| 摘要 |
Polyvinyl alcohol films are provided which are gelled, non-tacky, bubble-free and resistant to water at ambient temperatures. The polyvinyl alcohol film is obtained by plasticizing (fluxing) and melting granules of pure polyvinyl alcohol containing from 25 to 35% by weight of water at a temperature at least 100 DEG C. above the equilibrium melting point of the granules and less than or equal to 220 DEG C., and extruding the melted granules through a die at a temperature at least 5 DEG C. above the equilibrium melting point of the granules and less than or equal to 98 DEG C., optionally followed by monoaxial stretching or biaxial stretching of the unstretched film obtained. The stretched or unstretched film may be heat-treated to improve its properties. The polyvinyl alcohol film can be used to prepare with thermoplastic films composite films or sheets having a high gas impermeability. The invention also provides composite, biaxially oriented, impermeable barrier layer coated, thermoplastic hollow shaped articles useful as packaging material, e.g., as packages and bottles for flavored foods and carbonated beverages. The hollow shaped articles are produced by externally barrier covering a thermoplastic tubular blank, parison or preform with a relativley thick barrier layer consisting essentially of water-resistant and highly crystalline polyvinyl alcohol, said barrier layer having been prepared by shaping a melt of homogeneously shear fluxed and molten flakes of pure polyvinyl alcohol having a water content of 25 to 35% by weight thereof, with said shear fluxing and melting of said polyvinyl alcohol flakes being at a temperature above the equilibrium melting point of the polyvinyl alcohol/water admixture essentially constituting said flakes, and said shaping being at a temperature of at least said equilibrium melting point but less then that at which the vapor pressure of the component water would effect the surface expansion and bubbling of the desired barrier layer, and then biaxially orienting and blow molding into final configuration said barrier covered blank, parison or preform.
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