Rubber composition for studless tire and studless tire made thereof

Abstract

To provide a rubber composition having excellent on-ice performance, capable of improving on-ice performance (on-ice braking performance) of a studless tire against slipperiness on an icy road with a lower friction coefficient in comparison with that of an ordinary road surface.SOLUTION: A rubber composition for studless tires contains 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of powder of polyol having a molecular weight of 500 or less, relative to 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 having excellent 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 ordinary roads, making the road more slippery. Therefore, many methods have been proposed to improve the performance of studless tires on ice (braking performance on ice). Examples include the technologies disclosed in Patent Documents 1 to 3 listed below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2019 / 123749 Brochure [Patent Document 2] International Publication No. WO2020 / 129829 Brochure [Patent Document 3] International Publication No. WO2020 / 122073 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a rubber composition for studless tires having excellent 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 specific amount of a specific polyol powder with a diene rubber, and have been able to complete the present invention.

[0006] That is, the present invention provides a rubber composition for studless tires, characterized by containing 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polyol powder having a molecular weight of 500 or less per 100 parts by mass of diene rubber.

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

[0008] The rubber composition of the present invention contains 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polyol powder having a molecular weight of 500 or less per 100 parts by mass of diene rubber, and therefore it is possible to provide a rubber composition for studless tires with excellent performance on ice, and a studless tire using the same.

[0009] The polyol powder used in the present invention has a molecular weight of 500 or less and is moderately water-soluble. When on ice, it dissolves from the tire contact surface to form an uneven surface, efficiently imparting surface roughness and drainage effects to the tire contact surface, thereby improving performance on ice. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will now be described in further detail.

[0011] (Diene rubber) The diene rubber used in the present invention can be any diene rubber that can be compounded into a 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 terpolymer (EPDM). These may be used alone or in combination of two or more. There are no particular limitations on the molecular weight or microstructure, and the rubber may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, or hydroxyl group, or may be epoxidized. The molecular weight 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 molecular weight is a weight average molecular weight (Mw) calculated as a standard polystyrene standard obtained by gel permeation chromatography (GPC) measurement. Furthermore, from the viewpoint of improving performance on ice, it is preferable that the butadiene rubber accounts for 30 parts by mass or more, and preferably 40 parts by mass or more, per 100 parts by mass of diene rubber, and it is even more preferable that natural rubber is used in combination. 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.

[0012] (carbon black) Examples of carbon black that can be used in the present invention 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. 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."

[0013] (white filler) Specific examples of the white filler 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.

[0014] Specific examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate, which may be used alone or in combination of two or more. Silica made from biomass materials such as rice husks may also be used.

[0015] 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 200m 2 / g is more preferred. The CTAB adsorption specific surface area is a value obtained by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed onto the silica surface in accordance with JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[0016] (Polyol powder) The polyol powder used in the present invention is not particularly limited as long as it has a molecular weight of 500 or less, but from the viewpoint of improving performance on ice, it is preferable that it has the following form. (1) The molecular weight is preferably 400 or less, and more preferably 100 to 300. (2) The particle size is preferably 1 μm to 1000 μm, more preferably 1 μm to 300 μm, and particularly preferably 1 μm to 100 μm. By keeping the particle size within this range, excellent performance on ice can be imparted to a tire without impairing the breaking properties required for the tire. (3) The melting point is preferably 110° C. or higher, more preferably 150° C. or higher, and particularly preferably 180° C. or higher. In particular, when the melting point of the polyol powder is higher than the vulcanization temperature in the tire vulcanization process (for example, 150° C. or higher), the polyol powder remains in the tire in powder form (typically, while maintaining the crystallinity of the polyol molecules) without dissolving during the manufacturing process, and can impart excellent on-ice performance. (4) It is preferable that each molecule has four or more hydroxyl groups. The presence of hydroxyl groups increases affinity with silica, for example, making it easier to disperse in rubber and improving performance on ice. The more combinations of the conditions (1) to (4) are satisfied, the more the effects of the present invention are improved.

[0017] Examples of polyols suitable for use in the present invention are shown below.

[0018] [Table 1]

[0019] From the viewpoint of particularly enhancing the effects of the present invention, it is optimal that the polyol powder is composed of one or more selected from pentaerythritol and dipentaerythritol.

[0020] (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 carbon black and / or white filler and 1 to 30 parts by mass of polyol powder having a molecular weight of 500 or less per 100 parts by mass of diene rubber. If the amount of carbon black and / or white filler is less than 30 parts by mass per 100 parts by mass of the diene rubber, the mechanical properties and abrasion resistance of the rubber composition will deteriorate. Conversely, if the amount exceeds 100 parts by mass, the low-temperature flexibility of the rubber composition will decrease, resulting in poor performance on ice. If the amount of polyol powder mixed is less than 1 part by mass per 100 parts by mass of the diene rubber, the amount added is too small to achieve the effects of the present invention, and conversely, if it exceeds 30 parts by mass, the mechanical properties will decrease.

[0021] The amount of carbon black and / or white filler blended is preferably 30 to 100 parts by mass per 100 parts by mass of diene rubber. When carbon black is blended, the amount is preferably 2 to 90 parts by mass per 100 parts by mass of diene rubber. When silica is blended, the amount is preferably 5 to 90 parts by mass per 100 parts by mass of diene rubber. The total amount of carbon black and white filler (e.g., silica) is preferably 40 to 90 parts by mass, more preferably 50 to 85 parts by mass per 100 parts by mass of diene rubber. The amount of the polyol powder mixed is preferably 20 parts by mass or less, and more preferably 10 parts by mass or less, based on 100 parts by mass of the diene rubber.

[0022] (Other ingredients) In addition to the above-mentioned components, the rubber composition of the present invention may contain various additives that are generally compounded in rubber compositions, such as vulcanization or crosslinking agents, vulcanization or crosslinking accelerators, zinc oxide, antioxidants, plasticizers, silane coupling agents, and thermally expandable microcapsules, and these additives can be kneaded by a general method to form a composition, which can then be used for vulcanization or crosslinking. The amounts of these additives that can be compounded may be conventional amounts, provided that they do not deviate from the object of the present invention.

[0023] 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, an inert gas such as nitrogen, or other gases. The tire of the present invention is preferably applied to a tread, particularly a cap tread, to form a studless tire. [Example]

[0024] 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.

[0025] Standard Example 1, Examples 1 to 9, and Comparative Examples 1 and 2 Sample preparation The components excluding the vulcanization system (vulcanization accelerator, sulfur) were mixed in the formulation (parts by mass) shown in Table 2 in a 1.7-liter internal Banbury mixer for 5 minutes, then discharged from the mixer and cooled to room temperature. The resulting composition was then returned to the Banbury mixer, and the vulcanization system was added and mixed to obtain a rubber composition. The resulting rubber composition was press-vulcanized at less than 150°C for 10 minutes, and its physical properties were measured using the following test methods.

[0026] Performance on ice: The resulting vulcanized rubber test pieces were attached to flat, cylindrical rubber bases to create samples. The samples were immersed in room-temperature water for 24 hours. After immersion, the samples were measured for coefficient of friction on ice using an ice friction tester at a temperature of -1.5°C, a load of 98N, and a road speed of 20km / h. The obtained coefficient of friction on ice was expressed as an index, with the value for Standard Example 1 set at 100. A higher index indicates greater frictional force on ice and better performance on ice.

[0027] The results are also shown in Table 2. Table 2 also shows the breaking properties measured by conventional methods.

[0028] [Table 2]

[0029] *1: NR (STR20, manufactured by Bonbandit, glass transition temperature = -65°C) *2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., glass transition temperature = -110°C) *3: Carbon black (Cabot Japan N339) *4: Silica (ULTRASIL VN3 manufactured by Evonik Degussa) *5: Silane coupling agent (Si69, bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) *6: Oil (Extract No. 4 S manufactured by Showa Shell Sekiyu Co., Ltd.) *7: Polyol powder 1 (Voxtar M40 manufactured by Perstorp, pentaerythritol, melting point = 260 ° C, average particle size = 100 μm (particle size was adjusted using a sieve), molecular weight = 136) *8: Polyol powder 2 (Voxtar D40 manufactured by Perstorp, dipentaerythritol, melting point = 210 ° C, average particle size = 60 μm (particle size was adjusted using a sieve), molecular weight = 254) *9: Polyol powder 3 (PTMG2000 manufactured by Mitsubishi Chemical Corporation, polytetramethylene glycol, melting point = 20°C, average molecular weight = 2000) *10: Polyol powder 4 (product name meso-erythritol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., compound name = erythritol, melting point = 122 ° C, average particle size = 100 μm (particle size was adjusted using a sieve), molecular weight = 122) *11: Sulfur (Hosoi Chemical Industry Co., Ltd. oil refinery processing sulfur) *12: Vulcanization accelerator (Sansera CM-G, sulfenamide-based vulcanization accelerator manufactured by Sanshin Chemical Industry Co., Ltd.)

[0030] The results in Table 2 show that the rubber compositions of each example are characterized by containing 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polyol powder having a molecular weight of 500 or less per 100 parts by mass of diene rubber, and therefore have improved performance on ice compared to Standard Example 1. In contrast, Comparative Example 1 is an example in which polytetramethylene glycol with an average molecular weight of 2000 was used, and therefore the performance on ice was not improved to the same extent as in the examples. In Comparative Example 2, the blending amount of polyol powder exceeded the upper limit specified in the present invention, and therefore the mechanical properties (breaking properties) were reduced. On the other hand, the breaking properties of each Example showed results sufficient for practical use.

[0031] 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 carbon black and / or white filler and 1 to 30 parts by mass of polyol powder having a molecular weight of 500 or less, per 100 parts by mass of diene rubber. Embodiment 2: The rubber composition for a studless tire according to embodiment 1, wherein the particle size of the polyol powder is 1 μm to 1000 μm. Embodiment 3: 3. The rubber composition for a studless tire according to embodiment 1 or 2, wherein the polyol powder has a melting point of 110° C. or higher. Embodiment 4: 4. The rubber composition for a studless tire according to any one of embodiments 1 to 3, wherein the polyol powder has a melting point of 150° C. or higher. Embodiment 5: 5. The rubber composition for a studless tire according to any one of embodiments 1 to 4, wherein the polyol powder has four or more hydroxyl groups in one molecule. Embodiment 6: 6. The rubber composition for a studless tire according to any one of embodiments 1 to 5, wherein the polyol powder is composed of at least one selected from pentaerythritol and dipentaerythritol. Embodiment 7: 7. The rubber composition for a studless tire according to any one of embodiments 1 to 6, wherein the butadiene rubber accounts for 30 parts by mass or more per 100 parts by mass of the diene rubber. Embodiment 8: A studless tire using the rubber composition according to any one of embodiments 1 to 7.

Claims

1. A rubber composition for studless tires, comprising 30 to 100 parts by mass of carbon black and / or white filler and 1 to 30 parts by mass of polyol powder having a molecular weight of 500 or less, per 100 parts by mass of diene rubber.

2. 2. The rubber composition for studless tires according to claim 1, wherein the particle size of the polyol powder is 1 μm to 1000 μm.

3. 2. The rubber composition for a studless tire according to claim 1, wherein the polyol powder has a melting point of 110° C. or higher.

4. 2. The rubber composition for a studless tire according to claim 1, wherein the polyol powder has a melting point of 150° C. or higher.

5. 2. The rubber composition for studless tires according to claim 1, wherein the polyol powder has four or more hydroxyl groups in one molecule.

6. 2. The rubber composition for a studless tire according to claim 1, wherein the polyol powder is composed of at least one selected from the group consisting of pentaerythritol and dipentaerythritol.

7. 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.

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

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