The present invention relates to a polyester resin composition and a molded article thereof. More particularly, the present invention is directed to a polyester resin composition which has excellent toughness at low temperature and has improved heat stability and long-term stability in high-temperature service, in particular, resistance to discoloration, and which is useful for the preparation of a connector, switch or relay for automobiles or electrical appliances.
Crystalline thermoplastic polyester resins represented by polyalkylene terephthalates have been used as engineering plastics in various fields including automotive parts and electrical and electronic components by virtue of the excellent mechanical and electrical properties, excellent physical and chemical characteristics and good processability thereof. As the enlargement and diversification of the use of these resins have proceeded, however, polyalkylene terephthalates have been frequently required to show enhanced and specialized performance. For example, applications have increased where high heat stability, in particular, long-term stability of quality at high or low temperature is required.
More specifically, it is required in automotive fields from the standpoint of safety that the resin have excellent mechanical properties such as flexibility and impact resistance at low temperature and retain these excellent physical properties even after long-term service at high temperature.
In order to satisfy the above requirements, it has been proposed to add polycarbonate or thermoplastic elastomer such as an olefinic polymer or rubbery polymer to a thermoplastic polyester resin and simultaneously add an epoxy resin or polycarbodiimide. However, a polyester resin composition thus prepared containing an elastomer and an additive as described above is subject to surface peeling owing to poor compatibility and is problematic in that discoloration occurs in long-term service at high temperature. Accordingly, the utilization thereof is very limited, although the resin composition has somewhat improved mechanical properties.
For the purpose of overcoming the discoloration problem, it has also been proposed to add a stabilizer such as a specific phenol, amine, phosphate or phosphite compound to the polyester composition. Although the addition of a stabilizer is somewhat effective in depressing the discoloration, the effect is too insufficient to satisfy the performance as required of a connector for automobiles or electrical appliances, including high toughness (particularly, at low temperature) such as flexibility and impact resistance and excellent heat stability and long-term stability of quality at high temperature, in particular, resistance to discoloration. Accordingly, there is still an eager desire to solve the performance problems.