Rubber composition for metal bonding, rubber-metal composite, and tire using the same.

Abstract

The belt layer of a tire is subjected to strong impacts and heavy loads, so metal reinforcing cords, such as steel cords, are used as reinforcement. The rubber covering these steel cords needs to have good adhesion to the steel cords even when exposed to humid heat for long periods of time. [Solution] The above problem was solved by a rubber composition for metal bonding, which is obtained by blending 1 to 10 parts by mass of water-insoluble phytic acid with 100 parts by mass of diene rubber containing 50 parts by mass or more of natural rubber.

Description

Technical Field

[0001] The present invention relates to a rubber composition for metal adhesion, a rubber-metal composite, and a tire using the same. More specifically, the present invention relates to a rubber composition for metal adhesion, a rubber-metal composite, and a tire using the same, which have excellent adhesion after wet heat aging.

Background Art

[0002] A pneumatic tire is mainly composed of a pair of left and right bead portions, sidewall portions, and a tread portion continuous with both sidewall portions. A carcass layer is provided inside the tire, and both ends of the carcass layer are folded back so as to wrap the bead core from the inside to the outside of the tire. The tread portion consists of a cap tread and an under tread, and a belt layer is disposed between the under tread and the carcass layer. Since a strong impact or a large load is applied to this belt layer, a metal reinforcing cord such as a steel cord is used as a reinforcing material. The rubber coating such a steel cord requires good adhesion to the steel cord. Therefore, there is a method of applying brass plating to the steel cord and blending a specific compound into the rubber (see, for example, Patent Documents 1 and 2 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a rubber composition for metal adhesion, a rubber-metal composite, and a tire using the same, which can improve the adhesion after wet heat aging to a metal reinforcing cord. [Means for solving the problem]

[0005] The present invention provides a rubber composition for metal bonding, characterized in that it contains 100 parts by mass of a diene rubber containing 50 parts by mass or more of natural rubber and / or synthetic isoprene rubber, and a compound represented by the following formula (1) in amounts of more than 1 part by mass and 10 parts by mass.

[0006] [ka]

[0007] (In formula (1), A represents either an OPO3H2 group or an OH group. However, there are 1 to 6 OPO3H2 groups and 0 to 5 OH groups.) The present invention also provides a rubber composition for metal bonding, characterized by comprising 1 to 10 parts by mass of a water-insoluble compound represented by the following formula (2) in 100 parts by mass of a diene rubber containing 50 parts by mass or more of natural rubber and / or synthetic isoprene rubber.

[0008] [ka]

[0009] Furthermore, the present invention provides a rubber-metal composite comprising a metal reinforcing cord embedded in the aforementioned rubber composition for metal bonding. Furthermore, the present invention provides a tire using the aforementioned rubber-metal composite. [Effects of the Invention]

[0010] The rubber composition of the present invention incorporates a specific amount of the compound represented by (1) or (2) above into a diene rubber, thereby significantly improving the adhesion to metal reinforcing cords after moist heat aging.

[0011] As described above, the rubber used for bonding metal inside tires requires strong adhesion to, for example, brass-plated metal reinforcing cords. However, this adhesion is significantly reduced by humid heat aging. The inventors' research has shown that humid heat aging causes ionization of the brass components Cu and Zn, which then diffuse into the rubber, resulting in a significant decrease in adhesion. Cu ions, in particular, have a major impact on the decrease in adhesion. Therefore, in this invention, by incorporating the compound represented by (1) or (2) into the rubber, this suppresses the ionization of metals caused by humid heat, and as a result, the adhesion to metal reinforcing cords after humid heat aging can be significantly improved. [Modes for carrying out the invention]

[0012] The present invention will be described in more detail below. The diene rubber used in the metal adhesive rubber composition of the present invention is essential to natural rubber (NR) and / or synthetic isoprene rubber (IR). The amount of NR and / or IR must be 50 parts by mass or more when the total diene rubber is 100 parts by mass. If the amount of NR and / or IR is less than 50 parts by mass, the tensile strength deteriorates, which is undesirable. In addition to NR and IR, other diene rubbers can be used, such as butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and acrylonitrile-butadiene copolymer rubber (NBR). These may be used alone or in combination of two or more. Furthermore, their molecular weight and microstructure are not particularly limited, and they may be end-modified with amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl groups, etc., or epoxidized. The amount of NR and / or IR is preferably 80 parts by mass or more when the total diene rubber is 100 parts by mass. The weight-average molecular weight (Mw) of the diene rubber is not particularly limited, but for reasons that the effects of the present invention are superior, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000. In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values in terms of standard polystyrene obtained by gel permeation chromatography (GPC) measurement.

[0013] The rubber composition for metal adhesion of the present invention is blended with a compound represented by the following formula (1) or (2).

[0014]

Chemical formula

[0015] (In formula (1), A represents an OPO3H2 group or an OH group. However, the number of OPO3H2 groups is 1 to 6, and the number of OH groups is 0 to 5.)

[0016]

Chemical formula

[0017] (In formula (2), B represents an OPO3M group or an OH group. M represents Na, K, Fe, Mg, or Ca. However, the number of OPO3M groups is 1 to 6, and the number of OH groups is 0 to 5.)

[0018] Typical examples of the formula (1) include phytic acid (inositol hexaphosphate), inositol monophosphate, inositol trisphosphate, and the like. In addition, examples of the formula (2) include phyticin. Since phyticin is water-insoluble, it is difficult to migrate during wet heat deterioration, and the effect of suppressing the ionization of metals derived from wet heat can be further sustained. In this specification, water-insoluble means that the solubility in water (neutral) at 20°C is 5 g / liter or less. Also, phyticin can be a natural-derived material.

[0019] (Blending ratio of rubber composition) In one embodiment, the rubber composition of the present invention is characterized by containing more than 1 part by mass and 10 parts by mass of the compound represented by formula (1) with respect to 100 parts by mass of diene rubber. If the compound represented by formula (1) is 1 part by mass or less per 100 parts by mass of diene rubber, the amount is too small to achieve the effects of the present invention. Conversely, if it exceeds 10 parts by mass, the strength of the rubber decreases, and the metal adhesion after deterioration due to moist heat also decreases.

[0020] The amount of the compound represented by formula (1) is preferably 1 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of diene rubber.

[0021] In another embodiment, the rubber composition of the present invention is characterized by containing 1 to 10 parts by mass of a water-insoluble compound represented by formula (2) with respect to 100 parts by mass of diene rubber. If the compound represented by formula (2) is less than 1 part by mass per 100 parts by mass of diene rubber, the amount is too small to achieve the effects of the present invention. Conversely, if it exceeds 10 parts by mass, the strength of the rubber decreases, and the metal adhesion after deterioration due to moist heat also decreases.

[0022] The amount of the compound represented by formula (2) is preferably 1 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of diene rubber.

[0023] (Other ingredients) In addition to the components mentioned above, the rubber composition of the present invention may contain various additives commonly used in rubber compositions, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; zinc oxide; various fillers such as carbon black, silica, clay, talc, calcium carbonate, aluminum oxide, and titanium oxide; various oils; antioxidants; plasticizers; and fatty acid cobalt. These additives can be mixed in a conventional manner to form a composition which can then be used for vulcanization or crosslinking. The amounts of these additives can also be conventional amounts, as long as they do not contradict the purpose of the present invention.

[0024] Furthermore, when sulfur is used as a vulcanizing agent, from the viewpoint of improving the effects of the present invention, the amount of sulfur added is preferably 4 to 10 parts by mass per 100 parts by mass of diene rubber. Furthermore, when using zinc oxide, from the viewpoint of improving the effects of the present invention, the amount of zinc oxide added is preferably 5 to 12 parts by mass per 100 parts by mass of diene rubber.

[0025] The rubber-metal composite of the present invention is obtained by embedding a metal reinforcing cord in the rubber composition of the present invention. Examples of the metal reinforcing cord include steel wire, and it is preferable that the steel wire is coated with a plating compound. The plating compound is preferably brass plating, copper-tin plating, copper plating, zinc plating, nickel plating, chromium plating, or copper-zinc-cobalt ternary plating. Furthermore, applications of the rubber-metal composite of the present invention include, for example, tires, belt conveyors, electric wires, hoses, and seismic isolation rubber. In the case of tire applications, the rubber-metal composite may include belts embedded in the undertread, carcasses, and beads (including bead cores and steel cords housed therein).

[0026] The rubber-metal composite of the present invention can be obtained, for example, by mixing the various components mentioned above using a general-purpose mixer such as a Banbury mixer or a roll mixer to prepare a rubber composition, embedding a metal reinforcing cord therein, and then vulcanizing it according to a conventional method.

[0027] Furthermore, when the rubber-metal composite of the present invention is used for tire applications, the manufacturing method is not particularly limited, and tires can be manufactured according to known technologies. The tire is preferably a pneumatic tire, and can be filled with air, nitrogen or other inert gases, and other gases. [Examples]

[0028] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0029] Examples 1-6, Comparative Examples 1-5 In the formulations shown in Table 1 (parts by mass), the components excluding the vulcanization system (vulcanization accelerator, sulfur) were kneaded in a 1.7-liter sealed Banbury mixer for 5 minutes, then released from the mixer and cooled to room temperature. After that, the vulcanization accelerator and sulfur were mixed in a roll mill to obtain unvulcanized rubber.

[0030] 100% Modulus: The unvulcanized rubber was press-vulcanized in a predetermined mold at 170°C for 10 minutes to obtain a vulcanized rubber test specimen. A tensile test was performed at room temperature according to JIS K6251 (using a No. 3 dumbbell), and the 100% deformation modulus was measured. The results are shown as an index with the value of Comparative Example 1 set to 100. A larger index indicates that the deterioration of elongation is suppressed.

[0031] Breaking Strength: The unvulcanized rubber was press-vulcanized in a predetermined mold at 170°C for 10 minutes to obtain vulcanized rubber test specimens, which were then tested at room temperature according to JIS K 6251. The results are shown as an index, with the value for Comparative Example 1 set to 100. A higher index indicates higher breaking strength.

[0032] Pull-out force: The cord was pulled out in accordance with ASTM D-2, and the pull-out force was measured. Samples included one without a moist heat aging test (before aging) and one after a moist heat aging test conducted in a gear oven at 70°C, 96% relative humidity, for 2 or 4 weeks (after aging). The results are shown as an index, with the value for Comparative Example 1 set to 100. A higher index indicates better adhesion to rubber.

[0033] Rubber Adhesion Amount: Tests were conducted in accordance with ASTM D-2229. Brass-plated steel cords, arranged in parallel at 12.7 mm intervals, were coated with the unvulcanized rubber composition of each example. The cords were then embedded to a depth of 12.7 mm and vulcanized at 170°C for 10 minutes to prepare adhesive samples. Adhesion samples included those without a moist heat aging test (before aging) and those that underwent a moist heat aging test in a gear oven at 70°C, 96% relative humidity, for 2 or 4 weeks (after aging). The steel cords were pulled out of these adhesive samples, and the amount of rubber adhesion (%) was measured. The results are shown as an index, with the value for Comparative Example 1 set to 100. A higher index indicates better adhesion to rubber. The results are shown in Table 1.

[0034] [Table 1]

[0035] *1: NR (RSS#3) *2: Carbon black (Seas 300 manufactured by Tokai Carbon Co., Ltd.) *3: Zinc oxide (3 types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd.) *4: Anti-aging agent (Santoflex 6PPD manufactured by Flexis) *5: Cobalt stearate (manufactured by DIC Corporation) *6: Phytic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. In formula (1), all of A are OPO3H2 groups.) *7: Phytic acid (manufactured by Tokyo Chemical Industry Co., Ltd. Contains 80% or more by mass of magnesium inositol hexalate, sodium inositol hexalate, and calcium inositol hexalate. Non-water soluble.) *8: Sulfur (Crystex HT OT 20, manufactured by AkzoNobel Co., Ltd.) *9: Vulcanization accelerator DCBS (Noxeller DZ, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0036] The results in Table 1 show that, because each example's rubber composition contained a specific amount of the compound represented by formula (1) or (2), the adhesive properties were significantly improved even after moist heat aging compared to Comparative Example 1. The strength of the rubber was also improved. Comparative Examples 2 and 4 showed poor adhesion after moist heat aging because the blending ratio of the compound represented by formula (1) or (2) was below the range specified in the present invention. Comparative Examples 3 and 5 showed poor adhesion after moist heat aging because the blending ratio of the compound represented by formula (1) or (2) exceeded the range specified in the present invention. The strength of the rubber also decreased.

[0037] The present invention encompasses the following embodiments. Embodiment 1: A rubber composition for metal bonding, characterized by containing 100 parts by mass of a diene rubber containing 50 parts by mass or more of natural rubber and / or synthetic isoprene rubber, and a compound represented by the following formula (1) in amounts of more than 1 part by mass and 10 parts by mass.

[0038] [ka]

[0039] (In formula (1), A represents either an OPO3H2 group or an OH group. However, there are 1 to 6 OPO3H2 groups and 0 to 5 OH groups.) Embodiment 2: A diene rubber containing 50 parts by mass or more of natural rubber and / or synthetic isoprene rubber is blended with 1 to 10 parts by mass of a water-insoluble compound represented by the following formula (2). A rubber composition for metal bonding characterized by the following features.

[0040] [ka]

[0041] (In formula (2), B represents an OPO3M group or an OH group. M represents Na, K, Fe, Mg, or Ca. However, there are 1 to 6 OPO3M groups and 0 to 5 OH groups.) Embodiment 3: The metal bonding rubber composition according to Embodiment 1 or 2, characterized in that it comprises 100 parts by mass of diene rubber, 4 to 10 parts by mass of sulfur, and 5 to 12 parts by mass of zinc oxide. Embodiment 4: A rubber-metal composite comprising a metal-adhesive rubber composition according to any one of Embodiments 1 to 3, in which a metal reinforcing cord is embedded. Embodiment 5: A tire using a rubber-metal composite as described in any of Embodiments 1 to 4.

Claims

1. A rubber composition for metal bonding, characterized by containing 100 parts by mass of a diene rubber containing 50 parts by mass or more of natural rubber and / or synthetic isoprene rubber, and a compound represented by the following formula (1) in amounts of more than 1 part by mass and 10 parts by mass. 【Chemistry 1】 (In equation (1), A is OPO) ３ H ２ Represents a group or an OH group. However, OPO ３ H ２ The compound has 1 to 6 groups, and 0 to 5 OH groups.

2. A diene rubber containing 50 parts by mass or more of natural rubber and / or synthetic isoprene rubber is blended with 1 to 10 parts by mass of a water-insoluble compound represented by the following formula (2). A rubber composition for metal bonding characterized by the following features. 【Chemistry 2】 (In equation (2), B is OPO) ３ Represents an M group or an OH group. M represents Na, K, Fe, Mg, or Ca. However, OPO ３ (There are 1 to 6 M groups and 0 to 5 OH groups.)

3. The metal bonding rubber composition according to claim 1 or 2, characterized in that it comprises 100 parts by mass of diene rubber, 4 to 10 parts by mass of sulfur, and 5 to 12 parts by mass of zinc oxide.

4. A rubber-metal composite comprising a metal-adhesive rubber composition according to claim 1 or 2, in which a metal reinforcing cord is embedded.

5. A tire using the rubber-metal composite described in claim 4.

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