JP2024118688A - Pneumatic tires and vulcanization molds - Google Patents

Abstract

[Problem] To suppress uneven wear of the tread and prevent defects such as chipping of the tread and damage to sipe blades when the mold is opened. [Solution] The tread has a plurality of fine grooves (50) spaced apart in the tire circumferential direction and division marks provided at the division positions of the sectors, and the fine grooves have sipes (53A, 53C, etc.) extending in the tire axial direction and chamfers (54A, 54C, etc.) that widen the width of the open ends of the sipes toward the ground contact surface (8a). If the range from the division traces adjacent to each other in the tire circumferential direction to a first angle θ1 toward the tire circumferential center is defined as a first circumferential end region R1, and the region between the first circumferential end regions is defined as a central region Rm, then, among the multiple fine grooves provided in the first circumferential end region, the sipes 53A of the first fine groove 50A in which the chamfer is provided on the groove wall 53Aa on the sipe central region side are shallower than the sipes 53B1, 53B2 of the second fine grooves 50B1, 50B2 in which the chamfer is provided on the groove walls 53B1a, 53B2a on the sipe division trace side.

Description

The present invention relates to a pneumatic tire and a vulcanization mold.

Typically, a mold for vulcanizing and molding a pneumatic tire has multiple sectors divided in the tire circumferential direction. With such a mold, a green tire is placed inside the mold in an open state with the multiple sectors spaced radially outward from the center, and then the multiple sectors move toward the center to combine into a ring-shaped closed state, thereby vulcanizing and molding the green tire inside. Then, after vulcanization and molding is completed, the multiple sectors are moved radially outward to open the mold, and the vulcanized pneumatic tire is removed.

There is a known pneumatic tire with a narrow groove in the tread, which has a sipe and a chamfer that widens the open end of the sipe that contacts the ground. In a mold for vulcanizing a pneumatic tire with such a narrow groove, the chamfer forming protrusion that forms the chamfer is provided in contact with the base of the sipe blade that forms the sipe.

The sipe blades provided in the circumferential end regions of the sectors (i.e., the regions near the division positions of the sectors) protrude from the mold surface in a direction that is not parallel to the direction in which the sectors move when the mold is opened. As a result, the sipe blades provided in the circumferential end regions of the sectors and extending in the axial direction of the tire encounter relatively large resistance when the mold is opened and deform, which can cause defects in the shape of the vulcanized tire.

In response to this, it is known that the sipes provided in the circumferential end regions of the sector can be made shallower than the sipes provided in other regions of the sector, thereby reducing the resistance generated in the sipe blades when the mold is opened, thereby eliminating the above-mentioned problems (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2020-100002

However, parts of the tread with shallow sipes are more susceptible to wear than other parts and are more likely to cause uneven wear. To prevent uneven wear in the tread, it is preferable to reduce the number of shallow sipes.

The present invention was made in consideration of these circumstances, and aims to provide a pneumatic tire and a vulcanization molding die that can suppress uneven wear in the tread while also suppressing tire shape defects caused by deformation of the sipe blades.

In the pneumatic tire of this embodiment, the tread is formed by a plurality of sectors divided in the tire circumferential direction, the tread has a plurality of narrow grooves spaced apart in the tire circumferential direction and division marks provided at the division positions of the sectors, the narrow grooves have sipes extending in the tire axial direction and chamfers that widen the width of the open ends of the sipes toward the ground contact surface, and among the regions sandwiched between the division marks adjacent to each other in the tire circumferential direction, the range from the division marks to a first angle toward the tire circumferential center is defined as a first circumferential end region, and the region sandwiched between the first circumferential end regions is defined as a central region, the plurality of narrow grooves provided in the first circumferential end region include a first narrow groove in which the chamfer is provided on the groove wall of the sipe on the central region side, and a second narrow groove in which the chamfer is provided on the groove wall of the sipe on the division mark side, and the sipes of the first narrow grooves are shallower than the sipes of the second narrow grooves.

In addition, the vulcanization molding die of this embodiment is a vulcanization molding die having a plurality of sectors divided in the tire circumferential direction and a plurality of fine groove forming protrusions provided on the tread molding surface of the sectors, the fine groove forming protrusions having sipe blades that form sipes extending in the tire axial direction and chamfer forming protrusions provided in contact with the roots of the sipe blades, and in one of the sectors, the range from the sector circumferential end to a first angle toward the tire circumferential center is defined as a first sector end region, and the region sandwiched between the first sector end regions is defined as a sector central region. The plurality of narrow groove forming projections provided in the first sector end region include a first narrow groove forming projection in which the chamfer forming projection is provided on the sector central region side of the sipe blade, and a second narrow groove forming projection in which the chamfer forming projection is provided on the sector circumferential end side of the sipe blade, and the protrusion amount of the first narrow groove forming projection from the tread molding surface at the connection position between the chamfer forming projection and the sipe blade is smaller than the protrusion amount of the second narrow groove forming projection from the tread molding surface at the connection position between the chamfer forming projection and the sipe blade.

The above pneumatic tire can suppress uneven wear in the tread while preventing defects such as damage to the tread when the mold is opened or damage to the sipe blades that form the sipes.

1 is a cross-sectional view of a pneumatic tire according to an embodiment of the present invention; FIG. 2 is a development view showing the tread pattern of the pneumatic tire of FIG. 1; FIG. 1 is a side view of a pneumatic tire, showing the positions of division marks formed on the surface of the tread rubber. Enlarged view of the main part of Figure 2 A cross-sectional view of the inner center narrow groove taken along line A-A in FIG. 5A is a cross-sectional view of the outer center narrow groove taken along line B-B in FIG. 4, and FIG. 5B is a cross-sectional view of the outer center narrow groove taken along line C-C in FIG. 4. 5A is a cross-sectional view of the inner shoulder narrow groove taken along line DD in FIG. 4, and FIG. 5B is a cross-sectional view of the inner shoulder narrow groove taken along line EE in FIG. 4. Enlarged view of the main part of Figure 2 A cross-sectional view of the outer shoulder narrow groove taken along line F-F in FIG. FIG. 1 shows a sipe in a narrow groove near an end portion, where (a) is a view from the tire surface, (b) is a view showing one wall surface of the sipe, and (c) is a cross-sectional view taken along line G-G in (b). 1A is a diagram showing a sipe of a dividing end narrow groove, in which (a) is a diagram seen from the tire surface, (b) is a diagram showing one wall surface of the sipe, and (c) is a cross-sectional view taken along line H-H in (b). FIG. 2 is a half cross-sectional view of a vulcanization mold for vulcanizing the pneumatic tire of FIG. 1. Schematic diagram of a sector FIG. 14 is an enlarged view of a main part of FIG. 1A is a diagram showing a sipe of a first outer shoulder narrow groove according to a first modified example of the present invention, where FIG. 1A is a diagram seen from the tire surface, and FIG. 1B is a diagram showing one wall surface of the sipe.

The following embodiments are described with reference to the drawings. Note that the following embodiments are merely examples and are not intended to limit the scope of the invention.

In this specification, the ground contact state refers to a state in which the pneumatic tire 1 is mounted on a standard rim, has a standard internal pressure, and is subjected to a standard load. A standard rim is a rim that is determined for each tire by the standard system that includes the standard on which the tire is based, such as a standard rim for JATMA, or a "Measuring Rim" for TRA and ETRTO.

"Normal load" is the load specified for each tire by each standard in the system of standards on which the tire is based. For JATMA, it is the "maximum load capacity." For TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." For ETRTO, it is the "LOAD CAPACITY." If the tire is for passenger cars, it is a load equivalent to 88% of the above load. If the tire is for racing karts, the normal load is 392N.

The normal internal pressure is the air pressure set for each tire by each standard in the standard system on which the tire is based. For truck and bus tires and light truck tires, it is the maximum air pressure for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO.

In the figure, the symbol CL indicates the tire equatorial plane, which corresponds to the tire axial center. The symbol WD indicates the tire axial direction (also called the tire width direction). The axially inner side WDi refers to the direction approaching the tire equatorial plane CL, and the axially outer side WDo refers to the direction away from the tire equatorial plane CL. The symbol CD indicates the tire circumferential direction, which is the circumferential direction centered on the tire rotation axis. The symbol RD indicates the tire radial direction (direction perpendicular to the tire rotation axis). The radially inner side RDi refers to the direction approaching the tire rotation axis, and the radially outer side RDo refers to the direction away from the tire rotation axis.

(1) Cross-sectional structure of pneumatic tire 1 A pneumatic tire 1 according to one embodiment shown in FIG. 1 includes a pair of left and right beads 2, a pair of left and right sidewalls 4 extending radially outward from the beads 2, and a tread 3 connecting radially outer ends of the sidewalls 4 to form a contact surface 8 a.

A ring-shaped bead core 2a is embedded in each of the pair of beads 2. A hard rubber bead filler 2b is provided on the tire radial outer side RDo of the bead core 2a, tapering toward the tire radial outer side RDo.

The pneumatic tire has a carcass layer 5 that extends toroidally between a pair of beads 2. The carcass layer 5 extends from the tread 3 through both sidewalls 4 to the bead 2, and is folded back around the bead core 2a at the bead 2 from the inside to the outside in the tire axial direction, so that both ends of the carcass layer 5 are secured.

The carcass layer 5 is made up of at least one carcass ply, and in this example, it is made up of two carcass plies. The carcass ply that constitutes the carcass layer 5 is a rubber member in which carcass cords made of organic fiber cords arranged substantially perpendicular to the tire circumferential direction CD are covered with rubber. A sheet-shaped inner liner 6 made of rubber with low air permeability is attached to the inside of the carcass layer 5.

The tread 3 comprises a belt 7 provided on the outer circumferential side of the carcass layer 5, and a tread rubber 8 having a ground contact surface 8a that contacts the road surface. The belt 7 is made up of at least two cross belt plies in which belt cords are arranged at an inclination angle of 10° to 35° with respect to the tire circumferential direction CD. A belt reinforcing layer 9 may be provided on the tire radial outer side RDo of the belt 7, i.e., between the belt 7 and the tread rubber 8. The belt reinforcing layer 9 is made up of a cap ply having cords that extend substantially parallel to the tire circumferential direction CD.

As shown in FIG. 2, the surface of the tread rubber 8 has main grooves 10, 12 and narrow grooves 20, 30, 40, 50 that form the tread pattern, as well as stripe-like division marks 19 that correspond to the division positions of the tire vulcanization mold.

(2) Division mark 19
The division marks 19 are marks of division positions 102a of the sectors 102 of the vulcanization molding die 100 used in the tire vulcanization molding process described later (see Figs. 12 to 14). The division marks 19 are, for example, linear protrusions extending in the tire axial direction protruding from the surface of the tread rubber 8 with a width of 0.01 mm to 2 mm and a height of 0.01 mm to 5 mm. The division marks 19 are formed on the surface of the tread rubber 8 at intervals in the tire circumferential direction CD, the number of which is the same as the number of sectors 102 of the vulcanization molding die 100, as shown in Fig. 3.

As shown in Fig. 2 and Fig. 3, a plurality of regions are set on the surface of the tread rubber 8 based on a plurality of division marks 19. Specifically, in the surface of the tread rubber 8, of the region R0 sandwiched between the division marks 19 adjacent to each other in the tire circumferential direction CD, the range from the division marks 19 toward the tire circumferential center to a first angle θ1 is set as a first circumferential end region R1, the range from the division marks 19 toward the tire circumferential center to a second angle θ2 smaller than the first angle θ1 is set as a second circumferential end region R2, and the region sandwiched between the first circumferential end region R1 is set as a central region Rm. In other words, the second circumferential end region R2 is a region that overlaps with the division marks 19 side of the first circumferential end region R1.
For example, the first angle θ1 can be set to 10 degrees or more and 15 degrees or less, and the second angle θ2 can be set to 3 degrees or more and 5 degrees or less.

(3) Tread Pattern Configuration A plurality of (three in this embodiment) main grooves extending in the tire circumferential direction CD are provided at intervals in the tire axial direction WD in the tread pattern formed on the surface of the tread rubber 8. When three main grooves are provided, as shown in Fig. 2, a center main groove 10 disposed in the center of the tire axial direction and a pair of shoulder main grooves 12, 12 provided on the outer side WDo of the center main groove 10 in the tire axial direction are provided on the surface of the tread rubber 8.

The center main groove 10 is zigzag-shaped when viewed from the tire radial outside RDo. More specifically, as shown in Figures 2 and 4, the center main groove 10 consists of a long groove 10a that extends at an incline with respect to the tire circumferential direction CD, and a short groove 10b that is at an incline with respect to the tire circumferential direction CD and extends in a different direction from the long groove 10a. The center main groove 10 is formed by alternately arranging the long grooves 10a and the short grooves 10b. The shoulder main grooves 12 are not zigzag-shaped, but extend straight along the tire circumferential direction CD.

The three main grooves 10, 12, 12 provide the surface of the tread rubber 8 with a center rib 14 sandwiched between the center main groove 10 and the shoulder main groove 12, and a shoulder rib 16 sandwiched between the shoulder main groove 12 and the ground contact edge 18. The rib refers to the land that continues in the tire circumferential direction CD. The land here refers to the part that is defined by the grooves and has the ground contact surface 8a. The ground contact edge 18 refers to the axial end of the ground contact surface 8a under load.

The center rib 14 is provided with an inner center narrow groove 20 and an outer center narrow groove 30. The shoulder rib 16 is provided with an inner shoulder narrow groove 40 and an outer shoulder narrow groove 50. These narrow grooves 20, 30, 40, 50 are arranged in a row at equal or approximately equal intervals in the tire circumferential direction CD. Specifically, the inner center narrow grooves 20 form an inner center narrow groove row arranged in the tire circumferential direction at intervals on the center rib 14. The outer center narrow grooves 30 form an outer center narrow groove row arranged in the tire circumferential direction at intervals on the center rib 14. The inner shoulder narrow grooves 40 form an inner shoulder narrow groove row arranged in the tire circumferential direction at intervals on the shoulder rib 16. The outer shoulder narrow grooves 50 form an outer shoulder narrow groove row arranged in the tire circumferential direction at intervals on the shoulder rib 16. The structure of these narrow grooves 20, 30, 40, 50 will be described later.

As shown in FIG. 2, the narrow grooves 20, 30, 40, 50 are provided on both sides in the tire axial direction. However, the narrow grooves 20, 30, 40, 50 are in the opposite direction in the tire circumferential direction CD on one side and the other side in the tire axial direction WD, and are offset in the tire circumferential direction CD. That is, the position of the inner center narrow groove 20 on one side of the tire axial direction WD and the position of the inner center narrow groove 20 on the other side do not match the tire axial direction WD, the position of the outer center narrow groove 30 on one side of the tire axial direction WD and the position of the outer center narrow groove 30 on the other side do not match the tire axial direction WD, the position of the inner shoulder narrow groove 40 on one side of the tire axial direction WD and the position of the inner shoulder-narrow groove 40 on the other side do not match the tire axial direction WD, and the position of the outer shoulder narrow groove 50 on one side of the tire axial direction WD and the position of the outer shoulder narrow groove 50 on the other side do not match the tire axial direction WD.

(4) Inner center narrow groove 20
2 and 4, the inner center narrow groove 20 extends from the center main groove 10 toward the axially outer side WDo of the tire (toward the ground contact edge 18). One end of the inner center narrow groove 20 opens into the center main groove 10, and the other end terminates within the center rib 14. The inner center narrow groove 20 extends straight without bending.

As shown in Figures 2 and 5, the inner center narrow groove 20 has narrow sipes 23 and chamfers 24.

A sipe 23 is a groove in which at least a portion of the opposing groove walls 23a abuts when the tire is in contact with the ground, and is, for example, a narrow groove with a width of less than 2 mm (see Figure 5).

The chamfer 24 is provided on one of a pair of groove walls 23a that form the sipe 23. The chamfer 24 has a surface that is inclined relative to the groove wall 23a near the ground contact surface so as to widen the width of the opening end of the sipe 23 toward the ground contact surface 8a. The chamfer 24 is a surface that continues from the ground contact surface 8a to the back side of the sipe 23. The chamfer 24 may reach the ground contact surface 8a, but a step wall 24a of a small height (for example, about 0.5 mm) may be formed between the chamfer 24 and the ground contact surface 8a.

The chamfer 24 does not reach the bottom of the inner center narrow groove 20. The chamfer 24 gradually widens the width of the inner center narrow groove 20 as it approaches the ground contact surface 8a. The angle of the chamfer 24 with respect to the groove wall 23a of the sipe 23 is, for example, 40° or more and 50° or less. The width of the chamfer 24 gradually narrows as it moves from the center main groove 10 toward the outside in the tire axial direction.

In this embodiment, the multiple inner center narrow grooves 20 that make up the inner center narrow groove row are formed to have the same shape.

(5) Outer center narrow groove 30
2 and 4, the outer center narrow groove 30 extends from the shoulder main groove 12 toward the tire axial center (toward the tire equatorial plane CL). One end of the outer center narrow groove 30 opens into the shoulder main groove 12, and the other end terminates within the center rib 14.

The outer center narrow groove 30 has a bending point 31 and is bent at the bending point 31 when viewed from the outer side RDo in the tire radial direction.

The outer center narrow groove 30 has a relatively wide slit 32 provided closer to the shoulder main groove 12 than the bending point 31, and a sipe 33 and chamfer 34 provided closer to the tip side (center main groove 10 side) than the bending point 31.

A slit 32 is a groove in which the opposing groove walls 32a do not come into contact when the tire is in contact with the ground, and is, for example, a groove with a width of 2 mm or more (see FIG. 6(a)). A sipe 33 is a groove in which at least a portion of the opposing groove walls 33a come into contact when the tire is in contact with the ground, and is, for example, a narrow groove with a width of less than 2 mm (see FIG. 6(b)).

The chamfer 34 is provided on the groove wall 33a1 of the pair of groove walls 33a that form the sipe 33, which faces the inside of the bend of the outer center narrow groove 30 (the side that forms the minor angle). The chamfer 34 has a surface that is inclined with respect to the groove wall 31a near the ground contact surface 8a so as to widen the width of the opening end of the sipe 33 toward the ground contact surface 8a. The chamfer 34 is a surface that continues from the ground contact surface 8a to the back side of the sipe 33.

The chamfer 34 may reach the ground surface 8a, or a small step wall 34a (e.g., about 0.5 mm) may be formed between the chamfer 34 and the ground surface 8a. The chamfer 34 does not reach the bottom of the outer center narrow groove 30. By providing the chamfer 34, the width of the outer center narrow groove 30 gradually increases as it approaches the ground surface 8a.

The width of the chamfer 34 gradually increases from the tip of the outer center narrow groove 30 toward the bending point 31, and is widest at the bending point 31. As shown in Figures 4 and 6(a), the slit 32 does not have a chamfer 34.

In this embodiment, the multiple outer center fine grooves 30 that make up the outer center fine groove row are formed to have the same shape.

(6) Inner shoulder narrow groove 40
2 and 4 , the inner shoulder narrow groove 40 extends axially outward from the shoulder main groove 12. One end of the inner shoulder narrow groove 40 opens into the shoulder main groove 12, and the other end terminates within the shoulder rib 16.

The inner shoulder narrow groove 40 has a bending point 41 and is bent at the bending point 41 when viewed from the radially outer side RDo of the tire. The inner shoulder narrow groove 40 has a relatively wide slit 42 provided on the shoulder main groove 12 side of the bending point 41, and a sipe 43 and a chamfer 44 provided on the tip side (the ground contact edge 18 side) of the bending point 41.

The slit 42 is a groove in which the opposing groove walls 42a do not come into contact when the tire is in contact with the ground, and is, for example, a groove with a width of 2 mm or more (see FIG. 7(a)). The sipe 43 is a groove in which at least a portion of the opposing groove walls 43a come into contact when the tire is in contact with the ground, and is, for example, a narrow groove with a width of less than 2 mm (see FIG. 7(b)).

The chamfer 44 is provided on the groove wall 43a1 of the pair of groove walls 43a that form the sipe 43, which faces the inside of the bend of the inner shoulder narrow groove 40 (the side that forms the minor angle). The chamfer 44 has a surface that is inclined with respect to the groove wall 43a near the ground contact surface 8a so as to widen the width of the opening end of the sipe 43 toward the ground contact surface 8a. The chamfer 44 is a surface that continues from the ground contact surface 8a to the back side of the sipe 43.

The chamfer 44 may reach the ground surface 8a, or a small step wall 44a (e.g., about 0.5 mm) may be formed between the chamfer 44 and the ground surface 8a. The chamfer 44 does not reach the bottom of the inner shoulder narrow groove 40. By providing the chamfer 44, the width of the inner shoulder narrow groove 40 gradually increases as it approaches the ground surface 8a.

The width of the chamfer 44 gradually increases from the tip of the inner shoulder narrow groove 40 toward the bending point 41, and is widest at the bending point 41. As shown in Figures 4 and 7(a), the slit 42 does not have a chamfer 44.

In this embodiment, the multiple inner shoulder narrow grooves 40 that make up the inner shoulder narrow groove row are formed to have the same shape.

(7) Outer shoulder narrow groove 50
2 and 8 , the outer shoulder narrow groove 50 extends in the shoulder rib 16 in the tire axial direction W. One end of the outer shoulder narrow groove 50 is closed within the shoulder rib 26, and the other end opens from the ground contact edge 18 toward the tire axial direction outside.

2 and 8, the outer shoulder narrow groove 50 has a sipe 53 and a chamfer 54. The sipe 53 is a groove in which at least a portion of the opposing groove wall 53a abuts when the tire is in contact with the ground, and means, for example, a narrow groove with a width of less than 2 mm (see FIG. 9). The sipe 53 has a bending point 51 on its axially inner side, and is bent at the bending point 51 when viewed from the tire radially outer side RDo. The axially outer portion of the sipe 53 beyond the bending point 51 extends in the tire axial direction W. Here, extending in the tire axial direction WD includes not only the case where the extension direction of the sipe 53 is parallel to the tire axial direction WD, but also the case where the angle with respect to the tire axial direction WD is 5 degrees or less.

The chamfer 54 is provided over the entire tire axial direction WD of the groove wall 53a that faces the inner side (the side that forms the minor angle) of the bend of the sipe 53 out of the pair of groove walls 53a that form the sipe 53. As shown in FIG. 9, the chamfer 54 has a surface that is inclined with respect to the groove wall 53a near the ground contact surface 8a so as to widen the width of the opening end of the sipe 53 toward the ground contact surface 8a. The chamfer 54 is a surface that continues from the ground contact surface 8a to the back side of the sipe 53.

The chamfer 54 may reach the ground surface 8a, or a small step wall 54a (e.g., about 0.5 mm) may be formed between the chamfer 54 and the ground surface 8a. The chamfer 54 does not reach the bottom of the outer shoulder narrow groove 50. By providing the chamfer 54, the width of the outer shoulder narrow groove 50 gradually increases as it approaches the ground surface 8a.

The width of the chamfer 54 gradually increases from the ground contact edge 18 toward the bending point 51, and is widest at the bending point 51. The chamfer 54 is also provided axially inward of the bending point 51 of the sipe 53, continuing from the bending point 51.

The depth and shape of the sipes 53 of such outer shoulder narrow grooves 50 vary depending on their positional relationship with the division marks 19 formed on the surface of the tread rubber 8.

Specifically, as shown in Figures 2, 3, 8 and 9, the outer shoulder narrow groove 50 includes a first outer shoulder narrow groove 50A with a sipe 53A and a chamfer 54A, a divided end narrow groove 50B1 with a sipe 53B1 and a chamfer 54B1, an end vicinity narrow groove 50B2 with a sipe 53B2 and a chamfer 54B2, and a third outer shoulder narrow groove 50C with a sipe 53C and a chamfer 54C.

The first outer shoulder narrow groove 50A is provided in the first circumferential end region R1, and is an outer shoulder narrow groove 50 in which the chamfer 54A is provided on the groove wall 53Aa on the central region Rm side of the sipe 53A.

The dividing end narrow groove 50B1 is provided in the second circumferential end region R2, and is an outer shoulder narrow groove 50 in which the chamfer 54B1 is provided on the groove wall 53B1a on the dividing trace 19 side of the sipe 53B1.

The end-near narrow groove 50B2 is provided in the first circumferential end region R1 on the outside of the second circumferential end region R2, and is an outer shoulder narrow groove 50 in which the chamfer 54B2 is provided on the groove wall 53B2a on the division trace 19 side of the sipe 53B2.

The dividing end narrow groove 50B1 and the end vicinity narrow groove 50B2 are both outer shoulder narrow grooves 50 that constitute the second outer shoulder narrow groove. The second outer shoulder narrow groove is an outer shoulder narrow groove 50 that is provided in the first circumferential end region R1 and has chamfers 54B1, 54B2 on the groove walls 53B1a, 53B2a on the dividing trace 19 side of the sipes 53B1, 53B2.

The third outer shoulder narrow groove 50C is an outer shoulder narrow groove 50 provided in the central region Rm. In the third outer shoulder narrow groove 50C, a chamfer 54C is provided on one groove wall 53Ca of the sipe 53C. The sipe 53B2 of the end-nearby narrow groove 50B2 and the sipe 53C of the third outer shoulder narrow groove 50C have the same shape. The portions of both sipes 53B2 and 53C on the ground edge edge 18 side from the bending point 51 are three-dimensional sipes as shown in Figures 9 and 10.

The sipes 53A of the first outer shoulder narrow groove 50A are three-dimensional sipes in the portion closer to the ground edge 18 than the bending point 51, like the sipes 53B2 of the end-near narrow groove 50B2 and the sipes 53C of the third outer shoulder narrow groove 50C. The sipes 53A are shallower than the sipes 53B1 and 53B2 of the second outer shoulder narrow groove (division end narrow groove 50B1 and end-near narrow groove 50B2) and the sipes 53C of the third outer shoulder narrow groove 50C. The depth of the sipe 53A (the distance from the connection position PA between the chamfer 54A and the sipe 53A to the bottom surface of the sipe 53A) is preferably 50% to 70% of the depth of the sipe 53B1 of the dividing end narrow groove 50B1 (the distance from the connection position PB1 between the chamfer 54B1 and the sipe 53B1 to the bottom surface of the sipe 53B1), the depth of the sipe 53B2 of the end vicinity narrow groove 50B2 (the distance from the connection position PB2 between the chamfer 54B2 and the sipe 53B2 to the bottom surface of the sipe 53B2), or the depth of the sipe 53C of the third outer shoulder narrow groove 50C (the distance from the connection position PC between the chamfer 54C and the sipe 53C to the bottom surface of the sipe 53C).

The sipe 53B1 of the dividing end narrow groove 50B1 is a two-dimensional sipe as shown in Figs. 9 and 11 at the portion closer to the ground edge 18 than the bending point 51. This sipe 53B1 is provided at the same depth as the sipe 53B2 of the end vicinity narrow groove 50B2 and the sipe 53C of the third outer shoulder narrow groove 50C.

Here, a three-dimensional sipe refers to a sipe that has an inner wall surface that is curved in the axial direction of the sipe when viewed in a cross section perpendicular to the length of the sipe. In other words, it is a sipe whose shape changes in the depth direction of the sipe.

As shown in FIG. 10(c), the three-dimensional sipe of this embodiment is wavy with peaks 57 and valleys 58 on a cross section parallel to the ground contact surface 8a at a location deeper than the connection positions PA, PB2, and PC between the chamfers 54A, 54B2, and 54C and the sipes 53A, 53B2, and 53C. As shown in FIG. 10(b), the peaks 57 and valleys 58 extend in a zigzag pattern in the depth direction of the three-dimensional sipe. Compared to two-dimensional sipes, three-dimensional sipes have a stronger meshing force between the opposing sipe inner wall surfaces, which increases the rigidity of the land portion of the tread.

A two-dimensional sipe is a sipe that has a linear inner wall surface in a cross section perpendicular to the sipe length direction. As shown in FIG. 11(c), the two-dimensional sipe of this embodiment is wavy, consisting of peaks 59 and valleys 60, on a cross section taken along a plane parallel to the ground contact surface 8a at the connection position PB1 between the chamfer 54B1 and the sipe 53B1. As shown in FIG. 11(b), the peaks 59 and valleys 60 extend without changing in the depth direction of the sipe.

In this embodiment, as shown in FIG. 2, the outer shoulder narrow grooves 50 are arranged in opposite directions in the tire circumferential direction CD on both sides of the tire axial direction WD. Therefore, in one first circumferential end region R1, a first outer shoulder narrow groove 50A is provided on one side of the tire axial direction WD, and a division end narrow groove 50B1 and an end vicinity narrow groove 50B2 are provided on the other side of the tire axial direction WD.

(8) Vulcanization molding mold 100
Next, the vulcanization molding die 100 of this embodiment will be described with reference mainly to Fig. 12 to Fig. 14. In the following description, the tire radial direction RD, tire axial direction WD, and tire circumferential direction CD of the pneumatic tire 1 will also be described as the tire radial direction RD, tire axial direction WD, and tire circumferential direction CD of the vulcanization molding die 100.

The vulcanization mold 100 is a mold that vulcanizes and molds an unvulcanized green tire (raw tire) into a shape similar to the pneumatic tire 1 described above. The vulcanization mold 100 is attached to a vulcanizer via a container and constitutes a tire vulcanization device.

The vulcanization mold 100 comprises a plurality of sectors 102 arranged in a circular pattern, a pair of side plates 104 provided on both sides of the tire axial direction WD, and a pair of bead rings 106. The vulcanization mold 100 forms a cavity 108, which is a molding space for the pneumatic tire 1, inside the plurality of sectors 102, the pair of side plates 104, and the pair of bead rings 106.

The sectors 102 are molds that form the tread 3 of the pneumatic tire 1, and are divided into multiple parts in the tire circumferential direction CD. Note that, although FIG. 13 illustrates a vulcanization molding mold 100 that is composed of six sectors 102, the number of divisions of the vulcanization molding mold 100 is not limited to this.

The sectors 102 are arranged so that they can expand and contract in the radial direction of the tire (tire radial direction RD). In the mold closed state where each sector 102 is arranged in the mold closed position, the sectors 102 are gathered together and the circumferential ends 102a of the sectors 102 are in contact with each other to form a ring. In other words, the circumferential ends 102a of the sectors 102 are the division positions of the sectors 102.

A sector 102 corresponds to a portion of a tread pattern divided at a fixed or arbitrary pitch, and has a tread molding surface 110 for forming a portion of the tread pattern.

In addition, as shown in FIG. 13, the sector 102 is set with a first sector end region SR1, a second sector end region SR2, and a central region SRm corresponding to the first circumferential end region R1, the second circumferential end region R2, and the central region Rm set on the surface of the tread rubber 8 of the pneumatic tire 1. That is, in one sector 102, the range from the circumferential end 102a of the sector 102 to the first angle θ1 toward the center of the tire circumferential direction CD is set as the first sector end region SR1, the range from the circumferential end 102a of the sector 102 to the second angle θ2 smaller than the first angle θ1 toward the center of the tire circumferential direction CD is set as the second sector end region SR2, and the region sandwiched between the first sector end regions SR1 is set as the sector central region SRm.

The tread molding surface 110 of the sector 102 is provided with protrusions (not shown) connected in the tire circumferential direction CD for forming the main grooves 10, 12, 12 in the tread 3 of the pneumatic tire 1, protrusions (not shown) for forming the inner center narrow groove 20, the outer center narrow groove 30, and the inner shoulder narrow groove 40, and narrow groove forming protrusions 120 for forming the outer shoulder narrow groove 50.

The narrow groove forming protrusions 120 include sipe blades 121 that form the sipes 53 and chamfer forming protrusions 122 that form the chamfers 54, and are provided at intervals in the tire circumferential direction CD.

As shown in FIG. 14, the sipe blade 121 is a plate-shaped member made of a metal material, and is attached to the sector 102 so that a portion of the blade is fitted into a groove 111 formed in the sector 102 and protrudes from the tread molding surface 110.

The chamfer forming protrusion 122 is a protrusion that is integral with the sector 102. The chamfer forming protrusion 122 protrudes from the tread molding surface 110 toward the cavity 108 so as to contact the root of the sipe blade 121.

The shape of the sipe blade 121 of such a fine groove forming protrusion 120 varies depending on its positional relationship with the circumferential end (division position) 102a of the sector 102.

Specifically, as shown in Figures 13 and 14, the narrow groove forming projection 120 has a first narrow groove forming projection 120A having a sipe blade 121A and a chamfer forming projection 122A, a sector end narrow groove forming projection 120B1 having a sipe blade 121B1 and a chamfer forming projection 122B1, an end narrow groove forming projection 120B2 having a sipe blade 121B2 and a chamfer forming projection 122B2, and a third narrow groove forming projection 120C having a sipe blade 121C and a chamfer forming projection 122C.

The first narrow groove forming protrusion 120A is provided in the first sector end region SR1, and the chamfer forming protrusion 122A is a narrow groove forming protrusion 120 provided on the sector center region SRm side of the sipe blade 121A.

The sector end fine groove forming protrusion 120B1 is provided in the second sector end region SR2, and the chamfer forming protrusion 122B1 is a fine groove forming protrusion 120 provided on the circumferential end 102a side of the sector of the sipe blade 121B1.

The end narrow groove forming protrusion 120B2 is provided in the first sector end region SR1 outside the second sector end region SR2, and the chamfer forming protrusion 122B2 is a narrow groove forming protrusion 120 provided on the circumferential end 102a side of the sector of the sipe blade 121B2.

The sector end narrow groove forming protrusion 120B1 and the end narrow groove forming protrusion 120B2 are both narrow groove forming protrusions 120 that constitute the second narrow groove forming protrusion. The second narrow groove forming protrusion is a narrow groove forming protrusion 120 that is provided in the first sector end region SR1, and the chamfer forming protrusions 122B1 and 122B2 are provided on the circumferential end 102a side of the sector of the sipe blades 121B1 and 121B2.

The third narrow groove forming protrusion 120C is provided in the sector central region SRm, and the chamfer forming protrusion 122CD is a narrow groove forming protrusion 120 provided on one side of the sipe blade 121C.

The end narrow groove forming projection 120B2 and the third narrow groove forming projection 120C have the same shape. The sipe blade 121B2 of the end narrow groove forming projection 120B2 and the sipe blade 121C of the third narrow groove forming projection 120C have a portion that protrudes into the cavity 108 from the chamfer forming projections 122B2, 122C, which is a three-dimensional shape portion that has a waveform extending in the extension direction (tire axial direction WD) of the sipe blade 121B2 and the sipe blade 121C in a cross-sectional view perpendicular to the protruding direction, and the shape changes in the protruding direction. These sipe blades 121B2 and sipe blades 121C are intended to form three-dimensional sipes in the tread 3.

The sipe blade 121A of the first narrow groove forming projection 120A, like the sipe blade 121B2 of the end narrow groove forming projection 120B2 and the sipe blade 121C of the third narrow groove forming projection 120C, has a portion that protrudes from the chamfer forming projection 122A into the cavity 108, which is a three-dimensional portion whose shape changes in the protruding direction and forms a wave shape extending in the extension direction of the sipe blade 121A1 (tire axial direction WD) in a cross-sectional view perpendicular to the protruding direction. The sipe blade 121A of the first narrow groove forming projection 120A is for forming a three-dimensional sipe in the tread 3.

The sipe blade 121A of the first narrow groove forming projection 120A protrudes less from the tread molding surface 110 than the sipe blades 121B1 and 121B2 of the second narrow groove forming projection (sector end narrow groove forming projection 120B1 and end narrow groove forming projection 120B2) and the sipe blade 121C of the third narrow groove forming projection 120C.

The sipe blade 121B1 of the sector end narrow groove forming projection 120B1 has a portion that protrudes from the chamfer forming projection 122B1 into the cavity 108, which is a two-dimensional portion that forms a wave shape extending in the extension direction of the sipe blade 121B1 (tire axial direction WD) in a cross section perpendicular to the protruding direction, and extends linearly without changing shape in the protruding direction. The sipe blade 121B1 of the sector end narrow groove forming projection 120B1 is intended to form a two-dimensional sipe in the tread 3.

The sipe blade 121A of the first narrow groove forming projection 120A is formed of a material with higher strength than the sipe blade 121B1 of the sector end narrow groove forming projection 120B1, the sipe blade 121B2 of the end narrow groove forming projection 120B2, and the sipe blade 121C of the third narrow groove forming projection 120C. Here, the proof strength is the "stress when the plastic elongation becomes equal to the specified percentage of the extensometer gauge length Le (3.5)" as specified in "3.10.3 Proof strength (offset method), Rp (proof strength, plastic extension)" of JIS Z 2241:2022 (Metal material tensile test method).

The material of the sipe blade 121A of the first narrow groove forming projection 120A is preferably one having a strength 300% or more greater than that of the sipe blade 121B1 of the sector end narrow groove forming projection 120B1, the sipe blade 121B2 of the end narrow groove forming projection 120B2, and the sipe blade 121C of the third narrow groove forming projection 120C. For example, the material of the sipe blade 121A can be SUS631 or an alloy having a similar composition, and the material of the other sipe blades 121B1, 121B2, and 121C can be SUS304 or an alloy having a similar composition. As a specific numerical value, it is preferable that the strength of the sipe blade 121A of the first narrow groove forming projection 120A is 2205 N/mm2 or more. It is preferable that the yield strength of the sipe blade 121B1 of the sector end narrow groove forming projection 120B1, the sipe blade 121B2 of the end narrow groove forming projection 120B2, and the sipe blade 121C of the third narrow groove forming projection 120C is 1080 N/mm2 or more.

(9) Manufacturing Method of Pneumatic Tire 1 Next, a manufacturing method of the pneumatic tire 1 using the vulcanization molding die 100 according to the embodiment will be described.

An unvulcanized green tire is produced by combining various rubber components that make up the pneumatic tire 1 with various reinforcing components such as carcass plies and belt plies. Then, as shown in FIG. 12, the produced green tire is set in the vulcanization molding mold 100 and the mold is closed, and then the bladder 109 placed on the inside is expanded to press the green tire against the inner surface of the mold and maintain it in a heated state, thereby vulcanizing and molding the unvulcanized tire.

When the green tire is vulcanized and molded, the multiple sectors 102 are moved radially outward to open the vulcanization mold 100, and the vulcanized pneumatic tire 1 is removed.

(10) Effects In this embodiment, among the first outer shoulder narrow groove 50A and the second outer shoulder narrow groove (division end narrow groove 50B1 and end-nearby narrow groove 50B2) provided in the first circumferential region where a relatively large pull-out resistance occurs when the mold is opened, the sipes 53A of the first outer shoulder narrow groove 50A are set to be shallower than the sipes 53B1, 53B2 of the division end narrow groove 50B1 and end-nearby narrow groove 50B2. As a result, in this embodiment, the number of shallow sipes is reduced to suppress the occurrence of uneven wear, while deformation of the sipe blades 121 forming the sipes 53 of the outer shoulder narrow groove 50 is suppressed, and defective tire shapes can be suppressed.

That is, when the vulcanization molding die 100 is opened, in the vicinity of the circumferential end 102a of the sector 102, the rear of the movement direction of the sector 102 (the front of the relative movement direction of the pneumatic tire 1 with respect to the sector 102) is inclined toward the circumferential end 102a of the sector 102 with respect to the protruding direction (tire radial direction) of the sipe blade 121. Therefore, the tip portion of the sipe blade 121 is pressed against the circumferential end 102a of the sector 102 by the vulcanized pneumatic tire 1. The closer the sipe blade 121 is provided to the circumferential end 102a of the sector 102, the greater the pressing force acting on the sipe blade 121 when the die is opened, so the sipe blades 121A, 121B1, and 121B2 provided in the first sector end region SR1 are subjected to a relatively large pressing force when the die is opened.

Among the sipe blades 121A, 121B1, and 121B2 provided in the first sector end region SR1, the sipe blade 121A of the first narrow groove forming projection 120A in which the chamfer forming projection 122 is provided on the sector central region SRm side is pressed in a direction away from the chamfer forming projection 122A when the mold is opened. In this embodiment, the protrusion amount of the sipe blade 121A from the tread molding surface 110 is set to be smaller than the other sipe blades 121B1, 121B2, and 121C, so that the sipe blade 121A is less likely to deform away from the chamfer forming projection 122A, and a gap is less likely to occur between the sipe blade 121A and the chamfer forming projection 122A. Therefore, it is possible to suppress the occurrence of problems such as damage to the sipe blade 121A and rubber entering the gap generated between the sipe blade 121A and the chamfer forming projection 122A.

On the other hand, the sipe blades 121B1, 121B2 of the second narrow groove forming projections, in which the chamfer forming projections 122 are provided on the circumferential end 102a side of the sector 102, are pressed in a direction toward the chamfer forming projections 122B1, 122B2 when the mold is opened, so that the pressing force received from the pneumatic tire 1 can be distributed to the chamfer forming projections 122B1, 122B2. The sipe blades 121B1, 121B2 are provided near the circumferential end 102a of the sector 102, so they receive a relatively large pressing force when the mold is opened, but since the pressing force can be distributed as described above, they are unlikely to deform even if the amount of protrusion from the tread molding surface 110 is set to the same extent as the sipe blades 121C of the third narrow groove forming projections 120C provided in the sector central region SRm.

In this embodiment, the sipes 53A of the first outer shoulder narrow groove 50A are three-dimensional sipes, so that the sipe blades 121A forming the sipes 53A have a three-dimensional shape, which increases the rigidity and suppresses deformation of the sipe blades 121A. In addition, the sipes 53B1 of the dividing end narrow groove 50B1 provided in the second circumferential end region R2 of the second outer shoulder narrow groove are two-dimensional sipes, so that the resistance when the sipe blades 121B1 are pulled out of the pneumatic tire 1 during mold opening is small, and damage to the rubber can be suppressed.

(11) Modifications Next, modifications will be described. Various modifications can be made to the above embodiment without departing from the spirit of the invention. Several modifications will be described below, and any one of the modifications described below may be applied to the above embodiment, or any two or more of the modifications described below may be applied in combination. In addition to the following modifications, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention.

(11-1) Modification Example 1
In the embodiment described above, the chamfer 54 is provided in the outer shoulder narrow groove 50 over the entire extension direction of the sipe 53 (the entire tire axial direction WD). However, as shown in FIG. 15( a), the chamfer 154 may be provided only on a portion of the groove wall 53 a, and no chamfer may be provided on the remaining portion.

In the first outer shoulder narrow groove 50A provided in the first circumferential end region R1, if chamfer 154 is provided only on a portion of the groove wall 53a and the remaining portion is not chamfered, the sipe 53A may be shallower in the portion with chamfer 154 than in the portion without chamfer 154, as shown in FIG. 15(b).

When changing the depth of the sipe 53A of the first outer shoulder narrow groove 50A in its extension direction, the depth of the sipe 53A can be changed within the region P. The region P is a range of 5 mm or less in the extension direction of the sipe 53, centered on the boundary 154E of the chamfer 154, and preferably a range of 3 mm or less.

In this modified example, the sipes 53A are shallow in the areas where the chamfers 154 are provided, and the areas where the chamfers 154 are not provided are the same depth as the sipes 53B1 of the dividing end narrow grooves 50B1, the sipes 53B2 of the narrow grooves near the ends 50B2, and the sipes 53C of the third outer shoulder narrow grooves 50C. This reduces the shallow sipe depth areas and suppresses uneven wear, while also preventing damage to the sipe blades 121A and problems such as rubber getting in between the sipe blades 121A and the chamfer forming protrusions 122A.

(11-2) Modification Example 2
In the above embodiment, the sipes 53A, 53B2, and 53C in the first outer shoulder narrow groove 50A, the end-near narrow groove 50B2, and the third outer shoulder narrow groove 50C are three-dimensional sipes, and the sipe 53B1 in the dividing end narrow groove 50B1 is a two-dimensional sipe, but the sipes 53A, 53B1, 53B2, and 53C may all be three-dimensional sipes, two-dimensional sipes, or sipes whose shape does not change in the protruding direction and extension direction.

(11-3) Modification Example 3
In the embodiment described above, for the outer shoulder narrow groove 50, the depth and shape of the sipes 53 are changed depending on their positional relationship with the division marks 19 formed on the surface of the tread rubber 8. However, for the other narrow grooves 20, 30, 40, the depth and shape of the sipes 23, 33, 43 may also be changed depending on their positional relationship with the division marks 19, similar to the outer shoulder narrow groove 50.

That is, the depth of the sipes of the fine grooves 20, 30, 40 provided in the first circumferential end region R1 may be shallower than the depth of the sipes of the fine grooves 20, 30, 40 provided in the second circumferential end region R2 and the central region Rm. Also, the sipes of the fine grooves 20, 30, 40 provided in the first circumferential end region R1 may be three-dimensional sipes, and the sipes of the fine grooves 20, 30, 40 provided in the second circumferential end region R2 may be two-dimensional sipes.

In addition, for narrow grooves having sipes whose extension angle with respect to the tire axial direction WD is 5 degrees or less, the depth and shape of the sipes may be changed depending on the positional relationship with the division marks 19, and for narrow grooves having sipes whose extension angle with respect to the tire axial direction WD is greater than 5 degrees, the depth and shape of the sipes may be formed to be the same shape without changing in the tire circumferential direction.

1...pneumatic tire, 8...tread rubber, 8a...ground contact surface, 10...center main groove, 12...shoulder main groove, 14...center rib, 16...shoulder rib, 18...ground contact, 19...division marks, 20...inner center narrow groove, 30...outer center narrow groove, 40...inner shoulder narrow groove, 50...outer shoulder narrow groove, 50A...first outer shoulder narrow groove, 50B1...division end narrow groove, 50B2...narrow groove near end, 50C...third outer shoulder narrow groove, 51...bending point, 53...sipe, 54...chamfer, 100...vulcanization mold, 102...sector, 102a...division position, 104...upper side plate, 106...lower side plate , 108...cavity, 110...tread molding surface, 111...sipe blade groove, 120...narrow groove forming protrusion, 120A...first narrow groove forming protrusion, 120B...second narrow groove forming protrusion, 120B1...sector end narrow groove forming protrusion, 120B2...end narrow groove forming protrusion, 120C...narrow groove forming protrusion, 121...sipe blade, 121A...sipe blade, 121B1...sipe blade, 121B2...sipe blade, 121C...sipe blade, 122...chamfer forming protrusion, R1...first circumferential end region, R2...second circumferential end region, Rm...center region, SR1...first sector end region, SR2...second sector end region, SRm...center region

Claims (6)

In a pneumatic tire having a tread formed by a plurality of sectors divided in the tire circumferential direction,
The tread includes a plurality of narrow grooves spaced apart in the tire circumferential direction and division marks provided at division positions of the sectors,
The narrow groove includes a sipe extending in the tire axial direction and a chamfer that widens the width of an open end of the sipe toward the ground contact surface,
Among the regions sandwiched between the division marks adjacent to each other in the tire circumferential direction, a range from the division marks toward the tire circumferential center at a first angle is defined as a first circumferential end region, and a region sandwiched between the first circumferential end regions is defined as a central region.
The plurality of narrow grooves provided in the first circumferential end region include a first narrow groove in which the chamfer is provided on a groove wall of the sipe on the central region side, and a second narrow groove in which the chamfer is provided on a groove wall of the sipe on the division trace side,
The pneumatic tire, wherein the sipes of the first narrow groove are shallower than the sipes of the second narrow groove. The pneumatic tire of claim 1, wherein the first angle is 15 degrees or less. The first narrow groove is provided with the chamfer at a portion in an extension direction of the sipe,
3. The pneumatic tire according to claim 1, wherein in the first narrow groove, the sipes in the chamfered portion are shallower than the sipes in the non-chamfered portion, and the sipes in the non-chamfered portion have the same depth as the sipes in the second narrow groove. In a region sandwiched between the division traces adjacent to each other in the tire circumferential direction, a range from the division trace toward the tire circumferential center to a second angle smaller than the first angle is defined as a second circumferential end region,
the second narrow groove includes a divided end narrow groove provided in the second circumferential end region,
The sipes of the first narrow groove are three-dimensional sipes whose shape changes in a depth direction,
The pneumatic tire according to claim 1 , wherein the sipes of the division end narrow groove are two-dimensional sipes having a constant shape in a depth direction and are deeper than the sipes of the first narrow groove. A vulcanization molding die including a plurality of sectors divided in a tire circumferential direction and a plurality of fine groove forming projections provided on a tread molding surface of each of the sectors,
The narrow groove forming projection includes a sipe blade that forms a sipe extending in the tire axial direction, and a chamfer forming projection provided in contact with a root of the sipe blade,
In one of the sectors, a range from a sector circumferential end toward a tire circumferential center at a first angle is defined as a first sector end region, and a region between the first sector end regions is defined as a sector central region.
The plurality of narrow groove forming projections provided in the first sector end region include a first narrow groove forming projection in which the chamfer forming projection is provided on the sector central region side of the sipe blade, and a second narrow groove forming projection in which the chamfer forming projection is provided on the sector circumferential end side of the sipe blade,
a vulcanization molding die, wherein the sipe blade of the first narrow groove forming projection has a smaller protrusion amount from the tread molding surface than the sipe blade of the second narrow groove forming projection. The vulcanization molding die according to claim 5, wherein the sipe blade of the first narrow groove forming projection is made of a material having a higher strength than the sipe blade of the second narrow groove forming projection.

Images