Charging roller for electrophotographic equipment

Abstract

The present invention provides a charging roller for an electrophotographic device having excellent uniformity of discharge characteristics. In the charging roller 10, a groove portion 22 is formed on the outer peripheral surface of the elastomer layer 14, which regularly describes a spiral along the axial direction. The groove width w is 4 μm or more and 280 μm or less, and the groove depth d is 2 μm or more and 30 μm or less. The area ratio a / b of the bottom surface 221 of the groove portion 22 on the outer peripheral surface of the elastomer layer 14 to the area b of the flat surface portion 24 is 0.3 or more and 2.4 or less. The surface layer 16 contains a binder polymer 16a and roughness-forming particles 18. The particles 18 are respectively arranged on the plane portion 24 and the groove portion 22, the surface roughness Rz of the surface layer 16 in the area M on the groove portion 22 is greater than 2 μm and less than 16 μm, the surface roughness Rz of the entire surface layer 16 is greater than 5 μm and less than 26 μm, and the thickness t1 of the adhesive polymer 16a covering the roughness-forming particles 18a on the groove portion 22 is thicker than the thickness t2 of the adhesive polymer 16a covering the roughness-forming particles 18b on the plane portion 24.

Description

Technical Field

[0001] The present invention relates to a charging roller for an electrophotographic device that is preferably used in an electrophotographic device such as a copy machine, a printer, or a facsimile machine that adopts an electrophotographic method. Background Art

[0002] As charging rollers for electrophotographic equipment, there are known charging rollers comprising an elastomeric layer having rubber elasticity on the outer circumference of an axial body such as a core rod, and a surface layer on the outer circumference of the elastomeric layer. In some cases, for example, roughness-forming particles are added to the binder polymer in the surface layer of the charging roller to improve charging characteristics.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2018 / 025870 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, roughness-forming particles added to the surface layer tend to aggregate, so surface roughness uniformity can be reduced in roughness-forming methods that add roughness-forming particles. In particular, when two or more roughness-forming particles of different particle sizes are used to create surface irregularities, surface roughness uniformity is particularly susceptible to degradation due to aggregation of particles of varying particle sizes. This reduction in surface roughness uniformity can also lead to a decrease in the uniformity of the discharge characteristics of the charging roller.

[0008] An object of the present invention is to provide a charging roller for an electrophotographic apparatus having excellent uniformity in discharge characteristics.

[0009] Means used to solve problems

[0010] The charging roller for an electrophotographic device according to the present invention comprises a shaft, an elastomer layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastomer layer, wherein a groove portion regularly depicting a spiral along the axial direction is formed on the outer peripheral surface of the elastomer layer, the groove portion has a groove width of 4 μm or more and 280 μm or less, a groove depth of 2 μm or more and 30 μm or less, and an area ratio a / b of an area a of a bottom surface of the groove portion in the outer peripheral surface of the elastomer layer to an area b of a flat portion other than the groove portion is 0.3 or more. and 2.4 or less, the surface layer comprises an adhesive polymer and roughness-forming particles, the roughness-forming particles are respectively arranged on the planar portion and the groove portion of the elastomer layer, the surface roughness Rz of the surface layer in the area on the groove portion is greater than 2 μm and less than 16 μm, the surface roughness Rz of the entire surface layer is greater than 5 μm and less than 26 μm, and the thickness of the adhesive polymer covering the roughness-forming particles on the groove portion is thicker than the thickness of the adhesive polymer covering the roughness-forming particles on the planar portion.

[0011] Preferably, the roughness-forming particles are composed of one type of particles. Preferably, the material of the roughness-forming particles is any one of polyurethane, polyamide, and acrylic resin. Preferably, the average particle size of the roughness-forming particles is greater than or equal to 3 μm and less than or equal to 32 μm. Preferably, the difference between the thickness of the binder polymer covering the roughness-forming particles on the planar portion and the thickness of the binder polymer covering the roughness-forming particles on the groove portion is greater than or equal to 4 μm and less than or equal to 16 μm. Preferably, the elastomer layer contains at least one of isoprene rubber, nitrile rubber, and epichlorohydrin rubber. Preferably, the binder polymer of the surface layer is any one of polyurethane and polyamide. Preferably, a mesh-like groove portion is formed on the outer peripheral surface of the elastomer layer, and the mesh-like groove portion is formed by crossing a groove portion that regularly draws a spiral in a right-handed thread along the axial direction and a groove portion that regularly draws a spiral in a left-handed thread along the axial direction.

[0012] Effects of the Invention

[0013] According to the present invention, a charging roller for an electrophotographic device comprises a shaft, an elastomer layer formed on the outer peripheral surface of the shaft, and a surface layer formed on the outer peripheral surface of the elastomer layer, wherein grooves are formed on the outer peripheral surface of the elastomer layer in a regular spiral pattern along the axial direction, wherein the groove width is from 4 μm to 280 μm, and the groove depth is from 2 μm to 30 μm, and an area ratio a / b of an area a of a bottom surface of the groove to an area b of a flat surface portion other than the groove on the outer peripheral surface of the elastomer layer is from 0.3 to 2.4. The above-mentioned surface layer contains an adhesive polymer and roughness-forming particles, and the above-mentioned roughness-forming particles are respectively arranged on the above-mentioned plane portion and the above-mentioned groove portion of the above-mentioned elastomer layer. The surface roughness Rz of the above-mentioned surface layer in the area on the above-mentioned groove portion is greater than 2μm and less than 16μm, and the surface roughness Rz of the above-mentioned surface layer as a whole is greater than 5μm and less than 26μm. Compared with the thickness of the adhesive polymer covering the roughness-forming particles on the above-mentioned plane portion, the thickness of the adhesive polymer covering the roughness-forming particles on the above-mentioned groove portion is thicker, so the uniformity of the discharge characteristics is excellent.

[0014] If the roughness-forming particles are composed of a single type of particle, the uneven shape of the elastomer layer can be easily reflected in the uneven surface of the charging roller, making it easier to control the uneven surface of the charging roller. Furthermore, since the aggregation of the roughness-forming particles can be easily controlled, the uniformity of the surface roughness can be improved. Furthermore, since the thickness of the binder polymer covering the roughness-forming particles can be easily adjusted, the uniformity of the discharge characteristics can be improved.

[0015] 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 having a high dielectric constant, and thus the chargeability of the roller surface is improved.

[0016] When the average particle size of the roughness-forming particles is 3 μm or more and 32 μm or less, appropriate concavities and convexities can be easily formed, thereby improving the uniformity of discharge characteristics.

[0017] If the difference between the thickness of the binder polymer covering the roughness-forming particles on the planar surface and the thickness of the binder polymer covering the roughness-forming particles on the grooves is 4 μm or greater, the surface charge of the binder polymer covering the roughness-forming particles on the planar surface becomes relatively large, broadening the range of environments where black spot images are not generated. Furthermore, if the thickness difference is 16 μm or less, an appropriate thickness is maintained, making it easier to form appropriate irregularities. This improves the uniformity of discharge characteristics.

[0018] When the elastic layer includes at least one of isoprene rubber, nitrile rubber, and epichlorohydrin rubber, the compression set is small, and the generation of streaky images corresponding to the deformed portion when the charging roller is provided can be suppressed.

[0019] If the binder polymer in the surface layer is either polyurethane or polyamide, the binder polymer is composed of a material with a high dielectric constant, thereby improving the chargeability of the roller surface. Furthermore, the compression set is small, which can suppress the generation of streaked images corresponding to the deformed portion when the charging roller is installed.

[0020] If the outer peripheral surface of the elastomer layer is formed with a mesh of grooves formed by intersecting grooves that regularly trace a right-hand spiral along the axial direction and grooves that regularly trace a left-hand spiral along the axial direction, the uniformity of the surface roughness is improved, thereby improving the uniformity of the discharge characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 and 1. A schematic diagram (a) showing the appearance of a charging roller for an electrophotographic apparatus according to an embodiment of the present invention and a cross-sectional view taken along line AA thereof (b).

[0022] Figure 2 1 is a schematic external view of the elastic layer showing the shape of the groove portion formed on the outer peripheral surface of the elastic layer.

[0023] Figure 3 It is an enlarged cross-sectional view of the surface.

[0024] Figure 4 Schematic diagram of the external appearance of the elastic layer showing a modified example of the shape of the groove portion formed on the outer peripheral surface of the elastic layer. DETAILED DESCRIPTION

[0025] The charging roller for an electrophotographic apparatus (hereinafter, sometimes simply referred to as a charging roller) according to the present invention will be described in detail. Figure 1 1 and 1. A schematic diagram (a) showing the appearance of a charging roller for an electrophotographic apparatus according to an embodiment of the present invention and a cross-sectional view taken along line AA thereof (b). Figure 2 1 is a schematic external view of the elastic layer showing the shape of the groove portion formed on the outer peripheral surface of the elastic layer. Figure 3 It is an enlarged cross-sectional view of the surface.

[0026] The charging roller 10 includes a shaft 12, an elastomer 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 elastomer layer 14. The elastomer layer 14 is a layer (base layer) that serves as the base of the charging roller 10. The surface layer 16 is a layer that appears on the surface of the charging roller 10. Although not specifically shown in the figure, an intermediate layer such as a resistance adjustment layer may be formed between the elastomer layer 14 and the surface layer 16 as needed.

[0027] The shaft 12 is not particularly limited as long as it is conductive. Specifically, it can be a solid or hollow core rod made of a metal such as iron, stainless steel, or aluminum. An adhesive, primer, or the like can also be applied to the surface of the shaft 12 as needed. In other words, the elastomer layer 14 can also be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive, primer, etc. can be made conductive as needed.

[0028] like Figure 2 As shown, grooves 22 that regularly describe a spiral along the axial direction are formed on the outer peripheral surface of the elastomer layer 14. More specifically, mesh-like grooves 22 are formed on the outer peripheral surface of the elastomer layer 14, and the mesh-like grooves 22 are formed by crossing grooves 22a that regularly describe a spiral along the axial direction in a right-handed manner and grooves 22b that regularly describe a spiral along the axial direction in a left-handed manner. Regularly means that the grooves 22 are formed at constant intervals in the axial direction. In the outer peripheral surface of the elastomer layer 14, the portion other than the grooves 22 is a flat portion 24. As shown Figure 3 As shown, the flat portion 24 protrudes radially outward from the bottom surface 221 of the groove portion 22. The elastomer layer 14 is formed with surface irregularities on the outer peripheral surface by the bottom surface 221 of the groove portion 22 relatively arranged on the radial inner side and the flat portion 24 relatively arranged on the radial outer side. Moreover, since the groove portion 22 is formed to regularly describe a spiral along the axial direction, a uniform surface irregularity is formed on the outer peripheral surface of the elastomer layer 14. In addition, since the mesh-like groove portion 22 is formed by the intersection of the groove portion 22a that regularly describes a spiral in the manner of a right-hand thread and the groove portion 22b that describes a spiral in the manner of a left-hand thread, a more uniform surface irregularity is formed on the outer peripheral surface of the elastomer layer 14 compared to the case where the groove portion is not mesh-like.

[0029] The groove width w of the groove portion 22 is 4 μm or more and 280 μm or less. Furthermore, the groove depth d of the groove portion 22 is 2 μm or more and 30 μm or less. Furthermore, the area ratio a / b of the area a of the bottom surface 221 of the groove portion 22 to the area b of the flat surface portion 24 on the outer peripheral surface of the elastomer layer 14 is 0.3 or more and 2.4 or less.

[0030] 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. Therefore, the difference between the surface roughness Rz brought by the roughness forming particles 18b on the plane portion 24 and the surface roughness Rz brought by the roughness forming particles 18a on the groove portion 22 becomes smaller, resulting in horizontal stripes caused by insufficient charging. If roughness forming particles 18 of a size that can be accommodated in a smaller groove width w are used, it is impossible to form a roughness that ensures sufficient discharge. In addition, from this viewpoint, it is preferred to set the groove width w of the groove portion 22 to be 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, etc. in accordance with the size of the average particle size of the roughness forming particles 18 used.

[0031] If the groove width w of the groove portion 22 exceeds 280 μm, the groove width w is too large, and the roughness forming particles 18 cannot be evenly arranged in the groove portion 22. If the roughness forming particles 18 of a size that matches the larger groove width w are used, the convex portion caused by the roughness forming particles 18 becomes too large, and the surface roughness becomes too large, and it is impossible to form an appropriate surface roughness. As a result, uniform discharge characteristics cannot be obtained. In addition, if the groove width w is too large, the binder polymer 16a covering the roughness forming particles 18 on the groove portion 22 is easy to contact the photoreceptor, so not only the wear of the binder polymer 16a covering the roughness forming particles 18b on the plane portion 24 and the roughness forming particles 18b thereunder is generated, but also the wear of the binder polymer 16a covering the roughness forming particles 18a on the groove portion 22 and the roughness forming particles 18a thereunder is generated, so that the entire surface of the surface layer 16 is worn during durability, resulting in unevenness in the image. From this viewpoint, the groove width w of the groove portion 22 is preferably set to 250 μm or less, 200 μm or less, 150 μm or less, 100 μm or less, etc., in accordance with the average particle size of the roughness forming particles 18 used.

[0032] 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 horizontal streaks caused by insufficient charging. If smaller roughness-forming particles 18 are used in conjunction with a smaller groove depth d, it is impossible to achieve a roughness that ensures sufficient discharge. From this perspective, the groove depth d of the groove portion 22 is preferably set to 3 μm or greater, 5 μm or greater, 10 μm or greater, etc., in accordance with the average particle size of the roughness-forming particles 18 used.

[0033] If the groove depth d of the groove portion 22 exceeds 30 μm, the groove depth d is too large, and the surface roughness cannot be formed on the groove portion 22 by the roughness forming particles 18 arranged in the groove portion 22. Therefore, black spots (gray fog) are generated in the image after durability. If larger roughness forming particles 18 are used in conjunction with a larger groove depth d, the difference between the surface roughness Rz brought by the roughness forming particles 18b on the plane portion 24 and the surface roughness Rz brought by the roughness forming particles 18a on the groove portion 22 becomes too large, making it difficult to discharge. In addition, from this viewpoint, it is preferred to set the groove depth d of the groove portion 22 to be less than 25 μm, less than 20 μm, etc. in conjunction with the size of the average particle size of the roughness forming particles 18 used.

[0034] If the area ratio a / b of the area a of the bottom surface 221 of the groove portion 22 to the area b of the flat surface portion 24 is less than 0.3 or exceeds 2.4, the balance between the area a of the bottom surface 221 and the area b of the flat surface portion 24 deteriorates, reducing the uniformity of the surface unevenness. This can easily lead to uneven images after endurance testing. Furthermore, if the balance between the area a of the bottom surface 221 and the area b of the flat surface portion 24 deteriorates, the adhesion between the elastomer layer 14 and the surface layer 16 decreases. From this perspective, the area ratio a / b is preferably set to 0.5 or greater, 0.7 or greater, or, for example, 2.0 or less, 1.8 or less, or 1.5 or less.

[0035] The groove width w of the groove portion 22 is calculated by averaging the groove width w at 100 points of the groove portion 22 observed in the image obtained by photographing the outer peripheral surface of the elastomer layer 14 with a laser microscope. The groove depth d of the groove portion 22 is calculated by averaging the groove depth d at 100 points of the groove portion 22 observed in the image obtained by photographing a radial cross-section of the elastomer layer 14 with a laser microscope. The area ratio a / b of the area a of the bottom surface 221 of the groove portion 22 to the area b of the flat portion 24 is calculated as follows: the outer peripheral surface of the elastomer layer 14 is photographed at five arbitrary locations with a laser microscope, the area a of the bottom surface 221 of the groove portion 22 and the area b of the flat portion 24 observed within a predetermined range (0.1 mm x 0.1 mm) of the photographed image are calculated, and the area ratio a / b is calculated from the average of these ratios.

[0036] The elastomer layer 14 contains crosslinked rubber. The elastomer layer 14 is formed from a conductive rubber composition containing uncrosslinked rubber. The crosslinked rubber is obtained by crosslinking uncrosslinked rubber. The uncrosslinked rubber can be either polar or non-polar.

[0037] Polar rubber is a rubber having polar groups. Examples of polar groups include chloro groups, nitrile groups, carboxyl groups, and epoxy groups. Specific examples of polar rubber include epichlorohydrin rubber, nitrile rubber (NBR), urethane rubber (U), acrylic rubber (a copolymer of acrylate and 2-chloroethyl vinyl ether, ACM), chloroprene rubber (CR), and epoxidized natural rubber (ENR). Among polar rubbers, epichlorohydrin rubber and nitrile rubber (NBR) are more preferred because they tend to have a particularly low volume resistivity.

[0038] Examples of the epichlorohydrin rubber include epichlorohydrin homopolymer (CO), epichlorohydrin-ethylene oxide copolymer (ECO), epichlorohydrin-allyl glycidyl ether copolymer (GCO), and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO).

[0039] Examples of urethane rubber include polyether-type urethane rubbers having ether bonds within the molecule. Polyether-type urethane rubbers can be produced by reacting a polyether having hydroxyl groups at both ends with a diisocyanate. The polyether is not particularly limited, and examples thereof include polyethylene glycol and polypropylene glycol. Diisocyanates are not particularly limited, and examples thereof include toluene diisocyanate and diphenylmethane diisocyanate.

[0040] 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 aging (excellent elastic recovery).

[0041] The elastomer layer 14 preferably comprises at least one of isoprene rubber, nitrile rubber, and epichlorohydrin rubber. If the elastomer layer 14 comprises at least one of isoprene rubber, nitrile rubber, and epichlorohydrin rubber, the compression set is small, and the generation of streaked images corresponding to the deformed portion when the charging roller 10 is installed can be suppressed.

[0042] Examples of the crosslinking agent include sulfur crosslinking agents, peroxide crosslinking agents, and dechlorination crosslinking agents. These crosslinking agents may be used alone or in combination of two or more.

[0043] 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-based vulcanization accelerators, and high-molecular polysulfides.

[0044] Examples of the peroxide crosslinking agent include conventionally known peroxide crosslinking agents such as peroxyketal, dialkyl peroxide, peroxyester, ketone peroxide, peroxydicarbonate, diacyl peroxide, and hydroperoxide.

[0045] Examples of the dechlorination 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.

[0046] The amount of the crosslinking agent added is preferably 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 bleed-out.

[0047] When a dechlorination cross-linking agent is used as a cross-linking agent, a dechlorination cross-linking accelerator can also be used in combination. As a dechlorination cross-linking accelerator, 1,8-diazabicyclo-[5.4.0]-undec-7-ene (hereinafter referred to as DBU) or its weak acid salt can be listed. The dechlorination cross-linking accelerator can be used in the form of DBU, but from the perspective of its operation, it is preferably used in the form of its weak acid salt. As weak acid salts of DBU, carbonates, stearates, 2-ethylhexanoates, benzoates, salicylates, 3-hydroxy-2-naphthoates, phenolic resin salts, 2-mercaptobenzothiazole salts, 2-mercaptobenzimidazole salts, etc. can be listed.

[0048] The content of the dechlorination crosslinking accelerator is preferably within the 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.

[0049] In order to impart conductivity, a conductive agent may be added to the elastomer layer 14. Examples of the conductive agent include electronic conductive agents and ion 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 ion conductive agents include quaternary ammonium salts, borates, and surfactants. In addition, various additives may be appropriately added to the elastomer layer 14 as needed. Examples of additives include lubricants, vulcanization accelerators, anti-aging agents, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, defoaming agents, pigments, and release agents.

[0050] The volume resistivity of the elastic layer 14 can be adjusted to a predetermined value by adjusting the type of cross-linked rubber, the amount of ion conductive agent, the amount of electronic conductive agent, etc. The volume resistivity of the elastic layer 14 is appropriately set to 10 2 ~10 10 Ω·cm, 10 3 ~10 9 Ω·cm, 10 4 ~10 8 The range of Ω·cm may be sufficient.

[0051] The thickness of the elastic layer 14 is not particularly limited and may be appropriately set within a range of 0.1 to 10 mm depending on the intended use.

[0052] The surface layer 16 includes a binder polymer 16 a and roughness-forming particles 18 .

[0053] The binder polymer 16a is a base polymer constituting the surface layer 16. Examples of the binder polymer 16a include urethane resins, polyamide resins, acrylic resins, acrylic silicone resins, butyral resins (PVB), alkyd resins, polyester resins, fluororubbers, fluororesins, mixtures of fluororubbers and fluororesins, silicone resins, silicone-grafted acrylic polymers, acrylic-grafted silicone polymers, nitrile rubber, and urethane rubber.

[0054] The binder polymer 16a is preferably any one of polyurethane and polyamide. If the binder polymer 16a of the surface layer 16 is any one of polyurethane and polyamide, the binder polymer 16a is composed of a material with a high dielectric constant, thereby improving the chargeability of the roller surface. In addition, the compression set is small, which can suppress the generation of a striped image corresponding to the deformed portion when the charging roller 10 is installed. Polyurethane includes urethane resin, urethane rubber, and urethane elastomer. The polyamide can be a modified polyamide. Examples of modified polyamides include alkoxylated polyamides such as N-methoxymethylated nylon.

[0055] 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. Figure 3As shown, the roughness-forming particles 18 are arranged on the flat surface 24 and the groove 22 of the elastomer layer 14, respectively. Due to the height difference between the flat surface 24 of the elastomer layer 14 and the bottom surface 221 of the groove 22, the roughness-forming particles 18b on the flat surface 24 (the roughness-forming particles 18b arranged on the flat surface 24) and the roughness-forming particles 18a on the groove 22 (the roughness-forming particles 18a arranged on the groove 22) have different degrees of radial outward protrusion, even though they have the same particle size. Due to the height difference between the flat surface 24 of the elastomer layer 14 and the bottom surface 221 of the groove 22, the roughness-forming particles 18b on the flat surface 24 protrude radially outward more than the roughness-forming particles 18a on the groove 22.

[0056] The convex portions caused by the roughness-forming particles 18b on the plane portion 24, which protrude further radially outward, are formed as portions in contact with the photoreceptor, and the convex portions caused by the roughness-forming particles 18a on the groove portion 22, which are located further inward in the radial direction, are formed as portions not in contact with the photoreceptor. The convex portions caused by the roughness-forming particles 18a on the groove portion 22 become the starting point of discharge. The surface layer 16 includes the roughness-forming particles 18b on the plane portion 24, thereby ensuring an appropriate discharge space between the photoreceptor and the charging roller 10. In addition, the surface layer 16 includes the roughness-forming particles 18a on the groove portion 22, thereby ensuring a starting point of discharge. In this way, the surface unevenness of the surface layer 16 increases the discharge space between the photoreceptor and the charging roller 10, thereby promoting discharge. As a result, the chargeability can be improved, and image defects such as horizontal streaks and unevenness can be suppressed. In the charging roller 10 involved in the present invention, since there is a height difference between the planar portion 24 of the elastomer layer 14 and the bottom surface 221 of the groove portion 22, even if the roughness-forming particles 18 contained in the surface layer 16 have the same particle size, an appropriate discharge space and a starting point for discharge can be easily formed between the photosensitive body and the charging roller 10.

[0057] The surface roughness Rz of the surface layer 16 in the region M on the groove portion 22 is set to be 2 μm or more and 16 μm or less. Furthermore, the surface roughness Rz of the entire surface layer 16 is set to be 5 μm or more and 26 μm or less. This allows for the formation of an appropriate discharge space and a starting point for discharge between the photoreceptor and the charging roller 10.

[0058] If the surface roughness Rz of the surface layer 16 in the region M on the groove portion 22 is less than 2 μm, the surface roughness Rz is too small, the starting point of the discharge is insufficient, the discharge is insufficient, and black spots (gray fog) cannot be suppressed in the image after durability. In addition, from this point of view, the surface roughness Rz is more preferably 3 μm or more, and 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 portion 22 exceeds 16 μm, the surface roughness Rz of the entire surface layer 16 becomes too large, it becomes difficult to discharge, and black spots (gray fog) cannot be suppressed in the image after durability. In addition, from this point of view, the surface roughness Rz is more preferably 15 μm or less, and more preferably 12 μm or less.

[0059] If the surface roughness Rz of the entire surface layer 16 is less than 5 μm, the surface roughness Rz is too small, the starting point of discharge is insufficient, the discharge is insufficient, and black spots (gray fog) cannot be suppressed in the image after durability. In addition, from this point of view, the surface roughness Rz is more preferably 7 μm or more, and 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, it becomes difficult to discharge, and black spots (gray fog) cannot be suppressed in the image after durability. In addition, from this point of view, the surface roughness Rz is more preferably 25 μm or less, and more preferably 20 μm or less.

[0060] The surface roughness Rz is a 10-point average roughness, which is the average value of the 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 (such as "VK-9510" manufactured by KEYENCE). In the image captured at 400 times, the value calculated in the surface roughness mode in 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 area on the groove 22 can be measured by observation using a laser microscope (such as "VK-9510" manufactured by KEYENCE). In the captured image, 0.01 mm can be selected in the surface roughness mode in the analysis program (program name KEYENCE VK Analyzer analysis application). 2 The value calculated based on the groove portion is used as the surface roughness Rz of the surface layer 16 in the area above the groove portion 22.

[0061] The surface roughness Rz of the surface layer 16 can be adjusted by adjusting the groove width w, groove depth d, area ratio a / b of the bottom surface 221 of the groove 22 and the flat surface 24, particle size of the roughness forming particles 18, thickness of the binder polymer 16a, etc.

[0062] As the roughness-forming particles 18, resin particles, inorganic particles, or the like are used as particles added to the surface layer 16 of the charging roller. The material of the roughness-forming particles 18 is not particularly limited. The material of the roughness-forming particles 18 is preferably any one of polyurethane, polyamide, and acrylic resin. If the roughness-forming particles 18 are made of any one of polyurethane, polyamide, and acrylic resin, the roughness-forming particles 18 are formed of a material with a high dielectric constant, thereby improving the chargeability of the roller surface.

[0063] The size of the roughness-forming particles 18 is not particularly limited. From the perspective of forming appropriate irregularities and improving the uniformity of discharge characteristics, the average particle size is preferably 3 μm to 32 μm. More preferably, the average particle size is 5 μm to 30 μm, and even more preferably, 10 μm to 30 μm. The average particle size of the roughness-forming particles 18 is determined by observing the surface of the surface layer 16 using a laser microscope. The diameter of the roughness-forming particles 18 visible during surface observation is used as the particle size, and the average value is expressed as 20 points.

[0064] The roughness forming particles 18 may be composed of one type of particles or of two or more types of particles. A type of particle first refers to particles of the same material. The same material means that, in particles made of polymers, in a wider range, for example, substances included in polyurethane may be referred to as the same material, or in a narrower range, substances having the same monomer composition may be referred to as the same material. More preferably, in a narrower range, substances having the same monomer composition may be referred to as the same material. In addition, a type of particle secondly refers to particles of the same particle size. The same particle size means that the particle size is uniform. For example, it refers to the case where the diameter of the roughness forming particles 18 is measured at 50 points at any arbitrary position, the average thereof is set to μ, the deviation thereof is set to σ, and μ / σ is less than 4.97. The diameter of the roughness forming particles 18 can be measured by observing the diameter of the particles using a laser microscope (such as "VK-9510" manufactured by KEYENCE).

[0065] The roughness forming particles 18 are preferably composed of one type of particles. If the roughness forming particles 18 are composed of two or more particles with different materials and particle sizes, it is necessary to further consider the difference in the influence of the material and particle size of the roughness forming particles 18 on the discharge characteristics to adjust the thickness of the binder polymer 16a that covers the roughness forming particles 18. If the roughness forming particles 18 are composed of one type of particles in terms of material and particle size, it is easy to adjust the thickness of the binder polymer 16a that covers the roughness forming particles 18. Thus, the uniformity of the discharge characteristics can be improved. In addition, in the case of containing two particles with greatly different particle sizes, particles of different sizes are easily agglomerated, and the dispersibility is easily reduced. If the roughness forming particles 18 are composed of one type of particles in terms of particle size, it is easy to control the agglomeration of the roughness forming particles 18, and therefore the uniformity of the surface roughness can be improved. Furthermore, if the roughness forming particles 18 are composed of particles of the same particle size, the uneven shape of the elastic layer 14 is easily reflected on the uneven surface of the charging roller, making it easy to control the uneven surface of the charging roller.

[0066] In the surface layer 16, the thickness of the binder polymer 16a is 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 thicker than the thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat portion 24. As a result, 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, thereby improving the uniformity of the discharge characteristics. As a result, the generation of black dot images can be suppressed. This is because the portion where the roughness-forming particles 18 on the flat portion 24 are located is grounded to the photoreceptor, and thus the discharge amount is worse than the portion where the roughness-forming particles 18 on the groove portion 22 are located. Therefore, in order to make the discharge amount the same at each position, it is necessary to make the film thickness of the portion where the roughness-forming particles 18 on the flat portion 24 are located thinner than the film thickness of the portion where the roughness-forming particles 18 on the groove portion 22 are located, thereby increasing the electrostatic capacitance and increasing the surface charge.

[0067] 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. If 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 portion 24 becomes relatively large, and the range of environments in which no black spot images are generated becomes wider. From this point of view, the thickness difference (t1-t2) is more preferably 5 μm or more, and further preferably 6 μm or more. In addition, if the thickness difference (t1-t2) is 16 μm or less, it is maintained at an appropriate thickness, so it is easy to form appropriate bumps and depressions. Thus, the uniformity of the discharge characteristics can be improved. From this point of view, the thickness difference (t1-t2) is more preferably 15 μm or less, and further preferably 12 μm or less.

[0068] The thickness t1 of the binder polymer 16a covering the roughness-forming particles 18 on the grooves 22 is preferably 5 μm or greater and 20 μm or less. When the thickness t1 is 5 μm or greater, the resistance of the discharge portion becomes more uniform, and the discharge characteristics become more uniform. From this perspective, the thickness t1 is more preferably 6 μm or greater, and even more preferably 7 μm or greater. Furthermore, when the thickness t1 is 20 μm or less, the surface of the surface layer 16 on the grooves 22 maintains a suitable roughness, ensuring a discharge region. From this perspective, the thickness t1 is more preferably 18 μm or less, and even more preferably 15 μm or less.

[0069] The thickness t2 of the binder polymer 16a covering the roughness-forming particles 18 on the flat surface 24 is preferably 1.0 μm or greater and 4.0 μm or less. When the thickness t2 is 1.0 μm or greater, the resistance of the discharge portion tends to be uniform, and the discharge characteristics tend to be uniform. Furthermore, from this perspective, the thickness t2 is more preferably 1.5 μm or greater, and even more preferably 2.0 μm or greater. Furthermore, when the thickness t2 is 4.0 μm or less, a suitable roughness can be ensured on the surface of the surface layer 16, ensuring a discharge area. Furthermore, from this perspective, the thickness t2 is more preferably 3.5 μm or less, and even more preferably 3.0 μm or less.

[0070] The thicknesses t1 and t2 of the binder polymer 16a can be measured by observing a cross section using a laser microscope (e.g., "VK-9510" manufactured by KEYENCE). For example, the thickness of the binder polymer 16a can be measured at five arbitrary locations on the binder polymer 16a covered with the roughness-forming particles 18 on the groove portion 22, and the average of the measured values can be used to represent t1. Alternatively, the thickness of the binder polymer 16a can be measured at five arbitrary locations on the binder polymer 16a covered with the roughness-forming particles 18 on the flat portion 24, and the average of the measured values can be used to represent t2.

[0071] 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 possible to utilize both the instability of the surface energy of the roughness-forming particles 18 on the groove portion 22 and the instability of the energy of the base rubber of the groove portion 22. In other words, it is possible to utilize both the fact that the roughness-forming particles 18 on the groove portion 22 attempt to concentrate and stabilize the binder polymer 16a in large quantities, and the fact that the base rubber of the groove portion 22 attempts to concentrate and stabilize the binder polymer 16a in large quantities.

[0072] The content of the roughness-forming particles 18 in the surface layer 16 is not particularly limited. However, from the perspectives of improving the dispersibility of the roughness-forming particles 18 and ensuring uniform charging properties, 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, it is 5 parts by mass or more and 30 parts by mass or less.

[0073] In order to impart conductivity, a conductive agent may be added to the surface layer 16. Examples of conductive agents include electronic conductive agents and ion 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 ion conductive agents include quaternary ammonium salts, borates, and surfactants. In addition, 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 release agents.

[0074] From the viewpoint of chargeability, etc., it is preferable to set the volume resistivity of the surface layer 16 to the semi-conductive region. Specifically, for example, it is preferably set to 1.0×10 7 ~1.0×10 10 The volume resistivity can be measured in accordance with JIS K6911.

[0075] The elastomer layer 14 can be formed, for example, as follows: first, the shaft 12 is coaxially placed in the hollow portion of a roll forming mold, an uncrosslinked conductive rubber composition is injected, heated, cured (crosslinked), and then demolded, or the uncrosslinked conductive rubber composition is extruded onto the surface of the shaft 12, thereby forming the elastomer layer 14 on the outer periphery of the shaft 12.

[0076] As a method for forming the groove portion 22 on the outer peripheral surface of the elastomer layer 14, grinding, mold forming, etc. can be cited. In any method, it is possible to form a regular groove portion 22 on the outer peripheral surface of the elastomer layer 14. In the case of grinding, for example, while rotating the roller body having the elastomer layer 14 around the axis at a constant speed, the grinding wheel in contact with the outer peripheral surface of the elastomer layer 14 is moved in the axial direction of one side at a constant speed, thereby forming the groove portion 22 that regularly describes a spiral along the axial direction on the outer peripheral surface of the elastomer layer 14. In addition, for example, by moving the above-mentioned grinding wheel in the axial direction of one side and then in the axial direction of the other side, it is possible to form a mesh-like groove portion 22 on the outer peripheral surface of the elastomer layer 14, in which the groove portion 22a that regularly describes a spiral along the axial direction in a right-handed manner and the groove portion 22b that regularly describes a spiral along the axial direction in a left-handed manner intersect.

[0077] The surface layer 16 can be formed by applying a material for forming the surface layer 16 to the outer peripheral surface of the elastomer layer 14 and then drying the material as appropriate. The material for forming the surface layer 16 may include 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.

[0078] According to the charging roller 10 constructed as described above, grooves 22 are formed on the outer peripheral surface of the elastomer layer 14, regularly describing a spiral along the axial direction. The groove width w, groove depth d, and area ratio a / b of the groove 22 bottom surface 221 to the flat surface 24 are within specific ranges. This allows the roughness-forming particles 18 to be evenly and well-balancedly arranged on both the flat surface 24 and the grooves 22 of the elastomer layer 14, thereby achieving a desired surface roughness and a desired roughness difference between the flat surface 24 and the grooves 22 of the elastomer layer 14, thereby enabling adjustment of an appropriate discharge amount. 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. Consequently, excellent uniformity of discharge characteristics is achieved.

[0079] The charging roller 10 involved in the present invention does not form surface unevenness on the charging roller by arranging two types of roughness-forming particles of different sizes on the outer peripheral surface of the overall flat elastomer layer, but forms surface unevenness on the charging roller 10 by forming a predetermined uneven shape on the outer peripheral surface of the elastomer layer 14 in advance and arranging relatively uniform roughness-forming particles 18 of a predetermined size thereon. The roughness-forming particles 18 are arranged not only on the groove portion 22 of the elastomer layer 14, but also on the flat portion 24. As a result, the height difference of the surface unevenness of the elastomer layer 14 appears as the surface unevenness of the charging roller 10. If the roughness-forming particles 18 are relatively uniform, the surface unevenness of the elastomer layer 14 is easily reflected on the surface of the charging roller 10. In order to arrange the roughness-forming particles 18 not only on the groove portion 22 of the elastomer layer 14 but also on the flat portion 24, it is not preferred that the groove width w of the groove portion 22 is too large or too small relative to the size of the roughness-forming particles 18. By setting the groove width w of the groove portion 22 to a predetermined size, the roughness-forming particles 18 can be reliably and evenly arranged not only on the groove portion 22 but also on the plane portion 24. Similarly, it is not preferable that the width of the plane portion 24 is too large or too small. In order to reliably and evenly arrange the roughness-forming particles 18 on the plane portion 24, it is preferably set to a predetermined area ratio. Moreover, in the present invention, a predetermined concave-convex shape is formed on the outer peripheral surface of the elastomer layer 14, thereby further increasing the surface area of the outer peripheral surface of the elastomer layer compared to the outer peripheral surface of the elastomer layer that is flat as a whole. As a result, the ease of discharge is improved. This is an effect that can be exerted even if, for example, the groove portion 22 of the elastomer layer 14 is filled with the binder polymer 16a of the surface layer 16. This effect is a hitherto unknown concept. From this point of view, there are also advantages brought about by the configuration of the present invention.

[0080] As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment at all, Various changes are possible within the range which does not deviate from the summary of this invention.

[0081] For example, in the above embodiment, the outer peripheral surface of the elastomer layer 14 is formed with a mesh-like groove portion 22 formed by crossing the groove portion 22a that draws a spiral in a right-handed manner along the axial direction and the groove portion 22b that draws a spiral in a left-handed manner along the axial direction. However, the groove portion 22 formed on the outer peripheral surface of the elastomer layer 14 may be either the groove portion 22a that draws a spiral in a right-handed manner or the groove portion 22b that draws a spiral in a left-handed manner. For example, Figure 4 As shown, the groove portion 22 may include only the groove portion 22b that draws a spiral in a left-handed manner. Compared with either case, the mesh-shaped groove portion 22 is more advantageous in terms of uniformity of roughness.

[0082] Example

[0083] Hereinafter, the present invention will be described in detail using Examples and Comparative Examples.

[0084] (Example 1)

[0085] <Preparation of Conductive Rubber Composition>

[0086] 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-based vulcanization accelerator, 0.5 parts by mass of a thiuram-based vulcanization accelerator, and 50 parts by mass of heavy calcium carbonate were added to 100 parts by mass of isoprene rubber, and the mixture was kneaded for 10 minutes using a closed-type mixer adjusted to 50° C. to prepare a conductive rubber composition.

[0087] As materials for the conductive rubber composition, the following materials were prepared.

[0088] Isoprene rubber (IR): JSR IR2200 manufactured by JSR

[0089] Carbon black: "SHO BLACK N762" manufactured by Cabot Japan

[0090] Zinc oxide: "Zinc oxide type 2" manufactured by Sakai Chemical Industry

[0091] Stearic acid: "Stearic acid SAKURA" manufactured by NOF Corporation

[0092] Sulfur: "Powdered sulfur" manufactured by Tsurumi Chemical Industry

[0093] Thiazole vulcanization accelerator: "Nocceler DM" manufactured by Ouchi Shinko Chemical Industry

[0094] Thiuram-based vulcanization accelerator: "Nocceler TRA" manufactured by Ouchi Shinko Chemical Industry

[0095] Heavy calcium carbonate: "Whiton B" manufactured by Shiraishi Calcium, average particle size 3.6 μm

[0096] <Production of Elastomer Layer>

[0097] A core rod (8 mm in diameter) was placed in a forming mold (tubular), the composition was injected, and after heating at 180°C for 30 minutes, the mixture was cooled and demolded. An elastic layer of conductive rubber elastic body with a thickness of 1.9 mm was formed on the outer periphery of the core rod. Next, while the roller body having the elastic layer was rotated around the axis at a constant speed, a grinding wheel in contact with the outer peripheral surface of the elastic layer was moved in one axial direction at a constant speed. Then, the grinding wheel in contact with the outer peripheral surface of the elastic layer was moved in the other axial direction at a constant speed, thereby forming Figure 2As shown, the outer peripheral surface of the elastomer layer has a mesh-like groove portion formed by intersecting groove portions that regularly draw a right-hand spiral along the axial direction and groove portions that regularly draw a left-hand spiral along the axial direction. The conditions are as follows.

[0098] Roller rotation speed···500rpm

[0099] Grinding wheel moving speed···0.05m / s

[0100] Grinding wheel peripheral speed···72m / s

[0101] Grinding wheel grit number···#1500

[0102] Slot spacing···0.3mm

[0103] <Surface production>

[0104] The roughness-forming particles, a binder polymer, and carbon black as a conductive agent were blended in the composition (parts by mass) listed in the table. 200 parts by mass of methyl ethyl ketone (MEK) were added and mixed at a predetermined stirring speed to prepare a liquid composition for forming a surface layer. This liquid composition was then roller-coated onto the outer peripheral surface of the elastomer layer while continuing to stir. Heat treatment was then performed to form a 1.0 μm thick surface layer around the outer periphery of the elastomer layer. This produced the charging roller of Example 1.

[0105] (Example 2)

[0106] <Preparation of Conductive Rubber Composition>

[0107] 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 a peroxide crosslinking agent, and 20 parts by mass of carbon were added to 100 parts by mass of NBR and stirred and mixed in a stirrer to prepare a conductive rubber composition.

[0108] As materials for the conductive rubber composition, the following materials were prepared.

[0109] NBR: "Nipol 1041" manufactured by ZEON, Japan

[0110] Stearic acid: NOF Corporation's "Stearic Acid SAKURA"

[0111] Zinc oxide: "Zinc oxide type 2" manufactured by Sakai Chemical Industry

[0112] Hydrotalcite: "DHT4A" manufactured by Kyowa Chemical Industry

[0113] Peroxide crosslinking agent: NOF Corporation's "PERCUMYL D40"

[0114] Carbon: Ketjen Black EC300J manufactured by Ketjen Black International

[0115] <Production of Elastomer Layer>

[0116] The heating temperature was changed to 170° C., and an elastic layer composed of a conductive rubber elastic body was formed in the same manner as in Example 1. Next, in the same manner as in Example 1, mesh-like grooves were formed on the outer peripheral surface of the elastic layer by polishing.

[0117] <Surface production>

[0118] 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. Thus, a charging roller of Example 2 was produced.

[0119] (Example 3)

[0120] <Preparation of Conductive Rubber Composition>

[0121] To 100 parts by mass of epichlorohydrin rubber, 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 were added and stirred and mixed in a stirrer to prepare a conductive rubber composition.

[0122] As materials for the conductive rubber composition, the following materials were prepared.

[0123] Epichlorohydrin rubber (ECO, "Hydrin H1100" manufactured by ZEON Japan)

[0124] Vulcanizing accelerator (zinc oxide, "Zinc Oxide 2" manufactured by Mitsui Kinzoku)

[0125] Carbon (Ketjen Black EC300J manufactured by Ketjen Black International)

[0126] Vulcanization accelerator (2-mercaptobenzothiazole, "Nocceler MP" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0127] Sulfur (manufactured by Tsurumi Chemical Co., Ltd., "SULFAX PTC")

[0128] Filler (calcium carbonate, "Haiyanhua CC" manufactured by Shiraishi Industry)

[0129] <Production of Elastomer Layer>

[0130] An elastic layer made of a conductive rubber elastic body was formed in the same manner as in Example 1. Next, in the same manner as in Example 1, mesh-like grooves were formed on the outer peripheral surface of the elastic layer by polishing.

[0131] <Surface production>

[0132] 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. Thus, a charging roller of Example 3 was produced.

[0133] (Examples 4, 5, 7, and 8)

[0134] By changing the surface layer material, charging rollers of Examples 4, 5, 7, and 8 were produced in the same manner as in Example 3.

[0135] (Example 6)

[0136] Formed as Figure 4 As shown, spiral grooves were drawn regularly in a left-handed manner along the axial direction on the outer peripheral surface of the elastic layer, and a charging roller of Example 6 was produced in the same manner as in Example 3.

[0137] (Comparative Examples 1 to 8)

[0138] The charging rollers of Comparative Examples 1 to 8 were produced in the same manner as in Example 3 except that the surface layer material was changed.

[0139] The materials used as the surface layer material are as follows.

[0140] Binder polymer (PA): "FINE RESIN FR-101" manufactured in Japan

[0141] Adhesive polymer (PU): Negami Industries' "ART Resin UN-333"

[0142] ·Roughness forming particles (PU <1> ):Art-pearl TK-100TR manufactured by Negami Industry has an average particle size of 2 μm

[0143] ·Roughness forming particles (PU <2> ):Art-pearl C-1000 Transparent manufactured by Negami Industry has an average particle size of 3 μm

[0144] ·Roughness forming particles (PU <3> ):Art-pearl C-300 transparent manufactured by Negami Industry has an average particle size of 22μm

[0145] ·Roughness forming particles (PU <4> ):Art-pearl C-200 transparent graded product manufactured by Negami Industry has an average particle size of 32 μm

[0146] ·Roughness forming particles (PU <5> ) : Negami Industry's "ART-pearl C-200 transparent graded product" has an average particle size of 35 μm

[0147] Roughness forming particles (PA): Toray's "TR-2" with an average particle size of 22 μm

[0148] Roughness-forming particles (PMMA): Negami Industries' "ART-pearl GR-200 Transparent" with an average particle size of 22 μm

[0149] Carbon black: "SEAST 9H" manufactured by Tokai Carbon

[0150] Surface and cross-sectional analysis of the elastomer layer after polishing the charging roller were performed to calculate the groove width, groove depth, and the area ratio (a / b) of the groove bottom area (a) to the flat surface area (b). The surface roughness Rz and the thickness of the binder polymer in the surface layer of the produced charging roller were also measured.

[0151] (Concavoconvex shape of elastic layer)

[0152] The groove width is calculated by photographing the outer peripheral surface of the elastomer layer with a laser microscope and averaging the groove width at 100 points of the randomly observed groove in the photographed image. The groove depth is calculated by photographing a radial cross-section of the elastomer layer with a laser microscope and averaging the groove depth at 100 points of the randomly observed groove in the photographed image. The area ratio a / b of the groove bottom area a to the flat surface area b is calculated as follows: photographing five random locations on the outer peripheral surface of the elastomer layer with a laser microscope, calculating the groove bottom area a and the flat surface area b observed within a predetermined range (0.1 mm x 0.1 mm) of the photographed image, and calculating the area ratio a / b from the average of these ratios.

[0153] (Surface roughness Rz)

[0154] The surface roughness Rz is a 10-point average roughness, which is the average value of the values measured at any five locations in accordance with JIS B0601 (1994). The surface roughness Rz of the entire surface layer is measured by observation using a laser microscope ("VK-9510" manufactured by KEYENCE). In the image captured at 400 times, the value calculated in the surface roughness mode in the analysis program (program name KEYENCE VK Analyzer analysis application) is used as the surface roughness Rz of the entire surface layer. The surface roughness Rz of the surface layer in the area on the groove portion is measured by observation using a laser microscope ("VK-9510" manufactured by KEYENCE). In the captured image, 0.01 mm is selected in the surface roughness mode in the analysis program (program name KEYENCE VK Analyzer analysis application). 2 The value calculated based on the groove portion is taken as the surface roughness Rz of the groove portion.

[0155] (Adhesive thickness)

[0156] The measurement was performed by observing the radial cross section of the surface layer at 400 times magnification using a laser microscope ("VK-X100" manufactured by KEYENCE). Figure 2 As shown in FIG, the thickness of the binder polymer covering the roughness-forming particles on the groove portion (binder thickness t1) and the thickness of the binder polymer covering the roughness-forming particles on the flat portion (binder thickness t2) were measured. Measurements were made at five arbitrary locations, and the average of the measurements was expressed.

[0157] (Image rating: Uneven)

[0158] The produced charging roller was installed in the unit (black) of an actual machine (RICOH "MP C6004"). Images were output at 25% halftone density under a 10°C, 10% RH environment, and durability evaluation was performed after 500,000 prints. Images with no unevenness were rated "good" (0), while images with unevenness were rated "poor" (x).

[0159] (Image evaluation: horizontal stripes)

[0160] The produced charging roller was installed in the unit (black) of an actual machine (RICOH "MP C6004"). Images were output at 25% halftone density under a 10°C, 10% RH environment, and durability evaluation was performed after 500,000 prints. Images with no horizontal streaks were rated "very good" (0), while images with significant horizontal streaks affecting the image were rated "poor" (x).

[0161] (Image evaluation: Setting stripes)

[0162] The produced charging roller was installed in the unit (black) of an actual machine (RICOH "MP C6004") and allowed to stand for one week in a 50°C, 95% RH environment. Subsequently, with the charging roller installed in the unit (black) of an actual machine (RICOH "MP C6004"), an image was output at a 25% halftone density in a 10°C, 10% RH environment. Images with no streaks were rated "very good" (0), while images with streaks that significantly affected the image were rated "poor" (x).

[0163] (Image evaluation: black spots (gray fog))

[0164] The produced charging roller was installed in the unit (black) of an actual machine (RICOH "MP C6004"). Images were output at 25% halftone density under a 10°C, 10% RH environment. Durability evaluation was performed after 500,000 prints. Images with no black spots were rated as good (0), while images with even a single spot were rated as poor (x).

[0165]

[0166]

[0167] In Comparative Example 1, the groove width is too small, and the roughness forming particles do not enter the groove portion. Therefore, the difference between the surface roughness caused by the roughness forming particles on the plane portion and the surface roughness caused by the roughness forming particles on the groove portion is small, resulting in horizontal stripes caused by insufficient charging. In addition, if roughness forming particles of a size that can be accommodated in a smaller groove width are used, it is impossible to form a roughness that ensures sufficient discharge. The groove width of Comparative Example 2 is too large, and the roughness forming particles cannot be evenly arranged in the groove portion. Therefore, unevenness after durability occurs. In addition, if roughness forming particles of a size that matches the larger groove width are used, the convex portion brought by the roughness forming particles becomes too large, the surface roughness becomes too large, and it is impossible to form an appropriate surface roughness. Thus, uniform discharge characteristics cannot be obtained. In addition, in Comparative Example 2, the groove width is too large, and the adhesive polymer covering the roughness-forming particles on the groove portion easily contacts the photosensitive body. Therefore, not only the adhesive polymer covering the roughness-forming particles on the flat portion and the roughness-forming particles thereunder are worn, but also the adhesive polymer covering the roughness-forming particles on the groove portion and the roughness-forming particles thereunder are worn. During durability, the entire surface of the surface layer is worn, and the image becomes uneven.

[0168] In Comparative Example 3, the groove depth is too small, and the difference between the surface roughness on the plane portion caused by the roughness-forming particles and the surface roughness on the groove portion caused by the roughness-forming particles is small, resulting in horizontal stripes caused by insufficient charging. In addition, if smaller roughness-forming particles are used in conjunction with a smaller groove depth, it is impossible to form a roughness that ensures sufficient discharge. In Comparative Example 4, the groove depth is too large, and it is impossible to form surface roughness on the groove portion by the roughness-forming particles configured in the groove portion. Therefore, black spots (gray fog) are generated in the image after durability. In addition, if larger roughness-forming particles are used in conjunction with a larger groove depth, the difference between the surface roughness on the plane portion caused by the roughness-forming particles and the surface roughness on the groove portion caused by the roughness-forming particles becomes too large, making it difficult to discharge.

[0169] In Comparative Examples 5 and 6, the area ratio a / b of the groove bottom area a to the flat surface area b was not within the predetermined range, and either ratio was too large. This reduced the uniformity of the surface irregularities and resulted in uneven images after aging.

[0170] In Comparative Example 7, the surface roughness Rz of the entire surface layer was too small, failing to achieve a roughness sufficient for discharge. Consequently, horizontal streaks occurred due to insufficient charging. In Comparative Example 8, the surface roughness Rz of the entire surface layer and the surface roughness Rz of the surface layer in the area above the grooves were too large, making discharge difficult. Consequently, black spots (fog) appeared in the image after endurance testing.

[0171] On the other hand, in the embodiment, a groove portion that regularly depicts a spiral along the axial direction is formed on the outer peripheral surface of the elastomer layer, and the groove width, groove depth, and area ratio a / b of the bottom surface of the groove portion to the plane portion of the groove portion are within a specific range. The surface layer contains an adhesive polymer and roughness-forming particles, and the roughness-forming particles are respectively arranged on the plane portion and the groove portion of the elastomer layer. The surface roughness Rz of the surface layer in the area on the groove portion and the surface roughness Rz of the entire surface layer are within a specific range. The thickness of the adhesive polymer covering the roughness-forming particles on the groove portion is thicker than the thickness of the adhesive polymer covering the roughness-forming particles on the plane portion. Therefore, it can be seen that in the image evaluation of the embodiment, the problems of unevenness, horizontal stripes, and black spots (gray fog) after durability are suppressed, and the uniformity of the discharge characteristics is excellent. In addition, no setting stripes are generated in the image, and no peeling of the surface layer after durability is observed.

[0172] While the embodiments and examples of the present invention have been described above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

[0173] Description of Reference Numerals

[0174] 10: Charging roller;

[0175] 12: shaft;

[0176] 14: Elastomer layer;

[0177] 16: surface;

[0178] 18: particles for roughness formation;

[0179] 22: groove;

[0180] 24: plane part;

[0181] 16a: adhesive polymer;

[0182] 18a: Particles for forming roughness on the groove portion;

[0183] 18b: Particles for forming roughness on the flat surface;

[0184] 221: bottom surface of the groove;

[0185] 22a: The groove portion of the spiral is depicted in a right-handed thread;

[0186] 22b: The groove portion of the spiral is depicted in a left-handed thread manner;

[0187] w: slot width;

[0188] d: groove depth;

[0189] M: Area above the groove.

Claims

1. A charging roller for an electrophotographic device, wherein: The charging roller for an electrophotographic device includes 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. A groove portion is formed on the outer peripheral surface of the elastic layer, which regularly draws a spiral along the axial direction. The groove width of the groove portion is not less than 4 μm and not more than 280 μm, The groove depth of the groove portion is not less than 2 μm and not more than 30 μm, The area ratio a / b of the area a of the bottom surface of the groove portion in the outer peripheral surface of the elastomer layer to the area b of the flat portion other than the groove portion is 0.3 or more and 2.4 or less. The surface layer comprises a binder polymer and roughness-forming particles, The roughness forming particles are respectively arranged on the flat surface portion and the groove portion of the elastic layer. 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, The surface roughness Rz of the entire surface layer is 5 μm or more and 26 μm or less. 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.

2. The charging roller for an electrophotographic apparatus according to claim 1, wherein The roughness-forming particles are composed of one type of particles.

3. The charging roller for an electrophotographic apparatus according to claim 1 or 2, wherein The material of the roughness forming particles is any one of polyurethane, polyamide, and acrylic resin.

4. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 3, wherein The roughness-forming particles have an average particle size of 3 μm or more and 32 μm or less.

5. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 4, wherein The difference between the thickness of the binder polymer covering the roughness-forming particles on the planar 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.

6. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 5, wherein The elastic layer includes at least one of isoprene rubber, nitrile rubber, and epichlorohydrin rubber.

7. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 6, wherein The adhesive polymer of the surface layer is any one of polyurethane and polyamide.

8. The charging roller for an electrophotographic apparatus according to any one of claims 1 to 7, wherein The outer peripheral surface of the elastic layer is formed with mesh-like grooves formed by intersecting grooves that regularly spiral in a right-handed manner along the axial direction and grooves that regularly spiral in a left-handed manner along the axial direction.

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