TIRE HAVING A MULTILAYER TREAD CAP

Abstract

This invention discloses a tire tread comprising: (a) a first tread cap layer comprising a first rubber composition; and (b) a second tread cap layer arranged radially inside of the first tread cap layer comprising a second rubber composition; wherein at 0° C. the rebound resilience of the first rubber composition is within a range of 10% to 25%, the rebound resilience of the second rubber composition is within a range of 15% to 35% and is at least 5% lower than that of the second rubber composition; and wherein at 100° C. the rebound resilience of the first rubber composition is within a range of 45% to 65%, the rebound resilience of the second rubber composition is within a range of 60% to 75% and is at least 3% higher than that of the first rubber composition.

Claims

1. A tire having a tread comprising: (a) a first tread cap layer which is adapted to being ground contacting, wherein the first tread cap layer comprises a first rubber composition; and (b) a second tread cap layer arranged radially inside of the first tread cap layer and supporting the first tread cap layer, wherein the second tread cap layer comprises a second rubber composition which is different from the first rubber composition; wherein the rebound resilience of the first rubber composition, as determined at a temperature of 0° C. according to DIN 53512, is within the range of 10% to 25%, and wherein the rebound resilience of the second rubber composition, as determined at a temperature of 0° C. according to DIN 53512, is within the range of 15% to 35%, and wherein said rebound resilience of the first rubber composition is at least 5% lower than said rebound resilience of the second rubber composition as determined at a temperature of 0° C. according to DIN 53512, and wherein the rebound resilience of the first rubber composition, as determined at a temperature of 100° C. according to DIN 53512, is within the range of 45% to 65%, and a rebound resilience of the second rubber composition, as determined at a temperature of 100° C. according to DIN 53512, is within the range of 60% to 75%, and wherein said rebound resilience of the second rubber composition, as determined at a temperature of 100° C., is at least 3% higher than said rebound resilience of the first rubber composition, as determined at a temperature of 100° C. according to DIN 53512.

2. The tire of claim 1 wherein the tire is a snow tire, wherein the tread comprises at least one circumferential groove and/or at least one groove separating two tread ribs, and wherein the at least one groove has a radial depth d extending from the radially outermost surface of the unworn tread to a bottom of the groove, wherein the radial depth d is equal to 4 mm plus a radial length t, and wherein the first tread cap layer has over at least 80% of its axial width a radial thickness within a range of t−1 mm to t+1 mm.

3. The tire of claim 1 wherein a maximum radial thickness of the second tread cap layer is within a range of 60% to 90% of a maximum radial thickness of the first tread cap layer.

4. The tire of claim 2 wherein the first tread cap layer has over at least 80% of its axial width a radial thickness within a range of t to t+1 mm.

5. The tire of claim 4 wherein the first tread cap layer has over at least 90% of its axial width a radial thickness within a range of t to t+1 mm.

6. The tire of claim 4 wherein said radial thickness of the first tread cap layer is within a range of 3 mm to 5 mm.

7. The tire of claim 1 further comprising a tread base layer radially inside of the first and second tread cap layers and supporting the second tread cap layer, wherein the tread base layer is comprised of a third rubber composition which is different from said first and second rubber compositions, wherein the third rubber composition has a rebound resilience, as determined at a temperature of 100° C. according to DIN 53512, which is at least 10% higher than the rebound resilience of the second rubber composition, as determined at a temperature of 100° C. according to DIN 53512.

8. The tire of claim 7 wherein the tread base layer has over at least 70% of its axial width a radial thickness which is within the range of 5% to 30% of the maximum radial thickness of the first tread cap layer.

9. The tire of claim 7 wherein the tread base layer has over at least 70% of its axial width a radial thickness which is within a range of 0.2 mm to 2 mm.

10. The tire of claim 1 wherein the first rubber composition and the second rubber composition are further comprised of a reinforcing filer, wherein the reinforcing filler is comprised predominantly of silica which is present at a level which is within the range of 90 phr to 200 phr.

11. The tire of claim 10 wherein the tire is further comprised of a tread base layer, wherein the tread base layer is situated radially inside of the first and second tread cap layers, wherein the tread base layer supports the second tread cap layer, wherein the tread base layer is comprised of a third rubber composition having a filler, wherein the filler is comprised predominantly of carbon black which is present at a level of at least 30 phr, and wherein silica can be present in the tread base layer at a level of no more than 30 phr.

12. The tire of claim 1 wherein the first rubber composition is comprised of 50 phr to 100 phr of at least one diene-based rubber having a maximum glass transition temperature of −50° C., and from 100 phr to 200 phr of silica, and wherein the second rubber composition is comprised of 50 phr to 100 phr of at least one diene-based rubber having a maximum glass transition temperature of −50° C., and from 90 phr to 150 phr of silica.

13. The tire of claim 12 wherein the first rubber composition is comprised of 5 phr to 60 phr of at least one traction resin selected from the group consisting of styrene-α-methylstyrene resin, coumarone-indene resin, petroleum hydrocarbon resin, terpene polymer, terpene phenol resin, rosin derived resins and copolymers, and wherein said resin has a softening point as determined in accordance with ASTM E28 which is in a range of 60° C. to 150° C.

14. The tire of claim 12 wherein the first rubber composition is comprised of 3 phr to 20 phr of an oil having a glass transition temperature which is within the range of −70° C. to −115° C.

15. The tire of claim 14 wherein said oil is a vegetable oil selected from the group consisting of sunflower oil, soybean oil and canola oil.

16. The tire of claim 12 wherein the first rubber composition is comprised of 55 phr to 100 phr of a solution styrene-butadiene rubber.

17. The tire of claim 12 wherein the second rubber composition is comprised of silica at a level which is within the range of 90 phr to 115 phr, and wherein the silica is present at a level which is at least 5 phr less than the level of the silica in the first rubber composition.

18. The tire of claim 16 wherein the first rubber composition is comprised of 5 phr to 20 phr of polybutadiene rubber having a glass transition temperature within a range of −100° C. to −115° C., and 80 phr to 95 phr of the solution styrene butadiene rubber.

19. The tire of claim 15 wherein the second rubber composition comprises a pre-silanized precipitated silica.

20. The tire of claim 12 wherein the second rubber composition is comprised of 5 phr to 20 phr of polyisoprene rubber, 5 phr to 20 phr of polybutadiene rubber, and 60 to 90 phr of the solution styrene-butadiene rubber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The structure, operation, and advantages of the invention will become more apparent upon contemplation of the following description taken in conjunction with the accompanying drawings.

[0077] FIG. 1 is a schematic cross section of a tire tread in accordance with an embodiment of the present invention.

[0078] FIG. 2 is a magnified partial cross section of the tire tread shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0079] FIG. 1 is a schematic cross-section of a tire tread 10 in accordance with an embodiment of the present invention. The tire tread 10 comprises multiple grooves 2 and two tread cap layers 3, 4, wherein a radially outer tread cap layer, or in other words a first tread cap layer 3 is provided to contact the road when driving and a radially inner tread cap layer or second tread cap layer 4 is supporting the first tread cap layer 3. In the embodiment of FIG. 1, the second tread cap layer 4 has a smaller radial thickness than the first tread cap layer 3. A tread base layer 5 is arranged radially inside of the tread cap layers 3, 4, supporting the second tread cap layer 4. In particular, each one of these layers 3, 4, 5 is made of a different rubber composition. Each of the tread cap layers 3, 4 and the tread base layer 5 extend around the tire in a circumferential direction c and also in an axial direction a, wherein these directions are perpendicular to the radial direction r of the tire as indicated in FIG. 1. The term axial direction as used herein means a direction which is parallel to the axis of rotation of the tire. The circumferential direction c is essentially parallel to the circumference of the tire and/or parallel to the equatorial plane of the tire EP. The radial direction r is perpendicular to the axial direction a. While the tread 10 is shown with four circumferential grooves 2, it is also possible that the tire has more or less circumferential grooves, such as one, two, three or five circumferential grooves. Such grooves may extend essentially in the circumferential direction c and may also be referred to as main grooves. In particular, the tire tread 10 may have one (axially) central circumferential groove such as in a case where the tread pattern is an essentially V-shaped tread pattern extending away from the axial centerline, or in other words from the equatorial plane EP, of the tire. The tread pattern may also be essentially V-shaped. In such a case the tread has grooves separating two adjacent ribs of the tread which extend essentially in a V-shaped pattern.

[0080] Preferably, the radial thickness of the tread base layer 5 is along at least 80% of its axial width smaller than the maximum radial thickness of the first tread cap layer 3 and also the maximum radial thickness of the second tread cap layer 4. The tread base layer has in the present non-limiting embodiment at axially outermost portions radial extensions 7, which may also be called skirt portions. Moreover, it has another radial extension 8 extending up to the radially outermost surface of the tread in a rib and/or at least one tread block adjacent the equatorial plane EP of the tire. An average axial width of this extension along its radial length is preferably smaller than 5% of the total axial width of the tread base layer 5 and/or within a range of 0.5% and 5% of said total axial width. This extension may serve as conductive chimney, in particular in case of electrically non-conductive first and/or second tread cap layers 3, 4.

[0081] As depicted in FIG. 2, which shows a magnified part of the tread according to FIG. 1, the grooves 2 have a radial depth or height d (in mm), which can be described as a radial distance of 4 mm plus the radial distance t (also in mm). In many countries 4 mm is the minimum remaining groove height or depth which allows a tire to drive safely under winter conditions. In the preferred embodiment shown in FIG. 2, the first tread cap layer 3 extends from the radially outermost surface of the tread radially inwards to a position below the 4 mm line, with the latter measured from the bottom of the groove in a radially outer direction. Thus, when the tire wears, it is ensured that it is the rubber composition of the first tread cap layer 3 which is contacting the road when driving. Only when the tire tread 10 is worn more than 1 mm below the 4 mm threshold, the tire will roll on the rubber composition of the second tread cap layer 4 which is rather designed for an improved rolling resistance, whereas the first rubber composition of the first tread cap layer 3 is designed for an improved wet performance. Thus, in a preferred embodiment the thickness of the first tread cap layer 3 (of the unworn tread) is within a range of t to t+1 mm (with t=d−4 mm), measured from the radially outermost surface of the tread 10. Preferably the thickness of the first tread cap layer 3 is measured adjacent a circumferential center groove 2, such as extending along the equatorial plane EP of the tire. If such a groove 2 does not exist, the thickness of the first tread cap layer 3 is determined adjacent a groove 2 which is axially closest to the equatorial plane EP of the tire. Preferably, the thickness of the first tread cap layer 3 is not too large. In other words, it is less desirable to have a first tread cap layer 3 which extends further in an inner radial direction as described herein above. In particular, according to the present embodiment of the invention, it is desired that the second tread cap layer 4 is made of a rubber composition which has a reduced rolling resistance compared to the rubber composition of the first tread cap layer 3. Thus, the radial thickness of the first tread cap layer is preferably not larger than t+1 mm. Moreover, preferably the radial thickness of the second tread cap layer 4 is smaller than the radial thickness of the first tread cap layer. Preferably, the radial thickness of the second tread cap layer 4 is within a range of 60% to 90% of the radial thickness of the first tread cap layer 3. However, in other embodiments it could be within a range of 25% to 150%. In addition, or alternatively, the majority of the radial thickness of the second tread cap layer 4 extends radially above the position of the bottom of the grooves 2. In other words, the second tread cap layer 4 extends with more than 50% of its radial thickness, preferably more than 60% of its radial thickness, radially above the bottom of the grooves 2. Thus, the majority of the tread height of (the first) 4 mm measured radially from the bottom of a groove 2 in a radially outer direction is formed by the second rubber composition which is advantageous for the rolling resistance of the tire tread 10.

[0082] Apart from the above described geometry of the tread cap layers 3, 4 and/or the tread base layer 5, the rubber compositions of the respective tread layers 3, 4, 5 are different in their compositions, wherein a rebound resilience of the first rubber composition of the first tread cap layer 3, determined at a temperature of 0° C. according to DIN 53512, is within a range of 10% to 25% (preferably 10% to 20%, or 10% to 19%), and a rebound resilience of the second rubber composition of the second tread cap layer 4, determined at a temperature of 0° C. according to DIN 53512, is within a range of 20% to 35% (preferably 20% to 30%, or 21% to 30%). In particular, the said rebound resilience of the first rubber composition is at least 5%, preferably at least 10% (and optionally at most 20%), lower than said rebound resilience of the second rubber composition. Said rebound resilience at a temperature of 0° C. is an indicator for the wet traction behavior of the tire. In addition, the rebound resilience of the first rubber composition, determined at a temperature of 100° C. according to DIN 53512, is within a range of 45% to 60% (preferably 50% to 60%, or 50% to 59%), and a rebound resilience of the second rubber composition, determined at a temperature of 100° C. according to DIN 53512, is within a range of 60% to 75% (preferably 60% to 70%, or 61% to 70%), wherein said rebound resilience of the second rubber composition, determined at a temperature of 100° C., is at least 3%, preferably 4% or 5% higher (and optionally at most 20% higher) than said rebound resilience of the first rubber composition, determined at a temperature of 100° C. The latter rebound resilience measured at a temperature of 100° C. is considered as an indicator for the rolling resistance of the tread. The above combination has been found to be most preferable by the inventors to obtain a compromise between wet performance and rolling resistance.

[0083] The rebound resilience of the tread base layer 5, determined at a temperature of 100° C., is preferably within a range of 70% to 90% or 70% to 85% which is an indicator for an even further improved contribution to the rolling resistance of the tread 10.

[0084] This invention is illustrated by the following examples that are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

[0085] Examples, in accordance with embodiments of the present invention, for rubber compositions of the first tread cap layer 3 are given herein below in Table 1.

TABLE-US-00001 TABLE 1 Parts by weight (phr) Inventive Inventive Inventive Example 1 Example 2 Example 3 (first tread (first tread (first tread Material cap layer) cap layer) cap layer) SSBR .sup.1 90 80 58 PBR 1 (Tg −108° C.).sup.2 10 0 42 PBR 2 (Tg −87° C.).sup.3 0 20 0 Silica.sup.4 115 115 135 Resin 1.sup.5 28 20.5 0 Resin 2 .sup.6 0 0 52 Oil.sup.7 11.5 24 4 Antidegradants.sup.8 3 3 3 Waxes 1.5 1.5 1.5 Sulfur 1.2 1.3 1.2 Silane 1.sup.9 7.2 7.2 8.4 Silane 2.sup.10 2 2 2 Accelerators.sup.11 4.8 5.3 6.4 Stearic Acid 2 2 2 Zinc Oxide 2.5 2.5 2.5 .sup.1 Solution-polymerized styrene butadiene rubber as Sprintan ™ SLR 3402 from Trinseo ™ having a Tg of about −60° C. .sup.2Cis-1,4 polybutadiene rubber as Budene ™ 1223 from the Goodyear Tire and Rubber Company, having a Tg of about −108° C. .sup.31,4 polybutadiene rubber with 10%-12% vinyl content and a Tg of about −87° C. .sup.4Precipitated silica with a surface area of about 125 m.sup.2/g .sup.5Terpene (alpha pinene based) resin having a Tg of about 70° C. as Dercolyte ™ A 115 .sup.6 Aromatic modified aliphatic petroleum hydrocarbon resin having a softening point of about 90° C. as Oppera ™ PR 373 Exxon Mobil .sup.7Sunflower oil with a Tg of about −80° C. .sup.8Mixed p-phenylene diamine type .sup.9As SI266 ™ coupling agent from Evonik Industries .sup.10As X50S ™ coupling agent from Evonik Industries .sup.11Sulfenamide and guanidine types

[0086] Table 2 discloses mechanical test results for the Inventive Examples disclosed above in Table 1.

TABLE-US-00002 TABLE 2 Samples Inventive Inventive Inventive Example 1 Example 2 Example 3 (first tread (first tread (first tread Test cap layer) cap layer) cap layer) Rebound at 0° C. (%) .sup.a 19.5 19.6 13.8 Rebound at 100° C. (%) .sup.a 59.5 59.9 54.1 Abrasion .sup.b 95 50 116 E′ at −40° C. (MPa) .sup.c 103 185 180 Tangent Delta (10%) RPA .sup.d 0.15 0.21 0.19 .sup.a Rebound measured on a Zwick Roell 5109 rebound resilience tester according to DIN 53512 at given temperature. .sup.b Rotary drum abrasion test according to DIN 53516, smaller value means less abrasion. .sup.c The modulus E′ was determined by means of a GABO ™ Eplexor ™ tester. The test specimen is subjected to 0.25% sinusoidal deformation at 1 Hz and the temperature is varied. .sup.d Data obtained with an RPA 2000 ™ Rubber Process Analyzer of Alpha Technologies based on ASTM D5289.

[0087] As shown by the above data, the three inventive compounds have a low rebound value at 0° C. which is an indicator for an advanced wet performance of the rubber composition of the first layer. Rebound values at 100° C. are below 60% which is not considered to be optimal under rolling resistance considerations. While the abrasion of the second example is very low, its modulus is relatively high which means that snow performance can be less favorable than for the first example. Tangent delta (tan δ) is another indicator for the rolling resistance of the compound which can also be compared with the values of the below exemplary compositions of the second tread cap layer.

[0088] Table 3 discloses exemplary compositions, in accordance with embodiments of the present invention, for the second tread cap layer 4.

TABLE-US-00003 TABLE 3 Parts by weight (phr) Inventive Inventive Example 4 Example 5 (second tread (second tread Material cap layer) cap layer) SSBR .sup.1 75 90 PBR (Tg −108° C.).sup.2 10 10 Natural Rubber 15 0 Pre-silanized silica.sup.3 110 110 Resin 1.sup.4 27 0 Resin 2.sup.5 0 34 Oil.sup.6 17.5 10.5 Antidegradants.sup.7 3 2.5 Waxes 1.5 2.5 Sulfur 0.4 0.4 Silane 1.sup.8 0 7.2 Silane 2.sup.9 2 2 Accelerators.sup.10 2.3 2.2 Stearic Acid 0 2 Crosslinker 2.2 2.2 Zinc Oxide 2 2 Processing aids 4.5 0 .sup.1 Solution-polymerized styrene butadiene rubber as Sprintan ™ SLR 3402 from Trinseo ™ having a Tg of about −60° C. .sup.2Cis-1,4 polybutadiene rubber as Budene ™ 1223 from the Goodyear Tire and Rubber Company, having a Tg of about −108° C. .sup.3Pre-silanized, precipitated silica as Agilon 400 ™ of PPG Industries .sup.4Alpha methylstyrene resin with a softening point of 85° C. as Novares Pure 85 AS ™ .sup.5Terpene (alpha pinene based) resin having a Tg of about 70° C. as Dercolyte ™ A 115 .sup.6Sunflower oil, with a Tg of about −80° C. .sup.7Mixed p-phenylene diamine type .sup.8As SI266 ™ coupling agent from Evonik Industries .sup.9As X50S ™ coupling agent from Evonik Industries .sup.10Sulfenamide and guanidine types

[0089] Table 4 discloses mechanical test results for the Inventive Examples in relation to the second tread cap layer 4 as disclosed above in Table 2.

TABLE-US-00004 TABLE 4 Samples Inventive Inventive Example 4 Example 5 (second tread (second tread Test cap layer) cap layer) Rebound at 0° C. (%) .sup.a 22.6 20.0 Rebound at 100° C. (%) .sup.a 61.9 61.9 Abrasion .sup.b 87 86 E′ at −40° C. (MPa) .sup.c 70 145 Tangent Delta (10%) RPA .sup.d 0.14 0.18 .sup.a Rebound measured on a Zwick Roell 5109 rebound resilience tester according to DIN 53512 at given temperature. .sup.b Rotary drum abrasion test according to DIN 53516, smaller value means less abrasion. .sup.c The modulus E′ was determined by means of a GABO ™ Eplexor ™ tester. The test specimen is subjected to 0.25% sinusoidal deformation at 1 Hz and the temperature is varied. .sup.d Data obtained with an RPA 2000 ™ Rubber Process Analyzer of Alpha Technologies based on ASTM D5289.

[0090] In view of the above results shown in Table 4, the exemplary rubber compositions for the second tread cap layer 4 have higher rebound at 0° C. than the rubber compositions for the first tread cap layer 3. At the same time the compositions for the second tread cap layer 4 have a considerably higher rebound resilience at 100° C. than the rubber compositions for the radially outermost tread cap layer 3. The corresponding improvement in rolling resistance is also indicated by the tangent delta (tan δ) values which are much lower than respective values of the examples for the first rubber composition. The higher rebound resilience values at 0° C. of the Inventive Examples 4 and 5 compared to the Inventive Examples 1 to 3 are less important as a tire will usually not be driven on the radially inner tread cap layer. Apart from that, even the rebound resilience values at 0° C. are still acceptable for the fourth and fifth Inventive Examples.

[0091] In another embodiment, a tread base layer formulation may comprise from 50 phr to 80 phr of polyisoprene such as natural rubber, from 20 phr to 50 phr of polybutadiene, from 30 to 60 phr (preferably from 35 phr to 50 phr) of carbon black, and from 1 phr to 10 phr of a tackifier resin. In a specific example tested by the inventors, comprising 65 phr of natural rubber, 35 phr of polybutadiene, 40 phr of carbon black, 4 phr of a phenolic resin and further ingredients such a accelerators, processing aids, antidegradants and vulcanizing agents, a rebound resilience of 78%, measured at 100° C., was determined and a tangent delta of 0.07 based on the same measurement methods as described above for the other Inventive Examples.

[0092] Variations in the present invention are possible in light of the provided description. In any case, the above described embodiments and examples shall not be understood in a limiting sense. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention.