RUBBER COMPOSITION AND A TIRE

Abstract

In a first aspect, the present invention is directed to a tire comprising a belt portion and a tread portion radially outward of the belt portion, wherein the tread portion comprises a radially outer tread layer for contacting the road when driving and a radially inner tread layer arranged between the radially outer tread layer and the belt portion, wherein the radially outer tread layer comprises a first rubber composition having a first shear storage modulus G′1 and the radially inner tread layer comprises a second rubber composition having a second shear storage modulus G′2, wherein the second shear storage modulus G′2 is between 3 MPa and 9 MPa higher than the first shear storage modulus G′1, and wherein the first shear storage modulus G′1 ranges from 1 MPa to 3 MPa and the second shear storage modulus G′2 ranges from 4 MPa to 12 MPa.

Claims

1. A tire comprising a belt portion and a tread portion, wherein the tread portion is situated radially outward from the belt portion, wherein the tread portion comprises a radially outer tread layer, which is adapted to be ground contacting, and a radially inner tread layer arranged between the radially outer tread layer and the belt portion, wherein the radially outer tread layer comprises a first rubber composition having a first shear storage modulus G′1, the radially inner tread layer comprises a second rubber composition having a second shear storage modulus G′2, wherein the second shear storage modulus G′2 is between 3 MPa and 9 MPa higher than the first shear storage modulus G′1, and wherein the first shear storage modulus G′1 ranges from 1 MPa to 3 MPa and the second shear storage modulus G′2 ranges from 4 MPa to 12 MPa, and wherein the first shear storage modulus G′1 and the second shear storage modulus G′2 are determined according to ASTM D5992.

2. The tire of claim 1 wherein the first shear storage modulus G′1 is within the range of 1 MPa to 2.5 to MPa.

3. The tire of claim 1 wherein the second shear storage modulus G′2 is within the range of 5.5 MPa to 10 MPa.

4. The tire of claim 1 wherein the second shear storage modulus G′2 is within the range of 3.5 MPa to 6 MPa higher than the first shear storage modulus G′1.

5. The tire of claim 1 wherein the first shear storage modulus G′1 is within the range of 1 MPa to 2.5 to MPa, the second shear storage modulus G′2 is within the range of 5.5 MPa to 9 MPa, and wherein the second shear storage modulus G′2 is 3.5 MPa to 7 MPa higher than the first shear storage modulus G′1.

6. The tire of claim 1 wherein the tread portion comprises a tread cap and a tread base, and wherein the radially outer tread layer is a layer of the tread cap and wherein the radially inner tread layer is a (tread base) layer of the tread base.

7. The tire of claim 1 wherein the tread portion comprises a tread cap and a tread base arranged radially inward of the tread cap and wherein the radially outer tread layer and the radially inner tread layer are comprised in the tread cap.

8. The tire of claim 1 further comprising a plurality of circumferential grooves and circumferential ribs, wherein two neighboring circumferential grooves define a circumferential rib, and wherein the radially inner tread layer comprises an electrically conductive chimney extending to the radially outermost surface of the tread portion for contacting the road when driving, wherein the conductive chimney extends radially through one of the ribs and is axially spaced apart from the neighboring grooves.

9. The tire of claim 1 further comprising a plurality of circumferential grooves, wherein the radially inner tread layer is free of radial extensions contacting the circumferential grooves.

10. The tire of claim 1 wherein the radially inner tread layer is free of any radial extension extending radially into the radially outer tread layer.

11. The tire of claim 1 wherein the first rubber composition has a tangent delta which is higher than 0.2, as determined according to ASTM D5992.

12. The tire of claim 11 wherein the first rubber composition has a tangent delta that ranges from 0.2 to 0.4.

13. The tire of claim 1 wherein the first rubber composition has a tangent delta that ranges from 0.05 to 0.15 as, determined according to ASTM D5992.

14. The tire of claim 1 wherein the radially inner tread layer has over at least 90% of its axial width a radially thickness ranging from 20% to 80% of the maximum radial thickness of the radially outer tread layer.

15. The tire of claim 1 wherein the second rubber composition comprises: from 75 phr to 90 phr of an elastomer selected from one or more of cis-1,4-polyisoprene having a cis content of more than 90% and a solution polymerized styrene-butadiene rubber, from 10 phr to 25 phr of cis-1,4 polybutadiene rubber having a glass transition temperature ranging from −85° C. to −110° C., from 40 phr to 80 phr of a filler comprising from 40 phr to 80 phr carbon black and from 0 phr to 40 phr silica, less than 10 phr of plasticizer, from 20 phr to 50 phr of a methylene acceptor composition comprising a phenol formaldehyde and an alkyl phenol formaldehyde, and from 1 phr to 10 phr of a methylene donor composition comprising hexamethylenetetramine.

16. The tire of claim 15 wherein the second rubber composition comprises: from 45 phr to 70 phr of the filler comprising from 45 phr to 70 phr carbon black and from 0 phr to 25 phr silica, from 25 phr to 45 phr of the methylene acceptor composition comprising the phenol formaldehyde and the alkyl phenol formaldehyde, from 1 phr to 5 phr of the methylene donor composition comprising the hexamethylenetetramine, and from 1.5 phr to 4 phr of sulfur.

17. The tire of claim 15 wherein the methylene acceptor composition comprises from 15 phr to 25 phr of the phenol formaldehyde, from 12 phr to 17 phr of octyl phenol formaldehyde, and the second rubber composition comprises from 2 phr to 4 phr sulfur.

18. The tire of claim 15 wherein the second rubber composition comprises from 2 phr to 4 phr of the methylene donor composition comprising the hexamethylenetetramine, and wherein the ratio between the methylene acceptor composition and the methylene donor composition ranges from 10:1 to 15:1.

19. The tire of claim 15 wherein the alkyl phenol formaldehyde has a softening point ranging from 80° C. to 100° C. and the phenol formaldehyde has a softening point ranging from 100° C. to 120° C.

20. A rubber composition comprising: from 75 phr to 90 phr of an elastomer selected from one or more of cis-1,4-polyisoprene having a cis-microstructure content of more than 90% and a solution polymerized styrene-butadiene rubber, from 10 phr to 25 phr of cis-1,4 polybutadiene rubber having a glass transition temperature ranging from −85° C. to −110° C., from 45 phr to 70 phr of a filler comprising from 45 phr to 70 phr carbon black and from 0 phr to 25 phr silica, less than 10 phr of plasticizer, from 25 phr to 45 phr of a methylene acceptor composition comprising a phenol formaldehyde and an alkyl phenol formaldehyde, from 1 phr to 5 phr of a methylene donor composition comprising a hexamethylenetetramine, and from 2 phr to 4 phr of sulfur.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] 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, wherein:

[0066] FIG. 1 is a schematic cross section of a tire comprising multiple tread cap layers;

[0067] FIG. 2 is a schematic cross section of a tire comprising multiple tread cap layers and a tread base layer;

[0068] FIG. 3 is a schematic cross section of a tire comprising multiple tread cap layers and a tread base layer having an electrically conductive chimney extending to the radially outermost side of the tread; and

[0069] FIG. 4 is a schematic cross section of a tire comprising two tread cap layers wherein the radially inner tread cap layer, in accordance with an embodiment of the invention, comprises a conductive chimney extending to the radially outermost side of the tread.

DETAILED DESCRIPTION OF THE INVENTION

[0070] FIG. 1 is a schematic cross-section of a tire 1. The tire 1 has a tread (or tread portion) 10, an inner liner 13, a belt structure (or belt portion) comprising four belt plies 11, a carcass ply 9, two sidewalls 2, and two bead regions 3 comprising bead filler apexes 5 and beads 4. The example tire 1 is suitable, for example, for mounting on a rim of a vehicle, e.g. a truck or a passenger car. As shown in FIG. 1, the belt plies 11 may be covered by an overlay ply 12. The carcass ply 9 includes a pair of axially opposite end portions 6, each of which is associated with a respective one of the beads 4. Each axial end portion 6 of the carcass ply 9 may be turned up and around the respective bead 4 to a position to anchor each axial end portion 6. The turned-up portions 6 of the carcass ply 9 may engage the axial outer surfaces of two flippers 8 and axial inner surfaces of two chippers 7. As shown in FIG. 1, the example tread 10 may have four circumferential grooves 20, each groove typically defining a U-shaped opening in the tread 10. The tread 10 or tread portion comprises in accordance with FIG. 1 two tread cap layer layers 30, 40 arranged radially on top of each other, wherein the radially outer tread cap layer 30 is supported by the radially inner tread cap layer 40. Alternatively, the tread 10 could comprise one or more further tread cap layers and/or a tread base layer arranged radially inside of the tread cap (not shown). In accordance with the present embodiment of the invention, the radially inner tread layer 40 comprises a compound having a higher shear storage modulus (G′) than the radially outer tread layer 30. In particular, such a difference may amount to at least 4 MPa according to a nonlimiting example of the invention. Such an embodiment provides the radially outer tread layer 30 with a stiff base, stiffer than the compound of the radially outer tread layer 30. Preferably, the radial thickness of the radially inner tread layer 40 ranges over at least 80% of its axial width from 20% to 80% of the maximum radial thickness of the radially outer tread cap layer 30. This relatively large thickness helps to provide an even better support for the radially outer tread layer 30.

[0071] The radially outer tread layer 30 could comprise different tread compounds having a stiffness ranging from 1 MPa to 3 MPa. When reference is made to a stiffness herein in MPa, this shall be understood as the corresponding shear storage modulus G′. In other words, these compounds could for instance be high performance compounds or low rolling resistance compounds, depending on the intended use of the tire.

[0072] Tables 3 and 4 provide some examples of suitable compounds for a radially outer tread layer 30. While the embodiment of FIG. 1 suggests a plurality of tire components including for instance apexes 5, chippers 7, flippers 8 and overlay 12, such components are not mandatory for the invention. Also, the turned-up end of the carcass ply 9 is not necessary for the invention or may pass on the opposite side of the bead area 3 and end on the axially inner side of the bead 4 instead of the axially outer side of the bead 4. The tire could also have for instance more or less than four grooves.

[0073] The axial direction a (in other words a direction in parallel to the axis of rotation of the tire 1), the radial direction r and the circumferential direction c have been indicated as common in the tire art. The terms axial direction a, radial direction r and circumferential direction c shall not be limited to a specific orientation unless otherwise provided herein.

[0074] FIG. 2 shows another tire 1′ in accordance with another embodiment of the present invention. For the sake of easier reference, the same reference numerals as in FIG. 1 have been used in FIG. 2 where applicable. In contrast to the tread 10 or tread portion according to FIG. 1, the tread 10′ or tread portion of FIG. 2 comprises a tread base layer 41, and a tread cap radially outside of the tread base layer 41, wherein the tread cap comprises a first tread cap layer 31 radially outside of the tread base layer 41 and a second tread cap layer 32 arranged radially outside or on top of the first tread cap layer 31. In the present example, it is the tread base layer 41 having a shear storage modulus G′ that is at least 4 MPa larger than the shear storage modulus, preferably of each one, of the tread cap layers 31, 32.

[0075] FIG. 3 depicts a third embodiment of a tire 1″ comprising a tread 10″ with a tread base layer 42 having a (electrically conductive) chimney 50, radially extending to the outermost top of the tread 10″ in a rib formed between two grooves 20. Electrically conductive chimneys are known as such in order to provide electrical conductivity through radially outer(most) tread layers, such as tread layers 33, 34 shown in FIG. 3 to the base layer 42. For this purpose, the tread base layer 42 can for instance have a carbon black content which is at least 40 phr or at least 45 phr which is one way to render the compound of the base layer electrically conductive. This may be of particular, interest in case of not sufficiently conductive tread layers contacting the road when driving (e.g. in case of fully silica reinforced compounds). In particular, such a conductive chimney does not act as groove reinforcement of a tire as it typically does not contact the sidewalls of the grooves 20. Such an arrangement might increase the risk of groove cracking. In the depicted embodiment, the compounds of the tread cap layers 33, 34 and the tread base layer 42 could be the same as in the embodiment of FIG. 2.

[0076] FIG. 4 depicts a fourth embodiment of a tire 1′″ comprising a tread 10′″ with a radially inner tread cap layer 43 and a radially outer tread cap layer 35 supported by the radially inner tread cap layer 43. Similar to the embodiment of FIG. 3, the tread 10′″ of FIG. 4 comprises a conductive chimney 53, whereas the conductive chimney 53 of the embodiment of FIG. 4 extends from the inner tread cap layer 43 instead from the base layer 42. In particular, the embodiments according to FIGS. 1 and 4 do not have a tread base layer. Such tread base layers may be desired in some cases (e.g. for an increased tack between the belt and the tread cap) but are preferably not necessarily required for the compounds of the radially inner tread layers in accordance with the present invention. In particular, the second compound of the radially inner layer (such as radially inner tread layer 43) as described herein is deemed to have sufficient tack to omit a further base layer if desired.

[0077] Below Table 1 shows compositions which may be used for radially inner tread layers such as a tread base layer or radially inner tread cap layer supporting one or more radially outer tread layers. Control Sample 1, Control Sample 2 and the Inventive Examples comprise a combination of natural rubber, polybutadiene and carbon black. Control Sample 1 and the Inventive Examples comprise also silica and an amount of phenol/phenolic formaldehyde resin in combination with hexamethylenetetramine (i.e. a methylene donor). Control Sample 2 also includes syndiotactic-1,2-polybutadiene as further reinforcing agent. The Inventive Examples comprise an alkyl phenol formaldehyde resin and relatively high amounts of sulfur. Inventive Example 3 comprises in addition a higher amount of Hexamethylenetetramine than Inventive Examples 1 and 2. While the below Inventive Examples 1 to 3 show explicitly compositions comprising natural rubber, it is emphasized that also synthetic polyisoprene may be used in another embodiment of the present invention. Moreover, the inventors have discovered that the use of SSBR instead of natural rubber or synthetic polyisoprene or blends of all these polymers is possible and desirable. However, natural rubber may be considered as the most preferred non-limiting example. Moreover, it is emphasized that compositions comprising essentially carbon black and in particular less than 5 phr silica or even no silica have been found to be also particularly desirable.

TABLE-US-00001 TABLE 1 Parts by weight (phr) Control Control Inventive Inventive Inventive Sample Sample Example Example Example Material 1 2 1 2 3 Natural Rubber 80 72 80 80 80 Polybutadiene.sup.1 20 28 20 20 20 Syndiotactic 1,2-Polybutadiene.sup.2 0 6 0 0 0 Carbon Black 50 53 50 50 50 Precipitated silica 20 0 20 20 20 Silane 2 0 2 2 2 Stearic acid 3 1.5 3 3 3 Antidegradants 3 4 3 3 3 Oil 15 0 0 0 0 Phenol formaldehyde resin.sup.3 20 2 20 20 20 Alkyl phenol formaldehyde resin.sup.4 0 0 14.5 14.5 14.5 Hexamethylenetetramine 3 0 3 3 5 Sulfenamide accelerators 2.4 2.9 2.4 2.4 2.4 Fatty acid soap 2 0 2 2 2 ZnO 2.5 2.6 2.5 2.5 2.5 Waxes 1.5 1.5 1.5 1.5 1.5 Sulfur 1.6 2.3 2.3 3.2 2.5 Vulcanization inhibitor 0.3 0.2 0.3 0.3 0.3 .sup.1as Budene 1207 of the Goodyear Tire and Rubber Company .sup.2as UBEPOL-VCR412 of UBE INDUSTRIES, LTD. .sup.3as SMD 30207 M3 from SI group .sup.4octyl phenol formaldehyde resin as SP-1068 from SI Group

[0078] Below Table 2 shows the shear storage modulus values G′ of the compounds listed in Table 1. While Control Samples 1 and 2 show relatively high values of more than 2 and 3 MPa, the G′ value of the Inventive Example 1 is significantly higher, i.e. above 6 MPa. The G′ values of the Inventive Examples 2 and 3 are even higher than 7 MPa. However, the tangent delta values of the Inventive Examples are higher than the tangent delta values of the Control Samples 1 and 2, although deemed still acceptable for a radially inner tread layer.

TABLE-US-00002 TABLE 2 Control Control Inventive Inventive Inventive Physical Sample Sample Example Example Example properties 1 2 1 2 3 G′ 6% 70° C. 3.36 2.39 6.1 7.0 7.9 [MPa] tanδ 6% 70° C. 0.25 0.08 0.29 0.28 0.28

[0079] Below Table 3 shows some exemplary compounds which can be utilized in rubber formulations for the radially outer tread layer which is supported by a radially inner layer made of a relatively stiff compound, such as the compounds shown in Inventive Examples 1 to 3. In particular, below Examples 1 to 3 may be considered as examples for high performance compositions. The present invention is not limited to these specific examples of compounds for the radially outer tread layer.

TABLE-US-00003 TABLE 3 Parts by weight (phr) Example Example Example Material 1 2 3 Polybutadiene.sup.1 10 10 10 Solution SBR.sup.2 0 50 50 Solution SBR.sup.3 0 40 40 Solution SBR.sup.4 75 0 0 3,4-Polyisoprene 15 0 0 Silica.sup.5 95 105 56 Carbon black.sup.6 20 20 62 Oil.sup.7 31 49 44 Resin.sup.8 8 15 10 Resin.sup.9 0 5 5 Resin.sup.10 8 0 0 Low MW Styrene.sup.11- 0 0 11.76 Coupling agent.sup.12 6 7.6 4 Waxes.sup.13 1.5 1.5 1.5 Fatty acids.sup.14 3.5 5 5 Antidegradant.sup.15 0.5 4.5 4.5 Zinc oxide 2.5 2.5 2.5 Sulfur 1.8 1.9 1.9 Accelerators.sup.16 4.7 4.9 4.3 .sup.1Budene1207 from Goodyear Tire & Rubber Chemical .sup.2SE SLR6430 solution polymerized styrene-butadiene rubber, 40% styrene, 14% vinyl, Tg (OE) = −34° C., 37.5 phr TDAE oil, from Styron. .sup.3Tufdene E680 solution polymerized styrene-butadiene rubber, 34% styrene, 38% vinyl, Tg(OE) = −25° C., 37.5 phr SRAE oil, from Asahi Chemical .sup.4SE SLR 4630, partially silicon-coupled, solution-polymerized styrene butadiene rubber extended with 37.5 phr TDAE oil, typical properties reported as 25 percent by weight of styrene and 63 percent by weight vinyl (of butadiene segments), Tg = −28.9° C., Mooney ML 1 + 4 (100° C.) = 55, from the Dow Chemical Company .sup.5Precipitated Silica, BET Nitrogen Surface Area = 160 m2/g .sup.6Furnace black with iodine absorption number = 202 g/kg (ASTM D-1510), oil absorption number = 134 cm.sup.3/kg (ASTM D-2414) .sup.7RAE, SRAE & TDAE oil .sup.8Alphamethyl styrene resin, as Resin 2336 from Eastman .sup.9Dimerized gum rosin, as Dymerex from Eastman .sup.10coumarone-indene resin .sup.11Ricon 100, low molecular weight styrene-butadiene copolymer, 25% styrene, 70% vinyl, MW = 4500, from Cray Valley .sup.1250% Bis(triethoxysilylpropyl) tetrasulfide on carbon black .sup.13Microcrystalline & paraffinic waxes .sup.14fatty acids, fatty acid zinc salts, and fatty acid glycerides .sup.15p-phenylenediamine and quinoline types .sup.16Sulfenamide and guanidine type

[0080] A fourth example, Example 4, is given below in Table 4. This example may be considered as an example for a tread (cap) composition that is designed to have low rolling resistance.

TABLE-US-00004 TABLE 4 Parts by weight (phr) Material Example 4 SBR.sup.a 49 SBR.sup.b 30 Natural Rubber 21 Silica.sup.c 65 Silane.sup.d 5.2 Silane.sup.e 2 Liquid polymer.sup.f 4 TDAE oil 9 Sunflower oil 3 .sup.aSolution polymerized SBR with styrene content of 21% and 1,2-vinyl content of 50%, Tg = −23° C. obtained from Trinseo as SLR4602 .sup.bSolution polymerized SBR with styrene content of 30% and 1,2-vinyl content of 41%, Tg = −22.4° C. extended with 20 phr TDAE oil, obtained as SLF30H41-66C from The Goodyear Tire & Rubber Company .sup.cZeosil Premium 200MP from Solvay .sup.dS-octanoylmercaptopropyltriethoxysilane, as NXT* from Momentive .sup.eTESPD type silane coupling agent, 50% on carbon black as X50S from Evonik .sup.fPolybutadiene end functionalized with triethoxysilyl groups, Mw = 3000, Tg = −35 C., as Ricon 603 from Cray Valley

[0081] Below Table 5 provides G′ and tangent delta values for the exemplary radially outer tread layer compounds listed in Tables 3 and 4. The respective G′ values are considerably smaller than those of the base layer compounds in accordance with Table 2. The tangent delta values of Examples 1 to 3 are relatively high which is typical for high performance tread compounds, whereas the tangent delta value for Example 4 is very low in view of the fact that this compound is designed as low rolling resistance compound, in particular including a low filler amount and little to no carbon black.

TABLE-US-00005 TABLE 5 Physical Example Example Example Example properties 1 2 3 4 G′ 6% 70° C. 2 1.5 1.4 1.5 [MPa] tanδ 6% 70° C. 0.22 0.27 0.33 0.08

[0082] Below Table 6 shows tire test results for cornering stiffness and dry grip of the compounds according to Control Sample 1 and the Inventive Example 1. With the same tire construction including a tread base layer made of either the composition in accordance with Control Sample 1 or the Inventive Example 1 and one radially outer tread cap layer, the values for cornering stiffness and dry grip have significantly been improved by the Inventive Example 1 over the Control Sample.

TABLE-US-00006 TABLE 6 Inventive Control Example Tire Test Results Sample 1 1 Tire Cornering Stiffness @2.7 bar inflation [N/deg] 3388 3591 Tire Cornering Stiffness @2.9 bar inflation [N/deg] 3040 3253 F.sub.y max (dry grip) @2.7 bar inflation [N] 3212 3394 F.sub.y max (dry grip) @2.9 bar inflation [N] 2886 3106

[0083] Variations in the present invention are possible in light of the provided description. While certain representative embodiments, examples 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 invention. It is, therefore, to be understood that changes may be made in the particular example embodiments described which will be within scope of the invention as defined by the appended claims.