Rubber composition for studless tire and studless tire using the same

Abstract

To solve the following problem that: on ice and snow road surfaces, the coefficient of friction is reduced relative to general road surfaces, resulting in increased slipperiness; accordingly, improvement in ice performance has been demanded for studless tires; meanwhile, tires are required to maintain physical properties such as tensile strength (TB) and elongation at break (EB) at a certain level or higher.SOLUTION: The problem is solved by a rubber composition for studless tires, comprising, based on 100 pts.mass of diene rubber, 30 to 100 pts.mass of an inorganic filler, and 0.5 to 50 pts.mass of a metal powder having a specific gravity of 3.50 or more and containing iron oxide.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 can improve performance on ice without impairing tensile strength (TB) or elongation at break (EB), 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. Known methods for improving ice performance include adding a foaming agent made of hollow polymers with small particle sizes to remove water film, and adding high-hardness particles to provide a traction effect (see, for example, Patent Documents 1 and 2 listed below). However, the above-mentioned conventional techniques have the problem that physical properties such as tensile strength (TB) and elongation at break (EB) are reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-320427 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-105131 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 can improve performance on ice without impairing tensile strength (TB) or elongation at break (EB), 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 specific amount of inorganic filler and a specific amount of metal powder containing iron oxide and having a specific specific gravity into a diene-based rubber, and have thereby completed the present invention. That is, the present invention provides a rubber composition for studless tires, characterized by containing 30 to 100 parts by mass of an inorganic filler and 0.5 to 50 parts by mass of a metal powder containing iron oxide and having a specific gravity of 3.50 or more, per 100 parts by mass of diene rubber.

[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 50 parts by mass of a metal powder containing iron oxide and having a specific gravity of 3.50 or more per 100 parts by mass of diene rubber. Therefore, it is possible to provide a rubber composition for studless tires that can improve performance on ice without compromising tensile strength (TB) or elongation at break (EB), and a studless tire using the same.

[0008] As mentioned above, techniques for improving the ice performance of studless tires include compounding hollow polymer foaming agents or high-hardness particles into tires, but these methods have the problem of deteriorating tire physical properties. The former method also poses the problem of environmental issues arising from the hollow polymer particles detaching from the tire. The present invention uses a metal powder containing iron oxide, specifically a specific gravity of 3.50 or more, which reduces the volume of foreign matter present in the rubber, making it less likely to deteriorate physical properties such as tensile strength (TB) and elongation at break (EB). Furthermore, the metal powder used in the present invention exhibits sufficient road scratching properties, improving ice performance. Environmental issues are also less likely to arise. 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, etc., and these may be used alone or in combination of two or more. Of these, silica is preferred because of its better performance on ice. Specific examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate, and 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 / g is more preferred. 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 / g is more preferred. 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] (metal powder) The metal powder used in the present invention contains iron oxide as an essential component. While the composition of the iron oxide is not critical, ferrite is preferred in the present invention to enhance its effectiveness. Known ferrites include spinel ferrite and hexagonal ferrite. In particular, the present invention uses a ferrite having the composition AFe2O4 (where A represents Mn, Co, Ni, Cu, Zn, etc.), such as Ni-Zn-Cu ferrite and Ni-Zn ferrite. Commercially available ferrites can be used, including Ni-Zn-Cu ferrite (manufactured by Toda Kogyo Co., Ltd.) under the trade name FRX-952 and Ni-Zn ferrite (manufactured by Toda Kogyo Co., Ltd. under the trade name BSN-828). In addition to iron oxide alone or ferrite, the metal powder used in the present invention can also include pigments or other metals. The mass ratio of iron oxide to metals other than iron oxide is preferably 10:0 to 10:8. The metal powder used in the present invention has a specific gravity of 3.50 or more. By satisfying this condition, the volume of the metal powder present as foreign matter in the rubber is reduced, and physical properties such as tensile strength (TB) and elongation at break (EB) are less likely to deteriorate. Furthermore, sufficient road scratching effect is exhibited, improving performance on ice. The specific gravity of the metal powder is preferably 3.5 to 10. From the viewpoint of improving the effects of the present invention, the average particle size of the metal powder used in the present invention is preferably 0.005 μm to 200 μm, and more preferably 20 μm to 150 μm. The average particle size of the metal powder can be determined by measuring the lengths of two sides (vertical and horizontal) of a planar image of iron oxide particles observed under an electron microscope and calculating the average value. The metal powder used in the present invention preferably has a spherical shape, a polyhedral shape such as a hexahedron or an octahedron, or a cylindrical shape.

[0015] (Rubber composition for studless tires) The rubber composition for studless tires of the present invention is characterized by containing 30 to 100 parts by mass of an inorganic filler and 0.5 to 50 parts by mass of a metal powder containing iron oxide and having a specific gravity of 3.50 or more, per 100 parts by mass of diene rubber. If the content of the inorganic filler is less than 30 parts by mass, the mechanical properties and abrasion resistance of the rubber composition will deteriorate, and conversely, if it exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition will decrease and performance on ice will deteriorate. If the content of the metal powder is less than 0.5 parts by mass, the content is too small to achieve the effects of the present invention, and if it exceeds 50 parts by mass, physical properties such as tensile strength (TB) and elongation at break (EB) will decrease.

[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 manufacturing pneumatic tires according to conventional manufacturing methods for pneumatic tires, and is preferably a pneumatic tire, which can be filled with air, an inert gas such as nitrogen, or other gases. Furthermore, the rubber composition for studless tires of the present invention can improve performance on ice without impairing tensile strength (TB) or elongation at break (EB), and is therefore preferably applied to treads, particularly cap treads, to make 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] Standard Examples 1-2, Examples 1-8, and Comparative Examples 1-4 In the formulation (parts by mass) shown in Table 1, the components excluding the vulcanization accelerator and sulfur were mixed for 5 minutes in a 1.7-liter internal Banbury mixer, and then the vulcanization accelerator and sulfur were added and further mixed to obtain a rubber composition. The resulting unvulcanized rubber composition was then press-vulcanized in a specified 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 methods shown below.

[0020] Specific gravity: Measured in accordance with JIS K6250 and JIS K6268. 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 Standard Example 1 set to 100. A higher index indicates greater frictional force on ice and better performance on ice. Tensile strength (TB): Tensile tests were conducted at room temperature based on JIS K6250 and JIS K6251 (JIS No. 3 dumbbell). The higher the result, the better the tensile strength. A TB of 11 MPa or more is considered to be sufficient for practical use. Breaking elongation (EB): Breaking elongation was measured at room temperature according to JIS K6250 and JIS K6251. A higher value indicates better breaking elongation. An EB of 580% or more is considered to be 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: Foaming agent (FN-105 manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., thermal expansion microcapsules, particle size after foaming = average 150 μm) *7: Metal powder 1 (Fukuda Metal Foil and Powder Co., Ltd. FBMSn9Zn, spherical metal balls consisting of Cu, Ag, and Sn. Specific gravity = 7.30, average particle size = 500 μm) *8: Metal powder 2 (Kyowamag 150 manufactured by Kyowa Chemical Industry Co., Ltd., magnesium oxide, specific gravity = 3.65, average particle size = 150 μm or less) *9: Metal powder 3 (FRX-952 manufactured by Toda Kogyo Co., Ltd., ferrite, specific gravity = 3.00, average particle size = 0.65 μm) *10: Metal powder 4 (Toda Kogyo Co., Ltd. BSN-828, ferrite, specific gravity = 3.79, average particle size = 7.6 μm) *11: Metal powder 5 (large particle size ferrite manufactured by Powder Tech Co., Ltd., specific gravity = 5.20, average particle size = 200 μm) *12: Metal powder 6 (α-FeOOH (goethite) manufactured by Toda Kogyo Co., Ltd., specific gravity = 4.10, average particle size = 0.05 μm) *13: Metal powder 7 (α-Fe3O4 (magnetite) manufactured by Toda Kogyo Co., Ltd., specific gravity = 5.20, average particle size = 1.5 μm) *14: Metal powder 8 (Graphite Corporation mill scale #150, iron oxide, specific gravity = 5.60, average particle size = 150 μm) *15: Vulcanization accelerator (Noccela CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) *16: Sulfur (Kinka brand oil-filled fine sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.)

[0024] The results in Table 1 show that the rubber composition of each example contains 30 to 100 parts by mass of inorganic filler and 0.5 to 50 parts by mass of metal powder containing iron oxide and having a specific gravity of 3.50 or more per 100 parts by mass of diene-based rubber, and therefore can improve ice performance compared to Standard Example 1 without compromising tensile strength (TB) or elongation at break (EB). In contrast to this, Comparative Example 1 is an example in which a metal powder containing no iron oxide was used, and therefore the elongation at break (EB) was reduced. Comparative Example 2 is an example in which magnesium oxide was used as the metal powder, and therefore the elongation at break (EB) was reduced. In Comparative Example 3, the specific gravity was below the lower limit defined in the present invention, and therefore the elongation at break (EB) was reduced. In Comparative Example 4, the content of metal powder exceeded the upper limit specified in the present invention, and therefore the elongation at break (EB) decreased. Control example 2 is an example in which a foaming agent was used, and the tensile strength (TB) and elongation at break (EB) were reduced.

[0025] The present invention includes the following embodiments. Embodiment 1: A rubber composition for studless tires, characterized by containing 30 to 100 parts by mass of an inorganic filler and 0.5 to 50 parts by mass of a metal powder containing iron oxide and having a specific gravity of 3.50 or more, per 100 parts by mass of diene rubber. Embodiment 2: 2. The rubber composition according to embodiment 1, wherein the metal powder has an average particle size of 0.005 μm to 200 μm. Embodiment 3: 3. The rubber composition for a studless tire according to embodiment 1 or 2, wherein the butadiene rubber accounts for 30 parts by mass or more per 100 parts by mass of the diene rubber. Embodiment 4: A studless tire using the rubber composition for a studless tire according to any one of embodiments 1 to 3.

Claims

1. A rubber composition for studless tires, comprising 30 to 100 parts by mass of an inorganic filler and 0.5 to 50 parts by mass of a metal powder containing iron oxide and having a specific gravity of 3.50 or more, per 100 parts by mass of diene rubber.

2. 2. The rubber composition for studless tires according to claim 1, wherein the metal powder has an average particle size of 0.005 μm to 200 μm.

3. 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.

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

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