JP7636968B2 - Rubber composition for tires, tire tread and tire - Google Patents

Description

The present invention relates to a rubber composition for tires, a tire tread, and a tire.

In order to improve the grip of passenger car tires on dry and wet road surfaces, _a rubber composition is disclosed for use in the manufacture of treads, which is prepared by blending a rubber component (A) containing 70% by mass or more of natural rubber, ₅ to ₅₀ parts by mass of at least one thermoplastic resin (B) selected from C5 resin, C5 to _C9 resin, C9 resin, terpene resin, terpene-aromatic compound resin, rosin resin, dicyclopentadiene resin, and alkylphenol resin, and 20 to 120 parts by mass of a filler (C) containing silica, per 100 parts by mass of the rubber component, and in which the silica content in the filler (C) is 50 to 100% by mass (see, for example, Patent Document 1).

International Publication No. 2015/079703

However, although the rubber composition of Patent Document 1 can improve grip performance on wet road surfaces, there is room for improvement in terms of a high level balance between low rolling resistance and abrasion resistance.
The present invention aims to provide a tire tread and a tire having an improved balance of wet grip performance, low rolling resistance, and abrasion resistance, and a rubber composition for tires from which the tire tread and the tire can be obtained, and an object of the present invention is to achieve the above-mentioned object.

<1> A rubber composition for tires, comprising a rubber component including a conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine and a conjugated diene polymer B modified with a modifier including a compound represented by formula (1), and a filler.

In formula (1), R ¹ to R ⁸ are each independently an alkyl group having 1 to 20 carbon atoms; L ¹ and L ² are each independently an alkylene group having 1 to 20 carbon atoms; and n is an integer of 2 to 4.

<2> The rubber composition for tires according to <1>, wherein the conjugated diene-based polymer A modified with a functional group having a skeleton derived from hexamethyleneimine is one or more modified rubbers selected from the group consisting of polybutadiene rubber and styrene-butadiene copolymer rubber.
<3> The rubber composition for tires according to <1> or <2>, wherein the conjugated diene-based polymer A modified with a functional group having a skeleton derived from hexamethyleneimine is a modified rubber of a styrene-butadiene copolymer rubber.

<4> The rubber composition for a tire according to any one of <1> to <3>, wherein the filler contains carbon black.
<5> The rubber composition for a tire according to <4>, wherein the filler further contains silica, and a ratio of the silica to a total mass of the silica and the carbon black is 50% by mass or more and less than 100% by mass.

<6> A tire tread using the rubber composition for tires according to any one of <1> to <5>.
<7> A tire using the rubber composition for tires according to any one of <1> to <5>.

The present invention provides a tire tread and tire with an improved balance of wet grip performance, low rolling resistance, and abrasion resistance, as well as a rubber composition for tires from which the tire tread and tire are obtained.

<Rubber composition for tires>
The rubber composition for tires of the present invention contains a rubber component including a conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine and a conjugated diene polymer B modified with a modifier containing a compound represented by formula (1), and a filler.

In formula (1), R ¹ to R ⁸ are each independently an alkyl group having 1 to 20 carbon atoms; L ¹ and L ² are each independently an alkylene group having 1 to 20 carbon atoms; and n is an integer of 2 to 4.

Hereinafter, "conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine" may be referred to as "modified polymer A". Also, "conjugated diene polymer B modified with a modifying agent containing a compound represented by formula (1)" may be referred to as "modified polymer B". "Rubber composition for tires" may be simply referred to as "rubber composition".

The modified polymer A has the effect of improving the dispersibility of carbon black in the rubber composition, and the modified polymer B has the effect of improving the dispersibility of silica in the rubber composition. The type of filler contained in the rubber composition for tires of the present invention is not particularly limited, but carbon black and silica are generally used as fillers that reinforce the vulcanized rubber obtained from the rubber composition. It is believed that the rubber composition for tires of the present invention can improve the high balance of wet grip performance, low rolling resistance, and abrasion resistance of tire treads and tires by containing two types of modified copolymers that improve the dispersibility of various fillers.
The rubber composition and the pneumatic tire of the present invention will be described in detail below.

[Rubber component]
The rubber component contains a conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine, and a conjugated diene polymer B modified with a modifier containing a compound represented by formula (1).
The rubber component may further contain an unmodified conjugated diene-based polymer.

(Modified Polymer A)
The rubber component contains a conjugated diene polymer A (modified polymer A) modified with a functional group having a skeleton derived from hexamethyleneimine.
By containing the modified polymer A, the rubber component has high affinity for fillers, particularly carbon black, and improves the dispersibility of the filler in the rubber composition for tires, thereby enabling the tire tread and tire to have an excellent balance of wet grip performance, low rolling resistance, and abrasion resistance.
The phrase "modified with a functional group having a skeleton derived from hexamethyleneimine" means that the conjugated diene polymer is modified with a compound having a hexamethyleneimine skeleton. The modification site may be one end or both ends of the molecular chain of the conjugated diene polymer, or a side chain of the molecular chain.
Examples of compounds having a hexamethyleneimine skeleton include hexamethyleneimine, N-trimethylsilyl(hexamethyleneimin-2-yl)propyl(methyl)dimethoxysilane, and N-trimethylsilyl(hexamethyleneimin-2-yl)propyl(methyl)diethoxysilane. Of these, hexamethyleneimine (HMI) is preferred.

The conjugated diene polymer (unmodified conjugated diene polymer) modified with a compound having a hexamethyleneimine skeleton is not particularly limited, and examples of the conjugated diene polymer that can be used include natural rubber (NR), as well as synthetic rubbers such as polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), halogenated butyl rubber, and acrylonitrile-butadiene rubber (NBR).

The unmodified conjugated diene polymer may further contain a styrene-based thermoplastic elastomer.
Styrenic thermoplastic elastomers may include a diblock formed from a single styrene rigid segment bonded to a single diene flexible segment.
The diblock, which is composed of a single styrene rigid segment bonded to a single diene flexible segment, may be selected from the group including or consisting of styrene/butadiene (SB) block copolymers, styrene/isoprene (SI) block copolymers, styrene/butadiene/isoprene (SBI) block copolymers, and mixtures of these copolymers. In this indication, the diene flexible block is a random copolymer or a block copolymer.

The styrenic thermoplastic elastomer preferably comprises or consists of a styrenic thermoplastic elastomer containing at least two styrene rigid segments.More preferably, the styrenic thermoplastic elastomer mainly comprises a styrenic thermoplastic elastomer containing at least two styrene rigid segments.
When the styrene-based thermoplastic elastomer comprises at least two styrene rigid segments, generally, at least two chain ends of the styrene-based thermoplastic elastomer are provided with a styrene rigid segment, and the styrene rigid segments are bonded via the diene flexible segment(s).Preferably, the styrene-based thermoplastic elastomer comprising at least two styrene rigid segments is a triblock.In that case, the triblock is composed of two styrene rigid segments and one diene flexible segment.

The triblock consisting of two rigid styrene segments and one diene flexible segment may be selected from the group consisting of styrene/butadiene/styrene (SBS) block copolymers, styrene/isoprene/styrene (SIS) block copolymers, styrene/butadiene/isoprene/styrene (SBIS) block copolymers and mixtures of these copolymers. In this indication, the diene flexible block may be a random copolymer or a block copolymer. Preferably, the triblock consisting of two rigid styrene segments and one diene flexible segment is selected from the group consisting of styrene/isoprene/styrene (SIS) block copolymers, styrene/butadiene/isoprene/styrene (SBIS) block copolymers and mixtures of these copolymers; more preferably, the triblock consisting of two rigid styrene segments and a diene flexible segment is a styrene/isoprene/styrene (SIS) block copolymer.

In the case where the styrenic thermoplastic elastomer is a diblock, the reference "at least one rigid segment" refers to the rigid segment present in the styrenic thermoplastic elastomer. In the case where the styrenic thermoplastic elastomer is other than a diblock, such as a triblock, the reference "at least one rigid segment" refers to the rigid segment present in the styrenic thermoplastic elastomer.
If the styrenic thermoplastic elastomer is diblock or triblock, the reference "at least one flexible segment" refers to the flexible segment present in the styrenic thermoplastic elastomer. If the styrenic thermoplastic elastomer is not diblock or triblock, the reference "at least one flexible segment" refers to the flexible segment present in the thermoplastic styrenic elastomer.
A part of the diene units of the diene flexible segment may be hydrogenated. Alternatively, all of the diene units of the diene flexible segment may be hydrogenated. Those skilled in the art will understand that styrene-based thermoplastic elastomers in which some of the double bonds of the diene units of the diene flexible segment have been reduced to single bonds by methods other than hydrogenation may be used as well. Among the methods that allow the double bonds of the diene units to be reduced to single bonds, for example, reduction with aluminum hydride or diimine may be mentioned.

When all of the diene units of the diene flexible segments of the thermoplastic elastomer are hydrogenated, the diblock consisting of a single styrene rigid segment bonded to a single diene flexible segment can be selected from the group consisting of styrene/ethylene/butylene (SEB) block copolymers, styrene/ethylene/propylene (SEP) block copolymers, styrene/ethylene/ethylene/propylene (SEEP) block copolymers, and mixtures of these copolymers. In this indication, the flexible hydrogenated diene block is a random copolymer or a block copolymer.
When all of the diene units of the diene flexible segments of the thermoplastic elastomer are hydrogenated, the triblock consisting of two styrene rigid segments and one diene flexible segment can be selected from the group consisting of styrene/ethylene/butylene/styrene (SEBS) block copolymers, styrene/ethylene/propylene/styrene (SEPS) block copolymers, styrene/ethylene/ethylene/propylene/styrene (SEEPS) block copolymers and mixtures of these copolymers. In this indication, the flexible hydrogenated diene block is a random copolymer or a block copolymer.

The unmodified conjugated diene polymer used in the production of the modified polymer A may be one type or two or more types. For example, the modified polymer A may be a mixture of a modified rubber derived from unmodified natural rubber and a modified rubber derived from unmodified synthetic rubber.

Among these, from the viewpoint of further improving the balance between wet grip performance, low rolling resistance, and abrasion resistance of the tire tread and tire, polybutadiene rubber and styrene-butadiene copolymer rubber are preferred, and styrene-butadiene copolymer rubber is more preferred. In other words, the conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine is preferably one or more modified rubbers selected from the group consisting of polybutadiene rubber and styrene-butadiene copolymer rubber, and more preferably a modified rubber of styrene-butadiene copolymer rubber.

When modified polymer A is a modified rubber of styrene-butadiene copolymer rubber, the amount of bound styrene is preferably 20 to 50% by mass, more preferably 25 to 45% by mass, and even more preferably 30 to 40% by mass.

The bound styrene content of the modified polymer A can be measured as follows.
100 mg of the sample (modified polymer A) is dissolved in chloroform to prepare a measurement sample. Using a spectrophotometer, the amount of bound styrene (mass%) relative to 100 mass% of the sample is measured based on the amount of absorption of ultraviolet light at a wavelength (near 254 nm) by the phenyl group of styrene.
The amount of bound styrene in the modified polymer B described below may be measured in the same manner.

(Modified Polymer B)
The rubber component contains a conjugated diene polymer B (modified polymer B) modified with a modifier containing a compound represented by formula (1).
By containing modified polymer B, the rubber component has high affinity for fillers, particularly silica, and improves the dispersibility of the filler in the rubber composition for tires, thereby enabling an excellent balance of wet grip performance, low rolling resistance, and abrasion resistance of the tire tread and tire to be achieved.
The modified site may be one or both ends of the molecular chain of the conjugated diene polymer, or a side chain of the molecular chain.
The conjugated diene polymer in the modified polymer B can be modified, for example, according to the methods described in WO 2003/046020 and JP 2007-217562 A, by reacting various modifiers with the terminals of a conjugated diene polymer having an active terminal.

The conjugated diene polymer (unmodified conjugated diene polymer) modified with the modifying agent containing the compound represented by formula (1) is not particularly limited, and may be the same as the unmodified conjugated diene polymer used in the production of modified polymer A. Specifically, in addition to natural rubber, synthetic rubbers such as polybutadiene rubber (BR) and styrene-butadiene copolymer rubber (SBR); styrene-based thermoplastic elastomers, etc. may be used.
Among these, from the viewpoint of further improving the high balance of wet grip performance, low rolling resistance, and abrasion resistance of the tire tread and tire, polybutadiene rubber and styrene-butadiene copolymer rubber are preferred, and styrene-butadiene copolymer rubber is more preferred. In other words, the conjugated diene polymer B modified with a modifier containing a compound represented by formula (1) is preferably one or more modified rubbers selected from the group consisting of polybutadiene rubber and styrene-butadiene copolymer rubber, and more preferably a modified rubber of styrene-butadiene copolymer rubber.
Formula (1) is the following structure:

In formula (1), R ¹ to R ⁸ are each independently an alkyl group having 1 to 20 carbon atoms; L ¹ and L ² are each independently an alkylene group having 1 to 20 carbon atoms; and n is an integer of 2 to 4.

By using a conjugated diene polymer modified with a modifying agent containing a compound represented by formula (1) containing an oligosiloxane and a tertiary amino group, which are filler affinity functional groups, as the rubber component, the dispersibility of fillers such as silica in the rubber composition can be improved. As a result, tire treads and tires obtained from the tire rubber composition have a high level of balance between excellent wet grip performance, excellent low rolling resistance, and excellent abrasion resistance.

In formula (1), R ¹ to R ⁴ are each independently an alkyl group having 1 to 20 carbon atoms, and the number of carbon atoms in the alkyl group is preferably 1 to 10, and more preferably 1 to 6. The alkyl group may be linear, branched, or cyclic.
R ¹ to R ⁴ may each independently have a substituent or be unsubstituted.
Examples of the substituent include one or more substituents selected from the group consisting of an alkoxy group having 1 to 10 carbon atoms, a cycloalkoxy group having 4 to 10 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, an alkanoyloxy group having 2 to 12 carbon atoms (alkanoyloxy, R ^a COO ⁻ , where R ^a is an alkyl group having 1 to 9 carbon atoms), an aralkyloxy group having 7 to 13 carbon atoms, an arylalkyl group having 7 to 13 carbon atoms, and an alkylaryl group having 7 to 13 carbon atoms.

In formula (1), R ⁵ to R ⁸ are each independently an alkyl group having 1 to 20 carbon atoms, and the alkyl group preferably has 1 to 10 carbon atoms, and more preferably has 1 to 6 carbon atoms.
R ⁵ to R ⁸ may each independently have a substituent or may be unsubstituted. The substituents that R ⁵ to R ⁸ may have are the same as the substituents that R ¹ to R ⁴ may have.
When R ⁵ to R ⁸ are not alkyl groups but are hydrolyzable substituents, the bonds of N-R ⁵ R ⁶ and N-R ⁷ R ⁸ may be hydrolyzed to N-H in the presence of moisture, adversely affecting the processability of the modified polymer B and, in turn, the processability of the rubber composition for tires. For example, the viscosity of the modified polymer B may increase, which may increase the viscosity of other components, preventing the components in the rubber composition for tires from being mixed uniformly.

In addition, when R ⁵ to R ⁸ are not alkyl groups, but are protecting groups for protecting amino groups or are hydrogen atoms, the effect of the compound represented by formula (1) cannot be realized. When ^{R 5 to} R ⁸ are hydrogen atoms, the anions react with hydrogen during the modification process and lose reactivity, making the modification reaction itself impossible, and when R ⁵ to R ⁸ are protecting groups, the modification reaction takes place, but in the state bonded to the polymer end, they are deprotected by hydrolysis during post-processing to become primary or secondary amino groups, and the deprotected primary or secondary amino groups cause high viscosity of the compound during subsequent blending, resulting in reduced processability.

In the compound represented by formula (1), it is preferable that R ¹ to R ⁴ are each independently a methyl group or an ethyl group, and R ⁵ to R ⁸ are each independently an alkyl group having 1 to 10 carbon atoms.

In formula (1), L ¹ and L ² are each independently an alkylene group having 1 to 20 carbon atoms. The alkylene group may be linear, branched, or cyclic.
^L1 and ^L2 may each independently have a substituent or may be unsubstituted. The substituents that ^L1 and ^L2 may have are the same as the substituents that ^R1 to ^R4 may have.
L ¹ and L ² are each preferably an alkylene group having 1 to 10 carbon atoms, and more preferably an alkylene group having 1 to 6 carbon atoms.

Regarding L ¹ and L ² in formula (1), the closer the distance between the Si atom and the N atom in the molecule, the better the effect, so it is preferable that the carbon numbers of L ¹ and L ² are small. However, when the Si atom is directly bonded to the N atom, that is, when L ¹ and L ² are single bonds, there is a risk that the bond between the Si atom and the N atom will be broken during the subsequent processing steps. The secondary amino group generated at this time is likely to be washed away by water during the post-treatment. In such a modified polymer modified by a compound in which the Si atom is directly bonded to the N atom, it is difficult to bond with the silica filler due to the amino group member that promotes the bond with the silica filler, and as a result, the dispersion effect of the filler cannot be obtained. In this way, considering the improvement effect due to the length of the bond between the Si atom and the N atom, it is more preferable that L ¹ and L ² are each independently an alkylene group having 1 to 3 carbon atoms such as a methylene group, an ethylene group, or a propylene group, and even more preferably a propylene group.

In formula (1), n is an integer from 2 to 4. If n is less than 2, the number of amino groups in one molecule is small, making it impossible to sufficiently improve low rolling resistance, and if n is more than 4, the number of polymer chains that react with one molecule increases, reducing the number of modified groups per polymer chain, making it impossible to sufficiently improve low rolling resistance. It is preferable that n is 2 to 4.

The compound represented by formula (1) is preferably any one of the compounds represented by the following formulas (1a) to (1e). By using modified polymer B modified with these compounds, the low rolling resistance of the tire tread and tire can be further improved.

The compound represented by formula (1) has an alkoxysilane structure that bonds with the activated end of the conjugated diene polymer, while the Si-O-Si structure and three or more amino groups bonded to the end show affinity for fillers such as silica, and thus can promote the bonding between the filler and the modified polymer B compared to conventional modifiers containing one amino group in the molecule. In addition, the degree of bonding of the activated end of the conjugated diene polymer is uniform, and when the change in molecular weight distribution is observed before and after coupling, the molecular weight distribution is constant after coupling without increasing compared to before. Therefore, there is no deterioration in the physical properties of the modified polymer B itself, and the aggregation of the filler in the rubber composition for tires can be prevented, and the dispersibility of the filler can be increased, thereby improving the processability of the rubber composition for tires. As a result, the tire tread and tire can be further improved in a high balance of excellent wet grip performance, low rolling resistance, and abrasion resistance.

The compound represented by formula (1) can be produced through a condensation reaction represented by the following reaction scheme 1.

In reaction formula 1, R ¹ to R ⁸ , L ¹ , L ² , and n are the same as R ¹ to R ⁸ , L ¹ , L ² , and n in the above formula (1), and R' and R'' are any substituents that do not affect the condensation reaction. For example, R' and R'' can each independently be the same as any one of R ¹ to R ⁴ .

The reaction of Reaction Scheme 1 is carried out under acidic conditions, and any acid generally used in condensation reactions can be used without limitation. Those skilled in the art can select the most suitable acid depending on various process variables such as the type of reactor in which the reaction is carried out, the starting materials, and the reaction temperature.

When the modified polymer B is a polymer modified at both ends with alkoxysilane, for example, SBR modified at both ends with alkoxysilane, the glass transition point (Tg) is preferably about −45° C. to −15° C. The high Tg of the SBR modified at both ends with alkoxysilane increases the affinity with the filler, and better dispersibility of the filler can be obtained.
Furthermore, when the modified polymer B is a one-terminated alkoxysilane-modified polymer, for example, one-terminated alkoxysilane-modified SBR, the glass transition point (Tg) is preferably about −60° C. to −30° C. When the one-terminated alkoxysilane-modified SBR is at a moderate level, the high level of balance between wet grip performance, low rolling resistance, and abrasion resistance can be further improved.

The glass transition point (Tg) of the modified polymer B can be measured as follows.
Using a TA Instruments DSC250, a DSC curve is recorded while heating a sample (modified polymer B) 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 glass transition point (Tg) of the modified polymer B described below may be measured in the same manner.

When modified polymer B is a modified rubber of styrene-butadiene copolymer rubber, the amount of bound styrene is preferably 25 to 55 mass%, more preferably 30 to 50 mass%, and even more preferably 35 to 45 mass%.

The modified polymer B may have a narrow molecular weight distribution: Mw/Mn (also called polydispersity index (PDI or MWD)) of 1.1 to 3.0. By making the molecular weight distribution of the modified polymer B 1.1 to 3.0, it is possible to suppress the deterioration of the tensile properties and viscoelasticity when applied to a rubber composition. Considering the remarkable effect of improving the tensile properties and viscoelasticity of the polymer by controlling the molecular weight distribution of the modified polymer B, it is preferable to make the molecular weight distribution of the modified polymer B 1.3 to 2.0.

The molecular weight distribution of the modified polymer B can be calculated from the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the logarithm average molecular weight (Mn). In this case, the number average molecular weight (Mn) is the common average of the molecular weights of individual polymers calculated by measuring the molecular weights of n polymer molecules, calculating the sum of these molecular weights, and dividing by n, and the weight average molecular weight (Mw) represents the molecular weight distribution of the polymer composition. The average of the total molecular weight can be expressed in grams per mole (g/mol).
In the present invention, the weight average molecular weight and the number average molecular weight are each a polystyrene-equivalent molecular weight analyzed by gel permeation chromatography (GPC).

Modified polymer B satisfies the above-mentioned molecular weight distribution conditions, and at the same time, the number average molecular weight (Mn) is preferably 50,000 g/mol to 2,000,000 g/mol, and more preferably 200,000 g/mol to 800,000 g/mol. Modified polymer B preferably has a weight average molecular weight (Mw) of 100,000 g/mol to 4,000,000 g/mol, and more preferably 300,000 g/mol to 1,500,000 g/mol.

The weight average molecular weight (Mw) of the modified polymer B is 100,000 g/mol or more, and the number average molecular weight (Mn) is 50,000 g/mol or more, so that the deterioration of the tensile properties of the vulcanized rubber obtained from the rubber composition for tires can be suppressed. Also, the weight average molecular weight (Mw) is 4,000,000 g/mol or less, and the number average molecular weight (Mn) is 2,000,000 g/mol or less, so that the deterioration of the processability of the modified polymer B and the deterioration of the workability of the rubber composition can be suppressed, and therefore the physical properties of the rubber composition can be sufficiently improved.
When the modified polymer B simultaneously satisfies the conditions of weight average molecular weight (Mw) and number average molecular weight (Mn) as well as the molecular weight distribution, when a tire tread and a tire are produced from the rubber composition for tires, the tire tread and the tire can have a high level of balance between wet grip performance, low rolling resistance, and abrasion resistance.

The modified polymer B preferably has a Mooney viscosity (MV) at 100° C. of 40 to 140, more preferably 60 to 100. By having a Mooney viscosity in this range, the modified polymer B exhibits superior processability.
In the present invention, the Mooney viscosity can be measured using a Mooney viscometer, for example, Monsanto's MV2000E, with a rotor speed of 20.02 rpm and a large rotor at 100° C. The sample used here is left at room temperature (23±3° C.) for 30 minutes or more, and then 27±3 g of the sample is taken and filled into the die cavity, and the platen is operated to measure the viscosity.

In addition, when the modified polymer B is a one-terminated alkoxysilane modified polymer, one end is modified with a modifying agent containing a compound represented by formula (1), but the other end can also be further modified with a modifying agent containing a compound represented by formula (3). This can further improve the dispersibility of the filler in the rubber composition, thereby further improving the high level balance of wet grip performance, low rolling resistance, and abrasion resistance.

In formula (3), R ¹ to R ³ are each independently a hydrogen atom; an alkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms, a heteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30 carbon atoms.
R ⁴ is a single bond; an alkylene group having 1 to 20 carbon atoms; or an arylene group having 5 to 20 carbon atoms.
The alkylene group may be linear, branched, or cyclic. ^R4 may further have a substituent or may be unsubstituted.
For example, the alkylene group may further have an aryl group having 6 to 20 carbon atoms as a substituent, and the arylene group may further have an alkyl group having 1 to 10 carbon atoms as a substituent.
^R5 is an alkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic group having 3 to 30 carbon atoms; or a functional group represented by the following formula (3a) or formula (3b).
n is an integer from 1 to 5.
At least one of R ⁵ is a functional group represented by formula (3a) or formula (3b), and when n is an integer of 2 to 5, the multiple R _5s may be the same or different.

In formula (3a), ^R6 is an alkylene group having 1 to 20 carbon atoms; or an arylene group having 5 to 20 carbon atoms. The alkylene group may be linear, branched, or cyclic. ^R6 may further have a substituent or may be unsubstituted.
For example, the alkylene group may further have an aryl group having 6 to 20 carbon atoms as a substituent, and the arylene group may further have an alkyl group having 1 to 10 carbon atoms as a substituent.
R ⁷ and R ⁸ are each independently an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, or an alkylene group having 1 to 20 carbon atoms which is substituted or unsubstituted with an aryl group having 6 to 20 carbon atoms; R ⁹ is hydrogen; an alkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30 carbon atoms; X is an N atom, an O atom, or an S atom; and when X is an O atom or an S atom, R ⁹ does not exist.

In the above formula (3b), R ¹⁰ is an alkylene group having 1 to 20 carbon atoms; or an arylene group having 5 to 20 carbon atoms. The alkylene group may be linear, branched, or cyclic. R ¹⁰ may further have a substituent or may be unsubstituted.
For example, the alkylene group may further have an aryl group having 6 to 20 carbon atoms as a substituent, and the arylene group may further have an alkyl group having 1 to 10 carbon atoms as a substituent.
R ¹¹ and R ¹² are each independently an alkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30 carbon atoms.

In addition, in the compound represented by the above formula (3),
R ¹ to R ³ are each independently a hydrogen atom; an alkyl group having 1 to 10 carbon atoms; an alkenyl group having 2 to 10 carbon atoms; or an alkynyl group having 2 to 10 carbon atoms;
R ⁴ is a single bond; or an unsubstituted alkylene group having 1 to 10 carbon atoms;
^R5 is an alkyl group having 1 to 10 carbon atoms; an alkenyl group having 2 to 10 carbon atoms; an alkynyl group having 2 to 10 carbon atoms; or a functional group represented by formula (3a) or formula (3b),
In formula (3a),
^R6 is an unsubstituted alkylene group having 1 to 10 carbon atoms;
R ⁷ and R ⁸ each independently represent an unsubstituted alkylene group having 1 to 10 carbon atoms;
R ⁹ is an alkyl group having 1 to 10 carbon atoms; a cycloalkyl group having 5 to 20 carbon atoms; an aryl group having 6 to 20 carbon atoms; or a heterocyclic group having 3 to 20 carbon atoms;
In formula (3b),
R ¹⁰ is an unsubstituted alkylene group having 1 to 10 carbon atoms;
R ¹¹ and R ¹² may each independently be an alkyl group having 1 to 10 carbon atoms; a cycloalkyl group having 5 to 20 carbon atoms; an aryl group having 6 to 20 carbon atoms; or a heterocyclic group having 3 to 20 carbon atoms.

Furthermore, the compound represented by the above formula (3) can be a compound represented by the following formulas (3-1) to (3-3).

In addition, when the styrene-butadiene copolymer rubber is modified with a modifying agent containing the compound represented by formula (3), the modifying agent containing the compound represented by formula (3) is used as a modification initiator.
Specifically, for example, a butadiene monomer and a styrene monomer are polymerized in a hydrocarbon solvent in the presence of a modifying agent containing the compound represented by formula (3), whereby a modifying group derived from the compound represented by formula (3) can be imparted to a styrene-butadiene copolymer rubber.

(Other rubber components)
The rubber component may further contain a rubber component other than the modified polymer A and the modified polymer B.
The other rubber components are not particularly limited, and may be the same as the unmodified conjugated diene polymer used in the production of the modified polymer A. Specifically, in addition to natural rubber, synthetic rubbers such as polybutadiene rubber (BR) and styrene-butadiene copolymer rubber (SBR) and the like; styrene-based thermoplastic elastomers, etc. may be used.
Among these, from the viewpoint of further improving the balance between the wet grip performance, low rolling resistance, and abrasion resistance of the tire tread and tire, it is preferable that the other rubber component is a natural rubber.
The rubber component may be one of the modified polymer A, the modified polymer B, and the other rubber component, or two or more of them may be used in combination.

The content of the modified polymer A in the rubber composition is preferably 20 to 70 mass %, and more preferably 30 to 60 mass %, from the viewpoint of improving the dispersibility of carbon black in the rubber composition.
The content of the modified polymer B in the rubber composition is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass, from the viewpoint of improving the dispersibility of silica in the rubber composition.
From the viewpoint of further improving the balance between wet grip performance, low rolling resistance, and abrasion resistance of the tire tread and tire, it is preferable that the total of the modified polymer A and the modified polymer B is the main component (amount exceeding 50 mass%) in the rubber component. Specifically, the total content of the modified polymer A and the modified polymer B in the rubber composition is preferably 51 to 100 mass%, more preferably 60 to 100 mass%.

The ratio b/a of the mass a of modified polymer A to the mass b of modified polymer B varies depending on the type of filler used, and may be 1<b/a, b/a=1, or b/a<1. b/a may be 5/95 or more.

[Filler]
The rubber composition for tires of the present invention contains a filler.
When the rubber composition for tires contains a filler, the vulcanized rubber, tire tread and tire obtained from the rubber composition for tires have low rolling resistance and excellent abrasion resistance.
The filler is not particularly limited, and for example, a reinforcing filler that reinforces the rubber composition for tires is used. Examples of the reinforcing filler include silica, carbon black, etc., and either silica or carbon black may be used alone, or both silica and carbon black may be used.
From the viewpoint of further improving the low rolling resistance and abrasion resistance of the tire tread and the tire, it is preferable that the filler contains carbon black.
In order to further improve the low rolling resistance and abrasion resistance of the tire tread and the tire, it is preferable that the filler further contains silica, and the ratio of silica to the total mass of silica and carbon black is 50 mass% or more and less than 100 mass%. Hereinafter, the "ratio of silica to the total mass of silica and carbon black" may be referred to as the "silica ratio".
The silica percentage is more preferably from 60 to 99 mass %, and further preferably from 70 to 99 mass %.

(Carbon Black)
The carbon black is not particularly limited and can be appropriately selected depending on the purpose. For example, the carbon black is preferably FEF, SRF, HAF, ISAF, or SAF grade, and more preferably HAF, ISAF, or SAF grade.

(silica)
The silica is not particularly limited, and may be any type depending on the application, such as general-grade silica, special silica that has been surface-treated with a silane coupling agent, etc. As the silica, it is preferable to use, for example, wet silica.
When the filler contains silica, it may further contain a silane coupling agent.

The content of the filler in the rubber composition for tires of the present invention is preferably 30 to 80 parts by mass, and more preferably 40 to 70 parts by mass, per 100 parts by mass of the rubber component.
When the content of the filler in the rubber composition is 30 parts by mass or more per 100 parts by mass of the rubber component, the abrasion resistance of the obtained vulcanized rubber is excellent, and when the content is 80 parts by mass or less, the flexibility of the obtained vulcanized rubber is not easily impaired, and the wet grip performance of the tire tread and tire is excellent.

In addition to the above components, the rubber composition of the present invention may contain compounding agents commonly used in the rubber industry, such as vulcanizing agents, stearic acid, antioxidants, zinc oxide (zinc oxide), vulcanization accelerators, softeners, etc., as necessary, selected appropriately within the scope that does not impair the purpose of the present invention.

When the rubber composition for tires contains a softener (oil component, resin), the wet grip performance of the tire tread and the tire can be further improved.
Examples of the resin include C5 resin, C9 resin, C5C9 resin, dicyclopentadiene resin, rosin resin, alkylphenol resin, terpene phenol resin, etc. These resins may be hydrogenated or modified.
These resins may be used alone or in combination of two or more.

[C5 resin, C9 resin, C5C9 resin]
C5 resin refers to a C5 synthetic petroleum resin, and refers to a solid polymer obtained by polymerizing a C5 fraction using a Friedel-Crafts type catalyst such as AlCl ₃ or BF _3. Specific examples include copolymers mainly composed of isoprene, cyclopentadiene, 1,3-pentadiene and 1-pentene, copolymers of 2-pentene and dicyclopentadiene, and polymers mainly composed of 1,3-pentadiene.
The C9 resin refers to a C9 synthetic petroleum resin, and is a solid polymer obtained by polymerizing a C9 fraction using a Friedel-Crafts catalyst such as AlCl ₃ or BF _3. Specific examples include copolymers mainly composed of indene, methylindene, α-methylstyrene, vinyltoluene, etc.
C5C9 resin refers to C5 to C9 synthetic petroleum resin, and refers to a solid polymer obtained by polymerizing a C5 to C9 fraction using a Friedel-Crafts type catalyst such as AlCl ₃ or BF _3. Examples include copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc.

[Dicyclopentadiene resin, rosin resin]
Dicyclopentadiene resins are petroleum resins that use dicyclopentadiene in the C5 fraction as the main raw material. For example, Maruzen Petrochemical Co., Ltd.'s "Marukaretzu M" series (M-890A, M-845A, M-990A, etc.) can be mentioned.
Rosin-based resins include natural resin rosins such as gum rosin, tall oil rosin, and wood rosin contained in raw pine resin and tall oil, etc. In addition, modified rosins, rosin derivatives, and modified rosin derivatives include, for example, polymerized rosin, partially hydrogenated rosin thereof, glycerin ester rosin, partially hydrogenated rosin thereof, and fully hydrogenated rosin thereof, pentaerythritol ester rosin, partially hydrogenated rosin thereof, and polymerized rosin, etc.

[Alkylphenol resin, terpene phenol resin]
The alkylphenol resin refers to a phenol resin having an alkyl group.
For example, alkylphenol-acetylene resins such as p-tert-butylphenol-acetylene resin, and alkylphenol-formaldehyde resins having a low degree of polymerization can be used.
Terpene phenol resins are resins that can be obtained by reacting terpenes with various phenols using a Friedel-Crafts catalyst, or by further condensing them with formalin. There are no particular limitations on the terpenes used as raw materials, but monoterpene hydrocarbons such as α-pinene and limonene are preferred, those containing α-pinene are more preferred, and α-pinene is particularly preferred.

The amount of resin contained in the rubber composition for tires is not particularly limited, but from the viewpoint of improving the processability of the rubber composition for tires and the braking performance of the tire without deteriorating the abrasion resistance and reinforcement properties, the amount is preferably 2 to 10 parts by mass, and more preferably 3 to 8 parts by mass, per 100 parts by mass of the rubber component.

The rubber composition can be produced by blending the components including the rubber component and the filler, and kneading the blend using a kneading machine such as a Banbury mixer, a roll, or an internal mixer.
The kneading of each component may be performed in one stage or in two or more stages. When the kneading is performed in two or more stages, it is preferable to knead components that do not easily contribute to the vulcanization or vulcanization acceleration of the rubber component, such as the rubber component, filler, antioxidant, etc., in a stage before the final stage, and further compound and knead components that vulcanize the rubber component and accelerate vulcanization in the final stage. The kneading of components that do not easily contribute to the vulcanization or vulcanization acceleration of the rubber component may be further divided into two or more stages.
When kneading is performed in two stages, the maximum temperature in the first stage of kneading is preferably 140 to 160°C, and the maximum temperature in the second stage is preferably 90 to 120°C.

<Tire tread and tires>
The tire tread and tire of the present invention are made using the rubber composition for tires of the present invention. That is, the rubber composition for tires of the present invention is suitable as a rubber composition for tire treads.
It is preferable to produce a tire tread using the rubber composition for tires of the present invention, and then produce a tire having the tire tread.
The tire tread and tire of the present invention use the rubber composition for tires of the present invention having the above-mentioned configuration, and therefore exhibit an excellent balance of excellent wet grip performance, low rolling resistance, and abrasion resistance.
Depending on the type and components of the tire to be applied, a tire may be obtained by molding an unvulcanized rubber composition for tires and then vulcanizing the molded product, or by first obtaining a semi-vulcanized rubber from an unvulcanized rubber composition for tires through a pre-vulcanization step or the like, and then molding the rubber using the semi-vulcanized rubber and then vulcanizing the rubber.
For example, the rubber composition for tires of the present invention containing various components is processed into a tire tread in an unvulcanized state, and then the tread is attached and molded in a tire building machine by a normal method to form a green tire. The green tire is then heated and pressurized in a vulcanizer to obtain a tire.

The present invention will be described in more detail below with reference to examples. However, these examples are intended to illustrate the present invention and are not intended to limit the present invention in any way.

<Preparation of Rubber Composition>
[Comparative Example 1, Examples 1 and 2]
The components were blended and kneaded according to the blending ratio in Table 1 to obtain rubber compositions of Comparative Example 1 and Examples 1 and 2. In the table, a blank cell indicates that the blending amount was 0 parts by mass.
Details of the components in the table are as follows:

(Rubber component)
NR: Natural rubber, unmodified SBR: Unmodified styrene-butadiene copolymer rubber, manufactured by JSR Corporation, product name "JSR1500", bound styrene content = 24% by mass
Modified polymer A: A conjugated diene polymer modified with a functional group having a skeleton derived from hexamethyleneimine. Based on the method for producing polymer K described in JP-A-2007-70642, this is a hexamethyleneimine-modified SBR produced using a blend of styrene and butadiene monomers in different ratios, with a bound styrene content of 35% by mass and a vinyl bond content of 21% in the butadiene portion.
Modified polymer B: a conjugated diene polymer modified with a modifying agent containing a compound represented by formula (1) produced in Production Example 1 below, bound styrene content = 41% by mass

(fillers, etc.)
Carbon black: ISAF-HS grade, manufactured by Asahi Carbon Co., Ltd., product name "Asahi #78"
Silica: "NipSil (registered trademark) AQ" manufactured by Tosoh Silica Corporation, CTAB specific surface area = 165 m ² /g, BET specific surface area = 195 m ² /g
Silane coupling agent: silane coupling agent manufactured by Evonik, product name "Si363"

(Softeners, etc.)
Oil: Sankyo Yuka Kogyo Co., Ltd., product name "A/O Mix"
Anti-aging agent package: Includes product name "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization package: Contains sulfur, zinc oxide, and Sansera D (trade name) manufactured by Sanshin Chemical Industry Co., Ltd.

[Measurement of polymer properties]
The glass transition temperature (Tg), bound styrene content, vinyl bond content, weight average molecular weight and molecular weight distribution of the modified polymer were measured as follows.

(1) Glass transition temperature (Tg)
Using a TA Instruments DSC250, a DSC curve was recorded while heating the sample 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 was determined as the glass transition temperature.

(2) Bound styrene content 100 mg of a sample was dissolved in chloroform to make a measurement sample. The bound styrene content (mass%) relative to 100 mass% of the sample was measured based on the amount of ultraviolet light absorbed by the phenyl group of styrene (near 254 nm) (Shimadzu Corporation spectrophotometer "UV-2450").

The amount of bound styrene in unmodified SBR is the value given in the manufacturer's catalogue.

(3) Amount of Vinyl Bond in Butadiene Moiety 50 mg of a sample was dissolved in 10 mL of carbon disulfide to prepare a measurement sample.
Using a solution cell, an infrared spectrum was measured in the range of 600 to 1000 cm ^-1 , and the microstructure of the butadiene portion, i.e., the amount of 1,2-vinyl bonds, was determined from the absorbance at a predetermined wave number according to the calculation formula of the Hampton method (the method described in R.R. Hampton, Analytical Chemistry 21, 923 (1949)) (Fourier transform infrared spectrophotometer "FT-IR230" manufactured by JASCO Corporation).

(4) Molecular Weight Chromatograms were measured using a GPC measuring device (manufactured by Tosoh Corporation under the trade name "HLC-8320GPC") in which three columns packed with polystyrene gel were connected, and an RI detector (manufactured by Tosoh Corporation under the trade name "HLC8020"). The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) were determined based on a calibration curve obtained using standard polystyrene.
The eluent used was THF (tetrahydrofuran) containing 5 mmol/L triethylamine. Three columns, trade name "TSKgel SuperMultiporeHZ-H" manufactured by Tosoh Corporation, were connected, and a guard column, trade name "TSKguardcolumn SuperMP(HZ)-H" manufactured by Tosoh Corporation, was connected to the front stage. 10 mg of the sample for measurement was dissolved in 10 mL of THF to prepare a measurement solution, and 10 μL of the measurement solution was injected into the GPC measurement device and measured under conditions of an oven temperature of 40° C. and a THF flow rate of 0.35 mL/min.

2. Production Example 1 (Production Example of Modified Polymer B)
(1) Preparation of Unmodified SBR Into the first reactor of a continuous reactor having three reactors connected in series, a styrene solution in which styrene was dissolved at 60 mass% in n-hexane was injected at a rate of 7.99 kg/h, a 1,3-butadiene solution in which 1,3-butadiene was dissolved at 60 mass% in n-hexane was injected at a rate of 10.55 kg/h, n-hexane at 49.11 kg/h, a 1,2-butadiene solution in which 1,2-butadiene was dissolved at 2.0 mass% in n-hexane was injected at a rate of 40 g/h, a solution in which 2,2-(di-2(tetrahydrofuryl)propane was dissolved at 10 mass% in n-hexane as a polar additive was injected at a rate of 51.0 g/h, and an n-butyllithium solution in which n-butyllithium was dissolved at 10 mass% in n-hexane was injected at a rate of 59.0 g/h. At this time, the temperature of the first reactor was maintained at 50° C.
Then, a 1,3-butadiene solution in which 1,3-butadiene is dissolved in n-hexane at a concentration of 60% by mass is injected into the second reactor at a rate of 0.95 kg/h, while maintaining the temperature of the second reactor at 65°C.
The polymer is transferred from the second reactor to the third reactor, and a solution of dichlorodimethylsilane as a coupling agent is added to the third reactor (coupling agent: act. Li = 1: 1 mol). Then, the temperature of the third reactor is maintained at 65°C.
Then, a solution of IR1520 (BASF) dissolved at 30 mass% as an antioxidant is injected at a rate of 167 g/h into the polymerization solution discharged from the third reactor and stirred. The resulting polymer is put into hot water heated with steam and stirred to remove the solvent, thereby obtaining unmodified SBR.
Furthermore, the microstructure of the resulting unmodified SBR was measured to find that the styrene content was 41% by mass, the vinyl bond amount in the butadiene portion was 45%, the weight average molecular weight Mw was 440,000, and the molecular weight distribution MWD was 1.6.

(2) Example of preparation of modified initiator Two vacuum-dried 4 L stainless steel pressure vessels are prepared. 944 g of cyclohexane, 161 g of the compound represented by the following formula (3-1) , and 86 g of tetramethylethylenediamine are charged into the first pressure vessel to prepare a first reaction solution. At the same time, 318 g of liquid 20% by mass n-butyllithium and 874 g of cyclohexane are charged into the second pressure vessel to prepare a second reaction solution. At this time, the molar ratio of the compound represented by the following formula (3-1), n-butyllithium, and tetramethylethylenediamine is 1:1:1. With the pressure of each pressure vessel maintained at 7 bar, the first reaction solution is injected into the first continuous channel at an injection rate of 1.0 g/min, and the second reaction solution is injected into the second continuous channel at an injection rate of 1.0 g/min using a mass flow meter. At this time, the temperature of the continuous reactor is maintained at -10°C, the internal pressure is maintained at 3 bar using a back pressure regulator, and the residence time in the reactor is adjusted to within 10 minutes. The reaction is terminated to obtain a modified initiator.

(3) Production Example of Modified Polymer B Into the first reactor of the continuous reactor in which three reactors are connected in series, styrene solution in which styrene is dissolved at 60% by mass in n-hexane is 7.99 kg/h, 1,3-butadiene solution in which 1,3-butadiene is dissolved at 60% by mass in n-hexane is 10.55 kg/h, n-hexane is 47.66 kg/h, 1,2-butadiene solution in which 1,2-butadiene is dissolved at 2.0% by mass in n-hexane is 10 g/h, a solution in which 2,2-(di-2(tetrahydrofuryl)propane is dissolved at 10% by mass in n-hexane as a polar additive is 10.0 g/h, and the modified initiator prepared in the above Preparation Example is 292.50 g/h. At this time, the temperature of the first reactor is maintained at 50° C., and when the polymerization conversion rate reaches 43%, the polymer is transferred from the first reactor to the second reactor through the transfer pipe.
Subsequently, a 1,3-butadiene solution in which 1,3-butadiene is dissolved in n-hexane at a concentration of 60% by mass is injected into the second reactor at a rate of 0.95 kg/h. At this time, the temperature of the second reactor is maintained at 65° C., and when the polymerization conversion rate reaches 95% or more, the polymer is transferred from the second reactor to the third reactor through the transfer pipe.
The polymer is transferred from the second reactor to the third reactor, and a solution of the following formula (1a) is added as a modifier to the third reactor (modifier: act. Li=1:1 mol). The temperature of the third reactor is maintained at 65° C.

Then, a solution of IR1520 (BASF) dissolved at 30% by mass as an antioxidant is injected into the polymerization solution discharged from the third reactor at a rate of 170 g/h and stirred. The resulting polymer is placed in hot water heated with steam and stirred to remove the solvent, yielding modified polymer B with both ends modified.

<Evaluation>
Vulcanized rubber was obtained from each of the rubber compositions of Comparative Example 1 and Examples 1 and 2. The obtained vulcanized rubber was evaluated for the following performance properties. The evaluation results are shown in Table 1.

(1) Low rolling resistance Using a viscoelasticity measuring device [manufactured by Ueshima Seisakusho Co., Ltd.], the loss tangent (tan δ) of the vulcanized rubber was measured at a temperature of 50°C, an initial strain of 2%, a dynamic strain of 1%, and a frequency of 52 Hz. A relative evaluation was performed with the reciprocal of tan δ of the evaluation result of Comparative Example 1 taken as 100. The larger the index, the lower the rolling resistance, which means that the low rolling resistance of the tire obtained from the vulcanized rubber is excellent.

(2) Wet grip performance (braking performance on wet roads)
Using a viscoelasticity measuring device [manufactured by Ueshima Seisakusho Co., Ltd.], the loss tangent (tan δ) of the vulcanized rubber was measured at a temperature of 0°C, an initial strain of 2%, a dynamic strain of 1%, and a frequency of 52 Hz. The loss tangent (tan δ) of the evaluation result of Comparative Example 1 was set to 100, and a relative evaluation was performed. The higher the index, the better the wet grip property.

(3) Abrasion resistance The vulcanized rubber was processed into a JIS dumbbell-shaped No. 3 test piece, and a tensile test was carried out at 25°C in accordance with JIS K 6251:2004 to measure the elongation at break (Eb) and tensile stress at break (TSb). The toughness (TF) was calculated using the following formula, and the abrasion resistance index was also calculated. The larger the abrasion resistance index, the more excellent the vulcanized rubber is in rigidity and abrasion resistance.
Toughness (TF) = Elongation at break (Eb) x Tensile stress at break (TSb)
Abrasion resistance index={(TF of each test piece)/(TF of test piece of Comparative Example 1)}×100

As can be seen from Table 1, in the examples, the indices of low rolling resistance, wet grip performance and abrasion resistance are all greater than 100. This means that if tire treads and tires are manufactured using the rubber compositions of the examples, they will have excellent wet grip performance, low rolling resistance and abrasion resistance.
In addition, the average index values of the wet grip performance, low rolling resistance, and abrasion resistance each exceed 100, and it is evident that the tire treads and tires obtained from the rubber compositions of the examples can achieve a highly improved balance of wet grip performance, low rolling resistance, and abrasion resistance.

According to the present invention, it is possible to provide a rubber composition for tires that can be used to produce tire treads and tires that are excellent in wet grip performance, low rolling resistance, and abrasion resistance. In addition, according to the present invention, it is possible to provide tire treads and tires that are excellent in wet grip performance, low rolling resistance, and abrasion resistance.

Claims (7)

a rubber component comprising a conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine and a conjugated diene polymer B modified with a modifier containing a compound represented by formula (1);
and a filler.

[In formula (1), R ¹ to R ⁸ are each independently an alkyl group having 1 to 20 carbon atoms; L ¹ and L ² are each independently an alkylene group having 1 to 20 carbon atoms; and n is an integer of 2 to 4.] The rubber composition for tires according to claim 1, wherein the conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine is one or more modified rubbers selected from the group consisting of polybutadiene rubber and styrene-butadiene copolymer rubber. The rubber composition for tires according to claim 1 or 2, wherein the conjugated diene polymer A modified with a functional group having a skeleton derived from hexamethyleneimine is a modified rubber of a styrene-butadiene copolymer rubber. The rubber composition for tires according to any one of claims 1 to 3, wherein the filler contains carbon black. The rubber composition for tires according to claim 4, wherein the filler further contains silica, and the ratio of the silica to the total mass of the silica and the carbon black is 50% by mass or more and less than 100% by mass. A tire tread using the rubber composition for tires according to any one of claims 1 to 5. A tire using the rubber composition for tires according to any one of claims 1 to 5.