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
2000-12-04
2002-05-21
Boykin, Terressa M. (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...
Reexamination Certificate
active
06391976
ABSTRACT:
TECHNICAL FIELD
This invention relates to a processing aid for foam molding use and vinyl chloride resin compositions using the same. More particularly, it relates to a processing aid for foam molding use which can improve the foam moldability of vinyl chloride resin compositions, and vinyl chloride resin compositions using the same.
BACKGROUND ART
Since vinyl chloride resins not only have excellent properties such as chemical resistance, impact resistance and weather resistance, but also are inexpensive, they are being widely used as general-purpose resin materials of great utility value. Foam molding is one of their preferable uses and, for example, attempts are being made to produce foam-molded products useful as building components aiming at synthetic wood and the like. However, if a foam molded product is made from just a vinyl chloride resin, sufficient elongation characteristics and melt strength cannot be obtained at the molding temperature commonly employed for vinyl chloride resins, so that it is impossible to form a uniform foamed cell structure and achieve any desired high foaming ratio. Thus, it has been difficult to produce satisfactory foam-molded products. Moreover, since vinyl chloride resins have a narrow range of allowable molding conditions, it has also been difficult to produce satisfactory foam-molded products solely by modifying the molding conditions.
In order to improve the foam moldability of such vinyl chloride resins, there have heretofore been proposed various methods which involve adding a high-molecular-weight acrylic resin for the main purpose of imparting melt strength thereto.
However, with the recent spread and extension of the foam molding of vinyl chloride resins, there is a growing demand for foam-molded products having more excellent moldability and an attractive molding appearance.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a processing aid for foam molding use which permits vinyl chloride resin compositions to be melted and kneaded efficiently and imparts an increased melt strength thereto, so that fine and uniform foamed cells required for vinyl chloride resin-based foam molding compositions can be formed, a high foaming ratio can be achieved, and an attractive molding appearance can be produced, as well as vinyl chloride resin-based foam molding compositions using the same.
The present inventors made intensive investigations with a view to solving the above-described problem. As a result, it has now been found that the foam moldability of vinyl chloride resins can be improved by adding thereto a processing aid for foam molding use comprising a powder of a methacrylic ester copolymer having a specific weight-average molecular weight and a specific monomer composition. Moreover, it has also be found that, when this processing aid for foam molding use comprises a powder formed by spray drying so that the proportion of particles whose inner part has fused into a homogeneous state is less than 50% by weight, molded products having a uniform cell structure can be obtained even at a high foaming ratio. The present invention has been completed on the basis of these findings.
In order to improve the foam moldability of vinyl chloride resin-based foam molding compositions, it is necessary to melt and knead the vinyl chloride resin compositions efficiently. One method for melting and kneading vinyl chloride resin compositions efficiently comprises adding a high-molecular-weight acrylic resin thereto. It is described in Japanese Patent Laid-Open No. 169914/'96 that spray-dried acrylic resin powders having different surface conditions (i.e., a spray-dried acrylic resin powder comprising particles whose surface is closely united to form a smooth surface, and a spray-dried acrylic resin powder comprising particles in which primary particles derived from the dispersion and gathered together are distinctly recognized) show a difference in the effect of promoting the melting and kneading of vinyl chloride resins. Specifically, the spray-dried acrylic resin powder comprising particles in which primary particles derived from the dispersion and gathered together are distinctly recognized is said to be more suitable for the purpose of promoting the melting and kneading of vinyl chloride resins. In this connection, however, all that is described therein is that an acrylic processing aid suitable for the production of drink bottles comprising a vinyl chloride resin can be prepared. In order to improve the foam moldability of vinyl chloride resin compositions, it is necessary that not only the surface condition of particles formed by spray drying, but also the composition and molecular weight of the processing aid are suitable for the foam molding of the vinyl chloride resin compositions. In this respect, the present invention is different from the above-described prior art.
That is, the present invention relates to a processing aid (B) for foam molding use which comprises a powdered copolymer composed of 50 to 80% by weight of methyl methacrylate, 20 to 50% by weight of an alkyl methacrylate having an alkyl group of 3 to 5 carbon atoms, and 0 to 20% by weight of other copolymerizable monomers, the copolymer having a reduced viscosity (&eegr;
sp
/c) of 4 to 8.
The present invention also relates to a vinyl chloride resin-based foam molding composition comprising 100 parts by weight of a vinyl chloride resin (A) and 1 to 25 parts by weight of the aforesaid processing aid (B) for foam molding use.
BEST MODE FOR CARRYING OUT THE INVENTION
The processing aid (B) for foam molding use in accordance with the present invention comprises a powder of a copolymer obtained by the polymerization of methyl methacrylate, an alkyl methacrylate having an alkyl group of 3 to 5 carbon atoms, and other copolymerizable monomers. The content of methyl methacrylate is in the range of 50 to 80% by weight and preferably 60 to 80% by weight. If its content is less than 50% by weight, it will be impossible to melt and knead the vinyl chloride resin-based foam molding composition efficiently as desired in the present invention, and it will hence become difficult to produce a fine and uniform foamed cell structure and achieve a high foaming ratio. Moreover, the step of recovering the processing aid for foam molding use as a powder may encounter blocking with the powder, or the compound obtained by its blending with a vinyl chloride resin may show a reduction in bulk specific gravity. If its content is greater than 80% by weight, the resulting molded product will have a poor molding appearance.
Examples of the alkyl methacrylate having an alkyl group of 3 to 5 carbon atoms, which is used in the present invention, include propyl methacrylate, butyl methacrylate and pentyl methacrylate. Among others, n-butyl methacrylate is preferred. These alkyl methacrylates may be used alone or in admixture of two or more, depending upon the intended purpose. The content of the alkyl methacrylate having an alkyl group of 3 to 5 carbon atoms is in the range of 20 to 50% by weight and preferably 20 to 40% by weight. If its content is less than 20% by weight, the resulting molded product will have a poor molding appearance. If its content is greater than 50% by weight, it will be impossible to melt and knead the vinyl chloride resin-based foam molding composition efficiently as desired in the present invention, and it will hence become difficult to produce a uniform foamed cell structure and achieve a high foaming ratio. Moreover, the step of recovering the processing aid for foam molding use as a powder may encounter blocking with the powder, or the compound obtained by its blending with a vinyl chloride resin may show a reduction in bulk specific gravity.
Examples of the other monomers copolymerizable therewith include acrylic esters such as ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate and phenyl acrylate; aromatic vinyl compounds such as styrene, &agr;-methylstyrene and vinyltoluene; vinyl cyanide compounds such as acrylonitrile and metha
Naka Naho
Nakata Akira
Takei Seiji
Wakabayashi Shigeo
Boykin Terressa M.
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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