Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-04-06
2002-09-03
Kuhns, Allan R. (Department: 1732)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S097000, C525S191000, C264S050000
Reexamination Certificate
active
06444719
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a crystalline methacrylic resin, to a plastic foam made from the crystalline methacrylic resin and to a method for producing the plastic foam.
BACKGROUND ART
Methacrylic resins have excellent properties, that is, high transparency, weatherability and mechanical characteristics. Hence methacrylic resins are made into various forms for use in a wide range of applications including lighting fixtures, signboards, displays, construction materials, foam materials and optical tools such as lenses and optical disks.
In the meantime, it is well-known that when an isotactic poly(methyl methacrylate) (hereinafter referred to as IPMMA) is mixed with a syndiotactic poly(methyl methacrylate) (hereinafter referred to as SPMMA) in an appropriate condition, a crystalline methacrylic resin called a stereocomplex poly(methyl methacrylate) (hereinafter referred to as SCPMMA) is obtained.
Well-known methods for the production of such a crystalline methacrylic resin include (1) a method in which IPMMA is mixed with SPMMA in a specific solvent such as toluene, acetone and DMF, (2) a method in which a solid mixture consisting of IPMMA and SPMMA is heat-treated (Japan Chemical Society “Experimental Chemistry Lecture 28, Polymer Synthesis” pp129, lines 10-13 (1992), Maruzen, (3) a method in which IPMMA and SPMMA are respectively dissolved in methyl methacrylate, the resulting solutions are mixed with each other to obtain SCPMMA and thereafter methyl methacrylate is photo-polymerized to obtain poly(methyl methacrylate) containing SCPMMA (Japanese Patent Publication (JP-B) No. S47-14834) and (4) a method in which IPMMA is swollen using methyl methacrylate to conduct matrix polymerization thereby forming SCPMMA in the interface between them (H. Yau, and S. I. Stupp, J. Polym. Sci., Polym. Chem. Ed., 23, 813 (1985)). The crystalline methacrylic resin thus obtained is known to have higher solvent resistance than non-crystalline methacrylic resins (Japanese Patent Application Laid-Open (JP-A) No. H3-244651).
Applications of a methacrylic resin include use in products provided with a printed design or pattern on the surface thereof. For instance, a photoconductive plate made of a methacrylic resin is provided with a proper dot pattern on the surface thereof by means of screen printing to improve the luminance of the photoconductive plate. For printing in the above method, an organic solvent is usually used. In such a method, however, there is the case where the surface of the methacrylic resin is affected by the solvent with the result that a defect such as unclear printing is caused.
In the production of a decorative sheet in which the surface of a substrate, e.g., a metallic material is coated with a methacrylic resin film on which various designs are printed, the surface of the decorative plate is usually washed using an alcoholic solvent in a finishing step to remove an organic solvent used for printing. In this case, cracks are sometimes generated in the methacrylic resin film on account probably of residual stress in the coating stage when the surface of the decorative plate is washed with the alcoholic solvent.
For the applications as above, it is considered to apply a crystalline methacrylic resin, such as SCPMMA as aforementioned, having high solvent resistance. However, the foregoing well-known production methods (1)-(4) have the following problems and hence a crystalline methacrylic resin is not sufficiently obtained. For example, a crystalline methacrylic resin obtained in the above method (1) is reduced in crystallinity and allows a solvent to remain unremoved in a molded article thereof in which the solvent adversely affects the solvent resistance so that it can be used with difficulty for the purpose of improving the solvent resistance. In the above method (2), in the case of using IPMMA and SPMMA which have a relatively low molecular weight and high stereoregularity, crystallization of the resulting methacrylic resin may proceed rapidly but raw materials thereof are expensive. On the other hand, in the case of using IPMMA and SPMMA which have a relatively high molecular weight and low stereoregularity, crystallization of the resulting methacrylic resin may proceed with difficulty. The above methods (1), (3) and (4) have problems such that there is a limitation in a form of a molded article to which the resulting crystalline methacrylic resin can be applied.
SUMMARY OF THE INVENTION
Under these circumstances, the inventors of the present invention have made earnest studies to find a method for producing a crystalline methacrylic resin, which is not limited in a form applicable to a molded article thereof and has high crystallinity and excellent solvent resistance, in a simple process and found that a crystalline methacrylic resin which attains all of the above objects can be obtained when a mixture of IPMMA and SPMMA is treated in a specific condition. Also, the inventors have found that when a mixture of IPMMA and SPMMA is treated in a specific condition to foam the mixture, a plastic foam of crystalline methacrylic resin can be obtained in which the plastic foam exhibits high solvent resistance, embraces fine cells having an average cell diameter of about 10 &mgr;m or less and a cell number density of 10
9
to 10
15
cells/cm
3
and possesses excellent mechanical properties such as high impact resistance and bending strength. Thus the present invention has been completed.
According to a first aspect of the present invention, there is provided a method for producing a crystalline methacrylic resin, which comprises a step of bringing a mixture of an isotactic methyl methacrylate-type polymer and a syndiotactic methyl methacrylate-type polymer into contact with high pressure gas.
According to a second aspect of the present invention, there is provided a method for producing a plastic foam of a crystalline methacrylic resin, which comprises a step of bringing a mixture of an isotactic methyl methacrylate-type polymer and a syndiotactic methyl methacrylate-type polymer into contact with high pressure gas, followed by foaming the mixture.
According to a third aspect of the present invention, there is provided a plastic foam of a crystalline methacrylic resin, the plastic foam embracing fine cells having an average cell diameter of about 10 &mgr;m or less and a cell number density of 10
9
to 10
15
cells/cm
3
.
DETAIL DESCRIPTION OF THE INVENTION
The isotactic methyl methacrylate-type polymer used in the present invention means a polymer having a methyl methacrylate unit as a major component and the isotacticity (of its methyl methacrylate unit chain) of about 50% or more and preferably about 80% or more, in terms of triad expression. The isotactic methyl methacrylate-type polymer used in the present invention may be a homopolymer of a methyl methacrylate monomer and a copolymer of i) a monomer copolymerizable with a methyl methacrylate monomer and ii) a methyl methacrylate monomer.
The above-mentioned monomer copolymerizable with a methyl methacrylate monomer may be a well-known one and no particular limitation is imposed on the monomer. Examples of the monomer may include methacrylates such as ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate and 2-hydroxyethyl methacrylate, acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate, unsaturated acids such as methacrylic acid and acrylic acid, monofunctional monomers such as acrylonitrile, methacrylonitrile and styrene and polyfunctional monomers such as ethylene glycol dimethacrylate and trimethylpropane trimethacrylate. When the monomer among them is used to obtain the isotactic methyl methacrylate-type polymer in the present invention, the monomer is used singly or in combination of two or more, together with a methyl methacrylate monomer.
An amount of the copolymerizable monomer to be used to obtain the isotactic methyl methacrylate-typ
Mizumoto Tomohiro
Moritani Masahiko
Sugimura Norio
Kuhns Allan R.
Sughrue & Mion, PLLC
Sumitomo Chemical Company Limited
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