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
2002-06-18
2004-11-23
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S069000, C525S070000, C525S071000, C525S100000, C525S185000, C525S193000, C525S254000, C525S326500
Reexamination Certificate
active
06822045
ABSTRACT:
RELATED APPLICATIONS
This application is a nationalization of PCT application PCT/JP01/10465 filed Nov. 30, 2001. This application claims priority from the PCT application and Japan Application Ser. No. 2000-370273 filed Dec. 5, 2000.
TECHNICAL FIELD
The present invention relates to a rubber-modified resin useful as an impact modifier for thermoplastic resins, and a thermoplastic resin composition containing the same. More particularly, the present invention relates to a rubber-modified resin wherein a resin is modified with two rubbers of a silicone rubber and an acrylic rubber, and a thermoplastic resin composition having an excellent impact resistance.
BACKGROUND ART
It has been popularly practiced to improve the impact resistance of thermoplastic resins by incorporating a rubber-modified resin containing a rubber component into the thermoplastic resins.
It has been considered advantageous in exhibiting impact resistance to use a rubber component having a glass transition temperature (Tg) as low as possible. In practice, a resin composition incorporated with a resin modified with a polybutadiene-based rubber having a low Tg of about −80° C., e.g., acrylonitrile/butadiene/styrene copolymer (ABS resin), has a higher impact resistance than a resin composition incorporated with a resin modified with a polybutyl acrylate rubber having a Tg of about −50° C.
In respect of low Tg of rubbers, a polyorganosiloxane rubber (hereinafter also referred to as “silicone rubber”) can be expected to impart a higher impact resistance as compared with rubber-modified resins containing a polybutadiene-based rubber component if rubber-modified resins containing a silicone rubber can be utilized as impact modifier, since for example the Tg of polydimethylsiloxane rubber is about −120° C.
Use of silicone rubber is also advantageous from the viewpoint of weatherability as being superior to polybutyl acryalate rubber and polybutadiene-based rubber.
From such a point of view, recently, it has been variously investigated to use resins modified with silicone rubber or composite rubbers containing silicone rubber as an impact modifier for thermoplastic resins. For example, JP-A-4-100812 discloses using a graft copolymer prepared by graft-polymerizing a vinyl monomer onto a composite rubber wherein a silicone rubber component and a polyalkyl (meth)acrylate component are unseparably entangled with each other. Also, JP-A-11-100481 discloses using a graft copolymer prepared by co-agglomerating silicone rubber particles and acrylic rubber particles to give a composite rubber of enhanced particle size and graft-polymerizing a vinyl monomer onto the composite rubber.
The impact resistance of thermoplastic resins is further improved by incorporation of, as an impact modifier, these graft copolymers prepared using the composite rubbers as mentioned above in compared with single use of conventional rubbers such as polybutadiene-based rubber and acrylic rubber. However, the degree of improvement is not so large as one expects.
It is an object of the present invention to provide an impact modifier having a remarkably improved effect of imparting impact resistance.
A further object of the present invention is to provide a thermoplastic resin composition having an improved impact resistance.
DISCLOSURE OF INVENTION
The present inventors have found that a rubber-modified resin having a remarkably improved impact resistance-imparting effect can be prepared by polymerizing a vinyl monomer in the presence of a mixed rubber latex of a silicone rubber latex and an acrylic rubber latex and, during the polymerization, coagglomerating polymer particles present in the mixed latex to enhance the particle size.
Thus, the present invention provides a rubber-modified resin obtained by polymerizing a vinyl monomer in the presence of (A) a silicone rubber latex and (B) an acrylic rubber latex and, during the polymerization, coagglomerating polymer particles to enhance the particle size.
The rubber-modified resin of the present invention contains a silicone rubber and an acrylic rubber as the rubber component. The silicone rubber used in the present invention comprehends a polyorganosiloxane and a modified polyorganosiloxane wherein a polyorganosiloxane is partly replaced with an organic polymer having no polyorganosiloxane segment. It is preferable that the amount of silicone (polyorganosiloxane) in the total rubber component of the modified-rubber resin is from 1 to 90% by weight based on 100% by weight of the total of the silicone rubber and the acrylic rubber. Also, it is preferable that the amount of the total rubber latex is from 40 to 98 parts by weight (solid basis) and the amount of the vinyl monomer is from 2 to 60 parts by weight, respectively, based on 100 parts by weight of the total of the whole rubber component and the vinyl monomer. Preferably the particle size enhancement by coagglomeration is conducted by adding an electrolyte to the polymerization system on or before the polymerization conversion of the vinyl monomer reaches 90% by weight, especially when the polymerization conversion reaches 10 to 70% by weight.
The rubber-modified resin of the present invention can be incorporated into various thermoplastic resins, whereby the impact resistance of the thermoplastic resins is remarkably improved.
Thus, the present invention also provides a thermoplastic resin composition comprising a thermoplastic resin and 0.1 to 150 parts by weight of the above-mentioned rubber-modified resin per 100 parts by weight of the thermoplastic resin.
BEST MODE FOR CARRYING OUT THE INVENTION
The rubber-modified resins of the present invention are those prepared by polymerizing a vinyl monomer in the presence of a mixed rubber latex of (A) a silicone rubber latex and (B) an acrylic rubber latex and, during the polymerization, coagglomerating polymer particles in the latex to enhance the particle size. That is to say, the rubber-modified resins comprise particles formed by particle size-enhancing co-agglomeration, which is conducted in the course of the graft polymerization, of graft copolymer particles wherein a vinyl monomer is graft-polymerized onto a silicone rubber (or particles wherein the silicone rubber and a polymer of the vinyl monomer are physically coexist if the silicone rubber has no grafting site) and graft copolymer particles wherein the vinyl monomer is graft-polymerized onto an acrylic rubber (or particles wherein the acrylic rubber and the vinyl polymer are physically coexist if the acrylic rubber has no grafting site).
The rubber-modified resins of the present invention have the advantage of being superior in impact resistance-imparting effect as compared with a rubber-modified resin prepared in the same manner as the present invention but without conducting the particle size enhancing coagglomeration during the polymerization of vinyl monomer, and a rubber-modified resin prepared in such a manner as coagglomerating a latex of a mixed rubber (silicone rubber and acrylic rubber) prior to the polymerization of vinyl monomer, namely a graft copolymer prepared by graft-polymerizing a vinyl monomer onto a composite rubber of silicone rubber and acrylic rubber.
The term “silicone rubber” as used herein comprehends a polyorganosiloxane having rubber elasticity, namely a conventional silicone rubber, a modified silicone rubber composed of a silicone rubber and an organic polymer having no silicone (polyorganosiloxane) segment (e.g., butyl acrylate polymer rubber, butadiene polymer rubber, styrene polymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer or methyl methacrylate polymer), and the like. The modified silicone rubber includes a modified silicone rubber wherein a silicone rubber and an organic polymer having no silicone segment are chemically bonded, a modified silicone rubber wherein a silicone rubber and an organic polymer having no silicone segment are entangled, and a modified silicone rubber wherein a silicone rubber and an organic polymer having no silicone segment merely coex
Miyatake Nobuo
Takaki Akira
Brinks Hofer Gilson & Lione
Egwim Kelechi C.
Kaneka Corporation
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