tire

Abstract

To provide a tire that suppresses the occurrence of groove cracks in tires with identification lines, thereby achieving both crack resistance and identification functionality. [Solution] The stress relaxation layer (52) mainly consists of diene-based rubber material and non-diene-based rubber material and also contains a vulcanizing agent, and the stress relaxation layer contains a coloring pigment.

Description

[Technical Field]

[0001] This invention relates to tires. [Background technology]

[0002] To suppress groove cracks that occur at the bottom of the main grooves, tires are known that have a stress-relieving layer at the bottom of the main grooves. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-147115 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, in the tire disclosed in Patent Document 1, if the identification line applied to the tread for tire identification purposes is separately placed at the bottom of the groove (for example, on a stress relaxation layer), when stress is applied to the bottom of the groove during large steering maneuvers (of the vehicle to which the tire is mounted), peeling stress may occur between the identification line and the stress relaxation layer. In such cases, the identification line may peel off from the bottom of the groove, and consequently, the occurrence of groove cracks may not be suppressed.

[0005] Therefore, in recent years, there has been a demand to suppress the occurrence of groove cracks in tires that include identification lines.

[0006] The present invention aims to provide a tire that suppresses the occurrence of groove cracks in tires including identification lines, thereby achieving both crack resistance and identification functionality. [Means for solving the problem]

[0007] The present invention relates to a tire in which the tread surface of the tread rubber is divided into land areas by main grooves, and a stress-relieving layer is formed on the surface of at least one groove bottom of the main grooves, The stress-relieving layer is characterized in that it mainly consists of a diene-based rubber material and a non-diene-based rubber material and contains a vulcanizing agent, and the stress-relieving layer contains a coloring pigment. [Effects of the Invention]

[0008] According to the present invention, by providing a tire identification function to the stress relaxation layer formed at the bottom of the main groove, the occurrence of groove cracks can be suppressed in tires that include identification lines, thereby achieving both crack resistance and identification functionality. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an end view showing the meridional cross-sectional shape of the tire according to this embodiment. [Figure 2] Figure 2 is an enlarged view showing the region enclosed by the tire width direction range II and tire radial direction range II in Figure 1. [Figure 3] Figure 3 is a plan view of the tire showing the arrangement of the stress relaxation layer. [Figure 4] Figure 4 is a plan view of the tire showing the arrangement of the stress relaxation layer. [Figure 5] Figure 5 is a plan view of the tire showing the arrangement of the stress relaxation layer. [Figure 6] Figure 6 is a plan view of the tire showing the arrangement of the stress relaxation layer. [Figure 7] Figure 7 is a cross-sectional view in the width direction of the main groove showing variations in the cross-sectional shape of the stress relaxation layers 52g and 52h shown in Figure 6(A). [Figure 8] Figure 8 is a plan view of the tire showing the arrangement of the stress relaxation layer. [Figure 9] Figure 9 is a cross-sectional view in the groove width direction showing the arrangement of the stress relaxation layer. [Figure 10] Figure 10 is a plan view of the tire showing the arrangement of the stress relaxation layer. [Figure 11]FIG. 11 is a plan view of a tire showing an arrangement mode of a stress relaxation layer. [Figure 12] FIG. 12 is a plan view of a tire showing an arrangement mode of a stress relaxation layer. [Figure 13] FIG. 13 is a plan view of a tire showing an arrangement mode of a stress relaxation layer.

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] <Embodiment of the Present Invention> The present invention includes the following embodiments. [Embodiment 1] A tire in which on a tread surface of a tread rubber, land portions are partitioned by main grooves, and a stress relaxation layer is formed on a surface of at least one groove bottom of the main grooves, where the stress relaxation layer is mainly composed of a diene rubber material and a non-diene rubber material and contains a vulcanizing agent, and the stress relaxation layer contains a coloring pigment. [Embodiment 2] The tire according to Embodiment 1, wherein a color difference ΔE*ab in the L*a*b* color space is 12 or more between at least one of the stress relaxation layers and the tread surface. [Embodiment 3] The tire according to Embodiment 1 or 2, wherein a difference ΔL* in an L* index in the lightness axis direction in the L*a*b* color space is 7 or more between at least one of the stress relaxation layers and the tread surface. [Embodiment 4] Between at least one of the stress relaxation layers and the tread surface, in the L*a*b* color space, a difference Δa* in an a* index in the red direction and the green direction and a difference Δb* in a b* index in the yellow direction and the blue direction are such that [(Δa*) 2 +(Δb*) 2 1 / 2 ≧12 is satisfied. [Embodiment 5] The tire according to any one of Embodiments 1 to 4, wherein a plurality of the main grooves are formed, and the stress relaxation layer is formed in the outermost main groove in the tire width direction.​ [Form 6] A tire according to any one of embodiments 1 to 5, wherein a plurality of main grooves are formed, and the stress-relieving layers formed in different main grooves exhibit different colors. [Form 7] A tire according to any one of embodiments 1 to 6, wherein at least one of the main grooves has the stress-relieving layer of a different color formed therein. [Form 8] A tire according to any one of embodiments 1 to 7, wherein a plurality of main grooves are formed, and the stress-relieving layer is formed in all of the main grooves. [Form 9] In a cross-sectional view in the width direction of the main groove, of at least one groove wall surface of the main groove on which the stress relaxation layer is formed, A tire according to any one of embodiments 1 to 8, wherein the angle θ between a virtual line perpendicular to the outer contour of the tire and the groove wall surface is 5° or more and 25° or less. [Form 10] A tire according to any one of embodiments 1 to 9, wherein, in a plan view of the tire, the shortest distance Wc in the groove width direction from one end of the main groove in the groove width direction to one end of the stress relaxation layer in the groove width direction is 5 mm or less. [Form 11] A tire according to any one of embodiments 1 to 10, wherein, in a plan view of the tire, at least one lateral groove is formed that communicates with the main groove, and the groove width Wl of the lateral groove is 8 mm or less. [Form 12] A tire according to any one of embodiments 1 to 11, wherein, in a plan view of the tire, at least one end of the main groove in the groove width direction is straight. [Form 13] A tire according to any one of forms 1 to 12, wherein the thickness of the stress relaxation layer is 5 μm or more and 200 μm or less.

[0011] <Definition> The radial direction of a tire refers to the direction perpendicular to the tire's axis of rotation. The inner side of the tire's radial direction refers to the side facing the tire's axis of rotation, while the outer side of the tire's radial direction refers to the side moving away from the tire's axis of rotation. The circumferential direction of a tire refers to the direction around the tire's axis of rotation. The tire width direction refers to the direction parallel to the tire's axis of rotation. The inner side in the tire width direction refers to the side facing the tire's equator, while the outer side in the tire width direction refers to the side moving away from the tire's equator. The tire equatorial plane is a plane that is perpendicular to the tire's axis of rotation and passes through the center of the tire's width. The main groove is a groove with a wear indicator on its groove wall that shows the end of wear, such as a circumferential groove, and generally has a groove width of 3.0 mm or more and a groove depth of 5.0 mm or more. However, the groove width and groove depth of the circumferential main groove are not limited to the above ranges. The groove width is the maximum distance between opposing groove walls at the groove opening on the tread surface when the tire is mounted on a standard rim and filled to the standard internal pressure in an unloaded state (the distance measured in a direction perpendicular to the direction in which the groove extends). If there is a notch or chamfer at the groove opening, the groove width is the value measured with the endpoint being the intersection of the extension line of the tread surface and the extension line of the groove wall in a cross-sectional view parallel to the groove width direction and groove depth direction. The groove depth is the maximum distance from the tread surface to the bottom of the groove (measured in the radial direction of the tire) when the tire is mounted on a standard rim, filled to the standard internal pressure, and under no load. If the groove in question has partial unevenness or sipes at the bottom of the groove, the groove depth shall be the value measured excluding the unevenness or sipes. The tread edge refers to the ends of the tread pattern on a tire, and is also called the design end. In this specification, unless otherwise specified, the shape, position, and length (distance) of each component are based on the shape, position, and length in a meridional section (or plan view) of the tire (when mounted on a standard rim and filled with standard internal pressure in an unloaded state). A "regular rim" refers to an "applicable rim" as defined by JATMA, a "Design Rim" as defined by TRA, or a "Measuring Rim" as defined by ETRTO. Standard internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "INFLATION PRESSURES" specified by ETRTO. Standard load refers to the "maximum load capacity" specified by JATMA, the maximum value listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "LOAD CAPACITY" specified by ETRTO.

[0012] <Basic tire configurations> One embodiment of the present invention will be described below with reference to the drawings. Figure 1 is an end view showing the meridional cross-sectional shape of the tire according to this embodiment. Note that the figure shows the tire portion in an unloaded state, mounted on a regular rim and subjected to regular internal pressure.

[0013] The tire 10 of this embodiment, when viewed in a meridional cross-section of the tire, comprises a pair of bead portions 12, a pair of sidewall portions 14, a pair of shoulder portions 16, and a tread portion 18, arranged from the inside to the outside in the radial direction of the tire. The tire 10 comprises an inner liner 19, a carcass 20, a belt 22 (consisting of two belt layers 22a and 22b), a belt cover 24, sidewall rubber 36, and tread rubber 38, just like a typical tire.

[0014] The tread rubber 38 has a tread surface 37 that is exposed at the outermost part in the radial direction of the tire, and is made of a rubber material that has excellent contact characteristics and weather resistance. Preferably, the tread rubber 38 contains silica, wax, and an anti-aging agent.

[0015] As for the wax, plant-derived waxes, paraffin wax, microcrystalline wax, polyethylene wax, and mixtures thereof can be selected. In particular, to ensure crack resistance at low temperatures, a low-melting-point wax that can easily precipitate and spread on the groove bottom surface even at low temperatures is preferred, and for example, a wax with a melting point of 40 to 65°C is preferably selected. The tread rubber preferably contains 1.0 part by mass or more of wax when the rubber component is 100 parts by mass.

[0016] The anti-aging agent is preferably an amine-based anti-aging agent. Examples of amine-based anti-aging agents include "N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine" and "2,2,4-trimethyl-1,2-dihydroquinoline polymer". The tread rubber preferably contains 0.5 parts by mass or more of the anti-aging agent when the rubber component is 100 parts by mass.

[0017] The tread surface 37 is provided with multiple (four in Figure 1) circumferential main grooves 40 (forming a continuous annular shape in the circumferential direction of the tire). These circumferential main grooves 40 divide the tread surface 37 into multiple (five rows in Figure 1) land areas 42.

[0018] Figure 2 is an enlarged view showing the region enclosed by the tire width direction range II and the tire radial direction range II in Figure 1. As shown in Figure 2, the land area demarcated by the circumferential main groove 40 has a groove bottom 44 and a pair of groove walls 46. The groove bottom 44 is the bottom of the circumferential main groove 40 and serves as the reference for the groove depth of the circumferential main groove 40. The groove bottom 44 is composed of a surface that follows the tread surface 37, with the groove width direction (tire width direction in the example shown in Figure 2) as the short side and the direction perpendicular to both the groove width direction and the tire radial direction (tire circumferential direction in the example shown in Figure 2) as the long side. The pair of groove walls 46 are continuous with the outer edge of the groove bottom 44 in the tire width direction and serve as the reference for the groove width of the circumferential main groove 40. The pair of groove walls 46 are composed of a surface that intersects the tread surface 37, with the direction inclined in the groove width direction (tire width direction) relative to the tire radial direction as the short side and the tire circumferential direction as the long side.

[0019] [Characteristics of the basic form of a tire] (Stress relaxation layer) The tire 10 is provided with a stress-relieving layer 52 on the surface of at least the groove bottom 44 of the land portion demarcated by the circumferential main groove 40. The stress-relieving layer 52 includes a bottom portion 54 provided on the groove bottom 44. The bottom portion 54 is formed over the entire groove bottom 44. The bottom portion 54 forms a continuous annular shape in the circumferential direction of the tire.

[0020] The stress-relaxing layer 52 may include a wall portion 56 and a surface portion 58 in addition to the bottom portion 54 described above. The wall portion 56 is provided on each of the pair of groove walls 46. One end 56U of the wall portion 56 on the inner side in the tire radial direction is connected to the bottom portion 54, and the other end 56T on the outer side in the tire radial direction may be located within the groove wall 46 or may reach the edge 48. The surface portion 58 is provided on the tread surface 37, starting from the edge 48. One end 58G of the surface portion 58 in the tire width direction is connected to the other end 56T of the wall portion 56 on the outer side in the tire radial direction at the edge 48, and the other end 58L in the tire width direction is located at a predetermined length, for example, 0.5 mm to 5 mm, on the opposite side in the groove width direction from the edge 48 from the one end 56U.

[0021] The stress relaxation layer 52 mainly consists of a diene-based rubber material and a non-diene-based rubber material, and contains a vulcanizing agent. The diene-based rubber is selected from the group consisting of diene polymers including natural rubber and synthetic diene-based rubbers (isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), butadiene-isoprene rubber (BIR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene rubber (SBIR), chloroprene rubber (CR), etc.). The non-diene-based rubber is selected from the group consisting of non-diene polymers including synthetic non-diene-based rubbers (butyl rubber (IIR), ethylene-propylene rubber (EPDM, EPM), urethane rubber, silicone rubber, etc.). Furthermore, it is preferable that the stress relaxation layer 52 does not contain resin components in order to ensure weather resistance.

[0022] The stress relaxation layer 52 does not necessarily have to contain an anti-aging agent. This is because, since the stress relaxation layer 52 has a small thickness Ga, the anti-aging agent contained in the adjacent tread rubber 38 migrates to the stress relaxation layer 52 and compensates for this. The stress relaxation layer 52 can further suppress the occurrence of cracks by containing an anti-aging agent. If the stress relaxation layer 52 contains an anti-aging agent, it is preferable to use other anti-aging agents (e.g., phenolic, phosphite, organic thioacid, benzimidazole, etc.) in an amount of 0.1 parts by mass to 5 parts by mass per 100 parts by mass of the rubber component, rather than using amine-based anti-aging agents.

[0023] Under these premises, the stress relaxation layer 52 contains a coloring pigment. A coloring pigment other than carbon black is used so that the stress relaxation layer 52 exhibits a different color from the tread rubber (a color in which at least one of the saturation, hue, and lightness is different). Since the stress relaxation layer 52 is applied to the tread rubber before vulcanization, the coloring pigment used is one that does not decompose during vulcanization, i.e., one with a decomposition temperature of 125°C or higher.

[0024] As coloring pigments, zinc oxide, zinc powder, lead zinc, aluminum pigment, lead monoxide, mica-like iron oxide pigment, basic lead chromate, basic lead carbonate, red lead, lead white, yellow lead, ochre, kaolin, clay, ultramarine, turquoise, Prussian blue, iron oxide pigment, iron oxide powder, lead cyanamide, heavy calcium carbonate, zinc chromate, talc, earthenware powder, precipitated calcium carbonate, precipitated barium sulfate, iron yellow, turquoise powder, titanium dioxide, chalk, barite powder, etc. can be used.

[0025] Alternatively, azo pigments such as soluble azo red, monoazo yellow, monoazo red, disazo yellow, disazo orange, and condensed azo pigments can be used as coloring pigments; phthalocyanine pigments such as copper phthalocyanine blue, copper phthalocyanine green, and cobalt phthalocyanine blue can also be used.

[0026] <Functions and Effects of the Basic Form of Tires> Rubbers such as SBR, commonly used as tread rubber, do not have sufficient ozone resistance, making them susceptible to cracking caused by ozone. Traditionally, this cracking has been addressed by incorporating various compounding agents (such as anti-aging agents) into the tread rubber.

[0027] However, within the tread rubber, particularly near the bottom of the main grooves, residual stress is generated not only due to being extruded into the mold and exposed to high temperatures during tire manufacturing (vulcanization), but also because the molecular chains of the tread rubber tend to be oriented in the direction of extrusion. Therefore, depending on the usage conditions of the vulcanized tire, groove cracks (GC) may occur at the bottom of the main grooves.

[0028] Therefore, in the tire of this embodiment, a stress relaxation layer 52 is formed at the bottom of the groove 44 in the land portion that is partitioned by the main groove 40, in order to suppress the occurrence of groove cracks (GC).

[0029] Under these premises, in the tire of this embodiment, the stress relaxation layer 52, which is mainly composed of rubber, does not contain any resin components from the viewpoint of ensuring weather resistance. In addition to suppressing the occurrence of GC, the stress relaxation layer 52 is also made to contain a predetermined colored pigment in order to give the stress relaxation layer 52 an identification function.

[0030] In summary, in the tire 10 of this embodiment, a stress-relieving layer 52 is formed on the surface of the groove bottom 44, and the stress-relieving layer 52 mainly consists of diene-based rubber material and non-diene-based rubber material, contains a vulcanizing agent, and further contains a coloring pigment. With this configuration, crack resistance can be ensured by forming a stress-relieving layer 52 on the surface of the land area partitioned by the main groove 40, and by including a coloring pigment in the stress-relieving layer 52, the stress-relieving layer 52 formed at the bottom of the main groove can be given a tire identification function. Therefore, with the tire 10 of this embodiment, the occurrence of groove cracks can be suppressed in tires that include identification lines, and both crack resistance and identification function can be achieved.

[0031] Furthermore, the stress relaxation layer 52 may be a black color similar to the tread surface 37 (however, a black color with a different brightness than the tread surface 37), and by combining the color of the tread surface 37 with a different color, various identification variations can be achieved.

[0032] Figures 3-6, 8, and 10-13 are plan views of tires showing the arrangement of stress relaxation layers. All of the examples shown in these figures are examples in which four circumferential main grooves 40 are formed.

[0033] The example shown in Figure 3(A) is an example in which the stress relaxation layer 52 is not formed (not the tire of this embodiment), and in which the entire tread surface 37 is uniformly colored with tread rubber 38.

[0034] In contrast, the example shown in Figure 3(B) is one in which a stress-relieving layer 52 is formed in one of the four circumferential main grooves 40 (this is the tire of this embodiment), and the color of this stress-relieving layer 52 (for example, yellow) differs from the color of the tread rubber 38 (tread surface 37) in terms of chromaticity (at least one of hue and saturation).

[0035] The example shown in Figure 3(C) is one in which a stress-relieving layer 52 is formed in one of the four circumferential main grooves 40 (this is the tire of this embodiment), and the color (black) of this stress-relieving layer 52 is different in brightness from the color of the tread rubber 38 (tread surface 37).

[0036] The example shown in Figure 3(D) is one in which stress-relieving layers 52 are formed in all four circumferential main grooves 40 (this is the tire of this embodiment), and the colors of these stress-relieving layers 52 (for example, yellow, green, pink, and yellow from left to right in Figure 3(D)) differ in chromaticity (at least one of hue and saturation) from the color of the tread rubber 38 (tread surface 37). In this way, the chromaticity and brightness can be appropriately selected between multiple stress-relieving layers.

[0037] The example shown in Figure 3(E) is one in which stress-relieving layers 52 are formed in all four circumferential main grooves 40 (this is the tire of this embodiment), and in this example, three of these stress-relieving layers 52 have a different brightness from the tread rubber, and one has a different color from the tread rubber 38. For example, in Figure 3(E), from left to right, the layers are black (different brightness from the tread rubber), black (different brightness from the tread rubber), black (different brightness from the tread rubber), and yellow.

[0038] The example shown in Figure 3(F) is one in which stress relaxation layers 52 are formed in all four circumferential main grooves 40 (this is the tire of this embodiment), and it is conceivable that all of these stress relaxation layers 52 are black (different in brightness from the tread rubber).

[0039] Thus, in the tire of this embodiment, assuming that the stress relaxation layer 52 suppresses the occurrence of groove cracks, various variations can be provided to the stress relaxation layer 52 formed at the bottom of the main groove 40, thereby realizing a tire identification function for different types of tires.

[0040] <Preferred tire configuration> Typically, circumferential main grooves (grooves indicated by reference numeral 40 in Figure 1) are often formed on the tread surface 37 in a range of two to five grooves. Therefore, the stress relaxation layer 52 can be formed in at least one of these grooves, but considering the occurrence of cracks at the groove bottom 44, it is preferable to form it in all of the main grooves formed on the tread surface 37 (all four circumferential main grooves 40 as shown in Figure 1).

[0041] The preferred region for forming the stress relaxation layer 52 is the area between 0% and 30% from the inner side of the tire radially in the main groove depth. Therefore, in the case of the stress relaxation layer 52 shown in Figure 2, it is naturally preferable that the bottom portion 54 be formed, but it is also preferable that at least a part of the wall portion 56 be formed.

[0042] In the tires shown in Figures 1 and 2, it is preferable that the color difference ΔE*ab in the L*a*b* color space is 12 or more between at least one stress relaxation layer 52 and the tread surface 37. Here, the color difference ΔE*ab is [(ΔL*) 2 +(Δa*) 2 +(Δb*) 2 Defined by ].

[0043] The L*a*b* color space mentioned above is a color space standardized by the International Commission on Illumination (CIE) in 1976, and is also defined in JIS Z8781-4. Color evaluation in this color space can be performed using a fluorescence spectrometer (e.g., KONICA MINOLTA FD-7 / FD-5 fluorescence spectrometer) under the illumination of a D50 light source.

[0044] By setting ΔE*ab to 12 or more, the contrast in the L*a*b* color system between the tread rubber 38 and the stress relaxation layer 52 becomes clear, and the visibility of the stress relaxation layer 52 can be further enhanced.

[0045] Incidentally, the color difference ΔE*ab is more preferably 15 or more, and extremely preferably 18 or more.

[0046] In the tires shown in FIGS. 1 and 2, it is preferable that the difference ΔL* in the L* index in the lightness axis direction in the L*a*b* color space between at least one stress relaxation layer 52 and the tread surface 37 is 7 or more. Here, the lightness axis means a direction perpendicular to both the red direction or green direction and the yellow direction or blue direction in the L*a*b* color space.

[0047] By setting the difference ΔL to 7 or more, the contrast in the L*a*b* color system between the tread rubber 38 and the stress relaxation layer 52 becomes clear, and the visibility of the stress relaxation layer 52 can be further enhanced.

[0048] Incidentally, the color ΔL* is more preferably 9 or more, and extremely preferably 11 or more.

[0049] In the tires shown in FIGS. 1 and 2, between at least one stress relaxation layer 52 and the tread surface 37, in the L*a*b* color space, the difference Δa* in the a* index in the red direction and green direction and the difference Δb* in the b* index in the yellow direction and blue direction are such that [(Δa*) 2 +(Δb*) 2 1 / 2 ≧12 is satisfied, which is preferable.

[0050] Here, the difference Δa* represents the difference in the red direction (green direction), and the difference Δb* represents the difference in the yellow direction (blue direction). A larger difference Δa* means that there is a greater difference in saturation in the red direction (green direction) between the tread rubber 38 and the stress relaxation layer 52, and a larger difference Δb* means that there is a greater difference in saturation in the yellow direction (blue direction) between the tread rubber 38 and the stress relaxation layer 52.

[0051] [(Δa*) 2 +(Δb*) 2 ] 1 / 2 By satisfying the condition ≥ 12, the contrast in the L*a*b* color system between the tread rubber 38 and the stress relaxation layer 52 becomes clearer, further improving the visibility of the stress relaxation layer 52.

[0052] Note that [(Δa*) 2 +(Δb*) 2 ] 1 / 2 It is even more preferable that ≥ 14 be satisfied, [(Δa*) 2 +(Δb*) 2 ] 1 / 2 It is extremely preferable that the condition ≥ 16 be met.

[0053] The example shown in Figure 4(A) is one in which the circumferential main groove 40 is not formed at an equidistant distance from the tire equatorial plane CP on each side in the tire width direction, while the example shown in Figure 4(B) is one in which the circumferential main groove 40 is formed at an equidistant distance from the tire equatorial plane CP on each side in the tire width direction.

[0054] In the tires shown in Figures 1 and 2, it is preferable that multiple main grooves 40 are formed, as shown in Figures 4(A) and 4(B), and that stress relaxation layers 52 are formed in the outermost main grooves 40a, 40b, and 40c in the tire width direction.

[0055] When a tire is mounted on a vehicle, the visibility of the tread surface 37 deteriorates from the outside to the inside of the vehicle due to its relationship with the vehicle body. Therefore, in order to ensure the visibility of the stress relaxation layer 52, it is preferable to form a stress relaxation layer 52 in the outermost main grooves 40a, 40b, and 40c in the tire width direction, which has at least one difference in saturation, hue, and brightness from the tread rubber 38.

[0056] In the example shown in Figure 4(A), since the circumferential main grooves 40 are not formed at equidistant distances from the tire equatorial plane CP on each side in the tire width direction, it is preferable to form a stress relaxation layer 52 in the circumferential main groove 40a furthest from the tire equatorial plane CP and to mount the tire to the vehicle so that this stress relaxation layer 52 is located on the outside of the vehicle. The distance of the main groove 40 from the tire equatorial plane CP is determined by the center position of the main groove 40 in the width direction.

[0057] In the example shown in Figure 4(B), since the circumferential main grooves 40 are formed equidistant from the tire equatorial plane CP on each side in the tire width direction, it is preferable to form stress relief layers 52a and 52b in both the circumferential main grooves 40b and 40c, which are furthest from the tire equatorial plane CP, and to mount the tire to the vehicle so that one of these stress relief layers 52 (for example, stress relief layer 52a) is located on the outside of the vehicle. In the example shown in Figure 4(B), for example, even if the tire is removed from the vehicle after being used for a certain period of time, and then mounted on the vehicle so that the stress relief layer 52b is located on the outside of the vehicle, the visibility of the stress relief layer 52 can be continuously maintained.

[0058] The example shown in Figure 5(A) is one in which stress-relieving layers 52c and 52d, which have a different saturation from the tread rubber 38, are formed in multiple circumferential main grooves, and the example shown in Figure 5(B) is one in which stress-relieving layers 52e and 52f, which have a different brightness or saturation from the tread rubber 38, are formed in multiple circumferential main grooves 40.

[0059] For example, the stress relaxation layers 52c and 52d shown in Figure 5(A) can be pink and yellow, respectively, from left to right on the page. Also, the stress relaxation layers 52e and 52f shown in Figure 5(B) can be black and yellow, respectively, with a different brightness from the tread rubber 38, from left to right on the page.

[0060] In the tires shown in Figures 1 and 2, it is preferable that multiple main grooves 40 are formed, as shown in Figures 5(A) and 5(B), and that the stress-relieving layers 52 formed in different main grooves exhibit different colors.

[0061] Here, "different colors" refers to a color relationship between multiple stress relaxation layers where any of |ΔL*|, |Δa*|, and |Δb*| is 13 or greater.

[0062] In this embodiment, it is more preferable that any one of |ΔL*|, |Δa*|, and |Δb*| between the multiple stress relaxation layers is 14 or more, and it is extremely preferable that it is 15 or more.

[0063] The example shown in Figure 6(A) is one in which two types of stress-relieving layers 52g and 52h with different saturation from the tread rubber 38 are formed in one circumferential main groove 40, and the example shown in Figure 6(B) is one in which stress-relieving layers 52i and 52i with different brightness from the tread rubber 38 and a stress-relieving layer 52j with different saturation are formed in one circumferential main groove.

[0064] In the tires shown in Figures 1 and 2, it is preferable that a stress-relieving layer of a different color is formed in at least one main groove 40, as shown in Figures 6(A) and 6(B).

[0065] By composing the stress relaxation layer 52 within a single main groove with multiple colors (i.e., multiple colors that differ in at least one of the lightness, hue, and saturation), the visibility of the stress relaxation layer 52 can be further enhanced.

[0066] In the example shown in Figure 6(A), two types of stress-relieving layers 52g and 52h with different saturations from the tread rubber 38 (tread surface 37) are formed in one circumferential main groove. For example, the stress-relieving layer 52g can be yellow and the stress-relieving layer 52h can be pink.

[0067] Figure 7 is a cross-sectional view in the main groove width direction showing variations in the cross-sectional shape of the stress relaxation layers 52g and 52h shown in Figure 6(A). As shown in Figure 7, in a cross-sectional view in the main groove width direction, stress relaxation layers 52g and 52h of different colors may be arranged overlapping in the tire radial direction (Figure 7(A)) or butting against each other in the groove width direction (Figure 7(B)).

[0068] In the example shown in Figure 6(B), a stress-relieving layer 52i, 52i with a different brightness from the tread rubber 38 (tread surface 37) and a stress-relieving layer 52j with a different saturation are formed in one circumferential main groove. For example, the stress-relieving layer 52i can be made black and the stress-relieving layer 52j can be made yellow.

[0069] In the example shown in Figure 6(B), in particular, by combining a black stress-relieving layer 52i that is close in color to the tread rubber 38 with a stress-relieving layer 52j of a color other than black (yellow), the groove bottom of the circumferential main groove 40 can be covered with stress-relieving layers 52i and 52j while adjusting the thickness of the colored line (in this case, the yellow stress-relieving layer 52j).

[0070] The examples shown in Figures 8(A) and 8(B) both show cases in which stress relaxation layers 52 are formed in all main grooves 40. For example, in the example shown in Figure 8(A), the colors of the stress relaxation layers 52k, 52l, 52m, and 52n can be yellow, black (different in brightness from the tread rubber), black (different in brightness from the tread rubber), and yellow, respectively, from left to right on the page. Similarly, in the example shown in Figure 8(B), the colors of the stress relaxation layers 52o, 52p, 52q, and 52r can be pink, black (different in brightness from the tread rubber), green, and yellow, respectively, from left to right on the page.

[0071] In the tires shown in Figures 1 and 2, it is preferable that multiple main grooves 40 are formed, as shown in Figures 8(A) and 8(B), and that a stress-relieving layer is formed in all of the main grooves.

[0072] By forming a stress-relieving layer 52 in all main grooves 40, a wide variety of identification functions can be provided, and the visibility of the stress-relieving layer 52 can be further enhanced. In particular, increasing the proportion of stress-relieving layers 52 that are other colors than black can further enhance the visibility of the stress-relieving layer 52.

[0073] Figure 9 is a cross-sectional view in the groove width direction showing the arrangement of the stress relaxation layer. In the tires shown in Figures 1 and 2, as shown in Figure 9, it is preferable that the angle θ between the imaginary line L2 perpendicular to the tire outer contour line L1 and the groove wall surface P in a cross-sectional view in the width direction of the main groove 40 of at least one groove wall surface of the main groove 40 on which the stress relaxation layer 52 is formed is 5° or more and 25° or less. Here, if there is a chamfered portion near the groove opening (not shown), the angle θ is determined from the imaginary line L2 and the groove wall surface P, assuming that there is no chamfered portion.

[0074] By setting the angle θ to 5° or more, it is possible to suppress the formation of dark areas in the stress relaxation layer 52 that are not exposed to light when the tire is mounted on the vehicle, thereby further improving the visibility of the stress relaxation layer 52.

[0075] In contrast, by setting the angle θ to 25° or less, it is possible to suppress the extreme reduction in groove volume due to tire wear, and to ensure a high level of drainage performance even in the final stages of tire wear.

[0076] In this embodiment, the requirements only need to be satisfied on at least one groove wall surface of the main groove 40 on which the stress relaxation layer 52 is formed, but it is even more preferable that the requirements be satisfied on both groove wall surfaces of the main groove 40 on which the stress relaxation layer 52 is formed. Also, in the example shown in Figure 9, the same angle θ is shown on the wall surfaces on both sides in the groove width direction, but this embodiment is not limited to such an example, and the angle θ on each side in the groove width direction may be different.

[0077] Furthermore, the angle θ is more preferably 7° or more and 23° or less, and more preferably 9° or more and 21° or less.

[0078] The example shown in Figure 10 is one in which a stress-relieving layer 52 is formed in the main groove 40 through which the lateral grooves 62 are connected. Figure 10(A) is a plan view of the tire showing the state of the stress-relieving layer 52 when the tire is new, and Figure 10(B) is a plan view of the tire showing the state of the stress-relieving layer 52 at the end of the tire's wear cycle.

[0079] In the tires shown in Figures 1 and 2, as shown in Figure 10(A) (when the tire is new), it is preferable that the shortest distance Wc in the groove width direction from one end of the main groove 40 in the groove width direction to one end of the stress relaxation layer 52 in the groove width direction (up to a part of the lateral groove 62 communicating with the main groove 40) is 5 mm or less in a plan view of the tire.

[0080] By setting the shortest distance Wc in the groove width direction to 5 mm or less, the colored area (stress relaxation layer area) of the lateral groove 62 becomes almost nonexistent after tread wear as shown in Figure 10(B), and the stress relaxation layer 52 takes on a shape close to a line. As a result, this stress relaxation layer 52 becomes more distinguishable from the colored stress relaxation layers 52 provided in adjacent main grooves, further improving visibility.

[0081] The shortest distance Wc in the groove width direction is more preferably 4 mm or less, and most preferably 3 mm or less.

[0082] The example shown in Figure 11, similar to Figure 10(B), is an example in which a stress-relaxing layer 52 is formed in the main groove 40 through which the lateral grooves 62 communicate (end of tire wear). In the tires shown in Figures 1 and 2, as shown in Figure 11, it is preferable that at least one lateral groove 62 communicating with the main groove 40 is formed in a plan view of the tire, and that the groove width Wl of the lateral groove 62 is 8 mm or less.

[0083] By setting the groove width Wl, which is the opening width of the lateral groove, to 8 mm or less, the stress relief layer 52 maintains a shape close to linear even after tread wear as shown in Figure 11. This further enhances the identifiability of this stress relief layer 52 compared to the colored stress relief layers 52 provided in adjacent main grooves, thereby improving visibility.

[0084] The groove width Wl of the lateral groove is more preferably 7 mm or less, and most preferably 6 mm or less.

[0085] The example shown in Figure 12 is one in which a stress-relieving layer 52 is formed in a main groove 40 in which transverse grooves 62 are connected on one side in the groove width direction (end of tire wear). In the tires shown in Figures 1 and 2, as shown in Figure 12, it is preferable that at least one end in the groove width direction of the main groove 40 in which the stress-relieving layer 52 is formed is linear in shape.

[0086] Here, the statement that at least one end of the main groove 40 on which the stress relaxation layer 52 is formed is linear in the groove width direction means that no transverse groove is in communication with the main groove 40 at that end. As shown in Figure 12, for the main groove 40d on which the stress relaxation layer 52 is formed, a transverse groove 62 is in communication from the left side of the paper, but not from the right side of the paper. The tire of this embodiment has a distinctive feature at the end on which the transverse groove 62 is not in communication.

[0087] By making at least one end of the main groove 40, where the stress-relieving layer 52 is formed, in the groove width direction, a straight line is achieved. This ensures that the stress-relieving layer 52 remains nearly linear even after tread wear as shown in Figure 12. As a result, the stress-relieving layer 52 is more easily distinguishable from the colored stress-relieving layers 52 provided in adjacent main grooves 40, thereby further enhancing visibility.

[0088] The stress relaxation layer 52 described above preferably has a thickness of 5 μm or more and 200 μm or less. The thickness of the stress relaxation layer 52 shall be measured as the radial dimension of the stress relaxation layer 52 in the tire, as indicated by the symbol Ga in Figure 2.

[0089] By making the thickness of the stress relaxation layer 52 5 μm or more, the stress relaxation effect of the stress relaxation layer 52 is further enhanced, and crack resistance can be further improved. On the other hand, by making the thickness of the stress relaxation layer 52 200 μm or less, the ability of the stress relaxation layer 52 to follow the deformation of the tread rubber 38 can be ensured, and crack resistance can be further improved.

[0090] The thickness of the stress relaxation layer 52 is more preferably 7 μm or more and 150 μm or less, and more preferably 10 μm or more and 100 μm or less.

[0091] In the tires shown in Figures 1 and 2, as shown in Figure 13 (showing the final stage of tire wear), the relationship between the width WS of the main groove 40 in which the stress relaxation layer 52 is formed and the tire circumferential arrangement period L3 of the transverse groove 62 communicating with the main groove 40 is as follows: 0.5 ≤ L3 / WS ≤ 30 It is preferable to show this.

[0092] By setting the ratio L3 / WS to 0.5 or higher, the stress relaxation layer 52 takes on a shape that is close to linear. As a result, this stress relaxation layer 52 becomes more distinguishable from the colored stress relaxation layers 52 provided in the adjacent main grooves 40, and its visibility is further enhanced.

[0093] In contrast, by setting the L3 / WS ratio to 30 or less, it is possible to secure a certain amount of lateral grooves on the tire circumference and improve drainage performance.

[0094] The ratio L3 / WS is more preferably 3 to 28, and most preferably 5 to 25.

[0095] <Other suitable examples of tires> In the tires shown in Figures 1 and 2, the ratio R of the maximum thickness Hmax of the tread portion 18 to the minimum thickness Hg of the tread portion 18 is defined as Hg / Hmax. Preferably, the above ratio R, the minimum distance Gu in the radial direction of the tire from the groove bottom 44 to the belt cover 24 (or to the belt 22 if there is no belt cover 24), and the thickness Ga of the stress relaxation layer 52 satisfy the following formula (1). By satisfying the following formula (1), the tire 10 can achieve both durability of the stress relaxation layer 52 and suppression of tire rolling resistance.

[0096]

number

[0097] When the maximum thickness Hmax is large and the minimum thickness Hg is small, i.e., when R is small, the amount of deformation of the tread rubber 38 at the bottom of the groove 44 is large, making it difficult to obtain durability of the stress relaxation layer 52, and the rolling resistance of the tire 10 tends to increase. On the other hand, when R is large, the amount of deformation at the bottom of the groove 44 is kept small, making it easier to obtain durability of the stress relaxation layer 52, and the rolling resistance of the tire 10 tends to decrease.

[0098] Furthermore, when the minimum distance Gu is large and the thickness Ga is small (Ga / Gu is small), the thickness Ga of the stress relaxation layer 52 becomes small relative to the thickness of the tread rubber 38 at the minimum distance Gu, i.e., the groove bottom 44, making it difficult to obtain durability for the stress relaxation layer 52. On the other hand, when Ga / Gu is large, the thickness Ga of the stress relaxation layer 52 becomes thicker relative to the thickness of the tread rubber 38 at the groove bottom 44, making it easier to obtain durability for the stress relaxation layer 52.

[0099] By being above the lower limit of equation (1) above, the stress relaxation layer 52 has sufficient thickness relative to the thickness of the tread rubber 38 at the groove bottom 44. Therefore, the tire 10 can obtain the effect of suppressing the occurrence of groove cracks. In addition, because the tread rubber 38 at the groove bottom 44 has sufficient thickness, the amount of deformation at the groove bottom 44 can be suppressed. Therefore, the tire 10 can suppress the increase in rolling resistance.

[0100] By keeping the value below the upper limit of equation (1) above, the stress relaxation layer 52 does not become too thick relative to the thickness of the tread rubber 38 at the groove bottom 44, and can follow the deformation of the tread portion 18. Therefore, the tire 10 can obtain the effect of suppressing the occurrence of groove cracks. In addition, by maintaining the appropriate thickness of the tread rubber 38 at the groove bottom 44, an unnecessary increase in tire mass can be suppressed. Therefore, the tire 10 can suppress an increase in rolling resistance.

[0101] In the tires shown in Figures 1 and 2, the stress relaxation layer 52 is preferably provided in the circumferential main groove 40 located within the maximum belt width region WB. The maximum belt width region WB is the region from both outer ends in the tire width direction to the inner end in the tire width direction of the belt layer 22b or belt cover 24, which is formed as a reinforcing layer and located on the outermost side in the tire radial direction. The maximum belt width region WB has high rigidity and low strain during driving because the belt 22 or belt cover 24 is provided therein. Therefore, by providing the stress relaxation layer 52 in the circumferential main groove 40 located within the maximum belt width region WB, strain can be reduced and durability can be improved. The stress relaxation layer 52 is preferably provided in the circumferential main groove 40 located in the region where the belt cover 24 is provided within the maximum belt width region WB.

[0102] In the tires shown in Figures 1 and 2, among the circumferential main grooves 40 provided with a stress relaxation layer 52, the circumferential main groove 40 located on the outermost side in the tire width direction is specifically called the outermost main groove 40S. The distance between the center of the groove width of the outermost main groove 40S and the tire equatorial plane CP is denoted as Dg. The distance between the outer edge of the belt layer 22b or belt cover 24 located on the outermost side in the tire radial direction and the tire equatorial plane CP is denoted as Df. The ratio of Dg to Df (Dg / Df) is preferably 0.3 or more and 0.7 or less.

[0103] Generally, during the manufacturing process, when the green tire is inflated, when the tire 10 is mounted on the rim, and when the tire 10 is brought to the ground, the tread portion 18 experiences greater stress closer to the tread edge. As a result, the strain generated at the groove bottom 44 of the outermost main groove 40S, which is located near the tread edge, also increases. Therefore, by keeping the above ratio (Dg / Df) above the lower limit, the strain generated at the groove bottom 44 can be suppressed, thereby improving the durability of the stress relaxation layer 52. By keeping the above ratio (Dg / Df) below the upper limit, appropriate rigidity of the tread portion 18 can be obtained, resulting in excellent handling stability.

[0104] In the tires shown in Figures 1 and 2, the groove area ratio on the tread surface 37 is preferably 15% or more and 45% or less. The groove area ratio is a value (in %) defined by groove area / (contact area + groove area) × 100. Groove area refers to the opening area of ​​the grooves on the contact surface. Grooves include the circumferential main grooves of the tread but do not include sipes. If circumferential fine grooves and lug grooves are formed on the tread surface 37, these are included in the grooves. Contact area refers to the contact area between the tire and the contact surface. The groove area and contact area are measured at the contact surface between the tire 10 and the flat plate when the tire 10 is mounted on a regular rim, subjected to regular internal pressure, and placed perpendicular to a flat plate in a stationary state, with a load corresponding to a specified load (80% of the maximum load capacity) applied.

[0105] <Tire manufacturing method> The tire 10 of this embodiment, as described above, is obtained through the usual manufacturing processes, namely the mixing process of tire materials, the processing process of tire materials, the molding process of green tires, the vulcanization process, and the inspection process after vulcanization. When manufacturing the tire 10 of this embodiment, a coating agent for the stress relief layer 52 is applied to the green tire before vulcanization, to a predetermined location, namely the area including the location where the circumferential main grooves 40 are formed. The coating agent mainly consists of the above-mentioned diene-based rubber material and non-diene-based rubber material, and also contains at least a vulcanizing agent and a coloring pigment. Subsequently, by going through the vulcanization process, a tire 10 can be obtained in which a stress relief layer 52 is formed at least at the groove bottom 44 of the circumferential main grooves 40. In the vulcanization process, a vulcanization mold is used, which has convex and concave portions corresponding to a predetermined tread pattern formed on its inner wall. [Examples]

[0106] The following describes the results of evaluating the durability (GC resistance) of the stress relaxation layer and the visibility of the stress relaxation layer at a test temperature of 50°C for each of the test tires shown below.

[0107] (Preparation of test tires) Each test tire (the conventional example and Invention Examples 1 to 13 described later) was prepared with a tire size of 225 / 65R17, having the tread pattern shown in Figure 1, and having a stress-relieving layer formed on the surface of the groove bottom of all circumferential main grooves, in which these stress-relieving layers are mainly composed of butadiene rubber and also contain a vulcanizing agent and a coloring pigment. Each test tire was then mounted on a rim with a rim size of 17 × 6.5J, and an internal pressure of 230 [kPa] and a specified load of 6.0 [kN] were applied.

[0108] The conditions for the tires in the conventional example and Invention Examples 1 to 13 are as shown in Table 1 below. The terms in Table 1 are all the same as the terms explained in this embodiment, and their descriptions have been partially simplified.

[0109] (Evaluation of crack resistance at 50°C) Each test tire was left for 24 hours in a room maintained at an ozone concentration of 100±5 pphm, a temperature of 50±2°C, and an internal pressure of 230±2 kPa. The number of cracks that formed in the circumferential main grooves was then measured. Based on this measurement, an index evaluation was performed using a conventional example as the baseline (100). In this evaluation (see Table 1), a higher number indicates higher crack resistance.

[0110] (Evaluation of identifiable visibility) An evaluator, standing 1 meter away from each test tire, measured the time it took from opening their closed eyes while crouching down until they recognized the identification line. An index evaluation was then performed using the reciprocal of this measurement time, with the previous example set as the baseline (100). This evaluation (see Table 1) indicates that a higher numerical value indicates better identification visibility.

[0111] [Table 1]

[0112] As shown in Table 1, the tires of Invention Examples 1 to 13, which fall within the technical scope of the present invention (the stress relaxation layer mainly consists of a diene-based rubber material and includes not only a vulcanizing agent but also a coloring pigment), all have excellent crack resistance while ensuring identifiable visibility, compared to conventional tires that do not fall within the technical scope of the present invention. Therefore, it can be seen that Invention Examples 1 to 13 achieve both crack resistance and identification function. [Explanation of symbols]

[0113] 10 tires 12 Bead section 14 Sidewall section 16 Shoulder section 18 Tread section 19 Inner liner 20 Carcass 22 belts 22a, 22b Belt Layer 24 Belt Cover 36 Sidewall rubber 37 Tread surface 38 Tread Rubber 40 Circumferential main groove 40S outermost main groove 42 Land 44 Groove bottom 46 Ditch wall 48 Edge 52 Stress relaxation layer 54 Bottom 56 Wall 56U one end 56T other end 58 Surface part 58G one end 58L other end CP Tire Equatorial Plane Df is the distance between the outer edge of the belt layer 22b or belt cover 24 located on the outermost side in the tire's width direction and the tire's equatorial plane CP. Dg: The distance between the center of the groove width of the outermost main groove 40S and the tire's equatorial plane CP. Ga stress relaxation layer thickness Minimum tire radial distance from groove bottom 44 to belt cover 24 (or belt 22 if there is no belt cover) Hg tread section 18 minimum thickness Hmax tread section maximum thickness 18 WB Maximum Belt Width Area Area indicated by the dotted line X

Claims

1. A tire in which the tread surface of the tread rubber is divided into land areas by main grooves, and a stress-relieving layer is formed on the surface of at least one groove bottom of the main groove, The stress relaxation layer mainly consists of a diene-based rubber material and a non-diene-based rubber material, and also contains a vulcanizing agent. A tire characterized in that the stress-relieving layer contains a colored pigment.

2. The tire according to claim 1, wherein the color difference ΔE*ab in the L*a*b* color space is 12 or more between at least one of the stress relaxation layers and the tread surface.

3. The tire according to claim 1 or 2, wherein the difference ΔL* of the index L* in the lightness axis direction in the L*a*b* color space between at least one of the stress relaxation layers and the tread surface is 7 or more.

4. Between at least one of the stress relaxation layers and the tread surface, the difference Δa* between the index a* in the red and green directions and the difference Δb* between the index b* in the yellow and blue directions in the L*a*b* color space are, [(Δa*) ２ +(Δb*) ２ ] １／２ ≧12 A tire according to claim 1 or 2, satisfying the requirements.

5. The tire according to claim 1 or 2, wherein a plurality of main grooves are formed, and the stress relaxation layer is formed in the outermost main groove in the tire width direction.

6. The tire according to claim 1 or 2, wherein a plurality of main grooves are formed, and the stress-relieving layers formed in different main grooves exhibit different colors.

7. The tire according to claim 1 or 2, wherein at least one of the main grooves has the stress-relieving layer of a different color formed therein.

8. The tire according to claim 1 or 2, wherein a plurality of main grooves are formed, and the stress-relieving layer is formed in all of the main grooves.

9. In a cross-sectional view in the width direction of the main groove, of at least one groove wall surface of the main groove on which the stress relaxation layer is formed, The tire according to claim 1 or 2, wherein the angle θ between a virtual line perpendicular to the outer contour of the tire and the groove wall surface is 5° or more and 25° or less.

10. The tire according to claim 1 or 2, wherein, in a plan view of the tire, the shortest distance Wc in the groove width direction from one end of the main groove in the groove width direction to one end of the stress relaxation layer in the groove width direction is 5 mm or less.

11. The tire according to claim 1 or 2, wherein, in a plan view of the tire, at least one lateral groove is formed that communicates with the main groove, and the groove width Wl of the lateral groove is 8 mm or less.

12. The tire according to claim 1 or 2, wherein, in a plan view of the tire, at least one end of the main groove in the groove width direction is straight.

13. The tire according to claim 1 or 2, wherein the thickness of the stress relaxation layer is 5 μm or more and 200 μm or less.

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