To provide a biaxially stretched polyester film for solar battery backside protection which is suitable for a backside protection film and capable of keeping a good protective function even after a long-term use, and which is excellent in hydrolysis resistance, heat resistance and film appearance, and is arranged so that even after a long-term use under a harsh natural environment such as a high temperature and high humidity, the degradation of its mechanical property is suppressed and good UV discoloration resistance is maintained.
The biaxially stretched polyester film for solar battery backside protection is composed of a polyester film comprising polyester as a polymer component, and glycol oxalate represented by the formula (1), provided that the glycol oxalate is added to the polyester in a range between 0.1 and 5.0 mol% inclusive to all of acid components of the polyester: -C(O)-C(O)-ORO- (1). In the formula (1), R represents an alkylene group having 2-4 carbon atoms. The polyester film has a breaking ductility half-life time of 80 hours or longer under the environment that the temperature is 121°C and the humidity is 100%RH.
OYAMATSU ATSUSHI
OKADA SHINICHIRO
KAMEOKA AKIRA
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