JP6414248B2 - Rubber composition - Google Patents

Description

  The present invention relates to a rubber composition that improves adhesion performance with a steel cord and tire durability.

  Some pneumatic tires include a carcass layer and a belt layer in which a steel cord is coated with a coat rubber (rubber composition for coating a steel cord) and the tread portion thereof. If the adhesiveness between these steel cords and rubber members decreases with long-term use, failure tends to occur and tire durability may decrease. In recent years, however, tires have been used for a longer period of time, and it has become increasingly important to increase the reinforcement effect of steel cords and maintain durability over a long period of time.

  Patent document 1 has proposed improving the adhesiveness of a steel cord by the rubber composition which mix | blended organic acid cobalt salt with diene type rubber. However, the level demanded by consumers to improve the adhesion of steel cords and tire durability is higher, and further improvements have been demanded.

JP 2007-99868 A

  An object of the present invention is to provide a rubber composition in which the adhesion performance to a steel cord and the durability of a tire are improved to a conventional level or more.

The rubber composition of the present invention that achieves the above object is obtained by blending 40 to 80 parts by mass of carbon black, cobalt neodecanoate, cobalt resin and a curing agent in 100 parts by mass of a diene rubber containing natural rubber. The carbon black has a DBP oil absorption of 50 × 10 ⁻⁵ to 80 × 10 ⁻⁵ m ³ / kg, an iodine adsorption of 100 to 150 g / kg, and the rubber composition. For a vulcanized product having a dynamic strain of 2%, a dynamic storage elastic modulus (E ′) at 20 ° C. of 8 MPa or more, a tangent loss (tan δ) of 60 ° C. of 0.20 or less, a strain of 60%, and a constant strain fatigue of 400 rpm. It is characterized in that the number of repetitions until destruction in the test is 45,000 times or more.

The rubber composition of the present invention comprises 40 to 80 parts by mass of carbon black having a specific DBP oil absorption amount and iodine adsorption amount, 100 parts by mass of diene rubber containing natural rubber, cobalt borate neodecanoate, phenolic resin And the physical properties of the vulcanizate of the rubber composition, the dynamic storage elastic modulus (E ′) at 20 ° C. is 8 MPa or more, the tangent loss (tan δ) at 60 ° C. is 0.20 or less, Since the constant strain fatigue test at a strain of 60% and 400 rpm is broken at 45,000 times or more, the adhesion performance to the steel cord and the tire durability can be improved to the conventional level or more.

  The rubber composition of the present invention is 0.3 to 1.5 parts by mass of the cobalt neodecanoate borate and 0.5 to 3.0 parts by mass of the phenolic resin with respect to 100 parts by mass of the diene rubber. It is preferable that the curing agent is blended in an amount of 0.5 to 5.0 parts by mass.

  Furthermore, it is preferable to mix | blend 0.1-1.0 mass part of sulfenamide type | system | group vulcanization accelerators with respect to 100 mass parts of said diene rubbers.

  The pneumatic tire using the rubber composition of the present invention for the belt layer has improved adhesion performance to the steel cord, and the tire durability can be improved beyond the conventional level.

The rubber composition of the present invention has a DBP oil absorption of 50 × 10 ⁻⁵ to 80 × 10 ⁻⁵ m ³ / kg and an iodine adsorption of 100 to 150 g / kg on 100 parts by mass of diene rubber containing natural rubber. 40-80 parts by mass of carbon black, cobalt neodecanoate borate, phenolic resin and curing agent, dynamic strain 2%, dynamic storage elastic modulus (E ′) at 20 ° C. of 8 MPa or more, 60 The tangent loss (tan δ) at 0 ° C. is 0.20 or less, the strain is 60%, and the number of repetitions until breakage in a constant strain fatigue test at 400 rpm is 45,000 or more.

  In the present invention, the dynamic storage elastic modulus (E ′) at 20% at 2% dynamic strain of the rubber composition is 8 MPa or more, preferably 8 MPa or more and less than 14 MPa, more preferably 9 to 12 MPa. When the dynamic storage elastic modulus (E ′) is less than 8 MPa, the adhesion performance to the steel cord is inferior and the tire durability is insufficient. The dynamic storage elastic modulus (E ′) can be increased or decreased depending on the composition of the rubber composition and the vulcanization conditions such as temperature and time. In this specification, the dynamic storage elastic modulus (E ′) is based on the conditions of a frequency of 20 Hz, initial strain of 10%, dynamic strain of ± 2%, and temperature of 20 ° C. using a viscoelastic spectrometer in accordance with JIS-K6394. Shall be measured.

  The rubber composition of the present invention has a tangent loss (tan δ) at 60 ° C. of 0.20 or less, preferably 0.14 to 0.20, more preferably 0.15 to 0.19. If the tan δ at 60 ° C. exceeds 0.20, the adhesion performance to the steel cord tends to be lowered, resulting in insufficient tire durability. The tan δ at 60 ° C. can be increased or decreased depending on the composition of the rubber composition and the vulcanization conditions such as temperature and time. In the present specification, tan δ at 60 ° C. is measured according to JIS-K6394 using a viscoelastic spectrometer under the conditions of frequency 20 Hz, initial strain 10%, dynamic strain ± 2%, temperature 60 ° C. .

  In addition, the tensile fatigue characteristics of the rubber composition are such that the number of repetitions until fracture in a constant strain fatigue test at 60% strain and 400 rpm is 45,000 times or more, preferably 50,000 times or more. If the fatigue life with a 60% strain of the rubber composition is less than 45,000 times, the tire durability is insufficient. The tensile fatigue characteristics of the rubber composition can be adjusted by the composition of the rubber composition and the vulcanization conditions such as temperature and time. In this specification, the tensile fatigue characteristics of the rubber composition are as follows: JIS-K6270 is used, a dumbbell No. 3 type test piece (thickness 2 mm), 20 ° C., strain 60%, test frequency 6.67 Hz ( It shall be measured according to the condition of the number of rotations of 400 rpm.

  In the rubber composition of the present invention, the diene rubber necessarily contains natural rubber. The content of the natural rubber is preferably 80% by mass or more, more preferably 90 to 100% by mass in 100% by mass of the diene rubber. If the content of the natural rubber is less than 80% by mass, it is not possible to ensure adhesion to the steel cord (for example, cross-ply peeling force).

  The diene rubber other than natural rubber can be blended as the diene rubber in the rubber composition of the present invention. Examples of other diene rubbers include isoprene rubber, butadiene rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, butyl rubber, and halogenated butyl rubber. Of these, isoprene rubber, butadiene rubber, styrene-butadiene rubber, and halogenated butyl rubber are preferable. These diene rubbers can be used alone or as any blend. The content of the other diene rubber is preferably 20% by mass or less, more preferably 0 to 10% by mass in 100% by mass of the diene rubber.

  In the rubber composition of the present invention, 40 to 80 parts by mass of carbon black is blended with 100 parts by mass of the diene rubber described above. By blending carbon black in such a range, the mechanical properties of the rubber composition can be ensured and excellent tire durability can be obtained. The compounding amount of carbon black is preferably 43 to 75 parts by mass, more preferably 45 to 70 parts by mass. When the blending amount of the carbon black is less than 40 parts by mass, the fatigue life in the constant strain fatigue test is deteriorated and the tire durability is lowered. Moreover, when the compounding quantity of carbon black exceeds 80 mass parts, tan (delta) of 60 degreeC will deteriorate.

  The carbon black used in the present invention is an ISAF grade carbon black, particularly an ISAF grade carbon black having a small structure. When ISAF grade carbon black, which has a large structure, is used in the tread rubber composition, tire durability is inferior as a steel cord coating rubber composition.

In the rubber composition of the present invention, the DBP oil absorption of carbon black is 50 × 10 ⁻⁵ to 80 × 10 ⁻⁵ m ³ / kg, preferably 60 × 10 ^{−5 to} 78 × 10 ⁻⁵ m ³ / kg. . When the DBP oil absorption of carbon black is less than 50 × 10 ⁻⁵ m ³ / kg, the reinforcing property is lowered and the tire durability is lowered. On the other hand, if the DBP oil absorption exceeds 80 × 10 ⁻⁵ m ³ / kg, the fatigue life in the constant strain fatigue test deteriorates and the tire durability decreases. In this specification, CTAB adsorption specific surface area shall be measured according to JIS K6217-3.

  The iodine adsorption amount of carbon black is 100 to 150 g / kg, preferably 105 to 125 g / kg. When the iodine adsorption amount of carbon black is less than 100 g / kg, the reinforcing property is lowered and the tire durability is lowered. On the other hand, if the iodine adsorption amount exceeds 150 g / kg, tan δ at 60 ° C. deteriorates and durability deteriorates. In this specification, the iodine adsorption amount shall be measured in accordance with JIS K6217-1.

In the present invention, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 90 × 10 ^{−3 to} 115 × 10 ⁻³ m ² / kg, more preferably 95 × 10 ^{−3 to} 110 × 10 ^−3. It may be m ² / kg. When N ₂ SA of carbon black is less than 90 × 10 ⁻³ m ² / kg, the reinforcing property is lowered and the tire durability is lowered. On the other hand, when N ₂ SA of carbon black exceeds 115 × 10 ⁻³ m ² / kg, tan δ at 60 ° C. deteriorates and durability deteriorates. In the present specification, N ₂ SA is measured in accordance with JIS K6217-2.

The rubber composition of the present invention increases adhesion to steel cords by blending cobalt neodecanoate borate. Cobalt neodecanoate is a compound represented by the following general formula (1), and the blending amount thereof is preferably 0.3 to 1.5 parts by mass, more preferably 0.8 parts per 100 parts by mass of the diene rubber. It is good to make it more than 5 mass parts and 1.5 mass parts or less. If the blending amount of cobalt neodecanoate is less than 0.3 parts by mass, the initial adhesiveness and durable adhesiveness to the steel cord may not be sufficiently increased. Moreover, when the compounding quantity of cobalt neodecanoate borate exceeds 1.5 mass parts, a constant strain fatigue characteristic will fall on the contrary and there exists a possibility that tire durability may fall.

  The cobalt neodecanoate borate preferably has a cobalt content of 18 to 26 mass%, more preferably 20 to 24 mass%. Examples of cobalt neodecanoate borate include Manobond C22.5 and Manobond 680C manufactured by Rhodia, CoMend A and CoMend B manufactured by Shepherd, and DICATE NBC-II manufactured by DIC Corporation.

  The rubber composition of this invention mix | blends phenolic resin and its hardening | curing agent with diene rubber. By blending the phenolic resin and the curing agent, it is possible to improve the hardness, tensile elongation at break and adhesion performance to the steel cord of the rubber composition and to improve the tire durability.

  Examples of phenolic resins include cresol resins, resorcin resins, alkylphenol resins, and modified phenol resins. Examples of the modified phenol resin include cashew modified phenol resin, oil modified phenol resin, epoxy modified phenol resin, aniline modified phenol resin, melamine modified phenol resin and the like.

  The cresol resin is a compound obtained by reacting cresol and formaldehyde, and a compound using m-cresol is particularly preferable. Examples of the cresol resin include Sumicanol 610 manufactured by Sumitomo Chemical Co., Ltd. and SP7000 manufactured by Nippon Shokubai Co., Ltd.

  Resorcin resin is a compound obtained by reacting resorcin and formaldehyde. For example, Penacolite B-18-S, B-19-S, B-20-S, B-20-S, etc. manufactured by INDSPEC Chemical Corporation, etc. Can be illustrated. Further, as the resorcin resin, a modified resorcin resin may be used, and examples thereof include a resorcin resin modified with alkylphenol and the like, and a resorcin / alkylphenol / formalin copolymer can be exemplified.

  The cashew-modified phenol resin is a phenol resin modified with cashew oil, such as Sumitomo Bakelite's Sumilite Resin PR-YR-170, PR-150, Dainippon Ink & Chemicals Phenolite A4-1419, etc. Can be illustrated. The phenol resin is an unmodified resin obtained by a reaction between phenol and formaldehyde, and examples thereof include Sumikanol 620 manufactured by Sumitomo Chemical Co., Ltd.

  The blending amount of the phenolic resin is preferably 0.5 parts by mass or more and less than 3 parts by mass, more preferably 0.7 to 2.0 parts by mass with respect to 100 parts by mass of the diene rubber. When the blending amount of the phenolic resin is less than 0.5 parts by mass, the dynamic storage elastic modulus (E ′) decreases, the tan δ at 60 ° C. increases, the adhesion to the steel cord decreases, and the tire durability decreases. There may be a shortage. On the other hand, if the blending amount of the phenolic resin is 3 parts by mass or more, the tan δ at 60 ° C. increases, the constant strain fatigue characteristics are lowered, and the tire durability may be lowered.

  In this invention, the hardening | curing agent which hardens the phenol-type resin mentioned above is mix | blended. Examples of the curing agent include hexamethylenetetramine, hexamethoxymethyl melamine, hexamethoxymethylol melamine, pentamethoxymethyl melamine, hexaethoxymethyl melamine, para-formaldehyde polymer, melamine N-methylol derivative and the like. These methylene donors can be used alone or in any blend.

  Examples of hexamethylenetetramine include Sunseller HT-PO manufactured by Sanshin Chemical Industry Co., Ltd. Examples of hexamethoxymethylolmelamine (HMMM) include CYREZ 964RPC manufactured by CYTEC INDUSTRIES. Examples of pentamethoxymethylmelamine (PMMM) include BARA CHEMICAL Co. , LTD. An example is Sumikanol 507A manufactured by the company.

  The blending amount of the curing agent is preferably 0.5 to 5 parts by mass, more preferably 0.7 to 4.0 parts by mass with respect to 100 parts by mass of the diene rubber. When the compounding amount of the curing agent is less than 0.5 parts by mass, the dynamic storage elastic modulus (E ′) is decreased, the tan δ at 60 ° C. is increased, the adhesion to the steel cord is decreased, and the tire durability is insufficient. There is a risk of doing. Moreover, when the compounding quantity of a hardening | curing agent exceeds 5 mass parts, there exists a possibility that a constant strain fatigue characteristic may fall and tire durability may fall.

  The rubber composition of the present invention contains sulfur and a vulcanization accelerator in a diene rubber. The amount of sulfur is preferably 3.0 to 9.0 parts by mass, more preferably 4.0 to 8.0 parts by mass with respect to 100 parts by mass of the diene rubber. There exists a possibility that the adhesiveness with respect to a steel cord may fall that the compounding quantity of sulfur is less than 3.0 mass parts. Further, if the amount of sulfur exceeds 9.0 parts by mass, tire durability may be reduced. In this specification, the compounding amount of sulfur is the net compounding amount of sulfur contained for vulcanization and / or sulfur contained in the vulcanizing agent.

  Although it does not specifically limit as a vulcanization accelerator, Preferably a sulfenamide type | system | group vulcanization accelerator is preferable. Examples of the sulfenamide-based vulcanization accelerator include N, N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ), N-cyclohexyl-2-benzothiazole sulfenamide (CZ), N -Oxydiethylene-2-benzothiazole sulfenamide (OBS), N- (tert-butyl) benzothiazole-2-sulfenamide (NS) can be mentioned. These sulfenamide-based vulcanization accelerators can be blended singly or in combination. Among these, N, N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ) and / or N- (tert-butyl) benzothiazole-2-sulfenamide (NS) is preferably blended. .

  The blending amount of the vulcanization accelerator is preferably 0.1 to 1.0 part by mass, more preferably 0.2 to 0.8 part by mass with respect to 100 parts by mass of the diene rubber. If the blending amount of the vulcanization accelerator is less than 0.1 parts by mass, tan δ at 60 ° C. is increased, and tire durability may be reduced. Moreover, when the compounding quantity of a vulcanization accelerator exceeds 1.0 mass part, there exists a possibility that the adhesiveness at the time of deterioration may fall. As the vulcanization accelerator, a sulfenamide-based vulcanization accelerator is preferably added in an amount of 0.1 to 1.0 part by weight, more preferably 0.2 to 0.8 part by weight, based on 100 parts by weight of the diene rubber. .

  In the present invention, inorganic fillers other than carbon black can be blended. Examples of other inorganic fillers include silica, clay, talc, mica, and calcium carbonate. Of these, silica is preferable, and tan δ at 60 ° C. can be further reduced.

  The rubber composition can be blended with various additives commonly used in tire rubber compositions such as vulcanization accelerators, aging inhibitors, peptizers, various oils, and plasticizers, Such additives can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition of the present invention can be produced by mixing the above components using a normal rubber kneading machine, such as a Banbury mixer, a kneader, or a roll.

  The rubber composition of the present invention can be suitably used for constituting a steel cord covering portion of a pneumatic tire. It is preferable to use it for the coated rubber for covering the steel cord of the belt layer and / or the carcass layer. It is particularly preferable to use the coated rubber for covering the steel cord of the belt layer. Since the pneumatic tire using the rubber composition of the present invention for the coated rubber of the steel cord has improved the adhesion performance to the steel cord, it is possible to suppress the peeling between the steel cord and the covering rubber. Thereby, the durability of the pneumatic tire can be maintained and improved to a level higher than the conventional level.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  In preparing 15 types of rubber compositions (Examples 1 to 6, Standard Examples and Comparative Examples 1 to 7) having the common compositions shown in Table 3 and comprising the compositions shown in Tables 1 and 2, sulfur and additive were respectively used. The components excluding the sulfur accelerator were weighed and kneaded with a 1.7 L closed Banbury mixer for 5 minutes, and then the master batch was discharged and cooled at room temperature. This master batch was subjected to a 1.7 L hermetic Banbury mixer, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition. In Table 3, each compounding agent describes the compounding amount (part by mass) with respect to 100 parts by mass of the diene rubber described in Tables 1 and 2.

  The rubber composition obtained above was vulcanized in a mold having a predetermined shape at 170 ° C. for 10 minutes to prepare a test piece. A dynamic storage elastic modulus (E ′), 60 The tan δ at 0 ° C. and the constant strain fatigue test were evaluated. Further, steel cord adhesiveness (index rubber adhesion amount) and tire durability test were conducted by the method described later.

Dynamic storage elastic modulus (E ′), tan δ at 60 ° C.
Based on JIS K6394, the obtained test piece was dynamically stored at a temperature of 20 ° C. under the conditions of initial strain 10%, dynamic strain ± 2%, frequency 20 Hz, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. The elastic modulus (E ′) and loss tangent tan δ at a temperature of 60 ° C. were measured. The obtained results of E ′ and tan δ are shown in the columns “E ′ at 20 ° C.” and “tan δ at 60 ° C.” in Tables 1 and 2.

Constant strain fatigue test Using the obtained test piece, a dumbbell JIS No. 3 type test piece was prepared in accordance with JIS K6251, and 20 ° C., strain 60%, test frequency 6.67 Hz with reference to JIS-K6270. A tensile constant strain fatigue test was performed under the condition of (rotation speed: 400 rpm), and the number of repetitions until breaking was measured. The obtained results are listed in the column of “Tensile Constant Strain Fatigue Properties” in Tables 1 and 2.

Steel cord adhesion (index rubber adhesion)
A brass-plated steel cord arranged in parallel at 12.7 mm intervals is coated with the rubber composition, embedded at an embedding length of 12.7 mm, and vulcanized and bonded under vulcanization conditions at 170 ° C. for 10 minutes to produce a sample. did. In accordance with ASTM D-2229, a steel cord was drawn from the sample and evaluated based on the attached amount (%) of index rubber covering the surface. The obtained results are shown in the column of “index rubber adhesion amount” in Tables 1 and 2.

Tire Durability Test A pneumatic tire (size 295 / 35R21) was vulcanized using the rubber composition obtained as a coating rubber for the belt layer. The obtained tire was mounted on a rim (21 × 10.5 J), filled with a gas having an oxygen concentration of 100%, adjusted to an air pressure of 350 kPa, and allowed to stand in an environment at a temperature of 70 ° C. for 14 days. Thereafter, the air pressure is adjusted to 170 kPa, the drum diameter is 1707 mm, and the load is increased by 13% every 2 hours from 88% of the JIS D4230 indoor drum tester, while the speed is 60 km / h. Then, a running test of 6,000 km was conducted. After the running test, the tire was disassembled and the amount (mm) of edge separation in the belt layer was measured. The obtained results are shown in the column of “Tire durability (peeling amount)” in Tables 1 and 2.

The types of raw materials used in Tables 1 and 2 are shown below.
・ NR: Natural rubber, TSR20
CB-1: carbon black HAF grade LS, Toast Carbon Co., Ltd. Seest 300, DBP oil absorption is 75 × 10 ⁻⁵ m ³ / kg, iodine adsorption is 86 g / kg, nitrogen adsorption specific surface area is 84 × 10 ^{− 3} m ² / kg
CB-2: Carbon black ISAF grade LS, Tokai Carbon Co., Ltd. Seast 600, DBP oil absorption is 75.6 × 10 ⁻⁵ m ³ / kg, iodine adsorption is 112.8 g / kg, nitrogen adsorption specific surface area is 101.9 × 10 ⁻³ m ² / kg
CB-3: carbon black ISAF grade HS, Tokai Carbon Co., Ltd. Seest 5H, DBP oil absorption 129 × 10 ⁻⁵ m ³ / kg, iodine adsorption 104 g / kg, nitrogen adsorption specific surface area 99 × 10 ^{− 3} m ² / kg
Cobalt stearate: cobalt stearate, cobalt stearate manufactured by DIC Corporation (cobalt content: 9.5% by mass)
-Neodecanoic acid boric acid Co: Cobalt neodecanoic acid borate represented by the above general formula (1), DICRATE NBC-II (cobalt content 22.2% by mass) manufactured by DIC Corporation
・ Phenolic resin-1: Resorcin resin, PENACOLLITE RESIN B-18-S manufactured by INDSPEC
-Phenol resin-2: Cresol resin, Sumikanol 610 manufactured by Sumitomo Chemical Co., Ltd.
Curing agent: Hexamethoxymethylol melamine (HMMM), CYREZ 964RPC manufactured by CYTEC INDUSTRIES
Vulcanization accelerator: N, N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide, Nouchira DZ manufactured by Ouchi Shinsei Chemical Co., Ltd.

The types of raw materials used in Table 3 are shown below.
・ Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. ・ Anti-aging agent: Santoflex 6PPD manufactured by Flexis
・ Sulfur: Shikoku Kasei Kogyo Co., Ltd. Mukuron OT-20 (Sulfur content is 80% by mass)

  As is clear from Table 1, the rubber compositions of Examples 1 to 6 have a large amount (%) of rubber adhering to the steel cord, the amount of edge separation in the belt layer is suppressed, and the tire durability is higher than the standard example. It was confirmed that it improved.

  As is apparent from Table 2, the rubber composition of Comparative Example 1 has a specific DBP oil absorption amount and an iodine adsorption amount of carbon black CB-2 of less than 40 parts by mass, a constant strain fatigue life of 45, Since it is less than 000 times, the amount of edge separation is inferior.

  Since the rubber composition of Comparative Example 2 has a constant strain fatigue life of less than 45,000 times, the steel cord adhesion (index rubber adhesion amount) is inferior, and the amount of edge separation increases.

  Since the rubber composition of Comparative Example 3 has a constant strain fatigue life of less than 45,000 times, the steel cord adhesion (index rubber adhesion amount) and the amount of edge separation are inferior.

  The rubber composition of Comparative Example 4 has a dynamic storage elastic modulus (E ′) at 20 ° C. of less than 8 MPa and a constant strain fatigue life of less than 45,000 times. And the amount of edge separation increases.

  Since the rubber composition of Comparative Example 5 has a tan δ at 60 ° C. of more than 0.20 and a constant strain fatigue life of less than 45,000 times, the amount of edge separation increases.

  Since the rubber composition of Comparative Example 6 has a tan δ at 60 ° C. of more than 0.20 and a constant strain fatigue life of less than 45,000 times, the steel cord has poor adhesion (index rubber adhesion amount) and edge separation. The amount of increases.

  Since the rubber composition of Comparative Example 7 has a constant strain fatigue life of less than 45,000 times, the steel cord adhesion (index rubber adhesion amount) and the amount of edge separation increase.

In the rubber composition of Comparative Example 8, the DBP oil absorption of carbon black CB-3 exceeds 80 × 10 ⁻⁵ m ³ / kg and the constant strain fatigue life is less than 45,000 times. (Index rubber adhesion amount) and the amount of edge separation increase.

Claims (4)

A rubber composition comprising 40 to 80 parts by mass of carbon black, cobalt neodecanoate borate, a phenolic resin, and a curing agent in 100 parts by mass of a diene rubber containing natural rubber, wherein the DBP of the carbon black The oil absorption is 50 × 10 ⁻⁵ to 80 × 10 ⁻⁵ m ³ / kg, the iodine adsorption is 100 to 150 g / kg, and the vulcanizate of the rubber composition has a dynamic strain of 2%, 20 ° C. The dynamic storage elastic modulus (E ′) at 8 MPa is 8 MPa or more, the tangent loss (tan δ) at 60 ° C. is 0.20 or less, the strain is 60%, and the number of repetitions until it breaks in a constant strain fatigue test at 400 rpm is 45,000 The rubber composition characterized by the above.   The cobalt neodecanoate borate is 0.3 to 1.5 parts by mass, the phenolic resin is 0.5 parts by mass or more and less than 3.0 parts by mass, and the curing agent is 0 parts by mass with respect to 100 parts by mass of the diene rubber. The rubber composition according to claim 1, which is blended in an amount of 0.5 to 5.0 parts by mass.   The rubber composition according to claim 1, wherein 0.1 to 1.0 part by mass of a sulfenamide vulcanization accelerator is blended with 100 parts by mass of the diene rubber.   The pneumatic tire containing the belt layer which consists of a rubber composition in any one of Claims 1-3.