tire

Abstract

To provide a tire capable of suppressing peeling of the stress relaxation layer and also effectively suppressing occurrence of groove cracks.SOLUTION: A tire according to the present invention comprises: a tread rubber 4 exposed on a tread surface 3; a main groove 30 formed in the tread surface 3; and a stress relaxation layer 40 disposed on a surface of the groove bottom 31 of the main groove 30. The stress relaxation layer 40 contains a diene rubber material and a non-diene rubber material, as main components, as well as, carbon, a vulcanizing agent, and a vulcanization accelerator. The stress relaxation layer 40 has an average thickness TA of 5 to 200 [μm] inclusive in a span of a stress action length LS in an extension direction of the main groove 30 in which the stress relaxation layer 40 is disposed. A difference TMa - TMi between a maximum film thickness TMa and a minimum film thickness TMi of the stress relaxation layer 40 is in a range of 3 to 100 [μm] inclusive. A ratio TA / (TMa-TMi) of the average thickness TA to the difference TMa - TMi between a maximum film thickness TMa and a minimum film thickness TMi is in a range of 0.85 to 10 inclusive.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a tire. [Background technology]

[0002] Some conventional pneumatic tires have a resin layer or a rubber layer different from the tread rubber on the surface of the tread. For example, the pneumatic tire described in Patent Document 1 has a urethane resin layer that covers the surface of the rubber layer to form the tire's outer surface, thereby improving the crack resistance of the tire surface. In addition, the tire described in Patent Document 2 has a surface layer rubber with a different composition from the tread rubber arranged on the surface of the grooves in the tread, thereby suppressing the occurrence of surface cracks due to aging without significantly impairing rolling resistance.

[0003] In addition, in the protective film-coated tire described in Patent Document 3, a protective film formed by vulcanizing a predetermined rubber composition that does not contain antioxidants or wax is formed at least in the tread portion, thereby ensuring wear resistance and steering stability and maintaining the appearance even when exposed to the open air.In addition, in the pneumatic tire described in Patent Document 4, the tread has two layers, a surface layer and an inner layer, and by making the thickness of at least a portion of the surface layer 10 μm or more and less than 500 μm, performance deterioration before use is suppressed, and a tire is obtained that has high grip performance in the early stages of driving and also sufficient wear resistance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-105406 [Patent Document 2] Japanese Patent Application Publication No. 2018-30546 [Patent Document 3] Japanese Patent Application Publication No. 11-301210 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-240583 Summary of the Invention [Problem to be solved by the invention]

[0005] One example of cracks that occur in tires is groove cracks, which are cracks that occur at the bottom of the main grooves. In addition to rubber degradation due to ozone and other factors, repeated stresses are likely to occur at the bottom of the main grooves when the vehicle is running, which makes groove cracks more likely to occur. One method for suppressing groove cracks is to provide a stress relief layer at the bottom of the main grooves, which can relieve stress.

[0006] However, when groove cracking is suppressed by disposing a stress relaxation layer at the groove bottom of the main groove, if the thickness of the stress relaxation layer varies greatly, stress tends to concentrate in the thinner areas, which may result in ineffective suppression of groove cracking. On the other hand, if the thickness of the stress relaxation layer varies too little, the contact area between the tread rubber on which the stress relaxation layer is disposed and the stress relaxation layer becomes small, making it difficult to ensure contact force between the tread rubber and the stress relaxation layer, which may result in the stress relaxation layer being more susceptible to peeling. For this reason, the method of suppressing groove cracking by disposing a stress relaxation layer at the groove bottom of the main groove of a tire leaves room for improvement in terms of suppressing peeling of the stress relaxation layer and more effectively suppressing groove cracking.

[0007] The present invention has been made in view of the above, and has an object to provide a tire that can suppress peeling of a stress relaxation layer and effectively suppress the occurrence of groove cracks. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the tire according to the present invention is a tire comprising a tread rubber exposed on a tread surface, main grooves formed on the tread surface, and a stress relaxation layer disposed on a surface of the groove bottom of the main groove, the stress relaxation layer containing a diene rubber material and a non-diene rubber material as main components and also containing carbon, a vulcanizing agent and a vulcanization accelerator, and the groove width W of the main groove is G [mm] and groove depth H G [mm] and the value L calculated from the following formula (1) S The stress acting length L S In this case, the stress relaxation layer has a stress acting length L S The average thickness T A is in the range of 5 [μm] to 200 [μm], and the maximum thickness T Ma and minimum film thickness T Mi Difference with T Ma -T Mi is in the range of 3 [μm] or more and 100 [μm] or less, and the average thickness T A and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is in the range of 0.85 or more and 10 or less.

[0009]

number

[0010] In the tire, the stress relaxation layer has a tensile stress M M and the tensile stress M of the tread rubber at 100% elongation T and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi and preferably satisfy the relationship of the following formula (2). 1≦(M M / M T )×(T Ma -T Mi )≦70 (2)

[0011] In the tire, the stress relaxation layer has a rubber hardness H M and the rubber hardness H of the tread rubber T and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi and preferably satisfy the relationship of the following formula (3). -20≦(H T -H M )×(T Ma -T Mi )≦1000 (3)

[0012] In the tire, the stress relaxation layer has a stress acting length L S It is preferable that the coefficient of variation of thickness in this range is in the range of 2% to 40%.

[0013] In the tire, the stress relaxation layer has a stress acting length L S The maximum film thickness T Ma The surface point at the position of S Ma and the maximum film thickness T Ma The boundary point with the tread rubber at the position P Ma and the minimum film thickness T Mi The surface point at the position of S Mi and the minimum film thickness T Mi The boundary point with the tread rubber at the position P Mi When the boundary point P Mi and the boundary point P Ma The imaginary line L1 connecting the surface point S Mi and the surface point S Ma and the boundary point P Mi It is preferable that the angle θ formed by the imaginary line L2 passing through the line θ is in the range of 50°≦θ<90°. [Effects of the Invention]

[0014] The tire according to the present invention has the effect of suppressing peeling of the stress relaxation layer and effectively suppressing the occurrence of groove cracks. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a tire meridian cross-sectional view showing a main part of a pneumatic tire according to an embodiment. [Figure 2] FIG. 2 is a detailed view of part A in FIG. [Figure 3] FIG. 3 is a view taken along the arrow BB in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along CC in FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along the line CC in FIG. 3, and is an explanatory diagram of the conditions for the positional relationship between the maximum thickness portion and the minimum thickness portion in the stress relaxation layer. [Figure 6] FIG. 6 is a perspective view of a paint transfer roller provided in the tire building apparatus. [Figure 7] FIG. 7 is a perspective view of the paint transfer roller shown in FIG. 6 with the support portion omitted. [Figure 8] FIG. 8 is an explanatory diagram of the position of the paint transfer roller relative to the tread rubber extruder. [Figure 9] FIG. 9 is a view taken along the arrow DD in FIG. [Figure 10] FIG. 10 is an explanatory diagram showing the state in which paint is applied to the tread rubber by a paint transfer roller. [Figure 11] FIG. 11 is a cross-sectional view taken along the line E-E in FIG. [Figure 12] FIG. 12 is a table showing the results of a performance evaluation test of a pneumatic tire. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of a tire according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[0017] [Embodiment] In the following description, a pneumatic tire 1 will be used as an example of a tire according to the present invention. The pneumatic tire 1, which is an example of a tire, can be filled with air, an inert gas such as nitrogen, or other gases.

[0018] In the following description, the tire radial direction refers to the direction perpendicular to the tire rotational axis (not shown), which is the rotational axis of the pneumatic tire 1, the tire radial inner side refers to the side toward the tire rotational axis in the tire radial direction, and the tire radial outer side refers to the side away from the tire rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotational axis as the central axis. The tire width direction refers to the direction parallel to the tire rotational axis, the tire width inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the tire rotational axis and passes through the center of the tire width of the pneumatic tire 1, and the tire equatorial plane CL coincides in position in the tire width direction with the tire width centerline, which is the center position of the pneumatic tire 1 in the tire width direction. The tire width is the width in the tire width direction between the portions located outermost in the tire width direction, that is, the distance in the tire width direction between the portions farthest from the tire equatorial plane CL. The tire equator line refers to a line that is on the tire equatorial plane CL and extends along the tire circumferential direction of the pneumatic tire 1. In the following description, the tire meridian cross section refers to a cross section of the tire cut by a plane that includes the tire rotation axis.

[0019] [Pneumatic tires] FIG. 1 is a tire meridian cross-section showing a main portion of a pneumatic tire 1 according to an embodiment. When viewed in a tire meridian cross-section, the pneumatic tire 1 according to the embodiment has a tread portion 2 disposed at the outermost portion in the tire radial direction, and the tread portion 2 has tread rubber 4 made of a rubber composition. The surface of the tread portion 2, i.e., the portion that comes into contact with the road surface when a vehicle (not shown) equipped with the pneumatic tire 1 is traveling, is formed as a tread surface 3, and the tread rubber 4 is exposed on the tread surface 3. The tread surface 3 forms part of the contour of the pneumatic tire 1. The tread portion 2 has a plurality of main grooves 30 formed on the tread surface 3, extending in the tire circumferential direction. In this embodiment, four main grooves 30 are arranged side by side in the tire width direction. The surface of the tread portion 2 is partitioned by the plurality of main grooves 30 into a plurality of land portions 20 arranged side by side in the tire width direction.

[0020] The main grooves 30 referred to here are grooves that are required to display a wear indicator as defined by JATMA. The main grooves 30 have a groove width of 4.0 mm or more and a groove depth of 6.2 mm or more. The main grooves 30 may extend linearly along the tire circumferential direction, or may be formed in a zigzag pattern by repeatedly bending or curving in the tire width direction while extending in the tire circumferential direction. The number of main grooves 30 may be any number other than four.

[0021] In addition to the main grooves 30 extending in the tire circumferential direction, lug grooves (not shown) extending in the tire width direction are provided on the tread surface 3. The tread surface 3 may also be provided with circumferential narrow grooves (not shown) that extend in the tire circumferential direction with a groove width narrower than that of the main grooves 30, sipes (not shown) formed in the tread surface 3 in the form of cuts, and the like.

[0022] Shoulder portions 5 are located at both outer ends of the tread portion 2 in the tire width direction, and sidewall portions 8 are arranged on the tire radially inward sides of the shoulder portions 5. That is, the sidewall portions 8 are arranged on both sides of the tread portion 2 in the tire width direction. In other words, the sidewall portions 8 are arranged in two locations on both sides of the pneumatic tire 1 in the tire width direction, and form the outermost exposed portions of the pneumatic tire 1 in the tire width direction.

[0023] Bead portions 10 are located on the tire radially inward side of each sidewall portion 8 located on both sides in the tire width direction. Like the sidewall portions 8, the bead portions 10 are arranged in two locations on both sides of the tire equatorial plane CL; that is, a pair of bead portions 10 are arranged on both sides of the tire equatorial plane CL in the tire width direction. Each bead portion 10 is provided with a bead core 11, and a bead filler 12 is provided on the tire radially outer side of the bead core 11. The bead core 11 is an annular member formed by bundling bead wires, which are steel wires, into a circular shape, and the bead filler 12 is a rubber member located on the tire radially outer side of the bead core 11.

[0024] A belt layer 14 is also disposed in the tread portion 2. The belt layer 14 has a multi-layer structure in which a plurality of belts 141, 142 and a belt cover 143 are laminated, and in this embodiment, two layers of belts 141, 142 are laminated. The belts 141, 142 constituting the belt layer 14 are formed by coating a plurality of belt cords made of steel or organic fiber material such as polyester, rayon, or nylon with coating rubber and rolling them, and the belt angle, defined as the inclination angle of the belt cords with respect to the tire circumferential direction, is within a predetermined range (for example, 20° to 55°). The two layers of belts 141, 142 have different belt angles. Therefore, the belt layer 14 has a so-called cross-ply structure in which the two layers of belts 141, 142 are laminated with the inclination directions of the belt cords crossing each other. That is, the two-layer belts 141 and 142 are provided as so-called cross belts in which the belt cords of the respective belts 141 and 142 are arranged in a direction that crosses each other.

[0025] The belt cover 143 is formed by covering a plurality of belt cover cords made of steel or organic fiber material such as polyester, rayon, or nylon with coating rubber and rolling the covered cords, and the belt angle, defined as the inclination angle of the belt cover cords with respect to the tire circumferential direction, is within a predetermined range (for example, 0° to 10°). The belt cover 143 is, for example, a strip material formed by covering one or more belt cover cords with coating rubber, and is formed by winding this strip material spirally around the tire rotation axis from the outer side in the tire radial direction of the two-layered belts 141 and 142.

[0026] A carcass layer 13 containing the cords of the radial ply is provided continuously on the tire radially inward side of the belt layer 14 and on the tire equatorial plane CL side of the sidewall portion 8. Therefore, the pneumatic tire 1 according to the embodiment is configured as a so-called radial tire. The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of a plurality of carcass plies stacked together, and is toroidally spanned between a pair of bead portions 10 arranged on both sides in the tire width direction to form the framework of the tire.

[0027] Specifically, the carcass layer 13 is disposed from one of a pair of bead portions 10 located on both sides in the tire width direction to the other bead portion 10, and is wound back along the bead core 11 at the bead portion 10 toward the outside in the tire width direction so as to enclose the bead core 11 and the bead filler 12. The bead filler 12 is made of a rubber material that is disposed in a space formed on the outside in the tire radial direction of the bead core 11 by folding back the carcass layer 13 at the bead portion 10 in this manner. The belt layer 14 is disposed on the outside in the tire radial direction of the portion of the carcass layer 13 that is positioned in the tread portion 2 and that is stretched between the pair of bead portions 10 in this manner. The carcass ply of the carcass layer 13 is formed by covering a plurality of carcass cords made of steel or an organic fiber material such as aramid, nylon, polyester, or rayon with coating rubber and rolling the coated cords. The carcass cords constituting the carcass ply are arranged in parallel at a certain angle relative to the tire circumferential direction, along the tire meridian direction.

[0028] In the bead portion 10, a rim cushion rubber 17 that forms the contact surface of the bead portion 10 with the rim flange is disposed on the tire radially inner side and tire widthwise outer side of the bead core 11 and the turned-up portion of the carcass layer 13. Furthermore, an inner liner 16 is formed along the carcass layer 13 on the inner side of the carcass layer 13 or on the inner side of the carcass layer 13 in the pneumatic tire 1. The inner liner 16 forms a tire inner surface 18, which is the inner surface of the pneumatic tire 1.

[0029] [Stress relief layer] Fig. 2 is a detailed view of part A in Fig. 1. A stress relief layer 40 that suppresses groove cracks is disposed on the surface of the groove bottom 31 of the main grooves 30 formed on the tread surface 3. The stress relief layer 40 is disposed in each of the multiple main grooves 30 formed on the tread surface 3.

[0030] The stress relief layer 40 is primarily composed of a diene rubber material and a non-diene rubber material, and contains carbon, a vulcanizing agent, and a vulcanization accelerator. The diene rubber is selected from the group consisting of diene polymers including natural rubber and synthetic diene rubber (isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), etc.). The non-diene rubber is selected from the group consisting of non-diene polymers including synthetic non-diene rubber (butyl rubber (IIR), ethylene propylene rubber (EPDM, EPM), urethane rubber, silicone rubber, etc.). To ensure weather resistance, the stress relief layer 40 preferably does not contain a resin component.

[0031] It is also preferable that the stress relaxation layer 40 does not contain an antioxidant. This configuration is preferable in that in a configuration in which a paint P (see FIG. 10 ) for providing the stress relaxation layer 40 in the main groove 30, as described below, is applied to the unvulcanized tread rubber 4 and a vulcanization molding process is performed, transfer of the stress relaxation layer 40 to the mold is suppressed and coloring of the stress relaxation layer 40 is suppressed.

[0032] However, the present invention is not limited to this, and the stress relaxation layer 40 may contain an antioxidant. In this case, it is preferable to not use an amine-based antioxidant, but to compound another antioxidant (for example, a phenol-based, phosphorous-based, organic thioacid-based, or benzimidazole-based antioxidant) in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the rubber component.

[0033] The stress relaxation layer 40 extends continuously in the tire circumferential direction along the main groove 30. The main groove 30 has a curved portion 32 at the portion where the groove bottom 31 and the groove wall 33 are connected in the tire meridian cross section, which gently connects the two without a sudden change in the angle of the inner surface of the main groove 30 at the connecting portion, and the stress relaxation layer 40 is disposed on at least the surfaces of the groove bottom 31 and the curved portion 32. In other words, the stress relaxation layer 40 is disposed on at least the surfaces of the curved portions 32 and the groove bottom 31 on both sides of the main groove 30 in the groove width direction.

[0034] The stress relief layer 40 may be disposed in a portion other than the groove bottom 31 or the curved portion 32, for example, on the groove wall 33. Furthermore, the stress relief layer 40 may extend from the groove wall 33 to the tread surface 3, and may be disposed on the inner surface of the main groove 30 as well as at a position on the tread surface 3 near the main groove 30.

[0035] Fig. 3 is a view taken along the arrow BB in Fig. 2. Fig. 4 is a cross-sectional view taken along the line CC in Fig. 3. The stress relaxation layer 40 is disposed on the surface of the tread rubber 4, and the surface of the tread rubber 4 has minute irregularities. Therefore, the thickness of the stress relaxation layer 40 varies in accordance with the minute irregularities on the surface of the tread rubber 4. That is, the thickness of the stress relaxation layer 40, which is the distance from the outer layer of the stress relaxation layer 40 to the surface of the tread rubber 4, varies in accordance with the minute irregularities on the surface of the tread rubber 4. In other words, the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 has irregularities in accordance with the irregularities on the surface of the tread rubber 4, and the thickness of the stress relaxation layer 40 varies in accordance with the irregularities at the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4. In this embodiment, the thickness that varies in accordance with the irregularities on the surface of the tread rubber 4 satisfies a predetermined condition.

[0036] In this embodiment, the stress relaxation layer 40 has a stress acting length L in the extension direction of the main groove 30 at an arbitrary position of the main groove 30 where the stress relaxation layer 40 is arranged. S The average thickness T A In this case, the stress acting length L is in the range of 5 μm to 200 μm. SIn this embodiment, the stress acting length L is a length defined as a range in which stress that contributes to the occurrence of cracks at the groove bottom 31 of the main groove 30 acts. S is the groove width W of the main groove 30 in which the stress relaxation layer 40 is arranged. G [mm] and groove depth H G [mm] and the value L calculated from the following formula (1) S The stress acting length L calculated from the following formula (1) is S is, for example, in the range of 1.5 [mm] to 10.0 [mm].

[0037]

number

[0038] The thickness of the stress relaxation layer 40 is measured, for example, at a position near the center in the groove width direction at the groove bottom 31 of the main groove 30. S The average thickness T of the stress relaxation layer 40 in the range A is the stress acting length L S The average thickness T of the stress relaxation layer 40 is the average value of the thicknesses of the stress relaxation layer 40 measured at predetermined intervals in the extension direction of the main groove 30 within the range of . A For example, the stress acting length L S The average thickness T of the stress relaxation layer 40 calculated in this way is the average value of the thicknesses of the stress relaxation layer 40 measured at intervals of 10 μm within the range of A is preferably in the range of 8 μm or more and 180 μm or less.

[0039] The stress relaxation layer 40 has a stress acting length L S The maximum thickness of the stress relaxation layer 40 in the range of Ma and the minimum thickness, T Mi Difference with T Ma -T Mi The stress acting length L is in the range of 3 μm to 100 μm. S The maximum thickness T of the stress relaxation layer 40 in the range Ma and minimum film thickness TMi Difference with T Ma -T Mi is preferably in the range of 5 μm to 80 μm.

[0040] The stress relaxation layer 40 has a stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is in the range of 0.85 to 10. The stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is preferably in the range of 1 or more and 8 or less.

[0041] The stress relaxation layer 40 formed with such a varying thickness has a stress acting length L S The coefficient of variation of the thickness in the range of 2% to 40% is in the range of 2% to 40%. S The coefficient of variation of the thickness of the stress relaxation layer 40 is calculated from the average value and standard deviation of the thickness of the stress relaxation layer 40 measured at intervals of 10 μm within the range of S The thickness of the stress relaxation layer 40 is measured every 10 μm within the range of 10 μm, and the standard deviation / average value is calculated.

[0042] In addition, the stress acting length L S The coefficient of variation of the thickness of the stress relaxation layer 40 in this range is preferably in the range of 2.2% to 38% and more preferably in the range of 2.5% to 35%.

[0043] 5 is a cross-sectional view of the stress relaxation layer 40 taken along the CC line of FIG. Ma and the minimum thickness T Mi The stress relaxation layer 40 has a stress acting length L S In the range of Mi and boundary point P Ma The imaginary line L1 connecting the surface point S Mi and surface point S Ma A virtual line L0 extends perpendicularly from the line L0 and connects the two points P Mi The angle θ formed by the imaginary line L2 passing through the line θ is in the range of 50°≦θ<90°.

[0044] In this case, the boundary point P Mi is the stress acting length L S The minimum thickness T of the stress relaxation layer 40 in the range Mi This is the boundary point between the stress relaxation layer 40 and the tread rubber 4. Ma is the stress acting length L S The maximum thickness T of the stress relaxation layer 40 in the range Ma The surface point S Mi is the stress acting length L S The minimum thickness T of the stress relaxation layer 40 in the range Mi The surface point S Ma is the stress acting length L S The maximum thickness T of the stress relaxation layer 40 in the range Ma This is the surface point of the stress relaxation layer 40 at the position.

[0045] The virtual line L1 is at the boundary point P Mi and boundary point P Ma The imaginary line L0 is a line connecting the surface point S Mi and surface point S Ma The imaginary line L2 extends perpendicularly from the imaginary line L0 and is connected to the boundary point P MiIn the stress relaxation layer 40, the angle θ formed by the imaginary line L1 and the imaginary line L2 defined as above is in the range of 50°≦θ<90°.

[0046] In addition, the angle θ between the virtual lines L1 and L2 of the stress relaxation layer 40 is preferably within the range of 55°≦θ<90°, more preferably within the range of 60°≦θ<90°, and even more preferably within the range of 65°≦θ<90°.

[0047] The stress relaxation layer 40 disposed on the surface of the groove bottom 31 of the main groove 30 in this manner is resistant to the tensile stress M M [MPa] and the tensile stress M of tread rubber 4 at 100[%] elongation T [MPa] and the stress acting length L S The maximum thickness T of the stress relaxation layer 40 in the range Ma and minimum film thickness T Mi Difference with T Ma -T Mi and satisfy the relationship of the following formula (2). In other words, the stress relaxation layer 40 has a modulus M M and the modulus M of tread rubber 4 at 100% elongation T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi Difference with T Ma -T Mi and satisfy the relationship of the following formula (2). 1≦(M M / M T )×(T Ma -T Mi )≦70 (2)

[0048] In this case, the modulus M of the stress relaxation layer 40 M and the modulus M of tread rubber 4 T The modulus M of the tread rubber 4 is measured by a tensile test using a dumbbell-shaped test piece at a temperature of 20°C in accordance with JIS K6251 (using a No. 3 dumbbell). Tis measured as the modulus of the rubber material of the portion that comes into surface contact with the stress relaxation layer 40.

[0049] The modulus M of the stress relaxation layer 40 and the tread rubber 4 M , M T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi Difference with T Ma -T Mi The relationship is 1.5≦(M M / M T )×(T Ma -T Mi )≦68, and 2≦(M M / M T )×(T Ma -T Mi )≦65 is more preferred.

[0050] The stress relaxation layer 40 has a rubber hardness H M and tread rubber 4 rubber hardness H T and the stress acting length L S The maximum thickness T of the stress relaxation layer 40 in the range Ma and minimum film thickness T Mi Difference with T Ma -T Mi and satisfy the relationship of the following formula (3). -20≦(H T -H M )×(T Ma -T Mi )≦1000 (3)

[0051] In this case, the rubber hardness H of the stress relaxation layer 40 M and tread rubber 4 rubber hardness H T The hardness H of the tread rubber 4 is JIS-A hardness, which is measured at a temperature of -20°C using an A-type durometer in accordance with JIS K6253. T is measured as the rubber hardness of the rubber material that comes into surface contact with the stress relaxation layer 40 among the rubber materials that make up the tread rubber 4.

[0052] The rubber hardness H of the stress relaxation layer 40 and the tread rubber 4 M , H T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi Difference with T Ma -T Mi The relationship is -10≦(H T -H M )×(T Ma -T Mi )≦800, and 0≦(H T -H M )×(T Ma -T Mi )≦700 is more preferable.

[0053] [Paint transfer roller] The stress relaxation layer 40 disposed in the main groove 30 of the pneumatic tire 1 as described above is provided by applying a paint that will become the base of the stress relaxation layer 40 to the tread rubber 4 before vulcanization molding during the manufacture of the pneumatic tire 1. The paint that will become the base of the stress relaxation layer 40 is applied by a paint transfer roller 60 provided in a tire manufacturing apparatus 50 used in the manufacture of the pneumatic tire 1. Next, the paint transfer roller 60 will be described.

[0054] Fig. 6 is a perspective view of the paint transfer roller 60 provided in the tire building apparatus 50. Fig. 7 is a perspective view of the paint transfer roller 60 shown in Fig. 6 with the support unit 90 omitted. The paint transfer roller 60 includes a paint supply unit 65, a transfer unit 70, a rotating unit 80, and a support unit 90. In the following description, the upper side of the paint transfer roller 60 in its normal usage state will also be referred to as the upper side of the paint transfer roller 60, and the lower side of the paint transfer roller 60 in its normal usage state will also be referred to as the lower side of the paint transfer roller 60.

[0055] The paint supply unit 65 supplies the paint P (see FIG. 10) to be transferred by the paint transfer roller 60 to the transfer unit 70. A paint storage unit 66 that stores the paint P therein is connected to the paint supply unit 65. The paint storage unit 66 is formed in a so-called bottle shape that stores a liquid therein, and is connected to the upper side of the paint supply unit 65 with the opening facing downwards. This allows the paint P stored inside the paint storage unit 66 to be supplied to the paint supply unit 65 by gravity. The paint supply unit 65 supplies the paint P supplied from the paint storage unit 66 to the transfer unit 70.

[0056] The paint storage unit 66 is detachably connected to the paint supply unit 65. Therefore, when the paint P inside the paint storage unit 66 runs out, the paint storage unit 66 connected to the paint supply unit 65 can be replaced with another paint storage unit 66 in which the paint P is stored.

[0057] The transfer unit 70 is formed in a substantially cylindrical shape. The transfer unit 70 is capable of receiving the paint P (see FIG. 10) supplied from the paint supply unit 65 on an outer peripheral surface 71 of the transfer unit 70, and is capable of transferring the paint P received on the outer peripheral surface 71 to a surface to which the paint P is to be applied.

[0058] The rotating unit 80 is formed in a substantially cylindrical shape. The rotating units 80 are arranged on both sides of the transfer unit 70 in the axial direction of the transfer unit 70, which is formed in a cylindrical shape, and are each provided integrally with the transfer unit 70. The rotating units 80 arranged on both sides of the transfer unit 70 are arranged in a position and orientation such that the axis of the rotating unit 80 coincides with the axis of the transfer unit 70. The radius of the rotating unit 80 is larger than the radius of the transfer unit 70, and the two rotating units 80 arranged on both sides of the transfer unit 70 have the same maximum diameter.

[0059] The support unit 90 supports the transfer unit 70 and the rotating unit 80 so that they can rotate freely in the circumferential direction around the axis of the transfer unit 70. More specifically, a rotating shaft 95, which is an axial member that passes through the axis of the transfer unit 70 and the rotating unit 80, is inserted into the transfer unit 70 and the rotating unit 80, and the transfer unit 70 and the rotating unit 80 are rotatable about the rotating shaft 95. The length of the rotating shaft 95 is longer than the combined width of the transfer unit 70 and the rotating unit 80 in the axial direction of the transfer unit 70, and both ends of the rotating shaft 95 in the longitudinal direction protrude from the rotating units 80 that are arranged on both sides of the transfer unit 70.

[0060] The support section 90 has a shaft support section 91 that supports the rotation shaft 95, and a supply section support section 92 that supports the paint supply section 65. The shaft support sections 91 are arranged at two locations on both sides in the width direction of the two rotation sections 80 and the transfer section 70, and support the portions of the rotation shaft 95 that protrude from the rotation sections 80 that are arranged on both sides of the transfer section 70.

[0061] The supply unit support part 92 is disposed between the two shaft support parts 91 at a position outside the outer periphery of the transfer unit 70 or the rotation unit 80 in the radial direction of the transfer unit 70 or the rotation unit 80, and connects the two shaft support parts 91. The paint supply unit 65 is attached to the supply unit support part 92 and disposed at a position facing the outer periphery 71 of the transfer unit 70.

[0062] [Tire manufacturing method] Next, a method for manufacturing a tire using the tire manufacturing apparatus 50 equipped with the paint transfer roller 60 configured as described above will be described. When manufacturing a pneumatic tire 1, first, each of the components, such as the tread rubber 4 and the rubber constituting the sidewall portion 8, the inner liner 16, the rim cushion rubber 17, the carcass layer 13, the belt layer 14, the bead core 11, and the bead filler 12, is manufactured. After each of the components constituting the pneumatic tire 1 is manufactured, these are bonded together and assembled to manufacture a so-called green tire, which is the prototype of the pneumatic tire 1. Thereafter, the green tire is vulcanized and molded using a mold (not shown) and a bladder (not shown), thereby molding it into the shape of the pneumatic tire 1. As a result, each groove, such as the main groove 30, is formed in the tread surface 3 of the pneumatic tire 1 by the mold.

[0063] Here, the pneumatic tire 1 according to this embodiment has a stress relaxation layer 40 disposed in the main groove 30. The stress relaxation layer 40 is formed by applying a material that will become the stress relaxation layer 40 as paint P (see FIG. 10 ) to the tread rubber 4 before it is bonded to other members, and then bonding the tread rubber 4 to other members and performing vulcanization molding, thereby disposing the stress relaxation layer 40 in the main groove 30.

[0064] FIG. 8 is an explanatory diagram of the position of the paint transfer roller 60 relative to the extruder 100 for the tread rubber 4. FIG. 9 is a view seen from the arrow DD in FIG. 8. FIG. 10 is an explanatory diagram showing the state in which the paint P is applied to the tread rubber 4 by the paint transfer roller 60. FIG. 11 is a cross-sectional view taken along the line EE in FIG. 10. When applying the material that will become the stress relaxation layer 40 as paint P to the tread rubber 4, the paint transfer roller 60 is used to apply the paint P to the sheet-like tread rubber 4 before it is laminated with other components. For this reason, the paint transfer roller 60 that applies the paint P is arranged downstream of the extruder 100 in the direction of movement of the tread rubber 4 extruded from the extruder 100 that extrudes the tread rubber 4. More preferably, the paint transfer roller 60 is arranged between the extrusion process and the cooling process of the tread rubber 4.

[0065] That is, the rubber material that constitutes the tread rubber 4 is formed into a sheet shape and extruded from the extruder 100, and the paint transfer roller 60 is positioned downstream of the extruder 100 in the movement direction of the tread rubber 4, thereby applying the paint P to the sheet-like tread rubber 4 formed by the extruder 100. The sheet-like tread rubber 4 is extruded from the extruder 100 with its thickness direction oriented vertically, and the paint transfer roller 60 is positioned on the upper surface side of the tread rubber 4, thereby applying the paint P to the upper surface of the tread rubber 4.

[0066] The paint transfer roller 60 is arranged on the upper surface side of the tread rubber 4, with the side where the paint supply unit 65 is located facing up and the side where the transfer unit 70 and the rotating unit 80 are located facing up. Furthermore, the paint transfer roller 60 is arranged so that the extension direction of the axis of the transfer unit 70 and the rotating unit 80, i.e., the extension direction of the rotating shaft 95, is parallel to the surface of the tread rubber 4 and perpendicular to the moving direction of the tread rubber 4 extruded from the extruder 100.

[0067] The paint transfer roller 60 is also placed at a position corresponding to the main groove 30 in which the stress relaxation layer 40 is to be disposed in the tread rubber 4. In other words, the paint transfer roller 60 is placed at a position in the tread rubber 4 extruded from the extruder 100 where the main groove 30 will be formed after vulcanization molding, and more specifically, the paint transfer roller 60 is placed at a position in the sheet-like tread rubber 4 where the groove bottom 31 of the main groove 30 will be formed after vulcanization molding. Therefore, if the pneumatic tire 1 has a plurality of main grooves 30 in which the stress relaxation layer 40 is to be disposed, a plurality of paint transfer rollers 60 are placed at positions corresponding to the respective main grooves 30 in which the stress relaxation layer 40 is to be disposed.

[0068] Since the radius of the rotating part 80 of the paint transfer roller 60 is larger than the radius of the transfer part 70, the paint transfer roller 60 arranged on the upper surface side of the tread rubber 4 brings the rotating part 80 into contact with the surface of the tread rubber 4. When the rotating part 80 is in contact with the surface of the tread rubber 4, the transfer part 70 is spaced apart from the surface of the tread rubber 4.

[0069] The extruder 100 sequentially extrudes the sheet-shaped tread rubber 4, and the sheet-shaped tread rubber 4 is sequentially delivered from the extruder 100. The paint transfer roller 60 brings the rotating part 80 into contact with the surface of the tread rubber 4 downstream of the extruder 100, causing the rotating part 80 to rotate about the rotation axis 95 due to the frictional force between the rotating part 80 and the tread rubber 4. As a result, the transfer part 70 also rotates integrally with the rotating part 80 about the rotation axis 95.

[0070] A paint supply unit 65 is disposed above the transfer unit 70, and the paint supply unit 65 is capable of supplying the paint P stored in the paint storage unit 66 to the outer peripheral surface 71 of the transfer unit 70. Therefore, the paint P supplied from the paint supply unit 65 at an upper position in the transfer unit 70 moves downward as the outer peripheral surface 71 of the transfer unit 70 rotates integrally with the rotating unit 80. In other words, the paint P received by the outer peripheral surface 71 of the transfer unit 70 from the paint supply unit 65 moves toward the side where the tread rubber 4 is located as the transfer unit 70 rotates.

[0071] As the transfer unit 70 rotates, the paint P moves toward the side where the tread rubber 4 is located, and when it reaches the position of the tread rubber 4, it adheres to the surface of the tread rubber 4. As a result, the paint P received by the outer peripheral surface 71 of the transfer unit 70 is transferred to the surface of the tread rubber 4 and applied to the surface of the tread rubber 4.

[0072] At that time, the transfer unit 70 transfers the paint P to the tread rubber 4 without coming into contact with the tread rubber 4, and due to the difference between the radius of the rotating unit 80 and the radius of the transfer unit 70, the outer peripheral surface 71 of the transfer unit 70 is kept apart from the surface of the tread rubber 4. As a result, the paint applied by being transferred to the tread rubber 4 is applied while variations in thickness are suppressed.

[0073] As the sheet-like tread rubber 4 is sequentially extruded and sent out from the extruder 100, the paint transfer roller 60, whose rotating part 80 comes into contact with the surface of the tread rubber 4, continues to rotate both the rotating part 80 and the transfer part 70 as the tread rubber 4 moves. As a result, the paint P supplied from the paint supply part 65 to the transfer part 70 and received on the outer peripheral surface 71 is continuously transferred to the surface of the tread rubber 4 as the tread rubber 4 moves, and is continuously applied. In this way, by bringing the rotating part 80 into contact with the surface of the tread rubber 4 extruded from the extruder 100, the paint transfer roller 60 rotates the rotating part 80 and the transfer part 70 together as the tread rubber 4 moves, and continuously applies the paint P to the surface of the tread rubber 4.

[0074] The tread rubber 4 to which the paint P has been applied by the paint transfer roller 60 is then bonded to other components and then vulcanized. The paint P applied to the tread rubber 4 by the paint transfer roller 60 is applied to positions on the tread rubber 4 corresponding to positions where the main grooves 30 are formed, so when the tread rubber 4 is bonded to other components and vulcanized, the paint P covers the groove bottoms 31 of the main grooves 30. Because the paint P is made of the material of the stress relaxation layer 40, the paint P covering the main grooves 30 becomes the stress relaxation layer 40 and is disposed on the surface of the groove bottoms 31 of the main grooves 30.

[0075] Here, the sheet-like tread rubber 4 extruded from the extruder 100 has an arithmetic mean roughness Ra of the surface of the tread rubber 4 within a range of 1.5 μm to 35 μm. By applying paint P to the tread rubber 4 formed with a surface roughness within this range using a paint transfer roller 60 having a transfer unit 70 and a rotating unit 80, it is possible to arrange the stress relaxation layer 40, whose thickness variation satisfies the above-mentioned condition, at the groove bottom 31 of the main groove 30.

[0076] [Effects of the embodiment] As described above, in the pneumatic tire 1 according to the embodiment, the stress relaxation layer 40 made of a weather-resistant material is disposed on the surface of the groove bottom 31 of the main groove 30, and the stress relaxation layer 40 has a stress acting length L SThe average thickness T A Since the thickness is within the range of 5 μm or more and 200 μm or less, the thickness of the stress relaxation layer 40 can be ensured, and the stress relaxation layer 40 can suppress groove cracks.

[0077] In other words, the stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A When the average thickness T of the stress relaxation layer 40 is less than 5 μm, A is too thin, so even if the stress relaxation layer 40 is disposed on the groove bottom 31 of the main groove 30, it may be difficult for the stress relaxation layer 40 to suppress groove cracks occurring on the groove bottom 31 of the main groove 30. S The average thickness T of the stress relaxation layer 40 in the range A When the average thickness T of the stress relaxation layer 40 is greater than 200 μm, A is too thick, there is a risk that the stress relaxation layer 40 will not be able to follow the deformation of the tread rubber 4 when the pneumatic tire 1 rotates. In this case, the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 may peel off, and the stress relaxation layer 40 may not be able to suppress groove cracks that occur at the groove bottoms 31 of the main grooves 30.

[0078] In contrast, the stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A However, when the thickness is within the range of 5 μm or more and 200 μm or less, the stress relaxation layer 40 can suppress groove cracks that occur at the groove bottom 31 of the main groove 30 while ensuring the ability of the stress relaxation layer 40 to follow the deformation of the tread rubber 4.

[0079] The stress relaxation layer 40 has a stress acting length L S The maximum thickness T of the stress relaxation layer 40 in the range Ma and minimum film thickness T Mi Difference with T Ma -T Mi is in the range of 3 μm or more and 100 μm or less, the adhesive strength between the stress relaxation layer 40 and the tread rubber 4 is ensured, and the minimum thickness T MiIt is possible to suppress the occurrence of stress concentration in the portion where the stress is generated.

[0080] That is, the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi Difference with T Ma -T Mi If is less than 3 μm, the maximum film thickness T Ma and minimum film thickness T Mi Since the difference between the maximum thickness T of the stress relaxation layer 40 and the maximum thickness T of the stress relaxation layer 40 is too small, there is a risk that the stress relaxation layer 40 may easily peel off from the tread rubber 4. Ma and minimum film thickness T Mi As the difference between the thickness T Ma and minimum film thickness T Mi If the difference is small, the length of the adhesive interface 41 between the stress relief layer 40 and the tread rubber 4 will be short, making it difficult to ensure the adhesive strength between the stress relief layer 40 and the tread rubber 4, and there is a risk that the stress relief layer 40 will be easily peeled off from the tread rubber 4.

[0081] In addition, the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi Difference with T Ma -T Mi If is greater than 100 μm, the maximum film thickness T Ma and minimum film thickness T Mi Since the difference between the thickness of the stress relaxation layer 40 and the thickness of the stress relaxation layer 40 is too large, the thickness of the stress relaxation layer 40 at the groove bottom 31 of the main groove 30 is smaller than the minimum thickness T Mi Therefore, at the groove bottom 31 of the main groove 30, there is a risk that groove cracks will be more likely to occur in the portion where stress concentration occurs.

[0082] In contrast, the maximum thickness T Ma and minimum film thickness T Mi Difference with T Ma -T Miis in the range of 3 [μm] or more and 100 [μm] or less, the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 is secured to secure the adhesive strength between the stress relaxation layer 40 and the tread rubber 4, and the minimum film thickness T Mi This can suppress the occurrence of stress concentration in the portion where the stress relaxation layer 40 is in contact with the tread rubber 4, and can also suppress the likelihood of groove cracks occurring at the groove bottoms 31 of the main grooves 30.

[0083] The stress relaxation layer 40 has a stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is in the range of 0.85 or more and 10 or less, the minimum thickness T Mi This makes it possible to ensure the adhesive strength between the stress relaxation layer 40 and the tread rubber 4 while suppressing the occurrence of stress concentration in the portion where the stress relaxation layer 40 is weak.

[0084] That is, the average thickness T of the stress relaxation layer 40 A and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi The ratio of the difference between A / (T Ma -T Mi If the ratio is less than 0.85, the average thickness T A Maximum film thickness T Ma and minimum film thickness T Mi In this case, the thickness of the stress relaxation layer 40 at the groove bottom 31 of the main groove 30 is smaller than the minimum film thickness T Mi Stress concentration is likely to occur in the portion where this occurs, and groove cracks may be likely to occur in the portion where stress concentration occurs.

[0085] The average thickness T of the stress relaxation layer 40 Aand the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi The ratio of the difference between A / (T Ma -T Mi If the ratio is greater than 10, the average thickness T A Maximum film thickness T Ma and minimum film thickness T Mi In this case, the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 becomes too short, making it difficult to ensure adhesive strength between the stress relaxation layer 40 and the tread rubber 4, and there is a risk that the stress relaxation layer 40 will be easily peeled off from the tread rubber 4.

[0086] In contrast, the average thickness T A and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi The ratio of the difference between A / (T Ma -T Mi ) is in the range of 0.85 or more and 10 or less, the minimum thickness T Mi By ensuring the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 while suppressing the occurrence of stress concentration in the portion where the grooves are bent, the adhesive strength between the stress relaxation layer 40 and the tread rubber 4 can be secured. This reduces the likelihood of groove cracks occurring at the groove bottoms 31 of the main grooves 30, and also suppresses peeling of the stress relaxation layer 40 from the tread rubber 4. As a result, peeling of the stress relaxation layer 40 from the tread rubber 4 can be suppressed, and the occurrence of groove cracks can be effectively suppressed.

[0087] In addition, the stress relaxation layer 40 has a tensile stress M M and the tensile stress M of tread rubber 4 at 100% elongation T and the maximum film thickness T Ma and minimum film thickness T Mi Difference with T Ma -T MiIn order to satisfy the relationship of the above formula (2), the thickness of the stress relaxation layer 40 is set to the minimum thickness T Mi It is possible to suppress the occurrence of stress concentration in the portion where the stress is generated.

[0088] That is, (M M / M T )×(T Ma -T Mi )<1, the maximum thickness T Ma and minimum film thickness T Mi If the difference between the stress relaxation layer 40 and the tread rubber 4 is too small, it may be difficult to ensure the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4. In this case, it may be difficult to ensure an appropriate adhesive force between the stress relaxation layer 40 and the tread rubber 4, and the stress relaxation layer 40 may be easily peeled off from the tread rubber 4. M / M T )×(T Ma -T Mi )>70, the maximum thickness T Ma and minimum film thickness T Mi Since the difference between the thickness of the stress relaxation layer 40 and the thickness of the stress relaxation layer 40 at the groove bottom 31 of the main groove 30 is too large, Mi In this case, it may become difficult to prevent the occurrence of groove cracks in the portion where stress concentration occurs.

[0089] In contrast, the tensile stress M M , M T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi When the difference between the thickness of the stress relaxation layer 40 and the tread rubber 4 satisfies the relationship of the above formula (2), the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 is secured, and peeling of the stress relaxation layer 40 from the tread rubber 4 is suppressed, and the thickness of the stress relaxation layer 40 is within the minimum thickness T Mi As a result, peeling of the stress relaxation layer 40 can be suppressed and the occurrence of groove cracks can be more effectively suppressed.

[0090] The stress relaxation layer 40 has a rubber hardness H M and tread rubber 4 rubber hardness H T and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi In order to satisfy the relationship of the above formula (3), the thickness of the stress relaxation layer 40 is set to the minimum thickness T Mi It is possible to suppress the occurrence of stress concentration in the portion where the stress is generated.

[0091] That is, (H T -H M )×(T Ma -T Mi )<-20, the maximum thickness T Ma and minimum film thickness T Mi Since the difference between the stress relaxation layer 40 and the tread rubber 4 is too small, it may be difficult to ensure the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4. In this case, it may be difficult to ensure an appropriate adhesive strength between the stress relaxation layer 40 and the tread rubber 4, and in particular, it may be difficult to ensure adhesive strength at low temperatures, which may cause the stress relaxation layer 40 to easily peel off from the tread rubber 4 when running at low temperatures. T -H M )×(T Ma -T Mi )>1000, the maximum thickness T Ma and minimum film thickness T Mi Since the difference between the thickness of the stress relaxation layer 40 and the thickness of the stress relaxation layer 40 at the groove bottom 31 of the main groove 30 is too large, Mi In this case, it may become difficult to prevent groove cracks from occurring in the area where stress concentration occurs. In particular, stress relaxation in the stress relaxation layer 40 at low temperatures may become insufficient, making it difficult to prevent groove cracks from occurring at low temperatures.

[0092] In contrast, the rubber hardness H M , H T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness TMi When the difference between the thickness of the stress relaxation layer 40 and the tread rubber 4 satisfies the relationship of the above formula (3), the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 is secured, and peeling of the stress relaxation layer 40 from the tread rubber 4 during low-temperature running is suppressed, and the thickness of the stress relaxation layer 40 is within the minimum thickness T Mi This can prevent stress concentration at the portion where the groove cracks are formed, thereby preventing the occurrence of groove cracks at low temperatures. As a result, peeling of the stress relaxation layer 40 can be prevented, and the occurrence of groove cracks can be more effectively prevented.

[0093] The stress relaxation layer 40 has a stress acting length L S Since the coefficient of variation of the thickness in this range is within the range of 2% or more and 40% or less, it is possible to suppress the occurrence of stress concentration in the thin portions of the stress relaxation layer 40 while ensuring the adhesive strength between the stress relaxation layer 40 and the tread rubber 4. In other words, if the coefficient of variation of the thickness of the stress relaxation layer 40 is less than 2%, the variation in the thickness of the stress relaxation layer 40 is too small, which may make it difficult to ensure the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4. In this case, it may become difficult to ensure the appropriate adhesive strength between the stress relaxation layer 40 and the tread rubber 4, and the stress relaxation layer 40 may be prone to peeling off from the tread rubber 4. Furthermore, if the coefficient of variation of the thickness of the stress relaxation layer 40 is greater than 40%, the variation in the thickness of the stress relaxation layer 40 is too large, which may make it easy for stress concentration to occur in the thin portions of the stress relaxation layer 40 at the groove bottoms 31 of the main grooves 30. In this case, there is a risk that it will become difficult to prevent groove cracks from occurring due to long-term fatigue in the area where stress concentration occurs.

[0094] In contrast, when the coefficient of variation of the thickness of the stress relaxation layer 40 is within the range of 2% to 40%, the length of the adhesive interface 41 between the stress relaxation layer 40 and the tread rubber 4 is ensured, preventing peeling of the stress relaxation layer 40 from the tread rubber 4, and also preventing stress concentration in the thinner portions of the stress relaxation layer 40, thereby preventing groove cracks. As a result, peeling of the stress relaxation layer 40 can be prevented and groove cracks can be more effectively prevented.

[0095] In addition, since the angle θ between the virtual line L1 and the virtual line L2 of the stress relaxation layer 40 is in the range of 50°≦θ<90°, the thickness of the stress relaxation layer 40 is the minimum film thickness T Mi In other words, when the angle θ formed by the imaginary line L1 and the imaginary line L2 of the stress relaxation layer 40 is θ<50°, the thickness of the stress relaxation layer 40 is the maximum film thickness T Ma and the minimum thickness T Mi In this case, the thickness of the stress relaxation layer 40 at the groove bottom 31 of the main groove 30 is less than the minimum film thickness T Mi Stress concentration is likely to occur in the portion where this occurs, and there is a risk that it may become difficult to suppress the occurrence of groove cracks in the portion where stress concentration occurs.

[0096] On the other hand, when the angle θ formed by the imaginary line L1 and the imaginary line L2 of the stress relaxation layer 40 is in the range of 50°≦θ<90°, the thickness of the stress relaxation layer 40 is the minimum film thickness T Mi This can prevent stress concentration at the portion where the groove cracks are formed, and therefore groove cracks can be prevented from occurring. As a result, groove cracks can be prevented from occurring more effectively.

[0097] In the above-described embodiment, the pneumatic tire 1 has been described as an example of a tire according to the present invention, but the tire according to the present invention may be a tire other than the pneumatic tire 1. The tire according to the present invention may be, for example, a so-called airless tire that can be used without being filled with gas.

[0098] [Example] 12 is a table showing the results of performance evaluation tests of pneumatic tires. Hereinafter, performance evaluation tests will be described for the above-mentioned pneumatic tire 1, a conventional pneumatic tire, the pneumatic tire 1 according to the present invention, and a comparative pneumatic tire compared to the pneumatic tire 1 according to the present invention. The performance evaluation tests were conducted to test groove crack resistance and stress relaxation layer durability.

[0099] The performance evaluation test was conducted under the following conditions: the test tire was a pneumatic tire 1 with a nominal tire size of 225 / 65R17 as specified by JATMA, and the tire was mounted on a JATMA standard rim wheel with a rim size of 17 x 6.5J, with the air pressure adjusted to 180 kPa.

[0100] The evaluation method for each test item was as follows: for groove crack resistance, test tires were exposed to an ozone-supplied test chamber at a temperature of 50°C and an ozone concentration of 100 pphm for 8 hours each day for 3 days, and then the number of cracks that occurred in the main grooves 30 was counted. Groove crack resistance was evaluated by calculating the reciprocal of the number of cracks that occurred in the main grooves 30 and assigning an index to Comparative Example 1, described below, with 100. The larger the index value, the fewer groove cracks occurred in the main grooves 30, indicating better groove crack resistance.

[0101] The durability of the stress relaxation layer was evaluated using an indoor drum tester. The stress relaxation layer durability was evaluated by running 1,800 km of drum tires at a load specified by JATMA, a speed of 80 km / h, and a low ambient temperature of -10°C, followed by 3,600 km of drum tires in a high ambient temperature of 40°C. After the drum test, the number of cracked areas in the stress relaxation layer 40 that had peeled off from the tread rubber 4 was counted. The durability of the stress relaxation layer was evaluated using an index calculated by calculating the reciprocal of the number of cracked areas in the stress relaxation layer 40 that had peeled off from the tread rubber 4, with Comparative Example 1 (described later) being assigned an index of 100. The higher the index value, the less likely the stress relaxation layer 40 was to peel off, resulting in fewer groove cracks in the main grooves 30 and superior stress relaxation layer durability.

[0102] The performance evaluation test was carried out on 12 types of pneumatic tires, including Examples 1 to 9 which are pneumatic tires 1 according to the present invention, and Comparative Examples 1 to 3 which are pneumatic tires compared with pneumatic tire 1 according to the present invention. SThe maximum thickness T of the stress relaxation layer 40 in the range Ma and minimum film thickness T Mi Difference with T Ma -T Mi In Comparative Example 2, this difference T Ma -T Mi In Comparative Example 3, the stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A and the maximum film thickness T Ma and minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is smaller than 0.85.

[0103] In contrast, in Examples 1 to 9, which are examples of the pneumatic tire 1 according to the present invention, all of the stress acting length L S The average thickness T of the stress relaxation layer 40 in the range A The maximum thickness T of the stress relaxation layer 40 is in the range of 5 μm or more and 200 μm or less. Ma and minimum film thickness T Mi Difference with T Ma -T Mi The average thickness T of the stress relaxation layer 40 is in the range of 3 μm or more and 100 μm or less. A and the maximum film thickness T Ma and minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is in the range of 0.85 or more and 10 or less. Furthermore, in the pneumatic tires 1 according to Examples 1 to 9, the tensile stress M M and the tensile stress M of the tread rubber 4 T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness T Mi and the rubber hardness H of the stress relaxation layer 40. M and tread rubber 4 rubber hardness H T and the maximum thickness T of the stress relaxation layer 40 Ma and minimum film thickness TMi The value obtained by multiplying the difference between S The coefficient of variation of the thickness of the stress relaxation layer 40 in the range of S The angle θ formed by the imaginary line L1 and the imaginary line L2 in the stress relaxation layer 40 in this range is different for each of the stress relaxation layers 40 in this range.

[0104] As a result of conducting performance evaluation tests using these pneumatic tires 1, it was found that the pneumatic tires 1 according to Examples 1 to 9 were able to improve both groove crack resistance and stress relaxation layer durability compared to Comparative Example 1, as shown in Fig. 12. It was also found that the pneumatic tires 1 according to Examples 1 to 9 were able to improve at least one of the performances, groove crack resistance and stress relaxation layer durability, without deteriorating either performance compared to Comparative Examples 2 and 3. In other words, the pneumatic tires 1 according to Examples 1 to 9 can suppress peeling of the stress relaxation layer 40 and effectively suppress the occurrence of groove cracks.

[0105] The present disclosure encompasses the following inventions. Invention[1] Tread rubber exposed on the tread surface; A main groove formed on the tread surface; a stress relaxation layer disposed on a surface of the groove bottom of the main groove; A tire comprising: the stress relaxation layer contains a diene rubber material and a non-diene rubber material as main components, carbon, a vulcanizing agent, and a vulcanization accelerator; The groove width W of the main groove G [mm] and groove depth H G [mm] and the value L calculated from the above formula (1) S The stress acting length L S In this case, The stress relaxation layer is The stress acting length L in the extension direction of the main groove in which the stress relaxation layer is arranged S The average thickness T A is in the range of 5 μm or more and 200 μm or less, The maximum thickness T of the stress relaxation layerMa and minimum film thickness T Mi Difference with T Ma -T Mi is in the range of 3 μm or more and 100 μm or less, The average thickness T A and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi Ratio to T A / (T Ma -T Mi ) is in the range of 0.85 or more and 10 or less. Invention[2] The stress relaxation layer has a tensile stress M M and the tensile stress M of the tread rubber at 100% elongation T and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi The tire according to the invention [1], wherein the relationship of the above formula (2) is satisfied. Invention[3] The stress relaxation layer has a rubber hardness H M and the rubber hardness H of the tread rubber T and the maximum film thickness T Ma and the minimum film thickness T Mi Difference with T Ma -T Mi The tire according to the invention [1] or [2], wherein the relationship of the above formula (3) is satisfied. Invention[4] The stress relaxation layer has a stress acting length L S A tire according to any one of inventions [1] to [3], wherein the coefficient of variation of thickness within the range is in the range of 2% to 40%. Invention[5] The stress relaxation layer has a stress acting length L S In the range of Maximum film thickness T Ma The surface point at the position of S Ma year, Maximum film thickness T MaThe boundary point with the tread rubber at the position P Ma year, The minimum film thickness T Mi The surface point at the position of S Mi year, The minimum film thickness T Mi The boundary point with the tread rubber at the position P Mi In this case, The boundary point P Mi and the boundary point P Ma The imaginary line L1 connecting the surface point S Mi and the surface point S Ma and the boundary point P Mi The tire according to any one of the inventions [1] to [4], wherein the angle θ formed by the imaginary line L2 passing through the line L1 is within the range of 50°≦θ<90°. [Explanation of symbols]

[0106] 1 pneumatic tire 2 Tread section 3 Tread surface 4 Tread rubber 5 Shoulder section 8 Sidewall 10 Bead section 11 Bead core 12 Bead filler 13 Carcass layer 14 Belt Layer 141, 142 Belt 143 Belt cover 16 Inner liner 17 Rim cushion rubber 18 Tire inner surface 20 Land 30 Main groove 31 Groove bottom 32 Curved section 33 Groove Wall 40 Stress relief layer 41 Adhesive interface 50 Tire manufacturing equipment 60 Paint transfer roller 65 Paint supply section 66 Paint storage section 70 Transfer unit 71 Outer surface 80 Rotating part 90 Support part 95 Rotation axis 100 Extruder

Claims

1. Tread rubber exposed on the tread surface; A main groove formed on the tread surface; a stress relaxation layer disposed on a surface of the groove bottom of the main groove; A tire comprising: the stress relaxation layer contains a diene rubber material and a non-diene rubber material as main components, carbon, a vulcanizing agent, and a vulcanization accelerator; The groove width W of the main groove Ｇ [mm] and groove depth H Ｇ [mm] and the value L calculated from the following formula (1) Ｓ The stress acting length L Ｓ In this case, The stress relaxation layer is The stress acting length L in the extension direction of the main groove where the stress relaxation layer is arranged Ｓ The average thickness T Ａ is in the range of 5 μm or more and 200 μm or less, The maximum thickness T of the stress relaxation layer Ｍａ and minimum film thickness T Ｍｉ Difference with T Ｍａ -T Ｍｉ is in the range of 3 μm or more and 100 μm or less, Said average thickness T Ａ and the maximum film thickness T Ｍａ and the minimum film thickness T Ｍｉ Difference with T Ｍａ -T Ｍｉ Ratio to T Ａ / (T Ｍａ -T Ｍｉ ) is in the range of 0.85 or more and 10 or less. [Equation 1]

2. The stress relaxation layer has a tensile stress M Ｍ and the tensile stress M of the tread rubber at 100% elongation Ｔ and the maximum film thickness T Ｍａ and the minimum film thickness T Ｍｉ Difference with T Ｍａ -T Ｍｉ The tire according to claim 1, wherein the relationship of the following formula (2) is satisfied: 1≦(M Ｍ / M Ｔ )×(T Ｍａ -T Ｍｉ )≦70 ・・・(2)

3. The stress relaxation layer has a rubber hardness H Ｍ and the rubber hardness H of the tread rubber Ｔ and the maximum film thickness T Ｍａ and the minimum film thickness T Ｍｉ Difference with T Ｍａ -T Ｍｉ The tire according to claim 1 or 2, wherein and satisfy the relationship of the following formula (3): -20≦(H Ｔ -H Ｍ )×(T Ｍａ -T Ｍｉ )≦1000 ・・・(3)

4. The stress relaxation layer has a stress acting length L Ｓ 3. The tire according to claim 1, wherein the coefficient of variation of thickness in the range is in the range of 2% to 40%.

5. The stress relaxation layer has a stress acting length L Ｓ In the range of The maximum film thickness T Ｍａ The surface point at the position of S Ｍａ year, The maximum film thickness T Ｍａ The boundary point with the tread rubber at the position P Ｍａ year, The minimum film thickness T Ｍｉ The surface point at the position of S Ｍｉ year, The minimum film thickness T Ｍｉ The boundary point with the tread rubber at the position P Ｍｉ In this case, The boundary point P Ｍｉ and the boundary point P Ｍａ Imaginary line L connecting １ and the surface point S Ｍｉ and the surface point S Ｍａ An imaginary line L connecting ０ and extends perpendicularly from the boundary point P Ｍｉ A virtual line L passing through ２ 3. The tire according to claim 1, wherein the angle θ formed by the above is in the range of 50°≦θ<90°.

Images