Method of forming an improved battery separator

#The subject invention is directed to battery separators which exhibit a high degree of conductivity and inhibition to dendrite formation and which are capable of being formed in an economically improved manner.

#Storage batteries, in general, utilize either acid or alkaline electrolyte with compatible electrode systems. The term "acid battery system" or "alkaline battery system", as used in the present application, refers to battery systems which utilize, respectively, an acidic or an alkaline solution as the electrolyte. An example of an acid battery system is lead acid batteries which are in common use, which examples of alkaline battery systems are those which use silver-cadmium or nickel-zinc electrodes in an alkaline solution such as an aqueous solution of potassium hydroxide.

#Because of their high energy density, alkaline batteries, such as nickel-zinc secondary alkaline battery system, have great potential for replacing the more conventional lead acid battery system in a number of terrestrial applications. However, extending the cyclic life of the battery beyond that presently attainable and reducing the cost of the cell components are required criterias which must be met to make the alkaline battery system an effective energy source.

#The following examples are given for illustrative purposes only and are not meant to be a limitation on the subject invention except as made in the claims appended hereto. All parts and percentages are by weight unless otherwise indicated.

#A battery separator was formed by introducing into a Brabender mixer 44 parts of a commercially available styrene/butadiene/styrene triblock copolymer crumb material which has a 30:70 styrene:butadiene ratio, contains no plasticizer or oil, has a melt index of 1 gm/10 min, Condition G, a Brookfield viscosity (25 wt. % in Toluene) of 4000 at 25.degree. C., and a density of 0.94 gm/cc, with 54 parts a commercial TiO.sub.2 powder (DeGusso P-25) having a surface area of 65 m.sup.2 /gm and a density of 4.3 gm/cc, a rubber modifier or 2 parts of a polyester condensation product of azelaic acid and propanediol (Emergy Industries P-9720), and 0.5 part of tetra-bis methylene-3-(3,5-ditertiary-butyl-4-hydroxyphenyl)propionate methane. The materials were mixed at 160.degree. C. at 50 RPM in two passes until a substantially homogeneous mixture was obtained.

#Films of the material were formed by pressing small amounts of the resultant formulation in a Walash press at approximately 1,600 psi with both plates of the press being maintained at 145.degree. to 150.degree. C. The resultant film has a thickness of approximately 10 mils and is free of pinholes and imperfections, as observed. Random sections of the surface and cross-sectional area of the resultant film were observed using standard technique of electron microscopy and showed the film to be substantially free of pores.