Pneumatic tire

A pneumatic tire is provided with an electrically conductive portion at least extending continuously from a bead portion to a belt layer. The electrically conductive portion has a linear structure. The linear structure includes an electrically conductive linear member linearly formed of electrically conductive material with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm. The electrically conductive portion ensures an electrically conductive path from the bead portion to the belt layer.

TECHNICAL FIELD

The present technology relates to a pneumatic tire, and particularly relates to a pneumatic tire with enhanced electrostatic suppression performance.

BACKGROUND ART

Some pneumatic tires employ a structure provided with an earthing tread that suppresses electrostatic charging by discharging to the road surface static electricity produced in the vehicle when traveling. Such an earthing tread is an electrically conductive rubber disposed passing through the tread cap and is exposed to the ground contact surface. This electrostatic suppressing structure can suppress electrostatic charging in the vehicle by discharging static electricity in the vehicle from the belt layer to the road surface via the earthing tread.

However in recent years, the amount of silica contained in rubber compounds constituting tread caps, undertreads, sidewall rubbers, and the like has been increasing for the purpose of improving the fuel economy of tires. Because silica is a good insulator, the resistance value of a tread cap increases when the amount of silica contained therein increases. Consequently, the electrostatic suppression performance decreases.

In order to enhance the electrostatic suppression performance, conventional pneumatic tires provided with an electrically conductive layer extending in a region from a bead portion to the belt layer are known. Examples of conventional pneumatic tires with such a configuration include the technologies disclosed in Japanese Unexamined Patent Application Publication Nos. 2009-154608A and 2013-528525A.

SUMMARY

The present technology provides a pneumatic tire with enhanced electrostatic suppression performance.

A pneumatic tire is provided that comprises:

a pair of bead cores;

at least one carcass layer extending between the pair of bead cores continuously or with a divided portion at a tread portion;

a belt layer disposed outward of the carcass layer in a tire radial direction;

a tread rubber disposed outward of the belt layer in the tire radial direction;

a pair of sidewall rubbers disposed outward of the carcass layer in a tire width direction;

an innerliner disposed on an inner circumferential surface of the carcass layer; and

an electrically conductive portion extending continuously at least from a bead portion to the belt layer; wherein

the electrically conductive portion has a linear structure, the linear structure including an electrically conductive linear member made of a linear electrically conductive material with an electric line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm.

The pneumatic tire according to the present technology can suppress a reduction in electrical conductivity of the electrically conductive portion caused when the tire is manufactured or in service by the electrically conductive linear member of the electrically conductive portion being linearly formed of electrically conductive material with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm. As a result, there is an advantage that the electrostatic suppression performance of the tire is appropriately secured.

DETAILED DESCRIPTION

The technology is described in detail below, with reference to the accompanying drawings. However, the technology is not limited to the embodiments. In addition, the components of the embodiments include components that are replaceable while maintaining consistency with the technology, and obviously replaceable components. Furthermore, a plurality of modified examples described in the embodiments may be freely combined within the scope of obviousness to a person skilled in the art.

FIG. 1is a cross-sectional view along a tire meridian direction illustrating a pneumatic tire according to an embodiment of the technology.FIG. 1illustrates a region to one side in the tire radial direction. Also,FIG. 1illustrates a radial tire for a passenger vehicle as an example of a pneumatic tire.

Note that forFIG. 1, “cross section along a tire meridian direction” refers to a cross section of the tire taken along a plan that includes the tire rotation axis (not illustrated). In addition, the reference sign CL denotes the tire equatorial plane, which is a plane perpendicular to the tire rotation axis that passes through the center point of the tire in the tire rotation axis direction. “Tire width direction” refers to the direction parallel to the tire rotation axis. “Tire radial direction” refers to the direction perpendicular to the tire rotation axis.

A pneumatic tire1has an annular structure with the tire rotation axis as its center and includes a pair of bead cores11,11, a pair of bead fillers12,12, a carcass layer13, a belt layer14, a tread rubber15, a pair of sidewall rubbers16,16, a pair of rim cushion rubbers17,17, an innerliner18, and chafers20(seeFIG. 1).

The pair of bead cores11,11constitute the cores of the left and right bead portions, and are annular members made of a plurality of bead wires bundled together. The pair of bead fillers12,12are disposed on the outer periphery of the pair of bead cores11,11in the tire radial direction and reinforce the bead portions.

The carcass layer13extends between the left and right side bead cores11,11in a toroidal form, forming the framework for the tire. Additionally, both ends of the carcass layer13are folded outwardly in the tire width direction so as to wrap around the bead cores11and the bead fillers12, and fixed. The carcass layer13is constituted by a plurality of carcass cords formed from steel or organic fibers (e.g. aramid, nylon, polyester, rayon, or the like) covered by a coating rubber and subjected to a rolling process, and has a carcass angle (inclination angle of the fiber direction of the carcass cords with respect to the tire circumferential direction), as an absolute value, from 80 to 95 degrees, both inclusive.

The cord rubber of the carcass cord preferably has a value of tan δ at 60° C. of 0.20 or less. In addition, the cord rubber of the carcass cord preferably has a volume resistivity of 1×10{circumflex over ( )}8 Ω·cm or greater. The cord rubber having such a volume resistivity is made using a compound with low exothermic properties and low carbon content, or alternatively by increasing the silica content to improve the volume resistivity. Such a configuration is preferable because a low value of tan δ at 60° C. means low tire rolling resistance.

The value of tan δ at 60° C. is measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisaku-sho, Ltd. under the following conditions: 10% initial distortion, ±0.5% amplitude, 20 Hz frequency.

The volume resistivity is measured in accordance with the method specified in JIS (Japanese Industrial Standard) K6271 “Rubber, vulcanized or thermoplastic—Determination of volume and/or surface resistivity”. Typically, a member with a volume resistivity of less than 1×10{circumflex over ( )}8 Ω·cm can be considered to have electrical conductivity sufficient to suppress a buildup of static electricity.

Note that the configuration illustrated inFIG. 1includes the carcass layer13extending between the left and right bead cores11,11of the tire in a continuous manner.

However, the carcass layer13is not limited to such a configuration and may be divided in the tire width direction into a pair of left and right carcass plies, i.e. have a divided carcass structure (not illustrated). Specifically, radially inward end portions of the left-right pair of carcass plies are folded outwardly in the tire width direction so as to wrap around the left and right bead cores11and bead filler12, and fixed. In addition, radially outward end portions of the left-right pair of carcass plies are disposed separated at the center region of the tread portion.

Such a divided carcass structure includes an open section (region without carcass plies) formed at the center region of the tread portion. In such a case, the tension of the tire at this open section is supported by the belt layer14, and the rigidity at the left and right sidewall portions is ensured by the left and right carcass layers13,13. Thus, the tire internal pressure holding capacity and rigidity of the sidewall portions can be maintained, and reduction in tire weight achieved.

The belt layer14includes a pair of cross belts141,142and a belt cover143layered together, and is disposed around the outer periphery of the carcass layer13. The pair of cross belts141,142are constituted by a plurality of belt cords formed from steel or organic fibers, covered by coating rubber, and subjected to a rolling process, having a belt angle, as an absolute value, from 20 to 55 degrees, both inclusive. Furthermore, the pair of cross belts141,142have belt angles (inclination angle of the fiber direction of the belt cord with respect to the tire circumferential direction) of opposite signs, and the belts are layered so that the fiber direction of the belt cords intersect each other (cross-ply configuration). The belt cover143is configured by a plurality of cords formed from steel or an organic fiber material, covered by coating rubber, and subjected to a rolling process, having a belt angle, as an absolute value, from 0 to 10 degrees, both inclusive. Moreover, the belt cover143is disposed outward of the cross belts141,142in the tire radial direction.

The tread rubber15is disposed on the outer circumference in the tire radial direction of the carcass layer13and the belt layer14, and configures a tread portion of the tire. The tread rubber15includes a tread cap151and an undertread152.

The tread cap151is a rubber member that constitutes the ground contact surface and may have a single layer structure (seeFIG. 1) or a multi-layer structure (not illustrated). The tread cap151preferably has a value of tan δ at 60° C. of 0.25 or less. In addition, the tread cap151preferably has a volume resistivity of 1×10{circumflex over ( )}8 Ω·cm or greater, more preferably of 1×10{circumflex over ( )}10 Ω·cm or greater, and even more preferably of 1×10{circumflex over ( )}12 Ω·cm or greater. The tread cap151having such a volume resistivity is made using a compound with low exothermic properties and low carbon content, or alternatively by increasing the silica content to improve the volume resistivity. Such a configuration is preferable because a low value of tan δ at 60° C. means low tire rolling resistance.

The undertread152is a member layered inward of the tread cap151in the tire radial direction and preferably has a volume resistivity less than that of the tread cap151.

The pair of sidewall rubbers16,16are disposed outward of the carcass layer13in the tire width direction and constitute left and right sidewall portions. The sidewall rubber16preferably has a value of tan δ at 60° C. of 0.20 or less. In addition, the sidewall rubber16preferably has a resistivity of 1×10{circumflex over ( )}8 Ω·cm or greater, more preferably of 1×10{circumflex over ( )}10 Ω·cm or greater, and even more preferably of 1×10{circumflex over ( )}12 Ω·cm or greater. The sidewall rubber16having such a resistivity is made using a compound with low exothermic properties and low carbon content, or alternatively by increasing the silica content to improve the volume resistivity. Such a configuration is preferable because a low value of tan δ at 60° C. means low tire rolling resistance.

The pair of rim cushion rubbers17,17are disposed inward in the tire radial direction of the left and right bead cores11,11and the folded portion of the carcass layer13and constitute the contact surface of the left and right bead portions with the rim flange portion of the rim R. The rim cushion rubber17preferably has a resistivity of 1×10{circumflex over ( )}7 Ω·cm or less.

Note that the upper limit value for the resistivity of the tread cap151, the lower limit value for the resistivity of the undertread152, the upper limit value for the resistivity of the sidewall rubber16, and the lower limit value for the resistivity of the rim cushion rubber17are not particularly limited to the above-mentioned values, but are subject to physical constraints specific to being a rubber member.

The innerliner18is an air penetration preventing layer covering the carcass layer13disposed on the tire inner surface. The innerliner18also suppresses oxidation caused by exposure of the carcass layer13and prevents the air in the tire from leaking. In addition, the innerliner18is constituted by, for example, a rubber composition with butyl rubber as a main component, thermoplastic resin, thermoplastic elastomer composition made by blending an elastomer component with a thermoplastic resin, and the like. In particular, by using a thermoplastic resin or a thermoplastic elastomer composition to form the innerliner18, the innerliner18can be made thinner than in the case in which butyl rubber is used for the innerliner18. As such, tire weight can be greatly reduced. Note that the innerliner18is typically required to have an air penetration coefficient at of 100×10{circumflex over ( )}12 cc·cm/cm{circumflex over ( )}2·sec·cmHg or less when measured in accordance with JIS K7126-1 at a temperature of 30° C. In addition, the innerliner18preferably has a resistivity of 1×10{circumflex over ( )}8 Ω·cm or greater, and typically 1×10{circumflex over ( )}9 Ω·cm or greater.

Examples of a rubber composition with butyl rubber as a main component that can be used include butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), and the like. Butyl rubber is preferably a halogenated butyl rubber such as chlorinated butyl rubber and brominated butyl rubber.

Electrostatic Suppressing Structure

Some pneumatic tires employ a structure including an earthing tread that suppresses electrostatic charging by discharging to the road surface static electricity produced in the vehicle when traveling. Such an earthing tread is an electrically conductive rubber disposed passing through the tread cap and is exposed to the ground contact surface. This electrostatic suppressing structure can suppress electrostatic charging in the vehicle by discharging static electricity in the vehicle from the belt layer to the road surface via the earthing tread.

However in recent years, as described above, the amount of silica contained in rubber compounds constituting tread caps, undertreads, sidewall rubber, and the like has been increasing in order to reduce the tire rolling resistance and thus improve the fuel economy of tires. Because silica is a good insulator, the resistance value of a tread cap increases when the amount of silica contained therein increases. Consequently, the electrostatic suppression performance decreases.

In light of the above, the pneumatic tire1employs the following configuration to enhance the electrostatic suppression performance.

FIGS. 2 to 6are explanatory diagrams of an electrostatic suppressing structure of the pneumatic tire illustrated inFIG. 1.FIG. 2is a cross-sectional view in a tire meridian direction of the region to one side of the tire equatorial plane CL.FIG. 3is an enlarged cross-sectional view of an earthing tread51.FIG. 4is a cross-sectional view taken along A ofFIG. 2. A layered structure of an electrically conductive portion52, the carcass layer13, the innerliner18, and a tie rubber19is illustrated.FIG. 5schematically illustrates the region where the electrically conductive portion52is disposed in the tire circumferential direction. In these drawings, the electrically conductive portion52is indicated by hatching.FIG. 6illustrates the stranded wire structure of the electrically conductive portion52.

As illustrated inFIG. 1, the pneumatic tire1is provided with the earthing tread51and the electrically conductive portion52as an electrostatic suppressing structure5.

As illustrated inFIG. 2andFIG. 3, the earthing tread51is disposed passing through the tread cap151and undertread152, is exposed to the road contact surface of the tread rubber15, and is in contact with the belt layer14(belt cover143) in an electrically conductive manner. Consequently, an electrically conductive path is secured from the belt layer14to the road surface. In addition, the earthing tread51has an annular structure extending around the entire circumference of the tire. A portion of the earthing tread51is exposed to the tread road contact surface and extends continuously in the tire circumferential direction. As such, when the tire is driven, an electrically conductive path from the belt layer14to the road surface is always ensured by the earthing tread51being always in contact with the road surface.

In addition, the earthing tread51is made of electrically conductive rubber material having a lower volume resistivity than the tread rubber15. Specifically, the earthing tread51preferably has a volume resistivity of less than 1×10{circumflex over ( )}8 Ω·cm, and more preferably of 1×10{circumflex over ( )}6 Ω·cm or less.

The electrically conductive portion52extends at least from the bead portion to the belt layer14, as illustrated inFIG. 1andFIG. 2, and has an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm. At least one electrically conductive portion52is disposed. As a result, an electrically conductive path is ensured from the bead portion to the belt layer14.

“Bead portion” refers to the region from the rim diameter measuring position to a position at one third of the cross-sectional height SH of the tire.

“Cross-sectional height SH of the tire” refers to a height half of the difference between the tire external diameter and the rim diameter, and measured when the tire is assembled on a specified rim, inflated to a specified inner pressure, and no load is applied.

Here, “specified rim” refers to an “applicable rim” as defined by the Japan Automobile Tyre Manufacturers Association (JATMA), to a “Design Rim” as defined by the Tire and Rim Association (TRA), or to a “Measuring Rim” defined by the European Tyre and Rim Technical Organization (ETRTO). In addition, “specified internal pressure” refers to “maximum air pressure” as defined by JATMA, to a maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” as defined by TRA, and to “INFLATION PRESSURES” as defined by ETRTO. Also, “specified load” refers to a “maximum load capacity” defined by JATMA, to a maximum value in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” as defined by TRA, and to a “LOAD CAPACITY” as defined by ETRTO. However, according to JATMA, for a passenger vehicle tire, the specified internal pressure is an air pressure of 180 kPa, and a specified load is 88% of maximum load capacity.

As illustrated inFIGS. 4 to 6, the electrically conductive portion52has a linear structure and includes an electrically conductive linear member521. The electrically conductive portion52may have a stranded wire structure including an intertwined plurality of linear members including at least one electrically conductive linear member521(seeFIG. 6), or may be a monofilament cord made of electrically conductive material (not illustrated). An electrically conductive portion52with a linear structure is preferable because tire rolling resistance is reduced more than a configuration in which an electrically conductive portion is constituted by a rubber layer additionally added to the tire.

The electrically conductive linear member521is a linear member made of electrically conductive material linearly formed and has an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm. The electrically conductive linear member521may represent a monofilament, a strand, or a cord made of electrically conductive material. Accordingly, for example, the electrically conductive linear member521may correspond to a cord made of metal or carbon fiber, a metal fiber of fiberized metal such as stainless steel, and the like. However, the electrically conductive linear member521does not correspond to a non-electrically conductive linear member made of non-electrically conductive material with an electrical line resistivity of 1×10{circumflex over ( )}8 Ω/cm or greater, a linear member made of such a non-electrically conductive linear member with its surface coated with electrically conductive material, or the like.

Examples of the stranded wire structure of the electrically conductive portion52(seeFIG. 6) include:

(1) an intertwined plurality of carbon fibers;

(2) an electrically conductive linear member521with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm and a non-electrically conductive linear member522with an electrical line resistivity of 1×10{circumflex over ( )}8 Ω/cm or greater intertwined together. The stranded wire structure of the linear members is not limited to any particular structure, and any structure can be applied.

As the non-electrically conductive linear member522of above-mentioned (2), for example polyester fiber, nylon fiber, and the like can be used. In particular, the electrically conductive portion52is preferably a blended yarn of the electrically conductive linear member521made of metal fiber and the non-electrically conductive linear member522made of polyester fiber intertwined together.

The electrical line resistivity Ω/cm is measured by:

preparing a sample piece of the fiber 3 cm or greater in length in the filament length direction;

applying a voltage of 500 V across the sample piece (between both ends);

carrying out measurement using ohmmeter SME-8220 manufactured by Toa Dempa Kogyo K.K under conditions of measurement environment temperature 20° C. and 20% RH.

The electrically conductive portion52preferably has a total linear density from 20 to 1000 dtex, both inclusive, and more preferably from 150 to 350 dtex, both inclusive. Setting this lower limit of the total linear density to a value within the range described above ensures that the electrically conductive portion52is prevented from breaking when the tire is manufactured. In addition, setting this upper limit of total linear density to a value within the range described above ensures that the electrically conductive portion52is prevented from breaking when the tire is driven.

The total linear density is measured in accordance with JIS L 1017-8.3 “Test methods for chemical fibre tire cords—Fineness based on corrected weight”.

The electrically conductive portion52preferably has an elongation ratio of from 1.0 to 70.0%, both inclusive. Setting this lower limit of the elongation ratio to a value within the range described above ensures that the electrically conductive portion52is prevented from breaking when the tire is manufactured. In addition, setting this upper limit of the elongation ratio to a value within the range described above ensures that the electrically conductive portion52is prevented from breaking when the tire is driven.

The elongation ratio of the linear members is measured in accordance with JIS L 1017-8.5 “Test methods for chemical fibre tire cords—Tensile strength and Elongation ratio”.

In the configuration illustrated inFIG. 1for example, the electrically conductive portion52is disposed in each of the regions to the left and the right of the tire equatorial plane CL. In addition, in each region, a plurality of the electrically conductive portions52are disposed at predetermined intervals in the tire circumferential direction.

As illustrated inFIG. 2, the electrically conductive portion52extends continuously in the tire radial direction along the carcass layer13from the bead portion to the belt layer14. The radially inward end portion of the electrically conductive portion52is located in the vicinity of the bead core11in contact with the rim cushion rubber17. Consequently, an electrically conductive path is ensured from the rim fitting surface to the electrically conductive portion52via the rim cushion rubber17. In addition, the radially outward end portion of the electrically conductive portion52extends to a position at which the end portion overlaps with the belt layer14in the tire width direction. As a result, an electrically conductive path is ensured from the electrically conductive portion52to the belt layer14.

In such a case, a lap width La with which the belt layer14and the electrically conductive portion52overlap is preferably 3 mm or greater. The upper limit of the lap width La is not particularly limited to any value, and the electrically conductive portion52may extend, crossing the tire equatorial plane CL, to reach both left and right bead portions.

The lap width La, in a cross-sectional view in the tire meridian direction, is taken as the surface length of the electrically conductive portion52. This surface length of the electrically conductive portion52is measured from the bottom point of a vertical line drawn from the laterally outward end portion of belt ply141, which is the widest belt ply in the belt layer14, to the conductive portion52to the end portion of the electrically conductive portion52.

The electrically conductive portion52of the configuration illustrated inFIG. 1is yarn, and this electrically conductive portion52is disposed between the carcass layer13and the adjacent member. As illustrated inFIG. 6, the electrically conductive portion52has a stranded wire structure including the electrically conductive linear member521with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm and the non-electrically conductive linear member522with an electrical line resistivity of 1×10{circumflex over ( )}8 Ω/cm or greater intertwined together.

The yarn is a linear member disposed along the surface of the carcass layer13(seeFIG. 5). Upon forming of the green tire, this yarn forms a gap between the carcass layer13and the adjacent member for discharging enclosed air.

For example, the electrically conductive portion52of the configuration illustrated inFIG. 1is located on the inner circumferential surface side of the carcass layer13and disposed between the carcass layer13and the innerliner18and the tie rubber19, as illustrated inFIG. 2andFIG. 4. The electrically conductive portion52extends in a straight line along the carcass layer13in the tire radial direction.

In such a case, the distance from the electrically conductive portion52to the innerliner18is preferably 1.0 mm or less, and more preferably 0.5 mm or less. In particular, when the innerliner18is constituted by thermoplastic resin, static electricity is produced by friction when the tire is driven and the innerliner18builds up charge. Thus, by disposing the electrically conductive portion52approximate to the innerliner18, an electrically conductive path from the innerliner18to the electrically conductive portion52is appropriately ensured.

The configuration described above discharges static electricity produced in the vehicle through the rim R, the rim cushion rubber17, the electrically conductive portion52, and the belt layer14(and undertread152) to the road surface via the earthing tread51. Thus, electrostatic charge in the vehicle due to static electricity is suppressed.

Note that the rim cushion rubber17, the coating rubber of the carcass layer13and the belt layer14constitute the electrically conductive path from the rim R to the earthing tread51. Thus, these rubbers preferably have low volume resistivity. This causes the electrically conductive efficiency from the rim R to the earthing tread51to be improved.

MODIFIED EXAMPLES

FIG. 7andFIG. 8are explanatory diagrams illustrating modified examples for the pneumatic tire illustrated inFIG. 1. These diagrams illustrate modified examples of the structure with which the electrically conductive portion52is disposed.

The electrically conductive portion52of the configuration illustrated inFIG. 1, as illustrated inFIG. 2, includes a radially inward end portion that extends to the vicinity of the bead core11and is in contact with the rim cushion rubber17. Such a configuration is preferable because an electrically conductive path from the rim fitting surface to the electrically conductive portion52, via the rim cushion rubber17, is appropriately ensured.

In addition, as illustrated inFIG. 7, the radially inward end portion of the electrically conductive portion52may extend to the inner side of the bead core11in the tire radial direction. As illustrated inFIG. 8, the radially inward end portion of the electrically conductive portion52may be disposed to wind up and around the bead core11. These configurations further improve electrical conductivity from the rim fitting surface to the electrically conductive portion52.

However, the electrically conductive portion52is not limited to these configurations, and the radially inward end portion of the electrically conductive portion52may, for example, end in the vicinity of the bead filler12without coming into contact with the rim cushion rubber17(not illustrated). Such a configuration can ensure necessary and sufficient electrical conductivity from the rim fitting surface to the electrically conductive portion52.

FIG. 9andFIG. 10are explanatory diagrams illustrating modified examples for the pneumatic tire illustrated inFIG. 1. These diagrams illustrate modified examples of the structure with which the electrically conductive portion52is disposed.

The electrically conductive portion52of the configuration illustrated inFIG. 1, as illustrated inFIG. 2andFIG. 4, is disposed on the inner circumference of the carcass layer13between the carcass layer13and the innerliner18and the tie rubber19. Such a configuration can reduce the distance from the innerliner18to the electrically conductive portion52. Specifically, the distance from the electrically conductive portion52to the innerliner18can be reduced to 1.0 mm or less. This configuration is preferable, in particular when the innerliner18is made of thermoplastic resin, because static electricity produced in the innerliner18can efficiently dissipate through the electrically conductive portion52.

However the electrically conductive portion52is not limited to such a configuration and, as illustrated inFIG. 9andFIG. 10, may be disposed on the outer circumference of the carcass layer13.

For example, the electrically conductive portion52of the configuration illustrated inFIG. 9andFIG. 10is yarn for discharging air enclosed upon forming of the green tire. This electrically conductive portion52has a stranded wire structure including a plurality of linear members intertwined together, the plurality of linear members including an electrically conductive linear member (seeFIG. 6). In addition, the electrically conductive portion52is disposed along the outer circumferential surface of the carcass layer13(seeFIG. 5) and extends from the bead portion to the belt layer14. The radially outward end portion of the electrically conductive portion52extends to a position at which the end portion overlaps the belt layer14and is disposed between the belt layer14(the most radially inward belt ply141(seeFIG. 9)) and the carcass layer13.

In such a case, the radially inward end portion of the electrically conductive portion52may be located inward of the bead core11or the bead filler12in the tire width direction (seeFIG. 9). The radially inward end portion may also be located inward of the bead core11in the radial direction (not illustrated). Additionally, the radially inward end portion may wrap up and around the bead core11together with the carcass layer13(seeFIG. 10).

FIG. 11andFIG. 12are explanatory diagrams illustrating modified examples for the pneumatic tire illustrated inFIG. 1. These diagrams illustrate modified examples of the structure with which the electrically conductive portion52is disposed.

As described above, the electrically conductive portion52of the configuration illustrated inFIG. 1is a yarn for discharging air enclosed upon forming of the green tire and, as illustrated inFIG. 5, is disposed along the circumferential surface of the carcass layer13.

However the electrically conductive portion52is not limited to this configuration. The electrically conductive portion52may be a member that is not a yarn and may be disposed with a portion or the entirety thereof separated from the carcass layer13.

For example, the electrically conductive portion52of the configuration illustrated inFIG. 11andFIG. 12is disposed between the bead core11and the bead filler12and the sidewall rubber16and extends from the bead portion to the belt layer14. The radially outward end portion of the electrically conductive portion52extends to a position at which the end portion overlaps the belt layer14and is disposed between the belt layer14(the most radially inward belt ply141(seeFIG. 11)) and the carcass layer13.

In addition, in the configuration illustrated inFIG. 11, the radially inward end portion of the electrically conductive portion52is disposed between the wound up portion of the carcass layer13and the sidewall rubber16and is in contact with the rim cushion rubber17. By the electrically conductive portion52and the rim cushion rubber17being in contact in such a manner, the electrical conductivity from the rim fitting surface to the electrically conductive portion52is improved.

In the configuration illustrated inFIG. 12, the radially inward end portion of the electrically conductive portion52is disposed between the bead core11and bead filler12and the wound up portion of the carcass layer13. Such a configuration can ensure an electrically conductive path from the rim cushion rubber17to the electrically conductive portion52via the cord rubber of the carcass layer13.

FIGS. 13 to 16are explanatory diagrams illustrating modified examples of the pneumatic tire illustrated inFIG. 1. These diagrams illustrate modified examples of the structure with which the electrically conductive portion52is disposed.

The electrically conductive portion52of the configuration illustrated inFIG. 1is embedded in the tire without being exposed to the tire surface. Such a configuration is preferable because the electrically conductive portion52is not prone to breaking when the tire is manufactured or in service.

However, the electrically conductive portion52is not limited to this configuration and may be disposed exposed to the tire inner circumferential surface or the tire outer circumferential surface.

For example, the electrically conductive portion52of the configuration illustrated inFIGS. 13 to 15is disposed on the tire cavity side of the innerliner18and tie rubber19and is exposed to the tire inner circumferential surface. The electrically conductive portion52extends along the surface of the innerliner18from the bead portion to the belt layer14.

In the configuration illustrated inFIG. 13andFIG. 14, the radially inward end portion of the electrically conductive portion52extends with the innerliner18and the tie rubber19to the lower portion of the rim cushion rubber17and is disposed between the rim cushion rubber17and the carcass layer13. In addition, by the electrically conductive portion52being in contact with the rim cushion rubber17, electrical conductivity from the rim fitting surface to the electrically conductive portion52is increased. In such a case, the radially inward end portion of the electrically conductive portion52may be located inward of the bead core11or the bead filler12in the tire width direction (seeFIG. 13). The radially inward end portion of the electrically conductive portion52may be located inward of the bead core11in the radial direction (not illustrated). Additionally, the radially inward end portion of the electrically conductive portion52may wind up and around the bead core11conforming with the carcass layer13(seeFIG. 14).

In the configuration illustrated inFIG. 15, the radially inward end portion of the electrically conductive portion52extends to the inner side of the bead core11in the radial direction along the circumferential surface of the rim cushion rubber17and is exposed to the rim fitting surface. Such a configuration is preferable because, with the tire mounted on the rim, the electrically conductive portion52is in direct contact with the rim R, and thus electrical conductivity from the rim R to the electrically conductive portion52is improved.

Additionally, for example, the electrically conductive portion52of the configuration illustrated inFIG. 16is disposed on the outer circumference of the sidewall rubber16and is exposed to the tire outer circumferential surface. The electrically conductive portion52extends along the surface of the sidewall rubber16from the bead portion to the tread rubber15.

FIG. 17andFIG. 18are explanatory diagrams illustrating modified examples for the pneumatic tire illustrated inFIG. 1. These diagrams illustrate modified examples of the structure with which the electrically conductive portion52is disposed.

The electrically conductive portion52of the configuration illustrated inFIG. 1is disposed in each of the regions to the left and the right of the tire equatorial plane CL. In addition, the radially outward end portion of the electrically conductive portion52extends from the bead portion to a position at which the end portion overlaps the belt layer14and ends without crossing the tire equatorial plane CL.

In contrast, as illustrated inFIG. 17, the electrically conductive portion52may be disposed in the region to only one side of the tire equatorial plane CL. The electrically conductive portion52may alternatively be disposed across the entire width of the tire width direction, as illustrated inFIG. 18.

FIG. 19andFIG. 20are explanatory diagrams illustrating modified examples for the pneumatic tire illustrated inFIG. 1. These diagrams illustrate enlarged cross-sectional views of the earthing tread51.

As illustrated inFIG. 3, the earthing tread51of the configuration illustrated inFIG. 1, when viewed as a cross-section from the tire meridian direction, is disposed passing through the tread cap151and undertread152, is exposed to the road contact surface of the tread rubber15, and is in contact with the belt layer14(the belt cover143, which is the outermost layer) in an electrically conductive manner. The earthing tread51has a straight shape. Such a configuration is preferable because the effects of electrostatic suppression can be efficiently obtained by an electrically conductive path being ensured from the belt layer14, which has a low resistivity, to the road contact surface of the tread rubber15, via the earthing tread51.

In contrast to the configuration illustrated inFIG. 3, the earthing tread51of the configuration illustrated inFIG. 19is disposed passing through the tread cap151only and is in contact with the undertread152. Such a configuration can efficiently obtain effects of electrostatic suppression by the undertread152having a low resistivity.

In relation to the configuration illustrated inFIG. 3, the earthing tread51of the configuration illustrated inFIG. 20has a shape which widens from the road contact surface of the tread rubber15toward the belt layer14to increase the contact surface with the belt layer14. Such a configuration can suppress the amount of area of the earthing tread51exposed to the tread road contact surface while reliably ensuring greater contact area between the earthing tread51and the belt layer14than the configuration in which the earthing tread51has a straight shape (seeFIG. 3). Thus, the electrical conductivity from the belt layer14to the earthing tread51is improved.

Note that inFIG. 3,FIG. 19, andFIG. 20, the earthing tread51is employed as a discharge structure spanning from the belt layer14(or the undertread152) to the road contact surface of the tread rubber15. However, the discharge structure is not limited to this earthing tread51and other known discharge structures may be employed.

EFFECT

As described above, the pneumatic tire1is provided with the pair of bead cores11,11, the at least one carcass layer13extending between the pair of bead cores11,11continuously or with a divided portion at the tread portion, the belt layer14disposed outward of the carcass layer13in the tire radial direction, the tread rubber15disposed outward of the belt layer14in the tire radial direction, the pair of sidewall rubbers16,16disposed outward of the carcass layer13in the tire width direction on both sides, and the innerliner18disposed on the inner circumferential surface of the carcass layer13(seeFIG. 1). The pneumatic tire1is also provided with the electrically conductive portion52at least extending continuously from the bead portion to the belt layer14(seeFIG. 2). The electrically conductive portion52has a linear structure. The linear structure includes the electrically conductive linear member linearly formed of electrically conductive material with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm (seeFIGS. 4 to 6). Such a configuration:

(1) is advantageous because the electrically conductive portion52ensures that an electrically conductive path from the bead portion to the belt layer14is formed, and thus the electrostatic suppression performance of the tire is effectively improved; and

(2) is advantageous because by the electrically conductive linear member521of the electrically conductive portion52being linearly formed of electrically conductive material with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm, a reduction in electrical conductivity of the electrically conductive portion52caused when the tire is manufactured or in service is suppressed. Consequently, electrostatic suppression performance of the tire is appropriately ensured. A configuration, for example, in which the electrically conductive portion is a non-electrically conductive linear member coated with electrically conductive material is not preferable because the coating is susceptible to separation due to heat or strain that occurs when the tire is manufactured or in service, and thus the electrical conductivity of the electrically conductive portion may be reduced. In particular, in the case of a configuration in which the innerliner18is made of thermoplastic resin or a thermoplastic elastomer composition made by blending an elastomer component with a thermoplastic resin, the thin gauge of the innerliner18causes the electrically conductive portion52(for example, seeFIG. 2,FIG. 9, and the like) embedded in the tire to reach high temperatures. Thus, configurations in which the electrically conductive portion is a non-electrically conductive linear member coated with electrically conductive material are not preferable especially because the coating is susceptible to separation.

The electrically conductive portion52of the pneumatic tire1includes a plurality of intertwined linear members, the plurality of linear members including at least one electrically conductive linear member521(seeFIG. 6). Such a configuration is advantageous because, by the electrically conductive portion52having a stranded wire structure, repeated fatigue properties and elongation properties are more favorable than those of configurations in which the electrically conductive portion is a monofilament, and thus the durability of the electrically conductive linear member521is improved.

In addition, the electrically conductive portion52of the pneumatic tire1includes the electrically conductive linear member521with an electrical line resistivity of less than 1×10{circumflex over ( )}8 Ω/cm and the non-electrically conductive linear member522with an electrical line resistivity of 1×10{circumflex over ( )}8 Ω/cm or greater intertwined together (seeFIG. 6). This configuration is advantageous because the non-electrically conductive linear member522can, for example, compensate for the insufficiencies of the electrically conductive linear member521, and thus the strength, heat resistance, and dimensional stability of the electrically conductive portion52can be appropriately ensured.

The electrically conductive linear member521of the pneumatic tire1is a metal fiber (in particular, stainless steel fiber), and the non-electrically conductive linear member522is an organic fiber (in particular, polyester fiber) (seeFIG. 6). This configuration is advantageous because strength, heat resistance, and dimensional stability can be appropriately ensured.

The electrically conductive linear member521of the pneumatic tire1includes a plurality of carbon fibers intertwined together. This configuration is advantageous because reduction in weight can be achieved.

In addition, the electrically conductive linear member521of the pneumatic tire1is a monofilament cord made of carbon fiber. This configuration is advantageous because reduction in weight can be achieved.

The electrically conductive portion52of the pneumatic tire1is disposed between the carcass layer13and the adjacent member (examples include inFIGS. 2 and 4, the innerliner18and the tie rubber19, and inFIG. 9, the belt layer14and the sidewall rubber16). Such a configuration is advantageous because, by the electrically conductive portion52being embedded in the tire, the electrically conductive portion can be prevented from breaking upon the manufacture of the tire or when in service to a greater degree than a configuration in which the electrically conductive portion is exposed to the tire surface.

In the pneumatic tire1, the cord rubber of the carcass layer13has a volume resistivity of 1×10{circumflex over ( )}8 Ω·cm or greater. Such a configuration is advantageous because, by being able to reduce the amount of carbon blended in the cord rubber, the release of heat from the cord rubber when the tire is driven can be suppressed, and thus the tire rolling resistance can be reduced.

The innerliner18of the pneumatic tire1is constituted by a thermoplastic resin or a thermoplastic elastomer composition made by blending an elastomer component with a thermoplastic resin. Such a configuration is advantageous because air permeability of the innerliner18can be more favorably reduced than a configuration in which butyl rubber constitutes the innerliner18, and thus tire weight and tire rolling resistance are reduced. In the pneumatic tire1, the distance from the innerliner18to the electrically conductive portion52is 1.0 mm or less (seeFIG. 4). Such a configuration is advantageous because with a configuration in which the innerliner18is constituted by a thermoplastic resin, static electricity produced in the innerliner18can efficiently dissipate through the electrically conductive portion52.

In the pneumatic tire1, the total linear density of the electrically conductive portion52is from 20 to 1000 dtex, both inclusive. This configuration is advantageous because the total linear density of the electrically conductive portion52is made appropriate. In other words, when the total linear density is 20 dtex or greater, breaking of the electrically conductive portion52upon manufacture of the tire is prevented. When the total linear density is 1000 dtex or less, breaking of the electrically conductive portion52when the tire is driven is prevented.

In addition, the electrically conductive portion52of the pneumatic tire1has an elongation ratio of from 1.0 to 70.0%, both inclusive. This configuration is advantageous because the elongation ratio of the electrically conductive portion52is made appropriate. In other words, because the elongation ratio is 1.0% or greater, breaking of the electrically conductive portion52upon manufacture of the tire is prevented. Because the elongation ratio is 70.0% or less, breaking of the electrically conductive portion52when the tire is driven is prevented.

The tread rubber15of the pneumatic tire1includes the tread cap151constituting the ground contact surface, and the undertread152layered inward of the tread cap151in the tire radial direction (seeFIG. 1). The tread cap151has a value of tan δ at 60° C. of 0.25 or less and a volume resistivity of 1×10{circumflex over ( )}8 Ω·cm or greater. Such a configuration is advantageous because the tire rolling resistance is reduced when the amount of silica contained in the tread cap151is increased.

The tread rubber15of the pneumatic tire1includes the tread cap151constituting the ground contact surface, and the undertread152disposed inward of the tread cap151in the tire radial direction. The tread rubber15has an volume resistivity of less than 1×10{circumflex over ( )}8 Ω·cm and is provided with the earthing tread51that passes through at least the tread cap151and is exposed to the ground contact surface (seeFIGS. 1 to 3). Such a configuration is advantageous because an electrically conductive path from the belt layer14(or the undertread152) to the contact surface of the tread rubber15is ensured.

In the pneumatic tire1, the value of tan δ at 60° C. of the sidewall rubber16is 0.20 or less, and the volume resistivity of the sidewall rubber16is 1×10{circumflex over ( )}8 Ω·cm or greater. Such a configuration is advantageous because the tire rolling resistance is reduced when the amount of silica contained in the sidewall rubber16is increased.

EXAMPLES

FIGS. 21A-21Binclude a table showing results of performance testing of pneumatic tires according to embodiments of the present technology.

In the performance testing, a plurality of mutually differing test tires were evaluated for (1) low rolling resistance and (2) electrostatic suppression performance (electrical resistance value). For the performance testing, test tires of tire size 195/65R15 91H were manufactured.

(1) For the evaluation for low rolling resistance, the tire rolling resistance was measured using an indoor drum type tire rolling resistance tester with a drum diameter of 1707 mm in accordance with the measurement method defined in JATMA Y/B 2012 edition. Results of the evaluations were indexed with the results of the Conventional Example set as the reference (100). Higher values indicate lower rolling resistance (preferred result).

(2) For the evaluation of electrostatic suppression performance, electrical resistance (Ω) was measured using ADVANTEST R8340A ultra high resistance meter in accordance with measurement conditions specified by JATMA. The electrical resistance was measured when the tires were new and after travelling under predetermined conditions. The electrical resistance after travelling was measured as follows:

the test tires were assembled on an applicable rim as specified by JATMA,

inflated to an air pressure of 200 kPa,

loaded with 80% of a maximum load as specified by JATMA, and

run for 60 min at 81 km/h using an indoor drum type tire rolling resistance tester with a drum diameter of 1707 mm. Lower values indicate superior discharge properties (preferred result).

The test tires of Working Examples 1 to 10 had a configuration based on that illustrated inFIG. 1and were provided with the earthing tread51and the electrically conductive portion52including the electrically conductive linear member. The electrically conductive portion52was disposed at different positions: between the carcass layer13and the innerliner18and tie rubber19(FIG. 2), between the carcass layer13and the belt layer14and sidewall rubber16(FIG. 9), and on the surface of the sidewall portion (FIG. 16). In addition, the electrically conductive portion52was either a “blended yarn” made of intertwined polyester fiber and stainless steel fiber, or “carbon fiber” made of intertwined carbon fibers. “Electrical line resistivity of electrically conductive portion (Ω/cm)” refers to the electrical resistivity of the electrically conductive portion52, which is a stranded wire.

The test tire of the Conventional Example was the same as that of Working Example 2 except that the electrically conductive portion52was made of polyester fiber, which is a non-electrically conductive material, coated with a conducting polymer.

As shown in the test results, it can be seen that the low rolling resistance and electrostatic suppression performance of the test tires of Working Examples 1 to 10 are improved.