Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-03-07
2003-10-21
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...
C521S091000, C521S092000, C521S093000, C521S094000, C521S145000
Reexamination Certificate
active
06635687
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 strength and surface property.
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. If the expansion ratio is raised to more than 4 times, especially to more than 5 times, there arises a problem that the strength and surface property of foamed articles are deteriorated.
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 a resin “P-531” made by Mitsubishi Rayon Co., Ltd. having a weight average molecular weight of 4,700,000, and no evaluation is made with respect to monomer composition and expandability. Also, the obtained expansion ratios are at most about 2-3 times.
Also, Japanese Patent Publication Kokai No. 9-208732 discloses an expandable vinyl chloride resin composition obtained by incorporating a methacrylic ester resin, a chlorinated polyethylene resin, talc and a blowing agent into a vinyl chloride resin. It is disclosed that this expandable vinyl chloride resin composition is molded with good molding processability to give foamed articles having a small linear expansion coefficient and uniform cells. However, the obtained expansion ratios are at most about 2-3 times.
Thus, 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, and deterioration of strength and surface property of foamed articles caused by the increase in expansion ratio can be suppressed.
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 and capable of improving the strength and surface property of foamed articles is obtained by adding a specific (meth)acrylic acid ester copolymer, a thermally decomposable inorganic blowing agent, a thermally decomposable organic blowing agent and optionally a filler to a vinyl chloride resin.
Thus, in accordance with the present invention, there is provided an expandable vinyl chloride resin composition comprising (1) 100 parts by weight of a vinyl chloride resin, (2) 0.5 to 30 parts by weight of, as a processing aid, a two stage (meth)acrylic acid ester polymer having a specific viscosity of not less than 0.5 measured at 30° C. with respect to a solution of 0.1 g of the polymer dissolved in 100 ml of chloroform, the two stage polymer being obtained by emulsion-polymerizing (a) 50 to 99 parts by weight of a monomer mixture comprising 50 to 100% by weight of methyl methacrylate, 0 to 50% by weight of at least one monomer selected from the group consisting of an acrylic acid ester and a methacrylic acid ester excepting methyl methacrylate and 0 to 20% by weight of other vinyl monomer copolymerizable therewith to give a polymer having a specific viscosity of not less than 0.7 measured at 30° C. with respect to a solution of 0.1 g of the polymer dissolved in 100 ml of chloroform and polymerizing, in the presence of a latex of the obtained polymer, (b) 1 to 50 parts by weight of a monomer mixture comprising 0 to 50% by weight of methyl methacrylate, 50 to 100% by weight of at least one monomer selected from the group consisting of an acrylic acid ester and a methacrylic acid ester excepting methyl methacrylate and 0 to 20% by weight of other vinyl monomer copolymerizable therewith wherein the total of the monomer mixtures (a) and (b) is 100 parts by weight, (3) 0.3 to 25 parts by weight of a thermally decomposable inorganic blowing agent and (4) 0.01 to 15 parts by weight of a thermally decomposable organic blowing agent.
Sodium bicarbonate is particularly preferred as the thermally decomposable inorganic blowing agent.
The expandable vinyl chloride
Kadokura Mamoru
Sato Mitsutaka
Sunagawa Takenobu
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