PRODUCTION OF AIR PERMEABLE COMPOSITE SHEET

PURPOSE:To simultaneously perform the perforation of a thermoplastic resin film and the bonding thereof to a porous base material such as a nonwoven fabric, by using two porous base materials having specific roughness values and specific void ratio values and setting the thickness of a thermoplastic resin layer to the average specific roughness value of both porous base materials. CONSTITUTION:As the properties of a porous base material, it is pref. that surface roughness is 1-15mum, a thickness of a fiber is 1-20mumphi and a void ratio being the index of fiber density is 96% or less. Porous base materials A, B may be the same or different but the thickness of a molten resin film 2 is set to 5 times or less of the average Ra-value of both porous base materials A, B. The molten resin film 2 extruded from a T-die 1 is held between the porous base materials A3, B4 to be bonded under pressure by a cooling roll 5 and a rubber roll 6 and, at the same time, the molten resin film 2 is perforated by the effect of the surface roughness of the porous base materials A, B and the whole is taken up as an air permeable composite sheet 7 having a sandwich structure.