tire

Abstract

The present invention addresses the problem of providing a tire in which wet grip performance, low fuel consumption performance, and wear resistance performance are enhanced without degrading cut resistance, and which inhibits discoloration of the outer appearance. The solution is a tire (1) provided with a tread rubber layer (8) and belt layers (6A, 6B) positioned at the inner side in the radial direction of the tire. The tread rubber layer (8) comprises a rubber composite containing a specific modified SBR, an unmodified SBR, silica, a silane coupling agent (A) having a thiol group, and a silane coupling agent (B) having a sulfide bond. The contained amount of the silane coupling agent (A) and the total contained amount of the silane coupling agent (A) and the silane coupling agent (B) are within specific ranges. The belt layers (6A, 6B) include cords obtained by twisting together filaments which, when the diameter of the filaments is defined as X (mm) and the tensile strength is defined as Y (MPa), satisfy 4000-2000X≤Y≤4500-2000X.

Description

tire

[0001] The present invention relates to a tire.

[0002] Conventionally, from the viewpoint of improving vehicle safety, various studies have been conducted to improve braking performance on wet road surfaces (hereinafter abbreviated as "wet grip performance"). For example, Patent Document 1 listed below discloses that tire braking performance on both dry and wet road surfaces is improved by applying a rubber composition to tire tread rubber, the rubber composition being obtained by blending a rubber component containing 70% by mass or more of natural rubber with a thermoplastic resin and a filler containing silica.

[0003] On the other hand, in connection with the recent trend toward global carbon dioxide emission regulations accompanying growing interest in environmental issues, there is an increasing demand for improved fuel efficiency in automobiles. In order to meet such demands, tire performance is also required to be improved in terms of fuel efficiency (reduction of rolling resistance). Furthermore, from the viewpoint of tire economics, in the development of rubber compositions for tires, it is required to improve not only wet grip performance and fuel efficiency but also wear resistance.

[0004] In response to this, Patent Document 2 listed below discloses a rubber composition containing an emulsion-polymerized styrene-butadiene rubber and a solution-polymerized styrene-butadiene rubber, both of which have glass transition temperatures Tg of −25° C. or higher, and a polymer with a low Tg, with the aim of achieving both wet grip performance and low fuel consumption performance of a tire.

[0005] International Publication No. WO 2015 / 079703 International Publication No. WO 2017 / 188139

[0006] However, the inventors of the present invention have found that while the technology described in Patent Document 1 can improve the wet grip performance of tires, the addition of a resin (thermoplastic resin) as a softening component reduces the rigidity of the rubber, which in turn reduces the plunger level of the tire and can result in insufficient cut resistance. Furthermore, when an attempt is made to improve the cut resistance of a tire, the amount of resin (softening component) that can be added is limited, which can result in insufficient wet grip performance.

[0007] Furthermore, although the technology described in Patent Document 2 makes it possible to achieve both wet grip performance and fuel economy of a tire to some extent, further improvement in wet grip performance and fuel economy is required. In response to this, the present inventors conducted research and found that wet grip performance and fuel economy can be improved by compounding a silane coupling agent having a thiol group, but there was a problem in that rubber compositions containing a silane coupling agent having a thiol group are prone to discoloration of appearance, such as the generation of a black luster, over time.

[0008] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology, and to provide a tire that has improved wet grip performance, fuel efficiency, and wear resistance without deteriorating cut resistance, and furthermore, that is suppressed from discoloring its appearance.

[0009] The gist of the tire of the present invention that solves the above problems is as follows.

[0010] [1] A tire comprising a tread rubber layer located on the outermost surface of a tread portion, and a belt layer located radially inward of the tread rubber layer, wherein the tread rubber layer is made of a rubber composition including a rubber component, a filler, and a silane coupling agent, wherein the rubber component contains styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of −50° C. or less, and unmodified styrene-butadiene rubber (B) having a glass transition temperature 30° C. or higher than that of the styrene-butadiene rubber (A), wherein the filler contains at least silica, and the silane coupling agent contains at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, and the content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica, a tire characterized in that the total content of the silane coupling agent (A) and the silane coupling agent (B) is more than 1 part by mass and not more than 15 parts by mass per 100 parts by mass of the silica, the belt layer includes a cord having a structure formed by twisting filaments, and the filaments constituting the cord of the belt layer satisfy the following formula: 4000-2000X≦Y≦4500-2000X, where X (mm) is the diameter of the filament and Y (MPa) is the tensile strength of the filament.

[0011] [2] The tire according to [1], wherein the styrene-butadiene rubber (A) is modified with a modifier having a nitrogen atom and a silicon atom.

[0012] [3] The tire according to [1] or [2], wherein the styrene-butadiene rubber (A) is modified with a modifier having a functional group containing a nitrogen atom and an alkoxy group.

[0013] [4] The tire according to any one of [1] to [3], wherein the mass ratio (B / A) of the content of the silane coupling agent (B) to the content of the silane coupling agent (A) is 0.3 or more and less than 3.

[0014] [5] The tire according to any one of [1] to [4], wherein the filler further contains carbon black, and the content ratio of the silica in the total amount of the silica and the carbon black is 80 mass % or more and less than 100 mass %.

[0015] [6] The tire according to any one of [1] to [5], wherein the content of the silica is 20 parts by mass or more and less than 100 parts by mass per 100 parts by mass of the rubber component.

[0016] [7] The tire according to any one of [1] to [6], wherein the silane coupling agent (A) has a carbon number of 20 to 75.

[0017] [8] The tire according to any one of [1] to [7], wherein the rubber component contains 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (A).

[0018] [9] The tire according to any one of [1] to [8], wherein the rubber component contains 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (B).

[0019]

[10] The tire according to any one of [1] to [9], wherein the rubber composition constituting the tread rubber layer further contains a resin, and the content of the resin is 1 to 50 parts by mass per 100 parts by mass of the rubber component.

[0020]

[11] The tire according to

[10] , wherein the resin is a hydrogenated resin.

[0021]

[12] The tire according to any one of [1] to

[11] , wherein the cord of the belt layer has a 1×N structure (where N is an integer selected from 2 to 6) formed by twisting together N filaments.

[0022]

[13] The tire according to any one of [1] to

[12] , wherein the end density of the cords in the belt layer is 60 cords / dm or more and 95 cords / dm or less.

[0023]

[14] The tire according to any one of [1] to

[13] , wherein the diameter of the cords of the belt layer is 0.5 mm or more and 1.0 mm or less.

[0024] According to the present invention, it is possible to provide a tire that has improved wet grip performance, fuel economy, and wear resistance without deteriorating cut resistance, and furthermore, that is suppressed from discoloring its appearance.

[0025] 1 is a cross-sectional view of one embodiment of a tire of the present invention.

[0026] The tire of the present invention will be described in detail below by way of example based on an embodiment thereof.

[0027] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0028] In this specification, the glass transition temperature of styrene-butadiene rubber is determined in accordance with ISO 22768:2006 by recording a DSC curve while raising the temperature within a predetermined temperature range, and the peak top (inflection point) of the DSC differential curve is taken as the glass transition temperature.

[0029] In this specification, the softening point of a resin is measured in accordance with JIS-K2207-1996 (ring and ball method).

[0030] In this specification, the weight average molecular weight of a resin is measured by gel permeation chromatography (GPC) and calculated as a polystyrene equivalent value.

[0031] <Tire> Figure 1 is a cross-sectional view of one embodiment of a tire of the present invention. The tire 1 shown in Figure 1 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 4 continuous with both sidewall portions 3, and is equipped with a carcass 5 extending in a toroidal shape between the pair of bead portions 2 to reinforce these portions 2, 3, 4, and a belt 6 disposed on the radially outer side of a crown portion of the carcass 5.

[0032] The carcass 5 of the tire shown in FIG. 1 is composed of one carcass ply made of a plurality of parallel-arranged cords covered with a coating rubber, and the carcass 5 is composed of a main body portion extending in a toroidal shape between the bead cores 7 respectively embedded in the bead portions 2, and turned-up portions wound up radially outward around each bead core 7 from the inner side toward the outer side in the tire width direction, but the number of plies and structure of the carcass 5 in the tire of the present invention are not limited to this.

[0033] 1 is composed of two belt layers 6A and 6B, but in the tire of the present invention, the number of belt layers constituting the belt 6 is not limited to this and the number of belt layers may be three or more. Here, the belt layer is usually composed of a rubberized layer of metal cords (preferably steel cords) extending at an angle with respect to the tire equatorial plane, and the two belt layers are laminated to constitute the belt 6 such that the metal cords constituting the belt layers cross each other with the tire equatorial plane in between.

[0034] The tire 1 of this embodiment comprises a tread rubber layer 8 located on the outermost surface of a tread portion 4, and belt layers 6A, 6B located radially inward of the tread rubber layer 8, wherein the tread rubber layer 8 is made of a rubber composition including a rubber component, a filler, and a silane coupling agent, wherein the rubber component contains styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of −50° C. or less, and unmodified styrene-butadiene rubber (B) having a glass transition temperature 30° C. or higher than that of the styrene-butadiene rubber (A), wherein the filler contains at least silica, and wherein the silane coupling agent contains at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, and wherein the content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica, The total content of the silane coupling agent (A) and the silane coupling agent (B) is more than 1 part by mass and not more than 15 parts by mass per 100 parts by mass of the silica, the belt layers (6A, 6B) include cords having a structure formed by twisting filaments, and the filaments constituting the cords of the belt layers (6A, 6B) satisfy the following formula: 4000-2000X≦Y≦4500-2000X, where X (mm) is the diameter of the filament and Y (MPa) is the tensile strength of the filament.

[0035] The tire of the present invention may be modified in various ways as long as it includes a tread rubber layer located on the outermost surface of the tread portion and a belt layer located radially inward of the tread rubber layer. For example, it is possible to dispose a belt reinforcing layer on the outer side of the belt 6 of the tire 1 shown in Figure 1 in the tire radial direction, or to divide the tread rubber layer 8 into a cap rubber located on the outermost surface side and a base rubber located radially inward of the cap rubber.

[0036] The tire 1 of this embodiment has a tread rubber layer 8 made of a rubber composition containing a rubber component containing the specific modified styrene-butadiene rubber (A) and unmodified styrene-butadiene rubber (B), a filler containing silica, and a silane coupling agent, thereby improving wet grip performance, fuel economy, and wear resistance. Although the thiol group-containing silane coupling agent (A) is highly effective in increasing the dispersibility of silica, a high content may cause discoloration of the tire's appearance over time. In contrast, the tread rubber layer 8 of the tire 1 of this embodiment uses a thiol group-containing silane coupling agent (A) in combination with a sulfide bond-containing silane coupling agent (B). The content of the silane coupling agent (A) is 10 parts by mass or less per 100 parts by mass of silica, while the total content of the silane coupling agent (A) and the silane coupling agent (B) is 15 parts by mass or less per 100 parts by mass of silica, thereby suppressing discoloration of the appearance. However, if the rubber composition is applied to the tread rubber layer 8, the rigidity of the tread rubber layer 8 decreases, which may reduce the plunger level of the tire 1 and result in insufficient cut resistance. In contrast, in the tire 1 of the present embodiment, the belt layers 6A, 6B use cords having a structure formed by twisting filaments, where the filaments constituting the cord satisfy the following formula: 4000-2000X≦Y≦4500-2000X, where X (mm) is the diameter of the filament and Y (MPa) is the tensile strength of the filament. This improves the strength of the belt layers 6A, 6B, improves the plunger level, and compensates for the cut resistance of the tire 1. Therefore, the tire 1 of the present embodiment has improved wet grip performance, fuel efficiency, and abrasion resistance without deteriorating cut resistance, and furthermore, discoloration of the appearance is suppressed.

[0037] <<Tread Rubber Layer>> In the tire of this embodiment, the tread rubber layer is made of a rubber composition containing a rubber component, a filler, and a silane coupling agent. Hereinafter, each component constituting the rubber composition used in the tread rubber layer will be described.

[0038] (Rubber Component) The rubber component contains a styrene-butadiene rubber (A) (modified SBR) that has been modified with a modifier containing at least one atom of nitrogen, silicon, and tin and has a glass transition temperature of −50° C. or lower, and an unmodified styrene-butadiene rubber (B) (unmodified SBR) that has a glass transition temperature that is 30° C. or higher than that of the styrene-butadiene rubber (A).

[0039] By including the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B) in the rubber component, the wet grip performance of the tire can be improved. In addition, in this embodiment, by using the styrene-butadiene rubber (A) modified with a modifier containing at least one atom of nitrogen, silicon, and tin as the rubber component, the dispersibility of fillers such as silica in the rubber composition can be improved. As a result, the tire of this embodiment has significantly improved low heat buildup and improved filler dispersibility, which enables improvements in performance such as reinforcement, fuel economy, and wear resistance.

[0040] As described above, the styrene-butadiene rubber (A) is a styrene-butadiene rubber modified with a modifier having at least one atom of nitrogen, silicon, and tin, and having a glass transition temperature of −50° C. or lower.

[0041] The styrene-butadiene rubber (A) has a glass transition temperature of −50° C. or lower, preferably −55° C. or lower, and preferably higher than −90° C. When the styrene-butadiene rubber (A) has a glass transition temperature of −50° C. or lower, the fuel economy and wear resistance of the tire can be sufficiently improved. In addition, styrene-butadiene rubber having a glass transition temperature higher than −90° C. is easy to synthesize.

[0042] The glass transition temperatures of the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B) described below can be measured, for example, as follows: Using each styrene-butadiene rubber as a sample, a DSC curve is recorded using a DSC250 manufactured by TA Instruments, while increasing the temperature from −100° C. at a rate of 20° C. / min under a helium flow of 50 mL / min, and the peak top (inflection point) of the DSC differential curve is taken as the glass transition temperature.

[0043] The content of the styrene-butadiene rubber (A) in the rubber component is preferably 15% by mass or more and less than 85% by mass, more preferably 20 to 85% by mass, more preferably 30 to 80% by mass, and even more preferably 40 to 80% by mass. When the content of the styrene-butadiene rubber (A) in the rubber component is 15% by mass or more and less than 85% by mass, the fuel economy and wet grip performance of the tire can be further improved.

[0044] Furthermore, the styrene-butadiene rubber (A) preferably has a bound styrene content of less than 15% by mass. The bound styrene content of the styrene-butadiene rubber (A) refers to the proportion of styrene units contained in the styrene-butadiene rubber. If the bound styrene content is less than 15% by mass, the glass transition temperature is likely to be low. From the same viewpoint, the bound styrene content is more preferably 14% by mass or less, more preferably 13% by mass or less, and even more preferably 12% by mass or less. From the viewpoint of tire wear resistance, the bound styrene content is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. The bound styrene content of the styrene-butadiene rubber (A) can be adjusted by the amount of monomers used in polymerization of the styrene-butadiene rubber, the degree of polymerization, etc.

[0045] As described above, the styrene-butadiene rubber (A) is modified with a modifier having at least one atom of nitrogen, silicon, and tin. From the viewpoint of achieving a higher level of fuel economy, wear resistance, and wet grip performance of the tire, it is preferable that the rubber be modified with a modifier having a nitrogen atom and a silicon atom, and it is more preferable that the rubber be modified with a modifier having a functional group containing a nitrogen atom and an alkoxy group. When the styrene-butadiene rubber (A) is modified with a modifier having a nitrogen atom and a silicon atom, the balance between the tire's wet grip performance, fuel economy, and wear resistance is further improved, and in particular, the fuel economy and wear resistance can be further improved. When the styrene-butadiene rubber (A) is modified with a modifier having a functional group containing a nitrogen atom and an alkoxy group, the balance between the tire's wet grip performance, fuel economy, and wear resistance is further improved, and in particular, the fuel economy and wear resistance can be further improved.

[0046] Here, the "modifier having a nitrogen atom-containing functional group and an alkoxy group" is a general term for modifiers having at least one nitrogen atom-containing functional group and at least one alkoxy group. The nitrogen atom-containing functional group is preferably selected from the following: The monovalent hydrocarbon group having 1 to 30 carbon atoms and containing a linear, branched, alicyclic, or aromatic ring, has a functional group selected from the group consisting of a primary amino group, a primary amino group protected with a hydrolyzable protecting group, an onium salt residue of a primary amine, an isocyanate group, a thioisocyanate group, an imine group, an imine residue, an amide group, a secondary amino group protected with a hydrolyzable protecting group, a cyclic secondary amino group, an onium salt residue of a cyclic secondary amine, an acyclic secondary amino group, an onium salt residue of an acyclic secondary amine, an isocyanuric acid triester residue, a cyclic tertiary amino group, an acyclic tertiary amino group, a nitrile group, a pyridine residue, an onium salt residue of a cyclic tertiary amine, and an onium salt residue of an acyclic tertiary amine, or a monovalent hydrocarbon group having 1 to 30 carbon atoms and containing a linear, branched, alicyclic, or aromatic ring, which may contain at least one heteroatom selected from an oxygen atom, a sulfur atom, and a phosphorus atom.

[0047] Furthermore, the styrene-butadiene rubber (A) is preferably modified with an aminoalkoxysilane compound, and from the viewpoint of having a high affinity for fillers such as silica, it is more preferable that the terminals are modified with an aminoalkoxysilane compound. When the terminals of the styrene-butadiene rubber are modified with an aminoalkoxysilane compound, the interaction between the styrene-butadiene rubber (A) and the filler (particularly silica) becomes particularly strong.

[0048] The modified site of the styrene-butadiene rubber (A) may be the molecular terminal as described above, or may be the main chain. The styrene-butadiene rubber (A) having a modified molecular terminal can be produced, for example, by reacting various modifiers with the terminal of a styrene-butadiene copolymer having an active terminal, according to the methods described in WO 2003 / 046020 and JP 2007-217562 A. In one preferred embodiment, the styrene-butadiene rubber (A) having a modified molecular terminal can be produced, according to the methods described in WO 2003 / 046020 and JP 2007-217562 A, by reacting an aminoalkoxysilane compound with the terminal of a styrene-butadiene copolymer having an active terminal with a cis-1,4 bond content of 75% or more, and then reacting the resulting mixture with a carboxylic acid partial ester of a polyhydric alcohol for stabilization.

[0049] The carboxylic acid partial ester of a polyhydric alcohol refers to an ester of a polyhydric alcohol and a carboxylic acid, which has one or more hydroxyl groups. Specifically, esters of fatty acids with sugars or modified sugars having 4 or more carbon atoms are preferably used. More preferred examples of this ester include (1) fatty acid partial esters of polyhydric alcohols, particularly partial esters (monoesters, diesters, or triesters) of saturated or unsaturated higher fatty acids having 10 to 20 carbon atoms with polyhydric alcohols, and (2) ester compounds in which 1 to 3 partial esters of polycarboxylic acids and higher alcohols are bonded to a polyhydric alcohol. Polyhydric alcohols used as raw materials for the partial esters are preferably sugars (whether hydrogenated or unhydrogenated) having 5 or 6 carbon atoms and at least three hydroxyl groups, glycols, polyhydroxy compounds, and the like. Furthermore, the raw fatty acids are preferably saturated or unsaturated fatty acids having 10 to 20 carbon atoms, such as stearic acid, lauric acid, and palmitic acid. Among the fatty acid partial esters of polyhydric alcohols, sorbitan fatty acid esters are preferred, and specific examples include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate.

[0050] The aminoalkoxysilane compound is not particularly limited, but is preferably an aminoalkoxysilane compound represented by the following general formula (i): １１ ａ -Si-(OR １２ ) ４－ａ ... (i)

[0051] In general formula (i), R １１ and R １２ each independently represents a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms; R １１ and R １２ At least one of the groups is substituted with an amino group, a is an integer of 0 to 2, and OR １２If there are multiple, each OR １２ may be the same or different, and the molecule does not contain any active protons.

[0052] The aminoalkoxysilane compound is also preferably an aminoalkoxysilane compound represented by the following general formula (ii):

[0053] In the general formula (ii), n1+n2+n3+n4=4 (wherein n2 is an integer of 1 to 4, and n1, n3, and n4 are integers of 0 to 3). １ is at least one functional group selected from a saturated cyclic tertiary amine compound residue, an unsaturated cyclic tertiary amine compound residue, a ketimine residue, a nitrile group, a (thio)isocyanate group, an isocyanuric acid trihydrocarbyl ester group, a nitrile group, a pyridine group, a (thio)ketone group, an amide group, and a primary or secondary amino group having a hydrolyzable group. １ may be the same or different, and A １ may be a divalent group that bonds with Si to form a cyclic structure. ２１ represents a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when n1 is 2 or more, they may be the same or different. ２２ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, both of which may contain a nitrogen atom and / or a silicon atom. ２２ may be the same or different, or may be joined together to form a ring. ２３ represents a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom, and when n3 is 2 or greater, may be the same or different. ２４represents a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and may be the same or different when n4 is 2 or greater. As the hydrolyzable group in the primary or secondary amino group having a hydrolyzable group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

[0054] The aminoalkoxysilane compound represented by the above general formula (ii) is preferably an aminoalkoxysilane compound represented by the following general formula (iii).

[0055] In the general formula (iii), p1+p2+p3=2 (wherein p2 is an integer of 1 to 2, and p1 and p3 are integers of 0 to 1). ２ is NRa (Ra is a monovalent hydrocarbon group, a hydrolyzable group, or a nitrogen-containing organic group). ２５ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ２６ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a nitrogen-containing organic group, any of which may contain a nitrogen atom and / or a silicon atom. ２６ may be the same or different, or may be joined together to form a ring. ２７ R is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom. ２８ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. As the hydrolyzable group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

[0056] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (iv) or (v).

[0057] In the general formula (iv), q1+q2=3 (wherein q1 is an integer of 0 to 2, and q2 is an integer of 1 to 3). ３１ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３２ and R ３３ are each independently a hydrolyzable group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３４ are monovalent aliphatic or alicyclic hydrocarbon groups having 1 to 20 carbon atoms or monovalent aromatic hydrocarbon groups having 6 to 18 carbon atoms, and when q1 is 2, they may be the same or different. ３５ represents a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when q2 is 2 or more, may be the same or different.

[0058]

[0059] In the general formula (v), r1+r2=3 (where r1 is an integer of 1 to 3, and r2 is an integer of 0 to 2). ３６ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３７ represents a dimethylaminomethyl group, a dimethylaminoethyl group, a diethylaminomethyl group, a diethylaminoethyl group, a methylsilyl(methyl)aminomethyl group, a methylsilyl(methyl)aminoethyl group, a methylsilyl(ethyl)aminomethyl group, a methylsilyl(ethyl)aminoethyl group, a dimethylsilylaminomethyl group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and when r1 is 2 or more, they may be the same or different. R ３８represents a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and may be the same or different when r2 is 2. A specific example of the aminoalkoxysilane compound represented by general formula (v) is N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propanamine.

[0060] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (vi) or (vii):

[0061] In general formula (vi), R ４０ is a trimethylsilyl group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４１ R is a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４２ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, where TMS represents a trimethylsilyl group (the same applies hereinafter).

[0062]

[0063] In general formula (vii), R ４３ and R ４４ are each independently a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４５ is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, and each R ４５ may be the same or different.

[0064] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (viii) or the following general formula (ix).

[0065] In general formula (viii), s1+s2 is 3 (wherein s1 is an integer of 0 to 2, and s2 is an integer of 1 to 3). ４６ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４７ and R ４８ are each independently a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４７ or R ４８ may be the same or different.

[0066]

[0067] In general formula (ix), X is a halogen atom. ４９ is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ５０ and R ５１ are each independently a hydrolyzable group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or R ５０ and R ５１ are bonded to form a divalent organic group. ５２ and R ５３ are each independently a halogen atom, a hydrocarbyloxy group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ５０ and R ５１ As the hydrolyzable group, a hydrolyzable group is preferred, and as the hydrolyzable group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

[0068] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (x), the following general formula (xi), the following general formula (xii), or the following general formula (xiii).

[0069] In the general formulas (x) to (xiii), the symbols U and V are each an integer of 0 to 2 and satisfy U+V=2. ５４ ~ ９２ may be the same or different and are monovalent or divalent aliphatic or alicyclic hydrocarbon groups having 1 to 20 carbon atoms, or monovalent or divalent aromatic hydrocarbon groups having 6 to 18 carbon atoms. α and β in general formula (xiii) are integers of 0 to 5.

[0070] Among the compounds satisfying general formula (x), general formula (xi), and general formula (xii), N1,N1,N7,N7-tetramethyl-4-((trimethoxysilyl)methyl)heptane-1,7-diamine, 2-((hexyl-dimethoxysilyl)methyl)-N1,N1,N3,N3-2-pentamethylpropane-1,3-diamine, N1-(3-(dimethylamino)propyl)-N3,N3-dimethyl-N1-(3-(trimethoxysilyl)propyl)propane-1,3-diamine, and 4-(3-(dimethylamino)propyl)-N1,N1,N7,N7-tetramethyl-4-((trimethoxysilyl)methyl)heptane-1,7-diamine are particularly preferred. Among the compounds satisfying general formula (xiii), N,N-dimethyl-2-(3-(dimethoxymethylsilyl)propoxy)ethanamine, N,N-bis(trimethylsilyl)-2-(3-(trimethoxysilyl)propoxy)ethanamine, N,N-dimethyl-2-(3-(trimethoxysilyl)propoxy)ethanamine, and N,N-dimethyl-3-(3-(trimethoxysilyl)propoxy)propan-1-amine are particularly preferred.

[0071] The method for producing the styrene-butadiene rubber (A) is not particularly limited. In one embodiment, the method for producing the styrene-butadiene rubber (A) may include: 1) polymerizing styrene-butadiene rubber in a hydrocarbon solvent in the presence of an organic alkali metal compound to produce an activated polymer having an alkali metal bonded to at least one end thereof; and 2) reacting the activated polymer with a modifier such as the aminoalkoxysilane compound.

[0072] Step 1) is a step for preparing an activated polymer having an alkali metal bonded to at least one end thereof, and can be carried out by polymerizing a styrene-based monomer and a butadiene-based monomer in a hydrocarbon solvent in the presence of an organic alkali metal compound.

[0073] The hydrocarbon solvent is not particularly limited, but may be, for example, one or more selected from the group consisting of n-pentane, n-hexane, n-heptane, isooctane, cyclohexane, toluene, benzene, and xylene.

[0074] The organic alkali metal compound can be used in an amount of 0.1 mmol to 1.0 mmol based on 100 g of the total monomers. The organic alkali metal compound is not particularly limited, and examples thereof include at least one selected from the group consisting of methyl lithium, ethyl lithium, propyl lithium, n-butyl lithium, s-butyl lithium, t-butyl lithium, hexyl lithium, n-decyl lithium, t-octyl lithium, phenyl lithium, 1-naphthyl lithium, n-eicosyl lithium, 4-butylphenyl lithium, 4-tolyl lithium, cyclohexyl lithium, 3,5-di-n-heptylcyclohexyl lithium, 4-cyclopentyl lithium, naphthyl sodium, naphthyl potassium, lithium alkoxide, sodium alkoxide, potassium alkoxide, lithium sulfonate, sodium sulfonate, potassium sulfonate, lithium amide, sodium amide, potassium amide, and lithium isopropyl amide.

[0075] The polymerization in step 1 may be carried out by further adding a polar additive, if necessary. The polar additive may be added in an amount of 0.001 to 1.0 part by weight, based on 100 parts by weight of the total monomers. Specifically, the polar additive may be added in an amount of 0.005 to 0.5 parts by weight, more specifically, 0.01 to 0.3 parts by weight, based on 100 parts by weight of the total monomers. Examples of the polar additive include at least one selected from the group consisting of tetrahydrofuran, ditetrahydrofurylpropane, diethyl ether, cycloamethyl ether, dipropyl ether, ethylene dimethyl ether, ethylene dimethyl ether, diethyl glycol, dimethyl ether, tert-butoxyethoxyethane, bis(3-dimethylaminoethyl)ether, (dimethylaminoethyl)ethyl ether, trimethylamine, triethylamine, tripropylamine, and tetramethylethylenediamine.

[0076] In addition, in the above-mentioned preparation method, when a butadiene-based monomer and a styrene-based monomer are copolymerized by using the polar additive, the difference in reaction rate between them can be compensated for, thereby guiding the formation of a random copolymer easily.

[0077] The polymerization in step 1) can be carried out via adiabatic polymerization or isothermal polymerization. Here, the adiabatic polymerization refers to a polymerization method that involves polymerizing the organic alkali metal compound by heat of self-reaction without adding any heat after adding the organic alkali metal compound, while the isothermal polymerization refers to a polymerization method that maintains a constant temperature of the polymer by adding or removing heat after adding the organic alkali metal compound.

[0078] Furthermore, the polymerization may be carried out in a temperature range of 20°C to 200°C, specifically in a temperature range of 0°C to 150°C, more specifically in a temperature range of 10°C to 120°C.

[0079] The step 2) is a modification reaction step in which the activated polymer is reacted with a modifier such as the aminoalkoxysilane compound to produce styrene-butadiene rubber (A).

[0080] In this case, the modifying agent may be the same as that described above. The modifying agent may be used in a ratio of 0.1 to 2.0 moles per mole of the organic alkali metal compound. Furthermore, the reaction in step 2) is a modification reaction for introducing functional groups into the polymer, and each reaction may be carried out at a temperature ranging from 0°C to 90°C for 1 minute to 5 hours.

[0081]

[0033] The above-described preparation method may further include, after step 2), one or more steps of recovering the solvent and unreacted monomer and drying, if necessary.

[0082] Furthermore, the content ratio of the styrene-butadiene rubber (A) modified with a modifier such as the aminoalkoxysilane compound in the rubber component is not particularly limited, but is preferably 15% by mass or more, more preferably 20% by mass or more, preferably less than 85% by mass, more preferably 60% by mass or less, and even more preferably 50% by mass or less. When the content ratio of the styrene-butadiene rubber (A) in the rubber component is 15% by mass or more, the fuel economy and wear resistance of the tire can be further improved. On the other hand, when the content ratio of the styrene-butadiene rubber (A) in the rubber component is 60% by mass or less, the styrene-butadiene rubber (B) described below can be sufficiently contained, and the wet grip performance of the tire can be maintained well.

[0083] In addition to the styrene-butadiene rubber (A), the rubber component further contains unmodified styrene-butadiene rubber (B) having a glass transition temperature at least 30° C. higher than that of the styrene-butadiene rubber (A). By including the styrene-butadiene rubber (B) having a high glass transition temperature as the rubber component, the wet grip performance of the tire can be improved.

[0084] The glass transition temperature of the styrene-butadiene rubber (B) must be at least 30° C. higher than the glass transition temperature of the styrene-butadiene rubber (A), and is preferably at least 35° C. higher. By including the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B), the flexibility of the tread rubber layer can be increased, and the fuel economy and wear resistance of the tire can be sufficiently improved.

[0085] Furthermore, the content ratio of the styrene-butadiene rubber (B) in the rubber component is not particularly limited, but is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably less than 85% by mass, more preferably 80% by mass or less. When the content ratio of the styrene-butadiene rubber (B) in the rubber component is 15% by mass or more, the wet grip performance of the tire can be further improved. On the other hand, when the content ratio of the styrene-butadiene rubber (B) in the rubber component is less than 85% by mass, the fuel economy performance and wear resistance performance of the tire can be well maintained. Therefore, by having the rubber component contain the styrene-butadiene rubber (B) in an amount of 15% by mass or more but less than 85% by mass, the wet grip performance can be further improved while maintaining good fuel economy performance and wear resistance performance.

[0086] Furthermore, from the viewpoint of achieving wet grip performance, fuel economy, and wear resistance of the tire at a higher level, it is preferable that the content ratio of the styrene-butadiene rubber (B) is larger than the content ratio of the styrene-butadiene rubber (A) [content ratio of styrene-butadiene rubber (B) / content ratio of styrene-butadiene rubber (A)>1].

[0087] The rubber component may contain a rubber (other rubber) different from the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B) as a rubber component, for the purpose of improving the fuel economy and wear resistance of the tire. The other rubber can be appropriately selected depending on the required performance. For example, one or more of diene rubbers such as natural rubber (NR), butadiene rubber (BR), synthetic isoprene rubber (IR), and ethylene-propylene copolymer rubber, and non-diene rubbers such as butyl rubber, can be used. However, from the viewpoint of achieving a higher level of wet grip performance, fuel economy, and wear resistance of the tire, it is preferable that the rubber component consists of only the styrene-butadiene rubber (A) and the styrene-butadiene rubber (B).

[0088] (Filler) The rubber composition for the tread rubber layer contains, in addition to the rubber component described above, a filler containing at least silica. By using the filler together with the rubber component containing the styrene-butadiene rubber (A), the dispersibility of the filler is improved, and the fuel economy and wear resistance of the tire can be improved.

[0089] Here, the content of the filler is not particularly limited, but is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 150 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 120 parts by mass or less. By optimizing the amount of filler, wet grip performance, fuel economy, and wear resistance can be achieved at a higher level. When the content of filler is 20 parts by mass or more, sufficient wet grip performance, fuel economy, and wear resistance can be obtained, and when the content of filler is 150 parts by mass or less, deterioration of low heat generation performance and processability can be suppressed.

[0090] The silica contained in the filler is not particularly limited and can be appropriately selected depending on the required performance. For example, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. can be used as the silica, and among these, wet silica is preferred. These silicas may be used alone or in combination of two or more. Precipitated silica can also be used as the wet silica. Precipitated silica is silica obtained by reacting a reaction solution at a relatively high temperature in a neutral to alkaline pH range in the early stages of production to grow primary silica particles, and then adjusting the pH to the acidic side to cause the primary particles to aggregate.

[0091] From the viewpoint of reducing environmental impact, silica derived from siliceous plants is also preferred as the silica. Examples of siliceous plants include mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo, and sugarcane, with rice being preferred. Rice is widely cultivated for food and therefore can be procured locally over a wide area. Furthermore, rice husks are generated in large quantities as industrial waste, making it easy to secure a sufficient supply. Therefore, from the viewpoint of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. The use of rice husk silica allows for the effective use of rice husks, which are industrial waste, and also allows for the local procurement of raw materials near tire manufacturing plants, thereby reducing the energy and costs involved in transportation and storage, which is environmentally preferable from various viewpoints. The rice husk silica may be a powder of rice husk charcoal obtained by carbonizing rice husks by heating, or may be precipitated silica produced by a wet process using an alkali silicate aqueous solution, which is prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with an alkali. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by pyrolyzing rice husks by steaming them in a kiln. The rice husk charcoal obtained in this manner can be pulverized using a known pulverizer (e.g., a ball mill), and then sorted and classified into a predetermined particle size range to obtain rice husk charcoal powder. The rice husk-derived precipitated silica can be produced by the method described in JP 2019-38728 A, for example.

[0092] The silica preferably has a CTAB (cetyltrimethylammonium bromide) specific surface area of ​​50 m ２ / g~350m ２ / g. The CTAB specific surface area of ​​silica is 50 m ２ / g or more, the abrasion resistance is further improved, and the CTAB specific surface area of ​​the silica is 350 m ２ If the value is 0.1 / g or less, the rolling resistance is small.

[0093] Furthermore, the silica has a nitrogen adsorption specific surface area (BET method) of 80 m ２ / g or more 330m２ The nitrogen adsorption specific surface area (BET method) of silica is preferably less than 80 m ２ / g or more, the tread rubber layer can be sufficiently reinforced, and the fuel economy performance of the tire can be further improved. ２ When the modulus of elasticity of the tread rubber layer is less than 1 / g, the wet grip performance of the tire is further improved. From the viewpoint of further reducing the rolling resistance and further improving the wear resistance of the tire, the nitrogen adsorption specific surface area (BET method) of the silica is 130 m ２ / g or more, and ２ / g or more, and ２ / g or more, and ２ / g or more, and ２ / g or more, and ２ From the viewpoint of further improving the wet grip performance of the tire, the nitrogen adsorption specific surface area (BET method) of the silica is more preferably 300 m ２ / g or less, and ２ / g or less is more preferable, and 270m ２ It is more preferable that the tensile strength is 1 / g or less.

[0094] Furthermore, the content of the silica is preferably 20 parts by mass or more but less than 100 parts by mass per 100 parts by mass of the rubber component. By optimizing the amount of silica, wet grip performance, fuel economy, and abrasion resistance can be simultaneously achieved at higher levels. When the silica content is 20 parts by mass or more, sufficient wet grip performance, fuel economy, and abrasion resistance are obtained, while when the silica content is less than 100 parts by mass, deterioration of the low heat buildup and processability of the rubber composition can be suppressed. Therefore, when the silica content is 20 parts by mass or more but less than 100 parts by mass per 100 parts by mass of the rubber component, sufficient wet grip performance, fuel economy, and abrasion resistance can be obtained while deterioration of the low heat buildup and processability can be suppressed. From the same viewpoint, the content of the silica is more preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 62 parts by mass or more, even more preferably 65 parts by mass or more, and particularly preferably 68 parts by mass or more per 100 parts by mass of the rubber component. Additionally, the amount of silica is more preferably 90 parts by mass or less, further preferably 85 parts by mass or less, and particularly preferably 82 parts by mass or less, per 100 parts by mass of the rubber component.

[0095] Preferably, the filler further contains carbon black in addition to the silica. The carbon black reinforces the rubber composition and improves the abrasion resistance of the rubber composition. The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used alone or in combination of two or more. The carbon black may also be recycled carbon black.

[0096] In this specification, "recycled carbon black" refers to carbon black recovered from raw materials that are waste materials that have been recycled. Examples of the waste materials that have been recycled include rubber products (particularly vulcanized rubber products) containing carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" differs from carbon black that is produced directly from hydrocarbons such as petroleum and natural gas, i.e., non-recycled carbon black. Note that "used" here refers not only to carbon black that has been discarded after actual use, but also to carbon black that has been produced but discarded without actually being used.

[0097] In the filler, the content of silica in the total amount of the silica and the carbon black is preferably 80% by mass or more but less than 100% by mass, more preferably 85% by mass or more but less than 100% by mass, and even more preferably 90% by mass or more but less than 100% by mass. When the content of silica in the total amount of the silica and the carbon black is 80% by mass or more, it is possible to suppress a decrease in fuel economy performance due to an increase in carbon black, and when the content is less than 100% by mass, it is possible to reliably ensure the reinforcing effect of the carbon black. Therefore, when the filler further contains carbon black and the content of silica in the total amount of the silica and the carbon black is 80% by mass or more but less than 100% by mass, it is possible to reliably ensure the reinforcing effect of the carbon black while suppressing a decrease in fuel economy performance.

[0098] As the filler, in addition to the above-mentioned silica and carbon black, other inorganic compounds represented by the following formula (I) can also be used: nM.xSiO ｙ ・zH ２O ... (I) (In the formula, M is at least one selected from the group consisting of a metal selected from the group consisting of Al, Mg, Ti, Ca and Zr, an oxide or hydroxide of these metals, a hydrate thereof, and a carbonate of these metals; and n, x, y and z are integers of 1 to 5, an integer of 0 to 10, an integer of 2 to 5, and an integer of 0 to 10, respectively.) When the filler contains other inorganic compounds, the content thereof is preferably about 5 to 30 parts by mass per 100 parts by mass of the rubber component.

[0099] The inorganic compound of the above formula (I) includes alumina (Al) such as γ-alumina and α-alumina. ２ O ３ alumina monohydrate (Al) such as boehmite and diaspore; ２ O ３ ・H ２ O); aluminum hydroxides such as gibbsite and bayerite [Al(OH) ３ ]; aluminum carbonate [Al ２ (CO ３ ) ３ ], magnesium hydroxide [Mg(OH) ２ ], magnesium oxide (MgO), magnesium carbonate (MgCO ３ ), talc (3MgO.4SiO ２ ・H ２ O), attapulgite (5MgO.8SiO ２ ・9H ２ O), titanium white (TiO ２ ), titanium black (TiO ２ｎ－１ ), calcium oxide (CaO), calcium hydroxide [Ca(OH) ２ ], magnesium aluminum oxide (MgO.Al ２ O ３ ), clay (Al ２ O ３ 2SiO ２ ), kaolin (Al ２ O ３ 2SiO ２ ・2H ２ O), pyrophyllite (Al ２ O ３ 4SiO ２ ・H ２O), bentonite (Al ２ O ３ 4SiO ２ ・2H ２ O), aluminum silicate (Al ２ SiO ５ , Al ４ 3SiO ４ ・5H ２ O, etc.), magnesium silicate (Mg ２ SiO ４ , MgSiO ３ etc.), calcium silicate (Ca ２ SiO ４ etc.), calcium aluminum silicate (Al ２ O ３ CaO 2SiO ２ etc.), magnesium calcium silicate (CaMgSiO ４ ), calcium carbonate (CaCO ３ ), zirconium oxide (ZrO ２ ), zirconium hydroxide [ZrO(OH) ２ ・nH ２ O], zirconium carbonate [Zr(CO ３ ) ２ ], crystalline aluminosilicates containing hydrogen, alkali metals or alkaline earth metals to compensate for the charge, such as various zeolites, and the like.

[0100] (Silane Coupling Agent) The rubber composition for the tread rubber layer further contains a silane coupling agent in addition to the rubber component and the filler. The inclusion of the silane coupling agent improves the dispersibility of the silica contained as a filler, contributing to achieving both wet grip performance, fuel economy, and abrasion resistance.

[0101] In this embodiment, the silane coupling agent contains at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond.Although the silane coupling agent (A) having a thiol group has a high effect of increasing the dispersibility of silica as described above, if the content is large, it may cause discoloration such as blackening of the tire over time.Therefore, by further containing a silane coupling agent (B) having a sulfide bond as the silane coupling agent and adjusting the content of these silane coupling agents, it is possible to achieve both wet grip performance of the tire, low fuel consumption performance and wear resistance, while suppressing discoloration such as blackening (excellent discoloration resistance).

[0102] Here, the total content of the silane coupling agent (A) and the silane coupling agent (B) is more than 1 part by mass and not more than 15 parts by mass per 100 parts by mass of the silica. When the total content of the silane coupling agents exceeds 1 part by mass per 100 parts by mass of the silica, it is possible to sufficiently achieve both wet grip performance of the tire and fuel efficiency and wear resistance, and when the total content of the silane coupling agents is 15 parts by mass or less per 100 parts by mass of the silica, it is possible to sufficiently ensure discoloration resistance. From the same viewpoint, the total content of the silane coupling agents (A) and the silane coupling agents (B) is preferably 2 to 14 parts by mass, more preferably 3 to 13 parts by mass, and even more preferably 5 to 12 parts by mass per 100 parts by mass of the silica.

[0103] The content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica. When the content of the silane coupling agent (A) is 1 part by mass or more per 100 parts by mass of the silica, the tire's wet grip performance, fuel economy, and abrasion resistance can be sufficiently achieved, and when the content of the silane coupling agent (A) is 10 parts by mass or less per 100 parts by mass of the silica, discoloration resistance can be sufficiently ensured. From the same perspective, the content of the silane coupling agent (A) is preferably 2 to 9.5 parts by mass, more preferably 3 to 9 parts by mass, per 100 parts by mass of the silica. The content of the silane coupling agent (B) is appropriately selected within a range in which the content of the silane coupling agent (A) is 1 to 10 parts by mass per 100 parts by mass of the silica, and the total content of the silane coupling agent (A) and the silane coupling agent (B) is 15 parts by mass or less per 100 parts by mass of the silica. For example, the content of the silane coupling agent (B) is preferably 0.5 to 9.5 parts by mass, and more preferably 1 to 9 parts by mass, relative to 100 parts by mass of the silica.

[0104] Furthermore, from the viewpoint of achieving a good balance between the wet grip performance of the tire and fuel economy and wear resistance, as well as the effect of discoloration resistance, the mass ratio (B / A) of the content of the silane coupling agent (B) to the content of the silane coupling agent (A) is preferably 0.3 or more and less than 3.0. When the content mass ratio (B / A) of the silane coupling agents (A) and (B) is 0.3 or more, the effect of discoloration resistance is more reliably obtained, and when the content mass ratio (B / A) of the silane coupling agents (A) and (B) is less than 3.0, the wet grip performance, fuel economy and wear resistance are more reliably achieved. From the same viewpoint, the content mass ratio (B / A) of the silane coupling agents (A) and (B) is preferably 0.31 or more and 3.0 or less, more preferably 0.32 or more and 2.9 or less.

[0105] The silane coupling agent (A) is not particularly limited as long as it has a thiol group (—SH). For example, examples of the silane coupling agent (A) having a thiol group include 3-(trimethoxysilyl)-1-propanethiol, 3-(triethoxysilyl)-1-propanethiol, 3-(methyldimethoxysilyl)-1-propanethiol, 2-(trimethoxysilyl)-1-ethanethiol, 2-(triethoxysilyl)-1-ethanethiol, 2-(methyldimethoxysilyl)-1-ethanethiol, (trimethoxysilyl)methanethiol, (triethoxysilyl)methanethiol, (methyldimethoxysilyl)methanethiol, 3-[ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]-1-propanethiol {manufactured by Evonik Degussa, trade name “Si363” and [C １３ H ２７ O (CH ２ CH ２ O) ５ ] ２ (CH ３ CH ２ O)Si(CH ２ ) ３ SH} and the like.

[0106] Furthermore, among the above-mentioned silane coupling agents, the silane coupling agent (A) preferably has a carbon number of 20 to 75. When the silane coupling agent (A) has a carbon number of 20 to 75, wet grip performance, fuel economy, and wear resistance of the tire can be more reliably achieved at the same time.

[0107] The silane coupling agent (B) is not particularly limited as long as it has a sulfide bond (-S-). In addition, the sulfide bond may be a polysulfide bond [-(S) ｎ-, where n is a natural number of 2 or more)] may be formed, but this excludes -SH in which hydrogen is directly bonded to sulfur (i.e., the above-mentioned thiol group). For example, examples of the silane coupling agent (B) having a sulfide bond include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethyl thiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl)tetrasulfide, and the like.

[0108] Bioethanol can also be used as a raw material for silane coupling agents. Bioethanol is produced primarily using sugars and / or cellulose as biological resources, and does not effectively utilize other biological resources such as proteins, lipids, and amino acids. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, depending on the supply status of various biological resources, the supply status of renewable resources, the supply status of fossil resources, and market demands (e.g., demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources as the biological resource-derived monomer component, or to use a combination of a monomer component derived from a biological resource, a monomer component derived from a renewable resource, and a monomer component derived from a fossil resource. This allows for the effective use of a wide range of biological resources and renewable resources, such as sugars, proteins, and lipids, without relying on a single type of biological resource, and also allows for environmental considerations depending on the production conditions.

[0109] (Resin) The rubber composition for the tread rubber layer preferably further contains a resin. By further containing a resin, the processability of the rubber composition is improved and the wet grip performance of the tire can be further improved.

[0110] The type of the resin is not particularly limited. Examples of the resin include C ５ based resin, C ５ -C ９ based resin, C ９ These resins may be used alone or in combination of two or more.

[0111] Said C ５ As a resin based on C, there is C obtained by thermal decomposition of naphtha in the petrochemical industry. ５ and aliphatic petroleum resins obtained by (co)polymerizing the distillate. ５ The fraction usually contains olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, and diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene. ５ Commercially available resins can be used.

[0112] Said C ５ -C ９ The C-based resin is ５ -C ９ It refers to synthetic petroleum resin, ５ -C ９ Examples of the resin include petroleum-derived C ５ -C １１ The fraction was treated with AlCl ３ , B.F. ３ More specifically, copolymers containing styrene, vinyl toluene, α-methyl styrene, indene, etc. as the main component may be mentioned. ５ -C ９ As the resin, ９Resins containing less of the above components are preferred from the viewpoint of compatibility with the rubber component. ９ "Low amount of the above components" means that the C ９ This means that the above components are contained in an amount of less than 50% by mass, preferably 40% by mass or less. ５ -C ９ Commercially available resins can be used.

[0113] Said C ９ The C-based resin is ９ This refers to synthetic petroleum resins, such as AlCl ３ or BF ３ Using a Friedel-Crafts type catalyst such as C ９ It refers to a solid polymer obtained by polymerizing the fraction. ９ Examples of the resin include copolymers containing indene, α-methylstyrene, vinyltoluene, etc. as main components.

[0114] The terpene resin is a solid resin obtained by blending turpentine, which is obtained simultaneously with the extraction of rosin from pine trees, or a polymerization component separated from the blend, and polymerizing the blend using a Friedel-Crafts catalyst. Examples of such resins include β-pinene resin and α-pinene resin. Furthermore, a representative example of a terpene-aromatic compound resin is terpene-phenol resin. This terpene-phenol resin can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing the terpene with formalin. There are no particular limitations on the terpenes used as raw materials; monoterpene hydrocarbons such as α-pinene and limonene are preferred, with those containing α-pinene being more preferred, and α-pinene being particularly preferred. Styrene or the like may also be included in the skeleton.

[0115] The dicyclopentadiene resin is, for example, AlCl ３ or BF ３ This refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts catalyst such as

[0116] Furthermore, the resin is preferably at least partially hydrogenated, i.e., a hydrogenated resin. By at least partially hydrogenating the resin, the hysteresis loss (tan δ) in the low temperature range can be improved, thereby further improving the wet grip performance of the tire. Note that the at least partially hydrogenated resin refers to a resin obtained by reducing and hydrogenating a resin.

[0117] The resin that is the raw material for the hydrogenated resin is, for example, C ５ A resin (C) copolymerized with the fraction and dicyclopentadiene (DCPD) ５ -DCPD-based resin). When the dicyclopentadiene-derived component is 50% by mass or more in the total amount of the resin, C ５ - DCPD-based resins are included in dicyclopentadiene-based resins. When the dicyclopentadiene-derived component is less than 50% by mass in the total amount of resin, C ５ -DCPD resin is C ５ The same applies to cases where a small amount of a third component is contained.

[0118] The resin preferably has a softening point higher than 110°C and a weight average molecular weight in polystyrene equivalent of 200 to 1600 g / mol. By applying a rubber composition containing such a resin to the tread rubber layer of a tire, the wear resistance of the tire can be further improved. When the softening point of the resin is higher than 110°C, the tire tread rubber layer can be sufficiently reinforced, and the wear resistance can be further improved. From the viewpoint of the wear resistance of the tire tread rubber layer, the softening point of the resin is preferably 116°C or higher, more preferably 120°C or higher, more preferably 123°C or higher, and even more preferably 127°C or higher. Furthermore, from the viewpoint of the processability of the rubber composition, the softening point of the resin is preferably 160°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, more preferably 141°C or lower, and even more preferably 136°C or lower. The polystyrene-equivalent weight-average molecular weight of the resin can be calculated by measuring the average molecular weight by gel permeation chromatography (GPC) under the following conditions, for example: Column temperature: 40°C Injection volume: 50 μL Carrier and flow rate: tetrahydrofuran 0.6 mL / min Sample preparation: dissolving approximately 2.5 mg of resin in 10 mL of tetrahydrofuran The softening point of the resin can be measured, for example, in accordance with JIS-K2207-1996 (ring and ball method).

[0119] When the polystyrene-equivalent weight-average molecular weight of the resin is 200 g / mol or more, the resin is less likely to precipitate from the tire and the effects of the resin can be fully exhibited, and when it is 1600 g / mol or less, the resin is more likely to be compatible with the rubber component. From the viewpoint of suppressing the resin's precipitation from the tire and suppressing deterioration in tire appearance, the polystyrene-equivalent weight-average molecular weight of the resin is preferably 500 g / mol or more, more preferably 550 g / mol or more, even more preferably 600 g / mol or more, even more preferably 650 g / mol or more, and still more preferably 700 g / mol or more. Furthermore, from the viewpoint of increasing the compatibility of the resin with the rubber component and further enhancing the effects of the resin, the polystyrene-equivalent weight average molecular weight of the resin is preferably 1350 g / mol or less, more preferably 1330 g / mol or less, more preferably 1300 g / mol or less, more preferably 1200 g / mol or less, more preferably 1100 g / mol or less, more preferably 1000 g / mol or less, and even more preferably 950 g / mol or less.

[0120] The weight average molecular weight (Mw ＨＲ ) (unit: g / mol) to the softening point (Ts ＨＲ ) (unit: °C) ratio (Ts ＨＲ / Mw ＨＲ ) is preferably 0.07 or more, more preferably 0.083 or more, more preferably 0.095 or more, more preferably 0.104 or more, more preferably 0.125 or more, more preferably 0.135 or more, more preferably 0.14 or more, and even more preferably 0.141 or more. ＨＲ / Mw ＨＲ ) is preferably 0.25 or less, more preferably 0.24 or less, more preferably 0.23 or less, more preferably 0.19 or less, more preferably 0.18 or less, and even more preferably 0.17 or less.

[0121] The content of the resin is preferably 1 to 50 parts by mass per 100 parts by mass of the rubber component. When the content of the resin in the rubber composition is 1 part by mass or more per 100 parts by mass of the rubber component, the effect of the resin is fully exhibited, and when it is 50 parts by mass or less, the resin is less likely to precipitate from the tire and the effect of the resin can be fully exhibited. Therefore, when the content of the resin is 1 to 50 parts by mass per 100 parts by mass of the rubber component, the effect of the resin can be fully exhibited while suppressing the resin from precipitating from the tire. From the viewpoint of further enhancing the effect of the resin, the content of the resin in the rubber composition is preferably 5 parts by mass or more per 100 parts by mass of the rubber component, more preferably 7 parts by mass or more, and even more preferably 9 parts by mass or more. From the viewpoint of suppressing the resin from precipitating from the tire and suppressing deterioration of the tire appearance, the content of the resin in the rubber composition is preferably 45 parts by mass or less per 100 parts by mass of the rubber component, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less.

[0122] (Other Components) In addition to the rubber components, fillers, silane coupling agents, and resins described above, the rubber composition for the tread rubber layer may contain, as necessary, various components commonly used in the rubber industry, such as antioxidants, waxes, softeners, processing aids, stearic acid, zinc oxide (zinc white), vulcanization accelerators, vulcanizing agents, etc., appropriately selected within a range that does not impair the object of the present invention. Commercially available products can be suitably used as these compounding ingredients.

[0123] Examples of the antioxidant include N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6C), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (AW), N,N'-diphenyl-p-phenylenediamine (DPPD), etc. The content of the antioxidant is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0124] Examples of the wax include paraffin wax, microcrystalline wax, etc. The content of the wax is not particularly limited, but is preferably in the range of 0.1 to 5 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0125] The content of the zinc oxide (zinc white) is not particularly limited, but is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably less than 4 parts by mass, per 100 parts by mass of the rubber component. If the content of the zinc white is too high (more than 8 parts by mass), non-dispersion may occur, resulting in a decrease in fracture properties.

[0126] Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators, guanidine vulcanization accelerators, thiazole vulcanization accelerators, thiuram vulcanization accelerators, and dithiocarbamate vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. The content of the vulcanization accelerator is not particularly limited, and is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

[0127] The vulcanizing agent may be sulfur, etc. The content of the vulcanizing agent is preferably in the range of 0.1 to 10 parts by mass, more preferably 1 to 4 parts by mass, in terms of sulfur content, per 100 parts by mass of the rubber component.

[0128] (Method for producing rubber composition for tread rubber layer) The method for producing the rubber composition for the tread rubber layer is not particularly limited. For example, the rubber composition can be produced by blending various components appropriately selected as necessary with the above-mentioned rubber component, filler, and silane coupling agent, and kneading, heating, extruding, etc. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0129] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0130] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0131] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0132] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of vulcanization apparatus include a molding vulcanizer using a mold used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0133] <<Belt Layer>> The belt layer includes cords having a structure formed by twisting filaments together, and the cords of the belt layer are further coated with a belt coating rubber. The filaments constituting the cords of the belt layer satisfy the following formula: 4000-2000X≦Y≦4500-2000X, where X (mm) is the diameter of the filament and Y (MPa) is the tensile strength of the filament. By using cords having a structure formed by twisting filaments satisfying the formula in the belt layer, the strength of the belt layer can be improved, the plunger level can be improved, and the cut resistance of the tire can be supplemented.

[0134] From the viewpoint of fatigue resistance, the hardness of the surface layer of the filament constituting the cord of the belt layer is preferably 90 to 110% of the hardness of the inner layer, and particularly preferably 100%. The hardness can be measured, for example, by Vickers hardness. The surface layer of the filament refers to the layer extending from the outermost surface to a depth of 0.01 mm, and the inner layer refers to the layer extending further inside. The hardness can be measured in a region 0.005 mm deep from the outermost surface for the surface layer, and in a region 0.04 mm deep for the inner layer.

[0135] The method for producing the filaments constituting the cords of the belt layer is not particularly limited. The filaments may be obtained, for example, by refining iron ore and wiredrawing, by refining scrap iron and wiredrawing, or by recycling steel extracted from tires. Furthermore, in the belt layer, typically, a plurality of cords are wound in parallel. Such cords are generally steel cords. Furthermore, the structure of such cords is not particularly limited.

[0136] The cords of the belt layer preferably have a 1×N structure (where N is an integer selected from 2 to 6) formed by twisting together N filaments. When the cords of the belt layer have a 1×N structure formed by twisting together N filaments, it is possible to effectively achieve both cut resistance and fuel economy performance of the tire. In particular, for tires with a tire load index of less than 100, the cords are more preferably of a 1×2 structure, and for tires with a tire load index of 100 or more, the cords are more preferably of a 1×5 structure.

[0137] Furthermore, in the case of the 1xN structure, the cord may have a 1xN open structure in which the filaments are twisted together with a gap between them and do not come into contact with each other. Cords with an open structure have superior fatigue resistance compared to cords in which the filaments are twisted together while coming into contact with each other. Note that a cord with a 1xN open structure may be formed by sandwiching unvulcanized rubber between the filaments and twisting them together, or by coating the surfaces of the filaments with unvulcanized rubber and then twisting them together.

[0138] The placement density of the cords in the belt layer is preferably 60 cords / dm or more and 95 cords / dm or less, in which case the cut resistance and fuel economy of the tire can be effectively achieved at the same time.

[0139] The diameter of the cords of the belt layer is preferably 0.5 mm or more and 1.0 mm or less, in which case the cut resistance and fuel economy of the tire can be effectively achieved at the same time.

[0140] The coating rubber is not particularly limited as long as it is a general rubber composition capable of coating steel cords. Examples of rubber components include diene rubbers, with natural rubber or isoprene rubber being particularly preferred. The natural rubber may be modified. In the case of modified natural rubber, for example, a modified natural rubber with a nitrogen content of 0.1 to 0.3% by mass is preferred. Furthermore, the modified natural rubber is preferably one in which proteins have been removed by a centrifugation process, enzyme treatment, or urea treatment. Furthermore, the phosphorus content of the modified natural rubber is preferably greater than 200 ppm and less than or equal to 900 ppm. Furthermore, the coating rubber may contain a filler such as carbon black, as long as it does not affect the coating rubber's performance, such as adhesion and durability. The carbon black is preferably HAF-class carbon black, and the carbon black content in the coating rubber may be 50 to 70 parts by mass per 100 parts by mass of the rubber component. The carbon black may also be recycled carbon black. In addition to the above-mentioned components, the coating rubber may also contain, as appropriate, crosslinking agents such as vulcanization accelerators, sulfur, and zinc oxide; adhesion promoters such as cobalt compounds containing cobalt salts; antioxidants; oils; resins; etc. Examples of antioxidants include amine-based antioxidants such as 6PPD and bisphenol-based antioxidants such as o-MBp14. These antioxidants may be used alone or in combination of two or more.

[0141] <Tire Manufacturing Method> Depending on the type of tire to be applied, the tire of this embodiment may be obtained by molding an unvulcanized rubber composition or an unvulcanized treat (a cord-rubber composite in which cords are coated with rubber), etc., followed by vulcanization. Alternatively, the tire of this embodiment may be obtained by molding a semi-vulcanized rubber that has undergone a pre-vulcanization process or the like instead of the unvulcanized rubber composition, followed by full vulcanization. The components of the tire of this embodiment other than the tread rubber layer and belt layer are not particularly limited, and known components can be used. The tire of this embodiment is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0142] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0143] <Analysis Method of Rubber Component> The glass transition temperature (Tg) and bound styrene content of styrene-butadiene rubber were measured by the following methods.

[0144] (1) Glass Transition Temperature (Tg) Using the synthesized styrene-butadiene rubber as a sample, a DSC curve was recorded using a DSC250 manufactured by TA Instruments, while increasing the temperature from −100° C. at a rate of 20° C. / min under a helium flow of 50 mL / min, and the peak top (inflection point) of the DSC differential curve was determined as the glass transition temperature.

[0145] (2) Bound Styrene Amount The synthesized styrene-butadiene rubber was used as a sample, and 100 mg of the sample was diluted with chloroform to 100 mL and dissolved to prepare a measurement sample. The amount of bound styrene (mass%) relative to 100 mass% of the sample was measured based on the amount of absorption at the ultraviolet absorption wavelength (near 254 nm) by the phenyl group of styrene. A spectrophotometer "UV-2450" manufactured by Shimadzu Corporation was used as the measurement device.

[0146] <Method of Analyzing Resin> The softening point and weight average molecular weight of the resin were measured by the following methods.

[0147] (3) Softening Point The softening point of the resin was measured in accordance with JIS-K2207-1996 (ring and ball method).

[0148] (4) Weight-average molecular weight The average molecular weight of the resin was measured by gel permeation chromatography (GPC) under the following conditions, and the weight-average molecular weight in terms of polystyrene was calculated: Column temperature: 40°C, Injection volume: 50 μL, Carrier and flow rate: tetrahydrofuran 0.6 mL / min, Sample preparation: About 2.5 mg of resin was dissolved in 10 mL of tetrahydrofuran.

[0149] <Preparation of Belt Layer> Belt layers are prepared by covering cords with coating rubber, each having a structure and diameter shown in Table 1. The placement density of the cords in each belt layer is as shown in Table 1. The strength of the obtained belt layer and the strength of the cord itself are measured by the following method.

[0150] (5) Evaluation of Strength of Single Cord The breaking strength of the single cord is measured using a tensile tester. The evaluation results are expressed as an index, with the strength of a conventional single cord being set at 100. The larger the index value, the higher the strength of the single cord.

[0151] (6) Evaluation of belt layer strength The strength of the belt is calculated from the strength of the individual cord used and the placement density of the cord in the belt layer. The evaluation results are expressed as an index, with the strength of a belt using conventional cords being set at 100. The larger the index value, the stronger the belt.

[0152]

[0153] *1 Conventional cord: A cord with a 1x5 structure made by twisting together five filaments, the diameter of the filaments constituting the cord = 0.225 mm, and the tensile strength of the filaments = 3400 MPa. *2 UT grade cord: A cord with a 1x5 structure made by twisting together five filaments classified as UT grade as defined in ISO 17832:2009, the diameter of the filaments constituting the cord = 0.225 mm, and the tensile strength of the filaments = 3900 MPa.

[0154] <Preparation of Rubber Compositions> Rubber compositions of Examples and Comparative Examples were prepared by blending and kneading each component according to the formulations shown in Tables 2 and 3. The blending amounts of the rubber components shown in Tables 2 and 3 are shown as values ​​including the amount of oil extender. The blending amount of each component is shown as the amount (parts by mass) per 100 parts by mass of the rubber component. The obtained rubber compositions of Examples and Comparative Examples were vulcanized to obtain vulcanized rubber test pieces.

[0155] <Evaluation> The obtained vulcanized rubber test pieces were evaluated for wet grip performance, fuel economy, abrasion resistance, and discoloration of appearance by the following methods. Furthermore, cut resistance was evaluated by the following method. The results are shown in Tables 2 and 3.

[0156] (7) Wet Grip Performance The loss tangent (tan δ) of the test specimen was measured using a viscoelasticity measuring device (manufactured by GABO) under conditions of a temperature of -5 ° C, a strain of 1%, and a frequency of 15 Hz. The evaluation results are shown in Tables 2 and 3 as an index, with the tan δ of Comparative Example 1 set to 100. The larger the index value, the larger the tan δ and the better the wet grip performance.

[0157] (8) Fuel Economy Performance The loss tangent (tan δ) of the test specimen was measured using a viscoelasticity measuring device (manufactured by GABO) under conditions of a temperature of 50°C, a strain of 1%, and a frequency of 15 Hz, and the reciprocal of the measured value was calculated. The evaluation results are shown in Tables 2 and 3 as index values, with the reciprocal of tan δ of Comparative Example 1 set to 100. A larger index value indicates a smaller tan δ and better fuel economy.

[0158] (9) Abrasion Resistance Performance For the test specimens, sandpaper was attached to the grinding wheel using a Lambourn abrasion tester manufactured by Ueshima Seisakusho in accordance with JIS K 6264-2:2005, and the abrasion volume was measured at room temperature at slip ratios of 5%, 7%, 10%, 12%, and 15%. The reciprocal of the abrasion volume in Comparative Example 1 was set to 100, and the abrasion volume was calculated as an index using the following formula. The larger the index value, the smaller the abrasion volume and the better the abrasion resistance performance. The abrasion volume was calculated by multiplying it by a coefficient for the expected occurrence frequency for each slip ratio, and further correcting the value so that the contact area was constant, taking into account the elastic modulus of the rubber. Abrasion resistance performance index = {(abrasion volume of the test specimen in Comparative Example 1) / (abrasion volume of each test specimen)} x 100

[0159] (10) Discoloration of Appearance After storing the test piece for 7 days under the conditions of 40°C and 50 pphm ozone atmosphere, the presence or absence of discoloration on the surface was confirmed by visual inspection. The evaluation was performed according to the following criteria: Good: No black luster occurred. Bad: Black luster occurred.

[0160] (11) Evaluation of Cut Resistance The storage modulus (E') of the test piece was measured using a viscoelasticity measuring device (manufactured by GABO) under conditions of a temperature of 25°C, a strain of 1%, and a frequency of 15 Hz. The evaluation results were expressed as an index, with the storage modulus (E') of Comparative Example 1 set to 100. From the obtained storage modulus (E') index and the belt strength index, a cut resistance index was calculated according to the following formula: Cut resistance index = Storage modulus (E') index + Belt strength index - 100. In other words, the cut resistance index is the sum of the improvement in the storage modulus (E') index, the improvement in the belt strength index, and 100. Here, if each index is lower than the standard, the improvement will be a negative value. A larger cut resistance index value indicates better cut resistance.

[0161]

[0162]

[0163] *1, *2 Same as Table 1 *3 Low Tg modified SBR: Modified SBR obtained by synthesis using the following method, equivalent to styrene-butadiene rubber (A), glass transition temperature (Tg) = -65 ° C. *4 Medium Tg modified SBR: SBR obtained using butyllithium as an initiator, glass transition temperature (Tg) -38 ° C., styrene-butadiene rubber modified at the end with N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propanamine *5 High Tg unmodified SBR: Manufactured by ENEOS Materials Corporation, trade name "HP755B", glass transition temperature (Tg) = -19 ° C., blending amount includes 37.5 parts by mass of oil added to 100 parts by mass of SBR, equivalent to styrene-butadiene rubber (B) *6 Silica: Manufactured by Tosoh Silica Corporation, trade name "Nipsil AQ" *7 Carbon black: Asahi Carbon Co., Ltd., trade name "# 80" * 8 Inorganic filler: Aluminum hydroxide, Showa Denko K.K., "Higilite (registered trademark)" * 9 Silane coupling agent (A): Silane coupling agent having a thiol group, EVONIK Co., Ltd., trade name "Si 363" * 10 Silane coupling agent (B): Silane coupling agent having a sulfide bond, EVONIK Co., Ltd., trade name "S 2.5" * 11 Oil: Idemitsu Kosan Co., Ltd., trade name "Diana Process NH-70S" * 12 Hydrogenated C ５ Resin: Eastman Co., trade name "Impera E1780", softening point = 130°C, weight average molecular weight (Mw) = 909 g / mol *13 Other components: total amount of stearic acid, wax, antioxidant, zinc oxide, vulcanization accelerator, sulfur, retarder, and workability improver

[0164] (Synthesis of Low Tg Modified SBR (*3)) A cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added to a dried, nitrogen-purged 800 mL pressure-resistant glass vessel so that the total weight of the mixture was 67.5 g of 1,3-butadiene and 7.5 g of styrene. 0.6 mmol of 2,2-ditetrahydrofurylpropane and 0.8 mmol of n-butyllithium were then added, and polymerization was carried out at 50°C for 1.5 hours. To the polymerization reaction system, which had reached a polymerization conversion rate of nearly 100%, 0.72 mmol of N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl]propylamine was added as a modifier, and a modification reaction was carried out at 50°C for 30 minutes. Thereafter, 2 mL of a 5 mass % solution of 2,6-di-t-butyl-p-cresol (BHT) in isopropanol was added to terminate the reaction, and the mixture was dried in a conventional manner to obtain a modified SBR. Measurement of the microstructure of the resulting modified SBR revealed that the bound styrene content was 10% by mass and the glass transition temperature (Tg) was -65°C.

[0165] From the results in Tables 2 and 3, it can be seen that Examples 1 to 4 according to the present invention improve wet grip performance, fuel economy, and abrasion resistance without deteriorating cut resistance, and furthermore, discoloration of the appearance is suppressed. On the other hand, it can be seen that Comparative Examples 2 to 9 have at least one poor evaluation result.

[0166] 1: Tire 2: Bead portion 3: Sidewall portion 4: Tread portion 5: Carcass 6: Belt 6A, 6B: Belt layer 7: Bead core 8: Tread rubber layer

Claims

1. A tire comprising a tread rubber layer located on the outermost surface of a tread portion, and a belt layer located on the inner side of the tread rubber layer in the tire radial direction, wherein the tread rubber layer is made of a rubber composition including a rubber component, a filler, and a silane coupling agent, the rubber component includes a styrene-butadiene rubber (A) modified with a modifying agent having at least one atom of nitrogen, silicon, and tin and having a glass transition temperature of -50°C or less, and an unmodified styrene-butadiene rubber (B) having a glass transition temperature 30°C or higher than that of the styrene-butadiene rubber (A), the filler includes at least silica, the silane coupling agent includes at least a silane coupling agent (A) having a thiol group and a silane coupling agent (B) having a sulfide bond, and the content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 100 parts by mass of the silica, a total content of the silane coupling agent (A) and the silane coupling agent (B) is more than 1 part by mass and not more than 15 parts by mass per 100 parts by mass of the silica, the belt layer includes a cord having a structure formed by twisting together filaments, and a filament constituting the cord of the belt layer satisfies the following formula: 4000-2000X≦Y≦4500-2000X, where X (mm) is the diameter of the filament and Y (MPa) is the tensile strength of the filament.

2. The tire according to claim 1, wherein the styrene-butadiene rubber (A) is modified with a modifier having a nitrogen atom and a silicon atom.

3. The tire according to claim 1, wherein the styrene-butadiene rubber (A) is modified with a modifier having a functional group containing a nitrogen atom and an alkoxy group.

4. The tire according to claim 1, wherein a mass ratio (B / A) of the content of the silane coupling agent (B) to the content of the silane coupling agent (A) is 0.3 or more and less than 3.

5. The tire according to claim 1, wherein the filler further contains carbon black, and the content of the silica in the total amount of the silica and the carbon black is 80 mass % or more and less than 100 mass %.

6. The tire according to claim 1, wherein the content of the silica is 20 parts by mass or more and less than 100 parts by mass per 100 parts by mass of the rubber component.

7. The tire according to claim 1, wherein the silane coupling agent (A) has a carbon number of 20 to 75.

8. The tire according to claim 1, wherein the rubber component contains 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (A).

9. The tire according to claim 1, wherein the rubber component contains 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (B).

10. The tire according to claim 1, wherein the rubber composition constituting the tread rubber layer further contains a resin, and the content of the resin is 1 to 50 parts by mass per 100 parts by mass of the rubber component.

11. The tire of claim 10, wherein the resin is a hydrogenated resin.

12. The tire according to claim 1, wherein the cord of the belt layer has a 1×N structure (wherein N is an integer selected from 2 to 6) formed by twisting together N filaments.

13. The tire according to claim 1, wherein the cord density in the belt layer is 60 cords / dm or more and 95 cords / dm or less.

14. The tire according to claim 1, wherein the diameter of the cords of the belt layer is 0.5 mm or more and 1.0 mm or less.