Charging roll for electrophotographic apparatus

Abstract

Provided is a charging roll for an electrophotographic apparatus, the charging roll both reducing compression set and reducing wear of a photoreceptor, and comprising a surface layer capable of reducing a change in characteristics resulting from moisture absorption.　This charging roll 10 for an electrophotographic apparatus comprises a shaft 12, an elastic layer 14 formed on the outer circumferencial surface of the shaft 12, and a surface layer 16 formed on the outer circumferencial surface of the elastic layer 14. The surface layer 16 contains (a) to (c) below. (a) A crosslinked product of a water-dispersible polyurethane dispersion. (b) A crosslinked product of a water-dispersible isocyanate. (c) A crosslinked product of a water-dispersible polyurethane dispersion and a water-dispersible isocyanate.

Description

Charging Roll for Electrophotographic Apparatus

[0001] The present invention relates to a charging roll for an electrophotographic apparatus, which is suitably used in electrophotographic apparatuses such as copiers, printers, and facsimiles that employ an electrophotographic method.

[0002] As a charging roll for an electrophotographic apparatus, one having an elastic layer with rubber elasticity on the outer peripheral surface of a shaft body such as a core metal and having a surface layer on the outer peripheral surface of the elastic layer is known. When forming the surface layer, it is common to apply a material dissolved in an organic solvent and perform 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.

[0003] Japanese Patent Application Laid-Open No. 2008-70444

[0004] The surface layer of the charging roll is required to have both high hardness such that it is difficult to sag and easily elastically recovers (compression set is reduced) when contacting a mating member such as a photoreceptor, and low hardness such that wear of the roughness-forming particles incorporated in the surface layer and wear of the mating member such as a photoreceptor are suppressed. Since these are conflicting 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, it has intermediate hardness characteristics as a whole, and it is difficult to satisfy both high hardness and low hardness. On the other hand, when using an aqueous paint, it is likely to absorb moisture from the outside air, so the hardness characteristics are likely to change due to environmental influences.

[0005] The problem to be solved by the present invention is to provide a charging roll for an electrophotographic apparatus having a surface layer that can achieve both reduction of compression set and reduction of wear of the photoreceptor, and can reduce characteristic changes due to moisture absorption.

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

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

[0010] (3) In (2) above, 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 is preferably in the range of (a):(b) = 60:40 to 90:10 by mass ratio.

[0013] The electrostatic roll for electrophotographic equipment 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] Furthermore, if the surface layer contains water-dispersible carbon black as a conductive agent, the carbon black exhibits excellent dispersibility on the surface. This allows for the formation of a macroscopically uniform surface.

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

[0018] This is a schematic external view (a) of a charging roll for electrophotographic equipment according to one embodiment of the present invention, and a cross-sectional view (b) of the same roll along line A-A.

[0019] A charging roll for electrophotographic equipment (hereinafter sometimes simply referred to as a charging roll) according to the present invention will be described in detail. Figure 1 is a schematic external view (a) and a cross-sectional view (b) of the same as a charging roll for electrophotographic equipment according to one embodiment of the present invention.

[0020] The charging roll 10 comprises a shaft 12, an elastic layer 14 formed on the outer circumferential surface of the shaft 12, and a surface layer 16 formed on the outer circumferential surface of the elastic layer 14. The elastic layer 14 is the base layer of the charging roll 10. The surface layer 16 is the layer that appears on the surface of the charging roll 10. Although not specifically shown in the figures, an intermediate layer such as a resistance adjustment layer may be formed between the elastic layer 14 and the surface layer 16 as needed.

[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 generation 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, examples 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 to be 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 the following (a) to (c). (a) to (c) are 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 isocyanate (c) Crosslinked water-dispersible polyurethane dispersion and water-dispersible isocyanate

[0039] A water-dispersible polyurethane dispersion is a material in which polyurethane fine particles are dispersed in water. The water-dispersible polyurethane dispersion can be classified into a self-emulsifying type and a forced emulsifying type by an emulsification method. It can also be classified into an anionic type and a nonionic type according to the type of hydrophilic group introduced. The self-emulsifying type is obtained by introducing a hydrophilic group into polyurethane to make it self-dispersible. The forced emulsifying type is obtained by forcibly emulsifying hydrophobic polyurethane with a surfactant. The self-emulsifying type is preferred in that no surfactant is required. Also, as the type of hydrophilic group to be introduced, the anionic type is more preferred in terms of self-emulsifying power. Examples of anionic hydrophilic groups include carboxylate groups and sulfonate groups.

[0040] The water-dispersible polyurethane dispersion exists in the form of fine particles (particles of about 5 to 200 nm) in the dispersion liquid. By applying the dispersion liquid and drying and heat-curing it, a crosslinked body of polyurethane is formed in the state of fine particles. The water-dispersible polyurethane dispersion may be a thermally crosslinked type or a self-crosslinked type.

[0041] A water-dispersible isocyanate is a material in which isocyanate fine particles are dispersed in water. The water-dispersible isocyanate is preferably of the self-emulsifying type having a hydrophilic group. Preferred hydrophilic groups include anionic carboxylate groups and sulfonate groups. The water-dispersible isocyanate is preferably a blocked isocyanate in which the terminal isocyanate group is blocked with a blocking agent. Being a blocked isocyanate, the water-dispersible isocyanate has excellent stability. The blocked isocyanate is such that the blocking agent dissociates and the isocyanate is liberated at a temperature above a predetermined dissociation temperature.

[0042] The water-dispersible isocyanate exists in the form of fine particles (particles of about 5 to 200 nm) in the dispersion liquid. By applying the dispersion liquid and drying and heat-curing it, a crosslinked body of isocyanate is formed in the state of fine particles. The water-dispersible isocyanate may be a thermally crosslinked type or a self-crosslinked type.

[0043] The blocked isocyanate preferably has a dissociation temperature of 100 °C or higher, more preferably 120 °C or higher. Further, from the viewpoint of easily suppressing the heating temperature for the blocking agent to dissociate during curing, the dissociation temperature is preferably 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, phenols, and the like. These may be used alone as one kind of the blocking agent for forming the blocked isocyanate, or two or more kinds may be used in combination.

[0045] Examples of the oximes include aldoximes and ketoximes. Examples of the aldoximes include formaldehyde oxime and acetaldehyde oxime. Examples of the ketoximes include dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, acetone oxime, cyclohexanone oxime, and the like. Examples of the pyrazoles include pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, and the like. Examples of the carbazoles include carbazole. Examples of the 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, 2,2,6,6-tetramethylpiperidine, and the like. Examples of the 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 the lactams include ε-caprolactam. Examples of the phenols include phenol.

[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 having a relatively low dissociation temperature of the blocked isocyanate, 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 electrostatic 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 help to reduce compression set, and the soft areas help to 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 by mass ratio.

[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 particles that 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 easily ensuring uniform chargeability, 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. When the roughness-forming particles are non-porous particles, their surface structure makes it difficult for moisture absorbed from the outside air to be retained, 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 during 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 and other factors. Specifically, for example, 1.0 × 10 ７ ~1.0 x 10 １０ It 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 (for example, 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 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 a reduction in compression set in the high-hardness areas and a reduction in photoreceptor wear in the low-hardness areas, thus achieving both a reduction in compression set and a reduction in 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.

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

[0067] (Example 1) <Preparation of conductive rubber composition> 100 parts by mass of isoprene rubber was mixed 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 to prepare a conductive rubber composition.

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

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

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

[0071] <Preparation of the surface layer> The surface layer forming composition was roll-coated onto the outer surface of the elastic layer. After reducing the amount of water by evaporating the water in the solvent below the dissociation temperature of the blocking agent of the water-dispersible isocyanate, a partial crosslinking reaction of the water-dispersible isocyanate was carried out below the activation temperature of the polyurethane in the polyurethane dispersion. Subsequently, 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 were carried out 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.

[0072] (Example 2) <Preparation of conductive rubber composition> 100 parts by mass of NBR was mixed 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. These were stirred and mixed using a stirrer to prepare a conductive rubber composition.

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

[0074] <Preparation of the elastic layer> 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-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> In the same manner as in Example 1, a surface layer was formed 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 (thickness 1.0 μm).

[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 components for the conductive rubber composition: • Hydrin rubber (ECO, "Hydrin H1100" manufactured by Nippon Zeon Co., Ltd.) • Vulcanization aid (zinc oxide, "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd.) • Carbon ("Ketjenbrak EC300J" manufactured by Ketjenbrak International Co., Ltd.) • Vulcanization accelerator (2-mercaptobenzothiazole, "Noxellar M-P" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Sulfur ("Sulfax PTC" manufactured by Tsurumi Chemical Industry Co., Ltd.) • Filler (calcium carbonate, "Hakuenka CC" manufactured by Shiraishi Industries Co., Ltd.)

[0079] <Preparation of the elastic layer> 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-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> In the same manner as in Example 1, a surface layer was formed 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 (thickness 1.0 μm).

[0082] (Example 4) <Preparation of conductive rubber composition> 50 parts by mass of NBR and 30 parts by mass of carbon black were mixed and stirred with 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 mixed and stirred with 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: Nipol IR2200 (manufactured by Nippon Zeon Co., Ltd.) • Carbon black: Showblack N762 (manufactured by Cabot Japan Co., Ltd.) • Peroxide crosslinking agent: Parkmill D40 (manufactured by NOF Corporation) • Vulcanization aid (zinc oxide, Zinc Oxide Type 2 (manufactured by Mitsui Mining & Smelting Co., Ltd.)

[0084] <Preparation of the elastic layer> 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> In the same manner as in Example 1, a surface layer was formed 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 (thickness 1.0 μm).

[0087] (Comparative Example 1) A surface layer forming composition was prepared in the same manner as in Example 1, except that the stirring was performed in an environment of 85°C to 100°C instead of an environment of 10°C to 35°C. Next, in the preparation of 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). The electrostatic roll of Comparative Example 1 was thus prepared.

[0088] (Comparative Example 2) A surface layer forming composition was prepared in the same manner as in Example 2, except that a water-dispersible isocyanate was not included in the preparation of the surface layer forming composition, and the type and blending ratio of polyurethane dispersion and the type of water-dispersible carbon black were changed. Next, in the preparation of 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). The electrostatic roll of Comparative Example 2 was thus prepared.

[0089] (Comparative Example 3) A surface layer forming composition was prepared in the same manner as in Example 1, except that polyurethane dispersion was not included in the preparation of the surface layer forming composition. Next, in the preparation of 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). The electrostatic roll of Comparative Example 3 was thus produced.

[0090] The materials used for the surface layer are as follows: • Water-dispersible polyurethane dispersion 1 (PUD1): UBE's "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's "Trixene Aqua BI201", Blocked isocyanate / water-dispersible carbon black 1: Tokai Carbon's "Aqua-Black 204" • Water-dispersible carbon black 2: Tokushiki's "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): Sekisui Plastics Co., Ltd. "Techpolymer SBX-6" (average particle size 6.0 μm) - Roughness forming particles 3 (porous): Fuji Silysia Chemical Co., Ltd. "SYLYSIA 852" (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 for 5 days in a high-temperature, high-humidity environment (HH environment) of 40°C × 90% RH (relative humidity). 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] (Hygroscopicity) The manufactured 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 x 80% RH (relative humidity), and then the cartridge with the electrostatic roll still assembled was assembled into an HP "CLJ4525dn" and a halftone image was output in a high-temperature, high-humidity environment (HH environment) of 30°C x 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 manufactured 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, appear in the image.

[0095]

[0096] Examples 1 to 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 to 4 show 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 changes in properties 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 crosslinked water-dispersible isocyanate, but does not contain (a) a crosslinked water-dispersible polyurethane dispersion or (c) a crosslinked water-dispersible polyurethane dispersion and water-dispersible isocyanate. 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.

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

Claims

1. A charging roll for electrophotographic equipment comprising 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) a crosslinked body of water-dispersible polyurethane dispersion (b) a crosslinked body of water-dispersible isocyanate (c) a crosslinked body 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 for electrophotographic equipment according to any one of claims 1 to 3, wherein the surface layer contains water-dispersible carbon black as a conductive agent.

5. The electrophotographic roller for electrophotographic equipment according to any one of claims 1 to 4, 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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