Process for continuously producing heat-vulcanizable silicone rubber compound

A process for continuously producing a heat-vulcanizable silicone rubber compound which exhibits reduced plasticization reverse/crepe hardening which consists essentially of the steps of:

• (i) mixing (A) a diorganopolysiloxane having a viscosity as measured at 25.degree. C. of 1.times.10.sup.5 cP or more, (B) an inorganic filler and (C) a processing aid, as basic ingredients, by a high-speed mechanical shearing means, thereby to obtain a flowable particulate mixture which does not contain a vulcanizing agent and in which each ingredient is present in a substantially uniformly and finely dispersed state, and
• (ii) continuously feeding, at a constant feed rate, said particulate mixture to a continuously kneading and extruding machine through a feed opening thereof, which machine has two screws rotating in the same direction, wherein the screws of said continuously kneading and extruding machine are double-threaded or triple-threaded screws, thereby to obtain a homogenous silicone rubber compound from a discharge opening of said kneading and extruding machine, wherein said flowable particulate mixture is kneaded in the continuously kneading and extruding machine while the mixture is heated at 100 to 300.degree. C. and wherein cooling is conducted at the rear stage of the kneading step with the kneading and extruding machine, whereby the cooling diminishes the plasticization reverse/crepe hardening of the discharged silicone rubber compound.

A process for continuously producing a heat-vulcanizable silicone rubber compound which exhibits reduced plasticization reverse/crepe hardening which consists essentially of the steps of:

• (i) mixing (A) a diorganopolysiloxane having a viscosity as measured at 25.degree. C. of 1.times.10.sup.5 cP or more, (B) an inorganic filler and (C) a processing aid, as basic ingredients, by a high-speed mechanical shearing means, thereby to obtain a flowable particulate mixture which does not contain a vulcanizing agent and in which each ingredient is present in a substantially uniformly and finely dispersed state, and
• (ii) continuously feeding, at a constant feed rate, said particulate mixture to a continuously kneading and extruding machine through a feed opening thereof, which machine has two screws rotating in the same direction, wherein the screws of said continuously kneading and extruding machine are double-threaded or triple-threaded screws, thereby to obtain a homogeneous silicone rubber compound from a discharge opening of said kneading and extruding machine, wherein said flowable particulate mixture is kneaded in the continuously kneading and extruding machine while the mixture is heated at 100 to 300.degree. C. and wherein cooling is conducted at the rear stage of the kneading step with the kneading and extruding machine, wherein said diorganopolysiloxane (A) is formed into pellets by means of a rotary chopper provided at the discharge opening of a feed pump for said diorganopolysiloxane (A), before said diorganopolysiloxane (A) is mixed with the ingredients (B) and (C) to form the flowable particulate mixture, whereby the cooing diminishes the plasticization reverse/crepe hardening of the discharged silicone rubber compound.