Silicone manufacturing

A process for the preparation of an uncatalyzed (fluoro)silicone rubber base which is prepared by the introduction of reinforcing fillers and optionally hydrophobing treating agents into one or more silicone polymers, fluorosilicone polymers or copolymers thereof, in each instance the one or more silicone polymers, fluorosilicone polymers or copolymers thereof having a Williams plasticity of at least 100 mm/100 in accordance with ASTM D-926-08, which process comprises the steps of:

• (i) introducing, as a first starting ingredient the one or more silicone polymers, fluorosilicone polymers or copolymers thereof in each instance having a Williams plasticity of at least 100 mm/100 in accordance with ASTM D-926-08, into a mixing chamber of a mixer at approximately 25° C. optionally in an inert atmosphere and mixing;
• (ii) gradually introducing, as a second starting ingredient, one or more reinforcing fillers and optionally a third starting ingredient, one or more hydrophobing filler treating agents into the mixing chamber of the mixer while continuing mixing until the mixer has been charged with a predetermined amount of reinforcing filler of at least 38 wt. % of the total base starting ingredients to form a base mixture;
• (iii) optionally, maintaining the temperature of the base mixture in the mixing chamber within a pre-determined range of from 100° C. and 200° C. for a period of up to 6 hours to remove volatiles from the step (ii), base mixture, to form a step (iii) base mixture which step (iii), when utilized, may be carried out under vacuum;
• (iv) cooling the resulting step (ii) base mixture or step (iii) base mixture to a temperature between 25° C. and 120° C.;
• and prior to, during or subsequent to step (iv);
• (v) reducing the wt. % of reinforcing filler in the step (ii) base mixture or step (iii) base mixture to a pre-defined amount by mixing the step (ii) base mixture or step (iii) base mixture with additional one or more silicone polymers, fluorosilicone polymers or copolymers thereof having a Williams plasticity of at least 100 mm/100 in accordance with ASTM D-926-08, to form an uncatalyzed (fluoro)silicone rubber base;
• wherein the mixer utilized for at least steps (i), (ii) and (iii) is a conical screw dump extruder comprising a conical twin screw mixing chamber, the conical twin screw mixing chamber housing two counter-rotating conical screws converging towards an extrusion die having an entrance and an exit wherein passage through the extrusion die is controlled by an occlusion means such that the exit of the extrusion die is adapted to be closed by the occlusion means until the product of step (iii), (iv) or (v) is to be extruded from the conical screw dump extruder and opened subsequent to step (iii), (iv) or (v) if or when the uncatalyzed (fluoro)silicone rubber base is to be further processed or stored outside the conical screw dump extruder such that during mixing the base mixture is driven towards extrusion die by the pair of counter-rotating conical screws, and then forced to go back when the extrusion die is closed by the occlusion means and then subsequent to step (iii), (iv) or (v) is opened, to allow the product of the step (iii), (iv) or (v) to be extruded through the extrusion die for further processing and/or storage.