JP7494580B2 - Rubber composition for tires - Google Patents

Description

The present invention relates to a rubber composition and a tire having tire components made of the rubber composition.

Important tire performance factors include wet grip performance and abrasion resistance, which improve driving safety. In recent years, from the standpoint of resource conservation, there has been a need to improve fuel efficiency by improving tire rolling resistance. Known methods for achieving a good balance between low fuel consumption and wet grip performance include, for example, blending silica with a silane coupling agent (Patent Document 1).

JP 2004-59599 A

However, silica has a strong tendency to self-aggregate due to the formation of hydrogen bonds by silanol groups present on the particle surface, and because it has a lower affinity with rubber components than carbon black, it is prone to insufficient dispersion in the rubber composition.

On the other hand, isoprene-based rubber and styrene-butadiene rubber (SBR) have poor compatibility and are prone to layer separation in the rubber composition. Furthermore, in rubber compositions containing isoprene-based rubber and SBR, silica is easily incorporated into the isoprene-based rubber phase, and silica tends to be dispersed biased toward the isoprene-based rubber phase. For these reasons, rubber compositions containing isoprene-based rubber, SBR, and silica have the problem that it is difficult to obtain sufficient reinforcement.

When the above rubber composition is used in the tread of a tire, heat is likely to be generated between the silica aggregates in the isoprene-based rubber phase and the isoprene-based rubber, raising the temperature of the entire rubber composition and reducing the strength of the rubber. In particular, when the tire is driven continuously at high speed, friction per unit time increases and the time spent cooling without contacting the road surface is shortened, so it is believed that there is room for improvement in heat generation performance and wear resistance during high-speed driving.

The present invention aims to provide a rubber composition for tires that improves the dispersibility of silica and provides a well-balanced improvement in heat generation performance and wear resistance during high-speed driving.

After extensive research, the inventors discovered that the above problems can be solved by adding a specific phosphate ester compound to a rubber composition containing isoprene-based rubber, SBR, and silica. In a further preferred embodiment, they discovered that wet grip performance can also be improved, and thus completed the present invention.

［式中、Ｒ¹は、炭素数３～２１の直鎖状または分枝状のアルキル基を表し；ｎは１～１０の整数を表し；ｍは１または２を表し；－ＯＡ¹－は、オキシエチレン基、またはオキシプロピレン基を表し；Ｒ²は水素原子または炭素数１～１０の直鎖状または分枝状のアルキル基を表し、ｍが１である場合、複数のＲ²はそれぞれ同一であっても異なっていてもよく、ｍが２である場合、複数のＲ¹はそれぞれ同一であっても異なっていてもよい］で表される化合物からなる群より選択される１以上のリン酸エステル化合物を１～５０質量部含有するタイヤ用ゴム組成物であって、前記ゴム成分中のイソプレン系ゴムの含有量が８０質量％以下であり、スチレンブタジエンゴムの含有量が２０質量％以上である、タイヤ用ゴム組成物、
〔２〕シリカ１００質量部に対し、前記リン酸エステル化合物を２～１０質量部含有する、〔１〕記載のタイヤ用ゴム組成物、
〔３〕イソプレン系ゴム１００質量部に対し、前記リン酸エステル化合物を２～１０質量部含有する、〔１〕または〔２〕記載のタイヤ用ゴム組成物、
〔４〕シリカおよび前記リン酸エステル化合物を含むマスターバッチを含有する、〔１〕～〔３〕のいずれかに記載のタイヤ用ゴム組成物、
〔５〕前記ゴム組成物のガラス転移温度が－５０℃～－２０℃である、〔１〕～〔４〕のいずれかに記載のタイヤ用ゴム組成物、
〔６〕加硫後の前記ゴム組成物のアセトン抽出量が５質量％以上である、〔１〕～〔５〕のいずれかに記載のタイヤ用ゴム組成物、
〔７〕前記ゴム成分中が、ケイ素、窒素および酸素からなる群から選択される少なくとも一つの元素を含む官能基によって変性されたブタジエンゴムを含む、〔１〕～〔６〕のいずれかに記載のタイヤ用ゴム組成物、
〔８〕前記ゴム成分中に、変性ジエン系ゴムを２０質量％以上含む、〔１〕～〔７〕のいずれかに記載のタイヤ用ゴム組成物、
〔９〕〔１〕～〔８〕のいずれかに記載のタイヤ用ゴム組成物により構成されたトレッドを有するタイヤ、に関する。 That is, the present invention provides
[1] 30 to 120 parts by mass of silica and a rubber component represented by the following formula (1) or (2):

wherein R ¹ represents a linear or branched alkyl group having 3 to 21 carbon atoms; n represents an integer of 1 to 10; m represents 1 or 2; -OA ¹ - represents an oxyethylene group or an oxypropylene group; R ² represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, and when m is 1, a plurality of R ^2s may be the same or different, and when m is 2, a plurality of R ^1s may be the same or different, and wherein the rubber component of the rubber composition contains an isoprene-based rubber in an amount of 80% by mass or less and a styrene-butadiene rubber in an amount of 20% by mass or more.
[2] The rubber composition for tires according to [1], which contains 2 to 10 parts by mass of the phosphoric acid ester compound per 100 parts by mass of silica.
[3] The rubber composition for tires according to [1] or [2], which contains 2 to 10 parts by mass of the phosphoric acid ester compound per 100 parts by mass of isoprene-based rubber.
[4] The rubber composition for tires according to any one of [1] to [3], which contains a master batch containing silica and the phosphoric acid ester compound.
[5] The rubber composition for tires according to any one of [1] to [4], wherein the glass transition temperature of the rubber composition is −50° C. to −20° C.;
[6] The rubber composition for tires according to any one of [1] to [5], wherein the acetone extractable amount of the rubber composition after vulcanization is 5% by mass or more.
[7] The rubber composition for tires according to any one of [1] to [6], wherein the rubber component contains a butadiene rubber modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen.
[8] The rubber composition for tires according to any one of [1] to [7], wherein the rubber component contains 20% by mass or more of a modified diene rubber.
[9] A tire having a tread formed from the rubber composition for tires according to any one of [1] to [8].

The rubber composition for tires according to the present invention has improved silica dispersibility and provides a well-balanced improvement in heat generation performance and wear resistance during high-speed driving. In a preferred embodiment, the wet grip performance is also improved.

［式中、Ｒ¹は、炭素数３～２１（好ましくは５～１５、より好ましくは７～１３、さらに好ましくは９～１３）の直鎖状または分枝状のアルキル基を表し；ｎは１～１０の整数（好ましくは２～８の整数、より好ましくは３～６の整数）を表し；ｍは１または２を表し；－ＯＡ¹－は、オキシエチレン基、またはオキシプロピレン基を表し；Ｒ²は水素原子または炭素数１～１０の直鎖状または分枝状のアルキル基を表し、ｍが１である場合、複数のＲ²はそれぞれ同一であっても異なっていてもよく、ｍが２である場合、複数のＲ¹はそれぞれ同一であっても異なっていてもよい］で表される化合物からなる群より選択される１以上のリン酸エステル化合物を１～５０質量部含有するタイヤ用ゴム組成物であって、前記ゴム成分中のイソプレン系ゴムの含有量が８０質量％以下であり、スチレンブタジエンゴムの含有量が２０質量％以上である、タイヤ用ゴム組成物である。 The rubber composition for tires according to one embodiment of the present disclosure comprises 100 parts by mass of a rubber component including an isoprene-based rubber and a styrene-butadiene rubber, 30 to 120 parts by mass of silica, and a rubber component represented by the following formula (1) or (2):

wherein R ¹ represents a linear or branched alkyl group having 3 to 21 carbon atoms (preferably 5 to 15, more preferably 7 to 13, and even more preferably 9 to 13); n represents an integer of 1 to 10 (preferably an integer of 2 to 8, and more preferably an integer of 3 to 6); m represents 1 or 2; -OA ¹ - represents an oxyethylene group or an oxypropylene group; R ² represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, and when m is 1, multiple R ^2s may be the same or different, and when m is 2, multiple R ^1s may be the same or different, and the rubber component contains an isoprene-based rubber that is 80% by mass or less, and a styrene-butadiene rubber that is 20% by mass or more.

Although it is not intended to be bound by theory, the following is considered to be a mechanism that can improve heat generation performance and wear resistance performance in a balanced manner during high-speed driving in the present disclosure. That is, since the phosphate group of the phosphate ester compound is adsorbed to the silanol group on the silica surface, the phosphate ester compound and silica show high affinity, and the phosphate ester compound interacts with the silica and the rubber component, respectively, and can promote the dispersion of silica in the rubber. And, by promoting the dispersion of silica, it is possible to prevent the silica from becoming agglomerates, and it is possible to obtain sufficient reinforcement and reduce heat generation performance, which is considered to make it possible to reduce heat generation performance during high-speed driving. Furthermore, by reducing the viscosity of the rubber composition, the kneading time is shortened and the decrease in molecular weight due to the cleavage of the polymer having an isoprene skeleton is suppressed, so it is considered that sufficient wear resistance can be obtained at the same time even during high-speed driving. In addition, as the dispersibility of silica improves as described above, the elastic modulus of the rubber composition also decreases at the same time, and therefore, it is considered that the wet grip performance is also improved secondarily.

The rubber composition for tires preferably contains 2 to 10 parts by mass of the phosphate ester compound per 100 parts by mass of silica. By containing an appropriate amount of the phosphate ester relative to the silica content to hydrophobize the silica surface, the dispersibility of the silica improves, and better heat generation performance and wear resistance during high-speed driving tend to be obtained.

The rubber composition for tires preferably contains 2 to 10 parts by mass of the phosphate ester compound per 100 parts by mass of isoprene-based rubber. By containing an appropriate amount of the phosphate ester to hydrophobize the silica surface relative to the amount of isoprene-based rubber, the dispersibility of the silica improves, and better heat generation performance and wear resistance during high-speed driving tend to be obtained.

The rubber composition for tires preferably contains a masterbatch containing silica and the phosphate ester compound. By making the silica and the phosphate ester compound into a masterbatch, the phosphate ester compound can be uniformly bonded to the silica surface, which improves the dispersibility of the silica and tends to result in better heat generation performance and wear resistance during high-speed driving.

From the viewpoint of wet grip performance, the glass transition temperature of the rubber composition is preferably -50°C to -20°C.

The amount of acetone extractable from the rubber composition after vulcanization is preferably 5% by mass or more in order to obtain a sufficient effect of improving silica dispersion.

It is preferable that the rubber component contains a butadiene rubber modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen. In order to promote the coupling reaction of silica, it is effective to compound such a modified butadiene rubber.

The rubber component preferably contains 20% by mass or more of modified diene rubber.

Another aspect of the present disclosure is a tire having tire components made of the rubber composition for tires.

In this specification, when a numerical range is indicated using "~", it is meant to include both ends of the range.

<Rubber component>
The rubber component used in this embodiment contains isoprene-based rubber and styrene-butadiene rubber (SBR), and preferably contains butadiene rubber (BR). The rubber component may be a rubber component consisting of only isoprene-based rubber and SBR, or may be a rubber component consisting of only isoprene-based rubber, SBR, and BR.

(Isoprene rubber)
Examples of isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. As NR, for example, SIR20, RSS#3, TSR20, and other rubbers commonly used in the tire industry can be used. As IR, there is no particular limitation, and for example, IR2200 and other rubbers commonly used in the tire industry can be used. Examples of modified NR include deproteinized natural rubber (DPNR), high-purity natural rubber, and the like; examples of modified NR include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber; and examples of modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These isoprene-based rubbers may be used alone or in combination of two or more types.

From the viewpoint of the effects of the present disclosure, the content of isoprene-based rubber in the rubber component is 80% by mass or less, preferably 75% by mass or less, more preferably 70% by mass or less, even more preferably 65% by mass or less, and particularly preferably 60% by mass or less. On the other hand, from the viewpoint of the effects of the present disclosure, the content of isoprene-based rubber is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more.

(SBR)
The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Examples of modified SBR include SBR whose ends and/or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR), etc. can also be used. Of these, S-SBR is preferred, and modified S-SBR is more preferred.

The modified SBR may be modified SBR into which a functional group that is normally used in this field has been introduced. Examples of the functional group include an amino group (preferably an amino group in which the hydrogen atom of the amino group is replaced with an alkyl group having 1 to 6 carbon atoms), an amide group, a silyl group, an alkoxysilyl group (preferably an alkoxysilyl group having 1 to 6 carbon atoms), 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 (preferably an alkoxy group having 1 to 6 carbon atoms), a hydroxyl group, an oxy group, an epoxy group, and the like. These functional groups may have a substituent. Examples of the substituent include functional groups such as an amino group, an amide group, an alkoxysilyl group, a carboxyl group, and a hydroxyl group. Modified SBR includes hydrogenated, epoxidized, and tin-modified SBR.

Either oil-extended or non-oil-extended SBR can be used as the SBR. When oil-extended SBR is used, the amount of oil extension of the SBR, i.e., the amount of oil extension oil contained in the SBR, is preferably 10 to 50 parts by mass per 100 parts by mass of rubber solids of the SBR.

The SBRs listed above may be used alone or in combination of two or more. Examples of the SBRs listed above include SBRs manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, ZS Elastomers Co., Ltd., etc.

The styrene content of SBR is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, because the effects of the present disclosure can be more suitably obtained. The styrene content is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, and particularly preferably 40% by mass or less. In this specification, the styrene content of SBR is calculated by ¹ H-NMR measurement.

The vinyl content of SBR is preferably 10 mol% or more, more preferably 15 mol% or more, and even more preferably 20 mol% or more, because this allows the effects of the present disclosure to be more suitably achieved. The vinyl content is preferably 80 mol% or less, more preferably 75 mol% or less, and even more preferably 70 mol% or less. In this specification, the vinyl content (amount of 1,2-bonded butadiene units) is measured by infrared absorption spectroscopy.

The weight average molecular weight (Mw) of the SBR is preferably 200,000 or more, more preferably 250,000 or more, and even more preferably 300,000 or more, because this allows the effects of the present disclosure to be more suitably obtained. The Mw is preferably 2,000,000 or less, and more preferably 1,800,000 or less. In this specification, the weight average molecular weight (Mw) can be calculated in terms of standard polystyrene based on the measured value obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation).

From the viewpoint of the effects of the present disclosure, the content of SBR in the rubber component is 20% by mass or more, preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and particularly preferably 40% by mass or more. On the other hand, from the viewpoint of the effects of the present disclosure, the content of SBR is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less. Note that when oil-extended SBR is used as SBR, the content of SBR itself as rubber solids contained in the oil-extended SBR is regarded as the content of SBR in the rubber component.

(BR)
The BR is not particularly limited, and examples of the BR that can be used include BR having a cis-1,4 bond content (cis content) of 90% or more (high cis BR), rare earth butadiene rubber (rare earth BR) synthesized using a rare earth catalyst, BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high cis modified BR, low cis modified BR), etc. Examples of modified BR include BR modified with functional groups, etc., similar to those described above for SBR.

Examples of high cis BR include those manufactured by Zeon Corporation, Ube Industries, Ltd., and JSR Corporation. The inclusion of high cis BR can improve low temperature properties and wear resistance. The cis content of high cis BR is preferably 95% or more, more preferably 96% or more, even more preferably 97% or more, and particularly preferably 98% or more. In this specification, the cis content is a value calculated by infrared absorption spectrum analysis.

Rare earth BR is synthesized using a rare earth catalyst, and has a vinyl bond amount (amount of 1,2-bonded butadiene units) of preferably 1.8 mol% or less, more preferably 1.0 mol% or less, and even more preferably 0.8 mol% or less, and a cis content of preferably 95 mol% or more, more preferably 96% mol% or more, even more preferably 97% or more, and particularly preferably 98% or more. For example, rare earth BR manufactured by LANXESS can be used.

SPB-containing BR is one in which 1,2-syndiotactic polybutadiene crystals are not simply dispersed in BR, but are dispersed after being chemically bonded to the BR. Examples of such SPB-containing BR that can be used include those manufactured by Ube Industries, Ltd.

As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and/or the main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen is preferably used.

The functional group is not particularly limited, and examples thereof include silyl group, ^R1 ( ^R2O ) ₂ silyl group, ( ^R1 ) _2R2O ^silyl group, ( ^R2O ) ₃ silyl group, amino group, amide group, isocyanate group, imino group, imidazole group, urea group, ether group, carbonyl group, oxycarbonyl group, sulfonyl group, sulfinyl group, thiocarbonyl group, ammonium group, imide group, hydrazo group, azo group, diazo group, nitrile group, pyridyl group, alkoxy group, hydroxyl group, oxy group, carboxyl group, epoxy group, (meth)acrylic group, etc. Here, ^R1 and ^R2 constituting the substituent of the silyl group each independently represent an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms. The alkyl group having 1 to 10 carbon atoms may be linear, cyclic, or branched, and specific examples thereof include methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. Among these, linear alkyl groups are preferred, and methyl or ethyl groups are more preferred, from the viewpoint of the effects of the present disclosure. Specific examples of aryl groups having 6 to 10 carbon atoms include phenyl, α-naphthyl, and β-naphthyl groups.

From the viewpoint of the effect of the present disclosure, the functional group is preferably a functional group containing at ^least one element selected from the group consisting of silicon and oxygen, such as ^R1 ( ^R2O ) _2silyl group, ( ^R1 ) _2R2Osilyl group, ( ^R2O ) _3silyl group, etc., and among them, a trialkoxysilyl group is more preferable. Furthermore, as the trialkoxysilyl group, for example, a trimethoxysilyl group, a triethoxysilyl group, etc. can be mentioned.

Other modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, in which the ends of the modified BR molecules are further bonded with tin-carbon bonds (tin-modified BR). In addition, the modified BR may be either non-hydrogenated or hydrogenated.

The BRs listed above may be used alone or in combination of two or more.

When BR is contained, the 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. On the other hand, from the viewpoint of the effects of the present disclosure, the content is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less.

When modified diene rubber (preferably modified SBR and modified BR) is contained, the content in the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. On the other hand, from the viewpoint of the effects of the present disclosure, the content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

(Other rubber components)
The rubber component may contain other rubber components other than the SBR, BR, and isoprene-based rubber as long as the effects of the present disclosure are not affected. As the other rubber components, crosslinkable rubber components commonly used in the tire industry can be used, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, and the like. These other rubber components may be used alone or in combination of two or more.

<Filler>
The filler according to the present disclosure contains silica as an essential component, and may contain fillers other than silica.As fillers other than silica, any filler commonly used in the tire industry can be used, for example, carbon black, aluminum hydroxide, alumina (aluminum oxide), clay, calcium carbonate, mica, etc., and carbon black is preferred.In addition, the filler may be a filler containing silica and carbon black, or a filler consisting of only silica and carbon black.

(silica)
The silica is not particularly limited, and can be used as is commonly used in the tire industry, such as silica (anhydrous silica) prepared by a dry method, silica (hydrated silica) prepared by a wet method, etc. Among them, hydrated silica prepared by a wet method is preferred because it has a large number of silanol groups. As the silica, for example, those manufactured and sold by Evonik Degussa, Solvay, Tosoh Silica Co., Ltd., Tokuyama Co., Ltd., etc. can be used. These silicas can be used alone or in combination of two or more.

The average primary particle size of the silica used in the present disclosure is preferably 22 nm or less, more preferably 20 nm or less, even more preferably 18 nm or less, and particularly preferably 16 nm or less. The lower limit of the average primary particle size is not particularly limited, but is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. By having the average primary particle size of silica in the above range, the dispersibility of the silica can be further improved, and the reinforcement, wet grip performance, and abrasion resistance can be further improved. The average primary particle size of silica can be determined by observing with a transmission or scanning electron microscope, measuring 400 or more primary particles of silica observed within the field of view, and averaging the results.

From the viewpoints of fuel economy and wear resistance, the nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 140 m ² /g or more, more preferably 160 m ² /g or more, even more preferably 170 m ² /g or more, and particularly preferably 190 m ² /g or more. From the viewpoints of fuel economy and processability, it is preferably 350 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 250 m ² /g or less. In this specification, the N ₂ SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

The content of silica per 100 parts by mass of the rubber component is 30 parts by mass or more, preferably 40 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 70 parts by mass or more, from the viewpoint of wet grip performance. Also, from the viewpoint of fuel economy and abrasion resistance, the content is 120 parts by mass or less, preferably 115 parts by mass or less, more preferably 110 parts by mass or less, even more preferably 105 parts by mass or less, and particularly preferably 100 parts by mass or less.

(Silane coupling agent)
Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent that has been conventionally used in combination with silica in the tire industry can be used. Examples of such silane coupling agents include sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide and bis(3-triethoxysilylpropyl) tetrasulfide; mercapto-based silane coupling agents such as 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, and NXT manufactured by Momentive; vinyl-based silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyltriethoxysilane and 3-aminopropyltriethoxysilane; Examples of the silane coupling agents include amino-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane, chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane, etc. These silane coupling agents may be used alone or in combination of two or more.

When a silane coupling agent is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. The content per 100 parts by mass of the rubber component is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less.

When a silane coupling agent is included, the content per 100 parts by mass of silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and particularly preferably 8 parts by mass or more. The content is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, per 100 parts by mass of silica.

(Carbon black)
As the carbon black, those commonly used in the tire industry can be appropriately used. For example, GPF, FEF, HAF, ISAF, SAF, etc. can be mentioned, or N110, N115, N120, N125, N134, N135, N219, N220, N231, N234, N293, N299, N326, N330, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991, etc. can be mentioned. As these carbon blacks, for example, those manufactured and sold by Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Nippon Steel Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc. These carbon blacks may be used alone or in combination of two or more kinds.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² /g or more, more preferably 80 m ² /g or more, and even more preferably 100 m ² /g or more. By making it equal to or more than the lower limit, good abrasion resistance and wet grip performance tend to be obtained. Moreover, the above N ₂ SA is preferably 200 m ² /g or less, more preferably 160 m ² /g or less, and even more preferably 150 m ² /g or less. By making it equal to or less than the upper limit, good dispersion of carbon black tends to be obtained. The N ₂ SA of carbon black is determined according to JIS K 6217-2:2001.

From the viewpoint of reinforcement, the carbon black content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. From the viewpoint of processability and fuel efficiency performance, the carbon black content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 15 parts by mass or less.

The total filler content per 100 parts by mass of the rubber component is preferably 35 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 70 parts by mass or more, from the viewpoint of wet grip performance. Also, from the viewpoint of fuel economy and abrasion resistance, it is preferably 120 parts by mass or less, more preferably 115 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 105 parts by mass or less.

From the viewpoint of wet grip performance, the silica content in the filler is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Also, from the viewpoint of weather resistance and reinforcement, the silica content is preferably 99% by mass or less, and more preferably 95% by mass or less.

［式中、Ｒ¹は、炭素数３～２１（好ましくは５～１５、より好ましくは７～１３、さらに好ましくは９～１３）の直鎖状または分枝状のアルキル基を表し；ｎは１～１０の整数（好ましくは２～８の整数、より好ましくは３～６の整数）を表し；ｍは１または２を表し；－ＯＡ¹－は、オキシエチレン基、またはオキシプロピレン基を表し；Ｒ²は水素原子または炭素数１～１０の直鎖状または分枝状のアルキル基を表し、ｍが１である場合、複数のＲ²はそれぞれ同一であっても異なっていてもよく、ｍが２である場合、複数のＲ¹はそれぞれ同一であっても異なっていてもよい］で表される化合物からなる群より選択される１以上のリン酸エステル化合物を含有する。 <Phosphate Ester Compound>
The rubber composition according to the present disclosure has the following formula (1) or (2):

[in which R ¹ represents a linear or branched alkyl group having 3 to 21 carbon atoms (preferably 5 to 15, more preferably 7 to 13, and even more preferably 9 to 13); n represents an integer of 1 to 10 (preferably an integer of 2 to 8, and more preferably an integer of 3 to 6); m represents 1 or 2; -OA ¹ - represents an oxyethylene group or an oxypropylene group; R ² represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms, and when m is 1, the multiple R ^2s may be the same or different, and when m is 2, the multiple R ^1s may be the same or different].

The content of the phosphate ester compound per 100 parts by mass of the rubber component is 1 part by mass or more, preferably 2 parts by mass or more, and more preferably 3 parts by mass or more, from the viewpoint of improving the dispersibility of silica and obtaining good heat generation performance and wear resistance performance during high-speed driving. The content is 50 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, per 100 parts by mass of the rubber component.

The content of the phosphate ester compound relative to 100 parts by mass of isoprene-based rubber is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, from the viewpoint of improving the dispersibility of silica and obtaining good heat generation performance and wear resistance during high-speed driving. Moreover, the content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less, relative to 100 parts by mass of isoprene-based rubber.

The content of the phosphate ester compound relative to 100 parts by mass of silica is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, from the viewpoint of improving the dispersibility of silica and obtaining good heat generation performance and wear resistance during high-speed driving. Moreover, the content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, relative to 100 parts by mass of silica.

<Softener>
The rubber composition constituting the first layer preferably contains a softener in order to improve wet grip performance. Examples of the softener include a resin component, oil, and liquid rubber.

The resin component is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, phenol resins, etc., which are commonly used in the tire industry, and may be hydrogenated. These resin components may be used alone or in combination of two or more types.

In this specification, "C5 petroleum resin" refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene. As a C5 petroleum resin, a cyclopentadiene resin is preferably used. Examples of cyclopentadiene resins include dicyclopentadiene resin (DCPD resin), cyclopentadiene resin, methylcyclopentadiene resin (non-hydrogenated cyclopentadiene resin), and these cyclopentadiene resins that have been subjected to a hydrogenation treatment (hydrogenated cyclopentadiene resin). As a cyclopentadiene resin, for example, commercially available products from ExxonMobil Chemical Corporation can be used.

In this specification, "aromatic petroleum resin" refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified resin. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are preferably used include coumarone-indene resin, coumarone resin, indene resin, and aromatic vinyl resin.

As the aromatic vinyl resin, a homopolymer of an α-methylstyrene derivative or a styrene derivative, or a copolymer of an α-methylstyrene derivative and a styrene derivative and/or indene is preferred, and a copolymer of an α-methylstyrene derivative and indene is more preferred, because they are economical, easy to process, and have excellent heat generation properties. The above-mentioned "α-methylstyrene derivative" means an α-methylstyrene compound even if the benzene ring is substituted (preferably, an α-methylstyrene compound in which the benzene ring may be substituted with a saturated hydrocarbon group having 1 to 4 carbon atoms), and the above-mentioned "styrene derivative" means a styrene compound even if the benzene ring is substituted (preferably, a styrene compound in which the benzene ring may be substituted with a saturated hydrocarbon group having 1 to 4 carbon atoms). As the aromatic vinyl resin, for example, those commercially available from Mitsui Chemicals, Inc., Kraton, Eastman Chemical Co., etc. can be used.

In this specification, "C5C9 petroleum resin" refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above. As the C5C9 petroleum resin, for example, those commercially available from Tosoh Corporation, LUHUA Corporation, etc. can be used.

Examples of terpene resins include polyterpene resins made of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and other terpene compounds; aromatic modified terpene resins made from the above terpene compounds and aromatic compounds; terpene phenolic resins made from terpene compounds and phenolic compounds; and terpene resins that have been subjected to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds that are raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that are raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol. Examples of terpene resins that can be used include commercially available products from Yasuhara Chemical Co., Ltd., etc.

The rosin-based resin is not particularly limited, but examples thereof include natural rosin resin, modified rosin resin, etc. As the rosin-based resin, for example, commercially available products from Arakawa Chemical Industries, Ltd., Harima Chemical Industries, Ltd., etc. can be used.

Phenol-based resins include, but are not limited to, phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenol formaldehyde resin, etc.

From the viewpoint of wet grip performance, the softening point of the resin component is preferably 85°C or higher, more preferably 95°C or higher, even more preferably 105°C or higher, and particularly preferably 115°C or higher. From the viewpoint of processability and improved dispersibility of the rubber component and the filler, the softening point is preferably 165°C or lower, more preferably 160°C or lower, even more preferably 155°C or lower, and particularly preferably 150°C or lower. In this specification, the softening point may be defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point measuring device.

When a resin component is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and particularly preferably 12 parts by mass or more, from the viewpoint of wet grip performance. Also, from the viewpoint of suppressing heat generation, the content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less.

Examples of oils include process oils, vegetable oils and fats, and animal oils and fats. Examples of the process oils include paraffinic process oils, naphthenic process oils, and aromatic process oils. In addition, as an environmental measure, process oils with a low content of polycyclic aromatic compound (PCA) compounds can also be used. Examples of the low PCA content process oils include light extract solvates (MES), treated distillate aromatic extracts (TDAE), and heavy naphthenic oils.

When oil is contained, the content per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, the content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less. In this specification, the oil content includes the amount of oil contained in the oil-extended rubber.

The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), but examples include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. These liquid rubbers may be used alone or in combination of two or more types.

When liquid rubber is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more. The content of liquid rubber is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less.

When a softener is contained, the content per 100 parts by mass of the rubber component (the total amount when multiple softeners are used) is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, from the viewpoint of wet grip performance. Also, from the viewpoint of processability, it is preferably 130 parts by mass or less, more preferably 120 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 100 parts by mass or less.

<Other compounding agents>
In addition to the above-mentioned components, the rubber composition according to the present disclosure may appropriately contain compounding agents that are generally used in the tire industry, such as wax, processing aids, antioxidants, vulcanizing agents such as stearic acid, zinc oxide, and sulfur, and vulcanization accelerators.

The wax is not particularly limited, and any wax commonly used in the rubber industry can be suitably used, such as petroleum-based wax, mineral-based wax, and synthetic wax. Of these, petroleum-based wax is preferred. Examples of petroleum-based wax include paraffin wax and microcrystalline wax. Waxes that can be used include those manufactured by Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Paramelt Co., Ltd. These waxes may be used alone or in combination of two or more types.

When wax is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of weather resistance of the rubber. Also, from the viewpoint of whitening of the tire due to bloom, the content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, etc. These processing aids may be used alone or in combination of two or more. Of these, fatty acid metal salts, amide esters, mixtures of fatty acid metal salts and amide esters or fatty acid amides are preferred, and mixtures of fatty acid metal salts and fatty acid amides are more preferred. Examples of processing aids that can be used include fatty acid soap-based processing aids manufactured by Schill & Seilacher.

When a processing aid is included, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of improving processability. Also, from the viewpoint of abrasion resistance and breaking strength, the content is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less.

The anti-aging agent is not particularly limited, and examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as anti-aging agents such as metal carbamates, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N,N'-bis(1-methylheptyl)-p-phenylenediamine, N,N'-bis(1,4-dimethylphenyl ... Phenylenediamine-based antioxidants such as N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, N-4-methyl-2-pentyl-N'-phenyl-p-phenylenediamine, N,N'-diaryl-p-phenylenediamine, hindered diaryl-p-phenylenediamine, phenylhexyl-p-phenylenediamine, and phenyloctyl-p-phenylenediamine, and quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. These antioxidants may be used alone or in combination of two or more.

When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of the ozone crack resistance of the rubber. Also, from the viewpoint of abrasion resistance and wet grip performance, the content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of processability. Also, from the viewpoint of vulcanization speed, the content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, from the viewpoint of processability. Also, from the viewpoint of abrasion resistance, the content is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less.

Sulfur is preferably used as a vulcanizing agent. Examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

When sulfur is used as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, and more preferably 0.7 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction and obtaining good wet grip performance and abrasion resistance. In addition, from the viewpoint of suppressing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

Examples of vulcanizing agents other than sulfur include vulcanizing agents containing sulfur atoms, such as sodium 1,6-hexamethylene-dithiosulfate dihydrate and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and organic peroxides, such as dicumyl peroxide. Examples of vulcanizing agents other than sulfur that can be used include those manufactured by Taoka Chemical Co., Ltd., Flexsys, and Lanxess.

Examples of vulcanization accelerators include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, or xanthate-based vulcanization accelerators. These vulcanization accelerators may be used alone or in combination of two or more. Among them, one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators are preferred, and it is more preferred to use a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator in combination.

Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS). Of these, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS) is preferred.

Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, 1,3-diphenylguanidine (DPG) is preferred.

Examples of thiazole-based vulcanization accelerators include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and di-2-benzothiazolyl disulfide. Of these, 2-mercaptobenzothiazole is preferred.

When a vulcanization accelerator is contained, the content per 100 parts by mass of the rubber component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. The content per 100 parts by mass of the rubber component is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. By keeping the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

The acetone extraction amount (AE amount) of the rubber composition after vulcanization according to the present disclosure is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. The upper limit of the acetone extraction amount is not particularly limited, but is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. When the acetone extraction amount of the rubber composition after vulcanization is in the above range, the dispersibility of silica is further improved. The acetone extraction amount is an index of the concentration of organic low molecular weight compounds in the softener contained in the vulcanized rubber composition. The acetone extraction amount can be calculated by immersing each vulcanized rubber test piece in acetone for 24 hours to extract soluble components, measuring the mass of each test piece before and after extraction, and calculating it according to the following formula.
Acetone extractable amount (%)={(mass of rubber test piece before extraction−mass of rubber test piece after extraction)/(mass of rubber test piece before extraction)}×100

From the viewpoint of wet grip performance, the glass transition temperature of the rubber composition after vulcanization according to the present disclosure is preferably -55°C or higher, more preferably -50°C or higher, and even more preferably -45°C or higher. The glass transition temperature of the rubber composition after vulcanization is preferably -20°C or lower, more preferably -25°C or lower, and even more preferably -30°C or lower. The glass transition temperature (Tg) of the rubber composition after vulcanization can be determined by measuring a tan δ temperature distribution curve using an Iplexer series manufactured by GABO Corporation under the conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C/min, and determining it as the temperature (tan δ peak temperature) corresponding to the largest tan δ value in the measured temperature distribution curve.

<Production of rubber composition and tire>
The rubber composition according to the present embodiment can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading machine such as an open roll, a Banbury mixer, or an internal kneader, and then vulcanizing the mixture.

Here, the kneading process for kneading each component can be, for example, a kneading process consisting of a base kneading process in which compounding agents and additives other than the vulcanizing agent and vulcanization accelerator are kneaded with a kneading machine such as a Banbury mixer, a kneader, or an open roll, and a final kneading (F kneading) process in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading process and kneaded. From the viewpoint of more efficiently bonding the hydrophilic groups on the silica surface with the phosphate ester compound, it is preferable to divide the base kneading process into an X kneading process for producing a master batch containing silica and the phosphate ester compound, and a Y kneading process for adding the remaining compounding agents and additives other than the vulcanizing agent and vulcanization accelerator to the master batch and kneading them. Silica and the amphipathic compound may be added in their entirety or in part in the X kneading process.

The master batch may contain, in addition to silica and the phosphate ester compound, a silane coupling agent, oil, etc., as appropriate. When a silane coupling agent is blended, the content relative to the silica in the master batch is the same as the content relative to the silica described above.

The discharge temperature in the X-kneading step is preferably 140 to 170°C, more preferably 145 to 165°C, because this can sufficiently promote bonding between the silica and the phosphate ester compound.

The kneading time in the X kneading step is not particularly limited, but is preferably 2.0 to 10.0 minutes, more preferably 2.5 to 8.0 minutes, and even more preferably 3.0 to 7.0 minutes, because this allows efficient production of a kneaded product in which silica is well dispersed.

The kneading time is the time from the start of kneading until the kneading temperature reaches the discharge temperature, but in the X kneading step, it is preferable to knead for 1 to 5 minutes while maintaining the discharge temperature after the discharge temperature is reached, because this can further promote bonding between the silica and the phosphate ester compound.

The kneading temperature and time in the Y kneading process and the F kneading process are not particularly limited, and can be carried out under the conditions of the conventional base kneading process. For example, the Y kneading process can be performed at a discharge temperature of 150 to 170°C for 3 to 10 minutes, and the F kneading process can be performed at 70 to 110°C for 1 to 5 minutes. There are no particular limitations on the vulcanization conditions, and an example of the method is vulcanization at 150 to 200°C for 10 to 30 minutes.

The rubber composition for tires disclosed herein can be suitably used for various tire components (e.g., treads, sidewalls, carcass covering rubber, clinches, chafers, beads, breaker cushions, inner liners, etc.), and due to its properties, can be particularly suitably used as tire treads.

The tire according to this embodiment can be manufactured by a normal method using the above rubber composition. That is, the unvulcanized rubber composition obtained by kneading the above components is extruded to match the shape of a tire component such as a tread, and the extruded component is bonded together with other tire components on a tire building machine and molded by a normal method to form an unvulcanized tire, which can then be manufactured by heating and pressurizing the unvulcanized tire in a vulcanizer.

The tires disclosed herein may be pneumatic or non-pneumatic. They are also suitable for use as racing tires, passenger car tires, large passenger car tires, large SUV tires, motorcycle tires, etc., and can be used as summer tires, winter tires, and studless tires for each of these.

The present invention will be described based on examples, but the present invention is not limited to only the examples.

<Evaluation>
Assuming that a tread made of a rubber composition whose formulation was changed according to Tables 1 and 2 using various chemicals shown below is used in the tread of a tire having a tire size of 195/65R15, the glass transition temperature (Tg) and acetone extractable amount (AE amount) of the rubber composition, as well as the heat generation performance, wear resistance and wet grip performance of the tire during high-speed running were calculated based on the evaluation methods described below. The results are shown in the evaluation columns of Tables 1 and 2.

リン酸エステル２：下記式（４）で表されるリン酸エステル

リン酸エステル３：下記式（５）で表されるリン酸エステル

リン酸エステル４：トリエチルホスファイト
オイル：出光興産（株）製のダイアナプロセスＮＨ－７０Ｓ
樹脂成分：三井化学（株）製のＦＭＲ０１５０（４－メチル－α－メチルスチレンとインデンとの共重合体、軟化点：１４５℃、Ｍｗ：２０００）
酸化亜鉛：東邦亜鉛（株）製の「銀嶺Ｒ」
老化防止剤：住友化学（株）製のアンチゲン６Ｃ（Ｎ－（１，３－ジメチルブチル）－Ｎ’－フェニル－ｐ－フェニレンジアミン）
ステアリン酸：日油（株）製のビーズステアリン酸つばき
ワックス：日本精蝋（株）製のオゾエース０３５５
硫黄：細井化学工業（株）製のＨＫ－２００－５（５％オイル含有粉末硫黄）
加硫促進剤１：大内新興化学工業（株）製のノクセラーＤ（Ｎ，Ｎ’－ジフェニルグアニジン）
加硫促進剤２：大内新興化学工業（株）製のノクセラーＮＳ（Ｎ－ｔｅｒｔ－ブチル－２－ベンゾチアゾリルスルフェンアミド） Various chemicals used in the examples and comparative examples are listed below.
NR: TSR20
SBR1: SBR1502 manufactured by JSR Corporation (E-SBR, styrene content: 23.5% by mass, vinyl content: 18% by mole, Mw: 420,000)
SBR2: Modified S-SBR produced in Production Example 1 described later (styrene content: 30 mass%, vinyl content: 52 mol%, Mw: 250,000, non-oil extended product)
BR1: UBEPOL BR150B manufactured by Ube Industries, Ltd. (Mw: 440,000, high cis BR, cis content: 96%)
BR2: N103 manufactured by Asahi Kasei Chemicals Corporation (modified BR whose terminals are modified with a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane and its oligomer components, Mw: 550,000, cis content: 38% by mass)
Silica 1: Ultrasil 9100GR manufactured by Evonik Degussa ( _N2SA : 230 ^m2 /g, average primary particle size: 15 nm)
Silica 2: Ultrasil VN3 manufactured by Evonik Degussa ( _N2SA : 175 ^m2 /g, average primary particle size: 18 nm)
Masterbatch 1: Masterbatch prepared in Production Example 1 below. Carbon black: Show Black N220 ( _N2SA : 111 ^m2 /g) manufactured by Cabot Japan Co., Ltd.
Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa
Phosphate ester 1: a phosphate ester represented by the following formula (3)

Phosphate ester 2: a phosphate ester represented by the following formula (4)

Phosphate ester 3: a phosphate ester represented by the following formula (5)

Phosphate ester 4: Triethyl phosphite oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd.
Resin component: FMR0150 manufactured by Mitsui Chemicals, Inc. (copolymer of 4-methyl-α-methylstyrene and indene, softening point: 145° C., Mw: 2000)
Zinc oxide: "Ginrei R" manufactured by Toho Zinc Co., Ltd.
Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Beads of stearic acid manufactured by NOF Corp. Camellia wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd.
Sulfur: HK-200-5 (powdered sulfur containing 5% oil) manufactured by Hosoi Chemical Industry Co., Ltd.
Vulcanization accelerator 1: Noccelaer D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noccela NS (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

Production Example 1: Synthesis of SBR2 Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. The temperature of the reactor contents was adjusted to 20°C, and 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 rate reached 99%, 1,3-butadiene was added, and polymerization was continued for another 5 minutes, after which N,N-bis(trimethylsilyl)-3-aminopropyltrimethoxysilane was added as a modifier to carry out the reaction. After the polymerization reaction was completed, 2,6-di-tert-butyl-p-cresol was added. Next, the solvent was removed by steam stripping, and the mixture was dried with a heated roll adjusted to 110°C to obtain SBR2.

Production Example 1: Preparation of Masterbatch 1 Using a 1.0 L pressure kneader, 80 parts by mass of silica and 4.0 parts by mass of the phosphoric ester compound 1 are mixed with 100 parts by mass of a rubber component at 150° C. for 4 minutes to prepare masterbatch 1.

(Manufacturing method of test tires)
According to the compounding recipe shown in Table 1, chemicals other than sulfur and vulcanization accelerator are kneaded for 5 minutes at a discharge temperature of 150°C using a 1.7 L Banbury mixer. Next, sulfur and vulcanization accelerator are added to the kneaded mixture obtained, and the mixture is kneaded with an open roll for 4 minutes until the temperature reaches 105°C, to obtain an unvulcanized rubber composition. The unvulcanized rubber composition obtained is molded into a tread shape and laminated together with other tire components to prepare an unvulcanized tire, which is then press-vulcanized at 170°C for 12 minutes to obtain a test tire.

<Measurement of Glass Transition Temperature (Tg)>
For each rubber test piece after vulcanization, the glass transition temperature (Tg) is measured using an Iplexer series manufactured by GABO Corporation under the conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a heating rate of 2°C/min. A temperature distribution curve of tan δ is measured, and the temperature corresponding to the largest tan δ value in the measured temperature distribution curve (tan δ peak temperature) is determined. This temperature is regarded as the glass transition temperature (Tg) of the rubber composition after vulcanization.

<Measurement of acetone extractable amount (AE amount)>
In accordance with JIS K 6229-3:2015, each vulcanized rubber test piece is immersed in acetone for 24 hours to extract the soluble components. The mass of each test piece is measured before and after extraction. The amount of acetone extracted is then calculated using the following formula.
Acetone extractable amount (%)={(mass of rubber test piece before extraction−mass of rubber test piece after extraction)/(mass of rubber test piece before extraction)}×100

<Heat generation performance during high speed driving>
Using a rolling resistance tester, the rolling resistance was measured when the tire was run under the conditions of rim 15×6.0J, internal pressure 230 kPa, load 4.24 kN, and speed 120 km/h, and the reciprocal of the rolling resistance was expressed as an index, with Comparative Example 1 being set at 100. A larger value indicates a smaller rolling resistance and better heat generation performance during high-speed running.

<Wear resistance>
Each test tire was fitted to all wheels of a vehicle (domestic FF 2000cc), and the tire tread depth was measured after driving 5000 km at a speed of 120 km/h, and the running distance when the tire groove depth is reduced by 1 mm was calculated. The measurement results were expressed as an index using the following calculation formula. The higher the index, the better the wear resistance performance during high-speed driving.
(Wear resistance performance index) = (travel distance when tire tread of each compounding example is reduced by 1 mm) / (travel distance when tire tread of Comparative Example 3 is reduced by 1 mm) x 100

<Wet grip performance>
Each test tire is attached to all wheels of a vehicle (domestic FF 2000cc), and the vehicle is driven on a wet asphalt road surface at an initial speed of 100 km/h, and the braking distance is measured. The measurement results are expressed as an index using the following calculation formula. The higher the index, the better the wet grip performance.
(Wet grip performance index) =
(Braking distance of Comparative Example 1)/(Braking distance of each formulation)×100

By conducting the above tests based on the formulations in Tables 1 and 2, each index or a value close to it can be obtained.

The results in Tables 1 and 2 show that the rubber composition for tires of the present disclosure, which contains silica and a specific phosphate ester compound, has improved silica dispersibility and improved overall heat generation performance and wear resistance performance during high-speed driving (average values of heat generation performance and wear resistance performance during high-speed driving). It also shows that the overall heat generation performance, wear resistance performance, and wet grip performance during high-speed driving (average values of heat generation performance, wear resistance performance, and wet grip performance during high-speed driving) is also improved.

Claims (11)

A rubber component containing an isoprene-based rubber and a styrene-butadiene rubber is mixed with 30 to 120 parts by mass of silica and a rubber component represented by the following formula (1 ):

[wherein R ¹ represents a linear or branched alkyl group having 3 to 21 carbon atoms ; m represents 1 or 2 ; and when m is 2, a plurality of R ^1s may be the same or different],
The rubber composition for tires, wherein the content of the isoprene-based rubber in the rubber component is 20% by mass or more and 80% by mass or less, and the content of the styrene-butadiene rubber is 20% by mass or more and 80% by mass or less . The rubber composition for tires according to claim 1 , wherein the amount of acetone extractable from the rubber composition after vulcanization is 5% by mass or more. 30 to 120 parts by mass of silica and a rubber component having the following formula (2):

[Wherein, R ¹ represents a linear or branched alkyl group having 3 to 21 carbon atoms; n represents an integer of 1 to 10; m represents 1 or 2; ¹ - represents an oxyethylene group or an oxypropylene group; R ² represents a hydrogen atom or a linear or branched alkyl group having 1 to 10 carbon atoms; when m is 1, a plurality of R ² may be the same or different, and when m is 2, a plurality of R ¹ may be the same or different],
The rubber composition for tires, wherein the content of the isoprene-based rubber in the rubber component is 20% by mass or more and 80% by mass or less, and the content of the styrene-butadiene rubber is 20% by mass or more and 80% by mass or less. The rubber composition for tires according to claim 3, further comprising 1 to 30 parts by mass of carbon black per 100 parts by mass of the rubber component. The rubber composition for tires according to any one of claims 1 to 4 , comprising 2 to 10 parts by mass of the phosphoric acid ester compound per 100 parts by mass of silica. The rubber composition for tires according to any one of claims 1 to 5 , comprising 2 to 10 parts by mass of the phosphoric acid ester compound per 100 parts by mass of the isoprene-based rubber. The rubber composition for tires according to any one of claims 1 to 6 , comprising a master batch containing silica and the phosphoric acid ester compound. The rubber composition for tires according to any one of claims 1 to 7, wherein a tan δ peak temperature in a tan δ temperature distribution curve of the rubber composition measured under conditions of a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a temperature rise rate of 2°C/min is -50°C to -20°C. The rubber composition for a tire according to any one of claims 1 to 8 , wherein the rubber component contains a butadiene rubber modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen and oxygen. The rubber composition for tires according to any one of claims 1 to 9 , wherein the rubber component contains 20% by mass or more of a modified diene rubber. A tire having a tread formed from the rubber composition for tires according to any one of claims 1 to 10 .