Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-10-31
2003-08-26
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S095000, C521S145000, C521S139000, C521S093000, C521S079000, C521S081000
Reexamination Certificate
active
06610757
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an expandable vinyl chloride resin composition, and more particularly to an expandable vinyl chloride resin composition which is excellent in processability and provides cellular molded articles having a high expansion ratio and having excellent physical properties.
BACKGROUND ART
Polyvinyl chloride resins provide molded articles excellent in physical properties such as impact resistance and heat resistance and in chemical properties such as solvent resistance, acid resistance and alkali resistance and, therefore, have been widely used in the field of building materials and other various fields. In recent years, foaming method attracts attention as a means for lightening of vinyl chloride resins and cost reduction of molded articles. Cellular molded articles of vinyl chloride resins having a high expansion ratio have been demanded strongly from the market.
In foaming of vinyl chloride resins, generally known is a method using a blowing agent in combination with a processing aid comprising methyl methacrylate as a main component.
It is known that it is possible to achieve foaming in a high expansion ratio when an easily volatile organic solvent blowing agent such as an aliphatic hydrocarbon or a halogenated aliphatic hydrocarbon is used as the blowing agent mentioned above.
For example, Japanese Patent Publications Kokoku No. 60-10540 and Kokoku No. 58-40986 disclose that foamed articles having an expansion ratio of several tens of times are obtained by impregnating a vinyl chloride resin with an organic solvent having a boiling point of not more than 90° C. such as butane or dichlorofluoromethane as a blowing agent or by directly introducing the organic solvent to an extruder during extrusion processing.
However, the use of an organic solvent blowing agent is disadvantageous in cost as compared with a thermally decomposable blowing agent, since equipments for the impregnation and for explosion proof are required in carrying out the molding.
On the other hand, in case of using a thermally decomposable blowing agent such as a thermally decomposable organic blowing agent or a thermally decomposable inorganic blowing agent, it is difficult under existing circumstances to raise the expansion ratio to more than about 3-4 times so long as it is desired to produce foamed articles having a smooth surface and to keep the cells thereof uniform and fine.
For example, Japanese Patent Publication Kokoku No. 63-9540 discloses an expandable vinyl chloride resin composition obtained by adding a methacrylate resin (polymethyl methacrylate having a degree of polymerization of 2,000 to 30,000, that is, a weight average molecular weight of 200,000 to 3,000,000) with a thermally decomposable organic blowing agent such as azodicarbonamide and a thermally decomposable inorganic blowing agent such as sodium bicarbonate and further with a filler such as calcium carbonate to a vinyl chloride resin having an average degree of polymerization of 500 to 800. It is disclosed that this expandable vinyl chloride resin composition is molded to give foamed articles having uniform and fine cells and having excellent surface property and surface hardness, but the expansion ratio is at most about 3-4 times.
Also, Japanese Patent Publication Kokai No. 6-9813 discloses an expandable vinyl chloride resin composition obtained by adding a methacrylate resin and a bicarbonate having a particle size of not more than 10 &mgr;m as a thermally decomposable blowing agent to a vinyl chloride resin. It is disclosed that this expandable vinyl chloride resin composition is molded to give foamed articles having uniform and fine cells and having good heat stability and weatherability, but no detail of the average molecular weight of methacrylate resin and the expansion ratio is disclosed therein.
Further, Japanese Patent Publication Kokai No. 9-151269 discloses an expandable vinyl chloride resin composition obtained by adding a polymethyl methacrylate resin having a weight average molecular weight of 4,500,000 to 7,000,000 and a thermally decomposable blowing agent to a vinyl chloride resin. It is disclosed that this expandable vinyl chloride resin composition is molded to give injection-molded foams having uniform cells without occurrence of decomposition of the resins. However, in the working examples thereof, as the polymethyl methacrylate resin is used only P-531 made by Mitsubishi Rayon Co., Ltd. (weight average molecular weight 4,700,000) and no evaluation in the vicinity of 7,000,000 in weight average molecular weight is made. Also, the obtained expansion ratios are at most about 2-3 times.
It is an object of the present invention to provide an expandable vinyl chloride resin composition according to which the expansion ratio can be markedly increased by the use of a thermally decomposable blowing agent without using any organic solvent-based blowing agent in the foaming.
A further object of the present invention is to provide an expandable vinyl chloride resin composition which provides foamed articles having an expansion ratio of at least 4, especially at least 5, and having uniform and fine cells by the use of a thermally decomposable blowing agent.
DISCLOSURE OF INVENTION
The present inventors have found that a composition capable of greatly increasing the expansion ratio as compared with conventional compositions containing a thermally decomposable blowing agent is obtained by adding a specific (meth)acrylic acid ester polymer and a thermally decomposable inorganic blowing agent to a vinyl chloride resin.
In accordance with the present invention, there is provided an expandable vinyl chloride resin composition comprising (a) 100 parts by weight of a vinyl chloride resin, (b) 0.5 to 30 parts by weight of, as a processing aid, a (meth)acrylic acid ester polymer having a specific viscosity of not less than 0.73 measured at 30° C. with respect to a solution of 0.1 g of the polymer dissolved in 100 ml of chloroform, and (c) not less than 0.3 to less than 2 parts by weight of a thermally decomposable inorganic blowing agent.
Sodium bicarbonate is particularly preferred as the thermally decomposable inorganic blowing agent.
The feature of the present invention resides in that a polymer which is obtained by emulsion polymerization of a monomer mixture containing a predominant amount of a methacrylic acid ester and/or an acrylic acid ester and which has a high molecular weight is used as a processing aid for vinyl chloride resins. By using such a processing aid together with a thermally decomposable inorganic blowing agent, the effect that the expansion ratio in the foaming can be increased without impairing excellent physical and chemical properties that the vinyl chloride resins originally possess can be remarkably exhibited with the addition of small amounts thereof.
The present inventors already made an invention concerning an expandable vinyl chloride resin composition utilizing water or a material capable of generating steam by heating it as a blowing agent. Accordingly, the present invention excludes using water or a material capable of generating water by the heating in an amount capable of substantially expand a vinyl chloride resin.
BEST MODE FOR CARRYING OUT THE INVENTION
The vinyl chloride resins used in the present invention are not particularly limited, and any of conventionally used vinyl chloride resins can be used in the present invention. Homopolymer and copolymers composed of 80 to 100% by weight of units of vinyl chloride and 0 to 20% by weight of units of other monomers copolymerizable with vinyl chloride are preferable.
Examples of the other monomer copolymerizable with vinyl chloride are, for instance, vinyl acetate, propylene, styrene, an acrylic acid ester (e.g., alkyl acrylates having a C
1
to C
8
alkyl group such as methyl acrylate, ethyl acrylate, butyl acrylate and octyl acrylate), and other vinyl monomers. These vinyl monomers may be used alone or in admixture thereof.
The average degree of polymerization of the vinyl chloride resin is not particul
Kadokura Mamoru
Sakashita Noriko
Sato Mitsutaka
Sunagawa Takenobu
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