Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-12-18
2003-12-16
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S212000, C524S165000, C524S264000, C524S267000, C524S268000, C524S269000, C524S492000, C524S493000, C524S497000
Reexamination Certificate
active
06664313
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a polycarbonate resin composition and its molded articles. More particularly, it relates to a polycarbonate resin composition which is preferably used to reflectors and has improved flame retardancy without containing any halogenic or phosphate-based flame retardant which is causative of a corrosive action, burning of resin and lowering of heat resistance, and the articles molded from such a resin composition.
Polycarbonate resins are widely used in many fields of industry such as, typically, automobiles, OA equipment, and electric and electronic devices because of their excellent mechanical properties. The display-related devices required to have a high level of light reflectance, such as reflectors for backlight of liquid crystal displays, luminous push switches, photoelectic switches, etc., in various types of display devices for computers and television-related devices such as thin film transistors (TFT), have now become generalized, and the molded articles produced from the compositions comprising polycarbonate resins incorporated with a white pigment such as titanium oxide are being used for the light reflectors used in such devices.
Japanese Patent Application Laid-Open (KOKAI) No. 9-12853 proposes a polycarbonate resin composition with high light reflectance comprising (A) a polycarbonate resin, (B) titanium oxide, (C) a composite rubber-based graft polymer produced by graft polymerizing one or more vinyl monomers with a composite rubber having a structure in which a polyorganosiloxane rubber and an alkyl poly(meth)acrylate are inseparably entangled with each other, (D) a flame retardant and (E) polytetrafluoroethylene. This resin composition, however, involves the problems such as corrosive action to the cylinder, screw and mold of the molding machine, burning of the resin and deterioration of heat resistance as the composition contains a halogenic and/or a phosphate type flame retardant.
Also, a composition comprising a polyorganosiloxane polymer and polytetrafluoroethylene (Japanese Patent Application Laid-Open (KOKAI) No. 5-202280) and a composition comprising a polyorganosiloxane polymer and silica (Japanese Patent Application Laid-Open (KOKAI) No. 8-22371) have been proposed as the polycarbonate resin compositions improved in flame retardancy without containing a flame retardant such as mentioned above, but these resin compositions are not necessarily satisfactory in flame retardancy.
As a result of the present inventors' earnest study to solve the above problem, it has been found that by polycarbonate resin composition comprising aromatic polycarbonate resin, titanium oxide, silica, polyorganosiloxane polymer and polytetrafluoroethylene in a specific amount, the above problem can be solved.
The present invention has been attained on the basis of the above finding.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a polycarbonate resin composition with excellent heat stability, a high light reflectance, high reflecting properties, and excellent flame retardancy.
The second object of the present invention is to provide a polycarbonate resin composition with improved flame retardancy which is freed of such problems as corrosive action to the molding machine, mold, etc., burning of the resin and deterioration of heat resistance.
The third object of the present invention is to provide the molded articles having beautiful visual appearance, high light reflecting properties and excellent flame retardancy.
To attain the above aim, in the first aspect of the present invention, there is provided a polycarbonate resin composition comprising 100 parts by weight of an aromatic polycarbonate resin (a), 3 to 30 parts by weight of titanium oxide (b), 0.01 to 9 parts by weight of silica (c1), 0.01 to 9 parts by weight of a polyorganosiloxane polymer (c2), and 0.01 to 5 parts by weight of polytetrafluoroethylene (d).
In the second aspect of the present invention, there are provided the molded articles comprising the polycarbonate resin composition as defined in the first aspect.
DETAILED DESCRIPTION OF THE INVENTION
The invention is described in detail below.
The aromatic polycarbonate resin (a) used in the present invention is a thermoplastic aromatic polycarbonate polymer or copolymer which may be branched and can be produced by reacting an aromatic hydroxyl compound and/or a small quantity of a polyhydroxyl compound with phosgene or a carbonic acid diester. The method of producing this resin (a) is not specifically restricted; it may be produced by any usual method such as phosgene method (interfacial polymerization method) or melting method (ester exchange method). It is also possible to use an aromatic polycarbonate resin with a regulated amount of terminal OH groups, produced by the melting method.
The aromatic dihydroxyl compounds usable in the present invention include, for example, 2,2-bis(4-hydroxyphenyl)propane (=bisphenol A), tetramethylbisphenol A, &agr;,&agr;′-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene, hydroquinone, resorcinol and 4,4-dihydroxydiphenyl. Among them, bisphenol A is preferred. Use of an aromatic dihydroxyl compound having one or more tetraalkylphosphonium sulfonate bonded thereto is preferable as it provides further improvement of flame retardancy of the produced polycarbonate resin composition.
The branched aromatic polycarbonate resins can be obtained by using the following compounds as a partial substitution for the said aromatic dihydroxyl compounds. Examples of such substitute compounds include polyhydroxyl compounds such as fluoroglucin, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)-2-heptene, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane, 2,6-dimethyl-2,4,6-tri(4-hydroxypheyl)-3-heptene and 1,3,5-tri(4-hydroxyphenyl)benzene; 1,1,1-tri(4-hydroxyphenyl)ethane, 3,3-bis(4-hydroxydiaryl)oxyindole (=isatinbisphenol), 5-chloroisatin, 5,7-dichloroisatin, and 5-bromoisatin. These compounds are usually used in an amount of 0.01 to 10 mol %, preferably 0.1 to 2 mol %.
The particularly preferred aromatic polycarbonate resins for use in the present invention are the aromatic polycarbonate resins derived from 2,2-bis(4-hydroxyphenyl)propane and the polycarbonate polymers derived from 2,2-bis(4-hydroxyphenyl)propane and other aromatic dihydroxyl compounds. In the course of preparation of the aromatic polycarbonate resin, a polymer or an oligomer having a siloxane structure may be copolymerized for further improving flame retardancy of the produced polycarbonate resin composition. The aromatic polycarbonate resin used in the present invention may be a mixture of two or more types of aromatic polycarbonate resin differing in composition, molecular weight, etc.
A monovalent aromatic hydroxyl compound is preferably used for adjusting the molecular weight of the aromatic polycarbonate resin (a). Examples of such monovalent aromatic hydroxyl compounds are m- and p-methylphenol, m- and p-propylphenol, p-tert-butylphenol, and long-chain alkyl-substituted p-phenol. The molecular weight of the aromatic polycarbonate resin (a), when expressed in terms of viscosity-average molecular weight calculated from solution viscosity determined at 25° C. using methylene chloride as solvent, is usually in the range of 16,000 to 30,000, preferably 17,000 to 26,000, more preferably 18,000 to 23,000.
Titanium oxide (b) used in the present invention functions to improve light screening properties, whiteness, light reflecting properties, etc., of the molded articles of the polycarbonate resin composition. Titanium oxide (b) is not subject to any specific restrictions regarding its production method, crystal structure and average particle size. There are two types of production method of titanium oxide (b): (1) sulfuric acid method and (2) chlorine method. When titanium oxide produced by the sulfuric acid method is used, the produced composition tends to deteriorate in whiteness, so that titanium oxide produced by the chlorine method is preferably used for the effective attai
Hirai Yasuhiro
Ishii Kazuhiko
Buttner David J.
Conlin David G.
Edwards & Angell LLP
Hazzard Lisa Swiszcz
Mitsubishi Engineering-Plastics Corporation
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