tire

Abstract

To provide a tire that improves electrical conductivity without worsening rolling resistance, and reduces long-term electrical resistance. [Solution] The tire 1 comprises a pair of bead portions, at least one carcass layer spanning between the pair of bead portions, a belt layer disposed radially outward of the carcass layer, a tread portion disposed radially outward of the belt layer, an inner liner disposed on the inner surface of the tire along the carcass layer, tie rubber disposed between the carcass layer and the inner liner, and conductive rubber Earthtread rubber on the rib portion of the tread portion closest to the tire equator. The carcass layer includes carcass cords and carcass coat rubber enclosing the carcass cords. The tie rubber has portions that penetrate between the carcass cords of the carcass layer, at least within the area where the belt layer is arranged, and the volume resistivity of the tie rubber is less than 1 × 10^8 [Ω·cm].

Description

[Technical Field]

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

[0002] In recent years, demand for fuel-efficient tires has increased due to environmental concerns. One method used to improve tire fuel efficiency is to increase the silica content in the rubber compound that makes up the tire's cap tread, under tread, and sidewall rubber, thereby reducing the tire's rolling resistance. However, because silica has high insulating properties, increasing the silica content in the rubber compound used in the cap tread, etc., increases the electrical resistance of the cap tread, etc., reducing the tire's static electricity suppression performance. When the tire's static electricity suppression performance decreases, static electricity generated when the vehicle is in motion accumulates more easily, making it more susceptible to radio interference such as radio noise.

[0003] For this reason, some conventional pneumatic tires are equipped with conductive materials with low electrical resistance to improve static electricity suppression performance and to facilitate the release of static electricity generated on the vehicle during driving onto the road surface. For example, Patent Document 1 describes how a conductive layer with low electrical resistivity is placed between the carcass layer and the inner liner and extends from the bead to the belt layer to improve the static electricity suppression performance of the tire. Patent Document 1 also describes an example in which the conductive layer is made of a conductive rubber material and also serves as a tie rubber that is placed around the entire circumference of the inner cavity of the tire. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-40031 [Overview of the project] [Problems that the invention aims to solve]

[0005] When reducing electrical resistance using a tie rubber made of conductive rubber material, it is important to position the tie rubber in contact with the rim cushion. However, if the length of overlap of the tie rubber with respect to the rim cushion is long, there is a risk that rolling resistance will worsen. Also, because tie rubber made of conductive rubber material is relatively hard due to its high carbon content, if the length of overlap of the tie rubber with respect to the rim cushion is long, there is a risk that the fitting pressure when fitting the tire onto the rim wheel will increase. For these reasons, it is extremely difficult to reduce electrical resistance without worsening rolling resistance or increasing fitting pressure.

[0006] This disclosure has been made in view of the above, and its purpose is to provide a tire that can improve conductivity and reduce long-term electrical resistance without worsening rolling resistance. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the tire according to this disclosure comprises: a pair of bead portions arranged on both sides of the tire equatorial plane in the tire width direction; a bead core provided on each of the pair of bead portions; a rim cushion rubber constituting the rim fitting surface of the bead portion and arranged from the inside in the tire width direction to the outside in the tire width direction of the bead core; at least one carcass layer spanning between the pair of bead portions; a belt layer arranged on the tire radially outside the carcass layer; and a tread portion arranged on the tire radially outside the belt layer. The tire comprises an inner liner disposed on the inner surface of the tire along the carcass layer, tie rubber disposed between the carcass layer and the inner liner, and conductive rubber Earthtread rubber on the rib portion of the tread closest to the tire equator, wherein the carcass layer includes carcass cords and carcass coat rubber enclosing the carcass cords, the tie rubber has portions that penetrate between the carcass cords of the carcass layer, at least within the arrangement range of the belt layer, and the volume resistivity of the tie rubber is less than 1 × 10^8 [Ω·cm]. [Effects of the Invention]

[0008] The tire of this disclosure can improve conductivity and reduce long-term electrical resistance without worsening rolling resistance. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a cross-sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment. [Figure 2] Figure 2 shows a portion of the tire meridional cross-section shown in Figure 1. [Figure 3] Figure 3 shows an example of a cross-sectional structure including a two-ply carcass layer. [Figure 4] Figure 4 shows an example of the cross-sectional structure of a portion of the side rubber shown in Figure 1. [Figure 5] Figure 5 shows a schematic diagram of the tire's appearance. [Figure 6] Figure 6 illustrates the area of ​​the tie rubber portion that is inserted between the carcass cords in the carcass layer. [Figure 7] Figure 7 illustrates the variation in carcass layer thickness in the circumferential direction of the tire. [Figure 8] Figure 8 illustrates the height of the tie rubber inserted between the carcass cords. [Figure 9] Figure 9 shows a modified example of the cross-sectional structure of a portion of the tread shown in Figure 1. [Figure 10] Figure 10 illustrates the cross-sectional area and height of the tie rubber embedded in the carcass coat rubber. [Figure 11] Figure 11 shows a cross-section of the tire when it is cut circumferentially at the location of the Earthtread rubber in Figure 1. [Figure 12] Figure 12 is a cross-sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment in which a non-penetrating type Earthtread rubber is used. [Figure 13]FIG. 13 is a view showing a cross section when the tire is cut in the circumferential direction at the position of the ground tread rubber in FIG. 12. [Figure 14A] FIG. 14A is a chart showing the results of a performance evaluation test of a pneumatic tire. [Figure 14B] FIG. 14B is a chart showing the results of a performance evaluation test of a pneumatic tire. [Figure 14C] FIG. 14C is a chart showing the results of a performance evaluation test of a pneumatic tire. [MODE FOR CARRYING OUT THE INVENTION]

[0010] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In the description of each of the following embodiments, the same or equivalent components as those in other embodiments are denoted by the same reference numerals, and the description thereof is simplified or omitted. The present invention is not limited by each embodiment. In addition, the components of each embodiment include those that can be replaced by those skilled in the art and are easy to replace, or those that are substantially the same. In addition, the configurations described below can be combined as appropriate. In addition, omissions, substitutions, or changes in the configuration can be made without departing from the gist of the invention.

[0011] [Embodiment] [Pneumatic Tire] In the following description, as an example of the tire according to the present disclosure, a pneumatic tire 1 will be used for explanation. The pneumatic tire 1, which is an example of the tire according to the present disclosure, can be filled with air, an inert gas such as nitrogen, and other gases.

[0012] Furthermore, in the following explanation, the tire radial direction refers to the direction perpendicular to the tire rotation axis (not shown), which is the rotation axis of the pneumatic tire 1. The inner side of the tire radial direction refers to the side toward the tire rotation axis in the tire radial direction, and the outer side of the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side of the tire width direction refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the outer side of the tire width direction refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane perpendicular to the tire rotation axis and passing through the center of the tire width of the pneumatic tire 1. The position of the tire equatorial plane CL in the tire width direction coincides with the center line in the tire width direction, which is the center position of the pneumatic tire 1 in the tire width direction. The tire width is the distance in the tire width direction between the outermost parts in that direction, that is, the distance between the parts furthest from the tire equatorial plane CL in that direction. The tire equatorial line is a line on the tire equatorial plane CL that runs along the circumferential direction of the pneumatic tire 1. In this embodiment, the tire equatorial line is denoted by the same symbol "CL" as the tire equatorial plane. Furthermore, in the following description, the tire meridional section refers to the cross-section obtained when the tire is cut by a plane containing the tire rotation axis.

[0013] Figure 1 is a meridional cross-sectional view of a pneumatic tire 1 according to an embodiment. Figure 1 shows one side region in the radial direction of the tire. Figure 1 also shows a passenger car radial tire as an example of a pneumatic tire.

[0014] The pneumatic tire 1 according to this embodiment has an annular structure centered on the tire rotation axis and comprises a tread portion 2, a pair of sidewall portions 4, 4, a pair of bead portions 10, 10, a carcass layer 15, a belt layer 18, an inner liner 21, and a tie rubber 22. Of these, the pair of sidewall portions 4, 4 and the pair of bead portions 10, 10 are each arranged one on each side of the tire equatorial plane CL in the tire width direction.

[0015] The pair of bead portions 10, 10 are located on the radially inner side of the pair of sidewall portions 4, 4, and each has a bead core 11, a bead filler 14, and a rim cushion 30. That is, the pair of bead cores 11, 11, the pair of bead fillers 14, 14, and the pair of rim cushions 30, 30 are arranged on both sides of the tire equatorial plane CL in the tire width direction.

[0016] The pair of bead cores 11, 11 are annular members formed by bundling multiple bead wires, and constitute the core of the pair of bead portions 10, 10. The pair of bead fillers 14, 14 are positioned on the radially outer side of the pair of bead cores 11, 11 to reinforce the bead portion 10.

[0017] The carcass layer 15 has a single-layer structure consisting of one carcass ply, or a multi-layer structure consisting of multiple carcass plies stacked together, and is stretched in a toroidal manner between a pair of bead portions 10, 10 located on both sides in the tire width direction to form the tire's skeleton. The carcass ply of the carcass layer 15 is constructed by covering multiple carcass cords made of steel or organic fiber materials such as aramid, nylon, polyester, or rayon with a coating rubber and then rolling them. The carcass angle of the carcass ply of this carcass layer 15, which is defined as the inclination angle of the direction in which the carcass cord extends with respect to the circumferential direction of the tire, is within the range of 80 degrees to 95 degrees in absolute value.

[0018] In this embodiment, the carcass layer 15 has a single-layer structure and is continuously stretched between the bead cores 11, 11 on both sides in the tire width direction. Furthermore, both ends of the carcass layer 15 are wrapped back outward in the tire width direction and secured so as to enclose the bead cores 11 and bead filler 14. In other words, the carcass layer 15, near both ends in the tire meridional section, is wrapped back outward in the tire width direction, passing from the inside in the tire width direction to the inside in the tire radial direction of the bead cores 11 and bead filler 14.

[0019] Therefore, the carcass layer 15 has a carcass body portion 15a that is arranged between a pair of bead portions 10, and a turn-up portion 15b that is formed continuously from the carcass body portion 15a and is folded back from the inside in the tire width direction to the outside in the tire width direction of the bead core 11. The carcass body portion 15a is the portion of the carcass layer 15 that is formed between the inside in the tire width direction of a pair of bead cores 11, and the turn-up portion 15b is formed continuously from the carcass body portion 15a on the inside in the tire width direction of the bead core 11 and is folded back from the inside in the tire radial direction of the bead core 11 to the outside in the tire width direction. The bead filler 14 is arranged on the inside in the tire width direction of the turn-up portion 15b, which is the portion of the bead core 11 that is folded back to the outside in the tire width direction, and on the outside in the tire radial direction of the bead core 11.

[0020] Preferably, the carcass ply of the carcass layer 15 formed in this manner has a volume resistivity of less than 1 × 10^8 [Ω·cm] of the carcass coat rubber, which is the coating rubber of the carcass cord. In this specification, the symbol "^" means exponentiation.

[0021] Volume resistivity (volume resistivity) is measured according to JIS K6271, "Vulcanized rubber and thermoplastic rubber - Method for determining volume resistivity and surface resistivity." Generally, if the volume resistivity is less than 1 × 10^8 [Ω·cm] or the surface resistivity is less than 1 × 10^8 [Ω / cm], the material can be said to have conductivity that can suppress the accumulation of static electricity.

[0022] The pair of rim cushions 30, 30 of the pair of bead portions 10, 10 are respectively located on the inner side in the tire radial direction of the bead cores 11, 11 and the reversal portion of the carcass layer 15 on both sides in the tire width direction. More specifically, the rim cushion 30 is located at least from the inner side in the tire width direction to the outer side in the tire width direction of the bead core 11. That is, the rim cushion 30 is located in the bead portion 10, passing from the inner side in the tire width direction of the bead core 11 through the inner side in the tire radial direction of the bead core 11 to the outer side in the tire width direction of the bead core 11.

[0023] The rim cushion 30, arranged in this manner, is the part that contacts the rim flange R of the rim wheel when the pneumatic tire 1 is mounted onto the rim wheel, and constitutes the contact surface of the bead portion 10 with respect to the rim flange R. Of the contact surface of the rim cushion 30 with respect to the rim flange R, the portion that is the inner circumferential surface of the rim cushion 30 constitutes the rim fitting surface 32 of the bead portion 10, which is the surface that fits into the rim wheel.

[0024] The rim cushion 30 is composed of a rubber component, the rim cushion rubber 31. The rim cushion 30 has a volume resistivity of less than 1 × 10^8 [Ω·cm], that is, the rim cushion rubber 31 constituting the rim cushion 30 has a volume resistivity of less than 1 × 10^8 [Ω·cm]. It is more preferable that the volume resistivity of the rim cushion 30 is less than 1 × 10^7 [Ω·cm].

[0025] Furthermore, the rim cushion rubber 31 has a tanδ value at 60°C that is in the range of 0.085 to 0.35, and a rubber hardness Hs that is in the range of 35 to 111.

[0026] The tanδ value at 60°C mentioned here is measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., under the conditions of initial strain of 10%, amplitude of ±0.5%, and frequency of 20Hz. The rubber hardness Hs is measured at a temperature of 20°C in accordance with JIS K6253.

[0027] Furthermore, the rim cushion 30 may have components other than the rim cushion rubber 31. For example, the rim cushion 30 may include a chafer, which is made of fibrous material or rubber, that prevents the carcass layer 15 from coming into contact with the rim flange R and being damaged when the pneumatic tire 1 is fitted onto the rim wheel.

[0028] The belt layer 18 has one or more belt plies extending in the tire width direction, and in this embodiment, a plurality of belt plies 181 to 183 are laminated. That is, in this embodiment, the belt layer 18 is constructed by laminating a pair of cross belts 181 and 182 and a belt cover 183 in the tire radial direction, and is positioned on the outside of the carcass layer 15 in the tire radial direction and wrapped around the outer circumference of the carcass layer 15. The pair of cross belts 181 and 182 are constructed by covering a plurality of belt cords made of steel or organic fiber material with coated rubber and rolling them, and the belt angle, which is the inclination angle of the direction of extension of the belt cords with respect to the tire circumferential direction, is within the range of 20 [deg] to 65 [deg] in absolute value. Furthermore, the pair of cross belts 181 and 182 have belt angles with opposite signs to each other and are laminated with the directions of extension of the belt cords intersecting each other, forming a so-called cross-ply structure. Specifically, the pair of cross belts 181 and 182 have belt cords inclined in opposite directions relative to the tire width direction with respect to the tire circumferential direction. The belt cover 183 is constructed by rolling multiple cords made of steel or organic fiber material covered with coated rubber, and the belt angle is within the range of 0 [deg] to 10 [deg] in absolute value. The belt cover 183 is also arranged stacked on the outer side of the cross belts 181 and 182 in the tire radial direction.

[0029] The tread portion 2 is composed of tread rubber 3, which is a rubber composition, and is located on the radially outer side of the carcass layer 15 and belt layer 18, and is exposed at the outermost radial point of the pneumatic tire 1. For this reason, the outer surface of the tread portion 2 constitutes part of the contour of the pneumatic tire 1, and the tread portion 2 has multiple grooves, such as circumferential main grooves (not shown) and lug grooves (not shown), that extend in the circumferential direction of the tire. Furthermore, the tread rubber 3 that constitutes the tread portion 2 has a cap tread 3a and an under tread 3b.

[0030] The cap tread 3a is a rubber member located on the outermost side of the tread portion 2 in the tire radial direction and constitutes the tire contact surface 2a. It may have a single-layer structure (see Figure 1) or a multi-layer structure (not shown). The tanδ value of the cap tread 3a at 60°C is preferably 0.25 or less. Furthermore, the volume resistivity of the cap tread 3a is preferably 1 × 10^8 [Ω·cm] or more, more preferably 1 × 10^10 [Ω·cm] or more, and even more preferably 1 × 10^12 [Ω·cm] or more. These factors reduce the rolling resistance of the pneumatic tire 1. A cap tread 3a having such a volume resistivity is produced by using a low-heat-generating compound with a low carbon content and reinforcing it by increasing the silica content.

[0031] Furthermore, the undertread 3b is a component laminated on the inner side of the cap tread 3a in the tire radial direction. Preferably, the volume resistivity of the undertread 3b is lower than that of the cap tread 3a.

[0032] Each of the pair of sidewall sections 4, 4 is composed of sidewall rubber 5, and the pair of sidewall rubbers 5, 5 of the pair of sidewall sections 4, 4 are respectively arranged on the outer side in the tire width direction of the carcass layer 15. The tanδ value of the sidewall rubber 5 at 60 [℃] is preferably 0.20 or less. Furthermore, the volume resistivity of the sidewall rubber 5 is preferably 1 × 10^8 [Ω·cm] or more, more preferably 1 × 10^10 [Ω·cm] or more, and even more preferably 1 × 10^12 [Ω·cm] or more. These factors reduce the rolling resistance of the pneumatic tire 1. Sidewall rubber 5 having such volume resistivity is produced by using a low-heat generating compound with a low carbon content and reinforcing it by increasing the silica content.

[0033] While there are no specific limitations on the upper limit of the volume resistivity of the cap tread 3a, the lower limit of the volume resistivity of the under tread 3b, the upper limit of the volume resistivity of the sidewall rubber 5, and the lower limit of the volume resistivity of the rim cushion rubber 31, these are subject to physical constraints because they are rubber components.

[0034] The inner liner 21 is positioned on the inner surface 25 of the tire along the carcass layer 15. That is, the inner liner 21 constitutes the inner surface 25 of the tire, which is the inner surface of the pneumatic tire 1, and faces the inner cavity of the tire, which is the inner space of the pneumatic tire 1. The inner liner 21 that constitutes the inner surface 25 of the tire is a rubber layer positioned on the inner cavity side of the carcass layer 15, and covers the carcass layer 15 from the inner cavity side.

[0035] The tie rubber 22 is positioned between the carcass layer 15 and the inner liner 21. The tie rubber 22 is positioned along the carcass layer 15, similar to the inner liner 21, on the inner side of the tire cavity relative to the carcass layer 15. That is, the inner liner 21 and the tie rubber 22 are laminated and positioned along the carcass layer 15, on the inner side of the tire cavity relative to the carcass layer 15.

[0036] The inner liner 21, positioned on the inner surface 25 of the tire, is an air permeability-preventing layer. By covering the carcass layer 15, it suppresses oxidation of the carcass layer 15 due to exposure and prevents air leakage from the tire. The inner liner 21 is composed of, for example, a rubber composition mainly composed of butyl rubber, a thermoplastic resin, or a thermoplastic elastomer composition in which an elastomer component is blended into a thermoplastic resin. In particular, when the inner liner 21 is made of a thermoplastic resin or a thermoplastic elastomer composition, the inner liner 21 can be made thinner compared to when the inner liner 21 is made of butyl rubber, thus significantly reducing the tire weight.

[0037] Furthermore, the air permeability coefficient of the inner liner 21 is generally preferably 100 × 10⁻¹² [cc·cm / cm²·sec·cmHg] or less, and more preferably 50 × 10⁻¹² [cc·cm / cm²·sec·cmHg] or less, when measured at a temperature of 30 [°C] in accordance with JIS K7126-1.

[0038] Furthermore, the volume resistivity of the inner liner 21 is 1 × 10^8 [Ω·cm] or greater, preferably 1 × 10^9 [Ω·cm] or greater. In addition, the inner liner 21 has a tanδ value at 60 [℃] in the range of 0.115 to 0.35, and a rubber hardness Hs in the range of 27 to 90.

[0039] As rubber compositions mainly composed of butyl rubber, for example, butyl rubber (IIR) and butyl-based rubbers can be used. The butyl-based rubber is preferably a halogenated butyl rubber such as chlorinated butyl rubber (Cl-IIR) or brominated butyl rubber (Br-IIR).

[0040] Examples of thermoplastic resins include polyamide resins [e.g., nylon 6 (N6), nylon 66 (N66), nylon 46 (N46), nylon 11 (N11), nylon 12 (N12), nylon 610 (N610), nylon 612 (N612), nylon 6 / 66 copolymer (N6 / 66), nylon 6 / 66 / 610 copolymer (N6 / 66 / 610), nylon MXD6, nylon 6T, nylon 9T, nylon 6 / 6T copolymer, nylon 66 / PP copolymer, nylon 66 / PPS copolymer], polyester Polyethylene resins [e.g., polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyethylene isophthalate (PEI), polybutylene terephthalate / tetramethylene glycol copolymer, PET / PEI copolymer, polyarylate (PAR), polybutylene naphthalate (PBN), liquid crystal polyester, aromatic polyesters such as polyoxyalkylenediimidodic acid / polybutylene terephthalate copolymer], polynitrile resins [e.g., polyacrylonitrile (PAN), polymethacrylonitrile, acrylonitrile / styrene copolymer (AS), methacrylonitrile / styrene copolymer, methacrylonitrile / styrene / butadiene copolymer], poly(meth)acrylate resins [e.g., polymethyl methacrylate (PMMA), polyethyl methacrylate, ethylene ethyl acrylate copolymer (EEA), ethylene acrylic acid copolymer (EAA), ethylene methyl acrylate resin (EMA)], polyvinyl resins [e.g., vinyl acetate (EVA), polyvinyl alcohol (PVA), vinyl alcohol / ethylene Copolymers (EVOH), polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), vinyl chloride / vinylidene chloride copolymer, vinylidene chloride / methyl acrylate copolymer, cellulose resins (e.g., cellulose acetate, cellulose acetate butyrate), fluororesins (e.g., polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polychlorofluoroethylene (PCTFE), tetrafluoroethylene / ethylene copolymer (ETFE)), imide resins (e.g., aromatic polyimide (PI)), etc., can be used.

[0041] Examples of elastomers include diene rubbers and their hydrogenated versions [e.g., NR, IR, epoxidized natural rubber, SBR, BR (high-cis BR and low-cis BR), NBR, hydrogenated NBR, hydrogenated SBR], olefin rubbers [e.g., ethylene propylene rubber (EPDM, EPM), maleic acid-modified ethylene propylene rubber (M-EPM)], butyl rubber (IIR), isobutylene and aromatic vinyl or diene monomer copolymers, acrylic rubber (ACM), ionomers, halogen-containing rubbers [e.g., Br-IIR, Cl-IIR, brominated isobutylene-paramethylstyrene copolymer (Br-IPMS), chloroprene rubber (CR), hydrin rubber (CHC, CHR), chlorosulfur Polyethylene chloride (CSM), chlorinated polyethylene (CM), maleic acid-modified chlorinated polyethylene (M-CM), silicone rubber (e.g., methyl vinyl silicone rubber, dimethyl silicone rubber, methylphenyl vinyl silicone rubber), sulfur-containing rubber (e.g., polysulfide rubber), fluororubber (e.g., vinylidene fluoride rubber, fluorovinyl ether rubber, tetrafluoroethylene-propylene rubber, fluorosilicone rubber, fluorophosphazene rubber), thermoplastic elastomers (e.g., styrene elastomers, olefin elastomers, polyester elastomers, urethane elastomers, polyamide elastomers), etc., can be used.

[0042] Furthermore, the tie rubber 22, positioned between the inner liner 21 and the carcass layer 15, is a layer designed to prevent the carcass cords of the carcass layer 15 from biting into the inner liner 21 when the unvulcanized pneumatic tire 1 is inflated during tire manufacturing. In addition, the tie rubber 22 contributes to air permeability prevention and handling stability on dry road surfaces in the pneumatic tire 1 after manufacturing.

[0043] Thai Rubber 22 is a rubber composition containing 30 to 100 parts by mass of carbon black with a CTAB adsorption specific surface area of ​​25 [m2 / g] to 130 [m2 / g] per 100 parts by mass of diene rubber, with the carbon black being more preferably in the range of 40 to 70 parts by mass. Thai Rubber 22 containing carbon black is a rubber composition containing isoprene rubber in the range of 30 to 90 parts by mass and styrene-butadiene rubber in the range of 20 to 70 parts by mass. By having such a material composition, the electrical resistance of Thai Rubber 22 can be reduced.

[0044] The pneumatic tire 1 according to this embodiment has a charge suppression structure for releasing static electricity generated on the vehicle during vehicle operation to the road surface, and a tie rubber 22 is used for the charge suppression structure. The tie rubber 22 is arranged along the carcass layer 15 between a pair of bead portions 10, and has a volume resistivity of less than 1 × 10^8 [Ω·cm]. It is more preferable that the volume resistivity of the tie rubber 22 is less than 1 × 10^6 [Ω·cm]. In addition, the tie rubber 22 has a tanδ value at 60 [℃] in the range of 0.05 to 0.40, and a rubber hardness Hs in the range of 50 to 70.

[0045] The inner liner 21 is positioned on the inner side of the tire lumen 22, spanning between the pair of bead portions 10.

[0046] In this embodiment, the bead portion 10 refers to the area from the rim diameter measurement point to 1 / 3 of the tire cross-sectional height SH. The tire cross-sectional height SH refers to 1 / 2 of the difference between the tire outer diameter and the rim diameter, and is measured when the pneumatic tire 1 is mounted on a specified rim, a specified internal pressure is applied, and the measurement is taken under no-load conditions.

[0047] Here, "specified rim" refers to the "applicable rim" specified by JATMA, the "Design Rim" specified by TRA, or the "Measuring Rim" specified by ETRTO. Furthermore, "specified internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" specified by TRA, or the "INFLATION PRESSURES" specified by ETRTO.

[0048] [Earth Red Rubber] Earthtread rubber 50 is arranged in the tread portion 2. Earthtread rubber 50 is a conductive rubber member embedded in the tread rubber 3 and exposed on the tire contact surface. Earthtread rubber 50 penetrates the tread rubber 3 and contacts the belt layer 18, and is also exposed on the tire contact surface 2a, which is the surface of the tread rubber 3. Specifically, Earthtread rubber 50 is exposed on the tire contact surface 2a and penetrates the cap tread 3a and under tread 3b of the tread rubber 3 to make conductive contact with the belt layer 18. In this way, an conductive path from the belt layer 18 to the road surface is secured by Earthtread rubber 50.

[0049] Furthermore, the Earthtread rubber 50 has an annular structure that extends around the entire circumference of the tire, with a portion of it exposed to the tire contact surface 2a, and extends continuously in the circumferential direction of the tire. Therefore, when the pneumatic tire 1 rolls, the Earthtread rubber 50 can always be in contact with the road surface, and a conductive path from the belt layer 18 to the road surface can always be ensured. The Earthtread rubber 50 is formed with a width in the tire width direction that is narrower than, for example, the groove width of the circumferential main groove (not shown) that extends in the circumferential direction of the tire in the tread portion 2, and is positioned between adjacent circumferential main grooves in the tire width direction.

[0050] Figure 2 shows a portion of the meridional cross-section of the tire shown in Figure 1. Figure 2 shows an example of the cross-sectional structure of a portion of the tread portion 2 shown in Figure 1. Figure 2 shows a cross-section cut along the circumferential direction of the tire. Referring to Figure 2, the belt layer 18, carcass layer 15, tie rubber 22, and inner liner 21 are arranged in order on the radially inner side of the tread rubber 3. The tie rubber 22 is positioned between the carcass layer 15 and the inner liner 21.

[0051] The carcass layer 15 has carcass cords 16 and carcass coat rubber 17 that surrounds the carcass cords 16. Focusing on the tie rubber 22, a portion 221 of the tie rubber 22 extends outward in the tire radial direction and fits between the carcass cords 16. Specifically, if a portion 221 of the tie rubber 22 crosses a virtual line L1 that passes through the inside of each carcass cord 16 in the tire radial direction, it can be considered that the tie rubber 22 fits between the carcass cords 16. That is, the tie rubber 22 has a portion 221 that fits between the carcass cords 16 of the carcass layer 15, at least within the arrangement range of the belt layer 18. By the tie rubber 22 fitting between the carcass cords 16, the thickness of the carcass coat rubber 17 is reduced, the conductive distance is shortened, and thus conductivity is improved. In addition, by fitting into the carcass coat rubber 17, the adhesive area between the tie rubber 22 and the carcass layer 15 is increased. This improves the adhesion between the tie rubber 22 and the carcass layer 15, allowing low electrical resistance to be maintained even after driving.

[0052] [Modified carcass layer] With reference to Figure 2, the carcass layer 15 is preferably a single-ply structure, but is not limited thereto. Figure 3 shows an example of a cross-sectional structure including a two-ply carcass layer 150. The carcass layer 150 includes a ply consisting of a carcass cord 161 and a carcass coat rubber 171 surrounding it, and another ply consisting of a carcass cord 162 and a carcass coat rubber 172 surrounding it, thus having a two-ply structure.

[0053] Even in the case shown in Figure 3, portion 221 of the tie rubber 22 extends radially outward in the tire direction and is inserted between the carcass cords 161. In the case of a two-ply structure, a virtual line L12 is drawn between the ply consisting of carcass cord 161 and carcass coat rubber 171 and the ply consisting of carcass cord 162 and carcass coat rubber 172. If portion 221 of the tie rubber 22 crosses the virtual line L12, which passes through the radially inside of the carcass cord 161 of the inner ply in the tire direction, i.e., the ply closer to the tie rubber 22 in the tire radial direction, then it can be considered that it is inserted between the carcass cords 161.

[0054] When the tie rubber 22 is inserted between the carcass cords 161, the thickness of the carcass coat rubber 171 is reduced, shortening the conductive distance and thus improving conductivity. In addition, by being inserted into the carcass coat rubber 171, the adhesive area between the tie rubber 22 and the carcass layer 150 increases. As a result, the adhesion between the tie rubber 22 and the carcass layer 150 is improved, and low electrical resistance can be maintained even after driving.

[0055] Furthermore, the area around the side rubber may have the same configuration as in Figure 2. Figure 4 shows an example of the cross-sectional structure of a part of the sidewall rubber 5 shown in Figure 1. Referring to Figure 4, the carcass layer 15, tie rubber 22, and inner liner 21 are arranged in order from the tread rubber 3 toward the inner cavity of the tire.

[0056] In Figure 4, focusing on the tie rubber 22, portion 221 of the tie rubber 22 extends outward in the radial direction of the tire and is inserted between the carcass cords 16. That is, even within the area where the sidewall rubber 5 is placed, the tie rubber 22 has a portion 221 that is inserted between the carcass cords 16 of the carcass layer 15. By the tie rubber 22 being inserted between the carcass cords 16, the thickness of the carcass coat rubber 17 is reduced, and the conductive distance is shortened, thus improving conductivity. In addition, by being inserted into the carcass coat rubber 17, the adhesive area between the tie rubber 22 and the carcass layer 15 is increased. As a result, the adhesion between the tie rubber 22 and the carcass layer 15 is improved, and low electrical resistance can be maintained even after driving.

[0057] [Number of places where the tie rubber can be inserted] Figure 5 shows a schematic diagram of the appearance of tire 1. As shown in Figure 5, in this example of tire 1, four locations in the tire's circumferential direction are designated as measurement points S1, S2, S3, and S4. These four locations in the tire's circumferential direction are, for example, one location every 90 degrees in the tire's circumferential direction. Here, within a 50 mm circumferential length range of measurement point S1, it is preferable that there is at least one portion 221 in which the tie rubber 22 is inserted between the carcass cords 16 of the carcass layer 15. In other words, it is preferable that there is at least one location in which the tie rubber 22 is inserted between the carcass cords 16 for every 50 mm of circumferential length of the tire. The more locations in which the tie rubber 22 is inserted, the greater the adhesive area between the tie rubber 22 and the carcass layer 15. This improves the adhesion between the tie rubber 22 and the carcass layer 15, and allows low electrical resistance to be maintained even after driving.

[0058] Similarly, it is preferable that at least one measurement point is included in each of the other measurement points S2, S3, and S4 of tire 1. Note that the four measurement points S1, S2, S3, and S4 in Figure 5 are examples, and more measurement points may be used.

[0059] [Cross-sectional area of ​​Thai rubber] Figure 6 illustrates the area of ​​portion 221 of the tie rubber 22 that is embedded between the carcass cords 16 of the carcass layer 15. The average value of the intercord cross-sectional area Sc (50Ave), calculated from the average distance between the centers of the carcass cords 16 and the average thickness of the carcass layer 15, is shown for a 50mm circumferential length range of measurement points S1, S2, S3, and S4. The cross-sectional area St[mm²] of the tie rubber embedded within the carcass coat rubber in that range is also shown. 2 It is preferable that the relationship with the mean value St(50Ave) of ] satisfies the following equation (1). 0.02≦St(50Ave) / Sc(50Ave)≦0.5 …(1)

[0060] In equation (1) above, St(50Ave) is the cross-sectional area of ​​the tie rubber that is inserted between the carcass cords St[mm 2 This is the average value of Sc(50Ave). Area Sc[mm 2 The area Sc = Tc × Lc [mm²] is the cross-sectional area determined by the thickness Tc of the carcass layer 15 and the distance Lc between the centers of the carcass cords 16. 2 The thickness Tc [mm] is the length between point P18, where a perpendicular line drawn radially outward from the center of the carcass cord 16 toward the belt layer 18 intersects with the interface of the belt layer 18, and point P22, where a perpendicular line drawn radially inward intersects with the interface of the tie rubber 22.

[0061] By satisfying the conditions in (1) above, the conductivity can be improved while maintaining the durability of the tire, and the electrical resistivity can be reduced. If the above St(50Ave) / Sc(50Ave) is less than 0.02, the improvement in conductivity is small, and the electrical resistance does not decrease. Also, if the above St(50Ave) / Sc(50Ave) is greater than 0.4, the durability deteriorates due to the widening of the spacing between the carcass cords 16, and it is not possible to maintain low electrical resistance after driving. Note that the cross-sectional area St[mm 2 It is more preferable that the relationship between the average value St(50Ave) of ] and the average value Sc(50Ave) of area Sc is 0.1 ≤ St(50Ave) / Sc(50Ave) ≤ 0.35.

[0062] Here, the thickness Tc [mm] of the carcass layer 15 is not constant in the circumferential direction of the tire, but varies. This will be explained with reference to Figure 7. Figure 7 is a diagram illustrating that the thickness of the carcass layer 15 varies in the circumferential direction of the tire.

[0063] In Figure 7, a perpendicular line S16 is drawn from the center of the carcass cord 16 toward the radially inward direction of the tire. The distance along the tire radial direction from point P16, where this perpendicular line S16 intersects the interface between the tie rubber 22 and the carcass coat rubber 17, to the interface between the carcass coat rubber 17 and the belt layer 18, is not constant and varies depending on the height to which the portion 221 of the tie rubber 22 intrudes. For example, in Figure 7, thickness Tcmax is the maximum value, thickness Tcmin is the minimum value, and thickness Tcave is the average value. The above area Sc[mm] 2 This is calculated as the product of the average value thickness Tcave and the center-to-center distance Lc of the carcass code 16.

[0064] [Height of the inserted rubber band] Figure 8 illustrates the height of the tie rubber that is inserted between the carcass cords 16. In Figure 8, the thickness of the carcass layer 15 is denoted as Tc, and the height of the tie rubber that is inserted into the carcass coat rubber is denoted as Tt. It is preferable that the relationship between the thickness Tc and the height Tt satisfies the following equation (2). 0.014 ≤ Tt / Tc ≤ 0.8 …(2)

[0065] In equation (2), thickness Tc is the thickness [mm] of the carcass layer 15. Thickness Tc is the distance from the interface between the tie rubber 22 and the carcass layer 15 to the interface between the belt layer 18 and the carcass layer 15. In equation (2), height Tt is the height [mm] of the portion 221 of the tie rubber 22 that is inserted between the carcass cords 16. Height Tt is the distance from the interface between the tie rubber 22 and the carcass layer 15 to the outermost part of the portion 221 of the tie rubber 22 in the radial direction of the tire. If Tt / Tc in equation (2) is less than 0.014, the improvement in conductivity is small and the electrical resistance is not reduced. Also, if Tt / Tc is greater than 0.8, the durability deteriorates due to the opening of the carcass cords, and it is not possible to maintain low electrical resistance after driving. It is more preferable that the relationship between thickness Tc and height Tt is 0.2 ≤ Tt / Tc ≤ 0.6.

[0066] [Modified example of the coated rubber in the belt layer] The tie rubber 22 may penetrate into the carcass coat rubber 17, and the coat rubber of the belt layer 18 may also penetrate into the carcass coat rubber 17. Figure 9 shows a modified example of the cross-sectional structure of the tread portion 2 shown in Figure 1. As shown in Figure 9, portion 221 of the tie rubber 22 extends outward in the tire radial direction within the carcass coat rubber 17. That is, portion 221 of the tie rubber 22 crosses the imaginary line L1, and portion 221 penetrates between the carcass cords 16. Furthermore, a portion of the coat rubber 18b of the belt layer 18 crosses the imaginary line L2 passing on the radially outer side of the carcass cords 16, and the coat rubber 18b penetrates between the carcass cords 16. It is preferable that the volume resistivity of the coat rubber 18b of the belt layer 18 is less than 1 × 10^8 [Ω·cm].

[0067] [Cross-sectional area and height of the inserted rubber tie] Figure 10 illustrates the cross-sectional area and height of the tie rubber inserted into the carcass coat rubber. In Figure 10, the cross-sectional area of ​​the tie rubber inserted between the carcass cords is St[mm 2Let ] be the case. Also, let Tt be the height of the tie rubber inserted between the carcass cords. In this case, it is preferable that the relationship between the cross-sectional area St and the height Tt satisfies the following equation (3). That is, 0.02 mm ≤ St / Tt ≤ 2.0 mm …(3) It is preferable that the following conditions be met.

[0068] Furthermore, it is more preferable that the relationship between the cross-sectional area St and the height Tt satisfies the following: 0.2mm ≤ St / Tt ≤ 0.6mm It is more preferable that the following conditions be met. Note that the cross-sectional area St[mm 2 The height Tt [mm] and the cross-section observed when the tire is cut in the circumferential direction are both average values ​​along the circumferential direction of the tire, within a range of 50 mm in length.

[0069] [Rubber hardness] When the hardness of the carcass coat rubber 17 is Hc and the hardness of the tie rubber 22 is Ht, the ratio of hardness Ht to hardness Hc, Ht / Hc, is preferably 0.5 or more and 2.0 or less. Furthermore, the ratio Ht / Hc is more preferably 0.7 or more and 1.5 or less, and even more preferably 0.9 or more and 1.3 or less.

[0070] If the ratio of the hardness of the tie rubber to the hardness of the carcass coat rubber (Ht / Hc) is within the above range, the hardness difference will be reduced, suppressing the small delaminations that occurred in the tires after driving. This ensures conductivity, thus suppressing the deterioration of electrical resistance before and after driving.

[0071] The hardness Hc of the carcass coat rubber 17 is, for example, between 55 and 75 points. The hardness Ht of the tie rubber 22 is, for example, between 50 and 65 points. Here, hardness refers to the durometer hardness measured at a temperature of 23°C using a Type A durometer (rubber hardness tester) in accordance with JIS-K6253, and is also called JIS-A hardness. The hardness of the rubber is the average value measured at four or more locations using the above durometer on a cut sample tire.

[0072] Regarding the land portion of the tread section 2 closest to the tire equatorial plane CL, it is preferable that in the cross-section seen when the pneumatic tire 1 is cut in the circumferential direction, there is at least one location along the circumferential direction of the tire, within a circumferential length of 50 mm, where the tie rubber 22 is inserted between the carcass cords 16 of the carcass layer 15. Having at least one location where the tie rubber 22 is inserted helps maintain low electrical resistance while maintaining tire durability.

[0073] [Placement of Earth Red Rubber] The arrangement of the Earth Red Rubber 50 will be explained with reference to Figures 11 to 13. Figure 11 is a cross-section of the tire when it is cut circumferentially at the position of the Earth Red Rubber 50 in Figure 1. Figure 11 is a cross-section when the Earth Red Rubber 50 is a through-type Earth Rubber.

[0074] In Figure 11, the Earthtread rubber 50 is a through-type earthing rubber. Therefore, the Earthtread rubber 50 penetrates the tread rubber 3 and contacts the belt layer 18. Consequently, the conductivity is improved by the Earthtread rubber 50 contacting the road surface. As shown in Figure 11, a small portion of the cap tread 3a may remain on the outermost edge of the tread rubber 3 in the tire radial direction.

[0075] On the one hand, FIG. 12 is a cross-sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment when a non-penetrating type ground tread rubber is adopted. FIG. 13 is a view showing a cross-section when the tire is cut in the circumferential direction at the position of the ground tread rubber in FIG. 12. In FIGS. 12 and 13, the ground tread rubber 50a is a non-penetrating type ground rubber. Therefore, the ground tread rubber 50a does not penetrate the tread rubber 3 and contacts the under tread 3b and terminates. Although the ground tread rubber 50a does not contact the belt layer 18, if the volume resistivity of the under tread 3b is sufficiently low, the electrical conductivity can be maintained. As shown in FIG. 13, a slight amount of cap tread 3a may remain on the outermost side in the tire radial direction of the tread rubber 3.

[0076] In each cross-section shown in FIGS. 11 and 13, let the cross-sectional area of the tread portion be Str [mm 2 . The cross-sectional area Str is the total area of the cross-sectional area of the cap tread 3a, the cross-sectional area of the ground tread rubber 50 or 50a, and the cross-sectional area of the under tread 3b. Also, let the cross-sectional area of the ground tread rubber be Sea [mm 2 . At this time, it is preferable that the ratio Sea / Str of the cross-sectional area Sea to the cross-sectional area Str is 0.8 or more and 1 or less. When the ratio of the cross-sectional areas is within the above range and, as shown in FIGS. 11 and 13, the portion 221 of the tie rubber 22 enters the carcass coat rubber 17 of the carcass layer 15, the electrical conductivity is further improved. More preferably, the ratio Sea / Str is 0.9 or more and 1 or less.

[0077] The ground tread rubber 50 is made of a conductive rubber material having a volume resistivity lower than that of the tread rubber 3, and the volume resistivity of the ground tread rubber 50 is less than 1×10^8 [Ω·cm]. More preferably, the volume resistivity of the ground tread rubber 50 is 1×10^6 [Ω·cm] or less.

[0078] [Examples] Figures 14A to 14C are charts showing the results of performance evaluation tests of pneumatic tires. Below, we will describe the performance evaluation tests conducted on the above-mentioned pneumatic tire 1, comparing it to a conventional pneumatic tire and the pneumatic tire 1 described herein. In the performance evaluation tests, the electrical resistance of the pneumatic tire was measured before and after driving with the pneumatic tire.

[0079] Regarding the electrical resistance of the tires, the electrical resistance [Ω] of the test tires was measured using an R8340A ultra-high resistance meter manufactured by Advantest Corporation, based on the measurement conditions specified by JATMA. For running with pneumatic tires, an indoor drum-type tire rolling resistance tester with a drum diameter of 1707 [mm] was used. The test tires were mounted on rims conforming to the JATMA specifications, and the test tires were subjected to an air pressure of 200 [kPa] and 80% of the maximum load specified by JATMA. After running at a speed of 81 [km / h] for 60 minutes, the electrical resistance of the tires was measured using the method described above.

[0080] In Figure 14A, a tire in which tie rubber is not embedded in the carcass coat rubber is shown as a "conventional example." It is thought that the tie rubber embedded between the carcass cords peels off slightly as the tire runs, so the resistance value increases compared to before running. However, an increase in electrical resistance of 1.5 × 10^7 [Ω·cm] or less is considered to be within an acceptable range. In Figure 14A, the conventional tire shows an increase in resistance value of 1.9 × 10^7 [Ω·cm] after running compared to before running. In contrast, in Figures 14A to 14C, it can be seen that the tires of each embodiment of this disclosure maintain their electrical resistance value even after running.

[0081] This disclosure encompasses the following inventions: [1] A pair of bead portions are arranged on both sides of the tire's equatorial plane in the tire width direction, A bead core provided in each of the pair of bead portions, The rim cushion rubber is arranged to form the rim fitting surface in the bead portion and to extend from the inner side in the tire width direction to the outer side in the tire width direction of the bead core, A carcass layer of at least one layer is stretched between the pair of bead portions, A belt layer is disposed on the outer side of the carcass layer in the radial direction of the tire, The tread portion is positioned on the outer side of the belt layer in the radial direction of the tire, An inner liner arranged on the inner surface of the tire along the carcass layer, A tie rubber is disposed between the carcass layer and the inner liner, The rib portion of the tread section closest to the tire's equatorial plane is made of conductive rubber called Earthtread rubber, Equipped with, The carcass layer includes carcass cords and carcass coat rubber that encloses the carcass cords. The tie rubber has a portion that is inserted between the carcass cords of the carcass layer, at least within the arrangement range of the belt layer. The volume resistivity of the aforementioned rubber tie is less than 1 × 10^8 [Ω·cm]. tire. [2] In the cross-section of the tread portion closest to the tire's equatorial plane, as seen when the tire is cut in the circumferential direction, the tie rubber is inserted at least once between the carcass cords of the carcass layer, along the circumferential direction and within a circumferential length of 50 mm. The tire described in [1]. [3] The tire as described in [1] or [2], wherein the relationship between the intercord cross-sectional area Sc(50Ave), calculated by the average distance between the centers of the carcass cords and the average thickness of the carcass layer in a circumferential length of 50 mm along the tire's circumferential direction, and the cross-sectional area St(50Ave) of the tie rubber that has entered the carcass coat rubber in that range, is as follows in the cross-sectional area observed when the tire is cut in the circumferential direction of the rib portion of the tread portion closest to the tire's equatorial plane, and the relationship between the intercord cross-sectional area Sc(50Ave), calculated by the average distance between the centers of the carcass cords and the average thickness of the carcass layer in a circumferential length of 50 mm along the tire's circumferential direction, and the cross-sectional area St(50Ave) of the tie rubber that has entered the carcass coat rubber in that range, is as follows in the cross-sectional area observed when the tire is cut in the circumferential direction of the tire, with respect to the rib portion of the tread portion closest to the tire's equatorial plane, and the relationship between the intercord cross-sectional area Sc(50Ave), calculated by the average distance between the centers of the carcass cords and the average thickness of the carcass layer along the tire's circumferential direction, and the cross-sectional area of ​​the tie rubber that has entered the carcass coat rubber in that range, is as follows. 0.02≦St(50Ave) / Sc(50Ave)≦0.5 [4] The tire according to any one of [1] to [3], wherein the thickness Tc of the carcass layer and the height Tt of the tie rubber embedded in the carcass coat rubber are in the following relationship. 0.014 ≤ Tt / Tc ≤ 0.8 [5] The tire according to any one of [1] to [4], wherein the cross-sectional area St of the tie rubber inserted between the carcass cords and the height Tt of the tie rubber inserted between the carcass cords are in the following relationship. 0.02mm ≤ St / Tt ≤ 2.0mm [6] A tire according to any one of [1] to [5], wherein the ratio Ht / Hc of the hardness of the tie rubber to the hardness Hc of the carcass coat rubber is 0.5 or more and 2.0 or less. [7] A tire according to any one of [1] to [6], wherein, when the tire is cut in the circumferential direction through the Earthtread rubber, the Earthtread rubber is arranged such that the ratio of the cross-sectional area Sea of ​​the Earthtread rubber to the cross-sectional area Str of the tread portion is as follows, and the tie rubber is inserted between the carcass cords of the carcass layer on the inner side of the Earthtread rubber arrangement range in the radial direction of the tire. 0.8 ≤ Sea / Str ≤ 1 [Explanation of Symbols]

[0082] 1 tire 2 Tread section 3 Tread Rubber 3a Cap Tread 3b Undertread 4. Sidewall section 5 Sidewall rubber 10 Bead section 11 Bead core 14 Bead Filler 15, 150 Carcass Layer 16, 161, 162 Carcass chord 17, 171, 172 Carcass Coat Rubber 18 Belt Layer 18b Coated rubber 21 Inner Liner 22 Thai rubber 25 Inner surface of tire 30 Rim Cushion 31 Rim cushion rubber 32 Rim fitting surface 50, 50a Earth Red Rubber

Claims

1. A pair of bead portions are arranged on both sides of the tire's equatorial plane in the tire width direction, A bead core provided in each of the pair of bead portions, The rim cushion rubber is arranged to form the rim fitting surface in the bead portion and to extend from the inner side in the tire width direction to the outer side in the tire width direction of the bead core, At least one carcass layer is stretched between the pair of bead portions, A belt layer is disposed on the outer side of the carcass layer in the radial direction of the tire, The tread portion is positioned on the outer side of the belt layer in the radial direction of the tire, An inner liner arranged on the inner surface of the tire along the carcass layer, A tie rubber is disposed between the carcass layer and the inner liner, The rib portion of the tread section closest to the tire's equatorial plane is made of conductive rubber called Earthtread rubber, Equipped with, The carcass layer includes carcass cords and carcass coat rubber that encloses the carcass cords. The tie rubber has a portion that is inserted between the carcass cords of the carcass layer, at least within the arrangement range of the belt layer. The volume resistivity of the aforementioned rubber tie is less than 1 × 10⁸ [Ω·cm]. tire.

2. In the cross-section of the tread portion closest to the tire's equatorial plane, as seen when the tire is cut in the circumferential direction, the tie rubber is inserted at least once between the carcass cords of the carcass layer, along the circumferential direction and within a circumferential length of 50 mm. The tire according to claim 1.

3. The tire according to claim 1 or claim 2, wherein the relationship between the intercord cross-sectional area Sc(50Ave), calculated by the average distance between the centers of the carcass cords and the average thickness of the carcass layer in a range of 50 mm in the circumferential direction of the tire, and the cross-sectional area St(50Ave) of the tie rubber that has entered into the carcass coat rubber in the range, is as follows, in the cross-sectional area observed when the tire is cut in the circumferential direction of the rib portion of the tread portion closest to the tire equator, and the relationship between the intercord cross-sectional area Sc(50Ave), calculated by the average distance between the centers of the carcass cords and the average thickness of the carcass layer in a range of 50 mm in the circumferential direction of the tire, and the cross-sectional area St(50Ave) of the tie rubber that has entered into the carcass coat rubber in the range, is as follows. 0.02≦St(50Ave) / Sc(50Ave)≦0.5

4. The tire according to claim 1 or claim 2, wherein the thickness Tc of the carcass layer and the height Tt of the tie rubber embedded in the carcass coat rubber have the following relationship. 0.014 ≤ Tt / Tc ≤ 0.8

5. The tire according to claim 1 or claim 2, wherein the cross-sectional area St of the tie rubber inserted between the carcass cords and the height Tt of the tie rubber inserted between the carcass cords have the following relationship. 0.02mm≦St / Tt≦2.0mm

6. The tire according to claim 1 or claim 2, wherein the ratio Ht / Hc of the hardness of the tie rubber to the hardness Hc of the carcass coat rubber is 0.5 or more and 2.0 or less.

7. The tire according to claim 1 or 2, wherein, when the tire is cut in the circumferential direction through the Earthtread rubber, the Earthtread rubber is arranged such that the ratio of the cross-sectional area Sea of ​​the Earthtread rubber to the cross-sectional area Str of the tread portion is as follows, and the tie rubber is inserted between the carcass cords of the carcass layer on the inner side of the Earthtread rubber arrangement range in the radial direction of the tire. 0.8 ≤ Sea / Str ≤ 1

Images