Long-lasting tire tread

Abstract

The present invention provides a tread for a tire having a contact surface and at least a part of a plurality of grooves provided with wear indicating means for indicating a legal wear limit, the tread comprising at least two rubber layers, a first rubber layer arranged radially outside a second rubber layer and provided with a separation layer intended to be joined to the other rubber layer radially inside the first rubber layer, the second rubber layer provided without a separation layer, the constituent material of the separation layer being: (Formula 2) Fill in TIFF2024502256000012.tif1551, where G * is the elastic modulus G at 60°C of the material constituting the separation layer * , C is the wear amount (mm2) of the material constituting the separation layer measured in accordance with JIS K 7218, Method A 3 ).

Description

[Technical Field]

[0001] The present invention relates to a tread for a tire, and more particularly to a tread for a tire that is capable of maintaining high performance on winter and non-winter road surfaces until almost the end of its wear life. [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] Furthermore, 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] It is known that reducing the tread stiffness near the groove bottom is effective in maintaining performance on winter roads, especially on snow-covered roads, but this method is also known to adversely affect performance on non-winter roads.

[0005] EP 0 378 090 A1 discloses a tread for a tire having blocks (relief elements) with cuts having a cross section with a fork-shaped profile with at least two branches forming an extension of a single part, the number of cuts in the blocks (relief elements) increasing by at least 1.5 times starting from the depth of the cut with two branches.

[0006] Japanese Patent Application Laid-Open No. 2006-142843 discloses a tire having a block including a cap rubber layer and a base rubber layer overlapped in the radial direction, in which the cap rubber layer includes an alumina-containing cylindrical closed-cell foam and the base rubber layer includes a spherical closed-cell foam.

[0007] JP 2002-079807 A discloses a tire having a tread formed by at least two layers including a cap rubber layer and a base rubber layer, the base rubber layer containing hollow particles having an average particle size equal to a maximum of 500 μm mixed in a volume ratio of 2% to 40%.

[0008] Japanese Patent Application Laid-Open Publication No. 2007-168651 discloses a tire having multiple blocks, which has a three-layer rubber block including a cap rubber layer, an intermediate rubber layer, and a base rubber layer, and the 100% elastic modulus of each rubber layer is highest in the base rubber layer, followed by the cap rubber layer, and then the intermediate rubber layer.

[0009] JP 2006-306281 A discloses a tire tread having a cap tread and two layers of base tread, in which the cap tread has a JISA hardness of 40 to 50, the outer base tread has a JISA hardness of 70 to 80 and a thickness of 1.5 mm or more, and the inner base tread has a JISA hardness of 55 to 70 and a thickness of 0.3 mm or more.

[0010] Japanese Patent Application Laid-Open No. 2001-080314 discloses a tire in which a cap tread and a base tread having different hardnesses are laminated together, and a tread separation layer having a higher hardness than the cap tread and the base tread is provided between the cap tread and the base tread. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Publication No. 0378090 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-142843 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-079807 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-168651 [Patent Document 5] Japanese Patent Application Laid-Open No. 2006-306281 [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-080314 Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the solutions disclosed in these documents, the bottom of the tread (or block) containing double branched incisions, spherical closed-cell foam, or hollow particles is too soft due to the increased number of incisions, the closed-cell foam or hollow particles have a negative effect from the early stage of tire life, and the multi-layer tread solution is not satisfactory in terms of performance until almost the end of life, especially on winter roads. Therefore, it is desired to provide an improvement in performance until almost the end of tread life, especially on winter roads.

[0013] Therefore, there is a need for a tire tread that allows for improved performance, particularly on winter surfaces, while maintaining performance and durability on non-winter surfaces throughout most of its life.

[0014] definition

[0015] "Radial / Orientation" means the direction / orientation perpendicular to the tire's axis of rotation. This direction / orientation corresponds to the thickness orientation of the tread.

[0016] "Axial / orientation" is the direction / orientation parallel to the axis of rotation of the tire.

[0017] 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.

[0018] "Tire" means any type of resilient tire, whether or not under internal pressure.

[0019] The "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.

[0020] A "groove" is the space between two rubber surfaces / side walls that do not touch under normal rolling conditions because they are connected by another rubber surface / bottom surface. A groove has a width and a depth.

[0021] "Sipes," also known as "sipes," are narrow cutouts extending radially inward from the surface of the tread, typically made by a thin blade shaped like a knife blade. The width of the cuts at the surface of the tread is narrower than that of grooves, typically 2.0 mm or less. Unlike grooves, such cuts may close partially or completely within the tire's contact patch under normal rolling conditions.

[0022] "Tire contact patch" is the footprint of the tire as identified in a tire standard such as ETRTO, JATMA, TRA, etc. and mounted on its standard rim inflated to nominal pressure and nominal load. Tire contact patch "width TW" is the maximum contact width of the tire contact patch along the tire's axis of rotation.

[0023] Elastic modulus 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 viscoanalyzer (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 format) 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 2The thickness "L" of each portion of the rubber composition is 2 mm, resulting in a ratio "d / L" of 5 (as opposed to the ratio "d / L" of 2 recommended by standard ISO 2856, as stated in paragraph X2.4 of the ASTM standard). The test measures the response of a vulcanized rubber composition specimen 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 performed 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 specimen is allowed to stabilize at Tmin for approximately 20 minutes before the start of the test to ensure good temperature uniformity within the specimen. The results obtained are the storage modulus (G') and loss modulus (G'') at a given temperature. The complex modulus G * is defined in terms of the absolute values of the storage modulus and loss modulus by the following equation: (Formula 1) TIFF0007723747000001.tif1251

[0024] It is therefore an object of the present invention to provide a tread for a tire that is capable of providing improved performance, particularly on winter surfaces, while maintaining performance and durability capabilities on non-winter surfaces until nearly the end of its life. [Means for solving the problem]

[0025] 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 a plurality of grooves of depth D that open into the contact surface, a plurality of contact elements delimited by the plurality of grooves, each of the plurality of contact elements having an upper surface that constitutes part of the contact surface, at least some of the plurality of grooves comprising wear indicators that indicate the legal wear limit of the tread, the tread comprising at least two rubber layers, at least one first rubber layer and at least one second rubber layer, the first rubber layer being provided with a separation layer arranged radially outside the second rubber layer and intended to be joined to another rubber layer radially inside the first rubber layer, the second rubber layer being provided without a separation layer, the tread being characterized in that the materials that make up the separation layers are in the following relationship: (Formula 2) TIFF0007723747000002.tif1551, where G * is the elastic modulus G of the material that makes up the separation layer at 60°C * , C is the abrasion amount (mm ) of the material constituting the separation layer measured in accordance with JIS K 7218, Method A. 3 )

[0026] This configuration allows for improved performance, especially on winter roads, almost to the end of its life.

[0027] The tread comprises at least two rubber layers, at least one first rubber layer and at least one second rubber layer, the first rubber layer being arranged radially outward of the second rubber layer and provided with a separation layer intended to connect to another rubber layer radially inward of the first rubber layer, and the second rubber layer being provided without a separation layer, particularly at the bottom of the contact elements and shaped to extend radially beyond the wear indicators that indicate the legal wear limit of the tread, allowing for the continuous creation of upper surface roughness in the form of riblets or microgrooves that act as additional fine edges and volumes for trapping snow particles or water films until almost the end of the tread's life, thus improving performance on winter roads until almost the end of the tread's life.

[0028] The present inventors have determined that the material constituting the separation layer satisfies the following relationship: (Formula 2) TIFF0007723747000003.tif1551 Where, G * is the elastic modulus G at 60°C of the material constituting the separation layer 7 * , C is the wear amount of the material that makes up the separation layer measured in accordance with JIS K 7218 Method A mm 3 It was found that by satisfying the above condition, the separation layer wears faster than both the first and second rubber layers, and continues to generate / regenerate roughness on the upper surface, thereby improving performance on winter roads almost until the end of the tire's life.

[0029] If this value is less than 200, there is a risk that the separation layer 7 will wear slower than both the first rubber layer and the second rubber layer, which will lead to a significant decrease in the contact area of the upper surface. Also, if this value is greater than 1200, there is a risk that the separation layer will wear too quickly, resulting in a decrease in durability. The material constituting the separation layer is selected so as to satisfy the following relationship: (Formula 2) By setting it to meet TIFF0007723747000004.tif1551, performance on winter roads can be improved almost until the end of its life.

[0030] In another preferred embodiment, less than 20% of the volume of the separation layer exceeds the height corresponding to the wear indicator on each contact element.

[0031] Thus, if the volume of the separation layer that exceeds the height corresponding to the wear indicator in each contact element exceeds 20%, the contact surface with the first rubber layer or the second rubber layer will be reduced, which poses a risk of performance degradation, particularly in winter. By setting the volume of the separation layer that exceeds the height corresponding to the wear indicator in each contact element to less than 20%, it is possible to maintain performance, particularly on winter road surfaces.

[0032] The volume of the separation layer above the height corresponding to the wear indicator on each contact element is preferably less than 18%, more preferably less than 15%.

[0033] In another preferred embodiment, the radially outermost portion of the second rubber layer on each contact element in a plane perpendicular to both the upper surface and the axis of rotation of the tire is at least equal to 0.5 mm radially outward from a height corresponding to the wear indicating means.

[0034] If the radially outermost position of the second rubber layer of each contact element in a plane perpendicular to the tire's top surface and rotation axis is less than 0.5 mm radially outward from the wear indicating means, there is a risk that a sufficient amount of roughness will not be generated even near the end of life, and performance will not be improved until near the end of life.By making this radially outermost position of the second rubber layer equal to at least 0.5 mm radially outward from the wear indicating means in a plane perpendicular to the tire's top surface and rotation axis, performance can be improved until near the end of life.

[0035] This radially outermost extent of the second rubber layer in a plane perpendicular to both the upper surface and the axis of rotation of the tire at each contact element is preferably equal to at least 0.8 mm radially outward from a height corresponding to the wear indicating means, and more preferably equal to at least 1.0 mm radially outward from a height corresponding to the wear indicating means.

[0036] In another preferred embodiment, the separating layer is at least 0.2 mm away from any contour of the contact element.

[0037] If the separation layer is less than 0.2 mm away from the contour of the contact element, stress concentration during rotation can cause the separation layer to become a fracture origin, resulting in a risk of reduced durability. By separating this separation layer by at least 0.2 mm from the contour of the contact element, durability can be maintained.

[0038] The separating layer is preferably at least 0.5 mm from the contour of the contact element, more preferably at least 0.8 mm from the contour of the contact element, and even more preferably at least 1.0 mm from the contour of the contact element.

[0039] In another preferred embodiment, the tread comprises one first rubber layer and one second rubber layer.

[0040] This configuration allows the tread to be manufactured without any modifications or with minimal modifications to the manufacturing process.

[0041] In another preferred embodiment, the rubber composition constituting the first rubber layer is the same as the rubber composition constituting the second rubber layer.

[0042] According to this configuration, the rubber composition constituting the contact elements is the same except for the separating layer, so that the tread can be manufactured efficiently.

[0043] In another preferred embodiment, the tread further comprises a base rubber layer positioned radially inward at a height corresponding to the wear indicating means.

[0044] With this configuration, thanks to the base rubber layer being positioned radially inward at a height corresponding to the wear indicator means, it is possible to adjust performance other than grip performance, such as handling performance or rolling resistance, without affecting grip performance.

[0045] (Advantageous Effects of the Present Invention) The above-described configuration can provide improved performance, particularly on winter roads, while maintaining performance and durability on non-winter roads until almost the end of the tire's life.

[0046] Other characteristics and advantages of the invention emerge from the description that follows, with reference to the accompanying drawings, which show, by way of non-limiting example, embodiments of the invention. [Brief explanation of the drawings]

[0047] [Figure 1] 1 is a schematic plan view of a tread according to a first embodiment of the present invention. [Figure 2] 2A and 2B are schematic cross-sectional views taken along line II-II in FIG. 1 in (a) a new condition and (b) a worn condition. [Figure 3] FIG. 3 is an enlarged schematic view showing a portion indicated by III in FIG. 2(b). [Figure 4] 4 is a schematic cross-sectional view of a tread according to a second embodiment of the present invention, corresponding to a position along line IV-IV in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0048] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[0049] A tire tread 1 according to a first embodiment of the present invention will be described below with reference to Figures 1, 2 and 3. Figure 1 is a schematic plan view of the tread according to the first embodiment of the present invention. Figure 2 is a schematic cross-sectional view taken along line II-II in Figure 1 in (a) a new state and (b) a worn state. Figure 3 is an enlarged schematic view showing the part indicated by III in Figure 2(b).

[0050] The tread 1 has dimensions 225 / 45R17 and comprises a tread for a tire having a contact surface 2 intended to come into contact with the ground when rolling, and is provided with a plurality of grooves 3 of depth D (shown in FIG. 2 ) opening in the contact surface 2. The tread 1 comprises a plurality of contact elements 4 delimited by the plurality of grooves 3.

[0051] As shown in Figure 1, the tread 1 is provided to have a plurality of contact elements 4, and each contact element 4 close to the center of the tread 1, indicated by a line C-C' parallel to the circumferential direction of the tread 1, is provided with one notch 42 opening on an upper surface 41 constituting a part of the contact surface 2, and each contact element 4 axially outward from the contact element 4 with the notch 42 has no opening on the upper surface 41. In addition, one of the plurality of grooves 3 is provided with a wear indicating means 8 indicating the legal wear limit of the tread 1.

[0052] As shown in FIG. 2(a), the tread 1 comprises two rubber layers: at least one first rubber layer 5 and at least one second rubber layer 6. The first rubber layer 5 is provided with a separation layer 7 arranged radially outward of the second rubber layer 6 and intended to bond to the other rubber layers radially inward of the first rubber layer 5, while the second rubber layer 6 is provided without a separation layer. The tread 1 is provided on a ply 15, which, in the case of a radial tire structure, is generally a package of structural reinforcements for the tire, including at least a carcass and a belt. In this first embodiment, the tread 1 comprises one first rubber layer 5 with the separation layer 7 and one second rubber layer 6. The material constituting the first rubber layer 5 is different from the material constituting the second rubber layer 6.

[0053] 2(a), the volume of the separation layer 7 in each contact element 4 that exceeds the height corresponding to the wear indication means 8 is less than 20%, and the radially outermost portion of the second rubber layer 6 in each contact element 4 in a plane perpendicular to both the tire top surface 41 and the rotation axis is at least 0.5 mm from the height corresponding to the wear indication means 8. The separation layer 7 is also at least 0.2 mm away from any contours of the contact element 4. In this first embodiment, the volume of the separation layer 7 in each contact element 4 that exceeds the height corresponding to the wear indication means 8 is 13%, and the radially outermost portion of the second rubber layer 6 in each contact element 4 in a plane perpendicular to both the tire top surface 41 and the rotation axis is 4.0 mm.

[0054] 2(b) and 3, when the tread 1 is in a worn state near the end of its life as indicated by the wear indicator 8, both the first rubber layer 5 and the second rubber layer 6 appear on the worn upper surface 41' of the worn contact element 4' that constitutes part of the worn contact surface 2'. At the same time, riblets 71 having a small depth below the worn contact surface 2' are formed between the first rubber layer 5 and the second rubber layer 6 on the worn upper surface 41' due to the separation layer 7 wearing away faster than both the first rubber layer 5 and the second rubber layer 6.

[0055] The material constituting the separation layer 7 is different from both the material constituting the first rubber layer 5 and the material constituting the second rubber layer 6, and is designed to satisfy the following relationship. (Formula 2) TIFF0007723747000005.tif1551 where, G * is the elastic modulus G at 60°C of the material constituting the separation layer 7 * , C is the amount of wear of the material constituting the separation layer 7 measured in accordance with JIS K 7218 Method A mm 3 and in this first embodiment, this value for the separation layer 7 is 357, and G * is 1.29 and C is 0.0053.

[0056] 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 arranged radially outside the second rubber layer 6 and provided with a separation layer 7 intended to join with another rubber layer radially inside the first rubber layer 5, while the second rubber layer 6 is provided without a separation layer, in particular the separation layer 7 shaped to extend radially at the bottom of the contact element 4 and above the wear indicators 8 indicating the legal wear limit of the tread 1, making it possible to continuously form roughness in the form of riblets 71 or microgrooves on the upper surface 41, which act as additional fine edges and volumes for trapping snow particles or water films until approximately the end of the tread's life, thus improving performance on winter roads until approximately the end of the tread's life.

[0057] The present inventors have determined that the material constituting the separation layer 7 satisfies the following relationship: (Formula 2) TIFF0007723747000006.tif1551 where, G * is the elastic modulus G at 60°C of the material constituting the separation layer 7 * , C is the amount of wear of the material constituting the separation layer 7 measured in accordance with JIS K 7218 Method A mm 3It has been found that by satisfying the above condition, the separation layer 7 wears faster than both the first rubber layer 5 and the second rubber layer 6, and continues to generate / regenerate roughness on the upper surface 41. Therefore, it is possible to improve performance on winter roads almost until the end of the tire's life.

[0058] If this value is less than 200, there is a risk that the separation layer 7 will wear slower than both the first rubber layer 5 and the second rubber layer 6, which will lead to a significant decrease in the contact area of the upper surface 41. Also, if this value is greater than 1200, there is a risk that the separation layer 7 will wear too quickly, resulting in a decrease in durability. The material constituting the separation layer 7 is selected to satisfy the following relationship: (Formula 2) By setting it to meet TIFF0007723747000007.tif1551, performance on winter roads can be improved almost until the end of its life.

[0059] The volume of the separating layer 7 exceeding the height corresponding to the wear indicating means 8 in each contact element 4 is less than 20%, which makes it possible to maintain performance, particularly on winter roads.

[0060] If the volume of the separating layer 7 in each contact element 4 that exceeds the height corresponding to the wear indicator 8 exceeds 20%, there is a risk of performance degradation, particularly in winter, due to a reduction in the contact surface with the first rubber layer 5 or the second rubber layer 6.

[0061] Furthermore, the volume of the separating layer 7 above the height corresponding to the wear indicator means 8 on each contact element 4 is preferably less than 18%, more preferably less than 15%.

[0062] The radially outermost portion of each contact element 4 in a plane perpendicular to both the upper surface 41 of the second rubber layer 6 and the rotational axis of the tire is at least equal to 0.5 mm radially outward from the height corresponding to the wear indicator means 8, thereby improving performance almost until the end of life.

[0063] If this radially outermost point of each contact element 4 in a plane perpendicular to both the upper surface 41 of the second rubber layer 6 and the tire rotation axis is less than 0.5 mm radially outward from the height corresponding to the wear indicator means 8, there is a risk that a sufficient amount of roughness will not be generated near the end of life and performance will not be improved near the end of life.

[0064] The radially outermost position of each contact element 4 in a plane perpendicular to both the upper surface 41 of the second rubber layer 6 and the tire rotation axis is preferably at least equal to 0.8 mm radially outward from a height corresponding to the wear indicator means 8, and more preferably at least 1.0 mm radially outward from a height corresponding to the wear indicator means 8.

[0065] The separation layer 7 is at least 0.2 mm away from any contours of the contact element 4, so that durability performance can be maintained.

[0066] If the separation layer 7 is spaced less than 0.2 mm from the contour of the contact element 4, stress concentration during rotation may cause the separation layer 7 to become a fracture origin, which may result in a decrease in durability.

[0067] The separation layer 7 is preferably at least 0.5 mm away from any contour of the contact element 4, more preferably at least 0.8 mm away from any contour of the contact element 4, and even more preferably at least 1.0 mm away from any contour of the contact element 4.

[0068] Since the tread 1 comprises one first rubber layer 5 and one second rubber layer 6, the tread 1 can be manufactured without any modifications or with minimal modifications to the manufacturing process.

[0069] To manufacture the tread 1, comprising the first rubber layer 5 and the separating layer 7 and the second rubber layer 6, with a volume of riblets 71 or microgrooves on the worn upper surface 41' to act sufficiently as additional fine edges and volume for trapping snow particles or water films, it is preferable to make the shape of the separating layer 7 radially corrugated already in the green (uncured) state of the tread 1. This also helps to control the height of the second rubber layer 6 appearing too early or too late on the worn upper surface 41'.

[0070] In this first embodiment, the second rubber layer 6 is arranged so as to have only one radial peak within the contact element 4. The second rubber layer 6 can be arranged so as to have multiple radial peaks within the contact element 4, not only in the circumferential direction but also in the axial direction.

[0071] A tread 21 according to a second embodiment of the present invention will now be described with reference to Figure 4. Figure 4 is a schematic cross-sectional view of a tread according to the second embodiment of the present invention, corresponding to a position along line IV-IV in Figure 1. The configuration of this second embodiment is similar to that of the first embodiment, except for the arrangement shown in Figure 4, and will therefore be described with reference to Figure 4.

[0072] As shown in Figure 4, the tread 21 comprises a contact surface 22 intended to come into contact with the ground during rolling, and a plurality of grooves 23 of depth D. The tread 21 comprises contact elements 24 delimited by the plurality of grooves 23.

[0073] 4, the contact element 24 has a notch 42 extending radially inwards and opening into an upper surface 241 that forms part of the contact surface 22. The notch 42 has a depth corresponding to the height up to the level of the wear indicator 28.

[0074] As shown in Figure 4, the tread 21 comprises at least two rubber layers, namely two first rubber layers 25 and one second rubber layer 26, both of which are arranged radially outside the second rubber layer 6 and each of which is provided with a separation layer 27 intended to connect to the other rubber layer radially inside the first rubber layer 25, and the second rubber layer 26 is provided without a separation layer. The tread 21 further comprises a base rubber layer 9 arranged between the second rubber layer 26 and the ply 15, radially inside at a height corresponding to the wear indicator means 28. 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.

[0075] The tread 21 is configured so that the separation layer 27 is at least 0.2 mm away from any contour of the contact element 24, including the contour of the incision 42.

[0076] Since the rubber composition constituting the first rubber layer 25 and the rubber composition constituting the second rubber layer 26 are the same, the rubber composition constituting the contact element 24 is the same except for the separation layer 27, so the tread 21 can be manufactured efficiently.

[0077] The tread 21 further comprises a base rubber layer 9 arranged radially inward at a height corresponding to the wear indicating means 28, and thanks to the base rubber layer 9 arranged radially inward at a height corresponding to the wear indicating means 28, it is possible to adjust performance other than grip performance, such as handling performance or rolling resistance, without affecting grip performance.

[0078] The invention is not limited to the embodiments described and shown, but various modifications can be made thereto without departing from its framework. [Example]

[0079] In order to confirm the effect of the present invention, one type of tread of an example to which the present invention is applied and another type of tread of a reference example were prepared.

[0080] The Example is a tread described in the second embodiment, which employs the structure of the first embodiment, and each contact element has one incision, one first rubber layer, a separation layer, and one second rubber layer. The Reference Example is a tire having contact elements with one incision, one first rubber layer, and one second rubber layer without a separation layer. The material constituting the first rubber layer is the same in the Example and the Reference Example, and the material constituting the second rubber layer is also the same in the Example and the Reference Example. The internal structure of both the Example and the Reference Example was otherwise the same as that of a typical radial tire. Both the Example and the Reference Example were buffed and then driven 10,000 km to reproduce the wear condition of a tire with a remaining tread depth of 2.0 mm.

[0081] Winter performance test:

[0082] -Snow braking:

[0083] The prepared worn test tires were mounted on all four wheels of a 2,500cc front-wheel drive vehicle. 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.

[0084] The results are shown in Table 1. In Table 1, the results are expressed as an index with the reference example being 100, with larger values indicating better performance.

[0085] Non-winter performance tests:

[0086] -Wet road braking

[0087] The prepared worn test tires were mounted on all four wheels of a 2,500cc front-wheel drive vehicle. Braking was performed using the ABS (anti-lock braking system) at a speed of 100 km / h on a straight road with a wet surface 1 mm deep, and the distance traveled up to 10 km / h was measured.

[0088] The results are similarly shown in Table 1. In Table 1, the results are expressed as an index with the reference example being 100, with larger values indicating better performance.

[0089] (Table 1) TIFF0007723747000008.tif19158

[0090] As can be seen from Table 1, the Examples show a better compromise between winter and non-winter performance, with improved winter performance near the end of life that is not achievable with treads disclosed in the prior art.

[0091] Visual Observation:

[0092] Using the tread structure of the above example, G *2.5 Two other types of treads to which the present invention is applied and one type of comparative tread were prepared by changing the constituent materials of the separation layer with different / C values. Immediately after preparing the worn test tire as described above, a well-trained technician observed the condition of the upper surface to see whether there were riblets or fine grooves that act as sufficient additional fine edges and volume to capture snow particles or water films, and whether there were cracks in the separation layer.

[0093] The results are shown in Table 2. The technicians confirmed that if the riblets or microgrooves were formed in a way that acted sufficiently as extra fine edges and volume to trap snow particles or water films, they were marked "OK"; otherwise, they were marked "NO."

[0094] (Table 2) TIFF0007723747000009.tif24158

[0095] As can be seen from Table 2, the examples were found to form riblets or microgrooves that acted sufficiently as extra fine edges and volume to capture snow particles or water films without causing cracks in the separation layer, improving performance almost to the end of life. [Explanation of symbols]

[0096] 1, 21 tread 15 ply 2, 22 contact surface 3, 23 grooves 4, 24 contact elements 41, 241 top surface 42 Cutting 5, 25 First rubber layer 6, 26 Second rubber layer 7, 27 separation layer 71 Libretto 8, 28 Wear indicator 9 Base rubber layer

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 a plurality of grooves (3) of depth D opening into said contact surface (2), a plurality of contact elements (4) delimited by said grooves (3), each of said plurality of contact elements (4) having an upper surface (41) constituting part of said contact surface (2), at least some of said plurality of grooves (3) comprising wear indicator means (8) for indicating the legal wear limit of said tread (1), The tread (1) comprises at least two rubber layers, at least one first rubber layer (5) and at least one second rubber layer (6), the first rubber layer (5) being provided with a separation layer (7) arranged radially outside the second rubber layer (6) and intended to be joined to another rubber layer radially inside the first rubber layer (5), the second rubber layer (6) being provided without the separation layer (7), the tread being characterized in that the material constituting the separation layer (7) satisfies the following relationship: (Formula 2) where G * is the elastic modulus G of the material constituting the separation layer (7) at 60°C * (MPa), C is the abrasion amount (mm 3 ) Tread (1).

2. 2. A tread (1) according to claim 1, wherein the volume of said separating layer (7) above the height corresponding to said wear indicator means (8) in each of said contact elements (4) is less than 20%.

3. 3. The tread (1) according to claim 1 or 2, wherein the radially outermost part of the second rubber layer (6) of each of the contact elements (4) in a plane perpendicular to both the upper surface (41) and the rotation axis of the tire is located at a position that is 0.5 mm or more radially outward from a height corresponding to the wear indicator means (8).

4. A tread (1) according to any one of claims 1 to 3, wherein said separating layer (7) is at least 0.2 mm away from any contour of said contact element (4).

5. A tread (1) according to any one of claims 1 to 4, wherein said tread (1) comprises only one first rubber layer (5) and only one second rubber layer (6).

6. 6. The tread (1) according to any one of claims 1 to 5, wherein the rubber composition constituting the first rubber layer (5) is the same as the rubber composition constituting the second rubber layer (6).

7. 7. The tread (1) according to any one of claims 1 to 6, wherein the tread (1) further comprises a base rubber layer (9) arranged radially inward at a height corresponding to the wear indicator means (8).

8. A tire having a tread according to any one of claims 1 to 7.

Images