| 摘要 |
PURPOSE:To make it possible to enhance modulus of elasticity and breaking strength inexpensively, by dissolving an atactic polyvinyl alcohol(PVA) in ethylene glycol, rapidly cooling the resultant solution to effect gellation, removing the ethylene glycol by washing to obtain a dried gel, and stretching the gel with heating. CONSTITUTION:An atactic PVA to be used is a completely saponified high polymerization degree PVA having a saponification degree of at least 98mol% from which an ethylene glycol solution is prepared to have a low concentration of 1 to 6g/dl. The PVA is dissolved in ethylene glycol while being maintained at a temperature of 160 deg.C or above, and the resultant solution is cooled to or below 100 deg.C to form a gel form film. The gel form molded piece is washed sufficiently with a large amount of water, methanol or the like, thereby removing ethylene glycol therefrom. Then, the molded piece is dried, and the resultant dried gel is stretched to a length of 10 to 20 times the original length in a multiplicity ot stages under a temperature condition of 160 to 230 deg.C. In the first stage of the stretching operation, the dried gel is stretched in a high-temperature atmosphere to a length of about 80% based on the length at which the gel is broken, followed by relaxation at room temperature. Then, the stretched gel is again stretched in a high-temperature atmosphere to a length of about 110% based on the length attained upon the subsequent stage of stretching, followed by relaxation at room temperature. |
