Rubber composition

Abstract

To provide a rubber composition characterized by substantially retained hardness, maintained or improved elongation at break, and enhanced performance on ice.SOLUTION: The foregoing problem is solved by a rubber composition containing 100 pts.mass of diene rubber in combination with 30-100 pts.mass of carbon black and / or white fillers and 0.5-20 pts.mass of a polyester resin that is solid at room temperature and soluble in aqueous solvents at 60°C or higher.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 performance (ice performance) that provides high friction even on ice such as icy roads. Various rubber compositions have been developed to improve the ice performance of studless tires.

[0003] For example, Patent Document 1 discloses a pneumatic tire that satisfies all of the requirements for braking performance on rainy roads, braking performance on icy and snowy roads, and steering stability on dry roads, and a rubber composition that can be effectively used for the tread rubber thereof, which comprises a matrix rubber having a rubber component made of at least one type selected from natural rubber and diene-based synthetic rubber, and a water-soluble resin having a water solubility temperature of 10°C or lower, and is characterized in that at 100% elongation after vulcanization, 80% or more of the interface between the water-soluble resin and the matrix rubber is bonded. Patent Document 2 discloses a pneumatic tire in which a belt layer and a tread are sequentially arranged on the outside of a crown portion of a carcass that straddles a pair of bead cores in a toroidal shape, and the tread rubber that comes into contact with the ground is formed by dividing it into multiple layers in the circumferential direction of the tire, and at least one layer of the tread is made of a rubber composition that contains a water-soluble resin. This pneumatic tire satisfies both high levels of braking performance on ice and on wet roads, and also ensures stable driving performance on general roads and snowy and icy roads. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-191829 A [Patent Document 2] JP 2001-047815 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the water-soluble resins contained in the rubber compositions described in Patent Documents 1 and 2 are soluble in low-temperature water, and may therefore have a significant effect on the mechanical properties of the rubber composition. In addition, it is preferable for rubber compositions used in studless tires and the like to have improved friction on ice without a significant change in hardness, and to maintain or improve breaking elongation, 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 largely maintains its hardness, maintains or improves its breaking elongation, and further improves its performance 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 20 parts by mass of a polyester resin that is solid at room temperature and soluble in an aqueous solvent at 60°C or higher, per 100 parts by mass of diene rubber, largely maintains hardness, maintains or improves breaking elongation, and further improves performance on ice, thereby completing the present invention.

[0008] That is, the present invention is as follows: <1> ~ <6> 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 white filler, and 0.5 to 20 parts by mass of a polyester resin which is solid at room temperature and soluble in an aqueous solvent at 60°C or higher. <2> The polyester resin is a polyester resin containing a moiety derived from a chain polyol represented by the following formula (1): <1> The rubber composition according to claim 1. (1) -(CH2-CH2-O) n - (n=2~100) <3> The polyester resin has a melting point of 30° C. or more and 80° C. or less. <1> or <2> The rubber composition according to claim 1. <4> The diene rubber includes natural rubber (NR) and butadiene rubber (BR); <1> ~ <3> The rubber composition according to any one of the above. <5> The diene rubber has an average glass transition temperature of -100 to -50°C. <1> ~ <4> The rubber composition according to any one of the above. <6> <1> ~ <5> 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 generally maintains hardness, maintains or improves breaking elongation, and further improves performance 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 20 parts by mass of a polyester resin that is solid at room temperature and soluble in an aqueous solvent at 60° C. or higher, 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. Here, 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, the diene rubber contained in the rubber composition of the present invention has an average glass transition temperature (average Tg) of -100 to -50°C, since it is easy to improve the performance on ice. 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] [Polyester resin that is solid at room temperature and soluble in aqueous solvents at 60°C or higher] The polyester resin contained in the rubber composition of the present invention is a polyester resin (a copolymer having a plurality of ester bonds in the molecular main chain, which is a condensation polymerized polycarboxylic acid and polyalcohol) that is solid at room temperature and soluble in an aqueous solvent at 60°C or higher. By including a predetermined amount of such a polyester resin in a predetermined composition, the rubber composition of the present invention is able to improve its performance on ice without significantly affecting its hardness. Furthermore, this also makes it possible to maintain or improve its breaking elongation. Here, "solid at room temperature" means that the ambient temperature is room temperature (23°C), that is, that the resin is in a solid form (does not flow) under an atmosphere at room temperature. Also, "soluble in an aqueous solvent at 60°C or higher" means that when the polyester resin is mixed with an aqueous solvent (water, a water-soluble organic solvent, or a mixture thereof) at 60°C or higher in a mass ratio of 1:5 and stirred, the polyester resin is uniformly dispersed in the aqueous solvent and becomes liquid phase (dissolves). Note that the polyester resin is insoluble in an aqueous solvent at room temperature or lower (does not become uniformly dispersed liquid phase).

[0023] The polyester resin contained in the rubber composition of the present invention is not limited as long as it is a polyester resin having the above-mentioned physical properties, but is preferably a polyester resin obtained by condensation polymerization of a polyhydric alcohol and an aromatic polycarboxylic acid (i.e., a polyester resin containing a site derived from an aromatic polycarboxylic acid), and for example, a copolymer obtained by condensation polymerization of a polyhydric alcohol and terephthalic acid (C8H6O4, CAS No. 100-21-0) is shown as a preferred example. In addition, since the effects of the present invention are easily exhibited, it is preferable that the polyester resin is a nonionic polyester resin that does not ionize when dissolved in water.

[0024] Moreover, since the polyester resin is likely to be soluble in an aqueous solvent at 60° C. or higher and the effects of the present invention are more easily exhibited, it is more preferable that the polyester resin is a polyester resin containing a moiety derived from a chain polyol represented by the following formula (1). In other words, it is more preferable that the polyester resin is a polyester resin containing a moiety derived from a chain polyol (chain polyhydric alcohol) represented by the following formula (1) in the main chain of the molecule. (1) -(CH2-CH2-O) n - (n=2~100) The lower limit of n in this formula is more preferably 5 or more, even more preferably 10 or more, even more preferably 20 or more, even more preferably 30 or more, and even more preferably 40 or more. The upper limit may be 90 or less, or may be 80 or less. In addition, it is preferable that the mass ratio of the above-mentioned chain polyol-derived portion in this polyester resin is 70% or more and 90% or less. For example, a copolymer obtained by condensation polymerization of polyethylene glycol and terephthalic acid having a number average molecular weight of 200 to 4000 is shown as a preferred example (this "number average molecular weight" means a value calculated based on a hydroxyl value measured in accordance with JIS K 1557).

[0025] From the viewpoint of easily improving performance on ice, the weight average molecular weight of the polyester resin that is solid at room temperature and soluble in an aqueous solvent at 60° C. or higher is preferably 5,000 or more and 30,000 or less, although this is not limited thereto. The lower limit is more preferably 8,000 or more, and even more preferably 10,000 or more. The upper limit is more preferably 25,000 or less, and even more preferably 20,000 or less, and even more preferably 18,000 or less. Here, 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.

[0026] Furthermore, the polyester resin contained in the rubber composition of the present invention, which is solid at room temperature and soluble in an aqueous solvent at 60°C or higher, more preferably has a melting point of 30°C or higher and 80°C or lower. This is because it is easy to disperse during mixing of raw materials in the production of the rubber composition of the present invention, and its mechanical properties are easily improved. The upper limit is more preferably 70°C or lower, and even more preferably 60°C or lower. The lower limit may be 40°C or higher. Note that if the melting point exceeds 80°C, it tends to be difficult to disperse during mixing, and it tends to be difficult to maintain or improve the mechanical properties of the rubber composition. Here, the melting point refers to a value measured using a DSC (differential scanning calorimeter).

[0027] The rubber composition of the present invention contains 0.5 to 20 parts by mass of the polyester resin, which is solid at room temperature and soluble in an aqueous solvent at 60°C or higher, relative to 100 parts by mass of diene rubber. The lower limit is more preferably 1 part by mass or more, more preferably 3 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 18 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less. If the content of the polyester resin is less than 0.5 parts by mass relative to 100 parts by mass of diene rubber, the performance on ice of the rubber composition may not be sufficiently improved. If the content of the polyester resin is more than 20 parts by mass relative to 100 parts by mass of diene rubber, the rubber composition may become hard and the elongation at break may decrease.

[0028] Although not limited thereto, the rubber composition of the present invention more preferably contains 1 to 40 parts by mass of the polyester resin 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 polyester resin which is solid at room temperature and soluble in an aqueous solvent at 60° C. or higher 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 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less. In particular, when the rubber composition of the present invention contains carbon black and silica, and contains the polyester resin 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.

[0029] [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.

[0030] For example, the content of the aromatic oil in the rubber composition of the present invention is preferably 5 to 30 parts by mass, and more preferably 10 to 25 parts by mass, per 100 parts by mass of the diene rubber described above, which can further improve the processability, etc. of the rubber composition of the present invention. 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 ....

[0031] 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.

[0032] 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.

[0033] 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.

[0034] [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, the carbon black and / or the white filler, the polyester resin which is solid at room temperature and soluble in an aqueous solvent at 60°C or higher, and other components as necessary, in a predetermined ratio at room temperature or at a high temperature using a kneading machine such as a Banbury mixer, a kneader, or a roll. When a vulcanization-based component (sulfur, vulcanization accelerator, etc.) is used, it is preferable to first mix the other components at a high temperature and then mix the vulcanization-based component after cooling.

[0035] 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), the breaking elongation is maintained or improved, and performance on ice is improved due to the interaction between the diene rubber described above, the carbon black and / or white filler, and the polyester resin that is solid at room temperature and soluble in an aqueous solvent at 60°C or higher.

[0036] 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.

[0037] 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

[0038] (Preparation and Evaluation of Rubber Compositions) Rubber compositions having the ingredients shown in Table 1 below were prepared.

[0039] Specifically, first, the components (except sulfur and vulcanization accelerator) in the parts by mass 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 mixture was discharged from the mixer and cooled to room temperature to obtain a master batch. Furthermore, using the Banbury mixer, a predetermined amount of sulfur and 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 4, and Comparative Examples 1 to 3.

[0040] The rubber compositions (vulcanized rubber test pieces) obtained in the Standard Example, Examples 1 to 4, and Comparative Examples 1 to 3 were evaluated for hardness, elongation at break, and performance on ice as described below.

[0041] <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.

[0042] <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.

[0043] <Ice performance> 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 -1.5°C and a load of 5.5kg / cm 2 The coefficient of friction on ice was measured at a drum rotation speed of 25 km / h. The results are shown in the bottom row 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 ice and the better the performance on ice (the easier it is to stop on ice).

[0044] [Table 1]

[0045] 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) Carbon black: Show Black N339 (Nitrogen adsorption specific surface area (N2SA): 88m 2 / g, manufactured by Gabot Japan) ·Silica: ULTRASIL VN3 (CTAB adsorption specific surface area: 167m 2 / g, manufactured by Evonik Degussa) Silane coupling agent: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa) 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.) Polyester resin 1: A polyester resin that is solid at room temperature and soluble in aqueous solvents at 60°C or higher (PLASCOAT FR-550, a nonionic polyester resin containing approximately 80% by mass of a chain polyol derived from condensation polymerization of polyethylene glycol and terephthalic acid, weight average molecular weight approximately 15,500, melting point 45-55°C, manufactured by GOO Chemical Industry Co., Ltd.) Polyester resin 2: A polyester resin that is solid at room temperature and soluble in aqueous solvents at 60°C or higher (PLASCOAT FR-627, a nonionic polyester resin containing approximately 80% by mass of a chain polyol derived from condensation polymerization of polyethylene glycol and terephthalic acid, weight average molecular weight approximately 15,000, melting point 50°C, manufactured by GOO Chemical Industry Co., Ltd.) Polyester elastomer: A polyester resin that is solid at room temperature and insoluble in aqueous solvents above 60°C (Hytrel, manufactured by Toray Celanese)

[0046] From these results, it was shown that by using a composition containing 65 parts by mass of carbon black and silica in total and 5 to 10 parts by mass of a specific polyester resin 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 is generally maintained (does not change significantly), the breaking elongation is maintained or improved, and the performance on ice is improved, compared to the standard example, etc. These rubber compositions were recognized to be particularly suitable for use in studless tires. On the other hand, when the content of the specified polyester resin was too low, the breaking elongation decreased and the performance on ice did not improve (Comparative Example 1), and when the content of the specified polyester resin was too high, the hardness increased and the breaking elongation decreased (Comparative Example 2). Furthermore, a rubber composition containing a polyester resin that is insoluble in an aqueous solvent at 60°C or higher decreased the breaking elongation and did not improve the performance on ice (Comparative Example 3).

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 20 parts by mass of a polyester resin that is solid at room temperature and soluble in an aqueous solvent at 60°C or higher.

2. The rubber composition according to claim 1 , wherein the polyester resin is a polyester resin containing a moiety derived from a chain polyol represented by the following formula (1): (1) -(CH 2 -CH 2 -O) n - (n=2~100)

3. The rubber composition according to claim 1 or 2, wherein the polyester resin has a melting point of 30°C or higher and 80°C or lower.

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

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

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

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