Process for preparing powders from natural rubber and carbon black

摘要

Fine rubber powder is obtained by making an aqueous suspension of all the carbon black to be added, dividing into 3, mixing part 1 with a metal salt, especially aluminum sulfate, stirring with latex, acidifying to pH 5-8 and adding part 2, acidifying to 2-5 (preferably with sulfuric acid), reacting for 5-20 minutes, adding part 3 and working up the precipitate. A process for the production of finely divided, natural rubber-based powder (rubber powder) by precipitation from aqueous mixtures containing suspended carbon black (CB), water-soluble salts of Group IIa, IIb, IIIa or VIII metals and NR latex involves: (a) making a 0.5-10 wt% aqueous suspension of all the CB which is to be incorporated in the rubber; (b) dividing this suspension into 3 parts containing 10-80% (core CB), 10-70% (CB split 1) and 1-15% (CB split 2) of the total amount of CB respectively; (c) mixing the first part with 0.5-10 phr (parts per 100 parts rubber) metal salt as above (especially aluminum sulfate, Al2(SO4)3); (d) stirring this mixture thoroughly with the rubber latex; (e) reducing the pH to 5-8 and adding CB split 1) (preferably simultaneously); (f) further reducing the pH to 2.0 to below 5, preferably 2.5-4.5 by adding more acid, preferably sulfuric acid; (g) reacting for 5-20 minutes and then adding CB split 2; (h) separating the precipitated solid; (i) preferably washing; and (j) drying. An Independent claim is also included for non-sticky, finely divided rubber powder with a particle size of 300 microns to 5 mm, especially 500 microns to 2 mm, containing 30-250 (preferably 45-75) phr carbon black.