| 摘要 |
A method of manufacturing a multilayer polyolefinic film which is permeable to water vapor and impermeable to liquid by simultaneous extrusion of at least three layers At least three polyolefinic thermoplastic layers are simultaneously extruded in a structure A, B, C or A, B, A or C, B, C, where A is an outer layer, B is an central layer and C is an outer or adhesion layer to form a precursor film which is then drawn out into a film. Layer A is a thermoplastic polyolefin copolymer and/or a grafted polyolefin polymer having a modulus E by ASTM 882 below 50 mPa, a melt flow index by ASTM D1238 of 1.5-10 g/10min and a water vapor transmission speed of at least 100 g/m<2>/24hours at 38 deg C and 90% RH. Layer B contains a thermoplastic polyolefinic homo- or copolymer, at least one particulate filler and optionally one or more elastomers. Layer C contains at least one adhesion agent and/or a thermoplastic polyolefinic homo- or copolymer and at least one particulate filler. The ratio of the individual layers to the total thickness is A 5-30%, B 40- 90% and C 5-30%. An Independent claim is included for a breathable microporous multilayer film, obtained by the method, with a water vapor transport rate of at least 500 (preferably 2000- 5000) g/m<2>/24 hours at 38 deg C and 90% RH without loss of impermeability to liquids including one laminated to a non-woven fabric.
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