Mitsubishi Monsanto Chemical Co., Ltd.

Kazuharu Abe

Tsuguo Okumura

Kenji Mori

Naomichi Yamagishi

Hitoshi Matsuda

Masayoshi Sugiyama

Disclosed is a heat-shrinkable biaxially drawn polyamide film which is formed from a homopolymer or copolymer of .epsilon.-caprolactam or a polyblend thereof, by a sequential biaxial drawing method and which has a density of 1.129 to 1.136 g/cm.sup.3 and an in-plane orientation index of 0.0535 to 0.0580. This film is prepared by the steps of drawing in the machine direction a substantially amorphous unoriented polyamide film at 45.degree. to 65.degree. C., a deformation rate of at least 10,000%/min and a draw ratio of 2.7 to 3.5 by a roll type longitudinal drawing method, gripping the ends of the film by tenter clips, drawing the film in the transverse direction at a film temperature not higher than 100.degree. C., an average deformation rate of 2,000 to 10,000%/min and a draw ratio of 3 to 5, and heat-treating the film at 125.degree. to 170.degree. C. while gripping the ends of the film by the tenter clips.

Heat-shrinkable biaxially drawn polyamide film and process for

Biaxially drawn polyamide films having an excellent levelness are prepared as follows. A substantially unoriented polyamide film is heated at 45.degree.-65.degree. C., and then drawn in the longitudinal direction at a deformation rate of at least 10,000%/min. and a draw ratio of 2.7-3.5 by a roll stretcher. The drawn film is immediately transferred to the lateral drawing position at 45.degree.-60.degree. C. within a time (t):t=e.sup.(3.9-0.053T.sbsp.1.sup.) where e=the base of natural logarithm and T.sub.1 =film temperature during this period of time (t), which is 45.degree.-60.degree. C. The thickness profile of the film at the starting position of lateral drawing is gradually reduced from the side and portions toward the central portion of the width so that the film thickness at the central portion is 75-90% of the film thickness at the side end portions. The film is drawn in the lateral direction at an average deformation rate of 2,000-10,000%/min. and a draw ratio of 3-5 by a tenter type stretcher in such a manner that, until the mechanically set draw ratio between respective tenter clips exceeds 1.4 times the original distance, the film is expanded at an angle of up to 6.degree. with respect to the travelling direction at a tenter clip temperature T.sub.2 (T.sub.2 &lt;T.sub.1). The film temperature is elevated stepwise in the lateral drawing and the film temperature at the termination position of lateral drawing is 70.degree.-100.degree. C.

Process for preparing biaxially drawn polyamide films

A biaxially drawn laminated films having a good oxygen barrier property, a good mechanical strength and high thickness uniformity are made by a process comprising:

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Tsuchiura, Japan

Kazuharu Abe