Rubber composition

Abstract

To provide a rubber composition mostly maintaining hardness, and improved in any of breaking elongation, wet performance and on-ice friction.SOLUTION: A rubber composition contains, with respect to 100 pts.mass of a diene rubber, 30 to 100 pts.mass of carbon black and / or a white filler, and 0.5 to 30 pts.mass of a water-soluble phenol resin polymer including a phenolsulfonic acid or a salt thereof as a constitutional unit.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition and a studless tire using the rubber composition. [Background technology]

[0002] Studless tires, which are tires for icy and snowy roads, are required to have a high frictional force (friction on ice) even on ice such as icy roads. At the same time, wet performance (grip performance on wet road surfaces) is also required. Various rubber compositions have been developed to improve the performance of studless tires.

[0003] For example, Patent Document 1 discloses a rubber composition for treads that contains a rubber component containing an isoprene-based rubber, a terpene-based resin such as a terpene phenol resin, and a specific branched conjugated diene copolymer, and that has little temperature dependency of performance on ice and excellent wet grip performance. Furthermore, Patent Document 2 discloses a tread rubber composition for studless tires capable of improving performance on ice, which comprises a rubber component containing an isoprene-based rubber and a conjugated diene-based polymer, water-soluble fine particles, a hydrocarbon resin, and a liquid plasticizer, and is characterized in that the liquid plasticizer content and the hydrocarbon resin content satisfy a predetermined relationship. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-099656 A [Patent Document 2] JP 2020-063322 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the terpene resins and the like contained in the rubber composition for treads described in Patent Document 1 are insoluble in water, and therefore sufficient effects are not obtained, particularly in terms of improving friction on ice. In addition, the water-soluble fine particles contained in the rubber composition for treads for studless tires described in Patent Document 2 are water-soluble components (water-soluble inorganic salts, lignin derivatives, sugars), but have problems with affinity with rubber components, and therefore may not be sufficient in terms of improving friction on ice. In addition, it is preferable for rubber compositions used in studless tires and the like to have improved breaking elongation, wet performance, and friction on ice without a significant change in hardness, and it can be said that further improvement in this regard is required.

[0006] Therefore, an object of the present invention is to provide a rubber composition which generally maintains its hardness and has improved breaking elongation, wet performance, and friction on ice. [Means for solving the problem]

[0007] In order to solve the above problems, the present inventors conducted extensive research and found that a rubber composition containing 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of a water-soluble phenolic resin polymer containing phenolsulfonic acid or a salt thereof as a constituent unit, per 100 parts by mass of diene rubber, largely maintains hardness and improves breaking elongation, wet performance, and friction on ice, thereby completing the present invention.

[0008] That is, the present invention is as follows: <1> ~ <8> It is. <1> A rubber composition comprising 100 parts by mass of diene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of a water-soluble phenolic resin polymer containing phenolsulfonic acid or a salt thereof as a constituent unit. <2> The water-soluble phenolic resin polymer is a resol-type water-soluble phenolic resin polymer obtained by reacting in the presence of an alkali catalyst. <1> The rubber composition according to claim 1. <3> The water-soluble phenolic resin polymer is a water-soluble phenolic resin polymer containing dihydroxydiphenyl sulfone as a constituent unit. <1> or <2> The rubber composition according to claim 1. <4> The water-soluble phenolic resin polymer contains a salt of phenolsulfonic acid as a constituent unit and has a methylol group at a terminal thereof. <1> ~ <3> The rubber composition according to any one of the above. <5> the salt is a sodium salt, a magnesium salt, a potassium salt, an ammonium salt, a lithium salt, or a calcium salt; <4> The rubber composition according to claim 1. <6> The diene rubber includes natural rubber (NR) and butadiene rubber (BR); <1> ~ <5> The rubber composition according to any one of the above. <7> The diene rubber has an average glass transition temperature of -100 to -50°C. <1> ~ <6> The rubber composition according to any one of the above. <8> <1> ~ <7> A studless tire using the rubber composition described in any one of the above. Effect of the Invention

[0009] According to the present invention, it is possible to obtain a rubber composition that maintains the hardness of the tire and improves the breaking elongation, wet performance, and friction on ice. By using this rubber composition, it is possible to obtain a studless tire that has excellent performance on ice. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will now be described. The present invention relates to a rubber composition containing 30 to 100 parts by mass of carbon black and / or white filler, and 0.5 to 30 parts by mass of a water-soluble phenolic resin polymer containing phenolsulfonic acid or its salt as a constituent unit, relative to 100 parts by mass of diene rubber, and a studless tire using this rubber composition. Hereinafter, these are also referred to as the "rubber composition of the present invention" and the "studless tire of the present invention".

[0011] In the present invention, unless otherwise specified, a numerical range expressed using "~" means a numerical range having the numerical value before "~" as the lower limit and the numerical value after "~" as the upper limit.

[0012] The components contained in the rubber composition of the present invention, their contents, etc. will be described in detail below.

[0013] [Diene rubber] The diene rubber contained in the rubber composition of the present invention is a rubber component having a double bond in the polymer main chain, and specific examples thereof include natural rubber (NR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, isoprene-butadiene copolymer rubber, etc. In the rubber composition of the present invention, such diene rubbers can be used alone or in combination of two or more kinds.

[0014] In the rubber composition of the present invention, when the diene rubber contains natural rubber (NR) and butadiene rubber (BR), that is, when the rubber composition of the present invention contains a diene rubber containing natural rubber and butadiene rubber, the effects of the present invention are more easily exhibited, which is preferable. In particular, the diene rubber is more preferable when it contains natural rubber and butadiene rubber in a total amount of preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, and even more preferably 90 mass% or more, and may be made of natural rubber and butadiene rubber (made of a mixture of natural rubber and butadiene rubber containing natural rubber and butadiene rubber in a total amount of 100 mass%).

[0015] Furthermore, when the diene rubber contained in the rubber composition of the present invention contains natural rubber and butadiene rubber, the content of the butadiene rubber in the diene rubber is preferably 30% by mass or more, more preferably 40% by mass or more. The upper limit is not particularly limited, but is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less of the diene rubber. The content of natural rubber in the diene rubber is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. The lower limit is preferably 30% by mass or more, and more preferably 40% by mass or more.

[0016] The weight average molecular weight of the diene rubber contained in the rubber composition of the present invention is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. In the present invention, the "weight average molecular weight" refers to a value measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent. The GPC measurement is performed at 40°C using a column (MIXED-B, manufactured by Polymer Laboratories) as a measuring instrument.

[0017] In addition, since the diene rubber contained in the rubber composition of the present invention is likely to improve wet performance and friction on ice, its average glass transition temperature (average Tg) is preferably -100 to -50°C. The upper limit is more preferably -60°C or less, and even more preferably -70°C or less. The lower limit is more preferably -90°C or more. Here, the average glass transition temperature of this diene rubber is a value obtained by multiplying the glass transition temperature of each component contained in the diene rubber by the mass% of each component and adding them together. In this calculation, the sum of the mass% of each component is set to 1.0. The glass transition temperature of each diene rubber is determined by measuring a thermogram by differential scanning calorimetry (DSC) at a heating rate of 20°C / min, and the temperature at the intersection of the extension line of the low-temperature baseline and the slope of the transition region (inclined straight line). When the diene rubber is an oil-extended product, the glass transition temperature of the diene rubber is determined to be the temperature of the diene rubber without the oil-extending component (oil).

[0018] The rubber composition of the present invention may contain rubber components other than diene-based rubber, but it is preferable that 90% by mass or more of the rubber components contained are diene-based rubber, more preferably 95% by mass or more are diene-based rubber, and even more preferably the rubber components contained are made of diene-based rubber (100% by mass of diene-based rubber).

[0019] [Carbon black] The carbon black contained in the rubber composition of the present invention is not particularly limited, and any known carbon black that is blended in rubber compositions for use in tires and the like can be used. For example, specific examples of carbon black that can be used include various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, GPF, SRF, FT, and MT. The carbon black may be used alone or in combination of two or more types. The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited, but is preferably 50 to 200 m2 because the effects of the present invention are more easily achieved. 2 / g, and 70 to 150m 2 It is more preferable that the molecular weight is / g. The term "carbon black" means fine carbon particles with a diameter of about 3 to 500 nm that are industrially manufactured under quality control. The nitrogen adsorption specific surface area (N2SA) of carbon black is the amount of nitrogen adsorbed on the carbon black surface measured according to JIS K6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0020] [White filler] The white filler contained in the rubber composition of the present invention is not particularly limited, and any known white filler that is compounded in rubber compositions for use in tires and the like can be used. Specific examples include silica, calcium carbonate, magnesium carbonate, clay, mica, talc, alumina, aluminum hydroxide, titanium oxide, calcium sulfate, barium sulfate, and the like. The white filler may be used alone or in combination of two or more. In particular, in the rubber composition of the present invention, it is more preferable to use silica as the white filler, since the effect of the present invention is more easily exhibited. Specific examples of silica include wet silica, dry silica, fumed silica, diatomaceous earth, and the like, and such silica can be used alone or in combination of two or more. Furthermore, since the effect of the present invention is more easily exhibited, it is preferable to use a CTAB specific surface area of ​​the silica contained in the rubber composition of the present invention of 110 to 200 m. 2 / g is more preferable, and 150 to 180m 2 It is even more preferred that the weight ratio is / g. The term "silica" means a particulate material made of silicon dioxide (SiO2) or containing silicon dioxide as a main component (e.g., 80% by mass or more, or even 90% by mass or more). The CTAB specific surface area of ​​silica is a value measured according to "ISO 5794 / 1".

[0021] The rubber composition of the present invention contains at least one of the above-mentioned carbon black or white filler, and contains 30 to 100 parts by mass of the carbon black and / or white filler in total relative to 100 parts by mass of the diene rubber. Furthermore, the lower limit is more preferably 40 parts by mass or more, more preferably 50 parts by mass or more, more preferably 55 parts by mass or more, and even more preferably 60 parts by mass or more. The upper limit is more preferably 90 parts by mass or less, more preferably 85 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less. For example, a more preferred range is 55 parts by mass or more and 85 parts by mass or less. In particular, since the effects of the present invention are more easily exhibited, it is more preferred that the rubber composition of the present invention contains carbon black and silica, and the total content of the carbon black and the white filler (white filler including silica) is within the above range. If the total amount of carbon black and / or white filler is less than 30 parts by mass or more than 100 parts by mass per 100 parts by mass of diene rubber, the mechanical properties of the rubber composition may be insufficient.

[0022] [Water-soluble phenolic resin polymer containing phenolsulfonic acid or its salt as a structural unit] The water-soluble phenolic resin polymer contained in the rubber composition of the present invention is a water-soluble phenolic resin polymer containing phenolsulfonic acid or its salt (at least one of them) as a constituent unit. That is, it is a water-soluble phenolic resin polymer obtained by polymerizing (addition condensation) a component containing phenolsulfonic acid (C6H6O4S, CAS No. 98-67-9) or its salt as a monomer. The phenolsulfonate may be a salt after polymerization. By containing a predetermined amount of such a water-soluble phenolic resin polymer in a predetermined composition, the rubber composition of the present invention can improve the surface roughness when the rubber composition of the present invention comes into contact with snow or its melting water, and can improve wet performance and friction on ice. In addition, the environmental load is not increased at this time. Furthermore, the breaking elongation can be improved. And, this predetermined amount of water-soluble phenolic resin polymer does not significantly affect the hardness of the rubber composition of the present invention. In addition, this water-soluble phenolic resin polymer has high affinity with the rubber component. Here, "water-soluble" means that it is soluble in an aqueous solvent (water, a water-soluble organic solvent, or a mixture thereof) at room temperature (23°C), that is, when the water-soluble phenolic resin polymer is mixed with an aqueous solvent at room temperature in a mass ratio of 1:1 to 2.5 and stirred, the water-soluble phenolic resin polymer is completely dissolved in the aqueous solvent. Also, completely dissolved means that when observed with the naked eye, no water-soluble phenolic resin polymer remains in the aqueous solvent (a liquid phase state in which the water-soluble phenolic resin polymer cannot be visually confirmed).

[0023] From the viewpoint of achieving both water-soluble properties and affinity with rubber components, the water-soluble phenolic resin polymer is preferably a resol-type water-soluble phenolic resin polymer obtained by reacting (addition condensation reaction) in the presence of an alkali catalyst such as hydroxide of an alkali metal or alkaline earth metal, ammonia, or tertiary amine. This resol-type water-soluble phenolic resin polymer has many methylol groups (-CH2OH) in its molecule, so that it has both water-soluble properties and affinity with rubber components. In the case of a novolac-type water-soluble phenolic resin polymer obtained by reacting in the presence of an acid catalyst, the amount of methylol groups in its molecule is small, so that it tends to be difficult to maintain water-soluble properties.

[0024] For the same reason, the water-soluble phenolic resin polymer is more preferably a water-soluble phenolic resin polymer that contains a salt of phenolsulfonic acid as a constituent unit and has a methylol group at the end of the molecule, i.e., at least a part (more preferably all) of the phenolsulfonic acid contained as a constituent unit is a phenolsulfonate salt, and a methylol group is present at the end of the molecule.

[0025] Preferred examples of the salt of phenolsulfonic acid include sodium salt, magnesium salt, potassium salt, ammonium salt, lithium salt, and calcium salt, but from the standpoint of ease of production, it is more preferable to include sodium phenolsulfonate as a constituent unit.

[0026] The structural unit (monomer used in polymerization) constituting this water-soluble phenolic resin polymer is not limited as long as it contains phenolsulfonic acid or its salt and maintains the water-soluble property, but further includes dihydroxydiphenyl sulfone (C 12 H 10It is more preferable to include O4S, CAS No. 80-09-1) as a structural unit, because this also makes it easier to maintain high levels of water solubility and affinity with the rubber component. A more preferred example of the water-soluble phenolic resin polymer containing phenolsulfonic acid or a salt thereof as a constituent unit contained in the rubber composition of the present invention is a polycondensation product of sodium phenolsulfonate-dihydroxyphenylsulfone-formaldehyde (CAS No. 71832-81-0, resol-type phenolic resin polymer: WSR-SP82 manufactured by Konishi Chemical Industry Co., Ltd.), as shown in the following formula (1) (wherein m and n are both integers):

[0027] [ka]

[0028] The rubber composition of the present invention contains 0.5 to 30 parts by mass of the water-soluble phenolic resin polymer containing the above-mentioned phenolsulfonic acid or its salt as a constituent unit relative to 100 parts by mass of the diene rubber. Furthermore, the lower limit is more preferably 1 part by mass or more, more preferably 3 parts by mass or more, more preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 8 parts by mass or more. The upper limit is more preferably 25 parts by mass or less, and even more preferably 22 parts by mass or less. If the content of the water-soluble phenolic resin polymer is less than 0.5 parts by mass relative to 100 parts by mass of the diene rubber, the wet performance and friction on ice of the rubber composition may not be sufficiently improved, and the elongation at break may also be reduced. If the content of the water-soluble phenolic resin polymer is more than 30 parts by mass relative to 100 parts by mass of the diene rubber, the friction on ice of the rubber composition may not be sufficiently improved, and the elongation at break may also be reduced.

[0029] Although not limited thereto, it is more preferable that the rubber composition of the present invention contains 1 to 40 parts by mass of the water-soluble phenolic resin polymer relative to 100 parts by mass of the carbon black and the white filler in total, since the interaction between the carbon black and / or the white filler and the water-soluble phenolic resin polymer containing the phenolsulfonic acid or its salt as a constituent unit is more easily exhibited. The lower limit is more preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and the upper limit is more preferably 35 parts by mass or less, more preferably 30 parts by mass or less. In particular, when the rubber composition of the present invention contains carbon black and silica, and contains the water-soluble phenolic resin polymer in the above range relative to 100 parts by mass of the carbon black and the white filler (white filler including silica), it is more preferable from the viewpoint of their interaction.

[0030] [Other ingredients] The rubber composition of the present invention may further contain appropriate amounts of various additives that are generally used in rubber compositions, such as inorganic fillers other than those described above, resin components, aroma oils, zinc oxide (zinc white), stearic acid, wax, lecithin, antioxidants, plasticizers, curing agents, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and vulcanization acceleration aids, within the range that does not significantly affect the effects of the present invention, and these additives can be kneaded by a known method to form a rubber composition.

[0031] For example, the content of the aromatic oil in the rubber composition of the present invention is preferably 5 to 30 parts by mass, more preferably 10 to 25 parts by mass, based on 100 parts by mass of the diene rubber. This can improve the processability of the rubber composition of the present invention. The content of the stearic acid, zinc oxide, and antioxidant in the rubber composition of the present invention is preferably 1 to 5 parts by mass, based on 100 parts by mass of the diene rubber. The content of the vulcanizing agent in the rubber composition of the present invention is preferably 0.3 to 3.0 parts by mass, more preferably 0.5 to 2.5 parts by mass, based on 100 parts by mass of the diene rubber. The content of the vulcanization accelerator in the rubber composition of the present invention is preferably 0.3 to 3.0 parts by mass, more preferably 0.5 to 2.5 parts by mass, based on 100 parts by mass of the diene rubber ....

[0032] The rubber composition of the present invention may further contain a silane coupling agent in order to further increase the dispersibility of silica when silica is used as a white filler. The silane coupling agent is not particularly limited as long as it is a silane compound having a hydrolyzable group and an organic functional group. The hydrolyzable group is also not limited, and examples thereof include an alkoxy group, a phenoxy group, a carboxy group, and an alkenyloxy group, and more preferably an alkoxysilyl group in which the alkoxy group is bonded to a silicon atom. When the hydrolyzable group is an alkoxysilyl group, the number of carbon atoms in the alkoxy group is preferably 1 to 16, and more preferably 1 to 4. Examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and a propoxy group.

[0033] The organic functional group is not limited, but may be any group capable of forming a chemical bond with an organic compound, such as an epoxy group, a vinyl group, an acryloyl group, a methacryl group, an amino group, a sulfide group (particularly, a polysulfide group (-S n - (n is an integer of 2 or more), mercapto group, blocked mercapto group (protected mercapto group) (for example, octanoylthio group), etc., and among these, sulfide group (particularly disulfide group, tetrasulfide group), mercapto group, and blocked mercapto group are preferred. Such silane coupling agents may be used alone or in combination of two or more. The silane coupling agent is preferably a sulfur-containing silane coupling agent.

[0034] The rubber composition of the present invention preferably contains 1 to 20 parts by mass, and more preferably 2 to 10 parts by mass, of the silane coupling agent per 100 parts by mass of the above-mentioned silica.

[0035] [Manufacturing method etc.] The method for producing the rubber composition of the present invention may be a conventional method and is not particularly limited. As an example of the production method, the rubber composition of the present invention can be produced by kneading and mixing the diene rubber, carbon black and / or white filler, water-soluble phenolic resin polymer containing phenolsulfonic acid as a constituent unit, and other components as necessary at room temperature or at a high temperature using a kneading machine such as a Banbury mixer, a kneader, or a roll, in a predetermined blend. When using a vulcanization-based component (sulfur, vulcanization accelerator, etc.), it is preferable to first mix the other components at a high temperature, cool the mixture, and then mix the vulcanization-based component. The water-soluble phenolic resin polymer containing phenolsulfonic acid as a constituent unit can also be mixed in the form of an aqueous solution.

[0036] The rubber composition of the present invention obtained as described above is a rubber composition in which the hardness is generally maintained (does not change significantly) and the breaking elongation, wet performance, and friction on ice are all improved due to the interaction between the diene rubber, carbon black and / or white filler, and the water-soluble phenolic resin polymer containing phenolsulfonic acid as a structural unit as described above.

[0037] The rubber composition of the present invention can be used in, for example, the tire tread portion (cap tread portion) that comes into contact with the road surface to obtain a studless tire of the present invention that has excellent performance on ice. The rubber composition of the present invention may also be used in other tire components. The studless tire of the present invention is preferably a pneumatic tire, and the gas to be filled in the pneumatic tire may be, for example, air, inert gas such as nitrogen, argon, helium, or other gas.

[0038] Hereinafter, examples of the present invention will be described, however, the present invention is not limited to the following examples, and various modifications are possible within the technical concept of the present invention. EXAMPLES

[0039] (Preparation and Evaluation of Rubber Compositions) Rubber compositions having the ingredients shown in Table 1 below were prepared.

[0040] Specifically, first, the components (except sulfur and vulcanization accelerator) in the mass parts shown in the upper part of Table 1 below were mixed for 5 minutes after heating to about 150°C using a 1.7-liter closed Banbury mixer, and then the components were discharged from the mixer and cooled to room temperature to obtain a master batch. The water-soluble phenolic resin polymer was added in such a way that the solid content of the product (aqueous solution) with a solid content of 30% by mass was the mass shown in the upper part of Table 1 below as the solid content. Furthermore, using the Banbury mixer, a predetermined amount of sulfur and a vulcanization accelerator were mixed and kneaded into each of the obtained master batches, and the mixture was press-vulcanized at 170°C for 10 minutes in a predetermined mold to produce rubber compositions (vulcanized rubber test pieces) of the standard example, Examples 1 to 3, and Comparative Examples 1 to 4.

[0041] The rubber compositions (vulcanized rubber test pieces) obtained in the standard example, examples 1 to 3, and comparative examples 1 to 4 were evaluated for hardness, elongation at break, wet performance, and friction on ice as described below.

[0042] <Hardness> The rubber hardness (HS) of each of the obtained vulcanized rubber test pieces was measured at a temperature of 20°C using a durometer type A (manufactured by Toyo Seiki Seisakusho, Ltd.) in accordance with JIS K6253-3:2012. The results are shown in the lower part of Table 1. The results are expressed as an index with the standard value set at 100.

[0043] <Elongation at break> A tensile test was performed on each of the obtained vulcanized rubber test pieces at a tensile speed of 500 mm / min in accordance with JIS K6251:2010, and the breaking elongation (= elongation at break: Eb) was measured at room temperature (20° C.). The results are shown in the lower part of Table 1. The results are expressed as an index with the standard value set at 100.

[0044] <Wet performance> For each of the obtained vulcanized rubber test pieces, tan δ was measured under conditions of initial strain of 10%, amplitude of ±2%, frequency of 20 Hz, and temperature of 0° C. using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisakusho) in accordance with JIS K6394:2007. The results are shown in the lower part of Table 1 below. The results are expressed as an index with the standard example value being 100. A higher index value means better wet performance (wet grip performance).

[0045] <Friction on ice> Each 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 3 The coefficient of friction on ice was measured at a drum rotation speed of 25 km / h. The results are shown in the lower part of Table 1 below. The results are expressed as an index, with the standard example value being 100. The higher the index, the greater the friction force on the ice (the easier it is to stop on the ice).

[0046] [Table 1]

[0047] The details of each component in Table 1 above are as follows: NR: Natural rubber (STR20, glass transition temperature (Tg): -65°C, manufactured by Bonbandit) BR: Butadiene rubber (Nipol BR1220, glass transition temperature (Tg): -110°C, manufactured by Zeon Corporation) ·Silica: ULTRASIL VN3 (CTAB adsorption specific surface area: 167m 2 / g, manufactured by Evonik Degussa) Carbon black: Show Black N339 (Nitrogen adsorption specific surface area (N2SA): 88m 2 / g, manufactured by Gabot Japan Co., Ltd.) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) Zinc oxide: Three types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.) Stearic acid: Beads Stearic Acid YR (NOF Corporation) Antioxidant: Amine-based antioxidant (Santoflex 6PPD, manufactured by Flexis) Wax: Paraffin wax (manufactured by Ouchi Shinko Chemical Co., Ltd.) Aroma oil: Extract No. 4S (Shell Lubricants Japan) Sulfur: Oil-treated sulfur (Hosoi Chemicals) Vulcanization accelerator: Sulfenamide vulcanization accelerator (Suncerer CM-G, Sanshin Chemical Co., Ltd.) Water-soluble phenolic resin polymer: Sodium phenolsulfonate · dihydroxyphenylsulfone · formaldehyde polycondensate (WSR-SP82: CAS No. 71832-81-0, resol-type phenolic resin polymer, solid content 30% by mass, manufactured by Konishi Chemical Industry Co., Ltd.) *"Water soluble" has the meaning described above. Phenolic resin 1: Alkylphenol resin (Tamanol 521, resol type phenolic resin polymer, manufactured by Arakawa Chemical Industries, Ltd.) Phenolic resin 2: pt-butylphenol-acetylene condensate phenolic resin (KORESIN, novolac-type phenolic resin polymer, manufactured by BASF) *These are insoluble in aqueous solvents at room temperature (do not dissolve under the conditions mentioned above).

[0048] From these results, it was shown that by using a composition containing 70 parts by mass of carbon black and silica in total and 5 to 20 parts by mass of a specific water-soluble phenolic resin polymer per 100 parts by mass of diene rubber (natural rubber and butadiene rubber), it was possible to obtain a rubber composition in which the hardness was generally maintained (did not change significantly) and further the breaking elongation, wet performance, and friction on ice were all excellent, compared with the standard example, etc. These rubber compositions were recognized as being particularly suitable for use in studless tires. On the other hand, rubber compositions containing a water-insoluble phenolic resin instead of a specified water-soluble phenolic resin polymer showed reduced friction on ice and a large change in hardness (Comparative Examples 1 and 2). Also, some showed a decrease in breaking elongation (Comparative Example 1). When the content of the specified water-soluble phenolic resin polymer was too low, the breaking elongation decreased, and neither the wet performance nor the friction on ice improved (Comparative Example 3). When the content of the specified water-soluble phenolic resin polymer was too high, the hardness increased significantly, and the breaking elongation and the friction on ice decreased (Comparative Example 4).

Claims

1. The rubber composition contains, per 100 parts by mass of diene rubber, 30 to 100 parts by mass of carbon black and / or a white filler, and 0.5 to 30 parts by mass of a water-soluble phenolic resin polymer containing phenolsulfonic acid or a salt thereof as a constituent unit.

2. 2. The rubber composition according to claim 1, wherein the water-soluble phenolic resin polymer is a resol-type water-soluble phenolic resin polymer obtained by reacting in the presence of an alkali catalyst.

3. 3. The rubber composition according to claim 1, wherein the water-soluble phenolic resin polymer contains dihydroxydiphenyl sulfone as a constituent unit.

4. 3. The rubber composition according to claim 1, wherein the water-soluble phenolic resin polymer contains a salt of phenolsulfonic acid as a constituent unit and has a methylol group at a terminal thereof.

5. The rubber composition according to claim 4, wherein the salt is a sodium salt, a magnesium salt, a potassium salt, an ammonium salt, a lithium salt, or a calcium salt.

6. The rubber composition according to claim 1 or 2, wherein the diene-based rubber comprises natural rubber (NR) and butadiene rubber (BR).

7. 3. The rubber composition according to claim 1, wherein the diene rubber has an average glass transition temperature of -100 to -50°C.

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

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