PURPOSE: To simplify the structure of a die itself and the piping and wiring around the die, and to simplify a system of controlling the thickness, by providing cooling means for cooling the die approximately uniformly in the direction of the width thereof so that cooling by using a cooling medium under predetermined conditions may be effected.
CONSTITUTION: An extrusion die 1 and a thermoplastic resin 6 are kept at a prescribed temperature by a main heater 2. Local auxiliary heaters 4 are operated according to the ununiformity of the thickness of the discharged thermoplastic resin film thereby controlling locally the temperature near the die opening. The cooling amount of cooling means with a passage 3 through which a heating medium set to a prescribed temperature is passed can approximately cancel the whole heating amount of the local auxiliary heaters 4, so that the temperature of the die opening 5 is kept approximately equal to the temperature of the main heater 2. It is enough if the cooling capacity of the cooling apparatus is approximately balanced with the heating amount exerted by the auxiliary heaters.
KITAMURA YOSHIYUKI
OKASHIRO HIDETOSHI
