JPH0328004A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To improve duration life in a radial tire for heavy load by forming a carcass ply a steel cord consisting of a cobalt-plated filaments having specific carbon content and tensile strength, and a rubber containing a specific amount of organic cobalt metallic salt and having a specific 100% modulus. CONSTITUTION:Steel cord for making up a toroidal carcass layer 7 is formed by twisting plural filaments with carbon content of 0.75 to 0.9% by weight, filament-tensile strength of 320kg/mm<2> or more, and having a cobalt-plated layer. Further rubber for sheathing the cord is formed by a rubber-composite containing 0 to 0.1 parts by weight of organic cobalt metallic salt and 0.5 to 4.0 parts by weight of sulphur in comparison with 100 parts by weight of rubber component, and having a 100% modulus of 20kg/mm<2> or more after vulcanization. In this constitution, duration life of the tire can be improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention improves the metal cord and its coating rubber applied to the car force sply of pneumatic radial tires, especially heavy-duty radial tires, thereby significantly extending the durability life. This relates to a radial tire for heavy loads that has been improved.

(Prior Art) In recent years, as social needs have increased, demands have arisen for heavy-duty radial tires to be lighter in weight, longer in life, and flatter. For example, in response to the need for weight reduction, there has recently been an active movement toward increasing the strength of steel cords. Significant improvement in durability is desired.

When developing tires that meet these demands, there are various issues such as the problem of decreasing corrosion fatigue resistance due to the high strength of metal cords for carcass brazing materials, and the suppression of heat aging and crack propagation for covering rubber. It is essential to try to resolve the issue.

Furthermore, it goes without saying that sufficient adhesion performance between the metal cord of the carcass bly and the coating rubber is a major premise for tire durability. Conventionally, the most common method for bonding tire cords and rubber is the direct bonding method in which the tire cord is plated with a copper-zinc alloy plus, which reacts with the sulfur in the rubber. Efforts have been made to improve adhesion by adding organic cobalt salts such as acid cobalt.

(Problems to be Solved by the Invention) Techniques for improving the plating of steel cords to improve the adhesion between the cord and rubber are disclosed in Japanese Patent Application Laid-open Nos. 54-89939, 54-89940, and 57-56110.
This can be seen in the official gazettes such as No. However, in either case, there is only a small amount of cobalt on the outermost surface of the cord due to thermal diffusion caused by wire drawing after plating, and therefore the role of cobalt in adhesion on the cord surface is extremely small. There was a problem in that rubber without it did not exhibit good adhesion. In particular, the above-mentioned Japanese Patent Application Publication No. 57
After carefully studying the contents of Publication No. 56110 and forming a cobalt ternary alloy plating layer as described therein, a rich layer of cobalt was not formed on the surface but was diffused into the interior. Therefore, it was confirmed that rubbers containing no organic cobalt salts did not exhibit good adhesion.

In view of this situation, in order to develop a heavy-duty radial tire that can significantly improve the durability life, the inventors of the present invention have conducted extensive studies on the nature of reinforcing materials and rubber in tires. When used in combination with coated rubber containing organic acid cobalt salts, the corrosion fatigue resistance is not sufficient, and the crack propagation rate of the rubber is rapid. Radial tire for truck (L
When applied to carcass ply cords such as SR) and their covering rubber, there is a problem that the corrosion fatigue resistance decreases under severe usage conditions, and cracks tend to occur from the folded ends of the carcass cords, so the fracture resistance of the carcass ply ends It has been found that there is a problem in that (bright separation resistance) tends to decrease. Furthermore, when a high-strength cord with a filament tensile strength of 320 kg/m or more is used as the braai cord, a problem arises in that the above-mentioned corrosion fatigue resistance is significantly reduced.

Therefore, an object of the present invention is to provide a heavy-duty radial tire that can significantly reduce the weight of the tire, improve the corrosion fatigue resistance that is the problem mentioned above, and further improve the ply end separation resistance performance of the radial tire. Our goal is to provide tire improvement technology.

(Means for Solving the Problems) In the pneumatic radial tire of the present invention for achieving the above object, a toroidal carcass comprising steel cords arranged substantially parallel to the meridian section of the tire and rubber covering the steel cords is provided. and the steel cord is (1
) A steel material with a carbon content of 0.75 to 0.90% by weight, (2) a filament tensile strength of 320 kg/mm" or more, and (3) a plurality of filaments having a cobalt plating layer on the surface. Then, the covering rubber is
(5) For 100 parts by weight of the rubber component, the organic cobalt metal salt is O-0.1 part by weight as cobalt metal, and the sulfur is 0.
．． A rubber composition containing 5 to 4.0 parts by weight, (6)
And the 100% modulus after vulcanization is 20 kg/c or more.

The method of twisting the filaments of the steel cord according to the present invention may be single twist, layer twist, or double twist, and the filament diameter is 0.15 mmφ to 0.5 mm. 25 mmφ is preferable.

The high tensile strength steel filament of the present invention has a reduction in area of 97.5%, a lubricant with good wire drawability, and is drawn 3 to 4 times more than normal wire drawing. It can be made by performing stage nakasen.

The above cobalt plating method may be electroplating or various dry plating methods, and the coating step may be performed either before or after the twisting step. The thickness of the cobalt plating layer is preferably in the range of 0.05 to 0.40 μm when electroplating is used, and 0.001 to 0.15 μm when using dry plating.
A range of is preferred.

Note that the base material for cobalt plating may be iron or iron coated with copper, zinc, plasmid, or the like.

(Function) In the present invention, the filament tensile strength is set to 320 kg/mm.
The reason for this is that when considering a significant reduction in tire weight, practical effects cannot be obtained unless the tire has a tensile strength of 320 kg/lIlm2 or more.The upper limit is set from the viewpoint of productivity and processability. The limit is about 450 kg/mm.

In addition, the carbon content of the filament is 0.75 to 0.90.
The reason why the content is within the range of % by weight is that if it is less than -0.75% by weight, it is difficult to obtain a filament tensile strength of 320 kg/mm" or more, whereas if it exceeds 0.90% by weight, pro-eutectoid cementite will be formed. This is because the filament becomes brittle, making it unsuitable for use as a tire cord.

On the other hand, the reason why the amount of sulfur in the coated rubber is specified as 0.5 to 4.0 parts by weight per 100 parts by weight of the rubber component is that less than 0.5 parts by weight will cause a sufficient cross-linking reaction or adhesion reaction. On the other hand, if the amount exceeds 4 parts by weight, the effect of the present invention on improving corrosion fatigue resistance and end separation resistance will be diminished.

In addition, the reason why the organic cobalt salt in the coating rubber is 0.1 part by weight or less in terms of cobalt metal is that if it exceeds 0.1 part by weight, it will not improve the adhesion but will actually reduce the adhesion. This is because it accelerates aging and reduces the durability of rubber. Preferably it is less than 0.05 part by weight.

Furthermore, the reason why the modulus of the covering rubber is set to 20 kg/cm or more is because if the modulus is less than 20 kg/cm, the distortion of the covering rubber becomes too large in response to the input. This is because not only will it become thinner, but it will also cause problems in terms of durability.

Furthermore, in the present invention, the preferred thickness of the cobalt plating layer is defined as 0.05 to 0.40 μm when electroplating is used because if it is less than 0.05 μm, a stable film with a uniform plating thickness cannot be obtained. Sometimes the base material may be exposed, and the adhesion with the rubber may not be stabilized, while 0.40
This is because if the thickness exceeds μm, the gauge of cobalt plating becomes thick, which is unfavorable in terms of production efficiency and cost. Similarly, when using the dry plating method, the preferred thickness of the cobalt plated layer is defined as 0.001 to 0.15 μm.
If it is less than 0.001 tt m, stable adhesion with rubber cannot be obtained because the plating layer is in the form of islands or networks, while if it exceeds 0.15 μm, it is undesirable from the viewpoint of productivity and cost. This is because not only is it not possible, but it also causes a decrease in adhesiveness, which is not preferable.

In the present invention, by coating the surface of the outermost layer of the steel cord with cobalt plating, the organic cobalt salt contained in the coating rubber, which was conventionally contained in the coating rubber to improve the adhesion with the cord with the outermost layer coated with a positive layer, can be removed. It has become possible to create a rubber compound that can be removed or reduced to a very small amount, thereby suppressing deterioration of adhesive strength over time and thermal aging of breaking strength, elongation, etc. caused by the addition of organic cobalt salts.

In addition, in order to maintain stable heat-resistant adhesion, the amount of sulfur component, which was previously contained in a relatively large amount (4 to 8 parts by weight), can now be reduced to less than 4 parts by weight. Heat aging can be prevented, crack propagation resistance has been significantly improved, and it has also become possible to improve the corrosion fatigue resistance of adjacent steel cords by reducing the amount of corrosion.

Therefore, in the tire according to the present invention, not only the corrosion fatigue resistance, which has been a problem when using high-strength cords, is significantly improved, but also the ply end separation resistance can be significantly improved.

(Example) Hereinafter, the present invention will be specifically explained with reference to Examples.

As shown in FIG. 1, tire size 11/70R22. 5 truck/bus radial tire (TBR) 1 is used, and the carcass bridle structure is 3 + 9 x 0.20mm + 1 compact cord (stranded in the same direction) and I x 5 x 0.25n +
Two kinds of steel cords of 90 mm in the circumferential direction of the tire.
The tires were arranged at an angle of .degree. with the number of strokes determined to suit the case strength of the control tires (Comparative Examples 1 and 5 shown in Table 2 below). Here, in FIG. 1, 2 is a bead part, 3 is a sidewall part, 4 is a shoulder part, 5 is a tread part, 6 is a bead wire part, and 7
8 indicates a carcass layer, and 8 indicates a belt portion.

The rubber compositions shown in Tables 1 and 2 were used as coating rubber compositions for the carcass ply forming the tires. Also, the same type of Kaimono was used for the adjacent members at the end of the ply cord.

Two methods were used for plating: electroplating and dry plating (sputtering method).

Electroplating was performed under the following electroplating conditions after pretreatment of electrolytic degreasing and pickling. After the cobalt film was formed, it was thoroughly washed with ultrasonic waves and dried.

pH of O bath: 4 Bath temperature: 40°C Current density: 5 A/dm On the other hand, dry plating was performed using a magnetron sputtering device as follows.

First, the inside of the chamber was made to have a vacuum level of 10 to 1 Torr or less, and then a small amount of argon gas was introduced into the chamber to adjust the vacuum level to Q,1 Torr.
The surface of the test piece was cleaned for 5 minutes using high frequency glow discharge. After cleaning, stop the high frequency glow discharge and apply a DC voltage of -600 to the metal sample (cobalt) target.
V was applied and sputtering was performed with argon plasma at a target current of 0.5 A to form a cobalt film.

The following performance evaluations were performed on the above-mentioned prototype tire.

We prototyped tires using each type of steel cord in the car force sublime, filled about 300cc of water between the inner liner and tube of the tire when assembling the rim, and conducted drum tests on each sample tire. The lifespan (mileage) until cord breakage (CBU) failure occurred was compared with that of the control tire of Comparative Example 1, and was expressed as an index. The larger the value, the better the CBU resistance.

The tread rubber of a prototype tire with carcass sprue end separation was puffed, and the resistance to carcass sprue end separation was evaluated in a state where there was no failure of the belt layer due to heat generation in the belt layer.

Specifically, each prototype tire was rotated on a drum under the conditions of JIS 200% load, speed 60km/hr, and internal pressure 8.25kg/II1, and when separation occurred at the tip of the carcass ply cord and vibration became large. The drum running distance of each tire was compared with that of the control tire of Comparative Example 1 and expressed as an index.

The larger the value, the better the carcass blind separation resistance.

The steel cord used in the Toyoka Satoya Tatehashi trial tire was supplemented with carcass-coated rubber to make a plytreat composite, and each trial treat was The weight reduction effect when changing the driving number was expressed as an index compared to the control tire of Comparative Example 1 using the weight of steel cord used per tire. The smaller the value, the better the weight reduction effect.

The performance evaluation results of the above solid prototype tires are shown in Table 2 below.

The cobalt plating substrates shown in this example are all positive plated iron, but the substrates shown in Table 2 below can also be made of iron alone or iron plated with copper or zinc. There is no change in the evaluation results shown in .

(Effects of the Invention) As is clear from the tire performance evaluation results shown in Table 2 above, the pneumatic radial tire of the present invention has improved corrosion fatigue resistance and Kerr force splice resistance while significantly reducing tire weight. End separation performance is significantly improved, and as a result, the present invention can significantly improve the durability of heavy-duty radial tires such as radial tires for trucks and buses and radial tires for light trucks.

Furthermore, because the present invention has reduced the sulfur content in the rubber coating layer, it has become possible to reduce the sulfur in adjacent rubber members of the tire and to remove the adjacent members themselves, making it possible to create a new lightweight tire that has never existed before. can.

[Brief explanation of drawings]

Figure 1 is a partial cross-sectional view of the radial tire for trucks and buses used in the example. 2... Bead part 3... Sidewall part 4... Shoulder part 5... Tread part 6...
・Bead wire part 8...belt part

Claims (1)

[Scope of Claims] 1. A radial tire comprising a toroidal carcass made of steel cords arranged substantially parallel to the meridional cross section of the tire and their covering rubber, wherein the steel cords have: (1) carbon content; is 0.75 to 0.90% by weight, (2) has a filament tensile strength of 320 kg/mm^2 or more, and (3) is made of a plurality of filaments twisted together having a cobalt plating layer on the surface, (5) The coating rubber contains 0 to 0.1 parts by weight of organic cobalt metal salt as cobalt metal and 0 parts by weight of sulfur based on 100 parts by weight of the rubber component.
．． (6) and has a 100% modulus of 20 kg/c after vulcanization.
A pneumatic radial tire characterized by having a diameter of m^2 or more. 2. The pneumatic radial tire according to claim 1, wherein the cobalt plating layer is deposited by electroplating. 3. The thickness of the cobalt plating layer formed by the electroplating is 0.
．． The pneumatic radial tire according to claim 2, wherein the pneumatic radial tire has a particle size in the range of 0.05 to 0.40 μm. 4. The pneumatic radial tire according to claim 1, wherein the cobalt plating layer is adhered and formed by a dry plating method. 5. The pneumatic radial tire according to claim 4, wherein the thickness of the cobalt plating formed by the dry plating method is 0.001 to 0.15 μm.