A preferred rigid thermoplastic resin composition having high impact strength and resistance to thermal distortion includes a vinyl chloride resin/polycarbonate alloy and at least 3 parts by weight of butadiene-modified acrylic per 100 parts by weight of the alloy. A particularly preferred thermoplastic resin composition includes the alloy and both butadiene-modified acrylic and ethylene-vinyl acetate copolymer.
High Impact PVC/Polycarbonate Alloy Compositions, E. J. Termine, D. J. Honkomp, and N.A. Favstritsky, United States Patent No. 5,219,936.
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to impact and thermal distortion resistant thermoplastic resin compositions, and more particularly relates to impact-modified polyvinyl chloride/polycarbonate alloy compositions.
2. Description of the Prior Art
Polyvinylchloride (PVC) is a high volume, relatively inexpensive polymer. However, the use of PVC is often limited because it lacks properties required for many service applications. Efforts to develop PVC blends or alloys with other materials which meet the demands of commercial service applications have therefore continued.
For example, PVC alone lacks the dimensional stability under heat required for many service applications. To address this problem, it is known to alloy PVC with polycarbonate to form an alloy composition having dimensional stability under heat surpassing that of PVC alone. For example, Abdrakhmanova et al., SU 84-3788283, 31 Aug. 1984, describe a mixture of 100 parts polyvinyl chloride and 1-8 parts oligomeric bisphenol A polycarbonate. PVC/polycarbonate alloys, however, often lack acceptable impact strength. Efforts have therefore been made to discover impact modifiers that can be added to PVC/polycarbonate alloys to make an overall composition having both acceptable impact strength and dimensional stability under heat.
In this connection, U.S. Pat. No. 3,882,192 issued to Elghani et al. in 1975 describes molding compositions consisting of 5-95 parts by weight of a polycarbonate, 5-95 parts by weight of a vinyl chloride polymer, and 5-95 parts by weight of an acrylonitrile butadiene styrene copolymer or a styrene/maleic anhydride copolymer or an ethylene-vinyl acetate copolymer.
On the other hand, U.S. Pat. No. 4,680,343 issued to Lee in 1987 describes chlorinated polyvinyl chloride (CPVC) alloys containing aromatic polycarbonates, ethylene-based functional polymers and optionally an impact modifier. The Lee patent notes that CPVC and PVC are different materials and that PVC prior art is not analogous to patentability issues relating to CPVC since PVC processes easily and CPVC does not, since CPVC has heat resistance but PVC does not, and furthermore, since CPVC has a high melt viscosity but PVC does not.
Despite these and other efforts, the need continues for PVC/polycarbonate alloy compositions having high impact properties. Efforts to find such compositions have been frustrated because the effects of differing impact modifiers on PVC/polycarbonate blends vary greatly, and it is thus difficult to discover impact modifiers which provide overall alloys having high impact and other desirable properties.
The applicant’s invention now addresses this need and provides impact and thermal distortion resistant PVC alloys having other advantageous properties as well.
SUMMARY OF THE INVENTION
One preferred embodiment of the invention provides a rigid thermoplastic resin composition having high impact strength and resistance to thermal distortion. The thermoplastic resin composition includes an alloy of a vinyl chloride resin and a polycarbonate (hereinafter sometimes referred to as a “vinyl chloride resin/polycarbonate alloy”). The thermoplastic composition further includes at least about 3 parts by weight of a butadiene-modified acrylic (“BMA”) impact modifier per 100 parts by weight of the vinyl chloride resin/polycarbonate alloy. This composition demonstrates highly advantageous physical and chemical properties, including for instance superior impact strength as can be measured by the Gardner impact test, as well as high resistance to heat distortion.
As another feature of the invention, a particularly preferred thermoplastic resin composition includes both butadiene-modified acrylic and an ethylene-vinyl acetate (EVA) copolymer. It has been discovered that using these two impact modifiers together can provide synergistic results in which high impact properties are retained while the composition has greater ductility than similar compositions modified only with the individual impact modifiers.
Still another preferred embodiment of the invention provides a method for preparing a thermoplastic resin composition having high impact strength and resistance to heat distortion. This method includes the step of incorporating into a vinyl chloride resin/polycarbonate alloy an effective amount of butadiene-modified acrylic polymer to increase the impact strength of the alloy.
Additional aspects, features and preferred embodiments of the invention will be apparent from the following description.