Biaxially oriented polyester film
AssigneeTeijin Limited
InventorsKouhei Endo, Hiroshi Tokuda
Life of this patent
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Abstract
A biaxially oriented polyester film which has good thickness nonuniformity in both longitudinal and transverse directions, uniform physical properties in a transverse direction and high strength in a longitudinal direction. This film has such characteristic properties that (a) an F-5 value in a longitudinal direction of 13 kg/mm2 or more, (b) a thickness nonuniformity in each of both longitudinal and transverse directions of 8% or less, and (c) a difference in the heat shrinkage factor of 0.02 to 0.2% per 1 m in a transverse direction, said heat shrinkage factor being measured at 105° C. in the longitudinal direction.
Claims8
A biaxially oriented polyester film having (a) an F-5 value in a longitudinal direction of 13 kg/mm2 or more, (b) a thickness nonuniformity in each of both longitudinal and transverse directions of 8% or less, and (c) a difference in the heat shrinkage factor of 0.02 to 0.2% per 1 m in the transverse direction, said heat shrinkage factor being measured at 105° C. in the longitudinal direction.
A process for producing a biaxially oriented polyester film comprising the steps of:
- stretching an amorphous unstretched polyester film to 4.0 to 6.0 times in a longitudinal direction;
- stretching the so-obtained film to 3.0 times or more and less than 4.0 times in a transverse direction;
- stretching the so-obtained film to 1.01 to 1.20 times in a transverse direction while heat-setting it;
- and
- relaxing the so-obtained film by 0 to 20% in a transverse direction while cooling it,
- wherein the biaxially oriented polyester film has a width of 3 to 10 m, and
- the difference in the heat shrinkage factor is 0.05 to 0.2% per 1 m in the transverse direction, said heat shrinkage factor being measured at 105° C. in the longitudinal direction.
Dependencies are inferred from the claim text.