tire

Abstract

This tire comprises a tread, wherein: the tread has land parts partitioned by a plurality of circumferential grooves, and has locations where, in a tire meridian cross-section including the tire rotation axis, the widthwise length of the land part closest to the tire equatorial plane increases from the outside to the inside in the tire radial direction; the tread has at least one rubber layer; a first rubber layer constituting the tread surface is configured from a rubber composition containing a rubber component that includes a diene-based rubber; and the contact angle A1 of pure water measured after immersing the rubber composition constituting the first rubber layer in water for one hour at 23°C under normal pressure and furthermore leaving the rubber composition to dry for 24 hours at 23°C under normal pressure, and the contact angle A2 of pure water measured after measuring the contact angle A1 and then immersing the rubber composition in water for one hour at 23°C under normal pressure and furthermore leaving the rubber composition to dry for 24 hours at 23°C under normal pressure, are both 80° or less.

Description

[Technical Field]

[0001] The present disclosure relates to a tire that maintains wet grip performance over a long period of time. [Background technology]

[0002] As a method for improving the wet grip performance of a tire by increasing adhesion on a wet road surface, for example, a method of compounding a plasticizer such as a resin into the tread rubber is known (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-56137 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the plasticizer disappears from the tread rubber over time as the vehicle is driven, there is concern that the wet grip performance of the tire may deteriorate at the end of the driving period.

[0005] An object of the present disclosure is to provide a tire that maintains wet grip performance over a long period of time. [Means for solving the problem]

[0006] As a result of extensive research, it was discovered that the above-mentioned problems can be solved by providing a tire with a predetermined tread pattern in which the contact area increases with wear, and in which the contact angle of the rubber composition constituting the tread rubber is within a predetermined range.

[0007] Specifically, the present disclosure relates to a tire having a tread, the tread having land portions separated by a plurality of circumferential grooves, and in a tire meridian cross section including the tire rotation axis, the width direction length of the land portion closest to the tire equatorial plane increases from the outer side to the inner side in the tire radial direction, the tread having at least one rubber layer, a first rubber layer constituting the tread surface being composed of a rubber composition containing a rubber component including a diene rubber, the rubber composition constituting the first rubber layer being immersed in water at 23°C and normal pressure for 1 hour, and then left to dry at 23°C and normal pressure for 24 hours, and the pure water contact angle A1 measured after the rubber composition constituting the first rubber layer is 80° or less, and the pure water contact angle A2 measured after the rubber composition is immersed in water at 23°C and normal pressure for 1 hour, and then left to dry at 23°C and normal pressure for 24 hours, are both 80° or less. [Effects of the Invention]

[0008] According to the present disclosure, a tire is provided that maintains wet grip performance for a long period of time. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an enlarged cross-sectional view schematically illustrating a portion of a tread of a tire according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged cross-sectional view schematically showing a portion of the tread of a tire of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] A tire according to one embodiment of the present disclosure is a tire having a tread, the tread having land portions separated by a plurality of circumferential grooves, and in a tire meridian cross section including the tire rotation axis, the width direction length of the land portion closest to the tire equatorial plane increases from the outer side to the inner side in the tire radial direction. The tread has at least one rubber layer, and a first rubber layer constituting the tread surface is constituted by a rubber composition containing a rubber component including a diene rubber. The rubber composition constituting the first rubber layer is immersed in water at 23°C and normal pressure for 1 hour, and then allowed to stand at 23°C and normal pressure for 24 hours to dry. A pure water contact angle A1 measured after the rubber composition constituting the first rubber layer is immersed in water at 23°C and normal pressure for 1 hour, and then allowed to stand at 23°C and normal pressure for 24 hours to dry. A pure water contact angle A2 measured after the rubber composition constituting the first rubber layer is immersed in water at 23°C and normal pressure for 1 hour after the contact angle A1 measurement, and then allowed to stand at 23°C and normal pressure for 24 hours to dry is both 80° or less (preferably both 75° or less, more preferably both 70° or less, and even more preferably both 65° or less).

[0011] While not intending to be bound by theory, in the present disclosure, the mechanism by which wet grip performance can be maintained for a long period of time is believed to be as follows: By using a highly wettable rubber composition with a tread rubber contact angle of 80° or less in the rubber layer that constitutes the tread surface, the affinity between the tread rubber and wet road surfaces is maintained even when repeatedly driving on wet road surfaces, and the contact area can be increased as the tire wears with driving, so that braking performance on wet road surfaces can be maintained until the end of driving.

[0012] The rubber composition constituting the first rubber layer preferably contains a thermoplastic elastomer containing a hydrophilic functional group, and more preferably contains 0.5 to 50 parts by mass of a thermoplastic elastomer containing at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an ether group, a carbonyl group, and an amide group, per 100 parts by mass of the rubber component.

[0013] The rubber component contained in the rubber composition constituting the first rubber layer preferably contains an isoprene-based rubber modified with a hydrophilic functional group, and more preferably contains 10 to 90 mass % of an isoprene-based rubber modified with one or more functional groups selected from the group consisting of a hydroxyl group, an amino group, and an ether group.

[0014] The acetone extractable amount of the rubber composition constituting the first rubber layer is preferably 5 to 25% by mass.

[0015] The rubber composition constituting the first rubber layer preferably contains at least one selected from the group consisting of petroleum resins, terpene resins, and hydrogenated versions of these resins.

[0016] The rubber composition constituting the first rubber layer preferably contains a liquid polymer.

[0017] The rubber composition constituting the first rubber layer has a nitrogen adsorption specific surface area of ​​180 m 2 It is preferable that the silica content is at least 1 / g.

[0018] The width direction length L of the land portion closest to the tire equatorial plane when the tread portion is 90% worn relative to the width direction length L0 when the tire is new. 90 The ratio of L 90 / L0 is preferably 1.1 or more.

[0019] It is preferable that the contact angle A1 and the contact angle A2 of the rubber composition constituting the first rubber layer are both 70° or less.

[0020] A manufacturing procedure for a tire according to one embodiment of the present disclosure will be described in detail below. However, the following description is an example for explaining the present disclosure and is not intended to limit the technical scope of the present disclosure to the described range. In this specification, when a numerical range is indicated using "to" it is intended to include both ends of the numerical range.

[0021] 1 is an enlarged cross-sectional view showing a portion of a tire tread. In Fig. 1, the vertical direction is the tire radial direction, the horizontal direction is the tire width direction, and the direction perpendicular to the paper surface is the tire circumferential direction.

[0022] The tread of the present disclosure has a plurality of circumferential grooves 2 that extend continuously in the tire circumferential direction. The circumferential grooves 2 extend linearly along the circumferential direction, but are not limited to this form, and may extend, for example, in a wave-like, sinusoidal, or zigzag shape along the circumferential direction.

[0023] The tread of the present disclosure has land portions 3 separated by circumferential grooves 2, 2 in the tire width direction. The land portions 3 are not particularly limited as long as they have a portion where the width direction length of the land portion 3 closest to the tire equatorial plane C increases from the outer side to the inner side in the tire radial direction in a tire meridian cross section including the tire rotation axis. However, it is preferable that the width direction length of the land portion 3 gradually increases from the outer side to the inner side in the tire radial direction. Here, "the land portion closest to the tire equatorial plane" refers to a land portion on the tire equatorial plane C if such a land portion exists on the tire equatorial plane C. If no land portion exists on the tire equatorial plane C, it refers to a land portion of a circumferential groove 2 present on the tire equatorial plane C that has a groove edge 4 closest to the tire equatorial plane C. The groove wall 5 of the circumferential groove 2 of the present disclosure extends linearly from the outer side to the inner side in the tire radial direction, but is not limited to this form and may extend in a curved or stepped manner, for example.

[0024] The groove depth H of the circumferential groove 2 is determined by the distance between the tread surface 1 and an extension line of the deepest part of the groove bottom of the circumferential groove 2. Note that, for example, when there are multiple circumferential grooves 2, the groove depth H is the distance between the tread surface 1 and an extension line of the deepest part of the groove bottom of the circumferential groove 2 that has the deepest groove depth among the multiple circumferential grooves 2.

[0025] In the tire of the present disclosure, the width direction length L of the land portion 3 closest to the tire equatorial plane when the tread portion is 90% worn relative to the width direction length L0 of the land portion 3 when the tire is new is 90 The ratio of L 90 / L0 is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. 90 By setting / L0 in the above range, good wet grip performance can be maintained even after wear. 90 The upper limit of / L0 is not particularly limited, but may be, for example, 2.0 or less, 1.8 or less, or 1.5 or less. 90 As shown in the figure, is obtained from the width direction length of the land portion 3 at a position 0.90H inward from the tread surface 1 in the tire radial direction (a position that is 90% of the groove depth H of the circumferential groove 2).

[0026] The groove depth H of the circumferential grooves 2 is preferably more than 90% of the thickness of the entire tread portion, more preferably more than 92%, and even more preferably more than 94%. The groove depth H of the circumferential grooves 2 is preferably 99% or less of the thickness of the entire tread portion, and more preferably 97% or less. Note that the thickness of the entire tread portion in this disclosure refers to the total thickness of the rubber layers that make up the tread portion, and is determined by the shortest distance from the tread surface 1 to the belt layer.

[0027] From the viewpoint of the effects of the present disclosure, the groove depth H of the circumferential groove 2 is preferably 5.0 mm or more, more preferably 6.0 mm or more, and from the viewpoint of chipping resistance, it is preferably 10.0 mm or less, more preferably 9.0 mm or less.

[0028] The land portion 3 may be provided with lateral grooves and / or sipes that cross the land portion 3. In this specification, the term "groove", including circumferential grooves and lateral grooves, refers to a recess with a width of at least 2.0 mm. On the other hand, in this specification, the term "sipe" refers to a thin cut with a width of 2.0 mm or less, preferably 0.5 to 2.0 mm.

[0029] In the present disclosure, the tread has at least one rubber layer. The tread of the present disclosure may be a tread made of a single rubber layer, or may be a tread having a first rubber layer whose outer surface constitutes a tread surface 1 and one or more rubber layers present between the first rubber layer and the belt layer.

[0030] The thickness of the first rubber layer relative to the thickness of the entire tread portion can be, for example, more than 70%, more than 80%, more than 90%, or more than 95%, and the tread may be made up of only the first rubber layer.

[0031] In this disclosure, unless otherwise specified, the dimensions and angles of each component of a tire are measured when the tire is mounted on a standard rim and inflated to the standard internal pressure. No load is applied to the tire during measurement. Note that, in this specification, a "standard rim" refers to the rim specified for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it refers to the standard rim, in the case of TRA, it refers to the "Design Rim," and in the case of ETRTO, it refers to the "Measuring Rim." In this specification, the "standard internal pressure" refers to the air pressure specified for each tire by the standard, which refers to the maximum air pressure in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and it refers to the "INFLATION PRESSURE" in the case of ETRTO.

[0032] The "contact angle" in the present disclosure is determined by dropping 2.0 μL of pure water onto the surface of a rubber composition held horizontally, and measuring the angle formed by the edge of the droplet and the surface of the rubber composition 180 seconds after the drop is dropped using a commercially available contact angle meter.

[0033] The rubber composition constituting the first rubber layer is immersed in water at 23°C under normal pressure for 1 hour, then allowed to stand at 23°C under normal pressure for 24 hours and dried. The resulting rubber composition is measured for its pure water contact angle A1, and its pure water contact angle A2 is measured for the rubber composition obtained by immersing the rubber composition in water at 23°C under normal pressure for 1 hour after the contact angle A1 measurement and then allowing it to stand at 23°C under normal pressure for 24 hours and drying. Both of these angles are 80° or less, preferably 75° or less, more preferably 70° or less, and even more preferably 65° or less. By setting the contact angles A1 and A2 within the above ranges, good wet grip performance can be maintained until the end of the running. The lower limit of the contact angle of the rubber composition according to the present disclosure is not particularly limited, but is typically 30° or more. The contact angle of the rubber composition constituting the first rubber layer can be appropriately adjusted by the type and content of the plasticizer described below.

[0034] The "acetone extractable amount" in the present disclosure can be determined in accordance with JIS K 6229:2015 by immersing each vulcanized rubber test piece in acetone for 24 hours to extract the soluble components, measuring the mass of each test piece before and after extraction, and then calculating the amount of acetone extractable amount using the following formula: The acetone extractable amount is an index of the concentration of organic low-molecular-weight compounds in the plasticizer contained in the vulcanized rubber composition. Acetone extractable amount (mass%) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100

[0035] The acetone extractable amount of the rubber composition according to the present disclosure is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 9% by mass or more. The acetone extractable amount is preferably 25% by mass or less, more preferably 23% by mass or less, even more preferably 21% by mass or less, and particularly preferably 19% by mass or less. By keeping the acetone extractable amount within the above range, good wet grip performance can be maintained until the end of driving.

[0036] <Rubber component> The rubber component constituting the first rubber layer contains a diene rubber as an essential component. From the viewpoint of the effects of the present disclosure, the content of the diene rubber in the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more. The rubber component may also consist solely of the diene rubber.

[0037] Examples of diene rubbers include isoprene rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene rubber (SIR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). These rubber components may be used alone or in combination of two or more. Among these, it is preferable to contain at least one selected from the group consisting of SBR, BR, and isoprene rubber, more preferably to contain BR, and even more preferably to contain isoprene rubber or SBR and BR.

[0038] (Isoprene rubber) Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. Examples of NR include SIR20, RSS#3, and TSR20, which are commonly used in the tire industry. Examples of IR include IR2200 and other commonly used rubbers. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber. 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 isoprene-based rubbers may be used alone or in combination.

[0039] When an isoprene-based rubber is contained, the content in the rubber component is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. On the other hand, the upper limit of the isoprene-based rubber content is not particularly limited and can be, for example, 90% by mass or less, 85% by mass or less, 80% by mass or less, or 75% by mass or less.

[0040] The rubber component according to the present disclosure preferably includes an isoprene-based rubber modified with a hydrophilic functional group as the isoprene-based rubber. Examples of the hydrophilic functional group include one or more functional groups selected from the group consisting of hydroxyl, amino, and ether groups. Among these, modified natural rubber (ENR) or modified epoxidized isoprene rubber, which is further modified by adding a hydrophilic modifying compound having a hydroxyl, amino, or ether group to the epoxy groups of epoxidized natural rubber (ENR) or epoxidized isoprene rubber, is preferred, with modified ENR being more preferred. The incorporation of such isoprene-based rubber modified with a hydrophilic functional group reduces the contact angle of the rubber composition, making it easier to remove the water film that forms between the road surface and the tread rubber during driving, which is thought to improve wet grip performance.

[0041] The modified ENR is preferably ENR modified with one or more functional groups selected from the group consisting of hydroxyl groups, amino groups, and ether groups, and more preferably ENR having a polyethylene glycol monoalkyl ether residue on the side chain of the ENR. The modified epoxidized isoprene rubber is preferably epoxidized isoprene rubber modified with one or more functional groups selected from the group consisting of hydroxyl groups, amino groups, and ether groups, and more preferably epoxidized isoprene rubber having a polyethylene glycol monoalkyl ether residue on the side chain of the epoxidized isoprene rubber.

[0042] The epoxidation rate of ENR or epoxidized isoprene rubber is preferably 1 to 80 mol%, more preferably 5 to 65 mol%, even more preferably 25 to 50 mol%, and particularly preferably 30 to 50 mol%. Here, the epoxidation rate refers to the proportion of epoxidized double bonds to the total number of carbon-carbon double bonds in the natural rubber or isoprene rubber before epoxidation, and can be determined, for example, by titration analysis or nuclear magnetic resonance (NMR) analysis. As ENR, for example, commercially available products manufactured by Kempuran Guthrie Co., Ltd. can be used.

[0043] Modified ENR or modified epoxidized isoprene rubber having a polyethylene glycol monoalkyl ether residue on the side chain of ENR or epoxidized isoprene rubber can be obtained by reacting ENR or epoxidized isoprene rubber with a polyethylene glycol monoalkyl ether, and can be produced, for example, according to the methods described in RSC Adv., 2016, 6, 107021-107028 and Advanced Materials Research, 2013, 795, 251-255. The epoxy groups of the ENR or epoxidized isoprene rubber are partially or completely ring-opened by the addition of the polyethylene glycol monoalkyl ether. The degree of modification (ring-opening) of the epoxy groups can be adjusted by the charging ratio of the ENR or epoxidized isoprene rubber to the polyethylene glycol monoalkyl ether, but is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and particularly preferably 100%.

[0044] The weight-average molecular weight (Mw) of the polyethylene glycol monoalkyl ether is preferably 100 to 3000, more preferably 200 to 2000, and even more preferably 300 to 1000. From the viewpoint of hydrophilicity, the alkyl ether portion of the polyethylene glycol monoalkyl ether is preferably an alkyl ether having 1 to 4 carbon atoms (for example, methyl ether, ethyl ether, propyl ether, butyl ether), more preferably methyl ether and ethyl ether, and particularly preferably methyl ether.

[0045] When a modified isoprene-based rubber is contained, the content in the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 40% by mass or more. The content of the modified ENR in the rubber component is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, and particularly preferably 60% by mass or less.

[0046] (SBR) The SBR is not particularly limited, and examples thereof 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 whose ends and / or main chains are modified, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those having a branched structure, etc.). Furthermore, hydrogenated products of these SBRs (hydrogenated SBRs) can also be used. Of these, S-SBR is preferred, and modified S-SBR is more preferred.

[0047] The modified SBR is preferably modified SBR whose terminals and / or main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen.

[0048] The SBR may be either oil-extended or non-oil-extended. When oil-extended SBR is used, the amount of oil extension of the SBR, i.e., the content of the oil-extending oil contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of the rubber solids content of the SBR.

[0049] The SBRs listed above may be used alone or in combination of two or more. As the SBRs listed above, for example, commercially available products from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., ZS Elastomers Co., Ltd., etc. can be used.

[0050] The styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, because the effects of the present disclosure can be more suitably obtained. The styrene content is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, and even more preferably 40% by mass or less. In this specification, the styrene content of SBR is 1 It is calculated by H-NMR measurement.

[0051] The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, because the effects of the present disclosure can be more suitably obtained. The vinyl content is preferably 80 mol% or less, more preferably 75 mol% or less, and even more preferably 70 mol% or less. In this specification, the vinyl content (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

[0052] The weight-average molecular weight (Mw) of SBR is preferably 200,000 or more, more preferably 300,000 or more, and even more preferably 400,000 or more, because this more suitably achieves the effects of the present disclosure. Furthermore, the Mw is preferably 2,000,000 or less, more preferably 1,800,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight-average molecular weight (Mw) can be determined in terms of standard polystyrene based on measurements obtained by gel permeation chromatography (GPC) (for example, a GPC-8000 series manufactured by Tosoh Corporation, a differential refractometer as the detector, and a TSKGEL SUPERMALTIPORE HZ-M column manufactured by Tosoh Corporation).

[0053] When SBR is contained, the content in the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 40% by mass or more, from the viewpoint of the effects of the present disclosure. On the other hand, the upper limit of the SBR content is not particularly limited and can be, for example, 95% by mass or less, 90% by mass or less, 85% by mass or less, 80% by mass or less, or 75% by mass or less, and the rubber component may consist solely of SBR. When oil-extended SBR is used as SBR, the content of SBR itself as rubber solids contained in the oil-extended SBR is defined as the content of SBR in the rubber component.

[0054] (BR) The BR is not particularly limited, and examples include BR with a cis content of less than 50 mol% (low-cis BR), BR with a cis content of 90 mol% or more (high-cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR), which are commonly used in the tire industry. Modified BRs include BRs modified with functional groups similar to those described above for SBR. These BRs may be used alone or in combination of two or more.

[0055] As the high-cis BR, for example, commercially available products from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. The inclusion of high-cis BR can improve low-temperature properties and wear resistance. The cis content is preferably 95 mol% or more, more preferably 96 mol% or more, even more preferably 97 mol% or more, and particularly preferably 98 mol% or more. In this specification, the cis content (amount of cis-1,4-bonded butadiene units) is a value calculated by infrared absorption spectroscopy.

[0056] The rare earth BR is synthesized using a rare earth catalyst and has a vinyl content of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less, and a cis content of preferably 95 mol% or more, more preferably 96 mol% or more, even more preferably 97 mol% or more, and particularly preferably 98 mol% or more. As the rare earth BR, for example, commercially available products from Lanxess K.K. can be used.

[0057] The SPB-containing BR is not one in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in the BR, but one in which the 1,2-syndiotactic polybutadiene crystals are dispersed after being chemically bonded to the BR. As such SPB-containing BR, commercially available products from Ube Industries, Ltd. and the like can be used.

[0058] The modified BR preferably used is one whose terminals and / or main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen.

[0059] Other examples of modified BR include tin-modified BR, which is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the terminals of the modified BR molecule are further bonded with a tin-carbon bond (tin-modified BR).Modified BR may be either non-hydrogenated or hydrogenated.

[0060] The BRs listed above may be used alone or in combination of two or more.

[0061] From the viewpoint of abrasion resistance, the weight-average molecular weight (Mw) of the BR is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. From the viewpoint of crosslinking uniformity, it is preferably 2,000,000 or less, more preferably 1,000,000 or less. The weight-average molecular weight of the BR can be determined in terms of standard polystyrene based on measurements obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0062] When BR is contained, the content in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of the effects of the present disclosure. On the other hand, when BR is contained, the content in the rubber component is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0063] (Other rubber components) The rubber component may contain other rubber components besides diene rubber, as long as the effects of the present disclosure are not affected. Examples of other rubber components include crosslinkable rubber components commonly used in the tire industry, such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used alone or in combination of two or more.

[0064] <Thermoplastic elastomer> From the viewpoint of obtaining good wet grip performance, the rubber composition constituting the first rubber layer preferably contains a thermoplastic elastomer containing a hydrophilic functional group. Examples of the hydrophilic functional group include at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an ether group, a carbonyl group, and an amide group. The thermoplastic elastomer of the present disclosure has a large molecular weight similar to the rubber component, and is entangled with the rubber component, making it less likely to separate from the rubber composition over time. In addition, the thermoplastic elastomer exhibits partial hydrophilicity, which is thought to facilitate long-term maintenance of wet grip performance.

[0065] As used herein, the term "thermoplastic elastomer" refers to a polymeric compound having elasticity, a thermoplastic resin material composed of a copolymer having a polymer that constitutes a crystalline hard segment with a high melting point and a polymer that constitutes an amorphous soft segment with a low glass transition temperature. The crystalline hard segments of a thermoplastic elastomer, with a high melting point, act as pseudo-crosslinking points, thereby exhibiting elasticity. Rubber, on the other hand, contains double bonds in its molecular chain, and when crosslinked (vulcanized) by adding sulfur or the like, generates a three-dimensional network structure, thereby exhibiting elasticity. Therefore, when a thermoplastic elastomer is heated, the hard segments melt, and when cooled, the pseudo-crosslinking points are regenerated, making it reusable. On the other hand, when rubber is crosslinked (vulcanized), it generates a three-dimensional network structure, losing fluidity and making it difficult to reuse, even when heated. The thermoplastic elastomer of the present disclosure does not contain the rubber component.

[0066] The thermoplastic elastomer containing a hydrophilic functional group (preferably a thermoplastic elastomer containing at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an ether group, a carbonyl group, and an amide group) is not particularly limited, and examples thereof include polyurethane-based thermoplastic elastomers, polyester-based thermoplastic elastomers, and polyamide-based thermoplastic elastomers, with polyurethane-based thermoplastic elastomers being preferred. Copolymers of polyurethane-based thermoplastic elastomers, polyester-based thermoplastic elastomers, or polyamide-based thermoplastic elastomers with diene elastomers are also suitable. Among these, copolymers of polyurethane-based thermoplastic elastomers and diene elastomers are preferred, and copolymers of polyurethane-based thermoplastic elastomers and styrene-based thermoplastic elastomers are more preferred.

[0067] The polyurethane-based thermoplastic elastomer is not particularly limited, but for example, one prepared from a polyol and a diisocyanate can be suitably used. Examples of polyols include polyester-based polyols, polyester ether-based polyols, polycarbonate-based polyols, and polyether-based polyols. Examples of diisocyanates include tolylene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI).

[0068] The polyester-based thermoplastic elastomer is not particularly limited, but for example, one using an olefin-based elastomer as a soft segment and polyethylene terephthalate, polybutylene terephthalate, or the like as a hard segment is preferably used. Examples of the olefin-based elastomer include those obtained by homopolymerizing one type selected from the group consisting of linear alkenes, branched alkenes, and polyvinyl acetates having 1 to 8 carbon atoms, or copolymerizing two or more types, and specific examples include ethylene-vinyl acetate copolymers, ethylene-propylene resins, and linear low-density polyethylene.

[0069] The polyamide-based thermoplastic elastomer is not particularly limited, but examples thereof include polyamide (amide 6) obtained by ring-opening polycondensation of ε-caprolactam, polyamide (amide 11) obtained by ring-opening polycondensation of undecane lactam, polyamide (amide 12) obtained by ring-opening polycondensation of lauryllactam, polyamide (amide 66) obtained by polycondensation of diamine and dibasic acid, and polyamide having metaxylenediamine as a constituent unit (amide MX).

[0070] In this disclosure, the term "diene elastomer" refers to any homopolymer obtained by polymerization of a conjugated diene monomer, or any copolymer obtained by copolymerization of one or more conjugated dienes with each other or with a vinyl aromatic compound, which may be hydrogenated or whose ends may be modified with a modifying agent, such as a hydroxyl group, a carboxyl group, an acid anhydride group, an amino group, an epoxy group, etc. In the case of a copolymer, the latter contains 20% to 99% by weight of diene units and 1% to 80% by weight of vinyl aromatic units.

[0071] Examples of conjugated diene monomers include butadiene, isoprene, and 1,3-pentadiene.

[0072] Examples of aromatic vinyl monomers include styrene, o-methylstyrene, p-methylstyrene, pt (tertiary)-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene, and styrene is generally selected because it is readily available.

[0073] A styrene-based thermoplastic elastomer is a copolymer having at least one styrene block (hard segment) and at least one elastomer block (soft segment). The molecular structure of the styrene-based thermoplastic elastomer is not particularly limited, but a molecular structure having a styrene block at one or both ends and an elastomer block elsewhere is preferred. Having a styrene block at at least one end tends to provide better grip performance. Furthermore, it is more preferred that the styrene-based thermoplastic elastomer has a structure that does not have a styrene block in the main chain portion other than the end. This structure tends to prevent the rubber from becoming too hard at room temperature, providing better grip performance, as well as better fracture properties and abrasion resistance.

[0074] Examples of the elastomer block include vinyl-polydiene, polyisoprene, polybutadiene, polyethylene, polychloroprene, poly-2,3-dimethylbutadiene, etc. Furthermore, the elastomer block may also be a hydrogenated version of the above elastomer block.

[0075] Examples of styrene-based thermoplastic elastomers include styrene-isobutylene block copolymer (SIB), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene block copolymer (SEB), styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-butylene-ethylene block copolymer (SEBC), hydrogenated styrene-butadiene copolymer (HSBR), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), and styrene-butadiene-butylene-styrene block copolymer (SBBS).

[0076] The styrene unit content (styrene content) of the styrene-based thermoplastic elastomer is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of wet grip performance, and is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of suppressing heat buildup.

[0077] The content of the thermoplastic elastomer containing a hydrophilic functional group (preferably a thermoplastic elastomer containing at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an ether group, a carbonyl group, and an amide group) per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 10 parts by mass or more, from the viewpoint of hydrophilizing the rubber component. Furthermore, from the viewpoint of the balance with other performance properties such as wet grip performance, abrasion resistance, and breaking strength, the content is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less.

[0078] <Filler> The rubber composition constituting the first rubber layer preferably contains a filler containing carbon black and / or silica, and the filler may be a filler consisting of only carbon black and silica.

[0079] (silica) The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), which are commonly used in the tire industry. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. Examples of silica that can be used include those manufactured and sold by Evonik Degussa, Solvay, Tosoh Silica Co., Ltd., and Tokuyama Corporation. These silicas can be used alone or in combination of two or more.

[0080] The average primary particle size of silica is preferably 22 nm or less, more preferably 20 nm or less, even more preferably 18 nm or less, and particularly preferably 16 nm or less. The lower limit of the average primary particle size is not particularly limited, but is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. By having the average primary particle size of silica within the above range, the dispersibility of silica can be further improved, and reinforcement, wet grip performance, and abrasion resistance can be further improved. The average primary particle size of silica can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary silica particles observed within the field of view, and averaging the results.

[0081] The nitrogen adsorption specific surface area (N2SA) of silica is 140m from the viewpoint of fuel efficiency and wear resistance. 2 / g or more is preferable, and 160m 2 / g or more is more preferable, and 180m 2 / g or more is more preferable, and 200m 2 / g or more is particularly preferable. From the viewpoint of fuel efficiency and processability, 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 250m 2 / g or less is more preferable. In this specification, the N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0082] The content of silica per 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 55 parts by mass or more, from the viewpoint of wet grip performance, and is preferably 150 parts by mass or less, more preferably 130 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 95 parts by mass or less, from the viewpoint of silica dispersibility and abrasion resistance.

[0083] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used. Examples of such silane coupling agents include sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane and Momentive's NXT-Z100, NXT-Z45, and NXT; thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane; vinyltriethoxysilane, vinyltrimethy ... Examples of suitable silane coupling agents include vinyl-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; amino-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, preferred are at least one selected from the group consisting of sulfide-based silane coupling agents, mercapto-based silane coupling agents, and thioester-based silane coupling agents. These silane coupling agents may be used alone or in combination.

[0084] When a silane coupling agent is contained, the content relative to 100 parts by mass of silica is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, particularly preferably 5 parts by mass or more, and the content relative to 100 parts by mass of silica is preferably 20 parts by mass or less, more preferably 18 parts by mass or less.

[0085] When a silane coupling agent is contained, the amount thereof per 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, and particularly preferably 3 parts by mass or more. The amount thereof per 100 parts by mass of the rubber component is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0086] (carbon black) The carbon black is not particularly limited, and any carbon black commonly used in the tire industry can be used as appropriate, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more.

[0087] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m 2 / g or more is preferable, and 80m 2 / g or more is more preferable, and 100m 2 / g or more is more preferable. By making it equal to or more than the lower limit, good abrasion resistance and grip performance tend to be obtained. 2 / g or less is preferable, and 160m 2 / g or less is more preferable, and 150m 2 / g or less is more preferable. By setting it to the upper limit or less, good dispersion of the carbon black tends to be obtained. The N2SA of carbon black is determined according to JIS K 6217-2:2017.

[0088] From the viewpoint of reinforcement, the amount of carbon black is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component, and from the viewpoint of processability and fuel economy, the amount is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, still more preferably 15 parts by mass or less, and particularly preferably 9 parts by mass or less.

[0089] The total amount of filler per 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 55 parts by mass or more, from the viewpoint of wet grip performance, and is preferably 120 parts by mass or less, more preferably 120 parts by mass or less, more preferably 110 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 95 parts by mass or less, from the viewpoint of abrasion resistance.

[0090] From the viewpoint of fuel economy, the content of silica in the filler is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 85% by mass or more. From the viewpoint of weather resistance and reinforcing properties, the content is preferably 99% by mass or less, more preferably 95% by mass or less.

[0091] (Other reinforcing fillers) Fillers other than silica and carbon black that have been generally used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc, can be blended.

[0092] <Plasticizer> The rubber composition constituting the first rubber layer preferably contains a plasticizer, such as a resin component, oil, liquid polymer, or ester-based plasticizer.

[0093] The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenolic resins, etc., which are commonly used in the tire industry, and may be hydrogenated. These resin components may be used alone or in combination of two or more.

[0094] As used herein, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As the C5 petroleum resin, a cyclopentadiene resin is preferably used. Examples of cyclopentadiene resins include dicyclopentadiene resin (DCPD resin), cyclopentadiene resin, methylcyclopentadiene resin (non-hydrogenated cyclopentadiene resin), and products obtained by subjecting these cyclopentadiene resins to hydrogenation treatment (hydrogenated cyclopentadiene resin). Examples of cyclopentadiene resins that can be used include those commercially available from ExxonMobil Chemical Corporation and the like.

[0095] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified version of the C9 fraction. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins include: Coumarone-indene resin, coumarone resin, indene resin, and aromatic vinyl resin are preferably used.

[0096] As the aromatic vinyl resin, a homopolymer of an α-methylstyrene derivative or a styrene derivative, or a copolymer of an α-methylstyrene derivative with a styrene derivative and / or indene is preferred because of its economical efficiency, ease of processing, and excellent heat generation. The term "α-methylstyrene derivative" refers to an α-methylstyrene compound even if the benzene ring is substituted (preferably, an α-methylstyrene compound in which the benzene ring may be substituted with a saturated hydrocarbon group having 1 to 4 carbon atoms), and the term "styrene derivative" refers to a styrene compound even if the benzene ring is substituted (preferably, a styrene compound in which the benzene ring may be substituted with a saturated hydrocarbon group having 1 to 4 carbon atoms). Examples of the aromatic vinyl resin that can be used include those commercially available from Mitsui Chemicals, Inc., Kraton, Eastman Chemical Company, etc.

[0097] As used herein, the term "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, commercially available products from Tosoh Corporation, LUHUA, etc. can be used.

[0098] Examples of terpene resins include polyterpene resins composed of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and the like; aromatic-modified terpene resins made from the terpene compound and an aromatic compound; terpene phenolic resins made from a terpene compound and a phenolic compound; and hydrogenated terpene resins (hydrogenated terpene resins) obtained by hydrogenating these terpene resins. Examples of aromatic compounds used as raw materials for aromatic-modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol. Examples of terpene resins that can be used include commercially available terpene resins from Yasuhara Chemical Co., Ltd.

[0099] The rosin-based resin is not particularly limited, but examples thereof include natural rosin resin, modified rosin resin, etc. As the rosin-based resin, for example, commercially available products from Arakawa Chemical Co., Ltd., Harima Chemical Co., Ltd., etc. can be used.

[0100] The phenolic resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, and oil-modified phenol formaldehyde resin.

[0101] The resin component is preferably one or more selected from the group consisting of petroleum resins and terpene resins, and more preferably one or more selected from the group consisting of cyclopentadiene resins, aromatic vinyl resins, and terpene resins.

[0102] From the viewpoint of wet grip performance, the softening point of the resin component is preferably 80° C. or higher, more preferably 85° C. or higher, and even more preferably 90° C. or higher. From the viewpoint of processability and improving the dispersibility of the rubber component and the filler, the softening point is preferably 160° C. or lower, more preferably 150° C. or lower, and even more preferably 145° C. or lower. In this specification, the softening point may be defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point tester.

[0103] When a resin component is contained, the content 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 wet grip performance, and 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 from the viewpoint of suppressing heat buildup.

[0104] Examples of oils include process oil, vegetable oils, and animal fats. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Furthermore, as an environmental measure, process oil with a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of the low-PCA process oil include mild extract solvates (MES), treated distillate aromatic extracts (TDAE), and heavy naphthenic oil.

[0105] When oil is contained, the content 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 wet grip performance. Furthermore, from the viewpoint of abrasion resistance, the content 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. The amount of oil may be 0 parts by mass. In this specification, the oil content includes the amount of oil contained in the oil-extended rubber.

[0106] The liquid polymer is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof 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 may be hydrogenated, or modified liquid polymers (preferably terminally modified liquid polymers) in which the main chain and / or terminals of these polymers have been modified with modifying groups. These liquid polymers may be used alone or in combination of two or more.

[0107] The modified liquid polymer is not particularly limited, but examples thereof include liquid butadiene polymers modified at one or both ends (terminal-modified liquid BR) and liquid styrene-butadiene polymers modified at one or both ends (terminal-modified liquid SBR), which may be hydrogenated. Of these, optionally hydrogenated terminal-modified liquid BR is preferred.

[0108] The modifying group is not particularly limited, and examples thereof include a silyl group, a trialkoxysilyl group, an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imido group, a hydrazo group, an azo group, a diazo group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, a carboxyl group, an epoxy group, an acryl group, a methacryl group, an acryloyl group, a methacryloyl group, etc. Among these, one or more groups selected from the group consisting of a hydroxyl group, a carboxyl group, an acryloyl group, and a methacryloyl group are preferred.

[0109] When a liquid polymer is contained, the content thereof per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. The content of the liquid rubber 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.

[0110] Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), and trixylenyl phosphate (TXP). These ester-based plasticizers may be used alone or in combination of two or more.

[0111] The amount of plasticizer per 100 parts by mass of the rubber component (the total amount when multiple plasticizers are used in combination) 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 wet grip performance, and is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 90 parts by mass or less, and particularly preferably 80 parts by mass or less from the viewpoint of processability.

[0112] <Other compounding agents> In addition to the above-mentioned components, the rubber composition constituting the first rubber layer may appropriately contain compounding agents that are generally used in the tire industry, such as wax, processing aids, stearic acid, zinc oxide, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0113] When wax is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, from the viewpoint of preventing whitening of the tire due to bloom.

[0114] Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used alone or in combination of two or more. Examples of processing aids that can be used include those commercially available from Schill + Seilacher, Performance Additives, etc.

[0115] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of improving processability, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, from the viewpoint of abrasion resistance and breaking strength.

[0116] The antioxidant is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamates. Preferred are phenylenediamine-based antioxidants 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 antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. These antioxidants may be used alone or in combination of two or more.

[0117] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of ozone crack resistance of the rubber, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of abrasion resistance and wet grip performance.

[0118] When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, from the viewpoint of vulcanization rate.

[0119] When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 1.5 parts by mass or more from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less from the viewpoint of abrasion resistance.

[0120] As the vulcanizing agent, sulfur is preferably used, and examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0121] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0122] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylenedithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, etc.

[0123] Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based 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-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred, and a combination of a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator is more preferred.

[0124] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among these, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

[0125] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0126] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, etc. Among these, 2-mercaptobenzothiazole is preferred.

[0127] When a vulcanization accelerator is contained, the content thereof per 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 content thereof per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[0128] <Production of rubber composition and tire> The rubber composition according to the present disclosure can be produced by a known method, for example, by kneading the above-described components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or kneader).

[0129] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into multiple steps as desired.

[0130] The kneading conditions are not particularly limited, but examples include a method in which the base kneading step involves kneading for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and a method in which the final kneading step involves kneading for 1 to 5 minutes at 70 to 110°C. The vulcanization conditions are not particularly limited, but examples include a method in which vulcanization is carried out for 10 to 30 minutes at 150 to 200°C.

[0131] The tire of the present disclosure can be manufactured by a conventional method using the rubber composition described above. That is, an unvulcanized rubber composition obtained by blending the above-described components with a rubber component as needed is extruded into the shape of a tread using an extruder equipped with a die of a predetermined shape, and the extruded rubber composition is bonded together with other tire components in a tire building machine and molded by a conventional method to form an unvulcanized tire. The unvulcanized tire can then be heated and pressurized in a vulcanizer to manufacture the tire.

[0132] The tires disclosed herein may be pneumatic or non-pneumatic. They are also suitable for racing tires, passenger car tires, large passenger car tires, large SUV tires, motorcycle tires, and the like, and can be used as summer tires, winter tires, and studless tires for each of these. In this specification, passenger car tires refer to tires designed to be mounted on four-wheeled automobiles and having a maximum load capacity of 1000 kg or less. [Example]

[0133] The present disclosure will be described based on examples, but the present disclosure is not limited to only the examples.

[0134] The various chemicals used in the examples and comparative examples are listed below. NR:TSR20 Hydrophilized ENR50: Modified ENR produced in Production Example 1 described below Hydrophilized ENR 25: Modified ENR produced in Production Example 2 described below SBR: Nipol 1502 (E-SBR, styrene content: 23.5% by mass, vinyl content: 18% by mole, Mw: 500,000) manufactured by Zeon Corporation BR: UBEPOL BR (registered trademark) 150B (cis content: 97 mol%, Mw: 440,000) manufactured by Ube Industries, Ltd. Carbon black: Show Black N220 (N2SA: 111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Silica 1: Ultrasil VN3 (N2SA: 175 ml) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 18nm) Silica 2: Ultrasil 9100GR (N2SA: 230 ml) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 15nm) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Surfactant: Kao Corporation's Emulgen 306P (polyoxyethylene stearyl ether, non-ionic surfactant) Thermoplastic elastomer: Kuraray Co., Ltd.'s Kuramilon TU-S5265 (a copolymer of polyurethane-based thermoplastic elastomer and styrene-based thermoplastic elastomer) Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd. Resin component 1: Kraton Sylvares SA85 (α-methylstyrene / styrene resin, softening point: 85°C) Resin component 2: Oppa PR-140 (hydrogenated dicyclopentadiene resin, softening point: 100°C) manufactured by ExxonMobil Chemical Company Liquid BR: "NISSO-PB GI-3000" manufactured by Nippon Soda Co., Ltd. (hydrogenated polybutadiene with hydroxyl groups at both ends) Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Zinc oxide: "Ginrei R" manufactured by Toho Zinc Co., Ltd. Wax: Ozoace 355 manufactured by Nippon Seiro Co., Ltd. Antioxidant 1: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Antioxidant 2: Antigen RD (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Sumitomo Chemical Co., Ltd. Sulfur: HK-200-5 (powdered sulfur containing 5% oil) manufactured by Hosoi Chemical Industry Co., Ltd. Vulcanization accelerator 1: Noccelaer D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela CZ-G (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0135] Production Example 1: Synthesis of hydrophilic ENR50 A tetrahydrofuran solution of ENR50 (manufactured by Kempuran Guthrie, epoxidation rate: 50 mol%) was poured into methanol, washed with alcohol, and then dried. The purified ENR50 was dissolved in dimethylformamide, and polyethylene glycol monomethyl ether (Mw: 400) was added. The mixture was heated in an oil bath at 140°C and stirred under a nitrogen atmosphere for 8 hours. The solvent was then removed using an evaporator, and the mixture was vacuum dried at 80°C for 12 hours. This product was then subjected to Soxhlet extraction using methanol for 24 hours, and the purified product was vacuum dried in an oven at 25°C for 3 days to obtain hydrophilized ENR50. The resulting hydrophilized ENR50 had undergone ring-opening via the addition of polyethylene glycol monomethyl ether to all epoxy groups (ring-opening rate: 100%).

[0136] Production Example 2: Synthesis of hydrophilic ENR25 Hydrophilized ENR25 was obtained in the same manner as in Production Example 1, except that ENR25 (manufactured by Kempuran Guthrie, epoxidation rate: 25 mol%) was used. In the obtained hydrophilized ENR25, all epoxy groups were ring-opened by addition of polyethylene glycol monomethyl ether (ring-opening rate: 100%).

[0137] Examples and Comparative Examples According to the formulations shown in Tables 1 to 4, a 1.7 L closed-type Banbury mixer was used to knead the chemicals other than sulfur and the vulcanization accelerator for 4 minutes at a discharge temperature of 160°C to obtain a kneaded mixture. Next, using an open roll, sulfur and the vulcanization accelerator were added to the kneaded mixture, and the mixture was kneaded for 4 minutes until the temperature reached 105°C, obtaining an unvulcanized rubber composition. The resulting unvulcanized rubber composition was then press-vulcanized for 12 minutes at 170°C to obtain a vulcanized rubber sheet for testing. The resulting unvulcanized rubber composition was molded to fit the shape of the tread and bonded together with other tire components to produce an unvulcanized tire. The tire was then vulcanized at 170°C to obtain test tires (size: 205 / 65R15, rim: 15x6JJ, internal pressure: 230 kPa). As shown in Figure 2, the tires of Comparative Examples 1, 3, 5, 7 to 11, and 14 to 17 are tires in which the widthwise length of the land portion closest to the tire equatorial plane is constant from the outer side to the inner side in the tire radial direction in a tire meridian cross section including the tire rotation axis.

[0138] <Measurement of acetone extractables> After vulcanization, each rubber test piece was immersed in acetone for 24 hours to extract the soluble components. The mass of each test piece was measured before and after extraction, and the amount of acetone extracted was calculated using the following formula. Acetone extractable amount (%) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100

[0139] <Contact angle measurement> Each vulcanized rubber test specimen was cut from the first rubber layer of the tread portion of each test tire, measuring 20 mm in length, 30 mm in width, and 2 mm in thickness, with the long side aligned in the tire circumferential direction. The contact angle of each rubber test specimen, which had been subjected to the following treatments, was measured using a contact angle meter DMs-401 manufactured by Kyowa Interface Science Co., Ltd. Specifically, each rubber test specimen cut from the first rubber layer as described above was first immersed in water at 23°C and atmospheric pressure for 1 hour, and then allowed to dry at 23°C and atmospheric pressure for 24 hours. Subsequently, 2.0 μL of pure water was dropped onto the surface of each rubber test specimen held horizontally, and the angle (contact angle A1) formed by the edge of the droplet with the surface of the rubber composition 180 seconds after the drop was measured. After measuring the contact angle A1, each rubber test specimen was immersed in water at 23°C and atmospheric pressure for 1 hour, and then allowed to dry at 23°C and atmospheric pressure for 24 hours. Thereafter, 2.0 μL of pure water was dropped onto the surface of each rubber test piece held horizontally, and the angle (contact angle A2) formed by the edge of the drop and the surface of the rubber composition 180 seconds after the drop was measured.

[0140] <Wet grip performance of new and worn tires> Each test tire was mounted on all wheels of a vehicle (domestic FF2000cc), and the braking distance from the point where the brakes were applied at a speed of 100 km / h was measured on a wet asphalt circuit. Next, the tires were thermally aged at 80°C for 7 days, and then the treads were worn along the tread radius so that the tread thickness was 10% of that of the new tires. Each test tire was mounted on all wheels of the vehicle, and the vehicle was driven 10 laps around the wet asphalt circuit. The braking distance from the point where the brakes were applied at a speed of 100 km / h was then measured. The braking distance of the test tire of the reference comparative example (Comparative Example 1 in Tables 1 and 2, Comparative Example 13 in Tables 3 and 4) when new was set to 100, and the wet grip performance of each tire when new and after wear was expressed as an index using the following calculation formula. A higher index indicates better wet grip performance. (Wet grip performance index) = (braking distance of the standard comparative tire (when new)) / (braking distance of each test tire (when new and after wear)) × 100

[0141] [Table 1]

[0142] [Table 2]

[0143] [Table 3]

[0144] [Table 4]

[0145] The results in Tables 1 to 4 show that tires of the present disclosure, which have a specified tread pattern in which the contact area increases with wear and in which the contact angle of the rubber composition constituting the tread rubber is within a specified range, have excellent wet grip performance when new and significantly suppress deterioration of wet grip performance after wear.

[0146] <Embodiment> Examples of embodiments of the present disclosure are provided below.

[0147] [1] A tire having a tread, the tread having land portions separated by a plurality of circumferential grooves, and in a tire meridian cross section including the tire rotation axis, the width direction length of the land portion closest to the tire equatorial plane has a portion where it increases from the outer side to the inner side in the tire radial direction, the tread having at least one rubber layer, a first rubber layer constituting the tread surface being constituted by a rubber composition containing a rubber component including a diene rubber, the rubber composition constituting the first rubber layer being immersed in water at 23°C and normal pressure for 1 hour, and then left to dry at 23°C and normal pressure for 24 hours, and the pure water contact angle A1 measured after the rubber composition constituting the first rubber layer is immersed in water at 23°C and normal pressure for 1 hour, and then left to dry at 23°C and normal pressure for 24 hours, both of which are 80° or less (preferably 75° or less). [2] The tire according to [1], wherein the rubber component contained in the rubber composition constituting the first rubber layer contains an isoprene-based rubber modified with a hydrophilic functional group, and / or the rubber composition constituting the first rubber layer contains a thermoplastic elastomer containing a hydrophilic functional group. [3] The tire according to [1] or [2], wherein the rubber composition constituting the first rubber layer contains 0.5 to 50 parts by mass of a thermoplastic elastomer containing at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an ether group, a carbonyl group, and an amide group, per 100 parts by mass of the rubber component. [4] The tire according to any one of the above [1] to [3], wherein the rubber component contained in the rubber composition constituting the first rubber layer contains 10 to 90 mass % of an isoprene-based rubber modified with one or more functional groups selected from the group consisting of a hydroxyl group, an amino group, and an ether group. [5] The tire according to any one of the above [1] to [4], wherein the acetone extractable amount of the rubber composition constituting the first rubber layer is 5 to 25 mass% (preferably 7 to 23 mass%, more preferably 9 to 21 mass%). [6] The tire according to any one of the above [1] to [5], wherein the rubber composition constituting the first rubber layer contains at least one selected from the group consisting of petroleum resins, terpene resins, and hydrogenated versions thereof. [7] The tire according to any one of the above [1] to [6], wherein the rubber composition constituting the first rubber layer contains a liquid polymer. [8] The rubber composition constituting the first rubber layer has a nitrogen adsorption specific surface area of ​​180 m 2 / g or more (preferably 200m 2 The tire according to any one of the above [1] to [7], containing silica (at least 1 / g). [9] The width direction length L of the land portion closest to the tire equatorial plane when the tread portion is 90% worn relative to the width direction length L0 when the tire is new. 90 The ratio of L 90 The tire according to any one of the above [1] to [8], wherein / L0 is 1.1 or more (preferably 1.2 or more, more preferably 1.3 or more).

[10] The tire according to any one of the above [1] to [9], wherein the contact angle A1 and the contact angle A2 of the rubber composition constituting the first rubber layer are both 70° or less (preferably both 65° or less). [Explanation of symbols]

[0148] 1. Tread surface 2...Circumferential groove 3... land department 4 Groove edge 5. Groove wall C···Tire equatorial plane H: Circumferential groove depth L0: Width of new tire L 90 Width direction length when tread is 90% worn

Claims

1. A tire having a tread, the tread has land portions partitioned by a plurality of circumferential grooves, In a tire meridian cross section including the tire rotation axis, the width direction length of the land portion closest to the tire equatorial plane has a portion that increases from the outer side toward the inner side in the tire radial direction, the tread having at least one rubber layer, the first rubber layer constituting the tread surface is made of a rubber composition containing a rubber component including a diene rubber, a rubber composition constituting the first rubber layer is immersed in water at 23°C and normal pressure for 1 hour, and then left to stand at 23°C and normal pressure for 24 hours to dry, and thereafter a pure water contact angle A1 is measured; and a pure water contact angle A2 is measured after the rubber composition has been immersed in water at 23°C and normal pressure for 1 hour, and then left to stand at 23°C and normal pressure for 24 hours to dry, both of which are 80° or less.

2. 2. The tire according to claim 1, wherein the acetone extractable amount of the rubber composition constituting the first rubber layer is 5 to 25% by mass.

3. 3. The tire according to claim 1, wherein the rubber component contained in the rubber composition constituting the first rubber layer contains an isoprene-based rubber modified with a hydrophilic functional group, and / or the rubber composition constituting the first rubber layer contains a thermoplastic elastomer containing a hydrophilic functional group.

4. The tire according to any one of claims 1 to 3, wherein the rubber composition constituting the first rubber layer contains 0.5 to 50 parts by mass of a thermoplastic elastomer containing at least one functional group selected from the group consisting of a carboxyl group, a hydroxyl group, an ester group, an ether group, a carbonyl group, and an amide group, per 100 parts by mass of the rubber component.

5. A tire as described in claim 1 or 4, wherein the rubber component contained in the rubber composition constituting the first rubber layer includes an isoprene-based rubber modified with a hydrophilic functional group.

6. A tire as described in claim 3, wherein the thermoplastic elastomer containing the hydrophilic functional group is a copolymer of a polyurethane-based thermoplastic elastomer and a styrene-based thermoplastic elastomer.

7. A tire having a tread, the tread has land portions partitioned by a plurality of circumferential grooves, In a tire meridian cross section including the tire rotation axis, the width direction length of the land portion closest to the tire equatorial plane has a portion that increases from the outer side toward the inner side in the tire radial direction, the tread having at least one rubber layer, the first rubber layer constituting the tread surface is made of a rubber composition containing a rubber component including a diene rubber, the rubber component contained in the rubber composition constituting the first rubber layer contains an isoprene-based rubber modified with a hydrophilic functional group, and the acetone extractable amount of the rubber composition constituting the first rubber layer is 5 to 25% by mass; a rubber composition constituting the first rubber layer is immersed in water at 23°C and normal pressure for 1 hour, and then left to stand at 23°C and normal pressure for 24 hours to dry, and thereafter a pure water contact angle A1 is measured; and a pure water contact angle A2 is measured after the rubber composition has been immersed in water at 23°C and normal pressure for 1 hour, and then left to stand at 23°C and normal pressure for 24 hours to dry, both of which are 80° or less.

8. A tire as described in claim 7, wherein the rubber composition constituting the first rubber layer contains a thermoplastic elastomer having a hydrophilic functional group, and the thermoplastic elastomer having a hydrophilic functional group is a copolymer of a polyurethane-based thermoplastic elastomer and a styrene-based thermoplastic elastomer.

9. The tire according to any one of claims 1 to 8, wherein the rubber component contained in the rubber composition constituting the first rubber layer contains 10 to 90% by mass of an isoprene-based rubber modified with one or more functional groups selected from the group consisting of a hydroxyl group, an amino group, and an ether group.

10. The tire according to any one of claims 1 to 9, wherein the rubber composition constituting the first rubber layer contains at least one selected from the group consisting of petroleum resins, terpene resins, and hydrogenated versions thereof.

11. The tire according to any one of claims 1 to 10, wherein the rubber composition constituting the first rubber layer contains a liquid polymer.

12. The rubber composition constituting the first rubber layer has a nitrogen adsorption specific surface area of ​​180 m 2 12. The tire according to claim 1, comprising at least 1 / g of silica.

13. The width direction length L of the land portion closest to the tire equatorial plane when the tire is new 0 The width direction length L when the tread portion is 90% worn 90 The ratio L 90 / L 0 The tire according to any one of claims 1 to 12, wherein the σ is 1.1 or more.

14. The tire according to any one of claims 1 to 13, wherein the contact angle A1 and the contact angle A2 of the rubber composition constituting the first rubber layer are both 70° or less.

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