PURPOSE: To remove oligomer and prevent the generation of troubles for a film making by a method wherein air is supplied into the tubular film molten and extruded from an annular die while the contaminated air is discharged therefrom.
CONSTITUTION: While the tubular film 6 molten and extruded from the annular die 7 is cooled by an inside mandrel 8, a constant volume of air is poured into the tubular film to form a baloon 9. In this case, fresh air is supplied into the baloon 9 while the contaminated air is discharged therefrom, further, the supplying as well as the discharging amount of the air are controlled at a constant value so as not to generate the variation of the amount of air in the baloon. For this purpose, an air reserving ring 10, for examplem, having the same diameter as that of the inside mandrel 8 is provided above the mandrel 8 and a fine perforated member 11 is utilized for the outer wall thereof to permit the communication of the air while a discharging port 13 is provided on the annular die 7 in the baloon 9.
MITA AKIRA
SHIOMI TETSUYA
HIRAI TOSHIYUKI
