Rubber composition and studless tire using the same

Abstract

On icy and snowy roads, the coefficient of friction decreases compared to normal roads, making them more slippery. Therefore, numerous methods have been proposed to improve the ice performance of studless tires, but there is a need to further enhance ice performance. Furthermore, there is a need to reduce the environmental impact and ensure that physical properties such as elongation at break are practically sufficient. [Solution] The above problem was solved by a rubber composition characterized by comprising 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of alkaline earth metal salts having a particle size of 20 μm to 100 μm.

Description

[Technical Field]

[0001] The present invention relates to a rubber composition and a studless tire using the same, and more specifically, to a rubber composition that suppresses environmental impact, has sufficient physical properties for practical use, and has excellent ice performance, and a studless tire using the same. [Background technology]

[0002] On icy and snowy roads, the coefficient of friction decreases compared to normal roads, making them more slippery. Therefore, numerous methods have been proposed to improve the ice performance (braking ability on ice) of studless tires. Known techniques for improving ice performance include, for example, the addition of polymer microparticles to give the tread surface roughness. However, with the conventional technologies described above, the polymer compounds that detach from the tread surface are not decomposed, raising concerns about environmental problems. In addition, tires require sufficient physical properties such as elongation at break for practical use. Patent Document 1 discloses a rubber composition comprising 0.3 to 30 parts by weight of porous hydroxyapatite powder per 100 parts by weight of diene rubber. However, Patent Document 1 does not disclose any technical concept for improving ice performance by incorporating alkaline earth metal salts with particle sizes of 20 μm to 100 μm, as described below. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-285536 [Overview of the project] [Problems that the invention aims to solve]

[0004] The object of the present invention is to provide a rubber composition that suppresses environmental impact, has sufficient physical properties for practical use, and has excellent ice performance, as well as a studless tire using the same. [Means for solving the problem]

[0005] As a result of diligent research, the inventors of the present invention have discovered that a rubber composition obtained by blending carbon black and / or a white filler with a diene-based rubber having the measured composition, and by blending a specific amount of alkaline earth metal salt having a specific particle size, can solve the above problems, and have completed the present invention.

[0006] In other words, the present invention provides a rubber composition characterized by comprising 100 parts by mass of a diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of an alkaline earth metal salt having a particle size of 20 μm to 100 μm.

[0007] The present invention also provides a studless tire using the aforementioned rubber composition. [Effects of the Invention]

[0008] The rubber composition of the present invention is characterized by comprising 100 parts by mass of a diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of an alkaline earth metal salt with a particle size of 20 μm to 100 μm. Therefore, it is possible to provide a rubber composition and a studless tire using the same that suppresses environmental impact, has sufficient physical properties for practical use, and has excellent ice performance.

[0009] The alkaline earth metal salts used in this invention have a particle size of 20 μm to 100 μm. This particle size allows for an appropriate surface roughness on the tread surface, improving ice performance without impairing physical properties such as tensile strength. Furthermore, the alkaline earth metal salts used in this invention have sufficient hardness and exhibit a scratching effect on the road surface. This further enhances ice performance. In addition, the alkaline earth metal salts used in this invention can be natural products or derived from natural products, and even if they detach from the tread surface, they are less likely to cause environmental problems. [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. 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 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. In addition, it is preferable that the diene rubber is composed of natural rubber and butadiene 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] (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 50-150m 2 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. Among these, silica is preferred because of better ice performance.

[0013] Specific examples of silica include, for example, 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. Also, silica made from biomass materials such as rice husks may be used.

[0014] From the viewpoint of improving ice performance, silica preferably has a CTAB adsorption specific surface area of 50 to 300 m 2 / g, and more preferably 90 to 200 m 2 / g. The CTAB adsorption specific surface area is a value measured according to JIS K6217-3:2001 "Part 3: Method for determining specific surface area - CTAB adsorption method" for the adsorption amount of n-hexadecyltrimethylammonium bromide on the silica surface.

[0015] (Alkaline earth metal salt) The alkaline earth metal salt used in the present invention is preferably an inorganic alkaline earth metal salt, and examples thereof include calcium hydrogen phosphate, tricalcium phosphate, calcium pyrophosphate, calcium carbonate, calcium sulfate, magnesium phosphate, magnesium carbonate, etc. Among them, from the viewpoint of improving the effect of the present invention, an alkaline earth metal salt containing phosphorus is preferred, and it is more preferred that the alkaline earth metal salt is calcium, and calcium hydrogen phosphate, tricalcium phosphate, and calcium pyrophosphate are particularly preferred.

[0016] In addition, the alkaline earth metal salt used in the present invention has a particle size of 20 μm to 100 μm, preferably 20 μm to 60 μm, and more preferably 20 μm to 50 μm. When the particle size is less than 20 μm, the performance on ice deteriorates. Conversely, when it exceeds 100 μm, the tensile strength deteriorates. The adjustment of the particle size of the alkaline earth metal salt can be carried out according to a conventional method. For example, a sieving method can be mentioned. The above particle size can be measured according to a known measurement method. For example, it can be measured from 100 samples using an electron microscope, a laser microscope, etc. When the alkaline earth metal salt is irregular in shape, the equivalent circle diameter can be measured and calculated as the particle size. In addition, the alkaline earth metal salt used in the present invention allows a small amount of alkaline earth metal salts other than those with a particle size of 20 μm to 100 μm to be mixed in.

[0017] In addition, from the viewpoint of enhancing physical properties such as performance on ice and elongation at break, the alkaline earth metal salt used in the present invention preferably has the following form. (A) The alkaline earth metal salt used in the present invention is preferably a natural product or a product made from a natural product as a raw material. The alkaline earth metal salt prepared from a natural product or a natural product as a raw material generally includes irregularly shaped objects having various acute or obtuse angles in addition to the spherical form that forms a smooth arc in particle shape. This irregular shape suppresses the orientation of the alkaline earth metal salt in the rubber, exhibits an appropriate dispersion state, and can maintain or improve physical properties such as elongation at break. (B) The alkaline earth metal salt used in the present invention preferably has a specific surface area of less than 10.0 m 2 / g, and more preferably 0.1 to 5.0 m 2 / g. (C) The alkaline earth metal salt used in the present invention is preferably water-insoluble. By being water-insoluble, the irregular shape is maintained, and the performance on ice is further improved by the scratching effect. (D) From the viewpoint of improving the scratching effect on the road surface, the alkaline earth metal salt used in the present invention preferably has a specific gravity of 1.5 to 5.0, and more preferably 2.0 to 4.0. The more combinations of conditions (A) to (D) described above are met, the more the effects of the present invention are improved.

[0018] (Ratio of rubber composition) The rubber composition of the present invention is characterized by comprising 100 parts by mass of a diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of an alkaline earth metal salt having a particle size of 20 μm to 100 μm. If the amount of alkaline earth metal salt added to 100 parts by mass of the diene rubber is less than 0.5 parts by mass, the amount added is too small to achieve the effects of the present invention, while if it exceeds 30 parts by mass, physical properties such as elongation at break will deteriorate.

[0019] The amount of alkaline earth metal salt added is preferably 5 to 30 parts by mass, and more preferably 5 to 20 parts by mass, per 100 parts by mass of diene rubber.

[0020] The amount of carbon black and / or white filler added is 30 to 100 parts by mass, preferably 40 to 90 parts by mass, per 100 parts by mass of diene rubber. If the amount of carbon black and / or white filler added is less than 30 parts by mass per 100 parts by mass of diene rubber, the mechanical properties and abrasion resistance of the rubber composition deteriorate, while if it exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition decreases, resulting in poor ice performance. When carbon black is added, the amount is preferably 5 to 50 parts by mass per 100 parts by mass of diene rubber. Furthermore, when silica is added, the amount is preferably 20 to 80 parts by mass per 100 parts by mass of diene rubber.

[0021] (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.

[0022] Furthermore, the studless 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, an inert gas such as nitrogen, and other gases. The rubber composition of the present invention is also suitable for application to the tread of a studless tire, particularly the cap tread. [Examples]

[0023] 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.

[0024] Standard Example 1, Examples 1-4, Comparative Examples 1-2 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.

[0025] 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 exponent, with the value of Standard Example 1 set to 100. A larger exponent indicates greater friction on ice and superior ice performance. Breaking elongation (EB): Tested at room temperature in accordance with JIS K 6250 and 6251. The results are shown as indices with the value of Standard Example 1 being 100. A higher index indicates a higher breaking elongation. If the index is 100 or more, it can be judged that there is a practically sufficient breaking elongation. The results are shown in Table 1.

[0026]

Table 1

[0027] *1: NR (TSR20 manufactured by PT. NUSIRA (SAD)) *2: BR (Nipol BRX5000 manufactured by Zeon Corporation, Japan) *3: Carbon black (Shoublack N339 manufactured by Cabot Japan Ltd.) *4: Silica (ULTRASIL VN3GR manufactured by EVONIK WELLINK) [[ID=二十一]] *5: Silane coupling agent (Si69 manufactured by EVONIK LANXING (RIZHAO) Co., Ltd.) *6: Alkaline earth metal salt 1 (Calcium pyrophosphate prepared from natural products, manufactured by Taihei Chemical Industry Co., Ltd., particle size = 30 - 60 μm, specific surface area = 0.5 - 3.0 m 2 / g, water-insoluble.) *7: Alkaline earth metal salt 2 (Calcium hydrogen phosphate (anhydrous) prepared from natural products, manufactured by Taihei Chemical Industry Co., Ltd., particle size = 20 - 50 μm, specific surface area = 0.5 - 3.0 m 2 / g, water-insoluble.) *8: Alkaline earth metal salt 3 (Calcium carbonate, trade name RM#2, manufactured by Nitto Powder Industry Co., Ltd., particle size = 3 - 15 μm, specific surface area = 0.5 - 5.0 m 2 / g, water-insoluble.) *9: Vulcanization accelerator (Nocceler CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *10: Sulfur (Fine powder sulfur for Tsubaki Chemical Industry Co., Ltd. gold stamp ink)

[0028] As shown in Table 1, the rubber compositions of each example, which consist of 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of alkaline earth metal salts with a particle size of 20 μm to 100 μm, show improved ice performance compared to Standard Example 1. Furthermore, the elongation at break is maintained or improved. In contrast, Comparative Example 1 showed a decrease in elongation at break because the amount of alkaline earth metal salt used exceeded the upper limit specified in the present invention. Comparative Example 2 is an example in which calcium carbonate with a particle size below the lower limit specified in the present invention was used, resulting in a decrease in elongation at break.

[0029] This disclosure includes the following embodiments. Embodiment 1: A rubber composition characterized by comprising 100 parts by mass of a diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of an alkaline earth metal salt having a particle size of 20 μm to 100 μm. Embodiment 2: The rubber composition according to Embodiment 1, characterized in that the alkaline earth metal salt is a natural product or derived from a natural product. Embodiment 3: The specific surface area of ​​the aforementioned alkaline earth metal salt is 10.0 m². 2 The rubber composition according to Embodiment 1 or 2, characterized in that it is less than / g. Embodiment 4: The rubber composition according to any one of Embodiments 1 to 3, characterized in that the alkaline earth metal salt is water-insoluble. Embodiment 5: The rubber composition according to any one of Embodiments 1 to 4, characterized in that the alkaline earth metal salt contains phosphorus. Embodiment 6: The rubber composition according to any one of Embodiments 1 to 5, characterized in that the alkaline earth metal salt contains calcium. Embodiment 7: A studless tire using the rubber composition described in any of Embodiments 1 to 6.

Claims

1. A rubber composition characterized by comprising 100 parts by mass of diene rubber containing 30 parts by mass or more of butadiene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of an alkaline earth metal salt having a particle size of 20 μm to 100 μm.

2. The rubber composition according to claim 1, characterized in that the alkaline earth metal salt is a natural product or derived from a natural product.

3. The specific surface area of ​​the aforementioned alkaline earth metal salt is 10.0 m². ２ The rubber composition according to claim 1, characterized in that it is less than / g.

4. The rubber composition according to claim 1, characterized in that the alkaline earth metal salt is water-insoluble.

5. The rubber composition according to claim 1, characterized in that the alkaline earth metal salt contains phosphorus.

6. The rubber composition according to claim 1, characterized in that the alkaline earth metal salt contains calcium.

7. A studless tire using the rubber composition described in claim 1.

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