Microporous laminated membrane and method for producing the same

A microporous laminated membrane comprising:

• a nonwoven-fabric substrate;
• and
• a microporous membrane on at least one side of the nonwoven-fabric substrate,
• the microporous membrane comprising a multiplicity of interconnecting micropores, the micropores having an average pore diameter of from 0.01 to 10 μm,
• the microporous membrane having an arithmetic mean surface roughness Sa of 0.5 μm or less,
• the microporous laminated membrane having an air permeability of from 0.5 to 30 seconds,
• the microporous laminated membrane having a tensile strength of 4.0 N/15 mm or more,
• the microporous laminated membrane not undergoing interfacial peeling between the substrate and the microporous membrane as a result of a tape peel test,
• wherein the tape peel test is performed in a manner as follows:
• a masking tape [trade name Film Masking Tape No. 603 (#25) supplied by Teraoka Seisakusho Co., Ltd., having a width of 24 mm] is applied onto a microporous membrane surface of the microporous laminated membrane, compression-bonded to the microporous membrane using a roller having a diameter of 30 mm under a load of 200 gf to give a bonded assembly, and the bonded assembly is subjected to T-peel using a tensile tester at a peel rate of 50 mm/min;
• and
• wherein the arithmetic mean surface roughness Sa is measured by a method as follows:
• a surface profile of the microporous membrane is measured by optical interferometry using Non-contact Surface Measurement System VertScan 2.0 (Ryoka Systems Inc.) to calculate the surface roughness, where the measurement is performed in an area of 250 μm by 188 μm, at an objective lens magnification of 50-fold, at a lens barrel size of 0.5 time the body length, using a no-relay zoom lens and a 530 White wavelength filter in a wave measurement mode in a field of view with a size of 640 μm by 480 μm.