Electrostatic roller for electrophotographic equipment

Abstract

To provide a charging roll for an electro-photographic apparatus excellent in uniformity of discharge characteristics.SOLUTION: A charging roll 10 includes, formed regularly in an axial direction x, one or more groove parts 22 extending in a direction within ±5° to a circumferential direction y on an outer peripheral surface of an elastic body layer 14, in which a groove width w is 4 to 30 μm, inclusive, and a groove depth d is 2 to 12 μm, inclusive. An area ratio a / b is 0.3 to 2.4, inclusive, with regard to an area a of a bottom face 221 and an area b of a plane part 24 of the groove part 22 in the outer peripheral surface of the elastic body layer 14. In the charging roll, a surface layer 16 includes binder polymer 16a and roughness formation particles 18. The roughness formation particles 18 are arranged on the plane part 24 and the groove part 22, respectively.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic roller suitable for use in electrophotographic equipment such as photocopiers, printers, and facsimile machines that employ an electrophotographic method. [Background technology]

[0002] As a charging roll for electrophotographic equipment, a known type has an elastic layer with rubber elasticity on the outer surface of a shaft such as a core metal, and a surface layer on the outer surface of the elastic layer. In addition, in charging rolls, roughness-forming particles are sometimes added to the binder polymer of the surface layer, for example, based on the charge characteristics. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International release 2018 / 025870 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, since roughness-forming particles added to the surface tend to aggregate, surface roughness uniformity tends to decrease in roughness-forming methods that involve adding roughness-forming particles. In particular, when attempting to create surface irregularities using two or more types of roughness-forming particles with different particle sizes, the particles of different particle sizes tend to aggregate separately, resulting in a particularly significant decrease in surface roughness uniformity. A decrease in surface roughness uniformity may lead to a decrease in the uniformity of the discharge characteristics of the electrostatic roll.

[0005] The problem that this invention aims to solve is to provide a charging roll for electrophotographic equipment that exhibits excellent uniformity of discharge characteristics. [Means for solving the problem]

[0006] The electrophotographic roller according to the present invention comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer. The outer circumferential surface of the elastic layer has one or more grooves regularly formed in the axial direction, extending in a direction within ±5° of the circumferential direction. The groove width of each groove is 4 μm or more and 30 μm or less. The groove depth of each groove is 2 μm or more and 12 μm or less. The area ratio a / b of the outer circumferential surface of the elastic layer, which is the area a of the bottom surface of each groove and the area b of the flat portion other than the grooves, is 0.3 or more and 2.4 or less. The surface layer contains a binder polymer and roughness-forming particles, and the roughness-forming particles are arranged on the flat portion and the groove portion of the elastic layer, respectively.

[0007] The surface roughness Rz of the surface layer in the region above the grooves is preferably 2 μm or more and 16 μm or less, and the surface roughness Rz of the entire surface layer is preferably 5 μm or more and 26 μm or less. The average particle diameter of the roughness-forming particles is preferably 3 μm or more and 30 μm or less. The material of the roughness-forming particles is preferably one of polyurethane, polyamide, or acrylic resin. The thickness of the binder polymer covering the roughness-forming particles on the grooves is preferably greater than the thickness of the binder polymer covering the roughness-forming particles on the flat portion. The difference between the thickness of the binder polymer covering the roughness-forming particles on the flat portion and the thickness of the binder polymer covering the roughness-forming particles on the grooves is preferably 4 μm or more and 16 μm or less. The elastic layer may contain one or more of isoprene rubber, nitrile rubber, or hydrin rubber. The binder polymer of the surface layer is preferably one of polyurethane or polyamide. The roughness-forming particles may be composed of one type of particle. The outer surface of the elastic layer may have a mesh-like groove formed where grooves extending in a direction of +5° or less with respect to the circumferential direction intersect with grooves extending in a direction of -5° or less with respect to the circumferential direction.

[0008] (1) The electrophotographic roller according to the present invention comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer, wherein one or more grooves extending along a direction within ±5° of the circumferential direction are regularly formed in the axial direction on the outer circumferential surface of the elastic layer, the groove width of the grooves is 4 μm or more and 30 μm or less, the groove depth of the grooves is 2 μm or more and 12 μm or less, the area ratio a / b of the area a of the bottom surface of the grooves to the area b of the flat portion other than the grooves on the outer circumferential surface of the elastic layer is 0.3 or more and 2.4 or less, and the surface layer contains a binder polymer and roughness-forming particles, the roughness-forming particles are arranged on the flat portion and the grooves of the elastic layer, respectively.

[0009] (2) In (1) above, the surface roughness Rz of the surface layer in the region on the groove is preferably 2 μm or more and 16 μm or less, and the surface roughness Rz of the entire surface layer is preferably 5 μm or more and 26 μm or less.

[0010] (3) In (1) or (2) above, the average particle size of the roughness-forming particles is preferably 3 μm or more and 30 μm or less.

[0011] (4) In any of (1) to (3) above, the material of the roughness-forming particles may be one of polyurethane, polyamide, or acrylic resin.

[0012] (5) In any of (1) to (4) above, it is preferable that the thickness of the binder polymer covering the roughness-forming particles on the groove portion is greater than the thickness of the binder polymer covering the roughness-forming particles on the flat portion.

[0013] (6) In any of (1) to (5) above, the difference between the thickness of the binder polymer covering the roughness-forming particles on the flat portion and the thickness of the binder polymer covering the roughness-forming particles on the groove portion is preferably 4 μm or more and 16 μm or less.

[0014] (7) In any of the above (1) to (6), the elastic layer may contain one or more of isoprene rubber, nitrile rubber, and hydrin rubber.

[0015] (8) In any of the above (1) to (7), the binder polymer of the surface layer may be one of polyurethane or polyamide.

[0016] (9) In any of the above (1) to (8), the roughness-forming particles may consist of only one type of particle.

[0017] (10) In any of (1) to (9) above, it is preferable that a mesh-like groove is formed on the outer surface of the elastic layer, in which grooves extending in a direction of +5° or less with respect to the circumferential direction intersect with grooves extending in a direction of -5° or less with respect to the circumferential direction. [Effects of the Invention]

[0018] The electrostatic roll for electrophotographic equipment according to the present invention comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer. The outer circumferential surface of the elastic layer has one or more grooves regularly formed in the axial direction, extending in a direction within ±5° of the circumferential direction. The groove width of each groove is 4 μm to 30 μm, and the groove depth is 2 μm to 12 μm. The area ratio a / b of the outer circumferential surface of the elastic layer, which is the area a of the bottom surface of each groove and the area b of the flat portion other than the grooves, is 0.3 to 2.4. The surface layer contains a binder polymer and roughness-forming particles, and the roughness-forming particles are arranged on the flat portion and the groove portion of the elastic layer, respectively, resulting in excellent uniformity of discharge characteristics.

[0019] If the surface roughness Rz of the surface layer in the region above the groove is 2 μm or more and 16 μm or less, and the surface roughness Rz of the entire surface layer is 5 μm or more and 26 μm or less, then an appropriate discharge space and discharge initiation point can be formed between the photoreceptor and the charging roll.

[0020] When the average particle diameter of the particles for forming the roughness is 3 μm or more and 30 μm or less, appropriate irregularities are likely to be formed. Thereby, the uniformity of the discharge characteristics can be improved.

[0021] When the material of the particles for forming the roughness is any one of polyurethane, polyamide, and acrylic resin, the particles for forming the roughness are composed of a material with a high dielectric constant, so the charging property of the roll surface is improved.

[0022] When the thickness of the binder polymer covering the particles for forming the roughness on the flat portion is smaller than the thickness of the binder polymer covering the particles for forming the roughness on the groove portion, the discharge amount on the particles for forming the roughness on the groove portion and the discharge amount on the particles for forming the roughness on the flat portion can be adjusted to be the same, and the uniformity of the discharge characteristics can be improved.

[0023] When the difference between the thickness of the binder polymer covering the particles for forming the roughness on the flat portion and the thickness of the binder polymer covering the particles for forming the roughness on the groove portion is 4 μm or more, the amount of charge on the surface of the binder polymer covering the particles for forming the roughness on the flat portion becomes relatively large, and the environmental range in which no black dot image is generated is widened. Further, when the difference in the above thickness is 16 μm or less, since it is maintained at an appropriate thickness, appropriate irregularities are likely to be formed. Thereby, the uniformity of the discharge characteristics can be improved.

[0024] When the elastic layer contains any one or more of isoprene rubber, nitrile rubber, and hydrin rubber, the compression set is small, and the generation of streak images corresponding to the deformed portions at the time of setting the charged roll is suppressed.

[0025] When the binder polymer of the surface layer is any one of polyurethane and polyamide, the binder polymer is composed of a material with a high dielectric constant, so the charging property of the roll surface is improved. Further, the compression set is small, and the generation of streak images corresponding to the deformed portions at the time of setting the charged roll is suppressed.

[0026] If the roughness-forming particles consist of only one type of particle, the uneven shape of the elastic layer is easily reflected in the surface irregularities of the charging roll, making it easier to control the surface irregularities of the charging roll. Furthermore, because the aggregation of the roughness-forming particles is easily controlled, the uniformity of the surface roughness can be improved. In addition, because the thickness of the binder polymer covering the roughness-forming particles can be easily adjusted, the uniformity of the discharge characteristics can be improved.

[0027] If a mesh-like groove pattern is formed on the outer surface of the elastic layer, where grooves extending in a direction of +5° or less relative to the circumferential direction intersect with grooves extending in a direction of -5° or less relative to the circumferential direction, the uniformity of the surface roughness is improved. This makes it possible to improve the uniformity of the discharge characteristics. [Brief explanation of the drawing]

[0028] [Figure 1] This is a schematic external view (a) of a charging roll for electrophotographic equipment according to one embodiment of the present invention, and a cross-sectional view of the same along line AA (b). [Figure 2] This is a schematic diagram of the external appearance of an elastic layer, showing the shape of the grooves formed on the outer surface of the elastic layer. [Figure 3] This is a schematic diagram of the external appearance of an elastic layer, showing a modified example of the shape of the groove formed on the outer surface of the elastic layer. [Figure 4] This is a magnified cross-sectional view of the surface. [Figure 5] This is a schematic diagram of the external appearance of an elastic layer, showing a modified example of the shape of the groove formed on the outer surface of the elastic layer. [Modes for carrying out the invention]

[0029] A charging roll for electrophotographic equipment (hereinafter sometimes simply referred to as a charging roll) according to the present invention will be described in detail. Figure 1 is a schematic external view (a) and a cross-sectional view (b) of the charging roll for electrophotographic equipment according to one embodiment of the present invention. Figure 2 is a schematic external view of an elastic layer showing the shape of grooves formed on the outer surface of the elastic layer. Figure 3 is a schematic external view of an elastic layer showing a modified example of the shape of grooves formed on the outer surface of the elastic layer. Figure 4 is an enlarged cross-sectional view of the surface layer.

[0030] The electrostatic roll 10 comprises a shaft 12, an elastic layer 14 formed on the outer circumferential surface of the shaft 12, and a surface layer 16 formed on the outer circumferential surface of the elastic layer 14. The elastic layer 14 is the base layer of the electrostatic roll 10. The surface layer 16 is the layer that appears on the surface of the electrostatic roll 10. Although not specifically shown in the figures, an intermediate layer such as a resistance adjustment layer may be formed between the elastic layer 14 and the surface layer 16 as needed.

[0031] The shaft 12 is not particularly limited as long as it is conductive. Specifically, examples include a solid or hollow core made of metal such as iron, stainless steel, or aluminum. The surface of the shaft 12 may be coated with an adhesive or primer as needed. In other words, the elastic layer 14 may be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive or primer may be made conductive as needed.

[0032] In Figures 2 and 3, x (direction) is the axial direction of the charging roll 10, and y (direction) is the circumferential direction of the charging roll 10. As shown in Figures 2 and 3, one or more grooves 22 extending along a direction within ±5° of the circumferential direction y are regularly formed in the axial direction x on the outer circumferential surface of the elastic layer 14. More specifically, in Figure 2, two or more grooves 22 extending along a direction 0° of the circumferential direction y (extending along the circumferential direction) are regularly formed in the axial direction x on the outer circumferential surface of the elastic layer 14. In Figure 2, one groove 22 is connected in a circular fashion and is not helical. In Figure 3, one or more grooves 22 extending along a direction other than 0° of the circumferential direction y (direction θ) are regularly formed in the axial direction x on the outer circumferential surface of the elastic layer 14. In Figure 3, the connected grooves 22 are not helical and there are two or more of them. In Figure 3, the spiral groove 22 is considered a single unit because it is connected throughout. Regularity means that the grooves 22 are formed at regular intervals in the axial direction x. On the outer surface of the elastic layer 14, the parts other than the grooves 22 are flat surfaces 24. As shown in Figure 4, the flat surfaces 24 protrude radially outward from the bottom surfaces 221 of the grooves 22. The elastic layer 14 has surface irregularities formed on its outer surface by the bottom surfaces 221 of the grooves 22 which are positioned radially inward and the flat surfaces 24 which are positioned radially outward. Furthermore, since one or more grooves 22 extending along directions within ±5° of the circumferential direction y are regularly formed in the axial direction x, the outer surface of the elastic layer 14 has uniform surface irregularities. The directions within ±5° of the circumferential direction y refer to directions in the range of -5° to 0° and 0° to +5° with respect to the circumferential direction y.

[0033] The reason the direction in which the groove 22 extends is within ±5° of the circumferential direction y, and is close to the circumferential direction, is that if the angle of the direction in which the groove 22 extends with respect to the circumferential direction y becomes large (an angle exceeding 5° in absolute value), the edges of the protrusions formed by the groove 22 become more susceptible to shear stress in the rotational direction (circumferential direction y) of the charging roll 10 when the photoreceptor and the charging roll 10 rub against each other, causing the protrusions to wear down easily. When the protrusions wear down, the difference in charge between the bumps and depressions becomes larger during durability, making it easier for streaks to occur. As the lifespan of electrophotographic equipment is extended and longer durability is required for the charging roll 10, the impact of the above-mentioned wear becomes significant.

[0034] If the direction in which the grooves 22 extend is within ±5° of the circumferential direction y, and is close to the circumferential direction y, then with respect to rotation in the circumferential direction, the surface of the photoreceptor will be divided into areas where the protrusions formed by the grooves 22 constantly make contact, and areas where the grooves 22 (roughness-forming particles on the grooves 22) constantly make contact. Because there is a difference in charge between the protrusions and the grooves 22, images with grooves 22 extending close to the circumferential direction y are more prone to image defects (vertical streaks) due to the difference in charge than images with grooves 22 extending at a larger angle to the circumferential direction y. For this reason, the width w of the grooves 22 is narrowed to a specific range to reduce this effect.

[0035] The groove width w of the groove 22 is 4 μm or more and 30 μm or less. The groove depth d of the groove 22 is 2 μm or more and 12 μm or less. Furthermore, the area ratio a / b of the area a of the bottom surface 221 of the groove 22 to the area b of the flat surface 24 of the outer surface of the elastic layer 14 is 0.3 or more and 2.4 or less.

[0036] If the groove width w of the groove portion 22 is less than 4 μm, the groove width w is too small, and the roughness-forming particles 18 cannot enter the groove portion 22. As a result, the difference between the surface roughness Rz caused by the roughness-forming particles 18b on the flat portion 24 and the surface roughness Rz caused by the roughness-forming particles 18a on the groove portion 22 becomes small, and horizontal streaks occur due to insufficient charging. If roughness-forming particles 18 that are small enough to fit into a small groove width w are used, it becomes impossible to form roughness that ensures sufficient discharge. Also from this viewpoint, the groove width w of the groove portion 22 should be set to 5 μm or more, 10 μm or more, 20 μm or more, etc., in accordance with the average particle size of the roughness-forming particles 18 used.

[0037] If the groove width w of the groove portion 22 exceeds 30 μm, image defects (vertical streaks) are likely to occur, as described above. Also, if the groove width w of the groove portion 22 exceeds 30 μm, the groove width w is too large, making it impossible to uniformly distribute the roughness-forming particles 18 in the groove portion 22. If roughness-forming particles 18 of a size that matches the large groove width w are used, the protrusions caused by the roughness-forming particles 18 become too large, resulting in excessively high surface roughness, making it impossible to achieve the appropriate surface roughness. As a result, uniform discharge characteristics cannot be obtained. Furthermore, if the groove width w is too large, the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22 is more likely to come into contact with the photoreceptor. This causes wear not only on the binder polymer 16a covering the roughness-forming particles 18b on the flat portion 24 and the roughness-forming particles 18b beneath it, but also on the binder polymer 16a covering the roughness-forming particles 18a on the groove portion 22 and the roughness-forming particles 18a beneath it. As a result, during durability testing, the entire surface of the surface layer 16 is worn down, causing unevenness in the image. From this perspective, the groove width w of the groove portion 22 should be set to 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, etc., depending on the average particle size of the roughness-forming particles 18 used.

[0038] If the groove depth d of the groove portion 22 is less than 2 μm, the groove depth d is too small, and the difference between the surface roughness Rz caused by the roughness-forming particles 18b on the flat portion 24 and the surface roughness Rz caused by the roughness-forming particles 18a on the groove portion 22 becomes too small, resulting in lateral streaks due to insufficient charging. If small roughness-forming particles 18 are used to match a small groove depth d, it becomes impossible to form roughness that ensures sufficient discharge. From this viewpoint, the groove depth d of the groove portion 22 should be set to 3 μm or more, 5 μm or more, 10 μm or more, etc., depending on the average particle size of the roughness-forming particles 18 used.

[0039] If the groove depth d of the groove portion 22 exceeds 12 μm, the groove depth d is too large, and surface roughness cannot be formed on the groove portion 22 by the roughness-forming particles 18 placed in the groove portion 22. As a result, black spots (fogging) occur in the image after durability testing. Also, if the groove depth d of the groove portion 22 exceeds 12 μm, the groove depth d is too large, and the difference between the surface roughness Rz caused by the roughness-forming particles 18b on the flat portion 24 and the surface roughness Rz caused by the roughness-forming particles 18a on the groove portion 22 becomes too large, resulting in a large difference in chargeability, which makes image defects (vertical streaks) more likely to occur. If large roughness-forming particles 18 are used to match a large groove depth d, the difference between the surface roughness Rz caused by the roughness-forming particles 18b on the flat portion 24 and the surface roughness Rz caused by the roughness-forming particles 18a on the groove portion 22 becomes too large, making discharge difficult. Furthermore, from this perspective, the groove depth d of the groove portion 22 should be set to 10 μm or less, 8 μm or less, etc., in accordance with the average particle size of the roughness-forming particles 18 used.

[0040] If the area ratio a / b of the area a of the bottom surface 221 of the groove 22 to the area b of the flat surface 24 is less than 0.3 or greater than 2.4, the balance between the area a of the bottom surface 221 and the area b of the flat surface 24 becomes poor, and the uniformity of the surface irregularities decreases. As a result, uneven images are likely to occur after durability testing. Also, if the balance between the area a of the bottom surface 221 and the area b of the flat surface 24 becomes poor, the adhesion between the elastic layer 14 and the surface layer 16 decreases. From this viewpoint, it is preferable to set the area ratio a / b to 0.5 or more, 0.7 or more, or 2.0 or less, 1.8 or less, or 1.5 or less.

[0041] The angle of the groove 22 is calculated from the average angle of 100 points in the groove with respect to the circumferential direction y, obtained by photographing the outer surface of the elastic layer 14 with a laser microscope. The groove width w of the groove 22 is calculated from the average groove width w of 100 points in the groove 22, obtained by photographing the outer surface of the elastic layer 14 with a laser microscope. The groove depth d of the groove 22 is calculated from the average groove depth d of 100 points in the groove 22, obtained by photographing the radial cross-section of the elastic layer 14 with a laser microscope. The area ratio a / b between the area a of the bottom surface 221 of the groove 22 and the area b of the flat surface 24 is calculated by taking images of five arbitrary locations on the outer surface of the elastic layer 14 with a laser microscope, calculating the area a of the bottom surface 221 of the groove 22 and the area b of the flat surface 24 observed within a predetermined range (0.1 mm × 0.1 mm) of the captured image, and then averaging the ratio of these two areas.

[0042] The elastic layer 14 contains crosslinked rubber. The elastic layer 14 is formed from a conductive rubber composition containing uncrosslinked rubber. The crosslinked rubber is obtained by crosslinking the uncrosslinked rubber. The uncrosslinked rubber may be polar rubber or non-polar rubber.

[0043] Polar rubber is rubber having polar groups, and examples of polar groups include chloro groups, nitrile groups, carboxyl groups, and epoxy groups. Specifically, examples of polar rubber include hydrin rubber, nitrile rubber (NBR), urethane rubber (U), acrylic rubber (a copolymer of acrylic acid ester and 2-chloroethyl vinyl ether, ACM), chloroprene rubber (CR), and epoxidized natural rubber (ENR). Among polar rubbers, hydrin rubber and nitrile rubber (NBR) are more preferred from the viewpoint that they tend to have particularly low volume resistivity.

[0044] Examples of hydrin rubber include epichlorohydrin homopolymer (CO), epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO).

[0045] Examples of urethane rubber include polyether-type urethane rubber having ether bonds in its molecule. Polyether-type urethane rubber can be produced by the reaction of a polyether having hydroxyl groups at both ends with a diisocyanate. Examples of polyethers are not particularly limited, but include polyethylene glycol and polypropylene glycol. Examples of diisocyanates are not particularly limited, but include tolylene diisocyanate and diphenylmethane diisocyanate.

[0046] Examples of non-polar rubbers include silicone rubber (Q), isoprene rubber (IR), natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). Among non-polar rubbers, silicone rubber is more preferable from the viewpoint of low hardness and resistance to deformation (excellent elastic recovery).

[0047] The elastic layer 14 may contain one or more of isoprene rubber, nitrile rubber, or hydrin rubber. When the elastic layer 14 contains one or more of isoprene rubber, nitrile rubber, or hydrin rubber, the compression set is small, and the occurrence of streaks corresponding to the deformed parts when the charged roll 10 is set is suppressed.

[0048] Examples of crosslinking agents include sulfur crosslinking agents, peroxide crosslinking agents, and dechlorination crosslinking agents. These crosslinking agents may be used individually or in combination of two or more types.

[0049] Examples of conventionally known sulfur crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, sulfur chloride, thiram-based vulcanization accelerators, and polymeric polysulfides.

[0050] Examples of conventionally known peroxide crosslinking agents include peroxyketals, dialkyl peroxides, peroxyesters, ketone peroxides, peroxydicarbonates, diacyl peroxides, and hydroperoxides.

[0051] Examples of dechlorinating crosslinking agents include dithiocarbonate compounds. More specifically, these include quinoxaline-2,3-dithiocarbonate, 6-methylquinoxaline-2,3-dithiocarbonate, 6-isopropylquinoxaline-2,3-dithiocarbonate, and 5,8-dimethylquinoxaline-2,3-dithiocarbonate.

[0052] The amount of crosslinking agent added is preferably in the range of 0.1 to 2 parts by mass, more preferably in the range of 0.3 to 1.8 parts by mass, and even more preferably in the range of 0.5 to 1.5 parts by mass, per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding.

[0053] When using a dechlorinating crosslinking agent as a crosslinking agent, a dechlorinating crosslinking accelerator may be used in combination. Examples of dechlorinating crosslinking accelerators include 1,8-diazabicyclo(5,4,0)undecene-7 (hereinafter abbreviated as DBU) or its weak salt. The dechlorinating crosslinking accelerator may be used in the form of DBU, but it is preferable to use it in the form of its weak salt for ease of handling. Examples of weak salts of DBU include carbonate, stearate, 2-ethylhexylate, benzoate, salicylate, 3-hydroxy-2-naphthoate, phenol resin salt, 2-mercaptobenzothiazole salt, and 2-mercaptobenzimidazole salt.

[0054] The content of the dechlorination crosslinking accelerator is preferably in the range of 0.1 to 2 parts by mass per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding. More preferably, it is in the range of 0.3 to 1.8 parts by mass, and even more preferably, in the range of 0.5 to 1.5 parts by mass.

[0055] The elastic layer 14 may contain conductive agents to impart conductivity. Examples of conductive agents include electronic conductive agents and ionic conductive agents. Examples of electronic conductive agents include carbon black, graphite, and conductive metal oxides. Examples of conductive metal oxides include conductive titanium oxide, conductive zinc oxide, and conductive tin oxide. Examples of ionic conductive agents include quaternary ammonium salts, borates, and surfactants. In addition, various additives may be added to the elastic layer 14 as needed. Examples of additives include lubricants, vulcanization accelerators, antioxidants, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, defoamers, pigments, and mold release agents.

[0056] The elastic layer 14 can be adjusted to a predetermined volume resistivity by changing the type of crosslinked rubber, the amount of ionic conductive agent, the amount of electronic conductive agent, etc. The volume resistivity of the elastic layer 14 is 10 depending on the application, etc. 2 ~10 10 Ω·cm, 10 3 ~10 9 Ω·cm, 10 4 ~10 8 You can set it appropriately within the range of Ω·cm, etc.

[0057] The thickness of the elastic layer 14 is not particularly limited and can be set appropriately within the range of 0.1 to 10 mm depending on the application.

[0058] The surface layer 16 includes a binder polymer 16a and roughness-forming particles 18.

[0059] The binder polymer 16a is the base polymer that constitutes the surface layer 16. Examples of binder polymers 16a include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, butyral resin (PVB), alkyd resin, polyester resin, fluororubber, fluororesin, mixtures of fluororubber and fluororesin, silicone resin, silicone grafted acrylic polymer, acrylic grafted silicone polymer, nitrile rubber, and urethane rubber.

[0060] The binder polymer 16a is preferably one of polyurethane or polyamide. When the binder polymer 16a of the surface layer 16 is one of polyurethane or polyamide, the binder polymer 16a is composed of a material with a high dielectric constant, which improves the electrostatic properties of the roll surface. In addition, the compression set is small, and the occurrence of streaks corresponding to the deformed area when the charged roll 10 is set is suppressed. Polyurethane includes urethane resin, urethane rubber, and urethane elastomer. Polyamide may be a modified type. Examples of modified polyamides include alkoxy polyamides such as N-methoxymethylated nylon.

[0061] The roughness-forming particles 18 are particles that impart roughness to the surface of the surface layer 16. In other words, they are particles that impart irregularities to the surface of the surface layer 16. As shown in Figure 4, the roughness-forming particles 18 are arranged on the flat portion 24 and the groove portion 22 of the elastic layer 14, respectively. Due to the step difference between the flat portion 24 and the bottom surface 221 of the groove portion 22 of the elastic layer 14, the roughness-forming particles 18b on the flat portion 24 (roughness-forming particles 18b placed on the flat portion 24) and the roughness-forming particles 18a on the groove portion 22 (roughness-forming particles 18a placed on the groove portion 22) have different degrees of radial outward protrusion, even if they have the same particle diameter. Due to the step difference between the flat portion 24 and the bottom surface 221 of the groove portion 22 of the elastic layer 14, the roughness-forming particles 18b on the flat portion 24 protrude radially outward more than the roughness-forming particles 18a on the groove portion 22.

[0062] The protrusions caused by the roughness-forming particles 18b on the flat portion 24, which protrude more radially outward, become the parts that contact the photoreceptor, while the protrusions caused by the roughness-forming particles 18a on the groove portion 22, which are further radially inward, do not contact the photoreceptor. The protrusions caused by the roughness-forming particles 18a on the groove portion 22 become the starting points for discharge. The surface layer 16, by including the roughness-forming particles 18b on the flat portion 24, ensures an appropriate discharge space between the photoreceptor and the charging roll 10. In addition, the surface layer 16, by including the roughness-forming particles 18a on the groove portion 22, ensures the starting points for discharge. In this way, the surface irregularities of the surface layer 16 increase the discharge space between the photoreceptor and the charging roll 10, promoting discharge. This improves electrostatic properties and suppresses image defects such as horizontal streaks and unevenness. In the charging roll 10 according to the present invention, a step is present between the flat portion 24 of the elastic layer 14 and the bottom surface 221 of the groove portion 22. This makes it possible to easily form an appropriate discharge space and discharge initiation point between the photoreceptor and the charging roll 10, even if the roughness-forming particles 18 contained in the surface layer 16 have the same particle size.

[0063] The surface roughness Rz of the surface layer 16 in the region M on the groove 22 is preferably 2 μm or more and 16 μm or less. Furthermore, the surface roughness Rz of the entire surface layer 16 is preferably 5 μm or more and 26 μm or less. This allows for the formation of an appropriate discharge space and discharge initiation point between the photoreceptor and the charging roll 10.

[0064] If the surface roughness Rz of the surface layer 16 in the region M on the groove 22 is less than 2 μm, this surface roughness Rz is too small, resulting in insufficient discharge initiation points and insufficient discharge, which may result in black spots (fogging) not being suppressed in the image after durability testing. From this viewpoint, the surface roughness Rz is more preferably 3 μm or more, and even more preferably 5 μm or more. On the other hand, if the surface roughness Rz of the surface layer 16 in the region M on the groove 22 is greater than 16 μm, the overall surface roughness Rz of the surface layer 16 becomes too large, making discharge difficult, which may result in black spots (fogging) not being suppressed in the image after durability testing. From this viewpoint, the surface roughness Rz is more preferably 15 μm or less, and even more preferably 12 μm or less.

[0065] If the overall surface roughness Rz of the surface layer 16 is less than 5 μm, this surface roughness Rz is too small, resulting in insufficient discharge initiation points and insufficient discharge, which may result in black spots (fogging) not being suppressed in the image after durability testing. From this viewpoint, the surface roughness Rz is more preferably 7 μm or more, and even more preferably 10 μm or more. On the other hand, if the overall surface roughness Rz of the surface layer 16 exceeds 26 μm, this surface roughness Rz is too large, making discharge difficult, which may result in black spots (fogging) not being suppressed in the image after durability testing. From this viewpoint, the surface roughness Rz is more preferably 25 μm or less, and even more preferably 20 μm or less.

[0066] The surface roughness Rz is a 10-point average roughness, which is the average value of values ​​measured at any 5 locations in accordance with JIS B0601 (1994). The surface roughness Rz of the entire surface layer 16 can be measured by observation using a laser microscope (e.g., Keyence "VK-9510"). In the image taken at 400x magnification, the value calculated in the surface roughness mode of the analysis program (program name: KEYENCE VK Analyzer analysis application) can be used as the surface roughness Rz of the entire surface layer 16. The surface roughness Rz of the surface layer 16 in the region above the groove 22 can be measured by observation using a laser microscope (e.g., Keyence "VK-9510"). In the image taken, the value calculated in the surface roughness mode of the analysis program (program name: KEYENCE VK Analyzer analysis application) for the groove 0.01 mm 2 The value calculated by selecting this option can be used as the surface roughness Rz of the surface layer 16 in the region above the groove 22.

[0067] The surface roughness Rz of the surface layer 16 can be adjusted by adjusting the groove width w, groove depth d of the groove portion 22, the area ratio a / b of the bottom surface 221 of the groove portion 22 to the flat portion 24, the particle size of the roughness-forming particles 18, the thickness of the binder polymer 16a, and so on.

[0068] As the roughness-forming particles 18, any particles used as roughness-forming particles 18 added to the surface layer 16 of the electrostatic roll can be used, such as resin particles or inorganic particles. The material of the roughness-forming particles 18 is not particularly limited. Preferably, the material of the roughness-forming particles 18 is one of polyurethane, polyamide, or acrylic resin. If the material of the roughness-forming particles 18 is one of polyurethane, polyamide, or acrylic resin, the roughness-forming particles 18 are composed of a material with a high dielectric constant, which improves the electrostatic properties of the roll surface.

[0069] The size of the roughness-forming particles 18 is not particularly limited, but from the viewpoint of forming appropriate irregularities and improving the uniformity of discharge characteristics, an average particle diameter of 3 μm to 30 μm is preferred. More preferably, an average particle diameter of 5 μm to 30 μm is preferred, and even more preferably, an average particle diameter of 10 μm to 30 μm is preferred. The average particle diameter of the roughness-forming particles 18 is determined by observing the surface of the surface layer 16 with a laser microscope, and the diameter of the roughness-forming particles 18 visible during surface observation is defined as the particle size, expressed as the average of any 20 points.

[0070] The roughness-forming particles 18 may consist of one type of particle or two or more types of particles. One type of particle means, firstly, particles of the same material. Having the same material means that, in the case of polymer particles, particles containing polyurethane within a broad range may be considered the same, or particles with the same monomer composition within a narrow range may be considered the same. More preferably, particles with the same monomer composition within a narrow range should be considered the same. Secondly, one type of particle means particles with the same particle size. Having the same particle size means that the particle size is uniform. For example, this means that the diameter of the roughness-forming particles 18 is measured at 50 arbitrary locations, the average is taken as μ, the deviation is taken as σ, and μ / σ is 4.97 or less. The diameter of the roughness-forming particles 18 can be measured by observing the particle diameter using a laser microscope (for example, Keyence's "VK-9510").

[0071] Preferably, the roughness-forming particles 18 are composed of only one type of particle. If the roughness-forming particles 18 are composed of two or more types of particles with different materials or particle sizes, it becomes necessary to adjust the thickness of the binder polymer 16a covering the roughness-forming particles 18, taking into further consideration the differences in the effect of the material and particle size of the roughness-forming particles 18 on the discharge characteristics. If the roughness-forming particles 18 are composed of only one type of particle in terms of material and particle size, it is easier to adjust the thickness of the binder polymer 16a covering the roughness-forming particles 18. This makes it possible to improve the uniformity of the discharge characteristics. Also, if two types of particles with significantly different particle sizes are included, the particles of different sizes tend to aggregate, and dispersibility tends to decrease. If the roughness-forming particles 18 are composed of only one type of particle in terms of particle size, it is easier to control the aggregation of the roughness-forming particles 18, and thus the uniformity of the surface roughness can be improved. Furthermore, if the roughness-forming particles 18 are composed of only one type of particle in terms of particle size, the uneven shape of the elastic layer 14 is more easily reflected in the surface unevenness of the charging roll, making it easier to control the surface unevenness of the charging roll.

[0072] In the surface layer 16, the thickness of the binder polymer 16a is preferably set to a predetermined thickness. The thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22 is preferably greater than the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24. By doing so, the discharge amount on the roughness-forming particles 18 on the groove portion 22 and the discharge amount on the roughness-forming particles 18 on the flat portion 24 can be adjusted to be the same, improving the uniformity of the discharge characteristics. This makes it possible to suppress the generation of black spot images. This is because the portion of the flat portion 24 where the roughness-forming particles 18 are present is in contact with the photoreceptor, resulting in a lower discharge rate than the portion of the grooved portion 22 where the roughness-forming particles 18 are present. Therefore, in order to make the discharge rate the same at each position, it is necessary to make the film thickness of the portion of the flat portion 24 where the roughness-forming particles 18 are present thinner than that of the portion of the grooved portion 22, thereby increasing the capacitance and the amount of charge on the surface.

[0073] The difference (t1-t2) between the thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22 and the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24 is preferably 4 μm or more and 16 μm or less. When the above thickness difference (t1-t2) is 4 μm or more, the amount of charge on the surface of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24 becomes relatively larger, and the range of environments in which black dot images do not occur widens. From this viewpoint, the above thickness difference (t1-t2) is more preferably 5 μm or more, and even more preferably 6 μm or more. Furthermore, when the above thickness difference (t1-t2) is 16 μm or less, it is maintained at an appropriate thickness, making it easier to form appropriate irregularities. This can improve the uniformity of the discharge characteristics. From this viewpoint, the above thickness difference (t1-t2) is more preferably 15 μm or less, and even more preferably 12 μm or less.

[0074] The thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22 is preferably 5 μm or more and 20 μm or less. When the thickness t1 is 5 μm or more, the resistance at the discharge site tends to be uniform, and the discharge characteristics tend to be uniform. From this viewpoint, the thickness t1 is more preferably 6 μm or more, and even more preferably 7 μm or more. When the thickness t1 is 20 μm or less, an appropriate roughness is ensured on the surface of the surface layer 16 on the groove portion 22, and a discharge area can be secured. From this viewpoint, the thickness t1 is more preferably 18 μm or less, and even more preferably 15 μm or less.

[0075] The thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24 is preferably 1.0 μm or more and 4.0 μm or less. When the thickness t2 is 1.0 μm or more, the resistance at the discharge site tends to be uniform, and the discharge characteristics tend to be uniform. From this viewpoint, the thickness t2 is more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. When the thickness t2 is 4.0 μm or less, an appropriate roughness is ensured on the surface of the surface layer 16, and a discharge area can be secured. From this viewpoint, the thickness t2 is more preferably 3.5 μm or less, and even more preferably 3.0 μm or less.

[0076] The thicknesses t1 and t2 of the binder polymer 16a can be measured by observing the cross-section using a laser microscope (e.g., Keyence's "VK-9510"). For example, the thickness of the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22 can be measured at five arbitrary locations, and t1 can be represented by the average of these measurements. Similarly, the thickness of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24 can be measured at five arbitrary locations, and t2 can be represented by the average of these measurements.

[0077] To make the thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22 thicker than the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24, it is advisable to utilize both the surface energy instability of the roughness-forming particles 18 on the groove portion 22 and the energy instability of the base rubber of the groove portion 22. In other words, it is advisable to utilize the fact that the roughness-forming particles 18 on the groove portion 22 try to stabilize by accumulating a large amount of binder polymer 16a, and that the base rubber of the groove portion 22 also tries to stabilize by accumulating a large amount of binder polymer 16a.

[0078] The content in the surface layer 16 of the roughness-forming particles 18 is not particularly limited, but from the viewpoints such as improving the dispersibility of the roughness-forming particles 18 and easily ensuring uniform chargeability, it is preferably 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the binder polymer 16a in the surface layer 16. More preferably, it is 5 parts by mass or more and 30 parts by mass or less.

[0079] A conductive agent can be blended in the surface layer 16 for imparting conductivity. Examples of the conductive agent include an electron conductive agent and an ion conductive agent. Examples of the electron conductive agent include carbon black, graphite, and a conductive metal oxide. Examples of the conductive metal oxide include a conductive titanium oxide, a conductive zinc oxide, and a conductive tin oxide. Examples of the ion conductive agent include a quaternary ammonium salt, a borate, and a surfactant. Further, various additives may be appropriately added to the surface layer 16 as necessary. Examples of the additives include a plasticizer, a leveling agent, a filler, a vulcanization accelerator, a processing aid, and a mold release agent.

[0080] The volume resistivity of the surface layer 16 may be set in the semiconductive region from the viewpoint of chargeability and the like. Specifically, for example, it may be set within the range of 1.0×10 7 ~1.0×10 10 Ω·cm. The volume resistivity can be measured in accordance with JIS K6911.

[0081] The elastic body layer 14 can be formed, for example, as follows. First, the shaft body 12 is coaxially installed in the hollow part of a roll forming die, an uncrosslinked conductive rubber composition is injected, heated and cured (crosslinked), and then demolded, or the elastic body layer 14 is formed on the outer periphery of the shaft body 12 by extruding the uncrosslinked conductive rubber composition onto the surface of the shaft body 12.

[0082] Methods for forming grooves 22 on the outer surface of the elastic layer 14 include polishing and molding. In either method, regular grooves 22 can be formed on the outer surface of the elastic layer 14. When using polishing, the plunge method is preferable for forming circumferential grooves 22. The traverse method is preferable for forming helical grooves 22. In the traverse method, for example, by rotating a roll body having the elastic layer 14 around its axis at a constant speed, and moving a grinding wheel in contact with the outer surface of the elastic layer 14 in one axial direction at a constant speed, grooves 22 that regularly form a spiral along the axial direction can be formed on the outer surface of the elastic layer 14.

[0083] The surface layer 16 can be formed by using a surface layer 16 forming material, coating it onto the outer surface of the elastic layer 14, and performing appropriate drying treatments. The surface layer 16 forming material may contain a diluent. Examples of diluent solvents include ketone solvents such as methyl ethyl ketone (MEK) and methyl isobutyl ketone, alcohol solvents such as isopropyl alcohol (IPA), methanol, and ethanol, hydrocarbon solvents such as hexane and toluene, acetic acid solvents such as ethyl acetate and butyl acetate, ether solvents such as diethyl ether and tetrahydrofuran, and water.

[0084] With the above configuration of the charging roll 10, one or more grooves 22 extending along a direction within ±5° of the circumferential direction are regularly formed in the axial direction on the outer surface of the elastic layer 14. The groove width w and groove depth d of the grooves 22 and the area ratio a / b of the bottom surface 221 of the grooves 22 to the flat surface 24 are within a specific range. This allows the roughness-forming particles 18 to be uniformly and evenly distributed on both the flat surface 24 and the grooves 22 of the elastic layer 14, forming an appropriate surface roughness and creating an appropriate roughness difference between the flat surface 24 and the grooves 22 of the elastic layer 14, thereby adjusting to an appropriate discharge amount. As a result, the uniformity of the discharge characteristics is excellent. Furthermore, by making the thickness of the binder polymer 16a covering the roughness-forming particles 18 on the grooves 22 thicker than the thickness of the binder polymer 16a covering the roughness-forming particles 18 on the flat surface 24, the discharge amount can be made uniform. As a result, the uniformity of the discharge characteristics is excellent.

[0085] The electrostatic roll 10 according to the present invention does not form surface irregularities on the electrostatic roll by arranging two types of roughness-forming particles of different sizes on the outer surface of an overall flat elastic layer, but rather forms a predetermined irregular shape on the outer surface of the elastic layer 14 and then forms surface irregularities on the electrostatic roll 10 by arranging relatively uniform roughness-forming particles 18 of a predetermined size thereon. The roughness-forming particles 18 are arranged not only on the grooves 22 of the elastic layer 14 but also on the flat parts 24. As a result, the steps of the surface irregularities of the elastic layer 14 appear as surface irregularities on the electrostatic roll 10. If the roughness-forming particles 18 are relatively uniform, the surface irregularities of the elastic layer 14 are easily reflected on the surface of the electrostatic roll 10. In order to arrange the roughness-forming particles 18 not only on the grooves 22 but also on the flat parts 24 of the elastic layer 14, the groove width w of the grooves 22 should not be too large or too small relative to the size of the roughness-forming particles 18. By having a predetermined groove width w of the groove portion 22, the roughness-forming particles 18 can be reliably and uniformly placed not only on the groove portion 22 but also on the flat portion 24. Similarly, the width of the flat portion 24 is not good if it is too large or too small. To reliably and uniformly place the roughness-forming particles 18 on the flat portion 24 as well, a predetermined area ratio is desirable. Furthermore, in this invention, a predetermined uneven shape is formed on the outer circumferential surface of the elastic body layer 14, which allows the surface area of ​​the outer circumferential surface of the elastic body layer to be made larger compared to the outer circumferential surface of an elastic body layer that is entirely flat. This improves the ease of discharge. This effect is exhibited even if, for example, the groove portion 22 of the elastic body layer 14 is filled with the binder polymer 16a of the surface layer 16. This effect is a previously unknown finding. From this point of view as well, there are advantages to the configuration of the present invention.

[0086] Furthermore, in the charging roll 10 according to the present invention, the direction in which the groove portion 22 extends is within ±5° of the circumferential direction y, and is close to the circumferential direction. As a result, when the photoreceptor and the charging roll 10 rub against each other, the edges of the protrusions formed by the groove portion 22 are less susceptible to shear stress in the rotational direction (circumferential direction y) of the charging roll 10, wear of the protrusions is suppressed, and during durability, the difference in charge between the bumps and depressions due to wear of the protrusions is kept small, thereby suppressing the occurrence of streaky images. In this case, since the direction in which the groove portion 22 extends is close to the circumferential direction y, the surface of the photoreceptor tends to be divided into parts where the protrusions formed by the groove portion 22 are constantly in contact and parts where the groove portion 22 (roughness-forming particles on the groove portion 22) are constantly in contact with each other when rotating in the circumferential direction. However, by narrowing the width w of the groove portion 22 within a specific range, this effect is reduced, and the occurrence of image defects (vertical streaks) due to differences in charge is suppressed.

[0087] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0088] For example, in the above embodiment, one or more grooves 22 extending in a direction within ±5° of the circumferential direction y are regularly formed in the axial direction x on the outer circumferential surface of the elastic layer 14. However, as shown in Figure 5, a mesh-like groove pattern may be formed on the outer circumferential surface of the elastic layer 14, where grooves 22(22a) extending in a direction within +5° of the circumferential direction y intersect with grooves 22(22b) extending in a direction within -5° of the circumferential direction. This improves the uniformity of the surface roughness and the uniformity of the discharge characteristics.

[0089] The spiral groove 22 may consist only of grooves that regularly form a left-hand spiral along the axial direction, or it may consist only of grooves that regularly form a right-hand spiral along the axial direction, or it may have a mesh-like groove structure where grooves that regularly form a right-hand spiral along the axial direction and grooves that regularly form a left-hand spiral along the axial direction intersect.

[0090] The spiral, intersecting, mesh-like grooves can be formed on the outer surface of the elastic layer 14 by, for example, the grinding wheel moving in one axial direction and then in the other axial direction. This allows for the formation of a mesh-like groove 22 on the outer surface of the elastic layer 14, where grooves 22a that regularly form a right-hand spiral along the axial direction and grooves 22b that regularly form a left-hand spiral along the axial direction intersect. [Examples]

[0091] The present invention will be described in detail below using examples and comparative examples.

[0092] (Example 1) <Preparation of conductive rubber composition> A conductive rubber composition was prepared by mixing 100 parts by mass of isoprene rubber with 30 parts by mass of carbon black, 6 parts by mass of zinc oxide, 2 parts by mass of stearic acid, 1 part by mass of sulfur, 0.5 parts by mass of thiazole-based vulcanization accelerator, 0.5 parts by mass of thiraum-based vulcanization accelerator, and 50 parts by mass of heavy calcium carbonate. The mixture was kneaded for 10 minutes using a sealed mixer heated to 50°C.

[0093] The following materials were prepared as components for the conductive rubber composition. • Isoprene rubber (IR): JSR "JSR IR2200" • Carbon Black: Cabot Japan's "Show Black N762" • Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc Oxide Type 2" • Stearic acid: Nippon Oil & Fats Co., Ltd. "Sakura Stearic Acid" • Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries. • Thiazole-based vulcanization accelerator: "Noxellar DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Thiram-based vulcanization accelerator: "Noxellar TRA" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Heavy calcium carbonate: Shiraishi Calcium's "Whiten B", average particle size 3.6 μm

[0094] <Fabrication of elastic layers> A mandrel (8 mm in diameter) was set in a molding die (pipe-shaped), the above composition was injected, and after heating at 180°C for 30 minutes, it was cooled and demolded to form an elastic layer made of a conductive rubber elastic material with a thickness of 1.9 mm on the outer circumference of the mandrel. Next, while rotating the roll body having the elastic layer at a constant speed around its axis, a grinding wheel in contact with the outer surface of the elastic layer was moved at a constant speed in one axial direction, and then the grinding wheel in contact with the outer surface of the elastic layer was moved at a constant speed in the other axial direction, thereby forming a mesh-like groove on the outer surface of the elastic layer in which grooves that regularly form a right-hand spiral along the axial direction and grooves that regularly form a left-hand spiral along the axial direction intersect. The conditions for each were as follows. Roller rotation speed: 500 rpm Grinding wheel movement speed: 0.05 m / s Grinding wheel peripheral speed: 72 m / s Grit size of grinding wheel: #1500 Groove pitch: 0.3 mm

[0095] <Preparation of the surface layer> A liquid composition for surface layer formation was prepared by blending roughness-forming particles, a binder polymer, and carbon black as a conductive agent to the composition (parts by mass) shown in the table, adding 200 parts by mass of methyl ethyl ketone (MEK), and mixing and stirring at a predetermined stirring speed. Next, while continuing to stir, this liquid composition was roll-coated onto the outer surface of the elastic layer and heat-treated to form a surface layer with a thickness of 1.0 μm on the outer surface of the elastic layer. This produced the electrostatic roll of Example 1.

[0096] (Example 2) <Preparation of conductive rubber composition> A conductive rubber composition was prepared by mixing 100 parts by mass of NBR with 0.7 parts by mass of stearic acid, 5 parts by mass of zinc oxide, 2 parts by mass of hydrotalcite, 3 parts by mass of peroxide crosslinking agent, and 20 parts by mass of carbon, and stirring and mixing these ingredients with a stirrer.

[0097] The following materials were prepared as components for the conductive rubber composition. • NBR: "Nipol 1041" manufactured by Nippon Zeon Co., Ltd. • Stearic acid: NOF Corporation's "Sakura Stearic Acid" • Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc Oxide Type 2" • Hydrotalcite: Kyowa Chemical Industry Co., Ltd. "DHT4A" • Peroxide crosslinking agent: NOF Corporation's "Parkmill D40" • Carbon fiber: Ketjenbrak International "Ketjenbrak EC300J" <Fabrication of elastic layers> The heating temperature was changed to 170°C, and an elastic layer made of conductive rubber elastic material was molded in the same manner as in Example 1. Then, in the same manner as in Example 1, a mesh-like groove was formed on the outer surface of the elastic layer by polishing.

[0098] <Preparation of the surface layer> A surface layer with a thickness of 1.0 μm was formed on the outer periphery of the elastic layer in the same manner as in Example 1. This resulted in the production of the electrostatic roll of Example 2.

[0099] (Example 3) <Preparation of conductive rubber composition> A conductive rubber composition was prepared by adding 5 parts by mass of a vulcanization aid, 10 parts by mass of carbon, 0.5 parts by mass of a vulcanization accelerator, 2 parts by mass of sulfur, and 50 parts by mass of a filler to 100 parts by mass of hydrin rubber, and then stirring and mixing these with a stirrer.

[0100] The following materials were prepared as components for the conductive rubber composition. • Hydrin rubber (ECO, manufactured by Nippon Zeon, "Hydrin H1100") • Vulcanization aid (zinc oxide, Mitsui & Co. "Zinc Oxide Type 2") • Carbon fiber (Ketjenbrak International "Ketjenbrak EC300J") • Vulcanization accelerator (2-mercaptobenzothiazole, "Noxellar MP" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Sulfur (manufactured by Tsurumi Chemical Industries, Ltd., "Sulfax PTC") • Filler (calcium carbonate, Shiraishi Kogyo Co., Ltd. "Shiratsuka CC") <Fabrication of elastic layers> An elastic layer made of a conductive rubber elastic material was molded in the same manner as in Example 1. Then, in the same manner as in Example 1, a mesh-like groove was formed on the outer surface of the elastic layer by polishing.

[0101] <Preparation of the surface layer> A surface layer with a thickness of 1.0 μm was formed on the outer periphery of the elastic layer in the same manner as in Example 1. This resulted in the production of the electrostatic roll of Example 3.

[0102] (Examples 4, 5, 7, 8) By changing the surface material, the electrostatic rolls of Examples 4, 5, 7, and 8 were fabricated in the same manner as in Example 3.

[0103] (Example 6) A groove portion is formed on the outer surface of the elastic layer, regularly forming a left-hand thread-like spiral along the axial direction, and the electrostatic roll of Example 6 is manufactured in the same manner as in Example 3.

[0104] (Example 9) An electrostatic roll of Example 9 was manufactured in the same manner as in Example 4, except that the direction of groove formation was set to the circumferential direction and the area ratio between the groove bottom surface and the flat surface was changed.

[0105] (Example 10) The electrostatic roll of Example 10 was manufactured in the same manner as in Example 4, except that the groove formation angle was changed and the area ratio between the groove bottom and the flat surface was changed.

[0106] (Example 11) The electrostatic roll of Example 11 was manufactured in the same manner as in Example 6, except that the angle of groove formation was changed.

[0107] (Comparative Examples 1-7) The electrostatically charged rolls of Comparative Examples 1 to 7 were fabricated in the same manner as in Example 4.

[0108] (Comparative Examples 8-9) By changing the groove formation angle, the electrostatic rolls of Comparative Examples 8 and 9 were manufactured in the same manner as in Example 4.

[0109] The materials used as surface materials are as follows: • Binder polymer (PA): "Fine Resin FR-101" manufactured by Namichi • Binder polymer (PU): "ART Resin UN-333" manufactured by Negami Kogyo Co., Ltd. • Roughness-forming particles (PU) <1> ): Negami Kogyo Co., Ltd. "Art Pearl TK-100TR" Average particle size 2μm • Roughness-forming particles (PU) <2> ): Negami Kogyo Co., Ltd. "Art Pearl C-1000 Transparent" Average particle size 3μm • Roughness-forming particles (PU <3> ): Negami Kogyo Co., Ltd. "Art Pearl C-300 Transparent" Average particle size 22μm • Roughness-forming particles (PU) <4> ): Negami Kogyo Co., Ltd. "Art Pearl C-200 Transparent Graded Product" Average particle size 32μm • Roughness-forming particles (PU) <5> ): Negami Kogyo Co., Ltd. "Art Pearl C-200 Transparent Graded Product" Average particle size 35μm • Roughness-forming particles (PA): Toray "TR-2" with an average particle size of 22 μm • Roughness-forming particles (PMMA): Negami Kogyo Co., Ltd. "Art Pearl GR-200 Transparent" Average particle size 22 μm • Carbon Black: Tokai Carbon "Seast 9H"

[0110] Surface and cross-sectional analyses were performed on the polished elastic layer of the electrostatic roll to calculate the groove width, groove depth, area ratio a / b (area of ​​the groove bottom surface a to area of ​​the flat surface b), and groove angle. Furthermore, the surface roughness Rz and the thickness of the binder polymer on the surface layer were measured for the fabricated electrostatic roll.

[0111] (The uneven shape of the elastic layer) The groove width was calculated by taking a laser microscope image of the outer surface of the elastic layer and averaging the groove widths of 100 arbitrary groove points observed in the image. The groove depth was calculated by taking a laser microscope image of the radial cross-section of the elastic layer and averaging the groove depths of 100 arbitrary groove points observed in the image. The area ratio a / b of the groove bottom surface area a to the flat surface area b was calculated by taking a laser microscope image of five arbitrary locations on the outer surface of the elastic layer, calculating the area a of the groove bottom surface and the area b of the flat surface observed within a predetermined range (0.1 mm × 0.1 mm) of the image, and averaging the ratio. The groove angle was calculated by taking a laser microscope image of the outer surface of the elastic layer and averaging the angles of 100 arbitrary groove points observed in the image with respect to the circumferential direction.

[0112] (Surface roughness Rz) The surface roughness Rz is a 10-point average roughness, calculated in accordance with JIS B0601 (1994) and is the average of values ​​measured at any 5 locations. The surface roughness Rz of the entire surface layer was measured by observation using a laser microscope (KEYENCE "VK-9510"). In the image taken at 400x magnification, the value calculated using the surface roughness mode in the analysis program (program name KEYENCE VK Analyzer analysis application) was used as the surface roughness Rz of the entire surface layer. The surface roughness Rz of the surface layer in the groove area was measured by observation using a laser microscope (KEYENCE "VK-9510"). In the image taken, the value calculated using the surface roughness mode in the analysis program (program name KEYENCE VK Analyzer analysis application) for the groove area at 0.01 mm 2 The value calculated by selecting this option was taken as the surface roughness Rz of the groove.

[0113] (Binder thickness) The measurement was performed by observing the radial cross-section of the surface layer at 400x magnification using a laser microscope (Keyence "VK-X100"). As shown in Figure 4, the thickness of the binder polymer covering the roughness-forming particles on the grooves (binder thickness t1) and the thickness of the binder polymer covering the roughness-forming particles on the flat surfaces (binder thickness t2) were measured. Each was measured at five arbitrary locations, and the average of these measurements was used to represent the result.

[0114] (Image rating: Uneven) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000"), and images were produced at 25% density halftone under a 10°C x 10% RH environment. After 1 million prints, the roll was evaluated. Images without unevenness were rated as good ("〇"), and those with unevenness were rated as poor ("×").

[0115] (Image evaluation: horizontal lines) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000"), and images were produced at 25% density halftone under a 10°C x 10% RH environment. After 1 million prints, the roll was evaluated. Images without horizontal streaks were marked as particularly good ("○"), while images with horizontal streaks that significantly affected the image were marked as poor ("×").

[0116] (Image evaluation: Set lines) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000") and left for one week in a 50°C x 95%RH environment. After that, with the electrostatic roll still attached to the unit (black) of the real machine (RICOH "IM C8000"), images were produced at 25% density halftone in a 10°C x 10%RH environment. Images without set lines were marked as particularly good ("○"), while images with set lines that significantly affected the image were marked as poor ("×").

[0117] (Image evaluation: Sunspots (haze)) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000"), and images were produced at 25% density halftone under a 10°C x 10% RH environment. Evaluation was performed after 1 million prints. Images without black spots were rated as good ("○"), and images with even one black spot were rated as poor ("×").

[0118] (Image evaluation: vertical stripes) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000"), and images were produced at 25% density halftone under a 10°C x 10% RH environment. After 1 million prints, the roll was evaluated. Images without vertical streaks were rated as good ("○"), while images with vertical streaks that significantly affected the image were rated as poor ("×").

[0119] (Image evaluation: Lines following the uneven surface) The fabricated electrostatic roll was attached to the unit (black) of a real machine (RICOH "IM C8000"), and images were produced at 25% density halftone under a 10°C x 10% RH environment. Evaluation was performed after 1 million prints. Images without streaks following the uneven surface were rated as good ("○"), while images with streaks following the uneven surface that significantly affected the image were rated as poor ("×").

[0120] [Table 1]

[0121] [Table 2]

[0122] In Comparative Example 1, the groove width is too small, preventing the roughness-forming particles from entering the grooves. As a result, the difference between the surface roughness caused by the roughness-forming particles on the flat areas and the surface roughness caused by the roughness-forming particles on the grooves is small, resulting in horizontal streaks due to insufficient charging. Furthermore, using roughness-forming particles that are sized to fit within a small groove width makes it impossible to form a roughness sufficient to ensure adequate discharge. In Comparative Example 2, the groove width is too large, making the difference in charge between the concave and convex areas of the charging roll surface more apparent in the image, resulting in vertical streaks. Also, the groove width is too large, preventing the roughness-forming particles from being uniformly distributed within the grooves. As a result, unevenness occurs after durability testing. Furthermore, using roughness-forming particles that are sized to fit within a large groove width results in excessively large convex areas caused by the roughness-forming particles, making it impossible to achieve an appropriate surface roughness. This prevents the acquisition of uniform discharge characteristics. Furthermore, in Comparative Example 2, the groove width is too large, making it easier for the binder polymer covering the roughness-forming particles on the grooves to come into contact with the photoreceptor. As a result, not only does wear occur on the binder polymer covering the roughness-forming particles on the flat surfaces and the roughness-forming particles beneath them, but also on the binder polymer covering the roughness-forming particles on the grooves and the roughness-forming particles beneath them. This leads to wear across the entire surface layer during durability testing, resulting in unevenness in the image.

[0123] In Comparative Example 3, the groove depth was too small, resulting in a small difference between the surface roughness caused by the roughness-forming particles on the flat surface and the surface roughness caused by the roughness-forming particles on the groove, causing horizontal streaks due to insufficient charging. Note that using small roughness-forming particles in accordance with a small groove depth would prevent the formation of sufficient roughness to ensure adequate discharge. In Comparative Example 4, the groove depth was too large, resulting in a large difference between the surface roughness caused by the roughness-forming particles on the flat surface and the surface roughness caused by the roughness-forming particles on the groove, leading to a large difference in chargeability and image defects (vertical streaks). Furthermore, in Comparative Example 4, the groove depth was too large, preventing the roughness-forming particles placed in the groove from forming surface roughness. Therefore, black spots (fogging) appeared in the image after durability testing. Note that using large roughness-forming particles in accordance with a large groove depth would result in a large difference between the surface roughness caused by the roughness-forming particles on the flat surface and the surface roughness caused by the roughness-forming particles on the groove, making discharge difficult.

[0124] In Comparative Examples 5 and 6, the area ratio a / b of the area a of the bottom surface of the groove and the area b of the flat surface does not fall within the predetermined range, with the ratio of one of them being too large. As a result, the uniformity of the surface irregularities decreases, and uneven images occur after durability testing.

[0125] In Comparative Example 7, the groove depth is too large, resulting in a large difference in surface roughness between the roughness-forming particles on the flat surface and the roughness-forming particles on the groove. This leads to a large difference in electrostatic charge and causes image defects (vertical streaks).

[0126] In comparative examples 8 and 9, the groove formation angle is greater than ±5° with respect to the circumferential direction. As a result, the edges of the protrusions formed by the grooves are easily worn down by circumferential rotation, and during durability testing, the difference in charge between the protrusions and depressions becomes large due to the wear of the protrusions, resulting in the generation of streaks along the contours of the surface.

[0127] On the other hand, in the example, one or more grooves extending along a direction within ±5° of the circumferential direction are regularly formed in the axial direction on the outer surface of the elastic layer, and the groove width, groove depth, and the area ratio a / b of the groove bottom to the flat surface are within a specific range, and the surface layer contains a binder polymer and roughness-forming particles, with the roughness-forming particles arranged on the flat surface and grooves of the elastic layer, respectively. As a result, in the image evaluation, the example shows that problems such as unevenness, horizontal streaks, black spots (fogging), vertical streaks, and streaks along the uneven shape after durability are suppressed, and it can be seen that the uniformity of the discharge characteristics is excellent. Furthermore, no set streaks were observed in the images, and no peeling of the surface layer after durability was observed.

[0128] Although embodiments and examples of the present invention have been described above, the present invention is not limited in any way to the above embodiments and examples, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0129] 10 Electrostatic Rolls 12 Axis Body 14 Elastic layer 16 Surface layer 18. Particles for roughness formation 22 Groove 24 Plane section 16a Binder Polymer 18a Particles for forming roughness on grooves 18b Particles for forming roughness on a flat surface 221 Bottom surface of groove w Groove width d Groove depth Region on groove M

Claims

1. It comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer, On the outer circumferential surface of the elastic layer, one or more grooves extending along a direction within ±5° of the circumferential direction are regularly formed in the axial direction. The groove width of the groove portion is 4 μm or more and 30 μm or less. The groove depth of the groove portion is 2 μm or more and 12 μm or less. Of the outer surface of the elastic layer, the area ratio a / b of the area a of the bottom surface of the groove and the area b of the flat portion other than the groove is 0.3 or more and 2.4 or less. The surface layer contains a binder polymer and roughness-forming particles. The roughness-forming particles are arranged on the flat portion and the groove portion of the elastic layer, respectively. The average particle diameter of the roughness-forming particles is 3 μm or more and 30 μm or less. The surface roughness Rz of the surface layer in the region above the groove is 2 μm or more and 16 μm or less, and the surface roughness Rz of the entire surface layer is 5 μm or more and 26 μm or less. The roughness-forming particles on the flat portion protrude radially outward more than the roughness-forming particles on the groove portion. A electrostatic roll for electrophotographic equipment, wherein the difference between the surface roughness of the groove portion and the surface roughness of the entire surface layer is 3 μm or more and 10 μm or less.

2. The electrophotographic roller for electrophotographic equipment according to claim 1, wherein the material of the roughness-forming particles is one of polyurethane, polyamide, and acrylic resin.

3. The electrophotographic roller according to claim 1 or claim 2, wherein the thickness of the binder polymer covering the roughness-forming particles on the grooved portion is greater than the thickness of the binder polymer covering the roughness-forming particles on the flat portion.

4. The electrophotographic roller for electrophotographic equipment according to claim 3, wherein the difference between the thickness of the binder polymer covering the roughness-forming particles on the flat portion and the thickness of the binder polymer covering the roughness-forming particles on the groove portion is 4 μm or more and 16 μm or less.

5. The electrophotographic equipment charging roll according to claim 1 or claim 2, wherein the elastic layer comprises one or more of isoprene rubber, nitrile rubber, and hydrin rubber.

6. The electrophotographic roller according to claim 1 or claim 2, wherein the binder polymer of the surface layer is one of polyurethane and polyamide.

7. The electrophotographic roller according to claim 1 or claim 2, wherein the roughness-forming particles consist of one type of particle.

8. The electrophotographic roller according to claim 1 or 2, wherein a mesh-like groove is formed on the outer surface of the elastic layer, where grooves extending in a direction of +5° or less with respect to the circumferential direction intersect with grooves extending in a direction of -5° or less with respect to the circumferential direction.

9. The material of the roughness-forming particles is one of polyurethane, polyamide, and acrylic resin. The thickness of the binder polymer covering the roughness-forming particles on the grooved portion is greater than the thickness of the binder polymer covering the roughness-forming particles on the flat portion. The difference between the thickness of the binder polymer covering the roughness-forming particles on the flat portion and the thickness of the binder polymer covering the roughness-forming particles on the groove portion is 4 μm or more and 16 μm or less. The elastic layer comprises one or more of isoprene rubber, nitrile rubber, and hydrin rubber. The binder polymer of the surface layer is one of polyurethane or polyamide. The roughness-forming particles are composed of one type of particle. The electrophotographic roller for electrophotographic equipment according to claim 1, wherein a mesh-like groove is formed on the outer circumferential surface of the elastic layer, where grooves extending in a direction of +5° or less with respect to the circumferential direction intersect with grooves extending in a direction of -5° or less with respect to the circumferential direction.

Images