RUBBER COMPOSITION FOR TIRES, AND TIRES

Abstract

The present invention provides a tire rubber composition and a tire capable of changing tire performance in response to temperature changes. The present invention relates to a tire rubber composition comprising: a rubber component, comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber; a crosslinking agent; carbon black; a plasticizer; and a temperature-reactive material A, comprising a carboxyl group-containing polymer and a metal salt, wherein the tire rubber composition contains, per 100 parts by mass of the rubber component, the crosslinking agent in an amount of more than 0 parts by mass and less than 10 parts by mass, the carbon black in an amount of more than 0 parts by mass and less than 100 parts by mass, and the plasticizer in an amount of more than 5 parts by mass.

Description

TECHNICAL FIELD

[0001] The present invention relates to a tire rubber composition and a tire. STATE OF THE ART

[0002] Tires are required to perform in a variety of ways. All-season tires, in particular, must withstand significant changes in outside temperature and road surface conditions. SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0003] The present invention aims to solve the above problem and to provide a tire rubber composition and a tire capable of changing tire performance in response to temperature changes. SOLUTION TO THE PROBLEM

[0004] The present invention relates to a tire rubber composition containing: a rubber component comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber; a crosslinking agent; carbon black; a plasticizer; and a temperature-responsive material A containing a carboxyl group-containing polymer and a metal salt, wherein the tire rubber composition contains, per 100 parts by mass of the rubber component, the crosslinking agent in an amount of more than 0 parts by mass and less than 10 parts by mass, the carbon black in an amount of more than 0 parts by mass and less than 100 parts by mass, and the plasticizer in an amount of more than 5 parts by mass. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0005] According to the present invention, the tire has a structure having the above-described feature. The present invention can provide a tire rubber composition and a tire capable of changing tire performance in response to temperature changes. DESCRIPTION OF EMBODIMENTS

[0006] The present invention relates to a tire rubber composition which contains predetermined amounts of a rubber component comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber and styrene-butadiene rubber, a crosslinking agent, carbon black, a plasticizer and a temperature-reactive material A which contains a carboxyl group-containing polymer and a metal salt.

[0007] To date, the tire industry has not focused heavily on changing tire performance in response to temperature changes. Conventional methods have room for improvement in changing tire performance in response to temperature changes. In particular, ice grip performance on ice must be improved at low temperatures by reducing the elastic modulus, while handling stability at high temperatures must be improved by improving the elastic modulus. A method that uses a rubber that is flexible at low temperatures may be a possible solution. However, this method is disadvantageous for conventional rubber compositions in that the use of a rubber with high flexibility reduces handling stability.

[0008] Another possible method may be the addition of a temperature-responsive material, such as poly(N-isopropylacrylamide) (PNIPAM). This material has the disadvantage that it is soluble in water at low temperatures and can dissolve in water during rainy weather or on ice, causing it to disappear from a composition.

[0009] In contrast, the temperature-responsive material A in the present invention is a material that increases the elastic modulus when it absorbs water and subsequently increases the temperature from, for example, 0°C to 100°C, or decreases the elastic modulus when the temperature decreases. The use of this material can change tire performance in response to temperature changes.

[0010] The reason for the beneficial effect described above is not entirely clear, but is presumably as follows.

[0011] After the temperature-responsive material A in the present invention absorbs water, it changes the elastic modulus with temperature changes, thereby presumably changing the elastic modulus of the rubber composition.

[0012] It is believed that at least one of a water-soluble material B or a water-absorbing material B added as needed promotes the absorption of water into the temperature-responsive material A. This may be because at least one of a water-soluble material B or a water-absorbing material B immersed in water, for example, is dissolved in water or absorbs water, so that voids are formed in the rubber.

[0013] Thus, tire performance is likely to change in response to temperature changes caused by immersion in water, for example.

[0014] The tire rubber composition contains a rubber component comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber (BR), and styrene-butadiene rubber (SBR). To better achieve the advantageous effect, the tire rubber composition preferably contains at least one of an isoprene-based rubber and BR, and more preferably contains both an isoprene-based rubber and BR.

[0015] The rubber component used in the rubber composition contributes to crosslinking and is a polymer component that typically has a weight-average molecular weight (Mw) of 10,000 or more and is not extracted with acetone. The rubber component is in a solid state at room temperature (25°C).

[0016] The weight-average molecular weight of the rubber component is preferably 50,000 or more, more preferably 150,000 or more, even more preferably 200,000 or more, while it is preferably 2,000,000 or less, more preferably 1,500,000 or less, even more preferably 1,000,000 or less. When the weight-average molecular weight is within the above-specified range, the advantageous effect tends to be better achieved.

[0017] Here, the weight-average molecular weight (Mw) can be determined using a gel permeation chromatograph (GPC) (GPC-8000 series, available from Tosoh Corporation, detector: differential refractometer, column: TSKGel SuperMultipore HZ-M, available from Tosoh Corporation). The resulting value is calibrated using polystyrene standards.

[0018] Each rubber component, such as polyisoprene rubber, BR or SBR, can be an unmodified rubber or a modified rubber.

[0019] The modified rubber may be any rubber having a functional group that interacts with fillers such as silica. Examples of the modified rubber include a chain-end-modified rubber obtained by modifying at least one chain end of a rubber with a compound (modifier) ​​having the functional group (i.e., a chain-end-modified rubber ending with the functional group); a backbone-modified rubber having the functional group in the backbone; a backbone- and chain-end-modified rubber having the functional group in both the backbone and the chain end (e.g.,a backbone- and chain-end-modified rubber in which the backbone has the functional group and at least one chain end is modified by the modifier); and a chain-end-modified rubber into which a hydroxyl or epoxy group has been introduced by modification (coupling) with a polyfunctional compound having two or more epoxy groups in the molecule.

[0020] Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxy group, an oxy group, and an epoxy group. These functional groups may be substituted. Preferred among these are amino groups (preferably amino groups whose hydrogen atom is replaced by a C1-C6 alkyl group), alkoxy groups (preferably C1-C6 alkoxy groups) and alkoxysilyl groups (preferably C1-C6 alkoxysilyl groups).

[0021] Usable rubbers also include hydrogenated rubbers.

[0022] Examples of isoprene-based rubber include natural rubbers (NR), polyisoprene rubbers (IR), refined NR, modified NR, and modified IR. Examples of NR include those commonly used in the rubber industry, such as SIR20, RSS#3, and TSR20. Any IR can be used, and examples include those commonly used in the rubber industry, such as IR2200. Examples of refined NR include deproteinized natural rubbers (DPNR) and high-purity natural rubbers (UPNR). Examples of modified NR include epoxidized natural rubbers (ENR), hydrogenated natural rubbers (HNR), and grafted natural rubbers. Examples of modified IR include epoxidized polyisoprene rubbers, hydrogenated polyisoprene rubbers, and grafted polyisoprene rubbers.Modified isoprene-based rubbers containing the functional groups described above for modified rubbers are also usable. Each of these can be used alone or in combinations of two or more.

[0023] The amount of the isoprene-based rubber, if any, in the rubber composition, based on 100 mass % of the rubber component, is preferably 5 mass % or more, more preferably 20 mass % or more, still more preferably 30 mass % or more. The upper limit is preferably 60 mass % or less, more preferably 50 mass % or less, still more preferably 40 mass % or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0024] Non-limiting examples of the BR may include high-cis BR having a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using rare earth catalysts (rare earth-catalyzed BR). Each of these can be used alone or in combinations of two or more. The BR preferably includes high-cis BR having a cis content of 90 mass% or higher. The cis content is more preferably 95 mass% or higher, even more preferably 98 mass% or higher. The upper limit is not limited and is preferably 99 mass% or lower. The cis content can be determined by infrared absorption spectrometry.

[0025] The BR can be either unmodified BR or modified BR. Examples of modified BR include those in which the functional groups described above for modified rubbers have been introduced. The BR can comprise a hydrogenated polybutadiene rubber.

[0026] Applicable commercial products of BR may be available from Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc.

[0027] The amount of BR, if present, in the rubber composition, based on 100 mass % of the rubber component, is preferably 20 mass % or more, more preferably 50 mass % or more, still more preferably 55 mass % or more, particularly preferably 60 mass % or more. The upper limit is preferably 90 mass % or less, more preferably 80 mass % or less, still more preferably 75 mass % or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0028] Non-limiting examples of SBR include emulsion-polymerized styrene-butadiene rubbers (E-SBR) and solution-polymerized styrene-butadiene rubbers (S-SBR). Each of these can be used alone or in combinations of two or more.

[0029] The styrene content of the SBR is preferably 1 mass% or higher, more preferably 3 mass% or higher, even more preferably 5 mass% or higher. The styrene content is preferably 30 mass% or lower, more preferably 23.5 mass% or lower, even more preferably 20 mass% or lower, further preferably 15 mass% or lower, particularly preferably 10 mass% or lower. When the styrene content is within the above-specified range, the advantageous effect tends to be better achieved.

[0030] Here the styrene content can be 1 H-NMR analysis.

[0031] The vinyl bond content of the SBR is preferably 20 mass% or higher, more preferably 35 mass% or higher, even more preferably 40 mass% or higher, particularly preferably 42 mass% or higher. The vinyl bond content is preferably 70 mass% or lower, more preferably 60 mass% or lower, even more preferably 50 mass% or lower. When the vinyl bond content is within the above-specified range, the advantageous effects tend to be better achieved.

[0032] Here, the vinyl bond content (content of 1,2-bond butadiene units) can be determined by infrared absorption spectrometry.

[0033] The SBR may be an SBR product manufactured or sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, etc.

[0034] The amount of SBR, if present, in the rubber composition, based on 100 mass % of the rubber component, is preferably 5 mass % or more, more preferably 10 mass % or more, still more preferably 15 mass % or more. The upper limit is preferably 40 mass % or less, more preferably 30 mass % or less, still more preferably 25 mass % or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0035] Examples of usable rubber components other than isoprene-based rubber, BR, and SBR include styrene-isoprene-butadiene rubber (SIBR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR). Examples also include butyl-based rubbers and fluororubbers. Each of these can be used alone or in combinations of two or more.

[0036] The rubber composition contains a crosslinking agent.

[0037] The crosslinking agent can be any compound capable of crosslinking rubber components. Examples include known crosslinking agents in the tire field, such as sulfur, an organic crosslinking agent, an organic peroxide, and a resin crosslinking agent. To better achieve the beneficial effect, sulfur is desirable among these.

[0038] The amount of the crosslinking agent (total amount of crosslinking agents) per 100 parts by mass of the rubber component in the rubber composition is more than 0 parts by mass and less than 10 parts by mass. The lower limit is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, still more preferably 1.2 parts by mass or more, particularly preferably 1.5 parts by mass or more. The upper limit is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, still more preferably 2.5 parts by mass or less, particularly preferably 2.0 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0039] Examples of sulfur include those commonly used as crosslinking agents in the rubber industry, such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. Usable sulfur may include commercial products available from Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Corporation, Flexsys, Nippon Kanryu Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. Each of these can be used alone or in combinations of two or more.

[0040] The amount of sulfur per 100 parts by mass of the rubber component in the rubber composition is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.2 parts by mass or more, particularly preferably 1.5 parts by mass or more, while it is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.5 parts by mass or less, particularly preferably 2.0 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0041] Non-limiting examples of the organic crosslinking agent include maleimide compounds, alkylphenol-sulfur chloride condensates, organic peroxides, and amine organosulfides. Each of these can be used alone or in combinations of two or more.

[0042] The amount of organic crosslinking agents per 100 parts by mass of the rubber component in the rubber composition is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.2 parts by mass or more, particularly preferably 1.5 parts by mass or more, while it is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.5 parts by mass or less, particularly preferably 2.0 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0043] Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, and 1,3-bis(t-butylperoxypropyl)benzene. Each of these can be used alone or in combinations of two or more.

[0044] The amount of organic peroxides per 100 parts by mass of the rubber component in the rubber composition is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.2 parts by mass or more, particularly preferably 1.5 parts by mass or more, while it is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.5 parts by mass or less, particularly preferably 2.0 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0045] Non-limiting examples of the resin crosslinking agent include phenolic resins, melamine-formaldehyde resins, triazine-formaldehyde condensates, hexamethoxymethyl-melamine resins, and alkylphenol-sulfur chloride condensates. From the standpoint of the advantageous effect of the present invention, alkylphenol-sulfur chloride condensates are suitable.

[0046] The alkylphenol-sulfur chloride condensates are not limited. To obtain low heat generation properties, hardness, and the like, and to suppress reversion, the alkylphenol-sulfur chloride condensates are preferably compounds represented by the following formula (II).

[0047] In the formula, R 101 , R 102 and R 103 are the same or different from each other and each represents a C5-C12 alkyl group, x and y are the same or different from each other and each represents an integer from 1 to 3, and k represents an integer from 0 to 250.

[0048] In order to enable the alkylphenol-sulfur chloride condensates to disperse well in the rubber component, k is preferably an integer from 0 to 250, more preferably an integer from 0 to 100. In order to efficiently obtain high hardness, both x and y are preferably 2. In order to enable the alkylphenol-sulfur chloride condensates to disperse well in the rubber component, R 101 to R 103 each preferably a C6-C9 alkyl group.

[0049] The alkylphenol-sulfur chloride condensates can be prepared by a known method, such as a method involving a reaction of alkylphenol with sulfur chloride in a molar ratio of 1:0.9 to 1.25. Specific examples of the alkylphenol-sulfur chloride condensates include TACKIROL V200 (represented by the following formula (II-1)), available from Taoka Chemical Co., Ltd.

[0050] In the formula, k represents an integer from 0 to 100.

[0051] The amount of resin crosslinking agents per 100 parts by mass of the rubber component in the rubber composition is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.2 parts by mass or more, particularly preferably 1.5 parts by mass or more, while it is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.5 parts by mass or less, particularly preferably 2.0 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0052] Applicable commercial products of the crosslinking agent can be obtained from Tsurumi Chemical Industry Co., Ltd., Karuizawa sulfur Co., Ltd., Shikoku Chemicals Corporation, Flexsys, Nippon Kanryu Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. Each of these can be used alone or in combinations of two or more.

[0053] The rubber composition contains carbon black. Non-limiting examples of carbon black include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Usable commercial products can be obtained from Asahi Carbon Co., Ltd., Cabot Japan KK, Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, NSCC Carbon Co., Ltd., Columbia Carbon, etc. Each of these can be used alone or in combinations of two or more.

[0054] The specific nitrogen adsorption surface (N2SA) of the soot is preferably 30 m 2 / g or more, preferably 50 m 2 / g or more, more preferably 70 m 2 / g or more. The N2SA is preferably 200 m 2 / g or less, preferably 150 m 2 / g or less, more preferably 130 m 2 / g or less, particularly preferably 120 m 2 / g or less, most preferably 111 m 2 / g or less. When the N2SA is within the above range, the beneficial effect tends to be better achieved.

[0055] The N2SA of carbon black can be determined according to JIS K 6217-2:2001.

[0056] The amount of carbon black per 100 parts by mass of the rubber component in the rubber composition is more than 0 parts by mass and less than 100 parts by mass. The lower limit is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, still more preferably 7 parts by mass or more, particularly preferably 10 parts by mass or more. The upper limit is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 25 parts by mass or less, particularly preferably 20 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0057] The rubber composition desirably contains various fillers besides carbon black. Examples of the various fillers include inorganic fillers such as silica, calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica. Among these, silica is desirable to better achieve the beneficial effect.

[0058] Non-limiting examples of the silica include dry silica (anhydrous silica) and wet silica (hydrated silica). Wet silica is preferred among these because it contains a large number of silanol groups.

[0059] The nitrogen adsorption surface (N2SA) of the silica is preferably 30 m 2 / g or more, preferably 100 m 2 / g or more, more preferably 125 m 2 / g or more. The N2SA of the silicon dioxide is preferably 300 m 2 / g or less, preferably 250 m 2 / g or less, more preferably 200 m 2 / g or less, particularly preferably 175 m 2 / g or less. If the N2SA is within the above range, the beneficial effect can be adequately achieved.

[0060] The N2SA of silica is determined by the BET method according to ASTM D3037-93.

[0061] Usable commercial products of silica may be available from Evonik Degussa, Rhodia, Tosoh Silica Corporation, Solvay Japan, Tokuyama Corporation, etc.

[0062] The amount of silica per 100 parts by mass of the rubber component in the rubber composition is preferably 30 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 55 parts by mass or more, particularly preferably 60 parts by mass or more. The upper limit of the amount is not limited and is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 80 parts by mass or less, particularly preferably 70 parts by mass or less. When the amount is within the above-specified range, the advantageous effect can be suitably achieved.

[0063] The rubber composition desirably contains a silane coupling agent.

[0064] Non-limiting examples of useful silane coupling agents include silane coupling agents conventionally used in the rubber industry with silica, including: sulfide silane coupling agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(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,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-silane coupling agents such as 3-mercaptopropyltrimethoxysilane and 2-mercaptoethyltriethoxysilane;Vinyl silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino silane coupling agents such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Applicable commercial products can be obtained from Evonik Degussa, Momentive, Shin-Etsu Silicone, Tokyo Chemical Industry Co., Ltd., AZmax Co., Dow Corning Toray Co., Ltd., etc. Each of these can be used alone or in combinations of two or more.

[0065] The amount of silane coupling agents per 100 parts by mass of silica (a total of 100 parts by mass of silica, including surface-modified silica and silica other than silica) in the rubber composition is preferably 0.1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, particularly preferably 7 parts by mass or more. The upper limit of the amount is preferably 50 parts by mass, more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, particularly preferably 10 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0066] The rubber composition contains a plasticizer.

[0067] The term "plasticizer" refers to a substance that imparts plasticity to rubber components. Examples include liquid plasticizers (plasticizers that are liquid at room temperature (25°C)) and resins (resins that are solid at room temperature (25°C)).

[0068] The amount of the plasticizer (total amount of plasticizers) per 100 parts by mass of the rubber component in the rubber composition is more than 5 parts by mass. The lower limit is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less, most preferably 35 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0069] Liquid plasticizers (plasticizers that are liquid at room temperature (25°C)) usable in the rubber composition are not limited. Desirably, oils or liquid polymers (liquid resins, liquid diene-based polymers, liquid farnesene-based polymers, etc.) are used. To better achieve the beneficial effect, an oil is preferably included. Each of these can be used alone or in combinations of two or more.

[0070] The amount of liquid plasticizers per 100 parts by mass of the rubber component in the rubber composition is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less, most preferably 35 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0071] Examples of the oils include process oils, vegetable oils, and mixtures thereof. Examples of the process oils include paraffinic process oils, aromatic process oils, and naphthenic process oils. Examples of the vegetable oils include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, safflower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Usable commercial products may be available from Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo KK, ENEOS Corporation, Olisoy, H&R, Hokoku Corporation, Showa Shell Sekiyu KK, Fuji Kosan Co., Ltd., The Nisshin Oillio Group, etc. Process oils such as paraffinic process oils, aromatic process oils and naphthenic process oils, and vegetable oils are preferred among these.

[0072] The amount of oils per 100 parts by mass of the rubber component in the rubber composition is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less, most preferably 35 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0073] The amount of oils includes the amount of extender oils from oil-extended rubbers.

[0074] Examples of liquid resins among liquid polymers 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 resins based on coumarone or indene alone), phenolic resins, olefin resins, polyurethane resins, and acrylic resins. Hydrogenated products of these resins are also usable.

[0075] Examples of liquid diene-based polymers among liquid polymers include liquid styrene-butadiene copolymers (liquid SBR), liquid polybutadiene polymers (liquid BR), liquid polyisoprene 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 chain ends or backbones of these polymers can each be modified with a polar group. Hydrogenated products of these polymers are also usable.

[0076] Usable commercial products of liquid diene-based polymers may be available from Sartomer, Kuraray, etc.

[0077] The amount of liquid polymers per 100 parts by mass of the rubber component in the rubber composition is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0078] Examples of the resin (resin that is solid at room temperature (25°C)) usable in the rubber composition include aromatic vinyl polymers, coumarone-indene resin, coumarone resin, indene resin, phenolic resin, rosin resin, petroleum resins, terpene-based resins, and acrylic resins, all of which are solid at room temperature (25°C). The resin may be hydrogenated. Each of these can be used alone or in combinations of two or more. Aromatic vinyl polymers, petroleum resins, and terpene-based resins are preferred among them.

[0079] The amount of the resin per 100 parts by mass of the rubber component in the rubber composition is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved.

[0080] The softening point of the resin is preferably 50°C or higher, more preferably 55°C or higher, even more preferably 60°C or higher. The upper limit is preferably 160°C or lower, more preferably 150°C or lower, even more preferably 145°C or lower. When the softening point is within the above-specified range, the advantageous effect tends to be better achieved. The softening point of the resin is measured according to JIS K 6220-1:2001 using a ring-and-ball softening point measuring device, and the temperature at which the ball falls is defined as the softening temperature.

[0081] The term "aromatic vinyl polymers" refers to polymers containing aromatic vinyl monomers as structural units. Examples include resins produced by polymerizing α-methylstyrene and / or styrene. Specific examples include styrene homopolymers (styrene resins), α-methylstyrene homopolymers (α-methylstyrene resins), copolymers of α-methylstyrene and styrene, and copolymers of styrene and other monomers.

[0082] The term "coumarone-indene resins" refers to resins containing coumarone and indene as the main monomer components, forming the skeleton (backbone) of the resins. Examples of monomer components that may be present in the skeleton in addition to coumarone and indene include styrene, α-methylstyrene, methylindene, and vinyltoluene.

[0083] The term “coumarone resins” refers to resins that contain coumarone as the main monomer component, which forms the skeleton (backbone) of the resins.

[0084] The term “indene resins” refers to resins that contain indene as the major monomer component, which forms the skeleton (backbone) of the resins.

[0085] Examples of usable phenolic resins include known polymers prepared by reacting phenol with an aldehyde such as formaldehyde, acetaldehyde, or furfural in the presence of an acidic or alkaline catalyst. Preferred among these are those prepared by the reaction in the presence of an acidic catalyst, such as novolak phenolic resins.

[0086] Examples of the rosins include rosins typified by natural rosin, polymerized rosin, modified rosin, and esterified compounds thereof and hydrogenated products thereof.

[0087] Examples of petroleum resins include C5 resins, C9 resins, C5 / C9 resins, dicyclopentadiene (DCPD) resins, and hydrogenated products of these resins. DCPD resins and hydrogenated DCPD resins are preferred among them.

[0088] The term "terpene resins" refers to polymers containing terpenes as structural units. Examples include polyterpene resins produced by polymerizing terpene compounds, and aromatic-modified terpene resins produced by polymerizing terpene compounds and aromatic compounds. Examples of usable aromatic-modified terpene resins include terpene-phenol resins made from terpene compounds and phenol compounds, terpene-styrene resins made from terpene compounds and styrene compounds, and terpene-phenol-styrene resins made from terpene compounds, phenol compounds, and styrene compounds. Examples of terpene compounds include α-pinene and β-pinene. Examples of phenol compounds include phenol and bisphenol A. Examples of aromatic compounds include styrene compounds such as styrene and α-methylstyrene.

[0089] The term "acrylic resins" refers to polymers containing acrylic monomers as structural units. Examples include styrene-acrylic resins, such as those containing carboxyl groups, produced by copolymerizing aromatic vinyl monomer components and acrylic monomer components. Solvent-free, carboxyl-containing styrene-acrylic resins are suitably used among these.

[0090] Applicable commercial resins may be available from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical, Nitto Chemical Co., Ltd., Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., Taoka Chemical Co., Ltd., etc.

[0091] The rubber composition contains a temperature-reactive material A, which contains a carboxyl group-containing polymer and a metal salt.

[0092] Poly(N-isopropylacrylamide), or poly(NIPAAm), is known to be a typical temperature-responsive polymer. Poly(NIPAAm) exhibits a lower critical solution temperature (LCST), meaning that in an aqueous solution, poly(NIPAAm) is soluble at a temperature lower than the LCST and precipitates (undergoes phase separation) at a temperature higher than the LCST. Poly(N-isopropylacrylamide) hydrogels are also known to exhibit bulk phase change.

[0093] The temperature-responsive material A, which contains a carboxyl-containing polymer and a metal salt, exhibits the properties of a temperature-responsive hydrogel. It preferably has the following properties.

[0094] (1) It is transparent below the LCST, while above the LCST phase separation occurs and turbidity appears.

[0095] (2) It is soft below the LCST, while above the LCST it exhibits high strength and high toughness. The elastic modulus and toughness increase as the temperature rises above the LCST. At and above a certain temperature, the elastic modulus increases sharply (it becomes very hard), while the toughness decreases due to severe phase separation.

[0096] (3) It shows almost no volume change around the LCST and shows no volume phase change. The feature of the hydrogel in the present invention of showing no volume phase change or the feature of showing practically no volume change means that a ratio V 2 / V1 of a volume V2 at a temperature above the LCST (for example T2 ≥ LCST + 5°C) to a volume V1 at a temperature below the LCST (for example T1 ≤ LCST - 5°C) is in the range from 0.8 to 1.2, preferably from 0.85 to 1.15, more preferably from 0.98 to 1.02.

[0097] (4) The temperature-responsive phase separation is completely reversible.

[0098] The carboxyl group-containing polymer can be any carboxyl group-containing organic polymer compound. Examples include a homopolymer of a carboxyl group-containing monomer and a copolymer of a plurality of carboxyl group-containing monomers. Each of these can be used alone or in combinations of two or more.

[0099] Examples of the carboxyl group-containing monomer include an α,β-unsaturated carboxylic acid containing one carboxyl group or two or more carboxyl groups in the molecule. Examples of the α,β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, aconitic acid, fumaric acid, and crotonic acid.

[0100] Non-limiting examples of the homopolymer include polyacrylic acid and polymethacrylic acid.

[0101] Examples of the copolymer include a copolymer of a plurality of carboxyl group-containing monomers and a copolymer of a carboxyl group-containing monomer and a monomer other than the carboxyl group-containing monomer. Non-limiting examples of the monomer other than the carboxyl group-containing monomer include acrylate monomers (e.g., esters of α,β-ethylenically unsaturated carboxylic acids, hydroxyalkyl esters of α,β-ethylenically unsaturated carboxylic acids, and alkoxyalkyl esters of α,β-ethylenically unsaturated carboxylic acids), acrylamide monomers, and styrene monomers. Each of these can be used alone or in combinations of two or more.

[0102] Non-limiting examples of the acrylate monomers include esters of α,β-ethylenically unsaturated carboxylic acids, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, lauryl acrylate, and stearyl acrylate; hydroxyalkyl esters of α,β-ethylenically unsaturated carboxylic acids, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and 3-hydroxypropyl methacrylate; and alkoxyalkyl esters of α,β-ethylenically unsaturated carboxylic acids, such as diethylene glycol methacrylate.

[0103] Non-limiting examples of the acrylamide monomers include acrylamide and methylolmethacrylamide.

[0104] Non-limiting examples of the styrene monomers include styrene and alkylstyrene.

[0105] From the standpoint of temperature reactivity, the content of structural units derived from the carboxyl group-containing monomer in the monomer is desirably 50 mol% or higher. This content is preferably 60 mol% or higher, more preferably 70 mol% or higher, even more preferably 80 mol% or higher, particularly preferably 90 mol% or higher. The upper limit is not limited and is, for example, 98 mol% or lower, more preferably 95 mol% or lower.

[0106] From the viewpoint of temperature reactivity, the amount of carboxyl groups in the carboxyl group-containing polymer is preferably 0.001 mol / g or more, more preferably 0.005 mol / g or more, still more preferably 0.007 mol / g or more, while it is preferably 0.05 mol / g or less, more preferably 0.03 mol / g or less, still more preferably 0.014 mol / g or less.

[0107] The carboxyl group-containing polymer may have a cross-linked structure.

[0108] Examples of the crosslinked structure include a chemically crosslinked structure or a physically crosslinked structure. The chemically crosslinked structure can be formed by inducing crosslinking with a crosslinking agent for chemical crosslinking during polymer formation or after polymer formation.

[0109] In the present invention, the crosslinking agent for chemical crosslinking formation is not included in the crosslinking agent.

[0110] A difunctional or multifunctional monomer can be used as the crosslinking agent for chemical crosslinking to form a chemically crosslinked structure. Examples of the crosslinking agent include N,N'-methylenebisacrylamide (MbAAd), N,N'-ethylenebisacrylamide, diethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, and 1-acryloyloxy-3-methacryloyloxy-2-propanol. The amount of the crosslinking agent for chemical crosslinking can be determined depending on the desired degree of crosslinking and can, for example, range from 0 to 10 mol% relative to the monomer concentration.

[0111] The weight-average molecular weight of the carboxyl group-containing polymer is not limited. For example, the weight-average molecular weight is 1,000,000 or less, preferably 500,000 or less. The lower limit is, for example, 5,000 or more, preferably 10,000 or more. In some cases, it may be impossible to actually measure the weight-average molecular weight of the polymer having a crosslinked structure.

[0112] The physically cross-linked structure is formed by the formation of a salt between two carboxyl groups possessed by the carboxyl group-containing polymer and a divalent metal and / or by polymer interlacing. The formation of the physically cross-linked structure by the former method is carried out by forming a salt with a divalent metal in a polymer formed without using a cross-linking agent for chemical cross-linking. A phenomenon in which a physically cut hydrogel undergoes reunification after cutting is mainly due to salt formation between the carboxyl groups and the divalent metal. However, it is believed that with the lapse of a relatively long time, polymer interlacing also occurs, further enhancing the reunification caused by salt formation.The hydrogel having a chemically cross-linked structure may also have a physically cross-linked structure due to salt formation between two carboxyl groups possessed by the polymer and a divalent metal, as well as the presence of polymer interweaving.

[0113] Examples of the polymerization method used to produce the polymer include radical polymerization using a thermal initiator (thermal polymerization) and photopolymerization using a photoinitiator. Among them, photopolymerization is preferred. A known initiator can be suitably used as the polymerization initiator. Examples of the photoinitiator include α-ketoglutaric acid. The amount of the initiator, relative to the monomer concentration, can be, for example, in the range of 0.01 to 10 mol%.

[0114] The metal salt forming the thermoreactive material A is not limited. To better achieve the advantageous effect, the metal salt is preferably a metal salt of an organic acid, more preferably a divalent metal salt of an organic acid.

[0115] Non-limiting examples of the organic acid used to construct the divalent metal salt of an organic acid include fatty acids (fatty carboxylic acids), aromatic carboxylic acids, oxocarboxylic acids, and other organic acids.

[0116] Examples of fatty acids (fatty carboxylic acids) include the following compounds. Formic acid [methanoic acid] Acetic acid [ethanoic acid] Propionic acid [propanoic acid] Butyric acid [butanoic acid] Isobutyric acid Valeric acid [pentanoic acid] Isovaleric acid Caproic acid [hexanoic acid] Enanthic acid (heptylic acid) [heptanoic acid] Caprylic acid [octanoic acid] Pelargonic acid [nonanoic acid] Capric acid [decanoic acid] Lauric acid [dodecanoic acid] Myristic acid [tetradecanoic acid] Pentadecylic acid [pentadecanoic acid] Palmitic acid (cetanic acid) [hexadecanoic acid] Margaric acid [heptadecanoic acid] Stearic acid [octadecanoic acid] oleic acid Linoleic acid Linolenic acid Tuberculostearic acid [nonadecanoic acid] Arachidic acid [eicosanoic acid] Arachidonic acid Eicosapentaenoic acid Behenic acid [docosanic acid] Docosahexaenoic acid Lignoceric acid [tetracosanoic acid] Cerotinic acid [hexacosanoic acid] Montanic acid [octacosanoic acid] Melissinic acid [triacontanoic acid]

[0117] Examples of aromatic carboxylic acids include the following compounds. Salicylic acid [hydroxybenzoic acid] Gallic acid (trihydroxybenzoic acid) Benzoic acid [benzenecarboxylic acid] Phthalic acid Cinnamic acid (β-phenylacrylic acid) Mellitic acid (graphitic acid) [benzenehexacarboxylic acid]

[0118] Examples of oxocarboxylic acids include the following compound.

[0119] Pyruvic acid (oxopropionic acid, α-ketopropionic acid, pyruvic acid)

[0120] Examples of other organic acids include the following compounds. Oxalic acid [ethanedioic acid] Lactic acid (a-hydroxypropanoic acid) Tartaric acid Maleic acid Fumaric acid (paramaleic acid, boletic acid, lichen acid) Malonic acid [propanedioic acid] succinic acid Malic acid (hydroxysuccinic acid) citric acid Aconitic acid Glutaric acid Adipic acid [hexanedioic acid] Amino acids L-ascorbic acid (vitamin C)

[0121] Preferred organic acids are formic acid, acetic acid, and propionic acid, taking into account the solubility in an aqueous solution of the salt in the hydrogel and the solubility curve. For example, calcium formate exhibits a relatively moderately positive solubility curve in the range of 0°C to 100°C in its relationship with temperature (solubility increases as the temperature rises). In contrast, calcium acetate exhibits a negative solubility curve in the range of 0°C to about 60°C and a relatively moderately positive solubility curve in the range of about 50°C to about 85°C. Calcium propionate exhibits a negative solubility curve in the range of 0°C to about 50°C and a positive solubility curve in the range of about 50°C to 100°C in its relationship with temperature.

[0122] The divalent metal used to construct the divalent metal salt of an organic acid is not limited and is desirably an alkaline earth metal. Examples of alkaline earth metals include calcium (Ca), magnesium (Mg), strontium (Sr), and barium (Ba).

[0123] To better achieve the beneficial effect, the divalent metal salt of an organic acid is desirably Ca formate, Ca acetate, Ca propionate, Mg formate, Mg acetate, Mg propionate, or the like. The LCST of the hydrogel can be varied by the type of divalent metal salt of an organic acid used.

[0124] The total metal concentration in the temperature-reactive material A can be measured by inductively coupled plasma atomic emission analysis (ICP). The metal ion concentration can be determined by combusting a known volume of the temperature-reactive material A (for example, at approximately 1,000°C) to remove the organic component, dissolving the residue in a known volume of water, and analyzing the aqueous solution by ICP. In the case where the temperature-reactive material A contains a divalent metal salt of an organic acid, the concentration of free metals that do not form the organic acid salt in the temperature-reactive material A can be measured, for example, using a metal ion electrode.In the case where a metal ion forming the salt of an organic acid and a free metal ion are present in the temperature-reactive material A, they can be distinguished from each other using this method.

[0125] In the case where the temperature-responsive material A contains a divalent metal salt of an organic acid, the concentration of the divalent metal salt of an organic acid in the temperature-responsive material A can be appropriately adjusted, taking into account the physical properties required of the temperature-responsive hydrogel and the amount of carboxyl groups. For example, the concentration of an aqueous metal salt solution impregnated into the polymer ranges from 50 mM to the saturation concentration, preferably from 50 to 500 mM. The term "saturation concentration" refers to the saturation amount (equal equivalent) relative to the amount of carboxyl groups in the polymer. The LCST of the hydrogel can be varied by controlling the concentration of the metal salt in the polymer.The concentration of the metal in the polymer tends to be higher than the metal concentration of the aqueous metal salt solution with which the polymer is impregnated, and varies with conditions such as the concentration of carboxyl groups in the polymer and the concentration of the metal salt in the aqueous solution. For example, the concentration of the metal may be, for example, approximately 1.1 to 2.0 times higher, or more typically 1.2 to 1.5 times higher, than the metal concentration of the aqueous metal salt solution. In the case where the divalent metal is calcium, the concentration of the divalent metal in the polymer ranges from about 1 to about 100 mg, based on 1 g of the polymer (gel). The concentration is more typically in the range of about 10 to about 70 mg, even more typically in the range of about 15 to about 50 mg.

[0126] The thermoresponsive material A (hydrogel), which contains a carboxyl group-containing polymer and a metal salt, is a gel containing water or an aqueous solution and a polymer as the main components. Whether the polymer forms a hydrogel can be mainly determined by the length of the polymer (in other words, the concentration of the polymerization initiator). For the same polymer mass, a higher polymerization initiator concentration increases the tendency toward gel formation. From this point of view, for example, when the monomer is acrylic acid, gel formation tends to occur at 3 M or higher when the polymerization initiator concentration is 0.1 mol%, and at 2 M or higher when the polymerization initiator concentration is 0.01 mol%, which is approximately the same when the monomer is methacrylic acid.The polymerization initiator concentration can be appropriately selected in the range where hydrogel formation occurs, depending on the type of polymerization initiator and the type of monomer.

[0127] The temperature-responsive material A (hydrogel) has a low critical solution temperature (LCST). The LCST is the lower critical solution temperature at which the hydrogel develops turbidity due to phase separation and is an indicator of the phase separation temperature. For example, whether LCST is present or not can be assessed by measuring the turbidity (transmittance) using an ultraviolet-visible-near-infrared spectrophotometer, or alternatively, by measuring the endothermic / exothermic peak using a differential scanning calorimeter, or by measuring the temperature dependence of the dynamic elastic modulus using a rheometer (viscoelasticity meter). The LCST of the temperature-responsive material A (hydrogel) varies depending on the composition of the polymer, the type and concentration of the metal salt, and the like.For example, the LCST is in the range of 10°C to 80°C, preferably in the range of 25°C to 45°C.

[0128] The temperature-responsive material A (hydrogel) is transparent at a temperature below the LCST, while it is opaque above the LCST. In the present invention, the term "transparent" refers to a transmittance of 85% or higher at a wavelength of 550 nm. The term "opaque" refers to a transmittance of 30% or lower at a wavelength of 550 nm.

[0129] For example, the temperature-responsive material A (hydrogel) can be prepared by immersing a carboxyl group-containing polymer in the aqueous metal salt solution.

[0130] Immersion of the polymer into the aqueous metal salt solution can be performed at room temperature, for example, in the range of 4°C to 30°C. Taking into account the LCST of the temperature-responsive hydrogel to be obtained, immersion can be performed at a temperature above or below the LCST.

[0131] The metal salt concentration of the aqueous metal salt solution can be appropriately determined taking into account the types of the polymer and metal salt, and the desired LCST. For example, the metal salt concentration ranges from 50 mM to the saturation concentration. For example, the temperature-responsive hydrogel can be obtained by immersing a polymer in an aqueous metal salt solution having a metal salt concentration of 50 mM to the saturation concentration until approximate equilibrium is reached. Regarding the immersion time, for a chemically cross-linked gel, approximate equilibrium is reached in approximately 1 to 72 hours. In the case of a physically cross-linked gel, approximate equilibrium is reached in two to seven days. Immersion until equilibrium is reached may be unnecessary as long as the desired physical properties are maintained.

[0132] To better achieve the advantageous effect, the temperature-responsive material A is preferably a material that at least partially comprises a foam structure. The temperature-responsive material A that at least partially comprises a foam structure may partially or entirely comprise the foam structure. When the temperature-responsive material A is a material that at least partially comprises a foam structure, it can provide a space for swelling of a cavity where water originally existed. This can prevent an increase in volume due to swelling of the temperature-responsive material A during water absorption, so that the rubber composition can have improved hardness when dry.

[0133] The material at least partially comprising a foam structure can be obtained by further processing the hydrogel to have a foam structure. The material is obtained by foaming the hydrogel, and it at least partially comprises a foam structure having a large number of air bubbles. The hydrogel can be processed into a foam structure by any method that can provide a material at least partially comprising a foam structure. The hydrogel can be foamed by a known method. Examples of the method include a method in which the temperature-responsive material A (hydrogel) is heated, then frozen by rapid (for example, within one hour, preferably within 30 minutes, more preferably within 10 minutes, particularly preferably within 5 minutes) cooling with liquid nitrogen or the like, and freeze-dried.

[0134] Heating can be performed under any conditions that cause phase separation in the temperature-responsive material A (hydrogel). For example, the heating temperature is preferably 60°C or higher, more preferably 80°C or higher, while preferably 120°C or lower, more preferably 100°C or lower. The heating time is preferably one minute or longer, preferably five minutes or longer, while preferably 24 hours or shorter, more preferably 10 hours or shorter, and even more preferably 1 hour or shorter.

[0135] The drying time in freeze-drying is not limited. For example, the drying time is preferably one hour or longer, more preferably five hours or longer, even more preferably 10 hours or longer, particularly preferably 24 hours or longer, while it is preferably 72 hours or shorter, more preferably 48 hours or shorter, even more preferably 30 hours or shorter.

[0136] Another exemplary method for making the hydrogel have a foam structure comprises foaming the hydrogel by adding an inorganic foaming agent such as sodium bicarbonate or ammonium carbonate, or an organic foaming agent such as azodicarboxamide, dinitrosopentamethylenetetramine, or p,p'-oxybis(benzenesulfonylhydrazide) to the hydrogel.

[0137] The amount of the temperature-responsive material A per 100 parts by mass of the rubber component in the rubber composition 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, particularly preferably 20 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less. When the amount is within the above range, the advantageous effect tends to be better achieved.

[0138] In the present invention, the amount of the temperature-responsive material A means the amount of a temperature-responsive hydrogel (a gel containing water or an aqueous solution and a polymer as main components) containing a carboxyl group-containing polymer and a metal salt. This amount includes the amount of water contained in the temperature-responsive material (temperature-responsive hydrogel), as well as the amounts of the carboxyl group-containing polymer and the metal salt.

[0139] In order to better achieve the advantageous effect, the rubber composition desirably contains at least one of a water-soluble material B or a water-absorbing material B.

[0140] In the present invention, at least one of a water-soluble material B or a water-absorbing material B is different from the temperature-responsive material A containing a carboxyl group-containing polymer and a metal salt. Specifically, for example, when the rubber composition contains a temperature-responsive hydrogel comprising polyacrylic acid and calcium acetate as the temperature-responsive material A, and further contains calcium acetate monohydrate as at least one of a water-soluble material B and a water-absorbing material B, the calcium acetate in the temperature-responsive material A does not correspond to at least one of a water-soluble material B or a water-absorbing material B, while the separately added calcium acetate monohydrate corresponds to at least one of a water-soluble material B or a water-absorbing material B.

[0141] The water-soluble material B (hereinafter also simply referred to as water-soluble material) in at least one of a water-soluble material B or a water-absorbing material B is not limited and may be any known water-soluble material. For example, a material having a solubility in water at 20°C of 25 g / 100 g of water is usable. To better achieve the advantageous effect, the metal salt or its hydrate is preferable, and the divalent metal salt of an organic acid or its hydrate is more preferable. Examples of the organic acid and the divalent metal constituting the divalent metal salt of an organic acid include the compounds described above. A hydrate capable of forming a metal salt, such as a monohydrate or a dihydrate, can be suitably used as the hydrate.

[0142] In order to better achieve the advantageous effect, among the water-soluble materials, alkaline earth metal salts of organic acids and their hydrates are preferred, and more preferred are Ca formate, Ca acetate, Ca propionate, Mg formate, Mg acetate and Mg propionate and their hydrates.

[0143] The water-absorbing material B (hereinafter also referred to simply as water-absorbing material) in at least one of a water-soluble material B or a water-absorbing material B is not limited and may be any known water-absorbing material. For example, a material having a water absorption rate of 5% or higher as measured by the following method is usable. (measurement method)

[0144] The weights before and after immersion in water at 20°C for 24 hours are measured, and the water absorption rate is calculated using the following expression. Water absorption rate (%)=(weight after immersion−weight before immersion) / weight after immersion×100

[0145] Examples of the water-absorbing material include heteroatom-containing materials (fibers, elastomers, resins).

[0146] The term "heteroatom" refers to an atom other than a carbon atom and a hydrogen atom, and can be any heteroatom capable of forming a reversible molecular bond with water, such as a hydrogen bond or an ionic bond. The heteroatom is preferably at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom, a phosphorus atom, and halogen atoms, more preferably an oxygen atom, a nitrogen atom, or a silicon atom, even more preferably an oxygen atom.

[0147] Examples of structures or groups containing an oxygen atom include ether groups, esters, carboxy groups, carbonyl groups, alkoxy groups, and hydroxy groups. Ether groups are preferred among these, with oxyalkylene groups being more preferred.

[0148] Examples of structures or groups containing a nitrogen atom include amino groups (primary amino groups, secondary amino groups, and tertiary amino groups), amide groups, nitrile groups, and nitro groups. Amino groups are preferred among these, with tertiary amino groups being more preferred.

[0149] Examples of structures or groups containing a silicon atom include silyl groups, alkoxysilyl groups, and silanol groups. Silyl groups are preferred among these, with alkoxysilyl groups being more preferred.

[0150] Examples of structures or groups containing a sulfur atom include sulfide groups, sulfuric acid groups, sulfates, and sulfo groups.

[0151] Examples of structures or groups containing a phosphorus atom include phosphoric acid groups and phosphates.

[0152] Examples of structures or groups containing halogen atoms include halogen groups such as a fluoro group, a chloro group, a bromo group, and an iodo group.

[0153] Examples of water-absorbing fibers include cellulose fibers containing hydroxyl groups.

[0154] Cellulose microfibrils are preferred among cellulose fibers. Any cellulose microfibril derived from a naturally occurring material can be used. Examples include those derived from: biomass feedstock, such as fruits, grains, and root vegetables; wood, bamboo, hemp, jute, and kenaf, and wood pulp, paper, or cloth made from them; biomass waste, such as agricultural waste, food waste, and sewage sludge; unused biomass, such as rice straw, wheat straw, and thinning wood; and celluloses produced by ascidians, acetic acid bacteria, or other organisms. Each of these can be used alone or in combinations of two or more.

[0155] Examples of water-absorbent elastomers include oxyalkylene group-containing elastomers. Examples of the elastomers include epoxy / allyl glycidyl ether copolymers, amine / allyl glycidyl ether copolymers, and silyl / allyl glycidyl ether copolymers. Each of these can be used alone or in combinations of two or more.

[0156] Examples of water-absorbent resins include polyvinyl alcohol, polyurethane, polyvinyl acetate, epoxy resins, cellulose resins, polyethylene glycol, and sodium polyacrylate. Each of these can be used alone or in combinations of two or more.

[0157] The amount of at least one of a water-soluble material B or a water-absorbent material B (total amount of the water-soluble material and the water-absorbent material) per 100 parts by mass of the rubber component in the rubber composition is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 15 parts by mass or more, particularly preferably 20 parts by mass or more. The upper limit is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, still more preferably 50 parts by mass or less, particularly preferably 40 parts by mass or less, most preferably 30 parts by mass or less. When the amount is within the above-specified range, the advantageous effect tends to be better achieved. In the case where the rubber composition contains the water-soluble material and / or the water-absorbent material, the amount is desirably within the above-specified range.

[0158] In the present invention, the amount of at least one of a water-soluble material B or a water-absorbing material B refers to a total amount of the water-soluble material and the water-absorbing material. When the water-soluble material and the water-absorbing material are each a hydrate, the total amount includes the amount of the hydrate(s).

[0159] From the standpoint of properties such as crack resistance and ozone resistance, the rubber composition preferably contains an antioxidant.

[0160] Non-limiting examples of the antioxidant include naphthylamine antioxidants such as phenyl-α-naphthylamine; diphenylamine antioxidants such as octylated diphenylamine and 4,4'-bis(α,α'-dimethylbenzyl)diphenylamine; p-phenylenediamine antioxidants such as N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, and N,N'-di-2-naphthyl-p-phenylenediamine; quinoline antioxidants such as polymerized 2,2,4-trimethyl-1,2-dihydroquinoline; monophenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis-, tris-, or polyphenolic antioxidants, such as tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Preferred among these are p-phenylenediamine antioxidants and quinoline antioxidants, and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine or polymerized 2,2,4-trimethyl-1,2-dihydroquinoline is more preferred. Usable commercial products can be obtained from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industrial Co., Ltd., Flexsys, etc.

[0161] The amount of antioxidants per 100 parts by mass of the rubber component in the rubber composition is preferably 0.5 parts by mass or more, more preferably 2.0 parts by mass or more. The amount is preferably 7.0 parts by mass or less, more preferably 4.0 parts by mass or less.

[0162] The rubber composition may contain stearic acid.

[0163] The amount of stearic acid per 100 parts by mass of the rubber component in the rubber composition is preferably 0.5 to 10 parts by mass or more, more preferably 1.5 to 5 parts by mass.

[0164] The stearic acid can be conventional. Usable commercial products can be obtained from NOF Corporation, Kao Corporation, FUJIFILM Wako Pure Chemical Corporation, Chiba Fatty Acid Co., Ltd., etc.

[0165] The rubber composition may contain zinc oxide. The amount of zinc oxide per 100 parts by mass of the rubber component in the rubber composition is preferably 0.5 to 10 parts by mass, more preferably 2 to 6 parts by mass.

[0166] The zinc oxide can be conventional. Usable commercial products may be available from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., HakusuiTech Co., Ltd., Seido Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc.

[0167] The rubber composition may contain wax. The amount of wax per 100 parts by mass of the rubber component in the rubber composition is preferably 0.5 to 10 parts by mass, more preferably 2 to 5 parts by mass.

[0168] Non-limiting examples of wax include petroleum waxes and natural waxes, and also include synthetic waxes produced by purifying or chemically treating a plurality of waxes. Each of these waxes may be used alone or in combinations of two or more.

[0169] Examples of petroleum waxes include paraffin waxes and microcrystalline waxes. Natural waxes can be any wax derived from non-petroleum sources, and examples include vegetable waxes such as candelilla wax, carnauba wax, Japan wax, rice wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti; mineral waxes such as ozokerite, ceresin, and petrolatum; and purified products of these waxes. Usable commercial products may be available from Ouchi Shinko Chemical Industrial Co., Ltd., Nippon Seiro Co., Ltd., Seiko Chemical Co., Ltd., etc.

[0170] The rubber composition may contain a vulcanization accelerator.

[0171] The amount of vulcanization accelerators per 100 parts by mass of the rubber component in the rubber composition is usually 0.3 to 10 parts by mass, preferably 0.5 to 4 parts by mass.

[0172] Any type of vulcanization accelerator can be used, including commonly used ones. Examples of the vulcanization accelerator include thiazole vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiazylsulfenamide; thiuram vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, Nt-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide. and guanidine vulcanization accelerators such as diphenylguanidine, diorthotolylguanidine, and orthotolylbiguanidine. Each of these can be used alone or in combinations of two or more. Sulfenamide vulcanization accelerators and guanidine vulcanization accelerators are preferred among these.

[0173] In addition to the above-described components, the rubber composition may contain other suitable additives commonly used in the field of application, such as a release agent or a pigment. The amount of each additive per 100 parts by mass of the rubber component in the rubber composition is preferably 0.5 to 10 parts by mass, more preferably 2 to 5 parts by mass.

[0174] In order to better achieve the advantageous effect, in the rubber composition, a ratio of the amount of at least one of a water-soluble material B or a water-absorbing material B to the amount of the crosslinking agent (amount of at least one of a water-soluble material B or a water-absorbing material B / amount of crosslinking agent) is desirably 2.0 to 40.0. The lower limit is preferably 6.7 or higher, more preferably 10.0 or higher, further preferably 13.3 or higher, particularly preferably 16.7 or higher, most preferably 20.0 or higher. The upper limit is preferably 50.0 or lower, more preferably 40.0 or lower, even more preferably 30.0 or lower.

[0175] The rubber composition can be prepared by known methods. For example, it can be prepared by kneading the components in a rubber kneading machine, such as an open-roll mill or a Banbury mixer, optionally followed by crosslinking. The kneading conditions include a kneading temperature of usually 50°C to 200°C, preferably 80°C to 190°C, and a kneading time of usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes.

[0176] In order to better achieve the advantageous effect, the rubber composition desirably has a dynamic elastic modulus when immersed in water at 0°C (E*w at 0°C) and a dynamic elastic modulus when dry at 0°C (E*d at 0°C) which satisfy the following formula (1): E*w at 0°C / E*d at 0°C≤0.70.

[0177] The ratio "E*w at 0°C / E*d at 0°C" is preferably 0.56 or lower, more preferably 0.55 or lower, even more preferably 0.54 or lower, further preferably 0.53 or lower, further preferably 0.51 or lower, further preferably 0.49 or lower, further preferably 0.45 or lower, further preferably 0.44 or lower, further preferably 0.42 or lower, further preferably 0.40 or lower, further preferably 0.39 or lower, further preferably 0.33 or lower, further preferably 0.31 or lower, further preferably 0.30 or lower, further preferably 0.28 or lower, particularly preferably 0.27 or lower. The lower limit is not limited and is preferably 0.01 or higher, more preferably 0.05 or higher, still more preferably 0.10 or higher.

[0178] In order to better achieve the advantageous effect, the rubber composition desirably has a dynamic elastic modulus when immersed in water at 0°C (E*w at 0°C) and a dynamic elastic modulus when immersed in water at 30°C (E*w at 30°C) which satisfy the following formula (2): E*w at 30°C / E*w at 0°C≥0.80.

[0179] The ratio "E*w at 30°C / E*w at 0°C" is preferably 0.83 or higher, more preferably 0.85 or higher, even more preferably 0.87 or higher, further preferably 0.88 or higher, further preferably 0.89 or higher, further preferably 0.90 or higher, further preferably 0.95 or higher, further preferably 0.98 or higher, further preferably 1.04 or higher, further preferably 1.05 or higher, further preferably 1.06 or higher, further preferably 1.08 or higher, particularly preferably 1.10 or higher, particularly preferably 1.20 or higher, particularly preferably 1.23 or higher, particularly preferably 1.24 or higher, particularly preferably 1.25 or higher, most preferably 1.29 or higher. The upper limit is not limited and is preferably 3.00 or lower, more preferably 2.00 or lower, still more preferably 1.50 or lower.

[0180] The reason for the advantageous effect of the elastomer composition satisfying formulas (1) and (2) is not entirely clear, but is presumably as follows.

[0181] The formula "(1) E*w at 0°C / E*d at 0°C ≤ 0.70" means that at low temperatures, the elastic modulus when immersed in water is relatively lower than that when dry. The formula "(2) E*w at 30°C / E*w at 0°C ≥ 0.80" means that a practical elastic modulus is maintained when immersed in water even at high temperatures, compared to that at low temperatures. As described above, the rubber composition changes its behavior with respect to elastic modulus with temperature changes. Thus, it can change tire performance in response to temperature changes.

[0182] In this case, the problem (objective) of changing tire performance in response to temperature changes is solved by the rubber composition containing predetermined amounts of a rubber component comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber, a crosslinking agent, carbon black, a plasticizer, and a temperature-responsive material A containing a carboxyl group-containing polymer and a metal salt, and also satisfying the parameters of formulas (1) and (2). In other words, the parameters do not define the problem (objective). The problem here is to change tire performance in response to temperature changes. To solve this problem, a rubber composition was formulated to contain the predetermined amounts of the materials and satisfy the parameters of formulas (1) and (2).

[0183] In order to better achieve the advantageous effect, the rubber composition desirably has a dynamic elastic modulus when immersed in water at 0°C (E*w at 0°C) which satisfies the following formula: E*w at 0°C≤8.0 MPa.

[0184] The value of "E*w at 0°C" is preferably 5.0 MPa or less, more preferably 4.8 MPa or less, more preferably 4.6 MPa or less, even more preferably 4.5 MPa or less, further preferably 4.2 MPa or less, further preferably 4.0 MPa or less, further preferably 3.8 MPa or less, further preferably 3.7 MPa or less, further preferably 3.5 MPa or less, further preferably 3.3 MPa or less, particularly preferably 3.2 MPa or less, most preferably 3.1 MPa or less. The lower limit is not limited and is preferably 1.0 MPa or more, more preferably 1.3 MPa or more, even more preferably 1.5 MPa or more, further preferably 2.7 MPa or more, further preferably 2.8 MPa or more, further preferably 3.0 MPa or more.

[0185] In order to better achieve the advantageous effect, the rubber composition desirably has a dynamic elastic modulus when immersed in water at 30°C (E*w at 30°C) which satisfies the following formula: E*w at 30°C≤3.0 MPa.

[0186] The value of "E*w at 30°C" is preferably 3.3 MPa or more, more preferably 3.4 MPa or more, even more preferably 3.5 MPa or more, further preferably 3.6 MPa or more, further preferably 3.7 MPa or more, further preferably 3.8 MPa or more, particularly preferably 3.9 MPa or more, more preferably 4.0 MPa or more, even more preferably 4.1 MPa or more, even more preferably 4.3 MPa or more, most preferably 4.5 MPa or more. The upper limit is not limited and is preferably 10.0 MPa or less, more preferably 8.0 MPa or less, even more preferably 7.0 MPa or less, particularly preferably 6.0 MPa or less.

[0187] In order to better achieve the advantageous effect, the rubber composition desirably has a dynamic elastic modulus when dry at 0°C (E*d at 0°C) which satisfies the following formula: E*d at 0°C ≥ 5.0 MPa.

[0188] The value of “E*d at 0°C” is preferably 6.0 MPa or more, more preferably 6.9 MPa or more, even more preferably 7.0 MPa or more, further preferably 7.8 MPa or more, further preferably 8.0 MPa or more, further preferably 8.2 MPa or more, further preferably 8.3 MPa or more, further preferably 8.4 MPa or more, further preferably 8.5 MPa or more, further preferably 9.0 MPa or more, further preferably 10.0 MPa or more, further preferably 10.5 MPa or more, further preferably 10.7 MPa or more, further preferably 11.0 MPa or more, particularly preferably 11.6 MPa or more, most preferably 12.0 MPa or more, further preferably 12.3 MPa or more. The upper limit is not limited and is preferably 20.0 MPa or less, more preferably 18.0 MPa or less, still more preferably 16.0 MPa or less, further preferably 15.0 MPa or less.

[0189] In the present invention, the dynamic elastic modulus E* is measured by the method described in EXAMPLES.

[0190] In the present invention, the dynamic elastic modulus E* of the rubber composition refers to the dynamic elastic modulus E* of the vulcanized (crosslinked) rubber composition.

[0191] In the present invention, the dynamic elastic modulus E* when dry refers to the dynamic elastic modulus of the vulcanized rubber composition when dry; more specifically, the dynamic elastic modulus of the vulcanized rubber composition dried by the method described in EXAMPLES.

[0192] In the present invention, the dynamic elastic modulus E* when immersed in water refers to the dynamic elastic modulus of the rubber composition after being immersed in water; specifically, the dynamic elastic modulus of the vulcanized rubber composition after being immersed in water by the method described in EXAMPLES.

[0193] In the present invention, the dynamic elastic modulus E* of the vulcanized rubber composition is determined by measuring the dynamic elastic modulus E* of a vulcanized rubber test sheet at an elongation of 2% and a frequency of 10 Hz using ARES (a rheometer available from TA Instruments).

[0194] Next, the manufacturing guidelines are explained to satisfy the formulas “(1) E*w at 0°C / E*d at 0°C ≤ 0.70”, “(2) E*w at 30°C / E*w at 0°C ≥ 0.80”, “E*w at 0°C ≤ 8.0 MPa”, “E*w at 30°C ≥ 3.0 MPa”, and “E*d at 0°C ≥ 5.0 MPa”.

[0195] The formula "(1) E*w at 0°C / E*d at 0°C ≤ 0.70" means that at low temperatures, the elastic modulus when immersed in water is relatively lower than that when dry. The formula "(2) E*w at 30°C / E*w at 0°C ≥ 0.80" means that a practical elastic modulus when immersed in water is maintained even at high temperatures, compared to that at low temperatures. For example, a rubber composition satisfying formulas (1) and (2) can be prepared by incorporating a temperature-responsive material A containing a carboxyl group-containing polymer and a metal salt into the rubber composition.The production of such a rubber composition can be facilitated by incorporating into the rubber composition a material at least partially comprising a foam structure as the temperature-reactive material A, or additionally incorporating at least one of a water-soluble material B or a water-absorbing material B.

[0196] The formula "E*w at 0°C ≤ 8.0 MPa" means an improvement in grip performance on an icy road. For example, a rubber composition satisfying the formula can be prepared by incorporating temperature-responsive material A into the rubber composition. The preparation of such a rubber composition can be facilitated by incorporating a material having at least a partial foam structure into the rubber composition as temperature-responsive material A, or by additionally incorporating material B.

[0197] The formula "E*d at 0°C ≥ 5.0 MPa" means an improvement in dry road grip performance. For example, a rubber composition satisfying the formula can be prepared by incorporating temperature-responsive material A into the rubber composition. The preparation of such a rubber composition can be facilitated by incorporating a material having at least a partial foam structure into the rubber composition as temperature-responsive material A, or by additionally incorporating material B.

[0198] The dynamic elastic modulus E* (absolute value) when dry can be controlled by the types and amounts of chemicals (especially rubber components, fillers, plasticizers) incorporated into the rubber composition. For example, the dynamic elastic modulus when dry tends to decrease as the amount of plasticizer is increased, the dynamic elastic modulus E* when dry tends to increase as the amount of fillers is increased, and the dynamic elastic modulus E* when dry tends to decrease as the amount of sulfur is decreased. The dynamic elastic modulus E* when dry can also be controlled by varying the amounts of sulfur and vulcanization accelerators.Specifically, the dynamic elastic modulus E* when dry tends to increase as the amount of sulfur is increased, and the dynamic elastic modulus E* when dry tends to increase as the amount of vulcanization accelerators is increased.

[0199] Specifically, the formulas “(1) E*w at 0°C / E*d at 0°C ≤ 0.70”, “(2) E*w at 30°C / E*w at 0°C ≥ 0.80”, “E*w at 0°C ≤ 8.0 MPa”, “E*w at 30°C ≥ 3.0 MPa” and “E*d at 0°C ≥ 5.0 MPa” can be satisfied by controlling the dynamic elastic modulus E* when dry in the desired range and also incorporating a temperature-responsive material A containing a carboxyl group-containing polymer and a metal salt into the rubber composition, while optionally using a material at least partially comprising a foam structure as the temperature-responsive material A, or further incorporating at least one of a water-soluble material B or a water-absorbing material B into the rubber composition. becomes.

[0200] The rubber composition can be used (as a tire rubber composition) in tire components such as treads, sidewalls, tread bases, undertreads, shoulders, chafers, bead apices, breaker cushion rubbers, carcass cord rubbers, insulators, chafer strips, and inner liners and side reinforcement layers of run-flat tires. The rubber composition is suitable for treads.

[0201] The tire of the present invention can be manufactured using the rubber composition by a conventional method.

[0202] For example, a rubber composition containing various materials is extruded and processed into a tread shape or the like before vulcanization, and then molded with other tire components on a tire building machine by a usual method to form an unvulcanized tire, and the unvulcanized tire is heated and pressurized in a vulcanizer, thereby obtaining a tire.

[0203] The tire can be suitably used as a tire for passenger vehicles, large passenger vehicles, large SUVs, trucks and buses, or two-wheeled vehicles, or as a racing tire, a winter tire (studded winter tire, snow tire, studded tire), an all-season tire, a runflat tire, an aircraft tire, a mining tire, etc. The tire is suitably used as a winter tire (studded winter tire, snow tire, studded tire) or an all-season tire, among others. EXAMPLES

[0204] Examples (working examples) considered preferable for implementing the present invention are described below. However, the scope of the invention is not limited to the examples.

[0205] The chemicals used in the following examples and comparative examples are listed below. No.: TSR20 BR: BR150B (cis content: 98 mass%), available from Ube Industries, Ltd. SBR: Nipol SBR1502 (styrene content: 23.5 mass%), available from Zeon Corporation Soot: Seast N220 (N2SA: 111 m 2 / g), available from Mitsubishi Chemical Corporation Silicon dioxide: ULTRASIL VN3 (N2SA: 175 m 2 / g), available from Evonik Degussa Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide), available from Evonik Degussa Oil: Diana Process NH-70S, available from Idemitsu Kosan Co., Ltd. Plasticizer A: RICON 150 (liquid polybutadiene polymer), available from Sartomer Temperature reactive material A-1: Preparation example 1 (polyacrylic acid / calcium acetate gel) Temperature reactive material A-2: Production example 2 (foamed polyacrylic acid / calcium acetate gel) Temperature reactive material A-3: Preparation Example 3 (Polyacrylic acid / calcium propionate gel) Temperature reactive material A-4: Production example 4 (foamed polyacrylic acid / calcium propionate gel) Water-soluble material B: Calcium acetate monohydrate (solubility in water at 20°C: 34.7 g / 100 g water), available from WAKO Water-absorbing material B: Biomass nanofiber (product name “BiNFi-s cellulose”, microfibrillated cellulose fiber, water absorption rate: 10%), available from SUGINO MACHINE LIMITED Antioxidant: NOCRAC 6C, available from Ouchi Shinko Chemical Industrial Co., Ltd. Stearic acid: Stearic acid, available from NOF Corporation Zinc Oxide: Zinc Oxide #2, available from Mitsui Mining & Smelting Co., Ltd. Sulfur: powdered sulfur, available from Tsurumi Chemical Industry Co., Ltd. Crosslinking agent A: TACKIROL V200 (alkylphenol sulfur chloride condensate), available from Taoka Chemical Co., Ltd. Vulcanization accelerator CZ: NOCCELER CZ-G, available from Ouchi Shinko Chemical Industrial Co., Ltd. Vulcanization accelerator DPG: NOCCELER D, available from Ouchi Shinko Chemical Industrial Co., Ltd. (Production example 1)

[0206] With reference to Advanced Materials 2020, 32, 1905878, a temperature-responsive material A-1 was prepared by the following method.

[0207] An aqueous precursor solution was prepared by dissolving 1.0 M acrylic acid (AAc), potassium peroxodisulfate as an initiator in an amount of 1.0 mol% based on the monomer concentration, and N,N'-methylenebisacrylamide (MbAAd) as a crosslinking agent in an amount of 1.0 mol% based on the monomer concentration in ultrapure water.

[0208] Here, when the concentration of the crosslinking agent is 0 mol%, a physically crosslinked gel can be obtained. When the crosslinking agent is added, a chemically crosslinked gel can be obtained.

[0209] The solution was poured into a mold of any shape and heated in air at 60°C for six hours to form a gel.

[0210] The polymerized gel or a non-flowable, highly viscous substance was immersed in a sufficient volume of a 1,000 mM solution of calcium acetate in ultrapure water until equilibrium was reached. Thus, a temperature-responsive material A-1 was obtained. (Production example 2)

[0211] The temperature-responsive material A-1 was heated to 80°C for five minutes and then frozen in liquid nitrogen. The frozen temperature-responsive material A-1 was freeze-dried for 24 hours using a freeze-dryer (FDU-2110, available from EYELA). Thus, a temperature-responsive material A-2 comprising a foam structure was obtained. (Production example 3)

[0212] With reference to Advanced Materials 2020, 32, 1905878, a temperature-responsive material A-3 was prepared by the following method.

[0213] An aqueous precursor solution was prepared by dissolving 1.0 M acrylic acid (AAcc), potassium peroxodisulfate as an initiator in an amount of 1.0 mol% based on the monomer concentration, and N,N'-methylenebisacrylamide (MbAAd) as a crosslinking agent in an amount of 1.0 mol% based on the monomer concentration in ultrapure water.

[0214] Here, when the concentration of the crosslinking agent is 0 mol%, a physically crosslinked gel can be obtained. When the crosslinking agent is added, a chemically crosslinked gel can be obtained.

[0215] The solution was poured into a mold of any shape and heated in air at 60°C for six hours to form a gel.

[0216] The polymerized gel or a non-flowable, highly viscous substance was immersed in a sufficient volume of a 1,000 mM solution of calcium acetate in ultrapure water until equilibrium was reached.

[0217] Thus, a temperature-responsive material A-3 was obtained. (Production example 4)

[0218] The temperature-responsive material A-3 was heated to 80°C for five minutes and then frozen in liquid nitrogen. The frozen temperature-responsive material A-3 was freeze-dried for 24 hours using a freeze-dryer (FDU-2110, available from EYELA). Thus, a temperature-responsive material A-4 comprising a foam structure was obtained. <Beispiele und Vergleichsbeispiele>

[0219] According to the formulation shown in Table 1, the chemicals except sulfur and vulcanization accelerators were kneaded using a 1.7-L Banbury mixer (Kobe Steel, Ltd.) at 150°C for 5 minutes to obtain a kneaded mixture. Then, sulfur and vulcanization accelerator were added to the kneaded mixture, and they were kneaded in an open-roll mill at 80°C for 5 minutes to obtain an unvulcanized rubber composition.

[0220] The unvulcanized rubber composition was press-vulcanized at 170°C for 12 minutes to prepare a 1 mm thick vulcanized rubber composition sheet.

[0221] The unvulcanized rubber composition prepared as above was separately molded into a tread cover mold and combined with the other tire components to construct an unvulcanized tire. The unvulcanized tire was cured at 170°C for 15 minutes to produce a test tire (size: 195 / 65R15).

[0222] The vulcanized rubber composition and test tire prepared as above were stored at room temperature in the dark for three months and then subjected to the following evaluations. Table 1 shows the results. (Measurement of the dynamic elastic modulus E*)

[0223] The dynamic elastic modulus E* of the 1 mm thick vulcanized rubber composition film was measured.

[0224] Specifically, the 1 mm thick vulcanized rubber composition sheet was kept at a measurement temperature for 10 minutes, and then the dynamic elastic modulus E* (at 0°C or 30°C) of the vulcanized rubber composition sheet was measured at an elongation of 2% and a frequency of 10 Hz using ARES (a rheometer available from TA Instruments).

[0225] Here, the vulcanized rubber composition sheet was prepared for measurement as described below.

[0226] The 1 mm thick vulcanized rubber composition sheet was immersed in water at 25°C for 10 hours. Then, the sheet was dried under reduced pressure at 80°C and 1 kPa or lower to a constant weight to obtain a dried vulcanized rubber composition sheet. The temperature of the dried vulcanized rubber composition sheet was returned to 25°C, and the resulting sheet was used as the vulcanized rubber composition sheet for measuring the dynamic elastic modulus E* when dry.

[0227] Separately, the dried vulcanized rubber composition sheet was again immersed in water at 25°C for 10 hours, and the resulting sheet was used as the vulcanized rubber composition sheet for measuring the dynamic elastic modulus E* when immersed in water. (Ice grip performance)

[0228] A set of test tires was mounted on a Japanese-made front-engine, rear-wheel drive, 2,000 cc automobile. The automobile was driven on ice to evaluate ice grip performance. Specifically, the ice grip performance evaluation was conducted by measuring the stopping distance (braking stopping distance on ice) required to stop the automobile moving on ice after the locking brakes were applied at 30 km / h. The distance was expressed as an index (ice grip performance index) relative to that of Comparative Example 1, which was taken as 100. A higher index indicates better braking performance on ice (ice grip performance). (Dry grip performance)

[0229] The test tire was mounted on each wheel of a Japanese-made front-engine, front-wheel-drive, 2,000 cc automobile. The braking distance of the automobile at an initial speed of 100 km / h on a dry asphalt road was measured. The distance was expressed as an index (dry grip performance index) relative to that of Comparative Example 1, which was taken as 100. A higher index indicates a shorter braking distance and better dry grip performance. (Total performance)

[0230] The sum of the ice grip performance (index) and the dry grip performance (index) was defined as the overall performance in terms of ice grip performance and dry grip performance. Overall performance was evaluated. A higher index indicates better overall performance.

[0231] The present invention (1) relates to a tire rubber composition containing: a rubber component comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber; a cross-linking agent; Soot; a plasticizer; and a temperature-reactive material A containing a carboxyl group-containing polymer and a metal salt, wherein the tire rubber composition contains, per 100 parts by mass of the rubber component, the crosslinking agent in an amount of more than 0 parts by mass and less than 10 parts by mass, the carbon black in an amount of more than 0 parts by mass and less than 100 parts by mass, and the plasticizer in an amount of more than 5 parts by mass.

[0232] The present invention (2) relates to the tire rubber composition according to the present invention (1), which further contains at least one of a water-soluble material B or a water-absorbing material B.

[0233] The present invention (3) relates to the tire rubber composition according to the present invention (2), wherein a ratio of the amount of material B to the amount of crosslinking agent (amount of material B / amount of crosslinking agent) is 2.0 to 40.0.

[0234] The present invention (4) relates to the tire rubber composition according to any one of the present inventions (1) to (3), wherein the tire rubber composition has a dynamic elastic modulus when immersed in water at 0°C (E*w at 0°C), a dynamic elastic modulus when immersed in water at 30°C (E*w at 30°C), and a dynamic elastic modulus when dry at 0°C (E*d at 0°C) satisfying the following formulas (1) and (2): E*w at 0°C / E*d at 0°C≤0.70. E*w at 30°C / E*w at 0°C≥0.80.

[0235] The present invention (5) relates to the tire rubber composition according to any one of the present inventions (1) to (4), wherein the tire rubber composition has a dynamic modulus of elasticity when immersed in water at 0°C (E*w at 0°C) which satisfies the following formula: E*w at 0°C≤8.0 MPa.

[0236] The present invention (6) relates to the tire rubber composition according to any one of the present inventions (1) to (5), wherein the tire rubber composition has a dynamic modulus of elasticity when immersed in water at 30°C (E*w at 30°C) which satisfies the following formula: E*w at 30°C≥3.0 MPa.

[0237] The present invention (7) relates to the tire rubber composition according to any one of the present inventions (1) to (6), wherein the temperature-reactive material A is a material that at least partially comprises a foam structure.

[0238] The present invention (8) relates to a tire comprising a tread comprising the rubber composition according to any one of the present inventions (1) to (7).

[0239] The present invention (9) relates to the tire according to the present invention (8), which is a winter tire or an all-season tire. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] JIS K 6217-2:2001

[0055] JIS K 6220-1:2001

[0080]

Claims

[1] A tire rubber composition comprising: a rubber component comprising at least one selected from the group consisting of polyisoprene rubber, polybutadiene rubber, and styrene-butadiene rubber; a cross-linking agent; Soot; a plasticizer; and a temperature-reactive material A containing a carboxyl group-containing polymer and a metal salt, wherein the tire rubber composition comprises, per 100 parts by mass of the rubber component, the crosslinking agent in an amount of more than 0 parts by mass and less than 10 parts by mass, the carbon black in an amount of more than 0 parts by mass and less than 100 parts by mass, and the plasticizer in an amount of more than 5 parts by mass. [2] The tire rubber composition according to claim 1, which further comprises at least one of a water-soluble material B or a water-absorbing material B. [3] Tire rubber composition according to claim 2, wherein a ratio of the amount of material B to the amount of crosslinking agent (amount of material B / amount of crosslinking agent) is 2.0 to 40.

0. [4] Tire rubber composition according to any one of claims 1 to 3, wherein the tire rubber composition has a dynamic elastic modulus when immersed in water at 0°C (E*w at 0°C), a dynamic elastic modulus when immersed in water at 30°C (E*w at 30°C), and a dynamic elastic modulus when dry at 0°C (E*d at 0°C) satisfying the following formulas (1) and (2): E*w at 0°C / E*d at 0°C≤0.

70. E*w at 30°C / E*w at 0°C≥0.

80. [5] Tire rubber composition according to any one of claims 1 to 4, wherein the tire rubber composition has a dynamic modulus of elasticity when immersed in water at 0°C (E*w at 0°C) which satisfies the following formula: E*w at 0°C≤8.0 MPa. [6] Tire rubber composition according to any one of claims 1 to 5, wherein the tire rubber composition has a dynamic modulus of elasticity when immersed in water at 30°C (E*w at 30°C) which satisfies the following formula: E*w at 30°C≥3.0 MPa. [7] The tire rubber composition according to any one of claims 1 to 6, wherein the temperature-reactive material A is a material at least partially comprising a foam structure. [8] A tire comprising a tread comprising the rubber composition according to any one of claims 1 to 7. [9] A tyre according to claim 8, which is a winter tyre or an all-season tyre.