Rubber composition for tire, rubber member for tire, and tire

Abstract

The present invention addresses the problem of providing a rubber composition for tires which is able to give a rubber member for tires that has voids and combines on-ice performance with fracture resistance (particularly fracture resistance after exposure to high temperatures). This rubber composition for tires is characterized by comprising a rubber component, a void-introducing agent, and an amine-compound antioxidant represented by general formula (1) (wherein R1 and R2 are each independently a monovalent saturated hydrocarbon group), the content of the amine-compound antioxidant being 0.1-11 parts by mass per 100 parts by mass of the rubber component.

Description

Rubber composition for tires, rubber member for tires, and tires

[0001] The present invention relates to a rubber composition for a tire, a rubber member for a tire, and a tire.

[0002] Conventionally, in order to improve the performance of tires on ice, a technique for introducing voids such as foam holes into the rubber component of the tire tread that comes into contact with the road surface has been known. For example, Patent Document 1 listed below discloses a tire in which a foamed rubber layer is provided in the tire tread, the foamed rubber layer has a foaming rate of 3% to 50%, and the foamed rubber layer further uses a rubber composition containing ethylene-vinyl alcohol copolymer fibers coated with a resin that has affinity for the rubber component and inorganic compound powder with an average particle size of 10 μm or more.

[0003] International Publication No. 2014 / 024466

[0004] However, in general, when voids such as foamed holes are introduced into a rubber member, the fracture resistance of the rubber member is likely to decrease. Therefore, conventional tire rubber members having voids have room for improvement in fracture resistance. Furthermore, since tire treads generate heat during running, rubber members used in treads are exposed to high temperatures. Therefore, from the perspective of application to tire treads, tire rubber members having voids are required to have improved fracture resistance after exposure to high temperatures.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a rubber composition for a tire that can achieve both excellent ice performance and fracture resistance (particularly fracture resistance after exposure to high temperatures) for a rubber component for a tire having voids.A further object of the present invention is to provide a rubber component for a tire and a tire that have voids but are excellent in ice performance and fracture resistance (particularly fracture resistance after exposure to high temperatures).

[0006] The rubber composition for a tire, the rubber member for a tire, and the tire of the present invention that solve the above-mentioned problems are outlined below.

[0007] [1] A rubber component, a void-introducing agent, and a rubber composition represented by the following general formula (1): [In the formula, R １ and R ２and each independently represents a monovalent saturated hydrocarbon group, and the content of the amine antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component.

[0008] [2] The rubber composition for a tire according to [1], wherein the rubber component contains at least one rubber selected from the group consisting of an isoprene skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber.

[0009] [3] R in the above general formula (1) １ and R ２ are each independently a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms.

[0010] [4] A rubber member for a tire having voids, comprising a rubber component and a rubber compound represented by the following general formula (1): [In the formula, R １ and R ２ and each independently represents a monovalent saturated hydrocarbon group, and the content of the amine antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component.

[0011] [5] A tire comprising a rubber member made of the rubber composition for a tire according to any one of [1] to [3], or the rubber member for a tire according to [4].

[0012] According to the present invention, it is possible to provide a rubber composition for a tire that can achieve both excellent ice performance and fracture resistance for a rubber component for a tire having voids. Furthermore, according to the present invention, it is possible to provide a rubber component for a tire and a tire that have excellent ice performance and fracture resistance despite having voids.

[0013] The rubber composition for a tire, the rubber member for a tire, and the tire of the present invention will be described in detail below by way of example based on embodiments thereof.

[0014] <Rubber Composition for Tire> The rubber composition for tire of the present invention comprises a rubber component, a void-introducing agent, and a rubber compound represented by the following general formula (1): [In the formula, R １ and R ２ and each independently represents a monovalent saturated hydrocarbon group. The rubber composition for a tire of the present invention is characterized in that the content of the amine antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component.

[0015] Because the rubber composition for tires of the present invention contains a void-introducing agent, rubber components obtained from the rubber composition have voids derived from the void-introducing agent and exhibit excellent on-ice performance. Furthermore, by blending 0.1 parts by mass or more of an amine-based antiaging agent represented by the above general formula (1) per 100 parts by mass of the rubber component in the rubber composition for tires of the present invention, the aging resistance (ozone resistance) of the rubber composition is improved, and the deterioration of the tensile stress, elongation at break (EB), and tensile strength (TB) of the rubber composition after exposure to high temperatures is suppressed, thereby improving fracture resistance. Therefore, by applying the rubber composition for tires of the present invention, it is possible to achieve both on-ice performance and fracture resistance (particularly fracture resistance after exposure to high temperatures) of void-containing rubber components for tires. Furthermore, by applying the rubber composition for tires of the present invention to a tread, the fracture resistance and crack resistance of the tread, which generates heat during driving, can be improved.

[0016] (Rubber Component) The rubber composition for tires of the present invention contains a rubber component, and the rubber component provides rubber elasticity to the composition. As the rubber component, a diene rubber is preferred, and an isoprene-skeleton rubber, a styrene-butadiene rubber (SBR), a butadiene rubber (BR), or a chloroprene rubber (CR) is more preferred. Here, the isoprene-skeleton rubber is a rubber having an isoprene unit as the main skeleton, and specific examples include natural rubber (NR) and synthetic isoprene rubber (IR). When the rubber component contains at least one selected from the group consisting of an isoprene-skeleton rubber, a styrene-butadiene rubber, a butadiene rubber, and a chloroprene rubber, the rubber composition has excellent rubber elasticity and is more suitable for tire applications. Furthermore, when the rubber component contains at least one rubber selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber, the effects of the present invention (the effect of improving aging resistance by using an amine-based antioxidant, the effect of suppressing decreases in tensile stress, elongation at break (EB), and tensile strength (TB) after exposure to high temperatures, and, in an embodiment containing a foaming agent as a void-introducing agent, the effect of improving the balance between the reaction rate of the foaming agent and the vulcanization reaction rate of the rubber composition) are more likely to be significantly exhibited. The content of diene rubber, such as isoprene-skeleton rubber, styrene-butadiene rubber, butadiene rubber, or chloroprene rubber, in the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and may even be 100% by mass. The rubber component may contain one type alone or a blend of two or more types.

[0017] (Void-introducing agent) The rubber composition for tires of the present invention contains a void-introducing agent. When the rubber composition contains a void-introducing agent, the vulcanized rubber (rubber component) obtained by vulcanizing the rubber composition has voids on the surface or inside, or on the surface and inside. Therefore, a tire using this vulcanized rubber has flexibility and easily adheres to icy road surfaces. In addition, water on the road surface is absorbed into the voids on the tire surface, making it easier to remove water from icy and snowy road surfaces. Therefore, a tire using this rubber composition for tires can improve braking performance on ice.

[0018] Examples of the void-introducing agent include foaming agents, metal sulfates, thermally expandable microcapsules, porous cellulose particles, lignin derivatives, etc., and one of these may be used alone or two or more may be mixed together. Among these, foaming agents are preferred from the viewpoint of tire performance on ice.

[0019] The content of the void-introducing agent in the rubber composition is not particularly limited, but from the viewpoint of obtaining a desired void ratio and maintaining fracture resistance, abrasion resistance, etc., it is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component. The content ratio of the void-introducing agent to the amine-based antiaging agent described below is not particularly limited, but from the viewpoint of improving fracture resistance and performance on ice, the mass ratio of the void-introducing agent to the amine-based antiaging agent (void-introducing agent / amine-based antiaging agent) is preferably 0.1 or more, more preferably 0.3 or more, even more preferably 0.5 or more, and is preferably 10 or less, more preferably 7 or less, and even more preferably 6 or less.

[0020] --Foaming Agent-- By including a foaming agent as the void-introducing agent in the rubber composition, the foaming agent generates bubbles in the vulcanized rubber (rubber component) during vulcanization of the rubber composition, thereby converting the vulcanized rubber into foamed rubber. Because foamed rubber is flexible, tire surfaces made from vulcanized rubber can more easily adhere to icy road surfaces. Furthermore, the bubbles create holes (foam pores) in the vulcanized rubber surface and the tire surface, which function as water channels for draining water.

[0021] Specific examples of the foaming agent include inorganic foaming agents such as azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), dinitrosopentastyrenetetramine, benzenesulfonylhydrazide derivatives, p,p'-oxybisbenzenesulfonylhydrazide (OBSH), carbonates such as ammonium carbonate, sodium carbonate, and potassium carbonate, and bicarbonates (hydrogencarbonates) such as ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate, nitrogen-generating nitrososulfonylazo compounds, N,N'-dimethyl-N,N'-dinitrosophthalamide, toluenesulfonylhydrazide, p-toluenesulfonylsemicarbazide, and p,p'-oxybisbenzenesulfonylsemicarbazide. Among these, azodicarbonamide (ADCA), dinitrosopentamethylenetetramine (DPT), and inorganic foaming agents are preferred from the viewpoint of manufacturing processability. These foaming agents may be used alone or in combination of two or more.

[0022] The content of the foaming agent in the rubber composition is not particularly limited, but is preferably 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the rubber component.

[0023] --Metal Sulfate-- When the rubber composition contains a metal sulfate as the void-introducing agent, the metal sulfate protrudes from the surface of a rubber component (e.g., a tire surface) obtained by vulcanizing the rubber composition, performing a claw function without the disadvantage of being abrasive. Subsequently, the metal sulfate gradually leaves the rubber matrix, creating cavities that function as storage volumes and passageways for discharging the water film on the ice surface. Under these conditions, contact between the surface of the rubber component (e.g., a tire surface (particularly the tread surface)) and ice is no longer lubricated, thereby improving the coefficient of friction.

[0024] Examples of the metal sulfate include magnesium sulfate, calcium sulfate, and barium sulfate, and among these, magnesium sulfate is preferred.

[0025] The metal sulfate preferably has micrometer-sized particles. Specifically, the average particle size and median particle size (both expressed by mass) are preferably 1 μm to 1 mm, and the median particle size is more preferably 2 μm to 800 μm. When the average particle size and median particle size are 1 μm or more, the desired technical effect (i.e., the formation of an appropriate micro-roughness) is easily achieved. Furthermore, when the rubber composition is used as a tread, when the average particle size and median particle size are 1 mm or less, deterioration in aesthetics is suppressed (the appearance of too obvious particles on the tread surface can be suppressed) and grip performance on melting ice is less likely to be impaired. For all of these reasons, the median particle size of the metal sulfate is more preferably 2 μm to 500 μm, and particularly preferably 5 μm to 200 μm. This particularly preferred particle size range appears to correspond to the optimal compromise between the desired surface roughness on the one hand and good contact between the rubber composition and ice on the other hand.

[0026] Furthermore, for the same reason as above, the content of the metal sulfate in the rubber composition is preferably 5 to 40 parts by mass, more preferably 10 to 35 parts by mass, per 100 parts by mass of the rubber component.

[0027] Various known methods for analyzing particle size and calculating the median particle size of microparticles (or the average diameter of microparticles assuming a substantially spherical shape), for example by laser diffraction, can be applied (see, for example, standard ISO-8130-13 or standard JIS K5600-9-3).

[0028] Particle size analysis by mechanical sieving can also be used simply and preferably. This procedure consists in sieving a defined amount of sample (e.g., 200 g) for 30 minutes on a vibrating table through various sieve diameters (e.g., through meshes of 1000, 800, 630, 500, 400, ..., 100, 80, and 63 μm, according to a progression ratio equal to 1.26). The oversize particles collected on each sieve are weighed on a precision balance, and the percentage of oversize particles at each mesh diameter relative to the total mass of the substance is estimated from the weight. Finally, the median particle size (or median diameter) or average particle size (or average diameter) is calculated in a known manner from a histogram of the particle size distribution.

[0029] --Thermal-Expandable Microcapsules--The thermally expandable microcapsules are configured by encapsulating a thermally expandable substance within a shell material made of a thermoplastic resin. The shell material of the thermally expandable microcapsules can be formed from a nitrile-based polymer. The thermally expandable substance encapsulated within the microcapsule shell material has the property of vaporizing or expanding upon heat, and is exemplified by at least one type selected from the group consisting of hydrocarbons such as isoalkanes and normal alkanes. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, and 2,2,4-trimethylpentane. Examples of normal alkanes include n-butane, n-propane, n-hexane, n-heptane, and n-octane. These hydrocarbons may be used alone or in combination. A preferred form of the thermally expandable substance is one in which a hydrocarbon that is gaseous at room temperature is dissolved in a hydrocarbon that is liquid at room temperature. By using such a hydrocarbon mixture, sufficient expansion force can be obtained from low to high temperature ranges within the vulcanization molding temperature range (150°C to 190°C) of an unvulcanized tire.

[0030] Examples of such thermally expandable microcapsules include those manufactured by Expancel AB in Sweden under the trade names "EXPANCEL 091DU-80" and "EXPANCEL 092DU-120" and those manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. under the trade names "Matsumoto Microsphere F-85D" and "Matsumoto Microsphere F-100D".

[0031] The content of the thermally expandable microcapsules in the rubber composition is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0032] --Porous Cellulose Particles-- When the rubber composition contains porous cellulose particles as the void-introducing agent, if the porous cellulose particles are exposed on the surface of a rubber component (e.g., a tire surface) obtained by vulcanizing the rubber composition, water on an icy or snowy road surface is absorbed by the porous cellulose particles. Therefore, by applying the rubber component to a tire, water can be removed from between the tire and the road surface. Furthermore, the presence of cellulose, a polysaccharide, causes an interaction between the tire and water on the icy or snowy road surface, thereby further enhancing the interaction between the tire and water.

[0033] The porous cellulose particles have a porous structure with a porosity of 75 to 95%, and when incorporated into a rubber composition, they can significantly improve performance on ice. A porosity of 75% or more in the porous cellulose particles provides excellent performance improvement on ice, while a porosity of 95% or less enhances particle strength. The porosity is more preferably 80 to 90%. The porosity of the porous cellulose particles can be calculated by measuring the volume of a given mass of sample (i.e., porous cellulose particles) with a measuring cylinder, determining the bulk density, and then using the following formula: Porosity [%] = {1 - (bulk density of sample [g / mL]) / (true specific gravity of sample [g / mL])} × 100, where the true specific gravity of cellulose is 1.5.

[0034] The particle size of the porous cellulose particles is not particularly limited, but from the viewpoint of abrasion resistance, those having an average particle size of 1000 μm or less are preferably used. The lower limit of the average particle size is not particularly limited, but it is preferably 5 μm or more. The average particle size is more preferably 100 to 800 μm, and even more preferably 200 to 800 μm.

[0035] The porous cellulose particles are preferably spherical particles having a major axis / minor axis ratio of 1 to 2. The use of particles with such a spherical structure improves dispersibility in the rubber composition, contributing to improved performance on ice and maintenance of abrasion resistance, etc. The major axis / minor axis ratio is more preferably 1.0 to 1.5.

[0036] The average particle size and the major axis / minor axis ratio of the porous cellulose particles are determined as follows: the porous cellulose particles are observed under a microscope to obtain an image, and the major axis and minor axis (if the major axis and minor axis are the same, the length in a certain axis direction and the length in an axis direction perpendicular to the major axis) of 100 particles are measured using this image, and the average particle size is obtained by calculating the average value, and the major axis / minor axis ratio is obtained by averaging the values ​​obtained by dividing the major axis by the minor axis.

[0037] Such porous cellulose particles are commercially available from Rengo Co., Ltd. under the name "Viscopal" and are also described in JP-A Nos. 2001-323095 and 2004-115284, and these can be suitably used.

[0038] The content of the porous cellulose particles in the rubber composition is preferably 0.3 to 20 parts by mass per 100 parts by mass of the rubber component. A content of 0.3 parts by mass or more can enhance the effect of improving performance on ice, while a content of 20 parts by mass or less can prevent the rubber hardness from becoming too high and suppress a decrease in abrasion resistance. The content of the porous cellulose particles is more preferably 1 to 15 parts by weight, and even more preferably 3 to 15 parts by mass.

[0039] --Lignin Derivative-- When the rubber composition contains a lignin derivative as the void-introducing agent, the effect of improving performance on ice can be enhanced. Here, lignin sulfonates are preferably used as the lignin derivative. Examples of lignin sulfonates include alkali metal salts, alkaline earth metal salts, ammonium salts, and alcoholamine salts of lignin sulfonic acid, and at least one of these can be used. Preferred are alkali metal salts and / or alkaline earth metal salts of lignin sulfonic acid, such as potassium salt, sodium salt, calcium salt, magnesium salt, lithium salt, and barium salt, and mixed salts of these are also acceptable.

[0040] The content of the lignin derivative in the rubber composition is preferably 0.3 to 20 parts by mass per 100 parts by mass of the rubber component. A content of 0.3 parts by mass or more can enhance the effect of improving performance on ice, while a content of 20 parts by mass or less can prevent the rubber hardness from becoming too high and suppress a decrease in wear resistance. The content of the lignin derivative is more preferably 1 to 15 parts by mass, and even more preferably 3 to 15 parts by mass.

[0041] (Amine-Based Antiaging Agent) The rubber composition for tires of the present invention contains an amine-based antioxidant represented by the above general formula (1). The amine-based antioxidant represented by general formula (1) contains a phenylenediamine moiety, just like N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (antiaging agent 6PPD), but differs from antioxidant 6PPD in that it does not contain a double bond outside of the phenylenediamine moiety. The amine-based antioxidant represented by general formula (1) improves the aging resistance (ozone resistance) of the rubber composition and has the effect of suppressing decreases in tensile stress, elongation at break (EB), and tensile strength (TB) after exposure to high temperatures.

[0042] In the above general formula (1), R １ and R ２ are each independently a monovalent saturated hydrocarbon group. １ and R ２ may be the same or different, but from the viewpoint of synthesis, they are preferably the same.

[0043] The number of carbon atoms in the monovalent saturated hydrocarbon group is preferably 1 to 20, more preferably 3 to 10, and particularly preferably 6 or 7. When the number of carbon atoms in the saturated hydrocarbon group is 20 or less, the number of moles per unit mass increases, resulting in a greater anti-aging effect and improved aging resistance and fracture resistance of the rubber composition. １ and R ２ and each independently represent a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms, from the viewpoint of further improving the aging resistance and fracture resistance of the rubber composition.

[0044] Examples of the monovalent saturated hydrocarbon group include an alkyl group and a cycloalkyl group. The alkyl group may be linear or branched, and the cycloalkyl group may further have an alkyl group or the like bonded thereto as a substituent. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,3-dimethylbutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,2-dimethylpentyl group, a 1,3-dimethylpentyl group, a 1,4-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,4-dimethylpentyl group, an n-hexyl group, a 1-methylhexyl group, a 2-methylhexyl group, various octyl groups, various decyl groups, and various dodecyl groups. Of these, a 1,4-dimethylpentyl group is preferred. Examples of the cycloalkyl group include a cyclopentyl group, a methylcyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, a cycloheptyl group, and a cyclooctyl group, and among these, a cyclohexyl group is preferred.

[0045] Specific examples of the amine-based antioxidant represented by the general formula (1) include N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD), N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, and N,N'-dicyclohexyl-p-phenylenediamine (antiaging agent CCPD). Of these, N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD) and N,N'-dicyclohexyl-p-phenylenediamine (CCPD) are preferred, with N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine (antiaging agent 77PD) being particularly preferred. The amine-based antioxidants may be used alone or in combination of two or more.

[0046] The content of the amine-based antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component. If the content of the amine-based antioxidant is less than 0.1 part by mass per 100 parts by mass of the rubber component, the aging resistance of the rubber composition cannot be sufficiently ensured, and the decrease in the tensile stress, elongation at break (EB), and tensile strength (TB) of the rubber composition after exposure to high temperatures cannot be sufficiently suppressed. Furthermore, in an embodiment containing a foaming agent as a void-introducing agent, if the content of the amine-based antioxidant is less than 0.1 part by mass per 100 parts by mass of the rubber component, the effect of improving the balance between the reaction rate of the foaming agent and the vulcanization reaction rate of the rubber composition is insufficient. On the other hand, if the content of the amine-based antioxidant exceeds 11 parts by mass per 100 parts by mass of the rubber component, adverse effects on rubber physical properties other than aging resistance (heat buildup, etc.) become significant, making the rubber unsuitable for tire applications. The amount of the amine-based antiaging agent is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more, per 100 parts by mass of the rubber component from the viewpoint of aging resistance, and is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the rubber component from the viewpoint of influence on other rubber physical properties.

[0047] (Quinoline-Based Antiaging Agent) The rubber composition for a tire of the present invention may contain a quinoline-based antioxidant. The quinoline-based antioxidant is an antioxidant having a quinoline moiety or a derivative thereof (such as a dihydroquinoline moiety). The quinoline-based antioxidant has the effect of improving the aging resistance (ozone resistance) of the rubber composition and suppressing a decrease in the retention rate of elongation at break (EB) and tensile strength (TB) after exposure to high temperatures.

[0048] The quinoline-based antioxidant preferably has a dihydroquinoline moiety, and more preferably has a 1,2-dihydroquinoline moiety. Specific examples of the quinoline-based antioxidant include a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, and 6-anilino-2,2,4-trimethyl-1,2-dihydroquinoline. The quinoline-based antioxidant preferably contains a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline (antiaging agent TMDQ). Quinoline-based antioxidants containing a polymer of 2,2,4-trimethyl-1,2-dihydroquinoline are highly effective in improving the aging resistance of rubber compositions and also have the advantage of being less likely to discolor the rubber composition. The polymer of 2,2,4-trimethyl-1,2-dihydroquinoline includes a dimer, trimer, tetramer, etc. of 2,2,4-trimethyl-1,2-dihydroquinoline.

[0049] The content of the quinoline-based antioxidant is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component. When the content of the quinoline-based antioxidant is 0.1 part by mass or more per 100 parts by mass of the rubber component, the aging resistance of the rubber composition is improved, and the decrease in the elongation at break (EB) and tensile strength (TB) of the rubber composition after exposure to high temperatures can be further suppressed. On the other hand, when the content of the quinoline-based antioxidant is 5 parts by mass or less per 100 parts by mass of the rubber component, adverse effects on rubber physical properties other than aging resistance (heat buildup, etc.) can be suppressed, making the rubber more suitable for tire applications. From the viewpoint of aging resistance, the content of the quinoline-based antioxidant is more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of the effect on other rubber physical properties, the content is more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of the rubber component.

[0050] (Foaming Aid) The rubber composition for a tire of the present invention may contain a foaming aid. In particular, when the rubber composition contains a foaming agent as the void-introducing agent, it is preferable that the rubber composition contains a foaming aid. Examples of the foaming aid include urea, zinc stearate, zinc benzenesulfinate, zinc oxide, etc., and among these, urea is widely known. These may be used alone or in combination of two or more. By using the foaming aid in combination, it is possible to promote the foaming reaction, increase the degree of completion of the reaction, and suppress unnecessary deterioration over time.

[0051] The total content of the foaming agent and the foaming aid is preferably 1 to 30 parts by mass per 100 parts by mass of the rubber component. When the total content of the foaming agent and the foaming aid is 1 part by mass or more, the rubber composition can be sufficiently foamed during vulcanization, and the foaming rate of the vulcanized rubber can be maintained high. On the other hand, even when the total content of the foaming agent and the foaming aid is 30 parts by mass or less, a decrease in the foaming rate can be suppressed. Furthermore, from the viewpoint of improving the foaming rate, the total content of the foaming agent and the foaming aid is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, from the viewpoint of improving the foaming rate, the total content of the foaming agent and the foaming aid is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the rubber component.

[0052] In the rubber composition, the mass ratio of the foaming agent to the foaming aid (foaming agent:foaming aid) is preferably 1:1.1 to 1:3.3. When the mass ratio (foaming agent:foaming aid) is in the range of 1:1.1 to 1:3.3, the rubber composition is sufficiently foamed during vulcanization, and the foaming rate of the vulcanized rubber is improved. From the viewpoint of improving the foaming rate, the mass ratio of the foaming agent to the foaming aid (foaming agent:foaming aid) is preferably 1:1.2 or more, and more preferably 1:1.3 or more. From the viewpoint of improving the foaming rate, the mass ratio of the foaming agent to the foaming aid (foaming agent:foaming aid) is preferably 1:3.2 or less, more preferably 1:3.1 or less, even more preferably 1:2.9 or less, even more preferably 1:2.7 or less, even more preferably 1:2.5 or less, and particularly preferably 1:2.3 or less.

[0053] From the viewpoints of the foaming rate of the vulcanized rubber and the on-ice performance of the tire, the content of the foaming aid is preferably in the range of 4 to 14 parts by mass, and more preferably in the range of 6 to 14 parts by mass, per 100 parts by mass of the rubber component.

[0054] (Organic Acid) The rubber composition may contain an organic acid, if necessary. In this case, the SP value of the organic acid is 9.15 to 16.0 (cal / cm ３ ) １／２ The organic acid has the effect of improving the foaming rate of the vulcanized rubber by balancing the rate of the decomposition / foaming reaction of the foaming agent and the rate of the vulcanization reaction of the rubber composition during vulcanization of the rubber composition. Therefore, by compounding the organic acid into the rubber composition, the workability of the rubber composition is maintained good, while the decomposition / foaming reaction of the foaming agent is promoted, and the rate of the decomposition / foaming reaction and the rate of the vulcanization reaction of the rubber composition are balanced, thereby improving the foaming rate of the vulcanized rubber. By applying the rubber composition to a tire, the tire's performance on ice can be improved. The SP value of the organic acid is 9.15 (cal / cm ３ ) １／２ If the SP value of the organic acid is less than 16.0 (cal / cm), the decomposition of the foaming agent may not be sufficiently promoted. ３ ) １／２ If the content exceeds this range, the adhesiveness of the rubber composition containing the organic acid will be high, and the rubber composition may adhere to manufacturing equipment such as rolls during production of the rubber composition, which may deteriorate the workability of the rubber composition.

[0055] From the same viewpoint, the SP value of the organic acid is 10.5 to 14.3 (cal / cm ３ ) １／２ The SP value of the organic acid is preferably 10.5 (cal / cm ３ ) １／２ When the SP value of the organic acid is 14.3 (cal / cm or more), the effect of promoting the decomposition of the foaming agent is further increased. ３ ) １／２When the SP value is 9.12 (cal / cm), the adhesiveness of the rubber composition containing the organic acid can be further reduced, and the workability of the rubber composition can be further improved. ３ ) １／２ In this specification, the SP value (solubility parameter) of an organic acid is calculated according to the Fedors method.

[0056] The organic acid may be any of monocarboxylic acid, dicarboxylic acid, tricarboxylic acid, etc., and may be aliphatic or aromatic. Furthermore, it may have a functional group other than a carboxyl group, such as a hydroxyl group, a ketone group, or an ethylenically unsaturated group. The organic acid preferably has an aromatic ring (aromatic), and more preferably a monocarboxylic acid. When the organic acid has an aromatic ring, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition is less likely to adhere to manufacturing equipment such as rolls.

[0057] Examples of the aliphatic monocarboxylic acid include palmitic acid. Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Examples of the aromatic monocarboxylic acid include benzoic acid and salicylic acid. Examples of the aromatic dicarboxylic acid include phthalic acid. Examples of organic acids having a functional group other than a carboxyl group include tartaric acid, malic acid, maleic acid, glycolic acid, and α-ketoglutaric acid. The organic acids may be used alone or in combination of two or more.

[0058] It is particularly preferable to use benzoic acid as the organic acid. When benzoic acid is compounded into the rubber composition, the adhesion of the rubber composition can be further reduced, the workability of the rubber composition is further improved, and the rubber composition becomes even less likely to adhere to manufacturing equipment such as rolls.

[0059] From the viewpoints of workability of the rubber composition, the foaming rate of the vulcanized rubber, and the tire's performance on ice, the content of the organic acid is preferably 0.1 to 7 parts by mass, more preferably 1.5 to 7 parts by mass, and even more preferably 3 to 7 parts by mass, per 100 parts by mass of the rubber component. Furthermore, from the viewpoints of the foaming rate of the vulcanized rubber and the tire's performance on ice, the total content of the foaming agent and the organic acid is preferably 3 parts by mass or more and less than 15 parts by mass, more preferably 5 parts by mass or more and less than 15 parts by mass, and even more preferably 7 parts by mass or more and less than 15 parts by mass, per 100 parts by mass of the rubber component. Furthermore, from the viewpoints of the foaming rate of the vulcanized rubber and the tire's performance on ice, the mass ratio of the foaming agent to the organic acid (foaming agent:organic acid) is preferably in the range of 1:0.5 to 1:1.5, and more preferably 1:0.7 to 1:1.3.

[0060] (Wax) The rubber composition for a tire of the present invention preferably further contains a wax. When the rubber composition contains a wax, the aging resistance (ozone resistance) of the rubber composition is further improved. Examples of the wax include paraffin wax and microcrystalline wax. The content of the wax is preferably 0.1 to 5 parts by mass per 100 parts by mass of the rubber component. When the content of the wax is 0.1 part by mass or more per 100 parts by mass of the rubber component, the aging resistance of the rubber composition is further improved. Furthermore, when the content of the wax is 5 parts by mass or less per 100 parts by mass of the rubber component, the influence on rubber physical properties other than aging resistance is small. From the viewpoint of aging resistance, the content of the wax is more preferably 0.5 parts by mass or more per 100 parts by mass of the rubber component, and even more preferably 1 part by mass or more. Furthermore, from the viewpoint of the influence on other rubber physical properties, the content of the wax is more preferably 4 parts by mass or less per 100 parts by mass of the rubber component, and even more preferably 3 parts by mass or less.

[0061] (Sulfur) The rubber composition for a tire of the present invention preferably contains sulfur. The inclusion of sulfur in the rubber composition makes it possible to vulcanize the rubber composition, improving its fracture resistance (particularly, elongation at break (EB) and tensile strength (TB)). Various types of sulfur can be used as the sulfur; however, ordinary sulfur (soluble sulfur (powdered sulfur), etc.) is preferred over insoluble sulfur, and oil treat sulfur is also preferred. Here, insoluble sulfur refers to sulfur insoluble in carbon disulfide (amorphous polymeric sulfur), and soluble sulfur (powdered sulfur) refers to sulfur soluble in carbon disulfide. The sulfur content is preferably in the range of 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component. When the sulfur content is 0.1 part by mass or more per 100 parts by mass of the rubber component, the fracture resistance of the vulcanized rubber can be ensured. When the sulfur content is 10 parts by mass or less per 100 parts by mass of the rubber component, sufficient rubber elasticity can be ensured.

[0062] (Others) In addition to the rubber component, void-introducing agent, amine-based antioxidant, quinoline-based antioxidant, foaming aid, organic acid, wax, and sulfur described above, the rubber composition for tires of the present invention may contain, as needed, various components commonly used in the rubber industry, such as fillers (silica, carbon black, calcium carbonate, etc.), silane coupling agents, softeners, processing aids, resins, surfactants, and rubbers with an SP value of 9.15 to 16.0 (cal / cm ３ ) １／２The composition may contain an organic acid (e.g., stearic acid), zinc oxide (zinc white), a vulcanization accelerator, a vulcanizing agent other than sulfur, and the like, selected as appropriate within a range that does not impair the objectives of the present invention. Commercially available products can be suitably used as these compounding ingredients. The amine-based antiaging agent represented by the general formula (1) above may be supported on any carrier. For example, the amine-based antiaging agent represented by the general formula (1) above may be supported on an inorganic filler such as silica or calcium carbonate. The amine-based antiaging agent represented by the general formula (1) above may also constitute a masterbatch together with a rubber component. The rubber component used in the masterbatch is not particularly limited, and may be a diene rubber such as natural rubber (NR), or an ethylene-propylene-diene rubber (EPDM). The amine-based antiaging agent represented by the general formula (1) above may also be formed into a salt with an organic acid. The organic acid used in the salt formation is not particularly limited, but examples thereof include stearic acid.

[0063] (Method for Producing Rubber Composition) The method for producing the rubber composition is not particularly limited, but the rubber composition can be produced, for example, by blending the above-mentioned rubber component, void-introducing agent, and amine-based antiaging agent with various components appropriately selected as necessary, followed by kneading, heating, extrusion, etc. The obtained rubber composition can be vulcanized to produce a vulcanized rubber.

[0064] The conditions for the kneading are not particularly limited, and various conditions such as the input volume of the kneading device, the rotation speed of the rotor, the ram pressure, the kneading temperature, the kneading time, the type of kneading device, etc. can be appropriately selected depending on the purpose. Examples of the kneading device include a Banbury mixer, an intermix, a kneader, a roll, etc. that are usually used for kneading rubber compositions.

[0065] The conditions for the heat-in are not particularly limited, and various conditions such as the heat-in temperature, heat-in time, and heat-in device can be appropriately selected depending on the purpose. Examples of the heat-in device include a heat-in roll mill typically used for heat-in of rubber compositions.

[0066] The extrusion conditions are not particularly limited, and various conditions such as extrusion time, extrusion speed, extrusion device, and extrusion temperature can be appropriately selected depending on the purpose. Examples of the extrusion device include an extruder typically used for extruding rubber compositions. The extrusion temperature can be appropriately determined.

[0067] The vulcanization apparatus, method, conditions, etc. are not particularly limited and can be appropriately selected depending on the purpose. Examples of vulcanization apparatus include a molding vulcanizer using a mold used for vulcanizing rubber compositions. The vulcanization temperature is, for example, about 100 to 190°C.

[0068] <Rubber member for tire> The rubber member for tire of the present invention is a rubber member for tire having voids, and is a rubber member containing a rubber component and a rubber compound represented by the following general formula (1): [In the formula, R １ and R ２ and each independently represents a monovalent saturated hydrocarbon group, and the amount of the amine antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component.

[0069] The tire rubber member of the present invention has excellent on-ice performance due to the presence of voids. Furthermore, by containing 0.1 part by mass or more of the amine-based antioxidant represented by the general formula (1) above per 100 parts by mass of the rubber component, the tire rubber member of the present invention has improved aging resistance (ozone resistance), and can suppress decreases in tensile stress, elongation at break (EB), and tensile strength (TB) after exposure to high temperatures, thereby improving fracture resistance. Therefore, the tire rubber member of the present invention has excellent on-ice performance and fracture resistance (particularly fracture resistance after exposure to high temperatures), despite having voids. Furthermore, by applying the tire rubber member of the present invention to a tread, the fracture resistance and crack resistance of the tread, which generates heat during driving, can be improved.

[0070] The tire rubber component of the present invention can be formed, for example, from the tire rubber composition of the present invention described above. When a foaming agent or thermally expandable microcapsules is included as a void-introducing agent, voids can be formed by heating or the like to produce a tire rubber component having voids. When a metal sulfate, porous cellulose particles, or lignin derivative is included as a void-introducing agent, the metal sulfate, porous cellulose particles, and lignin derivative gradually leave the rubber matrix during use, thereby creating voids and producing a tire rubber component having voids.

[0071] The rubber component and the amine-based antiaging agent represented by general formula (1) contained in the rubber member for a tire of the present invention may be the same as the rubber component and the amine-based antiaging agent represented by general formula (1) used in the rubber composition for a tire described above, and the contents, blending ratios, etc. thereof are also the same. Similarly, the rubber member for a tire of the present invention may appropriately contain various compounding agents that can be blended in the rubber composition for a tire described above.

[0072] <Tire> The tire of the present invention is characterized by comprising a rubber member made of the above-mentioned rubber composition for a tire, or the above-mentioned rubber member for a tire. Because the tire of the present invention comprises a rubber member made of the above-mentioned rubber composition for a tire, or the above-mentioned rubber member for a tire, the tire has excellent performance on ice and fracture resistance (particularly fracture resistance after exposure to high temperatures) while having voids.

[0073] A suitable example of the rubber member is tread rubber that constitutes the tread of a tire. A tire having the rubber member in the tread has excellent fracture resistance and crack resistance.

[0074] Depending on the type of tire to be applied, the tire of the present invention may be obtained by molding an unvulcanized rubber composition and then vulcanizing it, or by molding a semi-vulcanized rubber that has been subjected to a pre-vulcanization step or the like and then further vulcanizing it. The tire of the present invention is preferably a pneumatic tire, and the gas to be filled into the pneumatic tire may be normal air or air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

[0075] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0076] <Preparation and Evaluation of Rubber Compositions> Rubber compositions were produced according to the formulations shown in Tables 1 and 2. The foaming ratio of the resulting rubber compositions was measured using the methods described below, and the on-ice performance and the retention rate of tensile stress (M300) at 300% elongation after aging were evaluated. Furthermore, the on-ice performance and fracture resistance were comprehensively evaluated from the sum of the on-ice performance index and the retention rate (%) of tensile stress (M300) at 300% elongation. The results are shown in Tables 1 and 2.

[0077] (1) Method for measuring foaming ratio A vulcanized rubber test piece was prepared by vulcanization in a conventional manner, and the density ρ1 (g / cm ３ ) was measured, while the density ρ0 (g / cm ３ ) was measured, and the foaming ratio (Vs) was calculated using the following formula: Vs = (ρ0 / ρ1-1) × 100 (%) In Table 1, a foaming ratio in the range of 10 to 20% was evaluated as "good."

[0078] (2) Evaluation method for on-ice performance Vulcanized rubber test pieces were prepared by conventional vulcanization, and the test pieces were pressed against fixed ice at -2°C and moved back and forth. The frictional force generated when the test pieces were pressed against ice was detected with a load cell, and the dynamic friction coefficient μ was calculated. In Table 1, the dynamic friction coefficient μ of Comparative Example 1 was set to 100, and in Table 2, the dynamic friction coefficient μ of Comparative Example 2 was set to 100. The higher the index value, the better the on-ice performance.

[0079] (3) Method for Evaluating the Percentage of Tensile Stress at 300% Elongation (M300) Retention Vulcanized rubber test pieces were prepared by conventional vulcanization, and the initial tensile stress (M300) at 300% elongation of the vulcanized rubber test pieces was measured in accordance with JIS K 6251. Similarly, vulcanized rubber test pieces were left to age in a constant temperature bath at 100°C for 24 hours, and the tensile stress (M300) at 300% elongation of the vulcanized rubber test pieces after aging was measured. The percent retention after aging was calculated from the initial tensile stress (M300) at 300% elongation of the vulcanized rubber test pieces prepared from the rubber composition of each example and the tensile stress (M300) at 300% elongation after aging according to the following formula: Percentage retention after aging (%) = (M300 after aging) / (initial M300) × 100. A higher percent retention after aging indicates better fracture resistance after exposure to high temperatures.

[0080]

[0081]

[0082] *1 NR: Natural rubber *2 BR: Butadiene rubber, manufactured by Nippon Zeon Co., Ltd., high cis BR *3 SBR: Solution polymerization styrene-butadiene rubber, styrene bond amount = 10 mass% *4 Carbon black: Manufactured by Asahi Carbon Co., Ltd., nitrogen adsorption specific surface area = 148 m ２ / g *5 Silica: manufactured by Tosoh Corporation, nitrogen adsorption specific surface area = 222 m ２ / g *6 Antioxidant 6PPD: R in general formula (1) １ and R ２ An amine-based antioxidant in which one of R is an unsaturated hydrocarbon group (phenyl group), N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, manufactured by Sumitomo Chemical Co., Ltd., trade name "Antigen 6C" *7 Antioxidant 77PD: １ and R ２is a saturated hydrocarbon group (1,4-dimethylpentyl group), N,N'-bis(1,4-dimethylpentyl)-p-phenylenediamine, manufactured by EASTMAN, trade name "Santoflex 77PD" *8 Softener: Total amount of softener components including resin, oil, and liquid polymer *9 Foaming agent: Dinitrosopentamethylenetetramine, manufactured by Eiwa Chemical Industry Co., Ltd., trade name "Cellular" *10 Other chemicals: Total amount of at least silane coupling agent, vulcanization accelerator, and other chemicals containing sulfur

[0083] Tables 1 and 2 show that the rubber compositions of the examples, which contain 0.1 to 11 parts by mass of the amine-based antioxidant represented by the general formula (1) above per 100 parts by mass of the rubber component together with a foaming agent (void-introducing agent), are able to achieve both good performance on ice and good fracture resistance (particularly good fracture resistance after exposure to high temperatures). While not wishing to be bound by theory, the fact that the M300 after aging is greater than the initial M300 in each example and comparative example is thought to be due to the progress of hardening of the foamed rubber due to heat.

Claims

1. A rubber component, a void-introducing agent, and a compound represented by the following general formula (1): 【Chemical 1】 [In the formula, R １ and R ２ and each independently represents a monovalent saturated hydrocarbon group; A rubber composition for tires, characterized in that the content of the amine-based antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component.

2. 2. The rubber composition for tires according to claim 1, wherein the rubber component comprises at least one rubber selected from the group consisting of isoprene-skeleton rubber, styrene-butadiene rubber, butadiene rubber, and chloroprene rubber.

3. R in the above general formula (1) １ and R ２ and each independently represent a linear or cyclic monovalent saturated hydrocarbon group having 1 to 20 carbon atoms.

4. A tire rubber member having a void, A rubber component and a compound represented by the following general formula (1): 【Chemistry 2】 [In the formula, R １ and R ２ and each independently represents a monovalent saturated hydrocarbon group; A rubber member for a tire, characterized in that the content of the amine-based antioxidant is 0.1 to 11 parts by mass per 100 parts by mass of the rubber component.

5. A tire comprising a rubber member made of the rubber composition for a tire according to any one of claims 1 to 3, or the rubber member for a tire according to claim 4.

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