Rubber composition for tires and tires

Abstract

To provide a tire rubber composition or the like that has excellent dispersibility of microfibrillated vegetable fibers and can improve tensile characteristics and fuel economy.SOLUTION: A tire rubber composition contains a rubber component, microfibrillated vegetable fibers, and a modifier that can form a covalent bond with the microfibrillated vegetable fibers.SELECTED DRAWING: None

Description

[Technology Field]

[0001] The present invention relates to a rubber composition for tires, a method for producing the same, and a tire having a tire component made of the rubber composition. [Background technology]

[0002] It is known that incorporating microfibrillated plant fibers, such as cellulose fibers, as fillers into rubber compositions can reinforce them and improve their modulus (complex modulus of elasticity). However, microfibrillated plant fibers have strong self-cohesive properties and poor compatibility with rubber components.

[0003] In response to this, a method has been disclosed to improve the compatibility between rubber components and microfibrillated plant fibers by chemically modifying the microfibrillated plant fibers (see, for example, Patent Document 1). Furthermore, a method has been disclosed to improve the dispersibility of cellulose fibers in rubber by blending them with rubber, thereby obtaining finely modified cellulose fibers obtained by treating cellulose fibers having carboxyl groups with an average fiber diameter of 1 to 200 nm, or fine cellulose fibers having carboxyl groups with an average fiber diameter of 0.1 to 200 nm, with a hydrophobic modification agent having hydrocarbon groups (see, for example, Patent Documents 2 and 3).

[0004] Thus, while techniques have been proposed to improve the affinity of microfibrillated plant fibers with rubber by modifying them, no improvement techniques using modifiers have yet been disclosed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 4581116 specification [Patent Document 2] Japanese Unexamined Patent Publication No. 2013-18918 [Patent Document 3] Japanese Unexamined Patent Publication No. 2014-125607 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention aims to solve the aforementioned problems and provide a tire rubber composition, etc., that has excellent dispersibility of microfibrillated plant fibers and can improve tensile properties and fuel efficiency. [Means for solving the problem]

[0007] The present invention relates to a rubber composition for tires comprising a rubber component, microfibrillated plant fibers, and a modifier that can covalently bond with the microfibrillated plant fibers.

[0008] Preferably, the content of the microfibrillated plant fibers is 1 to 50 parts by mass and the content of the modifying agent is 1 to 20 parts by mass per 100 parts by mass of the rubber component.

[0009] The modifier is preferably a liquid polymer. The liquid polymer is preferably a modified liquid polymer modified with an unsaturated carboxylic acid and / or its derivative.

[0010] The modifying agent preferably has a reaction site with diene rubber.

[0011] The present invention relates to a method for producing a rubber composition for tires, comprising the steps of kneading a rubber component, microfibrillated plant fibers, and a modifier capable of covalently bonding with the microfibrillated plant fibers to produce a kneaded product in which covalent bonds are formed between the microfibrillated plant fibers and the modifier, and vulcanizing the kneaded product.

[0012] The present invention also relates to a tire having a tire member made of the rubber composition. [Effects of the Invention]

[0013] According to the present invention, the tire rubber composition contains a rubber component, microfibrillated plant fibers, and a modifier that can covalently bond with the microfibrillated plant fibers. Therefore, it exhibits excellent dispersibility of the microfibrillated plant fibers and can improve tensile properties and fuel efficiency. [Modes for carrying out the invention]

[0014] The rubber composition for tires of the present invention contains a rubber component, microfibrillated plant fibers, and a modifier capable of covalent bonding with the microfibrillated plant fibers. The rubber composition has excellent dispersibility of the microfibrillated plant fibers, and the tensile properties (tensile strength, elongation at break) and low fuel consumption are significantly improved. Also, good processability and hardness can be obtained.

[0015] The reason for obtaining such effects is not clear, but it is speculated as follows. First, when using microfibrillated plant fibers and a modifier capable of covalent bonding with them, a material in which a covalent bond is formed between the plant fibers and the modifier during kneading and the like of these materials can be obtained. It is considered that the dispersibility of the microfibrillated plant fibers in the rubber component is improved by the modifier in this material. Furthermore, when this material in which the covalent bond is formed, a vulcanizing agent (such as sulfur), etc. are kneaded and vulcanized, it is considered that the modifier covalently bonded to the microfibrillated plant fibers further crosslinks with the rubber component via the vulcanizing agent (such as sulfur). Therefore, a material in which the plant fiber - the modifier - the vulcanizing agent (such as sulfur) - the rubber component are bonded is formed, and it is considered that the tensile properties and low fuel consumption are improved. From the above, it is speculated that the rubber composition has excellent dispersibility of the microfibrillated plant fibers, and the tensile properties and low fuel consumption are significantly improved. Also, it is speculated that good processability and hardness can be obtained.

[0016] As the rubber component, general rubbers used in the rubber industry can be used. For example, diene - based rubbers (diene - based polymers) such as natural rubber (NR), epoxidized natural rubber (ENR), hydrogenated natural rubber, isoprene rubber (IR), butadiene rubber (BR), styrene - butadiene rubber (SBR), styrene - isoprene - butadiene rubber (SIBR), acrylonitrile - butadiene rubber (NBR), chloroprene rubber (CR) are preferred. Also, as the rubber component, butyl - based rubbers such as halogenated butyl rubber (X - IIR), butyl rubber (IIR), etc. can be mentioned. These rubber components may be used alone or in combination of two or more. Among them, isoprene - based rubbers (NR, ENR, hydrogenated natural rubber, IR, etc.), SBR, and BR are preferred.

[0017] SBR and BR may be either unmodified diene rubber or modified diene rubber. Modified diene rubbers can be any diene rubber having a functional group that interacts with a filler such as silica. Examples include end-modified diene rubbers (end-modified diene rubbers having the functional group at the end) in which at least one end of the diene rubber is modified with a compound (modifier) ​​having the functional group, main-chain modified diene rubbers having the functional group in the main chain, main-chain end-modified diene rubbers having the functional group in both the main chain and the end (for example, main-chain end-modified diene rubbers having the functional group in the main chain and at least one end modified with the modifier), and end-modified diene rubbers that are modified (coupled) with a polyfunctional compound having two or more epoxy groups in the molecule, and in which hydroxyl groups or epoxy groups are introduced.

[0018] Examples of the above functional groups include amino groups, amide groups, silyl groups, alkoxysilyl groups, isocyanate groups, imino groups, imidazole groups, urea groups, ether groups, carbonyl groups, oxycarbonyl groups, mercapto groups, sulfide groups, disulfide groups, sulfonyl groups, sulfinyl groups, thiocarbonyl groups, ammonium groups, imide groups, hydrazo groups, azo groups, diazo groups, carboxyl groups, nitrile groups, pyridyl groups, alkoxy groups, hydroxyl groups, oxy groups, epoxy groups, and the like. These functional groups may have substituents. Among these, amino groups (preferably amino groups in which the hydrogen atoms of the amino group are substituted with C1-C6 alkyl groups), alkoxy groups (preferably C1-C6 alkoxy groups), and alkoxysilyl groups (preferably C1-C6 alkoxysilyl groups) are preferred.

[0019] The SBR is not particularly limited; for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR), etc., can be used. These may be used individually or in combination of two or more types.

[0020] BR is not particularly limited, and for example, high-cis BR with a high cis content, BR containing syndiotactic polybutadiene crystals, and BR synthesized using a rare-earth catalyst (rare-earth BR) can be used. These may be used individually or in combination of two or more. Among these, high-cis BR with a cis content of 90% by mass or more is preferred because it improves wear resistance.

[0021] As a source of the above-mentioned rubber components, rubber latex (in this case, the rubber solids contained in the rubber latex correspond to the rubber components) can also be suitably used. Suitable rubber latex options include, for example, natural rubber latex, modified natural rubber latex (saponified natural rubber latex, epoxidized natural rubber latex, etc.), and synthetic diene rubber latex (butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene-butadiene rubber (SIBR), isoprene rubber (IR), acrylonitrile-butadiene rubber, ethylene vinyl acetate rubber, chloroprene rubber, vinylpyridine rubber, butyl rubber, etc.). These rubber latex may be used individually or in combination of two or more. In particular, it is preferable to use natural rubber, SBR, BR, and IR, which are supplied using natural rubber latex, SBR latex, BR latex, and IR latex as sources.

[0022] The pH of the above rubber latex is preferably 8.5 or higher, more preferably 9.5 or higher. When the pH is 8.5 or higher, the rubber latex tends to be less unstable and less likely to solidify. The pH of the above rubber latex is preferably 12 or lower, more preferably 11 or lower. When the pH is 12 or lower, the rubber latex tends to be less likely to deteriorate.

[0023] The above-mentioned rubber latex can be prepared by conventionally known manufacturing methods, and various commercially available products can also be used. Preferably, the rubber latex used has a rubber solid content of 10 to 80% by mass. More preferably, it is 20% or more and 60% or less by mass.

[0024] Natural rubber latex is collected as the sap of natural rubber trees such as the Hevea tree, and contains rubber components as well as water, proteins, lipids, inorganic salts, etc. The gel content in the rubber is thought to be due to the complex presence of various impurities. In this invention, as natural rubber latex, raw latex (field latex) obtained by tapping the Hevea tree, concentrated latex obtained by centrifugal separation or creaming (purified latex, high-ammonia latex obtained by adding ammonia by conventional methods, LATZ latex stabilized with zinc oxide, TMTD and ammonia, etc.) can be used.

[0025] For SBR latex, emulsion polymerized styrene-butadiene rubber latex (E-SBR latex) can be used; for BR latex, emulsion polymerized butadiene rubber latex (E-BR latex) can be used; and for IR latex, emulsion polymerized isoprene rubber latex (E-IR latex) can be used. E-SBR latex, E-SBR latex, and E-IR latex can be prepared by conventionally known manufacturing methods, and various commercially available products can also be used.

[0026] In the rubber composition described above, it is preferable to use at least one of isoprene-based rubber, BR, and SBR, as described above. However, from the viewpoint of tensile properties, fuel efficiency, processability, and hardness, the total content of isoprene-based rubber, BR, and SBR in 100% by mass of the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.

[0027] When the aforementioned rubber composition is applied to the sidewall, it is preferable to use isoprene-based rubber, BR, as the rubber component, as this provides good resistance to flexural crack growth.

[0028] When the rubber composition is applied to the sidewall, the content of isoprene-based rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 60% by mass or more. Setting it above the lower limit tends to yield excellent fuel efficiency. Furthermore, the content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less. Setting it below the upper limit tends to yield good resistance to flexural crack growth.

[0029] When the rubber composition is applied to the sidewall, the BR content in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more, from the viewpoint of exhibiting the necessary low fuel consumption and resistance to flexural crack growth. Furthermore, from the viewpoint of processability, the content is preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 55% by mass or less.

[0030] When the aforementioned rubber composition is applied to the tread of a passenger car tire, it is preferable to use SBR or BR.

[0031] When the rubber composition is applied to the tread of a passenger car tire, the SBR content in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. A content above the lower limit tends to provide sufficient grip performance. The SBR content is preferably 90% by mass or less, more preferably 80% by mass or less. A content below the upper limit tends to provide good fuel efficiency.

[0032] When the rubber composition is applied to the tread of a passenger car tire, the BR content in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. Above the lower limit tends to yield excellent fuel efficiency. Furthermore, the content is preferably 80% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less. Below the upper limit tends to yield good grip performance.

[0033] When the aforementioned rubber composition is applied to the tread of a heavy-duty tire, it is preferable to use isoprene-based rubber.

[0034] When the aforementioned rubber composition is applied to the tread of a heavy-duty tire, from the viewpoint of wear resistance, durability, etc., the content of isoprene-based rubber in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass.

[0035] As the above-mentioned microfibrillated plant fiber, cellulose microfibrils are preferred in that they provide good reinforcing properties. The cellulose microfibrils are not particularly limited as long as they are derived from natural products, and examples include resource biomass such as fruits, grains, and root vegetables; wood, bamboo, hemp, jute, and kenaf, as well as waste biomass such as pulp, paper, cloth, agricultural residues, food waste, and sewage sludge obtained from these raw materials, unused biomass such as rice straw, wheat straw, and thinned wood, and cellulose produced by sea squirts, acetic acid bacteria, etc. One type of microfibrillated plant fiber may be used, or two or more types may be used in combination.

[0036] In this specification, cellulose microfibrils typically refer to cellulose fibers having an average fiber diameter of 10 μm or less, and more typically, cellulose fibers having a microstructure with an average fiber diameter of 500 nm or less, formed by an aggregate of cellulose molecules. Typical cellulose microfibrils can be formed, for example, as aggregates of cellulose fibers having the average fiber diameter described above.

[0037] The method for producing the above-mentioned microfibrillated plant fibers is not particularly limited, but examples include chemically treating the raw material for the cellulose microfibrils with an alkali such as sodium hydroxide as needed, and then mechanically grinding or beating it using a refiner, twin-screw kneader (twin-screw extruder), twin-screw kneading extruder, high-pressure homogenizer, media stirring mill, millstone, grinder, vibratory mill, sand grinder, etc. In these methods, lignin is separated from the raw material by chemical treatment, so microfibrillated plant fibers that are substantially free of lignin are obtained. In addition, other methods include treating the raw material for the cellulose microfibrils under ultra-high pressure.

[0038] As the above-mentioned microfibrillated plant fibers, for example, products from Sugino Machine Co., Ltd. can be used.

[0039] Furthermore, as microfibrillated plant fibers, those obtained by the above manufacturing method may be subjected to further oxidation treatment or various chemical modification treatments, or natural products that can be the source of the above-mentioned cellulose microfibrils (for example, wood, pulp, bamboo, hemp, jute, kenaf, agricultural waste, cloth, paper, ascidian cellulose, etc.) may be used as cellulose raw materials and subjected to oxidation treatment or various chemical modification treatments, followed by defibration treatment as necessary, or a dispersion of microfibrillated plant fibers may be subjected to further oxidation treatment or various chemical modification treatments (chemically modified microfibrillated plant fibers).

[0040] Examples of chemical modification of microfibrillated plant fibers include esterification, etherification, and acetalization. More specifically, preferred examples include acylation such as acetylation, cyanoethylation, amination, sulfone esterification, phosphate esterification, alkyl esterification, alkyl etherification, complex esterification, β-ketoesterification, alkylation such as butylation, and chlorination. Furthermore, alkylcarbamation and arylcarbamation can also be exemplified. All of these chemical modification treatments make the microfibrillated plant fibers hydrophobic, and by using microfibrillated plant fibers that have undergone such chemical modification treatments, the dispersibility of the microfibrillated plant fibers is improved.

[0041] The above-mentioned chemically modified microfibrillated plant fibers are preferably chemically modified such that the degree of substitution is within the range of 0.2 to 2.5. Here, the degree of substitution refers to the average number of hydroxyl groups per glucose ring unit that have been substituted with other functional groups by chemical modification among the hydroxyl groups of cellulose, and the theoretical maximum value is 3. When the degree of substitution is 0.2 or higher, the dispersibility of the chemically modified microfibrillated plant fibers is particularly good, and when it is 2.5 or lower, the chemically modified microfibrillated plant fibers are particularly excellent in dispersibility and flexibility, and the aforementioned effects are preferably obtained. The degree of substitution is more preferably within the range of 0.3 to 2.5, even more preferably within the range of 0.4 to 2.3, and particularly preferably within the range of 0.4 to 2.0.

[0042] Furthermore, if the above-mentioned chemically modified microfibrillated plant fibers consist of a combination of two or more types, the degree of substitution is calculated as the average of all chemically modified microfibrillated plant fibers.

[0043] The degree of substitution in the above-mentioned chemically modified microfibrillated plant fibers can be confirmed, for example, by titration using 0.5N-NaOH and 0.2N-HCl, or by measurements such as NMR and infrared absorption spectroscopy.

[0044] When the above chemically modified microfibrillated plant fiber is acetylated microfibrillated plant fiber, the degree of substitution is preferably within the range of 0.3 to 2.5; when it is amination microfibrillated plant fiber, the degree of substitution is preferably within the range of 0.3 to 2.5; when it is sulfone esterified microfibrillated plant fiber, the degree of substitution is preferably within the range of 0.3 to 1.8; when it is alkyl esterified microfibrillated cellulose, the degree of substitution is preferably within the range of 0.3 to 1.8; when it is complex esterified microfibrillated cellulose, the degree of substitution is preferably within the range of 0.4 to 1.8; when it is β-ketoesterified microfibrillated cellulose, the degree of substitution is preferably within the range of 0.3 to 1.8; when it is alkyl carbamateated microfibrillated cellulose, the degree of substitution is preferably within the range of 0.3 to 1.8; and when it is aryl carbamateated microfibrillated cellulose, the degree of substitution is preferably within the range of 0.3 to 1.8.

[0045] The above acetylation can be carried out, for example, by reacting microfibrillated plant fibers with acetic acid, concentrated sulfuric acid, or acetic anhydride. More specifically, it can be carried out by conventionally known methods, such as reacting microfibrillated plant fibers with acetic anhydride in a mixed solvent of acetic acid and toluene in the presence of a sulfuric acid catalyst to carry out the acetylation reaction, and then replacing the solvent with water.

[0046] The above amination can be carried out by known methods, such as a method in which tosyl esterification is followed by a reaction with an alkylamine in an alcohol to carry out a nucleophile substitution reaction.

[0047] The above sulfon esterification can be carried out by a simple procedure, for example, dissolving microfibrillated plant fibers in sulfuric acid and then adding them to water. Other methods include treatment with anhydrous sulfuric acid gas or treatment with chlorosulfonic acid and pyridine.

[0048] The above phosphate esterification can be carried out, for example, by treating microfibrillated plant fibers that have been treated with dimethylamine or the like with phosphoric acid and urea.

[0049] The alkyl esterification described above can be carried out, for example, by the Schotten-Baumann method, in which microfibrillated plant fibers are reacted with carboxylic acid chloride under basic conditions. The alkyl etherification described above can be carried out by the Williamson method, in which microfibrillated plant fibers are reacted with alkyl halides under basic conditions.

[0050] The above chlorination can be carried out, for example, by adding thionyl chloride in DMF (dimethylformamide) and heating it.

[0051] The above complex esterification can be carried out, for example, by reacting microfibrillated plant fibers with two or more types of carboxylic acid anhydrides or carboxylic acid chlorides under basic conditions.

[0052] The above β-ketoesterification can be carried out, for example, by reacting microfibrillated plant fibers with diketene or alkylketene dimers, or by transesterification of microfibrillated plant fibers with β-ketoester compounds such as alkylacetate.

[0053] The alkylcarbamate reaction described above can be carried out, for example, by reacting microfibrillated plant fibers with an alkyl isocyanate in the presence of a basic catalyst or a tin catalyst.

[0054] The above aryl carbamate reaction can be carried out, for example, by reacting microfibrillated plant fibers with an aryl isocyanate in the presence of a basic catalyst or a tin catalyst.

[0055] Examples of methods for oxidizing the above-mentioned microfibrillated plant fibers include oxidation treatment using an N-oxyl compound. This oxidation treatment using an N-oxyl compound can be carried out, for example, by using an N-oxyl compound as an oxidation catalyst in water and reacting the microfibrillated plant fibers with a co-oxidant.

[0056] Examples of the above N-oxyl compounds include 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its derivatives. Examples of the above-mentioned co-oxidizing agents include sodium hypochlorite.

[0057] The average fiber diameter of the microfibrillated plant fibers is preferably 4 to 100 nm. This range ensures sufficient dispersibility of the microfibrillated plant fibers, thus achieving the aforementioned effects. Furthermore, it suppresses damage to the microfibrillated plant fibers during processing. From the viewpoint of the aforementioned effects, the average fiber diameter is preferably 90 nm or less, and more preferably 50 nm or less. Additionally, because the microfibrillated plant fibers are less likely to untangle and disperse, a diameter of 10 nm or more is preferable, and more preferably 20 nm or more.

[0058] The average fiber length of the above-mentioned microfibrillated plant fibers is preferably 100 nm or more. More preferably 300 nm or more, and even more preferably 500 nm or more. Furthermore, it is preferably 5 mm or less, more preferably 1 mm or less, even more preferably 50 μm or less, particularly preferably 3 μm or less, and most preferably 2 μm or less. When the average fiber length is above the lower limit and below the upper limit, it exhibits a similar trend to that of the average fiber diameter described above.

[0059] Furthermore, if the above-mentioned microfibrillated plant fibers consist of a combination of two or more types, the above-mentioned average fiber diameter and average fiber length are calculated as the average of the entire microfibrillated plant fiber.

[0060] In this specification, the average fiber diameter and average fiber length of the above-mentioned microfibrillated plant fibers can be measured by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray scattering data analysis, pore electrical resistance method (Culter principle method), etc.

[0061] In the above rubber composition, the content (solids) of microfibrillated plant fibers is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, 50 parts by mass or less is preferred, 40 parts by mass or less is more preferred, and 30 parts by mass or less is even more preferred. The above effects can be suitably obtained within the above range.

[0062] The average fiber diameter of the microfibrillated plant fibers in the above rubber composition is preferably 4 to 100 nm. This range tends to improve the dispersibility of the microfibrillated plant fibers in the rubber composition, leading to the aforementioned effects. Furthermore, it tends to suppress damage to the microfibrillated plant fibers during processing. A suitable average fiber diameter is preferred if it is 90 nm or less, as this effectively achieves the aforementioned effects. Additionally, a diameter of 10 nm or more is preferred, and 20 nm or more, because it makes it difficult for the microfibrillated plant fibers to untangle and disperse.

[0063] The average fiber length of the microfibrillated plant fibers in the above rubber composition is preferably 100 nm or more. More preferably 300 nm or more, and even more preferably 500 nm or more. Furthermore, it is preferably 5 mm or less, more preferably 1 mm or less, even more preferably 50 μm or less, particularly preferably 3 μm or less, and most preferably 2 μm or less. When the average fiber length is above the lower limit and below the upper limit, it exhibits a similar tendency to the average fiber diameter described above.

[0064] The most frequent fiber diameter of the microfibrillated plant fibers in the above rubber composition is preferably 10 to 70 nm. This range allows for good dispersibility of the microfibrillated plant fibers in the rubber composition, leading to the aforementioned effects. From the viewpoint of obtaining these effects more favorably, the most frequent fiber diameter is preferably 15 nm or greater, more preferably 18 nm or greater. Furthermore, 65 nm or less is preferred, and 60 nm or less is more preferred.

[0065] In this specification, the mode of the fiber diameter of the above-mentioned microfibrillated plant fibers is the value obtained from the distribution obtained by observing and imaging 100 fibers with a transmission electron microscope and measuring their diameters.

[0066] The rubber composition contains a modifier capable of covalently bonding with microfibrillated plant fibers. The modifier is a compound capable of forming a covalent bond with microfibrillated plant fibers.

[0067] In the rubber composition, the content of the modifier is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, it is preferably 20 parts by mass or less, more preferably 18 parts by mass or less, and even more preferably 16 parts by mass or less. When the content is within the above range, the above effect can be suitably obtained.

[0068] As the modifying agent, for example, a liquid polymer can be suitably used from the viewpoint of being able to disperse microfibrillated plant fibers well in rubber.

[0069] From the viewpoint of the mechanical properties of the rubber composition, the number-average molecular weight (Mn) of the liquid polymer is preferably 1000 or more, preferably 5000 or more, and more preferably 10000 or more. From the viewpoint of processability, the Mn is preferably 70000 or less, and more preferably 50000 or less.

[0070] In this specification, Mw and Mn can be determined by converting them to standard polystyrene equivalents based on measurements obtained by gel permeation chromatography (GPC) (GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMULTIPORE HZ-M manufactured by Tosoh Corporation).

[0071] Examples of liquid polymers include unmodified liquid polymers and modified liquid polymers. Among these, modified liquid polymers are preferred, and it is particularly preferred to use modified liquid polymers obtained by modifying unmodified liquid polymers with unsaturated carboxylic acids and / or their derivatives.

[0072] Unmodified liquid polymers are unmodified liquid polymers (liquid diene polymers) obtained by polymerizing monomers containing conjugated dienes such as 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 2-methyl-1,3-pentadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. Examples of unmodified liquid polymers include liquid polybutadiene, liquid polyisoprene, liquid styrene-butadiene random copolymer, liquid styrene-butadiene block copolymer, liquid butadiene-isoprene random copolymer, liquid butadiene-isoprene block copolymer, liquid styrene-butadiene-isoprene random copolymer, and liquid styrene-butadiene-isoprene block copolymer. These can be used individually or in combination of two or more. Among them, liquid polyisoprene is preferred from the viewpoint of the effects mentioned above.

[0073] Examples of the above unsaturated carboxylic acids include maleic acid, fumaric acid, itaconic acid, and (meth)acrylic acid. Examples of the above unsaturated carboxylic acid derivatives include unsaturated carboxylic acid anhydrides such as maleic anhydride and itaconic anhydride; unsaturated carboxylic acid esters such as maleic acid esters, fumaric acid esters, itaconic acid esters, glycidyl (meth)acrylate and hydroxyethyl (meth)acrylate; unsaturated carboxylic acid amides such as maleic acid amide, fumaric acid amide and itaconic acid amide; and unsaturated carboxylic acid imides such as maleic acid imide and itaconic acid imide. The unsaturated carboxylic acid or unsaturated carboxylic acid derivative may be modified with one type, or with two or more types.

[0074] Modified liquid polymers can be produced by modifying an unmodified liquid polymer, which is used as a raw material, with an unsaturated carboxylic acid and / or its derivatives. The modification method is not particularly limited and can be produced by known methods, such as adding an unsaturated carboxylic acid and / or its derivatives to the unmodified liquid polymer, which is used as a raw material. Modified liquid polymers may be produced using only one type or by mixing two or more types.

[0075] Among these, from the viewpoint of economics, tensile properties, and the aforementioned effects such as low fuel consumption, maleic anhydride-modified liquid polymers are preferred, maleic anhydride-modified liquid diene polymers are more preferred, and maleic anhydride-modified liquid polyisoprene is even more preferred.

[0076] The modifier that can covalently bond with microfibrillated plant fibers preferably has a reaction site with diene rubber. When a modifier with a reaction site with diene rubber is used, for example, during the vulcanization stage, the modifier bonds with the diene rubber via a vulcanizing agent (such as sulfur), improving strength. Consequently, the dispersibility of the microfibrillated plant fibers is improved, and the tensile properties (tensile strength, elongation at break) and fuel efficiency are significantly improved.

[0077] The reaction site with the diene rubber (diene polymer) is a site (part) that can react with the diene rubber, and may also be a site (part) that reacts with the diene rubber via a vulcanizing agent (such as sulfur) if necessary. Examples of reaction sites for the diene rubber include the double bond site of the conjugated diene. In this case, there are cases where the double bond of the modifier reacts with the diene rubber, and cases where the double bond of the modifier reacts with the diene rubber via sulfur.

[0078] For example, products from companies such as Kuraray Co., Ltd. and Clay Valley Corporation can be used as the liquid polymer mentioned above.

[0079] The rubber composition preferably contains carbon black. A reinforcing effect can be obtained by incorporating carbon black.

[0080] The carbon black is not particularly limited, and examples thereof include GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more.

[0081] In the rubber composition, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 20 m 2 / g or more, more preferably 25 m 2 / g or more. Also, the N2SA is preferably 200 m 2 / g or less, more preferably 150 m 2 / g or less, and even more preferably 120 m 2 / g or less. By setting it above the lower limit, a sufficient reinforcing effect tends to be obtained. By setting it below the upper limit, excellent low fuel consumption property tends to be obtained. In this specification, the nitrogen adsorption specific surface area of the carbon black is determined by the method A of JIS K6217.

[0082] In the rubber composition, from the viewpoint of the above-described effects, the content of the carbon black is preferably 1 to 200 parts by mass, more preferably 3 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

[0083] When the rubber composition is applied to the sidewall, the content of the carbon black is preferably 5 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 50 parts by mass or less. Within the above range, good low fuel consumption property and flex crack growth resistance tend to be obtained.

[0084] When the rubber composition is applied to the sidewall, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 20 m 2 / g or more, more preferably 30 m 2 / g or more. Also, the N2SA is preferably 200 m 2 / g or less, more preferably 150 m 2It is less than / g. Raising it above the lower limit tends to provide sufficient reinforcement. Lowering it below the upper limit tends to provide excellent fuel efficiency.

[0085] When the rubber composition is applied to the tread of a passenger car tire, the carbon black content is preferably 1 part by mass or more, more preferably 2 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less. When the content is within the above range, good fuel efficiency tends to be obtained.

[0086] When the rubber composition is applied to the tread of a passenger car tire, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 50 m². 2 / g or more, more preferably 80m 2 / g or more, more preferably 100m 2 The amount is 1 / g or more. Furthermore, the N2SA is preferably 200m 2 Less than / g, more preferably 150m 2 It is less than / g. Raising it above the lower limit tends to provide sufficient reinforcement. Lowering it below the upper limit tends to provide excellent fuel efficiency.

[0087] When the rubber composition is applied to the tread of a heavy-duty tire, the carbon black content is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less. When the content is within the above range, good fuel efficiency tends to be obtained.

[0088] When the rubber composition is applied to the tread of a heavy-duty tire, the nitrogen adsorption specific surface area (N2SA) of the carbon black is preferably 50 m². 2 / g or more, more preferably 80m 2 / g or more, more preferably 100m 2 The amount is 1 / g or more. Furthermore, the N2SA is preferably 200m2 Less than / g, more preferably 150m 2 It is less than / g. Raising it above the lower limit tends to provide sufficient reinforcement. Lowering it below the upper limit tends to provide excellent fuel efficiency.

[0089] The aforementioned rubber composition may contain silica. By incorporating silica, good wet grip performance, wear resistance, and other properties can be obtained.

[0090] The silica used is not particularly limited; for example, dry-process silica (anhydrous silicic acid) and wet-process silica (hydrated silicic acid) can be used. However, wet-process silica is preferred because it contains a large number of silanol groups.

[0091] In the aforementioned rubber composition, the specific surface area (N2SA) of silica for nitrogen adsorption is 40 m². 2 Preferably 50m / g or more. 2 A value of 300m / g or higher is more preferable. A value above the lower limit tends to yield good fracture strength. Also, the N2SA of silica is 300m 2 Preferably less than / g, 250m 2 A value of less than / g is preferable. Keeping it below the upper limit tends to result in good low heat generation and rubber processability. In this specification, the specific surface area for nitrogen adsorption of silica is the value measured by the BET method in accordance with ASTM D3037-93.

[0092] If the rubber composition contains silica, its content is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the content is preferably 150 parts by mass or less, more preferably 100 parts by mass or less. Within this range, good fuel efficiency tends to be obtained.

[0093] When the rubber composition is applied to the tread of a passenger car tire, the silica content is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the silica content is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less. Within the above range, good fuel efficiency and other properties tend to be obtained.

[0094] When the aforementioned rubber composition is applied to the tread of a passenger car tire, the specific surface area (N2SA) of silica for nitrogen adsorption is 100m². 2 Preferably 150m / g or more 2 A value of 300m / g or higher is more preferable. A value above the lower limit tends to yield good fracture strength. Also, the N2SA of silica is 300m 2 Preferably less than / g, 250m 2 A value of less than / g is preferable. Keeping it below the upper limit tends to result in good low heat generation and rubber processability.

[0095] If the rubber composition contains silica, it is preferable that it further contains a silane coupling agent. The silane coupling agent is not particularly limited and includes, for example, 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, and 3-trimethoxysilylpropyl-N,N-dimethylthiocal Examples include sulfide-based compounds such as bamoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide and 3-triethoxysilylpropyl methacrylate monosulfide; mercapto-based compounds such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and Momentive's NXT and NXT-Z; vinyl-based compounds such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-based compounds such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-based compounds such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based compounds such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Commercially available products from companies such as Degussa, Momentive, Shin-Etsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., and Toray Dow Corning Co., Ltd. can be used. These can be used individually or in combination of two or more types.

[0096] The silane coupling agent content is preferably 3 parts by mass or more, and more preferably 6 parts by mass or more, per 100 parts by mass of silica. A content of 3 parts by mass or more tends to yield good fracture strength and other properties. Furthermore, the above content is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less. A content of 20 parts by mass or less tends to yield effects commensurate with the amount added.

[0097] The above rubber composition may contain other fillers besides silica and carbon black. Examples of other fillers, though not particularly limited, include calcium carbonate, talc, alumina, clay, aluminum hydroxide, aluminum oxide, and mica.

[0098] The above rubber composition may contain oil. One type of oil may be used, or two or more types may be used in combination.

[0099] The oil used is not particularly limited, and conventionally known oils can be used, such as paraffinic process oils, aromatic process oils, naphthenic process oils, low PCA (polycyclic aromatic) process oils such as TDAE and MES, vegetable oils, and mixtures thereof. Among these, aromatic process oils are preferred in terms of wear resistance and fracture characteristics. Specific examples of aromatic process oils include the Diana Process Oil AH series manufactured by Idemitsu Kosan Co., Ltd.

[0100] If oil is included, its content is preferably 3 parts by mass or more, and more preferably 6 parts by mass or more, per 100 parts by mass of rubber component. Furthermore, the above content is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less.

[0101] The rubber composition may also contain a solid resin (a polymer that is solid at room temperature (25°C)).

[0102] If a solid resin is included, its content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the rubber component. Furthermore, the above content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less.

[0103] The solid resin is not particularly limited, but examples include solid styrene resins, coumarone indene resins, terpene resins, pt-butylphenol acetylene resins, acrylic resins, dicyclopentadiene resins (DCPD resins), C5 petroleum resins, C9 petroleum resins, and C5C9 petroleum resins. These may be used individually or in combination of two or more.

[0104] Solid styrene resins are solid polymers that use styrene monomers as constituent monomers, and include polymers polymerized with styrene monomers as the main component (50% by mass or more). Specifically, examples include homopolymers obtained by polymerizing styrene monomers (styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.) individually, copolymers obtained by copolymerizing two or more styrene monomers, and copolymers of styrene monomers and other monomers that can copolymerize with them.

[0105] Examples of other monomers mentioned above include acrylonitriles such as acrylonitrile and methacrylonitrile, unsaturated carboxylic acids such as acrylics and methacrylic acid, unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate, dienes such as chloroprene and butadiene isoprene, olefins such as 1-butene and 1-pentene; α,β-unsaturated carboxylic acids such as maleic anhydride or their acid anhydrides; and so on.

[0106] Among these, solid α-methylstyrene resins (α-methylstyrene homopolymers, copolymers of α-methylstyrene and styrene, etc.) are preferred.

[0107] Examples of solid coumarone indene resins include solid resins having the same constituent units as the liquid coumarone indene resin described above.

[0108] Examples of solid terpene resins include polyterpenes, terpene phenols, and aromatically modified terpene resins. Polyterpenes are resins obtained by polymerizing terpene compounds and their hydrogenated products. Terpene compounds are (C5H8) n A hydrocarbon and its oxygen-containing derivative represented by the following composition, monoterpene (C 10 H 16 ), sesquiterpenes (C 15 H 24 ), diterpene (C 20 H 32 These are compounds with a terpene as their basic skeleton, classified as such, and examples include α-pinene, β-pinene, dipentene, limonene, myrcene, allocimene, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineol, β-terpineol, and γ-terpineol.

[0109] Examples of solid polyterpenes include terpene resins such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene / limonene resin, which are made from the terpene compounds mentioned above, as well as solid resins such as hydrogenated terpene resins, which are obtained by hydrogenating the terpene resins.

[0110] Examples of solid terpene phenols include solid resins obtained by copolymerizing the above-mentioned terpene compound with a phenolic compound, and solid resins obtained by hydrogenating the resin. Specifically, examples include solid resins obtained by condensing the above-mentioned terpene compound, a phenolic compound, and formalin. Examples of phenolic compounds include phenol, bisphenol A, cresol, and xylenol.

[0111] Examples of solid aromatically modified terpene resins include solid resins obtained by modifying terpene resins with aromatic compounds, and solid resins obtained by hydrogenating the resins. The aromatic compounds are not particularly limited as long as they are compounds having an aromatic ring, but examples include phenol compounds such as phenol, alkylphenol, alkoxyphenol, and phenol containing an unsaturated hydrocarbon group; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and naphthol containing an unsaturated hydrocarbon group; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, and styrene containing an unsaturated hydrocarbon group; coumarone, indene, and the like.

[0112] Examples of solid pt-butylphenol acetylene resins include solid resins obtained by a condensation reaction between pt-butylphenol and acetylene.

[0113] While there are no particular limitations on the solid acrylic resin, solvent-free acrylic solid resins are preferably used because they have fewer impurities and a sharper molecular weight distribution.

[0114] Examples of solid, solvent-free acrylic resins include (meth)acrylic resins (polymers) synthesized by high-temperature continuous polymerization (high-temperature continuous bulk polymerization) (as described in U.S. Patent No. 4,414,370, Japanese Patent Publication No. 59-6207, Japanese Patent Publication No. 5-58005, Japanese Patent Publication No. 1-313522, U.S. Patent No. 5,010,166, and the Toa Gosei Research Annual Report TREND2000 No. 3, pp. 42-45, etc.) with minimal use of polymerization initiators, chain transfer agents, organic solvents, and other auxiliary raw materials. In this specification, (meth)acrylic means methacrylic and acrylic.

[0115] The solid acrylic resin preferably does not contain substantially any secondary raw materials such as polymerization initiators, chain transfer agents, or organic solvents. Furthermore, the acrylic resin obtained by continuous polymerization preferably has a relatively narrow compositional distribution and molecular weight distribution.

[0116] As described above, the solid acrylic resin is preferably one that does not contain polymerization initiators, chain transfer agents, organic solvents, etc., which are substantially auxiliary raw materials, i.e., one with high purity. The purity of the solid acrylic resin (the proportion of resin contained in the resin) is preferably 95% by mass or more, more preferably 97% by mass or more.

[0117] Examples of monomer components that constitute solid acrylic resins include (meth)acrylic acid, (meth)acrylic acid esters (alkyl esters, aryl esters, aralkyl esters, etc.), (meth)acrylamide, and (meth)acrylic acid derivatives such as (meth)acrylamide derivatives.

[0118] Furthermore, as monomer components constituting the solid acrylic resin, aromatic vinyls such as styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, and divinylnaphthalene may be used along with (meth)acrylic acid and (meth)acrylic acid derivatives.

[0119] The solid acrylic resin may be a resin composed solely of (meth)acrylic components, or a resin that also contains components other than (meth)acrylic components. Furthermore, the solid acrylic resin may have hydroxyl groups, carboxyl groups, silanol groups, etc.

[0120] Examples of solid resins that can be used include products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Arizona Chemical Company, Nippon Paint Chemical Co., Ltd., Nippon Shokubai Co., Ltd., JX Energy Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Industries, Ltd.

[0121] The above rubber composition preferably contains an anti-aging agent from the viewpoint of crack resistance, ozone resistance, etc.

[0122] While not particularly limited, the following are examples of anti-aging agents: naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4′-bis(α,α′-dimethylbenzyl)diphenylamine; N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, and N,N′-di-2-naphthyl-p-phenylenediamine. Examples of anti-aging agents include p-phenylenediamine-based anti-aging agents such as amines; quinoline-based anti-aging agents such as polymers of 2,2,4-trimethyl-1,2-dihydroquinoline; monophenol-based anti-aging agents such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; and bis, tris, and polyphenol-based anti-aging agents such as tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane. Among these, p-phenylenediamine-based anti-aging agents and quinoline-based anti-aging agents are preferred, and polymers of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine and 2,2,4-trimethyl-1,2-dihydroquinoline are more preferred. Commercial products such as those from Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Co., Ltd., and Flexis Co., Ltd. can be used.

[0123] The content of the anti-aging agent is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the rubber component. A content above the lower limit tends to provide sufficient ozone resistance. The content is preferably 7.0 parts by mass or less, more preferably 4.0 parts by mass or less. A content below the upper limit tends to provide a good appearance.

[0124] The above rubber composition preferably contains stearic acid. The stearic acid content is preferably 0.5 to 10 parts by mass or more, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0125] In addition, conventionally known stearic acid can be used, such as products from NOF Corporation, NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Corporation, Chiba Fatty Acid Co., Ltd.

[0126] The above rubber composition preferably contains zinc oxide. The zinc oxide content is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0127] In addition, conventionally known zinc oxides can be used, such as products from Mitsui Mining & Smelting Co., Ltd., Toho Zinc Co., Ltd., Hakusui Tech Co., Ltd., Seido Chemical Industry Co., Ltd., and Sakai Chemical Industry Co., Ltd.

[0128] The above rubber composition may contain wax. From the viewpoint of performance balance, the wax content is preferably 0.5 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the rubber component.

[0129] The type of wax used is not particularly limited and includes petroleum-based waxes, natural waxes, and synthetic waxes obtained by refining or chemically processing multiple waxes. These waxes may be used individually or in combination of two or more types.

[0130] Examples of petroleum-based waxes include paraffin wax and microcrystalline wax. Examples of natural waxes are not limited to those derived from non-petroleum resources, and include plant-based waxes such as candelilla wax, carnauba wax, wood wax, rice wax, and jojoba wax; animal-based waxes such as beeswax, lanolin, and whale wax; mineral waxes such as ozokerite, ceresin, and petrolactam; and refined products thereof. Commercially available products include those from companies such as Ouchi Shinko Chemical Industry Co., Ltd., Nippon Seiro Co., Ltd., and Seiko Chemical Co., Ltd. The wax content should be set appropriately in terms of ozone resistance and cost.

[0131] The above rubber composition preferably contains sulfur, as it forms appropriate cross-linked chains in the polymer chains and imparts good performance.

[0132] The sulfur content is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.7 parts by mass or more, per 100 parts by mass of the rubber component. The content is preferably 6.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less.

[0133] Examples of sulfur commonly used in the rubber industry include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and soluble sulfur. Commercially available products include those from Tsurumi Chemical Industries, Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Co., Ltd., Flexis Co., Ltd., Nippon Dry Distillation Co., Ltd., and Hosoi Chemical Industry Co., Ltd. These can be used individually or in combination of two or more types.

[0134] The above rubber composition preferably contains a vulcanization accelerator. There are no particular restrictions on the amount of vulcanization accelerator; it can be freely determined according to the desired vulcanization rate and crosslinking density. However, it is usually 0.3 to 10 parts by mass, preferably 0.5 to 7 parts by mass, per 100 parts by mass of rubber component.

[0135] There are no particular restrictions on the type of vulcanization accelerator; commonly used ones can be used. Examples of vulcanization accelerators include thiazole-based vulcanization accelerators such as 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and N-cyclohexyl-2-benzothiadylsulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD), and tetrakis(2-ethylhexyl)thiuram disulfide (TOT-N); sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, Nt-butyl-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, and N,N'-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, diortotrilguanidine, and orthotrilbiguanidine. These may be used individually or in combination of two or more. Among them, sulfenamide-based vulcanization accelerators and guanidine-based vulcanization accelerators are preferred from the viewpoint of the aforementioned performance balance.

[0136] In addition to the above components, the above rubber composition may also contain, as appropriate, conventional additives used in the application field, such as mold release agents and pigments.

[0137] As a method for producing the above rubber composition, known methods can be used. For example, it can be produced by kneading each of the above components using a rubber kneading device such as an open roll or Banbury mixer, and then vulcanizing it. For example, it can be produced by a manufacturing method that includes the steps of kneading a rubber component, microfibrillated plant fibers, and a modifier that can covalently bond with the microfibrillated plant fibers to produce a kneaded product in which covalent bonds are formed between the microfibrillated plant fibers and the modifier, and then vulcanizing it.

[0138] In particular, from the viewpoint of the aforementioned properties such as the dispersibility, tensile properties, and low fuel consumption of microfibrillated plant fibers, it is preferable to prepare a mixture (masterbatch) of rubber components and microfibrillated plant fibers in advance before mixing the microfibrillated plant fibers and modifiers that can covalently bond with them. Specifically, it is preferable to first prepare a microfibrillated plant fiber / rubber composite (masterbatch) by a manufacturing method that includes a step of mixing an anionic surfactant with a dispersion of microfibrillated plant fibers to prepare a mixture (step (1)), and a step of mixing the mixture with rubber components (step (2)). Furthermore, it is preferable to produce a rubber composition (vulcanized) by kneading the obtained masterbatch and components such as the modifier to prepare a kneaded product in which covalent bonds are formed between the microfibrillated plant fibers and the modifier (step (3)), and a step of vulcanizing the unvulcanized rubber composition (step (4)). Furthermore, the manufacturing method may include other steps as long as it includes the above steps, and each of the above steps may be performed once or repeatedly.

[0139] (Process (1)) First, a step (1) is performed in which an anionic surfactant and a microfibrillated plant fiber dispersion are mixed to prepare a mixture.

[0140] The above-mentioned anionic surfactant has both hydrophobic and hydrophilic groups. It is presumed that by using such a surfactant, the hydrophobic group and the hydrophobic group of the rubber form a hydrophobic bond and exhibit affinity, and the hydrophilic group and the hydroxyl group of the microfibrillated plant fiber adsorb via hydrogen bonding and exhibit affinity, thereby increasing the dispersibility of the microfibrillated plant fiber, suppressing aggregation of the microfibrillated plant fiber in the rubber, and preventing the formation of aggregates. One type of anionic surfactant may be used, or two or more types may be used in combination.

[0141] The above hydrophobic group may be any hydrophobic functional group, but a hydrocarbon group is preferred. The hydrocarbon group may be linear, branched, or cyclic, and examples include aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups. Among these, aliphatic hydrocarbon groups and aromatic hydrocarbon groups are preferred. The number of carbon atoms in the above hydrocarbon group is preferably 4 to 20, more preferably 4 to 15, and even more preferably 4 to 12.

[0142] The above aliphatic hydrocarbon groups are preferably those having 1 to 20 carbon atoms, more preferably those having 1 to 10 carbon atoms, and even more preferably those having 1 to 6 carbon atoms. Preferred examples include alkyl groups with the above number of carbon atoms, specifically, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, octadecyl group, etc. In addition, alkenyl groups and alkynyl groups with the above number of carbon atoms are also acceptable, for example, alkenyl groups such as vinyl group, allyl group, 1-propenyl group, 1-methylethenyl group, and isobutylene group, and alkynyl groups such as ethynyl group and propagyl group. Among these, isobutylene group is preferred.

[0143] The above-mentioned alicyclic hydrocarbon groups are preferably those having 3 to 8 carbon atoms, and specifically include cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclopropenyl group, cyclobutenyl group, cyclopentenyl group, cyclohexenyl group, cycloheptenyl group, and cyclooctenyl group.

[0144] The above aromatic hydrocarbon groups are preferably those having 6 to 12 carbon atoms, and specifically include phenyl, benzyl, phenethyl, tolyl, xylyl, and naphthyl groups. Among these, phenyl, benzyl, and phenethyl groups are preferred, phenyl and benzyl groups are more preferred, and phenyl groups are particularly preferred. The substitution position of the methyl group on the benzene ring in tolyl and xyl groups may be at the ortho, meta, or para position.

[0145] The hydrophilic group is preferably at least one selected from the group consisting of a carboxyl group, a sulfonic acid group, a sulfate group, and a phosphate group. Among these, a carboxyl group is particularly preferred.

[0146] Among the above anionic surfactants, anionic surfactants having a phenyl group or isobutylene group as a hydrophobic group and a carboxyl group as a hydrophilic group are particularly preferred.

[0147] As for the anionic surfactants mentioned above, those having the functional groups described above are preferred, but specifically, they can be classified into surfactants such as carboxylic acid-based, sulfonic acid-based, sulfate ester-based, and phosphate ester-based surfactants.

[0148] Examples of the carboxylic acid-based surfactants mentioned above include fatty acid salts, polycarboxylic acid salts, rosinates, dimerates, polymerates, tall oil fatty acid salts, and polycarboxylic acid-type polymer surfactants having 6 to 30 carbon atoms. Preferably, the surfactants are carboxylic acid salts, polycarboxylic acid salts, and polycarboxylic acid-type polymer surfactants having 10 to 20 carbon atoms, and particularly preferably, polycarboxylic acid-type polymer surfactants. Examples of the above-mentioned sulfonic acid-based surfactants include alkylbenzene sulfonates, alkyl sulfonates, alkylnaphthalene sulfonates, naphthalene sulfonates, and diphenyl ethersulfonates. Examples of the above-mentioned sulfate ester surfactants include alkyl sulfate salts, polyoxyalkylene alkyl sulfate salts, polyoxyalkylene alkylphenyl ether sulfate salts, tristyrenelated phenol sulfate salts, distyrenelated phenol sulfate salts, α-olefin sulfate salts, alkyl succinate sulfate salts, polyoxyalkylene tristyrenelated phenol sulfate salts, and polyoxyalkylene distyrenelated phenol sulfate salts. Examples of the phosphate ester surfactants mentioned above include alkyl phosphate salts and polyoxyalkylene phosphate salts. Examples of salts of these compounds include metal salts (Na, K, Ca, Mg, Zn, etc.), ammonium salts, and amine salts (triethanolamine salt, etc.).

[0149] The alkyl group in the above-mentioned surfactant may be an alkyl group having 4 to 30 carbon atoms. The polyoxyalkylene group may be one having an alkylene group with 2 to 4 carbon atoms, and for example, one in which the number of moles of ethylene oxide added is about 1 to 50 moles can be used.

[0150] The above anionic surfactant preferably has a weight-average molecular weight (Mw) of 500 or more, more preferably 1000 or more. Furthermore, it is preferably 50000 or less, and more preferably 30000 or less.

[0151] Examples of anionic surfactants that can be used include products from companies such as Elementis, Kao Corporation, Daiichi Kogyo Seiyaku Co., Ltd., and Sanyo Chemical Industries, Ltd.

[0152] The above-mentioned microfibrillated plant fiber dispersion is a dispersion (slurry) in which microfibrillated plant fibers are dispersed in a solvent, and the solvent is not particularly limited, but can be water or the like.

[0153] The above-mentioned microfibrillated plant fiber dispersion can be produced by known methods, and the production method is not particularly limited. For example, it can be prepared by dispersing the microfibrillated plant fibers in a solvent such as water using a high-speed homogenizer, ultrasonic homogenizer, colloid mill, blender mill, etc. The temperature and time during preparation can also be set appropriately within the range of normal practice so that the microfibrillated plant fibers are sufficiently dispersed in the solvent such as water.

[0154] The content of microfibrillated plant fibers (solid content) in the above-mentioned microfibrillated plant fiber dispersion is not particularly limited, but is preferably 0.2 to 20% by mass, more preferably 0.5 to 10% by mass, and even more preferably 0.5 to 3% by mass.

[0155] In step (1) above, a method for preparing a mixture by mixing an anionic surfactant with a microfibrillated plant fiber dispersion includes, for example, a method of mixing the anionic surfactant with a microfibrillated plant fiber dispersion using a known stirring device such as a high-speed homogenizer, ultrasonic homogenizer, colloid mill, or blender mill, and by stirring thoroughly until the mixture is sufficiently dispersed, a mixture of the anionic surfactant and the microfibrillated plant fiber dispersion can be obtained. The temperature and time for preparing the mixture can be appropriately set within the range that is normally used until the anionic surfactant and the microfibrillated plant fiber dispersion are sufficiently dispersed, but for example, 10 to 40°C for 3 to 120 minutes is preferred, and 15 to 30°C for 5 to 90 minutes is more preferred.

[0156] In step (1) above, the amount of anionic surfactant added is preferably 8 to 50 parts by mass per 100 parts by mass of microfibrillated plant fiber (solid content) contained in the microfibrillated plant fiber dispersion. The amount added is more preferably 9 parts by mass or more, and even more preferably 10 parts by mass or more. Furthermore, it is more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less.

[0157] (Process (2)) Next, a step (2) is performed in which the mixture obtained in step (1) is mixed with the rubber component. As a source of the rubber component, the aforementioned rubber latex can be suitably used from the viewpoint of the dispersibility of microfibrillated plant fibers, etc.

[0158] In step (2) above, methods for mixing the mixture obtained in step (1) with the rubber component (rubber latex, etc.) include, for example, placing the rubber in a known stirring device such as a high-speed homogenizer, ultrasonic homogenizer, colloid mill, or blender mill and dropping the mixture obtained in step (1) while stirring, or dropping the rubber component into the mixture obtained in step (1) while stirring. By stirring thoroughly until the mixture is sufficiently dispersed, a mixture of the mixture obtained in step (1) and the rubber component (formulated latex, etc.) can be obtained. The temperature and time for preparing the mixture can be set appropriately within the range of normal practice until the mixture obtained in step (1) and the rubber component are sufficiently dispersed, but for example, 10 to 40°C for 3 to 120 minutes is preferred, and 15 to 30°C for 5 to 90 minutes is more preferred.

[0159] The pH of the mixture (formulated latex, etc.) obtained in step (2) above is preferably 9.0 or higher, more preferably 9.5 or higher. It is also preferably 12 or lower, and more preferably 11.5 or lower. When the pH of the mixture (formulated latex, etc.) of the mixed liquid obtained in step (1) above and the rubber component is within this range, deterioration is suppressed and the product can be made stable.

[0160] In step (2) above, it is preferable to mix the mixture obtained in step (1) such that the amount of microfibrillated plant fibers (solids) is 2 to 45 parts by mass per 100 parts by mass of rubber solids. The above range tends to favorably obtain the aforementioned effects. The content of the microfibrillated plant fibers (solids) is more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more. It is also more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less.

[0161] The mixture (such as blended latex) obtained in step (2) above is coagulated as needed, and the coagulated product (agglomerated rubber and agglomerated product containing microfibrillated plant fibers) is filtered and dried by a known method. After further drying, the rubber is kneaded using a twin-screw roller, Banbury machine, etc., to obtain a composite (microfibrillated plant fiber-rubber composite) in which the microfibrillated plant fibers are sufficiently dispersed in the rubber matrix. The microfibrillated plant fiber-rubber composite may contain other components.

[0162] The above solidification is usually carried out by adding an acid to the mixture (formulated latex, etc.) obtained in step (2) above. Examples of acids used for solidification include sulfuric acid, hydrochloric acid, formic acid, and acetic acid. The preferred temperature for solidification is 10 to 40°C.

[0163] During the above coagulation, it is preferable to adjust the pH of the mixture (compounded latex, etc.) obtained in step (2) above to 3 to 5, and more preferably to 3 to 4.

[0164] Furthermore, a flocculant may be added to control the state of coagulation (the size of the coagulated aggregated particles). Cationic polymers can be used as flocculants.

[0165] The microfibrillated plant fiber / rubber composite obtained by steps (1) and (2) can be used as a masterbatch. The above microfibrillated plant fiber / rubber composite has sufficient dispersion of microfibrillated plant fibers in the rubber, and the microfibrillated plant fibers can be sufficiently dispersed even in rubber compositions mixed with other components. Therefore, it has excellent dispersibility of microfibrillated plant fibers, good tensile properties (tensile strength, elongation at break), and low fuel consumption.

[0166] (Step (3)) The microfibrillated plant fiber / rubber composite (masterbatch) obtained in step (2), the modifier, and other rubber components other than rubber in the composite, carbon black, silica, etc., which are added as needed, are kneaded by a known method. Through kneading, a kneaded product is produced in which covalent bonds are formed between the microfibrillated plant fibers in the microfibrillated plant fiber / rubber composite and the modifier.

[0167] As for the mixing conditions, in the step of mixing additives other than the vulcanizing agent and vulcanization accelerator (base mixing step), the mixing temperature is usually 50 to 200°C, preferably 80 to 190°C, and the mixing time is usually 30 seconds to 30 minutes, preferably 1 minute to 30 minutes.

[0168] (Step (4)) In step (3), the mixture obtained, the vulcanizing agent, and the vulcanization accelerator are mixed to produce an unvulcanized rubber composition. Then, the vulcanization process in step (4) is carried out to produce the rubber composition (after vulcanization). In the process of mixing the vulcanizing agent and vulcanization accelerator (finishing mix), the mixing temperature is usually 100°C or lower, preferably room temperature to 80°C. Furthermore, when the composition mixed with the vulcanizing agent and vulcanization accelerator is subjected to a vulcanization treatment such as press vulcanization (the vulcanization process in step (4)), the vulcanization temperature is usually 120 to 200°C, preferably 140 to 180°C.

[0169] The rubber composition can be suitably applied to various components of pneumatic tires, including the sidewall, base tread, bead apex, clinch apex, inner liner, under tread, breaker topping, ply topping, and tread. It can be suitably used in pneumatic tires such as passenger car tires, truck and bus tires, and other heavy-duty tires.

[0170] The above rubber composition is suitably used for tires. The above tire is manufactured using the above rubber composition by a conventional method. That is, a rubber composition, which may contain various materials as needed, is extruded to match the shape of a tire component at the unvulcanized stage, and then molded together with other tire components on a tire molding machine in a conventional method to form an unvulcanized tire. After that, the tire (pneumatic tire, studless tire, run-flat tire, etc.) can be manufactured by heating and pressurizing it in a vulcanizing machine. [Examples]

[0171] The present invention will be specifically described based on the examples provided, but the present invention is not limited to these examples.

[0172] (Preparation of SBR latex) According to the composition shown in Table 1, water, emulsifier (1), emulsifier (2), electrolyte, styrene, butadiene, and molecular weight modifier were charged into a pressure reactor equipped with a stirrer. The reactor temperature was set to 5°C, and polymerization was started by adding aqueous solutions containing the radical initiator and SFS, and aqueous solutions containing EDTA and catalyst to the reactor. Five hours after the start of polymerization, the reaction was stopped by adding a polymerization arrestor to obtain SBR latex.

[0173] The chemicals used are listed below. Water: Distilled water Emulsifier (1): Rosinate soap manufactured by Harima Chemicals Co., Ltd. Emulsifier (2): Fatty acid soap manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Electrolyte: Sodium phosphate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Styrene: Styrene manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Butadiene: 1,3-butadiene manufactured by Takachiho Chemical Industry Co., Ltd. Molecular weight modifier: tert-dodecyl mercaptan manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Radical initiator: Paramentane hydroperoxide manufactured by NOF Corporation SFS: Sodium formaldehyde sulfoxylate manufactured by Fujifilm Wako Pure Chemical Corporation. EDTA: Sodium ethylenediaminetetraacetate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Catalyst: Ferric sulfate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Polymerization inhibitor: N,N'-dimethyldithiocarbamate manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0174] [Table 1]

[0175] The following describes the various chemicals used in the preparation of the microfibrillated plant fiber dispersion and the microfibrillated plant fiber-rubber composite. Natural rubber latex: We use field latex obtained from Muhibbah Latex. SBR latex: Prepared as described above. Microfibrillated plant fibers: Biomass nanofiber manufactured by Sugino Machine Co., Ltd. (product name "BiNFi-s Cellulose", average fiber length: approx. 2 μm, average fiber diameter: approx. 0.02 μm, solid content: 2% by mass) Surfactant: NUOSPERSE FX 600 manufactured by Elementis (anionic surfactant, polycarboxylate amine salt (containing a phenyl group as a hydrophobic group and a carboxyl group as a hydrophilic group), Mw: 2000)

[0176] (Preparation of microfibrillated plant fiber dispersion) 50 g of microfibrillated plant fiber (2% by weight) was mixed with 150 g of pure water to prepare a suspension of microfibrillated plant fiber with a solid content of 0.5% by mass. This suspension was then stirred and subjected to ultrasonic treatment for 10 minutes to obtain a dispersion of microfibrillated plant fiber.

[0177] (Preparation of microfibrillated plant fiber-rubber composite) A predetermined amount of surfactant was added to the prepared microfibrillated plant fiber dispersion according to the formulation in Table 2, and the mixture was stirred for 5 minutes at room temperature (20-30°C) using a high-speed homogenizer to obtain a mixture of the microfibrillated plant fiber dispersion and surfactant (mixture). The obtained mixture was added to a predetermined amount of rubber latex according to the formulation in Table 2, and the mixture was stirred for 5 minutes at room temperature using a high-speed homogenizer to obtain a latex formulation with a pH of 10.2. Next, a 2% by mass aqueous solution of formic acid was added at room temperature to adjust the pH to 3-4, and a solidified product was obtained. The obtained solidified product was filtered and dried to obtain microfibrillated plant fiber / rubber composites (MB1, MB2).

[0178] [Table 2]

[0179] The various chemicals used in the examples and comparative examples are described below. Microfibrillated plant fiber / rubber composite (MB1-MB3): Prepared as described above. NR:TSR20 BR: High-cis BR (cis content 97% by mass, Mw 400,000) SBR: SBR1502 manufactured by JSR Co., Ltd. (styrene unit content 23.5% by mass) Carbon Black: Show Black N220 (N2SA111m) manufactured by Cabot Japan Co., Ltd. 2 / g) Silica: Degussa's Ultrasil VN3 (N2SA175m 2 / g) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik DeGussa. Liquid polyisoprene (unmodified): LIR-30 (Mn=28000) manufactured by Kuraray Co., Ltd. Modified liquid polyisoprene: LIR-403 manufactured by Kuraray Co., Ltd. (maleic anhydride modified liquid polyisoprene, Mn=34000) Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Anti-aging agent: Ozonon 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Seiko Chemical Co., Ltd. Stearic acid: Stearic acid "Tsubaki" manufactured by NOF Corporation Zinc oxide: Zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Oil: Process X140 manufactured by Japan Energy Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Co., Ltd. Vulcanization accelerator 1: Noxellar NS (N-tert-butyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noxellar D (diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0180] <Examples and Comparative Examples> According to the formulations shown in Tables 3-5, all chemicals except sulfur and vulcanization accelerator were mixed in a 1.7L Banbury mixer at 130°C for 4 minutes. Next, sulfur and vulcanization accelerator were added to the resulting mixture using a roll and kneaded at 80°C for 4 minutes to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press-vulcanized at 170°C for 12 minutes to obtain a vulcanized product.

[0181] The obtained vulcanized and unvulcanized rubber compositions were evaluated as described below, and the results are shown in Tables 3 to 5. The reference comparative examples in Tables 3, 4, and 5 are Comparative Examples 1-1, 2-1, and 3-1, respectively.

[0182] (Most frequent value of fiber diameter for microfibrillated plant fibers) The obtained vulcanized material was observed using a transmission electron microscope to obtain images, and the mode of fiber diameter was determined from the distribution obtained by measuring the diameter of 100 microfibrillated plant fibers.

[0183] (Average fiber diameter of microfibrillated plant fibers) The obtained vulcanized material was observed using a transmission electron microscope to obtain images, and the average fiber diameter (average fiber diameter) was determined from the distribution obtained by measuring the diameter of 100 microfibrillated plant fibers.

[0184] (processability) For each unvulcanized rubber composition, the Mooney viscosity (ML1+4) was measured at a temperature of 130°C according to the Mooney viscosity measurement method conforming to JIS K 6300-1, "Unvulcanized rubber - Physical properties - Part 1: Method for determining viscosity and scorch time using a Mooney viscometer". The Mooney viscosity of the reference comparative example was set to 100 and expressed as an index (processability index). A higher index indicates lower Mooney viscosity and superior processability.

[0185] (hardness) The hardness of vulcanized rubber and thermoplastic rubber was measured using a Type A durometer in accordance with JIS K6253, "Test Method for Hardness of Vulcanized Rubber and Thermoplastic Rubber." Measurements were performed at 25°C. The results of the reference comparison were expressed as an index, with the result set to 100 (hardness index). A higher index indicates better hardness.

[0186] (Tensile test) No. 3 dumbbell-shaped rubber test specimens were prepared using vulcanized material, and tensile tests were performed in accordance with JIS K6251 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties" to measure the breaking strength (TB) and elongation at break (EB) (%). The TB and EB of the rubber test specimens of the reference comparative example were set to 100, and the TB and EB of each compound were expressed as indices (breaking strength index, elongation at break index). Higher TB and EB indices indicate superior breaking strength.

[0187] (Fuel efficiency) Using a viscoelastic spectrometer (VES, manufactured by Iwamoto Seisakusho Co., Ltd.), the tanδ of each compound (vulcanized material) was measured under conditions of 50°C, initial strain of 10%, dynamic strain of 2%, and frequency of 10Hz. The tanδ of the rubber test piece of the reference comparative example was set to 100, and the results were expressed as an index (fuel efficiency index). A higher index indicates better fuel efficiency.

[0188] (Dispersibility (ΔG*)) The shear modulus G* of the above unvulcanized rubber composition was measured using an RPA2000 manufactured by α Technology Co., Ltd. The measurement temperature was 100°C. Measurements were performed in the strain range of 4% to 64%, and ΔG* = G*(4%) - G*(64%) was calculated. The ΔG* of the rubber test piece of the reference comparative example was set to 100, and the result was expressed as an index (dispersibility index). A larger index indicates that the microfibrillated plant fibers in the rubber composition are well dispersed.

[0189] [Table 3]

[0190] [Table 4]

[0191] [Table 5]

[0192] Tables 3-5 show that the examples containing a rubber component, microfibrillated plant fibers, and a modifier that can covalently bond with the microfibrillated plant fibers exhibited good dispersibility of the microfibrillated plant fibers, as well as excellent tensile strength, elongation at break, and low fuel consumption. On the other hand, the comparative examples without the modifier exhibited inferior tensile strength, elongation at break, and low fuel consumption. The examples also showed good processability and hardness.

Claims

1. A rubber composition for tires comprising a rubber component, microfibrillated plant fibers, and a modifier capable of covalently bonding to the microfibrillated plant fibers.

2. 2. The rubber composition for tires according to claim 1, wherein the content of the microfibrillated plant fibers is 1 to 50 parts by mass and the content of the modifying agent is 1 to 20 parts by mass per 100 parts by mass of the rubber component.

3. 3. The rubber composition for a tire according to claim 1, wherein the modifying agent is a liquid polymer.

4. 4. The rubber composition for a tire according to claim 3, wherein the liquid polymer is a modified liquid polymer modified with an unsaturated carboxylic acid and / or a derivative thereof.

5. 4. The rubber composition for a tire according to claim 1, wherein the modifying agent has a reactive site with a diene rubber.

6. A method for producing a rubber composition for tires, comprising the steps of: kneading a rubber component, microfibrillated plant fibers, and a modifying agent capable of forming a covalent bond with the microfibrillated plant fibers to produce a kneaded product in which a covalent bond is formed between the microfibrillated plant fibers and the modifying agent; and vulcanizing the kneaded product.

7. A tire having a tire component made of the rubber composition according to any one of claims 1 to 5.