Battery separator

The operation of Example 1 was repeated except that a fiber web was formed by a conventional wet-laid web-forming method from a slurry prepared by mixing and dispersing

(i) 40 mass % of high Young's modulus polypropylene fibers (melting point: 174.degree. C.; fineness=1.2 denier (fiber diameter=13.7 .mu.m); fiber length=10 mm; tensile strength=12 g / d; Young's modulus=850 kg / mm.sup.2 and thermal shrinkage ratio=7%) manufactured in the same manner as in Example 1 and

(ii) 60 mass % of sheath-core type fusible fibers (fineness 1.1 denier (fiber diameter=13.1 .mu.m); fiber length=5 mm; and tensile strength=3.5 g / d) wherein the core component was polypropylene while the sheath component (low-melting component) was high-density polyethylene (melting point: 135.degree. C.) similarly to Example 1. As a result, a separator (mass per unit area=60 g / m.sup.2 ; and thickness=0.15 mm) was manufactured.

The operation of Example 1 was repeated except that a hydrophilization was carried out by dipping a fused nonwoven fabric for 10 minutes into a 39.degree. C. fuming sulfuric acid solution (15% SO.sub.3 solution) to manufacture a separator (mass per unit area=60 g / m.sup.2 ; and thickness=0.15 mm).

A fiber web was manufactured by a conventional wet-laid web-forming method from a slurry prepared by mixing and dispersing

(i) 30 mass % of high Young's modulus polypropylene fibers (melting point: 174.degree. C.; fineness=1.2 denier (fiber diameter=13.7 .mu.m); fiber length=10 mm; tensile strength=12 g / d; Young's modulus=850 kg / mm.sup.2 ; and thermal shrinkage ratio=7%) manufactured in the same manner as in Example 1 and

(ii) 70 mass % of sheath-core type fusible fibers (fineness=0.7 denier (fiber diameter=10.4 .mu.m); fiber length=5 mm; and tensile strength=3.5 g / d) where the core component was polypropylene while the sheath component low-melting component) was high-density polyethylene (melting point: 135.degree. C.).

Then this fiber web was heated for 10 seconds by an oven set to the temperature of 135.degree. C., and immediately thereafter pressurized (2.5 N / cm) by a water-cooled cooling roll to manufacture a fused nonwoven fabric wherein the fibers were fused with the sheath