Pulverulent rubbers comprising carbon black fillers and based on rubbers present in organic solvents, process for their preparation, and applications

A process for preparing fine-particle, free-flowing rubber powders composed of carbon black fillers and a rubber, which comprises:

• having prepared the rubber by solution polymerization which is present in an organic solvent solution:
• a) first suspending a carbon black in an appropriate amount as a filler for the rubber in water by means of a high-shear mixing device, without any other additives, and setting the solids content of the suspension to 0.5-15%;
• b) separating some of the suspended carbon black from the main amount of carbon black, the amount of carbon black separated (in suspension) in this step ranging from 0.5-20%, based on the total amount of carbon black in the finished product;
• c) finally heating the suspension which comprises most of the carbon black to a temperature approximately equal to the boiling point of the organic solvent in which the polymer has been dissolved;
• d) introducing the rubber solution into the carbon black suspension, with stirring, and in parallel with this introduction, removing solvent by distillation at atmospheric pressure or in vacuo, with the thermal energy necessary for the distillation being supplied to keep the temperature of the reaction mixture in the region where evaporation of the solvent is possible, and in this process converting the rubber/filler composite from a two-phase system to a single-phase system, and removing the organic phase by distillation in water to transfer the rubber into the aqueous carbon black suspension and form the rubber/filler composite, whereupon, once the solvent has been removed, the product is a rubber/carbon black composite in an aqueous single-phase system;
• e) mixing the aqueous suspension comprising the product with the carbon black suspension retained in b), with stirring;
• f) treating the suspension of d) and e) with 1-15 parts of a rubber emulsion, based on a total of 100 parts of rubber;
• g) adjusting the pH of the suspension of f) with a Brönsted or Lewis acid to 2-7, where steps e)-f) of the process form, around each grain of rubber powder, an effective carbon black release layer which is mechanically anchored to the solution-polymer-based carbon black/rubber core particle;
• h) removing most of the water from the product;
• and
• i) drying the moist product to a residual moisture level <2%.