JPH08218158A - Posttreatment of hot dip galvanized or hot dip galvannealed steel plate - Google Patents

Abstract

PURPOSE: To provide a method of applying a colored film in gray to grayish black which impresses a person favorably as a building roof material or the like onto a hot dip galvanized or hot dip galvannealed steel plate. CONSTITUTION: Treatment is executed by using a solution with 0.2-3g/l Fe<2+> ion, 0.2-3g/l Mn<2+> ion and 0.1-1g/l Ni<2+> ion added as special metal ions to a generally used zinc phosphate treating solution. To a hot dip galvanized steel plate or a hot dip galvannealed steel plate using a molten Zn alloy bath mixed with Al, Mg, Ni, Mn, La, Ce, Ti or the like, the coloring treatment of the above constitution is applied, and the obtained colored coating film has an outside color of gray or grayish black (L value=40-20), and the coating film is not peeled by bending or the like, and discoloration is not caused even when stored for a long-term in summer high humidity atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet or a post-treatment method for hot-dip galvanized steel sheet, which is mainly used for building materials (roofs, walls, etc.) electric appliances, furniture and the like.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets and hot-dip galvanized steel sheets are sometimes used as a coating material on building materials, electrical appliance materials, and furniture materials, although they may be painted (as-plated). ) Often used. However,
It is generally known that the plated steel sheet undergoes partial discoloration from gray to black during storage after manufacture, during storage or during transportation, and also during use in a bare state, which is extremely unsightly. This discoloration has been studied in various fields, and it has been clarified that the cause of discoloration is that the plating surface layer is corroded by moisture in the air and forms corrosion products such as zinc hydroxide and zinc carbonate on the surface. (The 69th Scientific Lecture Meeting of the Japan Institute of Metal Surface Technology (1984), P70-71).

The susceptibility to corrosion is more remarkable in a so-called hot-dip zinc alloy plated layer in which zinc contains Al, Mg, Ti, Ni, etc. than in a pure zinc plated layer.
(Iron and Steel, Vol. 71 (1985) A93 to A96)
Further, when the plated steel sheet is manufactured and subjected to a chromic acid treatment liquid application (chromate treatment) and a temper rolling process in the subsequent steps, the color is more likely to change from gray to black. It is said that the reason why this discoloration is promoted is that when a metal other than zinc is contained in zinc, a local battery occurs between Zn and another metal to promote the corrosion reaction on the surface of the galvanized layer. There is. Further, it is considered that the temper rolling process causes strain in the galvanized layer due to the process, so that local battery formation similarly increases and the discoloration (black change) is promoted. Further, in the case of chromate treatment, C contained in the chromate film
It is considered that the reaction of r ⁶⁺ ions with the surface zinc layer causes a reaction similar to the corrosion reaction to generate zinc chromate (Materials and Process, Vol. 1, No. 2 (1
988) P.O. 663-666).

As described above, detailed investigations have been made in various fields regarding the discoloration of gray or black that locally occurs on the surface of the hot dip galvanized surface and the surface of the hot dip galvanized alloy.
Therefore, various techniques have also been developed for this discoloration prevention technique. Among them, as the most effective and economical method, there is a method that is currently adopted, that is, a treatment liquid containing Ni ²⁺ or Co ²⁺ (Japanese Patent Publication No. 3-49982). This method uses a slight amount of Ni or C on the surface of the plating layer.
By attaching metal, the corrosion active points on the surface of the plating layer are inactivated to prevent discoloration. However, this Ni ²⁺ or Co ²⁺ ion-containing solution treatment method is quite effective in preventing discoloration, but when placed in a strict storage environment (when humidity and temperature are extremely high), black discoloration still occurs. I cannot escape.

Therefore, if the plated steel sheet having a metallic luster is locally discolored (gray to black) during storage, transportation or use of the plated steel sheet by changing the way of thinking, the same system color is applied in advance. I thought that not only would a solid appearance be obtained, but there would be no phenomenon of local discoloration that would reduce the product value. First, considering the use of the hot-dip galvanized steel sheet and the hot-dip galvanized steel sheet (roofs, walls, electric appliances, furniture, etc.), gray to black-gray coloring is suitable as the color tone.

Then, as a result of an investigation on the coloring technique of the galvanized steel sheet, it was found that a light gray coloring technique or a black coloring technique (excluding the coloring technique by painting) has already been proposed. Among them, light gray erosion is performed by the conventional zinc phosphate treatment method. Meanwhile black coloring, after subjected to electrical Zn-Ni alloy plating on the said galvanized steel NO ₃ ^- + Ni ²⁺ anodic electrolysis method for electrolytic oxidation in a solution containing (Plating and Surface
Finishing, Vol. 75 (1988) P.I.
108-111) and the galvanized steel sheet with Zn ²⁺ + Ni
There is a method of cathodic electrolysis in a solution containing ²⁺ + NO ₃ ⁻ . (Japanese Patent Application No. 5-141808). However, the above-mentioned anodic electrolysis method is disadvantageous in that the cost is high because electric Zn-Ni alloy plating is performed on the plated steel sheet, and the cathodic electrolysis method peels off the black film when bent after coloring. Therefore, it has not been practically used.

[0007]

As described above, light gray coloring and black coloring are possible, but gray to black gray coloring, which is the object of the present invention, could not be achieved. Here, since the expression of the degree of coloring becomes inaccurate when words are used for the expression of the color tone, the lightness index (also referred to as the L value) will be represented by a numeral. The lightness index (L value) is defined academically as follows.

Lightness index (L value) = 10Y ^1/2 (Y is one of three color tone tristimulus values specified in JIS Z8722) The relationship between the degree of coloring and the lightness index (L value) is as follows. . (Coloring degree) (Blackness (L value)) Black color: less than 20 Black gray: 20 to less than 30 Gray color: 30 to 40 Light gray:・ ・ ・ More than 40 to 50 Light white (metal color) ・ ・ ・ ・ ・ More than 50

The surface color tone of the above-mentioned existing galvanized steel sheet treated with zinc phosphate has a lightness index (L value) of more than 40.
The color tone is light gray of 50, and the surface color tone by the anodizing treatment after the Zn-Ni alloy plating is less than 20. Therefore, the coloring technology target color tone of the surface of the plated steel sheet is set to the lightness index (L value).
We decided to proceed with research and development with less than 40.

[0010]

[Means for Solving the Problems] Then, as a result of earnestly studying the coloring technology of the hot dip galvanized steel sheet and the hot dip galvanized alloy steel sheet, the target blackness (L value) of 20 to
The inventors have found a technique capable of arbitrarily coloring 40 black gray to gray. The summary is Fe ²⁺ : 0.2-3 g / l, M
n ²⁺ : 0.2-3 g / l and Ni ²⁺ : 0.1-1 g /
A hot-dip zinc or hot-dipped zinc alloy having a brightness index of 20 to 40 by subjecting the hot-dip galvanized steel sheet or hot-dip zinc alloy-plated steel sheet to a zinc phosphate treatment in a zinc phosphate treatment bath containing 1 This is a post-treatment method for plated steel sheets. However, the brightness index is represented by the L value, and the L value = 10Y.
^1/2 Y is one of the color tone tristimulus values defined in JIS Z8722.

That is, the present invention is generally used, for example, Zn ²⁺ , H ⁺ , H ₂ PO ₄ ⁻ , PO ₄ ⁻ , NO ₃
^- the phosphating solution containing, F as a special metal ion
This is a technique of treating with a treatment liquid containing an appropriate amount of e ²⁺ , Mn ²⁺ , and Ni ²⁺ added. This special 3 types of added metal ions are 3
It is necessary for both seeds and must be kept in an appropriate concentration range. If it is contrary to this, the resulting colored film property on the plated steel sheet does not exhibit the target lightness index (L value), and peels off when bent. However, problems such as new local discoloration occur during long-term storage. In the experimental process of the present invention, a means for producing a black film having a lightness index (L value) of less than 20 was tried, but it was unsuccessful. That is, as a technique on an extension of the means of the present invention, the range of the concentration of special metal ions and the treatment conditions (treatment time, treatment liquid temperature) were examined, but those having a lightness index (L value) of less than 20 can be produced, but the black film is It was found that peeling occurred by bending at 90 ° C. (later taping).

The details of the present invention will be described below. The galvanized steel sheet of the present invention is not particularly specified, and is generally referred to as a zinc-iron plate. In the galvanized layer, 0.10 to 0.15 wt% of Al is usually added to improve plating adhesion.
Hot-dip galvanized steel sheet containing, about 5 Al in the galvanized layer
wt% and further contains about 0.1 wt% of Mg, or about 0.03 wt% of misch metal (La, Ce) hot-dip galvanized steel sheet, about 55 wt% of Al and Si in the galvanized layer. It is possible to use a hot dip galvanized steel sheet containing about 5 wt%, a hot dip alloy plated steel sheet containing about 1 wt% Ni in the galvanized layer, and the like.

These hot dip galvanized or hot dip galvanized steel sheets are immersed in a commonly used weak alkaline type degreasing solution for degreasing and then washed with water. Subsequently, it is generally immersed in a liquid called a chemical conversion treatment surface conditioning liquid (an aqueous solution of the chemical PN-Z commercially available from Japan Parker Rising KK) and then washed with water. Subsequently, it is treated with the coloring treatment liquid of the present invention. Coloring treatment liquid is generally-used by being 0.2~3g the Fe ²⁺ zinc phosphate treatment solution / l for the zinc, the Mn ²⁺ 0.2
.About.3 g / l, and Ni.sup.2 ⁺ added in an amount of 0.1 to 1 g / l. Among the above special metal ions, Fe ²⁺ is important for the concentration balance of all ions (both cations and anions) in the treatment liquid, and when the Fe ²⁺ concentration is out of the proper range, the concentration balance is not only destroyed. On the other hand, if it is less than 0.2 g / l, the thickness of the colored film is too small, and if it exceeds 3 g / l, the reaction is excessively promoted, so that the film is easily peeled off.

Mn ²⁺ is an important element for adjusting the color tone,
If it is out of the proper range, the color tone becomes uneven. That is,
If it is less than 0.2 g / l, the thickness of the colored film becomes small, or the reaction points do not extend over the entire surface, resulting in uneven coloring. Further, if it exceeds 3 g / l, the color film becomes too thick, so that the film adhesion is insufficient and the color film is detached,
The color tone becomes uneven. Further, Ni ²⁺ is important for adjusting the crystal size of the colored film (phosphate film), and if it deviates from the proper range, the crystal size becomes abnormal. That is, 0.1
In both the range of less than g / l and the range of more than 1 g / l, the crystal size becomes abnormally large and the depth of color tone disappears. That is, a fine metallic luster is emitted.

Next, a method of adjusting the color tone will be described. As described above, the color tone width of the method of the present invention is in the range of the lightness index (L value) of 20 to 40, but the color tone adjustment in this color tone width is performed by adjusting the special metal ion concentration of Fe ²⁺ , Mn ²⁺ , Ni ^2+. It is possible by adjusting, and if you keep the concentration of 3 kinds of metal ions in the proper range, the color tone becomes gray →
It is possible to make an arbitrary color tone appear by changing in the direction of black gray (40 → 20 in terms of L value).

The coloring treatment liquid concentration control in the case of continuing processing the plated steel sheet, a high concentration of ^{_{Zn 2 +, H 2 PO 4}} -,
A basic bath stock solution which is a solution containing H ⁺ , PO ₄ ³⁻ and NO ₃ ⁻ and high concentration Fe ²⁺ , Mn ²⁺ , Ni ²⁺ , H ⁺ , H ₂ PO.
₄ ^- is adjusted by continuing supply of special metal ion stock solution is a solution containing a PO ₄ ^3-. The reason for the color development of the colored film in the present invention is light gray (L value 40 to less than 50)
Conventional zinc phosphate coating that presents (zinc phosphate crystal coating)
If it is treated with a special metal ion added coloring treatment liquid to generate zinc phosphate crystals _{(Zn 3 (PO 4) 2} · 4H
In addition to _{Zn 2 Fe (PO 4) 2} · 4H 2 O in ₂ O), Mn ₅
It is presumed that the color tone changes to the black side (toward the smaller L value) due to the precipitation of H ₂ (PO ₄ ) ₄ .4H ₂ O and fine grain Ni.

[0017]

Example A coloring treatment based on the present invention and an existing coloring treatment (comparison) were performed using a hot-dip zinc alloy-plated steel sheet (plating layer composition: Zn-5% Al-0.1% Mg system) having a plate thickness of 0.8 mm. I did. In the coloring treatment according to the present invention, 0.2 to 3 g / l of Fe ²⁺ and 0.2 to 3 of Mn ²⁺ ions are added to a commonly used zinc phosphate treatment solution as special metal ions.
Using a solution in which g / l and Ni ²⁺ were changed in the range of 0.1 to 1 g / l, the temperature was 50 ° C. to 80 ° C. as the immersion treatment condition.
Various color tone samples were prepared by changing the temperature and the immersion time from 10 seconds to 90 seconds. Further, as comparative examples, a sample deviated to the low concentration side and a sample deviated to the high concentration side as the addition concentration of the special metal ion were prepared. Furthermore, as a comparative example, an ordinary zinc phosphate treatment liquid was used, which was subjected to a dipping treatment at 50 ° C. for 30 seconds, and a cathode coloring treatment was carried out under the following conditions.

ZnSO ₄ .7H ₂ O 350 g / l Na ₂ SO ₄ 80 g / l NaNO ₃ 10 g / l NiSO ₄ .6H ₂ O 15 g / l pH 2 temperature 50 ° C. cathode current density 30 A / dm ² electrolysis time 5 seconds

[Test / Evaluation Method] The following characteristic evaluations were carried out on the colored steel sheets prepared in the above examples. Blackness measurement ... The brightness index (L value) was measured with a color computer (model SM-3) manufactured by Suga Test Instruments. Adhesion of Colored Film After the bending test (bending at 90 ° C.), taping was performed and the peeling condition was observed. The evaluation method is as follows: ◎ ... The colored layer is not peeled at all and the tape is not blackened. ◯: The colored layer was not peeled at all, but the tape was slightly blackened. Δ: The colored layer is slightly peeled off. X: The colored layer peels off over the entire bent portion.

Discoloration resistance test After shearing the colored steel sheets to 50 × 70 mm, 5 sheets are stacked and
After packing with packing paper, it was stored in a humidity tank at a temperature of 70 ° C. and a humidity of 99% or more for 3 days. The color change was observed by observing 5 samples. A: No discoloration is observed. A slight gray mottled discoloration is observed. Δ: A slight discoloration of gray to black is seen. X: A black discoloration is seen quite intensely. [Test Results] Table 1 shows the evaluation results of the color-treated test samples.

[0021]

[Table 1]

[0022]

As shown in Table 1, by performing the coloring treatment of the present invention, a colored film of gray to black gray (L value = 20 to 40) is obtained on the surface of the hot dip Zn-Al-Mg alloy plated steel sheet. It was clarified that the same coating did not peel off by bending (90 ° C.), and hot-dip galvanized steel sheets and hot-dip galvanized steel sheets were obtained which did not discolor even during long-term storage.

Claims (1)

[Claims] 1. Fe ²⁺ : 0.2-3 g / l, Mn ²⁺ :
Brightness index obtained by subjecting the hot-dip galvanized steel sheet or hot-dip galvanized steel sheet to zinc phosphate treatment in a zinc phosphate treatment bath containing 0.2 to 3 g / l and Ni ²⁺ : 0.1 to 1 g / l. 20-40, The post-treatment method of hot dip zinc or hot dip galvanized steel sheet. However,
The lightness index is represented by an L value, and the L value = 10Y ^1/2 Y is one of the color tone tristimulus values defined in JIS Z8722.