Rubber composition and tire

Abstract

To provide a rubber composition and a tire which can provide improved overall performance in terms of crack growth resistance and compression set.SOLUTION: The present invention relates to a rubber composition which satisfies the following relationship (1): 0.42≤Fw / Fa<1.00, wherein Fa and Fw denote the averages of stresses detected in atmospheric air at 23°C and water, respectively, using an atomic force microscope.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to rubber compositions and tires. [Background technology]

[0002] Various materials such as diene rubbers and fillers are used in rubber compositions for tires to improve tire performance (see, for example, Patent Document 1). However, methods for improving the overall performance of crack growth resistance and compression set have not been fully investigated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 125614 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a rubber composition and a tire that can solve the above problems and improve the overall performance of crack growth resistance and compression set. [Means for solving the problem]

[0005] The present disclosure relates to a rubber composition in which average stress values ​​Fa and Fw measured by an atomic force microscope in air and water at 23° C. satisfy the following formula (1): (1) 0.42≦Fw / Fa<1.00 [Effects of the Invention]

[0006] According to the present disclosure, the rubber composition has average stress values ​​Fa and Fw measured by an atomic force microscope in the air and in water at 23°C that satisfy the formula (1), and therefore a rubber composition and a pneumatic tire having good overall performance in terms of crack growth resistance and compression set can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0007] In the rubber composition of the present disclosure, the average stress values ​​Fa and Fw measured in air and water at 23° C. using an atomic force microscope satisfy the formula (1).

[0008] The reason why a rubber composition satisfying the above formula (1) improves the overall performance of crack growth resistance and compression set is not clear, but is presumed to be as follows. Stress detected by atomic force microscopy (AFM) is considered to indicate the hardness of the microstructure within a rubber composition. Satisfying the relationship of stress detected by AFM in water / stress detected by AFM in air < ​​1.00 is considered to indicate that the microscopic region within the rubber exhibits a decrease in hardness in water compared to air. Reversible hydrogen bonding is generally considered to be the cause of this change in hardness in water. Therefore, a rubber composition that satisfies this relationship is considered to have dispersed domains connected by hydrogen bonds within the rubber, which are capable of reversible bonding and cleavage. Because reversible bonds are formed within the rubber, the rubber composition is considered to be able to rebond within the rubber even when cracks occur, thereby improving crack growth resistance. On the other hand, such bonds have low resistance to strain such as compression deformation and are considered to be relatively weak bonds, but furthermore, since the relationship of stress detected by AFM in water / stress detected by AFM in air ≥ 0.43 is satisfied, the recovery force of the chemically strongly bonded domains such as ordinary diene rubbers is obtained, and good crack growth resistance and recovery rate against strain are imparted. Therefore, it is presumed that a rubber composition with significantly improved overall performance in crack growth resistance and compression set can be provided.

[0009] In this way, the problem (objective) of improving the overall performance of crack growth resistance and compression set is solved by configuring a rubber composition such that the average values ​​Fa and Fw of the respective stresses detected by AFM in the air and in water at 23°C satisfy the above formula (1). In other words, the parameter of formula (1), "0.42≦Fw / Fa<1.00," does not define the problem (objective); the object of the present application is to improve the overall performance of crack growth resistance and compression set, and a configuration that satisfies the parameter is used as a means to achieve this.

[0010] In the rubber composition, an average stress Fa measured by AFM in the air at 23° C. and an average stress Fw measured by AFM in water satisfy the following formula (1). (1) 0.42≦Fw / Fa<1.00

[0011] The lower limit of Fw / Fa is preferably 0.43 or more, more preferably 0.45 or more, even more preferably 0.50 or more, and particularly preferably 0.57 or more. The upper limit is preferably 0.90 or less, more preferably 0.85 or less, even more preferably 0.80 or less, and particularly preferably 0.75 or less. Within the above ranges, the effect tends to be favorably obtained.

[0012] In the rubber composition, it is preferable that Fa [MPa] satisfies the following formula: Fa≧3.0MPa Fa is preferably 4.0 MPa or more, more preferably 4.5 MPa or more, even more preferably 5.0 MPa or more, and particularly preferably 5.5 MPa or more. There is no particular upper limit for Fa, but it is preferably 8.0 MPa or less, more preferably 7.5 MPa or less, even more preferably 7.0 MPa or less, and particularly preferably 6.5 MPa or less. Within the above range, the effect tends to be preferably obtained.

[0013] In this specification, the average stress values ​​Fa and Fw can be measured using an AFM, and specifically, can be measured by the method described in the examples.

[0014] An atomic force microscope (AFM) is equipped with a cantilever with a probe attached to the tip. When a sample is observed with the AFM, the probe scans the surface of the sample. The probe moves along the surface of the sample. The movement of the probe is detected by the cantilever. The AFM can measure the mechanical properties of the sample surface, such as stress, hardness, and elastic modulus. The movement of the probe detected by the cantilever is visualized to obtain an AFM image, which allows the three-dimensional shape of the sample surface to be detected.

[0015] Examples of AFMs that can be used include the MultiMode8 manufactured by Bruker AXS and the E-sweep manufactured by Hitachi High-Tech Science, but these are not the only models available. The measurement conditions for the AFM are selected appropriately depending on the type of sample and its surface condition. For example, probes made of materials such as tungsten, iridium, and silicon nitride can be used.

[0016] Mechanical properties can be measured using any AFM mode, and the appropriate measurement mode can be selected. Examples include force modulation mode, force volume mode, and force curve measurement. Other modes include contact mode, tapping mode, and non-contact mode.

[0017] From the viewpoint of obtaining the desired effect, it is preferable that the hardness of the rubber composition be reversibly changed by water.

[0018] In this specification, the phrase "the hardness changes reversibly with water" means that the hardness of the rubber composition (after vulcanization) reversibly increases or decreases in the presence of water. Note that, for example, when the hardness changes from dry to wet to dry, it is sufficient that the hardness changes reversibly, and the hardness may be the same or different between the previous dry state and the subsequent dry state.

[0019] In this specification, the hardness before wetting with water means the hardness of a rubber composition (after vulcanization) that has been dried before wetting with water, and specifically means the hardness of a rubber composition (after vulcanization) that has been dried before wetting with water by the method described in the examples. In this specification, the hardness when wet with water means the hardness of a rubber composition (after vulcanization) in a state wet with water, and specifically means the hardness of a rubber composition (after vulcanization) wetted with water by the method described in the examples.

[0020] In this specification, the hardness (JIS-A hardness) of a rubber composition (after vulcanization) is measured at 25°C using a type A durometer in accordance with JIS K6253-3:2012 "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness."

[0021] In order to obtain the desired effect, the rubber composition preferably has a water-wet hardness Hsw and a water-wet hardness Hsa that satisfy the following formula (2). (2) Hsw / Hsa × 100≦98

[0022] Hsw / Hsa×100 (hardness of rubber composition (after vulcanization) when wetted with water / hardness of rubber composition (after vulcanization) before wetted with water×100) is preferably 97 or less, more preferably 96 or less, even more preferably 95 or less, and particularly preferably 93 or less, and is also preferably 85 or more, more preferably 88 or more, even more preferably 90 or more, and particularly preferably 91 or more. Within the above ranges, the effects tend to be favorably obtained.

[0023] The reason why a rubber composition satisfying the above formula (2) improves the overall performance of crack growth resistance and compression set is not clear, but is presumed to be as follows. The properties of formula (2) are brought about by the presence of reversible bonds in the rubber matrix that can be broken and recombined, such as ionic bonds and hydrogen bonds. Therefore, even if a crack occurs, it is thought that the formation of new bonds will prevent the crack from propagating. Therefore, it is presumed that the overall performance of crack growth resistance and compression set is significantly improved.

[0024] The hardness Hsa (hardness of the rubber composition (after vulcanization) before wetting with water) is preferably 30 or more, more preferably 35 or more, even more preferably 37 or more, and particularly preferably 39 or more, and is preferably 50 or less, more preferably 47 or less, even more preferably 45 or less, and particularly preferably 43 or less. Within the above ranges, the effects tend to be favorably obtained.

[0025] The rubber composition's formula (1) "0.43≦Fw / Fa<1.00" and formula (2) "Hsw / Hsa×100≦98" can be achieved by the rubber composition having bonds, such as hydrogen bonds or ionic bonds, that can be reversibly broken and recombined by adding water and drying. Specifically, this can be achieved by using a rubber modified with an ionic functional group in combination with a compound having an opposite charge to the ionic functional group to form an ionic bond between them.

[0026] The average stress value Fa detected by AFM in the air at 23°C can be adjusted by the types and amounts of chemicals (particularly rubber components, fillers, softeners, and sulfur) compounded into the rubber composition. For example, the average stress value Fa tends to increase when the amount of softener is reduced, the amount of filler is increased, or the amount of sulfur is increased, and tends to decrease when the amount of softener is increased, the amount of filler is reduced, or the amount of sulfur is reduced.

[0027] The average stress Fw detected by AFM in water can be made lower than that in the air at 23°C, for example, by using a rubber composition in which rubber molecules are crosslinked by ionic bonds. Also, it can be adjusted by the types and amounts of chemicals (particularly rubber components, fillers, softeners, and sulfur) compounded in the rubber composition; for example, it tends to increase when the amount of softener is reduced, the amount of filler is increased, or the amount of sulfur is increased, and tends to decrease when the amount of softener is increased, the amount of filler is reduced, or the amount of sulfur is decreased.

[0028] The hardness in a dry state (before wetting with water) can be adjusted by the type and amount of chemicals (particularly rubber components, fillers, softeners, and sulfur) compounded in the rubber composition. For example, the hardness tends to increase when the amount of softener is reduced, the amount of filler is increased, or the amount of sulfur is increased, and tends to decrease when the amount of softener is increased, the amount of filler is reduced, or the amount of sulfur is reduced.

[0029] The hardness when wet with water can be reduced compared to the dry state by, for example, using a rubber composition in which rubber molecules are crosslinked by ionic bonds. Furthermore, it can be adjusted by the types and amounts of chemicals (particularly rubber components, fillers, softeners, and sulfur) compounded in the rubber composition. For example, the hardness tends to increase when the amount of softener is reduced, the amount of filler is increased, or the amount of sulfur is increased, and tends to decrease when the amount of softener is increased, the amount of filler is reduced, or the amount of sulfur is decreased.

[0030] The following describes the chemicals that can be used.

[0031] The rubber component is not particularly limited, and examples thereof include rubbers that are mainly crosslinked with sulfur (sulfur-crosslinkable rubbers). Examples of sulfur-crosslinkable rubbers include diene rubbers such as isoprene-based rubbers, butadiene rubbers (BR), styrene-butadiene rubbers (SBR), and styrene-isoprene-butadiene rubbers (SIBR). Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. These may be used alone or in combination of two or more. Among these, SBR, BR, and isoprene-based rubbers are preferred, isoprene-based rubbers are more preferred, and NR is even more preferred.

[0032] In addition to sulfur-crosslinkable rubber, rubber that is crosslinked mainly by ionic bonds (ionic bond rubber) can also be used as the rubber component. The ionic bond rubber is a rubber having ionic functional groups, and the ionic functional groups include anionic functional groups and cationic functional groups. The ionic bond rubber may have one ionic functional group or two or more ionic functional groups.

[0033] Examples of the anionic functional group include a halogen group and an acidic functional group. Examples of the halogen group include a fluoro group, a chloro group, a bromo group, and an iodo group. Examples of the acidic functional group include a carboxylic acid group, a sulfonic acid group, a sulfate group, a phosphonic acid group, a phosphoric acid group, a phosphinic acid group, a maleic acid group, an acid anhydride group (such as a maleic anhydride group), a fumaric acid group, an itaconic acid group, an acrylic acid group, a methacrylic acid group, and a mercapto group. Among these, a halogen group and a carboxylic acid group are preferred, and a halogen group is more preferred.

[0034] Examples of cationic functional groups include basic functional groups. Examples of basic functional groups include amino groups, imino groups (=NH), ammonium bases, and heterocyclic groups having a basic nitrogen atom. The amino group may be a primary amino group (-NH2), a secondary amino group (-NHR), or a tertiary amino group (-NRR'). R and R' are alkyl groups, phenyl groups, aralkyl groups, or the like, and preferably have 1 to 8 carbon atoms. Examples of ammonium bases include tertiary ammonium bases and quaternary ammonium bases. Examples of heterocyclic groups having a basic nitrogen atom include nitrogen-containing heterocyclic groups such as pyridine groups, pyrimidine groups, pyrazine groups, imidazole groups, thiol-containing imidazole groups, triazole groups, and thiazole groups. In the case of heterocyclic groups, the presence of a double bond makes them more easily dispersed in rubber. Of these, a pyridine group, an imidazole group, a thiazole group, and an amino group (amine group) are preferred, and an imidazole group is more preferred.

[0035] Examples of rubbers into which ionic functional groups can be introduced include diene rubbers as described for sulfur-crosslinkable rubbers, as well as non-diene rubbers that do not contain diene compounds or contain very little diene compounds, such as butyl rubber, urethane rubber, and silicone rubber. These may be used alone or in combination of two or more. Of these, non-diene rubbers are preferred, and butyl rubber is more preferred.

[0036] The ionic bonding rubber is modified with an ionic functional group, and the content of the ionic functional group in 100% by mass of the ionic bonding rubber is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, and even more preferably 1.0% by mass or more, and is preferably 40% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. Within the above ranges, the effects tend to be favorably obtained. The content of the ionic functional group can be measured by performing NMR measurement and calculating the content (mass %) based on the peak corresponding to the ionic functional group.

[0037] From the viewpoint of obtaining the desired effect, the rubber composition preferably contains the ionic-bonding rubber as a rubber component, and more preferably contains the ionic-bonding rubber and the sulfur-crosslinkable rubber.

[0038] The content of the sulfur-crosslinkable rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more, and is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. Within the above ranges, the effects tend to be favorably obtained.

[0039] The content of the ionic-bonding rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more, and is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. Within the above ranges, the effects tend to be favorably obtained.

[0040] From the viewpoint of obtaining the desired effect, the content of the ionic-bonding rubber is preferably less than the content of the sulfur-crosslinkable rubber. The ratio of the content of the sulfur-crosslinkable rubber to the content of the ionic-bonding rubber is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, and is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0041] The ionic bonding rubber is preferably used in combination with an ionic compound having an ionic functional group 2 having an opposite charge to the ionic functional group (ionic functional group 1) of the ionic bonding rubber, thereby forming an ionic bond between the ionic bonding rubber and the ionic compound.

[0042] The ionic functional group 2 can be the same as the ionic functional group 1 described above. When the ionic functional group 2 is an anionic functional group, a halogen group or a carboxylic acid group is preferred, and a halogen group is more preferred. When the ionic functional group 2 is a cationic functional group, a pyridine group, an imidazole group, a thiazole group, or an amino group (amine group) is preferred, and an imidazole group is more preferred.

[0043] Examples of ionic compounds having anionic functional groups include dicarboxylic acids, specifically aliphatic dicarboxylic acids (adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, etc.); aromatic dicarboxylic acids (terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 5-sodiumsulfoisophthalic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, etc.); alicyclic dicarboxylic acids (1,4-cyclohexanedicarboxylic acid, etc.); etc. Among these, from the viewpoint of crack growth resistance (self-repairing ability), etc., aliphatic dicarboxylic acids are preferred, and suberic acid, adipic acid, sebacic acid, and dodecanedioic acid are more preferred.

[0044] Specific examples of ionic compounds having a cationic functional group include imidazoles (imidazole, N-isobutylimidazole, 1-methylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-n-propylimidazole, 2-isopropylimidazole, 1-butylimidazole, 2-butylimidazole, 2-phenylimidazole, 4-methylimidazole, 4-ethylimidazole, 4-nitroimidazole, 4-phenylimidazole, 2-methyl-4-phenylimidazole, 4,5-dimethylimidazole, 1- isobutyl-2-methylimidazole, 2,4,5-trimethylimidazole, 2,4,5-triphenylimidazole, benzimidazole, 2-methylbenzimidazole, 2-phenylbenzimidazole, etc.); pyridines (pyridine, 2-isobutylpyridine, 3-isobutylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 4-propylpyridine, 2-n-hexylpyridine, 3-n-hexylpyridine, 3,5-dimethylpyridine, 3,5-diethylpyridine, 2,6-di-tert-butylpyridine, 2-benzylpyridine, 4-benzylpyridine, 2-phenylpyridine, 3-phenylpyridine, 4-phenylpyridine, 2,6-diphenylpyridine, 2-(3-phenylpropyl)pyridine, 4-(3-phenylpropyl)pyridine, etc.); thiazoles (thiazole, 2-aminothiazole, 2-methylthiazole, 2-methoxythiazole, 2-ethoxythiazole, 2-isobutylthiazole, 2-trimethylsilylthiazole, 5-trimethylsilylthiazole, 4-methylthiazole, 4, 5-dimethylthiazole, 2-ethylthiazole, 2,4-dimethylthiazole, 2-amino-5-methylthiazole, 2-amino-4-methylthiazole, 2,4,5-trimethylthiazole, benzothiazole, 2-methylbenzothiazole, 2,5-dimethylbenzothiazole, etc.); alkylenediamines (methylenediamine, ethylenediamine, propylenediamine, butylenediamine, etc.); polyamines (diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, etc.); and the like.Among these, from the viewpoint of crack growth resistance (self-repairing property), methylimidazole, butylimidazole, pyridine, and ethylenediamine are preferred, and butylimidazole is more preferred.

[0045] In addition to the above-mentioned compounds, metal salts can also be used as the ionic compound. Examples of metal salts include sodium acetate, sodium carbonate, and potassium acetate. Of these, sodium acetate is preferred.

[0046] The ionic functional group 1 of the ionic bonding rubber is preferably an anionic functional group, and the ionic functional group 2 of the ionic compound is preferably a cationic functional group, because the effect tends to be more favorably obtained.

[0047] From the viewpoint of self-repairing property, the amount of the ionic compound per 100 parts by mass of the rubber component is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.2 parts by mass or more, particularly preferably 1.8 parts by mass or more, and is preferably 6.5 parts by mass or less, more preferably 4.5 parts by mass or less, and even more preferably 2.4 parts by mass or less.

[0048] The rubber composition preferably contains a filler. Examples of fillers include those known in the rubber field, such as silica, carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, mica, etc. Of these, silica and carbon black are preferred, and carbon black is more preferred.

[0049] Examples of carbon black include, but are not limited to, GPF, FEF, HAF, ISAF, SAF, etc. Commercially available products include those from Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin-Nichika Carbon Co., Ltd., Columbia Carbon Co., Ltd., etc.

[0050] The amount of carbon black per 100 parts by mass of the rubber component is preferably 12 parts by mass or more, preferably 16 parts by mass or more, more preferably 24 parts by mass or more, and is preferably 70 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 32 parts by mass or less.

[0051] The nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 80 m 2 / g or more, more preferably 100m 2 / g or more, more preferably 110m 2 / g or more, and preferably 160m 2 / g or less, more preferably 140m 2 / g or less, more preferably 125m 2 / g or less. The nitrogen adsorption specific surface area of ​​carbon black is a value measured in accordance with JIS K6217-2:2001.

[0052] Examples of silica include dry process silica (anhydrous silica), wet process silica (hydrated silica), etc. Among these, wet process silica is preferred because it has a large number of silanol groups.

[0053] The amount of silica per 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass, and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less.

[0054] The nitrogen adsorption specific surface area (N2SA) of the silica is preferably 30 m 2 / g or more, more preferably 100m 2 / g or more, more preferably 125m 2 / g or more, and preferably 300m 2 / g or less, more preferably 250m 2 / g or less, more preferably 200m 2 / g or less. The nitrogen adsorption specific surface area of ​​silica is a value measured by the BET method in accordance with ASTM D3037-81.

[0055] As silica, for example, products from Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used.

[0056] Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and examples thereof include bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(2-triethoxysilylethyl)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, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilylethyl)disulfide, bis(4-trimethoxysilylbutyl)disulfide, 3-trimethoxysilylpropyl methyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, and other sulfide-based compounds; mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products include those from Degussa, Momentive, Shin-Etsu Silicones, Tokyo Chemical Industry Co., Ltd., AZMAX Corporation, and Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more. Of these, sulfide-based and mercapto-based silane coupling agents are preferred.

[0057] The content of the silane coupling agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, per 100 parts by mass of silica.

[0058] The rubber composition preferably contains sulfur. Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, soluble sulfur, etc., which are commonly used in the rubber industry. These may be used alone or in combination of two or more.

[0059] As sulfur, for example, products from Tsurumi Chemical Industry Co., Ltd., Karuizawa Iso Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanritsu Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

[0060] The amount of sulfur per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, even more preferably 1.0 part by mass or more, and is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less.

[0061] The rubber composition may contain a vulcanization accelerator. Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazyl sulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazole sulfenamide, Nt-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazole sulfenamide, and N,N'-diisopropyl-2-benzothiazole sulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, di-orthotolylguanidine, and orthotolylbiguanidine. These may be used alone or in combination of two or more. Of these, sulfenamide vulcanization accelerators and guanidine vulcanization accelerators are preferred.

[0062] The amount of the vulcanization accelerator, relative to 100 parts by mass of the rubber component, is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, even more preferably 2.5 parts by mass or more, and is preferably 10.0 parts by mass or less, more preferably 6.0 parts by mass or less, even more preferably 4.0 parts by mass or less.

[0063] The rubber composition may contain oil. Examples of oils include process oils, vegetable oils, and mixtures thereof. Examples of process oils that can be used include paraffin-based process oils, aromatic process oils, and naphthenic process oils. Examples of vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combination of two or more. Among these, process oils are preferred, and aromatic process oils are particularly preferred.

[0064] The oil content, per 100 parts by mass of the rubber component, is preferably at least 2 parts by mass, more preferably at least 5 parts by mass, even more preferably at least 7 parts by mass, and is preferably at most 50 parts by mass, more preferably at most 30 parts by mass, even more preferably at most 20 parts by mass. The oil content also includes the amount of oil (extender oil) contained in the rubber (oil-extended rubber).

[0065] The rubber composition may contain a resin. The resin is not particularly limited as long as it is one commonly used in the tire industry, and examples thereof include rosin-based resins, coumarone-indene resins, α-methylstyrene-based resins, terpene-based resins, pt-butylphenol acetylene resins, acrylic resins, C5 resins, and C9 resins. Commercially available products include those from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., Taoka Chemical Co., Ltd., and Toagosei Co., Ltd. These resins may be used alone or in combination of two or more.

[0066] The amount of the resin per 100 parts by mass of the rubber component is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less.

[0067] The rubber composition may contain a wax. The wax is not particularly limited, and examples thereof include petroleum waxes such as paraffin wax and microcrystalline wax; natural waxes such as vegetable wax and animal wax; and synthetic waxes such as polymers of ethylene, propylene, etc. These may be used alone or in combination of two or more. Of these, petroleum waxes are preferred, and paraffin wax is more preferred.

[0068] As the wax, for example, products from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc. can be used.

[0069] The amount of wax per 100 parts by mass of the rubber component is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 10 parts by mass or less.

[0070] The rubber composition may contain an antioxidant. Examples of the antioxidant include naphthylamine-based antioxidants such as phenyl-α-naphthylamine; diphenylamine-based antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine. Examples of antioxidants include p-phenylenediamine antioxidants such as quinoline; quinoline-based antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol-based antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. These antioxidants may be used alone or in combination of two or more. Among these, p-phenylenediamine-based antioxidants and quinoline-based antioxidants are preferred.

[0071] As the antioxidant, for example, products available from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis, etc. can be used.

[0072] The amount of the antioxidant per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0073] The rubber composition may contain stearic acid. As the stearic acid, conventionally known ones can be used, for example, products available from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

[0074] The amount of stearic acid per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0075] The rubber composition may contain zinc oxide. As the zinc oxide, conventionally known products can be used, for example, products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

[0076] The amount of zinc oxide per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0077] In addition to the above components, the rubber composition may further contain other compounding agents (organic crosslinking agents, etc.) commonly used in the tire industry. The content of these compounding agents is preferably 0.1 to 200 parts by mass per 100 parts by mass of the rubber component.

[0078] The rubber composition can be produced, for example, by kneading the components using a rubber kneading device such as an open roll or a Banbury mixer, and then press-molding the resulting kneaded mixture.

[0079] The kneading conditions for kneading the components are such that the kneading temperature is usually 100 to 180°C, preferably 120 to 170°C, and the kneading time is usually 1 to 30 minutes, preferably 2 to 10 minutes. The conditions for press-molding (vulcanizing) the kneaded product obtained by kneading are such that the temperature is usually 140 to 190°C, preferably 150 to 185°C, and the kneading time is usually 1 to 60 minutes, preferably 5 to 30 minutes.

[0080] The rubber composition can be used (as a rubber composition for tires) for tire components such as treads (cap treads), sidewalls, base treads, undertreads, clinches, bead apexes, breaker cushion rubbers, carcass cord covering rubbers, insulations, chafers, inner liners, and side reinforcing layers of run-flat tires.

[0081] The tire (pneumatic tire, etc.) of the present disclosure is produced by a conventional method using the above rubber composition. That is, the rubber composition is extruded in an unvulcanized state to match the shape of tire components such as a tread, and molded together with other tire components in a tire building machine by a conventional method to form an unvulcanized tire. This unvulcanized tire is then heated and pressurized in a vulcanizer to obtain a tire.

[0082] The tire may be made of at least a part (for example, the tread) of the rubber composition, or may be made of the entire tire of the rubber composition.

[0083] The above-mentioned tires can be used as tires for passenger cars, large passenger cars, large SUVs, heavy-duty tires for trucks, buses, etc., tires for light trucks, tires for motorcycles, racing tires (high-performance tires), etc. They can also be used as all-season tires, summer tires, studless tires (winter tires), etc. [Example]

[0084] The present disclosure will be specifically described based on examples, but the present disclosure is not limited to these examples.

[0085] Bromobutyl rubber: BROMOBUTYL 2255 (butyl rubber having an anionic functional group (bromo group), anionic functional group: 1.0% by mass) manufactured by ExxonMobil Chemical Company Natural rubber: TSR20 Carbon black: Show Black N220 (N2SA: 111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Imidazole: 1-butylimidazole (cationic compound) manufactured by Tokyo Chemical Industry Co., Ltd. Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0086] Examples and Comparative Examples According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded for 5 minutes at 150°C using a 1.7L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded product (base kneading step). Next, sulfur and a vulcanization accelerator were added to the obtained kneaded mixture, and the mixture was kneaded using an open roll at 80° C. for 4 minutes to obtain an unvulcanized rubber composition (finish kneading step). The obtained unvulcanized rubber composition was press-molded in a 2 mm thick mold at 170° C. for 10 minutes to obtain a vulcanized rubber composition (sheet) (vulcanization step).

[0087] The prepared rubber compositions (vulcanized (crosslinked) rubber compositions) were evaluated by the following methods. The results are shown in Table 1.

[0088] <Stress measurement using an atomic force microscope> A sample with a measurement surface of 2 μm square and a thickness of 3 μm was measured in an air atmosphere at 23°C using an atomic force microscope equipped with a probe with a tip radius of 7 nm and spaced at 64 points along each side, and the stress was detected and averaged to obtain Fa. The measurement sample was then immersed in water for 24 hours, and then the stress was measured at 64 intervals per side in water using the liquid measurement holder attached to the device, in the same way as in air, and the average value was taken as Fw. (Measurement conditions) Equipment: Bruker AXS MultiMode8 Measurement range: 10 μm x 10 μm Cantilever: 0.5N / m Frequency: 5Hz

[0089] <Hardness measurement> In accordance with JIS K6253-3:2012, "Vulcanized rubber and thermoplastic rubber - Determination of hardness - Part 3: Durometer hardness," the Shore hardness (Hs) of test specimens (30 mm x 30 mm x 4 mm rectangular parallelepiped shape) prepared from the vulcanized rubber composition was measured using a Type A durometer (JIS-A hardness). Measurements were carried out at 25°C for both the hardness before wetting with water (Hsa) and the hardness after wetting with water (Hsw). The values ​​were averaged over five measurements. (Test piece processing conditions) Before wetting: Dry the test piece under reduced pressure at 80°C and 1 kPa or less until it reaches a constant weight. When wet: Test piece is immersed in 20 ml of water at 25°C for 6 hours

[0090] <Crack growth resistance> A flex crack growth test was conducted in accordance with JIS K6260:2017, in which the rubber composition (sheet) was bent by 70% elongation 1 million times, and the length of the crack that occurred was measured. The results were expressed as an index, with the reciprocal of the measurement value of Comparative Example 1 set to 100. A larger index indicates smaller cracks and better crack growth resistance.

[0091] <Strain recovery rate> The compression set (%) of the rubber composition was measured in accordance with JIS K6262:2013, and the strain recovery rate (%) was calculated as 100 minus the compression set (%). The results were expressed as an index, with the calculated value for Comparative Example 1 being 100. A larger index indicates a larger strain recovery rate, i.e., a smaller compression set.

[0092] <Overall performance> The overall performance of crack growth resistance and compression set was evaluated as the sum of the crack growth resistance (index) and the strain recovery rate (index). The larger the sum of the indexes, the better the overall performance.

[0093] [Table 1]

[0094] As can be seen from Table 1, the rubber compositions of the examples that satisfied the formula (1) "0.42≦Fw / Fa<1.00" were significantly superior in overall performance (expressed as the sum of two indices, crack growth resistance and strain recovery rate) of crack growth resistance and compression set resistance (expressed as the sum of two indices, crack growth resistance and strain recovery rate) compared to the comparative examples that did not satisfy the formula (1).

[0095] The present disclosure (1) is a rubber composition in which average values ​​Fa and Fw of stresses measured by an atomic force microscope in air and water at 23° C. satisfy the following formula (1): (1) 0.42≦Fw / Fa<1.00

[0096] The present disclosure (2) is the rubber composition according to the present disclosure (1) that satisfies the following formula: 0.50≦Fw / Fa<1.00

[0097] The present disclosure (3) is a rubber composition according to the present disclosure (1) or (2), in which the hardness Hsw and hardness Hsa when wetted with water and before wetted with water satisfy the following formula (2): (2) Hsw / Hsa × 100≦98

[0098] The present disclosure (4) is the rubber composition according to the present disclosure (3) that satisfies the following formula: 90≦Hsw / Hsa×100≦98

[0099] The present disclosure (5) is a tire using the rubber composition according to any one of the present disclosures (1) to (4).

Claims

1. The average values ​​Fa and Fw of the stresses measured by an atomic force microscope in the air and in water at 23°C satisfy the following formula (1): The rubber component includes isoprene rubber and butyl rubber, Contains 4.0 parts by mass or more of carbon black per 100 parts by mass of the rubber component, Contains sulfur, A rubber composition comprising an imidazole. (1) 0.42≦Fw / Fa<1.00

2. The rubber composition according to claim 1, which satisfies the following formula: 0.50≦Fw / Fa<1.00

3. 3. The rubber composition according to claim 1, wherein the hardness Hsw and hardness Hsa when wetted with water and before wetted with water satisfy the following formula (2): (2) Hsw / Hsa×100≦98

4. The rubber composition according to claim 3, which satisfies the following formula: 90≦Hsw / Hsa×100≦98

5. The rubber composition according to any one of claims 1 to 4, comprising 6.0 parts by mass or less of sulfur per 100 parts by mass of the rubber component.

6. The rubber composition according to any one of claims 1 to 5, further comprising zinc oxide.

7. The rubber composition according to any one of claims 1 to 6, comprising 70 parts by mass or less of carbon black per 100 parts by mass of the rubber component.

8. The rubber composition according to any one of claims 1 to 7, further comprising a vulcanization accelerator.

9. A tire using the rubber composition according to any one of claims 1 to 8.

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