JP2017203796A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing generation of vertical stripe images or interference fringes for a long period of time.SOLUTION: An image forming apparatus includes an image carrier, a charging member, an exposure device, a developing device and a cleaning member. The image carrier has a cylindrical support body having conductivity, and a photosensitive layer formed on a surface of the support body and having a monolayer structure containing a charge generating material and a charge transporting material. The charging member is disposed in contact with or in the proximity of the surface of the image carrier and charges the photosensitive layer in response to application of a charging bias. The exposure device irradiates the photosensitive layer charged by the charging member with light to form an electrostatic latent image on the surface of the photosensitive layer. The developing device develops the electrostatic latent image formed on the surface of the photosensitive layer. The cleaning member cleans the surface of the image carrier. In the image carrier, the support body has a maximum height Ry of surface roughness in a longitudinal direction of 0.5 μm or more and 2.0 μm or less and an average interval Sm of the roughness of 5 μm or more and 200 μm or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus provided with an image carrier on which a toner image is formed.

  In an image forming apparatus such as a printer, a copying machine, a facsimile machine, or a multifunction machine having these functions, a photosensitive drum that is an example of an electrophotographic photosensitive member, a charging device that charges the surface of the photosensitive drum, and a photosensitive member There is known a cleaning blade that is disposed in contact with the drum surface and has a cleaning blade that removes toner and external additives remaining on the surface of the photosensitive drum.

  The photosensitive drum uses a conductive substrate such as an aluminum alloy as a support. After the surface of the conductive substrate is cut by cutting or the like, a photosensitive layer is formed on the surface of the conductive substrate.

  Here, when the surface roughness of the conductive substrate cut by bite machining or the like is large, there is a problem that vertical stripes are generated in the formed image when used as a photosensitive drum. In particular, when a single-layer photosensitive layer containing a charge generation material and a charge transport material is formed on a conductive substrate, irregularities on the conductive substrate appear on the surface of the photosensitive layer, and vertical stripe images tend to be generated.

  Thus, as shown in Patent Document 1, a technique has been proposed in which image defects are suppressed by setting the surface roughness of a conductive substrate within a predetermined range.

JP-A-8-227170

  However, in the technique described in Patent Document 1, when a function-separated type photosensitive layer in which a charge generation layer and a charge transport layer are stacked is formed, there is an effect of suppressing generation of a vertical stripe image to some extent. In the case of a single-layer type photoreceptor having such a single-layer photosensitive layer, it is not possible to sufficiently suppress the vertical stripe image due to the cutting line such as bite processing, and a good image cannot be obtained. there were.

  Further, as a method for suppressing the generation of vertical stripes, a method of mirror-finishing the surface of a conductive substrate is known. However, when the surface of the conductive substrate is mirror-finished, in the exposure process in which the charged photosensitive layer surface is scanned with an exposure device to form an electrostatic latent image, interference fringes are formed on the image due to the interference of the light source of the exposure device. Occur.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of image defects such as vertical stripes and interference fringes over a long period of time.

  In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including an image carrier, a charging member, an exposure device, a developing device, and a cleaning member. The image carrier includes a cylindrical support having conductivity, and a photosensitive layer having a single layer structure including a charge generation material and a charge transport material formed on the surface of the support. The charging member is disposed in contact with or close to the surface of the image carrier, and charges the photosensitive layer by applying a charging bias. The exposure apparatus irradiates the photosensitive layer charged by the charging member with light to form an electrostatic latent image on the surface of the photosensitive layer. The developing device develops the electrostatic latent image formed on the surface of the photosensitive layer by the exposure device. The cleaning member is disposed so as to contact the surface of the image carrier, and cleans the surface of the image carrier. In the image carrier, the maximum height Ry of the surface irregularities in the longitudinal direction of the support is 0.5 μm or more and 2.0 μm or less, and the average interval Sm of the irregularities is 5 μm or more and 200 μm or less.

  According to the first configuration of the present invention, the maximum height Ry of the surface unevenness in the longitudinal direction of the support constituting the image carrier is 0.5 μm or more and 2.0 μm or less, and the average interval Sm of the unevenness is 5 μm or more and 200 μm. Due to the following, it is caused by interference of the light source of the exposure apparatus when the vertical streak image generated by the surface potential unevenness of the photosensitive layer when the surface unevenness of the photosensitive layer is large and the surface unevenness of the surface of the photosensitive layer are eliminated. Both interference fringes can be effectively suppressed.

A schematic cross-sectional view showing a schematic configuration of an image forming apparatus 11 on which the photosensitive drum 20 of the present invention is mounted. Schematic showing a configuration around the photosensitive drum 20 of the image forming apparatus 11

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing a schematic configuration of an image forming apparatus 11 on which a photosensitive drum of the present invention is mounted. FIG. 2 is a schematic diagram showing a configuration around the photosensitive drum 20 of the image forming apparatus 11 shown in FIG.

  As shown in FIG. 1, the image forming apparatus 11 according to the present embodiment is a tandem color printer. The image forming apparatus 11 includes, inside a printer main body 12, a paper feed cassette 13 that stores recording paper (not shown), a paper feeding unit 14 that feeds recording paper one by one from the paper feeding cassette 13, and paper feeding An image forming processing unit 15 that performs an image forming process on the recording paper supplied from the cassette 13 or the manual feed tray (not shown), and a recording paper transport path for transporting the recording paper supplied from the paper feed cassette 13 or the manual feed tray 16, a secondary transfer unit 17 that transfers the toner image formed in the image forming processing unit 15 to the recording paper conveyed along the recording paper conveyance path 16, and the toner image transferred in the secondary transfer unit 17 And a fixing unit 18 that fixes the recording paper.

  For example, the image forming processing unit 15 employs a tandem system that performs image forming processing using toner (developer) of four colors of yellow (Y), magenta (M), cyan (C), and black (K). ing. In the following explanation, only in the case of color designation, the symbol of each arithmetic numeral is attached with a color of (Y, M, C, K) in parentheses, and in the common case, only the arithmetic numeral is included. A description will be given with reference numerals.

  The image forming processing unit 15 corresponds to each color (Y, M, C, K) and print data (images) transmitted from a plurality of toner containers 19 containing replenishing toner and an externally connected device such as a personal computer. A plurality of photosensitive drums 20 for forming toner images of respective colors based on the data), an endless intermediate transfer belt 22 to which the toner images formed on the respective photosensitive drums 20 are primarily transferred, and the respective photosensitive members. And an exposure unit 25 for emitting beam light to the drum 20.

  The photoconductor drum 20 includes a base tube 20a that is a support (conductive base) and a photosensitive layer 20b formed on the surface of the base tube 20a. Examples of the metal forming the raw tube 20a include aluminum, iron, titanium, and magnesium. The photosensitive drum 20 of this embodiment is a positive electrode containing a charge generating agent, a charge transporting agent, a binder resin (binder), and a filler in the same layer as the photosensitive layer 20b on the surface of an aluminum cylindrical tube 20a. A charged single layer type organic photosensitive layer (OPC) is laminated. The surface shape of the raw tube 20a of the photosensitive drum 20 will be described later.

  As shown in FIGS. 1 and 2, a charging device 26, an exposure unit 25, a developing device 21, a cleaning device 28, and a charge eliminating device 29 are disposed around the photosensitive drum 20, and the intermediate transfer belt 22 is attached to the photosensitive drum 20. The primary transfer roller 27 is disposed opposite to the photosensitive drum 20 with the sandwich.

  The developing device 21 includes a developing roller 23 that is disposed to face the photosensitive drum 20 with a predetermined interval. The developing device 21 used in the present embodiment is a contact developing method using a two-component developer (hereinafter also simply referred to as a developer) containing a magnetic carrier and toner T, and is formed on the surface of the developing roller 23 with the developer. The magnetic brush is carried. By bringing the magnetic brush into contact with the photosensitive drum 20 while rotating the developing roller 23, the electrostatic latent image formed on the surface of the photosensitive drum 20 with toner T attached is developed into a toner image.

  The charging device 26 has a charging roller 42 in a charging housing (not shown). The charging roller 42 is formed of, for example, conductive rubber and is disposed so as to contact the photosensitive drum 20. As shown in FIG. 2, when the photosensitive drum 20 rotates in the clockwise direction, the charging roller 42 that contacts the surface of the photosensitive drum 20 is driven to rotate counterclockwise. At this time, by applying a predetermined voltage (charging bias) to the charging roller 42, the surface of the photosensitive drum 20 is uniformly charged. The charging roller 42 may be disposed so as to be close to the photosensitive drum 20.

  The cleaning device 28 includes a cleaning housing 50 having a depth in the recording paper width direction (a direction orthogonal to the recording paper conveyance direction), a cleaning blade 52 attached to the lower outside of the cleaning housing 50, and a photosensitive drum by the cleaning blade 52. A recovery spiral (not shown) that transports the residual toner recovered from the surface of 20 and sends it to a waste toner container (not shown). A toner seal 55 that prevents the collected toner from leaking outside from the cleaning housing 50 is provided at the upstream end of the cleaning housing 50.

  The cleaning blade 52 is made of urethane rubber or the like. The cleaning blade 52 is disposed so that the tip abuts against the surface of the photosensitive drum 20 from below the rotation axis of the photosensitive drum 20. At this time, the tip of the cleaning blade 52 abuts in the counter direction with respect to the rotation direction of the photosensitive drum 20 (see the arrow in FIG. 2).

  The neutralization device 29 is disposed on the downstream side of the primary transfer roller 27 along the rotation direction of the photosensitive drum 20. The neutralization device 29 removes residual charges on the surface of the photosensitive drum 20 by irradiating the photosensitive drum 20 with static elimination light.

  Next, an image forming procedure of the image forming apparatus 100 will be described. When image data is input from an externally connected device such as a personal computer, the charging device 26 first uniformly charges the surface of the photosensitive drum 20, and then the exposure unit 25 applies beam light to the surface of the photosensitive drum 20. Irradiation is performed to form an electrostatic latent image corresponding to the image data on each photosensitive drum 20. The developing device 21 is filled with a predetermined amount of a two-component developer containing toner of each color of yellow, magenta, cyan, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 21 is less than a predetermined value due to the formation of a toner image described later, the toner is supplied from the toner container 19 to each developing device 21. . The toner in the developer is supplied onto the photosensitive drum 20 by the developing device 21 and electrostatically adheres, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 25 is formed. It is formed.

  On the other hand, the recording paper is fed from the paper feed cassette 13 (or the manual feed tray) in accordance with the toner image formation timing in the image forming processing unit 15, and conveyed to the registration roller pair 30 a through the recording paper conveyance path 16. .

  The primary transfer roller 27 applies an electric field between the primary transfer roller 27 and the photosensitive drum 20 at a predetermined transfer voltage, and yellow, magenta, cyan, and black toner images on the photosensitive drum 20 are transferred to the intermediate transfer belt. 22 is primarily transferred onto 22. Thereafter, the toner remaining on the surface of the photosensitive drum 20 after the primary transfer is removed by the cleaning device 28. Further, the residual charge on the surface of the photosensitive drum 20 is removed by the static eliminator 29.

  When the intermediate transfer belt 22 starts to rotate counterclockwise, the recording paper is conveyed from the registration roller pair 30a to the secondary transfer unit 17 provided adjacent to the intermediate transfer belt 22 at a predetermined timing. The full-color image on 22 is secondarily transferred onto the recording paper. The recording paper on which the toner image is secondarily transferred is conveyed to the fixing unit 18. Residual toner or the like adhering to the surface of the intermediate transfer belt 22 is removed by the belt cleaning device 24.

  The recording paper conveyed to the fixing unit 18 is heated and pressurized to fix the toner image on the surface of the recording paper, thereby forming a predetermined full color image. The recording paper on which the full-color image is formed is guided to the end portion of the recording paper transport path 16 and is discharged onto the discharge tray 12a that also serves as the upper surface of the printer body 12 by the discharge roller pair 30b.

  As described above, when the surface roughness of the photosensitive drum 20 is large, vertical stripes are generated in the formed image. In particular, in the case of a single-layer type photoreceptor in which a charge generating material is exposed on the surface of the photosensitive layer 20b, the pressure on the surface of the photosensitive layer 20b is generated by the pressure of the cleaning blade 52, and the surface potential is lowered. Become. For this reason, if there are irregularities on the surface of the photosensitive layer 20b, the surface potential decreases at the convex portions, but the potential decrease does not occur at the concave portions and unevenness of the surface potential occurs. Due to the unevenness of the surface potential, streaks (vertical streaks) are generated in the circumferential direction of the photosensitive drum 20. On the other hand, when the surface of the base tube 20a of the photosensitive drum 20 is mirror-finished to eliminate the irregularities on the surface of the photosensitive layer 20b, the occurrence of vertical stripes is suppressed, but the exposure unit 25 applies the photosensitive drum 20 to the photosensitive drum 20. Interference fringes are generated when light is irradiated.

  In addition, the ease of occurrence of the above-mentioned problems varies depending on the charging method and the developing method. The charging method includes a non-contact charging method such as a scorotron charging method and a contact charging method using a charging member such as the charging roller 42 as in this embodiment. Since the non-contact charging method has a high charge imparting capability, no vertical stripe image is generated. On the other hand, since a large amount of discharge products such as ozone is discharged in the non-contact charging method, a contact charging method in which discharge of the discharge products is small is generally used. However, since the contact charging method has a low charge imparting capability, it tends to cause a vertical stripe image.

  Further, in the contact development method in which the magnetic brush formed on the developing roller 23 is brought into contact with the photosensitive drum 20 and developed as in the present embodiment, the toner is ejected from the developing roller 23 to the photosensitive drum 20 for development. Compared with the non-contact development method, the influence of uneven charging tends to appear in an image. For this reason, it is easy to generate a vertical stripe image due to the unevenness of the surface of the photosensitive layer.

  Therefore, the present invention has found that the occurrence of vertical stripe images and interference fringes can be effectively suppressed by defining the surface roughness of the raw tube 20a constituting the photosensitive drum 20 within a predetermined range. Hereinafter, the surface characteristics of the tube 20a, which is a characteristic part of the photosensitive drum 20 of the present invention, will be described.

  In the photosensitive drum 20 of the present embodiment, the maximum height Ry of surface irregularities in the longitudinal direction (axial direction) of the raw tube 20a is in the range of 0.5 [μm] to 2.0 [nm], The surface roughness is such that the average interval Sm of the unevenness is 5 [μm] or more and 200 [μm] or less. The maximum height Ry and the average interval Sm are measured by a surface roughness measuring method defined in 1994 edition JISB0601 using a stylus type two-dimensional roughness measuring device.

  The maximum height Ry is from the roughness line to the height Yp from the average line of the portion extracted by the reference length in the direction of the average line (longitudinal direction of the raw tube 20a) to the highest peak and the lowest valley bottom. It is represented by the sum (Ry = Yp + Yv) with the depth Yv. The maximum height Ry of the irregularities on the surface of the raw tube 20a may be in the range of 0.5 μm to 2.0 μm. When the maximum height Ry is smaller than 0.5 μm, interference fringes are likely to occur when the exposure unit 25 irradiates the photosensitive drum 20 with light. On the other hand, when the maximum height Ry is larger than 2.0 μm, the potential difference between the convex portion and the concave portion on the surface of the photosensitive layer 20b laminated on the surface of the raw tube 20a increases, and a vertical stripe image due to surface potential unevenness is generated. .

  Moreover, the average interval Sm of the unevenness in the longitudinal direction of the surface of the raw tube 20a may be 5 μm or more and 200 μm or less. When the average interval Sm exceeds 200 μm, the unevenness interval becomes too large, and the surface potential unevenness is output to the extent that it is visually recognized as a vertical stripe image. On the other hand, vertical stripe images are less likely to be generated as the average interval Sm is smaller. However, as the average interval Sm is decreased, it takes a longer time to form the raw tube 20a and the manufacturing cost increases, which is not preferable. In addition, since the unevenness period on the surface of the raw tube 20a becomes very fine, the unevenness acts as a diffraction grating, so that it is also considered that interference fringes are generated by exposure from the exposure unit 25. Therefore, in order to use the photosensitive drum 20 stably, there is a lower limit value in the average interval Sm, and as a result of examination, it has been found that 5 μm or more is appropriate.

  The vertical stripe image is generated because the irregularities on the raw tube 20a appear as irregularities on the surface of the photosensitive layer 20b. Therefore, it is considered that the surface level of the photosensitive layer 20b varies depending on the layer thickness of the photosensitive layer 20b, and that the vertical stripe image is less likely to be generated as the initial layer thickness is thicker. In addition, since the unevenness on the surface of the photosensitive layer 20b is worn by the use of the photosensitive drum 20 and is gradually uniformed, the vertical stripe image is most noticeably generated in the initial use of the photosensitive drum 20. As a result of the examination, it was found that the vertical stripe image is effectively suppressed when the initial film thickness of the photosensitive layer 20b is 28 μm or more.

  However, the layer thickness of the photosensitive layer 20b has a limit in the process of coating the raw tube 20a. In addition, if the layer thickness of the photosensitive layer 20b becomes too large, it is easy to cause image defects such as a ghost image due to the influence of the transfer bias. ing. Therefore, when the photosensitive drum 20 is a positively charged single-layer type photosensitive drum 20 and the charging method is a contact charging method, the layer thickness of the photosensitive layer 20b is 28 μm or more and 32 μm or less. .

  In addition, the maximum height Ry and the average interval Sm on the surface of the raw tube 20a are preferably in the above ranges over the entire image forming region on the surface of the raw tube 20a.

  As described above, the photosensitive drum 20 and the image forming apparatus 11 according to the present invention have been described by way of the embodiments. However, the present invention is not limited to the above-described embodiments, and design changes can be made without departing from the gist of the present invention. Even if it exists, it is included in this invention. For example, in the above-described embodiment, the developing device 21 using the two-component developer including the magnetic carrier and the toner is illustrated, but a one-component developing type developing device including only the toner component may be used.

  In the above embodiment, a tandem color printer has been described as an example of the image forming apparatus 11. However, the image forming apparatus 11 can be applied to, for example, a rotary color printer or a monochrome printer. Further, the present invention can also be applied to an image forming apparatus such as a copying machine, a facsimile, or a multifunction machine having these functions. The image forming apparatus 11 may have each configuration of the color printer described in the embodiment, or may have another configuration. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

<Relationship between surface potential unevenness of photosensitive drum and generation of vertical stripe image>
The relationship between surface potential unevenness caused by unevenness on the surface of the photosensitive layer and generation of vertical stripe images was investigated. As a test method, using a test machine (TASKalfa2550ci remodeling machine, manufactured by Kyocera Document Solutions) as shown in FIG. 20 is driven (empty). When the photosensitive drum 20 is idled, friction between the cleaning blade 52 and the surface of the photosensitive layer is generated, and the surface potential is lowered at the convex portion on the surface of the photosensitive layer, so that the surface potential is uneven. Then, after the photosensitive drum 20 was idled for a predetermined time, a test image (photo image) was output, and the relationship between the idle time of the photosensitive drum 20 and the generation level of the vertical stripe image was investigated.

  The system linear velocity of the testing machine is 160 mm / sec, and a positively charged single layer type organic photosensitive layer (OPC) having a layer thickness of 28 μm is formed as a photosensitive layer 20 b on the surface of an aluminum tube 20 a having a diameter of 30 mm as the photosensitive drum 20. What was formed was used. The charging roller 42 was made of epichlorohydrin rubber having a diameter of 12 mm, and a DC voltage (constant voltage) of +1400 V was applied to set the surface potential (white background portion potential) of the photosensitive drum 20 to +500 V. The developing device 21 is a two-component developing system, and a blade made of urethane rubber having a thickness of 2.0 mm, a JIS-A hardness of 75 °, a rebound resilience of 30% (23 ° C.), and a Young's modulus of 9.5 MPa is used as the cleaning blade 52.

  Since the surface potential unevenness is very small and cannot be measured with a surface potential meter, the occurrence of vertical stripes in the output image was visually observed. The evaluation criteria were ◯ when the occurrence of vertical streak was not observed visually, x when the occurrence of vertical streak was recognized, and xx when the occurrence of vertical streak was noticeable. The results are shown in Table 1.

  As is apparent from Table 1, it can be seen that the vertical stripes become deeper (the vertical stripe level becomes worse) as the idling time increases. This is because when the idling time is increased, the convex portion of the photosensitive layer causes a decrease in surface potential due to friction with the cleaning blade 52, and the concave portion of the photosensitive layer does not cause friction with the cleaning blade 52 and does not cause a decrease in surface potential. It is thought that. That is, it was confirmed that unevenness of the surface potential was generated due to the unevenness of the photosensitive layer, and developed as vertical stripes in the image.

<Relationship between the maximum height Ry and average interval Sm of the tube surface, and the occurrence of vertical stripes and interference fringes>
The relationship between the maximum height Ry of the irregularities on the surface of the raw tube 20a and the average interval Sm and the occurrence of vertical stripes and interference fringes was investigated. As a test method, an image is output using a test machine similar to that in Example 1 on which a plurality of types of photosensitive drums 20 having different maximum heights Ry and average intervals Sm of the surface irregularities in the longitudinal direction of the tube 20a are mounted. Before the operation, the photosensitive drum 20 was driven (idle) for 60 seconds with the voltage applied to the charging roller 42 turned off. Thereafter, a test image was output, and the occurrence of a vertical stripe image when the maximum height Ry and the average interval Sm were changed was investigated.

  The measurement environment was set to three environments: a high temperature and high humidity environment (32.5 ° C., 80%), a normal temperature and normal humidity environment (25 ° C., 50%), and a low temperature low humidity environment (10 ° C., 10%). The evaluation criteria were ○ when the occurrence of vertical stripes and interference fringes was not visually recognized, x1 when occurrence of vertical stripes was observed, and x2 when occurrence of interference fringes was observed. The results are shown in Tables 2-4.

  The surface roughness of the raw tube 20a was measured at a measurement length of 2.5 mm using a stylus type two-dimensional roughness measuring instrument (surfcom 1500DX, manufactured by Tokyo Seimitsu Co., Ltd.). The measurement terminal is a stylus type of 60 [°] conical diamond, and the tip radius is 2 [μm]. The measurement length is 2.5 [mm], and the cut-off value is 0.08 [mm]. The filter type is Gaussian, and the inclination correction is a least square line correction. The cut-off ratio is 300 and the measurement magnification is x100k.

  As shown in Table 2, in a high-temperature and high-humidity environment, both vertical streaks and interference fringes occur when the maximum unevenness height Ry is 0.5 μm to 3.5 μm and the average interval Sm is 400 μm or less. I did not. In addition, as shown in Table 3, both vertical streaks and interference fringes occur in the range where the maximum unevenness height Ry is 0.5 μm or more and 3 μm or less and the average interval Sm is 300 μm or less in a room temperature and humidity environment. I did not. Furthermore, as shown in Table 4, in a low-temperature and low-humidity environment, both vertical streaks and interference fringes occur when the maximum unevenness height Ry is 0.5 μm or more and 2 μm or less, and the average interval Sm of unevenness is 200 μm or less. There wasn't.

  From the above results, when the photosensitive drum 20 on which the positively charged single-layer type organic photosensitive layer having a layer thickness of 28 μm is charged by the contact charging method, the maximum height Ry of the irregularities on the surface of the base tube 20a is set to 0. It was confirmed that the occurrence of both vertical stripes and interference fringes can be suppressed regardless of the environmental conditions by setting the average interval Sm between 5 μm and 2 μm and the unevenness to 200 μm or less.

  The present invention can be used for an electrophotographic photosensitive member on which a toner image is formed. By utilizing the present invention, it is possible to provide an image forming apparatus capable of suppressing the occurrence of image defects such as vertical stripes and interference fringes over a long period of time.

11 Image forming apparatus 20 Photosensitive drum (image carrier)
20a Element tube (support)
20b Photosensitive layer 21 Developing device 25 Exposure unit (exposure device)
42 Charging roller (charging member)
52 Cleaning blade (cleaning member)

Claims (3)

An image carrier having a cylindrical support having conductivity and a photosensitive layer having a single layer structure including a charge generation material and a charge transport material laminated on the surface of the support;
A charging member that is disposed in contact with or close to the surface of the image carrier and charges the photosensitive layer by applying a charging bias;
An exposure apparatus that irradiates the photosensitive layer charged by the charging member with light to form an electrostatic latent image on the surface of the photosensitive layer;
A developing device for developing an electrostatic latent image formed on the surface of the photosensitive layer by the exposure device;
A cleaning member arranged to contact the surface of the image carrier and cleaning the surface of the image carrier;
With
The maximum height Ry of the surface irregularities in the longitudinal direction of the support is 0.5 μm or more and 2.0 μm or less, and the average interval Sm of the irregularities is 5 μm or more and 200 μm or less.   The image forming apparatus according to claim 1, wherein the layer thickness of the photosensitive layer in the initial use is 28 μm or more and 32 μm or less.   3. The image forming apparatus according to claim 1, wherein the developing device is a contact developing system in which a developer containing toner is brought into contact with the surface of the image carrier to develop.

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