Rubber composition and tire

Abstract

To provide a rubber composition that achieves improved overall performances including dry grip performance, wet grip performance and fuel economy, and a tire including the same.SOLUTION: A rubber composition contains modified rubber having at least one selected from the group consisting of carboxylic acid, sulfonic acid, and salts thereof in each molecule, and surface-modified silica having at least one selected from the group consisting of a basic molecule and a salt thereof on its surface.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] The grip performance of a tire is important because it is directly linked to safety, and various studies have been conducted to improve the grip performance (see, for example, Patent Document 1). Furthermore, from an environmental perspective, fuel economy is also important, and further improvements in grip performance (dry grip performance and wet grip performance) and fuel economy are required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-285524 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to solve the above problems and provide a rubber composition that improves the overall performance of dry grip performance, wet grip performance, and fuel economy, and a tire using the same. [Means for solving the problem]

[0005] The present disclosure relates to a rubber composition comprising a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, and a surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface. [Effects of the Invention]

[0006] According to the present disclosure, the rubber composition includes a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, and a surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface, thereby improving the overall performance of dry grip performance, wet grip performance, and fuel economy. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a pneumatic tire. DETAILED DESCRIPTION OF THE INVENTION

[0008] <Rubber composition> The present disclosure provides a rubber composition comprising a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, and a surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface. The rubber composition exhibits improved overall performance in terms of dry grip performance, wet grip performance, and fuel economy.

[0009] The reason why the rubber composition exhibits the above-mentioned effects is not entirely clear, but it is presumed to be due to the following mechanism. A modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and their salts in its molecule and surface-modified silica having at least one selected from the group consisting of basic molecules and their salts on its surface forms an ionic bond between the carboxylic acid, etc. and the basic molecule and / or its salt. While this ionic bond is formed when the rubber is dry, it dissociates when the rubber is wet (when the rubber comes into contact with water), which is thought to increase the E*, tan δ, and other properties of the rubber composition. Therefore, when the rubber is wet (when the rubber comes into contact with water), the increased contact area with the road surface and / or increased energy loss improve friction (μ) on wet roads (wet roads), which is thought to improve wet grip performance. Furthermore, because the dissociation and bonding of the ionic bond are reversible, the ionic bond reoccurs when the rubber dries, restoring E*, tan δ, and other properties. In other words, wet grip performance can be improved while maintaining good friction (μ) and fuel economy when driving on dry roads (dry roads). Therefore, it is presumed that the rubber composition improves the overall performance of dry grip performance, wet grip performance and fuel economy.

[0010] (rubber component) The rubber composition contains, as a rubber component, carboxylic acid (carboxylic acid group (-COOH)), sulfonic acid (sulfonic acid group (-SO3H)), and salts thereof (carboxylic acid ion (-COO - ) and / or sulfonate ions (-SO3 - The modified rubber includes a modified rubber having at least one selected from the group consisting of: a carboxylic acid group and a salt thereof (a salt formed from a counter cation thereof). The salt is not particularly limited, and examples thereof include monovalent metal salts such as alkali metal salts (sodium salt, potassium salt, etc.) and divalent metal salts such as alkaline earth metal salts (calcium salt, strontium salt, etc.). Among these, a carboxylic acid group is preferred from the viewpoint of obtaining a more effective effect.

[0011] The modified rubber has at least one ionic functional group 1 selected from the group consisting of carboxylic acid, sulfonic acid, and salts thereof in the molecule, and the content of the ionic functional group 1 in 100% by mass of the rubber (100% by mass of rubber having ionic functional group 1 in the molecule) 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. There is no particular upper limit, but it is preferably 40% by mass or less, more preferably 35% by mass or less. The content of the ionic functional group 1 can be measured by performing NMR measurement and calculating the content (mass %) based on the peak corresponding to the ionic functional group 1.

[0012] In the rubber composition, the content of the modified rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 20% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. There is no particular upper limit, but it is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less. Within the above range, the effects can be suitably obtained.

[0013] Examples of rubber constituting the skeleton of the modified rubber include isoprene-based rubber, butadiene rubber (BR), styrene-butadiene rubber (SBR), and styrene-isoprene-butadiene rubber (SIBR). The rubber components may be used alone or in combination of two or more. Among these, SBR, BR, and isoprene-based rubber are preferred from the viewpoint of tire physical properties.

[0014] The SBR is not particularly limited, and examples thereof include emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc. These may be used alone or in combination of two or more.

[0015] The styrene content of SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The styrene content is preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. Within the above range, the effect tends to be more favorable. In this specification, the styrene content of SBR is 1 It is calculated by H-NMR measurement.

[0016] The vinyl content of the SBR is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. The vinyl content is preferably 75% by mass or less, and more preferably 70% by mass or less. Within the above range, the effect tends to be more favorable. The vinyl content (amount of 1,2-bonded butadiene units) can be measured by infrared absorption spectroscopy.

[0017] As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Nippon Zeon Co., Ltd., etc. can be used.

[0018] When the rubber composition contains, as the modified rubber, a modified SBR having at least one ionic functional group 1 selected from the group consisting of carboxylic acid, sulfonic acid, and salts thereof in the molecule, the content of the modified SBR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 20% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more. There is no particular upper limit, but it is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less. Within the above range, the effects can be preferably obtained.

[0019] The BR is not particularly limited, and examples thereof include high-cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare earth catalyst (rare earth BR). These may be used alone or in combination of two or more. Among these, high-cis BR with a cis content of 90% by mass or more is preferred because it improves wear resistance.

[0020] When the rubber composition contains, as the modified rubber, a modified BR having at least one ionic functional group 1 selected from the group consisting of carboxylic acid, sulfonic acid, and salts thereof in the molecule, the content of the modified BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. There is no particular upper limit, but it is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and particularly preferably 75% by mass or less. Within the above range, the effects can be preferably obtained.

[0021] Examples of isoprene-based rubbers include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR, and modified IR. NRs such as SIR20, RSS#3, and TSR20 are commonly used in the rubber industry. IRs are not particularly limited, and examples of IRs such as IR2200 are commonly used in the rubber industry. Modified NRs include deproteinized natural rubber (DPNR) and highly purified natural rubber (UPNR). Modified NRs include epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Modified IRs include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber. These may be used alone or in combination of two or more.

[0022] When the rubber composition contains a modified isoprene-based rubber having at least one ionic functional group 1 selected from the group consisting of carboxylic acid, sulfonic acid, and salts thereof in the molecule as the modified rubber, the content of the modified isoprene-based rubber in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. There is no particular upper limit, but it is preferably 80% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less. Within the above range, the effects can be preferably obtained.

[0023] The rubber composition may contain a rubber component other than the modified rubber. Examples of the other rubber component include unmodified isoprene-based rubber, BR, and SBR. The rubber composition may also contain a modified rubber other than the modified rubber. Among these, unmodified isoprene-based rubber and BR are preferred.

[0024] When the rubber composition contains a rubber component other than the modified rubber, the content of the other rubber component in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more. There is no particular upper limit, but it is preferably 80% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and particularly preferably 35% by mass or less. Within the above ranges, the effects can be preferably obtained. Note that when an unmodified isoprene-based rubber or unmodified BR is used as the other rubber component, the content of the unmodified isoprene-based rubber and the content of the unmodified BR are also preferably in the same ranges.

[0025] (filler) The rubber composition contains surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface.

[0026] The silica constituting the surface-modified silica is not particularly limited, and examples thereof 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.

[0027] 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. The N2SA of the silica is preferably 300m 2 / g or less, more preferably 250m 2 / g or less, more preferably 200m 2 Within the above range, the effect can be suitably obtained. The N2SA of silica is a value measured by the BET method in accordance with ASTM D3037-93.

[0028] As silica, for example, products from Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., Tokuyama Corporation, etc. can be used.

[0029] The at least one selected from the group consisting of basic molecules and salts thereof that constitute the surface-modified silica can be any basic molecule and / or salt thereof, and for example, a compound having a basic functional group and / or salt thereof can be suitably used. Examples of the basic functional group and the base of the basic functional group include an amino group, an imino group (=NH), an ammonium base, and a heterocyclic group having a basic nitrogen atom.

[0030] The amino group may be any of a primary amino group (-NH2), a secondary amino group (-NHR), and a tertiary amino group (-NRR').

[0031] The R and R' may be substituted or unsubstituted monovalent hydrocarbon groups, which may be linear, branched, or cyclic. The R and R' may be saturated or unsaturated hydrocarbon groups, and may contain heteroatoms such as oxygen.

[0032] The substituted or unsubstituted monovalent hydrocarbon group of R and R' preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 1 to 6 carbon atoms.

[0033] The substituted or unsubstituted monovalent hydrocarbon groups represented by R and R′ include substituted or unsubstituted aliphatic, alicyclic, and aromatic hydrocarbon groups which may contain a heteroatom. Specific examples include substituted or unsubstituted linear alkyl groups, branched alkyl groups, cyclic alkyl groups, aryl groups, and aralkyl groups which may contain a heteroatom.

[0034] When R and R' are substituted or unsubstituted linear or branched alkyl groups which may contain heteroatoms, the number of carbon atoms is preferably 1 to 8, more preferably 1 to 4, and even more preferably 1 to 2. When R and R' are substituted or unsubstituted cyclic alkyl groups which may contain heteroatoms, the number of carbon atoms is preferably 3 to 12. When R and R' are substituted or unsubstituted aryl groups which may contain heteroatoms, the number of carbon atoms is preferably 6 to 10. When R and R' are substituted or unsubstituted aralkyl groups which may contain heteroatoms, the number of carbon atoms is preferably 7 to 10.

[0035] Examples of the substituted or unsubstituted linear or branched alkyl group that may contain a heteroatom include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, and groups containing these heteroatoms. Examples of the substituted or unsubstituted cyclic alkyl group that may contain a heteroatom include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, adamantyl, 1-ethylcyclopentyl, and 1-ethylcyclohexyl. Examples of the substituted or unsubstituted aryl group that may contain a heteroatom include phenyl, tolyl, xylyl, biphenyl, naphthyl, anthryl, phenanthryl, and groups containing these heteroatoms. Examples of the substituted or unsubstituted aralkyl group which may contain a hetero atom include a benzyl group, a phenethyl group, and groups containing these hetero atoms.

[0036] Examples of the ammonium base include a tertiary ammonium base and a quaternary ammonium base.

[0037] Examples of the heterocyclic group having a basic nitrogen atom include nitrogen-containing heterocyclic groups such as a pyridine group, a pyrimidine group, a pyrazine group, an imidazole group, an imidazole group containing a thiol, a triazole group, and a thiazole group. In the case of a heterocyclic group, the presence of a double bond makes it easy to disperse in the rubber.

[0038] Among the basic functional groups, a pyridine group, an imidazole group, a thiazole group, and an amino group (a primary amino group, a secondary amino group, a tertiary amino group) are preferred, and an amino group is more preferred.

[0039] The compound having an amino group as the basic compound is not particularly limited, but for example, a compound having a primary to tertiary amino group and an alkoxysilyl group in one molecule can be suitably used.Specific examples of the compound having an amino group include compounds represented by the following formulas (I) and (II).

[0040] (R 11 O) n R 12 3-n -Si-R 13 -NR 14 R 15 (I) (In the formula, R 11 , R 12 , R 14 and R 15 R each independently represents a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group. 13 represents a substituted or unsubstituted divalent hydrocarbon group, and n represents an integer of 1 to 3.

[0041] (R 21 O) p R 22 3-p -Si-R 23 -NR 24 -R 25 -Si-(R 26 O) q R 27 3-q (II) (In the formula, R 21 , R 22 , R 24 , R 26 and R 27 R each independently represents a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group. 23 and R 25 each independently represents a substituted or unsubstituted divalent hydrocarbon group; p and q each independently represent 1 to 3.

[0042] R in formula (I) and (II) 11 ~R 15 , R 21 ~R 27The substituted or unsubstituted monovalent and divalent hydrocarbon groups of R may be linear, branched, or cyclic. 11 ~R 15 The substituted or unsubstituted monovalent and divalent hydrocarbon groups may be saturated or unsaturated hydrocarbon groups, and may contain heteroatoms such as oxygen.

[0043] R in formula (I) 11 , R 12 , R 14 and R 15 , formula (II)R 21 , R 22 , R 24 , R 26 and R 27 The number of carbon atoms in the substituted or unsubstituted monovalent hydrocarbon group R is preferably 1 to 10, more preferably 1 to 8, and even more preferably 1 to 6. 13 The substituted or unsubstituted divalent hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 1 to 6 carbon atoms.

[0044] R in formula (I) 11 , R 12 , R 14 and R 15 , formula (II)R 21 , R 22 , R 24 , R 26 and R 27 Specific examples of the substituted or unsubstituted monovalent hydrocarbon group of R include the same as the substituted or unsubstituted monovalent hydrocarbon groups of R and R' described above.

[0045] R in formula (I) 13 , R in formula (II) 23 and R 25 Specific examples of the substituted or unsubstituted divalent hydrocarbon group include substituted or unsubstituted alkylene groups having 1 to 18 carbon atoms, which may contain a heteroatom, and cycloalkylene groups having 5 to 18 carbon atoms. Specific examples include a methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, octylene group, nonylene group, decylene group, and 1,2-propylene group.

[0046] Specific examples of the compound having an amino group represented by the above formula (I) include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-[3-(trimethoxysilyl)propyl]-1-butanamine, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminobutyl)-3-aminobutyltrimethoxysilane, and N-2-(aminoethyl)-3-aminopropylmethyltrimethoxysilane.

[0047] Specific examples of the compound having an amino group represented by the above formula (II) include bis(3-trimethoxysilylpropyl)amine, bis(3-triethoxysilylpropyl)amine, bis(4-trimethoxysilylbutyl)amine, bis(triethoxysilylmethyl)amine, and bis(6-trimethoxysilylhexyl)amine.

[0048] Specific examples of compounds having an amino group other than those mentioned above include amino group-containing aromatic compounds such as N-phenyl-3-aminopropyltrimethoxysilane; amino group-containing dialkoxysilane compounds such as 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and bis(3-methyldimethoxysilylpropyl)amine; and ethylenediamine compounds such as N,N'-bis[3-(trimethoxysilyl)propyl]ethylenediamine and N-(2-aminoethyl)-N'-(3-(trimethoxysilyl)propyl)ethylenediamine.

[0049] The compound having an ammonium base as a salt of a basic compound is not particularly limited, but for example, a compound having a tertiary or quaternary ammonium base and an alkoxysilyl group in one molecule can be suitably used. Examples of the compound having an ammonium base include compounds in which the amino group of the compound represented by the formula (I) or (II) is substituted with an ammonium base.

[0050] Examples of the compound having an ammonium base include quaternary ammonium salts of reaction products of N,N-dialkylamino aliphatic alcohols (N,N-dimethylaminoethanol, N,N-dimethylaminopropanol, etc.) with trialkoxysilanes containing an NCO group (γ-trimethoxysilylpropyl isocyanate, etc.), quaternary ammonium salts of reaction products of N,N-dialkylaminoalkyl (meth)acrylic acid esters (N,N-dimethylamino methacrylate, etc.) with trialkoxysilanes containing a mercapto group (γ-mercaptopropyltrimethoxysilane, etc.), monohydrolyzed condensates of these, and cohydrolyzed condensates of these with other silane coupling agents.

[0051] Among these, compounds in which the amino group of the compound represented by formula (I) is substituted with an ammonium base, and quaternary ammonium salts of reaction products of N,N-dialkylaminoaliphatic alcohols and trialkoxysilanes containing an NCO group are preferred, and 3-(trimethoxysilyl)propyldimethyloctadecylammonium salts (e.g., 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride) are more preferred.

[0052] The method for producing surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface (a method for treating (coating) the silica surface with basic molecules and / or salts thereof) can be any method capable of contacting basic molecules and / or salts thereof with silica. For example, the silica can be prepared by mixing basic molecules and / or salts thereof with silica using a known method. Specifically, the silica can be prepared by kneading the basic molecules and / or salts thereof, silica, and other components such as a rubber component using a rubber kneading device such as an open roll or Banbury mixer. Alternatively, the silica can be prepared by mixing only basic molecules and / or salts thereof with silica using a known method.

[0053] In the rubber composition, the content of the surface-modified silica is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 54 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit of the content is not particularly limited, but 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. Within the above range, the desired effect can be obtained. In addition, when the basic molecule is a compound having an amino group, the content of the silica having the compound having an amino group on its surface is also preferably within the same range.

[0054] In the rubber composition, the content of at least one selected from the group consisting of basic molecules and salts thereof (total amount of basic molecules and salts thereof) is preferably 2.0 parts by mass or more, more preferably 4.0 parts by mass or more, and even more preferably 6.0 parts by mass or more, per 100 parts by mass of the total silica contained in the rubber composition. Furthermore, the content is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less. Within the above range, the effects can be suitably obtained.

[0055] The rubber composition may further contain a silane coupling agent in addition to the basic molecule and the salt thereof. 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, 3-trimethoxysilylpropyl-N Examples of such compounds include sulfide-based compounds such as N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, and 3-triethoxysilylpropyl methacrylate monosulfide; 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 that can be used include, for example, products from Degussa, Momentive, Shin-Etsu Silicones Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more.

[0056] When a silane coupling agent is contained, the content of the silane coupling agent may be appropriately selected in consideration of the amount of silica in the surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface, the amount of basic molecules and salts thereof, the amount of silica to be separately blended, etc.

[0057] The rubber composition may contain a filler other than the surface-modified silica. Examples of such fillers include inorganic fillers such as untreated silica (silica having no basic molecules or salts thereof on the surface), carbon black, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica; and poorly dispersible fillers, all of which are well known in the rubber field. Of these, carbon black is preferred.

[0058] Usable carbon blacks include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. These may be used alone or in combination of two or more. Commercially available carbon blacks 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., and Columbia Carbon Co., Ltd.

[0059] The nitrogen adsorption specific surface area (N2SA) of carbon black is 50m 2 / g or more is preferable, and 80m 2 / g or more is more preferable, and 100m 2 / g or more is more preferable. 2 / g or less is preferable, and 150m 2 / g or less is more preferable, and 130m 2 Within the above range, the effect tends to be better. The nitrogen adsorption specific surface area of ​​carbon black can be determined according to JIS K6217-2:2001.

[0060] In the rubber composition, the carbon black content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. Within the above range, the effect tends to be more favorably obtained.

[0061] (metal oxides) The rubber composition preferably contains a metal oxide from the viewpoint of obtaining better effects. Examples of the metal oxide include a single oxide or a composite oxide of a metal, such as a compound represented by MxOy (M represents a metal atom, and x and y each independently represent an integer of 1 to 6). These may be used alone or in combination of two or more. The metal oxide is preferably other than zinc oxide.

[0062] In the rubber composition, the content of the metal oxide is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, particularly preferably 2.2 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 4.0 parts by mass or less, particularly preferably 3.0 parts by mass or less. Within the above ranges, the effect tends to be more favorably obtained.

[0063] Specific metal oxides include alkali metal oxides such as lithium oxide, sodium oxide, potassium oxide, rubidium oxide, and cesium oxide; alkaline earth metal oxides such as calcium oxide, strontium oxide, and barium oxide; transition metal oxides such as scandium oxide, titanium oxide, vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, technetium oxide, ruthenium oxide, rhodium oxide, palladium oxide, silver oxide, hafnium oxide, tantalum oxide, tungsten oxide, osmium oxide, iridium oxide, platinum oxide, and gold oxide; and base metal oxides such as beryllium oxide, magnesium oxide, aluminum oxide, gallium oxide, cadmium oxide, indium oxide, tin oxide, thallium oxide, lead oxide, bismuth oxide, and polonium oxide. Metal oxides can be used alone or as a mixture of two or more. Among these, oxides of divalent metals are preferred, magnesium oxide, calcium oxide and barium oxide are more preferred, and magnesium oxide is even more preferred.

[0064] The apparent specific gravity of magnesium oxide is preferably less than 0.4 g / ml, more preferably 0.3 g / ml or less, even more preferably 0.25 g / ml or less, and is preferably 0.05 g / ml or more, more preferably 0.15 g / ml or more. Within the above ranges, better effects tend to be obtained. The apparent specific gravity of the magnesium oxide was determined by measuring 30 ml of the apparent volume into a 50 ml measuring cylinder and calculating from the mass.

[0065] The d50 of magnesium oxide is preferably less than 10 μm, more preferably 4.5 μm or less, even more preferably 1.5 μm or less, particularly preferably less than 0.75 μm, and is preferably 0.05 μm or more, more preferably 0.45 μm or more. Within the above ranges, better effects tend to be obtained. The d50 of the magnesium oxide is the particle size at 50% of the integrated value in the mass-based particle size distribution curve obtained by the laser diffraction scattering method.

[0066] The nitrogen adsorption specific surface area (N2SA) of magnesium oxide is preferably 100 m 2 / g or more, more preferably 115m 2 / g or more, and preferably 250m 2 / g or less, more preferably 225m 2 / g or less, more preferably 200m 2 Within the above range, there is a tendency for the effect to be better obtained. The N2SA of the magnesium oxide is a value measured by the BET method in accordance with JIS Z8830:2013.

[0067] In the rubber composition, the content of magnesium oxide is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 2.0 parts by mass or more, particularly preferably 2.2 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 4.0 parts by mass or less, particularly preferably 3.0 parts by mass or less. Within the above ranges, the effect tends to be more favorably obtained.

[0068] Commercially available metal oxides include products from Kyowa Chemical Industry Co., Ltd., Fujifilm Wako Pure Chemical Industries Co., Ltd., Kishida Chemical Co., Ltd., Kyowa Chemical Industry Co., Ltd., Tateho Chemical Industry Co., Ltd., JHE Co., Ltd., Nippon Chemical Industry Co., Ltd., Ako Kasei Co., Ltd., etc.

[0069] (plasticizer) The rubber composition preferably contains a plasticizer, which is a material that imparts plasticity to the rubber component, and examples of the plasticizer include a liquid plasticizer (a plasticizer that is in a liquid state at room temperature (25°C)) and a resin (a resin that is in a solid state at room temperature (25°C)).

[0070] In the rubber composition, the content of the plasticizer (total amount of plasticizer) is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, and particularly preferably 30 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 120 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 90 parts by mass or less. Within the above range, the effect tends to be more favorably obtained.

[0071] Liquid plasticizers (plasticizers that are liquid at room temperature (25°C)) that can be used in the rubber composition are not particularly limited, and examples include oils, liquid polymers (liquid resins, liquid diene-based polymers, liquid farnesene-based polymers, etc.), etc. These may be used alone or in combination of two or more.

[0072] In the rubber composition, the content of the liquid plasticizer is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 8 parts by mass or more, and particularly preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. Within the above range, the effect tends to be more favorably obtained. Note that the content of the liquid plasticizer also includes the amount of oil contained in the oil-extended rubber. A similar range is also preferred for the content of the oil.

[0073] 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 that can be used 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. Commercially available products include those from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Corporation, Oriso Co., Ltd., H&R Corporation, Toyokuni Oil Mills Co., Ltd., Showa Shell Sekiyu K.K., Fuji Kosan Co., Ltd., and Nisshin Oillio Group, Ltd. Among these, process oils (paraffin-based process oils, aromatic process oils, naphthenic process oils, etc.) and vegetable oils are preferred.

[0074] Examples of liquid resins include terpene resins (including terpene phenol resins and aromatic modified terpene resins), rosin resins, styrene resins, C5 resins, C9 resins, C5 / C9 resins, dicyclopentadiene (DCPD) resins, coumarone-indene resins (including coumarone and indene simple resins), phenol resins, olefin resins, polyurethane resins, acrylic resins, etc. Hydrogenated products of these resins can also be used.

[0075] Examples of liquid diene polymers include liquid styrene butadiene copolymers (liquid SBR), liquid butadiene polymers (liquid BR), liquid isoprene polymers (liquid IR), liquid styrene isoprene copolymers (liquid SIR), liquid styrene butadiene styrene block copolymers (liquid SBS block polymers), liquid styrene isoprene styrene block copolymers (liquid SIS block polymers), liquid farnesene polymers, and liquid farnesene butadiene copolymers, all of which are liquid at 25°C. The terminals or main chains of these polymers may be modified with polar groups. Hydrogenated versions of these polymers can also be used.

[0076] Examples of the resins (resins that are solid at room temperature (25°C)) that can be used in the rubber composition include aromatic vinyl polymers, coumarone-indene resins, coumarone resins, indene resins, phenolic resins, rosin resins, petroleum resins, terpene resins, and acrylic resins that are solid at room temperature (25°C). The resins may also be hydrogenated. These may be used alone or in combination of two or more. Of these, aromatic vinyl polymers, petroleum resins, and terpene resins are preferred.

[0077] In the rubber composition, the content of the resin is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more, per 100 parts by mass of the rubber component. The upper limit is preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. Within the above range, the effect tends to be more favorably obtained.

[0078] The softening point of the resin is preferably 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. The upper limit is preferably 160°C or lower, more preferably 150°C or lower, and even more preferably 145°C or lower. Within the above range, the effect tends to be better obtained. The softening point of the resin is the temperature at which the ball drops when the softening point specified in JIS K6220-1:2001 is measured using a ring and ball softening point tester.

[0079] The aromatic vinyl polymer is a polymer containing an aromatic vinyl monomer as a constituent unit. For example, it may be a resin obtained by polymerizing α-methylstyrene and / or styrene, and specifically may be a homopolymer of styrene (styrene resin), a homopolymer of α-methylstyrene (α-methylstyrene resin), a copolymer of α-methylstyrene and styrene, or a copolymer of styrene and another monomer.

[0080] The coumarone-indene resin is a resin containing coumarone and indene as the main monomer components constituting the resin skeleton (main chain). Other monomer components contained in the skeleton besides coumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene, etc.

[0081] The coumarone resin is a resin containing coumarone as a main monomer component constituting the skeleton (main chain) of the resin.

[0082] The indene resin is a resin containing indene as a main monomer component constituting the skeleton (main chain) of the resin.

[0083] The phenolic resin may be a known polymer obtained by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural in the presence of an acid or alkali catalyst. Of these, those obtained by reacting with an acid catalyst (such as novolac phenolic resin) are preferred.

[0084] Examples of the rosin resin include rosin-based resins such as natural rosin, polymerized rosin, modified rosin, ester compounds thereof, and hydrogenated products thereof.

[0085] Examples of the petroleum resin include C5 resin, C9 resin, C5 / C9 resin, dicyclopentadiene (DCPD) resin, and hydrogenated versions of these resins. Of these, DCPD resin and hydrogenated DCPD resin are preferred.

[0086] The terpene resin is a polymer containing terpene as a structural unit, and examples thereof include polyterpene resins obtained by polymerizing a terpene compound and aromatic-modified terpene resins obtained by polymerizing a terpene compound and an aromatic compound. Examples of aromatic-modified terpene resins that can be used include terpene phenolic resins made from terpene compounds and phenolic compounds, terpene styrene resins made from terpene compounds and styrene compounds, and terpene phenol styrene resins made from terpene compounds, phenolic compounds, and styrene compounds. Examples of terpene compounds include α-pinene and β-pinene, phenolic compounds include phenol and bisphenol A, and aromatic compounds include styrene compounds (styrene, α-methylstyrene, etc.).

[0087] The acrylic resin is a polymer containing an acrylic monomer as a constituent unit. For example, a styrene-acrylic resin having a carboxyl group and obtained by copolymerizing an aromatic vinyl monomer component with an acrylic monomer component can be used. Among them, a solvent-free carboxyl-containing styrene-acrylic resin can be preferably used.

[0088] Examples of plasticizers that can be used include products 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., and Taoka Chemical Co., Ltd.

[0089] (Other ingredients) The rubber composition preferably contains an antioxidant from the viewpoint of crack resistance, ozone resistance, and the like.

[0090] The antioxidant is not particularly limited, but examples thereof 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, N,N'-di-2-naphthyl-p-phenylenediamine, and the like. Examples of suitable antioxidants include p-phenylenediamine antioxidants such as amines; quinoline antioxidants such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, and polyphenol antioxidants such as tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine antioxidants and quinoline antioxidants are preferred, with polymers of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline being more preferred. Commercially available products include those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., and Flexis.

[0091] In the rubber composition, the content of the antioxidant is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component, and is preferably 7.0 parts by mass or less, more preferably 4.0 parts by mass or less.

[0092] The rubber composition may contain stearic acid. The content of stearic acid in the rubber composition is preferably 0.5 to 10 parts by mass or more, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0093] As the stearic acid, conventionally known products can be used, for example, products available from NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Chiba Fatty Acid Co., Ltd., etc.

[0094] The rubber composition may contain zinc oxide. The content of zinc oxide in the rubber composition is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0095] 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.

[0096] The rubber composition may contain wax, and the content of the wax in the rubber composition is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0097] The wax is not particularly limited, and examples thereof include petroleum waxes, natural waxes, etc. Synthetic waxes obtained by refining or chemically treating multiple waxes can also be used. These waxes may be used alone or in combination of two or more types.

[0098] Examples of petroleum-based waxes include paraffin wax and microcrystalline wax. Natural waxes are not particularly limited as long as they are derived from non-petroleum resources, and include, for example, plant-based waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal-based waxes such as beeswax, lanolin, and spermaceti; mineral-based waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include those from Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd.

[0099] The rubber composition may contain sulfur in order to form appropriate crosslinked chains in polymer chains and to provide a good balance of the above performances.

[0100] In the rubber composition, the sulfur content is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and even more preferably 0.7 part by mass or more, per 100 parts by mass of the rubber component, and is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

[0101] 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. Commercially available products include those from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemical Industry Co., Ltd., Flexis Corporation, Nippon Kanzuri Kogyo Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. These may be used alone or in combination of two or more.

[0102] The rubber composition may contain a vulcanization accelerator. In the rubber composition, the content of the vulcanization accelerator is usually 0.3 to 10 parts by mass, and preferably 0.5 to 7 parts by mass, per 100 parts by mass of the rubber component.

[0103] The type of vulcanization accelerator is not particularly limited, and commonly used ones can be used. Examples of the vulcanization accelerator 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. Among these, sulfenamide vulcanization accelerators and guanidine vulcanization accelerators are preferred.

[0104] Among the vulcanization accelerators, sulfenamide vulcanization accelerators and guanidine vulcanization accelerators are preferred. The content of the sulfenamide vulcanization accelerator is not particularly limited, but is preferably 0.3 to 4.0 parts by mass, preferably 0.5 to 2.5 parts by mass, and more preferably 0.7 to 1.6 parts by mass, per 100 parts by mass of the rubber component. The content of the guanidine vulcanization accelerator is not particularly limited, but is preferably 0.5 to 5.0 parts by mass, preferably 0.8 to 3.0 parts by mass, and more preferably 1.0 to 2.3 parts by mass, per 100 parts by mass of the rubber component.

[0105] In addition to the above components, the rubber composition may contain additives such as a mold release agent and a pigment, which are commonly used in accordance with the field of application.

[0106] From the viewpoint of obtaining a more effective effect, it is desirable that the complex modulus (E*) and loss tangent (tanδ) of the rubber composition (after vulcanization) are reversibly changed by water and satisfy the formula (1) and / or (2) described below.

[0107] The reason why the rubber composition exhibits the above-mentioned effects is not entirely clear, but it is presumed to be due to the following mechanism. As described above, modified rubber containing at least one selected from the group consisting of carboxylic acids, sulfonic acids, and their salts in its molecule and surface-modified silica having at least one selected from the group consisting of basic molecules and their salts on its surface form ionic bonds between the carboxylic acids and the basic molecules and / or their salts. While these ionic bonds remain in place when dry, they dissociate when wet (upon contact with water), resulting in a decrease in E* and / or an increase in tan δ of the rubber composition. Therefore, when wet (upon contact with water), the increased contact area with the road surface and / or increased energy loss improve friction (μ) on wet (wet) surfaces, leading to improved wet grip performance. Furthermore, because the dissociation and bonding of the ionic bonds are reversible, ionic bonds reoccur upon drying, restoring E* and / or tan δ. In other words, wet grip performance can be improved while maintaining good friction (μ) and fuel economy when driving on dry surfaces. Therefore, it is presumed that the rubber composition significantly improves the overall performance of dry grip performance, wet grip performance and fuel economy.

[0108] As described above, the present disclosure solves the problem (objective) of improving the overall performance of dry grip performance, wet grip performance, and fuel economy by configuring a rubber composition that satisfies the parameters of formulas (1) and / or (2) described below. In other words, the parameters do not define the problem (objective), and the object of the present application is to improve the overall performance of dry grip performance, wet grip performance, and fuel economy, and a configuration that satisfies the parameters of formulas (1) and / or (2) described below is used as a means to achieve this.

[0109] In this specification, E* and tanδ of a rubber composition refer to the E* and tanδ of the rubber composition after vulcanization. Furthermore, E* and tanδ are values ​​obtained by conducting a viscoelasticity test on the rubber composition after vulcanization.

[0110] In this specification, "the complex modulus (E*) and loss tangent (tanδ) change reversibly due to water" means that the E* and tanδ of the rubber composition (after vulcanization) reversibly increase or decrease in the presence of water. Note that, for example, when changing from dry to wet to dry, it is sufficient that E* and tanδ change reversibly, and the E* and tanδ do not have to be the same in the previous drying state and the subsequent drying state, or they may be the same in the previous drying state and the subsequent drying state.

[0111] In this specification, E* and tanδ in a dry state refer to the E* and tanδ of a rubber composition (after vulcanization) in a dry state, and specifically refer to the E* and tanδ of a rubber composition (after vulcanization) dried by the method described in the examples. In this specification, E* and tanδ when wet with water refer to the E* and tanδ of a rubber composition (after vulcanization) in a state wet with water, and specifically refer to the E* and tanδ of a rubber composition (after vulcanization) wetted with water by the method described in the examples.

[0112] In this specification, E* and tan δ of a rubber composition (after vulcanization) are E* and tan δ measured under conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.

[0113] The rubber composition (after vulcanization) preferably satisfies the following formula (1). E* when wet / E* when dry≦0.90 (1) (In the formula, E* is the complex modulus measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.) The ratio of E* when wet to E* when dry is preferably 0.87 or less, more preferably 0.82 or less, even more preferably 0.80 or less, and particularly preferably 0.77 or less. There is no particular restriction on the lower limit of E* when wet to E* when dry, but it is preferably 0.50 or more, more preferably 0.60 or more, even more preferably 0.63 or more, and particularly preferably 0.65 or more. Within the above range, the effect can be suitably obtained.

[0114] The rubber composition (after vulcanization) has an E* value in a dry state of preferably 5.5 MPa or more, more preferably 6.5 MPa or more, even more preferably 7.0 MPa or more, particularly preferably 7.5 MPa or more, and most preferably 8.0 MPa or more. There are no particular restrictions on the upper limit of E* in a dry state, but it is preferably 20.0 MPa or less, more preferably 17.0 MPa or less, even more preferably 16.0 MPa or less, and particularly preferably 15.0 MPa or less. Within the above range, the effects can be suitably obtained.

[0115] The rubber composition (after vulcanization) preferably satisfies the following formula (2). Tan δ when wet / tan δ when dry ≧ 1.15 (2) (In the formula, tanδ is the loss tangent measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.) The ratio of wet tan δ to dry tan δ is preferably 1.20 or more, more preferably 1.25 or more, even more preferably 1.30 or more, and particularly preferably 1.33 or more. There are no particular limitations on the upper limit of wet tan δ to dry tan δ, but it is preferably 1.60 or less, more preferably 1.55 or less, even more preferably 1.50 or less, and particularly preferably 1.45 or less. Within the above range, the effects can be suitably obtained.

[0116] The rubber composition (after vulcanization) has a dry tan δ of preferably 2.2 or more, more preferably 2.7 or more, even more preferably 3.0 or more, and particularly preferably 3.3 or more. There is no particular upper limit to the dry tan δ, but it is preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.2 or less, and particularly preferably 5.0 or less. Within the above range, the effects can be suitably obtained.

[0117] The reversible changes in E* and tan δ of a rubber composition due to water, as represented by the above formulas (1) and / or (2), can be achieved, for example, by blending a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule with surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof. Specifically, the reversible changes in E* and tan δ of a rubber composition due to water, as represented by the above formulas (1) and / or (2), can be achieved by combining a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, such as carboxylic acid-modified SBR, with surface-modified silica having basic molecules and / or salts thereof on its surface, such as silica having a compound having a basic functional group and / or a base thereof on its surface. This is thought to be achieved by the following: when such a combination is used, an ionic bond is formed between the modified rubber and the surface-modified silica, for example, by a cation derived from a basic molecule and / or a salt thereof and an anion derived from a carboxylic acid, a sulfonic acid, or a salt thereof; and the ionic bond between the modified rubber and the surface-modified silica is cleaved by the addition of water, and recombined by drying the water, resulting in a decrease in E* and / or an increase in tan δ when wet with water, and an increase in E* and / or a decrease in tan δ when dry.

[0118] The dry E* can be adjusted by the type and amount of chemicals (especially rubber components, fillers, softeners such as oils) compounded into the rubber composition. For example, the dry E* tends to increase by reducing the amount of softener or increasing the amount of filler.

[0119] The dry tan δ can be adjusted by the type and amount of chemicals (particularly rubber components, fillers, softeners, resins, sulfur, vulcanization accelerators, and silane coupling agents) compounded into the rubber composition. For example, the dry tan δ tends to increase when a softener (e.g., resin) that is poorly compatible with the rubber component is used, when an unmodified rubber is used, when the amount of filler is increased, when oil as a plasticizer is increased, when sulfur is reduced, when vulcanization accelerators are reduced, or when silane coupling agents are reduced.

[0120] Furthermore, the E* and tanδ upon drying can be adjusted, for example, by the acidic functional group content of the modified rubber or the coating amount of the basic molecule and its salt on the surface-modified silica (in other words, the coating amount of the basic functional group and its base). Specifically, increasing the acidic functional group content of the modified rubber or the coating amount of the basic molecule and its base on the silica tends to increase the E* upon drying and decrease the tanδ upon drying.

[0121] Regarding E* and tan δ when wet, for example, by forming a rubber composition crosslinked by ionic bonds in which the modified rubber and the surface-modified silica are partially or entirely crosslinked by ionic bonds, the E* when wet can be lowered and / or tan δ can be increased compared to when dry, making it possible to adjust the E* and tan δ when wet and when dry. Specifically, by using the modified rubber in combination with the surface-modified silica, a rubber composition crosslinked by ionic bonds can be obtained, which can lower E* and / or increase tan δ when wet compared to when dry. Furthermore, the E* and tan δ when wet can be adjusted by the type and amount of chemicals blended into the rubber composition. For example, similar trends can be obtained for E* and tan δ when wet by using the same methods as those for adjusting E* and tan δ when dry described above.

[0122] Specifically, by adjusting the dry E* and tanδ to within the desired ranges and then using a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule in combination with surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface, it is possible to achieve reversible water-induced E* changes and / or tanδ changes of the rubber composition as represented by the above formulas (1) and / or (2).

[0123] The rubber composition can be produced by a known method. For example, the rubber composition can be produced by kneading the components using a rubber kneading device such as an open roll or a Banbury mixer, and optionally crosslinking the components. The kneading conditions are as follows: the kneading temperature is usually 50 to 200°C, preferably 80 to 190°C, and the kneading time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes.

[0124] The tire component for which the rubber composition is used is not particularly limited, but it can be suitably used for the tread (cap tread).

[0125] <Tires> The rubber composition can be suitably used for tires. Examples of tires include pneumatic tires and non-pneumatic tires, with pneumatic tires being preferred. In particular, the rubber composition can be suitably used as summer tires and winter tires (studless tires, snow tires, studded tires, etc.). Tires can be used for passenger car tires, large passenger car tires, large SUV tires, heavy-duty tires for trucks, buses, etc., light truck tires, motorcycle tires, racing tires (high-performance tires), etc.

[0126] A tire is manufactured by a conventional method using the above rubber composition. For example, a rubber composition containing various materials is extruded to fit the shape of tire components while still unvulcanized, and molded together with other tire components in a tire building machine by a conventional method to form an unvulcanized tire. The unvulcanized tire is then heated and pressurized in the vulcanizer to obtain a tire.

[0127] An example of a tire using the rubber composition will be described with reference to FIG. 1, the up-down direction is the radial direction of the tire 2, the left-right direction is the axial direction of the tire 2, and the direction perpendicular to the paper surface is the circumferential direction of the tire 2. The tread 4 includes a cap layer 30 and a base layer 28, and it is preferable that the cap layer 30 is made of the rubber composition.

[0128] Although FIG. 1 shows an example of a two-layer tread 4 consisting of a cap layer 30 and a base layer 28, a single-layer tread or a tread having a structure of three or more layers may also be used. In either case, it is desirable that the outermost layer that comes into contact with the road surface is made of the rubber composition.

[0129] In the tire 2, each sidewall 6 extends substantially radially inward from an end of the tread 4. A radially outer portion of each sidewall 6 is joined to the tread 4. A radially inner portion of each sidewall 6 is joined to a clinch 10. The sidewall 6 can prevent damage to the carcass 14.

[0130] Each wing 8 is located between the tread 4 and the sidewall 6. The wing 8 is joined to each of the tread 4 and the sidewall 6.

[0131] Each clinch 10 is located approximately radially inward of the sidewall 6. The clinches 10 are located axially outward of the beads 12 and the carcass 14.

[0132] Each bead 12 is located axially inward of the clinch 10. The bead 12 includes a core 32 and an apex 34 extending radially outward from the core 32. The core 32 is preferably ring-shaped and includes a wound non-extensible wire. The apex 34 tapers radially outward.

[0133] The carcass 14 includes a carcass ply 36. In the tire 2, the carcass 14 is made up of one carcass ply 36, but may be made up of two or more carcass plies.

[0134] In the tire 2, the carcass ply 36 is laid between the beads 12 on both sides and extends along the tread 4 and the sidewall 6. The carcass ply 36 is folded back from the inside to the outside in the axial direction around each core 32. This folding back forms a main portion 36a and a pair of folded back portions 36b in the carcass ply 36. That is, the carcass ply 36 includes the main portion 36a and the pair of folded back portions 36b.

[0135] Although not shown, the carcass ply 36 preferably comprises a large number of parallel cords and a topping rubber. The absolute value of the angle that each cord forms with respect to the equator plane is preferably 75° to 90°. In other words, the carcass 14 preferably has a radial structure.

[0136] The belt 16 is located radially inward of the tread 4. The belt 16 is laminated with the carcass 14. The belt 16 reinforces the carcass 14. The belt 16 is made up of an inner layer 38 and an outer layer 40. As is clear from FIG. 1 , it is desirable that the width of the inner layer 38 is slightly larger than the width of the outer layer 40 in the axial direction. In this tire 2, the axial width of the belt 16 is preferably 0.6 times or more and 0.9 times or less the cross-sectional width of the tire 2 (see JATMA).

[0137] Although not shown, each of the inner layer 38 and the outer layer 40 preferably comprises a large number of cords arranged in parallel and a topping rubber. In other words, the belt 16 includes a large number of cords arranged in parallel. Each cord is inclined with respect to the equatorial plane. The absolute value of the inclination angle is generally 10° or more and 35° or less. The inclination direction of the cords of the inner layer 38 with respect to the equatorial plane is opposite to the inclination direction of the cords of the outer layer 40 with respect to the equatorial plane.

[0138] The band 18 is located radially outside the belt 16. In the axial direction, the band 18 has a width equal to the width of the belt 16. The band 18 may also have a width greater than the width of the belt 16.

[0139] Although not shown, the band 18 is preferably made of a cord and a topping rubber. The cord is wound spirally. The band 18 has a so-called jointless structure. The cord extends substantially in the circumferential direction. The angle of the cord with respect to the circumferential direction is preferably 5° or less, and more preferably 2° or less. The cord restrains the belt 16, thereby suppressing lifting of the belt 16.

[0140] The belt 16 and the band 18 form a reinforcing layer. The reinforcing layer may be formed of the belt 16 alone.

[0141] The inner liner 20 is located inside the carcass 14. The inner liner 20 is bonded to the inner surface of the carcass 14. A typical base rubber of the inner liner 20 is butyl rubber or halogenated butyl rubber. The inner liner 20 maintains the internal pressure of the tire 2.

[0142] Each chafer 22 is located near a bead 12. In this embodiment, the chafer 22 is preferably made of a cloth with rubber impregnated into the cloth. The chafer 22 may be integral with the clinch 10.

[0143] In this tire 2, the tread 4 has main grooves 42 as the grooves 26. As shown in FIG. 1 , a plurality of main grooves 42, specifically three main grooves 42, are formed in the tread 4. These main grooves 42 are spaced apart in the axial direction. The three main grooves 42 formed in the tread 4 form four ribs 44 extending in the circumferential direction. In other words, the spaces between the ribs 44 constitute the main grooves 42.

[0144] Each main groove 42 extends in the circumferential direction. The main grooves 42 are continuous and uninterrupted in the circumferential direction. The main grooves 42 facilitate the drainage of water present between the road surface and the tire 2, for example, in rainy weather. This allows the tire 2 to maintain sufficient contact with the road surface even when the road surface is wet.

[0145] In the tire 2 having the tread 4 made of the rubber composition, the negative ratio (S) of the tread 4 is preferably 50% or less. The negative ratio (S) of the tread 4 is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less. The negative ratio is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. When it is within the above range, better effects tend to be obtained.

[0146] The reason why such an effect is obtained is not entirely clear, but it is presumed to be due to the following mechanism. As mentioned above, by satisfying the above formulas (1) and (2), when the tire is wet, the friction (μ) on a wet road surface is improved due to an increase in the contact area with the road surface and / or an increase in energy loss, improving wet grip performance. When the tire is dry, ionic bonding occurs again, and the complex modulus E* returns to its original state, presumably maintaining good friction (μ) and fuel economy when traveling on dry roads. However, it is believed that a low negative ratio of the tread further improves the friction (μ) on a wet road surface and further improves wet grip performance. Therefore, it is presumed that a tire having a tread made of the above rubber composition will have improved overall performance in terms of dry grip performance, wet grip performance, and fuel economy.

[0147] In a tire 2 having a tread 4 made of the rubber composition, it is preferable that the wet E* and dry E* of the rubber composition and the negative rate S (%) of the tread 4 satisfy the following formula (3). (E* when wet / E* when dry) × S≦28.0 (3) (E* when wet / E* when dry) x S is preferably 26.0% or less, more preferably 24.0% or less, and even more preferably 23.5% or less. There is no particular lower limit, but it is preferably 5.0% or more, more preferably 15.0% or more, and even more preferably 17.0% or more. Within the above range, better effects tend to be obtained.

[0148] The reason why such an effect is obtained is not entirely clear, but it is presumed to be due to the following mechanism. As mentioned above, it is presumed that by satisfying the formula (1), when the tire is wet, the contact area with the road surface increases, improving friction (μ) on wet roads and improving wet grip performance, and when the tire is dry, ionic bonding occurs again, restoring E*, thereby maintaining good friction (μ) and fuel economy when traveling on dry roads. However, it is believed that a low negative ratio of the tread further improves friction (μ) on wet roads and further improves wet grip performance. Therefore, it is presumed that a tire having a tread made of a rubber composition that satisfies the formula (3) will have improved overall performance in terms of dry grip performance, wet grip performance, and fuel economy.

[0149] In a tire 2 having a tread 4 made of the rubber composition, it is preferable that the tan δ of the rubber composition when wet and when dry, and the negative rate S (%) of the tread 4 satisfy the following formula (4). (tanδ when wet / tanδ when dry) / S≧0.035 (4) (tan δ when wet with water / tan δ when dry) / S is preferably 0.037 (1 / %) or more, more preferably 0.040 (1 / %) or more, and even more preferably 0.042 (1 / %) or more. There is no particular upper limit, but it is preferably 0.100 (1 / %) or less, more preferably 0.080 (1 / %) or less, and even more preferably 0.060 (1 / %) or less. Within the above range, better effects tend to be obtained.

[0150] The reason why such an effect is obtained is not entirely clear, but it is presumed to be due to the following mechanism. As mentioned above, it is presumed that by satisfying the formula (2), when the tire is wet, the friction (μ) on a wet road surface increases due to increased energy loss, improving wet grip performance, and when the tire is dry, ionic bonding occurs again, restoring tan δ, thereby maintaining good friction (μ) and fuel economy when traveling on dry roads. However, it is believed that a low negative ratio of the tread further improves the friction (μ) on a wet road surface, further improving wet grip performance. Therefore, it is presumed that a tire having a tread made of a rubber composition that satisfies the formula (4) will have improved overall performance in terms of dry grip performance, wet grip performance, and fuel economy.

[0151] The negative ratio (negative ratio within the contact area of ​​the tread portion) is the ratio of the total groove area within the contact area to the total area of ​​the contact area, and is measured by the following method. In this specification, if the tire is a pneumatic tire, the negative rate is calculated from the contact shape under normal load conditions with a normal rim and normal internal pressure. In the case of a non-pneumatic tire, the negative rate can be measured in the same way without requiring normal internal pressure. "Genuine rim" means a rim that is specified for each tire by the standard system that includes the standard on which the tire is based. For example, it means a standard rim in the case of JATMA, a "Design Rim" in the case of TRA, or a "Measuring Rim" in the case of ETRTO. "Normal internal pressure" refers to the air pressure specified for each tire by the above standards. In the case of JATMA, this means the maximum air pressure, in the case of TRA, it means the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it means "INFLATION PRESSURE". In the case of passenger car tires, it is 180kPa. "Normal load" refers to the load specified for each tire by the above standards, and means the load obtained by multiplying the maximum load capacity in the case of JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the case of TRA, and the "LOAD CAPACITY" in the case of ETRTO by 0.88. The contact shape is obtained by assembling the tire on a standard rim, applying the standard internal pressure, and leaving it to stand at 25°C for 24 hours. Then, ink is applied to the surface of the tire tread, and the tire is pressed against cardboard under a standard load (camber angle 0°) and transferred to the paper. The tire is rotated 72° in the circumferential direction and the pattern is transferred at five locations. In other words, the contact shape is obtained five times. For the five contact shapes, the average value of the maximum length in the tire axial direction is defined as L, and the average value of the length in the direction perpendicular to the axial direction is defined as W. The negative rate (%) is calculated as follows: [1-{average area of ​​five transferred contact shapes (ink areas) on cardboard / (L×W)}]×100(%). Here, the average value of the length or area is the simple average of the five values. [Example]

[0152] The present disclosure will be specifically described based on examples, but the present disclosure is not limited to these examples.

[0153] The various chemicals used in the examples and comparative examples will be collectively described below. Carboxylic acid modified SBR: Manufacturing example below NR:TSR20 SBR: Nipol 1502 (E-SBR) manufactured by ZEON Corporation BR: BR150B manufactured by Ube Industries, Ltd. Carbon black: Diablack I (N220, N2SA114m) manufactured by Mitsubishi Chemical Corporation 2 / g, DBP 114ml / 100g) Silica 1: Ultrasil VN3 (N2SA175m) manufactured by Evonik Degussa 2 / g) Silica 2: 9000GR (N2SA235m) manufactured by Evonik Degussa 2 / g) Stearic acid: NOF Corporation's "Tsubaki" stearic acid Magnesium oxide 1: Kyowamag 150 (apparent specific gravity 0.36 g / ml, d50: 4.46 μm, N2SA: 145 m) manufactured by Kyowa Chemical Industry Co., Ltd. 2 / g) Magnesium oxide 2: Kyowamag 150MF (apparent specific gravity: 0.23 g / ml, d50: 0.72 μm, N2SA: 119 m) manufactured by Kyowa Chemical Industry Co., Ltd. 2 / g) Oil: H&R VIVATEC 400 / 500 (TDAE oil) Basic molecule 1: Shin-Etsu Chemical's KBE-903 (3-aminopropyltriethoxysilane) Basic molecule 2: Shin-Etsu Chemical's KBM-903 (3-aminopropyltrimethoxysilane) Basic molecule 3: Shin-Etsu Chemical's KBM-603 (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by EVONIK-DEGUSSA Resin: SYLVARES SA85 (copolymer of α-methylstyrene and styrene, Tg 43°C, softening point 85°C) manufactured by Arizona Chemical Antiaging agent: Antigen 6C (antiaging agent, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator DPG: Noccela D (1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator NS: Noccela NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0154] (Manufacturing example) A pressure-resistant reactor equipped with a stirrer was charged with 2000 g of distilled water, 45 g of emulsifier (1), 1.5 g of emulsifier (2), 8 g of electrolyte, 250 g of styrene, 50 g of methacrylic acid, 700 g of butadiene, and 2 g of molecular weight modifier. The reactor temperature was adjusted to 5°C, and an aqueous solution containing 1 g of radical initiator and 1.5 g of SFS, and an aqueous solution containing 0.7 g of EDTA and 0.5 g of catalyst were added to the reactor to initiate polymerization. Five hours after the start of polymerization, 2 g of polymerization terminator was added to terminate the reaction, yielding a latex.

[0155] Unreacted monomers were removed from the obtained latex by steam distillation. Then, the latex was added to alcohol and coagulated while adjusting the pH to 3 to 5 with saturated sodium chloride aqueous solution or formic acid to obtain a crumb-like polymer. The polymer was dried in a vacuum dryer at 40°C to obtain a solid rubber (emulsion polymerized rubber) (carboxylic acid-modified SBR (carboxylic acid group content 5% by mass)).

[0156] The materials used in the production examples are as follows: Emulsifier (1): Rosin acid soap manufactured by Harima Chemical Co., Ltd. Emulsifier (2): Fatty acid soap manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Electrolyte: Sodium phosphate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Styrene: Styrene manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Methacrylic acid: methacrylic acid manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Butadiene: 1,3-butadiene manufactured by Takachiho Chemical Industry Co., Ltd. Molecular weight modifier: tert-dodecyl mercaptan manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Radical initiator: Paramenthane hydroperoxide manufactured by NOF Corporation SFS: Sodium formaldehyde sulfoxylate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. EDTA: Sodium ethylenediaminetetraacetate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Catalyst: Ferric sulfate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Polymerization terminator: N,N'-dimethyldithiocarbamate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Alcohol: Methanol and ethanol manufactured by Kanto Chemical Co., Ltd. Formic acid: Formic acid manufactured by Kanto Chemical Co., Ltd. Sodium chloride: Sodium chloride manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0157] <Reaction rate of basic molecules and their salts> By the following method, unreacted basic molecules and salts thereof from each surface-modified silica were eluted into water, and the reaction rate of the basic molecules was calculated by titration. (1) Prepare a calibration curve for the basic molecule and its salt. (2) The surface-modified silica is dispersed in water, and unreacted basic molecules and their salts are eluted, followed by titration. (3) The amount of unreacted basic molecules and their salts is calculated using the titration value and the calibration curve formula. (4) The reaction rate is calculated from the amount of basic molecule and its salt used in the synthesis. From the above, it was found that each of the surface-modified silicas in the examples had basic molecules on the silica surface.

[0158] <Carboxylic acid group content> The content of carboxylic acid groups in the carboxylic acid-modified SBR is 1 Calculation was performed using H-NMR.

[0159] Examples and Comparative Examples According to the formulations shown in each table, chemicals other than sulfur and vulcanization accelerator were kneaded for 4 minutes at 160°C using a 16L Banbury mixer manufactured by Kobe Steel, Ltd. to obtain a kneaded mixture. Next, sulfur and vulcanization accelerator were added to the obtained kneaded mixture, and the mixture was kneaded for 4 minutes at 80°C using an open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was molded into a tread shape and laminated together with other tire components in a tire building machine to form an unvulcanized tire, which was then vulcanized at 170°C for 12 minutes to produce a test tire (size: 195 / 65R15).

[0160] <Negative rate> The negative rate of the obtained test tires was measured by the following method (the measured negative rates are shown in Tables 1 and 2). The tread contact profile of a test tire was obtained by assembling it onto a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours. Then, ink was applied to the tire tread surface, and the tire was pressed against cardboard under a standard load (camber angle 0°) and transferred to the paper. The tire was rotated 72° circumferentially, and the transfer was performed at five locations, obtaining five contact profiles. For the five contact profiles, the average maximum length in the tire axial direction was defined as L, and the average length in the direction perpendicular to the axial direction was defined as W. The negative rate (%) was measured using the following formula. The average values ​​for length and area were calculated by simply averaging the five values. Negative rate (%) = [1-{average area of ​​five transferred contact shapes (ink areas) on cardboard / (L × W)}] × 100

[0161] The obtained test tires were subjected to the following physical property measurements and evaluations. The results are shown in the tables. The reference comparative example in Table 1 is Comparative Example 1-1, and the reference comparative example in Table 2 is Comparative Example 2-1.

[0162] <Viscoelasticity test> A viscoelasticity measurement sample measuring 40 mm in length, 3 mm in width, and 0.5 mm in thickness was taken from inside the rubber layer of the tread of each test tire, with the long side aligned in the tire circumferential direction. The tan δ and E* of the tread rubber were measured using a TA Instruments RSA series under the following conditions: temperature 30°C, initial strain 10%, dynamic strain 1%, frequency 10 Hz, extension mode, and measurement time 30 minutes. The measured values ​​were obtained 30 minutes after the start of measurement. The thickness direction of the sample was the radial direction of the tire.

[0163] <E* and tanδ when dry> The viscoelasticity measurement sample (length 40 mm × width 3 mm × thickness 0.5 mm) was dried at room temperature and normal pressure until it reached a constant weight. The complex modulus E* and loss tangent tanδ of the resulting dried vulcanized rubber composition (rubber piece) were measured using the methods described above, and these were defined as E* and tanδ in the dry state.

[0164] <E* and tanδ when wet> The above-mentioned viscoelasticity measurement sample (length 40 mm × width 3 mm × thickness 0.5 mm) was immersed in 100 ml of water at 23°C for 2 hours to obtain a vulcanized rubber composition when wet with water. The complex modulus E* and loss tangent tanδ of the obtained vulcanized rubber composition (rubber piece) when wet with water were measured in water using the RSA immersion measurement jig according to the above method, and these were recorded as E* and tanδ when wet with water. The water temperature was set at 30°C.

[0165] <Wet grip performance> Each test tire was mounted on all wheels of a vehicle (domestic FF 2000cc) and the braking distance from an initial speed of 100 km / h on a wet asphalt road surface was measured. The braking distance of the reference comparative example was set to 100, and each compounding was expressed as an index. The higher the index, the better the wet grip performance.

[0166] <Dry grip performance> Each test tire was mounted on all wheels of a vehicle (domestic FF 2000cc) and the braking distance from an initial speed of 100 km / h on a dry asphalt road was measured. The braking distance of the reference comparative example was set to 100, and each compounding was expressed as an index. The higher the index, the better the dry grip performance.

[0167] <Fuel efficiency (rolling resistance)> Using a rolling resistance tester, the rolling resistance was measured when the test tire was run on a rim (15x6JJ), with an internal pressure (230kPa), a load (3.43kN), and at a speed (80km / h), and the result was expressed as an index, with the reference comparative example being set at 100. The higher the index, the better the fuel economy on dry roads.

[0168] [Table 1]

[0169] [Table 2]

[0170] From each table, it can be seen that the tires of the examples, which contained modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, and surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on the surface, had significantly superior overall performance in dry grip performance, wet grip performance, and fuel economy (expressed as the sum of three indices of dry grip performance, wet grip performance, and fuel economy).

[0171] The present disclosure (1) is a rubber composition comprising a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, and a surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface.

[0172] The present disclosure (2) is a rubber composition according to the present disclosure (1), in which the complex modulus (E*) and the loss tangent (tanδ) are reversibly changed by water and the following formula (1) and / or formula (2) are satisfied: E* when wet / E* when dry≦0.90 (1) Tan δ when wet / tan δ when dry ≧ 1.15 (2) (In the formula, E* and tanδ are the complex modulus and loss tangent measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

[0173] The present disclosure (3) is a rubber composition according to the present disclosure (1) or (2) that satisfies the following formula: E*≧5.5MPa when dry

[0174] The present disclosure (4) is a rubber composition according to any one of the present disclosures (1) to (3) that satisfies the following formula: Dry tan δ≧2.2

[0175] The present disclosure (5) is a rubber composition according to any one of the present disclosures (1) to (4), wherein the rubber constituting the skeleton of the modified rubber is at least one selected from the group consisting of styrene-butadiene rubber and butadiene rubber.

[0176] The present disclosure (6) is the rubber composition according to any one of the present disclosures (1) to (5), wherein at least one selected from the group consisting of basic molecules and salts thereof is a compound having an amino group.

[0177] The present disclosure (7) is a rubber composition according to any one of the present disclosures (1) to (6), which contains a metal oxide.

[0178] The present disclosure (8) is the rubber composition according to the present disclosure (7), wherein the metal oxide is at least one selected from the group consisting of magnesium oxide, calcium oxide, and barium oxide.

[0179] The present disclosure (9) is a tire having a tread made of the rubber composition according to any one of the present disclosures (1) to (8).

[0180] The present disclosure (10) is the tire according to the present disclosure (9), wherein the wet E* and dry E* of the rubber composition and the negative rate S (%) of the tread satisfy the following formula (3): (E* when wet / E* when dry) × S≦28.0 (3)

[0181] The present disclosure (11) is the tire according to the present disclosure (9) or (10), in which the tan δ when wet and the tan δ when dry of the rubber composition, and the negative rate S (%) of the tread satisfy the following formula (4): (tanδ when wet / tanδ when dry) / S≧0.035 (4)

[0182] The present disclosure (12) is the tire according to any one of the present disclosures (9) to (11), wherein the negative ratio of the tread is 40% or less. [Explanation of symbols]

[0183] 2. Pneumatic tires 4 Tread 6 Sidewall 8 Wing 10 Clinch 12 beads 14 Carcass 16 Belt 18 bands 20 Inner liner 22 Chafer 24 Tread surface 26 Groove 28 base layer 30 cap layers 32 cores 34 Apex 36 Carcass ply 36a Main part 36b Folded part 38 Inner layer 40 outer layer 42 Main groove 44 Ribs CL Equatorial plane of tire 2

Claims

1. A tire having a tread constructed of a vulcanized rubber composition, The vulcanized rubber composition comprises a modified rubber having at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof in the molecule, and a surface-modified silica having at least one selected from the group consisting of basic molecules and salts thereof on its surface, A tire in which the wet E* and dry E* of the vulcanized rubber composition and the negative rate S (%) of the tread satisfy the following formula (3): (E* when wet / E* when dry) x S≦28.0 (3) (In the formula, E* is the complex modulus measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

2. A tire having a component made of a vulcanized rubber composition, The vulcanized rubber composition is a tire comprising: a modified rubber having, in its molecule, at least one selected from the group consisting of carboxylic acids, sulfonic acids, and salts thereof; surface-modified silica having, on its surface, at least one selected from the group consisting of basic molecules and salts thereof; and at least one metal oxide selected from the group consisting of magnesium oxide, calcium oxide, and barium oxide.

3. A tire according to claim 1 or 2, wherein the vulcanized rubber composition has a complex modulus (E*) and loss tangent (tan δ) that are reversibly changed by water, and satisfies the following formula (1) and / or the following formula (2): E* when wet / E* when dry ≦ 0.90 (1) Tan δ when wet with water / tan δ when dry ≧1.15 (2) (In the formula, E* and tanδ are the complex modulus and loss tangent measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

4. A tire described in any one of claims 1 to 3, wherein the vulcanized rubber composition satisfies the following formula: E*≧5.5 MPa when dry (In the formula, E* is the complex modulus measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

5. A tire described in any one of claims 1 to 4, wherein the vulcanized rubber composition satisfies the following formula: Dry tan δ≧2.2 (In the formula, tanδ is the loss tangent measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

6. The tire according to any one of claims 1 to 5, wherein the rubber constituting the skeleton of the modified rubber is at least one rubber selected from the group consisting of styrene-butadiene rubber and butadiene rubber.

7. 7. The tire according to claim 1, wherein the at least one selected from the group consisting of basic molecules and salts thereof is a compound having an amino group.

8. 10. The tire of claim 1, comprising a metal oxide.

9. 9. The tire according to claim 8, wherein the metal oxide is at least one selected from the group consisting of magnesium oxide, calcium oxide, and barium oxide.

10. The tire of claim 2, wherein the component is a tread.

11. The tire according to claim 10, wherein E* in a water-wet state and E* in a dry state of the vulcanized rubber composition, and the negative rate S (%) of the tread satisfy the following formula (3): (E* when wet / E* when dry) x S≦28.0 (3) (In the formula, E* is the complex modulus measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

12. 12. The tire according to claim 1, 10 or 11, wherein the wet tan δ and dry tan δ of the vulcanized rubber composition and the negative rate S (%) of the tread satisfy the following formula (4): (tan δ when wet with water / tan δ when dry) / S≧0.035 (4) (In the formula, tanδ is the loss tangent measured under the conditions of a temperature of 30°C, an initial strain of 10%, a dynamic strain of 1%, a frequency of 10 Hz, and an extension mode.)

13. The tire according to any one of claims 1 and 10 to 12, wherein the negative ratio of the tread is 40% or less.

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