| 摘要 |
PURPOSE:To easily obtain a polyester film which has little strain and has low shrinkage by heat-treating the polyester film having prescribed composition in the prescribed conditions in an infrared-heating furnace held at specified temp. or more. CONSTITUTION:A polyester film which has <=1.5% shrinkage factor in the longitudinal direction of the film after treatment at 150 deg.C for 60 minutes is heat-treated in an infrared-heating furnace held at >=150 deg.C so that the following expressions are simultaneously satisfied. 0.03A+3.75<=t<=0.06A+7.5 and T<=100, in the expression, A shows thickness (mum) of the film, (t) shows heat-treating time (sec) and T shows tension (g/mm<2>) of the film. When the low shrinkage film is to be obtained from a film having a heat shrinkage of 0.5% or more, the heat-treating conditions are made severe. As the result, strain of the obtained film is great and this film can not be utilized for the practical applications. The heat-treating time (t) is regulated to a range within (0.03A+3.75)-(0.06A+7.5) sec. In such a way, strain of the film is made small and effective low shrinking treatment can be performed in a time shorter than the ordinary heat treatment time. |
