Halogen-free flameproof thermoplastic molding materials

Details Halogen-free flameproof thermoplastic molding materials Halogen-free flameproof thermoplastic molding materials

1999-06-18

2001-01-16

Hoke, Veronica P. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S141000, C524S267000

Reexamination Certificate

active

06174945

ABSTRACT:

BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to halogen-free flameproof thermoplastic molding compounds which comprise an aromatic polycarbonate, a styrene-containing copolymer, a styrene-containing graft polymer, a phosphorus compound, a silicon compound, and a tetrafluoroethylene polymer.
(b) Description of the Related Art
Flameproof polycarbonate/styrenic resin molding materials are widely used for electrical appliances. Most known flameproof blends of polycarbonate and styrenic resin contain halogenated flame retardant, which results in the release of toxic gas in the event of fire. To overcome such safety problems, halogen-free flameproof polycarbonate/styrenic resin molding materials have been developed by using phosphorus compounds.
U.S. Pat. No. 4,692,488 discloses thermoplastic molding materials containing a halogen-free aromatic polycarbonate, a styrene-containing copolymer, a phosphorus compound, and tetrafluoroethylene polymer as a coagulated mixture of styrene-containing graft polymers. The molding materials described in the U.S. Pat. No. 4,692,488 have satisfactory flame retardancy, but have completely inadequate impact strengths.
To increase the impact strength of the polycarbonate molding compositions which contain phosphorus compounds as a flame retardant, styrene-containing graft polymers have been used in prior art.
For example, U.S. Pat. No. 5,061,745 discloses polymer blends prepared from an aromatic polycarbonate, acrylonitrile-butadiene-styrene (ABS) graft polymer and/or styrene-containing copolymer, a monophosphorus compound, and a tetrafluoroethylene polymer. The patent shows that the use of ABS graft polymer increases impact strength.
U.S. Pat. No. 4,914,144 discloses polymer mixtures which consist of an aromatic polycarbonate, styrene-containing graft polymer based on an acrylate rubber, a styrene-containing copolymer, a monophosphorus compound, and a tetrafluoroethylene polymer.
U.S. Pat. No. 5,204,394 discloses polymer mixtures comprising an aromatic polycarbonate, a styrene-containing copolymer and/or styrene-containing graft polymer, and an oligomeric phosphate or a blend of oligomeric phosphates as flame retardant.
Although the above listed prior technologies have an adequate flame retardancy and mechanical properties, they have problems in achieving sufficient stress crack resistance.
When molding materials have poor stress crack resistance, problems such as cracks in molded parts may occur. Good stress crack resistance of the molding material is particularly important when the molding materials are injection molded into thin-walled parts or subjected to contact with chemicals.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flameproof thermoplastic molding materials having stress crack resistance and impact resistance comprising an aromatic polycarbonate, styrene-containing copolymer, styrene-containing graft polymer, a monophorus compound and/or an oligomeric phosphorus compound, a silicon compound, and tetrafluoroethylene polymer.
It is another object of the present invention to provide a flameproof thermoplastic molding material characterized in that the polymer mixture contains conventional additives selected form antioxidants, dyes, pigments, lubricants, light stabilizers, and inorganic fillers.
The present invention is based on the discovery that the incorporation of a specific silicon compound as will be described here below results in an excellent stress crack resistance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following detailed description, only the preferred embodiment of the invention has been shown and described simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing form the invention. Accordingly, the descriptions are to be regarded as illustrative in nature, and not restrictive.
The present invention relates to flameproof thermoplastic molding materials comprising:
i) 40 to 90 parts by weight of an aromatic polycarbonate (Component A),
ii) 5 to 30 parts by weight of styrene-containing copolymer (Component B),
iii) 5 to 30 parts by weight of styrene-containing graft polymer (Component C),
iv) 1 to 25 parts by weight, based on 100 parts by weight of the above i) plus the above ii) plus the above iii), of a monophorus compound (Component D.1) and/or an oligomeric phosphorus compound (Component D.2),
v) 0.5 to 15 parts by weight, based on 100 parts by weight of the above i) plus the above ii) plus the above iii), of silicon compound (Component E) corresponding to Formula (I),
in which n and m range form 5 to 8, and the value of x and y range from 1 to 5, and
vi) 0.05 to 5 parts by weight, based on 100 parts by weight of the above i) plus the above ii) plus the above iii) of a tetrafluoroethylene polymer (Component F).
The polymer mixture according to the invention may contain inorganic fillers having flame-retarding synergistic effects. It has been found that the use of talc improves the flame-retarding properties, although it detracts form impact strength. As a result, the use of inorganic fillers appears to be inadequate in some applications which require high impact strength. It has now been found the addition of a specific silicon compound not only enhance stress crack resistance but also increases impact strength of the molding materials, particularly in case of organic filler incorporated compositions.
COMPONENT A
Thermoplastic halogen-free aromatic polycarbonates (Component A) of the present invention are derived form diphenols of the following Formula (II);
in which A is a single bond, C
1
-C
3
alkylene, C
2
-C
3
alkylidene, C
3
-C
6
cycloalkylidene, —S—, or —SO
2
—.
The diphenols are either known form literature or maybe produced by methods known from literature. Suitable diphenols, are, for example, hydroquinone, resorcinol, 4,4′-dihydroxydiphenyl, 2,2-bis-(4-hydroxyphenyl)-propane, or 1,1-bis-(4-hydroxyphenyl)-cyclohexane.
The production of the polycarbonates suitable for the present invention is known from literature and may be carried out, for example, with phosgene by the interfacial process or with phosgene by the homogeneous-phase process. The polycarbonates suitable for the present invention have average molecular weights (Mw) from 10,000 to 200,000, preferably from 20,000 to 80,000.
The polycarbonates A which are suitable according to this invention may be branched in a conventional manner, preferably by the incorporation of from 0.05 to 2.0 mol % (based on the sum of the diphenols used) of trifunctional or polyfunctional compounds.
COMPONENT B
A flameproof thermoplastic molding material of the present invention is characterized in that its styrene-containing copolymer (Component B) are those prepared from at least one monomer of a B1) group comprising styrene, &agr;-methylstyrene, ring-substituted styrenes, C
1
-C
8
alkyl methacrylate, and C
1
-C
8
alkyl acrylate and at least one monomer of a B2) group comprising acryloritnle, methacrylonitrile, maleic anhydride, maleimide, and N-substituted maleimids.
Component B copolymers are known and can be prepared by free radical polymerization, in particular by emulsion, suspension, solution, or mass polymerization.
The styrene-containing copolymers contain 50 to 98, preferably 60 to 95 parts by weight of B1) group monomer and 50 to 2, preferably 40 to 5 parts by weight of B2) group monomer.
These copolymers are thermoplastic and contain no rubber. Particularly preferred copolymers are those prepared from styrene with acrylonitrile and optionally methyl methacrylate.
These copolymers have average molecular weights of between 15,000 and 200,000, preferably between 60,000 to 200,000.
COMPONENT C
Styrene-containing graft polymers (Component C) of the present invention can be obtained by grafting a mixture of at least two monomers on a rubber. Suitable monomers are selected form at least one monomer of a group C

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