JPS61227199A - Method for supplying metal ion in electroplating - Google Patents

Abstract

PURPOSE:To accelerate the dissolution of a plating metal regardless of the pH value of a plating liquid by dissolving the plating metal in the plating liquid in the presence of a metal of which the oxidation-reduction potential is nobler than the plating metal in the stage of replenishing plating metal ions to the electroplating liquid for which an insoluble anode is used. CONSTITUTION:The plating metal is deposited on a cathode which is a material to be plated by using the insoluble anode and using the plating liquid contg. the ions of the metal to be plated, by which the plating metallic film is formed. The plating metal ions in the plating liquid decrease on progression of the plating and therefore the concn. of the plating metal ions is increased by dissolving the plating metal in the plating liquid. The dissolving rate of the plating metal decreases with an increase in the pH of the plating liquid and therefore the decrease in the dissolving rate of the plating metal is prevented even if the pH value increases by adding the metal having the oxidation-reduction potential nobler than the oxidation-reduction potential of the plating metal to co-exist with the plating metal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for supplying metal ions in electroplating, and particularly to a supply method that can promote dissolution of plating metal.
Used in the field of electroplating using insoluble anodes.

[Conventional technology]

As a recent trend in electroplating, so-called insoluble plating using an insoluble anode is often used. For example, considering insoluble zinc plating, a typical bath composition is as follows.

Zn80. ．． 7H, 0300~500g/VNa z
804 30 g/1lAJ(S
O2) s.17H, 050 g/l pH 1-3 The reaction between the negative and positive electrodes in insoluble zinc plating is as follows.

Cathode Zn + 21− →Zn ・
...(1) Anode SOa +H20→a, so4+
1 /20z↑+2ノ...(2) As the insoluble plating is energized, the Zn ions decrease according to formula (1) and the pH decreases according to formula (2), so metal ions must be continuously or periodically supplied from the outside. There is a need to do.

In the case of Zn plating, Zn metal or its oxides, hydroxides, carbonates, etc. are used as a metal ion supplier, but due to cost and workability reasons, Zn metal is used in a plating solution with reduced Zn ions. Many methods include immersion and dissolution.

The reaction at that time is shown in (3) 2 below; this is a convenient reaction in which the supply of metal ions (Zn) and pH recovery are carried out simultaneously.

Zn+H28044ZnSO4+H2↑ ・(3
The reaction of formula 1(3) theoretically occurs at pH HI3 where Zn(OH)z is produced, but as the pH increases, the reaction rate slows down, so in practical terms the reaction can only be expected up to around pH 4.

As a specific method of supplying metal ions to the plating solution,
Conventional methods include fluidized bed method and barrel method.

The fluidized bed method is disclosed in Japanese Patent Application Laid-Open No. 58-151489, and as shown in FIG. The reduced plating liquid 4 is continuously supplied so that metal powder does not carry over and a fluidized bed 6 is formed, and the plating liquid 8 whose pH has increased due to the increase in metal ions is discharged from the top to supply metal ions. However, it has the disadvantage that a hydroxide film is formed on the surface of the metal powder, and the generation of metal ions stops when a certain pH is reached, thus preventing the supply of metal ions.

Further, as an improved version of the fluidized bed method, for example, there is a barrel method disclosed in Japanese Utility Model Application No. 60-25761. As shown in FIG. 2, a hollow rotating body barrel 16 having a number of holes 14 is provided, immersed in a liquid tank 12 containing a plating solution 10. The plating metal particles 22 and the plating liquid 10 with reduced metal ion concentration are supplied from the left hopper 18 and the plating solution supply pipe 20 to the hollow rotating body 16, and the hollow rotating body 16 rotates to supply the metal particles 22.
In this method, the hydroxide film formed on the surface of the metal grains is destroyed by contacting the metal grains to promote dissolution of the metal grains 22, and the tamping liquid 10 with increased metal ion concentration is discharged from the liquid tank 12. . However, as mentioned above, what controls the supply rate of metal ions is H ions in the plating solution, so this method also has the fateful problem that the dissolution rate drops dramatically when the pH approaches 4. There is.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for supplying metal ions in electroplating, which solves the problems of the prior art described above and can promote dissolution of plating metals regardless of the pH in the plating solution.

[Means and effects for solving the problems] The present inventors have conducted various studies on promoting the dissolution of plated metals. In other words, the basic reaction for dissolving the plating metal is as shown in equation (3) above, and from the relationship diagram between the apparent solubility of zinc hydroxide and pH in Figure 3 (G. Charlow, Qualitative Analytical Chemistry If, p. 297). As is clear, the reaction rate slows down exponentially as the pH increases.

A corrosion cell is formed by solid contact or contact through a liquid medium between the plated metal and a metal with a higher redox potential than the plated metal and a smaller ionization tendency, and the dissolution of the plated metal ions is promoted regardless of pH. By paying attention to this and utilizing it to promote dissolution of plating metal ions, we were able to complete the present invention.

The gist of the present invention is as follows.

That is, in a method for supplying metal ions in electroplating in which the metal is dissolved in a solution in which plating metal ions are reduced, the electroplating method is characterized in that the dissolution is performed in the presence of a metal having a nobler redox potential than the plating metal. This is a method of supplying metal ions in plating.

Metal ionization tendency, i.e. redox potential E0 (V)
is shown in Table 1. In the present invention, a corrosion battery is formed by actively bringing a plating metal into contact with a nobler metal having a redox potential than that of the metal, and the plating metal is dissolved regardless of the presence of H ions. Since the effect is proportional to the difference in oxidation potential between the metals brought into contact, the metals to be contacted can be selected with reference to the oxidation-reduction potentials in Table 1. however,
Since the metal to be contacted is H ion, it dissolves slightly and mixes into the plating solution, so metals that have an adverse effect on plating must be excluded.

The following various embodiments can be considered for dissolving the plating metal in the presence of a noble metal having an oxidation-reduction potential.

The plated metal particles and the noble metal particles are mixed to form a fluidized bed in the fluidized bed method, or in the barrel method, they are charged into a barrel and subjected to a melting reaction.

(B) The main body or lining of a fluid tube or barrel is formed using a noble metal as a material, and the metal particles are plated and the metal is used alone to cause a melting reaction.

(Q: The plating metal and the noble metal are placed in separate containers and brought into indirect contact using a plating solution as a medium to cause a dissolution reaction.

In the barrel method shown in FIG. 2, the method of the present invention is applied to supply noble metal particles in addition to the plating metal particles 22 to the hollow rotating body (barrel) 16, and rotate the hollow rotating body 16 to form metal particles. By forcibly bringing them into contact and promoting contact wear, the dissolution of the plated metal can be significantly promoted due to the synergistic effect of the destruction of the hydroxide film and the corrosion cell.

Although the present invention has been explained mainly by taking zinc as an example, the present invention is not limited to zinc, but also uses noble metals in other plating metals to form a corrosion battery and promote dissolution of the plating metal. be able to.

〔Example〕

In pursuit of the present invention, the barrel method shown in FIG. 2 was improved to melt plated metal. That is, a hollow rotating body was charged with metal grains of various types as shown in Table 2, and a plating solution under the conditions shown in Table 3 was supplied at a flow rate of 501/min at 14 rpm.
It was dissolved by rotating at a speed of .

The metal particles charged into the hollow rotating body are Znsokg with a particle size of 5 to 1011II as the plated metal particles, and Znsokg according to the method of the present invention.
Particle size 5-101 as a noble metal with redox potential than n
m of Ni or Ag grains were added.

For reference, a conventional example was also conducted in which no noble metal was added, and the pH and Zn concentration of each were investigated.
The results are shown in Table 2.

From Table 2 and Table 3, it can be seen that Ni, which has a more noble redox potential than zn,
It can be seen that the examples of the present invention in which Ag and the like are added have a faster dissolution rate than the conventional examples without additives, and among the examples, Ag, which has a large difference in redox potential, has a faster dissolution rate than Ni.

The amount of noble metal added is K 2.5 kg for both Ni and Ag.
and 5 kg, but no difference was observed in the dissolution effect.

〔Effect of the invention〕

As is clear from the above examples, the present invention achieves the effect of promoting dissolution regardless of the pH level of the plating solution by dissolving the plating metal in the presence of a metal with a nobler redox potential than the plating metal. was completed.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view showing a conventional flow-type metal ion dissolving device, Figure 2 is a cross-sectional view showing a conventional barrel-type metal ion dissolving device, and Figure 3 shows the apparent solubility and pH of zinc hydroxide. FIG. 2... Fluidization cylinder 4... Plating solution 6 with decreased pH due to decreased metal ions
...Fluidized bed 8...Plating solution 1 with increased metal ions and increased pH
0...Plating solution 12...Liquid tank 16...Hollow rotating body 22...Metal particle agent Patent attorney Takeo Nakaji 1st ward, Figure 3 H

Claims (1)

[Claims] (1) In a metal ion supply method in electroplating in which the plating metal is dissolved in a solution with reduced plating metal ions, the dissolution is performed in the presence of a metal having a nobler redox potential than the plating metal. A method for supplying metal ions in electroplating, characterized by: