JPS60204888A - Zinc phosphate treatment of steel sheet hot dipped with zn-al alloy - Google Patents

Abstract

PURPOSE:To form a normal zinc phosphate film in the stage of forming the zinc phosphate film to a steel sheet hot-dipped with a Zn-Al alloy by etching the Zn- Al-plated steel sheet with an aq. alkali soln. then subjecting the steel sheet to a zinc phosphate treatment. CONSTITUTION:A steel plate on which a Zn-Al alloy hot-dipped layer contg. 3- 5% Al and having excellent durability is formed is preliminarily subjected to an etching treatment with an aq. alkali soln. having 10-13pH in the stage of forming a zinc phosphate film thereon by a zinc phosphate treating liquid. The steel sheet is then treated with the zinc phosphate treating liquid contg. 0.85-1.7g/l Zn ion, 1.0-2.5g/l Ni ion, 5.5-10g/l PO4 ion, 0.8-1.5g/l NO3 ion and 1.5-5.5g/ lF ion and having <=500ppm accumulated Al ion eluted from the Zn-Al plating layer. The zinc phosphate film having excellent properties is easily formed with decreased elution of Al in the treatment by the aq. alkali soln.

Description

Detailed Description of the Invention The present invention etches the plating surface layer in advance as a means to keep the amount of AI ions inevitably mixed into the zinc phosphate treatment solution from exceeding 5001) I'll. This is a zinc phosphate treatment method for an In-Al alloy hot-dip plated steel sheet.

2N plated steel sheets have been used for construction and civil engineering applications for a long time, and are widely trusted for their durability. However, in recent years, galvanized steel sheets with even greater durability have become desired, and In-Al alloy hot-dip galvanized steel sheets (2n
A hot-dip plated steel sheet containing 3 to 5% of Al as a base (hereinafter referred to as 2n-Al-based plated steel sheet) was developed. The In-Al plated steel sheet has excellent bare corrosion resistance, which is about twice that of conventional curved lead plated steel sheets.In particular, the coating layer has good visibility and spreadability, so the corrosion resistance of the IJOI area is extremely excellent. It has characteristics such as being present. In order to take advantage of this feature, application to coated steel plates is desired and is being considered. Conventionally, most pre-painting treatments for painted steel sheets have been carried out by a method using bent lead phosphate treatment. LinflI! ll! When treated with lead, some of Metsukien's 711 is eluted, which combines with phosphoric acid to form a zinc phosphate film. In the case of 1n-AI type plated steel sheet, the plating is approximately 20% lower than that of conventional ordinary lead plated steel sheet.
Since it contains ~25 times as much A1, a large amount of oral A1 is eluted into the zinc phosphate treatment solution. Therefore, there is concern that a problem may occur if a large amount of A1, which is not a constituent element of the zinc phosphate film, accumulates in the treatment solution.

In order to clarify the influence of this accumulated Al, an In-Al plated steel sheet was continuously passed through a continuous chemical conversion treatment apparatus capable of performing pre-painting treatment on ordinary colored galvanized iron sheets and investigated.

In the experiment, a certain amount of a commercially available zinc phosphate treatment solution was prepared, and 2
The n-Al plated steel sheet is continuously passed through, and the amount of treatment liquid consumed as a zinc phosphate film and the amount of liquid taken out by roll squeezing are continuously replenished with a separate replenishment liquid by measuring the total acidity of 9a saliva. did. In this experiment, the amount of eluted A1, accumulated All, amount of zinc phosphate film, amount of etching (amount of plating material eluted in zinc phosphate treatment solution), and morphological changes of the formed zinc phosphate film were measured for each amount of plate passing. confirmed.

We also confirmed the performance of zinc phosphate-treated steel sheets after coating with chrome sealing.

The results of this experiment revealed the following. That is, as shown in Fig. 1, in the conventional galvanized steel sheet, the amount of Al accumulated in the zinc phosphate treatment solution is approximately 2209 pm, whereas
-Al-based plated steel sheets had a significantly higher content, reaching a maximum of 700 ppm.

In addition, with the increase in the amount of accumulated A1, the amount of zinc skin g! The amount of etching and the amount of etching decreased as shown in Figure 2, especially when the amount of accumulated A
It was found that when the amount exceeded 500DDlll, the amount decreased significantly. This decrease in the amount of zinc phosphate coating is caused by the crystal morphology of zinc phosphate changing from tl-shaped crystals A, which is unique to zinc phosphate, to granular crystals B, and the growth of the crystals is suppressed, as shown in Figure 3 (photo). It is thought that this is because of this. Furthermore, the relationship between accumulated Al11 in the zinc phosphate treatment solution and paint film adhesion after painting is shown in Figure 4. Items treated with a treatment solution with accumulated Alfi exceeding 5ooppm have poor bending adhesion and scratch resistance. It was found that the performance of the coated steel sheet was extremely poor, and that it did not have the performance as a painted steel sheet. When a steel plate with a low A1 type plated steel plate is treated with bent lead phosphate, a normal zinc phosphate film is not formed due to the influence of A1 eluted from the plating layer and accumulated, so sufficient pre-painting treatment performance is provided. It turned out that it wasn't. However, as mentioned above, In--Al plated steel sheets have extremely excellent corrosion resistance in processed parts, and therefore their application to coated steel sheets is desired. Therefore, various methods for treating In-Al plated steel sheets with zinc phosphate were investigated.

As shown in Fig. 1, 1n-Al plated steel plate is
/! When treated, the amount of eluted A1 is about 50 ppm, which is 3
The amount of accumulated A1 after processing 01112/ is approximately 700 ppi+
Met. In contrast, the amount of eluted A1 from In-plated steel sheets is approximately 1
0ppn+ and 3 (accumulated All after 1m2# treatment was approximately 220111111).

In addition, zinc phosphate treatment of ZO-plated steel sheets is currently carried out in many manufacturing lines for colored galvanized iron sheets, but the accumulated All in the treatment solution is balanced at approximately 200 to 400111) II, and 1n-Al based Large amount of accumulation A1 like plated steel plate
was not observed, and a zinc phosphate film was also formed normally. Based on these facts, 1WI is also applied to 2n-Al plated steel sheets.
'71! It can be seen that normal zinc phosphate treatment is possible by suppressing the amount of eluted Al during treatment to 10 ppm or less, or suppressing or removing the accumulated Al amount to 500 pp- or less. As a result of various studies on methods for suppressing the amount of eluted AI to 10 ppm or less, the following method was found to be effective.

That is, as a method for suppressing elution A1, a Zn-Al plated steel sheet is treated in advance with an alkaline aqueous solution with a pH of 1o to 13.
We have developed an effective method of etching the plating surface (1) and then subsequently treating it with zinc phosphate.1.

The present invention will be explained in detail.

An auto-drain method is considered as a method for preventing the accumulation of eluted A1. This method reduces the accumulation All to 500 ppm
In this method, a pre-prepared zinc phosphate treatment solution is constantly replenished in a fixed amount to maintain the following conditions, and the overflow is disposed of as waste and the accumulated A1 is removed. Although it is possible to prevent the accumulation of A1 in this method, it is clear that the amount of zinc phosphate treatment solution used and the waste treatment cost increase.

Historically, the amount of replenishment and waste liquid management has become complicated and uneconomical.

The present invention solves these drawbacks.

That is, in the zinc phosphate treatment, a part of the plating layer is dissolved, and the eluted ln combines with phosphoric acid to form a zinc phosphate film. Therefore, in the case of a Zn--Al based plated T# board, A1 in the plating field inevitably accumulates in the zinc phosphate treatment solution.

The method of the present invention, in which the surface layer of the In-Al plating layer is cleaned with an alkaline aqueous solution before the zinc phosphate treatment, and then the zinc phosphate treatment is performed, is based on the property that the alkaline aqueous solution selectively etches the plated A1. be. That is, the In-rich β-c) phase and the Al-rich eutectic phase coexist in the plating 1 of the 2n-Al-based plated steel sheet. Therefore, after selectively etching the eutectic phase by cleaning with an alkaline aqueous solution and discharging the eluted A] out of the system, an attempt is made to suppress the eluting A11l into the zinc phosphate treatment solution that is subsequently carried out. be. The alkaline aqueous solution is prepared by adjusting the pH by adding alkaline compounds such as NaOH, KOH, Ga(O), etc.The etching effect varies depending on the volume of the aqueous solution and is larger on the high pH side. , Ni,
By adding Fe or the like, the etching effect can be enhanced by replacing and precipitating the added element.

Furthermore, effects such as improved coating film adhesion and corrosion resistance after painting can be expected due to the precipitation of Co, Ni, and Fe.

In addition, many ordinary production lines for colored zinc iron have preliminary equipment such as a pickling tank and an alkaline degreasing tank in addition to the zinc phosphate treatment tank as pre-painting equipment. has the advantage that it can be easily done without installing new equipment.

Hereinafter, the present invention will be described in detail based on Examples.

A 2N-Al-plated steel plate with a thickness of 0.4w and a width of 220m was mixed with an aqueous solution of 1) H8-13 to which an alkali compound such as Na0)1°KOH, Ca(01(), etc.) and aqueous solution of Go, etc. were added. After cleaning with an aqueous solution containing Ni,)e, the amount of 1 ions as the main component was 1.12g/
/, Ni ion amount is 1.26g/l, PO, ion f
! 1ff6. Gq/l, NO, Ian II is 1.1
1J#! , using a commercially available bent lead phosphate treatment solution (trade name Roll Bonderite 103; manufactured by Nippon Barker Rising Co., Ltd.) with a treated saliva composition containing an F ion content of 1.329/l and a small amount of other additives, and a conventional coloring process. 4I! The plate was passed through a continuous chemical conversion treatment equipment capable of pre-painting treatment of lead iron plates, and treated with zinc phosphate treatment solution 201 for 600 m'. In this example, the amount of eluted AI eluted into the alkaline aqueous solution (treatment of plated steel sheet! 11'), the amount of accumulated A in the zinc phosphate treatment solution (treatment of plated steel sheet fi600m'), and the form 1 distribution of the zinc phosphate film The condition and adhesion of the paint film after painting were investigated, and the etching effect of the alkaline aqueous solution was confirmed.

The distribution state of the zinc phosphate film was evaluated by taking an electron micrograph at a magnification of 1000 times. Also, the performance after painting is paint W
After coating A21 (manufactured by Dainippon Ink and Chemicals, film thickness 5 μm, baking temperature 215° C. for 30 seconds), it was evaluated based on the criteria shown in Table 1, and the results are shown in Table 2.

As a comparative example in Table 1 below, as is clear from the comparative examples in Table 2 in the margin below, after cleaning with an aqueous solution of 1189 or less, the phosphorus awakening was 0! For those treated with lead, the elution A11l in alkaline aqueous solution is 20 to 37.
As a result, A1 was eluted into the zinc phosphate treatment solution, and the accumulated A1 was 510 ppm.
1+pm or more. This means that in this pH range, A
This is thought to be because the etching effect on 1 is small.

As a result, the produced zinc phosphate film also becomes granular and its distribution is uneven, which is not preferable. Furthermore, the results of the 21 bending and coin scratch resistance tests after painting also showed extremely poor performance. However, by the method of the present invention, DH10-118
The amount of A1 eluted into the alkaline aqueous solution is
f 41 to 18011111, so the elution of A1 into the zinc phosphate treatment solution is small, and the amount of accumulated A1 is 50 in each case.
0 leaves - or less. As a result, the resulting film has acicular crystals unique to zinc phosphate evenly distributed, and the results of the 21-fold bending and coin scratch tests after coating are also excellent. Especially Go.

The material with N+ and Fe added has even better performance in the bending test. In this way p) 110~p
By cleaning with an alkaline aqueous solution of H13, etching the A1-rich areas, and subsequently treating with zinc phosphate, the accumulated All can be suppressed to 5001)11- or less, allowing normal zinc phosphate treatment.

However, if the alkaline aqueous solution has a pH of I) below 89, the etching effect on A1 will be small (if it exceeds 1813, the workability will decrease, etc.), so it is most preferable to have a pH of 0 to 13.

When In--Al plated steel sheets are treated with normal zinc phosphate, A1 eluted from the plating (1) accumulates in the treatment solution, making it impossible to form a normal zinc phosphate film. By applying the present invention, a normal zinc phosphate film is produced and can be applied to painted steel sheets.

The present invention can be applied when a plurality of materials such as aluminum, galvanized steel sheets, and cold rolled steel sheets are processed on four lines.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the amount of sheet passing and the amount of accumulated A1 when 1n-AI alloy hot-dipped steel and galvanized steel sheets are continuously passed through a zinc phosphate treatment solution, and A Ltln
- Accumulated AI of the AI-based alloy hot-dipped steel sheet [lB indicates the accumulated AIWJ of the In-plated steel sheet. Figure 2 shows the relationship between the accumulated A11l in the zinc phosphate treatment solution, the amount of zinc phosphate film, and the amount of etching, where A is the phosphorus Pl! of the 1n-AI alloy hot-dipped steel sheet. Zinc coating amount The amount of etching of the BLt70-A1 alloy hot-dip plated steel sheet is shown. Figure 3 (photograph) shows the crystal form and crystal distribution of the phosphorus@zinc film when treated with the zinc phosphate treatment solution with the accumulated All0ppi+ (bath preparation solution) and accumulated AAl1700ul1, where A indicates the accumulated A1. Amount 011+111 (crystal form and crystal distribution state when treated with accumulation bath liquid B shows the crystal form and crystal distribution state when treated with accumulation A ll 700 pp++. bath liquid) to 700
This shows the performance when painted on a board treated with lead phosphate treated with a treatment solution of up to ppm. Figure 1 Figure 2 1141 At Children (PPffI) Continued from page 1 0 Inventor Masaru Suzuki

Claims (1)

[Claims] The surface of the 11n-Al alloy hot-dipped steel plate is
After treatment with an aqueous alkaline solution of 10 to 13, the surface layer is etched and the main component has an ion content of 0.
85-1.7q/l, Ni ion amount 1°0-2.5q
/It, PO, ion amount is 5.5-10g #! . NO, the amount of ions is 0.8-1.517/j! , A treatment with a zinc phosphate treatment solution composition consisting of an F ion amount of 1.3 to 5.51 J/l and a small amount of other additives, and a treatment in which the amount of A1 ions that are inevitably mixed in is suppressed to an amount that does not exceed 5ooppn+ In-Al characterized by processing using a liquid
Zinc phosphate treatment method for alloy-plated steel sheets.