WO2025109840A1 - Tire - Google Patents

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

The present invention relates to tires.

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, the following Patent Document 1 discloses that applying a rubber composition made by compounding a rubber component containing 70% by mass or more of natural rubber with a thermoplastic resin and a filler containing silica to the tread rubber of a tire improves the braking performance of the tire on both dry and wet road surfaces.

On the other hand, in response to the recent trend toward global carbon dioxide emission regulations in response to growing interest in environmental issues, there is a growing demand for improved fuel efficiency in automobiles. In order to meet such demands, there is also a demand for improved fuel efficiency in tires (reduced rolling resistance).
From the viewpoint of tire economics, in the development of rubber compositions for tires, it is also required to improve abrasion resistance in addition to wet grip performance and fuel economy.

In response to this, the following Patent Document 2 discloses a rubber composition that contains emulsion-polymerized styrene-butadiene rubber and solution-polymerized styrene-butadiene rubber, both of which have a glass transition temperature 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 in tires.

International Publication No. 2015/079703 International Publication No. 2017/188139

However, after the inventors' investigations, they found that while the technology described in Patent Document 1 can improve the wet grip performance of tires, the addition of a softening component resin (thermoplastic resin) reduces the rigidity of the rubber, lowering the plunger level of the tire and resulting in insufficient cut resistance. Furthermore, when attempting to supplement the cut resistance of tires, the amount of resin, which is a softening component, that can be added is limited, resulting in insufficient wet grip performance.

In addition, while the technology described in Patent Document 2 makes it possible to achieve both wet grip performance and fuel economy to a certain extent, it is necessary to further improve wet grip performance and fuel economy. In response to this, the present inventors conducted research and found that wet grip performance and fuel economy can be improved by blending a silane coupling agent having a thiol group. However, there is a problem in that rubber compositions containing silane coupling agents having a thiol group are prone to discoloration of the appearance, such as becoming shiny black over time.

The present invention aims to solve the problems of the conventional technology described above, and to provide a tire that has improved wet grip performance, fuel efficiency, and wear resistance without compromising cut resistance, and that also suppresses discoloration of the exterior.

The essential features of the tire of the present invention that solves the above problems are as follows:

[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,
The tread rubber layer is made of a rubber composition containing a rubber component, a filler, and a silane coupling agent,
The rubber component contains a styrene-butadiene rubber (A) 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, 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 contains at least silica,
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,
The content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 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 relative to 100 parts by mass of the silica,
The belt layer includes a cord having a structure formed by twisting filaments together,
When the diameter of the filament constituting the cord of the belt layer is X (mm) and the tensile strength of the filament is Y (MPa), the following formula is satisfied:
4000-2000X≦Y≦4500-2000X
A tire characterized by satisfying the above.

[2] The tire described in [1], in which the styrene-butadiene rubber (A) is modified with a modifier having nitrogen atoms and silicon atoms.

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

[4] A tire according to any one of [1] to [3], in which 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.

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

[6] A tire according to any one of [1] to [5], in which 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] A tire according to any one of [1] to [6], in which the silane coupling agent (A) has a carbon number of 20 to 75.

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

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

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

[11] The tire according to [10], wherein the resin is a hydrogenated resin.

[12] A tire according to any one of [1] to [11], in which the cord of the belt layer has a 1 x N structure (where N is an integer selected from 2 to 6) formed by twisting together N filaments.

[13] A tire according to any one of [1] to [12], in which the cord density in the belt layer is 60 cords/dm or more and 95 cords/dm or less.

[14] A tire described in any one of [1] to [13], in which the diameter of the cord of the belt layer is 0.5 mm or more and 1.0 mm or less.

The present invention provides a tire that has improved wet grip performance, fuel economy, and wear resistance without compromising cut resistance, and also suppresses discoloration of the exterior.

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

The tire of the present invention will be described in detail below with reference to an embodiment.

<Definition>
The compounds described herein may be derived in whole or in part from fossil sources, from biological sources such as plant sources, from recycled sources such as used tires, or from a mixture of two or more of fossil, biological and/or renewable sources.

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 increasing the temperature within a specified temperature range, and the peak top (inflection point) of the DSC differential curve is taken as the glass transition temperature.

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

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

<Tires>
Fig. 1 is a cross-sectional view of one embodiment of a tire of the present invention. The tire 1 shown in Fig. 1 has a pair of bead portions 2, a pair of sidewall portions 3, and a tread portion 4 connected to both sidewall portions 3. The tire 1 also includes a carcass 5 extending in a toroidal shape between the pair of bead portions 2 to reinforce these portions 2, 3, and 4, and a belt 6 disposed on the outer side of a crown portion of the carcass 5 in the tire radial direction.

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

The tire belt 6 shown in FIG. 1 is made up 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 made up of a rubber-coated layer of metal cords (preferably steel cords) that extend at an angle to the tire equatorial plane, and the two belt layers are laminated so that the metal cords constituting the belt layers cross each other with the tire equatorial plane in between to form the belt 6.

The tire 1 of the present embodiment includes a tread rubber layer 8 located on the outermost surface of the tread portion 4, and belt layers 6A, 6B located on the inner side in the tire radial direction of the tread rubber layer 8.
The tread rubber layer 8 is made of a rubber composition containing a rubber component, a filler, and a silane coupling agent,
The rubber component contains a styrene-butadiene rubber (A) 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, 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 contains at least silica,
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,
The content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 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 relative to 100 parts by mass of the silica,
The belt layers 6A and 6B include cords having a structure formed by twisting filaments together, and the filaments constituting the cords of the belt layers 6A and 6B have a diameter of X (mm) and a tensile strength of Y (MPa) that satisfies the following formula:
4000-2000X≦Y≦4500-2000X
The present invention is characterized in that:

The tire of the present invention may be modified in various ways as long as it comprises 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 provide a belt reinforcing layer on the outer side of the belt 6 of the tire 1 shown in FIG. 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.

In the tire 1 of the present embodiment, the tread rubber layer 8 is formed from 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 efficiency, and wear resistance.
In addition, although the silane coupling agent (A) having a thiol group has a high effect of increasing the dispersibility of silica, if the content is large, it may cause the discoloration of the tire's appearance over time.On the other hand, in the tread rubber layer 8 of the tire 1 of this embodiment, the silane coupling agent (A) having a thiol group and the silane coupling agent (B) having a sulfide bond are used in combination, and 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 the discoloration of the appearance.
However, when the rubber composition is applied to the tread rubber layer 8, the rigidity of the tread rubber layer 8 is reduced, which reduces the plunger level of the tire 1 and may result in insufficient cut resistance. In contrast, in the tire 1 of the present embodiment, the cord has a structure in which filaments are twisted together, and the filaments constituting the cord have a diameter X (mm) and a tensile strength Y (MPa) that satisfies the following formula:
4000-2000X≦Y≦4500-2000X
By using the cord satisfying the above requirement in the belt layers 6A and 6B, the strength of the belt layers 6A and 6B is improved, the plunger level is improved, and the cut resistance of the tire 1 is compensated for.
Therefore, the tire 1 of the present embodiment has improved wet grip performance, fuel efficiency, and wear resistance without deteriorating cut resistance, and furthermore, discoloration of the appearance is suppressed.

<<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.

(Rubber component)
The rubber component contains a styrene-butadiene rubber (A) (modified SBR) that has been modified with a modifier having 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).

The inclusion of styrene-butadiene rubber (A) and styrene-butadiene rubber (B) in the rubber component can improve the wet grip performance of the tire. In addition, in this embodiment, the use of styrene-butadiene rubber (A) modified with a modifier having at least one atom of nitrogen, silicon, and tin as the rubber component can improve the dispersibility of fillers in the rubber composition, such as silica. As a result, the tire of this embodiment has significantly improved low heat generation and improved dispersibility of fillers, which can also improve performance such as reinforcement, fuel efficiency, and wear resistance.

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 has a glass transition temperature of -50°C or lower.

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. If the glass transition temperature of the styrene-butadiene rubber (A) is -50°C or lower, the fuel economy and wear resistance of the tire can be sufficiently improved. In addition, styrene-butadiene rubber with a glass transition temperature higher than -90°C is easy to synthesize.

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 TA Instruments DSC250 while heating from -100°C at 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.

The content ratio 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 ratio 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 performance and wet grip performance of the tire can be further improved.

Moreover, the styrene-butadiene rubber (A) preferably has a bound styrene amount of less than 15% by mass. The bound styrene amount of the styrene-butadiene rubber (A) means the ratio of styrene units contained in the styrene-butadiene rubber. When the bound styrene amount is less than 15% by mass, the glass transition temperature is likely to be low. From the same viewpoint, the bound styrene amount 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 the wear resistance performance of the tire, the bound styrene amount is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more.
The amount of bound styrene in the styrene-butadiene rubber (A) can be adjusted by the amount of monomers used in the polymerization of the styrene-butadiene rubber, the degree of polymerization, and the like.

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 is modified with a modifier having a nitrogen atom and a silicon atom, and it is more preferable that the rubber is 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 wet grip performance, fuel economy, and wear resistance of the tire 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 wet grip performance, fuel economy, and wear resistance of the tire is further improved, and in particular, the fuel economy and wear resistance can be further improved.

Here, the modifying agent having a functional group containing a nitrogen atom and an alkoxy group is a general term for modifying agents having at least one functional group containing a nitrogen atom and at least one alkoxy group.
The functional group containing a nitrogen atom is preferably selected from the following:
The monovalent hydrocarbon group having 1 to 30 carbon atoms and containing a straight-chain, branched, alicyclic or aromatic ring, and having 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, a non-cyclic secondary amino group, an onium salt residue of a non-cyclic secondary amine, an isocyanuric acid triester residue, a cyclic tertiary amino group, a non-cyclic tertiary amino group, a nitrile group, a pyridine residue, an onium salt residue of a cyclic tertiary amine, and an onium salt residue of a non-cyclic tertiary amine, or a monovalent hydrocarbon group having 1 to 30 carbon atoms and containing a straight-chain, branched, alicyclic or aromatic ring, which may contain at least one heteroatom selected from an oxygen atom, a sulfur atom, and a phosphorus atom.

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 even 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.

The modified site of the styrene-butadiene rubber (A) may be the molecular terminal as described above, but may also be the main chain.
The styrene-butadiene rubber (A) having a modified molecular end can be produced, for example, by reacting various modifiers with the ends of a styrene-butadiene copolymer having active ends according to the methods described in WO 2003/046020 and JP 2007-217562 A.
In a preferred embodiment, the styrene-butadiene rubber (A) having a modified molecular end can be produced by reacting an aminoalkoxysilane compound with an end of a styrene-butadiene copolymer having an active end 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, according to the methods described in WO 2003/046020 and JP 2007-217562 A.

The carboxylic acid partial ester of a polyhydric alcohol means an ester of a polyhydric alcohol and a carboxylic acid, which has one or more hydroxyl groups. Specifically, an ester of a sugar or modified sugar having 4 or more carbon atoms and a fatty acid is preferably used. More preferred examples of this ester include (1) a fatty acid partial ester of a polyhydric alcohol, in particular a partial ester (which may be a monoester, diester, or triester) of a saturated higher fatty acid or an unsaturated higher fatty acid having 10 to 20 carbon atoms and a polyhydric alcohol, and (2) an ester compound in which 1 to 3 partial esters of a polycarboxylic acid and a higher alcohol are bonded to a polyhydric alcohol.
The polyhydric alcohol used as a raw material for the partial ester is preferably a saccharide having 5 or 6 carbon atoms and at least three hydroxyl groups (which may or may not be hydrogenated), glycol, polyhydroxy compound, etc. The raw material fatty acid is preferably a saturated or unsaturated fatty acid having 10 to 20 carbon atoms, such as stearic acid, lauric acid, or palmitic acid.
Among the fatty acid partial esters of polyhydric alcohols, sorbitan fatty acid esters are preferred, and specific examples thereof include sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate.

The aminoalkoxysilane compound is not particularly limited, but is preferably an aminoalkoxysilane compound represented by the following general formula (i).
R ¹¹ _a -Si-(OR ¹² ) _4-a ... (i)

In general formula (i), R ¹¹ and R ¹² each independently represent a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, at least one of R ¹¹ and R ¹² is substituted with an amino group, a is an integer of 0 to 2, and when there are multiple OR ¹² , each OR ¹² may be the same or different, and no active proton is contained in the molecule.

As the aminoalkoxysilane compound, an aminoalkoxysilane compound represented by the following general formula (ii) is also preferred.

In general formula (ii), n1+n2+n3+n4=4 (wherein n2 is an integer from 1 to 4, and n1, n3 and n4 are integers from 0 to 3).
A 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. When n4 is 2 or more, A ¹ may be the same or different, and A ¹ may be a divalent group that bonds with Si to form a cyclic structure.
R ²¹ 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 when n1 is 2 or more, R 21 may be the same or different.
R 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, either of which may contain a nitrogen atom and/or a silicon atom. When n2 is 2 or greater, R ²² may be the same or different from each other, or may be joined together to form a ring.
R 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.
R ²⁴ 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, and when n4 is 2 or greater, R 24 may be the same or different.
As the hydrolyzable group in the hydrolyzable group-containing primary or secondary amino group, a trimethylsilyl group or a tert-butyldimethylsilyl group is preferred, and a trimethylsilyl group is particularly preferred.

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

In general formula (iii), p1+p2+p3=2 (wherein p2 is an integer of 1 or 2, and p1 and p3 are integers of 0 or 1).
^A2 is NRa (Ra is a monovalent hydrocarbon group, a hydrolyzable group, or a nitrogen-containing organic group).
R 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.
R 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. When p2 is 2, R ²⁶ may be the same or different from each other, or may be joined together to form a ring.
R ²⁷ 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.
R 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.

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).

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).
R 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.
R ³² and R ³³ each independently represent 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.
R ³⁴ 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 when q1 is 2, may be the same or different.
R ³⁵ 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 when q2 is 2 or greater, R 35 may be the same or different.

In general formula (v), r1+r2=3 (wherein r1 is an integer of 1 to 3, and r2 is an integer of 0 to 2).
R 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.
R ³⁷ is 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 dimethylsilylaminoethyl 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 ³⁸ 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, and when r2 is 2, they may be the same or different.
A specific example of the aminoalkoxysilane compound represented by the general formula (v) is N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propaneamine.

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).

In general formula (vi), R ⁴⁰ represents 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.
R ⁴¹ 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.
R 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.
Here, TMS represents a trimethylsilyl group (hereinafter the same).

In general formula (vii), R ⁴³ and R ⁴⁴ each independently represent 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.
R 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.

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).

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).
R 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.
R 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. Multiple R ^47s or R ^48s may be the same or different.

In general formula (ix), X is a halogen atom.
R 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.
R 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 combine together to form a divalent organic group.
R ⁵² and R ⁵³ each independently represent 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.
R ⁵⁰ and R ⁵¹ are preferably a hydrolyzable group, and the hydrolyzable group is preferably a trimethylsilyl group or a tert-butyldimethylsilyl group, and particularly preferably a trimethylsilyl group.

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).

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

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.

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; and 2) reacting the activated polymer with a modifier such as the aminoalkoxysilane compound.

The step 1) is a step for producing an activated polymer having an alkali metal bonded to at least one end, 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.

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.

The organic alkali metal compound may be used in an amount of 0.1 mmol to 1.0 mmol based on 100 g of the total monomer.
The organic alkali metal compound is not particularly limited, and for example, one or more compounds 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 isopropylamide can be used.

The polymerization in step 1) may be carried out by further adding a polar additive as necessary, and the polar additive may be added in an amount of 0.001 to 1.0 parts by weight based on 100 parts by weight of the total monomers, specifically, 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.
As the polar additive, for example, one or more selected from the group consisting of tetrahydrofuran, ditetrahydrofurylpropane, diethyl ether, cycloamyl 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 can be used.

In the above-mentioned manufacturing method, when butadiene-based monomers and styrene-based monomers are copolymerized using the polar additive, the difference in their reaction rates can be compensated for, making it possible to easily induce the formation of a random copolymer.

The polymerization in the step 1) can be carried out via adiabatic polymerization or isothermal polymerization.
Here, the adiabatic polymerization refers to a polymerization method including a step of polymerizing the organic alkali metal compound by self-reaction heat without adding any heat after the organic alkali metal compound is added, and the isothermal polymerization refers to a polymerization method in which the temperature of the polymer is kept constant by adding or removing heat after the organic alkali metal compound is added.

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

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

In this case, the modifier may be the same as that described above, and may be used in an amount 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 a functional group into the polymer, and each reaction can be carried out at a temperature range of 0° C. to 90° C. for 1 minute to 5 hours.

In addition, the above-mentioned manufacturing method may further include, after step 2), one or more steps of recovering the solvent and unreacted monomer and drying, if necessary.

The content ratio of the styrene-butadiene rubber (A) modified by a modifying agent 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 efficiency 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 well maintained.

The rubber component further contains, in addition to the styrene-butadiene rubber (A), an 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 a styrene-butadiene rubber (B) having a high glass transition temperature as the rubber component, the wet grip performance of the tire can be improved.

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.

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 also 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 15% by mass or more and less than 85% by mass of the styrene-butadiene rubber (B), the wet grip performance can be further improved while maintaining the fuel economy performance and wear resistance performance well.

Furthermore, from the viewpoint of achieving a higher level of wet grip performance, fuel efficiency, and wear resistance of the tire, it is preferable that the content ratio of the styrene-butadiene rubber (B) is greater 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].

In addition, 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 efficiency performance, wear resistance, etc. of the tire.
The other rubbers 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), ethylene-propylene copolymer rubber, and non-diene rubbers such as butyl rubber can be used.
However, from the viewpoint of achieving higher levels 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).

(Filler)
The rubber composition for the tread rubber layer contains, in addition to the above-mentioned rubber component, 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 increased, and the fuel economy and wear resistance of the tire can be improved.

Here, the amount 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, 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, per 100 parts by mass of the rubber component. By optimizing the amount of filler, wet grip performance, fuel efficiency, and abrasion resistance can be achieved at a higher level. When the filler amount is 20 parts by mass or more, sufficient wet grip performance, fuel efficiency, and abrasion resistance can be obtained, and when the filler amount is 150 parts by mass or less, deterioration of low heat generation performance and processability can be suppressed.

The silica contained in the filler is not particularly limited, and can be appropriately selected according to the required performance.For example, as the silica, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. can be used, and among these, wet silica is preferred.These silicas can be used alone or in combination of two or more kinds.
The wet silica may be precipitated silica, which is obtained by growing primary silica particles in a reaction solution at a relatively high temperature and in a neutral to alkaline pH range in the early stages of production, and then agglomerating the primary particles by controlling the reaction solution to an acidic pH range.

As the silica, silica derived from silicic acid plants is also preferred from the viewpoint of reducing the environmental load. The silicic acid plants are present, for example, in mosses, ferns, horsetails, Cucurbitaceae, Urticaceae, and Gramineae plants. Among these plants, Gramineae plants are preferred. Examples of the Gramineae plants include rice, bamboo, and sugarcane, and among these, rice is preferred. Since rice is widely cultivated for food, it can be procured locally in a wide area, and since rice husks are generated in large quantities as industrial waste, it is easy to secure the amount. Therefore, from the viewpoint of ease of availability, silica derived from rice husks (hereinafter also referred to as "rice husk silica") is particularly preferred as silica. By using the rice husk silica, rice husks that become industrial waste can be effectively utilized, and since the raw material can be procured locally near the tire manufacturing plant, the energy and cost of transportation and storage can be reduced, 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 method using an aqueous alkali silicate solution, which is prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with an alkali and extracting the rice husk ash with an alkali silicate solution. The method for producing the rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husks can be pyrolyzed by steaming them in a kiln to obtain rice husk charcoal. The rice husk charcoal thus obtained is 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 precipitated silica derived from rice husks can be produced by the method described in JP 2019-38728 A, etc.

The silica preferably has a CTAB (cetyltrimethylammonium bromide) specific surface area of 50 m ² /g to 350 m ² /g. When the CTAB specific surface area of the silica is 50 m ² /g or more, the abrasion resistance is further improved, and when the CTAB specific surface area of the silica is 350 m ² /g or less, the rolling resistance is reduced.

Furthermore, the silica preferably has a nitrogen adsorption specific surface area (BET method) of 80 m ² /g or more and less than 330 m ² /g. When the nitrogen adsorption specific surface area (BET method) of silica is 80 m ² /g or more, the tread rubber layer can be sufficiently reinforced, and the fuel efficiency performance of the tire can be further improved. When the nitrogen adsorption specific surface area (BET method) of silica is less than 330 m ² /g, the elastic modulus of the tread rubber layer does not become too high, and 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 preferably 130 m ² /g or more, preferably 150 m ² /g or more, preferably 170 m ² /g or more, preferably 180 m ² /g or more, preferably 190 m ² /g or more, and more preferably 195 m ² /g or more. Also, 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 preferably 300 m ² /g or less, more preferably 280 m ² /g or less, and even more preferably 270 m ² /g or less.

Furthermore, the amount of the silica is preferably 20 parts by mass or more and 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 efficiency and abrasion resistance can be achieved at a higher level, and when the silica content is 20 parts by mass or more, sufficient wet grip performance, fuel efficiency and abrasion resistance can be obtained, and when the silica content is less than 100 parts by mass, deterioration of low heat generation and processability of the rubber composition can be suppressed. Therefore, when the silica content is 20 parts by mass or more and less than 100 parts by mass with respect to 100 parts by mass of the rubber component, deterioration of low heat generation and processability can be suppressed while sufficient wet grip performance, fuel efficiency and abrasion resistance can be obtained.
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, relative to 100 parts by mass of the rubber component. In addition, the content of the silica is more preferably 90 parts by mass or less, even more preferably 85 parts by mass or less, and particularly preferably 82 parts by mass or less, relative to 100 parts by mass of the rubber component.

In addition to the silica, the filler preferably further contains carbon black, which can reinforce the rubber composition and improve 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.

In this specification, "recycled carbon black" refers to carbon black recovered from raw materials that are waste materials that have been recycled. Examples of waste materials that have been recycled include rubber products (especially vulcanized rubber products) that contain carbon black, such as used rubber and used tires, and waste oil. "Recycled carbon black" is different from carbon black that is produced directly from raw materials such as hydrocarbons, such as petroleum and natural gas, i.e., carbon black that is not recycled. Note that "used" here does not only include carbon black that has actually been used and then discarded, but also carbon black that has been produced but discarded without actually being used.

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 and less than 100% by mass, more preferably 85% by mass or more and less than 100% by mass, and even more preferably 90% by mass or more and 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 efficiency performance due to an increase in carbon black, and when it is less than 100% by mass, it is possible to reliably ensure the reinforcing effect of 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 and less than 100% by mass, it is possible to reliably ensure the reinforcing effect of carbon black while suppressing a decrease in fuel efficiency performance.

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 ₂ O... (I)
(In the formula, M is at least one selected from the group consisting of metals selected from the group consisting of Al, Mg, Ti, Ca, and Zr, oxides or hydroxides of these metals, and hydrates thereof, and carbonates of these metals; n, x, y, and z are integers of 1 to 5, integers of 0 to 10, integers of 2 to 5, and integers of 0 to 10, respectively.)
When the filler contains other inorganic compounds, the content thereof is preferably about 5 to 30 parts by mass based on 100 parts by mass of the rubber component.

Examples of the inorganic compound of the above formula (I) include alumina (Al ₂ O ₃ ) such as γ-alumina and α-alumina; alumina monohydrate (Al ₂ O ₃ .H ₂ O) such as boehmite and diaspore; aluminum hydroxide [Al(OH) ₃ ] such as gibbsite and bayerite; 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 ], aluminum magnesium 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 2 O), 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.), aluminum calcium 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.

(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 enhances the dispersibility of the silica contained as a filler, and contributes to achieving both wet grip performance, fuel efficiency and abrasion resistance.

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.
The silane coupling agent (A) having thiol group has a high effect of enhancing the dispersibility of silica described above, but when the content is large, it may cause discoloration such as black luster on tire with aging.Therefore, by further containing the silane coupling agent (B) having sulfide bond as the silane coupling agent and adjusting the content of these silane coupling agents, it is possible to suppress discoloration such as black luster while achieving both wet grip performance of tire, low fuel consumption performance and wear resistance (excellent discoloration resistance).

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 with respect to 100 parts by mass of the silica.The total content of the silane coupling agent is more than 1 part by mass with respect to 100 parts by mass of the silica, so that the wet grip performance of the tire can be sufficiently achieved, as well as the low fuel consumption performance and the wear resistance performance, and the total content of the silane coupling agent is not more than 15 parts by mass with respect to 100 parts by mass of the silica, so that the discoloration resistance can be sufficiently ensured.
From the same viewpoint, the total content of the silane coupling agent (A) and the silane coupling agent (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, relative to 100 parts by mass of the silica.

Moreover, the content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 100 parts by mass of the silica. When the content of the silane coupling agent (A) is 1 part by mass or more relative to 100 parts by mass of the silica, the tire wet grip performance, fuel efficiency performance and wear resistance can be sufficiently achieved, and when the content of the silane coupling agent (A) is 10 parts by mass or less relative to 100 parts by mass of the silica, discoloration resistance can be sufficiently ensured. From the same viewpoint, 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 relative to 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 within a range of 1 to 10 parts by mass relative to 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 relative to 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, more preferably 1 to 9 parts by mass relative to 100 parts by mass of the silica.

Furthermore, from the viewpoint of achieving a good balance between wet grip performance, fuel economy and abrasion resistance of the tire, and the effect of discoloration resistance, it is preferable that 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 3.0. 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, it is more reliably achieved that wet grip performance, fuel economy and abrasion resistance are compatible. 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.

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", [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.

Furthermore, among the above-mentioned silane coupling agents (A), it is preferable that the carbon number of the silane coupling agent (A) is 20 to 75. This is because when the carbon number of the silane coupling agent (A) is 20 to 75, it is possible to more reliably achieve a balance between wet grip performance, fuel efficiency, and wear resistance of the tire.

The silane coupling agent (B) is not particularly limited as long as it has a sulfide bond (-S-). A plurality of sulfide bonds may be connected to form a polysulfide bond [-(S) _n -, where n is a natural number of 2 or more], but this does not include -SH, in which hydrogen is directly bonded to sulfur (i.e., the above-mentioned thiol group).
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.

In addition, bioethanol can also be used as a raw material for the silane coupling agent. Bioethanol is produced mainly using sugars and/or cellulose as biological resources, and other biological resources such as proteins, lipids, and amino acids cannot be effectively utilized. Furthermore, sugars compete with food, and excessive use of cellulose leads to deforestation. Therefore, it is preferable to use multiple types of monomer components derived from biological resources as the monomer components derived from the biological resources, or to use a combination of monomer components derived from biological resources, monomer components derived from renewable resources, and monomer components derived from fossil resources, depending on the supply situation of various biological resources, the supply situation of renewable resources, the supply situation of fossil resources, and market demands (for example, demand for biomass resources as food). This makes it possible to effectively utilize 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 to take the environment into consideration depending on the situation at the time of production.

(resin)
It is preferable that the rubber composition for the tread rubber layer 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.

The type of the resin is not particularly limited. Examples of the resin include _C5 resins, _C5 - _C9 resins, _C9 resins, terpene resins, dicyclopentadiene resins, and terpene-aromatic compound resins. These resins may be used alone or in combination of two or more.

The _C5 resin may be an aliphatic petroleum resin obtained by (co)polymerizing a _C5 fraction obtained by thermal cracking of naphtha in the petrochemical industry.
The _C5 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, etc. Note that, as the _C5 resin, commercially available products can be used.

The _C5 - _C9 resin refers to a _C5 - _C9 synthetic petroleum resin. Examples of the _C5 - _C9 resin include solid polymers obtained by polymerizing a petroleum-derived _C5 - _C11 fraction using a Friedel-Crafts catalyst such as _AlCl3 or _BF3 . More specifically, examples of the C5-C9 resin include copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc.
As the _C5 - _C9 resin, a resin having a small amount of C9 _or more components is preferred from the viewpoint of compatibility with the rubber component. Here, "having a small amount of _C9 or more components" means that the amount of _C9 or more components in the total amount of the resin is less than 50 mass%, preferably 40 mass% or less. Commercially available _C5 - _C9 resins can be used.

The _C9 resin refers to a _C9 synthetic petroleum resin, for example, a solid polymer obtained by polymerizing a _C9 fraction using a Friedel-Crafts type catalyst such as _AlCl3 or _BF3 .
Examples of _C9 resins include copolymers containing indene, α-methylstyrene, vinyltoluene, or the like as main components.

The terpene resin is a solid resin obtained by blending turpentine, which is obtained at the same time as rosin is obtained from pine trees, or a polymerization component separated from this, and polymerizing it using a Friedel-Crafts catalyst, and examples of this include β-pinene resin and α-pinene resin. 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 with formalin. There are no particular restrictions on the terpenes used as raw materials, and monoterpene hydrocarbons such as α-pinene and limonene are preferred, and those containing α-pinene are more preferred, with α-pinene being particularly preferred. Styrene, etc. may also be included in the skeleton.

The dicyclopentadiene-based resin refers to a resin obtained by polymerizing dicyclopentadiene using a Friedel-Crafts type catalyst such as _AlCl3 or _BF3 .

In addition, the resin is preferably at least partially hydrogenated, i.e., a hydrogenated resin, which can improve the hysteresis loss (tan δ) in the low temperature range by at least partially hydrogenating the resin, thereby further improving the wet grip performance of the tire.
The at least partially hydrogenated resin means a resin obtained by reducing and hydrogenating a resin.

The resin that is the raw material for the hydrogenated resin may include, for example, a resin obtained by copolymerizing a _C5 fraction with dicyclopentadiene (DCPD) ( _C5 -DCPD-based resin).
Here, when the dicyclopentadiene-derived component in the total amount of resin is 50 mass% or more, the _C5- DCPD-based resin is considered to be included in the dicyclopentadiene-based resin. When the dicyclopentadiene-derived component in the total amount of resin is less than 50 mass%, the C5 _- DCPD-based resin is considered to be included in the _C5- based resin. The same applies to the case where a small amount of a third component or the like is further contained.

The resin preferably has a softening point higher than 110° C. and a weight average molecular weight in terms of polystyrene of 200 to 1600 g/mol. By applying a rubber composition containing such a resin to a 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 tread rubber layer of the tire can be sufficiently reinforced, and the wear resistance can be further improved. From the viewpoint of the wear resistance of the tread rubber layer of the tire, 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. 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: 50μL
Carrier and flow rate: Tetrahydrofuran 0.6 mL/min
Sample preparation: About 2.5 mg of resin was dissolved 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).

When the weight average molecular weight of the resin in terms of polystyrene 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 easily compatible with the rubber component.
From the viewpoint of suppressing precipitation of the resin from the tire and suppressing deterioration of the 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, more preferably 600 g/mol or more, more preferably 650 g/mol or more, and even more preferably 700 g/mol or more. Also, from the viewpoint of increasing the compatibility of the resin with the rubber component and further enhancing the effect 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.

The ratio (Ts _HR /Mw _HR ) of the softening point (Ts _HR ) (unit: ° C.) of the resin to the polystyrene-equivalent weight average molecular weight (Mw _HR ) (unit: g/mol) of the resin 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. The ratio (Ts _HR /Mw _HR ) is preferably 0.25 or less, preferably 0.24 or less, preferably 0.23 or less, preferably 0.19 or less, more preferably 0.18 or less, and even more preferably 0.17 or less.

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 expressed, 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 expressed. 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 expressed 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 the deterioration of the tire appearance, the content of the resin in the rubber composition is more 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.

(Other ingredients)
The rubber composition for the tread rubber layer may contain, in addition to the above-mentioned rubber components, fillers, silane coupling agents, and resins, various components commonly used in the rubber industry, such as antioxidants, waxes, softeners, processing aids, stearic acid, zinc oxide (zinc oxide), vulcanization accelerators, vulcanizing agents, etc., as necessary, 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 agents.

The antioxidants 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. There are no particular restrictions on the content of the antioxidant, and it is preferably in the range of 0.1 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component.

Examples of the wax include paraffin wax and microcrystalline wax. There are no particular limitations on the amount of the wax, but it 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.

The amount of zinc oxide (zinc white) is not particularly limited, and 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 amount of zinc white is too high (more than 8 parts by mass), it may not disperse and the fracture properties may deteriorate.

The vulcanization accelerator may be a sulfenamide-based vulcanization accelerator, a guanidine-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a dithiocarbamate-based vulcanization accelerator, or the like. These vulcanization accelerators may be used alone or in combination of two or more. There are no particular limitations on the content of the vulcanization accelerator, and the content is preferably in the range of 0.1 to 5 parts by mass, and more preferably in the range of 0.2 to 4 parts by mass, per 100 parts by mass of the rubber component.

The vulcanizing agent may be sulfur. 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.

(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 components, filler, and silane coupling agent, kneading, heating, extruding, etc. Also, the obtained rubber composition can be vulcanized to produce a vulcanized rubber.

There are no particular limitations on the conditions for the kneading, and the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, etc., as well as the conditions for the kneading temperature, kneading time, type of kneading device, etc., can be appropriately selected according to the purpose. Examples of kneading devices include Banbury mixers, intermixes, kneaders, rolls, etc., which are typically used for kneading rubber compositions.

There are no particular limitations on the conditions for the heat-in process, and the heat-in process temperature, heat-in process time, heat-in process equipment, and other conditions can be appropriately selected depending on the purpose. Examples of the heat-in process equipment include a heat-in process roll machine that is typically used for heat-in process of rubber compositions.

There are no particular limitations on the extrusion conditions, and various conditions such as extrusion time, extrusion speed, extrusion equipment, and extrusion temperature can be appropriately selected depending on the purpose. Examples of extrusion equipment include extruders that are typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

There are no particular limitations on the vulcanization equipment, method, conditions, etc., and they can be selected appropriately depending on the purpose. Typical vulcanization equipment includes a mold vulcanizer that uses a mold used to vulcanize rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

<<Belt layer>>
The belt layer includes a cord having a structure formed by twisting filaments, and the cord of the belt layer is further coated with a belt coating rubber. The filament constituting the cord of the belt layer has a diameter of X (mm) and a tensile strength of Y (MPa) that satisfies the following formula:
4000-2000X≦Y≦4500-2000X
By using a cord having a structure obtained by twisting together filaments that satisfy the above formula in a 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.

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 100% is particularly preferable. The hardness can be measured, for example, by Vickers hardness. Furthermore, the surface layer of the filament means the layer from the outermost surface to a depth of 0.01 mm, and the area inside this refers to the inner layer of the filament. The hardness can be measured in a region 0.005 mm deep from the outermost surface for the surface layer, and 0.04 mm deep for the inner layer.

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 drawing wire, by refining scrap iron and drawing wire, or by recycling steel extracted from tires.
In the belt layer, typically, a plurality of cords are arranged in parallel. Such cords are generally steel cords. There is no particular limitation on the structure of such cords.

The cords of the belt layer preferably have a 1xN 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 1xN structure formed by twisting together N filaments, the tire can effectively achieve both cut resistance and low fuel consumption performance. In particular, for tires with a tire load index of less than 100, it is more preferable that the cords have a 1x2 structure, and for tires with a tire load index of 100 or more, it is more preferable that the cords have a 1x5 structure.

In the case of the 1xN structure, the cord can have a 1xN open structure in which the filaments are twisted together with a gap between them and do not touch each other. A cord with an open structure has better fatigue resistance than a cord in which the filaments are twisted together while touching each other. A cord with a 1xN open structure can be formed by sandwiching unvulcanized rubber between the filaments and twisting them together, or by covering the surfaces of the filaments with unvulcanized rubber and then twisting them together.

The cord density in the belt layer is preferably 60 cords/dm or more and 95 cords/dm or less. In this case, the tire can effectively achieve both cut resistance and low fuel consumption performance.

The diameter of the cord of the belt layer is preferably 0.5 mm or more and 1.0 mm or less. In this case, the tire can effectively achieve both cut resistance and low fuel consumption performance.

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, and in particular, natural rubber or isoprene rubber is preferred. The natural rubber may be modified. In the case of modified natural rubber, it is preferable that the modified natural rubber has a nitrogen content of, for example, 0.1 to 0.3% by mass. It is also preferable that the modified natural rubber has had proteins removed by a centrifugation process, enzyme treatment, or urea treatment. It is also preferable that the phosphorus content of the modified natural rubber is more than 200 ppm and 900 ppm or less. The coating rubber may contain a filler such as carbon black as long as it does not affect the performance of the coating rubber, 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 be recycled carbon black. In addition to the above-mentioned components, the coating rubber may contain, as appropriate, crosslinking chemicals 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.

<Tire manufacturing method>
The tire of the present embodiment may be obtained by molding and then vulcanizing an unvulcanized rubber composition or an unvulcanized treat (a cord-rubber composite in which a cord is coated with rubber) or the like, depending on the type of tire to be applied, or may be obtained by molding and then vulcanizing a semi-vulcanized rubber that has been subjected to a pre-vulcanization process or the like instead of an unvulcanized rubber composition.
The components of the tire of the present embodiment other than the tread rubber layer and the belt layer are not particularly limited, and known components can be used.
In addition, the tire of this embodiment is preferably a pneumatic tire, and the gas 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.

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

<Analysis method of rubber components>
The glass transition temperature (Tg) and bound styrene content of the styrene-butadiene rubber were measured by the following method.

(1) Glass transition temperature (Tg)
The synthesized styrene-butadiene rubber was used as a sample, and a DSC curve was recorded using a TA Instruments DSC250 while heating from −100° C. at 20° C./min under a helium flow of 50 mL/min. The peak top (inflection point) of the DSC differential curve was determined as the glass transition temperature.

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

<Method of resin analysis>
The softening point and weight average molecular weight of the resin were measured by the following methods.

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

(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: 50μL
Carrier and flow rate: Tetrahydrofuran 0.6 mL/min
Sample preparation: Approximately 2.5 mg of resin was dissolved in 10 mL of tetrahydrofuran.

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

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

(6) Evaluation of belt layer strength The strength of the belt is calculated from the strength of the individual cord used and the density of the cord in the belt layer. The evaluation result is expressed as an index, with the strength of the belt using the conventional cord being set at 100. The higher the index value, the higher the strength of the belt.

*1 Conventional cord: A 1 x 5 cord made of 5 twisted filaments, the diameter of the filament constituting the cord = 0.225 mm, and the tensile strength of the filament = 3,400 MPa
*2 UT grade code: A 1x5 cord made by twisting together five filaments classified as UT grade as defined in ISO 17832:2009, the diameter of the filament constituting the cord = 0.225 mm, and the tensile strength of the filament = 3900 MPa

<Preparation of Rubber Composition>
Rubber compositions of the examples and comparative examples were prepared by blending and kneading each component according to the formulation shown in Tables 2 and 3. The blended amounts of the rubber components shown in Tables 2 and 3 are shown as values including the amount of oil extension. The blended 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 the Examples and Comparative Examples were vulcanized to obtain vulcanized rubber test pieces.

<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.

(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 index values, with the tan δ of Comparative Example 1 being set at 100. The larger the index value, the larger the tan δ and the better the wet grip performance.

(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 being set at 100. A larger index value indicates a smaller tan δ and better fuel economy performance.

(9) Abrasion resistance performance For the test specimens, sandpaper was attached to the grinding wheel using a Lambourn abrasion tester manufactured by Ueshima Seisakusho Co., Ltd., and the amount of abrasion was measured at room temperature at slip rates of 5%, 7%, 10%, 12% and 15% in accordance with JIS K 6264-2:2005. The reciprocal of the amount of abrasion in Comparative Example 1 was set to 100, and the amount of abrasion was calculated as an index using the following formula. A larger index value indicates a smaller amount of abrasion and better abrasion resistance.
The amount of wear was calculated by multiplying each slip ratio by a coefficient representing the frequency of occurrence in actual practice, and then using a value corrected to ensure that the contact area was constant, taking into account the elastic modulus of the rubber.
Abrasion resistance performance index={(amount of wear of test piece of Comparative Example 1)/(amount of wear of each test piece)}×100

(10) Discoloration of Appearance The test pieces were stored for 7 days under conditions of 40° C. and 50 pphm ozone atmosphere, and then visually inspected for the presence or absence of discoloration on the surface. The evaluation was performed according to the following criteria.
Good: No black shine Bad: Black shine

(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 being set at 100. From the obtained index of storage modulus (E') and the index of belt strength, the following formula was used:
Cut resistance index = storage modulus (E') index + belt strength index - 100
The cut resistance index is calculated according to the above formula. In other words, the cut resistance index is the sum of the improvement range of the storage modulus (E') index, the improvement range of the belt strength index, and 100, and here, when each index is lower than the standard, the improvement range is a negative value. The larger the cut resistance index value, the more excellent the cut resistance is.

*1, *2 Same as Table 1 *3 Low Tg modified SBR: Modified SBR synthesized by the following method, equivalent to styrene-butadiene rubber (A), glass transition temperature (Tg) = -65°C
* 4 Medium Tg modified SBR: SBR obtained using butyl lithium as an initiator, with a glass transition temperature (Tg) of -38 ° C., and a styrene-butadiene rubber modified with N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propaneamine at the end. * 5 High Tg unmodified SBR: ENEOS Materials Corporation, product 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: Tosoh Silica Corporation, product name "Nipsil AQ"
*7 Carbon black: Asahi Carbon Co., Ltd., product name "#80"
*8 Inorganic filler: Aluminum hydroxide, manufactured by Showa Denko K.K., "Hijilite (registered trademark)"
*9 Silane coupling agent (A): A silane coupling agent having a thiol group, manufactured by EVONIK, trade name "Si 363"
*10 Silane coupling agent (B): A silane coupling agent having a sulfide bond, manufactured by EVONIK Corporation, trade name "S 2.5"
*11 Oil: Idemitsu Kosan Co., Ltd., product name "Diana Process NH-70S"
*12 Hydrogenated _C5 resin: Manufactured by Eastman, trade name "Registered Trademark Impera E1780", softening point = 130°C, weight average molecular weight (Mw) = 909 g/mol
*13 Other ingredients: Total amount of stearic acid, wax, antioxidant, zinc oxide, vulcanization accelerator, sulfur, retarder, and workability improver.

(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 amounts of 1,3-butadiene and styrene were 67.5 g and 7.5 g, respectively, and 0.6 mmol of 2,2-ditetrahydrofurylpropane and 0.8 mmol of n-butyllithium were added, followed by polymerization at 50° C. for 1.5 hours. To the polymerization reaction system in which the polymerization conversion rate reached 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% by 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.

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 efficiency, and abrasion resistance without compromising 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.

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 (14)

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,
The tread rubber layer is made of a rubber composition containing a rubber component, a filler, and a silane coupling agent,
The rubber component contains a styrene-butadiene rubber (A) 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, 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 contains at least silica,
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,
The content of the silane coupling agent (A) is 1 to 10 parts by mass relative to 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 relative to 100 parts by mass of the silica,
The belt layer includes a cord having a structure formed by twisting filaments together,
When the diameter of the filament constituting the cord of the belt layer is X (mm) and the tensile strength of the filament is Y (MPa), the following formula is satisfied:
4000-2000X≦Y≦4500-2000X
A tire characterized by satisfying the above. The tire according to claim 1, wherein the styrene-butadiene rubber (A) is modified with a modifier having nitrogen atoms and silicon atoms. 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. The tire according to claim 1, 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. The filler further comprises carbon black;
The tire according to claim 1 , wherein a content ratio of the silica in a total amount of the silica and the carbon black is 80 mass % or more and less than 100 mass %. 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. The tire according to claim 1, wherein the silane coupling agent (A) has a carbon number of 20 to 75. 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). 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). The rubber composition constituting the tread rubber layer further contains a resin,
The tire according to claim 1, wherein the resin content is 1 to 50 parts by mass per 100 parts by mass of the rubber component. The tire according to claim 10, wherein the resin is a hydrogenated resin. The tire according to claim 1, wherein the cord of the belt layer has a 1 x N structure (where N is an integer selected from 2 to 6) formed by twisting together N filaments. 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. The tire according to claim 1, wherein the diameter of the cord of the belt layer is 0.5 mm or more and 1.0 mm or less.

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