Studless tire

Abstract

A studless tire having a tread composed of a rubber composition for a tread comprising 1 to 20 parts by mass of a farnesene resin and 1 to 20 parts by mass of a terpene resin based on 100 parts by mass of a rubber component.

Claims

1. A studless tire having a tread composed of a rubber composition for a tread comprising: a rubber component which comprises 20 to 60% by mass of a natural rubber, 10 to 50% by mass of an un-modified butadiene rubber and 30 to 70% by mass of a modified butadiene rubber that has an alkoxysilane condensate compound in an active terminal thereof; and 1 to 20 parts by mass of a farnesene resin and 1 to 20 parts by mass of a terpene resin, both based on 100 parts by mass of the rubber component.

2. The studless tire of claim 1, wherein the rubber composition for a tread further comprises 5 to 100 parts by mass of silica.

3. The studless tire of claim 1, wherein the rubber composition for a tread further comprises 1 to 20 parts by mass of a cyclopentadiene resin.

4. The studless tire of claim 1, wherein a ratio of a content of a modified butadiene rubber to a content of an un-modified butadiene rubber in the butadiene rubber (content of modified butadiene rubber/content of un-modified butadiene rubber) is 0.6 to 3.0.

Description

EXAMPLE

(1) The present invention will be described based on Examples, but the present invention is not limited thereto only.

(2) A variety of chemicals used in Examples and Comparative Examples will be explained below.

(3) NR: TSR20

(4) Un-modified BR: BR730 (Un-modified BR, cis content: 95%, ML.sub.1+4(100° C.): 55) manufactured by JSR Corporation

(5) Modified BR: Terminal-modified BR (Cis content: 40%, trans content: 50%, vinyl content: 10%, Mw: 600,000)

(6) Carbon black: DIABLACK I (ASTM No. N220, N.sub.2SA: 114 m.sup.2/g, DBP: 114 ml/100 g) available from Mitsubishi Chemical Corporation

(7) Silica: ULTRASIL VN3 (N.sub.2SA: 175 m.sup.2/g, average primary particle size: 15 nm) manufactured by Evonik Degussa GmbH

(8) Silane coupling agent: Si75 (bis(3-triethoxysilylpropyl)disulfide) manufactured by Evonik Degussa GmbH

(9) Cyclopentadiene resin: Oppera PR-120 (hydrogenated cyclopentadiene resin) manufactured by Exxon Mobil Corporation

(10) Farnesene resin: Farnesene-butadiene copolymer prepared by synthesis of a farnesene resin described below

(11) Terpene resin: PX1150N (polyterpene resin not hydrogenated, SP value: 8.26, softening point: 115° C., Tg: 62° C.) manufactured by Yasuhara Chemical Co., Ltd.

(12) Oil: Process X-140 (aromatic oil) manufactured by JX Nippon Oil & Energy Corporation

(13) Wax: OK5258H (available from PARAMELT, paraffin wax comprising 95% by mass or more of paraffin wax having 20 to 50 carbon atoms)

(14) Antioxidant 1: NOCRAC 6C (N-(1,3-dimethylbutyl)-N-phenyl-p-phenylenediamine, 6PPD) available from Ouchi Shinko Chemical Industrial Co., Ltd.

(15) Antioxidant 2: NOCRAC RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline) available from Ouchi Shinko Chemical Industrial Co., Ltd.

(16) Processing aid: Aflux16 (a mixture of calcium salt of fatty acid and amide ester) available from Rhein Chemie Corporation

(17) Stearic acid: Stearic acid “Tsubaki” available from NOF CORPORATION

(18) Zinc oxide: Zinc Oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd.

(19) Sulfur: 5% oil-treated powdered sulfur (soluble sulfur having an oil content of 5% by mass) available from Tsurumi Chemical Industry Co., Ltd.

(20) Vulcanization accelerator 1: Nocceler CZ (CBS, N-cyclohexyl-2-benzothiazolylsulfeneamide) manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.

(21) Vulcanization accelerator 2: Nocceler M-P (MBT, 2-mercaptobenzothiazole) manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.

(22) Vulcanization accelerator 3: Nocceler D (DPG, 1,3-diphenylguanidine) manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD.

(23) Synthesis of Farnesene Resin

(24) Chemicals used for synthesis of a farnesene resin are described below.

(25) Cyclohexane: Cyclohexane (special grade) available from Kanto Chemical Industry Co., Ltd.

(26) Isopropanol: Isopropanol (special grade) available from Kanto Chemical Industry Co., Ltd.

(27) TMEDA: Tetramethylethylenediamine (reagent) available from Kanto Chemical Industry Co., Ltd.

(28) Butadiene: 1,3-butadiene available from TAKACHIHO CHEMICAL INDUSTRIAL CO., LTD.

(29) Isoprene: Isoprene (reagent) available from Wako Pure Chemical Industries, Ltd.

(30) Farnesene: (E)-β-farnesene (reagent) available from Nippon Terpene Chemicals, Inc.

(31) <Preparation of Catalyst Solution>

(32) (1) After replacing inside of a 50 ml glass container with nitrogen gas, 8 ml of cyclohexane solution of butadiene (2.0 mol/L), 1 ml of neodymium(III) 2-ethylhexanoate/cyclohexane solution (0.2 mol/L) and 8 ml of PMAO (Al: 6.8% by mass) were poured into the container, followed by stirring of a mixture. Five minutes after, 5 ml of 1M hydrogenated diisobutyl aluminum/hexane solution was added to the mixture, and further five minutes after, 2 ml of 1M diethyl aluminum chloride/hexane solution was added to the mixture, followed by stirring to obtain a catalyst solution (1).

(33) (2) A catalyst solution (2) was obtained in the same manner as in (1) above except that butadiene was replaced with isoprene.

(34) <Synthesis of Farnesene Resin>

(35) After replacing inside of a 3 L pressure-resistant stainless steel container with nitrogen gas, 1,800 ml of cyclohexane, 60 g of farnesene and 40 g of butadiene were poured into the container, followed by 10-minute stirring. Thereafter, 2 ml of the catalyst solution (1) was added to a mixture, followed by stirring while keeping a temperature at 30° C. Three hours after, 10 ml of 0.01 M BHT (butylated hydroxytoluene)/isopropanol solution was added dropwise to terminate a reaction. After having been cooled, a reaction liquid was added to 3 L of methanol prepared separately and a thus-obtained precipitate was air-dried overnight and further was subjected to 2-day drying under reduced pressure to obtain 100 g of farnesene resin (farnesene/butadiene copolymer). A degree of polymerization (percentage of “dry weight/charged amount”) was substantially 100%.

(36) <Measurements of Farnesene Resin>

(37) With respect to the farnesene resin obtained above, a weight-average molecular weight Mw, a number-average molecular weight Mn, a glass transition temperature Tg, a Mooney viscosity and a copolymerization ratio (1) of a branched conjugated diene compound (1) were measured according to the following methods.

(38) (Measurements of Weight-Average Molecular Weight Mw and Number-Average Molecular Weight Mn)

(39) The Mw and Mn were calibrated with standard polystyrene based on measurement values determined with equipment of GPC-8000 series manufactured by Tosoh Corporation; detector: differential refractometer

(40) (Measurement of Glass Transition Temperature (Tg))

(41) The Tg of each copolymer was measured using a differential scanning calorimeter (DSC) while heating up from an initial temperature of −150° C. up to a final temperature of 150° C. at a temperature elevating rate of 10° C./min.

(42) (Measurement of Mooney Viscosity of Copolymer)

(43) A Mooney viscometer was used and an L-rotor was rotated under the temperature condition of 130° C. by 1-minute preheating, and after a lapse of four minutes, a Mooney viscosity ML.sub.1+4(130° C.) of each copolymer was determined according to JIS K 6300 “Test Method of Unvulcanized rubber”. The smaller the Mooney viscosity is, the better the processability is.

(44) (Copolymerization Ratio of Farnesene)

(45) A copolymerization ratio (weight %) was measured by a usual method with pyrolysis gas chromatography (PGC). Namely, a calibration curve of a refined farnesene was made, and a weight % of farnesene in the copolymer was calculated from an area ratio of a pyrolysis product derived from farnesene, in which the area ratio was obtained by PGC. A system comprising a gas chromatograph-gas spectrometer GCMS-QP5050A manufactured by Shimadzu Corporation and a pyrolyzer JHP-330 manufactured by Japan Analytical Industry Co., Ltd. was used for the pyrolysis chromatography.

EXAMPLES AND COMPARATIVE EXAMPLES

(46) Chemicals other than sulfur and vulcanization accelerators were subjected to kneading in accordance with compounding formulations shown in Table 1 at a discharge temperature of 150° C. for five minutes using a 1.7 L closed Banbury mixer to obtain a kneaded product. Subsequently sulfur and vulcanization accelerators were added to the obtained kneaded product, followed by 4-minute kneading with a biaxial open roll until the temperature became 105° C., to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was subjected to vulcanization and molding at 170° C. for 12 minutes at a pressure of 25 kgf/cm.sup.2 to produce test rubber compositions.

(47) The unvulcanized rubber composition was extruded and molded into a shape of a tire tread by an extruder equipped with a base having a predetermined shape, and then laminated with other tire members to form an unvulcanized tire, which was then press-vulcanized at 170° C. for 12 minutes to manufacture a tire for test (size: 195/65R15, studless tire).

(48) The obtained unvulcanized rubber compositions, vulcanized rubber compositions and test tires were subjected to the following evaluations. The evaluation results are shown in Table 1.

(49) Braking Performance On-Ice

(50) The test tires were mounted on a 2000 cc domestic FR car. In-vehicle running on ice surface was carried out under the following conditions, and braking performance on ice was evaluated. In the evaluation of braking performance on ice, the car was run on an ice surface and a lock brake was applied at a speed of 30 km/hr. A stopping distance required for stopping the car after putting on the lock brake (stopping distance on ice, stopping distance on snow) was measured, and was indicated by an index calculated by the following equation. The larger the index is, the better the performance on ice and snow (grip performance on ice and snow) is. It can be said that the performance on ice and snow has been improved when the index exceeds 100.
(Index of braking performance on-ice)=(Stopping distance of Comparative Example 1)/(Stopping distance of each formulation)×100
On-ice test site: Hokkaido Nayoro test course, temperature: −1 to −6° C.
Evaluation of Morphology

(51) A vulcanized rubber composition was subjected to surface shaping and observed with a scanning electron microscope (SEM). The morphology of each phase could be confirmed by comparison of a contrast. As a result, in Examples and Comparative Examples, it was confirmed that a contrast of Examples is lower than that of Comparative Examples. The morphology in each of Examples and Comparative Examples is indicated by an index, assuming that the morphology in Comparative Example 1 is 100. It shows that the larger the index is, the lower the contrast is, and the dispersibility of silica is good.

(52) Dispersibility of Silica

(53) Ultra thin slices were prepared from a test rubber composition using a microtome and were observed using a transmission electron microscope. Morphology of each phase could be confirmed by comparison of each contrast. As a result, it was confirmed that in Examples and Comparative Examples, the two BR and NR phases were incompatible with each other.

(54) Silica can be observed in the form of particulate. An area of silica per unit area of each phase was measured in ten regions of one sample, and an average value was determined. An amount of the silica of a phase comprising the BR was determined from the average value, and an abundance ratio of silica of the following equation 1 was calculated using a compounding amount (part by mass) of silica based on 100 parts by mass of the whole rubber components.

(55) An index of silica dispersion was indicated by the following equation 2, assuming that an abundance ratio of silica in Comparative Example 1 is 100. It shows that as the index is larger, a larger amount of silica is dispersed in the BR phase.
(Abundance ratio of silica)=(Amount of silica in a phase comprising BR)/(Compounding amount of silica(part by mass))×100  (Equation 1)
(Index of silica dispersion)=(Abundance ratio of silica)/(Abundance ratio of silica in Comparative Example 1)×100  (Equation 2)
Stability Over Time of Silica Dispersion

(56) For the same vulcanized rubber composition, an abundance ratio α of silica in the BR phase after a lapse of one year from completion of vulcanization was measured in the same manner as described above. Then, a change rate of an abundance ratio α of silica after a lapse of one year from completion of vulcanization was calculated by the following equation based on an abundance ratio α of silica in the BR phase after a lapse of 200 hours from completion of vulcanization. Stability over time of silica dispersion is indicated by an index, assuming that a change rate of Comparative Example 1 is 100. The larger the index is, the smaller the change rate of the abundance ratio α is, and the stability over time is good.
Change rate (%)=|α(one year after)−α(200 hours after)|/α(200 hours after)×100
Wet Grip Performance

(57) The tires for test were loaded on the whole wheels of a car (2000 cc FF car domestically produced), and on the wet asphalt road surface, a braking distance from an initial speed of 100 km/h was measured. The results are shown by an index. The larger the index is, the better the wet grip performance is. The index was obtained by the following equation.
(Index of wet grip performance)=(Braking distance of Comparative Example 1)/(Braking distance of each formulation)×100
Sticking of Snow

(58) The test tires were mounted on a test car (2000 cc domestic FR car), and in-vehicle running on snow surface was carried out. After the running, clogging of snow and sticking of snow on the lateral grooves of the test tires were observed with naked eyes, and indicated by an index, assuming that the result of Comparative Example 1 was 100. The larger the index is, the higher the effect of inhibiting clogging of snow and sticking of snow is. The test was performed at the test course of Sumitomo Rubber Industries, Ltd. in Nayoro, Hokkaido, and air temperature on snow was −2° C.-−10° C.

(59) Aging of Hardness

(60) Aging of hardness is shown by a value obtained by measuring a Mooney viscosity (ML.sub.1+4(125° C.)) after keeping the test rubber composition for two days in a thermostatic bath at 90° C. and calculating from the following formula. Aging of hardness is indicated by an index, assuming that the aging of hardness in Comparative Example 1 is 100. It shows that the larger the index is, the smaller the aging of hardness is.
[Mooney viscosity(ML.sub.1+4(125° C.)) after keeping the test rubber composition for two days in thermostatic bath at 90° C.]−[Mooney viscosity(ML.sub.1+4(125° C.)) measured immediately after synthesis]

(61) TABLE-US-00001 TABLE 1 Comparative Example Example 1 2 3 4 5 1 2 3 Compounding amount (part by mass) NR 40 40 40 40 40 40 40 40 Un-modified BR 25 25 25 25 25 25 25 25 Modified BR 35 35 35 35 35 35 35 35 Carbon black 5 5 5 5 5 5 5 5 Silica 60 60 60 60 60 60 60 60 Silane coupling agent 5 5 5 5 5 5 5 5 Cyclopentadiene resin — — — — 10 — — 25 Farnesene resin 5 10 15 20 10 — 25 — Terpene resin 20 15 10 5 5 25 — — Oil 15 15 15 15 15 15 15 15 Wax 2 2 2 2 2 2 2 2 Antioxidant 1 2 2 2 2 2 2 2 2 Antioxidant 2 1 1 1 1 1 1 1 1 Processing aid 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide 2 2 2 2 2 2 2 2 Sulfur 1 1 1 1 1 1 1 1 Vulcanization accelerator 1 2 2 2 2 2 2 2 2 Vulcanization accelerator 2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Vulcanization accelerator 3 2 2 2 2 2 2 2 2 Evaluation results Braking performance on ice 102 101 100 100 100 100 94 101 Morphology 104 104 101 100 102 100 95 102 Index of silica dispersion 101 100 100 100 101 100 95 100 Stability over time of silica dispersion 104 105 105 106 104 100 103 101 Wet performance 104 102 100 100 102 100 97 101 Sticking of snow 106 104 103 101 105 100 99 104 Aging of hardness 104 107 110 112 105 100 116 97

(62) From the results shown in Table 1, it is seen that the studless tire having a tread composed of the rubber composition for a tread comprising predetermined amounts of the farnesene resin and the terpene resin is good in processability, braking performance on ice, morphology, silica dispersibility and stability over time of silica dispersion.