Liquid silicone rubber sponge composition, high-open-cell silicone rubber sponge, and roll for electrophotographic image forming member

Abstract

To provide a liquid silicone rubber sponge composition that enables a reduction in the amount of open-cell forming agent, exhibits superior storage stability, and produces a high-open-cell silicone rubber sponge with uniform appearance, high hardness with little variation, and superior rubber properties.SOLUTION: A liquid silicone rubber sponge composition comprises: (A) an organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule and being liquid at 25°C; (B) an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule; (C) reinforcing silica; (D) an addition reaction catalyst; (E) pre-expanded resin microparticles having an organic resin shell, an average particle diameter of 10-200 μm, and a true specific gravity of 0.01-0.3; and (F) 1,2-propanediol as an open-cell forming agent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a liquid silicone rubber sponge composition, a highly cellular silicone rubber sponge which is a cured product thereof, and a roll for an electrophotographic image forming member having one or more layers made of the sponge.

Background Art

[0002] Silicone rubber sponge is a sponge having excellent physical properties such as heat resistance, cold resistance, electrical insulation, flame retardancy, etc. peculiar to silicone rubber, and having a small compression set. Silicone rubber sponge having such properties is used to promote low heat conduction and weight reduction in OA equipment, automobiles, building materials, etc.

[0003] Silicone rubber sponge is produced by combining a silicone rubber molding method and a foaming method according to its application. For example, a method has been proposed in which a liquid silicone rubber sponge composition containing pre-expanded resin fine particles is heat-cured to form a sponge (Patent Document 1). However, in the above method, sponge cells (air bubbles) become closed cells, and since it takes time for air to move between cells, the compression set deteriorates. In addition, when a large amount of the above pre-expanded resin fine particles is blended, it becomes possible to reduce the specific gravity of the silicone rubber sponge. However, since the resin component of the pre-expanded resin fine particles remains in the sponge, the hardness of the obtained sponge becomes very high, the rubber elasticity decreases, and the compression set also deteriorates.

[0004] On the other hand, those containing hollow powder of inorganic substances such as glass and ceramics in a silicone rubber composition are also known (Patent Document 2). However, the obtained molded product cannot be lightweight because the powder specific gravity is large, and also has insufficient cushioning properties and deterioration of thermal conductivity because the powder is an inorganic substance.

[0005] As a method for reducing the compression set of the sponge, there is a method of making the sponge into a cellular structure. As a technique for making a liquid silicone rubber sponge containing expanded resin fine particles into a cellular structure, a method of blending a polyhydric alcohol (glycols) as a foaming agent has been proposed (Patent Documents 3 to 5). In these methods, the volatilization temperature of the polyhydric alcohols is set to a temperature higher than the curing temperature of the rubber, and after curing, the polyhydric alcohols are volatilized and removed to foam the sponge.

[0006] However, in the above method, when the rubber strength of the cured product of the liquid silicone rubber composition is high, the sponge cells cannot be broken and the foam cannot be formed, or the foamed cell part and the single-cell part become mottled like an island-sea pattern. In addition, while better foamability can be obtained as the amount of the foaming agent increases, if the foaming agent cannot be completely removed and remains, it may have an adverse effect on durability.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention has been made in view of the above circumstances, and can reduce the amount of the blowing agent used, has excellent storage stability, and further provides a liquid silicone rubber sponge composition that gives a highly cellular silicone rubber sponge having a uniform appearance, high hardness, little variation in hardness, and excellent rubber properties, a cured product thereof, a highly cellular silicone rubber sponge, and a roll for an electrophotographic image forming member.

Means for Solving the Problems

[0009] As a result of intensive studies to achieve the above object, the present inventors have found that by blending 1,2-propanediol as a blowing agent into a liquid silicone rubber composition containing pre-expanded resin fine particles and reinforcing silica, the storage stability is excellent, and the silicone rubber sponge obtained by heat-curing this composition has no surface stains or hardness variations, and the compression set is improved, thus completing the present invention.

[0010] Therefore, the present invention provides the following liquid silicone rubber sponge composition, highly cellular silicone rubber sponge, and roll for an electrophotographic image forming member. [1] (A) An organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule and being liquid at 25°C: 100 parts by mass, (B) An organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule: an amount such that the number of hydrosilyl groups contained in the component (B) is 0.4 to 10 with respect to one alkenyl group bonded to a silicon atom contained in the component (A), (C) Reinforcing silica: 2.5 to 40 parts by mass, (D) An addition reaction catalyst: 0.0001 to 1 part by mass, (E) Pre-expanded resin fine particles having an organic resin shell, an average particle diameter of 10 to 200 μm, and a true specific gravity of 0.01 to 0.3: 0.2 to 30 parts by mass, (F) 1,2-Propanediol as a blowing agent: 1 to 30 parts by mass A liquid silicone rubber sponge composition containing the above components. [2] The liquid silicone rubber sponge composition according to [1], wherein the organic resin shell of the pre-expanded resin fine particles of the component (E) is composed of a polymer of any one monomer selected from the group consisting of vinylidene chloride, acrylonitrile, methacrylonitrile, acrylic ester and methacrylic ester, or a copolymer of two or more monomers. [3] A highly cellular silicone rubber sponge which is a cured product of the liquid silicone rubber sponge composition according to [1] or [2]. [4] A roll for an electrophotographic image forming member having at least one layer formed of the highly cellular silicone rubber sponge according to [3], wherein the variation in hardness of the highly cellular silicone rubber sponge is such that the difference between the maximum value and the minimum value measured by an Asker C hardness meter described in JIS S 6050:2008 is 2 points or less. [Advantages of the Invention]

[0011] The liquid silicone rubber sponge composition of the present invention can form highly cellular silicone rubber sponges such as rubber sponge rolls and rubber sponge sheets with good appearance, especially without mottled patterns and hardness variations, and low compression set, while maintaining fine cellular sponges. Moreover, it has excellent storage stability. In addition, since the amount of the foaming agent used can be reduced, it is possible to shorten the process time for volatilizing and removing the foaming agent after heat curing (primary cure) of the liquid silicone rubber sponge composition, and it is also possible to reduce the deterioration of durability due to the remaining foaming agent. In addition, the roll produced using the liquid silicone rubber sponge composition of the present invention is particularly suitable as an electrophotographic image forming member because the variation in hardness in the length direction of the roll is small. [Brief Description of the Drawings]

[0012]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail. [1] Liquid silicone rubber sponge composition The liquid silicone rubber sponge composition of the present invention contains the following components (A) to (F). (A) An organopolysiloxane that is liquid at 25°C and has two or more alkenyl groups bonded to silicon atoms in one molecule (B) An organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule (C) Reinforcing silica (D) Addition reaction catalyst (E) Pre-expanded resin fine particles (F) As a foam stabilizer, 1,2-propanediol

[0014] [Component (A)] (Component (A)) is an organopolysiloxane that is liquid at 25°C and contains two or more alkenyl groups bonded to silicon atoms in one molecule.

[0015] Examples of the molecular structure of the component (A) include linear, cyclic, branched, three-dimensional network (resin-like), etc. However, a linear diorganopolysiloxane in which the main chain basically consists of repeating units of diorganosiloxane and both ends of the molecular chain are blocked with triorganosiloxy groups is preferred. Further, when the molecular structure of the organopolysiloxane of the component (A) is linear or branched, the position of the silicon atom to which the alkenyl group binds in the molecule of the organopolysiloxane may be either at the end of the molecular chain (i.e., the triorganosiloxy group) or in the middle of the molecular chain (i.e., a bifunctional diorganosiloxane unit or a trifunctional monoorganosilsesquioxane unit located at a non-terminal position of the molecular chain), or both. As the component (A), a linear diorganopolysiloxane containing alkenyl groups bonded to silicon atoms at both ends of the molecular chain is particularly preferred.

[0016] Examples of the alkenyl group bonded to the silicon atom in the component (A) usually include those having 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms. Specific examples thereof include vinyl, allyl, butenyl, pentenyl, hexenyl, cyclohexenyl, heptenyl groups, etc., and among them, a vinyl group is preferred.

[0017] The content of the alkenyl group bonded to the silicon atom in the component (A) is preferably 1.0×10 -6 ~1.0×10 -2 mol / g with respect to the total groups bonded to the silicon atom, more preferably 1.0×10 -5 ~5.0×10 -3 mol / g, and even more preferably 1.0×10 -4 ~5.0×10 -3 mol / g.

[0018] As the group bonded to the silicon atom other than the alkenyl group in the component (A), a monovalent hydrocarbon group is preferred. The monovalent hydrocarbon group is not particularly limited, and examples thereof include monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 1 to 6 carbon atoms. The monovalent hydrocarbon group may be linear, branched or cyclic. Specific examples thereof include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, heptyl groups; aryl groups such as phenyl, tolyl, xylyl, naphthyl groups; aralkyl groups such as benzyl, phenethyl groups and the like. Among these, a methyl group is particularly preferred.

[0019] Specific examples of the component (A) include, for example, dimethylpolysiloxane blocked at both molecular chain ends with dimethylvinylsiloxy groups, dimethylsiloxane·diphenylsiloxane copolymer blocked at both molecular chain ends with dimethylvinylsiloxy groups, dimethylsiloxane·methylphenylsiloxane copolymer blocked at both molecular chain ends with dimethylvinylsiloxy groups, dimethylsiloxane·methylvinylsiloxane copolymer blocked at both molecular chain ends with dimethylvinylsiloxy groups, methylvinylpolysiloxane blocked at both molecular chain ends with trimethylsiloxy groups, dimethylsiloxane·methylvinylsiloxane copolymer blocked at both molecular chain ends with trimethylsiloxy groups, dimethylpolysiloxane blocked at both molecular chain ends with methylphenylvinylsiloxy groups, the formula: (CH3)3SiO 1 / 2 siloxane units represented by and the formula: (CH3)2(CH2=CH)SiO 1 / 2 siloxane units represented by and the formula: (CH3)2SiO 2 / 2 siloxane units represented by and the formula: CH3SiO 3 / 2 and organopolysiloxane copolymers composed of siloxane units represented by and the like can be mentioned. These may be used alone or in combination of two or more having different types, degrees of polymerization, viscosities, etc. Among these, dimethylpolysiloxane blocked at both molecular chain ends with dimethylvinylsiloxy groups and dimethylsiloxane·methylvinylsiloxane copolymer blocked at both molecular chain ends with trimethylsiloxy groups are preferred.

[0020] The number average degree of polymerization of component (A) is preferably from 10 to 1,500, more preferably from 10 to 1,200, and still more preferably from 10 to 1,000. In the present invention, the degree of polymerization (or molecular weight) refers to the value determined as the number average degree of polymerization (or number average molecular weight) in terms of polystyrene in gel permeation chromatography (GPC) analysis using toluene as the developing solvent measured under the following measurement conditions. <Measurement conditions> Developing solvent: Toluene Flow rate: 0.6 mL / min Detector: Differential refractive index detector (RI) Column: TSK Guardcolumn SuperH-H TSKgel SuperH5000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH4000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH3000 (6.0 mm I.D. × 15 cm × 1) (All are manufactured by Tosoh Corporation) Column temperature: 40 °C Sample injection volume: 50 μL (toluene solution with a concentration of 0.5 mass%)

[0021] The viscosity of component (A) at 25 °C is preferably from 5 to 500,000 mPa·s, more preferably from 10 to 200,000 mPa·s, and still more preferably from 10 to 10,000 mPa·s. When the viscosity is within this range, the handling workability of the resulting silicone rubber sponge composition is good, and the mechanical properties of the cured product of the resulting silicone rubber sponge composition are good. The above viscosity refers to the value measured by a rotational viscometer at 25 °C by the method described in JIS K 7117-1:1999.

[0022] [Component (B)] (Component (B) is an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule. The organohydrogenpolysiloxane of component (B) undergoes a hydrosilylation addition reaction with the alkenyl group in component (A) and acts as a crosslinking agent (curing agent).

[0023] There is no particular limitation on the molecular structure of component (B), and various conventionally produced ones such as linear, cyclic, branched-chain, three-dimensional network (resin-like) structures can be used, but it is necessary to have two or more hydrosilyl groups in one molecule. The organohydrogenpolysiloxane of component (B) may be used alone or in combination of two or more.

[0024] The hydrosilyl groups of component (B) are two or more in one molecule, preferably 2 to 300, more preferably 2 to 150. Further, the hydrosilyl groups may be located at either the molecular chain end or in the middle of the molecular chain, or may be located at both. Also, the molecular structure of this organohydrogenpolysiloxane may be any of linear, cyclic, branched-chain, and three-dimensional network structures, but the number of silicon atoms (or degree of polymerization) in one molecule is usually 2 to 300, preferably 3 to 150, more preferably about 4 to 100, and the viscosity at 25 °C is usually 0.1 to 1,000 mPa·s, preferably about 0.5 to 500 mPa·s, and those that are liquid at 25 °C are used. The method for measuring the viscosity is as described for component (A). Also, the amount of hydrosilyl groups (hydrosilyl group content) in one molecule is preferably 0.0001 to 0.016 mol / g, more preferably 0.0005 to 0.012 mol / g.

[0025] Examples of the groups other than the hydrosilyl groups of component (B) include alkyl groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms; aryl groups having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms; aralkyl groups having 7 to 10 carbon atoms, etc. Specific examples thereof include, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, decyl groups; aryl groups such as phenyl, tolyl, xylyl, naphthyl groups; aralkyl groups such as benzyl, phenylethyl, phenylpropyl groups and the like. Among these, an alkyl group and an aryl group are preferred, and a methyl group is more preferred.

[0026] Specific examples of such organohydrogenpolysiloxanes of component (B) include, for example, 1,1,3,3 - tetramethyldisiloxane, 1,3,5,7 - tetramethylcyclotetrasiloxane, tris(hydrogendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane - dimethylsiloxane cyclic copolymer, trimethylsiloxy group - blocked methylhydrogenpolysiloxane with both ends of the molecular chain, trimethylsiloxy group - blocked dimethylsiloxane - methylhydrogensiloxane copolymer with both ends of the molecular chain, trimethylsiloxy group - blocked dimethylsiloxane - methylhydrogensiloxane - methylphenylsiloxane copolymer with both ends of the molecular chain, trimethylsiloxy group - blocked dimethylsiloxane - methylhydrogensiloxane - diphenylsiloxane copolymer with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked methylhydrogenpolysiloxane with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked dimethylpolysiloxane with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked dimethylsiloxane - methylhydrogensiloxane copolymer with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked dimethylsiloxane - methylphenylsiloxane copolymer with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked dimethylsiloxane - diphenylsiloxane copolymer with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked methylphenylpolysiloxane with both ends of the molecular chain, dimethylhydrogensiloxy group - blocked diphenylpolysiloxane with both ends of the molecular chain, and in each of these exemplified compounds, those in which part or all of the methyl groups are substituted with other alkyl groups such as ethyl groups and propyl groups, the formula: R 3 3SiO 1 / 2 The siloxane unit represented by and the formula: R 3 2HSiO 1 / 2 The siloxane unit represented by and the formula: SiO 4 / 2 An organosiloxane copolymer composed of the siloxane unit represented by, the formula: R 3 2HSiO 1 / 2 The siloxane unit represented by and the formula: SiO 4 / 2An organosiloxane copolymer composed of siloxane units represented by, formula: R 3 HSiO 2 / 2 An organosiloxane copolymer composed of siloxane units represented by formula: R 3 SiO 3 / 2 Or an organosiloxane copolymer composed of siloxane units represented by formula: HSiO 3 / 2 Examples include mixtures composed of two or more of these organopolysiloxanes. Note that the above R 3 Is a group selected from alkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 10 carbon atoms, and aralkyl groups having 7 to 10 carbon atoms, and is particularly preferably a methyl group. Among these, a dimethylsiloxane·methylhydrogensiloxane copolymer blocked with trimethylsiloxy groups at both ends of the molecular chain is preferred.

[0027] The blending amount of component (B) is such that the number of hydrosilyl groups in component (B) is 0.4 to 10 (or moles) with respect to 1 (or 1 mole) of the alkenyl group bonded to a silicon atom in component (A), preferably 0.5 to 5 (or moles), and more preferably 0.5 to 2.5 (or moles). When the number of hydrosilyl groups in component (B) is less than 0.4 with respect to 1 alkenyl group bonded to a silicon atom in component (A), the silicone rubber sponge composition does not cure sufficiently, the amount of free oil increases, and the desired strength cannot be obtained. Also, when this exceeds 10, hydrogen gas is generated during heat curing, and the heat resistance of the cured product of the silicone rubber composition deteriorates extremely.

[0028] [Component (C)] Component (C) is reinforcing silica. The reinforcing silica of component (C) is a filler necessary for improving the processability, mechanical strength, etc. of the silicone rubber sponge.

[0029] The specific surface area of this reinforcing silica by the BET method is preferably 10 m 2 / g or more, more preferably 100 to 400 m 2 / g. Specific examples of this reinforcing silica include fumed silica (fumed silica or dry silica), precipitated silica (wet silica), etc. Among these, fumed silica (fumed silica or dry silica) is preferred. Further, the surface of these reinforcing silicas may be hydrophobized using organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, etc. with water or the like.

[0030] Examples of commercially available usable reinforcing silica fine powder include Aerosil 130, 200, 300 (product names manufactured by Nippon Aerosil Co., Ltd.), Cab-O-sil MS-5, MS-7, HS-5, HS-7 (product names manufactured by Cabot Corporation), Santocel FRC, CS (product names manufactured by Monsanto), Nipsil VN-3 (product name manufactured by Nippon Silica Industry Co., Ltd.), etc. Further, the surface of these may be hydrophobized using organopolysiloxane, organopolysilazane, disilazane, chlorosilane, alkoxysilane, etc. These silicas may be used alone or in combination of two or more.

[0031] The blending amount of the reinforcing silica in component (C) is 2.5 to 40 parts by mass, preferably 2.5 to 35 parts by mass, more preferably 2.5 to 30 parts by mass, and still more preferably 6.5 to 20 parts by mass with respect to 100 parts by mass of the organopolysiloxane in component (A). If the blending amount of this reinforcing silica is less than 2.5 parts by mass, it is too little and a sufficient reinforcing effect cannot be obtained. When the hardness becomes high, it becomes brittle and cannot withstand 25% compression in the compression set test and breaks. If it exceeds 40 parts by mass, the viscosity of the uncrosslinked liquid silicone rubber sponge composition becomes extremely high, and the processability deteriorates. Further, the cell ratio of the obtained silicone rubber sponge decreases, and it does not become cellular without using a large amount of foaming agent, and hardness variations occur.

[0032] [Component (D)] (D) component is an addition reaction catalyst. Specific examples of the addition reaction catalyst of component (D) include, for example, platinum (including platinum black), platinum dichloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and olefins, a complex of chloroplatinic acid and vinylsiloxane, platinum-based catalysts such as platinum bisacetylacetate; palladium-based catalysts; platinum group metal-based catalysts such as rhodium-based catalysts and the like. These may be used alone or in combination of two or more.

[0033] (D) The compounding amount of the addition reaction catalyst of the component can be a catalytic amount. Usually, based on 100 parts by mass of the organopolysiloxane of component (A), the platinum group metal mass is 0.0001 to 1 part by mass, and 0.0001 to 0.5 part by mass is preferable. If the addition amount is too small, the curability will decrease, and if the addition amount is too large, the cost will increase and it will be uneconomical.

[0034] [(E) component] (E) component is an already expanded resin fine particle having an organic resin shell, a true specific gravity of 0.01 to 0.3, and an average particle diameter of 10 to 200 μm. This fine particle (filler) reduces the specific gravity of the silicone rubber sponge by imparting sponge cells into the cured rubber (silicone rubber cured product).

[0035] The resin forming the organic resin shell of the already expanded resin fine particle is not particularly limited. For example, a polymer of any one monomer such as vinylidene chloride, acrylonitrile, methacrylonitrile, acrylic ester, and methacrylic ester, or a copolymer of two or more monomers is preferable. The already expanded resin fine particle used in the present invention is obtained by previously heating and expanding unexpanded resin fine particles containing a volatile substance or a low-boiling substance in this organic resin shell in a single powder state to obtain already expanded resin fine particles. In addition, in order to improve the strength of the already expanded resin fine particles, etc., those having an inorganic filler such as calcium carbonate or talc attached to the surface thereof can also be blended.

[0036] The above-mentioned pre-expanded resin microparticles have a true specific gravity of 0.01 to 0.3, preferably 0.01 to 0.25, in terms of reducing the specific gravity of the silicone rubber sponge and reducing the thermal conductivity. If the true specific gravity is less than 0.01, not only is compounding and handling difficult, but the pressure resistance of the pre-expanded resin microparticles is insufficient, and they will break during compounding or molding, making it impossible to reduce the weight of the silicone rubber sponge. On the other hand, if the true specific gravity is greater than 0.3, the specific gravity of the silicone rubber sponge will not be sufficiently reduced. The true specific gravity of the pre-expanded resin microparticles is determined from the mass of alcohol displaced by the pre-expanded resin microparticles, for example, by the liquid displacement method.

[0037] In addition, the average particle diameter of the pre-expanded resin microparticles is 10 to 200 μm, preferably 30 to 150 μm, more preferably 50 to 100 μm. If this average particle diameter is less than 10 μm, it is necessary to compound a large amount to reduce the specific gravity of the silicone rubber sponge, and the fluidity of the liquid silicone rubber sponge composition deteriorates. If the average particle diameter is greater than 200 μm, the pre-expanded resin microparticles will be broken by the pressure during molding, resulting in an increase in the specific gravity of the silicone rubber sponge or a decrease in durability. In the present invention, the average particle diameter refers to the value measured as the median diameter using a particle size distribution measuring device by the laser light diffraction method.

[0038] As the component (E), commercially available products can be used, and specific examples thereof include Microsphere F-80ED (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.).

[0039] The compounding amount of the pre-expanded resin microparticles (E) is 0.2 to 30 parts by mass, preferably 1.5 to 20 parts by mass, more preferably 2 to 10 parts by mass, based on 100 parts by mass of the liquid organopolysiloxane (A). Also, it is preferable to blend such that it is 20 - 80% by volume with respect to the total of components (A) to (D). When the volume ratio is within the above range, the specific gravity and the thermal conductivity of the silicone rubber sponge are sufficiently reduced, and the sponge can be easily foamed into a cellular structure. Furthermore, the molding and blending of the liquid silicone rubber sponge composition of the present invention become easy, and a molded article having sufficient rubber elasticity can be obtained. Note that the component (E) may be used alone or in combination of two or more.

[0040] [Component (F)] In the present invention, the component (F) is 1,2 - propanediol and acts as a foaming agent. The blending amount of the component (F) is 1 - 30 parts by mass, preferably 2 - 20 parts by mass, more preferably 5 - 20 parts by mass, and still more preferably 10 - 20 parts by mass with respect to 100 parts by mass of the component (A). If this blending amount is less than 1 part by mass, there is almost no effect of foaming into a cellular structure. On the contrary, if it is more than 30 parts by mass, the sponge cell diameter becomes large, and the adverse effect on rubber physical properties such as rubber strength becomes large. Also, the foaming agent may not be completely removed and may remain, which is likely to have an adverse effect on durability.

[0041] The component (F) is not compatible with the silicone rubber sponge composition of the present invention and exists around the (E) resin fine particles. It is added to connect the resin fine particles in the silicone rubber sponge composition with each other by the component (F). The silicone rubber sponge composition cures in a state where the resin fine particles are connected by the component (F), and then, by additional heating, the component (F) volatilizes to obtain a cured product in which the resin fine particles are connected, that is, a foamed silicone rubber sponge. Therefore, without the component (F), the resin fine particles are in an independent state, that is, single - celled, and the compression set deteriorates significantly. In addition, the component (F) also plays a role in assisting the decomposition of the resin fine particles. Moreover, since the component (F) exists around the resin fine particles, the component (F) remains on the inner wall of the silicone rubber cured product, and has the effect of not hindering foaming into a cellular structure.

[0042] (F) component has an insufficient blending amount, resulting in insufficient cell formation and the appearance of mottled patterns on the surface and inside of the rubber. The mottled patterns are caused by the pre-expanded resin fine particles that remained without being destroyed and were colored by heating. Therefore, the mottled part not only deteriorates the appearance, but also due to the remaining pre-expanded resin fine particles, it is in a single-cell state, and the compression set of the silicone rubber cured product deteriorates. In addition, the cell-formed part becomes hollow and the hardness decreases, but the mottled part has relatively high hardness because the pre-expanded resin fine particles remain, which becomes a factor in the variation of hardness.

[0043] If the general-purpose triethylene glycol as the cell-forming agent is also increased in amount, cell formation occurs, the mottles decrease, and the compression set improves. However, since it finally volatilizes, increasing the amount leads to an increase in cost and environmental load. On the other hand, when using 1,2-propanediol as the (F) component, even half the amount of triethylene glycol can cause cell formation, not only reducing the cell-forming agent but also having excellent stability over time. When using 1,2-propanediol, the cell-forming agent can be reduced while maintaining fine cells. In addition, it is possible to suppress the influence on the rubber physical properties due to the increase in the sponge cell diameter and the influence on durability due to the remaining cell-forming agent. Furthermore, since cell formation can be achieved with a small amount of the cell-forming agent, high cell formation is possible even with high-hardness silicone rubber sponges that are difficult to cell-form. In particular, when the hardness of the silicone rubber sponge is 40 or more, especially 45 or more in Asker C hardness, the cell-forming property deteriorates. Therefore, without using 1,2-propanediol as the (F) component, it is impossible to obtain a silicone rubber sponge with no mottled patterns on the appearance, good condition, no hardness variation, and low compression set.

[0044] [Other components] In the liquid silicone rubber sponge composition of the present invention, in addition to the essential components described above, a semi-reinforcing or non-reinforcing filler other than the reinforcing silica of the above (C) component can be blended within a range that does not inhibit the effects of the present invention. Specific examples of this semi-reinforcing or non-reinforcing filler include, for example, pulverized silica, diatomaceous earth, metal carbonate, clay, talc, mica, titanium oxide, and the like. In addition, heat-resistant additives such as iron oxide, flame retardants (including platinum complexes), antioxidants, processing aids, etc., which have been conventionally used in liquid silicone rubber sponge compositions, can also be blended. Furthermore, conductive sponges can be obtained by adding conductive carbon or fine particles of conductive metal oxides (conductive zinc white, titanium oxide, tin-antimony-based fine particles), etc. By blending ferrite powder, etc., molding by high-frequency dielectric heating is also possible.

[0045] In the liquid silicone rubber sponge composition of the present invention, if necessary, heat conductivity can also be imparted by further blending a heat-conductive substance. Examples of the heat-conductive substance include powders with a proven track record of addition to silicone compositions, such as crushed quartz, zinc oxide, aluminum oxide (alumina), aluminum hydroxide, metallic silicon powder, silicon carbide, and fibrous carbon fibers. Also, dispersants such as alkoxysilane, diphenylsilanediol, carbon-functional silane, and low-molecular siloxane with both ends blocked by silanol groups, and reaction control agents such as 1-ethynylcyclohexanol and acetylene alcohol compounds may be added to the liquid silicone rubber sponge composition within a range that does not impair the effects of the present invention.

[0046] The method for producing the liquid silicone rubber sponge composition of the present invention is not particularly limited, and all components may be mixed at once or each component may be mixed sequentially. For example, (A) liquid organopolysiloxane and (C) reinforcing silica may be mixed using a planetary mixer, kneader, Banbury mixer, etc., and then the remaining components may be added. Further, if necessary, the component (A) and the component (C) may be heat-treated (kneaded under heating). Specifically, the component (A), the component (C), and a hydrophobizing agent (organopolysiloxane, organopolysilazane, disilazane, chlorosilane, alkoxysilane, water, etc.) for the component (C) are kneaded and heat-treated, and then, after cooling, (B) organohydrogenpolysiloxane and a reaction control agent are added, and (D) an addition reaction catalyst is added to prepare an addition-crosslinking type silicone rubber composition in a liquid state at 25°C. Finally, (E) pre-expanded resin fine particles and (F) a foaming agent are added and mixed. A method in which the component (A) and the component (C) are kneaded, the component (D) is added and mixed, and then the reaction control agent, the component (B), the component (E), and the component (F) are sequentially added and mixed. A method in which the component (A), the component (C), and other additives are kneaded and heat-treated, then, after cooling, the component (E) and the component (F) are added, and finally, the component (B) and the component (D) are added, etc. may be mentioned. Further, the component (F) may be added last after adding and mixing the component (B) and the component (D). The temperature and time of the above heat treatment can be, for example, 100 to 250°C and 30 minutes to 5 hours.

[0047] The form of the silicone rubber sponge composition of the present invention may be a one-component type or a two-component type. In addition, the viscosity at 25°C of the mixture of the components (A) to (F) measured by a B-type (HAT type) rotational viscometer according to the method described in JIS K 7117-1:1999 is preferably 1 to 3,000 Pa·s, and more preferably 5 to 1,000 Pa·s.

[0048] 〔2〕Curing method and silicone rubber sponge The method for producing a highly foamed silicone rubber sponge, which is a cured product of the liquid silicone rubber sponge composition of the present invention, will be described below. The manufacturing method of the highly cellular silicone rubber sponge of the present invention is not particularly limited, but preferably has a crosslinking step of crosslinking and curing a liquid silicone rubber sponge composition and a cell formation step of promoting cell formation in the silicone rubber cured product.

[0049] The crosslinking step is a step of crosslinking and curing a liquid silicone rubber sponge composition. In the crosslinking step, the liquid silicone rubber sponge composition is filled into a mold by press molding, casting, injection or injection molding. For example, the crosslinking (primary cure) is carried out for several seconds to 180 minutes, preferably 1 to 60 minutes, under the condition that the actual temperature of the mold is 80 to 150 ° C, preferably 100 to 150 ° C. As the heating source, a heating wire heater, a ceramic heater, a hot air dryer, heated water, heated glass beads, etc. can be used.

[0050] The purpose of the cell formation step is to break the already expanded resin fine particles of the component (E) and volatilize and remove the remaining component (F), and it is a step of promoting cell formation in the silicone rubber cured product. Therefore, it is desirable to perform heat treatment at a temperature of, for example, 200 to 250 ° C, preferably 200 to 230 ° C for about 0.5 to 20 hours, preferably 1 to 6 hours, using a batch-type or continuous hot air dryer. In addition, the cell formation step is also a step called post-cure for completely reacting crosslinking or volatilizing volatile residues and low molecular weight siloxanes in the silicone rubber cured product. Further, in the liquid silicone rubber sponge composition of the present invention, since the amount of the cell forming agent used can be reduced compared to the conventional amount, the time required for the cell formation step can be shortened without the cell forming agent remaining in the produced silicone rubber sponge and deteriorating its durability.

[0051] The silicone rubber sponge of the present invention obtained in this way has high cell porosity and little hardness variation. The evaluation of the hardness variation of the highly cellular silicone rubber sponge of the present invention is carried out as follows. A cylindrical molded article with a diameter of 29 mm and a height of 12 mm is press-molded at 120°C for 10 minutes, and the obtained silicone rubber sponge is further heat-treated at 220°C for 4 hours using a hot air dryer. The sponge hardness is measured at one point each on the surface (one bottom surface) and the back surface (the other bottom surface) of 6 samples using an Asker C hardness meter according to the method specified in JIS S 6050:2008. The hardness variation is evaluated by the difference between the maximum and minimum measured values. In the present invention, if this measured value difference is 2 points or less, it can be determined that the sponge has little hardness variation.

[0052] 〔3〕Roll for electrophotographic image forming member Such a highly porous silicone rubber sponge is useful for rolls used in electrophotographic image forming members having at least one layer composed of the sponge, particularly for fixing members, drive rolls, paper feed and discharge rolls, etc. Specific examples of the fixing member include a fixing roll having a single layer made of a highly porous silicone rubber sponge, a fixing belt support roll; a multi-layer fixing roll having two or more layers made of a highly porous silicone rubber sponge and an adhesive surface release material such as a PFA tube; a fixing roll for toner melting and fixing having a multi-layer structure fixing roll structure in which a solid rubber, a sponge rubber layer, and a toner release layer are combined, and the like.

[0053] When a roll member is manufactured using the liquid silicone rubber sponge composition of the present invention, since the hardness variation in the length direction of the roll is particularly small, a roll member suitable as the above electrophotographic image forming member can be manufactured. The method for evaluating the hardness variation is as described above.

Examples

[0054] Hereinafter, preparation examples, examples and comparative examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

[0055] The evaluation methods for each example and each comparative example are shown below. · Density: Measured based on the description in JIS K6249:2003. · Sponge hardness: In accordance with the Asker C hardness specified in JIS S 6050:2008, a cylindrical molded product with a test piece shape of 29 mm in diameter and 12 mm in height was used. · Sponge cell state: The states of abnormal foaming, cracking, and mottled patterns were visually observed. Those without abnormal foaming, cracking, or mottled patterns were judged as "uniform", and those with any of abnormal foaming, cracking, or mottled patterns were judged as "non-uniform". · Average cell diameter of the sponge: It is the average value of the sponge cell diameters on the cut surface of the sponge, and the sponge cell diameter is the value measured with an optical microscope. · Presence or absence of mottled patterns: A 20-fold magnified photograph of the sponge cross-section was taken to confirm the presence or absence of mottled patterns. · Area of black mottled patterns: A 20-fold magnified photograph of the sponge cross-section was taken, the black mottled part of the photograph was cut out with scissors, and the area ratio was calculated from the mass ratio of the cut-out part to the normal part. · Compression set: In accordance with JIS K 6249:2003, the compression set after 22 hours at 180°C and 25% compression was measured.

[0056] The following describes each component used in the preparation examples, examples, and comparative examples. Note that the viscosity is the value measured with a rotational viscometer at 25°C by the method described in JIS K 7117-1:1999. The number average degree of polymerization is the value in terms of standard polystyrene measured by GPC under the following measurement conditions. <Measurement conditions> Apparatus: HLC-8320GPC manufactured by Tosoh Corporation Developing solvent: Toluene Flow rate: 0.6 mL / min Detector: Differential refractive index detector (RI) Column: TSK Guardcolumn SuperH-H TSKgel SuperH5000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH4000 (6.0 mm I.D. × 15 cm × 1) TSKgel SuperH3000 (6.0 mm I.D. × 15 cm × 1) (All are manufactured by Tosoh Corporation) Column temperature: 40 °C Sample injection volume: 50 μL (toluene solution with a concentration of 0.5 mass%)

[0057] [Component (A)] (A1) Dimethylpolysiloxane (number average degree of polymerization: 710) with both ends of the molecular chain blocked by dimethylvinylsiloxy groups, vinyl group content of 3.8×10 -5 mol / g, and a viscosity of 30,000 mPa·s (A2) Dimethylpolysiloxane (number average degree of polymerization: 180) with both ends of the molecular chain blocked by dimethylvinylsiloxy groups, vinyl group content of 1.5×10 -4 mol / g, and a viscosity of 550 mPa·s (A3) Dimethylpolysiloxane with both ends of the molecular chain blocked by dimethylvinylsiloxy groups, vinyl group content of 6.0×10 -4 mol / g, and a viscosity of 55 mPa·s (number average degree of polymerization: 45) (A4) A dimethylsiloxane·methylvinylsiloxane copolymer (number average degree of polymerization: 200) with both ends of the molecular chain blocked by trimethylsiloxy groups, having 20 vinyl groups only in the side chain, vinyl group content of 1.3×10 -3 mol / g, and a viscosity of 700 mPa·s [Component (B)] (B1) A linear dimethylsiloxane·methylhydrogensiloxane copolymer (hydrosilyl group content = 0.011 mol / g, viscosity 42 mPa·s) with both ends of the molecular chain blocked by trimethylsiloxy groups and having 45 silicon atom-bonded hydrogen atoms in the side chain [Component (C)] (C1) Fumed silica with a specific surface area of 300 m 2 / g (manufactured by Nippon Aerosil Co., Ltd., Aerosil 300) [Component (D)] (D1) A dimethylpolysiloxane solution containing 1 mass% of chloroplatinic acid / 1,3-divinyltetramethyldisiloxane complex as the platinum atom content [Component (E)] (E1) Expanded resin microparticles (Microspheres F-80ED manufactured by Matsumoto Yushi Seiyaku Co., Ltd., average particle diameter 100 μm, true specific gravity 0.022, organic resin shell: acrylonitrile copolymer) [Component (F)] (F1) 1,2-Propanediol (F’2) Triethylene glycol (comparative component) (F’3) 1,3-Butanediol (comparative component) [Other components] (Surface treatment agent) · Hexamethyldisilazane · Divinyltetramethyldisilazane (Reaction controller) · 1-Ethynylcyclohexanol (Heat-resistant additive) · Iron oxide paste

[0058] [Preparation Example 1] 60 parts by mass of dimethylpolysiloxane (A1) with both ends of the molecular chain blocked by dimethylvinylsiloxy groups, vinyl group content 3.8×10 -5 mol / g, viscosity 30,000 mPa·s, 40 parts by mass of fumed silica (C1) with a specific surface area of 300 m 2 / g (manufactured by Nippon Aerosil Co., Ltd., Aerosil 300), 8.0 parts by mass of hexamethyldisilazane, 0.5 parts by mass of divinyltetramethyldisilazane, and 2.0 parts by mass of water were mixed at room temperature (25 °C, the same below) for 60 minutes, then heated to 150 °C and stirred for 4 hours. Next, 20 parts by mass of dimethylpolysiloxane (A2) with both ends of the molecular chain blocked by dimethylvinylsiloxy groups, vinyl group content 1.5×10 -4 mol / g, viscosity 550 mPa·s was added, and after mixing until uniform, it was cooled to obtain a silicone rubber base.

[0059] [Example 1] 60 parts by mass of the silicone rubber base, with both ends of the molecular chain blocked by vinyldimethylsiloxy groups, vinyl group content 6.0×10 -460 parts by mass of dimethylpolysiloxane (A3) with a viscosity of 55 mPa·s and 0.1 part by mass of a dimethylpolysiloxane solution (D1) containing 1% by mass of platinum atoms as chloroplatinic acid / 1,3-divinyltetramethyldisiloxane complex, and 0.07 part by mass of 1-ethynylcyclohexanol were mixed at room temperature with a planetary mixer for 30 minutes. Then, 3.8 parts by mass of pre-expanded resin fine particles (Microsphere F-80ED manufactured by Matsumoto Yushi-Seiyaku Co., Ltd., average particle diameter 100 μm, true specific gravity 0.022, organic resin shell: acrylonitrile copolymer) (E1) were mixed at room temperature for 30 minutes. After that, 5.95 parts by mass of a dimethylsiloxane·methylhydrogensiloxane copolymer (B1) in which both ends of the molecular chain were blocked with trimethylsiloxy groups and having silicon atom-bonded hydrogen atoms in the side chain (silicon atom-bonded hydrogen atom content = 0.011 mol / g) and 16 parts by mass of 1,2-propanediol (F1) were added and mixed at room temperature for 15 minutes to prepare Composition A.

[0060] Next, the prepared Composition A was filled with a spatula into a mold having a diameter of 29 mmφ and a thickness of 12.5 mm in an amount equal to the mold volume, and primary curing was performed at 120°C for 15 minutes to obtain a cylindrical silicone molded body. Then, the obtained cylindrical silicone molded body with a thickness of 12 mm was heated with hot air at normal pressure in a hot air dryer at 220°C for 4 hours to obtain a silicone rubber sponge. The hardness of the obtained sponge, the state of the sponge cells, the average cell diameter of the sponge, the presence or absence of mottled patterns, the area of the black mottled patterns, and the compression set were examined as described above. Separately from this, to confirm the storage stability, the catalyst and the crosslinking agent were divided into two liquids so that they would be separated and would form Composition A when mixed at a mass ratio of 1 to 1. After storing at room temperature for 3 months, they were mixed at a mass ratio of 1 to 1, and the same tests were performed. The evaluation results are shown in Table 1.

[0061] [Examples 2 to 5, Comparative Examples 1 to 7] As described in Tables 1 to 3, the formulations of Examples 2 to 5 and Comparative Examples 1 to 7 were carried out to prepare a silicone rubber sponge composition. A silicone rubber sponge was produced in the same manner as in Example 1, and various rubber properties were evaluated. The results are also shown in Tables 1 to 3.

[0062] Further, FIG. 1 shows a photograph of a cross-sectional view of the silicone rubber sponge obtained after storage at room temperature for 3 months in Example 5. (A) is a photograph of a cross-section when the bottom surface of the cylindrical silicone rubber sponge is bisected by a diameter (magnification: 55 times, actual photograph horizontal width: 29 mm). Also, (B) is a black-and-white image obtained by setting a white / black threshold for the photograph data in FIG. 1(A) and performing binarization processing in order to distinguish the mottled pattern. FIG. 2 shows a photograph of a cross-sectional view of the silicone rubber sponge obtained after storage at room temperature for 3 months in Comparative Example 7. (A) is a photograph of a cross-section when the bottom surface of the cylindrical silicone rubber sponge is bisected by a diameter (magnification: 55 times), and (B) is a black-and-white image obtained by binarizing the photograph data in (A) in the same manner as in FIG. 1(B).

[0063] [Table 1]

[0064] [Table 2] * Since the initial value was not preferable, evaluation over time was not performed.

[0065] [Table 3] * Since the initial value was not preferable, evaluation over time was not performed.

[0066] [Example 6, Comparative Example 8] [Production of fixing roll] A cylindrical mold made of aluminum with an outer diameter of 26 mm, a length of 250 mm, and a wall thickness of 3 mm, having a fired fluorine treatment on the inner surface, was vertically arranged. A SUS304 mandrel with a diameter of 6 mm and a length of 300 mm (PRIMER-No31A / B manufactured by Shin-Etsu Chemical Co., Ltd. was already applied to the shaft (mandrel)) was vertically fixed at the center of the mold. The silicone rubber sponge compositions prepared in Example 2 and Comparative Example 4 were cast at room temperature under a pressure of 0.05 MPa through four holes with a diameter of 2 mm provided at the lower part of the mold, and the material was supplied from the upper part of the mold until it overflowed. Next, this mold was placed in a batch-type hot air dryer at 150 °C and crosslinked for 1 hour.

[0067] Next, after cooling the mold to room temperature, the shaft coated with the sponge was taken out from the mold, and the obtained single-layer sponge silicone rubber roll was further heat-treated in a hot air dryer at 220 °C for 4 hours.

[0068] This sponge rubber roll was coated with a fluorine PFA tube with a film thickness of 50 μm treated with an additional crosslinking type one-component silicone rubber adhesive KE-1884 (manufactured by Shin-Etsu Chemical Co., Ltd.) on the inner surface, heated and cured at 150 °C for 30 minutes, and further post-cured at 200 °C for 4 hours to produce a PFA resin-coated silicone rubber fixing roll with an outer diameter of 26 mm and a length of 250 mm.

[0069] [Evaluation of the fixing roll] The fixing roll thus obtained was measured for the Asker C hardness at 12 points at 10 mm intervals in the axial direction, and the minimum value - maximum value (hardness variation) and the standard deviation of the hardness were determined, and these results are shown in Table 4. The Asker C hardness meter was measured at the top part (the vertex of the arc) of the roll. As shown in Table 4, for the fixing roll (Example 6) using the silicone rubber sponge composition of Example 2, the actually measured values of the Asker C hardness were "49" - "51" for the "minimum value" - "maximum value", and the hardness variation was 2 points. On the other hand, in the fixing roll (Comparative Example 8) using the silicone rubber sponge composition of Comparative Example 4, the actually measured values of the Asker C hardness were "57" - "64" with "minimum value" - "maximum value", and the hardness variation was 7 points. Therefore, the fixing roll using the composition of Comparative Example 4 had a hardness variation such that there was a risk of letter smudging and fixing defects such as letter bleeding when used.

[0070]

Table 4

[0071] As can be seen from the results of the above Examples and Comparative Examples in Tables 1 to 4, the liquid silicone rubber sponge composition of this Example (the product of the present invention) can inexpensively and stably provide a highly foamed and uniform fine cell structure, a small compression set, and a high foamed silicone rubber sponge with little hardness variation.

Claims

1. (A) An organopolysiloxane that has two or more alkenyl groups bonded to silicon atoms in one molecule and is liquid at 25°C: 100 parts by mass, (B) An organohydropolysiloxane having two or more hydrosilyl groups in one molecule: an amount such that the number of hydrosilyl groups contained in the component (B) is 0.4 to 10 with respect to one alkenyl group bonded to a silicon atom contained in the component (A), (C) Reinforcing silica: 2.5 to 40 parts by mass, (D) An addition reaction catalyst: 0.0001 to 1 part by mass, (E) Expanded resin fine particles having an organic resin shell, an average particle diameter of 10 to 200 μm, and a true specific gravity of 0.01 to 0.3: 0.2 to 30 parts by mass, (F) As a foaming agent, 1,2 - propanediol: 1 to 30 parts by mass A liquid silicone rubber sponge composition containing the above.

2. The liquid silicone rubber sponge composition according to claim 1, wherein the organic resin shell of the expanded resin fine particles of the component (E) is composed of a polymer of any one monomer selected from the group consisting of vinylidene chloride, acrylonitrile, methacrylonitrile, acrylic esters, and methacrylic esters, or a copolymer of two or more monomers.

3. A highly foamed silicone rubber sponge that is a cured product of the liquid silicone rubber sponge composition according to claim 1 or 2.

4. A roll for an electrophotographic image forming member having one or more layers formed of the highly foamed silicone rubber sponge according to claim 3, wherein the variation in hardness of the highly foamed silicone rubber sponge is such that the difference between the maximum value and the minimum value measured with an Asker C hardness meter described in JIS S 6050:2008 is 2 points or less.

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