tire

Abstract

To provide a tire, which can exert stable conductive performance, without causing deterioration in steering stability and increase in road noise.SOLUTION: The tire comprises a tread, a pair of side walls, a pair of beads, a carcass 12, a belt, and a conductive yarn 50 fixed to the carcass 12 to make the first bead lead to the second bead. The tread has a tread surface grounding a road surface. The carcass 12 comprises a carcass ply 40. The conductive yarn 50 is sewn with sewing threads 52 to a surface at the tread side of the carcass ply 40. Complex elastic modulus E*s of the side walls is 4.0 MPa or more and 5.5 MPa or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] To reduce rolling resistance, low heat buildup rubber is used in tires. Low heat buildup rubber contains silica as a main reinforcing agent. Silica has poor electrical conductivity. The use of low heat buildup rubber increases the electrical resistance of the tire. Static electricity is likely to accumulate on vehicles equipped with tires with high electrical resistance. The accumulation of static electricity may result in radio interference, such as radio noise. Development is underway to develop tires with low electrical resistance even when low heat buildup rubber is used (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-133467 Summary of the Invention [Problem to be solved by the invention]

[0004] Conductive yarns are used to ensure the conductivity of tires. The carcass of a tire has a carcass ply. The carcass ply spans between the first bead and the second bead. The carcass ply is located radially inward of the tread that comes into contact with the road surface. The carcass ply is located axially inward of the clinch that contacts the rim. The carcass ply is used to form a conductive path that electrically connects the road surface and the rim. To form the conductive path, it is considered to fix conductive yarns to the surface of the carcass ply.

[0005] In tire manufacturing, heated rubber sheets are used to form the carcass ply. Immediately after completion, the carcass ply is soft and sticky. By pressing conductive threads onto the surface of the carcass ply, the conductive threads easily adhere to the carcass ply. During vulcanization, rubber flows within the mold. To prevent interface irregularities caused by this flow, the surface of the carcass ply may be irradiated with electron beams to crosslink the surface. This crosslinking hardens the surface of the carcass ply. In this case, conductive threads are difficult to adhere to the carcass ply. Even if conductive threads do adhere to the surface of the carcass ply, they tend to peel off.

[0006] If the conductive thread is sewn into the carcass ply with sewing thread, the conductive thread is reliably fixed to the surface of the carcass ply regardless of the surface condition of the carcass ply. On the other hand, sewing the conductive thread into the carcass ply with sewing thread increases the second moment of area of ​​the carcass. As the rigidity of the carcass increases, cornering power and vertical spring constant increase. There is concern that high cornering power and high vertical spring constant may lead to reduced handling stability and increased road noise.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tire that can exhibit stable electrical conductivity without causing a decrease in steering stability or an increase in road noise. [Means for solving the problem]

[0008] A tire according to one aspect of the present invention includes a tread, a pair of sidewalls connected to the ends of the tread and positioned radially inward of the tread, a pair of beads positioned radially inward of the sidewalls, a carcass spanning between a first bead and a second bead of the pair of beads, a belt laminated on the carcass radially inward of the tread, and a conductive thread fixed to the carcass and spanning between the first bead and the second bead. The tread has a tread surface that comes into contact with a road surface. The carcass includes a carcass ply. The conductive thread is sewn to the tread-side surface of the carcass ply with a sewing thread. The complex elastic modulus of the sidewall is 4.0 MPa or more and 5.5 MPa or less.

[0009] Preferably, the tire includes a full band located radially between the tread and the belt. The full band is made of a spirally wound strip. The full band includes a pair of shoulder portions including ends of the full band, and a center portion located between the shoulder portions. In the center portion, adjacent circumferential portions of the strip are disposed with a gap therebetween. The gap is 3.0 mm or more and 5.0 mm or less.

[0010] Preferably, in the tire, the tread includes a base layer and a cap layer located radially outward of the base layer, wherein a ratio of a thickness of the cap layer to a thickness of the tread is equal to or greater than 0.60 and is equal to or less than 0.80.

[0011] Preferably, in the tire, a ratio of a loss tangent at 30° C. of the base layer to a loss tangent at 30° C. of the cap layer is equal to or greater than 0.40 and is equal to or less than 0.80.

[0012] Preferably, in this tire, the conductive yarn is made of a blended yarn spun by mixing conductive staple fibers and non-conductive staple fibers. The conductive staple fibers have a length of 5 mm or more and 50 mm or less, and the non-conductive staple fibers have a length of 5 mm or more and 50 mm or less. The ratio of the mass of the conductive staple fibers to the mass of the conductive yarn is 10 mass% or more.

[0013] Preferably, in the tire, the conductive short fibers are made of stainless steel, and the non-conductive short fibers are made of organic fibers.

[0014] Preferably, in the tire, the sewing thread is a conductive thread. [Effects of the Invention]

[0015] According to the present invention, a tire can be obtained that can exhibit stable electrical conductivity without causing a decrease in steering stability or an increase in road noise. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing a part of the carcass ply. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a cross-sectional view illustrating the structure of the band. [Figure 6] FIG. 6 is a cross-sectional view showing a modified example of the band. [Figure 7] FIG. 7 is a cross-sectional view showing a part of the tread. [Figure 8] FIG. 8 is a schematic diagram illustrating an apparatus for measuring the electrical resistance of a tire. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0018] In this disclosure, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is referred to as a standard state.

[0019] In this disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part in a meridian cross section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured by cutting the tire along a plane including the rotation axis, and the distance between the left and right beads in the cross section is measured so that it matches the distance between the beads when the tire is mounted on a regular rim.

[0020] A genuine rim is a rim specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "design rim" in the TRA standard, and the "measuring rim" in the ETRTO standard are all genuine rims.

[0021] Normal tire pressure refers to the pressure specified in the standard on which the tire is based. The "maximum tire pressure" in the JATMA standard, the "maximum tire pressure" listed in the TRA standard's "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURE" and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0022] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0023] In this disclosure, a crosslinked rubber is a molded article of a rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. The crosslinked rubber is also called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0024] Examples of base rubbers include natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). Examples of chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of base rubber and chemicals, the content of the selected chemicals, etc. are determined appropriately depending on the specifications of each element to which the rubber composition is applied, such as the tread and sidewall.

[0025] In this disclosure, conductive rubber has a volume resistivity of 1.0×10 8 Non-conductive rubber means cross-linked rubber with a volume resistivity of less than 1.0×10 8 This refers to cross-linked rubber with a conductivity of Ω·cm or more. The conductivity of rubber is controlled by the amount of carbon black it contains. The main reinforcing agent in conductive rubber is carbon black, while the main reinforcing agent in non-conductive rubber is silica.

[0026] In the present disclosure, when a rubber composition contains silica and carbon black as reinforcing agents, if the silica content, expressed as the ratio of the amount of silica to the total amount of reinforcing agent, expressed as the sum of the amount of silica and the amount of carbon black, is 50% by mass or more, silica is the main component of the reinforcing agent. If the carbon black content is 50% by mass or more, carbon black is the main component of the reinforcing agent. The amount of chemicals such as silica and carbon black is expressed in parts by mass of the chemicals per 100 parts by mass of the base rubber.

[0027] In the present disclosure, the volume resistivity of an element made of crosslinked rubber among the elements constituting a tire is measured in accordance with the double ring electrode method specified in JIS K6271 at a temperature of 25°C. For this measurement, a sheet (thickness = 2 mm) is used, which is obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes.

[0028] In the present disclosure, the complex modulus and loss tangent at a temperature of 30°C or 70°C of an element made of crosslinked rubber among the elements constituting a tire are measured in accordance with the provisions of JIS K6394 using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions: Initial strain = 10% Dynamic strain = 2% Frequency = 10 Hz Deformation mode = tension In this measurement, test specimens are sampled from tires. If it is not possible to sample test specimens from tires, test specimens are sampled from a sheet of crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes.

[0029] In this disclosure, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The side portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of side portions.

[0030] 1 shows a portion of a tire 2 according to one embodiment of the present invention. The tire 2 is a pneumatic tire for passenger cars. FIG. 1 shows a portion of a cross section (hereinafter referred to as a meridian cross section) of the tire 2 taken along a plane including the rotation axis of the tire 2. In FIG. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. The dashed-dotted line CL represents the equatorial plane of the tire 2.

[0031] The tire 2 is mounted on a rim R. The rim R is a regular rim. Air is filled inside the tire 2, and the internal pressure of the tire 2 is adjusted. The tire 2 mounted on the rim R is also called a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 mounted on this rim R.

[0032] The rim R includes a seat S and a flange F. When the tire 2 is mounted on the rim R, the seat S comes into contact with the bead portion from the radially inner side. The flange F comes into contact with the bead portion from the axially outer side.

[0033] In FIG. 1, the position indicated by the symbol PW is the axial outer end of the tire 2. If there is a decoration such as a pattern or lettering on the outer surface, the outer end PW is identified based on a virtual outer surface obtained assuming that there is no decoration. The axial distance from the first outer end PW to the second outer end PW obtained in a normal state is the cross-sectional width of the tire 2 (see JATMA, etc.). The outer end PW is also referred to as the maximum width position.

[0034] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of clinches 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a band 16 , a pair of chafers 18 , and an inner liner 20 .

[0035] The tread 4 comes into contact with the road surface at a tread surface 22. The tread 4 has a tread surface 22 that comes into contact with the road surface. The tread surface 22 forms a part of the outer surface of the tire. Grooves 24 are cut into the tread 4. The tread 4 includes a tread body 26 , a terminal portion 28 , and a pair of wings 30 .

[0036] The terminal portion 28 penetrates the tread body 26. The outer end of the terminal portion 28 forms part of the tread surface 22. The inner end of the terminal portion 28 is connected to the band 16. The terminal portion 28 is made of conductive rubber.

[0037] Each wing 30 is located axially outward of the tread body 26. The wings 30 join the tread body 26 to the sidewall 6. The wings 30 are made of crosslinked rubber in consideration of adhesive properties.

[0038] The tread body 26 comprises a base layer 32 and a cap layer 34. The base layer 32 covers the band 16. The base layer 32 is made of a cross-linked rubber with low heat buildup. The base layer 32 is made of a non-conductive rubber. The base layer 32 may be made of a conductive rubber. The cap layer 34 is located radially outward of the base layer 32. The cap layer 34 covers the base layer 32. The cap layer 34 includes the above-mentioned tread surface 22. The cap layer 34 is made of a cross-linked rubber that takes into consideration wear resistance and grip performance. The cap layer 34 is made of a non-conductive rubber. The cap layer 34 may be made of a conductive rubber.

[0039] In the tire 2, the loss tangent LTb of the base layer 32 at 30° C. is smaller than the loss tangent LTc of the cap layer 34 at 30° C. From the viewpoint of reducing rolling resistance, the loss tangent LTb of the base layer 32 at 30° C. is preferably equal to or less than 0.15. From the viewpoint of improving grip performance and reducing rolling resistance, the loss tangent LTc of the cap layer 34 at 30° C. is preferably equal to or greater than 0.10 and equal to or less than 0.30.

[0040] Each sidewall 6 is continuous with the edge of the tread 4. The sidewalls 6 are located radially inward of the tread 4. The sidewalls 6 are made of crosslinked rubber for cut resistance. The thickness of the sidewalls 6 at the maximum width position PW is 1.5 mm or more and 3.0 mm or less.

[0041] In the tire 2, from the viewpoint of reducing rolling resistance, the loss tangent of the sidewall 6 at 30°C is preferably 0.08 or less, and more preferably 0.05 or less. In this case, the sidewall 6 is made of a low-heat-generating crosslinked rubber, in other words, a non-conductive rubber. The sidewall 6 may also be made of a conductive rubber.

[0042] Each clinch 8 is located radially inside the sidewall 6. The clinch 8 contacts the flange F of the rim R. The clinch 8 is made of cross-linked rubber that takes abrasion resistance into consideration. The clinch 8 is made of conductive rubber.

[0043] Each bead 10 is located axially inside the clinch 8. The beads 10 are located radially inside the sidewall 6. The bead 10 includes a core 36 and an apex 38. The core 36 extends in the circumferential direction. Although not shown, the core 36 includes a steel wire. The apex 38 is located radially outside the core 36. The apex 38 tapers radially outward. The apex 38 is made of crosslinked rubber with high rigidity.

[0044] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 bridges between the first bead 10 and the second bead 10 of the pair of beads 10. The carcass 12 includes at least one carcass ply 40.

[0045] The carcass 12 of this tire 2 is composed of one carcass ply 40. The carcass ply 40 includes a ply body 40a and a pair of turned-up portions 40b. The ply body 40a spans between the first bead 10 and the second bead 10. Each turned-up portion 40b is continuous with the ply body 40a and is turned up from the axially inner side to the axially outer side at each bead 10.

[0046] As will be described later, the carcass ply 40 includes a number of carcass cords arranged in parallel. Each carcass cord intersects with the equator plane. The carcass 12 of the tire 2 has a radial structure. The carcass cord is a cord made of organic fiber (hereinafter also referred to as organic fiber cord). Examples of organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0047] In this tire 2, the end of the turned-up portion 40b is located radially outward from the maximum width position PW. The end of the turned-up portion 40b may also be located radially inward from the maximum width position PW. The position indicated by the symbol PA is the outer end of the apex 38. The end of the turned-up portion 40b may also be located radially inward from the outer end PA of the apex 38. Although not shown, the carcass cord bridges between the first bead 10 and the second bead 10. An end of the carcass cord is located at the end of the turned-up portion 40b.

[0048] The belt 14 is laminated on the carcass 12 radially inside the tread 4. The belt 14 is made up of two layers 42 laminated in the radial direction. Although not shown, each of the two layers 42 is made up of a number of parallel belt cords and topping rubber. These belt cords are inclined relative to the equator plane. The belt cords are covered with topping rubber. The belt cords are made of steel. The topping rubber is conductive rubber. The belt 14 has good conductivity.

[0049] The band 16 is located between the tread 4 and the belt 14 in the radial direction. The band 16 of the tire 2 is composed of a full band 44 that covers the entire belt 14. The band 16 may be composed of a pair of edge bands that are spaced apart in the axial direction. The band 16 may be composed of a full band 44 and a pair of edge bands. In this case, each edge band covers an end of the full band 44.

[0050] The full band 44 includes a center portion 44c located on the equatorial plane and a pair of shoulder portions 44s. The shoulder portions 44s include the ends of the full band 44. The center portion 44c is located between the two shoulder portions 44s. The position indicated by the symbol PB in FIG. 1 is the boundary between the center portion 44c and the shoulder portions 44s. The length of the shoulder portions 44s is set within a range of 15 mm to 45 mm.

[0051] Although not shown, the band 16 includes a band cord. The band cord is covered with a topping rubber. The topping rubber is a conductive rubber. The band cord is wound spirally in the circumferential direction. The angle that the band cord forms with the circumferential direction is preferably 5° or less, more preferably 2° or less. The band cord extends substantially in the circumferential direction. The band 16 has a jointless structure. Cords made of organic fibers are used as band cords, and examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0052] Each chafer 18 is located radially inward of the bead 10. As shown in FIG. 1, the portion of each chafer 18 located radially inward of the core 36 comes into contact with the sheet S of the rim R. The axially outer portion of each chafer 18 is located between the turned-up portion 40b of the carcass ply 40 and the clinch 8. The axially inner portion of each chafer 18, together with the inner liner 20 described below, forms the inner surface of the tire 2. Each chafer 18 is made of cloth and rubber impregnated into the cloth. The rubber impregnated into the cloth is conductive rubber.

[0053] The inner liner 20 is located inside the carcass 12. The inner liner 20 constitutes the inner surface of the tire 2. The inner liner 20 is made of crosslinked rubber that has excellent air barrier properties. The inner liner 20 maintains the internal pressure of the tire 2.

[0054] Fig. 2 shows a portion of the carcass ply 40. In Fig. 2, the carcass ply 40 is shown with the surface (hereinafter also referred to as the first surface 40f) located on the tread 4 side on the inner side of the tread 4 of the tire 2 positioned on the upper side. The surface opposite the first surface 40f, that is, the surface located on the inner liner 20 side on the inner side of the tread 4 of the tire 2, is the second surface 40s.

[0055] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. In Fig. 3, the upper side of the paper corresponds to the tread 4 side, and the lower side corresponds to the inner liner 20 side.

[0056] As described above, the carcass ply 40 includes a large number of parallel carcass cords 46. These carcass cords 46 are covered with a topping rubber 48. The topping rubber 48 is a conductive rubber.

[0057] In the tire 2, a conductive thread is fixed to the carcass 12, specifically, to the first surface 40f of the carcass ply 40. In other words, the tire 2 further includes a conductive thread 50.

[0058] In the present disclosure, the conductive yarn 50 is a yarn having an electrical resistance of 10 8 The conductive yarn 50 is made of metal fiber or organic fiber and has a resistance of 1.0×10 7 Preferably, the yarn has a resistance value of Ω / cm or less.

[0059] 2 and 3, the conductive thread 50 is sewn to the first surface 40f of the carcass ply 40 with a sewing thread 52. As shown in Fig. 3, an upper thread 52n and a lower thread 52b are used as the sewing thread 52. After the conductive thread 50 is placed on the first surface 40f of the carcass ply 40, the upper thread 52n and the lower thread 52b are sewn into the carcass ply 40 by, for example, a sewing machine (not shown). The upper thread 52n and the lower thread 52b are entangled with each other, and the conductive thread 50 is fixed to the first surface 40f of the carcass ply 40.

[0060] 3, the portion indicated by the symbol PE is a portion where the upper thread 52n and the lower thread 52b are intertwined. In the tire 2, the portion PE where the upper thread 52n and the lower thread 52b are intertwined is located inside the carcass ply 40. The intertwined portion PE may be exposed to either the first surface 40f or the second surface 40s.

[0061] The conductive thread 50 is sewn to the carcass ply 40 with the sewing thread 52, thereby forming a large number of stitches 54 in the carcass ply 40. The large number of stitches 54 form rows 56 of stitches 54, as shown in FIG. 2, for example. The rows 56 of stitches 54 cross the conductive thread 50. The number of sewing threads 52 used to sew the conductive thread 50 is set appropriately in consideration of the specifications of the tire 2.

[0062] As shown in Fig. 3, each seam 54 includes one carcass cord 46. This seam 54 may include two or more carcass cords 46. In this case, from the viewpoint of enabling the conductive yarn 50 fixed to the carcass ply 40 to effectively contribute to the stable electrical conductivity of the tire 2, the number of carcass cords 46 included in the seam 54 is preferably five or less, more preferably four or less, and even more preferably three or less. When the number of carcass cords 46 included in the seam 54 is one, the row 56 of seams 54 may alternate between portions of the seam 54 that include a carcass cord 46 and portions of the seam 54 that do not include a carcass cord 46.

[0063] In this tire 2, the portion of the seam 54 that fixes the conductive thread 50 includes the carcass cord 46. In this tire 2, the conductive thread 50 extends along the carcass cord 46. As described above, the carcass cord 46 bridges between the first bead 10 and the second bead 10. The conductive thread 50 also bridges between the first bead 10 and the second bead 10.

[0064] The thickness of the carcass ply 40 is 0.8 mm or more and 1.5 mm or less. As described above, the sidewall 6 of this tire 2 is made of non-conductive rubber. Since the carcass ply 40 is thin, even if the topping rubber 48 of the carcass ply 40 is conductive rubber, the electrical resistance of the tire 2 is 10 8 Ω, there is a risk that tire 2 will not be able to exhibit stable conductive performance.

[0065] In this tire 2, a conductive thread 50 sewn with a sewing thread 52 to the first surface 40f (the surface on the tread 4 side) of the carcass ply 40 bridges between the first bead 10 and the second bead 10. As a result, the portion consisting of the terminal portion 28, the band 16, and the belt 14 is connected to the clinch 8 by the carcass to which the conductive thread 50 is fixed. The terminal portion 28, the band 16, the belt 14, and the clinch 8 are conductive, the terminal portion 28 comes into contact with the road surface, and the clinch 8 contacts the rim R. As a result, a conductive path is formed in the tire 2. This tire 2 can exhibit stable conductive performance.

[0066] For example, in order to reduce rolling resistance, when the topping rubber 48 of the carcass ply 40 is made of a low heat-generating rubber, the electrical resistance of the tire 2 can be reduced by 10% even when the carcass 12 has the conductive threads 50 fixed thereto. 8 If the resistance exceeds Ω, the tire 2 may not be able to exhibit stable electrical conductivity. In this case, the sewing thread 52 may be made of an electrically conductive thread. An example of this electrically conductive thread is a thread having a similar configuration to the electrically conductive thread 50.

[0067] FIG. 4 shows a cross-sectional view taken along line IV-IV in FIG. 1. FIG. 4 shows the overlapping portion of the ply body 40a and the folded-up portion 40b. As shown in FIG. 4, between the ply body 40a and the folded-up portion 40b, there are conductive threads 50 fixed to the ply body 40a and conductive threads 50 fixed to the folded-up portion 40b. At the folded-up portion 40b, the sewing threads 52 that secure the conductive threads 50 contact the clinches 8. As described above, the clinches 8 contact the rim R. In this tire 2, the sewing threads 52 are made of conductive threads, thereby forming a more stable conductive path in the tire 2. Even if the topping rubber 48 of the carcass ply 40 is made of low-heat-generating rubber, the sewing threads 52 are made of conductive threads, thereby allowing the conductive threads 50 to contribute to the formation of a conductive path. This tire 2 can exhibit stable conductive performance.

[0068] In this tire 2, the conductive thread 50 is sewn to the carcass ply 40 with a sewing thread 52, thereby forming a large number of stitches 54 in the carcass ply 40. The large number of stitches 54 increases the second moment of area of ​​the carcass 12. As the rigidity of the carcass 12 increases, the cornering power and the vertical spring constant increase. There is concern that high cornering power and a high vertical spring constant may lead to a decrease in handling stability and an increase in road noise.

[0069] In the tire 2, the complex modulus E*s of the sidewall 6 at 70° C. is 4.0 MPa or more and 5.5 MPa or less. The complex elastic modulus E*s of a conventional sidewall exceeds 6.0 MPa, so this sidewall 6 is softer than a conventional sidewall. In this tire 2, the rigidity of the entire side portion is appropriately adjusted, even though the rigidity of the carcass 12 is increased by the numerous seams 54. Cornering power and vertical spring constant are appropriately maintained, thereby suppressing a decrease in steering stability and an increase in road noise. From this viewpoint, in this tire 2, the complex modulus of elasticity E*s is preferably 4.5 MPa or more and 5.5 MPa or less.

[0070] The tire 2 can exhibit stable electrical conductivity without causing a decrease in steering stability or an increase in road noise.

[0071] From the viewpoint of properly adjusting the rigidity of the entire side portion and effectively suppressing a decrease in steering stability and an increase in road noise, the ratio (E*c / E*s) of the complex modulus E*c of the topping rubber 48 of the carcass ply 40 at 70°C to the complex modulus E*s of the sidewall 6 at 70°C is preferably 1.2 or more, more preferably 1.4 or more. This ratio (E*c / E*s) is preferably 2.5 or less, more preferably 2.3 or less.

[0072] Fig. 5 shows a part of the cross section of the tire 2 shown in Fig. 1. Fig. 5 shows the configuration of the band 16 (more specifically, the full band 44) ​​provided in the tread portion. In the tire 2, the full band 44 is configured by spirally winding band-shaped strips 58. In other words, the full band 44 is made up of spirally wound strips 58. In the tire 2, the strips 58 are wound densely without gaps. No gaps are formed between adjacent circumferential portions of the strips 58.

[0073] Although not shown, in this tire 2, the strip 58 includes the above-mentioned band cord. The strip 58 includes a plurality of band cords. These band cords are arranged in parallel in the width direction of the strip 58. These band cords are arranged at equal intervals. 5, the length indicated by the symbol WS is the width of the strip 58. In this tire 2, the width WS of the strip 58 is determined appropriately in consideration of the specifications of the tire 2 and the like.

[0074] In the tire 2, when the width WS of the strip 58 is 10 mm, the number of band cords included in the strip 58 is two or more. From the viewpoint that the band 16 can effectively increase the rigidity of the tread portion, the number of band cords is preferably five or more, more preferably eight or more, and even more preferably ten or more. In the tire 2, when the width WS of the strip 58 is 10 mm, the number of band cords included in the strip 58 is preferably 15 or less. This appropriately maintains the restraining force of the tread portion by the band 16, and effectively reduces the input that the tread portion receives from the road surface. In the tire 2, road noise is reduced. From this viewpoint, the number of band cords is more preferably 12 or less.

[0075] Fig. 6 shows a modified example of the band 16. In particular, Fig. 6 shows a modified example of the center portion 44c of the full band 44.

[0076] This full band 44 is also made up of spirally wound strips 58, similar to the full band 44 shown in Fig. 5. The strips 58 are wound with gaps in the center portion 44c of this full band 44. As shown in Fig. 6, in the center portion 44c, adjacent winding portions of the strips 58 are arranged with gaps in between.

[0077] The length indicated by the symbol WG in FIG. 6 is the width of the gap provided between adjacent circumferential portions of the strip 58.

[0078] In the tire 2, the width WG of the gap is preferably equal to or greater than 3.0 mm and equal to or less than 5.0 mm. Setting the width WG to 3.0 mm or greater effectively reduces the input that the tread portion receives from the road surface, thereby reducing road noise in the tire 2. From this viewpoint, it is more preferable that the width WG be 3.5 mm or greater. By setting the width WG to 5.0 mm or less, the band 16 has the necessary rigidity. Since the band 16 effectively restrains the tread portion, good durability is maintained in the tire 2. From this viewpoint, it is more preferable that the width WG be 4.5 mm or less.

[0079] 6, adjacent winding portions of the strips 58 are arranged with a gap between them in the center portion 44c, but in the shoulder portions 44s, the strips 58 are wound closely together with no gaps between them. In the tire 2, adjacent winding portions of the strips 58 may also be arranged with a gap between them in the shoulder portions 44s. From the viewpoint of stabilizing the ground contact shape, it is preferable that the strips 58 are wound closely together with no gaps between them in the shoulder portions 44s.

[0080] Fig. 7 shows a portion of the tread 4 of the tire 2 shown in Fig. 1. As described above, the tread 4 includes the base layer 32 and the cap layer 34. In Fig. 7, the length indicated by the symbol T is the thickness of the tread 4. The length indicated by the symbol Tc is the thickness of the cap layer 34.

[0081] In the tire 2, the ratio (Tc / T) of the thickness Tc of the cap layer 34 to the thickness T of the tread 4 is preferably equal to or greater than 0.60 and equal to or less than 0.80. By setting the ratio (Tc / T) to be 0.60 or greater, the cap layer 34 has a necessary thickness. Exposure of the base layer 32 due to wear is suppressed. In the tire 2, good uneven wear resistance is obtained. From this viewpoint, the ratio (Tc / T) is more preferably 0.65 or greater. Setting the ratio (Tc / T) to 0.80 or less appropriately maintains the volume of the base layer 32. In the tire 2, the tread 4 can contribute to reducing rolling resistance. From this viewpoint, the ratio (Tc / T) is more preferably 0.75 or less.

[0082] In this tire 2, at least two circumferential grooves 60 are formed in the tread 4. The circumferential grooves 60 are arranged in parallel in the axial direction and extend continuously in the circumferential direction. The tread 4 of the tire 2 shown in FIG. 1 has three circumferential grooves 60, and four land portions 62 are formed. Of the four land portions 62, the land portion 62 located axially outward is the shoulder land portion 62s, and the land portion 62 located axially inward of the shoulder land portion 62s is the middle land portion 62m. In this tire 2, the circumferential groove 60 is located on the equatorial plane. In the middle land portion 62m close to the equatorial plane, the thickness Tc of the cap layer 34 and the thickness T of the tread 4 are obtained. In FIG. 7, the solid line TL is the center line of the width of the middle land portion. The thickness Tc of the cap layer 34 and the thickness T of the tread 4 are measured along this center line TL. When the land portion 62 is located on the equatorial plane, the thickness Tc of the cap layer 34 and the thickness T of the tread 4 are measured along the equatorial plane.

[0083] In the tire 2, the ratio (LTb / LTc) of the loss tangent LTb of the base layer 32 at 30° C. to the loss tangent LTc of the cap layer 34 at 30° C. is preferably 0.40 or greater and 0.80 or less.

[0084] By setting the ratio (LTb / LTc) to 0.40 or greater, deterioration in grip performance is minimized even when the base layer 32 is exposed due to wear. From this viewpoint, the ratio (LTb / LTc) is more preferably 0.45 or greater, and further preferably 0.50 or greater. Setting the ratio (LTb / LTc) to be equal to or less than 0.80 allows the tread 4 to effectively contribute to reducing rolling resistance. In this respect, the ratio (LTb / LTc) is more preferably equal to or less than 0.75, and further preferably equal to or less than 0.70.

[0085] As described above, in this tire 2, the conductive thread 50 bridges between the first bead 10 and the second bead 10. If even one conductive thread 50 is included in the tire 2, the tire 2 will exhibit good conductive performance. The side portion of the tire 2 is bent due to the action of a load. This causes tension to be generated in the conductive thread 50. If a large tension is generated in the conductive thread 50, there is a concern that the conductive fiber that gives the conductive thread 50 conductivity will be cut. In this case, the conductive thread 50 will lose its conductivity, and the electrical resistance of the tire 2 will increase.

[0086] From the viewpoint of exhibiting stable conductive performance, it is preferable that the tire 2 be provided with a plurality of conductive threads 50. As a result, even if one conductive thread 50 loses conductivity, the other conductive threads 50 contribute to exhibiting the conductive performance of the tire. The tire 2 can exhibit stable conductive performance. From this viewpoint, the number of conductive threads 50 included in the tire 2 is preferably two or more, more preferably four or more, and even more preferably ten or more. From the viewpoint of being able to keep the increase in mass of the tire 2 small, the number of conductive threads 50 included in the tire 2 is preferably 20 or less, more preferably 13 or less, and even more preferably 15 or less.

[0087] When multiple conductive threads 50 are provided in the tire 2, it is preferable that the multiple conductive threads 50 be arranged at equal intervals in the circumferential direction, in order to obtain good uniformity and, as a result, improve the ride comfort of the tire 2.

[0088] Although not shown, the tire 2 can use a blended yarn spun from a mixture of conductive staple fibers and non-conductive staple fibers as the conductive yarn 50. In the conductive yarn 50, the conductive staple fibers are arranged intermittently in the longitudinal direction. This forms a conductive path within the conductive yarn 50. In the tire 2 using this conductive yarn 50, even if the side portion bends and tension is generated in the conductive yarn 50, the tension acting on each conductive staple fiber is small. Because the conductive staple fibers themselves do not break, the conductive path formed within the conductive yarn 50 is maintained without losing its function. The tire 2 including this conductive yarn 50 is prevented from losing its conductive performance due to running. The tire 2 can sustain its conductive performance. From this perspective, the conductive yarn 50 is preferably made of a blended yarn spun from a mixture of conductive staple fibers and non-conductive staple fibers.

[0089] In manufacturing the tire 2, the surface of the carcass ply 40 may be irradiated with an electron beam to crosslink the surface portion in order to prevent interface irregularities due to the flow of rubber during vulcanization molding. When the aforementioned blended yarn is used as the conductive yarn 50, if there is a conductive fiber with its end buried in the conductive yarn 50, sparks will occur during electron beam irradiation. Therefore, the surface portion is crosslinked by electron beam irradiation, and then the conductive yarn 50 is attached to the carcass ply 40. After electron beam irradiation, the surface of the carcass ply 40 is hard. It is difficult to attach the conductive yarn 50 to this carcass ply 40. In this case, there is a risk that the conductive yarn 50 cannot be positioned in the desired position.

[0090] In this tire 2, as described above, the conductive thread 50 is sewn to the carcass ply 40 with the sewing thread 52. The conductive thread 50 is firmly fixed to the carcass ply 40 even after electron beam irradiation. In this tire 2, the conductive thread 50 is arranged at a desired position. In this tire 2, stable conductive performance is exhibited even when a blended yarn is used as the conductive thread 50.

[0091] To ensure that the conductive yarn 50 can exhibit stable conductive performance, the length of the conductive short fibers is preferably 5 mm or more and 50 mm or less. The length is more preferably 10 mm or more, and even more preferably 20 mm or more. The length is more preferably 40 mm or less, and even more preferably 30 mm or less.

[0092] To ensure that the conductive yarn 50 can exhibit stable conductive performance, the length of the non-conductive short fibers is preferably 5 mm or more and 50 mm or less. The length is more preferably 10 mm or more, and even more preferably 20 mm or more. The length is more preferably 40 mm or less, and even more preferably 30 mm or less.

[0093] In the tire 2, the ratio (MS / MA) of the mass MS of the conductive short fibers to the mass MA of the conductive yarn 50 is preferably 10% by mass or more. This allows the conductive yarn 50 to contribute to stable conductive performance. From this viewpoint, the ratio (MS / MA) is more preferably 15% by mass or more, and further preferably 20% by mass or more. From the viewpoint of suppressing the effect on the mass of the tire 2, this ratio (MS / MA) is preferably equal to or less than 50 mass %, more preferably equal to or less than 45 mass %, and further preferably equal to or less than 40 mass %.

[0094] Examples of conductive short fibers include metal short fibers, metal oxide short fibers, and carbon short fibers. Of these, metal short fibers are preferred as conductive short fibers. Examples of materials for these metal short fibers include stainless steel, iron, aluminum, and copper. Of these, stainless steel is preferred from the viewpoints of having appropriate rigidity and being resistant to corrosion. In other words, stainless steel is preferred as the material for these conductive fibers.

[0095] Examples of non-conductive staple fibers include organic fibers made of cotton, nylon, polyester, polypropylene, etc. In other words, the non-conductive staple fibers are preferably made of organic fibers. From the viewpoint of versatility, the non-conductive staple fibers are preferably organic fibers made of polyester. Among organic fibers made of polyester, organic fibers made of polyethylene terephthalate (hereinafter referred to as PET staple fibers) are more preferred.

[0096] As described above, according to the present invention, a tire 2 can be obtained that can exhibit stable electrical conductivity without causing a decrease in steering stability or an increase in road noise. [Example]

[0097] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0098] [Example 1] A pneumatic tire for a passenger car (tire size = 205 / 55R16) having the basic structure shown in Fig. 1 and the specifications shown in Table 1 below was obtained.

[0099] In Example 1, a blended yarn made by mixing and spinning conductive staple fibers (material: stainless steel) and non-conductive staple fibers (PET fibers) was used as the conductive yarn. The number of conductive yarns was 10. The 10 conductive yarns were arranged at equal intervals in the circumferential direction. The length of the conductive fibers was 25 mm, and the length of the non-conductive fibers was 25 mm. The ratio of the mass MS of the conductive short fibers to the mass MS of the conductive yarn (MS / MA) was 20 mass%. The surface of the carcass ply was irradiated with an electron beam to crosslink the surface, and then a conductive thread was sewn to the carcass ply with a sewing thread. The topping rubber of the carcass ply was made of a conductive rubber. The sidewalls were made of non-conductive rubber and had a complex modulus of elasticity (E*s) of 4.5 MPa at 70°C. The band was constructed by tightly wrapping the strips, with the width WG of the gap between the turns of adjacent strips being 0.0 mm. The ratio (Tc / T) of the thickness Tc of the cap layer to the thickness T of the tread was 0.7. The ratio (LTb / LTc) of the loss tangent LTb of the base layer at 30°C to the loss tangent LTc of the cap layer at 30°C was 0.60.

[0100] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that no conductive yarn was used and the complex modulus of elasticity E*s of the sidewall at 70° C. was set to 6.5 MPa.

[0101] Comparative Example 2 A tire of Comparative Example 2 was obtained in the same manner as Example 1, except that a twisted yarn made by twisting together a stainless steel filament and a PET fiber filament was used as the conductive yarn, and the complex modulus of elasticity E*s of the sidewall at 70°C was set to 6.5 MPa.

[0102] [Example 2] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the width WG of the gap between the circumferential portions of adjacent strips in the center portion of the full band was set to 4.0 mm.

[0103] [Conductive performance] To evaluate the electrical conductivity, the electrical resistance of the prototype tire (new) was measured. The equipment and conditions for measuring the electrical resistance are as follows. For measuring the electrical resistance, a measuring device 72 having the configuration shown in FIG. 8 is used. The measuring device 72 includes an insulating plate 74, a metal plate 76, a tire mounting shaft 78, and an electrical resistance measuring instrument 80. The electrical resistance value of the insulating plate 74 is 10 12 Ω or more. The metal plate 76 is placed on the insulating plate 74. The surface of the metal plate 76 is polished, and the electrical resistance of the metal plate 76 is 10 Ω or less. A tire-rim assembly is held on the tire mounting shaft 78. Using this measuring device 72, the electrical resistance of the tire-rim assembly is measured in the following manner.

[0104] The procedure for measuring the electrical resistance of a tire is as follows. (1) Thoroughly remove any release agent or dirt adhering to the surface of the prototype tire SP. After removal, dry the tire T thoroughly. (2) The prototype tire SP is mounted on the rim R to prepare a tire-rim assembly. At this time, soapy water is used as a lubricant at the contact points between the two. (3) After leaving the tire-rim assembly in the test room for two hours, the tire-rim assembly is attached to the tire mounting shaft 78. (4) A load is applied to the tire-rim assembly for 0.5 minutes, and the tire-rim assembly is released from this load. Then, a load is applied to the tire-rim assembly for an additional 0.5 minutes, and the tire-rim assembly is released from this load. Then, a load is applied to the tire-rim assembly for an additional 2 minutes, and the tire-rim assembly is released from this load. (5) After five minutes have passed since the test voltage was applied, the electrical resistance between the tire mounting shaft 78 and the metal plate 76 is measured using an electrical resistance measuring device 80. The measurements are performed at 90° intervals (four locations) around the circumference of the tire T. The maximum value is used as the measured value of the electrical resistance of the tire T.

[0105] Other conditions for the measurement are as follows: Rim material: Aluminum alloy Rim size: 16x6.5J Internal pressure: 230kPa Load capacity: 4.8kN Test environment temperature (test room temperature): 25°C ·Humidity: 50% Electrical Resistance Meter 80 Measurement Range: 1.0 x 10 3 ~1.6×10 16 Ω Test voltage (applied voltage): 1000V

[0106] In the following Table 1, the measurement results of the electrical resistance are shown as an index, with Comparative Example 1 being set at 100. The larger the value, the lower the electrical resistance, and the better the tire's electrical conductivity performance.

[0107] [Conductive stability] The prototype tire was mounted on a rim (size = 16 x 6.5J) and inflated to adjust the internal pressure of the tire to 230 kPa. A load of 4.8 kN was applied to the tire in a drum testing machine, and the tire was run on a drum (drum diameter = 1707 mm) at a speed of 80 km / h (camber angle was set to -1°). The tire's electrical resistance was measured every 10,000 km as described above in the "Conductive Performance" section, and the running distance until an increase in the tire's electrical resistance was confirmed was obtained. The running distance of the tire of Comparative Example 2 was used as the reference distance, and it was confirmed whether the running distance of the tires of Examples 1 and 2 exceeded this reference distance. Cases where the running distance increased are indicated by "G."

[0108] [Handling stability] The prototype tire was mounted on a rim (size = 16 x 6.5J) and inflated to adjust the tire internal pressure to 230 kPa. The tire was mounted on a test vehicle (a domestic passenger car). The test vehicle was run on a test course with a dry asphalt road surface, and a sensory evaluation of the steering stability was performed. The results are shown in Table 1 below, where Comparative Example 1 is indexed to 100. The higher the value, the better the performance.

[0109] [Road noise] The prototype tire was mounted on a rim (size = 16 x 6.5J) and inflated to adjust the tire internal pressure to 230 kPa. The tire was mounted on a test vehicle (a domestic passenger car). The driver drove the car at a speed of 60 km / h on a rough asphalt road surface. The noise level (dB) in the 160 Hz band in the driver's seat while driving was measured using a sound-collecting microphone. The results are shown in Table 1 below, where Comparative Example 1 is indexed to 100. The higher the value, the lower the road noise, which is preferable.

[0110] [Table 1]

[0111] As shown in Table 1, it has been confirmed that the examples can exhibit stable conductive performance without causing a decrease in steering stability or an increase in road noise. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0112] The techniques described above for achieving stable electrical conductivity without reducing steering stability or increasing road noise can be applied to various types of tires. [Explanation of symbols]

[0113] 2. Tires 4. Tread 6. Sidewall 10 Bead 12. Carcass 14. Belt 16...Band 22 Tread surface 32 Base layer 34 Cap layer 40···Carcass ply 40f: First side of carcass ply 40 40s: Second side of carcass ply 40 44...Full Band 44c···Center section 44s···Shoulder part 46···Carcass cord 48···Topping rubber 50 Conductive thread 52 Sewing thread 52n···Needle thread 52b···Lower thread 54...Seam 56...row of 54 stitches 58...Strip

Claims

1. a pair of sidewalls connected to ends of the tread and positioned radially inward of the tread; a pair of beads positioned radially inward of the sidewalls; a carcass extending between a first bead and a second bead of the pair of beads; a belt laminated on the carcass on the radially inner side of the tread; and a conductive thread fixed to the carcass and extending between the first bead and the second bead, The tread has a tread surface that comes into contact with a road surface, the carcass comprises a carcass ply; The conductive thread is sewn with a sewing thread on the tread side surface of the carcass ply, The complex elastic modulus of the sidewall at 70°C is 4.0 MPa or more and 5.5 MPa or less, The tread includes a base layer and a cap layer located radially outward of the base layer, a ratio of a loss tangent at 30°C of the base layer to a loss tangent at 30°C of the cap layer is 0.40 or more and 0.80 or less; tire.

2. a full band positioned between the tread and the belt in the radial direction, the full band is made of a spirally wound strip; The full band includes a pair of shoulder portions including ends of the full band, and a center portion located between the shoulder portions, In the center portion, adjacent circumferential portions of the strip are arranged with a gap therebetween, The gap is 3.0 mm or more and 5.0 mm or less.

2. The tire of claim 1.

3. The ratio of the thickness of the cap layer to the thickness of the tread is 0.60 or more and 0.80 or less.

3. The tire according to claim 1 or 2.

4. the conductive yarn is made of a blended yarn spun by mixing conductive staple fibers and non-conductive staple fibers, The length of the conductive short fibers is 5 mm or more and 50 mm or less, The length of the non-conductive short fibers is 5 mm or more and 50 mm or less, The ratio of the mass of the conductive short fibers to the mass of the conductive yarn is 10 mass% or more. A tire according to any one of claims 1 to 3.

5. the conductive short fibers are made of stainless steel; The non-conductive short fibers are made of organic fibers.

5. The tire of claim 4.

6. The carcass ply comprises a number of carcass cords arranged in parallel and a topping rubber covering these carcass cords, The topping rubber is a conductive rubber, The complex elastic modulus of the topping rubber of the carcass ply is higher than the complex elastic modulus of the sidewall.

6. A tire according to any one of claims 1 to 5.

7. The sewing thread is a conductive thread.

7. A tire according to any one of claims 1 to 6.

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