PURPOSE: To improve the transparency, mechanical strengths, dimensional stability, and recovery from curling and inhibit the light piping phenomenon of a polyester film by copolymerizing a specific acid component with a specific diol component.
CONSTITUTION: An acid component comprising terephthalic acid, dimethyl terephthalate, naphthalene-2,6-dicarboxylic acid, dimethyl naphthalene-2,6- dicarboxylate, etc., is reacted with a diol component contg. 1-50mol% ester- forming deriv. having a fluorene, phenylindane, spiroglycol, or diphenyl sulfone group in the presence of a Ge compd. in an amt. 10-500ppm (in term of Ge) and at least one comtd. of a metal selected from among Ca, Mg, Ti, and Li in an amt. of 1-500ppm (in terms of metal) to give a modified polyester having a glass transition point (by differential scanning calorimetry) of 125°C or higher and a heat of crystallization (measured by decreasing temp.) of 4J/g or lower. The polyester is formed into sheet, stretched 2.0- to 5.0-fold in both longitudinal and transverse directions, and thermally treated, thus providing a film.
SHIMIZU YUZO
SUZUKI MASARU