JPS62146936A - Rubber composition for bonding steel cord - Google Patents

Abstract

PURPOSE:To obtain a rubber composition for bonding steel cord excellent in capability of bonding and age resistance, by mixing natural rubber or synthetic polyisoprene rubber with cobalt resinate and a specified cobalt compound. CONSTITUTION:A rubber composition formed by mixing 100pts.wt. rubber containing at least 70pts.wt. at least either natural rubber or synthetic polyisoprene rubber with cobalt resinate and at least one cobalt compound selected from cobalt acetylacetonate and a boron-cobalt compound of the formula in an amount of 0.05-0.7pt.wt. in terms of cobalt. In the formula, R1, R2 and R3 are each a resin acid residue, a naphthenic acid group or a 3-24C aliphatic monocarboxylic acid group. The ratio of the amount of the cobalt resinate used to that of the cobalt compound used is preferably 9/1-1/9 in terms of a cobalt content.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rubber composition, and more specifically, a rubber composition for adhering steel cords that has excellent adhesiveness and heat aging resistance when used as a steel cord coating rubber. It is related to.

(Prior Art) In recent years, the development of so-called steel tires using steel cords for belts and carcass plies has been remarkable, and various studies have been made to date regarding the adhesion between steel cords and rubber.

In general, there are two main ways to bond steel cords and rubber. One is the RH8 adhesive system using resorcinol/hexamethylenetetramine/silica, and the other method is to mix metal salts, especially organic acid cobalt salts. The latter method has been widely used, and rubber compositions containing such metal salts have been proposed as steel cord coating rubbers. For example, Japanese Patent Publication No. 56-39828, Japanese Patent Publication No. 54-'52188, Japanese Patent Publication No. 50-3
Cobalt naphthenate, cobalt stearate, cobalt oleate, etc. Rubber compositions containing cobalt tall oil acid, cobalt resin acid, etc. as adhesion promoters have been disclosed.

On the other hand, demands for safety, high-speed running performance, durability, etc. for automobile tires have been increasing more and more, and conventional technologies have not always been able to fully satisfy these demands.

In other words, if a tire reinforced with steel cords is used in a corrosive atmosphere, the steel cords will rust, the adhesive strength between the steel cords and the rubber will decrease, and the CBU phenomenon will occur. This causes the steel cord to break, causing a fatal tire failure.

Furthermore, in order to improve tire durability, it is necessary to reduce interlaminar shear strain that occurs between belt layers, but this interlaminar shear strain is a cause of major peeling failures at belt ends. This is because the Young's modulus of the belt cord at the end of the belt and the rubber covering the belt are greatly different, and this shear strain causes a large stress concentration, which causes peeling failure from this end. In order to prevent such destruction, structural improvements are being considered, and an effective method would be to further improve the durability of the belt cord coating rubber, but so far there has been no effective method. There is currently no way to do so.

(Problem to be solved by the invention) For this reason, the adhesive Zoro motor used for adhesion of steel cord and rubber has not only adhesion but also physical properties of rubber such as wet heat adhesion, heat resistant adhesion, and exothermic heat aging. Comprehensive performance, such as the influence of For example, cobalt salts incorporated into rubber compositions as adhesion promoters increase the thermal aging of rubber, and among them, cobalt naphthenate is particularly effective.
Not only does it reduce heat aging resistance, but it also has poor wet heat adhesion. In addition, fatty acid cobalt causes a decrease in tackiness during unvulcanization, resulting in poor adhesion between rubber members, resulting in poor adhesion after vulcanization.

Although the heat aging resistance of cobalt resinate is generally better than that of cobalt naphthenate, the present inventors have investigated that even if the same cobalt resinate is used, it is not always the case that
Performance is not always good, and even rubber compositions containing cobalt resin acid tend to have poor adhesion, particularly poor initial adhesion, and this is a major drawback of cobalt resin acid. Furthermore, it is known that compounds containing boron and cobalt can also be used as adhesion promoters, but although they have excellent wet heat adhesion properties, they cannot be expected to have much of an effect on improving the physical properties of the rubber, and in either case, they do not improve the properties of tires. There was a problem that the durability was not satisfactory.

(Another Means to Solve the Problem) The present inventors have focused on the fact that, as an adhesion promoter blended into a rubber composition, it does not have much of an adverse effect on the heat aging resistance of rubber compared to cobalt naphthenate and the like. As a result of intensive studies aimed at further improving the adhesion and heat aging resistance, we found that by using a specific cobalt compound in combination with cobalt resin acid, we were able to improve the adhesion, heat aging resistance, etc. of the resulting rubber composition. The present invention has been achieved based on the discovery that a comb composition can be obtained which is synergistically improved and has excellent overall properties.

That is, the rubber composition for adhering steel cords of the present invention comprises either natural rubber or synthetic polyisoprene rubber.
Rubber 10 containing 70 parts by weight or more of one or two types of rubber
0 parts by weight, (4) cobalt resin acid, (B) organic cobalt carginate, cobalt acetylacetonate and the following general formula, where R4, R2 and R3 are resin acid groups and naphthenic acid groups. ,
An aliphatic monocal having 3 to 24 carbon atoms represents a phosphoric acid group.

For adhesion of steel cords, characterized in that at least one cobalt compound selected from the group consisting of boron-cobalt compounds represented by: is combined in a cobalt element content of 0.05 to 0.7 parts by weight. The present invention relates to a rubber composition.

The rubber used in the present invention is preferably natural rubber, synthetic polyisoprene rubber, or a mixture of both.
If the amount is less than part by weight, it is also possible to substitute other diene-based combs, such as styrene-butadiene copolymer rubber, polybutadiene rubber, etc. If the amount of natural rubber, synthetic preisogrene rubber, or a mixture thereof is less than 70 parts by weight in the rubber, the adhesion to the steel cord will deteriorate, which is undesirable.

The cobalt resin acids used in the present invention include gum rosin, tall oil rosin, wood rosin, formylated rosin, polymerized rosin, disproportionated rosin, hydrogenated rosin, and simple abietic acid, neoabienoic acid, 4-last phosphoric acid, Alkali metal salts of resin acids such as sodium and potassium, such as legopimaric acid, dehydroabietic acid, dihydroabietic acid, pimaric acid, and isobimaric acid, and inorganic cobalt salts, preferably monovalent acids considering initial adhesive properties. Cobalt salts obtained by metathesis reactions of cobalt chloride, cobalt iodide, cobalt bromide, and cobalt acetate, for example, those having a metal element content of 1 to 9% in cobalt resin acid are effective.

The cobalt resin acid preferably has an oxidation degree of 60% or less, preferably 40% or less, as determined by gas chromatography analysis. If the degree of oxidation exceeds 60%, it is not preferable because not only the initial adhesion with the steel cord deteriorates, but also the heat aging resistance of the rubber deteriorates. It is also necessary that the sulfur concentration in the cobalt resin acid is 2000 ppm or less, preferably 11000 ppm or less. If the sulfur concentration exceeds 2000 ppm, the heat aging resistance of the rubber will deteriorate, which is not preferable. Also, cobalt resin acid is 14
It is necessary to have a melting point within the range of 0 to 180°C.

If the melting point is less than 140°C, the vulcanization rate and initial adhesiveness will be adversely affected, and if it exceeds 180°C, the compatibility with rubber, heat resistance, aging resistance, and initial adhesiveness will deteriorate, which is undesirable. In addition, the toluene/water insoluble part of the cobalt resin acid has a sharp characteristic absorption near 3600 cm in the infrared absorption spectrum, and when heated at 5 °C/min by DSC, it has a characteristic absorption of 250 to 350 °C and 300 to 420 °C. It is necessary that each of them has a pronounced endothermic peak in the temperature range of .degree.

Although it is currently not clear what causes the first endothermic peak in the range of 250 to 350°C and the characteristic absorption in the infrared absorption spectrum, cobalt sulfate was used as the cobalt salt. In some cases, these are not observed in the resin acid cobalt or in the toluene soluble part of the resin acid cobalt, but only in the toluene insoluble part, and in the DSC, the endothermic In the infrared absorption spectrum of the sample after the peak has passed, the characteristic absorption mentioned above disappears, indicating that crystal water is coordinated to the bonding part between calanoic acid and cobalt in the resin acid. , it is assumed that this is caused by withdrawal.

Furthermore, when cobalt chloride is used as the co-iR salt, the infrared absorption spectrum has a value of 850.740, which is presumed to be due to the elimination of chlorine.

Various characteristic absorptions at 400 cm-1 are observed, and it is assumed that chlorine further bonds to the divalent cobalt bonded to the carboxylic acid to form a normal salt, to which water of crystallization is coordinated. Ru. Here, the second endothermic peak at 300 to 420°C is due to decomposition of organic matter. Such cobalt resin acid is produced, for example, as follows.

A cobalt salt of a resin acid is produced by adding a cobalt salt of a monovalent acid, such as an aqueous solution of cobalt chloride, to a metal salt of a resin acid, such as an aqueous solution of sodium gum rosin, at a temperature of 50° C. or lower to proceed with a metathesis reaction. The generated metal salts are separated by mechanical methods such as sedimentation of the reactants and centrifugation or filter press without solvent extraction.
It is obtained by washing with water and drying the obtained cobalt salt of resin acid at a temperature of 60° C. or lower.

In the present invention, the cobalt compounds to be blended in combination with the cobalt resin acid include cobalt organic carboxylate,
Cobalt acetylacetonate or a cobalt compound represented by the general formula, and examples of the organic carboxylic acid conolate in which at least one of these cobalt compounds is used in combination with the above-mentioned cobalt resin acid include cobalt propionate, cobalt hexanoate, Cobalt octoate, cobalt decanoate, cobalt laurate, cobalt myristic acid, cobalt stearate, conoglut 2-ethylhexanoate, cobalt isostearate, conoglute pinoglyrate,
Cobalt neodecanoate, cobalt cyclohexanoate, cobalt acrylate, cobalt methacrylate, cobalt benzoate, cobalt timer acid, etc., and these organic acid cobalts are produced by the known double decomposition method or direct method. Also, among the boron-cobalt compounds represented by the general formula,
Resin acid groups include the aforementioned gum rosin, wood rosin, tall oil rosin, their formylated rosin, polymerized rosin, asymmetric rosin, hydrogenated rosin, and simple abietic acid, neoabietic acid, palustric acid, redevimaric acid, dehydroabietin. acid, dihydroabietic acid, bimaric acid, isobimaric acid, and other acid groups. Also, the number of carbon atoms is 3 to 2
Examples of the aliphatic monocarboxylic acid group of 4 include propionic acid, hexanoic acid 1, octanoic acid, 2,2-dimethylpentanoic acid, 2-ethylhentanoic acid, 4.4-dimethylpentanoic acid, 2.2-dimethylhexanoic acid, 2 -Ethylhexanoic acid, 4.4-dimethylhexanoic acid, 2,4.4-) dimethylpentanoic acid, 2,2-dimethylheptanoic acid, neodecanoic acid, undecanoic acid, thujarmitic acid, stearic acid, oleic acid, υnolic acid , linoleic acid, 7 raki)
These are acid groups such as phosphoric acid and behenic acid. These boron-cobalt compounds can be produced by, for example, reacting a cobalt salt of a mixed carganic acid, Co with an organic boron compound (ZO) 3B at a temperature of 100 to 250°C according to the following reaction formula, and the volatile by-product It is obtained by distilling off the ester ZX under normal pressure or reduced pressure.

(In the formula, X represents a lower monocarboxylic acid group, Z represents a lower alkyl group or an aryl group, and Rj + R2+ and R3
(same as above) In the present invention, cobalt resin acid and a cobalt compound are blended in combination, but the blending amount is 100% rubber.

0.05 to 0 as cobalt element content based on weight part
．． The amount is 7 parts by weight, preferably 0.07 to 0.4 parts by weight.

If the blending amount is less than 0.05 parts by weight, there is no effect of addition, and 0.
．． If it exceeds 7 parts by weight, it is not preferable because it not only deteriorates the adhesion but also significantly deteriorates the heat aging resistance of the rubber. Further, the combined ratio of cobalt resin acid and cobalt compound is preferably 9/1 to 1/9 in terms of cobalt element content, particularly preferably 7/3 to 3/7. If the ratio of combined use is outside the range of 9/1 to 1/9, the effect of combined use will not be apparent, which is not preferable.

In the present invention, in addition to the cobalt resin acid, the rubber component includes reinforcing agents and fillers such as carbon black, silica, and calcium carbonate, softening agents such as aroma oil, vulcanizing agents such as sulfur, vulcanization accelerators, and vulcanization. Compounding agents commonly used in the rubber industry, such as accelerator auxiliaries and anti-aging agents, can be blended as appropriate and within the range of usual blending amounts.

The rubber composition of the present invention having the above-mentioned structure is particularly suitable for adhesion to metals, and is used, for example, in coating compositions for tire steel belts, steel breakers, and slur carcass. It can also be applied to other industrial products such as conveyor belts, anti-vibration rubber, etc.

(Example) Hereinafter, the present invention will be explained in detail using Synthesis Examples, Examples, and Comparative Examples.

Synthesis Example 1 500℃ equipped with a 100℃ thermometer, stirrer, and dropping funnel
0ml! In a semi-quadrate type fourth flask with an acid value of 1.
Chinese gum rosin 300. ! i', 75 g of a 48% aqueous sodium hydroxide solution, and 4195.9 g of tap water, and a saponification reaction was carried out at an internal temperature of 80 to 90°C for 1 hour to prepare a Chinese gum rosin metal salt with a solid content of 7 t and a pH of 10.3. Obtained. The obtained metal salt was cooled to an internal temperature of 30°C, and 114.9 (cobal chloride) was added to 200 l of tap water! An aqueous solution of cobalt chloride dissolved in the solution was placed in a dropping funnel, and added dropwise over 10 minutes while stirring. After the dropwise addition, a double decomposition reaction was carried out with stirring at 30° C. for 20 minutes to obtain a slurry containing cobalt salt of Chinese gum rosin.

The slurry liquid was dehydrated using an experimental filter press at a liquid temperature of 30°C and a pressure of 4 kg/α2.
The cobalt salt of rosin acid having a solid content of 35% was obtained by repeating water washing and dehydration twice using No. 1.

The cobalt salt was dried in a hot air dryer at 40° C. for 8 hours to obtain a cobalt salt of rosin acid (sample A) with a volatile content of 18.2% and a cobalt content of 6.7 tons. OO! I got it.

Synthesis Example 2 In Synthesis Example 1, instead of Chinese gum rosin, acid value 1
65, U.S. wood rosin 300# with a softening point of 73°C and a conjugated dienoic acid content of 67.0%, an amount of 48% sodium hydroxide aqueous solution of 74.9, and an amount of cobalt chloride of 111 g. A cobalt salt of rosin acid (sample B) with a volatile content of 17.5% and a cobalt content of 6.7% was prepared under the same conditions as in Synthesis Example 1. I got li'.

Synthesis Example 3 In Synthesis Example 1, instead of Chinese gum rosin, acid value 169.5, softening point 76°C, conjugated citric acid content 65
Synthesis Example 1 was carried out under the same conditions as in Synthesis Example 1, except that a tall oil rosin having a quality of 7% was used, and the volatile content was 7% and the cobalt content was 7%.
6% cobalt salt of rosin acid (sample C) 340.9
I got it.

Synthesis Example 4 In Synthesis Example 1, an acid value of 183. 48% hydroxylation using 300 g of abietin having a quality of O1 conjugated dienoic acid content of 92) I
The amount of Jium aqueous solution used is 82g, and the amount of cobalt chloride used is 12g.
The process was carried out under the same conditions as in Synthesis Example 1 except that 5 g was used, and the volatile content was 1
Cobalt salt of rosin acid (sample D) 39011 with a cobalt content of 9.0% and a cobalt content of 7.1% was obtained.

Synthesis Example 5 The same conditions as Synthesis Example 1 were used except that 115 g of cobalt acetate was used instead of cobalt chloride, and a rosin having a volatile content of 8% and a cobalt content of 7.4% was produced. 340.9 of the co/S salt of the acid (sample E) was obtained.

Synthesis Example 6 In Synthesis Example 1, instead of Chinese gum rosin, acid value 158.5, conjugated dienoic acid content 0%, softening point 80°C
Synthesis Example 1 was carried out under the same conditions as in Synthesis Example 1, except that 70 g of sodium 48 hydroxide and 106 g of cobalt chloride were used.
A cobalt salt of rosin acid with a cobalt content of 6.4% (sample F) 360.9% was obtained.

Synthesis Example 7 Synthesis Example 1 was carried out under the same conditions as Synthesis Example 1, except that cobalt sulfur (126.9%) was used instead of cobalt chloride, and the quality was obtained with a volatile content of 5% and a cobalt content of 7.8%. 330 g of cobalt salt of rosin acid (sample G) was obtained.

Synthesis Example 8 In Synthesis Example 1, the metathesis reaction temperature was changed from 30°C to 60°C.
The same conditions as Synthesis Example 1 were used except that the volatile content was 8%.
A cobalt salt of rosin acid (sample H) 340I having a quality of 7.5% cobalt content was obtained.

Synthesis Example 9 In Synthesis Example 1, the metathesis reaction temperature was changed from 30°C to 80°C.
The same conditions as Synthesis Example 1 were used except that the volatile content was 4%.
, 320 g of cobalt salt of rosin acid (sample I) having a quality of 7.9% cobalt content were obtained.

Synthesis Example 10 The same conditions as Synthesis Example 1 were used except that the amount of cobalt chloride used in Synthesis Example 1 was changed from 114 g to 87 g. Cobalt salt (Sansol J) 350I was obtained.

Synthesis Example 11 In Synthesis Example 1, after the metathesis reaction, toluene 11 was added and stirred at 30°C for 1 hour, then transferred to a 10A separating funnel to separate into a solvent layer and an aqueous layer, and the solvent layer was placed under a vacuum of 100 m
mHg and a final desolvation temperature of 130°C, toluene was removed, and the cobalt salt of rosin acid (sample K) 320I! with a volatile content of 2% and a cobalt content of 8.0%! I got it.

Synthesis Example 12 In Synthesis Example 1, the drying temperature in the hot air dryer was set to 30
The conditions were the same as in Synthesis Example 1 except that the temperature was changed from .degree. C. to 80.degree. C., and 335 g of a cobalt salt of rosin acid (sample L) having a volatile content of 5 and a cobalt content of 7.8 was obtained.

Synthesis Example 13 In Synthesis Example 1, the drying temperature in the hot air dryer was set to 30
The conditions were the same as in Synthesis Example 1, except that the temperature was changed from .degree. C. to 100.degree. C., and 320 g of a cobalt salt of rosin acid (sample M) having a volatile content of 0.5% and a cobalt content of 8.1% was obtained.

Synthesis Example 14 Synthesis Example 1 was carried out under the same conditions as Synthesis Example 1 except that cohal sulfate (126,9) was used instead of cobalt chloride and the water washing step after dehydration of the filter press was omitted. A cobalt salt of rosin acid (sample N) 3 with a yield of 7.7% was obtained.

Next, the degree of oxidation, melting point, IR analysis of toluene dissolved content, DSC analysis, and sulfur content were determined for the various types of wood bart obtained in Synthesis Examples 1 to 14. The results obtained are shown in Table 1.

The measurement method is as follows.

<Oxidation degree> Cobalt rosin acid was acid decomposed with nitric acid, then neeed out, washed with water until the ether layer became neutral, dehydrated with nitrogen, and heated under reduced pressure at 40°C.
Add ether to this and add a specified amount of margaric acid (98% purity).
After addition, dimethylation was performed by the diazomethane method, followed by GLC analysis.

GLC conditions Column: DEGS -20 temperature: 205°C Detector: FID The rosin acid value after decomposition with diluted acid was determined by neutralization titration with potassium hydroxide.

The degree of oxidation was determined by the following formula.

Acid reduction rate - acid value of rosin after acid decomposition/acid value of raw material rosin
Melting point> Measured according to JIS KOO64.

(IR analysis, DSC analysis) Add toluene to cobalt rosin acid in a test tube,
After dissolution by shaking at ℃ for 2 hours, water was added, shaken well, and centrifuged for 10 minutes at 15,000 ppm to separate the toluene-dissolved portion. Furthermore, toluene was added to the remaining water portion, and after stirring, the centrifugation operation was repeated again until the toluene portion became transparent. The toluene/water insoluble portion was filtered and dried under reduced pressure. Further, in the toluene-dissolved portion, toluene was distilled off under reduced pressure using an evaporator. toluene·
The water-insoluble portion was subjected to IR analysis and DSC measurement at a heating rate of 5° C./min. For reference, the IR spectra of Sample A and Sample G are shown in FIG. 1, and the DSC curves of Sample A, Sample C1, and Sample G are shown in FIG. 2.

<Sulfur content in cobalt resin acid> Organic sulfur was measured using a Dorman microcoulometric titration device.

Synthesis Example 15 Chinese gum rosin
(acid value 170, softening point 75°C) 274.9 and high boiling point aromatic naphtha (b, p, 180-210°C) 100g, and a stirring device, nitrogen force blowing pipe, thermometer, and cooler were installed. The temperature was raised to 120° C. while passing nitrogen gas to dissolve the gum rosin. After cooling to below 100°C, acetic acid 52
．． After adding 9 and stirring thoroughly, cobalt hydroxide 79
g was added and aged at 150-160°C for 2 hours. 12
After cooling to 0°C, 41.9 g of triethyl borate was added, and after reacting at the same temperature for 3 hours, the temperature was raised to 230°C, high-boiling aromatic naphtha was recovered by vacuum distillation (degree of vacuum: 20 mmHg), and rosin acid groups were recovered. A boron-cobalt compound having (cobalt content 18.6%, rosin acid group/neodecanoic acid group =
773, sample O) was obtained.

Synthesis Example 16 Using 192 g of gum rosin X, and further adding 45 g of neodecanoic acid
A boron-cobalt compound (cobalt content: 21.0%, sample P) having a rosin acid group and a neodecanoic acid group was obtained in the same manner as in Synthesis Example 15, except that .

Synthesis Example 17 A boron-cobalt compound having a rosin acid group and a neodecanoic acid group (cobalt content 21.6%, rosin acid group/neodecanoic acid group) was prepared in the same manner as in Synthesis Example 15 except that gum rosin Base = 377
, sample Q) is 4.

Synthesis Example 18 Gum Rosin X274. ! 9 and further naphthenic acid 67
．． A boron-cobalt compound having a rosin acid group and a naphthenic acid group (cobalt content 8.0%, rosin acid group/naphthenic acid group = 7/
3. Sample R) was obtained.

Examples 1-12. Comparative Examples 1 to 4 80 parts by weight of natural rubber and synthetic polyisozolene rubber (IR2
200) 20 parts by weight, 50 parts by weight of HAF carbon black, 1 part by weight of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediami, 2 parts by weight of aroma oil, 8 parts by weight of zinc white. , N-oxydiethylene-2
--! 0.5 parts by weight of nzothiazole sulfenamide,
5 parts by weight of sulfur and various cobalt resin acids and cobalt compounds shown in Table 1 were mixed together in a Banbury mixer to give a cobalt element content of 0.2 parts by weight (Jul) Various rubber compositions was prepared. The obtained rubber composition was evaluated for initial adhesion, heat-resistant adhesion, wet heat adhesion, and heat aging characteristics. The results obtained are shown in Table 2. For comparison, resin acid co-glut alone and Kono R) Reto compound alone with the same cobalt element content were also evaluated at the same time, and the results are also listed in Table 2.

The initial adhesion, heat-resistant adhesion, wet heat adhesion, and heat aging properties were evaluated as follows.

<Initial adhesion> Steel cord I X 5 Xo with brass plated surface,
After vulcanizing the steel cord rubber composite with 23 layers embedded in unvulcanized rubber at 145°C for 30 minutes, it was vulcanized to JIS K 63.
A peel test was conducted between the steel cord and the buried comb layer in accordance with the 01 peel test, and the adhesion was evaluated based on the amount of comb remaining on the cord. 100 indicates that the cord is completely covered with rubber, and 0 indicates that no rubber is attached at all.

<Heat-resistant adhesion> A steel cord-rubber composite similar to that used in the initial adhesion test was left in an oven at 120° C. for 9 days, and then adhesion was evaluated in the same manner as the initial adhesion. However, the vulcanization time of the composite was 145° C. for 40 minutes.

<Wet heat adhesion> The same steel cord comb composite as used in the wet heat adhesion test was left in a constant temperature and humidity chamber at 70° C. and 90% RH for 14 days, and then evaluated in the same manner as the initial adhesion.

<Heat aging properties> Tensile strength was measured according to JIS K6301 using a comb sheet obtained by vulcanizing an unvulcanized rubber composition at 145° C. for 30 minutes. Furthermore, after heat aging these rubber sheets in a gear oven at 100° C. for 24 hours, the tensile strength was measured in the same manner, and the retention rate of the tensile strength after heat aging was evaluated.

As is clear from Table 2, the rubber composition for adhesion to steel cords of the present invention, which is formulated in combination with cobalt resin acid and a specific cobalt compound, has extremely excellent adhesion and heat aging resistance.

(Effects of the Invention) As explained above, the rubber composition of the present invention contains 100 parts by weight of rubber containing 70 parts by weight or more of one or both of natural rubber and synthetic polyinzolene rubber. On the other hand, by blending the cobalt resin acid with a specific cobalt compound, both adhesiveness and heat aging resistance are significantly improved, and the rubber is extremely useful as a rubber for bonding steel cords.

[Brief explanation of drawings]

Figure 1 is the IR spectrum diagram of Sample A and Sample G. Figure 2 is the IR spectrum diagram of Sample A, Sample C, and Sample G.
It is an SC curve diagram.

Claims (1)

[Claims] 1. Rubber 1 containing 70 parts by weight or more of one or both of natural rubber and synthetic polyisoprene rubber
00 parts by weight, cobalt resin acid, cobalt organic carboxylic acid, cobalt acetylacetonate and the following general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ In the formula, R_1, R_2 and R_3 are resin acid groups, naphthene An acid group represents an aliphatic monocarboxylic acid group having 3 to 24 carbon atoms. For adhesion of steel cords, characterized in that at least one cobalt compound selected from the group consisting of boron-cobalt compounds represented by: is combined in a cobalt element content of 0.05 to 0.7 parts by weight. Rubber composition. 2. Cobalt organic carboxylate is cobalt propionate,
Cobalt hexanoate, cobalt octoate, cobalt decanoate, cobalt laurate, cobalt myristate,
Cobalt stearate, cobalt 2-ethylhexanoate, cobalt isostearate, cobalt pivalate, cobalt neodecanoate, cobalt cyclohexanecarboxylate, cobalt acrylate, cobalt methacrylate, cobalt benzoate, and cobalt dimerate. The rubber composition for adhering steel cords according to item 1. 3. The aliphatic monocarboxylic acid group having 3 to 24 carbon atoms in the general formula is propionic acid, octanoic acid, 2,2-dimethylpentanoic acid, 2-ethylpentanoic acid, 4,4-dimethylhexanoic acid, 2,4 , 4-trimethylpentanoic acid, 2,2-
Dimethylheptanoic acid, neodecanoic acid, undecanoic acid, palmitic acid, stearic acid, oleic acid, linoleic acid,
The rubber composition for bonding steel cords according to claim 1, which contains acid groups of linoleic acid, arachidic acid, and behenic acid. 4. Cobalt resin acid has a melting point within the range of 140 to 180°C, and the degree of oxidation by gas chromatography is 60%.
Hereinafter, the sulfur concentration in the metal salt is 2000 ppm or less, and the toluene/water insoluble part of the metal salt has a characteristic absorption near 3600 cm^-^1 in the infrared absorption spectrum, and when measured in a differential scanning calorimeter. The rubber composition for bonding steel cords according to claim 1, which is a cobalt resin acid having endothermic peaks in the ranges of 250 to 350°C and 300 to 420°C when the temperature is raised at 5°C/min. 5. The rubber composition according to claim 1, wherein the cobalt resin acid and cobalt compound are used in a ratio of 9/1 to 1/9 in terms of cobalt content.