JP4766347B2 - Image carrier and image forming apparatus - Google Patents

Description

  The present invention relates to an image carrier and an image forming apparatus.

  Patent Document 1 discloses an image forming method for forming an electrostatic latent image on an electrophotographic photosensitive member having a plurality of dimple-shaped concave portions on the surface of an organic photosensitive layer provided on a cylindrical support. Patent Document 2 discloses an electrophotographic apparatus having a plurality of dimple-shaped concave portions formed by a process of causing powder to collide with the surface of an electrophotographic photosensitive member. Patent Document 3 discloses a charging roll in which the charging layer is formed of an elastic body in which elastic particles having a particle size of 7 to 30 μm are dispersed, and the surface roughness Rz is formed to be 7 to 30 μm.

JP 2006-330425 A JP 2006-267885 A Patent No. 3024248

  An object of the present invention is to provide an image carrier and an image forming apparatus that can suppress an increase in the roughness of an image.

According to the first aspect of the present invention, there is provided an image holding member, a developer supplying means for supplying a developer to which an external additive is added to the image holding member, and the image holding member in contact with the image holding member. A cylindrical charging device that charges the body, and a cleaning member that contacts the image carrier and cleans the image carrier, the image carrier comprising a cylindrical support and the support A photosensitive layer that covers the outer surface of the image holding member, and a polishing region in which the image holding member is polished by the accumulated external additive is upstream of a portion in contact with the cleaning member in the rotation direction of the image holding member. The surface is formed with a plurality of rows of recesses arranged at equal intervals in the circumferential direction over the entire image forming region. The recesses are formed by dissolving the surface of the photosensitive layer with a solvent, and have a depth. but the shallower than the average particle diameter of the developer supply means for supplying a developer, the average of the external additive Deeper than the diameter, the charging device has a plurality of rows of recesses arranged on the outer surface periodically at regular intervals over the entire image forming area, and the recesses of the charging device are provided with the developer supplying means. Is an image forming apparatus in which the height difference is smaller than the average particle diameter of the developer supplied and the height difference is larger than the average particle diameter of the external additive.

The present invention according to claim 2, wherein the charging device is an image forming apparatus according to claim 1, wherein the recess is arranged in the charging device in a direction different predetermined from the circumferential direction.

According to the first aspect of the present invention, it is possible to provide an image forming apparatus that suppresses an increase in the roughness of the image as compared with the case where the present configuration is not provided.

According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, it is possible to further suppress the occurrence of irregular moiré in the image as compared with the case without the present configuration. .

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes an image forming apparatus main body 12, and, for example, a one-stage sheet feeding unit 14 is disposed below the image forming apparatus main body 12.

  The paper feed unit 14 includes a paper feed cassette 16 that stores recording media such as paper. A pickup roll 18 for picking up paper is disposed in the upper part near the rear end of the paper feed cassette 16, and a feed roll 20 and a retard roll 22 are disposed in front of the pickup roll 18. The feed roll 20 rotates so as to feed the sheet toward the conveyance path 24. The retard roll 22 is pressed against the feed roll 20 and is rotated in accordance with the rotation of the feed roll 20, and rotates so as to feed the paper one by one together with the feed roll 20.

  The conveyance path 24 is a sheet path from the feed roll 20 to the discharge port 26, and the conveyance path 24 is in the vicinity of the back side (the left side surface in FIG. 1) of the image forming apparatus main body 12, and will be described later from the sheet feeding unit 14. The fixing device 68 is formed in a substantially vertical direction. A secondary transfer roll 64 and a secondary transfer backup roll 62, which will be described later, are arranged on the upstream side of the fixing device 68 in the conveyance path 24, and the registration roll 28 is located upstream of the secondary transfer roll 64 and the secondary transfer backup roll 62. Is arranged. In addition, a transport roll 30 that transports the paper from below to above is disposed in the transport path 24, and a discharge roll 32 is disposed in the vicinity of the discharge port 26.

  Accordingly, the sheet fed from the sheet feed cassette 16 of the sheet feed unit 14 by the feed roll 20 is turned by the retard roll 22 and only the uppermost sheet is guided to the transport path 24 and is temporarily stopped by the registration roll 28. Then, a toner image is transferred between a secondary transfer roll 64 and a secondary transfer backup roll 62, which will be described later, and the transferred toner image is fixed by the fixing device 68, and the discharge port 32 discharges the discharge port 26. Are discharged to a discharge portion 34 provided at the upper part of the image forming apparatus main body 12.

  In the image forming apparatus main body 12, for example, four image forming units 42a to 42d are arranged substantially horizontally. The image forming units 42a to 42d receive toners of four colors of yellow, yellow, magenta, cyan, and black contained in a toner box (not shown) provided on the upper portion of the image forming apparatus main body 14. Each is to accept. The image forming units 42a to 42d include, for example, image holders 44a to 44d, charging devices 46a to 46d including charging rolls, optical writing devices (ROS) 48a to 48d, developing devices 50a to 50d, and primary transfer devices 52a to 52d. In addition, the cleaning devices 53a to 53d are integrated with each other.

  An intermediate transfer belt 54 runs between the image carriers 44a to 44d and the primary transfer devices 52a to 52d. The intermediate transfer belt 54 is made of an endless belt-shaped resin film using, for example, polyimide or polyamide, and includes a drive roll 56, primary transfer devices 52a to 52d, a support roll 58, a tension roll 60, and a secondary transfer backup roll 62. The belt is stretched (supported) so as to be rotatable with a predetermined tension, and is rotated by the driving force of the driving roll 56. Accordingly, the primary transfer devices 52 a to 52 d are pressed against the image carriers 44 a to 44 d via the intermediate transfer belt 54, so that the toner images on the image carriers 44 a to 44 d are transferred onto the intermediate transfer belt 54.

  The secondary transfer backup roll 62 is in pressure contact with the secondary transfer roll 64 via (interposing) the intermediate transfer belt 54, and transfers the toner image on the intermediate transfer belt 54 to the paper supplied from the paper supply unit 14. I have to do it. That is, the secondary transfer position is between the secondary transfer roll 64 and the secondary transfer backup roll 62, and the secondary transfer roll 64 is primary to the intermediate transfer belt 54 with the assistance of the secondary transfer backup roll 62. The transferred toner image is secondarily transferred onto the paper at the secondary transfer position. Note that a predetermined potential difference is generated between the secondary transfer roll 64 and the secondary transfer backup roll 62. For example, when the secondary transfer roll 64 is set to a high voltage, the secondary transfer roll 64 has a secondary voltage difference. The transfer backup roll 62 is connected to a ground (GND) or the like.

  Further, a cleaning device 66 is pressed against the drive roll 56 via an intermediate transfer belt 54. The cleaning device 66 secondarily transfers the toner image primarily transferred to the intermediate transfer belt 54 to a sheet, and then cleans the toner remaining on the intermediate transfer belt 54.

  A fixing device 68 is disposed above the secondary transfer position. The fixing device 68 includes a heating roll 70 and a pressure roll 72, and fixes the toner image secondarily transferred to the sheet by the secondary transfer roll 64 and the secondary transfer backup roll 62 to the sheet by heat and pressure. Then, it is conveyed toward the discharge roll 32.

FIG. 2 shows details of the image forming unit 42a.
The image forming units 42a to 42d are configured in substantially the same manner except that the colors of images to be formed are different. Therefore, the image forming unit 42a will be described below.
The image holding member 44a is a roll-shaped photosensitive member having a cylindrical conductive support 80 made of, for example, grounded aluminum and the like, and a photosensitive layer 82 covering the outer surface of the conductive support 80. Rotate to.

  The charging device 46a rotates in contact with the image carrier 44a to uniformly charge the image carrier 44a. The optical writing device 48a is disposed below the image forming unit 42a, and forms an electrostatic latent image on the image holding body 44a by emitting scanning light toward the charged image holding body 44a. The developing device 50a supplies, for example, yellow toner added with an external additive such as silicon dioxide (SiO2) to the image carrier 44a, and the electrostatic latent image formed on the image carrier 44a. To a visualized toner image. Here, the average particle diameter of the external additive is, for example, 0.2 μm or less. The average particle diameter of the toner is, for example, about 5 μm. The primary transfer device 52a is, for example, a roll-shaped transfer device having elasticity.

  The cleaning device 53 a includes a cleaning blade 84 and a toner storage portion 86. The cleaning blade 84 is a plate-like cleaning member having elasticity, and cleans the image holding body 44a by scraping off the toner remaining on the image holding body 44a. The toner storage unit 86 stores the toner scraped off by the cleaning blade 84.

Next, the image carrier 44a will be described in detail.
FIG. 3 is a schematic diagram showing the surface shape of the image carrier 44a according to the embodiment of the present invention (surface shape of the photosensitive layer 82), where (A) is a schematic diagram showing an initial state, and (B). FIG. 3 is a schematic diagram showing a state after image formation is repeated (timed).
As shown in FIG. 3A, a plurality of rows of concave portions (dimples) 88 arranged in the rotation direction (circumferential direction) are formed on the surface of the photosensitive layer 82 in the initial state. The concave portion 88 has an axial width of the image carrier 44a of, for example, about 20 μm, and the depth to which the pressure of the cleaning blade 84 is applied to such an extent that the external additive slips through but the toner does not slip through is, for example, 0.2 to 1 μm. The recesses 88 are arranged in the rotation direction so as to be continuous at intervals of 32 μm (corresponding to a dot interval of 800 dpi), for example, and the mutual interval in the axial direction of the image carrier 44a is, for example, 42 μm (corresponding to a dot interval of 600 dpi). Has been. The recesses may be arranged at predetermined intervals in the circumferential direction. Examples of the surface material of the photosensitive layer 82 include polycarbonate.

As shown in FIG. 3B, when the image forming apparatus 10 repeats image formation, the image carrier 44a wears the surface of the photosensitive layer 82 in the rotational direction due to the external additive pressed by the cleaning blade 84 (FIG. 3B). 4), and the plurality of recesses 88 are connected in the rotation direction. In this way, even if the image forming apparatus 10 repeats image formation a predetermined number of times, the variation in wear of the concave portion 88 in the axial direction of the image holding body 44a is not increased, and thus this configuration is not provided. It is presumed that an increase in the roughness of the toner image held by the image holding body 44a is suppressed compared to the case.
For this reason, in the photosensitive layer 82, not only the periphery of the recess 88 (protruded portion) but also the recess 88 is worn in the circumferential direction by the external additive, so that the image forming apparatus 10 is predetermined. It is presumed that the variation in wear of the recess 88 in the axial direction of the image holding body 44a is not increased even when image formation is repeated a number of times. For example, even if the image forming apparatus 10 repeats image formation a predetermined number of times and the plurality of recesses 88 are connected in the rotation direction, the depth of the recesses 88 is, for example, 0.2 as shown in FIG. ˜1 μm.

  In the initial state, as shown in FIG. 3B, the image holding body 44a may have a plurality of recesses 88 connected in the rotation direction and a plurality of rows of grooves formed in the circumferential direction. In the initial state, the image carrier 44a may have a plurality of rows of linear grooves formed in the circumferential direction.

FIG. 4 is an enlarged view showing a state in which the external additive polishes the image holding body 44a when the cleaning blade 84 scrapes off the toner remaining on the image holding body 44a. FIG. It is an enlarged view which shows the state which an agent grind | polishes, (B) is an enlarged view which shows the state which the external additive which slips through grinds.
As shown in FIG. 4A, when the external additive is deposited on the upstream side of the portion (nip portion) where the cleaning blade 84 contacts the image carrier 44a, the portion where the external additive is deposited is the main part. The image holding member 44a is worn out as a polishing region. The external additive deposited on the upstream side of the nip portion has a small pressure (vertical load) on the image holding body 44a, but the image holding body 44a is always polished while the image holding body 44a rotates, and the image holding body 44a Forms numerous fine scratches. The state shown in FIG. 4A is presumed to occur in a place where there is little slippage of the external additive such as the periphery of the concave portion 88 (a convex portion or a smooth surface).

  As shown in FIG. 4B, when the external additive passes through the nip portion between the image holding body 44a and the cleaning blade 84, the external additive causes the image holding body 44a to be used with the nip portion as a main polishing area. Wear. The external additive that slips through the nip moves while applying a high pressure to the image carrier 44a while slipping through the nip, and forms deep scratches on the image carrier 44a. The state shown in FIG. 4B occurs when the contact pressure of the cleaning blade 84 with respect to the image carrier 44a is low, such as in the recess 88 and a place where the contact pressure of the cleaning blade 84 is locally low. Since the recesses 88 are arranged in the circumferential direction, it is presumed that the external additive slipping between the cleaning blade 84 and the image holding body 44a concentrates at a specific position in the axial direction of the image holding body 44a.

5A and 5B are schematic diagrams showing the surface shape of an image carrier as a comparative example, in which FIG. 5A is a schematic diagram showing an initial state, and FIG. 5B is a diagram after repeated image formation (over time). It is a schematic diagram which shows a state.
When concave portions are randomly formed on the surface of the image carrier as shown in FIG. 5A, when the image forming apparatus repeats image formation, the surface of the photosensitive layer is caused by the external additive pressed by the cleaning blade. As shown in FIG. 5B, the concave portions adjacent to each other in the rotation direction of the image carrier are connected and lengthened, and the isolated concave portions are reduced by peripheral wear. That is, it is presumed that the axial wear of the image holding member varies and unevenness occurs in the sliding between the image holding member and the cleaning blade.
As described above, when the image forming apparatus repeats image formation and the wear of the image holding member in the axial direction varies, the image quality of the toner image held by the image holding member is deteriorated, and horizontal stripes of the image are generated. Cause.

Next, the charging device 46a will be described in detail.
FIG. 6 is a schematic diagram showing the surface shape of the charging device 46a.
As shown in FIG. 6, a plurality of rows of recesses (dimples) 90 arranged so as to have a predetermined angle α with respect to the rotation direction (circumferential direction) are formed on the surface of the charging device 46a. Has been. The concave portion 90 has a width in the axial direction of the charging device 46a of, for example, about 20 μm, and the depth does not contact the external additive at the nip portion with the image holding body 44a and does not cause discharge abnormality. For example, 0.5 to 4 μm. The concave portions 90 are arranged so that the interval in the rotation direction is, for example, 32 μm (corresponding to a dot interval of 800 dpi), and the mutual interval in the axial direction of the charging device 46 a is, for example, 42 μm (corresponding to a dot interval of 600 dpi). Has been.
That is, the charging device 46a has the recesses arranged in a predetermined direction different from the circumferential direction. Here, the angle α is set to, for example, 15 degrees, 30 degrees, 45 degrees, or 75 degrees, similarly to the screen angle set in the case of preventing moire.

In the charging device 46a, a plurality of recesses 90 may be connected and arranged in a predetermined direction different from the circumferential direction, and a plurality of rows of grooves may be formed in a direction different from the circumferential direction. Further, in the charging device 46a, a plurality of rows of linear grooves may be formed in a direction different from the circumferential direction.
Examples of the surface material of the charging device 46a include alcohol-soluble copolymer nylon.

Next, the wear over time of the image carrier 44a according to the embodiment of the present invention will be described.
FIG. 7 is a graph showing the results of measuring wear over time of the image carrier 44a according to the embodiment of the present invention and a comparative example.
The image carrier wear rate is a value (unit: nm / kcyc) converted to a wear amount when the wear amount at the time of wear amount measurement is continued for 1000 cycles (image formation is 1000 times: 1 kcyc). Therefore, integrating the measured image carrier wear rate with the actual number of cycles gives the actual image carrier wear.

  As shown in FIG. 7, the image carrier 44a according to the embodiment of the present invention has an image carrier wear rate in an initial state (the number of cycles is substantially 0) and an image carrier wear rate after 1000 cycles of about 5 nm / kcyc, and the image carrier wear rate does not vary greatly with time, and wear continues until the wear limit of the photosensitive layer 82 reaches the lifetime of the image carrier 44a.

  On the other hand, in the image carrier of the comparative example, the image carrier wear rate greatly fluctuates (increases) with time, and the photosensitive layer reaches the wear limit before the image forming apparatus performs 1000 cycles of operation.

Next, the recess forming apparatus 100 that forms the recess 88 in the image carrier 44a will be described.
FIG. 8 is a configuration diagram showing an outline of the concave portion forming apparatus 100 for forming the concave portion 88 in the image holding body 44a, and FIG. It is a figure, (B) is the block diagram which looked at the recessed part formation apparatus 100 from the side surface.
The recess forming apparatus 100 includes a solvent ejection device 102, a drying device 104, a mirror finishing device 106, and a drive unit 108, and the recess 88 is mounted at a substantially central position so that the image forming body 44a not formed is rotated by the drive unit 108. Has been made possible.

  The solvent discharge device 102 includes, for example, a solvent tank 110 that stores a solvent (organic solvent) such as toluene, acetone, or methylene chloride, and, for example, a piezo solvent discharge head (inkjet head) that discharges the solvent stored in the solvent tank 110. 112, and discharges the solvent to the image carrier 44a that is rotated by the driving force of the driving unit 108 in accordance with control of a control unit (not shown). The piezo-type solvent discharge head 112 is configured to move parallel to the axial direction with respect to the image carrier 44a under the control of a control unit (not shown).

  The drying device 104 includes a fan 114, and dries the solvent ejected by the solvent ejection device 102 onto the image carrier 44a.

  The mirror finish device 106 includes, for example, a nonwoven fabric 116 and performs mirror finish by polishing the surface of the image carrier 44 a with the nonwoven fabric 116.

  The drive unit 108 includes a motor 118 and an encoder 120, and rotates the image carrier 44a in the circumferential direction at a predetermined speed in accordance with control of a control unit (not shown).

FIG. 9 is a schematic diagram showing the surface state of the photosensitive layer 82 in the process in which the recess forming apparatus 100 shown in FIG. 8 forms the recess 88 in the image carrier 44a.
When the solvent discharge device 102 discharges the solvent toward the image carrier 44a, the solvent adheres to the surface of the photosensitive layer 82 (solvent landing) as shown in FIG. 9A.

  While the solvent adhering to the surface of the photosensitive layer 82 is dried by the drying device 104, the surface of the photosensitive layer 82 is dissolved to form a recess 88. However, as shown in FIG. 9B, flash-shaped protrusions are formed around the recesses 88 in the recesses 88 formed of the solvent.

  The recess forming apparatus 100 polishes the surface of the photosensitive layer 82 with the mirror finishing device 106, thereby forming a recess 88 in which the flash-like protruding portion is removed on the surface of the photosensitive layer 82 as shown in FIG. 9C. To do.

  The recess forming apparatus 100 can also form the recess 90 in the charging device 46a. When the recess forming device 100 forms the recess 90 in the charging device 46a, the solvent discharge device 102 stores, for example, alcohol as a solvent and discharges it.

1 is a side view illustrating an outline of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a side view showing details of the image forming unit. 2A and 2B are schematic diagrams illustrating a surface shape of an image carrier according to an embodiment of the present invention, where FIG. 1A is a schematic diagram illustrating an initial state, and FIG. 2B is a schematic diagram illustrating a state after image formation is repeated. FIG. FIG. 4 is an enlarged view showing a state in which an external additive polishes the image carrier when the cleaning blade scrapes off toner remaining on the image carrier, and (A) shows a state in which the deposited external additive is polished. It is an enlarged view, (B) is an enlarged view showing a state in which the external additive slipping through is polished. FIG. 2 is a schematic diagram illustrating a surface shape of an image carrier as a comparative example, where (A) is a schematic diagram illustrating an initial state, and (B) is a schematic diagram illustrating a state after repeated image formation (over time). FIG. It is a schematic diagram which shows the surface shape of a charging device. It is a graph which shows the result of having measured abrasion over time of the image carrier concerning the embodiment of the present invention, and a comparative example. BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the outline | summary of the recessed part formation apparatus which forms a recessed part in an image carrier, Comprising: (A) is the block diagram which looked at the periphery of the image carrier formed with a recessed part from the upper direction, (B) is a recessed part. It is the block diagram which looked at the forming apparatus from the side. FIG. 9 is a schematic diagram illustrating a surface state of a photosensitive layer in a process in which the concave portion forming apparatus illustrated in FIG. 8 forms a concave portion on the image carrier.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 42a-42d Image forming unit 44a-44d Image holding body 46a-46d Charging apparatus 50a-50d Developing device 53a-53d Cleaning apparatus 80 Conductive support body 82 Photosensitive layer 84 Cleaning blade 86 Toner accommodating part 88,90 Recessed part

Claims (2)

An image carrier,
Developer supplying means for supplying a developer to which an external additive has been added to the image carrier;
A cylindrical charging device that contacts the image carrier and charges the image carrier;
A cleaning member that contacts the image carrier and cleans the image carrier;
Have
The image carrier is
A cylindrical support;
A photosensitive layer covering the outer surface of the support;
Have
A polishing region in which the image carrier is polished by the retained external additive is formed on the upstream side of the portion where the cleaning member contacts in the rotation direction of the image carrier,
A plurality of rows of recesses are arranged on the surface at equal intervals in the circumferential direction over the entire image forming area.
The recess is
Formed by dissolving the surface of the photosensitive layer with a solvent,
Depth, the shallower than the average particle diameter of the developer supply means for supplying developer, deeper than the average particle size of the external additive,
The charging device is:
A plurality of rows of concave portions arranged periodically at regular intervals over the entire image forming area
The concave portion of the charging device is an image forming apparatus in which a difference in height is smaller than an average particle diameter of a developer supplied by the developer supplying unit and a difference in height is larger than an average particle diameter of an external additive.   The image forming apparatus according to claim 1, wherein the charging device includes concave portions of the charging device arranged in a predetermined direction different from a circumferential direction.

Images