METHOD FOR STRETCHING THERMOPLASTIC RESIN FILM OR SHEET

PROBLEM TO BE SOLVED: To uniformize the stretching start and complesion positions of a sheet in the width direction thereof by dividing a heating furnace into respective preheating, heating, buffer and cooling zones and providing a mechanism discharging the atmospheres of the heating and cooling zones from the buffer zone to the outside of the heating furnace and set the respective zones to specific temps. SOLUTION: A heating furnace is divided into a preheating zone 1, a heating zone 2, a buffer zone 4 and a cooling zone 3 and the atmospheres of the heating and cooling zones 2, 3 are discharged from the buffer zone 4. During the passage of a thermoplastic resin film or sheet through a heating furnace, the temp. T1 of the preheating zone 1, the temp. T2 of the heating zone 2 and the temp. T3 of the cooling zone 3 are held to the ranges represented by the following formulae, that is Tg-50 deg.C