Rubber composition and pneumatic tire

Abstract

To provide a rubber composition which is a rubber composition containing a diene rubber and a polyrotaxane, prevents gelatinization caused by reaction of the diene rubber and the polyrotaxane in an unvulcanization blending process, and is excellent in durability of rubber after vulcanization.SOLUTION: A rubber composition containing a diene rubber and a polyrotaxane is such that: the polyrotaxane has a straight-chain molecule, a cyclic molecule including the straight-chain molecule, and a sealing group arranged at the terminal of the straight-chain molecule so as to prevent the cyclic molecule from being detached from the straight-chain molecule; and the cyclic molecule has a polysulfide group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition, and particularly to a rubber composition suitably used as a raw material for pneumatic tires, and a pneumatic tire obtained using the rubber composition as a raw material.

Background Art

[0002] In recent years, with the progress of higher output of automobiles, it has become essential to improve the durability of pneumatic tires. For this reason, in the rubber parts constituting pneumatic tires, it is required to improve mechanical strengths such as tensile strength.

[0003] Patent Document 1 below describes a rubber composition containing a polyrotaxane having a linear molecule, a cyclic molecule that clathrates the linear molecule in a skewer-like manner, and a sealing group disposed at both ends of the linear molecule to prevent the detachment of the cyclic molecule, and a diene-based rubber, wherein the cyclic molecule has a mercapto group.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The technique described in Patent Document 1 aims to form a chemical bond between the main chain of the diene rubber to be compounded and polyrotaxane by introducing a mercapto group into the cyclic molecule of polyrotaxane. However, as a result of the intensive study by the present inventor, in the technique described in Patent Document 1, the reactivity of the en-thiol reaction between the mercapto group of polyrotaxane and the diene rubber is high, and the two react with each other in the mixing step before the vulcanization step, so that a part of the unvulcanized rubber composition gels. As a result, it has been found that there is room for further improvement in terms of improving the durability of the rubber after vulcanization.

[0006] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a rubber composition containing a diene rubber and polyrotaxane, which prevents gelation due to the reaction of the diene rubber and polyrotaxane in the unvulcanized mixing step and has excellent durability of the rubber after vulcanization.

Means for Solving the Problems

[0007] The above object can be achieved by the present invention as follows. That is, the present invention is a rubber composition containing a diene rubber and polyrotaxane, wherein the polyrotaxane has a linear molecule, a cyclic molecule that clathrates the linear molecule, and a sealing group disposed at the terminal of the linear molecule to prevent the cyclic molecule from detaching from the linear molecule, and the cyclic molecule has a polysulfide group, and relates to a rubber composition (1).

[0008] In the above rubber composition (1), a rubber composition (2) in which the polyrotaxane has a cyclic molecule having a disulfide group is preferable.

[0009] In the above rubber composition (1) or (2), a rubber composition (3) in which the polyrotaxane has a crystallization temperature of -30 to -10 °C is preferable.

[0010] Among the rubber compositions (1) to (3) above, the rubber composition (4) in which the polyrotaxane has a cyclic molecule having a polysulfide group via an ester bond is preferable.

[0011] Among the rubber compositions (1) to (4) above, the rubber composition (5) in which the polyrotaxane is an ester compound of a hydroxyl group of the cyclic molecule and an aliphatic carboxylic acid having a disulfide group is preferable.

[0012] Among the rubber compositions (1) to (5) above, when the total amount of the diene rubber is 100 parts by mass, the rubber composition (6) containing 1 to 40 parts by mass of the polyrotaxane is preferable.

[0013] The present invention also relates to a pneumatic tire (7) provided with a vulcanized rubber obtained from any one of the rubber compositions (1) to (6) above as a raw material.

Advantages of the Invention

[0014] In a conventional rubber composition, polymer (rubber) chains form a crosslinked structure by covalent bonds in the vulcanization process, and the rubber strength (such as tensile strength) after vulcanization is improved. However, the crosslinking distance between polymer chains varies depending on the site, and a non-uniform polymer network is likely to be formed. For this reason, in the vulcanized rubber of a conventional rubber composition, the stress applied from the outside tends to concentrate at the location where the crosslinking distance between polymer chains is the shortest, and destruction and breakage are likely to progress starting from this location.

[0015] The rubber composition according to the present invention contains a diene rubber and a polyrotaxane. The polyrotaxane has a linear molecule, a cyclic molecule that includes the linear molecule, and a blocking group disposed at the end of the linear molecule to prevent the cyclic molecule from detaching from the linear molecule. The polymer chain can freely pass through the cross-linked structure caused by the cyclic molecule of the polyrotaxane (so-called "pulley effect"). Further, the cross-linking distance between the polymer chains is more easily made uniform compared to the chemical bonds formed by conventional vulcanization. As a result, the properties of the polymer material, such as the breaking strength, can be improved to the maximum and uniformly, so that the durability of the finally obtained vulcanized rubber is improved.

[0016] In addition, in order to use polyrotaxane and improve the properties of the polymer material to the maximum and uniformly, the cyclic molecule of the polyrotaxane needs to form a covalent bond (cross-linked structure) with the polymer chain. For example, in the prior art described in Patent Document 1 and the like, a mercapto group is introduced into the cyclic molecule of the polyrotaxane, and the mercapto group forms a covalent bond with the diene rubber, so that the polymer chain forms a cross-linked structure. However, the reactivity of the en-thiol reaction between the mercapto group of the polyrotaxane and the diene rubber is high, and the two react with each other in the mixing step before the vulcanization step, so that a part of the unvulcanized rubber composition gels, and as a result, the wear resistance and breaking strength of the vulcanized rubber may deteriorate.

[0017] On the other hand, in the rubber composition according to the present invention, the cyclic molecule of the polyrotaxane has a polysulfide group. The reactivity between the polysulfide group and the diene rubber is moderately suppressed, and in the mixing step of the rubber composition before the vulcanization step, that is, before the sulfur compounding, the polyrotaxane and the diene rubber are not particularly reactive and are mixed with each other. Then, when sulfur is compounded in the rubber composition and vulcanized while heating, the polysulfide group is activated by sulfur, so that the cyclic molecule of the polyrotaxane forms a covalent bond with the polymer chain.

[0018] As described above, in the prior art, gelation occurs due to the reaction between polyrotaxane and diene rubber in the mixing step before vulcanization. However, in the rubber composition according to the present invention, since the cyclic molecules of polyrotaxane have polysulfide groups, the reaction between polyrotaxane and diene rubber is suppressed in the mixing step, and it is only in the vulcanization step that the cyclic molecules of polyrotaxane form covalent bonds with the polymer chains. As a result, in the rubber composition according to the present invention, gelation of diene rubber and polyrotaxane can be prevented in the unvulcanized mixing step, and a rubber composition excellent in the breaking strength of the vulcanized rubber can be provided. In particular, when the cyclic molecules of polyrotaxane have disulfide groups, the length of the crosslinking chains forming the crosslinked structure becomes more uniform, which makes it difficult for the polymer chains to break, resulting in more improved durability of the finally obtained vulcanized rubber, which is preferable. Furthermore, when the cyclic molecules of polyrotaxane have disulfide groups via ester bonds, particularly when polyrotaxane is an ester compound of a cyclic molecule's hydroxyl group and an aliphatic carboxylic acid having a disulfide group, it is preferable because the durability of the finally obtained vulcanized rubber is particularly improved.

Embodiments for Carrying Out the Invention

[0019] The rubber composition according to the present invention contains a diene rubber and polyrotaxane.

[0020] Examples of the diene rubber include natural rubber (NR), polyisoprene rubber (IR), polystyrene butadiene rubber (SBR), polybutadiene rubber (BR), chloroprene rubber (CR), nitrile rubber (NBR), etc. If necessary, those with modified ends (for example, end-modified BR, end-modified SBR, etc.) or those modified to impart desired properties (for example, modified NR) can also be preferably used. Regarding polybutadiene rubber (BR), in addition to those synthesized using cobalt (Co) catalysts, neodymium (Nd) catalysts, nickel (Ni) catalysts, titanium (Ti) catalysts, and lithium (Li) catalysts, those synthesized using a polymerization catalyst composition containing a metallocene complex described in WO2007-129670 can also be used.

[0021] A polyrotaxane has a linear molecule, a cyclic molecule that inclusion complexes the linear molecule, and a capping group disposed at the ends of the linear molecule to prevent the cyclic molecule from detaching from the linear molecule. A representative structural formula of the polyrotaxane is shown below.

[0022] [Chemical formula]

[0023] In the above formula, 1 represents a linear molecule, 2 represents a cyclic molecule that inclusion complexes the linear molecule, and 3 represents a capping group disposed at the ends of the linear molecule to prevent the cyclic molecule from detaching from the linear molecule. The polyrotaxane compounded in the rubber composition according to the present invention has a cyclic molecule having a polysulfide group. However, when the cyclic molecule of the polyrotaxane has a disulfide group, it is preferable because the length of the crosslinking chain forming the crosslinked structure becomes more uniform, making it difficult for the polymer chain to break, and ultimately improving the durability of the vulcanized rubber obtained.

[0024] The above linear molecule is not particularly limited as long as it can be included in a pierced manner at the opening of the cyclic molecule. Examples include polyvinyl alcohol; polyvinyl pyrrolidone; poly(meth)acrylic acid; cellulose resins such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose; polyacrylamide; polyethylene oxide; polyethylene glycol; polypropylene glycol; polyvinyl acetal resins; polyvinyl methyl ether; polyamine; polyethyleneimine; casein; gelatin; starch, etc., alone and / or their copolymers, polyolefin resins such as polyethylene; polypropylene and copolymer resins with other olefin monomers, etc.; polyester resins; polyvinyl chloride resins; polystyrene resins such as polystyrene and / or acrylonitrile-styrene copolymer resins; acrylic resins such as polymethyl methacrylate, (meth)acrylate copolymer, acrylonitrile-methyl acrylate copolymer resins; polycarbonate resins; polyurethane resins; vinyl chloride-vinyl acetate copolymer resins; polyvinyl butyral resins, etc., alone, their derivatives or modified products; polyisobutylene; polytetrahydrofuran; polyaniline; acrylonitrile-butadiene-styrene copolymer (ABS resin); polyamides such as nylon; polyimides; polydienes such as polyisoprene and polybutadiene; polysiloxanes such as polydimethylsiloxane; polysulfones; polyimines; polyacetic anhydrides; polyureas; polysulfides; polyphosphazenes; polyketones; polyphenylenes; polyhaloolefins alone or their derivatives. At least one selected from the group consisting of polyethylene glycol, polyisoprene, polyisobutylene, polybutadiene, polypropylene glycol, polytetrahydrofuran, polydimethylsiloxane, polyethylene, polypropylene, polyvinyl alcohol, and polyvinyl methyl ether is preferred, and polyethylene glycol is particularly more preferred.

[0025] The linear molecule preferably has a mass average molecular weight of 3,000 or more, more preferably 5,000 to 100,000, and particularly preferably 10,000 to 50,000.

[0026] The above cyclic molecule is a molecule in which a linear molecule is included in a skewered manner at its opening. Examples of the cyclic molecule include cyclodextrins such as α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, crown ethers, benzo crowns, dibenzo crowns, dicyclohexano crowns, cyclophanes, calixarenes, cucurbiturils, pillararenes, cyclic amides, and the like. Among these, cyclodextrins are preferred.

[0027] In the present invention, the method for introducing a polysulfide group, more preferably a disulfide group, into the cyclic molecule of the polyrotaxane is not particularly limited and can be appropriately selected from known methods. However, a method of bonding an alcoholic hydroxyl group possessed by cyclic molecules such as cyclodextrins, which are cyclic molecules, and a compound having a disulfide group via an ester bond is preferable. Examples of the compound that can be used for introducing a polysulfide group, more preferably a disulfide group, into the cyclic molecule of the polyrotaxane via an ester bond include 3,3'-dithiodipropionic acid, 2,2'-dithiodipropionic acid, dithiodiglycolic acid, 4,4'-dithiobutyric acid, 2,2'-dithiobenzilic acid, 6,6'-dithiodinicotinic acid, 5,5'-dithiobis(2-nitrobenzoic acid), (R)-α-lipoic acid, 3-(2-pyridyldithio)propionic acid, cystine (DL-, meso-mixture), L-(-)-cystine, L-(-)-cystine dihydrochloride, DL-homocystine, 2,2'-dithiobis(6-fluorobenzoic acid), lipoamide-PEG12-carboxylic acid, and N,N'-dicarboxybenzoxy-L-cystine. In the present invention, the polyrotaxane is preferably an ester compound of the hydroxyl group of the cyclic molecule and an aliphatic carboxylic acid having the disulfide group exemplified above. Among the above aliphatic carboxylic acids, when 3,3'-dithiodipropionic acid is particularly used, it is preferable because a disulfide group can be easily and surely introduced into the cyclic molecule of the polyrotaxane. The structural formula of the polyrotaxane, which is an ester compound of the hydroxyl group of the cyclic molecule of the polyrotaxane and 3,3'-dithiodipropionic acid, is shown below.

[0028]

Chemical formula

[0029] In the above formula, 1 represents a linear molecule, 2 represents a cyclic molecule that inclusion complexes the linear molecule, 3 represents a capping group arranged at the end of the linear molecule to prevent the cyclic molecule from detaching from the linear molecule, and 4 represents a disulfide group introduced into the cyclic molecule.

[0030] When reacting a compound having a polysulfide group, more preferably a disulfide group and a carboxyl group with an alcoholic hydroxyl group possessed by cyclodextrins or the like which are cyclic molecules via an ester bond, a catalyst known to those skilled in the art may be used.

[0031] In addition, methods for introducing a polysulfide group, more preferably a disulfide group, into the cyclic molecule of the polyrotaxane other than the above include, for example, a method of reacting the alcoholic hydroxyl group of cyclic molecules such as cyclodextrins with a compound having a disulfide group via a diisocyanate compound. Examples of the compound having a disulfide group include bis(2-hydroxyethyl) disulfide, dithiodiglycolic acid, 3,3'-dithiodipropionic acid, 4,4'-dithiobutyric acid, 2,2'-dithiodipropionic acid, bis(4-hydroxyphenyl) disulfide, bis(6-hydroxy-2-naphthyl) disulfide, 2,2'-dithiobenzoic acid, 6,6'-dithiodinicotinic acid, 5,5'-dithiobis(2-nitrobenzoic acid), 2,2'-dithiodianiline, 4,4'-dithiodianiline, (R)-α-lipoic acid, xanthane hydride, 3-(2-pyridyldithio)propionic acid, cystamine dihydrochloride, formamidine disulfide dihydrochloride, cystine (DL-, meso-mixture), L-(-)-cystine, L-(-)-cystine dihydrochloride, L-cystine dimethyl dihydrochloride, DL-homocystine, bis[2-(4-azidosalicylamido)ethyl] disulfide, 2,2'-dithiobis(6-fluorobenzoic acid), lipoamide-PEG12-carboxylic acid, bis(2-benzamidophenyl) disulfide, N,N'-dicarboxybenzoxy-L-cystine, pyrithinol, and the like.Examples of the diisocyanate compound include aromatic diisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, and m-xylylene diisocyanate; aliphatic diisocyanates such as ethylene diisocyanate, 1,5-pentamethylene diisocyanate, 2,2,4-trimethylhexamethylene-1,6-diisocyanate, 2,4,4-trimethylhexamethylene-1,6-diisocyanate, and 1,6-hexamethylene diisocyanate; and alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and norbornane diisocyanate. The exemplified diisocyanate compounds may be used alone or in combination of two or more kinds.

[0032] The above-mentioned blocking group is not particularly limited as long as it is a group that is disposed at both ends of a linear molecule and acts so that a cyclic molecule does not leave. For example, it is preferably selected from the group consisting of dinitrophenyl groups, cyclodextrins, adamantane groups, trityl groups, fluoresceins, silsesquioxanes, pyrenes, substituted benzenes, polynuclear aromatics which may be substituted, and steroids. Among these examples, dinitrophenyl groups, cyclodextrins, adamantane groups, trityl groups, fluoresceins, silsesquioxanes, and pyrenes are preferable, and adamantane groups or trityl groups are more preferable.

[0033] In the present invention, since the cyclic molecules included in the polyrotaxane have polysulfide groups, the vulcanized rubber finally obtained is excellent in durability. Here, when the polyrotaxane is introduced with polysulfide groups, crystallization is inhibited and it becomes difficult to crystallize. Therefore, in the present invention, the modification amount of the polysulfide groups in the polyrotaxane can be inferred indirectly from the crystallization temperature of the polyrotaxane. In the present invention, when the crystallization temperature of the polyrotaxane to be used is -30 to -10°C, since the modification amount of the polysulfide groups in the polyrotaxane is sufficiently ensured, it is preferable because the durability of the finally obtained vulcanized rubber is excellent.

[0034] When the total amount of the rubber components including the diene rubber is 100 parts by mass, the blending ratio of the polyrotaxane in the rubber composition is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and particularly preferably 10 parts by mass or more. Also, it is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and particularly preferably 20 parts by mass or less.

[0035] In addition to the diene rubber and the polyrotaxane, various compounding agents such as carbon black, silica, silane coupling agent, anti-aging agent, zinc oxide, stearic acid, wax, softening agent such as oil, and processing aids can be compounded in the rubber composition according to the present invention.

[0036] As the carbon black, in addition to the carbon black usually used in the rubber industry such as SAF, ISAF, HAF, FEF, GPF, etc., conductive carbon black such as acetylene black and ketjen black can be used.

[0037] As the silica, wet silica and dry silica can be used, but in particular, it is preferable to use wet silica mainly composed of hydrous silicic acid.

[0038] As the silane coupling agent, a silane coupling agent having a reactive activity with respect to diene rubber is used. Examples of the silane coupling agent that can be used in the present invention include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (for example, "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl)disulfide (for example, "Si75" manufactured by Degussa), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)disulfide; mercapto silanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane; and protected mercapto silanes such as 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane.

[0039] As the anti-aging agent, anti-aging agents such as aromatic amine-based anti-aging agents, amine-ketone-based anti-aging agents, monophenol-based anti-aging agents, bisphenol-based anti-aging agents, polyphenol-based anti-aging agents, dithiocarbamate-based anti-aging agents, thiourea-based anti-aging agents, which are commonly used for rubber, can be used alone or mixed as appropriate.

[0040] After the step of mixing the compounding agents other than the vulcanization compounding agent, the vulcanization compounding agent is further mixed and dispersed. Examples of the vulcanization compounding agent used in the step of mixing the vulcanization compounding agent include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization accelerator aids, vulcanization retarders, and the like.

[0041] Sulfur as a sulfur-based vulcanizing agent may be ordinary sulfur for rubber, and for example, powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0042] As the vulcanization accelerator, a vulcanization accelerator such as a sulfenamide-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiourea-based vulcanization accelerator, a guanidine-based vulcanization accelerator, or a dithiocarbamate-based vulcanization accelerator, which is usually used for rubber vulcanization, may be used alone or in appropriate mixture.

[0043] The rubber composition according to the present invention is obtained by kneading a diene rubber, a polyrotaxane, and, if necessary, carbon black, silica, a silane coupling agent, a vulcanization compounding agent, an antioxidant, zinc oxide, stearic acid, wax, a softening agent such as oil, a processing aid, etc. using a kneader used in the normal rubber industry such as a Banbury mixer, a kneader, or a roll.

[0044] In addition, the compounding method of each of the above components is not particularly limited, and a method of pre-kneading compounding components other than the sulfur-based vulcanizing agent and vulcanization compounding agents such as vulcanization accelerators to form a masterbatch, adding the remaining components and further kneading, a method of adding and kneading each component in an arbitrary order, a method of adding all components simultaneously and kneading, etc. may be used.

[0045] The vulcanized rubber of the rubber composition according to the present invention is particularly excellent in breaking strength. Therefore, a pneumatic tire having a rubber part obtained from such a rubber composition disposed, for example, in a tread part is excellent in durability. For this reason, it is particularly useful as a tread member of a pneumatic tire.

Examples

[0046] Hereinafter, examples etc. specifically showing the configuration and effects of the present invention will be described. The evaluation items in the examples etc. were measured as follows.

[0047] <Crystallization temperature (Tc) and melting temperature (Tm)> Using a differential scanning calorimeter [DSC] (product name: X-DSC 7000, manufactured by Hitachi High-Technologies Corporation), the Tc and Tm of polyrotaxane were measured.

[0048] <Evaluation of the Durability of Vulcanized Rubber> For each rubber composition, vulcanization was carried out at 160 °C for 20 minutes to obtain a vulcanized rubber sheet with a thickness of 2 mm. A JIS No. 3 dumbbell-shaped test piece was punched out from the obtained vulcanized rubber sheet, and a tensile test at a tensile speed of 500 mm / min was carried out in accordance with JIS K6251, and the 300% modulus (M300) [MPa] and the breaking energy [J] were measured at 23 °C. The evaluation was carried out by index evaluation with Comparative Example 1 taken as 100 for both M300 and the breaking energy. The larger the numerical value, the better M300 and the breaking energy are, and it means that the durability of the vulcanized rubber is excellent.

[0049] (Production of Polyrotaxane) Polyrotaxane (trade name "SH2400P", manufactured by ASM), 3,3'-dithiodipropionic acid (an aliphatic carboxylic acid having a disulfide group), 4-dimethylaminopyridine (DMAP) (catalyst) were dissolved in N,N-dimethylformamide (DMF (low moisture content)), and then cooled to 5 °C or lower in an ice bath. At 5 °C or lower, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) (condensing agent) was added and stirred for 30 minutes. After dissolution, the ice bath was removed and the condensation reaction was carried out at room temperature for 6 hours to produce a polyrotaxane having a cyclic molecule with a polysulfide group. The blending ratios of the respective raw materials used are shown in Table 1.

[0050] [Table 1]

[0051] (Production of Rubber Compositions of Examples 1 to 3 and Comparative Examples 1 to 2) The obtained polyrotaxane (raw material reactants 1 to 2) or polyrotaxane (without introducing a polysulfide group into the cyclic molecule) was compounded into a diene rubber (SBR, trade name: SL563, manufactured by JSR Corporation) using a laboratory mixer (product name: Laboplastmill, manufactured by Toyo Seiki Seisakusho Co., Ltd.). The compounding procedure was carried out at the compounding ratios described in Table 2. First, as the first step, silica (trade name: Nipsil AQ, manufactured by Tosoh Silica Corporation), a silane coupling agent (bis(3-triethoxysilylpropyl)tetrasulfide, trade name: Si69, manufactured by Evonik Degussa), raw material reactants 1 to 2 or polyrotaxane (without introducing a polysulfide group into the cyclic molecule), zinc white (trade name: Zinc white No. 1, manufactured by Mitsui Mining & Smelting Co., Ltd.), stearic acid (trade name: Lunac S-20, manufactured by Kao Corporation), and an antioxidant (trade name: No Crack 6C, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added to SBR and kneaded at 150°C. Next, sulfur (powdered sulfur for rubber, 150 mesh, manufactured by Hosoi Chemical Industry Co., Ltd.) and a vulcanization accelerator (trade name: Nocceler CZ (primary vulcanization accelerator), Nocceler D (secondary vulcanization accelerator), both manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added to the obtained mixture and kneaded at 90°C, and the resulting product was used as the rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 2.

[0052]

Table 2

[0053] From the results in Table 2, it means that the vulcanized rubbers of the rubber compositions according to Examples 1 to 3 are excellent in M300 and breaking energy and have excellent durability.

Claims

1. A rubber composition containing a diene rubber and a polyrotaxane, wherein the polyrotaxane has a linear molecule, a cyclic molecule that clathrates the linear molecule, and a sealing group disposed at the ends of the linear molecule to prevent the cyclic molecule from detaching from the linear molecule, and the cyclic molecule has a polysulfide group. A rubber composition characterized by this.

2. The rubber composition according to Claim 1, wherein the polyrotaxane has a cyclic molecule having a disulfide group.

3. The rubber composition according to Claim 1, wherein the polyrotaxane has a crystallization temperature of -30 to -10°C.

4. The rubber composition according to Claim 1, wherein the polyrotaxane has a cyclic molecule having a polysulfide group via an ester bond.

5. The rubber composition according to Claim 1, wherein the polyrotaxane is an ester compound of a hydroxyl group of the cyclic molecule and an aliphatic carboxylic acid having a disulfide group.

6. The rubber composition according to Claim 1, containing 1 to 40 parts by mass of the polyrotaxane when the total amount of the diene rubber is 100 parts by mass.

7. A pneumatic tire comprising a vulcanized rubber obtained from the rubber composition according to Claim 1 as a raw material.

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