Method for preparing elastomer/silica composite
This invention relates to the preparation of a silica reinforced elastomer via preparation of a silica-elastomer masterbatch as a composite of synthetic silica and an emulsion polymerization prepared synthetic elastomer. Such masterbatch is prepared by introducing such silica and a silane into a latex of the synthetic elastomer and recovering the composite thereof The invention further includes a rubber composition of at least two elastomers wherein at least one of said elastomers is such masterbatched composite. A tire having a component of such rubber composition, particularly a tire tread, is specifically contemplated.
1. A method for preparing an elastomer/silica composite comprised of at least one elastomer and a homogeneously dispersed silica reinforcement therein and an emulsion of oil and an organosilane polysulfide dispersed therein which comprises, based upon parts by weight of an ingredient per 100 parts by weight rubber:
(A) preparing a water dispersion of a composite formed by blending an aqueous colloidal silica slurry, rubber latex comprised of colloidal elastomer particles therein, and an emulsion of oil and an organosilane polysulfide by blending:
(1) an aqueous suspension of negatively charged colloidal silica aggregates which contains from about 10 to about 100 phr of silica aggregates therein,
(2) an aqueous rubber latex which is comprised of water and colloidal particles of a diene-based rubber and which contains 100 phr of diene-based rubber colloidal particles therein, and
(3) an oil emulsion of an organosilane polysulfide having from 2 to 6, with an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge, which contains from 0.4 to about 4 phr of said organosilane polysulfide therein, wherein said organosilane component of said organosilane polysulfide is reactive with silanol groups contained on the surface of said silica aggregates, wherein the oil of said oil emulsion is chemically inert insofar as said organosilane polysulfide is concerned, wherein said oil emulsion protects said organosilane polysulfide from hydrolysis from exposure to the water of said aqueous emulsion of colloidal particles of said diene-based rubber, and
(B) recovering said elastomer/silica composite by coagulation to form a rubber composite.
2. The method of claim 1 wherein said aqueous rubber latex is a latex of an elastomer selected from the group consisting of at least one of cis 1,4-polyisoprene elastomer particles, styrene/butadiene elastomer particles and cis 1,4-polybutadiene elastomer particle.
3. The method of claim 1 wherein said organosilane polysulfide is of the general formula (I):
(OR) 3 —Si—R′—S x —R′—Si—(OR) 3 (I)
wherein R is selected from the group consisting of at least one of methyl and ethyl radicals and R′ is an alkylene radical having from 1 to 12 carbon atoms and x is a value of from 2 to 6 and an average of from 2 to 2.6 or from 3.5 to 4.
4. The method of claim 2 wherein said organosilane polysulfide is of the general formula (I):
(OR) 3 —Si—R′—S x —R′—Si—(OR) 3 (I)
wherein R is selected from the group consisting of the at least one of methyl and ethyl radicals and R′ is an alkylene radical having from 1 to 12 carbon atoms and x is a value of from 2 to 6 and an average of from 2 to 2.6 or from 3.5 to 4.
5. The method of claim 3 wherein said organosilane polysulfide contains an average of from 2 to 2.6 sulfur atoms in its polysulfidic bridge.
6. The method of claim 3 wherein said organosilane polysulfide contains an average of from 3.5 to 4 sulfur atoms in its polysulfidic bridge.
7. The method of claim 3 wherein said organosilane polysulfide is a bis(3-triethoxysilylpropyl)polysulfide.
8. The method of claim 5 wherein said organosilane polysulfide is a bis(3-triethoxysilylpropyl)polysulfide.