| abstract |
A microporous polyolefin membrane made of a polyethylene resin as a main component, and having (a) a shutdown temperature of 135° C. or lower, at which the air permeability measured while heating at a temperature-elevating speed of 5° C./minute reaches 1×10 5 sec/100 cm 3 , (b) an air permeability change ratio of 1×10 4 sec/100 cm 3 /° C. or more, which is a gradient of a curve representing the dependency of the above air permeability on a temperature at the air permeability of 1×10 4 sec/100 cm 3 , and (c) a meltdown temperature of 150° C. or higher, at which the air permeability measured while further heating after reaching the above shutdown temperature becomes 1×10 5 sec/100 cm 3 again. |