Fixing roll and silicone gel for use therein

Abstract: A low durometer fixing roll is described comprising a roller shaft, a peelable organic resin layer established on the external circumferential surface of the roller shaft, and a silicone gel layer interposed between them. The silicone gel composition comprises (A) an alkenyl-substituted organopolysiloxane, (B) an organohydrogenpolysiloxane, in a quantity sufficient to provide 0.1 to 5 moles of silicon-bonded hydrogen in component (B) per mole of alkenyl groups in component (A) and (C) a sufficient quantity of platinum catalyst for curing the silicone gel composition.

Description: This invention relates to a fixing roll and to a silicone gel composition for use therein. More particularly, this invention relates to a low durometer fixing roll having a peelable organic resin layer established on the external circumferential surface of a roller shaft with a silicone gel layer interposed between them. This invention also relates to a silicone gel composition which is usable as the silicone layer of the fixing roll. Fixing rolls with a fluorine resin layer established on the external circumferential surface of a metal roller shaft with a silicone rubber layer interposed between them are of superior toner peelability and are used as fixing rolls for devices such as electronic copying machines, printers and facsimiles. (See JP-As 53-74436, 57-89785, 59-74578 and 59-52269). As the aforementioned devices have been made smaller and lighter as a result of these fixing rolls, silicone rubbers of comparatively low durometer have been used as the silicone rubbers for forming the silicone rubber layer. (JP-A-07-207163). Specifically, while the thickness of the fixing roll has been reduced by use of silicone rubbers of comparatively low durometer, a suitable nip width can be obtained by low nip pressure, and, in turn, the aforementioned devices can further be made smaller and lighter. Also, silicone rubber films are used to form a silicone rubber layer for the purpose of decreasing the durometer of the fixing roll. (JP-A 63-139380). However, there remains the problem that fixing rolls in which silicone rubber films are used readily undergo permanent compression set due to nip pressure. EP-A-0,320,533 provides a silicone elastomer-covered roll consisting of a central roll axle which is in contact with an inner layer of cured silicone elastomer having a hardness value no greater than 30 on the JIS A scale and an outer layer of cured silicone material having a hardness in excess of that of the inner layer. EP-A-0,321,162 discloses an image fixing rotatable device which comprises a heating roller onto which is a silicone rubber layer. The silicone rubber layer has a hardness preferably lower than that of the heating roller, in particular, to a value of between 20 to 60 as measured on the JIS A scale. We have conducted intensive studies of the aforementioned problems, and, as a result, have arrived at this invention. Specifically, the objectives of this invention are to provide a fixing roll of superior durability and low durometer with a suitable nip width which can be obtained at a low nip pressure in spite of the fact that the thickness of the fixing roll is decreased. We also provide a silicone gel composition for making this fixing roll. The fixing roll of this invention comprises a roller shaft, a peelable organic resin layer established on the external circumferential surface of the roller shaft, and a layer of cured silicone gel interposed between the roller shaft and an organic resin layer, the cured silicone gel having a penetration value, as measured according to JIS K 2207, of 20 to 200. The present invention also relates to the fixing roll described above wherein the cured silicone gel is prepared by mixing a silicone gel composition comprising (A) an alkenyl-substituted organopolysiloxane having an average of at least two alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule, in a quantity sufficient to provide 0.1 to 5 moles of silicon-bonded hydrogen atoms in component (B) per mole of alkenyl groups in component (A); and (C) a sufficient quantity of platinum catalyst for curing the silicone gel composition; wherein the silicone gel composition is curable via an addition reaction and when so cured forms a silicone gel having a penetration value, as measured according to JIS K 2207, of 20 to 200. The present invention also relates to the silicone gel composition described above. We shall now present a detailed description of the fixing roll of this invention by reference to Figure 1 which is a cross-sectional view of the fixing roll of this invention. This fixing roll is characterized by the peelable organic resin layer 3 established on the external circumferential surface of the roller shaft 1 with the silicone gel layer 2 interposed between them. The roller shaft 1 can be made, for example, of iron, stainless steel, copper and aluminum. The organic resin that forms the peelable organic resin layer 3 for example, fluorine resins such as polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin (PFA), ethylene fluoride-polypropylene copolymer resin (FEP), tetrafluoroethylene-ethylene copolymer resins (ETFE), polychlorotrifluoroethylene copolymer resin (PCTFE), polyvinylidene fluoride resin (PVDF). polyvinyl fluoride resin (PVF) and ethylene trifluorochloride-ethylene copolymer resin (ECTFE), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), fluorine rubbers such as vinylidene fluoride-hexafluoropropylene copolymer rubber (VDF-HFP), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer rubber (VDF-HFP-TFE) and tetrafluoroethylene-propylene copolymer rubber (TFE-Pr) and polyolefin resins such as polyethylene resins and polypropylene resins, with fluorine resins or fluorine rubbers being particularly preferred. The thickness of the peelable organic resin layer 3 should be less than 0.1 mm, and, preferably, 0.1 to 50 µm. The silicone gel that forms the silicone gel layer 2 is characterized in that the penetration as measured according to JIS K 2207 is 20 to 200. In preferred embodiments, the penetration is 50 to 150. This silicone gel may also have a compression set as measured according to JIS C 2123 of less than 15%. The thickness of the silicone gel layer 2 should be 2 to 30 mm. Japanese Industrial Standard JIS K 2207 is used to determine the penetration value of the cured silicone gel used in the fixing roll of the present invention. The penetration value indicates hardness and is expressed by the penetrating length of a needle used in the test apparatus conventionally known as described in JIS K 2207, which penetrates into the test sample perpendicularly and wherein the test apparatus and sample are kept at a fixed temperature of approximately 25°C in a thermostatic water bath for a fixed time of the test. The needle is allowed to penetrate into the sample by self weight for approximately 5 seconds. 0.1 mm of penetration is defined as 1 unit. According to an embodiment of the invention, the cured silicone gel has a compression set of less than 15% as measured by JIS C 2123. The thickness specified for the test specimen is achieved by stacking 2 circular plates punched from a test sample (6.3-6.4 mm thick) and vulcanising the sample according to the conditions stipulated in JIS C 2123. Vulcanisation, therefore, may be carried out by first conducting press vulcanisation at a pressure of approximately 2.94 MPa at a temperature of 120± 2°C and for approximately 10 minutes followed by secondary vulcanisation at a constant temperature of approximately 200°C for 4 hours. The compression test is then carried out essentially as described in JIS K 6301, at 180± 2°C for approximately 22 hours. The test is carried out using a compression device consisting of 2 or more flat compression plates and spacers as is conventionally known. The thickness of the test sample is measured prior to the test at a central portion of the test sample. After the test sample and spacers are inserted, upper and lower compression plates are pressed until the plates come into close contact with the spacers. The compression rate of the test sample is approximately 25% of the thickness of the test sample. When the heat treatment is completed, the test sample is taken out of the compression device as quickly as possible and allowed to stand at room temperature for 30 minutes. Measurement of the thickness of the test sample is carried out as before. The rate of compression set is calculated by the formula: CS = t 0 -t 1 t 0 -t 2 x 100 where, CS is the rate of compression set (%) t 0 is the original thickness of the test sample (mm) t 1 is the thickness of the test sample measured 30 minutes after it was taken out from the compression device (mm) t 2 is the thickness of the spacer (mm). The silicone gel composition that forms our silicone gel can include, for example, silicone gel compositions that are cured by addition reactions, silicone gel compositions that are cured by condensation reactions and silicone gel compositions that are cured by organic peroxides. Silicone gel compositions that are cured by addition reactions are desirable because the fixing roll can be manufactured efficiently. The silicone gel compositions that are cured by addition reactions should be silicone gel compositions comprised of (A) an alkenyl-substituted organopolysiloxane having at least two alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, in a quantity that provides 0.1 to 5 moles of silicon-bonded hydrogen atoms in component (B) per mole of alkenyl groups in component (A); and (C) a sufficient quantity of platinum catalyst for curing this composition. The alkenyl-substituted organopolysiloxane comprising component (A) has an average of at least two alkenyl groups per molecule. The alkenyl groups in component (A) are, for example, vinyl, allyl, butenyl, pentenyl, hexenyl and heptenyl. Vinyl groups and hexenyl groups are particularly preferred. The bond positions of the alkenyl groups in component (A) are, for example, the terminals of the molecular chain and/or the side chains of the molecular chain. To minimize the compression set of the silicone gel, at least one alkenyl group is bonded to a side chain of the molecular chain. Groups that are bonded to silicon atoms other than the alkenyl groups in component (A) are, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups such as benzyl or phenethyl, alkyl halides such as chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl; alkoxy groups such as methoxy or ethoxy and hydroxyl groups. Of these, methyl groups and phenyl groups are particularly preferred. The molecular structure of component (A) is, for example, straight chain, straight chain having some branches, branched chain, cyclic or reticulate. Component (A) may be a single polymer having these molecular structures, or it may be a mixture of polymers having these molecular structures. When the organohydrogenpolysiloxane comprising component (B) is essentially straight chain, component (A) should essentially be straight chain also. The viscosity of component (A) at 25°C is 50 to 1,000,000 mPa.s, and, preferably 100 to 100,000 mPa.s. When the viscosity of component (A) at 25°C is less than 50 mPa.s, there is the possibility that the mechanical strength of the silicone gel obtained may be decreased. When it exceeds 1,000,000 mPa.s, there is the possibility that handling and workability of the silicone gel composition will be decreased. The alkenyl-substituted organopolysiloxanes comprising component (A) are, for example, dimethylsiloxane-methylvinylsiloxane copolymers both molecular chain terminals of which are blocked by trimethylsiloxy groups, methylvinyl polysiloxanes both molecular chain terminals of which are blocked by trimethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer both molecular chain terminals of which are blocked by trimethylsiloxy groups, methylvinylsiloxane-dimethylsiloxane-methyl (3,3,3-trifluoropropyl) siloxane copolymer both molecular chain terminals of which are blocked by trimethylsiloxy groups, methylvinylsiloxane-dimethylsiloxane copolymer both molecular chain terminals of which are blocked by silanol groups, methylvinyl polysiloxanes both molecular chain terminals of which are blocked by silanol groups, methylvinylsiloxane-dimethylsiloxane-methylphenylsiloxane copolymer both molecular chain terminals of which are blocked by silanol groups, methylvinylsiloxane-dimethylsiloxane-methyl (3,3,3-trifluoropropyl) siloxane copolymer both molecular chain terminals of which are blocked by silanol groups, dimethylpolysiloxanes both molecular chain terminals of which are blocked by dimethylvinylsiloxy groups, methylvinyl polysiloxanes both molecular chain terminals of which are blocked by dimethylvinylsiloxy groups, dimethylsiloxane-methylvinyl siloxane copolymer both molecular chain terminals of which are blocked by dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer both molecular chain terminals of which are blocked by dimethylvinylsiloxy groups, dimethylpolysiloxanes both molecular chain terminals of which are blocked by dimethylhexenyl groups, organopolysiloxane copolymer comprised of siloxane units as indicated by the formula R 1 3 SiO 1/2 , siloxane units as indicated by the formula R 1 2 R 2 SiO 1/2 and siloxane units as indicated by the formula SiO 4/2 , organopolysiloxane copolymer comprised of siloxane units as indicated by the formula R 1 2 R 2 SiO 1/2 and siloxane units as indicated by the formula SiO 4/2 , organopolysiloxane copolymer comprised of siloxane units as indicated by the formula R 1 R 2 SiO 2/2 , siloxane units as indicated by the formula R 1 SiO 3/2 or siloxane units as indicated by the formula R 2 SiO 3/2 and mixtures of two or more of these organopolysiloxanes. R 1 in these formulas is a monovalent hydrocarbon group other than an alkenyl group, including, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups such as benzyl or phenethyl; and alkyl halide groups such as chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl. In addition, R 2 is alkenyl groups, including, vinyl, allyl, butenyl, pentyl, hexenyl and heptyl. The organohydrogenpolysiloxane comprising component (B) is the cross linking agent of our silicone gel composition and has an average of at least two silicon-bonded hydrogen atoms per molecule. The bond position of the silicone-bonded hydrogen in the molecule may be, for example, the molecular chain terminal and/or a side chain of the molecular chain. Groups that may be bonded with the silicon atoms other than the hydrogen atoms of component (B) include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups such as benzyl or phenethyl; and alkyl halides such as chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl. Of these, methyl groups and phenyl groups are particularly preferred. The molecular structure of component (B) may be, for example, straight chain, straight chain having some branches, branched chain, cyclic or reticulate. Component (B) may be a single polymer having these molecular structures, or it may be a mixture of polymers having these molecular structures. When component (A) is essentially straight chain, component (B) should essentially be straight chain also. The viscosity of component (B) at 25°C is 1 to 500,000 mPa.s, and preferably 5 to 100,000 mPa.s. When the viscosity of component (B) at 25°C is less than 1 mPa.s, it readily volatilizes and the structure of the silicone gel composition that is obtained may not be stable. When it exceeds 500,000 mPa.s, there is the possibility that handling and workability of the silicone gel composition will be decreased. The organohydrogenpolysiloxanes of component (B) may be, for example, methylhydrogen polysiloxane both molecular chain terminals of which are blocked by trimethylsiloxy groups, dimethylsiloxane-methylhydrogen siloxane copolymer both molecular chain terminals of which are blocked by trimethylsiloxy groups, dimethylsiloxane-ethylhydrogensiloxane-methylphenylsiloxane copolymer both molecular chain terminals of which are blocked by trimethylsiloxy groups, dimethylpolysiloxane both molecular chain terminals of which are blocked by dimethylhydrogensiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymer both molecular chain terminals of which are blocked by dimethylhydrogensiloxy groups, methylphenyl polysiloxane both molecular chain terminals of which are blocked by dimethylhydrogensiloxy groups, organopolysiloxane copolymer comprised of siloxane units as indicated by the formula R 1 3 SiO 1/2 , siloxane units as indicated by the formula R 1 2 HSiO 1/2 and siloxane units as indicated by the formula SiO 4/2 , organopolysiloxane copolymer comprised of siloxane units as indicated by the formula R 1 2 HSiO 1/2 and siloxane units as indicated by the formula SiO 4/2 , organopolysiloxane copolymer comprised of siloxane units as indicated by the formula R 1 HSiO 2/2 and siloxane units as indicated by the formula R 1 SiO 3/2 or siloxane units as indicated by the formula HSiO 3/2 and mixtures of two or more of these organopolysiloxanes. R 1 is a monovalent hydrocarbon group other than an alkenyl group, including, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups such as benzyl or phenethyl; and alkyl halide groups such as chloromethyl, 3-chloropropyl and 3,3,3-trifluoropropyl. The quantity of component (B) should be such that provides 0.1 to 5 moles of silicon-bonded hydrogen atoms in component (B) per mole of alkenyl group in component (A). A silicone gel composition in which there is less than 0.1 mole of silicon-bonded hydrogen atoms in component (B) per 1 mole of alkenyl group in component (A) does not cure sufficiently. Further, a silicone gel composition in which this amount exceeds 5 moles cures to a silicone gel having a reduced heat resistance. The platinum catalyst comprising component (C) is a catalyst for the purpose of promoting curing of the silicone gel composition. The platinum catalyst includes, for example, platinum powder, platinum black, platinum carried on silica, platinum carried on carbon, chloroplatinic acid, alcohol solutions of chloroplatinic acid, complexes of platinum and olefins, complexes of platinum and alkenylsiloxanes and thermoplastic resins of particle diameters of less than 10 µm such as polystyrene resins, nylon resins, polycarbonate resins and silicone resins that contain these platinum catalysts. The quantity of component (C) compounded is that sufficient to cure the silicone gel composition. Practically, the platinum metal in component (C) is 0.1 to 1,000 ppm in terms of weight units. Quantities of 1 to 500 ppm are particularly preferred. When the platinum metal in component (C) is less than 0.1 ppm in terms of weight units, curing of our silicone gel composition is markedly slowed. Silicone gel compositions in which the quantity exceeds 1000 ppm do not exhibit any particular improvement in curing capacity. Rather, there is the possibility that the silicone gel that is obtained may undergo coloration. It is also desirable to compound a diorganopolysiloxane that is free of alkenyl groups and silicon-bonded hydrogen atoms with the above silicone gel composition [(components (A) through (C)]. This diorganopolysiloxane is for decreasing the durometer of the silicone gel and for increasing penetration as measured according to JIS K 2207. Groups that bind to the silicon atoms of the diorganopolysiloxane include, for example, alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups such as benzyl or phenethyl; and alkyl halide groups such as chloromethyl, 3-chloropropyl and 3,3,3-trichloropropyl. Of these, methyl groups and phenyl groups are particular preferred. These diorganopolysiloxanes are essentially straight chain and may also have some branched chains. It is preferred that the diorganopolysiloxane be liquid or rubbery with a viscosity at 25°C greater than 100 mPa.s. It is particularly preferred that it have a viscosity at 25°C of 1,000 to 10,000,000 mPa.s because the handling and workability of the silicone gel composition is superior. Also, the diorganopolysiloxane readily hardens and does not bleed from the silicone gel. When the viscosity of the diorganopolysiloxane at 25°C is less than 100 mPa.s, there is the possibility that it will bleed out of the silicone gel. This diorganopolysiloxane may have both molecular chain terminals blocked by trimethylsiloxy groups, or it may be dimethyl siloxane-methylphenyl siloxane copolymer both molecular chain terminals of which are blocked by trimethylsiloxy groups, dimethyl siloxane - methyl(3,3,3-trifluoropropyl)siloxane copolymer both molecular chain terminals of which are blocked by trimethylsiloxy groups, dimethylpolysiloxane both molecular chain terminals of which are blocked by silanol groups, dimethyl siloxane-methylphenyl siloxane copolymer both molecular chain terminals of which are blocked by silanol groups and mixtures of two or more of these diorganopolysiloxanes. The quantity in which these diorganopolysiloxanes is compounded should be 5 to 200 parts by weight, and, preferably, 10 to 150 parts by weight, per 100 parts by weight of component (A). When the quantity of diorganopolysiloxane is less than 5 parts by weight per 100 parts of component (A), the durometer of the silicone gel is not sufficiently lowered. When it exceeds 200 parts by weight, the diorganopolysiloxane may bleed from the silicone gel that is obtained. Addition reaction controlling agents can be compounded as optional components with our silicone gel composition for the purpose of improving storage stability and handling or workability. These agents include acetylene compounds such as 3-methyl-1-buten-3-ol, 3,5-dimethyl-1-hexen-3-ol and 3-phenyl-1-buten-3-ol; enine compounds such as 3-methyl-3-buten-1-ine or 3,5-dimethyl-3-hexen-1-ine; triazoles such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane or 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane; phosphines; mercaptans and hydrazines. The quantity in which these cure controlling agents is added is from 0.001 to 5 parts by weight per 100 parts by weight of component (A). Inorganic fillers can also be compounded as optional components with this silicone gel composition for the purpose of improving the mechanical strength, thermal conductivity and electroconductive properties of the silicone gel that is obtained. These inorganic fillers include, for example, dry silica, wet silica, crystalline silica, aluminosilicates, iron oxide, zinc oxide, calcium carbonate, carbon black, alumina, aluminum hydroxide, silver and nickel. These inorganic fillers may be compounded without being treated, or these fillers may be compounded after having been subjected to surface treatment in advance by an organic silicon compound such as an organoalkoxysilane, an organochlorosilane or an organodisilazane. In addition, these inorganic fillers may also be compounded while they are subjected to surface treatment by an organic silicon compound in the aforementioned component (A). The quantity in which these inorganic fillers is compounded is from 5 to 500 parts by weight, and preferably 10 to 300 parts by weight, per 100 parts by weight of component (A). When the quantity of inorganic filler compounded is less than 5 parts by weight per 100 parts by weight of component (A), the mechanical strength of the silicone gel is diminished. When it exceeds 500 parts by weight, the handling and workability of the silicone gel composition may be decreased. Six-membered ring compounds having carbon-nitrogen unsaturated bonds in the ring, such as pyridine, pyrazine and 1,3,5-triazine, or derivatives thereof may be compounded in extremely small quantities with our silicone gel composition for the purpose of decreasing the compression set. In addition, as required, known pigments, heat resistance agents and flame resistance agents can be compounded with this silicone gel composition in ranges that do not impair the objective of this invention. This silicone gel composition is obtained by uniform mixing of components (A) through (C), and, as required, other optional components. A method that can be used to prepare our silicone gel composition is, for example, a method in which the aforementioned components (A) through (C), and, as required, other optional components, are uniformly mixed with a known kneading apparatus such as double rollers, a kneader mixer or a ROSS mixer. ROSS is a registered trademark of Charles Ross & Sons Co. of Hauppauge, NY. Methods for making the fixing roll of this invention using our silicone gel composition include, for example, a method in which the shaft of a metal roller is placed inside a mold for forming rollers and a peelable organic resin tube is then set in the inside wall of the mold for forming rollers, after which the silicone gel composition is introduced under pressure into the cavity between the roller shaft and the peelable organic resin tube, and then the silicone gel composition is cured. Alternatively, a method may comprise the shaft of a metal roller inside a mold for forming rolls, after which the silicone gel composition is introduced under pressure and the silicone gel resin is cured, the peelable organic resin is then applied to the external circumferential surface of the silicone gel roller and subjected to heat treatment. Of these, the former method is particularly preferred. The external circumferential surface of the roller shaft and/or the internal circumferential surface of the peelable organic resin tube may be treated with primer in advance to improve the adhesiveness between the roller shaft and the silicone gel layer and the adhesiveness between the silicone gel layer and the peelable organic resin layer. The method whereby silicone gel composition is introduced under pressure into the cavity of the roller shaft and the peelable organic resin tube may be, for example, by use of a compression molding machine, a transfer molding machine or an injection molding machine. When the curing temperature of the silicone gel composition is markedly low, the curing rate is slowed and the productivity of producing the fixing roll is markedly decreased. When the curing temperature is markedly high, wrinkles are formed on the surface of the fixing roll. For these reasons, the curing temperature is in the range of 30 to 200°C, and preferably in the range of 50 to 150°C. Because the compression set of silicone gels obtained by curing at comparatively low temperatures is decreased, a further heat treatment at 150 to 250°C may also be performed. The peelable organic resin layer is established on the external circumferential surface of the roller shaft of the fixing roll of this invention with the silicone gel layer interposed between them. For this reason, in spite of the fact that the fixing roll is thin and of low durometer, a suitable degree of nip width is obtained even with a low nip pressure and superior durability is exhibited. Therefore, when this roller is used as a fixing roll in such devices as electronic copying machines, printers and facsimiles, these devices are produced in even smaller and lighter form. EXAMPLES We shall now describe the fixing roll of this invention in greater detail by means of examples. Viscosity in these examples is the value determined at 25°C. The silicone gel was evaluated as follows: The silicone gel composition was heated for 15 minutes at 120°C with a heat pressing machine to form a silicone gel. This silicone gel was then subjected to a further heating treatment for 4 hours at 200°C in an oven. The penetration of the silicone gel was determined in accordance with JIS K 2207. The compression set of the silicone gel was determined in accordance with the test method in JIS C 2123. The heat treatment temperature and time were set to 180°C and 22 hours. To determine the volume resistivity of the gel, a cylindrical silicone gel sample of 30 mm in diameter and 12 mm in thickness was used as a test strip, loads were applied to it and the load during 20% compression was measured. A fixing roll was made as indicated below. A commercially available primer was applied uniformly to the external circumferential surface of a cylindrical roller shaft of 10 mm in diameter made of iron, after which the roller shaft was allowed to stand for 30 minutes in an oven at 150°C. Therein, the primer was thoroughly dried. A commercially available primer was applied uniformly to the inside face of a tube made of tetrafluoroethylene-perfluoroalkylperfluorovinyl ether copolymer of a film thickness of 50 µm, which inside face had been treated with an alkali, after which the tube was allowed to stand for 1 hour at room temperature, with the primer being thoroughly dried. Next, the roller shaft was placed inside a mold for forming rollers, the tube was placed on the inside wall of the mold and the silicone gel composition was introduced under pressure into the cavity between the roller shaft and the tube. Thereafter, these materials were cured for 30 minutes at 100°C, with a fixing roll coated with fluorine resin of 10 mm in thickness being made. Next, the fixing roll was subjected to heat treatment for 4 hours in an oven at 200°C. EXAMPLE 1 100 parts by weight of dimethylsiloxane-methylvinyl siloxane copolymer (vinyl group content = 0.12 wt %) of a viscosity of 40,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups as indicated by the formula and 30 parts by weight of quartz powder of an average particle diameter of 5 µm were mixed uniformly with a ROSS ™ mixer, after which 4 parts by weight of dimethylpolysiloxane (content of silicon-bonded hydrogen atoms = 0.065 wt %) of a viscosity of 38 mPa.s both molecular chain terminals of which were blocked by dimethylhydrogensiloxy groups as indicated by the formula (the quantity of silicon-bonded hydrogen atoms in this dimethylpolysiloxane being 0.6 mole per 1 mole of vinyl groups in the aforementioned dimethylsiloxane-methylvinylsiloxane copolymer) and 0.5 part by weight of an isopropyl alcohol solution of chloroplatinic acid (content of platinum metal = 1 wt %) were mixed uniformly, an addition reaction was performed and a cured silicone gel composition was prepared. The penetration of the silicone gel obtained by curing this silicone gel composition was 55, its compression set was 5% and its compressive stress was 8.8 kPa (90 gf/cm 2 ). A fixing roll coated with fluorine resin was made using this silicone gel composition. The JIS A durometer of the surface of this fixing roll was 15. This fixing roll was installed in an electronic copying machine and 150,000 copies were run using size A4 copying paper. There was no wrinkling or jamming of the paper and the images that were reproduced were sharp. COMPARATIVE EXAMPLE 1 100 parts by weight of dimethylsiloxane-methylvinyl siloxane copolymer (vinyl group content = 0.12 wt %) of a viscosity of 40,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups as indicated by the formula and 30 parts by weight of quartz powder of an average particle diameter of 5 µm were mixed uniformly with a ROSS™ mixer, after which 1.2 parts by weight of dimethylpolysiloxane-methylhydrogensiloxane copolymer (content of silicon-bonded hydrogen atoms = 0.55 wt %) of a viscosity of 10 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups as indicated by the formula (the quantity of silicon-bonded hydrogen atoms in this dimethylpolysiloxane-methylhydrogensiloxane copolymer being 1.5 moles per 1 mole of vinyl groups in the aforementioned dimethylsiloxane-methylvinylsiloxane copolymer) and 0.5 part by weight of an isopropyl alcohol solution of chloroplatinic acid (content of platinum metal = 1 wt %) were mixed uniformly, an addition reaction was performed and a cured silicone gel composition was prepared. The penetration of the silicone gel obtained by curing this silicone gel composition was 7, its JIS A durometer was 15, its compression set was 5% and its compressive stress was 49.0 kPa (500 gf/cm 2 ). A fixing roll coated with fluorine resin was made using this silicone gel composition. The JIS A durometer of the surface of this fixing roll was 30. This fixing roll was installed in an electronic copying machine and 150,000 copies were run using size A4 copying paper. There was no wrinkling or jamming of the paper and the images that were reproduced were sharp. However, extremely high nip pressure was necessary to obtain a suitable degree of nip width with this fixing roll. EXAMPLE 2 100 parts by weight of dimethylsiloxane-methylvinyl siloxane copolymer (vinyl group content = 0.12 wt %) of a viscosity of 40,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups as indicated by the formula and 30 parts by weight of quartz powder of an average particle diameter of 5 µm were mixed uniformly with a ROSS™ mixer, after which 4 parts by weight of dimethylpolysiloxane (content of silicon-bonded hydrogen atoms = 0.065 wt %) of a viscosity of 38 mPa.s both molecular chain terminals of which were blocked by dimethylhydrogensiloxy groups as indicated by the formula (the quantity of silicon-bonded hydrogen atoms in this dimethylpolysiloxane being 0.6 mole per I mole of vinyl groups in the aforementioned dimethylsiloxane-methylvinylsiloxane copolymer), 70 parts by weight of dimethylpolysiloxane of a viscosity of 300,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups and 0.5 part by weight of an isopropyl alcohol solution of chloroplatinic acid (content of platinum metal = 1 wt %) were mixed uniformly, an addition reaction was performed and a cured silicone gel composition was prepared. The penetration of the silicone gel obtained by curing this silicone gel composition was 78, its compression set was 6% and its compressive stress was 4.90 kPa (50 gf/cm 2 ). A fixing roll coated with fluorine resin was made using this silicone gel composition. The JIS A durometer of the surface of this fixing roll was 12. This fixing roll was installed in an electronic copying machine and 150,000 copies were run using size A4 copying paper. There was no wrinkling or jamming of the paper and the images that were reproduced were sharp. EXAMPLE 3 100 parts by weight of dimethylsiloxane-methylvinyl siloxane copolymer (vinyl group content = 0.12 wt %) of a viscosity of 40,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups as indicated by the formula and 30 parts by weight of quartz powder of an average particle diameter of 5 µm were mixed uniformly with a ROSS™ mixer, after which 4 parts by weight of dimethylpolysiloxane (content of silicon-bonded hydrogen atoms = 0.065 wt %) of a viscosity of 38 mPa.s both molecular chain terminals of which were blocked by dimethylhydrogensiloxy groups as indicated by the formula (the quantity of silicon-bonded hydrogen atoms in this dimethylpolysiloxane being 0.6 mole per I mole of vinyl groups in the aforementioned dimethylsiloxane-methylvinylsiloxane copolymer), 70 parts by weight of dimethylpolysiloxane of a viscosity of 300,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups, 30 parts by weight of dimethylpolysiloxane of a viscosity of 100,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups, 15 parts by weight of carbon black (Denka™ Acetylene Black manufactured by Denki Kagaku Kogyo Co., Ltd.) and 0.5 part by weight of an isopropyl alcohol solution of chloroplatinic acid (content of platinum metal = 1 wt %) were mixed uniformly, an addition reaction was performed and a cured electroconductive silicone gel composition was prepared. The penetration of the silicone gel obtained by curing this electroconductive silicone gel composition was 80, its compression set was 10%, its volume resistivity was 1 x 10 4 Ω and its compressive stress was 4.4 kPa (45 gf/cm 2 ). A fixing roll coated with fluorine resin was made using this electroconductive silicone gel composition. The JIS A durometer of the surface of this fixing roll was 11. This fixing roll was installed in an electronic copying machine and 150,000 copies were run using size A4 copying paper. There was no wrinkling or jamming of the paper and the images that were reproduced were sharp. EXAMPLE 4 100 parts by weight of dimethylsiloxane-methylvinyl siloxane copolymer (vinyl group content = 0.12 wt %) of a viscosity of 400,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups as indicated by the formula and 30 parts by weight of fine pulverized quartz powder of an average particle diameter of 5 µm were mixed uniformly with a ROSS™ mixer, after which 1.2 parts by weight of dimethyl siloxane-methylhydrogensiloxane copolymer (content of silicon-bonded hydrogen atoms = 0.24 wt %) of a viscosity of 10 mPa.s both molecular chain terminals of which were blocked by dimethylhydrogensiloxy groups as indicated by the formula (the quantity of silicon-bonded hydrogen atoms in this dimethyl siloxane-methylhydrogensiloxane copolymer being 0.6 mole per 1 mole of vinyl groups in the aforementioned dimethylsiloxane-methylvinylsiloxane copolymer), 130 parts by weight of dimethylpolysiloxane of a viscosity of 100,000 mPa.s both molecular chain terminals of which were blocked by trimethylsiloxy groups and 0.5 part by weight of an isopropyl alcohol solution of chloroplatinic acid (content of platinum metal = 1 wt %) were mixed uniformly, an addition reaction was performed and a cured silicone gel composition was prepared. The penetration of the silicone gel obtained by curing this silicone gel composition was 90, its compression set was 9% and its compressive stress was 3.92 kPa (40 gf/cm 2 ). A fixing roll coated with fluorine resin was made using this silicone gel composition. The JIS A durometer of the surface of this fixing roll was 10. This fixing roll was installed in an electronic copying machine and 150,000 copies were run using size A4 copying paper. There was no wrinkling or jamming of the paper and the images that were reproduced were sharp. Because a peelable organic resin layer is established on the external circumferential surface of the roller shaft of the fixing roll of this invention with a silicone gel layer formed by a silicone gel of a penetration of 20 to 200 as measured according to JIS K 2207 interposed between them. The fixing roll is characterized in that a suitable degree of nip width can be obtained even at a low nip pressure and there is superior durability in spite of the fact that it is of low durometer and thin. In addition, the silicone gel composition of this invention is characterized in that this type of fixing roll can be made with it.

Claims: A fixing roll comprising A) a roller shaft (1), B) a peelable organic resin layer (3) established on the external circumferential surface of the roller shaft; and C) a layer of cured silicone gel (2) interposed between the roller shaft and the peelable organic resin layer; characterised in that said cured silicone gel has a penetration value, as measured according to JIS K 2207, of 20 to 200. The fixing roll of claim 1 wherein the cured silicone gel has a compression set of less than 15% as measured by JIS C 2123. The fixing roll of claim 1 or claim 2 wherein the layer of cured silicone gel has as a thickness of 2 to 30 mm. The fixing roll of any of claims 1 to 3 wherein the cured silicone gel is prepared by curing a silicone gel composition by an addition reaction. The fixing roll of claim 4 wherein the silicone gel composition comprises (A) an alkenyl-substituted organopolysiloxane having an average of at least two alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule, in an amount sufficient to provide 0.1 to 5 moles of silicone-bonded hydrogen atoms in component (B) per 1 mole of alkenyl groups in component (A); and (C) a sufficient quantity of platinum catalyst for curing the silicone gel composition. The fixing roll of claim 5 wherein the viscosity of component (A) is 50 to 1,000,000 mPa.s. The fixing roll of claim 5 wherein the viscosity of component (B) is I to 500,000 mPa.s. The fixing roll of claim 5, wherein the silicone gel composition further comprises a diorganopolysiloxane that is free of alkenyl groups and silicon-bonded hydrogen atoms. The fixing roll of claim 8, wherein the diorganopolysiloxane has a viscosity that is between 1,000 to 10,000,000 mPa.s. The fixing roll of claim 8, wherein the diorganopolysiloxane is present in an amount providing 5 to 200 parts by weight per 100 parts by weight of component (A). The fixing roll of any of claims 1 to 10 wherein the peelable organic resin layer is formed of fluorine resin or fluorine rubber. The fixing roll of any of claims 1 to 11 wherein the peelable organic resin layer has a thickness that is less than or equal to 0.1 mm.

Inventors: NAKAMURA AKITO, USHIO YOSHITO, NAKAMURA, AKITO, USHIO, YOSHITO, Nakamura, Akito, Dow Corning Silicone Co., Ltd., Ushio, Yoshito, Dow Corning Silicone Co., Ltd.
Applicants: DOW CORNING TORAY SILICONE, DOW CORNING TORAY SILICONE COMPANY, LIMITED
Application year: 1996
Main classification: G03G15
IPC codes: F16C13, C08L83, G03G15