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 braking performance (grip performance) on icy road surfaces and response performance such as steering response and driving stability (anti-wandering performance) on icy road surfaces (ice road surfaces). [Solution] A rubber composition containing a diene rubber, a filler, an oil, and water-soluble cellulose. Preferably, the composition contains 1 to 25 parts by mass of water-soluble cellulose per 100 parts by mass of diene rubber. Preferably, the water-soluble cellulose is such that at least some of the hydrogen atoms of the hydroxyl groups of cellulose are substituted with at least one substituent selected from the group consisting of carboxyalkyl groups and hydroxyalkyl groups. Preferably, the water-soluble cellulose has a viscosity of 5,000 to 15,000 mPa·s when prepared as a 1% aqueous solution at 23°C.

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 frozen road surfaces (ice roads). 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 the improvement of response performance such as steering response performance and driving stability performance (anti-wandering performance) on ice roads is required.

[0003] In Patent Document 1 below, a studless tire rubber composition is described, which comprises 2 to 30 parts by weight of cellulose fine powder having an average particle diameter of 100 μm or less with respect to 100 parts by weight of a rubber component composed of a diene rubber.

[0004] In Patent Document 2 below, a rubber composition for tires is described, which is characterized in that 25 to 125 parts by mass of a filler containing silica is blended with respect to 100 parts by mass of a rubber component composed of natural rubber and / or diene rubber, and 0.1 to 30 parts by mass of carboxyalkyl cellulose having an etherification degree of 0.1 to 1.0 and an average particle diameter of 20 to 100 μm is blended.

[0005] In Patent Document 3 below, a winter tire is described, the tread of which contains a rubber composition comprising at least a diene elastomer, 50 to 100 phr of a liquid plasticizer, and a reinforcing filler between 50 and 150 phr, and the composition further comprises magnesium sulfate fine powder as water-soluble fine particles between 2 and 50 phr, and PVA fibers as water-soluble short fibers between 2 and 50 phr.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-29708 [Patent Document 2] Patent No. 5694010 [Patent Document 3] Patent No. 5778172 [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 a diene rubber, a filler, an oil, and water-soluble cellulose.

[0010] In the above rubber composition (1), a rubber composition (2) containing 1 to 25 parts by mass of the water-soluble cellulose per 100 parts by mass of the diene rubber is preferred.

[0011] In the above rubber composition (1) or (2), a preferred rubber composition (3) is one in which the water-soluble cellulose is substituted with at least one substituent selected from the group consisting of carboxyalkyl groups and hydroxyalkyl groups, in which at least some of the hydrogen atoms of the hydroxyl groups of the cellulose are replaced.

[0012] Of the above rubber compositions (1) to (3), rubber composition (4) is preferred, wherein the water-soluble cellulose has a viscosity of 5,000 to 15,000 mPa·s when it is prepared as a 1% aqueous solution at 23°C.

[0013] The present invention also relates to a pneumatic tire (5) comprising at least the vulcanized rubber of the above rubber compositions (1) to (4), and more particularly to a studless tire (6) comprising at least the vulcanized rubber of the above rubber compositions (1) to (4) in the tread portion. [Effects of the Invention]

[0014] The rubber composition according to the present invention contains a filler, oil, and water-soluble cellulose in a diene-based rubber. A vulcanized rubber composition having this configuration can improve grip performance and responsiveness on icy surfaces in a well-balanced manner. While the reason for this effect is not entirely clear, the presence of the filler and oil improves the dispersibility of water-soluble cellulose in the diene-based rubber. Therefore, even on the tire surface in contact with the icy road, the water-soluble cellulose is uniformly dispersed, allowing it to efficiently absorb and remove water from the icy road surface during tire operation. As a result, it is believed that the grip performance and responsiveness of the vulcanized rubber on icy surfaces are improved in a well-balanced manner.

[0015] 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]

[0016] The rubber composition according to the present invention contains diene rubber, filler, oil, and water-soluble cellulose.

[0017] 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, and styrene-isoprene-butadiene copolymer rubber. These can be used individually or in combination of two or more.

[0018] Examples of fillers include silica and carbon black.

[0019] As silica, wet silica, dry silica, sol-gel silica, and surface-treated silica, which are commonly used for rubber reinforcement, can be used. Among these, wet silica is preferred. From the viewpoint of solving the problem, the rubber composition according to the present invention preferably contains 20 to 100 parts by mass of silica, and more preferably 30 to 80 parts by mass, when the total amount of diene-based rubber is 100 parts by mass.

[0020] 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 1 to 20% by mass, when the total amount of silica is considered to be 100% by mass.

[0021] As carbon black, in addition to carbon black commonly used in the rubber industry, such as SAF, ISAF, HAF, FEF, and GPF, conductive carbon blacks such as acetylene black and Ketjen black can be used. In the rubber composition according to the present invention, the carbon black content is preferably 1 to 30 parts by mass when the total amount of diene rubber is 100 parts by mass.

[0022] Examples of the oil include mineral oils such as paraffinic oil, naphthenic oil, and aromatic oil, and vegetable oils such as linseed oil, safflower oil, soybean oil, corn oil, castor oil, rapeseed oil, and cottonseed oil. Any one or a combination of two or more of these can be used. In the rubber composition according to the present invention, when the total amount of the diene rubber is 100 parts by mass, the oil content is preferably 0 to 30 parts by mass.

[0023] Cellulose has many hydroxyl groups (-OH) which are hydrophilic groups, but it is not soluble in water as it is. Water-soluble cellulose is obtained by using cellulose (pulp) widely distributed in nature as a raw material, treating it with caustic soda, and then performing various treatments to make it water-soluble. In the present invention, as the water-soluble cellulose, it is preferable that at least a part of the hydrogen atoms of the hydroxyl groups of the cellulose is substituted with at least one substituent selected from the group consisting of carboxyalkyl groups and hydroxyalkyl groups. Examples of the carboxyalkyl group include carboxymethyl group, carboxyethyl group, and carboxypropyl group. Examples of the hydroxyalkyl group include hydroxymethyl group, hydroxyethyl group, and hydroxypropyl group.

[0024] In the present invention, when the water-soluble cellulose efficiently absorbs and removes the water film on the ice road surface during tire running, the grip performance and response performance of the vulcanized rubber on the ice road surface are improved in a balanced manner. Particularly, when the water-soluble cellulose is a 1% aqueous solution at 23°C and has a viscosity of 5000 to 15000 mPa·s, the water-soluble cellulose can absorb and remove the water film on the ice road surface more efficiently during tire running. As a result, it is preferable because the grip performance and response performance of the vulcanized rubber on the ice road surface are improved in a balanced manner. In the present invention, from the viewpoint of solving the problem, it is more preferable to use water-soluble cellulose having a viscosity of 8000 to 15000 mPa·s when it is a 1% aqueous solution at 23°C.

[0025] From the viewpoint of solving the problem, in the rubber composition according to the present invention, it is preferable to contain 1 to 25 parts by mass of water-soluble cellulose per 100 parts by mass of diene rubber, and more preferably 2 to 20 parts by mass.

[0026] The rubber composition according to the present invention contains diene rubber, fillers, oils, and water-soluble cellulose. In addition to these, the rubber composition according to the present invention may also contain vulcanizing agents, vulcanization accelerators, antioxidants, stearic acid, softeners such as waxes and oils, processing aids, and the like.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The rubber composition according to the present invention is obtained by mixing diene rubber, fillers, oil, water-soluble cellulose, vulcanizing agents, vulcanization accelerators, zinc oxide, antioxidants, stearic acid, softeners such as wax, processing aids, etc., using a kneader commonly used in the rubber industry, such as a Banbury mixer, kneader, and rolls.

[0031] 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.

[0032] 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]

[0033] The present invention will be described in more detail below by illustrating some embodiments.

[0034] (Preparation of rubber composition for tires) To 100 parts by mass of rubber components, the rubber compositions of Examples 1-7 and Comparative Examples 1-4 were blended according to the formulations in Tables 1-2, and the mixture was kneaded using a standard Banbury mixer to prepare a rubber composition for tires. The compounding agents listed in Tables 1-2 are shown below.

[0035] (Diene-based rubber) • Natural rubber: RSS#3 • Butadiene rubber: Product name "BR730", manufactured by ENEOS Material Co., Ltd. (Filler) • Carbon Black: Product name "Seast 7HM", manufactured by Tokai Carbon Co., Ltd. • Silica: Product name "NipSeal AQ", manufactured by Tosoh Silica Co., Ltd. (oil) • Oil: Product name "Process P200", manufactured by ENEOS Corporation (Water-soluble cellulose) • Water-soluble carboxymethylcellulose (1): Product name "F1400MC", manufactured by Nippon Paper Industries, viscosity of 1% aqueous solution at 23°C: 13000 mPa·s • Water-soluble hydroxyethylcellulose (2): Product name "SE900", manufactured by Daicel Corporation, viscosity of 5000 mPa·s in a 1% aqueous solution at 23°C. • Water-soluble hydroxypropyl methylcellulose (3): Trade name "90SH", manufactured by Shin-Etsu Chemical Co., Ltd., viscosity of 1% aqueous solution at 23°C: 10,000 mPa·s • Water-soluble carboxymethylcellulose (4): Product name "F10MC", manufactured by Nippon Paper Industries, viscosity of 1% aqueous solution at 23°C: 100 mPa·s (Other combination drugs) • Insoluble carboxymethylcellulose: Product name "SLD-F1", manufactured by Nippon Paper Industries, viscosity of 1% aqueous solution at 23°C: 100 mPa·s • Unmodified cellulose: Product name "KC Floc", manufactured by Nippon Paper Industries, viscosity of 1% aqueous solution at 23°C is 10 mPa·s • Water-soluble polyvinyl alcohol: Product name "Poval", manufactured by Kuraray Co., Ltd., viscosity of 1% aqueous solution at 23°C is 5 mPa·s • Silane coupling agent: Product name "Si-75", manufactured by Evonik. • 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 Co., Ltd. • Terpene resin: Product name "SYLVATRAXX 4150", manufactured by Kraton. • Vulcanization accelerator 1: Product name "Soxinol CZ", manufactured by Sumitomo Chemical Co., Ltd. • Vulcanization accelerator 2: Product name "Noxellar DZ-G", manufactured by Ouchi Shinko Chemical Co., Ltd. • Sulfur: Product name "Powdered Sulfur", manufactured by Tsurumi Chemical Industry Co., Ltd.

[0036] After preparing unvulcanized samples of the rubber compositions obtained in Examples 1-7 and Comparative Examples 1-4, the braking performance and response performance on ice surfaces were evaluated under the following conditions.

[0037] (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.

[0038] (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.

[0039] [Table 1]

[0040] From the results in Table 1, it can be seen that in Example 1, the use of water-soluble carboxymethylcellulose (1), a water-soluble cellulose derivative, allows for a balance between ice braking performance and response performance compared to Comparative Example 1 (conventional technology). Furthermore, in Examples 2 to 4, it can be seen that even when varying the amount of water-soluble carboxymethylcellulose (1), a water-soluble cellulose derivative, a balance between ice braking performance and response performance can be achieved compared to Comparative Example 1 (conventional technology). On the other hand, in Comparative Example 2, even when insoluble carboxymethylcellulose is used, both ice braking performance and response performance do not improve or worsen compared to Comparative Example 1 (conventional technology). Furthermore, in Comparative Example 3, even when water-soluble polyvinyl alcohol is used, both ice braking performance and response performance do not improve or do not improve sufficiently compared to Comparative Example 1 (conventional technology).

[0041] [Table 2]

[0042] From the results in Table 2, it can be seen that in Examples 5 to 7, even when using water-soluble cellulose derivatives such as water-soluble hydroxyethylcellulose (2), water-soluble hydroxypropylmethylcellulose (3), and water-soluble carboxymethylcellulose (4), both ice braking performance and response performance can be achieved compared to Comparative Example 1 (prior art). On the other hand, in Comparative Example 4, even when using unmodified cellulose, both ice braking performance and response performance do not improve or worsen compared to Comparative Example 1 (prior art).

Claims

1. A rubber composition containing diene rubber, fillers, oil, and water-soluble cellulose.

2. The rubber composition according to claim 1, wherein the composition contains 1 to 25 parts by mass of the water-soluble cellulose with respect to 100 parts by mass of the diene rubber.

3. The rubber composition according to claim 1, wherein the water-soluble cellulose is substituted with at least one substituent selected from the group consisting of carboxyalkyl groups and hydroxyalkyl groups, wherein at least a portion of the hydrogen atoms of the hydroxyl groups of the cellulose are substituted with at least one substituent selected from the group consisting of carboxyalkyl groups and hydroxyalkyl groups.

4. The rubber composition according to claim 1, wherein the water-soluble cellulose has a viscosity of 5,000 to 15,000 mPa·s when it is prepared as a 1% aqueous solution at 23°C.

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

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

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