Process and apparatus for heat setting biaxially oriented tubular polyethylene terephthalate films

In the process which comprises heat setting a tubular biaxially oriented polyethylene terephthalate film by continuously heating a film bubble expanded by a gas pressure, and taking up on a winder, the improvement comprising:

• a. heat setting said film in a chamber by blowing hot gaseous blasts against the exterior surface of said film bubble;
• wherein the temperature of the hot blasts is about 220.degree. C.-240.degree. C, along the first 1/5-1/3 of the chamber and wherein the temperature of the blasts thereafter declines to about 195.degree. C.-215.degree. C. at the final stage of heat setting, and
• b. reducing the diameter of the tubular film during heat setting by about 5%-15% of that before heating and stretching the length thereof by about 2%- 7% of that before heat setting;
• whereby sway of the film is eliminated during heat setting, and
• c. taking the tubular heat set film up on a winder in a folded state while rotating said tubular film around the axis of the film.

In the process for producing polyethylene terephthalate films which comprises a step for heating setting a tubular biaxially oriented polyethylene terephthalate film by continuously heating a film bubble expanded by a gas pressure, the improvement comprising:

• a. heat setting said film in a chamber by blowing hot gaseous blasts against the exterior surface of said film bubble;
• wherein the temperature of the hot blasts is about 230.degree. C.-240.degree. C. along the first 1/5-1/3 of the chamber and wherein the temperature of the blasts thereafter declines to about 195.degree. C.- 205.degree. C. at the final stage of heat setting, and
• b. reducing the diameter of the tubular film during heat setting by about 5%-15% of that before heating and stretching the length thereof by about 2%- 7% of that before heat setting;
• whereby sway of the film is eliminated during heat setting.

In the process which comprises heat setting a tubular biaxially oriented polyethylene terephthalate film by continuously heating a film bubble expanded by a gas pressure and taking up on a winder, the improvement comprising:

• a. heat setting said film in a chamber by blowing hot gaseous blasts against the exterior surface of the film bubble;
• wherein the temperature of the hot blasts is about 230.degree. C.-240.degree. C. along the first 1/5-1/3 of the chamber and wherein the temperature of the blasts thereafter declines to about 195.degree. C.-205.degree. C. at the final stage of heat setting, and
• b. reducing the diameter of the tubular film during heat setting by about 5%- 15% of that before heating and stretching the length thereof by about 2%-7% of that before heat setting;
• whereby sway of the film is eliminated during heat setting.