JP6742203B2 - Rubber composition and pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition and a pneumatic tire using the same.

For example, in a rubber composition used for a tire, it is required to have excellent mechanical properties and fracture properties, and to have a high level of balance between the grip performance on wet road surfaces (wet grip performance) and the rolling resistance performance that contributes to low fuel consumption. ing. However, since these are antinomy characteristics, it is not easy to improve them at the same time.

Silica as a filler is said to be excellent in both fuel economy and wet grip performance. However, silica is generally difficult to disperse in the rubber component. Therefore, in order to improve the dispersibility of silica, it has been proposed to use a modified diene rubber in which a functional group such as a hydroxyl group, an amino group or a silyl group is contained in a diene rubber such as styrene butadiene rubber ( See Patent Documents 1 and 2.

By using such a modified diene rubber, the dispersibility of silica is enhanced, and the balance between low fuel consumption and wet grip performance can be improved. However, with the increasing interest in the environment and safety, it is required to improve these characteristics at a higher level.

On the other hand, in Patent Document 3, the weight average molecular weight is 5,000 to 1,000,000 and the glass transition point is −70 to 0° C. for the purpose of improving wet grip performance while suppressing deterioration of fuel economy. It is disclosed to incorporate a (meth)acrylate-based polymer. However, there is no disclosure of blending a fine particle (meth)acrylate polymer having a specific particle diameter.

Patent Document 4 discloses kneading a modified diene rubber having a hydrocarbyloxysilyl group, crosslinked rubber particles, and silica in order to obtain a rubber elastic body having a small rolling resistance and excellent impact resilience. There is. In this document, while the dispersibility of silica is increased by the modified diene rubber, the silica is partially displaced by the exclusion of the silica by the crosslinked rubber particles. The crosslinked rubber particles are mainly composed of a diene rubber, and it is not disclosed to mix fine particles of a specific (meth)acrylate polymer.

Patent Document 5 discloses that particles of a (meth)acrylic acid alkyl ester polymer are compounded in a rubber composition together with silica. However, the particles improve the frictional resistance on ice by forming micro unevenness on the tread surface of the studless tire. Therefore, it is necessary to use a relatively large particle diameter of 0.1 μm to 100 μm, preferably 1 μm to 30 μm. There is no disclosure that it is possible to improve the balance between fuel economy, wet grip performance and tear resistance by blending a fine particle (meth)acrylate polymer having a smaller particle size together with a modified diene rubber. ..

Patent Document 6 discloses that a non-aromatic vinyl polymer having a reactive silyl group represented by the formula ≡Si—X (wherein, X is hydroxyl or a hydrolyzable group) (for example, (meth)acrylate). It has been disclosed to incorporate nanoparticles of a polymer) into the rubber composition. However, in this document, the nanoparticles are used as a reinforcing filler, and it is essential to have a reactive silyl group in order to exert the reinforcing property when used in combination with a coupling agent. There is no disclosure that it is possible to improve the balance between low fuel consumption, wet grip performance, and tear resistance by using a combination of fine particles of a specific (meth)acrylate polymer and a modified styrene-butadiene rubber.

WO96/023027A1 JP, 2003-171418, A WO2015/155965A1 WO2012/111640A1 JP2012-158710A Japanese Patent Publication No. 2009-542827

An embodiment of the present invention has an object to provide a rubber composition having excellent fuel economy when used in a tire application, and excellent balance between wet grip performance and tear resistance.

The rubber composition according to the embodiment has 100 parts by mass of a diene rubber containing a styrene-butadiene rubber having at least one functional group selected from the group consisting of an amino group, a hydroxyl group, an epoxy group, a silyl group, and a carboxyl group. And 20 to 150 parts by mass of silica, and 1 to 100 parts by mass of fine particles having an average particle size of 10 nm or more and less than 100 nm and composed of a (meth)acrylate-based polymer having a structural unit represented by the following general formula (1): Is included.

式（１）中、Ｒ^１は水素原子又はメチル基であり、同一分子中のＲ^１は同一でも異なっていてもよく、Ｒ^２は炭素数４〜１８のアルキル基であり、同一分子中のＲ^２は同一でも異なっていてもよい。

In formula (1), R ¹ is a hydrogen atom or a methyl group, R ¹ in the same molecule may be the same or different, R ² is an alkyl group having 4 to 18 carbon atoms, and R ¹ in the same molecule is R ² may be the same or different.

The pneumatic tire according to the embodiment is produced using the rubber composition.

According to the embodiment, it is possible to provide a rubber composition having an excellent balance of low fuel consumption, wet grip performance and tear resistance when used for a tire application.

The rubber composition according to the present embodiment is a diene system containing (A) a styrene-butadiene rubber having at least one functional group selected from the group consisting of an amino group, a hydroxyl group, an epoxy group, a silyl group, and a carboxyl group. A rubber is prepared by blending (B) silica and (C) fine particles of a (meth)acrylate-based polymer having a structural unit represented by the above formula (1). It is considered that the rubber composition has high dispersion of silica and the specific fine particles in the diene rubber forming the matrix phase. Therefore, when used in a tire, the fuel economy and the wet grip performance are improved. The tear resistance can be improved in a balanced manner.

(A) Diene Rubber As the diene rubber as a rubber component, a styrene butadiene rubber having at least one functional group selected from the group consisting of an amino group, a hydroxyl group, an epoxy group, a silyl group, and a carboxyl group, That is, modified styrene butadiene rubber (modified SBR) is used. By using the modified SBR having such a functional group, the interaction between the silanol group on the particle surface of silica and the ester group of the above-mentioned fine particles (concept including intermolecular force such as hydrogen bond, chemical bond and affinity) It is thought to be obtained.

In these functional groups, the amino group may be not only a primary amino group but also a secondary amino group or a tertiary amino group. In the case of a secondary or tertiary amino group, the total number of carbon atoms of the hydrocarbon group as a substituent is preferably 15 or less. The silyl group is not only a silyl group in a narrow sense represented by -SiH ₃ , but at least one hydrogen atom bonded to a silicon atom is substituted with a substituent such as a hydroxyl group, an alkyl group, an alkoxyl group, an alkylene group or an ether group. It may be a substituted silyl group. For example, as a silyl group, -SiR ⁵ R ⁶ R ⁷ (wherein R ⁵ , R ⁶ , and R ⁷ are each independently a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, -(R ⁸ -O ) _p -R ^{9, or,} -O- (preferably one having 1 to 5 carbon atoms as a good. alkyl group any R ₁₀ -O) q ^{-R 11,} the alkoxyl group is those having 1 to 4 carbon atoms preferred ^.- (R 8 _-O) in the alkyl polyether group represented by p -R ⁹ and ^{_{-O- (R 10 -O) q -R}} 11, R 8 is an alkylene group having 1 to 4 carbon atoms, R ⁹ is an alkyl group having 1 to 16 carbon atoms, p is 1 to 20, R ¹⁰ is an alkylene group having 1 to 4 carbon atoms, R ¹¹ is an alkyl group having 1 to 16 carbon atoms, and q is 1 to 20. Preferred). The silyl group is preferably an alkylsilyl group or an alkoxysilyl group, more preferably an alkoxysilyl group. Examples of the alkoxysilyl group include a trialkoxysilyl group, an alkyldialkoxysilyl group, and a dialkylalkoxysilyl group, and a trialkoxysilyl group such as a triethoxysilyl group or a trimethoxysilyl group is preferable.

As one embodiment, the functional group of the modified SBR is preferably at least one selected from the group consisting of an amino group, a hydroxyl group, and a silyl group, more preferably an amino group, a hydroxyl group, and an alkoxy group. It is at least one selected from the group consisting of silyl groups.

The above-mentioned functional group may be introduced into at least one terminal of the styrene-butadiene rubber, or may be introduced into the molecular chain. That is, a terminal-modified SBR in which the functional group is introduced into at least one end of the molecular chain of SBR may be used, or a main chain-modified SBR in which the functional group is introduced into the main chain of SBR may be used. It may be a main chain terminal modified SBR having a functional group introduced. A modified SBR having such a functional group is known per se, and its production method and the like are not limited. For example, the functional group may be introduced by modifying a styrene-butadiene rubber synthesized by anionic polymerization with a modifier.

In one embodiment, the diene rubber may be the modified SBR alone or a blend of the modified SBR and another diene rubber. It should be noted that the diene rubber may include at least one modified SBR, that is, only one modified SBR may be used, or two or more modified SBR may be used in combination.

Examples of other diene rubbers include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), unmodified styrene butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), Butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, etc. are mentioned, and these are used individually by 1 type or in combination of 2 or more types. be able to. Among these, at least one selected from the group consisting of NR, BR, and unmodified SBR is preferable, and NR and/or BR is more preferable.

The amount of the modified SBR contained in the diene rubber is not particularly limited, and for example, 100 parts by mass of the diene rubber may contain 30 parts by mass or more, or 50 parts by mass or more of modified SBR. In one embodiment, 100 parts by mass of the diene rubber may be composed of 50 to 90 parts by mass of the modified SBR and 50 to 10 parts by mass of another diene rubber (preferably BR and/or NR). The modified SBR may be composed of 60 to 90 parts by mass and BR and/or NR of 40 to 10 parts by mass.

(B) Silica The silica is not particularly limited, but wet silica such as wet precipitation silica or wet gel silica is preferably used. The BET specific surface area (measured according to the BET method described in JIS K6430) of silica is not particularly limited and may be, for example, 90 to 250 m ² /g or 150 to 220 m ² /g.

The amount of silica compounded is preferably 20 to 150 parts by mass, more preferably 30 to 100 parts by mass, and further preferably 40 to 90 parts by mass with respect to 100 parts by mass of the diene rubber.

(C) Fine Particles As fine particles, those made of a (meth)acrylate polymer having an alkyl(meth)acrylate unit represented by the following general formula (1) as a constituent unit (also referred to as a repeating unit) are used. To be

式（１）中、Ｒ^１は、水素原子又はメチル基であり、同一分子中に存在するＲ^１は同一でも異なってもよい。Ｒ^２は、炭素数４〜１８のアルキル基であり、同一分子中に存在するＲ^２は同一でも異なってもよい。Ｒ^２のアルキル基は直鎖でも分岐していてもよい。Ｒ^２は、炭素数６〜１６のアルキル基であることが好ましく、より好ましくは炭素数８〜１５のアルキル基である。

In formula (1), R ¹ is a hydrogen atom or a methyl group, and R ¹ present in the same molecule may be the same or different. R ² is an alkyl group having 4 to 18 carbon atoms, and R ² existing in the same molecule may be the same or different. The alkyl group of R ² may be linear or branched. R ² is preferably an alkyl group having 6 to 16 carbon atoms, and more preferably an alkyl group having 8 to 15 carbon atoms.

The (meth)acrylate polymer is obtained by polymerizing a monomer containing one or more kinds of alkyl (meth)acrylate. Here, (meth)acrylate means one or both of acrylate and methacrylate. Further, (meth)acrylic acid means one or both of acrylic acid and methacrylic acid.

Examples of the alkyl (meth)acrylate include n-butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-nonyl acrylate, and n-acrylate. Decyl, n-undecyl acrylate, n-dodecyl acrylate, n-tridecyl acrylate, n-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, N-Alkyl (meth)acrylates such as n-nonyl methacrylate, n-decyl methacrylate, n-undecyl methacrylate, and n-dodecyl methacrylate; isobutyl acrylate, isopentyl acrylate, isohexyl acrylate, isoheptyl acrylate , Isooctyl acrylate, isononyl acrylate, isodecyl acrylate, isoundecyl acrylate, isododecyl acrylate, isotridecyl acrylate, isotetradecyl acrylate, isobutyl methacrylate, isopentyl methacrylate, isohexyl methacrylate, isoheptyl methacrylate, isooctyl methacrylate , Isononyl methacrylate, isodecyl methacrylate, isoundecyl methacrylate, isododecyl methacrylate, isotridecyl methacrylate, isotetradecyl methacrylate, and the like, isoalkyl (meth)acrylate; 2-methylbutyl acrylate, 2-ethylpentyl acrylate, acrylic 2-methylhexyl acid, 2-ethylhexyl acrylate, 2-ethylheptyl acrylate, 2-methylpentyl methacrylate, 2-methylhexyl methacrylate, 2-ethylhexyl methacrylate, 2-ethylheptyl methacrylate and the like. .. These can be used alone or in combination of two or more.

Here, isoalkyl refers to an alkyl group having a methyl side chain at the second carbon atom from the end of the alkyl chain. For example, isodecyl means an alkyl group having 10 carbon atoms with a methyl side chain at the second carbon atom from the chain end, and includes not only 8-methylnonyl group but also 2,4,6-trimethylheptyl group. Is.

As one embodiment, the (meth)acrylate-based polymer is preferably a polymer having a structural unit represented by the following general formula (2) as a structural unit represented by the formula (1).

式（２）中、Ｒ^３は、水素原子又はメチル基であり（好ましくはメチル基）、同一分子中のＲ^３は同一でも異なってもよい。Ｚは、炭素数１〜１５のアルキレン基（即ち、アルカンジイル基）であり、同一分子中のＺは同一でも異なってもよい。Ｚは直鎖でも分岐していてもよい。

In formula (2), R ³ is a hydrogen atom or a methyl group (preferably a methyl group), and R ³ in the same molecule may be the same or different. Z is an alkylene group having 1 to 15 carbon atoms (that is, alkanediyl group), and Z in the same molecule may be the same or different. Z may be linear or branched.

The constitutional unit of the formula (2) is a case where R ² in the formula (1) is represented by the following general formula (2A). Z in formula (2A) is the same as Z in formula (2).

このような構成単位を生じる（メタ）アクリレートとしては、上記の（メタ）アクリル酸イソアルキルが挙げられる。かかるイソアルキル基を有する（メタ）アクリレート（より好ましくは、メタクリレート）を用いることにより、本実施形態による効果を高めることができる。式（２）及び（２Ａ）中のＺは、炭素数５〜１２のアルキレン基であることが好ましく、より好ましくは炭素数６〜１０のアルキレン基である。

Examples of the (meth)acrylate that produces such a structural unit include the above-mentioned isoalkyl (meth)acrylate. By using (meth)acrylate (more preferably methacrylate) having such an isoalkyl group, the effect of the present embodiment can be enhanced. Z in formulas (2) and (2A) is preferably an alkylene group having 5 to 12 carbon atoms, and more preferably an alkylene group having 6 to 10 carbon atoms.

In another embodiment, the (meth)acrylate-based polymer may be a polymer having a structural unit represented by the following general formula (3) as a structural unit represented by the formula (1), or A polymer having a constitutional unit represented by the formula (2) and a constitutional unit represented by the formula (3) may be used. In the latter case, the addition form of both structural units may be random addition or block addition, preferably random addition.

式（３）中、Ｒ^４は、水素原子又はメチル基であり（好ましくはメチル基）、同一分子中のＲ^４は同一でも異なってもよい。Ｑ^１は、炭素数１〜６（より好ましくは１〜３）のアルキレン基であり、直鎖でも分岐でもよく（好ましくは直鎖）、同一分子中のＱ^１は同一でも異なってもよい。Ｑ^２は、メチル基又はエチル基であり（好ましくはエチル基）、同一分子中のＱ^２は同一でも異なっていてもよい。

In formula (3), R ⁴ is a hydrogen atom or a methyl group (preferably a methyl group), and R ⁴ in the same molecule may be the same or different. Q ¹ is an alkylene group having 1 to 6 carbon atoms (more preferably 1 to 3), and may be linear or branched (preferably linear), and Q ¹ in the same molecule may be the same or different. Q ² is a methyl group or an ethyl group (preferably an ethyl group), and Q ² in the same molecule may be the same or different.

The constitutional unit of the formula (3) is a case where R ² in the formula (1) is represented by the following general formula (3A). In formula (3A), Q ¹ and Q ² are the same as Q ¹ and Q ^{2 in} formula (3), respectively.

式（３）の構成単位を生じる（メタ）アクリレートの具体例としては、上記列挙のアルキル（メタ）アクリレートのうち、（メタ）アクリル酸ｎ−アルキルおよび（メタ）アクリル酸イソアルキルを除くものが挙げられ、特に好ましくは、メタクリル酸２−エチルヘキシルである。

Specific examples of the (meth)acrylate that gives rise to the structural unit of the formula (3) include the alkyl (meth)acrylates listed above, excluding n-alkyl (meth)acrylate and isoalkyl (meth)acrylate. And particularly preferably 2-ethylhexyl methacrylate.

When the (meth)acrylate-based polymer is a copolymer of the constitutional unit of formula (2) and the constitutional unit of formula (3), the ratio of the constitutional unit of formula (2) to the constitutional unit of formula (3) The (copolymerization ratio) is not particularly limited. For example, the molar ratio of the structural unit of the formula (2)/the structural unit of the formula (3) may be 30/70 to 90/10, or 40/60 to 85/15.

The (meth)acrylate-based polymer constituting the fine particles may be a polymer of only the above alkyl(meth)acrylate, but according to a more preferred embodiment, the alkyl(meth)acrylate is added by the presence of a polyfunctional vinyl monomer. It is a polymer having a crosslinked structure formed by crosslinking. That is, in a preferred embodiment, the (meth)acrylate-based polymer contains a structural unit represented by the formula (1) and a structural unit derived from a polyfunctional vinyl monomer, and a structural unit derived from the polyfunctional vinyl monomer. It has a cross-linked structure having a cross-linking point of.

Examples of the polyfunctional vinyl monomer include compounds having at least two vinyl groups that can be polymerized by free radical polymerization, and examples thereof include diols and triols (eg, ethylene glycol, propylene glycol, 1,4-butanediol, 1, 6-hexanediol, trimethylolpropane, etc.) di(meth)acrylate or tri(meth)acrylate; methylenebis-acrylamide, etc. alkylenedi(meth)acrylamide; diisopropenylbenzene, divinylbenzene, trivinylbenzene, etc. Examples thereof include vinyl aromatic compounds having one vinyl group, and these can be used alone or in combination of two or more.

The (meth)acrylate-based polymer is basically composed of the constitutional unit of the formula (1), that is, the constitutional unit of the formula (1) is the main component, but other vinyl-based compounds may be added within a range that does not impair the effect. You may use together. Although not particularly limited, it is preferable that the molar ratio of the constitutional unit of the formula (1) to all constitutional units (total repeating units) constituting the (meth)acrylate polymer is 50 mol% or more, and more preferable. Is 80 mol% or more, and more preferably 90 mol% or more. The upper limit of the molar ratio of the constituent units of formula (1) is not particularly limited, but when the above-mentioned polyfunctional vinyl monomer is added, for example, it may be 99.5 mol% or less, or 99 mol% or less. The molar ratio of the structural unit based on the polyfunctional vinyl monomer may be 0.5 to 20 mol %, 1 to 10 mol %, or 1 to 5 mol %.

In one embodiment, when the (meth)acrylate-based polymer is a polymer having the structural unit of the formula (2), the molar ratio of the structural unit of the formula (2) to all the structural units of the polymer is 25 mol%. It is preferably not less than 35 mol %, more preferably not less than 50 mol %, or not less than 80 mol %. The upper limit of the molar ratio is not particularly limited, but when the polyfunctional vinyl monomer is added in the above molar ratio, it may be 99.5 mol% or less, or 99 mol% or less.

In one embodiment, when the (meth)acrylate-based polymer is a polymer having the structural unit of the formula (3), the molar ratio of the structural unit of the formula (3) to all the structural units of the polymer is 25 mol%. It is preferably not less than 35 mol %, more preferably not less than 50 mol %, or not less than 80 mol %. The upper limit of the molar ratio is not particularly limited, but when the polyfunctional vinyl monomer is added in the above molar ratio, it may be 99.5 mol% or less, or 99 mol% or less.

In another embodiment, when the (meth)acrylate-based polymer is a copolymer of the structural unit of formula (2) and the structural unit of formula (3), the formula ( The molar ratio of the structural unit of 2) may be 25 to 90 mol %, the molar ratio of the structural unit of formula (3) may be 5 to 60 mol %, and the molar ratio of the structural unit of formula (2) is 35 to 85 mol %. %, the molar ratio of the structural unit of the formula (3) may be 8 to 55 mol %. Further, the total molar ratio of the constitutional unit of the formula (2) and the constitutional unit of the formula (3) may be 80 mol% or more, 90 mol% or more, and the upper limit thereof is, for example, the polyfunctional vinyl monomer described above. When added in a molar ratio, it may be 99.5 mol% or less, or 99 mol% or less.

As the above-mentioned (meth)acrylate-based polymer, one having no reactive silyl group, that is, one having no reactive silyl group at the molecular end or in the molecular chain of the (meth)acrylate-based polymer constituting the fine particles is used. It is preferable to use. Here, the reactive silyl group is a functional group represented by the formula ≡Si—X (wherein, X is a hydroxyl group or a hydrolyzable group), and 1 to 3 hydroxyl groups or It is a group having a structure in which a hydrolyzable monovalent group is bonded to a tetravalent silicon atom. Examples of X include a hydroxyl group, an alkoxy group, and a halogen atom.

The average particle size of the fine particles made of the (meth)acrylate polymer is preferably 10 nm or more and less than 100 nm. By adding a (meth)acrylate-based polymer containing the above-mentioned specific structural unit to a diene-based rubber as such fine particles, it is possible to improve fuel economy, wet grip performance and tear resistance in a well-balanced manner. You can The average particle size of the fine particles is more preferably 20 to 90 nm, further preferably 30 to 80 nm.

Further, it is preferable that the glass transition point (Tg) of the fine particles is −70 to 0° C. in order to enhance the effect of improving wet grip performance. The glass transition point can be set by the monomer composition of the (meth)acrylate polymer. The glass transition point of the fine particles is preferably -50 to -10°C, more preferably -40 to -20°C.

The method for producing the fine particles is not particularly limited, and for example, it can be synthesized by utilizing known emulsion polymerization. A preferred example is as follows. That is, (meth)acrylate is dispersed in an aqueous medium such as water in which an emulsifier is dissolved, together with a polyfunctional vinyl monomer as a cross-linking agent, and the resulting emulsion has a water-soluble radical polymerization initiator (for example, potassium persulfate). (Peroxide of 1) and radical polymerization are carried out to produce fine particles of the (meth)acrylate-based polymer in the aqueous medium. Therefore, fine particles are obtained by separating from the aqueous medium. As other methods for producing fine particles, known polymerization methods such as suspension polymerization, dispersion polymerization, precipitation polymerization, miniemulsion polymerization, soap-free emulsion polymerization (emulsifier-free emulsion polymerization), and microemulsion polymerization can be used.

The amount of the fine particles is not particularly limited, but is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, and further preferably 3 to 30 parts by mass with respect to 100 parts by mass of the diene rubber. And may be 5 to 20 parts by mass.

In the rubber composition according to the present embodiment, in addition to the above components, a silane coupling agent, a reinforcing filler other than silica, oil, zinc white, stearic acid, an antioxidant, a wax, a vulcanizing agent, Various additives generally used in rubber compositions, such as a vulcanization accelerator, can be blended.

The compounding amount of the silane coupling agent is not particularly limited, and may be, for example, 2 to 20% by mass or 4 to 15% by mass based on the mass of silica.

Examples of the reinforcing filler other than silica include carbon black. The amount of the reinforcing filler compounded is not particularly limited, and may be, for example, 20 to 150 parts by mass or 30 to 100 parts by mass with respect to 100 parts by mass of the diene rubber, as a total amount including silica.

Sulfur is preferably used as the vulcanizing agent. The compounding amount of the vulcanizing agent is not particularly limited, and may be, for example, 0.1 to 10 parts by mass, or 0.5 to 5 parts by mass with respect to 100 parts by mass of the diene rubber. Examples of the vulcanization accelerator include various vulcanization accelerators such as sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based accelerators. Any one of them may be used alone or two or more of them may be used in combination. You can The compounding amount of the vulcanization accelerator is not particularly limited, and may be, for example, 0.1 to 7 parts by mass, or 0.5 to 5 parts by mass with respect to 100 parts by mass of the diene rubber.

The rubber composition according to the present embodiment can be prepared by kneading according to a conventional method using a mixer such as a Banbury mixer, a kneader, and a roll that are commonly used. That is, for example, in the first mixing step, the diene rubber is mixed with silica and the above fine particles together with other additives other than the vulcanizing agent and the vulcanization accelerator, and then the resulting mixture is finally mixed. A rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator in the mixing stage.

The rubber composition thus obtained can be used for various rubber members for tires, anti-vibration rubbers, conveyor belts and the like. Preferably, it is for tires, and various uses such as tires for passenger cars, tires for heavy loads of trucks and buses, and pneumatic tires of various sizes can be mentioned. Examples of the application site of the tire include various parts of the tire such as a tread portion and a sidewall portion. A pneumatic tire is produced by molding the rubber composition into a predetermined shape by extrusion or the like in accordance with a conventional method, and by combining it with other parts to produce a green tire, the green tire is vulcanized at 140 to 180° C., for example. By doing so, it can be manufactured. Among these, it is particularly preferable to use it as a compound for tire tread.

Examples will be shown below, but the present invention is not limited to these examples.

[Measurement method of average particle size]
The average particle size of the fine particles is a particle size (50% diameter: D50) at an integrated value of 50% in a particle size distribution measured by a dynamic light scattering method (DLS), and dynamic light scattering luminous intensity manufactured by Otsuka Electronics Co., Ltd. It was measured by a photon correlation method (JIS Z8826 compliant) using a total of "DLS-8000" (angle between incident light and detector: 90°).

[Method of measuring Tg]
The Tg of the fine particles was measured by a differential scanning calorimetry (DSC) method according to JIS K7121 at a temperature rising rate of 20°C/min (measurement temperature range: -150°C to 150°C).

[Synthesis Example 1: Fine particles 1]
Mix 15.0 g of 2,4,6-trimethylheptyl methacrylate, 0.394 g of ethylene glycol dimethacrylate, 1.91 g of sodium dodecyl sulfate, 120 g of water and 13.5 g of ethanol and stir for 1 hour. The monomer was emulsified by, 0.179 g of potassium persulfate was added, nitrogen bubbling was carried out for 1 hour, and the solution was kept at 70° C. for 8 hours. Coagulation by adding methanol to the obtained solution gave 14.5 g of fine particles 1 (polymerization conversion rate (production amount/charge amount): 94%). The fine particles 1 had an average particle diameter of 60 nm and Tg of -37°C.

Regarding the fine particles 1, the chemical structure of the polymer was analyzed by ¹³ C-NMR. As a result, the structural unit of ethylene glycol dimethacrylate derived from the structural unit of the formula (2) derived from 2,4,6-trimethylheptyl methacrylate ((2)) was obtained. Hereinafter, the EGDM constitutional unit) was contained, and the molar ratio of each constitutional unit was 97 mol% for the constitutional unit of the formula (2) and 3.0 mol% for the EGDM constitutional unit.

[Synthesis Example 2: Fine particles 2]
Synthesis Example 1 using 15.0 g 2-ethylhexyl methacrylate, 0.450 g ethylene glycol dimethacrylate, 2.18 g sodium dodecyl sulfate, 0.205 g potassium persulfate, 120 g water and 13.5 g ethanol. 14.2 g of fine particles 2 were obtained by the same method as in (polymerization conversion rate: 92%). The fine particles 2 had an average particle diameter of 58 nm and Tg of -10°C. As a result of ¹³ C-NMR analysis of the fine particles 2, the constituent unit of the formula (3) derived from 2-ethylhexyl methacrylate was 97 mol% and the EGDM constituent unit was 3.0 mol %.

[Synthesis Example 3: Fine particles 3]
Synthesis Example 1 using 15.0 g n-dodecyl methacrylate, 0.351 g ethylene glycol dimethacrylate, 1.70 g sodium dodecyl sulfate, 0.159 g potassium persulfate, 120 g water and 13.5 g ethanol. By the same method as described above, 13.8 g of fine particles 3 were obtained (polymerization conversion rate: 90%). The fine particles 3 had an average particle diameter of 62 nm and Tg of −65° C. As a result of ¹³ C-NMR analysis of the fine particles 3, the constitutional unit of the formula (1) derived from n-dodecyl methacrylate was 97 mol %, and the EGDM constitutional unit was 3.0 mol %.

[Synthesis Example 4: Fine particles 4]
8.0 g of 2,4,6-trimethylheptyl methacrylate, 7.0 g of 2-ethylhexyl methacrylate (wherein 2,4,6-trimethylheptyl methacrylate/2-ethylhexyl methacrylate=50/50 (mol Ratio)), 0.420 g of ethylene glycol dimethacrylate, 2.04 g of sodium dodecyl sulfate, 120 g of water and 13.5 g of ethanol are mixed and stirred for 1 hour to emulsify the monomer, and After adding potassium sulfate, nitrogen bubbling was carried out for 1 hour, and the solution was kept at 70° C. for 8 hours. Fine particles 4 were obtained by coagulation by adding methanol to the obtained solution (polymerization conversion rate: 94%). The fine particles 4 had an average particle diameter of 60 nm and Tg of -24°C. As a result of ¹³ C-NMR analysis of the fine particles 4, 49 mol% of the constituent unit of the formula (2) derived from 2,4,6-trimethylheptyl methacrylate and the constituent unit of the formula (3) derived from 2-ethylhexyl methacrylate. Was 48 mol% and the EGDM constitutional unit was 3.0 mol %.

[Synthesis Example 5: Fine Particles 5 (Comparative Example)]
Fine particles 5 were obtained in the same manner as in Synthesis Example 1 except that ethyl acrylate was used instead of the 2,4,6-trimethylheptyl methacrylate used for the synthesis of the fine particles 1. The average particle size of the fine particles was 60 nm, and the Tg was -25°C.

[Synthesis example 6: fine particles 6 (comparative example)]
Fine particles 6 were obtained in the same manner as in Synthesis Example 1 except that methyl methacrylate was used instead of 2,4,6-trimethylheptyl methacrylate used for the synthesis of fine particles 1. The fine particles had an average particle diameter of 60 nm and a Tg of 105°C.

[Synthesis Example 7: Polymer 1 (Comparative Example)]
30 g of 2,4,6-trimethylheptyl methacrylate, 0.129 g of ethyl 2-bromoisobutyrate and 0.115 g of N,N,N',N",N"-pentamethyldiethylenetriamine are mixed. Nitrogen was bubbled for 1 hour. Then, 0.190 g of copper(I) bromide was added to the reaction solution, and the mixture was kept at 70° C. for 5 hours. The (meth)acrylate polymer (Polymer 1) was obtained by reprecipitation purification of the obtained solution in methanol. The Tg of polymer 1 was -41°C.

[Rubber composition evaluation]
Using a lab mixer, according to the composition (parts by mass) shown in Tables 1 and 2 below, first, in the first mixing step, other compounding agents except sulfur and a vulcanization accelerator are added to the diene rubber component and kneaded. (Discharge temperature=160° C.). Next, in the final mixing stage, sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded (exhaust temperature=90° C.) to prepare a rubber composition. Details of each component in Tables 1 and 2 are as follows.

・Unmodified SBR: "SL563" manufactured by JSR Corporation
-Modified SBR1: "HPR350" manufactured by JSR Corporation (amino group and alkoxysilyl group terminal modified SBR)
-Modified SBR2: "#9590" manufactured by Nippon Zeon Co., Ltd. (amino group-terminal modified SBR)
-Modified SBR3: "Toughden E580" manufactured by Asahi Kasei Corporation (hydroxyl terminal modified SBR)
-Modified SBR4: "Nipol LX421" manufactured by Nippon Zeon Co., Ltd. (carboxyl group terminal modified SBR)
・BR: "UBEPOL BR150B" manufactured by Ube Industries, Ltd.
・Silica: "Nipseal AQ" manufactured by Tosoh Silica Co., Ltd.
Silane coupling agent: bis(3-triethoxysilylpropyl) tetrasulfide, Evonik "Si69"
・Zinc flower: "Zinc flower type 1" manufactured by Mitsui Mining & Smelting Co., Ltd.
・Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
・Stearic acid: "Lunac S-20" manufactured by Kao Corporation
・Sulfur: Hosoi Chemical Co., Ltd. "Rubber powder sulfur 150 mesh"
・Vulcanization accelerator: "NOXCELLER CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
・Secondary vulcanization accelerator: "NOXCELLER D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
-Fine particles 1-6: Fine particles obtained by the method described in Synthesis Examples 1 to 6-Polymer 1: Polymer obtained by the method described in Synthesis Example 7-Crosslinked rubber particles: "Nanoprene BM350H" manufactured by LANXESS Styrene-butadiene rubber gel (Tg: -35°C).

Each rubber composition obtained was vulcanized at 160° C. for 20 minutes to prepare a test piece having a predetermined shape, and a dynamic viscoelasticity test was conducted using the obtained test piece to obtain 0° C. and 60° C. Tan δ was measured. The tear strength was also measured. The results are shown in Tables 1 and 2. The measuring method is as follows.

0° C. tan δ: loss coefficient tan δ was measured under the conditions of frequency 10 Hz, static strain 10%, dynamic strain 2%, and temperature 0° C. using a UBM Rheospectrometer E4000, and Table 1 shows the values of Comparative Example 1 In Table 2, the value of Comparative Example 10 is shown as an index, which is set to 100. The larger the index, the larger the tan δ, indicating that the wet grip performance is excellent.

60° C. tan δ: tan δ was measured in the same manner as 0° C. tan δ, except that the temperature was changed to 60° C., and the values of Comparative Example 1 in Table 1 and Comparative Example 10 in Table 2 were 100, respectively. displayed. The smaller the index, the less heat is generated, the smaller the rolling resistance on the tire, and the better the rolling resistance performance (that is, fuel economy).

-Tear strength: The tear strength of the test piece was measured according to JIS K6252, and the values of Comparative Example 1 in Table 1 and the value of Comparative Example 10 in Table 2 are shown as indices, each of which is 100. The larger the index, the better the tear resistance.

表２に示すように、未変性ＳＢＲを用いた配合系では、コントロールである比較例１０に対し、微粒子１を配合した比較例１１は、転がり抵抗性能の悪化を抑えながら、ウェットグリップ性能が改善されたが、引裂性能が低下した。

As shown in Table 2, in the compounding system using the unmodified SBR, in Comparative Example 11 in which the fine particles 1 were compounded, the wet grip performance was improved while suppressing the deterioration of the rolling resistance performance as compared to the control of Comparative Example 10. However, the tear performance deteriorated.

On the other hand, as shown in Table 1, in the compounding system using the modified SBR, the rolling resistance performance was deteriorated in Examples 1 to 7 in which the fine particles 1 to 4 were compounded in comparison with Comparative Example 1 as the control. It was possible to significantly improve the wet grip performance while suppressing the above and maintaining or improving the tear resistance.

On the other hand, in Comparative Examples 2 and 3 in which the fine particles 5 and 6 made of a non-specified (meth)acrylate-based polymer were blended, not only the effect of improving the wet grip performance was small, but also the rolling resistance performance was deteriorated. Also, the tear resistance was deteriorated. Further, in Comparative Example 4 in which the crosslinked rubber particles were blended instead of the fine particles made of the (meth)acrylate polymer, not only the effect of improving the wet grip performance was small, but also the rolling resistance performance and the tear resistance were deteriorated. Further, in Comparative Example 5 in which a non-fine particle (meth)acrylate polymer was blended, not only the effect of improving the wet grip performance was small, but also the tear resistance was deteriorated.

Claims (5)

100 parts by mass of a diene rubber containing styrene-butadiene rubber having at least one functional group selected from the group consisting of an amino group, a hydroxyl group, an epoxy group, a silyl group, and a carboxyl group, and 20 to 150 parts by mass of silica. A rubber composition comprising: 1 to 100 parts by mass of fine particles having an average particle size of 10 nm or more and less than 100 nm, which is composed of a (meth)acrylate-based polymer having a structural unit represented by the following general formula (1).

(In the formula (1), R ¹ is a hydrogen atom or a methyl group, R ¹ in the same molecule may be the same or different, R ² is an alkyl group having 4 to 18 carbon atoms, and R ^{2 s of} may be the same or different.) The rubber composition according to claim 1, wherein the glass transition point of the fine particles is -70 to 0°C. The (meth)acrylate-based polymer is a polymer having a structural unit represented by the following general formula (2) as a structural unit represented by the general formula (1). The rubber composition described.

(In formula (2), R ³ is a hydrogen atom or a methyl group, R ³ in the same molecule may be the same or different, Z is an alkylene group having 1 to 15 carbon atoms, and Z may be the same or different.) The said (meth)acrylate type polymer is a polymer which has a structural unit represented by the following general formula (3) as a structural unit represented by the said general formula (1), The polymer of Claims 1-3. The rubber composition according to any one of items.

(In formula (3), R ⁴ is a hydrogen atom or a methyl group, R ⁴ in the same molecule may be the same or different, Q ¹ is an alkylene group having 1 to 6 carbon atoms, and Q ¹ may be the same or different, Q ² is a methyl group or an ethyl group, and Q ² in the same molecule may be the same or different.) A pneumatic tire produced using the rubber composition according to any one of claims 1 to 4.