Silica reinforced rubber composition containing a multi-functional group functionalized elastomer and tire with tread

Abstract

This invention relates to a rubber composition containing filler reinforcement comprised of precipitated silica with silica coupling agent therefore and conjugated diene-based elastomer which contains end-chain functionalization with multi-functional groups. The groups functionalizing the elastomer are multi-functional in the sense of containing one group reactive with at least one of said precipitated silica and silica coupling agent and another different group reactive with diene-based elastomers through sulfur cure of the rubber composition. A sulfur cured rubber composition containing said end-chain functionalization is provided. A tire is provided having a component comprised of said rubber composition. Representative of said tire component is a tire tread.

Claims

1. A rubber composition comprised of: (A) at least one conjugated diene-based elastomer comprising at least one of a high vinyl and low vinyl polybutadiene; (B) filler reinforcement for said rubber composition comprised of a combination of precipitated silica and rubber reinforcing carbon black, together with silica coupling agent having a moiety reactive with silanol groups on said precipitated silica and another different moiety interactive with said diene-based elastomers, wherein at least one conjugated diene-based elastomer is an end-chain functionalized diene-based elastomer, wherein the end-chain functionalized conjugated diene-based elastomer is a reaction product, absent an intermediary, of a diene elastomer terminated with an alkoxyorganosilane polysulfide comprised of the general formula:
(R.sup.1O).sub.3—Si—R.sup.2—S.sub.x—R.sup.2—Si—(OR.sup.1).sub.3 wherein R1 represents the same or different aliphatic hydrocarbon radicals containing from 1 to 12 carbon atoms, R2 represents an aliphatic hydrocarbon containing from 1 to 8 carbon atoms and x represents a value of from 1 to and including 8 such that the polysulfide has an average of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge; and wherein the multi-functional groups are exclusive of alkoxyorganomercaptosilanes and alkoxyaminosilanes.

2. The rubber composition of claim 1 comprised of (A) 100 phr of conjugated diene-based elastomers comprised of: (1) about 10 to about 90 phr of a diene-based elastomer containing at least one end-chain multi-functional group of comprised of an alkoxyorganosilane polysulfide of claim 1, and (2) about 90 to about 10 phr of at least one additional diene-based elastomer; and (B) about 40 to about 200 phr of the rubber reinforcing filler.

3. The rubber composition of claim 2 wherein, for said end-chain multi-functionalized elastomer, said end-chain group is a bis(3-trialkoxysilylalkyl) polysulfide.

4. The rubber composition of claim 3 wherein, for said end-chain multi-functional elastomer, at least one of said R.sup.1 radicals of said bis(3-trialkoxysilylalkyl) polysulfide is an ethyl radical.

5. The rubber composition of claim 4 wherein, for said end-chain multi-functional elastomer, said alkoxyorganosilane polysulfide is a bis(3-triethoxysilylpropyl) polysulfide.

6. The rubber composition of claim 1 wherein, for said end-chain multi-functional elastomer, at least one of said R.sup.1 radicals of said alkoxyorganosilane polysulfide is an ethyl radical.

7. The rubber composition of claim 1 wherein, for said end-chain multi-functional elastomer, said conjugated diene-based elastomer containing at least one of said end-chain polyfunctional groups is comprised of at least one of polymers of at least one of isoprene and 1,3-butadiene monomers and of styrene with at least one of isoprene and 1,3-butadiene monomers.

8. The rubber composition of claim 1, wherein said elastomers are comprised of a mixture of end-chain functionalized and non-functionalized elastomers wherein at least 50 percent of said elastomers of said mixture are said end-chain functionalized elastomer.

9. The rubber composition of claim 1 further comprising, based on parts by weight per 100 parts by weight of rubber (phr): (A) 100 phr of conjugated diene-based elastomers comprised of; (1) about 10 to about 90 phr of at least one of diene-based elastomer containing at least one end-chain multi-functional group comprised of an alkoxyorganosilane polysulfide of claim 1 , and (2) about 90 to about 10 phr of at least one additional diene-based elastomer exclusive of styrene containing elastomers, and (B) about 40 to about 200 phr of rubber reinforcing filler comprised of a combination of precipitated silica and rubber reinforcing carbon black, together with silica coupling agent having a moiety reactive with silanol groups on said precipitated silica and another different moiety interactive with said diene-based elastomers.

10. The rubber composition of claim 1 wherein said end-chain multi-functional elastomer is comprised of a plurality of elastomer chains terminated by the same multi-functional group.

11. The rubber composition of claim 1 wherein said rubber composition is a sulfur cured rubber composition.

12. A tire having a component comprised of the rubber composition of claim 1 wherein said rubber composition is a sulfur cured rubber composition.

13. The tire of claim 12 wherein said component is a tire tread.

Description

EXAMPLE I

Preparation of End-chain Multi-functional Group Functionalized Polybutadiene Elastomer

(1) In this Example, a butyl-lithium catalyst was used to synthesize an end-chain multi-functional group functionalized relatively low vinyl containing polybutadiene elastomer from 1,3-butadiene monomer.

(2) A bis(3-triethoxysilylpropyl) polysulfide was introduced in an excess amount to thereby terminate the polymerization and to functionalize the terminal chain end of the polybutadiene elastomer.

(3) The end-chain terminated polybutadiene was recovered from the hexane solvent by stream stripping.

(4) The resulting end-functionalized polybutadiene elastomer was comprised of about 40 percent cis 1,4-isometric content, about 50 percent isometric trans 1,4-content, and 10 percent vinyl 1,2-content and was therefore considered to be a low vinyl polybutadiene elastomer. It had a weight average molecular weight (Mw) of about 200,000 and a Mooney (ML1+4), 100° C., viscosity of about 45.

EXAMPLE II

Evaluation of End-chain Multi-functional Group Functionalized Polybutadiene Elastomer in Rubber Composition

(5) A control rubber composition was prepared and identified as rubber Sample A as a precipitated silica reinforced rubber composition containing synthetic elastomers as a combination of styrene/butadiene rubber and cis 1,4-polybutadiene rubber.

(6) An experimental rubber composition was prepared as rubber Sample B as a precipitated silica reinforced rubber composition. Experimental rubber Sample B contained precipitated silica reinforced synthetic elastomers and a combination of end-chain multi-functional group functionalized polybutadiene elastomer of Example I together with styrene/butadiene rubber and filler reinforcement comprised of precipitated silica.

(7) The rubber compositions are illustrated in the following Table 1.

(8) TABLE-US-00001 TABLE 1 Parts by Weight (phr) Control Experimental Material Sample A Sample B Styrene/butadiene rubber.sup.1 40 40 Cis 1,4-Polybutadiene rubber.sup.2 60 0 End-Chain multi-functional group 0 60 functionalized low vinyl polybutadiene elastomer.sup.3 Rubber processing oil.sup.4 20 20 Precipitated silica.sup.5 65 65 Silica coupler.sup.6 5.2 5.2 Fatty acids.sup.7 3 3 Carbon black (N330) 5 5 Wax (paraffinic and microcrystalline) 1.5 1.5 Antioxidant 1.75 1.75 Zinc oxide 1.5 1.5 Sulfur 1.25 1.25 Sulfur cure accelerators.sup.8 3.25 3.25 .sup.1A styrene/butadiene rubber as SLF16S42 from The Goodyear Tire & Rubber Company .sup.2High cis 1,4-polybutadiene rubber as BUD1207 having a cis 1,4 content of at least 95 percent .sup.3End-chain multi-functional group functionalized low vinyl polybutadiene rubber of Example I .sup.4Rubber processing oil as a TDAE type petroleum based oil .sup.5Precipitated silica as Zeosil 1165MP ™ from Solvay .sup.6Silica coupler comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average in a range of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge as Si266 ™ from Evonik .sup.7Fatty acids comprised of stearic, palmitic and oleic acids .sup.8Sulfur cure accelerators as sulfenamide primary accelerator and diphenylguanidine secondary accelerator

(9) The rubber Samples were prepared by blending the ingredients, other than the sulfur curatives, in a first non-productive mixing stage (NP1) in an internal rubber mixer for about 6 minutes to a temperature of about 160° C. The rubber compositions were subsequently mixed in a productive mixing stage (P) in an internal rubber mixer with the sulfur curatives comprised of the sulfur and sulfur cure accelerators for about 3 minutes to a temperature of about 100° C. The rubber compositions were each removed from the internal mixer after each mixing step and cooled to below 40° C. between each non-productive mixing stage and before the final productive mixing stage.

(10) The following Table 2 illustrates cure behavior and various physical properties of rubber compositions based upon the basic formulation of Table 1 and reported herein as Control Sample A and Experimental rubber Sample B. Where cured rubber samples are reported, such as for the stress-strain, rebound and dynamical mechanical properties values, the rubber samples were cured for about 14 minutes at a temperature of about 160° C.

(11) TABLE-US-00002 TABLE 2 Evaluation of Rubber Compositions (Rubber Compounds) Parts by Weight (phr) Control Experimental Sample A Sample B Material Styrene/butadiene rubber 40 40 Cis 1,4-Polybutadiene rubber 60 0 End-chain multi-functional group 0 60 functionalized low vinyl polybutadiene elastomer (of Example I) Properties RPA.sup.1, cured storage modulus G' at 3258 3483 10% strain, 1 Hertz, 60° C., kPa RPA tan delta at 10% strain, 1 Hertz, 0.139 0.122 60° C. (lower is better) Rebound at 100° C., percent (higher is better) 62.8 66.9 Rebound at 23° C., percent (higher is better) 51.4 54.1 Rebound at 0° C., percent 40 39 Elongation at break (%) 582 574 Modulus 300% (MPa) 6.8 6.9 .sup.1Rubber Process Analyzer

(12) From Table 2 it is observed that sulfur cured Experimental rubber compound Sample B demonstrates a beneficially lower hysteresis as evidenced by both of a lower tan delta value of 0.122 and a higher rebound at 100° C. of 66.9 percent in comparison to the Control rubber compound Sample A having a higher tan delta value of 0.139 and a significantly lower rebound value of 62.8 percent. This shows a beneficial reduction (an improvement) of the hysteresis of the compound (rubber composition), Sample B, resulting from the utilization of the multi-functional group functionalized polybutadiene elastomer which is indicative of providing a beneficial reduction in rolling resistance for a vehicular tire having a tread of such rubber composition and a resulting beneficial reduction of fuel consumption of an associated vehicle.

(13) It is concluded that it has been discovered that an inclusion of the end-chain multi-functional group functionalized polybutadiene elastomer has resulted in a beneficial effect for the hysteresis of the rubber composition.

EXAMPLE III

Preparation of End-chain Multi-functional Group Functionalized High Vinyl Polybutadiene Rubber and Evaluation of Said Elastomer in Rubber Composition

(14) A 60 gallon (227 liter capacity) agitator containing jacketed reactor, having been dried and flushed with nitrogen, was charged with 210 pounds (95 kg) of a pre-dried 11.1 weight percent 1,3-butadiene monomer solution in hexane. During agitation, the solution temperature was increased to 135° F. (57° C.) by application of heat to the reactor jacket.

(15) To the agitated heated solution in the reactor was added 17.5 ml of TMEDA (tetramethylenediamine as a polymerization modifier) and 30 ml of dry hexane followed by addition of 36.6 ml of 15 weight percent n-butyl lithium polymerization catalyst (as a polymerization initiator) in hexane.

(16) The temperature of the solution in the reactor was allowed to increase to 152° F. (67° C.), and after 1.5 hours, the content of the reactor was slowly transferred to a second vessel that had been pre-charged with 82.5 ml of bis (3-triethoxysilylpropyl) polysulfide which contained a range of about 2 to 2.6 connecting sulfur atoms in its poly-sulfidic bridge.

(17) After 20 minutes of ageing, a polymerization stopping agent was added to stop the polymerization. The mixture was agitated for an additional 15 minutes to allow for the polymerization to discontinue.

(18) The resulting polymer product as an end-functionalized polybutadiene elastomer recovered by removing the hexane by steam stripping.

(19) The recovered product was a functionalized high Tg, high vinyl, polybutadiene elastomer determined to have a Tg of about −33° C. and a vinyl 1,2-isomeric content of about 70 percent with end-functional groups provided by the polymerization initiator.

(20) The final polymer (polybutadiene elastomer) had a weight average molecular weight (Mw) of about 200,000 and a Mooney (ML1+4), 100° C., viscosity of about 45.

(21) An Experimental rubber composition was prepared as rubber Samples D as a precipitated silica reinforced rubber composition. Experimental rubber Sample D contained precipitated silica reinforced synthetic elastomers as a combination of said end-chain functionalized high vinyl polybutadiene rubber (of this Example III) and filler reinforcement comprised of precipitated silica.

(22) The rubber compositions are illustrated in the following Table 3.

(23) TABLE-US-00003 TABLE 3 Formulation Used for Evaluation Parts by Weight (phr) Control Experimental Material Sample C Sample D Cis 1,4-Polybutadiene rubber.sup.1 20 20 Non functionalized high vinyl polybutadiene.sup.2 80 0 Multi-functional group functionalized high 0 80 vinyl polybutadiene elastomer (from this Example III).sup.3 Rubber processing oil.sup.4 20 20 Precipitated silica.sup.5 65 65 Silica coupler.sup.6 6.5 6.5 Fatty acids.sup.7 3 3 Carbon black (N330) 5 5 Wax (paraffinic and microcrystalline) 1.5 1.5 Antioxidant 2.5 2.5 Zinc oxide 2 2 Sulfur 1.5 1.5 Sulfur cure accelerators.sup.8 3.5 3.5 .sup.1High cis 1,4-polybutadiene rubber as BUD1207 ™ from The Goodyear Tire & Rubber Company having a cis 1,4-content of at least 95 percent .sup.2Non functionalized high vinyl polybutadiene synthesized in the same manner as the end-chain multi-functional group functionalized polybutadiene of this Example II without the end-functionalization step having a vinyl content of about 70 percent. .sup.3End-chain multi-functional group functionalized high vinyl polybutadiene rubber of this Example III. .sup.4Rubber processing oil as a TDAE type petroleum based oil .sup.5Precipitated silica as Zeosil 1165MP ™ from Solvay .sup.6Silica coupler comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average in a range of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge as Si266 ™ from Evonik .sup.7Fatty acids comprised of stearic, palmitic and oleic acids .sup.8Sulfur cure accelerators as sulfenamide primary accelerator and diphenylguanidine secondary accelerator

(24) The rubber Samples were prepared by blending the ingredients, other than the sulfur curatives, in a first non-productive mixing stage (NP1) in an internal rubber mixer for about 6 minutes to a temperature of about 160° C. The rubber compositions were subsequently mixed in a productive mixing stage (P) in an internal rubber mixer with the sulfur curatives comprised of the sulfur and sulfur cure accelerators for about 3 minutes to a temperature of about 100° C. The rubber compositions were each removed from the internal mixer after each mixing step and cooled to below 40° C. between each non-productive mixing stage and before the final productive mixing stage.

(25) The following Table 4 illustrates cure behavior and various physical properties of rubber compositions based upon the basic formulation of Table 3 and reported herein as Control Sample C and Experimental rubber Sample D. Where cured rubber samples are reported, such as for the stress-strain, rebound and dynamical mechanical properties values, the rubber samples were cured for about 14 minutes at a temperature of about 160° C.

(26) TABLE-US-00004 TABLE 4 Evaluation of rubber compositions (rubber compounds) Parts by Weight (phr) Control Experimental Sample C Sample D Material Cis 1,4-Polybutadiene rubber 20 20 Non functionalized high vinyl polybutadiene 80 0 End-chain multi-functional group 0 80 functionalized high vinyl polybutadiene (from this Example III) Properties RPA.sup.1, cured storage modulus G' at 10% strain, 1998 1958 1 Hertz, 60° C., kPa RPA tan delta at 10% strain, 1 Hertz, 60° C. 0.106 0.089 (lower is better) Rebound at 100° C., percent (higher is better) 66.8 71.7 Rebound at 23° C., percent (higher is better) 44.8 48.8 Rebound at 0° C., percent 11.2 9.4 Elongation at break (%) 426 379 Modulus 300% (MPa) 9.3 11.3 .sup.1Rubber Process Analyzer

(27) From Table 4 it is observed that cured experimental compound D demonstrates a beneficially lower hysteresis as evidenced by both of a lower tan delta value of 0.089 and a higher rebound at 100° C. of 71.7 percent in comparison to the Control rubber compound A having a higher tan delta value of 0.106 and lower rebound value of 66.8 percent. This shows a beneficial reduction (an improvement) of the hysteresis of the compound (rubber composition) resulting from the utilization of the multi-functional group functionalized elastomer which is indicative of providing a beneficial improvement in rolling resistance for a vehicular tire having a tread of such rubber composition and a resulting beneficial reduction of fuel consumption of an associated vehicle.

(28) It is concluded that it has been discovered that an inclusion of the end-chain multi-functional group functionalized polybutadiene elastomer has resulted in a beneficial effect of providing a lower hysteresis of the rubber composition.

(29) While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.