Tire

Abstract

This tire comprises bead cores 11 that are provided to each of a pair of bead parts 10, at least one carcass layer 15 that is continuously spanned between the pair of bead parts 10, a belt layer that is disposed on the outside of the carcass layer 15 in the tire radial direction, tread rubber that is disposed on the outside of the belt layer in the tire radial direction, an inner liner 21 that is disposed along the carcass layer 15 on a tire inner surface, and rim cushion rubber 31 that is provided on the outside of the carcass layer 15 in the tire width direction at the bead parts 10. The bead cores 11 have bead wires 12 and bead insulation rubber 13 that wraps the bead wires 12. The bead cores 11 have a volume resistivity of less than 1×10^8 [Ω・cm]. The bead insulation rubber 13 has a volume resistivity of less than 1×10^8 [Ω・cm].

Description

tire

[0001] The present invention relates to a tire.

[0002] In recent years, there has been an increasing demand for fuel-efficient tires due to environmental issues and other factors. One method for improving tire fuel efficiency is to increase the silica content in the rubber compounds that make up the tire's cap tread, undertread, sidewall rubber, etc., 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., and reduces the tire's anti-static performance. When the tire's anti-static performance decreases, static electricity generated during vehicle operation is more likely to accumulate, which can easily cause radio interference, such as radio noise.

[0003] For this reason, some conventional pneumatic tires are equipped with a conductive member with low electrical resistance to improve charge suppression performance and make it easier to release static electricity generated on a vehicle while the vehicle is running onto the road surface.For example, Patent Document 1 describes a configuration that includes a rim cushion rubber provided at a location of the bead portion that comes into contact with the rim, and a conductive rubber that is arranged together with the rim cushion rubber, one end of which is exposed on the outer surface of the rim cushion rubber so as to come into contact with the rim, and the other end of which is in contact with a tire component adjacent to the rim cushion rubber (for example, a carcass, inner liner, or bead filler), and has lower electrical resistance than the rim cushion rubber.

[0004] JP 2016-55660 A

[0005] However, in the conventional configuration, a conductive member with a lower volume resistivity than the rim cushion rubber is added to the rim cushion rubber, which increases the heat generated by adding the conductive member, and this may make the rolling resistance of the tire more susceptible to deterioration.

[0006] The present invention has been made in view of the above, and has an object to provide a tire that can reduce electrical resistance while suppressing deterioration of rolling resistance.

[0007] In order to solve the above-mentioned problems and achieve the objects, a tire according to the present invention includes a pair of bead portions arranged on both sides of the tire equatorial plane in the tire width direction, a bead core provided in each of the pair of bead portions, at least one carcass layer continuously spanning between the pair of bead portions, a belt layer arranged on the tire radially outer side of the carcass layer, a tread rubber arranged on the tire radially outer side of the belt layer, an inner liner arranged on the tire inner surface along the carcass layer, and a rim cushion rubber provided on the tire width outer side of the carcass layer in the bead portion, wherein the bead core has a bead wire and a bead insulation rubber wrapping the bead wire, and the bead core has a volume resistivity of less than 1×10^8 [Ω-cm], and the bead insulation rubber has a volume resistivity of less than 1×10^8 [Ω-cm].

[0008] In the above tire, it is preferable that the bead wire has a volume resistivity of less than 1×10 0 [Ω·cm].

[0009] In the tire, when tangents are drawn in the core outward direction to the adjacent bead wires at the outermost periphery of the bead core, and the area of ​​the region surrounded by these tangents and a part of the outer periphery of the bead wire is defined as the cross-sectional area S of the bead core, the total cross-sectional area of ​​the bead wires is defined as Sw, and the cross-sectional area of ​​the bead insulation rubber is defined as S-Sw, it is preferable that the average value of the ratio (S-Sw) / S of the cross-sectional area of ​​the bead insulation rubber to the cross-sectional area S of the bead core at a plurality of predetermined locations in the tire circumferential direction satisfies 0.1 or more and 0.8 or less.

[0010] In the tire, it is preferable that an average value of thicknesses Gi of the bead insulation rubber between adjacent bead wires at a plurality of predetermined locations in the tire circumferential direction is 1.5 mm or less.

[0011] In addition, in the above tire, it is preferable that the bead core has a plurality of bead wires that are different in the tire width direction, and that among the plurality of bead wires, there are at least two locations in the tire circumferential direction that satisfy the requirement that the thickness Gi of the bead insulation rubber between the bead wires adjacent in the tire width direction is 0.01 mm or less.

[0012] In addition, in the above tire, it is preferable that the bead core has a cover member that covers the bead core over an area of ​​at least 1 mm in the tire circumferential direction, and that the cover member has a volume resistivity of less than 1×10^8 Ω cm.

[0013] Furthermore, the above tire preferably includes a conductor extending from the belt to the bead portion, and at least one of the conductor and the inner liner has a volume resistivity of less than 1 x 10^8 [Ω-cm], and in at least one of the bead portions, at least one of the conductor and the inner liner overlaps the bead core, the overlap amount LAP between the conductor and at least one of the inner liner and the bead core is 3≦LAP [mm], and the rim cushion including the rim cushion rubber has a volume resistivity of less than 1 x 10^8 [Ω-cm].

[0014] In the tire, it is preferable that the thickness of the carcass coat rubber of the carcass layer located on both sides of the bead core in the tire width direction and in contact with the bead core is Gp [mm], and the thickness GP of the carcass coat rubber satisfies 0.1≦Gp≦5.0.

[0015] The tire preferably further comprises an earth tread having a volume resistivity of less than 1×10^8 [Ω·cm], penetrating the tread rubber to come into contact with the belt layer and exposed on the surface of the tread rubber.

[0016] Moreover, in the above tire, the rim cushion rubber forms a rim fitting surface in the bead portion and is arranged from the inner side in the tire width direction to the outer side in the tire width direction of the bead core, and further comprises a tread portion including the tread rubber, a tie rubber arranged between the carcass layer and the inner liner, and earth tread rubber which is a conductive rubber in a rib portion of the tread portion closest to the tire equatorial plane, the carcass layer includes carcass cords and carcass coat rubber wrapping the carcass cords, and the tie rubber has portions which are inserted between the carcass cords of the carcass layer at least in the arrangement range of the belt layer, and it is preferable that the volume resistivity of the tie rubber is less than 1 x 10^8 [Ω cm].

[0017] In addition, in the above tire, it is preferable that, in a cross section seen when the tire is cut in the tire circumferential direction for the rib portion of the tread portion closest to the tire equatorial plane, the tie rubber is inserted between the carcass cords of the carcass layer at at least one location along the tire circumferential direction within a range of 50 mm in the tire circumferential direction.

[0018] In the above tire, it is preferable that the relationship between the inter-cord cross-sectional area Sc(50Ave), calculated from the average center-to-center distance of the carcass cords and the average thickness of the carcass layer within a circumferentially long range of 50 mm along the tire circumferential direction in a cross section seen when the tire is cut in the tire circumferential direction at the rib portion of the tread portion closest to the tire equatorial plane, and the cross-sectional area St(50Ave) of the tie rubber embedded in the carcass coat rubber within the above range, is as follows: 0.02≦St(50Ave) / Sc(50Ave)≦0.5

[0019] In the tire, it is preferable that the thickness Tc of the carcass layer and the height Tt of the tie rubber embedded in the carcass coat rubber satisfy the following relationship: 0.014≦Tt / Tc≦0.8

[0020] In the tire, it is preferable that a cross-sectional area St of the tie rubber inserted between the carcass cords and a height Tt of the tie rubber inserted between the carcass cords satisfy the following relationship: 0.02 mm≦St / Tt≦2.0 mm

[0021] In the tire, it is preferable that a ratio Ht / Hc of a hardness Ht of the tie rubber to a hardness Hc of the carcass coat rubber is 0.5 or greater and 2.0 or less.

[0022] In the tire, when the tire is cut in the tire circumferential direction through the earth tread rubber, the earth tread rubber is arranged so that the ratio of a cross-sectional area Sea of ​​the earth tread rubber to a cross-sectional area Str of the tread portion satisfies the following relationship, and it is preferable that the tie rubber is inserted between the carcass cords of the carcass layer on the inner side in the tire radial direction of the arrangement range of the earth tread rubber: 0.8≦Sea / Str≦1

[0023] The tire according to the present invention has an effect of being able to reduce electrical resistance while suppressing deterioration in rolling resistance.

[0024] FIG. 1 is a cross-sectional view in the tire meridian direction showing a pneumatic tire 1 according to an embodiment. FIG. 2 is a detailed view of a region on one side of the tire equatorial plane in the tire width direction in FIG. 1. FIG. 3 is a detailed view of a bead portion shown in FIG. 2. FIG. 4 is a detailed view of the periphery of the bead core shown in FIG. 3 and is an explanatory diagram illustrating the definition of the cross-sectional areas of the bead core and the bead insulation rubber. FIG. 5 is a detailed view of the periphery of the bead core shown in FIG. 3 and is an explanatory diagram illustrating the calculation of the thickness of the bead insulation rubber between adjacent bead wires. FIG. 6 is a detailed view of the periphery of the bead core shown in FIG. 3 and is an explanatory diagram illustrating the thickness of the bead insulation rubber between adjacent bead wires in the tire width direction. FIG. 7 is a detailed view of a bead portion according to a modified example. FIG. 8 is a table showing the results of a performance evaluation test of a pneumatic tire. FIG. 9 is a table showing the results of a performance evaluation test of a pneumatic tire. FIG. 10 is a diagram showing a portion of the tire meridian cross-section shown in FIG. 1. FIG. 11 is a diagram showing an example of a cross-sectional structure including a two-ply carcass layer. FIG. 12 is a diagram showing an example of the cross-sectional structure of a portion of the side rubber shown in FIG. 1 . FIG. 13 is a diagram showing a schematic external view of a tire. FIG. 14 is a diagram explaining the area of ​​a portion of the tie rubber that is inserted between the carcass cords of the carcass layer. FIG. 15 is a diagram explaining that the thickness of the carcass layer varies in the tire circumferential direction. FIG. 16 is a diagram explaining the height of the tie rubber that is inserted between the carcass cords. FIG. 17 is a diagram showing a modified example of the cross-sectional structure of a portion of the tread portion shown in FIG. 1 . FIG. 18 is a diagram explaining the cross-sectional area and height of the tie rubber that is inserted into the carcass coat rubber. FIG. 19 is a diagram showing a cross-section of the tire when cut in the circumferential direction at the position of the earth tread rubber in FIG. 1 . FIG. 20 is a cross-section of a pneumatic tire according to an embodiment in which a non-penetrating type earth tread rubber is adopted, taken in the tire meridian direction. FIG. 21 is a diagram showing a cross-section of the tire when cut in the circumferential direction at the position of the earth tread rubber in FIG. 20 . FIG. 22A is a diagram showing the results of a performance evaluation test of a pneumatic tire. FIG. 22B is a diagram showing the results of a performance evaluation test of a pneumatic tire. FIG. 22C is a chart showing the results of a performance evaluation test of a pneumatic tire.

[0025] Hereinafter, embodiments of a tire according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[0026] [Embodiment] [Pneumatic Tire] In the following description, a pneumatic tire 1 will be used as an example of a tire according to the present invention. The pneumatic tire 1, which is an example of a tire, can be filled with air, an inert gas such as nitrogen, or other gases.

[0027] In the following description, 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 tire radially inner side refers to the side toward the tire rotation axis in the tire radial direction, and the tire radially outer side 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 tire widthwise inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire widthwise outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the tire rotation axis and passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL coincides in position in the tire width direction with the tire widthwise centerline, which is the center position of the pneumatic tire 1 in the tire width direction. The tire width is the width in the tire width direction between the portions located outermost in the tire width direction, that is, the distance in the tire width direction between the portions farthest from the tire equatorial plane CL. The tire equator line refers to a line that is on the tire equatorial plane CL and extends along the tire circumferential direction of the pneumatic tire 1. In the following description, the tire meridian cross section refers to a cross section obtained by cutting the tire along a plane that includes the tire rotation axis.

[0028] Fig. 1 is a cross-sectional view in the tire meridian direction showing a pneumatic tire 1 according to an embodiment. Fig. 2 is a detailed view of a region on one side from the tire equatorial plane in the tire width direction in Fig. 1. Figs. 1 and 2 show one side region in the tire radial direction. The figures also show a radial tire for passenger cars as an example of a pneumatic tire.

[0029] A pneumatic tire 1 according to the embodiment has an annular structure centered on the tire rotation axis, and includes 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 (conductor) 22. Of these, the pair of sidewall portions 4, 4 and the pair of bead portions 10, 10 are each disposed on either side of the tire equatorial plane CL in the tire width direction.

[0030] The pair of bead portions 10, 10 are located radially inward of the pair of sidewall portions 4, 4, and each includes a bead core 11, a bead filler 14, and a rim cushion 30. That is, a pair of bead cores 11, a pair of bead fillers 14, 14, and a pair of rim cushions 30, 30 are arranged on both sides of the tire equatorial plane CL in the tire width direction. In this embodiment, as shown in FIG. 2 , the bead portion 10 refers to the region from the rim diameter measurement point to one-third of the tire cross-sectional height SH. The tire cross-sectional height SH refers to one-half 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, pressurized to a specified internal pressure, and under no load.

[0031] Here, the specified rim refers to the "applicable rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. Also, the specified internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO.

[0032] The pair of bead cores 11, 11 are annular members formed by bundling a plurality of bead wires and constitute the cores of the pair of bead portions 10, 10. The pair of bead fillers 14, 14 are respectively arranged on the outer sides of the pair of bead cores 11, 11 in the tire radial direction to reinforce the bead portion 10.

[0033] 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 toroidally spanned between a pair of bead portions 10, 10 located on both sides in the tire width direction to form the tire framework. The carcass ply of the carcass layer 15 is formed by coating multiple carcass cords (not shown) made of steel or organic fiber material such as aramid, nylon, polyester, or rayon with carcass coat rubber 17 and rolling them. The carcass ply of the carcass layer 15 has a carcass angle, defined as the inclination angle of the extension direction of the carcass cords with respect to the tire circumferential direction, in the range of 80 degrees to 95 degrees in absolute value.

[0034] In this embodiment, the carcass layer 15 has a single-layer structure and is continuously laid between the bead cores 11, 11 on both sides in the tire width direction. Both end portions of the carcass layer 15 are wound back and secured to the outer side in the tire width direction so as to enclose the bead cores 11 and the bead fillers 14. That is, the carcass layer 15 is wound back near both end portions in a tire meridian cross section from the inner side in the tire width direction of the bead cores 11 and the bead fillers 14 to the inner side in the tire radial direction, and then wound back to the outer side in the tire width direction.

[0035] For this reason, the carcass layer 15 has a carcass main body portion 15a disposed between the pair of bead portions 10, and a turnup portion 15b formed continuously from the carcass main body portion 15a and folded back from the inner side in the tire width direction of the bead core 11 to the outer side in the tire width direction. The carcass main body portion 15a here is a portion formed in the carcass layer 15 between the inner sides in the tire width direction of the pair of bead cores 11, and the turnup portion 15b is formed continuously from the carcass main body portion 15a on the inner side in the tire width direction of the bead core 11, and is a portion folded back through the inner side in the tire radial direction of the bead core 11 to the outer side in the tire width direction. The bead filler 14 is disposed on the inner side in the tire width direction of the turnup portion 15b, which is a portion folded back to the outer side in the tire width direction of the bead core 11, and on the outer side in the tire radial direction of the bead core 11.

[0036] In the carcass ply of the carcass layer 15 formed in this manner, the volume resistivity of the carcass coat rubber 17, which is the coat rubber for the carcass cords, is preferably less than 1×10 8 [Ω·cm].

[0037] The volume resistivity (volume specific resistance) is measured based on "Vulcanized rubber and thermoplastic rubber - Determination of volume resistivity and surface resistivity" as specified in JIS K6271. 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], it can be said that the member has conductivity capable of suppressing static electricity buildup.

[0038] The pair of rim cushions 30, 30 owned by the pair of bead portions 10, 10 are respectively arranged on the tire radially inner side of the bead cores 11, 11 on both sides in the tire width direction and the turned-up portion of the carcass layer 15. The rim cushion 30 is provided on the tire width outer side of the carcass layer 15 in the bead portion 10. More specifically, the rim cushion 30 is arranged at least from the tire width inner side of the bead core 11 to the tire width outer side. In other words, the rim cushion 30 is arranged from the tire width inner side of the bead core 11 in the bead portion 10, passing through the tire radially inner side of the bead core 11, to the tire width outer side of the bead core 11.

[0039] The rim cushion 30 arranged in this manner is the part that comes into contact with the rim flange R of the rim wheel when the pneumatic tire 1 is mounted on the rim wheel, and constitutes the contact surface of the bead portion 10 that comes into contact with the rim flange R. Of the contact surface of the rim cushion 30 that comes into contact with the rim flange R, the part that forms the inner circumferential surface of the rim cushion 30 constitutes the rim fitting surface 32 of the bead portion 10 that fits into the rim wheel.

[0040] The rim cushion 30 is made up of a rubber member, a 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 that constitutes the rim cushion 30 has a volume resistivity of less than 1×10^8 [Ω·cm].

[0041] In this embodiment, the volume resistivity of the entire rim cushion rubber 31 that constitutes the rim cushion 30 is set to less than 1×10^8 Ω-cm. However, the volume resistivity of at least a portion of the rim cushion rubber 31, for example, a portion located on the outer side of the bead core 11 in the tire width direction and overlapping the bead core 11 in the tire radial direction, may also be set to less than 1×10^8 Ω-cm. Also, a configuration using the known technology described in JP 2016-55660 A may be used. Specifically, the rim cushion may be configured with a conductive rubber (not shown) that is disposed together with the rim cushion rubber 31 and has one end exposed on the outer surface of the rim cushion rubber 31 so as to come into contact with the rim, and the other end in contact with the bead core 11 via the carcass layer 15, and the volume resistivity of this conductive rubber may be set to less than 1×10^8 Ω-cm.

[0042] The rim cushion rubber 31 has a tan δ value at 60° C. in the range of 0.085 to 0.35, and a rubber hardness Hs in the range of 35 to 111.

[0043] The tan δ value at 60°C is measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho, Ltd. under conditions of an initial strain of 10%, an amplitude of ±0.5%, and a frequency of 20 Hz. The rubber hardness Hs is measured at a temperature of 20°C in accordance with JIS K6253.

[0044] The rim cushion 30 may also include a member other than the rim cushion rubber 31. For example, the rim cushion 30 may include a chafer, which is a member made of a fiber material or a rubber member, 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 a rim wheel.

[0045] The belt layer 18 has one or more belt plies extending in the tire width direction, and in this embodiment, multiple belt plies 181 to 183 are laminated. That is, in this embodiment, the belt layer 18 is configured by laminating a pair of cross belts 181, 182 and a belt cover 183 in the tire radial direction, and is disposed radially outward of the carcass layer 15 and wound around the outer periphery of the carcass layer 15. The pair of cross belts 181, 182 are configured by coating a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them, and the belt angle, which is the inclination angle of the extension direction of the belt cords with respect to the tire circumferential direction, is within the range of 20 degrees to 65 degrees in absolute value. Furthermore, the pair of cross belts 181, 182 have belt angles with opposite signs and are laminated so that the extension directions of the belt cords cross each other, forming a so-called cross-ply structure. That is, the inclination directions of the belt cords of the pair of cross belts 181, 182 in the tire width direction relative to the tire circumferential direction are opposite to each other. The belt cover 183 is formed by rolling a plurality of cords made of steel or organic fiber material coated with coated rubber, and the belt angle is in the range of 0 degrees to 10 degrees in absolute value. The belt cover 183 is also layered and disposed on the outer side of the cross belts 181, 182 in the tire radial direction. The belt layer 18 as a whole has a volume resistivity of less than 1×10^8 Ω-cm.

[0046] The tread portion 2 is configured with tread rubber 3, which is a rubber composition, and is arranged radially outward of the carcass layer 15 and the belt layer 18, and is exposed at the outermost portion in the radial direction of the pneumatic tire 1. Therefore, the outer peripheral surface of the tread portion 2 forms part of the contour of the pneumatic tire 1, and a plurality of grooves, such as circumferential main grooves 6 and lug grooves (not shown), that extend in the circumferential direction of the tire are formed in the tread portion 2. The tread rubber 3 that configures the tread portion 2 also has a cap tread 3a and an undertread 3b.

[0047] The cap tread 3a is a rubber member located at the outermost side of the tread portion 2 in the tire radial direction and constituting the tire contact surface 2a. It may have a single-layer structure (see FIG. 1) or a multi-layer structure (not shown). The tan δ value of the cap tread 3a at 60°C is preferably 0.25 or less. 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. This reduces the rolling resistance of the pneumatic tire 1. The 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 with an increased silica content.

[0048] The undertread 3b is a member laminated on the inner side of the cap tread 3a in the tire radial direction. The volume resistivity of the undertread 3b is preferably lower than the volume resistivity of the cap tread 3a.

[0049] Each of the pair of sidewall portions 4, 4 includes a sidewall rubber 5, and the pair of sidewall rubbers 5, 5 of the pair of sidewall portions 4, 4 are disposed on the outer side of the carcass layer 15 in the tire width direction. The tan δ value of the sidewall rubber 5 at 60 [°C] is preferably 0.20 or less. 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. This reduces the rolling resistance of the pneumatic tire 1. The sidewall rubber 5 having such a volume resistivity is produced by using a low-heat-generating compound with a low carbon content and reinforcing it with an increased silica content.

[0050] Although there are no particular limitations on the upper limit of the volume resistivity of the cap tread 3a, the lower limit of the volume resistivity of the undertread 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, they are subject to physical constraints since they are rubber members.

[0051] An earth tread 50 (hereinafter sometimes referred to as earth tread rubber) is also disposed in the tread portion 2. The earth tread 50 is a conductive rubber member that is embedded in the tread rubber 3 and exposed to the tire contact surface. The earth tread 50 penetrates the tread rubber 3 to come into contact with the belt layer 18, and is disposed so as to be exposed to the tire contact surface 2a, which is the surface of the tread rubber 3. More specifically, the earth tread 50 is exposed to the tire contact surface 2a, and penetrates the cap tread 3a and under tread 3b of the tread rubber 3 to come into conductive contact with the belt layer 18. This ensures a conductive path from the belt layer 18 to the road surface by the earth tread 50.

[0052] The earth tread 50 has an annular structure extending around the entire tire circumference, and extends continuously in the tire circumferential direction with a portion of it exposed to the tire contact patch 2a. Therefore, when the pneumatic tire 1 rolls, the earth tread 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 secured. In this embodiment, the width of the earth tread 50 in the tire width direction is narrower than the groove width of the circumferential main grooves 6 formed in the tread portion 2 and extending in the tire circumferential direction, and the earth tread 50 is formed between circumferential main grooves 6 adjacent in the tire width direction.

[0053] The earth tread 50 arranged in this manner is made of a conductive rubber material having a lower volume resistivity than the tread rubber 3, and the volume resistivity of the earth tread 50 is less than 1×10^8 [Ω·cm]. It is more preferable that the volume resistivity of the earth tread 50 is 1×10^6 [Ω·cm] or less.

[0054] The inner liner 21 is disposed on the tire inner surface 25 along the carcass layer 15. That is, the inner liner 21 constitutes the tire inner surface 25, which is the inner surface of the pneumatic tire 1, and faces the tire cavity, which is the space inside the pneumatic tire 1. The inner liner 21 that constitutes the tire inner surface 25 is a rubber layer that is disposed on the tire cavity side with respect to the carcass layer 15, and covers the carcass layer 15 from the tire cavity side.

[0055] The inner liner 21 is an air permeation prevention layer, and is disposed to cover the carcass layer 15, thereby suppressing oxidation due to exposure of the carcass layer 15 and preventing leakage of air filled in the tire. In general, the air permeability coefficient of the inner liner 21, when measured at a temperature of 30°C in accordance with JIS K7126-1, is preferably 100 x 10-12 [cc cm / cm^2 sec cmHg] or less, and more preferably 50 x 10-12 [cc cm / cm^2 sec cmHg] or less.

[0056] The tie rubber 22 is disposed between the carcass layer 15 and the inner liner 21. Like the inner liner 21, the tie rubber 22 is disposed along the carcass layer 15 on the tire cavity side of the carcass layer 15. That is, the inner liner 21 and the tie rubber 22 are laminated and disposed along the carcass layer 15 on the tire cavity side of the carcass layer 15.

[0057] The tie rubber 22 is a layer for preventing the carcass cords of the carcass layer 15 from digging into the inner liner 21 when the unvulcanized pneumatic tire 1 is inflated during tire manufacturing. The tie rubber 22 also contributes to air permeation prevention and steering stability on dry road surfaces in the manufactured pneumatic tire 1.

[0058] In this embodiment, the tie rubber 22 acts as a conductor that forms part of the conductive path from the rim cushion rubber 31 in contact with the rim flange R to the belt layer 18 and earth tread 50. This tie rubber 22 achieves reduced electrical resistance by compounding carbon black with diene-based rubber or isoprene-based rubber. The tie rubber 22 is disposed between a pair of bead portions 10 along the carcass layer 15, 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 be less than 1×10^6 [Ω-cm].

[0059] In this embodiment, the inner liner 21 is also electrically conductive and forms part of the conductive path from the rim cushion rubber 31 in contact with the rim flange R to the belt layer 18 and earth tread 50. The inner liner 21 achieves reduced electrical resistance by, for example, compounding carbon black into a rubber composition whose main component is butyl rubber. The inner liner 21 is disposed on the tire cavity side of the tie rubber 22, spanning between the 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 be less than 1×10^6 [Ω-cm].

[0060] In this embodiment, the inner liner 21 and the tie rubber 22 both have a volume resistivity of less than 1×10^8 [Ω-cm], but it is sufficient that the volume resistivity of at least one of the inner liner 21 and the tie rubber 22 is less than 1×10^8 [Ω-cm]. In other words, as long as the tie rubber 22 is disposed as a conductor, the volume resistivity of the inner liner 21 may be 1×10^8 [Ω-cm] or more.

[0061] FIG. 3 is a detailed view of the bead portion shown in FIG. 2 . In the bead portion 10, the inner liner 21 and the tie rubber 22 are laminated and arranged to overlap the bead core 11 in the tire radial direction, as shown in FIG. 3 . Specifically, the overlap amount LAP between the tie rubber 22 and the bead core 11, i.e., the distance between the end 22 a of the tie rubber 22 and the outermost diameter portion 11 a of the bead core 11 in the tire radial direction, is preferably 3 mm or more. If this overlap amount LAP is 3 mm or more, electrical resistance can be maintained low. While the rolling resistance worsens as the overlap amount LAP increases, lower electrical resistance can be achieved. In this configuration, the tie rubber 22 overlaps the bead core 11 in the tire radial direction by an overlap amount of 3 mm or more. Therefore, in at least one bead portion 10 of a pair of bead portions 10, the end 22 a of the tie rubber 22 contacts the bead core 11 via the carcass layer 15 (carcass coat rubber 17). In this embodiment, in the bead portions 10 on both sides in the tire width direction, the end portions 22a of the tie rubbers 22 are in contact with the bead cores 11 via the carcass layer 15 (carcass coat rubber 17).

[0062] Furthermore, the end 21a of the inner liner 21 extends radially inward of the tire than the end 22a of the tie rubber 22, and is in contact with the bead core 11 via the carcass layer 15 (carcass coat rubber 17). Like the tie rubber 22, the inner liner 21 overlaps the bead core 11 in the tire radial direction by an LAP amount of 3 mm or more. Therefore, in at least one bead portion 10 of a pair of bead portions 10, the end 21a of the inner liner 21 is in contact with the bead core 11 via the carcass layer 15 (carcass coat rubber 17). In this embodiment, in the bead portions 10 on both sides in the tire width direction, the end 21a of the inner liner 21 is in contact with the bead core 11 via the carcass layer 15 (carcass coat rubber 17).

[0063] In this embodiment, the inner liner 21 and the tie rubber 22 are both disposed to overlap the bead core 11 in the tire radial direction, and the overlap amount LAP with the bead core 11 is 3 mm or more. However, it is sufficient that at least one of the inner liner 21 and the tie rubber 22 overlaps the bead core 11 in the tire radial direction and the overlap amount LAP is 3 mm or more. In this case, the inner liner 21 or the tie rubber 22 with a volume resistivity of less than 1×10^8 Ω cm overlaps the bead core 11 in the tire radial direction by an overlap amount LAP of 3 mm or more.

[0064] The carcass layer 15 is located on both sides of the bead core 11 in the tire width direction and contacts the bead core 11. As shown in Figure 3, when the thickness of the carcass coat rubber 17 of the carcass layer 15 is Gp [mm], the thickness GP of the carcass coat rubber 17 satisfies 0.1 ≤ Gp ≤ 5.0. By specifying the range of the thickness GP of the carcass coat rubber 17 in this way, the conductive distance in the tire width direction is shortened, thereby further reducing the electrical resistance of the bead portion 10. It is more preferable that the thickness GP of the carcass coat rubber 17 satisfies 0.1 ≤ Gp ≤ 4.0. The smaller the thickness GP, the smaller the rolling resistance and the lower the electrical resistance can be achieved.

[0065] Fig. 4 is a detailed view of the periphery of the bead core 11 shown in Fig. 3 and is an explanatory diagram illustrating the definition of the cross-sectional areas of the bead core 11 and the bead insulation rubber 13. Fig. 5 is a detailed view of the periphery of the bead core 11 shown in Fig. 3 and is an explanatory diagram illustrating the calculation of the thickness of the bead insulation rubber 13 between adjacent bead wires 12, 12. Fig. 6 is a detailed view of the periphery of the bead core 11 shown in Fig. 3 and is an explanatory diagram illustrating the thickness of the bead insulation rubber 13 between adjacent bead wires 12, 12 in the tire width direction. Note that the number of bead wires 12 in the bead core 11 shown in Figs. 4 to 6 is an example and can be changed as appropriate.

[0066] The pneumatic tire 1 according to this embodiment has an anti-static structure for dissipating static electricity generated on the vehicle while the vehicle is running to the road surface, and the anti-static structure uses a bead core 11. As shown in Fig. 4, the bead core 11 has a bead wire 12 and bead insulation rubber 13 that wraps around the bead wire 12. Specifically, the bead core 11 is an annular member formed by bundling one or more bead wires 12 covered with the bead insulation rubber 13 in a tire circumferential direction. The bead insulation rubber 13 is tightly attached to each other by being bundled in a multiple number of windings.

[0067] In this embodiment, the bead core 11 has a volume resistivity of less than 1×10^8 Ω-cm. It is more preferable that the bead core 11 have a volume resistivity of less than 1×10^7 Ω-cm. In this configuration, the bead core 11 can be used as a conductive path for passing static electricity. Therefore, the following paths can be used as conductive paths for static electricity flowing to the rim cushion rubber 31 in contact with the rim flange R: from the rim cushion 30 to the carcass coat rubber 17 of the turnup portion 15b of the carcass layer 15, from the carcass coat rubber 17 of the turnup portion 15b to the bead core 11, from the bead core 11 to the carcass coat rubber 17 of the carcass main body portion 15a of the carcass layer 15, and from the carcass coat rubber 17 of the carcass main body portion 15a to the tie rubber 22 or the inner liner 21. This allows static electricity that flows from the rim flange R to the rim cushion 30 to flow more reliably to the tie rubber 22 or the inner liner 21, further reducing electrical resistance.

[0068] Furthermore, because the bead core 11 undergoes little deformation when a load is applied, it is possible to prevent a deterioration in rolling resistance even when the bead insulation rubber 13 constituting the bead core 11 becomes highly heated. Therefore, by ensuring electrical conductivity so that the volume resistivity of the bead core 11 is less than 1×10^8 [Ω cm], it is possible to reduce electrical resistance while preventing a deterioration in rolling resistance.

[0069] Furthermore, the bead insulation rubber 13 is made of a conductive rubber material and has a volume resistivity of less than 1×10^8 Ω·cm. In this embodiment, by specifying an upper limit for the volume resistivity of the bead insulation rubber 13, the electrical resistance of the bead core 11 can be further reduced. The volume resistivity of the bead insulation rubber 13 is preferably equal to or greater than 1×10^0 Ω·cm and less than 1×10^8 Ω·cm. Because the volume resistivity of the bead insulation rubber 13 of the bead core 11 is less than 1×10^8 Ω·cm, the bead insulation rubber 13 can be used as a conductive path for conducting static electricity. Static electricity flowing from the rim flange R to the rim cushion 30 can be more reliably conducted to the tie rubber 22 or the inner liner 21, further reducing electrical resistance.

[0070] Furthermore, since the bead core 11 having the bead insulation rubber 13 undergoes little deformation when a load is applied, it is possible to suppress a deterioration in rolling resistance even when a highly conductive rubber material is used for the bead insulation rubber 13 and the bead insulation rubber 13 generates high heat. Therefore, by ensuring conductivity so that the volume resistivity of the bead core 11 is less than 1×10^8 [Ω cm], it is possible to reduce electrical resistance while suppressing a deterioration in rolling resistance.

[0071] The bead wire 12 is a conductive linear body formed of a metal such as steel or a combination of an organic fiber material and a metal fiber material, and has a volume resistivity of less than 1×10^0 [Ω·cm]. In this embodiment, by specifying an upper limit for the volume resistivity of the bead wire 12, the electrical resistance of the bead core 11 can be further reduced. It is more preferable that the volume resistivity of the bead wire 12 be less than 1×10^-3 [Ω·cm]. Because the volume resistivity of the bead wire 12 in the bead core 11 is less than 1×10^0 [Ω·cm], the bead wire 12 can be used as a conductive path for conducting static electricity. Static electricity flowing from the rim flange R to the rim cushion 30 can be more reliably conducted to the tie rubber 22 or the inner liner 21, further reducing electrical resistance.

[0072] 4 , tangent lines 70 are drawn outward from the bead core 11 to the bead wires 12, 12 adjacent to each other at the outermost periphery, and the area of ​​a region 71 surrounded by these tangent lines 70 and a portion of the outer periphery of the bead wire 12 is defined as the cross-sectional area S of the bead core 11. If the total cross-sectional area of ​​the bead wires 12 is defined as Sw and the cross-sectional area of ​​the bead insulation rubber 13 is defined as S-Sw, the bead core 11 has a cross-sectional area S of the bead core 11, and the average value of the ratio (S-Sw) / S of the cross-sectional area S of the bead core 11 to the cross-sectional area S of the bead core 11 measured at eight equally spaced locations (predetermined multiple locations) around the tire circumferential direction is 0.1 or more and 0.8 or less. In this embodiment, the average value of the ratio (S-Sw) / S is calculated based on measurements at eight equally spaced locations around the tire circumferential direction, but the number and positions of the measurement locations may be changed as appropriate.

[0073] In this configuration, tangent lines 70 are drawn toward the outside of the bead core 11 for each of the adjacent bead wires 12, 12 at the outermost periphery. The area of ​​the region 71 enclosed by these tangent lines 70 and a portion of the outer periphery of the bead wire 12 is defined as the cross-sectional area S of the bead core 11. This allows the region of the bead core 11 to be easily defined, and the cross-sectional area S of the bead core 11 to be easily calculated. In this embodiment, the bead core 11 has an average ratio (S-Sw) / S of the cross-sectional area S of the bead core 11 to the cross-sectional area S of the bead core 11 at eight equally spaced locations (predetermined locations) around the tire circumference, which satisfies a value between 0.1 and 0.8. Therefore, by specifying the lower limit of the average value of this ratio (S-Sw) / S, a conductive path through the bead insulation rubber 13 can be ensured, further reducing electrical resistance. The smaller the average value of this ratio (S-Sw) / S, the lower the electrical resistance can be achieved, while having almost no effect on rolling resistance.

[0074] It is also preferable that the bead insulation rubber 13 is provided continuously from the outermost to the innermost in the tire width direction in the bead core 11. With this configuration, a conductive path can be secured by the bead insulation rubber 13 that is continuous in the tire width direction, thereby further reducing electrical resistance. It is also more preferable that the average value of the ratio (S-Sw) / S of the cross-sectional area S of the bead core 11 to the cross-sectional area S-Sw is 0.15 or more and 0.7 or less.

[0075] As shown in FIG. 5 , the bead core 11 has a bead insulation rubber 13 between adjacent bead wires 12, 12, with an average thickness Gi of 1.5 mm or less at eight evenly spaced locations (predetermined locations) around the tire circumferential direction. The thickness Gi of the bead insulation rubber 13 between the bead wires 12, 12 can be calculated, for example, as follows. At any location around the tire circumferential direction of the bead core 11, the center-to-center distance between adjacent bead wires 12, 12 when a straight line is drawn is defined as L [mm], and the radii of these two adjacent bead wires 12, 12 are defined as r1 [mm] and r2 [mm], respectively. The thickness Gi [mm] of the bead insulation rubber 13 between the bead wires 12, 12 on the straight line can be calculated as Gi = L - (r1 + r2). This formula allows for easy calculation of the thickness Gi of the bead insulation rubber 13.

[0076] Furthermore, since the average value of the thickness Gi is set to 1.5 mm or less, the upper limit of the average value of the thickness Gi is specified, and by bringing the bead wires 12, 12 closer to each other, a conductive path through the bead insulation rubber 13 can be secured, thereby further reducing electrical resistance. Furthermore, the average value of the thickness Gi is more preferably 0 mm or more and 1.0 mm or less. The smaller the average value of the thickness Gi, the lower the electrical resistance can be achieved.

[0077] In the above calculation formula, the radii r1 and r2 of the bead wire 12 may be different values ​​or may be the same value. In the above calculation formula, if the cross section of the bead wire 12 is not a perfect circle (circle), the thickness Gi may be calculated by setting the midpoint of the maximum width of the non-circular bead wire 12 as the center and using the distance between this midpoint and the edge with the maximum width (i.e., 1 / 2 of the maximum width) as the radius of the non-circular bead wire 12. In addition, the above calculation formula is one example of how to calculate the thickness Gi, and the thickness Gi may also be measured directly using a measuring instrument such as a ruler or vernier calipers.

[0078] As described above, the bead core 11 is an annular member formed by bundling one or more bead wires 12 covered with the bead insulation rubber 13 and winding them in the tire circumferential direction. As shown in FIG. 6 , when the bead core 11 has multiple bead wires 12A, 12B, 12C, and 12D that are different in the tire width direction and each of the bead wires 12A to 12D is wound radially outward, it is important to specify the thickness Gi of the bead insulation rubber 13 between adjacent bead wires 12 in the tire width direction in order to ensure a conductive path through the bead insulation rubber 13. In this embodiment, the bead core 11 has at least two locations in the tire circumferential direction where the thickness Gi of the bead insulation rubber 13 between adjacent bead wires 12 in the tire width direction is 0.01 mm or less. According to this configuration, different bead wires 12, 12 approach each other in the tire width direction, thereby ensuring a conductive path through the bead insulation rubber 13 and further reducing electrical resistance. The thickness Gi of the bead insulation rubber 13 between different bead wires 12, 12 adjacent to each other in the tire width direction is preferably 0 mm or more and 0.01 mm or less. It is also more preferable that the bead wires 12 are located at the innermost positions in the tire radial direction, i.e., that all bead wires 12 adjacent to the carcass layer 15 are in contact with each other. The thickness Gi of the bead insulation rubber 13 between different bead wires 12, 12 adjacent to each other in the tire width direction may be calculated using the calculation formula described in FIG. 5 or may be directly measured using a measuring instrument such as a ruler or vernier calipers.

[0079] When the pneumatic tire 1 according to this embodiment is mounted on a vehicle and the vehicle runs, the pneumatic tire 1 rotates while the lower portion of the surface of the tread portion 2 of the pneumatic tire 1 that faces the road surface comes into contact with the road surface. The tire contact surface 2a, which is the surface of the tread portion 2, successively comes into contact with the road surface in this manner, thereby generating frictional force between the pneumatic tire 1 and the road surface. This allows the vehicle to transmit driving force, braking force, and turning force to the road surface through the frictional force between the pneumatic tire 1 and the road surface, and the vehicle runs using these driving force, braking force, and turning force.

[0080] Furthermore, static electricity may be generated while the vehicle is running, and if static electricity builds up on the vehicle, it is likely to cause radio interference such as radio noise. In this embodiment, the pneumatic tire 1 includes a pair of bead portions 10 arranged on both sides of the tire equatorial plane CL in the tire width direction, a bead core 11 provided in each of the pair of bead portions 10, at least one carcass layer 15 continuously spanning between the pair of bead portions 10, a belt layer 18 arranged on the tire radial outer side of the carcass layer 15, a tread rubber 3 arranged on the tire radial outer side of the belt layer 18, an inner liner 21 arranged on the tire inner surface along the carcass layer 15, and a rim cushion rubber 31 provided on the tire width outer side of the carcass layer 15 in the bead portion 10, the bead core 11 having a bead wire 12 and a bead insulation rubber 13 wrapping the bead wire 12, and the volume resistivity of the bead core 11 and the bead insulation rubber 13 is each less than 1×10^8 [Ω-cm]. According to this configuration, the bead core 11 and the bead insulation rubber 13 are relatively easy to conduct electricity, so that static electricity can be released to the road surface.

[0081] In other words, the low volume resistivity of the bead core 11 and the bead insulation rubber 13 reduces the tire electrical resistance, which is the electrical resistance of the pneumatic tire 1. As a result, static electricity generated while the vehicle is running can flow from the rim flange R through the bead core 11, which has a low volume resistivity, and then from this bead core 11 through the carcass layer 15 and inner liner 21 to the belt layer 18, and from the belt layer 18 to the tread rubber 3, where it can be released to the road surface from the tread rubber 3. As a result, static electricity generated on the vehicle is released to the road surface, suppressing charging of the vehicle due to static electricity.

[0082] Furthermore, because the bead core 11 undergoes little deformation when a load is applied, it is possible to prevent a deterioration in rolling resistance even when the bead insulation rubber 13 constituting the bead core 11 generates high heat. Therefore, by setting the volume resistivity of the bead core 11 and the volume resistivity of the bead insulation rubber 13 to less than 1×10^8 [Ω cm], it is possible to reduce electrical resistance while preventing a deterioration in rolling resistance.

[0083] Furthermore, in the pneumatic tire 1 of this embodiment, the bead wires 12 have a volume resistivity of less than 1×10^0 [Ω·cm]. Therefore, by using these bead wires 12 and bead insulation rubber 13 having a volume resistivity of less than 1×10^8 [Ω·cm], the volume resistivity of the bead core 11 can be reduced, and the bead core 11 can be used as part of the conductive path from the rim flange R to the tread rubber 3.

[0084] In the pneumatic tire 1 of this embodiment, tangents 70 are drawn toward the outside of the core for adjacent bead wires 12 at the outermost periphery of the bead core 11, and if the area of ​​a region 71 surrounded by these tangents 70 and a portion of the outer periphery of the bead wire 12 is taken as the cross-sectional area S of the bead core 11, the total cross-sectional area of ​​the bead wires 12 is taken as Sw, and the cross-sectional area of ​​the bead insulation rubber 13 is taken as S-Sw, then the average value of the ratio (S-Sw) / S of the cross-sectional area S of the bead core 11 to the cross-sectional area S of the bead core 11 at a plurality of predetermined locations in the tire circumferential direction is 0.1 or more and 0.8 or less. According to this embodiment, the region 71 of the bead core 11 can be easily defined, and the cross-sectional area S of the bead core 11 can be easily determined. In addition, in this embodiment, the bead core 11 has an average ratio (S-Sw) / S of the cross-sectional area S-Sw of the bead insulation rubber 13 to the cross-sectional area S of the bead core 11 at eight equal locations (predetermined multiple locations) around the tire circumferential direction, which satisfies 0.1 or more and 0.8 or less. Therefore, by specifying the lower limit of the average value of this ratio (S-Sw) / S, it is possible to ensure a conductive path through the bead insulation rubber 13, and further reduce electrical resistance.

[0085] Furthermore, in the pneumatic tire 1 of this embodiment, the average value of the thickness Gi of the bead insulation rubber 13 between adjacent bead wires 12, 12 at predetermined locations around the tire is 1.5 mm or less. Therefore, by specifying the upper limit of the average value of this thickness Gi, it is possible to ensure a conductive path through the bead insulation rubber 13 by bringing the bead wires 12, 12 closer to each other, thereby further reducing electrical resistance.

[0086] Furthermore, in the pneumatic tire 1 of this embodiment, the bead core 11 has a plurality of bead wires 12A, 12B, 12C, 12D that are different in the tire width direction, and among these plurality of bead wires 12A to 12D, there are at least two locations in the tire circumferential direction where the thickness Gi of the bead insulation rubber between adjacent bead wires in the tire width direction is 0.01 mm or less. Therefore, different bead wires that are not electrically connected approach each other in the tire width direction, thereby ensuring a conductive path through the bead insulation rubber 13 and further reducing electrical resistance.

[0087] Furthermore, the pneumatic tire 1 of this embodiment is provided with a tie rubber 22 as a conductor extending from the belt layer 18 to the bead portion 10, and at least one of the tie rubber 22 and the inner liner 21 has a volume resistivity of less than 1×10^8 [Ω-cm], and in at least one bead portion 10, at least one of the tie rubber 22 and the inner liner 21 overlaps with the bead core 11 in the tire radial direction, and the overlap amount LAP between at least one of the tie rubber 22 and the inner liner 21 and the bead core 11 is 3≦LAP [mm], and the rim cushion 30 has a volume resistivity of less than 1×10^8 [Ω-cm]. According to this configuration, the volume resistivity of at least one of the tie rubber 22 and the inner liner 21 and the volume resistivity of the rim cushion 30 are each less than 1 x 10^8 [Ω-cm], and the overlap amount LAP between at least one of the tie rubber 22 and the inner liner 21 and the bead core 11 is 3≦LAP [mm], so that the rim cushion 30 and at least one of the tie rubber 22 and the inner liner 21 can be used as part of the above-mentioned conductive path.

[0088] Therefore, the paths from the rim cushion 30 to the bead core 11, and from the bead core 11 to at least one of the tie rubber 22 and inner liner 21 can be used as conduction paths for static electricity that has flowed to the rim cushion rubber 31 that is in contact with the rim flange R. This allows static electricity that has flowed from the rim flange R to the rim cushion 30 to be more reliably channeled to at least one of the tie rubber 22 and inner liner 21, further reducing electrical resistance.

[0089] Furthermore, in the pneumatic tire 1 of this embodiment, the thickness of the carcass coat rubber 17 of the carcass layer 15 located on both sides of the bead core 11 in the tire width direction and in contact with the bead core 11 is Gp [mm], and the thickness GP of the carcass coat rubber 17 satisfies 0.1≦Gp≦5.0, so the conductive distance from the rim cushion rubber 31 to at least one of the tie rubber 22 and the inner liner 21 in the tire width direction is shortened, thereby further reducing the electrical resistance of the bead portion 10.

[0090] Furthermore, in the pneumatic tire 1 of this embodiment, the tread portion 2 is provided with an earth tread 50 having a volume resistivity of less than 1×10^8 [Ω-cm], which penetrates the tread rubber 3 to contact the belt layer 18 and is exposed to the tire contact surface 2a, so that a conductive path from the belt layer 18 to the road surface can be secured by the earth tread 50. This makes it possible to more reliably reduce the electrical resistance between the rim wheel and the road surface and more reliably release static electricity generated on the vehicle to the road surface, thereby more reliably reducing the electrical resistance of the pneumatic tire 1.

[0091] Furthermore, by providing the earth tread 50, it is possible to suppress a decrease in charge-suppressing performance when the silica content of the rubber compound constituting the cap tread 3a, under tread 3b, sidewall rubber 5, etc. is increased in order to reduce the rolling resistance of the pneumatic tire 1 and improve fuel economy. In other words, because silica has high insulating properties, an increase in the silica content of the cap tread 3a increases the volume resistivity of the cap tread 3a and reduces charge-suppressing performance, but by providing the earth tread 50, a conductive path between the belt layer 18 and the road surface can be secured. As a result, it is possible to reduce the electrical resistance of the pneumatic tire 1 while more reliably reducing rolling resistance.

[0092] [Modification] Figure 7 is a detailed view of a bead portion according to a modification. In this modification, as shown in Figure 7, the bead portion 10A includes a cover member 60 that covers the periphery of the bead core 11. This cover member 60 is made of, for example, metal thread or organic fiber thread, and is wrapped around the periphery of the bead core 11 near the end of the bead wire 12 to cover the periphery of the bead core 11 in order to prevent the end of the bead wire 12 from protruding outside the bead core 11. The cover member 60 may be any member that covers the bead core 11 over an area of ​​at least 1 mm in the circumferential direction of the tire.

[0093] The cover member 60 has a volume resistivity of less than 1×10^8 [Ω-cm], and preferably less than 1×10^6 [Ω-cm]. With this configuration, the cover member 60 can partially protect at least a part of the bead core 11 while forming part of the conductive path from the rim cushion rubber 31 to at least one of the tie rubber 22 and the inner liner 21 in the tire width direction, thereby reducing the electrical resistance of the bead portion 10.

[0094] In this modification, the cover member 60 is made of metal thread or organic fiber thread, but it may be a metal plate or a plate made of an organic material as long as it has a volume resistivity of less than 1×10^8 [Ω-cm] and covers the periphery of the bead core 11. The cover member 60 does not need to cover the entire periphery of the bead core 11, and for example, a portion 60a facing the outermost diameter portion 11a of the bead core 11 in the tire radial direction may be removed to leave an open area.

[0095] In the above embodiment, the tie rubber 22 is described as an example of the conductor extending from the belt layer 18 to the bead portion 10, but the present invention is not limited to this. For example, the conductor may be a conductive rubber sheet, conductive thread, paint, or cement that satisfies the condition of a volume resistivity of less than 1×10^8 [Ω cm].

[0096] The conductive rubber sheet may be disposed between the inner liner 21 and the tie rubber 22, or between the tie rubber 22 and the carcass layer 15. In a pneumatic tire not including the tie rubber 22, the conductive rubber sheet may be disposed between the inner liner 21 and the carcass layer 15. The conductive rubber sheet may also be disposed between the carcass layer 15 and the sidewall rubber 5, and between the carcass layer 15 and the bead core 11 or the bead filler 14. This conductive rubber sheet may be provided over all or part of the tire circumferential direction.

[0097] The conductive thread may be arranged at the interface between the inner liner 21 and the tie rubber 22, or at the interface between the tie rubber 22 and the carcass layer 15. Furthermore, in a pneumatic tire configured without the tie rubber 22, the conductive thread may be arranged at the interface between the inner liner 21 and the carcass layer 15. Furthermore, the conductive thread may be arranged in parallel to the carcass cord of the carcass layer 15, or woven into the carcass cord, within the carcass coat rubber 17. Furthermore, the conductive thread may be arranged on the outer side of the carcass cord in the carcass layer 15, at the interface between the carcass coat rubber 17 and its adjacent members (such as the sidewall rubber 5, bead core 11, or bead filler 14).

[0098] The paint is a liquid or paste-like paint having electrical conductivity, which dries and solidifies after application. The paint may be applied between the inner liner 21 and the tie rubber 22, or between the tie rubber 22 and the carcass coat rubber 17 of the carcass layer 15. In a pneumatic tire configured without the tie rubber 22, the paint may be applied between the inner liner 21 and the carcass coat rubber 17 of the carcass layer 15. The paint may be applied to the carcass cords of the carcass layer 15 and then disposed within the carcass coat rubber 17. The paint may also be applied between the carcass coat rubber 17 of the carcass layer 15 and its adjacent components (such as the sidewall rubber 5, the bead core 11, and the bead filler 14). This paint may be applied to all or part of the tire circumferential direction.

[0099] The cement is a liquid obtained by dissolving a rubber composition (e.g., rubber / CB mast) in a solvent, and dries and solidifies after application. The cement may be applied between the inner liner 21 and the tie rubber 22, or between the tie rubber 22 and the carcass coat rubber 17 of the carcass layer 15. In a pneumatic tire configured without the tie rubber 22, the cement may be applied between the inner liner 21 and the carcass coat rubber 17 of the carcass layer 15. The cement may be applied to the carcass cords of the carcass layer 15 and then disposed within the carcass coat rubber 17. The cement may also be applied between the carcass coat rubber 17 of the carcass layer 15 and its adjacent components (such as the sidewall rubber 5, the bead core 11, and the bead filler 14). The cement may be applied to all or part of the tire circumferential direction.

[0100] Even with the above-described configuration, by providing a conductor, a conductive path is ensured from the rim cushion rubber 31 in contact with the rim flange R, through the carcass coat rubber 17, bead core 11, carcass coat rubber 17, conductor (at least one of tie rubber 22, conductive rubber sheet, conductive thread, paint, and cement), inner liner 21, and belt layer 18, to the earth tread 50. This allows static electricity from the vehicle to be released onto the road surface. This prevents static electricity from building up on the vehicle on which the pneumatic tire 1 is mounted. This allows the effect of reducing electrical resistance to be maintained over the long term.

[0101] In the above embodiment, the cap tread 3a of the tread portion 2 has a volume resistivity of 1×10^8 [Ω cm] or more, and the earth tread 50 has a volume resistivity of less than 1×10^8 [Ω cm]. However, if the cap tread 3a contains carbon and has a volume resistivity of less than 1×10^8 [Ω cm], the earth tread 50 does not need to be provided.

[0102] The above-described embodiments and modified examples may be combined as appropriate. In the above-described embodiments, the pneumatic tire 1 has been used as an example of a tire according to the present invention, but the tire according to the present invention may be a tire other than the pneumatic tire 1. The tire according to the present invention may be, for example, a so-called airless tire that can be used without being filled with gas.

[0103] 8 and 9 are tables showing the results of performance evaluation tests of pneumatic tires. Performance evaluation tests conducted on the pneumatic tire 1 of Conventional Example 1 and the pneumatic tire 1 according to the present invention will be described below. The performance evaluation tests were conducted to measure the electrical resistance and rolling resistance of the pneumatic tire.

[0104] The performance evaluation test was carried out using a pneumatic tire with a nominal tire size of 235 / 60R18 as specified by JATMA as the test tire. The evaluation test for the electrical resistance of the pneumatic tire was carried out by measuring the electrical resistance [Ω] of the test tire using an R8340A Ultra High Resistance Meter manufactured by Advantest Corporation, based on the measurement conditions specified by JATMA.

[0105] Furthermore, evaluation tests for the rolling resistance of pneumatic tires were performed by mounting the test tire on a rim wheel with a rim size of 15x6J, and performing an indoor drum test on the test tire using a drum testing machine with a drum diameter of 1707 mm, measuring the rolling resistance of the test tire under conditions of an air pressure of 210 kPa, a load of 4.82 kN, and a speed of 80 km / h. The rolling resistance of the pneumatic tires was evaluated using an index based on the reciprocal of the measured rolling resistance, with Conventional Example 1, described below, being set at 100. The larger the index evaluation value for the rolling resistance of the pneumatic tire, the lower the rolling resistance and the better the performance in terms of rolling resistance.

[0106] The performance evaluation test was conducted on 16 types of pneumatic tires, including a pneumatic tire of Conventional Example 1, which is an example of a conventional pneumatic tire, and Examples 1 to 15, which are pneumatic tires 1 according to the present invention. Of these, the pneumatic tire of Conventional Example 1 has a volume resistivity of less than 1×10^0 [Ω cm] for the bead wire, but the volume resistivities of the bead core, bead insulation rubber, and rim cushion rubber are 1×10^8 [Ω cm] or more.

[0107] In contrast, in all of Examples 1 to 15, which are examples of the pneumatic tire 1 according to the present invention, the volume resistivity of the bead core 11 and the volume resistivity of the bead insulation rubber 13 are each less than 1×10^8 [Ω·cm]. Furthermore, the pneumatic tires 1 according to Examples 1 to 15 differ in the average value of the ratio of the cross-sectional area of ​​the bead insulation rubber 13 to the bead core 11 (S-Sw) / S, the average value of the thickness of the bead insulation rubber between adjacent bead wires, whether there are two or more locations in the tire circumferential direction where the thickness of the bead insulation rubber between different bead wires adjacent in the tire width direction is 0.01 mm or less, the LAP amount between the bead core and at least one of the conductor and the inner liner, whether the volume resistivity of the cover member that covers the bead core over a range of 1 mm or more in the tire circumferential direction is less than 1 x 10^8 Ω-cm, the thickness of the carcass coat rubber that is located on both sides of the bead core in the tire width direction and in contact with the bead core, and whether the volume resistivity of the earth tread rubber is less than 1 x 10^8 Ω-cm.

[0108] Evaluation tests were conducted using these pneumatic tires 1, and as a result, it was found that the pneumatic tires 1 according to Examples 1 to 15 were able to maintain rolling resistance while reducing electrical resistance more than Conventional Example 1, as shown in Figures 8 and 9. In other words, the pneumatic tires 1 according to Examples 1 to 15 were able to reduce electrical resistance while suppressing deterioration in rolling resistance.

[0109] [Other Modifications] Fig. 10 is a diagram showing a portion of the meridian cross section of the tire shown in Fig. 1. Fig. 10 shows an example of the cross-sectional structure of a portion of the tread portion 2 shown in Fig. 1. Fig. 10 shows a cross section cut along the tire circumferential direction. Referring to Fig. 10, a belt layer 18, a carcass layer 15, a tie rubber 22, and an inner liner 21 are provided in this order on the inner side in the tire radial direction of the tread rubber 3. The tie rubber 22 is arranged between the carcass layer 15 and the inner liner 21.

[0110] The carcass layer 15 includes carcass cords 16 and a carcass coat rubber 17 that wraps around the carcass cords 16. Focusing on the tie rubber 22, a portion 221 of the tie rubber 22 extends radially outward and is embedded between the carcass cords 16. Specifically, if the portion 221 of the tie rubber 22 crosses an imaginary line L1 that passes through the radially inner side of each carcass cord 16, the portion 221 can be considered to be embedded between the carcass cords 16. That is, the tie rubber 22 has a portion 221 that is embedded between the carcass cords 16 of the carcass layer 15, at least within the range of the belt layer 18. The inclusion of the tie rubber 22 between the carcass cords 16 reduces the thickness of the carcass coat rubber 17, shortening the conductive distance and improving conductivity. Furthermore, the inclusion of the tie rubber 22 in the carcass coat rubber 17 increases the adhesion 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, making it possible to maintain low electrical resistance even after running.

[0111] [Modifications of Carcass Layer] The carcass layer 15 described with reference to Fig. 10 preferably has a one-ply structure, but is not limited to this. Fig. 11 is a diagram showing an example of a cross-sectional structure including a two-ply carcass layer 150. The carcass layer 150 has a two-ply structure, including a ply made of carcass cords 161 and carcass coat rubber 171 wrapping the same, and another ply made of carcass cords 162 and carcass coat rubber 172 wrapping the same.

[0112] 11 , the portion 221 of the tie rubber 22 also extends radially outward in the tire direction and enters between the carcass cords 161. In the case of a two-ply structure, an imaginary line L12 is drawn between the ply consisting of the carcass cords 161 and the carcass coat rubber 171 and the ply consisting of the carcass cords 162 and the carcass coat rubber 172. If the portion 221 of the tie rubber 22 crosses the imaginary line L1 that passes through the ply on the inner side in the tire radial direction of the imaginary line L12, i.e., the ply closest to the tie rubber 22 in the tire radial direction, it can be considered that the portion 221 of the tie rubber 22 enters between the carcass cords 161.

[0113] By inserting the tie rubber 22 between the carcass cords 161, the thickness of the carcass coat rubber 171 is reduced, shortening the conductive distance and improving conductivity. In addition, by inserting the tie rubber 22 into the carcass coat rubber 171, the adhesive area between the tie rubber 22 and the carcass layer 150 is increased. This improves the adhesiveness between the tie rubber 22 and the carcass layer 150, making it possible to maintain low electrical resistance even after running.

[0114] Also, the vicinity of the side rubber may have the same configuration as that shown in Fig. 10. Fig. 12 is a diagram showing an example of a cross-sectional structure of a portion of the sidewall rubber 5 shown in Fig. 1. Referring to Fig. 12, a carcass layer 15, a tie rubber 22, and an inner liner 21 are provided in this order from the tread rubber 3 toward the tire cavity side.

[0115] Focusing on the tie rubber 22 in FIG. 12 , a portion 221 of the tie rubber 22 extends radially outward and enters between the carcass cords 16. That is, the tie rubber 22 has a portion 221 that enters between the carcass cords 16 of the carcass layer 15, even within the area where the sidewall rubber 5 is disposed. By having the tie rubber 22 enter between the carcass cords 16, the thickness of the carcass coat rubber 17 is reduced, shortening the conductive distance and improving conductivity. Furthermore, by having the tie rubber 22 enter into the carcass coat rubber 17, the adhesive area between the tie rubber 22 and the carcass layer 15 is increased. This improves the adhesiveness between the tie rubber 22 and the carcass layer 15, allowing low electrical resistance to be maintained even after driving.

[0116] [Number of Locations Where Tie Rubber Inserts] FIG. 13 is a diagram showing a schematic external view of a tire 1. As shown in FIG. 13 , in the tire 1 of this example, four locations in the tire circumferential direction are designated as measurement locations S1, S2, S3, and S4. These four locations in the tire circumferential direction are, for example, one location every 90 degrees in the tire circumferential direction. Here, within a 50 mm circumferential length of measurement location S1, it is preferable that there is at least one portion 221 in which the tie rubber 22 inserts between the carcass cords 16 of the carcass layer 15. In other words, it is preferable that the tie rubber 22 inserts between the carcass cords 16 at at least one location per 50 mm circumferential length of the tire. The greater the number of locations where the tie rubber 22 inserts, the greater the adhesion area between the tie rubber 22 and the carcass layer 15. This improves adhesion between the tie rubber 22 and the carcass layer 15, allowing low electrical resistance to be maintained even after running.

[0117] Similarly, it is preferable that at least one portion of each of the other measurement portions S2, S3, and S4 of the tire 1 is embedded. Note that the four measurement portions S1, S2, S3, and S4 in Fig. 13 are examples, and more portions may be used as measurement portions.

[0118] 14 is a diagram illustrating the area of ​​a portion 221 of the tie rubber 22 that is inserted between the carcass cords 16 of the carcass layer 15. Within a range of 50 mm in the tire circumferential direction at measurement points S1, S2, S3, and S4, the average value Sc(50Ave) of the inter-cord cross-sectional area Sc calculated from the average center-to-center distance of the carcass cords 16 and the average thickness of the carcass layer 15, and the cross-sectional area St [mm ２ ] and the average value St(50Ave) preferably satisfy the following formula (1): 0.02≦St(50Ave) / Sc(50Ave)≦0.5 (1)

[0119] In the above formula (1), St(50Ave) is the cross-sectional area St [mm ２ ]. Sc(50Ave) is the average value of area Sc. Area Sc [mm ２ ] is the cross-sectional area of ​​the carcass layer 15 with the thickness Tc and the center-to-center distance Lc of the carcass cords 16. That is, the area Sc = Tc × Lc [mm ２ The thickness Tc [mm] is the length between a point P18 where a perpendicular line drawn from the center of the carcass cord 16 toward the belt layer 18 intersects with the interface of the belt layer 18 outward in the tire radial direction, and a point P22 where a perpendicular line drawn toward the inner side in the tire radial direction intersects with the interface of the tie rubber 22.

[0120] By satisfying the above condition (1), the conductivity can be improved and the electrical resistivity can be reduced while maintaining the durability of the tire. If the St(50Ave) / Sc(50Ave) is less than 0.02, the improvement in conductivity is small and the electrical resistance does not decrease. On the other hand, if the St(50Ave) / Sc(50Ave) is more than 0.5, the durability deteriorates due to the openings that widen the spaces between the carcass cords 16, and it is not possible to maintain low electrical resistance after running. Note that the cross-sectional area St [mm ２ It is more preferable that the relationship between the average value St(50Ave) of the area Sc and the average value Sc(50Ave) of the area Sc satisfies 0.1≦St(50Ave) / Sc(50Ave)≦0.35.

[0121] Here, the thickness Tc [mm] of the carcass layer 15 is not constant in the tire circumferential direction but varies. This will be explained with reference to Fig. 15. Fig. 15 is a diagram illustrating that the thickness of the carcass layer 15 varies in the tire circumferential direction.

[0122] In Figure 15, a perpendicular line S16 is drawn from the center of the carcass cord 16 toward the tire radially inward. The distance along the tire radial direction from point P16 where this perpendicular line S16 intersects with the boundary surface between the tie rubber 22 and the carcass coat rubber 17 to the boundary surface between the carcass coat rubber 17 and the belt layer 18 is not constant, but varies depending on the height to which the portion 221 of the tie rubber 22 enters. For example, in Figure 15, the thickness Tcmax is the maximum value, the thickness Tcmin is the minimum value, and the thickness Tcave is the average value. The above area Sc [mm ２ ] is calculated by multiplying the average thickness Tcave by the center-to-center distance Lc of the carcass cords 16.

[0123] [Height of the Tie Rubber] Figure 16 is a diagram illustrating the height of the tie rubber that has entered between the carcass cords 16. In Figure 16, the thickness of the carcass layer 15 is Tc, and the height of the tie rubber that has entered into the carcass coat rubber is Tt. It is preferable that the relationship between the thickness Tc and the height Tt satisfy the following formula (2): 0.014 ≤ Tt / Tc ≤ 0.8 (2)

[0124] In formula (2), the thickness Tc is the thickness [mm] of the carcass layer 15. The 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 formula (2), the height Tt is the height [mm] of the portion 221 of the tie rubber 22 that is sandwiched between the carcass cords 16. The height Tt is the distance from the interface between the tie rubber 22 and the carcass layer 15 to the outermost portion of the portion 221 of the tie rubber 22 in the tire radial direction. If Tt / Tc in formula (2) is less than 0.014, the improvement in conductivity is small and electrical resistance is not reduced. Furthermore, if Tt / Tc is greater than 0.8, durability deteriorates due to the opening of the carcass cords, making it impossible to maintain low electrical resistance after running. It is more preferable that the relationship between the thickness Tc and the height Tt be 0.2≦Tt / Tc≦0.6.

[0125] [Modification of Coat Rubber of Belt Layer] The tie rubber 22 may penetrate into the carcass coat rubber 17, and the coat rubber of the belt layer 18 may penetrate into the carcass coat rubber 17. FIG. 17 is a diagram showing a modification of the cross-sectional structure of a portion of the tread portion 2 shown in FIG. 1. As shown in FIG. 17, a portion 221 of the tie rubber 22 extends toward the tire radially outward in the carcass coat rubber 17. That is, the portion 221 of the tie rubber 22 crosses the imaginary line L1, and the 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 through the tire radially outer side of the carcass cords 16, and the coat rubber 18b penetrates between the carcass cords 16. Note that the volume resistivity of the coat rubber 18b of the belt layer 18 is preferably less than 1×10^8 [Ω cm].

[0126] [Cross-sectional area and height of the intruded tie rubber] Fig. 18 is a diagram for explaining the cross-sectional area and height of the tie rubber intruded into the carcass coat rubber. In Fig. 18, the cross-sectional area of ​​the tie rubber intruded between the carcass cords is expressed as St [mm ２]. The height of the tie rubber inserted between the carcass cords is defined as Tt. In this case, it is preferable that the relationship between the cross-sectional area St and the height Tt satisfies the following formula (3). That is, it is preferable that the following formula be satisfied: 0.02 mm≦St / Tt≦2.0 mm (3).

[0127] It is more preferable that the relationship between the cross-sectional area St and the height Tt satisfies the following: 0.2 mm≦St / Tt≦0.6 mm. ２ ] and height Tt [mm] are both average values ​​in a range of 50 mm in the circumferential direction of the tire, along the circumferential direction of the tire, at a cross section seen when the tire is cut in the circumferential direction of the tire.

[0128] [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 Ht / Hc of the hardness Ht to the hardness Hc is preferably 0.5 or more and 2.0 or less. 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.

[0129] If the ratio Ht / Hc of the tie rubber hardness to the carcass coat rubber hardness is within the above range, the hardness difference is small, and small peeling that occurs in the tire after running can be suppressed. This ensures electrical conductivity, and suppresses deterioration of electrical resistance before and after running.

[0130] The hardness Hc of the carcass coat rubber 17 is, for example, 55 points or more and 75 points or less. The hardness Ht of the tie rubber 22 is, for example, 50 points or more and 65 points or less. Here, hardness refers to 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 points using the durometer on a cut sample tire.

[0131] In the land portion of the tread portion 2 closest to the tire equatorial plane CL, it is preferable that there is at least one location where the tie rubber 22 is inserted between the carcass cords 16 of the carcass layer 15 within a tire circumferential length of 50 mm along the tire circumferential direction in a cross section seen when the pneumatic tire 1 is cut in the tire circumferential direction. By having at least one location where the tie rubber 22 is inserted, it is possible to maintain low electrical resistance while maintaining the durability of the tire.

[0132] [Arrangement of Earth Tread Rubber] The arrangement of the earth tread rubber 50 will be described with reference to Fig. 19 to Fig. 21. Fig. 19 is a diagram showing a cross section of the tire cut in the circumferential direction at the position of the earth tread rubber 50 in Fig. 1. Fig. 19 is a diagram showing a cross section when the earth tread rubber 50 is a through-type earth rubber.

[0133] In Figure 19, the earth tread rubber 50 is a penetrating type earth rubber. Therefore, the earth tread rubber 50 penetrates the tread rubber 3 and comes into contact with the belt layer 18. Therefore, the earth tread rubber 50 comes into contact with the road surface, improving electrical conductivity. Note that, as shown in Figure 19, a small amount of cap tread 3a may remain on the outermost side of the tread rubber 3 in the tire radial direction.

[0134] On the other hand, Figure 20 is a cross-sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment in which a non-penetrating type earth tread rubber is used. Figure 21 is a diagram showing a cross section of the tire cut in the circumferential direction at the position of the earth tread rubber in Figure 20. In Figures 20 and 21, the earth tread rubber 50a is a non-penetrating type earth rubber. Therefore, the earth tread rubber 50a does not penetrate the tread rubber 3, but terminates in contact with the undertread 3b. Although the earth tread rubber 50a does not contact the belt layer 18, electrical conductivity can be maintained as long as the volume resistivity of the undertread 3b is sufficiently low. Note that, as shown in Figure 21, a small amount of cap tread 3a may remain on the outermost side of the tread rubber 3 in the tire radial direction.

[0135] In each cross section shown in FIG. 19 and FIG. 21, the cross-sectional area of ​​the tread portion is expressed as 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 earth tread rubber 50 or 50a, and the cross-sectional area of ​​the under tread 3b. The cross-sectional area of ​​the earth tread rubber is expressed as Sea [mm ２ In this case, 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 cross-sectional area ratio is in the above range and the portion 221 of the tie rubber 22 penetrates into the carcass coat rubber 17 of the carcass layer 15 as shown in Figures 19 and 21, the electrical conductivity is further improved. It is more preferable that the ratio Sea / Str is 0.9 or more and 1 or less.

[0136] The earth tread rubber 50 is made of a conductive rubber material having a lower volume resistivity than the tread rubber 3, and the volume resistivity of the earth tread rubber 50 is less than 1×10^8 [Ω·cm]. The volume resistivity of the earth tread rubber 50 is more preferably 1×10^6 [Ω·cm] or less.

[0137] 22A to 22C are tables showing the results of performance evaluation tests of pneumatic tires. Performance evaluation tests conducted on the pneumatic tire of Conventional Example 2 and the pneumatic tire 1 according to the present disclosure will be described below for the pneumatic tire 1. In the performance evaluation tests, the electrical resistance of the pneumatic tire was measured before and after driving with the pneumatic tire.

[0138] Regarding the electrical resistance of the tire, the electrical resistance [Ω] of the test tire was measured based on the measurement conditions specified by JATMA using an R8340A Ultra High Resistance Meter manufactured by Advantest Corporation. For running with pneumatic tires, an indoor drum-type tire rolling resistance tester with a drum diameter of 1707 mm was used, and the test tire was mounted on a rim that conforms to the JATMA standard, and an air pressure of 200 kPa and 80% of the maximum load specified by JATMA were applied to the test tire. After running for 60 minutes at a speed of 81 km / h, the electrical resistance of the tire was measured using the above method.

[0139] In FIG. 22A , a tire without tie rubber embedded in the carcass coat rubber is designated "Conventional Example 2." It is believed that the tie rubber embedded between the carcass cords peels off slightly as the tire runs, resulting in an increase in resistance compared to before the tire runs. Note that an increase in electrical resistance of 1.5×10^7 [Ω·cm] or less is considered acceptable. In FIG. 22A , the tire of Conventional Example 2 exhibits an increase in resistance of 1.9×10^7 [Ω·cm] after running compared to before running. In contrast, FIGS. 22A to 22C show that the tires of each example of the present disclosure maintain their electrical resistance even after running.

[0140] The present disclosure includes the following inventions: Invention [1] A tire comprising: a pair of bead portions disposed on both sides of the tire equatorial plane in the tire width direction, a bead core provided in each of the pair of bead portions, at least one carcass layer continuously spanning the pair of bead portions, a belt layer disposed radially outward of the carcass layer, a tread rubber disposed radially outward of the belt layer, an inner liner disposed on the inner surface of the tire along the carcass layer, and a rim cushion rubber disposed on the bead portion outer side of the carcass layer in the tire width direction, wherein the bead core has a bead wire and a bead insulation rubber wrapping the bead wire, and the bead core has a volume resistivity of less than 1×10^8 [Ω-cm] and the bead insulation rubber has a volume resistivity of less than 1×10^8 [Ω-cm]. Invention [2] The tire according to Invention [1], wherein the bead wire has a volume resistivity of less than 1×10^0 [Ω-cm]. Invention [3] A tire according to Invention [1] or Invention [2], wherein, when tangents are drawn in a direction outward from the core to the adjacent bead wires at the outermost periphery of the bead core, and the area of ​​a region enclosed by these tangents and a part of the outer periphery of the bead wire is defined as the cross-sectional area S of the bead core, the total cross-sectional area of ​​the bead wires is defined as Sw, and the cross-sectional area of ​​the bead insulation rubber is defined as S-Sw, the bead core has an average ratio (S-Sw) / S of the cross-sectional area of ​​the bead insulation rubber to the cross-sectional area S of the bead core at a plurality of predetermined locations in the tire circumferential direction of the tire that satisfies 0.1 to 0.8. Invention [4] A tire according to any one of Inventions [1] to [3], wherein an average value of thicknesses Gi of the bead insulation rubber between adjacent bead wires at a plurality of predetermined locations in the tire circumferential direction is 1.5 mm or less.The tire according to any one of the inventions [1] to [4], wherein the bead core has a plurality of bead wires that are different in the tire width direction, and among the plurality of bead wires, there are at least two locations in the tire circumferential direction where a thickness Gi of the bead insulation rubber between the bead wires adjacent in the tire width direction is 0.01 mm or less.The tire according to any one of the inventions [1] to [5], wherein the bead portion has a cover member that covers the bead core over a range of at least 1 mm in the tire circumferential direction, and the cover member has a volume resistivity of less than 1 x 10^8 Ω cm. Invention [7] A tire according to any one of Inventions [1] to [6], comprising a conductor extending from the belt layer to the bead portion, wherein at least one of the conductor and the inner liner has a volume resistivity of less than 1 x 10^8 [Ω cm], at least one of the conductor and the inner liner overlaps the bead core in at least one of the bead portions, and an overlap amount LAP between the at least one of the conductor and the inner liner and the bead core is 3≦LAP [mm], and the rim cushion has a volume resistivity of less than 1 x 10^8 [Ω cm]. Invention [8] A tire according to any one of Inventions [1] to [7], wherein a thickness of carcass coat rubber of the carcass layer located on both sides of the bead core in the tire width direction and in contact with the bead core is Gp [mm], and the thickness GP of the carcass coat rubber satisfies 0.1≦Gp≦5.0. Invention [9] A tire according to any one of inventions [1] to [8], which has a volume resistivity of less than 1 x 10^8 [Ω cm], penetrates the tread rubber, contacts the belt layer, and is exposed on the surface of the tread rubber.Invention

[10] The tire according to invention [1], wherein the rim cushion rubber constitutes a rim fitting surface of the bead portion and is arranged from the inner side in the tire width direction of the bead core to the outer side in the tire width direction, and further comprises: a tread portion including the tread rubber, a tie rubber arranged between the carcass layer and the inner liner, and earth tread rubber which is a conductive rubber in a rib portion of the tread portion closest to the tire equatorial plane, the carcass layer includes carcass cords and carcass coat rubber wrapping the carcass cords, the tie rubber has a portion which enters between the carcass cords of the carcass layer at least in the area where the belt layer is arranged, and the volume resistivity of the tie rubber is less than 1 x 10^8 [Ω cm]. Invention

[11] The tire according to invention

[10] , wherein the tie rubber enters between the carcass cords of the carcass layer at least in one location within a circumferential length of 50 mm along the tire circumferential direction in a cross section seen when the tire is cut in the tire circumferential direction at the rib portion of the tread portion closest to the tire equatorial plane. Invention

[12] The tire according to invention

[10] or invention

[11] , wherein the relationship between an inter-cord cross-sectional area Sc(50Ave), calculated from the average center-to-center distances of carcass cords and the average thickness of carcass layers in a 50 mm circumferential length range along the tire circumferential direction in a cross section seen when the tire is cut in the tire circumferential direction at the rib portion of the tread portion closest to the tire equatorial plane, and a cross-sectional area St(50Ave) of tie rubber embedded in the carcass coat rubber in said range, is as follows: 0.02≦St(50Ave) / Sc(50Ave)≦0.5 Invention

[13] The tire according to any one of inventions

[10] to

[12] , wherein the relationship between the carcass layer thickness Tc and the height Tt of the tie rubber embedded in the carcass coat rubber is as follows: Invention

[14] The tire according to any one of Inventions

[10] to

[13] , wherein a cross-sectional area St of the tie rubber inserted between the carcass cords and a height Tt of the tie rubber inserted between the carcass cords satisfy the following relationship: 0.014≦Tt / Tc≦0.80.02 mm≦St / Tt≦2.0 mm Invention

[15] The tire according to any one of inventions

[10] to

[14] , wherein a ratio Ht / Hc of the hardness Ht of the tie rubber to the hardness Hc of the carcass coat rubber is 0.5 or more and 2.0 or less. Invention

[16] The tire according to any one of inventions

[10] to

[15] , wherein, when the tire is cut in the tire circumferential direction through the earth tread rubber, the ratio of the cross-sectional area Sea of ​​the earth tread rubber to the cross-sectional area Str of the tread portion satisfies the following relationship, and the tie rubber is inserted between the carcass cords of the carcass layer on the tire radially inner side of the arrangement range of the earth tread rubber. 0.8≦Sea / Str≦1.

[0141] DESCRIPTION OF SYMBOLS 1 Pneumatic tire (tire) 2 Tread portion 3 Tread rubber 3a Cap tread 3b Under tread 4 Sidewall portion 5 Sidewall rubber 10, 10A Bead portion 11 Bead core 12, 12A, 12B, 12C, 12D Bead wire 13 Bead insulation rubber 14 Bead filler 15, 150 Carcass layer 16, 161, 162 Carcass cord 17, 171, 172 Carcass coat rubber 18 Belt layer 18b Coat rubber 21 Inner liner 21a End portion 22 Tie rubber (conductor) 22a End portion 25 Tire inner surface 30 Rim cushion 31 Rim cushion rubber 50, 50a Earth tread rubber 32 Rim fitting surface 60 Cover member CL Tire equatorial plane R Rim flange

Claims

1. A tire comprising: a pair of bead portions arranged on both sides of the tire equatorial plane in the tire width direction; a bead core provided in each of the pair of bead portions; at least one carcass layer continuously spanning the pair of bead portions; a belt layer arranged on the tire radially outer side of the carcass layer; tread rubber arranged on the tire radially outer side of the belt layer; an inner liner arranged on the tire inner surface along the carcass layer; and a rim cushion rubber provided on the tire width outer side of the carcass layer in the bead portion, wherein the bead core has a bead wire and a bead insulation rubber wrapping the bead wire, and the bead core has a volume resistivity of less than 1 x 10^8 [Ω-cm], and the bead insulation rubber has a volume resistivity of less than 1 x 10^8 [Ω-cm].

2. The tire according to claim 1, wherein the bead wire has a volume resistivity of less than 1×10^0 [Ω·cm].

3. A tire as described in claim 1, wherein, when tangents are drawn in the outward direction of the core to adjacent bead wires at the outermost periphery of the bead core, and the area of ​​the region enclosed by these tangents and a part of the outer periphery of the bead wire is taken as the cross-sectional area S of the bead core, the total cross-sectional area of ​​the bead wires is taken as Sw, and the cross-sectional area of ​​the bead insulation rubber is taken as S-Sw, the bead core has an average ratio (S-Sw) / S of the cross-sectional area of ​​the bead insulation rubber to the cross-sectional area S of the bead core at a plurality of predetermined locations in the circumferential direction of the tire that satisfies 0.1 or more and 0.8 or less.

4. A tire according to claim 1, wherein the average thickness Gi of the bead insulation rubber between adjacent bead wires at a plurality of predetermined locations in the tire circumferential direction is 1.5 mm or less.

5. A tire according to claim 1, wherein the bead core has a plurality of bead wires that are different in the tire width direction, and among the plurality of bead wires, there are at least two locations in the tire circumferential direction where the thickness Gi of the bead insulation rubber between adjacent bead wires in the tire width direction is 0.01 mm or less.

6. A tire as described in claim 1, wherein the bead portion has a cover member that covers the bead core over an area of ​​at least 1 mm in the tire circumferential direction, and the cover member has a volume resistivity of less than 1 x 10^8 Ω-cm.

7. A tire as claimed in claim 1, comprising an electric conductor extending from the belt layer to the bead portion, wherein at least one of the electric conductor and the inner liner has a volume resistivity of less than 1 x 10^8 [Ω-cm], at least one of the electric conductor and the inner liner overlaps the bead core in at least one of the bead portions, and the overlap amount LAP between the at least one of the electric conductor and the inner liner and the bead core is 3≦LAP [mm], and the rim cushion including the rim cushion rubber has a volume resistivity of less than 1 x 10^8 [Ω-cm].

8. A tire as described in claim 1, wherein the thickness of the carcass coat rubber of the carcass layer located on both sides of the bead core in the tire width direction and in contact with the bead core is Gp [mm], and the thickness GP of the carcass coat rubber satisfies 0.1≦Gp≦5.

0.

9. A tire according to claim 1, comprising an earth tread having a volume resistivity of less than 1 x 10^8 [Ω·cm], penetrating the tread rubber to contact the belt layer and exposed on the surface of the tread rubber.

10. A tire as claimed in claim 1, wherein the rim cushion rubber forms a rim fitting surface in the bead portion and is arranged from the inner side in the tire width direction of the bead core to the outer side in the tire width direction, and further comprises: a tread portion including the tread rubber; a tie rubber arranged between the carcass layer and the inner liner; and earth tread rubber which is a conductive rubber in a rib portion of the tread portion closest to the tire equatorial plane, wherein the carcass layer includes carcass cords and carcass coat rubber wrapping the carcass cords, and the tie rubber has portions which are inserted between the carcass cords of the carcass layer at least in the arrangement range of the belt layer, and the volume resistivity of the tie rubber is less than 1 x 10^8 [Ω cm].

11. A tire as described in claim 10, wherein the tie rubber is inserted between the carcass cords of the carcass layer at least in one location within a circumferentially long range of 50 mm along the tire circumferential direction in a cross section seen when the tire is cut in the tire circumferential direction at the rib portion of the tread portion closest to the tire equatorial plane.

12. A tire according to claim 10 or 11, wherein the relationship between the inter-cord cross-sectional area Sc(50Ave), calculated from the average center-to-center distance of the carcass cords and the average thickness of the carcass layer within a circumferentially long range of 50 mm along the tire circumferential direction in a cross section seen when the tire is cut in the tire circumferential direction at the rib portion of the tread portion closest to the tire equatorial plane, and the cross-sectional area St(50Ave) of the tie rubber embedded in the carcass coat rubber within said range, is as follows: 0.02≦St(50Ave) / Sc(50Ave)≦0.5 13. A tire according to claim 10 or 11, wherein the thickness Tc of the carcass layer and the height Tt of the tie rubber embedded in the carcass coat rubber satisfy the following relationship: 0.014≦Tt / Tc≦0.8 14. A tire according to claim 10 or 11, 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 satisfy the following relationship: 0.02 mm≦St / Tt≦2.0 mm 15. A tire according to claim 10 or 11, wherein the ratio Ht / Hc of the hardness Ht of the tie rubber to the hardness Hc of the carcass coat rubber is 0.5 or more and 2.0 or less.

16. A tire according to claim 10 or 11, wherein the earth tread rubber is arranged so that, when the tire is cut in the circumferential direction through the earth tread rubber, the ratio of the cross-sectional area Sea of ​​the earth tread rubber to the cross-sectional area Str of the tread portion satisfies the following relationship, and the tie rubber is inserted between the carcass cords of the carcass layer on the tire radially inner side of the arrangement range of the earth tread rubber: 0.8≦Sea / Str≦1

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