Electrostatic roller for electrophotographic equipment

Abstract

The present invention provides a electrostatic roll for electrophotographic equipment that achieves both reduced compression set and reduced wear on the photoreceptor, while also having a surface layer that reduces changes in properties due to moisture absorption. [Solution] The electrophotographic electrostatic roll 10 comprises a shaft 12, an elastic layer 14 formed on the outer surface of the shaft 12, and a surface layer 16 formed on the outer 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 isocyanates (c) Crosslinked material 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 preferably used in electrophotographic equipment such as copiers, printers, and facsimiles that employ an electrophotographic method.

Background Art

[0002] As a charging roll for electrophotographic equipment, there is known one having an elastic body layer having rubber elasticity on the outer peripheral surface of a shaft body such as a core metal, and a surface layer on the outer peripheral surface of the elastic body layer. When forming the surface layer, it is common to apply a material dissolved in an organic solvent and perform a heat treatment. In this case, due to the use of an organic solvent, volatile organic compounds are discharged, so there are problems in terms of the environment and workability. On the other hand, it is also known to use an aqueous paint containing an aqueous urethane resin when forming the surface layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The surface layer of the charging roll is required to have both high hardness properties that are not easily deformed and easily elastically recovered (compression set is reduced) when contacting a mating member such as a photoreceptor, and low hardness properties that suppress wear of the roughness-forming particles blended in the surface layer and wear of the mating member such as the photoreceptor. Since these are contradictory characteristics, it is difficult to achieve both at a high level. When applying a material dissolved in an organic solvent during surface layer formation, it can be homogenized to the molecular level by dissolution, so it is good for the purpose of forming a uniform surface layer. However, since the material is homogenized, the overall hardness characteristics become intermediate, and it is difficult to satisfy both high hardness and low hardness. On the other hand, when using an aqueous paint, it is easy to absorb moisture from the outside air, so the hardness characteristics are likely to change due to environmental influences.

[0005] The problem that this invention aims to solve is to provide a charging roll for electrophotographic equipment that has a surface layer that can reduce both compression set and photoreceptor wear, as well as reduce changes in properties due to moisture absorption. [Means for solving the problem]

[0006] The electrostatic roller for electrophotographic equipment according to the present invention comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer, wherein the surface layer includes the following (a) to (c). (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanates (c) Crosslinked material of water-dispersible polyurethane dispersion and water-dispersible isocyanate

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

[0008] (1) The conductive roll for electrophotographic equipment according to the present invention comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer, wherein the surface layer includes the following (a) to (c). (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanates (c) Crosslinked material of water-dispersible polyurethane dispersion and water-dispersible isocyanate

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

[0010] (3) In the above (2), the roughness-forming particles are preferably non-porous particles.

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

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

[0013] The electrophotographic roller according to the present invention has a surface layer comprising (a) a crosslinked water-dispersible polyurethane dispersion, which is a component with relatively low hardness, and (b) a crosslinked water-dispersible isocyanate, which is a component with relatively high hardness. Since these are water-dispersible rather than dissolvable, they form a uniform surface at the macro level, while having both high-hardness and low-hardness areas at the micro level. This allows for the reduction of compression set in the high-hardness areas and the reduction of photoreceptor wear in the low-hardness areas, thus achieving both reduction of compression set and reduction of photoreceptor wear. Furthermore, the surface layer also comprises (c) a crosslinked water-dispersible polyurethane dispersion and a water-dispersible isocyanate. This area has a particularly high crosslink density. Due to its steric hindrance, moisture absorption from the outside air is suppressed. Therefore, even though it is a water-dispersible type, moisture absorption from the outside air is suppressed, and changes in properties due to moisture absorption can be reduced.

[0014] In this case, if the surface layer contains roughness-forming particles, suitable surface irregularities are formed on the surface layer, increasing the discharge space between the photoreceptor and the charging roll, thereby promoting discharge. This improves the electrostatic properties and suppresses image defects such as horizontal streaks and unevenness.

[0015] Furthermore, if the roughness-forming particles are non-porous particles, the surface structure is less likely to retain moisture absorbed from the outside air, thus reducing changes in properties due to moisture absorption.

[0016] When the surface layer contains water-dispersible carbon black as a conductive agent, the carbon black has excellent dispersibility in the surface layer. As a result, a macroscopically uniform surface can be formed.

[0017] When the ratio of (a) to (b) in the surface layer is within the range of (a):(b) = 60:40 to 90:10 in terms of mass ratio, it is possible to highly achieve both the reduction of compression set and the reduction of wear of the photoreceptor.

Brief Description of the Drawings

[0018] [Figure 1] It is an external schematic view (a) of a charging roll for an electrophotographic apparatus according to an embodiment of the present invention and a cross-sectional view taken along line A-A thereof (b).

Modes for Carrying Out the Invention

[0019] The charging roll for an electrophotographic apparatus according to the present invention (hereinafter, may be simply referred to as a charging roll) will be described in detail. FIG. 1 is an external schematic view (a) of a charging roll for an electrophotographic apparatus according to an embodiment of the present invention and a cross-sectional view taken along line A-A thereof (b).

[0020] The charging roll 10 includes a shaft body 12, an elastic body layer 14 formed on the outer peripheral surface of the shaft body 12, and a surface layer 16 formed on the outer peripheral surface of the elastic body layer 14. The elastic body layer 14 is a layer (base layer) that serves as the base of the charging roll 10. The surface layer 16 is a layer that appears on the surface of the charging roll 10. Although not particularly illustrated, an intermediate layer such as a resistance adjustment layer may be formed between the elastic body layer 14 and the surface layer 16 as necessary.

[0021] The shaft 12 is not particularly limited as long as it is conductive. Specifically, examples include a solid or hollow core made of metal such as iron, stainless steel, or aluminum. The surface of the shaft 12 may be coated with an adhesive or primer as needed. In other words, the elastic layer 14 may be bonded to the shaft 12 via an adhesive layer (primer layer). The adhesive or primer may be made conductive as needed.

[0022] The elastic layer 14 contains crosslinked rubber. The elastic layer 14 is formed from a conductive rubber composition containing uncrosslinked rubber. The crosslinked rubber is obtained by crosslinking the uncrosslinked rubber. The uncrosslinked rubber may be polar rubber or non-polar rubber.

[0023] Polar rubber is rubber having polar groups, and examples of polar groups include chloro groups, nitrile groups, carboxyl groups, and epoxy groups. Specifically, examples of polar rubber include hydrin rubber, nitrile rubber (NBR), urethane rubber (U), acrylic rubber (a copolymer of acrylic acid ester and 2-chloroethyl vinyl ether, ACM), chloroprene rubber (CR), and epoxidized natural rubber (ENR). Among polar rubbers, hydrin rubber and nitrile rubber (NBR) are more preferred from the viewpoint that they tend to have particularly low volume resistivity.

[0024] Examples of hydrin rubber include epichlorohydrin homopolymer (CO), epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO).

[0025] Examples of urethane rubber include polyether-type urethane rubber having ether bonds in its molecule. Polyether-type urethane rubber can be produced by the reaction of a polyether having hydroxyl groups at both ends with a diisocyanate. Examples of polyethers are not particularly limited, but include polyethylene glycol and polypropylene glycol. Examples of diisocyanates are not particularly limited, but include tolylene diisocyanate and diphenylmethane diisocyanate.

[0026] Examples of non-polar rubbers include silicone rubber (Q), isoprene rubber (IR), natural rubber (NR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). Among the non-polar rubbers, isoprene rubber is more preferred from the viewpoint of having excellent tensile strength.

[0027] The elastic layer 14 may contain one or more of isoprene rubber, nitrile rubber, or hydrin rubber. When the elastic layer 14 contains one or more of isoprene rubber, nitrile rubber, or hydrin rubber, the compression set is small, and the occurrence of streaks corresponding to the deformed parts when the charged roll 10 is set is suppressed.

[0028] Examples of crosslinking agents include sulfur crosslinking agents, peroxide crosslinking agents, and dechlorination crosslinking agents. These crosslinking agents may be used individually or in combination of two or more types.

[0029] Examples of conventionally known sulfur crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, sulfur chloride, thiram-based vulcanization accelerators, and polymeric polysulfides.

[0030] Examples of conventionally known peroxide crosslinking agents include peroxyketals, dialkyl peroxides, peroxyesters, ketone peroxides, peroxydicarbonates, diacyl peroxides, and hydroperoxides.

[0031] Examples of dechlorinating crosslinking agents include dithiocarbonate compounds. More specifically, these include quinoxaline-2,3-dithiocarbonate, 6-methylquinoxaline-2,3-dithiocarbonate, 6-isopropylquinoxaline-2,3-dithiocarbonate, and 5,8-dimethylquinoxaline-2,3-dithiocarbonate.

[0032] The amount of crosslinking agent added is preferably in the range of 0.1 to 2 parts by mass, more preferably in the range of 0.3 to 1.8 parts by mass, and even more preferably in the range of 0.5 to 1.5 parts by mass, per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding.

[0033] When using a dechlorinating crosslinking agent as a crosslinking agent, a dechlorinating crosslinking accelerator may be used in combination. Examples of dechlorinating crosslinking accelerators include 1,8-diazabicyclo(5,4,0)undecene-7 (hereinafter abbreviated as DBU) or its weak salt. The dechlorinating crosslinking accelerator may be used in the form of DBU, but it is preferable to use it in the form of its weak salt for ease of handling. Examples of weak salts of DBU include carbonate, stearate, 2-ethylhexylate, benzoate, salicylate, 3-hydroxy-2-naphthoate, phenol resin salt, 2-mercaptobenzothiazole salt, and 2-mercaptobenzimidazole salt.

[0034] The content of the dechlorination crosslinking accelerator is preferably in the range of 0.1 to 2 parts by mass per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding. More preferably, it is in the range of 0.3 to 1.8 parts by mass, and even more preferably, in the range of 0.5 to 1.5 parts by mass.

[0035] The elastic layer 14 may contain conductive agents to impart conductivity. Examples of conductive agents include electronic conductive agents and ionic conductive agents. Examples of electronic conductive agents include carbon black, graphite, and conductive metal oxides. Examples of conductive metal oxides include conductive titanium oxide, conductive zinc oxide, and conductive tin oxide. Examples of ionic conductive agents include quaternary ammonium salts, borates, and surfactants. In addition, various additives may be added to the elastic layer 14 as needed. Examples of additives include lubricants, vulcanization accelerators, antioxidants, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, defoamers, pigments, and mold release agents.

[0036] The elastic layer 14 can be adjusted to a predetermined volume resistivity by changing the type of crosslinked rubber, the amount of ionic conductive agent, the amount of electronic conductive agent, etc. The volume resistivity of the elastic layer 14 is 10 depending on the application, etc. 2 ~10 10 Ω·cm, 10 3 ~10 9 Ω·cm, 10 4 ~10 8 You can set it appropriately within the range of Ω·cm, etc.

[0037] The thickness of the elastic layer 14 is not particularly limited and can be set appropriately within the range of 0.1 to 10 mm depending on the application.

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

[0039] Water-dispersible polyurethane dispersions are materials in which polyurethane fine 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 preferable because they do not require the use of surfactants. Furthermore, in terms of self-emulsifying ability, anionic hydrophilic groups are more preferable. Examples of anionic hydrophilic groups include carboxylate groups and sulfonate groups.

[0040] Water-dispersible polyurethane dispersions exist in the form of fine particles (approximately 5-200 nm in size) in a dispersion liquid. By coating with the dispersion liquid and then drying and heat curing it, the fine particles become crosslinked polyurethane bodies. Water-dispersible polyurethane dispersions may be heat-crosslinkable or self-crosslinkable.

[0041] Water-dispersible isocyanates are materials in which isocyanate fine particles are dispersed in water. Water-dispersible isocyanates are preferably self-emulsifying types having hydrophilic groups. Preferred hydrophilic groups include anionic carboxylate groups and sulfonate groups. Water-dispersible isocyanates are preferably blocked isocyanates in which the terminal isocyanate groups are blocked by a blocking agent. Blocked isocyanates offer superior stability. In blocked isocyanates, the blocking agent dissociates and the isocyanates are released at temperatures above a predetermined dissociation temperature.

[0042] Water-dispersible isocyanates exist in the dispersion as fine particles (approximately 5-200 nm in size), and by coating the dispersion and drying / heat curing it, they become crosslinked isocyanates in their fine particle state. Water-dispersible isocyanates may be thermally crosslinked or self-crosslinked.

[0043] The blocked isocyanate preferably has a dissociation temperature of 100°C or higher, more preferably 120°C or higher. Furthermore, from the viewpoint of being able to keep the heating temperature required for the blocking agent to dissociate during curing low, it is preferable that the dissociation temperature be 160°C or lower, more preferably 140°C or lower.

[0044] Compounds containing active hydrogen are used as blocking agents. Examples of compounds containing active hydrogen include oximes, pyrazoles, carbazoles, secondary amines, β-dicarbonyl compounds, lactams, and phenols. These may be used individually as blocking agents that form blocked isocyanates, or two or more may be used in combination.

[0045] Examples of oximes include aldoximes and ketoximes. Examples of aldoximes include formaldehyde oxime and acetaldehyde oxime. Examples of ketoximes include dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, acetooxime, 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, ethyl isopropylamine, ethylbutylamine, ethyl isobutylamine, 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 acetoacetate esters such as methyl acetoacetate and acetate acetate. Examples of lactams include ε-caprolactam. Examples of phenols include phenols.

[0046] From the viewpoint of excellent stability of the blocked isocyanate and a suitable dissociation temperature of the blocked isocyanate, methyl ethyl ketoxime, diisopropylamine, phenol, ε-caprolactam, diethyl malonate, 3,5-dimethylpyrazole, and ethyl acetoacetate are preferred as blocking agents. Furthermore, from the viewpoint of the tendency for the dissociation temperature of the blocked isocyanate to be relatively low, 3,5-dimethylpyrazole and methyl ethyl ketoxime are preferred.

[0047] (c) A crosslinked product of a water-dispersible polyurethane dispersion and a 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 their interface.

[0048] The presence of (c) in the surface layer 16 can be determined, for example, by the weight change before and after placing the charged roll 10 in a high-temperature, high-humidity environment (HH environment) of 40°C × 90%RH (relative humidity) for 9 days. The surface layer 16 is hydrophilic and easily absorbs moisture from the atmosphere, but the presence of (c), which has a high crosslink density, suppresses the penetration of moisture into the interior of the surface layer 16. As a result, the weight increase is limited to the adsorption of moisture on the surface of the surface layer 16 and the absorption of moisture by the elastic layer 14 in the cross-section where the surface layer 16 is not present, and can be determined by the low weight increase rate before and after. The weight increase rate when (c) is present is less than 0.3 mass%.

[0049] (a) The water-dispersible polyurethane dispersion crosslinked material is the softest of (a) to (c). This property allows it to absorb pressure when in contact with the photoreceptor, suppressing wear of the roughness-forming particles and the photoreceptor. (b) The water-dispersible isocyanate crosslinked material is the hardest of (a) to (c). This property allows it to reduce compression set. Because these are water-dispersible rather than dissolved, they form a uniform surface at the macro level, while at the micro level they have both hard and soft areas. The hard areas reduce compression set, and the soft areas reduce wear of the photoreceptor, thus achieving both reduction of compression set and wear of the photoreceptor. (c) The water-dispersible polyurethane dispersion and water-dispersible isocyanate crosslinked material has the highest crosslink density among (a) to (c). Its steric hindrance suppresses moisture absorption from the outside air. Therefore, even in a water-dispersible type, moisture absorption from the outside air is suppressed, and changes in properties due to moisture absorption can be reduced.

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

[0051] The surface layer 16 may contain roughness-forming particles. These roughness-forming particles are used to impart roughness to the surface of the surface layer 16. In other words, they are used to create irregularities on 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 electrostatic properties and suppresses image defects such as horizontal streaks and unevenness.

[0052] Particles used to create roughness include inorganic particles, resin particles, and rubber particles. Examples of inorganic particles include silica particles. The material of the roughness-creating 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 ensuring uniform charging properties, an average particle diameter of 3.0 μm to 50 μm is preferred. More preferably, an average particle diameter of 3.0 μm to 30 μm is preferred. The average particle diameter of the roughness-forming particles is determined by observing the surface of the surface layer 16 with a laser microscope, and the diameter of the roughness-forming particles 16 visible during surface observation is defined as the particle size, expressed as the average of 20 arbitrary points.

[0054] The content of roughness-forming particles in the surface layer 16 is not particularly limited, but from the viewpoint of ensuring uniform electrostatic properties, it is preferably 3 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the binder polymer in the surface layer 16. More preferably it is 5 parts by mass or more and 40 parts by mass or less.

[0055] The roughness-forming particles are preferably non-porous particles. Non-porous particles have a surface structure that does not easily retain moisture absorbed from the outside air, thus reducing changes in properties due to moisture absorption. Non-porous particles can be particles with a porosity of 10% or less as defined in JIS Z 2506.

[0056] The surface layer 16 may contain a conductive agent. 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, quaternary phosphonium salts, imidazolium salts, borates, and surfactants.

[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 charge properties can be maintained even during durability without deterioration of durability due to bleed-out of the conductive agent, and a response speed that can handle the charging and discharging process can be achieved even in high-speed printing.

[0058] Water-dispersible carbon black is preferred. The inclusion of water-dispersible carbon black results in excellent dispersibility of the carbon black in the surface layer 16. This allows for the formation of a macroscopically uniform surface.

[0059] Water-dispersible carbon black preferably has anionic groups. This results in excellent water dispersibility.

[0060] The content of 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 per 100 parts by mass of the binder polymer in the surface layer 16. 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] Various additives may be added to the surface layer 16 as needed. Examples of additives include plasticizers, leveling agents, fillers, vulcanization accelerators, processing aids, and mold release agents.

[0062] The volume resistivity of the surface layer 16 should be set to the semiconducting region from the viewpoint of chargeability, etc. Specifically, for example, 1.0 × 10 7 ~1.0×10 10It is preferable to set the value within 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 (e.g., Keyence's "VK-9510"). For example, the distance from the surface of the elastic body layer 14 to the surface of the surface layer 16 can be measured at five arbitrary locations, and the thickness can be expressed by the average of these measurements.

[0063] The elastic layer 14 can be formed, for example, as follows: First, the shaft 12 is coaxially placed in the hollow part of a roll molding die, an uncrosslinked conductive rubber composition is injected and heated and cured (crosslinked), and then the mold is removed, or the uncrosslinked conductive rubber composition is extruded onto the surface of the shaft 12 to form the elastic layer 14 on the outer circumference of the shaft 12.

[0064] The surface layer 16 can be formed by using a surface layer 16 forming material, coating it onto the outer surface of the elastic layer 14, and performing drying and heating treatments as appropriate. In the drying and heating treatments, the water in the solvent is evaporated at a temperature below the dissociation temperature of the blocking agent of the water-dispersible isocyanate to reduce the amount of water, then a partial crosslinking reaction of the water-dispersible isocyanate is carried out at a temperature 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 between the polyurethane in the polyurethane dispersion and the water-dispersible isocyanate is carried out at a temperature above the activation temperature of the polyurethane in the polyurethane dispersion, thereby forming a surface layer 16 containing (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] In the electrostatic roll 10 with the above configuration, the surface layer 16 contains (a) a crosslinked water-dispersible polyurethane dispersion, which is a component with relatively low hardness, and (b) a crosslinked water-dispersible isocyanate, which is a component with relatively high hardness. Since these are water-dispersible rather than dissolvable, they form a uniform surface at the macro level, while having both high-hardness and low-hardness areas at the micro level. This allows for the reduction of compression set in the high-hardness areas and the reduction of photoreceptor wear in the low-hardness areas, thus achieving both reduction of compression set and reduction of photoreceptor wear. Furthermore, the surface layer 16 contains (c) a crosslinked water-dispersible polyurethane dispersion and water-dispersible isocyanate. This area has a particularly high crosslink density. Due to its steric hindrance, moisture absorption from the outside air is suppressed. Therefore, even though it is a water-dispersible type, moisture absorption from the outside air is suppressed, and changes in properties due to moisture absorption can be reduced. [Examples]

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

[0068] The following materials were prepared as components for the conductive rubber composition. • Isoprene rubber (IR): JSR "JSR IR2200" • Carbon Black: Cabot Japan's "Show Black N762" • Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc Oxide Type 2" • Stearic acid: Nippon Oil & Fats Co., Ltd. "Sakura Stearic Acid" • Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industries. • Thiazole-based vulcanization accelerator: "Noxellar DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Thiram-based vulcanization accelerator: "Noxellar TRA" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Heavy calcium carbonate: Shiraishi Calcium's "Whiten B", average particle size 3.6 μm

[0069] <Fabrication of elastic layers> A core metal (8 mm in diameter) was set in a molding die (pipe-shaped), the above composition was injected, and after heating at 180°C for 30 minutes, it was cooled and demolded to form an elastic layer made of a conductive rubber elastic material with a thickness of 1.9 mm on the outer circumference of the core metal.

[0070] <Preparation of surface-forming composition> Under conditions of 10°C to 35°C, polyurethane dispersion was stirred in water (solvent) for 1 hour. A water-dispersible isocyanate was then added, and stirring continued for another hour. Next, water-dispersible carbon black was added and stirred. After stirring, roughness-forming particles were added and the mixture was stirred further. The surface-forming composition was then prepared. The mixing ratios are as shown in Table 1.

[0071] <Preparation of the surface layer> The surface-forming composition was roll-coated onto the outer surface of the elastic layer. The water in the solvent was evaporated at a temperature below the dissociation temperature of the blocking agent for the water-dispersible isocyanate to reduce the water content. Then, a partial crosslinking reaction of the water-dispersible isocyanate was carried out at a temperature below the activation temperature of the polyurethane in the polyurethane dispersion. Subsequently, the crosslinking reaction of the polyurethane in the polyurethane dispersion and the crosslinking reaction between the polyurethane in the polyurethane dispersion and the water-dispersible isocyanate were carried out at a temperature above the activation temperature of the polyurethane in the polyurethane dispersion. As a result, a surface layer was formed (thickness 1.0 μm) containing (a) a crosslinked body of water-dispersible polyurethane dispersion, (b) a crosslinked body of water-dispersible isocyanate, and (c) a crosslinked body of water-dispersible polyurethane dispersion and water-dispersible isocyanate. The electrostatic roll of Example 1 was thus manufactured.

[0072] (Example 2) <Preparation of conductive rubber composition> A conductive rubber composition was prepared by mixing 100 parts by mass of NBR with 0.7 parts by mass of stearic acid, 5 parts by mass of zinc oxide, 2 parts by mass of hydrotalcite, 3 parts by mass of peroxide crosslinking agent, and 20 parts by mass of carbon, and stirring and mixing these ingredients with a stirrer.

[0073] The following materials were prepared as components for the conductive rubber composition. • NBR: "Nipol 1041" manufactured by Nippon Zeon Co., Ltd. • Stearic acid: NOF Corporation's "Sakura Stearic Acid" • Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc Oxide Type 2" • Hydrotalcite: Kyowa Chemical Industry Co., Ltd. "DHT4A" • Peroxide crosslinking agent: NOF Corporation's "Parkmill D40" • Carbon fiber: Ketjenbrak International "Ketjenbrak EC300J"

[0074] <Fabrication of elastic layers> The heating temperature was changed to 170°C, and an elastic layer made of conductive rubber elastic material was molded in the same manner as in Example 1.

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

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

[0077] (Example 3) <Preparation of conductive rubber composition> A conductive rubber composition was prepared by adding 5 parts by mass of a vulcanization aid, 10 parts by mass of carbon, 0.5 parts by mass of a vulcanization accelerator, 2 parts by mass of sulfur, and 50 parts by mass of a filler to 100 parts by mass of hydrin rubber, and then stirring and mixing these with a stirrer.

[0078] The following materials were prepared as components for the conductive rubber composition. • Hydrin rubber (ECO, manufactured by Nippon Zeon, "Hydrin H1100") • Vulcanization aid (zinc oxide, Mitsui & Co. "Zinc Oxide Type 2") • Carbon fiber (Ketjenbrak International "Ketjenbrak EC300J") • Vulcanization accelerator (2-mercaptobenzothiazole, "Noxellar MP" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Sulfur (manufactured by Tsurumi Chemical Industries, Ltd., "Sulfax PTC") • Filler (calcium carbonate, Shiraishi Kogyo Co., Ltd. "Shiratsuka CC")

[0079] <Fabrication of elastic layers> An elastic layer made of a conductive rubber elastic material was molded in the same manner as in Example 1.

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

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

[0082] (Example 4) <Preparation of conductive rubber composition> 50 parts by mass of NBR were mixed with 30 parts by mass of carbon black, and these were stirred and mixed using a stirrer. 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 added, and these were stirred and mixed using a stirrer to prepare a conductive rubber composition.

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

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

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

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

[0087] (Comparative Example 1) In preparing the surface layer-forming composition, the procedure was the same as in Example 1, except that the stirring was performed in an environment of 85°C to 100°C instead of 10°C to 35°C. Next, in preparing the surface layer, the surface layer-forming composition was roll-coated onto the outer surface of the elastic layer and heat-treated in an oven at 125°C for 60 minutes to form the surface layer (thickness 1.0 μm). Thus, the electrostatic roll of Comparative Example 1 was prepared.

[0088] (Comparative Example 2) In preparing the surface layer-forming composition, the surface layer-forming composition was prepared in the same manner as in Example 2, except that a water-dispersible isocyanate was not included, 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 surface of the elastic layer, as in Comparative Example 1, and the surface layer was formed by heat treatment in an oven at 125°C for 60 minutes (thickness 1.0 μm). Thus, the electrostatic roll of Comparative Example 2 was prepared.

[0089] (Comparative Example 3) In preparing the surface layer-forming composition, the composition was prepared in the same manner as in Example 1, except that polyurethane dispersion was not included. Next, in preparing the surface layer, the surface layer-forming composition was roll-coated onto the outer surface of the elastic layer and heat-treated in an oven at 125°C for 60 minutes to form the surface layer (thickness 1.0 μm). Thus, the electrostatic roll of Comparative Example 3 was prepared.

[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's "Hydran HW-350" • Water-dispersible isocyanate 1: Tosoh's "Aquanate 105", blocked isocyanate • Water-dispersible isocyanate 2: Lanxess "Trixene Aqua BI201", blocked isocyanate • Water-dispersible carbon black 1: Tokai Carbon's "Aqua-Black204" • Water-dispersible carbon black 2: Tokushiki "8652BLACK" • Roughness-forming particles 1 (non-porous): "SYLOSPHERE C-1504" manufactured by Fuji Silysia Chemical Co., Ltd. (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): "SYLYSIA 852" manufactured by Fuji Silysia Chemical Co., Ltd. (average particle size 5.0 μm)

[0091] The evaluation was performed using the fabricated electrostatic roll.

[0092] (Setting characteristics (compression set)) The manufactured electrostatic roll was assembled into an HP "CLJ4525dn K-color cartridge" and subjected to a compression set test by being left in a high-temperature, high-humidity environment (HH environment) of 40°C × 90%RH (relative humidity) for 5 days. After that, the cartridge with the electrostatic roll still assembled was assembled into an HP "CLJ4525dn" and a halftone image was output in a low-temperature, low-humidity environment (LL environment) of 10°C × 10%RH (relative humidity). If no uniaxial streaks caused by distortion of the electrostatic roll occurred, or if the occurrence was extremely slight and did not cause any practical problems, it was marked as "○". If the above streaks occurred in part or throughout the image, causing image defects, it was marked as "×".

[0093] (Moisture Absorption) The fabricated electrostatic roll was assembled into an HP "CLJ4525dn K-color cartridge," left for one day in a high-temperature, high-humidity environment (HH environment) of 30°C × 80%RH (relative humidity), and then the cartridge with the electrostatic roll still installed was assembled into an HP "CLJ4525dn" and a halftone image was output in a high-temperature, high-humidity environment (HH environment) of 30°C × 80%RH (relative humidity). If no uniaxial white streaks caused by distortion of the electrostatic roll occurred, or if the occurrence was extremely slight and did not pose a practical problem, it was marked as "◎". If the above streaks occurred in part of the image but did not pose a practical problem, it was marked as "○". If the above streaks occurred in part of or throughout the image and caused image defects, it was marked as "×". Note that the white streaks occur when the resistance drops drastically due to moisture absorption, resulting in an overcharged state.

[0094] (Abrasion Resistance) The fabricated electrostatic roll was assembled 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 that, a halftone image with a print density of 25% was printed. If no horizontal streaks were observed, it was judged as good ("○"), and if horizontal streaks were observed, it was judged as poor ("×"). "Abrasion" was judged by whether horizontal streaks, which occur when the discharge area decreases due to particle abrasion and the electrostatic properties deteriorate, appeared in the image.

[0095] [Table 1]

[0096] Examples 1-4 show that the surface layer comprises (a) a crosslinked water-dispersible polyurethane dispersion, (b) a crosslinked water-dispersible isocyanate, and (c) a crosslinked water-dispersible polyurethane dispersion and a water-dispersible isocyanate. Examples 1-4 demonstrate that it is possible to achieve both a reduction in compression set and a reduction in wear of the photoreceptor, as well as a reduction in changes in properties due to moisture absorption.

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

[0098] In Comparative Example 3, since polyurethane dispersion was not incorporated in the preparation of the surface layer forming composition, the surface layer contains (b) a water-dispersible isocyanate crosslinker, but does not contain (a) a water-dispersible polyurethane dispersion crosslinker, or (c) a water-dispersible polyurethane dispersion and a water-dispersible isocyanate crosslinker. According to Comparative Example 3, it is not possible to reduce wear on the photoreceptor or reduce changes in properties due to moisture absorption.

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

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

[0101] Although embodiments and examples of the present invention have been described above, the present invention is not limited in any way to the above embodiments and examples, and various modifications are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0102] 10 Electrostatic Rolls 12 Axis Body 14 Elastic layer 16 Surface layer

Claims

1. It comprises a shaft, an elastic layer formed on the outer circumferential surface of the shaft, and a surface layer formed on the outer circumferential surface of the elastic layer, A charging roll for electrophotographic equipment, wherein the surface layer includes (a) to (c) below. (a) Crosslinked water-dispersible polyurethane dispersion (b) Crosslinked water-dispersible isocyanates (c) Crosslinked material of water-dispersible polyurethane dispersion and water-dispersible isocyanate

2. The electrophotographic roller for electrophotographic equipment according to claim 1, wherein the surface layer contains roughness-forming particles.

3. The electrophotographic roller for electrophotographic equipment according to claim 2, wherein the roughness-forming particles are non-porous particles.

4. The electrophotographic roller according to claim 1 or claim 2, wherein the surface layer contains water-dispersible carbon black as a conductive agent.

5. The electrophotographic electrostatic roll according to claim 1 or claim 2, wherein the ratio of (a) to (b) in the surface layer is in the range of (a):(b) = 60:40 to 90:10 by mass ratio.

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

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