US20130053491A1

US20130053491A1 - Rubber composition for tire, and pneumatic tire

Info

Publication number: US20130053491A1
Application number: US13/641,954
Authority: US
Inventors: Yasuhisa Minagawa
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2010-04-19
Filing date: 2011-02-28
Publication date: 2013-02-28
Also published as: EP2562213A4; US10005893B2; EP2562213B1; JP5552158B2; US20150299423A1; EP2562213A1; CN102844368A; WO2011132461A1; BR112012026865A2; CN102844368B; JPWO2011132461A1

Abstract

The present invention provides a rubber composition for a tire, which has an increased rate of reaction between a silane coupling agent and silica so that its performances including fuel economy and abrasion resistance can be enhanced; and a pneumatic tire formed from the rubber composition. The present invention relates to a rubber composition for a tire, containing: diene rubber; silica; a silane coupling agent; and a carbonate salt and/or a hydrogen carbonate salt, wherein the rubber composition has a total content of the carbonate salt and the hydrogen carbonate salt of 0.3 to 25 parts by mass relative to 100 parts by mass of the silica.

Description

TECHNICAL FIELD

The present invention relates to a rubber composition for a tire, and a pneumatic tire formed from the rubber composition.

BACKGROUND ART

Conventionally, silica has been used as a reinforcing filler in order to enhance the performances of tires such as durability (abrasion resistance) and fuel economy. Also, because a satisfactory effect cannot be achieved by using silica alone, silica has been used in combination with a silane coupling agent that bonds silica to the rubber component.
In order for a silane coupling agent to react with silica, it is necessary for an alkoxy group or the like bonded to the silicon atom in the silane coupling agent to be hydrolyzed to form a silanol group. However, because hydrolysis reaction of an alkoxy group or the like will not proceed in a short period of time, it has been difficult to bring about sufficient hydrolysis of an alkoxy group or the like in a rubber kneading step. Conventionally, therefore, the rate of reaction between a silane coupling agent and silica is low and the performance of silica cannot be maximized.
As the method for solving the above-mentioned problem, Patent Literatures 1 to 3 disclose adding boric acid or the like in a rubber composition. Still, further improvement in terms of the rate of reaction and the like is desired.

CITATION LIST

Patent Literature

Patent Literature 1: JP-A 2007-77322
Patent Literature 2: JP-A 2001-247718
Patent Literature 3: JP-A 2005-232295

SUMMARY OF INVENTION

Technical Problem

An object of the present invention is to solve the aforementioned problem and provide a rubber composition for a tire, which has an increased rate of reaction between a silane coupling agent and silica so that its performances including fuel economy and abrasion resistance can be enhanced; and a pneumatic tire formed from the rubber composition.

Solution to Problem

As a result of diligent research into how to solve the aforementioned problem, the inventor of the present invention has found that a carbonate salt, a hydrogen carbonate salt or carbon dioxide, which is generated by the decomposition of these salts, promotes a hydrolysis reaction of an alkoxy group or the like, thereby improving the rate of reaction between a silane coupling agent and silica, and has thereby completed the present invention.
The present invention relates to a rubber composition for a tire, containing: diene rubber; silica; a silane coupling agent; and at least one of a carbonate salt and a hydrogen carbonate salt, wherein the rubber composition has a total content of the carbonate salt and the hydrogen carbonate salt of 0.3 to 25 parts by mass relative to 100 parts by mass of the silica.
Preferably, the carbonate salt is at least one selected from the group consisting of sodium carbonate, potassium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate, and the hydrogen carbonate salt is at least one selected from the group consisting of sodium hydrogen carbonate, potassium hydrogen carbonate and ammonium hydrogen carbonate.
Preferably, the carbonate salt is at least one selected from the group consisting of sodium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate, and the hydrogen carbonate salt is ammonium hydrogen carbonate.
Preferably, the potassium carbonate has an average particle size of 40 μm or smaller.
Preferably, the silane coupling agent is at least one selected from the group consisting of a sulfide-type silane coupling agent, a silane coupling agent represented by formula (1):
wherein R¹is a group represented by —O—(R⁵—O)_m—R⁶in which m pieces of R⁵are the same or different and each denote a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms, R⁶denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms, and m is an integer between 1 and 30; R²and R³are the same or different and each denote a group as defined for R¹, a branched or unbranched alkyl group having 1 to 12 carbon atoms, or a group represented by —O—R⁷in which R⁷denotes a hydrogen atom, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms; and R⁴denotes a branched or unbranched alkylene group having 1 to 30 carbon atoms, and
a silane coupling agent containing linking units A and B respectively represented by formulae (2) and (3):
wherein x is an integer of 0 or higher; y is an integer of 1 or higher; R⁸denotes a hydrogen atom, a halogen atom, a branched or unbranched alkyl or alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenyl or alkenylene group having 2 to 30 carbon atoms, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or a group in which a terminal of the alkyl or alkenyl group is substituted with a hydroxyl or carboxyl group; R⁹denotes a hydrogen atom, a branched or unbranched alkylene or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene or alkynyl group having 2 to 30 carbon atoms; and R⁸and R⁹may together form a ring structure.
Preferably, 5 to 150 parts by mass of the silica is contained relative to 100 parts by mass of the diene rubber, and 2 to 20 parts by mass of the silane coupling agent is contained relative to 100 parts by mass of the silica.
Preferably, the rubber composition for a tire is obtained by a production method including: a step (A) of kneading diene rubber, silica, a silane coupling agent, and at least one of a carbonate salt and a hydrogen carbonate salt, and discharging the resulting kneaded mixture A; a step (B) of kneading the kneaded mixture A discharged in the step (A), stearic acid and zinc oxide, and discharging the resulting kneaded mixture B; and a step (C) of kneading the kneaded mixture B discharged in the step (B), a vulcanizing agent and a vulcanization accelerator.
Preferably, the rubber composition for a tire is obtained by a production method including: a step (a) of kneading diene rubber, silica, a silane coupling agent, and at least one of a carbonate salt and a hydrogen carbonate salt, adding thereto stearic acid and zinc oxide, further kneading them, and discharging the resulting kneaded mixture a; and a step (b) of kneading the kneaded mixture a discharged in the step (a), a vulcanizing agent and a vulcanization accelerator.
The present invention also relates to a pneumatic tire formed from the rubber composition.

Advantageous Effects of Invention

According to the present invention, the rubber composition for a tire contains: diene rubber; silica; a silane coupling agent; and a predetermined amount of a carbonate salt and/or a hydrogen carbonate salt, and therefore has an increased rate of reaction between the silane coupling agent and silica so that its performances including fuel economy and abrasion resistance can be enhanced. Therefore, by using this rubber composition in various tire components, it is possible to provide pneumatic tires having excellent fuel economy and abrasion resistance.

DESCRIPTION OF EMBODIMENTS

The rubber composition for a tire of the present invention contains: diene rubber; silica; a silane coupling agent; and a predetermined amount of a carbonate salt and/or a hydrogen carbonate salt.
Rubbers able to be used as the diene rubber in the present invention are not particularly limited, and include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), styrene-isoprene-butadiene rubber (SIBR), styrene-isoprene rubber (SIR) and isoprene-butadiene rubber. It is possible to use one type of diene rubber or a combination of two or more types thereof. Of these, SBR, NR, IR and BR are preferred because they can enhance the abrasion resistance so that good abrasion resistance, fuel economy and wet grip performance can be obtained. Also, using oil-free SBR (non-oil-extended SBR) can also lead to such an effect.
Examples of SBR able to be used include emulsion polymerized styrene-butadiene rubber (E-SBR) and solution polymerized styrene-butadiene rubber (S-SBR). Of these, S-SBR is preferred because it can enhance the abrasion resistance so that both this performance and fuel economy can be satisfied.
The bound styrene content in SBR is preferably 40% by mass or lower, more preferably 35% by mass or lower, further preferably 30% by mass or lower, and particularly preferably 28% by mass or lower. If the bound styrene content exceeds 40% by mass, the glass transition temperature (Tg) tends to increase and the abrasion resistance tends to deteriorate. Also, the bound styrene content in SBR is preferably 10% by mass or higher, more preferably 20% by mass or higher, and further preferably 24% by mass or higher. If the bound styrene content is less than 10% by mass, the Tg value may be too low and it may not be possible to achieve satisfactory wet grip performance.
Here, the styrene content can be calculated by ¹H-NMR measurement.
The content of SBR is preferably 50% by mass or higher, and more preferably 60% by mass or higher, based on 100% by mass of the diene rubber. If the content is lower than 50% by mass, it may not be possible to achieve satisfactory wet grip performance. The content may be 100% by mass, but is preferably 90% by mass or lower, and more preferably 70% by mass or lower. If the content exceeds 90% by mass, the fuel economy may deteriorate.
Examples of NR able to be used include those commonly used in the tire industry, such as SIR20, RSS#3 and TSR20.
The content of NR is preferably 20% by mass or higher, and more preferably 30% by mass or higher, based on 100% by mass of the diene rubber. If the content is lower than 20% by mass, the rubber strength may deteriorate, which may cause separation of rubber pieces. The content is preferably 85% by mass or lower, more preferably 70% by mass or lower, further preferably 50% by mass or lower, and particularly preferably 40% by mass or lower. If the content exceeds 85% by mass, the wet grip performance may deteriorate.
Silica is used in the present invention. Compounding silica can lead to enhancement in wet grip performance and fuel economy and also improvement of abrasion resistance due to its reinforcing effect. The type of silica used is not particularly limited, and may be, for example, dry silica (silicic anhydride) or wet silica (hydrous silicic acid), but wet silica is preferred because it has a large amount of silanol groups.
The nitrogen adsorption specific surface area (N₂SA) of silica is preferably 40 m²/g or higher, more preferably 50 m²/g or higher, further preferably 100 m²/g or higher, and particularly preferably 150 m²/g or higher. If the nitrogen adsorption specific surface area is lower than 40 m²/g, it may not be possible to achieve satisfactory abrasion resistance. Also, the N₂SA of silica is preferably 220 m²/g or lower, and more preferably 200 m²/g or lower. If the N₂SA exceeds 220 m²/g, dispersion of the silica may be difficult so that dispersion problems may occur.
Here, the nitrogen adsorption specific surface area of silica is a value measured using the BET method in accordance with ASTM D3037-81.
The content of silica is preferably 5 parts by mass or higher, and more preferably 15 parts by mass or higher, relative to 100 parts by mass of the diene rubber. If the content is lower than 5 parts by mass, satisfactory rubber strength may not be obtained and the abrasion resistance may deteriorate. The content of silica is preferably 150 parts by mass or lower, and more preferably 120 parts by mass or lower. If the content exceeds 150 parts by mass, the silica dispersibility tends to deteriorate and the abrasion resistance tends to deteriorate.
A silane coupling agent is used in the present invention. Compounding a silane coupling agent brings about bonding between rubber and silica, thereby enhancing performance such as abrasion resistance.
The silane coupling agent is not particularly limited, and examples thereof include sulfide-type silane coupling agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(4-trimethoxysilylbutyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-triethoxysilylbutyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(2-trimethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide and 3-trimethoxysilylpropyl methacrylate monosulfide; mercapto-type silane coupling agents such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyl-type silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-type silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane and 3-(2-aminoethyl)aminopropyltrimethoxysilane; glycidoxy-type silane coupling agents such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane and γ-glycidoxypropylmethyldimethoxysilane; nitro-type silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chlorine-type silane coupling agents such as 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane and 2-chloroethyltriethoxysilane.
Of these, preferred are sulfide-type silane coupling agents (especially, bis(3-triethoxysilylpropyl)disulfide and bis(3-triethoxysilylpropyl)tetrasulfide), silane coupling agents represented by the following formula (1) and silane coupling agents containing linking units A represented by the following formula (2) and linking units B represented by the following formula (3) because they exhibit high rates of reaction with silica so that excellent abrasion resistance can be obtained.
In formula (1), R¹is a group represented by —O—(R⁵—O)_m—R⁶in which m pieces of R⁵are the same or different and each denote a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms, R⁶denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms, and m is an integer between 1 and 30; R²and R³are the same or different and each denote a group as defined for R¹, a branched or unbranched alkyl group having 1 to 12 carbon atoms, or a group represented by —O—R⁷in which R⁷denotes a hydrogen atom, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms; and R⁴denotes a branched or unbranched alkylene group having 1 to 30 carbon atoms.
In formulae (2) and (3), x is an integer of 0 or higher; y is an integer of 1 or higher; R⁸denotes a hydrogen atom, a halogen atom, a branched or unbranched alkyl or alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenyl or alkenylene group having 2 to 30 carbon atoms, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or a group in which a terminal of the alkyl or alkenyl group is substituted with a hydroxyl or carboxyl group; R⁹denotes a hydrogen atom, a branched or unbranched alkylene or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene or alkynyl group having 2 to 30 carbon atoms; and R⁸and R⁹may together form a ring structure.
By compounding the silane coupling agent represented by formula (1) above, it is possible to achieve excellent fuel economy and abrasion resistance.
In formula (1) above, R¹is a group represented by —O—(R⁵—O)_m—R⁶in which m pieces of R⁵are the same or different and each denote a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms, R⁶denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms, and m is an integer between 1 and 30.
The R⁵groups are the same or different and each denote a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms (preferably 1 to 15 carbon atoms, and more preferably 1 to 3 carbon atoms).
Examples of this hydrocarbon group include branched or unbranched alkylene groups having 1 to 30 carbon atoms, branched or unbranched alkenylene groups having 2 to 30 carbon atoms, branched or unbranched alkynylene groups having 2 to 30 carbon atoms and arylene groups having 6 to 30 carbon atoms. Of these, the alkylene groups are preferred because they can bond (react) readily with silica so that the fuel economy and abrasion resistance can be satisfactorily enhanced.
The branched or unbranched alkylene groups having 1 to 30 carbon atoms (preferably 1 to 15 carbon atoms, and more preferably 1 to 3 carbon atoms) of R⁵include, for example, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, a tridecylene group, a tetradecylene group, a pentadecylene group, a hexadecylene group, a heptadecylene group and an octadecylene group.
The branched or unbranched alkenylene groups having 2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, and more preferably 2 to 3 carbon atoms) of R⁵include, for example, a vinylene group, a 1-propenylene group, a 2-propenylene group, a 1-butenylene group, a 2-butenylene group, a 1-pentenylene group, a 2-pentenylene group, a 1-hexenylene group, a 2-hexenylene group and a 1-octenylene group.
The branched or unbranched alkynylene groups having 2 to 30 carbon atoms (preferably 2 to 15 carbon atoms, and more preferably 2 to 3 carbon atoms) of R⁵include, for example, an ethynylene group, a propynylene group, a butynylene group, a pentynylene group, a hexynylene group, a heptynylene group, an octynylene group, a nonynylene group, a decynylene group, an undecynylene group and a dodecynylene group.
The arylene groups having 6 to 30 carbon atoms (preferably 6 to 15 carbon atoms) of R⁵include, for example, a phenylene group, a tolylene group, a xylylene group and a naphthylene group.
The m denotes an integer between 1 and 30 (preferably between 2 and 20, more preferably between 3 and 7, and further preferably between 5 and 6). If m is 0, the bonding (reaction) with silica is adversely affected, whereas if m is 31 or higher, the reactivity with silica decreases, which is disadvantageous from the perspective of the process.
R⁶denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms. Among these, R⁶is preferably a branched or unbranched alkyl group having 1 to 30 carbon atoms because it leads to good reactivity with silica.
Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms (preferably 3 to 25 carbon atoms, and more preferably 10 to 15 carbon atoms) of R⁶include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group and an octadecyl group.
Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms (preferably 3 to 25 carbon atoms, and more preferably 10 to 15 carbon atoms) of R⁶include a vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 1-pentenyl group, a 2-pentenyl group, a 1-hexenyl group, a 2-hexenyl group, a 1-octenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group and an octadecenyl group.
Examples of the aryl group having 6 to 30 carbon atoms (preferably 10 to 20 carbon atoms) of R⁶include a phenyl group, a tolyl group, a xylyl group, a naphthyl group and a biphenyl group.
Examples of the aralkyl group having 7 to 30 carbon atoms (preferably 10 to 20 carbon atoms) of R⁶include a benzyl group and a phenethyl group.
Specific examples of R¹in formula (1) above include —O—(C₂H₄—O)₅—C₁₁H₂₃, —O—(C₂H₄—O)₅—C₁₂H₂₅, —O—(C₂H₄—O)₅—C₁₃H₂₇, —O—(C₂H₄—O)₅—C₁₄H₂₉, —O—(C₂H₄—O)₅—C₁₅H₃₁, —O—(C₂H₄—O)₃—C₁₃H₂₇, —O—(C₂H₄—O)₄—C₁₃H₂₇, —O—(C₂H₄—O)₆—C₁₃H₂₇and —O—(C₂H₄—O)₇—C₁₃H₂₇. Of these, —O—(C₂H₄—O)₅—C₁₁H₂₃, —O—(C₂H₄—O)₅—C₁₃H₂₇, —O—(C₂H₄—O)₅—C₁₅H₃₁and —O—(C₂H₄—O)₆—C₁₃H₂₇are preferred.
R²and R³are the same or different and each denote a group as defined for R¹(that is, a group represented by —O—(R⁵—O)_m—R⁶), a branched or unbranched alkyl group having 1 to 12 carbon atoms, or a group represented by —O—R⁷in which R⁷denotes a hydrogen atom, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms. Among these, R²and R³each are preferably a group as defined for R¹or a group represented by —O—R⁷in which R⁷denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms because they exhibit good reactivity with silica.
Examples of the branched or unbranched alkyl group having 1 to 12 carbon atoms (preferably 1 to 8 carbon atoms, and more preferably 1 to 5 carbon atoms) for R²and R³include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group and a nonyl group.
Examples of the branched or unbranched alkyl group having 1 to 30 carbon atoms (preferably 1 to 15 carbon atoms, and more preferably 1 to 3 carbon atoms) of R⁷include the same groups as mentioned as the branched or unbranched alkyl group having 1 to 30 carbon atoms of R⁶.
Examples of the branched or unbranched alkenyl group having 2 to 30 carbon atoms of R⁷include the same groups as mentioned as the branched or unbranched alkenyl group having 2 to 30 carbon atoms of R⁶.
Examples of the aryl group having 6 to 30 carbon atoms of R⁷include the same groups as mentioned as the aryl group having 6 to 30 carbon atoms of R⁶.
Examples of the aralkyl group having 7 to 30 carbon atoms of R⁷include the same groups as mentioned as the aralkyl group having 7 to 30 carbon atoms of R⁶.
Specific examples of R²and R³in formula (1) above include —O—(C₂H₄—O)₅—C₁₁H₂₃, —O—(C₂H₄—O)₅—C₁₂H₂₅, —O—(C₂H₄—O)₅—C₁₃H₂₇, —O—(C₂H₄—O)₅—C₁₄H₂₉, —O—(C₂H₄—O)₅—C₁₅H₃₁, —O—(C₂H₄—O)₃—C₁₃H₂₇, —O—(C₂H₄—O)₄C₁₃H₂₇, —O—(C₂H₄—O)₆—C₁₃H₂₇, —O—(C₂H₄—O)₇—C₁₃H₂₇, C₂H₅—O—, CH₃—O— and C₃H₇—O—. Of these, —O—(C₂H₄—O)₅—C₁₁H₂₃, —O—(C₂H₄—O)₅—C₁₃H₂₇, —O—(C₂H₄—O)₅—C₁₅H₃₁, —O—(C₂H₄—O)₆—C₁₃H₂₇and C₂H₅—O— are preferred.
Examples of the branched or unbranched alkylene group having 1 to 30 carbon atoms (preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms) of R⁴include the same groups as mentioned as the branched or unbranched alkylene group having 1 to 30 carbon atoms of R⁵.
The silane coupling agent represented by formula (1) above may be, for example, Si363 produced by Degussa. It is possible to use one of such silane coupling agents or a combination of two or more thereof.
Also, by compounding a silane coupling agent containing linking units B represented by formula (3) above and optionally linking units A represented by formula (2) above, it is possible to enhance the fuel economy and abrasion resistance compared with a case in which a conventional silane coupling agent, such as bis(3-triethoxysilylpropyl)tetrasulfide, is used.
The silane coupling agent containing linking units A and B is preferably a copolymer in which the proportion of linking units B is 1 to 70 mol % of the total molar amount of linking units A and B.
If the molar ratio of linking units A and B satisfies this condition, an increase in viscosity during processing can be suppressed compared with cases in which polysulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide are used. This is thought to be because the sulfide moiety in linking unit A is a C—S—C bond and is therefore more thermally stable than tetrasulfide or disulfide, which leads to less increase in Mooney viscosity.
Also, if the molar ratio of linking units A and B satisfies the condition, a reduction in scorch time can be suppressed compared with cases in which mercaptosilanes such as 3-mercaptopropyltrimethoxysilane are used. This is thought to be because although linking unit B has a mercaptosilane structure, the —C₇H₁₅moiety in linking unit A covers the —SH group in linking unit B, and the silane coupling agent is therefore less likely to react with the polymer, which leads to less scorching.
The halogen atom of R⁸may be chlorine, bromine, fluorine or the like.
Examples of the branched or unbranched alkyl groups having 1 to 30 carbon atoms (preferably 1 to 12 carbon atoms, and more preferably 1 to 5 carbon atoms) for R⁸and R⁹include the same groups as mentioned as the branched or unbranched alkyl group having 1 to 30 carbon atoms of R⁶.
Examples of the branched or unbranched alkylene groups having 1 to 30 carbon atoms (preferably 1 to 12 carbon atoms) for R⁸and R⁹include the same groups as mentioned as the branched or unbranched alkylene group having 1 to 30 carbon atoms of R⁵.
Examples of the branched or unbranched alkenyl groups having 2 to 30 carbon atoms (preferably 2 to 12 carbon atoms) for R⁸and R⁹include the same groups as mentioned as the branched or unbranched alkenyl group having 2 to 30 carbon atoms of R⁶.
Examples of the branched or unbranched alkenylene groups having 2 to 30 carbon atoms (preferably 2 to 12 carbon atoms) for R⁸and R⁹include the same groups as mentioned as the branched or unbranched alkenylene group having 2 to 30 carbon atoms of R⁵.
Examples of the branched or unbranched alkynyl groups having 2 to 30 carbon atoms (preferably 2 to 12 carbon atoms) for R⁸and R⁹include an ethynyl group, a propynyl group, a butynyl group, a pentynyl group, a hexynyl group, a heptynyl group, an octynyl group, a nonynyl group, a decynyl group, an undecynyl group and a dodecynyl group.
Examples of the branched or unbranched alkynylene groups having 2 to 30 carbon atoms (preferably 2 to 12 carbon atoms) for R⁸and R⁹include the same groups as mentioned as the branched or unbranched alkynylene group having 2 to 30 carbon atoms of R⁵.
In the silane coupling agent containing linking units A and B, the total number of repetitions (x+y) of the number of repetitions (x) of linking unit A and the number of repetitions (y) of linking unit B is preferably in the range of 3 to 300. If x+y is in this range and x is 1 or higher, the —C₇H₁₅moiety in linking unit A covers the mercaptosilane in linking unit B, and it is therefore possible to suppress a reduction in scorch time and to ensure good reactivity with silica and with the rubber component.
Examples of the silane coupling agent containing linking units A and B include NXT-Z30, NXT-Z45, NXT-Z60 and NXT-Z100 all of which are produced by Momentive. It is possible to use one of such silane coupling agents or a combination of two or more thereof.
The content of the silane coupling agent is preferably 2 parts by mass or higher, more preferably 4 parts by mass or higher, and further preferably 6 parts by mass or higher, relative to 100 parts by mass of the silica. If the content is lower than 2 parts by mass, it tends not be possible to produce a satisfactory effect to enhance the fuel economy. Also, the content of the silane coupling agent is preferably 20 parts by mass or lower, more preferably 15 parts by mass or lower, and further preferably 10 parts by mass or lower. If the content exceeds 20 parts by mass, the fuel economy and abrasion resistance tend to fail to be improved with increase in the content and therefore costs tend to increase.
In cases where two or more silane coupling agents are used in combination, the content means the total content of the silane coupling agents.
At least one compound selected from the group consisting of carbonate salts and hydrogen carbonate salts is compounded in the present invention. This promotes a hydrolysis reaction of an alkoxy group or the like in the silane coupling agent and therefore a hydrolysis reaction of an alkoxy group or the like will proceed sufficiently (that is, silanol groups will be sufficiently produced) in the rubber composition kneading step, which can lead to an increased rate of reaction between the silane coupling agent and silica. Therefore, the fuel economy and abrasion resistance of the resulting rubber composition (pneumatic tire) can be enhanced.
Suitable carbonate salts and hydrogen carbonate salts are inorganic carbonate salts and inorganic hydrogen carbonate salts from the perspective of increasing the rate of reaction between the silane coupling agent and silica. Examples of the inorganic carbonate salts include alkali metal carbonates such as sodium carbonate, potassium carbonate and lithium carbonate; ammonium carbonate; and alkaline earth metal carbonates such as calcium carbonate and magnesium carbonate. Examples of the inorganic hydrogen carbonate salts include alkali metal hydrogen carbonates such as sodium hydrogen carbonate, potassium hydrogen carbonate and lithium hydrogen carbonate; ammonium hydrogen carbonate; and alkaline earth metal hydrogen carbonates such as calcium hydrogen carbonate and magnesium hydrogen carbonate. Of these, sodium carbonate, potassium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate, magnesium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and ammonium hydrogen carbonate are preferred, and sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and ammonium hydrogen carbonate are more preferred, in terms of effectively increasing the reaction rate. In particular, ammonium hydrogen carbonate is very suitable because it has a lower melting temperature than metal salts and will decompose into carbon dioxide, ammonia and water, which will then vaporize, in a base kneading step, so that no adverse effect is caused on vulcanization in a final kneading step and therefore good vulcanization is ensured. Here, because ammonium hydrogen carbonate has a low decomposition temperature and some amount will vaporize in the step, it needs to be added in an amount somewhat larger than those of other inorganic carbonate salts and inorganic hydrogen carbonate salts.
Meanwhile, potassium carbonate having an average particle size of 40 μm or smaller is preferably used. The average particle size is more preferably 30 μm or smaller, and further preferably 20 μm or smaller. If the average particle size exceeds 40 μm, fracture nuclei tend to be formed due to poor dispersion of the potassium carbonate, in other words, foreign matter contaminates the rubber composition, and therefore breakage of the rubber composition tends to occur around foreign matter particles, thereby leading to poor abrasion resistance. Also, the lower limit of the average particle size is not particularly limited, but is preferably 3 μm or greater, and more preferably 5 μm or greater.
The average particle size of potassium carbonate herein is a value measured using a laser diffraction/scattering particle size distribution analyzer (LA-910 manufactured by Horiba, Ltd.).
The total content of the carbonate salt and the hydrogen carbonate salt is 0.3 parts by mass or higher, preferably 0.5 parts by mass or higher, more preferably 1 part by mass or higher, and further preferably 2 parts by mass or higher, relative to 100 parts by mass of the silica. If the total content is lower than 0.3 parts by mass, the rate of reaction between the silane coupling agent and silica tends not to be increased sufficiently, thereby failing to enhance the fuel economy and abrasion resistance. The total content is 25 parts by mass or lower, preferably 20 parts by mass or lower, more preferably 10 parts by mass or lower, and further preferably 6 parts by mass or lower. If the total content exceeds 25 parts by mass, the content of the carbonate salt and hydrogen carbonate salt is so high that the rolling resistance tends to increase to reduce the fuel economy.
In addition to the aforementioned components, compounding ingredients commonly used in the production of rubber compositions, such as carbon black, stearic acid, antioxidants, antiozonants, oil, wax, vulcanizing agents and vulcanization accelerators, may be compounded as appropriate in the rubber composition of the present invention.
Usable antioxidants include amine antioxidants, for example, diphenylamine derivatives such as p-(p-toluenesulfonylamide)-diphenylamine; and p-phenylenediamine derivatives such as N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) and N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD).
In the rubber composition of the present invention, the content of the antioxidant is preferably 5 parts by mass or lower, more preferably 4 parts by mass or lower, and further preferably 3 parts by mass or lower, relative to 100 parts by mass of the diene rubber.
The rubber composition of the present invention can be produced using an ordinary method. Specifically, the rubber composition can be produced by, for example, kneading the aforementioned components in a Banbury mixer, a kneader, an open roll mill or the like, and then vulcanizing the mixture.
In particular, Production Methods 1 and 2 mentioned below are preferred and Production Method 1 is more preferred because firstly kneading the rubber component, the silica, the silane coupling agent and the carbonate salt and/or hydrogen carbonate salt can lead to an increased rate of reaction between the silane coupling agent and silica and therefore excellent fuel economy and abrasion resistance.

(Production Method 1)

A production method that includes: a step (A) of kneading diene rubber, silica, a silane coupling agent, and a carbonate salt and/or a hydrogen carbonate salt, and discharging the resulting kneaded mixture A; a step (B) of kneading the kneaded mixture A discharged in the step (A), stearic acid and zinc oxide, and discharging the resulting kneaded mixture B; and a step (C) of kneading the kneaded mixture B discharged in the step (B), a vulcanizing agent and a vulcanization accelerator.

(Production Method 2)

A production method that includes: a step (a) of kneading diene rubber, silica, a silane coupling agent, and a carbonate salt and/or a hydrogen carbonate salt, adding thereto stearic acid and zinc oxide, further kneading them, and discharging the resulting kneaded mixture a; and a step (b) of kneading the kneaded mixture a discharged in the step (a), a vulcanizing agent and a vulcanization accelerator.
The kneading processes in the steps in Production Methods 1 and 2 can be carried out using a conventionally known kneading machine and the kneading temperature and time may be set as appropriate. With regard to the kneading temperature in particular, the kneading temperature in the steps (A) and (B) and the kneading temperature in the step (a) (the temperature at which diene rubber, silica, a silane coupling agent, and a carbonate salt and/or a hydrogen carbonate salt are kneaded and the temperature at which stearic acid and zinc oxide are added and further kneaded) each are preferably in the range of 120 to 160° C. Also, the kneading temperature in the steps (C) and (b) is preferably in the range of 70 to 120° C.
Oil, carbon black, an antioxidant, wax and the like may also be kneaded in the kneading process in the step (A) of Production Method 1. Here, it is preferable to knead oil together in this kneading process because the load on the kneading machine can be reduced. Also, an antioxidant, wax and the like may also be kneaded in the kneading process in the step (B).
Meanwhile, oil, carbon black, an antioxidant, wax and the like may also be kneaded in the kneading process in the step (a) of Production Method 2. Also, it is preferable to knead oil together in this kneading process for the same reason as that given above.
The kneading process in the steps (C) and (b) in Production Methods 1 and 2 is carried out, and then the resulting kneaded mixture (unvulcanized rubber composition) is vulcanized for 5 to 40 minutes at 140 to 185° C., whereby a vulcanized rubber composition can be obtained.
By using Production Method 1 or 2, it is possible to increase the rate of reaction between the silica and the silane coupling agent and thereby reduce the amount of unreacted silane coupling agent to 15% by mass or lower (preferably to 10% by mass or lower).
The amount of unreacted silane coupling agent can be measured using the method mentioned in examples given below.
The rubber composition of the present invention can be suitably used in various tire components. In particular, the rubber composition of the present invention is preferably used in treads (cap treads and base treads), sidewalls and clinches for which fuel economy, abrasion resistance and other performances are required.
The pneumatic tire of the present invention can be produced from the rubber composition by an ordinary method.
Specifically, an unvulcanized rubber composition with the aforementioned components compounded therein is extruded and processed into the shape of a tread or the like and then molded with other tire components in a tire building machine by an ordinary method to form an unvulcanized tire. A tire is obtained by heating and pressurizing this unvulcanized tire in a vulcanizer.
The pneumatic tire of the present invention can be suitably used as automotive tires, bus tires, truck tires and the like.

EXAMPLES

The present invention will now be explained in greater detail, referring to examples, but is in no way limited to these examples.
An explanation of the various chemicals used in the examples will now be given.
SBR: SBR Nipol NS210 produced by Zeon Corporation (bound styrene content: 25% by mass, Mooney viscosity (ML₁₊₄, 100° C.): 56) NR: RSS#3
Carbon black: Diablack I produced by Mitsubishi Chemical Corporation
Silica: Ultrasil VN3 produced by Degussa (N₂SA: 175 m²/g)
Silane coupling agent (1): Si266
(bis(3-triethoxysilylpropyl)disulfide) produced by Degussa
Silane coupling agent (2): Si363 produced by Degussa (silane coupling agent represented by formula below (in formula (1) above, R¹═—O—(C₂H₄—O)₅—C₁₃H₂₇, R²═C₂H₅—O—, R³═—O—(C₂H₄—O)₅—C₁₃H₂₇, R⁴═—C₃H₆—))
Silane coupling agent (3): NXT-Z45 produced by Momentive (copolymer of linking units A and B, linking unit A: 55 mol %, linking unit B: 45 mol %)
Aromatic oil: X140 produced by Jomo
Stearic acid: stearic acid beads “Tsubaki” produced by NOF Corporation
Zinc oxide: zinc oxide #2 produced by Mitsui Mining & Smelting Co., Ltd.
Sulfur: sulfur (200 meshes) produced by Tsurumi Chemical Industry Co., Ltd.
Vulcanization accelerator TBBS: Nocceler NS produced by Ouchi Shinko Chemical Industrial Co., Ltd.
Vulcanization accelerator DPG: Nocceler D produced by Ouchi Shinko Chemical Industrial Co., Ltd.
Sodium carbonate: produced by Wako Pure Chemical Industries, Ltd.
Potassium carbonate (1): produced by Wako Pure Chemical Industries, Ltd. (average particle size: 340 μm as measured using a laser diffraction/scattering particle size distribution analyzer (LA-910 manufactured by Horiba, Ltd.))
Potassium carbonate (2): produced by Asahi Glass Co., Ltd. (average particle size: 21 μm as measured described above)
Ammonium carbonate: produced by Wako Pure Chemical Industries, Ltd.
Lithium carbonate: produced by Wako Pure Chemical Industries, Ltd.
Calcium carbonate: produced by Wako Pure Chemical Industries, Ltd.
Magnesium carbonate: produced by Wako Pure Chemical Industries, Ltd.
Potassium hydrogen carbonate: produced by Wako Pure Chemical Industries, Ltd.
Sodium hydrogen carbonate: produced by Wako Pure Chemical Industries, Ltd.
Ammonium hydrogen carbonate: produced by Nissei Corporation

Examples and Comparative Examples

(Preparation of Rubber Test Pieces)

Production Example 1

Examples 1 to 50 and Comparative Examples 1 to 21 (Production Method 1)

100 parts by mass of SBR, 55 parts by mass of silica, 20 parts by mass of carbon black, 10 parts by mass of aromatic oil, and 4.4 parts by mass of silane coupling agent (1) were kneaded with various amounts of carbonate or hydrogen carbonate salts (relative to 100 parts by mass of the silica) shown in Table 1 in a 1.7 L Banbury mixer, followed by discharging when the kneading temperature was 150° C. Thus kneaded mixtures 1 were obtained.
Next, 2 parts by mass of stearic acid and 3 parts by mass of zinc oxide were kneaded with each kneaded mixture 1 in a 1.7 L Banbury mixer, followed by discharging when the kneading temperature was 130° C. Thus kneaded mixtures 2 were obtained.
Further, 1.5 parts by mass of sulfur, 1 part by mass of vulcanization accelerator TBBS and 0.5 parts by mass of vulcanization accelerator DPG were kneaded with each kneaded mixture 2 by a roller to give an unvulcanized rubber sheet (unvulcanized rubber composition).
The obtained unvulcanized rubber composition was press-vulcanized for 20 minutes at 170° C. to give a vulcanized rubber composition.

Production Example 2

Examples 51 to 70 and Comparative Examples 22 to 30 (Production Method 2)

100 parts by mass of SBR, 55 parts by mass of silica, 20 parts by mass of carbon black, 10 parts by mass of aromatic oil, and 4.4 parts by mass of silane coupling agent (1) were kneaded with various amounts of carbonate or hydrogen carbonate salts (relative to 100 parts by mass of the silica) shown in Table 2 in a 1.7 L Banbury mixer, and then 2 parts by mass of stearic acid and 3 parts by mass of zinc oxide were kneaded therewith, followed by discharging when the kneading temperature was 150° C. Thus kneaded mixtures 1 were obtained.
Further, 1.5 parts by mass of sulfur, 1 part by mass of vulcanization accelerator TBBS and 0.5 parts by mass of vulcanization accelerator DPG were kneaded with each kneaded mixture 1 by a roller to give an unvulcanized rubber sheet (unvulcanized rubber composition).
The obtained unvulcanized rubber composition was press-vulcanized for 20 minutes at 170° C. to give a vulcanized rubber composition.

Production Example 3

Examples 71 to 90 and Comparative Examples 31 to 39 (Production Method 3)

100 parts by mass of SBR, 55 parts by mass of silica, 20 parts by mass of carbon black, 10 parts by mass of aromatic oil, 4.4 parts by mass of silane coupling agent (1), 2 parts by mass of stearic acid, and 3 parts by mass of zinc oxide were kneaded with various amounts of carbonate or hydrogen carbonate salts (relative to 100 parts by mass of the silica) shown in Table 3 in a 1.7 L Banbury mixer, followed by discharging when the kneading temperature was 150° C. Thus kneaded mixtures 1 were obtained.
Further, 1.5 parts by mass of sulfur, 1 part by mass of vulcanization accelerator TBBS and 0.5 parts by mass of vulcanization accelerator DPG were kneaded with each kneaded mixture 1 by a roller to give an unvulcanized rubber sheet (unvulcanized rubber composition).
The obtained unvulcanized rubber composition was press-vulcanized for 20 minutes at 170° C. to give a vulcanized rubber composition.

Production Example 4

Examples 91 to 110 and Comparative Examples 40 to 48 (Production Method 1)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 1, except that 6.6 parts by mass of silane coupling agent (2) was used instead of 4.4 parts by mass of silane coupling agent (1) and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 4.

Production Example 5

Examples 111 to 130 and Comparative Examples 49 to 57 (Production Method 2)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 2, except that 6.6 parts by mass of silane coupling agent (2) was used instead of 4.4 parts by mass of silane coupling agent (1) and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 5.

Production Example 6

Examples 131 to 150 and Comparative Examples 58 to 66 (Production Method 1)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 1, except that 4.4 parts by mass of silane coupling agent (3) was used instead of 4.4 parts by mass of silane coupling agent (1) and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 6.

Production Example 7

Examples 151 to 170 and Comparative Examples 67 to 75 (Production Method 2)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 2, except that 4.4 parts by mass of silane coupling agent (3) was used instead of 4.4 parts by mass of silane coupling agent (1) and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 7.

Production Example 8

Examples 171 to 220 and Comparative Examples 76 to 96 (Production Method 1)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 1, except that the rubber component was changed to include 70 parts by mass of SBR and 30 parts by mass of NR and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 8.

Production Example 9

Examples 221 to 240 and Comparative Examples 97 to 105 (Production Method 1)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 1, except that the rubber component was changed to include 70 parts by mass of SBR and 30 parts by mass of NR, 6.6 parts by mass of silane coupling agent (2) was used instead of 4.4 parts by mass of silane coupling agent (1), and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 9.

Production Example 10

Examples 241 to 260 and Comparative Examples 106 to 114 (Production Method 1)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 1, except that the rubber component was changed to include 70 parts by mass of SBR and 30 parts by mass of NR, 4.4 parts by mass of silane coupling agent (3) was used instead of 4.4 parts by mass of silane coupling agent (1), and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 10.

Production Example 11

Examples 261 to 310 and Comparative Examples 115 to 135 (Production Method 2)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 2, except that the rubber component was changed to include 70 parts by mass of SBR and 30 parts by mass of NR and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 11.

Production Example 12

Examples 311 to 330 and Comparative Examples 136 to 144 (Production Method 2)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 2, except that the rubber component was changed to include 70 parts by mass of SBR and 30 parts by mass of NR, 6.6 parts by mass of silane coupling agent (2) was used instead of 4.4 parts by mass of silane coupling agent (1), and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 12.

Production Example 13

Examples 331 to 350 and Comparative Examples 145 to 153 (Production Method 2)

Unvulcanized rubber compositions and vulcanized rubber compositions were obtained in the same way as in Production Example 2, except that the rubber component was changed to include 70 parts by mass of SBR and 30 parts by mass of NR, 4.4 parts by mass of silane coupling agent (3) was used instead of 4.4 parts by mass of silane coupling agent (1), and various carbonate or hydrogen carbonate salts were used in amounts shown in Table 13.
The obtained unvulcanized rubber compositions and vulcanized rubber compositions were evaluated as follows. The results are shown in Tables 1 to 13.

(Amount of Unreacted Coupling Agent)

An unvulcanized rubber sheet was finely cut and subjected to extraction with ethanol for 24 hours. The amount of unreacted silane coupling agent in the resultant extract was measured by gas chromatography, and the amount (wt %) of unreacted silane coupling agent was calculated based on the charged amount of the silane coupling agent.
A smaller value for this content means that a smaller amount of the silane coupling agent exists in an unreacted state in the unvulcanized rubber composition after completion of kneading. In other words, this indicates that a composition in which the silane coupling agent has reacted sufficiently during the kneading has a small amount of unreacted silane coupling agent and is therefore good.

(Abrasion Index)

Using a Lambourn abrasion tester, the loss in volume of each vulcanized rubber composition was measured for a test period of 3 minutes under a load of 2.5 kgf at a slip ratio of 40%. With the loss in volume of Comparative Example 1 deemed to be 100 (abrasion index), abrasion indices of the examples were calculated using the following calculation formula. A higher abrasion index means better abrasion resistance.
(Abrasion index of each example)=(loss in volume of Comparative Example 1)/(loss in volume of each example)×100

(Rolling Resistance Index)

Using a VES viscoelasticity spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the tan δ of each vulcanized rubber composition was measured at 70° C. under conditions of initial strain 10% and dynamic strain 2%. With the tan δ value of Comparative Example 1 deemed to be 100 (rolling resistance index), rolling resistance indices of the examples were calculated using the following calculation formula. A higher index means better performance in terms of rolling resistance.
(Rolling resistance index of each example)=(tan δ value of Comparative Example 1)/(tan δ value of each example)×100

TABLE 1

Rubber component: SBR 100 parts by mass
(Production Example 1: Production Method 1 (Si266))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 2	ple 1	ple 2	ple 3	ple 4	ple 5	Example 3

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	14.6	5.5	0.5	0	0	0	0
	coupling agent
	Abrasion index	100	99	102	105	108	106	104	95
	Rolling resistance index	100	100	102	106	112	108	105	100

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 4	ple 6	ple 7	ple 8	ple 9	ple 10	Example 5

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	2	5	10	30
Evaluation	Amount of unreacted	18.4	14.3	0.7	0	0	0	0	0
	coupling agent
	Abrasion index	100	100	103	105	110	108	106	98
	Rolling resistance index	100	100	108	112	114	111	108	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 6	ple 11	ple 12	ple 13	ple 14	ple 15	Example 7

Formulation	Ammonium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	16.8	8.1	2.5	0	0	0	0
	coupling agent
	Abrasion index	100	99	106	108	112	110	105	94
	Rolling resistance index	100	101	105	112	114	110	104	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 8	ple 16	ple 17	ple 18	ple 19	ple 20	Example 9

Formulation	Lithium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	15.3	3.7	0.5	0	0	0	0
	coupling agent
	Abrasion index	100	99	103	105	108	103	102	97
	Rolling resistance index	100	101	102	105	110	106	105	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 10	ple 21	ple 22	ple 23	ple 24	ple 25	Example 11

Formulation	Calcium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	17.8	8.8	4.3	2	0	0	0
	coupling agent
	Abrasion index	100	100	102	104	105	106	105	97
	Rolling resistance index	100	99	101	102	108	112	105	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 12	ple 26	ple 27	ple 28	ple 29	ple 30	Example 13

Formulation	Magnesium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	16.9	8.4	3.6	0.2	0	0	0
	coupling agent
	Abrasion index	100	100	102	105	105	104	104	97
	Rolling resistance index	100	99	102	104	110	108	102	100

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 14	ple 31	ple 32	ple 33	ple 34	ple 35	Example 15

Formulation	Potassium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	14.3	2	0	0	0	0	0
	coupling agent
	Abrasion index	100	100	102	106	109	108	103	97
	Rolling resistance index	100	99	101	101	105	107	104	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 16	ple 36	ple 37	ple 38	ple 39	ple 40	Example 17

Formulation	Sodium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	14	1.7	0	0	0	0	0
	coupling agent
	Abrasion index	100	100	102	104	107	105	103	97
	Rolling resistance index	100	99	101	102	105	108	102	100

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 18	ple 41	ple 42	ple 43	ple 44	ple 45	Example 19

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	16.5	8.5	4.2	0	0	0	0
	coupling agent
	Abrasion index	100	100	101	104	110	108	103	97
	Rolling resistance index	100	99	103	108	113	110	108	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 1	Example 20	ple 46	ple 47	ple 48	ple 49	ple 50	Example 21

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.4	15.6	1.2	0.4	0	0	0	0
	coupling agent
	Abrasion index	100	99	101	102	103	103	100	98
	Rolling resistance index	100	100	107	112	113	110	108	101

TABLE 2

Rubber component: SBR 100 parts by mass
(Production Example 2: Production Method 2 (Si266))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 22	Example 23	ple 51	ple 52	ple 53	ple 54	ple 55	Example 24

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.6	15.6	7.2	2.5	0.7	0	0	0
	coupling agent
	Abrasion index	100	100	101	104	106	105	103	94
	Rolling resistance index	100	99	102	105	110	107	103	98

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 22	Example 25	ple 56	ple 57	ple 58	ple 59	ple 60	Example 26

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.6	14.8	1.5	0.2	0	0	0	0
	coupling agent
	Abrasion index	100	100	102	103	107	106	104	96
	Rolling resistance index	100	98	108	110	112	109	106	98

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 22	Example 27	ple 61	ple 62	ple 63	ple 64	ple 65	Example 28

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.6	15.8	2.9	1.5	0.6	0.1	0	0
	coupling agent
	Abrasion index	100	100	101	101	102	102	101	97
	Rolling resistance index	100	99	105	108	110	107	104	96

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 22	Example 29	ple 66	ple 67	ple 68	ple 69	ple 70	Example 30

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	18.6	16.9	9.2	5.2	2.5	0.8	0	0
	coupling agent
	Abrasion index	100	100	101	103	107	106	102	97
	Rolling resistance index	100	99	102	106	110	106	104	96

TABLE 3

Rubber component: SBR 100 parts by mass
(Production Example 3: Production Method 3 (Si266))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 31	Example 32	ple 71	ple 72	ple 73	ple 74	ple 75	Example 33

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.2	16.4	8.2	4.8	2.1	0.6	0	0
	coupling agent
	Abrasion index	100	99	101	103	104	103	102	93
	Rolling resistance index	100	98	101	104	107	105	102	97

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 31	Example 34	ple 76	ple 77	ple 78	ple 79	ple 80	Example 35

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.2	15.6	3.5	0.9	0.1	0	0	0
	coupling agent
	Abrasion index	100	99	101	102	105	104	102	95
	Rolling resistance index	100	98	105	107	109	106	104	96

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 31	Example 36	ple 81	ple 82	ple 83	ple 84	ple 85	Example 37

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.2	16.2	3.8	1.9	0.8	0.4	0	0
	coupling agent
	Abrasion index	100	100	101	101	101	102	101	97
	Rolling resistance index	100	100	103	106	107	105	102	95

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 31	Example 38	ple 86	ple 87	ple 88	ple 89	ple 90	Example 39

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.2	17.6	9.9	6.4	3.5	1.6	0.5	0
	coupling agent
	Abrasion index	100	100	101	102	105	105	102	96
	Rolling resistance index	100	99	102	105	107	105	103	94

TABLE 4

Rubber component: SBR 100 parts by mass
(Production Example 4: Production Method 1 (Si363))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 40	Example 41	ple 91	ple 92	ple 93	ple 94	ple 95	Example 42

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.2	11.8	4.6	0.4	0	0	0	0
	coupling agent
	Abrasion index	101	101	103	106	110	108	105	100
	Rolling resistance index	102	102	104	106	114	112	108	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 40	Example 43	ple 96	ple 97	ple 98	ple 99	ple 100	Example 44

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.2	11.3	0.6	0	0	0	0	0
	coupling agent
	Abrasion index	101	102	104	106	114	110	108	100
	Rolling resistance index	102	101	109	114	117	113	110	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 40	Example 45	ple 101	ple 102	ple 103	ple 104	ple 105	Example 46

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.2	12.1	1.5	0.1	0	0	0	0
	coupling agent
	Abrasion index	101	101	103	104	105	104	103	101
	Rolling resistance index	102	101	108	113	115	112	108	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 40	Example 47	ple 106	ple 107	ple 108	ple 109	ple 110	Example 48

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.2	12.8	7.4	3.0	0	0	0	0
	coupling agent
	Abrasion index	101	101	102	108	114	109	104	100
	Rolling resistance index	102	101	104	110	115	111	109	101

TABLE 5

Rubber component: SBR 100 parts by mass
(Production Example 5: Production Method 2 (Si363))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 49	Example 50	ple 111	ple 112	ple 113	ple 114	ple 115	Example 51

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.8	12.5	7.0	2.5	0.8	0.2	0	0
	coupling agent
	Abrasion index	101	101	102	104	107	106	102	100
	Rolling resistance index	101	101	103	106	112	109	105	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 49	Example 52	ple 116	ple 117	ple 118	ple 119	ple 120	Example 53

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.8	11.7	2.5	0.8	0.2	0	0	0
	coupling agent
	Abrasion index	101	101	103	105	112	107	105	101
	Rolling resistance index	101	101	109	112	114	110	106	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 49	Example 54	ple 121	ple 122	ple 123	ple 124	ple 125	Example 55

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.8	13.2	3.5	1.5	0.5	0	0	0
	coupling agent
	Abrasion index	101	101	102	103	104	104	102	101
	Rolling resistance index	101	101	105	108	111	106	104	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 49	Example 56	ple 126	ple 127	ple 128	ple 129	ple 130	Example 57

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	14.8	13.4	8.4	4.0	0.8	0	0	0
	coupling agent
	Abrasion index	101	101	101	106	110	106	103	100
	Rolling resistance index	101	101	103	108	114	107	105	101

TABLE 6

Rubber component: SBR 100 parts by mass
(Production Example 6: Production Method 1 (NXT-Z45))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 58	Example 59	ple 131	ple 132	ple 133	ple 134	ple 135	Example 60

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	11.2	10.8	2.5	0	0	0	0	0
	coupling agent
	Abrasion index	103	102	105	107	113	110	108	102
	Rolling resistance index	102	102	106	108	116	114	112	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 58	Example 61	ple 136	ple 137	ple 138	ple 139	ple 140	Example 62

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	11.2	10.4	0.6	0	0	0	0	0
	coupling agent
	Abrasion index	103	103	106	110	117	114	110	101
	Rolling resistance index	102	102	112	115	118	116	113	103

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 58	Example 63	ple 141	ple 142	ple 143	ple 144	ple 145	Example 64

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	11.2	10.6	1.3	0.1	0	0	0	0
	coupling agent
	Abrasion index	103	103	104	106	108	107	105	101
	Rolling resistance index	102	102	110	114	116	113	109	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 58	Example 65	ple 146	ple 147	ple 148	ple 149	ple 150	Example 66

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	11.2	10.5	6.4	2.5	0.4	0	0	0
	coupling agent
	Abrasion index	103	102	104	109	115	112	106	101
	Rolling resistance index	102	102	104	112	117	112	110	102

TABLE 7

Rubber component: SBR 100 parts by mass
(Production Example 7: Production Method 2 (NXT-Z45))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 67	Example 68	ple 151	ple 152	ple 153	ple 154	ple 155	Example 69

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.0	11.0	5.9	2.4	0.5	0	0	0
	coupling agent
	Abrasion index	102	102	103	105	109	106	104	101
	Rolling resistance index	102	102	105	107	113	111	106	101

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 67	Example 70	ple 156	ple 157	ple 158	ple 159	ple 160	Example 71

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.0	10.4	2.0	0.5	0.1	0	0	0
	coupling agent
	Abrasion index	102	102	105	108	114	112	106	101
	Rolling resistance index	102	102	108	112	115	113	108	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 67	Example 72	ple 161	ple 162	ple 163	ple 164	ple 165	Example 73

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.0	10.9	2.4	0.9	0.6	0.1	0	0
	coupling agent
	Abrasion index	102	102	103	104	105	105	104	101
	Rolling resistance index	102	102	106	110	108	107	104	102

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 67	Example 74	ple 166	ple 167	ple 168	ple 169	ple 170	Example 75

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.0	10.8	7.8	3.5	1.8	0.6	0	0
	coupling agent
	Abrasion index	102	102	104	105	108	104	103	101
	Rolling resistance index	102	102	103	108	115	109	104	102

TABLE 8

Rubber component: SBR 70 parts by mass, NR 30 parts by mass
(Production Example 8: Production Method 1 (Si266))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 77	ple 171	ple 172	ple 173	ple 174	ple 175	Example 78

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	17.8	7.6	4.5	2.1	0.5	0	0
	coupling agent
	Abrasion index	112	111	116	122	123	118	116	106
	Rolling resistance index	108	108	111	114	120	116	114	108

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 79	ple 176	ple 177	ple 178	ple 179	ple 180	Example 80

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	16.8	5.5	2.4	1.1	0	0	0
	coupling agent
	Abrasion index	112	111	115	116	123	121	117	110
	Rolling resistance index	108	108	116	121	125	120	115	109

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 81	ple 181	ple 182	ple 183	ple 184	ple 185	Example 82

Formulation	Ammonium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	16.8	8.1	2.5	0	0	0	0
	coupling agent
	Abrasion index	112	111	118	120	122	122	117	106
	Rolling resistance index	108	108	113	121	121	118	109	107

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 83	ple 186	ple 187	ple 188	ple 189	ple 190	Example 84

Formulation	Lithium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	16.3	6.5	3.4	1.5	0	0	0
	coupling agent
	Abrasion index	112	112	115	118	120	114	114	109
	Rolling resistance index	108	110	112	114	119	114	112	109

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 85	ple 191	ple 192	ple 193	ple 194	ple 195	Example 86

Formulation	Calcium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	17.8	8.8	4.3	2	0	0	0
	coupling agent
	Abrasion index	112	111	114	116	118	117	116	109
	Rolling resistance index	108	107	110	111	116	121	113	109

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 87	ple 196	ple 197	ple 198	ple 199	ple 200	Example 88

Formulation	Magnesium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	17.6	8.8	4.6	2.5	1.0	0	0
	coupling agent
	Abrasion index	112	112	115	116	116	116	115	109
	Rolling resistance index	108	108	111	112	119	117	113	107

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 89	ple 201	ple 202	ple 203	ple 204	ple 205	Example 90

Formulation	Potassium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	16.8	4.0	1.8	0	0	0	0
	coupling agent
	Abrasion index	112	111	114	118	121	119	116	109
	Rolling resistance index	108	107	110	110	114	115	112	109

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 91	ple 206	ple 207	ple 208	ple 209	ple 210	Example 92

Formulation	Sodium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	17.2	6.4	3.0	1.0	0	0	0
	coupling agent
	Abrasion index	112	111	114	117	120	115	114	109
	Rolling resistance index	108	109	111	112	114	116	111	109

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 93	ple 211	ple 212	ple 213	ple 214	ple 215	Example 94

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	17.6	8.9	5.6	2.4	0.8	0	0
	coupling agent
	Abrasion index	112	112	114	116	122	121	115	109
	Rolling resistance index	108	108	112	116	121	119	117	110

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 76	Example 95	ple 216	ple 217	ple 218	ple 219	ple 220	Example 96

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	19.7	18.2	9.6	6.5	3.2	2.6	0	0
	coupling agent
	Abrasion index	112	111	114	115	115	115	113	108
	Rolling resistance index	108	109	114	121	121	120	116	110

TABLE 9

Rubber component: SBR 70 parts by mass, NR 30 parts by mass
(Production Example 9: Production Method 1 (Si363))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 97	Example 98	ple 221	ple 222	ple 223	ple 224	ple 225	Example 99

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	15.4	12.6	6.0	2.9	0.8	0	0	0
	coupling agent
	Abrasion index	113	113	116	124	124	122	118	112
	Rolling resistance index	109	110	113	116	127	124	120	110

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 97	Example 100	ple 226	ple 227	ple 228	ple 229	ple 230	Example 101

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	15.4	12.7	2.6	0.8	0	0	0	0
	coupling agent
	Abrasion index	113	112	115	120	126	123	119	113
	Rolling resistance index	109	109	116	124	126	122	119	108

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 97	Example 102	ple 231	ple 232	ple 233	ple 234	ple 235	Example 103

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	15.4	12.8	4.5	1.6	0.5	0	0	0
	coupling agent
	Abrasion index	113	112	115	117	119	117	116	110
	Rolling resistance index	109	110	114	125	124	124	120	108

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 97	Example 104	ple 236	ple 237	ple 238	ple 239	ple 240	Example 105

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	15.4	12.8	7.4	3.0	0	0	0	0
	coupling agent
	Abrasion index	113	113	116	121	126	122	117	113
	Rolling resistance index	109	108	113	120	124	119	117	109

TABLE 10

Rubber component: SBR 70 parts by mass, NR 30 parts by mass
(Production Example 10: Production Method 1 (NXT-Z45))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 106	Example 107	ple 241	ple 242	ple 243	ple 244	ple 245	Example 108

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.5	11.2	6.5	3.1	1.2	0	0	0
	coupling agent
	Abrasion index	114	114	120	124	126	126	123	113
	Rolling resistance index	110	110	114	118	128	125	122	111

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 106	Example 109	ple 246	ple 247	ple 248	ple 249	ple 250	Example 110

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.5	11.0	5.6	2.3	0.6	0	0	0
	coupling agent
	Abrasion index	114	113	120	125	130	126	124	114
	Rolling resistance index	110	110	116	125	127	126	123	109

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 106	Example 111	ple 251	ple 252	ple 253	ple 254	ple 255	Example 112

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.5	11.5	7.8	4.6	2.0	0.9	0	0
	coupling agent
	Abrasion index	114	115	120	122	123	122	120	114
	Rolling resistance index	110	110	115	123	124	122	118	111

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 106	Example 113	ple 256	ple 257	ple 258	ple 259	ple 260	Example 114

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	12.5	12.0	8.9	6.1	3.6	0.8	0	0
	coupling agent
	Abrasion index	114	115	118	124	127	123	120	113
	Rolling resistance index	110	111	115	124	129	125	120	111

TABLE 11

Rubber component: SBR 70 parts by mass, NR 30 parts by mass
(Production Example 11: Production Method 2 (Si266))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 116	ple 261	ple 262	ple 263	ple 264	ple 265	Example 117

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	18.4	8.6	5.3	2.8	1.5	0.8	0
	coupling agent
	Abrasion index	110	109	113	120	121	114	114	107
	Rolling resistance index	106	106	110	113	115	114	113	107

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 118	ple 266	ple 267	ple 268	ple 269	ple 270	Example 119

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	17.8	6.9	3.2	1.2	0.1	0	0
	coupling agent
	Abrasion index	110	109	114	114	120	117	114	107
	Rolling resistance index	106	106	112	116	117	115	114	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 120	ple 271	ple 272	ple 273	ple 274	ple 275	Example 121

Formulation	Ammonium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	17.6	9.6	5.6	2.5	1.0	0	0
	coupling agent
	Abrasion index	110	110	116	118	121	118	115	108
	Rolling resistance index	106	105	112	118	117	116	109	105

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 122	ple 276	ple 277	ple 278	ple 279	ple 280	Example 123

Formulation	Lithium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	18.3	7.9	4.6	2.5	1.2	0	0
	coupling agent
	Abrasion index	110	108	114	116	118	114	113	108
	Rolling resistance index	106	105	110	112	116	113	111	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 124	ple 281	ple 282	ple 283	ple 284	ple 285	Example 125

Formulation	Calcium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	18.4	9.2	5.3	2.8	1.4	0.1	0
	coupling agent
	Abrasion index	110	110	112	114	116	114	113	109
	Rolling resistance index	106	105	110	111	114	116	110	104

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 126	ple 286	ple 287	ple 288	ple 289	ple 290	Example 127

Formulation	Magnesium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	19.4	9.8	5.4	3.1	1.4	0.5	0
	coupling agent
	Abrasion index	110	109	113	114	115	114	113	109
	Rolling resistance index	106	106	110	111	117	115	114	104

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 128	ple 291	ple 292	ple 293	ple 294	ple 295	Example 129

Formulation	Potassium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	18.4	6.5	2.7	1.1	0	0	0
	coupling agent
	Abrasion index	110	109	113	115	118	115	113	110
	Rolling resistance index	106	105	110	110	113	114	112	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 130	ple 296	ple 297	ple 298	ple 299	ple 300	Example 131

Formulation	Sodium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	18.4	7.4	4.2	2.0	0.6	0	0
	coupling agent
	Abrasion index	110	108	113	116	118	114	113	109
	Rolling resistance index	106	106	111	111	113	114	111	104

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 132	ple 301	ple 302	ple 303	ple 304	ple 305	Example 133

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	19.3	9.9	6.2	4.1	2.2	0.6	0
	coupling agent
	Abrasion index	110	108	113	115	120	119	114	107
	Rolling resistance index	106	105	111	114	118	116	114	105

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 115	Example 134	ple 306	ple 307	ple 308	ple 309	ple 310	Example 135

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	20.7	19.9	9.9	6.9	4.0	2.7	1.2	0.2
	coupling agent
	Abrasion index	110	109	113	114	114	114	112	107
	Rolling resistance index	106	106	112	116	114	115	112	105

TABLE 12

Rubber component: SBR 70 parts by mass, NR 30 parts by mass
(Production Example 12: Production Method 2 (Si363))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 136	Example 137	ple 311	ple 312	ple 313	ple 314	ple 315	Example 138

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	16.8	14.1	7.8	3.9	2.2	1.0	0.2	0
	coupling agent
	Abrasion index	111	111	114	121	123	119	116	110
	Rolling resistance index	107	108	112	114	123	119	115	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 136	Example 139	ple 316	ple 317	ple 318	ple 319	ple 320	Example 140

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	16.8	13.2	3.5	1.0	0.1	0	0	0
	coupling agent
	Abrasion index	111	110	114	118	122	118	114	108
	Rolling resistance index	107	106	112	120	118	116	115	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 136	Example 141	ple 321	ple 322	ple 323	ple 324	ple 325	Example 142

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	16.8	14.0	5.4	2.6	1.3	0.4	0	0
	coupling agent
	Abrasion index	111	110	114	116	117	115	113	107
	Rolling resistance index	107	106	113	115	115	116	113	103

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 136	Example 143	ple 326	ple 327	ple 328	ple 329	ple 330	Example 144

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	16.8	15.4	8.4	5.0	2.5	1.1	0	0
	coupling agent
	Abrasion index	111	109	114	118	120	118	114	108
	Rolling resistance index	107	107	112	118	122	118	114	105

TABLE 13

Rubber component: SBR 70 parts by mass, NR 30 parts by mass
(Production Example 13: Production Method 2 (NXT-Z45))

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 145	Example 146	ple 331	ple 332	ple 333	ple 334	ple 335	Example 147

Formulation	Sodium carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	13.8	11.9	7.6	3.8	1.8	0.5	0	0
	coupling agent
	Abrasion index	112	112	116	122	123	121	117	111
	Rolling resistance index	106	107	113	116	124	122	117	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 145	Example 148	ple 336	ple 337	ple 338	ple 339	ple 340	Example 149

Formulation	Potassium carbonate (2)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	13.8	11.7	7.4	3.4	1.6	0.1	0	0
	coupling agent
	Abrasion index	112	111	116	120	124	121	118	111
	Rolling resistance index	106	105	115	123	124	122	115	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 145	Example 150	ple 341	ple 342	ple 343	ple 344	ple 345	Example 151

Formulation	Potassium carbonate (1)	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	13.8	12.5	8.5	5.2	2.5	1.3	0.5	0
	coupling agent
	Abrasion index	112	111	115	118	120	118	116	111
	Rolling resistance index	106	106	113	120	120	117	115	106

		Comparative	Comparative	Exam-	Exam-	Exam-	Exam-	Exam-	Comparative
		Example 145	Example 152	ple 346	ple 347	ple 348	ple 349	ple 350	Example 153

Formulation	Ammonium hydrogen carbonate	—	0.2	0.5	1	5	10	20	30
Evaluation	Amount of unreacted	13.8	12.0	8.9	6.1	3.6	0.8	0	0
	coupling agent
	Abrasion index	112	112	117	120	122	120	118	111
	Rolling resistance index	106	106	114	122	125	121	116	105

In the examples in which silica, a silane coupling agent and a predetermined amount of a carbonate salt or hydrogen carbonate salt were contained, the amount of unreacted silane coupling agent was as small as at most 10% by mass, the rate of reaction between the silane coupling agent and the silica was increased, and the fuel economy and abrasion resistance were enhanced, as compared with the comparative examples. In addition, in the examples using silane coupling agent (2) or (3), excellent fuel economy and abrasion resistance were exhibited. In the examples using potassium carbonate (2) with an average particle size of 40 μm or smaller, an increased rate of reaction and superior abrasion resistance were exhibited compared with cases in which potassium carbonate (1) with an average particle size of 340 μm was used. With regard to Production Examples 1 to 3, in Examples 1 to 50 which were obtained by carrying out the first base kneading step, the second base kneading step and the final kneading step (Production Example 1 (Production Method 1)), good fuel economy and abrasion resistance were exhibited. Next to these examples, the improvement effect was large in the examples obtained according to Production Example 2 (Production Method 2) and Production Example 3 (Production Method 3). In contrast, in the comparative examples, the fuel economy and abrasion resistance could not be enhanced in a balanced manner.
In addition, if the content of the carbonate or hydrogen carbonate salt is increased too far, the abrasion resistance tends to deteriorate (for example, see Comparative Examples 3, 5, 7, 9, 11, 13, 15, 17 and 19).

Claims

1. A rubber composition for a tire, comprising: diene rubber; silica; a silane coupling agent; and at least one of a carbonate salt and a hydrogen carbonate salt,

wherein the rubber composition has a total content of the carbonate salt and the hydrogen carbonate salt of 0.3 to 25 parts by mass relative to 100 parts by mass of the silica.

2. The rubber composition for a tire according to claim 1, wherein the carbonate salt is at least one selected from the group consisting of sodium carbonate, potassium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate, and

the hydrogen carbonate salt is at least one selected from the group consisting of sodium hydrogen carbonate, potassium hydrogen carbonate and ammonium hydrogen carbonate.

3. The rubber composition for a tire according to claim 1, wherein the carbonate salt is at least one selected from the group consisting of sodium carbonate, ammonium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate, and

the hydrogen carbonate salt is ammonium hydrogen carbonate.

4. The rubber composition for a tire according to claim 1 or 2, wherein the potassium carbonate has an average particle size of 40 μm or smaller.

5. The rubber composition for a tire according to claim 1, wherein the silane coupling agent is at least one selected from the group consisting of a sulfide-type silane coupling agent, a silane coupling agent represented by formula (1):

wherein R¹is a group represented by —O—(R⁵—O)_m—R⁶in which m pieces of R⁵are the same or different and each denote a branched or unbranched divalent hydrocarbon group having 1 to 30 carbon atoms, R⁶denotes a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms, and m is an integer between 1 and 30; R²and R³are the same or different and each denote a group as defined for R¹, a branched or unbranched alkyl group having 1 to 12 carbon atoms, or a group represented by —O—R⁷in which R⁷denotes a hydrogen atom, a branched or unbranched alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms or an aralkyl group having 7 to 30 carbon atoms; and R⁴denotes a branched or unbranched alkylene group having 1 to 30 carbon atoms, and

a silane coupling agent comprising linking units A and B respectively represented by formulae (2) and (3):

wherein x is an integer of 0 or higher; y is an integer of 1 or higher; R⁸denotes a hydrogen atom, a halogen atom, a branched or unbranched alkyl or alkylene group having 1 to 30 carbon atoms, a branched or unbranched alkenyl or alkenylene group having 2 to 30 carbon atoms, a branched or unbranched alkynyl or alkynylene group having 2 to 30 carbon atoms, or a group in which a terminal of the alkyl or alkenyl group is substituted with a hydroxyl or carboxyl group; R⁹denotes a hydrogen atom, a branched or unbranched alkylene or alkyl group having 1 to 30 carbon atoms, a branched or unbranched alkenylene or alkenyl group having 2 to 30 carbon atoms, or a branched or unbranched alkynylene or alkynyl group having 2 to 30 carbon atoms; and R⁸and R⁹may together form a ring structure.

6. The rubber composition for a tire according to claim 1, wherein 5 to 150 parts by mass of the silica is contained relative to 100 parts by mass of the diene rubber, and

2 to 20 parts by mass of the silane coupling agent is contained relative to 100 parts by mass of the silica.

7. The rubber composition for a tire according to claim 1, which is obtained by a production method comprising:

a step (A) of kneading diene rubber, silica, a silane coupling agent, and at least one of a carbonate salt and a hydrogen carbonate salt, and discharging the resulting kneaded mixture A;

a step (B) of kneading the kneaded mixture A discharged in the step (A), stearic acid and zinc oxide, and discharging the resulting kneaded mixture B; and

a step (C) of kneading the kneaded mixture B discharged in the step (B), a vulcanizing agent and a vulcanization accelerator.

8. The rubber composition for a tire according to claim 1, which is obtained by a production method comprising:

a step (a) of kneading diene rubber, silica, a silane coupling agent, and at least one of a carbonate salt and a hydrogen carbonate salt, adding thereto stearic acid and zinc oxide, further kneading them, and discharging the resulting kneaded mixture a; and

a step (b) of kneading the kneaded mixture a discharged in the step (a), a vulcanizing agent and a vulcanization accelerator.

9. A pneumatic tire formed from the rubber composition according to claim 1.