JPH1085663A - Coated aluminum alloy plate excellent in edge corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coated Al alloy plate excellent in edge corrosion resistance. SOLUTION: The surface of an Al alloy plate is subjected to granular zinc or zinc alloy plating to form a lower layer and the plated surface is coated with an org. coating film as an upper layer in 1-100μm thickness after coating with a chromate coating film to obtain the objective coated Al alloy plate excellent in edge corrosion resistance. The granular plating is carried out so as to regulate the covering area of granules to <=300μm<2> , the ratio of (height):(width) of each granule to 1:>=20 and the rate of covering of the surface of the Al alloy plate with the granules to 5-70%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated aluminum plate, and more particularly to a coated aluminum alloy plate having excellent end face corrosion resistance and applicable to various uses, for example, an aluminum plate for home appliances and automobiles. is there.

[0002]

2. Description of the Related Art Compared to a method of forming a metal sheet first to form a complicated shape and then applying a coating, a coated metal sheet can streamline the coating process, achieve uniform quality, and consume less paint. Due to advantages such as savings, it has been widely used so far, and its usage is expected to increase in the future. In general, a coated metal sheet is one that is applied to a cold-rolled steel sheet, a galvanized steel sheet, or another metal sheet in advance, and then formed into an arbitrary shape and provided for final use, such as a refrigerator, a washing machine, and an electronic device. It is used for home appliances such as microwave ovens, vending machines, office equipment, automobiles, and metal products such as outdoor units for air conditioners. In such a variety of applications, especially for home appliances and automotive products used outdoors,
Since the coated steel sheet is used while being cut, the occurrence of corrosion on the end face tends to be disliked as deteriorating the commercial value. Therefore, it is necessary to improve the end face corrosion resistance. For this reason, in the coated steel sheet, the end face corrosion resistance has been ensured by increasing the plating adhesion amount.

[0003]

On the other hand, in the case of a coated aluminum alloy plate, for example, Japanese Unexamined Patent Publication No.
JP-A-07776 discloses a coated aluminum material having excellent corrosion resistance in which a coating film is formed on a film made of zinc phosphate or zinc iron phosphate, and JP-A-5-220450 discloses that a lower layer is a Zn layer and an upper layer is a An organic-coated Zn-plated aluminum alloy sheet having an organic coating via a zinc phosphate coating, JP-A-5-222549 discloses that the lower layer is made of Zn.
There is disclosed an organic-coated Zn-plated aluminum alloy sheet having a layer and an upper layer having an organic film via a chromate film. However, at present, it is difficult to sufficiently secure the corrosion resistance of the end face of the above and other coated aluminum alloy sheets disclosed so far. Then, this invention solves the said problem and provides the coating aluminum alloy board excellent in end surface corrosion resistance.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies on the development of a coated aluminum alloy plate which is low in cost and has excellent end face corrosion resistance in order to solve these problems. The present invention has been made by finding that excellent end face corrosion resistance can be obtained by forming a plating on the surface and then painting. That is, the present invention provides: (1) On the surface of an aluminum alloy plate, a granular zinc-based plating layer as a lower layer, a chromate coating layer as an intermediate layer, and an organic coating layer having a thickness of 1 to 100 μm as an upper layer. A coated aluminum alloy sheet with excellent end face corrosion resistance. (2) The shape of the granular zinc-based plating is
300 (μm) ² or less, the ratio of the height and width of the grains is height / width ≧ 1/20, and the coverage of the aluminum alloy plate surface with the grains is 5 to 70%. The coated aluminum alloy sheet having excellent end face corrosion resistance according to the above (1). (3) The coated aluminum alloy sheet having excellent end face corrosion resistance according to the above (1) or (2), wherein the organic coating is a thermosetting resin coating. Here, the aluminum alloy plate includes not only a plate shape but also a coil shape.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the following, the term "corrosion resistance" includes the corrosion resistance of the end face. In the present invention, the coated aluminum alloy plate is a plate in which a zinc-based plating, a chromate film, and an organic film are sequentially provided on an aluminum alloy plate. It is essential that the zinc plating of the lower layer is formed in a granular form on the surface of the aluminum alloy plate. Further, the zinc-based plating defined in the present invention includes zinc plating and F
It refers to zinc-based alloy plating containing 1 to 90% of one or more alloy elements such as e, Ni, Co, Cr, and Mn. The reason for using these platings is that while aluminum alloys alone tend to cause under-film corrosion called thread rust, zinc-based plating has an effect of suppressing the thread rust.

In the present invention, the term “granular” means that the plating thickness is 0.0
For a portion having a size of 1 μm or more, it means that a zinc-based alloy particle is attached in a convex shape on the surface of the aluminum alloy plate after plating. Further, the formation of plating grains widely covers both cases described below. (1) Some are independent and some are in contact with each other, and the plated particles are distributed on the surface of the aluminum alloy plate. (2) An extremely thin plating layer of less than 0.01 μm A state in which the plated layer is distributed after plating so that the protrusions are locally present on the surface.

In the present invention, the coating area of a plating grain means an area of the plating grain projected perpendicular to the surface of the aluminum plate. 300 (μm) ²
The reason for limiting to the following is that when the covering area is large, the tendency of individual grains to be connected increases, and it is not possible to obtain granular plating excellent in corrosion resistance. Preferably 100
(Μm) ² or less. Although the lower limit of the coating area is not particularly limited, if it is too small, the effect of attaching plating cannot be obtained. Desirably, it is 0.001 (μm) ² or more.

Next, in the present invention, the grain height and grain width are projected vertically to the maximum grain height and the grain surface of the aluminum plate in the portion where the plating thickness is 0.01 μm or more. Refers to the maximum length of the part. The reason why the height / width ratio of the plating grains is limited to height / width ≧ 1/20 is that if the height / width ratio is less than 1/20, the effect of improving the corrosion resistance is insufficient. More preferably, height / width ≧ 1/10. Although the upper limit of the ratio of height to width is not specified, the range that can be easily produced industrially is 2 or less.

Next, the coverage of the plate surface with the particles is the ratio of the area covered with the particles to the surface area of the aluminum plate. The reason why the coverage of the aluminum plate surface by the plated grains is limited to 5 to 70% is that if the coverage is less than 5%, the coverage is too small to obtain the effect of adhering the plating. This is because the tendency of individual grains to be connected increases, and granular plating excellent in corrosion resistance cannot be obtained. In the present invention, the reason why the corrosion resistance is improved by making the plating granular is that when the plating is layered, thread rust is suppressed, but in a high-humidity environment, corrosion of the plating occurs continuously, and a coating called a blister is formed. This is because film swelling occurs, but the generation of blisters can be suppressed when the film is made into a granular form.

In the present invention, the plating method is not particularly limited, and any method may be used as long as the above-mentioned granular plating can be obtained. Industrially, it is easy to electrochemically anodize the surface of the aluminum alloy plate with a current of 1 to 1000 C / dm ² and then to perform electroplating. Electrochemical anodic treatment is a process of forcibly energizing from the outside, a process of energizing using a potential difference between other metals, and a process of using ions in a solution and a redox reaction of the aluminum alloy plate surface. And so on.

Next, the chromate film as the intermediate layer is
It may be applied by a method such as electrolytic chromate, coating type chromate, and reaction type chromate. The role of the chromate film is to improve the adhesion between the plating and the aluminum alloy and the organic film, and this is also effective in improving the corrosion resistance. Next, as the upper organic coating, polyester resin,
Amino resins, epoxy resins, acrylic resins, urethane resins, fluororesins and the like are given as examples, and are not particularly limited, but when used for products that are particularly difficult to process, a thermosetting resin coating film is most preferable. . Examples of the thermosetting resin coating film include polyester paints such as epoxy polyester paints, polyester paints, melamine polyester paints, urethane polyester paints, and acrylic paints.

[0012] Polyester-based paints in which melamine resin or polyisocyanate resin is used as a curing agent in combination with alkyd resins in which a part of the acid component of the polyester resin is replaced by fatty acids, oil-free alkyd resins that are not modified with oil, and various crosslinks This is because the acrylic paint combined with the agent has better workability than other paints, so that cracks and the like do not occur in the coating film even after severe processing. The film thickness is 1μ
m to 100 μm is appropriate. The reason for setting the film thickness to 1 μm or more is that if the film thickness is less than 1 μm, corrosion resistance cannot be ensured. The reason for setting the film thickness to 100 μm or less is as follows.
This is because if the film thickness exceeds 100 μm, it is disadvantageous in terms of cost. Desirably, it is 20 μm or less. The organic coating layer may be a single layer or multiple layers. In addition, additives such as a plasticizer, an antioxidant, a heat stabilizer, inorganic particles, a pigment, and organic lubrication are added to the organic film used in the method of the present invention, if necessary.

[0013]

The present invention will be described below in detail with reference to examples. (Example 1) First, a rolled plate of AA6111-T4 material was prepared as a raw material, and granular electroplating as shown in Table 1 was applied to both surfaces. The granular plating was obtained by electrochemically anodizing the surface of the aluminum alloy plate and then performing electroplating using a plating bath containing each metal ion. Next, the aluminum alloy plate on which the granular plating was performed was immersed in a coating type chromate treatment solution to perform a chromate treatment. The adhesion amount of the chromate film was 50 mg / m ^{2 in} terms of Cr. On top of this, an epoxy polyester paint was applied as a primer with a bar coater and baked in a hot air drying oven to adjust the film thickness to 5 μm. The top coat is made of a polyester coating with a bar coater and baked in a hot air drying oven to a thickness of 20 μm.
Was adjusted. The coated aluminum alloy plate produced as described above was cut into 150 × 70 mm, and the corrosion resistance of the end face was evaluated as it was. In the evaluation test, a yarn rust test combining salt spray and a wet environment was performed. The evaluation was evaluated by Δ: no swelling from the end face, and X: swelling from the end face. The evaluation results are as shown in Table 1, and all the materials of the present invention showed good end face corrosion resistance.

[0014]

[Table 1]

(Example 2) First, Tables 2 to 6 were used as materials.
Prepared aluminum alloy rolled plate shown in Table 2
Granular Zn—Fe (10%) electric alloy plating as shown in Table 6 was performed. Granular plating involves electrochemically anodizing the aluminum plate surface, followed by Zn ²⁺ and Fe ²⁺
It was obtained by performing electroplating using a sulfuric acid bath containing. Next, the aluminum plate subjected to the granular plating was immersed in a coating type chromate treatment solution to perform a chromate treatment. The amount of chromate film adhered is 50 in terms of Cr.
mg / m ² . On top of this, an epoxy polyester paint was applied as a primer with a bar coater and baked in a hot air drying oven to adjust the film thickness to 5 μm. For the top coat, a polyester coating was applied with a bar coater and baked in a hot air drying oven to adjust the film thickness to 20 μm. The coated aluminum alloy plate produced as described above is 150 × 70
mm, and the end face corrosion resistance evaluation test was performed as it was.
In the evaluation test, a yarn rust test combining salt spray and a wet environment was performed. The evaluation was Δ: no swelling from the end face, ×:
Judgment was made based on the presence of swelling from the end face. Evaluation results are shown in Tables 2 to 6.
As shown in Table 2, the materials of the present invention all showed good end face corrosion resistance.

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

[Table 5]

[0020]

[Table 6]

(Embodiment 3) First, AA611 is used as a material.
1-T4 rolled plate is prepared, and the coated area of the grain is 1
(Μm) ² , granular Zn—Fe (10%) electric alloy plating was performed so that the ratio of the height and width of the grains was ２ and the coverage by the grains was 40%. Granular plating was obtained by electrochemically anodizing the surface of an aluminum plate and then performing electroplating using a sulfuric acid bath containing Zn ²⁺ and Fe ²⁺ . Next, the aluminum alloy plate on which the granular plating was performed was immersed in a coating type chromate treatment solution to perform a chromate treatment. The adhesion amount of the chromate film was 50 mg / m ^{2 in} terms of Cr. The coating was performed by coating each with an epoxy polyester paint, a polyester paint, a melamine polyester paint, a urethane polyester paint, and an acrylic paint with a bar coater and baking in a hot-air drying oven to adjust the film thickness as shown in Tables 7 and 8. As a comparative example, an AA6111-T4 material that was not plated was coated with the same material and used. The coated aluminum alloy plate produced as described above was cut into 150 × 70 mm, and the corrosion resistance of the end face was evaluated as it was. In the evaluation test, a yarn rust test combining salt spray and a wet environment was performed. The evaluation was evaluated by Δ: no swelling from the end face, ×: swelling from the end face. The evaluation results are as shown in Tables 7 and 8, and all the materials of the present invention showed good end face corrosion resistance.

[0022]

[Table 7]

[0023]

[Table 8]

[0024]

The coated aluminum alloy sheet of the present invention has a granular zinc-based alloy plating shape, a grain coverage of 300 (μm) ² or less, and a ratio of the height and width of the grains to the height / width ratio.
Excellent edge corrosion resistance by having a form of width ≥ 1/20, making the coverage of the aluminum alloy plate surface 5 to 70%, making the intermediate layer a chromate film and the upper layer an organic resin layer . As a result, it is possible for the consumer to complete the product by omitting the painting process.

Claims (3)

[Claims] 1. An aluminum alloy sheet having, on a surface thereof, a granular zinc-based plating layer as a lower layer, a chromate film layer as an intermediate layer, and an organic film layer having a thickness of 1 to 100 μm as an upper layer. Painted aluminum alloy plate with excellent edge corrosion resistance. 2. The shape of the granular zinc-based plating is such that the coverage area of the grains is 300 (μm) ² or less, and the ratio of the height to the width of the grains is:
2. The coated aluminum alloy sheet having excellent end face corrosion resistance according to claim 1, wherein the aluminum alloy sheet has a form of height / width ≧ 1/20, and the coverage of the aluminum alloy sheet surface with the grains is 5 to 70%. 3. The coated aluminum alloy sheet having excellent end face corrosion resistance according to claim 1, wherein the organic coating is a thermosetting resin coating.