Film thickness adjusting method and apparatus in inflation film forming, and forming die used therefor

摘要

PROBLEM TO BE SOLVED: To eliminate the sectional non-uniformity of a tubelike film in the peripheral direction in easy response to a change in various kinds of resins and molding conditions by dividing a rising part of a channel into a plurality of sections and adjusting the temperature of the sections independently of each other. SOLUTION: In molding the tubular film, the rising part 11 of each of spiral grooves which form resin feed channels for a molding die 10, is divided into a plurality of sections along the circumference of the molding die 10 and each section is heated by its heating means. In this case, the heating means 12 of each section is adjusted under control in accordance with the difference between a film thickness detected near a frost line and a set value and thereby, the sum of the overflow flow rates of the rising parts 11 of the spiral grooves in the circumferential direction is set to be constant. In addition, the flow variability of each of the spiral grooves in the entire circumference is eliminated and thereby, the wall thickness of the tubular film is made uniform on the entire circumference.