Tire

Abstract

To provide a tire which can prevent weather resistance from deteriorating and suppress an increase in electric resistance after traveling.SOLUTION: A tire 1 includes an electrical conduction body which is arranged in at least one splice part of a pair of side wall rubbers. The electrical conduction body is not exposed to a tire surface to be covered with the side wall rubber or a rim cushion rubber. A tread part includes an earth tread rubber which is arranged at an outer side of a belt layer in a tire radial direction. A volume resistivity of the electrical conduction body is less than 1×10^8 [Ω cm]. A volume resistivity of the rim cushion rubber is less than 1×10^8 [Ω cm]. A volume resistivity of the earth tread rubber is less than 1×10^8 [Ω cm]. A volume resistivity of the side wall rubber is 1×10^8 [Ω cm] or more. A volume resistivity of a cap tread rubber of the tread part is 1×10^8 [Ω cm] or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, there has been a growing demand for reduced rolling resistance coefficient (hereinafter referred to as RRC), which has led to a trend toward lower heat generation in casing compounds in addition to conventional cap compounds, and increased electrical resistance in the casing, resulting in increased electrical resistance in the entire tire. To solve this problem, Patent Document 1 requires the installation of a casing earth that connects from the rim cushion section to the tread section in the casing, in addition to the earth tread. In Patent Document 1, a conductor is sandwiched between the splice of the sidewall rubber as the casing earth from the rim to the contact surface, so that it is exposed on the outer surface of the sidewall rubber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-216115 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the technology described in Patent Document 1, the conductor is exposed on the outer surface of the sidewall rubber, which can reduce weather resistance, cause cracks or damage, and increase electrical resistance after driving.

[0005] The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a tire that does not deteriorate in weather resistance and can suppress an increase in electrical resistance after running. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a tire according to an aspect of the present disclosure includes a pair of bead portions, a carcass layer laid between the pair of bead portions, a belt layer provided on the tire radially outer side of the carcass layer, a tread portion provided on the radially outer side of the belt layer, a rim cushion rubber provided on the outer side of the carcass layer in the bead portion, a pair of sidewall rubbers provided in contact with the rim cushion rubber on the tire radially outer side of the rim cushion rubber and on the outer side of the carcass layer, and a conductor provided at a splice portion of at least one of the pair of sidewall rubbers, The conductor is not exposed on the tire surface and is covered by the sidewall rubber or the rim cushion rubber, the tread portion has earth tread rubber arranged radially outside the belt layer, the volume resistivity of the conductor is less than 1×10^8 [Ω·cm], the volume resistivity of the rim cushion rubber is less than 1×10^8 [Ω·cm], the volume resistivity of the earth tread rubber is less than 1×10^8 [Ω·cm], the volume resistivity of the sidewall rubber is 1×10^8 [Ω·cm] or more, and the volume resistivity of the cap tread rubber of the tread portion is 1×10^8 [Ω·cm] or more. [Effects of the Invention]

[0007] According to the tire of the present disclosure, the weather resistance is not reduced and an increase in electrical resistance after driving can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a tire 1 according to a first embodiment of the present disclosure in the tire meridian direction. [Figure 2] FIG. 2 is a diagram showing a contact state between the conductor and the belt layer in FIG. [Figure 3] FIG. 3 is a diagram showing a contact state between the conductor and the rim cushion rubber in FIG. [Figure 4] FIG. 4 is a diagram illustrating the arrangement of the conductors in FIG. [Figure 5]FIG. 5 is a diagram illustrating the arrangement of the conductors in FIG. [Figure 6] FIG. 6 is a diagram illustrating the arrangement of electrical conductors in a tire according to a second embodiment of the present disclosure. [Figure 7] FIG. 7 is a diagram illustrating the arrangement of electrical conductors in a tire according to a third embodiment of the present disclosure. [Figure 8] FIG. 8 is a diagram illustrating the arrangement of electrical conductors in a tire according to a fourth embodiment of the present disclosure. [Figure 9] FIG. 9 is a diagram illustrating the arrangement of electrical conductors in a tire according to a fifth embodiment of the present disclosure. [Figure 10A] FIG. 10A is a chart showing performance test results for tires of the present disclosure. [Figure 10B] FIG. 10B is a chart showing performance test results for tires of the present disclosure. [Figure 10C] FIG. 10C is a chart showing performance test results for tires of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of each embodiment, components that are the same as or equivalent to those in other embodiments will be given the same reference numerals, and their description will be simplified or omitted. The present invention is not limited to each embodiment. Furthermore, the components of each embodiment include those that are easily replaceable by those skilled in the art, or those that are substantially the same. Note that the configurations described below can be combined as appropriate. Furthermore, the configurations can be omitted, replaced, or modified within the scope of the gist of the invention.

[0010] (First embodiment) FIG. 1 is a cross-sectional view in the tire meridian direction of a tire 1 according to a first embodiment of the present disclosure. FIG. 1 is a cross-sectional view including a splice portion, which will be described later. FIG. 1 shows one side region in the tire radial direction. FIG. 1 shows a radial tire for passenger cars as an example of the tire 1. The tire 1 according to this embodiment is preferably a pneumatic tire. As the gas to be filled into the tire 1, normal air or air with an adjusted oxygen partial pressure, as well as an inert gas such as nitrogen, argon, or helium, can be used.

[0011] In the following description, a meridian section of a tire refers to a section of the tire cut by a plane including the tire's rotation axis (not shown). The tire radial direction refers to a direction perpendicular to the tire's rotation axis (not shown), the tire radially inner side refers to the side toward the rotation axis in the tire radial direction, and the tire radially outer side refers to the side away from the rotation axis in the tire radial direction. The tire circumferential direction refers to a direction around the rotation axis as the central axis. The tire width direction refers to a direction parallel to the 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 perpendicular to the rotation axis of the tire 1 and passing through the center of the tire width of the tire 1. The tire width is the width in the tire width direction between portions located on outer sides in the tire width direction, that is, the distance between portions farthest from the tire equatorial plane CL in the tire width direction. 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 tire 1. In this embodiment, the tire equator line is given the same symbol "CL" as the tire equatorial plane.

[0012] The tire 1 according to this embodiment has an annular structure centered on a rotation axis, and includes a tread portion 2, a pair of sidewall portions 3, 3, a pair of bead portions 10, 10, a carcass layer 13, a belt layer 14, and an inner liner layer 20. Of these, the pair of sidewall portions 3, 3 and the pair of bead portions 10, 10 are arranged one on each side of the tire equatorial plane CL in the tire width direction.

[0013] The pair of bead portions 10, 10 are located radially inward of the pair of sidewall portions 3, 3, and each has a bead core 11, a bead filler 12, and a rim cushion rubber 31. Therefore, the pair of bead cores 11, 11, the pair of bead fillers 12, 12, and the pair of rim cushion rubbers 31, 31 are arranged on both sides of the tire equatorial plane CL in the tire width direction.

[0014] The pair of bead cores 11, 11 are annular members formed by bundling a plurality of bead wires and form the cores of the pair of bead portions 10, 10. The pair of bead fillers 12, 12 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.

[0015] The carcass layer 13 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 laid between the 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 13 is formed by coating multiple carcass cords made of steel or organic fiber material such as aramid, nylon, polyester, or rayon with coating rubber and rolling them. The carcass ply of the carcass layer 13 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.

[0016] In this embodiment, a carcass layer 13 formed by laminating a plurality of carcass plies is continuously laid between the bead cores 11, 11 on both sides in the tire width direction. In addition, both end portions of the carcass layer 13 are wrapped back and secured to the outer side in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12. That is, the vicinity of both end portions of the carcass layer 13 in a cross section viewed in the tire meridian direction is wrapped back from the inner side in the tire width direction of the bead cores 11 and the bead fillers 12 to the inner side in the tire radial direction and then to the outer side in the tire width direction.

[0017] Furthermore, for the carcass ply of the carcass layer 13, the tan δ value at 60°C of the coating rubber of the carcass cord is preferably 0.20 or less. Furthermore, the volume resistivity of the coating rubber of the carcass cord is preferably 1×10^8 [Ω·cm] or more. This reduces the rolling resistance of the tire. Coating rubber with such volume resistivity can be produced, for example, by using a low-heat-generating compound with a low carbon content. Furthermore, the coating rubber may be constructed without using silica, or may be reinforced by incorporating silica.

[0018] The tan δ value at 60° C. is measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under the conditions of an initial strain of 10%, an amplitude of ±0.5%, and a frequency of 20 Hz.

[0019] Volume resistivity (volume specific resistance) is measured based on JIS K6271, "Vulcanized rubber and thermoplastic rubber - Determination of volume resistivity and surface resistivity." Generally, if the volume resistivity is less than 1 x 10^8 [Ω·cm] or the surface resistivity is less than 1 x 10^8 [Ω / cm], the material can be said to have conductivity that can suppress static electricity buildup.

[0020] The pair of bead portions 10, 10 have rim cushion rubbers 31. The rim cushion rubbers 31 are respectively arranged on the radially inner side of the bead cores 11, 11 on both sides in the tire width direction and the turnup portion of the carcass layer 13. The rim cushion rubber 31 of the bead portion 10 is the portion that abuts against the rim flange Ri of the rim when the tire 1 is mounted on the rim, and forms the contact surface of the bead portion 10 with the rim flange Ri. The volume resistivity of the rim cushion rubber 31 is preferably less than 1×10^8 [Ω·cm].

[0021] A rim cushion rubber 31 that forms the contact surface of the bead portion 10 with the rim flange is arranged on the radially inner side and the widthwise outer side of the bead core 11 and the turned-up portion of the carcass layer 13 in the bead portion 10. An inner liner layer 20 is formed along the carcass layer 13 on the inner side of the carcass layer 13 or on the inner side of the carcass layer 13 in the tire 1.

[0022] The belt layer 14 has one or more belt plies extending in the tire width direction, and in this embodiment, multiple belt plies are laminated. That is, in this embodiment, the belt layer 14 is configured by laminating a pair of cross belts 141, 142 and a belt cover 143 in the tire radial direction, and is disposed radially outward of the carcass layer 13 and wound around the carcass layer 13. The pair of cross belts 141, 142 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. The pair of cross belts 141, 142 have a so-called cross-ply structure in which the belt angles have opposite signs and are laminated so that the extension directions of the belt cords cross each other. That is, the pair of cross belts 141, 142 have the inclination directions of the belt cords with respect to the tire circumferential direction in the tire width direction opposite to each other. The belt cover 143 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 to 10 degrees in absolute value. The belt cover 143 is also arranged by being layered on the outer side of the cross belts 141 and 142 in the tire radial direction.

[0023] The tread portion 2 is configured with tread rubber 15, which is a rubber composition, and is arranged radially outward of the carcass layer 13 and the belt layer 14, and is exposed at the outermost portion in the radial direction of the tire 1. Therefore, the outer peripheral surface of the tread portion 2 forms part of the contour of the 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. In addition, the tread rubber 15 that configures the tread portion 2 has a cap tread 151 and an undertread 152.

[0024] The cap tread 151 is a rubber member located at the outermost position in the tire radial direction of the tread portion 2 and constituting the tire contact surface, and may have a single-layer structure (see FIG. 1) or a multi-layer structure (not shown). The tan δ value of the cap tread 151 at 60°C is preferably 0.25 or less. The volume resistivity of the cap tread 151 is preferably 1×10^8 Ω·cm or more. This reduces the rolling resistance of the tire 1. The cap tread 151 with 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.

[0025] The undertread 152 is a member laminated on the inner side in the tire radial direction of the cap tread 151. The volume resistivity of the undertread 152 is preferably lower than the volume resistivity of the cap tread 151.

[0026] Each of the pair of sidewall portions 3, 3 includes a sidewall rubber 16, and the pair of sidewall rubbers 16, 16 of the pair of sidewall portions 3, 3 are disposed on the outer side of the carcass layer 13 in the tire width direction. The tan δ value of the sidewall rubber 16 at 60°C is preferably 0.20 or less. The volume resistivity of the sidewall rubber 16 is preferably in the range of 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 tire 1. The sidewall rubber 16 with 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.

[0027] There are no particular limitations on the upper limit of the volume resistivity of the cap tread 151, the lower limit of the volume resistivity of the undertread 152, the upper limit of the volume resistivity of the sidewall rubber 16, and the lower limit of the volume resistivity of the rim cushion rubber 31, but these are subject to physical constraints because they are rubber components.

[0028] Here, a conductor 18 is provided at the splice portion of the sidewall rubber 16. The splice portion refers to the circumferential joint portion of the rim cushion rubber and the sidewall rubber material, and the joint portion formed during molding. Since the conductor 18 only needs to be provided at the splice portion, not around the entire circumference of the tire 1, it can be easily provided and does not deteriorate the RRC. The conductor 18 may be rubber, paint, adhesive, or cement, as long as it is conductive.

[0029] The conductor 18 extends from the rim cushion rubber 31 through the sidewall rubber 16 to the outside in the tire radial direction, and comes into contact with the belt coat rubber of the belt layer 14. As shown in Fig. 1, the conductor 18 is preferably provided straddling the rim cushion rubber 31 and the sidewall rubber 16. However, if the conductor 18 is not provided straddling the rim cushion rubber 31 and the sidewall rubber 16, and the inner end of the conductor 18 in the tire radial direction comes into contact with the rim cushion rubber 31, a conductive path can be ensured.

[0030] As shown in Figure 1, by eliminating exposure of the conductor 18 sandwiched in the splice portion on the outer surface of the tire, weather resistance is not reduced and an increase in electrical resistance after driving due to the occurrence of cracks or damage can be suppressed. If there are multiple splices in the sidewall rubber 16, a conductive path can be ensured by providing a conductor 18 in at least one of them. Note that in Figure 1, the conductor 18 is provided in the splice portion of one sidewall portion 3 in the tire width direction of the pair of sidewall portions 3, 3, but the conductor 18 may also be provided in the splice portion of the other sidewall portion 3. A conductive path can be ensured by providing a conductor 18 in the splice portion of at least one of the pair of sidewall portions 3, 3.

[0031] The volume resistivity of the conductor 18 is less than 1×10^8 [Ω·cm]. The volume resistivity of the rim cushion rubber 31 is less than 1×10^8 [Ω·cm]. The volume resistivity of the earth tread rubber 7 is less than 1×10^8 [Ω·cm]. The volume resistivity of the sidewall rubber 16 is 1×10^8 [Ω·cm] or more.

[0032] In this embodiment, the bead portion 10 refers to the region from the measurement point of the rim diameter to 1 / 3 of the tire cross-sectional height SH. The tire cross-sectional height SH refers to 1 / 2 of the difference between the tire outer diameter and the rim diameter, and is measured with the tire 1 mounted on a specified rim, pressurized to a specified internal pressure, and in an unloaded state.

[0033] 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. 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. The specified load refers to the "maximum load capacity" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity.

[0034] (Earth Red Rubber) As shown in FIG. 1, the tire 1 includes an earth tread rubber 7. The earth tread rubber 7 is made of a conductive rubber material having a volume resistivity lower than that of the tread rubber 15. Specifically, the volume resistivity of the earth tread rubber 7 is preferably less than 1×10^8 [Ω·cm], and more preferably 1×10^6 [Ω·cm] or less.

[0035] The earth tread rubber 7 is embedded in the tread rubber 15. A portion of the earth tread rubber 7 is exposed on the tread surface of the tread rubber 15. The earth tread rubber 7 penetrates the cap tread 151 and the under tread 152 and is in conductive contact with the belt layer 14 (belt cover 143). That is, in the tire meridian cross section, one end of the earth tread rubber 7 is in contact with the belt layer 14, and the other end of the earth tread rubber 7 is exposed on the tread surface of the tread portion 2. The earth tread rubber 7 is sometimes called earth rubber. The earth tread rubber 7 has an annular structure extending around the entire tire circumference, and extends continuously in the tire circumferential direction with a portion of it exposed on the tread surface. Therefore, as the tire rolls, the earth tread rubber 7 is always in contact with the road surface, thereby always ensuring a conductive path from the belt layer 14 to the road surface.

[0036] As described above, a conductive path is secured from the rim cushion rubber 31 in contact with the rim flange Ri, through the conductor 18 and the belt layer 14, to the earth tread rubber 7. 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 tire 1 is mounted. This allows the effect of reducing electrical resistance to be maintained over the long term.

[0037] (conductor and belt layer) Fig. 2 is a diagram showing a contact state between the conductor 18 and the belt layer 14 in Fig. 1. Fig. 2 shows an enlarged view of the vicinity of the outer end portion in the tire width direction of the belt layer 14 in Fig. 1.

[0038] 2, the outer end 181 of the conductor 18 in the tire radial direction is in contact with the coating rubber of the belt layer 14. This ensures a conductive path from the conductor 18 to the belt layer 14. The volume resistivity of the coating rubber of the belt layer 14 is preferably less than 1×10^8 [Ω·cm].

[0039] Here, the width in the tire width direction where the conductor 18 and the coating rubber of the belt layer 14 come into contact is defined as Lb. The width Lb is preferably 3 mm≦Lb. The width Lb is the minimum width necessary for contact with the coating rubber of the belt layer 14 to maintain low electrical resistance. The width Lb is smaller than the maximum width Lbmax in the tire width direction where the conductor 18 and the coating rubber of the belt layer 14 come into contact. The ratio Lb / Lbmax of the width Lb to the maximum width Lbmax in the tire width direction where the conductor 18 and the coating rubber of the belt layer 14 come into contact is preferably 0.9 or less. In other words, it is preferable that Lb / Lbmax≦0.9. It is not preferable that the ratio Lb / Lbmax exceeds 0.9 because the area of ​​the conductor becomes large, which may adversely affect the RRC.

[0040] It should be noted that even when the outer end 181 of the conductor 18 in the tire radial direction is not in contact with the coating rubber of the belt layer 14, it may be possible to ensure a conductive path from the conductor 18 to the belt layer 14. For example, if the volume resistivity of the sidewall rubber 16 is sufficiently low and the distance between the outer end 181 of the conductor 18 in the tire radial direction and the conductor 18 is short, electrical conduction occurs and a conductive path from the conductor 18 to the belt layer 14 can be ensured.

[0041] (conductor and rim cushion rubber) Figure 3 is a diagram showing the contact state between the conductor 18 and rim cushion rubber 31 in Figure 1. Referring to Figure 3, the conductor 18 is provided across the sidewall rubber 16 and the rim cushion rubber 31. Therefore, the conductor 18 is covered by the sidewall rubber 16 or the rim cushion rubber 31. A chafer may be provided on the surface of the rim cushion rubber 31 that comes into contact with the rim flange Ri (not shown). In that case, the chafer forms the contact surface with the rim flange Ri.

[0042] The inner end 182 of the conductor 18 in the tire radial direction contacts the rim cushion rubber 31. The width Lr of the conductor 18 in contact with the rim cushion rubber 31 is preferably 3 mm or more. If the width Lr is 3 mm or more, electrical resistance can be maintained low. If the conductor 18 extends too long, there is a concern that the RRC may deteriorate. For this reason, it is preferable that the ratio Lr / Lrmax of the width Lr to the maximum distance Lrmax from the tire inner end 31t of the rim cushion rubber 31 to the boundary end with the sidewall rubber 16 is 0.9 or less. In other words, it is preferable that Lr / Lrmax≦0.9. If the conductor 18 is too long, the volume of the conductor 18 increases, which may result in a deterioration of the RRC. By keeping the ratio Lr / Lrmax 0.9 or less, it is possible to suppress the deterioration of the RRC caused by the conductor 18.

[0043] (Arrangement of conductors) 4 and 5 are diagrams illustrating the arrangement of the conductor 18 in FIG. 1. FIG. 4 is a schematic diagram showing the position of the conductor 18 when the tire 1 is viewed from the direction of arrow Y1 in FIG. 1. As shown in FIG. 4, the conductor 18 is provided at a splice portion 25 of the sidewall rubber 16. At the splice portion 25, the conductor 18 extends in the tire radial direction.

[0044] Fig. 5 is a diagram showing a cross section of the conductor 18 at the AA portion in Fig. 4. In Fig. 5, the up-down direction in the drawing corresponds to the tire width direction, the left-right direction in the drawing corresponds to the tire circumferential direction, and the depth direction in the drawing corresponds to the tire radial direction. As shown in Fig. 5, the conductor 18 is provided at a splice portion 25 of the sidewall rubber 16. An inner end portion 18t of the conductor 18 in the tire width direction contacts the carcass layer 13.

[0045] In FIG. 5, the thickness t of the conductor 18 preferably satisfies the relationship 0.01 mm≦t≦2.0 mm. When the conductor 18 is formed using a conductive paint, the thickness of the paint film corresponds to the above-mentioned thickness t. The conductor 18 may be a thin rubber strip. In that case, the thickness of the rubber strip corresponds to the above-mentioned thickness t. The conductor 18 may be a conductive rubber cord. In that case, the diameter of the cord corresponds to the above-mentioned thickness t. By setting the thickness t of the conductor 18 to 0.01 mm≦t≦2.0 mm, the electrical resistance of the tire 1 can be more reliably reduced without deteriorating the rolling resistance. The thickness t of the conductor 18 may be uniform or may vary. For example, the thickness t may gradually decrease toward the end of the conductor 18.

[0046] In addition, in Figure 5, Wa denotes the length of the conductor 18 in the tire width direction from the contact position with the carcass layer 13. The ratio Wa / Wmax of the length Wa to the thickness of the sidewall rubber 16, i.e., the length Wmax in the tire width direction from the position of the carcass layer 13 in Figure 5, is preferably 0.9 or less. In other words, it is preferable that Wa / Wmax ≤ 0.9. If the conductor 18 is too long, the volume of the conductor 18 increases, which is undesirable because it may have a negative effect on the RRC. By setting the ratio Wa / Wmax to 0.9 or less, the conductor 18 is not exposed on the surface of the sidewall rubber 16. In other words, the conductor 18 is covered by the sidewall rubber 16 and not exposed on the tire surface.

[0047] 5, the length Wa is preferably 0.01 mm or more. That is, it is preferable that 0.01 mm≦Wa. If the length Wa is 0.01 mm or more, the minimum cross-sectional area necessary to maintain low electrical resistance from the rim cushion rubber 31 to the coating rubber of the belt layer 14 can be ensured.

[0048] In Figure 5, the length of the conductor 18 in contact with the sidewall rubber 16 is L1, the length of the conductor 18 in contact with the splice portion 25 is L2, and the length of the splice portion 25 is LP. The ratio L2 / L1 of the length L2 to the length L1 is preferably 0.05 or more and 400 or less. If the ratio L2 / L1 is 0.05 or more and 400 or less, it is possible to suppress deterioration of RRC due to the provision of the conductor 18. Furthermore, the ratio L2 / LP of the length L2 to the length LP is preferably 0.5 or more and 95 or less. If the ratio L2 / LP is 0.5 or more and 95 or less, it is possible to suppress deterioration of RRC due to the conductor 18.

[0049] The conductor 18 may have other forms as long as it is not exposed to the outside of the tire 1. Other forms of the conductor will be described below.

[0050] (Second embodiment) FIG. 6 is a diagram illustrating the arrangement of the conductor 18a in a tire 1a according to a second embodiment of the present disclosure. FIG. 6 is a diagram corresponding to a cross section of the conductor 18a taken along line AA in FIG. 4. In FIG. 6, the vertical direction in the diagram corresponds to the tire width direction, the horizontal direction in the diagram corresponds to the tire circumferential direction, and the depth direction in the diagram corresponds to the tire radial direction. As shown in FIG. 6, the conductor 18a is provided at a splice portion 25 of the sidewall rubber 16. The conductor 18a extends in the tire width direction and has a bent portion K1 at the boundary surface M between the sidewall rubber 16 and the carcass layer 13. The conductor 18a also extends in the tire circumferential direction along the boundary surface. Therefore, the inner end of the conductor 18a in the tire width direction contacts the carcass layer 13. The other portions of the tire 1a according to the second embodiment have the same configuration as that described with reference to FIG. 1. A thin sheet of conductive rubber is used as the conductor 18a, and by sandwiching part of the conductive rubber between the carcass layer 13 and the sidewall rubber 16, the conductive width is increased, thereby achieving lower electrical resistance.

[0051] In Figure 6, the length of the conductor 18a in contact with the sidewall rubber 16 is L1, the length of the conductor 18a in contact with the splice portion 25 is L2, and the length of the splice portion 25 is LP. The ratio L2 / L1 of the length L2 to the length L1 is preferably 0.05 or more and 400 or less. If the ratio L2 / L1 is 0.05 or more and 400 or less, deterioration of the RRC due to the conductor 18a can be suppressed. Furthermore, the ratio L2 / LP of the length L2 to the length LP is preferably 0.5 or more and 95 or less. If the ratio L2 / LP is 0.5 or more and 95 or less, deterioration of the RRC due to the conductor 18a can be suppressed.

[0052] In the tire 1a of the second embodiment, a conductive path is also ensured from the rim cushion rubber 31 through the conductor 18a and the belt layer 14 to the earth tread rubber 7. This allows static electricity in the vehicle to be released onto the road surface. This prevents static electricity from building up in the vehicle on which the tire 1a is mounted. This allows the effect of reducing electrical resistance to be maintained for a long period of time.

[0053] (Third embodiment) FIG. 7 is a diagram illustrating the arrangement of conductors in a tire 1b according to a third embodiment of the present disclosure. FIG. 7 is a diagram corresponding to a cross section of the conductor at the AA section in FIG. 4. In FIG. 7, the up-down direction in the diagram corresponds to the tire width direction, the left-right direction in the diagram corresponds to the tire circumferential direction, and the depth direction in the diagram corresponds to the tire radial direction. As shown in FIG. 7, the conductor 18b is provided at the splice portion 25 of the sidewall rubber 16. The conductor 18b has a smaller conductive width than the conductor 18 of the first embodiment and the conductor 18a of the second embodiment, and has a sheet width such that the conductor 18b does not come into contact with the carcass layer 13. The other portions of the tire 1b according to the third embodiment are similar to the configuration described with reference to FIG. 1. When a thin sheet-like conductive rubber having a sufficiently high volume resistivity is used, it is possible to reduce the volume of the conductive rubber sheet while suppressing heat generation and preventing deterioration of the RRC.

[0054] 7, the length of conductor 18b in contact with splice portion 25 is designated as L2, and the length of splice portion 25 is designated as LP. The ratio L2 / LP of length L2 to length LP is preferably equal to or greater than 0.5 and equal to or less than 95. If the ratio L2 / LP is equal to or greater than 0.5 and equal to or less than 95, it is possible to suppress deterioration of RRC due to conductor 18b.

[0055] In the tire 1b of the third embodiment, a conductive path is also secured from the rim cushion rubber 31 through the conductor 18b and the belt layer 14 to the earth tread rubber 7. This allows static electricity on the vehicle to be released onto the road surface. This suppresses static electricity buildup on the vehicle on which the tire 1b is mounted. This allows the effect of reducing electrical resistance to be maintained for a long period of time.

[0056] (Fourth embodiment) FIG. 8 is a diagram illustrating the arrangement of conductors in a tire 1c according to a fourth embodiment of the present disclosure. FIG. 8 is a diagram corresponding to a cross section of the conductor at section AA in FIG. 4. In FIG. 8, the up-down direction in the drawing corresponds to the tire width direction, the left-right direction in the drawing corresponds to the tire circumferential direction, and the depth direction in the drawing corresponds to the tire radial direction. In this embodiment, a conductive rubber cord is used as the conductor 18c. As shown in FIG. 8, the conductor 18c is provided at a splice portion 25 of the sidewall rubber 16. Other parts of the tire 1c according to the fourth embodiment have the same configuration as that described with reference to FIG. 1.

[0057] 8, the length of conductor 18c in contact with splice portion 25 is designated as L2, and the length of splice portion 25 is designated as LP. The ratio L2 / LP of length L2 to length LP is preferably equal to or greater than 0.1 and equal to or less than 95. If the ratio L2 / LP is equal to or greater than 0.1 and equal to or less than 95, deterioration of RRC due to conductor 18c can be suppressed.

[0058] In the tire 1c of the fourth embodiment, a conductive path is also ensured from the rim cushion rubber 31 through the conductor 18c and the belt layer 14 to the earth tread rubber 7. This allows static electricity in the vehicle to be released onto the road surface. This suppresses static electricity buildup in the vehicle on which the tire 1c is mounted. This allows the effect of reducing electrical resistance to be maintained for a long period of time.

[0059] (Fifth embodiment) FIG. 9 is a diagram illustrating the arrangement of conductors in a tire 1d according to a fifth embodiment of the present disclosure. FIG. 9 is a diagram corresponding to a cross section of the conductor at the AA section in FIG. 4. In FIG. 9, the up-down direction in the diagram corresponds to the tire width direction, the left-right direction in the diagram corresponds to the tire circumferential direction, and the depth direction in the diagram corresponds to the tire radial direction. As shown in FIG. 9, the conductor 18d is provided at the splice portion 25 of the sidewall rubber 16. The conductor 18d extends in the tire width direction and has a bent portion K2 at the boundary surface M between the sidewall rubber 16 and the carcass layer 13. Furthermore, the conductor 18d extends in the tire circumferential direction along the boundary surface M. Therefore, the inner end of the conductor 18d in the tire width direction comes into contact with the carcass layer 13. By using a thin sheet-like conductive rubber as the conductor 18d and sandwiching a portion of the conductive rubber between the carcass layer 13 and the sidewall rubber 16, the conductive width can be increased, thereby achieving lower electrical resistance. Other parts of the tire 1d of the fifth embodiment have the same configuration as that described with reference to FIG.

[0060] In Figure 9, the length of the conductor 18d in contact with the sidewall rubber 16 is L1, the length of the conductor 18d in contact with the splice portion 25 is L2, and the length of the splice portion 25 is LP. The ratio L2 / L1 of the length L2 to the length L1 is preferably 0.05 or more and 400 or less. If the ratio L2 / L1 is 0.05 or more and 400 or less, the deterioration of RRC due to the conductor 18d can be suppressed. Furthermore, the ratio L2 / LP of the length L2 to the length LP is preferably 0.5 or more and 95 or less. If the ratio L2 / LP is 0.5 or more and 95 or less, the deterioration of RRC due to the conductor 18d can be suppressed.

[0061] In the tire 1d of the fifth embodiment, a conductive path is also ensured from the rim cushion rubber 31 through the conductor 18d and the belt layer 14 to the earth tread rubber 7. This allows static electricity on the vehicle to be released onto the road surface. This suppresses static electricity buildup on the vehicle on which the tire 1d is mounted. This allows the effect of reducing electrical resistance to be maintained for a long period of time.

[0062] (Elongation at break of conductor) In each of the above-described embodiments, the breaking elongation EB of the conductors 18, 18a, 18b, 18c, and 18d is preferably 100%≦EB. If the breaking elongation is 100% or more, the conductor 18 will not break during running and can maintain low electrical resistance after running. The breaking elongation is measured by a tensile test at room temperature in accordance with JIS-K6251 (using a No. 3 dumbbell).

[0063] (Example) 10A to 10C are tables showing the results of performance tests on tires according to the present disclosure. Performance evaluation tests conducted on tires of comparative examples and tires according to the present disclosure are described below. Performance evaluation tests were conducted on the electrical resistance of new tires and tires after running.

[0064] (Evaluation method) Performance evaluation tests were conducted using pneumatic tires with a nominal tire size of 195 / 65R15 91H as specified by JATMA as test tires. Evaluation tests for the electrical resistance of new tires were conducted based on the measurement conditions specified in JIS K6271, using an R8340A Ultra High Resistance Meter manufactured by Advantest Corporation to measure the electrical resistance [Ω] of the test tires.

[0065] In addition, an indoor drum tire rolling resistance tester with a drum diameter of 1707 mm was used to evaluate electrical resistance after driving. The test tire was mounted on a rim specified by JATMA, and the test tire was inflated to 200 kPa and subjected to 80% of the maximum load specified by JATMA. After driving for 60 minutes at a speed of 81 km / h, measurements were taken using the same method as for new tires. The lower the measured value for electrical resistance of new tires and after driving, the lower the electrical resistance and the better the tire's performance in terms of electrical resistance.

[0066] Regarding RRC, in accordance with ISO standards, each test tire was mounted on a wheel with a rim size of 15 x 6J, and rolling resistance was measured using an indoor drum-type tire rolling resistance tester when the tire was driven under conditions of an air pressure of 210 kPa, a load of 4.82 kN, and a speed of 80 km / h.

[0067] Performance evaluation tests were conducted on a comparative tire and on tires of each example according to the present disclosure. Of these, the comparative tire is a tire in which a conductor is disposed at the splice portion of the sidewall rubber, with the conductor exposed to the outside of the sidewall rubber. The comparative tire was set as the reference value (100), and the tires of each example were evaluated. A higher value indicates better performance. Note that, although the provision of conductors in the tires of each example reduces the RRC below the reference value, an evaluation value of around "98" is considered to pose no problem in terms of tire performance.

[0068] As can be seen from Figures 10A to 10C, with the tire of the present disclosure, a conductive path is secured from the rim cushion rubber 31 through the conductor and belt layer 14 in this order to the earth tread rubber 7. This allows static electricity in the vehicle to be released onto the road surface. This prevents static electricity from building up in the vehicle on which the tire of the present disclosure is mounted. This allows the effect of reducing electrical resistance to be maintained over the long term.

[0069] The present disclosure includes the following inventions. <1> a pair of bead portions, a carcass layer laid between the pair of bead portions, a belt layer provided radially outward of the carcass layer, a tread portion provided radially outward of the belt layer, a rim cushion rubber provided outside the carcass layer in the bead portions, a pair of sidewall rubbers provided radially outward of the rim cushion rubber and outside the carcass layer in contact with the rim cushion rubber, and an electrical conductor provided at a splice portion of at least one of the pair of sidewall rubbers; Including, the conductor is not exposed on the tire surface but is covered by the sidewall rubber or the rim cushion rubber, the tread portion has an earth tread rubber disposed on the outer side of the belt layer in the tire radial direction, The volume resistivity of the conductor is less than 1×10^8 [Ω·cm], The volume resistivity of the rim cushion rubber is less than 1×10^8 [Ω·cm], The volume resistivity of the earthtread rubber is less than 1×10^8 [Ω·cm], The volume resistivity of the sidewall rubber is 1×10^8 [Ω·cm] or more, The volume resistivity of the cap tread rubber of the tread portion is 1×10^8 [Ω·cm] or more tire. <2> an inner end of the conductor in the tire radial direction contacts the rim cushion rubber; The outer end of the conductor in the tire radial direction extends to the vicinity of the belt layer, whether or not in contact with the belt layer. <1> A tire as described in <3> The width Lb in the tire width direction of the portion where the conductor and the coating rubber of the belt layer contact each other is in the range of 3 [mm]≦Lb. <2> A tire as described in <4> The thickness t of the conductor is 0.01 [mm] ≦ t ≦ 2.0 [mm] <1> from <3> 1. A tire according to any one of the preceding items. <5> The width Wa in the tire width direction of the cross section of the conductor along the tire circumferential direction is 0.01 [mm]≦Wa <1> from <4> 1. A tire according to any one of the preceding items. <6> The width Lr in the tire radial direction where the conductor contacts the rim cushion rubber is 3 [mm]≦Lr <1> from <5> 1. A tire according to any one of the preceding items. <7> The breaking elongation EB of the conductor is 100[%]≦EB <1> from <6> 1. A tire according to any one of the preceding items. [Explanation of symbols]

[0070] 1, 1a, 1b, 1c, 1d tires 2 Tread section 3 Sidewall 7 Earth Tread Rubber 10 Bead section 11 Bead core 12 Bead filler 13 Carcass layer 14 Belt Layer 15 Tread rubber 16 Sidewall rubber 18, 18a, 18b, 18c, 18d conductor 20 Inner liner layer 25 Splice 31 Rim cushion rubber 151 Cap Tread 152 Undertread CL Tire equatorial plane Ri rim flange

Claims

1. a pair of bead portions, a carcass layer laid between the pair of bead portions, a belt layer provided radially outward of the carcass layer, a tread portion provided radially outward of the belt layer, a rim cushion rubber provided outside the carcass layer in the bead portions, a pair of sidewall rubbers provided radially outward of the rim cushion rubber and outside the carcass layer in contact with the rim cushion rubber, and an electrical conductor provided at a splice portion of at least one of the pair of sidewall rubbers; Including, the conductor is not exposed on the tire surface but is covered by the sidewall rubber or the rim cushion rubber, the tread portion has an earth tread rubber disposed on the outer side of the belt layer in the tire radial direction, The volume resistivity of the conductor is less than 1×10 8 [Ω cm], The volume resistivity of the rim cushion rubber is less than 1×10^8 [Ω cm], The volume resistivity of the earthtread rubber is less than 1×10^8 [Ω cm], The volume resistivity of the sidewall rubber is 1×10^8 [Ω cm] or more, The volume resistivity of the cap tread rubber of the tread portion is 1×10^8 [Ω·cm] or more. tire.

2. an inner end of the conductor in the tire radial direction contacts the rim cushion rubber; The outer end of the conductor in the tire radial direction extends to the vicinity of the belt layer, whether or not in contact with the belt layer.

2. The tire of claim 1.

3. The tire according to claim 2, wherein a width Lb in the tire width direction of a portion where the conductor contacts the coating rubber of the belt layer is in a range of 3 mm≦Lb.

4. 4. The tire according to claim 1, wherein the thickness t of the conductor is in the range of 0.01 mm≦t≦2.0 mm.

5. The tire according to any one of claims 1 to 3, wherein a width Wa in the tire width direction of the cross section of the electrical conductor taken along the tire circumferential direction satisfies 0.01 mm≦Wa.

6. 4. The tire according to claim 1, wherein a width Lr in the tire radial direction where the conductor contacts the rim cushion rubber is 3 mm or less.

7. 4. The tire according to claim 1, wherein the breaking elongation EB of the conductor is 100%≦EB.

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