Tire tread and a tire comprising a tread

Abstract

The present invention relates to a tire tread comprising a tread cap comprising at least one tread cap rubber compound, at least three circumferential grooves, wherein at least portions of the sidewalls and the bottom of each of said grooves are formed by a circumferential groove reinforcement, and wherein a first groove reinforcement of a groove laterally next to the equatorial plane of the tire comprises a first reinforcement rubber compound which has a higher hardness than the tread cap rubber compound, and wherein a second groove reinforcement of a groove with a larger lateral distance to the equatorial plane of the tire than the first groove, comprises a second reinforcement rubber compound which has a higher hardness than the tread cap rubber compound and a lower hardness than the second reinforcement rubber compound.

Claims

1. A tire tread comprising: a tread cap comprising at least one tread cap rubber, at least three circumferential grooves, wherein at least portions of sidewalls and the bottom of each of said grooves are formed by a circumferential groove reinforcement, and wherein a first groove reinforcement of a groove laterally next to the equatorial plane of the tire comprises a first reinforcement rubber compound which has a higher hardness than the tread cap rubber compound, and wherein a second groove reinforcement of a groove with a larger lateral distance to the equatorial plane of the tire than the first groove, comprises a second reinforcement rubber compound which has a higher hardness than the tread cap rubber compound and a lower hardness than the first reinforcement rubber compound.

2. The tire tread of claim 1, wherein the first reinforcement rubber compound has a Shore A hardness which is within the range of 75 to 100 and wherein the Shore A hardness of the second reinforcement rubber compound is within the range of 60 to 90.

3. The tire tread of claim 1, wherein the tread cap rubber compound has a Shore A hardness which is within the range of 40 to 75.

4. The tire tread of claim 1, wherein at least one of the groove reinforcements comprises two groove sidewall layers, each sidewall layer extending from the outermost radial surface of the unworn tread down into the direction of the bottom of the groove formed by the groove reinforcement.

5. The tire tread of claim 1, wherein at least one of the groove reinforcements has two groove sidewall layers, each sidewall layer extending from the outermost radial surface of the unworn tread down into the direction of the bottom of the groove formed by the groove reinforcement, and wherein each sidewall layer has a uniform thickness along its length.

6. The tire tread of claim 1, wherein at least one of the groove reinforcements has a groove support portion forming a bottom portion of the groove and having a radially inner base side as well as a radially outer top side, wherein the groove support portion tapers from its base side to its top side and has optionally an essentially trapezoidal shape tapering from the base side to the top side.

7. The tire tread of claim 1, wherein at least one groove reinforcement comprising the first reinforcement rubber compound is embedded in a groove reinforcement comprising the second reinforcement rubber compound, and wherein the groove reinforcement comprising the second reinforcement rubber compound extends laterally below multiple grooves from one lateral side of the equatorial plane of the tire to the other lateral side of the equatorial plane of the tire.

8. The tire tread of claim 1, wherein at least one of the groove reinforcements has two groove sidewall layers, each sidewall layer extending from the outermost radial surface of the unworn tread down into the direction of the bottom of the groove formed by the groove reinforcement, and wherein each sidewall layer has a uniform thickness which is within the range of 0.5 mm to 4 mm along its length.

9. The tire tread of claim 1, wherein at least one of the groove reinforcements has two groove sidewall layers, each sidewall layer extending from the outermost radial surface of the unworn tread down into the direction of the bottom of the groove formed by the groove reinforcement, and wherein each sidewall layer has a uniform thickness along its length, and wherein the groove sidewall layers extend from the top of the unworn tread at least over 70% of the depth of the groove measured in parallel to the sidewall of the groove.

10. The tire tread of claim 1, wherein at least one of the groove reinforcements has two groove sidewall layers, each sidewall layer extending from the outermost radial surface of the unworn tread down into the direction of the bottom of the groove formed by the groove reinforcement, and wherein each sidewall layer has a uniform thickness along its length, and wherein a ratio between thickness of the sidewall layer and length of the sidewall layer having uniform thickness is at most 1:10.

11. The tire tread of claim 1, wherein at least one of the groove reinforcements has two groove sidewall layers, each sidewall layer extending from the outermost radial surface of the unworn tread down into the direction of the bottom of the groove formed by the groove reinforcement, and wherein each sidewall layer has a uniform thickness along its length, wherein both have at least one of the same uniform thickness and the same length when the tread is unworn.

12. The tire tread of claim 1, wherein at least one of the groove reinforcements has two groove sidewall layers, each sidewall layer extending from the bottom of the reinforced groove into the direction of the outermost surface of the tread, wherein the length of a first sidewall layer of the groove which is further away from the equatorial plane of the tire is shorter than a second sidewall layer of the same groove.

13. The tire tread of claim 1, further comprising a tread base layer arranged radially below the tread cap, wherein at least one of the reinforcements extends in the radial direction at least until the radially outer surface of the base layer, and optionally also radially through the base layer.

14. The tire tread of claim 1, further comprising a tread base arranged radially below the tread cap, wherein at least one of the reinforcements extends in the radial direction from the radially outermost top of the tread entirely through the base layer and wherein the reinforcement compound of the at least one reinforcement extending through the base layer has a carbon black content of at least 40 phr so as to provide electrical conductivity through the tread.

15. The tire tread of claim 1, wherein the first groove reinforcement has an elongation at break of at least 300%.

16. The tire tread of claim 1, wherein ribs formed between the sidewalls of adjacent groove reinforcements comprise a first tread cap compound with higher hysteresis than the first and second reinforcement compounds, and optionally higher than the remaining tread cap compound.

17. The tire tread of claim 1, wherein the tread cap comprises at least two tread cap compounds arranged radially on top of each other, including a first tread cap compound for contacting the road when the tire is unworn and a second tread cap compound for contacting the road upon wear of the first tread cap compound.

18. A tire having a tread comprising: a tread cap comprising at least one tread cap rubber compound, at least three circumferential grooves, wherein at least portions of the sidewalls and the bottom of each of said grooves are formed by a circumferential groove reinforcement, and wherein a first groove reinforcement of a groove laterally next to the equatorial plane of the tire comprises a first reinforcement rubber compound which has a higher hardness than the tread cap rubber compound, and wherein a second groove reinforcement of a groove with a larger lateral distance to the equatorial plane of the tire than the first groove comprises a second reinforcement rubber compound which has a higher hardness than the tread cap rubber compound and a lower hardness than the first reinforcement rubber compound.

19. The tire of claim 18, wherein the tire has a carcass connecting two circumferential bead portions and one or more belts arranged between the carcass and the tread in a crown area of the tire.

20. The tire of claim 18, wherein the tire is a pneumatic tire.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 represents a schematic cross section of a tire tread comprising groove reinforcement and tread cap compounds in accordance with an example of the present invention.

(3) FIG. 2 represents a schematic cross section of another tire tread comprising groove reinforcement and tread cap compounds in accordance with another example of the present invention in which sidewall layers of the groove reinforcements have essentially a uniform width.

(4) FIG. 3 represents a schematic cross section of still another tire tread comprising groove reinforcement and tread cap compounds in accordance with still another example of the present invention in which tread groove reinforcements integrally extend over the width of multiple grooves.

(5) FIG. 4 represents a schematic cross section of still another tire tread comprising groove reinforcement and tread cap compounds in accordance with still another example of the present invention in which the tread cap comprises a different tread cap compound in the ribs between the grooves compared to the compound in the shoulder regions of the tread.

(6) FIG. 5 represents a schematic cross section of still another tire tread comprising groove reinforcement and tread cap compounds in accordance with still another example of the present invention in which the tread cap comprises a different compound in a radially outer layer compared to a radially inner layer of the tread.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(7) FIG. 1 shows a schematic cross section of a tire tread 10 in accordance with a first embodiment of the present invention, wherein the tread 10 has a tread cap 2 with a plurality of circumferential ribs and/or tread blocks 8 between circumferential (main) grooves 5. Moreover, said tread 10 has a support portion having a tread base 4. The tread base 4 or tread base layer 4, if present, is preferably made of a different compound than the cap 2 and it supports the tread cap 2 on a radially inner side of the tread 10. The tread base layer 4 also has in the present and non-limiting example radial extensions in axially outer regions 7 of the shoulder regions 6 of the tire, in other words in the skirt regions 7 of the tread 10. The grooves 5 are reinforced by a plurality of axially or laterally separated groove reinforcements 3, 3′ which extend in a circumferential direction. In other words, the groove reinforcements form the bottoms of the grooves 5 as well as at least parts of their sidewalls (cover at least a portion of the sides of the grooves 5), i.e. the sidewalls of the ribs or blocks 8. The portions of the groove reinforcements covering the groove sidewalls are optionally tapered and have a decreasing thickness along their length in an outer radial direction. The groove reinforcements 3, 3′ will normally cover at least about 80% of surface area of the groove sidewalls and will more typically cover at least 90% or 95% of the surface area of the groove sidewalls. In many cases, the groove reinforcements 3, 3′ will totally cover the surface are of the groove sidewalls. In the embodiment of the invention depicted in FIG. 1, the outside walls of the outside grooves are only partially covered with the groove reinforcements 3′ with the inside walls of the outside grooves and the walls of the inside grooves being totally covered with the groove reinforcements 3, 3′. In such an embodiment of the invention the surface area of outside walls of the outside grooves will typically be from 50% to 95%, and more typically from about 55% to 90% covered with the groove reinforcements 3′. In some cases, the surface area of outside walls of the outside grooves will be from 60% to 80% or from 60% to 70% covered with the groove reinforcements 3′.

(8) As shown in FIG. 1, the equatorial plane EP of the tire tread is indicated by dashed lines. Alternatively, one could also refer to the center line of the tread which would run circumferentially in the equatorial plane EP. In accordance with the invention, the compound of the groove reinforcements 3 which are closest to the equatorial plane EP have a higher hardness than the compounds of the groove reinforcements 3′ which are more far away from that plane. In addition, the compound in the tread cap 2 is even less hard than the compounds in the areas 3, 3′. It is contemplated herein that the tire could also have three main grooves 5 or five or more grooves 5. Furthermore, one of the groove reinforcements 3 comprises an extension 11 extending radially through the tread base layer 4. This feature may help to provide a conductive passage through the tire tread to a belt region of the tire (not shown in FIG. 1).

(9) FIG. 2 shows another example of a tread 110 in accordance with the invention. The tread 110 has a tread cap 2 made of a tread cap compound, a plurality of tread blocks and/or ribs 8 largely made of tread cap compound, a shoulder portion 6, a skirt portion 7 and a plurality of circumferential tread grooves 5 which are formed in the tread cap 2 by the groove reinforcements 103, 103′. In other words, one may also say that the groove reinforcements 103, 103′ are embedded in the tread cap 2. Radially below the tread cap 2, there is a tread base layer 4 supporting the radially above arranged groove reinforcements 103, 103′ and tread cap 2. In contrast to the embodiment shown in FIG. 1, the embodiment of FIG. 2 has differently shaped reinforcements 103, 103′. Thus, while the compound of the two laterally innermost reinforcements 103 is harder than the compound of the two laterally outer groove reinforcements 103′, as it is also the case for the embodiment of FIG. 1, the thickness of the sidewall layers of the groove reinforcements 103, 103′ is constant over the height of the groove, in this example down to the bottom of the reinforced grooves. The groove reinforcements 103, 103′ have below the bottom of the reinforced grooves a support portion which has a top side, in this example forming the bottom of the groove and a base side, wherein the support portion tapers from the bottom side to the top side. Both sides are interconnected at their lateral edges by the lateral sides. The lateral sides have in the example an angle α between an axial direction or the axial base side which is smaller than 90°. In other words, the groove support portion tapers from its base side to its top side or top portion. As the support portion of the groove reinforcement tapers in an outer radial direction, there may be an angle β between the lateral side of the support portion and the sidewall layer of the groove reinforcement which is smaller than 180°, preferably smaller than 175°, which may improve support of the groove. While in the example of FIG. 2 the support portion extends in an outer radial direction until the bottom of the reinforced groove, this extension could be different. According to FIG. 2, all sidewall layers of a groove and the sidewall layers of all grooves have in this example the same uniform thickness. However, it is emphasized that the sidewall layers could also have different thicknesses, while each layer as such could have still uniform thickness.

(10) In the example in accordance with the present invention shown in FIG. 3, the tread 210 has a reinforcement 203 covering the two center grooves of the tire and a reinforcement 203′ which extends laterally below multiple grooves 5, in this example all four grooves 5, and forms the sidewalls and the bottoms of the two axially outermost grooves 5. At the same time, the central groove reinforcement 203 is embedded in or supported by the laterally wider groove reinforcement 203′.

(11) In another example within the scope of the present invention, the tread 310 shown in FIG. 4, has an arrangement of reinforcements 303, 303′ similar to that of FIG. 2. In contrast to the embodiment described already in relation to FIG. 2, the tread cap is made of different tread cap compounds 302, 302′. In particular, shoulder regions or zones 6 of the tread cap have a first tread cap compound 302 while central regions, in particular in the ribs/tread blocks 8 (between the reinforcement sidewall layers) have a different compound 302′. For instance, the compound 302′ may be optimized for wet grip compared to the tread cap compound 302 in the shoulder region 6 of the tread 310. This compound could be a low hysteresis compound compared with the tread cap compound in the ribs/tread blocks 8 of the tread 310. Apart from providing stiffness to the tread, the groove reinforcements 303, 303′ avoid also that the different compounds 302, 302′ are smeared into the grooves upon extrusion of the tread or the further building and curing steps.

(12) FIG. 5 shows another example of a tire tread 410 having again similar groove reinforcements 403, 403′ as already discussed with regards to FIGS. 2 and 4. However, in contrast to other embodiments described herein, the embodiment of FIG. 5 has two tread cap layers arranged on top of each other. In particular, a radially lower tread cap layer has a first compound 402 while a radially upper tread cap layer has a compound 402′. Such compounds could be provided by the person skilled in the rubber art in dependency of the desired application.

(13) While the present invention does not focus on the chemical composition of the tread compounds in the groove reinforcement, tread cap compounds or tread base layers, a few examples are given herein below. Those shall however not be understood as necessarily limiting the invention to these examples.

(14) In this context, Table 1 provides examples of suitable base layer compounds. However, it shall be re-emphasized that the main focus of the invention is not directed to the specific compounds used.

(15) TABLE-US-00001 TABLE 1 Base layer compound examples Sample number i ii iii iv Polybutadiene 65 50 0 0 Natural Rubber 35 50 100 100 Carbon Black 50 45 0 0 Pre-Silanized Silica.sup.1 0 0 30 30 Phenol Formaldehyde resins 3 0 5 5 TDAE Oil 11.3 16 10 45 Waxes 2 1.5 3.8 3.8 Antidegradants 7 5.5 6.7 6.7 Stearic Acid 1 0.75 1 1 Sulfenamide Accelerator 0.6 1.4 0.9 0.9 Zinc oxide 3.5 2 2 2 Sulfur 2.8 1.9 2.5 2.5 .sup.1Agilon 400 ® pre-silanized silica from PPG Industries.
Table 2 shows the Shore A hardness values of the samples shown above in Table 1.

(16) TABLE-US-00002 TABLE 2 Base layer compound examples Sample number i ii iii iv Shore A Hardness .sup.a 49 54 29 17 .sup.a Shore A hardness was measured according to ASTM D2240.

(17) Table 3 gives examples of suitable tread cap compounds. As mentioned already in the context of tread base layer compounds, it is emphasized again that such tread cap compounds mentioned herein are essentially considered as examples while other tread cap compounds could be used as long as they fall within the scope of the present invention.

(18) TABLE-US-00003 TABLE 3 Tread cap compound examples Sample number v vi vii Functionalized SSBR.sup.1 60 49 0 Natural Rubber 40 21 60 ESBR.sup.2 0 0 40 Non-functionalized SSBR.sup.3 0 30 0 Tackifier Resin.sup.4 0 0 6 Carbon Black 3 1 0 Silica 80 66 30 Oils 16 12 0 Waxes 1.5 2 1.5 Fatty Acid Soap 0 0 2 Silane 6.4 5.2 5 Fatty Acid 0 0 3 Antidegradants 3.5 0 3.5 Stearic Acid 2 4 0 Sulfenamide Accelerator 2.4 2.4 3 Dithiophosphate Zinc Salt 0.8 0.8 0 Zinc oxide 3 3 3 Sulfur 1.5 1.5 1.2 Diphenylguanidine 0 0 1.5 .sup.1Thio-functionalized, tin coupled, solution polymerized copolymer of butadiene and styrene .sup.2Emulsion Styrene Butadiene Rubber, 50.8% (by weight) styrene, 8.2% vinyl 1,2; 4.2% cis 1,4; 36.8% trans 1,4; Tg (inflection) = −13° C.; 1% styrene sequences ≥5; from The Goodyear Tire & Rubber Co. .sup.3Non-functionalized, solution polymerized copolymer of butadiene and styrene .sup.4unreactive alkylphenol/formaldehyde resin, as SP 1068 from SI Group
Table 4 shows Shore A hardness values of the example compositions of Table 3.

(19) TABLE-US-00004 TABLE 4 Tread cap compound examples Sample number v vi vii Shore A Hardness .sup.a 67 55 60 .sup.a Shore A hardness was measured according to ASTM D2240.

(20) Examples for suitable groove reinforcement rubber compounds may for instance be found in U.S. Pat. No. 10,427,463 B2 (also see United States Patent Publication No. 2018/0134086 A1) and note in particular in Examples 1, 2, 3, 4 and 5. Such compounds have high Shore A hardness covered by the ranges of the present disclosure. For the sake of illustration, two of the examples of that publication are listed herein below in Tables 5 to 8. The teachings of U.S. Pat. No. 10,427,463 B2 and United States Patent Application Publication No. 2018/0134086 A1 are incorporated herein by reference for the purpose of teaching rubber formulations which are suitable in the practice of this invention as groove reinforcement materials.

(21) TABLE-US-00005 TABLE 5 Groove reinforcement compounds Sample number 1 2 3 4 polybutadiene 10 10 10 10 styrene-butadiene copolymer (oil extended) 97.5 97.5 97.5 97.5 carbon black 50 50 50 50 silica 20 20 20 20 silane 2 2 2 2 phenol-formaldehyde resin.sup.1 20 20 20 20 hexamethylene tetramine 3 3 3 3 styrene-alpha methyl styrene resin.sup.2 8 12 16 8 carbamic resin.sup.3 0 0 0 4 wax 1.5 1.5 1.5 1.5 antioxidants 3 3 3 3 stearic acid 3 3 3 3 processing aid 2 2 2 2 zinc oxide 2.5 2.5 2.5 2.5 sulfur 1.6 1.6 1.6 1.6 N-tertbutyl-2benzothiazolesulfenamide 1.63 1.63 1.63 1.63 N-Cyclohexylthiophthalimide 0.3 0.3 0.3 0.3 .sup.1SMD 30207 from Schenectedy Chemicals .sup.2Resin 2336 from Eastman .sup.3Alnovol ® UF410, from Allnex
Table 6 shows high Shore A hardness values above 80 as well as considerable elongation at break values over 300% for the compounds 1 to 4 of Table 5.

(22) TABLE-US-00006 TABLE 6 Groove reinforcement compounds Sample number 1 2 3 4 Shore A .sup.a 83.3 81.8 83 85.6 Elongation at break (%) .sup.b 329 359 390 426 .sup.a Shore A hardness measured according to ASTM D2240. .sup.b Ring sample test based on ASTM D412 and DIN 53504.

(23) In view of the relatively high Shore A Hardness such compounds would be preferably suitable for the first reinforcement compound described herein.

(24) Table 7 lists further examples of potential compounds that could be used as groove reinforcement rubber compounds.

(25) TABLE-US-00007 TABLE 7 Groove reinforcement compounds continued Sample number 5 6 7 8 9 Polybutadiene 20 20 20 20 20 Natural Rubber 80 80 80 80 80 Carbon Black 50 50 50 50 50 Waxes 1.5 1.5 1.5 1.5 1.5 Antidegradant 2.5 2.5 2.5 2.5 2.5 Ricon 184.sup.5 0 15 0 35 0 Ricon 100.sup.6 0 0 15 0 35 Oil 15 0 0 0 0 Stearic Acid 3 3 3 3 3 Silica 20 20 20 20 20 silane disulfide 2 2 2 2 2 phenol formaldehyde resin 20 20 20 20 20 fatty acid soap 2 2 2 2 2 hexamethylenetetramine 3 3 3 3 3 Antidegradant 0.5 0.5 0.5 0.5 0.5 Sulfenamide Accelerator 2.36 2.36 2.36 2.36 2.36 zinc oxide 2.5 2.5 2.5 2.5 2.5 sulfur 1.6 1.6 1.6 1.6 1.6 vulcanization inhibitor 0.3 0.3 0.3 0.3 0.3 .sup.5liquid styrene-butadiene, Mn = 8600 .sup.6liquid styrene-butadiene, Mn = 4000
Table 8 shows again high Shore A hardness values as well as considerable elongation at break values for the materials 5-9 of Table 7.

(26) TABLE-US-00008 TABLE 8 Groove reinforcement compounds continued Sample number 5 6 7 8 9 Shore A Hardness 86 85.4 86.6 89.3 90.6 Elongation at Break (%) 508 518 508 481 502

(27) In addition, the compound of Example v of Tables 3 and 4 could also be used as relatively soft second reinforcement rubber compound.

(28) As visible in these examples for the groove reinforcement compounds, Shore A hardness values are higher than in the base layer compound or the tread cap compound. Moreover, elongation at Break is higher than 300% in all samples. However, this is not indispensable for the scope of the invention.

(29) In general, the tread cap layer, the groove reinforcement and tread base layer may be extruded together to form the tread as known to the person skilled in the art of extrusion and/or tire building. In particular, gear pumps and/or triplex or quadruplex extruders could be used.

(30) 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 following appended claims.

(31) In any case the above described embodiments and examples shall not be understood in a limiting sense. In particular, the features of the above embodiments may also be replaced or combined with one another.