Footwear and rubber sole containing dual silica moieties

Abstract

The invention relates to footwear with a rubber sole and to such rubber sole where the sole is provided with a rubber composition which contains dual precipitated silica moieties. The dual precipitated silica moieties are provided in a sense of being comprised of hydrophilic precipitated silica and hydrophobic precipitated silica.

Claims

1. A footwear rubber sole intended for ground engagement comprised of a rubber composition which contains at least one conjugated diene-based rubber and filler reinforcement, the filler reinforcement comprising: dual silica moieties in the form of an in situ hydrophobic precipitated silica and a hydrophilic precipitated silica; the hydrophobic precipitated silica being formed by a combination of a hydrophilic silica and a silica coupler in a first step and the hydrophilic precipitated silica being formed by addition of a hydrophilic silica absent the coupling agent in a different step; the hydrophilic precipitated silica for promoting wet traction of the footwear rubber sole on a wet surface; wherein said rubber composition contains rubber processing oil comprised of a combination of petroleum-based rubber processing oil and vegetable triglyceride oil.

2. The footwear rubber sole of claim 1 wherein said hydrophobic precipitated silica is a precipitated silica treated with silica coupler comprised of at least one of bis(3-triethoxysilylpropyl) polysulfide and organomercaptoalkoxysilane.

3. The footwear rubber sole of claim 2 where said silica coupler is used together with an alkoxysilane.

4. The footwear rubber sole of claim 1 wherein said hydrophobic precipitated silica is provided as a pre-treated hydrophilic precipitated silica with a silica coupler comprised of at least one of bis(3-triethoxysilylpropyl) polysulfide and organomercaptoalkoxysilane.

5. The footwear rubber sole of claim 4 wherein said pre-treatment of said hydrophilic precipitated silica additionally includes treatment with an alkoxysilane.

6. The footwear rubber sole of claim 1 wherein said hydrophobic precipitated silica is provided as a hydrophylic precipitated silica treated in situ within said rubber composition with a silica coupler comprised of at least one of bis(3-triethoxysilylpropyl) polysulfide and organomercaptoalkoxysilane prior to separate, subsequent addition of a hydrophilic precipitated silica and optionally an alkoxysilane.

7. The footwear rubber sole of claim 1 wherein said conjugated diene-based rubber is comprised of polymer(s) 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 footwear rubber sole of claim 7 where said rubber composition contains at least one of cis 1,4-polyisoprene, cis 1,4-polybutadiene, styrene/butadiene rubber and block polymers comprised of styrene-isoprene-styrene or styrene-butadiene-styrene polymer blocks.

9. The footwear rubber sole of claim 7 where said rubber composition contains cis 1,4-polybutadiene rubber and at least one of cis 1,4-polyisoprene and styrene/butadiene rubber.

10. The footwear rubber sole of claim 8 where said rubber composition also contains up to 25 phr of primarily saturated elastomers comprised of at least one of EPDM (ethylene/propylene/non-conjugated diene terpolymer rubber), butyl rubber, halobutyl rubber and brominated copolymers of paramethylstyrene and isobutylene and their mixtures, wherein non-conjugated dienes for said EPDM are comprised of at least one of ethylidene norbornadiene, trans 1,4-hexadiene and dicyclopentadiene.

11. The footwear rubber sole of claim 1 wherein said rubber composition contains a rubber processing oil comprised of: (A) petroleum based rubber processing oil, (B) vegetable triglyceride oil, or (C) combination of petroleum-based rubber processing oil and vegetable triglyceride oil.

12. The footwear rubber sole of claim 11 which contains vegetable triglyceride oil comprised of at least one of soybean oil, sunflower oil, palm oil and rapeseed oil.

13. The footwear rubber sole of claim 1 wherein said rubber composition is cured with at least one of elemental sulfur and organic peroxide.

14. The footwear rubber sole of claim 1 wherein said rubber composition is cured with elemental sulfur together with at least one sulfur cure accelerator.

15. The footwear rubber sole of claim 1 wherein said rubber composition contains traction promoting resin comprised of as least one of styrene/alphamethylstyrene resin, coumarone-indene resin petroleum hydrocarbon resin, terpene polymer, terpene phenol resin and rosin derived resin and copolymers thereof.

16. The footwear rubber sole of claim 1 where the rubber composition of said sole further contains from about 1 to about 10 phr of zinc rosinate as a product of zinc oxide and freely added rosin acid in situ within said rubber composition.

17. The footwear rubber sole of claim 1 which comprises, based upon parts by weight per 100 parts by weight of rubber (phr): (A) at least one conjugated diene-based elastomer, and (B) about 20 to about 120 phr of reinforcing filler comprised of: (1) precipitated silica, or (2) a combination of precipitated silica and rubber reinforcing carbon black containing up to about 60 phr of rubber reinforcing carbon black; wherein said precipitated silica of (B)(1) and (B)(2) is comprised of: (3) about 50 to about 95 weight percent of composite of hydrophobic precipitated silica, and (4) about 5 to about 50 weight percent hydrophilic precipitated silica.

18. A method for providing a footwear rubber sole of a rubber composition containing a combination of hydrophobic precipitated silica and hydrophilic precipitated silica which comprises: (A) pre-treating a hydrophilic precipitated silica with a silica coupler to form a composite thereof, where said silica coupler comprises at least one of bis(3-triethoxysilylpropyl) polysulfide and organomercaptoalkoxysilane optionally including alkoxysilane, addition of said composite to a rubber composition containing at least one diene-based elastomer and wherein a hydrophilic precipitated silica is added to the rubber composition without additional silica coupler either prior to, coincidentally with or subsequent to said hydrophobic precipitated silica, (B) treating a hydrophilic precipitated silica with a silica coupler in situ within a rubber composition containing at least one diene-based elastomer with a silica coupler to form a composite thereof within the rubber composition wherein said silica coupler comprises at least one of bis(3-triethoxysilylpropyl) polysulfide and organomercaptoalkoxysilane optionally including an alkoxysilane, and thereafter adding a hydrophilic precipitated silica to the rubber composition without additional silica coupler wherein said subsequently added hydrophilic precipitated silica is added to said rubber composition in a separate and subsequent mixing step from said in situ treatment of said hydrophilic precipitated silica to form a hydrophobic precipitated silica.

19. An article of footwear comprised of a combination of an upper portion and a sole portion where said sole portion is comprised of the footwear rubber sole of claim 1.

Description

EXAMPLE I

(1) This Example, derived from Example I of U.S. Pat. No. 8,522,847, relates to providing dual silica moieties in a rubber composition for a tire tread in a sense of a hydrophilic precipitated silica and hydrophobic precipitated silica where the hydrophobic precipitated silica is formed in situ within the rubber composition by treatment of a hydrophilic precipitated silica. The Example from U.S. Pat. No. 8,522,847 is presented here for said evaluation of dual precipitated silica moieties in a footwear rubber sole rubber composition.

(2) The experimental rubber composition Sample B was prepared by hydrophobating a hydrophilic precipitated silica in situ within the rubber composition to form an in situ hydrophobated precipitated silica with a silane based hydrophobating agent, namely a bis(3-triethoxysilylpropyl) polysulfide silica coupler, followed by adding additional hydrophilic precipitated silica to the rubber composition in a separate, subsequent, mixing step.

(3) In this manner, then, the second addition of the hydrophilic precipitated silica is completely separate and disconnected from the first addition of hydrophilic silica and coupling agent to form hydrophobated precipitated silica. It is therefore considered herein that little or no hydrophobation of the separately added hydrophilic precipitated silica occurs.

(4) Control rubber Sample A, and comparative rubber compositions Samples C and D, and experimental Sample B, the invention, were prepared by:

(5) (A) control rubber Sample A was provided with only a hydrophilic precipitated silica without a hydrophobated precipitated silica.

(6) (B) comparative rubber Samples C and D were provided with dual in situ hydrophobated precipitated silicas in a manner of first hydrophobating a precipitated silica in situ within a rubber composition followed by then sequentially hydrophobating a second precipitated silica in situ within the same rubber composition.

(7) (C) for experimental rubber Sample B, which represents this invention, addition of hydrophilic precipitated silica and coupling agent in the first mixing stage to produce a hydrophobated silica followed be the separate addition of additional hydrophilic silica in a second non-productive mixing stage (NP2) without an accompanying addition of the silica coupler.

(8) The basic formulations for the Control rubber Sample A, the invention experimental rubber Sample B and comparative rubber Samples C and D are presented in the following Table 1 expressed in parts by weight per 100 parts of rubber unless otherwise indicated.

(9) TABLE-US-00001 TABLE 1 Samples A B C D First Non-Productive Mixing Stage (NP1) Synthetic polyisoprene rubber.sup.1 100 100 100 100 Carbon black.sup.2 20 20 20 20 Processing oil 6 6 6 6 Fatty acid.sup.3 2 2 2 2 Antidegradant(s).sup.4 2 2 2 2 Precipitated (hydrophilic) precipitated silica.sup.5 15 15 15 15 Zinc oxide 5 5 5 5 Silica coupler (50/50 carbon black 0 2.5 3 4 composite).sup.6 Second Non-Productive Mixing Stage (NP2) Precipitated (hydrophilic) silica.sup.5 15 15 15 15 Silica coupler (50/50 carbon black 0 0 2 3.5 composite).sup.6 Productive Mixing Stage (P) Sulfur 1.4 1.4 1.4 1.4 Accelerator(s).sup.7 2.2 2.2 2.2 2.2 .sup.1Cis 1,4-polyisoprene rubber as NAT 2200 from The Goodyear Tire & Rubber Company 1 .sup.2N299, rubber reinforcing carbon black, ASTM identification .sup.3Primarily stearic acid (at least 90 percent by weight stearic acid) .sup.4Quinoline based antidegradant .sup.5Pre-hydrophobated precipitated silica composite as Agilon 400 ™ from PPG .sup.6Precipitated silica as HiSil 210 ™ from PPG .sup.7Sulfenamide and diphenyl guanidine sulfur cure accelerators

(10) The following Table 2 illustrates cure behavior and various physical properties of rubber compositions based upon the basic recipe of Table 1 and reported herein as control Sample A, invention Sample B and comparative Samples C and D. Where cured rubber samples are examined, such as for the stress-strain, hot rebound and hardness values, the rubber samples were cured for about 12 minutes at a temperature of about 170° C.

(11) The heading for Table 2 shows the respective non-productive mixing steps, namely NP1 and NP2, in which the hydrophilic silica and hydrophobating agent (silica coupler) were added.

(12) TABLE-US-00002 TABLE 2 Samples Control A B C D Carbon black (added in NP1) 20 20 20 20 Silica, hydrophilic (added in NP1) 15 15 15 15 Silica coupler (added inNP1) 0 2.5 3 4 Silica, hydrophilic (added inNP2) 15 15 15 15 Silica coupler (added in NP2) 0 0 2 3.5 Coefficient of Friction.sup.1 Wet substrate 2.6 2.4 1.5 1.2 Dry substrate 2.8 2.8 2.9 2.6 Stress-strain, ATS.sup.2 14 min, 160° C. Tensile strength (MPa) 20.7 22.8 23.3 23.7 Elongation at break (%) 666 581 557 535 300% modulus, ring (MPa) 3.9 8.2 9.7 11 Rebound  23° C. 46 51 50 50 100° C. 60 65 64 65 Shore A hardness, 23° C. 57 64 67 69 RPA.sup.3 (100° C.), Storage Modulus G′, MPa Uncured G′ 15% strain 0.18 0.18 0.18 0.18 Cured G′ modulus, 10% strain 1.2 1.4 1.5 1.6 .sup.1ASTM D-1894. A coefficient of friction (COF) value for a rubber sample may be measured, for example, on a Model SP-2000 slip/peel tester from IMASS Inc. at six inches (about 15.2 cm) per minute using a 200 g sled against a substrate surface such as, for example, a polished aluminum surface. .sup.2Automated testing system (ATS) instrument by the Instron Corporation which can incorporate as many as six tests in one system. Such instrument may determine ultimate tensile, ultimate elongation, moduli, etc. .sup.3Rubber Process Analyzer as RPA 2000 ™ instrument by Alpha Technologies

(13) In the above Table 2, it can be seen that the hydrophilic precipitated silica was added in both the first (NP1) and the second (NP2) separate non-productive mixing stages (it was removed from the internal rubber mixer of the NP1 mixing stage, cooled to below 40° C. and then mixed in the NP2 mixing stage in an internal rubber mixer).

(14) It can be observed in Table 2 that, for the dry coefficient of friction, addition of increasing levels of silica coupler to Control rubber Sample A, namely for rubber Samples B, C and D, had no significant effect, although physical properties such as tensile strength, 300 percent modulus, rebound and cured storage modulus (G′) at 10 percent strain were significantly improved.

(15) It can further be observed in Table 2 for the wet coefficient of friction, a combined addition of both hydrophilic silica and silica coupler (hydrophobating agent) to both of the sequential non-productive mixing stages (NP1 and NP2) in Samples C and D to therefore form an in situ hydrophobated silica in both the NP1 and NP2 mixing stages had a significant and rather dramatic negative effect on the wet coefficient of friction (wet COF) with reduced values of only 1.5 and 1.2 as compared to a value of 2.6 for the Control rubber Sample A.

(16) In sharp contrast, it can next be observed in Table 2 that, for Sample B, which represents the invention of U.S. Pat. No. 8,522,847, addition of hydrophilic precipitated silica in the separate, second non-productive mixing stage (NP2) without an accompanying addition of the silica coupler (hydrophobating agent) resulted in a comparable wet coefficient of friction (wet COF), namely a value of 2.4, to that of the Control rubber Sample A which has a desirably high wet coefficient of friction (wet COF) value of 2.6.

(17) The sharp contrast becomes even more evident when observing that the beneficial wet coefficient of friction (wet COF) of the surface of rubber Sample B was obtained while other physical properties were significantly improved as compared to Control rubber Sample A, a combination which was not observed for rubber Samples C and D which, instead, had dramatically poorer wet coefficients of friction.

(18) It is concluded from the Example of U.S. Pat. No. 8,522,847 that the addition of the hydrophilic silica and silica coupler (hydrophobation agent) in the first non-productive mixing step (NP1), followed by a separated sequential addition of hydrophilic silica in a second non-productive mixing step (NP2) without the coupling agent addition (hydrophobation agent addition), enabled the preparation of a rubber composition which contained dual silica moieties in a form of an in situ hydrophobated precipitated silica (hydrophobated in situ within the rubber composition) and a hydrophilic precipitated silica where the in situ hydrophobated silica promoted enhanced physical properties of the rubber composition (rubber Sample B) and where the presence of the hydrophilic precipitated silica promoted a suitable wet coefficient of friction (wet COF) for the surface of the rubber composition suitable for a cured tire tread, particularly including its running surface.

(19) Accordingly, it is concluded herein that a footwear rubber sole of a rubber composition containing dual precipitated silica moieties in a sense of the dual precipitated silica moieties provided in a sense of being comprised of hydrophilic precipitated silica and hydrophobic precipitated silica will provide improved wet traction of the footwear rubber sole on a wet surface.

EXAMPLE II

(20) This Example, derived from an example presented in U.S. Pat. No. 9,163,126, relates to providing zinc rosinate in a rubber composition as a product of zinc oxide with rosin acid formed in situ within the rubber composition and thereby relates to the aforesaid evaluation of providing such zinc rosinate in a footwear rubber sole rubber composition.

(21) For this Example, Tables 1 and 2 of said example provided in U.S. Pat. No. 9,163,126 have been re-labeled as Tables 3 and 4, respectively, to present the Tables herein in a chronological sequence.

(22) For this Example, rubber compositions E through J of said example provided in U.S. Pat. No. 9,163,126 have been re-labeled as rubber compositions E through J, respectively, to present the labels herein in a chronological sequence.

(23) For this Example of U.S. Pat. No. 9,163,126, rosin acid was introduced in a rubber composition in combination with zinc oxide to enable an in situ formation of zinc rosinate within the rubber composition,

(24) Silica-rich rubber compositions were prepared as rubber Samples E through J. Rubber Sample E was a control rubber sample formulated with 3 phr of zinc oxide and 1 phr of fatty acids comprised of stearic, palmitic and oleic acids to form salts of such fatty acids in situ within the rubber composition. Rubber Samples F and G were formulated with 3 phr and 6 phr of the fatty acids, respectively, while maintaining 3 phr of zinc oxide, rubber Samples H, I, and J were formulated with 3 phr zinc oxide and rosin acid (instead of the aforesaid fatty acids) in amounts of 1, 3 and 6 phr of rosin acid, respectively, to form zinc rosinate in situ within the rubber composition.

(25) The following Table 3 derived from the aforesaid U.S. patent illustrates a summary of the formulations.

(26) TABLE-US-00003 TABLE 3 phr Non-Productive Mixing Stage (4 min to 170° C. drop temperature) Solution styrene/butadiene rubber (SBR).sup.1 74 Cis 1,4-polybutadiene rubber.sup.2 26 Precipitated silica.sup.3 73 Carbon black 10 Processing oil, wax 9 Silane coupling agent.sup.4 6.5 Antidegradant.sup.5 3 Zinc oxide 3 Traction resin.sup.6 5 Fatty acids (E-G) or rosin acid.sup.7 (H-J) 1, 3 and 6 Second Non-productive mixing stage (3 minutes to 160° C. drop temperature) No additional ingredients added Productive mixing stage (2 minutes to 120° C. drop temperature) Sulfur 1.9 Sulfenamide accelerator 1.7 Diphenyl guanidine accelerator 1.5 .sup.1SLF31X22 from The Goodyear Tire & Rubber Company .sup.2Budene 1207 from The Goodyear Tire & Rubber Company .sup.3Z1165MP ™ from Rhone-Poulenc .sup.4NXT ™ from GE Silicones .sup.5Amine type .sup.6Coumarone-indene resin .sup.7Gum rosin

(27) The rubber composition Samples for the U.S. patent example were prepared by mixing the elastomers together with the identified rubber compounding ingredients in a first non-productive mixing stage (NP) in an internal rubber mixer for about 4 minutes at a temperature of about 170° C. The mixture was then further sequentially mixed in a second non-productive mixing stage (NP) in an internal rubber mixer, with no additional ingredients added, for about 3 more minutes at a temperature of about 160° C. The resulting mixture was then mixed in a productive mixing stage (P) in an internal rubber mixer with curatives for about 2 minutes at a temperature of about 120° C. The rubber composition was cooled to below 40° C. between the non-productive mixing steps and between the second non-productive mixing step and the productive mixing step.

(28) The following Table 4 derived from the aforesaid U.S. patent illustrates the cure behavior and various physical properties of the silica-rich rubber compositions based on the basic recipe of Table 3 and reported herein as rubber Samples E through J.

(29) TABLE-US-00004 TABLE 4 Samples Control A B C D E F Fatty acids,(phr)—(fatty acid 1 3 6 0 0 0 emphasis added here) Rosin acid (phr)—(rosin acid 0 0 0 1 3 6 emphasis added here) Processing (uncured rubber processing indicator) Uncured (G’).sup.1 256 203 184 249 224 187 Wet (indicative wet traction).sup.2  0° C. Rebound 19 18 19 18 17 15 23° C. Rebound 36 38 34 34 31 28 Handling.sup.3 G’ at 10% 2261 1854 1598 2157 2100 1477 Modulus at 300% 10.4 9.1 8.3 10.6 9.1 7.4 Hot hardness 60 59 59 59 59 60 RR (indicative rolling resistance).sup.4 Rebound, 100° C. 56 58 61 55 52 51 TD (tan delta) at 100° C., RPA 0.14 0.12 0.11 0.14 0.14 0/.13 Wear (indicative resistance to wear).sup.5 DIN abrasion 108 137 135 115 131 143 COF (coefficient of friction).sup.6 Dry (dry surface) 1.54 1.53 1.57 1.62 1.56 1.64 Wet (wet surface) 0.32 0.34 0.33 0.35 0.43 0.52 Tear Original 82 77 76 81 97 135 .sup.1Uncured G’ was measured using ASTM D6601 on an RPA 2000 .sup.2Rebound was measured using ASTM D1054 .sup.3Modulus at 300 was measured using ASTM D1042 .sup.4Rebound at 100° C. was measured using ASTM D1415 .sup.5DIN abrasion was measured using ASTM 596.3 .sup.6Coefficient of friction (COF) measured using ASTM D1894. COF value for a rubber sample may be measured, for example, on a Model SP-200 slip/peel tester from IMASS, Inc. at six inches (about 15.2 cm) per minutes using a 200 g sled against a substrate surface such as, for example, a polished aluminum surface.

(30) From Table 4 it can be seen in Samples E through G that the increase of fatty acid provides no appreciable change in either of the dry or wet coefficient of friction (COF) values.

(31) However, the coefficient of friction values for Samples H, I and J (which contained the zinc rosinate formed in situ within the rubber compositions as a product of rosin acid, instead of the fatty acid and zinc oxide) were dramatically improved for wet substrate conditions as compared to Samples E, F and G and also showed a small improvement for dry COF (dry COF emphasis added here).

(32) Accordingly, it is concluded herein that a footwear rubber sole of a rubber composition containing dual precipitated silica moieties provided in a sense of being comprised of hydrophilic precipitated silica and hydrophobic precipitated silica which also contains a zinc soap in the form of zinc rosinate as a product of zinc oxide and freely added rosin acid, which may be in addition to any residual rosin acid which might be contained in an elastomer in the rubber composition can promote a coefficient of friction of the sole's surface intended for contacting or engaging a substrate surface.

EXAMPLE III

(33) This Example, derived from Example II of U.S. Pat. No. 9,212,275, relates to providing dual silica moieties in a rubber composition and tire with tread thereof in a sense of providing a combination of pre-hydrophobated precipitated silica (hydrophobic precipitated silica) and hydrophilic precipitated silica. The Example is presented here for said evaluation of dual precipitated moieties in a sense of hydrophobic precipitated silica and hydrophilic precipitated silica in a footwear rubber sole rubber composition.

(34) For this Example, Tables 3 and 4 of said Example II of U.S. Pat. No. 9,212,275 have been re-labeled as Tables 5 and 6, respectively, to present the Tables herein in a chronological sequence.

(35) For this Example, rubber compositions C through F of said Example II of U.S. Pat. No. 9,212,275 have been re-labeled as rubber compositions K through N, respectively, to present the labels herein in a chronological sequence.

(36) For this Example of U.S. Pat. No. 9,212,275, experiments are shown as being conducted to evaluate the effect of adding hydrophilic, not pre-treated, precipitated silica to the pre-hydrophobated, (pre-treated), precipitated silica in the internal rubber mixer (Banbury mixer) without addition of silica coupling agent to the compounds (rubber composition Samples). Control rubber Sample K contained 84 phr of the pre-treated silica, whereas rubber Samples L, M and N contained in addition to the 84 phr of the pre-treated silica, 5, 10 and 15 phr, respectively, of the not pre-treated, therefore hydrophilic, precipitated silica.

(37) This example represents an attempt to increase the low strain stiffness of the compound containing pre-treated (pre-hydrophobated) precipitated silica by the addition of various levels of not-treated (therefore hydrophilic) precipitated silica, without the addition of silica coupling agent. The success of this approach and others listed in the following examples demonstrates an ability to increase low strain stiffness, without a significant penalty to hysteresis, to the rubber composition for which a lower hysteresis of the rubber composition is desired to promote an improvement in (lower) tire rolling resistance for the tire with a tread of such rubber composition.

(38) The rubber composition (rubber compound) base is illustrated in the following Table 5 where the parts and percentages are reported in terms parts by weight unless otherwise indicated.

(39) TABLE-US-00005 TABLE 5 First Non-Productive Mixing Stage (NP1) Parts by weight (phr) Functionalized SBR rubber.sup.1 60 Natural rubber .sup.2 40 Hydrophilic (not pre-treated) precipitated silica.sup.3 0, 5, 10, 15 Pre-hydrophobated precipitated silica.sup.4 84, 84, 84, 84

(40) Ingredients used are as identified in Table 1 of Example I of U.S. Pat. No. 9,212,275 except for amounts and unless otherwise identified.

(41) The following Table 6 illustrates cure behavior and various physical properties of the rubber compositions based upon the compounds of Table 5. Where cured rubber samples are examined, such as for the stress-strain, hot rebound and hardness values, the rubber samples were cured for about 12 minutes at a temperature of about 170° C.

(42) TABLE-US-00006 TABLE 6 Samples (phr) K L M N Materials (phr) Functionalized SBR elastomer 60 60 60 60 Hydrophilic (not pre-treated) precipitated silica 0 5 10 15 Pre-hydrophobated precipitated silica 84 84 84 84 Silica coupling agent 0 0 0 0 Properties Tire Tread Predictive Handling Properties Cured storage modulus (G′).sup.1 at 100° C., 11 Hertz (RPA).sup.1 1 percent strain (MPa) 1220 1367 1599 2338 10 percent strain (MPa) 1000 1076 1183 1489 Tire Tread Rolling Resistance Predictive Properties (higher values for rebound and lower values for tan delta are predictive of beneficial reduction in tire rolling resistance) Rebound (100° C.) 63 60 59 59 Tan delta (100° C., 10% strain, 11 Hertz) 0.121 0.118 0.114 0.091 Tire Tread Predictive Wet Traction Property Rebound, 0° C. 7.3 7.6 7.7 7.8 Tire Treadwear Predictive Property Abrasion Resistance(rate of abrasion, lower is better) Grosch abrasion.sup.2, Medium, mg/km 53 59 65 74 Tear Strength.sup.3, (peal strength) N At 95° C. for testing 61 72 55 64 .sup.1,2,3Test procedures as in Example I (of U.S. Pat. No. 9,212,275 which is incorporated herein in its entirety)

(43) It can be seen in Table 6 that the low strain stiffness of rubber Sample (Compound) K, the control, can be significantly increased with only a minor penalty to hysteresis, as indicated by rebound and as indicated by tan delta physical properties, by the addition of low levels of not-treated precipitated silica (therefore hydrophilic precipitated silica), in Compounds (rubber Samples) L, M, N.

(44) This is considered to be significant in a sense that it is seen that an advantage can therefore be taken of the low hysteresis properties of the rubber promoted by the pre-treated precipitated silica (pre-hydrophobated precipitated silica), through small additions of the hydrophilic precipitated silica with a resulting improvement of the low strain stiffness properties which are significant for promoting wet and dry handling tire performance for a tire tread.

(45) Accordingly, it is concluded herein that a footwear rubber sole of a rubber composition containing dual precipitated silica moieties in a sense of a combination of hydrophobic precipitated silica (as a pre-hydrophobated precipitated silica prior to addition to the rubber composition), together with a hydrophilic precipitated silica (a precipitated silica which is provided to the rubber composition without being pre-hydrophobated) can provide beneficial physical property(ies) for the footwear rubber sole.

(46) While 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.