JP2002365941A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device, capable of preventing the deterioration of an image by surely preventing the occurrence of filming due to long-term use and faulty cleaning caused by the adhesion of silicone oil at the time of fixing, without complicating structure. SOLUTION: This imaging device is equipped with a photoreceptor drum (image carrier) 1a having a movable surface, a toner imaging means (primary electrifier 2a and developing device 4a) for forming a toner image on the surface of the drum 1a, a transfer belt (transfer body) 7 for transferring the toner image to transfer material, and a cleaning device (cleaning means) 8a removing residual toner left on the surface of the drum 1a, after transferring the toner image. The device is constituted, so that the abutting pressure of the belt 7 disposed on the upstream side of the device 8a in the moving direction of the surface of the drum 1a to the surface of the drum 1a can be changed, and also the pressing surface of a pressing member for pressing the belt 7a at the imaging time and the abutting surface of the pressing member at the image non-forming time are made different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer which employs an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a laser beam printer, a method of forming a toner image on the surface of a photosensitive drum and transferring the toner image to a transfer material such as paper is known. The residual toner remaining on the surface of the photosensitive drum is removed by a cleaning device.

[0003] The cleaning device includes, for example, a cleaning blade in which an elastic member such as urethane rubber is formed in a plate shape, and the edge of the cleaning blade is brought into contact with the surface of the photosensitive drum at a predetermined pressure to contact the surface of the photosensitive drum. The attached residual toner is scraped off. A cleaning device using this cleaning blade has a relatively simple structure, is small in size, and has an advantage of excellent toner removal performance in spite of being advantageous in cost, and therefore has been widely put to practical use. ing.

[0004]

However, in the conventional image forming apparatus, since the cleaning blade is in contact with the surface of the photosensitive drum, the residual toner on the cleaning blade becomes strong with the long-term use of the image forming apparatus. There is a problem that filming occurs due to the adhesion and deteriorates the subsequent image. Alternatively, there is a problem in that a rubbing scratch is generated by a developer or the like at the time of paper jam adhered to the surface of the photosensitive drum on the transfer belt surface, and a starting point of toner rubbing-through or an image defect (flaw image) is generated.

Further, recently, in an image forming apparatus,
After an image is formed on the front surface (first surface) of the transfer material, the transfer material is turned upside down in the image forming apparatus and the back surface (second surface) is formed.
Those having a double-sided image forming function for forming an image again are often used.

In such an image forming apparatus, when a general fixing device having a configuration in which a transfer material is passed through a nip portion of a pair of rollers is used for fixing a toner image, it is difficult for toner to adhere to the rollers. Apply silicone oil to the roller surface to prevent it. The silicone oil adheres to the transfer material when the toner image on the first surface is fixed, and adheres to the photosensitive drum when the image on the second surface is formed. Then, there is a problem that the silicone oil attached to the surface of the photosensitive drum causes poor charging, or mixes with the toner present at the edge of the cleaning blade and slips through the edge of the cleaning blade to cause poor cleaning. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to prevent filming due to long-term use and adhesion of silicone oil at the time of fixing without complicating the structure. An object of the present invention is to provide an image forming apparatus capable of reliably preventing defective cleaning and preventing image deterioration.

[0008]

In order to achieve the above object, the present invention provides an image carrier having a movable surface, a toner image forming means for forming a toner image on the surface of the image carrier, and the image forming apparatus. A transfer member that is in contact with the surface of the carrier and transfers the toner image on the surface of the image carrier to a transfer material; and a cleaning unit that removes residual toner remaining on the surface of the image carrier after transfer of the toner image. In the image forming apparatus,
The transfer member disposed on the upstream side of the cleaning unit in the moving direction of the surface of the image carrier is configured to be capable of changing a contact pressure of the transfer member against the surface of the image carrier, and the transfer member during image formation is changed. The pressing surface of the pressing member to be pressed and the contact surface of the pressing member during non-image formation are different surfaces.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 4 is a block diagram showing an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is a four-color full-color image forming apparatus (copier), and transports a transfer material such as paper inside an image forming apparatus main body (hereinafter simply referred to as “apparatus main body”) 100. Four image forming units in order from the upstream side (right side in the figure) to the downstream side (left side in the figure), that is, a first image forming unit Pa, a second image forming unit Pb, and a third image forming unit. And a fourth image forming unit Pd. FIG. 1 shows an enlarged view of the first image forming unit Pa on the most upstream side. The other second, third, and fourth image forming apparatuses Pb, Pc, and Pd have substantially the same configuration as that of the first image forming unit Pa, and a description thereof will be omitted. However, in FIG. 2, members and the like common to the first to fourth image forming apparatuses Pa to Pd are distinguished from each other by the same numerals followed by reference numerals a to d.

As shown in FIG. 1, a first image forming unit Pa
Includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) 1a as an image carrier. As the photosensitive drum 1a, on the surface of a cylindrical aluminum base,
Carrier generation layer (CGL) and carrier transport layer (CTL)
Is coated so that the thickness of the CTL is 40 μm, and the photosensitive layer having a JIS surface roughness (B0601) of R
Those having z (10-point average roughness) of 2 μm or less in an initial state were used. The photosensitive drum 1a is rotatably supported by the apparatus main body 100 and is rotationally driven by a driving unit (not shown) at a process speed of 160 mm / sec in the direction of arrow R1. Here, a photosensitive drum 1a having a diameter of 60 mm was used.

A primary charger (toner image forming means) 2a is disposed above the photosensitive drum 1a, and the surface of the photosensitive drum 1a is uniformly charged by the primary charger 2a. The surface of the charged photosensitive drum 1a is exposed to an optical system (toner image forming means) H disposed above the image forming unit to form an electrostatic latent image, and thereafter, is exposed to light by a blank exposing unit 3a.

Subsequently, the toner in the developer is attached to the electrostatic latent image by a developing device (toner image forming means) 4a, and is developed as a toner image. As a developer, a two-component developer mainly composed of a toner and a ferrite-based carrier was used.

When the toner image reaches a transfer portion where the photosensitive drum 1a and the transfer blade 5a face each other, the transfer material P fed from the transfer material supply / conveyance section 6 (see FIG. 2) by this time is transferred to the transfer belt ( Transfer member) 7 carried on the surface and arrow K
The toner is conveyed in seven directions, arrives at the transfer site in a timely manner with the toner image on the photosensitive drum 1a, and is transferred from the surface of the photosensitive drum 1a onto the transfer material P by the action of an electric field formed by the transfer blade 5a. Transcribed. The above-described transfer belt 7 is configured to pass through respective transfer sites of the four image forming units Pa to Pd with the transfer material P being carried on the surface thereof.

On the photosensitive drum 1a after the transfer of the toner image, residual toner remaining on the surface without being transferred to the transfer material P is
The cleaning blade (9a) of the cleaning device (cleaning means) 8a scrapes off and removes the remaining charge. Further, the pre-exposure lamp 10a removes the residual charge, and is used for the next image formation.

The transfer material P on which the first toner image has been formed by the first image forming unit Pa as described above is conveyed to the downstream side by the conveying belt 7, and is transferred to the second image forming unit P.
b, third image forming unit Pc, and fourth image forming unit P
The toner image is transferred by d in the same manner as in the first image forming unit Pa. However, the toner colors of the toner images transferred in the first to fourth image forming units Pa to Pd are different from each other, and the four color toner images are superimposed on the surface of the transfer material P and pass through a fixing device 13 described later. As a result, a four-color full-color image is formed. The edge of the cleaning blade 9a is set at one edge with respect to the surface of the photosensitive drum 1a.
The contact is performed at a contact pressure of 0 to 40 gr / cm.

Transfer material P on which transfer of four color toner images has been completed
Then, as shown in FIG. 2, a separation bias is applied by a separation charger 11 to separate the transfer belt 7 from the transfer belt 7.
The toner image is conveyed to the fixing device 13 via the conveyance belt 12, and is heated and pressed by the fixing roller 13a and the pressure roller 13b to fix the toner image. At this time, for example, silicone oil is applied as a release agent to the surface of the fixing roller 13a, so that the toner on the transfer material P does not adhere to the surface of the fixing roller 13a.

The transfer material P having the toner image formed on the front surface (first surface) has a flapper 15 when the image is formed on one side.
And is discharged onto the paper discharge tray 14 after passing through the upper side. On the other hand, when image formation is performed on both surfaces (the first surface and the second surface), the transfer material P having the toner image fixed on the first surface is
By switching the flapper 15, the flapper 15 is guided to the lower re-feeding unit 16 without being discharged to the paper discharge tray 14. Then, after being turned upside down by the reversing device 17, it is supplied again to the first to fourth image forming units Pa, Pb, Pc, Pd, and after the toner images of four colors are transferred to the second surface, Fixing device 13
And is discharged onto the paper discharge tray 14 through above the flapper 15. Thereby, image formation on both sides is completed. The relative speed of the transfer belt 7 to the photosensitive drums 1a to 1d during the above operation is set to zero.

In the cleaning device 8a, residual toner (waste toner) removed from the surface of the photosensitive drum 1a by the cleaning blade 9a is temporarily stored between the sheet member 9e and the toner holding member 9f, and is sequentially stored.
The cleaning blade 9a is configured to be supplied little by little to the edge of the cleaning blade 9a to act as a lubricant, to reduce friction between the photosensitive drum 1a and the cleaning blade 9a, and to maintain a good cleaning action. During the cleaning process by the cleaning blade 9a, there is a possibility that the photosensitive drum la may be unevenly worn or damaged as described below. In the present invention, such uneven wear and damage are prevented. This will be described below.

As described above, when an image is formed on both surfaces of the transfer material P, when the toner image on the first surface of the transfer material P is fixed, the silicone oil adhering to the first surface removes the image on the second surface. At the time of formation, they adhere to the photosensitive drums la to ld via the transfer belt 7. Thus, the photosensitive drums 1a to 1d
Silicon oil adhering to the surface lowers the toner removing function of the edge of the cleaning blade 9a.

For example, for an A4 size transfer material P, 1
Transfer material P holding 10 mg of silicone oil per sheet
It has been confirmed by the present inventors that if five or more sheets are continuously passed through the cleaning blade 9a, cleaning failure will occur if the normal contact pressure (set pressure) of the cleaning blade 9a is 10 to 40 gr / cm. Therefore, when the contact pressure of the cleaning blade 9a is not changed, it is necessary to remove the silicon oil before reaching the cleaning blade 9a.

For this reason, in the present embodiment, the cleaning device 8a for the rotation direction of the photosensitive drums 1a to 1d is used.
8d, the transfer belt 7 wipes off the silicon oil on the surfaces of the photosensitive drums 1a to 1d. That is, the transfer belt 7 is rotated after the photosensitive drums la to ld during non-image formation (after the toner remaining on the photosensitive drums 1a to 1d is scraped off by the cleaning devices 8a to 8d after the image formation, the The transfer blade 5a is rotated to the upstream side of the transfer bell 7 during the rotation until the drums la to ld are stopped), and after changing the pressing surface of the transfer blade 5a (see FIG. 2), the transfer belt 7 is exposed again. 2.55 sec for drums la ~ ld
After the contact (for a period corresponding to three rotations of the photosensitive drums 1a to ld), the transfer belt 7 was separated from the photosensitive drums la to ld. Thereafter, the photosensitive drums la to ld rotate five times to complete a predetermined operation. The transport rotation speed of the transfer belt 7 when cleaning the photosensitive drums la to 1d was set to 80% of the peripheral speed of the photosensitive drums 1a to 1d.

Here, the transfer belt 7 in contact with the photosensitive drums 1a to 1d is a chargeable endless belt to which carbon is added, and has a total circumference of 1500 mm and a width of 400 m.
m and a thickness of 200 μm. As for the surface roughness, the one having a surface roughness of 5 μm or more on the outer peripheral surface of the transfer belt 7 (that is, the surface that comes into contact with the photosensitive drums la to ld) was used.

The surface roughness of the transfer belt 7 was measured by using a surface roughness measuring device (SE-3300 manufactured by Kosaka Laboratories Co., Ltd.) and the stylus was moved in a thrust direction perpendicular to the running direction of the transfer belt 7. The measurement was performed by running the transfer belt 7 in a state where the transfer belt 7 was contacted in the direction. Thereby, JIS surface roughness (B0601)
Rz (10-point average roughness) was measured according to.

The transfer blade 5a is disposed inside the transfer belt 7 having the above configuration. Transfer blade 5a
Is a urethane blade formed in a plate shape of urethane rubber having a thickness of l mm and a thrust length (length along the axial direction of the photosensitive drum la) of 360 mm, and having a rubber hardness of 70 on the surface.
°. During transfer of the toner image, a high transfer voltage is applied by a power supply (not shown).

The transfer blade 5a is swingably supported in the direction of arrow R5 with its base end as a center, and is configured to be located at the operating position A and the retracted position B. The transfer blade 5a moves to the operating position A during image formation (during a transfer operation), urges the transfer belt 7 from the back side, and places the front side on the surface of the photosensitive drum la and the linear pressure P1.
= 10 gr / cm (pressurized). In this state, a high transfer voltage is applied to the transfer blade 5a by a power supply (not shown) when transferring the toner image.

Here, the linear pressure is defined as follows.

That is, when the total length of the blade thrust of the transfer belt 7 uniformly contacted with the photosensitive drum 1a by the transfer blade 5a is Lcm, and the total pressure of the blade added to the total thrust of the photosensitive drum 1a is Pgr, Pressure = P / L (gr / cm).

When the transfer operation is completed, the transfer blade 5a
Moves in the direction away from the back surface of the transfer belt 7 and moves to the retreat position B, whereby the pressing operation of the transfer belt 7 on the photosensitive drum la is released.

On the other hand, after the completion of the transfer operation, the photosensitive drum 1a carrying the residual toner is rotated to the cleaning device 8a, and the residual toner is scraped off by the cleaning blade 9a in the cleaning device 8a. The cleaning blade 9a has a thickness of 2 mm and a thrust length of 34 mm.
It is constituted by a 5 mm plate-like urethane blade, the surface hardness is set to 65 °, and the contact pressure (linear pressure) against the surface of the photosensitive drum la is set to P3 = 30 gr / cm.

The photosensitive drum 1a, from which the residual toner has been scraped off by the cleaning blade 9a of the cleaning device 8a, is moved to the operating position A so as to come into contact with the post-rotation operation.
Placed in As a result, the surface of the transfer belt 7 comes into contact with the surface of the photosensitive drum 1a, and rubs the surface of the photosensitive drum la to wipe off the silicon oil.

At this time, the time during which the surface of the transfer belt 7 is in contact with the surface of the photosensitive drum la is 2.55 as described above.
After that, the transfer blade 5a is separated from the transfer belt 7 to be disposed at the retreat position B, and the photosensitive drum 1a is further rotated by a predetermined rotation to complete the entire image forming operation.

In the above description, an example has been described in which the transfer belt 7 and the transfer blade 5a for the first image forming unit Pa wipe the silicon oil on the surface of the photosensitive drum la. The same applies to the second, third, and fourth image forming units Pb, Pc, and Pd), and a description thereof will be omitted.

Here, the contact pressure (linear pressure) of the transfer belt 7 against the photosensitive drums 1a to 1d by the transfer blades 5a to 5d is P2 = 20 gr / c when the silicon oil is wiped.
m, P1 at the time of image formation (at the time of transfer) = 10 gr / cm
The experiment was conducted by setting a larger value than the above to enhance the wiping property.

As a result, although the image defect occurred before the image formation of 10,000 sheets, the image defect did not occur even after the image formation of 35,000 sheets (A size, laterally fed image). Duty 25%, environmental temperature 25 ° C, humidity 50
%).

<Second Embodiment> In the present embodiment, the photosensitive drums 1a to 1d in the first embodiment are used.
The transfer belt 7 is applied to the photosensitive drum during non-image formation in order to further improve the rubbing and polishing force and increase the ability to remove foreign substances on the surface of the photosensitive drum by maximizing the relative transport rotation speed of the transfer belt 7 with respect to the transfer belt 7. After the contact, the transport rotation is stopped.

In addition, by minimizing the transfer rotation of the transfer belt 7 other than during image formation, it is possible to prevent the transfer belt 7 from being moved or wrinkled, and to prevent the transfer belt driving roller from being worn. Cleaning stability of one or more 40,000 sheets was secured.

<Embodiment 3> In this embodiment, the cleaning devices 8a to 8a to
The linear pressure at which the 8d cleaning blades 9a to 9d contact the photosensitive drums la to ld is set to 30 gr / cm,
Transfer belt 7 when wiping silicon oil during post-rotation
Reduce the linear pressure in contact with each of the photosensitive drums la to ld to 35 gr /
cm. That is, the linear pressure of the transfer belt 7 is set higher than the linear pressures of the cleaning blades 9a to 9d, and the transfer belt 7 scrapes off the deposits on the photosensitive drums 1a to 1d that have not been scraped off by the cleaning blades 9a to 9d. The configuration has been further enhanced.

However, the linear pressure of the transfer belt 7 is 35 gr / cm.
Is significantly higher than the linear pressure generally considered necessary for image formation (transfer of a toner image), and the life of the transfer belt 7 is likely to be shortened due to breakage of the transfer belt 7.
The contact of the transfer belt 7 during the post-rotation of d was set so as to be performed in sequence every time the number of image formation reached 1,000. As a result, the number of durable sheets was 450,000 or more.

<Embodiment 4> In this embodiment, when the transfer belt 7 abuts during the post-rotation of the photosensitive drums 1a to 1d in the first embodiment, the photosensitive drums la to ld are placed before the abutment. After a toner image (toner band: thrust length 280 mm, entire circumference of the photosensitive drum 188.4 mm) is formed on the transfer belt 7, the transfer belt 7 is brought into contact with the toner image, and toner is interposed between the photosensitive drums 1a to 1d and the transfer belt 7. Thus, the polishing power of the photosensitive drums la to 1d by the transfer belt 7 was further enhanced by using the abrasive contained in the toner. Thereby, the number of durable sheets could be increased from 30,000 to 45 or more.

At this time, the transfer current applied to the transfer blade 5a was set to the off state so as to minimize the residual toner on the transfer belt 7 and soiling of the transfer belt 7.

<Embodiment 5> In this embodiment, a transfer efficiency of 90% (temperature 2
(5 ° C., humidity 50%) was improved to 95%, and the effect of the present invention was examined in a cleaning-less configuration in which untransferred toner was collected by the developing device 4a.

According to the prior art, the photosensitive drum 1a is scratched by the intermittent 10K (the developer is pressed against the transfer blade 5a).
The growth nuclei of the rubbing scratches could be scraped off, and the durability of 20K sheets could be cleared (the transfer efficiency was increased by increasing the transfer current value).

[0044]

As is apparent from the above description, according to the present invention, an image carrier having a movable surface, a toner image forming means for forming a toner image on the surface of the image carrier, A transfer member that is in contact with the surface of the carrier and transfers the toner image on the surface of the image carrier to a transfer material; and a cleaning unit that removes residual toner remaining on the surface of the image carrier after transfer of the toner image. In the image forming apparatus, the contact pressure of the transfer member, which is disposed on the upstream side of the cleaning unit with respect to the moving direction of the surface of the image carrier, with respect to the surface of the image carrier can be changed, and at the time of image formation, Since the pressing surface of the pressing member for pressing the transfer member and the contact surface of the pressing member during non-image formation are different surfaces, filming associated with long-term use without complicating the structure. Departure The cleaning failure due and adhesion during fixation of the silicone oil reliably preventing effect is obtained that it is possible to prevent deterioration of the image.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image forming unit of an image forming apparatus according to Embodiments 1 to 4 of the present invention.

FIG. 2 is a sectional view of an image forming unit of the image forming apparatus according to Embodiments 1 to 4 of the present invention.

FIG. 3 is a sectional view of an image forming unit of an image forming apparatus according to Embodiment 5 of the present invention.

FIG. 4 is a cross-sectional view of the image forming apparatus according to the present invention.

[Explanation of symbols]

 1a to 1d Photosensitive drum (image carrier) 2a to 2d Primary charger (toner image forming means) 4a to 4d Developing device (toner image forming means) 5a to 5d Transfer blade 7 Transfer belt (transfer body) 8a to 8d Cleaning device (Cleaning unit) 9a Cleaning blade Pa to Pd Image forming unit P Transfer material

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H134 GA01 GB02 GB07 GB08 HD04 HD11 HD19 KD08 KG04 KG08 KH01 KJ02 2H200 FA07 GA23 GA45 GA47 GA66 GB12 HA02 HA12 HB03 HB14 JA02 JA29 JB07 JB08 JB40 JB45 JB47 JB49 MC03 MC03 MC20 PA10 PA14 PA19 PA26

Claims (7)

[Claims] An image carrier having a movable surface; a toner image forming means for forming a toner image on the surface of the image carrier; An image forming apparatus comprising: a transfer member that transfers a toner image onto a transfer material; and a cleaning unit that removes residual toner remaining on the surface of the image carrier after transfer of the toner image. The contact pressure of the transfer member disposed on the upstream side of the cleaning unit with respect to the surface of the image carrier is changeable, and a pressing surface of a pressing member that presses the transfer member during image formation and a non-image An image forming apparatus, wherein a contact surface of the pressing member at the time of formation is a different surface. 2. The contact pressure of the transfer member at the time of image formation is P
1. An image forming apparatus, wherein a relationship of P1 <P2 is established between the contact pressures P1 and P2 when the contact pressure during non-image formation is P2. 3. The image forming apparatus according to claim 1, wherein the transfer member rotates in contact with the surface of the image carrier with a relative speed difference.
Or the image forming apparatus according to 2. 4. The image forming apparatus according to claim 1, wherein the transport rotation is stopped while the transfer member is in contact with the image carrier during non-image formation. 5. The cleaning unit includes a cleaning member that is in contact with the surface of the image carrier.
When a contact pressure of the cleaning member against the surface of the image carrier is P3, a relationship of P3 <P2 is established between the contact pressure P3 and the contact pressure P2. Item 1
Or the image forming apparatus according to 2. 6. A non-image forming method, wherein a toner image is electrostatically attached to the surface of the image carrier before the transfer body is brought into contact with the surface of the image carrier. The image forming apparatus according to any one of claims 1 to 4, 7. The image forming apparatus according to claim 1, wherein a cleaning member abutting on the surface of the image carrier is omitted.