JP6132862B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus capable of forming an image by electrophotography.

  In an image forming apparatus such as a printer capable of forming an image by electrophotography, a photosensitive layer portion of an image carrier such as a photosensitive drum is charged by a charging portion such as a charging roller. An electrostatic latent image is formed on the photosensitive layer portion of the image carrier charged by the charging portion by the light irradiated from the light irradiation portion. The electrostatic latent image formed on the photosensitive layer portion of the image carrier is developed with, for example, toner charged to the same polarity as the charged polarity of the photosensitive layer portion supplied from the developing device. Thereafter, the toner image developed by the developing device is transferred to a transfer medium by a transfer unit such as a transfer roller to which a voltage having a polarity opposite to the charging polarity of the toner is applied. The photosensitive layer portion of the image carrier is formed by coating a photosensitive material on the base portion. As a method for coating the photosensitive material with the image carrier, a dipping method or a ring coating method is known.

  On the other hand, the toner image formed on the photosensitive layer portion of the image carrier may be transferred to the intermediate transfer belt, which is a transfer target, by the transfer portion. The intermediate transfer belt has a base material layer portion and a surface layer portion. For example, the base material layer portion is formed of a thermoplastic resin, and the surface layer portion is formed by coating the base material layer portion with a thermosetting resin as a surface layer material. As a method for coating the surface layer material onto the intermediate transfer belt, a dipping method or a ring coating method is known (see Patent Document 1).

JP 2003-270962 A

  By the way, when the photosensitive layer portion of the image carrier is formed by the dipping method or the ring coating method, the photosensitive layer portion has a layer thickness of the first end portion on one side in the rotation axis direction of the image carrier on the other side. It is formed thicker than the layer thickness of the second end. For this reason, the amount of charge accumulated at the second end of the photosensitive layer portion during charging by the charging portion is greater than the amount of charge accumulated at the first end. Here, in the image forming apparatus, when development is performed using toner charged to the same polarity as the charged polarity of the photosensitive layer portion, the light emitted from the light irradiation portion in the photosensitive layer portion is transferred during transfer by the transfer portion. Discharge may occur between the outside of the irradiation region and the transfer portion. In this case, a larger current flows than the first end portion at the second end portion of the photosensitive layer portion where the accumulated charge amount is larger than that of the first end portion. As a result, the second end portion of the photosensitive layer portion is more deteriorated than the first end portion. When the photosensitive layer portion deteriorates, wear of the photosensitive layer portion due to contact with the cleaning member or the like proceeds.

  On the other hand, when the surface layer portion of the intermediate transfer belt is formed by the dipping method or the ring coating method, the surface layer portion is the third end on one side in the width direction of the intermediate transfer belt, similarly to the photosensitive layer portion of the image carrier. Is formed thicker than the layer thickness of the fourth end on the other side. In this case, the intermediate transfer belt in the photosensitive layer portion on the side facing the fourth end of the surface layer portion of the intermediate transfer belt due to discharge generated between the photosensitive layer portion and the transfer portion during transfer by the transfer portion. A larger current flows than the photosensitive layer portion on the side facing the third end portion of the surface layer portion. For this reason, the deterioration of the second end of the photosensitive layer portion whose thickness is thinner than the first end portion of the photosensitive layer portion may proceed from the first end portion, and the service life of the image carrier may be shortened.

  An object of the present invention is to provide an image forming apparatus capable of extending the service life of an image carrier.

  An image forming apparatus according to the present invention includes an image carrier, a charging unit, a light irradiation unit, a developing unit, an intermediate transfer body, and a transfer unit. The image carrier is provided so as to be rotatable by receiving a driving force, and the layer thickness of the first end portion on one side in the rotation axis direction is larger than the layer thickness of the second end portion on the other side in the rotation axis direction. It has a layer part. The charging unit charges the photosensitive layer unit to a potential having a predetermined polarity. The light irradiation unit irradiates light to the photosensitive layer portion charged by the charging unit to form an electrostatic latent image. The developing unit develops the electrostatic latent image formed on the photosensitive layer unit with toner charged to the same polarity as the polarity. The intermediate transfer member has a surface layer portion in which the layer thickness of the third end portion on one side in the same width direction as the rotation axis direction is thicker than the layer thickness of the fourth end portion on the other side in the width direction. Three end portions are disposed to face the second end portion of the photosensitive layer portion, and the fourth end portion is disposed to face the first end portion of the photosensitive layer portion. The transfer unit is disposed to face the image carrier with the intermediate transfer member interposed therebetween, and a toner image developed on the surface of the photosensitive layer unit by applying a voltage having a polarity opposite to the polarity is applied to the intermediate transfer unit. Transfer to the surface layer of the body.

  According to the present invention, it is possible to extend the service life of the image carrier.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of an image forming unit of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram showing the configuration of the intermediate transfer device of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram showing the configuration of the photosensitive drum of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram showing the configuration of the intermediate transfer belt of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram showing the positional relationship between the photosensitive drum and the intermediate transfer belt of the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

[Schematic Configuration of Image Forming Apparatus 10]
First, the configuration of an image forming apparatus 10 according to an embodiment of the present invention will be described with reference to FIG. Here, FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 10.

  As shown in FIG. 1, the image forming apparatus 10 includes an ADF 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, and an operation display unit 5. The image forming apparatus 10 is a multifunction machine having a plurality of functions such as a scan function, a facsimile function, and a copy function, as well as a print function for forming an image based on image data. The present invention is also applicable to image forming apparatuses such as printers, facsimile machines, and copiers.

  The ADF 1 is an automatic document conveyance device that includes a document setting unit (not shown), a plurality of conveyance rollers, a document pressing unit, and a paper discharge unit, and conveys a document read by the image reading unit 2. The image reading unit 2 includes a document table (not shown), a light source, a plurality of mirrors, an optical lens, and a CCD, and can read image data from the document.

  The operation display unit 5 includes a display unit such as a liquid crystal display that displays various types of information in response to control instructions from a control unit (not shown), and operation keys that input various types of information to the control unit in response to user operations. An operation unit such as a touch panel is provided.

  Next, the image forming unit 3 will be described with reference to FIGS. Here, FIG. 2 is a schematic cross-sectional view showing the configuration of the image forming unit 31. FIG. 3 is a schematic cross-sectional view showing the configuration of the intermediate transfer device 36.

  The image forming unit 3 can execute an image forming process (printing process) for forming a color or monochrome image by electrophotography based on the image data read by the image reading unit 2. The image forming unit 3 can also execute the printing process based on image data input from an information processing apparatus such as an external personal computer.

  Specifically, as shown in FIG. 1, the image forming unit 3 includes a plurality of image forming units 31 to 34, optical scanning devices 35A to 35B, an intermediate transfer device 36, a secondary transfer roller 37, a fixing device 38, and a discharge device. A paper tray 39 is provided.

  The image forming unit 31 corresponds to Y (yellow), the image forming unit 32 corresponds to C (cyan), the image forming unit 33 corresponds to M (magenta), and the image forming unit 34 corresponds to K (black). is there. As illustrated in FIG. 1, the image forming units 31 to 34 are provided in the order of yellow, cyan, magenta, and black from the front of the image forming apparatus 10 along the front-rear direction of the image forming apparatus 10.

  As shown in FIGS. 1 and 2, the image forming unit 31 includes a photosensitive drum 311, a charging roller 312, a developing device 313, a primary transfer roller 314, and a drum cleaning unit 315.

  The photosensitive drum 311 has an electrostatic latent image formed on the surface. Here, the photosensitive drum 311 is an example of an image carrier in the present invention.

  Specifically, the photosensitive drum 311 includes a base portion 311A and a photosensitive layer portion 311B as shown in FIG. For example, the base 311A is an aluminum tube. The photosensitive layer portion 311B is formed by coating the surface of the base portion 311A with an organic photosensitive material made of an organic compound whose conductivity is improved by light irradiation. A method for forming the photosensitive layer portion 311B will be described later. The photoconductive drum 311 rotates along the rotation direction 311C shown in FIG. 2 in response to a driving force supplied from a power source (not shown).

  The charging roller 312 charges the photosensitive layer portion 311B of the photosensitive drum 311 to a potential having a predetermined polarity. For example, the charging roller 312 charges the photosensitive layer portion 311B to a positive polarity potential. Here, the charging roller 312 is an example of the charging unit in the present invention. Note that the charging roller 312 may charge the photosensitive layer portion 311B to a negative polarity potential.

  For example, the charging roller 312 is provided in contact with the photosensitive layer portion 311B as shown in FIG. A positive polarity voltage is applied to the charging roller 312 from a power supply device (not shown). As a result, a discharge occurs between the charging roller 312 and the photosensitive layer portion 311B, and the photosensitive layer portion 311B is charged with a positive polarity.

  The developing device 313 develops the electrostatic latent image formed on the photosensitive layer portion 311B of the photosensitive drum 311 with yellow toner charged to the same polarity as the charged polarity of the photosensitive layer portion 311B. Here, the developing device 313 is an example of a developing unit in the present invention.

  Specifically, the developing device 313 includes a stirring screw 313A, a magnet roller 313B, and a developing roller 313C. A developer containing toner and a carrier is accommodated in the housing of the developing device 313. The developer is stirred by a stirring screw 313A. As a result, the toner contained in the developer is triboelectrically charged to a positive polarity. The magnet roller 313B acquires the developer stirred by the stirring screw 313A and supplies the toner contained in the developer to the developing roller 313C. The developing roller 313C acquires the toner supplied from the magnet roller 313B and supplies the toner to the photosensitive layer portion 311B. The developing device 313 is supplied with yellow toner from the toner container 313D shown in FIG.

  The primary transfer roller 314 is applied with a voltage having a polarity opposite to the charged polarity of the photosensitive layer portion 311B, and the surface layer of the intermediate transfer belt 361 provided in the intermediate transfer device 36 to be described later is a toner image developed on the surface of the photosensitive layer portion 311B. Transfer to the part 361B. Here, the primary transfer roller 314 is an example of a transfer portion in the present invention.

  Specifically, as shown in FIG. 2, the primary transfer roller 314 is disposed to face the photosensitive layer portion 311 </ b> B of the photosensitive drum 311 with the intermediate transfer belt 361 interposed therebetween. A negative polarity voltage is applied to the primary transfer roller 314 from a power supply device (not shown). As a result, an electric field is formed between the primary transfer roller 314 and the photosensitive layer portion 311B, and the toner image formed on the surface of the photosensitive layer portion 311B is transferred to the surface of the surface layer portion 361B of the intermediate transfer belt 361.

  The drum cleaning unit 315 removes the toner remaining on the surface of the photosensitive layer unit 311B of the photosensitive drum 311. For example, in the drum cleaning unit 315, the toner remaining on the surface of the photosensitive layer unit 311B is removed by the blade-shaped cleaning member 315A. The toner removed by the cleaning member 315A is transported to a toner storage container (not shown) by the transport screw 315B and collected.

  The image forming units 32 to 34 have the same configuration as the image forming unit 31. That is, the image forming units 32 to 34 are provided with photosensitive drums 321 to 341, primary transfer rollers 324 to 344, and toner containers 323D to 343D, as shown in FIGS.

  The optical scanning devices 35A to 35B irradiate each of the photosensitive layer portions of the photosensitive drums 311 to 341 to form an electrostatic latent image. Here, the optical scanning devices 35 </ b> A to 35 </ b> B are an example of a light irradiation unit in the present invention.

  Specifically, the optical scanning device 35A is provided corresponding to the photosensitive drums 311 to 321 of the image forming units 31 to 32, as shown in FIG. The optical scanning device 35B is provided corresponding to the photosensitive drums 331 to 341 of the image forming units 33 to 34. The optical scanning device 35 </ b> A irradiates light based on image data to the photosensitive layer portion 311 </ b> B of the photosensitive drum 311 charged by the charging roller 312. Thereby, an electrostatic latent image corresponding to the image data is formed on the photosensitive layer portion 311B.

  The intermediate transfer device 36 uses the intermediate transfer belt 361 to convey the toner image transferred from the photosensitive drums 311 to 341 to the intermediate transfer belt 361. As shown in FIGS. 1 and 3, the intermediate transfer device 36 includes an intermediate transfer belt 361, a driving roller 362, a stretching roller 363, and a belt cleaning unit 364.

  The intermediate transfer belt 361 is an endless belt member to which a toner image formed on the surface of each photosensitive layer portion of the photosensitive drums 311 to 341 is transferred. The intermediate transfer belt 361 is an example of the intermediate transfer member in the present invention.

  Specifically, as shown in FIG. 2, the intermediate transfer belt 361 has a base material layer portion 361A and a surface layer portion 361B. The base material layer portion 361A is formed of a thermoplastic resin. For example, the thermoplastic resin is PC (polycarbonate), PVDF (polyvinylidene fluoride), PA (nylon), PBT (polybutylene terephthalate), or the like. The surface layer portion 361B is formed by coating the base material layer portion 361A with an insulating thermosetting resin. For example, the thermosetting resin is PI (polyimide), PAI (polyamideimide), AC (acrylic), or the like. A method for forming the surface layer portion 361B will be described later.

  As illustrated in FIGS. 1 and 3, the intermediate transfer belt 361 is stretched by a driving roller 362 and a stretching roller 363 that are spaced apart from each other in the front-rear direction of the image forming apparatus 10. Specifically, the intermediate transfer belt 361 is stretched in a state where the base material layer portion 361A is in contact with the driving roller 362 and the stretching roller 363. The primary transfer rollers 314 to 344 of the image forming units 31 to 34 are arranged in contact with the base material layer portion 361 </ b> A of the intermediate transfer belt 361. The photosensitive layer portions of the photosensitive drums 311 to 341 of the image forming units 31 to 34 are arranged in contact with the surface layer portion 361B of the intermediate transfer belt 361.

  The driving roller 362 is driven to rotate by a driving force supplied from a power source (not shown) to cause the intermediate transfer belt 361 to travel. Accordingly, the surface layer portion 361B of the intermediate transfer belt 361 is conveyed along the same conveyance direction 36A as the front-rear direction of the image forming apparatus 10, as shown in FIGS.

  The belt cleaning unit 364 removes the toner remaining on the surface of the surface layer portion 361B of the intermediate transfer belt 361. For example, in the belt cleaning unit 364, the toner remaining on the surface of the surface layer unit 361B is removed by the blade-shaped cleaning member 364A. The toner removed by the cleaning member 364A is transported to a toner storage container (not shown) by the transport screw 364B and collected.

  The secondary transfer roller 37 transfers the toner image attached to the surface of the surface layer portion 361B of the intermediate transfer belt 361 onto the sheet. The secondary transfer roller 37 is provided in contact with the surface layer portion 361B of the intermediate transfer belt 361. A voltage is applied to the secondary transfer roller 37 from a power supply device (not shown). As a result, an electric field is formed between the secondary transfer roller 37 and the surface layer portion 361B, and the toner image attached to the surface of the surface layer portion 361B is transferred to the sheet.

  The fixing device 38 melts and fixes the toner image transferred to the sheet by the secondary transfer roller 37 on the sheet. For example, the fixing device 38 includes a fixing roller 38A and a pressure roller 38B. The fixing roller 38A is provided in contact with the pressure roller 38B, and heats the toner image transferred to the sheet to fix it on the sheet. The pressure roller 38B presses the sheet that passes through the contact portion formed between the pressure roller 38B and the fixing roller 38A.

  The sheet on which the toner image is fixed by the fixing device 38 is discharged to the paper discharge tray 39.

  In the image forming unit 3, a color image is formed on the sheet supplied from the paper feeding unit 4 according to the following procedure. The sheet is a sheet material such as paper, coated paper, postcard, envelope, and OHP sheet.

  First, in the image forming unit 31, the surface of the photosensitive layer portion 311 </ b> B of the photosensitive drum 311 is uniformly charged to a positive polarity potential by the charging roller 312. The surface of the photosensitive layer portion 311B charged by the charging roller 312 is irradiated with light based on image data by the optical scanning device 35A. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive layer portion 311B. The electrostatic latent image formed on the surface of the photosensitive layer portion 311B is developed (visualized) as a toner image with yellow toner charged to a positive polarity supplied from the developing device 313. That is, the toner supplied from the developing device 313 adheres to the light irradiation area by the optical scanning device 35A on the surface of the photosensitive layer portion 311B to form a toner image.

  The yellow toner image formed on the surface of the photosensitive layer portion 311B is conveyed to the primary transfer position P1 by the primary transfer roller 314 by the photosensitive drum 311 rotating along the rotation direction 311C. Here, the primary transfer position P1 is a position where the surface of the photosensitive layer portion 311B and the surface layer portion 361B of the intermediate transfer belt 361 contact each other as shown in FIG. The toner image attached to the surface of the photosensitive layer portion 311B is caused by an electric field formed between the primary transfer roller 314 and the photosensitive layer portion 311B by a negative polarity voltage applied to the primary transfer roller 314 at the primary transfer position P1. Affected. As a result, the yellow toner image formed on the surface of the photosensitive layer portion 311B is transferred to the surface of the surface layer portion 361B of the intermediate transfer belt 361. Note that the toner remaining on the surface of the photosensitive layer portion 311B is removed by the drum cleaning portion 315.

  Next, in the image forming units 32 to 34, toner images of the respective colors are formed on the surfaces of the photosensitive layer portions of the photosensitive drums 321 to 341 in the same processing procedure as that of the image forming unit 31. The toner images of the respective colors formed on the surfaces of the photosensitive layer portions of the photosensitive drums 321 to 341 are surface layers of the intermediate transfer belt 361 by the primary transfer rollers 324 to 344 at the primary transfer positions P2 to P4 shown in FIG. Transferred to the surface of the portion 361B. As a result, the toner images of the respective colors formed on the photosensitive drums 311 to 341 are transferred onto the surface of the surface layer portion 361B in the order of yellow, cyan, magenta, and black.

  The toner image transferred to the surface of the surface layer portion 361B by the image forming units 31 to 34 is transported to the secondary transfer position P5 by the secondary transfer roller 37 by the intermediate transfer belt 361 traveling along the transport direction 36A. Here, the secondary transfer position P5 is a position where the intermediate transfer belt 361 and the secondary transfer roller 37 are in contact with each other, as shown in FIG. The secondary transfer roller 37 transfers the toner image attached to the surface of the surface layer portion 361B to a sheet supplied from the paper feeding unit 4 and passing the secondary transfer position P5.

  Thereafter, the toner image is melt-fixed by the fixing device 38 to form an image on the sheet on which the toner image is transferred. The sheet after image formation is discharged to the paper discharge tray 39.

  Next, a method for forming the photosensitive layer portion 311B of the photosensitive drum 311 will be described with reference to FIG. Here, FIG. 4 is a sectional view taken along arrows IV-IV in FIG.

  In the image forming apparatus 10, the photosensitive layer portion 311B of the photosensitive drum 311 is formed by a ring coating method. Here, the ring coating method is a method in which a ring-shaped coating film device or an object is moved in the vertical direction, and a coating material delivered from the inner peripheral side of the coating film device is applied to the surface of the object. It is. By using the ring coating method as a method for forming the photosensitive layer portion 311B of the photosensitive drum 311, the productivity of the photosensitive drum 311 is improved as compared with the case where other methods such as a spray coating method and a blade coating method are used. It is possible to make it. Instead of the ring coating method, a dipping method may be used as a method for forming the photosensitive layer portion 311B of the photosensitive drum 311. Also in this case, it is possible to improve the productivity of the photosensitive layer portion 311B of the photosensitive drum 311 as compared with the case where other methods are used.

  When the photosensitive layer portion 311B of the photosensitive drum 311 is formed by a ring coating method or a dipping method, the photosensitive layer portion 311B of the photosensitive drum 311 has a rotating shaft 311C of the photosensitive drum 311 as shown in FIG. The layer thickness of the first end portion 311E on one side in the rotation axis direction 311D is thicker than the layer thickness of the second end portion 311F on the other side in the rotation axis direction 311D. Note that the shape of the photosensitive layer portion 311B of the photosensitive drum 311 is not limited to the shape in which the first end portion 311E is swollen as shown in FIG. For example, the shape of the photosensitive layer portion 311B of the photosensitive drum 311 may be a shape that is linearly inclined from the first end portion 311E toward the second end portion 311F.

  Next, a method for forming the surface layer portion 361B of the intermediate transfer belt 361 will be described with reference to FIG. Here, FIG. 5 is a cross-sectional view taken along line VV in FIG.

  In the image forming apparatus 10, the surface layer portion 361 </ b> B of the intermediate transfer belt 361 is formed by a ring coating method in the same manner as the photosensitive layer portion 311 </ b> B of the photosensitive drum 311. By using the ring coating method as a method for forming the surface layer portion 361B of the intermediate transfer belt 361, the productivity of the intermediate transfer belt 361 is improved as compared with the case where other methods such as a spray coating method and a blade coating method are used. It is possible. Instead of the ring coating method, a dipping method may be used as a method for forming the surface layer portion 361B of the intermediate transfer belt 361. Also in this case, the productivity of the intermediate transfer belt 361 can be improved as compared with the case where other methods are used.

  When the surface layer portion 361B of the intermediate transfer belt 361 is formed by a ring coating method or a dipping method, the surface layer portion 361B of the intermediate transfer belt 361 is shown in FIG. 5 in the same manner as the photosensitive layer portion 311B of the photosensitive drum 311. As described above, the layer thickness of the third end 361D on one side in the width direction 361C of the intermediate transfer belt 361 that is the same as the rotation axis direction 311D is thicker than the layer thickness of the fourth end 361E on the other side in the width direction 361C. The Note that the shape of the surface layer portion 361B of the intermediate transfer belt 361 is not limited to the shape in which the third end portion 361D swells as shown in FIG. For example, the shape of the surface layer portion 361B of the intermediate transfer belt 361 may be a shape that is linearly inclined from the third end portion 361D toward the fourth end portion 361E.

The surface layer portion 361B of the intermediate transfer belt 361 is preferably formed of the thermosetting resin having a Martens hardness of 100 N / mm ² or more and 350 N / mm ² or less. That is, when the surface layer portion 361B of the intermediate transfer belt 361 is formed of the thermosetting resin having a Martens hardness of less than 100 N / mm ² , sufficient toner releasability cannot be obtained, and the toner image is transferred to the sheet. Efficiency is reduced. Further, when the surface layer portion 361B of the intermediate transfer belt 361 is formed of the thermosetting resin having a Martens hardness of 350 N / mm ² , coating by a dipping method or a ring coating method becomes difficult.

  By the way, in the photosensitive layer portion 311B of the photosensitive drum 311, when the layer thickness of the first end portion 311E is thicker than the layer thickness of the second end portion 311F, the photosensitive layer portion 311 is charged during charging by the charging roller 312. The amount of charge accumulated in the second end 311F of 311B is larger than the amount of charge accumulated in the first end 311E. That is, when the layer thickness of the second end 311F of the photosensitive layer portion 311B is thinner than the layer thickness of the first end 311E, the capacitance at the second end 311F is larger than the capacitance at the first end 311E. growing. As a result, the amount of charge accumulated in the second end 311F of the photosensitive layer portion 311B becomes larger than the amount of charge accumulated in the first end 311E.

  Here, in the image forming apparatus 10, when development is performed using toner charged to the same polarity as the charged polarity of the photosensitive layer portion 311 </ b> B, at the time of transfer by the primary transfer roller 314, Discharge may occur between the primary transfer roller 314 and the outside of the light irradiation area by the optical scanning device 35A. In this case, a current larger than that of the first end 311E flows in the second end 311F of the photosensitive layer portion 311B in which the accumulated charge amount is larger than that of the first end 311E. Thereby, the deterioration of the second end 311F of the photosensitive layer portion 311B progresses more than the first end 311E. That is, the current flowing through the photosensitive layer portion 311B weakens the bond between the components such as the organic compound constituting the photosensitive layer portion 311B, thereby reducing the wear resistance. When the photosensitive layer portion 311B deteriorates, wear of the photosensitive layer portion 311B due to contact with the cleaning member 315A and the like proceeds.

  On the other hand, in the surface layer portion 361B of the intermediate transfer belt 361, when the layer thickness of the third end portion 361D is thicker than the layer thickness of the fourth end portion 361E, the photosensitive layer portion is transferred during the transfer by the primary transfer roller 314. The photosensitive layer portion 311B on the side facing the fourth end 361E of the surface layer portion 361B of the intermediate transfer belt 361 by the discharge generated between 311B and the primary transfer roller 314 causes the first layer of the surface layer portion 361B of the intermediate transfer belt 361 to be A larger current flows than the photosensitive layer portion 311B on the side facing the three end portions 361D. That is, in the intermediate transfer belt 361 interposed between the primary transfer roller 314 and the photosensitive layer portion 311B, the thinner the surface layer portion 361B formed of the thermosetting resin having insulation, the smaller the primary transfer roller 314 and The amount of charge flowing out from the photosensitive layer portion 311B due to the discharge generated between the photosensitive layer portion 311B and the photosensitive layer portion 311B increases. Therefore, the deterioration of the second end 311F of the photosensitive layer portion 311B, which is thinner than the first end portion 311E of the photosensitive layer portion 311B, proceeds from the first end portion 311E, and the useful life of the photosensitive drum 311 is shortened. Sometimes.

  Specifically, the intermediate transfer belt 361 is arranged such that the fourth end 361E of the surface layer portion 361B of the intermediate transfer belt 361 is opposed to the second end 311F of the photosensitive layer portion 311B of the photosensitive drum 311, and the surface layer portion 361B. When the third end portion 361D of the photosensitive layer portion 311B is disposed to face the first end portion 311E, the second end portion 311F of the photosensitive layer portion 311B deteriorates more than the first end portion 311E. Therefore, in the image forming apparatus in which the third end portion 361D or the fourth end portion 361E of the surface layer portion 361B of the intermediate transfer belt 361 can be disposed on either one side or the other side in the rotation axis direction 311D of the photosensitive drum 311. When the intermediate transfer belt 361 is assembled, the third end portion 361D and the fourth end portion 361E of the surface layer portion 361B of the intermediate transfer belt 361, the first end portion 311E and the second end portion 311F of the photosensitive layer portion 311B of the photosensitive drum 311, and If the positional relationship is not conscious, the life of the photosensitive drum 311 varies for each of the image forming apparatuses.

  On the other hand, in the image forming apparatus 10 according to the present invention, as shown in FIG. 6, the fourth end 361E of the surface layer portion 361B of the intermediate transfer belt 361 is the first end of the photosensitive layer portion 311B of the photosensitive drum 311. The third end portion 361D of the surface layer portion 361B is disposed to face the second end portion 311F of the photosensitive layer portion 311B. 6 is a side view from the left side of the drawing showing the positional relationship between the surface layer portion 361B of the intermediate transfer belt 361 and the photosensitive layer portion 311B of the photosensitive drum 311 at the primary transfer position P1 in FIG. In FIG. 6, the primary transfer roller 314, the intermediate transfer belt 361, and the photosensitive drum 311 are arranged apart from each other.

  Accordingly, the fourth end portion 361E of the surface layer portion 361B is disposed to face the first end portion 311E of the photosensitive layer portion 311B, and the photosensitive layer portion due to discharge generated between the primary transfer roller 314 and the photosensitive layer portion 311B. The third end portion 361D of the surface layer portion 361B in which the amount of charge outflow from the 311B is smaller than that of the fourth end portion 361E is opposed to the second end portion 311F of the photosensitive layer portion 311B where the accumulated charge amount is larger than that of the first end portion 311E. Be placed. Therefore, the difference between the amount of current flowing through the first end 311E of the photosensitive layer portion 311B and the amount of current flowing through the second end portion 311F is reduced by the discharge generated between the primary transfer roller 314 and the photosensitive layer portion 311B. Is possible. Accordingly, the progress of deterioration at the second end 311F of the photosensitive layer portion 311B is suppressed, and the service life of the photosensitive drum 311 is prolonged. In addition, for each image forming apparatus 10, variations in the life of the photosensitive drum 311 are suppressed.

  In the image forming apparatus 10 according to the embodiment of the present invention, an experiment was conducted to investigate whether or not an image defect occurred when 200,000 sheets were continuously printed. In the experiment, the photosensitive drum 311 having the first end 311E of the photosensitive layer portion 311B having a layer thickness of 32 μm and the second end 311F having a layer thickness of 28 μm, and the thermosetting resin mainly composed of a polyimide resin. The intermediate transfer belt 361 having the layer thickness of the third end portion 361D of the surface layer portion 361B and the layer thickness of the fourth end portion 361E of 3.5 μm formed in step 361 was used. As a result of the experiment, the occurrence of image defects was not confirmed.

  On the other hand, in the image forming apparatus 10 used in the experiment, an experiment similar to the above experiment was performed with the positional relationship between the photosensitive drum 311 and the intermediate transfer belt 361 reversed. That is, in the image forming apparatus 10 used in the experiment, the fourth end 361E of the surface layer portion 361B of the intermediate transfer belt 361 is disposed to face the second end 311F of the photosensitive layer portion 311B, and the third end 361D. Was placed opposite to the first end 311E, and the same experiment as the above experiment was performed. As a result, it was confirmed that image defects such as black spots appeared when the number of printed sheets exceeded 150,000. The occurrence of the image defect is considered to be because the second end 311F of the photosensitive layer portion 311B of the photosensitive drum 311 is worn by continuous printing.

1: ADF
2: Image reading unit 3: Image forming units 31 to 34: Image forming units 311 to 341: Photosensitive drum 311 A: Base unit 311 B: Photosensitive layer unit 312: Charging roller 313: Developing devices 314 to 344: Primary transfer roller 35 A to 35B: optical scanning device 36: intermediate transfer device 361: intermediate transfer belt 361A: substrate layer portion 361B: surface layer portion 37: secondary transfer roller 38: fixing device 39: paper discharge tray 4: paper supply portion 5: operation display portion 10: Image forming apparatus

Claims (5)

An image carrier which is provided so as to be rotatable by receiving a driving force and has a photosensitive layer portion whose first end portion on one side in the rotation axis direction is thicker than the second end portion on the other side in the rotation axis direction. Body,
A charging portion for charging the photosensitive layer portion to a potential of a predetermined polarity;
A light irradiation unit that irradiates light to the photosensitive layer unit charged by the charging unit to form an electrostatic latent image; and
A developing unit for developing the electrostatic latent image formed on the photosensitive layer unit with toner charged to the same polarity as the polarity;
A layer thickness of a third end portion on one side in the same width direction as the rotation axis direction has a surface layer portion thicker than a layer thickness of a fourth end portion on the other side in the width direction, and the surface layer portion is the image carrier. The third end portion is disposed opposite to the second end portion of the photosensitive layer portion, and the fourth end portion is the first end portion of the photosensitive layer portion. An intermediate transfer member disposed opposite to
A toner that is disposed opposite to the image carrier with the intermediate transfer member interposed therebetween, is in contact with the intermediate transfer member, and is developed on the surface of the photosensitive layer portion by applying a voltage having a polarity opposite to the polarity. A transfer part for transferring an image to the surface layer part of the intermediate transfer member;
With
The photosensitive layer portion and the surface layer portion are formed by a dipping method or a ring coating method,
The first end portion of the photosensitive layer portion is formed by bulging from an outer surface of a portion of the photosensitive layer portion between the first end portion and the second end portion by the dipping method or the ring coating method. And
The third end portion of the surface layer portion is formed by bulging from the outer surface of the portion between the third end portion and the fourth end portion of the surface layer portion by the dipping method or the ring coating method. Forming equipment. The photosensitive layer portion is formed with a uniform layer thickness between the first end portion and the second end portion by the dipping method or the ring coating method.
The second end portion of the photosensitive layer portion is formed with a layer thickness thinner than a layer thickness of a portion between the first end portion and the second end portion in the photosensitive layer portion,
The surface layer portion is formed with a uniform layer thickness between the third end portion and the fourth end portion by the dipping method or the ring coating method,
The fourth end portion of the surface layer portion is formed with a layer thickness thinner than the layer thickness of the portion between the third end portion and the fourth end portion in the surface layer portion,
The image forming apparatus according to claim 1. The photosensitive layer unit, an image forming apparatus according to claim 1 or 2 is formed by an organic photosensitive material. The surface layer portion, an image forming apparatus according to any one of claims 1 to 3 which is formed of an insulating resin. The intermediate transfer body, the thermoplastic resin base layer portion formed in, and an image forming apparatus according to any one of claims 1 to 4 having a surface layer portion formed of a thermosetting resin.

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