Rubber composition and studless tire using the same

Abstract

On icy and snowy roads, the coefficient of friction is lower than on normal roads, making them more slippery. Therefore, conventionally, studless tires have been required to have improved performance on ice. [Solution] The above problem was solved by a rubber composition comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler, and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or fewer vertices.

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 road surfaces, the friction coefficient is lower than that on general road surfaces, making it easier to slip. Therefore, conventionally, many methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. Techniques for blending metals into rubber compositions for the purpose of improving ice performance are disclosed in, for example, Patent Documents 1 to 4 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] An 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 Problems

[0005] As a result of intensive research by the present inventors, it has been found that the above problems can be solved by blending a specific amount of an inorganic filler and a specific amount of a metal oxide having a specific shape into a diene - based rubber, and the present invention has been completed. 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 an inorganic filler, and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or fewer vertices.

[0006] The present invention also provides a studless tire using the above-mentioned rubber composition in the tread. [Effects of the Invention]

[0007] 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 an inorganic filler, and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or fewer vertices. Therefore, it is possible to provide a rubber composition with excellent ice performance and a studless tire using the same.

[0008] The metal oxide used in this invention has a polyhedral structure with six or fewer vertices, resulting in the presence of sharp angles within the metal oxide. This provides a sufficient scratching effect on the road surface, improving performance on ice. [Modes for carrying out the invention]

[0009] The present invention will be described in more detail below.

[0010] (Diene-based rubber) Examples of diene rubbers used in the present invention include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and acrylonitrile-butadiene copolymer rubber (NBR). Furthermore, the molecular weight and microstructure of the diene rubber used in the present invention are not particularly limited, and it may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or it may be epoxidized. The weight-average molecular weight (Mw) of the above diene rubber is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000. In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are standard polystyrene equivalent values ​​obtained by gel permeation chromatography (GPC) measurement. Furthermore, from the viewpoint of improving performance on ice, it is preferable that butadiene rubber accounts for 50 parts by mass or more in 100 parts by mass of diene rubber. 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] (Inorganic fillers) Examples of inorganic 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. Examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These may be used alone or in combination of two or more. Silica made from biomass materials such as rice husks may also be used.

[0012] From the viewpoint of improving ice performance, silica preferably has a CTAB adsorption specific surface area of 50 to 300 m 2 / g, more preferably 90 to 220 m 2 / g. The CTAB adsorption specific surface area is a value measured in accordance with JIS K6430:2008.

[0013] (Carbon black) In addition, it is preferable to incorporate carbon black into the rubber composition of the present invention. Specific examples of carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF. These may be used alone or in combination of two or more. From the viewpoint of improving ice performance, carbon black preferably has a nitrogen adsorption specific surface area (N2SA) of 10 to 300 m 2 / g, more preferably 50 to 150 m 2 / g. The nitrogen adsorption specific surface area (N2SA) is a value measured in accordance with JIS K 6217-2:2001, "Part 2: Method for determining specific surface area - Nitrogen adsorption method - Single point method".

[0014] [[ID=]]](Metal oxide) The metal oxide used in the present invention has a polyhedral structure with 6 or fewer vertices. Such polyhedral structures typically include tetrahedral structures, octahedral structures, etc. In other words, it can be said that the metal oxide used in the present invention has two or more acute corners in one particle. - From the viewpoint of exerting a sufficient scratching effect on the road surface, it is preferable that the metal oxide used in the present invention satisfies one or more of the following forms. (1) The average particle size is preferably from 0.1 μm to 200 μm, more preferably from 0.1 μm to 80 μm. The average particle size is determined by measuring the length of the perpendicular formed by sandwiching the particles with two parallel lines in a certain direction under electron microscope observation and calculating the average value thereof. That is, it is the so-called Feret diameter. (2) It is preferably an oxide of a transition metal of Group 3 to Group 11, more preferably iron oxide. (3) Those containing 80% by mass or more of iron are preferred. In the form of (2) above, the composition of the iron oxide is not limited, but from the viewpoint of improving the effects of the present invention, it is preferable to use ferrite. Ferrite typically has a composition of AFe2O4 (A represents Mn, Co, Ni, Cu, Zn, etc.). As the ferrite having the forms of (1) to (3) above, commercially available ones can be used. For example, the product name EPT-1002 manufactured by Toda Kogyo Corporation (containing iron (Group 8) and manganese (Group 7) as metals, having an octahedral shape, average particle size = 0.23 μm, containing 99.6% by mass of iron), EPT-4L (containing iron (Group 8) and manganese (Group 7) as metals, having an octahedral shape, average particle size = 1.5 μm, containing 99.6% by mass of iron), etc. can be mentioned. Note that the metal oxide having a polyhedral structure with 6 or less vertices in the present invention does not include acicular substances having an aspect ratio of 10:1 or more and amorphous structures having no specific shape such as crushed shapes.

[0015] (Blending ratio of rubber composition) The rubber composition of the present invention is characterized in that 30 to 100 parts by mass of an inorganic filler and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or less vertices are blended with respect to 100 parts by mass of a diene rubber. When the content of the inorganic filler is less than 30 parts by mass, the mechanical properties and abrasion resistance of the rubber composition deteriorate. On the contrary, when it exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition decreases and the performance on ice deteriorates. If the content of the aforementioned metal oxide is less than 0.5 parts by mass, the content is too low to achieve the effects of the present invention, and if it exceeds 50 parts by mass, physical properties such as fracture strength and elongation will decrease. The inorganic filler content is preferably 30 to 70 parts by mass per 100 parts by mass of diene rubber. Furthermore, the content of the metal oxide is preferably 10 to 50 parts by mass per 100 parts by mass of diene rubber.

[0016] (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; silane coupling agents; zinc oxide; various fillers; antioxidants; plasticizers; and reinforcing materials. 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.

[0017] The rubber composition of the present invention is suitable for manufacturing pneumatic tires according to conventional methods for manufacturing pneumatic tires, and is preferably used to manufacture pneumatic tires that can be filled with air, nitrogen or other inert gases, and other gases. Furthermore, since the rubber composition of the present invention has excellent ice performance, it is preferable to apply it to the tread, especially the cap tread, to make a studless tire. [Examples]

[0018] 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.

[0019] Standard example, Examples 1-5, and Comparative Examples 1-4 In the formulations (parts by mass) shown in Table 1, the components excluding the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 1.7-liter sealed Banbury mixer. Then, the vulcanization accelerator and sulfur were added and kneaded further to obtain a rubber composition. Next, the obtained unvulcanized rubber composition was press-vulcanized in a predetermined mold at 160°C for 20 minutes to obtain vulcanized rubber test pieces, and the physical properties of the vulcanized rubber test pieces were measured using the test method described below.

[0020] Ice performance: The obtained vulcanized rubber test piece (2 mm thick) was attached to a flat cylindrical rubber base, and tested using an inside drum type ice friction tester at a temperature of -1.5°C and a load of 5.5 kg / cm². 2 The coefficient of friction on ice was measured under the condition of a drum rotation speed of 25 km / h. The obtained coefficient of friction on ice is shown as an index, with the standard example value set to 100. A larger index indicates greater friction on ice and superior ice performance.

[0021] The results are shown in Table 1.

[0022] [Table 1]

[0023] *1: NR (TSR20 manufactured by PT.NUSIRA (SAD)) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd.) *3: Carbon black (Show Black N339 manufactured by Cabot Japan Co., Ltd.) *4: Silica (EVONIK WELLINK ULTRASIL VN3GR) *5: Silane coupling agent (EVONIK Si69) *6: Metal oxide 1 (MTH-310 manufactured by Toda Kogyo Co., Ltd., ferrite, contains iron (Group 8) and manganese (Group 7) as metals, has a hexahedral shape, average particle size = 0.20 μm, contains 99.6% by mass of iron) *7: Metal oxide 2 (MAT-503 manufactured by Toda Kogyo Co., Ltd., ferrite, containing iron (Group 8) and manganese (Group 7) as metals, spherical in shape, average particle size = 0.23 μm, containing 99.6% by mass of iron) *8: Metal oxide 3 (140ED manufactured by Toda Kogyo Co., Ltd., ferrite, contains iron (Group 8) as a metal, amorphous, average particle size = 0.21 μm, contains 100% iron by mass) *9: Metal oxide 4 (TSY-1 manufactured by Toda Kogyo Co., Ltd., ferrite, contains iron (Group 8) as a metal, needle-shaped, average particle size (long axis) = 1.0 μm, contains 100% iron by mass) *10: Metal oxide 5 (EPT-1002 manufactured by Toda Kogyo Co., Ltd. (contains iron (Group 8) and manganese (Group 7) as metals, has an octahedral shape, average particle size = 0.23 μm, contains 99.6% by mass of iron)) *11: Metal oxide 6 (EPT-4L manufactured by Toda Kogyo Co., Ltd. (contains iron (Group 8) and manganese (Group 7) as metals, has an octahedral shape, average particle size = 1.5 μm, contains 99.6% by mass of iron)) *12: Vulcanization accelerator (Noxellar CZ-G, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *13: Sulfur (Finely powdered sulfur containing Kinka oil, manufactured by Tsurumi Chemical Industries Co., Ltd.)

[0024] The results in Table 1 show that the rubber compositions of each example contain 30 to 100 parts by mass of inorganic filler and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or fewer vertices, per 100 parts by mass of diene rubber, resulting in improved ice performance compared to the standard example. In contrast, the metal oxide used in Comparative Example 1 has a hexahedral shape with more than six vertices, so no improvement in ice performance was observed. The metal oxide used in Comparative Example 2 exhibited a spherical shape, and therefore no improvement in ice performance was observed. The metal oxide used in Comparative Example 3 exhibited an amorphous structure, and therefore no improvement in ice performance was observed. The metal oxide used in Comparative Example 4 exhibited a needle-like shape, and therefore no improvement in ice performance was observed.

[0025] The present invention encompasses the following embodiments. Embodiment 1: A rubber composition characterized by comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler, and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or fewer vertices. Embodiment 2: The rubber composition according to Embodiment 1, characterized in that the average particle size of the metal oxide is 0.1 μm to 200 μm. Embodiment 3: The rubber composition according to Embodiment 1 or 2, characterized in that the metal oxide is an oxide of a transition metal of Group 3 to Group 11. Embodiment 4: The rubber composition according to any one of Embodiments 1 to 3, characterized in that the metal oxide contains 80% by mass or more of iron. Embodiment 5: The rubber composition according to any one of Embodiments 1 to 4, characterized in that butadiene rubber accounts for 50 parts by mass or more in 100 parts by mass of the diene rubber. Embodiment 6: A rubber composition according to any one of embodiments 1 to 5, characterized in that it is used in studless tires. Embodiment 7: A studless tire using the rubber composition described in any of Embodiments 1 to 6 for the tread.

Claims

1. A rubber composition characterized by comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler, and 0.5 to 50 parts by mass of a metal oxide having a polyhedral structure with 6 or fewer vertices.

2. The rubber composition according to claim 1, characterized in that the average particle size of the metal oxide is 0.1 μm to 200 μm.

3. The rubber composition according to claim 1, characterized in that the metal oxide is an oxide of a transition metal belonging to Group 3 to Group 11.

4. The rubber composition according to claim 1, characterized in that the metal oxide contains 80% by mass or more of iron.

5. The rubber composition according to claim 1, characterized in that butadiene rubber accounts for 50 parts by mass or more of 100 parts by mass of the diene rubber.

6. The rubber composition according to claim 1, characterized in that it is used in studless tires.

7. A studless tire using the rubber composition described in claim 6 for the tread.

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