JPS61151249A - Rubber composition for covering steel cord - Google Patents

Abstract

PURPOSE:To provide the titled compsn. having excellent heat aging characteristics, water-resistant adhesion and initial adhesion to steel cord, by blending sulfur and N-nitrosodiphenylamine with a specified raw rubber. CONSTITUTION:3-6pts.wt. sulfur, 1-5pts.wt. N-nitrosodiphenylamine and optionally additives such as carbon black, process oil, vulcanization accelerator, etc. are blended with 100pts.wt. raw rubber composed of at least 80pts.wt. natural rubber and/or polyisoprene rubber and optionally not more than 20pts.wt. synthetic diene rubber such as polybutadiene rubber or a styrene/butadiene rubber to obtain a rubber compsn. for covering steel cord. The compsn. is useful as a rubber material for covering steel cord such as carcass and belt of a steel radial tire and brass-plated steel cords of rubber goods such as steel-reinforced core-covering rubber of a conveyor belt.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a rubber composition for coating steel cords, and more specifically, the present invention relates to a rubber composition for coating steel cords, and more specifically, the main rubber is natural rubber and/or polyisoprene rubber, and sulfur and N-nitrosodiphenylamine are respectively added to the rubber composition. The present invention relates to a rubber composition for covering steel cords which has high heat aging resistance and excellent initial adhesion and water-resistant adhesion to steel cords coated with plus plating etc.

[Prior Art] Conventionally, when bonding rubber and steel cords, the common method is to plate the steel cords with brass, zinc, or the like. Rubber composite materials reinforced with such steel cords have recently been applied to vehicle tires, steel conveyor belts, etc., and have been put into practical use in a wide range of fields.

Particularly in vehicle tires, the demand for high speed and high durability has increased with the development of expressways, and the prevalence of steel radial tires that use steel cord for the belt and carcass has increased. With the spread of such steel radial tires, the required performance of physical properties such as adhesion between rubber and steel cord and heat aging resistance has diversified, and the demand for higher performance has become stronger. Specifically, the rubber for covering the steel cord of a steel radial tire has a disadvantage in that it is susceptible to so-called separation, in which the physical properties of the rubber for covering the steel cord deteriorate and break due to the heat generated during tire travel. In order to prevent this separation, it is necessary to use a rubber composition with excellent heat aging resistance as the rubber for covering the steel cord. Furthermore, since the vulcanization conditions for the rubber used to cover the steel cords of steel radial tires vary depending on the location of use, such as the tire belt or carcass, stable initial adhesion is required under a wide range of vulcanization conditions. Furthermore, when tires are left unattended such as during storage, the adhesive strength tends to decrease due to moisture in the air, so stable water-resistant adhesion is required.

Therefore, the rubber for covering steel cords must simultaneously satisfy good heat aging resistance, stable initial adhesion to steel cords, and water-resistant adhesion.

Conventionally, as a rubber composition for coating steel cords, an IRH-containing rubber composition in which white carbon, resorcinol, and hexamethylenetetramine are simultaneously blended with raw rubber has been used. HRH-containing rubber compositions are characterized by good initial adhesion and heat aging resistance, but have a drawback of poor water-resistant adhesion.

Furthermore, organic acid cobalt salt-containing rubber compositions containing organic acid cobalt salts have been used. Rubber compositions containing organic acid cobalt salts have good initial adhesion and water-resistant adhesion, but have the disadvantage of poor heat aging resistance because of the need to incorporate a large amount of sulfur.

In order to improve the drawbacks of both rubber compositions, HR
Rubber compositions containing both H and an organic acid cobalt salt have also been used, but these do not improve heat aging resistance, which is a drawback of rubber compositions containing organic acid cobalt salts.

As described above, a rubber composition for coating steel cords that has all of these characteristics, such as good heat aging resistance, stable initial adhesion to steel cords, and water-resistant adhesion, has not yet been obtained.

[Object of the invention] The present invention has been made to solve the above-mentioned problems.
The purpose is to provide a rubber composition for coating steel cords that has excellent initial adhesion and water-resistant adhesion to steel cords that have been subjected to plus plating, etc., and has good heat aging resistance, especially for steel cords of steel radial tires. It is used for coating rubber for steel cords coated with a plus plated coating, such as coating rubber for steel cord reinforcing cores of conveyor belts.

[Background of the Invention] In line with the above objectives, the present inventors have developed a rubber composition that does not contain HRH or organic acid cobalt salt, which has been used conventionally, that has good heat aging resistance and that is similar to steel cord. As a result of research into methods for obtaining stable initial adhesion and water-resistant adhesion, the following facts were discovered.

In other words, a rubber composition obtained by blending only a large amount of sulfur without using the conventionally used HRH or organic acid cobalt salt does not meet the basic performance requirements for steel cord coating rubber. Practical use is difficult due to poor initial adhesion.

Furthermore, N-nitrosodiphenylamine has conventionally been used as a vulcanization retarder or scorch inhibitor, and is usually blended in an amount of 0.5 to 0.75 parts by weight per 100 parts by weight of raw rubber. However, even if 0.5 to 0.75 parts by weight of N-nitrosodiphenylamine is added to the rubber composition containing only sulfur in a large amount as mentioned above, the initial adhesion to the steel cord is still poor. It is inferior and inadequate.

On the other hand, when N-nitrosodiphenylamine is blended into an IRH-containing rubber composition, the water-resistant adhesion, which is a drawback of HRH-containing rubber compositions, cannot be improved.

Further, even when N-nitrosodiphenylamine is blended into a rubber composition containing a cobalt salt of an organic acid, the heat aging resistance, which is a drawback of the rubber composition containing a cobalt salt of an organic acid, cannot be improved.

As a result of intensive studies based on the above research results, the present inventors used a rubber mainly composed of natural rubber and/or polyisoprene rubber as the raw material rubber, and added a specific amount of sulfur and N-nitrosodiphenylamine to this rubber. The present invention was achieved based on the discovery that good heat aging resistance, as well as stable initial adhesion and water-resistant adhesion to steel cords, can be obtained by incorporating the above.

[Structure of the Invention] That is, the present invention provides 3 to 6 parts by weight of sulfur and 1 to 5 parts by weight of N-nitrosodiphenylamine to 100 parts by weight of raw rubber containing 80 parts by weight or more of natural rubber and/or polyisoprene rubber. This is a rubber composition for coating steel cords, which is characterized by having a combination of: It also prevents deterioration of physical properties due to heat generation generated during tire running, making it suitable for parts that require high adhesion performance and physical properties, such as steel radial tires.

The present invention will be described in further detail below.

The raw material rubber used in the present invention is preferably natural rubber (NR), polyisoprene rubber (IR), or a mixture of both, but 20 parts by weight or less of 100 parts by weight of the raw material rubber is polybutadiene rubber (BR), styrene rubber, etc. Butadiene rubber (
It is also possible to replace it with a diene-based synthetic rubber such as SBR). If less than 80 parts by weight of natural rubber, polyisoprene rubber, or a mixture thereof is contained in the suspended portion of the raw rubber 100, the adhesion of the steel cord will deteriorate, which is undesirable.

The amount of sulfur blended in the present invention is 3 to 6 parts by weight per 100 parts by weight of raw rubber. If the amount of sulfur is less than 3 parts by weight, the initial adhesion will decrease, and if it exceeds 6 parts by weight, the heat aging resistance will decrease, which is not preferable.

The amount of N-nitrosodiphenylamine blended in the present invention is 1 to 5 parts by weight per 100 parts by weight of raw rubber. If the amount of N-nitrosodiphenylamine blended is less than 1 part by weight, initial adhesion will be poor, which is not preferred. In addition, if the amount of N-nitrosodiphenylamine added exceeds 5 parts by weight, the exothermic property increases and the heat aging resistance decreases.

In the present invention, in addition to these compounding agents, various compounding agents commonly used as rubber compounding agents, such as carbon black, process oil, vulcanization accelerator, anti-aging agent, etc., may be added in appropriate amounts. can.

[Description of Examples] The present invention will be specifically described below based on Examples and Comparative Examples.

All the blending values in Table 1 are parts by weight, and the numbers in parentheses in the sulfur column indicate the actual amount of sulfur blended.

, Flow Sides 1 to 9 and Comparative Examples 1 to 12 A vulcanizing agent was added to a masterbatch obtained by mixing compounding agents other than the vulcanizing agent shown in Table 1 and raw rubber in a normal Banbury type mixer. A rubber composition was prepared by adding on a roll.

The physical properties of this rubber composition were evaluated in accordance with JIS K6301 under vulcanization conditions of 150°C and 30 minutes.

Regarding heat aging resistance, vulcanized rubber was cured at 150° C. for 30 minutes in a 100° C. gear oven, and the physical properties were evaluated after the rubber was left to stand for 24 hours.

In addition, the adhesion evaluation with the steel cord was conducted using a brass-plated steel cord with a 3+9+15 structure according to ASTM D2229.
The initial adhesion after vulcanization at 160℃ for 20 minutes according to
Evaluation was made based on pull-out force (Ky/25M) and rubber coverage (%).

In addition, water-resistant adhesion was evaluated using a constant temperature and humidity chamber adjusted to 70°C and 90% relative humidity.The sample was cured at 160°C for 20 minutes, and after being left for 2 weeks, the pulling force (Kg725m) and rubber coating Evaluation was made in percentage (%).

Table 1 shows the measurement results for each characteristic.

-X- Six Sacred Treasures -1+ As shown in Table 1, Examples 1 to 4 and Comparative Example 1
~3 uses NR as the raw material rubber, and contains 5 parts by weight of sulfur (actually 4 parts by weight, hereinafter described as the actual amount blended)
The amount of N-nitrosodiphenylamine blended is varied in the range of 0 to 6 parts by weight. As shown in Comparative Examples 1 and 2, 0 to 0.5 parts by weight of N-nitrosodiphenylamine has good heat aging resistance, but both initial adhesion and water resistance are low. Moreover, at 6 parts by weight, although the adhesion is good, the heat aging resistance is poor. It can be seen that Examples 1 to 4, in which N-nitrosodiphenylamine was blended in an amount of 1 to 5 parts by weight, were in good ranges in terms of initial adhesion, water resistance adhesion, and heat aging resistance.

Examples 2 and 5 and Comparative Examples 4 and 5 are rubber compositions with varying amounts of sulfur. As shown in Comparative Example 4, when the amount of sulfur is less than 3 parts by weight, both initial adhesion and water-resistant adhesion are low, and as shown in Comparative Example 5, when the amount of sulfur is more than 6 parts by weight, the adhesion is poor. Although it is improved, the heat aging resistance is greatly reduced. Therefore, it can be seen that 3 to 6 parts by weight of sulfur is required to satisfy heat aging resistance and adhesiveness at the same time.

Comparative Examples 6 to 8 are rubber compositions in which 2 parts by weight of cobalt naphthenate were blended and the amount of sulfur blended was varied.
Comparative Example 7 contains double portions of N-nitrosophenylamine, and Comparative Example 8 contains no N-nitrosodiphenylamine. In Comparative Example 6, in which 4 parts by weight of sulfur was added, both initial adhesion and water-resistant adhesion showed low values. On the other hand, when sulfur is increased to 6 parts by weight as in Comparative Examples 7 and 8, the initial adhesion and water-resistant adhesion are satisfactory, but the heat aging resistance decreases, regardless of whether N-nitrosodiphenylamine is added or not. Heat aging resistance is not improved.

Comparative Examples 9 and 10 are rubber compositions containing I-I Rl-1. The HRH-containing rubber composition has good initial adhesion and excellent heat aging resistance even when the sulfur content is 4 parts by weight. However, the water-resistant adhesiveness shows a low value regardless of whether N-nitrosodiphenylamine is blended or not.

13- Examples 6 and 7 are based on the formulation of Example 2, in which the vulcanization accelerator OBS or the vulcanization accelerator P is used instead of the vulcanization accelerator DZ.
Although this is a rubber composition containing SA, almost the same results as in Example 2 are obtained.

In Examples 8 and 9 and Comparative Examples 11 and 12, the type and blending amount of the raw rubber were changed, and Example 8
In Comparative Example 11, IR was blended alone as the raw rubber, and in Example 9 and Comparative Example 12, NR/NR was blended as the raw rubber.
It uses a blend of BR. In Example 8, in which N-nitrosodiphenylamine was blended, N was used as the raw material rubber.
Almost the same results as in Example 2 using R are obtained. However, in Comparative Example 11, in which N-nitrosodiphenylamine was not blended, the initial adhesiveness decreased. On the other hand, BR is 200
In Example 9, in which BR was added in parts by weight, the heat aging resistance, initial adhesion, and water resistant adhesion were both in good ranges, but in Comparative Example 12, in which 300 parts by weight of BR was added, the water resistant adhesion was unfavorable.

[Effect of the invention] As explained above, sulfur and N-
The steel cord rubber composition of the present invention, which contains specific amounts of nitrosodiphenylamine, exhibits stable initial adhesion and water-resistant adhesion to steel cords when used as a steel cord coating rubber, and also has good heat resistance. Has aging properties. Moreover, the N-nitrosodiphenylamine used in the present invention is more stably available and cheaper than conventionally used cobalt salts of organic acids. It is also extremely advantageous in terms of sex.

Therefore, the rubber composition of the present invention can be used as a rubber for coating steel cords such as belts and carcass of steel radial tires, and can also be used for plus plating of rubber products such as rubber for coating steel reinforcing cores of conveyor belts. Suitable for use as a rubber material for covering steel cords.

Claims (1)

[Claims] 1. 80% natural rubber and/or polyisoprene rubber
3 to 6 parts by weight of sulfur and 1 part by weight of N-nitrosodiphenylamine to 100 parts by weight of raw rubber containing at least parts by weight.
5 parts by weight of a rubber composition for coating a steel cord.