JP2014054925A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire 2 achieving reduction of rolling resistance without impairing steering stability.SOLUTION: A tire 2 includes: a pair of beads 10 each of which is located on a substantially inner side in the radial direction than an end of a tread 4; a pair of side sections 6 each of which is located at the outside of a carcass 12 in an axial direction; and a pair of reinforcing layers 18 each of which is located at the inside of the side sections 6 in the axial direction. Each of the side sections 6 includes side walls 30 and a clinch section 32. The side walls 30 extend substantially inward in the radial direction from the end of the tread 4. The clinch section 32 is located at the inside of the side walls 30 in the radial direction. A complex elastic modulus of the clinch section 32 is 7.2 MPa or more and 8.8 MPa or below. Loss tangent of the clinch section 32 is 0.10 or more and 0.12 or below.

Description

  The present invention relates to a pneumatic tire.

  The tire includes a tread and a sidewall extending substantially inward in the radial direction from the end of the tread. From the viewpoint of improving the fuel consumption efficiency in the vehicle, the thickness of the sidewall may be reduced. This reduction in thickness affects the rigidity of the tire. If the thickness is too small, the steering stability is impaired.

  A strip apex that extends along the carcass may be provided on the inner side of the sidewall of the tire from the viewpoint of both handling stability and ride comfort. In this tire, the thickness of the sidewall is effectively reduced without impairing the steering stability. An example of such a tire is disclosed in Japanese Patent Application Laid-Open No. 2010-149677.

JP 2010-149677 A

  The tire includes a clinch portion on the radially inner side of the sidewall. This clinch portion is made of a crosslinked rubber. From the viewpoint of improving fuel consumption efficiency, a clinching portion having a low loss tangent may be employed to reduce the rolling resistance of the tire. However, the low-loss tangent clinch portion has a low complex elastic modulus, and thus reduces the rigidity of the tire. Adoption of a clinching portion having a low complex elastic modulus has a problem that steering stability is lowered.

  An object of the present invention is to provide a pneumatic tire in which a reduction in rolling resistance is achieved without impairing steering stability.

  The pneumatic tire according to the present invention has a tread whose outer surface forms a tread surface, a pair of beads positioned substantially radially inward of the end of the tread, and between one bead and the other bead. A carcass that is bridged and is located inside the tread in the radial direction, a pair of side portions that are located outside the carcass in the axial direction, and a pair that is located inside the side portions in the axial direction. And a reinforcing layer. Each side portion includes a sidewall and a clinch portion. The sidewall extends substantially inward in the radial direction from the end of the tread. The clinch portion is located inside the sidewall in the radial direction. The complex elastic modulus of this clinching part is 7.2 MPa or more and 8.8 MPa or less. The loss tangent of this clinch portion is 0.10 or more and 0.12 or less. Each bead includes a core and an apex extending substantially outward in the radial direction from the core. The hardness of this apex is 65 or more and 80 or less. Each reinforcing layer extends substantially outward in the radial direction along the carcass from the tip portion of the apex. The hardness of this reinforcing layer is 65 or more and 80 or less.

  Preferably, in this pneumatic tire, the ratio of the thickness of the clinch portion to the thickness of the apex is 0.36 or more and 0.44 or less.

  Preferably, in the pneumatic tire, a line extending in the axial direction through the inner edge is used as a reference, a radial height H1 from the reference line to the equator, and from the reference line to the outer end of the reinforcing layer. When the radial height H2 and the radial height H3 from the reference line to the outer end of the clinch portion are measured without being attached to the regular rim, the ratio of the height H2 to the height H1 is It is 0.54 or more and 0.66 or less, and the ratio of the height H3 to the height H1 is 0.36 or more and 0.44 or less.

  Preferably, in the pneumatic tire, the thickness of the reinforcing layer in a portion where the tip of the apex is located is 0.9 mm or more and 1.1 mm or less.

  In the pneumatic tire according to the present invention, a reduction in rolling resistance is achieved without impairing steering stability.

FIG. 1 is a cross-sectional view showing a part of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged sectional view showing a part of the tire shown in FIG.

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

  The tire 2 shown in FIG. 1 includes a tread 4, a side portion 6, a wing 8, a bead 10, a carcass 12, a belt 14, a band 16, a reinforcing layer 18, a cushion 20, an inner liner 22 and a chafer 24. . The tire 2 is a tubeless type. The tire 2 is mounted on a passenger car. In FIG. 1, the vertical direction is the radial direction, the horizontal direction is the axial direction, and the direction perpendicular to the paper surface is the circumferential direction. The tire 2 has a substantially left-right symmetric shape centered on a one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator plane of the tire 2.

  The tread 4 is made of a crosslinked rubber having excellent wear resistance. The tread 4 has a shape protruding outward in the radial direction. The tread 4 includes a tread surface 26. The tread surface 26 is in contact with the road surface. A groove 28 is carved in the tread surface 26. The groove 28 forms a tread pattern. The groove 28 may not be cut on the tread surface 26.

  The side part 6 is located outside the carcass 12 in the axial direction. The side portion 6 includes a sidewall 30 and a clinching portion 32. The sidewall 30 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 30 is made of a crosslinked rubber. The sidewall 30 absorbs an impact from the road surface by bending. Furthermore, the sidewall 30 prevents the carcass 12 from being damaged.

  The clinch portion 32 is located inside the sidewall 30 in the radial direction. Although not shown, when the tire 2 is mounted on a regular rim (hereinafter referred to as a rim), the clinch portion 32 comes into contact with the flange of the rim. Thereby, the bead 10 is protected.

  The clinching part 32 is made of a crosslinked rubber composition. In the tire 2, the loss tangent (tan δ) of the clinch portion 32 is 0.12 or less. The loss tangent of the clinch portion 32 is low. The low-loss tangent clinch portion 32 can contribute to reduction of rolling resistance. In the tire 2, the loss tangent of the clinch portion 32 is 0.10 or more. The clinch portion 32 has appropriate rigidity. In the tire 2, a delay in response is suppressed and a good linear feeling of response is maintained. In the tire 2, the influence on the steering stability by the clinching portion 32 is suppressed. This clinching part 32 can contribute to reduction of rolling resistance without impairing steering stability.

  In the tire 2, the complex elastic modulus of the clinch portion 32 is 7.2 MPa or more and 8.8 MPa or less. This clinching part 32 can contribute to reduction of rolling resistance without impairing steering stability. In this respect, the complex elastic modulus of the clinching portion 32 is preferably 7.5 MPa or more, and preferably 8.5 MPa or less.

In this specification, the loss tangent and the complex elastic modulus are measured in accordance with the provisions of “JIS K 6394”. The measurement conditions are as follows.
Viscoelastic spectrometer: "VESF-3" from Iwamoto Seisakusho
Initial strain: 10%
Dynamic strain: ± 1%
Frequency: 10Hz
Deformation mode: Tensile Measurement temperature: 70 ° C

  The bead 10 is located substantially inward in the radial direction from the end of the tread 4. The bead 10 is located inside the clinch portion 32 in the axial direction. The bead 10 includes a core 34 and an apex 36 that extends radially outward from the core 34. The core 34 has a ring shape. The core 34 is formed by winding a non-stretchable wire. Typically, a steel wire is used for the core 34. The apex 36 is tapered outward in the radial direction.

  The apex 36 is made of a crosslinked rubber composition. In the tire 2, the hardness of the apex 36 is 65 or more and 80 or less. The apex 36 can effectively contribute to the rigidity of the tire 2. The tire 2 is excellent in handling stability and ride comfort.

  In this specification, the hardness is JIS-A hardness. This hardness is measured with a type A durometer in an environment of 23 ° C. in accordance with the provisions of “JIS-K6253”.

  In the tire 2, the complex elastic modulus is preferably 45 MPa or more, and preferably 65 MPa or less, from the viewpoint that the apex 36 can effectively contribute to steering stability and riding comfort. The loss tangent of the apex 36 is preferably 0.10 or more, and preferably 0.20 or less.

  The carcass 12 includes a carcass ply 38. The carcass ply 38 is spanned between the beads 10 on both sides, and extends along the inside of the tread 4 and the sidewall 30. The carcass ply 38 is folded around the core 34 from the inner side to the outer side in the axial direction. The carcass ply 38 includes a main body 40 extending from the equator toward each bead 10, and a pair of folded portions 42 extending from the main body 40 substantially outward in the radial direction.

  Although not shown, the carcass ply 38 includes a large number of cords arranged in parallel and a topping rubber. The absolute value of the angle formed by each cord with respect to the equator plane is usually 70 ° to 90 °. In other words, the carcass 12 has a radial structure. The cord is made of organic fiber. Examples of preferable organic fibers include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

  The belt 14 is located on the radially outer side of the carcass 12. The belt 14 is laminated with the carcass 12. The belt 14 reinforces the carcass 12. The belt 14 includes an inner layer 44 and an outer layer 46. Although not shown, each of the inner layer 44 and the outer layer 46 is composed of a plurality of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equator plane. The absolute value of the tilt angle is not less than 10 ° and not more than 35 °. The cord inclination direction of the inner layer 44 is opposite to the cord inclination direction of the outer layer 46. The material of this cord is steel. An organic fiber may be used for this cord. From the viewpoint that the carcass 12 can be effectively reinforced, a cord whose material is steel is preferable.

  The band 16 covers the end portion of the belt 14. This band 16 is also referred to as an edge band 16. Although not shown, the band 16 is composed of a cord and a topping rubber. The cord extends substantially in the circumferential direction and is wound spirally. The band 16 has a so-called jointless structure. Since the belt 14 is restrained by this cord, lifting of the belt 14 is suppressed. The cord is made of organic fiber. Examples of the organic fiber include nylon fiber, polyester fiber, rayon fiber, polyethylene naphthalate fiber, and aramid fiber. From the viewpoint of effectively suppressing lifting of the belt 14 and excellent versatility, the organic fiber is preferably a nylon fiber.

  The reinforcing layer 18 is located inside the side portion 6 in the axial direction. The reinforcing layer 18 extends substantially outward in the radial direction along the carcass 12 from the tip 48 of the apex 36. An end 50 (hereinafter referred to as “inner end”) located on the radially inner side of the reinforcing layer 18 is located on the inner side of the tip 48 of the apex 36 in the radial direction. The reinforcing layer 18 overlaps the apex 36 in the axial direction. An end 52 (hereinafter referred to as an outer end) located on the outer side in the radial direction of the reinforcing layer 18 is located on an outer side than an end 54 of the folded portion 42 that forms a part of the carcass ply 38 in the radial direction. The outer end 52 of the reinforcing layer 18 may be located inside the end 54 of the folded portion 42 in the radial direction. In this case, the outer end 52 of the reinforcing layer 18 is covered with the folded portion 42.

  As shown in the figure, in the tire 2, the reinforcing layer 18 is sandwiched between the main body 40 constituting the carcass ply 38 and the folded portion 42. The inner end 50 of the reinforcing layer 18 is located between the apex 36 and the main body 40. The reinforcing layer 18 may be configured such that the inner end 50 thereof is located between the apex 36 and the folded portion 42.

  The reinforcing layer 18 is made of a crosslinked rubber composition. In the tire 2, the hardness of the reinforcing layer 18 is 65 or more and 85 or less. The reinforcing layer 18 can effectively contribute to the rigidity of the tire 2. The tire 2 is excellent in handling stability and ride comfort.

  In the tire 2, the complex elastic modulus is preferably 45 MPa or more and preferably 65 MPa or less from the viewpoint that the reinforcing layer 18 can effectively contribute to steering stability and riding comfort. The loss tangent of the reinforcing layer 18 is preferably 0.10 or more, and preferably 0.20 or less.

  In the tire 2, it is preferable that the rubber composition of the reinforcing layer 18 is equivalent to the rubber composition of the apex 36. Thereby, the rigidity of the tire 2 is effectively improved. In addition, the use of a rubber composition equivalent to the rubber composition of the apex 36 for the reinforcing layer 18 can contribute to the aggregation of materials used for manufacturing the tire 2. The tire 2 can contribute to a reduction in production cost.

  In the tire 2, the thickness of the clinch portion 32 is smaller than the thickness of the apex 36. The clinch portion 32 can contribute to reduction of rolling resistance. As described above, the reinforcing layer 18 can effectively contribute to the rigidity of the tire 2. In the tire 2, the rolling resistance is reduced without impairing the steering stability by reducing the thickness of the clinching portion 32 and adopting the reinforcing layer 18. Moreover, the clinch portion 32 having a small thickness can suppress an increase in mass of the tire 2 due to the adoption of the reinforcing layer 18.

  In FIG. 1, a solid line BL represents a reference line. The symbol PE represents the inner edge of the tire. The reference line BL is a line extending in the axial direction passing through the inner edge PE of the tire 2. A double-headed arrow H1 represents the height in the radial direction from the reference line BL to the equator 56 of the tire 2. This height H1 is referred to as a cross-sectional height of the tire 2. A double-headed arrow H2 represents the height in the radial direction from the reference line BL to the outer end 52 of the reinforcing layer 18. A double-headed arrow H3 represents the height in the radial direction from the reference line BL to the outer end 58 of the clinch portion 32. A double-headed arrow H4 represents the height in the radial direction from the reference line BL to the inner end 50 of the reinforcing layer 18. A double-headed arrow H5 represents the height in the radial direction from the reference line BL to the tip 48 of the apex 36. A double-headed arrow H6 represents the height in the radial direction from the reference line BL to the end 54 of the folded portion 42. The height H1, the height H2, the height H3, the height H4, the height H5, and the height H6 are measured in a state where the tire 2 is not attached to the regular rim. In other words, these are measured in a deflated state.

  In the tire 2, the ratio of the height H2 to the height H1 is preferably 0.54 or more and 0.66 or less. By setting this ratio to 0.54 or more, the reinforcing layer 18 can effectively contribute to the rigidity of the tire 2. In the tire 2, the response delay is suppressed and the linearity of the response is improved. The tire 2 is excellent in handling stability. In this respect, the ratio is more preferably equal to or greater than 0.58. By setting this ratio to 0.66 or less, excessive rigidity due to the reinforcing layer 18 is suppressed. In the tire 2, good riding comfort is maintained. In this respect, the ratio is more preferably equal to or less than 0.62.

  In the tire 2, the ratio of the height H4 to the height H1 is preferably 0.13 or more and 0.20 or less. By setting this ratio to be equal to or greater than 0.13, excessive rigidity due to the reinforcing layer 18 is suppressed. In the tire 2, good riding comfort is maintained. By setting this ratio to 0.20 or less, the reinforcing layer 18 can effectively contribute to the rigidity of the tire 2. The tire 2 is excellent in handling stability.

  In the tire 2, the ratio of the height H3 to the height H1 is preferably 0.36 or more and 0.44 or less. By setting this ratio to be 0.36 or more, the clinch portion 32 can effectively contribute to the rigidity of the tire 2. The tire 2 is excellent in handling stability. In this respect, the ratio is more preferably equal to or greater than 0.38. By setting this ratio to 0.44 or less, the influence on the steering stability by the clinch portion 32 is suppressed. Moreover, the clinch portion 32 can effectively contribute to the reduction of rolling resistance. In this respect, the ratio is more preferably equal to or less than 0.42.

  In the tire 2, the ratio of the height H5 to the height H1 is preferably 0.20 or more and 0.30 or less. By setting this ratio to 0.20 or more, the apex 36 can effectively contribute to the rigidity of the tire 2. The tire 2 is excellent in handling stability. By setting this ratio to 0.30 or less, excessive rigidity due to the apex 36 is suppressed. In the tire 2, excellent riding comfort is maintained.

  In the tire 2, the ratio of the height H6 to the height H1 is preferably 0.45 or more and 0.50 or less. By setting this ratio to 0.45 or more, the folded-back portion 42 can effectively contribute to the rigidity of the tire 2. The tire 2 is excellent in handling stability. By setting this ratio to 0.50 or less, excessive rigidity due to the folded portion 42 is suppressed. In the tire 2, excellent riding comfort is maintained.

  FIG. 2 shows a cross-sectional view in which a part of the tire 2 shown in FIG. 1 is enlarged. In FIG. 2, what is indicated by a double arrow a <b> 1 is the thickness of the clinching portion 32. The thickness a1 is represented by the maximum thickness of the clinching portion 32 when there is no clincher line 60 protruding outward from the outer surface of the clinching portion 32. What is indicated by a double-headed arrow a2 is the thickness of the apex 36. The thickness a2 is represented by the maximum thickness of the apex 36. In the tire 2, the apex 36 has a maximum thickness at a position close to the core 34. What is indicated by a double-headed arrow a3 is the thickness of the reinforcing layer 18. This thickness a3 is represented by the thickness of the reinforcing layer 18 at the tip 48 of the apex 36.

  In the tire 2, the ratio of the thickness a1 to the thickness a2 is preferably 0.36 or more and 0.44 or less. By setting this ratio to 0.36 or more, the clinch portion 32 can effectively contribute to the rigidity of the bead 10 portion. The tire 2 is excellent in handling stability. In this respect, the ratio is more preferably equal to or greater than 0.38. By setting this ratio to 0.44 or less, the tire 2 including the clinch portion 32 having a small thickness can be obtained. The clinch portion 32 can contribute to reduction of rolling resistance. In addition, the influence of the clinching portion 32 on the steering stability is suppressed. In this respect, the ratio is more preferably equal to or less than 0.42.

  In the tire 2, the thickness a3 is preferably 0.9 mm or greater and 1.1 mm or less. In the tire 2 in which the thickness a2 is set to 0.9 mm or more, the reinforcing layer 18 can effectively contribute to the rigidity of the tire 2. In the tire 2, response delay is improved while maintaining a linear sense of response. The tire 2 is excellent in handling stability. In the tire 2 in which the thickness a2 is set to 1.1 mm or less, excessive rigidity due to the reinforcing layer 18 is suppressed. In the tire 2, the response linearity is improved while suppressing a decrease in response delay. The tire 2 is excellent in handling stability. In addition, in the tire 2, rolling resistance is reduced.

  In the present invention, unless otherwise specified, the size and angle of each member of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures. In the case of the passenger car tire 2, the dimensions and angles are measured in a state where the internal pressure is 180 kPa.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
Passenger car tires having the basic configuration shown in FIG. 1 and the specifications shown in Table 2 below were obtained. The size of this tire is 175 / 65R15 84S. In this tire, the ratio (H2 / H1) of the radial height H2 to the outer end of the reinforcing layer to the tire cross-sectional height H1 was 0.6. The ratio (H3 / H1) of the radial height H3 to the outer end of the clinching portion with respect to the tire cross-section height H1 was 0.4. The ratio (a1 / a2) of the clinch portion thickness a1 to the apex thickness a2 was 0.4. The thickness a3 of the reinforcing layer was 1.0 mm. The loss tangent (tan δ) of the clinch portion was set to 0.11. The complex elastic modulus E * of this clinching part was set to 8.0 MPa. In this tire, the apex and the reinforcing layer are made of the same rubber composition. The tan δ of each of the apex and the reinforcing layer was 0.15. The hardness of each of the apex and the reinforcing layer was 70.

[Example 2-3 and Comparative Example 6-7]
Tires of Example 2-3 and Comparative Example 6-7 were obtained in the same manner as in Example 1 except that the tan δ of the clinch portion and the complex elastic modulus E * were set as shown in Table 2 below.

[Example 4-7]
A tire of Example 4-7 was obtained in the same manner as in Example 1 except that the ratio (H2 / H1) was as shown in Table 3 below.

[Example 8-11]
A tire of Example 8-11 was obtained in the same manner as in Example 1 except that the ratio (H3 / H1) was as shown in Table 4 below.

[Example 12-15]
Tires of Examples 12-15 were obtained in the same manner as Example 1, except that the ratio (a1 / a2) was as shown in Table 5 below.

[Examples 16-19]
Tires of Examples 16-19 were obtained in the same manner as in Example 1 except that the thickness a3 was set as shown in Table 6 below.

[Example 20-21 and Comparative Example 8-9]
Tires of Example 20-21 and Comparative Example 8-9 were obtained in the same manner as in Example 1 except that the tan δ and hardness of the apex and the reinforcing layer were as shown in Table 7 below.

[Comparative Example 1-5]
Except that the ratio H3 / H1, the ratio (a1 / a2), the tan δ of the clinch portion, its complex elastic modulus E *, the tan δ of the apex, and its hardness were set as shown in Table 1 without providing a reinforcing layer. In the same manner as in Example 1, a tire of Comparative Example 1-5 was obtained. Note that Comparative Example 1 is a conventional tire.

[Response delay and response linearity]
The tire was assembled in a rim of 15 × 5.5 JJ, the front tire was filled with air so that the internal pressure was 230 kPa, and the rear tire was filled with air so that the internal pressure was 220 kPa. This tire was mounted on a front-wheel drive passenger car having a displacement of 1300 cc. The driver was driven on the racing circuit to evaluate the response delay and response linearity. The results are shown in Tables 1 to 7 below as indices. Larger numbers are preferable.

[Rolling resistance]
Using a rolling resistance tester, rolling resistance was measured under the following measurement conditions.
Rim used: 15 × 6-J (aluminum alloy)
Internal pressure: 220 kPa
Load: 4.6kN
Speed: 80km / h
The results are shown in Tables 1 to 7 below as indices based on Example 1. A smaller numerical value is preferable.

  As shown in Tables 1 to 7, the tire of the example has a higher evaluation than the tire of the comparative example. From this evaluation result, the superiority of the present invention is clear.

  The pneumatic tire described above can be applied to various vehicles.

2 ... tyre 4 ... tread 6 ... side 8 ... wing 10 ... bead 12 ... carcass 14 ... belt 16 ... band 18 ... reinforcing layer 30 ... -Side wall 32 ... Clinch part 34 ... Core 36 ... Apex 38 ... Carcass ply 40 ... Main body 42 ... Folded part 44 ... Inner layer 46 ... Outer layer

Claims (4)

A tread whose outer surface forms a tread surface, a pair of beads each positioned substantially inward in the radial direction from the end of the tread, and spanned between one bead and the other bead. A carcass positioned inside the tread, a pair of side portions each positioned outside the carcass in the axial direction, and a pair of reinforcing layers each positioned inside the side portion in the axial direction,
Each side has a side wall and a clinch part,
This sidewall extends substantially inward in the radial direction from the end of the tread,
This clinch part is located inside this sidewall in the radial direction,
The complex elastic modulus of this clinching part is 7.2 MPa or more and 8.8 MPa or less,
The loss tangent of this clinch part is 0.10 or more and 0.12 or less,
Each bead includes a core and an apex extending substantially outward in the radial direction from the core,
The hardness of this apex is 65 or more and 80 or less,
Each reinforcing layer extends radially outward from the tip of the apex along the carcass,
A pneumatic tire in which the hardness of the reinforcing layer is 65 to 80.   The pneumatic tire according to claim 1, wherein a ratio of the thickness of the clinch portion to the thickness of the apex is 0.36 or more and 0.44 or less. A line extending in the axial direction through the inner edge is used as a reference. A radial height H1 from the reference line to the equator, a radial height H2 from the reference line to the outer end of the reinforcing layer, and the reference line. When the height H3 in the radial direction from the clinch portion to the outer end is measured in a state where it is not attached to the regular rim,
The ratio of the height H2 to the height H1 is not less than 0.54 and not more than 0.66,
The pneumatic tire according to claim 1 or 2, wherein a ratio of the height H3 to the height H1 is not less than 0.36 and not more than 0.44.   The pneumatic tire according to any one of claims 1 to 3, wherein a thickness of the reinforcing layer in a portion where a tip of the apex is located is 0.9 mm or more and 1.1 mm or less.

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