JP2007009343A - Steel wire for reinforcing rubber article and steel cord - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for further improving the durable adhesiveness of a steel wire to rubbers. <P>SOLUTION: This steel wire to whose peripheral surface a brass plating is applied is characterized by controlling the surface roughness of the brass plating to 4 to 12 nmRa. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a steel wire subjected to brass plating, which is used for reinforcing rubber articles such as tires and industrial belts, and intends to achieve improvement in adhesion to rubber, particularly durability adhesion.
Here, the durable adhesive property refers to peeling of the adhered rubber after the active component of moisture or oxygen from the outside enters during storage or use in a humid atmosphere and the interface between the steel wire and the rubber deteriorates. Each can be evaluated based on the strength against and the rubber adhesion rate when peeled.

  In pneumatic radial tires, which are typical examples of rubber articles, steel cords made of twisted steel wires with brass plating on the belt or carcass or consisting of a single wire of steel wire are covered with rubber. Applied, and mainly reinforced with steel cords. In order to use the steel cord as a tire reinforcing material, it is necessary to securely bond the steel cord to the covering rubber. For this purpose, the peripheral surface of the wire constituting the steel cord is subjected to brass plating. Yes.

  By the way, since the use conditions of pneumatic tires are severe, the cord (rubber initial adhesion) between the cord and rubber when finished is good, as well as the cord due to temperature rise and moisture penetration during subsequent use. It is desired to avoid as much as possible the decrease in durability adhesion.

  For this brass plating, in order to ensure adhesion to rubber, it has been studied to optimize the ratio of copper and zinc in the brass and the plating thickness, and certain knowledge about these has been established.

  By applying brass plating optimized based on such knowledge to the wire constituting the steel cord, the initial adhesion to rubber is improved, but the durable adhesion is still insufficient.

In this regard, Patent Document 1 proposes a technique that also improves the durability adhesion property by defining the surface roughness of the wire peripheral surface that forms a boundary with the brass plating.
JP-A-6-49783

Although the initial adhesiveness and the durable adhesiveness were uniformly improved by the technique proposed in Patent Document 1, with the recent improvement in the durability performance of the tire, the durable adhesiveness between the wire and the rubber as the reinforcing material There is a need to further improve the above.
Accordingly, an object of the present invention is to pioneer ways to further improve the durable adhesion of steel wires to rubber.

  Now, it is generally known that the plating surface applied to the wire is significantly different from the composition of the plating. For example, as schematically shown in FIG. 1, the surface of the plating is heated even when wet wire drawing is performed, so that the plating outermost surface is made of zinc as a plating component. An oxide film also exists, and a reaction product (lubricant film) with the lubricant component also exists. Therefore, in order to aim at further improvement of durable adhesiveness, it is guessed that the property and form of the plating outermost surface are involved.

  Under such circumstances, the inventors have intensively studied the factors affecting the adhesion, and the lubricant film exists between the wire and the rubber and affects the adhesion. If there is a part containing phosphate partially, the brass surface will be almost exposed if it does not exist as a coating layer, and the adhesion reaction proceeds quickly and uniformly. It has been found that the reaction occurs simultaneously at any place as well as the initial adhesiveness, and as a result of forming a uniform adhesive layer, the durable adhesiveness is also greatly improved.

  That is, in order to solve the above-mentioned problems, various components in the lubricating liquid during wet wire drawing are changed, and the surface area reduction rate and die material selection for each die, especially the wire surface mechanical cutting action during wire drawing. In various studies, such as the morphological characteristics of the brass plating surface, specifically, to the extent that the lubricating coating layer is not formed, or even if generated, the lubricating coating layer is removed using the cutting action of the final wire drawing die, for example. It has been found that the durability adhesion as well as the initial adhesion can be surely improved by making the polycrystalline brass appear on the surface to cause certain ultra-fine irregularities.

  Based on this knowledge, the inventors have made the surface of the steel wire of the steel radial tire ultra-fine, that is, brass plating so as to reflect the size that the polycrystalline body of the brass has shrunk according to the reduction in drawing. The present invention has been completed by making the surface. The gist of the present invention is as follows.

(1) A steel wire for reinforcing rubber articles, characterized in that it is a steel wire that is subjected to brass plating on the peripheral surface of the wire, and the surface roughness of the brass plating is 4 nmRa or more and 12 nmRa or less.

(2) The steel wire for reinforcing rubber articles according to (1), wherein the brass plating layer has an average thickness of 0.15 to 0.35 μm.

(3) The steel wire for reinforcing rubber articles according to (1) or (2) above, wherein the ratio of copper to the total amount of copper and zinc in the brass plating layer is 50 to 70 mass%.

(4) The steel wire for reinforcing rubber articles according to (1), (2) or (3), wherein the wire has a diameter of 0.4 mm or less.

(5) A steel cord for reinforcing rubber articles formed by twisting a plurality of wires according to any one of (1) to (4).

  According to the present invention, by restricting the surface roughness of the brass plating and causing the appearance of brass polycrystal on the surface, an adhesion reaction occurs uniformly and simultaneously, and a uniform adhesive layer is formed. Can be improved.

  By the way, the brass plating layer applied to the surface of the wire has an average thickness of about 200 nm, but it never forms a uniform thickness layer, and it is inevitable to have a thickness distribution. . Conventionally, obtaining a uniform plating layer by suppressing the surface unevenness in the μm range and reducing the thickness distribution has been considered effective for adhesion to rubber.

  However, according to the research by the inventors, it is natural to ensure such uniformity, and it is important to control the surface morphology in a finer form, that is, in the range of nm. It came to be suggested from. That is, no matter how uniform the plating layer is, if the surface is covered with a lubricating film with a thickness of several nm, the adhesion reaction is inhibited, and even if the amount of phosphoric acid forming the lubricating film is reduced, If the lubricating coating is partially present, the adhesion reaction proceeds non-uniformly, and the adhesive layer is also formed non-uniformly and non-uniformly. As a result, when an active species that degrades the adhesive layer such as water or oxygen enters from the outside, it is expected that a local battery is formed between the plating and the adhesive layer, thereby promoting the corrosion reaction. is there.

  Therefore, it is important to create a state in which the plating surface has no lubricant-derived film and consists only of the brass plating component (even if the outermost surface is covered with zinc oxide), that is, to bring out the true appearance of brass. Become. This means that the crystal grain size of brass that has been micronized by wire drawing is exposed on the surface, and a certain fine roughness appears on the surface. If the plating surface is completely covered with a lubricating coating, the surface does not show fine irregularities, and the adhesion reaction is delayed. On the other hand, if the lubricating film partially remains, the surface roughness is apparently increased, and a non-uniform adhesion reaction proceeds.

That is, it is important to adjust the surface roughness of the brass plating to 4 nmRa to 12 nmRa, preferably 6 nmRa to 10 nmRa.
This is because if the thickness is less than 4 nmRa, the lubricating coating forms a continuous layer that can be regarded as a complete film. As a result, the plating surface becomes smooth, the surface loses conductivity, and the adhesion reaction, which is an ionic reaction, is difficult to proceed. Under the conditions, sufficient initial adhesion cannot be secured.
On the other hand, if it exceeds 12 nmRa, the lubricating coating will be present discontinuously, and the adhesive layer will develop unevenly, resulting in a decrease in durability adhesion.

Next, a method for adjusting the surface roughness of the brass plating to 4 nmRa or more and 12 nmRa or less will be specifically described below.
As shown in FIG. 1, there is a ZnO layer under the lubricating film on the plating surface, but this ZnO layer is an oxide, but has conductivity, so an ultra-thin lubricating film is being drawn during the wire drawing process. If it is removed after wire drawing, the roughness of the plating surface can be controlled within the above-described range, and as a result of ensuring electrical conductivity, the interfacial reaction is activated.

  Here, although an extreme pressure lubricating liquid that completely removes the lubricating film generated at the time of wire drawing has not yet been found, the formation of the lubricating film can be suppressed by adjusting the components in the phosphoric acid based lubricating liquid. In addition, if a sintered diamond die is used for the final several passes in the final wire drawing step and the diamond cutting action or self-lubricating action is used, the lubricating coating on the plated surface of the wire can be removed.

  In other words, in the latter half of the final wire drawing using a phosphoric acid extreme pressure lubricant, the wire diameter is reduced and strong processing is performed to increase heat generation on the surface. In addition, oxidation tends to proceed, and the control of conditions in this process is the most important point. As specific conditions, in addition to controlling the amount of zinc ions and phosphate ions in the lubricating liquid, effective control means is to use sintered diamond for the die and effectively utilize the cutting action. In particular, an appropriate selection of the area reduction ratio of the final several passes and the material of the die, that is, a fine sintered diamond die, is an extremely effective means for preventing the lubricant film from remaining.

  Furthermore, the roughness of the plating outermost surface can also be controlled by mechanically polishing the surface of the wire drawn under normal conditions with, for example, a cotton cloth impregnated with acetone.

  The plated surface treated in this way has a surface roughness with ultra-fine irregularities and never becomes a smooth surface. That is, it is presumed that the brass crystal is refined as the surface is reduced during wire drawing, but exhibits an ultrafine roughness corresponding to the refinement. As a typical example, FIG. 2 shows an ultra-high resolution SEM image of a wire surface without a lubricating coating, and FIG. 2 shows a three-dimensional concavo-convex image thereof. For comparison, FIG. 3 shows an ultra-high resolution SEM image of a wire surface manufactured under normal conditions, and FIG. 4 shows a three-dimensional concavo-convex image thereof.

  In addition, such adjustment of the plating surface was caused by the fine surface of the brass because the plating layer was damaged when the lubricating film layer was removed in the method of dissolving the surface using acid or alkali. It is impossible to create an ultra-fine surface, and no improvement in adhesion is realized.

  Moreover, it is preferable that the average thickness of a plating layer is 0.15-0.35 micrometer. That is, when the average thickness of the plating layer is less than 0.15 μm, the portion where the iron base is exposed is increased and the fatigue resistance is lowered, and the initial adhesiveness is also inhibited. On the other hand, if it exceeds 0.35 μm, the adhesion reaction proceeds excessively due to heat during use of the rubber article, and only brittle adhesion can be obtained.

  Furthermore, it is preferable that the ratio of copper to the total amount of copper and zinc in the brass plating layer is 50 to 70 mass%. First, when the ratio of copper to the total amount of copper and zinc in the entire plating layer is less than 50 mass%, the wire drawing property deteriorates and the productivity due to disconnection is hindered, making mass production difficult. On the other hand, if it exceeds 70 mass%, the adhesion stability under high moisture in the summer will deteriorate.

  The diameter of the wire is advantageously 0.40 mm or less. This is because if the thickness exceeds 0.40 mm, the used rubber article is repeatedly strained under bending deformation, the surface strain becomes large and is likely to cause buckling, which also deteriorates fatigue resistance. is there.

  A treat material in which a steel cord twisted with a wire having plating characteristics according to the present invention and a cord produced under normal conditions is coated with an appropriate rubber composition (A) is produced, and after vulcanization treatment at 160 ° C. for 7 minutes The rubber adhesion was measured in accordance with the rubber adhesion test method defined in JIS G3510 (1992).

In addition, durable adhesiveness is deteriorated by treating the treating material after vulcanization treatment at 160 ° C for 15 minutes, leaving it in an atmosphere of humidity (100%) and temperature: 75 ° C in the presence of air (oxygen). The rubber adhesive test was conducted to investigate the number of days until the adhesiveness was reduced to half, and the result of Comparative Example 1 was expressed as an index when the result was 100.
The above evaluation results are shown in Table 1.

  The roughness of the wire surface was measured in a contact atomic force measurement mode (AFM mode) of an ultra-high resolution three-dimensional scanning electron microscope or scanning probe microscope (SPM) equipped with a field emission gun.

It is a schematic diagram which shows the structure of brass plating. It is a photograph which shows the ultrahigh resolution SEM image of the wire surface without a lubricating film. It is a figure which shows the three-dimensional uneven | corrugated image of the wire surface without a lubricating film. It is a photograph which shows the ultrahigh resolution SEM image of the wire surface manufactured on normal conditions. It is a figure which shows the three-dimensional uneven | corrugated image of the wire surface manufactured on normal conditions.

Claims (5)

  A steel wire for reinforcing rubber articles, characterized in that it is a steel wire that has been subjected to brass plating on the peripheral surface of the wire, and the surface roughness of the brass plating is 4 nmRa or more and 12 nmRa or less.   The steel wire for reinforcing rubber articles according to claim 1, wherein the brass plating layer has an average thickness of 0.15 to 0.35 µm.   The steel wire for reinforcing rubber articles according to claim 1 or 2, wherein the ratio of copper to the total amount of copper and zinc in the brass plating layer is 50 to 70 mass%.   4. The steel wire for reinforcing rubber articles according to claim 1, wherein the diameter of the wire is 0.4 mm or less.   A steel cord for reinforcing rubber articles, comprising a plurality of wires according to any one of claims 1 to 4 twisted together.