Patent Application
20120148307
The present invention relates to a blade-like charging member for charging a surface of an image bearing member, the charging member being moved relative to an image bearing member (member to be charged) carrying an electrostatic latent image in contact thereto while being supplied with a voltage, and to an image forming apparatus using the charging member.
Here, a typical example of the image bearing member on which the electrostatic latent image is formed is an electrophotographic photosensitive member or a dielectric member for electrostatic recording. As for the image forming apparatus, there are an electrophotographic type or electrostatic recording type copying machine, printer, facsimile machine or a complex machine thereof, and an image display device or the like.
The description will be made as to a transfer type electrophotographic image forming apparatus, taking for example. Generally, in such an apparatus, the electrostatic latent image of image information is formed by charging means for charging uniformly a surface of the image bearing member (rotatable drum type electrophotographic photosensitive member) to a predetermined polarity and potential and by exposure means for selectively exposing the thus charged drum surface to the light of the image information. The latent image is visualized (developed) into a toner image using a developer (toner) by developing means. The toner image is transferred onto a recording material (recording material) by transferring means. The transferred toner image is fixed by fixing means into a fixed image on the recording material, and then the recording material is outputted as a print.
A recently dominant charging means (charging device) is a contact-charging type means using a fixed type charging member such as a blade or film, or a rotating type charging member such as a brush, roller, belt of semiconductive rubber or resin material.
The contact-charging type does not necessitate an ozone removing filter because the amount of produced ozone is small. The required voltage applied to provide the surface of the drum with a predetermined potential may be small, and therefore, the cost can be reduced.
A charging mechanism of the contact-charging type will be described. It is known that the charging mechanism for the drum surface in the contact charging system is ruled by the Paschen law relating to the electric discharge in a small gap.
Referring to
The charging roller 21 has a length to cover an image forming region (maximum image region width) G of the surface of the drum 1 and is rotated by the rotation of the drum 1. To the core metal 21a of the charging roller 21, a predetermined charging bias voltage is applied from the charging bias voltage applying source E so that a bias voltage is applied to the elastic layer 21b through the core metal 21a. By this, the surface of the rotation drum 1 is charged uniformly to the predetermined polarity and potential.
Part (c) of
Vair=C2/(C1+C2) (1)
The air layer has a dielectric breakdown voltage determined by the Paschen law, and it is as follows when the thickness of the air layer is g [micron]:
312+6.2 g [V] (2)
When Vair exceeds this, the discharge occurs.
The minimum discharging voltage is that when formula (1) is equal to formula (2) and the air layer thickness g obtained by the equation has a double root (C1 is also a function of g), and a DC voltage value at this time is a discharge starting voltage Vth. The theoretical value Vth thus obtained is very close to an experiment value.
The charging roller tends to be complicated in the structure since it requires a rotatable supporting member 211, an urging spring 212 and so on for the charging roller 21. A brush charging member (charging brush) is time-consuming in manufacturing the brush irrespective of whether it is rotating type or fixing type, and tracks of the brush fibers may result in unevenness of charging.
Part (a) of
A predetermined charging bias voltage is applied from a charging bias voltage applying source to the supporting member 223, so that the bias voltage is applied to the blade portion 220 through is supporting member 223. By this, the surface of the rotation drum 1 is charged uniformly to predetermined polarity and potential. The discharge occurs in the wedged small gap formed between the blade portion 220 and the drum 1, and a relatively stable small gap can be formed. The rotation supporting member 211 and the urging spring 212 and so on required by the charging roller are unnecessary, and therefore, the blade type is inexpensive.
However, a part of the blade portion 220 of the charging blade 22 is always in contact with the drum 1, and therefore, involves the following problems.
A: as shown in part (b) of
B: in order to prevent pin hole leakage which is a leakage of the voltage applied to the blade portion 220 through pin holes existing on the surface of the drum 1, a protection layer is provided on the blade portion 220 at the position contacting the drum 1 in many cases. In such cases, the protection layer is worn with long term use, and then the pin hole leakage may occur.
Japanese Laid-open Patent Application Hei 09-319183 proposes a structure of a charging blade comprising a semiconductive portion for effecting discharge, and an insulative portion for contacting the drum o position the semiconductive portion with a small gap from the drum. With such a structure, the semiconductive portion and the drum are always kept non-contact, and therefore, the pin hole leakage is suppressed for long term use.
Japanese Laid-open Patent Application Hei 08-62937 proposes a having comprising a blade of an insulative elastic member and a charging electrode layer provided on the surface of the blade opposing the drum. By setting properly a distance from a free end of the blade to the free end of the charging electrode layer, the influence of the accumulation of the toner or the like on the charging electrode layer suppressed to form images without the image defect.
Japanese Laid-open Patent Application Hei 08-62938 proposes a structure comprising a blade of an insulative elastic member, and a charging electrode layer provided on the surface of the blade opposing the drum, wherein a convex portion is provided which separates from the drum surface and then approaches to the drum. This is advantageous in that the distance through free end of the blade to the free end of the charging electrode layer can be made longer than in Japanese Laid-open Patent Application Hei 08-62937, thus stabilizing the image formation without the stripes.
Because of the recent demand for downsizing of the image forming apparatus and for reducing the weight, the following problems arise. When the charging blade and the drum are press-contacted to each other, virtual bites of the blade at the longitudinal end and central portions of the drum are different, as shown in part (a) of
In the above-described prior art, there is a relation shown in part (c) of
Accordingly, it is a object of the present invention to provide a blade-like charging member capable of effecting stabilized charging with suppressed influence of a flexure of an image bearing member, and an image forming apparatus using the charging member.
According to an aspect of the present invention, there is provided a blade-like charging member for charging a surface of an image bearing member by contacting thereto and by being supplied with a voltage, said charging member comprising a charging portion for effecting electric discharge to the surface of the image bearing member; a non-charging portion not effecting the electric discharge to the surface of the image bearing member; wherein non-charging portion capable of contacting said image bearing member with maintaining an electrically dischargeable gap between said charging portion and said image bearing member, at least a part of said non-charging portion is made of a material having a higher resistance than that of said charging portion so as to prevent electric discharge between said non-charging portion and the surface of said image bearing member, and an amount of deformation of said charging member when a force is applied to said non-charging portion in a longitudinally central portion is larger than an amount of deformation of said charging member when the same force is applied to said non-charging portion in a longitudinally end portion.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
In
In
Referring first to
The recording material P is a sheet on which an image can be formed by an electrophotographic process, and is a sheet of paper, a resin material sheet, a label or the like. The control circuit portion 200 exchange various electrical information with an operating portion 300 or the host apparatus 400, and controls overall image forming operation of the device 100 in accordance with predetermined control program and reference table stored in a storing portion.
In a main assembly of the apparatus of the device 100, there is provided a cartridge accommodating portion 100A. A process cartridge 50 is demountably mounted to the cartridge accommodating portion 100A through a predetermined operation manner. In this embodiment, the cartridge 50 is an integral type process cartridge. More particularly, an electrophotographic photosensitive drum as an image bearing member on which an electrostatic latent image developed with a developer T is formed, charging means 22, developing means 10 and cleaning means 7 are mounted to a common casing into a unit.
In this embodiment, the charging means 22 is a charging blade. The charging blade 22 will be described hereinafter. The developing means 10 is a non-contact-type developing device operable with one component magnetic toner as the developer T. In the following, the developer T will be called toner, too. The cleaning means 7 is a blade cleaning device using an elastic blade 7a as a cleaning member.
The developing device 10 includes a developing container 10a as a developer accommodating portion accommodating the toner T. It also includes a developing sleeve 10b as a developer carrying member for developing an electrostatic latent image formed on the drum 1 into a toner image, a non-rotatable magnet roller 10c provided in the sleeve 10b, a developing blade 10d for regulating an amount of the toner on the developing sleeve 10b, and so on.
Above the cartridge accommodating portion 100A, there is provided a laser scanner unit 3 as image exposure means. The unit 3 outputs a laser beam L modulated in accordance with the image information inputted to the control circuit portion 200 from the host apparatus 400. The laser beam L enters the cartridge 50 through an exposure window provided in a top side. By doing so, the surface of the drum 1 is scanningly exposed to a laser beam.
To the drum 1 in the cartridge 50, a transfer roller 9 is contacted to form a transfer nip N. The cartridge 50 accommodated in the cartridge accommodating portion 100A is urged to a positioning portion (unshown) in the main assembly side of the apparatus by an urging means (unshown) is correctly positioned. In addition, a drive outputting portion (unshown) of the main assembly side of the apparatus is connected to a drive inputting portion (unshown) of the cartridge 50. To various electrical contacts (unshown) of the cartridge 50, the corresponding electrical contacts (unshown) of the main assembly side of the apparatus are contacted.
The image forming operation is as follows. Drum 1 is rotated in the clockwise direction indicated by arrow R at a predetermined peripheral speed (process speed). The unit 3 is also driven. In synchronism with the drive, a predetermined charging bias voltage is applied from a charging bias voltage applying source E to the charging blade 22 at predetermined control timing so that the surface of the drum 1 is charged uniformly to the predetermined polarity and potential by the charging blade 22 by a non-contact type charging. The unit 3 scans and exposes the surface of the drum 1 by a laser beam L modulated in accordance with the image signal. By this, an electrostatic latent image is formed in accordance with the image signal on the surface of the drum 1.
The electrostatic latent image thus formed is developed into a toner image by the toner carried on the developing sleeve 10b of the developing device 10. The developing sleeve 10b is rotated in a counterclockwise direction indicated by an arrow at a predetermined speed. To the developing sleeve 10b, a predetermined developing bias voltage is applied at predetermined control timing from a developing bias applying voltage source portion (unshown).
On the other hand, one recording material P is separated and fed out of a sheet feeding mechanism portion (unshown) and is introduced into the transfer nip N at predetermined control timing and is nipped and fed through the nip N. During the recording material P moving the nip N, a predetermined transfer bias is applied to the transfer roller 9 from a transfer bias application voltage source portion (unshown) By this, the toner image is transferred from the drum 1 onto the surface of the recording material P sequentially.
The recording material P having passed through the nip N is separated from the surface of the drum 1 and is introduced into the fixing device 8. In this embodiment, the fixing device 8 is a heat roller fixing device, and the recording material P is nipped and fed by a fixing nip and is subjected to heat and pressure. By this, the unfixed toner image on the recording material P is heat-pressure fixed into a fixed image. The recording material P discharged from the fixing device 8 is discharged from the device 100 as a print. The surface of the drum 1 after the recording material is separated, is cleaned by a cleaning blade 7a so that deposited residual matter such as untransferred toner is removed therefrom, thus it is prepared for the next image formation.
The charging blade 22 is contacted to the drum counterdirectionally with respect to the rotation of the drum 1 at a position of β degree from a horizontal line passing through the center of the drum 1 (the angle β is formed between the horizontal line and a line connecting the drum center and the contact position between the drum 1 and the blade 22)
As shown in
Here, an example of determining an actual virtual bite δ and a setting angle θ. The charging blade 22 and the drum 1 are set in the state of image forming operation, and the drum 1 is removed, and then the virtual bite δ and the θ are measured. In
As shown in
δ=√(r̂2−X̂2) (1)
θ=tan−1(X/r) (2)
Part (a) of
The non-charging portion 221 contacts the drum 1 to provide a gap between the charging portion 222 and the drum 1, across which the electric discharge occurs. At least a part of the non-charging portion 221 is made of a high resistance material having a resistance higher than that of the charging portion 222 to prevent discharge between the non-charging portion 221 and the surface of the drum 1. Designated by 220 is a discharging position where the drum is charged through the fine gap g (
Designated by 223 is an elastic member of metal (metal leaf spring), and), 224 is a holder. The elastic member 223 supports the charging portion 222 and the non-charging portion 221. In this embodiment, the holder 224 is made of electroconductive material, and the holder 224 and the charging portion 222 are electrically conduced by the elastic member 223, so that the charging voltage is applied from the voltage source E to the charging portion 222 through the holder 224 and the elastic member 223.
The charging portion 222 is elongate in a generatrix direction of the drum 1 (drum axis direction), and is long enough to cover the entirety of an image forming region G of the drum 1 (charging region width in part (a) of
If the resistance of the charging portion 222 is smaller than 1×10̂3 Ωcm, the current leakage may occur when the drum 1 has a defect such as a pin hole, with the result of image defect white strips or black stripes. If, on the contrary, it is not less than 1×10̂9 Ωcm, the attenuation of applied voltage is so large that the chargeable is poor. Therefore, the resistance value of the charging portion 222 is desirably 1×10̂3 Ωcm -1×10̂9 Ωcm.
Part (a) and part (b) of
In this contact state, the charging portion 222 is out of contact to the drum 1. And, the discharging position 220 of the charging portion 222 is out of contact with a dischargeable gap g (g1, g2) from the drum 1.
In the charging blade 22 of this embodiment, the discharging position 220 of the charging portion 222 is a meeting portion between a connection end surface of the charging portion 222 relative to the non-charging portion 221 and a surface of the charging portion 222 opposing the drum 1. That is, the discharging position 220 is the closest position between the charging portion 222 and the drum 1.
The predetermined charging bias voltage is applied to the electroconductive holder 224 from charging bias voltage applying source E, and the bias voltage is applied to the charging portion 222 through the holder 224 and the metal elastic member 223. By this, the discharge occurs to the surface of drum 1 across the small gap g between the discharging position 220 of the charging portion 222 and the drum 1 to charge uniformly the surface of the rotating drum 1 to the predetermined polarity and potential.
In order to effect the charging stably, the small gap g is not less than 7.5 μm and not more than 150 μm, desirably not less than 7.5 μm and not more than 100 μm. If the small gap g is less than 7.5 μm, the discharge does not occur as will be understood from the Paschen law. If, on the other hand, the small gap g is not less than 150 μm, the discharge occur, but is non-uniform with the result of defective image having spots. Therefore, for the stabilized discharge, the gap g is desirably not more than 100 μm.
The lower limit value of the small gap g for generating the discharge is constant irrespective of the applied voltage or the discharging member. The lower limit value of the small gap g for the generation of the discharge changes to a certain extent by the ambient pressure. In this embodiment, the above-mentioned 7.5 μm is based on (760 torr). This ambient pressure is an ordinary condition.
In this embodiment, the distance between the drum 1 and the charging portion 222 is not less than 7.5 μm and not more than 150 μm, and the position on the charging portion 222 at the closest position between the drum 1 and the charging portion 222 is the discharging position 220.
verification has been made as to whether or not the theoretical discharging position 220 and the actual discharging position are the same. In the state that the charging blade 22 is press-contacted to the drum 1 which is not rotating, a predetermined charging potential is applied for a predetermined duration. A position of a trace of discharging on the charging portion 222 (discharging trace) is deemed as the actual discharging position. The applied charging potential is enough if the discharge continues, and by applying a sine wave AC voltage having a peak-to-peak voltage 2.0 kV, for example, for 10 minutes, a discharging trace is produced on the charging portion 222.
The result exhibited the position of the discharging trace and the theoretical discharging position are substantially the same. From the foregoing, the above-described theoretical determination of the discharging position is correct.
The non-charging portion 221 will be described. The non-charging portion 221 is directly contacted to the drum 1 at the free end portion of the charging blade 22. In this embodiment, the non-charging portion 221 of the charging blade 22 is made of an urethane rubber having a volume resistivity not less than 1×10̂11 Ωcm and a micro rubber hardness of 72♂o♂ (JIS-A). Other insulative rubber material such as a silicone rubber is usable.
The charging blade (charging member) 22 of the present invention is such that an amount of deformation of the charging blade when a force is applied to the non-charging portion 221 is larger in the central portion in the longitudinal direction of the charging blade (charging member) than in the end portions thereof.
In this embodiment, in order to provide the charging blade with such a property, the charging member is provided with a groove or a cut-away portion extending in the longitudinal direction of the charging member. A depth of the groove or a depth of the cut away portion is larger in the central portion than in the end portions with respect to longitudinal direction of the charging member.
As shown in part (b) of
In this case, as shown in (a) of
The deformation amount of the charging blade will be described. A distance S1 between a point N1 and a point N2 in the non-contact state relative to the drum as shown in part (a) of
A deformation amount Z1 in the central portion of the image region of the charging blade when the charging blade is contacted to the metal drum of the 30 mmφ with the predetermined set angle and virtual bite δ and a deformation amount Z2 in an end portion (20 mm inside from the end of the maximum image forming region) in the same condition, are measured. That is, a difference ΔZ=(deformation amount Z1−deformation amount Z2) when the same force is applied to the non-charging portion 221 of the charging blade satisfy ΔZ>0.
This will be described in more detail. The measurement of the deformation amount Z is made using a cut out test piece (longitudinally central portion piece and longitudinally end portion piece). The test pieces are observed facing the sectional surface using a laser microscope to measure the deformation amount Z and the difference ΔZ.
Image formation tests were carried out using an image forming apparatus 100 to which the cartridge 50 provided with the charging blade 22 is mounted. For these tests, 6 cartridges 50 having different virtual blade bites δ were prepared, and 8000 sheets image formation tests were carried out under the normal temperature and normal humidity ambient condition (N/N ambient condition), that is, 23° C./50%. For the comparison, the same tests were carried out using a charging blade not employing the present invention. The specific data of the charging blade are as follows:
<Charging Blade 22 of this Embodiment>
Conventional charging blade not provided with the groove portion U1 between the charging portion and the free end portion, and an insulative urethane rubber is formed at the free end contacting the drum 1.
a) Charging Blade Set Condition
The results are shown in Table 1. In the image forming tests using the 22 of this embodiment, the proper charging property has been kept up to 8000 sheets even when the virtual blade bite δ is different. In the case of the charging blade 22 of comparison example 1 not using this embodiment, non-uniform density image between the central portion and the end portions.
The causes of the facts are considered as follows.
When the virtual blade bite δ is about 0.5 mm, the small gap difference Δg arises, but the non-uniform density in the images is practically not problematic. When δ is larger than 0.7 mm, the flexure or deformation of the drum and therefore the gap difference are so large that the charged potential is uneven along the longitudinal direction. As a result, the formed images are non-uniform in the density.
On the other hand, in the charging blade 22 of this embodiment, the density uniformity of the image in the longitudinal direction is satisfactory. As shown in
As described in the foregoing, according to this embodiment, even when the drum flexes, satisfactory output images can be provided stably in a broad range of the virtual bite δ of the charging blade. In this embodiment, the groove portion U1 is provided in a side opposing the drum 1, but the uniform image density can be provided also when the groove portion U1 is provided in the side not opposing the drum 1 as shown in part (a) of
In this embodiment, the charging blade is provided with the groove portion U1, but in an alternative example, a cut away portion U2 is formed between the free end of the blade and the discharging position 220 as shown in part (b) of
The position of the groove portion U1 or the cut away portion is not limited to the non-charging portion 221. In the case of the charging blade 22 having a convex or protruding discharging position 220 as shown in part (c) of
The non-charging portion 221 will suffice if no discharge resulting in charging of the surface of the drum 1, and as shown in part (d) of
Part (a) of
More particularly, in the charging member 22 of this embodiment, a first charging member portion 222 and a second charging member portion 221 are bonded with each other by an adhesive material along the longitudinal direction of the charging member while a non-bonded portion Ba is provided. That is, the first charging member portion 222 and the second charging member portion 221 are bonded to each other by the bonded portion B. And, a non-bonding width Ba which is a width of the non-bonded portion Ba measured in the thickness direction of the charging member is larger in the longitudinally central portion than in the longitudinally end portion.
In this embodiment, the non-charging portion 221 and the charging portion 222 are bonded to each other by applying a primer (adhesive material) such that a distance from the surface of the side opposing the drum 1 to the bonded portion B is larger in the central portion than in the end portion. The details of the bonded portion B are as follows. The structures other than the bonded portion B are the same as with Embodiment 1.
With this structure, as shown in parts (a) and (b) of
Image formation tests were carried out using an image forming apparatus 100 to which the cartridge 50 provided with the charging blade 22 is mounted, similarly to Embodiment 1. The results are shown in Table 2.
Part (a) of
As described in the foregoing, according to this embodiment, even when the drum 1 flexes, the satisfactory output images can be produced stably in a wide range of the virtual bite δ of the charging blade 22.
Part (a) of
Elastic metal member 223: phosphor bronze having a thickness of 0.1 mm.
End configuration: arcuate (the longitudinally central portion is recessed by 0.4 mm as compared with the end portions).
Protruding amount (distance between a free end of the elastic metal member 223 and the charging portion 220) H:
A distance L4 between the free end portion and the discharging position 220: 0.7 mm.
By this, as shown in
Image formation tests were carried out using an image forming apparatus 100 to which the cartridge 50 provided with the charging blade 22 is mounted, similarly to Embodiment 1. In this embodiment, the non-charging portion (insulative portion) 221 of the charging blade 22 functions to clean the surface of the drum, and therefore, the charging blade 22 of this embodiment is a cleaning and charging blade as shown in
As will be understood, with the virtual bite δ=0.3 mm, the image uniformity is satisfactory, but the cleaning property us insufficient. This will be because the contact pressure between the cleaning and charging blade 22 and the drum is insufficient. When the virtual bite δ is not less than 1.5 mm, the cleaning property is practically acceptable, but the flexure of the drum 1 is so large that the image uniformity is not satisfactory. In the case of the virtual bite 6=0.5 mm-1.5 mm, both of the image density uniformity and the cleaning property are satisfactory, and the satisfactory images can be provided.
As described in the foregoing, according to this embodiment of the present invention, the charging blade can charge the drum stably in a wider range of the virtual bite δ of the charging blade, and the cleaning property is satisfactory, and therefore, a downsized image forming apparatus capable of forming satisfactory images with a smaller number of parts. In addition, the charging blade contacts to and slides on the drum 1 stably all over the image region of the surface of the drum, and therefore, the output images are uniform along the longitudinal direction.
1) the image bearing member on which the electrostatic latent image is formed is not limited to the electrophotographic photosensitive member for an electrophotographic type apparatus of the embodiments. It may be a dielectric member for electrostatic recording for an electrostatic recording type apparatus. The image bearing member is not limited to the drum type. It may be an endless rotatable belt, a traveling non-endless belt or the like. The image bearing member may be a sheet-like member (electro-facsimile machine paper, electrostatic recording paper) fed by a feeding means.
2) the relative movement between the image bearing member and the charging member is not limited to the case in which the image bearing member moves relative to the fixed charging member as in the foregoing embodiments, but the charging member may move relative to the fixed image bearing member, or both of the charging member and the image bearing member move with relative movement therebetween.
3) the contact of the charging member relative to the image bearing member is not limited to the counterdirectional contact as in the foregoing embodiments, but the codirectional contact may be employed. In addition, the edge contact is not inevitable, but convex contact can be employed.
4) in the present invention, the charging of the surface of the image bearing member by the charging member is not limited to applying the electric charge thereto, but includes the case of electrically discharging the image bearing member, that is, removing the electric charge from the image bearing member.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 278184/2010 filed Dec. 14, 2010 which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-278184 | Dec 2010 | JP | national |
