Rubber composition for studless tire and studless tire using the same

Abstract

On an icy and snowy road surface, the friction coefficient is lower than that on a general road surface, and the road surface is slippery. Thus, studless winter tires have been required to have improved performance on ice. On the other hand, tires are also required to have practically sufficient physical properties at a certain level or higher.SOLUTION: The above problem is solved by a rubber composition for a studless tire containing 30 to 100 parts by mass of an inorganic filler and 0.5 to 30 parts by mass of a melt of amorphous aluminum oxide having an average particle diameter of more than 50 μm and 500 μm or less based on 100 parts by mass of a diene rubber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for studless tires and a studless tire using the same, and more particularly to a rubber composition for studless tires that has sufficient physical properties for practical use and can improve performance on ice, and a studless tire using the same. [Background technology]

[0002] On snowy and icy roads, the coefficient of friction is lower than on regular roads, making the tires more slippery. Therefore, numerous methods have been proposed to improve the ice performance (braking performance on ice) of studless tires. One known method of improving ice performance is to add polymer microparticles to the tread surface to create surface roughness. However, the above-mentioned conventional techniques have the problem of deteriorating physical properties such as breaking characteristics and tensile characteristics. The technology of compounding aluminum oxide into a rubber composition for tires to improve performance on ice is disclosed in, for example, Patent Documents 1 and 2 listed below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-60548 [Patent Document 2] Patent No. 5363739 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, an object of the present invention is to provide a rubber composition for studless tires that has sufficient physical properties for practical use and can improve performance on ice, and a studless tire using the same. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by blending a diene rubber with an inorganic filler and a molten aluminum oxide satisfying specific conditions in specific amounts, and have thus completed the present invention. That is, the present invention provides a rubber composition for studless tires, characterized by containing, per 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler, and 0.5 to 30 parts by mass of molten aluminum oxide that is amorphous and has an average particle size of more than 50 μm and not more than 500 μm.

[0006] The present invention also provides a studless tire using the rubber composition for a studless tire. [Effects of the Invention]

[0007] The rubber composition of the present invention is characterized by containing 30 to 100 parts by mass of an inorganic filler and 0.5 to 30 parts by mass of molten amorphous aluminum oxide having an average particle size of more than 50 μm and not more than 500 μm per 100 parts by mass of diene rubber. Therefore, it is possible to provide a rubber composition for studless tires that has sufficient physical properties for practical use and can improve performance on ice, and a studless tire using the same.

[0008] As mentioned above, a technique for compounding polymeric microparticles into studless tires with the aim of improving their performance on ice is known, but this approach has the problem of deteriorating tire physical properties. Another issue is that the polymeric microparticles may detach from the tire, causing environmental problems. The present invention uses a melt of amorphous aluminum oxide, particularly one with an average particle size of more than 50 μm and not more than 500 μm, which provides sufficient road scratching performance and improves performance on ice. Furthermore, this method can prevent deterioration of tire physical properties and is less likely to cause environmental problems. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will now be described in further detail.

[0010] (Diene rubber) Examples of the diene rubber used in the present invention include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), etc. The diene rubber used in the present invention is not particularly limited in terms of molecular weight or microstructure, and may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group, or the like, or may be epoxidized. The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but in order to obtain better effects of the present invention, 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 values ​​calculated as standard polystyrene obtained by gel permeation chromatography (GPC) measurement. From the viewpoint of improving performance on ice, it is preferable that the butadiene rubber accounts for 30 parts by mass or more, and more preferably 40 parts by mass or more, per 100 parts by mass of the diene rubber. Furthermore, the diene rubber preferably has a glass transition temperature (Tg) of not more than −50° C. By specifying the Tg in this way, performance on ice is improved. In the case where multiple diene rubbers are contained, the Tg referred to in this specification is a value calculated based on the sum of the products obtained by multiplying the glass transition temperature of each rubber by the weight fraction of each rubber, i.e., the weighted average. In the calculation, the sum of the weight fractions of each component is set to 1.0. The glass transition temperature (Tg) referred to in this invention refers to the midpoint temperature of the transition region measured by differential scanning calorimetry (DSC) at a heating rate of 20°C / min. More preferably, the average Tg is −60° C. or lower.

[0011] (inorganic filler) Specific examples of inorganic fillers used in the present invention include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, calcium sulfate, and the like, excluding the molten aluminum oxide described below. These may be used alone or in combination of two or more. Of these, silica is preferred because of its better performance on ice. The silica is not particularly limited, but examples thereof include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Silica made from biomass materials such as rice husks may also be used. These may be used alone or in combination of two or more.

[0012] To improve performance on ice, silica is used with a CTAB adsorption specific surface area of ​​50 to 300 m 2 / g, and 90 to 220m 2 More preferably, it is / g. The CTAB adsorption specific surface area is a value measured in accordance with JIS K6430:2008.

[0013] The rubber composition of the present invention preferably contains carbon black, specifically furnace carbon black such as SAF, ISAF, HAF, FEF, GPE, and SRF, which may be used alone or in combination of two or more. In addition, carbon black is used with a nitrogen adsorption specific surface area (N2SA) of 10 to 300 m to improve performance on ice. 2 / g, and 50 to 150m 2 More preferably, it is / g. The nitrogen adsorption specific surface area (N2SA) is a value measured in accordance with JIS K 6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0014] (aluminum oxide melt) The molten aluminum oxide used in the present invention has an average particle size of more than 50 μm and not more than 500 μm and is amorphous. While general aluminum oxide is crystallized by firing, the molten aluminum oxide used in the present invention is amorphous, which differs from the prior art. From the viewpoint of improving the effects of the present invention, the molten aluminum oxide used in the present invention preferably satisfies one or more of the following requirements (1) to (4), and more preferably satisfies more requirements. (1) The average particle size of the melt is preferably 50 μm to 400 μm, and more preferably 50 μm to 200 μm. (2) The shape of the molten material is preferably spherical, acicular, a polyhedral shape such as a hexahedron or octahedron, a cylindrical shape, a prismatic shape, or the like, and is preferably a shape having so-called corners that form acute or obtuse angles anywhere in the molten material. Such a molten aluminum oxide material in a suitable shape has high hardness and toughness, exhibits sufficient scratching effect on road surfaces, and can suppress deterioration of tire physical properties such as strength at break (TB) and elongation at break (EB). (3) Vickers hardness (HV) is 1700 to 2500, and more preferably 2150 to 2500. (4) Contains 90.00 to 99.70 mass% Al2O3, 0.10 to 5.00 mass% Cr2O3, 0.10 to 1.00 mass% Na2O, and 0.01 to 0.10 mass% Fe2O3. Such a melt of aluminum oxide is commercially available as fused alumina from, for example, JCT Abrasives. The fused alumina is obtained by melting aluminum oxide in the presence of Cr2O3. The average particle size can be measured according to known measurement methods, for example, by measuring 100 samples using an electron microscope, a laser microscope, or the like. If the powder has an irregular shape, the equivalent circle diameter can be regarded as the particle size of the powder, and the average particle size can be calculated. In the case of an acicular shape with an aspect ratio of, for example, 2 or more, the average particle size refers to the average value of the maximum length in a planar image observed under an electron microscope.

[0015] (Rubber composition for studless tires) The rubber composition for studless tires of the present invention is characterized by containing, per 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler and 0.5 to 30 parts by mass of molten aluminum oxide that is amorphous and has an average particle size of more than 50 μm and not more than 500 μm. If the content of the molten aluminum oxide is less than 0.5 parts by mass, the content is too small to achieve the effects of the present invention, whereas if it exceeds 30 parts by mass, the physical properties will be reduced. From the viewpoint of improving the effects of the present invention, the content of the inorganic filler is preferably 30 to 60 parts by mass relative to 100 parts by mass of the diene rubber. From the viewpoint of improving the effects of the present invention, the content of the molten aluminum oxide is preferably 0.5 to 20 parts by mass relative to 100 parts by mass of the diene rubber. When carbon black is compounded, the content thereof is preferably 5 to 60 parts by mass per 100 parts by mass of the diene rubber.

[0016] (Other ingredients) In addition to the above-mentioned components, the rubber composition for studless tires of the present invention can be blended with various additives that are generally blended into rubber compositions, such as vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, silane coupling agents, zinc oxide, various fillers, antioxidants, plasticizers, and reinforcing materials, and these additives can be kneaded by a general method to form a composition that can be used for vulcanization or crosslinking. The blending amounts of these additives can also be conventionally general blending amounts, as long as they do not contradict the object of the present invention.

[0017] The rubber composition for studless tires of the present invention is suitable for producing pneumatic tires according to conventional pneumatic tire production methods, and is preferably a pneumatic tire that can be filled with air, an inert gas such as nitrogen, or other gases. The rubber composition for studless tires of the present invention is also preferably applied to treads, particularly cap treads, to produce studless tires. [Example]

[0018] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0019] Comparative Examples 1-2 and Examples 1-7 The components excluding the vulcanization system (vulcanization accelerator, sulfur) were mixed in the formulation (parts by mass) shown in Table 1 in a 1.7-liter internal Banbury mixer for 5 minutes, then discharged from the mixer and cooled to room temperature. The composition was then returned to the same Banbury mixer, and the vulcanization system was added and mixed to obtain a rubber composition. The resulting rubber composition was press-vulcanized at 170°C for 10 minutes to obtain vulcanized rubber test pieces, and the physical properties were measured using the test methods described below.

[0020] Performance on ice: 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 measurement temperature of -1.5°C and a load of 5.5 kg / cm. 2 The coefficient of friction on ice was measured under conditions of 25 km / h drum rotation speed. The obtained coefficient of friction on ice was expressed as an index, with the value for Comparative Example 1 set to 100. A higher index indicates greater frictional force on ice and better performance on ice. Strength at break (TB) and elongation at break (EB): JIS No. 3 dumbbell-shaped test pieces (2 mm thick) were punched out of the obtained vulcanized rubber sheet in accordance with JIS K6251:2010, and the strength at break (TB) and elongation at break (EB) were evaluated at a temperature of 20°C and a tensile speed of 500 mm / min. The results were expressed as an index, with the value of Comparative Example 1 being 100. A larger index indicates better strength at break (TB) and elongation at break (EB). An index of 90 or more can be determined to have strength at break (TB) and elongation at break (EB) sufficient for practical use.

[0021] The results are shown in Table 1.

[0022] [Table 1]

[0023] *1:NR (PT.NUSIRA (SAD) TSR20) *2: BR (Nipol BRX5000 manufactured by Nippon Zeon Co., Ltd.) *3: Carbon black (Cabot Japan Co., Ltd. Show Black N339) *4: Silica (EVONIK WELLINK ULTRASIL VN3GR) *5: Silane coupling agent (Si69 manufactured by EVONIK LANXING (RIZHAO)) *6: Aluminum oxide melt 1 (Fused alumina manufactured by JCT Abrasive. Amorphous, needle-shaped. Particle size: 106-125 μm. Composition (mass%): Al2O3:Cr2O3:Na2O:Fe2O3 = 97.80:0.45-1.00:0.40:0.01-0.05. Vickers hardness (HV) = 2200-2300) *7: Aluminum oxide melt 2 (fused alumina manufactured by JCT Abrasive. Amorphous, needle-shaped. Particle size: 106-125 μm, composition (mass%): Al2O3:Cr2O3:Na2O:Fe2O3 = 98.80:0.20-0.45:0.40:0.01-0.05, Vickers hardness (HV) = 2200-2300) *8: Aluminum oxide melt 3 (Fused alumina manufactured by JCT Abrasive. Amorphous, needle-shaped. Particle size: 106-125 μm. Composition (mass%): Al2O3:Cr2O3:Na2O:Fe2O3 = 96.50:1.00-2.00:0.40:0.01-0.05. Vickers hardness (HV) = 2200-2300) *9: Aluminum oxide melt 4 (Fused alumina manufactured by JCT Abrasive. Amorphous, needle-shaped. Particle size = 150-250 μm, composition (mass%) Al2O3:Cr2O3:Na2O:Fe2O3 = 98.20:0.45-1.00:0.35:0.01-0.05, Vickers hardness (HV) = 2200-2300) *10: Burned aluminum oxide 1 (manufactured by Zhengzhou Haixu Abrasives Co., Ltd., trade name: White fused alumina. Average particle size = 29 μm, Vickers hardness (HV) = 2100) *11: Vulcanization accelerator (Noccela CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *12: Sulfur (Kinka brand oil-filled fine sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.)

[0024] As can be seen from the results in Table 1, the rubber composition of each example contains 30 to 100 parts by mass of inorganic filler and 0.5 to 30 parts by mass of molten aluminum oxide that is amorphous and has an average particle size of more than 50 μm and not more than 500 μm per 100 parts by mass of diene-based rubber, and therefore has improved performance on ice compared to Comparative Example 1 and has physical properties that are sufficient for practical use. In contrast, Comparative Example 2 used fused alumina with an average particle size below the lower limit specified by the present invention, and therefore did not demonstrate as much improvement in performance on ice as in the Examples.

[0025] The present invention includes the following embodiments. Embodiment 1: A rubber composition for studless tires, characterized by containing, per 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler, and 0.5 to 30 parts by mass of molten aluminum oxide, which is amorphous and has an average particle size of more than 50 μm and not more than 500 μm. Embodiment 2: 2. The rubber composition according to embodiment 1, wherein the aluminum oxide melt has a shape having corners. Embodiment 3: 3. The rubber composition for a studless tire according to embodiment 1 or 2, wherein the molten aluminum oxide contains 0.05 to 5% by mass of Cr2O3. Embodiment 4: The rubber composition for studless tires according to any one of Embodiments 1 to 3, wherein the butadiene rubber accounts for 30 parts by mass or more per 100 parts by mass of the diene rubber. Embodiment 5: A studless tire using the rubber composition for a studless tire according to any one of embodiments 1 to 4.

Claims

1. A rubber composition for studless tires, comprising, per 100 parts by mass of diene rubber, 30 to 100 parts by mass of an inorganic filler, and 0.5 to 30 parts by mass of molten aluminum oxide, which is amorphous and has an average particle size of more than 50 μm and not more than 500 μm.

2. 2. The rubber composition for a studless tire according to claim 1, wherein the molten aluminum oxide has a shape having corners.

3. The aluminum oxide melt is Cr ２ O ３ The rubber composition for a studless tire according to claim 1, characterized in that it contains 0.05 to 5 mass % of

4. 2. The rubber composition for studless tires according to claim 1, wherein the butadiene rubber accounts for 30 parts by mass or more per 100 parts by mass of the diene rubber.

5. A studless tire using the rubber composition for a studless tire according to claim 1.

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