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: A rubber composition comprising: 0.1 to 10 parts by mass of a compound having XLogP of 0.5 or more and 10 or less; and 20 to 150 parts by mass of silica, based on 100 parts by mass of a rubber component comprising at least a diene rubber. Preferably, the hydrophilic compound is a naturally occurring compound. In addition, it is preferable that the compound having XLogP of 0.5 to 10 is at least one of 3, 4-dihydroxycinnamic acid or 3, 4-dimethoxycinnamic acid.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 relates to a rubber composition (1) characterized by containing, per 100 parts by mass of a rubber component containing at least a diene rubber, 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less, and 20 to 150 parts by mass of silica.

[0010] In the rubber composition (1), the compound having an XLogP of 0.5 or more and 10 or less is preferably a rubber composition (2) of natural origin.

[0011] In the rubber composition (1) or (2), the compound having an XLogP of 0.5 or more and 10 or less is preferably a rubber composition (3) which 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 a compound having an XLogP of 0.5 or more and 10 or less, 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] Compounds having an XLogP of 0.5 or more and 10 or less have moderate hydrophilicity and tend to aggregate in the rubber component, thereby increasing the viscosity of the rubber composition. As a result, during rubber kneading, a high shear state of the rubber composition can be maintained while suppressing excessive temperature rise. This allows the reaction between the compound having an XLogP of 0.5 or more and 10 or less 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 having an XLogP of 0.5 or more and 10 or less has moderate hydrophilicity, 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 having an XLogP of 0.5 or more and 10 or less 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. In the present invention, when a compound with an XLogP of less than 0.5 is used, it is believed that such a compound is too hydrophilic and the dispersion of the filler becomes poor, whereas when a compound with an XLogP of more than 10 is used, it is believed that such a compound has low hydrophilicity and therefore has good compatibility with the rubber, making it impossible to maintain a high shear state.

[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 a compound having an XLogP of 0.5 or more and 10 or less together with silica, and the compound having an XLogP of 0.5 or more and 10 or less has appropriate hydrophilicity, which improves the dispersibility of 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 contains, per 100 parts by mass of a rubber component containing at least a diene rubber, 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less. The compounding amount of the compound having an XLogP of 0.5 or more and 10 or less is more preferably 0.5 to 5 parts by mass when the total amount of the rubber component is taken as 100 parts by mass.

[0017] XLogP in the present invention will be described below. The lipid solubility of a compound significantly influences its solubility as well as its pharmacokinetics, including absorption and metabolism. A typical descriptor of a compound's lipid solubility is the octanol / water partition coefficient (LogP). The P in LogP is the ratio of the molecule's concentration at equilibrium in the organic layer (octanol layer) and the aqueous layer, and LogP is its common logarithm. A larger value indicates a higher concentration in the organic layer, indicating higher lipid solubility. However, LogP has practical limitations. For example, while LogP values ​​can be determined experimentally for individual compounds, this is not very practical due to time and cost considerations, and only a limited number of compounds have been reported. Another drawback is that LogP values ​​cannot be obtained experimentally for compounds that have not yet been synthesized.

[0018] To solve the problems with LogP mentioned above, there is an approach that estimates LogP by breaking down the molecule into individual atoms and calculating the sum of each contribution, and the XLogP algorithm is the only atom-based approach that adds a correction term, and the latest model in the XLogP series is described in the paper "Computation of Octanol-Water Partition Coefficients by Guiding an Additive Model with Knowledge." XLogP is based on the LogP values ​​contained in PubChem, a chemical molecule database maintained by the National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) under the National Institutes of Health (NIH).

[0019] In the present invention, it is more preferable from the viewpoint of environmental protection if the compound having an X Log P of 0.5 or more and 10 or less is a naturally occurring compound. Examples of naturally occurring compounds include 3,4-dihydroxycinnamic acid (caffeic acid) (X Log P = 1.2), 3,4-dimethoxycinnamic acid (X Log P = 1.8), curcumin (X Log P = 3.2), sesamol (X Log P = 1.2), coumaric acid (X Log P = 1.5), cinnamic acid (X Log P = 2.1), rosmarinic acid (X Log P = 2.4), ferulic acid (X Log P = 1.5), sinapic acid (X Log P = 1.5), and 4-(4-hydroxy-3-methoxyphenyl)-2-butanone (X Log P = 0.8). Among these compounds, in the present invention, it is more 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), for example, are thought to be the cause.

[0020] (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 having an XLogP of 0.5 or more and 10 or less has moderate hydrophilicity, which contributes to improving the dispersibility of silica in the rubber composition, enhancing the reinforcing effect of silica, while promoting a higher level of reaction between the compound having an XLogP of 0.5 or more and 10 or less and the rubber component. This further increases tan δ at 0°C (tan δ(0°C)), while further 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.

[0021] In addition, compounds that are not naturally occurring can also be used as compounds with an X Log P of 0.5 or more and 10 or less. Examples of non-naturally occurring compounds include 2,3-dimethoxycinnamic acid (X Log P = 1.8), 2,4-dimethoxycinnamic acid (X Log P = 1.8), 2,5-dimethoxycinnamic acid (X Log P = 1.8), 2,3,4-trimethoxycinnamic acid (X Log P = 1.7), 3,4,5-triethoxycinnamic acid (X Log P = 1.4), and protocatechuic acid (X Log P = 1.1). , catechol (XLogP=0.9), 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (XLogP=5.1), carvacrol (XLogP=3.1), 3,4-dimethoxyhydrocinnamic acid (XLogP=1.2), and 5,6-dimethoxy-1-indanone (XLogP=1.6).

[0022] 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.

[0023] The rubber composition according to the present invention contains silica as a filler. Compounds having an XLogP of 0.5 or more and 10 or less have an effect of improving the dispersibility of silica, which ultimately results in a vulcanized rubber with excellent wet performance and fuel economy, and are therefore preferred. 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 preferred. 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.

[0024] 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.

[0025] 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.

[0026] The rubber composition according to the present invention may contain, in addition to the rubber component, the compound having an XLogP of 0.5 or more and 10 or less, 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, and the like.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The rubber composition according to the present invention can be obtained by kneading together components other than the rubber component, the compound having an XLogP of 0.5 or more and 10 or less, and silica, as well 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.

[0031] 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.

[0032] 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]

[0033] Examples that specifically illustrate the configuration and effects of the present invention will be described below.

[0034] (Preparation of Rubber Composition) Rubber compositions were prepared by compounding the rubber compositions of Examples 1 to 8 and Comparative Examples 1 to 6 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 (XLogP=1.8) 3,4-Dihydroxycinnamic acid (XLogP=1.2) Catechol (XLogP=0.9) Cinnamic acid (XLogP=2.1) 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (XLogP=5.1) Acetamidocinnamic acid (XLogP=0) Tocopherol (XLogP=10.7) Sulfur: Powdered sulfur, manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd., product name "Noccela CZ"

[0035] The processability of the rubber compositions of Examples 1 to 8 and Comparative Examples 1 to 6 and the vulcanized rubbers thereof were evaluated for tan δ (0° C.) and tan δ (60° C.) by the following method.

[0036] <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.

[0037] <Vulcanized rubber tan δ (0℃) and tan δ (60℃)> The rubber compositions of Examples 1 to 8 and Comparative Examples 1 to 6 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%

[0038] [Table 1]

[0039] 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 have improved tan δ (0°C) and tan δ (60°C) when used in the tread of a pneumatic tire due to the synergistic effect of silica and 3,4-dimethoxycinnamic acid (XLogP=1.8), which has an XLogP of 0.5 or more and 10 or less. This improves both tan δ (0°C) and tan δ (60°C), resulting in a balanced improvement in both wet performance and fuel economy. 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. It is noted that the vulcanized rubber of the rubber composition of Comparative Example 3 contains an excessive amount of 3,4-dimethoxycinnamic acid, which causes excessive aggregation of the 3,4-dimethoxycinnamic acid, resulting in a deterioration in tan δ (60°C).

[0040] [Table 2]

[0041] The results in Table 2 show that in Examples 4 to 8, even when the rubber compositions contained 3,4-dihydroxycinnamic acid (X Log P = 1.2), catechol (X Log P = 0.9), cinnamic acid (X Log P = 2.1), and 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (X Log P = 5.1), the synergistic effect with silica improved both tan δ (0°C) and tan δ (60°C) when used in the tread of a pneumatic tire, resulting in a balanced improvement in both wet performance and fuel economy. Additionally, the rubber compositions of Examples 4 to 8 also showed improved processability due to the improved silica dispersibility resulting from the 3,4-dihydroxycinnamic acid, catechol, cinnamic acid, and 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane. On the other hand, the vulcanized rubbers of the rubber compositions of Comparative Examples 4 and 5 show a deterioration in tan δ (60°C) because the compounded acetamidocinnamic acid does not correspond to compounds having an XLogP of 0.5 or more and 10 or less. The vulcanized rubber of the rubber composition of Comparative Example 6 shows a deterioration in tan δ (0°C) and tan δ (60°C) because the compounded tocopherol does not correspond to compounds having an XLogP of 0.5 or more and 10 or less.

Claims

1. A rubber composition characterized by containing, per 100 parts by mass of a rubber component containing at least a diene rubber, 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less, and 20 to 150 parts by mass of silica.

2. 2. The rubber composition according to claim 1, wherein the compound having an XLogP of 0.5 or more and 10 or less is a naturally occurring compound.

3. 2. The rubber composition according to claim 1, wherein the compound having an XLogP of 0.5 or more and 10 or less 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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