JP2636645B2 - Zinc supply method and apparatus for Zn-Ni alloy plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for supplying zinc in Zn-Ni alloy plating, and more particularly to a method and an apparatus for supplying zinc in continuous electroplating of a Zn-Ni alloy in an acidic bath using an insoluble anode.

[0002]

2. Description of the Related Art In recent years, electroplating on steel materials has been widely performed due to a demand for further improvement of corrosion resistance of automobiles or home electric appliances. In particular, Zn-Ni-based alloy plating has been rapidly applied to steel materials for automobile bodies and the like due to its excellent corrosion resistance. In order to respond to such an increase in demand, in recent years, the speed of electroplating lines and the current density have been increased, and in order to reduce electrode replacement time or eliminate electrode replacement, conventional soluble anodes have been replaced with insoluble anodes. The conversion is progressing.

In the case where an insoluble anode is used, it is necessary to supply metal ions consumed by plating. Particularly, in an electroplating line with high productivity, a large amount of metal ions are consumed. Therefore, a system capable of supplying a large amount of metal ions to replenish the metal ions is desired.

[0004] Further, in the production of alloy plating such as a Zn-Ni system, the corrosion resistance of the plating film is inferior to that of Zn in the plating bath.
Since it depends on the molar ratio of Ni, a metal ion supply system with excellent solubility is required to quickly respond to fluctuations in the molar ratio.

[0005] In order to meet such demands, as a method for supplying metal ions in electroplating, particularly in electroplating of alloys, a method of dissolving a metal salt has been often used.

However, in recent years, in order to reduce costs,
In the supply of zinc ions, instead of metal salts, metals themselves, that is, electrorefined zinc metal before producing the metal salts, have been used as a zinc metal supply source.

In such a supply system using metallic zinc, a system is provided in which a dissolving tank for metallic zinc is separately provided, and a plating solution from a plating system is circulated through the dissolving tank to dissolve metallic zinc. The reaction equation at this time is as shown in equation (1).

Zn + 2H ⁺ → Zn ²⁺ + H ₂ (1) However, as can be seen from the above equation, the progress of this reaction is extremely disadvantageous on Zn with a high hydrogen overvoltage. As described in JP 61-600, ψ _Ni (hydrogen overvoltage of Ni) <ψ _Zn (hydrogen overvoltage of Zn)
By utilizing the fact that 5 to 1000 ppm of nickel ions are present in the plating bath, as shown by the following formulas (2) and (3), generation of hydrogen is performed by , A method for promoting the dissolution of Zn has been proposed.

Ni ²⁺ + 2e → Ni (on zinc) ··· (2) Zn → Zn ^{2 +} + 2e (3) As can be seen from these equations (2) and (3), This means that Ni precipitates on zinc and inhibits dissolution of Zn thereafter. On the other hand, in the case of Zn-Ni alloy plating,
Similarly, when dissolving metallic zinc using a plating solution as a dissolving solution, Ni is deposited on metallic zinc by the reaction of the following formula (4), and this coating significantly reduces the dissolving rate of metallic zinc.

Zn + Ni ²⁺ → Zn ²⁺ + Ni (4) Accordingly, when zinc metal is used for supplying zinc ions in Zn-Ni alloy plating, it is disclosed in JP-A-63-238300.
As disclosed in Japanese Unexamined Patent Application Publication No. H11-163, a method of controlling the amount of free sulfuric acid in a Zn-Ni plating bath to 10 to 20 g / l has been proposed.However, it is difficult to control the plating bath in such a manner. It was extremely difficult and there was a problem in applying it to an actual alloy plating line.

Japanese Patent Application Laid-Open No. Sho 62-174400 discloses a technique for dissolving zinc metal by disposing a roughened zinc metal plate in layers to dissolve the zinc. In the dissolution of metallic zinc in gold plating, the dissolution rate of metallic zinc decreases with time only by arranging a rough zinc plate in a layer, and the dissolution rate is small even when saturation is reached. This is because, as already described, the film of Ni in the Zn-Ni bath is deposited on the metallic zinc, and in order to realize the cost reduction by the metallic zinc and to realize the compact melting equipment. Aggressive Ni or alloy
It is necessary to remove the Ni layer.

[0012]

The object of the present invention is to provide a Zn-
When dissolving and supplying metallic zinc to Ni alloy electroplating bath,
An object of the present invention is to provide a method and an apparatus for dissolving and supplying zinc metal, which prevent a reduction in the dissolution rate of zinc metal due to coating of the surface of the zinc metal with Ni.

[0013]

Means for Solving the Problems The present inventors have solved the above-mentioned problems in supplying Zn ions to a Zn-Ni alloy electroplating system, and have solved the problem of dissolving Zn ions using metallic zinc. , And studied repeatedly for practical use of the supply system.

As a result, in the Zn-Ni-based alloy plating using an acidic plating bath, when dissolving metallic zinc in a dissolving solution which is a plating bath to be circulated and recovered, the metal zinc is dissolved from within the dissolving solution and from above the dissolving solution. Spraying a gas such as oxygen, air, or nitrogen onto the metallic zinc removes or makes the Ni layer coated on the metallic zinc, so the dissolution rate of the metallic zinc does not decrease. The present invention was completed by knowing that it was possible to supply.

Here, the gist of the present invention is a method of supplying zinc in continuous electroplating of a Zn—Ni alloy using an acid plating bath using an insoluble anode. When dissolving, gas is blown on the metallic zinc from within or from the solution,
This is a method for supplying zinc in Zn-Ni-based alloy plating, wherein the dissolution of the metal zinc is promoted by removing or making the Ni layer or the Ni alloy layer coated on the metal zinc.

The Ni layer coated on the metal zinc or Ni layer
The alloy layer may be separately mechanically removed as necessary. As the mechanical removal in that case, a method of rubbing the metal zinc surface with a brush roll or other mechanical polishing means can be considered.

Further, the flow rate of the solution in the metal zinc dissolution tank may be set to 1 m ³ / min or more to further promote the removal or porosity of the Ni layer or the Ni alloy layer coated on the metal zinc. .

Another aspect of the present invention is a zinc supply apparatus in a continuous electroplating system for a Zn—Ni alloy using an acid plating bath using an insoluble anode, the zinc electroplating system comprising: A dissolving tank containing a dissolving solution, which is an acidic plating bath recovered from the dissolving solution, and metal zinc; and a dissolving solution provided adjacent to the dissolving tank and dissolving the metal zinc, temporarily dissolving the overflow dissolving solution from the dissolving tank. The dissolving tank is provided with a plurality of gas jet nozzles and a dissolving liquid supply nozzle, and is a zinc supply apparatus for Zn-Ni-based alloy plating.

[0019]

The operation of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic explanatory view of a zinc supply apparatus for a Zn-Ni-based alloy plating system according to the present invention. In the drawing, an overflow tank 2 is provided in addition to a zinc dissolution tank 1 provided separately from the plating system. And overflow tank 2
Are partitioned by a partition plate 3. A solution in which a sufficient amount of metallic zinc is dissolved is supplied to a plating tank 8 constituting a plating system via a filter 4.

The zinc dissolving tank 1 is provided with a plating solution supply nozzle 5 and a gas nozzle 6, and a plurality of nozzles are arranged in the tank, for example, on the inner peripheral wall of the zinc dissolving tank 1 in a vertical line toward the inner center. The gas and dissolved liquid continue to dissolve while impinging on the metallic zinc arranged in the form of a packed bed. An H ₂ diffusion blower 7 is provided at the upper part of the dissolution tank 1. In the case of the present invention, it is preferable that the nozzles 5 and 6 have the same structure, and that both of them can be appropriately switched for gas and dissolution.

The plating solution collected and supplied from the plating tank 8 is quantified by a flow meter 9 to determine the amount of dissolution, and is supplied into the zinc dissolution tank 1 through one or more nozzles 5.

Next, it was evaluated how the gas injection and the solution injection affect the dissolution of metallic zinc.

In the test of this example, the metal zinc shown in FIG. 2 (dimensions: width 30 mm, length
Dissolution tank 1 filled with 30 mm and a thickness of 1 mm) was used.

A dissolving solution, which is a plating solution, is accommodated in the dissolving tank 1, and a metal zinc lump is charged therein, while a gas (air, nitrogen, oxygen, etc.) is blown from the nozzle 6 into the solution. The solution in which the metallic zinc is dissolved overflows from the dissolution tank 1 and is temporarily stored in the adjacent overflow tank 2. The solution from the overflow tank 2 is appropriately returned to the plating system through the filter 4.

After the flow of the dissolving solution has passed through the dissolving tank,
Enter the overflow tank 2 and plating tank (not shown)
Returned to the method. The gas nozzle 6 was provided with an openable / closable nozzle every 50 mm in a stainless steel pipe. The gas pressure is
It was changed to 0, 5, and 10 kg / cm ² . The type of gas is N ₂
And air was used.

FIG. 3 shows the relationship between gas pressure and metal zinc dissolution rate. Here, the filling amount of metal zinc was 5000 kg, the dissolving tank capacity was 5 m ³ , and the liquid circulation amount was 1 m ³ / min. The gas nozzle 6 was fully opened.

As is clear from FIG. 3, the dissolution rate of metallic zinc decreases as time elapses from the start of dissolution, but the gas pressure increases from 0 → 5 kg / cm ² → 10 kg / cm ^{2 due} to an increase in gas pressure. It can be seen that the degree of reduction can be suppressed. Preferably it is 2 to 5 kg / cm ² .

The reason for this is that the present inventors performed SEM observation or mapping of the dissolved zinc metal plate, and found that as the gas pressure increased, the Ni layer on the zinc metal became porous, I confirmed that it was thin.
Therefore, it can be seen that by blowing gas onto the metallic zinc, the Ni layer on the metallic zinc is made porous or removed, thereby promoting the dissolution of the metallic zinc.

When the position of the gas nozzle was examined, no difference was observed in the height direction. Also, N ₂
The same tendency was observed even when gas was used, and no difference was observed in the change in dissolution rate depending on the type of gas.

Removal of Ni Layer by Mechanical Removal A metal zinc plate was immersed in the same dissolution tank as in FIG. In this example, no gas injection was used. Instead, the zinc plate surface was polished every hour using a polishing brush. Thus, it was found that the dissolution rate of the metal Zn plate could be maintained.

The experiment was repeated using the dissolving tank shown in FIG. 2 to determine the relationship between the flow rate of the plating solution supplied to the dissolving tank and the dissolving rate.
Is shown in the graph. The injection of the solution was performed by one nozzle provided at the bottom of the solution tank.

In this embodiment, gas injection from a gas nozzle is not used. The dissolution rate was measured two hours after the start of dissolution. At a flow rate of 1 m ³ / min or more, an increase in the dissolution rate was confirmed. This is due to the fact that, through the porous Ni coating on the metallic zinc, the plating solution has increased contact with the metallic zinc, and also the Ni coating has a reduced thickness.

When the thickness of the Ni film was measured in the same manner, it was found that the thickness of the Ni film decreased as shown in FIG. 5 at a flow rate of 1 m ³ / min or more of the dissolving solution. .

The filling form and size of the metallic zinc are not particularly limited, but are preferably about 10 to 40% with respect to the dissolving tank, as little contact between the metallic zinc plates as possible, and the metallic zinc has a thickness of 1%. ~ 2 mm is desirable. Next, the present invention will be described more specifically with reference to examples.

[0035]

EXAMPLE In this example, a metal zinc dissolution test was performed using the metal zinc dissolution supply apparatus shown in FIG. Zinc dissolution tank 1
The gas nozzle 6 and the plating solution supply nozzle 5 were mounted on the inner wall of the dissolution tank 1.5 m, 3 m, and 4 m from the upper surface, respectively, at the center of each side wall at 15 m ³ and air pressure of 2.0 kg / cm ² ,
A melting operation was performed.

As a result, by blowing gas and dissolving solution and maintaining the filling degree of metallic zinc in the dissolving tank at 20 to 25%, zinc is stably supplied at a dissolving rate of 166 kg / Hr. It was found that ions could be supplied. The supply rate of the lysis solution was 5 m ³ / min. In addition, there was concern about the influence of Ni sludge by air and the plating solution. However, as a result of operation for 6 months, there was no such problem, and it was found that these Ni layers were redissolved.

[0037]

As described in detail above, the use of the zinc dissolution apparatus according to the present invention makes it possible to use metal Zn in the production of Zn-Ni alloy plating, thereby achieving a significant cost reduction.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a metal zinc supply apparatus according to the present invention.

FIG. 2 is a schematic explanatory view of a device used in a test for demonstrating the effect of the present invention.

FIG. 3 is a graph showing test results.

FIG. 4 is a graph showing test results.

FIG. 5 is a graph showing test results.

[Explanation of symbols]

1: dissolution vessel 2: overflow tank 3: partition plate 4: Filter 5: supply nozzle 6: gas nozzle 7: H ₂ dissipation blower 8: Plating Tank 9: flow meter

Claims (4)

(57) [Claims] 1. An acidic plating bath using an insoluble anode.
A method for supplying zinc in continuous electroplating of a Zn-Ni-based alloy, in which when dissolving metallic zinc in a dissolving solution that is an acidic plating bath, a gas is blown onto the metallic zinc from within the dissolving solution or from the surface of the dissolving solution. A zinc supply method in Zn-Ni-based alloy plating, wherein the dissolution of the metallic zinc is promoted by removing or making the Ni layer or the Ni alloy layer coated on the zinc. 2. The zinc supply method according to claim 1, wherein
A zinc supply method in Zn-Ni-based alloy plating, wherein a Ni layer or a Ni alloy layer coated on metallic zinc is mechanically removed. 3. The zinc supply method according to claim 1, wherein the flow rate of the solution in the metal zinc dissolving tank is 1 m ³ / min or more to remove the Ni layer or the Ni alloy layer coated on the metal zinc. A zinc supply method in Zn-Ni-based alloy plating, characterized by being porous. 4. An acidic plating bath using an insoluble anode.
A zinc supply apparatus in a Zn-Ni-based alloy continuous electroplating system, a melting tank containing a solution and a metal zinc, which are an acidic plating bath recovered from the Zn-Ni-based alloy continuous electroplating system, An overflow tank provided adjacent to the dissolving tank and temporarily containing an overflow dissolving solution from the dissolving tank in which the metallic zinc has been dissolved, wherein the dissolving tank has a plurality of gas jet nozzles and a dissolving liquid supply. A zinc supply device for plating Zn-Ni alloy provided with a nozzle.