Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-02-24
2002-04-30
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S09200D
Reexamination Certificate
active
06380303
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to compositions containing a branched carbonate polymer and a rubber-modified monovinylidene aromatic copolymer. This invention relates particularly to a blend composition having improved processability and when molded, having improved impact strength.
BACKGROUND OF THE INVENTION
Carbonate polymers derived from reactions of dihydroxyorganic compounds, particularly the dihydric phenols, and carbonic acid derivatives such as phosgene have found extensive commercial application because of their excellent physical properties. These thermoplastic polymers appear suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance, excellent electrical properties, glass-like transparency and good clarity are required.
Unfortunately, however, these polymers are expensive in price and require a high amount of energy expenditure in extrusion and molding processes. In order to reduce the cost of processing carbonate polymers, said polymers may contain additives that reduce costs and lower the temperatures required for molding processes. The blends resulting from the processing of carbonate polymer and additive generally exhibit improved melt flow properties at the sacrifice of other desirable features such as heat resistance, impact strength and the like. In addition, blends of carbonate polymer and additive often do not exhibit a desirable glossy finish.
In view of the deficiencies of the conventional carbonate polymers and blends thereof, it would be highly desirable to provide an economical carbonate polymer composition which exhibits improved processability while retaining, to some degree, the desirable properties characteristic of carbonate polymers such as impact strength and heat resistance, and exhibiting a glossy finish.
SUMMARY OF THE INVENTION
The present invention is such a desirable polymer blend composition. The composition possesses a desirable balance of good processability, improved gloss, good thermal and physical properties, and especially, improved impact resistance. The composition is a heterogeneous blend comprising a branched aromatic carbonate polymer blended with an effective amount of a rubber-modified copolymer comprising a monovinylidene aromatic monomer, an ethylenically unsaturated nitrile monomer, and a rubber component comprising a star-branched rubber having three or more arms and optionally, a linear rubber. Preferably the branched aromatic carbonate polymer comprises a branched aromatic carbonate polymer component and a linear aromatic carbonate polymer component. Preferably, the rubber-modified copolymer is a composition prepared using bulk, mass-solution or mass-suspension polymerization techniques. Optionally, the polymer blend composition further comprises an impact modifier such as methylmethacrylate, butadiene and styrene-type core/shell grafted copolymer.
In another aspect, the present invention is a process for preparing a polymer blend composition which exhibits a desirable balance of good processability, improved gloss, good thermal and physical properties, and especially, improved impact resistance wherein a branched aromatic carbonate polymer is blended with an effective amount of a rubber-modified copolymer comprising a monovinylidene aromatic monomer, an ethylenically unsaturated nitrile monomer, and a rubber component comprising a star-branched rubber having three or more arms and optionally, a linear rubber.
In a further aspect, the present invention involves a method of molding or extruding a polymer blend composition whereby a branched aromatic carbonate polymer is blended with an effective amount of a rubber-modified copolymer comprising a monovinylidene aromatic monomer, an ethylenically unsaturated nitrile monomer, and a rubber component comprising a star-branched rubber having three or more arms and optionally, a linear rubber.
In yet a further aspect, the invention involves molded or extruded articles of a polymer blend composition comprising a branched aromatic carbonate polymer blended with an effective amount of a rubber-modified copolymer comprising a monovinylidene aromatic monomer, an ethylenically unsaturated nitrile monomer, and a rubber component comprising a star-branched rubber having three or more arms and optionally, a linear rubber.
The polymer blend compositions of the present invention are especially useful in the preparation of molded objects notably parts having large surfaces prepared by injection molding techniques and having predictable finished dimensions, good heat resistance, and good room temperature and low temperature impact resistance. Such properties are particularly desired for exterior automotive body panel applications such as door panels and fascia, or other automotive applications such as instrument panels, fenders, hoods, trunk lids, side cladding parts, mirror housings, cowl vent grills, etc. These compositions can even find use in instrument housings such as for power tools or information technology equipment such as telephones, computers, copiers, hand held computers, personal data assistants, cell phones, etc.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Suitable carbonate polymers employed in the present invention are well known in the literature and can be prepared by known techniques, for example several suitable methods are disclosed in U.S. Pat. Nos. 3,028,365, 4,529,791, and 4,677,162, which are hereby incorporated by reference in their entirety. In general, carbonate polymers can be prepared from one or more multihydric compounds by reacting the multihydric compounds, preferably an aromatic dihydroxy compound such as a diphenol, with a carbonate precursor such as phosgene, a haloformate or a carbonate ester such as diphenyl or dimethyl carbonate. Preferred diphenols are 2,2-bis(4-hydroxyphenyl)-propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, 3,3-bis(para-hydroxyphenyl)-phthalide and bishydroxyphenylfluorene. The carbonate polymers can be prepared from these raw materials by any of several known processes such as the known interfacial, solution or melt processes. As is well known, suitable chain terminators and/or branching agents can be employed to obtain the desired molecular weights and branching degrees.
It is understood, of course, that the carbonate polymer may be derived from (1) two or more different dihydric phenols or (2) a dihydric phenol and a glycol or a hydroxy- or acid-terminated polyester or a dibasic acid in the event a carbonate copolymer or heteropolymer rather than a homopolymer is desired. Thus, included in the term “carbonate polymer” are the poly(ester-carbonates) of the type described in U.S. Pat. No. 3,169,121, 4,156,069, and 4,260,731, which are hereby incorporated by reference in their entirety. Also suitable for the practice of this invention are blends of two or more of the above carbonate polymers. Of the aforementioned carbonate polymers, the polycarbonates of bisphenol-A are preferred.
As compared to linear carbonate polymers having otherwise similar melt flow rates (melt viscosity at low shear conditions) branched carbonate polymers are known to be more shear sensitive, exhibiting significantly decreased viscosity at higher shear processing conditions. In general, it has been found that the branched carbonate polymer is sufficiently branched if it has a higher degree of “shear thinning” than a linear carbonate polymer of the same molecular weight and will preferably provide a higher degree of “shear thinning” in the final polymer blend composition at an appropriate level of incorporation. It has been found that branched components with higher degrees of branching will provide shear sensitivity improvements at lower levels while lower degrees of branching will conversely require use of the component in larger amounts to provide shear sensitivity improvements.
Preferably, the carbonate polymer of the present invention is an aromatic carbonate polymer, more preferably a branched carbonate polymer and most preferably a branched aromatic carbonate polymer. Branched aromatic car
Hus Michael E.
Johnson Brenda G.
Ogoe Samuel A.
Pham Hoang T.
Buttner David J.
The Dow Chemical Company
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