Rubber composition and pneumatic tire

Abstract

To provide a rubber composition to be a raw material of a vulcanized rubber excellent in wet performance and low fuel consumption when used as a rubber part of a pneumatic tire.SOLUTION: (In the formula, at least one of R1 to R5 is a - OH group or a - OCH3 group, and the others are - H groups or hydrocarbon groups having 1 to 20 carbon atoms. A is an alkylene group having 1 to 20 carbon atoms which may have unsaturated bonds or -H groups, - CH3 groups, - NH2 groups, - O - groups, or - OH groups, and n is an integer of 0 to 10. B represents a -COOH group, an -OH group, or a = O group, and may be bonded to an adjacent R1 or R5 to form a ring structure. A rubber composition comprising 0.1 to 10 parts by mass of the compound according to [1], and 20 to 150 parts by mass of silica.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a pneumatic tire having a rubber portion made of a vulcanized rubber of the rubber composition. [Background technology]

[0002] In general, tires are used in a variety of driving environments, and there is a demand for improving wet grip performance (hereinafter also simply referred to as "wet performance"), which is the grip performance on wet road surfaces in the rain, for example. However, when rubber compositions are formulated with the aim of improving wet performance, the fuel economy of the resulting vulcanized rubber may deteriorate. Therefore, there has been a demand for a technology that can improve these in a balanced manner.

[0003] Incidentally, Patent Document 1 listed below describes a rubber composition in which a specific compound is blended in a predetermined amount when the total amount of rubber components is taken as 100 parts by mass, with the aim of improving the heat aging resistance of vulcanized rubber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-089553 Summary of the Invention [Problem to be solved by the invention]

[0005] When aiming to achieve both wet performance and fuel economy in pneumatic tires, it is important to optimize the loss tangent (tan δ) of the raw material rubber composition. Generally, wet performance is highly dependent on the tan δ of the raw material rubber composition at 0°C (hereinafter also referred to as "tan δ(0°C)"), and the larger the tan δ(0°C), the better the wet performance of the pneumatic tire. On the other hand, fuel economy is highly dependent on the tan δ of the raw material rubber composition at 60°C (hereinafter also referred to as "tan δ(60°C)"), and the smaller the tan δ(60°C), the better the fuel economy of the pneumatic tire.

[0006] The vulcanized rubber of the rubber composition described in Patent Document 1 has excellent heat aging resistance, but as a result of extensive research by the present inventors, it has been found that there is room for further improvement in terms of wet performance and fuel economy in order to use it as the rubber portion of a pneumatic tire.

[0007] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a rubber composition that can be used as a raw material for vulcanized rubber that has excellent wet performance and fuel efficiency when used as the rubber portion of a pneumatic tire.

[0008] Another object of the present invention is to provide a pneumatic tire that is excellent in wet performance and fuel economy. [Means for solving the problem]

[0009] The above object can be achieved by the present invention as described below. That is, the present invention provides a rubber composition comprising a compound represented by the following general formula (1): [ka] (In the above general formula (1), at least one of R1 to R5 is a -OH group or a -OCH3 group, and the others are a -H group or a hydrocarbon group having 1 to 20 carbon atoms. A is an alkylene group having 1 to 20 carbon atoms which may have an unsaturated bond, a -H group, a -CH3 group, a -NH2 group, a -O- group, or a -OH group, and n is an integer of 0 to 10. B is a -COOH group, a -OH group, or a ═O group, and may be bonded to an adjacent R1 or R5 to form a ring structure.)

[0010] In the rubber composition (1), the compound represented by the general formula (1) is preferably a rubber composition (2) that is a naturally occurring compound.

[0011] In the rubber composition (1) or (2), a rubber composition (3) is preferred in which the compound represented by the general formula (1) is at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid.

[0012] The present invention also relates to a pneumatic tire (4) having a rubber portion made of a vulcanized rubber of any one of the rubber compositions (1) to (3). [Effects of the Invention]

[0013] The rubber composition according to the present invention contains 0.1 to 10 parts by mass of the compound represented by the general formula (1) and 20 to 150 parts by mass of silica per 100 parts by mass of a rubber component containing at least a diene rubber. This dramatically improves the wet performance and fuel economy of the final vulcanized rubber. The following are thought to be the reasons for this effect.

[0014] Because the compound represented by the general formula (1) is highly hydrophilic, it tends to aggregate in the rubber component, thereby increasing the viscosity of the rubber composition. As a result, during rubber kneading, the rubber composition can be maintained in a high shear state while suppressing excessive temperature rise. This allows the reaction between the compound represented by the general formula (1) and the rubber component to proceed at a high level. In addition, the rubber composition according to the present invention contains silica, and the compound represented by the general formula (1) is highly hydrophilic, which contributes to improving the dispersibility of silica in the rubber composition, enhancing the reinforcing effect of silica, while allowing the reaction between the compound represented by the general formula (1) and the rubber component to proceed at a high level. This increases tan δ at 0°C (tan δ(0°C)) while decreasing tan δ(60°C). As a result, it is believed that the wet performance and fuel economy of the vulcanized rubber are further improved.

[0015] When silica is compounded into a rubber composition, the silica tends to aggregate in the rubber component, which can excessively increase the viscosity of the rubber composition and deteriorate processability. However, the rubber composition according to the present invention contains the compound represented by general formula (1) together with silica, and the high hydrophilicity of the compound represented by general formula (1) improves the dispersibility of the silica in the rubber composition. Therefore, the rubber composition according to the present invention also has excellent processability. DETAILED DESCRIPTION OF THE INVENTION

[0016] The rubber composition according to the present invention comprises a compound represented by the following general formula (1): [ka] (In the above general formula (1), at least one of R1 to R5 is an -OH group or an -OCH3 group, and the others are an -H group or a hydrocarbon group having 1 to 20 carbon atoms. A is an alkylene group having 1 to 20 carbon atoms which may have an unsaturated bond or an -H group, -CH3 group, -NH2 group, -O- group or an -OH group, and n is an integer of 0 to 10. B is a -COOH group, -OH group or ═O group and may combine with adjacent R1 or R5 to form a ring structure.) The compounding amount of the compound described in the above general formula (1) is more preferably 0.5 to 5 parts by mass when the total amount of the rubber component is 100 parts by mass.

[0017] From the viewpoint of environmental protection, it is more preferable that the compound represented by the general formula (1) is a naturally occurring compound. Examples of naturally occurring compounds include 3,4-dihydroxycinnamic acid (caffeic acid), 3,4-dimethoxycinnamic acid, curcumin, sesamol, coumaric acid, ferulic acid, sinapic acid, chlorogenic acid, rosmarinic acid, 4-(4-hydroxy-3-methoxyphenyl)-2-butanone, naringin, hesperidin, quercetin, and tocopherol. Among these compounds, in the present invention, it is particularly preferable to use at least one of 3,4-dihydroxycinnamic acid (caffeic acid) and 3,4-dimethoxycinnamic acid from the viewpoint of improving the wet performance and fuel economy of the vulcanized rubber. The reason why the wet performance and fuel economy of the vulcanized rubber are improved when at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid is used is not clear, but the following reasons (1) to (3) are considered.

[0018] (1) When compounded with zinc compounds such as zinc oxide in a rubber composition as a raw material, two or more molecules of 3,4-dihydroxycinnamic acid or 3,4-dimethoxycinnamic acid coordinate to zinc through the hydroxyl or methoxy groups at the R2 and R3 positions in the rubber composition, forming a complex that increases the molecular weight. (2) Two or more molecules of 3,4-dihydroxycinnamic acid or 3,4-dimethoxycinnamic acid form a complex, which increases the tendency of the complex to aggregate in the rubber composition, thereby more effectively increasing the viscosity of the rubber composition. (3) In addition, the rubber composition according to the present invention contains silica, and the compound represented by general formula (1) is highly hydrophilic, which contributes to improving the dispersibility of silica in the rubber composition, enhancing the reinforcing effect of silica, while also promoting a higher level of reaction between the compound represented by general formula (1) and the rubber component. This further increases tan δ at 0°C (tan δ(0°C)) while further decreasing tan δ(60°C). This is believed to result in further improvements in the wet performance and fuel economy of the vulcanized rubber.

[0019] It should be noted that compounds of non-natural origin can also be used as the compound represented by the general formula (1). Examples of non-naturally occurring compounds include 2,3-dimethoxycinnamic acid, 2,4-dimethoxycinnamic acid, 2,5-dimethoxycinnamic acid, 2,3,4-tritoxycinnamic acid, 3,4,5-tritoxycinnamic acid, protocatechuic acid, 3-(3,4-dihydroxyphenyl)-L-alanine, 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane, carvacrol, 3,4-dimethoxyhydrocinnamic acid, 5,6-dimethoxy-1-indanone, and 3,4-dihydroxyhydrocinnamic acid.

[0020] As the rubber component, for example, a diene rubber can be suitably used. The diene rubber is not particularly limited, and examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, and styrene-isoprene-butadiene copolymer rubber. These can be used alone or in combination of two or more. The diene rubber is preferably butadiene rubber, styrene-butadiene rubber, or a blend of two or more thereof.

[0021] The rubber composition according to the present invention contains silica as a filler. The compound represented by the general formula (1) has the effect of improving the dispersibility of silica, which is preferable because it ultimately results in a vulcanized rubber with excellent wet performance and fuel economy. Examples of silica that can be used include wet silica, dry silica, sol-gel silica, and surface-treated silica, which are commonly used for rubber reinforcement. Of these, wet silica is preferable. The amount of silica in the rubber composition is 20 to 150 parts by mass, preferably 20 to 100 parts by mass, more preferably 30 to 100 parts by mass, and even more preferably 40 to 90 parts by mass, per 100 parts by mass of the rubber component.

[0022] When silica is contained as a filler, it is also preferable to contain a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples of the silane include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Degussa), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0023] The rubber composition according to the present invention may contain carbon black as a filler. Examples of carbon black that can be used include carbon blacks commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, as well as conductive carbon blacks such as acetylene black and ketjen black. Among these, the rubber composition according to the present invention preferably contains carbon black having a nitrogen adsorption specific surface area (N2SA) of 140 to 250 m2. 2 When carbon black having a carbon black content of 1 / g is blended, a vulcanized rubber excellent in wet performance and fuel economy can be obtained, which is preferable. The amount of carbon black blended in the rubber composition is not particularly limited, and may be, for example, 20 to 150 parts by mass or 30 to 100 parts by mass in total including silica per 100 parts by mass of the diene rubber.

[0024] The rubber composition according to the present invention may contain, in addition to the rubber component, the compound represented by the general formula (1) and silica, carbon black, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, petroleum resin, a softener such as wax or oil, a processing aid, etc.

[0025] As the vulcanizing agent, sulfur can be suitably used. The sulfur may be any ordinary sulfur for rubber, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. The amount of sulfur in the rubber composition according to the present invention is preferably 0.5 to 5 parts by mass per 100 parts by mass of the rubber component.

[0026] As the vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators and dithiocarbamate-based vulcanization accelerators, may be used alone or in appropriate mixtures.

[0027] The rubber composition according to the present invention may use, as the antioxidant, antioxidants commonly used for rubber, such as aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, and thiourea-based antioxidants, either alone or in appropriate mixtures.

[0028] The rubber composition according to the present invention can be obtained by kneading together the rubber component, the compound represented by the general formula (1), silica, and other ingredients, such as carbon black, a vulcanizing agent, a vulcanization accelerator, an antioxidant, stearic acid, petroleum resin, a softener such as wax or oil, and a processing aid, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0029] The method for compounding the above-mentioned components is not particularly limited, and any of the following may be used: a method in which the compounding components other than the vulcanization-based compounding agents, such as the vulcanizing agent and vulcanization accelerator, are pre-mixed to form a master batch, and the remaining components are then added and further kneaded; a method in which the components are added in any order and kneaded; or a method in which all the components are added simultaneously and kneaded.

[0030] The vulcanized rubber of the rubber composition according to the present invention has excellent wet performance and fuel economy. Therefore, the rubber composition according to the present invention is useful as a raw material for pneumatic tires, and is particularly useful as a raw material for the rubber portion constituting the tread portion of pneumatic tires that require high wet performance and fuel economy. [Example]

[0031] Examples that specifically illustrate the configuration and effects of the present invention will be described below.

[0032] (Preparation of Rubber Composition) Rubber compositions were prepared by compounding the rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 5 according to the compounding recipes in Tables 1 and 2 and kneading them using a conventional Banbury mixer. The compounding ingredients listed in Tables 1 and 2 are shown below (in Tables 1 and 2, the compounding amount of each compounding ingredient is shown in parts by mass per 100 parts by mass of the rubber component). Styrene-butadiene rubber: JSR Corporation, product name "HPR350" (amino and alkoxysilyl group-terminated SBR) Butadiene rubber: Ube Industries, Ltd., "UBEPOL BR150B" Silica: Tosoh Silica Corporation, product name "Nipsil AQ" Silane coupling agent: bis(3-triethoxysilylpropyl)tetrasulfide, Evonik "Si69" Carbon black: Tokai Carbon Co., Ltd., product name "Seast 3", nitrogen adsorption specific surface area (N2SA) 79m 2 / g Zinc oxide: manufactured by Mitsui Mining & Smelting Co., Ltd., product name "Zinc oxide type 1" Stearic acid: Kao Corporation, product name "Lunac S-20" Anti-aging agent: Ouchi Shinko Chemical Industry Co., Ltd., product name "Nocrac 6C" 3,4-Dimethoxycinnamic acid 3,4-Dihydroxycinnamic acid (caffeic acid) Acetamidocinnamic acid (a compound not corresponding to the compound represented by general formula (1)) Sulfur: Powdered sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela CZ"

[0033] The processability of the rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 5 and the vulcanized rubbers thereof were evaluated for tan δ (0° C.) and tan δ (60° C.) by the following method.

[0034] <Processability of rubber composition> In accordance with JIS K6300, unvulcanized rubber was preheated at 100°C for 1 minute and the torque value was measured after 4 minutes using a rotorless Mooney viscometer manufactured by Toyo Seiki Seisakusho Co., Ltd. In Tables 1 and 2, the processability is expressed as an index, with the Mooney viscosity value of Comparative Example 1 set at 100. A smaller index indicates better processability.

[0035] <Vulcanized rubber tan δ (0℃) and tan δ (60℃)> The rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 5 were heated and vulcanized at 160°C for 30 minutes using a predetermined mold to obtain sample rubbers. For each sample, the storage modulus (E') and loss modulus (E") were measured using a dynamic viscoelasticity measuring device (product name: "Fully Automatic Viscoelasticity Analyzer VR-7110," manufactured by Ueshima Seisakusho Co., Ltd.), and tan δ (0°C) and tan δ (60°C) were also measured. In Tables 1 and 2, the values ​​of tan δ (0°C) and tan δ (60°C) for Comparative Example 1 are expressed as an index, with the values ​​being 100. For tan δ (0°C), a larger index indicates better wet grip performance when used in the tread of a pneumatic tire. For tan δ (60°C), a smaller index indicates better fuel economy when used in the tread of a pneumatic tire. The measurement conditions were as follows: Measurement sample size: length 40 mm, width 3 mm, thickness 2 mm Measurement mode: Tensile mode Measurement temperature: 0℃, 60℃ Frequency: 100Hz Dynamic distortion: 0.15%

[0036] [Table 1]

[0037] The results in Table 1 show that the rubber composition of Comparative Example 2 has poorer processability due to an increased silica content. Additionally, the vulcanized rubber of Comparative Example 2 has poorer tan δ (0°C) and tan δ (60°C). On the other hand, the vulcanized rubbers of Examples 1 to 3, when used in the tread portion of a pneumatic tire, have improved tan δ (0°C) and tan δ (60°C) due to the synergistic effect of 3,4-dimethoxycinnamic acid, which corresponds to the compound represented by general formula (1), and silica, resulting in improved wet performance and fuel economy in a balanced manner. Additionally, the rubber compositions of Examples 1 to 3 have improved processability due to the improved dispersibility of silica resulting from 3,4-dimethoxycinnamic acid, which corresponds to the compound represented by general formula (1).

[0038] [Table 2]

[0039] The results in Table 2 show that the vulcanized rubber of the rubber composition of Comparative Example 3 contains an excessive amount of 3,4-dimethoxycinnamic acid, which corresponds to the compound represented by general formula (1), and therefore the 3,4-dimethoxycinnamic acid, which corresponds to the compound represented by general formula (1), aggregates excessively, resulting in a deterioration in tan δ (60°C). The vulcanized rubbers of Comparative Examples 4 to 5 contain acetamidocinnamic acid, which does not correspond to the compound represented by general formula (1), and therefore also show a deterioration in tan δ (60°C). On the other hand, the results in Examples 4 to 5 show that rubber compositions containing 3,4-dihydroxycinnamic acid, which corresponds to the compound represented by general formula (1), have excellent processability, and similar effects can be obtained with the vulcanized rubbers.

Claims

1. With respect to 100 parts by mass of a rubber component containing at least a diene rubber, a compound represented by the following general formula (1): 【Chemistry 1】 (In the above general formula (1), R １ ~R ５ At least one of the groups is an —OH group or an —OCH ３ A is an unsaturated bond, a —H group, a —CH ３ group, -NH ２ is an alkylene group having 1 to 20 carbon atoms which may have a —COOH group, an —O— group, or an —OH group, and n is an integer of 0 to 10. B is a —COOH group, an —OH group, or an ═O group, and the adjacent R １ or R ５ and 20 to 150 parts by mass of silica.

2. The rubber composition according to claim 1, wherein the compound represented by the general formula (1) is a naturally occurring compound.

3. 2. The rubber composition according to claim 1, wherein the compound represented by the general formula (1) is at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid.

4. A pneumatic tire having a rubber portion comprising a vulcanized rubber of the rubber composition according to claim 1.

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