PURPOSE: To provide a film for optical material improved in transparency, optical isotropy, heat resistance and production cost by making it from a specified polyester.
CONSTITUTION: The film having a thickness of 5-2000μm and a double refractive index (Δn) of 1×10-3 or below at an elongation of 5% is made from a polyester obtained by polycondensation such as dehydrative condensation of a diol with an aromatic dicarboxylic acid, transesterification of a diol with a dimethyl aromatic dicarboxylate or dehydrohalogenation of a diol with an aromatic dicarboxylic acid halide and comprising repeating units of formula I [wherein R1 is a residue derived from a mixture of 50-100mol% alicyclic diol of formula II (wherein n is 1 or 2; and a and b are each 0 or 1) with 50-0mol% alicyclic diol other than the above; and R2 is an aromatic dicarboxylic acid residue derived from phenylindandicarboxylic acid of formula III]. The film formation is carried out by using a solvent such as a cyclic ether according to dry film formation process.
HANADA SUSUMU
IWATA KAORU
