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
1999-12-06
2001-10-30
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S085000, C525S227000, C525S228000
Reexamination Certificate
active
06310137
ABSTRACT:
TECHNICAL FIELD
This invention relates to multilayered acrylic polymers having excellent falling-ball or falling-weight impact strength, resistance to impact whitening, and transparency, and to methacrylic resin compositions using the same.
BACKGROUND ART
Methacrylic resins are being used for automobile parts, lighting equipment, various panels and the like, because of their excellent transparency, weather resistance, moldability and other properties. However, methacrylic resins generally have insufficient impact resistance, so that many propositions have hitherto been made in order to improve their impact resistance.
For example, Japanese Patent Publication No. 27576/′80 has proposed a technique in which the impact resistance of hard resins such as methacrylic resins is improved by adding thereto a multilayered polymer having a specific basic structure consisting of hard-soft-hard three layers. Moreover, Japanese Patent Publication No. 88903/′93 has proposed a thermoplastic acrylic resin composition containing a hard-soft-hard polymer having a specific structure and specific properties, with a view to improving impact resistance, transparency, and the lowering the variation of haze with temperature. Moreover, Japanese Patent Laid-Open No. 230841/′87 has proposed a method for improving the balance of transparency, gloss, rigidity and impact resistance in multilayered graft copolymers having a semisoft-soft-hard three layers structure. Furthermore, Japanese Patent Laid-Open No. 93056/′94 has proposed a method for improving the Izod impact strength and resistance to impact whitening of a hard-soft-hard three layers emulsion polymer by using an arylalkyl (meth)acrylate in place of styrol (styrene) serving as a component of the elastomer layer, so as to create a well-defined interface between the hard core and the elastomer layer.
However, the term “impact resistance” as used in these propositions exclusively means the impact strength (Izod impact strength) of a specimen having a notch (or cutout). Although this is a common method for evaluating the impact resistance of molded articles having a complicated shape with corners or the like, no particular consideration is given to falling-ball or falling-weight impact strength which is an index to the impact strength of molded articles used chiefly in the form of flat plates such as signboards and various covers. Accordingly, there is room for improvement.
Japanese Patent Publication No. 11970/′85 has proposed a method for improving falling-weight impact strength, solvent resistance and other properties by disposing an intermediate layer respectively between adjacent layers of a specific hard-soft-hard three-layer structure and controlling the particle diameter. Moreover, Japanese Patent Publication No. 17406/'85 has proposed a method for improving falling-weight impact strength, solvent resistance and other properties by controlling the molecular weight of the third layer in a specific hard-soft-hard three-layer structure. However, the degree of improvement brought about by these methods is less than satisfactory, and still leaves room for improvement.
Furthermore, Japanese Patent Laid-Open No. 17654/'93 has proposed a method for improving the gloss, transparency, falling-weight impact strength and processability of a multilayered graft copolymer having a semisoft-soft-hard three layers structure in which, during preparation of the graft copolymer, the addition and polymerization of the monomer to form the third layer is started at the time when the polymer of the second layer has reached a specific degree of polymerization. However, this proposition still fails to achieve sufficiently high transparency and falling-weight impact strength, and resistance to impact whitening also remains to be improved.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a multilayered acrylic polymer which can improve the falling-ball or falling-weight impact strength, resistance to impact whitening, transparency and other properties of thermoplastic resin compositions, as well as a methacrylic resin composition containing this multilayered acrylic polymer.
The present inventors made intensive investigations with a view to solving the above-described problems, and have now discovered that the above-described problems can be solved by a multilayered acrylic polymer having a specific composition and a specific morphological feature. The present invention has been completed on the basis of this discovery.
Specifically, the subject matter of the present invention comprehends a multilayered acrylic polymer comprising an innermost layer polymer (A) obtained by polymerizing a mixture composed of 100 parts by weight of a monomer or monomer mixture comprising 40 to 100% by weight of an alkyl methacrylate having an alkyl group of 1 to 4 carbon atoms, 0 to 60% by weight of an alkyl acrylate having an alkyl group of 1 to 8 carbon atoms, and 0 to 20% by weight of another copolymerizable monomer, and 0.1 to 10 parts by weight of a multifunctional monomer; an intermediate layer polymer (B) obtained by polymerizing a mixture composed of 100 parts by weight of a monomer mixture comprising 70 to 90% by weight of an alkyl acrylate having an alkyl group of 1 to 8 carbon atoms, 10 to 30% by weight of an aromatic vinyl monomer, and 0 to 20% by weight of another copolymerizable monomer, and 0.1 to 5 parts by weight of a multifunctional monomer, in the presence of the innermost layer polymer (A); and an outermost layer polymer (C) obtained by polymerizing a monomer or monomer mixture comprising 50 to 100% by weight of an alkyl methacrylate having an alkyl group of 1 to 4 carbon atoms, 0 to 50% by weight of an alkyl acrylate having an alkyl group of 1 to 8 carbon atoms, and 0 to 20% by weight of another copolymerizable monomer, in the presence of the innermost layer polymer (A) and the intermediate layer polymer (B); and wherein the average value of the coating ratio as defined by the following equation is not less than 30%.
Coating ratio=[(minimum thickness of the intermediate layer)÷(maximum thickness of the intermediate layer)]×100(%)
Moreover, the subject matter of the present invention also comprehends a methacrylic resin composition comprising 5 to 95% by weight of the above-described multilayered acrylic polymer, and 95 to 5% by weight of a methacrylic resin composed chiefly of methyl methacrylate.
As described above, the multilayered acrylic polymer of the present invention has a strictly controlled structure. This structure has been controlled with special attention to the uniformity of coverage of the intermediate layer coating the innermost layer, and its relationship with impact properties, resistance to impact whitening, and transparency. In particular, the present invention defines the coating ratio as a criterion for the uniformity of coverage of the intermediate layer and is based on the discovery that, if this value is not less than 30%, the resulting acrylic polymer will show a marked improvement in impact properties (in particular, falling-ball or falling weight impact strength) and also an improvement in resistance to impact whitening and transparency.
When incorporated into thermoplastic resin compositions such as methacrylic resin compositions, the multilayered acrylic polymer of the present invention can significantly improve their falling-ball or falling-weight impact strength, resistance to impact whitening, transparency and other properties. Moreover, the methacrylic resin compositions of the present invention containing this multilayered acrylic polymer are resin materials having very excellent properties as described above.
BEST MODE FOR CARRYING OUT THE INVENTION
The innermost layer polymer (A) is obtained by polymerizing a mixture composed of 100 parts by weight of a monomer or monomer mixture comprising 40 to 100% by weight, preferably 40 to 95% by weight and more preferably 50 to 70% by weight of an alkyl methacrylate having an alkyl group of 1 to 4 carb
Nakauchi Jun
Uno Hirofumi
Asinovsky Olga
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seidleck James J.
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