Polyethylene terephthalate (PET) is a low cost high performance thermoplastic material. In its crystalline state, the plastic has a very high flexural modulus and a high heat deflection temperature. Being a thermoplastic it can be economically processed by an injection molding process. The major use of polyethylene terephthalates today is in the beverage-bottle-making industry.
An injection molded polyethylene terephthalate article has excellent surface finish and low surface porosity making it suitable for painting processes. The inherent high heat deflection temperature of PET assures that a painted article can go through a paint bake cycle without thermal distortion. Based on these benefits, polyethylene terephthalate seems to be a good candidate for many automotive exterior body panel applications. However, a serious shortcoming of PET which disqualifies it from automotive applications is its very low impact strength.
One method that has been used to improve the physical properties of polyethylene terephthalate is to blend it with other thermoplastic materials. Since PET has good compatibility with many other thermoplastics, it can be easily blended with other plastic materials to give it desirable properties. For instance, impact modifiers of elastomeric base materials and high temperature plastics have been used to improve the impact property and the heat resistance property of polyethylene terephthalate. Many of these polyethylene terephthalate polyblends having improved physical properties are still inadequate to meet automotive application requirements. To be qualified for an automotive exterior body panel application, a plastic material must have high impact strength, high tensile strength, high flexural properties and easy processability.
It is therefore an object of the present invention to provide a polyblend of polyethylene terephthalate having improved impact property to meet automotive exterior panel application requirements.
It is yet another object of the present invention to provide a polyblend of polyethylene terephthalate having high impact strength and can be economically processed by the injection molding method.
It is a further object of the present invention to provide an injection moldable, high impact strength polyblend of polyethylene terephthalate capable of producing articles having readily paintable surfaces to meet automotive finishing requirements.
It is still another object of the present invention to provide a polyblend of polyethylene terephthalate having high impact strength and high temperature resistance such that a painted article can be cured in a paint bake cycle without thermal distortion.