JPH01153783A - Bonding accelerator for steel cord - Google Patents

Abstract

PURPOSE:To obtain the title bonding accelerator capable of maintaining bonding force for a long period of time and improving rubber elasticity, having a boron content of <= a fixed value, comprising a reaction mixture of an organic cobalt.boron carboxylate metallic soap as an essential component. CONSTITUTION:The aimed accelerator comprises a reaction mixture consisting essentially of an organic cobalt.boron carboxylate metallic soap, resulted in a reaction of (B) (i) organic carboxylic acid, (ii) inorganic cobalt compound and (iii) organic boric acid ester, having <=0.06% water-extracted boron content. The amount of the accelerator used is 0.02-0.5pt.wt. calculated as cobalt metal based on (A) 100pts.wt. rubber.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an improvement in adhesion promoters between rubber and steel.
In particular, the present invention relates to an improved adhesion promoter capable of maintaining long-term adhesive strength between rubber and steel cord under high temperature and high humidity conditions, and improving the elastic modulus of rubber.

(Prior Art) Steel cords have conventionally been used as reinforcing materials to improve the performance of automobile tires, conveyor belts, and the like. These steel cords are coated with metal plating, such as brass plating, zinc plating, or bronze plating, to increase their adhesion to the rubber in order to enhance their reinforcing effect, and the embedded rubber composition of the steel cord is made of steel cord and rubber. Adhesion promoters, such as cobalt salts of organic acids, have been used to improve the adhesive strength, but there is a problem in that the adhesive strength decreases when exposed to high temperature conditions for a long period of time. Therefore, as a method to improve this problem,
No. 1 and JP-A-60-158230 disclose the use of organic carboxylic acid cobalt-boron metal soap as an adhesion promoter to improve the adhesion between rubber-reinforcing steel cords and rubber, especially after thermal aging. It is proposed to do so.

(Problems to be Solved by the Invention) However, cobalt-boron metal soaps of organic carboxylic acids show a remarkable improvement effect on thermal deterioration of adhesives, but they do not improve initial adhesion strength, adhesive strength against thermal deterioration, and elastic modulus of rubber. It has been found that there is a drawback that the values are easily fluctuated.

That is, in JP-A-60-158230, an adhesion test was conducted by embedding a steel cord in a rubber composition containing an organic carboxylic acid cobalt-boron metal soap and vulcanizing it at 145°C for 30 minutes. Since vulcanization takes a long time, it is not preferable from an industrial production point of view. Also, JP-A-60
-124640 describes the use of an organic cobalt-boron complex as an adhesion promoter;
An adhesion evaluation sample was prepared by vulcanization at C for 23 minutes.

Furthermore, JP-A-60-238326 also discloses a rubber-to-metal adhesion promoter comprising a reaction product of a cobalt carboxylate and an alkaline earth metal borate.
In this case as well, an adhesion evaluation sample was prepared by vulcanizing the adhesion promoter-containing rubber composition in which the steel cord was embedded at 153° C. for 25 minutes, and an adhesion test was conducted.

If the adhesion quality is to be evaluated in this way, it is sufficient to perform the judgment on a sample that has been vulcanized at a constant temperature for a predetermined time.
Since various vulcanization temperatures and times are used for industrially produced steel cord reinforced rubber products, it is also necessary to evaluate product performance based on the vulcanization conditions. In particular, high temperature, short time vulcanization is preferred for improving productivity. Therefore, it has been desired to develop an adhesion promoter that can improve the adhesion between steel cord and rubber under such high-temperature, short-time vulcanization conditions.

(Means for Solving the Problems) Under these current circumstances, the present inventors developed a rubber composition containing a cobalt-boron metal soap, which is an organic carboxylic acid, in order to improve the adhesion between the steel cord and the rubber. The present invention was achieved by focusing on the fact that the elastic modulus and adhesiveness of rubber decrease when vulcanized at high temperature for a short time, and by attempting to improve these problems. In this way, the steel cord adhesion promoter of the present invention is added to a sulfur vulcanizable rubber composition in order to improve the adhesion between steel cord and rubber. The adhesion promoter is a reaction product of an organic carboxylic acid, an inorganic cobalt compound, and an organic boric acid ester, and contains boron, which is extracted with water. The ratio is 0.06% by weight or less.

Here, "the content of boron extracted in water" means that the above reaction mixture is dissolved in a non-polar organic solvent, water is added and mixed, and the amount of boron extracted into the aqueous layer is quantified. It is expressed as a weight percentage.

(Function) In the present invention, the amount of boron extracted with water from the organic carboxylic acid cobalt-boron metal soap is limited to 0.06% by weight or less. This is because the rate decreases too much and product performance is adversely affected.

For example, when the elastic modulus of the rubber in the steel cord belt layer of a radial tire for a passenger car decreases, the rigidity of the belt layer decreases, cornering power decreases, and steering response deteriorates. It also has a negative effect on durability and riding comfort.

Large radial tires used under high internal pressure and high loads are particularly required to have durability, but if the elastic modulus of the rubber in which the steel cord is embedded decreases, the durability deteriorates, which is undesirable.

The degree to which the elastic modulus of rubber decreases due to boron extracted with water is noticeable at high vulcanization temperatures, and there is almost no difference at low vulcanization temperatures.

The reason for this is unknown, but it is presumed that boron compounds extracted into water become more likely to react with sulfur as the temperature increases, reducing the formation of rubber grains.

The adhesion promoter of the present invention is blended in a proportion ranging from 0.02 to 0.5 parts by weight in terms of cobalt per 100 parts by weight of rubber.

(Example) The present invention will be explained below with reference to Examples and Comparative Examples.

Versatic R10 synthetic acid (manufactured by Shell Chemical, trade name)
After adding 3 moles of cobalt hydroxide to a mixture of 3 moles of propionic acid and 3.1 moles of propionic acid, the reaction was carried out at 190"C and heating was continued until about 6 moles of water was produced and distilled off. After adding 1 mole of n-butyl orthoborate to the solution, the reaction was carried out at 220"C, and the produced butyl propionate was distilled off under reduced pressure. Heating was continued until the distilled butyl propionate amounted to about 3 moles, and cobalt versatate. A boron metal soap was obtained.

The obtained cobalt/boron versatate metal soap Lo
Accurately weigh g to the nearest 0.1 mg and add 300 ml of toluene.
It was dissolved in Add 100 d of precisely weighed distilled water to this solution, stir at room temperature for 1.5 minutes, and then transfer to a separatory funnel for 30 min.
After standing for a minute, the aqueous layer was collected. Precisely weigh 5 relatives from the collected water layer and get 100m1! After transferring the mixture to a volumetric flask, distilled water was added to prepare a sample for atomic absorption measurement. Quantification by atomic absorption was determined by creating a calibration curve using a boron atomic absorption standard solution.

The content of boron extracted into water for the above cobalt boron versatate metal soap was 0.04% by weight.

As can be seen from the synthesis example, the above-mentioned versatile cobalt boron metal soap is strictly a reaction mixture containing unreacted substances and by-products, and these are presumed to be the cause of the formation of boron extracted into water. Ru.

In the same manner as in the above synthesis example, by varying the amount of versatic acid and butyl orthoborate with respect to cobalt hydroxide, compounds having different boron contents extracted in water as shown in Table 1 were synthesized.

Each of the cobalt cobalt oxides obtained as described above
Examples 1 to 5 were prepared by blending boron metal soap with a rubber composition having the following composition. Rubber compositions of Comparative Examples 1 and 2 were prepared and their physical properties were evaluated, and the results are shown in Table 1.

Rubber compounding ingredients in the buds Compound (parts by weight) Natural rubber
100 carbon black (HAF
) 50 zinc white
8 Sulfur 5 The 100% modulus of the rubber and the adhesion between the steel cord and the rubber were evaluated in accordance with JIS-6301.

The adhesion force index is 10 the peel resistance of Comparative Example 2 under each vulcanization condition.
It is shown as an index with 0 as the index, and the larger the index, the better the adhesion. The type of teal code that starts to be used is I.
X 5 Xo, 23.

Figure 1 is a diagram plotting the content (wt%) of boron extracted with water and the 100% modulus of the rubber composition vulcanized at 170°C for 8 minutes in Table 1. It can be seen that the degree to which the rubber elasticity modulus decreases due to boron is remarkable during high-temperature vulcanization.

A cobalt naphthenate/boron metal soap and a cobalt/rosin acid metal soap were produced in the same manner as in Example 1 except that naphthenic acid and rosin acid were used instead of the Versatic" 10 synthetic acid. did.

Next, cobalt naphthenate and cobalt naphthenate were added to the rubber composition used in Example 1 instead of the cobalt versatate and boron metal soap.
Rubber compositions of Examples 6 and 7 were prepared by adding 0.5 parts by weight of boron metal soap and cobalt rosin acid boron metal soap, each having a cobalt element content of 0.5 parts by weight. The physical properties of these rubber compositions were evaluated in the same manner as in Example 1, and the results are shown in Table 2 below.

Using the cobalt and boron versatate metal soap of Example 5, the rubber composition used for evaluation was as follows: The combination of the cobalt and boron versatate (parts by weight)
Four types of rubber compositions with a cobalt element content of 0.1, 0.3, 0.5, and 0.6 (No. 1 to 4)
was created. These rubber compositions were heated at 155°C for 2 hours.
Vulcanized for 0 minutes, heat aged in air at 100°C for 24 hours according to JIS K6301, measured the tensile strength of the rubber, and measured the ratio (strength retention) to the strength before heat aging. .

Rubber compounding ingredients on the tongue Compound (parts by weight) Natural rubber
100 carbon black (HAF
) 50 zinc white
8-13 = As shown in Table 3, the results show that cobalt versatate.
It was found that as the amount of boron metal soap added increases, the strength retention rate decreases, but when it exceeds 0.5 parts by weight, the decrease is severe.

When the amount of cobalt soap added to the rubber composition is increased,
-The elastic modulus of rubber increases during boat fishing. However, in the case of cobalt/boron versatate metal soap, as shown in Table 3, as the blending amount increases, the amount of boron extracted into the water contained in the rubber composition increases, and as a result, the amount of boron extracted into the water contained in the rubber composition increases. It was confirmed that the elastic modulus upon vulcanization was reduced at 0.6 PHR.

(Effects of the Invention) As explained above, the steel cord adhesion promoter of the present invention mainly contains an organic carboxylic acid cobalt/boron metal soap with a water-extractable boron content of 0.06% by weight or less. By being composed of a reaction mixture as a component,
Along with maintaining the adhesion between rubber and steel cord at high temperatures,
It improves the modulus during high-temperature vulcanization, which is an essential requirement for increasing the number of tires produced per vulcanization mold, or improves the elastic modulus, and reduces the decrease in tire maneuverability (cornering power) and tire belt durability. The effect is that it can be prevented.

[Brief explanation of the drawing]

Figure 1 shows the boron content (wt%) extracted with water when the rubber compositions of Examples 1 to 5 and Comparative Examples 1 to 2 were vulcanized at a high temperature of 170°C for 18 minutes and the 100% of the rubber. It is a graph showing the relationship between modulus.

Claims (1)

[Claims] 1. In a steel cord adhesion promoter that is blended in an amount of 0.02 to 0.5 parts by weight in terms of cobalt metal per 100 parts by weight of rubber, the promoter is a mixture of an organic carboxylic acid, an inorganic cobalt compound, and an organic borate ester. A steel cord adhesion promoter consisting of a reaction mixture whose main components are organic carboxylic acid cobalt/boron metal soap, which is a reaction product, and characterized in that the content of boron extracted with water is 0.06% by weight or less. agent.