Normally, a silicone rubber is produced either by heating and curing a composition comprising a diorganopolysiloxane gum, a reinforcing silica filler, an organic peroxide, etc., or by heating and curing a liquid silicone rubber composition comprising a liquid vinyl-containing organopolysiloxane, a reinforcing silica filler, an organohydrogenpolysiloxane, a platinum catalyst, etc. Methods of manufacturing silicone elastomers from aqueous silicone emulsions and silicone emulsions for the above purposes are known in the art. For example, unexamined Japanese Patent Application Publication (hereinafter JP Kokai) S56-36546 teaches a method of obtaining a silicone elastomer by preparing an emulsion obtained by emulsifying in water an organohydrogenpolysiloxane and a polyorganosiloxane capped at both molecular terminals with vinyl groups, adding a platinum catalyst to the emulsion, forming a cross-linked latex by heating the catalyst-added emulsion, adding a colloidal silica to the latex, and evaporating the water from the latex. JP Kokai 2000-169590 teaches a method of manufacturing a silicone rubber by heating and curing an emulsion prepared from a vinyl-containing diorganopolysiloxane, an organohydrogenpolysiloxane, a platinum catalyst, a silicone resin, an emulsifier, water, carbon black, etc.
However, the method disclosed in JP Kokai S56-36546 involves complicated operations and makes it difficult to obtain a uniform elastomer with repeatable properties. On the other hand, the method disclosed in JP Kokai 2000-169590 allows obtaining of silicone rubber with colors only between gray and black.
Furthermore, a silicone rubber sponge, which is a porous silicone rubber, is normally produced by heating and curing a silicone rubber composition comprising a diorganopolysiloxane gum, a reinforcing silica filler, a blowing agent, an organic peroxide, etc., or by heating and curing a liquid silicone rubber composition comprising a liquid vinyl-containing diorganopolysiloxane, a reinforcing silica filler, a blowing agent, an organohydrogenpolysiloxane, a platinum catalyst, etc.
Also known is JP Kokai S59-12832 that relates to a novel method and a composition therefor that teaches a method of manufacturing a silicone rubber sponge by freezing a condensation-reaction-curable silicone emulsion consisting of a diorganopolysiloxane capped at both molecular terminals with hydroxyl groups, an organotin catalyst, and a colloidal silica to a hard state, and then thawing and dehydrating the frozen composition. Japanese Patent Publication H7-122000 discloses a method of manufacturing a silicone rubber sponge by combining a hydrosilation-curable or organoperoxide-curable silicone rubber composition with an emulsion consisting of an organopolysiloxane, an emulsifier, water, and thickener, and then heating the combined composition to form a silicone rubber sponge where expansion action of evaporating water is utilized for forming a sponge. JP Kokai 2002-114860 describes a method of manufacturing a silicone rubber sponge by heating a hydrosilation reaction-, i.e. an addition reaction-curable silicone rubber sponge composition comprising an alkenyl-containing diorganopolysiloxane, an organohydrogenpolysiloxane, a platinum catalyst, and a water-absorbing organic polymer powder.
However, the method disclosed in JP Kokai S59-12832 is not suitable for commercial application as it is time-consuming and requires a significant amount of energy for freezing the silicone emulsion and thawing the frozen silicone emulsion. Furthermore, the use of the organotin catalyst does not allow obtaining a silicone rubber with heat-resistant properties. The method disclosed in Japanese Patent Publication H7-122000 indispensably needs a thickener which is an aqueous organic polymer, while the method of JP Kokai 2002-114860 indispensably needs a water-absorbing organic polymer powder. Therefore, the problem associated with both last-mentioned methods is that silicone rubber sponges produced by these methods will have poor resistance to heat and low mechanical strength.
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