JP7679649B2 - tire - Google Patents

Description

The present invention relates to a tire.

In recent years, in tires with a tread structure of two or more layers, Tread Groove Cracks (TGC) have been occurring at the bottom of the circumferential grooves of the tread, and cracks at the bottom of the grooves have become an issue.

The present invention aims to solve the above problems and provide a tire that improves the ability to suppress the progression of cracks at the bottom of the grooves at the end of the running period (TGC resistance).

The present invention provides a tire having at least one circumferential groove and a tread portion having two or more rubber layers,
The rubber layer has at least a rubber layer 1 disposed on an outermost surface of the tread, and a rubber layer 2 disposed adjacent to the rubber layer 1 on an inner side in the tire radial direction,
A groove width L0 (mm) at the outermost surface in the radial direction of the tire in a cross-sectional view of the circumferential groove and a groove width L95 (mm) at a position 95% from the outermost surface in the radial direction of the tire of the circumferential groove satisfy the following formula (1),
(1) 0.00<L95/L0<1.00
The hardnesses H1 and H2 of the rubber layer 1 and the rubber layer 2 at the groove bottoms of the circumferential grooves satisfy the following formula (2):
(2) H1>H2
The rubber layer 1 at the groove bottom of the circumferential groove relates to a tire in which a slope a of log _e (dc/dn [mm/cycle]) to log _e (tear energy [J]) is 2.0 or less within a log _e (tear energy [J]) range of 0.0 to 0.3.
(where dc/dN represents the value obtained by differentiating the crack length with respect to cycleN (the number of times the voltage is applied).)

It is preferable that the tire satisfies the following formula.
0.10≦L95/L0≦0.30

In the tire, it is preferable that the L95/L0 and the slope a satisfy the following formulas.
{a/(L95/L0)}≦10.0

In the tire, it is preferable that the L95/L0, the inclination a, and the groove depth D of the circumferential groove satisfy the following formula.
{a/(L95/L0)}/D≦2.00

It is preferable that the tire has L0 of 5 to 20 mm.

It is preferable that the tire has a groove depth D of the circumferential groove of 6.0 to 12.0 mm.

In the tire, it is preferable that H1 and H2 satisfy the following formula.
1.04≦H1/H2≦1.20

It is preferable that the H2 of the tire is 44 to 53.

According to the present invention, in a tire having at least one circumferential groove and a tread portion having at least two or more rubber layers, including a rubber layer 1 arranged on the outermost surface of the tread and a rubber layer 2 arranged adjacent to the inner side of the rubber layer 1 in the tire radial direction, the tire satisfies the above formulas (1) and (2) and the slope a is 2.0 or less, so that a tire having excellent TGC resistance performance at the end of the running period can be provided.

FIG. 1 is a cross-sectional view showing a portion of a pneumatic tire. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the tread 4 of the tire 2 of FIG. 1 is an example of a graph obtained by logarithmically transforming tear energy [J] and crack growth rate [mm/cycle]. 13A is a graph showing the relationship between cycleN (number of applications) and crack length, and FIG. 13B is an example of a graph obtained by differentiating the crack length with respect to cycleN in FIG.

The present invention relates to a tire having at least one circumferential groove and a tread portion having two or more rubber layers, including at least a rubber layer 1 disposed on the outermost surface of the tread and a rubber layer 2 disposed adjacent to the inner side in the tire radial direction of the rubber layer 1, which satisfies the above formulas (1) and (2), and the rubber layer 1 at the groove bottom of the circumferential groove has a slope a of crack growth tendency [mm/cycle] versus tear energy [J] of ^2.0 or less in a tear energy range of 1.0×10 0.1 to 2.0×10 ^0.1 [J]. The tire has excellent TGC resistance at the end of running.

The reason why such an effect is obtained is not clear, but is presumed to be as follows.
As a method for ensuring drainage while ensuring the rigidity of the tread portion, a method of making the circumferential grooves V-shaped and widening the block portion radially inward is considered, but it is considered that the larger the V-shape angle, the more deformation is concentrated at the groove bottom during running and the larger the deformation amount is. Therefore, by making the "slope a of the crack growth tendency [mm/cycle] with respect to the tear energy [J] 2.0 or less in the range of tear energy 1.0×10 ^0.1 to 2.0×10 ^0.1 [J]", the parameter (slope a) of the crack growth tendency with respect to deformation is reduced as the groove width (L0) on the tread surface increases with respect to the groove width (L95) at the groove bottom, so that cracks are less likely to occur due to repeated deformation, and TGC is less likely to occur even at the end of running. In addition, by making the hardness H2 of the second rubber layer 2 disposed adjacent to the outermost rubber layer 1 on the radially inner side of the tire smaller than the hardness H1 of the outermost rubber layer 1 at the bottom of the circumferential grooves, it is believed that stress concentration in the outermost rubber layer 1 is alleviated, improving the TGC resistance. Therefore, it is presumed that the TGC resistance of the tire at the end of the running period is significantly improved.

In this way, the tire satisfies "0.00<L95/L0<1.00" and has a configuration in which "H1>H2" and "rubber layer 1 at the groove bottom of the circumferential groove has a slope a of log _e (dc/dn [mm/cycle]) relative to log _e (tear energy [J]) of 2.0 or less in the range of log _e (tear energy [J]) of 0.0 to 0.3 (where dc/dN represents the value obtained by differentiating crack length with cycleN (number of applications))")," thereby solving the problem (objective) of improving TGC resistance at the end of running. That is, the parameters "H1>H2" and "In the rubber layer 1 at the groove bottom of the circumferential groove, the slope a of log _e (dc/dn [mm/cycle]) relative to log _e (tear energy [J]) is 2.0 or less in the range of log _e (tear energy [J]) of 0.0 to 0.3 (where dc/dN represents the value obtained by differentiating crack length with cycleN (number of applications))" do not define the problem (purpose), and the problem of the present application is to improve TGC resistance performance at the end of running, and a configuration that satisfies the parameters is used as a means to achieve this.

The present invention will be described in detail below based on one preferred embodiment, with reference to the drawings as appropriate, but the present invention is not limited to this embodiment and includes all tires within the scope of the claims.

Figure 1 shows an example of a cross-sectional view of a pneumatic tire 2. In Figure 1, the up-down direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. In Figure 1, the dashed dotted line CL represents the equatorial plane of the tire 2. The shape of this tire 2 is symmetrical with respect to the equatorial plane, except for the tread pattern.

The tire 2 includes a tread 4, a pair of sidewalls 6, a pair of wings 8, a pair of clinches 10, a pair of beads 12, a carcass 14, a belt 16, a band 18, an inner liner 20, and a pair of chafers 22. The tire 2 is a tubeless type. The tire 2 is mounted on a passenger vehicle.

The tread 4 has a shape that is convex outward in the radial direction. The tread 4 forms a tread surface 24 that comes into contact with the road surface. The tread 4 has circumferential grooves 26. The circumferential grooves 26 are grooves that are provided along the circumferential direction of the tire. The circumferential grooves 26 may be zigzag, curved, or straight, as long as they are connected in the circumferential direction. The circumferential grooves 26 form a tread pattern. The tread 4 has a base layer 28 and a cap layer 30. The base layer 28 is located adjacent to the cap layer 30 on the radially inner side of the tire. In the embodiment shown in FIG. 1, the cap layer 30 corresponds to the "rubber layer 1 arranged on the outermost surface of the tread" and the base layer 28 corresponds to the "rubber layer 2 arranged adjacent to the rubber layer 1 on the radially inner side of the tire".

Note that while FIG. 1 shows an example of a two-layer tread 4 consisting of a cap layer 30 and a base layer 28, the present invention is not limited to this and can be applied to any multi-layer tread having two or more layers. In the case of a tread 4 having a three or more layer structure, the rubber layer arranged on the outermost surface of the tread constitutes rubber layer 1, and the rubber layer arranged adjacent to the inner side in the tire radial direction of rubber layer 1 arranged on the outermost surface of the tread constitutes rubber layer 2.

In the tire 2 of FIG. 1, each sidewall 6 extends radially inward from the end of the tread 4. The radially outer portion of the sidewall 6 is joined to the tread 4. The radially inner portion of the sidewall 6 is joined to the clinch 10. The sidewall 6 is made of, for example, crosslinked rubber that has excellent cut resistance and weather resistance.

Each wing 8 is located between the tread 4 and the sidewall 6. The wing 8 is bonded to each of the tread 4 and the sidewall 6. The wing 8 is made of, for example, a crosslinked rubber with excellent adhesive properties.

Each clinch 10 is located approximately radially inward of the sidewall 6. In the axial direction, the clinch 10 is located outward of the bead 12 and the carcass 14. The clinch 10 is made of, for example, crosslinked rubber with excellent abrasion resistance.

Each bead 12 is located axially inside the clinch 10. The bead 12 includes a core 32 and an apex 34 extending radially outward from the core 32. The core 32 is ring-shaped and includes a wound non-stretchable wire. A typical material for the wire is, for example, steel. The apex 34 tapers radially outward. The apex 34 is made of, for example, high-hardness crosslinked rubber.

The carcass 14 has a carcass ply 36. In this tire 2, the carcass ply 36 is bridged between the beads 12 on both sides and runs along the tread 4 and sidewall 6. The carcass ply 36 is folded back around each core 32 from the inside to the outside in the axial direction. By this folding back, the carcass ply 36 has a main portion 36a and a pair of folded back portions 36b. That is, the carcass ply 36 has a main portion 36a and a pair of folded back portions 36b.

Although not shown, the carcass ply 36 is made of, for example, a large number of parallel cords and a topping rubber. The absolute angle that each cord makes with respect to the equatorial plane is preferably 75° to 90°. The cords are made of, for example, organic fibers, and specific examples include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

The belt 16 is located radially inward of the tread 4. The belt 16 is laminated with the carcass 14. The belt 16 reinforces the carcass 14. The belt 16 is composed of an inner layer 38 and an outer layer 40.

Although not shown, each of the inner layer 38 and the outer layer 40 is made of, for example, a number of parallel cords and a topping rubber. Each cord is inclined with respect to the equatorial plane. The typical absolute value of the inclination angle is 10° or more and 35° or less. The inclination direction of the cords of the inner layer 38 with respect to the equatorial plane is opposite to the inclination direction of the cords of the outer layer 40 with respect to the equatorial plane. The cords are made of, for example, steel and organic fibers, and examples of the organic fibers include those mentioned above.

The band 18 is located radially outside the belt 16. In the axial direction, the band 18 has a width equal to the width of the belt 16. The band 18 may also have a width greater than the width of the belt 16.

Although not shown, the band 18 is made of, for example, a cord and a topping rubber. The cord is wound, for example, in a spiral shape. An example of this band 18 is one having a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is, for example, 5° or less, or even 2° or less. The belt 16 is restrained by this cord, so that lifting of the belt 16 is suppressed. The cord is made of, for example, organic fiber, and examples of the organic fiber include those mentioned above.

The belt 16 and the band 18 form a reinforcing layer. The reinforcing layer may also be formed from the belt 16 alone.

The inner liner 20 is located inside the carcass 14. The inner liner 20 is bonded to the inner surface of the carcass 14. The inner liner 20 is made of, for example, crosslinked rubber with excellent air barrier properties. Typical examples of the base rubber of the inner liner 20 include butyl rubber and halogenated butyl rubber. The inner liner 20 maintains the internal pressure of the tire 2.

Each chafer 22 is located near the bead 12. The chafer 22 is made of, for example, cloth and rubber impregnated into the cloth. The chafer 22 may be integrated with the clinch 10. In this case, the material of the chafer 22 is, for example, the same as the material of the clinch 10.

Figure 2 is an enlarged cross-sectional view showing the vicinity of the tread 4 of the tire 2 in Figure 1. In Figure 2, the up-down direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2.

2, a groove width L0 (mm) at the position of the outermost surface in the radial direction of the tire in the cross-sectional view of the circumferential groove 26 and a groove width L95 (mm) at a position of 95% depth from the outermost surface in the radial direction of the tire of the circumferential groove 26 satisfy the following formula (1). It is preferable that all of the circumferential grooves 26 of the tire 2 satisfy the relationship of formula (1), but it is also possible that one circumferential groove 26 satisfies the relationship of formula (1).
(1) 0.00<L95/L0<1.00
The lower limit of L95/L0 is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more. The upper limit of L95/L0 is preferably 0.70 or less, more preferably 0.50 or less, and even more preferably 0.30 or less. Within the above range, there is a tendency that a better effect can be obtained.

In the tire 2, the groove width L0 of the circumferential groove 26 is preferably 20 mm or less, more preferably 15 mm or less, and even more preferably 12 mm or less, from the viewpoint of reducing deformation at the bottom of the groove and suppressing the occurrence of cracks, and is also preferably 5 mm or more, more preferably 6 mm or more, and even more preferably 8 mm or more.

In the tire 2, the groove depth D of the circumferential groove 26 is preferably 13.0 mm or less, more preferably 12.0 mm or less, and even more preferably 11.5 mm or less, from the viewpoint of reducing deformation at the bottom of the groove and suppressing the occurrence of cracks, and is also preferably 3.5 mm or more, more preferably 6.0 mm or more, and even more preferably 8.0 mm or more.

In this specification, the groove depth of the circumferential groove 26 is measured along the normal of the surface that forms the ground contact surface of the outermost tread surface, and means the distance from the surface that forms the ground contact surface to the deepest groove bottom. In FIG. 2, the groove depth of the circumferential groove 26 means the length of D. The position of the outermost surface in the tire radial direction of the circumferential groove 26 in the tire cross-sectional view means the position of the surface that forms the ground contact surface of the outermost tread surface, and the position of 95% depth from the outermost surface in the tire radial direction of the circumferential groove 26 means the position that is 95% of the distance (100%) from the surface that forms the ground contact surface of the outermost tread surface to the deepest groove bottom.

In the tire 2, the hardness H1 of the cap layer 30A (cap layer 30A located radially inward of the groove bottom 27: cap layer 30A within the dashed line) at the groove bottom 27 of the circumferential groove 26 and the hardness H2 of the base layer 28A (base layer 28A located radially inward of the groove bottom 27: base layer 28A within the dashed line) at the groove bottom 27 satisfy the following formula (2). In the embodiment in Fig. 1, the cap layer 30A corresponds to "rubber layer 1 at the groove bottom of the circumferential groove" and the base layer 28A corresponds to "rubber layer 2 at the groove bottom of the circumferential groove".
(2) H1>H2

H1/H2 is preferably 1.02 or more, more preferably 1.04 or more, and even more preferably 1.06 or more. The upper limit of H1/H2 is preferably 1.30 or less, more preferably 1.20 or less, and even more preferably 1.10 or less. If it is within the above range, it is believed that stress concentration at the bottom of the groove is alleviated, making it easier to suppress the occurrence of cracks.

H1 is preferably 45 or more, more preferably 49 or more, even more preferably 50 or more, and particularly preferably 51 or more. The upper limit of H1 is preferably 60 or less, more preferably 58 or less, and even more preferably 55 or less. If it is within the above range, it is believed that stress concentration at the bottom of the groove is alleviated, making it easier to suppress the occurrence of cracks.

H2 is preferably 40 or more, more preferably 44 or more, even more preferably 46 or more, and particularly preferably 48 or more. The upper limit of H2 is preferably 55 or less, more preferably 53 or less, and even more preferably 50 or less. If it is within the above range, it is believed that stress concentration at the bottom of the groove is alleviated, making it easier to suppress the occurrence of cracks.

In this specification, the hardness H1 and H2 of the rubber layer (after vulcanization) are measured at 25°C using a type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness." In principle, test pieces for measuring physical properties are obtained by measuring a rubber piece cut out from the tire 2 in the cross-sectional direction. However, if it is not possible to cut out a test piece from the tire 2, it is possible to calculate the hardness by determining the correlation, for example, from the relationship between the elastic modulus of extension-type dynamic viscoelasticity and hardness.

The hardness H of the rubber layer can be adjusted by the type and amount of chemicals (particularly rubber components, fillers, plasticizers, silane coupling agents, soft particles, etc.) that are blended into the rubber composition that constitutes the rubber layer. For example, the hardness H tends to increase when the amount of filler is increased or the amount of plasticizer is decreased, and tends to decrease when the amount of filler is decreased or the amount of plasticizer is increased. In addition, it is possible to increase or decrease the hardness by utilizing the hardness of the soft particles and blending the particles.

In the tire 2 shown in the enlarged cross-sectional view of FIG. 2, the cap layer 30A at the groove bottom 27 of the circumferential groove 26 (the cap layer 30A located on the radially inner side of the groove bottom 27: the cap layer 30A within the dashed line) has a slope a [(mm/cycle)/J] of log _e (dc/dn [mm/cycle]) relative to log _e (tear energy [J]) in the range of 0.0 to 0.3 for log _e (tear energy [J]) of 2.0 or less (where dc/dN represents the value obtained by differentiating the crack length with respect to cycleN (the number of applications)). The slope a [(mm/cycle)/J] is preferably 1.9 or less, more preferably 1.8 or less, and even more preferably 1.7 or less. The lower limit of the slope a [(mm/cycle)/J] is not particularly limited, and the smaller the slope a, the more preferable, but it may be 0.3 or more, 0.5 or more, or 0.7 or more. In the embodiment shown in FIG. 1, the cap layer 30A corresponds to the "rubber layer 1 at the groove bottom of the circumferential groove."

Here, examples of a method for satisfying the characteristic that "within the range of log _e (tear energy [J]) of 0.0 to 0.3, the slope a of log _e (dc/dn [mm/cycle]) relative to log _e (tear energy [J]) is 2.0 or less" include blending styrene-butadiene rubber, blending soft particles, blending a vulcanizing agent and/or a vulcanization accelerator, and adjusting the contents of these components.

The slope a [(mm/cycle)/J] can be measured, for example, by measuring each crack growth rate [mm/cycle] at each tear energy [J], logarithmically transforming the measured values, and then applying the least squares method.

3 is an example of a graph obtained by logarithmically transforming the values of each tear energy [J] and each crack growth rate [mm/cycle] obtained by measurement. In this logarithmically transformed graph, the range of tear energy 1.0×10 ^0.1 to 2.0×10 ^0.1 [J] corresponds to the range of log _e (tear energy [J]) of 0.0 to 0.3, and by applying the least squares method to this range, a slope a (1.7509 (mm/cycle)/J) is obtained.

Specifically, for example, the logarithmically transformed graph of FIG. 3 is created by the following method, and the slope a can be measured by applying the least squares method.
A plurality of test pieces are prepared, and for each test piece, an amplitude is repeatedly applied at each tear energy until each test piece breaks. Then, for each test piece, a graph is prepared showing the relationship between cycleN (number of applications) and crack length during the repeated application of the amplitude, and the crack length is differentiated by cycleN in the graph to obtain dc/dN.

Figure 4(a) is a graph showing the relationship between cycleN (number of applications) and crack length for a certain test piece, and Figure 4(b) is a graph showing how the crack length is differentiated by cycleN, the change in the slope of Figure 4(a) is measured, and dc/dn is calculated. Although there are differences depending on the rubber composition compound, as shown in Figure 4(a), the crack length c tends to rise suddenly when N is small, then change at a constant slope for a while, and then rise again suddenly. Figure 4(b) was created from the change in slope in Figure 4(a), and the average value during the period when the slope is constant is defined as dc/dn, as shown in Figure 4(b).

Then, for each test piece, the measured values of tear energy and dc/dn obtained are logarithmically converted to obtain a logarithmic graph as shown in FIG. 3 or the like, which shows the relationship between log _e (tear energy [J]) and log _e (dc/dn [mm/cycle]). Furthermore, by applying the least squares method, the slope a [(mm/cycle)/J] of the logarithmic graph can be measured.

The crack length can be measured by any method that allows for observation and measurement of the crack length. For example, it can be measured using a tension-compression type fatigue tester or a fatigue tester with a thermostatic chamber, both of which are sold by various companies, and an image processing system equipped with a CCD camera. It is also possible to measure the crack length after each application (repetition) using a microscope, calipers, etc.

In the tire 2, it is preferable that the L95/L0 and the slope a [(mm/cycle)/J] satisfy the following formula: By making the slope a smaller as the value of L95/L0 becomes smaller (the angle at the groove bottom becomes smaller) so as to satisfy the relationship in the following formula, it is possible to obtain sufficient crack resistance even if stress concentration is likely to occur at the groove bottom, and it is considered possible to improve the crack resistance performance at the groove bottom.
{a/(L95/L0)}≦20.0
{a/(L95/L0)} is preferably 17.8 or less, more preferably 10.0 or less, even more preferably 8.0 or less, and particularly preferably 6.0 or less. The lower limit of {a/(L95/L0)} is not particularly limited, but is preferably 1.0 or more, more preferably 2.0 or more, and even more preferably 3.0 or more.

In the tire 2, it is preferable that the L95/L0, the slope a [(mm/cycle)/J], and the groove depth D of the circumferential groove 26 satisfy the following formula: In addition to the above relationship, it is considered that the longer the distance from the tire surface to the bottom surface of the groove, the easier it is for the force received by the tread portion from the road surface to be absorbed within the tread, making it possible to reduce the input at the bottom of the groove, and making it easier to improve the crack resistance at the bottom of the groove.
{a/(L95/L0)}/D≦2.50
{a/(L95/L0)}/D is preferably 2.23 or less, more preferably 2.00 or less, even more preferably 1.50 or less, and particularly preferably 0.99 or less. The lower limit of {a/(L95/L0)}/D is not particularly limited, but is preferably 0.30 or more, more preferably 0.50 or more, even more preferably 0.70 or more, and particularly preferably 0.74 or more.

As shown in FIG. 1, the tread 4 of the tire 2 is provided with multiple circumferential grooves 26, specifically three circumferential grooves 26. These circumferential grooves 26 are spaced apart in the axial direction. The three circumferential grooves 26 formed in the tread 4 form four ribs 44 that extend in the circumferential direction. In other words, the circumferential grooves 26 are formed between the ribs 44.

Each circumferential groove 26 extends in the circumferential direction. The circumferential grooves 26 are continuous in the circumferential direction without interruption. The circumferential grooves 26 facilitate the drainage of water that exists between the road surface and the tire 2, for example, in rainy weather. Therefore, even if the road surface is wet, the tire 2 can make sufficient contact with the road surface.

In the manufacture of tire 2, multiple rubber components are assembled to obtain a raw cover (unvulcanized tire 2). This raw cover is placed into a mold. The outer surface of the raw cover abuts against the cavity surface of the mold. The inner surface of the raw cover abuts against a bladder or core. The raw cover is pressurized and heated in the mold. The pressure and heat cause the rubber composition of the raw cover to flow. The heat causes a crosslinking reaction of the rubber, and tire 2 is obtained. A mold having an uneven pattern on its cavity surface is used, forming the uneven pattern in tire 2.

As described above, in the example of tire 2 in Figures 1 and 2, cap layer 30 corresponds to "rubber layer 1 arranged on the outermost surface of the tread," and base layer 28 corresponds to "rubber layer 2 arranged adjacent to rubber layer 1 on the radially inner side of the tire," and the rubber composition for rubber layer 1 and the rubber composition for rubber layer 2 that constitute rubber layer 1 contain a rubber component.

As a rubber component that can be used in the rubber composition for rubber layer 1 and rubber layer 2, for example, diene-based rubber can be used. Examples of diene-based rubber include isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). Other examples include butyl-based rubber and fluororubber.

The diene rubber may be a non-modified diene rubber or a modified diene rubber.
The modified diene rubber may be any diene rubber having a functional group that interacts with a filler such as silica. Examples of the modified diene rubber include terminal-modified diene rubber (terminal-modified diene rubber having the functional group at the terminal) in which at least one terminal of the diene rubber has been modified with a compound (modifier) having the functional group, main-chain modified diene rubber having the functional group in the main chain, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal (for example, main-chain terminal-modified diene rubber having the functional group in the main chain and at least one terminal modified with the modifier), and terminal-modified diene rubber modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule and having a hydroxyl group or epoxy group introduced therein.

The above-mentioned functional groups include, for example, amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, and epoxy groups. These functional groups may have a substituent. Among them, amino groups (preferably amino groups in which the hydrogen atoms of the amino groups are substituted with alkyl groups having 1 to 6 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 6 carbon atoms), and alkoxysilyl groups (preferably alkoxysilyl groups having 1 to 6 carbon atoms) are preferred.

The rubber components usable in the rubber composition for rubber layer 1 and rubber layer 2 preferably contain SBR, BR, and isoprene-based rubber from the viewpoint of obtaining a better effect, and may be a combination of these. More preferably, it contains SBR, and may contain only SBR.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. can be used. These may be used alone or in combination of two or more types.

The styrene content of the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the styrene content is within the above range, the effect tends to be better obtained.
In this specification, the styrene content of SBR is calculated by H ¹ -NMR measurement.

The vinyl content of the SBR is preferably 5% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more. The vinyl content is preferably 75% by mass or less, and more preferably 70% by mass or less. When it is within the above range, the effect tends to be more favorably obtained.
The vinyl content (amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy.

As SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

The SBR may be unmodified or modified. Examples of modified SBR include modified SBR into which functional groups similar to those of modified diene rubber have been introduced.

In the rubber composition for the rubber layer 1, the content of SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, and may be 100% by mass. If it is within the above range, the effect tends to be better.

In the rubber composition for the rubber layer 2, the content of SBR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, and may be 100% by mass. Within the above range, the effect tends to be better obtained.

The BR is not particularly limited, and examples of the BR that can be used include high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare earth catalyst (rare earth BR). These may be used alone or in combination of two or more. Of these, high cis BR with a cis content of 90% by mass or more is preferred because it improves abrasion resistance.

The BR may be unmodified or modified. Examples of modified BR include modified BR into which functional groups similar to those of modified diene rubber have been introduced.

When the rubber composition for the rubber layer 1 contains BR, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The upper limit is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 2 contains BR, the content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The upper limit is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be better obtained.

For example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used as BR.

Isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, modified IR, etc. NR can be, for example, SIR20, RSS#3, TSR20, etc., which are common in the rubber industry. IR is not particularly limited, and can be, for example, IR2200, etc., which are common in the rubber industry. Modified NR can be, for example, deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), etc. Modified NR can be, for example, epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, etc. Modified IR can be, for example, epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, etc. These can be used alone or in combination of two or more.

When the rubber composition for the rubber layer 1 contains an isoprene-based rubber, the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The upper limit is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 2 contains an isoprene-based rubber, the content of the isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The upper limit is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be better obtained.

The rubber compositions for rubber layer 1 and rubber layer 2 preferably contain soft particles in order to obtain better effects.

From the viewpoint of obtaining a better effect, it is preferable that the soft particles have an average particle diameter of 0.08 to 50 μm. From the viewpoint of obtaining a better effect, it is preferable that the average particle diameter of the soft particles is . The lower limit is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. The upper limit is preferably 45 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less. Here, when the soft particles are "expanded particles expanded to form a cavity inside" as described below, the above average particle diameter is the value after expansion.

In this specification, the method for measuring the average particle size of soft particles is a value obtained by a light scattering method or a light diffraction method using a laser or the like. In the examples, the values are measured by a light scattering method using a laser. The measuring device used may be a laser diffraction type particle size distribution measuring device SALD-2300 manufactured by Shimadzu Corporation.

In the rubber composition for the rubber layer 1, the content of the soft particles is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. Within the above range, the effect tends to be better obtained.

In the rubber composition for the rubber layer 2, the content of the soft particles is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. Within the above range, the effect tends to be better obtained.

The hardness of the soft particles may be less than or greater than the hardness of the rubber component, but from the standpoint of obtaining better effects, it is preferable that the hardness be greater than the hardness of the rubber component.

The structure of the soft particles is not particularly limited, and examples include solid structures, hollow structures, and solid/hollow structures (such as a core-shell structure composed of multiple layers). In addition, soft particles whose particle surfaces have been surface-modified (such as soft particles whose particle surfaces have been modified with a modifier to improve affinity with rubber) can also be used.

Specifically, resin beads (resin particles) such as melamine beads, acrylic beads, acrylic-styrene beads, polycarbonate beads, polyethylene beads, polystyrene beads, PVC beads, urethane crosslinked fine particles, and silicone-based beads can be suitably used as soft particles.

As the soft particles, expanded particles that are expanded to form a cavity inside can also be suitably used. The expanded particles are preferably expanded particles obtained by expanding particles having thermal expansion properties, and more preferably expanded particles obtained by thermally expanding a thermally expandable microcapsule. Here, the thermally expandable microcapsule has a volatile substance such as a low boiling point solvent encapsulated inside the shell resin, and the shell resin softens when heated, causing the encapsulated volatile substance to volatilize or expand, and the shell expands under the pressure, increasing the particle diameter and becoming a foamed particle. The temperature at which the thermally expandable microcapsule is expanded is not particularly limited, but is preferably higher than the foaming start temperature described below and lower than the maximum foaming temperature.

The outer shell of the thermally expandable microcapsule is preferably formed from a thermoplastic resin. Examples of thermoplastic resins include vinyl polymers and copolymers thereof, such as ethylene, styrene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, butadiene, and chloroprene; polyamides, such as nylon 6 and nylon 66; and polyesters, such as polyethylene terephthalate. Among these, copolymers of acrylonitrile are preferred.

Examples of volatile substances that can be encapsulated inside the thermally expandable microcapsules include low-boiling point liquids such as hydrocarbons having 3 to 7 carbon atoms, such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, hexane, and heptane; petroleum ether; methane halides, such as methyl chloride and methylene chloride; chlorofluorocarbons, such as CCl ₃ F and CCl ₂ F ₂ ; and tetraalkylsilanes, such as tetramethylsilane and trimethylethylsilane.

A suitable example of a thermally expandable microcapsule is a microcapsule that uses a copolymer of acrylonitrile and vinylidene chloride as the shell resin and encapsulates a hydrocarbon with 3 to 7 carbon atoms, such as isobutane.

The thermally expandable microcapsules preferably expand 2 to 10 times their average particle diameter to become the foamed particles. The foaming start temperature of the thermally expandable microcapsules is preferably 95 to 150°C, more preferably 105 to 140°C. The maximum foaming temperature is preferably 120 to 200°C, more preferably 135 to 180°C.

As soft particles, commercially available products such as "Hyper" and "Art Pearl" manufactured by Negami Chemical Industries, Ltd., "Technopolymer" (solid particles) manufactured by Sekisui Chemical Co., Ltd., "EXPANCEL" manufactured by Nippon Fillerlite Co., Ltd., "Advancell" manufactured by Sekisui Chemical Co., Ltd., "Matsumoto Microsphere" manufactured by Matsumoto Yushi Seiyaku Co., Ltd., and "Microsphere" (thermally expandable microcapsules) manufactured by Kureha Corporation can be used.

The rubber composition for the rubber layers 1 and 2 may contain a filler other than the soft particles.
As the filler, materials known in the rubber field can be used, for example, inorganic fillers such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, etc.; poorly dispersible fillers, etc. Among them, silica and carbon black are preferred.

Examples of silica that can be used in the rubber composition for the rubber layer 1 and the rubber layer 2 include dry process silica (anhydrous silica) and wet process silica (hydrated silica). Among these, wet process silica is preferred because it has a large number of silanol groups. Examples of silica that can be used include products from Degussa, Rhodia, Tosoh Silica, Solvay Japan, and Tokuyama.

The nitrogen adsorption specific surface area ( _N2SA ) of silica is preferably ^70m2 /g or more, more preferably ^100m2 /g or more, and even more preferably ^150m2 /g or more. The upper limit of the _N2SA of silica is not particularly limited, but is preferably ^300m2 /g or less, more preferably ^250m2 /g or less, and even more preferably ^200m2 /g or less. Within the above range, the effect tends to be better obtained.
The N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

When the rubber composition for the rubber layer 1 contains silica, the content of silica is preferably 5 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 2 contains silica, the content of silica is preferably 5 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 1 and the rubber layer 2 contains silica, a silane coupling agent may be blended together with the silica.
Usable silane coupling agents include any silane coupling agents that have been conventionally used in combination with silica in the rubber industry, and are not particularly limited. Examples of such silane coupling agents include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxy ... Examples of the mercapto-based compounds include trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. As commercially available products, products of Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., Dow Corning Toray Co., Ltd., etc. can be used. These may be used alone or in combination of two or more. Among them, sulfide-based and mercapto-based products are preferred.

In the rubber composition for rubber layer 1 and rubber layer 2, the content of the silane coupling agent is preferably 3 parts by mass or more, and more preferably 6 parts by mass or more, relative to 100 parts by mass of silica. The content is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. Within the above range, the effect tends to be better obtained.

Examples of carbon black that can be used in the rubber composition for rubber layer 1 and rubber layer 2 include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. These may be used alone or in combination of two or more. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like.

The nitrogen adsorption specific surface area ( _N2SA ) of carbon black is preferably 50 ^m2 /g or more, more preferably 80 ^m2 /g or more, and even more preferably 100 ^m2 /g or more. The _N2SA is preferably 200 ^m2 /g or less, more preferably 150 ^m2 /g or less, and even more preferably 130 ^m2 /g or less. When the N2SA is within the above range, the effect tends to be better.
The nitrogen adsorption specific surface area of carbon black is determined in accordance with JIS K6217-2:2001.

When the rubber composition for the rubber layer 1 contains carbon black, the content of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 2 contains carbon black, the carbon black content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. Within the above range, the effect tends to be better obtained.

The rubber compositions for the rubber layers 1 and 2 may contain a plasticizer.
A plasticizer is a material that imparts plasticity to a rubber component, and examples of such a plasticizer include liquid plasticizers (plasticizers that are in a liquid state at room temperature (25° C.)) and resins (resins that are in a solid state at room temperature (25° C.)).

When the rubber composition for the rubber layer 1 contains a plasticizer, the content of the plasticizer (total amount of plasticizer) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. There is no particular lower limit and it may be 0 parts by mass, but it is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 2 contains a plasticizer, the content of the plasticizer (total amount of plasticizer) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. There is no particular lower limit and it may be 0 parts by mass, but it is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. Within the above range, the effect tends to be better obtained.

Liquid plasticizers (plasticizers that are in a liquid state at room temperature (25°C)) that can be used in the rubber compositions for rubber layer 1 and rubber layer 2 are not particularly limited, and examples include oils and liquid polymers (liquid resins, liquid diene-based polymers, liquid farnesene-based polymers, etc.). These may be used alone or in combination of two or more types.

When the rubber composition for the rubber layer 1 contains a liquid plasticizer, the content of the liquid plasticizer is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. There is no particular lower limit and it may be 0 parts by mass, but it is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. Within the above range, the effect tends to be better obtained. The content of the liquid plasticizer also includes the amount of oil contained in the oil extender oil.

When the rubber composition for the rubber layer 2 contains a liquid plasticizer, the content of the liquid plasticizer is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the rubber component. There is no particular lower limit and it may be 0 parts by mass, but it is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. If it is within the above range, the effect tends to be better obtained. The content of the liquid plasticizer also includes the amount of oil contained in the oil extender oil.

Examples of the oil include process oil, vegetable oil, or a mixture thereof. Examples of the process oil include paraffin-based process oil, aromatic process oil, and naphthenic process oil. Examples of the vegetable oil include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Examples of commercially available products include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Seiyu Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and Nisshin Oillio Group Co., Ltd. Among these, process oils (paraffin-based process oils, aromatic process oils, naphthenic process oils, etc.) and vegetable oils are preferred.

Liquid resins include terpene resins (including terpene phenol resins and aromatic modified terpene resins), rosin resins, styrene resins, C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, coumarone-indene resins (including coumarone and indene simple resins), phenol resins, olefin resins, polyurethane resins, acrylic resins, etc. Hydrogenated versions of these resins can also be used.

Liquid diene polymers include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), liquid styrene isoprene styrene block copolymers (liquid SIS block polymers), liquid farnesene polymers, liquid farnesene butadiene copolymers, etc. that are liquid at 25°C. The ends or main chains of these may be modified with polar groups. Hydrogenated versions of these may also be used.

Examples of the above resins (resins in a solid state at room temperature (25°C)) that can be used in the rubber compositions for rubber layer 1 and rubber layer 2 include aromatic vinyl polymers in a solid state at room temperature (25°C), coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, and acrylic resins. The resins may also be hydrogenated. These may be used alone or in combination of two or more. Of these, aromatic vinyl polymers, petroleum resins, and terpene resins are preferred.

When the rubber composition for the rubber layer 1 contains a liquid plasticizer, the content of the resin is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component. There is no particular lower limit and it may be 0 parts by mass, but it is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. Within the above range, the effect tends to be better obtained.

When the rubber composition for the rubber layer 2 contains a liquid plasticizer, the content of the resin is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the rubber component. There is no particular lower limit and it may be 0 parts by mass, but it is preferably 0.5 parts by mass or more, and more preferably 1.0 parts by mass or more. Within the above range, the effect tends to be better obtained.

The softening point of the resin is preferably 60° C. or higher, more preferably 70° C. or higher, and even more preferably 80° C. or higher. The upper limit is preferably 160° C. or lower, more preferably 130° C. or lower, and even more preferably 115° C. or lower. By keeping the softening point within the above range, cut resistance during running at high load and high speed tends to be improved.
The softening point of the resin is the temperature at which the ball drops when the softening point specified in JIS K6220-1:2001 is measured using a ring and ball softening point tester.

The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, it can be a resin obtained by polymerizing α-methylstyrene and/or styrene, and specifically, it can be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, a copolymer of styrene and another monomer, etc.

The above-mentioned coumarone-indene resin is a resin containing coumarone and indene as the main monomer components that make up the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

The above coumarone resin is a resin that contains coumarone as the main monomer component that constitutes the resin skeleton (main chain).

The above-mentioned indene resin is a resin that contains indene as the main monomer component that constitutes the resin skeleton (main chain).

The phenolic resin may be, for example, a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural using an acid or alkali catalyst. Among these, those obtained by reacting with an acid catalyst (such as novolac-type phenolic resin) are preferred.

The above-mentioned rosin resins include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

The petroleum resins include C5 resins, C9 resins, C5/C9 resins, dicyclopentadiene (DCPD) resins, and hydrogenated versions of these resins. Of these, DCPD resins and hydrogenated DCPD resins are preferred.

The terpene resin is a polymer containing terpene as a structural unit. Examples include polyterpene resins obtained by polymerizing terpene compounds, and aromatic modified terpene resins obtained by polymerizing terpene compounds and aromatic compounds. Examples of aromatic modified terpene resins include terpene phenol resins made from terpene compounds and phenolic compounds, terpene styrene resins made from terpene compounds and styrene compounds, and terpene phenol styrene resins made from terpene compounds, phenolic compounds, and styrene compounds. Examples of terpene compounds include α-pinene, β-pinene, etc., examples of phenolic compounds include phenol, bisphenol A, etc., and examples of aromatic compounds include styrene compounds (styrene, α-methylstyrene, etc.).

The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, there is a styrene-acrylic resin such as a styrene-acrylic resin that has a carboxyl group and is obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component. Among them, a solvent-free carboxyl group-containing styrene-acrylic resin can be preferably used.

Examples of the plasticizers that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries Co., Ltd., and Taoka Chemical Co., Ltd.

The rubber composition for rubber layer 1 and rubber layer 2 preferably contains an antioxidant from the viewpoints of crack resistance, ozone resistance, etc.

The anti-aging agent is not particularly limited, but may be naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, Examples of such antioxidants include p-phenylenediamine antioxidants such as amines; quinoline antioxidants such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and polymerized 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercially available products include those manufactured by Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd.

In the rubber composition for rubber layer 1 and rubber layer 2, the content of the antioxidant is preferably 0.2 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, and more preferably 4.0 parts by mass or less.

The rubber composition for rubber layer 1 and rubber layer 2 may contain stearic acid. In the rubber composition for rubber layer 1 and rubber layer 2, the content of stearic acid is preferably 0.5 to 10 parts by mass or more, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

The stearic acid used may be any known product, such as products from NOF Corp., NOF Corporation, Kao Corp., Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

The rubber composition for rubber layer 1 and rubber layer 2 preferably contains zinc oxide. The content of zinc oxide is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

As zinc oxide, any conventionally known product can be used, for example, products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

Wax may be blended into the rubber composition for rubber layer 1 and rubber layer 2. The wax content is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

The wax is not particularly limited, and examples include petroleum-based waxes and natural waxes. Synthetic waxes obtained by refining or chemically processing multiple waxes can also be used. These waxes may be used alone or in combination of two or more types.

Petroleum-based waxes include paraffin wax and microcrystalline wax. Natural waxes are not particularly limited as long as they are derived from resources other than petroleum, and examples include vegetable waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd. The wax content may be appropriately set in terms of ozone resistance and cost.

The rubber compositions for the rubber layers 1 and 2 may contain sulfur.
The amount of sulfur per 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and even more preferably 0.7 part by mass or more. The amount is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur, which are commonly used in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., and Hosoi Chemical Industry Co., Ltd. These may be used alone or in combination of two or more types.

The rubber composition for the rubber layer 1 and the rubber layer 2 may contain a vulcanization accelerator.
The content of the vulcanization accelerator is not particularly limited and may be freely determined according to the desired vulcanization speed and crosslink density, but is usually 0.3 to 10 parts by mass, preferably 0.5 to 7 parts by mass, per 100 parts by mass of the rubber component.

There are no particular restrictions on the type of vulcanization accelerator, and any commonly used accelerator can be used. Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, N-t-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenyl guanidine, di-orthotolyl guanidine, and orthotolyl biguanidine. These may be used alone or in combination of two or more. Among them, from the viewpoint of the balance of performance, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred.

In addition to the above components, the rubber compositions for rubber layer 1 and rubber layer 2 may contain appropriate additives, such as release agents and pigments, that are commonly used in the field of application.

The rubber composition for rubber layer 1 and rubber layer 2 can be produced by a known method. For example, the components are kneaded using a rubber kneading device such as an open roll or a Banbury mixer, and crosslinked as necessary. As for the kneading conditions, the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes.

The pneumatic tire of the present invention can be used as passenger car tires, large passenger car tires, large SUV tires, heavy load tires such as trucks and buses, light truck tires, two-wheeled vehicle tires, racing tires (high performance tires), etc. It can also be used as all-season tires, summer tires, studless tires (winter tires), etc. Among these, it is preferable to use it as a passenger car tire. Note that a passenger car tire is a tire that is intended to be mounted on a four-wheeled vehicle and has a maximum load capacity of 1000 kg or less. Here, maximum load capacity refers to the maximum load capacity determined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of the JATMA standard (Japan Automobile Tire Manufacturers Association standard), it is the maximum load capacity based on the load index (LI), in the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it is the "LOAD CAPACITY".

The present invention will be specifically explained based on examples, but the present invention is not limited to these.

SBR: HPR850 (styrene content 27.5% by mass, vinyl bond content 59.0% by mass) manufactured by JSR Corporation
BR: BR150B (cis content 98% by mass) manufactured by Ube Industries, Ltd.
NR: TSR20
Soft particles 1: Art Pearl JB-800 manufactured by Negami Chemical Industries, Ltd. (urethane beads (hollow structure), average particle diameter 6 μm)
Soft particles 2: Art Pearl JB-400 (urethane beads (hollow structure), average particle diameter 15 μm) manufactured by Negami Chemical Industries, Ltd.
Soft particles 3: C-200 manufactured by Negami Chemical Industries, Ltd. (urethane beads (hollow structure), average particle diameter 32 μm)
Soft particles 4: C-100 manufactured by Negami Chemical Industries, Ltd. (urethane beads (hollow structure), average particle diameter 50 μm)
Stearic acid: NOF Corporation's "Tsubaki" stearic acid
Antioxidant: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Sulfur: Powdered sulfur (containing 5% oil) manufactured by Tsurumi Chemical Industry Co., Ltd.
Vulcanization accelerator: Soxinol CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Sumitomo Chemical Co., Ltd.

<Examples and Comparative Examples>
According to the compounding recipes shown in Tables 1 and 3, materials other than sulfur and vulcanization accelerator were added using a 1.7 L Banbury mixer, and the mixture was kneaded for 3 minutes under the condition of 150°C to obtain a kneaded product. Next, sulfur and vulcanization accelerator were added, and the mixture was kneaded for 2 minutes under the condition of 100°C using an open roll to obtain an unvulcanized rubber composition.
Using each of the obtained unvulcanized rubber compositions, a cap tread (corresponding to rubber layer 1) and a base tread (corresponding to rubber layer 2) were molded in accordance with the specifications in Tables 2 and 4, and the resulting shapes were laminated together with other tire components and vulcanized at 170°C for 15 minutes to produce test tires (tire size: 195/65R15).

The following physical property measurements and evaluations were performed on the obtained test tires, and the results are shown in the tables. Note that in Tables 2 and 4, Comparative Examples 1-1 and 2-1 were used as the reference comparative examples, respectively.

<Tilt a [(mm/cycle)/J]>
For each sample taken from the cap tread at the bottom of the circumferential groove of each test tire, the slope a [(mm/cycle)/J] of the crack growth rate [mm/cycle] versus tear energy [J] in the tear energy range of 1.0× ^{10 0.1} to 2.0×10 ^0.1 [J] was measured for each crack growth rate [mm/cycle] at each tear energy [J], and the measured values were logarithmically converted according to Figures 3 and 4, and then the least squares method was applied to measure. The following equipment and test conditions were used.
(Device)
Coesfeld Tear Fatigue Analyzer (fatigue testing machine with crack observation system)
(Test conditions)
In an environment of room temperature (approximately 23° C.), a pulse wave with a frequency of 5 Hz and a cycle of 10 Hz is applied to the smooth portion of a test piece having a smooth portion of 15 mm at amplitudes of 10, 15, 20, 25, 30, and 35% until the smooth portion breaks.

<Hardness>
For each sample taken from the cap tread and base tread at the bottom of the circumferential grooves of each test tire, the hardness (JIS-A hardness) at 25°C was measured using a Type A durometer in accordance with JIS K6253-3 (2012) "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness".

<TGC resistance at the end of driving>
The rim-mounted test tire was heat-treated at 80°C for two weeks while irradiating the tread with 30 pphm of ozone, and then mounted on a domestic FF vehicle and driven around on an asphalt road surface, and the occurrence of cracks at the bottom of the grooves after the lap was observed. The length of the cracks that occurred at the bottom of the grooves was measured and indexed by the following formula. The higher the index, the better the resistance to cracks at the bottom of the grooves.
(crack length of the tire of the reference comparative example)/(crack length of the tire of each specification)×100

From each table, it can be seen that the example tires that satisfy the above formulas (1) and (2) and have a slope a of 2.0 or less had superior TGC resistance at the end of the running period compared to the comparative example tires that do not satisfy the above formulas.

2 Pneumatic tire 4 Tread 6 Sidewall 8 Wing 10 Clinch 12 Bead 14 Carcass 16 Belt 18 Band 20 Inner liner 22 Chafer 24 Tread surface 26 Circumferential groove 27 Groove bottom 28 Base layer 28A Base layer 30 at bottom of circumferential groove Cap layer 30A Cap layer 32 at bottom of circumferential groove Core 34 Apex 36 Carcass ply 36a Main portion 36b Turn-up portion 38 Inner layer 40 Outer layer 44 Rib CL Equatorial plane L0 of tire 2 Groove width L95 at the position of the outermost surface in the radial direction of the tire in a cross-sectional view of the circumferential groove Groove width D at a position 95% deep from the outermost surface in the radial direction of the tire Groove depth of the circumferential groove

Claims (8)

A tire having at least one circumferential groove and a tread portion having two or more rubber layers,
The rubber layer has at least a rubber layer 1 disposed on an outermost surface of the tread, and a rubber layer 2 disposed adjacent to the rubber layer 1 on an inner side in the tire radial direction,
The rubber layer 1 is composed of a rubber composition for the rubber layer 1, the rubber composition including 0.5 parts by mass or more and 30 parts by mass or less of soft particles relative to 100 parts by mass of a rubber component,
A groove width L0 (mm) at the outermost surface in the radial direction of the tire in a cross-sectional view of the circumferential groove and a groove width L95 (mm) at a position 95% from the outermost surface in the radial direction of the tire of the circumferential groove satisfy the following formula (1),
(1) 0.00<L95/L0<1.00
The hardnesses H1 and H2 of the rubber layer 1 and the rubber layer 2 at the groove bottoms of the circumferential grooves satisfy the following formula (2):
(2) H1>H2
The rubber layer 1 at the groove bottom of the circumferential groove has a slope a of log _e (dc/dn [mm/cycle]) to log _e (tear energy [J]) of 2.0 or less within a log _e (tear energy [J]) range of 0.0 to 0.3.
(where dc/dN represents the value obtained by differentiating the crack length with respect to cycleN (the number of times the voltage is applied).) 2. The tire according to claim 1, which satisfies the following formula:
0.10≦L95/L0≦0.30 The tire according to claim 1 or 2, wherein the L95/L0 and the slope a satisfy the following formula:
{a/(L95/L0)}≦10.0 The tire according to any one of claims 1 to 3, wherein the L95/L0, the inclination a, and the groove depth D of the circumferential groove satisfy the following formula:
{a/(L95/L0)}/D≦2.00 A tire according to any one of claims 1 to 4, wherein L0 is 5 to 20 mm. A tire according to any one of claims 1 to 5, wherein the groove depth D of the circumferential groove is 6.0 to 12.0 mm. The tire according to any one of claims 1 to 6, wherein the H1 and the H2 satisfy the following formulas:
1.04≦H1/H2≦1.20 A tire according to any one of claims 1 to 7, wherein H2 is 44 to 53.

Images