JPH03249200A - Production of composite electroplated steel sheet - Google Patents

Abstract

PURPOSE:To allow the continuous production of the subject plated steel sheet which is stable over a long period of time by bringing an aq. soln. contg. Cr<6+> ions into contact with metallic Zn to reduce the ions to Cr<3+> ions, then supplying the aq. soln. to a plating bath at the time of subjecting a steel sheet to Zn composite electroplating contg. respectively specific ratios of Cr, iron family metals and cation polymer. CONSTITUTION:The Zn composite electroplated steel sheet contg. 5 to 30wt. % Cr, 1 to 10wt. % iron family metal and 0.001 to 5wt.% cation polymer is produced by using the acidic Zn plating bath contg. the Cr<3+> ions, the iron family metal ions (Ni, etc.), the cation polymer (quaternary amine polymer, etc.). The aq. soln. contg. the Cr<3+> ions and Zn<2+> ions prepd. by bringing the aq. soln. contg. the Cr6+ ions into contact with metal Zn to reduce the Cr<6+> ions to the Cr<3+> ions and to dissolve the metal Zn is supplied to the Zn-plating bath at this time. The Zn composite electroplated steel sheet having extremely high corrosion resistance and a high Cr content is produced with the quality stable over a long period of time in this way.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing Zn-based composite electroplated steel sheets with high Cr content and excellent corrosion resistance, which are used in automobiles, home appliances, building materials, etc. The present invention relates to an ion replenishment method and a maintenance management method for a plating bath for stable and long-term continuous production.

(Prior Art) It is well known that electrogalvanized steel sheets are widely used as surface-treated steel sheets that improve the corrosion resistance of cold-rolled steel sheets and the corrosion resistance after painting, and can be mass-produced without impairing workability.

In recent years, attempts have been made to use galvanized steel sheets as a rust-proofing measure for automobiles against salt sprayed to prevent roads from freezing during the winter in cold regions, and a high degree of corrosion resistance is required in harsh corrosive environments.

In order to meet the demand for improving the corrosion resistance of galvanized steel sheets, one method is to increase the amount of zinc plating (adhesion: 1:), but this has many problems in terms of weldability and workability.

Therefore, many alloy platings have been proposed as a method of suppressing the dissolution of zinc itself and extending the life of zinc plating.

Many of these contain iron group metals such as Fe, Co, and N1 as alloy components.

In addition, attempts to obtain highly corrosion-resistant electroplated steel sheets by incorporating Cr into Zn or Zn-based alloy plating have been made, for example, in Japanese Patent Publication Nos. 59-311313 and 59-4.
No. 0234, JP-A-81-270398, and JP-A-82-54099 are disclosed.

Since all of these have a low Cr content of 5% or less, no particular consideration has been given to maintenance management such as a method of replenishing Cr ions in the plating bath.

(Problems to be Solved by the Invention) The present inventors have achieved an unprecedented high content by adding a cationic polymer as a Cr precipitation promoter to an acidic Zn-based plating bath containing Cr3+ ions and iron group metal ions. Corrosion resistance, processability, containing Cr and a small amount of cationic polymer.
A guideline for obtaining a Zn-based composite electroplated steel sheet with excellent surface appearance was obtained.

However, in order to manufacture plated steel sheets of stable quality over a long period of time on an industrial scale, a manufacturing technology that can replenish metal ions consumed by plating and maintain them at a predetermined concentration is required.

Regarding Z n "4-one and iron group metal ions, known methods such as replenishing them as acid-soluble carbonates or hydroxides that do not increase the anion concentration, or dissolving the metal can be used in this plating system. Applicable.

However, these conventional methods cannot be applied to replenishment of Cr3+ ions for the following reasons. ■Salts such as chromium sulfate or chromium chloride cause SO2− in the plating bath.
ions, Cg ions accumulate and interfere with long-term continuous production. (2) Carbonates such as Cr(CO3)2 or hydroxides such as Cr(OH)a have extremely slow dissolution rates in acidic plating baths and are not practical.

It is also disadvantageous in that raw material costs are high. ■ Oxides such as metal C and Cr2O3 cannot be applied because they do not dissolve even in strongly acidic plating baths with p)11 or less.

■It is possible to use metallic Cr as an anode and dissolve it electrically, but since Cr3+ ions will dissolve in excess of the amount of Cr”+ ions consumed during plating, the Cr3+ ion concentration must be maintained constant. It is not possible.

As described above, there has been no practical and efficient method for replenishing Cr3+ ions that can be applied industrially.

In view of such circumstances, the present invention has been developed with 5 to 30% by weight of Cr, 1 to 10% by weight of iron group metals, and 0.001 to 5% of cationic polymer.
In the production of a new Zn-based composite electroplated steel sheet containing Cr"+ ions, the problem of supplying and maintenance management of Cr"+ ions can be advantageously solved, and the Zn-based composite electroplated steel sheet can be industrially produced stably. The present invention provides a manufacturing method for obtaining.

(Means for Solving the Problems) The present inventors have discovered that C
We believe that an aqueous solution of r6+ ions is optimal, and continuously
We have discovered a method for replenishing r3+ ions by reducing them.

The present invention was made based on this knowledge, and the gist thereof is (1) Cr3+ ion, iron group metal ion, and cationic polymer-containing acidic Zn-based plating bath.
When producing a Zn-based composite electroplated steel sheet containing 5 to 30% by weight of r, 1 to 10% by weight of iron group metal, and 0.001 to 5% by weight of cationic polymer, an aqueous solution containing Cr6+ ions is brought into contact with metal Zn. (2) Cr3 is reduced to Cr”+ ions and supplied to the plating bath;
Using an acidic Zn-based plating bath containing + ions, iron group metal ions, and cationic polymers, 5 to 30% by weight of Cr, 1 to 10% by weight of iron group metals, cationic polymers o, oot to
When manufacturing a Zn-based composite electroplated steel sheet containing 5% by weight, the plating bath in which Cr6+ ions are generated is brought into contact with metallic Zn to be reduced to Cr"d ions, which is then supplied to the plating bath. , (3) Using an acidic Zn-based plating bath containing Cr3+ ions, iron group metal ions, and cationic polymers, 5 to 30% by weight of Cr, 1 to 10% by weight of iron group metals, and 0.001 to 5% by weight of cationic polymers are applied. When manufacturing a Zn-based composite electroplated steel sheet containing Zn, an aqueous solution containing Cr8+ ions and a plating bath in which Cr6+ ions are generated are mixed, brought into contact with metal Zn to be reduced to Cr3+ ions, and this is supplied to the plating bath. It is characterized by (
4) Supplying a part of Cr3+ ions as chromium sulfate,
and (5) the iron group metal is N1, and (6) the cationic polymer is a quaternary amine polymer.

(Function) 5 to 30% by weight of Cr, 1 to IO by weight of iron group metals, and 0.001 to 0.001% of cationic polymer, which are the targets of the production method of the present invention.
A Zn-based composite electroplated steel sheet containing 5% by weight will be described.

The high corrosion resistance of the composite electroplated steel sheet is expressed by the action of C. The Cr content is preferably 5 to 30% by weight. If it is less than 5% by weight, a slight corrosion resistance improvement effect is observed, but red rust occurs. The tendency to easily rust remains, and the corrosion resistance is not sufficient.When the amount exceeds 5% by weight, the occurrence of red rust is suppressed,
Corrosion resistance is greatly improved. For example, a salt spray test of 500
Red rust does not easily occur even if the process is continued for more than an hour.

Such high corrosion resistance is at a level that cannot be obtained not only with conventionally known Zn plating, but also with alloy plating such as Zn--Ni and Zn--Fe.

When Cr coexists with Zn, it does not become passivated and exhibits a sacrificial anticorrosion effect together with Zn, and corrosion products form a poorly soluble protective film to cover the surface and suppress the progress of corrosion. It is presumed that this is the reason why it exhibits revolutionary high corrosion resistance.

C: Even if the content exceeds 30% by weight, it has a high degree of corrosion resistance, but even with the eutectoid effect of the cationic polymer described below, powdering (powdery peeling of the plating layer) occurs during processing.
cannot prevent the deterioration of the material, making it difficult to apply in practice.

The composite electroplated steel sheet further contains an iron group metal. Here, the iron group metals are Ni, Co, and so on.

It refers to Fe, and the content thereof is preferably 1 to IO weight % in the total amount of one or more types.

The function of iron group metals is mainly to improve spot weldability. Composite plating consisting of Zn high C-cationic polymer that does not contain iron group metals is superior to conventional Zn-Ni.
, the spot weldability is slightly inferior to that of Zn-Fe alloy plating.

The reason for this is not clear, but the composite plating has a low electrical resistance and is easily melted by heat generated by electricity, or the plating layer is soft and easily deforms under the pressure of the welding tip, making it difficult for current to concentrate in the welding area. There are many things that can be considered.

When iron group metals are included, the electrical resistance increases and the plating layer becomes appropriately hard, so spot weldability is reliably improved. If the amount of the iron group metal is less than 1% by weight, the above effect will not be significant, and if it exceeds 10% by weight, the properties of the iron group metal will become stronger and the effect of C' will be reduced.

Considering powdering properties during processing, the total amount of Cr and iron group metals is preferably 30% by weight or less. Note that among iron group metals, Ni is particularly effective for corrosion resistance and is the most advantageous.

The cationic polymer contained in the composite electroplated steel sheet of the present invention is added to the plating bath as a C precipitation accelerator, and by eutectoiding a small amount of it together with C into the plating layer, it is can improve the powdering resistance of

Such eutectoid effect of cationic polymers is due to the fact that Cr is Zn
It is presumed that the purpose of this is to inhibit uniform electrodeposition growth and prevent a plating structure lacking in uniformity and smoothness.

That is, it is thought that a dense plating layer in which Zn, iron group metal, and Cr are uniformly mixed or alloyed is formed through the eutectoid cationic polymer. The content of the organic polymer is preferably 0.001 to 5% by weight. 0.0
If the content is less than 1% by weight, the effect of improving powdering resistance is poor, and if the content exceeds 5% by weight, it is not only difficult to obtain even if the concentration of cationic polymer in the plating bath is increased, but if a large amount is eutectoid, the adhesion of the plating will be adversely affected. Sexuality decreases. In order to ensure powdering resistance, 1/100 of the C content must be
It is desirable to eutectoid the organic polymer at a content of 0 or more.

As the cationic polymer used in the present invention, polymers of quaternary amines are particularly effective. In this case, the molecular weight is 10
3-10B is desirable. Specifically, among the following amine polymers, polyamine sulfone (abbreviated as PAS) and polyamine (abbreviated as PA) are the most effective as Cr precipitation promoters.

This is thought to be due to the adsorption effect of the amine group on the cathode surface and the coordination bond of Cr'-1'one to the sulfone group. These are basically the following 4
It is composed of a homopolymer or copolymer containing a salt of a class amine (ammonium salt) in its main chain.

Some compounds will be specifically listed below.

First, the following polymers obtained from diallylamine are mentioned.

/ \ or / \ N...X ／　＼ 2 ／　＼ RI R2 →Abbreviated as PAS.

Rt, R2 represents a lower alkyl group, X is CN
, H3O, HPO, R-5O3424 (R is a c-c alkyl group), and an anion of NO3.

Another example is a polymer synthesized from vinylbenzine.

N...X/1\RI R2R3 R1, R2, Rs represent a lower alkyl group, X is C#-
, H3O-, HPO, R-NO3424 (R is an alkyl group of cl-c4), and NO3 anion.

Further examples include allylamine polymers.

N...X / 1\RI R2R8 R,, R2, R3 represent a lower alkyl group, X is C,9
-, H5O"-, HPO, R-NO3424 (R is a c-c alkyl group), and an anion of NO3.

In addition, polymers of primary, secondary, and tertiary amines are also effective as Cr precipitation promoters, although they are not as effective as the above-mentioned quaternary amine polymers.

A coating weight of 10 to 50g1rd can ensure sufficient corrosion resistance.

When manufacturing a composite electroplated steel sheet having the composition as described above, it is necessary to maintain a predetermined concentration of Cr3+ ions. To achieve this, we need to: ■ Replenish Cr8' ions consumed by electroplating; ■ Re-reduce Cr'' K ions produced by oxidation of Cr3+ ions at the anode;
These needs to be accomplished efficiently and economically by applying the method of the present invention.

First, there is a method for replenishing Cr"+ ions consumed by electroplating. For this purpose, an effective method is to bring an aqueous solution containing Cr6+ ions into contact with metal Zn, and this is the first aspect of the present invention. When an aqueous solution containing ``4on'' is brought into contact with metal Zn, the metal Zn dissolves while generating hydrogen gas, but Cr'!on promotes the dissolution of metal Zn and is itself reduced to Cr3+ ions. When Cr6+ ions and metal Zn are brought into sufficient contact under appropriate conditions, Cr
' ions are mostly reduced to Cr"l' ions.

The aqueous solution containing Cr6+ ions desirably does not contain other cations or anions in view of the ion balance of the plating bath, and chromic acid, chromic anhydride, dichromic acid, and chromium chromate are suitable.

Chromium chromate is a combination of chromic acid and chromic anhydride with starch,
Organic substances such as alcohols and formic acid are added as reducing agents to reduce one part of Cr"l' ions to C"3+ ions.

As the metal Zn, highly pure Zn such as electrolytically refined Zn is desirable. Further, as for the shape, any of plate-like, granular and powder-like shapes can be used, but granular shapes are preferable in order to increase the contact area with Cr6+ ions and increase the rate of reduction to LCr""4-on.

As a reaction tank for bringing an aqueous solution containing Cr6+ ions into contact with metal Zn, there is a circulation system in which the tank is filled with metal Zn, the aqueous solution containing Cr6+ ions is introduced from the top or bottom of the tank, and after the reaction is discharged from the bottom or top of the tank. It is preferable to use one having the following, since it allows continuous ion replenishment.

The entire amount of the effluent from the reaction tank can be replenished into the plating bath circulation tank, or one part can be replenished and the rest can be stored in the storage tank.
Alternatively, if the reduction reaction is insufficient, it may be allowed to flow into the reaction tank again.

At this time, it is preferable to install perforated plates at the top and bottom of the reaction tank so that metal Zn is not moved by the liquid flow or hydrogen gas. In addition, the inflow of an aqueous solution containing Cr6+ ions prevents air from remaining in the reaction tank and promotes the floating of hydrogen gas.
It is more advantageous to do this from the bottom of the tank. At this time, the outflow from the reaction tank may be passed through a pipe attached to the top of the reaction tank, or may be recovered by overflowing at the top of the reaction tank.

Next, Cr8 produced by oxidation of Cr""4 on at the anode
The method for reducing + ions will be described.

Cr'M' on in the plating bath occurs when an insoluble anode is used as the anode. As is well known, insoluble anodes do not wear out even if electroplating is performed continuously, so they do not require frequent replenishment or replacement unlike soluble anodes, and can be operated under constant plating conditions over long periods of time, resulting in high productivity. The economic advantages of securing such facilities are enormous.

However, when an insoluble anode is used, oxygen generation and oxidation reactions of plating bath components occur at the anode due to electrolysis of water. In a plating bath containing Cr3+ ions, Cr"+ ions are oxidized to generate Cr6+ ions.

When Cr6+ ions accumulate in the plating bath, they cause not only a decrease in plating current efficiency but also a decrease in performance such as surface appearance and workability, so it is necessary to reduce them to Cr'' ions again.

For this purpose, the plating bath itself is brought into contact with the metal Zn, and the Cr
The method of reducing Cr'' to Cr'' is advantageous.

This is the second aspect of the present invention, in which a plating bath in which Cr'-(on is produced) is flowed into a reaction tank filled with metallic Zn, and Cr'!-on in the plating bath is dissolved while metallic Zn is dissolved. This is a method of reducing Cr to Cr.

The metal Zn used and the reaction tank are the same as those described above.

As an insoluble anode, pb or pb-based S
Pb-based electrodes containing n, In, Ag, etc.; Pt-based electrodes containing Ir, Pd, Rh, etc. with Pi or Pt as the main component; ceramic electrodes containing oxides such as Ir, Pd, Rh, etc. as the main component. etc. are applicable. Among them, the pb-based electrode is the most economically advantageous, but the production rate of Cr6'' ions is higher than other electrodes, so the application effect of the present invention is the greatest.

As described above, the replenishment of Cr"!on consumed during electroplating is the first aspect of the present invention, and the Cr6+ produced during plating is
The reduction of ions to Cr''+ ions can be carried out efficiently and economically according to the second aspect of the invention.

These may be applied independently by installing separate reaction vessels. As a more preferred method, it is also possible to replenish Cr3+ ions and reduce Cr' ions during plating using the same reaction tank, which is the third aspect of the present invention.

That is, in this method, an aqueous solution containing Cr6+ ions and a plating bath in which Cr6+ ions are generated are mixed and flowed into a reaction tank filled with metal Zn, thereby simultaneously reducing the solution to Cr''-4 ions.

By doing so, the C consumed by electroplating is
Although it is possible to replenish r3+ ions and reduce Cr ions generated by oxidation at an insoluble anode to Cr"6+ ions, in order to perform more stable long-term continuous production, Zn2" by electroplating. ! on,
With the consumption of Cr3+ ions and iron group metal ions, it is also necessary to consider the accumulation of sulfate ions, which are counter anions thereof.

Sulfate ions can be removed by supplying Sr carbonate and/or Ba carbonate to the plating bath. That is,
Since these are insolubilized as sulfates in the sulfuric acid plating solution, by separating them, the sulfate ions can be removed from the system.

30 This converts some of the Cr ions into C'2(SO4)
It is now possible to replenish Cr' ions as sulfates such as 3 and Cr (OH) (SO4), reducing the burden of reducing and replenishing Cr' ions with metal Zn, and making it possible to maintain and manage ion concentrations with greater precision. .

Another advantage of supplying carbonate and/or Ba carbonate is that it has the effect of adsorbing PB when it is insolubilized as a sulfate.

That is, when using a pb-based electrode, a very small amount of pb is inevitably dissolved in the plating bath;
If it exceeds lOppm, the surface appearance and corrosion resistance of the plating layer tend to deteriorate, which is not preferable. Therefore,
Although it is necessary to remove PB in the plating bath to the outside of the system, Sr
This problem can be solved at the same time by the action of carbonate and Ba carbonate.

The plating bath to which the present invention is applied includes Zn"I' ion, Cr ion, Ni2+ ion, Fe"+43
10 each of iron group metal ions such as +, on, and CO ions.
~100g/i) and P as a Cr precipitation promoter.
A sulfuric acid acid plating bath having a pH of 0.5 to 3 and containing 0.1 to 20 g/l of a cationic polymer such as AS is preferred.

In addition to these components, N a , K , N H4”
5i02゜TiO2, Af to further improve the corrosion resistance.
The present invention is effective even if oxide particles such as I203 or chromate particles such as B a Cr O4 are contained.

Cr6+ ions have no substantial effect and are tolerable as long as they are less than 1/10 of the Cr”d ion concentration.
ions and iron group metal ions can be supplied using carbonates, hydroxides,
Although it is possible by known methods such as metal melting, Z n "K
Since ion is also replenished by the method of the present invention, it is also possible to simultaneously maintain and manage the Z n 2''<on concentration and the Cr3+ ion concentration by adjusting the reaction tank.

Next, an example of a process embodying the manufacturing method of the present invention will be explained using the drawings.

Figure j@1 shows the first aspect of the invention.

Reference numeral 1 denotes a plurality of cells equipped with insoluble anodes. 2
is an insoluble anode, 3 is an energizing roll that passes electricity through the copper strip, 4
is a copper band. Reference numeral 5 denotes a plating bath circulation tank from which the plating bath is circulated to the plating cell 1 for electroplating. Reference numeral 6 denotes a reaction tank, into which metal Zn is charged and filled from a hopper 7, and an aqueous solution containing Cr6+ ions is supplied from a tank 8.

In this reaction tank, Cr6+ ions undergo a contact reaction with metal Zn and are reduced to Cr3+ ions, and metal Zn dissolves and becomes Zn.
n 2”< turns on. This C “3+ ion and Zn2
An aqueous solution containing + ions is supplied to the circulation tank 5. Here, if the reduction reaction is insufficient, the supply is again supplied to the reaction tank from 9, and when there is no need to supply to the circulation tank, the supply is made to the storage tank 10.
Store it in the tank and supply it to the circulation tank as needed.

Further, the hopper 11 may be charged with an aqueous solution of chromium sulfate, and the hopper 12 may be charged with carbonate of Sr and/or Ba, and may be supplied to the plating bath as required.

Carbonates of Sr and/or Ba are insolubilized as sulfates, and when a PB-based electrode is used as an anode, they adsorb PB eluted into the plating bath, but this is separated by a filter 16 and removed from the system.

A cationic polymer such as PAS, a carbonate of an iron group metal such as Ni, and zinc carbonate are respectively charged into the hoppers 13 to 15, and are charged into a circulation tank as required.

Zinc carbonate is produced by dissolving Zn2+ (
It can be used as an auxiliary when the supply of on is insufficient.

FIG. 2 shows a second aspect of the invention.

The explanations for 1 to 7 and 11 to 16 in the figure are the same as in FIG. 1, but the reaction tank 6 is supplied with a plating bath from a circulation tank. The C'6+ ions contained in the plating bath are reduced to Cr'K ions by reaction with metal Zn filled in the reaction tank and returned to the circulation tank.

FIG. 3 shows a third aspect of the invention.

The explanations for 1 to 8 and IO to 16 in the figure are the same as in FIG. supply to.

As a result, Cr"" ions consumed in electroplating are replenished and Cr6+ ions generated at the anode are reduced to Cr3+ ions at the same time.

As described above, by applying the present invention, plating bath temperature of 30 to 70°C and current density of 50 to 300 A/dw can be achieved.
Under the conditions of 2, it is possible to stably produce a highly corrosion-resistant Zn-based composite electroplated steel sheet containing 5 to 30% by weight of Cr, 1 to 10% by weight of iron group metals, and 5% by weight of cationic polymer o,oot over a long period of time. can.

(Example 1) A cold-rolled steel sheet was degreased with alkali, pickled with a 5% aqueous sulfuric acid solution, and then electroplated under the following conditions. As a plating bath, Zn2"-45g/fl, 3+ Cr = LOg/II, Ni2"-22sr/IIS
PAS (average molecular weight IO million) = 5 g/D,
Na 2”-16g/p1 Bath temperature 50°C, I) Hl, 5
A sulfuric acid acid bath was used.

Current density 100A/d using I r O2 electrode as anode
12. Continuous plating was performed at 10,000 coulombs/I at a liquid flow rate of 100 m/gin.

Plating layer composition: CrlO%, Ni 2%, PAS 1%
, the remainder was Zn. After applying a current of 10,000 corons/g, there was only a trace amount of Cr6+ in the plating bath.

Next, 2g of metal Zn powder and total C per plating bath 111
A chromium chromate aqueous solution containing 2 g of rO (38% of the total 30 Cr was Cr, the remainder Cr') was sufficiently reacted at 50° C. to dissolve metal Zn. There was only a trace of Cr6+ in the aqueous solution after the reaction, and almost the entire amount was reduced to Cr3+.

When this aqueous solution was added to the plating bath, the 2+ Z n Cr 3''s concentration was restored to approximately the initial concentration.

Continuous plating at 10,000 coulombs/p and ion replenishment were performed again under the same conditions as above, and this was repeated up to 500,000 coulombs/g. During this time, the correction of N i '2a degree is Ni
The experiment was carried out using CO3, and slight fluctuations in added components due to drag-out etc. were appropriately adjusted using reagents.

Z n 2” after energizing 500,000 cr/p, Cr
``9 degrees is almost the same as the initial concentration, and Cr6+ is 0.
It was 1g/g. In addition, the plating layer composition up to 500,000 coulombs/1 is approximately CrlO%, Ni 2%, PA 51%,
The balance remained stable with Zn, and the surface appearance and workability (powdering property) were also good.

(Example 2) As a plating bath, Z n"=45 g/N, Cr""
-20g/l, Co"=44g/II, FA
(Average molecular weight 10,000) = 10g/l, Na2”-1
8g/j! , using a sulfuric acid acid bath with a bath temperature of 80°C and a pH of 1.8, with a Pt electrode as an anode, and a current density of 200 A/d.
12. Continuous plating was performed at 10,000 coulombs/fl at a liquid flow rate of 100 m/sin.

The plating layer composition was Cr2O%, Co7%, PA2%, balance Zn. There was only a trace of Cr6+ in the plating bath after 11,000 Coron/11 current was applied.

Next, 2g of metal Zn powder and Cr per plating bath 11 were added.
' A chromic acid aqueous solution containing 0.5 g was sufficiently reacted at 50°C to dissolve metal Zn. C in the aqueous solution after the reaction
There was only a trace of r6+, and almost all of it was reduced to Cr''+.

When this aqueous solution was added to the plating bath, 2+ Zn, Cr3+m degrees recovered to almost the initial concentration.

Continuous plating and ion replenishment at 10,000 coulombs/II were performed again under the same conditions as above, and this was repeated up to 500,000 coulombs/II. During this time, the Co2''tli degree was corrected using Co2COs, and slight fluctuations in the added components due to drug-out etc. were adjusted as appropriate using reagents.

Z n "" after energizing 500,000 cron/g, Cr
``9 degrees is almost the same as the initial concentration, and Cr6+ is 0.
It was 15g/Ill. In addition, the plating layer composition up to 500,000 coulombs/ρ is approximately Cr2O%, Co 7%, PA2
% and the remaining Zn remained stable, and the surface appearance and workability (powderability) were also good.

(Example 3) As a plating bath, Zn -45g/l), Cr3"5
-10g/II, N i 2+ ~ 45g/I, P
AS (half-average molecular weight 3500) -2fr/II,
Using a sulfuric acid acid bath with a bath temperature of 60°C and a pH of 2.0, using a Pb-5%Sn electrode as an anode, current density of 150A/da + 2 liquid flow rate of 100m/■1n
Continuous plating was performed at 10,000 coulombs/p under the following conditions.

The plating layer composition is CrlO%, Ni 5%, PASO1
1%, the balance was Zn. C during plating after energizing 10,000 Clon/g 6+ is 0.2g/fl, Pb is 10p
It was pm.

Next, during plating, 2g of metal Zn was added per 1g of plating bath.
A chromic acid aqueous solution containing the powder and 0.2 g of Cr' was added and sufficiently reacted at 50° C. to dissolve metal Zn.

There is only a trace of Cr6+ in the plating bath after the reaction, and Z
n'', Cr''8 degrees recovered to almost the initial concentration.

(Example 4) As a plating bath, Z n ""-45 g / I s
Cr""=20z/I, Ni2"-22g/
I, PAS (average molecular weight 3500) = 2
g/l, Na ""-32tr/1, bath temperature 55℃
, Pb-3% In- using a sulfuric acid acid bath with pH 1.5
Current density 150A/d using 0.5%Ag electrode as anode
112, continuous plating was performed at a liquid flow rate of 10,000 coulombs/II under the conditions of Loom/win.

The plating layer composition is Cr2O%, Ni 2%, PASO0
2%, the balance being Zn. After applying a current of 10,000 corons/g, Cr6+ in the plating bath is Q, 3tr/II, and Pb is 5
It was ppm.

Next, 2 g of metal Z per plating bath lit was added to the plating bath.
A chromic acid aqueous solution containing n powder and 0.5 g of Cr' was added, and the mixture was sufficiently reacted at 50° C. to dissolve metal Zn.

There is only a trace of Cr6+ in the plating bath after the reaction, and Z
n2+ and Cr"6 degrees recovered to almost their initial concentrations.

(Example 5) In the plating bath after continuous plating at 10,000 coulombs/II in Example 3, 2 g of metal Zn powder and C were added per plating bath lit.
50 by adding a chromic acid aqueous solution containing 1 g of r'O.
The reaction was carried out sufficiently at 0.degree. C. to dissolve the metal Zn.

Furthermore, in the plating bath, Cr per plating bath III”
An aqueous solution of chromium sulfate containing 1 g of O and 0.5 g of S r
COs powder was added and dissolved. C in the glazing bath after reaction
r6+ was at a trace level, and pb was less than 1 ppm.

Furthermore, Zn2+ and Cr3+a concentrations were recovered to almost their initial concentrations. Continuous plating at 10,000 coulombs/g and ion replenishment were carried out again under the same conditions as above, and this was repeated at 1 million coulombs/g.
Repeated until 1. During this time, the N i ''fi degree was corrected using NiC0, slight fluctuations in added components due to drug-out, etc. were appropriately adjusted with reagents, and insolubilized S r SO 4 was removed with a filter.

After applying 1 million coulombs/g, the Zn and Cr"@2+ degrees were almost the same as the initial concentration, Cr6+ was only a trace, and pb was less than 1 ppI11.
The plating layer composition up to 00,000 coulombs/p is approximately CrlO%
, N15%, PASo, 1%, balance Zn, and the surface appearance and workability (powdering property) were also good.

(Example 6) In the plating bath after the continuous plating of 10,000 Cr/g in Example 4, 2 g of metal Zn powder and Cr were added per 1 g of the plating bath.
' Add a chromic acid aqueous solution containing 0.3g and heat at 50°C.
The reaction was carried out sufficiently to dissolve the metal Zn.

Furthermore, in the plating bath, Cr per plating bath Ig
An aqueous solution of chromium sulfate containing 0.2 g and 1 g of B a CO
Powder a was added and dissolved. Cr6 in the plating bath after reaction
+ indicates only a trace, and PB was 1 ppm or less.

Furthermore, Z n ” and Cr ” at 78 degrees recovered to almost their initial concentrations. 10,000 kron/g again under the same conditions as above.
Continuous plating and ion replenishment were performed, and this was repeated up to 1 million coulombs/g.

, 2+ During this time, the Ni concentration was corrected using N t COs, slight fluctuations in added components due to drug-out etc. were adjusted appropriately with reagents, and insolubilized B a S O4 was removed with a filter.

After applying 2+ 1 million coulombs/I, Zn and Cr3"6 degrees were almost the same as the initial concentration, Cr6+ was at the level of a wolf's trace, and pb was less than 1 pp-. Also, up to 1 million coulombs/g Plating layer composition is approximately Cr2O%, Ni 2%
, PASo, 2%, balance Zn, and the surface appearance and processability (powdering property) were also good.

(Comparative Example 1) In Example 1, the adjustment of Zn2'', Cr''+ concentration was
When replenishing C0 and chromium sulfate, a tendency for the C content to decrease began to appear around 200,000 cr/g, and after 500,000 cr/g, the plating layer composition became Cr7.
%, Ni 2%, PAS O, 1%, and the balance Zn.

(Comparative Example 2) In Example 6, Z n2", Cr" was adjusted by 6 degrees.
n Performed by supplementing COa and chromium sulfate, and S r
When no CO3 powder was added, the Cr content began to decrease from around 200,000 coulombs/g, and the plating layer composition after 1 million coulombs/g was Cr1.
5%, Ni 1%, PASO 1%, and the balance Zn.

Also, Cr6+ in the plating bath is 10g/II SPb is 2
It had increased to 0 ppm. The surface appearance of the plating had uneven gloss, and the plating current efficiency and workability were also reduced.

(Example 7) 2+ As a plating bath, Zn -45g/l, Cr''-20
tr/I, Ni""-22g/l), PAS
(Average molecular weight 3500) = 2g/I, Na2”-
Continuous plating was carried out using the electroplating equipment shown in FIG. 1 using a sulfuric acid acid bath of 32 g/fl, bath temperature 50° C., and I) H1. In the plating cell 1, the anode 2 is Pb-3
%In-0.5%Ag electrode, current density 80A/d■
2. The test was carried out under the conditions of a liquid flow rate of 100 m/Maro In.

The reaction tank 6 is filled with metal Zn plates, and the storage tank 8 is filled with Cr'
A 30 g/I chromic acid aqueous solution was flowed into the bottom of the reaction tank 6. Hoppers 11 to 14 were charged with PAS, nickel carbonate, a chromium sulfate aqueous solution of Cr 3"Jog /1, and S r COs. By operating these, the continuous current flow was up to 1 million coulombs/g.
", Cr3", and N i 2"s were able to be maintained at almost their initial values, Cr6+ was suppressed to a trace level, and PB was suppressed to 1 ppm or less.

In addition, the plating layer composition up to 1 million coulombs/II remains stable with approximately CrlO%, Ni 2%, PASO, 1%, and the balance Zn, and the surface appearance and workability (powdering property)
was also good.

(Effects of the Invention) As described above, according to the present invention, it is possible to manufacture a Zn-based composite electroplated steel sheet with high Cr content and excellent corrosion resistance with stable quality over a long period of time, and it is suitable for industrial production. It shows excellent effects.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are explanatory diagrams each showing an example of the process of the present invention. 1: Plating cell 2: Insoluble anode 3: Current roll 4: Steel strip 5: Plating bath circulation tank 6: Reaction tank 7: Hopper
8 = Tank 9: Mixing point l
O: Storage tanks 11-15: Hopper-16: Filter fee
Attorney Patent Attorney Tate Chanogi Mistake Diagram Figure 3 Procedural Amendment (Spontaneous) April 1, 1990 1990 Patent Application No. 47 No. 34 2, Title of Invention Method for Manufacturing Composite Electroplated Steel Sheet 3, Relationship with the case of the person making the amendment

Claims (1)

[Claims] 1. Cr5~ using an acidic Zn-based plating bath containing Cr^3^+ ions, iron group metal ions, and cationic polymers.
When manufacturing a Zn-based composite electroplated steel sheet containing 30% by weight, 1 to 10% by weight of iron group metals, and 0.001 to 5% by weight of cationic polymer, an aqueous solution containing Cr^6^+ ions is brought into contact with metallic Zn. and reduce it to Cr^3^+ ions,
A method for producing a composite electroplated steel sheet, which comprises supplying this to a plating bath. 2. The plating bath in which Cr^6^+ ions are generated is treated with metal Zn.
2. The method for producing a composite electroplated steel sheet according to claim 1, wherein the Cr^3^+ ions are reduced by contacting with Cr^3^+ ions, and the Cr^3^+ ions are supplied to the plating bath. 3. Aqueous solution containing Cr^6^+ ions and Cr^6^
The method of manufacturing a composite electroplated steel sheet according to claim 1, characterized in that the plating bath in which + ions are generated is mixed and brought into contact with metal Zn to be reduced to Cr^3^+ ions, which is then supplied to the plating bath. Method. 4. Production of a composite electroplated steel sheet according to claims 1 to 3, further comprising supplying a part of the Cr^3^+ ions as chromium sulfate, and supplying Sr carbonate and/or Ba carbonate to the plating bath. Method. 5. The method for producing a composite electroplated steel sheet according to claims 1 to 3, wherein the iron group metal is Ni. 6. The method for producing a composite electroplated steel sheet according to claims 1 to 3, wherein the cationic polymer is a quaternary amine polymer.