Abstract: A separator for a lead-acid battery enabling the lead acid battery to infallibly have a predetermined capacity after the initial charging and a prolonged service life by limiting the maximum quantity of reducing substance liberated or produced from the separator at or below a given level. The separator for a lead-acid battery comprising a porous membrane made mainly from a polyolefin resin, an inorganic powder and a mineral oil and containing a surface active agent as an auxiliary material, characterized in that the amount of any reducing substance liberated or eluted after 24 hours of electrolysis carried out at about 25° C. with a direct current of 1.2 A by using an electrolytic cell composed of the porous membrane, a positive electrode, a negative electrode and diluted sulfuric acid is 1.0 ml or less per 100 cm2 when calculated from the consumption of a (1/100)N potassium permanganate solution per 100 cm2 of the porous membrane.

Abstract: A separator for a lead-acid battery enabling the lead acid battery to infallibly have a predetermined capacity after the initial charging and a prolonged service life by limiting the maximum quantity of reducing substance liberated or produced from the separator at or below a given level. The separator for a lead-acid battery comprising a porous membrane made mainly from a polyolefin resin, an inorganic powder and a mineral oil and containing a surface active agent as an auxiliary material, characterized in that the amount of any reducing substance liberated or eluted after 24 hours of electrolysis carried out at about 25° C. with a direct current of 1.2 A by using an electrolytic cell composed of the porous membrane, a positive electrode, a negative electrode and diluted sulfuric acid is 1.0 ml or less per 100 cm2 when calculated from the consumption of a (1/100)N potassium permanganate solution per 100 cm2 of the porous membrane.

Abstract: A separator for a valve regulated lead acid battery is composed mainly of fine glass fibers and also contains inorganic powder, beaten natural pulp, and heat-weldable organic fibers. The heat-weldable organic fibers have a fineness of 1.5 d (deniers) or less and a fiber length of 1 mm or more, and the amount of the heat-weldable organic fibers is from 3% to 15% by weight. A valve regulated lead acid battery employs the separator.

Abstract: A separator for a valve regulated lead acid battery is composed mainly of fine glass fibers 1 and also contains inorganic powder 3, beaten natural pulp 2, and heat-weldable organic fibers 4. The heat-weldable organic fibers 4 have a fineness of 1.5 d (deniers) or less and a fiber length of 1 mm or more, and the amount of the heat-weldable organic fibers is from 3% to 15% by weight. The separator is excellent in resistance against a short circuit between a positive electrode plate and a negative electrode plate of the battery such as an electrochemical short circuit, for example a short circuit due to lead penetration, and a mechanical short circuit. The separator is also excellent in folding endurance, in durability against repetition of folding, and in tearing strength, and allows easy formation of envelope-like separator, thus preventing active materials from being coming off at the sides thereof.