TIRE WITH TREAD

Abstract

This invention relates to a tire with a tread of a rubber composition containing a combination of high and low glass transition temperature (Tg) synthetic elastomers. The high Tg elastomer is comprised of a high Tg, high vinyl content, functionalized polybutadiene rubber and the low Tg elastomer is comprised of a low Tg, low vinyl content, functionalized polybutadiene rubber. The tread rubber may contain traction resins, may contain rosin acid and may contain triglyceride vegetable rubber processing oil.

Claims

1. A pneumatic tire having a circumferential rubber tread of a rubber composition containing precipitated silica reinforcement comprised of, based on parts by weight per 100 parts by weight elastomer (phr): (A) 100 phr of conjugated diene-based elastomers comprised of; (1) about 20 to about 80 phr of a functionalized high Tg, high vinyl polybutadiene rubber having a Tg in a range of from about 40 C. to about 10 C. and an isomeric vinyl 1,2-content in a range of from about 65 to about 85 percent, where said functionalized high vinyl polybutadiene rubber contains functional groups reactive with hydroxyl groups on said precipitated silica reinforcement, (2) about 80 to about 20 phr of a functionalized low Tg, low vinyl polybutadiene rubber having a Tg in a range of from about 108 C. to about 90 C. and an isomeric vinyl 1,2-content in a range of from about 0 to about 15 percent, where said functionalized low vinyl polybutadiene rubber contains functional groups reactive with hydroxyl groups on said precipitated silica reinforcement, provided that the weight ratio of low vinyl to high vinyl functionalized polybutadiene rubber is at least 1/1 and alternately at least 1.5/1, (B) about 60 to about 200 phr of rubber reinforcing filler comprised of a combination of precipitated silica (amorphous synthetic precipitated silica) and rubber reinforcing carbon black in a weight ratio of precipitated silica to rubber reinforcing carbon black of at least 9/1, together with a silica coupling agent having a moiety reactive with hydroxyl groups (e.g. silanol groups) on said precipitated silica and another different moiety interactive with said diene-based elastomers, and (C) zero to about 60 phr of a traction promoting resin comprised of at least one of styrene-alphamethylstyrene resin, coumarone-indene resin, petroleum hydrocarbon resin, terpene polymer, terpene phenol resin, rosin derived resin and copolymers.

2. The tire of claim 1 wherein, for said tread rubber composition, said-end functionalized high vinyl polybutadiene elastomers is the polymerization product of 1,3-butadiene monomer end-functionalized by a functionalized polymerization initiator.

3. The tire of claim 1 wherein, for said tread rubber composition, said end-functionalized high vinyl polybutadiene elastomers is the polymerization product of 1,3-butadiene monomer end-functionalized by a functionalized polymerization terminator.

4. The tire of claim 1 wherein, for said tread rubber composition, is at least one of end-functionalized high vinyl polybutadiene elastomers is a bi-functionalized high vinyl polybutadiene elastomer and is the polymerization product of 1,3-butadiene monomer end-functionalized by a combination of functionalized polymerization initiator and polymerization terminator.

5. The tire of claim 1 wherein, for said tread rubber composition, said functional high vinyl and low vinyl polybutadiene elastomers contain at least one functional group reactive with hydroxyl groups on said precipitated silica comprised of: (A) Amine functional group reactive with hydroxyl groups on said precipitated silica, (B) Siloxy functional group reactive with hydroxyl groups on said precipitated silica, (C) Combination of amine and siloxy groups reactive with hydroxyl groups on said precipitated silica, (D) Combination of siloxy and thiol groups reactive with hydroxyl groups on said precipitated silica, (E) Combination of imine and siloxy groups reactive with hydroxyl groups on said precipitated silica, (F) Hydroxyl functional groups reactive with said precipitated silica, (G) Epoxy groups reactive with hydroxyl groups on said precipitated silica, (H) Carboxyl groups reactive with hydroxyl groups on said precipitated silica, and (I) Alkyl or Aryl silylamine groups reactive with hydroxyl groups on said precipitated silica.

6. The tire of claim 1 wherein said tread rubber composition further contains up to about 25 phr of at least one additional diene based elastomer exclusive of styrene containing elastomers.

7. The tire of claim 1 wherein said tread rubber composition further contains up to about 15 phr of at least one of cis 1,4-polyisoprene and copolymers of isoprene and butadiene.

8. The tire of claim 1 wherein said precipitated silica is provided as a composite of pre-reacted precipitated silica and silica coupling agent prior to addition to the rubber composition.

9. The tire of claim 1 wherein said precipitated silica is a product of precipitated silica and silica coupling agent reacted in situ within the rubber composition.

10. The tire of claim 1 wherein said silica coupling agent is comprised of: (A) bis(3-trialkoxysilylalkyl) polysulfide containing an average in range of from about 2 to about 4 sulfur atoms in its polysulfide connecting bridge, or (B) an organoalkoxymercaptosilane, or (C) their combination.

11. The tire of claim 1 wherein said silica coupling agent is comprised of a bis(3-triethoxysilylpropyl) polysulfide.

12. The tire of claim 1 wherein said silica coupling agent is comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average of from about 2 to about 2.6 sulfur atoms in its polysulfidic bridge.

13. The tire of claim 1 wherein said silica coupling agent is comprised of an organoalkoxymercaptosilane.

14. The tire of claim 1 wherein said tread rubber composition contains traction promoting resin comprised of at least one of styrene/alphamethylstyrene resin, coumarone-indene resin, petroleum hydrocarbon resin, terpene polymer, terpene phenol resin and rosin derived resin and copolymers thereof and hydrogenated rosin acid.

15. The tire of claim 1 where said tread rubber composition contains rosin acid to the substantial exclusion of fatty carboxylic acids.

16. The tire of claim 1 where said tread rubber composition contains rubber processing oil comprised of triglyceride based vegetable oil.

17. The tire of claim 15 where said tread rubber composition contains rubber processing oil comprised of triglyceride based vegetable oil.

18. The tire of claim 1 where said rubber composition contains rubber processing oils as a combination of triglyceride vegetable oil and petroleum based oil.

19. The tire of claim 1 wherein said tread rubber composition is sulfur cured.

20. The tire of claim 2 wherein said tread rubber composition is sulfur cured.

Description

EXAMPLE I

Preparation of Non-Functionalized and Functionalized High Vinyl Polybutadiene Elastomer

[0068] 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 solution in hexane. During agitation, the solution temperature was increased to 135 F. (57 C.) by application of heat to the reactor jacket.

[0069] 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.

[0070] 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 3,3-bis(triethoxysilylpropyl) polysulfide, which may be referred to as bis(3-triethoxysilylpropyl) polysulfide, having a range of about 2 to 2.6 connecting sulfur atoms in the polysulfidic bridge.

[0071] 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

[0072] The resulting polymer product is an end functionalized polybutadiene elastomer recovered by removing the hexane by steam stripping.

[0073] 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.

[0074] In a similar fashion, a non-functionalized version of a high Tg polybutadiene elastomer (Polymer B) was made in which the disulfide, the bis(3-triethoxysilylpropyl) polysulfide, was omitted from the polymerization reaction procedure. The recovered polymer product was a non-functionalized high Tg high vinyl polybutadiene elastomer determined to have a Tg of about 36 C. and a vinyl 1,2-isomeric content of about 69 percent.

EXAMPLE II

[0075] This study was conducted to evaluate the comparative use of the functionalized, high Tg, high vinyl polybutadiene elastomer (Polymer A) prepared via Example I herein with the non-functionalized high Tg, high vinyl polybutadiene elastomer (Polymer B) also prepared in Example I.

[0076] In this Example, exemplary rubber compositions for a tire tread were prepared for evaluation for promoting a combination of wet traction and cold weather (winter) performance for a tire tread. Of further interest is the impact of functionalization of the polybutadiene elastomer on the laboratory determined properties of abrasion resistance and hysteresis that are predictive of treadwear and rolling resistance, respectively, of a tire tread.

[0077] A first control rubber composition (Sample X) was prepared as a precipitated silica reinforced rubber composition containing a combination of 38 phr of commercially available functionalized styrene/butadiene rubber having a Tg of about 23 C. and 62 phr of a commercially available functionalized low Tg, 12 per cent vinyl polybutadiene rubber having a Tg of about 90 C.

[0078] A second control rubber composition (Sample Y) was prepared as a precipitated silica reinforced rubber composition containing a combination of 38 phr of a non-functionalized high Tg high vinyl polybutadiene rubber (Polymer B from Example I herein) having a Tg of about 36 C. and 62 phr of a functionalized low Tg, low vinyl polybutadiene rubber having a Tg of about 90 C. The second control rubber composition (Sample Y) is similar to the first control rubber composition (Sample X), except the commercially available functionalized styrene/butadiene rubber is replaced with a non-functionalized high vinyl polybutadiene rubber (Polymer B).

[0079] An Experimental rubber composition (Sample Z) was prepared as a precipitated silica reinforced rubber composition containing a combination of 38 phr of a functionalized high Tg, high vinyl polybutadiene rubber (Polymer A from Example I herein) having a Tg of about 33 C. and 62 phr of a functionalized low Tg, low vinyl polybutadiene rubber having a Tg of about 90 C. This experimental rubber composition is similar to Sample Y except that the high vinyl polybutadiene rubber (Polymer A) is a functionalized polybutadiene elastomer.

[0080] The rubber compositions are illustrated in the following Table 1.

TABLE-US-00001 TABLE 1 Parts by Weight (phr) Control Control Exp'1 Material Sample X Sample Y Sample Z Functionalized styrene/butadiene 38 0 0 rubber.sup.1 Functionalized low vinyl 62 62 62 polybutadiene.sup.2 High vinyl polybutadiene.sup.3 0 38 0 Functionalized high vinyl 0 0 38 polybutadiene.sup.4 Precipitated silica.sup.5 80 80 80 Silica coupler.sup.6 6.4 6.4 6.4 Rubber processing oil, fatty acids 30 30 30 and waxes.sup.7 Antidegradants 3 3 3 Carbon black (N330) 10 10 10 Cure system: zinc oxide, sulfur, 7 7 7 accelerators.sup.8 .sup.1Functionalized styrene/butadiene rubber having a styrene content of about 20 percent and a vinyl content of about 50 percent with a Tg of about 26 C. as Sprintan 4602 from Trinseo understood to be end functionalized with functional groups comprised of siloxane and thiol groups reactive with hydroxyl groups on precipitated silica .sup.2Functionalized low vinyl (12 percent) polybutadiene rubber as BR1261 from Zeon having a Tg of about 92 C. and functional groups reactive with hydroxyl groups on precipitated silica .sup.3Non functionalized high Tg, high vinyl polybutadiene elastomer as Polymer B prepared in Example I .sup.4Functionalized high Tg, high vinyl polybutadiene elastomer as Polymer A prepared in Example I .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.7Rubber processing oil, fatty acids containing stearic, palmitic and oleic acids and waxes comprised of paraffinic and microcrystalline waxes .sup.8Zinc oxide, sulfur and sulfur cure accelerators as sulfenamide primary accelerator and diphenyl guanidine secondary accelerator

[0081] 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 four minutes to a temperature of about 160 C. The resulting mixtures were subsequently individually mixed in a second sequential non-productive mixing stage (NP2) in an internal rubber mixer for about three 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 two minutes to a temperature of about 115 C. The rubber compositions were each removed from the internal mixer after each non-productive mixing step and cooled to below 40 C. before the final productive mixing stage.

[0082] 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 first Control rubber Sample X, second Control rubber sample Y and Experimental rubber Sample Z. Where cured rubber samples are reported, such as for the stress-strain, hot rebound and hardness values, the rubber samples were cured for about 14 minutes at a temperature of about 160 C.

[0083] To evaluate the predictive wet traction, a tangent delta (tan delta) test was run at 0 C.

[0084] To evaluate the predictive low temperature performance (e.g. winter and snow conditions) performance, the rubber's storage modulus E physical property (a measure of its stiffness) was determined at 20 C. to provide a stiffness value of the rubber composition at lower ambient temperatures.

TABLE-US-00002 TABLE 2 Parts by Weight (phr) Control Control Exp'1 Material Sample X Sample Y Sample Z Functionalized styrene/butadiene 38 0 0 rubber Functionalized low Tg, low vinyl 62 62 62 polybutadiene Non-functionalized high Tg, high 0 38 0 vinyl polybutadiene rubber (Polymer B) Functionalized high Tg, high vinyl 0 0 38 polybutadiene rubber (Polymer A) Cured Properties Wet Traction Laboratory Prediction Tan delta at 0 C. (higher is better) 0.15 0.13 0.13 Cold Weather (Winter) Performance (Stiffness) Laboratory Prediction Storage modulus (E'), (MPa) at 9.7 8.7 5.9 20 C., 10 Hertz, 0.25% strain (lower stiffness values are better) Rolling Resistance (RR) Laboratory Prediction Rebound at 100 C., percent 64 64 66 Additional properties Tensile strength (MPa) 18 17 15 Elongation at break (%) 367 361 327 Modulus 300% (MPa) 14 13 14 DIN abrasion loss, cc (lower is 59 58 54 better).sup.1 .sup.1DN53516, relative volume loss (relative to a control)

[0085] From Table 2 it is observed that:

[0086] (A) Experimental Sample Z has a predictive wet traction based on its tan delta property at 0 C. of 0.13 which is similar to Control Samples Y and X.

[0087] (B) Experimental Sample Z has a predictive rolling resistance for a tire tread of such rubber composition, based on hot rebound property at 100 C. of 66, which is beneficially better than the hot rebound properties of Control Samples X and Y which have hot rebound values of 64.

[0088] (C) Experimental Sample Z has a DIN abrasion wear resistance value of 54 which is an improvement over the values of 58 for Control Sample Y and 59 for Control Sample X.

[0089] (D) Experimental Sample Z has a predictive winter (cold weather) performance based on its stiffness value (E) at 20 C. of 5.9 which is a significant improvement over the values of 8.7 for Control Sample Y and 9.7 for Control Sample X.

[0090] Therefore, it is concluded that the replacement of a functionalized high Tg styrene/butadiene rubber with a functionalized high Tg, high vinyl polybutadiene rubber in a blend with a functionalized low vinyl, low Tg, low vinyl polybutadiene rubber for a silica reinforced tread composition will provide similar wet traction and improvements in winter performance, rolling resistance and treadwear based on laboratory determined predictive properties. It is also demonstrated that a non-functionalized high Tg, high vinyl polybutadiene rubber will also improve winter performance, but without improvement in predictive treadwear and rolling resistance for a tire tread. It is also observed that the predictive improvement of winter performance of the non-functionalized high Tg, high vinyl polybutadiene rubber is further improved when compared to a functionalized version of the same polymer as the stiffness value at 20 C. is lowered from 8.7 to 5.9. This lowering of stiffness is a key discovery of this functionalized rubber.

[0091] 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.