High barrier biaxially oriented polypropylene film

摘要

A biaxially-oriented polypropylene film has at least one base layer contg. polypropylene with the following properties: (i) a statistical ave. for the isotactic block length between 2 chain breaks of at least 40; (ii) an n-heptane insols. fraction having a chain-isotacticity index (measured by 13C NMR spectroscopy) of at least 95 (esp. at least 97)%; (iii) an Mw/Mn ratio below 4, esp. below 2.7; (iv) an n-heptane soluble fraction below 1%; and (v) a water vapour transmission no more than 24/micron thickness g/m<2>.d and an O2 transmission no more than 34,000/meter thickness cm<3>/(m<2>.d.bar). Claimed prodn. is by multi-layer melt extrusion, followed by cooling on a roller and orienting at ratios 3-9:1 lengthwise and 4-12:1 transversely. Pref. the film is 4-100 microns thick,being solely of the above polypropylene layer(s) or having its thickness 40-60% made up of such layer(s). Any other layers (on one or both sides of the polypropylene base layer(s) are of polyolefins which can be heat-sealable. The various layers can also contain neutralising agents, stabilisers, antistats and/or anti-blocking agents. Appropriate polypropylene for the base layer(s) is obtd. using metallocene catalysts.