JPH09164604A - Production of cord/rubber composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cord/rubber composite excellent in corrosion fatigue resistance under wet environment suitable from an aspect using the belt layer or carcass layer of a tire and not substantially damaging the adhesiveness of cords and rubber. SOLUTION: In this method, a steel wire plated with brass by a diffusion method is drawn and subsequently heat-treated at 250-350 deg.C. A plurality of the heat-treated steel wires are intertwisted to form a steel cord which is, in turn, embedded in an unvulcanized rubber compsn. containing 0.6% or more of moisture to be vulcanized and integrated.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a cord / rubber composite suitable for use in a belt layer, a carcass layer or the like of a tire.

[0002]

2. Description of the Related Art As one of the needs that has been increasing due to the recent problem of global warming, there is a reduction in fuel consumption of automobiles. In order to achieve low fuel consumption, weight reduction of automobile parts is also an important measure. Against this background, there is a strong demand for reducing the weight of tires, which are automobile parts. Currently, most of the most commonly used pneumatic radial tires use a steel cord for their belt layers. Therefore, in order to reduce the weight of the tire, the amount of rubber is reduced and
Reducing the amount of rucode used is a major issue.

To reduce the amount of steel cord used,
In order to secure the durability of the tire, it is necessary to increase the strength of the steel cord. Therefore, by applying a higher wire drawing workability to the high carbon steel having a higher carbon content than before, a high strength steel wire is manufactured, and one or more steel wires are twisted together to form a steel. Attempts have been made to code.

However, when high workability is applied using high carbon steel, the strength of the steel cord is increased but the corrosion fatigue resistance in a wet environment tends to deteriorate. Further, in order to reduce the weight of the tire, the amount of rubber is reduced together with the steel cord. As a result, water easily penetrates into the inside due to external damage on the tread surface, and the environment surrounding the steel cord is exposed to a humid atmosphere. There are many things. Therefore, in order to achieve the weight reduction of the tire while ensuring the durability of the tire, it is an essential task to improve the corrosion fatigue resistance of the high strength steel cord in a wet environment.

In order to solve such a problem, an open structure of steel cords, application of plating other than brass plating, and surface treatment of steel wires are taken as countermeasures. However, none of these methods has been able to prevent deterioration of corrosion fatigue resistance in a humid environment.

[0006]

An object of the present invention is to provide excellent corrosion fatigue resistance in a wet environment suitable for use in a belt layer, a carcass layer, etc. of a tire and to substantially improve the adhesion between a cord and rubber. To provide a method for producing a cord / rubber composite that does not impair the physical properties.

[0007]

In order to solve this problem, as a result of examination by the present inventors, as a result of drawing a brass-plated steel wire by a diffusion method and then heat-treating it under specific conditions, It was found that the corrosion / fatigue resistance of the cord / rubber composite in a wet environment is dramatically improved. However, it has been found that when a steel cord made of a steel wire thus heat-treated is embedded in a normal unvulcanized rubber composition and integrated by vulcanization, the adhesiveness with rubber is significantly reduced.

In order to solve the above problems, the present inventor has conducted extensive studies, and as a result, in order to prevent the decrease in the adhesiveness between the steel cord and the rubber, an unvulcanized rubber composition in which the steel cord is embedded is used. It has been found that increasing the amount of water contained in a product is effective. As a result, a brass-plated steel wire was drawn, then heat-treated under specific conditions, and then the steel wires were twisted together to form a steel cord, and this steel cord was made into an unvulcanized rubber composition containing a specific amount of water. By embedding it in an object and integrating it by vulcanization,
The inventors have found that it is possible to provide a cord / rubber composite having excellent corrosion fatigue resistance in a wet environment without lowering the adhesiveness between the cord and rubber, and completed the present invention.

Therefore, according to the present invention, after the steel wire plated with brass by the diffusion method is drawn, 250 to 350
An unvulcanized rubber composition obtained by heat-treating the steel wire at a temperature of ℃, and then twisting one or a plurality of the steel wires thus heat-treated into a steel cord, the steel cord containing water of 0.6% or more. It is characterized in that it is embedded in and is integrated with vulcanization.

As described above, the steel wire plated with brass by the diffusion method is drawn and then heat-treated at a temperature of 250 to 350 ° C. to change the structure of the wire surface layer and to form a coating having high corrosion resistance on the wire surface layer. Together, it is estimated that the corrosion resistance and fatigue resistance in a humid environment are improved. Here, "heat treatment" means performing a heating treatment. In addition, the steel wires thus heat treated are twisted together to form a steel cord, and the steel cord is embedded in an unvulcanized rubber composition containing 0.6% or more of water to vulcanize and integrate, It is considered that the extreme surface layer of the wire forming the boundary surface with the rubber is activated by the water content in the rubber composition, and the adhesiveness with the rubber is improved.

Therefore, it is possible to improve the corrosion fatigue resistance in a wet environment while ensuring the adhesiveness between the cord and the rubber. Further, by increasing the carbon content of the steel cord to increase its strength, the usage amount of the steel cord can be reduced, so that the weight of the tire or the like can be reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a steel wire plated with brass by a diffusion method is drawn and then heated at 250 to 350 ° C.
The heat treatment is performed at a temperature in the range of, preferably, a temperature in the range of 275 to 325 ° C. Then, one or a plurality of steel wires thus heat-treated are twisted together to form a steel cord, and the steel cord has a moisture content of 0.6% or more, preferably 0.6 to 1.5%. It is embedded in the unvulcanized rubber composition containing it and integrated by vulcanization.
The content of the unvulcanized rubber composition is not specified, and examples thereof include natural rubber (NR), styrene-butadiene copolymer rubber (SBR), butadiene rubber (B).
R) and other raw material rubbers are blended with carbon black, a vulcanizing agent and the like. Further, this unvulcanized rubber composition,
It is preferable to contain a partial condensate of cresol resin and hexamethylol melamine pentamethyl ether, and it is preferable to add 1.0 part of the partial condensate of hexamethylol melamine pentamethyl ether to 100 parts by weight of the raw rubber.
˜5 parts by weight, 0.5 to 5 parts by weight of cresol resin, 4 to 7 parts by weight of sulfur, and 0.1 to 0.8 parts by weight of organic acid cobalt salt as a cobalt element.

Here, as a method of brass-plating a steel wire, usually, a method of simultaneously electrodepositing copper and zinc using a cyan bath (cyan method), and a method of individually electrodepositing copper and zinc, After that, there is a method (diffusion method) of thermally diffusing into brass. However, since the cyan method uses a cyan bath, it has problems of pollution and environmental hygiene, while the diffusion method does not have such problems. Therefore, in the present invention, brass plating is performed by the diffusion method.

If the heat treatment is carried out at a temperature of 250 to 350 ° C., if it is less than 250 ° C., a sufficient effect for improving the corrosion fatigue resistance in a wet environment cannot be obtained. On the other hand, when heat-treated at a temperature higher than 350 ° C., the corrosion fatigue resistance of the brass-plated steel cord in a wet environment is not improved, and further the tensile strength of the brass-plated steel cord is significantly reduced. It becomes impossible to reduce the weight of the rubber composite.

The heat treatment temperature is more preferably 275 to 275.
It is the range shown at 325 ° C. The heat treatment time is not particularly limited, but in order to secure the corrosion fatigue resistance,
It is more preferably 5 to 30 minutes. The heat treatment method is not particularly limited. It is necessary to set the moisture content in the unvulcanized rubber composition in which the heat treatment cord is embedded to be 0.6% or more. When it is less than 0.6%, the adhesiveness between the cord and the rubber is lowered, and it is difficult to secure the durability of the cord / rubber composite. The upper limit of the water content is not particularly limited, but 1.
5% or less is preferable. If it exceeds 1.5%, problems such as foaming due to water when the unvulcanized rubber is vulcanized occur. Here, the method of adjusting the water content contained in the unvulcanized rubber composition to a predetermined amount is not particularly limited, and for example,
There is a method of leaving the unvulcanized rubber composition in a high-humidity atmosphere, or mixing water with the unvulcanized rubber composition.

In the present invention, the brass plating thickness of the steel wire plated by the diffusion method is not particularly limited, but the final plating thickness is 0.1 to 0.5.
It is preferable to set the thickness to μm from the viewpoint of adhesion to rubber. The brass plating composition may be in a range usually used, and is a composition of 60 to 70% of copper and 30 to 40% of zinc. The high carbon steel used in the present invention is not particularly limited, but a more remarkable effect is obtained when a wire having a carbon content of 0.82% by weight or more is used.

[0017]

EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples. Example 1 Brass plating was performed by a diffusion method so that the Cu / Zn alloy ratio was 0.64 / 0.36, and the carbon content was 0.82% by weight.
The steel wire of No. 1 was drawn to have a diameter of 0.30 mm. This brass-plated steel wire was heat-treated at the heat-treatment temperature shown in Table 1. Five pieces of the steel wires after the heat treatment are twisted together to form a steel cord, and the steel cord is embedded in an unvulcanized rubber composition of the compound A shown in Table 2 with various moisture contents changed, and integrated by vulcanization. To produce a cord / rubber composite. The unvulcanized rubber composition of the compound A is 4.0 parts by weight of a partial condensate of hexamethylol melamine pentamethyl ether, 1.0 part by weight of a cresol resin and 6.0 parts by weight of sulfur with respect to 100 parts by weight of a raw rubber. By weight, 0.3 parts by weight of an organic acid cobalt salt is used as a cobalt element.

Table 1 shows the results of evaluating the corrosion fatigue resistance of these heat-treated brass-plated steel wires and the adhesion with rubber. Corrosion fatigue resistance is a temperature of 2 as an accelerated evaluation.
The brass-plated steel wire subjected to the heat treatment at the heat treatment temperature shown in Table 1 in an atmosphere of 0 to 25 ° C was subjected to a rotating bending fatigue test (load stress: about 1176 N / mm ² ) in a 3 wt% sodium chloride aqueous solution. The breaking life evaluated by was expressed by an index. Adhesion between cord and rubber is ASTM
The brass-plated steel cord was pulled out in accordance with D2229, and the rubber coverage at that time was evaluated and expressed as an index. In each case, the larger the number, the better.

No. 1 in Table 1. 4, 6, 8, 10, and 12 are examples of the present invention, and others are comparative examples. As can be seen from the table, the brass-plated steel cord of the present invention example has excellent corrosion fatigue resistance and secures adhesion with rubber.
On the other hand, in Comparative Example No. Nos. 2 and 3 are examples in which the temperature of the heat treatment condition for the brass-plated steel cord is less than 250 ° C., and the corrosion fatigue resistance is inferior to the examples of the present invention. No. of Comparative Example. 5,7,9,13
In both cases, the temperature of the heat treatment condition for the brass-plated steel cord is in the range of 250 to 350 ° C., but the moisture content of the unvulcanized rubber composition burying them is less than 0.6%. is there. Since the amount of water contained in the unvulcanized rubber composition is low, the adhesiveness with rubber is lowered.
Furthermore, No. No. 14 is an example in which the temperature of the heat treatment condition for brass plated steel exceeds 350 ° C. The effect of improving the corrosion fatigue resistance is not sufficiently exerted, and the adhesiveness between the cord and the rubber is also reduced. Moreover, the temperature of the heat treatment condition for the brass-plated steel cord is 350.
If the temperature exceeds ℃, the mechanical properties of the cord itself, particularly the tensile strength, will be significantly reduced, and the mechanical properties of the cord / rubber composite will also be reduced.

Example 2 The same brass-plated steel cord as in Example 1 was embedded in an unvulcanized rubber composition of formulation B shown in Table 2 by specifying its water content, and integrated by vulcanization. The unvulcanized rubber composition of the compound B is a compounding agent and the compounding amount is almost the same as that of the compound A, but the compound A has a partial condensate of hexamethylol melamine pentamethyl ether per 100 parts by weight of the raw rubber. It is 0 part by weight, but the difference is that compound B is 4.0 parts by weight of hexamethylolmelamine per 100 parts by weight of the raw rubber. The unvulcanized rubber composition whose moisture content was specified was prepared in the same manner as in Example 1.

The adhesion between the cord of the obtained cord / rubber composite and the rubber was evaluated in the same manner as in Example 1, and the result was expressed as an index. No. No. 11 is No. The same brass-plated steel cord as 10 was embedded in the unvulcanized rubber composition of the compound B. In addition, the water content contained in the unvulcanized rubber composition is also as shown in No. Same as 10. as a result,
No. No. 11 shows the adhesiveness with rubber. Although it is superior to No. 9, No. 9 having the same moisture content in the unvulcanized rubber composition. Inferior to 10. That is, the combination A is
It can be seen that the compound B has better adhesion to rubber than the compound B.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As described above, according to the present invention, after drawing the brass-plated steel wire by the diffusion method,
Heat treatment is carried out at a temperature of 250 to 350 ° C., and then one or a plurality of the steel wires thus heat treated are twisted together to form a steel cord.
Since it is embedded in an unvulcanized rubber composition containing 6% or more of water and is vulcanized and integrated, it is excellent in corrosion fatigue resistance in a wet environment and at the same time substantially improves the adhesion between the cord and the rubber. It is possible to obtain a cord / rubber composite that is not damaged. Further, by increasing the carbon content to increase the strength of the steel cord, it is possible to reduce the usage amount of the steel cord, so that it is possible to reduce the weight of the tire or the like.

Claims (3)

[Claims] 1. A steel cord obtained by drawing a brass-plated steel wire by a diffusion method, heat-treating the wire at a temperature of 250 to 350 ° C., and then twisting one or more of the heat-treated steel wires together. The steel cord is embedded in an unvulcanized rubber composition containing 0.6% or more of water and vulcanized and integrated to produce a cord / rubber composite. 2. The unvulcanized rubber composition is 0.6% to 1.5.
The method for producing a cord / rubber composite according to claim 1, wherein the cord / rubber composite contains 100% of water. 3. The cord / code according to claim 1 or 2, wherein the unvulcanized rubber composition contains a partial condensate of a cresol resin and hexamethylolmelamine pentamethyl ether.
Method for producing rubber composite.