To enhance the steam and oxygen barrier properties of a biaxially stretched polypropylene film by specifying the average isotactic block length of polypropylene molecules, n-heptane insoluble and soluble fractions, a ratio of a wt. average mol.wt. to a number average mol.wt. in mol.wt. distribution, humidity permeability and oxygen permeability.
In polypropylene of a biaxially stretched polypropylene film, the average isotactic block length of polypropylene molecules between two structural carbon chain flaws exceeds 40 on an average and an n-heptane insoluble fraction measured by a 13C-NMR spectral method has a carbon chain isotactic index of at least 95%, a ratio of a wt. average mol.wt. Mw to a number average mol.wt. Mn in mol.wt. distribution is below 4 and an n-heptane soluble fraction is below 1%. The humidity permeability of the film is set to ≤24/thickness (μm) [g/m2.d] and the oxygen permeability thereof is set to ≤34000/thickness (m) [cm3/(m2.d.bar)].
DETOREFU BUTSUSHIYU
TOOMASU DORIIZU
GUNTAA SHIYUREEGURU
ANDOREASU BUINTAA
