Patent ID: 8710121

Claim:
A biaxially oriented polyester film comprising (i) polyester, (ii) 0.25-6% by weight, based on the weight of the film, of hydrolysis stabilizer based on epoxidized fatty acid esters and/or epoxidized fatty acid glycerides, and (ii) a chain extender having a polymer of formula 5 where R 9 -R 13 are each independently H or a C1-C12-alkyl radical, R 14 is a C1-C12-alkyl group, x and y are each independently selected from 0 to 100, x+y is greater than 0 and z is from 2 to 100; wherein the sum of the hydrolysis stabilizer and the chain extender ranges from at least 1% by weight to less than 12% by weight, based on the weight of the film; and wherein more than 80% by weight of the epoxidized fatty acid glycerides are mixtures of glyceryl esters of the formula 1: CH 2 OR 1 —CHOR 2 —CH 2 OR 3 where the R 1 , R 2 and R 3 radicals are each independently defined as follows where R E =CH 3 or H and m=1-40 n=0-10 o=0-4 and where the sequence of the individual methylene (CH 2 )— (1), epoxy (CHOCH)— (2) and (CHCH 3 )— (3) groups is independently selected, and where R 1,2,3 radicals where m=0 are present in glyceryl ester mixtures to an extent of less than 30% by weight, based on the total weight of the glyceryl esters, and where at least one said glyceryl ester includes at least one epoxidized fatty acid moiety; and wherein the film exhibits a modulus of elasticity in both directions of greater then 3000 N/mm 2 ; and wherein the film has standard viscosity (SV) of more than 500 after 96 hours in an autoclave with steam saturation at 110° C.; and wherein the hydrolysis stabilizer is a mixture of epoxidized fatty acid esters and epoxidized fatty acid glycerides and the proportion of the fatty acid glycerides described by formula 1 in the overall hydrolysis stabilizer content is >50% by weight.