JP2003342883A - Steel wire for reinforcing rubber material, steel cord for reinforcing rubber material, and tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel wire plated with brass for constituting a steel cord, capable of imparting an excellent adhering property between the steel cord and covering rubber, especially improving both initial adhesion and adhesion after its deterioration as the adhering properties, and further improving corrosion resistance of the wire. <P>SOLUTION: The steel wire plated with brass on its circumferential surface is provided by setting ≤5 atomic % amount of phosphorus contained as an oxide in a domain until 5 nm depth from the brass plated surface to its inside in wire radial direction, ≤(-)0.2 [atomic %/(nm)<SP>2</SP>] factor of a quadric variable term in a quadric function on approximating the wire radial directional distribution of the ratio of number of atoms of copper to the total number of atoms of copper, zinc, carbon and oxygen in a domain until 6 nm depth from the brass plated surface to its inside in the wire radial direction to the quadric function, and further 20-60 mg/m<SP>2</SP>amount of ZnO in a surface layer domain until 10 nm depth from the brass-plated surface to its inside in the wire radial direction. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel wire and a steel cord used as a reinforcing material for rubber articles such as pneumatic tires and industrial belts, and more particularly to a steel wire and a steel cord having excellent adhesion to rubber. It is a thing.

[0002]

2. Description of the Related Art A pneumatic radial tire, which is a typical example of a rubber article, has a belt or carcass formed by twisting a plurality of brass-plated steel filaments or a steel cord made of a single wire of steel filament. It is coated with rubber and is mainly reinforced with steel cords. And, in order to utilize the steel cord as a reinforcing material of the tire, it is necessary to securely bond it to the rubber covering the steel cord,
Therefore, brass plating is applied to the peripheral surface of the filaments that make up the steel cord.

Regarding this brass plating, in order to secure adhesiveness with rubber, optimization of the ratio of copper and zinc in the brass and the plating thickness have been studied, and certain knowledge about these has been established. .

It is generally known that the surface of brass plating is significantly different from the composition of brass plating. That is, the brass-plated surface is exposed to a high temperature in the wire-drawing process in spite of wet drawing, and as a result, a reaction product with a lubricant component is generated on the outermost surface of the plating, and further zinc oxidation which is a component of plating is oxidized. It also produces a film.

Various studies have hitherto been made on various relations between the components on the plated surface and the rubber adhesion by various studies. For example, in International Publication WO9723311, the relationship between the amount of phosphoric acid and the amount of zinc oxide has been studied from the viewpoint of improving the initial adhesiveness of the wire, but it is only a technique related to improving the initial adhesiveness.

However, the sulfur-containing adhesion promoter added in this manner is effective in promoting the adhesion reaction, but rubber and cord composites of tires and the like are exposed to water, oxygen (or air) under a hot environment. It does not contribute to the suppression of the deterioration of adhesion when exposed to the active gas inside) for a long period of time, and may accelerate the adhesion deterioration in some cases. Therefore, when tires are used in a relatively harsh environment where a relatively large amount of water and air coexist and are thermally harsh, such as in hot and humid areas such as the subtropical regions of Southeast Asia, in addition to improving the initial adhesion, It is also important to improve the so-called post-deterioration adhesiveness such as the resistance to moist heat, but it was difficult to achieve both initial adhesiveness and post-deteriorating adhesiveness.

[0007] During use of the tire, reactive components such as water and oxygen from the outside gradually enter, so it is said that the cord embedded inside the tire is bonded to rubber. However, the corrosion reaction is always proceeding, albeit gradually. Therefore, as the tire runs, the adhesion of the cord deteriorates, and the corrosion fatigue of the wire also decreases.As a result, when an extreme strain input occurs, the adhesive breaks and the wire breaks at the same time. The wire jumped out of the cord, impeding the durability of the cord.
Since the wire bending phenomenon reduces the durability of the cord, it is important to improve the bending property. Then, in order to improve the bending property of the wire, improving the corrosion fatigue resistance of the wire is an effective means. In particular, when used in a moisture environment, when the tire is repeatedly subjected to bending deformation, the corrosion fatigue resistance of the wire is important as the residual durability.

[0008]

Therefore, the present invention is
A method of imparting excellent adhesion between the steel cord and the coated rubber, in particular, improving both the initial adhesion and the adhesion after deterioration as the adhesion, and further improving the corrosion fatigue resistance of the wire, The purpose is to establish the brass plating applied to the wires that make up the cord.

[0009]

Means for Solving the Problems The inventors of the present invention have made extensive studies as to a method for improving the corrosion fatigue resistance of a wire. As a result, it has been found that the ZnO content on the plated surface and the corrosion fatigue resistance are closely related. Heading, it came to complete this invention.

That is, in order to solve the above-mentioned problems, the inventors of the present invention changed various components in the lubricating liquid during wet drawing, and changed each die based on the degree of thermal diffusion of the wire before drawing. While considering various factors such as reduction of surface area and selection of die material, adhesion was improved by controlling the amount of phosphoric acid on the plating surface and the distribution of copper in the depth direction. It has been found that controlling the amount of ZnO is effective in improving the corrosion fatigue resistance of the cord.

Further, ZnO on the plated surface does not depend so much on the degree of oxidation of the intermediate wire before drawing and the zinc concentration of brass, and is mainly determined during drawing, especially by the surface-reducing method after the final drawing. I was able to understand that. This is considered to be because the wire diameter of the wire becomes thin in the latter stage of the final wire drawing, and strong processing is performed, so the heat generated on the wire surface is large and the oxidation of the plating surface easily progresses. The ZnO amount control on the plating surface became possible for the first time by setting the conditions in the process. For example, one of the effective means is to use sintered diamond in a die at the same time as controlling the zinc ion amount and the phosphate ion amount in the plating solution.

[0012] Based on the above knowledge, a method that can solve the above problems is under consideration from a thorough examination of how to incorporate the ZnO amount on the plating surface, which is one of the plating characteristics of the steel wire used for steel radial tires. I came to find out.

That is, the gist of the present invention is as follows. (1) A steel wire having a brass surface plated with brass, wherein the amount of phosphorus contained as an oxide is 1.5 atomic% in a region from the surface of the brass plating to a depth of 5 nm inward in the radial direction of the wire. The distribution of the atomic ratio of copper to the total atomic number of copper, zinc, carbon, and oxygen in the radial direction of the wire in the area from the surface of the brass plating to the depth of 6 nm inward in the radial direction of the wire is approximated to a quadratic function. Then, the coefficient in the quadratic variable term of the quadratic function is −0.2 [atomic% / (nm) ² ] or less, and further from the surface of the brass plating to the depth of 10 nm inward in the wire radial direction. The amount of ZnO in the surface layer region is
A steel wire for reinforcing a rubber article, characterized in that it is ²⁰ to 60 mg / m ² for reinforcing a rubber article.

(2) The average thickness of the brass plating layer is 0.13 to
The steel wire for reinforcing a rubber article according to (1) above, which has a thickness of 0.35 μm.

(3) The steel wire for reinforcing a rubber article 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 60 to 70% by weight. .

(4) The steel wire for reinforcing rubber articles as described in (1), (2) or (3) above, wherein the diameter of the wire is 0.40 mm or less.

(5) A steel cord for reinforcing a rubber article, comprising a plurality of the wires according to any one of the above (1) to (4) twisted together.

(6) In a tire having a carcass extending in a toroidal shape between a pair of bead portions as a skeleton and having a belt radially outside the carcass, one or both of the carcass and the belt have the above (1) ) To (4) or the steel cord according to (5) above is applied to the tire.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION A steel wire is generally manufactured by drawing a wire having a diameter of, for example, about 5 mm. Of course, a lubricant is used in this manufacturing process, but in the final wire drawing step, the wire is thinned using a die of about 20 passes arranged in the liquid lubricant. In this final wire drawing process, extreme pressure is generated between the cord and the die, and the temperature becomes very high. Therefore, in order to ensure lubricity under extreme pressure and high temperature, a lubricant based on phosphoric acid is used. It is customary to use.

This lubricant reacts with the wire surface during wire drawing to form a lubricating film layer, that is, a phosphoric acid compound layer,
The input is eased under extreme pressure and high temperature conditions, and wire mass production is realized. Therefore, in the manufacturing process, it is inevitable that phosphoric acid is taken in during the plating of the wire.

[0021] Therefore, the inventors of the present invention have found that copper in brass plating containing phosphoric acid diffuses to the rubber side to form CuxS for adhesion, and phosphoric acid on the plating side particularly adheres to rubber. The mechanism of inhibition was eagerly investigated.
And it is not the phosphoric acid taken into the entire plating that hinders the adhesion with the rubber, but the very surface layer of the plating that comes into contact with the rubber, specifically, the surface layer from the surface of the plating to the depth of 5 nm inward in the radial direction of the wire. It was newly found that it is limited to the phosphoric acid compound existing in the region. That is, the essence of improving the rubber adhesiveness is that the phosphate compound does not remain in the surface layer region of the wire after the final wire drawing,
It has been clarified that the problem cannot be solved by controlling the amount of phosphoric acid or phosphorus in the entire plating layer, for example, the amount of phosphoric acid or phosphorus as measured by dissolving with dilute hydrochloric acid as in the conventional case.

The process of obtaining the above knowledge will be described below. First, in the wire drawing step for obtaining the wire, the rubber adhesion of the wire manufactured by variously changing the pass schedule, the material of the die, the component composition of the lubricant, the aging condition or the liquid temperature, etc. was evaluated. However, it became clear that rubber adhesion differs depending on the wire. Next, as a result of investigating the conditions common to the wire having good rubber adhesiveness, it was found that the content of copper and phosphorus in the plating layer, which is a conventional general index for rubber adhesiveness, cannot be completely covered. Therefore, as a result of diligent research into the factors that affect the rubber adhesiveness, it was found that as an oxide in the very surface region of the plating layer, specifically, in the surface region from the surface of the plating to a depth of 5 nm inward in the radial direction of the wire. It has been found that the amount of phosphorus contained correlates with rubber adhesion.

Here, the amount of phosphorus contained as an oxide in the surface layer region can be measured by X-ray photoelectron spectroscopy. That is, in the photoelectron escape depth region measured according to X-ray photoelectron spectroscopy, the number of atoms of all elements and the number of atoms of phosphorus in the oxide are detected, and oxidation is performed when the number of atoms of all elements is 100. Atomic% of phosphorus contained in the oxide in the region was expressed as an index of the number of phosphorus atoms in the substance. Note that the distinction between phosphorus as an oxide and other phosphorus can be made based on the chemical shift of the binding energy of P = p photoelectrons measured by the X-ray photoelectron spectrum of phosphorus atoms. Further, the surface layer region up to the depth of 5 nm can be recognized by the kinetic energy of electrons and the escape depth, which is shown in a general document on photoelectron spectroscopy of solids.

In the surface layer region, it is important to suppress the amount of phosphorus contained as an oxide to 1.5 atomic% or less. Because, as the amount of phosphorus increases beyond 1.5 atomic%, the adhesion speed with rubber becomes slower, and difficult operation such as strictly controlling the rubber composition is required to secure desired rubber adhesion. Moreover, the influence of the water content in the rubber becomes large, and the rubber adhesiveness cannot be ensured in the winter manufacturing when the water content decreases. Then, by setting the amount of phosphorus to 1.5 atomic% or less, it becomes possible to stably obtain excellent rubber adhesiveness regardless of the water content in the rubber.

Next, regarding the post-deterioration adhesiveness, for example, when the rubber article is used in a high temperature and humid environment, the adhesiveness between the cord and the rubber deteriorates because the CuxS involved in the initial adhesion is deteriorated.
However, it is caused by the fact that it is decomposed by water and oxygen, and that zinc in the plating reacts with water and oxygen to proceed with dezincification. Therefore, in order to improve the adhesiveness after deterioration, it is effective that the initial adhesive layer is uniform and dense, and that the plating composition is such that dezincification does not easily proceed. Specifically, as shown below, In addition, it is important to control the copper concentration distribution from the surface of the plating layer to the depth direction.

First, the copper concentration distribution in the region from the surface of plating to the depth of 6 nm inward in the radial direction of the wire is regulated. Here, the range that regulates the copper concentration distribution is defined as a region from the plating surface to a depth of 6 nm, because the region is copper in the plating that controls the uniformity and denseness of the adhesive layer,
That is, it is a Cu diffusible region necessary for forming CuxS.

When the distribution in the wire radial direction of the ratio of the number of atoms of copper to the total number of atoms of copper, zinc, carbon and oxygen in the region up to the depth of 6 nm is approximated to a quadratic function, the quadratic function is obtained. The coefficient in the quadratic variable term of the function −
It is important to set it to 0.2 [atomic% / (nm) ² ] or less.

That is, as shown in FIG. 1, an example of the distribution of the atomic ratio of copper to the total atomic number of copper, zinc, carbon and oxygen in the radial direction of the wire is shown in FIG. In the region up to this point, for example, a line segment L connecting the measured values of the copper concentration at every 1 nm depth is taken as a quadratic function, and the line segment L is quadratic equation y = a (x + b / 2a) ² -{(b ² -4ac) / 4
a}, the coefficient a in the quadratic variable term is −
0.2 [atomic% / (nm) ² ] or less,
Control the concentration distribution of copper.

Now, as shown as a comparative example in FIG. 1, in the conventional plating layer, the copper concentration distribution increases linearly from the plating surface to the inside (the coefficient of the quadratic variable term approaches 0). However, in the plating layer in which the copper concentration distribution is regulated according to the present invention, the coefficient in the quadratic variable term of the quadratic function is negative, that is, the copper concentration is inclined downward toward the inside of the plating. It is characterized by a sharp increase. The concentration distribution shown in FIG. 1 shows the result of quantitative determination of copper atoms at each depth while repeating ion etching from the plating surface to the inside.

The reason why the adhesion after deterioration is improved by providing such a copper concentration distribution to the surface layer of plating is C
It is presumed that, when the uxS is formed, the copper concentration inside the plating is higher than that of the surface layer, so that the copper on the rubber side easily diffuses. The higher the absolute value of copper, the better the adhesiveness after deterioration does not always become. Above all,
The coefficient of the quadratic variable term is -0.2 [atomic% /
(Nm) ² ] or less has the effect of rapidly improving the wet heat resistance.

By the way, although the surface of the wire is plated, the plated layer has a thickness of at most about 200 nm on average, so that the presence of plating spots is unavoidable, and electrochemically It can be said that the surface is extremely easy to form a local battery. Therefore, in order to improve the corrosion fatigue resistance of the wire, it is an important point to pre-treat the wire in order to make its surface inactive.

As such a chemically stable layer, it is conceivable to increase the amount of the lubricating film layer formed during wire drawing and to increase the thickness of the ZnO layer, but the lubricating film layer cannot be made so thick in manufacturing. , Its effect is less. On the other hand, since the ZnO layer is an original component of the plating, the reaction proceeds to a relatively deep layer, and therefore it is presumed that the effect of preventing corrosion from the external active component is great.

As a means for simply thickening the ZnO layer on the plating surface, a direction in which the wire surface temperature is high due to friction during drawing in a lubricant gives a desirable result.
This also causes a disconnection. Therefore, a detailed investigation of the relationship between ZnO and corrosion fatigue resistance revealed that instead of simply thickening the ZnO layer, optimizing the ZnO amount in the plating surface layer, especially up to about 10 nm depth of the final wire drawing wire. It has been found that controlling the amount of ZnO present in the surface layer is effective.

That is, ZnO in the surface layer region from the surface of plating to the depth of 10 nm inward in the radial direction of the wire
It is important to control the amount in the range of ²⁰ to 60 mg / m ² . This is because, as shown in FIG. 2, the relationship between the above ZnO amount and the residual fatigue limit strain of the wire is 20 mg / m 2.
^If it is less than ² , the fatigue resistance of the wire cannot be improved, while 60 mg
This is because if it exceeds / m ² , the effect of improving the fatigue resistance of the wire is saturated and more wire breakage occurs during wire drawing. The definition of the residual fatigue limit strain is as described later.

The average thickness of the plating layer is 0.13 to 0.35 μm.
It is preferably m. That is, when the average thickness of the plating layer is less than 0.13 μm, the exposed portion of the iron material increases and the initial adhesiveness is hindered. On the other hand, when it exceeds 0.35 μm, the adhesive reaction proceeds excessively due to heat during use of the rubber article. This is because only weak bonds can be obtained.

Further, the ratio of copper to the total amount of copper and zinc in the brass plating layer is preferably 60 to 70% by weight. First, when the ratio of copper to the total amount of copper and zinc in the entire plating layer is less than 60% by weight, wire drawability deteriorates, productivity due to wire breakage is hindered, and mass production becomes difficult. Copper content
It becomes difficult to control at 15 atomic% or more. On the other hand, if it exceeds 70% by weight, it becomes difficult to control the amount of ZnO no matter how the various conditions during wire drawing are controlled.

Advantageously, the wire diameter is 0.40 mm or less. Because, when it exceeds 0.40 mm, when the used rubber article is repeatedly strained under bending deformation, the surface strain becomes large and buckling easily occurs, which also deteriorates fatigue resistance. is there.

By twisting a plurality of the above-mentioned wires, a steel cord suitable for a rubber article, especially a carcass for tires or a reinforcing material for a belt can be obtained. In particular, when it is applied to a belt for a passenger car tire, especially a passenger car radial tire, the vulcanization time of the tire can be significantly shortened by increasing the adhesion speed with rubber. On the other hand, when applied to the carcass of truck and bus tires, especially radial tires for trucks and buses, the adhesion speed with the rubber at the bead portion becomes faster, so the vulcanization time is shortened and the bead portion durability is improved. It is possible to improve.

When wire drawing is performed under the above-mentioned extreme pressure and high temperature conditions, the temperature between the die and the wire is high by several hundreds of degrees, so that the copper during plating re-diffuses, resulting in a depth direction of plating. The concentration distribution of copper is easily changed. Therefore, since it is difficult to regulate the copper concentration distribution of the plating surface layer as described above,
It is advantageous to manufacture the wire in the following way. Further, in order to control the amount of phosphorus contained in the oxide in the surface layer region to 1.5 atomic% or less and further control the amount of ZnO in the surface layer region for plating, the following manufacturing process is recommended.

That is, the pass schedule for wire drawing,
Shape and angle of entrance and approach of dice,
The amount of phosphorus contained in the oxide in the surface region can be suppressed and the copper concentration distribution can be controlled by adjusting the material of the die and the composition of the lubricant alone or in combination. In particular, in the final wire drawing process, a lubricant containing an extreme pressure additive is used in the same manner as usual, and it is excellent in the final pass of the approximately 20-pass die of the final wire drawing process or the number of subsequent stages including the final pass. It is extremely effective to perform wire drawing by applying a die made of a material having excellent machinability in addition to self-lubricating property, for example, a sintered diamond die.

[0041]

[Examples] With respect to the steel cords manufactured in accordance with the specifications shown in Table 1, the rubber adhesion test was conducted in accordance with the rubber adhesion test method defined by the reference of JIS G3510 (1992). The post-deterioration adhesiveness was evaluated by allowing it to stand in an atmosphere of humidity (95%) and temperature (75 ° C.) for 3 weeks in the presence of air (oxygen), and then performing the above rubber adhesiveness test. The results are also shown in Table 1. The rubber composition used in this adhesion test is as shown in Table 2.

Further, a steel cord was adopted as a belt for passenger cars and allowed to run for 60,000 km in a market environment until it was completely worn. Then, the cord was taken out from the belt and the residual fatigue limit strain due to the rotational bending of the cord was measured. The residual fatigue limit strain is a strain at which the wire in the cord does not break after 1 million rotations, and the cord is subjected to rotational bending fatigue,
It is obtained by experimentally determining that the wire in the cord is not broken.

Further, in order to investigate the relation with the cord breakability, after the tire was run for 1000 km on the drum with a slip angle (5 °) after the running, the tire was dissected and the wire breakage ratio in the cord was measured. did.

The amount of ZnO was determined by sampling 5 g of wire and adding 6 g of it in 10 ml of 1.2N aqueous hydrochloric acid at room temperature.
The ZnO on the surface was dissolved by immersing it for 0 second, and the solute Zn in this solution was quantified by inductively coupled emission plasma analysis, and based on the obtained results, it was converted to the amount attached per wire surface area.

The amount of phosphorus in the surface layer region of the plating layer was determined by X-ray photoelectron spectroscopy in an area of 20 to 30 μmφ so as not to be affected by the curvature of the wire. Existing atoms, ie C, C
The number of atoms of u, Zn, O, P and N was measured, and C, C
When the total number of atoms of u, Zn, O, P and N was 100, the ratio of the number of P atoms was calculated. The number of atoms in each atom is
C: C _1S , O: O _1S , P: P _2P , Cu: Cu _{2p3 / 2} , Z
The photoelectron counts of n: Zn _{2p3 / 2} and N: N _1S were used, and the values were corrected with the respective sensitivity coefficients. For example, the number of detected atoms [P] of phosphorus can be calculated by the following formula. [P] = F _p (sensitivity coefficient of P _2p ) × (P per fixed time
_2p photoelectron count) Then, if the number of detected atoms is similarly calculated for other atoms, the relative atomic% of phosphorus can be calculated from these results as P% = {[P] / ([Cu] + [Zn] + [C] ＋ [O] ＋ [N] ＋ [P]
)} × 100.

When the surface of the wire before analysis is covered with oil or the like or is contaminated with an organic substance, it is washed with an appropriate solvent, and if necessary, the surface of the wire is not so modified as to be mild. Perform dry cleaning.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

According to the present invention, the amount of phosphorus contained as an oxide in the surface region of brass plating applied to a wire forming a steel cord is suppressed, and the concentration distribution of copper in the depth direction is regulated. Further, by controlling the amount of ZnO, not only excellent adhesiveness with the coating rubber with reduced or no addition of the adhesion promoter, that is, initial adhesiveness, but also adhesiveness after deterioration is ensured and corrosion resistance is ensured. It is possible to improve fatigue.

[Brief description of drawings]

FIG. 1 is a graph showing a copper concentration distribution in a depth direction of a plating layer.

FIG. 2 is a graph showing the relationship between the amount of ZnO in the plating layer and the residual fatigue limit strain.

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Claims (6)

[Claims] 1. A steel wire in which the peripheral surface of the wire is brass-plated, wherein the amount of phosphorus contained as an oxide is 1.5 in a region from the surface of the brass plating to a depth of 5 nm radially inward of the wire. Atomic% or less, and 6 nm from the surface of brass plating inward in the radial direction
When the wire radial distribution of the ratio of the number of copper atoms to the total number of atoms of copper, zinc, carbon and oxygen in the region up to the depth of is approximated to a quadratic function, the quadratic variable term of the quadratic function is obtained. Coefficient is -0.2 [atomic% / (n
m) ² ] or less, and further, the ZnO amount in the surface layer region from the surface of the brass plating to the depth of 10 nm inward in the radial direction of the wire is 20 to 60 mg / m ² for reinforcing rubber articles. Steel wire for reinforcing rubber articles. 2. The brass plating layer has an average thickness of 0.13 to 0.35.
The steel wire for reinforcing a rubber article according to claim 1, wherein the steel wire is μm. 3. The steel wire for reinforcing a rubber article according to claim 1, wherein a ratio of copper to the total amount of copper and zinc in the brass plating layer is 60 to 70% by weight. 4. The steel wire for reinforcing a rubber article according to claim 1, 2 or 3, wherein the diameter of the wire is 0.40 mm or less. 5. A steel cord for reinforcing a rubber article, comprising a plurality of the wires according to claim 1 twisted together. 6. A tire having a carcass extending in a toroidal shape between a pair of bead portions as a skeleton and having a belt radially outside the carcass, wherein either or both of the carcass and the belt are provided. A steel wire to which the steel wire according to claim 4 or the steel cord according to claim 5 is applied.