Rubber composition and studless tire using same

Abstract

To provide a rubber composition having low heat-generating properties and having excellent on-ice performance and a studless tire including the same.SOLUTION: A rubber composition contains, relative to 100 pts.mass of (I) a diene rubber, (II) carbon black and / or white filler of 30-100 pts.mass, and (III) a polyolefin elastomer of 0.5-20 pts.mass, which has a JIS A hardness of 0-50 and a compression set of 10-30%. Preferably, in the (I) diene rubber 100 pts.mass, a butadiene rubber is 30 pts.mass or more.SELECTED DRAWING: None

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 which has low heat generation and 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 normal roads, making the roads more slippery. For this reason, numerous methods have been proposed to improve the performance of studless tires on ice (braking performance on ice). For example, one known method is to compound hard foreign matter or hollow polymers into the rubber, which creates microscopic irregularities on the rubber surface, thereby removing the water film that forms on the ice surface and improving friction on ice. On the other hand, there is also a method that uses rubber that has flexibility at low temperatures.

[0003] However, the use of rubber having low-temperature flexibility causes a problem of deterioration in heat build-up, and the industry is calling for further improvement in on-ice performance. Meanwhile, the following Patent Document 1 discloses a rubber composition in which 1 to 20 parts by mass of silicone-modified polyolefin is blended with 100 parts by mass of diene rubber. Here, the following Patent Document 1 describes the finding that when unmodified polyolefin or maleic acid-modified polyolefin is blended, performance on ice is reduced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-135454 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a rubber composition which has low heat build-up and excellent performance on ice, and a studless tire using the same. [Means for solving the problem]

[0006] As a result of extensive research, the inventors have discovered that the above-mentioned problems can be solved by a rubber composition comprising a diene rubber, carbon black and / or a white filler, and a specific amount of a polyolefin elastomer having a specific hardness and compression set, and have thus completed the present invention.

[0007] That is, the present invention provides a rubber composition characterized by blending (I) 100 parts by mass of diene rubber with (II) 30 to 100 parts by mass of carbon black and / or white filler, and (III) 0.5 to 20 parts by mass of a polyolefin elastomer having a JIS A hardness of 0 to 50 and a compression set of 10 to 30%. Effect of the Invention

[0008] The rubber composition of the present invention is characterized by comprising 100 parts by mass of (I) diene rubber, 30 to 100 parts by mass of (II) carbon black and / or white filler, and 0.5 to 20 parts by mass of (III) polyolefin elastomer having a JIS A hardness of 0 to 50 and a compression set of 10 to 30%, blended therewith. Therefore, it is possible to provide a rubber composition having low heat build-up and excellent performance on ice, and a studless tire using the same.

[0009] The polyolefin-based elastomer (III) in the present invention has a JIS A hardness of 0 to 50 and a compression set of 10 to 30%, and therefore imparts low-temperature flexibility to studless tires and improves their performance on ice. The polyolefin-based elastomer (III) in the present invention also enhances the dispersibility of the carbon black and / or white filler (II) in the diene rubber (I), and therefore can impart low heat generation properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will now be described in further detail. (I) Diene Rubber The diene rubber used in the present invention may be any diene rubber that can be blended in a rubber composition, such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene-diene terpolymer (EPDM), etc. These may be used alone or in combination of two or more. In addition, the molecular weight and microstructure are not particularly limited, and the end may be modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group, etc., or may be epoxidized. From the viewpoint of improving performance on ice, it is preferred that polybutadiene accounts for 30 parts by mass or more, and preferably 40 parts by mass or more, per 100 parts by mass of the diene rubber (I). The diene rubber (I) preferably has a glass transition temperature (Tg) of not higher than −50° C. By specifying the Tg in this way, the performance on ice is improved. In the case where a plurality of diene rubbers are contained, the Tg referred to in this specification is the sum of the products of the glass transition temperatures of each rubber multiplied by the weight fraction of each rubber, i.e., a value calculated based on a 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 temperature at the midpoint 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] (II) Carbon black and / or white fillers Specific examples of the carbon black 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 required to have a nitrogen adsorption specific surface area (N2SA) of 10 to 300 m from the viewpoint of improving performance on ice. 2 / g, and 50 to 150m 2 It is even more preferred that the weight ratio 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."

[0012] 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.

[0013] Specific examples of silica include wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc., and these may be used alone or in combination of two or more kinds.

[0014] From the viewpoint of improving performance on ice, silica is selected to have a CTAB adsorption specific surface area of ​​50 to 300 m 2 / g, and 90 to 200m 2 It is even more preferred that the weight ratio is / g. The CTAB adsorption specific surface area is a value obtained by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed on the silica surface in accordance with JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[0015] (III) Polyolefin elastomer The polyolefin elastomer (III) used in the present invention has a JIS A hardness of 0 to 50 and a compression set of 10 to 30%. The JIS A hardness in the present invention is a JIS A hardness measured at 25°C according to the durometer hardness test (type A) of JIS K6253. The compression set was measured in accordance with JIS K6262 (issued in 2013) by hot pressing the polyolefin elastomer at 200°C for 10 minutes to prepare a sheet having a thickness of about 2 mm, punching out the obtained sheet into a disk shape having a diameter of 29 mm, stacking seven sheets, and preparing a sample having a height (thickness) of 12.5±0.5 mm, compressing the obtained sample by 25% with a dedicated jig, and leaving it at 70°C for 22 hours, and then measuring the compression set (unit: %) according to JIS K6262 (issued in 2013).

[0016] The polyolefin elastomer (III) used in the present invention is not particularly limited as long as it satisfies the above JIS A hardness and compression set, and includes homopolymers or copolymers of modified or unmodified olefin monomers, specifically ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-vinyl acetate copolymers, polybutene, polyisobutylene, etc. These polyolefin elastomers may be crosslinked. The above JIS A hardness and compression set can be adjusted by adjusting the amount of oil impregnated into the polyolefin elastomer (III).

[0017] On the other hand, a publicly known example of a polyolefin-based elastomer that satisfies the above-mentioned JIS A hardness and compression set is a polyolefin-based elastomer disclosed in JP 2017-57393 A, which is obtained by impregnating oil with "at least one selected from the group consisting of an elastomeric polymer (A) having a side chain (a) containing a hydrogen-bond cross-linkable moiety having a carbonyl-containing group and / or a nitrogen-containing heterocycle and having a glass transition point of 25° C. or less, and an elastomeric polymer (B) having a side chain containing a hydrogen-bond cross-linkable moiety and a covalent-bond cross-linking moiety and having a glass transition point of 25° C. or less" so as to satisfy the above-mentioned JIS A hardness and compression set.

[0018] In addition, the polyolefin-based elastomer (III) used in the present invention may be a commercially available product, such as the Gelatic series manufactured by ENEOS Corporation.

[0019] (Rubber composition blend ratio) The rubber composition is characterized in that it comprises 100 parts by mass of (I) diene rubber, 30 to 100 parts by mass of (II) carbon black and / or white filler, and 0.5 to 20 parts by mass of (III) polyolefin elastomer having a JIS A hardness of 0 to 50 and a compression set of 10 to 30%. If the amount of (II) carbon black and / or white filler is less than 30 parts by mass per 100 parts by mass of (I) 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 (III) polyolefin-based elastomer is less than 0.5 parts by mass per 100 parts by mass of (I) diene-based rubber, the amount is too small to achieve the effects of the present invention. Conversely, if it exceeds 20 parts by mass, the breaking properties will deteriorate.

[0020] The amount of carbon black mixed is preferably 5 to 80 parts by mass based on 100 parts by mass of the diene rubber. The amount of the white filler to be mixed is preferably 15 to 80 parts by mass based on 100 parts by mass of the diene rubber. The blending amount of the (III) polyolefin-based elastomer is preferably 1 to 20 parts by mass based on 100 parts by mass of the diene-based rubber.

[0021] (Other ingredients) In addition to the above-mentioned components, the rubber composition of the present invention may contain various additives that are generally incorporated in rubber compositions, such as vulcanizing or crosslinking agents, vulcanizing or crosslinking accelerators, zinc oxide, antioxidants, plasticizers, silane coupling agents, and thermally expandable microcapsules, and these additives can be kneaded in a general manner to form a composition, which can be used for vulcanization or crosslinking. The amounts of these additives may be conventional amounts, provided that they do not violate the object of the present invention.

[0022] 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. 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, Examples 1-5, Comparative Examples 1-3 In the formulation (parts by mass) shown in Table 1, the components other than the vulcanization system (vulcanization accelerator, sulfur) and the curing agent were mixed in a 1.7-liter closed Banbury mixer for 5 minutes, then discharged from the mixer and cooled at room temperature. The composition was then placed back into the Banbury mixer, and the vulcanization system was added and mixed to obtain a rubber composition. The rubber composition obtained was press-vulcanized at 170°C for 10 minutes, and its physical properties were measured using the test methods shown below.

[0025] Breaking strength (TB): Tested at room temperature according to JIS K 6251. The results are expressed as an index with the standard value being 100. The larger the index, the better the breaking strength. An index of 80 or more can be considered sufficient for practical use. Storage modulus (E'): According to JIS K6394, the storage modulus (E') at -10°C was determined using a Toyo Seiki Seisakusho viscoelasticity spectrometer under conditions of 10% initial strain, ±0.5% amplitude, and 20Hz frequency. The results are expressed as an index, with the standard value being 100. The smaller the index, the more excellent the low-temperature flexibility. Heat generation: Using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., tan δ (60°C) was measured under the conditions of initial strain = 10%, amplitude = ±2%, and frequency = 20Hz, and heat generation was evaluated based on this value. The results were expressed as an index, with the standard example value being 100. The smaller the index, the lower the heat generation. Performance on ice: The vulcanized rubber test piece obtained was attached to a flat cylindrical rubber base and tested using an inside drum type ice friction tester at a measurement temperature of -3.0°C and a load of 5.5 kg / cm. 2 The coefficient of friction on ice was measured under conditions of a drum rotation speed of 25 km / h. The obtained coefficient of friction on ice was expressed as an index, with the standard example value set at 100. A higher index value indicates greater frictional force on ice and better performance on ice. The results are shown in Table 1.

[0026] [Table 1]

[0027] *1:NR(RSS#3) *2: BR (Nipol BR1220 manufactured by Zeon Corporation) *3: Carbon black (Seest KHA manufactured by Tokai Carbon Co., Ltd.) *4: Silica (Rhodia Zeosil 1165MP, CTAB specific surface area = 159 m 2 / g) *5: Silane coupling agent (Evonik Degussa Si69, bis(3-triethoxysilylpropyl)tetrasulfide) *6: Oil (Extract No. 4 S manufactured by Showa Shell Sekiyu K.K.) *7: TPE (styrene-based thermoplastic elastomer, AR-SC-30, manufactured by Aronkasei Co., Ltd.) *8: Polyolefin elastomer 1 (ENEOS Corporation Gelatic Hs0, JIS A hardness = 0, compression set = 18%) *9: Polyolefin elastomer 2 (ENEOS Corporation Gelatic Hs5, JIS A hardness = 5, compression set = 27%) *10: Polyolefin elastomer 3 (ENEOS Corporation Gelatic Hs20, JIS A hardness = 20, compression set = 25%) *11: Sulfur (Kinka-in oil-filled fine sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.) *12: Vulcanization accelerator (Noccela CZ-G manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0028] As can be seen from the results in Table 1, the rubber composition of each Example is composed of 100 parts by mass of (I) diene rubber, 30 to 100 parts by mass of (II) carbon black and / or white filler, and 0.5 to 20 parts by mass of (III) polyolefin elastomer having a JIS A hardness of 0 to 50 and a compression set of 10 to 30%, and therefore has lower heat build-up and better performance on ice compared to the standard example. In contrast, Comparative Example 1 is an example in which a styrene-based elastomer was used instead of the (III) polyolefin-based elastomer, and therefore showed little improvement in performance on ice and heat build-up compared to the standard example. In Comparative Example 2, the amount of (III) polyolefin-based elastomer blended was less than the lower limit specified in the present invention, and a styrene-based elastomer was used instead, so no improvement was observed in any of the properties compared to the standard example. In Comparative Example 3, the blend amount of (III) polyolefin-based elastomer exceeded the upper limit specified in the present invention, and therefore the rubber strength was reduced compared to the control example.

Claims

1. (I) per 100 parts by mass of diene rubber, (II) 30 to 100 parts by weight of carbon black and / or white filler, and (III) 0.5 to 20 parts by mass of a polyolefin-based elastomer having a JIS A hardness of 0 to 50 and a compression set of 10 to 30% measured by the following measurement method. A rubber composition comprising: Measurement method for the compression set: The polyolefin elastomer is heat-pressed at 200°C for 10 minutes to prepare a sheet having a thickness of about 2 mm. The obtained sheet is punched out into a disk shape having a diameter of 29 mm, and seven sheets are stacked together to prepare a sample having a height (thickness) of 12.5±0.5 mm. The obtained sample is compressed by 25% using a dedicated jig, and the compression set (unit: %) after leaving it at 70°C for 22 hours is measured in accordance with JIS K6262 (issued in 2013).

2. 2. The rubber composition 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 (I).

3. A studless tire using the rubber composition according to claim 1 or 2.

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