JP2022059837A - Rubber composition for studless tire, and studless tire using the same - Google Patents

Abstract

To provide a studless tire that solves the problem in which, on an ice-snow road surface, the coefficient of friction becomes lower than that on a general road surface, making it slippery, and then, conventionally, many methods have been proposed to improve the on-ice performance of studless tires, but there is room for improvement in the on-ice performance.SOLUTION: The problem is solved by a rubber composition for studless tire that is characterized, for 100 pts.mass of (A) diene-based rubber, (B) carbon black and/or white filler by 30 to 100 pts.mass, and (C) ethylene/propylene/VNB copolymer having a constitutional unit derived from ethylene (a), propylene (b) and 5-vinyl-2-norbornene (VNB) (c) and satisfying specific requirement by 1 to 50 pts.mass are compounded to yield the composition.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rubber composition for a studless tire and a studless tire using the same, and more particularly to a rubber composition for a studless tire capable of further improving on-ice performance as compared with the prior art and a studless tire using the same. It is a thing.

On an ice-snow road surface, the coefficient of friction is lower than that on a general road surface, making it slippery. Therefore, in the past, many methods have been proposed for improving the on-ice performance (braking performance on ice) of studless tires. For example, there is known a method of blending a hard foreign substance or a hollow polymer with rubber to form micro-concavities and convexities on the rubber surface to remove a water film generated on the surface of ice and improve friction on ice (. For example, see Patent Document 1). On the other hand, there is also a method such as using rubber having low temperature flexibility.

However, further improvement in on-ice performance is required in the industry.

Japanese Unexamined Patent Publication No. 11-35736

Therefore, an object of the present invention is to provide a rubber composition for a studless tire capable of further improving the performance on ice as compared with the prior art, and a studless tire using the same.

As a result of diligent research, the present inventors have found a rubber composition in which a carbon black and / or white filler is blended with a diene rubber and an ethylene / propylene / VNB copolymer is blended in a specific amount. It was found that the above problems could be solved, and the present invention could be completed.

The present invention relates to (A) 100 parts by mass of diene rubber.
(B) 30 to 100 parts by mass of carbon black and / or white filler, and (C) composition derived from ethylene (a), propylene (b) and 5-vinyl-2-norbornene (VNB) (c). Have a unit,
Provided is a rubber composition for a studless tire, which comprises 1 to 50 parts by mass of an ethylene / propylene / VNB copolymer satisfying the following requirements (i) to (vii).
(I) The molar ratio of ethylene / propylene is 60/40 to 80/20;
(Ii) The ultimate viscosity [η] is 2 to 4 dL / g.
(Iii) The weight fraction of the constituent unit derived from VNB (c) is 1% by weight to 2% by weight in 100% by weight of the ethylene / propylene / VNB copolymer;
(Iv) Weight average molecular weight (Mw) of ethylene / propylene / VNB copolymer, weight fraction of structural unit derived from VNB (c) (weight fraction (% by weight) of (c)), and VNB ( The molecular weight of c) (the molecular weight of (c)) satisfies the following formula (1);
4.5 ≤ Mw x weight fraction of (c) / 100 / molecular weight of (c) ≤ 40 ... Equation (1)
(V) Complex viscosity η ^* ₍ ω _{= 0.1)} (Pa · sec) at frequency ω = 0.1 rad / s and frequency ω = obtained by linear viscous elasticity measurement (190 ° C) using a leometer. Ratio P (η ^* ₍ ω _{= 0.1)} / η ^* ₍ ω _{= 100)} ) to complex viscosity η ^* ₍ ω _{= 100)} (Pa · sec) at 100 rad / s, extreme viscosity [η], and VNB The weight fraction of the structural unit derived from (c) (the weight fraction of (c)) satisfies the following formula (2);
P / ([η] ^2.9 ) ≤ (c) weight fraction x 6 ... Equation (2)
(Vi) The ratio (molecular weight distribution; Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is in the range of 8 to 30;
(Vii) The number average molecular weight (Mn) is 30,000 or less;
(Viii) The chart obtained by GPC measurement shows two or more peaks, and the area of the peak appearing on the side with the smallest molecular weight is in the range of 1 to 20% of the total peak area.

The rubber composition for studless tires of the present invention comprises (A) 100 parts by mass of diene-based rubber, (B) 30 to 100 parts by mass of carbon black and / or white filler, and (C) ethylene, propylene, VNB. Since it is characterized by blending 1 to 50 parts by mass of the copolymer, it is possible to provide a rubber composition capable of further improving on-ice performance as compared with the prior art and a studless tire using the rubber composition.
The mechanism of action of the above effect in the present invention is, for example, that the ethylene / propylene / VNB copolymer of the component (C) has a vinyl group at the terminal, and the terminal vinyl group does not participate in sulfur cross-linking, so that vulcanization is performed. It is presumed that it exists as an unvulcanized portion in the rubber and may improve the low temperature flexibility of the rubber. On the other hand, the terminal vinyl group of the component (C) can react with, for example, a silane coupling agent to enhance the dispersibility of a white filler such as silica in rubber, thereby improving the performance on ice. It is presumed to be.

It is a schematic diagram of the continuous polymerization apparatus used in an Example.

Hereinafter, the present invention will be described in more detail.
(A) Diene-based rubber As the diene-based rubber used in the present invention, any diene-based rubber that can be blended in the rubber composition can be used, and for example, natural rubber (NR) and isoprene rubber (IR) can be used. , Butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), ethylene-propylene-dienter polymer (EPDM) and the like. These may be used alone or in combination of two or more. The molecular weight and microstructure thereof are not particularly limited, and may be terminal-modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or may be epoxidized.
The (A) diene-based rubber referred to in the present invention does not contain the (C) ethylene / propylene / VNB copolymer described below.
Further, the diene rubber (A) preferably has a glass transition temperature (Tg) of −50 ° C. or lower. By defining Tg in this way, the performance on ice is improved.
When a plurality of types of diene rubber are contained, Tg referred to in the present specification is a value calculated based on the total product of the glass transition temperature of each rubber multiplied by the weight fraction of each rubber, that is, a weighted average. And. At the time of calculation, the total weight fraction of each component is 1.0. The glass transition temperature (Tg) referred to in the present invention is measured by a differential scanning calorimetry (DSC) under a heating rate condition of 20 ° C./min, and refers to the temperature at the midpoint of the transition region.
A more preferable average Tg is −60 ° C. or lower.

(B) Carbon Black and / or White Filler Specific examples of the carbon black used in the present invention include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPE, and SRF. May be used alone or in combination of two or more.
Further, from the viewpoint of improving the performance on ice, the carbon black preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 10 to 300 m ² / g, and more preferably 50 to 150 m ² / g.
The nitrogen adsorption specific surface area (N ₂ SA) is a value measured according to JIS K 6217-2: 2001 "Part 2: How to obtain the specific surface area-Nitrogen adsorption method-Single point method".

Specific examples of the white filler used in the present invention include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, calcium sulfate and the like. The species may be used alone, or two or more species may be used in combination.
Of these, silica is preferred because it has better on-ice performance.

Specific examples of the silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, and the like, and these may be used alone. Two or more types may be used in combination.

From the viewpoint of improving the performance on ice, silica preferably has a CTAB adsorption specific surface area of 50 to 300 m ² / g, and more preferably 90 to 200 m ² / g.
The CTAB adsorption specific surface area is a value obtained by measuring the amount of n-hexadecyltrimethylammonium bromide adsorbed on the silica surface according to JIS K6217-3: 2001 "Part 3: How to determine the specific surface area-CTAB adsorption method". Is.

(C) Ethylene / propylene / VNB copolymer The ethylene / propylene / VNB copolymer used in the present invention includes ethylene (a), propylene (b) and 5-vinyl-2-norbornene (VNB) (c). It has a structural unit derived from and, and is characterized by satisfying the following requirements (i) to (viii).

(I) The molar ratio of ethylene / propylene is 60/40 to 80/20. By satisfying this requirement (i), heat resistance, cold resistance and wear resistance are excellent. The molar ratio can be determined by ¹³ C-NMR.

(Ii) The ultimate viscosity [η] is 2 to 4 dL / g. By satisfying this requirement (ii), the mechanical properties are excellent.

(Iii) The weight fraction of the constituent unit derived from VNB (c) is 1% by weight to 2% by weight in 100% by weight of the ethylene / propylene / VNB copolymer. By satisfying this requirement (iii), the hardness is sufficient and the mechanical properties are excellent.

(Iv) Weight average molecular weight (Mw) of ethylene / propylene / VNB copolymer, weight fraction of structural unit derived from VNB (c) (weight fraction (% by weight) of (c)), and VNB ( The molecular weight of c) (the molecular weight of (c)) satisfies the following formula (1).
4.5 ≤ Mw x weight fraction of (c) / 100 / molecular weight of (c) ≤ 40 ... Equation (1)
By satisfying this requirement (iv), the mechanical properties are excellent.

(V) Complex viscosity η ^* ₍ ω _{= 0.1)} (Pa · sec) at frequency ω = 0.1 rad / s and frequency ω = obtained by linear viscous elasticity measurement (190 ° C) using a leometer. Ratio P (η ^* ₍ ω _{= 0.1)} / η ^* ₍ ω _{= 100)} ) to complex viscosity η ^* ₍ ω _{= 100)} (Pa · sec) at 100 rad / s, extreme viscosity [η], and VNB The weight fraction of the structural unit derived from (c) (the weight fraction of (c)) satisfies the following formula (2);
P / ([η] ^2.9 ) ≤ (c) weight fraction x 6 ... Equation (2)
In the present invention, the P value is a complex viscosity at 0.1 rad / s obtained by measuring the viscoelasticity measuring device Ares (manufactured by Rheometric Scientific) at 190 ° C., strain 1.0%, and changing the frequency. And the complex viscosity at 100 rad / s, the ratio (η ^* ratio) was calculated. The ultimate viscosity [η] means a value measured in decalin at 135 ° C.

(Vi) The ratio (molecular weight distribution; Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is in the range of 8 to 30. By satisfying this requirement (vi), the workability becomes excellent.

(Vii) The number average molecular weight (Mn) is 30,000 or less, preferably 3,000 to 26,000. By satisfying this requirement (vii), the workability becomes excellent.

(Viii) The chart obtained by GPC measurement shows two or more peaks, and the area of the peak appearing on the side with the smallest molecular weight is in the range of 1 to 20% of the total peak area, preferably 2 to 18%. Is. By satisfying this requirement (viii), the workability becomes excellent.

Method for Producing Ethylene / Propropylene / VNB Copolymer The ethylene / propylene / VNB copolymer may be prepared by any production method as long as the above requirements (i) to (viii) are satisfied, but ethylene / propylene / VNB copolymer may be prepared. -As a method for producing a VNB copolymer, for example, it is disclosed and known in JP-A-2020-63381. That is, a method of copolymerizing a monomer in the presence of a polymerization catalyst system containing at least one metallocene compound selected from the compounds represented by the following general formula [A1] can be mentioned. When the copolymerization of the monomers is carried out using a polymerization catalyst system containing such a metallocene compound, the long-chain branching contained in the obtained copolymer is suppressed, and the ethylene / propylene / VNB copolymer weight satisfying the above requirements is satisfied. The coalescence can be easily prepared.

In the formula [A1], R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁸ , R ⁹ and R ¹² are independently heteroatoms other than hydrogen atom, hydrocarbon group, silicon-containing group or silicon-containing group, respectively. It indicates an atom-containing group, and two adjacent groups of R ¹ to R ⁴ may be bonded to each other to form a ring. R ⁶ and R ¹¹ are the same atom or the same group selected from heteroatom-containing groups other than hydrogen atom, hydrocarbon group, silicon-containing group and silicon-containing group, and R ⁷ and R ¹⁰ are hydrogen atom and hydrocarbon. The same atom or the same group selected from a group, a silicon-containing group and a heteroatom-containing group other than a silicon-containing group, and R ⁶ and R ⁷ may be bonded to each other to form a ring, and R ¹⁰ and R ¹¹ may be coupled to each other to form a ring. However, R ⁶ , R ⁷ , R ¹⁰ and R ¹¹ are not all hydrogen atoms. R ¹³ and R ¹⁴ each independently represent an aryl group. M ¹ represents a zirconium atom. Y ¹ represents a carbon atom or a silicon atom. Q is a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a neutral conjugated or unconjugated diene having 4 to 20 carbon atoms, an anionic ligand, or a neutral ligand that can be coordinated with a lone electron pair. Shown, j indicates an integer of 1 to 4, and when j is an integer of 2 or more, a plurality of Qs may be the same or different.

The metallocene compound represented by the above formula [A1] can be produced by any method without particular limitation. For example, J. Organomet. Chem. , 63,509 (1996), WO2005 / 100410, WO2006 / 123759, WO01 / 27124, JP-A-2004-168744, JP-A-2004-175759, JP-A-2000-212194, etc. It can be manufactured in accordance with the method described in 1.

Examples of the polymerization catalyst that can be suitably used for producing an ethylene / propylene / VNB copolymer include those containing the above-mentioned metallocene compound [A1] and capable of copolymerizing a monomer. For example, (a) a metallocene compound represented by the general formula [A1], (b) (b-1) an organometallic compound, (b-2) an organoaluminum oxy compound, and (b-3) the metallocene compound. Examples thereof include a polymerization catalyst composed of at least one compound selected from compounds that react with (a) to form an ion pair, and, if necessary, (c) a particulate carrier. The method for producing an ethylene / propylene / VNB copolymer can be carried out by any of a liquid phase polymerization method such as solution (dissolution) polymerization and suspension polymerization or a gas phase polymerization method, and the above-mentioned components and polymerization conditions can be used. Is also disclosed and known in, for example, Japanese Patent Application Laid-Open No. 2020-63381.

(Silane coupling agent)
The rubber composition of the present invention can contain a silane coupling agent. The silane coupling agent is not particularly limited, but a sulfur-containing silane coupling agent is preferable, and for example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, and 3-trimethoxysilyl are preferable. Examples thereof include propylbenzothiazole tetrasulfide, γ-mercaptopropyltriethoxysilane, 3-octanoylthiopropyltriethoxysilane, and the like. The silane coupling agent may be used alone or in combination of two or more.

(Thermal expandable microcapsules)
The rubber composition of the present invention can include heat-expandable microcapsules. The heat-expandable microcapsules are composed of a shell material made of a thermoplastic resin containing a heat-expandable substance. The shell material of the heat-expandable microcapsules can be formed of a nitrile-based polymer.
Further, the heat-expandable substance contained in the shell material of the microcapsules has a property of being vaporized or expanded by heat, and for example, at least one selected from the group consisting of hydrocarbons such as isoalkane and normalalkane is exemplified. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, and examples of normal alkanes include n-butane, n-propane, and n-hexane. Examples thereof include n-heptane and n-octane. These hydrocarbons may be used alone or in combination of two or more. As a preferable form of the heat-expandable substance, a hydrocarbon obtained by dissolving a gaseous hydrocarbon at room temperature in a liquid hydrocarbon at room temperature is preferable. By using such a mixture of hydrocarbons, a sufficient expansion force can be obtained from a low temperature region to a high temperature region in the vulcanization molding temperature range (150 ° C to 190 ° C) of the unvulcanized tire.
Examples of such heat-expandable microcapsules include the trade name "EXPANCEL 091DU-80" or "EXPANCEL 092DU-120" manufactured by EXPANCEL, Sweden, or the trade name "Matsumoto Micros" manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd. "Fair F-85D" or "Matsumoto Microsphere F-100D" or the like can be used.

(Rubber composition compounding ratio)
The rubber composition of the present invention comprises (A) 100 parts by mass of diene-based rubber, (B) 30 to 100 parts by mass of carbon black and / or white filler, and (C) ethylene / propylene / VNB copolymer. Is characterized by blending 1 to 50 parts by mass.
(A) If the blending amount of the carbon black and / or white filler is less than 30 parts by mass with respect to 100 parts by mass of the diene-based rubber, the mechanical properties and wear resistance of the rubber composition deteriorate, and conversely, 100 parts by mass. If it exceeds the portion, the low temperature flexibility of the rubber composition decreases and the performance on ice deteriorates.
(A) If the blending amount of the ethylene / propylene / VNB copolymer is less than 1 part by mass with respect to 100 parts by mass of the diene rubber, the addition amount is too small to achieve the effect of the present invention, and conversely 50. If it exceeds the mass part, the mechanical properties and workability deteriorate.

The blending amount of the carbon black is preferably 5 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.
The blending amount of the white filler is preferably 15 to 80 parts by mass with respect to 100 parts by mass of the diene rubber.
The blending amount of the ethylene / propylene / VNB copolymer is preferably 5 to 30 parts by mass with respect to 100 parts by mass of the diene rubber.

When a silane coupling agent is blended, the blending amount thereof is preferably 3 to 20% by mass, more preferably 3 to 15% by mass, based on silica.
When the heat-expandable microcapsules are blended, the blending amount is preferably 2 to 15 parts by mass with respect to 100 parts by mass of the diene rubber.

(Other ingredients)
In addition to the above-mentioned components, the rubber composition in the present invention is generally blended in a rubber composition such as a vulcanization or cross-linking agent; a vulcanization or cross-linking accelerator; zinc oxide; an antiaging agent; a plasticizer. Various additives can be blended, and such additives can be kneaded by a general method to form a composition, which can be used for vulcanization or cross-linking. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.
When sulfur is blended as a vulcanizing agent, the blending amount is preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the diene rubber.

Further, the rubber composition of the present invention is suitable for manufacturing a pneumatic tire according to a conventional method for manufacturing a pneumatic tire, and is preferably applied to a tread, particularly a cap tread, to be a studless tire.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to the following examples. In the following example, "part" means "part by mass".

(Preparation Example 1: Preparation of ethylene / propylene / VNB copolymer)
<Composition of ethylene / propylene / VNB copolymer>
The weight fraction (% by weight) of each constituent unit of the ethylene / propylene / VNB copolymer was determined by the measured value by ¹³ C-NMR. The measured values were measured using an ECX400P type nuclear magnetic resonance apparatus (manufactured by JEOL Ltd.) at a measurement temperature of 120 ° C., a measurement solvent: orthodichlorobenzene / dehydrogenated benzene = 4/1, and a total number of times of 8000 times. It was obtained by measuring the spectrum of ¹³ C-NMR of the polymer.

<Ultimate viscosity>
The ultimate viscosity [η] was measured using a fully automatic ultimate viscometer manufactured by Rigo Co., Ltd. at a temperature of 135 ° C. and a measuring solvent: decalin.

<Weight average molecular weight (Mw), number average molecular weight (Mn), molecular weight distribution (Mw / Mn)>
The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) are polystyrene-equivalent numerical values measured by gel permeation chromatography (GPC). The measuring device and conditions are as follows. In addition, the molecular weight was calculated based on a conversion method by preparing a calibration curve using commercially available monodisperse polystyrene.

Equipment: Gel permeation chromatograph Alliance GP2000 type (manufactured by Waters),
Analyst: Emper2 (manufactured by Waters),
Column: TSKgel GMH6-HT x 2 + TSKgel GMH6-HTL x 2 (7.5 mm ID x 30 cm, manufactured by Tosoh Corporation),
Column temperature: 140 ° C,
Mobile phase: o-dichlorobenzene (containing 0.025% BHT),
Detector: Differential Refractometer (RI), Flow Velocity: 1.0 mL / min,
Injection volume: 400 μL,
Sampling time interval: 1s,
Column calibration: Monodisperse polystyrene (manufactured by Tosoh),
Molecular weight conversion: Old method EPR conversion / Calibration method considering viscosity.

When the number of peaks is measured from the chart obtained by the above GPC measurement and two or more peaks are shown, the ratio (%) of the area of the peak appearing on the side with the smallest molecular weight to the total peak area. I checked.

<Complex viscosity η ^* >
A viscoelasticity measuring device Ares (manufactured by Rheometric Scientific) was used as a reometer, and the complex viscosity η ^* ₍ ω _{= 0.01)} at a frequency of ω = 0.01 rad / s under the conditions of 190 ° C. and 1.0% strain. Complex Viscosity η ^* at Frequency ω _{= 0.1} rad / s, Complex Viscosity η * _at Frequency ω = 10 rad / s ^* ₍ ω _{= 10)} and Complex Viscosity η ^* at Frequency ω = 100 rad / s ₍ Ω _{= 100)} (In each case, the unit is Pa · sec) was measured. Also, from the obtained results, the P value (η ^* ₍ ω _{= 0.1)} / η ^* ₍ ω), which is the ratio (η ^* ratio) of the complex viscosity of η ^* ₍ ω _{= 0.1)} and η ^* ₍ ω _{= 100)} . _{= 100)} ) was calculated.

Preparation of Ethylene / Propylene / VNB Copolymer The ethylene / propylene / VNB copolymer was produced as follows using the continuous polymerization apparatus shown in FIG.

In a polymerization reactor C having a volume of 300 liters, 58.3 L / hr of hexane solvent dehydrated and purified from tube 6, 4.5 mmol / hr of triisobutylaluminum (TiBA) from tube 7, (C ₆ H ₅ ) ₃ CB ( C ₆ F ₅ ) ₄ was continuously supplied at 0.150 mmol / hr, and di (p-tolyl) methylene (cyclopentadienyl) (octamethyloctahydrodibenzofluorenyl) zirconium dichloride was continuously supplied at 0.030 mmol / hr. .. At the same time, ethylene is continuously supplied into the polymerization reactor C at 6.6 kg / hr, propylene at 9.3 kg / hr, hydrogen at 18 liters / hr, and VNB at 340 g / hr, respectively, from tubes 2, 3, 4, and 5, respectively. Then, the copolymerization was carried out under the conditions of a polymerization temperature of 87 ° C., a total pressure of 1.6 MPaG, and a residence time of 1.0 hour.

The solution of the ethylene / propylene / VNB copolymer produced in the polymerization reactor C is continuously discharged through the tube 8 at a flow rate of 88.0 liters / hr and raised to a temperature of 170 ° C. (pressure is 4.1 MPaG). It was supplied to the phase separator D. At this time, ethanol, which is a polymerization inhibitor, was continuously introduced into the tube 8 in an amount of 0.1 mol times the amount of TiBA in the liquid component extracted from the polymerization reactor C.

In the phase separator D, the solution of the ethylene / propylene / VNB copolymer is mixed with a concentrated phase (lower phase portion) containing most of the ethylene / propylene / VNB copolymer and a dilute phase (upper phase portion) containing a small amount of polymer. ) And separated.

The separated concentrated phase is led to the heat exchanger K via the tube 11 at 85.4 liters / hr, and further led into the hopper E, where the solvent is evaporated and separated to form an ethylene / propylene / VNB copolymer. Was obtained in an amount of 7.8 kg / hr.

The physical characteristics of the obtained ethylene / propylene / VNB copolymer were evaluated as described above. The results are shown below. The molecular weight distribution of the obtained copolymer was bimodal.

(I) Ethylene / propylene molar ratio = 64/36.
(Ii) Extreme viscosity [η] = 2.6 dL / g.
(Iii) The weight fraction of the constituent unit derived from VNB (c) was 1.5% by mass in 100% by weight of the ethylene / propylene / VNB copolymer.
(Iv) Mw × (c) weight fraction / 100 / (c) molecular weight = 37.3
(V) P / ([η] ^2.9 ) = 5.3, and the weight fraction of (c) × 6 = 8.9.
(Vi) Mw / Mn = 22.9
(Vii) Mn = 13300
The chart obtained by (viii) GPC measurement showed two or more peaks, and the area of the peak appearing on the side with the smallest molecular weight was in the range of 10% of the total peak area.

Standard Example, Examples 1-2, Comparative Examples 1-2
In the formulation (part by mass) shown in Table 1, the vulcanization accelerator and the components excluding sulfur are kneaded with a 1.7 liter closed rubbery mixer for 5 minutes, then the vulcanization accelerator and sulfur are added and further kneaded. A rubber composition was obtained. Next, the obtained unvulcanized rubber composition was press-vulcanized in a predetermined mold at 160 ° C. for 20 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were obtained by the following test method. Was measured.

Performance on ice: The obtained vulture rubber test piece was attached to a flat cylindrical base rubber, and a measurement temperature of -3.0 ° C, a load of 5.5 kg / cm ² , and a drum were used using an inside drum type on-ice friction tester. The coefficient of friction on ice was measured under the condition of a rotation speed of 25 km / h. The coefficient of friction on ice obtained was shown exponentially with the value of the standard example as 100. The larger the index, the larger the frictional force on ice and the better the performance on ice.
The results are shown in Table 1.

* 1: NR (RSS # 3)
* 2: BR (Nipol BR1220 manufactured by Nippon Zeon Corporation)
* 3: Carbon black (Tokai Carbon Co., Ltd. Seest KHA)
* 4: Silica (Zeosil 1165MP manufactured by Rhodia, CTAB specific surface area = 159m ² / g)
* 5: Silane coupling agent (Si69 manufactured by Evonik Degussa, bis (3-triethoxysilylpropyl) tetrasulfide)
* 6: Oil (Extract No. 4S manufactured by Showa Shell Sekiyu Co., Ltd.)
* 7: EPDM (trade name Mitsui EPT4070 manufactured by Mitsui Chemicals, Inc.)
* 8: Ethylene / propylene / VNB copolymer (ethylene / propylene / VNB copolymer prepared as described above)
* 9: Sulfur (fine sulfur powder containing Jinhua Ink oil manufactured by Tsurumi Chemical Industry Co., Ltd.)
* 10: Vulcanization accelerator CZ (Noxeller CZ-G manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)

From the results in Table 1, the rubber composition of each example contains 30 to 100 parts by mass of (B) carbon black and / or white filler with respect to 100 parts by mass of (A) diene-based rubber, and (C) ethylene. -Since 1 to 50 parts by mass of the propylene / VNB copolymer is blended, the performance on ice is improved as compared with the standard example.
On the other hand, in Comparative Examples 1 and 2, since EPDM was blended instead of the ethylene / propylene / VNB copolymer, the degree of improvement in the performance on ice was poor.

C Polymerization reactor D Phase separator E Hopper F Pump G Heat exchanger H Heat exchanger I Heat exchanger J Heat exchanger K Heat exchanger

Claims (4)

(A) For 100 parts by mass of diene rubber
(B) 30 to 100 parts by mass of carbon black and / or white filler, and (C) composition derived from ethylene (a), propylene (b) and 5-vinyl-2-norbornene (VNB) (c). Have a unit,
A rubber composition for a studless tire, which comprises 1 to 50 parts by mass of an ethylene / propylene / VNB copolymer satisfying the following requirements (i) to (vii).
(I) The molar ratio of ethylene / propylene is 60/40 to 80/20;
(Ii) The ultimate viscosity [η] is 2 to 4 dL / g.
(Iii) The weight fraction of the constituent unit derived from VNB (c) is 1% by weight to 2% by weight in 100% by weight of the ethylene / propylene / VNB copolymer;
(Iv) Weight average molecular weight (Mw) of ethylene / propylene / VNB copolymer, weight fraction of structural unit derived from VNB (c) (weight fraction (% by weight) of (c)), and VNB ( The molecular weight of c) (the molecular weight of (c)) satisfies the following formula (1);
4.5 ≤ Mw x weight fraction of (c) / 100 / molecular weight of (c) ≤ 40 ... Equation (1)
(V) Complex viscosity η ^* ₍ ω _{= 0.1)} (Pa · sec) at frequency ω = 0.1 rad / s and frequency ω = obtained by linear viscous elasticity measurement (190 ° C) using a leometer. Ratio P (η ^* ₍ ω _{= 0.1)} / η ^* ₍ ω _{= 100)} ) to complex viscosity η ^* ₍ ω _{= 100)} (Pa · sec) at 100 rad / s, extreme viscosity [η], and VNB The weight fraction of the structural unit derived from (c) (the weight fraction of (c)) satisfies the following formula (2);
P / ([η] ^2.9 ) ≤ (c) weight fraction x 6 ... Equation (2)
(Vi) The ratio (molecular weight distribution; Mw / Mn) between the weight average molecular weight (Mw) and the number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is in the range of 8 to 30;
(Vii) The number average molecular weight (Mn) is 30,000 or less;
(Viii) The chart obtained by GPC measurement shows two or more peaks, and the area of the peak appearing on the side with the smallest molecular weight is in the range of 1 to 20% of the total peak area. The rubber composition for a studless tire according to claim 1, wherein the white filler is silica. The rubber composition for a studless tire according to claim 1 or 2, wherein the (A) diene-based rubber has a glass transition temperature (Tg) of −50 ° C. or lower. A studless tire using the rubber composition for a studless tire according to any one of claims 1 to 3.

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