Modified butadiene polymer and rubber composition

Abstract

An object of the present invention is to provide a compounding agent that exhibits excellent dispersibility, processability, toughness, low heat generation, and abrasion resistance when used in a rubber composition containing a reinforcing filler, and a rubber composition containing the above compounding agent. The modified butadiene polymer of the present invention has a functional group containing a nitrogen atom and a silicon atom at the terminal, a weight average molecular weight of 1,000 or more and 15,000 or less, and a molecular weight distribution of 2.0 or less.

Description

Technical Field

[0001] The present invention relates to a modified butadiene polymer and a rubber composition. Background Art

[0002] Generally, reinforcing fillers such as carbon black and silica are incorporated into rubber compositions used in tires and the like. On the other hand, due to the interaction between the reinforcing fillers, the reinforcing fillers sometimes aggregate in the rubber composition, and sufficient properties (for example, processability, toughness, low heat build-up property, abrasion resistance) cannot be obtained.

[0003] Among them, for example, in Patent Document 1, a modified low-molecular-weight conjugated diene polymer (claims, etc.) is disclosed as a compounding agent for a rubber composition containing a reinforcing filler.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-287018 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] The inventors of the present invention studied the use of a modified conjugated diene rubber as a compounding agent with reference to the examples of Patent Document 1, and as a result, found that the dispersibility (hereinafter, also simply referred to as "dispersibility") and properties of the reinforcing filler in the obtained rubber composition do not necessarily meet the recently required levels.

[0009] Therefore, in view of the above actual situation, an object of the present invention is to provide a compounding agent that exhibits excellent dispersibility, processability, toughness, low heat build-up property, and abrasion resistance when used in a rubber composition containing a reinforcing filler, and a rubber composition containing the above compounding agent.

[0010] Means for Solving the Problems

[0011] As described above, from the research results of the inventors of the present invention, it can be seen that when the modified conjugated diene rubber used in the examples of Patent Document 1 is used as a compounding agent, the dispersibility of the reinforcing filler becomes insufficient. More specifically, it can be seen that even when a rubber composition containing a reinforcing filler is compounded with a modified butadiene polymer (modified BR) having a weight average molecular weight of 80,000 used in the examples of Patent Document 1, the dispersibility of the reinforcing filler becomes insufficient.

[0012] The present inventors have conducted research focusing on the size of modified butadiene polymers and have found that there is a significant correlation between the weight-average molecular weight and molecular weight distribution of the modified butadiene polymer and the dispersibility of the reinforcing filler. Furthermore, by controlling the weight-average molecular weight and molecular weight distribution within specific ranges, the dispersibility of the reinforcing filler is significantly improved.

[0013] The present invention is based on the above-mentioned knowledge, and its specific structure is as follows.

[0014] (1) A modified butadiene polymer having a functional group containing a nitrogen atom and a silicon atom at a terminal,

[0015] The modified butadiene polymer has a weight average molecular weight of 1,000 to 15,000, and a molecular weight distribution of 2.0 or less.

[0016] (2) The modified butadiene polymer according to (1) above, wherein the viscosity is 150 to 240% of the viscosity of the butadiene polymer before modification, wherein the viscosity is measured using a cone-plate viscometer.

[0017] (3) The modified butadiene polymer according to (1) or (2) above, which is used in a rubber composition comprising: a rubber component having a weight-average molecular weight exceeding 15,000; and a reinforcing filler comprising at least one selected from carbon black and silica.

[0018] (4) A rubber composition comprising: a rubber component having a weight average molecular weight exceeding 15,000; a reinforcing filler; and the modified butadiene polymer described in any one of (1) to (3) above.

[0019] The content of the reinforcing filler is 50 to 200 parts by mass relative to 100 parts by mass of the rubber component.

[0020] The content of the modified butadiene polymer is 1 to 25% by mass relative to the content of the reinforcing filler.

[0021] (5) A rubber composition comprising: a rubber component having a weight-average molecular weight exceeding 15,000; a reinforcing filler comprising at least one selected from carbon black and silica; and the modified butadiene polymer according to any one of (1) to (3) above.

[0022] (6) The rubber composition according to (4) or (5) above, wherein the reinforcing filler contains at least one selected from carbon black and silica.

[0023] The nitrogen adsorption specific surface area of the above silicon dioxide is 194m 2 / g or more, CTAB adsorption specific surface area is 185m2 When it is more than / g, the ratio of the nitrogen adsorption specific surface area to the CTAB adsorption specific surface area is 0.9 to 1.4.

[0024] (7) The rubber composition according to (5) or (6) above further contains a silane coupling agent.

[0025] The content of the silane coupling agent is 1 to 20% by mass based on the content of the above silica.

[0026] (8) In the rubber composition according to any one of (4) to (7) above, the glass transition temperature of the rubber component is -60°C or higher.

[0027] Effects of the Invention

[0028] As shown below, according to the present invention, it is possible to provide a compounding agent that exhibits excellent dispersibility, processability, toughness, low heat generation, and abrasion resistance when used in a rubber composition containing a reinforcing filler, and a rubber composition containing the above compounding agent. Detailed Description of the Invention

[0029] Hereinafter, a modified butadiene polymer as a compounding agent of the present invention and a rubber composition containing the above modified butadiene polymer will be described.

[0030] In addition, in this specification, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0031] [Specific Modified BR]

[0032] The modified butadiene polymer as a compounding agent of the present invention is a butadiene polymer (butadiene polymer) having a functional group containing a nitrogen atom and a silicon atom (hereinafter, also referred to as "specific functional group") at the terminal, a weight average molecular weight of 1,000 or more and 15,000 or less, and a molecular weight distribution of 2.0 or less.

[0033] Hereinafter, the modified butadiene polymer as a compounding agent of the present invention will also be referred to as "specific modified BR".

[0034] By adopting such a configuration, it can be considered that the specific modified BR exhibits excellent dispersibility of the reinforcing filler in the rubber composition when used in a rubber composition containing a reinforcing filler.

[0035] The reason in detail is not yet clear, but it can be considered that the agglomeration of the reinforcing filler is prevented by the interaction between the nitrogen atom and the silicon atom in the specific functional group of the specific modified BR and the reinforcing filler. Here, as described above, from the research results of the present inventors, a criticality can be seen between the size (weight average molecular weight, molecular weight distribution) of the modified BR and the dispersibility of the reinforcing filler. It is speculated that this is because when the size (weight average molecular weight, molecular weight distribution) of the modified BR is within the above-mentioned specific range, it is extremely easy to intervene in the gaps between the aggregates of the reinforcing fillers, and as a result, the dispersibility of the reinforcing filler is greatly improved.

[0036] Hereinafter, the specific modified BR will be described in detail.

[0037] As described above, the specific modified BR is a butadiene polymer (modified butadiene polymer) having a functional group containing a nitrogen atom and a silicon atom (specific functional group) at the terminal, a weight average molecular weight of 1,000 or more and 15,000 or less, and a molecular weight distribution of 2.0 or less.

[0038] [Specific functional group]

[0039] As described above, the specific modified BR has a functional group containing a nitrogen atom and a silicon atom (specific functional group) at the terminal. In addition, the specific functional group only needs to be present at at least one terminal.

[0040] <Preferred embodiment>

[0041] The specific functional group is not particularly limited as long as it is a functional group containing a nitrogen atom and a silicon atom. However, for the reason that the effects of the present invention are more excellent, it is preferred to contain a nitrogen atom in the form of an amino group (-NR2: R is a hydrogen atom or a hydrocarbon group), and it is preferred to contain a silicon atom in the form of a hydrocarbyloxysilyl group (≡SiOR: R is a hydrocarbon group).

[0042] For the reason that the effects of the present invention are more excellent, the specific functional group is preferably a group represented by the following formula (M).

[0043]

[0044] In the above formula (M), R1 and R2 each independently represent a hydrogen atom or a substituent.

[0045] In the above formula (M), L represents a divalent organic group.

[0046] The above-mentioned substituent is not particularly limited as long as it is a monovalent substituent, and examples thereof include a halogen atom, a hydroxyl group, a nitro group, a carboxyl group, an alkoxy group, an amino group, a mercapto group, an acyl group, an imide group, a phosphino group, a phosphonyl group, a silyl group, and a hydrocarbon group that may have a heteroatom.

[0047] Examples of the above-mentioned halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.

[0048] Examples of the hetero atoms of the above-mentioned hydrocarbon group which may have a hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, etc.

[0049] Examples of the above-mentioned hydrocarbon group which may have a hetero atom include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, a group combining them, etc.

[0050] The above-mentioned aliphatic hydrocarbon group may be any of linear, branched, and cyclic. Specific examples of the above-mentioned aliphatic hydrocarbon group include a linear or branched alkyl group (particularly having 1 to 30 carbon atoms), a linear or branched alkenyl group (particularly having 2 to 30 carbon atoms), a linear or branched alkynyl group (particularly having 2 to 30 carbon atoms), etc.

[0051] Examples of the above-mentioned aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms such as a phenyl group, a tolyl group, a xylyl group, a naphthyl group, etc.

[0052] In the above formula (M), for the reason that the effects of the present invention are more excellent, R1 is preferably a hydrogen atom, an alkyl group (preferably having 1 to 10 carbon atoms), an alkylsilyl group (preferably having 1 to 10 carbon atoms), an aromatic hydrocarbon group (preferably having 6 to 18 carbon atoms), and more preferably a hydrogen atom.

[0053] A plurality of R1s may be the same or different.

[0054] For the reason that the effects of the present invention are more excellent, R2 is preferably a hydrocarbyloxy group (-OR group: R is a hydrocarbon group), and more preferably an alkoxy group (preferably having 1 to 10 carbon atoms).

[0055] As described above, in the above formula (M), L represents a single bond or a divalent organic group.

[0056] Examples of the divalent organic group include an aliphatic hydrocarbon group (e.g., an alkylene group. Preferably having 1 to 10 carbon atoms), an aromatic hydrocarbon group (e.g., an arylene group. Preferably having 6 to 18 carbon atoms), -O-, -S-, -SO2-, -N(R)- (R: alkyl group), -CO-, -NH-, -COO-, -CONH-, or a group combining them (e.g., an alkyleneoxy group (-C m H 2m O-: m is a positive integer), an alkyleneoxycarbonyl group, an alkylcarbonyloxy group, etc.).

[0057] For the reason that the effects of the present invention are more excellent, L is preferably an alkylene group (preferably having 1 to 10 carbon atoms).

[0058] In the above formula (M), n represents an integer from 0 to 2.

[0059] For reasons of even better effects of the present invention, n is preferably 2.

[0060] In the above formula (M), m represents an integer from 1 to 3.

[0061] For reasons of even better effects of the present invention, m is preferably 1.

[0062] In the above formula (M), n and m satisfy the relation of n + m = 3.

[0063] In the above formula (M), * represents the bonding position.

[0064] 〔Weight-average molecular weight〕

[0065] As described above, the weight-average molecular weight (Mw) of the specific modified BR is 1,000 or more and 15,000 or less. Among them, for reasons of even better effects of the present invention, it is preferably 5,000 or more and less than 10,000.

[0066] 〔Number-average molecular weight〕

[0067] Regarding the number-average molecular weight of the specific modified BR, as long as the weight-average molecular weight and molecular weight distribution of the specific modified BR are within a specific range, there is no particular limitation. However, for reasons of even better effects of the present invention, it is preferably 1,000 or more and 15,000 or less, and more preferably 5,000 or more and less than 10,000.

[0068] 〔Molecular weight distribution〕

[0069] As described above, the molecular weight distribution (Mw / Mn) of the specific modified BR is 2.0 or less. Among them, for reasons of even better effects of the present invention, it is preferably 1.7 or less, more preferably 1.5 or less, and further preferably 1.3 or less.

[0070] There is no particular limitation on the lower limit, and it is usually 1.0 or more.

[0071] In addition, in this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are standard polystyrene conversion values obtained by gel permeation chromatography (GPC) under the following conditions.

[0072] · Solvent: Tetrahydrofuran

[0073] · Detector: RI detector

[0074] 〔Microstructure〕

[0075] <Vinyl structure>

[0076] In the specific modified BR, the proportion of the vinyl structure is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 10 to 50 mol%, more preferably 20 to 40 mol%.

[0077] Here, the proportion of the vinyl structure means the proportion (mol%) of the repeating units having a vinyl structure among the repeating units derived from butadiene.

[0078] <1,4-trans structure>

[0079] In the specific modified BR, the proportion of the 1,4-trans structure is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 10 to 70 mol%, more preferably 30 to 50 mol%.

[0080] Here, the proportion of the 1,4-trans structure means the proportion (mol%) of the repeating units having a 1,4-trans structure among all the repeating units derived from butadiene.

[0081] <1,4-cis structure>

[0082] In the specific modified BR, the proportion of the 1,4-cis structure is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 10 to 50 mol%, more preferably 20 to 40 mol%.

[0083] Here, the proportion of the 1,4-cis structure means the proportion (mol%) of the repeating units having a 1,4-cis structure among all the repeating units derived from butadiene.

[0084] In addition, hereinafter, the "proportion of vinyl structure (mol%), proportion of 1,4-trans structure (mol%), proportion of 1,4-cis structure (mol%)" is also expressed as "vinyl / trans / cis".

[0085] 〔Glass transition temperature〕

[0086] The glass transition temperature (Tg) of the specific modified BR is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably -100 to -60 °C, more preferably -90 to -70 °C, and further preferably -85 to -75 °C.

[0087] In addition, in this specification, the glass transition temperature (Tg) is measured using a differential scanning calorimeter (DSC) at a heating rate of 10 °C / minute and calculated by the midpoint method.

[0088] 〔Viscosity〕

[0089] The viscosity of the specific modified BR is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 1,000 to 10,000 mPa·s, and more preferably 3,000 to 6,000 mPa·s.

[0090] In addition, the viscosity of the butadiene polymer before the specific modified BR is modified is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 500 to 5,000 mPa·s, and more preferably 1,500 to 3,000 mPa·s.

[0091] In addition, for the reason that the effects of the present invention are more excellent, the viscosity of the specific modified BR is preferably 150 to 240% of the viscosity of the butadiene polymer before modification. Hereinafter, the viscosity of the modified specific modified BR relative to the specific modified BR before modification is also referred to as "viscosity (after modification / before modification)".

[0092] In addition, in this specification, the viscosity is measured using a cone-plate viscometer in accordance with JIS K5600-2-3.

[0093] 〔Method for producing specific modified BR〕

[0094] The method for producing the specific modified BR is not particularly limited, and a conventionally known method can be used. The method for making the molecular weight and molecular weight distribution within a specific range is not particularly limited, and examples include methods of adjusting the amount ratio of the initiator, monomer, and terminator, the reaction temperature, and the rate of adding the initiator.

[0095] <Preferred embodiment>

[0096] As a preferred embodiment of the method for producing the specific modified BR, for example, a method of polymerizing butadiene using an organolithium compound and then terminating the polymerization using an electrophilic reagent containing a nitrogen atom and a silicon atom (hereinafter, also referred to as "the method of the present invention") can be cited. When the method of the present invention is used, the resulting specific modified BR exhibits more excellent dispersibility, processability, toughness, low heat generation, and abrasion resistance when used in a rubber composition containing a reinforcing filler.< /

[0097]

[0097] (Organolithium compound)

[0098] The above-mentioned organolithium compounds are not particularly limited. Specific examples thereof include mono-organolithium compounds such as n-butyllithium, sec-butyllithium, tert-butyllithium, n-propyllithium, isopropyllithium, and benzyllithium; polyfunctional organolithium compounds such as 1,4-dilithiobutane, 1,5-dilithiopentane, 1,6-dilithiohexane, 1,10-dilithiodecane, 1,1-dilithiodiphenylene, dilithiopolybutadiene, dilithiopolyisoprene, 1,4-dilithiobenzene, 1,2-dilithio-1,2-diphenylethane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene, and 1,3,5-trilithio-2,4,6-triethylbenzene. Among them, from the reason that the effects of the present invention are more excellent, mono-organolithium compounds such as n-butyllithium, sec-butyllithium, and tert-butyllithium are preferred.

[0099] The amount of the organolithium compound used is not particularly limited, but from the reason that the effects of the present invention are more excellent, it is preferably 0.001 to 10 mol% relative to butadiene.

[0100] (Copolymerization of butadiene)

[0101] The method for polymerizing butadiene using an organolithium compound is not particularly limited. Examples thereof include a method of adding the above-mentioned organolithium compound to an organic solvent solution containing butadiene and stirring in a temperature range of 0 to 120 °C (preferably 30 to 100 °C).

[0102] (Specific electrophilic reagent)

[0103] In the method of the present invention, the polymerization of butadiene is terminated using an electrophilic reagent containing a nitrogen atom and a silicon atom (hereinafter, also referred to as "specific electrophilic reagent"). By terminating the polymerization using a specific electrophilic reagent, a modified butadiene polymer having the above-mentioned specific functional group at the terminal can be obtained.

[0104] The specific electrophilic reagent is not particularly limited as long as it is a compound containing a nitrogen atom and a silicon atom. However, from the reason that the effects of the present invention are more excellent, it preferably contains a nitrogen atom in the form of an amino group (-NR2: R is a hydrogen atom or a hydrocarbon group), and preferably contains a silicon atom in the form of a hydrocarbyloxysilyl group (≡SiOR: R is a hydrocarbon group).

[0105] From the reason that the effects of the present invention are more excellent, the specific electrophilic reagent is preferably a silazane, and more preferably a cyclic silazane. Here, the so-called silazane refers to a compound having a structure in which a silicon atom and a nitrogen atom are directly bonded (a compound having a Si-N bond).

[0106] From the reason that the effects of the present invention are more excellent, the above-mentioned cyclic silazane is preferably a compound represented by the following formula (S).

[0107]

[0108] In the above formula (S), R1 to R3 each independently represent a hydrogen atom or a substituent. Specific examples and preferred embodiments of the substituent are the same as those of R1 and R2 in the above formula (M).

[0109] In the above formula (S), L represents a divalent organic group. Specific examples and preferred embodiments of the divalent organic group are the same as those of L in the above formula (M).

[0110] In the above formula (S), for the reason that the effects of the present invention are more excellent, R1 is preferably an alkyl group (preferably having 1 to 10 carbon atoms), an alkylsilyl group (preferably having 1 to 10 carbon atoms), an aromatic hydrocarbon group (preferably having 6 to 18 carbon atoms), and more preferably an alkylsilyl group.

[0111] In the above formula (S), for the reason that the effects of the present invention are more excellent, R2 and R3 each independently are preferably a hydrocarbyloxy group (-OR group: R is a hydrocarbyl group), and more preferably an alkoxy group (preferably having 1 to 10 carbon atoms).

[0112] In the above formula (S), for the reason that the effects of the present invention are more excellent, L is preferably an alkylene group (preferably having 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and further preferably 3 to 5 carbon atoms).

[0113] Examples of the compound represented by the above formula (S) include N-n-butyl-1,1-dimethoxy-2-azasilacyclopentane, N-phenyl-1,1-dimethoxy-2-azasilacyclopentane, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane, N-trimethylsilyl-1,1-diethoxy-2-azasilacyclopentane, and the like.

[0114] In addition, the silicon atom of the cyclic silazane can be considered to exhibit electrophilicity.

[0115] The amount of the specific electrophilic reagent relative to the organolithium compound is not particularly limited, but for the reason that the effects of the present invention are more excellent, the molar ratio is preferably 0.1 to 10, and more preferably 1 to 5.

[0116] [Rubber Composition]

[0117] The rubber composition of the present invention (hereinafter, also referred to as "the composition of the present invention") is a rubber composition containing a rubber component having a weight average molecular weight exceeding 15,000, a reinforcing filler, and the above-mentioned specific modified BR.

[0118] [Rubber Component]

[0119] The above rubber component is not particularly limited as long as it is a rubber component having a weight average molecular weight (Mw) exceeding 15,000.

[0120] For the reason that the effects of the present invention are more excellent, the above rubber component is preferably a diene rubber. Specific examples of the diene rubber include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Among them, for the reason that the effects of the present invention are more excellent, SBR and BR are preferred.

[0121] The content (styrene unit content) of the styrene unit (repeating unit derived from styrene) of the above SBR is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 5 to 50% by mass.

[0122] In addition, the proportion of the vinyl structure of the above SBR is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 5 to 80%, more preferably 10 to 75%, and further preferably 20 to 70%. Here, the proportion of the vinyl structure refers to the proportion (mol%) of the repeating units having a vinyl structure among the repeating units derived from butadiene.

[0123] <Weight average molecular weight>

[0124] As described above, the weight average molecular weight (Mw) of the rubber component exceeds 15,000. For the reason that the effects of the present invention are more excellent, the Mw of the rubber component is preferably 100,000 to 10,000,000.

[0125] The measurement method of the weight average molecular weight is as described above.

[0126] <Glass transition temperature>

[0127] The glass transition temperature (Tg) of the rubber component is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably -60 °C or higher. The upper limit is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 0 °C or lower, and more preferably -20 °C or lower. The measurement method of Tg is as described above.

[0128] In addition, when the rubber component is an oil-extended rubber, the glass transition temperature of the rubber component is the glass transition temperature in the state without the oil-extended component (oil). Further, when the rubber component contains two or more rubber components, the glass transition temperature of the rubber component is the average glass transition temperature. Here, the so-called average glass transition temperature is the sum of the glass transition temperatures of each rubber component multiplied by the mass fraction of each rubber component (weighted average value of the glass transition temperature), and the sum of the mass fractions of all rubber components is set to 1.

[0129] 〔Reinforcement fillers〕

[0130] The reinforcing filler contained in the composition of the present invention is not particularly limited, but is preferably at least one selected from silica and carbon black.

[0131] In the composition of the present invention, the content of the reinforcing filler is not particularly limited, but is preferably 50 to 200 parts by mass, more preferably 60 to 100 parts by mass, relative to 100 parts by mass of the rubber component, for the purpose of achieving more excellent effects of the present invention.

[0132] When the composition of the present invention contains two or more reinforcing fillers, the content of the reinforcing fillers refers to the total content.

[0133] <Silicon dioxide>

[0134] The composition of the present invention preferably contains silica as a reinforcing filler because the effects of the present invention are more excellent.

[0135] The silica is not particularly limited, and any conventionally known silica can be used.

[0136] Examples of the silica include wet silica, dry silica, fumed silica, and diatomaceous earth. As the silica, one type may be used alone, or two or more types may be used in combination.

[0137] The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of the silica (hereinafter, "CTAB adsorption specific surface area" is also referred to as "CTAB") is not particularly limited, but is preferably 100 to 300 m2 for the purpose of achieving the best effect of the present invention. 2 / g, more preferably 185m 2 / g or above.

[0138] Here, the CTAB adsorption specific surface area is a value obtained by measuring the amount of CTAB adsorbed on the silica surface in accordance with JIS K6217-3:2001 “Part 3: Method for determining specific surface area - CTAB adsorption method”.

[0139] The nitrogen adsorption specific surface area (N2SA) of the silica is not particularly limited, but is preferably 100 to 300 m2 for the purpose of achieving the best effect of the present invention. 2 / g, more preferably 194m 2 / g or above.

[0140] Here, N2SA is a surrogate property of the surface area of silica that can be utilized for adsorption to rubber molecules, and is a value obtained by measuring the amount of nitrogen adsorbed on the silica surface in accordance with JIS K6217-2:2001 "Part 2: Methods for determining specific surface area - Nitrogen adsorption method - Single-point method".

[0141] The ratio of the nitrogen adsorption specific surface area of silica to the CTAB adsorption specific surface area of silica (N2SA / CTAB) is not particularly limited, but is preferably 0.9 to 1.4 because the effects of the present invention are more excellent.

[0142] The content of silica in the composition of the present invention is not particularly limited, but is preferably 10 to 150 parts by mass, more preferably 50 to 100 parts by mass, relative to 100 parts by mass of the rubber component, for the purpose of achieving more excellent effects of the present invention.

[0143] Carbon black

[0144] The composition of the present invention preferably contains carbon black as a reinforcing filler because the effects of the present invention are more excellent. The carbon black may be used alone or in combination of two or more.

[0145] The carbon black is not particularly limited, and various grades of carbon black such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, GPF, and SRF may be used.

[0146] The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited, but is preferably 50 to 200 m2 for the purpose of achieving the best effect of the present invention. 2 / g, more preferably 70 to 150 m 2 / g.

[0147] Here, the nitrogen adsorption specific surface area (N2SA) is a value obtained by measuring the amount of nitrogen adsorbed on the carbon black surface in accordance with JIS K6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single-point method".

[0148] In the composition of the present invention, the content of carbon black is not particularly limited, but is preferably 1 to 100 parts by mass, more preferably 2 to 10 parts by mass, relative to 100 parts by mass of the rubber component, because the effects of the present invention are more excellent.

[0149] 〔Specific modified BR〕

[0150] As described above, the composition of the present invention contains the specific modified BR described above.

[0151] In the composition of the present invention, the content of the specific modified BR is not particularly limited. However, for the reason that the effects of the present invention are more excellent, it is preferably 1 to 25% by mass, more preferably 2.0 to 10.0% by mass, relative to the content of the above-mentioned reinforcing filler.

[0152] Furthermore, for the reason that the effects of the present invention are more excellent, the content of the specific modified BR is preferably 1 part by mass or more and less than 10 parts by mass relative to 100 parts by mass of the above-mentioned rubber component.

[0153] 〔Silane Coupling Agent〕

[0154] For the reason that the effects of the present invention are more excellent, the composition of the present invention preferably contains a silane coupling agent. The above-mentioned silane coupling agent may be used alone or in combination of two or more.

[0155] The above-mentioned silane coupling agent is not particularly limited as long as it is a silane compound having a hydrolyzable group and an organic functional group.

[0156] The above-mentioned hydrolyzable group is not particularly limited, and examples thereof include an alkoxy group, a phenoxy group, a carboxyl group, an alkenyloxy group, etc. Among them, an alkoxy group is preferred. When the hydrolyzable group is an alkoxy group, the number of carbon atoms of the alkoxy group is preferably 1 to 16, more preferably 1 to 4. Examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, etc.

[0157] The above-mentioned organic functional group is not particularly limited, and is preferably a group capable of forming a chemical bond with an organic compound. Examples thereof include an epoxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group, a thioether group, a mercapto group, etc. Among them, a thioether group and a mercapto group are preferred.

[0158] The above-mentioned silane coupling agent is preferably a sulfur-containing silane coupling agent.

[0159] Specific examples of the above-mentioned silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, trimethoxysilylpropyl-mercaptobenzothiazole tetrasulfide, triethoxysilylpropyl-methacrylate-monosulfide, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl-tetrasulfide, etc. Among them, one kind may be used alone, or two or more kinds may be used in combination.

[0160] In the composition of the present invention, the content of the silane coupling agent is not particularly limited. However, from the reason that the effects of the present invention are more excellent, it is preferably 1 to 20% by mass, more preferably 5 to 10% by mass, relative to the content of the above-mentioned silica.

[0161] 〔Other components〕

[0162] The composition of the present invention may contain components other than the above-mentioned components (other components) as needed within the range not impairing its effects and purposes.

[0163] Examples of such components include various additives generally used in rubber compositions, such as terpene resins (preferably aromatic-modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc oxide), stearic acid, anti-aging agents, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), vulcanization accelerators, etc.

[0164] 〔Use〕

[0165] The composition of the present invention is preferably used for tires, conveyor belts, hoses, vibration-proof materials, rubber rollers, outer waterproof cloths of railway vehicles, etc. It is particularly preferably used for tires.

[0166] Examples

[0167] Hereinafter, the present invention will be described in further detail by way of examples, but the present invention is not limited thereto.

[0168] 〔Synthesis example〕

[0169] As described below, Comparative Modified BR1-2 and Specific Modified BR1-4 were synthesized.

[0170] Here, Specific Modified BR1-4 are all modified BRs having a functional group represented by the following formula (m1) equivalent to a specific functional group at the terminal, with Mw of 1000 or more and 15,000 or less, and Mw / Mn of 2.0 or less, so they are equivalent to the above-mentioned "Specific Modified BR". On the other hand, Comparative Modified BR1 is a modified BR having a functional group represented by the following formula (m1) at the terminal, with Mw / Mn of 2.0 or less, but Mw exceeding 15,000, so it does not belong to the above-mentioned "Specific Modified BR". In addition, Comparative Modified BR2 is a modified BR having a functional group represented by the following formula (m1) at the terminal, with Mw of 1000 or more and 15,000 or less, but Mw / Mn exceeding 2.0, so it does not belong to the above-mentioned "Specific Modified BR".

[0171] <Comparative Modified BR1>

[0172] n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 21 mL, 33.6 mmol) was added to a mixed solution of 1,3-butadiene (230 g, 4259 mmol) and 2,2-bis(2-tetrahydrofuryl)propane (manufactured by Tokyo Chemical Industry Co., Ltd., 0.1 mL, 0.55 mmol) in cyclohexane (3.0 kg), and the mixture was stirred at room temperature for 6 hours. After the reaction, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane (the following structure) (15 g, 68.5 mmol) was added to terminate the polymerization.

[0173]

[0174] The resulting solution was taken out and concentrated under reduced pressure. The concentrated solution was poured into methanol (5.0 L), and the methanol-insoluble component was separated. As a result, modified BR (Comparative Modified BR1) (212 g, Mn = 17,400, Mw = 19,200, Mw / Mn = 1.1) having a functional group represented by the following formula (m1) (where * represents the bonding position) at the terminal was obtained in a yield of 92%. In addition, by IR analysis, cis / trans / vinyl was estimated to be 21 / 33 / 46. Furthermore, Tg was -70°C.

[0175]

[0176] <Comparative Modified BR2>

[0177] n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 23.2 mL, 37.2 mmol) was added to a mixed solution of 1,3-butadiene (461 g, 8518 mmol) and 2,2-bis(2-tetrahydrofuryl)propane (manufactured by Tokyo Chemical Industry Co., Ltd., 0.2 mL, 1.09 mmol) in cyclohexane (4.20 kg), and the mixture was stirred at room temperature. Every 1 hour and 30 minutes, 23.2 mL of n-BuLi was added each time for a total of 92.8 mL. After 6 hours from the start of the reaction, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane (60 g, 274 mmol) was added to terminate the polymerization. The resulting solution was taken out and concentrated under reduced pressure. The concentrated solution was poured into methanol (10 L), and the methanol-insoluble component was separated. As a result, modified BR (Comparative Modified BR2) (740 g, Mn = 4,000, Mw = 8,800, Mw / Mn = 2.2) having a functional group represented by the above formula (m1) at the terminal was obtained in a yield of 97%. In addition, by IR analysis, cis / trans / vinyl was estimated to be 23 / 38 / 39. Furthermore, Tg was -77°C.

[0178] <Specific Modified BR1>

[0179] n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 50 mL, 80 mmol) was added to a mixed solution of 1,3-butadiene (198 g, 3667 mmol) and 2,2-bis(2-tetrahydrofuryl)propane (manufactured by Tokyo Chemical Industry Co., Ltd., 0.1 mL, 0.55 mmol) in cyclohexane (2.96 kg), and the mixture was stirred at room temperature for 6 hours. After the reaction, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane (30 g, 137 mmol) was added to terminate the polymerization. The resulting solution was taken out and concentrated under reduced pressure. The concentrated solution was poured into methanol (5.0 L) to separate the methanol-insoluble component. As a result, modified BR (specific modified BR1) having a functional group represented by the above formula (m1) at the terminal was obtained in a yield of 92% (182 g, Mn = 4,100, Mw = 4,400, Mw / Mn = 1.1). In addition, by IR analysis, cis / trans / vinyl = 31 / 45 / 24 was estimated. Furthermore, Tg was -83°C. In addition, the viscosity (after modification / before modification) was 196%.

[0180] <Specific Modified BR2>

[0181] n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 27 mL, 43.2 mmol) was added to a mixed solution of 1,3-butadiene (205 g, 3786 mmol) and 2,2-bis(2-tetrahydrofuryl)propane (manufactured by Tokyo Chemical Industry Co., Ltd., 0.1 mL, 0.55 mmol) in cyclohexane (2.96 kg), and the mixture was stirred at room temperature for 6 hours. After the reaction, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane (15 g, 137 mmol) was added to terminate the polymerization. The resulting solution was taken out and concentrated under reduced pressure. The concentrated solution was poured into methanol (10 L) to separate the methanol-insoluble component. As a result, modified BR (specific modified BR2) having a functional group represented by the above formula (m1) at the terminal was obtained in a yield of 97% (199 g, Mn = 7,600, Mw = 8,100, Mw / Mn = 1.1). In addition, by IR analysis, cis / trans / vinyl = 24 / 40 / 36 was estimated. Furthermore, Tg was -80°C. In addition, the viscosity (after modification / before modification) was 204%.

[0182] <Specific Modified BR3>

[0183] n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 17 mL, 27.2 mmol) was added to a mixed solution of 1,3-butadiene (256 g, 4732 mmol) and 2,2-bis(2-tetrahydrofuryl)propane (manufactured by Tokyo Chemical Industry Co., Ltd., 0.1 mL, 0.55 mmol) in cyclohexane (3.5 kg), and the mixture was stirred at room temperature for 3 hours. Then, 17 mL of n-BuLi was added and stirred for 3 hours. After the reaction, N-trimethylsilyl-1,1-dimethoxy-2-azasilacyclopentane (25 g, 114 mmol) was added to terminate the polymerization. The resulting solution was taken out and concentrated under reduced pressure. The concentrated solution was poured into methanol (5.0 L), and the methanol-insoluble component was separated. As a result, modified BR (specific modified BR3) (740 g, Mn = 6,300, Mw = 9,400, Mw / Mn = 1.5) having the functional group represented by the above formula (m1) at the terminal was obtained in a yield of 95%. In addition, by IR analysis, cis / trans / vinyl was estimated to be 24 / 38 / 38. Further, Tg was -76°C. Further, the viscosity (after modification / before modification) was 181%.

[0184] <Specific Modified BR4>

[0185] n-BuLi (manufactured by Kanto Chemical Co., Inc.: 1.60 mol / L (hexane solution), 92 mL, 147.2 mmol) was added to a mixed solution of 1,3-butadiene (762 g, 14078 mmol) and 2,2-bis(2-tetrahydrofuryl)propane (manufactured by Tokyo Chemical Industry Co., Ltd., 0.25 mL, 1.36 mmol) in cyclohexane (4.15 kg), and the mixture was stirred at room temperature for 6 hours. After the reaction, 1,1,1-trimethyl-N-[3-(trimethoxysilyl)propyl]-N-(trimethylsilyl)silanamine (the following structure) (59 g, 185 mmol) was added to terminate the polymerization.

[0186]

[0187] The resulting solution was taken out and concentrated under reduced pressure. The concentrated solution was poured into methanol (10 L), and the methanol-insoluble component was separated. As a result, modified BR (specific modified BR4) (740 g, Mn = 8,000, Mw = 9,500, Mw / Mn = 1.2) having the functional group represented by the above formula (m1) at the terminal was obtained in a yield of 97%. In addition, by IR analysis, cis / trans / vinyl was estimated to be 26 / 45 / 29. Further, Tg was -82°C. Further, the viscosity (after modification / before modification) was 163%.

[0188] 〔Preparation of Rubber Composition〕

[0189] Mix the components shown in Table 1 below in the proportions (parts by mass) shown in the table.

[0190] Specifically, first, mix the components other than sulfur and vulcanization accelerators shown in Table 1 below using a Banbury mixer at 80°C for 5 minutes. Next, using an open mill, mix sulfur and vulcanization accelerators to obtain a rubber composition.

[0191] In addition, in Table 1, regarding the amount of SBR, the upper value is the amount of SBR (oil-extended) (unit: parts by mass), and the lower value is the net weight amount of SBR contained in the SBR (unit: parts by mass).

[0192] 〔Evaluation〕

[0193] Regarding each of the obtained rubber compositions, evaluation was carried out as described below.

[0194] <Dispersibility>

[0195] For each of the obtained rubber compositions (unvulcanized), press vulcanize at 160°C for 15 minutes in a mold (15 cm × 15 cm × 0.2 cm) to produce a vulcanized rubber sheet.

[0196] Furthermore, regarding the produced vulcanized rubber sheet, using a strain shear stress measuring machine (RPA2000, manufactured by α-Technology Co., Ltd.), measure the strain shear elastic modulus G' at a strain of 0.28% and the strain shear elastic modulus G' at a strain of 30.0%, and calculate the difference G'0.28 (MPa) - G'30.0 (MPa) as the Payne effect.

[0197] The results are shown in Table 1. The results are expressed as an index with Comparative Example 1 set to 100. The smaller the index, the more excellent the dispersibility of the reinforcing filler.

[0198] <Processability>

[0199] Regarding each of the obtained rubber compositions (unvulcanized), according to JIS K6300-1:2013, measure the Mooney viscosity (ML 1+4 ) at 100°C.

[0200] The results are shown in Table 1. The results are expressed as an index with Comparative Example 1 set to 100. The smaller the index, the lower the viscosity and the more excellent the processability.

[0201] <Elongation at break>

[0202] Regarding the vulcanized rubber sheet produced as described above, punch out JIS No. 3 dumbbell test pieces (thickness 2 mm) according to JIS K6251:2010, and evaluate the elongation at break under the conditions of a temperature of 20°C and a tensile speed of 500 mm / minute.

[0203] The results are shown in Table 1. The results are expressed as an index with the elongation at break of Comparative Example 1 set to 100. The larger the index, the more excellent the toughness.

[0204] <Low heat generation>

[0205] Regarding the vulcanized rubber sheet produced as described above, using a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.), the loss tangent tanδ(60°C) at a temperature of 60°C was measured under the conditions of an initial strain of 10%, an amplitude of ±2%, and a frequency of 20 Hz.

[0206] The results are shown in Table 1. The results are expressed as an index with Comparative Example 1 set to 100. The smaller the index, the more excellent the low heat generation.

[0207] <Abrasion resistance>

[0208] Regarding the vulcanized rubber sheet produced as described above, in accordance with JIS K6264-1,2:2005, using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho), the abrasion loss was measured under the conditions of a temperature of 20°C and a sliding rate of 50%. Furthermore, the abrasion resistance index was calculated by the following formula.

[0209] The results are shown in Table 1. The larger the index, the smaller the abrasion loss and the more excellent the abrasion resistance.

[0210] Abrasion resistance index = (abrasion loss of Comparative Example 1 / abrasion loss of each vulcanized rubber sheet) × 100

[0211] [Table 1]

[0212]

[0213] The details of each component shown in Table 1 above are as follows.

[0214] · SBR: Toughden F3420 (SBR, Mw = over 15,000, styrene unit content = 36% by mass, Tg = -27°C, oil-extended product containing 25 parts by mass of oil relative to 100 parts by mass of the rubber component, manufactured by Asahi Kasei Chemicals Corporation)

[0215] · BR: Nipol BR1220 (BR, Mw = 490,000, Tg = -105°C, manufactured by Zeon Corporation, Japan)

[0216] · Carbon black: Sheet KH manufactured by Tokai Carbon Co., Ltd.

[0217] · Silica: Zeosil Premium 200MP (silica, N2SA = 200 m 2 / g, CTAB = 200 m 2 / g, N2SA / CTAB = 1.0 (manufactured by Rhodia)

[0218] · Silane coupling agent: Si69 manufactured by Evonik Degussa

[0219] · Unmodified BR1: LBR-302 (unmodified BR, Mw = 5,500, Mw / Mn = 1.1, Tg = -85°C, viscosity = 1,199 mPa·s, manufactured by Kuraray)

[0220] · Unmodified BR2: LBR-307 (unmodified BR, Mw = 8,000, Mw / Mn = 1.1, Tg = -95°C, viscosity = 2,350 mPa·s, manufactured by Kuraray)

[0221] · Comparative modified BR1: Comparative modified BR1 synthesized as described above (modified BR having the functional group shown in the above formula (m1) at the end, Mw = 19,200, Mw / Mn = 1.1, vinyl / trans / cis = 21 / 33 / 46, Tg = -70°C, viscosity = 7,584 mPa·s)

[0222] · Comparative modified BR2: Comparative modified BR2 synthesized as described above (modified BR having the functional group shown in the above formula (m1) at the end, Mw = 8,800, Mw / Mn = 2.2, vinyl / trans / cis = 23 / 38 / 39, Tg = -77°C, viscosity = 2,157 mPa·s)

[0223] · Specific modified BR1: Specific modified BR1 synthesized as described above (modified BR having the functional group shown in the above formula (m1) at the end, Mw = 4,400, Mw / Mn = 1.1, vinyl / trans / cis = 31 / 45 / 24, Tg = -83°C, viscosity = 2,350 mPa·s)

[0224] · Specific modified BR2: Specific modified BR2 synthesized as described above (modified BR having the functional group shown in the above formula (m1) at the end, Mw = 8,100, Mw / Mn = 1.1, vinyl / trans / cis = 24 / 40 / 36, Tg = -80°C, viscosity = 4,794 mPa·s)

[0225] · Specific modified BR3: Specific modified BR3 synthesized as described above (modified BR having the functional group shown in the above formula (m1) at the end, Mw = 9,400, Mw / Mn = 1.5, vinyl / trans / cis = 24 / 38 / 38, Tg = -76°C, viscosity = 4,251 mPa·s)

[0226] · Specific modified BR4: The specific modified BR4 synthesized as described above (modified BR having a functional group represented by the above formula (m1) at the terminal, Mw = 9,500, Mw / Mn = 1.2, vinyl / trans / cis = 26 / 45 / 29, Tg = -82 °C, viscosity = 4,876 mPa·s)

[0227] · Stearic acid: Stearic acid YR (manufactured by NOF Corporation)

[0228] · Processing aid: Actiplast ST (manufactured by Rhein Chemie)

[0229] · Antioxidant: Santoflex 6PPD (manufactured by Soltia Europe)

[0230] · Oil: Extract No. 4S (manufactured by Showa Shell Sekiyu)

[0231] · Zinc oxide: Zinc oxide No. 3 (manufactured by Shodo Chemical)

[0232] · Sulfur: Oil-treated sulfur (manufactured by Karuizawa Refinery)

[0233] · Vulcanization accelerator CZ: Nocceler CZ-G (manufactured by Ouchi Shinko Chemical Industry)

[0234] · Vulcanization accelerator DPG: Soxinol D-G (manufactured by Sumitomo Chemical)

[0235] In addition, in Table 1, "Tg of the rubber component" represents the "Tg of the rubber component" described above.

[0236] As can be seen from Table 1, Examples 1 to 6 containing the specific modified BR showed excellent dispersibility, processability, toughness, low heat generation, and abrasion resistance compared to Comparative Example 1 not containing the specific modified BR.

[0237] On the other hand, in Comparative Examples 2 and 3 containing a butadiene polymer having no specific functional group at the terminal, Comparative Example 4 containing a modified BR having a specific functional group at the terminal but Mw exceeding 15,000, and Comparative Example 5 containing a modified BR having a specific functional group at the terminal but Mw / Mn exceeding 2.0, the dispersibility was insufficient.

[0238] Here, from the comparison between Examples 1 to 4, Comparative Example 4, and Comparative Example 5, it can be seen that by making the Mw of the modified BR 1,000 or more and 15,000 or less and making Mw / Mn 2.0 or less, the dispersibility is significantly improved. That is, a significant criticality is observed between the size (Mw, Mw / Mn) of the modified BR and the dispersibility of the reinforcing filler.

[0239] From the comparison of Examples 1 to 4 (comparison between the cases where the content of the specific modified BR is 6.7% by mass relative to the content of the reinforcing filler), Examples 1 to 3 in which the terminal of the specific modified BR is modified with a cyclic silazane showed excellent dispersibility, processability, toughness, and low heat generation. It is presumed that this is because the modification rate of the specific modified BR whose terminal is modified with a cyclic silazane is higher. Among them, Examples 1 and 2 in which the Mw / Mn of the specific modified BR is 1.3 or less showed more excellent processability, low heat generation, and abrasion resistance. Among them, Example 2 in which the Mw of the specific modified BR is 5,000 or more showed excellent dispersibility, processability, low heat generation, and abrasion resistance.

[0240] From the comparison of Examples 2, 5, and 6 (comparison between the cases where specific modified BR2 is used as the specific modified BR), in Example 2 where the content of the specific modified BR is 2.0 to 10.0% by mass relative to the content of the reinforcing filler, the balance of dispersibility, processability, toughness, low heat generation, and abrasion resistance is excellent at an extremely high level.

Claims

1. A rubber composition containing: a rubber component having a weight-average molecular weight exceeding 15,000; a filler for reinforcement; and a modified butadiene polymer, The content of the filler for reinforcement is 50 to 200 parts by mass relative to 100 parts by mass of the rubber component, The content of the modified butadiene polymer is 1 to 25% by mass relative to the content of the filler for reinforcement, The filler for reinforcement is selected from at least one of carbon black and silica, The modified butadiene polymer has a functional group containing a nitrogen atom and a silicon atom at the terminal, The weight-average molecular weight of the modified butadiene polymer is 1,000 or more and 15,000 or less, the molecular weight distribution is 2.0 or less, and the proportion of the vinyl structure is 20 to 40 mol%.

2. The rubber composition according to claim 1, wherein the viscosity of the modified butadiene polymer is 150 to 240% of the viscosity of the butadiene polymer before modification, wherein, The viscosity is measured using a cone-plate viscometer.

3. The silica in the rubber composition according to claim 1 or 2 has a nitrogen adsorption specific surface area of 194 m 2 / g or more, a CTAB adsorption specific surface area of 185 m 2 / g or more, and the ratio of the nitrogen adsorption specific surface area to the CTAB adsorption specific surface area is 0.9 to 1.

4.

4. The rubber composition according to claim 1, further containing a silane coupling agent, The content of the silane coupling agent is 1 to 20% by mass relative to the content of the silica.

5. The rubber composition according to claim 3, further containing a silane coupling agent, The content of the silane coupling agent is 1 to 20% by mass relative to the content of the silica.

6. The rubber composition according to any one of claims 1, 2, 4, and 5, wherein the glass transition temperature of the rubber component is -60°C or higher.

7. The rubber composition according to claim 3, wherein the glass transition temperature of the rubber component is -60°C or higher.

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