To provide a relaxation heat treatment method for a thermoplastic resin film small in size change and used in a packaging material, an industrial material, an electric insulation material, a capacitor material, a magnetic material, an optical material or the like excellent in flatness.
In the method for producing the thermoplastic resin film, the thermoplastic resin film stretched at least uniaxially by a tenter method is heat-set in the heat setting zone of a tenter and the heat-set film is separated from tenter clips to be subjected to relaxation heat treatment by using the difference between a film take-over speed and a film supply speed. In a film cooling process in a relaxation zone where the speed difference occurs, the wind speed Y(m/s) of cooling air blown against the film and the sum value X(m) of the installation distance a(m) in the width direction between two tentering devices surrounding a film cooling zone and the installation distance b(m) in the film traveling direction meet formulae Y ≤-15X+24 and 2≤X≤ 8 (wherein X=a+b, 1≤a≤7, and 1≤b≤5).
SASAKI YASUSHI
MURAKAMI HIDEO
Kakehi Yuro
Takeshi Ohara
Hiroji Nakagawa
Yasumitsu Tate
Kenji Saito
Jun Fujii
Hitoshi Seki
Mutsuko Nakano