JP7823381B2 - Rubber composition for tires and tires - Google Patents

Description

This disclosure relates to a rubber composition for tires and a tire.

Various methods for improving wet grip performance and fuel economy have been investigated to date (see, for example, Patent Documents 1 and 2). However, in recent years, further improvements in these areas of performance have been required.

Special Publication No. 2013-544936 Japanese Patent Application Laid-Open No. 2000-344955

The present disclosure aims to solve the above-mentioned problems and provide a rubber composition for tires and a tire that can improve the overall performance of wet grip performance and fuel economy during high-speed driving.

The present disclosure relates to a rubber composition for tires that contains a rubber component containing styrene-butadiene rubber and butadiene rubber, silica, and a resin containing an aromatic resin, wherein the content of the styrene-butadiene rubber exceeds 60% by mass per 100 parts by mass of the rubber component, the average particle size of the silica is 16 nm or less, the content of the silica exceeds 80 parts by mass per 100 parts by mass of the rubber component, and the content of the resin > the content of the butadiene rubber > the content of the liquid plasticizer.

The present disclosure provides a rubber composition for tires that contains a rubber component containing styrene-butadiene rubber and butadiene rubber, silica, and a resin containing an aromatic resin, wherein the styrene-butadiene rubber content exceeds 60% by mass per 100 parts by mass of the rubber component, the silica has an average particle size of 16 nm or less, the silica content exceeds 80 parts by mass per 100 parts by mass of the rubber component, and the resin content > butadiene rubber content > liquid plasticizer content, thereby achieving good overall wet grip performance and fuel economy during high-speed driving.

The rubber composition for tires disclosed herein contains a rubber component containing styrene-butadiene rubber and butadiene rubber, silica, and a resin containing an aromatic resin, wherein the content of the styrene-butadiene rubber exceeds 60% by mass per 100 parts by mass of the rubber component, the average particle diameter of the silica is 16 nm or less, the content of the silica exceeds 80 parts by mass per 100 parts by mass of the rubber component, and the content of the resin > the content of the butadiene rubber > the content of the liquid plasticizer.

The reason why the above-mentioned effects can be obtained with the above rubber composition is presumed to be as follows.
Silica having an average particle size of 16 nm or less (fine particle silica) has an excellent reinforcing effect, but it usually tends to be difficult to disperse uniformly in a rubber composition.
In contrast, in the rubber composition, the styrene-butadiene rubber content in the rubber component is more than 60% by mass, and an aromatic resin is used as the resin, which allows the rubber component and the resin to be well compatible and the silica to be well dispersed. As a result, even when a large amount of fine particle silica, which is difficult to disperse, is blended, the fine particle silica can be uniformly dispersed, effectively reinforcing the rubber composition.
Furthermore, by satisfying the relationship of resin content > butadiene rubber content > liquid plasticizer content, the liquid plasticizer is less likely to be released, and changes in the state of the rubber component due to deterioration are suppressed.
It is believed that the above effects improve the overall wet grip performance and fuel economy during high-speed driving.

In the above rubber composition, the acetone extractables (AE) are preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and are preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, better effects tend to be obtained.

In the above rubber composition, the polymer content (PC) is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. Within the above ranges, better effects tend to be obtained.

In the above rubber composition, the carbon black content (BC) is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, and is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. Within the above ranges, better effects tend to be obtained.

In the above rubber composition, the ash content (Ash) is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 42% by mass or less. Within the above ranges, better effects tend to be obtained.

The acetone extractable amount (AE), polymer amount (PC), carbon black amount (BC), and ash amount (Ash) are measured by the following methods.
First, the acetone extractable amount (AE) of the rubber composition (sample) is measured by a method for measuring acetone extractable amount in accordance with JIS K 6229:2015 (unit: mass% of the rubber composition (sample)).
The polymer content (PC) is calculated from the weight loss (mass) when the organic matter in the sample remaining after the acetone extraction is thermally decomposed and vaporized by heating in nitrogen (raising from room temperature to 750°C) in accordance with JIS K6226-1:2003 (unit: mass% in the rubber composition (sample)).
The carbon black content (BC) is calculated from the amount (mass) of carbon black lost when the sample after thermal decomposition and vaporization is subjected to oxidative combustion by heating in air (unit: mass % in the rubber composition (sample)).
The ash content (Ash) is calculated from the mass of the components (ash content) that do not burn in the oxidative combustion (unit: mass % in the rubber composition (sample)).
From the above definitions, the total of AE, PC, BC and Ash is 100% by mass.

Methods known to those skilled in the art can be used to adjust AE, PC, BC, and Ash. For example, AE tends to increase as the amount of plasticizers such as oil in the rubber composition increases. PC tends to increase as the amount of rubber components in the rubber composition increases. BC tends to increase as the amount of carbon black in the rubber composition increases. Ash tends to increase as the amount of components that do not burn by oxidative combustion, such as silica, in the rubber composition increases.

The rubber composition contains a rubber component.
Here, the rubber component is a component that contributes to crosslinking, and generally has a weight average molecular weight (Mw) of 10,000 or more.

The weight average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more, and is preferably 2,000,000 or less, more preferably 1,500,000 or less, and even more preferably 1,000,000 or less. Within the above ranges, better effects tend to be obtained.

In this specification, the weight average molecular weight (Mw) can be determined by converting it into standard polystyrene based on measurements obtained using a gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corporation; detector: differential refractometer; column: TSKGEL SUPERMULTIPORE HZ-M, manufactured by Tosoh Corporation).

The total styrene content in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably less than 30% by mass. Within the above ranges, better effects tend to be obtained.

Here, the total styrene amount in the rubber component is the total content of styrene moieties contained in the entire rubber component (unit: mass %) and can be calculated by Σ (content of each rubber component × styrene amount in each rubber component/100). For example, if 100% by mass of the rubber component contains 85% by mass of SBR with a styrene content of 40% by mass, 5% by mass of SBR with a styrene content of 25% by mass, and 10% by mass of BR with a styrene content of 0% by mass, the total styrene amount in the rubber component is 35.25% by mass (= 85 × 40/100 + 5 × 25/100 + 10 × 0/100).

The total vinyl content in the rubber component is preferably 10% by mass or more, more preferably 13% by mass or more, and even more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. Within the above ranges, better effects tend to be obtained.

Here, the total vinyl content in the rubber component is the total content (unit: parts by mass) of vinyl bonds in the butadiene moieties of the SBR and BR contained in the rubber component, assuming the total mass of the rubber component to be 100. It can be calculated by Σ (content of each rubber component × proportion of vinyl bond content in the butadiene moieties in the rubber component to the total mass of each rubber component [% by mass]). For example, if 100 parts by mass of the rubber component contains 85 parts by mass of SBR with 40% styrene and 30% vinyl, 5 parts by mass of SBR with 20% styrene and 20% vinyl, and 10 parts by mass of BR with 10% vinyl, the total vinyl content in the rubber component is 17.1 parts by mass (= 85 × (100 [% by mass] - 40 [% by mass]) × 30 [% by mass] + 5 × (100 [% by mass] - 20 [% by mass]) × 20 [% by mass] + 10 × 10 [% by mass]).

The styrene content and vinyl content in each rubber component can be measured by nuclear magnetic resonance (NMR) method.
In the examples of this specification, the total styrene amount and the total vinyl amount in the rubber component are calculated according to the above-mentioned formulas, but they may also be analyzed from the tire using, for example, a pyrolysis gas chromatograph mass spectrometer (Py-GC/MS) or the like.

The rubber composition contains styrene-butadiene rubber (SBR) as a rubber component.
The SBR is not particularly limited, and examples thereof include emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. Commercially available products include those from Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, and Zeon Corporation.

The SBR may be an oil-extended rubber or a resin-extended rubber. These may be used alone or in combination of two or more. Of these, resin-extended SBR is preferred.
The oil used in the oil-extended rubber and the resin used in the resin-extended rubber are the same as those described below. The oil content in the oil-extended rubber and the resin content in the resin-extended rubber are not particularly limited, but are usually about 5 to 50 parts by mass per 100 parts by mass of rubber solids.

SBR may be modified to introduce a functional group that interacts with a filler such as silica.
Examples of the functional group include a silicon-containing group (-SiR ₃ (R may be the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, or the like), an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imido group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, and the like. These functional groups may have a substituent. Among these, a silicon-containing group is preferred, and -SiR ₃ (R's may be the same or different and each represent a hydrogen atom, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)), or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R's is more preferably a hydroxyl group).

Specific examples of compounds (modifiers) that introduce the above-mentioned functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

As the SBR, hydrogenated SBR to which hydrogen has been added can also be used.
When the SBR is hydrogenated SBR, the hydrogenation method and reaction conditions are not particularly limited, and hydrogenation may be carried out by a known method and under known conditions. Typically, hydrogenation is carried out at 20 to 150°C under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. Other production methods and conditions are also not particularly limited, and the contents described in WO 2016/039005, for example, can be applied.
Note that hydrogenated SBR has the same structure as a copolymer of ethylene, butadiene, and styrene as a result of hydrogen being added to the butadiene portion of SBR. Therefore, in this specification, hydrogenated SBR includes not only hydrogenated products of copolymers of butadiene and styrene (SBR), but also copolymers of ethylene, butadiene, and styrene.

The hydrogenation rate of the hydrogenated SBR is preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and is preferably 95 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less, based on 100 mol% of the total butadiene units before hydrogenation. When the hydrogenation rate is within the above range, better effects tend to be obtained.
The hydrogenation rate can be calculated from the rate of decrease in the unsaturated bond portion of the spectrum obtained by measuring ¹ H-NMR.

The styrene content of the SBR is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. Within the above ranges, better effects tend to be achieved.

The vinyl content of the SBR is preferably 15% by mass or more, more preferably 25% by mass or more, and even more preferably 35% by mass or more, and is preferably 70% by mass or less, more preferably 65% by mass or less, and even more preferably 60% by mass or less. Being within the above ranges tends to produce better effects.

The styrene content of the SBR mentioned above means the styrene content of the SBR when there is one type of SBR, and means the average styrene content when there are multiple types of SBR.
The average styrene content of the SBR can be calculated by {Σ(content of each SBR × styrene content of each SBR)}/total content of all SBRs. For example, when 100% by mass of the rubber component contains 85% by mass of SBR with a styrene content of 40% by mass and 5% by mass of SBR with a styrene content of 25% by mass, the average styrene content of the SBR is 39.2% by mass (=(85×40+5×25)/(85+5)).

The vinyl content of the SBR is the proportion of vinyl bonds (unit: mass%) when the total mass of the butadiene parts in the SBR is taken as 100, and is expressed as vinyl content [mass%] + cis content [mass%] + trans content [mass%] = 100 [mass%]. When one type of SBR is used, it means the vinyl content of that SBR, and when multiple types of SBR are used, it means the average vinyl content.
The average vinyl content of the SBR can be calculated by Σ{content of each SBR×(100[% by mass]−styrene content of each SBR[% by mass])×vinyl content of each SBR[% by mass]}/Σ{content of each SBR×(100[% by mass]−styrene content of each SBR[% by mass])}. For example, in 100 parts by mass of the rubber component, 75 parts by mass of SBR having a styrene content of 40% by mass and a vinyl content of 30% by mass, and a styrene content of 25% by mass, Vinyl content: In a case where 20% by mass of SBR is 15 parts by mass and the remaining 10 parts by mass is a component other than SBR, the average vinyl content of the SBR is 28% by mass (= {75 × (100 [% by mass] - 40 [% by mass]) × 30 [% by mass] + 15 × (100 [% by mass] - 25 [% by mass]) × 20 [% by mass])} / {75 × (100 [% by mass] - 40 [% by mass]) + 15 × (100 [% by mass] - 25 [% by mass])}.

The SBR content per 100% by mass of the rubber component should be more than 60% by mass, but is preferably 62% by mass or more, more preferably 64% by mass or more, and even more preferably 65% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. Within the above range, better effects tend to be achieved.

The rubber composition contains butadiene rubber (BR) as a rubber component.
The BR is not particularly limited, and examples thereof include BRs commonly used in the tire industry, such as BR1220 manufactured by Zeon Corporation, BR150B manufactured by Ube Industries, Ltd., and BR1280 manufactured by LG Chem, BRs containing 1,2-syndiotactic polybutadiene crystals (SPB) such as VCR412 and VCR617 manufactured by Ube Industries, Ltd., and butadiene rubbers synthesized using rare earth catalysts (rare earth BRs). These may be used alone or in combination of two or more.

The BR may be an oil-extended rubber or a resin-extended rubber. These may be used alone or in combination of two or more. Resin-extended rubber is preferred.
The oil used in the oil-extended rubber and the resin used in the resin-extended rubber are the same as those described below. The oil content in the oil-extended rubber and the resin content in the resin-extended rubber are not particularly limited, but are usually about 5 to 50 parts by mass per 100 parts by mass of rubber solids.

The BR may be modified to introduce a functional group that interacts with a filler such as silica.
Examples of the functional group include a silicon-containing group (-SiR ₃ (R may be the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, or the like), an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imido group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, and the like. These functional groups may have a substituent. Among these, a silicon-containing group is preferred, and -SiR ₃ (R's may be the same or different and each represent a hydrogen atom, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)), or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R's is more preferably a hydroxyl group).

Specific examples of compounds (modifiers) that introduce the above-mentioned functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

As the BR, hydrogenated BR to which hydrogen has been added can also be used.
When the BR is hydrogenated BR, the hydrogenation method and reaction conditions are not particularly limited, and hydrogenation may be carried out by a known method and under known conditions. Typically, hydrogenation is carried out at 20 to 150°C under a hydrogen pressure of 0.1 to 10 MPa in the presence of a hydrogenation catalyst. Other production methods and conditions are also not particularly limited, and the contents described in WO 2016/039005, for example, can be applied.
Note that hydrogenated BR has the same structure as an ethylene-butadiene copolymer as a result of hydrogen being added to the butadiene moiety of BR, and therefore, in this specification, hydrogenated BR includes not only hydrogenated BR but also an ethylene-butadiene copolymer.

The hydrogenation rate of the hydrogenated BR is preferably 65 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, and is preferably 95 mol% or less, more preferably 92 mol% or less, and even more preferably 90 mol% or less, based on 100 mol% of all butadiene units before hydrogenation. When the hydrogenation rate is within the above range, better effects tend to be obtained.
The hydrogenation rate can be calculated from the rate of decrease in the unsaturated bond portion of the spectrum obtained by measuring ¹ H-NMR.

The cis amount (cis content) of the BR is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, and is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. When the cis amount is within the above range, the effect tends to be more favorably obtained.
The cis amount of BR can be measured by infrared absorption spectroscopy.

The above-mentioned cis amount of BR means the cis amount of the BR when there is one type of BR, and means the average cis amount when there are multiple types of BR.
The average cis amount of BR can be calculated by {Σ(content of each BR × cis amount of each BR)}/total amount of all BRs. For example, when 100% by mass of the rubber component contains 20% by mass of BR with a cis amount of 90% by mass and 10% by mass of BR with a cis amount of 40% by mass, the average cis amount of BR is 73.3% by mass (=(20×90+10×40)/(20+10)).

Within 100% by mass of the rubber component, the BR content is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. Within the above ranges, better effects tend to be obtained.

The rubber composition preferably contains an isoprene-based rubber as a rubber component.
Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. NR, for example, SIR20, RSS#3, TSR20, and other commonly used rubbers in the tire industry, can be used. IR is not particularly limited, and for example, IR2200 and other commonly used rubbers in the tire industry can be used. Modified NR includes deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and other such rubbers. Modified NR includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, and other such rubbers. Modified IR includes epoxidized isoprene rubber, hydrogenated isoprene rubber, grafted isoprene rubber, and other such rubbers. These may be used alone or in combination of two or more. Of these, NR is preferred.

Within 100% by mass of the rubber component, the content of isoprene-based rubber is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. Within the above ranges, better effects tend to be achieved.

Other rubber components include diene rubbers such as acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), and styrene-isoprene-butadiene copolymer rubber (SIBR). These may be used alone or in combination of two or more.

The other rubber component may be an oil-extended rubber or a resin-extended rubber. These may be used alone or in combination of two or more. Of these, resin-extended rubber is preferred.
The oil used in the oil-extended rubber and the resin used in the resin-extended rubber are the same as those described below. The oil content in the oil-extended rubber and the resin content in the resin-extended rubber are not particularly limited, but are usually about 5 to 50 parts by mass per 100 parts by mass of rubber solids.

The other rubber components may be modified to introduce functional groups that interact with fillers such as silica.
Examples of the functional group include a silicon-containing group (-SiR ₃ (R may be the same or different and is hydrogen, a hydroxyl group, a hydrocarbon group, an alkoxy group, or the like), an amino group, an amide group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imido group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group, an epoxy group, and the like. These functional groups may have a substituent. Of these, a silicon-containing group is preferred, and -SiR ₃ (R's may be the same or different and each represent a hydrogen atom, a hydroxyl group, a hydrocarbon group (preferably a hydrocarbon group having 1 to 6 carbon atoms (more preferably an alkyl group having 1 to 6 carbon atoms)), or an alkoxy group (preferably an alkoxy group having 1 to 6 carbon atoms)), and at least one of R's is more preferably a hydroxyl group).

Specific examples of compounds (modifiers) that introduce the above-mentioned functional groups include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxysilane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyltriethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethylaminopropyltriethoxysilane.

The raw materials (monomers) for synthetic rubbers such as SBR and BR may be derived from petroleum or biomass. Whether a raw material is biomass-derived can be determined by measuring the pMC (percent modern carbon) in accordance with ASTM D6866-10.

pMC is the ratio of the ¹⁴ C concentration of a sample to the ¹⁴ C concentration of a modern standard reference, and this value is used as an index of the biomass ratio of a compound (rubber). The significance of this value is described below.

In one mole of carbon atoms (6.02 x 10 ^atoms ), there are approximately 6.02 x 10 atoms of ^14C , which is about one trillionth of ^{the number of normal carbon atoms. 14C is} called a radioactive isotope and its half-life is 5,730 years, causing it to decay regularly. It takes 226,000 years for all of it to decay. Therefore, in fossil fuels such as coal, oil, and natural gas, which are thought to have been absorbed and fixed by plants and other organisms more than 226,000 years ago, all of the ^14C contained in these fuels at the time of fixation has decayed. Therefore, in the 21st century, fossil fuels such as coal, oil, and natural gas do not contain any ^14C at all. Therefore, chemicals produced using these fossil fuels do not contain any ^14C at all.

On the other hand, ^14C is constantly produced as a result of nuclear reactions caused by cosmic rays in the atmosphere, and this balances with the decrease due to radioactive decay, resulting in a constant amount of ^14C in the Earth's atmospheric environment. Therefore, as mentioned above, the ^14C concentration of substances derived from biomass resources circulating in the current environment is approximately 1 x ^10-12 mol% relative to the total C atoms. Therefore, the difference between these values can be used to calculate the ratio (biomass ratio) of compounds derived from natural resources (compounds derived from biomass resources) in a certain compound (rubber).

This ¹⁴ C is generally measured as follows: Accelerator mass spectrometry based on a tandem accelerator is used to measure the ¹³ C concentration ( ¹³ C/ ¹² C) and the ¹⁴ C concentration ( ¹⁴ C/ ¹² C). In the measurement, the ¹⁴ C concentration in circulating carbon in nature as of 1950 is used as the modern standard reference for the ¹⁴ C concentration. As a specific standard substance, an oxalic acid standard provided by NIST (National Institute of Standards and Technology) is used. The specific radioactivity of carbon in this oxalic acid (radioactivity intensity of ^14C per gram of carbon) is separated for each carbon isotope, corrected to a constant value for ^13C , and the value corrected for decay from 1950 to the date of measurement is used as the standard ^14C concentration value (100%). The ratio of this value to the value of the actually measured sample is the pMC value.

Therefore, if rubber is made from 100% biomass (natural) derived materials, it will show a value of approximately 110 pMC, although there may be regional differences (currently, under normal conditions, it is often not 100). On the other hand, when the ^14C concentration of chemical substances derived from fossil fuels such as petroleum is measured, it will show almost 0 pMC (for example, 0.3 pMC). This value corresponds to the biomass ratio of 0% mentioned above.

For these reasons, using materials such as rubber with a high pMC value, i.e., materials such as rubber with a high biomass ratio, in rubber compositions is advantageous from an environmental perspective.

The rubber composition may contain a thermoplastic elastomer as an elastomer other than the rubber component.
Thermoplastic elastomers are copolymers (block copolymers) composed of hard segments that act as crosslinking points and soft segments that exhibit rubber elasticity, and are usually solid at room temperature (25°C).

Hard segments include polystyrene, polypropylene, polyester, polyamide, polyvinyl chloride, polyurethane, etc., while soft segments include vinyl-polydiene, polyisoprene, polybutadiene, polyethylene, polychloroprene, poly 2,3-dimethylbutadiene, etc. These may be used alone or in combination of two or more types.

The thermoplastic elastomer may be used alone or in combination of two or more kinds. Commercially available products available from Kuraray Co., Ltd., Asahi Kasei Corporation, etc. may be used.
In this specification, the thermoplastic elastomer is not included in the rubber component.

The thermoplastic elastomer is preferably a thermoplastic elastomer having a styrene block (a styrene-based thermoplastic elastomer).
Specific examples of styrene-based thermoplastic elastomers include styrene-vinylisoprene-styrene triblock copolymer (SIS), styrene-isobutylene diblock copolymer (SIB), styrene-butadiene-styrene triblock copolymer (SBS), styrene-ethylene-butylene-styrene triblock copolymer (SEBS), styrene-ethylene-propylene-styrene triblock copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene triblock copolymer (SEEPS), and styrene-butadiene-butylene-styrene triblock copolymer (SBBS). These may be used alone or in combination of two or more. Among these, copolymers having styrene blocks at both ends are preferred, and styrene-ethylene-propylene-styrene triblock copolymer (SEPS) is more preferred.
The SEPS may be a hydrogenated styrene-vinylisoprene-styrene triblock copolymer (SIS) obtained by adding hydrogen to SIS.

The styrene content of the styrene-based thermoplastic elastomer is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above ranges, better effects tend to be achieved.

The content of the thermoplastic elastomer is preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component.

The rubber composition contains silica.
Examples of silica include dry-process silica (silicic anhydride) and wet-process silica (hydrated silicic acid), with wet-process silica being preferred due to its high silanol group content. The silica raw material may be water glass (sodium silicate) or a biomass material such as rice husks. Commercially available products include those from Evonik Degussa, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., and Tokuyama Corporation. These may be used alone or in combination of two or more.

The average particle size of the silica should be 16 nm or less, but is preferably 15 nm or less, more preferably 14 nm or less, and is preferably 6 nm or more, more preferably 9 nm or more, and even more preferably 12 nm or more. Within the above ranges, better effects tend to be obtained.

In this specification, the average particle size of silica is measured by observation with a transmission electron microscope (TEM). Specifically, silica particles are photographed with a transmission electron microscope, and if the particles are spherical, the diameter of the sphere is taken as the particle size. If the particles are needle-shaped or rod-shaped, the minor axis is taken as the particle size. If the particles are irregular, the average particle size from the center is taken as the particle size. The average particle size is the average value of the diameters of 100 microparticles.

The silica content may be more than 80 parts by mass per 100 parts by mass of the rubber component, but is preferably at least 82 parts by mass, more preferably at least 85 parts by mass, and even more preferably at least 90 parts by mass, and is preferably at most 140 parts by mass, more preferably at most 130 parts by mass, and even more preferably at most 120 parts by mass. Within the above ranges, better effects tend to be achieved.

In the rubber composition, the ratio of silica content to SBR content is preferably 0.5 or more, more preferably 1.0 or more, and even more preferably 1.4 or more, and is preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 2 or less.
Within the above range, better effects tend to be obtained.
In this relationship, the silica content is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the SBR content is the content (unit: % by mass) in 100% by mass of the rubber component.

The rubber composition may contain carbon black.
Carbon black is not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. The raw material for carbon black may be a biomass material such as lignin or vegetable oil, or may be obtained by recycling tires. Carbon black may be produced by combustion, such as a furnace method, or by hydrothermal carbonization (HTC). Commercially available carbon black products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., and the like. These carbon blacks may be used alone or in combination of two or more.

The cetyltrimethylammonium bromide (CTAB) specific surface area of the carbon black is preferably 90 m ² /g or more, more preferably 100 m ² /g or more, even more preferably 110 m ² /g or more, and is preferably 160 m ² /g or less, more preferably 140 m ² /g or less, even more preferably 120 m ² /g or less. Within the above ranges, better effects tend to be obtained.
The CTAB specific surface area of carbon black is a value measured in accordance with JIS K6217-3:2001.

The carbon black content, per 100 parts by mass of the rubber component, is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and even more preferably at least 5 parts by mass, and is preferably at most 20 parts by mass, more preferably at most 15 parts by mass, and even more preferably at most 10 parts by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition preferably contains a silane coupling agent.
The silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products include those from Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more. Of these, mercapto-based products are preferred.

In addition to compounds having a mercapto group, compounds in which the mercapto group is protected by a protecting group (for example, a compound represented by the following formula (S1)) can also be used as mercapto-based silane coupling agents.

Particularly suitable mercapto-based silane coupling agents include silane coupling agents represented by the following formula (S1) and silane coupling agents containing a bonding unit A represented by the following formula (I) and a bonding unit B represented by the following formula (II).
(wherein R ¹⁰⁰¹ is a monovalent group selected from -Cl, -Br, -OR ¹⁰⁰⁶ , -O(O═)CR ¹⁰⁰⁶ , -ON═CR ¹⁰⁰⁶ R ¹⁰⁰⁷ , -NR ¹⁰⁰⁶ R ¹⁰⁰⁷ and -(OSiR ¹⁰⁰⁶ R ¹⁰⁰⁷ ) _h (OSiR ¹⁰⁰⁶ R ¹⁰⁰⁷ R ¹⁰⁰⁸ ) (R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ may be the same or different and each is a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, and h has an average value of 1 to 4), R ¹⁰⁰² is R ¹⁰⁰¹ , a hydrogen atom or a monovalent hydrocarbon group having 1 to 18 carbon atoms, R ¹⁰⁰³ is -[O(R ¹⁰⁰⁹ O) _j ]- group (R ¹⁰⁰⁹ is an alkylene group having 1 to 18 carbon atoms, and j is an integer of 1 to 4), R ¹⁰⁰⁴ is a divalent hydrocarbon group having 1 to 18 carbon atoms, and R ¹⁰⁰⁵ is a monovalent hydrocarbon group having 1 to 18 carbon atoms, and x, y, and z are numbers that satisfy the relationships x + y + 2z = 3, 0≦x≦3, 0≦y≦2, and 0≦z≦1).
(In the formula, v is an integer of 0 or more, and w is an integer of 1 or more. R ¹¹ represents hydrogen, halogen, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, a branched or unbranched alkynyl group having 2 to 30 carbon atoms, or an alkyl group in which the terminal hydrogen atom has been substituted with a hydroxyl group or a carboxyl group. R ¹² represents a branched or unbranched alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenylene group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene group having 2 to 30 carbon atoms. R ¹¹ and R ¹² may together form a ring structure.)

In formula (S1), R ¹⁰⁰⁵ , R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ are preferably each independently a group selected from the group consisting of a linear, cyclic or branched alkyl group, alkenyl group, aryl group and aralkyl group having 1 to 18 carbon atoms. Furthermore, when R ¹⁰⁰² is a monovalent hydrocarbon group having 1 to 18 carbon atoms, it is preferably a group selected from the group consisting of a linear, cyclic or branched alkyl group, alkenyl group, aryl group and aralkyl group. R ¹⁰⁰⁹ is preferably a linear, cyclic or branched alkylene group, with a linear one being particularly preferred. Examples of R ¹⁰⁰⁴ include alkylene groups having 1 to 18 carbon atoms, alkenylene groups having 2 to 18 carbon atoms, cycloalkylene groups having 5 to 18 carbon atoms, cycloalkylalkylene groups having 6 to 18 carbon atoms, arylene groups having 6 to 18 carbon atoms, and aralkylene groups having 7 to 18 carbon atoms. The alkylene groups and alkenylene groups may be linear or branched, and the cycloalkylene groups, cycloalkylalkylene groups, arylene groups, and aralkylene groups may have a functional group such as a lower alkyl group on the ring. R ¹⁰⁰⁴ is preferably an alkylene group having 1 to 6 carbon atoms, and particularly preferably a linear alkylene group, such as a methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, or hexamethylene group.

Specific examples of R ¹⁰⁰² , R ¹⁰⁰⁵ , R ¹⁰⁰⁶ , R ¹⁰⁰⁷ and R ¹⁰⁰⁸ in formula (S1) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a cyclopentyl group, a cyclohexyl group, a vinyl group, a propenyl group, an allyl group, a hexenyl group, an octenyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, a phenethyl group and a naphthylmethyl group.
Examples of R ¹⁰⁰⁹ in formula (S1) include linear alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and hexylene, and branched alkylene groups such as isopropylene, isobutylene, and 2-methylpropylene.

Specific examples of silane coupling agents represented by formula (S1) include 3-hexanoylthiopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, 3-decanoylthiopropyltriethoxysilane, 3-lauroylthiopropyltriethoxysilane, 2-hexanoylthioethyltriethoxysilane, 2-octanoylthioethyltriethoxysilane, 2-decanoylthioethyltriethoxysilane, 2-lauroylthioethyltriethoxysilane, 3-hexanoylthiopropyltrimethoxysilane, 3-octanoylthiopropyltrimethoxysilane, 3-decanoylthiopropyltrimethoxysilane, 3-lauroylthiopropyltrimethoxysilane, 2-hexanoylthioethyltrimethoxysilane, 2-octanoylthioethyltrimethoxysilane, 2-decanoylthioethyltrimethoxysilane, 2-lauroylthioethyltrimethoxysilane, etc. These may be used alone or in combination of two or more. Of these, 3-octanoylthiopropyltriethoxysilane is particularly preferred.

In the silane coupling agent comprising the bond unit A represented by formula (I) and the bond unit B represented by formula (II), the content of bond unit A is preferably 30 mol% or more, more preferably 50 mol% or more, preferably 99 mol% or less, more preferably 90 mol% or less.In addition, the content of bond unit B is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, preferably 70 mol% or less, more preferably 65 mol% or less, even more preferably 55 mol% or less.In addition, the total content of bond unit A and B is preferably 95 mol% or more, more preferably 98 mol% or more, particularly preferably 100 mol%.
The content of the bonding units A and B includes the case where the bonding units A and B are located at the terminals of the silane coupling agent. When the bonding units A and B are located at the terminals of the silane coupling agent, the form of the bonding units A and B is not particularly limited, as long as they form units corresponding to the formulas (I) and (II) representing the bonding units A and B.

With respect to ^R11 in formulas (I) and (II), examples of halogen include chlorine, bromine, and fluorine. Examples of branched or unbranched alkyl groups having 1 to 30 carbon atoms include methyl and ethyl groups. Examples of branched or unbranched alkenyl groups having 2 to 30 carbon atoms include vinyl and 1-propenyl groups. Examples of branched or unbranched alkynyl groups having 2 to 30 carbon atoms include ethynyl and propynyl groups.

With respect to ^R12 in formulas (I) and (II), examples of branched or unbranched alkylene groups having 1 to 30 carbon atoms include an ethylene group, a propylene group, etc. Examples of branched or unbranched alkenylene groups having 2 to 30 carbon atoms include a vinylene group, a 1-propenylene group, etc. Examples of branched or unbranched alkynylene groups having 2 to 30 carbon atoms include an ethynylene group, a propynylene group, etc.

In a silane coupling agent containing a bonding unit A represented by formula (I) and a bonding unit B represented by formula (II), the total number of repetitions (v+w) of bonding unit A (v) and bonding unit B (w) is preferably in the range of 3 to 300.

The content of the silane coupling agent is preferably at least 6 parts by mass, more preferably at least 8 parts by mass, and even more preferably at least 10 parts by mass, per 100 parts by mass of silica, and is preferably at most 15 parts by mass, more preferably at most 13 parts by mass, and even more preferably at most 11 parts by mass. Within the above range, better effects tend to be obtained.

The rubber composition preferably contains vulcanized rubber particles.
The vulcanized rubber particles are particles made of vulcanized rubber, and specifically, rubber powder or the like specified in JIS K 6316:2017 can be used. From the viewpoint of environmental considerations and cost, recycled rubber powder produced from crushed waste tires or the like is preferred. These may be used alone or in combination of two or more types.

Commercially available vulcanized rubber particles include those from Lehigh Corporation and Muraoka Rubber Industries Co., Ltd. Note that, in this specification, vulcanized rubber particles are not included in the rubber component.

The average particle size of the vulcanized rubber particles is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more, and is preferably 1000 μm or less, more preferably 900 μm or less, and even more preferably 800 μm or less.
The average particle size of the vulcanized rubber particles is an average particle size on a mass basis calculated from the particle size distribution measured in accordance with JIS Z 8815:1994.

The content of vulcanized rubber particles is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and even more preferably at least 5 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 20 parts by mass, more preferably at most 15 parts by mass, and even more preferably at most 10 parts by mass. Within the above ranges, better effects tend to be achieved.

In the rubber composition, the content of vulcanized rubber particles/total styrene content in the rubber component is preferably 0.10 or more, more preferably 0.13 or more, even more preferably 0.16 or more, and is preferably 0.22 or less, more preferably 0.20 or less, even more preferably 0.18 or less. Within the above ranges, the effect tends to be more favorable.
In this relationship, the content of vulcanized rubber particles is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total amount of styrene in the rubber component is the content (unit: % by mass) relative to 100% by mass of the rubber component.

The rubber composition preferably contains water-soluble particles.
The water-soluble particles are not particularly limited as long as they are particles that are soluble in water. For example, a material having a solubility in water at room temperature (20° C.) of 1 g/100 g water or more can be used.

Examples of water-soluble particles include water-soluble inorganic salts and water-soluble organic substances. Examples of water-soluble inorganic salts include metal sulfates such as magnesium sulfate and potassium sulfate; metal chlorides such as potassium chloride and sodium chloride; metal hydroxides such as potassium hydroxide and sodium hydroxide; carbonates such as potassium carbonate and sodium carbonate; and phosphates such as sodium hydrogen phosphate and sodium dihydrogen phosphate. Examples of water-soluble organic substances include lignin derivatives and sugars. These may be used alone or in combination of two or more. Of these, water-soluble inorganic salts are preferred, metal sulfates are more preferred, and magnesium sulfate is even more preferred.

Commercially available water-soluble particles include products from Mai Chemical Industry Co., Ltd. and Tokyo Chemical Industry Co., Ltd.

The median particle size (median diameter, D50) of the water-soluble particles is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more, and is preferably 800 μm or less, more preferably 500 μm or less, and even more preferably 300 μm or less. Within the above ranges, better effects tend to be obtained.
In this specification, the median particle size can be measured by laser diffraction.

The content of the water-soluble particles is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and even more preferably at least 5 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 20 parts by mass, more preferably at most 15 parts by mass, and even more preferably at most 10 parts by mass. Within the above ranges, better effects tend to be obtained.

In the rubber composition, the content of the water-soluble particles/the total amount of styrene in the rubber component is preferably 0.10 or more, more preferably 0.13 or more, and even more preferably 0.16 or more, and is preferably 0.22 or less, more preferably 0.20 or less, and even more preferably 0.18 or less. Within the above ranges, the effect tends to be more favorable.
In this relationship, the content of water-soluble particles is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total amount of styrene in the rubber component is the content (unit: % by mass) relative to 100% by mass of the rubber component.

The rubber composition may contain talc.
The average particle size of the talc is preferably 50 μm or less, more preferably 30 μm or less. There is no particular lower limit to the average particle size of the talc, but it is preferably 1 μm or more.

The talc content is preferably 1 to 50 parts by mass per 100 parts by mass of the rubber component.

The rubber composition may contain aluminum hydroxide.
In this specification, aluminum hydroxide means Al(OH) ₃ or _Al2O3.3H2O . Commercially available products available from Sumitomo Chemical Co., Ltd., Showa Denko K.K., Nabaltec _, etc. may be used. These may be used alone or in combination of two or _more .

The average particle size of the aluminum hydroxide is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 0.8 μm or more, and is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less. Within the above ranges, better effects tend to be obtained.
The average particle size of aluminum hydroxide is a value measured in the same manner as the average particle size of silica.

The BET specific surface area (nitrogen adsorption specific surface area, _N2SA ) of the aluminum hydroxide is preferably 5 ^m2 /g or more, more preferably 8 ^m2 /g or more, even more preferably 10 ^m2 /g or more, and is preferably 40 ^m2 /g or less, more preferably 30 ^m2 /g or less, even more preferably 20 ^m2 /g or less.
The BET specific surface area of aluminum hydroxide is a value measured by the BET method in accordance with ASTM D3037-81.

The aluminum hydroxide content is preferably 1 to 25 parts by mass per 100 parts by mass of the rubber component.

The rubber composition may contain a calcium compound.
The calcium compound is a compound containing calcium, and examples thereof include inorganic salts such as calcium oxide, calcium hydroxide, and calcium carbide; and oxoacid salts such as calcium carbonate, calcium nitrate, and calcium sulfate. Oxoacid salts also include fatty acid salts such as calcium acetate and calcium stearate. Examples of calcium compounds include eggshells (main component: calcium carbonate) and WB16 (a mixture of fatty acid calcium, fatty acid amide, and fatty acid amide ester) manufactured by Struktol. These may be used alone or in combination of two or more. Among these, oxoacid salts are preferred, and calcium carbonate is more preferred.

The calcium compound content is preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component.

The rubber composition may contain short fibers.
Examples of short fibers that can be used include organic short fibers and inorganic short fibers. Specific examples of organic short fibers include nanocelluloses such as cellulose nanofibers (CNF) and cellulose nanocrystals (CNC); chitin nanofibers; and biomass nanomaterials such as chitosan nanofibers. Specific examples of inorganic short fibers include metal fibers and glass fibers. Commercially available products include those from Nippon Paper Industries Co., Ltd. and Sugino Machine Co., Ltd. These may be used alone or in combination of two or more. Of these, organic short fibers are preferred, and nanocellulose is more preferred.

The particle size of nanocellulose is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 25 nm or more, and particularly preferably 28 nm or more, and is preferably 50 nm or less, more preferably 40 nm or less, even more preferably 35 nm or less, and particularly preferably 32 nm or less. Within the above ranges, better effects tend to be obtained.

The particle size of nanocellulose is the average fiber diameter measured by image analysis using scanning electron microscope photographs, transmission electron microscope photographs, atomic force microscope photographs, X-ray scattering data analysis, pore electrical resistance method (Coulter principle method), etc. Furthermore, in this specification, the average fiber diameter of nanocellulose (cellulose fibers) is typically the average fiber diameter of an aggregate of cellulose fibers formed by the aggregation of cellulose molecules.

The short fiber content is preferably 1 to 40 parts by mass per 100 parts by mass of the rubber component.

The rubber composition contains an aromatic resin as a resin.
Aromatic resins are polymers containing aromatic monomers as constituent monomers, and examples thereof include homopolymers obtained by polymerizing one type of aromatic monomer alone, copolymers obtained by copolymerizing two or more types of aromatic monomers, and copolymers of an aromatic monomer and another monomer copolymerizable therewith.

Examples of aromatic monomers include styrene-based monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, and p-chlorostyrene; phenol-based monomers such as phenol, alkylphenol, and alkoxyphenol; naphthol-based monomers such as naphthol, alkylnaphthol, and alkoxynaphthol; coumarone, indene, and the like. These may be used alone or in combination of two or more. Of these, styrene-based monomers are preferred, and styrene and α-methylstyrene are more preferred.

Other monomers include, for example, non-conjugated olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. These may be used alone or in combination of two or more.

To achieve better results, the aromatic resin is preferably an α-methylstyrene resin (such as an α-methylstyrene homopolymer or a copolymer of styrene and α-methylstyrene), and more preferably a styrene-α-methylstyrene resin (a copolymer of styrene and α-methylstyrene).

The content of the aromatic resin is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less. Within the above ranges, better effects tend to be obtained.

Examples of resins other than aromatic resins that can be used include C5 resins, C5/C9 resins, C9 resins, cyclopentadiene resins, and terpene resins. These may be used alone or in combination of two or more.

C5 resins are polymers containing a C5 fraction as a constituent monomer, and examples thereof include polymers obtained by polymerizing a C5 fraction obtained by thermal cracking of naphtha in the petrochemical industry using a Friedel-Crafts catalyst such as AlCl ₃ or BF _3. C5 fractions typically include olefinic hydrocarbons such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene; diolefinic hydrocarbons such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, and 3-methyl-1,2-butadiene; and the like.

The amount of C5 resin per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less.

The C5/C9 resin is a polymer containing a C5 fraction and a C9 fraction as constituent monomers, and examples thereof include polymers obtained by polymerizing a petroleum-derived C5 fraction and a C9 fraction using a Friedel-Crafts catalyst such as AlCl ₃ or BF _3. Specific examples include copolymers containing styrene, vinyltoluene, α-methylstyrene, indene, or the like as main components.
In this specification, C5/C9 resins are treated as resins different from aromatic resins, C5 resins, and C9 resins.

The amount of C5/C9 resin is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less.

C9 resins are polymers containing a C9 fraction as a constituent monomer, and examples thereof include polymers obtained by polymerizing a C9 fraction, which is by-produced together with petrochemical base materials such as ethylene and propylene during the thermal decomposition of naphtha in the petrochemical industry, using a Friedel-Crafts catalyst such as AlCl ₃ or BF _3. Specific examples of C9 fractions include vinyltoluene, α-methylstyrene, β-methylstyrene, γ-methylstyrene, o-methylstyrene, p-methylstyrene, and indene. C9 resins may also be obtained by copolymerizing a mixture of these C8 to C10 fractions, etc., as raw materials together with the C9 fraction, such as C8 fractions such as styrene, C10 fractions such as methylindene and 1,3-dimethylstyrene, and even naphthalene, vinylnaphthalene, vinylanthracene, and p-tert-butylstyrene, using a Friedel-Crafts catalyst, for example.
In this specification, C9 resins are treated as resins separate from aromatic resins.

The amount of C9 resin per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less.

Terpene resins are polymers that contain terpene compounds (terpene monomers) as constituent monomers. Examples include homopolymers in which one type of terpene compound is polymerized alone, copolymers in which two or more types of terpene compounds are copolymerized, and copolymers of terpene compounds and other monomers that can be copolymerized with them.

Terpene compounds are hydrocarbons represented by the formula (C ₅ H ₈ ) _n and their oxygen-containing derivatives, and are compounds having a basic skeleton of a terpene classified as monoterpene (C ₁₀ H ₁₆ ), sesquiterpene (C ₁₅ H ₂₄ ), diterpene (C ₂₀ H ₃₂ ), etc. Examples include α-pinene, β-pinene, dipentene, limonene, myrcene, alloocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, γ-terpineol, etc. These may be used alone or in combination of two or more.

To obtain a better effect, the terpene resin is preferably a homopolymer of a terpene compound (polyterpene resin) or a copolymer of a terpene compound and a styrene-based monomer, more preferably a copolymer of a terpene compound and a styrene-based monomer. Furthermore, the copolymer of a terpene compound and a styrene-based monomer is preferably a copolymer of a terpene compound and styrene (terpene-styrene resin).
In this specification, a polymer containing a terpene compound and a styrene-based monomer as constituent monomers, such as a terpene-styrene resin, is treated as a terpene-based resin, not an aromatic resin.

The amount of terpene resin per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less.

Cyclopentadiene-based resins are polymers that contain cyclopentadiene-based monomers as constituent monomers. Examples include homopolymers obtained by polymerizing one type of cyclopentadiene-based monomer alone, copolymers obtained by copolymerizing two or more types of cyclopentadiene-based monomers, and copolymers of a cyclopentadiene-based monomer with another monomer that can copolymerize with it.

Examples of cyclopentadiene-based monomers include cyclopentadiene, dicyclopentadiene, and tricyclopentadiene. These may be used alone or in combination of two or more. Of these, dicyclopentadiene is preferred. That is, the cyclopentadiene-based resin is preferably a polymer (DCPD-based resin) containing dicyclopentadiene (DCPD) as a constituent monomer, and a hydrogenated DCPD-based resin is more preferred.

The amount of cyclopentadiene resin per 100 parts by mass of the rubber component is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less.

The resin is also preferably a modified resin into which a functional group has been introduced (functionalized resin).
The modified resin can be produced by a known method, for example, by a slurry method, a metathesis method, etc. Specifically, for example, the modified resin can be produced by reacting a polymer that will become the polymer skeleton of the modified resin with a functional compound that can introduce a functional group, by a known method.

The polymer that forms the polymer backbone is not particularly limited and may be, for example, the aromatic resins described above or other resins. These may be used alone or in combination of two or more. Of these, aromatic resins are preferred, α-methylstyrene resins are more preferred, and styrene-α-methylstyrene resins (copolymers of styrene and α-methylstyrene) are even more preferred.

The functional group is preferably a functional group containing at least one element selected from the group consisting of oxygen, silicon, and nitrogen, and more preferably a functional group containing silicon.

The amount of modified resin per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. Within the above ranges, better effects tend to be obtained.

In the rubber composition, the ratio of the content of the modified resin to the total amount of styrene in the rubber component is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.8 or more, and is preferably 1.1 or less, more preferably 1.0 or less, and even more preferably 0.9 or less.
Within the above range, better effects tend to be obtained.
In this relationship, the content of the modified resin is the content (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the total amount of styrene in the rubber component is the content (unit: % by mass) relative to 100% by mass of the rubber component.

Commercially available resins include those from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JXTG Nippon Oil & Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd.

The resin content, per 100 parts by mass of the rubber component, is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 45 parts by mass or less. Within the above ranges, better effects tend to be obtained.

In the rubber composition, the ratio of the silica content to the resin content is preferably more than 2, more preferably 2.2 or more, and even more preferably 2.4 or more, and is preferably 5.0 or less, more preferably less than 4.0, and even more preferably 3 or less. When the ratio is within the above range, the effect tends to be more favorably obtained.
In this relationship, the silica content and the resin content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component.

The rubber composition may contain a liquid plasticizer.
The liquid plasticizer is a plasticizer that is in a liquid state at room temperature (25° C.), and oil, liquid polymer, ester-based plasticizer, etc. The liquid plasticizer may be used alone or in combination of two or more kinds.

Examples of oils include process oils, vegetable oils, and mixtures thereof. Examples of process oils that can be used include paraffin-based process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Waste vegetable oils recovered from vegetable oils used as cooking oils may also be used. Commercially available products include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., JXTG Nippon Oil & Energy Corporation, Oriso Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., and Fuji Kosan Co., Ltd. These may be used alone or in combination of two or more.

The oil content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component. There is no particular lower limit, and it may be 0 parts by mass. Within the above range, better effects tend to be obtained.

The liquid polymer is a (co)polymer that is in a liquid state at room temperature (25°C). For example, at least one (co)polymer selected from the group consisting of butadiene, isoprene, styrene, farnesene, and derivatives thereof can be used. Specific examples include liquid styrene-butadiene copolymer (liquid SBR), liquid butadiene polymer (liquid BR), liquid isoprene polymer (liquid IR), liquid styrene-isoprene copolymer (liquid SIR), liquid farnesene polymer, and liquid farnesene-butadiene copolymer. The liquid polymer may also be modified or hydrogenated. Commercially available products include those from Cray Valley, Kuraray Co., Ltd., and other companies. These may be used alone or in combination.

The weight average molecular weight (Mw) of the liquid polymer is preferably 9000 or less, more preferably 6000 or less, and even more preferably 4500 or less, and is preferably 100 or more, more preferably 1000 or more, and even more preferably 2000 or more. Within the above ranges, the effect tends to be more favorably obtained.
In this specification, the liquid polymer is not included in the rubber component.

The liquid polymer content is preferably 0.5 to 25 parts by mass per 100 parts by mass of the rubber component.

The ester plasticizer is not particularly limited as long as it is a compound having an ester group that is liquid at room temperature (25°C), and examples thereof include phthalic acid derivatives, long-chain fatty acid derivatives, phosphoric acid derivatives, sebacic acid derivatives, and adipic acid derivatives. These may be used alone or in combination of two or more. Among these, phosphoric acid derivatives, sebacic acid derivatives, and adipic acid derivatives are preferred, and sebacic acid derivatives are more preferred.
The phthalic acid derivatives are not particularly limited, but examples thereof include phthalate esters such as di-2-ethylhexyl phthalate (DOP) and diisodecyl phthalate (DIDP). The long-chain fatty acid derivatives are not particularly limited, but examples thereof include long-chain fatty acid glycerin esters. The phosphoric acid derivatives are not particularly limited, but examples thereof include phosphoric acid esters such as tris(2-ethylhexyl)phosphate (TOP) and tributylphosphate (TBP). The sebacic acid derivatives are not particularly limited, but examples thereof include sebacic acid esters such as di(2-ethylhexyl)sebacate (DOS) and diisooctylsebacate (DIOS). The adipic acid derivatives are not particularly limited, but examples thereof include adipic acid esters such as di(2-ethylhexyl)adipate (DOA) and diisooctyladipate (DIOA).
Among these, phosphate ester, sebacate ester, and adipate ester are preferred, and sebacate ester is more preferred. Specific compounds are preferably TOP, DOS, and DOA, and more preferably DOS.
As the ester-based plasticizer, for example, products manufactured by Daihachi Chemical Industry Co., Ltd., Taoka Chemical Industry Co., Ltd., etc. can be used.

The glass transition temperature (Tg) of the ester-based plasticizer is preferably −110° C. or higher, more preferably −100° C. or higher, even more preferably −80° C. or higher, and is preferably −20° C. or lower, more preferably −40° C. or lower, even more preferably −55° C. or lower. By keeping the Tg within the above range, the above-mentioned effects tend to be more suitably obtained.
In this specification, the glass transition temperature is a value measured in accordance with JIS-K7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan at a temperature rise rate of 10°C/min.

The content of the ester-based plasticizer is preferably 1 to 20 parts by mass per 100 parts by mass of the rubber component.

In the above rubber composition, the content of liquid plasticizer (total content of oil, etc.) is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the rubber component. There is no particular lower limit, and it may be 0 parts by mass. Within the above range, better effects tend to be obtained.

In the rubber composition, the relationship is resin content>BR content>liquid plasticizer content.
The resin content - BR content is preferably 2 or more, more preferably 5 or more, and even more preferably 30 or more, and is preferably 55 or less, more preferably 50 or less, and even more preferably 45 or less. Within the above ranges, the effect tends to be better obtained.
The ratio of the content of BR to the content of the liquid plasticizer is preferably at least 1, more preferably at least 2, and even more preferably at least 3, and is preferably at most 25, more preferably at most 20, and even more preferably at most 15. Within the above ranges, better effects tend to be obtained.
Furthermore, the ratio of the resin content to the liquid plasticizer content is preferably 5 or more, more preferably 15 or more, and even more preferably 30 or more, and is preferably 55 or less, more preferably 50 or less, and even more preferably 45 or less. Within the above ranges, better effects tend to be obtained.
In this relationship, the resin content and the liquid plasticizer content are expressed as contents (unit: parts by mass) relative to 100 parts by mass of the rubber component, and the BR content is expressed as the content (unit: % by mass) in 100% by mass of the rubber component.

The rubber composition may contain a processing aid.
Examples of processing aids include metal salts (compounds in which the hydrogen atoms of an acid are substituted with metal ions), fatty acid amides, amide esters, and fatty acid esters. These may be used alone or in combination of two or more. Among these, metal salts and fatty acid amides are preferred, and metal salts are more preferred.

Metals used in metal salts include, for example, alkali metals such as potassium and sodium, and alkaline earth metals such as calcium and barium. Magnesium, zinc, nickel, molybdenum, etc. can also be used. Of these, alkali metals are preferred.

Acids used in metal salts include, for example, fatty acids such as lauric acid, myristic acid, and palmitic acid. Other acids that can also be used include boric acid, carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid.

Commercially available processing aids include products from Kishida Chemical Co., Ltd., Kenei Pharmaceutical Co., Ltd., Struktol, Performance Additives, etc.

The content of the processing aid per 100 parts by mass of the rubber component is preferably at least 1 part by mass, more preferably at least 2 parts by mass, and even more preferably at least 4 parts by mass, and is preferably at most 15 parts by mass, more preferably at most 12 parts by mass, and even more preferably at most 8 parts by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain a dibenzylamine compound.
The dibenzylamine compound is a compound having at least one group (dibenzylamine group) represented by the following formula:

Specific examples of dibenzylamine compounds include dibenzylamine, tetrabenzylthiuram disulfide (TBzTD), zinc dibenzyldithiocarbamate, and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. Commercially available products include those from Sanshin Chemical Industry Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and Lanxess. These compounds may be used alone or in combination. Of these, compounds having two dibenzylamine groups are preferred, with tetrabenzylthiuram disulfide being more preferred.

The amount of the dibenzylamine compound per 100 parts by mass of the rubber component is preferably at least 0.01 part by mass, more preferably at least 0.1 part by mass, and even more preferably at least 0.2 part by mass, and is preferably at most 1.0 part by mass, more preferably at most 0.7 part by mass, and even more preferably at most 0.5 part by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain an antioxidant.
Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine;N-isopropyl-N'-phenyl-p-phenylenediamine,N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Examples of such antioxidants include p-phenylenediamine-based antioxidants such as quinolone; quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Commercially available products include those available from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis, and the like. These antioxidants may be used alone or in combination of two or more.

The content of the antioxidant is preferably at least 1 part by mass, more preferably at least 3 parts by mass, and even more preferably at least 4.5 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 12 parts by mass, more preferably at most 10 parts by mass, and even more preferably at most 8 parts by mass. Within the above ranges, better effects tend to be obtained.

The rubber composition may contain a wax.
The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. These may be used alone or in combination of two or more.

The wax content is preferably at least 1 part by mass, more preferably at least 2 parts by mass, per 100 parts by mass of the rubber component, and is preferably at most 10 parts by mass, more preferably at most 5 parts by mass. Within the above ranges, better effects tend to be achieved.

The rubber composition may contain stearic acid.
As the stearic acid, conventionally known ones can be used, and commercially available products that can be used include those available from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc. These may be used alone or in combination of two or more.

The amount of stearic acid per 100 parts by mass of the rubber component is preferably at least 1 part by mass, more preferably at least 1.5 parts by mass, and is preferably at most 10 parts by mass, more preferably at most 6 parts by mass. Within the above ranges, better effects tend to be achieved.

The rubber composition may contain zinc oxide.
As the zinc oxide, conventionally known ones can be used, and commercially available products include those available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more.

The zinc oxide content, per 100 parts by mass of the rubber component, is preferably at least 0.1 part by mass, more preferably at least 0.3 part by mass, and even more preferably at least 0.5 part by mass, and is preferably at most 6 parts by mass, more preferably at most 3 parts by mass, and even more preferably at most 2 parts by mass. Within the above ranges, better effects tend to be obtained.

In the rubber composition, (zinc oxide content/silica content)×100 is preferably 3.5 or less, more preferably less than 2.0, even more preferably 0.8 or less, and is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.4 or more. When it is within the above range, the effect tends to be more favorable.
In this relationship, the zinc oxide content and the silica content are the contents (unit: parts by mass) relative to 100 parts by mass of the rubber component.

The rubber composition may contain sulfur.
Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, and the like, which are commonly used as crosslinking agents in the rubber industry. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., and the like. These may be used alone or in combination of two or more.

The sulfur content, per 100 parts by mass of the rubber component, is preferably at least 0.3 parts by mass, more preferably at least 0.6 parts by mass, and even more preferably at least 1.1 parts by mass, and is preferably at most 3.5 parts by mass, more preferably at most 2.8 parts by mass, and even more preferably at most 2 parts by mass. Within the above ranges, better effects tend to be obtained.

In the rubber composition, the ratio of the zinc oxide content to the sulfur content is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.4 or more, and is preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. When the ratio is within the above ranges, better effects tend to be obtained.
In this relationship, the zinc oxide content and sulfur content are expressed as the content (unit: parts by mass) relative to 100 parts by mass of the rubber component.

The rubber composition may contain an organic crosslinking agent.
The organic cross-linking agent is not particularly limited, and examples thereof include maleimide compounds, alkylphenol-sulfur chloride condensates, organic peroxides, amine organic sulfides, etc. These may be used alone or in combination of two or more.

The content of the organic crosslinking agent is preferably 1 to 15 parts by mass per 100 parts by mass of the rubber component.

The rubber composition may contain a vulcanization accelerator.
Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD) and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-oxyethylene-2-benzothiazolesulfenamide and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. Commercially available products include those from Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and the like. These may be used alone or in combination of two or more.

The content of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 2.5 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less. Within the above ranges, better effects tend to be obtained.

The rubber composition preferably contains a dialkyldithiophosphate compound.
As the dialkyldithiophosphate compound, for example, a salt of a dialkyldithiophosphate with a metal such as zinc or molybdenum can be used. Commercially available products include TP-50 manufactured by Rhein Chemie. These may be used alone or in combination of two or more. Of these, the compound represented by the following formula (1) (zinc dialkyldithiophosphate) is preferred.
(In the formula, R ¹ to R ⁴ each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, or a cycloalkyl group having 5 to 12 carbon atoms.)

In formula (1), examples of the linear or branched alkyl group represented by R ¹ to R ⁴ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a 4-methylpentyl group, a 2-ethylhexyl group, an octyl group, an octadecyl group, etc., while examples of the cycloalkyl group include a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, etc. Among these, from the viewpoints of ease of dispersion in the rubber composition and ease of production, R ¹ to R ⁴ are preferably linear or branched alkyl groups having 2 to 8 carbon atoms, more preferably an n-butyl group, an n-propyl group, an isopropyl group, or an n-octyl group, and even more preferably an n-butyl group.

The amount of the dialkyldithiophosphate compound per 100 parts by mass of the rubber component is preferably at least 0.1 part by mass, more preferably at least 0.5 part by mass, and even more preferably at least 1 part by mass, and is preferably at most 6 parts by mass, more preferably at most 4 parts by mass, and even more preferably at most 2 parts by mass. Within the above ranges, better effects tend to be obtained.

In addition to the above components, the rubber composition may further contain additives commonly used in the tire industry, such as organic peroxides. The content of these additives is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

The rubber composition can be produced, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or Banbury mixer, followed by vulcanization.

As for kneading conditions, in the base kneading process, in which additives other than the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is typically 100 to 180°C, preferably 120 to 170°C. In the finish kneading process, in which the vulcanizing agent and vulcanization accelerator are kneaded, the kneading temperature is typically 120°C or lower, preferably 85 to 110°C. Furthermore, the composition kneaded with the vulcanizing agent and vulcanization accelerator is typically subjected to a vulcanization process such as press vulcanization. The vulcanization temperature is typically 140 to 190°C, preferably 150 to 185°C. The vulcanization time is typically 5 to 15 minutes.

The above rubber composition can be used (as a rubber composition for tires) in tire components such as treads, sidewalls, base treads, undertreads, shoulders, clinches, bead apexes, breaker cushion rubber, carcass cord covering rubber, insulation, chafers, inner liners, and side reinforcing layers of run-flat tires. It is particularly suitable for treads (particularly the portion (cap tread) that comes into contact with the road surface during driving).

The tire of the present disclosure is manufactured by a conventional method using the above rubber composition.
That is, the rubber composition is extruded in an unvulcanized state to match the shape of the tread, etc., and molded together with other tire components in a tire building machine by a conventional method to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizer to obtain a tire.

The above-mentioned tires (pneumatic tires, etc.) can be used for passenger car tires; truck and bus tires; motorcycle tires; high-performance tires; winter tires such as studless tires; run-flat tires with side reinforcing layers; tires with sound-absorbing material that has sound-absorbing material such as sponge in the tire cavity; tires with sealing material that has a sealant inside or in the tire cavity that can seal in the event of a puncture; and tires with electronic components that have electronic components such as sensors and wireless tags inside or in the tire cavity, and are suitable for passenger car tires.

The size of the above tire is not particularly limited, and can be selected appropriately, for example, with a tire width in the range of 100 to 400 mm, an aspect ratio in the range of 25 to 85%, and a rim diameter in the range of 10 to 25 inches. Specific examples include 105/50R16, 115/50R17, 125/55R20, 135/45R21, 145/45R21, 155/45R18, 165/45R22, 175/45R23, 185/60R20, 195/55R14, 205/40R16, 215/40R16, 225/40R17, 235/40R17, 245/40R16, 255/40R17, 265/40R17, 275/35R18, 285/30R19, and 295/45R20.

It is preferable that the tire outer diameter Dt and the tire section width Wt of the tire satisfy the following relational expression.
The tire outer diameter (Dt) is the outer diameter of the tire when mounted on an applicable rim and under an internal pressure of 250 kPa with no load. The tire cross-sectional width (Wt) is the linear distance between the sidewalls, including any markings or letters on the tire sidewalls, when mounted on an applicable rim and under an internal pressure of 250 kPa with no load, i.e., the width excluding the markings and letters on the tire sidewalls from the total width.

Specific examples of tires that can satisfy the above formula include 145/60R18, 145/60R19, 155/55R18, 155/55R19, 155/70R17, 155/70R19, 165/55R20, 165/55R21, 165/60R19, 165/65R19, 165/70R18, 175/55R19, 175/55R20, 175/55R22, 175/60R18, 185/55R19, 185/60R20, 195/50R20, and 195/55R20.

Tires that satisfy the above formula are preferably used as pneumatic tires for passenger cars. This is because pneumatic tires for passenger cars that satisfy the above formula tend to be more suitable for solving the problem at hand.

The present disclosure will be specifically explained based on examples, but the present disclosure is not limited to these examples.

The various chemicals used in the examples and comparative examples are described below.

(Rubber component)
NR: TSR20
SBR1: Modified SBR synthesized in Production Example 1 below (styrene content: 40% by mass, vinyl content: 25% by mass)
SBR2: HPR850 (styrene content: 27.5% by mass, vinyl content: 59% by mass) manufactured by JSR Corporation
SBR3: Styrene-α-methylstyrene resin-extended SBR synthesized in Production Example 2 below (styrene content: 40% by mass, vinyl content: 25% by mass, resin content: 30 parts by mass per 100 parts by mass of rubber solids)
BR: BR150B manufactured by Ube Industries, Ltd. (vinyl content: 1 mass%, cis content: 97 mass%)

(Chemicals other than rubber components)
Carbon black: N220 (CTAB specific surface area: 111 m ² /g)
Silica 1: Ultrasil VN3 (average particle size: 17 nm) manufactured by Evonik Degussa
Silica 2: Zeosil Premium 200MP (average particle size 14 nm) manufactured by Solvay Japan Co., Ltd.
Silane coupling agent 1: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa
Silane coupling agent 2: NXT-Z45 manufactured by Momentive (a copolymer of bonding unit A and bonding unit B (bonding unit A: 55 mol %, bonding unit B: 45 mol %))
Resin 1: Marucaretz M-845A (dicyclopentadiene resin) manufactured by Maruzen Petrochemical Co., Ltd.
Resin 2: SYLVARES SA85 (styrene α-methylstyrene resin (copolymer of styrene and α-methylstyrene)) manufactured by Arizona Chemical Company
Resin 3: Modified styrene-α-methylstyrene resin produced in Production Example 3 below. Oil: A/O Mix manufactured by Sankyo Yuka Kogyo Co., Ltd. Magnesium sulfate: USN-00 manufactured by Mai Chemical Industry Co., Ltd. (ultrafine magnesium sulfate, median particle size: 3 μm).
Vulcanized rubber particles: Ekodyne from Lehigh
Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Stearic acid: NOF Corporation's "Tsubaki" stearic acid
Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Antioxidant 2: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Processing aid 1: ULTRA-FLOW 440 (fatty acid zinc salt) manufactured by Performance Additives
Processing aid 2: ULTAR-LUBE 160 (a mixture of fatty acid soap and fatty acid amide) manufactured by Performance Additives
Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: HK-200-5 (powdered sulfur containing 5% by mass of oil) manufactured by Hosoi Chemical Industry Co., Ltd.
Vulcanization accelerator: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Dibenzylamine compound: Sancerer TBzTD (tetrabenzyl thiuram disulfide) manufactured by Sanshin Chemical Industry Co., Ltd.
Dialkyldithiophosphate compound: TP-50 manufactured by Rhein Chemie (a mixture of zinc dithiophosphate and polymer, R ¹ to R ⁴ in formula (1) are n-butyl groups, active ingredient: 50% by mass)

(Production Example 1)
Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-purged autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium was added to initiate polymerization. Polymerization was carried out under adiabatic conditions, with the maximum temperature reaching 85°C. When the polymerization conversion reached 99%, 1,3-butadiene was added, and the polymerization was continued for an additional 5 minutes. N,N-bis(trimethylsilyl)-3-aminopropyltriethoxysilane was then added as a modifier, and the reaction was continued. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried using a heated roll adjusted to 110°C to obtain SBR1.

(Production Example 2)
Styrene-α-methylstyrene resin (Resin 2) and SBR1 were added to cyclohexane in a predetermined ratio and stirred at a stirring speed of 400 rpm for 2 hours under a nitrogen pressure of 0.4 bar while heating. The resulting solution was dried to obtain styrene-α-methylstyrene resin-extended SBR (SBR3).

(Production Example 3)
Aluminum chloride and toluene were added to a glass flask whose atmosphere had been replaced with an inert gas, and styrene and α-methylstyrene were added dropwise. Subsequently, an isoprene/toluene solution to which allyltriethoxysilane had been added by a slurry method was added dropwise to the reaction liquid, and water was added to the reaction liquid to terminate the reaction. After repeating the process of removing the aqueous layer by liquid separation, the organic layer obtained by liquid separation was dried with air to volatilize the toluene, and then dried under reduced pressure to obtain a modified styrene-α-methylstyrene resin (Resin 3).

Examples and Comparative Examples
According to the formulations shown in Tables 1 and 2, materials other than sulfur, vulcanization accelerator, and dibenzylamine compound were kneaded for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded mixture. Next, sulfur, vulcanization accelerator, and dibenzylamine compound were added to the obtained kneaded mixture, and the mixture was kneaded for 5 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was molded into a tread shape and laminated with other tire components to form an unvulcanized tire. The tire was press-vulcanized for 12 minutes at 150°C to produce a test tire (size: 175/60R18). The obtained test tire was subjected to the following evaluations, and the results are shown in Tables 1 and 2.

In Tables 1 and 2, the rubber content in the resin-extended rubber is listed in the rubber column, and the resin content in the resin-extended rubber is added to the resin 2 column.

In the following evaluations, the evaluation criteria for calculating the index are as follows:
(Wet grip performance at high speeds)
Table 1: Comparative Example 5
Table 2: Examples 9 and 10 are Comparative Example 7, Example 11 is Comparative Example 8, and Example 12 is Comparative Example 9
(low fuel consumption at high speeds)
Table 1: Comparative Example 4
Table 2: Examples 9 and 10 are Comparative Example 7, Example 11 is Comparative Example 8, and Example 12 is Comparative Example 9

(Acetone extractables (AE))
For rubber test pieces (samples) cut out from the tread of the test tire, the amount of substances contained in the rubber test pieces that could be extracted with acetone was measured in accordance with the method for measuring acetone extractables in accordance with JIS K 6229:2015.
Acetone extractable amount (mass%)=(mass of sample before extraction−mass of sample after extraction)/mass of sample before extraction×100

(Polymer content (PC))
For the sample after acetone extraction in the above acetone extractable amount (AE), the organic matter was pyrolyzed and vaporized by heating in nitrogen (heating from room temperature to 750°C) in accordance with JIS K6226-1:2003, and the weight loss (mass) was measured, and PC (mass%) was calculated based on the result.

(Carbon black content (BC))
The sample after pyrolysis and vaporization at the above polymer amount (PC) was subjected to oxidative combustion by heating in air, and the weight loss (mass) was measured, and BC (mass %) was calculated based on the result.

(Ash content (Ash))
The mass of the component (ash content) that did not burn in oxidative combustion in the above amount of carbon black (BC) was measured, and Ash (mass %) was calculated based on this.

(Wet grip performance at high speeds)
Each test tire was mounted on a vehicle, and the braking distance from an initial speed of 100 km/h on a wet asphalt road surface was measured and expressed as an index, with the evaluation standard being 100. A larger index indicates a shorter braking distance and better wet grip performance.

(low fuel consumption at high speeds)
Using a rolling resistance tester, the rolling resistance of each test tire was measured when it was run at a speed of 100 km/h, and the result was expressed as an index, with the evaluation standard being 100. A larger index indicates lower rolling resistance and better fuel economy.

Tables 1 and 2 show that the Examples were superior to the Comparative Examples in terms of the overall performance (total of all indexes) of wet grip performance and fuel economy during high-speed driving, which were the objectives.

The present disclosure (1) relates to a rubber composition for tires, which contains a rubber component containing styrene-butadiene rubber and butadiene rubber, silica, and a resin containing an aromatic resin, wherein the content of the styrene-butadiene rubber exceeds 60% by mass per 100 parts by mass of the rubber component, the average particle size of the silica is 16 nm or less, the content of the silica exceeds 80 parts by mass per 100 parts by mass of the rubber component, and the content of the resin > the content of the butadiene rubber > the content of the liquid plasticizer.

Disclosure (2) is a rubber composition for tires according to Disclosure (1), which contains a mercapto-based silane coupling agent.

The present disclosure (3) is a rubber composition for tires according to the present disclosure (1) or (2), which contains a dialkyldithiophosphate compound.

The present disclosure (4) is a rubber composition for tires, which is any combination of any of the present disclosures (1) to (3), in which the total amount of styrene in the rubber component is less than 30% by mass.

The present disclosure (5) is a rubber composition for tires, which is any combination of the present disclosures (1) to (4) in which the rubber component contains an isoprene-based rubber.

The present disclosure (6) is a rubber composition for tires that is any combination with any of the present disclosures (1) to (5), in which (zinc oxide content/said silica content) x 100 < 2.

The present disclosure (7) is a rubber composition for tires, which is any combination with any of the present disclosures (1) to (6), in which 2 < the silica content / the resin content < 4.

The present disclosure (8) is a rubber composition for tires, which is any combination with any of the present disclosures (1) to (7), in which the silica content/styrene-butadiene rubber content is ≥ 1.4.

The present disclosure (9) is a rubber composition for tires, which is any combination of the resin of the present disclosures (1) to (8) containing a modified resin.

The present disclosure (10) is a rubber composition for tires, which is any combination of the rubber component of the present disclosures (1) to (9) containing a resin-extended rubber.

The present disclosure (11) is a rubber composition for tires containing water-soluble particles, in any combination with any of the present disclosures (1) to (10).

The present disclosure (12) is a rubber composition for tires containing vulcanized rubber particles, in any combination with any of the present disclosures (1) to (11).

The present disclosure (13) is a tire using a rubber composition in any combination with any of the present disclosures (1) to (12).

Claims (14)

The rubber composition contains a rubber component including styrene butadiene rubber and butadiene rubber, silica, a resin including an aromatic resin , and a liquid plasticizer ,
The content of the styrene-butadiene rubber in 100% by mass of the rubber component is 82 % by mass or more ,
The average particle size of the silica is 16 nm or less,
the content of the silica is more than 80 parts by mass per 100 parts by mass of the rubber component,
the content of the liquid plasticizer is 15 parts by mass or more per 100 parts by mass of the rubber component,
A rubber composition for a tire, wherein the content of the resin > the content of the butadiene rubber > the content of the liquid plasticizer. The rubber composition for tires according to claim 1, which contains a mercapto-based silane coupling agent. The rubber composition for tires according to claim 1 or 2, which contains a dialkyldithiophosphate compound. The rubber composition for tires according to any one of claims 1 to 3, wherein the total amount of styrene in the rubber component is less than 30% by mass. The rubber composition for tires according to any one of claims 1 to 4, wherein the rubber component contains an isoprene-based rubber. The rubber composition for tires according to any one of claims 1 to 5, wherein (zinc oxide content/said silica content) x 100 < 2. The rubber composition for tires according to any one of claims 1 to 6, wherein 2 < content of said silica / content of said resin < 4. The rubber composition for tires according to any one of claims 1 to 7, wherein the silica content/styrene-butadiene rubber content is ≥ 1.4. The rubber composition for a tire according to any one of claims 1 to 8, wherein the content of the resin is 35 parts by mass or less per 100 parts by mass of the rubber component. The rubber composition for a tire according to any one of claims 1 to 9 , wherein the resin contains a modified resin. The rubber composition for a tire according to any one of claims 1 to 10 , wherein the rubber component contains a resin-extended rubber. The rubber composition for a tire according to any one of claims 1 to 11 , which contains water-soluble particles. The rubber composition for tires according to any one of claims 1 to 12 , which contains vulcanized rubber particles. A tire using the rubber composition according to any one of claims 1 to 13 .