JP2020186476A - Metal wire for rubber reinforcement, and method for producing metal wire for rubber reinforcement - Google Patents

Abstract

To provide a technique capable of improving strength characteristics of an adhesive interface between a metal wire for rubber reinforcement and rubber and improving durability of rubber by suppressing oxidative deterioration of the rubber.SOLUTION: There is provided a metal wire 1 for rubber reinforcement in which a brass plating layer containing copper and zinc is provided on a surface of the wire. Cobalt is contained in the surface layer of the brass plating layer 30b, and the cobalt concentration on the surface of the brass plating layer 30b is set to 3 at% or more and 7 at% or less. Thus, it is not necessary to preliminarily contain cobalt in the rubber, and deterioration of the rubber due to oxidation of cobalt can be suppressed.SELECTED DRAWING: Figure 3

Description

The present invention relates to a metal wire for reinforcing rubber such as a steel cord used as a reinforcing material for rubber such as a tire, and a method for manufacturing the same.

Conventionally, steel radial tires have used brass-plated steel cords for belts and carcass body plies to reinforce rubber. The steel cord is coated with brass plating (Cu-Zn alloy), and the interface reaction between brass and rubber occurs during rubber vulcanization, which strengthens the adhesion between brass and rubber, and as a result, the tire is reinforced. .. As described above, the strength characteristic of the adhesive interface between the steel cord and the rubber is an important factor in determining the life of the tire.

With respect to this technique, a layer having a first metal coating layer and a second metal coating layer, the second layer covering at least a part of the first layer, and two bonding layers containing at least one non-metal component. The invention relating to the steel substrate existing between the two is known (see Patent Document 1).

Here, in order to improve the strength characteristics of the adhesive interface between the steel cord and the rubber, it is necessary to optimize the rubber component and the metal component constituting the plating. For example, in the vulcanization production of tires, it is known to add Co salt to rubber in order to promote the adhesion reaction between the steel cord and the rubber. Regarding this technology, it is a rubber cord composite in which rubber is vulcanized and bonded to a metal cord composed of a plated wire having a brass plating layer provided on the surface of the wire before plating and the rubber and the brass plating layer. An invention having an adhesion reaction layer in which sulfur and copper are crosslinked with each other is known (see Patent Document 2).

In the present invention, the average thickness of the adhesive reaction layer is 50 nm in a moist heat-deteriorated state after the rubber is calcified and bonded and held in an atmosphere of a temperature of 50 to 100 ° C. and a humidity of 60 to 100% for 1 hour to 20 days. The fractal dimension of the interface between the adhesive reaction layer and the rubber is in the range of 1.001 to 1.300, and the brass plating layer is 0.1 to 5.0 weight based on 100 parts by weight of the plating. A portion of cobalt or 1.0 to 10.0 parts by weight of nickel is included.

Further, the following invention is known regarding a rubber-steel cord composite composed of a rubber composition and a brass-plated steel filament or a steel cord formed by twisting them (see Patent Document 3). .. In the present invention, the rubber composition comprises 100 parts by weight of a rubber component and 0.1 parts by weight or less of a cobalt salt as a cobalt metal. Further, the brass-plated steel filament or the steel cord formed by twisting these is a filament radial direction from the peripheral surface of the steel filament having a copper concentration of 15 to 45 atomic% on the peripheral surface. The surface region to a depth of 15 nm on the inside contains at least one of a cobalt (Co) atom and a nickel (Ni) atom.

However, the addition of Co salt oxidizes the vulcanized rubber and causes deterioration, which also causes a decrease in tire durability. In addition, Co salt is expensive, and it is desired to reduce the amount of Co salt used.

Japanese Unexamined Patent Publication No. 1-294873 JP-A-2007-186840 JP-A-2002-13085

An object of the present invention is to solve the above problems, and it is possible to improve the strength characteristics of the adhesive interface between the rubber reinforcing metal wire and the rubber, and to suppress the deterioration due to the oxidation of the rubber to improve the durability of the rubber. It is to provide technology that can be improved.

The present invention for solving the above problems is a metal wire for rubber reinforcement provided with a brass plating layer containing copper and zinc on the surface thereof.
Cobalt is contained in the surface layer of the brass plating layer,
The rubber reinforcing metal wire is characterized in that the cobalt concentration on the surface of the brass plating layer is 3 atomic% or more and 7 atomic% or less.

In the present invention, cobalt is contained in the surface of the brass-plated layer provided on the surface of the rubber reinforcing metal wire at a concentration of 3 atomic% or more and 7 atomic% or less. According to this, when the rubber is reinforced with the metal wire, cobalt having an appropriate concentration can be present in the reaction layer formed between the rubber and the metal wire. As a result, it is not necessary to contain cobalt in the rubber before the reaction, and deterioration of the rubber due to the oxidation of cobalt can be suppressed.

Further, in the present invention, the cobalt may be contained in a region having a depth of 9 nm or less from the surface of the brass plating layer. By doing so, cobalt can be concentrated near the surface of the brass plating layer, and when the rubber is reinforced by the metal wire, the cobalt is reliably supplied to the rubber during the vulcanization reaction between the rubber and the metal wire. be able to.

Further, in the present invention, the copper concentration in the region from the surface of the brass plating layer to a depth of 9 nm may be 45 atomic% or more.

Here, the cobalt present in the brass plating layer is the sulfur (S) in the rubber and the copper (S) in the brass plating layer in the reaction layer between the rubber and the metal wire when the rubber is reinforced by the metal wire. Since the reaction of Cu) is inhibited, if the copper concentration in the surface layer of the brass plating layer is too low, the reaction between the rubber and the metal wire becomes poor, and it becomes difficult to obtain sufficient initial adhesive strength.

Therefore, in the present invention, the copper concentration in the region from the surface of the brass-plated layer of the metal wire to the depth of 9 nm is set to 45 atomic% or more. According to this, even if cobalt is contained in the surface layer of the brass plating layer, sulfur (S) in the rubber and copper (Cu) in the brass plating layer are separated in the reaction layer between the rubber and the metal wire. It can be sufficiently reacted and a sufficient initial adhesive strength can be obtained.

Further, in the present invention, the cobalt concentration in the entire brass plating layer may be 0.1% by weight or less. Here, when the cobalt concentration in the entire brass plating layer exceeds 0.1% by weight, the cobalt concentration in the reaction layer between the rubber and the metal wire may be too high, and the thickness of the reaction layer may become too thick. .. It is known to cause the destruction of the reaction layer.

On the other hand, according to the present invention, it is possible to appropriately maintain the cobalt concentration in the reaction layer between the rubber and the metal wire, suppress the excessive expansion of the thickness of the reaction layer, and cause the reaction layer to be destroyed. It can be suppressed.

Further, in the present invention, the cobalt atom may be contained in the surface layer of the brass plating layer by substitution plating. According to this, it is possible to control the concentration of cobalt atoms in the surface layer of the brass plating layer more precisely, and it is possible to more reliably improve the initial adhesion state between the rubber and the metal wire, and further. More reliably, the excessive expansion of the reaction layer due to cobalt can be suppressed.

Further, the present invention includes a multi-stage wire drawing process for drawing a wire rod and
In the stranded wire process of twisting a plurality of wire rods drawn in the wire drawing process,
Of the plurality of stages of wire drawing steps, a brass plating step of performing brass plating on the wire rod at least before the final wire drawing step, and
A cobalt plating step in which cobalt is contained in the surface layer of the brass plating layer formed in the brass plating step by replacement plating, and
Have,
The cobalt plating step may be a method for producing a metal wire for rubber reinforcement, which is carried out after all the wire drawing steps and the stranded wire steps.

According to this manufacturing method, it is possible to prevent the wire from being drawn or stranded while the cobalt plating is formed on the surface of the metal wire, and the relatively brittle cobalt plating is peeled off or cracked in these steps. Can be prevented.

In the present invention, the above means for solving the problem can be used in combination as much as possible.

According to the present invention, the strength characteristics of the adhesive interface between the rubber reinforcing metal wire and the rubber can be improved, and the oxidative deterioration of the rubber can be suppressed to improve the durability of the rubber.

It is a figure which shows the example of the sectional view of the steel cord in this invention. It is a figure which shows the example of the adhesive state between the conventional steel cord and rubber. It is a figure which shows the example of the adhesive state between a steel cord and rubber in this invention. It is a 2nd figure which shows the example of the adhesive state between a steel cord and rubber in this invention. It is a flowchart which shows the manufacturing process of the steel cord in this invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are examples for carrying out the present invention, and the present invention is not limited to the embodiments described below.

<Example 1>
FIG. 1 shows an example of a cross-sectional view of a tire reinforcing steel cord 1 (hereinafter, also simply referred to as a steel cord 1) in this embodiment. The steel cord 1 as shown in FIG. 1 has a structure in which a plurality of filaments 2 are twisted together, and further, the plurality of steel cords 1 are covered with a rubber material in a state of being aligned in parallel at predetermined intervals. This reinforces the tires. Therefore, the indispensable conditions for the steel cord 1 are excellent mechanical strength and good chemical adhesion to the rubber material.

Conventionally, brass plating is often formed on the surface of the filament 2 of the steel cord 1 in FIG. This brass plating is a binary alloy plating containing copper and zinc as main components. When the rubber material is reinforced by the steel cord 1, the plurality of steel cords 1 are aligned in parallel, and the front and back surfaces of the arranged steel cords 1 are covered with the rubber material and vulcanized and bonded. .. This "vulcanization adhesion" is carried out by the heat of vulcanization when vulcanizing and molding an unvulcanized raw tire in a mold. As the rubber material at that time, a diene rubber such as natural rubber, isoprene rubber, butadiene rubber, and styrene / butadiene rubber is suitable. This diene rubber is used alone or in a blend of two or more.

Here, in the vulcanization adhesion between the rubber material and the steel cord 1, from the viewpoint of the adhesion speed and the adhesion strength, a considerable proportion of Co salt or Ni salt is added to the rubber as an adhesion promoter and sulfur is high. May be mixed. However, although the adhesive promoter and sulfur added in this way are effective in promoting the adhesive reaction, they cause deterioration of the vulcanized rubber, that is, return to vulcanization, and also cause a decrease in tire durability.

<Dispersion of cobalt (Co) in rubber>
FIG. 2 is a diagram showing an adhesive state between the conventional steel cord 1 and rubber. More specifically, FIG. 2 shows the vicinity of the interface where the plating layer 10b is formed on the steel surface 10a of the surface layer portion 10 of the steel cord 1 and further adhered to the rubber 12. FIG. 2A shows an unvulcanized state, FIG. 2B shows an initial bonding state after the vulcanization reaction, and FIG. 2C shows a moist heat deterioration state after use. Further, in FIG. 2, the plating layer 10b is brass-plated (Cu—Zn), and in addition to sulfur (S), cobalt (Co) for improving adhesiveness is dispersed in the rubber 12.

After the vulcanization reaction of FIG. 2B, copper (Cu) and zinc (Zn) in the plating layer 10b are diffused to the rubber 12 side, and sulfur (S) in the rubber 12 is transferred to the plating layer 10b side. By diffusing, a reaction layer composed of a ZnO layer and a CuxS layer is formed. The rubber 12 and the steel cord 1 are firmly adhered to each other by this reaction layer. Then, after use as shown in FIG. 2C, copper (Cu) and zinc (Zn) in the plating layer 10b are further thermally diffused to the rubber 12 side. As a result, the thickness of the ZnO layer is increased, and the ZnS component is increased in the CuxS layer to increase the thickness. This increases the thickness of the reaction layer. On the other hand, in the rubber 12, the oxidation of cobalt (Co) causes deterioration of the rubber 12 and causes peeling of the rubber 12.

In this way, in the conventional structure in which the steel cord 1 is brass-plated and cobalt (Co) is dispersed and bonded in the rubber 12, the adhesive strength between the steel cord 1 and the rubber 12 is improved. .. However, on the other hand, there is a disadvantage that the deterioration of the rubber 12 due to the oxidation of cobalt (Co) is promoted, and the adhesive strength is weakened due to the enlargement of the reaction layer.

<Use of ternary plating>
Further, as the plating layer of the steel cord 1, cobalt (Co) is supplied from the plating layer to the rubber 12 side by performing ternary plating of copper, zinc and cobalt (Co). However, in this case, since the plating layer contains cobalt (Co), there is a problem that the wire drawing workability of the plating layer is inferior to that of the current brass plating. Further, since the plating layer contains excess cobalt (Co) than the amount that reacts with the rubber 12, there is also a problem that the rubber 12 deteriorates faster.

<Addition of cobalt (Co) plating layer>
In response to the above inconvenience, in this embodiment, the steel cord 1 is subjected to brass plating (Cu-Zn) and further formed with cobalt (Co) plating to form a brass plating (Cu-Zn) layer. After containing cobalt in the surface layer of the above, it was decided to adhere to the rubber.

FIG. 3 shows the state of adhesion between the steel cord 1 and the rubber 32 in this embodiment. More specifically, FIG. 3 shows the vicinity of the interface where the plating layer 30b is formed on the steel surface 30a in the surface layer portion 30 of the steel cord 1 and further adhered to the rubber 32. Further, FIG. 3A shows an unvulcanized state, and FIG. 3B shows an initial state of the vulcanization reaction.

In this embodiment, as shown in FIG. 3A, a very small amount of cobalt (Co) plating layer 31 is replaced on the surface of the brass plating (Cu-Zn) plating layer 30b in an unvulcanized state. It is formed so that the surface layer of the plating layer 30b contains cobalt. According to this, as shown in FIG. 3B, in the initial state after the vulcanization reaction, cobalt (Co) can be intensively dispersed in the rubber near the adhesion interface of the rubber 32 with the steel cord 1. it can. In this embodiment, the cobalt (Co) plating layer 31 is formed by replacement plating, and is concentrated in a region having a depth of 9 nm or less from the surface of the plating layer 30b having a total thickness of about 200 to 300 nm. It is contained.

Next, FIG. 4 shows the state after FIG. 3 in the bonded state of the steel cord 1 and the rubber 32 in this embodiment. FIG. 4A shows an early state after the vulcanization reaction, and FIG. 4B shows a moist heat deterioration state after use.

In the early state after the vulcanization reaction of FIG. 4A, copper (Cu) and zinc (Zn) of the plating layer 30b are diffused to the rubber 32 side, and sulfur (S) in the rubber 32 is plated. By diffusing to the layer 30b side, a reaction layer 33 composed of a ZnO layer and a CuxS layer is formed. The rubber 32 and the steel cord 1 are firmly adhered to each other by the reaction layer 33. Then, after use as shown in FIG. 4B, copper (Cu) and zinc (Zn) of the plating layer 30b are further diffused toward the rubber 32 side. As a result, the thickness of the ZnO layer is increased, and the ZnS component is increased in the CuxS layer to increase the thickness of the reaction layer 33. Even in this state, since the dispersion of cobalt (Co) in the rubber 32 is limited, the deterioration of the rubber 32 due to the oxidation of cobalt (Co) is suppressed.

In the moist heat deterioration state after use shown in FIG. 4 (b), the relationship between the copper (Cu) concentration and the zinc (Zn) concentration in the reaction layer consisting of the CuxS layer + ZnS component is such that copper (Cu) concentration> zinc ( A relationship of Zn) concentration was observed (in FIG. 2C, copper (Cu) concentration <zinc (Zn)).

As described above, in this embodiment, the reaction layer composed of the ZnO layer and the CuxS layer can be sufficiently expanded, and the excessive diffusion of cobalt (Co) into the rubber 32 can be suppressed. Therefore, the adhesive strength of the rubber 32 to the steel cord 1 can be sufficiently maintained even in a moist heat deteriorated state after use. Further, since the rubber 32 does not contain cobalt (Co), it is possible to suppress deterioration and peeling of the rubber 32 due to oxidation of the cobalt (Co).

Next, an example of actual measurement results of each characteristic value when the steel cord 1 to which the present invention is applied is actually bonded to rubber will be described.

<Preparation of rubber composition>
In this actual measurement, a rubber composition was prepared by kneading with a Banbury mixer according to the formulation shown in Table 1 below.

<Evaluation of adhesiveness after moist heat aging>
Steel cord 1 is coated with the rubber composition shown in Table 1, press vulcanized under the condition of 150 ° C. for 30 minutes, and then subjected to a wet heat deterioration test for 96 hours in saturated steam at a temperature of 105 ° C. and evaluated. A test piece was prepared. Then, when the cobalt surface concentration (atomic%) on the cobalt-plated surface of the steel cord 1 is 0%, 3%, 7%, 11%, and 17%, respectively, the X of CuxS at the time of initial bonding and after moist heat deterioration , The value of the Cu / Zn concentration ratio, and the value of the reaction layer thickness (μm) were actually measured with an Auger analyzer (manufactured by PHI700 ULVAC PFI Co., Ltd.). In the evaluation of the reaction layer, it can be said that it is good if the value of X of CuxS is 1 or more and the thickness of the reaction layer is less than 0.30 μm. Further, it can be said that the value of the Cu / Zn concentration ratio after moist heat deterioration is good if it is 1 or more as described above.

Table 2 shows the actual measurement results of the above characteristic values. As shown in Table 2, when the cobalt surface concentration on the surface of the plating layer was 3% or more and 7% or less, good results were obtained both at the time of initial adhesion and after moist heat deterioration.

Table 3 shows the other characteristics of the sample having a cobalt concentration of 3% on the surface of the plating layer and the sample having a cobalt concentration of 7% in Table 2.

As shown in Table 3, in this example, cobalt (Co) was contained in a region having a depth of 9 nm or less from the surface of the plating layer 30b by brass plating (Cu—Zn). As a result, cobalt (Co) can be concentrated near the surface of the plating layer 30b, and when the rubber 32 is reinforced by the steel cord 1, the rubber 32 is vulcanized during the vulcanization reaction between the rubber 32 and the steel cord 1. Cobalt (Co) could be reliably supplied to and the adhesiveness could be improved.

Further, in this embodiment, since the copper concentration in the region from the surface of the plating layer 30b to the depth of 9 nm is 45 atomic% or more, even if the surface layer of the plating layer 30b contains cobalt (Co). In the reaction layer between the rubber 32 and the steel cord 1, the sulfur (S) in the rubber 32 and the copper (Cu) in the plating layer 30b can be sufficiently reacted to obtain sufficient initial adhesive strength. Was done.

Further, in this embodiment, since the cobalt concentration in the entire plating layer 30b is 0.1% by weight or less, the cobalt (Co) concentration in the reaction layer between the rubber 32 and the steel cord 1 can be appropriately maintained. Excessive expansion of the thickness of the reaction layer could be suppressed, and the occurrence of reaction layer destruction could be suppressed.

Next, FIG. 5 shows a flowchart of the manufacturing process of the steel cord 1 in this embodiment. According to this manufacturing method, first, in S101, the wire rod which is the material of the filament 2 is washed with an acid. More specifically, by treating the surface of a wire rod formed through wire making, steel making, and rolling processes with an acid, "rust" and fine "scale" generated on the metal surface are removed. Then, in S102, the primary wire drawing and the primary burning wire are performed. In this primary wire drawing, for example, a wire rod having a diameter of 5.5 mm is stretched at an initial stage to make it thinner and improve its strength. Further, the toughness is restored and the linearity and rollability are maintained by performing the burning wire on the primary drawn wire.

Next, in S103, secondary drawing and secondary burning are further performed, and necessary physical property values are secured. In S104, brass plating is performed. This brass plating is often formed by sequentially forming a copper plating layer and a zinc plating layer on the surface of a wire rod, and then alloying both metals by thermal diffusion. The ratio of brass-plated copper to zinc and the plating thickness are appropriately selected in order to maintain the basic adhesion between rubber and steel wire.

In S105, the final wire drawing, the tertiary wire drawing, is performed. Then, in S106, a stranded wire is formed by twisting the wire rods pulled out in S105. As a result, the final cross-sectional structure of the steel cord 1 is formed. Then, after all the wire drawing steps and the stranded wire steps are completed, cobalt substitution plating is performed in S107.

As shown in FIG. 5, in this embodiment, cobalt plating is performed after the tertiary wire drawing and stranded wire. In this way, by performing cobalt plating with poor ductility after the tertiary wire drawing and stranded wire, it is possible to suppress peeling and cracking of the cobalt plating and reduce the burden of adding or changing the manufacturing process. ing. Although the present invention has been applied to the reinforcement of tires in the above examples, the present invention can also be applied to the reinforcement of rubber other than tires.

1 ... Steel cord 10a, 20a, 30a ... Metal wire 10b, 20b, 30b ... Plating layer 11, 21, 33 ... Reaction layer 12, 22, 32 ... Rubber

Claims (6)

A metal wire for rubber reinforcement provided with a brass-plated layer containing copper and zinc on the surface.
Cobalt is contained in the surface layer of the brass plating layer,
A metal wire for rubber reinforcement, wherein the cobalt concentration on the surface of the brass plating layer is 3 atomic% or more and 7 atomic% or less. The rubber reinforcing metal wire according to claim 1, wherein the cobalt is contained in a region having a depth of 9 nm or less from the surface of the brass plating layer. The rubber reinforcing metal wire according to claim 2, wherein the copper concentration in the region from the surface of the brass plating layer to a depth of 9 nm is 45 atomic% or more. The rubber reinforcing metal wire according to any one of claims 1 to 3, wherein the cobalt concentration in the entire brass plating layer is 0.1% by weight or less. The rubber reinforcing metal wire according to any one of claims 1 to 4, wherein the cobalt atom is contained by being substituted-plated on the surface layer of the brass plating layer. A multi-stage wire drawing process for wire drawing and
In the stranded wire process of twisting a plurality of wire rods drawn in the wire drawing process,
Of the plurality of stages of wire drawing steps, a brass plating step of performing brass plating on the wire rod at least before the final wire drawing step, and
A cobalt plating step in which cobalt is contained in the surface layer of the brass plating layer formed in the brass plating step by replacement plating, and
Have,
A method for producing a metal wire for rubber reinforcement, wherein the cobalt plating step is carried out after all the wire drawing steps and stranded wire steps.

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