POLYESTER FILM AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To prevent the generation of a twist curl in a use laminating a polyester film chiefly used for an IC card. SOLUTION: In a differential curve of the real shrinkage quantity of a polyester film in its machine direction calculated from shrinkage quantities at times of a temp. rise and a temp. drop due to TMA by heat-treating the polyester film in a tenter after longitudinal stretching and lateral stretching and subsequently cooling the heated film to a temp. range from (glass transition temp. +50 deg.C)-(heat treatment temp. -30 deg.C) and applying relax to the film in its machine direction within a range of±10% in the shrinkage quantity at a time of a temp. drop due to TMA corresponding to the temp. drop of the cooling process up to the outlet of the tenter, a shrinkage quantity differential value dL/dT within a range from glass transition temp.-150 deg.C is always 0.02%/ deg.C or less and the heat shrinkage factor of the film in the machine direction at 150 deg.C for 30 min is 1.0% or less and the lateral distribution of this heat shrinkage factor is 0.1% or less.