Method for manufacturing polyester films
AssigneeToray Industries, Inc.
InventorsMasahiko Motegi, Kazuhiro Tanaka, Saburo Fujita
Life of this patent
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Abstract
The present invention relates to a process for preparing a polyester film which has not only uniaxially enhanced mechanical properties but also biaxially enhanced mechanical properties. The process involves heat-setting a biaxially oriented polyester film at a temperature above that used for the machine and transverse direction stretching and above that used for the machine direction re-stretching, but at least 10.degree. C. below the melting point of the polyester, then re-stretching the film in both the machine and transverse directions, and re-heat-setting the film.
Claims8
In a process for preparing a polyester film having an F-5 value in the TD which is above 14 kg/mm.sup.2, the steps which comprise heat-setting a biaxially oriented polyester film obtained by stretching the film at a ratio of more than 2.0 in both the MD and TD, at a temperature above the MD-, TD-, and re-MD stretching temperature but below T.sub.m (the melting point of the polyester) -10.degree. C., then restretching the film at a ratio of 1.05-2.5 in MD and then at a ratio of 1.05-2.5 in TD at a temperature between T.sub.g (glass transition temperature of the polyester) +10.degree. C. and T.sub.m -40.degree. C., and reheat-setting the film at a temperature between T.sub.g +50.degree. C. and T.sub.m -10.degree. C.
Dependencies are inferred from the claim text.