Rubber compositions and pneumatic tires

Abstract

To provide a rubber composition that serves as a raw material for vulcanized rubber for tires, and a pneumatic tire equipped with vulcanized rubber of the rubber composition, which improves the balance between ice braking performance (grip performance) and response performance such as steering response and driving stability (anti-wandering performance) on frozen road surfaces (icy road surfaces). [Solution] A rubber composition containing diene rubber, porous cellulose particles, and vegetable oil, wherein the vegetable oil is a fatty acid ester triglyceride in which a fatty acid containing at least saturated and unsaturated fatty acids is ester-bonded to glycerin, and the ratio of unsaturated fatty acids in the fatty acid is 50% by mass or more. Preferably, the ratio of polyunsaturated fatty acids in the fatty acid is 15% by mass or more.

Description

Technical Field

[0001] The present invention relates to a rubber composition and a pneumatic tire.

Background Art

[0002] Pneumatic tires are required to have driving performance in various scenarios. In particular, for studless tires, for example, it is required to improve the braking performance (grip performance) on ice on a frozen road surface (ice road surface). In addition, in recent years, the required characteristics for studless tires in the market have become increasingly strict, and not only the grip performance, but also improvements in response performance such as steering response performance and driving stability performance (anti-wandering performance) on an ice road surface are required.

[0003] In Patent Document 1 below, 3 to 30 parts by mass of a diene rubber that is liquid at room temperature and 0.3 to 20 parts by mass of porous cellulose particles that are spherical particles having a porosity of 75 to 95% and a ratio of major axis / minor axis of 1 to 1.5 are contained with respect to 100 parts by mass of a diene rubber that is solid at room temperature. A rubber composition for tires is described.

[0004] In Patent Document 2 below, a raw material rubber containing 20 to 50 parts by weight of a first styrene-butadiene rubber, 20 to 50 parts by weight of a second styrene-butadiene rubber, and 10 to 40 parts by weight of a butadiene rubber (BR), and, with respect to 100 parts by weight of the raw material rubber, 80 to 180 parts by weight of a reinforcing filler, 2 to 50 parts by weight of natural oil, and 2 to 30 parts by weight of a hydrocarbon resin are contained. A rubber composition for a tire tread is described.

[0005] Patent Document 3 below contains 100 parts by weight of raw rubber, 70 to 120 parts by weight of reinforcing filler, and 10 to 60 parts by weight of natural oil with a linoleic acid:oleic acid ratio of 1:0.5 to 1:5. The raw rubber contains 5 to 10 parts by weight of natural rubber, 40 to 70 parts by weight of solution-polymerized styrene-butadiene rubber, and 20 to 50 parts by weight of neodymium-butadiene rubber. The solution-polymerized styrene-butadiene rubber has a styrene content of 20 to 50% by weight, a vinyl content of 10 to 40% by weight, a Tg of -50 to -20°C, and contains 20 to 40 parts by weight of SRAE oil. The reinforcing filler contains 65 to 100 parts by weight of silica and 5 to 20 parts by weight of carbon black. The silica has a nitrogen adsorption value of 160 to 180 m 2 The value is / g, and the CTAB adsorption titer is 150-170m 2 A rubber composition for tire treads is described, which has a DBP oil absorption rate of 180-200cc / 100g. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 7357841 [Patent Document 2] Japanese Patent Publication No. 2019-172957 [Patent Document 3] Patent No. 6522716 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Through diligent research by the inventors, it was found that the technologies described in Patent Documents 1 to 3 above have difficulty in achieving a good balance between grip performance and response performance on icy surfaces.

[0008] The present invention has been made in view of the above circumstances, and its purpose is to provide a rubber composition that serves as a raw material for vulcanized rubber for tires, and a pneumatic tire equipped with vulcanized rubber of the rubber composition, which improves the braking performance (grip performance) on frozen road surfaces (icy road surfaces) and response performance such as steering response performance and driving stability performance (anti-wandering performance) in a well-balanced manner. [Means for solving the problem]

[0009] The above problems can be solved by the following configuration. That is, the present invention relates to a rubber composition (1) containing diene rubber, porous cellulose particles and vegetable oil, wherein the vegetable oil is a fatty acid ester triglyceride in which a fatty acid containing at least a saturated fatty acid and an unsaturated fatty acid is ester-bonded to glycerol, and the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more.

[0010] In the above rubber composition (1), the rubber composition (2) is preferable, wherein the vegetable oil has a ratio of polyunsaturated fatty acids in the unsaturated fatty acids of 15% by mass or more.

[0011] In the above rubber composition (1) or (2), the vegetable oil is preferably a rubber composition (3) having an iodine value of 100 or more.

[0012] Of the above rubber compositions (1) to (3), rubber composition (4) is preferred in which the amount of vegetable oil is 5 to 20 parts by mass when the total amount of diene rubber is 100 parts by mass.

[0013] Of the above rubber compositions (1) to (4), rubber composition (5) is preferred, in which, when the total amount of diene rubber is 100 parts by mass, the amount of porous cellulose particles is 0.5 to 5.0 parts by mass.

[0014] The present invention also relates to a pneumatic tire (6) comprising at least the vulcanized rubber of the above rubber compositions (1) to (5), and more particularly to a studless tire (7) comprising at least the vulcanized rubber of the above rubber compositions (1) to (5) in the tread portion. [Effects of the Invention]

[0015] The rubber composition according to the present invention contains at least porous cellulose particles and a vegetable oil with a specific ratio of unsaturated fatty acids. More specifically, the rubber composition according to the present invention is a diene rubber blended with porous cellulose particles and a vegetable oil which is a fatty acid ester triglyceride in which a fatty acid containing at least saturated and unsaturated fatty acids and glycerin are ester-bonded, and in which the ratio of unsaturated fatty acids in the fatty acid is 50% by mass or more. The vulcanized rubber of the rubber composition having such a configuration can improve grip performance and response performance on icy surfaces in a well-balanced manner.

[0016] The vulcanized rubber of the rubber composition according to the present invention exhibits a well-balanced improvement in grip performance and responsiveness on icy surfaces. For this reason, the vulcanized rubber of the rubber composition according to the present invention is suitably usable in pneumatic tire applications, and is particularly useful as a vulcanized rubber for use in the tread of studless tires. [Modes for carrying out the invention]

[0017] The rubber composition according to the present invention contains diene rubber, porous cellulose particles, and vegetable oil.

[0018] Diene rubbers are not particularly limited and include, for example, natural rubber (NR), isoprene rubber (IR), butadiene rubber without modifying groups (functional groups) (BR), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. These can be used individually or in combination of two or more.

[0019] As the porous cellulose particles, porous cellulose particles with a porosity of 75 to 95% can be preferably used. The pores of the porous cellulose particles with such a porosity can effectively absorb and remove the water film on the road surface when contacting the ice road surface. Further, due to the edge effect of the pore wall surface, in order to exert the effect of scraping the ice road surface, when used for pneumatic tire applications, particularly for the tread application of studless tires, it greatly contributes to the improvement of grip performance and response performance on the ice road surface.

[0020] The average particle diameter of the porous cellulose particles is not particularly limited, but from the viewpoint of solving the problems of the present invention, it is preferably 1000 μm or less, more preferably 100 to 800 μm, and still more preferably 200 to 800 μm.

[0021] From the viewpoint of improving the dispersibility in the rubber composition, the porous cellulose particles are preferably spherical particles with an aspect ratio (long diameter / short diameter) of 1 to 2, and more preferably spherical particles with an aspect ratio of 1 to 1.5.

[0022] The rubber composition according to the present invention is a fatty acid ester triglyceride in which a specific vegetable oil, specifically a fatty acid containing at least saturated fatty acid and unsaturated fatty acid, and glycerin are ester-bonded, and contains a vegetable oil in which the ratio of unsaturated fatty acid in the fatty acid is 50% by mass or more. In the present invention, the vegetable oil is represented by the following formula (1).

[0023]

Chemical formula

[0024] In formula (1) above, R1, R2, and R3 are fatty acid residues of either saturated or unsaturated fatty acids. Examples of saturated fatty acids include palmitic acid (C16:0) and stearic acid (C18:0). Examples of unsaturated fatty acids include oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3). The rubber composition according to the present invention contains a fatty acid ester triglyceride (vegetable oil) in which the ratio of unsaturated fatty acids in the fatty acid is 50% by mass or more. In order to improve the grip performance and response performance of vulcanized rubber on icy surfaces in a balanced manner, it is preferable to use a fatty acid ester triglyceride in which the ratio of unsaturated fatty acids in the fatty acid is 50% by mass or more, and it is more preferable to use a fatty acid ester triglyceride in which the ratio is 70% by mass or more.

[0025] From the viewpoint of solving the problem, the rubber composition according to the present invention preferably contains 5 to 30 parts by mass of fatty acid ester triglycerides (vegetable oil) when the total amount of diene rubber is 100 parts by mass, and more preferably 10 to 25 parts by mass.

[0026] Among fatty acid ester triglycerides (vegetable oils), fatty acid ester triglycerides (vegetable oils) with a high proportion of linoleic acid or linolenic acid, which are polyunsaturated fatty acids (hereinafter also referred to as "PUFAs") having two or more unsaturated bonds, are preferred because they can improve the wet grip performance, low-temperature performance, and rolling performance of the final vulcanized rubber in a particularly well-balanced manner. In particular, in the present invention, from the viewpoint of solving the problem, it is preferable to use fatty acid ester triglycerides (vegetable oils) in which the proportion of polyunsaturated fatty acids (PUFAs) in the unsaturated fatty acids is 15% by mass or more, it is preferable to use fatty acid ester triglycerides in which the proportion is 20% by mass or more, and it is more preferable to use fatty acid ester triglycerides in which the proportion is 70% by mass or more.

[0027] In the present invention, rapeseed oil, soybean oil, safflower oil, and sunflower oil can be suitably used as fatty acid ester triglycerides (vegetable oils). Table 1 shows the fatty acid composition and iodine value of each vegetable oil.

[0028] [Table 1]

[0029] As shown in Table 1, rapeseed oil (with a polyunsaturated fatty acid (PUFA) ratio of 30.8% by mass) and soybean oil (with a polyunsaturated fatty acid (PUFA) ratio of 72.3% by mass) have high PUFA ratios. Therefore, when the rubber composition according to the present invention contains rapeseed oil or soybean oil as the fatty acid ester triglyceride (vegetable oil), it is preferable because it can improve the grip performance and response performance of the final vulcanized rubber on icy surfaces in a particularly well-balanced manner. The reason for obtaining such an effect is not clear, but it is thought that the presence of rapeseed oil or soybean oil in the diene-based rubber improves the dispersibility of porous cellulose particles, and as a result, the effects of the porous cellulose particles (such as the water absorption and removal effect of the water film on the road surface and the edge effect of the pore walls) are further enhanced.

[0030] Among fatty acid ester triglycerides (vegetable oils), using those with an iodine value of 100 or higher is preferable because it increases the amount of double bonds in the fatty acid ester triglycerides (vegetable oils), which in turn improves the grip performance and responsiveness of the resulting vulcanized rubber on icy surfaces in a particularly well-balanced manner.

[0031] When the rubber composition according to the present invention contains silica as a filler, the reinforcing effect of silica is more effectively exhibited due to the dispersion effect of silica by certain vegetable oils. As a result, the vulcanized rubber obtained in the end is preferable because it can improve grip performance and response performance on icy surfaces in a particularly well-balanced manner. As silica, wet silica, dry silica, sol-gel silica, and surface-treated silica, which are normally used for rubber reinforcement, can be used. Among these, wet silica is preferred. From the viewpoint of solving the problem, when the total amount of diene-based rubber in the rubber composition according to the present invention is 100 parts by mass, the amount of silica blended is preferably 20 to 100 parts by mass, and more preferably 30 to 80 parts by mass.

[0032] When silica is included as a filler, it is also preferable to include a silane coupling agent. The silane coupling agent is not particularly limited as long as it contains sulfur in its molecule, and various silane coupling agents that are compounded together with silica in rubber compositions can be used. Examples include sulfidosilanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Evonik Japan), bis(3-triethoxysilylpropyl) disulfide (e.g., "Si75" manufactured by Evonik Japan), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triecethoxysilylbutyl) 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. The amount of silane coupling agent is preferably 5 to 20% by mass, when the total amount of silica is considered to be 100% by mass.

[0033] The rubber composition according to the present invention contains diene rubber, porous cellulose particles, and vegetable oil, and preferably further contains silica and a silane coupling agent. In addition to these, the rubber composition according to the present invention may also contain carbon black, vulcanizing agents, vulcanization accelerators, antioxidants, stearic acid, softeners such as waxes and oils, processing aids, and the like.

[0034] The rubber composition according to the present invention may contain carbon black as a filler. In addition to carbon black commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, conductive carbon black such as acetylene black or Ketjen black can be used. The pneumatic tire rubber composition according to the present invention preferably contains 1 to 30 parts by mass of carbon black when the total amount of diene rubber is 100 parts by mass.

[0035] Preferably, sulfur can be used as the vulcanizing agent. Any ordinary sulfur for rubber can be used, such as powdered sulfur, precipitated sulfur, insoluble sulfur, or highly dispersible sulfur. In the tire rubber composition according to the present invention, the content of the vulcanizing agent is preferably 0.1 to 10 parts by mass when the total amount of diene rubber is 100 parts by mass.

[0036] As a vulcanization accelerator, vulcanization accelerators commonly used for rubber vulcanization, such as sulfenamide-based vulcanization accelerators, thiram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators, may be used individually or in appropriate mixtures.

[0037] As an anti-aging agent, you may use, individually or in appropriate combinations, any anti-aging agent commonly used for rubber, such as aromatic amine-based anti-aging agents, amine-ketone-based anti-aging agents, monophenol-based anti-aging agents, bisphenol-based anti-aging agents, polyphenol-based anti-aging agents, dithiocarbamate-based anti-aging agents, or thiourea-based anti-aging agents.

[0038] The rubber composition according to the present invention contains diene rubber, porous cellulose particles, and vegetable oil, and preferably further contains silica and a silane coupling agent, as well as carbon black, a vulcanizing agent, a vulcanization accelerator, zinc oxide, an antioxidant, stearic acid, a softening agent such as wax, and processing aids, which are obtained by kneading using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and roll.

[0039] Furthermore, the method of blending each of the above components is not particularly limited. It may be a method in which the components other than vulcanizing agents such as vulcanizing agents and vulcanization accelerators are kneaded in advance to form a masterbatch, and the remaining components are added and kneaded further; a method in which each component is added and kneaded in any order; or a method in which all components are added and kneaded simultaneously.

[0040] The vulcanized rubber of the rubber composition according to the present invention exhibits particularly well-balanced improvements in grip performance and responsiveness on icy surfaces. For this reason, the vulcanized rubber of the rubber composition according to the present invention is suitably usable in pneumatic tire applications, and is particularly useful as a vulcanized rubber for use in the tread of studless tires. [Examples]

[0041] The present invention will be described in more detail below by illustrating some embodiments.

[0042] (Preparation of rubber composition for tires) To 100 parts by mass of rubber components, the rubber compositions of Examples 1-6 and Comparative Examples 1-5 were blended according to the formulations shown in Tables 2-3, and the mixture was kneaded using a standard Banbury mixer to prepare a rubber composition for tires. The compounding agents listed in Tables 2-3 are shown below.

[0043] (Diene-based rubber) • Natural rubber: RSS#3 • Butadiene rubber: Product name "BR730", manufactured by ENEOS Material Co., Ltd. (Porous cellulose particles) • Porous cellulose particles: Product name "ViscoPearl Mini", manufactured by Rengo. (vegetable oil) • Rapeseed oil: Product name "Rapeseed White Pressed Oil", manufactured by Nisshin Oillio Co., Ltd. • Soybean oil: Product name "Soybean Salad Oil (S)", manufactured by Nisshin Oillio Co., Ltd. • Palm oil: Product name "Refined Palm Oil (S)", manufactured by Nisshin Oillio Co., Ltd. • Safflower oil: Product name "Benibana Oil (High Ole)", manufactured by Nisshin Oillio Co., Ltd. • Sunflower oil: Product name "Sunflower Oil (S)", manufactured by Nisshin Oillio Co., Ltd. (Filler) • Carbon Black: Product name "N234 Seast 7HM", manufactured by Tokai Carbon Co., Ltd. • Silica: Product name "NipSeal AQ", manufactured by Tosoh Corporation (Other combination drugs) • Silane coupling agent: Product name "Si-75", manufactured by Evonik Industries, Inc. • Zinc oxide: Product name "Zinc Oxide Type 2", manufactured by Mitsui Mining & Smelting Co., Ltd. • Stearic acid: Product name "Lunaq S-20", manufactured by Kao Corporation. • Wax: Product name "OZOACE0355", manufactured by Nippon Seiro Co., Ltd. • Anti-aging agent: Product name "Nocrac 6C", manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Terpene resin: Product name "SYLVATRAX4150", manufactured by Kraton. • Oil: Product name "Process P200", manufactured by ENEOS Corporation • Liquid rubber: Product name "LBR305", manufactured by Kuraray Co., Ltd. • Vulcanization accelerator 1: Product name "Noxellar D", manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Vulcanization accelerator 2: Product name "Soxinol CZ", manufactured by Sumitomo Chemical Co., Ltd. • Sulfur: Product name "Powdered Sulfur", manufactured by Tsurumi Chemical Industry Co., Ltd.

[0044] After preparing unvulcanized samples of the rubber compositions obtained in Examples 1-6 and Comparative Examples 1-5 above, the braking performance and response performance on ice surfaces were evaluated under the following conditions.

[0045] (Braking performance on icy surfaces) Studless tires with the obtained rubber composition applied to the tread were mounted on a 2000cc 4WD vehicle, and the braking distance on ice was measured (average value of n=10) with the ABS activated from 40 km / h at temperatures of -2°C to -6°C. The reciprocal of the measured braking distance was expressed as an index with Comparative Example 1 set to 100. A larger index indicates a shorter braking distance and better braking performance on ice.

[0046] (Responsiveness on icy surfaces) A driver in charge of sensory testing drove on an icy test course at temperatures of -2°C to -6°C, paying attention to steering responsiveness and driving stability (wandering), and evaluated the response performance subjectively (evaluation of feeling performance). The results are shown in the table, with +2 indicating superiority, +1 indicating slight superiority, ±0 indicating equivalentity, -1 indicating slight inferiority, and -2 indicating inferiority, compared to Control Comparison Example 1.

[0047] [Table 2]

[0048] Rapeseed oil has a high ratio of unsaturated fatty acids (91.8% by mass) and polyunsaturated fatty acids (30.8% by mass). Soybean oil also has a high ratio of unsaturated fatty acids (84.2% by mass) and polyunsaturated fatty acids (72.3% by mass). From the results in Table 2, it can be seen that the vulcanized rubber of the rubber composition according to Example 1 using rapeseed oil, and the vulcanized rubber of the rubber composition according to Example 2 using soybean oil, improve ice braking performance and response performance on icy surfaces in a balanced manner. Furthermore, it can be seen that the vulcanized rubber of the rubber composition according to Example 3 using safflower oil, and the vulcanized rubber of the rubber composition according to Example 4 using sunflower oil, also improve ice braking performance and response performance on icy surfaces in a balanced manner. However, since safflower oil and sunflower oil both have a low ratio of polyunsaturated fatty acids in their unsaturated fatty acids, their effects are inferior to those of rapeseed oil and soybean oil. On the other hand, the vulcanized rubber of the rubber composition according to Comparative Example 3, which uses palm oil with a low ratio of unsaturated fatty acids (49.8% by mass), shows particularly poor braking performance on icy surfaces.

[0049] [Table 3]

[0050] The results in Table 3 show that the vulcanized rubber compositions of Examples 5-6, in which the amount of rapeseed oil varied, also showed a good balance of improved braking performance and response performance on icy surfaces. On the other hand, the vulcanized rubber compositions of Comparative Examples 3 and 4, which used liquid rubber, showed particularly poor response performance on icy surfaces, indicating that it was not possible to achieve both good braking performance and response performance on icy surfaces.

Claims

1. A rubber composition containing diene rubber, porous cellulose particles, and vegetable oil, The rubber composition is characterized in that the vegetable oil is a fatty acid ester triglyceride in which a fatty acid containing at least a saturated fatty acid and an unsaturated fatty acid is ester-bonded to glycerol, and the ratio of the unsaturated fatty acid in the fatty acid is 50% by mass or more.

2. The rubber composition according to claim 1, wherein the vegetable oil has a ratio of polyunsaturated fatty acids in the unsaturated fatty acids of 15% by mass or more.

3. The rubber composition according to claim 1, wherein the vegetable oil has an iodine value of 100 or more.

4. The rubber composition according to claim 1, wherein the amount of vegetable oil added is 5 to 20 parts by mass when the total amount of diene rubber is 100 parts by mass.

5. The rubber composition according to claim 1, wherein the amount of porous cellulose particles is 0.5 to 5.0 parts by mass when the total amount of diene rubber is 100 parts by mass.

6. A pneumatic tire comprising vulcanized rubber of the rubber composition described in claim 1.

7. A studless tire comprising vulcanized rubber of the rubber composition described in claim 1 in the tread portion.

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