JP2008038059A - Rubber composition, its composite, and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition which is excellent in the workability, adhesion to a metal such as steel, and thermal aging resistance, and to provide a composite using the composition. <P>SOLUTION: The rubber composition comprises (A) a diene-based rubber and (B) a low-molecular-weight, high-cis, diene-based rubber with an acid anhydride group of 0.1 to 10 parts by weight relative to 100 parts by weight of the above diene-based rubber. The metal-rubber composite is formed by the vulcanization-adhesion of the composition concerned to a metallic material. It is preferable that the above metallic material is a steel wire or a steel cord. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition excellent in processability, adhesion to a metal such as steel and heat aging resistance, a metal-rubber composite obtained by vulcanizing and bonding the rubber composition to a metal body, and the metal -It relates to a pneumatic tire using a rubber composite.

  In recent years, metal reinforcing materials have been used for rubber products such as tires, belts, hoses, and the like as necessary in order to enhance their durability. In these rubber products, if the adhesion between the reinforcing material and the rubber composition is not sufficient, or if the rubber deteriorates due to long-term use under high temperature conditions, the adhesiveness will decrease significantly. The quality of the product will be seriously affected. Therefore, conventionally, for the purpose of improving the adhesion between the metal and the rubber composition, for example, with respect to 100 parts by weight of the raw rubber, the amount of 1,2-vinyl bond is 60% or more and is terminated with maleic anhydride. 1 to 10 parts by weight of the modified butadiene rubber, 1 to 5 parts by weight of a partial condensate of hexamethylol melamine pentamethyl ether, 0.5 to 5 parts by weight of metacresol resin, and 4 to 7 parts by weight of sulfur are blended. A rubber composition having improved adhesion to steel cords has been proposed (Patent Document 1), hydrogenated acrylonitrile-butadiene copolymer (NBR), ethylene-methyl acrylate copolymer, and organic sulfur-containing compound A rubber composition having improved adhesion stability with brass has been proposed by blending maleic anhydride-modified polybutadiene with ( Patent Document 2). Furthermore, as a method for firmly bonding a metal and a rubber, the rubber has a cis-1,4-bond amount of 96% or more and is modified with maleic anhydride and / or a maleic anhydride derivative. It has been proposed to use a rubber containing cis-1,4-polyisoprene (Patent Document 3). Synthetic cis in which 0.08 to 2.5 mol of maleic anhydride is introduced with respect to 100 isoprene monomer units. An unvulcanized rubber compound composed of 1,4-polyisoprene rubber or a mixed rubber of at least 20% by weight of the above synthetic cis-1,4-polyisoprene rubber with another diene rubber is bonded to a metal material. It is proposed to vulcanize (Patent Document 4). And (i) a functionalized polymer having a functional group selected from a carboxylic acid or anhydride, an epoxy group, an amino group, an oxazoline group, and a hydroxyl group; and (ii) a copolyamide, a copolyester, and a polyamide or a blend thereof. It has been proposed to adhere a thermoplastic elastomer to a metal element comprising a metal substrate that is wholly or partially coated with an outer layer comprising a selected compound (Patent Document 5).

  In order to ensure adhesion to metals such as steel, it has been proposed to mix various acid anhydride-modified diene rubbers in rubber compositions containing diene rubber as the main rubber component. There is a problem that the adhesiveness with the rubber composition is insufficient, or the rubber deteriorates due to use for a long time under a high temperature condition and the adhesiveness is remarkably lowered.

JP-A-7-102121 JP-A-10-87888 JP 51-98785 A Japanese Patent Laid-Open No. 51-116884 Special table 2003-517386

  Accordingly, an object of the present invention is to provide a rubber composition that exhibits good processability before vulcanization and exhibits good heat aging resistance and good adhesion to a metal such as steel after vulcanization.

As a result of diligent research, the present inventor has found that when a certain amount of a low molecular weight high cis-diene rubber containing an acid anhydride group is blended in a rubber composition mainly composed of a diene rubber, the processability before vulcanization is increased. And improved heat aging resistance after vulcanization and adhesion to metals such as steel. That is, according to the present invention,
(A) a diene rubber,
(B) 0.1 to 10 parts by weight of a low molecular weight high cis-diene rubber containing an acid anhydride group with respect to 100 parts by weight of the diene rubber;
A rubber composition is provided.

  The present invention further provides a metal-rubber composite obtained by vulcanizing and bonding the rubber composition to a metal body, and a pneumatic tire using the metal-rubber composite.

  Surprisingly, the rubber composition of the present invention, as described above, even when using sulfur that is usually used as a vulcanizing agent for the diene rubber component in a considerably smaller amount than the conventional compounding amount, Good adhesion to metals such as steel after vulcanization.

  As the diene rubber (A) used in the rubber composition of the present invention, natural rubber or diene synthetic rubber can be used alone or in combination of two or more thereof. Examples of the diene synthetic rubber that can be used include various butadiene rubbers (BR), isoprene rubbers (IR), styrene-butadiene copolymer rubbers (SBR), acrylonitrile-butadiene copolymer rubbers (NBR), A chloroprene rubber (CR) is mentioned.

  The low molecular weight high cis-diene rubber (B) containing an acid anhydride group may be a diene rubber (A) as long as it satisfies the conditions regarding the weight average molecular weight, cis-1,4-bond content and the like described later. ) May be any of those obtained by modification with an acid anhydride, but the high cis-diene rubber (B) is preferably derived from butadiene rubber or isoprene rubber. By blending the high cis-diene rubber (B) in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the diene rubber, the heat aging resistance is improved, and particularly good tensile strength even after heat aging. Strength and tear strength and good adhesion to metals such as steel are achieved. When the blending amount of the high cis-diene rubber (B) is less than 0.1 parts by weight with respect to 100 parts by weight of the diene rubber, a sufficient effect cannot be achieved. The mechanical strength is lowered due to plasticizing action of the rubber (B), and the acid anhydride group contained in the high cis-diene rubber (B) inhibits the vulcanization acceleration reaction of the vulcanization accelerator. As a result, the vulcanization rate is lowered. The high cis-diene rubber (B) has a weight average molecular weight of 1,000 to 30,000, a cis-1,4-bond content of 70 to 100%, and an average per 100 monomer repeating units. 1 to 15 acid anhydride groups. When the weight average molecular weight of the high cis-diene rubber (B) is less than 1,000, the number of reaction sites with the rubber becomes too small, and the weight average molecular weight of the high cis-diene rubber (B) is 30, When the molecular weight exceeds 000, the molecular mobility of the high cis-diene rubber becomes low, and there is a drawback that the reactivity for adhesion is insufficient.

  The high cis-diene rubber (B) is obtained by adding a peroxide such as dicumyl peroxide (DCP) and maleic anhydride to a low molecular weight high cis liquid diene rubber according to a conventional method, and biaxially kneading. It can be obtained by reacting using a reaction apparatus such as a machine. Such high cis-diene rubbers are commercially available, for example, POLYBEST OC-800S (weight average molecular weight 2000, acid value = 80, cis content 75%, trans content 24%, vinyl content, manufactured by Degussa Japan Co., Ltd. 1% maleic anhydride-modified polybutadiene) and LIR-410A (maleic anhydride-modified polyisoprene having a weight average molecular weight of 25,000, an acid value = 22.4, and a cis content of 100%) manufactured by Kuraray Co., Ltd.

  Even if the amount of sulfur compounded as a cross-linking agent is reduced by including the high cis-diene rubber (B) in the above compounding amount, the rubber composition of the present invention can be applied to a metal body such as a steel wire. Shows high heat aging resistance without reducing adhesiveness. Surprisingly, the rubber composition of the present invention also exhibits high heat aging resistance to metal reinforcing materials such as a metal body having a brass plating layer, for example, a steel wire having a brass plating layer. Generally, a rubber composition that does not contain sulfur or has an insufficient amount of sulfur has poor adhesion after vulcanization with a metal body having a brass plating layer, for example, a steel wire having a brass plating layer. When a composite formed by vulcanizing and bonding with a metal body such as the above is used under high temperature and high pressure, there is a drawback that peeling occurs at the interface of the metal body and the composite is destroyed. However, in the present invention, the acid anhydride group contained in the high cis-diene rubber (B) reacts with the metal surface, and the high cis-diene rubber (B) is diene rubber (A) during vulcanization. It is considered that the adhesive force between the rubber composition and the metal is improved in order to generate a crosslink by reacting with. Furthermore, since the high cis-diene rubber has a molecular structure with a high cis content, the amount of sulfur is small due to high reactivity due to the high mobility of acid anhydride groups in the molecule. It is considered that sufficient adhesive strength is obtained, and as a result, heat aging resistance is improved.

  Furthermore, since the high cis-diene rubber (B) has a characteristic that the vinyl content is high, that is, the viscosity is lower than that of the diene rubber having a low cis content, a diene rubber having a lower cis content is used. The processability of the resulting rubber composition is improved compared to the case.

  The rubber composition of the present invention is preferably 1 to 4 parts by weight, more preferably 1 to 2 parts by weight with respect to 100 parts by weight of the total amount of the diene rubber (A) and the high cis-diene rubber (B). Contains sulfur. The rubber composition of the present invention contains a high cis-diene rubber (B) in the above-mentioned predetermined amount, so that the sulfur compounding amount is higher than the compounding amount in a conventional rubber composition intended to adhere to a metal. Despite generally little, good heat aging can be achieved without losing adhesion to the metal after vulcanization.

  In the rubber composition of the present invention, an adhesion promoter such as an organic acid cobalt salt that is known to enhance the adhesion of the rubber composition to a metal such as steel can be further used. Specific examples of the organic acid cobalt salt include cobalt stearate and cobalt naphthenate. When the organic acid cobalt salt is used, the blending amount is 0.1 to 10 parts by weight per 100 parts by weight of the total amount of the above (A) diene rubber and (B) high cis-diene rubber.

  The rubber composition of the present invention further includes a resin known to improve the adhesion between rubber and metal (hereinafter referred to as “adhesion promoting resin” in order to enhance the adhesion of the rubber composition to a metal body. Can be blended). Examples of the adhesion promoting resin include, for example, a condensate of m-cresol and formaldehyde (for example, Sumikanol 610 manufactured by Sumitomo Chemical Co., Ltd.) and a polyvalent methylol melamine derivative (for example, Sumikanol 507A manufactured by Sumitomo Chemical Co., Ltd.). It is done. When the adhesion promoting resin is used, the blending amount is 1 to 20 parts by weight per 100 parts by weight of the total amount of the (A) diene rubber and (B) high cis-diene rubber.

  The rubber composition of the present invention further includes various additives such as a reinforcing agent such as carbon black, a vulcanization or crosslinking agent, a vulcanization or crosslinking accelerator, an anti-aging agent, various oils, a filler, a plasticizer, and a softening agent. Agents and additives can be formulated by conventional compounding methods in commonly used amounts.

  In the rubber composition of the present invention, for example, an appropriate amount of a reinforcing filler such as a high cis-diene rubber (B) and carbon black, and other compounding agents are blended into the diene rubber (A) as necessary, and kneaded. Can be obtained.

  The rubber composition of the present invention thus obtained exhibits excellent adhesion and heat aging resistance, particularly when bonded to brass as a metal. Furthermore, by vulcanizing the rubber composition of the present invention obtained as described above and a metal body such as a steel wire having a brass plating layer in close contact with each other, a composite of the rubber and the metal body is obtained. Can be manufactured. This composite is excellent in heat aging resistance and can be suitably used for products such as hoses, belts, rolls and tires.

  In addition to the steel wire, the metal body may have any form such as a line, a tube, or a plate as long as it has a form that can be suitably used for products such as the hose, belt, roll, and tire. May be. As described above, since the rubber composition of the present invention exhibits excellent heat aging resistance and adhesion after vulcanization with respect to a metal body having a brass plating layer, the metal body preferably has a brass plating layer. . When the metal body is in the form of a steel wire, it may be a single-strand steel wire having a brass plating layer or a steel cord formed by braiding a plurality of steel wires having a brass plating layer. preferable. The wire diameter of the steel wire is appropriately selected according to the use of the rubber-metal composite obtained using the rubber composition of the present invention.

  The rubber-metal composite of the present invention includes, for example, a tire belt layer, an anti-vibration rubber such as an engine mount, a belt, a hose, a crawler, an anti-vibration material for construction, a sound-proof material, a vibration-damping material, a vibration-isolating material Can be used for industrial products. For example, the belt layer of a tire is obtained by cutting steel wires into a predetermined length and arranging them at predetermined intervals, and forming the steel wires into two sheets obtained by molding the rubber composition of the present invention into a sheet shape. Laminate a plurality of long rubber sheets containing steel wires, placed between unvulcanized rubber sheets and cut diagonally in the tire bias direction, and combine them with other tire members to vulcanize Can be formed.

  When a rubber-metal composite obtained by vulcanizing and bonding a single-strand steel wire or a steel cord obtained by braiding a plurality of steel wires with the rubber composition of the present invention is used as a tire belt layer. Can prevent separation of the belt layer. The rubber-metal composite of the present invention can be applied not only to the tire belt layer but also to other uses such as a conveyor belt.

  The present invention will be described in more detail with reference to the following examples and comparative examples, but it goes without saying that the technical scope of the present invention is not limited to these examples.

Preparation of rubber composition Among the ingredients shown in Table 1 and Table 2 below, natural rubber, carbon black, maleic anhydride-modified polybutadiene or maleic anhydride-modified isoprene, an anti-aging agent and an adhesion promoting resin are placed in a closed mixer. Mix for 5 minutes, release the mixer contents when the temperature reaches 150 ° C., make the contents a masterbatch, then add other ingredients such as insoluble sulfur and vulcanization accelerator, open roll The rubber compositions of Examples 1 to 11 and Comparative Examples 1 to 5 were obtained by kneading.

Table 1 and Table 2:
(1): STR-20
(2): HAF grade carbon black manufactured by Tokai Carbon Co., Ltd. (3): Ginseng R manufactured by Toho Zinc Co., Ltd.
(4): Sumikanol 610 (condensate of m-cresol and formaldehyde) manufactured by Sumitomo Chemical Co., Ltd.
(5): Sumikanol 507A manufactured by Sumitomo Chemical Co., Ltd. (mixture of 65% by weight of polymethylol melamine derivative, 32% by weight of silica, and 3% by weight of paraffinic oil)
(6): Nocrack 224 manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
(7): Cobalt stearate manufactured by Dainippon Ink & Chemicals, Inc. (8): Cobalt naphthenate manufactured by Dainippon Ink & Chemicals, Inc. (9): POLYBEST OC-800S manufactured by Degussa Japan. (Maleic anhydride modified cis polybutadiene, molecular weight 2,000, acid value = 80 mg KOH / g, cis content 75%, trans content 24%, vinyl content 1%)
(10): M-2000-80 (maleic anhydride-modified polybutadiene, molecular weight 2,000, acid value = 80 mg KOH / g, cis content 20%, trans content 15%, vinyl content 65, manufactured by Nippon Oil Corporation %)
(11): LIR-410A manufactured by Kuraray Co., Ltd. (maleic anhydride-modified cis polyisoprene, molecular weight 25,000, acid value = 22.4 mg KOH / g, cis content 100%)
(12): Insoluble sulfur christex HS OT 20 manufactured by Akzo Nobel Co., Ltd.
(13): Noxeller DZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

Test Method 1) Adhesion test to wire A brass-plated steel wire was embedded in the unvulcanized rubber composition of each comparative example or example so that one end of the steel wire was exposed and heated at 150 ° C. for 30 minutes. A test piece was prepared by sulfuration. Ten test pieces were prepared using the unvulcanized rubber compositions of the comparative examples and examples. Five of the prepared test pieces were used as unaged test pieces, and the other test piece was left in a constant temperature and humidity chamber at a temperature of 70 ° C. and a humidity of 96% for 5 weeks and then taken out and bonded to each test piece after aging. Seeking sex. Adhesion was evaluated based on the rubber coverage (%) of the surface of the drawn steel wire after drawing the wire at 50 mm / min in accordance with ASTM D2229. Tables 3 and 4 show the results of this test. The test results obtained from the unaged test piece are indicated as “wire bonding (unaged)” and aged for 5 weeks at a temperature of 70 ° C. and a humidity of 96%. The test result obtained from the strip is indicated as “wire adhesion (wet aging)”. The test results of “wire bonding (unaged)” and “wire bonding (wet aging)” indicate that the larger the value, the better the adhesion of the rubber composition to the wire.

2) Tear test after heat aging:
The unvulcanized rubber compositions of the comparative examples and examples were rolled into a sheet shape and press vulcanized at 150 ° C. for 30 minutes to prepare rubber sheets. Each rubber sheet was punched into a not-cut angle shape as defined in JIS K6252 to prepare a test piece. Three test pieces were prepared for each of the comparative examples and the examples, and one of the three test pieces was used as a test piece before aging, and the other two test pieces were 192 hours in a thermostat at 80 ° C. The specimen was stored to obtain a test piece after aging, and a tear test was performed on each of the test piece before aging and the test piece after aging in accordance with JIS K6252. The test results represented the tear strength after aging as a relative value when the tear strength retention after aging (%) with respect to the tear strength before aging, that is, the tear strength before aging was defined as 100. . The results are shown in Tables 3 and 4 below as “tear strength retention”. “Tear strength retention” indicates that the closer the value is to 100, the smaller the degradation of the tear property of the vulcanized rubber composition due to heat aging.

3) Tensile test after heat aging:
The unvulcanized rubber compositions of the comparative examples and examples were rolled into a sheet shape and press vulcanized at 150 ° C. for 30 minutes to prepare rubber sheets. Each rubber sheet is punched into JIS No. 3 dumbbells to produce three dumbbell specimens. One dumbbell specimen is used as a specimen before aging, and the other two specimens are kept in a constant temperature bath at 80 ° C. Each specimen was stored for 192 hours to obtain a test specimen after aging, and a tensile strength test was conducted in accordance with JIS K6251. Tensile stress and cutting at 100% elongation for each of the specimen before aging and the specimen after aging Time elongation was sought. The test result of tensile stress at 100% elongation is the retention rate (%) of tensile stress at 100% elongation after aging relative to the tensile stress at 100% elongation before aging, that is, at 100% elongation before aging. The tensile stress at 100% elongation after aging was expressed as a relative value when the tensile stress was 100. The test result of elongation at break is the retention rate (%) of elongation at break after aging with respect to the elongation at break before aging, that is, at the time of cutting after aging as a relative value when the elongation at break before aging is 100 Expressed elongation. The tensile stress test results at 100% elongation are shown as “Tensile Strength Retention Ratio (M100)” in Tables 3 and 4, and the test results of elongation at break are shown in Tables 3 and 4 as “Elongation retention at break”. Rate (EB) ". Both “tensile strength retention (M100)” and “elongation retention at break (EB)” indicate that the closer the value is to 100, the smaller the decrease in tensile properties of the vulcanized rubber composition due to heat aging. Show.

4) Mooney viscosity In accordance with JIS K6300, Mooney viscometer equipped with L-shaped rotor was used, Mooney 4 minutes after starting the rotor rotation under the conditions of preheating time 1 minute and test temperature 100 ° C. Viscosity ML _{(1 + 4)} was measured. The Mooney viscosity was calculated based on 100 Mooney units when the torque acting on the rotor shaft was 8.30 N · m. The smaller the Mooney viscosity value, the better the workability.

Examples 1-11 and Comparative Examples 1-5
The test results are shown in Tables 3 and 4 below.

  From the results of Table 3 and Table 4, in Examples 1 to 11, compared to Comparative Examples 1 to 5, the tearing properties and tensile properties after aging were improved in a well-balanced manner while maintaining or improving the adhesion to the wire. I understand that. Furthermore, it turns out that Examples 1-11 are excellent in workability compared with Comparative Examples 1-5. In particular, the smaller the sulfur content, the better the tensile and tear properties after aging, but the sulfur content is less than 1 part by weight relative to 100 parts by weight of the total amount of diene rubber and high cis-diene rubber. Then, it turns out that the adhesiveness with respect to a wire is comparatively low, and when it exceeds 2 weight part, heat aging resistance will fall considerably.

Claims (9)

(A) a diene rubber,
(B) 0.1 to 10 parts by weight of a low molecular weight high cis-diene rubber containing an acid anhydride group with respect to 100 parts by weight of the diene rubber;
A rubber composition comprising:   The rubber composition according to claim 1, wherein the high cis-diene rubber (B) has a cis-1,4-bond content of 70 to 100%.   The rubber composition according to claim 1 or 2, wherein the high cis-diene rubber (B) has a weight average molecular weight of 1,000 to 30,000.   The rubber composition according to any one of claims 1 to 3, wherein the high cis-diene rubber (B) is selected from the group consisting of a high cis-butadiene rubber, a high cis-isoprene rubber, and a mixture thereof. .   5. The rubber composition according to claim 1, wherein the rubber composition contains 1 to 4 parts by weight of sulfur per 100 parts by weight of the total amount of the diene rubber (A) and the high cis-diene rubber (B). The rubber composition as described.   5. The rubber composition according to claim 1, wherein the rubber composition contains 1 to 2 parts by weight of sulfur per 100 parts by weight of the total amount of the diene rubber (A) and the high cis-diene rubber (B). The rubber composition as described.   A metal-rubber composite formed by vulcanizing and bonding the rubber composition according to any one of claims 1 to 6 to a metal body.   The metal-rubber composite according to claim 7, wherein the metal body is a single-strand steel wire having a brass plating layer or a steel cord formed by braiding a plurality of steel wires having a brass plating layer. body.   A pneumatic tire using the metal-rubber composite according to claim 7 or 8.