Rubber composition and pneumatic tire

Abstract

To provide a rubber composition to be a raw material of a vulcanized rubber excellent in steering stability and wet grip performance when used as a rubber part of a pneumatic tire.SOLUTION: The rubber composition comprises 100 pts.mass of a rubber component containing at least one of a natural rubber and an isoprene rubber and a styrene-butadiene rubber having a glass transition point of -70°C to -20°C, and 0.1-10 pts.mass of a compound having XLogP of 0.5-10. The rubber composition preferably contains 20 to 150 parts by mass of silica and 1 to 70 parts by mass of carbon black per 100 parts by mass of the rubber component.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] Pneumatic tires are required to have excellent handling stability and grip performance on wet road surfaces (hereinafter also referred to as "wet grip performance"). One method for improving the former is to increase the rigidity of vulcanized rubber even at high temperatures (increasing hardness), and one method for improving the latter is to increase the tan δ of the vulcanized rubber, particularly tan δ at 0°C (tan δ(0°C)).

[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] 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 steering stability and wet grip performance in order to use the vulcanized rubber as the rubber portion of a pneumatic tire.

[0006] 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 steering stability and wet grip performance when used as the rubber portion of a pneumatic tire.

[0007] Another object of the present invention is to provide a pneumatic tire that is excellent in steering stability and wet grip performance. [Means for solving the problem]

[0008] The above object can be achieved by the present invention as described below. Specifically, the present invention relates to a rubber composition (1) characterized by containing 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less, per 100 parts by mass of a rubber component containing at least one of natural rubber and isoprene rubber, and a styrene-butadiene rubber having a glass transition point of −70°C to −20°C.

[0009] In the rubber composition (1), a rubber composition (2) containing 20 to 150 parts by mass of silica and 1 to 70 parts by mass of carbon black per 100 parts by mass of the rubber component is preferred.

[0010] 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) of natural origin.

[0011] In any one of the rubber compositions (1) to (3), a rubber composition (4) is preferred in which 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.

[0012] The present invention also relates to a pneumatic tire (5) having a rubber portion made of a vulcanized rubber of any one of the rubber compositions (1) to (4). [Effects of the Invention]

[0013] The rubber composition according to the present invention contains a compound having an XLogP of 0.5 or more and 10 or less in a rubber component containing at least one of natural rubber and isoprene rubber, and styrene-butadiene rubber having a glass transition temperature of -70°C to -20°C. This dramatically improves the handling stability and wet grip performance of the final vulcanized rubber. The following are thought to be the reasons for this effect.

[0014] Compounds with an XLogP of 0.5 or more and 10 or less have moderate hydrophilicity and tend to aggregate in rubber components containing at least one of natural rubber and isoprene rubber and styrene-butadiene rubber with a glass transition temperature of -70°C to -20°C, thereby increasing the viscosity of the rubber composition. As a result, during rubber mixing, the rubber composition can be maintained in a high shear state while suppressing excessive temperature rise. This allows the reaction between the compound with an XLogP of 0.5 or more and 10 or less and the rubber component to proceed at a high level, resulting in increased rubber hardness and an increase in tan δ, particularly tan δ at 0°C (tan δ(0°C)). This is believed to result in improved handling stability and wet grip performance of the vulcanized rubber.

[0015] When the rubber composition according to the present invention further contains 20 to 150 parts by mass of silica and 1 to 70 parts by mass of carbon black per 100 parts by mass of the rubber component, the handling stability and wet grip performance of the final vulcanized rubber are particularly improved. The reason for this effect is that compounds with an XLogP of 0.5 or more and 10 or less have moderate hydrophilicity, which contributes to improving the dispersibility of silica in the rubber composition and enhances the reinforcing effect of silica, while promoting a higher level of reaction between the compound with an XLogP of 0.5 or more and 10 or less and the rubber component. This further increases the rubber hardness of the final vulcanized rubber and tan δ, particularly tan δ at 0°C (tan δ(0°C)). This is believed to result in further improvements in the handling stability and wet grip performance of the vulcanized rubber. In the present invention, when a compound with an XLogP of less than 0.5 is used, such a compound is thought to be too hydrophilic, resulting in poor filler dispersion. On the other hand, when a compound with an XLogP of more than 10 is used, such a compound becomes less hydrophilic and therefore more compatible with rubber, which is thought to make it impossible to maintain a high shear state.

[0016] The vulcanized rubber of the rubber composition according to the present invention is excellent in handling stability and wet grip performance, and is therefore useful as a raw material for pneumatic tires. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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, relative to 100 parts by mass of a rubber component containing at least one of natural rubber and isoprene rubber, and a styrene-butadiene rubber having a glass transition point of −70° C. to −20° C. The compounding amount of the compound having an XLogP of 0.5 or more and 10 or less is, when the total amount of the rubber component is taken as 100 parts by mass,

[0018] 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.

[0019] To solve the problems with LogP mentioned above, there is an approach that estimates LogP by breaking down molecules 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, with the latest model in the XLogP series being 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).

[0020] 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 handling stability and wet grip performance of the vulcanized rubber. The reason why the handling stability and wet grip performance 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 thought to be the cause.

[0021] (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) When silica is compounded into a rubber composition, the dispersibility of silica improves in a rubber component containing styrene-butadiene rubber with a glass transition temperature of -70°C to -20°C. Furthermore, the reaction between the compound with an XLogP of 0.5 or more and 10 or less and the rubber component proceeds more effectively, resulting in a higher rubber hardness and a higher tan δ, particularly tan δ at 0°C (tan δ(0°C)). As a result, it is believed that the handling stability and wet grip performance of the vulcanized rubber are further improved.

[0022] 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).

[0023] The rubber composition according to the present invention contains, as rubber components, at least one of natural rubber (NR) and isoprene rubber (IR), and styrene-butadiene rubber (SBR) having a glass transition point of −70° C. to −20° C. The ratio of these rubbers per 100 parts by mass of the rubber component is not particularly limited, and may be, for example, 20 to 70 parts by mass of natural rubber and / or isoprene rubber and 30 to 80 parts by mass of SBR, 20 to 50 parts by mass of natural rubber and / or isoprene rubber and 50 to 80 parts by mass of SBR, or 20 to 40 parts by mass of natural rubber and / or isoprene rubber and 60 to 80 parts by mass of SBR. The rubber composition according to the present invention may contain, as a rubber component, natural rubber, isoprene rubber, and diene rubbers other than styrene-butadiene rubber having a glass transition point of −70° C. to −20° C., such as butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, and styrene-isoprene-butadiene copolymer rubber.

[0024] The rubber composition according to the present invention preferably contains silica as a filler, because the improved dispersibility of the silica, particularly due to a compound having an XLogP of 0.5 or more and 10 or less, ultimately results in a vulcanized rubber with excellent handling stability and wet grip performance. As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, and the like, which are commonly used for rubber reinforcement, are used. Of these, wet silica is preferred. The amount of silica in the rubber composition is preferably 20 to 150 parts by mass, more preferably 50 to 100 parts by mass, per 100 parts by mass of the rubber component.

[0025] 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.

[0026] 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. The amount of carbon black added is preferably 1 to 70 parts by mass, more preferably 5 to 40 parts by mass, per 100 parts by mass of the rubber component.

[0027] 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, silica, and 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The rubber composition according to the present invention can be obtained by kneading a rubber component, a compound having an XLogP of 0.5 or more and 10 or less, silica and carbon black, as well as 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, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0032] 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.

[0033] The vulcanized rubber of the rubber composition according to the present invention has excellent handling stability and wet grip performance. 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 handling stability and wet grip performance. [Example]

[0034] Examples that specifically illustrate the configuration and effects of the present invention will be described below.

[0035] (Preparation of Rubber Composition) Rubber compositions were prepared by compounding the rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4 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 1: Unmodified SBR, Tg = -40°C, manufactured by JSR Corporation, product name "JSR0122" Styrene-butadiene rubber 2: Alkoxysilyl and amino group-terminated solution polymerized SBR, Tg = -33°C, manufactured by JSR Corporation, product name "HPR350" Styrene-butadiene rubber 3: Unmodified SBR, Tg = -53°C, manufactured by JSR Corporation, product name "JSR1723" Styrene-butadiene rubber 4: Unmodified SBR, Tg = -4°C, manufactured by Sumitomo Chemical Co., Ltd., "SE-6529" Natural rubber; RSS#3 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" (N2SA: 79m 2 / g) Oil: JX Nippon Oil & Energy Corporation, product name "Process NC140" Zinc oxide: manufactured by Mitsui Mining & Smelting Co., Ltd., product name "Zinc Oxide No. 3" Stearic acid: Kao Corporation, product name "Lunac S-20" Anti-aging agent: Sumitomo Chemical Co., Ltd., product name "Antigen 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"

[0036] For the vulcanized rubbers of the rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4, the rubber hardness (Hs.) and tan δ (0° C.) were evaluated by the following methods.

[0037] <Rubber hardness of vulcanized rubber (Hs.)> The rubber hardness was evaluated by measuring the hardness of sample rubber test pieces obtained by heating and vulcanizing the rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4 in a predetermined mold at 160°C for 30 minutes using a type A durometer in accordance with JIS K6253 at a temperature of 23°C, and expressing the hardness as an index with the value of Comparative Example 1 set to 100. The larger the index, the higher the rubber hardness at room temperature, indicating excellent steering stability when used in the tread portion of a pneumatic tire.

[0038] <tan δ(0℃) of vulcanized rubber> The rubber compositions of Examples 1 to 12 and Comparative Examples 1 to 4 were heated and vulcanized at 160°C for 30 minutes using a predetermined mold to obtain sample rubbers for measurement. 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) was measured. In Tables 1 and 2, the values ​​are expressed as an index, with the tan δ (0°C) value of Comparative Example 1 set to 100. The higher the index, the better the wet grip performance when used in the tread of a pneumatic tire. The measurement conditions are as follows: Measurement sample size: length 40 mm, width 3 mm, thickness 2 mm Measurement mode: Tensile mode Measurement temperature: 0℃ Frequency: 100Hz Dynamic distortion: 0.15%

[0039] [Table 1]

[0040] The results in Table 1 show that the vulcanized rubber of the rubber composition of Comparative Example 2 does not improve wet grip performance when used in the tread of a pneumatic tire because the XLogP of the compounded acetamidocinnamic acid is 0. The vulcanized rubber of the rubber composition of Comparative Example 3 does not improve steering stability or wet grip performance when used in the tread of a pneumatic tire because the XLogP of the compounded tocopherol is 10.7. Furthermore, the vulcanized rubber of the rubber composition of Comparative Example 4, which contains styrene-butadiene rubber 4 with a Tg of -4°C, does not improve steering stability when used in the tread of a pneumatic tire. On the other hand, the vulcanized rubbers of the rubber compositions of Examples 1 to 3 exhibit a balanced improvement in both steering stability and wet grip performance when used in the tread of a pneumatic tire due to the synergistic effect of 3,4-dimethoxycinnamic acid (XLogP=1.8), which has an XLogP of 0.5 or more and 10 or less, and styrene-butadiene rubber and silica, which have a glass transition temperature of -70°C to -20°C. Furthermore, the results of Examples 4 to 7 show that similar effects can be obtained with vulcanized rubbers of rubber compositions blended with 3,4-dihydroxycinnamic acid (XLogP=1.2), catechol (XLogP=0.9), cinnamic acid (XLogP=2.1), and 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (XLogP=5.1).

[0041] [Table 2]

[0042] The results in Table 2 show that the vulcanized rubbers of the rubber compositions of Examples 8 to 12, even when blended with a specified amount of styrene-butadiene rubber with different glass transition points in the range of -70°C to -20°C, exhibit a balanced improvement in both steering stability and wet grip performance when used in the tread portion of a pneumatic tire due to the synergistic effect of 3,4-dimethoxycinnamic acid (XLogP=1.8) with an XLogP of 0.5 or more and 10 or less, and silica.

Claims

1. A rubber composition characterized by containing 0.1 to 10 parts by mass of a compound having an XLogP of 0.5 or more and 10 or less, relative to 100 parts by mass of a rubber component containing at least one of natural rubber and isoprene rubber, and a styrene-butadiene rubber having a glass transition point of -70°C to -20°C.

2. 2. The rubber composition according to claim 1, comprising 20 to 150 parts by mass of silica and 1 to 70 parts by mass of carbon black per 100 parts by mass of the rubber component.

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 a naturally occurring compound.

4. 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.

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

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