixture solvent containing 50 parts of monochloro benzene and 50 parts of dichloromethane to prepare a liquid for application for a surface protective layer. This liquid for application was applied to the charge transport layer mentioned above by a spray coating method. The resultant was cured by a metal halide lamp with a light intensity of 500mW/cm2 for 30 seconds to form a surface protective layer having a thickness of 5 μm.
[Chemical Formulae 1]
The structures illustrated in
In addition to the structure illustrated in
The structure illustrated in
The structure illustrated in
The structure illustrated in
The structure illustrated in
The structure illustrated in
The blade for use in lubricant layer uniforming device can be formed of materials forming a cleaning blade. That is, known materials such as polyurethane rubber, silicon rubber, nitrile rubber, chloroprene rubber can be used. In addition, such a blade preferably has an elasticity of from 20 to 80%, a thickness of from 1 to 6 mm, and a contact angle against an image bearing member of from 15° to 45°.
The rotation direction of the fur brush 7-1 contacting with the lubricant supplying device 103 or the lubrication member 102 illustrated in
0.5×V1≦V2≦5×V1(V1#V2) (8).
When such a brush roller is used, the brush roller preferably has a density of from 2,000 to 10,000 strings/cm2 and more preferably from 3,000 to 8,000 strings/cm2. The lower limit thereof is determined based on the result of an experiment for the occurrence of an abnormal image by an image bearing member. The upper limit thereof simply represents the limit in terms of the current manufacturing technology and can be higher as the manufacturing technology is improved. Therefore, the upper limit thereof is not necessarily limited.
What state of the lubricant should be achieved on the image bearing member 2 by the lubricant removing mode and the lubricant supplying mode mentioned above is not completely understood. However, it is found that it is possible to prevent degeneration (white turbidity) of the surface of a charged body (the image bearing member 2) when the ratio (%) of the metal elements contained in a metal salt of a fatty acid present on the surface of the image bearing member 2 is not less than the value represented by (9) based on XPS measurement:
1.52×10−4×{Vpp−2×Vth}×f/v(%) (9).
In the relationship (9), Vpp represents the amplitude (V) of the AC component applied to a charging member, f represents the frequency (Hz) of the AC component applied to a charging member, Gp represents the closest distance (μm) between the surface of a charging member and the surface of a charged body, v represents the moving speed (mm/sec) of the surface of a charged body opposing a charging member, and Vth represents the initial discharging voltage. In addition, the value of Vth is 312+6.2×(d/∈opc+Gp/εair)+√(7737.6×d/∈), wherein d (μm) represents the pressure of the layer of a charged body, ∈opc represents the specific dielectric constant of a charged body, and ∈air represents the specific dielectric constant of the space between a charged body and a charging member.
In the image forming apparatus illustrated in
In addition, the image formation unit of the embodiment has another member contacting with the image bearing member 2 in addition to the charging device 3. As illustrated in
These members form members contacting the image bearing member 2 can be detached or attached to the main body of an image forming apparatus on a separate occasion with the image bearing member 3. However, when a contacting member is detached or attached, these contacting members move while in contact with the image bearing member 2. Therefore, the image bearing member 2 receives a great stress from outside, which may change the minute gap G. To the contrary, when the contacting members such as the cleaning blade, the lubricant supplying device 103, and the lubricant supplying device are contained as the elements of an image formation unit, the contacting members are detached or attached together when the image formation unit is detached or attached to the main body of an image bearing member. Therefore, these contacting members are relatively immovable based on the image bearing member 2. Therefore, the minute gap G does not vary so that the image bearing member 2 is prevented from being scarred or scratched by the contact.
In addition, when the image bearing member 2 is structured as an organic photoreceptor having a surface layer reinforced by a filling material such as aluminum powder having a diameter of not greater than 0.1 μm, an organic photoreceptor using a cross-linkage charge transport material, or an organic photoreceptor having both characteristics, its surface hardness is improved. Therefore, anti-abrasion property thereof is improved, which leads to a long life of the image bearing member 2.
In one embodiment, the degraded lubricant or the nonfunctional lubricant remaining on the surface of the image bearing member 2 can be surely removed to prevent the deterioration of the quality of images and the occurrence of abnormal images.
In addition, the lubricant layer on the image bearing member 2 can be easily removed by suitably controlling the attachment of toner to the image bearing member 2.
In one embodiment, it is possible to prevent the lubricant from entering into the developing device (unit) by applying a DC developing bias. Further, by applying a lubricant to the image bearing member 2, the image bearing member is protected from discharging of the developing device. The image bearing member 2 has a protective layer on its surface so that the amount of layer scraping decreases.
In one embodiment, the scraped amount of layer of the image bearing member 2 further can be decreased due to the binder resin having a cross-linkage structure contained in the protective layer of the image bearing member 2. In addition, the quality of images can be improved because the binder resin having a cross-linkage structure contained in the protective layer of the image bearing member 2 includes a charge transport portion.
In one embodiment, by forming a process cartridge for use in an image forming apparatus integrally including the image bearing member 2, the lubricant removal device and the lubricant supplying device, the serviceability is improved as well as it becomes easy to maintain the contacting state between the image baring member 2 and the lubricant supplying device 103.
This document claims priority and contains subject matter related to Japanese Patent Application No. 2005-074351, filed on Mar. 16, 2005, the entire contents of which are incorporated herein by reference.
Having now fully described embodiments of the present invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit and scope of embodiments of the invention as set forth herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-074351 | Mar 2005 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20030044201 | Kosuge | Mar 2003 | A1 |
| 20050191099 | Yamaguchi et al. | Sep 2005 | A1 |
| 20070166087 | Yamaguchi et al. | Jul 2007 | A1 |
| 20070212139 | Sugiura et al. | Sep 2007 | A1 |
| 20070218383 | Seshita et al. | Sep 2007 | A1 |
| 20070218385 | Kojima et al. | Sep 2007 | A1 |
| 20080070148 | Awamura et al. | Mar 2008 | A1 |
| 20080076055 | Sawada et al. | Mar 2008 | A1 |
| 20090074467 | Seshita et al. | Mar 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 10-142897 | May 1998 | JP |
| 10-312098 | Nov 1998 | JP |
| 2001-051571 | Feb 2001 | JP |
| 2001-228668 | Aug 2001 | JP |
| 2002-006689 | Jan 2002 | JP |
| 2002-055580 | Feb 2002 | JP |
| 2002-156877 | May 2002 | JP |
| 2002-229227 | Aug 2002 | JP |
| 2002-244516 | Aug 2002 | JP |
| 2002-357983 | Dec 2002 | JP |
| 3507277 | Dec 2003 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20060210334 A1 | Sep 2006 | US |
