Electrophotographic rollers, process cartridges, and electrophotographic image forming apparatus

Abstract

To provide a roller for electrophotography that can prevent adhesion of dirt to end areas of the roller for electrophotography even in an accelerated electrophotographic device.SOLUTION: A roller for electrophotography has a shaft core body, and an elastic layer on the shaft core body. The roller for electrophotography has a crown shape in which its diameter is reduced from the center position O in a longitudinal direction toward an end of the core shaft body. When the position of the end in the longitudinal direction of the elastic layer is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, L1=0.6×(L1+L2). When the outer diameters of the roller for electrophotography at O, X1, and X2 are Do, DX1, and DX2, respectively, and Z1=(Do-DX1) / 2 and Z2=(DX1-DX2) / 2 are defined, Z1, Z2, L1, and L2 satisfy the relationship represented by the following formula (1). (1) (Z2 / L2)<α×(Z1 / L1). α in the formula (1) is 1.931.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an electrophotographic roller, a process cartridge using the same, and an electrophotographic image forming apparatus.

Background Art

[0002] An electrophotographic image forming apparatus (hereinafter also referred to as an "electrophotographic apparatus") adopting an electrophotographic method mainly includes an electrophotographic photoreceptor (hereinafter also referred to as a "photoreceptor"), a charging device, an exposure device, a developing device, a transfer device, and a fixing device. Members such as roller shapes and blade shapes are preferably used for the charging device, the developing device, and the transfer device. Among these devices, a roller-shaped member (hereinafter also referred to as an "electrophotographic roller") is particularly preferably used.

[0003] The outer diameter shape of the electrophotographic roller used in the electrophotographic apparatus is required to have high precision in both the circumferential direction and the longitudinal direction. Here, the shape required for the electrophotographic roller (hereinafter also referred to as a "charging roller") used in the charging device will be described. When the charging roller is brought into contact with the photoreceptor, it is common to apply a predetermined force to both end portions of the axis of the charging roller and press them against the photoreceptor. At this time, a "crown shape" is known as the shape of the charging roller adopted for the purpose of making the "nip width" uniform in the longitudinal direction (see Patent Document 1 and Patent Document 2). The "nip width" refers to the width at which the charging roller and the photoreceptor drum are in contact. The "crown shape" refers to a shape in which the outer diameter of the charging roller decreases from the central portion to both end portions, that is, a shape in which the diameter decreases from the center position of the length in the direction orthogonal to the circumferential direction of the charging roller (hereinafter also referred to as the "longitudinal direction") toward both ends.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] However, according to the inventors' research, crown-shaped electrostatic rollers sometimes develop stains on their end surfaces due to the adhesion of toner and toner additives during use. This phenomenon was particularly pronounced in recent high-speed electrophotographic devices. One aspect of this disclosure aims to provide an electrophotographic roller that can suppress the adhesion of dirt to the end region of the electrophotographic roller even in high-speed electrophotographic apparatuses. Furthermore, other aspects of this disclosure are aimed at providing process cartridges that contribute to the stable formation of high-quality electrophotographic images. Furthermore, other aspects of this disclosure are toward providing an electrophotographic apparatus capable of stably forming high-quality electrophotographic images. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, an electrophotographic roller having a core body and an elastic layer on the core body, wherein the core body has a crown shape in which the diameter decreases from the longitudinal center position O toward the end, When the position of the longitudinal end of the elastic layer is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, then L1 = 0.6 × (L1 + L2), The outer diameters of the electrophotographic rollers in O, X1, and X2 are Do, DX1, and DX2, respectively, and Z1 = (Do - DX1) / 2, When Z2 = (DX1 - DX2) / 2 is defined, An electrophotographic roller is provided in which Z1, Z2, L1, and L2 satisfy the relationship shown in the following formula (1). (Z2 / L2) < α × (Z1 / L1) (1) (In formula (1), α is 1.931).

[0007] According to other aspects of this disclosure, a process cartridge is provided having the above-mentioned electrophotographic roller and an electrophotographic photoreceptor, and configured to be detachably attached to the body of an electrophotographic apparatus. According to yet another aspect of this disclosure, an electrophotographic apparatus is provided having the above-described electrophotographic roller and an electrophotographic photoreceptor. [Effects of the Invention]

[0008] According to one aspect of this disclosure, an electrophotographic roller can be obtained that can suppress the adhesion of dirt in the edge region even in a high-speed electrophotographic apparatus. According to another aspect of this disclosure, a process cartridge that contributes to the stable formation of high-quality electrophotographic images can be obtained. According to yet another aspect of this disclosure, an electrophotographic image forming apparatus that can stably form high-quality electrophotographic images can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is an external view of an electrophotographic roller. [Figure 2] This figure illustrates the shape of a charging roller according to one embodiment of the present disclosure. [Figure 3] This figure shows the difference in roller shape due to the difference in the constant β. [Figure 4] This diagram shows a method for measuring the shape of an electrophotographic roller. [Figure 5] This figure shows a load-displacement curve to explain the elastic deformation power. [Figure 6] This diagram illustrates the state of soiling when the elastic deformation power of electrophotographic rollers differs. [Figure 7] This diagram shows a schematic configuration of a crosshead extruder. [Figure 8] This is a cross-sectional view of a process cartridge according to one embodiment of the present disclosure. [Figure 9]A cross-sectional view of an electrophotographic apparatus according to an embodiment of the present disclosure.

Embodiment for Carrying out the Invention

[0010] The inventors of the present invention have speculated as follows about the cause of dirt adhesion to the end region of the charging roller having the crown shape described above. That is, generally, the charging roller is in contact with and driven by the driving of the photoreceptor. At this time, in the charging roller having the crown shape, a peripheral speed difference occurs between the charging roller and the photoreceptor depending on the position in the longitudinal direction. And in the end region, the peripheral speed difference becomes large, and toner on the photoreceptor and external additives of the toner are rubbed against the surface of the charging roller. Thereby, it is considered that the end region is more likely to get dirty. Therefore, the inventors of the present invention have repeatedly studied to prevent dirt adhesion caused by the peripheral speed difference in the end region of the electrophotographic roller having the crown shape. As a result, it has been found that an electrophotographic roller having a specific crown shape as described above contributes to the achievement of the above object.

[0011] Hereinafter, embodiments according to the present disclosure will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions, etc., and the scope of this invention is not intended to be limited to the following embodiments. FIG. 2 shows the shape of the electrophotographic roller according to the present disclosure. FIG. 2 shows an enlarged view from the center in the longitudinal direction of the electrophotographic roller to one end of the shaft core body 1. An electrophotographic roller according to one aspect of the present disclosure has a shaft core body and an elastic layer on the shaft core body, and has a crown shape in which the diameter decreases from the central portion toward the end in the longitudinal direction of the shaft core body. And when the position of the longitudinal end of the elastic layer is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, L1 = 0.6×(L1 + L2), Let the outer diameters of the electrophotographic roller at O, X1, and X2 be Do, DX1, and DX2, respectively, and Z1 = (Do - DX1) / 2, Z2 = (DX1 - DX2) / 2, when defined as such, Z1, Z2, L1, and L2 satisfy the relationship shown in the following calculation formula (1): (Z2 / L2) < α × (Z1 / L1) (1) (α in the calculation formula (1) is 1.931). Hereinafter, the electrophotographic roller according to one aspect of the present disclosure will be described in detail.

[0012] [Crown amount] First, the crown amount will be described. Generally used charging rollers are brought into contact with the photoreceptor by applying a predetermined pressure to both ends of the shaft core 1. Therefore, if the outer diameter of the elastic layer of the charging roller is constant from the center position in the longitudinal direction of the shaft core to the end of the elastic layer, the pressing force at the end will be greater than that at the central part. In order to reduce this uneven pressure distribution in the longitudinal direction, as shown in Fig. 2, it has a crown shape in which the diameter decreases from the center in the longitudinal direction of the shaft core towards both ends.

[0013] The crown amount in the present disclosure is defined as (Do - DX2) / 2. Here, Do and DX2 represent the average values of the diameters at respective arbitrary points. In order to uniformly contact the roller body with the photoreceptor, when the length of the elastic body in the longitudinal direction is 220 mm or more and 340 mm or less, the crown amount is preferably 0.01 mm or more and 0.26 mm or less. Also, the suitable crown amount varies depending on the pressing load applied to both ends of the shaft core. For example, when a pressing force of 200 g or more and 500 g or less is applied to both ends of the shaft core respectively, in order to improve the pressure uniformity, the crown amount is preferably 0.15 mm or more and 0.25 mm or less, and more preferably 0.20 mm or more and 0.25 mm or less.

[0014] [Detailed shape] When the position of the end of the elastic body in the longitudinal direction is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, we define L1 = 0.6 × (L1 + L2). This means that the range from the center position O to position X1 is the central region of the roller, and the range from position X1 to position X2 is the end region of the roller. Furthermore, the outer diameters at O, X1, and X2 are defined as Do, DX1, and DX2, respectively, and defined as follows. Z1 = (Do - DX1) / 2 Z2 = (DX1 - DX2) / 2 Z1 is the decrease in the radius at position X1 relative to the radius at the center position O of the axis body. Z2 is the decrease in radius at position X2 relative to the radius at position X1. Z1 and Z2 are the arithmetic mean values ​​calculated at 180 locations with a 1° pitch in the circumferential direction of the roller. in particular, First, calculate the initial Z1 (hereinafter also referred to as Z1(1)), Next, with the roller rotated 1° in the circumferential direction, the second Z1 (hereinafter also referred to as Z1(2)) is calculated. In this way, the process of calculating Z1 each time the roller is rotated 1° in the circumferential direction is repeated until the 180th Z1 (hereinafter also referred to as Z1(180)), The arithmetic mean is calculated by dividing the sum of the values ​​from Z1(1) to Z1(180) (Z1(1) + Z1(2) + ... + Z1(180)) by 180. The same method is used to calculate the arithmetic mean for Z2. The electrophotographic roller in this disclosure has a shape in which Z1, Z2, L1, and L2 satisfy the following formula (1). (Z2 / L2) < α × (Z1 / L1) (1) (In formula (1), α is 1.931.) The constant α represents the rate of change in curvature between the central and end regions of the roller.

[0015] Figure 3 shows roller shapes with different curvatures in the end regions. The shapes of rollers B and C according to one embodiment of this disclosure are shown by dashed and dotted lines, respectively. The shape of roller A, which has the general crown shape shown in Figure 3, is shown by a solid line. Table 1 shows the values ​​of Z1, L1, Z2, and L2 for rollers A to C, and the value of β calculated from these values ​​using the following formula. β = (Z2 / L2) / (Z1 / L1) The longitudinal length of the roller's elastic layer 2 was set to 240 mm, and its diameter at the center position O was set to 7.67 mm. Figure 3 shows the diameter at various positions along the roller's longitudinal direction. Furthermore, the shape of the contour line of the elastic layer of roller A, shown as a solid line in Figure 3, can be expressed as a quadratic function of X, where Y is the diameter of the roller and X is the position along the longitudinal direction of the roller. Y=a(X―b) 2 +c(a, b, c are arbitrary constants)

[0016] Roller A, which has a typical crown shape, also has a gradually decreasing diameter in its end region (between X1 and X2), resulting in a large difference in peripheral speed between the photoreceptor and the roller in the end region. When an electrophotographic roller with a typical crown shape like Roller A is used as a charging roller, a large difference in peripheral speed occurs between the photoreceptor and the electrophotographic roller (charging roller) in its end region. This difference in peripheral speed causes toner and external additives interposed between the photoreceptor and the electrophotographic roller to rub against and adhere to the outer surface of the electrophotographic roller. Such adhesions can lead to abnormal discharge from the electrophotographic roller to the photoreceptor, resulting in the formation of spots (hereinafter also referred to as "white spots") in the electrophotographic image that should not be formed. This phenomenon is particularly pronounced in low-temperature, low-humidity environments, such as at a temperature of 15°C and a relative humidity of 10%.

[0017] Similarly, when an electrophotographic roller with a common crown shape, such as roller A, is used as a developing roller, a large peripheral speed difference occurs between the photoreceptor and the electrophotographic roller (developing roller) in its edge region. This peripheral speed difference causes the toner interposed between the photoreceptor and the electrophotographic roller to rub against and adhere to the surface of the electrophotographic roller. Such adhesion reduces the electrophotographic roller's ability to impart charge to the toner. As a result, the toner cannot acquire sufficient charge on the developing roller. The insufficiently charged toner is transferred to the surface of the photoreceptor, where it should not be transferred, causing fogging in the electrophotographic image. This phenomenon is particularly pronounced in high-temperature and high-humidity environments, such as at a temperature of 40°C and a relative humidity of 95%.

[0018] On the other hand, the curvature of the outer diameter of rollers B and C according to this disclosure is smaller in the end region than in the central region. That is, the radius of curvature is larger. As a result, the central region has a more uniform nip width in the longitudinal direction. Also, in the end region, the peripheral speed difference with the photoreceptor is smaller compared to roller A. Therefore, even when rollers B and C are used as charging rollers and applied to a high-speed image forming process, the occurrence of contamination in the end region is less severe compared to roller A. Furthermore, even in low-temperature and low-humidity environments, the occurrence of white spots at the position corresponding to the end region of the electrophotographic image can be suppressed. In addition, when these electrophotographic rollers are used as developing rollers, the occurrence of contamination in the end region can be reduced or prevented, and the occurrence of fogging at the position corresponding to the end region of the electrophotographic image can be suppressed.

[0019] In Figure 3, the curvature of the central region is the same in all cases of β, ensuring contact stability in the central region. As mentioned above, the smaller the difference in outer diameter in the longitudinal direction, the smaller the difference in peripheral speed in the end region. Therefore, roller C is advantageous, followed by roller B (roller C is the most advantageous). On the other hand, if the β value is small, the outer diameter of the end increases, which improves the occurrence of dirt caused by the difference in peripheral speed, but the contact pressure at the end increases, which may cause dirt to adhere. Therefore, in order to suppress dirt caused by the difference in peripheral speed in the end region and to equalize the contact pressure on the photoreceptor, β must be less than 1.931. That is, [(Z2 / L2) / (Z1 / L1)] must be less than 1.931. Preferably, 1.000 < [(Z2 / L2) / (Z1 / L1)] < 1.931. Furthermore, although the above example shows Z2 being changed while Z1 is kept nearly constant, Z1 may also be changed while Z2 is kept nearly constant. In that case as well, as long as the relationship in equation (1) is satisfied, fouling caused by peripheral speed differences in the end region can be suppressed.

[0020] [Table 1]

[0021] [Method for evaluating circumferential speed difference] The magnitude of vibration when an electrophotographic roller rotates in accordance with the photoreceptor is proportional to the difference in peripheral speed between the electrophotographic roller and the photoreceptor. By utilizing this property, the magnitude of the peripheral speed difference can be evaluated by assessing the magnitude of vibration when the electrophotographic roller is driven by the photoreceptor. The amplitude of vibration of the electrophotographic roller can be measured using a laser Doppler vibrometer (product name LV-1710, manufactured by Ono Sokki Co., Ltd.). The measurement position is 5 mm from the end of the elastic part of the electrophotographic roller towards the center, and is opposite (180° opposite) to the contact position with the photoreceptor. The electrophotographic roller is assembled into the electrophotographic process cartridge, and the vibration is measured when the electrophotographic device is in operation. The amplitude is determined by frequency analysis of the vibration of the electrophotographic device, and the frequency with the largest amplitude is evaluated. Since amplitude and peripheral speed difference are proportional, a small amplitude indicates a small peripheral speed difference, but from the viewpoint of preventing contamination caused by peripheral speed difference, an amplitude of 12 nm or less is preferable.

[0022] [Method for evaluating overlap] The amount of toner fouling after durability when an electrophotographic roller is incorporated as a developing roller can be measured using a reflectance densitometer (product name TC-6DS / A; manufactured by Tokyo Denshoku Co., Ltd.). The electrophotographic roller is incorporated as a developing roller into an electrophotographic process cartridge, and 1000 sheets of paper are fed through continuously. The reflectance R1 at a position 5 mm from the edge of the 1000th image is measured using a reflectance densitometer. The reflectance R0 of an unprinted sheet of paper is also measured using a reflectance densitometer. Then, the decrease in reflectivity, "R0-R1" (%), relative to unprinted paper is used as the cover value for evaluation. If the fogging value is 7% or less, it is determined that the impact of the reduced charge transfer ability on the developing roller is small, and no fogging has occurred.

[0023] <Method for measuring shape> A non-contact laser measuring instrument can be used to measure the outer diameter of electrophotographic rollers. An example of a non-contact laser measuring instrument is the "LS-5000" (product name), a laser scan type dimension / outer diameter measuring instrument manufactured by Keyence Corporation.

[0024] Figure 4 shows the method for measuring the outer diameter using the laser scan type dimension / outer diameter measuring instrument described above. Figure 4(a) is a perspective view of the measuring instrument with the electrophotographic roller 49 and reference roller 50, which are to be measured, placed on it, and Figure 4(b) is a side view thereof. The light receiving unit 52 receives the laser light 53 (shaded area) emitted from the laser light emitting unit 51. First, the reference roller 50 is placed on the measuring instrument so that its axis and the laser light 53 are perpendicular to each other. Next, the electrophotographic roller 49, which is to be measured, is placed on the measuring instrument so that it is parallel to the axis of the reference roller 50. In this state, the width 54 of the laser light emitted from the laser light emitting unit 51 and transmitted between the reference roller 50 and the electrophotographic roller 49 is measured. The measurement pitch is preferably 2 mm or less in the longitudinal direction and within 5 degrees in the rotational direction, but a pitch of 1 mm in the longitudinal direction and a pitch of 1 degree in the rotational direction is more preferable. As shown in Figure 2, when defining the longitudinal position of the measured shape data, the center position of the electrophotographic roller 49 is O, the position of one end of the elastic part is X2, and the length from O to X2 is L. Then, the length L1 from O to X1 is set to L1 = 0.6 × L. Also, the length between X1 and X2 is set to L2.

[0025] [Diameter measurement] The diameter of the electrophotographic roller 49 is measured as the width of the laser obstructed by the electrophotographic roller 49. The diameter is measured each time the electrophotographic roller 49 is rotated, and the diameter of one full rotation of the electrophotographic roller 49 at one measurement cross-section is determined. In this disclosure, diameter is defined as the average value of the diameter of one full rotation at each cross-section. Next, the electrophotographic roller 49 is moved in the longitudinal direction, and the diameter at other positions in the longitudinal direction is measured. Furthermore, the diameters at the center positions O, X1, and X2 of the electrophotographic roller 49 described above are denoted as Do, DX1, and DX2, respectively, and Z1 and Z2 are calculated using the following formulas. Z1 = (Do - DX1) / 2 Z2 = (DX1 - DX2) / 2

[0026] <Elastic deformation power> [Elastic deformation power] Next, we will discuss the elastic deformation power (hereinafter also referred to as "ηIT"). ηIT can be calculated from physical quantities that can be measured by the nanoindentation method (international standard: ISO 14577). Detailed measurement conditions for the electrophotographic roller are described in Example 1 and are therefore omitted here. Figure 5 shows an example of a load-displacement curve necessary in the derivation process of the elastic deformation power. The load application curve 301 (curve from point A to point B) profiles the behavior of displacement with respect to load when a load is applied to the object. The load removal curve 302 (curve from point B to point C) profiles the behavior of displacement with respect to load when the load is removed from the object. Let Wp (plastic deformation work) be the amount of work done when a load is applied (the area of ​​region 303 enclosed by the load application curve 301, the load removal curve 302, and the straight line from point A to point C). Let We (elastic deformation work) be the amount of work done when the load is removed (the area of ​​region 304 enclosed by the load removal curve 302, the straight line from point B to point D, and the straight line from point C to point D). Let Wt (total deformation work) be the total amount of work. ηIT can be calculated using We, Wt, and the following formula. Wt = Wp + We ηIT(%) = (We / Wt) × 100

[0027] A high ηIT of an electrophotographic roller means that it has a high elastic recovery rate, meaning it tends to return to its original shape even after deformation. On a roller surface with a high ηIT, even if dirt such as toner, toner shells, and external additives such as silica adheres to it and stress is applied due to pressure or differences in peripheral speed, the high elastic recovery rate of the roller makes it difficult for toner and external additives to adhere. Therefore, it is more advantageous for preventing dirt from adhering to the edge areas.

[0028] Figure 6 schematically shows the state after an electrophotographic roller was incorporated into an electrophotographic apparatus as a charging roller, subjected to a durability evaluation of 1000 images, and then removed, cut, and its cross-section observed. Figure 6(a) shows the state when ηIT is 40%, and Figure 6(b) shows the state when ηIT is 55. Detailed durability conditions are described in Example 1. As shown in Figure 6(a), when ηIT is 40, the toner shell and external additive contaminants 61 are embedded in the elastic layer 62. On the other hand, as shown in Figure 6(b), when ηIT is 56, the toner shell and external additive contaminants 61 are not embedded in the elastic layer 62, and image defects are less likely to occur compared to the case where ηIT is 40. In this disclosure, ηIT is set to 56% or more, which is effective against the embedding of external additive contaminants on the charging roller, but 65% or more is preferred for the purpose of more effectively suppressing embedding, and 75% or more is more preferred from the same viewpoint.

[0029] To improve the ηIT of a charged roller, it is necessary to promote crosslinking only near the surface of the elastic layer while maintaining the hardness within the elastic layer at an appropriate crosslinking density. One specific method for promoting crosslinking near the surface of the elastic layer is electron beam irradiation (hereinafter also referred to as "EB treatment"). By performing EB treatment, it is possible to crosslink only the outermost surface of the charged roller while maintaining the crosslinking density within the elastic layer. Furthermore, ηIT can be easily improved by changing the electron beam irradiation intensity during EB treatment. The above describes means for improving ηIT, but the means for improving ηIT are not limited to these methods.

[0030] <Electrophotographic roller> Figure 1 schematically shows the external view of an electrophotographic roller. The electrophotographic roller has an elastic layer 2 on the outer circumference of a shaft 1, and both ends of the shaft 1 are exposed without being covered by the elastic layer 2. The charging roller is provided in the electrophotographic image forming apparatus as a charging means for charging the photoreceptor. Specifically, it is in contact with the photoreceptor drum, moves in accordance with the photoreceptor on the photoreceptor drum, and charges by friction at the contact point between the photoreceptor drum and the charging roller. The developing roller is provided as a means for stably supplying toner to the photoreceptor.

[0031] [Core body] The core body 1 used in the elastic roller of this disclosure is conductive and has the function of supporting the elastic layer provided on its outer circumference. Examples of materials include metals such as iron, copper, stainless steel, aluminum, and nickel, and their alloys. Furthermore, plating or other treatments may be applied to the surface of these materials for the purpose of providing scratch resistance. In addition, as the core body, a core body in which the surface of a resin base material is coated with metal or the like to provide surface conductivity, or a core body manufactured from a conductive resin composition can also be used.

[0032] Furthermore, an adhesive layer (not shown) may be provided between the core body 1 and the elastic layer 2. In this case, the adhesive is preferably conductive. To achieve conductivity, the adhesive can be appropriately selected from known conductivity imparters (e.g., ionic conductivity imparters or electronic conductivity imparters) and used alone or in combination of two or more types. Examples of adhesive binders include thermosetting resins and thermoplastic resins, and known types such as urethane-based, acrylic-based, polyester-based, polyether-based, and epoxy-based adhesives can be used. Examples of adhesives include Metalock N33 (a conductive epoxy adhesive, manufactured by Toyo Chemical Research Institute Co., Ltd.). Known methods for applying the adhesive, such as roll coating, sponge coating, and spray coating, can be used. The adhesive layer between the core body 1 and the elastic layer 2 may be provided over the entire surface where the core body 1 and the elastic layer 2 are in contact, or it may be provided only at both ends of the surface where the core body 1 and the elastic layer 2 are in contact, with a width of 5 mm to 20 mm. The thickness of the adhesive layer is preferably 1 μm to 10 μm.

[0033] [Elastic layer] The elastic layer 2 provided on the outer surface of the core body 1 may be a solid or a foam, and may be a single layer or composed of multiple layers. The hardness of the elastic layer 2 is preferably between 10 and 70 degrees on the Asker C hardness scale. If the Asker C hardness of the elastic layer 2 is 10 degrees or higher, it becomes easier to suppress the seepage of oil components from the rubber material constituting the elastic layer 2, thereby suppressing contamination of contact members such as the photoreceptor drum. Furthermore, if the Asker C hardness of the elastic layer 2 is 70 degrees or lower, the contact of the elastic roller with the contact member becomes stable, thereby suppressing a decrease in the quality of the output image. Here, the Asker C hardness can be defined by the measured value obtained using an Asker rubber hardness tester (manufactured by Polymer Instruments Co., Ltd.) using a test piece separately prepared according to the standard Asker C type SRIS (Japan Rubber Association standard) 0101.

[0034] [Materials for forming elastic layers] The material for forming the elastic layer contains a binder resin and conductive particles. Examples of binder resins include: natural rubber, butadiene rubber, styrene-butadiene rubber (SBR), nitrile rubber, ethylene-propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), epichlorohydrin rubber, butyl rubber, silicone rubber, urethane rubber, fluororubber, chlorine rubber, and other rubbers and thermoplastic elastomers. Among these, NBR can be suitably used from the viewpoint of compression set and hardness. Furthermore, among NBRs, so-called medium-high nitrile NBRs with a nitrile content of 30% or more and less than 36% are preferred. As such a medium-high nitrile, for example, commercially available products such as "N230SV" (product name, manufactured by JSR Corporation) can be used.

[0035] Conductive particles that can be used include conductive carbon such as Ketjenblack EC, acetylene black, carbon for rubber, oxidized carbon for color (ink), and pyrolysis carbon. Specifically, examples of carbon for rubber include the following: Super Abrasion Furnace (SAF), Intermediate Super Abrasion Furnace (ISAF), High Abrasion Furnace (HAF), Fast Extruding Furnace (FEF), General Purpose Furnace (GPF), Semi Reinforcing Furnace (SRF), Fine Thermal (FT), and Medium Thermal (MT). In addition, graphite such as natural graphite and artificial graphite can also be used.

[0036] Furthermore, various known conductive particles can be used, including metal oxide particles such as TiO2, SnO2, and ZnO, complex oxide particles such as solid solutions of ZnO and Al2O3, and metal powders such as Cu and Ag. These may be used individually or blended together.

[0037] [Coarse particles] For example, spherical particles with a particle size in the range of 1 μm to 90 μm may be added to the material for forming the elastic layer. For example, at least one spherical particle selected from the following particles is an example. Phenolic resin particles, silicone resin particles, polyacrylonitrile resin particles, polystyrene resin particles, polyurethane resin particles, nylon resin particles, polyethylene resin particles, polypropylene resin particles, acrylic resin particles, silica particles, and alumina particles. By using such rubber compositions, a charging roller can be made in which the outer surface of the elastic layer has protrusions derived from spherical particles.

[0038] [Other additives] Furthermore, vulcanizing agents, vulcanization accelerators, conductivity imparters, charge control agents, plasticizers, antioxidants, etc. may be added as needed. In addition, antistatic agents, UV absorbers, reinforcing agents, fillers, lubricants, mold release agents, pigments, dyes, flame retardants, etc. may be added as needed.

[0039] <Method for manufacturing electrophotographic rollers> [Electrophotographic roller precursor manufacturing process] One embodiment of the present disclosure is a method for manufacturing an electrophotographic roller, in which an elastic layer-forming material is applied to the shaft core using an extruder having a crosshead. Figure 7 is an explanatory diagram illustrating the process of forming a layer of elastic layer-forming material on the outer surface of a shaft core by co-extruding the shaft core and the elastic layer-forming material using an extrusion molding machine 7 equipped with a crosshead 74. The extrusion molding machine 7 is equipped with a crosshead 74 into which the shaft core 71 and the elastic layer forming material 72 are fed, a feed roller 75 that feeds the shaft core 71 into the crosshead 74, and a cylinder 76 that feeds the elastic layer forming material 72 into the crosshead 74.

[0040] The screw 77 in the cylinder 76 feeds the elastic layer-forming material 72 into the crosshead 74, and simultaneously feeds the shaft core 71 into the crosshead 74, thereby discharging the shaft core 71, which has a layer of elastic layer-forming material formed on its outer surface, from the crosshead. Hereafter, the shaft core with a layer of elastic layer-forming material formed on its outer surface will also be referred to as a "coated roller".

[0041] The outer diameter of an electrophotographic roller according to one aspect of this disclosure can be controlled by changing the relative ratio between the feed speed of the shaft core 71 to the crosshead by the feed roller 75 and the feed speed of the material for forming the elastic layer from the cylinder 76. For example, the thickness of the elastic layer in the longitudinal direction of the shaft core can be adjusted by keeping the feed speed of the material for forming the elastic layer from the cylinder to the crosshead constant and changing the feed speed of the shaft core 71 to the crosshead. Specifically, by increasing the feed speed of the shaft core, the thickness of the elastic layer can be made relatively thinner, that is, the diameter can be reduced. Here, in order to more accurately adjust the thickness of the elastic layer in the longitudinal direction of the shaft core, i.e., the diameter of the electrophotographic roller, it is preferable to use a manufacturing method having the following four steps.

[0042] (Step 1) A step in which the feed rate of the material for forming the elastic layer to the crosshead is kept constant, and the feed rate of the shaft core to the crosshead is varied to perform pre-forming, thereby obtaining the relationship between the feed rate of the shaft core to the crosshead and the thickness of the layer of the material for forming the elastic layer that is formed on the shaft core. (Second step) A step of measuring the outer diameter of the coating roller extruded from the crosshead. (Third step) A step in which the feed rate of the shaft body to form the crown shape is determined from the outer diameter measurement obtained in the second step, in light of the information obtained in the first step. (Fourth step) A step in which the rotational speed of the feed roller 75 is controlled based on the feed rate of the shaft determined in the third step.

[0043] I will now explain the third and fourth steps in detail. If the measured thickness of the elastic layer-forming material at a predetermined position in the longitudinal direction of the shaft is determined to be larger than the target crown shape, the rotational speed of the feed roller 75 is increased to increase the feed rate of the shaft, thereby reducing the outer diameter. Conversely, if the thickness is determined to be smaller than the target crown shape, the rotational speed of the feed roller 75 is decreased to decrease the feed rate of the shaft, thereby increasing the outer diameter. By performing this feedback control, for example, at 0.01-second intervals, the outer shape of the elastic layer can be made to the target crown shape with high precision without polishing. Furthermore, when obtaining a crown-shaped electrophotographic roller according to the above method, it is preferable to determine the target shape during extrusion molding, taking into consideration that the elastic layer may shrink during the subsequent vulcanization process.

[0044] In addition to the above method, another method involves using a mold having a cavity shape corresponding to a crown shape according to one aspect of this disclosure, filling the cavity with an elastic layer-forming material around a core body placed inside the mold, and then curing it. Furthermore, when using a crosshead, the feed rate of the shaft core to the crosshead and the feed rate of the material for forming the elastic layer are kept constant to produce a coated roller having an outer diameter equal to or greater than the outer diameter of the widest central part of the target crown shape. The elastic layer-forming material can also be produced by polishing the outer surface of the hardened rubber layer using a grinding wheel or the like.

[0045] [Vulcanization process, parting process] The molded electrophotographic roller precursor is heated and vulcanized by means of a hot air furnace, vulcanizing can, heating plate, far- and near-infrared radiation, induction heating, etc. The heating temperature varies depending on the material for forming the elastic layer, but is preferably 130 to 250°C for 5 to 240 minutes, and more preferably 140 to 220°C for 10 to 60 minutes. The vulcanized rubber composition at both ends of the vulcanized rubber roller is removed in a later process, completing the electrophotographic roller. Therefore, the completed electrophotographic roller has both ends of the core metal exposed.

[0046] [Surface treatment process] The surface layer may be subjected to surface treatments such as ultraviolet irradiation to reduce the surface friction coefficient or electron beam irradiation to improve ηIT.

[0047] <Processing Cartridge> Figure 8 shows an example of an electrophotographic process cartridge equipped with a charging roller according to one embodiment of the present disclosure. The process cartridge 100 shown in Figure 8 integrates a developing device and a charging device and is configured to be detachably attached to the main body of an electrophotographic apparatus. The developing device integrates at least a developing roller 103, a toner container 106, and toner 109. The photosensitive drum 101 is an example of an electrophotographic photoreceptor. The developing device may optionally include a toner supply roller 104, a developing blade 108, and a stirring blade 110. The charging device integrates at least a photosensitive drum 101 and a charging roller 102. The charging roller 102 is positioned to charge the photosensitive drum 101. The charging device may also include a cleaning blade 105 and a waste toner container 107. Voltage is applied to the charging roller 102, the developing roller 103, the toner supply roller 104, and the developing blade 108.

[0048] <Electrophotographic device> Figure 9 shows an example of an electrophotographic apparatus using a charging roller according to one embodiment of the present disclosure. The electrophotographic apparatus 200 shown in Figure 9 is configured to have four process cartridges 100 that can be detachably mounted. Each process cartridge 100 corresponds to a black, magenta, yellow, and cyan color, and uses toner of the corresponding color. Each process cartridge 100 has the same configuration except for the color of toner used.

[0049] Each process cartridge 100 has basically the same configuration as shown in Figure 8. The process cartridge 100 comprises a photosensitive drum 201, a charging roller 202, a developing roller 203, a toner supply roller 204, a cleaning blade 205, a toner container 206, a waste toner container 207, a developing blade 208, toner 209, and an agitator blade 210.

[0050] The photosensitive drum 201 rotates in the direction of the arrow (clockwise) and is uniformly charged by the charging roller 202 to which a voltage is applied from the charging bias power supply. When exposure light 211 is shone on the surface of the photosensitive drum 201, an electrostatic latent image is formed on its surface. Meanwhile, the toner 209 stored in the toner container 206 is supplied to the toner supply roller 204 by the agitator blade 210. The toner supply roller 204 supplies the toner 209 to the developing roller 203. The developing blade 208, positioned in contact with the developing roller 203, uniformly coats the surface of the developing roller 203 with the toner 209, and also imparts an electric charge to the toner 209 through triboelectric charging. The electrostatic latent image described above is developed when toner 209, which is transported by a developing roller 203 positioned in contact with the photosensitive drum 201, is applied to it, and it is made visible as a toner image.

[0051] The visualized toner image on the photosensitive drum is transferred to the intermediate transfer belt 215 by the primary transfer roller 212, to which a voltage is applied by the primary transfer bias power supply. The intermediate transfer belt 215 is supported and driven by the tension roller 213 and the intermediate transfer belt drive roller 214. The toner images of each color are sequentially superimposed to form a color image on the intermediate transfer belt 215.

[0052] The transfer material 219 is fed into the device by a paper feed roller. The transfer material 219 is transported between the intermediate transfer belt 215 and the secondary transfer roller 216. The secondary transfer roller 216 receives voltage from the secondary transfer bias power supply and transfers the color image on the intermediate transfer belt 215 to the transfer material 219. The transfer material 219, on which the color image has been transferred, is fixed by the fuser 218. The fixed transfer material 219 is discharged from the device. Meanwhile, any toner remaining on the photosensitive drum 201 without being transferred is scraped off by the cleaning blade 205 and stored in the waste toner container 207. Additionally, any toner remaining on the intermediate transfer belt 215 without being transferred is scraped off by the cleaning device 217.

[0053] (Composition 1) An electrophotographic roller having a core body and an elastic layer on the core body, The electrophotographic roller has a crown shape in which the diameter decreases from the longitudinal center position O of the shaft body toward the end, When the position of the longitudinal end of the elastic layer is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, then L1 = 0.6 × (L1 + L2), The outer diameters of the electrophotographic rollers in O, X1, and X2 are Do, DX1, and DX2, respectively, and Z1 = (Do - DX1) / 2, When Z2 = (DX1 - DX2) / 2 is defined, An electrophotographic roller characterized in that Z1, Z2, L1, and L2 satisfy the relationship shown in the following calculation formula (1): (Z2 / L2) < α × (Z1 / L1) (1) (In formula (1), α is 1.931).

[0054] (Configuration 2) The electrophotographic roller is the electrophotographic roller according to configuration 1, wherein 1.000 < [(Z2 / L2) / (Z1 / L1)] < 1.931.

[0055] (Composition 3) An electrophotographic roller according to configuration 1 or 2, wherein (Do-DX2) / 2 is 0.01 mm or more and 0.26 mm or less.

[0056] (Composition 4) An electrophotographic roller according to any one of configurations 1 to 3, wherein the elastic deformation power of the elastic layer is 56% or more.

[0057] (Composition 5) An electrophotographic roller according to any configuration 1 to 4, wherein the elastic layer comprises acrylonitrile butadiene rubber. (Composition 6) An electrophotographic roller according to any of configurations 1 to 5, wherein the Asker C hardness of the elastic layer is 10 degrees or more and 70 degrees or less. (Composition 7) An electrophotographic roller according to any of configurations 1 to 6, wherein the longitudinal length of the elastic layer is 220 mm or more and 340 mm or less.

[0058] (Composition 8) A process cartridge that is detachable from the main body of an electrophotographic image forming apparatus, Electrophotographic photoreceptor, The electrophotographic roller in contact with the electrophotographic photoreceptor, It is equipped with, A process cartridge characterized in that the electrophotographic roller is an electrophotographic roller described in any of configurations 1 to 7. (Composition 9) The process cartridge according to configuration 8, wherein the electrophotographic roller is a charging roller that charges the electrophotographic photoreceptor.

[0059] (Composition 10) Electrophotographic photoreceptor, The electrophotographic roller in contact with the electrophotographic photoreceptor, An electrophotographic image forming apparatus comprising, An electrophotographic image forming apparatus characterized in that the electrophotographic roller is an electrophotographic roller described in any of configurations 1 to 7.

[0060] (Composition 11) The electrophotographic image forming apparatus according to configuration 10, wherein the electrophotographic roller is a charging roller for charging the electrophotographic photoreceptor. (Composition 12) The electrophotographic image forming apparatus according to configuration 11, wherein the electrophotographic photoreceptor is driven and the charging roller rotates in accordance with the rotation of the electrophotographic photoreceptor. [Examples]

[0061] The present disclosure will be described in detail below with reference to examples, but will not be limited thereto. [Example 1] (Preparation of unvulcanized rubber composition for elastic layer) Composition A of kneaded rubber was obtained by mixing the materials shown in Table 2 below. A 6-liter pressurized kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used as the mixer. The mixing conditions were a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and a mixing time of 16 minutes.

[0062] [Table 2]

[0063] Next, the materials shown in Table 3 were mixed to obtain unvulcanized rubber composition 1. A 12-inch (0.30 m) open roll mixer (product name: 12×30 test roll, manufactured by Kansai Roll) was used. The mixing conditions were a front roll rotation speed of 10 rpm and a rear roll rotation speed of 8 rpm, with a roll gap of 2 mm. After a total of 20 left-right turns, the roll gap was reduced to 0.5 mm and thin passes were made 10 times.

[0064] [Table 3]

[0065] <Fabrication of rollers for electrophotography> A stainless steel rod with a diameter of 4.975 mm and a length of 250 mm was prepared as the core body. To form the unvulcanized rubber composition 1 around the core body, an extrusion molding apparatus (manufactured by Mitsuba Seisakusho Co., Ltd.) with a crosshead as shown in Figure 7 was used. The extruder of the extrusion molding apparatus was an extruder with a vent, having a cylinder inner diameter of 70 mm and a cylinder length-to-diameter ratio of 20.

[0066] The extrusion molding temperature was set to 100°C for the cylinder, screw, and crosshead die. The screw rotation speed was set to 10 revolutions per minute. Under these conditions, the shaft core was coated with unvulcanized rubber composition 1. Furthermore, when coating, the electrophotographic roller precursor is vulcanized, and the shape of the charging roller after removing the elastic layer edges is crown-shaped, The electrophotographic roller was formed by controlling the feed speed of the feed roll and adjusting the wall thickness so that the L1, L2, Z1, and Z2 values ​​shown in Figure 2 were the values ​​shown in Table 4, after the elastic layer at the end was removed.

[0067] in particular, The inflow rate of the material for forming the elastic layer into the crosshead is 5.20 × 10⁻⁶. -4 mm 3 Let it be constant at / seconds. On the other hand, when forming a layer of the material for forming an elastic layer, When forming the central portion of the shaft in the longitudinal direction, the feed speed of the shaft to the crosshead is set to 4.70 mm / second. During the formation of both ends, the feed rate of the shaft core to the crosshead was set to 5.80 mm / second. Furthermore, the thickness (diameter) of the elastic layer-forming material surrounding the shaft core immediately after it was extruded from the crosshead was measured using a laser measuring instrument, and feedback control of the shaft core feed rate was performed based on the relationship between the shaft core feed rate and diameter, which had been previously obtained during pre-forming.

[0068] The obtained electrophotographic roller precursor was heated in a 160°C hot air furnace for 1 hour. Then, 10 mm of the elastic layer-forming material layer was removed from both ends of the electrophotographic roller precursor to obtain the electrophotographic roller 1. The length of the elastic layer in the longitudinal direction of the electrophotographic roller 1 was 230 mm, with L1 = 69 mm and L2 = 46 mm.

[0069] <Surface treatment> The surface of the obtained electrophotographic roller was irradiated with ultraviolet light to obtain an electrophotographic roller 1' having a UV-treated region on the surface of the elastic layer. A low-pressure mercury lamp (product name: GLQ500US / 11, manufactured by Toshiba Lighting & Technology Corporation) was used for ultraviolet irradiation, and the electrophotographic roller was uniformly irradiated while rotating the shaft core 1 at a constant speed around the axis of rotation. The amount of ultraviolet light was 9000 mJ / cm² with a sensitivity of 254 nm on the sensor. 2 I made it so that it would be like that.

[0070] <Measurement of the outer diameter of electrophotographic rollers> The outer diameter of the electrophotographic roller 1' was measured using a non-contact laser measuring instrument with the configuration shown in Figure 4. In this example, the shape of the roller was measured using a non-contact laser measuring instrument (LS-5000; manufactured by Keyence Corporation), and measurements were taken by moving the roller in 1 mm increments in the longitudinal direction and 1 degree increments in the rotational direction. In this disclosure, diameter is defined as the average value of the diameter around each cross-section. In Figure 2, the diameters at the center positions O, X1, and X2 of the charged roller 1' are denoted as Do, DX1, and DX2, respectively, and Z1 = (Do - DX1) / 2 and Z2 = (DX1 - DX2) / 2 were used to calculate the diameters. The calculated results were Do = 7.69 mm, and Z1 and Z2 are as shown in Table 4.

[0071] <Measuring ηIT> Using a nanoindentation device (manufactured by Fischer Instruments, model name: Picodenter, model number: HM500), an indentation test was performed on the fabricated electrophotographic roller 1' in accordance with ISO 145177, and ηIT was analyzed. The measurement conditions were an indenter approach speed of 100 nm / s, a maximum load of 1 mN, and an indentation time of 3 s. The unloading conditions were the reverse of the load conditions.

[0072] Measurements were taken at three points: the center of the longitudinal direction of the electrophotographic roller and two points 10.0 mm from the center of each end of the elastic layer. Measurements were taken at 12 points in the circumferential direction at 30-degree intervals, for a total of 36 measurements. The test was conducted under the above conditions, and the load-displacement curve of the electrophotographic roller 1' was obtained, and the ηIT for each curve was calculated. In this disclosure, the median value of the 36 ηITs is defined as ηIT. As shown in Table 6, in this example, ηIT was 45%.

[0073] <Measurement of amplitude and evaluation of peripheral velocity difference> The electrophotographic roller 1' was incorporated as the charging roller of the process cartridge, and the vibration of the charging roller was measured when the electrophotographic device was in operation. The amplitude was evaluated as the magnitude of the peripheral speed difference. A laser Doppler vibrometer (product name LV-1710, manufactured by Ono Sokki Co., Ltd.) was used as the measuring instrument. The measurement position was 5 mm from the end of the elastic part of the electrophotographic roller towards the center, and was the opposite position (180° opposite) from the contact position with the photoreceptor. A Laserjet M608dn (manufactured by HP) was prepared as the electrophotographic device for amplitude measurement, and in order to perform evaluation in a high-speed process, it was modified to output 75 pages / minute (A4 portrait output), which is higher than the original output rate. The electrophotographic process cartridge used was the electrophotographic process cartridge for the aforementioned printer. When the vibration was measured when the printer was in operation and frequency analysis was performed, the amplitude was large at a frequency of 2700 Hz, so the amplitude at a frequency of 2700 Hz was taken as the magnitude of the vibration of the charging roller 1. The measurement results are shown in Table 6.

[0074] <Image evaluation and observation of dirt on the electrostatic roller> An electrophotographic roller 1' was incorporated into an electrophotographic apparatus as a charging roller, and a paper feed durability test was conducted under low temperature and low humidity conditions. A laser printer (product name: Laserjet M608dn; manufactured by HP) was used as the electrophotographic apparatus. To perform evaluation in a high-speed process, the printer was modified to output 75 pages / minute (A4 portrait output), which is higher than the original output. The image resolution of the laser printer was 600 dpi, and the primary charging output was a DC voltage of -1100V. An electrophotographic process cartridge for the aforementioned printer was used as the electrophotographic process cartridge. The electrophotographic process cartridge has a drum-shaped electrophotographic photoreceptor and a charging roller positioned in contact with the electrophotographic photoreceptor. Furthermore, a pressure of 250g is applied to each end of the axis of the charging roller, thereby pressing the charging roller against the electrophotographic photoreceptor.

[0075] First, the electrophotographic roller 1', the electrophotographic apparatus, and the process cartridge were left undisturbed for 48 hours in an environment with a temperature of 15°C and a relative humidity of 10% in order to acclimate them to the measurement environment. Next, the electrophotographic roller 1' was incorporated as a charging roller in the process cartridge. The output image was then evaluated using this setup. Specifically, a 1% print density E character image was subjected to a continuous durability test (image output) of 1000 images under low temperature and low humidity conditions (temperature 15°C, relative humidity 10%). After outputting 1000 images, a halftone image (an image in which horizontal lines with a width of 1 dot and spacing of 2 dots are drawn perpendicular to the rotation direction of the electrophotographic photoreceptor) was output. The obtained images were visually observed, and image defects caused by dirt adhering to the surface of the charging roller were identified.

[0076] After outputting the evaluation image, the surface of the electrophotographic roller 1' was observed using a digital microscope (Keyence Corporation, model VH-8000) to check the degree of toner and external additive contamination. Two observation points were taken, 10 mm inward from the edge of the elastic layer, and the areas with poor contamination were designated as evaluation points. The results of observing image defects caused by dirt adhesion in halftone images and the results of microscopic observation of the surface of the electrophotographic roller 1' were evaluated according to the criteria shown in Table 5. The results are shown in Table 6.

[0077] [Example 2] An electrophotographic roller 1' was obtained in the same manner as in Example 1, except that the values ​​of Z1, Z2, and (Do-DX2) / 2 were as shown in Table 4. The obtained electrophotographic roller 1' was evaluated in the same manner as in Example 1. The results are shown in Table 6.

[0078] [Examples 3-6] An electrophotographic roller 1' was obtained in the same manner as in Example 1, except that the values ​​of Z1, Z2, and (Do-DX2) / 2 were as shown in Table 4. The amplitude measurement, image evaluation, and observation of contamination of the electrophotographic roller 1' were performed using a Laserjet M608dn (HP) electrophotographic system. To perform evaluations in a high-speed process, the system was modified to output 100 frames per minute (A4 portrait output), which is higher than the original output rate.

[0079] [Example 7] The surface of the obtained electrophotographic roller was irradiated with an electron beam to obtain an electrophotographic roller having an EB-treated region on the surface of the elastic layer. For electron beam irradiation, an electron beam irradiation device with a maximum acceleration voltage of 70 kV (product name: "Low Energy Electron Beam Irradiation Source EB-ENGINE," manufactured by Hamamatsu Photonics K.K.) was used. Before irradiation with the electron beam, the air in the irradiation chamber was purged with nitrogen gas to adjust the oxygen concentration in the irradiation chamber. The processing conditions were: acceleration voltage: 70 kV, electron current (irradiation current): 1.5 mA, processing speed (scanning speed): 0.6 m / min, oxygen concentration: 800 ppm. At this time, the device constant of the electron beam irradiation device at an acceleration voltage of 70 kV was 218, and the dose calculated from equation (1) was 1635 kGy. D = (K·I) / V ···Formula (1) Otherwise, the electrophotographic roller 1'' shown in Table 4 was obtained in the same manner as in Example 1. The obtained electrophotographic roller 1'' was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6.

[0080] [Example 8] An electrophotographic roller 1'' having an EB-treated region on the surface of the elastic layer was obtained in the same manner as in Example 1, except that the electron beam irradiation conditions in Example 7 were performed with an electron current of 3.0 mA. Z1, Z2, etc. are shown in Table 4. The obtained electrophotographic roller 1'' was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6.

[0081] [Example 9] An electrophotographic roller 1'' having an EB-treated region on the surface of the elastic layer was obtained in the same manner as in Example 1, except that the electron beam irradiation conditions in Example 7 were performed with an electron current of 4.5 mA. Z1, Z2, etc. are shown in Table 4. The obtained electrophotographic roller 1'' was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6. [Example 10] An electrophotographic roller was obtained in the same manner as in Example 1, except that no surface treatment was applied to the electrophotographic roller. Z1, Z2, etc., are shown in Table 4. The evaluation results are shown in Table 6.

[0082] [Example 11] Using the crosshead extrusion molding machine used in Example 1, a straight shape with an outer diameter of 8.00 mm was formed when extruded from the molding machine. The material was then heated in a 160°C hot air furnace for 60 minutes to produce an electrophotographic roller precursor. Next, 10 mm was removed from both ends of the vulcanized rubber layer, and the surface of the vulcanized rubber layer of the electrophotographic roller precursor was polished using a plunge-cut grinding machine to obtain an electrophotographic roller 1'''' with Z1, Z2, and (Do-DX2) / 2 values ​​as shown in Table 4. Otherwise, the procedure was the same as in Example 1. The evaluation results are shown in Table 6.

[0083] [Example 12] In Example 1, the electrophotographic roller 1' was incorporated into an electrophotographic apparatus as a developing roller, and a paper feed durability test was conducted. The electrophotographic apparatus used was a Laserjet Pro M102w Printer (manufactured by HP), and fogging was evaluated. First, the electrophotographic apparatus with the electrophotographic roller 1' installed was placed in an environment with a temperature of 40°C and a relative humidity of 95%, and left undisturbed for more than 12 hours. Next, the reflectance R0 (%) of unprinted paper was measured. Next, 1000 images with a black ink density of 1% were printed consecutively, and then the reflectance R1 (%) at the edge of the 1000th image was measured. A reflectance densitometer (product name TC-6DS / A; manufactured by Tokyo Denshoku Co., Ltd.) was used for the measurements. The overlap values ​​calculated using the following formula are shown in Table 6. Coverage = R0(%) - R1(%)

[0084] [Example 13] In Example 1, the rubber material of the unvulcanized rubber composition was changed from NBR (grade N230SV, manufactured by JSR Corporation) to NBR (grade N230SL, manufactured by JSR Corporation). Otherwise, it was the same as Example 1. Z1, Z2, etc., are shown in Table 4. The evaluation results are shown in Table 6. [Example 14] The rubber material of the unvulcanized rubber composition in Example 1 was changed from NBR (grade N230SV, manufactured by JSR Corporation) to NBR (grade N230S, manufactured by JSR Corporation). Otherwise, it was the same as Example 1. Z1, Z2, etc., are shown in Table 4. The evaluation results are shown in Table 6.

[0085] [Comparative Examples 1-2] An electrophotographic roller 1' was obtained in the same manner as in Example 1, except that the values ​​of Z1, Z2, and (Do-DX2) / 2 were as shown in Table 4. The obtained electrophotographic roller 1' was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6.

[0086] [Comparative Example 3] An electrophotographic roller 1' was obtained in the same manner as in Example 1, except that the values ​​of Z1, Z2, and (Do-DX2) / 2 were as shown in Table 4. The obtained electrophotographic roller 1' was evaluated in the same manner as in Examples 3 to 6. The evaluation results are shown in Table 6.

[0087] [Table 4]

[0088] [Table 5]

[0089] [Table 6]

Claims

1. A process cartridge that is detachable from the main body of an electrophotographic image forming apparatus, It comprises an electrophotographic photoreceptor and an electrophotographic roller in contact with the electrophotographic photoreceptor, The electrophotographic roller has a core body and an elastic layer on the core body, and has a crown shape in which the diameter decreases from the longitudinal center position O toward the end of the core body. When the position of the longitudinal end of the elastic layer is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, then L1 = 0.6 × (L1 + L2), The outer diameters of the electrophotographic rollers in O, X1, and X2 are Do, DX1, and DX2, respectively, and Z1=(Do-DX1) / 2, When Z2 is defined as (DX1 - DX2) / 2, A process cartridge characterized in that Z1, Z2, L1, and L2 satisfy the relationship shown in the following calculation formula (1), and 1.000 < [(Z2 / L2) / (Z1 / L1)] < 1.931: (Z2 / L2)<α×(Z1 / L1) (1) (In formula (1), α is 1.931).

2. The process cartridge according to claim 1, wherein the electrophotographic roller is a charging roller for charging the electrophotographic photoreceptor.

3. An electrophotographic image forming apparatus comprising an electrophotographic photoreceptor and an electrophotographic roller in contact with the electrophotographic photoreceptor, The electrophotographic roller has a core body and an elastic layer on the core body, and has a crown shape in which the diameter decreases from the longitudinal center position O toward the end of the core body. When the position of the longitudinal end of the elastic layer is X2, the position between the center position O and X2 is X1, the distance between the center position O and X1 is L1, and the distance between X1 and X2 is L2, then L1 = 0.6 × (L1 + L2), The outer diameters of the electrophotographic rollers in O, X1, and X2 are Do, DX1, and DX2, respectively, and Z1=(Do-DX1) / 2, When Z2 is defined as (DX1 - DX2) / 2, An electrophotographic image forming apparatus characterized in that Z1, Z2, L1, and L2 satisfy the relationship shown in the following calculation formula (1), and 1.000 < [(Z2 / L2) / (Z1 / L1)] < 1.931: (Z2 / L2)<α×(Z1 / L1) (1) (In formula (1), α is 1.931).

4. The electrophotographic image forming apparatus according to claim 3, wherein the electrophotographic roller is a charging roller for charging the electrophotographic photoreceptor.

5. The electrophotographic image forming apparatus according to claim 4, wherein the electrophotographic photoreceptor is driven and the charging roller rotates in accordance with the rotation of the electrophotographic photoreceptor.

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