tire

Abstract

To provide a tire for improving performance (TGC resistance performance) for suppressing progress of groove bottom cracks during a travel end stage.SOLUTION: A tire includes a tread part having at least one circumferential groove, and two or more rubber layers, wherein the rubber layer has at least a rubber layer 1 on the outermost surface of the tread and a rubber layer 2 adjacent to inside in a tire radial direction, a groove width L0 on the outermost surface in the tire radial direction and a groove width L95 at 95% from the outermost surface in tire cross-sectional view of the circumferential groove satisfy (1) 0.00<L95 / L0<1.00, hardnesses H1 and H2 of the rubber layers 1 and 2 in the groove bottom of the circumferential groove satisfy (2) H1>H2, and the rubber layer 1 in the groove bottom of the circumferential groove has an inclination a of loge(dc / dn[mm / cycle]) to loge(tear energy[J]) of 2.0 or less, in the range of 0.0-0.3 of the loge(tear energy[J]). (dc / dN is value obtained by differentiating crack length by number of times of application).SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] In recent years, in tires having a tread with a multi-layer structure of two or more layers, there has been a problem in that tread groove cracks (TGCs) occur at the bottom of circumferential grooves in the tread, and cracks progress at the bottom of the grooves. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to solve the above problems and to provide a tire that has improved performance (TGC resistance) in suppressing the progression of cracks at the groove bottom at the final stage of running. [Means for solving the problem]

[0004] 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 the outermost surface of the tread, and a rubber layer 2 disposed adjacent to the rubber layer 1 on the 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 has a length of log e In the range of 0.0 to 0.3 for (tear energy [J]), log e log(tear energy[J]) eThis relates to tires in which the slope a of (dc / dn [mm / cycle]) is 2.0 or less. (Note that dc / dN represents the value obtained by differentiating the crack length with respect to cycleN (the number of times the voltage is applied).)

[0005] It is preferable that the tire satisfies the following formula. 0.10≦L95 / L0≦0.30

[0006] In the tire, it is preferable that the L95 / L0 and the slope a satisfy the following formulas. {a / (L95 / L0)}≦10.0

[0007] 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

[0008] In the tire, the L0 is preferably from 5 to 20 mm.

[0009] In the tire, it is preferable that the groove depth D of the circumferential groove is 6.0 to 12.0 mm.

[0010] In the tire, it is preferable that the H1 and the H2 satisfy the following formulas. 1.04≦H1 / H2≦1.20

[0011] It is preferable that the H2 of the tire is 44-53. Effect of the Invention

[0012] According to the present invention, in 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 arranged on the outermost surface of the tread and a rubber layer 2 arranged adjacent to the rubber layer 1 on the radially inner side of the tire, the tire satisfies the formulas (1) and (2) and has the slope a of 2.0 or less, so that a tire having excellent TGC resistance performance at the end of running can be provided. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing a portion of a pneumatic tire. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the tread 4 of the tire 2 of FIG. [Diagram 3] This is an example of a graph obtained by logarithmic conversion of tear energy [J] and crack growth rate [mm / cycle]. [Figure 4] Graph (a) shows the relationship between cycleN (number of applications) and crack length, and graph (b) shows an example of the graph in (a) obtained by differentiating crack length with cycleN. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to a tire having at least one circumferential groove and a tread portion having two or more rubber layers, the rubber layer 1 being disposed on the outermost surface of the tread and a rubber layer 2 being disposed adjacent to the inner side in the tire radial direction of the rubber layer 1. The rubber layer 1 at the groove bottom of the circumferential groove satisfies the above formulas (1) and (2), and has a tear energy of 1.0×10 0.1 ~2.0×10 0.1 The tire has an inclination a of 2.0 or less of the crack growth rate [mm / cycle] versus tear energy [J] in the range of [J]. The tire has excellent TGC resistance at the end of the running period.

[0015] The reason why such an effect is obtained is not clear, but is presumed to be as follows. One method of ensuring drainage while maintaining the rigidity of the tread is to make the circumferential grooves V-shaped and to widen the block section radially inward. However, the larger the V-shape, the more deformation is concentrated at the bottom of the groove during driving, and the greater the deformation amount. 0.1 ~2.0×10 0.1In the range of [J], by setting the slope a of the crack growth property [mm / cycle] with respect to the tear energy [J] to 2.0 or less, as the groove width (L0) of the tread surface increases with respect to the groove width (L95) at the bottom of the groove, by reducing the parameter (slope a) of the crack growth property with respect to deformation, it is considered that cracks are less likely to occur due to repeated deformation, and it is possible to make TGC less likely to occur even at the end of running. Also, by making the hardness H2 of the second rubber layer 2 disposed adjacent to the inner side in the tire radial direction of the rubber layer 1 smaller than the hardness H1 of the outermost rubber layer 1 at the bottom of the circumferential groove, it is considered that the stress concentration in the outermost rubber layer 1 is alleviated and the TGC resistance performance is improved. Therefore, it is presumed that the TGC resistance performance at the end of running is significantly improved in the tire.

[0016] Thus, the tire is configured to solve the problem (objective) of improving the TGC resistance performance at the end of running in a tire that satisfies "0.00 < L95 / L0 < 1.00" with "H1 > H2", and "the rubber layer 1 at the bottom of the circumferential groove has, in the range of 0.0 to 0.3 of log e (tear energy [J]), the slope a of log e (dc / dn [mm / cycle]) with respect to log e (tear energy [J]) is 2.0 or less (where dc / dN represents the value obtained by differentiating the crack length with respect to the number of cycles N). That is, "H1 > H2", and "the rubber layer 1 at the bottom of the circumferential groove has, in the range of 0.0 to 0.3 of log e (tear energy [J]), the slope a of log e (dc / dn [mm / cycle]) with respect to log eThe parameter "the slope a of (dc / dn [mm / cycle]) is 2.0 or less (where dc / dN represents the value obtained by differentiating the crack length with respect to cycleN (number of applications))" does not define the problem (purpose). The problem of this application is to improve the TGC resistance performance at the end of the running period, and a configuration that satisfies this parameter is used as a means to solve this problem.

[0017] Hereinafter, the present invention will be described in detail based on one example of a preferred embodiment, with reference to the drawings as appropriate. However, the present invention is not limited to this embodiment, and includes all tires within the scope of the claims.

[0018] Fig. 1 shows an example of a cross-sectional view of a pneumatic tire 2. In Fig. 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 Fig. 1, a dashed dotted line CL represents the equatorial plane of the tire 2. The shape of the tire 2 is symmetrical with respect to the equatorial plane, except for the tread pattern.

[0019] 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.

[0020] 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 linear 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 adjacent to the cap layer 30 on the inner side in the tire radial direction. In the embodiment of 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 inner side in the tire radial direction."

[0021] 1 shows an example of a two-layer tread 4 consisting of a cap layer 30 and a base layer 28, but 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 rubber layer 1 arranged on the outermost surface of the tread on the radially inner side of the tire constitutes rubber layer 2.

[0022] In the tire 2 of Fig. 1, each sidewall 6 extends substantially radially inward from an end of the tread 4. A radially outer portion of each sidewall 6 is joined to the tread 4. A radially inner portion of each sidewall 6 is joined to a clinch 10. Each sidewall 6 is made of, for example, a crosslinked rubber having excellent cut resistance and weather resistance.

[0023] Each wing 8 is located between the tread 4 and the sidewall 6. The wing 8 is joined to each of the tread 4 and the sidewall 6. The wing 8 is made of, for example, a crosslinked rubber having excellent adhesiveness.

[0024] Each clinch 10 is located approximately radially inward of the sidewall 6. In the axial direction, the clinch 10 is located outward of the beads 12 and the carcass 14. The clinch 10 is made of, for example, a crosslinked rubber having excellent abrasion resistance.

[0025] 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 inelastic 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.

[0026] The carcass 14 includes a carcass ply 36. In the tire 2, the carcass ply 36 is laid between the beads 12 on both sides and extends along the tread 4 and the sidewall 6. The carcass ply 36 is folded back around each of the cores 32 from the inside to the outside in the axial direction. By this folding back, the carcass ply 36 is formed with a main portion 36a and a pair of folded back portions 36b. That is, the carcass ply 36 includes the main portion 36a and a pair of folded back portions 36b.

[0027] Although not shown, the carcass ply 36 is made of, for example, a large number of parallel cords and a topping rubber. The absolute value of the angle that each cord makes with respect to the equator plane is preferably 75° to 90°. The cords are made of, for example, organic fibers, and specific examples thereof include polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, and aramid fibers.

[0028] 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.

[0029] Although not shown, each of the inner layer 38 and the outer layer 40 is made of, for example, a large number of cords arranged in parallel and a topping rubber. Each cord is inclined with respect to the equatorial plane. The general 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 or organic fibers, and examples of the organic fibers include those mentioned above.

[0030] 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.

[0031] 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. Since the belt 16 is restrained by the cord, lifting of the belt 16 is suppressed. The cord is made of, for example, organic fiber, and examples of the organic fiber include those described above.

[0032] The belt 16 and the band 18 form a reinforcing layer. The reinforcing layer may be formed of the belt 16 alone.

[0033] 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, a crosslinked rubber having 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.

[0034] Each chafer 22 is located near the bead 12. The chafer 22 is made of, for example, a 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.

[0035] Fig. 2 is an enlarged cross-sectional view showing the vicinity of the tread 4 of the tire 2 in Fig. 1. In Fig. 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.

[0036] 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 tire 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 of the circumferential grooves 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 for better effects to be obtained.

[0037] 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 groove bottom and suppressing the occurrence of cracks, and is preferably 5 mm or more, more preferably 6 mm or more, and even more preferably 8 mm or more.

[0038] 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, even more preferably 11.5 mm or less, from the viewpoint of reducing deformation at the groove bottom and suppressing the occurrence of cracks, and is preferably 3.5 mm or more, more preferably 6.0 mm or more, even more preferably 8.0 mm or more.

[0039] In this specification, the groove depth of the circumferential groove 26 is measured along a normal to 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, and 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 a cross-sectional view of the tire 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.

[0040] 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 the "rubber layer 1 at the groove bottom of the circumferential groove" and the base layer 28A corresponds to the "rubber layer 2 at the groove bottom of the circumferential groove". (2) H1>H2

[0041] 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.

[0042] H1 is preferably at least 45, more preferably at least 49, even more preferably at least 50, and particularly preferably at least 51. The upper limit of H1 is preferably at most 60, more preferably at most 58, and even more preferably at most 55. 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.

[0043] H2 is preferably at least 40, more preferably at least 44, even more preferably at least 46, and particularly preferably at least 48. The upper limit of H2 is preferably at most 55, more preferably at most 53, and even more preferably at most 50. When H2 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.

[0044] 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 determined 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 a correlation from the relationship between the elastic modulus of extension-type dynamic viscoelasticity and hardness, for example.

[0045] Here, 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.) blended in the rubber composition constituting 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 soft particles and blending the particles.

[0046] 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 inner side in the tire radial direction of the groove bottom 27: the cap layer 30A within the dashed line) has a loge In the range of 0.0 to 0.3 for (tear energy [J]), log e log(tear energy[J]) e The slope a [(mm / cycle) / J] of (dc / dn [mm / cycle]) is 2.0 or less (where dc / dN represents the value obtained by differentiating the crack length with respect to cycleN (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. There is no particular lower limit to the slope a [(mm / cycle) / J], and the smaller the better, but it may be 0.3 or more, 0.5 or more, or 0.7 or more. In the embodiment of FIG. 1, the cap layer 30A corresponds to the "rubber layer 1 at the bottom of the circumferential groove."

[0047] Here, "log e In the range of 0.0 to 0.3 for (tear energy [J]), log e log(tear energy[J]) e Methods for satisfying the characteristic "slope a of (dc / dn [mm / cycle]) 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 content of these components.

[0048] 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 value, and then applying the least squares method.

[0049] Figure 3 shows 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 tear energy of 1.0×10 0.1 ~2.0×10 0.1 The range of [J] corresponds to log eThe range of (tear energy [J]) is 0.0 to 0.3, and by applying the least squares method to this range, the slope a (1.7509 (mm / cycle) / J) is obtained.

[0050] Specifically, for example, the logarithmic 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 number 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 created showing the relationship between cycleN (number of applications) and crack length while the amplitude is repeatedly applied, and the crack length is differentiated with respect to cycleN in the graph to obtain dc / dN.

[0051] Figure 4(a) is a graph showing the relationship between cycle N (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 cycle N in that graph, 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).

[0052] Then, the measured values ​​of tear energy and dc / dn for each specimen were logarithmically transformed to obtain log e (tear energy[J]) and log e A logarithmic graph showing the relationship between (dc / dn [mm / cycle]) and the applied current is obtained, as shown in FIG. 3, and the slope a [(mm / cycle) / J] of the logarithmic graph can be measured by applying the least squares method.

[0053] The crack length can be measured by any method that allows observation and measurement of the crack length. For example, it can be measured by using a tension-compression type fatigue tester or a fatigue tester with a thermostatic chamber, 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 using a microscope or calipers for each applied number (repetition number).

[0054] In the tire 2, it is preferable that the L95 / L0 and the slope a [(mm / cycle) / J] satisfy the following formula: By decreasing the slope a as the value of L95 / L0 decreases (the angle at the groove bottom decreases) 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.

[0055] 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 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.

[0056] As shown in Fig. 1, a plurality of circumferential grooves 26, specifically three circumferential grooves 26, are formed in the tread 4 of the tire 2. These circumferential grooves 26 are arranged at intervals in the axial direction. The three circumferential grooves 26 are formed in the tread 4, forming four ribs 44 extending in the circumferential direction. In other words, the circumferential grooves 26 are formed between the ribs 44.

[0057] Each of the circumferential grooves 26 extends in the circumferential direction. The circumferential grooves 26 are continuous in the circumferential direction without interruption. The circumferential grooves 26 promote the drainage of water present 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.

[0058] In manufacturing the tire 2, a plurality of rubber components are assembled to obtain a raw cover (unvulcanized tire 2). This raw cover is placed in 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 a 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 the tire 2 is obtained. The uneven pattern is formed in the tire 2 by using a mold having an uneven pattern on its cavity surface.

[0059] As described above, in the example of tire 2 in FIGS. 1 and 2 , 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," and the rubber composition for rubber layer 1 and the rubber composition for rubber layer 2 that constitute rubber layer 1 each contain a rubber component.

[0060] As the rubber component usable in the rubber composition for the rubber layer 1 and the rubber layer 2, for example, a diene-based rubber can be used. Examples of the 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), acrylonitrile butadiene rubber (NBR), etc. Other examples include butyl-based rubber, fluororubber, etc.

[0061] 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.

[0062] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, and an epoxy group. These functional groups may have a substituent. Among them, an amino group (preferably an amino group in which a hydrogen atom of an amino group is substituted with an alkyl group having 1 to 6 carbon atoms), an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms), and an alkoxysilyl group (preferably an alkoxysilyl group having 1 to 6 carbon atoms) are preferred.

[0063] From the viewpoint of obtaining a better effect, the rubber component usable in the rubber composition for the rubber layer 1 and the rubber layer 2 preferably contains SBR, BR, and isoprene-based rubber, or may contain a combination of these. More preferably, it contains SBR, or may contain only SBR.

[0064] There are no particular limitations on the SBR, and examples of the SBR that can be used include emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. These may be used alone or in combination of two or more kinds.

[0065] The styrene content of 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. Within the above range, the effect tends to be better obtained. In this specification, the styrene content of SBR is H 1 - Calculated by NMR measurement.

[0066] 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, more preferably 70% by mass or less. Within the above range, the effect tends to be better obtained. The vinyl content (amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy.

[0067] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., and the like can be used.

[0068] The SBR may be unmodified or modified, and the modified SBR may be modified SBR having the same functional group as the modified diene rubber introduced therein.

[0069] 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, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be better obtained.

[0070] 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, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and may be 100% by mass. When it is within the above range, the effect tends to be better obtained.

[0071] The BR is not particularly limited, and for example, high cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, BR synthesized using a rare earth catalyst (rare earth BR), etc. can be used. These may be used alone or in combination of two or more. Among them, high cis BR with a cis content of 90% by mass or more is preferred because it improves wear resistance.

[0072] The BR may be either unmodified or modified. The modified BR may be a modified BR having the same functional group as the modified diene rubber introduced therein.

[0073] 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.

[0074] 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.

[0075] As the BR, for example, products from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc. can be used.

[0076] Examples of isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. Examples of NR include SIR20, RSS♯3, TSR20, and other rubber industry-standard rubbers. Examples of IR include IR2200 and other rubber industry-standard rubbers. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and other rubbers. Examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination of two or more.

[0077] 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.

[0078] 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.

[0079] From the viewpoint of obtaining better effects, the rubber compositions for the rubber layers 1 and 2 preferably contain soft particles.

[0080] From the viewpoint of obtaining better effects, the soft particles preferably have an average particle diameter of 0.08 to 50 μm. From the viewpoint of obtaining better effects, the average particle diameter of the soft particles is preferably 0.5 μm or more. 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.

[0081] In this specification, the average particle size of the soft particles is measured 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.

[0082] 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, based on 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. When the content is within the above range, the effect tends to be better obtained.

[0083] 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, based on 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. When the content is within the above range, the effect tends to be better obtained.

[0084] The hardness of the soft particles may be smaller or larger than the hardness of the rubber component, but from the viewpoint of obtaining a better effect, it is preferable that the hardness is larger than the hardness of the rubber component.

[0085] The structure of the soft particles is not particularly limited, and examples thereof include a solid structure, a hollow structure, a solid / hollow structure (such as a core-shell structure composed of multiple layers), etc. In addition, soft particles whose surface has been modified (such as soft particles whose surface has been modified with a modifier to improve affinity with rubber) can also be used.

[0086] Specifically, examples of soft particles that can be suitably used include 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 silicon-based beads.

[0087] 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 is one in which a volatile substance such as a low boiling point solvent is encapsulated inside the shell resin, and the shell resin is softened by heating, and the encapsulated volatile substance evaporates or expands, so that the shell expands under the pressure and the particle diameter becomes large, 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.

[0088] The shell of the thermally expandable microcapsule is preferably made of a thermoplastic resin. Examples of the thermoplastic resin 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.

[0089] Examples of volatile substances that can be encapsulated in the thermally expandable microcapsules include 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; CCl 3 F, CCl 2 F 2 chlorofluorocarbons such as chlorofluorocarbons, etc.; tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, etc.; and low-boiling point liquids.

[0090] A suitable example of the thermally expandable microcapsule is a microcapsule having a copolymer of acrylonitrile and vinylidene chloride as the shell resin and encapsulating a hydrocarbon having 3 to 7 carbon atoms, such as isobutane.

[0091] The thermally expandable microcapsules preferably expand 2 to 10 times their average particle diameter to become the above-mentioned expanded particles. The expansion start temperature of the thermally expandable microcapsules is preferably 95 to 150° C., more preferably 105 to 140° C. The maximum expansion temperature is preferably 120 to 200° C., more preferably 135 to 180° C.

[0092] 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.

[0093] The rubber composition for the rubber layers 1 and 2 may contain a filler other than the soft particles. As the filler, a material 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.

[0094] 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 them, 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.

[0095] The nitrogen adsorption specific surface area of ​​silica (N 2 SA) is preferably 70m 2 / g or more, more preferably 100m 2 / g or more, more preferably 150m 2 / g or more. In addition, the N content of silica 2 The upper limit of SA is not particularly limited, but is preferably 300 m 2 / g or less, more preferably 250m 2 / g or less, more preferably 200m 2 Within the above range, there is a tendency for the effect to be better obtained. In addition, the N of silica 2 SA is a value measured by the BET method in accordance with ASTM D3037-93.

[0096] 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, based on 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.

[0097] 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, based on 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.

[0098] 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 ...4-trimethoxysilylbutyl)disulfide, bis Examples of the silylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide and other sulfide-based silylsilylsilanes; mercapto-based silylsilanes such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based silylsilanes such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based silylsilanes such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based silylsilanes such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silylsilanes such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silylsilanes such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products include those from Degussa, Momentive, Shin-Etsu Silicone, Tokyo Chemical Industry, Azumax, and Dow Corning Toray. These may be used alone or in combination of two or more. Of these, sulfide-based and mercapto-based products are preferred.

[0099] In the rubber composition for the rubber layer 1 and the rubber layer 2, the content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, based on 100 parts by mass of silica. The content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less. When the content is within the above range, the effect tends to be better.

[0100] Examples of carbon black that can be used in the rubber composition for the rubber layer 1 and the 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 Co., Ltd., Lion Co., Ltd., Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like.

[0101] The nitrogen adsorption specific surface area of ​​carbon black (N 2 SA) is 50m 2 / g or more is preferable, and 80m 2 / g or more is more preferable, and 100m 2 / g or more is more preferable. 2 SA is 200m 2 / g or less is preferable, and 150m 2 / g or less is more preferable, and 130m 2 Within the above range, there is a tendency that the effect is better obtained. The nitrogen adsorption specific surface area of ​​carbon black is determined in accordance with JIS K6217-2:2001.

[0102] 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, based on 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.

[0103] When the rubber composition for the rubber layer 2 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, based on 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.

[0104] 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. Examples of the 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)).

[0105] When the rubber composition for the rubber layer 1 contains a plasticizer, the content of the plasticizer (total amount of the 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, relative to 100 parts by mass of the rubber component. The lower limit is not particularly limited and may be 0 parts by mass, but 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.

[0106] When the rubber composition for the rubber layer 2 contains a plasticizer, the content of the plasticizer (total amount of the 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, relative to 100 parts by mass of the rubber component. The lower limit is not particularly limited and may be 0 parts by mass, but 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.

[0107] Liquid plasticizers (plasticizers in a liquid state at room temperature (25° C.)) that can be used in the rubber compositions for the rubber layer 1 and the rubber layer 2 are not particularly limited, and examples thereof include oils, liquid polymers (liquid resins, liquid diene-based polymers, liquid farnesene-based polymers, etc.), etc. These may be used alone or in combination of two or more kinds.

[0108] 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, relative to 100 parts by mass of the rubber component. The lower limit is not particularly limited and may be 0 parts by mass, but 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 extension oil.

[0109] 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, relative to 100 parts by mass of the rubber component. The lower limit is not particularly limited and may be 0 parts by mass, but 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 extension oil.

[0110] 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 products from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H&R Co., Ltd., Toyokuni Oil Mill 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.

[0111] Examples of 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 products of these resins can also be used.

[0112] Examples of 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, and liquid farnesene butadiene copolymers that are in a liquid state at 25°C. The ends or main chains of these may be modified with polar groups. Hydrogenated versions of these may also be used.

[0113] Examples of the resins (resins in a solid state at room temperature (25°C)) that can be used in the rubber compositions for the rubber layer 1 and the rubber layer 2 include aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, and acrylic resins that are in a solid state at room temperature (25°C). The resins may 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.

[0114] 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, based on 100 parts by mass of the rubber component. The lower limit is not particularly limited and may be 0 parts by mass, but 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.

[0115] 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, based on 100 parts by mass of the rubber component. The lower limit is not particularly limited and may be 0 parts by mass, but 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.

[0116] 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.

[0117] The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a structural 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.

[0118] The coumarone-indene resin is a resin containing coumarone and indene as main monomer components constituting the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

[0119] The coumarone resin is a resin containing coumarone as a main monomer component constituting the skeleton (main chain) of the resin.

[0120] The indene resin is a resin containing indene as a main monomer component constituting the skeleton (main chain) of the resin.

[0121] The phenolic resin may be a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural in the presence of an acid or alkali catalyst. Among these, those obtained by reacting with an acid catalyst (such as novolac-type phenolic resin) are preferred.

[0122] Examples of the rosin resin include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0123] Examples of the petroleum resin include C5 resin, C9 resin, C5 / C9 resin, dicyclopentadiene (DCPD) resin, and hydrogenated versions of these resins. Of these, DCPD resin and hydrogenated DCPD resin are preferred.

[0124] The terpene resin is a polymer containing terpene as a constituent unit. For example, polyterpene resin obtained by polymerizing a terpene compound, aromatic modified terpene resin obtained by polymerizing a terpene compound and an aromatic compound, etc. can be mentioned. As the aromatic modified terpene resin, terpene phenol resin made from terpene compounds and phenolic compounds, terpene styrene resin made from terpene compounds and styrene compounds, and terpene phenol styrene resin made from terpene compounds, phenolic compounds, and styrene compounds can also be used. In addition, examples of the terpene compound include α-pinene, β-pinene, etc., examples of the phenolic compound include phenol, bisphenol A, etc., and examples of the aromatic compound include styrene compounds (styrene, α-methylstyrene, etc.).

[0125] The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, a styrene-acrylic resin having a carboxyl group and obtained by copolymerizing an aromatic vinyl monomer component and an acrylic monomer component, such as a styrene-acrylic resin, can be used. Among them, a solventless carboxyl group-containing styrene-acrylic resin can be preferably used.

[0126] Examples of the plasticizer 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, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

[0127] The rubber composition for the rubber layers 1 and 2 preferably contains an antioxidant from the viewpoints of crack resistance, ozone resistance, and the like.

[0128] The antiaging agent is not particularly limited, and examples thereof include naphthylamine-based antiaging agents such as phenyl-α-naphthylamine; diphenylamine-based antiaging 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 the antioxidant 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 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 from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd.

[0129] In the rubber composition for the rubber layers 1 and 2, the content of the antioxidant is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, based on 100 parts by mass of the rubber component. The content is preferably 7.0 parts by mass or less, more preferably 4.0 parts by mass or less.

[0130] The rubber composition for the rubber layer 1 and the rubber layer 2 may contain stearic acid. The content of stearic acid in the rubber composition for the rubber layer 1 and the rubber layer 2 is preferably 0.5 to 10 parts by mass or more, and more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the rubber component.

[0131] As the stearic acid, any known stearic acid can be used, for example, products available from NOF Corporation, NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., and the like.

[0132] The rubber composition for the rubber layers 1 and 2 preferably contains zinc oxide. The content of zinc oxide is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, based on 100 parts by mass of the rubber component.

[0133] As the zinc oxide, any known zinc oxide can be used, for example, products available 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.

[0134] Wax may be blended into the rubber composition for the rubber layers 1 and 2. The content of the wax is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, based on 100 parts by mass of the rubber component.

[0135] The wax is not particularly limited, and examples thereof include petroleum waxes, natural waxes, etc. Also, synthetic waxes obtained by refining or chemically treating multiple waxes can be used. These waxes may be used alone or in combination of two or more kinds.

[0136] Examples of petroleum 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 thereof 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. Examples of commercially available products include 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.

[0137] 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.

[0138] Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., 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., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more kinds.

[0139] 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.

[0140] The type of vulcanization accelerator is not particularly limited, 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, Nt-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 vulcanization accelerators and guanidine vulcanization accelerators are preferred.

[0141] In addition to the above-mentioned components, the rubber composition for the rubber layers 1 and 2 may contain appropriate additives, such as a release agent and a pigment, that are commonly used in the field of application.

[0142] A known method can be used to produce the rubber composition for the rubber layers 1 and 2. For example, the rubber composition can be produced by kneading each component using a rubber kneading device such as an open roll or a Banbury mixer, and crosslinking 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.

[0143] The pneumatic tire of the present invention can be used as a passenger car tire, a large passenger car tire, a large SUV tire, a heavy load tire such as a truck or a bus tire, a light truck tire, a two-wheeled vehicle tire, a racing tire (high performance tire), etc. It can also be used as an all-season tire, a summer tire, a studless tire (winter tire), etc. Among them, it is preferable to use it as a passenger car tire. In addition, a passenger car tire refers to a tire that is assumed to be mounted on a four-wheeled vehicle and has a maximum load capacity of 1000 kg or less. Here, the maximum load capacity is the maximum load capacity determined for each tire by the standard system including 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 the TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of the ETRTO, it is "LOAD CAPACITY". EXAMPLES

[0144] The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0145] SBR: HPR850 manufactured by JSR Corporation (styrene content: 27.5% by mass, vinyl bond content: 59.0% by mass) BR: BR150B (cis content 98% by mass) manufactured by Ube Industries, Ltd. NR:TSR20 Flexible particle 1: Art Pearl JB-800 manufactured by Negami Chemical Industries, Ltd. (urethane beads (hollow structure), average particle diameter 6 μm) Flexible particles 2: Art Pearl JB-400 manufactured by Negami Chemical Industries, Ltd. (urethane beads (hollow structure), average particle diameter 15 μm) Flexible particles 3: C-200 manufactured by Negami Chemical Industries, Ltd. (urethane beads (hollow structure), average particle diameter 32 μm) Flexible 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 Anti-aging agent: 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.

[0146] <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 according to the specifications in Tables 2 and 4, and the resulting compositions were laminated together with other tire components and vulcanized at 170°C for 15 minutes to produce test tires (tire size: 195 / 65R15).

[0147] The obtained test tires were subjected to the following physical property measurements and evaluations, and the results are shown in the tables. In addition, in Tables 2 and 4, Comparative Examples 1-1 and 2-1 were used as the reference comparative examples, respectively.

[0148] <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 tear energy was 1.0×10 0.1 ~2.0×10 0.1 The slope a [(mm / cycle) / J] of the crack growth rate [mm / cycle] versus tear energy [J] in the range of [J] was measured by measuring the crack growth rate [mm / cycle] at each tear energy [J], converting the measured values ​​logarithmically according to Figures 3 and 4, and then applying the least squares method. The following equipment and test conditions were used. (Device) Coesfeld Tear Fatigue Analyzer (fatigue testing machine with crack observation system) (Test conditions) At room temperature (approximately 23°C), the frequency is 5Hz and the period is 10Hz. P A pulse wave with amplitudes of 10, 15, 20, 25, 30, and 35% is applied to the smooth portion of a test piece having a smooth surface of 15 mm until the specimen breaks.

[0149] <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".

[0150] <TGC resistance at the end of driving period> The rim-mounted test tires were heat-treated at 80°C for two weeks while irradiating the tread with 30 pphm of ozone, then mounted on a domestic FF vehicle and driven around on an asphalt road surface, after which the occurrence of cracks at the bottom of the grooves was observed. The length of the cracks that occurred at the bottom of the grooves was measured and indexed using the following formula. The higher the index, the better the resistance to cracks at the bottom of the grooves. (Crack length of the standard comparative tire) / (Crack length of each tire specification) x 100

[0151] [Table 1]

[0152] [Table 2]

[0153] [Table 3]

[0154] [Table 4]

[0155] From each table, it can be seen that the example tires which satisfied the formulas (1) and (2) and the slope a of 2.0 or less had superior TGC resistance at the end of the running period compared to the comparative examples which did not satisfy these formulas. [Explanation of symbols]

[0156] 2. Pneumatic tires 4 Tread 6 Sidewall 8 Wing 10. Clinch 12 Beads 14 Carcass 16 Belt 18 Bands 20 Inner Liner 22 Chafer 24 Tread surface 26 Circumferential groove 27 Groove bottom 28 Base Layer 28A Base layer at the bottom of the circumferential groove 30 Cap Layer 30A Cap layer at the bottom of the circumferential groove 32 cores 34 Apex 36 Carcass ply 36a Main part 36b Folded part 38 Inner layer 40 outer layer 44 Ribs CL Equatorial plane of tire 2 L0: Circumferential groove width at the radially outermost surface of the tire in a cross-sectional view L95 Circumferential groove width at 95% depth from the outermost surface in the radial direction of the tire D Circumferential groove depth

Claims

1. 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 log ｅ (tear energy [J]) in the range of 0.0 to 0.3, log ｅ (tear energy [J]) vs. log ｅ A tire in which the slope a of (dc / dn [mm / cycle]) is 2.0 or less. (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. 2. The tire according to claim 1, which satisfies the following formula: 0.10≦L95 / L0≦0.30

3. 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

4. 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

5. The tire according to any one of claims 1 to 4, wherein the L0 is 5 to 20 mm.

6. The tire according to any one of claims 1 to 5, wherein the circumferential groove has a groove depth D of 6.0 to 12.0 mm.

7. 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

8. The tire according to any one of claims 1 to 7, wherein the H2 is 44 to 53.

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