The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 18, 1992
Filed:
Jul. 22, 1991
Shigeo Utsumi, Yamato, JP;
Kichinojyo Tomitaka, Yokohama, JP;
Yujiro Fukuda, Machida, JP;
Takatoshi Miki, Nagahama, JP;
Daifoil Company, Limited, , US;
Abstract
The present invention relates to a process for producing a biaxially oriented polyester film. The process is carried out using the following steps: (a) stretching an amorphous film substantially comprising polyethylene terephthalate 1.2 to 4.0 times in the machine direction by single-stage or multi-stage process to obtain a film having an index of birefringence of 1.times.10.sup.-3 to 2.5.times.10.sup.-2 ; (b) stretching the thus obtained film 1.1 to 3.5 times in the machine direction by single-stage or multi-stage process of 3.0.times.10.sup.-2 to 8.0.times.10.sup.-2 without cooling the film to the glass transition temperature thereof or below; (c) cooling the thus obtained film to the glass transition temperature thereof or below; (d) heating the thus obtained film to the glass transition temperature or higher and stretching the film in the machine direction by a single-stage or multi-stage process at a stretching ratio which brings the overall stretching ratio of 4.0 to 9.0 times; and (e) stretching the thus obtained film at least 3.2 times in the transverse direction. According to the method of the present invention, a biaxially oriented polyester film which is excellent in thickness uniformity and flat and slippery properties can be easily produced and high-speed production thereof is possible, therefore, the present invention has a great industrial value.