Rubber composition for tire tread, and tire

Abstract

A rubber composition for a tire tread, said composition comprising a rubber component (A) and a filler (B), wherein: the filler (B) contains recovered carbon black; and when the recovered carbon black is measured with a grind gauge, at least three lines are confirmed to have a length of at least 10 mm, and the particle size of the third-largest particles among particles producing the lines having a length of at least 10 mm is at most 20 μm.

Description

Rubber composition for tire treads, and tires

[0001] This invention relates to a rubber composition for tire treads and to tires.

[0002] Tire treads require particularly high wear resistance, and performance is being improved by optimizing the materials used in tread manufacturing.

[0003] For example, Patent Document 1 discloses that wear resistance can be improved by blending predetermined amounts of a reinforcing filler such as carbon black, a tetrazine-based compound, and a hydrocarbon resin with a predetermined rubber component.

[0004] International Publication No. 2018 / 190427

[0005] Incidentally, in recent years, from the perspective of social sustainability, there has been a demand for the use of so-called sustainable materials in businesses and products, such as materials derived from biological resources (biomass resources) and materials derived from recycled resources. There is also a demand to increase the proportion of sustainable materials (hereinafter sometimes referred to as the "sustainability rate") in the various components used in tires. For example, recycled carbon black is known as a material derived from recycled resources.

[0006] Here, if conventional recycled carbon black is used as a filler in the tread rubber instead of unused carbon black in order to increase the proportion of sustainable materials in the tire, there is a risk that other tire rubber properties other than wear resistance (e.g., crack resistance after thermal degradation, high-temperature tensile strength after degradation) may deteriorate.

[0007] Therefore, the present invention aims to provide a rubber composition for tire treads that, compared to conventional methods using recycled carbon black, contributes to improved sustainability while minimizing adverse effects on tire rubber properties and maintaining performance. Furthermore, the present invention aims to provide a tire that maintains tire performance while increasing the proportion of sustainable materials.

[0008] In other words, the gist of the present invention that solves the above problems is as follows.

[0009] [1] A rubber composition for tire treads comprising a rubber component (A) and a filler (B), wherein the filler (B) contains recycled carbon black, and the recycled carbon black is such that, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

[0010] [2] The tire tread rubber composition according to [1], wherein, in the measurement of the recycled carbon black using a grind gauge, a paste of the recycled carbon black is prepared as a measurement sample in accordance with JIS K5101-1-5.

[0011] [3] The tire tread rubber composition according to [1] or [2], wherein, in the measurement of the recycled carbon black using a grind gauge, the recycled carbon black paste is prepared as a measurement sample by setting the applied load to 0.4 to 0.5 kN and the rotation speed of the glass plate to 90 to 110 r / min in accordance with JIS K5101-1-5.

[0012] [4] The tire tread rubber composition according to any one of [1] to [3], wherein the recycled carbon black comprises one or more selected from the group consisting of Zn, Fe, and Cu.

[0013] [5] The tire tread rubber composition according to any one of [1] to [4], wherein the recycled carbon black comprises Zn.

[0014] [6] The tire tread rubber composition according to any one of [1] to [5], wherein the Zn content in the recycled carbon black is 2.5% by mass or less.

[0015] [7] The rubber composition for tire treads according to any one of [1] to [6], wherein the recycled carbon black has an ash content of 20% by mass or less.

[0016] [8] A tire comprising a tread rubber including a cap tread rubber layer located on the outermost surface of the tread portion and a base tread rubber layer located radially inward of the cap tread rubber layer, wherein the cap tread rubber layer is made of the tire tread rubber composition described in any of [1] to [7].

[0017] [9] The storage modulus (E') of the cap tread rubber layer at 25°C Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ The tire described in [8], wherein the ratio is 0.50 or higher.

[0018]

[10] The tire according to [8] or [9], wherein the rubber component (A) is modified with a modifier having at least one atom from nitrogen, silicon, and tin, and comprises a modified styrene-butadiene rubber (a2-1) having a glass transition temperature of -50°C or lower, and an unmodified styrene-butadiene rubber (a2-2) having a glass transition temperature 30°C or higher than the modified styrene-butadiene rubber (a2-1).

[0019] According to the present invention, compared to conventional methods using recycled carbon black, it is possible to provide a tire tread rubber composition that contributes to improved sustainability while minimizing adverse effects on tire rubber properties and maintaining performance. Furthermore, according to the present invention, it is possible to provide a tire that maintains tire performance while increasing the proportion of sustainable materials.

[0020] This is an explanatory diagram illustrating an example of measurement results using a grind gauge. This is a cross-sectional view of one embodiment of the tire of the present invention.

[0021] The rubber composition for tire treads and the tire of the present invention will be described in detail below, based on embodiments thereof.

[0022] <Definitions> The compounds described herein may be derived in part or in whole from fossil resources, from biological resources such as plant resources, or from recycled resources such as used tires. They may also be derived from a mixture of two or more of fossil resources, biological resources, or recycled resources.

[0023] In this specification, "sustainable material ratio" refers to the total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources in the tire in question.

[0024] In this specification, the term "biomass resources" refers to carbon-neutral organic resources of biological origin, excluding fossil resources (such as petroleum, coal, and natural gas). These biological resources may be edible or inedible, but are preferably inedible, as they do not compete with food resources and are considered to be resources that can be used effectively.

[0025] In this specification, the term "recycled resources" refers to resources obtained by recycling products that have been used, collected without being used, or discarded. For example, recycled resources include resources obtained by recycling used rubber products such as used tires.

[0026] <Rubber Composition for Tire Treads> A rubber composition for tire treads according to one embodiment of the present invention (hereinafter sometimes referred to as "the rubber composition of this embodiment") is a rubber composition for tire treads containing a rubber component (A) and a filler (B), wherein the filler (B) contains recycled carbon black, and the recycled carbon black, when measured with a grind gauge, shows three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

[0027] The rubber composition of this embodiment not only uses recycled carbon black as the filler (B), but also uses recycled carbon black in which, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce such lines of 10 mm or more is 20 μm or less. In this way, by using at least recycled carbon black, the rubber composition of this embodiment can contribute to improved sustainability. Furthermore, in the grind gauge measurement of recycled carbon black, there is a high correlation between the evaluation results and the durability of the rubber composition, particularly the performance after degradation. By using recycled carbon black that is judged to have good dispersibility in grind gauge measurement (recycled carbon black in which the particle size of the third largest particle is 20 μm or less), the deterioration of the durability of the rubber composition, particularly the performance after degradation, can be suppressed. In other words, by using recycled carbon black in which the third largest particle size is 20 μm or less, the adverse effects on tire rubber properties (e.g., crack resistance after thermal degradation, high-temperature tensile strength after degradation) are significantly smaller compared to using conventional recycled carbon black, and performance can be maintained.

[0028] (Rubber component (A)) The rubber composition of this embodiment contains rubber component (A), which provides rubber elasticity to the composition. The sustainability rate of rubber component (A) is preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass. Hereinafter, in this specification, "sustainability rate" refers to the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources in the material in question.

[0029] The rubber component (A) is preferably the rubber derived from biological resources and the rubber derived from recycled resources. Here, the proportion of the monomer component derived from biological resources in 100 mol% of the monomer component constituting the rubber derived from biological resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol%. Furthermore, the proportion of the monomer component derived from recycled resources in 100 mol% of the monomer component constituting the rubber derived from recycled resources is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, particularly preferably 95 mol% or more, and may also be 100 mol%.

[0030] The rubber component (A) is a component that contributes to crosslinking, and typically has a weight-average molecular weight (Mw) of 10,000 or more, preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, and also preferably 5,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,500,000 or less. In this specification, the weight-average molecular weight (Mw) of the rubber component can be determined, for example, by converting it to standard polystyrene based on measurements obtained by gel permeation chromatography (GPC).

[0031] The rubber component (A) is preferably a diene-based rubber, and isoprene-based rubber and butadiene-based rubber are preferred as the diene-based rubber.

[0032] Examples of isoprene-based rubbers include natural rubber and synthetic isoprene rubber. The origin of natural rubber is not particularly limited; for example, it may be derived from the Para rubber tree, guayule, or Russian dandelion. Natural rubber may be modified or altered, and synthetic isoprene rubber may also be altered. These isoprene-based rubbers may be used individually or in combination of two or more. Natural rubber is preferred as the isoprene-based rubber.

[0033] Examples of the butadiene-based rubber include butadiene rubber and styrene-butadiene rubber. Here, it is preferable that the butadiene used as a raw material for the butadiene-based rubber is derived from biological resources or recycled resources.

[0034] Examples of the styrene-butadiene rubber include emulsion-polymerized styrene-butadiene rubber and solution-polymerized styrene-butadiene rubber.

[0035] The isoprene-based rubber and the butadiene-based rubber preferably have a sustainability rate of 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass.

[0036] Furthermore, in order to ensure that the overall sustainability rate of the rubber component (A) is within the aforementioned range, it is preferable to use natural rubber as the rubber component (A), or to use a polymer synthesized using monomer components derived from biological resources or recycled resources. It is also possible to use mass balance certified synthetic rubber to ensure that the sustainability rate is within the aforementioned range.

[0037] The ratio of each monomer unit (for example, units derived from isoprene, units derived from butadiene, and units derived from aromatic vinyl compounds) in the entire rubber component (A) can be appropriately adjusted depending on the member to which it is applied. The ratio of each monomer unit in the entire rubber component (A) can be adjusted, for example, by appropriately combining the isoprene-based rubber and butadiene-based rubber described above. The ratio of cis-bonded units in the butadiene-derived units can also be appropriately adjusted depending on the member to which it is applied. In this specification, "monomer unit" means a constituent unit of a polymer, "unit derived from isoprene" means a constituent unit in a polymer composed of isoprene, which is a monomer (including isoprene units in natural rubber), "unit derived from butadiene" means a constituent unit in a polymer composed of butadiene, which is a monomer, and "unit derived from aromatic vinyl compounds" means a constituent unit in a polymer composed of aromatic vinyl compounds, which are monomers. In this specification, the ratio of each monomer unit is measured by NMR.

[0038] The rubber component (A) may include, in addition to the isoprene-based rubber, butadiene rubber, and styrene-butadiene rubber (styrene-butadiene copolymer) mentioned above, diene-based rubbers such as acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, and styrene-isoprene-butadiene copolymer rubber. These rubber components may be used individually or in combination of two or more.

[0039] At least a portion of the rubber components constituting the rubber component (A) may have functional groups that interact with fillers such as carbon black and silica introduced through modification. That is, rubber component (A) may contain modified rubber components. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups. These functional groups may also have substituents. These functional groups may be introduced into the rubber component individually or in combination of two or more. Among these, amino groups, alkoxy groups, and alkoxysilyl groups are preferred, and substituted amino groups in which the hydrogen atoms of the amino group are replaced by alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and alkoxysilyl groups having 1 to 6 carbon atoms are even more preferred.

[0040] The functional group can be introduced, for example, by reacting a compound having the functional group (modifier) ​​with the rubber component. The compound having the functional group (modifier) ​​is a modifying functional group that interacts with fillers such as silica and carbon black, and can be a nitrogen-containing functional group, a silicon-containing functional group, or an oxygen-containing functional group. Examples of nitrogen-containing functional groups include amino group-containing compounds, examples of silicon-containing functional groups include silicon halides and hydrocarbyloxysilane compounds, and examples of oxygen-containing functional groups include alkoxy group-containing compounds, alkylene oxide group-containing compounds, and trialkylsilyloxy group-containing compounds. More specifically, examples include compounds described in WO2016 / 194316 and WO2019 / 117256. These modifiers may be used individually or in combination of two or more.

[0041] The aforementioned rubber derived from sustainable materials (materials derived from biological resources or materials derived from recycled resources) can be manufactured, for example, using monomer components derived from biological resources or monomer components derived from recycled resources, and, if necessary, monomer components derived from fossil resources, in the same manner as conventional methods for manufacturing synthetic rubber derived from fossil resources.

[0042] For example, the method described in Japanese Patent Publication No. 2022-179158 can be used to prepare rubber derived from biological resources.

[0043] As the butadiene obtained from the aforementioned biological resources, butadiene derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadiene derived from alkenes (preferably ethylene), and butadiene derived from unsaturated carboxylic acids (preferably tigric acid) can be suitably used.

[0044] -Modified Polymer (a1)- Preferably, the above rubber component (A) contains a modified polymer (a1) modified with a modifying agent having a functional group containing a nitrogen atom and an alkoxy group. By incorporating a modified polymer (a1) modified with a modifying agent having a functional group containing a nitrogen atom and an alkoxy group, the wear resistance of the tire to which the rubber composition is applied can be improved.

[0045] The modifying agent having a functional group containing a nitrogen atom and an alkoxy group is a general term for modifying agents having a functional group containing at least one nitrogen atom and at least one alkoxy group. The functional group containing a nitrogen atom is preferably selected from the following. A monovalent hydrocarbon group having 1 to 30 carbon atoms, including a linear, branched, alicyclic, or aromatic ring, having a functional group selected from the group consisting of a primary amino group, a primary amino group protected by 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 by a hydrolyzable protecting group, a cyclic secondary amino group, an onium salt residue of a cyclic secondary amine, an acyclic secondary amino group, an onium salt residue of an acyclic secondary amine, an isocyanuric acid triester residue, a cyclic tertiary amino group, an acyclic tertiary amino group, a nitrile group, a pyridine residue, an onium salt residue of a cyclic tertiary amine, and an onium salt residue of an acyclic tertiary amine, and which may contain a linear, branched, alicyclic, or aromatic ring, or a monovalent hydrocarbon group having 1 to 30 carbon atoms, including a linear, branched, alicyclic, or aromatic ring.

[0046] The content of the modified polymer (a1) is preferably 20 to 99 parts by mass, more preferably 30 to 99 parts by mass, more preferably 40 to 99 parts by mass, more preferably 50 to 99 parts by mass, and even more preferably 60 to 99 parts by mass, per 100 parts by mass of the rubber component (A). When the content of the modified polymer (a1) is 60 to 99 parts by mass per 100 parts by mass of the rubber component (A), the wear resistance of the tire to which the tire rubber composition is applied can be effectively improved.

[0047] The modified polymer (a1) is not particularly limited and may be any of the above-mentioned rubber types modified with the above-mentioned modifying agent. However, it is preferable that the modified polymer (a1) is a modified styrene-butadiene rubber, i.e., modified styrene-butadiene rubber (modified SBR) (a1-1). In this case, the wear resistance of the tire to which the rubber composition is applied can be further improved, and the rolling resistance can also be improved.

[0048] Furthermore, it is preferable that the modified styrene-butadiene rubber (a1-1) has a glass transition temperature of less than -40°C. By incorporating modified styrene-butadiene rubber with a glass transition temperature of less than -40°C, the dispersibility of the filler (B) can be improved, and the wear resistance of the tire to which the rubber composition is applied can be further improved. From a similar viewpoint, the glass transition temperature of the modified styrene-butadiene rubber (a1-1) is preferably -45°C or lower, more preferably -50°C or lower, and also preferably higher than -90°C. In addition, modified styrene-butadiene rubber (a1-1) with a glass transition temperature higher than -90°C is easier to synthesize.

[0049] The modified styrene-butadiene rubber (a1-1) preferably has a bound styrene content of less than 15% by mass. The bound styrene content of the modified styrene-butadiene rubber (a1-1) refers to the proportion of styrene units contained in the styrene-butadiene rubber that constitutes the modified styrene-butadiene rubber (a1-1). When the bound styrene content of the modified styrene-butadiene rubber is less than 15% by mass, the glass transition temperature tends to be low. The bound styrene content of the modified styrene-butadiene rubber is more preferably 14% by mass or less, more preferably 13% by mass or less, and even more preferably 12% by mass or less. Furthermore, from the viewpoint of further improving the wear resistance of tires to which the rubber composition is applied, the bound styrene content of the modified styrene-butadiene rubber (a1-1) is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. The bound styrene content of the modified styrene-butadiene rubber (a1-1) can be adjusted by the amount of monomer used in the polymerization of the styrene-butadiene rubber, the degree of polymerization, etc.

[0050] The modified styrene-butadiene rubber (a1-1) is preferably one obtained by modifying styrene-butadiene rubber (SBR) with an aminoalkoxysilane compound. Further, from the viewpoint of having a high affinity for the filler (B), the modified styrene-butadiene rubber (a1-1) is more preferably one in which the terminal of the styrene-butadiene rubber is modified with an aminoalkoxysilane compound. When the terminal of the styrene-butadiene rubber is modified with an aminoalkoxysilane compound, the interaction between the modified styrene-butadiene rubber and the filler (B) (particularly silica) becomes particularly large.

[0051] Further, the modified styrene-butadiene rubber (a1-1) is also preferably one obtained by modifying styrene-butadiene rubber (SBR) with a coupling agent represented by the following general formula (I). In this case, the low fuel consumption property and wear resistance of the tire to which the rubber composition is applied can be further improved.

[0052]

[0053] In the above general formula (I), R １ , R ２ and R ３ each independently represent a single bond or an alkylene group having from 1 to 20 carbon atoms. R ４ , R ５ , R ６ , R ７ and R ９ each independently represent an alkyl group having from 1 to 20 carbon atoms. R ８ and R １１ each independently represent an alkylene group having from 1 to 20 carbon atoms. R １０ represents an alkyl group or a trialkylsilyl group having from 1 to 20 carbon atoms. m represents an integer from 1 to 3, and p represents 1 or 2. R １ to R １１m and p are independent of each other if there are multiple. i, j and k each independently represent integers from 0 to 6, where (i + j + k) is an integer from 3 to 10. A represents a hydrocarbon group having 1 to 20 carbon atoms, or an organic group having at least one atom selected from the group consisting of oxygen, nitrogen, silicon, sulfur, and phosphorus atoms, and lacking active hydrogen. Here, in general formula (I), the hydrocarbon group represented by A includes saturated, unsaturated, aliphatic, and aromatic hydrocarbon groups. Examples of organic groups lacking active hydrogen include hydroxyl groups (-OH), secondary amino groups (>NH), and primary amino groups (-NH). ２ Examples include functional groups having active hydrogen, such as sulfhydryl groups (-SH), and organic groups that do not have active hydrogen.

[0054] Furthermore, it is also preferable that the modified styrene-butadiene rubber (a1-1) is obtained by modifying at least one end of styrene-butadiene rubber (SBR) with a modifying agent containing a compound represented by the following general formula (1) (alkoxysilane).

[0055]

[0056] By using styrene-butadiene rubber modified with a modifier containing an oligosiloxane and a tertiary amino group, which are filler affinity groups, as the rubber component, the dispersibility of fillers such as silica can be improved. As a result, the rubber composition of this embodiment has improved filler dispersibility, which greatly improves low loss, reduces the rolling resistance of tires to which this rubber composition is applied, and improves fuel efficiency.

[0057] In the above general formula (1), R １ ~R ８ Each of these is independently an alkyl group having 1 to 20 carbon atoms; L １ and L ２ Each of these is an alkylene group having 1 to 20 carbon atoms; and n is an integer from 2 to 4.

[0058] -Modified styrene-butadiene rubber (a2-1) and unmodified styrene-butadiene rubber (a2-2)- Preferably, the rubber component (A) includes modified styrene-butadiene rubber (a2-1) which has a glass transition temperature of -50°C or lower, modified with a modifying agent having at least one atom from nitrogen, silicon, and tin, and unmodified styrene-butadiene rubber (a2-2) which has a glass transition temperature 30°C or higher than that of the modified styrene-butadiene rubber (a2-1). By blending these modified styrene-butadiene rubber (a2-1) and unmodified styrene-butadiene rubber (a2-2), the wet grip performance of the tire can be improved. In addition, by using modified styrene-butadiene rubber (a2-1) which has been modified with a modifying agent having at least one atom from nitrogen, silicon, and tin as the rubber component, the dispersibility of fillers in the rubber composition, such as silica, can be improved. Therefore, tires to which the above-mentioned modified styrene-butadiene rubber (a2-1) and the above-mentioned unmodified styrene-butadiene rubber (a2-2) are applied to the cap tread rubber layer exhibit significantly improved low heat generation and improved dispersibility of fillers, thus enabling improvements in performance such as reinforcement, fuel efficiency, and wear resistance.

[0059] The modified styrene-butadiene rubber (a2-1) is, as described above, a styrene-butadiene rubber having a glass transition temperature of -50°C or lower, which has been modified with a modifier having at least one atom from nitrogen, silicon, and tin.

[0060] The modified styrene-butadiene rubber (a2-1) has a glass transition temperature of -50°C or lower, preferably -55°C or lower, and preferably higher than -90°C. When the glass transition temperature of the modified styrene-butadiene rubber (a2-1) is -50°C or lower, the fuel efficiency and wear resistance of the tire can be sufficiently improved. Furthermore, styrene-butadiene rubber with a glass transition temperature higher than -90°C is easier to synthesize.

[0061] The glass transition temperatures of the modified styrene-butadiene rubber (a2-1) and the unmodified styrene-butadiene rubber (a2-2) can be measured, for example, as follows: Using each styrene-butadiene rubber as a sample, a TA Instruments DSC250 is used to record the DSC curve while increasing the temperature from -100°C to 20°C / min under a helium flow of 50 mL / min. The peak top (influence point) of the DSC differential curve is defined as the glass transition temperature.

[0062] The content ratio of the modified styrene-butadiene rubber (a2-1) described above in the rubber component (A) 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 80% by mass or less, even more preferably 60% by mass or less, and even more preferably 50% by mass or less. When the content ratio of the modified styrene-butadiene rubber (a2-1) in the rubber component (A) 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 modified styrene-butadiene rubber (a2-1) in the rubber component (A) is 60% by mass or less, the unmodified styrene-butadiene rubber (a2-2) described later can be sufficiently contained, and the wet grip performance of the tire can be maintained well.

[0063] Furthermore, the modified styrene-butadiene rubber (a2-1) preferably has a bound styrene content of less than 15% by mass. The bound styrene content of the modified styrene-butadiene rubber (a2-1) refers to the proportion of styrene units contained in the styrene-butadiene rubber. When the bound styrene content is less than 15% by mass, the glass transition temperature tends to be low. From a similar viewpoint, the bound styrene content is more preferably 14% by mass or less, more preferably 13% by mass or less, and even more preferably 12% by mass or less. Also, from the viewpoint of the wear resistance performance of the tire, the bound styrene content is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. The bound styrene content of the modified styrene-butadiene rubber (a2-1) can be adjusted by the amount of monomer used in the polymerization of the styrene-butadiene rubber, the degree of polymerization, etc.

[0064] Furthermore, as described above, the modified styrene-butadiene rubber (a2-1) is modified with a modifying agent having at least one atom from nitrogen, silicon, and tin. However, from the viewpoint of achieving an even higher level of balance between the tire's fuel efficiency, wear resistance, and wet grip performance, it is preferable that it be modified with a modifying agent having nitrogen and silicon atoms, and more preferably with a modifying agent having a functional group containing nitrogen atoms and an alkoxy group. When the modified styrene-butadiene rubber (a2-1) is modified with a modifying agent having nitrogen and silicon atoms, the balance between the tire's wet grip performance, fuel efficiency, and wear resistance is further improved, and in particular, the fuel efficiency and wear resistance can be further improved. Also, when the modified styrene-butadiene rubber (a2-1) is modified with a modifying agent having a functional group containing nitrogen atoms and an alkoxy group, the balance between the tire's wet grip performance, fuel efficiency, and wear resistance is further improved, and in particular, the fuel efficiency and wear resistance can be further improved.

[0065] Here, the modifying agent having a functional group containing a nitrogen atom and an alkoxy group is as described above.

[0066] The modified styrene-butadiene rubber (a2-1) is preferably modified with an aminoalkoxysilane compound, and it is even more preferable that its ends are modified with an aminoalkoxysilane compound, from the viewpoint of having a high affinity for fillers such as silica. When the ends of the styrene-butadiene rubber are modified with an aminoalkoxysilane compound, the interaction between the modified styrene-butadiene rubber (a2-1) and the filler (especially silica) becomes particularly large.

[0067] The modified sites of the modified styrene-butadiene rubber (a2-1) may be at the molecular ends as described above, or they may be on the main chain. The modified styrene-butadiene rubber (a2-1) with modified molecular ends can be produced, for example, by reacting various modifying agents with the ends of a styrene-butadiene copolymer having active ends, according to the method described in International Publication No. 2003 / 046020 and Japanese Patent Application Publication No. 2007-217562. In one preferred embodiment, the modified styrene-butadiene rubber (a2-1) with modified molecular ends can be produced by reacting an aminoalkoxysilane compound with the ends of a styrene-butadiene copolymer having active ends with a cis-1,4 bond content of 75% or more, and then stabilizing it by reacting it with a carboxylic acid partial ester of a polyhydric alcohol, according to the method described in International Publication No. 2003 / 046020 and Japanese Patent Application Publication No. 2007-217562.

[0068] The carboxylic acid partial ester of the polyhydric alcohol refers to a partial ester of a polyhydric alcohol and a carboxylic acid, and having one or more hydroxyl groups. Specifically, esters of sugars or modified sugars having four or more carbon atoms and fatty acids are preferably used. More preferably, these esters include (1) fatty acid partial esters of polyhydric alcohols, particularly partial esters of saturated or unsaturated higher fatty acids having 10 to 20 carbon atoms and polyhydric alcohols (monoesters, diesters, or triesters), and (2) ester compounds in which one to three partial esters of polyhydric carboxylic acids and higher alcohols are bonded to a polyhydric alcohol. The polyhydric alcohol used as a raw material for the partial ester is preferably a sugar having five or six carbon atoms and at least three hydroxyl groups (which may or may not be hydrogenated), glycols, or polyhydroxy compounds. The raw material fatty acid is preferably a saturated or unsaturated fatty acid having 10 to 20 carbon atoms, for example, stearic acid, lauric acid, or palmitic acid. Among the fatty acid partial esters of polyhydric alcohols, sorbitan fatty acid esters are preferred, specifically including sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, and sorbitan trioleate.

[0069] The above aminoalkoxysilane compound is not particularly limited, but an aminoalkoxysilane compound represented by the following general formula (i) is preferred. １１ ａ -Si-(OR １２ ) ４－ａ ... (i)

[0070] In general formula (i), R １１ and R １２ Each independently represents a monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, R １１ and R １２ At least one of them is substituted with an amino group, a is an integer from 0 to 2, OR １２If there are multiple ORs, each OR １２ These elements may be identical or different from each other, and the molecule does not contain an active proton.

[0071] Among the above aminoalkoxysilane compounds, aminoalkoxysilane compounds represented by the following general formula (ii) are also preferred.

[0072] In general formula (ii), n1 + n2 + n3 + n4 = 4 (where n2 is an integer from 1 to 4, and n1, n3, and n4 are integers from 0 to 3). A １ This is at least one functional group selected from saturated cyclic tertiary amine compound residues, unsaturated cyclic tertiary amine compound residues, ketimine residues, nitrile groups, (thio)isocyanate groups, isocyanuric acid trihydrocarbyl ester groups, nitrile groups, pyridine groups, (thio)ketone groups, amide groups, and first or second amino groups having hydrolyzable groups. When n4 is 2 or more, A １ They may be the same or different, A １ R may be a divalent group that bonds with Si to form a cyclic structure. ２１ R 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 may be the same or different when n1 is 2 or more. 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, and may contain a nitrogen atom and / or a silicon atom. When n2 is 2 or more, R ２２ These elements may be identical or different from each other, or they may come together to form a ring. ２３ R is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom, and may be the same or different if n3 is 2 or more. ２４This 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 may be the same or different when n4 is 2 or more. The hydrolyzable group in the first or second amino group having a hydrolyzable group is preferably a trimethylsilyl group or a tert-butyldimethylsilyl group, and the trimethylsilyl group is particularly preferred.

[0073] The aminoalkoxysilane compound represented by the above general formula (ii) is preferably an aminoalkoxysilane compound represented by the following general formula (iii).

[0074] In general formula (iii), p1 + p2 + p3 = 2 (where p2 is an integer between 1 and 2, and p1 and p3 are integers between 0 and 1). A ２ R is NRa (where Ra is a monovalent hydrocarbon group, a hydrolyzable group, or a nitrogen-containing organic group). ２５ R is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ２６ This 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, all of which may contain a nitrogen atom and / or a silicon atom. When p2 is 2, R ２６ These elements may be identical or different from each other, or they may come together to form a ring. ２７ R is a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms, or a halogen atom. ２８ This 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.

[0075] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (iv) or the following general formula (v).

[0076] In the general formula (iv), q1 + q2 = 3 (where q1 is an integer from 0 to 2, and q2 is an integer from 1 to 3). ３１ R is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３２ and R ３３ Each of these is independently a hydrolyzable group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３４ This 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 may be the same or different when q1 is 2. ３５ This 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 may be the same or different if q2 is 2 or more.

[0077]

[0078] In the general formula (v), r1 + r2 = 3 (where r1 is an integer from 1 to 3, and r2 is an integer from 0 to 2). ３６ R is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ３７ R 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 may be the same or different when r1 is 2 or more. ３８is 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, it may be the same or different. A specific example of an aminoalkoxysilane compound represented by general formula (v) is N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propaneamine.

[0079] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (vi) or the following general formula (vii).

[0080] In general formula (vi), R ４０ R is a trimethylsilyl group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４１ This is a hydrocarbyloxy group having 1 to 20 carbon atoms, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４２ This 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 (the same applies hereinafter).

[0081]

[0082] In general formula (vii), R ４３ and R ４４ Each of these is independently a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４５ R 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 They may be the same or different.

[0083] The aminoalkoxysilane compound represented by the above general formula (ii) is also preferably an aminoalkoxysilane compound represented by the following general formula (viiii) or the following general formula (ix).

[0084] In the general formula (viiii), s1 + s2 is 3 (where s1 is an integer from 0 to 2, and s2 is an integer from 1 to 3). ４６ R is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４７ and R ４８ Each of these is independently a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ４７ or R ４８ They may be the same or different.

[0085]

[0086] In the general formula (ix), X is a halogen atom. ４９ R is a divalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ５０ and R ５１ Each of these is 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 They are bonded together to form a divalent organic group. ５２ and R ５３ Each of these is independently a halogen atom, a hydrocarbyl oxy group, a monovalent aliphatic or alicyclic hydrocarbon group having 1 to 20 carbon atoms, or a monovalent aromatic hydrocarbon group having 6 to 18 carbon atoms. ５０ and R ５１ As for the hydrolyzable group, a hydrolyzable group is preferred, and among the hydrolyzable groups, a trimethylsilyl group and a tert-butyldimethylsilyl group are preferred, with a trimethylsilyl group being particularly preferred.

[0087] 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 (xiiiii).

[0088] In the general formulas (x) to (xiii), the symbols u and v are integers from 0 to 2 and satisfying u + v = 2, respectively. ５４ ~ ９２ These may be the same or different, and are monovalent or divalent aliphatic or alicyclic hydrocarbon groups having 1 to 20 carbon atoms, or monovalent or divalent aromatic hydrocarbon groups having 6 to 18 carbon atoms. In general formula (xiiii), α and β are integers from 0 to 5.

[0089] Among the compounds satisfying general formula (x), general formula (xi), and general formula (xii), N1,N1,N7,N7-tetramethyl-4-((trimethoxysilyl)methyl)heptan-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)heptan-1,7-diamine are particularly preferred. Furthermore, among the compounds satisfying general formula (xiiii), 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)propane-1-amine are particularly preferred.

[0090] The method for producing the modified styrene-butadiene rubber (a2-1) is not particularly limited. In one embodiment, the method for producing the modified styrene-butadiene rubber (a2-1) may include the steps of: 1) polymerizing styrene-butadiene rubber in a hydrocarbon solvent in the presence of an organoalkali metal compound to produce an active polymer in which an alkali metal is bonded to at least one end; and 2) reacting the active polymer with a modifying agent such as the above-mentioned aminoalkoxysilane compound.

[0091] The step in 1) above is a step for producing an active polymer in which an alkali metal is bonded to at least one end, and can be carried out by polymerizing a styrene monomer and a butadiene monomer in a hydrocarbon solvent in the presence of an organoalkali metal compound.

[0092] The hydrocarbon solvent is not particularly limited, but for example, one or more selected from the group consisting of n-pentane, n-hexane, n-heptane, isooctane, cyclohexane, toluene, benzene, and xylene can be used.

[0093] The organoalkali metal compound can be used in an amount of 0.1 mmol to 1.0 mmol based on 100 g of the monomer. The organoalkali metal compound is not particularly limited, but for example, one or more selected from the group consisting of methyllithium, ethyllithium, propyllithium, n-butyllithium, s-butyllithium, t-butyllithium, hexyllithium, n-decyllithium, t-octyllithium, phenyllithium, 1-naphthyllithium, n-eicosyllithium, 4-butylphenyllithium, 4-tolylllithium, cyclohexyllithium, 3,5-di-n-heptylcyclohexyllithium, 4-cyclopentyllithium, sodium naphthyl, potassium naphthyl, lithium alkoxide, sodium alkoxide, potassium alkoxide, lithium sulfonate, sodium sulfonate, potassium sulfonate, lithium amide, sodium amide, potassium amide, and lithium isopropylamide can be used.

[0094] The polymerization in step 1) above may be carried out by further adding a polar additive as needed, and the polar additive can be added in an amount of 0.001 to 1.0 part by mass per 100 parts by mass of the monomer. Specifically, it can be added in an amount of 0.005 to 0.5 parts by mass, more specifically 0.01 to 0.3 parts by mass, per 100 parts by mass of the monomer. As the polar additive, for example, one or more selected from the group consisting of tetrahydrofuran, ditetrahydrofurylpropane, diethyl ether, cycloamal ether, dipropyl ether, ethylene dimethyl ether, ethylene dimethyl ether, diethyl glycol, dimethyl ether, tertiary butoxyethoxyethane, bis(3-dimethylaminoethyl) ether, (dimethylaminoethyl) ethyl ether, trimethylamine, triethylamine, tripropylamine, and tetramethylethylenediamine can be used.

[0095] Furthermore, in the above-described manufacturing method, when copolymerizing butadiene monomers and styrene monomers using the aforementioned polar additive, it is possible to facilitate the formation of random copolymers by compensating for the difference in their reaction rates.

[0096] Furthermore, the polymerization in step 1) above can be carried out via adiabatic polymerization or isothermal polymerization. Here, adiabatic polymerization refers to a polymerization method that includes a step in which polymerization is carried out by the heat of self-reaction without adding any heat after the organoalkali metal compound has been added, and isothermal polymerization refers to a polymerization method in which the temperature of the polymer is kept constant by adding or removing heat after the organoalkali metal compound has been added.

[0097] Furthermore, the polymerization may be carried out in a temperature range of 20°C to 200°C, more specifically in a temperature range of 0°C to 150°C, and more specifically in a temperature range of 10°C to 120°C.

[0098] Furthermore, step 2) above is a modification reaction step in which the active polymer is reacted with a modifying agent such as the above-mentioned aminoalkoxysilane compound in order to produce modified styrene-butadiene rubber (a2-1).

[0099] In this case, the modifying agent may be the same as that described above. The modifying agent can be used in a ratio of 0.1 to 2.0 moles per mole of the organic alkali metal compound. Furthermore, the reaction in step 2) is a modification reaction for introducing functional groups into the polymer, and each of the above reactions can be carried out at a temperature range of 0°C to 90°C for 1 minute to 5 hours.

[0100] Furthermore, the manufacturing method described above may, if necessary, further include one or more steps after step 2) above, such as solvent collection, recovery of unreacted monomers, and drying.

[0101] Furthermore, the content ratio of the modified styrene-butadiene rubber (a2-1) modified with the above-mentioned aminoalkoxysilane compound or other modifying agent in the rubber component (A) 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 modified styrene-butadiene rubber (a2-1) in the rubber component (A) 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 modified styrene-butadiene rubber (a2-1) in the rubber component (A) is 60% by mass or less, the unmodified styrene-butadiene rubber (a2-2) described later can be sufficiently contained, and the wet grip performance of the tire can be maintained well.

[0102] Furthermore, the rubber component (A) may further contain, in addition to the modified styrene-butadiene rubber (a2-1), unmodified styrene-butadiene rubber (a2-2) having a glass transition temperature 30°C or higher than that of the modified styrene-butadiene rubber (a2-1). By including unmodified styrene-butadiene rubber (a2-2) with a high glass transition temperature as the rubber component (A), the wet grip performance of the tire can be improved.

[0103] Here, the unmodified styrene-butadiene rubber (a2-2) must have a glass transition temperature at least 30°C higher than that of the modified styrene-butadiene rubber (a2-1), and preferably at least 35°C higher. By including both the modified styrene-butadiene rubber (a2-1) and the unmodified styrene-butadiene rubber (a2-2), the flexibility of the tread rubber layer can be increased, and the fuel efficiency and wear resistance of the tire can be significantly improved.

[0104] Furthermore, the content ratio of the unmodified styrene-butadiene rubber (a2-2) in rubber component (A) 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, and more preferably 80% by mass or less. When the content ratio of the unmodified styrene-butadiene rubber (a2-2) in rubber component (A) 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 unmodified styrene-butadiene rubber (a2-2) in rubber component (A) is less than 85% by mass, the fuel efficiency and wear resistance of the tire can be maintained well. Therefore, by having rubber component (A) contain 15% by mass or more and less than 85% by mass of unmodified styrene-butadiene rubber (a2-2), it is possible to further improve wet grip performance while maintaining fuel efficiency and wear resistance well.

[0105] Furthermore, from the viewpoint of achieving a higher level of balance between the tire's wet grip performance, fuel efficiency, and wear resistance, it is preferable that the content ratio of unmodified styrene-butadiene rubber (a2-2) is greater than the content ratio of modified styrene-butadiene rubber (a2-1) [Content ratio of unmodified styrene-butadiene rubber (a2-2) / Content ratio of modified styrene-butadiene rubber (a2-1) > 1].

[0106] Furthermore, the rubber component (A) may also include rubbers other than the modified styrene-butadiene rubber (a2-1) and the unmodified styrene-butadiene rubber (a2-2) for the purpose of improving the tire's fuel efficiency, wear resistance, etc. The other rubbers can be appropriately selected according to the required performance, but for example, one or more types of diene rubbers such as natural rubber (NR), butadiene rubber (BR), synthetic isoprene rubber (IR), and ethylene-propylene copolymer rubber, or non-diene rubbers such as butyl rubber can be used. However, from the viewpoint of achieving a higher level of balance between the tire's wet grip performance, fuel efficiency, and wear resistance, it is preferable that the rubber component (A) consists only of the modified styrene-butadiene rubber (a2-1) and the unmodified styrene-butadiene rubber (a2-2).

[0107] -Modified conjugated diene polymer (a3)- Furthermore, the rubber component (A) includes a modified conjugated diene polymer (a3) ​​having a functional group that has affinity with the filler (B), and it is preferable that the modified conjugated diene polymer (a3) ​​includes a modified conjugated diene polymer (a3-1) supplied by a mass balance method. The modified conjugated diene polymer (a3-1) supplied by a mass balance method is a modified conjugated diene polymer (modified synthetic rubber) to which biological resource-derived characteristics or recycled resource-derived characteristics have been assigned by a mass balance method, and the proportion of sustainable material can be treated as 100% by mass. By including a modified conjugated diene polymer to which biological resource-derived characteristics or recycled resource-derived characteristics have been assigned by a mass balance method in the rubber component (A), it is possible to contribute to reducing the environmental burden when considering the entire process of manufacturing, using, and disposing of the modified conjugated diene polymer.

[0108] The content of the modified conjugated diene polymer (a3) ​​is preferably 10 to 90 parts by mass, and more preferably 20 to 80 parts by mass, per 100 parts by mass of the rubber component (A). When the content of the modified conjugated diene polymer (a3) ​​per 100 parts by mass of the rubber component (A) is 10 parts by mass or more, it becomes easier to improve the performance of the tire using the rubber composition according to its purpose. Furthermore, when the content of the modified conjugated diene polymer (a3) ​​per 100 parts by mass of the rubber component (A) is 90 parts by mass or less, the flexibility of the source of the rubber component (A) is improved by increasing the amount of natural rubber or unmodified synthetic rubber blended in, making it easier to produce the rubber composition.

[0109] Furthermore, the proportion of the modified conjugated diene polymer (a3-1) supplied by the mass balance method in the modified conjugated diene polymer (a3) ​​is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass. When the proportion of the modified conjugated diene polymer (a3-1) supplied by the mass balance method in the modified conjugated diene polymer (a3) ​​is 10% by mass or more, the proportion of sustainable material in the tire using the rubber composition can be further improved.

[0110] One example of the mass balance method certification is ISCC PLUS certification. ISCC PLUS certification can certify bio-based raw materials, circular raw materials, and renewable raw materials, and among these, circular raw materials can be classified into biocircular and non-biocircular circular materials.

[0111] The aforementioned bio-raw materials and renewable raw materials are derived from unused biomass from related industries, including agriculture, forestry, and fisheries / aquaculture. Examples include fermented or biodegradable fractions of products such as corn, sugarcane, and rapeseed.

[0112] The aforementioned circular raw materials are materials at the beginning of the supply chain that are considered waste / processing residues but are reused or recycled instead of being landfilled or used for energy purposes. Within circular raw materials, "biocircular" refers to waste and residues of biological origin from related industries including agriculture, forestry, fisheries and aquaculture, as well as biodegradable fractions of industrial and municipal waste. Examples include used cooking oil (UCO), tall oil (a mixture of fatty acids, resin acids, unsaponifiable matter, etc., produced as a by-product when pulp raw materials are digested and fibers are separated during pulp production), and food waste. On the other hand, "circular materials other than biocircular" refers to raw materials derived from mechanical and / or chemical processing of recyclable materials (fossil-based) of non-biological origin, such as plastic waste and used tires.

[0113] Furthermore, the bio-raw material is preferably a plant-derived material, and the circular raw material is preferably a plant-derived by-product, a raw material obtained from the recycling of plant-derived materials, and a raw material obtained from the recycling of fossil resource-derived materials. In other words, the modified conjugated diene polymer (a3) ​​preferably contains a modified conjugated diene polymer derived from at least one of the plant-derived raw material, plant-derived by-product, a raw material obtained from the recycling of plant-derived materials, and a raw material obtained from the recycling of fossil resource-derived materials. Since plant-derived raw material, plant-derived by-product, a raw material obtained from the recycling of plant-derived materials, and a raw material obtained from the recycling of fossil resource-derived materials are abundant, it is easy to secure the quantity, and a tire rubber composition containing a modified conjugated diene polymer (a3) ​​derived from at least one of these raw materials can greatly contribute to reducing the environmental burden when considering the entire process of manufacturing, using, and disposing of the modified conjugated diene polymer.

[0114] The modified conjugated diene polymer (a3) ​​preferably contains both a modified conjugated diene polymer derived from biological resources and a modified conjugated diene polymer derived from fossil resources. Here, the modified conjugated diene polymer (a3) ​​preferably contains 0.1 to 99% by mass of a modified conjugated diene polymer derived from biological resources and 99.9 to 1% by mass of a modified conjugated diene polymer derived from fossil resources. By including 0.1% by mass or more of a modified conjugated diene polymer derived from biological resources in the modified conjugated diene polymer (a3), the proportion of sustainable materials in tires to which the rubber composition is applied can be significantly improved. Furthermore, by including 1% by mass or more of a modified conjugated diene polymer derived from fossil resources in the modified conjugated diene polymer (a3), the flexibility of the origin of the modified conjugated diene polymer (a3) ​​is improved, and the production of the rubber composition becomes easier. Therefore, a tire rubber composition containing a modified conjugated diene polymer (a3) ​​comprising 0.1 to 99% by mass of a modified conjugated diene polymer derived from biological resources and 99.9 to 1% by mass of a modified conjugated diene polymer derived from fossil resources offers an excellent balance between reducing environmental impact and productivity.

[0115] The modified conjugated diene polymer (a3) ​​has functional groups that have affinity for the filler (B). The presence of functional groups that have affinity for the filler (B) in the modified conjugated diene polymer (a3) ​​improves the dispersibility of the filler (B) in the rubber composition.

[0116] Examples of the modified conjugated diene polymer (a3) ​​include modified polybutadiene, modified styrene-butadiene copolymer, modified butadiene-isoprene copolymer (BIR), and modified styrene-butadiene-isoprene copolymer.

[0117] Examples of functional groups having affinity with the filler (B) include functional groups having one or more atoms selected from nitrogen atoms, oxygen atoms, sulfur atoms, metalloid atoms, and metal atoms. The metalloid atoms are preferably one or more atoms selected from boron, silicon, germanium, arsenic, antimony, and tellurium, more preferably one or more atoms selected from boron, silicon, and germanium, and silicon is particularly preferred. The metal atoms are preferably one or more atoms selected from tin, titanium, zirconium, bismuth, and aluminum, more preferably one or more atoms selected from tin and titanium, and tin is particularly preferred. The functional group having affinity with the filler (B) preferably contains at least one selected from the group consisting of nitrogen atoms, oxygen atoms, and silicon atoms.

[0118] A functional group having one or more atoms selected from nitrogen atoms, oxygen atoms, sulfur atoms, metalloid atoms, and metal atoms is a residue of a compound having one or more atoms selected from nitrogen atoms, oxygen atoms, sulfur atoms, metalloid atoms, and metal atoms (hereinafter sometimes referred to as a "heteroatom-containing compound"). The heteroatom-containing compound may react with the active end of a conjugated diene polymer as a modifying agent to form a modified conjugated diene polymer, or a nitrogen-containing compound as a heteroatom-containing compound may react with an alkali metal to form a polymerization initiator for anionic polymerization to form a modified conjugated diene polymer having a nitrogen-containing compound residue at the starting end of the conjugated diene polymer.

[0119] Modifying agents that react with the active end of the conjugated diene polymer include one or more modifying agents selected from the following: modifying agents having a tin atom (tin-containing compound), modifying agents having a nitrogen atom and a silicon atom (nitrogen and silicon-containing compound), modifying agents having an oxygen atom and a silicon atom (oxygen and silicon-containing compound), modifying agents having a sulfur atom and a silicon atom (sulfur and silicon-containing compound), and modifying agents having a nitrogen atom but no silicon atom (silicon-free nitrogen-containing compound).

[0120] As the denaturing agent (tin-containing compound) having a tin atom, a tin compound selected from one or more of tin tetrachloride and tin tributylchloride is preferably exemplified.

[0121] The aforementioned modifying agents (nitrogen and silicon-containing compounds) having nitrogen and silicon atoms include N,N-bis(trimethylsilyl)aminopropylmethyldimethoxysilane, 1-trimethylsilyl-2,2-dimethoxy-1-aza-2-silacyclopentane, N,N-bis(trimethylsilyl)aminopropyltrimethoxysilane, N,N-bis(trimethylsilyl)aminopropyltriethoxysilane, N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane, and N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane. Suitable examples include silane compounds having a protected primary amino group, selected from noethyltrimethoxysilane, N,N-bis(trimethylsilyl)aminoethyltriethoxysilane, N,N-bis(trimethylsilyl)aminoethylmethyldimethoxysilane, and N,N-bis(trimethylsilyl)aminoethylmethyldiethoxysilane, such as N-methyl-N-trimethylsilylaminopropyl(methyl)dimethoxysilane, N-methyl-N-trimethylsilylaminopropyl(methyl)diethoxysilane, and N-trimethyl Lucilyl(hexamethyleneimine-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(hexamethyleneimine-2-yl)propyl(methyl)diethoxysilane, N-trimethylsilyl(pyrrolidine-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(pyrrolidine-2-yl)propyl(methyl)diethoxysilane, N-trimethylsilyl(piperidine-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(piperidine-2-yl)propyl( Suitable examples include silane compounds having a protected secondary amino group, selected from methyl)diethoxysilane, N-trimethylsilyl(imidazole-2-yl)propyl(methyl)dimethoxysilane, N-trimethylsilyl(imidazole-2-yl)propyl(methyl)diethoxysilane, N-trimethylsilyl(4,5-dihydroimidazole-5-yl)propyl(methyl)dimethoxysilane, and N-trimethylsilyl(4,5-dihydroimidazole-5-yl)propyl(methyl)diethoxysilane.

[0122] Suitable examples of the modifying agent (oxygen and silicon-containing compound) having the oxygen atom and silicon atom include epoxy group-containing hydrocarbyl oxysilane compounds selected from one or more of the following: 2-glycidoxyethyltrimethoxysilane, 2-glycidoxyethyltriethoxysilane, (2-glycidoxyethyl)methyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyl(methyl)dimethoxysilane.

[0123] Suitable examples of the modifying agent (sulfur and silicon-containing compound) having sulfur and silicon atoms include modified thioepoxy group-containing hydrocarbyloxysilane compounds obtained by substituting the epoxy group of the epoxy group-containing hydrocarbyloxysilane compound with a thioepoxy group.

[0124] Examples of modifying agents having nitrogen atoms but not silicon atoms (nitrogen-containing compounds that do not contain silicon) include one or more compounds selected from bis(diethylamino)benzophenone, dimethylimidazolidinone, N-methylpyrrolidone, and 4-dimethylaminobenzylideneaniline.

[0125] Preferably, the modified conjugated diene polymer (a3) ​​is modified with a modifying agent having nitrogen atoms and silicon atoms. When the modified conjugated diene polymer (A1) is modified with a modifying agent having nitrogen atoms and silicon atoms, the balance between the wet grip performance, fuel efficiency, and wear resistance of the tire to which the rubber composition is applied is further improved, and in particular, the fuel efficiency and wear resistance can be further improved.

[0126] The conjugated diene polymer before modification that forms the modified conjugated diene polymer (a3) ​​may be a conjugated diene homopolymer obtained by polymerizing one type of conjugated diene monomer, or a conjugated diene copolymer obtained by polymerizing two or more monomers. The conjugated diene copolymer may be obtained by polymerizing two or more types of conjugated diene monomers, or it may be obtained by copolymerizing one or more conjugated diene monomers with one or more aromatic vinyl compounds. Examples of the conjugated diene monomers include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, and 1,3-hexadiene. Among these, 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene are particularly preferred. Examples of the aromatic vinyl compounds include styrene, α-methylstyrene, 1-vinylnaphthalene, 3-vinyltoluene, ethylvinylbenzene, divinylbenzene, 4-cyclohexylstyrene, and 2,4,6-trimethylstyrene. Among these, the styrene group is particularly preferred.

[0127] The conjugated diene polymer before modification that forms the modified conjugated diene polymer (a3) ​​is preferably polybutadiene, styrene-butadiene copolymer, polyisoprene, isoprene-butadiene copolymer, styrene-isoprene copolymer, etc.

[0128] The polymerization method for the aforementioned conjugated diene polymer may be anionic polymerization or coordination polymerization.

[0129] Modified conjugated diene polymers (a3-1) supplied by assigning biological resource-derived characteristics or recycled resource-derived characteristics using a mass balance method can be treated as having a sustainable material ratio [total mass ratio of materials derived from biological resources (biomass resources) and materials derived from recycled resources] of 100% by mass, even if some monomer components derived from fossil resources are used. Because it is a mass balance method, even if some monomer components derived from fossil resources are used in the modified conjugated diene polymers (a3-1) supplied by assigning biological resource-derived characteristics or recycled resource-derived characteristics, modified conjugated diene polymers that use some monomer components derived from biological resources or recycled resources, or modified conjugated diene polymers that are assigned fossil resource-derived characteristics and treated as having a sustainable material ratio of 0% by mass, are supplied separately from the modified conjugated diene polymers (a3-1). Therefore, by using the modified conjugated diene polymers (a3-1), it is possible to significantly contribute to reducing the environmental burden when considering the entire process of manufacturing, using, and disposing of the modified conjugated diene polymers.

[0130] Regarding the method for preparing bio-derived rubber from the above-mentioned biological resources, for example, the method described in Japanese Patent Application Publication No. 2022-179158 can be used. For example, by using butadiene obtained from biological resources as a monomer component, bio-derived butadiene rubber (B-BR) can be obtained, and by using styrene obtained from biological resources and butadiene obtained from biological resources as monomer components, bio-derived styrene-butadiene rubber (B-SBR) can be obtained. Here, methods for obtaining B-BR and B-SBR from biological resources include artificial polymerization, polymerization in vivo, and polymerization using biologically derived enzymes. The molecular weight, branching, microstructure, etc. of the obtained B-BR and B-SBR can be appropriately adjusted by changing the polymerization conditions according to known methods, depending on the desired tire performance.

[0131] As the butadiene obtained from the aforementioned biological resources, butadiene derived from alkyl alcohols (preferably ethanol and butanol, more preferably butanol), butadiene derived from alkenes (preferably ethylene), and butadiene derived from unsaturated carboxylic acids (preferably tigric acid) can be suitably used. Two or more of these butadienes may also be used in combination. As the styrene obtained from the aforementioned biological resources, styrene obtained from plants (preferably plants belonging to the Hamamelidaceae, Styracaceae, and Apocynaceae families, more preferably plants belonging to the genera Liquidambar, Styrax, and Vinca, even more preferably Liquidambar formosana, Styrax japonica, and Vinca) and styrene obtained from microorganisms (preferably microorganisms belonging to the genera Penicillium and Escherichia, more preferably P. citrinum and transformed E. coli) can be suitably used. Two or more of these styrenes may also be used in combination.

[0132] Recently, biomass complexes focusing on bioethanol and bioethylene are being planned. However, bioethanol and bioethylene are produced using mainly sugars and / or celluloses 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, depending on the supply situation of various biological resources, as well as the supply situation of recycled resources, the supply situation of fossil resources, and market demands (for example, the demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources, or to use monomer components derived from biological resources, recycled resources, and fossil resources in combination, and to adjust the ratio of these monomer components as appropriate. This allows for the effective utilization of a wide range of biological resources such as sugars, proteins, and lipids, as well as recycled resources, without relying on a single type of biological resource. It also enables a stable supply of rubber derived from sustainable materials and allows for environmental considerations depending on the circumstances during production. Furthermore, when using multiple types of monomer components derived from biological resources, it is preferable to use monomer components derived from different biological resources, i.e., monomer components obtained from different biological resources. Specifically, it is preferable to use a mixture of multiple types of butadiene derived from different biological resources as the butadiene derived from biological resources, and / or to use a mixture of multiple types of styrene derived from different biological resources as the styrene derived from biological resources. This allows for the effective utilization of multiple types of biological resources.

[0133] -Isoprene-based rubber- Furthermore, it is preferable that the rubber component (A) further contains isoprene-based rubber (as described above). By incorporating such isoprene-based rubber, the fracture strength of the rubber composition can be increased. In addition, by incorporating isoprene-based rubber in addition to the modified rubber components, including the modified polymer (a1) described above, as rubber component (A), the wear resistance of the tire to which the rubber composition is applied can be further improved, and the rolling resistance can also be improved, thereby improving fuel efficiency. Note that the isoprene-based rubber referred to here is essentially unmodified isoprene-based rubber.

[0134] The isoprene rubber preferably has a difference in SP value from the modified polymer (a1) of 0.3 (cal / cm ３ ). １／２ or more, and more preferably 0.35 (cal / cm ３ ). １／２ When the difference in SP value between the isoprene rubber and the modified polymer (a1) is 0.3 (cal / cm ３ ), １／２ the isoprene rubber and the modified polymer (a1) tend to be incompatible.

[0135] When the rubber composition of the present embodiment further contains the resin component (C) described later, the isoprene rubber preferably has a difference in SP value from the resin component (C) of 1.40 (cal / cm ３ ). １／２ or less. When the difference in SP value is 1.40 (cal / cm ３ ), １／２ the compatibility with the isoprene rubber is increased, the mobility of the rubber component is controlled, and the hysteresis loss (tan δ) in the low temperature region can be improved. Therefore, the wet grip performance of the tire to which the rubber composition is applied is improved. From the same viewpoint, the difference in SP value between the isoprene rubber and the resin component (C) is preferably 1.35 (cal / cm ３ ), １／２ more preferably 0.50 (cal / cm ３ ), １／２ still more preferably 0.45 (cal / cm ３ ), １／２ still more preferably 0.30 (cal / cm ３ ), １／２ still more preferably 0.25 (cal / cm ３ ), １／２ and still more preferably 0.25 (cal / cm) or less.

[0136] If the rubber composition of this embodiment further contains a resin component (C) described later, and the rubber component (A) further contains isoprene-based rubber, it is preferable that the following formula: Mass ratio of resin component (C) / isoprene-based rubber ≥ 0.5 is satisfied. By having a mass ratio of resin component (C) to isoprene-based rubber [mass ratio of resin component (C) / isoprene-based rubber] of 0.5 or more, the wet grip performance of the tire to which the rubber composition is applied can be improved. The mass ratio of resin component (C) to isoprene-based rubber [mass ratio of resin component (C) / isoprene-based rubber] is preferably 0.65 or more, more preferably 0.7 or more, more preferably 0.8 or more, preferably 2.0 or less, more preferably 1.9 or less, and even more preferably 1.8 or less.

[0137] -Styrene-butadiene rubber- When the rubber component (A) contains styrene-butadiene rubber (as described above), it is preferable that the styrene-butadiene rubber contains styrene-butadiene rubber (SBR-1) having a weight-average molecular weight (Mw) of 700,000 or more. In this case, the styrene-butadiene rubber contains at least styrene-butadiene rubber (SBR-1) having a weight-average molecular weight of 700,000 or more, and may consist only of styrene-butadiene rubber (SBR-1) having a weight-average molecular weight of 700,000 or more, or may further contain styrene-butadiene rubber with a weight-average molecular weight of less than 700,000. A rubber composition containing styrene-butadiene rubber (SBR-1) having a weight-average molecular weight of 700,000 or more has an uneven rubber surface, suppresses adhesion to production equipment, and has good workability. From the viewpoint of workability, it is preferable that the styrene-butadiene rubber (SBR-1) has a weight-average molecular weight of 700,000 or more and 1,000,000 or less.

[0138] The styrene-butadiene rubber (SBR-1) having a weight-average molecular weight (Mw) of 700,000 or more is preferably emulsion-polymerized styrene-butadiene rubber (E-SBR). When emulsion-polymerized styrene-butadiene rubber (E-SBR) is incorporated into the rubber composition, the rubber composition tends to have an uneven rubber surface, further suppressing adhesion to production equipment and improving workability.

[0139] The emulsion polymerized styrene-butadiene rubber (E-SBR) preferably has a bound styrene content of less than 50% by mass. The bound styrene content of styrene-butadiene rubber refers to the proportion of styrene units contained in the styrene-butadiene rubber. When the bound styrene content of emulsion polymerized styrene-butadiene rubber (E-SBR) is less than 50% by mass, the glass transition temperature tends to be lower, which can further improve the fuel efficiency of tires to which the rubber composition is applied. From the viewpoint of the fuel efficiency of tires, the bound styrene content of styrene-butadiene rubber is more preferably 48% by mass or less, and more preferably 46% by mass or less. Furthermore, from the viewpoint of wet grip performance and wear resistance performance of tires to which the rubber composition is applied, the bound styrene content of styrene-butadiene rubber is preferably 20% by mass or more, and more preferably 22% by mass or more.

[0140] The emulsion polymerized styrene-butadiene rubber (E-SBR) can be produced, for example, by emulsion polymerization of styrene and 1,3-butadiene (monomer) at a predetermined temperature in the presence of an emulsifier, a dispersant, and a polymerization initiator, in an optionally chosen manner.

[0141] The conditions for emulsion polymerization are not particularly limited. For example, when the total amount of monomer used is 100 parts by mass, typically 100 to 500 parts by mass of water is used as a dispersant, and the polymerization can be carried out at a polymerization temperature of 0 to 100°C, preferably 0 to 80°C. As for the polymerization method for emulsion polymerization, a batch method, a method of supplying monomers in divided or continuous portions, etc., can be appropriately selected.

[0142] The emulsion polymerized styrene-butadiene rubber (E-SBR) may be unmodified or modified. Furthermore, the emulsion polymerized styrene-butadiene rubber (E-SBR) may also be an oil-expandable rubber to which an expanding oil has been added.

[0143] The styrene-butadiene rubber preferably further contains solution-polymerized styrene-butadiene rubber (S-SBR). When solution-polymerized styrene-butadiene rubber (S-SBR) is incorporated into the rubber composition, the fuel efficiency and wear resistance of the tire to which the rubber composition is applied can be significantly improved. The solution-polymerized styrene-butadiene rubber (S-SBR) preferably has a weight-average molecular weight (Mw) of less than 700,000, more preferably 400,000 or less from the viewpoint of workability, even more preferably 300,000 or less, and more preferably 200,000 or more from the viewpoint of fuel efficiency and wear resistance.

[0144] The solution-polymerized styrene-butadiene rubber (S-SBR) preferably has a bound styrene content of less than 30% by mass. The bound styrene content of styrene-butadiene rubber refers to the proportion of styrene units contained in the styrene-butadiene rubber. When the bound styrene content of the solution-polymerized styrene-butadiene rubber (S-SBR) is less than 30% by mass, the glass transition temperature tends to be lower, which can further improve the fuel efficiency of tires to which the rubber composition is applied. From the viewpoint of the fuel efficiency of tires, the bound styrene content of styrene-butadiene rubber is more preferably 28% by mass or less, more preferably 26% by mass or less, and even more preferably 24% by mass or less. Furthermore, from the viewpoint of wet grip performance and wear resistance of tires to which the rubber composition is applied, the bound styrene content of styrene-butadiene rubber is preferably 5% by mass or more, more preferably 7% by mass or more, and even more preferably 8% by mass or more. The bound styrene content of the styrene-butadiene rubber can be adjusted by the amount of monomer used in the polymerization of styrene-butadiene rubber, the degree of polymerization, etc.

[0145] The solution-polymerized styrene-butadiene rubber is preferably modified with a modifying agent having a functional group containing a nitrogen atom and an alkoxy group. Here, the modifying agent having a functional group containing a nitrogen atom and an alkoxy group is as described above.

[0146] (Filler (B)) The rubber composition of this embodiment contains filler (B). The inclusion of filler (B) improves the reinforcing properties of the rubber composition. Examples of fillers include carbon black, silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, and the like.

[0147] The content of the filler (B) in the rubber composition is preferably in the range of 20 to 150 parts by mass per 100 parts by mass of the rubber component (A). If the content of the filler (B) in the rubber composition is 20 parts by mass or more per 100 parts by mass of the rubber component (A), the reinforcement of the tire to which the rubber composition is applied is sufficient and the wear resistance can be improved. If it is 150 parts by mass or less, the elastic modulus of the rubber composition does not become too high, and the wet grip performance of the tire to which the rubber composition is applied is improved. From the viewpoint of further improving the rolling resistance of the tire (from the viewpoint of improving fuel efficiency), the content of the filler (B) in the rubber composition is more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 55 parts by mass or more, per 100 parts by mass of the rubber component (A). Furthermore, from the viewpoint of improving the wet grip performance of the tire, the content of filler (B) in the rubber composition is more preferably 140 parts by mass or less, even more preferably 120 parts by mass or less, even more preferably 105 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 95 parts by mass or less, per 100 parts by mass of rubber component (A).

[0148] -Carbon Black- Carbon black can reinforce rubber compositions and improve their abrasion resistance. As carbon black, plant-derived carbon black or carbon black obtained through recycling (also called "recycled carbon black") can be used.

[0149] From the viewpoint of further improving the wear resistance of the rubber composition and the tire to which it is applied, the carbon black content in the rubber composition is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of rubber component (A). Furthermore, from the viewpoint of the workability of the rubber composition, the carbon black content in the rubber composition is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less, per 100 parts by mass of rubber component (A).

[0150] --Recycled Carbon Black-- As stated above, the rubber composition of this embodiment requires that the filler (B) contains recycled carbon black. Since recycled carbon black is a material derived from recycled resources, including recycled carbon black can improve the proportion of sustainable materials in the tire.

[0151] In this specification, recycled carbon black refers to carbon black obtained by recovering from raw materials that are waste materials submitted for recycling. Examples of such waste materials include waste rubber, used tires, and waste oil. Waste rubber refers to all discarded rubber, including not only that generated from rubber products, but also unwanted scraps generated during the production or repair of rubber products. Examples of scraps include buffing powder and peeling rubber. Buffing powder is fine rubber generated, for example, in the buffing process of retreading tires, where the tread portion remaining on the base tire is scraped off. Peeling rubber is long pieces of rubber, for example, 1 to 2 cm wide, that are peeled off from the surface of rubber products such as tires. Peeling rubber is generated by scraping the surface of rubber products such as tires using a U-shaped or V-shaped knife like a peeler. Furthermore, waste rubber includes not only cross-linked rubber, but also unvulcanized rubber. Rubber products include, for example, final products such as tires and rubber hoses, and rubber parts or components at the manufacturing stage of final products. Used tires may include, for example, tires that have been retreaded, tires generated from tire replacement or vehicle scrapping, and End-of-Life Tires (ELTs) that have reached the end of their lifespan, or any other type of tire that has been discarded for any reason. Waste oil is not limited to that generated when plastics and rubber are decomposed, but also includes used oils discharged from industry, such as animal and vegetable oils, lubricating oils, insulating oils, and cutting oils. Among these, waste oil that does not contain any non-organic composition, such as those derived from silicone rubber or polyvinyl chloride, is preferable. Furthermore, waste oil that is mixed with carbon black or rubber containing carbon black is preferable. "Recycled carbon black" is different from carbon black that is directly manufactured using hydrocarbons such as petroleum, natural gas, and coal as raw materials, i.e., carbon black that is not recycled. Note that "used" here includes not only those that have been actually used and then discarded, but also those that were manufactured but discarded without actually being used.

[0152] Furthermore, it is preferable that the recycled carbon black is obtained by thermal decomposition of a vulcanized rubber product containing carbon black. Recycled carbon black obtained by thermal decomposition of a vulcanized rubber product containing carbon black is readily available because a large amount of vulcanized rubber product containing carbon black exists and it can be easily obtained by thermal decomposition. Moreover, it is preferable that the recycled carbon black is obtained from the solid residue generated by the thermal decomposition of the vulcanized rubber product containing carbon black. When a rubber product containing carbon black is thermally decomposed, solid residue and volatile components (oil) are obtained, and recycled carbon black can be recovered from either. When recovering carbon black from volatile components, it is possible to recover oil with a specific gravity suitable for producing carbon black and use it to produce carbon black using an existing carbon black production method (for example, Japanese Patent Publication No. 2015-520259). In this case, unlike carbon black recovered from solid residue, there are advantages such as the absence of impurities and the absence of mixtures of different grades. Furthermore, in the production of environmentally friendly carbon black, there are various options besides the oil obtained by recovering volatile components from the thermal decomposition of rubber mentioned above, such as using vegetable oil or oil derived from waste plastics. However, edible resources such as vegetable oil present challenges in securing sufficient quantities due to other uses such as food, and the environmental impact associated with the expansion of cultivated land must also be considered. Similarly, oil derived from waste plastics is used for other purposes such as horizontal recycling of plastics, so supply issues are also a concern. On the other hand, when using volatile components (oil) produced by the thermal decomposition of vulcanized rubber products, particularly tires, the tire industry has a system for continuing to use existing materials, making it possible to continue using existing materials and reduce the consumption of new materials in new tire manufacturing, thereby contributing to reducing the environmental burden on the industry. The grade of carbon black is not particularly limited, but examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762.

[0153] Furthermore, when recycled carbon black is recovered from solid residue, it is more preferably carbon black that has undergone surface treatment or surface modification. Examples of surface treatment or surface modification include hydrofluoric acid treatment, acid treatment such as hydrochloric acid or sulfuric acid, or treatment with peroxides. Surface treatment or surface modification may be carried out at room temperature, preferably at 70°C or higher, more preferably at 90°C or higher, and particularly preferably at 90°C to 100°C.

[0154] Furthermore, recycled carbon black can be obtained from the pyrolysis process of used pneumatic tires. For example, European Patent Application Publication No. 3427975, "Rubber Chemistry and Technology," Vol. 85, No. 3, pp. 408-449 (2012), particularly pp. 438, 440, and 442, states that it can be obtained by the pyrolysis of organic materials at 550-800°C in the absence of oxygen, or by vacuum pyrolysis at relatively low temperatures (paragraph

[0027] ). Carbon black obtained from such pyrolysis processes typically lacks functional groups on its surface, as mentioned in

[0004] of Patent No. 6856781 (Comparison of Surface Morphology and Chemistry of Pyrolysis Carbon Black and Commercial Carbon Black, PowderTechnology 160 (2005) 190-193).

[0155] Recycled carbon black may lack functional groups on its surface, or it may be treated to contain functional groups on its surface. Treatment to contain functional groups on the surface of recycled carbon black can be carried out by conventional methods. For example, in European Patent Application Publication No. 3173251, carbon black obtained from a thermal decomposition process is treated with potassium permanganate under acidic conditions to obtain carbon black containing hydroxyl and / or carboxyl groups on its surface. In addition, in Japanese Patent No. 6856781, carbon black obtained from a thermal decomposition process is treated with an amino acid compound containing at least one thiol group or disulfide group to obtain carbon black with an activated surface. The recycled carbon black according to this embodiment also includes carbon black that has been treated to contain functional groups on its surface.

[0156] Furthermore, for the thermal decomposition of cross-linked rubber products (vulcanized rubber products) such as used tires, one example is a thermal decomposition method at a temperature of 650°C or higher.

[0157] The cross-linked rubber products used in the aforementioned decomposition may be grouped by the type of rubber component they contain beforehand, and the decomposition process may be carried out for each group separately. Alternatively, they may be grouped by the type of filler they contain beforehand (for example, the type of carbon black, the type of silica, the mixing ratio of carbon black and silica, etc.), and the decomposition process may be carried out for each group separately. Furthermore, they may be grouped by both the type of rubber component and the type of filler, and the decomposition process may be carried out for each group separately. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again incorporated into the rubber component, a rubber composition with better performance can be obtained.

[0158] Furthermore, if the cross-linked rubber product used in the decomposition is derived from a tire, it may be grouped in advance by tire type (for example, for passenger cars, trucks and buses, heavy vehicles such as off-road vehicles, aircraft, agricultural vehicles, etc.) and then the decomposition process may be carried out for each group. Alternatively, it may be grouped in advance by tire component (for example, tread rubber, sidewall rubber, bead rubber, steel cord coated rubber, organic fiber coated rubber, pad rubber, cushion rubber, etc.) and then the decomposition process may be carried out for each group. Moreover, it may be possible to group by both tire type and tire component and then carry out the decomposition process for each group. When the decomposition process is carried out for each group in this way, recycled carbon black with more uniform physical properties can be obtained, and when it is again blended into the rubber component, a rubber composition with better performance can be obtained.

[0159] Furthermore, the recycled carbon black used in this embodiment must, when measured with a grind gauge, produce three or more lines with a length of 10 mm or more, and the particle size of the third largest particle among the particles producing these lines of 10 mm or more is 20 μm or less. By incorporating such recycled carbon black as a filler (B), tire performance can be maintained.

[0160] The measurement using the grind gauge described above is for evaluating the dispersibility of carbon black and can be performed in accordance with the descriptions in JIS K5101-1-5 (especially regarding the preparation of paste) and JIS K5400 (especially regarding the method of evaluation by the manner in which linear traces are generated).

[0161] In evaluating recycled carbon black using a grind gauge, as described later, from the viewpoint of the durability of the rubber composition applied to the cap tread rubber layer (high-temperature tensile strength after degradation, crack propagation resistance after thermal degradation, etc.), it is important whether the particle size of the third largest particle in the recycled carbon black being measured is 20 μm or less. Therefore, from the viewpoint of accurately measuring particle size and the ease of measurement, the range of the grind gauge used is preferably 0 to 25 μm. However, if the upper limit of the range of the grind gauge is greater than 20 μm, it is possible to determine whether the particle size of the third largest particle is 20 μm or less, and thus it can be used. Furthermore, when used for other purposes (maintaining performance other than durability of the rubber composition containing recycled carbon black), the range of the grind gauge used can be appropriately selected according to the purpose.

[0162] JIS K5101-1-5 describes a method for preparing a paste of recycled carbon black as a measurement sample in grind gauge measurement. It is preferable to prepare the paste of recycled carbon black according to JIS K5101-1-5 as a measurement sample for grind gauge measurement. By preparing the paste of recycled carbon black according to JIS K5101-1-5, the accuracy of grind gauge measurement can be further improved. Furthermore, tires in which recycled carbon black evaluated using such a measurement sample is applied to the cap tread rubber layer can more reliably maintain tire performance.

[0163] In one embodiment, the accuracy of grind gauge measurement can be further improved by appropriately adjusting the viscosity of the paste. In one embodiment, it is preferable to prepare a paste (measurement sample) containing recycled carbon black by blending recycled carbon black and zinc oxide with epoxidized soybean oil. Here, the blending ratio of the paste is not particularly limited, but it is preferable to use about 8 to 12 g of recycled carbon black and about 160 to 200 g of zinc oxide per 100 mL of epoxidized soybean oil.

[0164] Furthermore, in the measurement of recycled carbon black using a grind gauge, it is preferable to prepare the recycled carbon black paste as a measurement sample by setting the applied load to 0.4 to 0.5 kN and the rotation speed of the glass plate to 90 to 110 r / min, in accordance with JIS K5101-1-5. By using recycled carbon black paste prepared with the applied load and rotation speed of the glass plate within the above range, it is possible to further suppress variations in measurement results and further improve measurement accuracy. In addition, tires to which recycled carbon black evaluated using such measurement samples is applied to the cap tread rubber layer can maintain tire performance more reliably. Note that the method for preparing the recycled carbon black paste is not particularly limited, as long as it does not affect the measurement results, even if it is a method other than the one conforming to the JIS standard.

[0165] When the recycled carbon black is measured with a grind gauge, three or more lines with a length of 10 mm or more can be observed. If the number of lines with a length of 10 mm or more is less than three, it is considered that the recycled carbon black being measured is too minute, and therefore cannot be sufficiently detected. In addition, while several lines caused by particles in the sample are observed when measuring with a grind gauge, in this embodiment, in accordance with JIS standards, lines with a length of 10 mm or more are not considered, and lines with a length of 10 mm or more are considered.

[0166] Furthermore, in this embodiment, in accordance with JIS standards, among the lines with a length of 10 mm or more, the line caused by the largest particle and the line caused by the second largest particle are judged to be abnormal values, and from the viewpoint of improving measurement accuracy, attention is paid to the line caused by the third largest particle and its particle size is confirmed. Here, the smaller the particle size of the third largest particle in the recycled carbon black, the better the dispersibility of the recycled carbon black in the rubber composition when the recycled carbon black is blended into the rubber composition, and the more likely it is that the durability of the rubber composition will improve. As described above, in the case of the recycled carbon black, if the particle size of the third largest particle among the particles that cause the line with a length of 10 mm or more is 20 μm or less, the dispersibility of the recycled carbon black in the rubber composition is improved, and the durability of the rubber composition can be effectively improved.

[0167] Figure 1 shows an explanatory diagram of an example of measurement results using a grind gauge. In the measurement using grind gauge 1, several lines are observed that are attributable to particles in the sample being measured. In this embodiment, in accordance with JIS standards, lines 2 with a length of less than 10 mm are not considered, and lines 3 with a length of 10 mm or more are considered. Furthermore, among the lines 3 with a length of 10 mm or more, line 31 at the largest particle and line 32 at the second largest particle are judged to be abnormal values, and in this embodiment, from the viewpoint of improving measurement accuracy, attention is paid to line 33 at the third largest particle. The scale 4 at the location where line 33 at the third largest particle appears is read, and this reading is taken as the particle size of the third largest particle. If the particle size of the third largest particle is 20 μm or less, even if recycled carbon black is applied, the decrease in the durability of the cap tread rubber layer, in particular the high-temperature tensile strength after degradation and the crack propagation resistance after thermal degradation, can be suppressed. In this specification, the measurement of recycled carbon black using a grind gauge is performed by the method described in the examples.

[0168] The recycled carbon black in which the third largest particle size is 20 μm or less can be manufactured by various methods. For example, recycled carbon black in which the third largest particle size is 20 μm or less can be manufactured by further grinding the recycled carbon black produced by a general method from recycled waste by extending the grinding process for a longer time or increasing the grinding intensity.

[0169] The recycled carbon black preferably has an ash content of 20% by mass or less. If the ash content in the recycled carbon black is 20% by mass or less, a tire with sufficient reinforcement can be obtained. Considering the reinforcement of the tire, the ash content of the recycled carbon black is more preferably 10% by mass or less, even more preferably 6% by mass or less, even more preferably 5% by mass or less, even more preferably 4% by mass or less, even more preferably 3% by mass or less, still even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. Furthermore, the ash content of the recycled carbon black is preferably 0.5% by mass or more. In other words, the ash content of the recycled carbon black is preferably 0.5% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, even more preferably 0.5% by mass or more and 6% by mass or less, even more preferably 0.5% by mass or more and 5% by mass or less, even more preferably 0.5% by mass or more and 4% by mass or less, even more preferably 0.5% by mass or more and 3% by mass or less, even more preferably 0.5% by mass or more and 2% by mass or less, and particularly preferably 0.5% by mass or more and 1% by mass or less. Here, in this specification, the ash content of the carbon black is determined according to ASTM D8474 / D1506.

[0170] The aforementioned ash content specifically includes zinc oxide, zinc sulfide, silica, iron compounds (iron oxide), calcium oxide, aluminum oxide, magnesium oxide, and the like. In the case of recycled carbon black produced from solid residue obtained by thermal decomposition of waste, a certain amount of ash remains even after various processes to remove it. In this embodiment, the presence of ash in recycled carbon black is permitted. The lower limit of the ash content of the recycled carbon black used in this embodiment may be 0.5% by mass.

[0171] The recycled carbon black preferably contains one or more elements selected from the group consisting of Zn (zinc), Fe (iron), and Cu (copper). Since recycled carbon black is obtained from recycled waste as raw material, it contains various elements other than carbon (C), and zinc (Zn), copper (Cu), and iron (Fe) are elements that are easily contained in recycled carbon black. Therefore, recycled carbon black containing at least one of the elements Zn, Cu, and Fe can maintain the physical properties of the rubber composition while leaving components that may affect the deterioration of the rubber composition's physical properties, thus simplifying processing steps such as purification to completely remove components that may affect the deterioration of the rubber composition's physical properties. In other words, recycled carbon black containing at least one of the elements Zn, Cu, and Fe does not require special removal operations, and tires having a cap tread rubber layer containing such recycled carbon black are easy to manufacture.

[0172] Furthermore, the recycled carbon black may contain Zn (zinc). The Zn in the recycled carbon black originates from, for example, zinc oxide used as a vulcanization aid, and is an element that is particularly likely to be present in recycled carbon black. If the Zn content in the recycled carbon black exceeds a certain amount, the physical properties of the rubber composition will deteriorate, but if it is below a certain amount, the deterioration of the physical properties of the rubber composition can be suppressed. However, the recycled carbon black may also not contain Zn.

[0173] If the recycled carbon black contains Zn, the Zn content in the recycled carbon black is preferably 2.5% by mass or less. A lower Zn content in the carbon black is preferable, but if the Zn content is 2.5% by mass or less, the deterioration of the physical properties of the rubber composition and tire performance can be suppressed. From the viewpoint of suppressing the deterioration of the physical properties of the rubber composition and tire performance, the Zn content is more preferably 2.0% by mass or less, even more preferably 1.5% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.5% by mass or less. The Zn content may also be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate.

[0174] Methods to keep the Zn content in recycled carbon black within the above range include, for example, acid treatment and analyzing the amount of Zn contained in the raw rubber to be recycled in advance, and using some or all of the raw rubber with a low Zn content.

[0175] The Fe content in the recycled carbon black is preferably 0% by mass or more and 0.1% by mass or less. A lower Fe content in the recycled carbon black is preferable, but if the Fe content is 0.1% by mass or less, the deterioration of the physical properties of the rubber composition and tire performance can be suppressed. From the viewpoint of suppressing the physical properties of the rubber composition and tire performance, the Fe content in the recycled carbon black is more preferably 0.09% by mass or less, even more preferably 0.08% by mass or less, even more preferably 0.07% by mass or less, even more preferably 0.06% by mass or less, even more preferably 0.05% by mass or less, still even more preferably 0.04% by mass or less, and most preferably 0.03% by mass or less. Furthermore, the Fe content in the recycled carbon black may be 0.01% by mass or more, or 0.02% by mass or more. The above upper and lower limits can be combined as appropriate.

[0176] The Cu content in the recycled carbon black is preferably 0% by mass or more and 0.05% by mass or less. A lower Cu content in the recycled carbon black is preferable, but if the Cu content is 0.05% by mass or less, the deterioration of the physical properties of the rubber composition and tire performance can be suppressed. From the viewpoint of suppressing the physical properties of the rubber composition and tire performance, the Cu content in the recycled carbon black is more preferably 0.04% by mass or less, even more preferably 0.03% by mass or less, even more preferably 0.02% by mass or less, and even more preferably 0.01% by mass or less. Furthermore, the Cu content in the recycled carbon black may be 0.01% by mass or more, or 0.02% by mass or more. The above upper and lower limits can be combined as appropriate.

[0177] The recycled carbon black may contain components other than Zn, Fe, and Cu as described above. "Components other than Zn, Fe, and Cu" refers to components other than Zn, Fe, and Cu in the ash. Examples of components other than Zn, Fe, and Cu in the ash include Si (silicon), S (sulfur), Ca (calcium), K (potassium), Br (bromine), Mg (magnesium), Cl (chlorine), P (phosphorus), Co (cobalt), Na (sodium), and Al (aluminum).

[0178] The recycled carbon black may contain silicon (Si). Preferably, the Si content in the recycled carbon black is 0% by mass or more and 1.0% by mass or less. A Si content of 1.0% by mass or less in the recycled carbon black can suppress the deterioration of the physical properties of the rubber composition and tire performance. From a similar viewpoint, it is more preferable that the Si content in the recycled carbon black be 0.5% by mass or less, and even more preferable that be 0.3% by mass or less. It is also preferable that the Si content in the recycled carbon black be 0% by mass, i.e., that the recycled carbon black is substantially Si-free. On the other hand, the Si content in the recycled carbon black may be 0.01% by mass or more, or 0.05% by mass or more. The above upper and lower limits can be combined as appropriate.

[0179] The recycled carbon black may contain sulfur (S). The S content in the recycled carbon black is preferably 0.4% by mass or more, and more preferably 0.5% by mass or more. Furthermore, the S content in the recycled carbon black is preferably 2.0% by mass or less, more preferably 1.8% by mass or less, and even more preferably 1.0% by mass or less. The above upper and lower limits can be combined as appropriate.

[0180] The recycled carbon black may contain Ca (calcium). The Ca content in the recycled carbon black is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, and even more preferably 0.8% by mass or more. Furthermore, the Ca content in the recycled carbon black is preferably 1.5% by mass or less, more preferably 1.2% by mass or less, and even more preferably 1.1% by mass or less. The above upper and lower limits can be combined as appropriate.

[0181] The recycled carbon black used in this embodiment has a nitrogen adsorption specific surface area (N) determined by the BET method. ２ SA) 40-100m ２ It is preferable that the amount be / g, and 50 to 90 m ２ It is more preferable that the amount be / g, and 55 to 75 m ２ It is particularly preferable that the nitrogen adsorption specific surface area (N) of carbon black by the BET method is specified in this specification. ２ SA) is the statistical thickness specific surface area (STSA), which is determined according to ASTM D6556.

[0182] The recycled carbon black preferably has a pH of 4 to 12, more preferably 5 to 11, and particularly preferably 6 to 10. Herein, the pH of the recycled carbon black is determined according to ASTM D1512.

[0183] The recycled carbon black preferably has a toluene staining transmittance of 60% or more, more preferably 70% or more, and particularly preferably 80% or more. Herein, in this specification, the toluene staining transmittance of recycled carbon black is determined according to ASTM D1618.

[0184] The recycled carbon black preferably has a heating loss of 3% by mass or less at 125°C, more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less. Hereinafter, the heating loss of the recycled carbon black at 125°C is determined according to ASTM D1509.

[0185] The recycled carbon black preferably has a sulfur content of 5% by mass or less, more preferably 3.5% by mass or less, and particularly preferably 3% by mass or less.

[0186] The recycled carbon black preferably has a 35-mesh sieve residue of 20 ppm by mass or less, more preferably 15 ppm by mass or less, and particularly preferably 10 ppm by mass or less. Here, in this specification, the 35-mesh sieve residue of the recycled carbon black is determined according to ASTM D1514.

[0187] The recycled carbon black preferably has a 325-mesh (44 μm) sieve residue of 1,000 ppm by mass or less, more preferably 700 ppm by mass or less, and particularly preferably 300 ppm by mass or less. Here, in this specification, the 325-mesh (44 μm) sieve residue of the recycled carbon black is determined according to ASTM D1514.

[0188] The recycled carbon black preferably has a pellet hardness of 100 cN or less, more preferably 90 cN or less, and particularly preferably 80 cN or less. Hereinafter, the pellet hardness of the recycled carbon black is determined according to ASTM D5230.

[0189] The recycled carbon black preferably has a pellet fine powder content of 10% by mass or less, more preferably 7% by mass or less, and particularly preferably 5% by mass or less. Hereinafter, the pellet fine powder content of the recycled carbon black is determined according to ASTM D1508.

[0190] The recycled carbon black preferably has a particle size (D97) of 25 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. Hereinafter, the particle size (D97) of the recycled carbon black is determined using a laser diffraction particle size analyzer, with the refractive index of water being 1.33 and the refractive index of the filler being 1.75.

[0191] The recycled carbon black preferably contains 50% or more by volume of particles 5 μm or smaller, more preferably 70% or more by volume, and particularly preferably 80% or more by volume.

[0192] The recycled carbon black preferably has an oil absorption rate (OAN) of 70 to 120 mL / 100 g, more preferably 75 to 110 mL / 100 g, and particularly preferably 80 to 100 mL / 100 g. Hereinafter, the oil absorption rate (OAN) of the recycled carbon black is determined according to ASTM D2414.

[0193] The recycled carbon black preferably has an oil absorption rate (COAN) of 50 to 110 mL / 100 g, more preferably 60 to 100 mL / 100 g, and particularly preferably 70 to 90 mL / 100 g. Hereinafter, the oil absorption rate (COAN) of the compressed sample of recycled carbon black is determined according to ASTM D3493.

[0194] The amount of recycled carbon black in the rubber composition of this embodiment is preferably 1 to 100 parts by mass, more preferably 5 to 80 parts by mass, even more preferably 5 to 50 parts by mass, even more preferably 5 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the rubber component (A). When the amount of recycled carbon black is 5 parts by mass or more per 100 parts by mass of the rubber component (A), it has a great effect in improving the ratio of sustainable materials in the tire, and when it is 50 parts by mass or less, the tire performance can be maintained more reliably.

[0195] --Carbon Black Other Than Recycled Carbon Black-- The rubber composition of this embodiment may further contain, in addition to the recycled carbon black described above, carbon black other than recycled carbon black (virgin carbon black) as a filler (B). Examples of carbon black other than recycled carbon black include plant-derived carbon black, such as that derived from castor oil and pine resin oil. The grade of the carbon black is not particularly limited, and examples include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, N762, etc. Commercially available carbon black can be used, and examples of commercially available carbon black include products from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Birla Carbon, etc. These carbon blacks may be used individually or in combination of two or more types.

[0196] The nitrogen adsorption specific surface area of ​​the carbon black (N ２ SA) is not particularly limited and can be adjusted as appropriate. For example, the specific surface area (N) of nitrogen adsorption of carbon black. ２ SA) is 20m ２ Preferably 30 m ２ More preferably 50 m ２ More preferably 70 m ２ More preferably 90m / g or more. ２ A value of 250m or more is even more preferable. ２ Preferably less than / g, 200m ２ More preferably less than / g, and 150m ２ It is even more preferable to be less than or equal to 130m ２ A value of less than or equal to / g is even more preferable.

[0197] The carbon black content is not particularly limited, but is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component (A). Furthermore, the carbon black content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 90 parts by mass or less, per 100 parts by mass of the rubber component (A).

[0198] -Silica- The filler (B) may contain silica. The silica is not particularly limited and can be appropriately selected according to the required performance. For example, wet silica (hydrated silica), dry silica (anhydrous silica), colloidal silica, calcium silicate, aluminum silicate, etc. can be used as the silica, and among these, wet silica is preferred. These silicas may be used individually or in combination of two or more.

[0199] Furthermore, precipitated silica can be used as the wet silica. Precipitated silica is silica obtained by first reacting the reaction solution at a relatively high temperature and in a neutral to alkaline pH range during the initial stages of production to grow primary silica particles, and then controlling the pH to the acidic side to aggregate the primary particles.

[0200] As for the silica, from the viewpoint of reducing environmental impact, silica derived from silicate plants is also preferred. These silicate plants include, for example, mosses, ferns, horsetails, cucurbitaceae, nettleaceae, and grasses. Among these plants, grasses are preferred. Examples of grasses include rice, bamboo grass, and sugarcane, with rice being preferred among these. Rice is widely cultivated for food, so it can be procured locally in a wide area, and rice hulls are generated in large quantities as industrial waste, making it easy to secure a sufficient amount. Therefore, from the viewpoint of availability, silica derived from rice hulls (hereinafter also referred to as "rice hull silica") is particularly preferred. By using this rice hull silica, rice hulls that would otherwise be industrial waste can be effectively utilized, and since the raw material can be procured locally near the tire manufacturing plant, the energy and costs of transportation and storage can be reduced, which is environmentally friendly from various perspectives. The aforementioned rice husk silica may be powder of rice husk charcoal obtained by carbonizing rice husks by heating, or it may be precipitated silica produced by a wet method using an alkaline aqueous solution of silicate prepared by extracting rice husk ash generated when rice husks are burned as fuel in a biomass boiler with alkali. The method for producing the aforementioned rice husk charcoal is not particularly limited, and various known methods can be used. For example, rice husk charcoal can be obtained by thermal decomposition by steam-roasting rice husks in a kiln. The rice husk charcoal obtained in this way can be crushed using a known crusher (for example, a ball mill), sorted into a predetermined particle size range, and classified to obtain powder of rice husk charcoal. Furthermore, the aforementioned precipitated silica derived from rice husks can be produced by the method described in Japanese Patent Application Publication No. 2019-38728, etc.

[0201] The aforementioned silica can also include silica recycled from silicon wafer scraps used as raw materials for semiconductors, glass bottles, etc.

[0202] Furthermore, the silica preferably has a CTAB (cetyltrimethylammonium bromide) specific surface area of ​​50 m². ２ / g to 350m ２ / g, more preferably 70m ２ / g ~ 250m ２ It is / g. The CTAB specific surface area of ​​silica is 50 m². ２When the amount is greater than / g, the wear resistance is further improved, and the CTAB specific surface area of ​​silica is 350 m². ２ When the value is less than or equal to / g, the rolling resistance decreases. Note that the CTAB specific surface area refers to the value measured in accordance with ASTM D3765-92. However, the adsorption cross-section per molecule of cetyltrimethylammonium bromide on the silica surface is 0.35 nm. ２ The specific surface area (m²) is calculated from the amount of adsorption of CTAB. ２ Let the CTAB specific surface area be ( / g).

[0203] Furthermore, the silica has a nitrogen adsorption specific surface area (BET method) of 80 m². ２ / g or more 330m ２ It is preferable that the amount is less than / g. The specific surface area of ​​silica for nitrogen adsorption (BET method) is 80 m². ２ If the nitrogen adsorption specific surface area (BET method) of silica is 330 m² or higher, the tread rubber layer can be sufficiently reinforced, further improving the tire's fuel efficiency. ２ If the value is less than / g, the elastic modulus of the tread rubber layer does not become too high, further improving the wet grip performance of the tire. From the perspective of further reducing rolling resistance and improving the wear resistance of the tire, the nitrogen adsorption specific surface area (BET method) of silica is 100m². ２ It is preferable that it be 130m or more per g. ２ Preferably, it is 150m or more per gram. ２ It is preferable that it be 170 m or more ２ It is preferable that it be 180m or more per gram. ２ It is preferable that it be 190 m or more per g. ２ It is preferable that it be 195 m or more per g. ２ It is even more preferable that the amount is greater than or equal to 1 / g. Furthermore, from the viewpoint of further improving the wet grip performance of the tire, the nitrogen adsorption specific surface area of ​​silica (BET method) should be 300 m². ２ It is preferable that the amount is less than or equal to 280m ２ It is more preferable that it be less than or equal to 270m ２ It is even more preferable that it be less than or equal to 250m ２ It is particularly preferable that the amount be less than or equal to / g.

[0204] The silica content is preferably 20 parts by mass or more and less than 100 parts by mass per 100 parts by mass of the rubber component (A). By optimizing the amount of silica, a higher level of wet grip performance, fuel efficiency, and wear resistance can be achieved simultaneously. When the silica content is 20 parts by mass or more, sufficient wet grip performance, fuel efficiency, and wear 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 per 100 parts by mass of the rubber component (A), sufficient wet grip performance, fuel efficiency, and wear resistance can be obtained while suppressing deterioration of low heat generation and processability. From a similar viewpoint, the silica content is more preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 62 parts by mass or more, even more preferably 65 parts by mass or more, and particularly preferably 68 parts by mass or more, per 100 parts by mass of the rubber component (A). In addition, the silica content 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, based on 100 parts by mass of the rubber component (A).

[0205] In the filler (B), the silica content in the total amount of silica and 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. By having a silica content of 80% by mass or more in the total amount of silica and carbon black, the decrease in fuel efficiency due to the increase in carbon black can be suppressed, and by having a silica content of less than 100% by mass, the reinforcing effect of carbon black can be reliably ensured.

[0206] (Silane coupling agent) If the filler (B) contains silica, the rubber composition of this embodiment preferably further contains a silane coupling agent. By using the silane coupling agent, the dispersibility of the silica contained in the filler (B) is improved, contributing to achieving both wet grip performance, low fuel consumption performance and wear resistance performance.

[0207] Preferably, the silane coupling agent contains at least a silane coupling agent having a thiol group (SC-A) and a silane coupling agent having a sulfide bond (SC-B). Although the silane coupling agent having a thiol group (SC-A) is highly effective in improving the dispersibility of silica as described above, if the content is high, it may cause discoloration such as blackening of the tire over time. Therefore, by further including a silane coupling agent having a sulfide bond (SC-B) as the silane coupling agent and adjusting the content of these silane coupling agents, it is possible to suppress discoloration such as blackening while achieving a balance between the wet grip performance of the tire and fuel efficiency and wear resistance (excellent discoloration resistance).

[0208] The total content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) is preferably more than 1 part by mass and 15 parts by mass or less per 100 parts by mass of silica. This is because a total content exceeding 1 part by mass per 100 parts by mass of silica allows for a sufficient balance between the wet grip performance of the tire and low fuel consumption and wear resistance, and a total content of 15 parts by mass or less per 100 parts by mass of silica ensures sufficient resistance to discoloration. From a similar viewpoint, the total content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) is preferably 2 to 14 parts by mass, more preferably 3 to 13 parts by mass, and even more preferably 5 to 12 parts by mass per 100 parts by mass of silica.

[0209] Furthermore, the content of the silane coupling agent (SC-A) is preferably 1 to 10 parts by mass per 100 parts by mass of silica. When the content of the silane coupling agent (SC-A) is 1 part by mass or more per 100 parts by mass of silica, it is possible to sufficiently achieve both wet grip performance, fuel efficiency, and wear resistance of the tire, and when the content of the silane coupling agent (SC-A) is 10 parts by mass or less per 100 parts by mass of silica, sufficient discoloration resistance can be ensured. From a similar viewpoint, the content of the silane coupling agent (SC-A) is preferably 2 to 9.5 parts by mass, and more preferably 3 to 9 parts by mass, per 100 parts by mass of silica. The content of the silane coupling agent (SC-B) is appropriately selected while considering the content of the silane coupling agent (SC-A) and the total content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B). For example, the content of the silane coupling agent (SC-B) is preferably 0.5 to 9.5 parts by mass, and more preferably 1 to 9 parts by mass, per 100 parts by mass of silica.

[0210] Particularly preferably, the silane coupling agent comprises at least a silane coupling agent having a thiol group (SC-A) and a silane coupling agent having a sulfide bond (SC-B), wherein the content of the silane coupling agent (SC-A) is 1 to 10 parts by mass per 100 parts by mass of silica, and the total content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) is greater than 1 part by mass and 15 parts by mass or less per 100 parts by mass of silica. Although the silane coupling agent having a thiol group (SC-A) is highly effective in improving the dispersibility of silica, if the content is high, it may cause discoloration of the tire's appearance over time. In contrast, by using a silane coupling agent having a thiol group (SC-A) and a silane coupling agent having a sulfide bond (SC-B) in combination, and keeping the content of the silane coupling agent (SC-A) at 10 parts by mass or less per 100 parts by mass of silica, and keeping the total content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) at 15 parts by mass or less per 100 parts by mass of silica, discoloration of the appearance can be suppressed. Therefore, a tire having a cap tread rubber layer containing a silane coupling agent having a thiol group (SC-A) and a silane coupling agent having a sulfide bond (SC-B), with the content of the silane coupling agent (SC-A) at 10 parts by mass or less per 100 parts by mass of silica, and the total content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) at 15 parts by mass or less per 100 parts by mass of silica, can suppress discoloration of the appearance.

[0211] Furthermore, from the viewpoint of achieving a good balance between wet grip performance, fuel efficiency, and wear resistance of the tire, as well as providing a good balance of discoloration resistance, the mass ratio of the content of the silane coupling agent (SC-B) to the content of the silane coupling agent (SC-A) (SC-B / SC-A) is preferably 0.3 or more and less than 3.0. This is because when the mass ratio of the content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) (SC-B / SC-A) is 0.3 or more, the discoloration resistance effect is more reliably obtained, and when the mass ratio of the content of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) (SC-B / SC-A) is less than 3.0, a better balance of wet grip performance, fuel efficiency, and wear resistance is achieved. From a similar viewpoint, the mass ratio of the silane coupling agent (SC-A) and the silane coupling agent (SC-B) (SC-B / SC-A) is preferably 0.31 or more and 3.0 or less, and more preferably 0.32 or more and 2.9 or less.

[0212] The silane coupling agent (SC-A) is not particularly limited as long as it has a thiol group (-SH). For example, silane coupling agents (SC-A) having a thiol group include 3-(trimethoxysilyl)-1-propantheol, 3-(triethoxysilyl)-1-propantheol, 3-(methyldimethoxysilyl)-1-propantheol, 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-propantheol {manufactured by Evonik De Gussa, trade name "Si363", [C １３ H ２７ O(CH ２ CH ２ O) ５ ] ２ (CH ３ CH ２ O)Si(CH２ ) ３ Examples include SH, etc.

[0213] Furthermore, among those described above, the silane coupling agent (SC-A) preferably has 20 to 75 carbon atoms. When the silane coupling agent (SC-A) has 20 to 75 carbon atoms, it is possible to more reliably achieve a balance between the wet grip performance, fuel efficiency, and wear resistance of the tire.

[0214] Furthermore, the silane coupling agent (SC-B) is not particularly limited as long as it has a sulfide bond (-S-). Note that multiple sulfide bonds can be linked together, forming a polysulfide bond [-(S) ｎ -, where n is a natural number greater than or equal to 2) may form, but -SH (i.e., the thiol group mentioned above) in which hydrogen is directly bonded to sulfur shall be excluded. For example, as silane coupling agents having sulfide bonds (SC-B), there are 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-di Examples include methylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, and bis(3-diethoxymethylsilylpropyl)tetrasulfide.

[0215] Furthermore, bioethanol can also be used as a raw material for silane coupling agents. Bioethanol is produced using mainly sugars and / or celluloses as biological resources, and does not allow for the effective utilization of other biological resources such as proteins, lipids, and amino acids. Moreover, sugars compete with food, and excessive use of celluloses leads to deforestation. For this reason, depending on the supply situation of various biological resources, as well as the supply situation of recycled resources, the supply situation of fossil resources, and market demands (for example, the demand for biomass resources as food), it is preferable to use multiple types of monomer components derived from biological resources, or to use monomer components derived from biological resources, recycled resources, and fossil resources in combination as monomer components derived from fossil resources. This allows for the effective utilization of a wide range of biological resources such as sugars, proteins, and lipids, as well as recycled resources, without relying on a single type of biological resource, and also allows for environmental considerations depending on the circumstances during production.

[0216] (Resin component (C)) The rubber composition of this embodiment preferably contains a resin component (C) in order to further improve the wear resistance and wet grip performance of the tire while maintaining various properties. Also, from the same viewpoint, it is preferable that the resin component (C) is at least partially hydrogenated.

[0217] The content of the resin component (C) is preferably 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of the rubber component (A). When the content of the resin component (C) in the rubber composition is 1 part by mass or more per 100 parts by mass of the rubber component (A), the effect of the resin component (C) is fully expressed, and when it is 100 parts by mass or less, the resin component (C) is less likely to precipitate from the tire, and the effect of the resin component (C) can be fully expressed. From the viewpoint of further enhancing the effect of the resin component (C), the content of the resin component (C) in the rubber composition is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, more preferably 9 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 17 parts by mass or more per 100 parts by mass of the rubber component (A). Furthermore, from the viewpoint of suppressing the precipitation of resin component (C) from the tire and suppressing deterioration of the tire appearance, the content of resin component (C) in the rubber composition is more preferably less than 50 parts by mass, even more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less, per 100 parts by mass of rubber component (A).

[0218] The resin component (C) preferably has a softening point of 30°C or higher and a weight-average molecular weight in polystyrene terms of 200 to 1600 g / mol. Applying a rubber composition containing such resin component (C) to a tire can further improve the wear resistance of the tire. From a similar viewpoint, the softening point of the resin component (C) is preferably 60°C or higher, more preferably 90°C or higher, even more preferably higher than 110°C, and even more preferably 120°C or higher. In this specification, the softening point of the resin component (C) is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2015 (ISO 28641:2010) is measured using a ring-type softening point analyzer. The weight-average molecular weight of the resin component is measured by gel permeation chromatography (GPC) and the polystyrene equivalent value is calculated.

[0219] Furthermore, if the softening point of the resin component (C) is higher than 110°C, the tire to which the rubber composition is applied can be sufficiently reinforced, and the wear resistance can be further improved. From the viewpoint of tire wear resistance, the softening point of the resin component (C) is more preferably 116°C or higher, more preferably 120°C or higher, more preferably 123°C or higher, and even more preferably 127°C or higher. Furthermore, from the viewpoint of processability, the softening point of the resin component (C) is preferably 160°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, more preferably 141°C or lower, even more preferably 140°C or lower, and even more preferably 136°C or lower.

[0220] If the weight-average molecular weight of the resin component (C) on a polystyrene basis is 200 g / mol or more, the resin component (C) is less likely to precipitate from the tire, and the effects of the resin component (C) can be fully expressed. If it is 1600 g / mol or less, the resin component (C) is more compatible with the rubber component (A). From the viewpoint of suppressing the precipitation of the resin component (C) from the tire and suppressing the deterioration of the tire appearance, the weight-average molecular weight of the resin component (C) on a polystyrene basis 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. Furthermore, from the viewpoint of improving the compatibility of the resin component (C) with the rubber component (A) and further enhancing the effects of the resin component (C), the weight-average molecular weight of the resin component (C) in terms of polystyrene is more preferably 1570 g / mol or less, more preferably 1530 g / mol or less, more preferably 1500 g / mol or less, more preferably 1470 g / mol or less, more preferably 1430 g / mol or less, more preferably 1400 g / mol or less, more preferably 1370 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.

[0221] The weight-average molecular weight (Mw) of the aforementioned resin component (C) on a polystyrene basis. ＨＲ The softening point (Ts) of the resin component (C) relative to (unit is g / mol) ＨＲ ) (unit is °C) ratio (Ts ＨＲ / Mw ＨＲThe ratio (Ts) is preferably 0.07 or higher, more preferably 0.083 or higher, more preferably 0.095 or higher, more preferably 0.104 or higher, more preferably 0.125 or higher, more preferably 0.135 or higher, more preferably 0.14 or higher, and even more preferably 0.141 or higher. ＨＲ / Mw ＨＲ The softening point and weight-average molecular weight in terms of polystyrene can be determined by the method described in the examples below.

[0222] The above-mentioned resin component that is at least partially hydrogenated refers to a resin obtained by reducing and hydrogenating a resin. Examples of resins that serve as raw materials for hydrogenated resin component (C) include terpene resins, rosin resins, and C ５ based resin, C ５ -C ９ based resin, C ９ Examples include terpene resins, cyclopentadiene resins, aromatic resins, coumarone resins, indene resins, coumarone-indene resins, olefin resins, polyurethane resins, and acrylic resins. These resins may be used individually or in combination of two or more. Furthermore, terpene resins and rosin resins are naturally derived and sustainable resins, thus further reducing environmental impact and improving tire performance, such as grip performance on various road surfaces including dry, wet, snowy, and icy surfaces. ５ based resin, C ９ based resin, C ５ -C ９ Aromatic resins, such as cyclopentadiene resins, can improve wear resistance and fuel efficiency in a balanced way. Aromatic resins, on the other hand, can improve grip performance, wear resistance, and rubber strength in a balanced way.

[0223] The aforementioned terpene resins are solid resins obtained by polymerizing turpentine oil, which is obtained simultaneously when rosin is obtained from pine trees, or polymer components separated therefrom, using a Friedel-Crafts type catalyst. Examples include β-pinene resin and α-pinene resin. Terpene resins also include terpene-aromatic compound resins, and typical examples of such terpene-aromatic compound resins include terpene-phenol resin and styrene-terpene resin. Terpene-phenol resins can be obtained by reacting terpenes with various phenols using a Friedel-Crafts type catalyst, or by further condensation with formalin. Styrene-terpene resins can be obtained by reacting styrene with terpenes using a Friedel-Crafts type catalyst. There are no particular restrictions 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.

[0224] Examples of rosin-based resins include natural resin rosins such as gum rosin contained in raw pine resin and tall oil, tall oil rosin, and wood rosin. Examples of modified rosins, rosin derivatives, and modified rosin derivatives include polymerized rosin and its partially hydrogenated rosin; glycerol ester rosin and its partially hydrogenated or fully hydrogenated rosin; pentaerythritol ester rosin and its partially hydrogenated or polymerized rosin; and so on.

[0225] Said C ５ As for resins, C obtained by the thermal decomposition of naphtha in the petrochemical industry. ５ Examples include aliphatic petroleum resins obtained by (co)polymerizing the fractions. ５ The fraction typically includes olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene, as well as diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene.

[0226] Said C ５ -C ９ C resins are C ５ -C９ This refers to synthetic petroleum resins, C ５ -C ９ Examples of resins include petroleum-derived C ５ -C １１ The fraction is AlCl ３ BF ３ Examples include solid polymers obtained by polymerization using Friedel-Crafts catalysts such as [list of catalysts], and more specifically, copolymers mainly composed of styrene, vinyltoluene, α-methylstyrene, indene, etc. ５ -C ９ As for resin systems, C ９ Resins containing fewer of the above components are preferred from the viewpoint of compatibility with rubber component (A). Here, "C ９ "The above components are low" means that the total amount of C in the resin is low. ９ This means that the above components are present in an amount of less than 50% by mass, preferably 40% by mass or less.

[0227] Said C ９ C resins are C ９ This refers to synthetic petroleum resins, such as AlCl ３ Ya BF ３ Using Friedelcrafts type catalysts such as C ９ This refers to a solid polymer obtained by polymerizing a fraction. ９ Examples of resin compounds include copolymers mainly composed of indene, α-methylstyrene, vinyltoluene, etc.

[0228] The cyclopentadiene-based resin refers to a resin containing units derived from cyclopentadiene monomers as monomer units. Examples of the cyclopentadiene-based resin include homopolymers of cyclopentadiene monomers, copolymers of two or more cyclopentadiene monomers, and copolymers of cyclopentadiene monomers and other monomers. Examples of cyclopentadiene monomers include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene, among which dicyclopentadiene is preferred, that is, a dicyclopentadiene-based resin is preferred as the cyclopentadiene-based resin. Examples of the dicyclopentadiene-based resin include AlCl ３ Ya BF ３This refers to resins obtained by polymerizing dicyclopentadiene using Friedel-Crafts type catalysts such as the above. Dicyclopentadiene-based resins include homopolymers of dicyclopentadiene, copolymers of dicyclopentadiene and aromatic monomers, and copolymers of dicyclopentadiene and C ９ Copolymers with fractions (such as vinyltoluene and indene) are examples.

[0229] The aforementioned aromatic resin refers to a resin that contains units derived from aromatic monomers as monomer units. Examples of such aromatic resins include homopolymers of aromatic monomers, copolymers of two or more aromatic monomers, and copolymers of aromatic monomers with other monomers. Examples of aromatic monomers include styrene monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-phenylstyrene; phenol monomers such as phenol, alkylphenol, and alkoxyphenol; and naphthol monomers such as naphthol, alkylnaphthol, and alkoxynaphthol.

[0230] Furthermore, the resin that serves as the raw material for the hydrogenated resin component (C) is, for example, C ５ A resin obtained by copolymerizing the fraction with dicyclopentadiene (DCPD) (C ５ - It may contain DCPD-based resins. Here, if the dicyclopentadiene-derived component in the total amount of resin is 50% by mass or more, C ５ - DCPD resins are included in dicyclopentadiene resins. If the dicyclopentadiene-derived component in the total amount of resin is less than 50% by mass, C ５ - DCPD resin is C ５ This refers to the components included in the resin system. The same applies even if a small amount of a third component or other elements are present.

[0231] From the viewpoint of improving the compatibility between the rubber component (A) and the resin component (C), improving the rolling resistance of the tire to which the rubber composition is applied, and improving the wet grip performance, the resin component (C) is a hydrogenated terpene resin, hydrogenated C ５based resin, hydrogenated C ５ -C ９ Preferably, it is at least one selected from the group consisting of hydrogenated C resins and hydrogenated dicyclopentadiene resins (hydrogenated DCPD resins), ５ Resin systems and hydrogenated C ５ -C ９ It is more preferably at least one selected from the group consisting of hydrogenated C resins. ５ It is even more preferable that the resin is a type of resin. Furthermore, it is preferable that the resin component (C) is a resin having at least a monomer with a hydrogenated DCPD structure or a hydrogenated cyclic structure.

[0232] Furthermore, the resin component (C) may be modified to introduce functional groups that interact with fillers (B) such as carbon black and silica. Examples of such functional groups include amino groups, amide groups, isocyanate groups, imino groups, imidazole groups, urea groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, ether groups, carbonyl groups, oxycarbonyl groups, silyl groups, alkoxysilyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, and thiocarbonyl groups.

[0233] As the aforementioned resin component (C), commercially available products can be used. Examples of commercially available resin component (C) include products from Eastman, ENEOS Corporation, Arakawa Chemical Industries, Ltd., ExxonMobil, Kraton, Yasuhara Chemical Co., Ltd., Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Corporation, Tosoh Corporation, Rutgers Chemicals, BASF, Kraton Polymers, Nippon Paint Chemicals Co., Ltd., Nippon Shokubai Co., Ltd., Taoka Chemical Industries, Ltd., and others.

[0234] In addition to those mentioned above, alkylphenol resins can be used as the resin component (C). By including alkylphenol resin in the rubber composition, the grip performance of the tire can be improved.

[0235] The alkylphenol resins are not particularly limited and include alkylphenol aldehyde condensation resins obtained by reacting alkylphenols with aldehydes such as formaldehyde, acetaldehyde, and furfural using an acid or alkali catalyst; alkylphenol alkyne condensation resins obtained by reacting alkylphenols with alkynes such as acetylene; and modified alkylphenol resins obtained by modifying these resins with compounds such as cashew oil, tall oil, linseed oil, various animal and vegetable oils, unsaturated fatty acids, rosin, alkylbenzene resins, aniline, and melamine. Among these, alkylphenol alkyne condensation resins are preferred as alkylphenol resins, and alkylphenol acetylene condensation resins are particularly preferred.

[0236] Examples of alkylphenols that constitute alkylphenol resins include cresol, xylenol, t-butylphenol, octylphenol, and nonylphenol. Among these, phenols having branched alkyl groups such as t-butylphenol are preferred, and t-butylphenol is particularly preferred.

[0237] Examples of commercially available alkylphenol resins include the product names "Hitanol 1502P" (alkylphenol formaldehyde resin, manufactured by Hitachi Chemical Co., Ltd.), "Tackiroll 201" (alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), "Tackiroll 250-I" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), "Tackiroll 250-III" (brominated alkylphenol formaldehyde resin, manufactured by Taoka Chemical Industry Co., Ltd.), and "R7521P", "SP1068", "R7510PJ", "R7572P", and "R7578P" (manufactured by SI GROUP INC.).

[0238] The alkylphenol resin described above is preferably used in combination with the hydrogenated resin component (hydrogenated resin) described above. In other words, the resin component (C) preferably contains both the alkylphenol resin and the hydrogenated resin. By including both the alkylphenol resin and the hydrogenated resin in the rubber composition, the grip performance of the tire can be improved. Furthermore, when using the resin component (C) which includes both the alkylphenol resin and the hydrogenated resin, it is preferable to use a rubber component (A) which contains styrene-butadiene rubber with a weight-average molecular weight (Mw) of 660,000 or more. While there is a concern that the fracture resistance may decrease when using the resin described above, by using styrene-butadiene rubber with a weight-average molecular weight (Mw) of 660,000 or more as the rubber component (A), the decrease in fracture resistance can be effectively suppressed.

[0239] (Other components) In addition to the components described above, the rubber composition of this embodiment may further contain various additives used in rubber products, especially tires, such as oils, liquid softeners such as liquid polymers, antioxidants, zinc oxide, sulfur, vulcanization accelerators, waxes, stearic acid, organic peroxides, cellulose nanofibers, cellulose particles, solid fine particles such as eggshells, rice husks, and walnut powder, and rubber powder obtained by crushing used rubber products.

[0240] (Method for producing the rubber composition) The method for preparing the rubber composition of this embodiment is not particularly limited, and known methods can be used. For example, it can be obtained by mixing a predetermined rubber component (A), a filler such as carbon black (B), and other components using a mixer such as a Banbury mixer, roll mixer, or internal mixer. Alternatively, components other than the crosslinking accelerator and crosslinking agent may be mixed in a non-production (non-pro) stage, and the crosslinking accelerator and crosslinking agent may be added to the mixture and mixed in a production (pro) stage to prepare the rubber composition.

[0241] The rubber composition of this embodiment can be crosslinked or vulcanized. The conditions for crosslinking or vulcanizing the rubber composition can be adjusted as appropriate, for example, a temperature of 120 to 200°C and a heating time of 1 minute to 900 minutes.

[0242] <Tire> A tire according to one embodiment of the present invention (hereinafter sometimes referred to as "the tire of this embodiment") comprises a tread rubber including a cap tread rubber layer located on the outermost surface of the tread portion and a base tread rubber layer located radially inward of the cap tread rubber layer. The tire of this embodiment is characterized in that the cap tread rubber layer is made of the rubber composition of this embodiment described above.

[0243] In the tire of this embodiment, the recycled carbon black applied to the cap tread rubber layer is derived from recycled resources, thus improving the proportion of sustainable materials in the tire of this embodiment. However, applying general recycled carbon black to the cap tread rubber layer would degrade tire performance. In contrast, in the tire of this embodiment, tire performance can be maintained by applying the rubber composition of this embodiment described above, particularly recycled carbon black that, when measured with a grind gauge, shows three or more lines with a length of 10 mm or more, and the third largest particle among the particles that produce these lines has a particle size of 20 μm or less, to the cap tread rubber layer. Therefore, the tire of this embodiment improves the proportion of sustainable materials while maintaining tire performance.

[0244] Next, an embodiment of the tire of the present invention will be described in detail with reference to the drawings. Figure 2 is a cross-sectional view of an embodiment of the tire of the present invention. The tire 101 shown in Figure 2 has a pair of bead portions 102 and a pair of sidewall portions 103, a tread portion 106 connected to both sidewall portions 103 and having a cap tread rubber layer 104 and a base tread rubber layer 105 in order from the radially outer side of the tire, a carcass 107 that extends in a toroidal shape between the pair of bead portions 102 and reinforces these portions 102, 103, and 106, and a belt 108 arranged on the radially outer side of the crown portion of the carcass 107.

[0245] The tire carcass 107 shown in Figure 2 is composed of a single carcass ply made of multiple parallel-arranged cords covered with coating rubber. The carcass 107 consists of a main body that extends in a toroidal shape between bead cores 109 embedded in the bead portion 102, and folded-over portions that are wound radially outward from the inside to the outside in the tire width direction around each bead core 109. However, the number of plies and structure of the carcass 107 in the tire of the present invention are not limited to this.

[0246] Furthermore, although the tire belt 108 shown in Figure 2 consists of two belt layers, the number of belt layers constituting the belt 108 in the tire of this embodiment is not limited to this, and the number of belt layers may be three or more. Here, the belt layers usually consist of rubberized layers of metal cords (preferably steel cords) that extend at an inclination with respect to the tire's equatorial plane, and the two belt layers are stacked so that the metal cords constituting the belt layers intersect each other with the tire's equatorial plane in between, thereby constituting the belt 108.

[0247] Furthermore, the tire of this embodiment comprises a tread rubber 110 including a cap tread rubber layer 104 located on the outermost surface of the tread portion 106 and a base tread rubber layer 105 located radially inward of the cap tread rubber layer 104.

[0248] The tire of this embodiment only needs to have a tread rubber that includes a cap tread rubber layer located on the outermost surface of the tread portion and a base tread rubber layer located radially inward of the cap tread rubber layer, and various modifications can be made. For example, a belt reinforcing layer can be provided on the radially outward side of the belt 108 of the tire 101 shown in Figure 2.

[0249] In the tire of this embodiment, the base tread rubber layer is not particularly limited.

[0250] In the tire of this embodiment, the storage modulus (E') of the cap tread rubber layer at 25°C is Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E'Ｃ / E' Ｂ Preferably, the storage modulus (E') of the base tread rubber layer 5 at 25°C is 0.50 or higher. Ｂ If the storage modulus (E') of the cap tread rubber layer at 25°C becomes too high, it may not be possible to sufficiently improve the overall fuel efficiency of the tire. In contrast, if the storage modulus (E') of the cap tread rubber layer at 25°C becomes too high, Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ By setting the storage modulus (E') of the base tread rubber layer at 25°C to 0.50 or higher, that is, the storage modulus (E') of the base tread rubber layer at 25°C is increased. Ｂ By lowering the storage modulus (E') of the cap tread rubber layer at 25°C (in other words, by not making it too high), the overall fuel efficiency of the tire can be sufficiently improved. Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ Tires with a ratio of 0.50 or higher can significantly improve fuel efficiency.

[0251] Here, the storage modulus (E') of the cap tread rubber layer at 25°C is shown. Ｃ The storage modulus (E') of the cap tread rubber layer at 25°C is preferably in the range of 4.5 to 8.5 MPa, and more preferably in the range of 5.0 to 7.5 MPa. Ｃ If the tire pressure is less than 4.5 MPa, the handling stability of the tire deteriorates, and if it exceeds 8.5 MPa, the quietness of the tire deteriorates. Within the aforementioned range, both the handling stability and quietness of the tire can be achieved.

[0252] Furthermore, the storage modulus (E') of the base tread rubber layer at 25°C is also important. Ｂ The storage modulus (E') of the base tread rubber layer at 25°C is preferably in the range of 2.25 to 18 MPa, more preferably in the range of 2.5 to 17.5 MPa, even more preferably in the range of 2.75 to 15 MPa, and still more preferably in the range of 3.0 to 8.0 MPa. ＢIf the pressure is below 2.25 MPa, the tire's handling stability deteriorates, and if it exceeds 18 MPa, there are concerns that the tire's quietness and durability may deteriorate.

[0253] The storage modulus (E') of the aforementioned cap tread rubber layer at 25°C Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ The ratio (E') is more preferably 0.76 or higher. Ｃ / E' Ｂ If the storage modulus (E') of the cap tread rubber layer at 25°C is 0.76 or higher, the tire's fuel efficiency performance is further improved. Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ The upper limit of ) is not particularly limited, but the ratio (E' Ｃ / E' Ｂ The ratio (E') is preferably 1.30 or less. Ｃ / E' Ｂ If the storage modulus of the cap tread rubber layer at 25°C (E') is 1.30 or less, Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ The difference between the two layers is small, meaning the difference in rigidity between the cap tread rubber layer and the base tread rubber layer is small, which improves the durability of the tire.

[0254] The base tread rubber layer can be formed from a rubber composition, the rubber composition for the base tread rubber layer having a storage modulus (E') of the cap tread rubber layer at 25°C. Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ It is preferable to select such that the ratio is 0.50 or higher. Below, an example of an embodiment of the rubber composition used for the base tread rubber layer is given.

[0255] In one embodiment, the rubber composition for the base tread rubber layer preferably contains a rubber component and carbon black.

[0256] The rubber component preferably contains natural rubber (NR). The rubber component may also contain other rubber components, such as synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). The amount of natural rubber (NR) is preferably in the range of 10 to 100 parts by mass, and more preferably in the range of 15 to 90 parts by mass, per 100 parts by mass of the rubber component.

[0257] The carbon black is not particularly limited, and examples include GPF, FEF, HAF, ISAF, and SAF grade carbon black. These carbon blacks may be used individually or in combination of two or more. The carbon black may also be the recycled carbon black mentioned above. The carbon black content is preferably in the range of 30 to 60 parts by mass per 100 parts by mass of rubber component. If the carbon black content is less than 30 parts by mass, the durability of the tire deteriorates, and if it exceeds 60 parts by mass, the fuel efficiency performance of the tire deteriorates.

[0258] The rubber composition for the base tread rubber layer may, in addition to the rubber components and carbon black described above, optionally contain various components commonly used in the rubber industry, such as silica, silane coupling agents, antioxidants, waxes, softeners, processing aids, stearic acid, zinc oxide (zinc oxide), vulcanization accelerators, vulcanizing agents, etc., selected appropriately within a range that does not impair the purpose of the present invention. Commercially available products can be suitably used as these compounding agents, and the same as those used in the rubber composition for the cap tread rubber layer described above can also be applied.

[0259] The method for producing the rubber composition for the base tread rubber layer is not particularly limited. For example, it can be produced by blending various components as needed with a rubber component, then kneading, heating, extruding, etc. The obtained rubber composition can also be vulcanized to produce vulcanized rubber. The conditions and equipment for kneading, heating, extrusion, vulcanization, and other related conditions are the same as those for the rubber composition for the cap tread rubber layer described above.

[0260] (Manufacturing of Tires) The tires of this embodiment can be manufactured by conventional methods using the rubber composition described above. For example, depending on the type of tire to be applied, the tires of this embodiment may be obtained by molding using an unvulcanized rubber composition (rubber composition for each component, including the rubber composition for the cap tread rubber layer and the rubber composition for the base tread rubber layer) and reinforcing materials, followed by vulcanization, or by molding using semi-vulcanized rubber that has undergone a pre-vulcanization process, and then further vulcanizing. The components of the tires of this embodiment other than the cap tread rubber layer and the base tread rubber layer are not particularly limited, and known components can be used. Furthermore, the tires of this embodiment are preferably pneumatic tires, and as the gas to be filled into the pneumatic tire, in addition to ordinary air or air with adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used.

[0261] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the present invention in any way.

[0262] <Evaluation 1> Two types of rubber compositions having the compound compositions shown in Table 1 were prepared, and these rubber compositions were vulcanized at 145°C for 33 minutes to obtain vulcanized rubber test pieces.

[0263] (Sustainable Material Ratio) For each rubber composition prepared, the sustainable material ratio was evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources. The results are shown in Table 1.

[0264] (Breaking Strength (Crack Resistance)) The obtained vulcanized rubber test pieces were punched into JIS-3 dumbbells, and the resulting samples were subjected to tensile tests at room temperature according to JIS K 6251:2004. The breaking strength (TB) before thermal degradation (initial) and after thermal degradation (100°C × 24 hours) was measured. The results are shown in Table 1. A higher value indicates better fracture resistance, i.e., better crack resistance.

[0265]

[0266] *1 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *2 Virgin carbon black: Manufactured by Asahi Carbon, product name "N550", nitrogen adsorption specific surface area (N ２ SA) = 40m ２ / g, OAN oil absorption = 121 mL / 100 g *3 Recycled carbon black: Enrestec, product name "PB365", ash content = 17% by mass *4 Anti-aging agent A: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C" *5 Anti-aging agent B: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 224" *6 Oil: ENEOS, product name "A / Omix" *7 Fatty acid: Miyoshi Oil & Fat Co., Ltd., product name "MXST" *8 Other chemicals: Total amount of sulfur, vulcanization accelerator, resin, and wax, same ratio in each rubber composition

[0267] Table 1 shows that replacing carbon black (virgin carbon black) with recycled carbon black among the various materials contained in the rubber composition contributes to improved sustainability, but reduces the tensile strength before and after thermal degradation.

[0268] <Evaluation 2> Recycled carbon black 1 and recycled carbon black 2 were prepared as test carbon blacks.

[0269] Next, 3.75 g of zinc oxide, 0.20 g of the carbon black under test, and 2.00 mL of epoxidized soybean oil were mixed to obtain a mixture. The obtained mixture was kneaded for 5 to 10 minutes to form a paste, and the sample paste was prepared. In accordance with JIS K5101-1-5, the paste was prepared using a Toyo Seiki Huber Mahler (model: H3) under conditions of a load of 0.4536 kN and a glass plate rotation speed of 100 r / min. In accordance with JIS K5400, each sample paste was placed on a grind gauge and stretched with a scraper. The grind gauge used had a range of 0 to 25 μm. It was confirmed that three or more continuous lines of 10 mm or more appeared, and the scale reading at the location where the line caused by the third largest particle among the particles that produced the continuous lines of 10 mm or more appeared was read, and this reading was taken as the particle size of the third largest particle. The same procedure was performed a total of four times, and the average particle size of the third largest particle from the four measurements was calculated. The results are shown in Table 2.

[0270] Furthermore, regarding the carbon black used in the test, the nitrogen adsorption specific surface area (N) was calculated according to ASTM D6556. ２ SA was measured. The results are shown in Table 2.

[0271] Furthermore, the Zn, Fe, and Cu content of the tested carbon black was measured by X-ray fluorescence analysis (XRF). The results are shown in Table 2.

[0272] Furthermore, the ash content of the tested carbon black was measured according to ASTM D8474 and D1506. The results are shown in Table 2.

[0273]

[0274] (Preparation of Rubber Composition) Using recycled carbon black 1 or recycled carbon black 2 as described above, rubber compositions were prepared according to the formulations shown in Table 3. Other chemicals included antioxidants, oils, fatty acids, sulfur, and vulcanization accelerators, and the same types and amounts were added in the comparative examples and examples. Commercially available chemicals commonly used in the preparation of rubber compositions were used. The amounts added were those commonly used in the preparation of rubber compositions.

[0275] (Sustainable Material Ratio) For each rubber composition prepared, the sustainable material ratio was evaluated by calculating the total mass ratio of components derived from biological resources (biomass resources) and components derived from recycled resources. The results are shown in Table 3.

[0276] (High-temperature tensile strength after degradation) Each rubber composition was vulcanized at 145°C for 33 minutes to obtain vulcanized rubber. The obtained vulcanized rubber was thermally degraded at 100°C for 48 hours in an air atmosphere. A tensile test was performed at 100°C in accordance with JIS K6251:2017 and the tensile strength was measured. The high-temperature tensile strength (fracture resistance) after degradation was expressed as an index using the following formula, with the tensile strength of the test piece from Example 1 set to 100. The results are shown in Table 3. High-temperature tensile strength index after degradation = (Tensile strength of the test piece / Tensile strength of the test piece from Example 1) × 100 A higher high-temperature tensile strength index after degradation indicates that the vulcanized rubber is less prone to fracture and has superior post-degradation performance (fracture resistance).

[0277] (Crack resistance after thermal degradation) The rubber composition to be tested was pre-treated by thermal degradation at 100°C for 24 hours in an air atmosphere. A strip-shaped test piece was prepared from the rubber composition with a 0.5 mm hole drilled in the lengthwise direction in the center. Using this test piece, a dc / dn test (using Shimadzu Corporation's "ServoPulsa") was performed, applying repeated fatigue at a frequency of 5 Hz and 80°C with a strain of 30-100%, and the tear energy [J / m] after 1950 cycles was measured. ２ The crack propagation rate was calculated when the common logarithm of [ ] was 3.9. The crack propagation rate obtained by the above process was normalized by the reciprocal of the formulation data for each example, with the formulation data of Example 1 used as a control (index value 100). The results are shown in Table 3. A larger index value indicates a lower crack propagation rate and superior crack resistance after thermal degradation.

[0278]

[0279] *11 Natural rubber: RSS#3 *12 Butadiene rubber: Manufactured by UBE Elastomers, product name "BR150L" *13 Virgin carbon black: Manufactured by Asahi Carbon, N550

[0280] Tables 2 and 3 show that even when rubber compositions containing recycled carbon black with the same ash content, the example using recycled carbon black with a third-largest particle size of 20 μm or less exhibits better high-temperature tensile strength after degradation compared to the comparative example using recycled carbon black with a third-largest particle size exceeding 20 μm. Furthermore, the example also showed better crack resistance after thermal degradation compared to the comparative example.

[0281] Based on these evaluations, it can be seen that by applying recycled carbon black, specifically one in which the third largest particle size measured with a grind gauge is 20 μm or less, to the cap tread rubber layer, the proportion of sustainable materials can be increased while maintaining tire performance.

[0282] <Evaluation 3 (Relationship between Zn content in carbon black and rubber properties)> Carbon black (CB) and styrene-butadiene rubber with different ash, Zn, and sulfur content were kneaded according to the formulations shown in Table 4 to prepare rubber compositions for each example.

[0283] Furthermore, the Zn and S content of the carbon black used was measured by X-ray fluorescence analysis. The results are shown in Table 4.

[0284] Furthermore, the ash content of the carbon black used was measured by thermogravimetric analysis (TGA, RIGAKU Corporation) using the following procedure. The sample was heated from room temperature to 550°C under a nitrogen atmosphere, and then heated to maintain 550°C under an air atmosphere, and the loss on heating was measured. The loss on heating (mass%) when the sample was heated from room temperature to 550°C under a nitrogen atmosphere was defined as "Loss on heating 1," and the loss on heating (mass%) when heated to maintain 550°C under an air atmosphere was defined as "Loss on heating 2." The ash content was calculated using the following formula. The results are shown in Table 4. Ash content (mass%) = 100 - Loss on heating 1 - Loss on heating 2

[0285] For each example of rubber composition, vulcanized rubber was obtained by vulcanization at 145°C for 33 minutes. Tensile strength was measured for each vulcanized rubber by performing a tensile test at room temperature in accordance with JIS K6301-1995. The tensile strength of the test specimen of the standard rubber composition was set to 100, and the index was expressed using the following formula. The results are shown in Table 4. Tensile strength index = (Tensile strength of test specimen other than the standard rubber composition / Tensile strength of test specimen of the standard rubber composition) × 100 A larger index indicates that the vulcanized rubber is less prone to fracture and has superior tensile strength.

[0286] For each example of rubber composition, a viscoelasticity test was performed using TA Instruments' "ARES-G2" under the conditions of a frequency of 15 Hz, shear strain of 10%, and temperature of 50°C, and the storage modulus (G') was measured. The evaluation results were indexed with the standard rubber composition as the control (index value 100). The results (viscoelasticity) are shown in Table 4. A higher index indicates a higher G', and a better rubber property when applied to tires.

[0287]

[0288] *21 SBR: Styrene-butadiene rubber, manufactured by ENEOS Material Co., Ltd., product name "#1500" *22 CB1: Carbon black, recycled carbon black equivalent to N330 *23 CB2: Carbon black, recycled carbon black equivalent to N330 *24 CB3: Carbon black, recycled carbon black equivalent to N330 *25 CB5: Carbon black, virgin (new) carbon black equivalent to N330

[0289] Table 4 shows that when carbon black with a Zn content of 2.5% by mass or less, or an ash content of 6% by mass or less, is applied to a rubber composition, the deterioration of the rubber composition's physical properties can be suppressed.

[0290] According to the present invention, compared to conventional methods using recycled carbon black, it is possible to provide a tire tread rubber composition that contributes to improved sustainability while minimizing adverse effects on tire rubber properties and maintaining performance. Furthermore, according to the present invention, it is possible to provide a tire that maintains tire performance while increasing the proportion of sustainable materials.

[0291] 1: Grind gauge 2: Line less than 10 mm in length 3: Line 10 mm or longer 31: Line caused by the largest particle 32: Line caused by the second largest particle 33: Line caused by the third largest particle 4: Scale mark where the line caused by the third largest particle appears 101: Tire 102: Bead area 103: Sidewall area 104: Cap tread rubber layer 105: Base tread rubber layer 106: Tread area 107: Carcass 108: Belt 109: Bead core 110: Tread rubber

Claims

1. A rubber composition for tire treads comprising a rubber component (A) and a filler (B), wherein the filler (B) contains recycled carbon black, and the recycled carbon black is characterized in that, when measured with a grind gauge, three or more lines with a length of 10 mm or more are confirmed, and the particle size of the third largest particle among the particles that produce the lines with a length of 10 mm or more is 20 μm or less.

2. The tire tread rubber composition according to claim 1, wherein, in the measurement of the recycled carbon black using a grind gauge, a paste of the recycled carbon black is prepared as the measurement sample in accordance with JIS K5101-1-5.

3. The tire tread rubber composition according to claim 1, wherein, in the measurement of the recycled carbon black using a grind gauge, the applied load is set to 0.4 to 0.5 kN and the rotation speed of the glass plate to 90 to 110 r / min in accordance with JIS K5101-1-5, and the paste of the recycled carbon black is prepared as the measurement sample.

4. The tire tread rubber composition according to claim 1, wherein the recycled carbon black comprises one or more selected from the group consisting of Zn, Fe, and Cu.

5. The tire tread rubber composition according to claim 4, wherein the recycled carbon black contains Zn.

6. The tire tread rubber composition according to claim 5, wherein the Zn content in the recycled carbon black is 2.5% by mass or less.

7. The rubber composition for tire treads according to claim 1, wherein the recycled carbon black has an ash content of 20% by mass or less.

8. A tire comprising a tread rubber including a cap tread rubber layer located on the outermost surface of the tread portion and a base tread rubber layer located radially inward of the cap tread rubber layer, wherein the cap tread rubber layer is made of the tire tread rubber composition described in claim 1.

9. Storage modulus (E') of the cap tread rubber layer at 25°C. Ｃ ) and the storage modulus of the base tread rubber layer at 25°C (E' Ｂ ) ratio (E' Ｃ / E' Ｂ The tire according to claim 8, wherein the ratio is 0.50 or greater.

10. The tire according to claim 8, wherein the rubber component (A) comprises a modified styrene-butadiene rubber (a2-1) having a glass transition temperature of -50°C or lower, which is modified with a modifying agent having at least one atom among nitrogen, silicon, and tin, and an unmodified styrene-butadiene rubber (a2-2) having a glass transition temperature 30°C or higher than that of the modified styrene-butadiene rubber (a2-1).

Images