To enhance mechanical and gas barrier properties by stretching a mixed polymer of a salt consisting of a specific ratio of an aliphatic polyamide, m-xylylene diamine and adipic acid and a salt consisting of hexamethylene diamine and terephthalic acid at a specific temperature and stretching the mixed polymer orthogonally.
An unstretched film is obtained based on a mixed polymer containing 2-80wt.% of a copolymer obtained by polymerizing 85-55wt.% of a salt consisting of 98-20wt.% of an aliphatic polyamide (A), m-xylylene diamine (B) and adipic acid and 15-45wt.% of a salt consisting of hexamethylene diamine and terephthalic acid. Next, this unstretched film is stretched 2-6-fold at the glass transition temperatures or higher of the film material and the melting point or lower of the film material. After that, this stretched film is orthogonally stretched 2-6-fold at stretching temperatures or higher and the melting points of -5°C or lower. The molecular weight of each of the components A, B should preferably stay in the range of 1.8-4.0 as a relative viscosity so that a melt viscosity high enough to maintain a uniform film face is obtained.
YAMASHITA ATSUSHI
SUGIMOTO KOJI
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