Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-04-29
2004-05-25
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S141000
Reexamination Certificate
active
06740696
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to flame retardant thermoplastic compositions, and more particularly relates to flame retardant thermoplastic compositions containing polycarbonate resins and a graft copolymer.
2. Description of the Related Art
Flame retarded compositions containing a acrylonitrile-butadiene-styrene (ABS) copolymers, a phosphate, and a polytetrafluoroethylene material are known, see Haaf et al., U.S. Pat. No. 4,107,232, issued Aug. 15, 1978. Flame resistant thermoplastic molding compositions containing (a) an aromatic polycarbonate (b) a styrene-acrylonitrile-butadiene graft copolymer, (c) a thermoplastic polymer such as styrene-acrylonitrile copolymer, (d) a halogen compound, (e) a flame retardant synergist and (f) a tetrafluoroethylene polymer (PTFE) are known, see Lindner et al., U.S. Pat. No. 4,810,739, issued Mar. 7, 1989. The utilization of phosphate flame retardants in ABS/aromatic polycarbonate blend compositions with PTFE is also known, but such compositions can exhibit less than desired levels of weatherability. Shipment and storage of thermoplastic (polycarbonate/graft copolymer (ABS) blends) articles such as business machining housings in extremely hot humid climates such as Southeast Asia can expose the articles to prolonged exposure to heat and humidity which can undesirably result in embrittlement and the loss of impact properties in the article.
Consequently, there is a need to develop polycarbonate/ABS graft copolymer compositions which exhibit enhanced retention of impact properties upon prolonged exposure to heat and humidity.
SUMMARY OF THE INVENTION
The present invention involves flame retardant thermoplastic compositions containing aromatic polycarbonate resin and a rubber modified vinyl aromatic-unsaturated nitrile-diene rubber graft copolymer. The compositions contain a high rubber graft copolymer or optionally contain in combination a low viscosity polycarbonate resin and a low molecular weight vinyl aromatic-unsaturated nitrile rigid copolymer. The compositions exhibit enhanced resistance to loss of IZOD impact properties upon exposure to heat and humidity aging.
DETAILED DESCRIPTION OF THE INVENTION
A thermoplastic composition is provided comprising (a) an aromatic polycarbonate resin, (b) a vinyl aromatic-unsaturated nitrile-diene rubber graft copolymer, (c) a vinyl aromatic-unsaturated nitrile rigid copolymer, (d) a phosphate and (e) a tetrafluoroethylene polymer. The graft copolymer preferably has a high rubber loading, and the polycarbonate resin is preferably a combination of a moderate molecular weight polycarbonate resin and a low molecular weight polycarbonate resin, and the vinyl aromatic-vinyl cyanide rigid copolymer is preferably a low molecular weight copolymer.
The aromatic polycarbonate resin preferably comprises a moderate molecular weight polycarbonate polymer and a low molecular weight polycarbonate. Preferably the aromatic polycarbonate resin is present at a level of from 60 to 90 percent by weight based on the total weight of the composition, more preferably from 75 to 85 percent by weight thereof, and most preferably from 78 to 82 percent by weight thereof. The use of low molecular weight aromatic polycarbonate resin allows for higher rubber levels for a given composition viscosity level. Preferably the moderate molecular weight polycarbonate polymer is present in the composition at a level of from 60 to 80 percent by weight based on the total weight of the composition, more preferably from 70 to 75 percent by weight thereof, and most preferably from 71 to 73 percent by weight thereof; and preferably the low molecular weight polycarbonate resin is present at a level of from 0 to 15 percent by weight based on the total weight of the composition, more preferably from 2 to 15 percent by weight thereof, and most preferably from 3 to 8 percent by weight thereof.
Polycarbonate resins suitable for use in this invention, are preferably aromatic polycarbonate resins. With respect to aromatic polycarbonate resins, these can be made by those skilled in this art or can be obtained from a variety of commercial sources. They may be prepared by reacting a dihydric phenol with a carbonate precursor, such as phosgene, a haloformate or a carbonate ester. Typically, they will have recurring structural units of the formula:
wherein A is a divalent aromatic radical of the dihydric phenol employed in the polymer producing reaction. Preferably, the aromatic carbonate polymers have an intrinsic viscosity ranging from 0.30 to 1.0 dl/g (measured in methylene chloride at 25° C.). By dihydric phenols is meant mononuclear or polynuclear aromatic compounds containing two hydroxy radicals, each of which is attached to a carbon atom of an aromatic nucleus. Typically, dihydric phenols include 2,2-bis-(4-hydroxyphenyl)propane; 2,2-bis-(3,5dimethyl-4-hydroxyphenyl) propane; 4,4′-di-hydroxydiphenyl ether, bis(2-hydroxyphenyl) methane, mixtures thereof and the like. The preferred aromatic carbonate polymer is a homopolymer derived from 2,2-bis-(4-hydroxyphenyl) propane (bisphenol-A).
The aromatic polycarbonate resin may be replaced in whole or in part with a poly(ester carbonate) resin. Poly(ester carbonates) for use in the invention are known and can be obtained commercially. Generally, they are copolyesters comprising recurring carbonate groups
carboxylate groups
and aromatic carbocyclic groups in the linear polymer chain, in which at least some of the carboxylate groups and at least some of the carbonate groups are bonded directly to ring carbon atoms of the aromatic carbocyclic groups. These poly(ester carbonates) in general, are prepared by reacting a difunctional carboxylic acid, such as phthalic acid, isophtalic acid, terephthalic acid, homophthalic acid, o-, m-, and p-phenylenediacetic acid, the polynuclear aromatic acids, such as diphenic acid, 1,4-naphthalic acid, mixtures of any of the foregoing, and the like, with a dihydric phenol and a carbonate precursor, of the types described above. A particularly useful poly(ester carbonate) is derived from bisphenol-A, isophthalic acid, terephthalic acid, or a mixture of isophthalic acid and terephthalic acid, or the reactive derivatives of these acids such as terephthaloyl dichloride, or a mixture thereof, and phosgene. The molar proportions of dihydroxy diaryl units can range from 1:0.30-0.80:0.70-0.20 and the molar range of terephthalate units to isophthalate units can range from 9:1 to 2:8 in this preferred family of resins.
The moderate molecular weight aromatic polycarbonate resin preferably has a number average molecular weight of between 25,000 and 80,000, for example, between 30,000 and 60,000, and for further example, between 35,000 and 40,000.
The low molecular weight aromatic polycarbonate resin preferably has a number average molecular weight of between 2,000 and 21,000, for example, between 5,000 and 10,000, and further for example, between 6,000 and 9,000.
The rubber graft copolymer comprises (i) the rubber substrate, (ii) a rigid polymeric superstrate portion grafted to the rubber substrate. The rubber substrate is preferably present in the graft copolyiner at a level of from 40 to 90 percent by weight based on the total weight of the graft copolymer composition, more preferably from 45 to 75 percent by weight thereof, and most preferably 50 to 60 percent by weight thereof; the rigid superstrate (and optional ungraded (free) rigid in combination) is preferably present at a level of from 10 to 40 percent by weight based on the total weight of the graft copolymer, preferably from 25 to 55 percent by weight thereof, and most preferably from 40 to 50 percent by weight thereof.
Examples of rubbery polymers for the substrate include: conjugated dienes, copolymers of a diene with styrene, acrylonitrile, methacrylonitrile or C
1
to C
8
alkyl acrylate which contain at least 50% (preferably at least 65% by weight) conjugated dienes, polyisoprene or mixtures thereof.
The diene rubbers may preferably be polybutadiene, polyisoprene a
Chen Fuh-Sheng
Gaggar Satish Kumar
General Electric Company
Szekely Peter
LandOfFree
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