Film formed from polyethylene-2,6-naphthalate resin, process for producing said film and package using said film

A cover film for a press-through pack comprising polyethlylene-2,6-naphthalate, said film being prepared by a process comprising the steps of:

• providing an unstretched film comprising polyethylene-2,6-naphthalate having an intrinsic viscosity .eta. in the range of from 0.31 to 0.6,
• stretching the film at 120.degree. to 170.degree. C. in mutually perpendicular directions each with drawing ratios of 1 to 3 times, and
• heat-treating the stretched film at 170.degree. to 270.degree. C. for 1 sec to 30 min to heat-set the film, thereby preparing a stretched film having a final thickness in the range of from 5 to 150 .mu.m.

A cover film for a press-through pack comprising polyethylene-2,6-naphthalate, said film being prepared by a process comprising the steps of:

• providing an unstretched film comprising polyethylene-2,6-naphthalate having an intrinsic viscosity .eta. in the range of from 0.31 to 0.6,
• stretching the film at 120.degree. to 170.degree. C. in the longitudinal direction at draw ratios of 3 to 6 times and in the transverse direction at draw ratios of 1 to 1.8 times, and
• heat-treating the stretched film at 170.degree. to 270.degree. C. for 1 sec to 30 min to heat-set the film, thereby preparing a stretched film having a final thickness in the range of from 5 to 150 .mu.m.