Abstract: A method of producing a base compound for a liquid fluoroelastomer which is unaffected by the storage state of the added silica powder, and yields minimal fluctuation in the viscosity between production lots. Specifically, a method of producing a base compound for a liquid fluoroelastomer containing: (A) a linear fluoropolyether compound having at least two alkenyl groups within each molecule and having a perfluoroalkyl ether structure within the main chain, and (B) a hydrophobic silica powder, the method including: (1) heating the component (A) under normal pressure at a temperature of 50 to 100 ° C., (2) adding 20 to 60 parts by mass of the component (B) to 100 parts by mass of the component (A) that has been heated in step (1) while performing kneading to obtain a kneaded product, and (3) kneading the kneaded product obtained in step (2) at a temperature exceeding 100° C., either under conditions of heat and reduced pressure or under conditions of heat and pressure.

Abstract: A method of producing a base compound for a liquid fluoroelastomer which is unaffected by the storage state of the added silica powder, and yields minimal fluctuation in the viscosity between production lots. Specifically, a method of producing a base compound for a liquid fluoroelastomer containing: (A) a linear fluoropolyether compound having at least two alkenyl groups within each molecule and having a perfluoroalkyl ether structure within the main chain, and (B) a hydrophobic silica powder, the method including: (1) heating the component (A) under normal pressure at a temperature of 50 to 100° C., (2) adding 20 to 60 parts by mass of the component (B) to 100 parts by mass of the component (A) that has been heated in step (1) while performing kneading to obtain a kneaded product, and (3) kneading the kneaded product obtained in step (2) at a temperature exceeding 100° C., either under conditions of heat and reduced pressure or under conditions of heat and pressure.

Abstract: A sealing material comprising (A) an organopoly-siloxane containing at least two alkenyl groups in a molecule, (B) a resinous copolymer composed mainly of R3SiO1/2 and SiO2 units in a molar ratio of 0.5-1.5:1, wherein R is a monovalent hydrocarbon group, and containing 5×10?3 to 1×10?4 mol/g of vinyl groups, (C) an organohydrogenpolysiloxane containing at least two Si—H groups in a molecule, (D) fumed silica having a specific surface area of 150-400 m2/g, and (E) an addition reaction catalyst is suited for sealing one side edge of a polymer electrolyte fuel-cell separator since it has excellent acid resistance and improved compression set in acidic solutions, and exerts satisfactory seal effects.

Abstract: An addition reaction-curable liquid silicone rubber composition includes an organopolysiloxane containing at least one Si-bonded vinyl group only at each end of its backbone and having a viscosity of from 1 to 1,000 Pa·s at 25° C., an organopolysiloxane containing at least two Si-bonded vinyl groups only in side chains on its backbone and having a viscosity of from 0.1 to 100 Pa·s at 25° C., the amount of siloxane units bonded to the vinyl groups being from 2 to 20 mole % of its total siloxane units, finely divided silica having a specific surface area of at least 50 m2/g, hexamethyldisilazane, water, an organohydrogenpolysiloxane containing at least two Si-bonded hydrogen atoms per molecule, and a hydrosilation catalyst. Another addition reaction-curable liquid silicone rubber composition additionally includes a specific non-functional dimethylpolysiloxane.

Abstract: A rubber composition comprising (A) an organopolysiloxane end-capped with alkenyldialkylsiloxy, dialkenylalkylsiloxy or trialkenylsiloxy radicals and free of aliphatic unsaturation on any side chain, (B) an organopolysiloxane containing at least three alkenyl radicals on molecular side chains, (C) an organohydrogenpolysiloxane having at least three Si—H radicals, (D) fumed silica, and (E) an addition reaction catalyst forms a seal member having improved strength and reduced compression set and useful for sealing a polymer electrolyte fuel-cell separator.

Abstract: An addition reaction-curable liquid silicone rubber composition includes an organopolysiloxane containing at least one Si-bonded vinyl group only at each end of its backbone and having a viscosity of from 1 to 1,000 Pa·s at 25° C., an organopolysiloxane containing at least two Si-bonded vinyl groups only in side chains on its backbone and having a viscosity of from 0.1 to 100 Pa·s at 25° C., the amount of siloxane units bonded to the vinyl groups being from 2 to 20 mole % of its total siloxane units, finely divided silica having a specific surface area of at least 50 m2/g, hexamethyldisilazane, water, an organohydrogenpolysiloxane containing at least two Si-bonded hydrogen atoms per molecule, and a hydrosilation catalyst. Another addition reaction-curable liquid silicone rubber composition additionally includes a specific non-functional dimethylpolysiloxane.

Abstract: A rubber composition contains an organopolysiloxane having at least two alkenyl radicals, an organohydrogenpolysiloxane having at least three Si—H radicals, a catalyst and optionally, fumed silica and an acid resistant inorganic filler. On a periphery of one side of a polymer electrolyte fuel-cell separator, the composition forms a seal member which allows for little leaching of non-functional organopolysiloxane fraction and has improved acid resistance and compression set.

Abstract: A sealing material comprising (A) an organopoly-siloxane containing at least two alkenyl groups in a molecule, (B) a resinous copolymer composed mainly of R3SiO1/2 and SiO2 units in a molar ratio of 0.5-1.5:1, wherein R is a monovalent hydrocarbon group, and containing 5×10−3 to 1×10−4 mol/g of vinyl groups, (C) an organohydrogenpolysiloxane containing at least two Si—H groups in a molecule, (D) fumed silica having a specific surface area of 150-400 m2/g, and (E) an addition reaction catalyst is suited for sealing one side edge of a polymer electrolyte fuel-cell separator since it has excellent acid resistance and improved compression set in acidic solutions, and exerts satisfactory seal effects.

Abstract: A sealing material for sealing the edges on at least one side of a solid polymer fuel cell separator is provided. This sealing material includes (A) an organopolysiloxane with at least two alkenyl groups bonded to silicon atoms within each molecule, (B) an organohydrogenpolysiloxane with at least two hydrogen atoms bonded to silicon atoms within each molecule, (C) a fumed silica with a specific surface area of 50 to 250 m2/g which has undergone surface treatment with at least two different surface treatment agents, and (D) an addition reaction catalyst. This sealing material displays excellent moldability, heat resistance and elasticity, has a compression set within air and within an acidic aqueous solution which can be suppressed to a low value, and produces an excellent seal, particularly in an acidic aqueous solution.

Abstract: A rubber composition comprising (A) an organopolysiloxane end-capped with alkenyldialkylsiloxy, dialkenylalkylsiloxy or trialkenylsiloxy radicals and free of aliphatic unsaturation on any side chain, (B) an organopolysiloxane containing at least three alkenyl radicals on molecular side chains, (C) an organohydrogenpolysiloxane having at least three Si—H radicals, (D) fumed silica, and (E) an addition reaction catalyst forms a seal member having improved strength and reduced compression set and useful for sealing a polymer electrolyte fuel-cell separator.

Abstract: A rubber composition contains an organopolysiloxane having at least two alkenyl radicals, an organohydrogenpolysiloxane having at least three Si—H radicals, a catalyst and optionally, fumed silica and an acid resistant inorganic filler. On a periphery of one side of a polymer electrolyte fuel-cell separator, the composition forms a seal member which allows for little leaching of non-functional organopolysiloxane fraction and has improved acid resistance and compression set.

Abstract: A sealing material for sealing the edges on at least one side of a solid polymer fuel cell separator is provided. This sealing material includes (A) an organopolysiloxane with at least two alkenyl groups bonded to silicon atoms within each molecule, (B) an organohydrogenpolysiloxane with at least two hydrogen atoms bonded to silicon atoms within each molecule, (C) a fumed silica with a specific surface area of 50 to 250 m2/g which has undergone surface treatment with at least two different surface treatment agents, and (D) an addition reaction catalyst. This sealing material displays excellent moldability, heat resistance and elasticity, has a compression set within air and within an acidic aqueous solution which can be suppressed to a low value, and produces an excellent seal, particularly in an acidic aqueous solution.

Abstract: A sealing material comprising (A) an organopolysiloxane containing at least two alkenyl groups in a molecule, (B) a resinous copolymer composed mainly of R3SiO1/2 and SiO2 units in a molar ratio of 0.5-1.5:1, wherein R is a monovalent hydrocarbon group, and containing 5×10−3 to 1×10−4 mol/g of vinyl groups, (C) an organohydrogenpolysiloxane containing at least two Si—H groups in a molecule, (D) fumed silica having a specific surface area of 150-400 m2/g, and (E) an addition reaction catalyst is suited for sealing one side edge of a polymer electrolyte fuel-cell separator since it has excellent acid resistance and improved compression set in acidic solutions, and exerts satisfactory seal effects.

Abstract: A liquid addition curing type silicone rubber composition comprising (A) an addition curing type organopolysiloxane component and (B) reinforcing silica fines having a specific surface area of 50-600 m2/g and surface treated with an organosilicon compound so as to bear 3-20% by weight of carbon on their surfaces prevents thickening after mixing and has an extended pot life.