Particle size control of SBR/carbon black powder

Claim 1

A process for the production of tack-free, pourable, filler containing elastomer powder which comprises (a) dispersing a reinforcing type carbon black filler in water, said carbon black being selected from the group consisting of high abrasion furnace (HAF), intermediate super abrasion fuurnace (ISAF), and fast extrusion furnace (FEF), (b) mixing the thus dispersed carbon black filler with an elastomer latex, said latex being selected from the group of styrene/butadiene rubbers, acrylonitrile/butadiene rubbers, polypropylene rubbers, polybutadiene rubbers, polyisoprene rubbers, and copolymers of dimethyl butadiene/butadiene rubbers, the improvement comprising (c) coagulating the thus produced mixture of elastomer latex and carbon black with a two-stage coagulating process, comprising first coagulating the mixture of elastomer latex and carbon black by the use of a dilute salt/acid solution at a pH 3-5, at temperatures varying from 30 to 90° C. wherein the concentration of salt varies between 2-20 parts per hundred of rubber, and the concentration of the salt in the solution may vary between 0.1 and 1.0 percent, and then conducting the second stage coagulation of the mixture by adding sufficient alum to give a concentration of 1 to 10 parts of alum per 100 parts of rubber, adjusting the pH of the mixture to a pH of 2 to 3 with dilute sulfuric acid, (d) partitioning the thus coagulated suspension with a coating resin by adding a dilute solution of a coating resin to the coagulated particles formed during the first stage coagulation while maintaining the temperature between 70° C. and 90° C. and (e) filtering, washing and drying the resultant powder dispersion, an additional improvement comprising using as a coating resin a mixture of a styrene/butadiene resin and a styrene/α-methylstyrene or a polystyrene resin wherein the weight ratio of the styrene/butadiene resin to the styrene/α-methylstyrene or polystyrene resin ranges between 4/1 and 1/4, said resins containing a mixture of added surfactants, the first being sodium lauryl sulfate and the second being a nonionic isooctyl phenoxy polyethoxy ethanol which contains 10 moles of ethylene oxide in the polyethoxy portion thereof, said mixture of surfactants being added in an amount at least 4 percent by weight and being in a weight ratio of sodium lauryl sulfate to the nonionic surfactant ranging from 2/1 to 1/2.