tire

Abstract

To provide a tire capable of maintaining wet performance and steering stability even when wear of a tread part progresses.SOLUTION: Provided is a tire with a tread part 2. The tread part 2 includes a first cap rubber layer 11, and a second cap rubber layer 12. A loss tangent tanδ2 of the second cap rubber layer 12 is larger than a loss tangent tanδ1 of the first cap rubber layer 11. A plurality of sipings 15 which open on a ground contact surface 2s are disposed on the tread part 2. The plurality of sipings 15 extends from the ground contact surface 2s to a position beyond at least a boundary between the first cap rubber layer 11 and the second cap rubber layer 12. In the plurality of sipings 15, a largest length L2 on the second cap rubber layer 12 of the sipings 15 is smaller than a length L1 on the ground contact surface 2s of the sipings 15.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 below proposes a pneumatic tire in which the loss tangent of the base rubber layer in the tread portion is specified. The pneumatic tire is expected to have improved wear resistance and fuel economy performance by including in the base rubber layer a low heat-generating rubber with a smaller loss tangent than the cap rubber layer that forms the outer surface of the tread. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-013539 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, with increasing environmental awareness and the practical application of autonomous driving technology, there has been a demand for tires that are maintenance-free over the long term. In particular, there is a demand for tires that can exhibit sufficient wet performance and handling stability until the end of tread wear.

[0005] The present invention has been devised in view of the above-described circumstances, and has as its main object to provide a tire that can maintain wet performance and handling stability even as wear of the tread portion progresses. [Means for solving the problem]

[0006] The present invention is a tire having a tread portion, the tread portion including a first cap rubber layer constituting a contact surface and a second cap rubber layer arranged radially inward of the first cap rubber layer, the loss tangent tanδ2 of the second cap rubber layer being larger than the loss tangent tanδ1 of the first cap rubber layer, the tread portion being provided with a plurality of sipes opening at the contact surface, the plurality of sipes extending from the contact surface to a position at least beyond the boundary between the first cap rubber layer and the second cap rubber layer, and the maximum length L2 of the plurality of sipes at the second cap rubber layer being smaller than the length L1 of the sipes at the contact surface.

[0007] In the tire of the present invention, the loss tangent tanδ1 is preferably 0.13 to 0.29.

[0008] In the tire of the present invention, the loss tangent tanδ2 is preferably 0.30 to 0.40.

[0009] In the tire of the present invention, it is preferable that the tread portion includes a base rubber layer disposed radially inward of the second cap rubber layer, and that the loss tangent tanδb of the base rubber layer is smaller than the loss tangent tanδ1.

[0010] In the tire of the present invention, the loss tangent tanδb is preferably 0.12 or less.

[0011] In the tire of the present invention, it is preferable that the tread portion is provided with a plurality of circumferential grooves extending continuously in the tire circumferential direction, and the maximum depth of the sipes is 75% to 100% of the maximum depth of the circumferential grooves.

[0012] In the tire of the present invention, the maximum length L2 of the sipe in the second cap rubber layer is preferably 60% to 80% of the length L1 of the sipe at the contact surface.

[0013] In the tire of the present invention, it is desirable that the sipes extend in a wavy shape in the radial direction of the tire in a cross section of the sipes.

[0014] In the tire of the present invention, it is desirable that the wavelength of the sipe in the tire radial direction is 20% to 60% of the thickness of the second cap rubber layer in the tire radial direction.

[0015] In the tire of the present invention, the sipes preferably include lateral sipes extending in the tire axial direction.

[0016] In the tire of the present invention, the sipes preferably include longitudinal sipes extending in the tire circumferential direction. [Effects of the Invention]

[0017] By adopting the above-described configuration, the pneumatic tire of the present invention can maintain wet performance and steering stability even when wear of the tread portion progresses. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a tire meridian cross-sectional view showing one embodiment of a tire of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a land portion of FIG. [Figure 3] FIG. 2 is an enlarged cross-sectional view of a land portion and a sipe. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a land portion when a second cap rubber layer is exposed. [Figure 5] FIG. 10 is an enlarged cross-sectional view of a land portion and a sipe according to another embodiment. [Figure 6] FIG. 10 is a cross-sectional view of a sipe according to another embodiment. [Figure 7] FIG. 2 is an enlarged cross-sectional view of a vertical sipe. [Figure 8] FIG. 2 is an enlarged cross-sectional view of a land portion and a sipe of a tire of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a tire meridian cross-sectional view of a tire 1 in a normal state, showing one embodiment of the present invention. As shown in Fig. 1, the present invention is preferably applied to, for example, a pneumatic tire for a passenger car. However, the present invention is not limited to this embodiment, and may also be applied to, for example, a tire for a motorcycle or a heavy load.

[0020] The "normal condition" refers to a state in which, in the case of a pneumatic tire for which various standards are established, the tire is mounted on a normal rim, inflated to the normal internal pressure, and no load is applied. In the case of a tire for which various standards are not established, the normal condition refers to a standard use state according to the intended use of the tire, in which the tire is not mounted on a vehicle and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are values measured in the normal condition.

[0021] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "design rim," and in the case of ETRTO, it is called a "measuring rim."

[0022] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0023] Tire constituent members such as a carcass 6 and a belt layer 7 are arranged inside the tire 1 of this embodiment. Known embodiments are appropriately adopted for these tire constituent members.

[0024] The carcass 6 extends from the bead portion 4 on one side, through the sidewall portion 3 on one side, the tread portion 2, and the sidewall portion 3 on the other side, to the bead portion 4 on the other side. The carcass 6 of this embodiment is made up of, for example, two carcass plies 6A and 6B. The two carcass plies 6A and 6B are made up of carcass cords made of organic fibers arranged at an angle of 75 to 90 degrees with respect to the tire circumferential direction, for example.

[0025] The belt layer 7 is composed of, for example, two belt plies 7A and 7B. The belt plies 7A and 7B are composed of belt cords arranged at an angle of, for example, 10 to 45 degrees with respect to the tire circumferential direction. For example, organic fiber cords or steel cords may be used as the belt cords as appropriate. In another embodiment, a tread reinforcing layer such as a band layer may be further disposed on the outer side of the belt layer 7.

[0026] The tread portion 2 of this embodiment is provided with a plurality of circumferential grooves 8 that extend continuously in the tire circumferential direction. As a result, the tread portion 2 includes a plurality of land portions 9 that are divided by the plurality of circumferential grooves 8. However, the present invention is not limited to this embodiment.

[0027] FIG. 2 shows an enlarged cross-sectional view of the land portion 9 as a diagram for explaining the configuration of the tread portion 2. As shown in FIG. 2, the tread portion 2 includes a first cap rubber layer 11 constituting the contact patch 2s and a second cap rubber layer 12 disposed radially inward of the first cap rubber layer 11. The tread portion 2 of this embodiment further includes a base rubber layer 10 disposed radially inward of the second cap rubber layer 12. As a result, the tread portion 2 of this embodiment is configured with three rubber layers: the first cap rubber layer 11, the second cap rubber layer 12, and the base rubber layer 10. However, the present invention is not limited to this embodiment. Note that in FIG. 2 and the subsequent figures, each rubber layer is hatched differently, but in FIG. 1, the hatching is omitted to avoid cluttering the drawing.

[0028] In the present invention, the loss tangent tanδ2 of the second cap rubber layer 12 is larger than the loss tangent tanδ1 of the first cap rubber layer 11. In this specification, the loss tangent tanδ is a value measured in accordance with the provisions of JIS-K6394 using a dynamic viscoelasticity measuring device (Iplexar series) manufactured by GABO under the following conditions: Initial strain: 5% Dynamic strain amplitude: ±1% Frequency: 10Hz Deformation mode: Stretch Measurement temperature: 30℃

[0029] The tread portion 2 is provided with a plurality of sipes 15 that open at the contact surface. The sipes 15 in this embodiment are configured as lateral sipes that extend in the tire axial direction. However, in the present invention, the length direction of the sipes 15 is not particularly limited. Therefore, the sipes 15 may be longitudinal sipes that extend in the tire circumferential direction. Also, one tread portion 2 may be provided with both lateral sipes and longitudinal sipes. Note that, since FIG. 2 is a cross section of the land portion 9 at a position that does not include sipes, the bottoms 15d of the sipes 15 are indicated by dashed lines in FIG. 2.

[0030] In this specification, the term "sipe" refers to a narrow cut element having a width of 1.5 mm or less between two inner walls that face each other and extend substantially parallel to each other. Furthermore, "substantially parallel" refers to an embodiment in which the angle between the two inner walls is 10° or less. The width of the sipe is preferably 0.5 to 1.5 mm, and more preferably 0.4 to 1.0 mm. The configuration of the sipe is not particularly limited, and in another embodiment, at least one of the sipe edges on both sides may be configured as a chamfered portion. Furthermore, the bottom of the sipe may be connected to a flask bottom having a width of more than 1.5 mm.

[0031] FIG. 3 shows an enlarged cross-sectional view of the land portion 9 and the sipes 15. The cross-section of the sipes 15 shown in FIG. 3 corresponds to a cross-section along the length of the sipes 15. As shown in FIG. 3, the plurality of sipes 15 extend from the ground contact surface 2s to a position beyond at least the boundary 16 between the first cap rubber layer 11 and the second cap rubber layer 12. Furthermore, the maximum length L2 of the plurality of sipes 15 at the second cap rubber layer 12 is smaller than the length L1 of the sipes 15 at the ground contact surface 2s. The lengths L1 and L2 are each measured parallel to the ground contact surface 2s of the tread portion 2 and refer to the so-called periphery length along the length of the sipes 15.

[0032] By adopting the above-described configuration, the present invention can maintain wet performance and steering stability even with progress of wear in the tread portion 2. The following mechanism is presumed to be the reason for this.

[0033] Fig. 4 shows an enlarged cross-sectional view of the land portion 9 when the tread portion 2 is worn and the second cap rubber layer 12 is exposed as the contact patch 2s. As shown in Fig. 4, in the present invention, the loss tangent tanδ2 of the second cap rubber layer 12 is larger than the loss tangent tanδ1 of the first cap rubber layer 11. Therefore, when the wear of the tread portion 2 progresses and the second cap rubber layer 12 is exposed, the second cap rubber layer 12 can exert a large grip force on wet roads. This makes it possible to maintain wet performance.

[0034] On the other hand, in the present invention, as shown in Fig. 3, the maximum length L2 of the sipe 15 in the second cap rubber layer 12 is smaller than the length L1 of the sipe 15 at the contact surface, and therefore, as shown in Fig. 4, the length of the sipe 15 when the second cap rubber layer 12 is exposed is relatively short. Therefore, even in a worn state in which the second cap rubber layer 12 is exposed, the rigidity of the tread portion 2 can be maintained, and thus steering stability can be maintained. Furthermore, in the present invention, by maintaining the rigidity of the tread portion 2, it can be expected that the progression of wear from a state in which the second cap rubber layer 12 is exposed can be slowed.

[0035] For the reasons described above, it is believed that the present invention can maintain wet performance and steering stability even when wear of the tread portion 2 progresses.

[0036] The following describes the configuration of this embodiment in more detail. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-described effects even if it does not have the configuration described below. Furthermore, even if any one of the configurations described below is applied alone to a tire of the present invention having the above-described characteristics, an improvement in performance corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, an improvement in combined performance corresponding to each configuration can be expected.

[0037] 2, the thickness t1 of the first cap rubber layer 11 is, for example, 25% to 35% of the total tread rubber thickness Ta (shown in FIG. 1 and the same applies hereinafter) from the ground contact surface of the tread portion 2 to the outer surface of the belt layer 7. The thickness t2 of the second cap rubber layer 12 is, for example, 15% to 25% of the total tread rubber thickness Ta.

[0038] As a result, the radial distance L3 from the ground contact surface 2s of the tread portion 2 to the boundary 17 between the second cap rubber layer 12 and the base rubber layer 10 is 60% to 80% of the depth d1 of the circumferential groove 8. With the rubber layers arranged in this manner, the second cap rubber layer 12, which is expected to have a high gripping force, is exposed from the latter to final stages of wear of the tread portion 2. This ensures that wet performance is maintained. In this embodiment, the boundary 16 between the first cap rubber layer 11 and the second cap rubber layer 12 and the boundary 17 between the second cap rubber layer 12 and the base rubber layer 10 each extend parallel to the ground contact surface 2s of the tread portion 2.

[0039] The loss tangent tanδ1 of the first cap rubber layer 11 is preferably 0.13 or more, more preferably 0.15 or more, and preferably 0.29 or less, and more preferably 0.25 or less. The loss tangent tanδ2 of the second cap rubber layer 12 is preferably 0.30 or more, more preferably 0.33 or more, and preferably 0.40 or less, and more preferably 0.37 or less. The loss tangent tanδ1 is 50% to 65% of the loss tangent tanδ2. Such first cap rubber layer 11 and second cap rubber layer 12 can achieve a well-balanced overall tire performance and can suppress rubber peeling at the boundary 16 between the first cap rubber layer 11 and the second cap rubber layer 12.

[0040] The loss tangent tanδb of the base rubber layer 10 is preferably smaller than the loss tangent tanδ1 of the first cap rubber layer 11. Specifically, the loss tangent tanδb is, for example, 0.12 or less, and preferably 0.07 to 0.12. This suppresses excessive heat generation in the tread portion 2 and improves tire durability. However, the loss tangent tanδb of the base rubber layer 10 is not limited to this range.

[0041] The loss tangent tan δ of each of the rubber layers can be obtained by appropriately combining known materials, and the explanation thereof will be omitted here.

[0042] As shown in Fig. 3, the sipes 15 of this embodiment are configured as lateral sipes extending in the tire axial direction, and in a preferred embodiment, extend parallel to the tire axial direction (not shown). Furthermore, the sipes 15 completely traverse the tread portion 2 in the tire axial direction at the contact surface of the tread portion 2. On the other hand, as shown in Fig. 4, the sipes 15 of this embodiment are discontinued at both ends within the land portion 9 when the second cap rubber layer 12 is exposed. This ensures that the rigidity of the tread portion 2 is maintained when the second cap rubber layer 12 is exposed.

[0043] 3, the maximum length L2 of the sipe 15 in the second cap rubber layer 12 is preferably 60% or more, more preferably 65% or more, and preferably 80% or less, more preferably 75% or less of the length L1 of the sipe 15 in the contact patch 2s. Such sipes 15 are useful for improving wet performance and steering stability in a balanced manner when the tread portion 2 is worn.

[0044] The bottoms 15d of the sipes 15 are disposed, for example, in the base rubber layer 10. However, the bottoms 15d of the sipes 15 may also be disposed in the second cap rubber layer 12. The maximum depth d2 of the sipes 15 is preferably, for example, 75% to 100% of the maximum depth d1 of the circumferential grooves 8. Such sipes 15 are useful for improving wet performance.

[0045] The cross-sectional configuration of the sipe 15 along its length is not limited to the above-described embodiment. Fig. 5 shows another embodiment of the sipe 15. As shown in Fig. 5, in this embodiment, one end of the sipe 15 communicates with the circumferential groove 8 in the contact patch 2s of the tread portion 2, and the other end terminates within the land portion 9. Also, in this embodiment, when the second cap rubber layer 12 is exposed, both ends of the sipe 15 terminate within the land portion. Such sipes 15 help to achieve excellent driving stability.

[0046] FIG. 6 shows a cross-sectional view of a sipe 15 according to another embodiment. Note that FIG. 6 shows a cross section perpendicular to the longitudinal direction of the sipe 15. As shown in FIG. 6, in the cross section of the sipe 15, the sipe 15 may extend in a wavy manner in the radial direction of the tire. Such a sipe 15 can increase the rigidity of the land portion 9 when opposing sipe walls come into contact with each other, thereby achieving excellent steering stability. It goes without saying that the above-described configurations shown in FIG. 3 and the like can be applied to the cross-sectional configuration of the sipe 15 along the longitudinal direction shown in FIG. 6.

[0047] 6, the wavelength A1 in the tire radial direction of the sipe 15 is preferably 20% to 60% of the thickness t2 in the tire radial direction of the second cap rubber layer 12. This can reliably enhance the above-mentioned effects.

[0048] Fig. 7 shows an enlarged cross-sectional view of a longitudinal sipe 20 extending in the tire circumferential direction. In Fig. 7, arrow A corresponds to the tire circumferential direction. As shown in Fig. 7, the sipes 15 of the present invention may be longitudinal sipes 20 extending in the tire circumferential direction. In this case, the longitudinal sipes 20 provide friction force in the tire axial direction, thereby improving cornering performance on wet roads.

[0049] Although a tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be modified and practiced in various aspects. [Example]

[0050] As the tire of the example, a pneumatic tire of size 235 / 65R16C was manufactured. The tire of the example had the basic structure shown in FIG. 1, and the rubber layers shown in FIG. 2 were arranged in the tread portion, and furthermore, it had a plurality of sipes shown in FIG. 3. In addition, as a comparative example, a tire having a land portion a and sipe b shown in FIG. 8 was manufactured. In the comparative example tire, the loss tangent tanδ1 of the first cap rubber layer is larger than the loss tangent tanδ2 of the second cap rubber layer, and the entire sipe b completely crosses the land portion a in the tire axial direction. Except for the above-mentioned points, the comparative example tire is substantially the same as the tire of the example. These test tires were tested for wet performance and handling stability when new, and wet performance and handling stability when 50% worn. Note that the 50% worn state refers to a tire in a state where the remaining depth of the circumferential grooves is 50% of that when new. The common specifications and test methods for each test tire are as follows. Rim: 16 x 7.0J Tire pressure: 475kPa Test vehicle: 3000cc, rear-wheel drive Test tire mounting position: All wheels

[0051] <Wet performance (new and 50% worn)> The wet performance of test vehicles fitted with new or 50% worn test tires was evaluated by the driver's senses when driving on wet roads. The results are rated based on the wet performance of the comparative tire when new, which is 100 points. The higher the score, the better the wet performance.

[0052] <Driving stability (new and 50% worn)> The handling stability of a test vehicle fitted with a new or 50% worn test tire was evaluated by the driver's senses when driving on a dry road. The results are given as a score, with the handling stability of the comparative tire when new being 100, and the higher the score, the better the handling stability. The test results are shown in Tables 1-2.

[0053] [Table 1]

[0054] [Table 2]

[0055] As shown in Tables 1 and 2, the comparative example had a wet performance of 60 points at 50% wear and a handling stability of 80 points at 50% wear. In contrast, the tires of the examples maintained high wet performance of 77 to 85 points at 50% wear. Furthermore, the tires of the examples maintained high handling stability of 87 to 92 points at 50% wear. As described above, it was confirmed that the tires of the examples maintained wet performance and handling stability even as wear of the tread progressed. [Explanation of symbols]

[0056] 2 Tread section 2s ground plane 11 First cap rubber layer 12 Second cap rubber layer 15 sipes L1 Length of sipe at contact surface L2 Maximum length of the sipe in the second cap rubber layer

Claims

1. A tire having a tread portion, the tread portion includes a first cap rubber layer constituting a ground contact surface, a second cap rubber layer disposed radially inward of the first cap rubber layer, and a base rubber layer disposed radially inward of the second cap rubber layer, the loss tangent tanδ2 of the second cap rubber layer measured in accordance with the provisions of JIS-K6394 under the conditions of initial strain: 5%, dynamic strain amplitude: ±1%, frequency: 10 Hz, deformation mode: extension, and measurement temperature: 30°C is larger than the loss tangent tanδ1 of the first cap rubber layer measured under the same conditions, a loss tangent tanδb of the base rubber layer measured under the above conditions is smaller than the loss tangent tanδ1, The tread portion is provided with a plurality of sipes that open at the contact surface and a circumferential groove that extends continuously in the tire circumferential direction, the base rubber layer has a portion extending in the tire axial direction and radially outward of the groove bottom of the circumferential groove, the plurality of sipes extend from the ground contact surface to the base rubber layer beyond at least a boundary between the first cap rubber layer and the second cap rubber layer, The plurality of sipes have a maximum length L2 of the sipe at the second cap rubber layer that is smaller than a length L1 of the sipe at the ground contact surface, a maximum depth of the sipe from the ground contact surface is 75% to 100% of a maximum depth of the circumferential groove, a portion of the bottom of the sipe is located in the portion of the base rubber layer; tire.

2. 2. The tire according to claim 1, wherein the loss tangent tanδ1 is 0.13 to 0.

29.

3. The tire according to claim 1 or 2, wherein the loss tangent tanδ2 is 0.30 to 0.

40.

4. The tire according to any one of claims 1 to 3, wherein the loss tangent tan δb is equal to or less than 0.

12.

5. 5. The tire according to claim 1, wherein a maximum length L2 of the sipe in the second cap rubber layer is 60% to 80% of a length L1 of the sipe at the contact surface.

6. The tire according to claim 1 , wherein in a cross section of the sipe, the sipe extends in a wavy manner in the tire radial direction.

7. The tire according to claim 6, wherein a wavelength of the sipe in the tire radial direction is 20% to 60% of a thickness of the second cap rubber layer in the tire radial direction.

8. The tire according to claim 1 , wherein the sipes include lateral sipes extending in the tire axial direction.

9. The tire according to claim 1 , wherein the sipes include longitudinal sipes extending in the tire circumferential direction.

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