JPH03260092A - Production of zinc-silica composite electroplated steel sheet - Google Patents

Abstract

PURPOSE:To produce a zinc-silica composite electroplated steel sheet with a plating layer whose workability is not deteriorated by adding a complexing agent stable to zinc as well as silica particles and nitrate ions to an electroplating bath. CONSTITUTION:An acidic zinc (alloy) electroplating bath contg. silica particles and nitrate ions is prepd., a complexing agent stable to zinc is added to the bath by 0.001-10mol/l and a steel sheet is composite-electroplated with the resulting bath. since the complexing agent is present, the excessive rise of the pH of the bath is inhibited, the rate of codeposition of silica in a plating layer is not excessively increased and the deterioration of the workability of the plating layer can be prevented. Disodium ethylenediaminetetraacetate or sodium citrate is suitable for use as the complexing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a zinc-silica composite electroplated steel sheet having excellent corrosion resistance.

[Conventional technology]

In order to further improve the corrosion resistance of zinc-based electroplated steel sheets, many attempts have been made in recent years to improve the corrosion resistance of the coating layer by uniformly dispersing silica particles in the zinc-based coating layer made of zinc or zinc alloy. It is.

In this way, by uniformly dispersing silica particles in the zinc-based plating layer, the corrosion resistance of the dumbbell-based plating layer is improved. However, it is difficult to uniformly disperse silica particles in the zinc-based plating layer.

It's not easy. This is because silica particles, like other oxide particles, tend to be negatively charged in zinc electroplating baths and are less likely to deposit on the surface of the steel sheet as a cathode.

As a method for solving the above-mentioned problems and manufacturing a sub-silica composite electroplated S plate in which silica particles are uniformly dispersed in the zinc-based plating layer, 1 is disclosed, for example, in JP-A-63-1998.
No. 99 of the newsletter discloses a method consisting of F.

A zinc or zinc alloy acidic electroplating bath containing silica particles and nitrate ions is used to form a zinc-based plating layer in which silica particles are dispersed on the surface of the steel plate by electroplating using the steel plate as a cathode (hereinafter referred to as , "prior art"
).

[Problem to be solved by the invention]

According to the prior art described above, zinc is activated on silica particles by nitrate ions contained in the electroplating bath. As a result, the eutectoid rate of silica increases in the plating layer and on the surface of the steel sheet.

A zinc-based plating layer in which silica particles are uniformly dispersed can be formed.

However, the above-mentioned prior art has the following problems.

Zn-5i when performing electroplating using a Zn-3in2 acidic electroplating bath containing nitrate ions.
The eutectoid behavior of n is estimated to be first-order, and Zn2゛+2
0H-→Zn(OH)2...”(I)7, n(Off)
, + 2e−−+Zn+ 20H−・”(2) No3
-+98"+80--+NH,+3f(20"...(
3) Due to the one-element Zn reaction in (1) and (2) above, p)I of the plating bath at the cathode interface becomes approximately 5.6, but does not increase beyond that. However, in (3) above
Due to the reduction reaction of No□゛, the pH of the plating bath is .

It rises to about 5.6 or more. As a result, silica particles are adsorbed by zinc ions, and silica and zinc are eutectoid in the plating layer.

As shown in item 2, the pH of the plating bath increases due to nitrate ions, and the eutectoid rate of silica increases, but on the other hand, if the eutectoid rate of silica increases too much, the workability of the plating layer deteriorates.

Since the content of nitrate ions sensitively reacts to the pH of the plating bath and the eutectoid rate of silica, it is possible to increase the eutectoid rate of silica without deteriorating the workability of the plating layer. The appropriate range for the concentration of nitrate ions in the plating bath is extremely narrow.

It is extremely difficult to maintain the concentration of nitrate ions in the plating bath within the narrow appropriate range mentioned above, so silica particles are uniformly dispersed in sufficient quantities to improve the corrosion resistance, and at the same time, the deterioration of processability. It has a plating layer that does not cause any damage. It is extremely difficult to stably produce zinc-silica composite electroplated steel sheets.

Therefore, an object of the present invention is to solve the above-mentioned problems when forming a zinc-based plating layer in which silica particles are dispersed on the surface of a steel sheet by using a zinc or zinc alloy electroplating bath containing silica particles and nitrate ions. Stable production of zinc-silica composite electroplated steel sheets that have a sufficient amount of silica particles uniformly dispersed to improve corrosion resistance and have a plating layer that does not deteriorate workability. The goal is to provide a way to do so.

[Means to solve the problem]

The present inventors have conducted extensive research in order to solve the above-mentioned problems. As a result, if a predetermined amount of a zinc-stable complexing agent is added to a zinc or zinc alloy acid electroplating solution containing silica particles and nitrate ions, and electroplating is performed using this plating bath, It has a plating layer in which a sufficient amount of silica particles is uniformly dispersed to improve corrosion resistance, and the processability does not deteriorate. It has been found that zinc-silica composite electroplated steel sheets can be stably produced.

This invention was made based on the above findings, and uses a zinc or zinc alloy acidic electroplating bath containing silica particles and nitrate ions.

A method for producing a zinc-silica composite electroplated steel sheet, which comprises forming a zinc-based plating layer in which silica particles are dispersed on the surface of the steel sheet by electroplating using a steel sheet as a cathode, in the acidic electroplating bath. together with the silica particles and the nitrate ions, zinc-stable, 0.001~0.
It is characterized in that it contains a complexing agent in an amount within the range of mol/l and conducts electroplating using such an acidic electroplating bath.

The reason for adding a complexing agent to the plating bath containing silica particles and nitrate ions in this invention is as follows. That is, when zinc and a stable complexing agent coexist in the plating bath, an excessive increase in the pH of the plating bath caused by the reaction (3) described above is suppressed. Therefore, the eutectoid rate of silica in the plating layer does not increase excessively, and deterioration of the workability of the plating layer can be prevented. Thus, by the addition of complexing agents into the plating bath.

The eutectoid rate of silica can be increased and the corrosion resistance can be improved without deteriorating the workability of the plating layer. The appropriate range of nitrate ion concentration in plating is greatly expanded.

The complexing agent has the ability to form a complex with zinc, and the degree of stability of the complex with zinc is required to be 1.0 or more when the pH of the plating bath is 6.

When the stability number is less than 1.0, the ability to suppress the increase in pH is small, and the desired purpose cannot be achieved.

The content of the complexing agent in the plating bath should be within the range of 0.001 to 10 mol/l. If the content of the complexing agent is less than o, ooi mol/e, an increase in the pH of the plating bath cannot be appropriately suppressed.

On the other hand, if the content of the complexing agent exceeds 10 mol/l.

This causes a problem in that the electrolytic efficiency decreases, plating burn occurs, and the quality deteriorates.

An example of a suitable complexing agent for use in this invention is shown below.

EDTA-Na (Disodium ethylenediaminetetraacetate) Citric acid ion Oxalate ion Tartrate ion Cy DTA (Trans-1,2-Cycle)
ohexar+e-diamine-N, N, N', N
'-tetraacetic Ac1d) D T P
A (Diethylene trjamine P
entaacetic Acid) G E D T A (EthyLenedioxyb
js(ethylao+1ne)-N.

N+N'+N' -tetraacetic Ac1d
) rjen It is preferable to use colloidal silica as the silica particles because of ease of handling when adding them to the plating bath. The particle size of the silica particles is preferably limited to 1 μm or less. When the particle size exceeds 1 μm, it becomes difficult to uniformly disperse the silica particles in the plating layer. The content of silica particles in the plating bath is preferably within the range of 0.5 to 10g/(l).
Below 0.

The eutectoid efficiency of silica decreases, making it impossible to obtain high corrosion resistance in the plating layer. On the other hand, if it exceeds 100 g/n, @
The transfer rate decreases.

As the nitrate ion, NaN0. , K〜O,, Zn(
No, )2゜)INO, etc. can be used.

The content of nitrate ions in the plating bath is 100-300
0. It is preferably within the range of pm. Nitrate ion content is 1
If it is less than 100 pp, the eutectoid efficiency of silica decreases, and high corrosion resistance cannot be obtained in the plating layer. On the other hand, 3000
If it exceeds pp111, a dense plating layer cannot be obtained.

The eutectoid rate of silica in the plating layer is 0.2iit, % or more
7 is preferable. The eutectoid rate of silica is ]2Wj
,%, high corrosion resistance cannot be obtained in the plating layer. As the eutectoid rate of silica increases, the corrosion resistance of the plating layer improves, but on the other hand, the workability of the plating layer deteriorates. Therefore, the upper limit of the eutectoid rate of silica is.

It is preferable to set it to 15ilt,%, which does not deteriorate the workability (OT bending) of a normal galvanized steel sheet (plating amount 40 g/rf).

In this invention, the plating layer in which silica particles are uniformly dispersed contains only zinc as the gold gL component, and if necessary, iron and nickel.

At least one component of cobalt and chromium can be included.

The basic galvanizing bath is a normal sulfuric acid bath.

A chloride bath or a mixture of both can be used. These basic baths may also contain conductivity aids, brighteners, and the like.

Next, the present invention will be explained by way of examples while comparing with comparative examples which are outside the scope of the present invention.

〔Example〕

An acidic dumbbell electroplating bath consisting of the following was used as the basic bath.

Zinc sulfate Sodium sulfate Sodium acetate Colloidal silica: Sodium nitrate pH: 2 To the above basic bath, a method according to the scope of this invention shown in Table 1 (
A complexing agent was added according to NGI-14 (hereinafter referred to as "method of the present invention") to prepare a zinc electroplating bath. Silica particles are uniformly dispersed on the surface of the steel plate by electroplating at a current density of 50 A/di using the zinc electroplating bath produced in Y4 as described above and using the cold rolled steel plate as a cathode. 40g#r? A zinc-silica composite electroplated layer was formed in an amount of .

For comparison purposes, it is outside the scope of this invention. Methods shown in Table 1 (hereinafter referred to as “comparative methods”) llk11-3
Accordingly, a zinc-silica composite electroplating layer was formed on the surface of a cold-rolled steel sheet under the same conditions as above.

300g/Q.

30g/i).

12g/(1, 70g/l, 1.6g/l.

Table 1 Sodium nitrate (
Proper concentration range (ΔX) of NaNO,), i.e., zinc-
The content of sodium nitrate and the eutectoid rate of silica when the workability of the silica composite electroplated layer (○T bending) is worse than that of a normal galvanized steel sheet (coating amount: 40 g/m) , 0,2 sufficient to improve corrosion resistance.
The difference between the content of sodium nitrate and the content of sodium nitrate when it exceeds uL, % was investigated, and this is also shown in Table 1.

As is clear from Table 1, the appropriate range concentration (Δ×) of sodium nitrate is 0.02 gI
The zinc-silica composite electroplating layer has a very narrow Q or less, and therefore has a sufficient amount of silica particles uniformly dispersed on the surface of the steel sheet to improve corrosion resistance, and does not deteriorate workability. It was extremely difficult to form it stably.

Even if a complexing agent is added to the plating bath, in comparative method Na 3, the amount of complexing agent is outside the range of the present invention, and although the appropriate concentration range (△×) of sodium nitrate is wide, the electrolytic efficiency is low. Although not shown in Table 1, plating burn occurred and the quality of the plating layer deteriorated.

On the other hand, in methods Nos. 1 to 14 of the present invention, in which plating was carried out using a plating bath to which an amount of complexing agent was added within the range of this invention, the appropriate concentration of 1 to 1 to 1 lithium nitrate was determined. The range (△×) is wide from 0.04 to 1.0 g/l, so a sufficient amount of silica particles is uniformly dispersed on the surface J- of the steel sheet to improve corrosion resistance, and also to improve workability. It was possible to stably form a zinc-silica composite electroplated layer of excellent quality without deterioration.

〔Effect of the invention〕

As described above, according to the present invention, a zinc or zinc alloy electroplating bath containing silica particles and nitrate ions is used to form a zinc-based plating layer in which 5J particles are dispersed on the surface of a steel sheet. During formation, the appropriate range of nitrate ion concentration in the plating bath is expanded, and a sufficient amount of silica particles are uniformly dispersed to improve corrosion resistance.
It has a plating layer that does not deteriorate workability. Zinc-
It is possible to stably produce Shitsuka composite electroplated steel sheets. Industrially useful effects are produced.

Claims (1)

[Claims] 1. Zinc with silica particles dispersed on the surface of the steel plate by electroplating using a zinc or zinc alloy acidic electroplating bath containing silica particles and nitrate ions and using the steel plate as a cathode. In the method for manufacturing a zinc-silica composite electroplated steel sheet, which comprises forming a zinc-silica composite electroplating layer, 0.001 to 10 mol of zinc-stable material is added to the acidic electroplating bath together with the silica particles and the nitrate ions. 1. A method for producing a zinc-silica composite electroplated steel sheet, which comprises containing a complexing agent in an amount within the range of /l and performing electroplating using such an acidic electroplating bath.