| 摘要 |
A process for preparing synthetic rubber master batches containing carbon black from which tyre-treads having improved physical properties may be manufactured, comprises subjecting wet synthetic rubber crumb or coagulum, e.g. containing 30% to 60% moisture, preferably butadiene-styrene oracrylonitrile polymer adjusted to a pH between 2 and 6, to mastication and shearing, e.g. for 1/2 to 2 minutes, in an internal mixer under a pressure of 50 to 120 p.s.i., thereby reducing its moisture content to less than 2% in a single mixing cycle of less than 6 minutes. The escape of steam &c. from the mixer is facilitated by the lifting of the mixer ram (80 to 120 r.p.m. rotor speed) for the purpose of adding in less than half a minute 30 to 90 parts of fine reinforcing carbon black, e.g. H.A.F. or S.A.F. black, per hundred parts of rubbery material, the black having a particle size of 10 to 40 millimicrons and a surface area of at least 70 sq. metres per gram. The moisture content of the material in the mixer at the time of adding the black is preferably 5 to 15% of the total weight of rubbery material and the mixer ram is allowed to "float" under its own weight for 1/2 to 1 minute before continuing the mastication and dispersion of the black to a temperature of at least 320 DEG F., but not higher than 375 DEG F. If desired, the rubber/black mixture can be heated during mastication. Preferably 5 to 60 parts of a compatible hydrocarbon oil are added to the wet crumb during the mixing cycle so as to give a raw Mooney viscosity of between 40 and 90 to the dry polymer-oil mixture compared with a figure of 100 to 200 for the dry polymer, and preferably an organic liquid antoxidant is also added before the black. Other compounding ingredients may be added after the black but preferably the addition of sulphur and accelerator i.e. curing additives, is effected after cooling in a second mixing operation. Specifications 737,086 and 794,770 are referred to. |
