Tire tread

Abstract

The present invention relates to a tread for a tire having a contact surface intended to come into contact with the ground during rotation, the material constituting the contact elements having a modulus of elasticity G at 60° C., Mb. * and a glass transition temperature Tgb, at least one of the contact elements is provided with a coating layer covering at least one of the side surfaces of the contact element facing at least partially in the circumferential direction, the coating layer including at least two layers, an outer coating layer facing the outside of the contact element and an inner coating layer facing the inside of the contact element, the material constituting the outer coating layer having a modulus of elasticity G of Mo at 60° C. * and a glass transition temperature Tgo, and the material constituting the inner coating layer has an elastic modulus G of Mi at 60°C. * and a glass transition temperature Tgi.

Description

[Technical field]

[0001] The present invention relates to a tire tread, and more particularly to a tire tread for achieving improved performance on non-winter road surfaces while maintaining performance on winter road surfaces. [Background technology]

[0002] In recent years, so-called "all-season" tires, which have driving performance on winter road surfaces while maintaining high-speed driving performance on non-winter road surfaces, have begun to become popular.

[0003] In addition, even in so-called studless tires that are suitable for driving on winter roads covered with ice or snow, it is desired to improve performance on winter road surfaces while also improving performance on non-winter road surfaces that are not covered with ice or snow.

[0004] To improve performance in both winter and non-winter conditions, it is effective to introduce a hard layer on the side of the block, which effectively increases the so-called edge pressure.

[0005] WO 2013 / 088570 discloses a tread for a pneumatic tire and a pneumatic tire having such a tread, in which a reinforcing layer 6 is provided on a sidewall of a ground-contacting element of the tire tread, the reinforcing layer having an average thickness of less than 0.5 mm, being provided over an area of ​​at least 50% or more of the sidewall, and having a material modulus of elasticity of at least 200 MPa or more.

[0006] Japanese Patent Laid-Open Publication No. 07-047814 discloses a tire tread having a reinforcing layer made of rubber with a JIS A hardness of 80 to 95 degrees on the block sidewalls facing the lateral groove and auxiliary groove, the block having three thin cuts and one auxiliary groove, in order to improve performance on winter road surfaces.

[0007] JP 2010-105509 A discloses a tire that includes a composition in which 100 parts by weight of diene rubber containing 30% by weight or more of a rubber component having a glass transition temperature equal to at least -60°C is blended with 50 parts by weight or more of at least one of carbon black and silica, and that has a reinforcing layer made of rubber having a brittle temperature of up to -30°C on the sidewalls of the blocks in order to improve performance on both winter and non-winter road surfaces. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2013 / 088570 [Patent Document 2] Japanese Patent Application Publication No. 07-047814 [Patent Document 3] JP 2010-105509 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, the solutions disclosed in these documents do not provide satisfactory improvements in non-winter performance, especially wet performance, because the hard / reinforced layer that provides a good edge effect has a temperature dependency, and those that do provide improvements in winter performance have a negative effect on wet performance at low road temperatures. Therefore, it is desirable to provide improved performance on non-winter roads over a wide temperature range while maintaining or even improving performance on winter roads.

[0010] Therefore, there is a need for a tire tread that provides improved performance on non-winter surfaces over a wide temperature range while maintaining or even improving performance on winter surfaces.

[0011] definition

[0012] "Radial / orientation" is the direction / orientation perpendicular to the axis of rotation of the tire. This direction / orientation corresponds to the thickness orientation of the tread.

[0013] "Axial / orientation" is the direction / orientation parallel to the axis of rotation of the tire.

[0014] A "circumferential direction / orientation" is a direction / orientation that is tangential to some circle about the axis of rotation. This direction / orientation is perpendicular to both the axial direction / orientation and the radial direction / orientation.

[0015] "Tire" means any type of resilient tire, whether or not subject to internal pressure.

[0016] "Tread" of a tire means the volume of rubber material bounded by sides and two major surfaces, one of which is intended to contact the ground as the tire rolls.

[0017] A "groove" is the space between two rubber surfaces / side walls that do not themselves touch under normal rolling conditions when they are joined by another rubber surface / bottom surface. A groove has a width and a depth.

[0018] A "sipe", also called a "sipe", is a narrow cut radially inward from the surface of the tread, made by a thin blade, e.g., having a knife-edge shape. The width of the cut at the surface of the tread is narrower than that of a groove, e.g., 2.0 mm or less. This cut differs from a groove in that such cuts may be partially or completely closed in the tire contact patch under normal rolling conditions.

[0019] "Tire Contact Patch" is the footprint of a tire mounted on its standard rim as identified in a tire standard such as ETRTO, JATMA, TRA, etc. and inflated to its nominal pressure and nominal load. The "Width" of the tire contact patch, TW, is the maximum contact width of the tire contact patch along the tire's axis of rotation.

[0020] Elasticity G *is the dynamic shear complex modulus of the material at 60°C. The storage modulus, denoted G', and the loss modulus, denoted G'', which are dynamic properties well known to those skilled in the art, are measured by a viscoanalyser (microanalyzer: Metravib VB4000) using specimens molded from the raw composition or combined with the composition after vulcanization. The specimens used are those described in Figure X2.1 (circular method) of ASTM D 5992-96 (version originally approved in 1996, published in September 2006). The diameter "d" of the specimen is 10 mm (so that the specimen is 78.5 mm 2 The thickness "L" of each part of the rubber composition is 2 mm, and the ratio "d / L" is 5 (as opposed to the ratio "d / L" of 2 recommended in the standard ISO 2856, as stated in paragraph X2.4 of the ASTM standard). The test measures the response of a test specimen of the vulcanized rubber composition subjected to a simple alternating sinusoidal shear load at a frequency of 10 Hz. The maximum shear stress imposed during the test is 0.7 MPa. The test is carried out by changing the temperature at a rate of 1.5°C per minute from Tmin, a temperature below the glass transition temperature (Tg) of the rubber material, to a maximum temperature Tmax near 100°C. The test specimen is stabilized at Tmin for about 20 minutes before the start of the test in order to obtain a good uniformity of temperature within the specimen. The results obtained are the storage modulus (G') and the loss modulus (G'') at a given temperature. The complex modulus G * is defined in terms of the absolute values ​​of the storage modulus and the loss modulus by the following equation: (Formula 1) TIFF0007676550000001.tif1150

[0021] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide a tread for a tire which provides improved performance on non-winter surfaces over a wide temperature range while maintaining or even improving performance on winter surfaces. [Means for solving the problem]

[0022] The present invention provides a tread for a tire having a contact surface intended to come into contact with the ground during rotation, the tread comprising at least one main groove of depth Dp and a plurality of minor grooves of depth Ds extending at an angle to the direction in which the at least one main groove extends, the at least one main groove and the plurality of minor grooves defining a plurality of contact elements, the material constituting the plurality of contact elements having a modulus of elasticity G at 60° C. of Mb. * and a glass transition temperature Tgb, at least one of the contact elements comprises a coating layer covering at least one of the contact element's side surfaces facing at least partially in the circumferential direction, the coating layer including at least two layers, an outer coating layer facing the outside of the contact element and an inner coating layer facing the inside of the contact element, the material constituting the outer coating layer having a modulus of elasticity G of Mo at 60° C. * and a glass transition temperature Tgo, and the material constituting the inner coating layer has an elastic modulus G of Mi at 60°C. * and the glass transition temperature Tgi, and the modulus of elasticity G at 60°C Mb of the material constituting the contact element * is the elastic modulus G of the material constituting the inner coating layer at 60°C Mi * The elastic modulus G of the material constituting the outer coating layer at 60°C is higher than * is the modulus of elasticity G at 60 °C in Mb of the material that constitutes the contact element * and / or the glass transition temperature Tgb of the material constituting the contact element is higher than the glass transition temperature Tgi of the material constituting the inner coating layer and the glass transition temperature Tgo of the material constituting the outer coating layer is higher than the glass transition temperature Tgb of the material constituting the contact element.

[0023] This configuration allows for improved performance on non-winter surfaces over a wide temperature range while maintaining or even improving performance on winter surfaces.

[0024] Since at least one of the contact elements is provided with a coating layer which at least partially covers at least one of the circumferentially facing side surfaces of the contact element, the coating layer generates a good edge effect, particularly on winter road surfaces, and thus the performance on winter road surfaces can be improved.

[0025] The coating layer includes at least two layers, an outer coating layer facing the outside of the contact element and an inner coating layer facing the inside of the contact element, and the material constituting the outer coating layer has a modulus of elasticity of Mo at 60° C. G * and a glass transition temperature Tgo, and the material constituting the inner coating layer has an elastic modulus G of Mi at 60°C. * and glass transition temperature Tgi, the coating layer has different elastic modulus G * The combination of different glass transition temperatures allows for a wide temperature range, especially on non-winter roads, and therefore improves performance on non-winter roads over a wide temperature range.

[0026] The elastic modulus G in Mb at 60 °C of the material constituting the contact element 5 * The elastic modulus G of the material constituting the inner coating layer 62 at 60° C. * The elastic modulus G of Mo at 60° C. of the material constituting the outer coating layer 61 is higher than * is the modulus of elasticity G of the material constituting the contact element 5 at 60 °C Mb * Since the elastic modulus G of Mo at 60° C. of the material constituting the outer layer 61 is higher, it is possible to improve the performance on non-winter road surfaces over a wide temperature range while maintaining or even improving the performance on winter road surfaces. * is the modulus of elasticity G of the material constituting the contact element 5 at 60 °C Mb * In particular, the edge effect can be efficiently generated on winter road surfaces and non-winter road surfaces with relatively low temperatures. Furthermore, the elastic modulus G of the material constituting the contact element 5 at 60° C. * The elastic modulus G of the material constituting the inner coating layer 62 at 60° C. *5C is higher than 100° C. because the relatively low modulus of elasticity of the inner coating layer at 60° C. helps to generate a high mu by the outer coating layer 61 by inducing bending in the inner coating layer 62, especially on relatively hot non-winter road surfaces, and / or because the glass transition temperature Tgb of the material constituting the contact element 5 is higher than the glass transition temperature Tgi of the material constituting the inner coating layer 62 and the glass transition temperature Tgo of the material constituting the outer coating layer 61 is higher than the glass transition temperature Tgb of the material constituting the contact element 5, thereby improving the performance on non-winter road surfaces over a wide temperature range while maintaining or even improving the performance on winter road surfaces. This is because the glass transition temperature Tgb of the material constituting the contact element 5 is higher than the glass transition temperature Tgi of the material constituting the inner coating layer 62, which helps to generate a high mu through the outer coating layer 61 by generating bending in the inner coating layer 62, especially on relatively high temperature non-winter road surfaces, thanks to the relatively high glass transition temperature of the inner coating layer, and further because the glass transition temperature Tgo of the material constituting the outer coating layer 61 is higher than the glass transition temperature Tgb of the material constituting the contact element 5, which makes it possible to efficiently generate an edge effect, especially on winter road surfaces and relatively low temperature non-winter road surfaces.

[0027] In another preferred embodiment, the thickness of the coating layer measured on a plane parallel to the contact surface in a direction perpendicular to the extension direction of the major or minor groove facing the coating layer is at most equal to 2.0 mm.

[0028] A coating thickness of more than 2.0 mm leads to an inappropriate distribution of contact pressure on the contact surfaces of the contact elements, which leads to poor performance on winter surfaces, especially on icy surfaces. A coating thickness of up to 2.0 mm improves performance on non-winter surfaces over a wide temperature range while maintaining or even improving performance on winter surfaces.

[0029] The thickness of this coating layer, measured on a plane parallel to the contact surface in a direction perpendicular to the extension direction of the major or minor groove which it faces, is preferably at most equal to 1.5 mm, more preferably at most equal to 1.0 mm.

[0030] In another preferred embodiment, the thickness of the inner coating layer measured on a plane parallel to the contact surface in a direction perpendicular to the extension direction of the main groove or sub-groove facing the coating layer is thicker than the thickness of the outer coating layer measured on the same plane.

[0031] With this configuration, the inner coating layer increases the ability of the outer coating layer to generate a high mu by inducing bending in the inner coating layer, particularly on relatively high temperature non-winter road surfaces, thereby improving performance on non-winter road surfaces over a wide temperature range while maintaining or even improving performance on winter road surfaces.

[0032] In another preferred embodiment, the thickness of the inner coating layer measured on a plane parallel to the contact surface in a direction perpendicular to the extension direction of the main groove or minor groove facing the coating layer is thinner than the thickness of the outer coating layer measured on the same plane.

[0033] According to this configuration, the side coating layer increases the scraping power and the contact area, thereby more reliably generating the edge effect, especially on winter road surfaces, thereby further improving performance on winter road surfaces.

[0034] In another preferred embodiment, the width of the covering layer is at least equal to 35% of the width of the contact element.

[0035] If the width of this coating layer is less than 35% of the width of the contact element, there is a risk of high mu generation through the outer coating layer on non-winter surfaces and of edge effects on both winter and non-winter surfaces due to insufficient volume of the coating layer.By making the width of the coating layer at least 35% of the width of the contact element, it is possible to improve the performance on non-winter surfaces over a wide temperature range while maintaining or even improving the performance on winter surfaces.

[0036] The width of this covering layer is preferably equal to at least 50% of the width of the contact element, more preferably at least 60% of the width of the contact element, and even more preferably at least 80% of the width of the contact element.

[0037] (Advantageous Effects of the Invention) According to the above-mentioned configuration, it is possible to provide a tire tread which improves performance on non-winter road surfaces over a wide temperature range while maintaining or even improving performance on winter road surfaces.

[0038] Other characteristics and advantages of the invention emerge from the description that follows with reference to the attached drawings which show, by way of non-limiting example, an embodiment of the invention. [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 is a schematic plan view of a tread according to a first embodiment of the present invention. [Diagram 2] 2A to 2C are schematic cross-sectional views taken along line II-II in FIG. 1 in different modified examples (a), (b) and (c). [Diagram 3] FIG. 4 is a schematic plan view of a tread according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0041] A tread 1 for a tire according to a first embodiment of the invention will be described below with reference to Figures 1 and 2. Figure 1 is a schematic plan view of the tread according to the first embodiment of the invention. Figure 2 is a schematic cross-sectional view along the line II-II in Figure 1 in different variants (a), (b) and (c).

[0042] The tread 1 is a tread for a tire having dimensions 225 / 45R17 and comprises a contact surface 2 intended to come into contact with the ground during rolling, at least one main groove 3 (shown in FIG. 2) of depth Dp, and a plurality of minor grooves 4 (shown in FIG. 2) of depth Ds extending at an angle to the direction in which the at least one main groove 3 extends. The tread 1 comprises a plurality of contact elements 5 bounded by the at least one main groove 3 and the plurality of minor grooves 4. The material constituting the plurality of contact elements 5 has a modulus of elasticity G at 60° C. of Mb. * and a glass transition temperature Tgb. In this first embodiment, the tread 1 has at least two main grooves 3 extending in a circumferential direction, which is the up-down direction in FIG. 1 parallel to the centerline indicated by the line C-C', and a plurality of sub grooves 4 extending in an axial direction perpendicular to the circumferential direction.

[0043] 1, at least one of the contact elements 5 is provided with a coating layer 6 which covers at least one of the side surfaces 7 of the contact element 5 which face at least partially in the circumferential direction. In this first embodiment, the coating layer 6 covers the entire width of the contact element 5.

[0044] 1 and 2, the coating layer 6 includes at least two layers: an outer coating layer 61 facing the outside of the contact element 5, and an inner coating layer 62 facing the inside of the contact element 5. The material constituting the outer coating layer 61 is selected from a group consisting of a material having a modulus of elasticity G of Mo at 60° C. * and a glass transition temperature Tgo, and the material constituting the inner coating layer 62 has an elastic modulus G of Mi at 60° C. * and a glass transition temperature Tgi.

[0045] The contact element 5, the outer coating layer 61 and the inner coating layer 62 have a modulus of elasticity G at 60° C. Mb of the material constituting the contact element 5. * The elastic modulus G of the material constituting the inner coating layer 62 at 60° C. * The elastic modulus G of Mo at 60° C. of the material constituting the outer coating layer 61 is higher than * is the modulus of elasticity G of the material constituting the contact element 5 at 60 °C Mb * It is configured to be higher.

[0046] In addition, the contact element 5, the outer coating layer 61 and the inner coating layer 62 are configured so that the glass transition temperature Tgb of the material constituting the contact element 5 is higher than the glass transition temperature Tgi of the material constituting the inner coating layer 62, and the glass transition temperature Tgo of the material constituting the outer coating layer 61 is higher than the glass transition temperature Tgb of the material constituting the contact element 5.

[0047] As shown in Figures 1 and 2, the thickness of the coating layer 6 measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or the sub-groove 4 that the coating layer 6 faces is at most equal to 2.0 mm.

[0048] As shown in Figures 1 and 2(a), the thickness of the inner coating layer 62 measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or the sub-groove 4 on which the coating layer 6 faces is equal to the thickness of the outer coating layer 61 measured on the same plane. As a variant, as shown in Figure 2(b), the thickness of the inner coating layer 62 measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or the sub-groove 4 on which the coating layer 6 faces can be thinner than the thickness of the outer coating layer 61 measured on the same plane, or as shown in Figure 2(c), the thickness of the inner coating layer 62 measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or the sub-groove 4 on which the coating layer 6 faces can be thicker than the thickness of the outer coating layer 61 measured on the same plane.

[0049] Since at least one of the contact elements 5 is provided with a coating layer 6 covering at least one of the circumferentially facing side surfaces 7 of the contact element 5, the coating layer 6 generates a good edge effect, particularly on winter roads, and thus the performance on winter roads can be improved.

[0050] The coating layer 6 includes at least two layers, an outer coating layer 61 and an inner coating layer 62. The outer coating layer 61 facing the outside of the contact element 5 is made of a material having a modulus of elasticity G of Mo at 60° C. * and a glass transition temperature Tgo, and the inner coating layer 62 facing the inside of the contact element 5 has a modulus of elasticity G of Mi at 60° C.* and glass transition temperature Tgi, the coating layer 6 has different elastic moduli G * The combination of different glass transition temperatures allows for a wide temperature range, especially on non-winter roads, and therefore improves performance on non-winter roads over a wide temperature range.

[0051] The elastic modulus G in Mb at 60 °C of the material constituting the contact element 5 * The elastic modulus G of the material constituting the inner coating layer 62 at 60° C. * The elastic modulus G of Mo at 60° C. of the material constituting the outer coating layer 61 is higher than * However, since the elastic modulus G* of Mb at 60° C. of the material constituting the contact element 5 is higher than that of Mb, it is possible to improve the performance on non-winter road surfaces over a wide temperature range while maintaining or even improving the performance on winter road surfaces. This is because the elastic modulus G* of Mo at 60° C. of the material constituting the outer covering layer 61 is higher than that of Mb at 60° C. * is the modulus of elasticity G of the material constituting the contact element 5 at 60 °C Mb * In particular, the edge effect can be efficiently generated on winter road surfaces and non-winter road surfaces with relatively low temperatures. Furthermore, the elastic modulus G of the material constituting the contact element 5 at 60° C. * The elastic modulus G of the material constituting the inner coating layer 62 at 60° C. * is higher because the relatively low elastic modulus at 60° C. of the inner coating layer helps to generate bending in the inner coating layer 62, thereby generating a high mu by the outer coating layer 61, especially on relatively high temperature non-winter road surfaces.

[0052] Since the glass transition temperature Tgb of the material constituting the contact element 5 is higher than the glass transition temperature Tgi of the material constituting the inner coating layer 62 and the glass transition temperature Tgo of the material constituting the outer coating layer 61 is higher than the glass transition temperature Tgb of the material constituting the contact element 5, it is possible to improve the performance on non-winter road surfaces over a wide temperature range while maintaining or even improving the performance on winter road surfaces, because the glass transition temperature Tgb of the material constituting the contact element 5 is higher than the glass transition temperature Tgi of the material constituting the inner coating layer 62, which helps to generate a high mu through the outer coating layer 61 by generating bending in the inner coating layer 62, especially on relatively high temperature non-winter road surfaces, thanks to the relatively high glass transition temperature of the inner coating layer, and further, the glass transition temperature Tgo of the material constituting the outer coating layer 61 is higher than the glass transition temperature Tgb of the material constituting the contact element 5, which allows an edge effect to be efficiently generated, especially on winter road surfaces and relatively low temperature non-winter road surfaces.

[0053] In addition, the thickness of the coating layer 6 measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or sub-groove 4 that the coating layer 6 faces is at most equal to 2.0 mm, so that it is possible to improve performance on non-winter road surfaces over a wide temperature range while maintaining or even improving performance on winter road surfaces.

[0054] If the thickness of the coating layer 6 exceeds 2.0 mm, the distribution of the contact pressure on the contact surface 2 of the contact element 5 will be inappropriate, leading to a decrease in performance on winter roads, particularly on icy roads.

[0055] The thickness of this coating layer 6, measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or the secondary groove 4 facing the coating layer 6, is preferably at most equal to 1.5 mm, more preferably at most equal to 1.0 mm.

[0056] If the thickness of the inner coating layer 62 measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or secondary groove 4 facing the coating layer 6 is designed to be thicker than the thickness of the outer coating layer 61 measured on the same plane, it is possible to improve the performance on non-winter road surfaces over a wide temperature range while maintaining or even improving the performance on winter road surfaces, because the inner coating layer 62 enhances the ability of the outer coating layer 61 to generate a high mu by generating bending in the inner coating layer 62, especially on non-winter road surfaces with relatively high temperatures.

[0057] If the thickness of the inner coating layer 62, measured on a plane parallel to the contact surface 2 in a direction perpendicular to the extension direction of the main groove 3 or the secondary groove 4 facing the coating layer 6, is designed to be thinner than the thickness of the outer coating layer 61, measured on the same plane, the performance on winter roads can be improved, because the outer coating layer 61 increases the scraping power and the contact surface, thereby more reliably generating an edge effect, especially on winter roads.

[0058] The depth Dp of the main groove 3 and the depth Ds of the minor groove 4 can be the same, as in this first embodiment, or can be different.

[0059] The covering layer 6 may be provided to cover other side surfaces 7, including side surfaces 7 not facing in the circumferential direction.

[0060] The thickness of the overall coating layer 6, the outer coating layer 61 or the inner coating layer 62 may vary radially and / or axially.

[0061] In the radial direction, the outer coating layer 61 and the inner coating layer 62 can have different lengths. Preferably, the entire coating layer 6, the outer coating layer 61 or the inner coating layer 62 can be made available up to a level corresponding to a measure indicating the legal wear limit of the tread 1.

[0062] A tread 21 according to a second embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 is a schematic plan view of a tread according to a second embodiment of the present invention. The configuration of this second embodiment is the same as that of the first embodiment except for the arrangement shown in Fig. 3, so it will be described with reference to Fig. 3.

[0063] As shown in Figure 3, the tread 21 comprises a contact surface 22 intended to come into contact with the ground during rolling, at least one main groove 23 of depth D (not shown) extending obliquely to the axial direction from the centre to a shoulder, and a plurality of minor grooves 24 of depth Ds (not shown) extending at an angle to the direction of extension of the at least one main groove 23. The at least one main groove 23 and the plurality of minor grooves 24 define a plurality of contact elements 25. The material from which the plurality of contact elements 25 is made has a modulus of elasticity G of Mb at 60°C. * and a glass transition temperature Tgb.

[0064] 3, at least one of the contact elements 25 includes a coating layer 26 covering at least one of the side surfaces 27 of the contact element 25 that are at least partially circumferentially oriented, the coating layer 26 including at least two layers: an outer coating layer 261 facing the outside of the contact element 25 and an inner coating layer 262 facing the inside of the contact element 25. The material constituting the outer coating layer 261 has a modulus of elasticity G of Mo at 60° C. * and a glass transition temperature Tgo, and the material constituting the inner coating layer 262 has an elastic modulus G of Mi at 60° C. * and a glass transition temperature Tgi. In this second embodiment, the covering layer 26 covers the two lateral sides 27 of the contact element 25 located in the central region of the tread 21.

[0065] As shown in FIG. 3, the width of the covering layer 26 is at least equal to 35% of the width of the contact element 25 .

[0066] The width of the covering layer 26 is at least equal to 35% of the width of the contact element 25, thereby improving performance on non-winter surfaces over a wide temperature range while maintaining or even improving performance on winter surfaces.

[0067] If the width of this coating layer 26 is less than 35% of the width of the contact element 25, there is a risk that due to insufficient volume of the coating layer 26, a high mu will be generated through the outer coating layer 261 on non-winter surfaces and that the edge effect will function both on winter and non-winter surfaces.

[0068] The width of this covering layer 26 is preferably equal to at least 50% of the width of the contact element 25 , more preferably at least 60% of the width of the contact element 25 , and even more preferably at least 80% of the width of the contact element 25 .

[0069] Even if the multiple side surfaces 27 face in the circumferential direction, the coating layer 26 may be provided on only one of the multiple side surfaces 27.

[0070] The invention is not limited to the embodiments described and shown, but various modifications can be made thereto without departing from its framework. EXAMPLES

[0071] In order to confirm the effect of the present invention, two types of tires as examples to which the present invention is applied, and other types of tires as reference examples and comparative examples were prepared.

[0072] The examples have a tread as described in the first embodiment above, where the contact element is provided with a cut that is open at the contact surface and extends completely in the axial direction. The covering layer includes an outer covering layer and an inner covering layer. Example 1 is configured to have a glass transition temperature Tgb of the material constituting the contact element that is higher than the glass transition temperature Tgi of the material constituting the inner covering layer (Tgb is indicated by "=" and Tgi is indicated by "-"), and a glass transition temperature Tgo of the material constituting the outer covering layer that is higher than the glass transition temperature Tgb of the material constituting the contact element (Tgb is indicated by "=" and Tgo is indicated by "+"). Example 2 is configured to have a modulus of elasticity G of Mi at 60°C of the material constituting the inner covering layer. * The elastic modulus G of the material that constitutes the contact element at 60 °C Mb is higher than *(Mb is indicated by "=" and Mi is indicated by "-"), and the elastic modulus G of the material constituting the contact element at 60 °C * The elastic modulus G of the material constituting the outer coating layer at 60 °C is higher than * (Mb is indicated by "=" and Mo is indicated by "+"). The comparative example is the same as Example 2, but the elastic modulus G of Mi at 60°C of the material constituting the inner coating layer is * The elastic modulus G of the material that constitutes the contact element at 60 °C Mb is higher than * (Mb is indicated by "=" and Mi is indicated by "-"), and the elastic modulus G of the material constituting the contact element at 60 °C * The elastic modulus G of the material constituting the outer coating layer at 60 °C is lower than * (Mb is represented by "=" and Mo is represented by "--"). The Reference Example is a tire having a single covering layer. All of the internal structures of the Examples, Comparative Examples, and Reference Example are the same as that of a typical radial tire, except for the above.

[0073] Winter performance test:

[0074] -Snow braking:

[0075] A 2,000cc front-wheel drive vehicle was fitted with brand new test tires on all four wheels. On a straight packed snow road, braking was performed using the ABS (anti-lock braking system) at a speed of 50 km / h, and the distance traveled up to 5 km / h was measured.

[0076] The results are shown in Tables 1 and 2. In these Tables 1 and 2, the results are expressed as an index with the Reference Example being set at 100, with a larger value indicating better performance.

[0077] Non-winter performance tests:

[0078] -Wet braking:

[0079] A 2,000cc front-wheel drive vehicle was fitted with brand new test tyres on all four wheels. The vehicle was placed on a straight road with a wet surface 1mm deep, and braking was performed using the ABS (anti-lock braking system) at a speed of 100km / h, and the distance travelled up to 10km / h was measured.

[0080] The results are similarly shown in Tables 1 and 2. In these Tables 1 and 2, the results are expressed as an index with the Reference Example being set at 100, with a larger value indicating better performance.

[0081] (Table 1) TIFF0007676550000002.tif40160

[0082] (Table 2) TIFF0007676550000003.tif39128

[0083] As can be seen from Tables 1 and 2, the examples demonstrate improved performance on non-winter surfaces over a wide temperature range while maintaining or even improving performance on winter surfaces that is not achievable with treads disclosed in the prior art. [Explanation of symbols]

[0084] 1, 21 Tread 2, 22 contact surface 3, 23 Main groove 4, 24 minor groove 5, 25 contact elements 6, 26 Covering layer 61, 261 Outer coating layer 62, 262 Inner coating layer 7, 27 Side

Claims

1. A tread (1) for a tire having a contact surface (2) intended to come into contact with the ground during rotation, said tread (1) comprising at least one main groove (3) of depth Dp and a number of secondary grooves (4) of depth Ds extending at an angle to the direction in which said at least one main groove (3) extends, said at least one main groove (3) and said secondary grooves (4) delimiting a number of contact elements (5), said number of contact elements (5) being made of a material having a modulus of elasticity G at 60° C. or less. * (Mb) and a glass transition temperature Tgb, at least one contact element (5) of the plurality of contact elements (5) comprising a coating layer (6) covering at least one of the side surfaces (7) of the contact element (5) facing at least partially in the circumferential direction, The tread has a covering layer (6) which comprises at least two layers, an outer covering layer (61) facing the outside of the contact element (5) and an inner covering layer (62) facing the inside of the contact element (5), and the material constituting the outer covering layer (61) has an elastic modulus G at 60° C. or less. * (Mo) and a glass transition temperature Tgo, and the material constituting the inner coating layer (62) has an elastic modulus G at 60° C. * (Mi) and a glass transition temperature Tgi, and the elastic modulus G at 60° C. of the material constituting the contact element (5) * (Mb) is the elastic modulus G at 60° C. of the material constituting the inner coating layer (62). * (Mi) is higher than the elastic modulus G at 60 ° C of the material constituting the outer coating layer (61). * (Mo) is the elastic modulus G at 60° C. of the material constituting the contact element (5). * (Mb), and / or the glass transition temperature Tgb of the material constituting the contact element (5) is higher than the glass transition temperature Tgi of the material constituting the inner coating layer (62) and the glass transition temperature Tgo of the material constituting the outer coating layer (61) is higher than the glass transition temperature Tgb of the material constituting the contact element (5).

2. 2. The tread (1) according to claim 1, wherein the thickness of the covering layer (6), measured on a plane parallel to the contact surface (2) in a direction perpendicular to the extension of the main groove (3) or the secondary groove (4) facing the covering layer (6), is at most equal to 2.0 mm.

3. 3. The tread (1) according to claim 1 or 2, wherein the thickness of the inner covering layer (62) measured on a plane parallel to the contact surface (2) in a direction perpendicular to the extension direction of the main groove (3) or the sub-groove (4) facing the covering layer (6) is greater than the thickness of the outer covering layer (61) measured on the same plane.

4. 3. The tread (1) according to claim 1 or 2, wherein the thickness of the inner covering layer (62) measured on a plane parallel to the contact surface (2) in a direction perpendicular to the extension direction of the main groove (3) or the sub-groove (4) facing the covering layer (6) is smaller than the thickness of the outer covering layer (61) measured on the same plane.

5. The tread (1) according to any one of the preceding claims, wherein the width of said covering layer (6) is at least equal to 35% of the width of said contact element (5).

6. A tire having a tread according to any one of claims 1 to 5.

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