A tire tread with durability performance

Abstract

The present invention provides a tread for a tire, the tread having a contact surface, at least a portion of a plurality of grooves being provided with a wear indicator, the wear indicator indicating a legal wear limit, the tread comprising at least two rubber layers, a first rubber layer being radially located on the outside of a second rubber layer and being arranged together with a separation layer, the separation layer being intended to be connected to another rubber layer on the radial inside of the first rubber layer, and the second rubber layer being arranged without a separation layer, the material constituting the separation layer satisfying the following relationship: [Mathematical Formula 2], wherein G* is the modulus G* of the material constituting the separation layer at 60°C, and C is the modulus in mm of the material constituting the separation layer measured by method A according to JIS K 7218 3 The amount of wear and tear. #imgabs0#

Description

Technical Field

[0001] The present invention relates to a tread for a tire, and more particularly to a tire tread that can maintain a high level of performance until near the end of its wear life on both winter and non-winter surfaces. Background Art

[0002] In recent years, a type of tire called an "all-season" tire has become popular, which has the ability to travel on winter surfaces while maintaining the ability to travel at high speeds on non-winter surfaces.

[0003] Furthermore, for tires called "studless" tires suitable for traveling on ice-covered and / or snow-covered winter surfaces, it is desirable to enhance performance on non-winter surfaces not covered with ice and snow while also improving performance on winter surfaces.

[0004] In order to maintain performance on winter ground (especially snow performance), it is known to be effective to reduce the stiffness of the tread in the area close to the bottom of the groove. It is also known that this approach can have a negative impact on performance on non-winter ground.

[0005] EP0378090 discloses a tread for a tire, the tread having a pattern block (raised element) arranged with grooves, the cross section of which has a forked profile with at least two branches, the branches forming an extension of a single part, the number of grooves in the pattern block (raised element) being multiplied by a factor at least equal to 1.5 starting from the depth of the double-branched groove.

[0006] JP2006-142843 discloses a tire having a pattern block composed of a cap rubber layer and a base rubber layer stacked in a radial direction, the cap rubber layer comprising a cylindrical closed-cell foam containing aluminum oxide, and the base rubber layer comprising a spherical closed-cell foam.

[0007] JP2002-079807 discloses a tire having a tread formed of at least two layers consisting of a cap rubber layer and a base rubber layer including hollow particles having an average particle diameter of at most 500 μm mixed in a volume ratio of 2% to 40%.

[0008] JP2007-168651 discloses a tire having a plurality of tread blocks, the tread blocks comprising a three-layer rubber tread block, the three-layer rubber tread block consisting of a cap rubber layer, an intermediate rubber layer and a base rubber layer, the 100% modulus of each rubber layer being highest at the base rubber layer, followed by the cap rubber layer, and then the intermediate rubber layer.

[0009] JP2006-306281 discloses a tread for a tire, the tread having a cap tread and two base tread layers, the cap tread having a JISA hardness of 40 to 50, the outer base tread having a JISA hardness of 70 to 80 and a thickness greater than or equal to 1.5 mm, and the inner base tread having a JISA hardness of 55 to 70 and a thickness greater than or equal to 0.3 mm.

[0010] JP2001-080314 discloses a tire having a laminated structure of a cap tread and a base tread having different hardnesses from each other, with a tread separator layer having a higher hardness than the cap tread and the base tread disposed between the cap tread and the base tread.

[0011] Citation List

[0012] Patent Literature

[0013] Patent document 1: EP0378090

[0014] Patent Document 2: JP2006-142843

[0015] Patent document 3: JP2002-079807

[0016] Patent Document 4: JP2007-168651

[0017] Patent Document 5: JP2006-306281

[0018] Patent document 6: JP2001-080314.

[0019] However, for the solutions disclosed in these documents, the bottom portion of the tread (or pattern block) composed of double-branch grooves, spherical closed-cell foams or hollow particles is too soft due to the increase in the number of grooves, closed-cell foams or hollow particles, which has a negative impact from the beginning of the tire life, and the multi-layer tread solution is not satisfactory for performance near the end of life, especially on winter ground. Therefore, it is desirable to provide performance improvement near the end of the life of the tread, especially on winter ground.

[0020]

[0006] Therefore, there is a need for a tread for a tire that provides improved performance near the end of life, particularly on winter surfaces, while maintaining performance and durability properties on non-winter surfaces.

[0021] definition:

[0022] A “radial direction” is a direction perpendicular to the axis of rotation of the tire. This direction corresponds to the thickness direction of the tread.

[0023] An "axial orientation / direction" is an orientation / direction parallel to the tire's axis of rotation.

[0024] A "circumferential direction" is a direction tangent to any circle centered on the axis of rotation. This direction is perpendicular to the axial direction and the radial direction.

[0025] "Tyre" means all types of resilient tyres, whether or not subjected to internal pressure.

[0026] “Tread” of a tire means the mass of rubber material delimited by lateral surfaces and two major surfaces, one of which is intended to come into contact with the ground when the tire rolls.

[0027] A "groove" is the space between two rubber faces / side walls connected by another rubber face / base, which do not touch each other under normal rolling conditions. A groove has a width and a depth.

[0028] A "groove" (also called a "sipe") is a narrow cut formed radially inward from the surface of the tread, which is made, for example, by a thin blade having a shape similar to a blade. The width of the groove on the surface of the tread is smaller than that of the groove, for example less than or equal to 2.0 mm. Unlike the groove, when such a groove is in the contact patch and under normal rolling conditions, the groove can be partially or completely closed.

[0029] The "contact patch" is the footprint of a tire under nominal load, mounted on a standard rim (as identified in tire standards such as ETRTO, JATMA or TRA) and inflated to nominal pressure. The "width TW" of the contact patch is the maximum contact width of the contact patch along the tire's axis of rotation.

[0030] The modulus G* is the dynamic shear complex modulus of the material at 60°C. The storage elastic modulus represented by G' and the loss elastic modulus represented by G", which are dynamic properties well known to those skilled in the art, are measured by a viscosity analyzer (microanalyzer: Metravib VB4000) using a test piece molded from the raw material composition or a test piece combined with the composition after vulcanization. The test piece used is the test piece described in Figure X2.1 (circular method) of the standard ASTM D 5992-96 (version published in September 2006, which was originally approved in 1996). The diameter "d" of the test piece is 10 mm (so the test piece has a circular cross section of 78.5 mm2), the thickness "L" of each part of the rubber compound is 2 mm, and the ratio "d / L" is 5 (described in Section X2.4 of the ASTM standard, compared to the standard ISO 2856 is 2). In the test, the response of a specimen containing a vulcanized rubber composition subjected to a simple alternating sinusoidal shear load is measured at a frequency of 10 Hz. The maximum shear stress applied during the test is 0.7 MPa. The test is performed by changing the temperature from Tmin (which is a temperature below the glass transition temperature (Tg) of the rubber material) to a maximum temperature Tmax (near 100°C) at a rate of 1.5°C / min. Before starting the test, the specimen is stabilized at Tmin for about 20 minutes in order to obtain satisfactory temperature uniformity within the specimen. The results obtained are the storage modulus (G') and loss modulus (G") at the specified temperature. The complex modulus G* is defined according to the absolute values ​​of the storage modulus and the loss modulus using the following formula:

[0031] [Mathematical formula 1]

[0032]

[0033] It is therefore an object of the present invention to provide a tread for a tire that can provide improved performance near the end of life, particularly on winter terrain, while maintaining performance and durability properties on non-winter terrain. Summary of the invention

[0034] The present invention provides a tread for a tire, the tread having a contact surface intended to come into contact with the ground when rolling, the tread being arranged with a plurality of grooves having a depth D leading to the contact surface and a plurality of contact elements defined by the plurality of grooves, each of the plurality of contact elements having a top surface, the top surface constituting a portion of the contact surface, at least a portion of the plurality of grooves being arranged with a wear indicator, the wear indicator indicating the legal wear limit of the tread, the tread comprising at least two rubber layers, namely at least one first rubber layer and at least one second rubber layer, the first rubber layer being radially located on the outside of the second rubber layer and being arranged together with a separation layer, the separation layer being intended to be connected to another rubber layer on the radial inside of the first rubber layer, the second rubber layer being arranged without a separation layer, the material constituting the separation layer satisfying the following relationship:

[0035] [Mathematical formula 2]

[0036]

[0037] wherein G* is the modulus G* at 60° C. of the material constituting the partition layer, and C is the modulus in mm of the material constituting the partition layer measured by method A according to JIS K 7218. 3 The amount of wear measured.

[0038] This arrangement provides improved performance near the end of life, particularly on winter ground.

[0039] The tread comprises at least two rubber layers, namely at least one first rubber layer and at least one second rubber layer, the first rubber layer being radially located on the outside of the second rubber layer and being arranged together with a separator layer intended to be connected to another rubber layer radially inside the first rubber layer, the second rubber layer being arranged without a separator layer, the separator layer being molded to extend radially, in particular in the bottom part of the contact elements and above the wear indicating means indicating the legal wear limit of the tread, making it possible to continuously produce on the top face roughness in the form of grooves or microgrooves, said grooves or microgrooves acting as additional microedges and volumes for capturing snow particles or water films until the end of life. Thus, the performance on winter grounds until close to the end of life can be improved.

[0040] The present inventors have found that the separation layer is worn faster than the first rubber layer and the second rubber layer and continuously generates / regenerates the roughness on the top surface by making the material constituting the separation layer satisfy the following relationship:

[0041] [Mathematical formula 2]

[0042]

[0043] wherein G* is the modulus G* at 60° C. of the material constituting the partition layer, and C is the modulus in mm of the material constituting the partition layer measured by method A according to JIS K 7218. 3 The performance on winter ground can thus be further improved towards the end of its service life.

[0044] If the value is less than 200, there is a risk that the partition layer wears slower than the first rubber layer and the second rubber layer, resulting in a significant reduction in the contact area of ​​the top surface. If the value is greater than 1200, there is a risk that the partition layer wears too quickly, resulting in reduced durability performance. By setting the material constituting the partition layer to satisfy the following relationship:

[0045] [Mathematical formula 2]

[0046]

[0047] Performance on winter ground surfaces may be improved towards the end of life.

[0048] In another preferred embodiment, the volume of the separating layer in each contact element above the height corresponding to the wear indicating device is less than 20%.

[0049] If this volume of the separator layer in each contact element above the height corresponding to the wear indication device is greater than 20%, there is a risk that the performance is reduced, especially on winter ground, due to the reduced contact surface with the first rubber layer or the second rubber layer. By setting the volume of the separator layer in each contact element above the height corresponding to the wear indication device to less than 20%, the performance can be maintained, especially on winter ground.

[0050] The volume of the separating layer in each contact element above the height corresponding to the wear indicating device is preferably less than 18%, more preferably less than 15%.

[0051] In another preferred embodiment, in a plane perpendicular to both the top surface and the axis of rotation of the tyre, the radially outermost portion of the second rubber layer in each contact element is located radially at least equal to 0.5 mm outside from a height corresponding to the wear indicating means.

[0052] If the radially outermost portion of the second rubber layer in each contact element, in a plane perpendicular to both the top surface and the axis of rotation of the tire, is located radially less than 0.5 mm on the outside from the height corresponding to the wear indicating means, there is a risk that even near the end of life a sufficient volume of roughness will not be created, and therefore the performance near the end of life will not be improved. The performance near the end of life can be improved by arranging this radially outermost portion of the second rubber layer in each contact element, in a plane perpendicular to both the top surface and the axis of rotation of the tire, to be located radially at least equal to 0.5 mm on the outside from the height corresponding to the wear indicating means.

[0053] This radially outermost portion of the second rubber layer in each contact element is preferably located radially at least equal to 0.8 mm on the outside from a height corresponding to the wear indicating means, more preferably at least equal to 1.0 mm on the outside from a height corresponding to the wear indicating means, on a plane perpendicular to both the top surface and the axis of rotation of the tyre.

[0054] In a further preferred embodiment, the distance of the separating layer from any contour of the contact element is at least equal to 0.2 mm.

[0055] If the distance between the separator layer and any contour of the contact element is less than 0.2 mm, there is a risk that the separator layer becomes a failure starting point due to stress concentration during rolling, resulting in a decrease in durability performance. By setting the distance between the separator layer and any contour of the contact element to at least 0.2 mm, the durability performance can be maintained.

[0056] The distance of the separating layer from any contour of the contact element is preferably at least equal to 0.5 mm, more preferably at least equal to 0.8 mm, still more preferably at least equal to 1.0 mm.

[0057] In another preferred embodiment, the tread includes a first rubber layer and a second rubber layer.

[0058] According to this arrangement, the tread can be manufactured without any or with minimal adjustments to the manufacturing method.

[0059] In another preferred embodiment, the rubber composition constituting the first rubber layer is the same as the rubber composition constituting the second rubber layer.

[0060] According to this arrangement, the tread can be manufactured efficiently because the rubber composition constituting the contact elements except the separator layer is the same.

[0061] In another preferred embodiment, the tread further comprises a base rubber layer which is located radially inwardly at a height corresponding to the wear indicating device.

[0062] According to this arrangement, since the base rubber layer is located radially inwardly corresponding to the height of the wear indicating device, performance other than the grip performance (such as handling performance or rolling resistance) can be adjusted without affecting the grip performance.

[0063] Advantageous Effects of the Invention

[0064] According to the above arrangement, it is possible to provide improved performance towards the end of life, particularly on winter terrain, while maintaining performance on non-winter terrain and durability properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Other characteristics and advantages of the invention emerge from the following description made with reference to the accompanying drawings which show an embodiment of the invention as a non-limiting example.

[0066] In these drawings:

[0067] [ Figure 1 ] Figure 1 is a schematic plan view of a tread according to a first embodiment of the present invention;

[0068] [ Figure 2 ] Figure 2 = The following table shows the relationship between the (a) new state and (b) worn state. Figure 1 A schematic cross-sectional view taken along line II-II in FIG.

[0069] [ Figure 3 ] Figure 3 To show Figure 2 An enlarged schematic diagram of the portion shown in III in (b);

[0070] [ Figure 4 ] Figure 4 For and along Figure 1 Schematic cross-sectional view of a tread according to a second embodiment of the present invention corresponding to a position taken along line IV-IV in FIG. DETAILED DESCRIPTION

[0071] Preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

[0072] Will refer to Figure 1 , Figure 2 and Figure 3 A tread 1 for a tire according to a first embodiment of the present invention is described. Figure 1 is a schematic plan view of a tread according to a first embodiment of the present invention. Figure 2for (a) new state and (b) worn state along Figure 1 Schematic cross-sectional view taken along line II-II in FIG. Figure 3 To show Figure 2 (b) is an enlarged schematic diagram of the portion shown in III.

[0073] The tread 1 is a tread for a tire of size 225 / 45R17, having a contact surface 2 intended to come into contact with the ground when rolling, and having a plurality of treads with a depth D ( Figure 2 The tread 1 comprises a plurality of contact elements 4 defined by the plurality of grooves 3.

[0074] like Figure 1 As shown, the tread 1 is provided with a plurality of contact elements 4, each contact element 4 close to the center of the tread 1 indicated by a line CC' parallel to the circumferential direction of the tread 1 is provided with a groove 42, the groove 42 leading to a top surface 41 constituting a part of the contact surface 2, and each contact element 4 axially located outside the contact element 4 provided with the groove 42 is not provided with any part leading to the top surface 41. One groove 3 of the plurality of grooves 3 is provided with a wear indicator 8, the wear indicator 8 indicating the legal wear limit of the tread 1.

[0075] like Figure 2 As shown in (a), the tread 1 comprises at least two rubber layers, namely at least one first rubber layer 5 and at least one second rubber layer 6, the first rubber layer 5 being radially located on the outside of the second rubber layer 6 and being arranged together with a separator 7, the separator 7 being intended to be connected to another rubber layer on the radial inside of the first rubber layer 5, and the second rubber layer 6 being arranged without a separator. The tread 1 is arranged above a ply 15, which is usually a component of the structural reinforcement of the tire and comprises at least a carcass and a belt layer (if it is a radial tire construction). In this first embodiment, the tread 1 comprises a first rubber layer 5 arranged with a separator 7 and a second rubber layer 6. The material constituting the first rubber layer 5 is different from the material constituting the second rubber layer 6.

[0076] like Figure 2As shown in (a), the volume of the separating layer 7 in each contact element 4 above the height corresponding to the wear indicating device 8 is less than 20%, and the radially outermost portion of the second rubber layer 6 in each contact element 4 is located at least 0.5 mm radially outward from the height corresponding to the wear indicating device 8 in a plane perpendicular to both the top surface 41 and the rotation axis of the tire. The distance between the separating layer 7 and any contour of the contact element 4 is at least 0.2 mm. In this first embodiment, the volume of the separating layer 7 in each contact element 4 above the wear indicating device 8 is 13%, and the radially outermost portion of the second rubber layer 6 in each contact element 4 is at 4.0 mm in a plane perpendicular to both the top surface 41 and the rotation axis of the tire.

[0077] like Figure 2 (b) and Figure 3 As shown, in the worn state of the tread 1 and near the end of life as shown by the wear indicator 8, both the first rubber layer 5 and the second rubber layer 6 appear on the worn top surface 41' of the wear contact element 4', and the worn top surface 41' constitutes a part of the wear contact surface 2'. In addition, at the same time, on the worn top surface 41', between the first rubber layer 5 and the second rubber layer 6, since the separation layer 7 wears faster than the first rubber layer 5 and the second rubber layer 6, a thin groove 71 with a small depth below the wear contact surface 2' is generated.

[0078] The material constituting the partition layer 7, which is different from both the material constituting the first rubber layer 5 and the material constituting the second rubber layer 6, is designed to satisfy the following relationship:

[0079] [Mathematical formula 2]

[0080]

[0081] wherein G* is the modulus G* at 60° C. of the material constituting the partition layer 7, and C is the modulus in mm of the material constituting the partition layer 7 measured by method A according to JIS K 7218. 3 In this first embodiment, the value of the separation layer 7 is 357, wherein G* is 1.29 and C is 0.0053.

[0082] The tread 1 comprises at least two rubber layers, namely at least one first rubber layer 5, radially on the outside of the second rubber layer 6 and arranged together with a separator layer 7, intended to be connected to another rubber layer radially inside the first rubber layer 5, the second rubber layer 6 being arranged without a separator layer, said separator layer 7 being molded so as to extend radially, in particular in the bottom part of the contact elements 4 and above the wear indicator means 8 indicating the legal wear limit of the tread 1, making it possible to continuously produce on the top face 41 roughness in the form of grooves 71 or microgrooves, said grooves 71 or microgrooves acting as additional microedges and volumes for capturing snow particles or water films until the end of life. Thus, the performance on winter grounds can be improved until close to the end of life.

[0083] The present inventors have found that the separation layer 7 is worn faster than the first rubber layer 5 and the second rubber layer 6 and continuously generates / regenerates the roughness on the top surface 41 by making the material constituting the separation layer 7 satisfy the following relationship:

[0084] [Mathematical formula 2]

[0085]

[0086] wherein G* is the modulus G* at 60° C. of the material constituting the partition layer 7, and C is the modulus in mm of the material constituting the partition layer 7 measured by method A according to JIS K 7218. 3 The performance on winter ground can thus be further improved towards the end of its service life.

[0087] If the value is less than 200, there is a risk that the partition layer 7 wears slower than the first rubber layer 5 and the second rubber layer 6, resulting in a significant reduction in the contact area of ​​the top surface 41. If the value is greater than 1200, there is a risk that the partition layer 7 wears too quickly, resulting in a decrease in durability performance. By setting the material constituting the partition layer 7 to satisfy the following relationship:

[0088] [Mathematical formula 2]

[0089]

[0090] Performance on winter ground surfaces may be improved towards the end of life.

[0091] Since the volume of the separating layer 7 in each contact element 4 above the height corresponding to the wear indicating device 8 is less than 20%, the performance can be maintained, in particular on winter ground.

[0092] If this volume of separating layer 7 in each contact element 4 above the height corresponding to wear indicating device 8 is greater than 20%, there is a risk of reduced performance, in particular on winter ground, due to the reduced contact surface with first rubber layer 5 or second rubber layer 6.

[0093] The volume of the separating layer 7 in each contact element 4 above the height corresponding to the wear indicating device 8 is preferably less than 18%, more preferably less than 15%.

[0094] Since the radially outermost portion of second rubber layer 6 in each contact element 4 is located at least 0.5 mm radially outside from a height corresponding to wear indicating means 8 in a plane perpendicular to both top surface 41 and the axis of rotation of the tyre, performance near the end of life can be improved.

[0095] If this radially outermost portion of the second rubber layer 6 in each contact element 4 is located less than 0.5 mm radially outside from a height corresponding to the wear indicating means 8 in a plane perpendicular to both the top surface 41 and the axis of rotation of the tyre, there is a risk that even near the end of life a sufficient volume of roughness will not be created, and therefore the performance near the end of life will not be improved.

[0096] This radially outermost portion of the second rubber layer 6 in each contact element 4 is preferably located at least 0.8 mm radially outside from a height corresponding to the wear indicating device 8, more preferably at least 1.0 mm radially outside from a height corresponding to the wear indicating device 8, on a plane perpendicular to both the top surface 41 and the axis of rotation of the tire.

[0097] Since the distance of the separation layer 7 from any contour of the contact element 4 is at least equal to 0.2 mm, the durability properties can be maintained.

[0098] If the distance between the separation layer 7 and any contour of the contact element 4 is less than 0.2 mm, there is a risk that the separation layer 7 becomes a failure starting point due to stress concentration during rolling, resulting in a decrease in durability performance.

[0099] The distance between the separation layer 7 and any contour of the contact element 4 is preferably at least 0.5 mm, more preferably at least 0.8 mm, and even more preferably at least 1.0 mm.

[0100] Since the tread 1 comprises a first rubber layer 5 and a second rubber layer 6, the tread 1 can be manufactured without any or with minimal adjustments to the manufacturing method.

[0101] In order to manufacture the following tread 1, it is preferred that the shape of the separator layer 7 is already wavy in the radial direction in the green (uncured) state of the tread 1: the tread 1 includes the first rubber layer 5 and the second rubber layer 6 together with the separator layer 7, so that the volume of the fine grooves 71 or micro grooves on the wear top surface 41 'is sufficient to serve as additional micro edges and volume for capturing snow particles or water film. This also helps to control the height of the second rubber layer 6 from appearing too early or too late on the wear top surface 41 '.

[0102] In this first embodiment, the second rubber layer 6 is arranged to have only one radial peak in the contact element 4. The second rubber layer 6 may be arranged to have a plurality of radial peaks in the contact element 4 not only in the circumferential direction but also in the axial direction.

[0103] Will refer to Figure 4 A tread 21 according to a second embodiment of the present invention is described. Figure 4 For and along Figure 1 A schematic cross-sectional view of a tread according to a second embodiment of the present invention corresponding to the position of the line IV-IV in FIG. The construction of the second embodiment is similar to that of the first embodiment, except that Figure 4 The arrangement shown will therefore refer to Figure 4 Give a description.

[0104] like Figure 4 As shown, the tread 21 comprises a contact surface 22 intended to come into contact with the ground when rolling, and a plurality of grooves 23 having a depth D. The tread 21 comprises contact elements 24 delimited by the plurality of grooves 23 .

[0105] like Figure 4 As shown, the contact element 24 has a groove 42 which opens into a top surface 241 and extends in the radially inner direction, the top surface 241 forming part of the contact surface 22. The depth of the groove 42 is equal to the height up to the level of the wear indicator 28.

[0106] like Figure 4 As shown, the tread 21 includes at least two rubber layers, namely, two first rubber layers 25 and one second rubber layer 26, both of which are radially located outside the second rubber layer 6 and are each arranged together with a separation layer 27, the separation layer 27 is intended to be connected to another rubber layer radially inside the first rubber layer 25, and the second rubber layer 26 is arranged without a separation layer. The tread 21 also includes a base rubber layer 9, which is radially located inside the height corresponding to the wear indicator 28 and is interposed between the second rubber layer 26 and the cord layer 15. In this second embodiment, the rubber composition constituting the first rubber layer 25 is the same as the rubber composition constituting the second rubber layer 26.

[0107] The tread 21 is configured such that the distance between the separating layer 27 and any contour of the contact elements 24 , including the contour of the grooves 42 , is at least equal to 0.2 mm.

[0108] Since the rubber composition constituting the first rubber layer 25 is the same as the rubber composition constituting the second rubber layer 26 , the tread 21 can be efficiently manufactured because the rubber composition constituting the contact elements 24 except for the separator 27 is the same.

[0109] Since the tread 21 also includes a base rubber layer 9 located radially on the inside of the height corresponding to the wear indicator 28, since the base rubber layer 9 is located radially on the inside of the height corresponding to the wear indicator 28, performance other than grip performance (such as handling performance or rolling resistance) can be adjusted without affecting the grip performance.

[0110] The invention is not limited to the described and illustrated embodiments and various modifications can be made without departing from its principles.

[0111] Example

[0112] In order to confirm the effects of the present invention, one type of tread to which an example of the present invention is applied and other types of reference treads were prepared.

[0113] The example is a tread as described in the above second embodiment to which the construction of the above first embodiment is applied; each contact element is arranged with a groove and has a first rubber layer and a second rubber layer together with a separator. The reference is a tire having a contact element, the contact element is arranged with a groove, and has a first rubber layer and a second rubber layer, without a separator. The material constituting the first rubber layer is the same between the example and the reference, and the material constituting the second rubber layer is also the same between the example and the reference. Except for the above, the internal construction of the example and the reference is the same typical radial tire construction. The example and the reference are polished and then run for 10,000 km to reproduce the wear state of the tire with a remaining tread depth of 2.0 mm.

[0114] Winter performance test:

[0115] -Snow Braking:

[0116] The prepared wear test tires were mounted on all four wheels of a 2500cc front-wheel drive vehicle. On a compacted snow surface on a straight path, ABS (anti-lock braking system) braking was applied at a speed of 50 km / h, and the distance up to 5 km / h was measured.

[0117] The results are shown in Table 1. In this Table 1, the results are expressed with an index of 100 for reference, and a higher value indicates better performance.

[0118] Non-winter performance test:

[0119] -Wet Braking:

[0120] The prepared wear test tires were mounted on all four wheels of a 2500cc front-wheel drive vehicle. On a 1 mm deep wet ground on a straight path, ABS (anti-lock braking system) braking was applied at a speed of 100 km / h, and the distance up to 10 km / h was measured.

[0121] The results are also shown in Table 1. In this Table 1, the results are expressed with an index of 100 for reference, and a higher value indicates better performance.

[0122] [Table 1]

[0123] Example Reference Winter performance (index) 110 100 Non-winter performance (index) 99 100

[0124] As can be seen from Table 1, the examples show a better compromise between winter performance and non-winter performance, and the winter performance is improved towards the end of life, which cannot be achieved with the treads disclosed in the prior art.

[0125] Visual observation:

[0126] Using the tread structure of the above embodiment, by changing the tread structure with different G *2.5 Two other types of treads applying the present invention and one type of comparative example were further prepared using materials constituting the separator layer with values ​​of 0.1% / C. Just after preparing the above wear test tires, a trained technician observed the state of the top surface, i.e., whether there were fine grooves or micro grooves with sufficient volume as additional micro edges and volume for capturing snow particles or water films, and whether there were cracks in the separator layer.

[0127] The results are shown in Table 2. If sufficient fine grooves or micro-grooves were created as additional micro-edges and volume for capturing snow particles or water film, the technician determined it as "good", otherwise it was "bad". If no cracks were observed in the separator layer, the technician also determined it as "good", otherwise it was "cracks".

[0128] [Table 2]

[0129] Example 1 Example 2 Example 3 Reference Comparative Example <![CDATA[G *2.5 / C]]> 357 207 517 77 1347 Fine groove good good good not good OK crack good good good good crack

[0130] As can be seen from Table 2, the examples show that sufficient fine grooves or micro-grooves are created as additional micro-edges and volume for capturing snow particles or water film, which leads to improved performance near the end of life without creating cracks in the separator layer.

[0131] Reference numerals

[0132] 1, 21 tread

[0133] 15 Ply

[0134] 2.22 Contact surface

[0135] 3.23 Grooves

[0136] 4, 24 contact elements

[0137] 41, 241 top surface

[0138] 42 grooves

[0139] 5.25 First rubber layer

[0140] 6.26 Second rubber layer

[0141] 7, 27 separation layer

[0142] 71 Fine groove

[0143] 8.28 Wear indicator

[0144] 9 Base rubber layer.

Claims

1. A tread (1) for a tyre, the tread (1) having a contact surface (2) intended to come into contact with the ground when rolling, the tread (1) being arranged with a plurality of grooves (3) leading to the contact surface (2) and a plurality of contact elements (4) delimited by the plurality of grooves (3), the grooves (3) having a depth D, each of the plurality of contact elements (4) having a top surface (41) constituting part of the contact surface (2), at least a portion of the plurality of grooves (3) being arranged with wear indicating means (8), the wear indicating means (8) indicating the legal wear limit of the tread (1), The tread (1) comprises at least two rubber layers, namely at least one first rubber layer (5) and at least one second rubber layer (6), the first rubber layer (5) being radially located on the outside of the second rubber layer (6) and being arranged together with a separation layer (7), the separation layer (7) being intended to be connected to another rubber layer on the radial inside of the first rubber layer (5), and the second rubber layer (6) being arranged without the separation layer (7), The tread is characterized in that the material constituting the separation layer (7) satisfies the following relationship: [Mathematical formula 2] wherein G* is the dynamic shear complex modulus G* of the material constituting the partition layer (7) measured at 60°C under a simple alternating sinusoidal shear load with a frequency of 10 Hz and a maximum shear stress of 0.7 MPa, and C is the dynamic shear complex modulus G* of the material constituting the partition layer (7) measured in mm according to JIS K 7218 by method A. 3 The wear amount of the meter, in, The separation layer (7) wears faster than the first rubber layer (5) and the second rubber layer (6), and the separation layer (7) enables the roughness in the form of fine grooves or micro grooves to be continuously generated on the top surface (41).

2. The tread (1) according to claim 1, wherein: The volume of the separation layer (7) in each contact element (4) above the height corresponding to the wear indication device (8) is less than 20%.

3. The tread (1) according to claim 1 or claim 2, wherein: In a plane perpendicular to both the top surface (41) and the axis of rotation of the tire, the radially outermost portion of the second rubber layer (6) in each contact element (4) is located radially at least 0.5 mm outside from a height corresponding to the wear indicating device (8).

4. The tread (1) according to claim 1, wherein: The distance between the separating layer (7) and any contour of the contact element (4) is at least equal to 0.2 mm.

5. The tread (1) according to claim 1, wherein: The rubber composition constituting the first rubber layer (5) is the same as the rubber composition constituting the second rubber layer (6).

6. The tread (1) according to claim 1, wherein: The tread (1) further comprises a base rubber layer (9) which is radially located on the inner side corresponding to the height of the wear indicating device (8).

7. A tire having the tread according to claim 1.

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