tire

Abstract

To provide a tire configured so that ride comfort performance is maintained over a long time.SOLUTION: A tire comprises a tread part 3 in which a direction of mounting on a vehicle is designated. The tread part 3 has an inner tread rubber layer 52 that constitutes an inner end part side of the vehicle when the tread part is mounted on the vehicle, and an outer tread rubber layer 53 constituting an outer end part side of the vehicle. The inner tread rubber layer 52 and the outer tread rubber layer 53 are constituted of rubber compositions including rubber components. The rubber components constituting the inner tread rubber layer 52 include copolymers in which aromatic vinyl compounds and conjugated diene compounds are copolymerized and some of the conjugated diene compounds are hydrogenated. Contents of silica with respect to 100 pts.mass of the rubber components of the rubber compositions constituting the inner tread rubber layer 52 are larger than contents of silica with respect to 100 pts.mass of the rubber components of the rubber compositions constituting the outer tread rubber layer 53 in the tire.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to tires. [Background technology]

[0002] Patent Document 1 describes how wet grip performance can be improved by blending a relatively large amount of highly dispersible silica with a liquid plasticizer such as oleic sunflower oil. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2014-506277 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the invention described in Patent Document 1 had the problem that, over time, the liquid plasticizer, which is an oil, would leach out, causing the rubber to harden. Consequently, it was also difficult to maintain ride comfort over a long period of time.

[0005] This disclosure aims to provide a tire that maintains ride comfort performance over a long period of time. [Means for solving the problem]

[0006] After thorough investigation, it was found that the aforementioned problem can be solved in a tire having a tread portion with a specified mounting direction on a vehicle by dividing the tread portion into an inner tread rubber layer that constitutes the inner end side of the vehicle when mounted on the vehicle and an outer tread rubber layer that constitutes the outer end side of the vehicle, by compounding a specific hydrogenated rubber component into the inner tread rubber layer, and by making the silica content of the inner tread rubber layer greater than that of the outer tread rubber layer.

[0007] In other words, the present disclosure relates to a tire having a tread portion for which the mounting direction to a vehicle is specified, wherein the tread portion comprises an inner tread rubber layer that constitutes the inner end side of the vehicle when mounted on the vehicle, and an outer tread rubber layer that constitutes the outer end side of the vehicle, wherein the inner tread rubber layer and the outer tread rubber layer are composed of a rubber composition containing rubber components, wherein the rubber component constituting the inner tread rubber layer includes a copolymer in which an aromatic vinyl compound and a conjugated diene compound are copolymerized, and a portion of the conjugated diene portion is hydrogenated, and the silica content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer. [Effects of the Invention]

[0008] According to this disclosure, a tire is provided that maintains ride comfort performance over a long period of time. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of a tire according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0010] A tire according to one embodiment of the present disclosure is a tire having a tread portion for which the mounting direction to a vehicle is specified, wherein the tread portion has an inner tread rubber layer that constitutes the inner end side of the vehicle when mounted on the vehicle, and an outer tread rubber layer that constitutes the outer end side of the vehicle, wherein the inner tread rubber layer and the outer tread rubber layer are composed of a rubber composition containing rubber components, wherein the rubber component constituting the inner tread rubber layer includes a copolymer in which an aromatic vinyl compound and a conjugated diene compound are copolymerized, and a portion of the conjugated diene portion is hydrogenated, and the silica content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer.

[0011] By incorporating a specific hydrogenated rubber component into the inner tread rubber layer and making the silica content of the inner tread rubber layer higher than that of the outer tread rubber layer, the resulting tire has less change in ride comfort performance before and after wear of the tread portion, and the ride comfort performance at the time of new product is maintained. Although not intending to be restricted by theory, the reason is considered as follows.

[0012] (1) When the rubber inside the tread deteriorates, the distance between crosslinking points in the rubber composition becomes shorter, the mobility of the polymer is suppressed, and it becomes difficult to relieve the impact from the outside, so the ride comfort performance deteriorates. Since the hydrogenated copolymer has few double bonds and few crosslinking points, it can prevent the distance between crosslinking points from becoming shorter due to deterioration. From this, it is considered that it becomes easier to absorb the impact from the outside regardless of time. (2) Also, by making the silica content of the inner tread rubber layer higher than that of the outer tread rubber layer, the thermal conductivity of the inner tread rubber layer is suppressed, so heat from the outer tread rubber layer, where the temperature is likely to rise during cornering, is less likely to be transmitted, and it is considered that deterioration of the tread rubber can be more effectively suppressed. And, by the cooperation of these, even when accompanied by movements such as cornering or changes over time, it is possible to suppress the heat transmitted to the inner tread rubber layer that is mainly in contact with the ground during driving and the change in the distance between crosslinking points, so it is considered that the remarkable effect of maintaining the ride comfort performance over a long period is achieved.

[0013] From the viewpoint of easily absorbing the impact during rolling, the rubber composition constituting the inner tread rubber layer preferably contains 90 parts by mass or more of silica with respect to 100 parts by mass of the rubber component.

[0014] From the viewpoints of suppressing deterioration due to heat and absorbing impact by the resin component, the rubber composition constituting the inner tread rubber layer preferably contains a hydrogenated petroleum resin.

[0015] The content of butadiene rubber in the rubber component constituting the inner tread rubber layer is preferably 15% by mass or less from the viewpoint of making it difficult to transmit impact inside the tire.

[0016] The distance W between both ground contact ends

[0020] , , , , ,

[0019] , L ,

[0018] , , ,

[0021] , , ,

[0017] , The ratio of D (D / W L ) from the inner vehicle-side ground contact end to the interface between the inner tread rubber layer and the outer tread rubber layer with respect to W is preferably 0.50 or more.

[0017] D / W L By setting D / W within the above range, it is considered that the inner tread rubber layer is likely to come into contact with the ground during rolling, and the riding comfort performance can be further improved.

[0018] The groove area ratio of the ground contact surface of the inner tread rubber layer is preferably larger than the groove area ratio of the ground contact surface of the outer tread rubber layer. Further, the difference between the groove area ratio of the ground contact surface of the inner tread rubber layer and the groove area ratio of the ground contact surface of the outer tread rubber layer (groove area ratio of the ground contact surface of the inner tread rubber layer - groove area ratio of the ground contact surface of the outer tread rubber layer) is preferably 2% or more and 10% or less.Is preferably within the range of.

[0019] By making the groove area ratio of the ground contact surface of the inner tread rubber layer larger than the groove area ratio of the ground contact surface of the outer tread rubber layer, deformation of the outer tread rubber layer is suppressed, and it becomes easier to suppress excessive heat generation in the outer tread rubber layer even during turning. From this, since the heat transmitted to the inner tread rubber layer is suppressed, it is considered that the curing of the inner tread rubber layer can be suppressed.

[0020] The tire of the present disclosure has land portions partitioned by two or more circumferential grooves in which the tread portion continuously extends in the tire circumferential direction, and the widthwise length of the land portion closest to the tire equatorial plane on the tread surface of the land portion is preferably 18% or more of the contact width.

[0021] By setting the widthwise length of the tread surface on the land portion closest to the tire's equatorial plane within the aforementioned range, deformation in the center of the tread can be suppressed. This is thought to reduce heat generation in the central portion that contacts the road surface during rolling, thereby making it easier to suppress deterioration.

[0022] <Definition> A "standard rim" is the rim specified for each tire within the standardization system that includes the standard on which the tire is based. For example, it is called a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO.

[0023] "Regular internal pressure" refers to the air pressure specified for each tire by each standard within the tire standard system, including the standard on which the tire is based. For example, it is the "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO.

[0024] "Normal condition" refers to a state in which the tire is mounted on a normal rim, filled to the normal internal pressure, and under no load. In this specification, unless otherwise specified, the dimensions of each part of the tire are measured under the aforementioned normal condition.

[0025] "Regular load" refers to the load specified for each tire by each standard within the standards system that the tire is based on. For example, it is the "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0026] The "tread contact point" is the outermost contact point in the tire's width direction when a tire in its normal state is subjected to a normal load, has a camber angle of 0 degrees, and is in contact with a flat surface.

[0027] "The distance D from the inner contact edge of the vehicle to the interface between the inner tread rubber layer and the outer tread rubber layer" refers to the straight-line distance from the inner contact edge of the vehicle on the contact surface to the extension of the rubber interface between the inner tread rubber layer and the outer tread rubber layer on the tread surface.

[0028] The "groove area ratio" is the ratio of the total area of ​​all grooves to the total surface area of ​​each contact surface formed by the outer tread rubber layer and the inner tread rubber layer separated at the interface, assuming that all grooves are filled.

[0029] An "aromatic vinyl unit" refers to a unit in a copolymer derived from an aromatic vinyl compound. Here, an aromatic vinyl compound refers to an aromatic compound substituted with at least a vinyl group, and does not include the conjugated diene compounds described below. Specific examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, and 2,4,6-trimethylstyrene, with styrene being preferred. These may be used individually or in combination of two or more.

[0030] "Aromatic vinyl unit content in rubber components" refers to the total amount (mass%) of aromatic vinyl units, such as styrene, contained in 100% by mass of the rubber components. For each rubber component, the aromatic vinyl unit content (mass%) is multiplied by the mass fraction in the rubber components to obtain the value, and these values ​​are then summed up. Specifically, it is calculated as Σ(aromatic vinyl unit content (mass%) of each aromatic vinyl unit-containing rubber × content in the rubber components of each aromatic vinyl unit-containing rubber (mass%) / 100). Note that if the aromatic vinyl unit-containing rubber is styrene-butadiene rubber, it is referred to as "styrene content".

[0031] "Oil content" includes the amount of oil contained in the oil-applied rubber.

[0032] <Measurement method> The "groove area ratio" is calculated from the contact shape when the tread is pressed against a flat surface under normal conditions with a normal load. The contact shape is obtained by mounting the tire on a normal rim, maintaining the normal internal pressure, applying ink to the tread, applying a normal load, pressing it perpendicularly against cardboard or similar material (camber angle 0°), and transferring the ink applied to the tread. Then, by dividing the obtained contact shape at the interface between the outer tread rubber layer and the inner tread rubber layer, the groove area ratio of the contact surface of the outer tread rubber layer and the groove area ratio of the contact surface of the inner tread rubber layer can be determined, respectively.

[0033] "Aromatic vinyl unit content" is, 1 This value is calculated by 1H-NMR measurement and is applied to rubber components (aromatic vinyl unit-containing rubber) that have repeating units derived from aromatic vinyl compounds, such as copolymers of aromatic vinyl compounds and conjugated diene compounds (including hydrogenated products of said copolymers).

[0034] "Cis content (amount of cis-1,4-bonded butadiene units)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2:2017, and is applied, for example, to rubber components having repeating units derived from butadiene, such as BR.

[0035] The glass transition temperature (Tg) of hydrogenated copolymers and SBR is measured in accordance with JIS K 7121, using a differential scanning calorimeter (Q200) manufactured by T.A. Instruments Japan Co., Ltd., while increasing the temperature at a heating rate of 10°C / min.

[0036] The "weight-average molecular weight (Mw)" can be determined by converting the measured value using gel permeation chromatography (GPC) (for example, the GPC-8000 series from Tosoh Corporation, with a differential refractometer as the detector and TSKGEL SUPERMALTIPORE HZ-M column from Tosoh Corporation) to a standard polystyrene equivalent. This method is applicable, for example, to SBR, BR, etc.

[0037] The nitrogen adsorption specific surface area (N2SA) of carbon black is measured in accordance with JIS K 6217-2:2017. The oil absorption capacity (DBP oil absorption capacity (OAN)) of carbon black is measured in accordance with JIS K6217-4:2017.

[0038] The nitrogen adsorption specific surface area (N2SA) of silica is measured by the BET method in accordance with ASTM D3037-93. The mean primary particle diameter 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 taking the average.

[0039] The "softening point of the resin component" is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2015 7.7 is measured using a ring-type softening point measuring device.

[0040] A tire manufacturing procedure, which is one embodiment of this disclosure, will be described in detail below. However, the following description is illustrative for the purpose of explaining this disclosure and is not intended to limit the technical scope of this disclosure to this scope only.

[0041] <Tires> Hereinafter, a tire according to one embodiment of this disclosure will be described with reference to the drawings.

[0042] As shown in Figure 1, the tire T comprises a pair of bead portions 1, a sidewall portion 2 extending outward from each bead portion 1 in the tire radial direction RD (vertical direction in Figure 1; hereinafter simply referred to as the tire radial direction), a tread portion 3 connected to the outer ends of both sidewall portions 2 in the tire radial direction RD, and a toroidal carcass layer 4 extending from the tread portion 3 through the sidewall portions 2 to the bead portion 1. The bead portion 1 is provided with a bead core 1a and a bead filler 1b. The carcass layer 4 is provided between the pair of bead portions 1 and is composed of at least one carcass ply, whose end is locked in a wound state via the bead core 1a. The carcass ply is formed by covering a cord extending approximately perpendicular to the tire equator with topping rubber. Inside the carcass layer 4, an inner liner rubber 4a is provided to maintain air pressure. Furthermore, a sidewall rubber 6 is provided outside the carcass layer 4 in the sidewall portion 2. Furthermore, a rim strip rubber 7 is provided on the outside of the carcass layer 4 in the bead portion 1, which comes into contact with the rim (not shown) when the wheel is mounted on the rim.

[0043] The tires of this disclosure have a specified mounting direction for the vehicle, and the mounting direction for the vehicle (for example, whether it is the inside or outside) is indicated on the side of the tire.

[0044] The tread portion 3 has an outer tread edge To and an inner tread edge Ti. The outer tread edge To is located on the outside of the vehicle (left side in Figure 1) when mounted on the vehicle. The inner tread edge Ti is located on the inside of the vehicle (right side in Figure 1) when mounted on the vehicle. Each tread edge To and Ti is the outermost contact point in the tire width direction W (left-right direction in Figure 1; hereinafter simply referred to as the width direction W) when a normal load is applied to a tire in a normal state with a camber angle of 0 degrees and contact with a flat surface.

[0045] In Figure 1, the tread portion 3 has a cap portion 50 that constitutes the contact surface and a base portion 51 provided on the inner side of the cap portion 50 in the tire radial direction. The cap portion 50 is the inner tread rubber layer that constitutes the inner end side of the vehicle when mounted on the vehicle. 53and the outer tread rubber layer that constitutes the outer edge of the vehicle 52 It has the inner tread rubber layer. 53 and outer tread rubber layer 52 A wing rubber may be provided on the outside of the tread. However, even if a wing rubber is provided, or if the sidewall portion overlaps the radially outer side of the tread, and these form a contact surface, they do not fall under the inner tread rubber and outer tread rubber of this disclosure. In Figure 1, the interface P between the inner tread rubber layer and the outer tread rubber layer from the outer contact end of the vehicle is located below the circumferential groove 5a, but is not limited to this configuration and may be located below the land portion 5. The "land portion" refers to the area of ​​the tread portion 3 partitioned by the tread contact end To, Ti and a plurality of circumferential grooves 5a that extend continuously in the circumferential direction of the tire.

[0046] The distance W between the contact points of the outer tread edge To and the inner tread edge Ti. L The ratio (D / W) of the distance D from the inner contact edge of the vehicle to the interface P between the inner tread rubber layer and the outer tread rubber layer. L ) is preferably 0.40 or higher, more preferably 0.45 or higher, even more preferably 0.50 or higher, and particularly preferably 0.55 or higher. D / W L By setting the range as described above, the inner tread portion is more likely to make contact with the ground during rolling, which is thought to further improve ride comfort. Also, D / W L From the viewpoint of the effects of this disclosure, a value of 0.90 or less is preferred, 0.86 or less is more preferred, 0.83 or less is even more preferred, and 0.80 or less is particularly preferred.

[0047] It is preferable that the groove area ratio of the contact surface of the inner tread rubber layer is greater than the groove area ratio of the contact surface of the outer tread rubber layer. By making the groove area ratio of the contact surface of the inner tread rubber layer greater than that of the outer tread rubber layer, deformation of the outer tread rubber layer is suppressed, and it becomes easier to suppress excessive heat generation of the outer tread rubber layer even during cornering. As a result, it is thought that the heat transmitted to the inner tread rubber layer is suppressed, and thus hardening of the inner tread rubber layer can be suppressed.

[0048] The groove area ratio of the contact surface of the outer tread rubber layer is preferably 4% or more, more preferably 7% or more, and even more preferably 10% or more. Furthermore, the groove area ratio of the contact surface of the outer tread rubber layer is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less.

[0049] The groove area ratio of the contact surface of the inner tread rubber layer is preferably 8% or more, more preferably 10% or more, and even more preferably 12% or more. Furthermore, the groove area ratio of the contact surface of the inner tread rubber layer is preferably 45% or less, more preferably 40% or less, and even more preferably 35% or less.

[0050] From the viewpoint of the effects of this disclosure, the difference between the groove area ratio of the contact surface of the inner tread rubber layer and the groove area ratio of the contact surface of the outer tread rubber layer is preferably 2% to 10%, more preferably 3% to 9%, and even more preferably 4% to 8%.

[0051] [Rubber composition] Inner tread rubber layer 53 and outer tread rubber layer 52 Each of the rubber compositions constituting the inner tread rubber layer (hereinafter referred to as the rubber composition of this disclosure unless otherwise specified) will be described in detail below. Unless otherwise specified, the following description of the rubber composition refers to the inner tread rubber layer. 53 and outer tread rubber layer 52 This is common to both.

[0052] <Rubber components> The rubber composition of this disclosure is characterized in that the rubber component constituting the inner tread rubber layer contains, as an essential component, a copolymer (hereinafter sometimes simply referred to as a hydrogenated copolymer) obtained by copolymerizing an aromatic vinyl compound and a conjugated diene compound, with a portion of the conjugated diene portion being hydrogenated. Furthermore, it is preferable that the rubber component of this disclosure contains a diene rubber. The rubber component constituting the inner tread rubber layer may consist only of the hydrogenated copolymer and the diene rubber. The rubber component constituting the outer tread rubber layer may consist only of a diene rubber.

[0053] (Hydrogenated copolymer) The hydrogenated copolymers disclosed herein can be synthesized by hydrogenating a polymer obtained by polymerizing an aromatic vinyl compound and a conjugated diene compound by a known method (for example, the method described in Japanese Patent Application Publication No. 2020-79340). There are no particular limitations on the order of copolymerization, and either random copolymerization or block copolymerization may be used. Furthermore, the hydrogenated copolymer may be synthesized by copolymerizing monomers having the structure after hydrogenation.

[0054] Aromatic vinyl compounds refer to aromatic compounds that are substituted with at least one vinyl group, and do not include the conjugated diene compounds described below. Specific examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, and 2,4,6-trimethylstyrene, with styrene being preferred. These may be used individually or in combination of two or more.

[0055] Examples of conjugated diene compounds include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene, with 1,3-butadiene and isoprene being preferred, and 1,3-butadiene being more preferred. These may be used individually or in combination of two or more.

[0056] As the copolymer of an aromatic vinyl compound and a conjugated diene compound, a styrene-butadiene copolymer (SBR) is preferred. Therefore, as the hydrogenated copolymer, a copolymer in which a part of the conjugated diene portion of the styrene-butadiene copolymer is hydrogenated (hydrogenated SBR) is preferred.

[0057] The hydrogenation rate of the hydrogenated copolymer (preferably hydrogenated SBR) is preferably 40 mol% or more, more preferably 50 mol% or more, still more preferably 60 mol% or more, and particularly preferably 70 mol% or more. Also, the hydrogenation rate of the hydrogenated copolymer is preferably 99 mol% or less, more preferably 98 mol% or less. When within the above range, the effects of the present disclosure tend to be more suitably obtained. The hydrogenation rate can be adjusted by adjusting reaction conditions such as the hydrogen gas supply pressure and reaction temperature in the hydrogenation reaction as described in Production Examples 1 and 2 below. The hydrogenation rate refers to the ratio of the double bonds in the conjugated diene portion of the copolymer of the aromatic vinyl compound and the conjugated diene compound that have been hydrogenated, 1 and can be calculated from the spectral reduction rate of the unsaturated bond portion of the spectrum obtained by measuring 1H-NMR.

[0058] The aromatic vinyl unit content of the hydrogenated copolymer (when the hydrogenated copolymer is hydrogenated SBR, it is the styrene content) can be appropriately selected, for example, so that the aromatic vinyl unit content in the rubber component satisfies the range described below. Preferably it is 5% by mass or more, more preferably 8% by mass or more, still more preferably 11% by mass or more. Also, the aromatic vinyl unit content of the hydrogenated copolymer is preferably 40% by mass or less, more preferably 35% by mass or less, still more preferably 32% by mass or less. The aromatic vinyl unit content of the hydrogenated copolymer is measured by the above measurement method.

[0059] The weight average molecular weight (Mw) of the hydrogenated copolymer, from the viewpoint of the effects of the present disclosure, is preferably 100,000 or more, more preferably 200,000 or more, still more preferably 300,000 or more. Also, from the viewpoint of processability, the Mw of the multi-polymer is preferably 2,000,000 or less, more preferably 1,000,000 or less, still more preferably 800,000 or less.

[0060] From the viewpoint of wear resistance, the glass transition temperature (Tg) of the hydrogenated copolymer is preferably -90°C or higher, more preferably -80°C or higher, even more preferably -70°C or higher, and particularly preferably -60°C or higher. Furthermore, the Tg of the hydrogenated copolymer is preferably -10°C or lower, more preferably -15°C or lower, even more preferably -20°C or lower, and particularly preferably -25°C or lower.

[0061] Hydrogenated copolymers can also be modified by introducing functional groups that interact with silica. Suitable functional groups include any of those commonly used in this field, such as amino groups, silanol groups, and alkoxysilyl groups.

[0062] The content of hydrogenated copolymer (preferably hydrogenated SBR, more preferably hydrogenated SBR with a hydrogenation rate of 50 mol% or more) in the rubber component constituting the inner tread rubber layer is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more, from the viewpoint of suppressing the shortening of the distance between crosslinking points, hardening, and increased vibration transmission. Furthermore, there is no particular upper limit to the content, but for example, it can be 100% by mass, 99% by mass or less, 95% by mass or less, or 90% by mass or less. The content of hydrogenated copolymer in the rubber component constituting the outer tread rubber layer is not particularly limited, and for example, it can be appropriately selected so that the aromatic vinyl unit content in the rubber component satisfies the range described below.

[0063] (Diene-based rubber) 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). The rubber component constituting the inner tread rubber layer preferably contains at least one selected from the group consisting of isoprene rubber, BR, and SBR, and more preferably contains BR. The rubber component constituting the outer tread rubber layer preferably contains at least one selected from the group consisting of isoprene rubber, BR, and SBR, more preferably contains SBR, even more preferably contains both SBR and BR, and may consist only of SBR and BR. These diene rubbers may be used individually or in combination of two or more.

[0064] (SBR) There are no particular limitations on SBR, and examples include unmodified solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs of these (modified S-SBR, modified E-SBR). Modified SBRs include SBRs with modified terminals and / or main chains, and modified SBRs coupled with tin, silicon compounds, etc. (condensates, those with branched structures, etc.).

[0065] The SBRs listed above may be used individually or in combination of two or more. Examples of the SBRs listed above include those commercially available from companies such as Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Corporation, and ZS Elastomer Co., Ltd.

[0066] The styrene content of SBR can be appropriately selected, for example, so that the aromatic vinyl unit content in the rubber component satisfies the range described below, but is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 11% by mass or more. Furthermore, the styrene content of SBR is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 32% by mass or less. The styrene content of SBR is measured by the method for measuring aromatic vinyl unit content described above.

[0067] The glass transition temperature (Tg) of SBR is preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -60°C or higher, from the viewpoint of making it easier to mitigate vibrations from the road surface. Furthermore, the Tg of SBR is preferably -20°C or lower, more preferably -25°C or lower, and even more preferably -30°C or lower.

[0068] The SBR content in the rubber components constituting the outer tread rubber layer is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. While there is no particular upper limit to the content, it can be, for example, 100% by mass, 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less. The SBR content in the rubber components constituting the inner tread rubber layer is also not particularly limited; for example, it can be appropriately selected so that the aromatic vinyl unit content in the rubber components satisfies the range described below.

[0069] (BR) The BR is not particularly limited, and for example, 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 synthesized using a rare-earth element catalyst (rare-earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are common in the tire industry, can be used. These BRs may be used individually or in combination of two or more. The cis content of the BR is measured by the measurement method described above.

[0070] High-cis BR can be commercially available from companies such as Nippon Zeon Co., Ltd., Ube Industries, Ltd., and JSR Corporation. Including high-cis BR can improve low-temperature properties and wear resistance. The cis content of high-cis BR 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. The cis content of BR is measured by the measurement method described above.

[0071] The BR content in the rubber component constituting the inner tread rubber layer is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less. Furthermore, there is no particular lower limit to the content, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 7% by mass or more.

[0072] The BR content in the rubber components constituting the outer tread rubber layer is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 15% by mass or less. The lower limit of the content is not particularly limited, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 7% by mass or more.

[0073] (Isoprene rubber) Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. For NR, for example, commonly used rubbers in the tire industry such as SIR20, RSS#3, and TSR20 can be used. For IR, there are no particular limitations, and commonly used rubbers in the tire industry such as IR2200 can be used. Examples of modified NR include deproteinized natural rubber (DPNR) and high-purity natural rubber, while examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber, and examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These isoprene-based rubbers may be used individually or in combination of two or more types.

[0074] When isoprene-based rubber is included, its content in the rubber component is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of the effects of this disclosure. Furthermore, there is no particular lower limit to the content, but for example, it can be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more.

[0075] (Other rubber components) The rubber component may contain other rubber components besides the hydrogenated copolymer and diene rubber, to the extent that they do not affect the effects of this disclosure. Other rubber components that can be crosslinkable are commonly used in the tire industry, such as butyl rubber (IIR), halogenated butyl rubber, ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. These other rubber components may be used individually or in combination of two or more. Furthermore, known thermoplastic elastomers may or may not be included in addition to the above rubber components.

[0076] The aromatic vinyl unit content in the rubber component of this disclosure is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of facilitating shock absorption by domains formed by aromatic vinyl units. Furthermore, from the viewpoint of the effects of this disclosure, the aromatic vinyl unit content in the rubber component is preferably 30% by mass or less, and more preferably 25% by mass or less.

[0077] <Filler> The rubber composition of this disclosure preferably contains silica as a filler, and more preferably contains silica and carbon black. Alternatively, the filler may consist only of silica and carbon black.

[0078] (silica) The silica used is not particularly limited, and common silica used in the tire industry can be used, such as silica prepared by the dry method (anhydrous silica) or silica prepared by the wet method (hydrated silica). Among these, hydrated silica prepared by the wet method is preferred because it contains a large amount of silanol groups. In addition to the silica mentioned above, silica made from biomass materials such as rice husks may also be used as appropriate. These silicas may be used individually or in combination of two or more types.

[0079] The nitrogen adsorption specific surface area (N2SA) of silica is considered to be 100m² from the viewpoint of ensuring reinforcing properties and grip performance. 2 Preferably 120m / g or more. 2 More preferably 140m / g or more. 2 More preferably 160m / g or more. 2 A value of 1 / g or more is particularly preferred. Furthermore, from the viewpoint of heat generation and processability, 350m 2 Preferably less than / g, 300m 2 More preferably less than / g, 250m 2 A value of less than / g is even more preferable. The N2SA of silica is measured by the measurement method described above.

[0080] The average primary particle diameter of silica is preferably 10 nm or more, more preferably 12 nm or more, and even more preferably 14 nm or more. Furthermore, the average primary particle diameter is preferably 22 nm or less, more preferably 20 nm or less, and even more preferably 18 nm or less. The average primary particle diameter of silica is measured by the measurement method described above.

[0081] The rubber composition of this disclosure is characterized in that the silica content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer. By increasing the silica content of the inner tread rubber layer compared to the silica content of the outer tread rubber layer, the thermal conductivity of the inner tread rubber layer is suppressed, making it difficult for heat to be transferred from the outer tread rubber layer, which tends to heat up during cornering, and thus effectively suppressing the deterioration of the tread rubber. The difference between the silica content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer and the silica content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more.

[0082] The silica content of the rubber composition constituting the inner tread rubber layer, relative to 100 parts by mass of rubber components, is preferably 80 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, and particularly preferably 95 parts by mass or more, from the viewpoint of facilitating absorption of impact from the road surface. Furthermore, from the viewpoint of reducing the specific gravity of the rubber and achieving weight reduction, it is preferably 140 parts by mass or less, more preferably 130 parts by mass or less, and even more preferably 120 parts by mass or less.

[0083] From the viewpoint of grip performance, the silica content of the rubber composition constituting the outer tread rubber layer, per 100 parts by mass of rubber components, is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 70 parts by mass or more. Furthermore, from the viewpoint of the effects of this disclosure, the silica content of the rubber composition constituting the outer tread rubber layer, per 100 parts by mass of rubber components, is preferably 120 parts by mass or less, more preferably 105 parts by mass or less, and even more preferably 90 parts by mass or less.

[0084] (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. In addition to carbon black produced by burning common mineral oil, carbon black made from biomass materials such as lignin may also be used. These carbon blacks may be used individually or in combination of two or more types.

[0085] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m from the perspective of reinforcement and grip performance. 2 Preferably 70m / g or more. 2 More preferably 100m / g or more, 2 More preferably 120m / g or more. 2 A concentration of 250m or more is particularly preferred. Furthermore, from the viewpoint of dispersibility, 250m is preferable. 2 Preferably less than / g, 220m 2 A value of less than / g is more preferable. The N2SA of carbon black is measured by the measurement method described above.

[0086] From the viewpoint of reinforcing properties, the carbon black content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 7 parts by mass or more. From the viewpoint of fuel efficiency, the carbon black content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more. Furthermore, from the viewpoint of low fuel consumption performance, the carbon black content per 100 parts by mass of rubber components is preferably 90 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 50 parts by mass or less. In addition, from the viewpoint of suppressing heat transfer from the outer tread rubber layer to the inner tread rubber layer, the carbon black content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is preferably less than the carbon black content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer.

[0087] (Other fillers) Other fillers besides silica and carbon black can be those commonly used in the tire industry, such as aluminum hydroxide, calcium carbonate, alumina, clay, and talc. In addition to these fillers, biochar may be used as appropriate.

[0088] From the viewpoint of reinforcing properties and grip performance, the total content of fillers per 100 parts by mass of rubber component is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, even more preferably 100 parts by mass or more, and particularly preferably 110 parts by mass or more. From the viewpoint of dispersibility, it is preferably 160 parts by mass or less, more preferably 150 parts by mass or less, even more preferably 140 parts by mass or less, and particularly preferably 130 parts by mass or less.

[0089] (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 that has conventionally been used in combination with silica in the tire industry can be used, for example: mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, and 2-mercaptoethyltriethoxysilane; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. Examples include thioester silane coupling agents such as lan; vinyl silane coupling agents such as vinyltriethoxysilane 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, it is preferable to contain a sulfide silane coupling agent and / or a mercapto silane coupling agent. As silane coupling agents, for example, those commercially available from Momentive, etc., can be used. These silane coupling agents may be used individually or in combination of two or more.

[0090] When a silane coupling agent is included, the 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, even more preferably 2.0 parts by mass or more, and particularly preferably 4.0 parts by mass or more, from the viewpoint of improving silica dispersibility. Furthermore, from the viewpoint of preventing a decrease in wear resistance, the content 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.

[0091] <Softener> The rubber composition relating to this disclosure preferably contains a softening agent. Examples of softening agents include resin components, oils, liquid rubber, ester-based plasticizers, and the like.

[0092] (Resin components) The resin components are not particularly limited, but examples include petroleum resins, terpene resins, rosin resins, and phenolic resins commonly used in the tire industry. These resin components may be used individually or in combination of two or more.

[0093] In this specification, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions with 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5 petroleum resin.

[0094] In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of C9 fractions include petroleum fractions with 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are preferably used include coumarone indene resin, coumarone resin, indene resin, and aromatic vinyl resins. As aromatic vinyl resins, homopolymers of α-methylstyrene or styrene, or copolymers of α-methylstyrene and styrene are preferred, and copolymers of α-methylstyrene and styrene are more preferred, for reasons of being economical, easy to process, and having excellent heat generation properties. As aromatic vinyl resins, commercially available products from companies such as Kraton, Eastman Chemical Company, and Mitsui Chemicals, Inc. can be used.

[0095] In this specification, "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and C9 fraction include the petroleum fractions mentioned above. As C5C9 petroleum resin, commercially available products from companies such as Tosoh Corporation and LUHUA can be used.

[0096] As for the resin components, the above petroleum resins are partially or completely hydrogenated. re Petroleum resins can also be used. Such hydrogenated petroleum resins are suitably used in rubber compositions constituting the inner tread rubber layer from the viewpoint of suppressing degradation due to heat and absorbing shock due to the resin components. In the case of hydrogenated petroleum resins used in this disclosure, the unsaturated bonds within the molecule are partially or completely hydrogenated. For example, when a petroleum resin having an aromatic ring such as a benzene ring in the main chain or side chain is hydrogenated, the aromatic ring is reduced (for example, if the aromatic ring is a benzene ring, it is reduced to a cyclohexane ring, etc.).

[0097] Examples of terpene resins include polyterpene resins consisting of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, etc.; aromatically modified terpene resins made from the terpene compound and an aromatic compound; terpene-phenol resins made from the terpene compound and a phenolic compound; and these terpene resins that have been hydrogenated (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatically modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene-phenol resins include phenol, bisphenol A, cresol, and xylenol.

[0098] Rosin-based resins are not particularly limited, but examples include natural resin rosin and rosin-modified resins obtained by hydrogenation, disproportionation, dimerization, esterification, etc.

[0099] Phenolic resins are not particularly limited, but examples include phenol-formaldehyde resin, alkylphenol-formaldehyde resin, alkylphenol-acetylene resin, and oil-modified phenol-formaldehyde resin.

[0100] From the viewpoint of grip performance, the softening point of the resin component is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°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 component is measured by the measurement method described above.

[0101] When a resin component is included, the content of the resin component per 100 parts by mass of rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 25 parts by mass or more, from the viewpoint of grip performance. Furthermore, from the viewpoint of suppressing heat generation, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, and even more preferably 80 parts by mass or less.

[0102] (oil) Examples of oils include process oils, vegetable oils, and animal fats. Examples of process oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. Furthermore, for environmental reasons, process oils with a low content of polycyclic aromatic compounds (PCA) can be used. Examples of low-PCA process oils include light extraction solvates (MES), processed distillate aromatic extracts (TDAEs), and heavy naphthenic oils. Additionally, from a life cycle assessment perspective, refined waste oil from rubber mixers and engines, or waste cooking oil used in restaurants, may be used.

[0103] When oil is included, the content of the oil per 100 parts by mass of rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more, from the viewpoint of processability. Furthermore, from the viewpoint of wear resistance, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 70 parts by mass or less, and particularly preferably 50 parts by mass or less.

[0104] (Liquid rubber) 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.

[0105] From the viewpoint of grip performance, the content of the softening agent per 100 parts by mass of the rubber component (total amount if multiple softening agents are used in combination) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 25 parts by mass or more. From the viewpoint of processability, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, and particularly preferably 70 parts by mass or less.

[0106] <Other compounding agents> In addition to the components mentioned above, the rubber composition relating to this disclosure may appropriately contain compounding agents commonly used in the tire industry, such as waxes, processing aids, antioxidants, stearic acid, zinc oxide, vulcanizing agents, and vulcanization accelerators.

[0107] When wax is included, 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. Furthermore, from the viewpoint of preventing whitening of the tire due to bloom, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0108] 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 individually or in combination of two or more.

[0109] When an anti-aging agent is included, the 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 the rubber's resistance to ozone cracking. Furthermore, from the viewpoint of wear resistance and wet grip performance, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0110] When stearic acid is included, its content 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 processability. Furthermore, from the viewpoint of vulcanization rate, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0111] When zinc oxide is included, its content 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 processability. Furthermore, from the viewpoint of wear resistance, it is preferably 10 parts by mass or less, and more preferably 5.0 parts by mass or less.

[0112] 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.

[0113] When sulfur is included, the sulfur content per 100 parts by mass of 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, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and particularly preferably 2.5 parts by mass or less. When oil-containing sulfur is used as a crosslinking agent, the content of the vulcanizing agent shall be the total content of pure sulfur contained in the oil-containing sulfur.

[0114] As a vulcanizing agent other than sulfur, known organic crosslinking agents can also be used. When an organic crosslinking agent is incorporated, the distance between crosslinking points becomes longer compared to crosslinking with sulfur, allowing for greater energy loss and resulting in good peak grip performance.

[0115] The organic crosslinking agent is not particularly limited as long as it can form crosslinking chains other than polysulfide bonds, but examples include alkylphenol-sulfur chloride condensates, 1,6-hexamethylene-dithiosulfate sodium dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and dicumyl peroxide.

[0116] Examples of vulcanization accelerators include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiram-based vulcanization accelerators, guanidine-based vulcanization accelerators, dithiocarbamate-based vulcanization accelerators, and caprolactam disulfide. These vulcanization accelerators may be used individually or in combination of two or more. In particular, from the viewpoint of obtaining the desired effect more favorably, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred, and the combination of sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators is even more preferred.

[0117] 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, TBBS and CBS are preferred.

[0118] Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole (MBT) or its salts, di-2-benzothiazolyl disulfide (MBTS), 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole. Of these, MBTS and MBT are preferred, with MBTS being more preferred.

[0119] 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, DPG is preferred.

[0120] When a vulcanization accelerator is included, its content per 100 parts by mass of 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. Furthermore, the content of the vulcanization accelerator per 100 parts by mass of rubber component 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 the above range, it tends to be possible to ensure fracture strength and elongation.

[0121] <Manufacturing> The rubber composition relating to this disclosure can be manufactured by known methods. For example, it can be manufactured by kneading each of the above components using a rubber kneading device such as an open roll or a closed kneader (Banbury mixer, kneader, etc.).

[0122] The mixing process includes, for example, a base mixing process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are mixed, and a final mixing (F mixing) process in which the vulcanizing agent and vulcanization accelerator are added to the mixture obtained in the base mixing process and mixed. Furthermore, the base mixing process can be divided into multiple processes as desired.

[0123] There are no particular limitations on the mixing conditions, but for example, in the base mixing process, mixing is performed at a discharge temperature of 150-170°C for 3-10 minutes, and in the final mixing process, mixing is performed at 70-110°C for 1-5 minutes. There are no particular limitations on the vulcanization conditions, but for example, vulcanization is performed at 150-200°C for 10-30 minutes.

[0124] A tire of the present disclosure, having a tread made of the aforementioned rubber composition, can be manufactured by conventional methods. That is, an unvulcanized rubber composition, in which the above components are blended with the rubber component as needed, is extruded to match the shape of each rubber layer constituting the tread, bonded together with other tire components on a tire molding machine, and molded in a conventional method to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizing machine to manufacture the tire. The vulcanization conditions are not particularly limited, and for example, a method of vulcanization at 150 to 200°C for 10 to 30 minutes can be cited.

[0125] <Application> The tires disclosed herein can be used as general-purpose tires for passenger cars, trucks and buses, motorcycles, etc., or as racing tires. Passenger car tires refer to tires intended for use on four-wheeled vehicles with a maximum load capacity of 1000 kg or less. Furthermore, the tires disclosed herein can be used as all-season tires, summer tires, and winter tires such as studless tires. [Examples]

[0126] The following examples (implementations) are considered preferable for implementation, but the scope of this disclosure is not limited to these examples.

[0127] Table 2 shows the results calculated based on the evaluation method below, assuming a tire having a tread made of a rubber composition obtained according to Table 1 using the various chemicals listed below.

[0128] The various chemicals used in the examples and comparative examples are summarized below. NR:TSR20 SBR: SBR1502 manufactured by JSR Corporation (unmodified E-SBR, styrene content: 23.5% by mass, Tg: -56℃, Mw: 440,000, non-oil-based) Hydrogenated SBR: Hydrogenated SBR produced in Production Example 1 described below (hydrogenation rate: 80%, styrene content: 30% by mass, Tg: -30℃, Mw: 480,000) BR: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (unmodified BR, cis content: 97 mol%, Mw: 440,000) Carbon Black: Dia Black N220 (N2SA: 114m) manufactured by Mitsubishi Chemical Corporation. 2 / g) Silica: Evonik Degussa's UltraSil VN3 (N2SA: 175m 2 / g, average primary particle diameter: 15nm) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa. Resin component 1: T-REZ PR801 (hydrogenated DCPD / C9 resin, softening point: 91℃) manufactured by ENEOS Corporation. Resin component 2: Sylvares SA85 manufactured by Kraton (a copolymer of α-methylstyrene and styrene, softening point: 85°C) Liquid rubber: RICON100 (liquid SBR) manufactured by Clay Valley Corporation. Oil: VivaTec500 (TDAE oil) manufactured by H&R Co., Ltd. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads of stearic acid manufactured by NOF Corporation Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Noxellar CZ-G (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0129] Manufacturing Example 1: Production of Hydrogenated SBR In a thoroughly nitrogen-purged heat-resistant reaction vessel, 2000 ml of n-hexane, 60 g of styrene, 140 g of 1,3-butadiene, 0.93 g of TMEDA, and 0.45 mmol of n-butyllithium were added, and the mixture was stirred at 50°C for 5 hours to carry out the polymerization reaction. Next, hydrogen gas was supplied at a pressure of 0.4 MPa-Gauge while stirring for 20 minutes to react with the unreacted lithium at the polymer ends to form lithium hydride. The hydrogen gas supply pressure was set to 0.7 MPa-Gauge and the reaction temperature to 90°C, and hydrogenation was carried out using a catalyst mainly composed of titanocene dichloride. When the hydrogen absorption reached the cumulative amount that would result in the desired hydrogenation rate, the reaction temperature was reduced to room temperature, the hydrogen pressure was returned to atmospheric pressure, and the mixture was withdrawn from the reaction vessel. The reaction solution was then stirred into water and the solvent was removed by steam stripping to obtain hydrogenated SBR.

[0130] (Examples and Comparative Examples) According to the formulation shown in Table 1, the chemicals other than sulfur and vulcanization accelerator were mixed in a 1.7 L closed Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C to obtain a mixture. Next, using a twin-screw open roll mixer, sulfur and vulcanization accelerator were added to the obtained mixture and mixed for 4 minutes until the temperature reached 105°C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was extruded using an extruder equipped with a die of a predetermined shape to form a composite of the inner tread rubber layer and the outer tread rubber layer (both 7.5 mm thick) to form an outer tread layer and inner tread layer. This composite was then bonded together with the base (thickness: 1.5 mm) and other tire components to produce an unvulcanized tire, which was then press-vulcanized for 12 minutes under conditions of 170°C to produce each test tire.

[0131] <Performance in maintaining ride comfort after wear> Each test tire, both new and worn, was mounted on the four wheels of a 2000cc front-wheel-drive passenger car, and the vehicle was driven on a dry asphalt test course. Ride comfort performance was evaluated based on the feeling of straight driving, lane changes, and acceleration / deceleration while driving at 120 km / h by test drivers. The evaluation was given as an integer value from 1 to 10, with higher scores indicating better ride comfort performance. The total scores of 20 test drivers were calculated. For each test tire, the maintenance index of the ride comfort performance score before and after wear was calculated using the following formula, and the maintenance index of Comparative Example 7 was set to 100 to represent the ride comfort maintenance performance after wear for each test tire. A higher value indicates less change in ride comfort performance before and after wear, and that the ride comfort performance of the new tire has been maintained, indicating good performance. (Ride comfort performance maintenance index of the target tire) = (Ride comfort performance rating of the target tire after wear) / (Ride comfort performance rating of the target tire when new) (Ride comfort performance maintenance index for each test tire) = (Ride comfort performance score of each test tire after wear) / (Ride comfort performance score of each test tire when new) (Ride comfort maintenance performance of each test tire) = (Ride comfort maintenance index of each test tire) / (Ride comfort maintenance index of the target tire) × 100

[0132] Each test tire after wear is prepared by first wearing down the tread so that the depth of the deepest main groove of a new tire is 50% of that of a new tire, and then thermally degrading the tire at 80°C for 7 days.

[0133] [Table 1]

[0134] [Table 2]

[0135] <Embodiment> Examples of embodiments of this disclosure are shown below.

[0136] [1] A tire having a tread portion for which the mounting direction to a vehicle is specified, wherein the tread portion comprises an inner tread rubber layer that constitutes the inner end side of the vehicle when mounted on the vehicle, and an outer tread rubber layer that constitutes the outer end side of the vehicle, wherein the inner tread rubber layer and the outer tread rubber layer are composed of a rubber composition containing rubber components, wherein the rubber component constituting the inner tread rubber layer includes a copolymer in which an aromatic vinyl compound and a conjugated diene compound are copolymerized, and a portion of the conjugated diene portion is hydrogenated, and the silica content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer. [2] The tire according to [1] above, wherein the rubber composition constituting the inner tread rubber layer contains 90 parts by mass or more of silica per 100 parts by mass of rubber components. [3] The tire according to [1] or [2] above, wherein the rubber composition constituting the inner tread rubber layer contains hydrogenated petroleum resin. [4] The tire according to any one of [1] to [3] above, wherein the rubber component constituting the inner tread rubber layer contains 50% by mass or more of hydrogenated styrene-butadiene rubber with a hydrogenation rate of 50 mol% or more. [5] The tire according to any one of [1] to [4] above, wherein the content of butadiene rubber in the rubber component constituting the inner tread rubber layer is 15% by mass or less. [6] Distance W between the grounding ends on both sides L The ratio of D (D / W) from the vehicle's inner contact edge to the interface between the inner and outer tread rubber layers. L A tire as described in any of the above [1] to [5], having a value of 0.50 or higher. [7] A tire according to any one of [1] to [6] above, wherein the ratio of groove area of ​​the contact surface of the inner tread rubber layer is greater than the ratio of groove area of ​​the contact surface of the outer tread rubber layer. [8] A tire according to any of [1] to [7] above, wherein the difference between the groove area ratio of the contact surface of the inner tread rubber layer and the groove area ratio of the contact surface of the outer tread rubber layer is 2% or more and 10% or less. [9] The tire according to any one of [1] to [8] above, wherein the tread portion has a land portion separated by two or more circumferential grooves that extend continuously in the circumferential direction of the tire, and the widthwise length of the tread surface of the land portion closest to the tire equator is 18% or more of the contact width. [Explanation of Symbols]

[0137] 1. Bead section 1a. Bead core 1b... Bead filler 2. Sidewall section 3. Tread section 4. Carcass layer 4a...Inner liner rubber 4b...belt 4c... Belt reinforcement layer 5... land department 5a...Circumferential groove 6. Sidewall rubber 7. Rim strip rubber 50... Cap part 51...Base section 53 ...Inner tread rubber layer 52...Outer tread rubber layer

Claims

1. A tire having a tread portion in which the mounting direction to the vehicle is specified, The tread portion has an inner tread rubber layer that forms the inner end side of the vehicle when mounted on the vehicle, and an outer tread rubber layer that forms the outer end side of the vehicle. The inner tread rubber layer and the outer tread rubber layer divide the tread portion into inner and outer sections in the tire width direction. The inner tread rubber layer and the outer tread rubber layer are composed of a rubber composition containing rubber components. The rubber component constituting the inner tread rubber layer includes a copolymer in which an aromatic vinyl compound and a conjugated diene compound are copolymerized, and a portion of the conjugated diene portion is hydrogenated. A tire in which the silica content per 100 parts by mass of rubber components in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber components in the rubber composition constituting the outer tread rubber layer.

2. A tire having a tread portion in which the mounting direction to the vehicle is specified, The tread portion has an inner tread rubber layer that forms the inner end side of the vehicle when mounted on the vehicle, and an outer tread rubber layer that forms the outer end side of the vehicle. The inner tread rubber layer and the outer tread rubber layer are composed of a rubber composition containing rubber components. The rubber component constituting the inner tread rubber layer includes a copolymer in which an aromatic vinyl compound and a conjugated diene compound are copolymerized, and a portion of the conjugated diene portion is hydrogenated. The silica content per 100 parts by mass of rubber component in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber component in the rubber composition constituting the outer tread rubber layer. A tire in which the difference between the groove area ratio of the contact surface of the inner tread rubber layer and the groove area ratio of the contact surface of the outer tread rubber layer is 2% or more and 10% or less.

3. A tire having a tread portion in which the mounting direction to the vehicle is specified, The tread portion has an inner tread rubber layer that forms the inner end side of the vehicle when mounted on the vehicle, and an outer tread rubber layer that forms the outer end side of the vehicle. The inner tread rubber layer and the outer tread rubber layer are composed of a rubber composition containing rubber components. The rubber component constituting the inner tread rubber layer includes a copolymer in which an aromatic vinyl compound and a conjugated diene compound are copolymerized, and a portion of the conjugated diene portion is hydrogenated. The silica content per 100 parts by mass of rubber component in the rubber composition constituting the inner tread rubber layer is greater than the silica content per 100 parts by mass of rubber component in the rubber composition constituting the outer tread rubber layer. A tire in which the tread portion has a land portion separated by two or more circumferential grooves that extend continuously in the circumferential direction of the tire, and the widthwise length of the tread surface of the land portion closest to the tire equator is 18% or more of the contact width.

4. The tire according to any one of claims 1 to 3, wherein the rubber composition constituting the inner tread rubber layer contains 90 parts by mass or more of silica per 100 parts by mass of rubber components.

5. The tire according to any one of claims 1 to 4, wherein the rubber composition constituting the inner tread rubber layer contains a hydrogenated petroleum resin.

6. The tire according to any one of claims 1 to 5, wherein the rubber component constituting the inner tread rubber layer contains 50% by mass or more of hydrogenated styrene-butadiene rubber with a hydrogenation rate of 50 mol% or more.

7. The tire according to any one of claims 1 to 6, wherein the butadiene rubber content in the rubber component constituting the inner tread rubber layer is 15% by mass or less.

8. Distance W between the grounding ends on both sides L The ratio of D (D / W) from the vehicle's inner contact edge to the interface between the inner and outer tread rubber layers. L A tire according to any one of claims 1 to 7, wherein the coefficient of force () is 0.50 or greater.

9. The tire according to any one of claims 1 to 8, wherein the difference between the groove area ratio of the contact surface of the inner tread rubber layer and the groove area ratio of the contact surface of the outer tread rubber layer is 3% or more and 9% or less.

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