JP2018039867A - Rubber composition and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition excellent in balance of fuel economy, wet grip performance, and tear resistance characteristics.SOLUTION: The rubber composition contains: 100 pts.mass of a diene rubber which contains 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; 20-150 pts.mass of silica; and 1-100 pts.mass of fine particles which comprise a (meth)acrylate-based polymer having a constituent unit represented by general formula (1) and have a specific average particle diameter. A pneumatic tire using the rubber composition is also provided. (Ris H or a methyl group; and Ris a C4-18 alkyl group.)SELECTED DRAWING: None

Description

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

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

  Silica as a filler is said to be excellent in both low fuel consumption 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 a styrene butadiene rubber ( (See Patent Documents 1 and 2).

  By using such a modified diene rubber, the dispersibility of silica is increased, and the balance between low fuel consumption and wet grip performance can be improved. However, with 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 efficiency. It is disclosed that a (meth) acrylate polymer is blended. However, there is no disclosure of blending a particulate (meth) acrylate polymer having a specific particle size.

  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 rebound resilience. Yes. In this document, while the dispersibility of silica is increased by the modified diene rubber, the silica is partially unevenly distributed by eliminating the silica by the crosslinked rubber particles. The crosslinked rubber particles are mainly composed of a diene rubber, and it is not disclosed that fine particles composed of a specific (meth) acrylate polymer are blended.

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

  Patent Document 6 discloses a non-aromatic vinyl polymer (for example, (meth) acrylate) having a reactive silyl group represented by the formula ≡Si-X (wherein X is hydroxyl or a hydrolyzable group). It is disclosed that polymer nanoparticles) are blended into a 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 exhibit reinforcing properties when used in combination with a coupling agent. There is no disclosure that the balance between low fuel consumption, wet grip performance, and tear resistance can be improved by the combined use of fine particles made of a specific (meth) acrylate polymer and a modified styrene butadiene rubber.

WO96 / 023027A1 JP 2003-171418 A WO2015 / 155965A1 WO2012 / 111640A1 JP 2012-158710 A Special table 2009-542827

  An object of an embodiment of the present invention is to provide a rubber composition that is excellent in balance between low fuel consumption, wet grip performance, and tear resistance when used in tire applications.

  The rubber composition according to the embodiment includes 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 comprising a (meth) acrylate polymer having a structural unit represented by the following general formula (1): It contains.

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 in the same molecule R ² may be the same or different.

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

  According to the embodiment, it is possible to provide a rubber composition excellent in the balance between low fuel consumption, wet grip performance and tear resistance when used in tire applications.

  The rubber composition according to the present embodiment includes (A) a diene system including 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 blended with (B) silica and (C) fine particles made of a (meth) acrylate polymer having a structural unit represented by the above formula (1). When the rubber composition is used, it is considered that the silica and the specific fine particles are highly dispersed in the diene rubber forming the matrix phase. Therefore, low fuel consumption and wet grip performance when used in a tire are obtained. The tear resistance can be improved in a well-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 a modified SBR having such a functional group, interaction with silanol groups on the surface of silica particles and ester groups of the fine particles (concepts including intermolecular forces such as hydrogen bonds, chemical bonds, and affinity) Is considered 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 groups that are substituents is preferably 15 or less. In the silyl group, not only a silyl group in a narrow sense represented by —SiH ₃ but also at least one of hydrogen atoms 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 the 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 In the alkyl polyether group represented by — (R ⁸ —O) _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). Preferably, the silyl group is an alkylsilyl group or an alkoxysilyl group, more preferably an alkoxysilyl group. Examples of the alkoxysilyl group include a trialkoxysilyl group, an alkyl dialkoxysilyl group, and a dialkylalkoxysilyl group, and a trialkoxysilyl group such as a triethoxysilyl group or a trimethoxysilyl group is preferable.

  In 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, and 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 functional group may be introduced into at least one end of the styrene butadiene rubber, or may be introduced into the molecular chain. That is, it may be a terminal-modified SBR in which the functional group is introduced into at least one end of the molecular chain of the SBR, or a main-chain modified SBR in which the functional group is introduced into the main chain of the SBR. It may be a main chain terminal-modified SBR having a functional group introduced therein. Modified SBR itself having such a functional group is known, 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 a modified SBR alone or a blend of the modified SBR and another diene rubber. The diene rubber only needs to contain at least one type of modified SBR, that is, only one type of modified SBR may be used, or two or more types of 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), Examples thereof include butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and these are used alone or in combination of two or more. 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. For example, the modified SBR may be contained in 30 parts by mass or more in 50 parts by mass in 100 parts by mass of the diene rubber. In one embodiment, 100 parts by weight of the diene rubber may be 50 to 90 parts by weight of the modified SBR and 50 to 10 parts by weight of another diene rubber (preferably BR and / or NR). Further, it may be composed of 60 to 90 parts by mass of modified SBR and 40 to 10 parts by mass of BR and / or NR.

(B) Silica Silica is not particularly limited, but wet silica such as wet precipitated 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.

  It is preferable that the compounding quantity of a silica is 20-150 mass parts with respect to 100 mass parts of said diene rubber, More preferably, it is 30-100 mass parts, More preferably, it is 40-90 mass parts.

(C) Fine particles As fine particles, those composed of a (meth) acrylate polymer having an alkyl (meth) acrylate unit represented by the following general formula (1) as a structural unit (also referred to as a repeating unit) are used. It is done.

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 present in the same molecule may be the same or different. The alkyl group for 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 alkyl (meth) acrylates. Here, (meth) acrylate means one or both of acrylate and methacrylate. (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, methacrylic acid Isoalkyl (meth) acrylates such as isononyl, isodecyl methacrylate, isoundecyl methacrylate, isododecyl methacrylate, isotridecyl methacrylate, and isotetradecyl methacrylate; 2-methylbutyl acrylate, 2-ethylpentyl acrylate, 2-acrylate Methylhexyl, 2-ethylhexyl acrylate, 2-ethylheptyl acrylate, 2-methylpentyl methacrylate, methacrylate Le acid 2-methylhexyl, 2-ethylhexyl methacrylate, and methacrylic acid 2-ethyl-heptyl and the like. Any of these may 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 a C10 alkyl group having a methyl side chain at the second carbon atom from the chain end, and includes not only an 8-methylnonyl group but also a 2,4,6-trimethylheptyl group. It is.

  As one embodiment, the (meth) acrylate 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 (ie, alkanediyl group), and Z in the same molecule may be the same or different. Z may be linear or branched.

The structural 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 generates 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 this embodiment can be enhanced. Z in the 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 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 alternatively: The polymer which has a structural unit represented by Formula (2) and a structural unit represented by Formula (3) may be sufficient. In the latter case, the addition form of both structural units may be random addition or block addition, and is 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 (more preferably 1 to 3) carbon atoms, which 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 structural 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 (meth) acrylates that produce the structural unit of formula (3) include those of the above-listed alkyl (meth) acrylates excluding n-alkyl (meth) acrylates and isoalkyl (meth) acrylates. Particularly preferred is 2-ethylhexyl methacrylate.

  When the (meth) acrylate polymer is a copolymer of the structural unit of the formula (2) and the structural unit of the formula (3), the ratio of the structural unit of the formula (2) and the structural unit of the formula (3) (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. A polymer having a crosslinked structure formed by crosslinking. That is, in a preferred embodiment, the (meth) acrylate polymer includes a structural unit derived from a polyfunctional vinyl monomer together with a structural unit represented by the formula (1), and is a structural unit derived from the polyfunctional vinyl monomer. Has a cross-linking structure having a cross-linking point.

  Polyfunctional vinyl monomers include compounds having at least two vinyl groups that can be polymerized by free radical polymerization, such as diols or triols (eg, ethylene glycol, propylene glycol, 1,4-butanediol, 1, Di (meth) acrylate or tri (meth) acrylate of 6-hexanediol, trimethylolpropane, etc .; alkylene di (meth) acrylamide such as methylenebis-acrylamide; at least 2 of diisopropenylbenzene, divinylbenzene, trivinylbenzene, etc. Examples thereof include vinyl aromatic compounds having a single vinyl group, and these can be used alone or in combination of two or more.

  The (meth) acrylate polymer is basically composed of the structural unit of the formula (1), that is, the main component is the structural unit of the formula (1), but other vinyl compounds are included within a range not impairing the effect. You may use together. Although it does not specifically limit, It is preferable that the molar ratio of the structural unit of Formula (1) with respect to all the structural units (all repeating units) which comprise a (meth) acrylate type polymer is 50 mol% or more, More preferably Is 80 mol% or more, more preferably 90 mol% or more. Although the upper limit of the molar ratio of the structural unit of Formula (1) is not specifically limited, For example, when adding said polyfunctional vinyl monomer, 99.5 mol% or less may be sufficient and 99 mol% or less may be sufficient. The molar ratio of the structural units 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 polymer is a polymer having a 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%. Preferably, it is 35 mol% or more, more preferably 50 mol% or more, or 80 mol% or more. Although the upper limit of the molar ratio is not particularly limited, for example, when the polyfunctional vinyl monomer is added at the above molar ratio, it may be 99.5 mol% or less, or 99 mol% or less.

  In one embodiment, when the (meth) acrylate polymer is a polymer having a 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%. Preferably, it is 35 mol% or more, more preferably 50 mol% or more, or 80 mol% or more. Although the upper limit of the molar ratio is not particularly limited, for example, when the polyfunctional vinyl monomer is added at the above molar ratio, it may be 99.5 mol% or less, or 99 mol% or less.

  In another embodiment, when the (meth) acrylate polymer is a copolymer of the structural unit of the formula (2) and the structural unit of the formula (3), the formula for all the structural units of the copolymer ( 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%. %, And the molar ratio of the structural unit of the formula (3) may be 8 to 55 mol%. Further, the total molar ratio of the structural unit of the formula (2) and the structural unit of the formula (3) may be 80 mol% or more, and may be 90 mol% or more, and the upper limit thereof is, for example, the polyfunctional vinyl monomer described above. When added at a molar ratio, it may be 99.5 mol% or less, or 99 mol% or less.

  As the (meth) acrylate polymer, a polymer having no reactive silyl group, that is, a polymer having no reactive silyl group in the molecular terminal or molecular chain of the (meth) acrylate polymer constituting the fine particles. It is preferable to use it. 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 This 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 diameter of the fine particles made of the (meth) acrylate polymer is preferably 10 nm or more and less than 100 nm. By adding the (meth) acrylate polymer containing the above specific structural unit to the diene rubber as such fine particles, the fuel economy, wet grip performance and tear resistance are improved in a balanced manner. Can do. The average particle size of the fine particles is more preferably 20 to 90 nm, still more preferably 30 to 80 nm.

  Further, the glass transition point (Tg) of the fine particles is preferably −70 to 0 ° C. in order to enhance the effect of improving wet grip performance. The glass transition point can be set according to the monomer composition constituting 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 can be synthesized using, for example, 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 crosslinking agent, and a water-soluble radical polymerization initiator (for example, potassium persulfate or the like) is obtained in the obtained emulsion. In this case, fine particles made of a (meth) acrylate polymer are produced in the aqueous medium, and the fine particles can be obtained by separating from the aqueous medium. As other fine particle production methods, known polymerization methods such as suspension polymerization, dispersion polymerization, precipitation polymerization, miniemulsion polymerization, soap-free emulsion polymerization (non-emulsifier emulsion polymerization), and microemulsion polymerization can be used.

  Although the compounding quantity of microparticles | fine-particles is not specifically limited, It is preferable that it is 1-100 mass parts with respect to 100 mass parts of diene rubbers, More preferably, it is 2-50 mass parts, More preferably, it is 3-30 mass parts. It may be 5 to 20 parts by mass.

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

  The compounding quantity of a silane coupling agent is not specifically limited, For example, 2-20 mass% of silica mass may be sufficient, and 4-15 mass% may be sufficient.

  Examples of the reinforcing filler other than silica include carbon black. The compounding quantity of a reinforcing filler is not specifically limited, For example, it is 20-150 mass parts with respect to 100 mass parts of diene rubbers, and may be 30-100 mass parts with the total amount containing a silica.

  Sulfur is preferably used as the vulcanizing agent. The compounding quantity of a vulcanizing agent is not specifically limited, For example, 0.1-10 mass parts may be sufficient with respect to 100 mass parts of diene rubbers, and 0.5-5 mass parts may be sufficient. Moreover, as a vulcanization accelerator, various vulcanization accelerators, such as a sulfenamide type | system | group, a thiuram type | system | group, a thiazole type | system | group, and a guanidine type | system | group, are mentioned, for example, any 1 type is used individually or in combination of 2 or more types. Can do. The compounding quantity of a vulcanization accelerator is not specifically limited, For example, 0.1-7 mass parts may be sufficient with respect to 100 mass parts of diene rubbers, and 0.5-5 mass parts may be sufficient.

  The rubber composition according to the present embodiment can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. That is, for example, in the first mixing stage, to the diene rubber, together with silica and the above fine particles, other additives excluding the vulcanizing agent and the vulcanization accelerator are added and mixed. In the mixing stage, a rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator.

  The rubber composition thus obtained can be used for various rubber members for tires, vibration-proof rubbers, conveyor belts and the like. Preferably, it is for tires, and includes various uses such as passenger car tires, heavy duty tires for trucks and buses, and pneumatic tires of various sizes. Applicable parts of the tire include each part of the tire such as a tread part and a sidewall part. For a pneumatic tire, according to a conventional method, the rubber composition is molded into a predetermined shape by extrusion or the like and combined with other parts to produce a green tire. Then, for example, the green tire is vulcanized at 140 to 180 ° C. By doing so, it can be manufactured. Among these, it is particularly preferable to use as a tire tread formulation.

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

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

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

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

The fine particle 1 was analyzed by ¹³ C-NMR for the chemical structure of the polymer. As a result, the structural unit derived from ethylene glycol dimethacrylate (2) and the structural unit derived from ethylene glycol dimethacrylate ( Hereinafter, the molar ratio of each structural unit was 97 mol% for the structural unit of the formula (2) and 3.0 mol% for the EGDM structural unit.

[Synthesis Example 2: Fine Particle 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 In the same manner as above, 14.2 g of fine particles 2 were obtained (polymerization conversion rate: 92%). The average particle diameter of the fine particles 2 was 58 nm, and Tg was −10 ° C. As a result of ¹³ C-NMR analysis of the fine particles 2, the constitutional unit of the formula (3) derived from 2-ethylhexyl methacrylate was 97 mol%, and the EGDM constitutional unit was 3.0 mol%.

[Synthesis Example 3: Fine Particle 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 In the same manner as above, 13.8 g of fine particles 3 were obtained (polymerization conversion rate: 90%). The average particle diameter of the fine particles 3 was 62 nm, and Tg was −65 ° C. As a result of ¹³ C-NMR analysis of the fine particles 3, the structural unit of the formula (1) derived from n-dodecyl methacrylate was 97 mol%, and the EGDM structural unit was 3.0 mol%.

[Synthesis Example 4: Fine Particle 4]
8.0 g of 2,4,6-trimethylheptyl methacrylate, 7.0 g of 2-ethylhexyl methacrylate (where 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, and the mixture is stirred for 1 hour to emulsify the monomer, and 0.191 g of excess After adding potassium sulfate, nitrogen bubbling for 1 hour was performed and the solution was held 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 average particle diameter of the fine particles 4 was 60 nm, and Tg was −24 ° C. As a result of ¹³ C-NMR analysis of fine particles 4, the structural unit of formula (2) derived from 2,4,6-trimethylheptyl methacrylate was 49 mol%, and the structural unit of formula (3) derived from 2-ethylhexyl methacrylate. Was 48 mol%, and the EGDM structural unit was 3.0 mol%.

[Synthesis Example 5: Fine Particle 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 2,4,6-trimethylheptyl methacrylate used for the synthesis of fine particles 1. The average particle diameter of the fine particles was 60 nm, and Tg was −25 ° C.

[Synthesis Example 6: Fine Particle 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 average particle diameter of the fine particles was 60 nm, and Tg was 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 were mixed. Nitrogen was bubbled for 1 hour. Thereafter, 0.190 g of copper (I) bromide was added to the reaction solution and kept at 70 ° C. for 5 hours. A (meth) acrylate polymer (Polymer 1) was obtained by reprecipitation purification of the resulting solution in methanol. The Tg of polymer 1 was -41 ° C.

[Evaluation of rubber composition]
Using a laboratory mixer, according to the blending (parts by mass) shown in Tables 1 and 2 below, first, in the first mixing stage, other blending agents except for sulfur and 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 (discharge 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" (amino group and alkoxysilyl group terminal modified SBR) manufactured by JSR Corporation
Modified SBR2: “# 9590” (amino group-modified SBR) manufactured by Nippon Zeon Co., Ltd.
-Modified SBR3: "Toughden E580" manufactured by Asahi Kasei Corporation (hydroxyl terminal-modified SBR)
-Modified SBR4: "Nippol LX421" (carboxyl terminal-modified SBR) manufactured by Nippon Zeon Co., Ltd.
・ BR: “UBEPOL BR150B” manufactured by Ube Industries, Ltd.
・ Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd.
Silane coupling agent: bis (3-triethoxysilylpropyl) tetrasulfide, “Si69” manufactured by Evonik
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting
Anti-aging agent: “NOCRACK 6C” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Sulfur: Hosoi Chemical Co., Ltd. “Powder sulfur for rubber 150 mesh”
・ Vulcanization accelerator: “Noxeller CZ” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Secondary vulcanization accelerator: “Noxeller D” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Fine particles 1-6: Fine particles obtained by the method described in Synthesis Examples 1-6 Polymer 1: Polymer obtained by the method described in Synthesis Example 7 Crosslinked rubber particle: “Nanoprene BM350H” manufactured by LANXESS Styrene butadiene rubber gel (Tg: -35 ° C).

  About each obtained rubber composition, the test piece of a predetermined shape is produced by vulcanizing in 160 degreeC x 20 minutes, and the dynamic viscoelasticity test is done using the obtained test piece, and 0 degreeC and 60 degreeC The tan δ was measured. Further, the tear strength was measured. The results are shown in Tables 1 and 2. The measuring method is as follows.

  0 ° C. tan δ: The loss factor tan δ was measured under the conditions of a frequency of 10 Hz, a static strain of 10%, a dynamic strain of 2%, and a temperature of 0 ° C. using a rheometer E4000 manufactured by UBM. In Table 2, the value of Comparative Example 10 is shown as an index with each value being 100. The larger the index, the larger the tan δ, and the better the wet grip performance.

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

  -Tear strength: The tear strength of the test piece was measured in accordance with JIS K6252, and the values of Comparative Example 1 in Table 1 and the values of Comparative Example 10 in Table 2 were each expressed as an index. A larger index indicates better 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 blending system using unmodified SBR, the comparative example 11 in which the fine particles 1 are blended improves the wet grip performance while suppressing the deterioration of the rolling resistance performance, compared to the comparative example 10 which is a control. However, the tearing performance decreased.

  On the other hand, as shown in Table 1, in the blending system using the modified SBR, when it is Examples 1 to 7 in which fine particles 1 to 4 were blended with respect to Comparative Example 1 as a control, the rolling resistance performance was deteriorated. The wet grip performance was remarkably improved while suppressing or maintaining or improving the tear resistance.

  On the other hand, in Comparative Examples 2 and 3 in which fine particles 5 and 6 composed of a non-regulated (meth) acrylate polymer are blended, not only the improvement effect of the wet grip performance is small, but also the rolling resistance performance is deteriorated, Also, the tear resistance was deteriorated. In Comparative Example 4 in which crosslinked rubber particles were blended in place of fine particles made of a (meth) acrylate polymer, not only the effect of improving wet grip performance was small, but also rolling resistance performance and tear resistance were deteriorated. In Comparative Example 5 in which a (meth) acrylate polymer that is not fine particles was blended, not only the effect of improving wet grip performance was small, but also the tear resistance was deteriorated.

Claims (5)

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 A rubber composition containing 1 to 100 parts by mass of fine particles having an average particle diameter of 10 nm or more and less than 100 nm, comprising a (meth) acrylate polymer having a structural unit represented by the following general formula (1)

(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 in the same molecule R ² 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 said (meth) acrylate type polymer is a polymer which has a structural unit represented by the following general formula (2) as a structural unit represented by the said General formula (1). The rubber composition as 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 following General formula (3) as a structural unit represented by the said General formula (1). The rubber composition according to any one of the above.

(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, and Q ¹ is an alkylene group having 1 to 6 carbon atoms, 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.)   The pneumatic tire produced using the rubber composition of any one of Claims 1-4.