JPH0853794A - Method for producing zinc-chromium alloy electroplated steel sheet with excellent corrosion resistance - Google Patents

Abstract

(57) [Summary] [Purpose] To stably produce zinc-chromium alloy electroplated steel sheets with excellent corrosion resistance for a long period of time. [Constitution] Zinc ion, trivalent chromium ion and 4m
Polyoxyalkylene derivative 0.01 consisting of +2 (m = 1 or 2) π-electron aromatic and / or heteroaromatic hydrocarbon group having 20 or less carbon atoms and ethyleneoxy group having 15 or less additional moles The steel sheet is electroplated at a current density of 50 A / dm ² or more using an acidic plating bath containing ˜20 g / l. It is preferable that the polyoxyalkylene derivative has an anion group and / or a cation group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a zinc-chromium alloy electroplated steel sheet for use in automobiles, home appliances, building materials, etc., which has excellent corrosion resistance and corrosion resistance after painting.

[0002]

2. Description of the Related Art An electroplated steel sheet containing Cr in Zn or a Zn-based alloy plating is, for example, Japanese Patent Publication No.
There are those described in JP-A-36078, JP-A-61-270398, JP-B-58-56039 and the like, but the eutectoid ratio of Cr is extremely small up to 0.005 to 5%, and corrosion resistance is high. For Cr, the effect of Cr can only be incidental, and there is a drawback that dramatic corrosion resistance is not exhibited.

In addition, Zn is made to contain 5% or more of Cr,
As a method for producing a zinc-chromium alloy plated steel sheet having improved corrosion resistance, JP-A-1-55398 and JP-A-1-
There are those described in Japanese Patent Application Laid-Open No. 191798 and Japanese Patent Laid-Open No. 3-120393, but when these are industrially implemented, Zn ²⁺ ions and Cr ³⁺ ions consumed by plating, and supplementation of additives However, there is a drawback in that stable plating cannot be performed semipermanently for a long period of time even if the above is performed.

[0004]

In view of the above problems, the present invention is a method for semi-permanently and stably producing a zinc-chromium alloy electroplated steel sheet containing 5% or more of Cr in Zn. Is intended to provide.

[0005]

The present invention provides zinc ions,
Polyoxy consisting of a hydrocarbon group having 20 or less carbon atoms and an ethyleneoxy group having 15 or less added moles, which has a trivalent chromium ion and an aromatic and / or heteroaromatic 4m + 2 (m = 1 or 2) π electron A method for producing a zinc-chromium alloy electroplated steel sheet having excellent corrosion resistance, which comprises plating at an electric current density of 50 A / dm ² or more using an acidic plating bath containing 0.01 to 20 g / l of an alkylene derivative. . It is preferable that the polyoxyalkylene derivative has an anion group and / or a cation group. Further, the zinc ion concentration is 10 to 150 g / l, the trivalent chromium ion concentration is 10 to 150 g / l, the hydrocarbon group concentration is 0.01 to 20 g / l, and the pH is 0.5 to 3, and , NH ₄ ⁺ ions and / or Li ⁺ ,
It is preferable to add one or two or more kinds of Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , and Al ³⁺ ions as ions at a concentration of 1 g / l or more and 50 g / l or less.

[0006]

The above problem is caused by the fact that the additive decomposes due to an electrolytic reaction caused by long-term plating, and the stability of the plating is impaired by the accumulation of substances produced by the decomposition. Is greatly influenced by the structure of the hydrophobic base and the structure of the hydrophilic base of the additive. Therefore, the size of the hydrocarbon group, which is the hydrophobic group of the additive, and the stability of the bond due to the resonance π bond are ensured, and the ethyleneoxy group, which is the hydrophilic group, is made small so that the decomposition product of the additive by electrolysis can be generated. It is extremely small, and even if a long-term electrolysis is performed, the additive is reduced and the effect of decomposition on the plating is rendered harmless,
Further, it is possible to semi-permanently and stably manufacture a zinc-chromium alloy electroplated steel sheet containing 5% or more of Cr in Zn.

The present invention will be described in detail below.

From the hydrocarbon group having 20 or less carbon atoms and the ethyleneoxy group having 15 or less additional moles, which has 4m + 2 (m = 1 or 2) π-electron aromatic and / or heteroaromatic groups used in the present invention. The polyoxyalkylene derivative is represented by the chemical formula 1.

[0009]

Embedded image R ₁ — (OCH ₂ CH ₂ ) _n —OH

In the above rational formula, the number of added moles n is 1 or more and 15 or less as an average molecular weight. The reason why the average molecular weight is used is that, in the synthesis of ethylene oxide, since it has a distribution in addition polymerization, industrially, it becomes impossible to obtain a single addition mole number as n becomes larger. Method The average molecular weight is the distribution average known by gas chromatography, liquid chromatography, and critical liquid chromatography. R ₁ is a hydrocarbon group having 4m + 2 (m = 1 or 2) π-electron aromatic and / or heteroaromatic groups. Specifically, R ₁ is a phenyl group (C ₆ H ₅ —), Benzyl group (C ₆ H ₅ CH
₂ -), naphthyl (C ₁₀ H ₇ -), phenethyl group (C
₆ H ₅ CH ₂ CH ₂ —) and other aromatic hydrocarbon groups, furyl groups (C ₄ H ₃ O—), furfuryl groups (C ₄ H ₃ OC)
H ₂ -), a pyrrolyl group (C ₄ H ₄ N-), pyridyl group (C ₅ H ₃ N-), thienyl (C ₄ H ₄ S-), Seniru group _{(C 4 H 3 SCH 2 -} ) , such as Heteroaromatic hydrocarbon groups and those having non-benzenoid aromatic hydrocarbon groups such as tropolone group inside. These have a π-electron number of 4 m + 2, exhibit aromaticity, and chemically stabilize the bond. Even if an alkyl side chain such as a methyl group is introduced into these aromatic and / or heteroaromatic rings, the effects described below will not change as long as the number of carbon atoms is 20 or less. And these are called nonionic additives.

Further, it may be an anionic additive in which an acid group such as a sulfonic acid group, a carboxyl group, a sulfuric ester group or a phosphoric acid ester group is introduced into the polyoxyalkylene derivative, or a cationic additive in which an amino group is introduced. , The effects described below do not change.

First, if R ₁ does not exist, the number of moles n of ethyleneoxy group addition is 15 or less and 5% or more of sufficient Cr.
The eutectoid rate cannot be obtained. R ₁ must be a hydrocarbon group having 4m + 2 π-electron aromatic and / or heteroaromatic groups, that is, a group exhibiting aromaticity. These bonds chemically stabilize the bond by resonance and improve the stability of the additive against electrolysis during plating. If the number of π electrons is 4 × m + 2 and m is 3 or more, the hydrocarbon group becomes too large and the hydrophobicity becomes high, so that it is difficult to secure the dissolution of the additive in the plating solution, and foaming due to the circulation of the plating solution occurs. Violent and not industrial. When the carbon number of R ₁ exceeds 20, the hydrophobicity is similarly high, it is difficult to secure the dissolution of the additive in the plating solution, and the foaming due to the circulation of the plating solution is severe.
Poor plating caused by bubbles and increased load on plating circulation equipment are not industrial.

When the added mole number n of the ethyleneoxy group is 0, no co-deposition of Cr occurs. If it exceeds 15, the molecular length becomes long and the CH ₂ O bond is likely to be cleaved by an electrolytic reaction.
The eutectoid rate fluctuates drastically, and the consumption of additives increases, which is not a cost effective measure. Further, in the case of methylene oxide other than ethyleneoxy group, CH ₂ O
The bond is likely to be cleaved by an electrolytic reaction, and the Cr eutectoid ratio fluctuates drastically. With propylene oxide or more (alkylene oxide having 3 or more carbon atoms), even if the added mole number is 15 or less, C
The eutectoid of r becomes insufficient.

In the polyoxyalkylene derivative, if R ₁ is the above-mentioned hydrocarbon group and an ethyleneoxy group having a number of addition moles of 15 or less, anionic addition of anion groups introduced to R ₁ and / or ethyleneoxy group is carried out. Even as an agent, it does not affect the long-term stability of the plating, and the anionization can further improve the plating adhesion.

In the polyoxyalkylene derivative, when R ₁ is an ethyleneoxy group having a number of moles of addition of 15 or less with the above-mentioned hydrocarbon group, cationic addition of cationic groups into R ₁ and / or ethyleneoxy group is added. Even as an agent, it does not affect the long-term stability of the plating, and the cationization can improve the gloss of the plating.

Further, even if plural kinds of the above additives are mixed, long-term stability of plating can be secured.

The concentration of these additives is 0.01 to 20 g.
/ L. If it is less than 0.01 g / l, almost no eutectoid effect of Cr is recognized. Moreover, when it exceeds 20 g / l,
The eutectoid effect of Cr is saturated, which is not a cost effective measure.

The concentration of zinc ions and trivalent chromium ions in the plating solution is preferably 10 to 150 g / l, and more preferably 20 to 130 g / l. Zinc ion, 3
When the amount of valent chromium ions is 10 g / l or less, plating burn is likely to occur, and when it is 150 g / l or more, the ion concentration reaches saturation and precipitation occurs in the plating solution. Furthermore, each 20 g /
If it is 1 or less, uneven plating is likely to occur, and if it is 130 g / l or more, the effect is already saturated, which is industrially disadvantageous in cost. Regarding the anion of the plating solution, both a sulfuric acid bath and a chloride bath can be used. The pH of the plating solution is preferably in the range of 0.5-3. If the pH exceeds 3, ion precipitation will occur, and if the pH is less than 0.5, the current efficiency will decrease, which is not industrially advantageous.

Furthermore, NH ₄ ⁺ ions and / or L
Addition of one or more irrelevant salts of i ⁺ , Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , and Al ³⁺ ions enhances the electrical conductivity of the plating solution and increases the coexistence of the additive Cr. The analysis effect is remarkably advantageous. These unrelated salts are 1
It is preferably g / l or more and 50 g / l or less. If it is less than 1 g / l, the Cr eutectoid amplification effect by the addition is not sufficient. 50 g
Above 1 / l, the electric conductivity of the plating solution is increased and Cr
The effect of making the eutectoid of (1) is saturated, and a large amount of extraneous ions causes a decrease in current efficiency.

In this ion concentration range, the optimum conditions can be determined in consideration of the intended plating composition and current efficiency.

Further, depending on the purpose, Cr ⁶⁺ , Ni, C
In the case where ions such as o, Fe, Mn, Cu, Pb, Sn, and Cd are added in a range not ^{exceeding the} Cr ³⁺ ion concentration, or inevitably present, a range not exceeding the Cr content in the plating layer Even if a small amount of eutectoid is used, the effect of the present invention is essentially unchanged.

Next, the current density is set to 50 A / dm ² or more. When it is less than 50 A / dm ² , Cr is hardly codeposited. Co-deposition of Cr becomes easy in the high current density region, but it is practically 2
It is preferable to operate at up to 50 A / dm ² . 250
When it exceeds A / dm ² , the voltage load becomes a problem, and the current load becomes large, which makes it difficult to carry out in a practical cell.

In the actual operation, the flow velocity of the plating solution is 30 to 300 m / min as a relative velocity to the steel strip, and the plating temperature is 40 to 70 ° C.

[0024]

EXAMPLES Next, examples of the present invention will be given together with comparative examples.

Under the plating solution components shown in Tables 1 and 2 and the plating conditions shown in Tables 3 and 4, ordinary degreasing and pickling were performed on a 0.8 mm thick cold rolled steel sheet having a basis weight of 20 g / m ² . Plated and evaluated plating layer composition (initial Cr composition I, Cr composition II after electrolytic load test, Cr composition III after repeating ion replenishment and electrolytic load test, third element), plating adhesion, plating appearance The results are shown in Tables 3 and 4.

[0026]

[Table 1]

[0027]

[Table 2]

Note 1) 4-octylphenylhe
xaoxyethylene dihydrogenph
osphate

The _{C 8 H 17 -C 6 H 4} - (OCH 2 CH 2)
_6- OPO ₃ H ₂

Note 2) 2-methylphenyltr
ioxyethylenehydrogensulfa
te

CH ₃ —C ₆ H ₄ — (OCH ₂ CH ₂ ) ₃ —OSO ₃ H

[0032]

[Table 3]

[0033]

[Table 4]

Note 3) The plating composition was analyzed by dissolving the plating layer.

The initial Cr composition I is the initial C of the plating composition.
When the r composition was 5% or more, it was evaluated as ◯, and when the Cr composition was less than 5%, it was evaluated as x.

The Cr composition II after the electrolytic load test is the initial C
For the example in which the r composition I was ○, under the same conditions as the initial plating conditions, up to an accumulated load electricity amount of 10,000 c / l,
After performing electrolysis without replenishing ions or additives,
The plating was performed under the same conditions as the initial conditions, and the change in Cr composition was evaluated. When the change in Cr composition was less than 5% compared to I, it was evaluated as ◯, and when more than 5% was evaluated as x.

Regarding the Cr composition III after repeating the ion replenishment and the electrolytic load test, for the example in which the Cr composition II after the electrolytic load test was ◯, Zn and Cr consumed by plating and taking out of the liquid by the plating were used. Supplement was made with zinc carbonate and chromium sulfate, pH was further supplemented with sulfuric acid, and the additive was supplemented with a shortage corresponding to the carried-out portion of the liquid by plating, and an electrolytic load test of 10000 c / l was conducted again. This operation was set to 1 cycle, performed up to 100 cycles, plated under the same conditions as the initial conditions, and evaluated the change in the Cr composition. Cr
When the change in composition was less than 5% compared to I, it was evaluated as ◯, and when more than 5% was evaluated as x.

Note 4) The plating adhesion is such that the Cr composition is 5%.
A white vinyl tape was adhered to the above, a plated steel plate was closely bent with the tape portion as the inner center, then the tape was peeled off and the presence or absence of a peeling plating layer on the back surface of the tape was evaluated. The case where there is no trace of peeling was marked with ⊚, the thin streak had no problem in practical use, and the case where there was plating peeling and which was not practical was marked with ×.

Note 5) The appearance of plating was evaluated by visually observing the surface of the plated steel sheet, and a uniform and glossy one was evaluated as ⊚, a uniform one was evaluated as ◯, and an uneven one was evaluated as x.

In Examples 1 to 15, the initial Cr composition was maintained even when electrolytic loading or ion supplementation was performed, and zinc-chromium alloy electroplating could always be stably performed. further,
In Examples 10 to 14, since the additive has an anionic group, the adhesiveness of the plating was not observed and the peeling of the plating was not observed at all.
In No. 5, the additive had a cationic group, so that the plating appearance was uniform and glossy.

On the other hand, since Comparative Example 1 has no hydrocarbon group,
Further, since Comparative Example 3 does not have an ethyleneoxy group, the codeposition of Cr on the plating was a trace from the initial stage and hardly occurred. Since Comparative Examples 2 and 4 have long ethyleneoxy groups,
In the initial stage of plating, Cr was sufficiently codeposited, but 100
After the electrolytic loading of 00 c / l, the Cr composition of the plating layer was extremely reduced compared to the initial stage, and stable zinc-chromium alloy electroplating maintaining the initial plating composition could not be performed.

[0042]

INDUSTRIAL APPLICABILITY The present invention enables a zinc-chromium alloy electroplated steel sheet to be manufactured semi-permanently and stably for a long period of time and dramatically improves the life of the plating solution. Enables manufacturing. In addition, the amount of plating waste liquid is reduced to minimize the impact on the environment. Further, plating adhesion and plating appearance can be improved.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Akira Takahashi 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Corporate Technology Development Division

Claims (5)

[Claims] 1. A hydrocarbon group having 20 or less carbon atoms and 15 or less added moles, which has a zinc ion, a trivalent chromium ion and 4m + 2 (m = 1 or 2) π-electron aromatic and / or heteroaromatic groups. Zinc-chromium alloy excellent in corrosion resistance, characterized by plating at a current density of 50 A / dm ² or more using an acidic plating bath containing 0.01 to 20 g / l of a polyoxyalkylene derivative consisting of an ethyleneoxy group. Manufacturing method of electroplated steel sheet. 2. The method for producing a zinc-chromium alloy electroplated steel sheet having excellent corrosion resistance according to claim 1, wherein the polyoxyalkylene derivative has an anion group. 3. The method for producing a zinc-chromium alloy electroplated steel sheet having excellent corrosion resistance according to claim 1, wherein the polyoxyalkylene derivative has a cation group. 4. A zinc ion concentration of 10 to 150 g / l,
Zinc excellent in corrosion resistance according to claim 1, 2 or 3 having a trivalent chromium ion concentration of 10 to 150 g / l, a hydrocarbon group concentration of 0.01 to 20 g / l, and a pH of 0.5 to 3. -A method for producing a chromium-based alloy electroplated steel sheet. 5. NH ₄ ⁺ ions and / or Li ⁺ ,
The Na ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Al ³⁺ ions as ions are added in one or two or more kinds at a concentration of 1 g / l or more and 50 g / l or less. A method for producing a zinc-chromium alloy electroplated steel sheet having excellent corrosion resistance.