JP4242893B2 - Electrophotographic photoreceptor and image forming apparatus provided with the same - Google Patents

Description

  The present invention relates to an electrophotographic photosensitive member and an image forming apparatus including the same.

  An image forming apparatus such as an electrophotographic copying machine or printer includes an electrophotographic photosensitive member. In such an image forming apparatus, an electrophotographic photosensitive member is rotated by a drive transmission mechanism, and an image is formed on a recording medium by repeating operations such as charging, exposure, development, transfer, and cleaning in synchronization with the rotation cycle. Is done.

  More specifically, in the image forming apparatus, the surface of the electrophotographic photosensitive member is electrostatically exposed by irradiating with laser light according to the image pattern while rotating the electrophotographic photosensitive member having a charged surface. A latent image is formed. The electrostatic latent image is developed by attaching toner. The toner attached to the electrophotographic photosensitive member is transferred to a recording medium. After the toner is transferred to the recording medium, the remaining toner is removed by pressing the cleaning blade against the surface of the electrophotographic photosensitive member while rotating the electrophotographic photosensitive member.

  As the electrophotographic photosensitive member, a photosensitive member having a photosensitive layer formed on a cylindrical base made of metal is used. The photosensitive layer includes, for example, a photoconductive layer containing an inorganic material formed on a cylindrical substrate, and a surface layer containing an inorganic material covering the photoconductive layer. When the photoconductive layer and the surface layer are charged with the same charging ability along the axial direction, the dark potential in the axial direction in the latent image forming region of the photosensitive layer is the first end portion of the substrate. , Approximately the same at any part of the central part and the second end part (primary obtained when the dark potential value is measured along the axial direction and the measured value is linearly approximated along the axial direction) The absolute value of the slope of the approximate straight line was 0.3 V / cm or less.

  As shown in FIG. 12, the electrophotographic photosensitive member 8 has an end portion 80 that receives rotational power from a drive transmission mechanism 81 and an end portion 82 that is rotatably supported by a bearing flange 83. ing.

  The drive transmission mechanism 81 includes a drive transmission flange 84 fixed to the electrophotographic photosensitive member 8 and a gear 85 that meshes with the drive transmission flange 84. The drive transmission flange 84 has a function of rotating the electrophotographic photosensitive member 8, and is thus firmly fixed to the inlay portion 86 of the electrophotographic photosensitive member 8. On the other hand, the bearing flange 83 provides a slight play (gap) 88 to the spigot portion 87 of the electrophotographic photosensitive member 8 so as to support the rotation of the electrophotographic photosensitive member 8 and not hinder the rotation. It is arranged and arranged.

Japanese Patent Laid-Open No. 11-265098 JP-A-8-272190

  However, the drive transmission flange 84 is firmly fixed to the spigot portion 86 of the electrophotographic photosensitive member 8, while the bearing flange 83 is connected to the spigot portion 87 of the electrophotographic photosensitive member 8 via a gap 88. It is fixed. Therefore, when charging the photosensitive layer 89 of the electrophotographic photosensitive member 8 by the charger 9 while rotating the electrophotographic photosensitive member 8, the state in which the electrophotographic photosensitive member 8 and the charger 9 are arranged in parallel is shown. The distance between the two tends not to be maintained, and the drive transmission flange 84 side tends to be closer than the bearing flange 83 side.

  In the case of a non-contact type charger, the dark potential of the electrophotographic photosensitive member 8 depends on the distance between the electrophotographic photosensitive member 8 and the charger 9. On the other hand, in the case of a contact-type charger (not shown), the dark potential of the electrophotographic photosensitive member 8 depends on the circumferential width in the contact area between the electrophotographic photosensitive member 8 and the charger 9 called the nip width. The nip width depends on the distance between the axial centers of the electrophotographic photosensitive member 8 and the charger 9. Therefore, when the distance between the electrophotographic photosensitive member 8 and the charger 9 tends to be closer on the drive transmission flange 84 side than on the bearing flange 83 side, the charger 9 is a non-contact type or a contact type. Regardless of the type, the dark potential on the drive transmission flange 84 side tends to be higher than the dark potential on the bearing flange 83 side.

  Such a bias in the dark potential in the axial direction causes a bias in the electrostatic adhesion force of the toner. The bias of the electrostatic adhesion force becomes apparent as the bias of the density of the image formed on the recording medium.

  The present invention provides an electrophotographic photosensitive member that suppresses uneven electrostatic adhesion of toner caused by dark potential unevenness in an electrophotographic photosensitive member, and that hardly causes image defects, and an image forming apparatus including the same. It is an issue.

  In the first aspect of the present invention, a substantially cylindrical shape is formed on the outer peripheral surface of the base body that is rotated by the rotational driving force transmitted from the first end portion in the image forming apparatus. A photosensitive layer having a latent image forming region, and the photosensitive layer has a dark potential in the latent image forming region when charged with the same charging ability along the axial direction of the substrate. In the axial direction of the base, an electrophotographic photosensitive member is provided which is gradually larger from the first end toward the second end opposite to the first end.

  In the second aspect of the present invention, an electrophotographic photosensitive member, a driving force transmitting portion that transmits a rotational driving force to a first end portion in the axial direction of the electrophotographic photosensitive member, and the axial direction. A charging device having the same charging ability, and the electrophotographic photosensitive member includes a substantially cylindrical substrate and a photosensitive layer having a latent image forming region formed on an outer peripheral surface of the substrate. And when the photosensitive layer is charged with the same charging ability along the axial direction of the substrate, a dark potential in the latent image forming region is reduced in the first end in the axial direction of the substrate. An image forming apparatus is provided that gradually increases from the portion toward the second end opposite to the first end.

The photosensitive layer includes, for example, a photoconductive layer. In this case, when the dark potential in the latent image forming region is charged with the same charging ability along the axial direction , the photoconductive layer is changed from the first end portion to the second end portion. It is preferable that the size gradually increases.

The photosensitive layer includes, for example, a photoconductive layer and a surface layer. In this case, when the dark potential in the latent image forming region is charged with the same charging ability along the axial direction , the surface layer moves from the first end portion toward the second end portion. It is preferable that it is gradually larger.

  The axial darkness when the photosensitive layer is charged with a distance in the axial direction from the end on the first end side of the substrate and a voltage value selected from 300V to 600V. For example, the slope of the first-order approximation line indicating the relationship with the measured potential value is 0.4 V / cm or more and 1.5 V / cm or less. The absolute value of the difference between the value obtained from the first-order approximate straight line and the measured value is preferably 10 V or less.

  The photosensitive layer contains, for example, a silicon-based inorganic material.

  The charger is, for example, a non-contact type charger. In this case, the distance from the latent image forming region to the charger in the photosensitive layer is gradually increased, for example, from the first end toward the second end.

  A primary relationship between a distance in the axial direction from the end on the first end side of the substrate and a measured value of a distance from the photosensitive layer to the non-contact charger in the latent image forming region. The approximate straight line has, for example, an absolute value of the slope of 10 μm / cm or more and 100 μm / cm or less. Preferably, the absolute value of the difference between the value obtained by the first-order approximate straight line and the measured value is 700 μm or less.

  The charger may be a contact charger. In this case, the nip width, which is the dimension in the circumferential direction of the substrate, in the contact region between the photosensitive layer and the contact charger is the first end portion in the axial direction from the first end in the latent image forming region. It is made to become small gradually as it goes to the edge part of 2.

  For example, the linear approximation line indicating the relationship between the axial distance from the end on the first end side of the substrate and the measured value of the nip width has an inclination of 0.004 mm / cm or more and 0.00. It is set to 08 mm / cm or less. The absolute value of the difference between the value obtained from the first-order approximate straight line and the measured value is preferably 0.5 mm or less.

  In the electrophotographic photosensitive member of the present invention, the photosensitive layer (photoconductive layer and surface layer) forms a latent image when charged in the latent image forming region with the same charging ability along the axial direction of the cylindrical substrate. The dark potential in the region is gradually increased from the first end toward the second end in the axial direction of the cylindrical substrate. Therefore, even when the distance from the charger gradually increases from the first end toward the second end, or even when the nip width gradually decreases, the electrostatic adhesion force of the toner is biased. Can be suppressed. As a result, in the electrophotographic photosensitive member of the present invention and the image forming apparatus including the same, it is possible to suppress the uneven density of the image formed on the recording medium.

  In particular, measurement of the axial dark potential when the photosensitive layer is charged with a distance in the axial direction from the end on the first end side of the substrate and one voltage value selected from 300 V to 600 V. When the photosensitive layer is formed so that the slope of the first-order approximation line indicating the relationship with the value is 0.4 V / cm or more and 1.5 V / cm or less, the bias of the electrostatic adhesion force of the toner is more appropriately adjusted. Can be suppressed. Even when the photosensitive layer is formed so that the absolute value of the difference between the value obtained from the first-order approximation straight line and the measured value is 10 V or less, the bias of the electrostatic adhesion force of the toner is more appropriately reduced. Can be suppressed. As a result, in the electrophotographic photosensitive member of the present invention and the image forming apparatus including the same, it is possible to more appropriately suppress the density deviation of the image formed on the recording medium.

  Hereinafter, an image forming apparatus and an electrophotographic photosensitive member according to the present invention will be specifically described with reference to the accompanying drawings.

  The image forming apparatus 1 shown in FIGS. 1 and 2 employs the Carlson method as an image forming method, and includes an electrophotographic photosensitive member 2, a rotating mechanism 3, a charging roller 41 ′, an exposure device 42, a developing device 43, A transfer device 44, a fixing device 45, a cleaning device 46, and a static eliminator 47 are provided.

  As shown in FIG. 2, the electrophotographic photosensitive member 2 forms an electrostatic latent image and a toner image based on an image signal, and can be rotated in the direction of arrow A in FIG. ing. As shown in FIG. 3, the electrophotographic photosensitive member 2 has a photosensitive layer 21 formed on the surface of a cylindrical substrate 20.

  The cylindrical substrate 20 forms a skeleton of the electrophotographic photosensitive member 2 and carries an electrostatic latent image on the outer peripheral surface thereof. The length L in the axial direction of the cylindrical substrate 20 is slightly longer than the maximum length of the recording medium P such as recording paper to be used. Specifically, the axial length L of the cylindrical substrate 20 is set to be longer than the end of the recording medium P by about 0.5 cm to 5 cm, for example. For this reason, the photosensitive layer 21 includes a latent image forming region 22 corresponding to the maximum length of the recording medium P, non-latent image property regions 23 provided at both ends adjacent to the latent image forming region 22, It will have. In other words, the non-latent image forming area 23 is an area of the photosensitive layer 21 that is not planned to be used (in the axial direction of the latent image forming area 22) no matter what image size is formed on the photosensitive layer 21. Outside).

  The cylindrical base 20 has inlay portions 24 and 25 having a relatively large inner diameter. The inlay portion 24 is a portion to which a drive transmission flange 30E of the rotation mechanism 3 described later is fitted, and the inlay portion 25 is a portion to which a bearing flange 31 of the rotation mechanism 3 described later is fitted. The illustrated inlay portions 24 and 25 are accommodated in a portion corresponding to the non-latent image forming region 23, but may extend to a portion corresponding to the latent image forming region 22.

Such a cylindrical substrate 20 is at least conductive on the surface. That is, the cylindrical base body 20 may be entirely formed of a conductive material, or may be formed by forming a conductive film on the surface of a cylindrical body formed of an insulating material. Examples of the conductive material for the cylindrical substrate 20 include metal materials such as Al or SUS (stainless steel), Zn, Cu, Fe, Ti, Ni, Cr, Ta, Sn, Au, and Ag, and those metals. Alloy materials can be used. Examples of the insulating material for the cylindrical substrate 20 include resin, glass, and ceramic. Examples of the material for the conductive film include transparent conductive materials such as ITO (Indium Tin Oxide) and SnO _{2 in} addition to the metals exemplified above. These transparent conductive materials can be deposited on the surface of an insulating cylinder by a known method such as vapor deposition. However, it is preferable that the cylindrical base body 20 is entirely formed of an Al alloy material. Then, the electrophotographic photosensitive member 2 can be manufactured at a low weight and at a low cost. In addition, the charge injection blocking layer 27 and the photoconductive layer 28 of the photosensitive layer 21 described later are made of an amorphous silicon (a-Si) material. In the case of forming, the adhesiveness with the layers 27 and 28 is increased, and the reliability is improved.

  The photosensitive layer 21 is formed by laminating a charge injection blocking layer 27, a photoconductive layer 28, and a surface layer 29. In the latent image forming region 22, the photosensitive layer 21 has a first end 22 </ b> A on the drive transmission flange 30 </ b> E side of the rotation mechanism 3 to be described later and a second end on the bearing flange 31 side of the rotation mechanism 3 to be described later. The thickness is made smaller than 22B. Further, when the photosensitive layer 21 is charged with the same charging ability along the axial direction of the cylindrical substrate 20, the dark potential in the latent image forming region 22 is the first end in the axial direction of the cylindrical substrate 20. The size is gradually increased from the portion 22A toward the second end portion 22B. More specifically, the photosensitive layer 21 is sensitive to an axial distance from the end 20A on the first end 22A side of the cylindrical substrate 20 and one voltage value selected from 300V to 600V. The slope of the primary approximate line indicating the relationship with the measured value of the dark potential in the axial direction when the layer 21 is charged is set to 0.4 V / cm or more and 1.5 V / cm or less, for example. The absolute value of the difference between the value obtained from the first-order approximate straight line and the measured value is preferably 10 V or less.

  Here, the same charging ability in the present invention means that, for example, two electrophotographic photosensitive members 2 having the same configuration of the photosensitive layer 21 are charged in the same charging state (distance to the charger 41, charging voltage, etc.). This is the ability to make the dark potential of the photosensitive layer 21 the same dark potential (the difference in dark potential is 3 V or less).

  The dark potential in the photosensitive layer 21 of the electrophotographic photosensitive member 2 is, for example, in a dark state (a state where light is blocked), and the surface of the photosensitive layer 21 charged by the charger 41 is a non-contact type surface potential meter (“MODEL 344”: The value measured by TREK) can be used.

  For example, the first-order approximate straight line represents a measurement value obtained when the dark potential is measured along the axial direction of the cylindrical substrate 20, for example, as a distance from the end 20A of the cylindrical substrate 20 on the first end 22A side. Can be calculated by the method of least squares.

  The charge injection blocking layer 27 is for suppressing injection of electrons and holes from the cylindrical substrate 20 into the photoconductive layer 28. Various layers can be used for the charge injection blocking layer 27 depending on the material of the photoconductive layer 28. The charge injection blocking layer 27 is formed of, for example, an inorganic material. If an a-Si based material is used for the photoconductive layer 28, an a-Si based material is used as the inorganic material for the charge injection blocking layer 27. Are preferably used. By doing so, it is possible to obtain electrophotographic characteristics with excellent adhesion between the cylindrical substrate 20 and the photoconductive layer 28.

  In the case where the a-Si based charge injection blocking layer 27 is provided, as compared with the a-Si based photoconductive layer 28, more Group 13 elements of the periodic table (hereinafter abbreviated as “Group 13 element”) and The conductivity type is adjusted by adding a Group 15 element (hereinafter abbreviated as “Group 15 element”) in the periodic table, and a large amount of boron (B), nitrogen (N), or oxygen (O) is included. To increase the resistance.

  The electric field injection blocking layer 27 is optional and is not always necessary. Further, instead of the charge injection blocking layer 27, a long wavelength light absorption layer may be provided. When this long-wavelength light absorption layer is provided, long-wavelength light incident during exposure (referred to as light having a wavelength of 0.8 μm or more) is reflected on the surface of the cylindrical substrate 20, and interference fringes are generated in the recorded image. Can be suppressed.

  The photoconductive layer 28 is for generating electrons such as free electrons or holes when electrons are excited by irradiation of laser light from the exposure device 42. The thickness of the photoconductive layer 28 may be set as appropriate depending on the photoconductive material to be used and desired electrophotographic characteristics, but the thickness at the second end 22B on the bearing flange 31 side in the latent image forming region 22 is as follows. It is larger than the thickness at the first end 22A on the drive transmission flange 30E side in the latent image forming region 22. In the illustrated example, the thickness of the photoconductive layer 28 is gradually increased from the first end 22A toward the second end 22B, but the thickness of the photoconductive layer 28 is the first end 22A. To the second end 22B.

  The ratio of the thickness at the second end 22B to the thickness at the first end 22A in the photoconductive layer 28 is set to, for example, 1.03 times or more and 1.25 times or less. When the photoconductive layer 28 is formed using an a-Si-based material, the thickness at the first end 22A is set to 5 μm to 100 μm, preferably 15 μm to 80 μm. The thickness at the second end 22B is set to 5.15 μm to 125 μm, preferably 15.45 μm to 100 μm. The difference in thickness between the thickness at the second end 22B and the thickness at the first end 22A in the photoconductive layer 3 is 1.0 μm or more and 9.0 μm or less, preferably 1.0 μm or more and 6. 0 μm or less.

  If the thickness of the photoconductive layer 28 is gradually increased from the first end portion 22A toward the second end portion 22B, the photosensitive layer 21 and the charger can be used when the electrophotographic photoreceptor 2 is incorporated into the image forming apparatus 1. Even if the distance between the first end 22A and the second end 22B becomes smaller than the second end 22B due to play on the bearing flange 31 side, the difference in distance can be reduced.

  Here, the first end 22A of the latent image forming region 22 is 0 from the axial end 20A of the cylindrical substrate 20 in the photosensitive layer 21 when the length of the cylindrical substrate 20 in the axial direction is L. The second end portion 22B of the latent image forming region 22 is 0.75L or more and 0.9L from the axial end portion 20B of the cylindrical substrate 20 in the photosensitive layer 21. The area is as follows.

  The thickness at the first and second end portions 22A and 22B of the photoconductive layer 28 in the latent image forming region 22 is measured at any five points along the circumferential direction of the respective end portions 22A and 22B. The average value of 5 points. However, in the thickness measurement, special parts such as film defects or film breakage are excluded. The thickness of the photoconductive layer 28 is calculated by a light interference method. More specifically, light of 1000 nm or more and 1100 nm or less is incident on the measurement location to draw a transmittance curve, and the thickness is calculated from the maximum and minimum transmittance and the refractive index of the surface layer (reference: measurement and evaluation of thin film material) Published by Japan Society for Technology Information (P42-46).

  Further, when the photoconductive layer 28 is charged with the same charging ability along the axial direction of the cylindrical substrate 20, the dark potential in the latent image forming region 22 becomes the first in the axial direction of the cylindrical substrate 20. The size is gradually increased from the end 22A toward the second end 22B. More specifically, the photoconductive layer 28 has an axial distance from the end 20A on the first end 22A side of the cylindrical substrate 20 and one voltage value selected from 300V to 600V. The slope of the primary approximation line indicating the relationship with the measured value of the dark potential in the axial direction when the photosensitive layer 21 is charged is set to 0.4 V / cm or more and 1.5 V / cm or less, for example. The absolute value of the difference between the value obtained from the first-order approximate straight line and the measured value is preferably 10 V or less.

  The dark potential of the photoconductive layer 28 is, for example, in a dark state (a state where light is blocked), and the surface of the photoconductive layer 28 charged by the charger 41 is a non-contact type surface potentiometer (“MODEL 344”: manufactured by TREK). The value measured in can be adopted.

  For example, the first-order approximate straight line represents a measurement value obtained when the dark potential is measured along the axial direction of the cylindrical substrate 20, for example, as a distance from the end 20A of the cylindrical substrate 20 on the first end 22A side. Can be calculated by the method of least squares.

The photoconductive layer 28 is formed of, for example, an a-Si-based material, an amorphous selenium-based (a-Se-based) material such as a-Se, Se-Te, and As ₂ Se ₃ or a periodic table such as ZnO, CdS, or CdSe. It is formed of a compound of a group 12 element and a group 16 element of the periodic table. As the a-Si material, a-Si, a-SiC, a-SiN, a-SiO, a-SiGe, a-SiCN, a-SiNO, a-SiCO, a-SiCNO, and the like can be used. . In particular, when the photoconductive layer 28 is formed of a-Si or an a-Si alloy material in which elements such as C, N, and O are added to a-Si, high photosensitivity characteristics, high-speed response, and repetition Excellent electrophotographic characteristics such as stability, heat resistance, and durability can be stably obtained, and the compatibility with the surface layer 29 when the surface layer 29 is formed of a-SiC: H is excellent. It will be a thing. The photoconductive layer 28 may be formed as a form in which the above-mentioned inorganic material is made into particles and dispersed in a resin, or as an OPC photoconductive layer.

  In the case where the photoconductive layer 28 is formed as an inorganic material as a whole, for example, a glow discharge decomposition method, various sputtering methods, various vapor deposition methods, an ECR method, a photo CVD method, a catalytic CVD method, or a reactive vapor deposition method is known. It can be formed by a film formation technique. In forming the photoconductive layer 28, hydrogen (H) or halogen elements (F, Cl) may be contained in the film for 1 to 40 atom% for dangling bond termination. Further, in forming the photoconductive layer 28, in order to obtain desired characteristics such as electrical characteristics such as dark conductivity and photoconductivity of each layer and optical band gap, group 13 elements and group 15 elements are added. The above characteristics are adjusted by adding or adjusting the content of elements such as C, N, and O.

Further, as the group 13 element and the group 15 element, boron (B) and phosphorus (P) are used in that they are excellent in covalent bonding, can change the semiconductor characteristics sensitively, and can provide excellent photosensitivity. Is desirable. When a Group 13 element and a Group 15 element are contained together with elements such as C, N, and O, the Group 13 element is preferably 0.1 ppm or more and 20000 ppm or less, and the Group 15 element is 0.1 ppm. It is preferably 10000 ppm or less.

  When the photoconductive layer 28 does not contain an element such as C, N, or O, or contains a trace amount (0.01 ppm or more and 100 ppm or less), the content of the Group 13 element is 0.01 ppm or more and 200 ppm or less, The content of the group element is preferably 0.01 ppm or more and 100 ppm or less. The content of these elements may have a concentration gradient in the layer thickness direction. In that case, the average content of the entire layer may be within the above range.

  When the photoconductive layer 28 is formed of an a-Si-based material, μc-Si (microcrystalline silicon) may be included, and in that case, dark conductivity and photoconductivity can be increased. There is an advantage that the degree of freedom of design of the photoconductive layer 3 is increased. Such μc-Si can be formed by adopting the same formation method as described above and changing the film formation conditions. For example, in the glow discharge decomposition method, it can be formed by setting the temperature and high-frequency power of the cylindrical substrate 20 higher than in the case of a-Si and increasing the flow rate of hydrogen as a dilution gas. Further, when μc-Si is included, an impurity element similar to the above may be added.

  Such a photoconductive layer 28 can be formed using, for example, the glow discharge decomposition apparatus 5 shown in FIGS. In the illustrated glow discharge decomposition apparatus 5, a cylindrical substrate 20 is supported on a substrate support 51 disposed in the center of a cylindrical vacuum vessel 50, and an a-Si film is formed on the cylindrical substrate 20 by glow discharge plasma. It is a film. In this glow discharge decomposition apparatus 5, the substrate support 51 is grounded, and the vacuum vessel 50 is connected to the high frequency power source 52, and between the vacuum vessel 50 and the substrate support 51 (cylindrical substrate 20). High frequency power can be applied. The substrate support 51 is rotatable by a rotation mechanism 53, and is heated by a heater 54 disposed therein. Further, a plurality (eight in the drawing) of gas introduction pipes 55 are arranged in the glow discharge decomposition apparatus 5 so as to surround the substrate support 51 (cylindrical substrate 20). Each gas introduction pipe 55 is provided with a plurality of gas introduction ports 56 so as to be aligned in the axial direction. The plurality of gas introduction ports 56 in each gas introduction pipe 55 are arranged so as to face the cylindrical substrate 20, and the raw material gas introduced through the plurality of gas introduction ports 56 is directed toward the cylindrical substrate 20. It is configured to blow out.

  In forming an a-Si-based film on the cylindrical substrate 20 using the glow discharge decomposition apparatus 5, a raw material gas set at a predetermined flow rate and gas ratio is supplied from a gas introduction pipe 55 to a gas introduction port 56. It introduce | transduces toward the cylindrical base | substrate 20 via. At this time, the cylindrical substrate 20 is rotated together with the substrate support 51 by the rotation mechanism 53. Then, a high frequency power is applied between the vacuum vessel 50 and the substrate support 51 (cylindrical substrate 20) by a high frequency power source 52, and a raw material gas is decomposed by glow discharge between them to set a desired temperature. An a-Si film is formed on the cylindrical substrate 20.

  When such a glow discharge decomposition apparatus 5 is used, the thickness and charging ability of the photoconductive layer 28 are changed by gradually or stepwise changing the arrangement density of the plurality of gas inlets 56 in the gas inlet tube 55. It can be changed gradually or stepwise in the axial direction. For example, as shown in FIG. 6, in the corresponding Y region including the first end portion 22A of the photoconductive layer 28 in the gas introduction pipe 55, a plurality of gases are compared with the X region including the second end portion 22B. By reducing the arrangement density of the introduction ports 56, the thickness at the second end 22B can be made larger than the thickness at the first end 22A. Further, when the gas introduction pipe 55 shown in FIG. 6 is used, the charging ability (at the second end portion 22B of the photoconductive layer 28) is obtained by including boron (B) in the source gas (see FIG. 6). The dark potential during charging) can be made larger than that of the first end 22A of the photoconductive layer 28.

  It should be noted that the ratio of the arrangement density of the X region to the Y region depends on the thickness of the photoconductive layer 28 at the first and second end portions 22A and 22B and the thickness of the photoconductive layer 28 at the end portions 22A and 22B. The ratio may be set according to the desired charging characteristics, but is set to 1.06 times or more and 2.25 times or less, for example. As the gas introduction pipe 55 for forming the photoconductive layer 28, as shown in FIG. 7, a plurality of gas introduction ports 56 are arranged so that the arrangement density gradually becomes closer to one end. Can be used.

  Further, the arrangement density of the plurality of gas introduction ports 56 in the gas introduction pipe 55 is not limited to the dense configuration of the lower portion as shown in FIG.

  Further, the heater 54 has a temperature distribution in the axial direction with respect to the cylindrical base body 20 so that the thickness at the second end 22B of the photoconductive layer 28 is larger than the thickness at the first end 22A. You can also. More specifically, the temperature of the portion corresponding to the second end portion 22B of the cylindrical base body 20 is set higher than the temperature of the portion corresponding to the first end portion 22A, whereby the second end portion 22B. The thickness at can be larger than the thickness at the first end 22A.

  The surface layer 29 shown in FIG. 3 is for preventing friction and wear of the photoconductive layer 28, and is laminated on the surface of the photoconductive layer 28. The surface layer 29 is made of an inorganic material typified by an a-Si material such as a-SiC and has a thickness of 0.2 μm or more and 1.5 μm or less. By making the thickness of the surface layer 29 0.2 μm or more, it becomes possible to prevent image scratches and image density unevenness due to printing durability, and by making the thickness of the surface layer 29 1.5 μm or less, the initial characteristics ( It is possible to improve image defects due to residual potential. The thickness of the surface layer 29 is preferably 0.5 μm or more and 1.0 μm or less.

  In the surface layer 29, the thickness at the first end 22A on the drive transmission flange 30E side is smaller than the thickness at the second end 22B on the bearing flange 31 side. The ratio of the thickness at the second end 22B to the thickness at the first end 22A of the surface layer 29 is set to, for example, 1.03 times or more and 1.25 times or less, and the thickness at the second end 22B is set. The difference between the thickness and the thickness at the first end 22A is 0.03 μm or more and 0.21 μm or less, preferably 0.09 μm or more and 0.14 μm or less.

  If the thickness of the surface layer 29 is gradually increased from the first end 22A toward the second end 22B, the photosensitive layer 21 and the charger 41 when the electrophotographic photosensitive member 2 is incorporated into the image forming apparatus 1. Even if the distance between the first end 22A becomes smaller than the second end 22B due to play on the bearing flange 31 side, the difference in distance can be reduced.

  The thicknesses of the surface layer 29 at the first and second end portions 22A and 22B are defined in the same manner as the thickness of the photoconductive layer 28, and are calculated by the same optical interference method. However, the wavelength of light used when measuring the thickness of the surface layer 29 is set to 400 nm or more and 700 nm or less.

  Further, when the surface layer 29 is charged with the same charging ability along the axial direction of the cylindrical substrate 20, the dark potential in the latent image forming region 22 becomes the first end in the axial direction of the cylindrical substrate 20. The size is gradually increased from the portion 22A toward the second end portion 22B. More specifically, the surface layer 29 is sensitive to an axial distance from the end 20A on the first end 22A side of the cylindrical substrate 20 and a voltage value selected from 300V to 600V. The slope of the primary approximate line indicating the relationship with the measured value of the dark potential in the axial direction when the layer 21 is charged is set to 0.4 V / cm or more and 1.5 V / cm or less, for example. The absolute value of the difference between the value obtained from the first-order approximate straight line and the measured value is preferably 10 V or less.

  The dark potential of the surface layer 29 is measured by, for example, a non-contact surface potentiometer (“MODEL 344”: manufactured by TREK) on the surface of the surface layer 29 charged by the charger 41 in a dark state (light blocked state). Values can be adopted.

  For example, the first-order approximate straight line represents a measurement value obtained when the dark potential is measured along the axial direction of the cylindrical substrate 20, for example, as a distance from the end 20A of the cylindrical substrate 20 on the first end 22A side. Can be calculated by the method of least squares.

Such a surface layer 29 is preferably formed of a-SiC: H containing hydrogen in a-SiC. When the element ratio is expressed as a composition formula a-Si _1-X C _X : H, a-SiC: H has an X value of 0.55 or more and less than 0.93, for example. By setting the X value to 0.55 or more, it is possible to obtain appropriate hardness as the surface layer 29, and the durability of the surface layer 29 and thus the electrophotographic photosensitive member 2 can be secured, and the X value is set to less than 0.93. Thus, it is possible to obtain appropriate hardness as the surface layer 29 in the same manner. Preferably, the X value is 0.6 or more and 0.7 or less. When the surface layer 29 is formed of a-SiC: H, the H content may be set to about 1 atomic% or more and 70 atomic% or less. Within this range, the number of Si—H bonds is smaller than that of Si—C bonds, and trapping of charges generated when the surface of the surface layer 29 is irradiated with light can be suppressed, thereby preventing residual potential. It is preferable in that it can be performed. According to the knowledge of the present inventors, better results can be obtained when the H content is about 45 atomic% or less.

Such a surface layer 29 of a-SiC: H is formed using the glow discharge decomposition apparatus 5 shown in FIGS. 4 and 5 in the same manner as when the photoconductive layer 28 is formed of an a-Si material. be able to. In this case, when the thickness at the second end 22B of the surface layer 29 is made larger than the thickness at the first end 22A, a Si-containing gas such as silane gas (SiH ₄ ), methane gas ( A C-containing gas such as CH ₄ ) and a diluting gas such as H ₂ gas are used if necessary, and the gas introduction pipe 55 illustrated in FIG. 6 or FIG. 7 is used as in the case of forming the photoconductive layer 28. That's fine. Further, the thickness of the surface layer 29 at the second end 22B is such that the temperature of the portion corresponding to the second end 22B of the cylindrical substrate 20 is higher than the temperature of the portion corresponding to the first end 22A. By making it higher, the thickness can be made larger than the thickness at the first end 22A.

When the thickness at the second end 22B is made larger than the thickness at the first end 22A by using the gas introduction pipe 55 shown in FIG. 6 or FIG. 7, for example, between CH ₄ and SiH ₄ The gas ratio is such that SiH ₄ is 1 and CH ₄ is 10 or more and 300 or less, the dilution rate with H ₂ gas is 0% or more and 50% or less, and the gas pressure during film formation is 0.15 Torr or more and 0.65 Torr. The high frequency power is set to about 100 W or more and 350 W or less per cylindrical base body 20, and the temperature of the cylindrical base body 20 is set to 200 ° C. or higher and 300 ° C. or lower. The high frequency power is applied, for example, with a frequency of 13.56 MHz or a pulse modulation of a 13.56 MHz high frequency at 1 kHz.

  The rotation mechanism 3 of the image forming apparatus 1 shown in FIG. 2 is for rotating the electrophotographic photosensitive member 2 and includes a rotation drive system 30 and a bearing flange 31.

  The rotational drive system 30 is for transmitting the rotational power of the motor 30A to the electrophotographic photosensitive member 2 to rotate the electrophotographic photosensitive member 2. The rotary drive system 30 includes drive gears 30B, 30C, 30D and a drive transmission flange 30E in addition to the motor 30A.

  The drive gears 30B, 30C, and 30D are made of large and small gears, and are for transmitting the rotational force of the motor 30A to the drive transmission flange 30E. The rotational speed of the electrophotographic photosensitive member 2 through the drive gears 30B, 30C, and 30D is a constant speed of, for example, 320 mm / sec at the peripheral speed on the surface.

  The drive transmission flange 30E is for transmitting the rotational power from the drive gears 30B, 30C, 30D to the electrophotographic photosensitive member 2. The drive transmission flange 30E includes a fitting portion 30Ea that is fitted into the spigot portion 24 of the cylindrical base body 20, and a gear portion 30Eb that meshes with the gear 30D. The fitting portion 30 </ b> Ea has an outer diameter that substantially matches the inner diameter of the spigot portion 24, and is fixed so as not to rotate substantially with respect to the cylindrical base body 20.

  The bearing flange 31 is for rotatably supporting the electrophotographic photosensitive member 2. The bearing flange 31 is fitted into the inlay portion 25 of the cylindrical base body 20 via the gap 6 (with so-called “play”).

  The rotational drive system 30 is not limited to the one including the drive gears 30B, 30C, and 30D, and may have another structure as long as it can apply a predetermined rotational force to the electrophotographic photosensitive member 2. You may employ | adopt the structure which transmits a rotational force with a rotating belt, a wire, or a chain.

  The charger 41 is a non-contact type called a scorotron. In the charger 41, a wire 41C is arranged substantially parallel to the axial direction of the electrophotographic photosensitive member 2 with respect to a wire holding portion 41B provided on a base 41A. In the illustrated example, there is one wire 41C, but a plurality of wires 41C may be arranged. The distance between the charger 41 and the electrophotographic photosensitive member 2 is maintained by the wheel 41D. The wheel 41 </ b> D is brought into contact with the non-latent image forming region 23 in the photosensitive layer 21 of the electrophotographic photosensitive member 2.

  The distance from the surface of the electrophotographic photosensitive member 2 (photosensitive layer 21) to the charger 41 (wire 41C) is set to, for example, 0.1 mm or more and 1.0 mm or less, and from the first end 22A to the second. It becomes larger as it goes to the end 22B. More specifically, the axial distance from the end 20A on the first end 22A side of the cylindrical substrate 20 and the distance from the photosensitive layer 21 to the charger 41 (wire) in the latent image forming region 22 are as follows. The slope of the first-order approximate straight line indicating the relationship with the measured value is, for example, 10 μm / cm or more and 100 μm / cm or less. Preferably, the absolute value of the difference between the value obtained from the first-order approximation line and the measured value is 700 μm or less.

  In such a charger 41, by applying a bias voltage to the wire 41C, the photosensitive layer 21 of the electrophotographic photosensitive member 2 can be charged with the same charging ability along the axial direction. The bias voltage is one voltage value selected from 300V to 600V. As described above, in the latent image forming region 22 of the photosensitive layer 21, the relationship between the axial distance from the end 20A and the measured value of the axial dark potential when the photosensitive layer 21 is charged is shown. The inclination of the approximate straight line is, for example, 0.4 V / cm or more and 1.5 V / cm or less. Moreover, the absolute value of the difference between the value obtained from the primary approximation line and the measured value is 10 V or less.

  As the charger, the contact-type charging roller 41 ′ shown in FIGS. 8 and 9 can also be used. The charging roller 41 ′ is disposed in close contact with the electrophotographic photosensitive member 2 so as to be pressed. For example, the charging roller 41 ′ is formed by covering a cored bar with a conductive rubber and PVDF (polyvinylidene fluoride). Yes.

  The nip width, which is the circumferential dimension of the cylindrical substrate 20 in the contact area between the electrophotographic photosensitive member 2 and the charging roller 41 ′, is, for example, from the first end 22 A to the second end in the latent image forming area 22. It becomes smaller gradually toward 22B. More specifically, the linear approximation line indicating the relationship between the axial distance from the end 20A on the first end 22A side of the cylindrical base body 20 and the measured value of the nip width has an inclination, For example, it is 0.004 mm / cm or more and 0.08 mm / cm or less. Preferably, the absolute value of the difference between the value obtained from the first-order approximate straight line and the measured value is 0.5 mm or less.

  Even when the charging roller 41 'is used, the charging voltage is set to one voltage value selected from 300V to 600V. As described above, in the latent image forming region 22 of the photosensitive layer 21, the relationship between the axial distance from the end 20A and the measured value of the axial dark potential when the photosensitive layer 21 is charged is shown. The inclination of the approximate straight line is, for example, 0.4 V / cm or more and 1.5 V / cm or less. Moreover, the absolute value of the difference between the value obtained from the primary approximation line and the measured value is 10 V or less.

  The exposure device 42 is for forming an electrostatic latent image on the electrophotographic photosensitive member 2 and can emit light having a specific wavelength (for example, 650 nm or more and 780 nm or less). According to this exposure device 42, an electrostatic latent image as a potential contrast is formed by irradiating the surface of the electrophotographic photosensitive member 2 with light in accordance with an image signal to attenuate the potential of the light irradiation portion. As the exposure unit 42, for example, an LED head in which LED elements capable of emitting light having a wavelength of about 680 nm are arranged at a density of 600 dpi can be employed.

  Of course, as the exposure device 42, a device capable of emitting laser light can be used. Further, in place of the exposure device 42 such as an LED head, an image of the structure of the copying machine can be obtained by using an optical system composed of a laser beam, a polygon mirror, etc., or an optical system composed of a lens, a mirror, etc. that transmits reflected light from the document. It can also be a forming device.

  The developing device 43 is for developing the electrostatic latent image of the electrophotographic photosensitive member 2 to form a toner image. The developing unit 43 includes a magnetic roller 43A for magnetically holding developer (toner), a wheel (not shown) called a roller for holding a gap (Gap) with the electrophotographic photosensitive member 2 substantially constant, and the like. I have.

  The developer is for constituting a toner image formed on the surface of the electrophotographic photosensitive member 2 and is frictionally charged in the developing device 43. As the developer, a two-component developer composed of a magnetic carrier and an insulating toner or a one-component developer composed of a magnetic toner can be used.

  The magnetic roller 43 </ b> A plays a role of transporting the developer to the surface (development region) of the electrophotographic photosensitive member 2.

  In the developing unit 43, the toner frictionally charged by the magnetic roller 43 </ b> A is conveyed in the form of a magnetic brush adjusted to a constant spike length, and in the developing area of the electrophotographic photoreceptor 2, the toner is statically charged with the electrostatic latent image. It is visualized by adhering to the surface of the photoreceptor due to the electric attractive force. The charge polarity of the toner image is opposite to the charge polarity of the surface of the electrophotographic photosensitive member 2 when image formation is performed by regular development. When the image formation is performed by reversal development, the electrophotographic photosensitive member is charged. The surface of the body 2 has the same polarity as the charged polarity.

  The developing device 43 employs a dry development method, but may employ a wet development method using a liquid developer.

  The transfer device 44 is for transferring the toner image of the electrophotographic photosensitive member 2 to the recording medium P supplied to the transfer region between the electrophotographic photosensitive member 2 and the transfer device 44. The transfer unit 44 includes a transfer charger 44A and a separation charger 44B. In the transfer device 44, the back surface (non-recording surface) of the recording medium P is charged with a polarity opposite to that of the toner image in the transfer charger 44A, and the toner is applied onto the recording medium P by electrostatic attraction between the charged charge and the toner image. The image is transferred. In the transfer device 44, simultaneously with the transfer of the toner image, the back surface of the recording medium P is AC-charged in the separation charger 44B, and the recording medium P is quickly separated from the surface of the electrophotographic photosensitive member 2.

  As the transfer device 44, it is also possible to use a transfer roller that is driven by the rotation of the electrophotographic photosensitive member 2 and disposed with a small gap (usually 0.5 mm or less) from the electrophotographic photosensitive member 2. It is. The transfer roller in this case is configured to apply a transfer voltage that attracts the toner image on the electrophotographic photosensitive member 2 onto the recording medium P by, for example, a DC power source. When a transfer roller is used, a transfer separation device such as the separation charger 44B is omitted.

  The fixing device 45 is for fixing the toner image transferred to the recording medium P to the recording medium P, and includes a pair of fixing rollers 45A and 45B. The fixing rollers 45A and 45B are, for example, coated on a metal roller with Teflon (registered trademark) or the like. In the fixing device 45, the toner image can be fixed to the recording medium P by heat, pressure or the like by passing the recording medium P between the pair of fixing rollers 45A and 45B.

  The cleaning device 46 shown in FIGS. 1 and 2 is for removing the toner remaining on the surface of the electrophotographic photosensitive member 2, and includes a cleaning blade 46A.

  The cleaning blade 46 </ b> A serves to scrape residual toner from the surface of the surface layer 29 of the electrophotographic photosensitive member 2. The cleaning blade 46A is supported by the case 46C via an urging means such as a spring 46B so that the tip of the cleaning blade 46A presses the latent image forming region 22 of the electrophotographic photosensitive member 2. The cleaning blade 46A is made of, for example, a rubber material whose main component is polyurethane resin, the thickness of the tip portion in contact with the surface layer 29 is 1.0 mm or more and 1.2 mm or less, and the blade linear pressure is 14 gf / cm (generally 5 gf / Cm or more and 30 gf / cm or less), and the hardness is 74 degrees in JIS hardness (preferable range 67 degrees or more and 84 degrees or less).

  The static eliminator 47 is for removing the surface charge of the electrophotographic photosensitive member 2. The static eliminator 47 uniformly irradiates the entire surface (surface layer 29) of the electrophotographic photosensitive member 2 with a light source such as an LED, so that the surface charge (residual electrostatic latent image) of the electrophotographic photosensitive member 2 is irradiated. ).

  In the image forming apparatus 1, in the electrophotographic photosensitive member 2, the drive transmission flange 30E is closely fixed by the inlay portion 24 corresponding to the first end portion 22A, and the inlay portion 25 corresponding to the second end portion 22B. The bearing flange 31 is supported via the gap 6. For this reason, when the non-contact type charger 41 is employed, the distance between the photosensitive layer 21 and the charger 41 is larger at the second end 22B than at the first end 22A. When the contact type charger 41 is employed, the nip width in the contact area between the photosensitive layer 21 and the charger 41 is smaller at the second end 22B than at the first end 22A.

  In contrast, in the electrophotographic photosensitive member 2, the photosensitive layer 21 (the photoconductive layer 28 and the surface layer 29) is charged with the same charging ability along the axial direction of the cylindrical substrate 20 in the latent image forming region 22. In this case, the dark potential in the latent image forming region 22 is gradually increased from the first end 22A toward the second end 22B in the axial direction of the cylindrical substrate 20. Therefore, even when the distance from the charger 41 gradually increases from the first end portion 22A toward the second end portion 22B, or even when the nip width gradually decreases, the uneven electrostatic adhesion force of the toner Can be suppressed, and unevenness in the density of the image formed on the recording medium P can be suppressed.

  In particular, the axial distance from the end 20A on the first end 22A side of the cylindrical substrate 20 in the axial direction and the axis when the photosensitive layer 21 is charged with one voltage value selected from 300V to 600V. When the photosensitive layer 21 is formed so that the slope of the first-order approximation line showing the relationship with the measured value of the dark potential in the direction is 0.4 V / cm or more and 1.5 V / cm or less, the electrostatic charge of the toner It is possible to more appropriately suppress the bias of the applied force. Further, even when the photosensitive layer 21 is formed so that the absolute value of the difference between the value obtained from the first-order approximation line and the measured value is 10 V or less, the bias of the electrostatic adhesion force of the toner is more appropriate. Can be suppressed. As a result, in the electrophotographic photoreceptor 2 and the image forming apparatus 1 including the same, it is possible to more appropriately suppress the density deviation of the image formed on the recording medium P.

  The present invention is not limited to the embodiment described above, and various design changes can be made. For example, in the present invention, it is sufficient that the dark potential when the photosensitive layer 21 is charged gradually increases from the first end 22A to the second end 22B, and at least the photoconductive layer 28 and the surface layer 29 The dark potential on one side may be gradually increased from the first end 22A toward the second end 22B.

Further, as shown in FIG. 10, the thickness of the photosensitive layer 70 of the electrophotographic photosensitive member 7 is the same at the first end 72 and the second end 73 of the latent image forming region 71. When the photosensitive layer 70 is charged with the same charging ability along the axial direction, the dark potential of the first end 72 may be made smaller than the dark potential of the second end 73. Good. Such a photosensitive layer 70 can be formed, for example, by making the content of boron (B) in the first end portion 72 larger than the content of boron (B) in the second end portion 73. More specifically, the temperature of the cylindrical substrate 74 when forming the photosensitive layer 70 is set so that the first end 72 is higher than the second end 73, so that The photosensitive layer 70 in which the boron (B) content is larger than the boron (B) content in the second end portion 73 can be formed. Further, when the photosensitive layer 70 (photoconductive layer and surface layer) is formed of a material mainly composed of a-SiC, for example, glow discharge decomposition using a Si-containing gas such as silane gas (SiH ₄ ) as a source gas. In the method, the boron (B) content in the first end portion 72 in the axial direction of the photosensitive layer 70 (photoconductive layer and surface layer) is 6 ppm to 50 ppm, and the boron (B) content in the second end portion 73 is It can also be formed by setting to 0 ppm to 5 ppm. The boron (B) content may be gradually reduced within the range of 0 ppm to 50 ppm from the first end 72 toward the second end 73.

  In this example, the influence of the change rate of the dark potential in the axial direction when various electrophotographic photosensitive members are charged on image unevenness was examined.

(Creation of electrophotographic photoreceptor)
The electrophotographic photosensitive member is a photosensitive layer (charge injection blocking layer, photoconductive layer, and surface layer) under the conditions shown in Table 2 below with respect to an aluminum drawing tube (cylindrical substrate) having the dimensions shown in Table 1 below. ).

  However, as the cylindrical substrate, a substrate whose outer peripheral surface was mirror-finished and cleaned was used.

  Further, in forming the photoconductive layer and the surface layer in the photosensitive layer, the glow discharge decomposition apparatus 5 shown in FIGS. 4 and 5 was used, and the gas introduction tube 55 shown in FIG. 6 was used. As the gas introduction pipes, six types of electrophotographic photosensitive members 1 to 6 were prepared by using gas introduction ports 56 having different arrangement densities.

(Calculation of change rate of dark potential)
The dark potential of the photosensitive layer is determined by incorporating the electrophotographic photosensitive member into an image forming apparatus (trade name “IRC5800” manufactured by Canon Inc.) and charging the photosensitive layer of the electrophotographic photosensitive member, and then the surface of the photosensitive layer is contactless. It was measured with a type surface potential meter (“MODEL 344”: manufactured by TREK). The charged voltage of the electrophotographic photosensitive member was 500V. The dark potential measurement points are 5 cm (point 1), 15 cm (point 2), 25 cm (point 3), and 35 cm (point 4) from the end of the cylindrical substrate (reference numeral “20A” in FIG. 3). The four places.

  The change rate of the dark potential is obtained by performing a first-order linear approximation by the least square method on the relationship between the distance from the end (symbol “20A” in FIG. 3) and the measured value of the dark potential at the four previous measurement points. Calculated by performing. The calculation results of the primary approximate line are shown in Table 3 below together with the measurement result of the dark potential. In Table 3 below, the slope of the primary approximate line and the difference Δ between the calculated value obtained from the primary approximate line and the actually measured value are also shown. Further, as an example, the electrophotographic photoreceptor No. A graph showing measured values and first-order approximate straight lines for 3 is shown in FIG.

(Evaluation of image unevenness)
Image unevenness is evaluated by mounting an electrophotographic photosensitive member on an image forming apparatus (trade name “IRC5800” manufactured by Canon Inc.) and performing printing durability on 300,000 blank sheets of A4 size office equipment, resulting in uneven image output. It was performed by confirming visually whether or not this occurred. As a result of visual confirmation, the case where no image unevenness was confirmed was evaluated as “◯”, the case where slight unevenness was observed was evaluated as “Δ”, and the case where clear image unevenness was confirmed was evaluated as “x”. The evaluation results are shown in Table 3.

  As can be seen from Table 3, the electrophotographic photosensitive member No. 1 in which the slopes of the primary approximation lines are 1.4 V / cm, 1.1 V / cm, and 0.43 V / cm. 2, no. 3, No. For No. 5, no image unevenness occurred.

  Electrophotographic photoreceptor No. 2, no. 3, No. 5 has a slope of the primary approximation line in the range of 0.43 V / cm to 1.4 V / cm.

  On the other hand, the electrophotographic photosensitive member No. 1 having an inclination of the primary approximation line of 1.8 V / cm. In the electrophotographic photosensitive member No. 1 in which slight image unevenness occurred and the slopes of the primary approximation line were 1.0 V / cm and 0.05 V / cm. 4, no. For image 6, image unevenness occurred.

  Here, the electrophotographic photoreceptor No. No. 4 is an electrophotographic photosensitive member No. 4 in which the inclination of the primary approximation line was 1.0 V / cm and no image unevenness occurred. 2, no. 3, No. In the range of the slope of the primary approximation line defined by 5 (0.43 V / cm to 1.4 V / cm). However, the electrophotographic photoreceptor No. 4, the distance from the end of the cylindrical substrate (reference numeral “20A” in FIG. 3) is smaller at 35 cm (point 4) than at 25 cm (point 3). The dark potential did not gradually increase from the end of the first to the second end.

  In addition, the electrophotographic photosensitive member No. 2, no. 3, No. 5 shows that the absolute value of the difference Δ between the value obtained from the first-order approximation straight line and the actual measurement value is 5.5 V at the maximum, whereas the electrophotographic photosensitive member No. The difference Δ of 4 was 16.5 V at the maximum.

  From the above results, the electrophotographic photosensitive member can suppress the occurrence of image unevenness when the dark potential gradually increases from the first end portion to the second end portion of the electrostatic latent image forming region. The slope of the primary approximation line is preferably 0.4 V / cm or more and 1.5 V / cm or less, and the absolute value of the difference Δ between the value obtained by the primary approximation line and the actual measurement value is 10 V or less. Is more preferable.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view of a main part for explaining the relationship between an electrophotographic photosensitive member and a charger in the image forming apparatus shown in FIG. 1. 1 is a cross-sectional view showing an example of an electrophotographic photosensitive member according to the present invention and an enlarged view of a main part thereof. It is sectional drawing which shows an example of the glow discharge decomposition apparatus for manufacturing the electrophotographic photosensitive member shown in FIG. It is sectional drawing which follows the VV line of FIG. FIG. 6 is a front view showing an example of a gas introduction tube in the glow discharge decomposition apparatus shown in FIGS. 4 and 5. FIG. 6 is a front view showing another example of the gas introduction tube in the glow discharge decomposition apparatus shown in FIGS. 4 and 5. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on this invention. FIG. 9 is a cross-sectional view of a main part for explaining the relationship between the electrophotographic photosensitive member and the charger in the image forming apparatus shown in FIG. 8. FIG. 4 is a cross-sectional view for explaining another example of the electrophotographic photosensitive member according to the present invention and a cross-sectional view showing an enlarged main part thereof. It is a graph which shows the measurement result of a dark potential in an Example, and a primary approximate line. FIG. 3 is a cross-sectional view corresponding to FIG. 2 showing an image forming apparatus provided with a conventional electrophotographic photosensitive member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Electrophotographic photosensitive member 20,74 Cylindrical base | substrate 20A (End of cylindrical base | substrate) 21,70 Photosensitive layer 22,71 Latent image formation area 22A, 72 (Latent image formation area | region) 1st edge part 22B, 73 Second end of latent image forming region 28 Photoconductive layer 29 Surface layer 41 Charger 41 ′ Charging roller (charger)

Claims (18)

A cylindrical substrate that is rotated by a rotational driving force transmitted from the first end in the image forming apparatus, and a photosensitive layer that is formed on the cylindrical substrate.
The dark potential in the latent image forming region is a second potential opposite to the first end portion from the first end portion when charged with the same charging ability along the axial direction of the cylindrical substrate. An electrophotographic photosensitive member characterized by gradually increasing toward an end of the electrophotographic photosensitive member. The photosensitive layer comprises a photoconductive layer,
The dark potential in the latent image formation region of the photoconductive layer is gradually increased from the first end toward the second end when charged with the same charging ability along the axial direction. The electrophotographic photosensitive member according to claim 1. The photosensitive layer comprises a photoconductive layer and a surface layer,
The dark potential in the latent image forming region of the surface layer is gradually increased from the first end toward the second end when charged with the same charging ability along the axial direction. The electrophotographic photosensitive member according to claim 1. Measurement of the dark potential in the axial direction when the photosensitive layer is charged with a distance from the end on the first end side in the axial direction and a voltage value selected from 300V to 600V. The electrophotographic photosensitive member according to any one of claims 1 to 3, wherein a slope of a first-order approximation line indicating a relationship with a value is 0.4 V / cm or more and 1.5 V / cm or less.   Measurement of the dark potential in the axial direction when the photosensitive layer is charged with a distance from the end on the first end side in the axial direction and a voltage value selected from 300V to 600V. The electrophotographic photosensitive member according to claim 4, wherein an absolute value of a difference between a value obtained by a first-order approximation line indicating a relationship with the value and the measured value is 10 V or less.   The electrophotographic photosensitive member according to claim 1, wherein the photosensitive layer contains a silicon-based inorganic material. An electrophotographic photosensitive member comprising a cylindrical substrate and a photosensitive layer formed on the cylindrical substrate, and a driving force transmission for transmitting a rotational driving force to a first end portion in the axial direction of the electrophotographic photosensitive member. And a charger having the same charging ability along the axial direction,
The dark potential of the latent image forming region in the electrophotographic photosensitive member is opposite to the first end portion from the first end portion when charged with the same charging ability along the axial direction of the substrate. An image forming apparatus that gradually increases toward a second end portion on the side. The photosensitive layer comprises a photoconductive layer,
The dark potential in the latent image formation region of the photoconductive layer is gradually increased from the first end toward the second end when charged with the same charging ability along the axial direction. The image forming apparatus according to claim 7. The photosensitive layer comprises a photoconductive layer and a surface layer,
The dark potential in the latent image forming region of the surface layer is gradually increased from the first end toward the second end when charged with the same charging ability along the axial direction. The image forming apparatus according to claim 7.   Measurement of the dark potential in the axial direction when the photosensitive layer is charged with a distance from the end on the first end side in the axial direction and a voltage value selected from 300V to 600V. 10. The image forming apparatus according to claim 7, wherein the slope of the first-order approximation line indicating the relationship with the value is 0.4 V / cm or more and 1.5 V / cm or less.   The image forming apparatus according to claim 10, wherein an absolute value of a difference between a value obtained by the first-order approximate straight line and the measured value is 10 V or less.   The image forming apparatus according to claim 7, wherein the photosensitive layer includes a silicon-based inorganic material. The charger is a non-contact charger,
The distance from the photosensitive layer to the charger in the latent image forming region gradually increases in the axial direction from the first end toward the second end. The image forming apparatus according to any one of the above.   A first-order approximate straight line indicating the relationship between the distance from the end on the first end side in the axial direction and the measured value of the distance from the photosensitive layer to the non-contact charger in the latent image forming region. The image forming apparatus according to claim 13, wherein an absolute value of the inclination is 10 μm / cm or more and 100 μm / cm or less.   By a first-order approximation straight line indicating the relationship between the distance from the end on the first end side in the axial direction and the measured value of the distance from the photosensitive layer to the non-contact type charger in the latent image forming region. The image forming apparatus according to claim 14, wherein an absolute value of a difference between the obtained value and the measured value is 700 μm or less. The charger is a contact charger,
The nip width between the photosensitive layer and the contact charger in the latent image forming region is gradually decreased from the first end toward the second end in the axial direction. 13. The image forming apparatus according to any one of items 12 to 12.   The slope of the first-order approximate line indicating the relationship between the distance from the end on the first end side in the axial direction and the measured value of the nip width is 0.004 mm / cm or more and 0.08 mm / cm or less. The image forming apparatus according to claim 16.   The absolute value of the difference between the measured value and the value obtained from the linear approximation line indicating the relationship between the distance from the end on the first end side in the axial direction and the measured value of the nip width is 0 The image forming apparatus according to claim 17, wherein the image forming apparatus is 5 mm or less.

Images