tire

Abstract

To provide a tire 2 that can exhibit good wet performance even when the base layer 30 is exposed. [Solution] The tread 4 of the tire 2 comprises a base layer 30. The base layer 30 contains a filler. The filler contains carbon black and silica. The ratio Sr of silica content to the sum of carbon black content BCB and silica content BSi is greater than 0.20. The tread 4 comprises a plurality of land sections 12 separated by circumferential main grooves 10. The ratio Ur of the thickness TU of the base layer 30 to the depth DGm of the circumferential main grooves 10 is 0.20 or more and 0.60 or less. At least one land section 12 comprises a sipe 26 having a bottom 26T within the base layer 30. The ratio Sr, the thickness TU of the base layer 30, and the depth DU of the sipe 26 in the base layer 30 satisfy the following relationship: Sr × DU ​​ / TU ≥ 0.010

Description

Technical Field

[0001] The present invention relates to a tire.

Background Art

[0002] A technique for forming a tread with two layers of a cap layer and a base layer located inside it is known. Patent Document 1 discloses that, in order to improve grip performance (hereinafter, wet performance) on a wet road surface, the cap layer is formed of a crosslinked rubber that is softer than the crosslinked rubber of the base layer. The tread contacts the road surface. As a result, the tread wears. In a two-layer tread, when the cap layer disappears due to wear, the base layer is exposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a tire that can exhibit good wet performance even when the base layer is exposed.

Means for Solving the Problems

[0005] The tire according to the present invention comprises a tread located radially on the outermost side and extending circumferentially. The tread comprises a cap layer and a base layer located radially inward from the cap layer. The base layer is composed of a rubber composition comprising a rubber component and a filler. The filler comprises carbon black and silica. The ratio Sr of the silica content to the sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is greater than 0.20. The tread comprises a plurality of land portions separated by circumferential main grooves. The ratio Ur of the thickness TU of the base layer to the depth DGm of the circumferential main grooves is 0.20 or more and 0.60 or less. At least one of the land portions comprises a sipe having a bottom within the base layer. The ratio Sr, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relational expression. Sr × DU ​​ / TU ≥ 0.010 [Effects of the Invention]

[0006] The present invention provides a tire that can exhibit good wet performance even when the base layer is exposed. [Brief explanation of the drawing]

[0007] [Figure 1] This is an exploded view showing a portion of the tire tread according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view along line II-II in Figure 1. [Figure 3] This is a cross-sectional view along line III-III in Figure 1. [Figure 4] This is a diagram showing a modified example of a sipe. [Figure 5] This is a cross-sectional view along the VV line in Figure 4. [Figure 6] This is a cross-sectional view showing other variations of the sipe. [Figure 7] This is a cross-sectional view illustrating the positional relationship between the sipe body and the tubular section boundary PB with respect to the boundary between the cap layer and the base layer. [Figure 8]This is a cross-sectional view illustrating the positional relationship between the sipe body and the tubular section boundary PB with respect to the boundary between the cap layer and the base layer. [Figure 9] This is a cross-sectional view showing yet another variation of the sipe. [Modes for carrying out the invention]

[0008] The present invention will now be described in detail, with reference to drawings as appropriate, based on preferred embodiments.

[0009] The tire of this invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is regulated. A tire mounted on a rim is also called a tire-rim assembly. A tire-rim assembly comprises a rim and a tire mounted on this rim.

[0010] In this invention, the state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to the tire is referred to as the standard state.

[0011] In this invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured under normal conditions. The dimensions and angles of each part of the tire in the meridional cross-section, which cannot be measured when the tire is mounted on a standard rim, are measured at the tire's cross-section, obtained by cutting the tire along a plane containing the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in a tire mounted on a standard rim. The tire's structure, which cannot be confirmed when the tire is mounted on a standard rim, is confirmed at the aforementioned cross-section.

[0012] A genuine rim refers to a rim defined in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are all considered genuine rims.

[0013] Regular tire pressure refers to the internal pressure specified in the tire's standard. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are all considered regular tire pressures.

[0014] The standard load refers to the load specified in the tire's specifications. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are all considered standard loads.

[0015] In the present invention, crosslinked rubber is a crosslinked product of a rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is a material obtained by mixing rubber components with chemicals such as fillers in a kneading machine such as a Banbury mixer.

[0016] In this invention, the loss tangent (tanδ) and complex modulus of the cross-linked rubber element among the components constituting the tire are measured using a viscoelastic spectrometer in accordance with the provisions of JIS K6394. The measurement conditions are as follows. Initial distortion = 10% Dynamic strain = ±1% Frequency = 10Hz Mode = Extension Mode Temperature = 0°C or 70°C In this measurement, the test specimen (40 mm long x 4 mm wide x 1 mm thick) is sampled from the tire. The length of the test specimen is aligned with the circumferential direction of the tire. If it is not possible to sample a test specimen from the tire, a test specimen is sampled from a sheet of cross-linked rubber (hereinafter also referred to as a rubber sheet) obtained by pressurizing and heating the rubber composition used to form the element to be measured at a temperature of 170°C for 12 minutes. In this invention, "loss tangent" is expressed as the loss tangent at 0°C, and "complex modulus" is expressed as the complex modulus at 70°C.

[0017] In this invention, the tread portion of a tire is the part of the tire that comes into contact with the road surface. The bead portion is the part of the tire that is fitted onto the rim. The sidewall portion is the part of the tire that bridges the gap between the tread portion and the bead portion. The tire comprises the tread portion, a pair of bead portions, and a pair of sidewall portions. The tread portion includes the tread as a component of the tire. The sidewall portion includes the sidewall as a component of the tire. The bead portion includes the bead as a component of the tire.

[0018] [Practices that formed the basis of this invention] For example, the tread of a studless tire (more specifically, the blocks that make up the tread) has sipes. Sipes function as edge components. Sipes can contribute to improved wet performance. In tires, deformation and recovery are repeated. When the cap layer is made of soft cross-linked rubber, the movement of the tread increases. If sipes are cut into such a tread, the risk of damage such as chipping increases. To reduce the risk of damage, the depth of the sipes can be adjusted, but if the cap layer disappears, the base layer will be exposed. The base layer is harder than the cap layer. Therefore, there is a concern that the wet performance will decrease when the base layer is exposed.

[0019] Therefore, the inventors diligently studied technologies that enable tires to exhibit good wet performance even when the base layer is exposed, and have completed the present invention described below.

[0020] [Summary of Embodiments of the Invention] The present invention relates to a tire comprising a tread located radially on the outermost side and extending circumferentially, wherein the tread comprises a cap layer and a base layer located radially inside the cap layer, the base layer is composed of a rubber composition comprising a rubber component and a filler, the filler comprising carbon black and silica, the ratio Sr of the silica content to the sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is greater than 0.20, the tread comprises a plurality of land portions separated by circumferential main grooves, the ratio Ur of the thickness TU of the base layer to the depth DGm of the circumferential main grooves is 0.20 or more and 0.60 or less, at least one of the land portions comprises a sipe having a bottom within the base layer, and the ratio Sr, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relational expression. Sr × DU ​​ / TU ≥ 0.010

[0021] The tire of the present invention can exhibit good wet performance even when the base layer is exposed. Although the mechanism by which the tire achieves this effect has not been fully elucidated, it is presumed to be as follows.

[0022] Sipes are carved into the land portion of the tide so that their bottoms are located within the base layer. Even if the cap layer disappears and the base layer is exposed, the sipes can still contribute to wet performance. Since a base layer is used that has been adjusted for silica content (BSi) while taking into account the carbon black content (BCB), the base layer itself can also contribute to achieving wet performance. Furthermore, since the base layer thickness TU is adjusted based on the circumferential main groove depth DGm, the occurrence of damage caused by the presence of sipes is effectively suppressed. Because the base layer is exposed at an effective timing, the deterioration of wet performance is suppressed. Furthermore, by balancing the sipe depth DU and silica content BSi in the base layer, this tire can effectively enhance both the contribution of the sipes and the base layer to wet performance after the base layer is exposed, while suppressing damage caused by the presence of sipes. This tire can perform well in wet conditions even when the base layer is exposed.

[0023] Preferably, the loss tangent LTu of the base layer at a temperature of 0°C, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relationship. LTu × DU ​​ / TU ≥ 0.0090 This allows the tire to effectively enhance both the contribution of sipes and the base layer to wet performance.

[0024] Preferably, the sipes extend in a zigzag pattern in their longitudinal and depth directions. This allows the walls to restrain each other when the land area deforms and the sipe walls come into close contact with each other. The rigidity of the land area is effectively increased. Since the movement of the land area is suppressed, the occurrence of damage caused by the presence of the sipes is suppressed. The sipes and base layer can effectively contribute to the performance of good wet performance.

[0025] Preferably, the sipe comprises a sipe body and a tubular portion located radially inward of the sipe body and having a bottom, wherein the tubular portion has a width wider than the width of the sipe body. This suppresses the concentration of strain at the bottom of the sipe. The occurrence of damage caused by the presence of the sipe is effectively suppressed. The sipe and base layer can effectively contribute to the performance of good wet performance.

[0026] More preferably, the tubular portion exhibits its maximum width within the base layer. This increases the groove volume as the tubular portion appears in the exposed base layer, improving the tire's drainage performance. Sipes including this tubular portion can contribute to improved wet performance when the base layer is exposed. This suppresses the decrease in wet performance when the tread in contact with the road surface switches from the cap layer to the base layer.

[0027] Preferably, the sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is less than 40 parts by mass. This results in a base layer with appropriate strength. This tire can reduce the risk of damage such as chipping to the tread. The base layer can stably perform its function.

[0028] Preferably, the rubber component contains natural rubber, and the CNR (Chemical Neutral Ratio) of the natural rubber in 100 parts by mass of the rubber component is 95 parts by mass or more. This results in a base layer with appropriate strength. This tire can reduce the risk of damage such as chipping to the tread. The base layer can stably perform its function.

[0029] Thus, according to the present invention, a tire can be obtained that exhibits good wet performance even when the base layer is exposed. This will be explained in detail below.

[0030] [Details of the Embodiments of the Invention] [tire] Figure 1 is a plan view showing a portion of the tread 4 of a tire 2 according to one embodiment of the present invention. This tire 2 is mounted on vehicles such as trucks and buses. This tire 2 is a heavy-duty tire. This tire 2 is also a studless tire designed with ice performance in mind. This tire 2 is a studless type heavy-duty tire.

[0031] Although the present invention will be explained using heavy-duty tires as an example, the present invention can also be applied to passenger car tires, small truck tires, and motorcycle tires. The present invention is preferably applied to heavy-duty tires, and more preferably to studless type heavy-duty tires.

[0032] In Figure 1, the direction indicated by the double-headed arrow AD is the axial direction of tire 2. The axial direction of tire 2 means the direction parallel to the rotation axis of tire 2. The direction indicated by the double-headed arrow CD is the circumferential direction of tire 2. The circumferential direction of tire 2 is also the rotation direction of tire 2. The direction perpendicular to the plane of paper in Figure 1 is the radial direction of tire 2. In Figure 1, the dashed line EL extending in the circumferential direction represents the equatorial plane of tire 2. In the axial direction, the direction away from the equatorial plane is the axial outward direction of tire 2, and the direction towards the equatorial plane is the axial inward direction of tire 2.

[0033] The tire 2 is equipped with a tread 4. The tread 4 is one of the elements that constitute the internal structure of the tire 2. In this invention, the internal structure of the tire 2 is not particularly limited. Although not described in detail, this tire 2 has an internal structure that is common for heavy-duty tires.

[0034] The tread 4 is made of cross-linked rubber. The tread 4 is located on the radially outermost part of the tire 2. The tread 4 extends in the circumferential direction. The tire 2 contacts the road surface at the tread 4. The surface of the tread 4 that contacts the road surface is the tread surface 6. The tread 4 has a tread surface 6 that contacts the road surface.

[0035] The solid line TE extending in the circumferential direction represents the edge of the tread surface 6. In the case of a tire where the edge of the tread surface is not identifiable by appearance, the position on the outer surface of the tire corresponding to the axial outer edge of the contact patch obtained by applying a normal load to a tire in a normal state, setting the camber angle to 0°, and contacting the tire with a plane, is used as the edge of the tread surface.

[0036] In Figure 1, the length indicated by the double-headed arrow TW represents the width of the tread 4. The width TW of the tread 4 is the axial distance from one end TE to the other end TE of the tread surface 6. The width TW of the tread 4 is measured along the tread surface 6.

[0037] Tread 4 has grooves 8 cut into it. This forms the tread pattern. The tread pattern shown in Figure 1 is an example of a tread pattern that makes up the tread 4 of the tire 2 of the present invention. The tread pattern shown in Figure 1 is the tread pattern of a new tire 2 that is not worn.

[0038] Figure 2 shows a cross-section of the groove 8. The direction indicated by the double arrow RD is the radial direction of the tire 2. The side indicated by arrow RD1 is the radially outer side of the tire 2, and the side indicated by arrow RD2 is the radially inner side of the tire 2. In this specification, the cross-section of the groove 8 is represented as a cross-section along a plane perpendicular to the longitudinal direction of the groove 8. The cross-section of groove 8 shown in Figure 2 is the cross-section of the circumferential main groove, which will be described later. The main structure of groove 8 will be explained based on the cross-section of the circumferential main groove.

[0039] The groove 8 has a pair of wall surfaces 8S including an opening 8M and a bottom surface 8B including a bottom 8T. The base 8T is, unless otherwise specified, represented by the position where the distance from the reference plane RP to the base 8B is maximized, measured along the normal to the reference plane RP, which is the plane containing the pair of edges 8E that constitute the opening 8M. If the base 8B is a plane, the base 8T is represented by the center position of the base 8B. If the base 8B has a projection, the base 8T is determined based on a virtual base obtained by assuming the absence of the projection. The normal to the reference plane RP, which connects the reference plane RP and the bottom 8T, is the reference normal RN, and the direction of this reference normal RN is the depth direction of the groove 8. The width of the groove 8 is expressed as the shortest distance between one wall surface 8S and the other wall surface 8S (hereinafter referred to as the inter-wall distance). Unless otherwise specified, the inter-wall distance is measured along a line perpendicular to the reference normal RN. If the profile of the tread surface 6 can be confirmed, the profile of the tread surface 6 may be used as the reference surface RP to determine the bottom 8T and width of the groove 8.

[0040] In Figure 2, the length indicated by the double arrow WG is the width of the groove 8 at the opening 8M. If the opening 8M portion of the groove 8 is tapered, the width of the groove 8 at the opening 8M is expressed based on a virtual edge obtained assuming that it is not tapered. The length indicated by the double arrow DG is the depth of the groove 8. Unless otherwise specified, the depth DG of the groove 8 is expressed as the distance from the reference surface RP to the bottom 8T of the groove 8, measured along the reference normal RN. The position, width WG, and depth DG of the groove 8 are determined as appropriate according to the specifications of the tire 2.

[0041] Grooves 8 with a width WG of less than 1.0 mm in opening 8M are called sipes. Grooves 8 other than sipes are called ordinary grooves. Ordinary grooves have a width WG of 1.0 mm or more in their opening 8M. Even among ordinary grooves, those with a wide width and a pair of walls that do not come into contact with each other when the tire is in contact with the road surface are also called main grooves. Ordinary grooves with a narrow width and a pair of walls that can come into contact with each other when the tire is in contact with the road surface are also called narrow grooves.

[0042] The tread 4 is provided with circumferential main grooves 10. The circumferential main grooves 10 extend continuously in the circumferential direction. The circumferential main grooves 10 are the main grooves described above. The circumferential main grooves 10 have a wide width. The pair of wall surfaces 10S of the circumferential main grooves 10 do not come into contact with each other even when the tire 2 is in contact with the road surface.

[0043] The depth DGm of the circumferential main groove 10 is, for example, 8 mm or more and 21 mm or less. From the viewpoint of enabling the tire 2 to exhibit good wet performance, it is preferable that the depth DGm of the circumferential main groove 10 is 13 mm or more and 18 mm or less. The width WGm of the circumferential main groove 10 is preferably 4.0% or more and 10% or less of the width TW of the tread 4.

[0044] The tread 4 is provided with multiple circumferential main grooves 10. The tread 4 shown in Figure 1 has three circumferential main grooves 10. The three circumferential main grooves 10 are aligned in the axial direction. The two circumferential main grooves 10 located on the outermost axial side are the shoulder circumferential main grooves 10s. The circumferential main groove 10 located between the two shoulder circumferential main grooves 10s is the main circumferential main groove 10m. There is one main circumferential main groove 10m provided in this tread 4. The main circumferential main groove 10m is located on the equatorial plane. This main circumferential main groove 10m is also called the center circumferential main groove.

[0045] Multiple circumferential main grooves 10 constitute multiple land areas 12 on the tread 4. The tread 4 comprises multiple land areas 12 separated by the circumferential main grooves 10. The tread 4 shown in Figure 1 has three circumferential main grooves 10, which constitute four land areas 12. The two outermost land sections 12 in the axial direction are the shoulder land sections 12s. The shoulder land sections 12s include the edge TE of the tread surface 6. The land section 12 located between the two shoulder land sections 12s is the main land section 12m. This tread 4 has two main land sections 12m. The two main land sections 12m are each located between the equatorial surface and the shoulder land sections 12s.

[0046] Each of the multiple land sections 12 that make up the tread 4 may be provided with longitudinal grooves 14 that extend continuously in the circumferential direction. The longitudinal grooves 14 carved into the main land area 12m are called the main longitudinal grooves 14m. The main longitudinal grooves 14m of this tire 2 are the aforementioned narrow grooves. The main longitudinal grooves 14m are also called longitudinal narrow grooves. The main land area 12m is equipped with longitudinal narrow grooves 14m. The longitudinal narrow grooves 14m have a depth approximately the same as the depth of the circumferential main grooves 10. The longitudinal narrow grooves 14m may be shallower than the circumferential main grooves 10. The longitudinal grooves 14 etched into the shoulder area 12s are called shoulder longitudinal grooves 14s. The shoulder longitudinal grooves 14s of this tire 2 are the aforementioned sipes. Shoulder longitudinal grooves 14s are also called longitudinal sipes. The shoulder area 12s is equipped with longitudinal sipes 14s. The longitudinal sipes 14s have a depth approximately the same as the depth of the circumferential main grooves 10. The longitudinal sipes 14s may be shallower than the circumferential main grooves.

[0047] The longitudinal grooves 14 form two narrow land sections 16 on the land section 12. The land section 12 comprises two narrow land sections 16 separated by the longitudinal grooves 14. The tread 4 of this tire 2 comprises four land sections 12, and each land section 12 comprises two narrow land sections 16.

[0048] In this invention, for the sake of explanation, of the two narrow land portions 16 that each land portion 12 has, the narrow land portion 16 located on one end TE side of the tread surface 6 is called the first narrow land portion, and the narrow land portion 16 located on the other end TE side of the tread surface 6 is called the second narrow land portion.

[0049] In the tread 4 shown in Figure 1, the edge TE of the tread surface 6 located on the left side of the paper is called the first edge TE1, and the narrow area 16 located on this first edge TE1 side is called the first narrow area. The edge TE of the tread surface 6 located on the right side is also called the second edge TE2, and the narrow area 16 located on this second edge TE2 side is called the second narrow area. Alternatively, the edge TE of the tread surface 6 located on the right side of the paper may be called the first edge TE1, and the narrow area 16 located on this first edge TE1 side may be called the first narrow area. Alternatively, the edge TE of the tread surface 6 located on the left side of the paper may be called the second edge TE2, and the narrow area 16 located on this second edge TE2 side may be called the second narrow area.

[0050] The narrow land portion 16 may be provided with a plurality of lateral grooves 18. The plurality of lateral grooves 18 are arranged at predetermined intervals in the circumferential direction. In this tire 2, in each land portion 12, the plurality of lateral grooves 18 of the first narrow land portion 16 and the plurality of lateral grooves 18 of the second narrow land portion 16 are arranged alternately in the circumferential direction.

[0051] The transverse grooves 18 traverse the narrow land sections 16. Of the two narrow land sections 16 that make up the shoulder land section 12s, the transverse groove 18 of the narrow land section 16 located on the edge TE side of the tread surface 6 spans between the edge TE of the tread surface 6 and the longitudinal grooves 14. The other transverse grooves 18 span between the circumferential main grooves 10 and the longitudinal grooves 14.

[0052] Multiple lateral grooves 18 are carved into the narrow land area 16, forming multiple blocks 20 arranged in the circumferential direction. In this tire 2, each of the two narrow land areas 16 of the land area 12 is equipped with multiple blocks 20. The multiple blocks 20 formed in the first narrow land area 16 and the multiple blocks 20 formed in the second narrow land area 16 are arranged alternately in the circumferential direction.

[0053] Each of the multiple blocks 20 that make up the narrow section 16 may be provided with a lateral sipe 22. The lateral sipe 22 is the sipe described above. In the tread 4 shown in Figure 1, multiple lateral sipes 22 are carved into each block 20. The multiple lateral sipes 22 are arranged in the circumferential direction. The lateral sipes 22 traverse the block 20. The block 20 of this tire 2 is provided with multiple small blocks 24 separated by the lateral sipes 22. Of the two narrow sections 16 that make up the shoulder section 12s, the lateral sipes 22 carved into the blocks 20 of the narrow section 16 located on the edge TE side of the tread surface 6 bridge the gap between the edge TE of the tread surface 6 and the longitudinal grooves 14. The other lateral sipes 22 bridge the gap between the circumferential main grooves 10 and the longitudinal grooves 14.

[0054] In this tire 2, the blocks 20 form part of the narrow land section 16, and the narrow land section 16 forms part of the land section 12. As previously mentioned, the blocks 20 are provided with transverse sipes 22. The land section 12 is provided with transverse sipes 22. The shoulder land section 12s, as part of the land section 12, is further provided with longitudinal sipes 14s. In this specification, the transverse sipes 22 and longitudinal sipes 14s are also simply referred to as sipes 26. The land section 12 of this tire 2 is provided with sipes 26.

[0055] How the sipes 26 are cut into the land portion 12 is determined appropriately according to the specifications of the tire 2. If the tire 2 is a studless type heavy load tire, it is preferable that the sipes 26 (specifically, lateral sipes 22) are cut into the blocks 20 that make up the land portion 12, as shown in Figure 1; in other words, it is preferable that the blocks 20 are equipped with lateral sipes 22.

[0056] In the tread 4 shown in Figure 1, all land areas 12 constituting the tread 4 are provided with sipes 26. In this tire 2, it is sufficient that at least one of the multiple land areas 12 constituting the tread 4 is provided with sipes 26. The land area 12 on which the sipes 26 are provided is determined appropriately according to the specifications of the tire 2.

[0057] Figure 3 shows a cross-section of the transverse sipe 22, or sipe 26. The sipe 26 shown in Figure 3 extends straight from the opening 26M to the bottom 26T, that is, in the depth direction. As shown in Figure 1, the sipe 26 also extends straight in the length direction. This sipe 26 is a two-dimensional sipe that extends straight in both its length and depth directions.

[0058] The tread 4 of this tire 2 comprises a cap layer 28 and a base layer 30. The cap layer 28 comprises the aforementioned tread surface 6. The base layer 30 is located radially inward of the cap layer 28. The cap layer 28 is laminated on the base layer 30. When the cap layer 28 is worn away, the base layer 30 is exposed.

[0059] The cap layer 28 is softer than the base layer 30. More specifically, the ratio of the complex modulus of the cap layer 28 at a temperature of 70°C to the complex modulus of the base layer 30 at a temperature of 70°C is between 0.40 and 0.90.

[0060] The tread 4 of this tire 2 is composed of two layers: a cap layer 28 and a base layer 30. The inner surface of the cap layer 28 and the outer surface of the base layer 30 form the boundary 32 between the cap layer 28 and the base layer 30 in the tread 4. The boundary 32 usually forms a flat surface inside the land portion 12 (specifically, the block 20).

[0061] In Figure 2, the solid line TBL is the thickness reference line. The thickness reference line TBL is a line drawn such that the distance from the tread surface 6, measured along the normal to the tread surface 6, coincides with the groove depth DGm of the circumferential main groove 10. The double arrow TU is the thickness of the base layer 30. The thickness TU is represented by the maximum length from the bottom 10T of the circumferential main groove 10 to the outer surface of the base layer 30. More specifically, the thickness TU is represented by the maximum length from the thickness reference line TBL, measured along the normal to the tread surface 6, to the outer surface of the base layer 30 (in other words, the boundary 32 between the cap layer 28 and the base layer 30). In the case of land 12 located between two circumferential main grooves 10, where the depths of the two circumferential main grooves 10 are different, the aforementioned thickness reference line TBL is determined using the depth DGm of the deeper circumferential main groove 10.

[0062] As mentioned above, the tread 4 is made of cross-linked rubber. Although not described in detail here, the cap layer 28 of the tread 4 is made of a cross-linked rubber that is common as the cross-linked rubber for the cap layer of a tire. The cap layer 28 is softer than the base layer 30. The base layer 30 is formed using a rubber composition described later. The cross-linked rubber that makes up the base layer 30 is a cross-linked product of the rubber composition described later.

[0063] [Rubber composition] The base layer 30 is composed of the rubber composition described below. The base layer 30 is a crosslinked product of the rubber composition described below, i.e., crosslinked rubber. The rubber composition contains rubber components and fillers.

[0064] [Rubber components] The rubber component is not particularly limited, and any crosslinkable rubber component commonly used in the tire industry can be used. Examples of such rubber components include isoprene rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. One of these rubber components may be selected and used alone, or two or more may be selected and used in combination.

[0065] The rubber component of the rubber composition for the base layer 30 preferably contains isoprene rubber. The rubber component may also contain rubber components other than isoprene rubber, or it may consist solely of isoprene rubber.

[0066] [Isoprene rubber] Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. For NR, examples include SIR20, RSS#3, TSR20, etc., which are commonly used in the tire industry. For IR, there are no particular limitations, but examples include IR2200, which are commonly used in the tire industry. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber (UPNR). 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 individually or in combination of two or more. Among these, NR is preferred.

[0067] When the rubber component contains NR, a base layer 30 with appropriate strength is formed, and from the viewpoint of reducing the risk of damage such as chipping occurring in the tread 4, the NR content CNR in 100 parts by mass of the rubber component is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 97 parts by mass or more. Particularly preferably, the NR content CNR in 100 parts by mass of the rubber component is 100 parts by mass, that is, the rubber component consists only of NR.

[0068] The rubber component of the rubber composition for the base layer 30 preferably includes either butadiene rubber or styrene-butadiene rubber, or both butadiene rubber and styrene-butadiene rubber, as rubber components other than isoprene-based rubber.

[0069] [Butadiene rubber] Butadiene rubber (BR) is not particularly limited, and common types used in the tire industry can be used, such as BR with a cis content of less than 50% by mass (low-cis BR), BR with a cis content of 90% by mass or more (high-cis BR), rare-earth butadiene rubber synthesized using a rare-earth element catalyst (rare-earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR). These may be used individually or in combination of two or more types. The cis content of BR is calculated by infrared absorption spectroscopy.

[0070] When the rubber component contains BR, from the viewpoint of improving abrasion resistance, the BR content CBR in 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more. The BR content CBR is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less.

[0071] [Styrene-butadiene rubber] There are no particular limitations on the styrene-butadiene rubber (SBR), and examples include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs in which the ends and / or main chain are modified, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, branched structures, etc.). Among these, it is preferable that the SBR contained in the rubber component be S-SBR and modified SBR. Furthermore, hydrogenated SBRs (hydrogenated SBR) can also be used as SBR in this rubber composition. One type of SBR may be selected from these and used alone, or two or more types may be selected and used in combination.

[0072] SBR exhibits excellent viscoelastic properties in the region highly correlated with wet performance (specifically, grip performance on wet surfaces), and has excellent compatibility and responsiveness with silica, as described later. SBR is expected to contribute to improvements in wet performance and wear resistance.

[0073] When the rubber component contains SBR, from the viewpoint of improving abrasion resistance and wet performance, the SBR content (CSBR) in 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more. From the viewpoint of maintaining a good ride comfort, the SBR content (CSBR) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less.

[0074] [Filler] As mentioned above, the rubber composition for the tread includes a filler, which includes carbon black and silica. In other words, the rubber composition includes carbon black and silica as fillers. The filler may also consist of only carbon black and silica. In other words, the rubber composition may include a filler consisting only of carbon black and silica.

[0075] [Carbon Black] The carbon black used is not particularly limited; for example, common types used in the tire industry such as GPF, FEF, HAF, ISAF, and SAF can be used. Furthermore, from the perspective of reducing environmental impact and reducing friction between the carbon black surface and rubber molecular chains, thereby suppressing heat generation, this tire may also use recycled carbon black (rCB) obtained from the thermal decomposition of used tires. These carbon blacks may be used individually or in combination of two or more types. In this invention, to distinguish it from recycled carbon black (rCB), the aforementioned carbon black commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, and SAF, is also called standard carbon black (sCB).

[0076] As mentioned above, recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, cited in "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly on pp. 438, 440, and 442, describes that it can be obtained by the pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (

[0027] ). Carbon black obtained from such pyrolysis processes usually lacks functional groups on its surface, as mentioned in

[0004] of Patent No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolysis Carbon Black and Commercial Carbon Black, Powder Technology 160 (2005) 190-193).

[0077] Recycled carbon black may lack functional groups on its surface, or it may be treated to contain functional groups on its surface. Treatment to contain functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black containing hydroxyl and / or carboxyl groups on its surface is obtained by treating carbon black obtained from a thermal decomposition process with potassium permanganate under acidic conditions. In addition, in Japanese Patent No. 6856781, carbon black with an activated surface is obtained by treating carbon black obtained from a thermal decomposition process with an amino acid compound containing at least one thiol group or disulfide group. Recycled carbon black according to this embodiment also includes carbon black treated to contain functional groups on its surface. Recycled carbon black can be purchased from companies such as Strebl Green Carbon and LDCarbon.

[0078] From the viewpoint of improving wear resistance and durability, the average primary particle diameter of carbon black is preferably 25 nm or less, more preferably 22 nm or less, and even more preferably 19 nm or less. This average primary particle diameter is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0079] The average primary particle size of carbon black can be determined by observing the carbon black using a transmission or scanning electron microscope, measuring the outer diameter of 400 or more primary particles of carbon black observed within the field of view, and averaging these measurements.

[0080] From the perspective of improving wear resistance and durability, the nitrogen adsorption specific surface area (N2SA) of carbon black is 10 m². 2 Preferably 20m / g or more. 2 More preferably 30m 2 A value of 1 / g or more is even more preferable. The nitrogen adsorption specific surface area (N2SA) is 250 m². 2 Preferably less than / g, 200m 2More preferably less than / g, 150m 2 A value of less than / g is even more preferable. The nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K6217-2:2017.

[0081] The carbon black content (BCB) per 100 parts by mass of rubber component is preferably 10 parts by mass or more, and more preferably 15 parts by mass or more, from the viewpoint of exhibiting a reinforcing effect and preventing degradation due to ultraviolet rays. From the viewpoint of the tread gaining flexibility and relieving stress, it is preferably 26 parts by mass or less, more preferably 23 parts by mass or less, and even more preferably 20 parts by mass or less.

[0082] The amount of recycled carbon black in 100 parts by mass of carbon black is not particularly limited, but can be, for example, more than 1 part by mass, more than 5 parts by mass, more than 10 parts by mass, more than 20 parts by mass, more than 25 parts by mass, or more than 30 parts by mass. From the viewpoint of exhibiting the reinforcing effect of carbon black, it is preferable to have less than 95 parts by mass, more preferably less than 90 parts by mass, and even more preferably less than 85 parts by mass.

[0083] [silica] The silica used is not particularly limited; for example, silica prepared by the dry process (anhydrous silica) or silica prepared by the wet process (hydrated silica), which are common in the tire industry, can be used. Furthermore, from the viewpoint of environmental impact, silica made from biomass materials (for example, amorphous silica refined from rice husks) may also be used. Among these, hydrated silica prepared by the wet process is preferred because it contains a large number of silanol groups. These silicas may be used individually or in combination of two or more types.

[0084] Silica derived from biomass materials can be obtained, for example, by extracting silicates from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then using these silicates to react with sulfuric acid in the same way as conventional wet silica, the precipitate of silicon dioxide is filtered, washed with water, dried, and pulverized. Note that when silica crystallizes, it becomes insoluble in water and the silicic acid, which is its component, cannot be utilized. By controlling the combustion temperature and combustion time, the crystallization of silica in rice husk ash is suppressed (see, for example, Japanese Patent Laid-Open No. 2009-2594, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.). The amorphous silica extracted from rice husks may be commercially available from companies such as Wilmar.

[0085] From the viewpoint of improving abrasion resistance and durability, the average primary particle diameter of silica is preferably 22 nm or less, more preferably 19 nm or less, and even more preferably 16 nm or less. This average primary particle diameter is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more.

[0086] The average primary particle diameter of silica can be determined by observing silica with a transmission or scanning electron microscope, measuring the outer diameters of 400 or more primary particles of silica observed in the field of view, and calculating the average.

[0087] From the viewpoint of improving abrasion resistance and durability, the nitrogen adsorption specific surface area (N2SA) of silica is preferably 100 m 2 / g or more, more preferably 110 m 2 / g or more, and even more preferably 120 m 2 / g or more. This nitrogen adsorption specific surface area is preferably 500 m 2 / g or less, more preferably 350 m 2 / g or less, and even more preferably 250 m 2 / g or less. The nitrogen adsorption specific surface area (N2SA) of silica is measured by the BET method in accordance with ASTM D3037-93.

[0088] The silica content BSi per 100 parts by mass of rubber component is preferably 4 parts by mass or more. Silica can effectively reinforce the tread. As the rigidity of the tread increases, wear resistance and durability are improved. From this viewpoint, a silica content BSi of 7 parts by mass or more is more preferable. From the viewpoint of obtaining flexibility and relieving stress, a silica content BSi of 20 parts by mass or less is preferred, and 15 parts by mass or less is more preferable.

[0089] The total amount of carbon black (BCB) and silica (BSi) is preferably less than 40 parts by mass. This ensures that the base layer 30 has appropriate strength, reducing the risk of damage such as chipping to the tread 4. The base layer 30 can effectively contribute to the performance of wet surfaces. From this viewpoint, the total amount of carbon black (BCB) and silica (BSi) is more preferably 35 parts by mass or less. From the viewpoint of improving wear resistance and durability, this total is preferably 15 parts by mass or more, and more preferably 20 parts by mass or more.

[0090] [Other fillers] Other fillers besides silica and carbon black can be used, including aluminum hydroxide, calcium carbonate, alumina, clay, talc, and other materials commonly used in the tire industry.

[0091] [Silane coupling agent] As mentioned above, the rubber composition contains silica as a filler. Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, but any silane coupling agent that has conventionally been used in combination with silica in the tire industry can be used. Examples of silane coupling agents include mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, Momentive's NXT-Z100, NXT-Z45, and NXT(3-octanoylthiopropyltriethoxysilane); sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane; and vinyltriethoxy Examples include vinyl silane coupling agents such as silanes and vinyltrimethoxysilane; amino silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, sulfide silane coupling agents and / or mercapto silane coupling agents are preferred, and mercapto silane coupling agents are more preferred. These silane coupling agents may be used individually or in combination of two or more.

[0092] A mercapto-silane coupling agent refers to a silane coupling agent having a mercapto group and a silane coupling agent in which the mercapto group is protected by a protecting group. A mercapto-silane coupling agent is not particularly limited and is, for example, at least one selected from the group consisting of a compound represented by the following chemical formula (1), a compound represented by the following chemical formula (2), and a compound containing a bonding unit A shown in the following chemical formula (3) and a bonding unit B shown in the following chemical formula (4). Among these, at least one compound represented by the following chemical formula (1) and a compound containing a bonding unit A shown in the following chemical formula (3) and a bonding unit B shown in the following chemical formula (4) are preferred, and the compound represented by the following chemical formula (1) is more preferred, in order to better exhibit the effects of the present invention.

[0093] [ka] (In the formula, R 1001 -Cl, -Br, -OR 1006 -O(O=)CR 1006 , -ON=CR 1006 R 1007 , -ON=CR 1006 R 1007 , -NR 1006 R 1007 , and -(OSiR 1006 R 1007 ) h (OSiR 1006 R 1007 R 1008 A monovalent group (R) selected from ) 1006 , R 1007 , and R 1008 These may be the same or different, and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, with h having an average value of 1 to 4. 1002 R 1001 , hydrogen atom, or monovalent hydrocarbon group having 1 to 18 carbon atoms, R 1003 is -[O(R 1009 O) j ]-group(R 1009 is an alkylene group with 1 to 18 carbon atoms, and j is an integer from 1 to 4. ), R 1004R is a divalent hydrocarbon group having 1 to 18 carbon atoms. 1005 (where represents a monovalent hydrocarbon group with 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationships x + y + 2z = 3, 0 ≤ x ≤ 3, 0 ≤ y ≤ 2, and 0 ≤ z ≤ 1.)

[0094] [ka] (In the formula, R 101 , R 102 , and R 103 Each of these is independently an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, or -O-(R 111 -O) z -R 112 (z R 111 Each of these independently represents a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 R represents a group represented by ) an alkyl group with 1 to 30 carbon atoms, an alkenyl group with 2 to 30 carbon atoms, an aryl group with 6 to 30 carbon atoms, or an aralkyl group with 7 to 30 carbon atoms; z represents an integer from 1 to 30. 104 (This represents alkylenes with 1 to 6 carbon atoms.)

[0095] [ka] [ka] (In the formula, x represents an integer greater than or equal to 0; y represents an integer greater than or equal to 1; R 201 R represents a hydrogen atom, an alkyl group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkynyl group having 2 to 30 carbon atoms (the alkyl group, alkenyl group, and alkynyl group may be substituted with a halogen atom, hydroxyl group, or carboxyl group); R 202 R represents alkylene with 1 to 30 carbon atoms, alkenylene with 2 to 30 carbon atoms, or alkynylene with 2 to 30 carbon atoms; here, R 201 and R 202 (They may form a ring structure.)

[0096] The compound represented by chemical formula (1) is R1005 , R 1006 , R 1007 , and R 1008 Preferably, each of these groups is independently selected from the group consisting of linear, cyclic, or branched alkyl, alkenyl, aryl, and aralkyl groups having 1 to 18 carbon atoms. 1002 If is a monovalent hydrocarbon group having 1 to 18 carbon atoms, it is preferably a group selected from the group consisting of linear, cyclic, or branched alkyl groups, alkenyl groups, aryl groups, and aralkyl groups. 1009 The alkylene group is preferably linear, cyclic, or branched, and is particularly preferred to be linear. 1004 Examples of R include alkylene groups having 1 to 18 carbon atoms, alkenylene groups having 2 to 18 carbon atoms, cycloalkylene groups having 5 to 18 carbon atoms, cycloalkylalkylene groups having 6 to 18 carbon atoms, arylene groups having 6 to 18 carbon atoms, and aralkylene groups having 7 to 18 carbon atoms. The alkylene groups and alkenylene groups may be linear or branched, and the cycloalkylene groups, cycloalkylalkylene groups, arylene groups, and aralkylene groups may have functional groups such as lower alkyl groups on their rings. 1004 Preferably, the alkylene group has 1 to 6 carbon atoms, and in particular, linear alkylene groups such as methylene, ethylene, trimethylene, tetramethylene, pentamethylene, and hexamethylene groups are preferred.

[0097] R in chemical formula (1) 1002 , R 1005 , R 1006 , R 1007 , and R 1008Specific examples include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, octyl group, decyl group, dodecyl group, cyclopentyl group, cyclohexyl group, vinyl group, propenyl group, allyl group, hexenyl group, octenyl group, cyclopentenyl group, cyclohexenyl group, phenyl group, tolyl group, xylyl group, naphthyl group, benzyl group, phenethyl group, naphthylmethyl group, and the like.

[0098] R in chemical formula (1) 1009 Examples of linear alkylene groups include methylene, ethylene, n-propylene, n-butylene, and hexylene groups, while examples of branched alkylene groups include isopropylene, isobutylene, and 2-methylpropylene groups.

[0099] Specific examples of silane coupling agents represented by chemical formula (1) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, and 2-lauroylthioethyltrimethoxysilane. Among these, 3-octanoylthiopropyltriethoxysilane is preferred.

[0100] The silane coupling agent represented by chemical formula (1) has a thioester structure (i.e., a protected mercapto group) within its molecule, exhibits low reactivity with rubber components up to high temperatures, can suppress the strong bonding between the rubber components, the silane coupling agent, and silica during mixing, and can appropriately disperse silica, thus tending to exhibit the effects of the present invention more effectively.

[0101] Examples of compounds represented by chemical formula (2) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the compound represented by the following chemical formula (5) (Si363 manufactured by Evonik Degussa). The compound represented by the following chemical formula (5) can be preferably used. These may be used individually or in combination of two or more. [ka]

[0102] Compounds containing the bonding unit A shown in chemical formula (3) and the bonding unit B shown in chemical formula (4) include, for example, those manufactured and sold by Momentive, Inc. These may be used individually or in combination of two or more types.

[0103] The content of the silane coupling agent relative to 100 parts by mass of silica (total amount when multiple silane coupling agents are used in combination) is preferably more than 1 part by mass, more preferably more than 3 parts by mass, even more preferably more than 5 parts by mass, and even more preferably more than 7 parts by mass, from the viewpoint of improving the dispersibility of silica. Furthermore, from the viewpoint of preventing a decrease in wear resistance, the content is preferably less than 20 parts by mass, more preferably less than 15 parts by mass, and even more preferably less than 12 parts by mass.

[0104] [Other compounding agents] In addition to the components mentioned above, the rubber composition according to this embodiment may also appropriately contain compounding agents commonly used in the tire industry, such as softeners, waxes, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0105] Examples of softening agents include resin components, oils, and liquid rubber.

[0106] The resin components that can be used in this embodiment are not particularly limited, but resins commonly used in the tire industry can be used, such as adhesive resins such as C9 resins, C5 resins, C5C9 resins, dicyclopentadiene resins, aromatic vinyl resins, coumarone resins, indene resins, terpene resins, rosin resins, and phenolic resins. These resin components may be used individually or in combination of two or more.

[0107] C9 resins refer to resins obtained by polymerizing a C9 fraction. These resins may be obtained by polymerizing the C9 fraction alone, or by copolymerizing the C9 fraction with other components. For example, a resin copolymerized with dicyclopentadiene (DCPD) and a C9 fraction is called a DCPD / C9 resin. These resins may also be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, coumarone, indene, methylindene, and dicyclopentadiene. These C9 resins may be used individually or in combination of two or more.

[0108] C5 resins refer to resins obtained by polymerizing C5 fractions, and may be hydrogenated or modified versions of these fractions. Examples of C5 fractions other than dicyclopentadiene include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, isoprene, pentane, isopentane, neopentane, pentene, and pentadiene. These C5 resins may be used individually or in combination of two or more types.

[0109] C5C9 resins refer to resins obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified versions of these resins. As C5C9 petroleum resins, for example, those commercially available from Tosoh Corporation, LUHUA, etc., can be used. These C5C9 resins may be used individually or in combination of two or more types.

[0110] A dicyclopentadiene resin refers to a resin containing cyclopentadiene (CPD) or dicyclopentadiene (DCPD) as a monomer component, and may be hydrogenated or modified. Examples of dicyclopentadiene resins include DCPD / C9 resins containing dicyclopentadiene and the C9 fraction as monomer components (the DCPD / C9 resin may be hydrogenated or modified), and DCPD / C9 resins containing dicyclopentadiene and styrene as monomer components are preferred, and DCPD / C9 resins containing dicyclopentadiene, styrene, and indene as monomer components are particularly preferred. Examples of dicyclopentadiene resins that can be used are those commercially available from ExxonMobil, ENEOS Corporation, Nippon Zeon Corporation, Maruzen Petrochemical Co., Ltd., etc. These dicyclopentadiene resins may be used individually or in combination of two or more types.

[0111] Aromatic vinyl resins refer to resins containing aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and p-chlorostyrene as the most abundant monomer component, and may also be hydrogenated or modified versions of these compounds. For aromatic vinyl resins, α-methylstyrene or a homopolymer of styrene, or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, due to their economical nature, ease of processing, and excellent heat generation properties. Aromatic vinyl resins that can be used are commercially available from companies such as Kraton, Eastman Chemical Company, and Mitsui Chemicals, Inc. These aromatic vinyl resins may be used individually or in combination of two or more types.

[0112] Coumarone-based resins refer to resins containing coumarone as a monomer component, and may be hydrogenated or modified resins. Examples of coumarone-based resins include coumarone-indene resins containing coumarone and indene as monomer components, and coumarone-indene-styrene resins containing coumarone, indene, and styrene as monomer components. These coumarone-based resins may be used individually or in combination of two or more types.

[0113] Indene resins refer to resins containing indene as a monomer component, and may be hydrogenated or modified resins. Examples of indene resins include coumarone-indene resins containing coumarone and indene as monomer components, and coumarone-indene-styrene resins containing coumarone, indene, and styrene as monomer components. These indene resins may be used individually or in combination of two or more types.

[0114] Terpene resins are resins that contain terpene compounds such as α-pinene, β-pinene, limonene, and dipentene as the most abundant monomer component, and may be hydrogenated or modified versions of these compounds. Specific examples of terpene resins include, for example, polyterpene resins containing only one or more of the aforementioned terpene compounds as monomer components; aromatically modified terpene resins containing the aforementioned terpene compounds and aromatic compounds as monomer components; and terpene-phenol resins containing the aforementioned terpene compounds and phenolic compounds as monomer components. Examples of aromatic compounds that serve as monomer components in aromatically modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that serve as monomer components in terpene-phenol resins include phenol, bisphenol A, cresol, and xylenol. These terpene resins may be used individually or in combination of two or more types.

[0115] Rosin resins refer to resins containing rosin acid compounds such as abietic acid, neoabietic acid, palastic acid, and isopimal acid, and may be hydrogenated or modified versions of these compounds. Rosin resins are not particularly limited, but examples include natural resin rosin and rosin-modified resins obtained by hydrogenation, disproportionation, dimerization, esterification, etc. These rosin resins may be used individually or in combination of two or more types.

[0116] Phenolic resins refer to resins that contain phenol compounds such as phenol and cresol as the most abundant monomer component. Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resins, alkylphenol-formaldehyde resins, alkylphenol-acetylene resins, and oil-modified phenol-formaldehyde resins. These phenolic resins may be used individually or in combination of two or more types.

[0117] From the viewpoint of ride comfort and wet performance, the softening point of the resin component is preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher. Furthermore, from the viewpoint of processability and improved dispersibility between the rubber component and filler, it is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. The softening point of the resin is determined by measuring the softening point specified in JIS K 6220-1:2015 7.7 using a ring-type softening point measuring device, and it is the temperature at which the sphere descends.

[0118] When the rubber composition contains a resin component, the content of the resin component per 100 parts by mass of the rubber component 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, from the viewpoint of ride comfort and wet performance. From the viewpoint of suppressing heat generation, the content of the resin component is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0119] Examples of oils include process oils, vegetable oils, and animal oils. Examples of process oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. Process oils with a low content of polycyclic aromatic compounds (PCA), which are environmentally friendly, can also be used. Examples of low-PCA process oils include light extraction solvates (MES), processed distillate aromatic extracts (TDAEs), and heavy naphthenic oils.

[0120] If the rubber composition contains oil, the oil content per 100 parts by mass of rubber component 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, from the viewpoint of improving processability. From the viewpoint of improving wear resistance, the oil content is preferably 90 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less.

[0121] Liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), but examples include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used individually or in combination of two or more types.

[0122] When the rubber composition contains liquid rubber, the liquid rubber content per 100 parts by mass 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. The liquid rubber content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

[0123] The wax is not particularly limited and can be any petroleum-based wax such as paraffin wax or microcrystalline wax; or synthetic wax such as polymers of ethylene or propylene. Commercially available products from companies such as Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd. can be used. These may be used individually or in combination of two or more types.

[0124] When the rubber composition contains wax, the amount of wax per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of weather resistance of the rubber. From the viewpoint of preventing whitening of the tire due to bloom, the amount of wax is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0125] While not particularly limited, examples of anti-aging agents include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamate salts. Phenylenediamine-based anti-aging agents such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These anti-aging agents may be used alone or in combination of two or more.

[0126] When a rubber composition contains an anti-aging agent, the amount of the anti-aging agent per 100 parts by mass of rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of the rubber's resistance to ozone cracking. From the viewpoint of wear resistance and wet grip performance, the amount of the anti-aging agent is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0127] Conventional known stearic acid can be used, and commercially available products from companies such as NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries Ltd., and Chiba Fatty Acid Co., Ltd. can be used. These may be used individually or in combination of two or more types.

[0128] When the rubber composition contains stearic acid, the stearic acid content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability. From the viewpoint of vulcanization rate, the stearic acid content is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0129] Conventional known zinc oxides can be used, and commercially available products from companies such as Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., and Sakai Chemical Industry Co., Ltd. can be used. These may be used individually or in combination of two or more types.

[0130] When the rubber composition contains zinc oxide, the zinc oxide content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and even more preferably 1.5 parts by mass or more, from the viewpoint of processability. From the viewpoint of wear resistance, the zinc oxide content is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0131] Sulfur is preferably used as a vulcanizing agent. Suitable sulfur varieties include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0132] When a rubber composition contains sulfur as a vulcanizing agent, the sulfur content per 100 parts by mass of rubber component is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. From the viewpoint of preventing deterioration, the sulfur content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.5 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is expressed by the amount of pure sulfur contained in the oil-containing sulfur.

[0133] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensates, 1,6-hexamethylenedithiosulfate sodium dihydrate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. These non-sulfur vulcanizing agents can be purchased commercially from companies such as Taoka Chemical Industries, Ltd., Lanxess Corporation, and Flexis.

[0134] Examples of vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamate, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among these, one or more vulcanization accelerators selected from the group consisting of sulfenamide, guanidine, and thiazole vulcanization accelerators are preferred, with sulfenamide vulcanization accelerators being more preferred, as they more favorably yield the desired effect.

[0135] Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS), N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolyl sulfenamide (DCBS). Among these, N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS) and N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS) are preferred.

[0136] Examples of guanidine-based vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salts of dicatecholborate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, and 1,3-di-o-cumenyl-2-propionylguanidine. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0137] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and di-2-benzothiazolyl disulfide. Among these, 2-mercaptobenzothiazole is preferred.

[0138] When a rubber composition contains a vulcanization accelerator, the content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more. The content of the vulcanization accelerator is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, even more preferably 6.0 parts by mass or less, and particularly preferably 5.0 parts by mass or less. By keeping the content of the vulcanization accelerator within these ranges, it tends to be possible to ensure fracture strength and elongation.

[0139] The rubber composition is manufactured, for example, by kneading the aforementioned components using a rubber mixing device such as an open roll or Banbury mixer. Regarding the mixing conditions, in the base mixing step where additives other than the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 100 to 180°C, preferably 120 to 170°C. In the finish mixing step where the vulcanizing agent and vulcanization accelerator are mixed, the mixing temperature is usually 120°C or lower, preferably 85 to 110°C.

[0140] The manufactured rubber composition is processed into a predetermined shape using an extruder or the like. In a molding machine, it is combined with sidewalls and the like to prepare a green tire (a tire in an uncrosslinked state). The green tire is vulcanized in a mold incorporated into a vulcanizing machine to obtain a tire. The tire is a crosslinked product of the green tire. The vulcanization temperature is usually 140 to 190°C, preferably 150 to 185°C. The vulcanization time is usually 5 to 15 minutes.

[0141] As mentioned above, the land portion 12 is provided with sipes 26. As shown in Figure 3, the bottom 26T of the sipes 26 is located within the base layer 30. In Figure 3, the length indicated by the double-headed arrow DU represents the depth of the sipe 26 in the base layer 30. The depth DU of the sipe 26 in the base layer 30 is expressed as the distance in the depth direction from the outer surface of the base layer 30 (in other words, the boundary 32 between the cap layer 28 and the base layer 30) to the bottom 26T of the sipe 26.

[0142] Of the multiple land sections 12 of the tread 4, at least one land section 12 is equipped with a sipe 26 having a bottom 26T within the base layer 30. Even if the cap layer 28 disappears due to wear and the base layer 30 is exposed, the sipe 26 can still contribute to the performance of wet surfaces.

[0143] The base layer 30 is composed of the aforementioned rubber composition. As described above, the rubber composition for the base layer 30 includes rubber components and fillers, the fillers including carbon black and silica. The ratio Sr of silica content to the sum of carbon black content BCB and silica content BSi per 100 parts by mass of rubber components is greater than 0.20. The tread 4 of this tire 2 uses a base layer 30 in which the silica content BSi is adjusted while taking into account the carbon black content BCB. Therefore, when the base layer 30 is exposed, the base layer 30 itself can contribute to the performance of wet surfaces.

[0144] Furthermore, the ratio Ur of the thickness TU of the base layer 30 to the depth DGm of the circumferential main groove 10 is between 0.20 and 0.60. Since the thickness TU of the base layer 30 is adjusted based on the depth DGm of the circumferential main groove 10, the occurrence of damage caused by the presence of the sipes 26 is effectively suppressed. Because the base layer 30 is exposed at an effective timing, the deterioration of wet performance is suppressed.

[0145] Furthermore, the ratio Sr, the thickness TU of the base layer 30, and the depth DU of the sipe 26 in the base layer 30 satisfy the following relationship. Sr × DU ​​ / TU ≥ 0.010 Since the depth DU of the sipes 26 and the silica content BSi in the base layer 30 are well-balanced, this tire 2 can effectively enhance the contribution of both the sipes 26 and the base layer 30 to wet performance after the base layer 30 is exposed, while suppressing the occurrence of damage caused by the presence of the sipes 26.

[0146] This tire 2 can exhibit good wet performance even when the base layer 30 is exposed.

[0147] From the viewpoint of improving wet performance when the base layer 30 is exposed, the product SDT of the ratio Sr and the ratio DU / TU of the depth DU of the sipe 26 in the base layer 30 to the thickness TU of the base layer 30 is preferably 0.013 or higher, more preferably 0.015 or higher, and even more preferably 0.020 or higher. Furthermore, from the viewpoint of reducing the risk of damage caused by the presence of the sipe 26, this product SDT is preferably 0.25 or lower, more preferably 0.15 or lower, and even more preferably 0.050 or lower.

[0148] As mentioned above, the ratio Sr of silica content BSi to the sum of carbon black content BCB and silica content BSi is greater than 0.20. From the viewpoint of improving wet performance when the base layer 30 is exposed, the ratio Sr is preferably 0.20 or higher, and more preferably 0.25 or higher. From the viewpoint of reducing the risk of damage caused by the presence of sipes 26, the ratio Sr is preferably 0.60 or lower, and more preferably 0.55 or lower.

[0149] As mentioned above, the ratio Ur of the thickness TU of the base layer 30 to the depth DGm of the circumferential main groove 10 is between 0.20 and 0.60. From the viewpoint that the exposed base layer 30 can effectively contribute to the performance of wet properties, the specific Ur is preferably 0.25 or higher, and more preferably 0.30 or higher. From the viewpoint that the occurrence of damage caused by the presence of the sipes 26 can be effectively suppressed, the specific Ur is preferably 0.55 or lower, and more preferably 0.50 or lower.

[0150] If the bottom 26T of the sipe 26 is within the base layer 30, the sipe 26 can contribute to improved wet performance even when the base layer 30 is exposed. Since the depth of the sipe 26 also affects the rigidity of the land portion 12, the lower limit of the depth DU of the sipe 26 in the base layer 30 is appropriately determined according to the specifications of the tire 2. If the sipe 26 can contribute to improved wet performance even when the base layer 30 is exposed, the depth DU of the sipe 26 in the base layer 30 may be 0.5 mm. The deeper the sipe 26, the more strain is concentrated at the bottom 26T, increasing the risk of damage such as chipping in the tread 4. From the viewpoint of reducing the risk of damage, the ratio DU / TU of the depth of the sipe 26 in the base layer 30 to the thickness TU of the base layer 30 is preferably 1.0 or less, and more preferably 0.9 or less.

[0151] In this tire 2, it is preferable that the loss tangent LTu of the base layer 30 at a temperature of 0°C, the thickness TU of the base layer 30, and the depth DU of the sipe 26 in the base layer 30 satisfy the following relationship. LTu × DU ​​ / TU ≥ 0.0090 This allows tire 2 to effectively enhance the contribution of both the sipes 26 and the base layer 30 to wet performance. From this viewpoint, it is preferable that the value obtained by the aforementioned relation, i.e., the product LDT of the loss tangent LTu and the ratio of depth DU to thickness TU DU / TU, be 0.0094 or greater. From the viewpoint of reducing the risk of damage caused by the presence of the sipes 26, it is preferable that the product LDT be 0.0100 or less.

[0152] In this tire 2, the loss tangent LTu of the base layer 30 at a temperature of 0°C is preferably 0.140 or more and 0.170 or less. By setting the loss tangent LTu to 0.140 or higher, the base layer 30 can effectively contribute to achieving wet performance. From this perspective, a loss tangent LTu of 0.145 or higher is more preferable. Setting the loss tangent LTu to 0.170 or less reduces the risk of damage caused by the presence of sipe 26. From this perspective, a loss tangent LTu of 0.165 or less is more preferable.

[0153] Figure 4 shows a modified example of sipe 26 (specifically, transverse sipe 22). Figure 5 shows a cross-section of sipe 26 along the VV line in Figure 4. As shown in Figure 4, the sipe 26 extends in a zigzag pattern along its length. As shown in Figure 5, the sipe 26 also extends in a zigzag pattern along its depth. The amplitude of the zigzag pattern is preferably, for example, 0.5 mm to 3.0 mm.

[0154] The sipes 26 shown in Figures 4 and 5 are three-dimensional sipes. When the tread 4 deforms and the wall surfaces 26S of the sipes 26 come into close contact with each other, the wall surfaces 26S restrain each other, effectively increasing the rigidity of the tread 4. Since the movement of the tread 4 is suppressed, the occurrence of damage caused by the presence of the sipes 26 is suppressed. The sipes 26 and the base layer 30 can effectively contribute to the performance of good wet performance. From this viewpoint, it is preferable that the sipes 26 extend in a zigzag pattern in their length and depth directions.

[0155] Figure 6 shows other variations of the sipe 26 (specifically, the transverse sipe 22). This sipe 26 has a sipe body 34 and a tubular portion 36. The sipe body 34 includes the opening 26M of the sipe 26. The tubular portion 36 includes the bottom 26T of the sipe 26. The sipe 26 shown in Figure 3 is a sipe composed only of the sipe body 34.

[0156] Although not shown in the figure, the sipe body 34 extends straight in the longitudinal direction of the sipe 26, just like the sipe 26, i.e., the transverse sipe 22, shown in Figure 1. As shown in Figure 6, the sipe body 34 extends straight in the depth direction of the sipe 26. The length indicated by the double arrow WGp in Figure 6 is the width of the sipe body 34. The sipe body 34 has a uniform width WGp in the depth direction. The tubular portion 36 is located radially inward of the sipe body 34. The tubular portion 36 extends along the length of the sipe 26.

[0157] In Figure 6, the solid line LB is the boundary line between the sipe body 34 and the tubular portion 36. The length indicated by the double arrow WB is the width of the sipe 26 measured along this boundary line LB. The boundary line LB is set at a position where the width WB of the sipe 26 is 1.0 mm. In Figure 6, the position indicated by the symbol PB is the boundary between the sipe body 34 and the tubular portion 36. The width WGp of the outer portion of the boundary line LB (i.e., the sipe body 34) is less than 1.0 mm. The width of the inner portion of the boundary line LB (i.e., the tubular portion 36) is 1.0 mm or more. The width of the tubular portion 36 is wider than the width of the sipe body 34.

[0158] The tubular portion 36 extends inward from the boundary line LB. In Figure 6, the length indicated by the double arrow WX is the maximum width of the tubular portion 36. In Figure 6, the position indicated by the symbol PX is the position where the tubular portion 36 shows its maximum width WX. The tubular portion 36 tapers outward from the portion showing its maximum width WX. The tubular portion 36 tapers inward from the portion showing its maximum width WX.

[0159] The cross-sectional shape of the tubular portion 36 may be circular or elliptical. The cross-sectional shape may be such that the portion indicating the maximum width WX is represented by a straight line, and the sipe body 34 side and the bottom 26T side of the straight portion are represented by arcs (hereinafter this shape is also called the track shape).

[0160] The sipe body 34 can function as an edge component. The sipe body 34 can contribute to the performance of wet conditions. When the sipe body 34 disappears, the tubular portion 36 is exposed. The tubular portion 36 has a wide width. After the sipe body 34 disappears, this tubular portion 36 can contribute to maintaining wet conditions. In the sipe 26 shown in Figure 6, the strain occurring at the bottom 26T of the sipe 26 is reduced compared to a sipe without a tubular portion 36, as shown in Figure 3. A sipe 26 having both a sipe body 34 and a tubular portion 36 can contribute to reducing the risk of damage such as chipping to the tread 4. From this viewpoint, it is preferable that the sipe 26 comprises a sipe body 34 and a tubular portion 36 located radially inward of the sipe body 34 and having a bottom 26T, with the tubular portion 36 having a width wider than the width of the sipe body 34.

[0161] As mentioned earlier, the cap layer 28 is softer than the base layer 30. There is a concern that wet performance will decrease as the tread 4 that contacts the road surface changes from the cap layer 28 to the base layer 30. However, as shown in Figure 6, the maximum width position PX of the tubular portion 36 is located within the base layer 30. When the base layer 30 is exposed, the tubular portion 36 can contribute to an increase in groove volume. This improves the drainage performance of the tire 2. The sipe 26, including this tubular portion 36, can contribute to improved wet performance when the base layer 30 is exposed. The decrease in wet performance that is a concern when the tread 4 in contact with the road surface changes from the cap layer 28 to the base layer 30 is suppressed. This tire 2 can exhibit good wet performance even when the base layer 30 is exposed. From this viewpoint, when the sipe 26 has a tubular portion 36, it is preferable that the tubular portion 36 shows its maximum width WX within the base layer 30.

[0162] When the sipe 26 has a tubular portion 36 and the tubular portion 36 exhibits its maximum width WX within the base layer 30, as shown in Figure 6, the boundary PB between the sipe body 34 and the tubular portion 36 may be located radially inward of the boundary 32 between the cap layer 28 and the base layer 30. As shown in Figure 7, when the cap layer 28 is thick, the boundary PB between the sipe body 34 and the tubular portion 36 may be located radially outward of the boundary 32 between the cap layer 28 and the base layer 30. As shown in Figure 8, even when a shallow sipe 26 is used, the boundary PB between the sipe body 34 and the tubular portion 36 may be located radially outward of the boundary 32 between the cap layer 28 and the base layer 30. From the viewpoint of enabling the tubular portion 36 to effectively contribute to the performance of wetness, it is more preferable that the boundary PB between the sipe body 34 and the tubular portion 36 be located radially inward of the boundary 32 between the cap layer 28 and the base layer 30.

[0163] In Figure 6, the length indicated by the double arrow DB is the depth distance from the boundary 32 between the cap layer 28 and the base layer 30 to the boundary PB between the sipe body 34 and the tubular portion 36. Distance DB is expressed as a positive number when the boundary PB between the sipe body 34 and the tubular portion 36 is located inside the boundary 32 between the cap layer 28 and the base layer 30. As shown in Figure 7 or 8, if the boundary PB between the sipe body 34 and the tubular portion 36 is located outside the boundary 32 between the cap layer 28 and the base layer 30, distance DB is expressed as a negative number. If distance DB is 0 (zero) mm, it means that the boundary PB between the sipe body 34 and the tubular portion 36 and the boundary 32 between the cap layer 28 and the base layer 30 are in the same position in the depth direction of the sipe 26.

[0164] From the viewpoint of minimizing the change in wet performance when the tread 4 in contact with the road surface changes from the cap layer 28 to the base layer 30, the depth-direction distance DB from the boundary 32 between the cap layer 28 and the base layer 30 to the boundary PB between the sipe body 34 and the tubular portion 36 is preferably -10 mm or more and 15 mm or less, more preferably -5 mm or more and 10 mm or less, and more preferably 0 mm or more and 5 mm or less.

[0165] The maximum width WX of the tubular section 36 is preferably four times or more the width WGp of the sipe body 34, and more preferably five times or more. This allows the tubular section 36 to contribute to maintaining wet performance. The maximum width WX of the tubular section 36 is preferably 13 times or less the groove width WGp of the sipe body 34, and more preferably 12 times or less. This ensures that the size of the tubular section 36 is appropriately maintained. This suppresses a decrease in the rigidity of the land section 12 (specifically, the block 20).

[0166] The tubular portion 36 has a bottom surface 26B that includes the bottom 26T of the sipe 26. In the cross-section shown in Figure 6, the contour of the bottom surface 26B of the tubular portion 36 is represented by an arc passing through the bottom 26T. The arrow Rb in Figure 6 is the radius of this arc.

[0167] The radius Rb of the arc representing the contour of the bottom surface 26B of the tubular portion 36 is preferably 1.5 mm or more and 3.5 mm or less. By setting the radius Rb to 1.5 mm or more, the strain occurring in the bottom 26T portion of the sipe 26 is reduced. This tubular portion 36 can contribute to reducing the risk of damage such as chipping to the tread 4. From this viewpoint, a radius Rb of 2.0 mm or more is more preferable. By setting the radius Rb to 3.5 mm or less, the reduction in rigidity of the land portion 12 caused by the provision of tubular sections 36 in the sipes 26 is suppressed. The rigidity of the land portion 12 is appropriately maintained. This tire 2 can improve resistance to uneven wear. From this viewpoint, a radius Rb of 3.0 mm or less is more preferable.

[0168] In Figure 6, the length indicated by the double-headed arrow DGb is the depth of the sipe body 34. The length indicated by the double-headed arrow DGp is ​​the depth of the sipe 26.

[0169] The ratio (DGb / DGp) of the depth DGb of the sipe body 34 to the depth DGp of the sipe 26 is preferably 0.50 or more and 0.80 or less. By setting the ratio (DGb / DGp) to 0.50 or higher, the influence on the rigidity of the land portion 12 due to the provision of tubular sections 36 in the sipes 26 is minimized and suppressed. The rigidity of the land portion 12 is appropriately maintained. This tire 2 can improve resistance to uneven wear. From this viewpoint, a ratio (DGb / DGp) of 0.60 or higher is more preferable. By setting the ratio (DGb / DGp) to 0.80 or less, the tubular portion 36 can contribute to the performance of wet surfaces. From this viewpoint, a ratio (DGb / DGp) of 0.70 or less is more preferable.

[0170] Figure 9 shows yet another modification of the sipe 26. As shown in Figure 9, the sipe body 34 shown in Figure 6 may be composed of a three-dimensional sipe, as shown in Figure 9. In this case, when the tread 4 deforms and the wall surfaces 26S of the sipe 26 come into contact with each other, the two wall surfaces 26S adhere tightly to each other. The deformation of the land portion 12 is effectively suppressed. This tire 2 can effectively increase the contribution of the sipe 26 and the base layer 30 to the wet performance after the base layer 30 is exposed, while suppressing the occurrence of damage caused by the presence of the sipe 26.

[0171] As is clear from the above description, according to the present invention, a tire 2 is obtained that can exhibit good wet performance even when the base layer is exposed. [Examples]

[0172] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0173] The various chemicals used in the examples and comparative examples are described. NR:TSR20 Carbon Black: Mitsubishi Chemical Corporation's Dia Black N134 (N2SA: 148ml) 2 / g) Silica: UltraSil VN3 (N2SA: 175m) manufactured by Eponic Industries. 2 / g, average primary particle diameter: 17nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa. Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Anti-aging agent 1: Nocrack 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Anti-aging agent 2: Nocrack RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (5% oil-containing powdered sulfur) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator: Noxellar NS (Nt-butyl-2-benzothiazole sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0174] [Examples and Comparative Examples] According to the formulation shown in Table 1, the materials other than sulfur and vulcanization accelerator are mixed for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a mixture. Next, sulfur and vulcanization accelerator are added to the mixture and mixed for 5 minutes at 80°C using an open roll to obtain a rubber composition (uncrosslinked rubber composition). The obtained rubber composition is molded into the base layer of the tread and bonded together with other parts such as the sidewall to form an unvulcanized tire. The unvulcanized tire is press-vulcanized for 12 minutes at 150°C to produce a test tire (size: 275 / 80R22.5, for trucks and buses) having the basic configuration shown in Figure 1. The tread pattern of the test tire is the one shown in Figure 1. In Examples 1-3 and Comparative Example 1, the bottom of the lateral sipe is located within the base layer, while in Comparative Example 2, it is located within the cap layer.

[0175] [Preparation before evaluation] The tread of the test tire is buffed. Specifically, the tread is polished until the cap layer disappears and the base layer is exposed. This reproduces the condition in which 0.5 mm deep lateral sipes remain in the exposed base layer. In Comparative Example 2, the bottom of the lateral sipes is located within the cap layer, so no lateral sipes remain in the exposed base layer.

[0176] Table 1 shows the calculation results based on the evaluation method described below for a test tire in which the base layer was exposed by buff polishing.

[0177] [Wet performance (WET)] The following test vehicle will be used to conduct wet performance (wet braking performance) tests in accordance with R117-02 (ECE Regulation No. 117 Revision 2). Test tires that simulate the later stages of wear will be mounted on all wheels of the test vehicle. In this wet performance test, the braking distance will be measured from a specified initial speed until the vehicle comes to a complete stop on a water-sprayed road surface. Test vehicle: 10-ton truck (2-D vehicle) Load: 75% of standard load capacity Wet surface: Water depth 0.5-2mm Speed: 65km / h The measured values ​​for Examples 1-3 and Comparative Example 2 are expressed exponentially, with Comparative Example 1 set to 100, using the following formula. (Wet performance index) = (Braking distance of the tire in Comparative Example 1) / (Braking distance of each test tire) × 100 The results are shown in the "WET" column of Table 1 below. A higher number indicates better wet performance.

[0178] [Table 1] [Industrial applicability]

[0179] The technology described above, which enables good wet performance even when the base layer is exposed, can be applied to various types of tires.

[0180] [Note] The present invention includes the following embodiments.

[0181] [1] A tire comprising a tread located radially on the outermost side and extending circumferentially, wherein the tread comprises a cap layer and a base layer located radially inside the cap layer, the base layer is composed of a rubber composition comprising a rubber component and a filler, the filler comprising carbon black and silica, the ratio Sr of the silica content to the sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is greater than 0.20, the tread comprises a plurality of land portions separated by circumferential main grooves, the ratio Ur of the thickness TU of the base layer to the depth DGm of the circumferential main grooves is 0.20 or more and 0.60 or less, at least one of the land portions comprises a sipe having a bottom in the base layer, and the ratio Sr, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relationship. Sr × DU ​​ / TU ≥ 0.010 [2] The tire according to [1] above, wherein the loss tangent LTu of the base layer at a temperature of 0°C, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relationship. LTu × DU ​​ / TU ≥ 0.0090 [3] The tire according to [1] or [2] above, wherein the sipes extend in a zigzag pattern in the longitudinal and depth directions. [4] The tire according to [1] or [2] above, wherein the sipe comprises a sipe body and a tubular portion located radially inward of the sipe body and having a bottom, the tubular portion having a width wider than the width of the sipe body. [5] The tire according to [4] above, wherein the tubular portion has its maximum width within the base layer. [6] The tire according to any one of [1] to [5] above, wherein the sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is less than 40 parts by mass. [7] A heavy-duty tire according to any one of the above [1] to [6], wherein the rubber component contains natural rubber, and the CNR of the natural rubber content in 100 parts by mass of the rubber component is 95 parts by mass or more. [Explanation of Symbols]

[0182] 2... Tires 4. Tread 6. Tread surface 8...Groove 10...Circumferential main groove 12... Rikubu 14.. Vertical grooves 16.. Narrow continental area 18.. Yokomizo 20 blocks 22... Horizontal sipes 24... Small Blocks 26... Sipes 28... Cap layer 30...Base layer 32...boundary 34.. Sipe body 36...Tubular part

Claims

1. Located on the outermost radial side, and featuring a tread that extends circumferentially, The tread comprises a cap layer and a base layer located radially inward of the cap layer. The base layer is composed of a rubber composition containing a rubber component and a filler. The filler comprises carbon black and silica. The ratio of the silica content BSi to the sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is greater than 0.

20. The tread comprises a plurality of land portions separated by circumferential main grooves, The ratio Ur of the thickness TU of the base layer to the depth DGm of the circumferential main groove is 0.20 or more and 0.60 or less. At least one of the land portions comprises a sipe having a bottom within the base layer, The ratio Sr, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relationship: tire. Sr × DU ​​ / TU ≥ 0.010

2. The loss tangent LTu of the base layer, the thickness TU of the base layer, and the depth DU of the sipe in the base layer satisfy the following relationship at a temperature of 0°C: The tire according to claim 1. LTu × DU ​​ / TU ≥ 0.0090

3. The sipe extends in a zigzag pattern in its length and depth directions. The tire according to claim 1.

4. The sipe comprises a sipe body and a tubular portion located radially inward of the sipe body and having the bottom, The tubular portion has a width wider than the width of the sipe body. The tire according to claim 1.

5. Within the base layer, the tubular portion shows its maximum width. The tire according to claim 4.

6. The sum of the carbon black content BCB and the silica content BSi per 100 parts by mass of the rubber component is less than 40 parts by mass. The tire according to claim 1.

7. The aforementioned rubber component includes natural rubber, The CNR content of natural rubber in 100 parts by mass of the rubber component is 95 parts by mass or more. A tire according to any one of claims 1 to 6.

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