JP2626850B2 - Continuous zinc coating method for aluminum strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous zinc coating method for an aluminum strip, and more particularly, to an aluminum strip as a pretreatment for zinc phosphate treatment for improving the coating corrosion resistance of an aluminum sheet for an automobile outer panel. The present invention relates to a continuous zinc coating method for an aluminum strip in which zinc coating is continuously performed using a coil.

[0002]

2. Description of the Related Art In recent years, aluminum plates (including aluminum alloy plates) have attracted attention as automotive outer plates from the viewpoint of weight reduction. For aluminum plates for automotive outer panels, painting is required in the same way as conventionally used steel plates.
In order to improve coating corrosion resistance, zinc phosphate treatment and chromate chromate treatment have been put to practical use as pretreatments for coating.

[0003] Among them, zinc phosphate treatment is basically known to be excellent particularly as a pretreatment for coating aluminum plates, but zinc phosphate treatment is a treatment originally developed for steel sheets or surface-treated steel sheets. Technology,
When applied to aluminum, there are various problems in quality.

[0004] In order to solve this problem and improve the zinc phosphate treatability of the aluminum plate, a method of previously coating the aluminum plate with zinc has been proposed. (JP-A-61-157693, JP-A-63-153262, JP-A-63-1669)
No. 64). The zinc coating formed on the aluminum plate surface by these methods improves the chemical conversion of zinc phosphate,
It suppresses the elution of Al ions.

[0005]

The zincate treatment is the easiest method for performing the zinc coating, but the zincate treatment is mainly performed on a small-scale treatment by immersion in a batch system, and the mass treatment with high productivity is performed. At present, the technology has not been established. However, in the case of automobile outer panels, it is necessary to establish an excellent mass production technique for surface treatment.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and has been made in order to develop a surface treatment technique which is highly productive. As pretreatment of zinc treatment,
An object of the present invention is to provide a continuous zinc coating method for an aluminum strip which can continuously apply zinc coating using an aluminum strip coil.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, a continuous zinc coating method for an aluminum strip according to the present invention is provided by a zinc phosphate treatment as a pretreatment for coating an aluminum or aluminum alloy strip for an automobile outer panel. A method of performing zinc coating prior to the above, wherein while the aluminum or aluminum alloy strip coil is rewound, an acid solution is supplied to the surface of the strip by a spray method and pickled, and then the pickled surface of the strip is removed. To a zincate treatment by supplying an alkali-based treating agent by spraying to a coating amount of 0.2.
It is characterized by forming a zinc film of up to 1.5 g / m ² , washing with water, drying and winding.

The aluminum strip or aluminum alloy strip used as the raw material is used in the form of a coil. As an aluminum alloy for automotive outer panels, the main alloy component is Mg
Al-Mg based alloy containing 4-5%, Mg 0.2-0.6%,
An Al-Mg-Si alloy containing 1.0 to 1.5% of Si is applied.

Aluminum is generally covered with a strong oxide film. Particularly, in the case of an aluminum alloy containing Mg, an oxide film rich in Mg is formed by heat treatment in the manufacturing process. Since the quality of the zincate treatment is easily affected by these oxide films, it is necessary to remove the oxide films. For removing the oxide film, pickling by a spray method is most preferable, and sulfuric acid, nitric acid, phosphoric acid and other acids can be used. The type, concentration, temperature, treatment time and the like of the acid used are appropriately selected according to the material to be treated.

Typical conditions for the pickling treatment are as follows. Acid: 3 to 5% sulfuric acid Temperature: 50 to 70 ° C Time: 10 seconds Treatment method: Spray method Washing with water and draining after pickling must be performed sufficiently,
It is desirable not to dry the surface of the aluminum strip until the next step. In addition, alkali washing is not preferable because unevenness in processing is likely to occur.

The zincate treatment in the next step is performed by supplying an alkali-based treating agent to the surface of the transferred aluminum strip by a spray method. The basic composition of the processing solution is composed of NaOH, ZnO, a chelating agent and the like. In this case, in order to densify the deposited zinc film, F
The addition of e-ion does not interfere.

Typical zincate treatment conditions are as follows. Liquid composition: NaOH 20 to 200 g / l, ZnO 2 to 20 g / l Temperature: 10 to 50 ° C. Time: 3 to 30 seconds Spray treatment: pressure 0.3 to ² kg / cm ² , pattern is elliptical or circular Zinc coating amount : 0.2 to 1.5 g / m ²

Under the above conditions, if the amount of the zinc film is too small, the effect as a pretreatment of the zinc phosphate treatment cannot be exhibited, and if it is too large, the coating corrosion resistance is reduced and blisters are liable to occur. Therefore, the amount of the zinc film is appropriately in the range of 0.2 to 1.5 g / m ² . On the other hand, if the spray pressure is too high, the processing liquid is scattered more and spot-like unevenness is likely to occur.
It is desirable that the spray patterns be properly overlapped with no excess or shortage and have no gap between the sprays.

When the zincate treatment of the aluminum strip is carried out by the conventional immersion method, powdering is apt to occur due to poor adhesion of the zinc coating, and the powder of the coating adheres to the transfer roll of the aluminum strip to prevent inconvenience. Occurs.

Washing with water after the zincate treatment is sufficiently performed. In order to enhance the effect of washing with water and speed up drying, washing with hot water may be appropriately used in combination. After drying, the aluminum strip is wound around a coil and subjected to processing such as oiling, straightening, slitting, and cutting, depending on the subsequent process.

[0016]

The zincate treatment is a substitution reaction in which Al is dissolved and zinc is precipitated. The diffusion process of the reactive species is important in order to form a film with good adhesion by the substitution reaction.However, if the spray method is applied, the powder generated by the gradual adhesion of the diffusion layer with a low degree of adhesion is generated. The film-like film is quickly removed from the system by the mechanical action of the processing liquid supplied with the spray method and having a high liquid flow rate, and does not remain as a film. Therefore, in the spray method, the diffusion layer becomes thin,
Only a layer that is compact and has good adhesion will be present as a coating.

FIG. 1 shows an electron microscope (SEM) photograph of the surface of an Al-4.5% Mg-0.35% Cu alloy plate zincated by a spray method. According to FIG. 1, it is clearly recognized that the zincate film has a strong crystal form. On the other hand, in the immersion method, the diffusion layer is thick, and the electron micrograph of FIG.
As shown in (4.5% Mg-0.35% Cu alloy plate surface), the deposited films are gently stacked in a state of low adhesion, resulting in poor adhesion and powder. A ring is likely to occur.

[0018]

Hereinafter, examples of the present invention will be described in comparison with comparative examples.

Examples 1-4, Comparative Examples 1-4 Aluminum alloy plates having the compositions shown in Table 1 (dimensions: width 70 mm,
A sample having a thickness of 1 mm) was subjected to zinc coating using a continuous surface treatment facility for testing.

[0020]

[Table 1]

Table 2 shows the test conditions. The alloy A used was a softened material (O material), and the alloy B used was T4 tempered.

[0022]

[Table 2]

The adhesion and powdering properties of the zinc films formed on the test materials prepared under the test conditions shown in Table 2 were examined. The evaluation method was as follows. The test material was extruded by 5 mm with an Erichsen tester, and the peeling state was examined with "Scotch tape # 610" (equivalent to cellophane adhesive tape specified in JISZ 1522) manufactured by Sumitomo 3M Limited. This was done by observing the situation.
Table 3 shows the evaluation results. In addition, the evaluation result of the adhesiveness was displayed according to the following criteria. ○: No peeling, no powdering △: Partial peeling, powdering ×: Fully peeling, powdering

Next, each test material on which the zinc film was formed was degreased, and then a zinc phosphate film was formed by dipping using a commercially available zinc phosphate treating agent [“Palbond L-3020” manufactured by Nippon Parkerizing Co., Ltd.]. . Furthermore, using a commercially available paint for automobile exterior panels on its surface, cationic electrodeposition coating, intermediate coating and top coating are sequentially applied in the usual manner to a thickness of 90μ.
m was formed. In order to examine the coating corrosion resistance of this coating film, a diagonal cross cut was made to reach the aluminum alloy material of the test material, and then SST for 6 hours—drying at 50 ° C.
× 8 hours → 50 ° C constant temperature, 80% constant humidity 10 hours → Cold air drying 1 hour as 1 cycle, conduct 60 cycles of corrosion resistance test,
The state of occurrence of swelling was observed. The evaluation results are also shown in Table 3. In addition, the evaluation result of this coating corrosion resistance was displayed based on the following criteria. ○: no swelling △: partial swelling ×: overall swelling

[0025]

[Table 3]

From the results shown in Table 3, all of the test materials on which the zinc film was formed according to the present invention showed good adhesion of the zinc film and excellent coating corrosion resistance. On the other hand, the test materials of Comparative Examples 2 and 3 in which the zincate treatment was performed by the immersion method had poor adhesion of the zinc film and poor coating corrosion resistance. The test material of Comparative Example 4 in which the pre-cleaning was performed by alkali cleaning instead of acid cleaning also partially swelled in the corrosion resistance test. Further, Comparative Example 1 in which the amount of the zinc film was too large did not show good results.

[0027]

As described above, since the zinc film formed according to the present invention has excellent adhesion and no powdering, continuous treatment using an aluminum strip coil becomes possible. Therefore, the establishment of mass production technology for aluminum plates for automobile outer panels is expected.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing a metal structure of a zinc film formed according to the present invention.

FIG. 2 is an electron micrograph showing a metal structure of a zinc film formed by an immersion method as a comparison.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Takahashi 3-1-1-12, Minato-ku, Nagoya-shi, Aichi Prefecture Inside the Nagoya Works, Sumitomo Light Metal Industries Co., Ltd. No. 3-Chome 1-112 Sumitomo Light Metal Industries, Ltd. Nagoya Works (56) References JP-A-2-70071 (JP, A) JP-A 64-83673 (JP, A) JP-B-61-36596 (JP , B2)

Claims (4)

(57) [Claims] 1. A method of performing zinc coating prior to zinc phosphate treatment as a pre-coating treatment of an aluminum or aluminum alloy strip for an automobile outer panel, wherein the aluminum or aluminum alloy strip coil is rewound while rewinding the coil. The surface of the strip is pickled by supplying an acid solution by a spray method, and then the surface of the pickled strip is zincated by supplying an alkali-based treating agent by a spray method. A continuous zinc coating method for an aluminum strip, comprising forming a zinc film of 5 g / m ² , washing with water, drying and winding. 2. A continuous zinc coating method for an aluminum strip according to claim 1, wherein the spray pressure in the zincate treatment is 0.3 to ² kg / cm ² . 3. Use of 3 to 5% sulfuric acid at 50 to 70 ° C. for pickling, 20 to 200 g / l of NaOH, 2 to ZnO 2 for zincate treatment.
The method for continuous zinc coating of an aluminum strip according to claim 1, wherein a treatment agent of 20 g / l at 10 to 50 ° C is used. 4. The continuous zinc coating method for an aluminum strip according to claim 1, wherein the aluminum alloy is an Al-Mg alloy or an Al-Mg-Si alloy.