DETAILED DESCRIPTION OF THE INVENTION The PVA used in the present invention generally has a polymerization degree of 100 to 2000, preferably 200 to 1000 and a saponification degree of not less than 80%, preferably not less than 90%, more preferably not less than 95%.
If the saponification degree is less than 80%, the barrier property is unfavorably lowered.
If the polymerization degree is less than 100, the viscosity is lowered too much for an ordinary molding apparatus.
As the metal compound, any metal compound is usable so long as it is capable of raising the Td of the PVA higher than a flow beginning temperature (hereinunder referred to as "Tf") by not less than 15.
degree.
C.
, preferably 20.
degree.
to 70.
degree.
C.
Alkaline metal compounds such as lithium, sodium and potassium compounds; alkaline earth metal compounds such as calcium, magnesium and strontium compounds; and divalent to quadrivalent heavy metal compounds such as cobalt, tin, manganese, nickel, iron and titanium compounds are preferably used.
As to the compound of any of these metals, halides such as chloride, bromide and iodide; inorganic acid salts such as carbonate, sulfate and nitrate; and organic acid salts such as acetate, lactate and stearate of these metals are usable.
These metal compounds may be used either singly or in the form of a mixture.
Concrete examples of a metal compound which is mixed with PVA are LiCl, NaCl, KCl, MgCl.
sub.
2, CaCl.
sub.
2, SrCl.
sub.
2, CoCl.
sub.
2, SnCl.
sub.
2, LiBr, NaI, Mg(NO.
sub.
3).
sub.
2, NaNO.
sub.
3, KNO.
sub.
3, K.
sub.
2 CO.
sub.
3, MgSO.
sub.
4, CH.
sub.
3 COOLi and CH.
sub.
3 COONa.
The metal compounds have different actions depending upon the kind of a metal.
Generally, lithium has a Tm lowering activity and a Td raising activity, and sodium and potassium have a Td raising activity while magnesium and calcium have a Tm lowering activity.
The amount of metal compound added is different depending upon the kind of a metal compound, but 0.
01 to 3.
0 mmol, preferably 0.
1 to 2.
0 mmol of the metal compound based on 1 g of PVA is used
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Manufacturing Materials 
