JP2003167416A - Image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which uses a contact electrifier as an electrifier for an image carrier and copes with wide sheets of paper without drastically increasing the sizes of the image carrier and contact electrifying member and without shortening the life of an image carrier, and to provide a process cartridge. <P>SOLUTION: In the image forming apparatus having the image carrier 1 and an image forming unit including the electrifiers for electrifying the image carrier layer surface of the image carrier, the electrifiers has a first electrifier 2 and a second electrifier 3. The first electrifier 2 electrifies the layer surface by externally applying a voltage to the contact electrifying member disposed in contact with the image carrier 1. The second electrifier 3 electrifies a range wider than the electrifying width of the first electrifier 2. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor,
The present invention relates to an image forming apparatus having an image forming device including an image carrier such as an electrostatic recording dielectric and a charging device that charges an image carrying layer surface of the image carrier.

Further, the present invention relates to a process cartridge which includes at least an image bearing member and a charging device for charging the image bearing layer surface of the image bearing member and which is attachable to and detachable from the main body of the image forming apparatus.

[0003]

2. Description of the Related Art Electrophotographic image forming apparatuses such as electrophotographic copying machines, laser beam printers, and plain paper FAX machines use electrophotographic photoreceptors such as selenium, cadmium sulfide, zinc oxide, amorphous silicon, and organic photoconductors. An image is obtained by performing basic processes such as charging, exposure, development, transfer, fixing and cleaning.

As a charging device for an electrophotographic photoreceptor, a non-contact charging (indirect charging) type corona charger has been widely used.

Recently, a contact charging (direct charging) type charging device for applying a voltage from the outside to a contact charging member arranged in contact with an image carrier to put it into practical use (for example, a special charging device). JP-A-57-178267 and JP-A-56
-104351, JP-A-58-40566, JP-A-58-139156, JP-A-58-1
50975 publication).

Specifically, the surface of the photoconductor has 1 to 2 KV.
A contact charging member such as a conductive elastic roller to which a DC voltage of about 2 KV _{PP and} an AC voltage of 2 KV _PP are applied is brought into contact with each other, and thereby the surface of the photoreceptor is charged to a predetermined potential. The contact charging member comprises a shaft, a base layer, a resistance layer and a surface layer. Further, the photoreceptor has a structure in which a photosensitive layer is provided on a conductive support.

[0007]

However, in general, this type of contact charging member has a drawback in that the diameter of the tip of the rubber, that is, both ends of the charging width is larger than that of the central portion because of covering the rubber.

For this reason, the amount of discharge at both ends of the contact charging member becomes large, and as a result, an excessive current flows in only a small part of the electrophotographic photosensitive member.

If the thickness of the charge transport layer, which determines the capacity of the electrophotographic photosensitive member, can be made smooth over the entire charging width, aS
In the case of an electrophotographic photosensitive member such as i, the amount of excess current does not become so large and problems do not occur.

However, in recent years, when the dip coating method which is generally used as the optimum manufacturing method for mass production of electrophotographic photoreceptors using organic semiconductors is used, the upper end portion of the electrophotographic photoreceptor, that is, the portion at the beginning of coating is the coating material. Phenomenon occurs due to its own weight. As a result, there is a thin portion of the charge transport layer on only one side of the electrophotographic photosensitive member. This is an unavoidable problem as long as it is manufactured under gravity.

Further, in recent years, with the downsizing of electrophotographic apparatuses, the tendency that the end portion of the contact charging member contacts the thin film portion has become extremely high. That is, when the thin film portion comes within the charging width, the thin film portion is abnormally scraped, and the base of the electrophotographic photoreceptor and the contact charging member eventually come into contact with each other and leak.

In order to avoid this, conventionally, the design has been made such that the end portion of the contact charging member does not hit the thin film portion, but as a recent tendency, it is premised on the use of wide paper such as full bleed paper. The required design has become necessary. In this case, it is possible to deal with the problem by increasing the size of the electrophotographic photosensitive member and the contact charging member, but it is inevitable that the image forming apparatus becomes large and the cost increases.

Further, when only the contact charging member is enlarged, the thin film portion is abnormally shaved as described above, and finally the base of the electrophotographic photosensitive member and the contact charging member come into contact with each other and leak. Occur.

As a recent trend, electrophotographic photoconductors are also negatively charged in order to cope with digitization, and an exposure system such as a laser or LED is used to lower the photoconductor potential of a printed portion to attach a developer to this portion. The so-called reversal development method is becoming mainstream. Not only printers, but also copying machines have been converted to MFPs, and many are equipped with printers and facsimile functions, and the reversal development method is widely used. In addition, as another trend, there is a need for a wide paper width, so-called full-bleed correspondence and novi correspondence. As is common in the printing industry and the like, a paper having a width of 10 mm to 20 mm wider than a normal paper size is used to make a mark for positioning outside the image area. Although it often remains the same as the image guarantee area, the electrophotographic apparatus must be able to pass at least this width of paper. Further, if possible, it is desirable to provide a mark for positioning so that printing can be performed even if the image quality is not guaranteed. However, when the reversal development is used, it is necessary to negatively charge the image non-guaranteed or non-printed area because of the property that the toner does not adhere to the negatively charged surface of the photoreceptor.

When this area is covered by the direct charging member for primary charging, the charging member becomes long, and the end portion of the charging member comes to a portion of the surface layer of the photosensitive member where the film thickness is thin, called sagging. As is known in the art, the roller type charging member that directly performs charging has a large discharge amount at both ends of the charging member due to the shape of the ends, etc., and as a result, excessive current is applied to only a small portion of the photoconductor. The phenomenon of flowing occurs. When this occurs in the thin portion of the surface layer, the life of the photoreceptor is significantly impaired.

Specifically, FIG. 3 shows the relationship between the area widths of respective parts of an electrophotographic copying machine capable of vertically feeding and copying A3 paper as a conventional image forming apparatus. A is the total width of the photosensitive layer of the electrophotographic photosensitive member, which is 340 mm here. B is the width of the charging area by the charging roller as the contact charging member, which is 310 mm here. C is a developing area width by the developing device, which is 300 mm here. D is A3
The width of the paper in the vertical feed direction is 297 mm. E is the image guarantee area width, which is 290 mm here. The image guarantee area width E becomes narrower than the paper width D by excluding the margin portion. However, the charging area width B and the developing area width C are set to be wider than the paper width D. Further, generally, the charging area width B is set to be wider than the developing area width C.

On the other hand, for wide paper, the paper width D is assumed to be about 320 mm. At this time, if only the size of the charging roller as the contact charging member is used, as shown in FIG. 4, paper width D: 320 mm, image guarantee area E: 290 mm, charging area width B by the charging roller:
It is 332 mm and the developing area width C is 300 mm.

To print the positioning marks and the like, refer to FIG.
As described above, it is necessary to further widen the developing area width C to about 313 mm.

On the other hand, the total width 34 of the photosensitive layer of the electrophotographic photosensitive member
At 0 mm, the sag of the photosensitive layer thickness is 4 from the edge of the photosensitive layer.
The film thickness is 10 μm at the position of 10 mm and the film thickness is 15 at the position of 10 mm.
After 15 μm, the film thickness becomes 25 μm. Therefore, it is most effective for the life of the photoconductor to design the charging roller to have a film thickness of 15 mm or more. But,
When the paper width is 320 mm, the charging area width is 332 as shown in FIG.
mm, the end of the charging roller is 4 mm from the end of the photosensitive layer
Will come to the position. The thickness of the photosensitive layer at the position of 4 mm is less than half the film thickness of 25 μm at the center of the photosensitive layer, which is less than half.
.mu.m, the life of the photoconductor is significantly reduced.

Therefore, by increasing the size of the charging roller as the contact charging member in the state where the width of the photosensitive layer is fixed, it is possible to deal with a wide paper width, which causes the above-mentioned problems.

In view of this, the present invention relates to an image forming apparatus using a contact charging device as a charging device for the image carrier, without significantly increasing the size of the image carrier or the contact charging member, and reducing the life of the image carrier. It is an object of the present invention to provide an image forming apparatus and a process cartridge that can handle a wide paper width without curling.

[0022]

SUMMARY OF THE INVENTION The present invention is an image forming apparatus and process cartridge characterized by the following configurations.

(1) In an image forming apparatus having an image forming device including an image bearing member and a charging device for charging an image bearing layer surface of the image bearing member, a first charging device and a second charging device are provided as the charging device. The first charging device is a contact charging device that charges the contact charging member disposed in contact with the image carrier by applying a voltage from the outside, and the second charging device charges the first charging device. An image forming apparatus characterized by being charged in a range wider than the width.

(2) The image forming apparatus according to (1), wherein the second charging device has less abrasion of the image carrying layer by the charging device than the abrasion of the image carrying layer by the first charging device.

(3) The image forming apparatus according to (1) or (2), wherein the second charging device is a corona charger.

(4) The image forming apparatus according to (1) or (2), wherein the second charging device is a brush charger.

(5) The image forming apparatus according to (1) or (2), wherein the second charging device is a needle electrode charger.

(6) The image forming apparatus according to (1) or (2), wherein the second charging device is a blade charger.

(7) The image carrier is an electrophotographic photoreceptor having a photosensitive layer containing an organic photoconductor on a conductive support, and the image carrier is any one of (1) to (6). Image forming device.

(8) At least the image carrier and the first and second charging devices are collectively configured as a process cartridge which can be attached to and detached from the main body of the image forming apparatus. The image forming apparatus according to any one of 7).

(9) A process cartridge which includes at least an image bearing member and a charging device for charging the image bearing layer surface of the image bearing member and which is attachable to and detachable from the main body of the image forming apparatus. The second charging device has a second charging device, the first charging device is a contact charging device that applies a voltage from the outside to a contact charging member that is disposed in contact with the image carrier, and the second charging device is a first charging device. A process cartridge which is electrified and charged in a range wider than a charging width of one charging device.

(10) The process cartridge according to (9), wherein the second charging device has less abrasion of the image carrying layer by the charging device than the abrasion of the image carrying layer by the first charging device.

(11) The process cartridge according to (9) or (10), wherein the second charging device is a corona charger.

(12) The process cartridge according to (9) or (10), wherein the second charging device is a brush charger.

(13) The process cartridge according to (9) or (10), wherein the second charging device is a needle electrode charger.

(14) The process cartridge according to (9) or (10), wherein the second charging device is a blade charger.

(15) The image carrier is an electrophotographic photoreceptor having a photosensitive layer containing an organic photoconductor on a conductive support, and the image carrier is any one of (9) to (14). Process cartridge.

<Operation> That is, as a result of repeated studies on the above-mentioned problems, a range wider than the first charging device for performing contact charging (direct charging) and the charging width for performing contact charging by the first charging device. It has been found that this problem can be solved by equipping the second charging device for charging.

That is, since the thin portion of the image bearing layer at the edge of the image bearing member is a region where the image quality is not guaranteed or the image need not be formed, the charging potential at the edge of the image bearing layer is not required. Need only be a potential from the developing bias to the dark part potential, and the uniformity is not limited. Therefore, the charging process of the end portion of the image bearing layer is performed by the second charging device that charges a wider range than the charging width where the contact charging is performed by the first charging device, and the image charging is performed by the second charging device. Corona charging that does not easily scratch or damage the carrier layer, non-contact charging (indirect charging) such as needle electrode charging, or charging that does not cause damage such as applying a DC bias to the blade or roller to softly contact In addition, it is possible to prevent the life of the image bearing member from being shortened due to the scraping of the edge portion of the image bearing layer, and it is possible to cope with a paper having a wide paper width with a conventional lifetime.

The second charging device is preferably arranged immediately before the first charging device, but it can be arranged from the transfer to the development if it does not interfere with other functions.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a schematic diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, a process cartridge attaching / detaching method, a copying machine, a facsimile machine, or a combination machine thereof.

Reference numeral 1 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, and an image bearing layer containing an organic photoconductor on the outer peripheral surface of a drum type conductive support. It has a photosensitive layer as a (charge holding layer). The photosensitive drum 1 is rotationally driven in the clockwise direction indicated by the arrow at a predetermined peripheral speed.

Reference numeral 2 is a contact charging roller (conductive elastic roller) as a first charging device. The charging roller 2 has a core metal and a conductive elastic rubber roller layer formed concentrically with the core metal as a basic structure. Both ends of the core metal are rotatably supported by bearings so that the axis line of the photosensitive drum 1 can be held. They are arranged substantially parallel to the axis and are pressed against the surface of the photosensitive drum 1 with a predetermined pressing force. The charging roller 2 rotates following the rotation of the photosensitive drum 1. S1 is a power supply for applying a charging bias to the charging roller 2, and this power supply S
1 applies a predetermined charging bias to the core of the charging roller 2, for example, a DC voltage of about 1 to 2 KV and an AC voltage of 2 KV _PP , so that the photosensitive layer of the photosensitive drum 1 has a predetermined polarity and potential. Is uniformly charged to the surface potential Vd.

Reference numeral 3 denotes a second charging device, which is a non-contact type corona charging device in this embodiment. S2 is a charging bias application power source for the corona charger 3. The voltage applied from the power source S2 to the corona charger 3 was adjusted so that the surface potential of the photosensitive layer of the photosensitive drum 1 was the same as the charging polarity by the charging roller 2 which is the first charging device, and was Vd setting. As will be described later, the corona charger 3 as the second charging device has a charging width wider than the charging width of the charging roller 2 as the first charging device.

A laser beam scanner 4 serves as an image exposure device. This laser beam scanner modulates image information input from a host device such as a computer (not shown), an image reader (not shown), or an external device (not shown) such as a facsimile machine of the other party in response to a time series electric digital pixel signal. Then, the laser beam L is output to scan and expose the photosensitive layer surface of the photosensitive drum 1 charged by the first and second charging devices 2.3. By this scanning exposure, the surface potential of the light exposed portion of the photosensitive layer is attenuated to form an electrostatic latent image corresponding to the scanning exposure pattern of the image information.

Reference numeral 5 is a developing device. S3 is a power source for applying a developing bias to the developing roller 5a of the developing device.
The electrostatic latent image formed on the photosensitive layer of the photosensitive drum 1 is subjected to reversal development (toner is attached to the light-exposed light-sensitive portion of the photosensitive layer) as a toner image by the developing device 5 in this embodiment.

Reference numeral 6 denotes a transfer roller as a transfer device, which presses the photosensitive drum 1 with a predetermined pressing force to form a transfer nip portion. S4 is a transfer bias application power source for the transfer roller 6. A recording paper (transfer material) P is fed from a paper feed mechanism (not shown) to the transfer nip at a predetermined control timing, and is nipped and conveyed in the transfer nip. During this time, a transfer bias of a predetermined potential having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 6 from the power source S4, so that the photosensitive drum 1 at the transfer nip portion.
The toner images on the surface side are sequentially transferred to the surface side of the recording paper P.

The recording paper P that has passed through the transfer nip portion is separated from the surface of the photosensitive drum 1 and is introduced into the fixing device 8, where it is subjected to the fixing process of the toner image and printed out.

The surface of the photosensitive drum 1 after the recording paper is separated is cleaned by a cleaning device 7 to remove residual contaminants such as transfer residual toner and paper dust, and is repeatedly used for image formation.

Reference numeral 9 is a process cartridge which can be attached to and detached from the main body of the image forming apparatus. In this embodiment, the photosensitive drum 1, the first and second charging devices 2 and 3, the developing device 5, and the cleaning device 7 are collectively configured as a process cartridge that can be attached to and detached from the image forming apparatus main body. Configured.

The process cartridge is a cartridge in which the charging means, the developing means or the cleaning means and the electrophotographic photosensitive member are integrally formed, and the cartridge can be attached to and detached from the main body of the image forming apparatus. Also, at least one of the charging means, the developing means, and the cleaning means and the electrophotographic photosensitive member are integrally made into a cartridge so as to be attachable to and detachable from the main body of the image forming apparatus. Furthermore,
At least the developing means and the electrophotographic photosensitive member are integrally made into a cartridge so that it can be attached to and detached from the apparatus main body.

The image forming apparatus of the present embodiment is an apparatus capable of vertically feeding and copying A3 paper, and is a so-called full bleed compatible and novi compatible apparatus having a wider paper width. FIG. 2 shows the relationship between the area widths of the respective parts of the image forming apparatus of this embodiment. A is the total width of the photosensitive layer of the electrophotographic photosensitive member, which is 340 mm as before. B is the width of the charging area by the charging roller 2 as the contact charging member which is the first charging device, and is 310 mm as in the conventional case. B'denotes a width of the charging area by the corona charger 3 which is the second charging device, and in this embodiment, 330 mm which is wider than the width 310 mm of the charging area by the charging roller 2 which is the first charging device.
Was set. C is a developing area width by the developing device, which is 313 mm here. D is the width of the paper wider than the width of the A3 paper lengthwise feed, and here 320 mm
Is. E is the image guarantee area width, which is 290 as before.
mm.

(Embodiment 2) The width B of the charging area by the charging roller 2 which is the first charging device is 310 mm as before, and the brush roller charging device is used as the second charging device 3 instead of the corona charging device. The brush roller charger was installed so that the width B ′ of the charging area was 330 mm.

(Embodiment 3) The width B of the charging area by the charging roller 2 which is the first charging device is 310 mm as in the conventional case, and the discharging charger needle charger is used as the second charging device 3 instead of the corona charger. It was set so that the width B ′ of the charging area by the charge eliminating needle charger was 330 mm.

(Embodiment 4) The width B of the charging area by the charging roller 2 which is the first charging device is 310 mm as before, and the blade charging device is used as the second charging device 3 instead of the corona charging device. It was set so that the charging area width B'by the charger was 330 mm.

(Embodiment 5) The charging area width B by the charging roller 2 which is the first charging device is 310 mm as in the conventional case, and the corona charger 3 is used as the second charging device by the charging area width 310 mm by the charging roller 2. Externally charged width 1
It was set so as to be 0 mm.

(Embodiment 6) The charging area width B by the charging roller 2 which is the first charging device is 310 mm as before, and the brush roller charging device as the second charging device has a charging area width of 310 mm by the charging roller 2. The charging width was set to 10 mm on both outer sides.

(Embodiment 7) The width B of the charging area by the charging roller 2 which is the first charging device is 310 mm as in the conventional case, and the discharging needle charger as the second charging device is 310 mm wide by the charging area of the charging roller 2. Charge width 1 on both outer sides
It was set so as to be 0 mm.

(Embodiment 8) The width B of the charging area by the charging roller 2 as the first charging device is 310 mm as in the conventional case, and the blade charging device as the second charging device has a width of 310 mm by the charging roller 2 as the charging area. It was installed outside so that the charging width was 10 mm.

(Comparative Example 1) The charging area width B of the charging roller 2 which is the first charging device was set to 332 mm, and the second charging device was not attached.

Table 1 shows the results of a durability test conducted by modifying the Canon digital copying machine GP405 so that a paper having a width of 320 mm can be passed by using a drum unit (process cartridge) modified to the above apparatus configuration.

[0062]

[Table 1]

In the prior art (FIG. 3), the end of the charging roller as a contact charging device is located at a position where the photosensitive layer is sufficiently thick, so the service life was 50 K. However, in Comparative Example 1 in which the charging roller is long, the end of the charging roller is The life of the photosensitive layer was remarkably shortened because the photosensitive layer was thin.

In the charging area of the second charging device, which is less scraped than the contact charging other than that, the scraping is about half or less, and the life is not rate-controlled, and the life as usual can be secured. In Examples 1 to 4, since the image area was also charged as compared with Examples 5 to 8, the abrasion of the image area was slightly increased, but it was smaller than the abrasion of the contact charging end portion and the rate-determining was not obtained. Further, in each of the examples, there was no fog in the non-image area (image non-guaranteed area), and the image was good.

The present invention can also be applied to an electrostatic recording apparatus using an electrostatic recording dielectric as an image carrier.

[0066]

As described above, by adopting the configuration of the present invention, the image forming apparatus and the process cartridge using the contact charging device as the charging device for the image bearing member can be used as shown in the experimental results. It is possible to provide an image forming apparatus and a process cartridge that can cope with a wide paper without causing any adverse effects without causing a deterioration in life.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a region width relationship of each part.

FIG. 3 is a diagram showing a region width relationship of each part of the conventional image forming apparatus.

FIG. 4 is a diagram showing a region width relationship (1) for coping with wide paper.

FIG. 5 is a diagram showing a region width relationship (part 2) for coping with wide paper.

[Explanation of symbols]

1 ... Image carrier, 2 ... 1st charging device (contact charging roller), 3 ... 2nd charging device (corona charger), 4 ...
・ Laser beam scanner, 5 ・ ・ Developing device, 6 ・ ・ Transfer roller, 7 ・ ・ Cleaning device, 8 ・ ・ Fixing device, 9 ・ ・ Process cartridge

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H200 FA02 FA09 FA19 GA03 GA16                       GA23 GA34 GA59 GB12 HA02                       HA12 HA28 HB06 HB07 HB12                       HB14 HB22 HB41 HB46 HB47                       HB48 JA02 JB10 LA01 LA13                       LA38 MB01 MC01 NA06

Claims (15)

[Claims] 1. An image forming apparatus having an image forming device including an image bearing member and a charging device for charging an image bearing layer surface of the image bearing member, wherein the charging device has first and second charging devices. The first charging device is a contact charging device that applies a voltage from the outside to a contact charging member that is arranged in contact with the image carrier to charge it, and the second charging device is a charging width of the first charging device. An image forming apparatus characterized by being charged in a wider range. 2. The image forming apparatus according to claim 1, wherein the second charging device has less abrasion of the image carrying layer by the charging device than the abrasion of the image carrying layer by the first charging device. 3. The image forming apparatus according to claim 1, wherein the second charging device is a corona charger. 4. The image forming apparatus according to claim 1, wherein the second charging device is a brush charger. 5. The image forming apparatus according to claim 1, wherein the second charging device is a needle electrode charger. 6. The image forming apparatus according to claim 1, wherein the second charging device is a blade charger. 7. The image forming apparatus according to claim 1, wherein the image carrier is an electrophotographic photoreceptor having a photosensitive layer containing an organic photoconductor on a conductive support. apparatus. 8. The process cartridge according to claim 1, wherein at least the image carrier and the first and second charging devices are collectively configured as a process cartridge that can be attached to and detached from the image forming apparatus main body. The image forming apparatus according to any one of claims. 9. A process cartridge which includes at least an image carrier and a charging device for charging an image carrying layer surface of the image carrier and which is attachable to and detachable from a main body of an image forming apparatus. And a first charging device is a contact charging device that applies a voltage from the outside to a contact charging member disposed in contact with the image carrier to charge the member.
A process cartridge characterized in that the second charging device charges a wider range than the charging width of the first charging device. 10. The process cartridge according to claim 9, wherein the second charging device has less abrasion of the image bearing layer by the charging device than the abrasion of the image bearing layer by the first charging device. 11. The process cartridge according to claim 9, wherein the second charging device is a corona charger. 12. The process cartridge according to claim 9, wherein the second charging device is a brush charger. 13. The process cartridge according to claim 9, wherein the second charging device is a needle electrode charger. 14. The process cartridge according to claim 9, wherein the second charging device is a blade charger. 15. The process cartridge according to claim 9, wherein the image carrier is an electrophotographic photoreceptor having a photosensitive layer containing an organic photoconductor on a conductive support. .