Charging rolls for electrophotographic equipment

Abstract

To provide a charging roll for electrophotographic apparatuses, excellent in the uniformity of discharge characteristics.SOLUTION: In a charging roll 10, one or two or more groove parts 22 extended in a direction having an angle of ±46° or less with respect to the circumferential direction y on the outer peripheral surface of an elastic body layer 14 and having a groove width w1 of 4 μm or more and 30 μm or less and a groove depth d of 2 μm or more and 12 μm or less are regularly formed in an axial direction x; the width w2 of a plane part 24 being a part except the groove part 22 on the outer peripheral surface of the elastic body layer 14 is 4 μm or more and 30 μ or less; a relationship between an angle θ between the extended direction of the groove part 22 and the circumferential direction y and a ratio w2 / w1 of the groove width w1 of the groove part 22 to the width w2 of the plane part 24 is specific; and a surface layer 16 includes a binder polymer 16a and roughness formation particles 18 arranged on the plane part 24 and the groove part 22.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a charging roll for electrophotographic equipment, which is suitably used in electrophotographic equipment such as copying machines, printers, and facsimiles that employ an electrophotographic system. [Background technology]

[0002] Known charging rolls for electrophotographic devices include those having an elastic layer having rubber elasticity on the outer peripheral surface of a shaft such as a core metal, and a surface layer on the outer peripheral surface of the elastic layer. Furthermore, in charging rolls, for example, roughness-forming particles may be added to the binder polymer of the surface layer in order to improve charging characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 025870 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the roughness-forming particles added to the surface layer tend to aggregate, the uniformity of the surface roughness is likely to decrease in roughness formation methods that add roughness-forming particles. In particular, when attempting to form surface irregularities using two or more types of roughness-forming particles with different particle sizes, the particles with different particle sizes tend to aggregate, which is particularly likely to decrease the uniformity of the surface roughness. If the uniformity of the surface roughness decreases, there is a risk that the uniformity of the discharge characteristics of the charging roll will decrease.

[0005] The problem to be solved by the present invention is to provide a charging roll for electrophotographic equipment which has excellent uniformity in discharge characteristics. [Means for solving the problem]

[0006] The charge roll for an electrophotographic device according to the present invention comprises a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein one or more grooves extending in a direction within ±46° of the circumferential direction are formed regularly in the axial direction on the outer peripheral surface of the elastic layer, the grooves having a groove width w1 of 4 μm or more and a groove depth of 2 μm or more and 12 μm or less, the width w2 of a flat portion of the outer peripheral surface of the elastic layer other than the grooves being 4 μm or more and 30 μm or less, the relationship between the angle θ of the direction in which the grooves extend with respect to the circumferential direction and the ratio w2 / w1 of the groove width w1 of the grooves to the width w2 of the flat portion satisfy the relationships (A) to (C) below, and the surface layer contains a binder polymer and roughness-forming particles, and the roughness-forming particles are disposed on the flat portions and the grooves of the elastic layer, respectively. (A) When -5°≦θ≦+5°, 0.7≦w2 / w1≦1.3 (B) When -22°≦θ<-5° or +5°<θ≦+22°, 1.0≦w2 / w1≦2.0 (C) When -46°≦θ<-22° or +22°<θ≦+46°, 1.2≦w2 / w1≦2.6

[0007] The surface roughness Rz of the surface layer in the region above the groove portion may be 2 μm or more and 16 μm or less, and the surface roughness Rz of the entire surface layer may be 5 μm or more and 26 μm or less. The average particle diameter of the roughness-forming particles may be 3 μm or more and 30 μm or less. The material of the roughness-forming particles may be any one of polyurethane, polyamide, and acrylic resin. The thickness of the binder polymer covering the roughness-forming particles on the groove portion may be thicker 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 may be 4 μm or more and 16 μm or less. The elastic layer may contain any one or more of isoprene rubber, nitrile rubber, and hydrin rubber. The binder polymer of the surface layer may be any one of polyurethane and polyamide. The roughness-imparting particles may be composed of one type of particle. The outer peripheral surface of the elastic layer may be formed with a mesh-like groove portion in which groove portions extending in a direction within +46° to the circumferential direction intersect with groove portions extending in a direction within -46° to the circumferential direction.

[0008] (1) A charging roll for an electrophotographic device according to the present invention comprises a shaft, an elastic layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastic layer, wherein one or more grooves extending in a direction within ±46° with respect to the circumferential direction are regularly formed in the axial direction on the outer peripheral surface of the elastic layer, the grooves having a groove width w1 of 4 μm or more and a groove depth of 2 μm or more and 12 μm or less, a width w2 of a flat portion of the outer peripheral surface of the elastic layer other than the grooves being 4 μm or more and 30 μm or less, and a relationship between an angle θ of the direction in which the grooves extend with respect to the circumferential direction and a ratio w2 / w1 of the groove width w1 of the grooves to the width w2 of the flat portion satisfies the following relationships (A) to (C), and the surface layer contains a binder polymer and roughness-forming particles, and the roughness-forming particles are disposed on the flat portions and the grooves of the elastic layer, respectively. (A) When -5°≦θ≦+5°, 0.7≦w2 / w1≦1.3 (B) When -22°≦θ<-5° or +5°<θ≦+22°, 1.0≦w2 / w1≦2.0 (C) When -46°≦θ<-22° or +22°<θ≦+46°, 1.2≦w2 / w1≦2.6

[0009] (2) In the above (1), 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.

[0010] (3) In the above (1) or (2), the average particle diameter of the roughness-imparting particles may be 3 μm or more and 30 μm or less.

[0011] (4) In any one of the above (1) to (3), the material of the roughness-imparting particles may be any one of polyurethane, polyamide, and 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 thicker 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 may be 4 μm or more and 16 μm or less.

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

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

[0016] (9) In any one of the above (1) to (8), the roughness-imparting particles may be composed of one type of particle.

[0017] (10) In any of the above (1) to (9), the outer peripheral surface of the elastic layer may be formed with a mesh-like groove portion in which groove portions extending along a direction within +46° of the circumferential direction intersect with groove portions extending along a direction within -46° of the circumferential direction. [Effects of the Invention]

[0018] According to the present invention, there is provided a charging roll for an electrophotographic device, comprising: a shaft; an elastic layer formed on the outer peripheral surface of the shaft; and a surface layer formed on the outer peripheral surface of the elastic layer; one or more grooves are formed in the outer peripheral surface of the elastic layer in a regular axial pattern, the grooves extending in a direction within ±46° of the circumferential direction; the groove width w1 of the grooves is 4 μm or more and 30 μm or less; the groove depth is 2 μm or more and 12 μm or less; the width w2 of a flat portion of the outer peripheral surface of the elastic layer other than the grooves is 4 μm or more and 30 μm or less; the relationship between the angle θ of the direction in which the grooves extend with respect to the circumferential direction and the ratio w2 / w1 of the groove width w1 of the grooves to the width w2 of the flat portion satisfies the relationships (A) to (C) above; the surface layer contains a binder polymer and roughness-forming particles, and the roughness-forming particles are disposed on the flat portions and the grooves of the elastic layer, respectively; and therefore, the charging roll has excellent uniformity in discharge characteristics.

[0019] When the surface roughness Rz of the surface layer in the region above the groove portion 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, an appropriate discharge space and a discharge starting point can be formed between the photosensitive member and the charging roll.

[0020] When the average particle diameter of the roughness-forming particles is 3 μm or more and 30 μm or less, appropriate unevenness is easily formed, thereby improving the uniformity of the discharge characteristics.

[0021] When the material of the roughness-forming particles is any one of polyurethane, polyamide, and acrylic resin, the roughness-forming particles are made of a material with a high dielectric constant, which improves the chargeability of the roll surface.

[0022] If the thickness of the binder polymer covering the roughness-forming particles on the groove portion is thicker than the thickness of the binder polymer covering the roughness-forming particles on the flat portion, the amount of discharge on the roughness-forming particles on the groove portion and the amount of discharge on the roughness-forming particles on the flat portion can be adjusted to be the same, thereby improving the uniformity of the discharge characteristics.

[0023] When the difference between the thickness of the binder polymer covering the roughness-forming particles on the flat surface and the thickness of the binder polymer covering the roughness-forming particles on the grooves is 4 μm or more, the amount of charge on the surface of the binder polymer covering the roughness-forming particles on the flat surface becomes relatively large, widening the range of environments in which black dots do not occur. Furthermore, when the difference in thickness is 16 μm or less, an appropriate thickness is maintained, making it easier to form appropriate unevenness. This improves the uniformity of the discharge characteristics.

[0024] When the elastic layer contains at least one of isoprene rubber, nitrile rubber, and hydrin rubber, the compression set is small, and the occurrence of streak images corresponding to deformed portions when the charging roll is set is suppressed.

[0025] When the binder polymer of the surface layer is either polyurethane or polyamide, the binder polymer is made of a material with a high dielectric constant, which improves the charging property of the roll surface. In addition, the compression set is small, which prevents streaks from occurring in the roll surface due to deformation when the charging roll is set.

[0026] When the roughness-forming particles are composed of one type of particle, the uneven shape of the elastic layer is easily reflected in the surface unevenness of the charging roll, making it easy to control the surface unevenness of the charging roll. Furthermore, since it is easy to control the aggregation of the roughness-forming particles, it is possible to improve the uniformity of the surface roughness. Furthermore, since it is easy to adjust the thickness of the binder polymer covering the roughness-forming particles, it is possible to improve the uniformity of the discharge characteristics.

[0027] When a mesh-like groove is formed on the outer peripheral surface of the elastic layer, the grooves extending in a direction within +46° to the circumferential direction intersect with the grooves extending in a direction within -46° to the circumferential direction, the uniformity of the surface roughness is improved, and the uniformity of the discharge characteristics can be improved. [Brief explanation of the drawings]

[0028] [Figure 1] 1A is a schematic view of the appearance of a charging roll for an electrophotographic apparatus according to one embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA thereof. [Figure 2] 3 is a schematic view of the appearance of an elastic layer, showing the shape of a groove formed in the outer peripheral surface of the elastic layer. FIG. [Figure 3] 10A and 10B are schematic external views of an elastic layer showing modified shapes of grooves formed on the outer peripheral surface of the elastic layer. [Figure 4] FIG. [Figure 5] 10A and 10B are schematic external views of an elastic layer showing modified shapes of grooves formed on the outer peripheral surface of the elastic layer. DETAILED DESCRIPTION OF THE INVENTION

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

[0030] The charge roll 10 comprises a shaft 12, an elastic layer 14 formed on the outer peripheral surface of the shaft 12, and a surface layer 16 formed on the outer peripheral surface of the elastic layer 14. The elastic layer 14 is a layer (base layer) that forms the base of the charge roll 10. The surface layer 16 is a layer that appears on the surface of the charge roll 10. Although not specifically shown, an intermediate layer such as a resistance adjustment layer may be formed between the elastic layer 14 and the surface layer 16, if necessary.

[0031] The shaft 12 is not particularly limited as long as it is electrically conductive. Specific 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, a primer, or the like, as needed. That is, the elastic layer 14 may be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive, primer, or the like may be made electrically conductive as needed.

[0032] In Figures 2 and 3, the x direction is the axial direction of the charge roll 10, and the y direction is the circumferential direction of the charge roll 10. As shown in Figures 2 and 3, one or more grooves 22 extending in a direction within ±46° with respect to the circumferential direction y are regularly formed in the axial direction x on the outer peripheral surface of the elastic layer 14. More specifically, two or more grooves 22 extending in a direction at 0° with respect to the circumferential direction y (extending along the circumferential direction) are regularly formed in the axial direction x on the outer peripheral surface of the elastic layer 14 in Figure 2. In Figure 2, each groove 22 is connected around the circumference and is not spirally shaped. In Figure 3, one or more grooves 22 extending in a direction other than 0° with respect to the circumferential direction y within ±46° (direction θ) are regularly formed in the axial direction x. In Figure 3, the grooves 22 that are connected around the circumference are not spirally shaped, and there are two or more grooves 22. In FIG. 3, the spiral groove 22 is connected as a whole and is therefore one. Regularly forming the grooves 22 at regular intervals in the axial direction x means that the grooves 22 are formed at regular intervals in the axial direction x. The portions of the outer peripheral surface of the elastic layer 14 other than the grooves 22 are flat surfaces 24. As shown in FIG. 4, the flat surfaces 24 protrude radially outward from the bottom surfaces 221 of the grooves 22. The bottom surfaces 221 of the grooves 22, which are positioned relatively radially inward, and the flat surfaces 24, which are positioned relatively radially outward, form surface irregularities on the outer peripheral surface of the elastic layer 14. One or more grooves 22 extending along a direction within ±46° of the circumferential direction y are regularly formed in the axial direction x, resulting in uniform surface irregularities on the outer peripheral surface of the elastic layer 14. A direction within ±46° of the circumferential direction y refers to a direction in the range of −46° to 0° and 0° to 46° with respect to the circumferential direction y.

[0033] The reason why the extension direction of the grooves 22 is within ±46° with respect to the circumferential direction y is that if the angle of the extension direction of the grooves 22 with respect to the circumferential direction y becomes large (exceeding 46° in absolute value), the edges of the convex portions formed by the grooves 22 are more likely to be subjected to shear stress in the direction of rotation of the charging roll 10 (circumferential direction y) when the photosensitive member and the charging roll 10 rub against each other, and the convex portions are more likely to wear. When the convex portions wear, the difference in charging properties between the convex and concave portions increases during durability, making streaked images more likely to occur. As the lifespan of electrophotographic devices increases and longer durability is also required of the charging roll 10, the impact of this wear becomes significant.

[0034] If the extension direction of the grooves 22 is within ±46° with respect to the circumferential direction y, when either the width of the convex portions formed by the grooves 22 or the width of the grooves 22 (groove width) becomes too large, the difference in charge between the convex portions and the grooves 22 within one circumference of the charging roll 10 becomes more visible, which is likely to affect charging unevenness. For this reason, the ratio of the width of the convex portions to the width of the grooves 22 (groove width) is set within a specific range, thereby suppressing the effects of charging unevenness.

[0035] The groove width w1 of the groove portions 22 is 4 μm or more and 30 μm or less. The groove depth d of the groove portions 22 is 2 μm or more and 12 μm or less. The width w2 of the flat portions 24 is 4 μm or more and 30 μm or less. There is a specific relationship between the angle θ of the extension direction of the groove portions 22 with respect to the circumferential direction y and the ratio w2 / w1 of the groove width w1 of the groove portions 22 to the width w2 of the flat portions 24.

[0036] If the groove width w1 of the groove portion 22 is less than 4 μm, the groove width w1 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, resulting in horizontal streaks due to insufficient charging. If roughness-forming particles 18 that fit within the small groove width w1 are used, it will be impossible to form a roughness that ensures sufficient discharge. From this perspective, the groove width w1 of the groove portion 22 should be set to 5 μm or more, 10 μm or more, or 20 μm or more, depending on the average particle diameter of the roughness-forming particles 18 used.

[0037] If the groove width w1 of the groove portion 22 exceeds 30 μm, image defects (vertical stripes) are likely to occur, as described above. Furthermore, if the groove width w1 of the groove portion 22 exceeds 30 μm, the groove width w1 is too large, making it impossible to uniformly arrange the roughness-forming particles 18 in the groove portion 22. If roughness-forming particles 18 of a size that matches the large groove width w1 are used, the convex portions resulting from the roughness-forming particles 18 become too large, resulting in excessive surface roughness and making it impossible to achieve an appropriate surface roughness. This makes it impossible to obtain uniform discharge characteristics. Furthermore, if the groove width w1 is too large, the binder polymer 16a covering the roughness-forming particles 18 on the groove portions 22 is more likely to come into contact with the photoreceptor, which causes wear not only of the binder polymer 16a covering the roughness-forming particles 18b on the flat portions 24 and the roughness-forming particles 18b underneath, but also of the binder polymer 16a covering the roughness-forming particles 18a on the groove portions 22 and the roughness-forming particles 18a underneath, resulting in wear of the entire surface of the surface layer 16 during durability testing and unevenness in the image. From this perspective, the groove width w1 of the groove portions 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 grooves 22 is less than 2 μm, the difference between the surface roughness Rz caused by the roughness-forming particles 18b on the flat surface 24 and the surface roughness Rz caused by the roughness-forming particles 18a on the grooves 22 will be too small, resulting in horizontal streaks due to insufficient charging. If small roughness-forming particles 18 are used to match the small groove depth d, it will be impossible to form a roughness that ensures sufficient discharge. From this perspective, the groove depth d of the grooves 22 should be set to 3 μm or more, 5 μm or more, 10 μm or more, etc., depending on the average particle diameter of the roughness-forming particles 18 used.

[0039] If the groove depth d of the grooves 22 exceeds 12 μm, the groove depth d is too large, making it impossible for the roughness-forming particles 18 disposed in the grooves 22 to form a surface roughness on the grooves 22. This results in black spots (fog) on ​​the image after endurance testing. Furthermore, if the groove depth d of the grooves 22 exceeds 12 μm, the groove depth d is too large, resulting in a large difference in surface roughness Rz between the roughness-forming particles 18b on the flat surfaces 24 and the roughness-forming particles 18a on the grooves 22. This results in a large difference in charging properties, making image defects (vertical stripes) more likely to occur. If large roughness-forming particles 18 are used in accordance with a large groove depth d, the difference in surface roughness Rz between the roughness-forming particles 18b on the flat surfaces 24 and the roughness-forming particles 18a on the grooves 22 becomes too large, making it difficult to discharge. From this viewpoint, the groove depth d of the grooves 22 is preferably set to 10 μm or less, 8 μm or less, etc., in accordance with the average particle size of the roughness-imparting particles 18 used.

[0040] The width w2 of the flat portion 24 is set to 4 μm or more and 30 μm or less, the same as the groove width w1 of the groove portion 22, in order to ensure uniform charging by having the same width range as the groove width w1 of the groove portion 22. The width w2 of the flat portion 24 is preferably set to match the groove width w1 of the groove portion 22, more preferably 5 μm or more, 10 μm or more, 20 μm or more, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, etc.

[0041] The relationship between the angle θ of the extension direction of the groove portions 22 and the width ratio w2 / w1 satisfies the following relationships (A) to (C): The following relationships suppress the occurrence of streaky images due to wear of the convex portions (flat portions 24) formed by the groove portions 22, and charging unevenness due to the charge difference between the convex portions and the groove portions 22 within one rotation of the charging roll 10. (A) When -5°≦θ≦+5°, 0.7≦w2 / w1≦1.3 (B) When -22°≦θ<-5° or +5°<θ≦+22°, 1.0≦w2 / w1≦2.0 (C) When -46°≦θ<-22° or +22°<θ≦+46°, 1.2≦w2 / w1≦2.6

[0042] The angle of the groove portions 22 is calculated by photographing the outer peripheral surface of the elastic layer 14 with a laser microscope and averaging the angles of 100 groove portions observed in the photographed image relative to the circumferential direction y. The groove width w1 of the groove portions 22 is calculated by photographing the outer peripheral surface of the elastic layer 14 with a laser microscope and averaging the groove widths w1 of 100 groove portions 22 observed in the photographed image. The groove depth d of the groove portions 22 is calculated by photographing the radial cross section of the elastic layer 14 with a laser microscope and averaging the groove depths d of 100 groove portions 22 observed in the photographed image. The groove width w2 of the flat portion 24 is calculated by photographing the outer peripheral surface of the elastic layer 14 with a laser microscope and averaging the widths w2 of 100 flat portion 24 observed in the photographed image.

[0043] The elastic layer 14 contains a crosslinked rubber. The elastic layer 14 is formed from a conductive rubber composition containing an uncrosslinked rubber. The crosslinked rubber is obtained by crosslinking the uncrosslinked rubber. The uncrosslinked rubber may be a polar rubber or a non-polar rubber.

[0044] Polar rubber is a rubber having a polar group, and examples of the polar group include a chloro group, a nitrile group, a carboxyl group, and an epoxy group. Specific 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.

[0045] Examples of hydrin rubbers 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).

[0046] Examples of urethane rubber include polyether-type urethane rubber having an ether bond in the molecule. Polyether-type urethane rubber can be produced by reacting a polyether having hydroxyl groups at both ends with a diisocyanate. Examples of polyethers include, but are not limited to, polyethylene glycol and polypropylene glycol. Examples of diisocyanates include, but are not limited to, tolylene diisocyanate and diphenylmethane diisocyanate.

[0047] Examples of non-polar rubbers include silicone rubber (Q), isoprene rubber (IR), natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), etc. Among non-polar rubbers, silicone rubber is more preferred from the viewpoints of low hardness and resistance to settling (excellent elastic recovery).

[0048] The elastic layer 14 preferably contains one or more of isoprene rubber, nitrile rubber, and hydrin rubber. When the elastic layer 14 contains one or more of isoprene rubber, nitrile rubber, and hydrin rubber, the compression set is small, and the occurrence of streak images corresponding to deformed portions when the charging roll 10 is set is suppressed.

[0049] Examples of the crosslinking agent include a sulfur crosslinking agent, a peroxide crosslinking agent, and a dechlorination crosslinking agent. These crosslinking agents may be used alone or in combination of two or more.

[0050] Examples of the sulfur crosslinking agent include conventionally known sulfur crosslinking agents such as powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, sulfur chloride, thiuram vulcanization accelerators, and polymeric polysulfides.

[0051] Examples of the peroxide crosslinking agent include conventionally known peroxide crosslinking agents such as peroxyketals, dialkyl peroxides, peroxyesters, ketone peroxides, peroxydicarbonates, diacyl peroxides, and hydroperoxides.

[0052] Examples of the dechlorinating crosslinking agent include dithiocarbonate compounds, more specifically, quinoxaline-2,3-dithiocarbonate, 6-methylquinoxaline-2,3-dithiocarbonate, 6-isopropylquinoxaline-2,3-dithiocarbonate, and 5,8-dimethylquinoxaline-2,3-dithiocarbonate.

[0053] The amount of crosslinking agent to be added is preferably within a range of 0.1 to 2 parts by mass, more preferably within a range of 0.3 to 1.8 parts by mass, and even more preferably within a range of 0.5 to 1.5 parts by mass, per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding.

[0054] When a dechlorination crosslinking agent is used as the crosslinking agent, a dechlorination crosslinking accelerator may be used in combination. Examples of the dechlorination crosslinking accelerator include 1,8-diazabicyclo(5,4,0)undecene-7 (hereinafter abbreviated as DBU) or a weak acid salt thereof. The dechlorination crosslinking accelerator may be used in the form of DBU, but from the viewpoint of handling, it is preferable to use it in the form of a weak acid salt thereof. Examples of weak acid salts of DBU include carbonate, stearate, 2-ethylhexyl salt, benzoate, salicylate, 3-hydroxy-2-naphthoate, phenol resin salt, 2-mercaptobenzothiazole salt, and 2-mercaptobenzimidazole salt.

[0055] The content of the dechlorination crosslinking accelerator is preferably within a range of 0.1 to 2 parts by mass, more preferably 0.3 to 1.8 parts by mass, and even more preferably 0.5 to 1.5 parts by mass, per 100 parts by mass of the uncrosslinked rubber, from the viewpoint of preventing bleeding.

[0056] A conductive agent can be blended into the elastic layer 14 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. Various additives may also 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, antifoaming agents, pigments, and mold release agents.

[0057] The elastic layer 14 can be adjusted to a predetermined volume resistivity by adjusting the type of crosslinked rubber, the amount of ionic conductive agent, the amount of electronic conductive agent, etc. 2 ~10 10 Ω·cm, 10 3 ~10 9 Ω·cm, 10 4 ~10 8 It can be set appropriately to the range of Ω·cm.

[0058] The thickness of the elastic layer 14 is not particularly limited, and may be set appropriately within the range of 0.1 to 10 mm depending on the application.

[0059] The surface layer 16 includes a binder polymer 16 a and roughness-imparting particles 18 .

[0060] The binder polymer 16a is a base polymer that constitutes the surface layer 16. Examples of the binder polymer 16a include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, butyral resin (PVB), alkyd resin, polyester resin, fluororubber, fluororesin, a mixture of fluororubber and fluororesin, silicone resin, silicone-grafted acrylic polymer, acrylic-grafted silicone polymer, nitrile rubber, and urethane rubber.

[0061] The binder polymer 16a is preferably either polyurethane or polyamide. When the binder polymer 16a of the surface layer 16 is either polyurethane or polyamide, the binder polymer 16a is made of a material with a high dielectric constant, improving the charging properties of the roll surface. Furthermore, the compression set is small, suppressing the occurrence of streak images corresponding to deformations when the charging roll 10 is set. Polyurethanes include urethane resins, urethane rubbers, and urethane elastomers. Polyamides may also be modified. Examples of modified polyamides include alkoxylated polyamides such as N-methoxymethylated nylon.

[0062] The roughness-forming particles 18 are particles for imparting roughness to the surface of the surface layer 16. In other words, they are particles for imparting irregularities to the surface of the surface layer 16. As shown in FIG. 4 , the roughness-forming particles 18 are arranged on the flat portions 24 and the groove portions 22 of the elastic layer 14. Due to the step between the flat portions 24 of the elastic layer 14 and the bottom surfaces 221 of the groove portions 22, the roughness-forming particles 18b on the flat portions 24 (the roughness-forming particles 18b arranged on the flat portions 24) and the roughness-forming particles 18a on the groove portions 22 (the roughness-forming particles 18a arranged on the groove portions 22) have different degrees of radial outward protrusion, even though they have the same particle diameter. Due to the step between the flat portions 24 of the elastic layer 14 and the bottom surfaces 221 of the groove portions 22, the roughness-forming particles 18b on the flat portions 24 protrude radially outward more than the roughness-forming particles 18a on the groove portions 22.

[0063] The convex portions caused by the roughness-forming particles 18b on the flat portion 24, which protrude radially outward, are the portions that come into contact with the photosensitive member, while the convex portions caused by the roughness-forming particles 18a on the grooves 22, which are located further inward in the radial direction, are the portions that do not come into contact with the photosensitive member. The convex portions caused by the roughness-forming particles 18a on the grooves 22 serve as starting points for discharge. The surface layer 16 contains the roughness-forming particles 18b on the flat portion 24, ensuring an appropriate discharge space between the photosensitive member and the charging roll 10. The surface layer 16 also contains the roughness-forming particles 18a on the grooves 22, ensuring starting points for discharge. In this way, the surface irregularities of the surface layer 16 increase the discharge space between the photosensitive member and the charging roll 10, promoting discharge. This improves charging performance and reduces image defects such as horizontal streaks and unevenness. In the charging roll 10 according to the present invention, there is a step between the flat portion 24 of the elastic layer 14 and the bottom surface 221 of the groove portion 22, so that even if the roughness-forming particles 18 contained in the surface layer 16 have the same particle diameter, it is possible to easily form an appropriate discharge space and a discharge starting point between the photosensitive member and the charging roll 10.

[0064] The surface roughness Rz of the surface layer 16 in the region M above the groove portion 22 is preferably 2 μm or more and 16 μm or less. The surface roughness Rz of the entire surface layer 16 is preferably 5 μm or more and 26 μm or less. This makes it possible to form an appropriate discharge space and discharge starting point between the photoreceptor and the charging roll 10.

[0065] If the surface roughness Rz of the surface layer 16 in the region M above the grooves 22 is less than 2 μm, the surface roughness Rz is too small, resulting in insufficient discharge starting points, and insufficient discharge, which may result in insufficient suppression of black spots (fog) in the image after durability testing. From this perspective, 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 above the grooves 22 exceeds 16 μm, the surface roughness Rz of the entire surface layer 16 becomes too large, making discharge difficult, and may result in insufficient suppression of black spots (fog) in the image after durability testing. From this perspective, the surface roughness Rz is more preferably 15 μm or less, and even more preferably 12 μm or less.

[0066] If the surface roughness Rz of the entire surface layer 16 is less than 5 μm, the surface roughness Rz is too small, resulting in insufficient discharge starting points, and insufficient discharge, which may result in insufficient suppression of black spots (fog) in images after durability testing. From this perspective, 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 surface roughness Rz of the entire surface layer 16 exceeds 26 μm, the surface roughness Rz becomes too large, making discharge difficult, and may result in insufficient suppression of black spots (fog) in images after durability testing. From this perspective, the surface roughness Rz is more preferably 25 μm or less, and even more preferably 20 μm or less.

[0067] The surface roughness Rz is a 10-point average roughness, and is the average value of values ​​measured at any five 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 (for example, a Keyence VK-9510). In an image taken at 400x magnification, the value calculated in the surface roughness mode of an 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 portion 22 can be measured by observation using a laser microscope (for example, a Keyence VK-9510). In the captured image, the value calculated in the surface roughness mode of an analysis program (program name: KEYENCE VK Analyzer analysis application) can be used as the surface roughness Rz of the entire surface layer 16. 2 The value calculated by selecting the above formula can be used as the surface roughness Rz of the surface layer 16 in the region above the groove portion 22.

[0068] The surface roughness Rz of the surface layer 16 can be adjusted by adjusting the groove width w1 and groove depth d of the groove portion 22, the width w2 of the flat portion 24, the particle diameter of the roughness-forming particles 18, the thickness of the binder polymer 16a, etc.

[0069] The roughness-forming particles 18 are particles such as resin particles or inorganic particles that are used as roughness-forming particles 18 added to the surface layer 16 of the charging roll. There are no particular limitations on the material of the roughness-forming particles 18. The material of the roughness-forming particles 18 is preferably any one of polyurethane, polyamide, and acrylic resin. When the material of the roughness-forming particles 18 is any one of polyurethane, polyamide, and acrylic resin, the roughness-forming particles 18 are made of a material with a high dielectric constant, which improves the charging properties of the roll surface.

[0070] The size of the roughness-forming particles 18 is not particularly limited, but from the viewpoint of forming appropriate unevenness and improving the uniformity of discharge characteristics, an average particle diameter of 3 μm to 30 μm is preferable. An average particle diameter of 5 μm to 30 μm is more preferable, and an average particle diameter of 10 μm to 30 μm is even more preferable. The average particle diameter of the roughness-forming particles 18 is expressed as the average of 20 arbitrary points when the surface of the surface layer 16 is observed with a laser microscope, and the diameter of the roughness-forming particles 18 visible during surface observation is defined as the particle size.

[0071] The roughness-imparting particles 18 may be composed of one type of particle, or two or more types of particles. First, "one type of particle" refers to particles made of the same material. "Same material" refers to polymer particles that are broadly classified as "same" within a range, such as polyurethane, or particles that have the same monomer composition within a narrow range. More preferably, particles that have the same monomer composition within a narrow range are considered to be the same. Second, "one type of particle" refers to particles with the same particle diameter. "Same particle diameter" refers to particles that are uniform in diameter. For example, the diameter of the roughness-imparting particles 18 is measured at 50 random locations, and the average is μ, the deviation is σ, and μ / σ is 4.97 or less. The diameter of the roughness-imparting particles 18 can be measured by observing the particle diameter using a laser microscope (such as Keyence's "VK-9510").

[0072] The roughness-forming particles 18 are preferably composed of 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 consideration the differences in the effects on discharge characteristics due to the material and particle size of the roughness-forming particles 18. If the roughness-forming particles 18 are composed of one type of particle in terms of material and particle size, it is easy to adjust the thickness of the binder polymer 16a covering the roughness-forming particles 18. This improves the uniformity of the discharge characteristics. Furthermore, if two types of particles with significantly different particle sizes are included, the particles of different sizes tend to aggregate, which reduces dispersibility. If the roughness-forming particles 18 are composed of one type of particle in terms of particle size, it is easy to control the aggregation of the roughness-forming particles 18, thereby improving the uniformity of the surface roughness. Furthermore, if the roughness-forming particles 18 are composed of one type of particle in terms of particle diameter, the uneven shape of the elastic layer 14 is easily reflected in the surface unevenness of the charging roll, making it easy to control the surface unevenness of the charging roll.

[0073] In the surface layer 16, the binder polymer 16a preferably has a predetermined thickness. The thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portions 22 is preferably thicker than the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portions 24. This makes it possible to adjust the amount of discharge on the roughness-forming particles 18 on the groove portions 22 to be the same as the amount of discharge on the roughness-forming particles 18 on the flat portions 24, thereby improving the uniformity of the discharge characteristics. This makes it possible to suppress the occurrence of black dot images. This is because the portions of the flat surface 24 where the roughness-forming particles 18 are present are grounded to the photosensitive body, and therefore have a lower discharge amount than the portions of the grooves 22 where the roughness-forming particles 18 are present. Therefore, in order to make the discharge amount the same at each position, it is necessary to make the film thickness of the portions of the flat surface 24 where the roughness-forming particles 18 are present thinner than the portions of the grooves 22 where the roughness-forming particles 18 are present, thereby increasing the electrostatic capacitance and increasing the amount of charge on the surface.

[0074] The difference (t1-t2) between the thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portions 22 and the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portions 24 is preferably 4 μm or more and 16 μm or less. When the 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 portions 24 becomes relatively large, thereby widening the range of environments in which black dots do not occur. From this perspective, the thickness difference (t1-t2) is more preferably 5 μm or more, and even more preferably 6 μm or more. Furthermore, when the thickness difference (t1-t2) is 16 μm or less, an appropriate thickness is maintained, making it easier to form appropriate unevenness. This improves the uniformity of the discharge characteristics. From this perspective, the thickness difference (t1-t2) is more preferably 15 μm or less, and even more preferably 12 μm or less.

[0075] The thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the grooves 22 is preferably 5 μm or more and 20 μm or less. When the thickness t1 is 5 μm or more, the resistance of the discharge points 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 grooves 22, and a discharge region can be secured. From this viewpoint, the thickness t1 is more preferably 18 μm or less, and even more preferably 15 μm or less.

[0076] The thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat surface 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 of the discharge points 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 region 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.

[0077] The thicknesses t1 and t2 of the binder polymer 16a can be measured by observing the cross section using a laser microscope (such as a Keyence VK-9510). For example, the thickness of the binder polymer 16a can be measured at five arbitrary positions on the binder polymer 16a covering the roughness-forming particles 18 on the groove portion 22, and t1 can be expressed as the average of the measured thicknesses. Furthermore, the thickness of the binder polymer 16a can be measured at five arbitrary positions on the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24, and t2 can be expressed as the average of the measured thicknesses.

[0078] To make the thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the groove portions 22 thicker than the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portions 24, it is advisable to utilize both the instability of the surface energy of the roughness-forming particles 18 on the groove portions 22 and the instability of the energy of the base rubber of the groove portions 22. In other words, it is advisable to utilize the fact that the roughness-forming particles 18 on the groove portions 22 tend to gather and stabilize a large amount of binder polymer 16a, and the fact that the base rubber of the groove portions 22 tend to gather and stabilize a large amount of binder polymer 16a.

[0079] The content of the roughness-forming particles 18 in the surface layer 16 is not particularly limited, but from the viewpoint of improving the dispersibility of the roughness-forming particles 18 and making it easier to ensure uniform charging, the content is preferably 3 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the binder polymer 16a in the surface layer 16. More preferably, the content is 5 parts by mass or more and 30 parts by mass or less.

[0080] A conductive agent can be blended into the surface layer 16 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. Furthermore, various additives may be appropriately added to the surface layer 16 as needed. Examples of additives include plasticizers, leveling agents, fillers, vulcanization accelerators, processing aids, and mold release agents.

[0081] The volume resistivity of the surface layer 16 is preferably set to a semiconductive region from the viewpoint of electrostatic chargeability, etc. Specifically, for example, 1.0×10 7 ~1.0×10 10 It is recommended to set it within the range of Ω·cm. Volume resistivity can be measured in accordance with JIS K6911.

[0082] The elastic layer 14 can be formed, for example, as follows: First, the shaft 12 is placed coaxially in the hollow portion of a roll molding die, and an uncrosslinked conductive rubber composition is injected and heated and cured (crosslinked), and then the composition is demolded, or the uncrosslinked conductive rubber composition is extruded onto the surface of the shaft 12, thereby forming the elastic layer 14 on the outer periphery of the shaft 12.

[0083] Methods for forming the grooves 22 on the outer peripheral surface of the elastic layer 14 include polishing and molding. Either method can form regular grooves 22 on the outer peripheral surface of the elastic layer 14. When polishing, a plunge method is preferably used to form circumferential grooves 22. A traverse method is preferably used to form spiral grooves 22. The traverse method, for example, rotates a roll having the elastic layer 14 at a constant speed around its axis while moving a grindstone in contact with the outer peripheral surface of the elastic layer 14 in one axial direction at a constant speed, thereby forming regular spiral grooves 22 on the outer peripheral surface of the elastic layer 14 along the axial direction.

[0084] The surface layer 16 can be formed by applying a material for forming the surface layer 16 to the outer peripheral surface of the elastic layer 14 and then performing a drying process as appropriate. The material for forming the surface layer 16 may contain a diluent solvent. Examples of the diluent solvent 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.

[0085] With the charging roll 10 configured as described above, one or more grooves 22 extending in a direction within ±46° of the circumferential direction are formed regularly in the axial direction on the outer peripheral surface of the elastic layer 14, the groove width w1 and groove depth d of the grooves 22 and the width w2 of the flat portions 24 are within specific ranges, and there is a specific relationship between the angle θ of the extension direction of the grooves 22 with respect to the circumferential direction and the ratio w2 / w1 of the groove width w1 of the grooves 22 to the width w2 of the flat portions 24. This allows the roughness-forming particles 18 to be uniformly and balanced on both the flat portions 24 and the grooves 22 of the elastic layer 14, forming an appropriate surface roughness and creating an appropriate difference in roughness between the flat portions 24 and the grooves 22 of the elastic layer 14, making it possible to adjust the discharge amount appropriately. This results in excellent uniformity in the discharge characteristics. Furthermore, the amount of discharge can be made uniform by making the thickness of the binder polymer 16a covering the roughness-forming particles 18 on the groove portions 22 thicker than the thickness of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24. This results in excellent uniformity of the discharge characteristics.

[0086] The charge roll 10 according to the present invention does not form surface irregularities on the charge roll by disposing two types of roughness-forming particles, one large and one small, of different sizes on the outer peripheral surface of the generally flat elastic layer, but rather forms a predetermined uneven shape on the outer peripheral surface of the elastic layer 14 and then disposes relatively uniform roughness-forming particles 18 of a predetermined size thereon to form surface irregularities on the charge roll 10. The roughness-forming particles 18 are disposed not only on the grooves 22 of the elastic layer 14 but also on the flat surface 24. As a result, the steps of the surface irregularities of the elastic layer 14 appear as surface irregularities on the charge roll 10. If the roughness-forming particles 18 are relatively uniform, the surface irregularities of the elastic layer 14 are likely to be reflected on the surface of the charge roll 10. To dispose the roughness-forming particles 18 not only on the grooves 22 of the elastic layer 14 but also on the flat surface 24, the groove width w1 of the grooves 22 should not be too large or too small relative to the size of the roughness-forming particles 18. By setting the groove width w1 of the groove portion 22 to a predetermined size, the roughness-forming particles 18 can be reliably and uniformly arranged not only on the groove portion 22 but also on the flat portion 24. Similarly, the width w2 of the flat portion 24 should not be too large or too small. A predetermined area ratio is desirable to ensure uniform arrangement of the roughness-forming particles 18 on the flat portion 24. Furthermore, in the present invention, a predetermined uneven shape is formed on the outer peripheral surface of the elastic layer 14, which allows for a larger surface area of ​​the outer peripheral surface of the elastic layer compared to an outer peripheral surface of an elastic layer that is generally flat. This improves the ease of discharge. This effect is exerted even when the groove portion 22 of the elastic layer 14 is filled with the binder polymer 16a of the surface layer 16. This effect is a previously unknown finding. This point also provides an advantage of the configuration of the present invention.

[0087] The extension direction of the grooves 22 is within ±46° with respect to the circumferential direction y. As a result, when the photoconductor and the charging roll 10 rub against each other, the edges (edges) of the convex portions formed by the grooves 22 are less likely to be subjected to shear stress in the rotational direction (circumferential direction y) of the charging roll 10, reducing wear on the convex portions. During durability testing, the difference in chargeability between the convex and concave portions due to wear on the convex portions is kept small, thereby reducing the occurrence of streaky images. In this case, if either the width of the convex portions formed by the grooves 22 or the width (groove width) of the grooves 22 becomes too large, the charge difference between the convex portions and the grooves 22 within one rotation of the charging roll 10 becomes more visible, which can easily affect charging unevenness. However, because the ratio of the width of the convex portions to the width (groove width) of the grooves 22 is within a specific range, the occurrence of charging unevenness is reduced.

[0088] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0089] For example, in the above embodiment, one or more grooves 22 extending in a direction within ±46° with respect to the circumferential direction y are regularly formed in the axial direction x on the outer peripheral surface of the elastic layer 14. However, as shown in Fig. 5, the outer peripheral surface of the elastic layer 14 may be formed with a mesh-like groove in which grooves 22 (22a) extending in a direction within +46° with respect to the circumferential direction y intersect with grooves 22 (22b) extending in a direction within -46° with respect to the circumferential direction. This improves the uniformity of the surface roughness and the uniformity of the discharge characteristics.

[0090] The spiral groove portion 22 may be a groove portion having only groove portions that spiral regularly in a left-handed manner along the axial direction, or a groove portion having only groove portions that spiral regularly in a right-handed manner along the axial direction, or a mesh-like groove portion formed by intersecting groove portions that spiral regularly in a right-handed manner along the axial direction and groove portions that spiral regularly in a left-handed manner along the axial direction.

[0091] The spiral intersecting mesh-like grooves can be formed, for example, by moving the grinding wheel in one axial direction and then in the other axial direction on the outer surface of the elastic layer 14, in which grooves 22a that regularly spiral in a right-handed manner along the axial direction intersect with grooves 22b that regularly spiral in a left-handed manner along the axial direction. [Example]

[0092] The present invention will be described in detail below using examples and comparative examples.

[0093] Example 1 <Preparation of Conductive Rubber Composition> A conductive rubber composition was prepared by compounding 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 a thiazole vulcanization accelerator, 0.5 parts by mass of a thiuram vulcanization accelerator, and 50 parts by mass of heavy calcium carbonate, and kneading the mixture for 10 minutes using an internal mixer adjusted to a temperature of 50°C.

[0094] The following materials were prepared as materials for the conductive rubber composition. Isoprene rubber (IR): JSR "JSR IR2200" Carbon black: Cabot Japan "Show Black N762" Zinc oxide: Sakai Chemical Industry's "Zinc oxide type 2" Stearic acid: "Sakura Stearic Acid" manufactured by Nippon Oil & Fats Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Thiazole vulcanization accelerator: "Noccela DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Thiamin-based vulcanization accelerator: "Noccela TRA" manufactured by Ouchi Shinko Chemical Industry Heavy calcium carbonate: "Whiten B" manufactured by Shiraishi Calcium, average particle size 3.6 μm

[0095] <Preparation of Elastic Layer> A core (8 mm in diameter) was placed in a pipe-shaped mold, and the composition was poured into the mold. The mold was heated at 180°C for 30 minutes, cooled, and demolded. A 1.9 mm-thick elastic layer made of a conductive rubber elastic material was molded around the core. A roll bearing the elastic layer was then rotated at a constant speed around its axis. A grindstone in contact with the outer surface of the elastic layer was then moved at a constant speed in one axial direction. The grindstone in contact with the outer surface of the elastic layer was then moved at a constant speed in the other axial direction. This resulted in the formation of a mesh-like groove pattern on the outer surface of the elastic layer, consisting of a regular right-handed spiral groove along the axial direction and a regular left-handed spiral groove along the axial direction. The conditions were as follows: Roll rotation speed: 500 rpm Grinding wheel speed: 0.05 m / s Grinding wheel peripheral speed: 72 m / s Grit size: #1500 Groove pitch: 0.3 mm

[0096] <Creating the surface layer> A liquid composition for forming a surface layer was prepared by blending the roughness-imparting particles, binder polymer, and carbon black as a conductive agent to obtain 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 periphery of the elastic layer. In this way, the charging roll of Example 1 was produced.

[0097] Example 2 <Preparation of Conductive Rubber Composition> A conductive rubber composition was prepared by compounding 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 with a stirrer.

[0098] The following materials were prepared as materials for the conductive rubber composition. NBR: Nipol 1041 manufactured by Nippon Zeon Stearic acid: NOF's "Sakura Stearic Acid" Zinc oxide: Sakai Chemical Industry's "Zinc oxide type 2" Hydrotalcite: Kyowa Chemical Industry's "DHT4A" Peroxide crosslinking agent: NOF's "Perkmyl D40" Carbon: Ketjenblack International "Ketjenblack EC300J" <Preparation of Elastic Layer> The heating temperature was changed to 170°C, and an elastic layer made of a conductive rubber elastic material was molded in the same manner as in Example 1. Next, in the same manner as in Example 1, a mesh-like groove was formed on the outer peripheral surface of the elastic layer by polishing.

[0099] <Creating the surface layer> A surface layer having a thickness of 1.0 μm was formed on the outer periphery of the elastic layer in the same manner as in Example 1. In this way, a charging roll of Example 2 was produced.

[0100] Example 3 <Preparation of Conductive Rubber Composition> To 100 parts by mass of hydrin rubber, 5 parts by mass of vulcanization aid, 10 parts by mass of carbon, 0.5 parts by mass of vulcanization accelerator, 2 parts by mass of sulfur, and 50 parts by mass of filler were added, and these were stirred and mixed with a stirrer to prepare a conductive rubber composition.

[0101] The following materials were prepared as materials for the conductive rubber composition. Hydrin rubber (ECO, Zeon Corporation "Hydrin H1100") Vulcanization aid (zinc oxide, Mitsui Metals "Zinc Oxide Type 2") Carbon fiber (Ketjenblack International "Ketjenblack EC300J") Vulcanization accelerator (2-mercaptobenzothiazole, "Noccela MP" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Sulfur (Tsurumi Chemical Co., Ltd., "Sulfax PTC") Filler (calcium carbonate, Shiraishi Kogyo's "Hakuenka CC") <Preparation of Elastic Layer> An elastic layer made of a conductive rubber elastic body was molded in the same manner as in Example 1. Next, in the same manner as in Example 1, a mesh-like groove was formed on the outer peripheral surface of the elastic layer by polishing.

[0102] <Creating the surface layer> A surface layer having a thickness of 1.0 μm was formed on the outer periphery of the elastic layer in the same manner as in Example 1. In this way, a charging roll of Example 3 was produced.

[0103] (Examples 4, 5, 7, and 8) Charging rolls of Examples 4, 5, 7, and 8 were produced in the same manner as in Example 3, except that the surface layer material was changed.

[0104] Example 6 A charging roll of Example 6 was produced in the same manner as in Example 3, except that grooves were formed on the outer peripheral surface of the elastic layer in a regular, left-handed spiral shape along the axial direction.

[0105] Example 9 The charging roll of Example 9 was produced in the same manner as in Example 4, except that the grooves were formed in the circumferential direction.

[0106] Example 10 A charging roll of Example 10 was produced in the same manner as in Example 4, except that the angle at which the grooves were formed was changed.

[0107] Example 11 A charging roll of Example 11 was produced in the same manner as in Example 6, except that the angle at which the grooves were formed was changed.

[0108] (Examples 12 to 15) Charging rolls were produced in the same manner as in Examples 9 and 10, except that the ratio of the groove width of the groove portion to the width of the flat portion (w2 / w1) was changed.

[0109] (Examples 16 to 23) Charging rolls were produced in the same manner as in Example 10, except that the ratio of the groove width to the width of the flat portion (w2 / w1) and the angle at which the grooves were formed were changed.

[0110] (Comparative Examples 1 to 6) A charging roll was produced in the same manner as in Example 4, except that the groove width of the grooves, the groove depth of the grooves, or the width of the flat portion was changed.

[0111] (Comparative Examples 7 to 14) Charging rolls were produced in the same manner as in Examples 16 to 23, except that the ratio of the groove width of the groove portion to the width of the flat portion (w2 / w1) was changed.

[0112] (Comparative Example 15) A charging roll was produced in the same manner as in Example 23, except that the angle at which the grooves were formed was changed.

[0113] The materials used for the surface layer are as follows: Binder polymer (PA): Lead City "Fine Resin FR-101" Binder polymer (PU): Negami Industrial Co., Ltd. "ART Resin UN-333" Roughness forming particles (PU): Negami Industrial Co., Ltd. "Art Pearl C-1000 Transparent" average particle diameter 3 μm Roughness forming particles (PU): Negami Industrial Co., Ltd. "Art Pearl C-200 transparent graded product" average particle diameter 30 μm Roughness forming particles (PU): Negami Industrial Co., Ltd. "Art Pearl C-300 Transparent" average particle diameter 22 μm Roughness forming particles (PU): Negami Industrial Co., Ltd. "Art Pearl C-300 transparent graded product" average particle diameter 20 μm Roughness forming particles (PU): Negami Industrial Co., Ltd. "Art Pearl C-400 Transparent" average particle size 15 μm Roughness forming particles (PU): Negami Industrial Co., Ltd. "Art Pearl C-600 Transparent" average particle size 11 μm Roughness forming particles (PA): Toray "TR-2" average particle diameter 22 μm Roughness forming particles (PMMA): Negami Industrial Co., Ltd. "Art Pearl GR-200 Transparent" average particle diameter 20 μm Carbon black: Tokai Carbon "Seast 9H"

[0114] The surface and cross-section of the polished elastic layer of the charging roll were analyzed, and the groove width, groove depth, width of the flat surface, and groove angle were calculated. The surface roughness Rz and the thickness of the binder polymer in the surface layer were also measured for the produced charging roll. The following evaluations were also performed.

[0115] (Uneven shape of elastic layer) The groove width of the groove portion was calculated by photographing the outer peripheral surface of the elastic layer with a laser microscope and averaging the groove widths of 100 arbitrary groove portions observed in the photographed image. The groove depth of the groove portion was calculated by photographing the radial cross section of the elastic layer with a laser microscope and averaging the groove depths of 100 arbitrary groove portions observed in the photographed image. The width of the flat portion was calculated by photographing the outer peripheral surface of the elastic layer with a laser microscope and averaging the widths of 100 arbitrary flat portions observed in the photographed image. The groove angle was calculated by photographing the outer peripheral surface of the elastic layer with a laser microscope and averaging the angle relative to the circumferential direction of 100 arbitrary groove portions observed in the photographed image.

[0116] (surface roughness Rz) The surface roughness Rz is the 10-point average roughness, and is the average value of values ​​measured at any five locations in accordance with JIS B0601 (1994). The surface roughness Rz of the entire surface layer was measured by observation using a laser microscope (Keyence VK-9510). The value calculated in the surface roughness mode of the analysis program (program name: KEYENCE VK Analyzer analysis application) for an image taken at 400x magnification was taken as the surface roughness Rz of the entire surface layer. The surface roughness Rz of the surface layer in the area above the grooves was measured by observation using a laser microscope (Keyence VK-9510). The surface roughness Rz of the image taken was measured in the surface roughness mode of the analysis program (program name: KEYENCE VK Analyzer analysis application) for an area 0.01 mm from the grooves. 2 The calculated value was used as the surface roughness Rz of the groove.

[0117] (binder thickness) Measurements were made 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-imparting particles on the grooves (binder thickness t1) and the thickness of the binder polymer covering the roughness-imparting particles on the flat surfaces (binder thickness t2) were measured. Each was measured at five randomly selected locations, and the average was used to represent the thickness.

[0118] (Image rating: uneven) The produced charging roll was attached to the unit (black) of an actual machine (RICOH "IM C8000"), and images were printed at 25% density halftone in an environment of 10°C x 10% RH, and evaluation was carried out after 1 million sheets were printed. Images with no unevenness were rated as good (◯), and images with unevenness were rated as poor (×).

[0119] (Image rating: horizontal streaks) The produced charging roll was attached to the unit (black) of an actual machine (RICOH "IM C8000"), and images were printed at 25% density halftone in an environment of 10°C x 10% RH, and an evaluation was carried out after 1 million sheets were printed. Images with no horizontal streaks were rated as particularly good (○), and images with horizontal streaks that appeared and had a significant impact on the image were rated as poor (×).

[0120] (Image evaluation: black spots (fogging)) The produced charging roll was attached to the unit (black) of an actual machine (RICOH "IM C8000"), and images were printed at 25% density halftone in an environment of 10°C x 10% RH, and evaluation was carried out after 1 million sheets were printed. Images with no black spots were rated as good (○), and images with even one spot were rated as bad (×).

[0121] (Image rating: vertical streaks) The produced charging roll was attached to the unit (black) of an actual machine (RICOH "IM C8000"), and images were printed at 25% density halftone in an environment of 10°C x 10% RH, and evaluation was carried out after 1 million sheets were printed. Images with no vertical streaks were rated as good (○), and images with vertical streaks that appeared and had a significant effect on the image were rated as poor (×).

[0122] (Image evaluation: lines that follow the uneven surface) The produced charging roll was attached to the unit (black) of an actual machine (RICOH "IM C8000"), and images were printed at 25% density halftone in an environment of 10°C x 10% RH, and an evaluation was carried out after 1 million sheets were printed. Images that had no streaks following the uneven shape were rated as good (○), and images that had streaks following the uneven shape and were significantly affected by the image were rated as poor (×).

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] [Table 4]

[0127] In Comparative Example 1, the groove width was 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 surface and the surface roughness caused by the roughness-forming particles on the grooves was small, resulting in horizontal streaks due to insufficient charging. Using roughness-forming particles large enough to fit within the small groove width would prevent the formation of a roughness sufficient to ensure sufficient discharge. In Comparative Example 2, the groove width was too large, making the difference in chargeability between the concave and convex portions of the charging roll surface more likely to appear in the image, resulting in vertical streaks. Furthermore, the groove width was too large, preventing the roughness-forming particles from being uniformly distributed in the grooves. As a result, unevenness occurred after durability testing. Using roughness-forming particles large enough to fit the large groove width would result in the convex portions caused by the roughness-forming particles becoming too large, resulting in excessive surface roughness and making it impossible to achieve an appropriate surface roughness. This resulted in insufficient discharge characteristics. In addition, in Comparative Example 2, the groove width is too large, so the binder polymer covering the roughness-forming particles on the grooves is more likely to come into contact with the photosensitive member, resulting in wear not only of the binder polymer covering the roughness-forming particles on the flat surface and the roughness-forming particles underneath, but also of the binder polymer covering the roughness-forming particles on the grooves and the roughness-forming particles underneath, resulting in wear of the entire surface of the surface layer during endurance testing and unevenness in the image.

[0128] In Comparative Example 3, the groove depth is too small, so the difference between the surface roughness caused by the roughness-forming particles on the flat portions and the surface roughness caused by the roughness-forming particles on the groove portions is small, resulting in horizontal streaks due to insufficient charging. Note that, if small roughness-forming particles are used in accordance with a small groove depth, a roughness sufficient to ensure sufficient discharge cannot be formed. In Comparative Example 4, the groove depth is too large, so the difference between the surface roughness caused by the roughness-forming particles on the flat portions and the surface roughness caused by the roughness-forming particles on the groove portions becomes too large, resulting in a large difference in charging properties and image defects (vertical streaks). Note that, if large roughness-forming particles are used in accordance with a large groove depth, the difference between the surface roughness caused by the roughness-forming particles on the flat portions and the surface roughness caused by the roughness-forming particles on the groove portions becomes too large, making it difficult to discharge.

[0129] In Comparative Examples 5 and 6, the groove width w1 of the groove portion is within the appropriate range (4 to 30 μm), but the width w2 of the flat portion is outside the appropriate range (4 to 30 μm). As a result, the uniformity of the surface irregularities is reduced, and uneven images occur after the durability test.

[0130] In Comparative Examples 7 to 10, the groove angle is within ±5° relative to the circumferential direction, and when the groove angle is relatively small, the ratio of the groove width to the flat surface width (w2 / w1) is not within the specified range, and either the groove width or the flat surface width becomes too large. As a result, the difference in chargeability between the groove and flat surface portions is easily visible in the image, causing vertical stripes.

[0131] In Comparative Examples 11 and 12, the groove angle was greater than 5° and less than 22° relative to the circumferential direction. When the groove angle was slightly larger, the ratio of the groove width to the width of the flat surface (w2 / w1) was not within the specified range, and either the groove width or the width of the flat surface was too large. This resulted in a difference in charge between the groove and flat surface, resulting in uneven images after durability testing. Furthermore, in Comparative Example 12, when the groove formation angle was greater than ±5° relative to the circumferential direction, the width of the flat surface was smaller than that of the groove. This resulted in the edges of the flat surface, which are the convex portions, being easily worn away by rotation in the circumferential direction. During durability testing, the difference in charge between the convex and concave portions due to wear of the convex portions increased, resulting in streaky images along the concave and convex shapes.

[0132] In Comparative Examples 13 and 14, the groove angle was greater than 22° and less than 46° relative to the circumferential direction. When the groove angle was relatively large, the ratio of the groove width to the width of the flat surface (w2 / w1) was not within the specified range, resulting in either the groove width or the width of the flat surface being too large. This resulted in a difference in charge between the groove and flat surface, resulting in uneven images after endurance testing. Furthermore, in Comparative Example 14, when the groove formation angle was greater than ±5° relative to the circumferential direction, the width of the flat surface was smaller than that of the groove. This resulted in the edges of the flat surface, which are the convex portions, being easily worn away by rotation in the circumferential direction. During endurance testing, the difference in charge between the convex and concave portions due to wear of the convex portions became greater, resulting in streaky images along the convex and concave portions.

[0133] In Comparative Example 15, the groove angle was too large, exceeding 46° relative to the circumferential direction, so that the edges of the convex portions formed by the grooves were easily worn away by rotation in the circumferential direction, and during durability testing, the difference in chargeability between the convex and concave portions due to the wear of the convex portions increased, resulting in streaky images along the convex and concave shapes.

[0134] On the other hand, in the examples, one or more grooves extending along a direction within ±46° relative to the circumferential direction are regularly formed in the axial direction on the outer peripheral surface of the elastic layer, the groove width, groove depth, and flat portion width are within specific ranges, and the relationship between the angle θ of the groove extension direction relative to the circumferential direction and the ratio w2 / w1 of the groove width w1 to the flat portion width w2 is specific, the surface layer contains a binder polymer and roughness-imparting particles, and the roughness-imparting particles are disposed on the flat portion and the grooves of the elastic layer, respectively. Therefore, in the examples, image evaluation showed that the problems of unevenness, horizontal streaks, black spots (fog), vertical streaks, and streaks along the uneven shape after durability testing were suppressed, indicating excellent uniformity of discharge characteristics.

[0135] Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and various modifications are possible within the scope of the invention. [Explanation of symbols]

[0136] 10 Charging roll 12 shaft body 14 Elastic layer 16 Surface layer 18 Roughness forming particles 22 Groove 24 Plane section 16a Binder polymer 18a Particles for forming roughness on grooves 18b Particles for forming roughness on flat surface 221 Bottom of groove w1 groove width w2 Width of the flat surface d Groove depth M groove area

Claims

1. a shaft body, an elastic layer formed on an outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic layer, One or more grooves extending along a direction within ±46° with respect to the circumferential direction are regularly formed in the axial direction on the outer peripheral surface of the elastic layer, The groove width w of the groove １ 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, The width w of the flat portion of the outer peripheral surface of the elastic layer other than the groove portion ２ is 4 μm or more and 30 μm or less, The angle θ of the direction in which the groove portion extends with respect to the circumferential direction, and the groove width w of the groove portion １ and the width w of the plane portion ２ The ratio w ２ / w １ The relationship between and satisfies the following relationships (A) to (C): the surface layer includes a binder polymer and roughness-forming particles; The charging roll for an electrophotographic device, wherein the roughness-forming particles are disposed on the flat portion and the groove portion of the elastic layer. (A) When -5°≦θ≦+5°, 0.7≦w ２ / w １ ≦1.3 (B) When -22°≦θ<-5° or +5°<θ≦+22°, 1.0≦w ２ / w １ ≦2.0 (C) When -46°≦θ<-22° or +22°<θ≦+46°, 1.2≦w ２ / w １ ≦2.6

2. 2. The charging roll for an electrophotographic device according to claim 1, wherein the surface roughness Rz of the surface layer in the region above the grooves 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.

3. 3. The charging roll for an electrophotographic device according to claim 1, wherein the average particle diameter of the roughness-imparting particles is 3 [mu]m or more and 30 [mu]m or less.

4. 3. The charging roll for an electrophotographic device according to claim 1, wherein the roughness-imparting particles are made of any one of polyurethane, polyamide, and acrylic resin.

5. 3. The charging roll for an electrophotographic device according to claim 1, wherein the thickness of the binder polymer covering the roughness-forming particles on the groove portions is greater than the thickness of the binder polymer covering the roughness-forming particles on the flat portions.

6. 3. The charging roll for an electrophotographic device according to claim 1, wherein a difference between a thickness of the binder polymer covering the roughness-forming particles on the flat portion and a thickness of the binder polymer covering the roughness-forming particles on the groove portion is 4 μm or more and 16 μm or less.

7. 3. The charging roll for an electrophotographic apparatus according to claim 1, wherein the elastic layer contains at least one rubber selected from the group consisting of isoprene rubber, nitrile rubber, and hydrin rubber.

8. 3. The charging roll for an electrophotographic device according to claim 1, wherein the binder polymer of the surface layer is one of polyurethane and polyamide.

9. 3. The charging roll for an electrophotographic device according to claim 1, wherein the roughness-forming particles are composed of one type of particles.

10. 3. The charging roll for an electrophotographic device according to claim 1, wherein a mesh-like groove portion is formed on the outer peripheral surface of the elastic layer, in which groove portions extending in a direction at an angle of +46° or less with respect to the circumferential direction intersect with groove portions extending in a direction at an angle of −46° or less with respect to the circumferential direction.

11. the surface roughness Rz of the surface layer in the region above the groove portion 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 average particle diameter of the roughness-forming particles is 3 μm or more and 30 μm or less, the roughness-imparting particles are made of any one of polyurethane, polyamide, and acrylic resin; the thickness of the binder polymer covering the particles for forming roughness on the groove portion is thicker than the thickness of the binder polymer covering the particles for forming roughness on the flat portion, a difference between a thickness of the binder polymer covering the roughness-forming particles on the flat portion and a 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 contains at least one of isoprene rubber, nitrile rubber, and hydrin rubber, the binder polymer of the surface layer is any one of polyurethane and polyamide, The roughness-imparting particles are composed of one type of particle, 2. The charging roll for an electrophotographic device according to claim 1, wherein a mesh-like groove portion is formed on the outer peripheral surface of the elastic layer, in which groove portions extending in a direction within +46° to the circumferential direction intersect with groove portions extending in a direction within −46° to the circumferential direction.

Images