Masticating and heating of mixtures comprising wet rubber crumb, carbon black and softener

Claim 1

IN A MULTI-STAGE PROCESS OF MAKING A VULCANIZABLE TIRE TREAD COMPOSITION COMPRISING 100 PARTS BY WEIGHT OF A COPLYMER OF A MAJOR PORTION OF BUTADIENE AND A MINOR PORTION OF STYRENE HAVING A RAW MOONEY VISCOSITY OF AT LEAST 100. 30 TO 90 PARTS OF FINE REINFORCING CARBON BLACK HAVING A SURFACE AREA OF ABOUT 60 TO 180 SQURE METERS PER GRAM, ABOUT 5 TO 60 PARTS OF A COMPATIBLE PLASTICIZING OIL, ABOUT 2 TO 8 PARTS OF ZINC OXIDE, ABOUT 1 TO 3 PARTS OF STEARIC ACID, LESS THAN 5 PARTS OF AN ANTIOXIDANT, A VULCANIZATION ACCELERATOR, AND ABOUT 1 TO 4 PARTS OF SULFUR, SAID COMPOSITION BEING FORMED FROM A WET RUBBER CRUMB COMPRISING A COAGULUM OF SAID COPOLYMER WHOSE MOISTURE CONTENT WAS REDUCED AT LEAST 50% BY MECHANICAL SEPARATION OF WATER THEREFROM, SAID TIRE TREAD COMPOSITION BEING FORMED BY REDUCING THE MOISTURE CONTENT OF SAID WET CRUMB TO BELOW 2% MIXING SAID FINE REINFORCING CARBON BLACK WITH THE RUBBER IN THE FIRST MIXING STAGE OF AN INTERNAL MIXER, THEREAFTER COOLING THE RUBBER MIXTURE AND MIXING THE SULFUR AND ACCELERATOR WITH THE RUBBER IN A LATER MIXING STAGE TO PRODUCE SAID VULCANIZABLE TIRE TREAD COMPOSITION, THE IMPROVEMENT WHICH COMPRISES: MIXING SAID FINE REINFORCING CARBON BLACK WITH SAID WET CRUMB IN SAID MIXER DURING THE FIRST MIXING STAGE WHILE THE MOISTURE CONTENT OF THE RUBBER IS ABOUT 5 TO ABOUT 15%. ADDING COMPOUNDING INGRDIENTS OF SAID RUBBER COMPOSITION TO THE WET CRUMB BEFORE THE CARBON BLACK IS COMPLETELY DISPERSED IN THE RUBBER, SUBJECTING THE RUBBER MIXTURE TO MASTICATION AND AN INTENSE SHEARING ACTION IN THE CLOSED RECEPTACLE OF SAID MIXER AT A ROTOR SPEED OF 50 TO 150 REVOLUTIONS PER MINUTE AND A PRESSURE OF ABOUT 60 TO 120 POUNDS PER SQUARE INCH TO DISPERSE THE CARBON BLACK AND THE COMPOUNDING INGREDIENTS, TO INCREASE THE TEMPERATURE TO 320* TO 575*F. AND TO REDUCE THE MOISTURE CONTENT OF THE RUBBER TO LESS THAN 1% AT THE END OF THE FIRST MIXING STAGE, COOLING THE RUBBER MIXTURE, AND THEREAFTER ADDING AND DISPERSING THE SULFUR AND ACCELERATOR TO COMPLETE THE TIRE TREAD COMPOSITION DURING A SECOND AND FINAL MIXING CYCLE, ESSENTIALLY ALL OF THE COMPOUNDING INGREDIENTS OF SAID COMPOSITION, EXCEPT THE SULFUR AND ACCELERATOR, BEING ADDED BEFORE THE END OF THE FIRST MIXING CYCLE.