winter tires

Abstract

Winter tires comprising a tread which is made from a rubber composition for a tread, wherein the rubber composition contains: a rubber component containing natural rubber and butadiene rubber, Aromatic oil with an aromatic hydrocarbon content, in mass percent, of 15 mass percent or more, Silica and Soot, wherein the total amount of natural rubber and butadiene rubber, based on 100% by mass of the rubber component, is 30% by mass or more, wherein the amount of aromatic oil per 100 parts by mass of the rubber component is 30 to 85 parts by mass and the amount of silica per 100 parts by mass of the rubber component is 60 to 85 parts by mass, and where the proportion of silica, based on 100% by mass of the total amount of silica and carbon black, is 45% by mass or more.

Description

TECHNICAL FIELD

[0001] The present invention relates to a rubber composition for a winter tire (for a studless tire) and a winter tire. STATE OF THE ART

[0002] The use of studded tires has been banned by law in Japan to prevent the powdery dust pollution resulting from the use of studded tires. Therefore, studless or winter tires are now used instead of studded tires in cold regions. Winter tires have been improved in their materials and construction for driving on icy or snowy roads, which have a rougher surface than conventional roads. For example, a rubber composition has been developed that contains diene rubber with excellent low-temperature properties and contains a plasticizer in an increased amount to enhance the softening effect. Mineral oil is generally used as the plasticizer to improve low-temperature properties.

[0003] When the amount of mineral oil is increased to improve low-temperature properties, abrasion resistance typically deteriorates. One way to solve this problem is to replace mineral oil with aromatic oil; however, this deteriorates low-temperature properties, making it difficult to achieve sufficient performance on ice and snow. In contrast, the combined use of aromatic oil and silica enables an improvement in low-temperature properties without reducing abrasion resistance; however, sufficient levels of these properties still cannot be achieved. Furthermore, an improvement in wet grip, ice and snow performance, and an improvement in abrasion resistance are also described.

[0004] For example, Patent Document 1 discloses a rubber composition for a tread containing components such as natural rubber, butadiene rubber, silica, and aromatic oil. However, this composition still has room for improvement in achieving sufficient wet grip performance in addition to both sufficient abrasion resistance and sufficient performance on ice and snow (low-temperature properties).

[0005] Tires whose treads contain rubber compositions containing natural rubber, butadiene rubber, silica and carbon black are known from US 200810 105 346 A1, JP H09-255813 A, JP 2006-131714 A, JP 2007-277437 A, JP 2008 106113 A, JP 2006-056967 A, JP 2006-241338 A and JP 2008-163234 A.

[0006] Patent Document 1: JP H06-240052 A SUMMARY OF THE INVENTION

[0007] The present invention aims to solve the above-mentioned problems and thus aims to provide a winter tire having a tread made of the rubber composition recited in claim 1, which can achieve, in a balanced manner, sufficiently high abrasion resistance, sufficiently high performance on ice and snow, and excellent wet grip performance.

[0008] The present invention relates to a winter tire comprising a tread made from a rubber composition for a tread, the rubber composition containing: a rubber component containing natural rubber and butadiene rubber, aromatic oil having an aromatic hydrocarbon content, in mass percent, of 15 mass% or more, silica, and carbon black, wherein the total amount of the natural rubber and the butadiene rubber, based on 100 mass% of the rubber component, is 30 mass% or more, the amount of the aromatic oil, based on 100 parts by mass of the rubber component, being 30 to 85 parts by mass, and the amount of silica, based on 100 parts by mass of the rubber component, being 60 to 85 parts by mass, and the proportion of silica being 45 mass% or more, based on 100 parts by mass of the total amount of the silica and the carbon black.

[0009] The present invention relates to a winter tire whose tread is made from a rubber composition containing specific amounts of natural rubber, butadiene rubber, aromatic oil, silica, and carbon black. The use of this rubber composition for a tread results in the provision of a winter tire that achieves, in a balanced manner, excellent abrasion resistance, excellent performance on ice and snow, and excellent wet grip performance. BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

[0010] The winter tire according to the present invention contains a rubber component including natural rubber and butadiene rubber, aromatic oil, silica, and carbon black. Here, the natural rubber and butadiene rubber are contained in the rubber component in a total amount equal to or greater than a specific value, and the aromatic oil and silica are also contained in specific amounts. Furthermore, the proportion of silica relative to the total amount of silica and carbon black is equal to or greater than a specific value. Accordingly, abrasion resistance, ice and snow performance, and wet grip performance can be improved in a balanced manner.

[0011] The rubber composition used to manufacture the tread of the winter tire according to the present invention contains both natural rubber and butadiene rubber as rubber components. This makes it possible to improve low-temperature properties and thus enhance performance on ice and snow. In particular, butadiene rubber is an important component for achieving sufficiently high performance on ice.

[0012] Examples of natural rubber (NR) include rubbers commonly used in the tire industry, such as SIR20, RSS#3, and TSR20. Examples of natural rubber (NR) also include modified natural rubbers, such as deproteinized natural rubber (DPNR), high-purity natural rubber (HPNR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Each of these can be used alone, or two or more of them can be used in blends.

[0013] The butadiene rubber (BR) preferably contains a cis amount of 80 mass% or more. This leads to an increase in abrasion resistance. The cis amount is preferably 85 mass% or more, more preferably 90 mass% or more, and most preferably 95 mass% or more.

[0014] Furthermore, the BR in the form of a 5% solution in toluene at 25°C preferably has a viscosity of 30 cps or more. A viscosity of less than 30 cps can severely impair processability and may also impair abrasion resistance. The viscosity of the BR solution in toluene is preferably 100 cps or less, and more preferably 70 cps or less. A viscosity of more than 100 cps can also impair processability.

[0015] Furthermore, in view of improving both processability and abrasion resistance, BR with a ratio of Mw / Mn of 3.0 to 3.4 is preferred.

[0016] Examples of the BR include, but are not limited to, BR's with a high cis content, such as BR1220 manufactured by Zeon Corporation, and BR130B and BR150B manufactured by Ube Industries, Ltd., and BR's containing a syndiotactic polybutadiene crystal, such as VCR412 and VCR617 manufactured by Ube Industries, Ltd.

[0017] The amount of NR is preferably 30 mass% or more, more preferably 40 mass% or more, even more preferably 50 mass% or more, and most preferably 55 mass% or more, based on 100 mass% of the rubber component. An amount of NR less than 30 mass% may greatly reduce tear strength and thus make it difficult to ensure sufficiently high abrasion resistance. The amount of NR is preferably 80 mass% or less, more preferably 70 mass% or less, and particularly preferably 65 mass% or less, based on 100 mass% of the rubber component. An amount of NR exceeding 80 mass% may deteriorate low-temperature properties, and thus, it may be unable to achieve on-ice performance necessary for a winter tire.

[0018] The amount of BR is preferably 10 mass% or more, more preferably 20 mass% or more, even more preferably 30 mass% or more, and particularly preferably 35 mass% or more, based on 100 mass% of the rubber component. The amount of BR of 10 mass% or more enables the rubber composition for a winter tire to exhibit its required performance on ice. The amount of BR is preferably 80 mass% or less, more preferably 70 mass% or less, and even more preferably 60 mass% or less, based on 100 mass% of the rubber component. An amount of BR exceeding 80 mass% may severely deteriorate processability and may lead to the occurrence of fading due to the bleeding of chemical compounds.

[0019] The total amount of NR and BR, based on 100 mass% of the rubber component, is 30 mass% or more, preferably 60 mass% or more, more preferably 80 mass% or more, and most preferably 100 mass%. The larger the total amount of NR and BR, the better the low-temperature properties, resulting in the required performance on ice being achieved.

[0020] The rubber composition of the tread of the winter tire according to the invention may contain other rubbers as long as they do not inhibit the effects of the present invention. Examples of the other rubbers include styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene-diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), butyl rubber (IIR), and halogenated butyl rubber (X-IIR).

[0021] The rubber composition of the tread of the winter tire according to the present invention contains a comparatively large amount of aromatic oil. When mineral oil, which has excellent low-temperature properties, is used, it ensures excellent performance on ice and snow, but deteriorates abrasion resistance. If the amount of mineral oil is reduced to ensure high abrasion resistance, the low-temperature properties are deteriorated, and consequently, the performance on ice and snow is impaired. Accordingly, sufficiently good performance on ice and snow and sufficiently high abrasion resistance, which are contradictory properties, cannot be achieved simultaneously.In contrast, an aromatic oil does not significantly impair abrasion resistance, even when blended in large quantities, which can lead to the achievement of both good ice and snow performance and good abrasion resistance. Aromatic oil, incorporated into the rubber composition along with large amounts of silica and carbon black, can contribute to achieving both good ice and snow performance and good abrasion resistance to a higher degree, and can also contribute to achieving good wet grip.

[0022] The aromatic oil according to the present invention in the tread of the winter tire is an oil having an aromatic hydrocarbon content, in mass percent, of 15 mass% or more, which content is determined according to ASTM Standard D2140. More specifically, the process oil contains aromatic hydrocarbon (C A ), paraffinic hydrocarbon (C P ) and naphthenic hydrocarbon (C N ). The process oil is based on the weight ratio between C A (mass%), C P (mass%) and C N (mass%) is roughly considered as aromatic oil, paraffinic oil, or naphthenic oil. In view of this, the process oil according to the present invention has a C A-content of 15 mass% or more, and more preferably 17 mass% or more. Furthermore, the aromatic oil according to the present invention is preferably an oil having a C A -content of 70 mass% or less, and more preferably 65 mass% or less.

[0023] Examples of commercially available aromatic oil products include AC-12, AC-460, AH-16, AH-24 and AH-58, manufactured by Idemitsu Kosan Co., Ltd., and process NC330S, manufactured by Japan Energy Corporation.

[0024] The amount of the aromatic oil is 30 parts by mass or more, particularly preferably 45 parts by mass or more, and most preferably 60 parts by mass or more, based on 100 parts by mass of the rubber component. A larger amount of the aromatic oil results in a better softening effect and better low-temperature properties, leading to improved performance on ice and snow. The amount of the aromatic oil is 85 parts by mass or less, particularly preferably 80 parts by mass or less, based on 100 parts by mass of the rubber component. An amount of the aromatic oil exceeding 85 parts by mass may deteriorate properties such as processability, abrasion resistance, and aging resistance.

[0025] The tread rubber composition of the winter tire according to the present invention contains a comparatively large amount of silica. The tread rubber composition of the winter tire according to the present invention, which contains silica together with aromatic oil, can achieve both sufficient abrasion resistance and sufficient performance on ice and snow, while simultaneously improving wet grip, which has been considered a weak point of a winter tire. Examples of the silica include, but are not limited to, silica produced by a wet process and silica produced by a dry process.

[0026] The specific surface area (N2SA) of the silica, determined by nitrogen adsorption, is preferably 80 m 2 / g or more, particularly preferably 120 m 2 / g or more and particularly preferably 150 m2 / g or more. A N2SA of the silica of less than 80 m 2 / g can significantly reduce the tensile strength and consequently make it difficult to ensure sufficiently high abrasion resistance. Furthermore, the N2SA of the silica is preferably 250 m 2 / g or less, particularly preferably 220 m 2 / g or less and particularly preferably 180 m 2 / g or less. A N2SA of the silica of greater than 250 m 2 / g can greatly increase the viscosity of the rubber composition containing silica, which impairs the processability.

[0027] The N2SA of silica is determined here by the BET method in accordance with ASTM standard D3037-81.

[0028] The amount of silica is 60 parts by mass or more based on 100 parts by mass of the rubber component. Blending the silica in an amount of 12 parts by mass or more can lead to achieving sufficient ice and snow performance required for a winter tire. Furthermore, the amount of silica is 85 parts by mass or less based on 100 parts by mass of the rubber component, more preferably 80 parts by mass or less, particularly preferably 70 parts by mass or less, and most preferably 60 parts by mass or less. An amount of silica exceeding 85 parts by mass may deteriorate processability and workability and may lead to poor low-temperature properties due to the increase in the filler amount.

[0029] The rubber composition of the tread of the winter tire according to the invention preferably contains a silane coupling agent together with silica.

[0030] As the silane coupling agent, all silane coupling agents which are conventionally used with silica in the rubber industry can be used. Examples thereof include sulfide-type silane coupling agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)tetrasulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, bis(2-trimethoxysilylethyl)tetrasulfide, bis(4-trimethoxysilylbutyl)tetrasulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(2-triethoxysilylethyl)trisulfide, bis(4-triethoxysilylbutyl)trisulfide, bis(3-trimethoxysilylpropyl)trisulfide, bis(2-trimethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)trisulfide, bis(2-trimethoxysilylethyl)trisulfide, bis(4-trimethoxysilylbutyl)trisulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)disulfide, Bis(4-triethoxysilyl-butyl)disulfide, bis(3-trimethoxysilylpropyl)disulfide, bis(2-trimethoxysilyl-ethyl)disulfide and bis(4-trimethoxysilylbutyl)disulfide, mercapto-type silane coupling agents,such as 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane; vinyl-type silane coupling agents such as vinyltriethoxysilane and vinyltrimethoxysilane; amino-type silane coupling agents such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy-type silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-type silane coupling agents such as 3-nitropropyltrimethoxysilane; and chlorine-type silane coupling agents such as 3-chloropropyltrimethoxysilane. Of these, bis(3-triethoxysilylpropyl) disulfide, which is inexpensive and readily available, is preferred. Each of these silane coupling agents can be used alone, or two or more of them can be used in admixture with each other.

[0031] The amount of the silane coupling agent is preferably 2 parts by mass or more, and more preferably 3 parts by mass or more, based on 100 parts by mass of silica. An amount of the silane coupling agent of less than 2 parts by mass may not achieve a sufficient effect intended to be achieved by adding the silane coupling agent. Furthermore, the amount of the silane coupling agent is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less, based on 100 parts by mass of silica. An amount of the silane coupling agent of more than 20 parts by mass may reduce reinforcement and abrasion resistance.

[0032] The rubber composition of the tread of the winter tire according to the present invention contains carbon black, which provides reinforcement. The rubber composition of the tread of the winter tire according to the present invention, which further contains NR and BR, as well as aromatic oil and silica, can improve abrasion resistance, ice and snow performance, and wet grip performance in a balanced manner. Examples of the carbon black include, but are not limited to, SAF, ISAF, HAF, FF, and GPF.

[0033] The carbon black typically has an average particle size of 31 nm or less and / or a DBP oil absorption of 100 ml / 100 g or more. The addition of such carbon black provides the necessary reinforcement for the rubber composition, can ensure sufficiently good block stiffness, uneven wear resistance, and fracture toughness, and leads to achieving the excellent effects of the present invention.

[0034] An average particle size of carbon black greater than 31 nm can greatly deteriorate the tensile strength and make it difficult to ensure sufficient abrasion resistance. The average particle size of carbon black is more preferably 25 nm or less, and even more preferably 23 nm or less. Further, the average particle size of carbon black is preferably 15 nm or larger, and particularly preferably 19 nm or larger. An average particle size of carbon black less than 15 nm can greatly increase the viscosity of the rubber composition containing carbon black and can deteriorate processability. In the present invention, the average particle size is the number-average particle size, and this can be measured using a transmission electron microscope.

[0035] A DBP (dibutyl phthalate oil) absorption of carbon black of less than 100 ml / 100 g may result in poor reinforcement and may make it difficult to ensure sufficient abrasion resistance. The DBP oil absorption of carbon black is more preferably 105 ml / 100 g or more, and particularly preferably 110 ml / 100 g or more. Furthermore, the DBP oil absorption of carbon black is preferably 160 ml / 100 g or less, and particularly preferably 150 ml / 100 g or less. An amount of DBP oil absorption exceeding 160 ml / 100 g poses difficulties in the production of the carbon black itself.

[0036] The DBP oil absorption of soot can be measured according to the measurement method described in JIS standard K6217-4.

[0037] The specific surface area (N2SA) of the soot, measured by nitrogen adsorption, is preferably 80 m 2 / g or more and particularly preferably 110 m 2 / g or more. A N2SA of less than 80 m 2 / g can significantly reduce the tensile strength and make it difficult to ensure sufficient abrasion resistance. Furthermore, the N2SA of the carbon black is preferably 200 m 2 / g or less and particularly preferably 150 m 2 / g or less. An N2SA of greater than 200 m 2 / g can greatly increase the viscosity of the rubber composition containing the carbon black and consequently worsens the processability.

[0038] The N2SA of carbon black can be measured here according to Method A described in JIS Standard K6217.

[0039] The amount of carbon black is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and most preferably 5 parts by mass or more, based on 100 parts by mass of the rubber component. An amount of carbon black of less than 2 parts by mass may seriously deteriorate weather resistance and ozone resistance. Further, the amount of carbon black is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and most preferably 15 parts by mass or less, based on 100 parts by mass of the rubber component. An amount of carbon black exceeding 50 parts by mass may deteriorate low-temperature properties, and thus, it may not be possible to ensure sufficient on-ice performance required for a winter tire.

[0040] The proportion of silica, based on 100 mass % of the total amount of silica and carbon black, is 45 mass % or more, preferably 50 mass % or more, and particularly preferably 55 mass % or more. A proportion of silica of less than 45 mass % cannot achieve both sufficient ice performance and sufficient abrasion resistance, which is an object of the present invention. Furthermore, the proportion of silica, based on 100 mass % of the total amount of silica and carbon black, is preferably 95 mass % or less, more preferably 93 mass % or less, and most preferably 90 mass % or less. A proportion of silica of more than 95 mass % can severely deteriorate weather resistance and ozone resistance.

[0041] The rubber composition of the tread of the winter tire according to the invention may optionally contain, in addition to the aforementioned components, blending components conventionally used in the rubber industry. Examples of such blending components include other fillers, stearic acid, antioxidants, anti-aging agents, zinc oxide, peroxides, vulcanizing agents such as sulfur and sulfur-containing compounds, and vulcanization accelerators.

[0042] Preferably, the vulcanization accelerators are sulfenamide vulcanization accelerators (such as N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), and N,N-diisopropyl-2-benzothiazolylsulfenamide), and guanidine vulcanization accelerators (such as diphenylguanidine (DPG), di-o-tolylguanidine, triphenylguanidine, o-tolylbiguanide, and diphenylguanidine phthalate). Of these, a mixture of TBBS and DPG is particularly preferred.

[0043] The winter tire is a winter tire for motor vehicles, such as trucks and buses, and is particularly preferably a winter tire for passenger cars which require high steering stability on ice and snow.

[0044] With the winter tire tread rubber composition according to the present invention, a winter tire can be manufactured by a conventional method. That is, the winter tire can be manufactured by preparing tire components such as a tread using the aforementioned composition, assembling the manufactured tire components with other components on a tire molding machine, and heating the assembled components under pressure. EXAMPLES

[0045] The present invention will be described more specifically below based on examples. It should be noted that the present invention is not limited to these examples.

[0046] The chemical substances used in the examples and comparative examples are listed below: No.: RSS#3 BR: BR150B manufactured by Ube Industries, Ltd. (Amount of cis-1,4 bonds: 97 mass%, ML 1+4 (100 °C): 40, viscosity of a 5% solution in toluene at 25 °C: 48 cps, Mw / Mn: 3.3) Soot: N220 (N2SA: 120 m 2 / g, average particle size: 23 nm, DBP oil absorption: 115 ml / 100 g) manufactured by Cabot Japan KK Silica: Ultrasil VN3 (N2SA: 175 m 2 / g) manufactured by Degussa AG Silane coupling agent: Si266 (Bis(3-triethoxysilylpropyl)disulfide) manufactured by Degussa AG Mineral oil: PS-32 (paraffinic process oil) manufactured by Idemitsu Kosan Co., Ltd. Aromatic oil: Process oil NC300S (content of aromatic hydrocarbons (C A ): 29 mass%) manufactured by Japan Energy Corporation Stearic acid: Kiri manufactured by NOF Corporation Zinc oxide: Zinc oxide #2 manufactured by Mitsui Mining & Smelting Co., Ltd. Antiaging agent: NOCRAC 6C (N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. Wax: OZOACE wax manufactured by Nippon Seiro Co., Ltd. Sulfur: Sulfur powder manufactured by Tsurumi Chemical Industry Co., Ltd. Vulcanization accelerator TBBS: NOCCELER NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. Vulcanization accelerator DPG: NOCCELER D (N,N'-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. Examples 1 to 4 and Comparative Examples 1 to 6

[0047] The chemical compounds in the amounts according to the formulation amounts shown in Process 1 in Table 1 were mixed and kneaded in a Banbury mixer for five minutes to raise the outlet temperature to approximately 150°C. Subsequently, sulfur and vulcanization accelerators in the amounts shown in Process 2 were added to the mixture prepared by Process 1, and they were mixed and kneaded together for three minutes at approximately 80°C by an open roll mill, thereby preparing an unvulcanized rubber composition. The prepared unvulcanized rubber composition was press-vulcanized for ten minutes at 170°C to produce a vulcanized rubber composition (vulcanized rubber sheet).

[0048] Furthermore, the prepared unvulcanized rubber composition was molded into a tread shape and assembled with the other tire components. The assembled components were then vulcanized for 15 minutes at 170°C, thus producing a winter tire.

[0049] The vulcanized rubber sheets and the test winter tires were examined in the following ways. (1) Hardness

[0050] According to JIS Standard K 6253 "Rubber, Unvulcanized or Thermoplastic - Determination of Hardness," the hardness of the vulcanized rubber sheets was determined at 0 °C using a Type A durometer. The determined hardness values ​​were each expressed as an index based on the value of Comparative Example 1, which was taken as 100 as a reference. (2) Glass transition temperature (Tg)

[0051] A test piece of a predetermined size was cut from each of the vulcanized rubber sheets. Then, the temperature dependence curve of the tan δ (from -100 °C to 100 °C) of each test piece was determined using a VES viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under the following conditions: an initial load of 10%, a dynamic load of 0.5%, a frequency of 10 Hz, an amplitude of ±0.25%, and a temperature increase rate of 2 °C / min. From the obtained temperature dependence curve, the tan δ peak temperature was determined, and this temperature was taken as the Tg. (3) Tensile strength test

[0052] A No. 3 dumbbell-shaped sample was punched from each of the vulcanized rubber compositions and subjected to a tensile strength test according to JIS Standard K6251 "Rubber, Vulcanized or Thermoplastic - Determination of Tensile Stress-Elongation Properties" to determine the ultimate tensile strength (TB) of each sample. The larger the TB value, the higher the strength. The determined TB values ​​were each expressed as an index based on the value of Comparative Example 1, which was taken as 100 as a reference. (4) Performance on ice and snow

[0053] The winter test tires were evaluated for driving performance on ice and snow under the following conditions. The winter tires used were passenger car winter tires with a size of 195 / 65R15 and a DS-2 pattern, and the tires were fitted to a Japanese-made front-wheel drive vehicle with a 2000 cm 3 -engine. The test was conducted on a test course operated by Sumitomo Rubber Industries, Ltd. in Nayoro, Hokkaido, Japan. The temperature on ice was between -6°C and -1°C, and the temperature on snow was between -10°C and -2°C.

[0054] Braking performance (braking stopping distance on ice): The braking stopping distance on ice was measured, which is the distance required for a motor vehicle to stop after the brakes are locked at 30 km / h. The braking performance index was then calculated according to the following formula, using Comparative Example 1 as a reference: (Braking performance index)=(braking stop distance in the comparison example1) / (braking stop distance of each tire)×100

[0055] The higher the index, the better the braking performance. (5) Wet grip performance

[0056] Using the aforementioned winter test tires (size 195 / 65R15), an actual vehicle driving test was conducted on a test track with a wet asphalt surface. In the test, the grip performance (grip feel, braking performance, traction performance) was evaluated by feel. In the evaluation, the performance of the tire in Comparative Example 1 was considered the standard and was assumed to be 100. Then, a ranking was made such that the tires were classified as 120 when the test driver considered their performance to be clearly improved, and the tires were classified as 140 when the test driver judged their performance to be unprecedented. (6) Abrasion resistance

[0057] The aforementioned winter test tires (size 195 / 65R15) were each mounted on a Japanese-made front-wheel drive vehicle, and the groove depth of the tire tread portion was measured after the vehicle had driven 8,000 km. From the measured value, the running distance at which the tire groove depth decreased by 1 mm was calculated. The obtained running distance was then used in the following formula to calculate the abrasion resistance index: (Abrasion resistance index) = (running distance at which the tire groove depth decreased by 1 mm) / (running distance at which the tire groove depth decreased by 1 mm in Comparative Example 1) × 100

[0058] The higher the index, the better the abrasion resistance.

[0059] Table 1 shows the evaluation results of the respective studies.

[0060] In the examples, the vulcanized rubber sheets and winter test tires exhibited low Tg's, excellent ice and snow performance, good tear strength, and excellent abrasion resistance. Furthermore, each winter test tire in the examples exhibited excellent wet grip performance. On the other hand, the winter test tires in Comparative Examples 1 and 2, which contained mineral oil instead of aromatic oil, exhibited inferior abrasion resistance and wet grip performance. The winter test tires in Comparative Example 3, which contained excessive amounts of silica and aromatic oil, exhibited a reduction in ice and snow performance and abrasion resistance.

[0061] The winter test tire of Comparative Example 4, which contained silica at a low proportion relative to the total filler content, exhibited poorer performance on ice and snow and poorer wet grip performance. The winter test tire of Comparative Example 5, which contained a small amount of silica, similarly exhibited poorer performance on ice and snow and poorer wet grip performance. The winter test tire of Comparative Example 6, which contained small amounts of silica and aromatic oil, exhibited poorer abrasion resistance and poorer wet grip performance.

Claims

[1] A winter tyre comprising a tread made from a rubber composition for a tread, the rubber composition containing: a rubber component containing natural rubber and butadiene rubber, aromatic oil containing 15% or more of aromatic hydrocarbons by mass, Silica and Soot, wherein the total amount of natural rubber and butadiene rubber, based on 100 mass% of the rubber component, is 30 mass% or more, wherein the amount of the aromatic oil is 30 to 85 parts by mass per 100 parts by mass of the rubber component and the amount of the silica is 60 to 85 parts by mass per 100 parts by mass of the rubber component, and wherein the proportion of silica based on 100 mass% of the total amount of silica and carbon black is 45 mass% or more.