Rubber composition and pneumatic tire

Abstract

To provide a rubber composition to be a raw material of a vulcanized rubber excellent in wet grip performance and ice performance when used as a rubber part of a pneumatic tire traveling especially on a wet road surface and an ice road surface.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 5 to 50 parts by mass of a paraffin-based oil.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 used in a variety of environments, including roads wet with rain (wet roads), snow-covered roads, and even frozen roads (icy roads). Therefore, they require good grip performance on wet roads (hereinafter also referred to as "wet grip performance") and braking performance on icy roads (hereinafter also referred to as "ice performance"). One method for improving the former is to increase the tan δ of the vulcanized rubber, particularly the tan δ at 0°C (tan δ(0°C)), while one method for improving the latter is to decrease the storage modulus E' of the vulcanized rubber at low temperatures (e.g., -5°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 wet grip performance and ice performance, particularly for use as the rubber portion of pneumatic tires that run on wet or icy roads.

[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 wet grip performance and ice performance, particularly when used as the rubber portion of a pneumatic tire that runs on wet or icy roads.

[0007] Another object of the present invention is to provide a pneumatic tire, particularly a studless tire, that has excellent wet grip performance and ice performance. [Means for solving the problem]

[0008] 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), and 5 to 50 parts by mass of a paraffinic oil.

[0009] In the rubber composition (1), a rubber composition (2) containing 3 to 40 parts by mass of silica and 10 to 80 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), a rubber composition (3) containing 30 to 70 parts by mass of natural rubber and 30 to 70 parts by mass of butadiene rubber is preferred, where the total amount of the rubber components is taken as 100 parts by mass.

[0011] In any one of the rubber compositions (1) to (3), a rubber composition (4) is preferred in which the compound represented by the general formula (1) is a naturally occurring compound.

[0012] In any of the rubber compositions (1) to (4), a rubber composition (5) 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.

[0013] The present invention also relates to a pneumatic tire (6) having a rubber portion made of a vulcanized rubber of any one of the rubber compositions (1) to (5), and further relates to a studless tire (7) having a tread portion made of a vulcanized rubber of any one of the rubber compositions (1) to (5). [Effects of the Invention]

[0014] The rubber composition according to the present invention contains the compound represented by the general formula (1) and a paraffinic oil. This dramatically improves the wet grip performance and ice performance of the final vulcanized rubber. The reasons for this effect are thought to be as follows.

[0015] Because the compound represented by general formula (1) is highly hydrophilic, it tends to aggregate in the rubber composition, thereby increasing the viscosity of the rubber composition. Therefore, 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 represented by general formula (1) and the rubber component to proceed at a high level, resulting in an increase in the rubber hardness of the final vulcanized rubber and an increase in tan δ, particularly tan δ at 0°C (tan δ(0°C)). In addition, the rubber composition according to the present invention contains paraffinic oil, which can reduce the storage modulus E' of the final vulcanized rubber at low temperatures (e.g., -5°C). These factors are believed to improve the wet grip performance and ice performance of the vulcanized rubber.

[0016] When the rubber composition according to the present invention contains 3 to 40 parts by mass of silica and 10 to 80 parts by mass of carbon black per 100 parts by mass of the rubber component, the wet grip performance and ice performance of the final vulcanized rubber are particularly improved. The reason for this effect is that the compound represented by general formula (1) is highly hydrophilic, which contributes to improving the dispersibility of silica in a rubber composition containing paraffinic oil, enhancing the reinforcing effect of silica while promoting a higher level of reaction between the compound represented by general formula (1) and the rubber component. This further increases the rubber hardness of the final vulcanized rubber and further increases tan δ, particularly tan δ at 0°C (tan δ(0°C)), while further reducing the storage modulus E' of the vulcanized rubber at low temperatures (e.g., -5°C). This is believed to result in further improvements in the wet grip performance and ice performance of the vulcanized rubber. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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.

[0018] From the perspective of environmental protection, it is more preferable for the compound represented by the general formula (1) to be 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 grip performance and ice performance of the vulcanized rubber. The reasons why the wet grip performance and ice performance of the vulcanized rubber are improved when at least one of 3,4-dihydroxycinnamic acid and 3,4-dimethoxycinnamic acid is used are unclear, but the following reasons (1) to (3) are considered.

[0019] (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 the silica improves in a rubber component containing paraffinic oil, and the reaction between the compound of general formula (1) and the rubber component proceeds more effectively, resulting in a higher rubber hardness for the final vulcanized rubber, a further increase in tan δ, particularly tan δ at 0°C (tan δ(0°C)), and a further decrease in the storage modulus E' of the vulcanized rubber at low temperatures (e.g., -5°C). As a result, it is believed that the wet grip performance and ice performance of the vulcanized rubber are further improved.

[0020] 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.

[0021] The rubber composition according to the present invention contains at least a diene rubber as a rubber component. Among the diene rubbers, natural rubber (NR) and butadiene rubber (BR) are preferably contained in the present invention, and the blending amounts thereof are preferably 30 to 70 parts by mass of the natural rubber and 30 to 70 parts by mass of the butadiene rubber, assuming the total amount of the rubber components to be 100 parts by mass. The rubber composition according to the present invention may also contain, as a rubber component, a diene rubber other than natural rubber and butadiene rubber, such as isoprene rubber (IR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, or styrene-isoprene-butadiene copolymer rubber.

[0022] In order to reduce the storage modulus E' of the finally obtained vulcanized rubber at low temperatures (e.g., -5°C), the rubber composition according to the present invention preferably contains a paraffinic oil. The paraffinic oil is an oil having a paraffin component content (%CP) of 50% or more as determined by ring analysis (ndM), and for example, a paraffinic mineral oil commercially available as a paraffinic process oil can be used. The blending amount of the paraffinic oil is preferably 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, per 100 parts by mass of the rubber component.

[0023] The rubber composition according to the present invention preferably contains silica as a filler, because the compound represented by the general formula (1) has the effect of improving the dispersibility of the silica, ultimately resulting in a vulcanized rubber with excellent wet grip performance and ice 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 3 to 40 parts by mass, more preferably 3 to 30 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 10 ...

[0026] The rubber composition according to the present invention may contain, in addition to the rubber component, the compound represented by the general formula (1), paraffinic oil, 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.

[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 a rubber component, the compound represented by the general formula (1), paraffinic oil, 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, 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 grip performance and ice 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 studless tires, which require high wet grip performance and ice performance. [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 7 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). Butadiene rubber: JSR Corporation, product name "BR01" (high cis BR, cis 1,4 bond content 95%) 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 "Seat KH" Paraffin oil: JX Nippon Oil & Energy Corporation, product name "Process P200" Aroma 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 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"

[0035] For the vulcanized rubbers of the rubber compositions of Examples 1 to 7 and Comparative Examples 1 to 4, tan δ (0° C.) and storage modulus E′ were evaluated by the following methods.

[0036] <tan δ(0℃) of vulcanized rubber> The rubber compositions of Examples 1 to 7 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 value of tan δ (0°C) for 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%

[0037] <Storage modulus E' of vulcanized rubber> The rubber compositions of Examples 1 to 7 and Comparative Examples 1 to 4 were heated and vulcanized at 160°C for 30 minutes using a specified mold to obtain sample rubbers for measurement. A viscoelasticity tester manufactured by Toyo Seiki Seisakusho was used to measure the storage modulus E' at a frequency of 10 Hz, static strain of 10%, dynamic strain of ±0.25%, and temperature of -5°C, and the value was expressed as an index, with the value for Comparative Example 1 set to 100. The smaller the index, the smaller the storage modulus E', and therefore the larger the contact area at low temperatures and the better the ice performance.

[0038] [Table 1]

[0039] The results in Table 1 show that the vulcanized rubber of the rubber composition of Comparative Example 2, which contains acetamidocinnamic acid that does not fall under the general formula (1) compound, deteriorates wet grip performance and ice performance when used in the tread of a pneumatic tire. The vulcanized rubber of Comparative Example 3, which contains aromatic oil instead of paraffinic oil, does not improve ice performance when used in the tread of a pneumatic tire. The vulcanized rubber of Comparative Example 4, which does not contain the general formula (1) compound, deteriorates wet grip performance even when the compounding ratio of natural rubber and butadiene rubber is changed. On the other hand, the vulcanized rubbers of Examples 1 to 3, which contain 3,4-dimethoxycinnamic acid, which falls under the general formula (1) compound, paraffinic oil, and silica, exhibit a synergistic effect when used in the tread of a pneumatic tire, improving both wet grip performance and ice performance in a balanced manner.

[0040] [Table 2]

[0041] The results in Table 2 show that the vulcanized rubber of the rubber composition of Example 4, which is compounded with 3,4-dihydroxycinnamic acid, which corresponds to the compound represented by general formula (1), exhibits a synergistic effect with paraffinic oil and silica, resulting in a balanced improvement in both wet grip performance and ice performance when used in the tread of a pneumatic tire. Furthermore, the results of Examples 5 to 7 show that even when the compounding amounts of silica and carbon black are changed, the synergistic effect of 3,4-dimethoxycinnamic acid, which corresponds to the compound represented by general formula (1), paraffinic oil, and silica results in a balanced improvement in both wet grip performance and ice performance when used in the tread of a pneumatic tire.

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 5 to 50 parts by mass of a paraffinic oil.

2. 2. The rubber composition according to claim 1, comprising 3 to 40 parts by mass of silica and 10 to 80 parts by mass of carbon black per 100 parts by mass of the rubber component.

3. 2. The rubber composition according to claim 1, comprising 30 to 70 parts by mass of natural rubber and 30 to 70 parts by mass of butadiene rubber, where the total amount of the rubber components is 100 parts by mass.

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

5. 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.

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

7. A studless tire having a tread portion comprising a vulcanized rubber of the rubber composition according to claim 1.

Images