Rubber composition and studless tire using the same

Abstract

To solve the problem in which: icy and snowy roads tend to have a lower friction coefficient than general roads, leading to slipperiness; numerous techniques have been proposed to improve the on-ice performance of studless tires, but further enhancements are still needed for their on-ice performance.SOLUTION: The foregoing problem is solved by a rubber composition that contains 100 pts.mass of diene rubber, blended with carbon black and / or white filler of 30-100 pts.mass and elastic graphitized carbon of 0.5-30 pts.mass.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a rubber composition and a studless tire using the same, and more particularly, to a rubber composition having excellent ice performance and a studless tire using the same.

Background Art

[0002] On icy and snowy roads, the friction coefficient is lower than that on ordinary roads, making it easier to slip. Therefore, conventionally, many methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. For example, a method is known in which hard foreign substances or hollow polymers are blended into a studless compound, and by forming micro irregularities on the rubber surface, the water film generated on the ice surface is removed to improve the ice friction. There are also methods such as blending polymer fine particles into the studless compound to impart roughness to the tread surface. Currently, there is a need for a method to more efficiently impart roughness to the tread surface.

[0003] For example, Patent Documents 1 and 2 below disclose a technique of blending expanded graphite to enhance the ice performance of a rubber composition for tires. However, expanded graphite does not have the elasticity possessed by elastic graphitized carbon as described below.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of the present invention is to provide a rubber composition having excellent ice performance and a studless tire using the same. [Means for solving the problem]

[0006] As a result of diligent research, the inventors of the present invention have discovered that a rubber composition comprising diene-based rubber, carbon black and / or a white filler, and a specific amount of elastographitized carbon can solve the above problems, and have completed the present invention.

[0007] In other words, the present invention provides a rubber composition characterized by comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of elastic graphitized carbon. [Effects of the Invention]

[0008] The rubber composition of the present invention is characterized by comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of elastic graphitized carbon, thereby providing a rubber composition with excellent ice performance and a studless tire using the same.

[0009] The elastic graphitized carbon in this invention has numerous voids within its particles, which imparts elasticity. Although the detailed mechanism is not yet clear, it is presumed that these voids and elasticity contribute to the imparting of roughness to the rubber itself and improve its grip. This, in turn, enhances performance on ice. [Modes for carrying out the invention]

[0010] The present invention will be described in more detail below. (Diene-based rubber) The diene rubber used in this invention can be any diene rubber that can be blended into the rubber composition, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and ethylene-propylene-diene polymer (EPDM). These may be used individually or in combination of two or more. Furthermore, their molecular weight and microstructure are not particularly limited, and they may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or epoxidized. Furthermore, from the viewpoint of improving ice performance, it is preferable that butadiene rubber accounts for 30 parts by mass or more, preferably 40 parts by mass or more, of 100 parts by mass of diene rubber, and a form that uses natural rubber in combination is even more preferable. Furthermore, it is preferable that the diene-based rubber has a glass transition temperature (Tg) of -50°C or lower. By specifying the Tg in this way, the performance on ice is improved. When multiple types of diene rubber are included, the Tg as used herein is calculated based on the weighted average, which is the sum of the products obtained by multiplying the glass transition temperature of each rubber by the weight fraction of each rubber. For calculation purposes, the sum of the weight fractions of each component is assumed to be 1.0. In this invention, the glass transition temperature (Tg) refers to the temperature at the midpoint of the transition region, measured by differential scanning calorimetry (DSC) at a heating rate of 20°C / min using a thermogram. A more preferable average Tg is -60°C or lower.

[0011] (Carbon black and / or white filler) Examples of carbon blacks used in the present invention include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF, which may be used individually or in combination of two or more. Furthermore, carbon black has a nitrogen adsorption specific surface area (N2SA) of 10-300 m², which is beneficial for improving ice performance. 2 It is preferable that the amount is / g, and 50-150m2 It is even more preferable that it be / g. The nitrogen adsorption specific surface area (N2SA) was measured according to JIS K 6217-2:2001 "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0012] Examples of white fillers used in the present invention include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium dioxide, calcium sulfate, etc. These may be used individually or in combination of two or more. Of these, silica is preferred because it provides better performance on ice.

[0013] Examples of silica include wet silica (hydrated silica), dry silica (anhydrous silica), calcium silicate, and aluminum silicate. These can be used individually or in combination of two or more.

[0014] From the perspective of improving ice performance, silica has a CTAB adsorption specific surface area of ​​50-300 m². 2 It is preferable that the amount is / g, and 90-200m 2 It is even more preferable that it be / g. The CTAB adsorption specific surface area is the value obtained by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed onto the silica surface according to JIS K6217-3:2001 "Part 3: Method for determining specific surface area - CTAB adsorption method".

[0015] (Elastic graphitized carbon) The elastic graphitized carbon used in this invention is obtained by expanding and foaming a carbon material consisting of carbonaceous mesoface or coke, and then graphitizing it at a temperature of 1900°C to 2700°C so that the degree of graphitization measured by X-ray diffraction is 80 to 95%. It has the characteristic of having a large volume recovery rate when a compressive load is applied and then removed. Superior Graphite's RGC series and others can be used as elastic graphitized carbon.

[0016] Moreover, the elasticity of the graphitized carbon is preferably 50% or more. Here, the elasticity referred to in the present invention means that when a pressure of 5000 psi (34.47 MPa) is applied to the graphitized carbon, the height of the sample when the pressure is released is 150% or more compared to the height of the sample during pressurization. The method for measuring the elasticity of the graphitized carbon is known and is described in, for example, the book (Advances in Ceramics for Environmental, Functional, Structural, and Energy Applications).

[0017] Moreover, the average particle size of the graphitized carbon is preferably 300 μm or less, more preferably 1 μm or more and 200 μm or less, and particularly preferably 1 μm or more and 100 μm or less. By defining the average particle size in this way, the effect of further improving the performance on ice can be achieved. The average particle size in the present invention refers to the average value of the equivalent circle diameters measured using an electron microscope, a laser microscope, etc. For example, it can be measured with a laser diffraction scattering type particle size distribution measuring device LA-300 (manufactured by Horiba, Ltd.), a laser microscope VK-8710 (manufactured by Keyence Corporation), etc.

[0018] (Blending ratio of rubber composition) The rubber composition of the present invention is characterized in that 30 to 100 parts by mass of carbon black and / or white filler and 0.5 to 30 parts by mass of graphitized carbon are blended with respect to 100 parts by mass of the diene rubber. When the blending amount of the carbon black and / or white filler is less than 3 parts by mass with respect to the 100 parts by mass of the diene rubber, the mechanical properties and abrasion resistance of the rubber composition deteriorate. Conversely, when it exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition decreases and the performance on ice deteriorates. When the blending amount of the graphitized carbon is less than 0.5 parts by mass with respect to the 100 parts by mass of the diene rubber, the addition amount is too small to achieve the effect of the present invention. Conversely, when it exceeds 30 parts by mass, the mechanical properties deteriorate.

[0019] The amount of carbon black and / or white filler added is preferably 40 to 90 parts by mass per 100 parts by mass of diene rubber. The amount of elastic graphitized carbon added is preferably 5 to 20 parts by mass per 100 parts by mass of diene rubber.

[0020] (Other ingredients) In addition to the components mentioned above, the rubber composition of the present invention may contain various additives commonly used in rubber compositions, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; zinc oxide; antioxidants; plasticizers; silane coupling agents; and thermally expandable microcapsules. These additives can be mixed in a conventional manner to form a composition which can then be used for vulcanization or crosslinking. The amounts of these additives can also be conventional amounts, as long as they do not contradict the purpose of the present invention.

[0021] Furthermore, the tire of the present invention can be prepared using the rubber composition of the present invention, and is preferably a pneumatic tire, which can be filled with air, nitrogen or other inert gases, and other gases. The tire of the present invention is also preferably applied to a tread, especially a capped tread, to form a studless tire. [Examples]

[0022] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0023] Standard example, Examples 1-7, Comparative example 1 In the formulations (parts by mass) shown in Table 1, the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then released from the mixer and cooled to room temperature. Subsequently, the composition was put back into the same Banbury mixer, the vulcanization system was added and kneaded to obtain a rubber composition. The obtained rubber composition was press-vulcanized at 170°C for 10 minutes, and its physical properties were measured using the test methods described below.

[0024] Ice Performance: Samples were prepared by attaching the obtained vulcanized rubber test pieces to a flattened cylindrical rubber base. The ice friction coefficient was measured using an ice friction tester under the conditions of a measurement temperature of -1.5°C, a load of 98N, and a road surface speed of 20km / h. The obtained ice friction coefficient is expressed as an index, with the standard example value set to 100. A larger index indicates greater ice friction and superior ice performance. Sdr: Sdr was measured in accordance with ISO 25178. The results are shown as an exponent, with the standard example value set to 100. A larger exponent indicates a larger surface area. The results are shown in Table 1.

[0025] [Table 1]

[0026] *1: NR (RSS#3) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd.) *3: Carbon black (Seast KHA manufactured by Tokai Carbon Co., Ltd.) *4: Silica (Zeosil 1165MP manufactured by Rhodia, CTAB specific surface area = 159 m²) 2 / g) *5: Silane coupling agent (Si69 manufactured by Evonik DeGussa, bis(3-triethoxysilylpropyl)tetrasulfide) *6: Oil (Extract No. 4S manufactured by Showa Shell Sekiyu K.K.) *7: Graphite (GR-15 manufactured by Nippon Graphite Industries Co., Ltd., non-elastic) *8: Elastic graphitized carbon 1 (RGC14A manufactured by Superior Graphite, average particle size = approximately 250 μm) *9: Elastic graphitized carbon 2 (RGC39A manufactured by Superior Graphite, average particle size = 8-10 μm) *10: Sulfur (Finely powdered sulfur containing Kinka oil, manufactured by Tsurumi Chemical Industries Co., Ltd.) *11: Vulcanization accelerator (Noxellar CZ-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0027] As shown in Table 1, the rubber compositions of each example consist of 100 parts by mass of diene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of elastic graphitized carbon. Compared to the standard example, the Sdr is increased and the ice performance is improved. In contrast, Comparative Example 1, which incorporated graphite that does not have elasticity, was unable to improve ice performance compared to the standard example.

[0028] This disclosure encompasses the following inventions: Invention [1]: A rubber composition characterized by comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of elastic graphitized carbon. Invention [2]: The rubber composition according to Invention 1, characterized in that the elasticity of the elastic graphitized carbon is 50% or more. Invention [3]: The rubber composition according to Invention 1 or 2, characterized in that the average particle size of the elastic graphitized carbon is 300 μm or less. Invention [4]: ​​The rubber composition according to any one of Inventions 1 to 3, characterized in that butadiene rubber accounts for 30 parts by mass or more in 100 parts by mass of the diene rubber. Invention [5]: A studless tire using the rubber composition described in any of Inventions 1 to 4.

Claims

1. Per 100 parts by mass of diene rubber, add 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of elastic graphitized carbon. A rubber composition for studless tires characterized by being formulated in a specific way.

2. The rubber composition for studless tires according to claim 1, characterized in that the elasticity of the elastic graphitized carbon is 50% or more.

3. The rubber composition for studless tires according to claim 1, characterized in that the average particle size based on the particle sizes of a plurality of elastographite carbon particles measured with a laser microscope is 300 μm or less.

4. The rubber composition for studless tires according to claim 1, characterized in that butadiene rubber accounts for 30 parts by mass or more of the diene-based rubber in 100 parts by mass.

5. A studless tire using the rubber composition for studless tires described in claim 1.

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