JP2017088148A - Pneumatic tire for motor cycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire for a motor cycle which can early exert performance thereof when the tire is brand new and allows abrasion of the tire to be visually checked before the brand-new tire sufficiently exerts performance.SOLUTION: In a tread part 1 are provided shallow grooves 2 whose width is between 0.1 and 2.0 mm and whose depth is between 0.1 and 2.0 mm, where the depths of the shallow grooves 2 vary in an extending direction.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire for a motorcycle (hereinafter, also simply referred to as “tire”). Specifically, until the performance of a new tire can be exhibited at an early stage and the new tire can sufficiently exhibit performance. The present invention relates to a pneumatic tire for a motorcycle capable of visually confirming wear.

  In the vulcanization process in the manufacturing process of a pneumatic tire, generally, a tire vulcanization bladder is arranged inside an unvulcanized tire arranged in a mold, and the tire vulcanization bladder is expanded by steam. This is performed by bringing an unvulcanized tire into close contact with the mold. The vulcanized tire is taken out from the vulcanizer, and at this time, the vulcanized tire needs to be smoothly peeled off from the vulcanizer.

  In order to deal with such problems, conventionally, the adhesion of the vulcanized tire has been prevented by spraying a mold release agent such as silicone in advance on the upper mold part of the vulcanizer. In addition to this, for example, in Patent Document 1, a modification is provided in which a peeling jig is provided without using a mold release agent, and a contrivance is made such as peeling off the adhered vulcanized tire.

JP-A-6-218734

  Tires manufactured using a release agent during vulcanization of unvulcanized tires will exhibit the original performance of the tire when it is new because the silicone, which is a component of the release agent, is transferred to the tread. I can't do it. Therefore, in order to fully demonstrate the performance of a new tire, it is necessary to wear a certain amount of the tread portion and remove the silicone and the like that have moved to the tread portion.

  Accordingly, an object of the present invention is to provide a pneumatic tire for a motorcycle that can exhibit the performance of a new tire at an early stage and can visually confirm that the new tire has been worn until it can fully perform. Is to provide.

  As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge. In other words, by providing a shallow groove in the tread portion, the wear of the tread portion at the time of a new article is promoted, the performance of the new tire can be exhibited at an early stage, and the new tire is worn until the performance can be sufficiently exhibited. This can be confirmed visually, and it has been found that the above-mentioned problems can be solved, and the present invention has been completed.

That is, the pneumatic tire for motorcycles of the present invention is a pneumatic tire for motorcycles having a tread portion formed in an annular shape,
The tread portion is provided with a shallow groove having a width of 0.1 to 2.0 mm and a depth of 0.1 to 2.0 mm, and the depth of the shallow groove changes in the extending direction of the shallow groove. It is characterized by doing.

  In the tire of the present invention, when the straight contact area of the tread portion is a center region and both outer sides in the tire width direction of the center region are shoulder regions, the depth of the shallow groove in the center region is the shoulder region. The depth of the shallow groove in the shoulder region may be deeper than the depth of the shallow groove in the center region, and the extension of the shallow groove may be greater than the depth of the shallow groove in the shoulder region. The depth in the intermediate portion in the current direction may be the deepest.

  Here, the center region of the tread portion is a straight contact region when the tire is mounted on a specified rim, filled with a specified internal pressure, and a maximum load is applied, and the shoulder region is a region in the tread portion. An area outside the center area in the tire width direction. In addition, the “specified rim” here refers to a standard rim (or “Applied Rim” or “Recommended Rim”) at an applicable size described in a predetermined industrial standard. Air pressure corresponding to the maximum load (maximum load capacity) of a single wheel in the described application size. Further, the maximum load load is the maximum load (maximum load capacity) of a single wheel at the applicable size described in the same standard. For such industrial standards, valid standards are established for each region where tires are produced or used. For example, in the United States, “The Tire and Rim Association Inc. Year Book” (including design guides) ) In Europe by “The European Tire and Rim Technical Organizations Manual”, and in Japan by “JATMA YEAR BOOK” of the Japan Automobile Tire Association.

  According to the present invention, there is provided a pneumatic tire for a motorcycle that can exhibit the performance of a new tire at an early stage and that can be visually confirmed that the new tire has been worn until it can fully perform. can do.

1 is a schematic development view of a tread portion of a pneumatic tire for a motorcycle according to a preferred embodiment of the present invention. FIG. 3 is a schematic sectional view showing an example of a change in depth in the extending direction of the shallow groove according to the pneumatic tire for a motorcycle of the present invention. FIG. 2 is a schematic plan view showing an example of a shape of a circumferential shallow groove according to the pneumatic tire for a motorcycle of the present invention. It is a schematic plan view showing an example of the shape of the widthwise shallow groove according to the pneumatic tire for motorcycles of the present invention. It is a schematic plan view showing an example of a change in width in the extending direction of the shallow groove according to the pneumatic tire for a motorcycle of the present invention. It is a schematic sectional view showing an example of a cross-sectional shape in the groove width direction of the shallow groove according to the pneumatic tire for motorcycles of the present invention. 1 is a schematic cross-sectional view in the width direction of a pneumatic tire for a motorcycle according to a preferred embodiment of the present invention.

  Hereinafter, the pneumatic tire for motorcycles of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic development view of a tread portion of a pneumatic tire for a motorcycle according to a preferred embodiment of the present invention. In addition, the arrow in a figure is a rotation direction, and a tire will be earth | grounded from the arrow side during driving | running | working. The tire of the present invention includes a tread portion 1 formed in an annular shape, and a shallow groove 2 is provided in the tread portion 1. In the illustrated example, a plurality of shallow grooves 2 are provided in the tire width direction. The tire of the present invention is not limited to this. That is, in the tire of the present invention, the type of the shallow groove 2 is not limited to the width direction shallow groove but may be a circumferential direction shallow groove. Here, the tire circumferential direction used when indicating the extending direction of the shallow groove 2 means a range of ± 45 ° with respect to the tire equator E, and the tire width direction is perpendicular to the tire equator E. It means a range greater than −45 ° and less than 45 ° with respect to the direction. When the shape of the shallow groove is not a straight line, the direction of the shallow groove is the direction of a line connecting both ends of the shallow groove.

  In the illustrated example, the two main grooves 3a and 3b are periodically provided at an equal pitch. However, the shape of the main groove 3 is not particularly limited and is not limited to the above example. . For example, a circumferential groove formed continuously in the circumferential direction may be provided as the main groove.

  In the tire of the present invention, the following effects can be obtained by providing the shallow groove 2 in the tread portion 1. First, in a new tire, since the silicone used in the tire vulcanization process is present on the surface layer, it is slippery when new. Therefore, in order to fully exhibit the performance of the tire, the surface layer of the tread portion 1 must be worn to some extent. In the tire according to the present invention, by providing the shallow groove 2 in the tread portion 1, the tread portion 1 can be easily worn, whereby the performance of the new tire can be exhibited at an early stage. Further, the drainage performance is improved by the shallow groove 2, and the rubber of the tread portion 1 becomes easy to move at the time of ground contact, and by promoting heat generation, the grip performance can be exhibited at an early stage. Moreover, the appearance can be improved by the shallow groove 2.

  In the tire of the present invention, the width of the shallow groove 2 is 0.1 to 2.0 mm, preferably 0.5 to 1.5 mm. When the width of the shallow groove 2 is less than 0.1 mm, sufficient drainage may not be obtained. On the other hand, when the width exceeds 2.0 mm, the rigidity of the tread portion 1 is lowered and steering stability is deteriorated. Since the ground contact area is small, a sufficient grip may not be obtained. Here, the width of the shallow groove 2 refers to the width of the opening in a cross section perpendicular to the extending direction of the shallow groove 2. Further, when the width of the shallow groove 2 changes in the extending direction of the shallow groove 2, the shallow groove 2 is the widest portion.

  The depth of the shallow groove 2 is 0.1 to 2.0 mm, preferably 0.2 to 0.5 mm. If the depth of the shallow groove 2 is less than 0.1 mm, sufficient drainage performance may not be obtained. On the other hand, if the depth exceeds 2.0 mm, the rigidity of the tread portion 1 is lowered, and the steering is reduced. There is a risk that stability will deteriorate. Here, when the depth of the shallow groove 2 changes in the extending direction of the shallow groove 2, it means the deepest portion of the shallow groove 2. If a deep groove having a depth exceeding 2.0 mm is provided, uneven wear may occur, but such a problem does not occur in the tire of the present invention. The depth of the shallow groove 2 refers to the distance from the tread surface of the tread portion 1 to the groove bottom of the shallow groove 2 and does not include the protrusion provided on the groove bottom of the shallow groove 2. Here, the protrusions are those whose peripheral contour shape is circular, elliptical, or other curved shape, or parallelogram, rhombus, or other polygonal shape.

  In the tire of the present invention, the depth of the shallow groove 2 changes in the extending direction. For example, the depth may be different at the position in the width direction of the tread portion 1. As described above, by appropriately adjusting the depth of the shallow groove 2, the drainage can be adjusted, and the grip performance can be adjusted by adjusting the rigidity of the tread portion.

  FIG. 2 is a schematic cross-sectional view showing an example of a change in depth in the extending direction of the shallow groove according to the pneumatic tire for a motorcycle of the present invention. 2A shows a shape in which the groove depth linearly decreases toward both ends of the shallow groove, and FIG. 2B shows that the groove depth increases linearly toward the both ends of the shallow groove. Shape. (C) is a curved surface convex outward in the tire radial direction in the vicinity of the center of the groove bottom, and a curved surface concave inward in the tire radial direction in the vicinity of both sides of the groove bottom, forming a corrugated shape as a whole. ing.

  When the depth of the shallow groove 2 on the center region Tc side is increased, the drainage performance is further improved, so that the grip performance on the wet road surface can be improved. On the other hand, if the shoulder region Ts side of the shallow groove 2 is deepened, the rubber in the shoulder region Ts can move easily when touching the ground, and by further promoting heat generation, it is possible to further improve the grip performance at the time of turning and at the time of turning. Drainability can also be improved. Moreover, the shallow part of the groove bottom of the shallow groove 2 is a standard for knowing the degree of wear of the tire.

  In the tire of the present invention, all of the circumferential shallow grooves and the widthwise shallow grooves having an angle with respect to the circumferential direction may extend to the tread end, and may be open at the tread end. Only 2 may be open at the tread end. By setting it as such a structure, favorable initial drainage property can be obtained. In the tire of the present invention, it is preferable that the angle of the shallow groove 2 is provided so as to be perpendicular to the input direction from the viewpoint of increasing the edge component. Moreover, a part or all of the shallow groove 2 may terminate about 20 mm before the tread end.

  In the tire of the present invention, the type of the shallow groove 2 is not limited, and may be a circumferential shallow groove or a widthwise shallow groove. FIG. 3 is a schematic plan view showing an example of the shape of a circumferential shallow groove according to the pneumatic tire for motorcycles of the present invention. FIG. 4 is a schematic plan view of the widthwise shallow groove according to the pneumatic tire for motorcycles of the present invention. The schematic plan view which shows the example of a shape is shown.

  3A is a shallow groove extending linearly in the circumferential direction, FIG. 3B is a shallow groove extending zigzag in the circumferential direction, and FIG. 3C is a wavy shape extending in the circumferential direction. A shallow groove (d) is a shallow groove extending alternately in the circumferential direction and the width direction but extending in the circumferential direction as a whole. (E) in FIG. 3 is a shallow groove extending linearly in a discontinuous manner in the circumferential direction, and (f) is a plurality of shallow grooves formed in a substantially elliptical shape in the circumferential direction. (G) is a shallow groove having a plurality of shallow grooves provided in the circumferential direction and extending in the circumferential direction as a whole. (H) is a substantially parallelogram. A plurality of shallow grooves are provided in the circumferential direction, and the shallow grooves extend in the circumferential direction as a whole. In addition, it is preferable to form the groove in the arrow shape toward the rotation direction of the tire because the mounting direction of the tire can be easily seen, but it is not always necessary to have the shape as shown in FIG. An arrow-shaped shallow groove may be added to the linear shallow groove shown in FIG.

  4A is a shallow groove extending linearly in the tire width direction, FIG. 4B is a shallow groove extending zigzag in the width direction, and FIG. 4C is a wavy shape in the width direction. (D) is a shallow groove extending in the tire width direction as a whole, although extending alternately in the width direction and the circumferential direction. 4 (e) shows shallow grooves extending linearly in a discontinuous manner in the width direction, and FIG. 4 (f) shows a plurality of shallow grooves formed in a substantially elliptical shape in the tire width direction. (G) is a shallow groove extending in the width direction as a whole, although both ends of the linear shallow groove extending in the width direction extend in the circumferential direction. Although it is a curved shape, it is a shallow groove extending in the width direction as a whole, and (i) is a shallow groove having branches at both ends of the shallow groove extending linearly in the width direction. The shapes of (g) and (h) have the advantage that they can be easily repelled by nails and the like.

  Furthermore, in the tire of the present invention, it is preferable that the distance between the substantially parallel shallow grooves 2, in the illustrated example, L1 is 10 to 100 mm. Here, the space | interval of the shallow groove | channel 2 says the length of the surface of a tread part at the time of normal internal pressure and no load. If the distance between the shallow grooves 2 is less than 10 mm, the rigidity of the tread portion 1 may be reduced and steering stability may be deteriorated. Moreover, since the area of the shallow groove 2 which occupies the whole grounding surface becomes large, there exists a possibility that grip performance may fall. On the other hand, if the distance between the shallow grooves 2 is greater than 100 mm, the drainage and traction properties deteriorate, and the tread portion 1 becomes difficult to move, so that the effects of the present invention may not be sufficiently obtained. In addition, when the shallow groove has a zigzag shape or the like, the interval between the intervals is the distance between the center positions of the swing width of the shallow groove.

  Furthermore, in the tire of the present invention, the width of the shallow groove 2 may change in the extending direction. For example, it is good also as a different width | variety in the position of the width direction of the tread part 1. FIG. As described above, the drainage can be adjusted by adjusting the width of the shallow groove 2 as appropriate, and the grip performance can be adjusted by adjusting the rigidity of the tread portion. In the tire of the present invention, the shape of the shallow groove 2 is not particularly limited.

  FIG. 5 is a schematic plan view showing an example of a change in width in the extending direction of the shallow groove according to the pneumatic tire for a motorcycle of the present invention. In the tire of the present invention, the shape of the shallow groove 2 is However, it is not limited to these. FIG. 5A shows a shallow groove in which the middle portion has the largest groove width and linearly narrows toward both ends of the shallow groove, and FIG. 5B shows the middle portion having the smallest groove width. The shallow groove has a groove width that increases linearly as it goes to both ends of the shallow groove, and (c) is a shallow groove in which both ends of the shallow groove are gradually narrowed. Further, (d) is an elliptical middle portion and both shallow groove ends are straight shallow grooves, and (e) is an intermediate portion linear and shallow groove both ends are elliptical shallow grooves, (F) is a shallow groove in which the middle part is linear and both ends of the shallow groove are substantially circular. (G) is a shallow groove having a shape in which two elliptical shallow grooves are arranged in the extending direction. As shown in (e), (f), and (g), cracks can be prevented by providing no acute angle portions at both ends of the shallow groove. The intermediate portion refers to an intermediate portion when the extending direction of the shallow groove is divided into three equal parts.

  If the shallow groove 2 is widened on the center region Tc side, the drainage performance is further improved, so that the grip performance on the wet road surface can be improved. On the other hand, if the shoulder region Ts side of the shallow groove 2 is widened, the rubber in the shoulder region Ts is easy to move at the time of ground contact, and by further promoting heat generation, the grip performance at the time of turning can be further improved. Drainability can also be improved.

  Further, in the tire of the present invention, in the center region Tc, the sum of the lengths of the contour lines of the circumferential shallow grooves may be longer than the sum of the lengths of the contour lines of the width direction shallow grooves, and the center region Tc. In this case, the sum of the lengths of the contour lines of the widthwise shallow grooves may be longer than the sum of the lengths of the contour lines of the circumferentially shallow grooves. That is, the drainage can be improved satisfactorily by mainly disposing the circumferential shallow groove in the center region Tc. On the other hand, the traction property can be improved satisfactorily by mainly disposing the shallow grooves in the width direction in the center region Tc.

  FIG. 6 is a schematic plan view showing an example of a change in the width in the extending direction of the shallow groove according to the pneumatic tire for a motorcycle of the present invention. In the tire of the present invention, the contour line 4 of the tread portion 1, a pair of groove walls 5 substantially perpendicular to the contour line 4, and a groove bottom substantially parallel to the contour line 4 connecting the pair of groove walls 5. 6 may be a shape different from the virtual cross-sectional shape composed of Here, the groove wall 5 and the groove bottom 6 may be connected vertically, or may be connected with a curve. That is, in the tire of the present invention, the cross-sectional shape of the shallow groove 2 is different from a general shape, and at least a part of the pair of groove walls 5 is tapered or in the depth direction of the shallow groove (tire radial direction). It may be a shape that narrows in stages. Moreover, the convex part 7 may be formed in the opening edge of the shallow groove | channel 2 of a tread part. Further, the groove wall 5 or the groove bottom 6 may be formed with unevenness extending in the extending direction of the shallow groove 2.

  6A, only the vicinity of the opening in the groove wall 5 has a tapered shape, and in FIG. 6B, the entire groove wall 5 has a tapered shape. Thus, by making the opening part of the shallow groove | channel 2 into a taper shape, drainage can be made more favorable, without impairing an edge effect. FIG. 6C shows a shape in which the width of the shallow groove 2 is gradually reduced in the groove depth direction. With such a shape, the degree of wear of the tread portion 1 can be determined in stages. 6D and 6E show a shape in which the convex portion 7 is provided at the opening edge of the shallow groove 2, and FIG. 6D shows a shape that gradually rises as the opening edge of the shallow groove 2 is approached. (E) has a shape in which the opening edge of the shallow groove 2 swells substantially vertically. Thus, by providing the convex part 7 at the opening edge of the shallow groove 2, the contact pressure at the end of the shallow groove 2 is increased, and a better edge effect can be expected. In addition, an effect of improving visibility can be obtained. In this case, the height of the convex portion is made lower than the depth of the shallow groove. Furthermore, FIG. 6F has a shape in which the front groove wall 5 is low and the rear groove wall 5 is high with respect to the input direction. Thus, a favorable edge effect can be acquired by providing a step in the groove wall 5. 6 (g) and 6 (h) are shapes in which irregularities are provided on the groove bottom 6 and the groove wall 5, respectively. Thus, the visibility of the shallow groove 2 is improved by further providing the groove inside the shallow groove 2. In addition, by providing irregularities on the groove bottom 6, since the irregularities on the groove bottom 6 appear after the shallow groove 2 is worn, the design is excellent. When the shallow groove has a tapered cross section, or when the groove wall 5 or the groove bottom 6 is provided with irregularities extending in the extending direction of the shallow groove 2, the depth of the shallow groove 2 is reduced. The reference is the outline 4 of the virtual cross-sectional shape, and the width of the shallow groove 2 is also based on the width of the opening of the virtual cross-sectional shape.

  In the tire of the present invention, a decoration pattern called serration in which a plurality of ridges are arranged at a predetermined pitch in the shallow groove 2 may be applied. In addition, the tread portion 1 may be provided with information such as a character or symbol such as a manufacturer name, or a pattern or a decoration pattern that can be used to understand the usage state of a figure or a camber angle in a shallow groove. Furthermore, when providing a circumferential shallow groove or a widthwise shallow groove inclined in the circumferential direction, these shapes may be an arrow shape and a rotation mark.

  In the tire of the present invention, it is only important that the shallow groove 2 formed in the tread portion 1 satisfies the above requirements, and there is no particular limitation other than that, and a known structure is adopted for other configurations. be able to. For example, as shown in the figure, when the main groove 3 is provided, the width and depth of the main groove 3 may be larger than the depth and width of the shallow groove 2. Moreover, there is no restriction | limiting in particular also about structures other than the tread part 1, A known structure is employable. FIG. 7 is a schematic cross-sectional view in the width direction of a pneumatic tire for a motorcycle according to a preferred embodiment of the present invention.

  The illustrated tire 10 of the present invention includes a tread portion 11, a pair of sidewall portions 12 connected to both sides of the tread portion 11, a pair of bead portions 13 respectively connected to the pair of sidewall portions 12, and each of these portions is a bead portion. 13 carcass 14 composed of carcass plies of at least one layer (one layer in the illustrated example) that reinforces each other. In the illustrated example, the end portion of the carcass 14 is folded and locked to the bead core 15 from the tire inner side to the outer side. However, the carcass 14 may be pinched and locked by bead wires from both sides.

  In the illustrated tire, a belt layer 16 is provided on the outer side of the carcass 14 in the tire radial direction. The belt cord of the belt layer 16 is not particularly limited, and a known non-extensible high elastic cord can be used. For example, aromatic polyamide (aramid, for example, trade name: Kevlar manufactured by DuPont) or polyethylene naphthalate ( PEN), polyethylene terephthalate (PET), organic fibers such as rayon and nylon, steel, glass fibers, carbon fibers and other materials can be appropriately selected and used. Such a belt may be composed of two or more inclined belt layers arranged so that the cord directions cross each other between the layers, and more than one layer whose cord direction is substantially the tire circumferential direction. It may consist of a spiral belt layer. In FIG. 7, a spiral belt layer 17 is provided outside the belt layer 16 in the tire radial direction.

  The tire of the present invention can be applied to both a front tire and a rear tire for a motorcycle, and can be applied to any tire having a radial structure and a bias structure.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Example 1>
A pneumatic tire for a motorcycle having a tread pattern shown in FIG. 1 was produced with a tire size of 120 / 70ZR17M / C. The cross-sectional shape of the shallow groove is the shape of FIG. 2A. The depth of the shallow groove is 0.5 mm at the deepest part, 0.3 mm at the shallowest part, and the width of the shallow groove is 1.0 mm. The angle of the shallow grooves was 0 ° with respect to the tire width direction, and the distance between the shallow grooves was 24 mm.

<Example 2>
A pneumatic tire for a motorcycle having a tread pattern shown in FIG. 1 was produced with a tire size of 120 / 70ZR17M / C. The cross-sectional shape of the shallow groove is the shape shown in FIG. 2B. The depth of the shallow groove is 0.5 mm at the deepest portion, 0.3 mm at the shallowest portion, and the width of the shallow groove is 1.0 mm. The angle of the shallow grooves was 0 ° with respect to the tire width direction, and the distance between the shallow grooves was 24 mm.

<Comparative example>
A comparative example tire was produced in the same manner as the example tire except that no shallow groove was provided in the shoulder region.

  The obtained tires were evaluated for grip properties and traction properties according to the following procedures.

<Grip properties>
This was done by running on a wet road with a vehicle fitted with each tire. The grip performance was evaluated by the driver's feeling. At that time, the evaluation of the tire of the comparative example was set to 100, and the tire of the example was indexed.

<Traction characteristics>
Traction performance was evaluated based on driver feeling. At that time, the evaluation of the tire of the comparative example was set to 100, and the tire of the example was indexed.

  From Table 1, it can be seen that the tire of the present invention in which a predetermined shallow groove is provided in the shoulder region of the tread portion is excellent in drainage, grip and traction.

DESCRIPTION OF SYMBOLS 1 Tread part 2 Shallow groove 3a, 3b Main groove 4 Contour line 5 Groove wall 6 Groove bottom 7 Convex part 10 Pneumatic tire for motorcycles (tire)
DESCRIPTION OF SYMBOLS 11 Tread part 12 Side wall part 13 Bead part 14 Carcass 15 Bead core 16 Belt layer 17 Spiral belt layer

Claims (4)

In a pneumatic tire for a motorcycle having a tread portion formed in an annular shape,
The tread portion is provided with a shallow groove having a width of 0.1 to 2.0 mm and a depth of 0.1 to 2.0 mm, and the depth of the shallow groove changes in the extending direction of the shallow groove. A pneumatic tire for a motorcycle, characterized by   When the straight contact area of the tread portion is a center region, and both outer sides in the tire width direction of the center region are shoulder regions, the depth of the shallow groove in the center region is greater than the depth of the shallow groove in the shoulder region. The pneumatic tire for a motorcycle according to claim 1.   When the straight contact area of the tread portion is a center region, and both outer sides in the tire width direction of the center region are shoulder regions, the depth of the shallow groove in the shoulder region is greater than the depth of the shallow groove in the center region. The pneumatic tire for a motorcycle according to claim 1.   The pneumatic tire for a motorcycle according to claim 1, wherein a depth in an intermediate portion in the extending direction of the shallow groove is deepest.

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