JPH0977931A - Rubber composition for tire tread - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rubber composition for tire treads excellent in dynamic fatigue resistance, braking performances on frozen road surface and their persistence by mixing a specified ethylene random copolymer rubber with a diene rubber, carbon black and a vulcanizing agent. SOLUTION: This rubber composition for tire treads comprises a random copolymer rubber comprising ethylene, a 3-20C α-olefin and a branched polyene compound of the formula (wherein (n) is an integer of 1-5; R<1> is a 1-5C alkyl; R<2> and R<3> are each H or a 1-5C alkyl), a diene rubber, carbon black and a vulcanizing agent. The random copolymer should have an ethylene/3-20C α-olefin molar ratio of 60/40 to 90/10, an iodine value of 20-50 and an intrinsic viscosity [η]of 1.0-6.0dl/g (as measured in decalin at 135 deg.C).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rubber composition for a tire tread, and more specifically, a rubber composition for a tire tread having excellent braking performance on an icy road surface and capable of maintaining the excellent braking performance for a long period of time. Regarding things.

[0002]

BACKGROUND OF THE INVENTION Since the tires of automobiles generally generate heat during running, the temperature inside the tread rises above 60 ° C., and the tread surface is 100% during normal running due to friction on the road surface during acceleration and deceleration. It is estimated that the temperature is higher than ℃. It is known that the tire tread is deteriorated by reacting with oxygen in the air in such a high temperature atmosphere, and the deterioration reaction causes the tread to deteriorate and the braking performance on the icy road surface, that is, the friction resistance with time. descend.

Conventionally, oil-extended natural rubber and polybutadiene rubber have been reported as rubbers having excellent braking performance on icy road surfaces. When these rubbers are blended with a rubber having a low glass transition temperature (Tg), the braking performance on an icy road surface can be further improved.

However, even if an oil-extended natural rubber or a polybutadiene rubber is blended with a rubber having a low glass transition temperature, excellent braking performance on an icy road surface can be maintained for a long time, and particularly, it can be used satisfactorily for a long period of time at low temperatures. No rubber composition for tire tread has been obtained.

By the way, most of the parts such as tires and anti-vibration rubber which require mechanical strength against dynamic fatigue are
Diene rubbers such as NR, SBR and BR, or blends thereof are used. On the other hand, the static resistance of automobile parts such as weather stripping, door glass run channel, radiator hose, ozone resistance,
EPT having excellent heat aging resistance is used. EPT
Although has excellent weather resistance, ozone resistance, and heat aging resistance, EPT cannot be used alone in tires, anti-vibration rubbers, etc. because of poor dynamic fatigue resistance.

[0006] Therefore, in order to make the best use of the advantages of both materials by blending EPT and diene rubber, many studies have been conducted on blends of diene rubber and EPT, but the blends proposed so far. The product had poor co-vulcanizability and had not reached the level of practical use.

The present inventors have greatly improved the vulcanization rate of EPT and have good covulcanizability with diene rubber.
By developing PT, a rubber composition for a tire tread, which has excellent dynamic fatigue resistance and braking performance on an icy road surface, and which maintains the excellent braking performance for a long time, and can be satisfactorily used particularly in a low temperature condition for a long period of time. 4-ethylidene-8-as a polyene that constitutes EPT
By selecting a specific branched polyene compound such as methyl-1,7-nonadiene (EMN), an EPT having excellent co-vulcanization properties with a diene rubber can be obtained, and this EPT and a diene rubber It was found that even when co-vulcanized with, the excellent dynamic mechanical strength characteristics originally possessed by the diene rubber are not impaired, and the present invention has been completed.

[0008]

SUMMARY OF THE INVENTION The present invention is intended to solve the problems associated with the prior art as described above, and is excellent in dynamic fatigue resistance and braking performance on an icy road surface. An object of the present invention is to provide a rubber composition for a tire tread, which can be maintained for a long time and can be favorably used for a long time particularly in a low temperature state.

[0009]

SUMMARY OF THE INVENTION A rubber composition for a tire tread according to the present invention comprises ethylene, an α-olefin having 3 to 20 carbon atoms, and at least one branched polyene compound represented by the following general formula [I]. A random copolymer rubber (A), a diene rubber (B), carbon black (C), and a vulcanizing agent (D). , (I) ethylene and 3 carbon atoms
The molar ratio (ethylene / α-olefin) to the α-olefin of 20 to 60 is in the range of 60/40 to 90/10,
(Ii) the iodine value is in the range of 20 to 50, and (iii) 1
The intrinsic viscosity [η] measured in decalin at 35 ° C is 1.0 to
It is characterized by being in the range of 6.0 dl / g.

[0010]

Embedded image

[In the formula [I], n is an integer of 1 to 5,
R ¹ is an alkyl group having 1 to 5 carbon atoms, and R ² and R ³ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ]

[0012]

DETAILED DESCRIPTION OF THE INVENTION The rubber composition for a tire tread according to the present invention will be specifically described below. The rubber composition for a tire tread according to the present invention comprises a specific random copolymer rubber (A), a diene rubber (B), carbon black (C) and a vulcanizing agent (D). It is a possible rubber composition.

Random Copolymer Rubber (A) The random copolymer rubber (A) used in the present invention comprises ethylene, an α-olefin having 3 to 20 carbon atoms, and a branched polyene compound.

Examples of such α-olefins having 3 to 20 carbon atoms include propylene, 1-butene,
1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-
Pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene,
Examples thereof include 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. Among them, propylene, 1-butene, 1-hexene and 1-octene are preferably used.

These α-olefins can be used alone or in combination of two or more. The branched polyene compound is represented by the following general formula [I].

[0016]

Embedded image

In the formula [I], n is an integer of 1 to 5;
¹ is an alkyl group having 1 to 5 carbon atoms, and R ² and R ³ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

As the alkyl group having 1 to 5 carbon atoms,
Specifically, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t-butyl group, n-pentyl group, i-pentyl group, etc. Is mentioned.

Examples of such a branched polyene compound (hereinafter also referred to as a branched polyene compound [I]) include the following compounds (1) to (24). Among them, (5), (6), (9),
The branched polyene compounds (11), (14), (19) and (20) are preferably used. (1) 4-ethylidene-1,6-octadiene (2) 7-methyl-4-ethylidene-1,6-octadiene (3) 7-methyl-4-ethylidene-1,6-nonadiene (4) 7-ethyl -4-Ethylidene-1,6-nonadiene (5) 6,7-Dimethyl-4-ethylidene-1,6-octadiene (6) 6,7-Dimethyl-4-ethylidene-1,6-nonadiene (7) 4 -Ethylidene-1,6-decadiene (8) 7-methyl-4-ethylidene-1,6-decadiene (9) 7-Methyl-6-propyl-4-ethylidene-1,6-octadiene (10) 4-ethylidene -1,7- Nonadiene (11) 8-Methyl-4-ethylidene-1,7-nonadiene (EM
N) (12) 4-ethylidene-1,7-undecadiene (13) 8-methyl-4-ethylidene-1,7-undecadiene (14) 7,8-dimethyl-4-ethylidene-1,7-nonadiene (15 ) 7,8-Dimethyl-4-ethylidene-1,7-decadiene (16) 7,8-Dimethyl-4-ethylidene-1,7-undecadiene (17) 8-Methyl-7-ethyl-4-ethylidene-1 , 7-Undecadiene (18) 7,8-Diethyl-4-ethylidene-1,7-decadiene (19) 9-Methyl-4-ethylidene-1,8-decadiene (20) 8,9-Dimethyl-4-ethylidene -1,8-decadiene (21) 10-methyl-4-ethylidene-1,9-undecadiene (22) 9,10-dimethyl-4-ethylidene-1,9-undecadiene (23) 11-methyl-4-ethylidene -1,10-dodecadiene (24) 10,11-dimethyl-4-ethylidene-1,10-dodecadiene These can be used alone or in combination of two or more.

The above branched polyene compound [I] is
It may be a mixture of the trans form and the cis form, or may be the trans form alone or the cis form alone. Such a branched polyene compound can be prepared by the method described in Japanese Patent Application No. 6-154952 filed by the present applicant.

That is, it can be produced by reacting a compound having a conjugated diene represented by the following [Ia] with ethylene in the presence of a catalyst comprising a transition metal compound and an organoaluminum compound.

[0022]

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(In the formula [Ia], n, R ¹ , R ² and R
³ represents n in the general formula [I] described above,
Same as R ¹ , R ² and R ³ . In the random copolymer rubber (A) used in the present invention, the structural units derived from the monomers of ethylene, α-olefin and branched polyene compound as described above are randomly arranged and bonded. The main chain has a substantially linear structure while having a branched structure caused by the branched polyene compound.

The fact that the copolymer rubber has a substantially linear structure and substantially does not contain a gel-like crosslinked polymer means that the copolymer rubber is dissolved in an organic solvent and the insoluble matter is substantially reduced. It can be confirmed by not including it. For example, when the intrinsic viscosity [η] is measured, it can be confirmed that the copolymer rubber is completely dissolved in decalin at 135 ° C.

In such a random copolymer rubber (A), the structural unit derived from the branched polyene compound has a structure substantially represented by the following formula [II].

[0026]

Embedded image

[In the formula [II], n, R ¹ , R ² and R ³
Are n, R ¹ , and R in the general formula [I], respectively.
Same as R ² and R ³ . It should be noted that the fact that the structural unit derived from the branched polyene compound has the above structure means that the ¹³ C-
It can be confirmed by measuring the NMR spectrum.

The random copolymer rubber (A) used in the present invention, for example, ethylene propylene 4-ethylidene
-8-Methyl-1,7-nonadiene (EMN) copolymer rubber has about 3 times faster vulcanization rate than existing ethylene / propylene / 5-ethylidene-2-norbornene (ENB) copolymer rubber. Since the vulcanization rate is almost the same as that of the diene rubber, it is possible to maintain the initial physical properties of the tire tread without impairing the excellent dynamic mechanical strength characteristics originally possessed by the diene rubber. it can.

The random copolymer rubber (A) used in the present invention has the following composition and properties. (I) This random copolymer rubber has a molar ratio of ethylene to an α-olefin having 3 to 20 carbon atoms (ethylene /
The α-olefin) is in the range of 60/40 to 90/10, preferably 70/30 to 80/20.

When the molar ratio of ethylene to the α-olefin having 3 to 20 carbon atoms is less than 60/40, the glass transition point of the random copolymer shifts to a high temperature and the rubber elasticity is lost, which is preferable. Absent. Further, the molar ratio of ethylene and the α-olefin having 3 to 20 carbon atoms is 90 /
When it exceeds 10, the random copolymer becomes a resin-like substance and loses rubber elasticity, which is not preferable.

(Ii) This random copolymer rubber (A)
Has an iodine value of 20 to 50, preferably 25 to 40. When the iodine value of the random copolymer rubber is within the above range, the heat resistance is excellent and the vulcanization rate is high,
Cost performance is good.

(Iii) This random copolymer rubber (A)
Has an intrinsic viscosity [η] measured in decalin of 135 ° C. of 1.0 to 6.0 dl / g, preferably 2.0 to 5.0 d.
1 / g.

When the random copolymer rubber (A) having an intrinsic viscosity [η] in the above range is used, the resulting rubber composition has excellent blendability with a diene rubber and is required as a tire tread. The mechanical strength can be expressed.

In the present invention, the random copolymer rubber (A) is 20 to 80 parts by weight based on 100 parts by weight of the total amount of the random copolymer rubber (A) and the diene rubber (B). It is preferably used in an amount of 30 to 70 parts by weight, more preferably 40 to 60 parts by weight. When the random copolymer rubber (A) is used in the above proportions, it does not impair the excellent mechanical strength characteristics of the diene rubber under the dynamic use conditions inherently, and has weather resistance and heat resistance. It is possible to obtain a rubber composition that can provide a tire tread excellent in heat resistance. If the proportion of the random copolymer rubber (A) is less than 20 parts by weight, the proportion of the random copolymer rubber (A) is too low, and it becomes impossible to maintain excellent vibration damping performance. . On the other hand, if it exceeds 80 parts by weight, the proportion of the diene rubber is too low, and the physical properties required for the tire tread cannot be satisfied, which is not preferable.

Random copolymer rubber (A) as described above
Can be obtained by copolymerizing ethylene, an α-olefin having 3 to 20 carbon atoms, and a branched polyene compound represented by the above general formula [I] in the presence of a catalyst.

As such a catalyst, a Ziegler catalyst comprising a transition metal compound such as vanadium (V), zirconium (Zr), or titanium (Ti) and an organic aluminum compound (organic aluminum oxy compound) can be used.

In the present invention, [a] a catalyst comprising a soluble vanadium compound and an organoaluminum compound, or [b] a metallocene compound of a transition metal selected from Group IVB of the periodic table, and an organoaluminum oxy compound or an ionized ionic compound A catalyst comprising a compound is particularly preferably used.

In the present invention, the catalyst [a] (a catalyst comprising a soluble vanadium compound and an organoaluminum compound) or the catalyst [b] (a metallocene compound of a transition metal selected from Group IV of the periodic table) and an organic Ethylene in the presence of an aluminum oxy compound or a catalyst comprising an ionized ionic compound) and ethylene having an α of 3 to 20 carbon atoms.
-The olefin and the branched polyene compound are usually copolymerized in the liquid phase.

In this case, a hydrocarbon solvent is generally used, but an α-olefin such as propylene may be used as the solvent. Specific examples of such hydrocarbon solvents include pentane, hexane, heptane, octane, decane, dodecane, aliphatic hydrocarbons such as kerosene and halogen derivatives thereof, cyclohexane, methylcyclopentane,
Alicyclic hydrocarbons such as methylcyclohexane and halogen derivatives thereof, aromatic hydrocarbons such as benzene, toluene and xylene, and halogen derivatives such as chlorobenzene are used.

These solvents may be used in combination.
The copolymerization of ethylene, an α-olefin having 3 to 20 carbon atoms and a branched polyene compound may be performed by a batch method or a continuous method. When the copolymerization is carried out by a continuous method, the above-mentioned catalyst is used in the following concentration.

In the present invention, when the above-mentioned catalyst [a], that is, a catalyst comprising a soluble vanadium compound and an organoaluminum compound is used, the concentration of the soluble vanadium compound in the polymerization system is usually 0.01 to 5%. Mmol / liter (polymerization volume), preferably 0.05 to 3 mmol / liter. This soluble vanadium compound is desirably supplied at a concentration of 10 times or less, preferably 1 to 7 times, more preferably 1 to 5 times the concentration of the soluble vanadium compound present in the polymerization system.

The organoaluminum compound has a ratio of aluminum atom to vanadium atom in the polymerization system (A
1 / V), and is supplied in an amount of 2 or more, preferably 2 to 50, more preferably 3 to 20.

The catalyst [a] consisting of a soluble vanadium compound and an organoaluminum compound is usually diluted with the above-mentioned hydrocarbon solvent and / or liquid α-olefin having 3 to 20 carbon atoms and a branched polyene compound. Supplied. At this time, the soluble vanadium compound is desirably diluted to the concentration described above, and the organoaluminum compound is diluted to, for example, 50% of the concentration in the polymerization system.
It is desirable to adjust the concentration to an arbitrary concentration of 2 times or less and supply it to the polymerization system.

In the present invention, when a catalyst [b] comprising a metallocene compound and an organic aluminum oxy compound or an ionized ionic compound (also referred to as an ionic ionized compound or an ionic compound) is used, a polymerization system is used. The concentration of the metallocene compound in is usually 0.1.
0.0005-0.1 mmol / liter (polymerization volume),
Preferably it is 0.0001-0.05 mmol / l.

The organic aluminum oxy compound is
It is supplied in an amount of 1 to 10,000, preferably 10 to 5,000 in terms of the ratio of aluminum atoms to the metallocene compound in the polymerization system (Al / transition metal).

In the case of the ionized ionic compound, the molar ratio of the ionized ionic compound to the metallocene compound in the polymerization system (ionized ionic compound / metallocene compound) is 0.5 to 20, preferably 1 to 10. Supplied.

When an organoaluminum compound is used, it is generally used in an amount of about 0 to 5 mmol / l (polymerization degree), preferably about 0 to 2 mmol / l.

In the present invention, when ethylene, an α-olefin having 3 to 20 carbon atoms and a branched polyene compound are copolymerized in the presence of a catalyst [a] consisting of a soluble vanadium compound and an organoaluminum compound. Has
In the copolymerization reaction, the temperature is usually -50 ° C to 100 ° C, preferably -30 ° C to 80 ° C, more preferably -20 ° C to
At 60 ° C., the pressure is 50 kg / cm ² or less, preferably ² kg / cm 2.
It is performed under the condition of 0 kg / cm ² or less. However, the pressure is not zero.

In the present invention, ethylene, an α-olefin having 3 to 20 carbon atoms and a branched chain polyene compound are present in the presence of a catalyst [b] comprising a metallocene compound and an organoaluminum oxy compound or an ionizable ionic compound. In the case of copolymerizing and, the temperature of the copolymerization reaction is usually -20 ° C to 150 ° C, preferably 0 ° C to 12 ° C.
0 ° C., more preferably 0 ° C. to 100 ° C., and a pressure of 80 ° C.
It is carried out under the condition of not more than kg / cm ² , preferably not more than 50 kg / cm ² . However, the pressure is not zero.

The reaction time (average residence time when the copolymerization is carried out by a continuous method) varies depending on conditions such as the catalyst concentration and the polymerization temperature, but is usually 5 minutes to 5 hours, preferably 10 minutes. ~ 3 hours.

In the present invention, ethylene, C 3 -C 2
The α-olefin of 0 and the branched polyene compound are
It is supplied to the polymerization system in such an amount that a random copolymer rubber having the above-mentioned specific composition can be obtained. Further, upon copolymerization, a molecular weight regulator such as hydrogen may be used.

As described above, ethylene and carbon atoms 3
When an α-olefin of from 20 to 20 and a branched polyene compound are copolymerized, a random copolymer rubber is usually obtained as a polymerization solution containing this. This polymerization liquid is treated by a conventional method to obtain a random copolymer rubber.

The method for preparing the random copolymer rubber (A) [unsaturated ethylenic copolymer] as described above is described in detail in Japanese Patent Application No. 7-69986 filed by the applicant of the present application. Has been done.

Diene Rubber (B) The diene rubber (B) used in the present invention is not particularly limited, and may be a rubber usually used for tire treads. Specific examples thereof include natural rubber (NR) and isoprene. Examples thereof include rubber (IR), butadiene rubber (BR) and styrene-butadiene rubber (SBR). Above all, isoprene-based rubber having a good balance of mechanical strength, that is, natural rubber (NR) and isoprene rubber (IR) are preferably used.

These diene rubbers can be used alone or in combination. In the present invention, the diene rubber (B) is based on 100 parts by weight of the total amount of the random copolymer rubber (A) and the diene rubber (B).
It is used in a proportion of 20 to 80 parts by weight, preferably 30 to 70 parts by weight, more preferably 40 to 60 parts by weight.

Carbon Black (C) The carbon black (C) used in the present invention includes
There is no particular limitation as long as it is carbon black normally used for tire treads, and specifically, SRF, GP
Carbon blacks such as F, FEF, HAF, ISAF, SAF, FT and MT can be mentioned.

In the present invention, the carbon black (C) is 20 to 12 per 100 parts by weight of the total amount of the random copolymer rubber (A) and the diene rubber (B).
It is used in an amount of 0 part by weight, preferably 30 to 100 parts by weight, more preferably 40 to 90 parts by weight. When the carbon black (C) is used in the above proportion, a rubber composition capable of providing a tire tread excellent in wear resistance and dynamic fatigue resistance can be obtained.

Vulcanizing Agent (D) The vulcanizing agent (D) preferably used in the present invention is sulfur or a sulfur compound.

Specific examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur and the like. As sulfur compounds,
Specific examples include sulfur chloride, sulfur dichloride, polymer polysulfide, and the like. Further, a sulfur compound that releases active sulfur at the vulcanization temperature and vulcanizes, for example, morpholine disulfide, alkylphenol disulfide, tetramethylthiuram disulfide, dipentamethylenethiuram tetrasulfide and the like can also be used.

In the present invention, powdered sulfur is preferably used. In the present invention, the vulcanizing agent (D) is the total amount 1 of the random copolymer rubber (A) and the diene rubber (B).
0.5 to 10 parts by weight, preferably 1 to 10 parts by weight, and more preferably 1.0 to 5.0 parts by weight with respect to 00 parts by weight.
Used in proportions by weight.

Rubber composition for tire tread The rubber composition for tire tread according to the present invention comprises the above-mentioned random copolymer rubber (A), diene rubber (B), carbon black (C) and a vulcanizing agent. (D) is contained.

The tire tread obtained from the rubber composition for a tire tread according to the present invention can maintain excellent braking performance on an icy road surface for a long period of time. Whether or not the excellent braking performance on an icy road surface according to the present invention can be maintained for a long time depends on the loss tangent (t
It can be confirmed by how much the value of an δ) changes with heat aging.

The rubber composition for a tire tread according to the present invention can be produced by adopting a well-known rubber-like polymer mixing method such as a mixing method using a mixer such as a Banbury mixer. Further, in the present invention, the random copolymer rubber (A), the diene rubber (B), the carbon black (C) and the vulcanizing agent (D) at the time of compounding the rubber.
In addition to the above, usual rubber compounding agents can be used within a range that does not impair the object of the present invention.

Examples of such compounding agents include softening agents; rubber reinforcing agents such as finely divided silicic acid; fillers such as light calcium carbonate, heavy calcium carbonate, talc, clay, silica; tackifiers; waxes; binding agents. Resins; zinc oxide; antioxidants; antiozonants; processing aids and vulcanization activators. These compounding agents may be used alone or in combination of two or more.

The vulcanized product of the rubber composition for a tire tread according to the present invention is a random copolymer rubber (A), a diene rubber (B), a carbon black (C), a vulcanizing agent (D). ) And, if necessary, other compounding agents are heated at a temperature of 150 to 200 ° C. for 5 to 60 minutes to be vulcanized, and a conventional vulcanization method can be employed.

[0066]

The rubber composition for a tire tread according to the present invention contains a specific ethylene / α-olefin / branched chain polyene copolymer rubber, a diene rubber, carbon black, and a vulcanizing agent. Therefore, it is possible to provide a tire tread which is excellent in dynamic fatigue resistance and braking performance on an icy road surface, maintains the excellent braking performance for a long time, and can be satisfactorily used particularly in a low temperature state for a long period of time.

The present invention will be described below with reference to examples.
The present invention is not limited to these examples. The test methods performed on the vulcanized rubbers in Examples and Comparative Examples are as follows.

[1] Dynamic Viscoelasticity Test The dynamic viscoelasticity test was carried out on a 2 mm thick vulcanized rubber sheet by a rheometric viscoelasticity tester (model RDS-
2), the measurement temperature is 0 ° C., the frequency is 10 Hz, and the strain rate is 1%, and the dynamic elastic modulus (kg / cm ² ) and the dynamic loss elastic modulus (kg / cm ² ) are obtained, and the loss tangent is calculated. ta
nδ (index of vibration damping property) was calculated by the following formula.

G _s = G ′ + ιG ″ (G _s : static elastic modulus, real part G ′: dynamic elastic modulus, imaginary part G ″: dynamic loss elastic modulus) tan δ = G ″ / G ′ at 0 ° C. Loss tangent (tan δ) is JIS K 63
The test pieces before and after 01 of the air heating aging test (100 ° C., 72 hours) were obtained, and the rate of change was obtained.

[2] Tensile test JIS K 6301 (198) was prepared by punching out a vulcanized rubber sheet.
No. 3 type dumbbell test piece described in 9 years) was prepared, and using this test piece, a measuring temperature of 25 ° C. and a pulling speed of 50 were measured according to the method defined in JIS K 6301, item 3.
Subjected to tensile test at 0 mm / min conditions, the 100% modulus (M _100), 200% modulus (M _200), 3
The 00% modulus (M ₃₀₀ ), the tensile stress at break T _B and the elongation at break E _B were measured.

[3] Hardness Test The hardness test was carried out according to JIS K 6301 (1989), and the spring hardness H _S (JIS A hardness) was measured.

[4] Elongation Fatigue Test (Monsanto Fatigue Test) A vulcanized rubber sheet was punched out to prepare a No. 1 type dumbbell test piece described in JIS K 6301. I made a scratch. Of 60 test pieces obtained in this way, 20 pieces were made to have an elongation rate of 40%, elongation fatigue was performed under conditions of a set temperature of 40 ° C. and a rotation speed of 300 rpm, and the average value of the number of times of dumbbell cutting and its The average value of stress during cutting was obtained. Also, the growth rate is 8
The elongation fatigue test was similarly conducted under the conditions of 0% and 150%. Monsanto Fatigue Testing Machine: Frequency 5Hz, Temperature 27 ℃

[5] Crack Growth Test (Dematcher Bending Test) In the crack growth test, resistance to crack growth was examined by a dematcher tester according to ASTM D813. That is, the number of times of bending until a crack was generated and the number of times of bending until the test piece was completely cut was measured (measurement temperature 40 ° C.,
Rotation speed 300 rpm).

The random copolymer rubber (EPT) used in Examples and Comparative Examples is as shown in Table 1.

[0075]

[Table 1]

[0076]

Examples 1 to 4 [Production of Vulcanized Rubber] As the random copolymer rubber (A), the above ethylene / propylene / 4-ethylidene-8-methyl-
1,7-nonadiene copolymer rubber (EMN-EPT),
A commercially available RSS # 1 (NR) as a diene rubber (B) was blended at a blend ratio (NR / EMN-EPT1) of 70/30 according to Table 2 to obtain an unvulcanized blended rubber.

In this compounding, in addition to the above copolymer rubber (EMN-EPT) and NR, Zinc Hua No. 1;
Stearic acid, carbon black [trade name: carbon black N339, manufactured by Asahi Carbon Co., Ltd.], paraffin oil [trade name: Sansen 4240, manufactured by Nippon San Oil Co., Ltd.], antiaging agent [trade name: Nocrac 810-
NA, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.] was added and kneaded with a Banbury mixer having a capacity of 1.7 liters (manufactured by Kobe Steel, Ltd.). This kneading was performed at a filling rate of 70%.

Next, the obtained kneaded product was mixed with a vulcanization accelerator [trade name: Nocrac TS, Ouchi Shinko Chemical Industry Co., Ltd.].
], A vulcanization accelerator [trade name: Nocrac NOBS, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.] and sulfur, and kneaded with an 8-inch roll (front roll / back roll: 65 ° C./65° C.) to obtain a compounded rubber. Obtained.

[0079]

[Table 2]

The compounded rubber obtained as described above is taken out into a sheet and t is pressed by a press heated to 160 ° C.
_A vulcanized sheet having a thickness of 2 mm was prepared by heating and pressing for ₉₀ (min) +2 minutes, and the above dynamic viscoelasticity test, tensile test, hardness test, extension fatigue test and crack growth test were conducted.

The results are shown in Table 3.

[0082]

Comparative Example 1 A vulcanized sheet having a thickness of 2 mm was prepared in the same manner as in Example 1 except that ENB-EPT was used instead of EMN-EPT-1, and the above dynamic viscoelasticity was obtained. Tests, tensile tests, hardness tests, elongation fatigue tests and crack growth tests were performed.

The results are shown in Table 3.

[0084]

[Table 3]

EMN-EPT-1 used in Examples 1 to 4
Since Nos. 4 to 4 have a vulcanization rate equivalent to that of natural rubber (NR), they have excellent co-vulcanizability with natural rubber, and as a result, the loss tangent (tan δ) at 0 ° C is ENB-E.
The value is lower than that of Comparative Example 1 using PT.

The braking property on ice is better as the tan δ is higher. In Comparative Example 1, tan δ at 0 ° C. is from Examples 1 to 1.
Although the value is larger than 4, the dynamic fatigue resistance is inferior. Further, in Examples 1 to 4, the change rate of tan δ at 0 ° C. before and after the aging test was small as compared with Comparative Example 1, and excellent braking performance on an icy road surface can be maintained for a long period of time.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Tsutsui 6-1-2 Waki, Waki-cho, Kuga-gun, Yamaguchi Mitsui Petrochemical Industry Co., Ltd.

Claims (2)

[Claims] 1. A random copolymer rubber (A) comprising ethylene, an α-olefin having 3 to 20 carbon atoms, and at least one branched polyene compound represented by the following general formula [I]: A diene rubber (B), carbon black (C), and a vulcanizing agent (D) are contained, and the random copolymer rubber (A) comprises (i) ethylene and 3 to 20 carbon atoms. The molar ratio of the α-olefin (ethylene / α-olefin) is in the range of 60/40 to 90/10, (ii) the iodine value is in the range of 20 to 50,
(Iii) intrinsic viscosity [η] measured in decalin at 135 ° C.
Is in the range of 1.0 to 6.0 dl / g, and a rubber composition for a tire tread; [In Formula [I], n is an integer of 1 to 5, R ¹ is an alkyl group having 1 to 5 carbon atoms, and R ² and R ³ are each independently a hydrogen atom or a carbon atom number. 1 to 5 alkyl groups]. 2. The content of the random copolymer rubber (A) is 20 to 80 parts by weight based on 100 parts by weight of the total amount of the random copolymer rubber (A) and the diene rubber (B). The rubber composition for a tire tread according to claim 1, wherein the content of the diene rubber (B) is 20 to 80 parts by weight.