| 摘要 |
PURPOSE:To provide a method of realizing the high draw ratio progressive biaxial stretching of poly(4-methylpentene-1) (PMP) without developing uneven stretching and breakage of film by a method wherein unstretched film made of resin mainly consisting of PMP is laterally stretched and, after that, longitudi nally stretched at the respective specified temperature. CONSTITUTION:Homopolymer of PMP, copolymer consisting of PMP as main component and another alpha-olefin as copolymeric component, a mixture of PMP and polyalpha-olefin such as polyethylene, polypropylene or the like are preferable as the resin mainly consisting of PMP. Firstly, unstretched film made of resin mainly consisting of PMP is laterally stretched at a temperature ranging film 130 deg.C or higher to under the melting point of the film with the draw ratio of 300% or more. Secondly, the resultant film is longitudinally stretched at a temperature ranging from 100 deg.C or higher to under the melting point of the film with the draw ratio of 300% or more. Because PMP is progressively and biaxially stretched as mentioned above, the satisfactory stretching is realized. Consequently, the obtained film has excellent mechanical properties as biaxially stretched film and no unevenly stretched portion.
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