Multilayer breathable microporous film with reinforced impermeability to liquids and production method

A process for producing a multilayer polyolefinic film having simultaneously the properties of being water vapor permeable and of having a liquids reinforced impermeability, said process comprising the steps of:

• coextrusion from a die of polyolefinic polymers and/or copolymers mixtures, one of which at least contains inorganic fillers, to form a multilayer precursor film,
• stretching of the precursor film to form a breathable multilayer film,
• characterized in that said precursor film is a base multilayer film, comprising at least two contiguous layers of same polyolefinic composition, having at least the structure “B”-“B”, associated with at least one other polyolefinic layer having a composition different from that of at least two contiguous layers “B”-“B”.

A process for producing a multilayer polyolefinic film with a multilayer structure having simultaneously a combination of the properties, of being water vapor permeable and of having a liquids reinforced impermeability, said process comprising the steps of:

• coextrusion from a die of at least two contiguous layers of same polyolefinic composition comprising mineral fillers to form a multilayer base film having at least the following structure:
• “B”-“B”, with at least one other polyolefinic layer having another specific property in order to form a precursor film of at least three layers having, as a minimum, the following structure “A”-“B”-“B” or “C”-“B”-“B” where “A” is a specific skin layer, “B” is one of the base layers and “C” is a specific skin/adhesion layer.
• stretching of the multilayer precursor film to thereby form a water vapor permeable multilayer film, without loss of its liquids impermeability property.