Process for preparing rubber compositions and articles made therefrom
A process for preparing a rubber composition comprises: (a) forming a mixture of: (i) at least one thiocarboxyl-functional hydrolyzable silane, (ii) at least one rubber containing carbon-carbon double bonds, (iii) at least one silane-reactive filler, (iv) at least one activating agent, and (v) water; (b) mixing the composition formed in step (a) under reactive-mechanical-working conditions and in the absence of vulcanizing agent(s); (c) adding at least one vulcanizing agent (vi) to the composition of step (b); (d) mixing the composition of step (c) under non-reactive-mechanical-working conditions; and, (e) optionally, curing the rubber composition of step (d).
1. A process for preparing a rubber composition which comprises:
a) providing a mixture of:
(i) at least one thiocarboxyl-functional hydrolyzable silane having the general formula:
(R 1 O) 3-a (CH 3 ) a Si—R 2 SC(═O)R 3
wherein:
each occurrence of R 1 is independently an alkyl group containing from 2 to 4 carbon atoms;
R 2 is a divalent alkylene group containing from 1 to 10 carbon atoms;
R 3 is an alkyl group containing from 5 to 9 carbon atoms; and,
a is 0 to 2, and in the amount of from 0.2 to 20 weight percent, based on the total weight of the rubber composition;
(ii) at least one rubber containing carbon-carbon double bonds selected from the group consisting of polybutadiene rubber, emulsion polymerization-prepared styrene/butadiene copolymer rubber, organic solution polymerization-prepared styrene/butadiene rubber, in the amount of from 30 to 98 weight percent, based on the total weight of the rubber composition;
(iii) at least one silane-reactive filler having a BET surface area between 100 m 2 /g and 600 m 2 /g in the amount of from 2 to 70 weight percent, based on the total weight of the rubber composition;
(iv) at least one activating agent, wherein said activating agent (v) is at least one guanidine-containing base of the general formula:
R 4 R 5 N—C(═NR 6 )—NR 7 R 8
wherein each occurrence of R 4 , R 5 , R 6 , R 7 and R 8 is independently hydrogen or a monovalent hydrocarbyl selected from the group consisting of alkyl, aryl, aralkyl and arenyl containing from 1 to 10 carbon atoms in the amount of from 0.2 to 5 weight percent, based on the total weight of the rubber composition; and
(v) water, wherein said water (v) is added in an amount of from 2 to 6 weight percent to the silane-reactive filler (iii) to form a hydrated silane-reactive filler, where the amount is based on the total weight of the hydrated silane-reactive filler,
wherein said thiocarboxyl-functional hydrolyzable silane is added to the rubber mix during the mixing of the rubber (ii);
b) subjecting the mixture provided in step (a) to reactive-mechanical-working conditions in the substantial absence of vulcanizing agent(s), wherein said reactive-mechanical-working conditions are an elevated temperature of from 140° C. to 180° C., residence times and shear prevailing with a mechanical-working apparatus selected from the group consisting of an extruder, intermeshing mixer, and tangential mixer;
c) cooling the mixture of step (b) to a temperature of 50° C. or less;
d) adding at least one vulcanizing agent (vi) in the amount of from 0.2 to 5 weight percent, based on the total weight of the rubber composition to the composition of step (c) and a combination of at least one primary accelerator used in the amount of from 0.5 to 4 parts by weight per hundred parts rubber and at least one secondary accelerator used in the amount of from 0.05 to 3 parts by weight per hundred parts of rubber;
e) mixing the composition of step (d) under non-reactive-mechanical-working conditions, wherein said non-reactive-mechanical-working conditions comprises a temperature of from 30° C. to 100° C. and a residence time of from 0.5 to 30 minutes; and
f) optionally, curing the rubber composition of step (e) at a temperature of from 130° up to 200° C.
2. The process of claim 1 wherein R 1 is a straight chain alkyl of 2 to 4 carbon atoms, R 2 is a straight chain alkylene of from 3 to 6 carbon atoms and R 3 is a straight chain alkyl of from 5 to 9 carbon atoms.
3. The process of claim 2 wherein R 1 is an ethyl or n-propyl, R 2 is n-propylene and R 3 is n-hexyl, n-heptyl or n-octyl.
4. The process of claim 1 wherein thiocarboxyl-functional hydrolysable silane (i) is at least one member selected from the group consisting of hexanethioic acid S-[2-(triethoxysilanyl)-methyl]ester; heptanethioic acid S-[2-(diethoxy-methyl-silanyl)-ethyl]ester; heptanethioic acid S-[2-(triethoxysilanyl)-ethyl]ester; heptanethioic acid S-[2-(tributoxysilanyl)-ethyl]ester; heptanethioic acid S-[3-(diethoxy-methyl-silanyl)-propyl]ester; heptanethioic acid S-[2-(triethoxysilanyl)-propyl]ester; octanethioic acid S-[3-(diethoxy-methyl-silanyl)-propyl]ester; octanethioic acid S-[3-(triethoxysilanyl)-propyl]ester; octanethioic acid S-[3-(triethoxysilanyl)-hexyl]ester; octanethioic acid S-[3-(ethoxy-dimethyl-silanyl)-propyl]ester; decanethioic acid S-[3-(diethoxy-methyl-silanyl)-propyl]ester; and, decanethioic acid S-[3-(triethoxysilanyl)-propyl]ester.
5. The process of claim 1 wherein rubber (ii) is at least one rubber is selected from group consisting of emulsion polymerization-prepared styrene/butadiene copolymer rubber and organic solution polymerization-prepared styrene/butadiene rubber.
6. The process of claim 1 wherein rubber (ii) is at least one polybutadiene rubber.
7. The process of claim 6 wherein rubber (ii) is at least one polybutadiene rubber selected from the group consisting of cis-1,4-polybutadiene, 35-50 percent vinyl content vinyl polybutadiene rubber and 50-75 vinyl content vinyl polybutadiene rubber.
8. The process of claim 1 wherein rubber (ii) is at least one emulsion polymerization-derived styrene/butadiene rubber selected from the group consisting of emulsion polymerization-derived styrene/butadiene rubber of 20 to 29 weight percent bound styrene and emulsion polymerization-derived styrene/butadiene rubber of 30 to 45 weight percent bound styrene.
9. The process of claim 1 wherein the organic solution polymerization-prepared styrene/butadiene rubber of 5 to 50 weight percent bound styrene.
10. The process of claim 1 wherein the organic solution polymerization-prepared styrene/butadiene rubber has from 9 to 36 weight percent bound styrene.
11. The process of claim 1 wherein rubber (ii) is at least one tin-coupled styrene/butadiene rubber.
12. The process of claim 1 wherein rubber (ii) is at least one silane-functionalized organic solution polymerization-prepared 1,4-polybutadiene rubber.
13. The process of claim 1 wherein silane-reactive filler (iii) is at least one member selected from the group consisting of metal oxide, silica and siliceous material.
14. The process of claim 13 wherein silane reactive filler (iii) is at least one member selected from the group consisting of pyrogenic silica, precipitated silica, hydrated silica, titanium dioxide, alumina, aluminosilicate, clay and talc.
15. The process of claim 14 wherein the mixture of step (a) further comprises a filler that is essentially non-reactive with thiocarboxyl-functional hydrolyzable silane (i).
16. The process of claim 15 wherein the non-reactive filler is at least one member selected from the group consisting of porous organic polymer, carbon black, diatomaceous earth and silica characterized by a differential of less than 1.3 between the infrared absorbance at 3502 cm −1 taken at 105° C. and taken at 500° C.
17. The process of claim 1 wherein each R 4 , R 6 and R 8 is hydrogen and each R 5 and R 7 is an alkyl or aryl group containing up to 6 carbon atoms.
18. The process of claim 1 wherein the guanidine-containing base is at least one member selected from the group consisting of 1,3-dimethyl guanidine; 1,3-diethyl-guanidine; 1-methyl-3-phenyl guanidine; 1,3-diphenyl guanidine; 1,1,3,3-tetramethyl guanidine; 1 1,1,3,3-tetraphenyl guanidine; 1,1,3,3-tetrabutyl guanidine; and, 1,3-di-o-tolylguanidine.
19. The process of claim 1 wherein vulcanizing agent (vi) is at least one member selected from the group consisting of elemental sulfur and sulfur-donating compound.
20. The process of claim 1 wherein in step (a), the mixture contains from 0.5 to 3 weight percent activating agent (iv) based on the total weight of the rubber composition.
21. The process of claim 1 wherein in step (a), the mixture contains from 0.5 to 15 weight percent thiocarboxyl-functional hydrolyzable silane (i) based on the total weight of the rubber composition.
22. The process of claim 1 wherein in step (a), the mixture contains from 5 to 50 weight percent silane-reactive filler (iii) based on the total weight of the rubber composition.
23. The process of claim 1 , wherein the organic solution polymerized-prepared styrene-butadiene rubber is organic solution polymerized-prepared styrene-butadiene rubber functionalized by an alkoxysilane derivative or a tin derivative.
24. The process of claim 1 wherein the thiocarboxyl-functional hydrolyzable silane (i) is octanethioic acid S-[3-(triethoxysilanyl)-propyl] ester, the rubber (ii) is organic solution polymerization-prepared styrene/butadiene rubber or polybutadiene, the one silane-reactive filler (iii) is particulate precipitated silica having reactive surface silanols, and the activating agent (iv) is diphenyl guanidine.
25. The process of claim 1 wherein the thiocarboxyl-functional hydrolyzable silane (i) is octanethioic acid S-[3-(triethoxysilanyl)-propyl] ester, the rubber (ii) is emulsion polymerization-prepared styrene/butadiene copolymer rubber, organic solution polymerization-prepared styrene/butadiene rubber or polybutadiene, the one silane-reactive filler (iii) is particulate precipitated silica having reactive surface silanols, the activating agent (iv) is diphenyl guanidine, the vulcanizating agent is sulfur, the primary accelerator is a sulfonamide and the secondary accelerators is a guanidine, dithiocarbamate or thiuram compound.
26. The process of claim 1 wherein the mechanical-working apparatus is a tangential mixer.
27. The cured rubber resulting from step (e) of claim 1 .
28. The process of claim 1 wherein the mixture of step (a) further comprises a filler that is essentially non-reactive with thiocarboxyl-functional hydrolyzable silane (i).