Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-10-12
2002-01-15
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S100000, C525S479000, C525S063000, C524S837000
Reexamination Certificate
active
06339127
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an aqueous emulsion containing silicone rubber particles which has a number average particle size of at most 0.1 &mgr;m and a narrow particle size distribution, and which is suitable for use in impact modifier, softener, fiber treating agent, hair treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material and the like, and also to a process for the preparation of the aqueous emulsion.
BACKGROUND ART
Silicone rubbers have good properties such as elasticity, water resistance, thermal stability, weatherability, flame resistance and lubricity and, therefore, aqueous emulsions containing them have been widely used in impact modifier, softener, fiber treating agent, hair treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material and the like. In these uses, it is effective in exhibiting higher performances to adjust the number average particle size of the aqueous emulsions of silicone rubber particles to not more than 0.1 &mgr;m and to make the particle size distribution of the emulsions narrow. Some proposals to obtain such aqueous emulsions of silicone rubber particles have been made, but satisfactory emulsions have not yet been obtained.
Japanese Patent Publication Kokai No. 62-141029 discloses a process for preparing an aqueous emulsion containing silicone rubber particles having a particle size of at most 0.1 &mgr;m which comprises adding an emulsion composed of an organosiloxane, an emulsifier and water to a reaction system containing water and a polymerization catalyst and carrying out the polymerization.
Japanese Patent Publication Kokai No. 5-194740 discloses a process for preparing an aqueous emulsion containing silicone rubber particles having a particle size of at most 0.1 &mgr;m which comprises adding dropwise an emulsion composed of a mixture of an organosiloxane, a siloxane-based crosslinking agent and a siloxane-based graftlinking agent, an emulsifier and water to a reaction system containing water and a polymerization catalyst, while carrying out the polymerization.
However, in both processes disclosed in Japanese Patent Publications Kokai No. 62-141029 and Kokai No. 5-194740, at least 13 parts by weight of an emulsifier is required per 100 parts by weight of the silicone rubber in the aqueous silicone rubber emulsion when it is desired to adjust the particle size of the emulsion to not more than 0.1 &mgr;m and to make the particle size distribution narrow, for example, to adjust the variation coefficient (standard deviation/average particle size (%)) which is a measure of the particle size distribution to not more than 65%. Thus, in case of using aqueous silicone rubber emulsions obtained by such conventional processes as impact modifier, slipping agent or flame retardant, there arises a problem that molded articles are easy to be colored. Also, in case of using them as coating material or fiber treating agent, there arises a problem that the water repellency is deteriorated.
Thus, it is an object of the present invention to provide an aqueous emulsion of silicone rubber particles having a number average particle size of at most 0.1 &mgr;m and a narrow particle size distribution (variation coefficient of at most 65%) which has a small content of an emulsifier.
A further object of the present invention is to provide a process for preparing an aqueous emulsion of silicone rubber particles according to which an aqueous emulsion of silicone rubber particles having a number average particle size of at most 0.1 &mgr;m and a narrow particle size distribution can be prepared with use of a small amount of an emulsifier.
Another object of the present invention is to provide an aqueous emulsion containing silicone rubber-based graft copolymer particles, which is prepared from silicone rubber particles having a number average particle size of at most 0.1 &mgr;m and a narrow particle size distribution.
Still another object of the present invention is to provide a resin composition wherein such silicone rubber particles and/or graft copolymer particles are incorporated into a thermoplastic resin.
DISCLOSURE OF THE INVENTION
The present inventors have found, as a result of making an intensive study in view of the problems mentioned above, that an aqueous emulsion containing silicone rubber particles having a number average particle size of 0.008 to 0.1 &mgr;m and a variation coefficient in particle size distribution of at most 65% is obtained with use of a small amount of an emulsifier, while maintaining properties of conventional aqueous emulsions containing silicone rubber particles, by polymerizing silicone rubber-forming components in an aqueous emulsion of a vinyl polymer or copolymer, and that an aqueous emulsion of silicone rubber-based graft copolymer particles wherein a vinyl polymer is grafted onto silicone rubber-containing polymer particles having a small number average particle size and a small variation coefficient of the particle size distribution is obtained by polymerizing a vinyl monomer in the above-mentioned aqueous emulsion containing silicone rubber particles.
Thus, the present invention provides a silicone rubber particle-containing aqueous emulsion which contains polymer particles comprising (A) 0.1 to 45% by weight of a vinyl homopolymer or copolymer and (B) 55 to 99.9% by weight of a silicone rubber, wherein said polymer particles have a number average particle size of 0.008 to 0.1 &mgr;m and a variation coefficient in particle size distribution of at most 65%, and said emulsion contains at most 10 parts by weight of an emulsifier per 100 parts by weight of said silicone rubber (B).
The silicone rubber particle-containing aqueous emulsion is prepared by adding (b) 60 to 99.9 parts by weight of a silicone rubber-forming component comprising 50 to 100% by weight of a mixture of an organosiloxane and a difunctional silane compound, 0 to 50% by weight of a silane compound having a functionality of at least 3 and 0 to 50% by weight of a polymerizable vinyl group-containing silane compound to an aqueous emulsion containing the vinyl homopolymer or copolymer (A) obtained by emulsion-polymerizing (a) 0.1 to 40 parts by weight of at least one vinyl monomer selected from the group consisting of an aromatic vinyl monomer, a vinyl cyanide monomer, a halogen-containing vinyl monomer, a (meth)acrylic ester monomer, a carboxyl group-containing vinyl monomer and a conjugated diene monomer so that the total amount of the vinyl monomer (a) and the silicone rubber-forming component (b) is 100 parts by weight, and polymerizing the silicone rubber-forming component (b). The silicone rubber particles are obtained by coagulating the silicone rubber particle-containing aqueous emulsion followed by dehydration and drying.
The present invention also provides an aqueous emulsion containing silicone rubber-based graft copolymer particles, which is prepared by polymerizing a vinyl monomer (c) in an aqueous emulsion containing the above-mentioned silicone rubber particle-containing aqueous emulsion. The graft copolymer particles are obtained by coagulating the graft copolymer particle-containing aqueous emulsion followed by dehydration and drying.
These aqueous emulsion of silicone rubber and aqueous emulsion of silicone rubber-based graft copolymer have a small average particle size, a narrow particle size distribution and a low content of an emulsifier. Therefore, they efficiently exhibit desirable properties without causing problems owing to an emulsifier and are very useful for various purposes, for example, as impact modifier, softener, fiber treating agent, hair treating agent, slipping agent, water repellent, processing aid for molding materials, flame retardant, coating material, and the like.
Thus, the present invention further provides a thermoplastic resin composition comprising a thermoplastic resin and the silicone rubber particles and/or silicone rubber-based graft copolymer particles as mentioned a
Hamaguchi Shigeki
Miyatake Nobuo
Takikawa Kazunori
Armstrong Westerman Hattori McLeland & Naughton LLP
Dawson Robert
Kaneka Corporation
Zimmer Marc S.
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