Charging rolls for electrophotographic equipment

Abstract

Provided is a charging roll for electrophotographic equipment that is provided with a surface layer that can reduce both compression set and wear of a photosensitive member, and that can also reduce changes in characteristics due to moisture absorption. [Solution] A charging roll 10 for an electrophotographic device 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, wherein the surface layer 16 includes the following (a) to (c): (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanate (c) Crosslinked composite of water-dispersible polyurethane dispersion and water-dispersible isocyanate

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 have a rubber-elastic elastic layer on the outer surface of a shaft such as a core bar, and a surface layer on the outer surface of the elastic layer. The surface layer is typically formed by coating a material dissolved in an organic solvent and then heat-treating it. The use of organic solvents results in the release of volatile organic compounds, posing environmental and workability challenges. Alternatively, it is also known to use a water-based paint containing a water-based urethane resin when forming the surface layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-70444 Summary of the Invention [Problem to be solved by the invention]

[0004] The surface layer of a charging roll requires both high hardness, which resists set and facilitates elastic recovery upon contact with a mating component such as a photoreceptor (reducing compression set), and low hardness, which limits wear on the surface roughness-forming particles and on the mating component such as a photoreceptor. Because these are contradictory properties, achieving both at a high level is difficult. Coating the surface layer with a material dissolved in an organic solvent is effective for forming a uniform surface layer, as dissolution homogenizes the material down to the molecular level. However, because the material is homogenized, the overall hardness is intermediate, making it difficult to achieve both high and low hardness requirements. On the other hand, when using water-based paints, the material is prone to moisture absorption from the outside air, making the hardness characteristics susceptible to environmental influences.

[0005] The problem to be solved by the present invention is to provide a charging roll for an electrophotographic device that is provided with a surface layer that can reduce both compression set and wear of the photoreceptor, and that can also reduce changes in characteristics due to moisture absorption. [Means for solving the problem]

[0006] The 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 the surface layer contains the following (a) to (c): (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanate (c) Crosslinked composite of water-dispersible polyurethane dispersion and water-dispersible isocyanate

[0007] The surface layer may contain particles for providing roughness. The particles for providing roughness may be non-porous particles. The surface layer may contain water-dispersible carbon black as a conductive agent. The mass ratio of (a) to (b) in the surface layer may be within a range of (a):(b)=60:40 to 90:10.

[0008] (1) The conductive 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 the surface layer contains the following (a) to (c): (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanate (c) Crosslinked composite of water-dispersible polyurethane dispersion and water-dispersible isocyanate

[0009] (2) In the above (1), the surface layer may contain particles for providing roughness.

[0010] (3) In the above (2), the roughness-imparting particles may be non-porous particles.

[0011] (4) In any one of the above (1) to (3), the surface layer may contain water-dispersible carbon black as a conductive agent.

[0012] (5) In any one of the above (1) to (4), the mass ratio of (a) to (b) in the surface layer may be within the range of (a):(b)=60:40 to 90:10. [Effects of the Invention]

[0013] According to the charging roll for electrophotographic devices of the present invention, the surface layer contains (a) a crosslinked product of a water-dispersible polyurethane dispersion, which is a relatively low-hardness component, and (b) a crosslinked product of a water-dispersible isocyanate, which is a relatively high-hardness component. Because these components are water-dispersed rather than dissolved, they form a uniform surface macroscopically and have both high-hardness and low-hardness regions microscopically. The high-hardness regions can reduce compression set, while the low-hardness regions can reduce photoreceptor wear, achieving both reduced compression set and reduced photoreceptor wear. Furthermore, the surface layer contains (c) a crosslinked product of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate. This region has a particularly high crosslink density. This steric hindrance suppresses moisture absorption from the ambient air. Therefore, even though the roller is water-dispersed, moisture absorption from the ambient air is suppressed, reducing changes in properties due to moisture absorption.

[0014] When the surface layer contains roughness-forming particles, suitable surface irregularities are formed on the surface layer, which increases the discharge space between the photoreceptor and the charging roll and promotes discharge, thereby improving charging properties and suppressing image defects such as horizontal streaks and unevenness.

[0015] Furthermore, when the roughness-imparting particles are non-porous particles, the surface structure is such that moisture absorbed from the outside air is not easily retained, and therefore, changes in properties due to moisture absorption can be reduced.

[0016] When the surface layer contains water-dispersible carbon black as a conductive agent, the dispersibility of the carbon black in the surface layer is excellent, thereby forming a macroscopically uniform surface.

[0017] When the ratio of (a) to (b) in the surface layer is within the range of (a):(b)=60:40 to 90:10 by mass, it is possible to achieve a high degree of reduction in both compression set and wear of the photosensitive member. [Brief explanation of the drawings]

[0018] [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. DETAILED DESCRIPTION OF THE INVENTION

[0019] The charging roll for electrophotographic equipment (hereinafter, sometimes simply referred to as the charging roll) according to the present invention will be described in detail. Fig. 1 shows a schematic external view (a) of the charging roll for electrophotographic equipment according to one embodiment of the present invention, and a cross-sectional view (b) of the same taken along line AA.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] 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.

[0026] 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, isoprene rubber is more preferred from the viewpoint of excellent tensile properties.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The surface layer 16 includes the following (a) to (c): (a) to (c) are binder components of the surface layer 16. The binder is a base material that constitutes the surface layer 16. (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanate (c) Crosslinked composite of water-dispersible polyurethane dispersion and water-dispersible isocyanate

[0039] Water-dispersible polyurethane dispersions are materials in which polyurethane particles are dispersed in water. Water-dispersible polyurethane dispersions can be classified into self-emulsifying and forced-emulsifying types depending on the emulsification method. They can also be classified into anionic and nonionic types depending on the type of hydrophilic group introduced. Self-emulsifying types are made self-dispersible by introducing hydrophilic groups into polyurethane. Forced-emulsifying types are made by forcibly emulsifying hydrophobic polyurethane with a surfactant. Self-emulsifying types are preferred because they do not require the use of a surfactant. Furthermore, anionic types are more preferred in terms of the type of hydrophilic group introduced, due to their self-emulsifying ability. Examples of anionic hydrophilic groups include carboxylate groups and sulfonate groups.

[0040] Water-dispersible polyurethane dispersions exist in the form of fine particles (particles of about 5 to 200 nm) in the dispersion liquid, and when the dispersion liquid is applied and then dried and heat-cured, the fine particles become crosslinked polyurethane. The water-dispersible polyurethane dispersion may be of the thermal crosslinking type or the self-crosslinking type.

[0041] Water-dispersible isocyanate is a material in which isocyanate particles are dispersed in water. The water-dispersible isocyanate is preferably a self-emulsifying type having a hydrophilic group. The hydrophilic group is preferably an anionic carboxylate group, sulfonate group, or the like. The water-dispersible isocyanate is preferably a blocked isocyanate in which the terminal isocyanate group is blocked with a blocking agent. Blocked isocyanates have excellent stability. Blocked isocyanates are those in which the blocking agent dissociates and the isocyanate is liberated at a temperature equal to or higher than a predetermined dissociation temperature.

[0042] Water-dispersible isocyanate exists in the form of fine particles (particles of about 5 to 200 nm) in the dispersion, and when the dispersion is applied and then dried and heat-cured, the fine particles become a crosslinked isocyanate. The water-dispersible isocyanate may be a thermal crosslinking type or a self-crosslinking type.

[0043] The blocked isocyanate preferably has a dissociation temperature of 100°C or higher, more preferably 120°C or higher. From the viewpoint of being able to easily keep the heating temperature for dissociating the blocking agent during curing low, the blocked isocyanate preferably has a dissociation temperature of 160°C or lower, more preferably 140°C or lower.

[0044] As the blocking agent, a compound having active hydrogen is used. Examples of the compound having active hydrogen include oximes, pyrazoles, carbazoles, secondary amines, β-dicarbonyl compounds, lactams, and phenols. These may be used alone or in combination as blocking agents to form blocked isocyanates.

[0045] Examples of oximes include aldoximes and ketoximes. Examples of aldoximes include formaldoxime and acetaldoxime. Examples of ketoximes include dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, acetoxime, and cyclohexanone oxime. Examples of pyrazoles include pyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole. Examples of carbazoles include carbazole. Examples of secondary amines include dipropylamine, diisopropylamine, dibutylamine, diisobutylamine, di(tert-butyl)amine, ethylpropylamine, ethylisopropylamine, ethylbutylamine, ethylisobutylamine, ethyl(tert-butyl)amine, dicyclohexylamine, N-methylaniline, diphenylamine, piperidine, 2-methylpiperidine, 2,6-dimethylpiperidine, and 2,2,6,6-tetramethylpiperidine. Examples of β-dicarbonyl compounds include malonic acid diesters such as dimethyl malonate and diethyl malonate, and acetoacetic acid esters such as methyl acetoacetate and ethyl acetoacetate. Examples of lactams include ε-caprolactam. Examples of phenols include phenol.

[0046] As the blocking agent, from the viewpoints of excellent stability of the blocked isocyanate, suitable dissociation temperature of the blocked isocyanate, etc., methyl ethyl ketoxime, diisopropylamine, phenol, ε-caprolactam, diethyl malonate, 3,5-dimethylpyrazole, ethyl acetoacetate, etc. are preferred. Furthermore, from the viewpoints of the tendency of the blocked isocyanate to have a relatively low dissociation temperature, etc., 3,5-dimethylpyrazole and methyl ethyl ketoxime are preferred.

[0047] (c) The crosslinked product of the water-dispersible polyurethane dispersion and the water-dispersible isocyanate is a crosslinked product obtained as a result of a crosslinking reaction between the water-dispersible polyurethane dispersion and the water-dispersible isocyanate at the interface between them.

[0048] Whether the surface layer 16 contains (c) can be determined, for example, by the change in weight before and after placing the charging roll 10 in a high-temperature, high-humidity environment (HH environment) of 40°C x 90% RH (relative humidity) for nine days. The surface layer 16 is hydrophilic and easily absorbs moisture from the atmosphere, but the presence of (c) with a high crosslink density prevents moisture from penetrating into the interior of the surface layer 16, and the only moisture absorbed is that from the surface of the surface layer 16 or the elastic layer 14 in cross-sectional areas where the surface layer 16 is not present, so this can be determined from the low rate of weight increase before and after. When (c) is included, the rate of weight increase is less than about 0.3% by mass.

[0049] The crosslinked product of (a) water-dispersible polyurethane dispersion is the softest of (a) to (c). This property allows it to absorb pressure when in contact with the photoreceptor, reducing wear on the roughness-forming particles and on the photoreceptor. The crosslinked product of (b) water-dispersible isocyanate is the hardest of (a) to (c). This property reduces compression set. Because these are water-dispersed rather than dissolved, they form a uniform surface at the macro level and possess both high-hardness and low-hardness areas at the micro level. The high-hardness areas reduce compression set, while the low-hardness areas reduce wear on the photoreceptor, achieving both reduced compression set and reduced wear on the photoreceptor. The crosslinked product of (c) water-dispersible polyurethane dispersion and water-dispersible isocyanate is the crosslinked product with the highest crosslink density of (a) to (c). This steric hindrance reduces moisture absorption from the ambient air. Therefore, even if the composition is a water dispersion type, moisture absorption from the outside air is suppressed, and changes in properties due to moisture absorption can be reduced.

[0050] The mass ratio of (a) to (b) in the surface layer 16 is preferably within a range of (a):(b)=60:40 to 90:10. When the mass ratio of (a):(b) is within this range, it is possible to achieve a high degree of both reduction in compression set and reduction in wear of the photoreceptor. Furthermore, the mass ratio of (a) to (b) in the surface layer 16 is more preferably within a range of (a):(b)=60:40 to 85:15, and even more preferably within a range of (a):(b)=60:40 to 80:20.

[0051] The surface layer 16 may contain roughness-forming particles. The roughness-forming particles 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. The surface irregularities of the surface layer 16 increase the discharge space between the photoreceptor and the charging roll 10, promoting discharge. This improves charging properties and reduces image defects such as horizontal streaks and unevenness.

[0052] The roughness-forming particles may be inorganic particles, resin particles, rubber particles, or the like. Examples of inorganic particles include silica particles. The material of the roughness-forming particles is not particularly limited. Examples of resins and rubbers include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, silicone-grafted acrylic polymer, acrylic-grafted silicone polymer, urethane rubber, and polystyrene.

[0053] The size of the roughness-forming particles is not particularly limited, but from the viewpoint of easily ensuring uniform charging, an average particle diameter of 3.0 μm to 50 μm is preferable. An average particle diameter of 3.0 μm to 30 μm is more preferable. The average particle diameter of the roughness-forming particles is expressed as the average of 20 arbitrary points, where the surface of the surface layer 16 is observed with a laser microscope, and the diameter of the roughness-forming particles 16 visible during surface observation is taken as the particle size.

[0054] The content of the roughness-imparting particles in the surface layer 16 is not particularly limited, but from the viewpoint of easily ensuring uniform charging properties, it 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 in the surface layer 16. It is more preferably 5 parts by mass or more and 40 parts by mass or less.

[0055] The particles for providing roughness are preferably non-porous particles. When the particles for providing roughness are non-porous particles, they have a surface structure that is less likely to retain moisture absorbed from the outside air, thereby reducing changes in properties due to moisture absorption. The non-porous particles can be particles with a porosity of 10% or less as defined by JIS Z 2506.

[0056] The surface layer 16 may contain a conductive agent. Examples of the conductive agent include an electronic conductive agent and an ionic conductive agent. Examples of the electronic conductive agent include carbon black, graphite, and conductive metal oxides. Examples of the conductive metal oxide include conductive titanium oxide, conductive zinc oxide, and conductive tin oxide. Examples of the ionic conductive agent include a quaternary ammonium salt, a quaternary phosphonium salt, an imidazolium salt, a borate, and a surfactant.

[0057] The surface layer 16 preferably contains carbon black as a conductive agent. When the surface layer 16 contains carbon black as a conductive agent, high chargeability can be maintained even during use without deterioration in durability due to bleed-out of the conductive agent, and a response speed that can accommodate the charge / discharge process can be achieved even in high-speed printing.

[0058] The carbon black is preferably water-dispersible carbon black. When water-dispersible carbon black is contained, the dispersibility of the carbon black is excellent in the surface layer 16. This allows the formation of a macroscopically uniform surface.

[0059] The water-dispersible carbon black preferably has an anionic group, which provides excellent water dispersibility.

[0060] The content of the water-dispersible carbon black in the surface layer 16 is not particularly limited, but is preferably 10 parts by mass or more and 90 parts by mass or less relative to 100 parts by mass of the binder polymer in the surface layer 16. It is more preferably 15 parts by mass or more and 70 parts by mass or less, and even more preferably 20 parts by mass or more and 50 parts by mass or less.

[0061] If necessary, various additives may be added appropriately to the surface layer 16. Examples of the additives include a plasticizer, a leveling agent, a filler, a vulcanization accelerator, a processing aid, and a mold release agent.

[0062] 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 10The volume resistivity can be measured in the range of Ω·cm. The volume resistivity can be measured in accordance with JIS K6911. The thickness of the surface layer 16 is not particularly limited, and can be set in the range of 0.1 to 30 μm. The thickness of the surface layer 16 can be measured by observing the cross section using a laser microscope (such as Keyence's "VK-9510"). For example, the distance from the surface of the elastic layer 14 to the surface of the surface layer 16 can be measured at five arbitrary positions, and the thickness can be expressed as the average.

[0063] 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.

[0064] Surface layer 16 can be formed by using a material for forming surface layer 16, applying this to the outer peripheral surface of elastic layer 14, and then appropriately performing drying and heating treatments. In the drying and heating treatments, the water solvent is volatilized below the dissociation temperature of the blocking agent for the water-dispersible isocyanate to reduce the water content, and then a crosslinking reaction of the water-dispersible isocyanate is partially carried out below the activation temperature of the polyurethane in the polyurethane dispersion, and then a crosslinking reaction of the polyurethane in the polyurethane dispersion and a crosslinking reaction of the polyurethane in the polyurethane dispersion with the water-dispersible isocyanate are carried out at a temperature equal to or higher than the activation temperature of the polyurethane in the polyurethane dispersion, thereby forming surface layer 16 including (a) a crosslinked body of the water-dispersible polyurethane dispersion, (b) a crosslinked body of the water-dispersible isocyanate, and (c) a crosslinked body of the water-dispersible polyurethane dispersion and the water-dispersible isocyanate.

[0065] According to the charging roll 10 configured as described above, the surface layer 16 contains (a) a crosslinked body of a water-dispersible polyurethane dispersion, which is a relatively low-hardness component, and (b) a crosslinked body of a water-dispersible isocyanate, which is a relatively high-hardness component. Because these components are water-dispersed rather than dissolved, they form a uniform surface at the macro level and have both high-hardness and low-hardness areas at the micro level. The high-hardness areas reduce compression set, while the low-hardness areas reduce photoreceptor wear, achieving both reduced compression set and reduced photoreceptor wear. Furthermore, the surface layer 16 contains (c) a crosslinked body of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate. This area has a particularly high crosslink density. This steric hindrance suppresses moisture absorption from the ambient air. Therefore, even though the material is water-dispersed, moisture absorption from the ambient air is suppressed, reducing changes in properties due to moisture absorption. [Example]

[0066] The present invention will be described in detail below using examples and comparative examples.

[0067] 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.

[0068] 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

[0069] <Preparation of Elastic Layer> A core metal (diameter 8 mm) was set in a molding die (pipe-shaped), the above composition was injected, and the die was heated at 180°C for 30 minutes, after which it was cooled and demolded, and an elastic layer made of a conductive rubber elastic material and having a thickness of 1.9 mm was molded around the outer periphery of the core metal.

[0070] <Preparation of Composition for Forming Surface Layer> The polyurethane dispersion was stirred in water (solvent) at 10 to 35°C for 1 hour, and then water-dispersible isocyanate was added and stirred for another hour. Water-dispersible carbon black was then added and stirred, followed by the addition of roughness-imparting particles and further stirring. This completed the preparation of a surface layer-forming composition. The blending ratios are shown in Table 1.

[0071] <Creating the surface layer> The surface layer-forming composition was roll-coated onto the outer peripheral surface of the elastic layer, and the water content was reduced by volatilizing the solvent water below the dissociation temperature of the blocking agent of the water-dispersible isocyanate. After that, a partial crosslinking reaction of the water-dispersible isocyanate was carried out below the activation temperature of the polyurethane of the polyurethane dispersion. Subsequently, a crosslinking reaction of the polyurethane of the polyurethane dispersion and a crosslinking reaction of the polyurethane of the polyurethane dispersion with the water-dispersible isocyanate were carried out above the activation temperature of the polyurethane of the polyurethane dispersion. This resulted in a surface layer (thickness 1.0 μm) containing (a) a crosslinked product of the water-dispersible polyurethane dispersion, (b) a crosslinked product of the water-dispersible isocyanate, and (c) a crosslinked product of the water-dispersible polyurethane dispersion and the water-dispersible isocyanate. The charging roll of Example 1 was thus produced.

[0072] 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.

[0073] 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"

[0074] <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.

[0075] <Preparation of Composition for Forming Surface Layer> A surface layer-forming composition was prepared in the same manner as in Example 1, except that the type and blending ratio of the polyurethane dispersion, the type and blending ratio of the water-dispersible isocyanate, the type of water-dispersible carbon black, and the type of roughness-forming particles were changed.

[0076] <Creating the surface layer> In the same manner as in Example 1, a surface layer (thickness 1.0 μm) containing (a) a crosslinked body of a water-dispersible polyurethane dispersion, (b) a crosslinked body of a water-dispersible isocyanate, and (c) a crosslinked body of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate was formed.

[0077] 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.

[0078] 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")

[0079] <Preparation of Elastic Layer> In the same manner as in Example 1, an elastic layer made of a conductive rubber elastic material was formed.

[0080] <Preparation of Composition for Forming Surface Layer> A surface layer-forming composition was prepared in the same manner as in Example 1, except that the blending ratio of the polyurethane dispersion, the blending ratio of the water-dispersible isocyanate, the type of water-dispersible carbon black, and the type of roughness-forming particles were changed.

[0081] <Creating the surface layer> In the same manner as in Example 1, a surface layer (thickness 1.0 μm) containing (a) a crosslinked body of a water-dispersible polyurethane dispersion, (b) a crosslinked body of a water-dispersible isocyanate, and (c) a crosslinked body of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate was formed.

[0082] Example 4 <Preparation of Conductive Rubber Composition> 50 parts by mass of NBR and 30 parts by mass of carbon black were blended and stirred and mixed using a mixer. Next, 50 parts by mass of isoprene rubber (IR), 5 parts by mass of peroxide crosslinking agent, 3 parts by mass of vulcanization aid, and 3 parts by mass of catalyst were blended and stirred and mixed using a mixer to prepare a conductive rubber composition.

[0083] The following materials were prepared as materials for the conductive rubber composition. NBR: Nipol 1041 manufactured by Nippon Zeon IR: Nipol IR2200 manufactured by Nippon Zeon Carbon black: Cabot Japan "Show Black N762" Peroxide crosslinking agent: NOF's "Perkmyl D40" Vulcanization aid (zinc oxide, Mitsui Metals "Zinc Oxide Type 2")

[0084] <Preparation of Elastic Layer> The heating temperature was changed to 180° C., and an elastic layer made of a conductive rubber elastic material was molded in the same manner as in Example 1.

[0085] <Preparation of Composition for Forming Surface Layer> A surface layer-forming composition was prepared in the same manner as in Example 1, except that the type and blending ratio of the polyurethane dispersion, the blending ratio of the water-dispersible isocyanate, and the type of roughness-imparting particles were changed.

[0086] <Creating the surface layer> In the same manner as in Example 1, a surface layer (thickness 1.0 μm) containing (a) a crosslinked body of a water-dispersible polyurethane dispersion, (b) a crosslinked body of a water-dispersible isocyanate, and (c) a crosslinked body of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate was formed.

[0087] (Comparative Example 1) A surface layer-forming composition was prepared in the same manner as in Example 1, except that the stirring was carried out in an environment of 85°C to 100°C instead of an environment of 10°C to 35°C. Next, in producing the surface layer, the surface layer-forming composition was roll-coated onto the outer peripheral surface of the elastic layer, and heat-treated in an oven at 125°C for 60 minutes to form a surface layer (thickness 1.0 μm). In this way, the charging roll of Comparative Example 1 was produced.

[0088] (Comparative Example 2) A surface layer-forming composition was prepared in the same manner as in Example 2, except that the water-dispersible isocyanate was not blended, and the type and blending ratio of the polyurethane dispersion and the type of water-dispersible carbon black were changed. Next, in preparing the surface layer, the surface layer-forming composition was roll-coated onto the outer peripheral surface of the elastic layer, as in Comparative Example 1, and heat-treated in an oven at 125°C for 60 minutes to form a surface layer (thickness 1.0 μm). In this way, the charging roll of Comparative Example 2 was prepared.

[0089] (Comparative Example 3) A surface layer-forming composition was prepared in the same manner as in Example 1, except that no polyurethane dispersion was added. Next, in producing the surface layer, the surface layer-forming composition was roll-coated onto the outer peripheral surface of the elastic layer and heat-treated in an oven at 125°C for 60 minutes to form a surface layer (thickness 1.0 μm). In this way, the charging roll of Comparative Example 3 was produced.

[0090] The materials used for the surface layer are as follows: Water-dispersible polyurethane dispersion 1 (PUD1): UBE "UW-1527DF" Water-dispersible polyurethane dispersion 2 (PUD2): DIC "Hydran HW-350" Water-dispersible isocyanate 1: Tosoh "Aquanate 105", blocked isocyanate Water-dispersible isocyanate 2: LANXESS "Trixene Aqua BI201", blocked isocyanate Water-dispersible carbon black 1: Tokai Carbon's "Aqua-Black 204" Water-dispersible carbon black 2: Tokushiki "8652BLACK" Roughness-forming particles 1 (non-porous): Fuji Silysia Chemical's "SYLOSPHERE C-1504" (average particle size 4.5 μm) ·Roughness forming particles 2 (non-porous): "Techpolymer SBX-6" manufactured by Sekisui Plastics (average particle size 6.0 μm) Roughness-forming particles 3 (porous): Fuji Silysia Chemical's "SYLYSIA 852" (average particle size 5.0 μm)

[0091] The produced charging roll was used for evaluation.

[0092] (Setting ability (compression set)) The produced charging roll was incorporated into an HP "CLJ4525dn K-color cartridge," and a compression set test was performed in which the charge roll was left for 5 days in a high temperature, high humidity environment (HH environment) of 40°C x 90% RH (relative humidity). After that, the cartridge with the charging roll still incorporated was incorporated into an HP "CLJ4525dn," and a halftone image was output in a low temperature, low humidity environment (LL environment) of 10°C x 10% RH (relative humidity). When no uniaxial streak images due to distortion of the charging roll occurred, or the occurrence was extremely slight and did not pose any practical problems, the result was marked "O," and when the above streaks occurred in part or all of the image, causing image problems, the result was marked "X."

[0093] (Moisture absorption) The manufactured charge roll was incorporated into an HP CLJ4525dn K-color cartridge and left in a high-temperature, high-humidity environment (HH environment) at 30°C and 80% RH (relative humidity) for one day. After that, the cartridge with the charge roll still incorporated was incorporated into an HP CLJ4525dn printer, and a halftone image was printed in a high-temperature, high-humidity environment (HH environment) at 30°C and 80% RH (relative humidity). When a white streak on one axis caused by distortion of the charge roll did not occur or the occurrence was very slight and did not cause any practical problems, it was evaluated as "◎". When the above streak occurred in part of the image but did not cause any practical problems, it was evaluated as "○". When the above streak occurred in part or the entire image and caused image problems, it was evaluated as "×". Note that the white streak occurs when resistance drops drastically due to moisture absorption, resulting in an overcharged state.

[0094] (Wear resistance) The manufactured charging roll was incorporated into an HP "CLJ4525dn K color cartridge" and printed 600,000 sheets in a 10°C x 10% RH environment in ruled line mode with a print density of 1%, after which a halftone image with a print density of 25% was printed. If no horizontal streaks were observed in the image, it was rated as "good" (○), and if horizontal streaks were observed, it was rated as "poor". "Wear resistance" was judged by whether horizontal streaks appeared in the image, which are caused by a decrease in the discharge area due to particle wear and a deterioration in charging properties.

[0095] [Table 1]

[0096] In Examples 1 to 4, the surface layer contains (a) a crosslinked product of a water-dispersible polyurethane dispersion, (b) a crosslinked product of a water-dispersible isocyanate, and (c) a crosslinked product of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate. Examples 1 to 4 demonstrate that both reduction in compression set and reduction in wear of the photoreceptor can be achieved, and that changes in properties due to moisture absorption can be reduced.

[0097] On the other hand, in Comparative Example 2, water-dispersible isocyanate was not blended in the preparation of the surface layer-forming composition, so the surface layer contains (a) a crosslinked product of water-dispersible polyurethane dispersion, but does not contain (b) a crosslinked product of water-dispersible isocyanate, or (c) a crosslinked product of water-dispersible polyurethane dispersion and water-dispersible isocyanate. According to Comparative Example 2, it is not possible to reduce compression set and changes in properties due to moisture absorption.

[0098] In Comparative Example 3, no polyurethane dispersion was added in the preparation of the surface layer-forming composition, so the surface layer contains (b) a crosslinked product of water-dispersible isocyanate, but does not contain (a) a crosslinked product of water-dispersible polyurethane dispersion or (c) a crosslinked product of water-dispersible polyurethane dispersion and water-dispersible isocyanate. Comparative Example 3 fails to reduce wear of the photoreceptor and to reduce changes in properties due to moisture absorption.

[0099] In Comparative Example 1, the surface layer contains (a) a crosslinked product of a water-dispersible polyurethane dispersion and (b) a crosslinked product of a water-dispersible isocyanate, but does not contain (c) a crosslinked product of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate. According to Comparative Example 1, it is not possible to reduce the change in properties due to moisture absorption.

[0100] Furthermore, a comparison between Example 1 and Example 4 reveals that non-porous particles for providing roughness are more effective in suppressing the reduction of changes in characteristics due to moisture absorption than porous particles.

[0101] 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]

[0102] 10 Charging roll 12 shaft body 14 Elastic layer 16 Surface layer

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, The charging roll for an electrophotographic device, wherein the surface layer comprises the following (a) to (c): (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked product of water-dispersible isocyanate (c) Crosslinked product of water-dispersible polyurethane dispersion and water-dispersible isocyanate

2. 2. The charge roll for an electrophotographic device according to claim 1, wherein the surface layer comprises roughness-forming particles.

3. 3. The charge roll for an electrophotographic device according to claim 2, wherein the roughness-forming particles are non-porous particles.

4. 3. The charging roll for an electrophotographic device according to claim 1, wherein the surface layer contains water-dispersible carbon black as a conductive agent.

5. 3. The charging roll for an electrophotographic device according to claim 1, wherein a ratio of (a) to (b) in the surface layer is in a range of (a):(b)=60:40 to 90:10 by mass.

6. the surface layer comprises non-porous roughness-forming particles; the surface layer contains water-dispersible carbon black as a conductive agent, 2. The charging roll for an electrophotographic device according to claim 1, wherein a ratio of (a) to (b) in the surface layer is in the range of (a):(b)=60:40 to 90:10 by mass.

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