JP3260564B2 - Method for producing Zn-Cr alloy electroplated steel sheet - 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 for producing a rust-preventing electroplated steel sheet having excellent corrosion resistance and corrosion resistance after painting used in automobiles, home appliances, building materials, etc., and more particularly to a method for producing a Zn--Cr alloy electroplated steel sheet. It is about.

[0002]

2. Description of the Related Art As a method for producing an electroplated steel sheet containing chromium in zinc or a zinc-based alloy plating, for example, JP-A-63-243295 and JP-A-1-19 are disclosed.
As disclosed in JP-A-1797 and JP-A-3-120393, it is common that chromium is eutectoidized by using an organic additive in a plating bath. Although the mechanism of action of this additive is not clear, the following two points are presumed. The additive exhibits its eutectoid action by being adsorbed on the electrode interface. The additive forms a complex with the Cr ³⁺ ion, and this complex exerts an eutectoid action.

[0003] In the hypothesis described above, the additive may be taken into the plating film at the time of electrodeposition of the alloy, and may change the physical properties of the plating or deteriorate the plating adhesion. In addition, this may reduce the concentration of the additive, making it impossible to produce an alloy having a constant composition. On the other hand, the hypothesis is not suitable for economical production due to the large amount of additives required to form a complex with Cr ³⁺ ions. Furthermore, when Cr ³⁺ ions are supplied during continuous operation, it takes time to form a complex, and it is difficult to control the plating bath. Regarding additives to the plating bath, no measures have been taken so far to solve the above problems.

[0004]

The additives in the plating bath are:
As is evident from the above, it is involved in alloy electrodeposition without being taken into plating during electrodeposition, returns to the bulk from near the steel sheet surface immediately after alloy electrodeposition, and changes in the concentration of additives before and after electrodeposition. It is required to have a mechanism that does not come into contact, to be effective with a small amount of this additive, and to be easy to manage without pretreatment such as pre-electrolysis and aging of the plating bath. In view of the above problems, the present invention does not adversely affect the physical properties of the plating, is economical and advantageous in operation, can use the plating bath immediately after it is built, and by using an additive whose management is simple, An object of the present invention is to provide a method for producing a Zn—Cr alloy electroplated steel sheet.

[0005]

SUMMARY OF THE INVENTION The present invention provides Zn²⁺ion
And Cr³⁺Immersion of steel sheet in acid bath containing ions
In the method of manufacturing Zn-Cr alloy electroplated steel sheet
A sulfonic acid group (-SO_Three
H), a sulfate group (—SO_FourH), amino group (-NH _Two),
Carboxylic acid group (-COOH), nitro group (-NO_Two),
Any of halogen groups (-F, -Cl, -Br, -I)
A polyethyleneoxyphenol derivative compound having
Alternatively, an alkylsulfonic acid compound and polyethylene
Selected from hydroxyalkylsulfonic acid compounds
Add one or more of 0.01g / l to 20g / l
And performing electroplating.

[0006]

In the present invention, a polyethyleneoxyphenol derivative compound added as an additive to a plating bath,
The alkylsulfonic acid compound and the polyethyleneoxyalkylsulfonic acid compound have the following chemical structures.

[0007]

Embedded image

[0008]

Embedded image

[0009]

Embedded image

It is considered that these additives in the present invention form molecular aggregates such as micelles in an aqueous solution. In this case, the hydrophilic group is directed to the aqueous solution side. Although the details of the molecular assembly structure of the compound are not clear, the hydrophilic group has a site for adsorbing Cr ³⁺ ions. The adsorption force at this time is different from the coordination bond in complex formation,
Because of the weak electrostatic coupling, electrolysis of Cr ³⁺ ions is easy to perform, and therefore, the current efficiency of plating is higher than before. The mechanism by which Zn and Cr are deposited is not yet clear, but is presumed as follows. That is, when the micelles adsorbing the Cr ³⁺ ions approach the steel sheet surface, the Cr ³⁺ ions are electrodeposited, and the micelles having lost the metal ions move to the bulk again. Then, Cr ³⁺ ions are adsorbed again in bulk and the same action is repeated. On the other hand, Zn ²⁺ ions are originally ions that are easily deposited, so that they are deposited without any interaction with additives. Then, the deposited Cr and Zn are alloyed to form a Zn-Cr alloy.

The additive in the present invention is not taken into the plating film together with the alloy at the time of electrodeposition. The reason is that firstly, this additive does not have a mechanism of alloy electrodeposition by directly adsorbing on the steel sheet, and the micelles that adsorb Cr ³⁺ ions deposit near the steel sheet surface to cause electrodeposition. It is. Also, in general, the size of micelles is
Since it is much larger than the atoms of zinc and chromium, it is unlikely that the molecular aggregate is taken into the plating film. The size of the micelle is not specified because it varies depending on the type and concentration of the additive. From the above, since the concentration of the additive in the present invention is not reduced by being taken into the film, the plating composition is always constant during continuous production, and the physical properties of the plating do not change.

In the present invention, a sulfonic acid group (—SO 2) is used as the substituent for the polyethyleneoxyphenol derivative compound having a substituent on the benzene ring.
₃ H), a sulfate group (—SO ₄ H), an amino group (—N
H ₂ ), carboxylic acid group (—COOH), nitro group (—N
O ₂ ) and halogen groups (-F, -Cl, -Br, -I) for the following reasons.
If the substituent is a strong hydrophobic substance such as an alkyl group, micelles cannot be formed and the micelles may be suspended.
In this case, there is a concern about uneven plating. Therefore, it is necessary for the substituent to have a certain degree of hydrophobicity. As a result of intensive studies, a sulfonic acid group (—SO ₃ H), a sulfate group (—SO ₄ H), and an amino group (—NH ₂ ), A carboxylic acid group (—COOH), a nitro group (—NO ₂ ), and a halogen group (—F, —Cl, —Br, —I).

[0013] For these substituents,
(-SO_FourR, R: alkyl group)
Salts may be used as long as they do not cause the salt to be used. example
For example, sodium sulfonate (-SO_ThreeNa), sulfone
Ammonium (-SO_ThreeNH _Four), Sodium sulfate
(-SO_FourNa), ammonium sulfate (-SO_FourN
H_Four), Amine hydrochloride (-NH_ThreeCl), carboxylic acid
Thorium (-COONa), ammonium carboxylate
(-COONH_Four) And the like. Additives mentioned above
Can be used alone to produce an effect, and
Can be used without interfering with each other even if the top is mixed
You.

Further, according to the present invention, it becomes easy to manage the plating bath. In the conventional Zn-Cr alloy electroplating baths, the complex structure of the Cr3 ⁺ ion has a complex with an additive, a hydrated complex, a hydrated complex partially containing an anion. Since a nucleus and a polynuclear complex are formed, the proportion of the nucleus and polynuclear complex varies depending on the temperature and time of the plating bath. As a result, there has been a problem that the composition of the obtained plating is unstable while the proportion of the complex in the bath is not constant. However, the present invention utilizes the phenomenon of adsorption of Cr ³⁺ ions into micelles to develop the mechanism of electrodeposition of Cr, so that an alloy having the same composition is always used regardless of the state of existence of Cr ³⁺ ions. It can be manufactured constantly. Next, the minimum amount of the additive necessary for forming micelles is 0.1.
It is an extremely small amount of 01 g / l or more, and is suitable for economical operation. However, adding a large amount increases the viscosity of the liquid,
20 g / l or less is desirable because the additive may be suspended without dissolving in some cases due to a decrease in electric conductivity.

In the present invention, if necessary, N
^{i 2+, Co 2+, Fe 2+} , Mn 2+, a small amount of metal ions Pb ²⁺ and the like in the plating bath (0.1 mol / l or less) Power as a third component in the plating film by adding Can be analyzed. The composition of the Zn—Cr alloy plating obtained by the present invention can be changed by changing the plating bath composition and the current density. However, considering corrosion resistance, it is desirable that Cr be contained at 5% by weight or more.
When the content is 0% by weight or more, the so-called powdering property in which the plating becomes powdery at the time of processing is deteriorated. The plating bath may be either a sulfuric acid acidic bath or a hydrochloric acid acidic bath. Further, the base steel sheet for plating is not specified, and the steel composition and the method of manufacturing the steel sheet are not limited.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments. In order to apply a Zn-Cr alloy plating to a cold-rolled steel sheet having a thickness of 0.8 mm, the plating bath contains 0.6 mol / l of Zn ²⁺ ions,
Using an acidic bath having a pH of 1.5 containing 0.4 mol / l of Cr ³⁺ ions, a bath temperature of 50 ° C. and a current density of 100 A / dm ²
Was plated. At that time, various Zn-additives were added to the plating bath by adding additives as shown in Tables 1 to 6.
A Cr alloy plated steel sheet was obtained. The characteristics of the obtained plated steel sheet were evaluated in terms of workability and corrosion resistance. Workability is Zn-Cr
It deteriorated when the additive was eutectoid and contained carbon in the alloy plating layer. Therefore, the judgment was made to judge the presence or absence of the additive eutectoid. The evaluation was performed based on the state of peeling of the plating at the bent portion after the close contact bending was performed. The evaluation was performed in three stages of ◎ (no plating peeling), Δ (slight plating peeling), and Δ (plating peeling). Tables 1 to 6 show these results.
Shown in The corrosion resistance of the plating was measured by the salt spray method in accordance with JIS2371. The percentage of red rust occurrence for 1008 hours was measured.
Was evaluated. The ease of plating bath management was evaluated by the stability over time of the resulting plating composition. That is, the plating composition obtained when the plating bath was plated immediately after the bath was set up and the plating temperature was 50 ° C.
Was evaluated by the difference in plating composition obtained when plating was performed after aging for 48 hours. When the difference was 1% or less, it was evaluated as ○, and at other times, it was evaluated as x.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

[Table 5]

[0022]

[Table 6]

In Examples 1 to 83, Cr in the plating film
A predetermined Zn-Cr alloy having a weight percentage of 6% to 34% was obtained. And the corrosion resistance and plating adhesion of the plating were both excellent. Further, the stability of the plating composition over time is also excellent. On the other hand, as shown in Comparative Examples 1 to 22, when the amount of the additive is too small and too small, chromium is hardly precipitated in the plating film, so that it does not show good corrosion resistance, and is shown in Comparative Examples 23 to 26. In the case of an additive that forms a complex with Cr ³⁺ ions as described above, if the additive is small, chromium does not precipitate in the plating layer and the corrosion resistance is poor, and if the additive is large, chromium precipitates and the corrosion resistance improves Deterioration of workability. Further, the stability of the plating composition over time is poor.

[0024]

As is apparent from the above description, the additive of the present invention can produce Zn-Cr alloy electroplating at low cost without adversely affecting the physical properties of the plating. This is the most suitable method for plating.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-53794 (JP, A) JP-A-6-41781 (JP, A) JP-A-8-85897 (JP, A) JP-A-8-858 53792 (JP, A) Patent 2647833 (JP, B2) Patent 2543578 (JP, B2) JP 6-35673 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 3 / 56

Claims (1)

(57) [Claims] 1. A method for producing a Zn—Cr alloy electroplated steel sheet by immersing a steel sheet in an acidic bath containing Zn ²⁺ ions and Cr ³⁺ ions, wherein the acid bath contains sulfone as a substituent on a benzene ring. acid group (-SO ₃ H), sulfuric acid group (-SO ₄ H), amino group (-NH _2), a carboxylic acid group (-COOH), nitro group (-NO _2), a halogen group (-F, -Cl , -Br, -I) in an amount of 0.01 g / l of one or more selected from a polyethyleneoxyphenol derivative compound having at least one of the above, an alkylsulfonic acid compound, and a polyethyleneoxyalkylsulfonic acid compound. A method for producing a Zn-Cr alloy electroplated steel sheet, comprising adding about 20 g / l.