JP2009091691A - Steel wire for reinforcing rubber article, method for producing the same, steel cord, rubber composite material, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve improvement in adhesiveness of a wire to rubber in a manner having reduced environmental load to avoid the problems of rubber material. <P>SOLUTION: The steel wire plated with brass on the circumference of a wire and the concentration of transition metals excluding Zn and Cu on the surface of the brass plating is set to 0.01 mass% or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  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 excellent in adhesion to rubber.

  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 made of a single wire of steel wire are covered with rubber. The rubber composite is applied and is mainly reinforced with steel cord. 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.

That is, so-called direct vulcanization adhesion is widely used, in which a brass-plated steel cord is embedded in a rubber composition containing sulfur and adhered at the same time as vulcanization of rubber during heat vulcanization. So far, various studies have been made to improve the adhesion between the cord and rubber in this direct vulcanization adhesion.
For example, in order to ensure adhesion to rubber, it has been studied to optimize the ratio of copper and zinc in 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 adhesion to rubber is improved. Conditions are required. For example, in order to vulcanize and mold a tire within a certain period of time, it is required to secure a sufficient adhesive force by the speed of bonding between a cord and rubber or by their complete bonding. That is, since so-called initial adhesiveness is required, it is necessary to add a Co salt or Ni salt as an adhesion promoter in the rubber in a considerable proportion, or to blend sulfur in a high proportion.

  However, when a Co salt is compounded with rubber, there are significant problems with physical properties such as rubber deterioration, rubber deterioration, and crack growth resistance, compared with rubber not containing Co. Therefore, various proposals have been made not for adjusting the composition of the rubber but for the wire that is the bonding partner of the rubber.

For example, the surface of steel wires and steel cords to be used is washed with an acidic or alkaline aqueous solution, and the phosphorus compound (derived from the lubricant used in the manufacture of steel wires) is removed by removing the adhesion reaction inhibitor. There is known a technique for improving the adhesiveness of the film (see Patent Document 1).
However, the pretreatment solutions used are acidic and alkaline solutions, which are not environmentally preferable, and safety may be a problem when considering the manufacturing process. Therefore, it is required to be able to process with a solution in a more neutral region.
JP 2001-234371 A

Further, Patent Document 2 discloses a method of adding resorcin to the surface of a steel filament by adding resorcin, which is considered as a steel cord / rubber adhesion improver, in a wet lubricant used in manufacturing a steel cord. Yes. However, since resorcin is altered by heat generation during wire drawing, it is difficult to sufficiently improve the durability of adhesion between the steel filament and the rubber.
JP 2004-66298 A

When considering adhesion between rubber and cord in direct vulcanization adhesion used for tires, etc., it is common to add an adhesion promoter to the rubber, but this is a problem that inhibits rubber properties such as rubber deterioration and crack growth resistance There is.
Therefore, an object of the present invention is to achieve an improvement in adhesion of a wire to rubber by a method with a small environmental load in order to avoid such a problem on the rubber material side.

  Inventors remove adhesion reaction inhibitors with rubber existing on the wire side, such as phosphorus compounds derived from lubricants used in the production of steel wires and ZnO formed on the surface of the plating layer after brass plating. As a result of intensive studies on pretreatment, it has been found that, by improving this steel wire pretreatment technique, the rubber-cord adhesion more than the conventional one can be secured without adding an adhesion promoter to the rubber. Furthermore, by devising the pretreatment technique, it has been found that a function as an adhesion promoter can be imparted to the wire surface, and the present invention has been completed.

The gist of the present invention is as follows.
(1) Reinforcement of rubber articles, characterized in that the steel wire is brass-plated on the peripheral surface of the wire, and the concentration of transition metals excluding Zn and Cu on the surface of the brass plating is 0.01 mass% or more. Steel wire for

(2) The steel wire for reinforcing rubber articles according to (1), wherein the phosphorus concentration on the surface of the brass plating is 2.5 mass% or less and the zinc concentration is 15 mass% or less.

(3) A steel cord for reinforcing rubber articles formed by twisting a plurality of steel wires according to (1) or (2).

(4) A rubber article obtained by coating the steel wire according to (1) or (2) or the steel cord according to (3) with rubber.

(5) In the above (4), the coated rubber is a rubber article obtained by blending 1 to 10 parts by mass of sulfur with respect to 100 parts by mass of the rubber component.

(6) In the above (4) or (5), the coated rubber is a rubber article not containing cobalt.

(7) A pneumatic tire in which the rubber article according to (4), (5) or (6) is applied as a reinforcing material.

(8) The pneumatic tire according to (7), wherein the reinforcing material is a carcass ply or a belt ply.

(9) The steel wire is subjected to brass plating and then subjected to wire drawing, and then the surface of the steel wire is washed with an aqueous solution containing a transition metal as a salt. Steel wire manufacturing method.

(10) A method for producing a steel wire for reinforcing rubber articles, wherein, in (9), the transition metal is cobalt.

(11) A method for producing a steel wire for reinforcing rubber articles, wherein, in (10), the salt of cobalt is cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt citrate, cobalt gluconate or acetylacetonato cobalt .

  According to the present invention, the steel wire or steel cord subjected to brass plating is pretreated by washing with an aqueous solution containing a transition metal as a salt. A steel wire and a steel cord with brass plating excellent in adhesiveness can be provided.

  In addition, by using the steel wire or steel cord of the present invention, the initial adhesion can be sufficiently applied to the rubber from which the adhesion promoter has been removed. And it becomes possible to enjoy the improvement of crack growth resistance.

  Now, a steel wire used to reinforce a rubber article is generally manufactured by, for example, drawing a wire material subjected to brass plating having a diameter of about 5 mm. In this manufacturing process, a lubricant is naturally used, but in particular, in the final wire drawing step, thinning is performed using a die having about 20 passes disposed in the liquid lubricant. In this final wire drawing process, an extreme pressure is generated between the cord and the die, and the temperature becomes very high. Therefore, a lubricant based on phosphoric acid is used to ensure lubricity at extreme pressure and high temperature. It is customary to use

  This lubricant reacts with the wire surface during wire drawing to form a lubricant film layer, that is, a phosphoric acid compound layer, and relaxes input under extreme pressure and high temperature conditions, realizing mass production of wires. Therefore, in the manufacturing process, it is inevitable that phosphoric acid is taken in during the plating of the wire. If this phosphoric acid compound layer is present on the plating surface, copper in the brass plating diffuses to the rubber side and forms CuxS, thereby inhibiting the adhesion reaction in which adhesion is performed.

  In addition, when brass plating, which is an alloy of Cu and Zn, is applied, the surface is oxidized over time to produce ZnO, which, like the phosphate compound layer, also inhibits the adhesion reaction. .

  Therefore, removing the phosphate compound layer and the ZnO layer from the plating surface before bonding with the rubber is effective for improving the adhesion with the rubber. For that purpose, it is important to remove the phosphate compound layer and ZnO layer on the surface of the steel wire after drawing, but it is important to perform a cleaning treatment, but cleaning with an acidic or alkaline aqueous solution becomes a problem. As described above.

  Therefore, as a result of diligent research on cleaning treatment with a small environmental load, it was found that surface treatment with an aqueous solution containing a transition metal as a salt is extremely effective. That is, when a steel wire subjected to brass plating or a cord obtained by twisting the wire is washed with an aqueous solution containing a transition metal as a salt, a phosphate compound layer or a ZnO layer that inhibits the adhesion reaction with the rubber described above Can be dissolved.

Here, the transition metals are scandium (Sc) to zinc (Zn) in the fourth period of the periodic table, yttrium (Y) to cadmium (Cd) in the fifth period, and lutetium (Lu) in the sixth period. Refers to metal elements from mercury to mercury (Hg).
Cobalt is a typical example of the transition metal, and examples of the aqueous solution containing cobalt as a salt include cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt citrate, cobalt gluconate, and acetylacetonato cobalt. . In addition, as a typical aqueous solution containing a transition metal as a salt, nitric acid, sulfuric acid or acetate containing Fe and Ag can be used.

  At that time, the pH of the aqueous solution is preferably about 5 to 8. This is because if the pH of the aqueous solution is out of this range, the plating is adversely affected and the adhesion to rubber is reduced. In addition, when the pH is in a neutral range of about 5 to 8, the load on the environment is reduced, and safety against exposure to the user during production and reagent safety can be ensured.

  The cleaning condition may be set as appropriate depending on the concentration of the aqueous solution. For example, in the case of a cobalt acetate-containing aqueous solution, the cleaning time is preferably 30 to 60 seconds at a concentration of 10 g / l.

Steel wire that has undergone a cleaning treatment with an aqueous solution containing a transition metal as a salt as described above does not have an oxide layer such as a ZnO layer or a phosphate compound layer on the surface of the brass plating, and further uses an aqueous solution in which the transition metal is cobalt. If it is, 0.01 mass% or more of cobalt is present on the plating surface. That is, by performing the above-described washing treatment, in addition to the absence of an inhibitor of adhesion reaction with rubber, a plating surface having cobalt functioning as an adhesion promoter is obtained, and as a result, the adhesion of wire to rubber is greatly improved. It is. Therefore, even if the adhesion promoter on the rubber side is omitted, the adhesion between the wire and the rubber can be ensured. On the other hand, since the adhesion promoter on the rubber side can be omitted, it is also possible to improve the deterioration resistance and crack growth resistance of the rubber.
On the other hand, if Co exceeding 20 mass% is present on the plating surface, it functions as an adhesion inhibiting factor with rubber rather than functioning as an adhesion promoter, so the upper limit of Co concentration is 20 mass%.

  In addition, the plating surface here is the surface layer region up to a depth of 10 mm inside the filament radial direction.

Moreover, about brass plating, it is preferable that the phosphorus density | concentration in the surface is 2.5 mass% or less, and zinc concentration is 15 mass% or less. This is because if the phosphorus concentration on the plating surface exceeds 2.5 mass%, the adhesion inhibiting effect is increased, and if the Co salt is removed from the rubber, sufficient adhesion performance may not be obtained.
Similarly, if the zinc concentration exceeds 15 mass%, the adhesion inhibiting effect is increased, and if the Co salt is removed from the rubber, sufficient adhesion performance may not be obtained.

  The steel wire or steel cord subjected to the washing treatment is coated with rubber to form a rubber article such as a pneumatic tire or an industrial belt. In this case, the coated rubber contains sulfur with respect to 100 parts by mass of the rubber component. It is good to use what mix | blended 1-10 mass parts. This is because, if sulfur is less than 1 part by mass, it becomes difficult to secure the original adhesive strength of vulcanized adhesion between sulfur and rubber, whereas if it exceeds 10 parts by mass, the heat aging resistance of rubber properties and the heat-resistant adhesive properties deteriorate. This is not preferable.

  Furthermore, it is preferable that the coating rubber does not contain cobalt. That is, while cobalt acts as an adhesion promoter, it also becomes a factor that inhibits the resistance to degradation caused by heat, moisture or oxygen of rubber, and crack growth resistance, so if the wire of the present invention is a bonding partner, Is preferably not included.

  When the rubber article is a pneumatic tire, the tire structure itself may be a general structure, and the wire or cord of the present invention is applied as a reinforcing material for a carcass ply or a belt ply.

Hereinafter, the present invention will be described more specifically, but the present invention is not limited to the following examples.
(Invention example)
A steel filament coated with brass plating (thickness: 0.25 μm) with a composition of Cu: 63 mass% and Zu: 37 mass% is twisted to produce a cord of 1 × 5 structure. And then dried at 50 ° C. for 1 minute. Table 1 shows the results obtained by examining the composition of the wire plating surface of the steel cord after the cleaning treatment by X-ray photoelectron spectroscopy (XPS).
Using the steel cord thus finished, the initial adhesion and wet heat adhesion were evaluated by the following methods using the rubbers shown in Table 2.

(Comparative Examples 1 and 2)
Using steel cord not subjected to cleaning treatment after brass plating similar to the above, using the rubber composition shown in Table 2, the initial adhesion and wet heat adhesion were measured by the following methods to evaluate the adhesion. did. The results are also shown in Table 1.

Adhesion test The steel cords were arranged in parallel, and the steel cords were coated with each rubber composition from the upper and lower sides, and vulcanized under the conditions shown in Table 1 to prepare samples. For each of the following adhesive properties of each sample, in accordance with ASTM D-2229, pull out the steel cord from each sample, visually observe the rubber coating state, display 0-100%, each adhesive index It was.

  Regarding the deterioration resistance of rubber, after vulcanizing unvulcanized rubber at 160 ° C for 20 minutes, after aging under wet heat conditions at 100 ° C for 2 days and then at 70 ° C and 100% humidity for 4 days, By performing a tensile test according to JIS K6251, Eb and Tb were measured, and toughness TF (= Eb × Tb) was obtained.

  For evaluation of crack growth resistance, a constant stress fatigue test was performed using a Uejima fatigue tester, and the number of times until fracture occurred was measured.

  As is apparent from Table 1, the use of a wire that has been subjected to a cleaning treatment according to the present invention can significantly improve the adhesion to rubber.

Claims (11)

  A steel wire for reinforcing rubber articles, wherein the peripheral surface of the wire is subjected to brass plating, and the concentration of transition metal excluding Zn and Cu on the surface of the brass plating is 0.01 mass% or more. .   The steel wire for reinforcing rubber articles according to claim 1, wherein a phosphorus concentration on the surface of the brass plating is 2.5 mass% or less and a zinc concentration is 15 mass% or less.   A steel cord for reinforcing rubber articles formed by twisting a plurality of steel wires according to claim 1 or 2.   A rubber article obtained by coating the steel wire according to claim 1 or 2 or the steel cord according to claim 3 with rubber.   5. The rubber article according to claim 4, wherein the covering rubber is compounded with 1 to 10 parts by mass of sulfur with respect to 100 parts by mass of the rubber component.   6. The rubber article according to claim 4, wherein the coated rubber does not contain cobalt.   A pneumatic tire in which the rubber article according to claim 4 is applied to a reinforcing material.   The pneumatic tire according to claim 7, wherein the reinforcing material is a carcass ply or a belt ply.   A steel wire for reinforcing rubber articles, characterized in that after the steel wire is subjected to brass plating and then subjected to wire drawing, the surface of the steel wire is washed with an aqueous solution containing a transition metal as a salt. Production method.   The method for manufacturing a steel wire for reinforcing rubber articles according to claim 9, wherein the transition metal is cobalt.   The method for producing a steel wire for reinforcing rubber articles according to claim 10, wherein the cobalt salt is cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt citrate, cobalt gluconate or acetylacetonato cobalt.