Electrophotographic roller, process cartridge, and electrophotographic image forming apparatus

Abstract

The present invention relates to an electronic photographic roller, a processing box and an electronic photographic image forming device. An electronic photographic roller comprises: a core shaft and an elastic layer on the core shaft, and has a convex shape with a diameter decreasing from a central position O in the length direction of the core shaft toward an end portion. When the position of the end portion in the length direction of the elastic layer is defined as X2, the position between O and X2 is defined as X1, the distance between O and X1 is defined as L1, and the distance between X1 and X2 is defined as L2, L1=0.6×(L1+L2). When the outer diameters of the electronic photographic roller at O, X1 and X2 are defined as Do, DX1 and DX2, respectively, and Z1=(Do‑DX1) / 2 and Z2=(DX1‑DX2) / 2 are defined, Z1, Z2, L1 and L2 satisfy (Z2 / L2)<1.931×(Z1 / L1).

Description

Technical Field

[0001] The present disclosure relates to a roller for electrophotography, and a process cartridge and an electrophotographic image forming apparatus including the same. Background Art

[0002] An electrophotographic image forming apparatus using an electrophotographic method (hereinafter, also referred to as an "electrophotographic apparatus") mainly includes an electrophotographic photosensitive member (hereinafter, also referred to as a "photosensitive member"), a charging device, an exposure device, a developing device, a transfer device, and a fixing device.

[0003] A member having a roller shape or a blade shape or the like is suitable for use in a charging device, a developing device, and a transfer device. Among these devices, a member having a roller shape (hereinafter also referred to as an "electrophotographic roller") is particularly preferably used.

[0004] The outer diameter shape of the electrophotographic roller used in the electrophotographic apparatus needs to be highly accurate in both the circumferential direction and the longitudinal direction.

[0005] Here, the shape required for an electrophotographic roller (hereinafter, also referred to as a "charging roller") used in a charging device will be described. When the charging roller is brought into contact with a photosensitive member, a predetermined force is generally applied to both ends of the shaft of the charging roller, and the charging roller is pressed toward the photosensitive member. In this case, as a shape of the charging roller adopted for the purpose of making the "nip width" in the length direction uniform, a "convex shape" is known (refer to Japanese Patent Application Laid-Open No. 2000-206762 and Japanese Patent Application Laid-Open No. 2006-323163). Note that the "nip width" refers to the width at which the charging roller and the photosensitive drum contact each other. The "convex shape" refers to a shape in which the outer diameter of the charging roller decreases from the central portion to both ends, specifically, a shape in which the diameter decreases from the center position of the length in a direction orthogonal to the circumferential direction of the charging roller (hereinafter, also referred to as the "length direction") toward both ends.

[0006] However, according to the research of the present inventors, there are cases where the charging roller having a convex shape generates blotting (blot) on the surface of the end area due to the fixation of toner or external additives of toner during use. In particular, this phenomenon is more significant in recent high-speed electronic photographic equipment. Summary of the invention

[0007] Problem that the invention aims to solve

[0008] At least one aspect of the present disclosure is directed to providing a roller for electrophotography that can suppress adhesion of stains in an end region of the roller for electrophotography even in a high-speed electrophotographic apparatus.

[0009] In addition, another aspect of the present disclosure is directed to providing a process cartridge that facilitates stable formation of high-quality electrophotographic images.

[0010] Furthermore, another aspect of the present disclosure is directed to providing an electrophotographic apparatus that can stably form high-quality electrophotographic images.

[0011] According to one aspect of the present disclosure, there is provided a roller for electrophotography, comprising a core shaft and an elastic layer on the core shaft, and the roller for electrophotography has a convex shape in which the diameter decreases from a center position O in the length direction of the core shaft toward both ends thereof, wherein

[0012] When the position of the end of the elastic layer in the length direction is defined as X2,

[0013] The position between the center position O and X2 is defined as X1,

[0014] The distance between the center position O and X1 is defined as L1, and

[0015] When the distance between X1 and X2 is defined as L2,

[0016] L1 = 0.6 × (L1 + L2), and

[0017] When the outer diameters of the roller for electrophotography at O, X1, and X2 are defined as Do, DX1, and DX2, respectively, and Z1 and Z2 are defined as follows:

[0018] Z1=(Do-DX1) / 2, and

[0019] Z2=(DX1-DX2) / 2,

[0020] Z1, Z2, L1 and L2 satisfy the relationship expressed by the following calculation formula (1):

[0021] (Z2 / L2)<α×(Z1 / L1)(1),

[0022] The α in the calculation formula (1) is 1.931.

[0023] According to another aspect of the present disclosure, there is provided a process cartridge including the above-mentioned roller for electrophotography and an electrophotographic photosensitive member and configured to be detachably mounted to a main body of an electrophotographic apparatus.

[0024] According to still another aspect of the present disclosure, there is provided an electrophotographic apparatus including the above-mentioned roller for electrophotography and an electrophotographic photosensitive member.

[0025] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This figure shows the appearance of an electrophotographic roller.

[0027] Figure 2 A diagram for describing the shape of a charging roller according to an embodiment of the present disclosure is shown.

[0028] Figure 3 A graph showing the difference in roller shape due to the difference in the constant β is shown.

[0029] Figure 4A and Figure 4B A diagram showing a method for measuring the shape of an electrophotographic roller is shown.

[0030] Figure 5 A graph showing a load-displacement curve for describing elastic deformation power is shown.

[0031] Fig. 6A and Figure 6B A graph for describing the state of stain when the elastic deformation power of the roller for electrophotography is different is shown.

[0032] Figure 7 A diagram showing a schematic configuration of a crosshead extrusion device is shown.

[0033] Figure 8 A sectional view showing a process cartridge according to an embodiment of the present disclosure.

[0034] Fig. 9 A cross-sectional view showing an electrophotographic apparatus according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0035] Preferred embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings.

[0036] The inventors of the present invention presume that the reason why the above-mentioned stains adhere to the end region of the charging roller having a convex shape is as follows. Specifically, the charging roller is usually in contact with the photosensitive member and driven by it. At this time, in the charging roller having a convex shape, a peripheral speed difference is generated between the charging roller and the photosensitive member according to the position in the length direction. Then, the peripheral speed difference becomes larger in the end region, and the toner on the photosensitive member and the external additive of the toner rub against the surface of the charging roller. It is considered that it becomes easier to make the end region more dirty thereby.

[0037] Then, the present inventors repeatedly studied to prevent stain adhesion caused by the peripheral speed difference in the end area of ​​the electrophotographic roller having a convex shape. As a result, the present inventors found that an electrophotographic roller having a specific convex shape as described above contributes to achieving the above purpose.

[0038] The following will describe in detail an embodiment according to the present disclosure with reference to the accompanying drawings. However, the size, material, shape, and relative configuration of the constituent parts described in the embodiment should be appropriately changed according to the composition of the equipment to which the present disclosure is applied, various conditions, etc., and the scope of the present disclosure is not intended to be limited to the following embodiments.

[0039] Figure 2 The shape of the roller for electrophotography according to the present disclosure is shown. Figure 2 An enlarged view from the center of the roller for electrophotography in the longitudinal direction to one end of the mandrel 1 is shown.

[0040] The roller for electrophotography according to one aspect of the present disclosure includes a core shaft and an elastic layer on the core shaft; and has a convex shape in which the diameter decreases from the central portion toward both ends in the length direction of the core shaft. In addition, when the position of the end portion in the length direction of the elastic layer is defined as X2, the position between the center position O and X2 is defined as X1, the distance between the center position O and X1 is defined as L1, and the distance between X1 and X2 is defined as L2, L1=0.6×(L1+L2), and

[0041] When the outer diameters of the roller for electrophotography at O, X1, and X2 are defined as Do, DX1, and DX2, respectively, and

[0042] When Z1 = (Do-DX1) / 2 and Z2 = (DX1-DX2) / 2 are defined,

[0043] Z1, Z2, L1 and L2 satisfy the relationship expressed by the following calculation formula (1):

[0044] (Z2 / L2)<α×(Z1 / L1)(1),

[0045] Where α is 1.931.

[0046] Hereinafter, a roller for electrophotography according to one aspect of the present disclosure will be described in detail.

[0047] [Amount of protrusion]

[0048] First, the amount of protrusion will be described. A commonly used charging roller is brought into contact with the photosensitive member so that a predetermined pressure is applied to both end portions of the mandrel 1. Therefore, when the outer diameter of the elastic layer of the charging roller is constant from the center position in the length direction of the mandrel to the end portions of the elastic layer, the pressure at the end portions becomes greater than the pressure at the center portion. In order to reduce the unevenness of the pressure distribution in the length direction, as Figure 2 As shown in , the charging roller has a convex shape in which the diameter decreases from the center of the core shaft in the length direction toward both ends.

[0049] The amount of projection in the present disclosure is defined as (Do-DX2) / 2. Here, Do and DX2 represent average values ​​of diameters at each arbitrary point.

[0050] In order to make the main body of the roller uniformly contact with the photosensitive member, when the length of the elastic body in the longitudinal direction is 220 mm or more and 340 mm or less, the protrusion amount is preferably 0.01 mm or more and 0.26 mm or less.

[0051] In addition, the appropriate amount of protrusion varies depending on the pressure load applied to both ends of the mandrel. For example, when a pressure of 200 g or more and 500 g or less is applied to each of the two ends of the mandrel, in order to improve the uniformity of the pressure, the amount of protrusion 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.

[0052] [Detailed shape]

[0053] When the position of the end of the elastic body in the length direction is defined as X2, the position between the center position O and X2 is defined as X1, the distance between the center position O and X1 is defined as L1, and the distance between X1 and X2 is defined as L2, L1 is defined as L1=0.6×(L1+L2). This means that the range from the center position O to the position X1 is the central area of ​​the roller, and the range from the position X1 to the position X2 is the end area of ​​the roller. In addition, the outer diameters at O, X1, and X2 are defined as Do, DX1, and DX2, respectively, and the following is defined:

[0054] Z1=(Do-DX1) / 2, and

[0055] Z2=(DX1-DX2) / 2.

[0056] Z1 is the reduction of the "radius at position X1" of the mandrel relative to the "radius at the center position O".

[0057] Z2 is the reduction of the "radius at position X2" relative to the "radius at position X1".

[0058] Z1 and Z2 are each determined as the arithmetic mean of values ​​calculated at 180 positions at intervals of 1 degree in the circumferential direction of the roller.

[0059] Specifically, the first Z1 (hereinafter also referred to as Z1(1)) is calculated, and

[0060] Next, the second Z1 (hereinafter also referred to as Z1(2)) is calculated in a state where the roller is rotated 1 degree in the circumferential direction;

[0061] Therefore, the calculation of Z1 is repeated each time the roller is rotated 1 degree in the circumferential direction until the 180th Z1 (hereinafter also referred to as Z1 (180)), and then

[0062] The arithmetic mean is calculated by dividing the total value of Z1(1) to Z1(180) (Z1(1)+Z1(2)+...+Z1(180)) by 180.

[0063] The arithmetic mean of Z2 is calculated in the same way.

[0064] The roller for electrophotography in the present disclosure has a shape in which Z1, Z2, L1 and L2 satisfy the following calculation formula (1):

[0065] (Z2 / L2)<α×(Z1 / L1) (1),

[0066] Where α is 1.931.

[0067] The constant α represents the rate of change of curvature in the center region and the end regions of the roller.

[0068] Figure 3 The shapes of the rollers B and C according to one aspect of the present disclosure are represented by dashed lines and alternating long and short dashed lines, respectively. Figure 3 The shape of the roller A having a general convex shape shown in is indicated by a solid line. Table 1 shows the respective values ​​of Z1, L1, Z2, and L2 of rollers A to C, and β values ​​calculated from these values ​​using the following calculation formula.

[0069] β=(Z2 / L2) / (Z1 / L1)

[0070] The length of the elastic layer 2 of the roller in the longitudinal direction was set to 240 mm, and the diameter thereof at the center position O was set to 7.67 mm. Figure 3 The diameter of the roller at each position in the length direction is shown.

[0071] For reference, when Y represents the diameter of the roller and X represents the position of the roller in the length direction, Figure 3 The shape of the contour line of the elastic layer of roller A indicated by the solid line in φ represents the following quadratic function of X.

[0072] Y=a(Xb) 2 +c (where a, b and c are arbitrary constants)

[0073] In roller A having a general convex shape, the diameter of the end region (between X1 and X2) also gradually decreases, and the peripheral speed difference between the photosensitive member and the roller is large in the end region. When an electrophotographic roller having a general convex shape such as roller A is used as a charging roller, a large peripheral speed difference is generated between the photosensitive member and the electrophotographic roller (charging roller) in the end region. Then, due to the peripheral speed difference, the toner and external additives between the photosensitive member and the electrophotographic roller rub against the outer surface of the electrophotographic roller and adhere thereto. Such fixing substances cause abnormal discharge from the electrophotographic roller to the photosensitive member, and as a result, spots (hereinafter also referred to as "white spots") that should not have been formed on the electrophotographic image are formed in some cases. In particular, this phenomenon occurs significantly in a low-temperature and low-humidity environment such as a temperature of 15°C and a relative humidity of 10%.

[0074] Similarly, when an electrophotographic roller having a generally convex shape, such as roller A, is used as a developing roller, a large peripheral speed difference is generated between the photosensitive member and the electrophotographic roller (developing roller) in the end region. Then, due to the peripheral speed difference, the toner between the photosensitive member and the electrophotographic roller rubs against the surface of the electrophotographic roller and adheres thereto. Such fixing substances reduce the ability of the electrophotographic roller to impart charge to the toner. As a result, the toner cannot be fully charged on the developing roller. The insufficiently charged toner is transferred to the surface of the photosensitive member to which the toner should not have been transferred, and causes fogging in the electrophotographic image. This phenomenon occurs particularly significantly in a high temperature and high humidity environment, such as a temperature of 40°C and a relative humidity of 95%.

[0075] In contrast, in roller B and roller C according to the present disclosure, the curvature of the outer diameter of the end region is smaller than the curvature of the outer diameter of the central region. In other words, the radius of curvature is larger. As a result, in the central region, the roller gap width is more uniform in the length direction. In addition, in the end region, the circumferential speed difference with the photosensitive member is smaller than the circumferential speed difference of roller A. Therefore, even when roller B or roller C is used as a charging roller and applied to a high-speed image forming process, compared with roller A, stains are less likely to appear in the end region. In addition, even in a low temperature and low humidity environment, the appearance of white spots at the position corresponding to the end region of the electronic photographic image can be suppressed. In addition, when the roller for electronic photography is used as a developing roller, the roller for electronic photography can also reduce or prevent the appearance of stains in the end region and suppress the appearance of fogging at the position corresponding to the end region of the electronic photographic image.

[0076] Figure 3In the case of any β, the curvature of the central area is the same, and the contact stability of the central area is ensured. As described above, the smaller the difference in the outer diameter in the length direction, the smaller the circumferential speed difference in the end area. Therefore, roller C and roller B are favorable in this order (roller C is the most favorable). On the other hand, when the β value is small, there is a situation where the contact pressure at the end becomes high, whereby stains will adhere, although the outer diameter of the end becomes larger and the appearance of stains caused by the circumferential speed difference is improved. Therefore, in order to make the contact pressure relative to the photosensitive member uniform, in addition to suppressing the stains caused by the circumferential speed difference in the end area, it is also necessary to control the constant β to be less than 1.931. In other words, it is necessary to control [(Z2 / L2) / (Z1 / L1)] to be less than 1.931. In addition, it is preferably 1.000<[(Z2 / L2) / (Z1 / L1)]<1.931. In addition, although the above example shows that Z2 changes while Z1 is roughly constant, Z1 can be changed while Z2 is roughly constant; and even in this case, as long as the relationship of formula (1) is satisfied, the stain in the end area caused by the peripheral speed difference can be suppressed.

[0077] [Table 1]

[0078] Z1(mm) L1(mm) Z2(mm) L2(mm) β Roller A 0.0448 72.0 0.0797 48.0 2.669 Roller B 0.0446 72.0 0.0574 48.0 1.930 Roller C 0.0443 72.0 0.0442 48.0 1.497

[0079] [Evaluation method of peripheral speed difference]

[0080] The magnitude of the vibration of the electrophotographic roller as it rotates with the photosensitive member is proportional to the magnitude of the peripheral speed difference of the electrophotographic roller relative to the photosensitive member. By utilizing this property, the magnitude of the vibration is evaluated when the electrophotographic roller is driven by the photosensitive member, and the magnitude of the peripheral speed difference is thereby evaluated.

[0081] The magnitude (amplitude) of the vibration of the roller for electrophotography can be measured with a laser Doppler vibrometer (trade name: LV-1710, manufactured by Ono Sokki Co., Ltd.). The measurement position is set at a position close to the center of 5 mm from the end of the elastic portion of the roller for electrophotography, and is a position opposite to the contact position of the photosensitive member (180 degrees opposite side). The roller for electrophotography is loaded into the electrophotographic process box, and when the electrophotographic device is operated, the vibration is measured. The amplitude is evaluated by performing frequency analysis on the vibration of the electrophotographic device and evaluating the frequency with the maximum amplitude. The amplitude and the peripheral speed difference are proportional to each other, and therefore, the smaller the amplitude means the smaller the peripheral speed difference; however, from the viewpoint of preventing stains caused by the peripheral speed difference, the amplitude is preferably 12 nm or less.

[0082] [Evaluation method of fogging]

[0083] When the electrophotographic roller is loaded as a developing roller, the amount of fogging caused by the toner after endurance can be measured by a reflection densitometer (trade name: TC-6DS / A; manufactured by Tokyo Denshoku Co., Ltd.). The electrophotographic roller is loaded into an electrophotographic process box as a developing roller, and 1000 sheets of paper are passed continuously. The reflectivity R1 at a position 5 mm from the end in the 1000th image is measured by the reflection densitometer. In addition, the reflectivity R0 of the unprinted paper is also measured with the reflection densitometer.

[0084] Then, the amount of reflectance reduction "R0-R1" (%) relative to the unprinted paper was evaluated as the fogging value.

[0085] When the fog value is 7% or less, it is determined that the influence of the reduction in charge imparting ability on the developing roller is small, and fogging does not occur.

[0086] <Shape measurement method>

[0087] A non-contact laser length measuring instrument can be used for measuring the outer diameter of the roller for electrophotography. As a non-contact laser length measuring instrument, for example, there is a laser scanning type size / outer diameter measuring instrument "LS-5000" (trade name) manufactured by Keyence Corporation.

[0088] Figure 4A and Figure 4B A method of measuring the outer diameter using the above-mentioned laser scanning type dimension / outer diameter measuring instrument is shown. Figure 4A A perspective view showing a state in which an electrophotographic roller 49 and a reference roller 50 as measurement objects are placed on a measuring instrument, and Figure 4B Its side view is shown. The light receiving portion 52 receives the laser beam 53 (diagonal line portion) emitted from the laser emitting portion 51. First, the reference roller 50 is placed on the measuring instrument so that its axis and the laser beam 53 are orthogonal to each other. Next, the electrophotographic roller 49 as the measurement object is placed on the measuring instrument so as to be parallel to the axis of the reference roller 50. In this state, the width 54 of the laser beam emitted from the laser emitting portion 51 and transmitted between the reference roller 50 and the electrophotographic roller 49 is measured. The measurement interval is preferably less than 2 mm in the length direction, and less than 5 degrees in the rotation direction, and more preferably 1 mm interval in the length direction, and 1 degree interval in the rotation direction. As Figure 2 As shown in , when specifying the position of the measurement shape data in the length direction, when the center position of the roller 49 for electrophotography is represented by O, the position of one end portion of the elastic portion is represented by X2, and the distance from O to X2 is represented by L, the distance L1 from O to X1 is determined as L1=0.6×L. The distance between X1 and X2 is represented by L2.

[0089] [Diameter measurement]

[0090] The diameter of the electrophotographic roller 49 is measured as the width of the laser light blocked by the conductive base roller 49. Specifically, the diameter is measured each time the electrophotographic roller 49 is rotated, and the diameter of one circumference of the electrophotographic roller 49 is determined in one measurement section. The diameter in the present disclosure is defined as the average value of the diameter of one circumference in each section. Next, the electrophotographic roller 49 is moved in the length direction, and the diameter is measured at other positions in the length direction. In addition, the diameters at the center position O of the electrophotographic roller 49, the above-mentioned X1 and X2 are represented by Do, DX1 and DX2, respectively, and Z1 and Z2 are calculated using the following expressions:

[0091] Z1=(Do-DX1) / 2, and

[0092] Z2=(DX1-DX2) / 2.

[0093] <Elastic deformation power>

[0094] [Elastic deformation power]

[0095] Subsequently, the elastic deformation power (hereinafter, also referred to as “ηIT”) will be described.

[0096] ηIT can be calculated from a physical quantity that can be measured by measurement by a nanoindentation method (International Standard: ISO 14577). Detailed measurement conditions for the roller for electrophotography will be described in Example 1 and will therefore be omitted here. Figure 5 An example of a load-displacement curve required in the derivation of elastic deformation power is shown. The load application curve 301 (the curve from point A to point B) describes the behavior of displacement relative to load when a load is applied to an object. The load-unloading curve 302 (the curve from point B to point C) describes the behavior of displacement relative to load when the load is unloaded from the object.

[0097] The amount of work done when a load is applied (the area of ​​a region 303 enclosed by the load application curve 301, the load-unloading curve 302, and the straight line from point A to point C) is represented by Wp (the amount of work done by plastic deformation). The amount of work done when the load is unloaded (the area of ​​a region 304 enclosed by the load-unloading curve 302, the straight line from point B to point D, and the straight line from point C to point D) is represented by We (the amount of work done by elastic deformation). The total amount of work done is represented by Wt (the total amount of deformation work done). ηIT can be calculated using We, Wt, and the following expression:

[0098] Wt=Wp+We, and

[0099] ηIT(%)=(We / Wt)×100.

[0100] In the case where the ηIT of the electrophotographic roller is high, it means that the electrophotographic roller has a high performance of being able to recover to the original state even if deformed, in other words, has a high elastic recovery rate. For the roller surface with high ηIT, in a state where stains such as toner or external additives such as toner shell or silica are attached to the roller surface, even if stress is applied thereto due to pressure or peripheral speed difference, the toner or external additive is difficult to adhere due to the high elastic recovery rate of the roller. Therefore, the roller surface with high ηIT is more conducive to preventing stains from adhering to the end area.

[0101] Fig. 6A and Figure 6B The following state is schematically shown: when the roller for electrophotography is incorporated into the electrophotographic apparatus as a charging roller, the durability of 1,000 sheets is evaluated, and then the roller for electrophotography is taken out and cut, and the cross section is observed. Fig. 6A The case where ηIT is 40% is shown, and Figure 6B The case where ηIT is 55% is shown. The detailed endurance conditions will be described in Example 1.

[0102] like Fig. 6A As shown in FIG. 1 , when ηIT is 40, the shell of the toner and the stain 61 of the external additive are buried in the elastic layer 62. On the other hand, as Figure 6B As shown in , when ηIT is 56, the shell of the toner and the stain 61 of the external additive are not buried in the elastic layer 62, and image defects are less likely to be caused compared with the case where ηIT is 40. In the present disclosure, ηIT is set to 56% or more, which is effective for suppressing the burying of the stain of the external additive in the charging roller, but for the purpose of more effectively suppressing the burying, it is preferably 65% ​​or more, and from the same viewpoint, it is more preferably 75% or more.

[0103] In order to improve the ηIT of the charging roller, it is necessary to promote crosslinking only near the surface of the elastic layer while maintaining the hardness inside the elastic layer at an appropriate crosslinking density. As a specific method for promoting crosslinking near the surface of the elastic layer, for example, electron beam irradiation (hereinafter, also referred to as "EB treatment") is used. By performing EB treatment, only the outermost surface of the charging roller can be crosslinked while maintaining the crosslinking density inside the elastic layer. In addition, EB treatment can easily improve ηIT by changing the intensity of electron beam irradiation. The above has described the way to improve ηIT, but the way to improve ηIT is not limited to these techniques.

[0104] <Electronic Photography Roller>

[0105] Figure 1The appearance diagram of the roller for electrophotography is schematically shown. The roller for electrophotography has a structure in which an elastic layer 2 is provided on the outer periphery of a core shaft 1, wherein both ends of the core 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 unit for charging a photosensitive member. Specifically, the charging roller is in contact with a photosensitive drum, is driven by the photosensitive member of the photosensitive drum, and is charged by friction at a contact portion between the photosensitive drum and the charging roller. In addition, a developing roller is provided as a unit for stably supplying toner to the photosensitive member.

[0106] [Mandrel]

[0107] The core shaft 1 used in the elastic roller of the present disclosure has electrical conductivity and has the function of supporting an elastic layer disposed on its periphery, etc. Examples of materials include metals such as iron, copper, stainless steel, aluminum and nickel, and alloys thereof. In addition, these materials may be subjected to plating treatments, etc., thereby imparting scratch resistance to these surfaces. In addition, as the core shaft, a core shaft in which the surface of a substrate formed of a resin is coated with a metal or the like to impart surface conductivity may also be used, or a core shaft produced from a conductive resin composition may also be used.

[0108] In addition, an adhesive layer (not shown) may be provided between the mandrel 1 and the elastic layer 2. In this case, it is preferred that the adhesive is conductive. In order to impart conductivity, an agent suitable for the adhesive is selected from known conductivity imparting agents (e.g., ionic conductivity imparting agents and electronic conductivity imparting agents), and may be used alone or in combination of two or more thereof.

[0109] Examples of the adhesive of the adhesive include thermosetting resins or thermoplastic resins, and known adhesives such as polyurethane, acrylic, polyester, polyether, and epoxy adhesives can be used. Examples of the adhesive include METALOCN33 (an epoxy adhesive having conductivity, produced by Toyokagaku Kenkyusho Co., Ltd.). As a coating method of the adhesive, known methods such as roller coating, wiping, and spraying can be used.

[0110] The adhesive layer between the mandrel 1 and the elastic layer 2 may be provided on the entire surface where the mandrel 1 and the elastic layer 2 are in contact with each other, or may be provided only within a range of 5 mm to 20 mm in width from both ends of the surface where the mandrel 1 and the elastic layer 2 are in contact with each other. The thickness of the adhesive layer is preferably 1 μm to 10 μm.

[0111] [Elastic layer]

[0112] The elastic layer 2 provided on the outer peripheral surface of the core shaft 1 may be a solid body or a foamed body, and may be a single layer or may be formed of a plurality of layers.

[0113] It is preferred that the hardness of the elastic layer 2 is 10 degrees or more and 70 degrees or less in terms of Asker C hardness. When the Asker C hardness of the elastic layer 2 is 10 degrees or more, it is possible to easily suppress the oil component from seeping out of the rubber material constituting the elastic layer 2, and it is possible to suppress the contamination of the contact member such as the photosensitive drum. In addition, when the Asker C hardness of the elastic layer 2 is 70 degrees or less, the contact between the elastic roller and the contact member becomes stable, and it is possible to suppress the reduction in the image quality of the output image. Here, the Asker C hardness can be defined by a measurement value measured by an Asker rubber hardness meter (manufactured by Kobunshi Keiki Co., Ltd.) using a test piece prepared separately according to the standard specification Asker C type SRIS (The society of Rubber Industry, Japan standard) 0101.

[0114] [Material for forming elastic layer]

[0115] The elastic layer forming material contains a binder resin and conductive particles.

[0116] The example of binder resin includes the following. Rubber and thermoplastic elastomer, it includes: 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, polyurethane rubber, fluororubber and chlororubber. Among these substrates, from the viewpoint of compression set and hardness, NBR can be suitably used. In addition, among NBR, nitrile content is 30% or more and less than 36% and is called so-called medium high nitrile NBR is preferred. As this type of medium high nitrile, for example, commercially available nitrile such as "N230SV" (trade name, manufactured by JSR Corporation) can be used.

[0117] As the conductive particles, conductive carbon such as Ketjen Black EC, acetylene black, carbon for rubber, carbon for pigment (ink) subjected to oxidation treatment, and pyrolytic carbon can be used. Specific examples of carbon for rubber include the following carbon for rubber. SuperAbrasion Furnace (SAF: super wear resistance), Intermediate Super Abrasion Furnace (ISAF: quasi-super wear resistance), High Abrasion Furnace (HAF: high wear resistance), Fast Extruding Furnace (FEF: good extrudability), General Purpose Furnace (GPF: general purpose), Semi Reinforcing Furnace (SRF: medium reinforcement), Fine Thermal (FT: fine particle thermal decomposition), and Medium Thermal (MT: medium particle thermal decomposition) can also be used. In addition, graphite such as natural graphite and artificial graphite can also be used.

[0118] Examples of usable conductive particles include particles of metal oxides such as TiO2, SnO2, and ZnO; particles of composite oxides such as a solid solution of ZnO and Al2O3; powders of metals such as Cu and Ag; and various known particles. The particles may be used alone, or a blend of two or more thereof may be used.

[0119] [Roughening particles]

[0120] For the elastic layer-forming material, spherical particles having a particle size in the range of, for example, 1 μm to 90 μm may be added. Examples of the spherical particles include at least one spherical particle selected from the following particles:

[0121] 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 aluminum oxide particles. By using such a rubber composition, a charging roller having convex portions derived from spherical particles on the outer surface of the elastic layer can be produced.

[0122] [Other additives]

[0123] In addition, as required, vulcanizing agents, vulcanization accelerators, conductivity imparting agents, charge control agents, plasticizers, and anti-aging agents can be appropriately added. In addition, as required, antistatic agents, ultraviolet absorbers, reinforcing agents, fillers, lubricants, mold release agents, pigments, dyes, and flame retardants can be appropriately added.

[0124] <Method for producing roller for electrophotography>

[0125] [Production Steps of Precursor of Electrophotographic Roller]

[0126] As a method of manufacturing a roller for electrophotography according to one aspect of the present disclosure, there is, for example, a method of coating a mandrel with an elastic layer-forming material using an extruder having a cross head.

[0127] Figure 7 This is a diagram for explaining a process of forming a layer of the elastic layer forming material on the outer peripheral surface of the mandrel by co-extruding the mandrel and the elastic layer forming material using the extrusion molding machine 7 provided with a cross head 74 .

[0128] The extrusion molding machine 7 is provided with a cross head 74 feeding a mandrel 71 and an elastic layer forming material 72 , a feed roller 75 feeding the mandrel 71 into the cross head 74 , and a cylinder 76 feeding the elastic layer forming material 72 into the cross head 74 .

[0129] The elastic layer forming material 72 is fed into the crosshead 74 by the screw 77 in the barrel 76, and at the same time, the mandrel 71 is fed into the crosshead 74; thereby, the mandrel 71 having a layer of the elastic layer forming material formed on the outer peripheral surface is discharged from the crosshead. Hereinafter, the mandrel having a layer of the elastic layer forming material formed on the outer peripheral surface is also referred to as a "coated roller 73".

[0130] The outer diameter of the roller for electrophotography according to one aspect of the present disclosure can be controlled by changing the relative ratio between the feeding speed of the mandrel 71 fed to the crosshead by the feed roller 75 and the feeding speed of the elastic layer forming material from the barrel 76. For example, the thickness of the elastic layer in the length direction of the mandrel can be adjusted by keeping the feeding speed of the elastic layer forming material from the barrel to the crosshead constant and changing the feeding speed of the mandrel 71 to the crosshead. Specifically, by increasing the feeding speed of the mandrel, the thickness of the elastic layer can be relatively thinned, in other words, the diameter can be reduced. Here, in order to more accurately adjust the thickness of the elastic layer in the length direction of the mandrel, that is, the diameter of the roller for electrophotography, it is preferred to use a manufacturing method having the following four steps.

[0131] (first step) performing preforming by maintaining a constant feed speed of the elastic layer forming material to the crosshead and changing a feed speed of the mandrel to the crosshead, thereby obtaining a relationship between the feed speed of the mandrel to the crosshead and the thickness of the layer of the elastic layer forming material formed on the mandrel;

[0132] (Second step) a step of measuring the outer diameter of the coated roller extruded from the crosshead;

[0133] (Third step) a step of determining a feed speed of a mandrel for forming a convex shape based on the measured value of the outer diameter obtained in the second step in view of the information obtained in the first step; and

[0134] (Fourth Step) A step of controlling the rotation speed of the feed roller 75 based on the feed speed of the mandrel determined in the third step.

[0135] The third and fourth steps will be described in detail below.

[0136] When it is determined that the measured value of the thickness of the layer of the elastic layer forming material at a predetermined position in the longitudinal direction of the mandrel is larger than the target convex shape, the rotation speed of the feed roller 75 is increased to increase the feed speed of the mandrel, thereby reducing the outer diameter. On the other hand, when it is determined that the thickness is smaller, the rotation speed of the feed roller 75 is reduced to reduce the feed speed of the mandrel, thereby increasing the outer diameter. This feedback control is performed at intervals of, for example, 0.01 seconds, whereby the outer shape of the elastic layer can be controlled to the target convex shape with high accuracy without grinding.

[0137] For reference, when the roller for electrophotography having a convex shape according to the present disclosure is obtained by the above method, it is preferred to determine a target shape at the time of extrusion molding in consideration of the fact that there is a case where the elastic layer shrinks in a subsequent vulcanization step.

[0138] In addition to the above method, there is a method of using a mold having a cavity shape corresponding to the convex shape according to one aspect of the present disclosure, filling the cavity around the mandrel arranged in the mold with an elastic layer forming material, and curing the material.

[0139] In addition, when a crosshead is used, a roller for electrophotography can also be manufactured by the following operations: while keeping the feed speed of the mandrel to the crosshead and the feed speed of the elastic layer forming material constant, a coated roller having an outer diameter equal to or larger than the outer diameter of the thickest central portion of the target convex shape is produced; and the outer peripheral surface of the rubber layer obtained by curing a layer of the elastic layer forming material is ground using a grindstone or the like.

[0140] [Vulcanization step and cutting step]

[0141] The formed electrophotographic roller precursor is heated and vulcanized by a hot air furnace, a vulcanizing pot, a hot plate, far / near infrared rays, and induction heating, etc. The heating temperature varies depending on the elastic layer-forming material, but is preferably 130 to 250° C., and more preferably 140 to 220° C.; and the heating time is preferably 5 to 240 minutes, and more preferably 10 to 60 minutes.

[0142] The vulcanized rubber composition at both ends of the vulcanized rubber roller is removed in another subsequent step, and the roller for electrophotography is completed. Therefore, both ends of the core metal are exposed in the completed roller for electrophotography.

[0143] [Surface treatment steps]

[0144] The surface layer may be subjected to surface treatment such as ultraviolet irradiation for the purpose of reducing the friction coefficient of the surface or electron beam irradiation for the purpose of increasing ηIT.

[0145] <Processing cartridge>

[0146] Figure 8 An example of a process cartridge for electrophotography provided with a charging roller according to an embodiment of the present disclosure is shown. Figure 8 The process cartridge 100 shown in FIG. 1 is configured to integrate a developing device and a charging device, and is detachably mountable to a main body of an electrophotographic apparatus.

[0147] The developing device is formed by integrating at least a developing roller 103, a toner container 106, and a toner 109. The photosensitive drum 101 is an example of an electrophotographic photosensitive member. The developing device may include a toner supplying roller 104, a developing blade 108, and a stirring blade 110 as necessary.

[0148] The charging device is formed by integrating at least the photosensitive drum 101 and the charging roller 102. The charging roller 102 is arranged at a position where the photosensitive drum 101 can be charged. The charging device may be provided with a cleaning blade 105 and a waste toner container 107. The charging roller 102, the developing roller 103, the toner supplying roller 104, and the developing blade 108 are configured so that voltages are applied thereto, respectively.

[0149] <Electronic Photographic Equipment>

[0150] Fig. 9 A diagram showing one example of an electrophotographic apparatus using a charging roller according to one embodiment of the present disclosure is shown. Fig. 9 The electronic photographic apparatus 200 shown in FIG. 1 is configured to detachably mount four process cartridges 100. Each process cartridge 100 corresponds to each color of black, magenta, yellow, and cyan, and uses a toner corresponding to each color. Each process cartridge 100 has the same configuration except that the color of the toner used is different.

[0151] Each process cartridge 100 has Figure 8The process box 100 has a substantially same structure as that shown in FIG. The process box 100 includes 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 storage container 207, a developing blade 208, a toner 209, and a stirring blade 210.

[0152] The photosensitive drum 201 rotates in the arrow direction (clockwise) and is uniformly charged by a charging roller 202 to which a voltage is applied from a charging bias power source. When the surface of the photosensitive drum 201 is irradiated with exposure light 211, an electrostatic latent image is formed on the surface.

[0153] On the other hand, the toner 209 stored in the toner container 206 is supplied to the toner supply roller 204 by the stirring blade 210. The toner supply roller 204 supplies the toner 209 to the developing roller 203. The surface of the developing roller 203 is uniformly coated with the toner 209 by the developing blade 208 arranged in contact with the developing roller 203, and the toner 209 is given an electric charge by friction charging.

[0154] The electrostatic latent image is developed by being given toner 209 conveyed by a developing roller 203 arranged in contact with the photosensitive drum 201 , and is visualized as a toner image.

[0155] The visualized toner image on the photosensitive drum is transferred onto 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 driving roller 214. The toner images of each color are sequentially superimposed to form a color image on the intermediate transfer belt 215.

[0156] The transfer material 219 is fed to the device through a paper feed roller. The transfer material 219 is conveyed between the intermediate transfer belt 215 and the secondary transfer roller 216. A voltage is applied from a secondary transfer bias power supply to the secondary transfer roller 216, and the color image on the intermediate transfer belt 215 is transferred to the transfer material 219. The transfer material 219 to which the color image is transferred is subjected to a fixing process by a fixing device 218. The transfer material 219 subjected to the fixing process is discharged to the outside of the device.

[0157] On the other hand, the toner remaining on the photosensitive drum 201 without being transferred is scraped off by the cleaning blade 205 and stored in the waste toner storage container 207. In addition, the toner remaining on the intermediate transfer belt 215 without being transferred is also scraped off by the cleaning device 217.

[0158] According to one aspect of the present disclosure, an electrophotographic roller can be obtained that can suppress the adhesion of stains in the end region of the electrophotographic roller even in a high-speed electrophotographic device. In addition, according to another aspect of the present disclosure, a processing box that contributes to the stable formation of high-quality electrophotographic images can be obtained. According to yet another aspect of the present disclosure, an electrophotographic image forming device that can stably form high-quality electrophotographic images can be obtained.

[0159] [Example]

[0160] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to the examples.

[0161] [Example 1] (Preparation of unvulcanized rubber composition for elastic layer)

[0162] A kneaded rubber composition was obtained by mixing the materials shown in the following Table 2. As a mixer, a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used. The mixing conditions were set to a filling rate of 70 vol%, a blade rotation speed of 30 rpm, and a time of 16 minutes.

[0163] [Table 2]

[0164]

[0165] Next, an unvulcanized rubber composition 1 was obtained by mixing the materials shown in Table 3 below. As a mixer, an open roll (product name: 12×30 test roll, manufactured by Kansai Roll Co., Ltd.) with a roll diameter of 12 inches (0.30 m) was used. Regarding the mixing conditions, the number of revolutions of the front roll was set to 10 rpm, the number of revolutions of the rear roll was set to 8 rpm, and the roll gap was set to 2 mm; a total of 20 back and forth movements were made; then the roll gap was set to 0.5 mm, and 10 thin passes were performed.

[0166] [Table 3]

[0167]

[0168] <Production of roller for electrophotography>

[0169] As a mandrel, a stainless steel rod having a diameter of 4.975 mm and a length of 250 mm was prepared. In order to form the unvulcanized rubber composition 1 around the mandrel, a Figure 7 An extrusion forming apparatus with a cross head shown in (manufactured by Mitsuba Mfg. Co., Ltd.) was used. As an extruder of the extrusion forming apparatus, an extruder provided with a vent having an inner diameter of a barrel of 70 mm and a ratio of barrel length to diameter of 20 was used.

[0170] The extrusion molding temperature of each of the barrel, the screw and the crosshead die was set to 100° C. The number of revolutions of the screw was set to 10 revolutions per minute. These conditions were adopted, and the mandrel was coated with the unvulcanized rubber composition 1 .

[0171] For reference, when coating the mandrel, the feed speed of the feed roller is controlled and the wall thickness is adjusted so that after the electrophotographic roller precursor is vulcanized and the end of the elastic layer is removed, the shape of the charging roller becomes a convex shape. In addition, the shape of the electrophotographic roller after the end of the elastic layer is removed is shown. Figure 2 The values ​​of L1, L2, Z1 and Z2 shown in are respectively the values ​​shown in Table 4; and a roller precursor for electrophotography is formed.

[0172] Specifically, the inflow rate of the elastic layer forming material into the crosshead was kept constant at 5.20×10 -4 mm 3 / sec; and on the other hand, when forming a layer of the elastic layer forming material and forming a central portion in the longitudinal direction of the core shaft, the feed speed of the core shaft to the crosshead is set to 4.70 mm / sec, and when forming both end portions, the feed speed of the core shaft to the crosshead is set to 5.80 mm / sec.

[0173] In addition, the thickness (diameter) of the layer of the elastic layer forming material around the mandrel immediately after extrusion from the crosshead is measured using a laser measuring device, and feedback control of the mandrel feed speed is performed based on the relationship between the mandrel feed speed and diameter obtained in advance in preforming.

[0174] The obtained electrophotographic roller precursor was heated in a hot air oven at 160° C. for 1 hour, and then both end portions of the layer of the elastic layer forming material in the electrophotographic roller precursor were removed by 10 mm; and an electrophotographic roller 1 was obtained. The length of the elastic layer in the longitudinal direction of the electrophotographic roller 1 was 230 mm; and L1 was 69 mm and L2 was 46 mm.

[0175] <Surface treatment>

[0176] The surface of the obtained roller for electrophotography was irradiated with ultraviolet rays, and an electrophotographic roller 1' having a UV-treated area on the surface of the elastic layer was obtained. A low-pressure mercury vapor lamp (trade name: GLQ500US / 11, manufactured by Toshiba Lighting & Technology Corporation Co., Ltd.) was used for the irradiation of ultraviolet rays, and the roller for electrophotography was uniformly irradiated while rotating the mandrel 1 as a rotating shaft at a constant speed. The light amount of ultraviolet rays was set to 9000 mJ / cm with a sensor sensitivity of 254 nm. 2 .

[0177] <Measurement of Outer Diameter of Electrophotographic Roller>

[0178] The outer diameter of the electrophotographic roller 1' is determined according to Figure 4A and Figure 4B In this embodiment, the shape of the roller was measured using a non-contact laser measuring instrument (LS-5000; manufactured by Keyence Corporation) by moving the roller at 1 mm pitch in the length direction and 1 degree pitch in the rotation direction.

[0179] The diameter in this disclosure is defined as the average value of the diameter of a circle in each cross section. Figure 2 The diameters at the center positions O, X1, and X2 of the charging roller 1' are defined as Do, DX1, and DX2, respectively, and Z1 and Z2 are defined as Z1 = (Do-DX1) / 2 and Z2 = (DX1-DX2) / 2; and the values ​​are calculated. As a result of the calculation, Do is 7.69 mm, and Z1 and Z2 become as shown in Table 4.

[0180] <Measurement of ηIT>

[0181] The produced roller 1 ′ for electrophotography was subjected to an indentation test according to a method based on ISO 145177 using a nanoindentation apparatus (apparatus name: PICODENTOR, model: HM500, manufactured by Fischer Instruments K.K.), and ηIT was analyzed.

[0182] Regarding the measurement conditions, the approach speed of the indenter was 100 nm / s; regarding the load conditions, the maximum load was 1 mN, and the indentation time was 3 s; and the unloading conditions were the opposite conditions of the load conditions.

[0183] The measurement points were 36 points in total, including the center position in the longitudinal direction of the electrophotographic roller and two positions close to the center 10.0 mm from both ends of the elastic layer, and 12 points at intervals of 30 degrees in the circumferential direction.

[0184] The test was conducted under the above-mentioned conditions to obtain a load-displacement curve of the roller 1 ′ for electrophotography, and ηIT was calculated for each curve. In the present disclosure, the median value of ηIT at 36 points is represented by ηIT.

[0185] As a result, in the present embodiment, ηIT is 45[%] as shown in FIG. 6 .

[0186] <Measurement of amplitude and evaluation of peripheral speed difference>

[0187] The roller 1' for electrophotography is loaded into the process box as a charging roller, and the vibration of the charging roller is measured when the electrophotographic device is running, and the magnitude of the amplitude is evaluated as the magnitude of the peripheral speed difference. As a measuring instrument, a laser Doppler vibrometer (trade name: LV-1710, manufactured by Ono Sokki Co., Ltd.) is used. The measuring position is set at a position close to the center of 5 mm from the end of the elastic portion of the roller for electrophotography, at a position opposite to the position in contact with the photosensitive member (a position on the opposite side of 180 degrees). As an electrophotographic device for amplitude measurement, a Laserjet M608dn (manufactured by HP Inc.) is prepared, and in order to evaluate in high-speed processing, the number of output sheets per unit time is converted to 75 sheets / minute (A4 longitudinal output) greater than the original number of output sheets to be used. The electrophotographic process box used for the above-mentioned printer is used as the electrophotographic process box. The vibration was measured while the printer was running, and the frequency was analyzed; as a result, the amplitude was large at a frequency of 2700 Hz; and the magnitude of the amplitude at a frequency of 2700 Hz was adopted as the magnitude of the vibration of the charging roller 1. The measurement results are shown in Table 6.

[0188] <Image Evaluation and Observation of Smudge on Charging Roller>

[0189] The roller 1' for electrophotography was loaded as a charging roller into an electrophotographic device, and a paper-passing durability test was performed under a low-temperature and low-humidity environment. As an electrophotographic device, a laser printer (trade name: Laserjet M608dn; manufactured by HP Inc.) was prepared. In order to evaluate in high-speed processing, the laser printer was used after the number of output sheets per unit time was modified to 75 sheets / minute (A4 longitudinal output) which was greater than the original number of output sheets. The resolution of the image of the above-mentioned laser printer was 600dpi, and the output of the primary charge was a DC voltage of -1100V. The electrophotographic process box used for the above-mentioned printer was used as the electrophotographic process box. For reference, the electrophotographic process box includes an electrophotographic photosensitive member in the shape of a drum, and a charging roller configured to contact the electrophotographic photosensitive member. In addition, a pressure of 250g was applied to each of the two ends of the core shaft body of the charging roller, thereby pressing the charging roller to the electrophotographic photosensitive member.

[0190] First, for the purpose of acclimation to the measurement environment, the roller 1 ′ for electrophotography, the electrophotographic apparatus, and the process cartridge were left to stand for 48 hours in an environment having a temperature of 15° C. and a relative atmospheric humidity of 10%.

[0191] Subsequently, the roller 1' for electrophotography was incorporated into a process cartridge as a charging roller. An output image was evaluated using the process cartridge.

[0192] Specifically, in a low temperature and low humidity environment (temperature of 15° C., and relative humidity of 10%), an E-character image with a print density of 1% was subjected to endurance (image output) of 1,000 consecutive sheets. After outputting 1,000 sheets of the image, a halftone image (an image in which horizontal lines each having a 1-dot width and a 2-dot interval are drawn in a direction perpendicular to the rotation direction of the electrophotographic photosensitive member) was output. The obtained image was visually observed, and image defects caused by adhesion of stains on the surface of the charging roller were observed.

[0193] After the evaluation image is output, the degree of adhesion of stains of toner and external additives on the surface of the electrophotographic roller 1' is observed with a digital microscope (Model VH-8000, manufactured by Keyence Corporation). As for the observation position, observation is made at two positions 10 mm inside the end of the elastic layer, respectively, and the position where the adhesion state of the stain is poor is determined as the site to be evaluated.

[0194] The observation results of image defects caused by adhesion of stains on the halftone image and the microscopic observation results of the surface of the roller 1 ′ for electrophotography were evaluated according to the criteria shown in Table 5. The results are shown in Table 6.

[0195] [Example 2]

[0196] A roller 1 ′ for electrophotography was obtained in the same manner as in Example 1 except that the values ​​of Z1, Z2 and (Do-DX2) / 2 were controlled as shown in Table 4.

[0197] The obtained roller 1 ′ for electrophotography was evaluated in the same manner as in Example 1. The results are shown in Table 6.

[0198] [Examples 3 to 6]

[0199] A roller 1 ′ for electrophotography was obtained in the same manner as in Example 1 except that the values ​​of Z1, Z2 and (Do-DX2) / 2 were controlled as shown in Table 4.

[0200] In order to measure the amplitude of the obtained electrophotographic roller 1', evaluate the image, and observe the smudge of the charging roller, a Laserjet M608dn (manufactured by HP Inc.) was prepared as an electrophotographic apparatus, and in order to perform evaluation in high-speed processing, the output number per unit time was modified to 100 sheets / minute (A4 longitudinal output) greater than the original output number for use.

[0201] [Example 7]

[0202] The surface of the obtained roller for electrophotography was irradiated with an electron beam, and an electrophotographic roller having an EB-treated area on the surface of the elastic layer was obtained. For the electron beam irradiation, an electron beam irradiation device (trade name: "low-energy electron beam irradiation source EB-ENGINE", manufactured by Hamamatsu Photonics KK) with a maximum acceleration voltage of 70 kV was used. For reference, before the electron beam irradiation, the air in the irradiation chamber was purged with nitrogen, and the oxygen concentration in the irradiation chamber was adjusted. The treatment conditions were as follows: acceleration voltage: 70 kV, current (irradiation current): 1.5 mA, treatment speed (scanning speed): 0.6 m / min, and oxygen concentration: 800 ppm. At this time, the device constant at an acceleration voltage of 70 kV in the electron beam irradiation device was 218, and the radiation dose calculated by formula (1) was 1635 kGy.

[0203] D=(K·I) / V ... Formula (1)

[0204] The roller 1 ″ for electrophotography shown in Table 4 was obtained in the same manner as in Example 1 except for the above. The obtained roller 1 ″ for electrophotography was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6.

[0205] [Example 8]

[0206] An electrophotographic roller 1" having an EB-treated area on the surface of the elastic layer was obtained in the same manner as in Example 1, except that in the conditions of the electron beam irradiation in Example 7, the current was set to 3.0 mA and the electron beam irradiation was performed. Z1, Z2, etc. are shown in Table 4.

[0207] The obtained roller 1'' for electrophotography was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6.

[0208] [Example 9]

[0209] An electrophotographic roller 1" having an EB-treated area on the surface of the elastic layer was obtained in the same manner as in Example 1, except that in the conditions of the electron beam irradiation in Example 7, the current was set to 4.5 mA and the electron beam irradiation was performed. Z1, Z2, etc. are shown in Table 4.

[0210] The obtained roller 1'' for electrophotography was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 6.

[0211] [Example 10]

[0212] A roller for electrophotography was obtained in the same manner as in Example 1 except that the surface of the roller for electrophotography was not treated. Z1, Z2, etc. are shown in Table 4. The evaluation results are shown in Table 6.

[0213] [Example 11]

[0214] Using the crosshead extruder used in Example 1, a coated roller was formed so that the outer diameter of 8.00 mm became a straight shape when extruded from the molding machine. Thereafter, the coated roller was heated in a hot air oven at 160°C for 60 minutes, and a roller precursor for electronic photography was produced. Subsequently, 10 mm was removed from each of the two end portions of the vulcanized rubber layer, and the surface of the vulcanized rubber layer of the roller precursor for electronic photography was ground by a grinder using a cut-in grinding method, and an electronic photography roller 1'' was obtained, whose values ​​of Z1, Z2, and (Do-DX2) / 2 are as shown in Table 4. Other than this, the same steps as those of Example 1 were adopted. The evaluation results are shown in Table 6.

[0215] [Example 12]

[0216] The electrophotographic roller 1' produced in Example 1 was loaded into an electrophotographic apparatus as a developing roller, and a paper-passing durability test was performed. A Laserjet Pro M102w Printer (manufactured by HP Inc.) was used as an electrophotographic apparatus to evaluate fogging. First, the electrophotographic apparatus loaded with the electrophotographic roller 1' was set in an environment with a temperature of 40°C and a relative atmospheric humidity of 95%, and then left to stand for more than 12 hours.

[0217] Next, the reflectance R0 (%) of the unprinted paper was measured.

[0218] Subsequently, a black image having a printing rate of 1% was continuously output on 1000 sheets, and then the reflectance R1 (%) was measured at the end of the image on the 1000th sheet.

[0219] For the measurement, a reflection densitometer (trade name: TC-6DS / A; manufactured by Tokyo Denshoku Co., Ltd.) was used.

[0220] Then, the fogging values ​​calculated using the following expression are shown in Table 6.

[0221] Fogging value = R0 (%) - R1 (%)

[0222] [Example 13]

[0223] The rubber in the material of the unvulcanized rubber composition in Example 1 was changed from NBR (grade N230SV, produced by JSR Corporation) to NBR (grade N230SL, produced by JSR Corporation). Other than this, the same procedures as those of Example 1 were adopted. Z1 and Z2, etc. are shown in Table 4. The evaluation results are shown in Table 6.

[0224] [Example 14]

[0225] The rubber in the material of the unvulcanized rubber composition in Example 1 was changed from NBR (grade N230SV, produced by JSR Corporation) to NBR (grade N230S, produced by JSR Corporation). Other than this, the same procedures as those of Example 1 were adopted. Z1 and Z2, etc. are shown in Table 4. The evaluation results are shown in Table 6.

[0226] [Comparative Examples 1 and 2]

[0227] 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 controlled 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.

[0228] [Comparative Example 3]

[0229] 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 controlled 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.

[0230] [Table 4]

[0231]

[0232] [Table 5]

[0233]

[0234] [Table 6]

[0235]

[0236] While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An electrophotographic roller comprising a core shaft and an elastic layer on the core shaft; wherein the electrophotographic roller has a convex shape with a diameter decreasing from a center position O in the longitudinal direction of the core shaft toward both ends thereof, characterized in that: When the position of the end of the elastic layer in the length direction is defined as X2, The position between the center position O and the X2 is defined as X1, The distance between the center position O and the X1 is defined as L1, and The distance between the X1 and the X2 is defined as L2, L1 = 0.6 × (L1 + L2), and When the outer diameters of the roller for electrophotography at O, X1, and X2 are defined as Do, DX1, and DX2, respectively, and Z1 and Z2 are defined as follows: Z1=(Do-DX1) / 2, and Z2=(DX1-DX2) / 2, Z1, Z2, L1 and L2 satisfy the relationship expressed by the following calculation formula (1): (Z2 / L2)<α×(Z1 / L1) (1), where α is 1.931, The roller for electrophotography is a charging roller or a developing roller. 2 . The roller for electrophotography according to claim 1 , wherein the roller for electrophotography satisfies 1.000<[(Z2 / L2) / (Z1 / L1)]<1.

931. 3 . The roller for electrophotography according to claim 1 , wherein (Do-DX2) / 2 is 0.01 mm or more and 0.26 mm or less. 4 . The roller for electrophotography according to claim 1 , wherein the elastic layer has an elastic deformation power of 56% or more. 5 . The roller for electrophotography according to claim 1 , wherein the elastic layer comprises acrylonitrile butadiene rubber. 6 . The roller for electrophotography according to claim 1 , wherein the elastic layer has an Asker C hardness of 10 degrees or more and 70 degrees or less. 7 . The roller for electrophotography according to claim 1 , wherein the length of the elastic layer in the longitudinal direction is 220 mm or more and 340 mm or less.

8. A process cartridge detachably mounted to a main body of an electrophotographic image forming apparatus, the process cartridge comprising: Electrophotographic photosensitive member; and an electrophotographic roller in contact with the electrophotographic photosensitive member, characterized in that The electrophotographic roller is the electrophotographic roller according to any one of claims 1 to 7. 9 . The process cartridge according to claim 8 , wherein the roller for electrophotography is a charging roller for charging the electrophotographic photosensitive member.

10. An electrophotographic image forming apparatus comprising: An electrophotographic photosensitive member; and an electrophotographic roller in contact with the electrophotographic photosensitive member, characterized in that The electrophotographic roller is the electrophotographic roller according to any one of claims 1 to 7.

11. The electrophotographic image forming apparatus according to claim 10, wherein the roller for electrophotography is a charging roller for charging the electrophotographic photosensitive member.

12. The electrophotographic image forming apparatus according to claim 11, wherein the electrophotographic photosensitive member is driven, and the charging roller is rotated following the rotation of the electrophotographic photosensitive member.

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