Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-07-31
2002-12-24
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S267000, C524S268000, C524S301000, C524S394000, C524S504000, C524S506000, C524S515000, C524S523000, C525S063000, C525S064000, C525S070000, C525S078000, C525S100000, C525S101000, C525S326100
Reexamination Certificate
active
06498206
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a powdery resin useful as an impact modifier for thermoplastic resins, and more particularly to an impact modifier having an improved blocking resistance.
Various proposals have been made to improve the impact resistance of thermoplastic resins. Crazing and shearing yield play an important part in the improvement of impact resistance, and stress concentration in molded articles is inevitable for the generation thereof. For this purpose, graft copolymers containing a rubber component have been popularly incorporated into thermoplastic resins to improve the impact resistance. It is also known to perforate rubber particles (“Impact Resistance of Plastics” by Ikuo Narisawa, pages 131 and 155, published by Siguma Shuppan). Further, in recent years, it has been investigated to improve the impact resistance of thermoplastic resins by using graft copolymers having a hollow rubber component.
For example, JP-A-10-310714 proposes a process of the synthesis of a hollow rubber-containing graft copolymer useful for improving the impact resistance of thermoplastic resins, wherein the graft copolymer is prepared utilizing a technique of synthesis of hollow particles. However, the graft copolymer prepared by this process is poor in powder characteristics and in particular has a blocking problem that the powdery polymer aggregates to a mass during storage, transfer or transportation.
In order to solve this problem, JP-A-11-315587 proposes adding a crosslinked polymer of 0.1 to 100% by weight of a crosslinking monomer and 0 to 99.9% by weight of a vinyl monomer to the graft copolymer. The blocking resistance of the graft copolymer is improved by the addition of this crosslinked polymer.
It is an object of the present invention to further improve the blocking resistance of the hollow rubber-containing graft copolymer.
A further object of the present invention is to provide a graft copolymer which is prepared by graft polymerization of a vinyl monomer onto hollow rubber particles and which can be suitably used as an impact modifier for thermoplastic resins without causing blocking during storage, transfer or transportation.
These and other objects of the present invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
It has now been found that the blocking resistance of the hollow rubber-containing graft copolymer can be remarkably improved by incorporating the crosslinked polymer of 0.1 to 100% by weight of a crosslinking monomer and 0 to 99.9% by weight of a vinyl monomer into the graft copolymer together with at least one of a higher fatty acid soap and a silicone oil, or by incorporating the higher fatty acid soap and the silicone oil into the graft copolymer.
Thus, in accordance with the present invention, there is provided an impact modifier having an improved blocking resistance which comprises (A) a graft copolymer prepared by polymerization of a vinyl monomer in the presence of hollow rubber particles, and at least two additives selected from the group consisting of (B) 0.1 to 10 parts of a higher fatty acid soap, (C) 0.1 to 10 parts of a crosslinked polymer of 0.1 to 100% by weight of a crosslinking monomer and 0 to 99.9% by weight of a vinyl monomer and (D) 0.001 to 5 parts of a silicone oil, the parts of (B), (C) and (D) being parts by weight per 100 parts by weight of the graft copolymer (A).
The higher fatty acid soap used in the present invention is anionic surface active agents of carboxylic acid type having a C
7
to C
25
alkyl group, preferably a C
10
to C
20
alkyl group.
DETAILED DESCRIPTION
The hollow rubber particle is a rubber particle having rubber component-non-filled part or parts therein, namely a rubber particle having hollow part or parts therein, unlike a conventional rubber particle the whole of which is formed by a rubber component. A typical hollow particle is hollow in the core part of the particle. The hollow rubber particles can be prepared by various known methods as disclosed in Takaaki Sugimura et al, Application of Synthetic Latex, page 285, published by Kobunshi Kankokai, Japan, e.g., (a) a method wherein a W/O/W emulsion is formed (O: lipophilic, W: hydrophilic) and a monomer of the O-layer is polymerized, (b) a method wherein core-shell polymer particles having a swellable core is swollen at a temperature of not less than Tg (glass transition temperature) of the shell layer, thereby forming a hollow part, (c) a method wherein polymers having different solubility parameters are produced by a two stage polymerization, (d) a method wherein an oily material and a monomer mixture containing a crosslinking monomer and a hydrophilic monomer are dispersed into water to form an O/W emulsion, the monomer mixture is polymerized and the oily material is removed from the produced polymer particles, and (e) a method utilizing a phenomenon that carboxylic acid units copolymerized into a rubber particle move in the particle under acidic or alkaline conditions.
The rubber particles used in the present invention which have a hollow part in the state of a latex can be prepared by any methods without particular restriction. For example, the hollow rubber particles can be prepared by emulsion polymerization of a monomer such as a diene monomer for forming a rubber in the presence of a swellable seed polymer and a swelling material which are used for forming a hollow part in a resulting rubber particle.
Examples of the seed polymer are, for instance, a rubber such as diene rubber, acrylic rubber, silicone rubber or olefin rubber; a semi-hard polymer such as butyl acrylate-styrene copolymer or ethyl acrylate-styrene copolymer; and a hard polymer such as styrene-methyl methacrylate. These seed polymers may be those prepared in the presence of a chain transfer agent such as t-dodecylmercaptan or n-dodecylmercaptan in order to decrease the molecular weight thereof.
The rubber which substantially constitutes the hollow particles is preferably a rubbery elastomer having a Tg of not more than 0° C., more preferably a much lower Tg. The rubber includes, for instance, a diene rubber, an acrylic rubber, a silicone rubber and an olefin rubber. Examples of the diene rubber are, for instance, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, and the like. Examples of the acrylic rubber are, for instance, butyl acrylate rubber, butadiene-butyl acrylate rubber, 2-ethylhexyl acrylate-butyl acrylate rubber, and the like. A typical example of the silicone rubber is polydimethylsiloxane rubber. Examples of the olefin rubber are, for instance, ethylene-propylene rubber, ethylene-propylene-diene rubber, and the like.
In the polymerization for preparing the rubber, a crosslinking monomer can be used as a comonomer. The crosslinking monomer serves to prevent the rubber particles from breaking to pieces when a thermoplastic resin incorporated with an impact modifier is thermally molded. If the amount of the crosslinking monomer is too large, the rubber particles do not break at the time of molding, but the impact strength of the molded article is not greatly improved since a void is hard to extend when the molded article receive an impact (under stress).
Examples of the crosslinking monomer are, for instance, allyl methacrylate, divinyl benzene, diallyl phthalate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, ethylene glycol dimethacrylate, and other known crosslinking monomers.
The preparation of the hollow rubber particles is not limited to a particular method, but emulsion polymerization method is preferred since the preparation can be efficiently conducted.
The hollow rubber particles may be directly used in the preparation of a graft copolymer by graft polymerization of a vinyl monomer onto the rubber particles, or may be subjected to a particle size enhancement treatment in a known manner, wherein the rubber particles are agglomerated by the use of an acid or a salt to enhance the particle size of the rubber particles, for the purpose of obtaining
Hashimoto Tomomichi
Kakutani Mitsuo
Mizuta Tosio
Sato Akio
Takaki Akira
Armstrong Westerman & Hattori, LLP
Dawson Robert
Kaneka Corporation
Robertson Jeffrey B.
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