JPS6038444A - Adhesive rubber composition - Google Patents

Abstract

PURPOSE:An adhesive rubber composition being good in adhesion to steel cords and having a high elastic modulus, a high strength at break and a high elongation at break, prepared by compounding a rubber with sulfur, an organic acid cobalt salt and hard carbon. CONSTITUTION:100pts.wt. rubber (e.g., natural rubber, polybutadiene rubber, or SBR) is compounded with 3-7pts.wt. sulfur, 0.5-5pts.wt. organic acid cobalt salt (e.g., cobalt naphthenate or cobalt stearate), and 50-70pts.wt. hard carbon (particle diameter <=about 40mmu, e.g., LS-HAF). When the resulting rubber composition is vulcanized, the culcanizate has a 100% modulus of 40-70kg/cm<2>, a strength at break >=200kg/cm<2>, and an elongation at break >=380%.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an adhesive rubber composition having good adhesion to steel cords, high elastic modulus, high breaking strength and high breaking elongation, especially adhesive suitable for rubber for belt layer of pneumatic tires. The present invention relates to a rubber composition for use.

In recent years, with the development and popularization of expressways, there has been an increased demand for high-speed durability of pneumatic tires. In particular, high-load tires such as tires for trucks and buses are required to have high load durability at high speeds, and conventional bias tires are being replaced by radial tires. The belt layer of a radial tire uses multiple plies with embedded steel cords to maintain high rigidity, and the steel cords are arranged so as to intersect between the plies, so the belt layer does not tighten during internal pressure filling or load application. When shearing strain occurs between the plies of the layer and the belt layer is run for a long time, ply separation may occur between the plies of the belt layer, particularly at both ends of the belt layer, leading to breakage.

To solve this problem, attempts have been made to change the design of tire structural factors such as tread radius and belt layer structure carcass profile as a way to reduce distortion, but satisfactory results have not yet been obtained. . Therefore, the present invention was achieved by conducting studies from the viewpoint of compounding design of the rubber embedded in the belt layer.

Until now, it has been thought that the required characteristics of the rubber embedded in the belt layer are good adhesion with the steel cord, and that the hardness and modulus of the rubber are high because the highly rigid steel cord is embedded. Embedded rubber with high hardness and modulus can be said to be effective from the perspective of reducing distortion during driving, but on the other hand, the belt layer has constant strain when momentary high loads are applied during cornering or braking. Because of this behavior, embedded rubber is required to have high elongation and strength. However, the commonly used embedded rubbers with high hardness and modulus have low elongation and are not necessarily strong, which may actually accelerate the failure.

Therefore, the present invention has developed a rubber composition that has high hardness and modulus, excellent elongation and strength, and has good adhesive properties as embedded rubber for the belt layer. This made it possible to significantly improve high-speed durability.

The present invention uses 3 to 7 parts by weight of sulfur per 100 parts by weight of rubber;
Organic acid cobalt salt 0.5-5 parts by weight, hard carbon 5
Contains 0 to 0 parts by weight, and has a 100% modulus of 4.
0-70 kg/ctl, breaking strength 200 kg
/cut or more, and the elongation at break is 380% or more, and is a rubber composition that has good adhesion to steel cords.

First, the rubbers used in the present invention include non-polar synthetic rubbers such as natural rubber, polyisoprene rubber, polybutadiene rubber, styrene-butadiene copolymer rubber (5BR), and copolymer rubber of olefins and non-conjugated diene. For example, EPD
MSEPT) or a mixture thereof.

Next, the organic acid cobalt salt used in the present invention includes cobalt naphthenate, cobalt oleate, cobalt maleate, cobalt stearate, etc., and cobalt naphthenate is particularly preferred. Organic acid cobalt salt is rubber 100
It is contained in an amount of 0.5 to 5 parts by weight. This organic acid cobalt salt contributes to the adhesion to the steel cord, and if it is less than 0.5 parts by weight, the adhesion is low, while if it exceeds 5 parts by weight, it will not bond with the steel cord after heat aging of the vulcanized rubber. adversely affects the adhesion of the

Next, the amount of hard carbon used in the present invention is 50 to 70 parts by weight per 100 parts by weight of rubber. Here, hard carbon has a particle size of about 40 mμ or less, and is used to maintain a high modulus and breaking strength after vulcanization of the composite material, and to improve adhesion to the steel cord.

Soft carbon with large particle size has sufficient modulus,
Strength cannot be achieved, and the same is true when the carbon content is less than 50 parts by weight. On the other hand, if the amount of carbon exceeds 70 parts by weight, sufficient elongation may not be obtained, and the scorch time may be too short (making processing difficult).For the same reason, 3 to 7 parts by weight of sulfur may be added. If it is less than 3 parts by weight, the modulus and strength after vulcanization will be low, and if it exceeds 7 parts by weight, the elongation will not be sufficient and the blooming of sulfur in the unvulcanized rubber will be intense, making it impractical.

Next, the vulcanization accelerator used in the present invention is N0BS (N-oxydiethylene, benzothiazyl, sulfenamide).
is suitable. The type of vulcanization accelerator is influenced by the use of the organic acid cobalt salt and the amount of sulfur blended, and within the above-mentioned range of the present invention, it is recommended to use rvoBs of 050 to 150 from the viewpoint of adhesion to the steel cord. desirable.

The steel cord used in the present invention is preferably a steel cord plated with brass, and the plating components are copper (Cu) and zinc (Zn) with a weight ratio of Cu/Zn of 5.
Those with Cu/Zn ratio of 5/45 to 80/20 are generally used, and those with Cu/Zn ratio of 70/30 are particularly preferred.

In addition, when actually compounding rubber, vulcanizing agents, vulcanizing aids, accelerators, fillers, softeners, plasticizers, anti-aging agents, and their low processing aids are used as ordinary rubber compounding agents. Of course, they may also be blended together.

Next, in the present invention, based on the above-mentioned composition, the 100 modulus after vulcanization is 40 to 70 kg/c++t, and the breaking strength is 20
0kg/co! As described above, rubber having a breaking elongation of 380% or more is used as the embedded rubber for the belt layer. 1
The reason why the 00% modulus is in the range of 40 to 70 kg/c++t is because cords with high elastic modulus such as steel cords and Kevlar (trade name, DuPont) are used for the cords in the belt layer. In order not to form a step in rigidity, the 100% modulus must be 40 kg/c++ or more, and on the other hand, in order not to form a step in rigidity with the adjacent tread rubber, it needs to be 70 kg/cJ or less. In addition, the belt layer is subjected to deformation strain during internal pressure filling and load loading, but especially at both ends of the belt layer, the gap between the carcass ply and the carcass ply widens, forming a structural fault in this area, causing large deformation strain. Become. Therefore, the embedded rubber in the belt layer has high elongation and strength, that is, the elongation at break is 3.
80% or more, and the breaking strength is 200kg, l'cn
1 or more is required. If these values are not met, the steel cord and rubber will separate, making it impossible to maintain durability.

However, by specifying the composition and physical properties of the rubber embedded in the belt layer as described above, the present invention maintains adhesion to the steel cord, suppresses peeling between the plies of the belt layer during high-speed running, and provides high durability. Demonstrate your sexuality.

The present invention will be described below with reference to Examples.

Example 1 A composition having the formulation shown in Table 1 was prepared as an embedded rubber for the belt layer, and using this formulation, +000R20,1
A 4PR steel radial tire for trucks and buses, and a 165SR 3 steel radial tire for passenger cars were prototyped. A test piece was taken from this tire and its tensile properties were evaluated according to JIS-6301.
Shown in the table. Adhesion was evaluated by peeling the tread rubber from the belt layer, visually observing the state of rubber adhesion on the cord surface, and rating it on a scale of 1 to 10. The larger the number, the
Show excellence.

(b) Effects due to the type and amount of carbon From Tables 1 and 2, samples B, C, and L show the effect of varying LS-11ΔF, and when the amount of carbon exceeds 70 parts by weight, the modulus is high and the elongation at break is high. On the other hand, if it is less than 50, the modulus is low and the breaking strength is insufficient. Moreover, sample A uses soft carbon (FEF) and has low breaking strength and breaking elongation.

(b) Effect of varying sulfur content Sample H shows the effect of varying sulfur content; when sulfur is too low, adhesion, breaking strength, and breaking elongation are all low, while when it is too high, modulus is high and breaking elongation is low. The degree becomes lower.

(c) Effect of cobalt naphthenate Test No. 11E, FSG, shows a random effect of cobalt naphthenate, and when the amount blended is small, the adhesion becomes significantly poor.

Tires prototyped using the samples shown in Table 1 were subjected to an indoor running test under the following conditions and evaluated in order of loose length at the end of the belt layer), and the results are shown in Table 3. From the same table, it is clear that the examples of the present invention have almost no looseness and exhibit good durability.

Indoor running test conditions 100 R20 tires, internal pressure 7.5 kg/ant, speed 4 okm/h, running ratio n 20,000 km 1 (i5sR13 tires, internal pressure 2.0 kg/cat, speed 6 ok/h, mileage 10,000 km)

Claims (4)

[Claims] (1) Contains 3 to 7 parts by weight of sulfur, 0.5 to 5 parts by weight of organic acid cobalt salt, and 50 to 0 parts by weight of hard carbon to 100 parts by weight of rubber, and has a 100% modulus after vulcanization. is 40 to 70 kg/c [111 breaking strength is 20
0 kg/c++! The above is a rubber composition that has good adhesion to a steel cord and has an elongation at break of 380% or more. (2) The rubber composition according to claim 1, wherein the organic acid cobalt is cobalt stearate or cobalt naphthenate. (3) The rubber composition according to claim 1, which contains 60 to 70 parts by weight of hard carbon. (4) The rubber composition according to claim 1, which has a breaking strength of 250 kg/cut or more.