tire

Abstract

To provide a tire that ensures the same antistatic effect as conventional tires, can be obtained through a relatively simple manufacturing process, and can suppress the occurrence of groove cracks at the bottom of the main grooves. [Solution] The stress relaxation layer (52) mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains carbon and a vulcanizing agent, and the surface resistivity of the stress relaxation layer is 1.0 × 10 8 The stress relaxation layer is less than or equal to [Ω / sq] and is in contact with the tire body (TMP), thereby forming a conductive path from the tire body to the tread surface (37) of the tire surface layer (TSP).

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] A dredge is formed by a non-conductive rubber exposed on the tread surface portion of the tire and a conductive rubber disposed inside the non-conductive rubber and partially exposed on the tread surface portion, which contributes to antistatic electricity. A tire having a so-called earth tread structure is known in which the base portion of the conductive rubber is disposed near the end of the belt layer of the shoulder portion except for the center portion region in the tread width direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the tire disclosed in Patent Document 1, the structure of the tread portion composed of non-conductive rubber and conductive rubber is relatively complicated. Therefore, especially at the time of green tire molding, it is not only complicated to arrange these different rubber materials at predetermined positions, but it may also be difficult to accurately maintain the above-mentioned predetermined positions after vulcanization due to rubber flow that may occur during vulcanization.

[0005] In recent years, there has also been a widespread demand for the development of a tire that suppresses the occurrence of groove cracks at the bottom of the main groove.

[0006] The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a tire that can ensure an antistatic electricity effect equivalent to that of a conventional tire, can be obtained by a relatively easy manufacturing process, and can suppress the occurrence of groove cracks at the bottom of the main groove.

Means for Solving the Problems

[0007] The tire of the present invention comprises a tire body portion having a carcass, belts and a belt reinforcing layer, and a tire surface portion disposed radially outward of the tire body portion and including a base tread, cap tread and wingtip, wherein the tread surface of the tread rubber is divided into land areas by main grooves, a stress relaxation layer is formed on the surface of at least one groove bottom of the main grooves, the stress relaxation layer mainly consists of a diene-based rubber material and a non-diene-based rubber material and also contains carbon and a vulcanizing agent, and the surface resistivity of the stress relaxation layer is 1.0 × 10⁻⁶ 8 The stress relaxation layer is less than or equal to [Ω / sq], and is characterized in that a conductive path is formed from the tire body to the tread surface of the tire surface layer due to the contact of the stress relaxation layer with the tire body. [Effects of the Invention]

[0008] According to the present invention, by controlling the material, surface resistivity, and formation position of the stress relaxation layer, a conductive path is formed from the tire body to the tread surface of the tire surface layer, thereby providing a tire that can be manufactured using a relatively simple process while ensuring an antistatic effect equivalent to that of conventional tires, and that can suppress the occurrence of groove cracks at the bottom of the main grooves. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is an end view showing the meridional cross-sectional shape of the tire of 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 shows an example of a conductive path by the stress relaxation layer in this embodiment. Figure 3(A) is a perspective view showing a part of the tire surface TSP in a sheet state before green tire molding, and Figure 3(B) is a meridional cross-sectional view of the tire showing the tire surface TSP in the finished tire. [Figure 4]Figure 4 shows an example of a conductive path by the stress relaxation layer in this embodiment. Figure 4(A) is a perspective view showing a part of the tire surface TSP in a sheet state before green tire molding, and Figure 4(B) is a meridional cross-sectional view of the tire showing the tire surface TSP in the finished tire. [Figure 5] Figure 5 is a plan view of the tire of this embodiment, where Figure 5(A) shows the new state and Figure 5(B) shows the end-of-wear state. [Figure 6] Figure 6 is a perspective view showing variations in the application state of the stress relaxation layer material in the sheet state of the tire surface TSP before green tire molding. [Figure 7] Figure 7 is a perspective view showing variations in the application state of the stress relaxation layer material in the sheet state of the tire surface TSP before green tire molding. [Figure 8] Figure 8 is a perspective view showing variations in the application state of the stress relaxation layer material in the sheet state of the tire surface TSP before green tire molding. [Figure 9] Figure 9 is a meridional cross-sectional view of the tire according to this embodiment, showing the tire body TMP and the tire surface layer TSP separated. [Figure 10] Figure 10 is a perspective view showing the state of application of the stress relaxation layer material to the TSP (Total Stress Patch) in the sheet state before green tire molding. [Figure 11] Figure 11 is a meridional cross-sectional view of the tire according to this embodiment, showing the tire body TMP and the tire surface layer TSP separated. [Figure 12] Figure 12 is a meridional cross-sectional view of the tire according to this embodiment, showing the tire body TMP and the tire surface layer TSP separated. [Figure 13] Figure 13 is a meridional cross-sectional view of the tire according to this embodiment. [Figure 14] Figure 14 is a meridional cross-sectional view of a tire showing the formation of stress relaxation layers made of different materials in the tire surface layer TSP of this embodiment. [Modes for carrying out the invention]

[0010] <Aspects of the Present Invention> The present invention includes the following aspects. [Aspect 1] A tire main body portion including a carcass, a belt, and a belt reinforcing layer, and a tire surface layer portion disposed on the outer side in the tire radial direction of the tire main body portion and including a base tread, a cap tread, and a wing tip. On the tread surface of the tread rubber, land portions are partitioned by main grooves, and a stress relaxation layer is formed on the surface of at least one groove bottom of the main grooves. The tire is characterized in that the stress relaxation layer is mainly composed of a diene rubber material and a non-diene rubber material and contains carbon and a vulcanizing agent, the surface resistivity of the stress relaxation layer is 1.0×10 8 [Ω / sq] or less, and a conductive path is formed from the tire main body portion to the tread surface of the tire surface layer portion by the stress relaxation layer contacting the tire main body portion. [Aspect 2] The tire according to Aspect 1, wherein the stress relaxation layer extends from the groove bottom of the main groove through the splice portion of the tire surface layer portion to the inner surface in the tire radial direction of the tire surface layer portion. [Aspect 3] The tire according to Aspect 1 or 2, wherein the stress relaxation layer extends from the groove bottom of the main groove through the tread surface and the end portion in the tire width direction to the inner surface in the tire radial direction of the tire surface layer portion. [Aspect 4] On at least one side in the tire width direction of the tire equatorial plane, a stress relaxation layer is formed on the tread surface of the main groove outer region, which is at least a part of the region in the tire circumferential direction in the tire width direction region from the opening end of the main groove closest to the grounding end to the end portion in the tire width direction of the tread surface. The tire according to any one of Aspects 1 to 3, wherein a transverse groove or a sipe extending from the main groove to the grounding end is formed in the main groove outer region. [Aspect 5] A tire according to any one of embodiments 1 to 4, wherein separate stress-relieving layers provided in different main grooves are connected to each other at least one of the outer surface portion, inner surface portion, and splice portion of the tire surface layer. [Form 6] The tire according to any one of embodiments 1 to 5, wherein the tire width direction forming region of the stress relaxation layer on the inner surface portion of the tire surface layer overlaps with the tire width direction forming region of at least one of the belt and the belt reinforcement layer. [Form 7] A tire according to any one of embodiments 1 to 6, wherein the thickness of the stress relaxation layer at the center of the tire width direction of the bottom of the main groove is 5 μm or more and 200 μm or less. [Form 8] A tire according to any one of embodiments 1 to 7, wherein the circumferential dimension Wt of the stress relaxation layer on the inner surface of the tire surface layer is 1.1 times or more and 10 times or less the widthwise dimension Wg of the stress relaxation layer formed in the main groove.

[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 refer to the shape, position, and length in the meridional cross-section of the tire (in an unloaded state with the tire mounted on a standard rim and filled to standard internal pressure). 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 of this embodiment. Note that the figure shows the tire portion in an unloaded state, mounted on a standard rim and subjected to standard 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 reinforcement layer 24, sidewall rubber 36, and tread rubber 38, just like a typical tire.

[0014] The tread rubber 38 includes an undertread 38a, a cap tread 38b, and a wingtip 38c, and has a tread surface 37 exposed at the outermost radial end of the tire. It is formed of a rubber material with 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 38 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. The amine-based anti-aging agent is selected from, for example, "N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine" and "2,2,4-trimethyl-1,2-dihydroquinoline polymer". The tread rubber 38 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] In the following, with respect to the tire 10 shown in Figure 1, the tread rubber 38 (consisting of the undertread 38a, cap tread 38b, and wingtip 38c in the same figure) will be referred to as the tire surface layer TSP, and the parts other than the tire surface layer TSP (consisting of the inner liner 19, carcass 20, belt 22, belt reinforcement layer 24, and sidewall rubber 36 in the same figure) will be referred to as the tire body TMP.

[0019] 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 42 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 both edges of the groove bottom 44 in the tire width direction, and (the outermost position of the groove walls 46 in the tire radial direction) serves as the reference for the groove width of the circumferential main groove 40. The pair of groove walls 46 are composed of surfaces that intersect the tread surface 37, with the shorter side being the direction inclined in the groove width direction (tire width direction in the example shown in Figure 2) relative to the tire diameter direction, and the longer side being the tire circumferential direction.

[0020] [Characteristics of the basic form of a tire] (Stress relaxation layer) As shown in Figure 2, 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 42, which is partitioned 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.

[0021] The stress-relaxing layer 52 may include a wall portion 56 and an outer 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 outer surface portion 58 is provided on the tread surface 37, starting from the edge 48. One end 58G of the outer 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 in the tire width direction (not shown) is located spaced apart from the main groove 40 starting from the edge 48, but there are no particular restrictions on its specific position.

[0022] The stress relaxation layer 52 mainly consists of diene-based rubber material and 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 rubber (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 rubber (butyl rubber (IIR), ethylene-propylene rubber (EPDM, EPM), urethane rubber, silicone rubber, etc.). Furthermore, in order to ensure weather resistance, the stress relaxation layer 52 basically does not contain resin components.

[0023] The stress relaxation layer 52 does not need to contain vulcanization accelerators or anti-aging agents. This is because, as shown in Figure 2, the thickness Ga (shortest distance from the surface of the stress relaxation layer 52 to the land area 42) of the stress relaxation layer 52 is small, and anti-aging agents contained in the adjacent tread rubber 38 migrate to the stress relaxation layer 52, thus compensating for the absence of these agents. Furthermore, by not including vulcanizing agents or anti-aging agents, it is possible to prevent staining such as discoloration caused by their adhesion to the mold.

[0024] The stress relaxation layer 52 can further suppress crack formation by containing an anti-aging agent. When 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.

[0025] Under these conditions, the surface resistivity of the stress relaxation layer 52 is 1.0 × 10⁻⁶. 8 It is less than or equal to [Ω / sq]. Since the surface resistivity of the stress relaxation layer 52 is lower than that of the other rubber layers (tread rubber) on which the stress relaxation layer 52 is formed, the stress relaxation layer 52 helps to efficiently form the conductive paths described later.

[0026] Furthermore, in the tire 10 of this embodiment, although not shown in Figure 2, the stress relaxation layer 52 is in contact with the tire body TMP, thereby forming a conductive path (specifically shown in Figure 3 and later) from the tire body TMP to at least the vicinity of the tread surface 37 of the tire surface TSP.

[0027] Specifically, regarding this conductive path, as shown in Figure 3A (referring to the sheet state of a part of the tire surface layer TSP before green tire molding) and Figure 3B (referring to the tire surface layer TSP in the finished tire), the stress relaxation layer 52 has a bottom portion 54, a wall portion 56, and an outer surface portion 58, and the outer surface portion 58 reaches the tire widthwise end E of the tread surface 37. Furthermore, the stress relaxation layer 52 can be extended so that it folds back at the end E to the inner surface portion 60 of the tire surface layer TSP. Note that in Figure 3(A), the parts corresponding to the bottom portion 54, wall portion 56, outer surface portion 58, and inner surface portion 60 shown in Figure 3(B) are denoted by the same reference numerals as the parts shown in Figure 3(B).

[0028] Alternatively, this conductive path can be formed such that, as shown in Figure 4A (referring to the sheet state of a part of the tire surface layer TSP before green tire molding) and Figure 4B (referring to the tire surface layer TSP in the finished tire), the stress relaxation layer 52 has a bottom portion 54 and a wall portion 56, and extends from the bottom portion 54 and the wall portion 56 to the inner surface portion 60 (of the tire surface layer TSP) via a splice portion 62 (formed on the joint surface of the tread rubber). Note that in Figure 4(A), the parts corresponding to the bottom portion 54, wall portion 56, and inner surface portion 60 shown in Figure 4(B) are denoted by the same reference numerals as the parts shown in Figure 4(B).

[0029] As shown in the examples in Figures 3 and 4, a conductive path is formed by the stress relaxation layer 52 from the groove surface including the bottom 54 to the inner surface 60 of the tire surface layer TSP, although the route taken differs. Therefore, the stress relaxation layer 52 in the finished tire extends to at least the vicinity of the tire body TMP shown in Figures 1 and 2 (specifically, at least one of the outermost belt layer 22b and belt reinforcement layer 24 in the radial direction of the tire), and consequently a conductive path is formed from the tire body TMP to the tread surface 37 (or the vicinity of the tread surface 37) of the tire surface layer TSP.

[0030] <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 changing various compounding agents (such as anti-aging agents) in the tread rubber.

[0031] 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.

[0032] Therefore, in the tire of this embodiment, as shown in Figures 1 to 4, a stress relaxation layer 52 is formed at least at the bottom of the groove 44 in the land portion partitioned by the main groove 40 to suppress the occurrence of groove cracks (GC).

[0033] Under these premises, in the tire 10 of this embodiment, the stress relaxation layer 52, which is mainly composed of rubber, does not contain resin components from the viewpoint of ensuring weather resistance, and the occurrence of groove cracks (GC) can be suppressed by using the above-mentioned predetermined diene-based rubber material and non-diene-based rubber material as the main components. Furthermore, in the tire 10 of this embodiment, in order to also provide an antistatic effect to the stress relaxation layer 52, the surface resistivity of the stress relaxation layer 52 is set to 1.0 × 10⁻⁶ 8 The stress level is set to [Ω / sq] or less, and the stress relaxation layer 52 is responsible for one end of the conductive path from the tire body TMP to the tread surface 37 of the tire surface TSP.

[0034] Furthermore, as will be described later, since the stress relaxation layer 52 is formed by applying a stress relaxation layer material to a predetermined location on the green tire before vulcanization, the tire 10 of this embodiment is easier to manufacture compared to conventional tires employing an earth-tread structure.

[0035] Furthermore, in the tire 10 of this embodiment, a stress-relieving layer 52 is formed on the surface of at least the groove bottom 44, and the stress-relieving layer 52 contains a vulcanizing agent mainly composed of diene-based rubber material and non-diene-based rubber material, and the stress-relieving layer 52 not only has a predetermined surface resistivity but also forms part of the predetermined conductive path described above. With this configuration, the stress-relieving layer 52, which can be easily manufactured and suppress the occurrence of groove cracks, can also be given a so-called antistatic effect, which is to release the electric charge accumulated on the tire from the vehicle body through the wheel to the outside.

[0036] Accordingly, according to the tire 10 of this embodiment, by controlling the material, surface resistivity, and formation position of the stress relaxation layer 52, a conductive path can be formed from the tire body TMP to the tread surface 37 of the tread surface layer TSP. This makes it possible to provide a tire that can be manufactured using a simpler process than conventional tires, while ensuring the same antistatic effect as conventional tires (tires employing a conventional earth tread structure), and that can suppress the occurrence of groove cracks (GC) at the bottom of the main grooves 40.

[0037] According to the tire 10 of this embodiment, since the stress relaxation layer 52 is conductive, a conductive rubber layer like that in conventional Earth Red structures is unnecessary, and static electricity can be discharged to the outside at low cost.

[0038] In particular, in the example shown in Figure 4, the stress relaxation layer 52 is formed on both sides of the tire surface layer TSP via the splice portion 62, making it easy to form a conductive path from the tire body TMP to the tread surface 37 of the tire surface layer TSP. That is, in the example shown in Figure 4, the stress relaxation layer can be formed simply by applying the stress relaxation layer material (paint) in a straight line to the rubber sheet for the tire surface layer TSP after the sheet cutting process for the tread surface layer TSP and before the molding of the green tire, making the manufacturing process simpler (compared to the example shown in Figure 3).

[0039] In contrast, in the example shown in Figure 3, unlike the example shown in Figure 4, the stress-relieving layer material is not applied to the jointed surface of the tread rubber. Therefore, the adhesion between the jointed surfaces of the sheets shown in Figure 3(A) after overlapping and vulcanization can be maintained better than in the example shown in Figure 4, and consequently, the tire can achieve superior durability. In the example shown in Figure 3, the stress-relieving layer 52 (especially the inner surface portion 60) is brought in close proximity to either the belt 22 or the belt reinforcement layer 24 of the tire body TMP. More specifically, the inner surface portion 60 of the stress-relieving layer 52 extends from the bottom portion 54, the wall portion 56, and the outer surface portion 58, through the tire width direction end E, to a position close to at least one of the belt 22 or the belt reinforcement layer 24. However, the inner surface portion 60 can also be further extended inward in the tire width direction.

[0040] The surface resistivity of the stress relaxation layer 52 is 5.0 × 10⁻⁶ (from the viewpoint of efficiently releasing the charge accumulated on the tire from the vehicle body via the wheel to the outside through tire contact). 8 It is preferable that the value is less than or equal to [Ω / sq], and 1.0 × 10 7 It is even more preferable that the value be less than or equal to [Ω / sq], and 5.0 × 10 6 It is extremely preferable that the value be less than or equal to [Ω / sq].

[0041] <Preferred tire configuration> Figure 5 is a plan view of the tire of this embodiment, where (A) shows the new state and (B) shows the end-of-wear state. Here, the end-of-wear state refers to the state in which the so-called "wear indicator" is exposed on the circumference of the tire.

[0042] In the tire of this embodiment, it is preferable that a stress relaxation layer 52 is formed on the tread surface 37 of the outer main groove region RO, which is at least a portion of the tire circumferential region (the lightly colored region in Figure 5(A)) of the tire width region from the opening end of the main groove 40S closest to the contact end GE to the tire width end E, E of the tread surface 37, on at least one side in the tire width direction of the tire equatorial plane CP (both sides in the example shown in Figure 5), and that a lateral groove 64 (or sipe) extending from the main groove 40S to at least the contact end GE is formed in the outer main groove region RO.

[0043] Here, the lateral groove 64 can be any groove that extends from the main groove 40S to at least the ground edge GE, as shown in Figure 5. The same applies to the sipe.

[0044] In a new condition (Figure 5(A)), a stress-relieving layer 52 is formed in the outer region RO of the main groove. The stress-relieving layer 52 is formed not only on the tread surface 37 and the lateral grooves 64 (groove bottom and groove walls) in the outer region RO of the main groove, but also on all other grooves (groove bottom and groove walls). Furthermore, in the outer region RO of the main groove, the lateral groove 64 extends from the innermost position in the tire width direction adjacent to the main groove 40S to at least the contact edge GE (in Figure 5(A), beyond the contact edge GE to the vicinity of the tire width direction end E of the tread surface 37), and at least one lateral groove 64 with a certain depth is formed. Therefore, even in the final stages of wear, the stress-relieving layer 52 formed on the groove bottom and groove walls of the lateral groove 64 remains, so that a conductive path by the stress-relieving layer 52 is maintained from the surface of the main groove 40S through the surface of the lateral groove 64 to the contact edge. In Figure 5(A), the stress relaxation layer 52 formed in the region RO outside the main groove is shown with a relatively light color, while the conductive paths formed by the main groove 40S and the transverse groove 64 are shown with a relatively dark color.

[0045] Furthermore, although not shown in Figure 5(A), the stress relaxation layer 52 extends from the outer region RO of the main groove, through the tire widthwise end E of the tread surface 37, and folds back to the inner surface of the tire surface layer TSP, extending to at least the vicinity of at least one of the belt and belt reinforcement layer of the tire body TMP.

[0046] In contrast, in the final wear stage (Figure 5(B)), the stress relaxation layer 52 has disappeared due to wear in the area outside the main groove RO (the area enclosed by two parallel dotted lines in the tire circumferential direction), except for the lateral groove 64. However, the stress relaxation layer 52 remains on the inner surface (at least the groove bottom) of the lateral groove 64. Therefore, the stress relaxation layer 52 extends continuously from the groove bottom of the lateral groove 64, through the tire widthwise end E of the tread surface 37, and folds back to the inner surface of the tire surface layer TSP. Similar to the example shown in Figure 5(A), it can extend to at least the vicinity of at least one of the belt and belt reinforcement layer of the tire body TMP.

[0047] In this way, by forming lateral grooves 64 (or sipes) in the outer region RO of the main groove, extending from the main groove 40 to at least the contact edge GE, a conductive path can be maintained from the tire body TMP to the tread surface 37 of the tire surface TSP even in the final stages of wear. This ensures an antistatic effect equivalent to that of conventional tires, while suppressing the occurrence of groove cracks (GC) not only in the main groove 40 but also at the bottom of the lateral grooves 64.

[0048] Figure 6 is a perspective view showing variations in the application state of the stress relaxation layer material in the sheet state of the tire surface TSP before green tire molding.

[0049] In the four examples shown in Figures 6(A) to 6(D), two circumferential main grooves 40 are formed on the tread surface 37 of the tire surface layer TSP, and a stress-relaxing layer material is applied to these circumferential main grooves 40 from the groove bottom to the opening end of the groove wall. Note that each part of the sheet-like tire surface layer TSP shown in Figures 6(A) and later is denoted by a reference numeral corresponding to the part of the actual finished tire.

[0050] Under these premises, in the example shown in Figure 6(A), the stress relaxation layer material is applied to one groove outer region RO (a predetermined region in the tire width direction, from one circumferential main groove 40 to the tire width direction end E of the tread surface 37). The stress relaxation layer material is then folded back from the tire width direction end E and applied to the inner surface portion 60 of the tire surface layer TSP.

[0051] In the example shown in Figure 6(B), the stress relaxation layer material is applied to two outer groove regions RO (the tire width region from each circumferential main groove 40, 40 to each tire width direction end E, E of the tread surface 37, each a predetermined region in the tire circumferential direction). The stress relaxation layer material is then folded back from these two tire width direction ends E, E and applied to the inner surface portion 60 of the tire surface layer TSP, thus connecting them.

[0052] In the example shown in Figure 6(C), in addition to the example shown in Figure 6(B), the stress relaxation layer material is also applied to the region between the two circumferential main grooves 40, 40 (main groove region RI) so as to connect these two circumferential main grooves 40, 40.

[0053] In the example shown in Figure 6(D), the outer groove region RO and inner surface portion 60 shown in Figure 6(A) are provided at two locations on the tire circumference, and the stress relaxation layer material is applied at these two locations in the same manner as in the example shown in Figure 6(A).

[0054] Thus, it is preferable to provide multiple main groove outer regions RO to which the stress relaxation layer material is applied, or to apply the material to both the main groove outer regions RO and the main groove inner regions IR. By applying the stress relaxation layer material to multiple main groove outer regions RO, multiple conductive paths can be created between the tire body TMP and the tire surface layer TSP. Even if one conductive path is lost due to uneven wear, the antistatic effect can be reliably maintained by continuing to use the other conductive paths.

[0055] Furthermore, by applying stress-relaxing layer material to both the outer RO region and the inner IR region of the main groove, the conductive paths can be made even more complex, and the antistatic effect can be more reliably maintained even when partial conductive paths are lost (for example, due to uneven wear).

[0056] Although not shown in Figures 6(A) to 6(D), a circumferential main groove 40 coated with a stress-relaxing layer material may be separately formed, which is not electrically connected to the outer region RO or the inner region RI of the main groove.

[0057] Figures 7 and 8 are perspective views showing variations in the application state of the stress-relieving layer material in the sheet state of the tire surface layer TSP before green tire molding, respectively. In particular, the examples shown in Figure 7 are cases where the stress-relieving layer material is applied to both the front and back surfaces of the tire surface layer TSP via the splice portion 62, while the examples shown in Figure 8 are cases where the stress-relieving layer material is applied to both the front and back surfaces of the tire surface layer TSP via the tire widthwise end E.

[0058] Looking at each figure in Figure 7, the example shown in Figure 7(A) is an example in which the stress-relieving layer material applied to two circumferential main grooves 40 is connected to the tread surface 37 of the tire surface layer TSP via the main groove region RI. The example shown in Figure 7(B) is an example in which the stress-relieving layer material applied to the inner surface portion 60 of the tire surface layer TSP is connected to the inner surface portion 60. Furthermore, the example shown in Figure 7(C) is an example in which the stress-relieving layer material applied to two circumferential main grooves 40 is connected to a splice portion 62 and a part of the inner surface portion 60 adjacent to it. The example shown in Figure 7(D) is an example in which the width of the splice portion 62 is narrower than that of the example shown in Figure 7(C).

[0059] Similarly, looking at each figure in Figure 8, the example shown in Figure 8(A) is an example in which the stress-relieving layer material applied to the two circumferential main grooves 40 extends to the inner surface portion 60 via the outer groove region RO and is connected to each other. The example shown in Figure 8(B) is an example in which, unlike the example shown in Figure 8(A), the stress-relieving layer material applied to the two circumferential main grooves 40 is also connected to the tread surface 37 of the tire surface portion TSP via the inner groove region RI. Furthermore, the example shown in Figure 8(C) is an example in which, unlike the example shown in Figure 8(B), only one of the stress-relieving layer materials applied to the circumferential main grooves 40 extends to the inner surface portion 60 via the outer groove region RO.

[0060] In the tire of this embodiment, as shown in Figures 7 and 8, it is preferable that the separate stress-relieving layer materials applied to different main grooves 40, 40 are connected at least one of the tread outer surface portion (RO or RI), the tread inner surface portion 60, and the splice portion 62.

[0061] As shown in the examples in Figures 7 and 8, groove cracks (GC) are suppressed in multiple circumferential main grooves 40, 40, and at the same time, even when the tire deforms during vehicle operation, a conductive path is reliably formed from the tire body TMP to the tread surface 37 of the tire surface TSP, thereby achieving an antistatic effect equivalent to that of conventional tires.

[0062] For example, if a stone or other object gets caught in one of the main grooves while the vehicle is in motion, the stress-relaxing layer may be interrupted midway along its longitudinal direction. Also, if the steering wheel is turned suddenly, the tire may not make sufficient contact with the road surface. However, even in these cases, a tire with the configuration shown in Figures 7 and 8 can maintain a high level of antistatic effect by having multiple conductive paths from the inner surface portion 60 to the outer surface portion (RO or RI).

[0063] As mentioned above, the example shown in Figure 7(D) is an example in which the width of the stress relaxation layer material in the splice portion 62 is narrower than the example shown in Figure 7(C). In the example shown in Figure 7(D), the vulcanization adhesion of the sheet edge of the tread rubber including the splice portion 62 is better, but the resistance value at the sheet edge increases. For this reason, in the example shown in Figure 7(D), it is even more preferable to increase the thickness of the stress relaxation layer material in order to reduce the resistance value at the sheet edge.

[0064] Figure 9 is a meridional cross-sectional view of the tire according to this embodiment, showing the tire body TMP and the tire surface layer TSP separated. In the example shown in Figure 9, the stress relaxation layer 52 extends across the bottom 54, wall 56, outer surface 58, tire widthwise end E, and inner surface 60.

[0065] In the tire of this embodiment, as shown in Figure 9, it is preferable that the tire width direction forming region R1 of the stress relaxation layer 52 on the inner surface portion 60 of the tire surface portion TSP overlaps with the tire width direction forming region R2 of at least one of the belt 22 and belt reinforcement layer 24, which are components of the tire body portion TMP.

[0066] The belt 22 and belt reinforcement layer 24 included in the tire body TMP tend to have lower electrical resistance compared to other rubber layers included in the tire body TMP. By overlapping the forming region R1 and the forming region R2, the stress relaxation layer 52 formed on the inner surface portion 60 of the tire surface layer TSP can be reliably brought into contact with at least one of the belt 22 and the belt reinforcement layer 24. This allows the electric charge accumulated on the tire from the vehicle body via the wheel to be released to the outside more efficiently by contact with the ground, further enhancing the antistatic effect of the stress relaxation layer 52.

[0067] Next, in the tire of this embodiment, it is preferable that the thickness of the stress relaxation layer 52 at the center in the tire width direction of the groove bottom 44 of the main groove 40 shown in Figure 2 is 5 μm or more and 200 μm or less.

[0068] By making the stress relaxation layer 52 thicker than 5 μm, the stress relaxation effect of the stress relaxation layer 52 is further enhanced, and the occurrence of groove cracks at the bottom of the main groove 40 can be further suppressed. On the other hand, by making the stress relaxation layer 52 thicker than 200 μm, the conformability of the stress relaxation layer 52 during deformation of the tread rubber 38 can be ensured, preventing the stress relaxation layer 52 from peeling off from the tread rubber 38, thereby improving their adhesion and ultimately increasing the durability of the tire.

[0069] 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.

[0070] Figure 10 is a perspective view showing the state of application of the stress relaxation layer material to the TSP (Total Stress Patch) in the sheet state before green tire molding.

[0071] In the tire of this embodiment, as shown in Figure 10, it is preferable that the circumferential dimension Wt of the inner surface portion 60 of the stress relaxation layer material applied to the tire surface portion TSP is 1.1 times or more and 10 times or less of the tire widthwise dimension Wg of the stress relaxation layer material applied to the main groove 40.

[0072] Here, the tire widthwise dimension Wg of the stress relaxation layer material formed in the main groove 40 refers to the total tire widthwise dimension of the bottom portion 54 and wall portion 56 shown in Figure 2, and does not include the tire widthwise dimension of the outer surface portion 58 shown in Figure 2.

[0073] The stress-relaxing layer material applied to the inner surface portion 60 of the tread surface layer TSP tends to decrease in thickness due to rubber flow during vulcanization, which may lead to an increase in electrical resistance. To overcome this, by making the tire circumferential dimension Wt 1.1 times or more the tire width dimension Wg, a better antistatic effect can be achieved, especially on the inner surface portion 60.

[0074] In contrast, by making the tire circumferential dimension Wt 10 times or less of the tire widthwise dimension Wg, the circumferential dimension Wt is not made excessively large, and the adhesion between the tire body TMP and the tire surface layer TSP can be maintained even better, thereby achieving even greater durability of the tire.

[0075] Furthermore, it is even more preferable that the tire circumferential dimension Wt be 1.2 times or more and 8.0 times or less the tire widthwise dimension Wg, and it is extremely preferable that it be 1.3 times or more and 7.0 times or less.

[0076] <Other suitable examples of tires> The above describes in detail the conductive path using the stress relaxation layer 52 in the tire surface layer TSP of the tire 10 of this embodiment. Below, an example of a conductive path using the stress relaxation layer 66 in the tire body TMP (see Figures 11 and 12) will be described.

[0077] Figures 11 and 12 are meridional cross-sectional views of the tire of this embodiment, showing the tire body TMP and the tire surface layer TSP separated, respectively.

[0078] The tire shown in Figure 11 is an example of Case 1 (C1), in which the stress relaxation layer 66 is provided along the outer edge of the carcass 20 in the tire width direction. In this example, extending the stress relaxation layer 66 to the outer edge of the belt 22 in the tire width direction is preferable in that it can form a better conductive path. That is, in this example, a conductive path can be formed from the stress relaxation layer 66 to the stress relaxation layer 52 formed as the inner surface portion 60 of the tire surface portion TSP via the belt 22 and belt reinforcement layer 24. Furthermore, it is sufficient to form at least one such path on the circumference of the tire.

[0079] In contrast, the tire shown in Figure 12 is an example of Case 2 (C2), in which the stress relaxation layer 66 is provided at the outermost position in the tire width direction of the tire body TMP, extending from the bead portion 12 to the shoulder portion 16. In this example, it is preferable to bring the stress relaxation layer 66 into contact with the stress relaxation layer 52 formed as the inner surface portion 60 of the tire surface portion TSP, as this allows for the formation of a better conductive path. That is, in this example, the stress relaxation layer 66 and the stress relaxation layer 52 can be in direct contact to form a conductive path. Furthermore, while it is sufficient to form such a path at least in one location on the circumference of the tire, it may also be formed around the entire circumference of the tire.

[0080] Similarly, the tire shown in Figure 12 is an example of case 3 (C3), in which the stress relaxation layer 66 is provided at the innermost position in the tire width direction, extending from the bead portion 12 to the tread portion 18. In this example, it is preferable to extend the stress relaxation layer 66 to the tire width direction forming region of the belt reinforcement layer 24, as this allows for the formation of a better conductive path. That is, in this example, a conductive path can be formed from the stress relaxation layer 66 to the stress relaxation layer 52 formed as the inner surface portion 60 of the tire surface portion TSP via the inner liner 19, carcass 20, belt 22, and belt reinforcement layer 24. Furthermore, it is sufficient to form at least one such path on the tire circumference.

[0081] Figure 13 is a meridional cross-sectional view of the tire of this embodiment. As shown in the figure, on either side of the tire equatorial plane CP in the tire width direction, two belt reinforcing layers 24 are formed on the radially outer side of the belt 22. Belt reinforcing layer 24a is formed over the tire width direction forming region of the belt 22, while belt reinforcing layer 24b is formed only near the outer edge of the belt 22 in the tire width direction. The installation of the belt reinforcing layers 24 increases the rigidity of the tread portion 18, reducing the strain when stress acts on the stress relaxation layer 52 formed in the circumferential main groove 40a to 40c during vehicle operation. This further suppresses the occurrence of groove cracks (GC) at the bottom of the main groove. Based on these findings, it is preferable to form a stress relaxation layer (not shown in Figure 13) in the circumferential main groove 40a to 40c formed in the tire width direction region RW between the two outer ends of the belt reinforcing layer 24 in the tire width direction, as shown in Figure 13. A separate stress relaxation layer can also be formed at the bottom of the circumferential sub-groove 66 shown in Figure 13.

[0082] In such an example, as shown in Figure 13, when multiple belt reinforcing layers 24 are formed, it is preferable to form a stress relaxation layer 52 in the main groove 40 located in the tire width direction region where two or more belt reinforcing layers 24 are formed, as this can further suppress the occurrence of groove cracks (GC) at the bottom of the main groove. In the example shown in Figure 13, the belt reinforcing layers 24 are not formed in the tire width direction region where two or more belt reinforcing layers 24 are formed in any of the main grooves 40a to 40c.

[0083] Figure 14 is a meridional cross-sectional view of a tire showing the formation of stress relaxation layers made of different materials in the tire surface layer TSP of this embodiment. Figure 14(A) is an example in which the material of the stress relaxation layer is different at the tire widthwise end E of the tire surface layer TSP, and Figure 14(B) is an example in which the material of the stress relaxation layer is different at an arbitrary point P on the outer surface portion 58 of the tire surface layer TSP.

[0084] Typically, the stress relaxation layer 52 formed on the tire surface TSP has the advantage of being able to be manufactured at a low cost by forming its constituent parts, the bottom 54, wall 56, and outer surface 58, and the inner surface 60, from the same material. On the other hand, the stress relaxation layer 52 formed as the inner surface 60 is located inside the tire after tire manufacturing, and therefore does not contribute to suppressing groove crack formation, so it only needs to have excellent conductivity.

[0085] Based on these findings, the stress-relieving layer formed as the inner surface portion 60 can be made to reduce the components that decrease the adhesion between rubbers while increasing the components that enhance conductivity, compared to the stress-relieving layers formed as the bottom portion 54 and the wall portion 56. This allows for further reduction of electrical resistance while maintaining adhesion between the tire body portion TMP and the tire surface portion TSP and ensuring tire durability.

[0086] More specifically, regarding the stress relaxation layer formed as the inner surface portion 60, unlike the stress relaxation layers formed as the bottom portion 54 and the wall portion 56, by reducing (or eliminating) the use of non-diene rubber and increasing the amount of carbon black blended in, it is possible to further reduce electrical resistance while maintaining the durability of the tire. Furthermore, to further enhance the conductivity of the stress relaxation layer formed as the inner surface portion 60, it is preferable to replace the carbon black with a grade that has high conductivity.

[0087] Thus, when forming the stress relaxation layer with two types of materials, for example, as shown in Figure 14(A), the material can be changed at the outer edge E in the tire width direction of the tire surface layer TSP, and as shown in Figure 14(B), the material can also be changed at any point P on the outer surface portion 58 of the tire surface layer TSP. In both examples of Figure 14(A) and Figure 14(B), it is preferable that the material used for the stress relaxation layer inside the tire radial direction from the positions E and P where the material is changed is a material that has fewer components that reduce the adhesion between rubbers and more components that enhance conductivity compared to the material used for the stress relaxation layer outside the tire radial direction from the positions E and P.

[0088] <Tire manufacturing method> The tire 10 of this embodiment, as described above, is obtained through the usual manufacturing processes, namely the mixing process of the tire material, the processing process of the tire material, the molding process of the green tire, the vulcanization process, and the inspection process after vulcanization. The manufacturing of the tire 10 of this embodiment is particularly characterized by the formation of conductive paths by stress relaxation layers 52 and 66, as shown in Figures 11 and 12. The formation of conductive paths will be described in detail below, with reference to Figures 11 and 12, divided into the tire body TMP and the tire surface layer TSP.

[0089] (Formation of conductive paths in the tire body TMP) In the case of Case 1 (C1) shown in Figure 11, during the molding process of the green tire, after winding the carcass sheet around the bead core, a coating material for the stress relaxation layer 66 is applied along the outer side of the carcass sheet in the tire width direction, and then the belt material and belt reinforcement layer material are formed sequentially. Alternatively, after manufacturing (rolling) the carcass sheet, the coating material for the stress relaxation layer 66 may be applied to a predetermined position on the sheet, and this sheet may then be wound around the bead core.

[0090] In the case of Case 2 (C2) shown in Figure 12, during the molding process of the green tire, a carcass sheet is wrapped around the bead core, and the belt material, belt reinforcement layer material, and sidewall rubber material are sequentially laminated. Then, a coating material for the stress relaxation layer 66 is applied to the outermost part in the tire width direction, from the bead portion to the shoulder portion of the molded body (part of the green tire). Alternatively, after manufacturing (extruding) the sidewall rubber material, the coating material for the stress relaxation layer 66 may be applied to a predetermined position on the rubber material, and the green tire may be molded using this rubber material.

[0091] In the case of Case 3 (C3) shown in Figure 12, before molding the green tire, a coating material for the stress-relieving layer 66 is applied to a predetermined position on the inner liner material, and the tire body is formed by laminating the carcass and other components using this inner liner material as usual.

[0092] (Formation of conductive paths in the tire surface TSP) In contrast, for the conductive path of the tire surface TSP, in both Figure 11 and Figure 12, after extruding the sheet-like tread member, a stress-relieving layer coating material is applied to the predetermined position of the stress-relieving layer 52 shown in Figures 11 and 12.

[0093] In this way, the tire 10 of this embodiment can be obtained by vulcanizing a green tire using a stress-relaxing layer coating material applied to the tire surface portion TSP (and in some cases, a stress-relaxing layer coating material applied to the tire body portion TMP). Since the material, surface resistivity, and formation position of the stress-relaxing layer are suitably controlled, such a tire can be obtained through a relatively easy manufacturing process while ensuring an antistatic effect equivalent to that of conventional tires by forming a conductive path from the tire body portion to the tread surface of the tire surface portion, and can also suppress the occurrence of groove cracks at the bottom of the main grooves. [Examples]

[0094] Each of the test tires shown below was prepared, and the durability (GC resistance) and antistatic effect (conductivity) of the stress relaxation layer at a test temperature of 50°C were evaluated.

[0095] (Preparation of test tires) Tires were prepared with a tire size of 225 / 65R17, having the tire meridional cross-sectional shape shown in Figure 1, and having stress-relieving layers formed on the surface of the groove bottoms of all circumferential main grooves. These stress-relieving layers were mainly composed of butadiene rubber and butyl rubber, as well as carbon and a vulcanizing agent. These were the tires (Comparative Examples 1 and 2, and the tires from Invention Examples 1-1 to 8-4). In contrast, conventional tires were also prepared, which instead of stress-relieving layers, were equipped with conductive rubber with the structure disclosed in Figure 1 of Patent Document 1, and the rest of the structure was the same as that of the tire in Invention Example 1-1. Each test tire (conventional example, each comparative example, and each invention example) 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 to evaluate the crack resistance and tire electrical resistance at a test temperature of 50°C.

[0096] The conditions for each test tire are as shown in Table 1 below. All terms in Table 1 are equivalent to those explained in this specification, although some descriptions have been simplified.

[0097] (Evaluation of crack resistance at a test temperature of 50°C) Each test tire was left for 240 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.

[0098] (Evaluation of tire electrical resistance) Under conditions of 23°C temperature and 50% humidity, a voltage of 1000[V] was applied, and the electrical resistance value Ω, which is the resistance between the tread surface and the rim, was 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 value indicates lower tire electrical resistance (i.e., higher conductivity).

[0099] [Table 1]

[0100] As shown in Table 1, the technical scope of the present invention is as follows: (The stress relaxation layer mainly consists of diene-based rubber material and non-diene-based rubber material, and also contains carbon and a vulcanizing agent, and the surface resistivity of the stress relaxation layer is 1.0 × 10 8 The tires of Invention Examples 1-1 to 8-4, which are included in the category of (where the stress relaxation layer is less than or equal to [Ω / sq] and the stress relaxation layer is in contact with the tire body, thereby forming a conductive path from the tire body to the tread surface of the tire surface layer), all have been found to have an equivalent antistatic effect compared to conventional tires that are not included in the technical scope of the present invention, while suppressing the occurrence of groove cracks at the bottom of the main grooves. [Explanation of Symbols]

[0101] 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, 24a, 24b Belt reinforcement layer 36 Sidewall rubber 37 Tread surface 38 Tread Rubber 38a Undertread 38b Cap Tread 38c Wingtip 40, 40a, 40b, 40c Circumferential main groove 40S Main groove closest to the grounding end GE 42 Land 44 Groove bottom 46 Ditch wall 48 Edge 52, 66 Stress relaxation layer 54 Bottom 56 Wall 56U one end 56T other end 58 Outer surface 58G one end 60 Inner surface 62 Splice section 64 Yokomizo 66 Circumferential minor groove CP Tire Equatorial Plane E End of tire width direction on tread surface 37 Ga stress relaxation layer thickness GE ground end Any location on the outer surface portion 58 of P R1 Tire width direction formation region of stress relaxation layer 52 on inner surface portion 60 of tire surface layer TSP R2 Belt 22 and belt reinforcement layer 24 at least one of the tire width direction forming regions RI main groove area RO outside main groove area RW tire width direction area TMP Tire Body TSP Tire Surface

Claims

1. A tire comprising a tire body having a carcass, belts and a belt reinforcing layer, and a tire surface portion disposed radially outward of the tire body and including a base tread, cap tread and wingtip, wherein 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 relaxation layer mainly consists of a diene-based rubber material and a non-diene-based rubber material, and also contains carbon and a vulcanizing agent. The surface resistivity of the stress relaxation layer is 1.0 × 10⁻⁶. ８ [Ω / sq] or less, A tire characterized in that the stress-relieving layer is in contact with the tire body, thereby forming a conductive path from the tire body to the tread surface of the tire surface layer.

2. The tire according to claim 1, wherein the stress-relieving layer extends from the bottom of the main groove through the splice portion of the tire surface layer to the radially inner surface of the tire surface layer.

3. The tire according to claim 1 or 2, wherein the stress-relieving layer extends from the bottom of the main groove through the tread surface and the tire widthwise end to the radially inner surface of the tire surface layer.

4. On at least one side of the tire's equatorial plane in the tire's width direction, A stress-relieving layer is formed on the tread surface in the outer region of the main groove, which is at least a portion of the tire circumferential region within the tire width direction, from the opening end of the main groove closest to the contact edge to the tire width direction end of the tread surface. The tire according to claim 1 or 2, wherein a transverse groove or sipe is formed in the region outside the main groove, extending from the main groove to the ground edge.

5. The tire according to claim 1 or 2, wherein separate stress-relieving layers provided in different main grooves are connected to each other at least one of the outer surface portion of the tire surface layer, the inner surface portion of the tread, and the splice portion.

6. The tire according to claim 2, wherein the tire width direction forming region of the stress relaxation layer on the inner surface portion of the tire surface layer overlaps with the tire width direction forming region of at least one of the belt and the belt reinforcement layer.

7. The tire according to claim 1 or 2, wherein the thickness of the stress relaxation layer at the center of the tire width direction of the bottom of the main groove is 5 μm or more and 200 μm or less.

8. The tire according to claim 2, wherein the circumferential dimension Wt of the stress relaxation layer on the inner surface of the tire surface layer is 1.1 times or more and 10 times or less the widthwise dimension Wg of the stress relaxation layer formed in the main groove.

Images