Battery separator, and method for producing same

A battery separator comprising:

• a porous membrane A comprising a polyolefin resin, and a porous membrane B laminated thereon comprising a fluororesin and inorganic particles or cross-linked polymer particles,
• wherein the particles are contained in an amount of 80 wt % to 97 wt % of the porous membrane B and have an average diameter being not less than 1.5 times and less than 50 times the average pore size of the porous membrane A, and Expression 1 and Expression 2 are satisfied:
• 0.01≦absT(1200)≦0.30 (1)
• absT(1200):
• Absorbance of an absorption having a peak at or near 1,200 cm −1 per 10 thickness of the porous membrane A, as measured by infrared spectroscopy (transmission method) after peeling the porous membrane B off the porous membrane A;
• and
• 0.001≦absR(1200)≦0.030 (2)
• absR(1200):
• Absorbance of a maximum peak at or near 1,200 cm −1, as measured by infrared spectroscopy (reflection method) on the surface of the porous membrane A that is opposite to the porous membrane B.