Storage battery separator

DETAILED DESCRIPTION OF THE INVENTION It has been hitherto known in general that synthetic monofilament fiber, that is, a mass of synthetic monofilament fibers, can be formed into fibril-formed fiber by means of a beater or a refiner.
However, a storage battery separator for attaining the foregoing objects cannot be obtained even if glass fiber, that is, a mass of glass fibers, is simply mixed with the synthetic fibril-formed fiber.
A fibril-formed fiber of the synthetic fibril-formed fiber comprises a trunk fiber part having innumerable fine fibers spread therefrom in the form of branches and, therefore, it can be presumed that there is such tendencies that intertwining of the fibril-formed synthetic fiber and the glass fiber become better and more tight through the innumerable branched fine fibers thereof than the conventional case using the synthetic monofilament fiber and that the maximum pore size of fine pores formed between those intertwined fibers becomes smaller, and at the same time there can be obtained innumerable fine pores which are finer in size and are increased in number over the conventional case.
However, it has been found as a result of many experimental efforts that, in fact, it is not always possible to obtain better results than in the cases of conventional separators according to change of the value of freeness or an additional amount of fibril-formed fibers.
These experiments were carried out as follows: A mass of acrylic monofilament fibers by a conventional beater was beated while a beating time and a beating pressure were being changed at every batch, so that there were obtained various kinds of acrylic fibril-formed fibers which are different in various values of freeness ranging from 100 to 600 c.
c.
at every batch.
In regard to every kind of those the fibril-formed acrylic fibers, a mass of the fibril-formed acrylic fibers was mixed with a mass of glass fibers of 2 m.
sup.
2 /g in specific surface area while the addition or mixing amount of the acrylic fibers was changed in the range of 2-20 wt% at every batch, and every resultant mixture thereof was formed by a conventional paper making machine into a separator sheet of 1 mm in thickness and with a grammage of 180 g/m