Semi-crystalline thermoplastic polyester for producing bioriented films

A biaxially oriented film comprising a semicrystalline thermoplastic polyester comprising:

• at least one 1,4:3,6-dianhydrohexitol unit (A);
• at least one alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A);
• and
• at least one terephthalic acid unit (C);
• wherein the (A)/[(A)+(B)] molar ratio is at least 0.05 and at most 0.30;
• said polyester not containing any aliphatic non-cyclic diol units or comprising a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 5%, and the reduced viscosity in solution (25° C.;
• phenol (50%m):
• ortho-dichlorobenzene (50%m);
• 5 g/l of polyester) of said polyester being greater than 50 ml/g.

A method for the production of a biaxially oriented film, comprising the following steps of:

• provision of a semicrystalline thermoplastic polyester comprising at least one 1,4:3,6-dianhydrohexitol unit (A), at least one alicyclic diol unit (B) other than the 1,4:3,6-dianhydrohexitol units (A), at least one terephthalic acid unit (C), wherein the (A)/[(A)+(B)] molar ratio is at least 0.05 and at most 0.30, said polyester not containing any aliphatic non-cyclic diol units or comprising a molar amount of aliphatic non-cyclic diol units, relative to all the monomer units of the polyester, of less than 5%, and the reduced viscosity in solution (25° C.;
• phenol (50%m):
• ortho-dichlorobenzene (50%m);
• 5 g/l of polyester) of said polyester being greater than 50 ml/g;
• and
• preparation of said biaxially oriented film from the semicrystalline thermoplastic polyester obtained in the preceding step.