Patent ID: 7063764

Claim:
A method for producing a polyolefinic double layer transpiring film which allows vapour and air to pass therethrough while being impermeable to liquids, said method comprising the steps of: bubble extruding a mix of a filler, which filler imparts transpirability upon stretching, and a polyolefin to form a tube; flattening the tube to obtain a double layer flat film having two layers; heating the double layer flat film to its softening temperature, wherein said heating of the double layer flat film to its softening temperature comprises first heating by conduction and then heating by irradiation; compressing the heated double layer flat film to unite the layers of the double layer film and thereby form a double layer laminate; then cooling the double layer flat film having united layers to a temperature between 8–30° C.; and then transversely and longitudinally stretching the cooled double layer flat film to impart transpirability to the double layer flat film.