JPH0232355B2 - ARUMINIUMUUAENGOKINMETSUKIKOHANOKIBANTOSHITATOSOKOHAN - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coated steel plate using an aluminum-zinc alloy plated steel plate that has been subjected to chromate-based chemical conversion treatment,
An undercoat is applied on top, which is a mixture of a paint film-forming resin, an extender, a chromate-based rust-preventing pigment with low water solubility, and a chromate-based rust-preventive pigment with high water solubility, and a top coat is applied on top of this undercoat. The present invention relates to a coated steel plate using an aluminum-zinc alloy plated steel plate as a substrate, which is coated with a paint. Aluminum-zinc alloy plated steel sheets are conventionally known, for example, from Japanese Patent Publication No. 7161/1983. This aluminum-zinc alloy plated steel plate has the characteristics of both aluminum plated steel plate and galvanized iron plate, and is attracting attention as a durable steel plate. Taking advantage of its excellent durability, heat resistance, and workability, it can be used in buildings without painting. It is used as a processed material mainly for roofing and wall materials. By the way, painted aluminum-zinc alloy plated steel sheets are made to look beautiful by taking advantage of the characteristics of the material and have excellent durability. ) are more likely to cause blistering of the paint film. Generally, galvanized steel sheets and aluminum plates are painted using a roll coater or curtain flow coater with an undercoat paint with a dry film thickness of approximately 2 to 10 μm, baked and dried, and then a top coat paint with a dry film thickness of approximately 8 to 30 μm. It is a 2-coat, 2-bake system where the paint is baked and dried.
These paints can also be used to paint aluminum-zinc alloy plated steel sheets, but with conventional paint systems, the blistering of the paint film from the end face in a corrosive atmosphere is more pronounced than in the case of galvanized iron sheets. Here, the swelling state of the coating film from the end surface (cut surface) of an aluminum-zinc alloy plated steel plate coated with a coating material will be explained. Figures 1 to 4 show EPMA (electron probe micro analysis) results on the end surface of a steel plate 6 coated with aluminum-zinc alloy plating 3 and a coating film 2 formed on an aluminum-zinc alloy plated steel plate 1. These are characteristic X-ray photographs. Figure 1 is a cross-sectional photograph at a magnification of 1000 times, Figure 2 is a photograph (at a magnification of 1000 times) showing the presence of Al in the three layers of aluminum-zinc alloy plating, and the third The figure is also a photograph (1000x magnification) showing the presence of Zn, and Figure 4 is also a photo showing the presence of Zn.
This is a photograph (1000x magnification) showing the presence of Si. Here, the aluminum-zinc alloy plating 3 is Al
This aluminum-zinc alloy plating 3 contains 55% by weight of Zn, 43.4% by weight of Zn, and 1.6% by weight of Si, as is clear from Figures 1 to 4.
Al and Zn are not uniformly dispersed, and there are areas where Al is present in larger amounts than Zn (hereinafter referred to as the aluminum-rich phase) and areas where Zn is present in greater amounts than Al (hereinafter referred to as the zinc-rich phase). ).
That is, the zinc-rich phase 4 is shaped like an ant's nest, and the portion other than the ant's nest-shaped zinc-rich phase 4 is an aluminum-rich phase 5. Figure 5~
Figure 8 shows aluminum-zinc alloy plated steel plate 1.
The results of a salt spray test (100 hours) on an end surface with coating film 2 formed on it.
This is a characteristic X-ray photograph of EPMA (Electron Probe Micro Analysis). Figure 5 is a photograph of the end face at a magnification of 1000 times, and Figure 6 shows the presence of Al in the three layers of aluminum-zinc alloy plating. It is a photograph (1000x magnification), and Figure 7 is the same.
This is a photograph (1000x magnification) showing the presence of Zn, and Figure 8 is a photograph (1000x magnification) also showing the presence of Si.
It is. As is clear from the photographs shown in FIGS. 5 to 8, zinc is intensively corroded in the ant-nest-shaped 4 parts of the zinc-rich phase, and corrosion products and gas are transferred to the interface with the coating film 2. It can be seen that the particles come out and swell the coating film 2, causing the coating film 2 to peel and tear. Corrosion from the end faces of the aluminum-zinc alloy plating coated steel sheet 1 is caused by batteries occurring between the aluminum-rich phase in the aluminum-zinc alloy plating layer and the iron on the end faces, and between the zinc-rich phase and the iron on the end faces. It is estimated that However, in the case of iron and aluminum, or iron and zinc, in the case of non-alloys, the potential difference between iron and aluminum is larger than that between iron and zinc, so aluminum corrodes more, but in the case of aluminum-zinc alloy plating, As is clear from the photographs in Figures 5 to 8, there is a phenomenon in which the zinc-rich phase 4, which contains more zinc, is more corroded, but the reason for this is currently unknown. In any case, as is clear from the photographs in Figs. 5 to 8, in the case of the aluminum-zinc alloy plated steel sheet 1, the ant-nest-like zinc-rich phase 4 corrodes at the ends (cut ends). This causes the coating film 2 to peel off. The object of the present invention is to provide a coated steel plate using an aluminum-zinc alloy plated steel plate as a substrate, which can prevent blistering of the coating film from the end face of the coated steel plate using the aluminum-zinc alloy plated steel plate as a substrate. . The present invention will be explained in detail below. In the present invention, in order to prevent blistering of the coating film 2, strontium chromate and calcium chromate (here, calcium chromate has higher water solubility than strontium chromate) are used as the undercoat. be. Chromate ions react with the zinc in the three layers of aluminum-zinc alloy plating to form insoluble salts or oxides, thereby acting as an anode inhibitor and suppressing the elution of zinc in the three layers of aluminum-zinc alloy plating. It is thought to suppress blistering of the paint film. By the way, chromate-based rust-preventive pigments containing chromate ions include strontium chromate, zinc chromate, calcium chromate, barium chromate, etc., and each rust-preventive pigment is converted to chromic acid as a measure of rust-preventive power. Comparing the solubility in water, it is generally said that the ratio of calcium chromate/zinc chromate/strontium chromate/barium chromate is approximately 30/1/0.5/0.1 or less. Among these anti-rust pigments, strontium chromate has good boiling water resistance as a coated steel sheet, but its anti-rust effect against blistering of the coating film 2 from the end surface is somewhat poor. Zinc chromate is slightly more effective than strontium chromate in preventing blistering of the paint film from the edges, but
Boiling water resistance decreases. Calcium chromate has high water solubility and can be expected to be effective against blistering of paint films while maintaining boiling water resistance, but there are concerns about its long-lasting effects. In order to make the blistering and boiling water resistance of the paint film from the edge of the aluminum-zinc alloy coated steel sheet in a corrosive atmosphere equivalent to that of the galvanized steel sheet, it is necessary to It is necessary to control the elution rate, and for this reason, in the invention, we selected a chromate-based pigment that does not reduce boiling water resistance among the above-mentioned chromate-based rust-preventing pigments, and calcium chromate, which has a fast dissolution rate in water. By using this together with strontium chromate, which has a slower dissolution rate than calcium chromate and therefore has a long-lasting effect, it is possible to suppress blistering from the edge of the paint film in a corrosive atmosphere to the same extent as with galvanized steel sheets. became possible. The undercoat used in the present invention is obtained by dispersing titanium oxide, finely powdered clay, extender pigments such as calcium carbonate, and antirust pigments in an epoxy resin varnish or epoxy urethane resin varnish. The rust-preventive pigment in the undercoat is used in an amount of 5 to 60 parts by weight based on 100 parts by weight of the solid content of the paint (the sum of the resin solid content and all the pigments). As the chromate rust-preventing pigment used in the present invention, strontium chromate and calcium chromate are used in combination at a weight ratio of strontium chromate/calcium chromate = 80/20 to 5/95. When the amount of calcium chromate increases to a weight ratio of strontium chromate/calcium chromate of 5/95 or more, the rust prevention effect decreases, and when the amount decreases to 80/20 or less, the rust prevention effect decreases. In the present invention, a chromate-based chemical conversion treatment is applied to an aluminum-zinc alloy plated steel sheet, and then the above-mentioned undercoat is applied, and then a topcoat is applied. Here, the aluminum-zinc alloy plated steel sheet 1 used in the present invention is a steel plate 6 coated with aluminum-zinc alloy plating 3, and the aluminum-zinc alloy plating 3 includes, for example, 55% by weight of Al and 43.4% by weight of Zn. , Si is 1.6
Although the alloy plating is by weight%, it is not necessarily limited to the above-mentioned formulation examples. As the top coating, for example, synthetic resin coatings such as oil-free polyester, silicone polyester, thermosetting acrylic resin, and melamine alkyd are used. However, in the present invention, an undercoat paint containing a mixture of a coating film-forming resin, an extender pigment, strontium chromate, and calcium chromate is applied to an aluminum-zinc alloy plated steel sheet that has been subjected to chromate-based chemical conversion treatment. However, since the top coat is applied on top of this undercoat, the calcium chromate in the undercoat prevents the initial blistering of the paint film at the edges, and the strontium chromate prevents the blistering of the paint film at the edges. It is something that can be made sustainable. Next, an example will be explained. Example 1 Chromate, finely powdered clay, titanium oxide, epoxy urethane resin varnish (manufactured by Mitsui Toatsu Chemical Co., Ltd.)
EP7931), xylol, celloacetate, and butanol were mixed and dispersed using a dispersion machine so that the pigment particle size was 20 μm or less, and then melamine resin (Cymer 301 manufactured by American Cyanamid Co., Ltd.) was added. Thinner (xylol/celloacetate/butanol = 1/
1/1) was added to adjust the viscosity to obtain a test primer. Six types of test primers 1 to 6 were prepared depending on the type and blending ratio of chromate (see Attached Table 1). Next, chromate-based chemical conversion treatment (Alodine, a chromate-based treatment agent manufactured by Nippon Paint Co., Ltd.)
The test primers (1 to 6) were applied to an aluminum-zinc alloy plated steel plate (galvalume steel plate manufactured by Bethlehem Steel Co., Ltd., plate thickness 0.4 mm) that had been pre-painted with a coating method (1225) to a dry film thickness of 5 μm. It was painted using a natural roll coater and baked for 60 seconds at the maximum temperature the material could reach, 200°C. Next, oil-free polyester paint (Nippon Paint Co., Ltd.'s Super Lux DIEE-80 Sorairo) was used as the top coat.
The dry film thickness is 10μ using a natural roll coater.
The maximum temperature the material can reach is 200℃.
The sample coated plates (1 to 6) were obtained by baking for 60 seconds. On the other hand, test primer 1 was used on a galvanized steel plate (thickness: 0.4 mm) that had been pre-painted with a zinc phosphate treatment agent (Granozin 46, manufactured by Nippon Paint Co., Ltd.) and treated in the same manner as in the previous example. It was coated to obtain a supplied coated board 7. The performance of the aluminum-zinc alloy coated steel sheet prepared based on the above examples and the galvanized coated steel sheet was compared, and the results are shown in Attached Table 2. Example 2 Test primers 1 to 1 obtained in the same manner as Example 1
6 was applied to an aluminum-zinc alloy plated steel plate (galvalume steel plate manufactured by Bethlehem Steel Co., Ltd., plate thickness 0.4 mm) which was subjected to chromate-based chemical conversion treatment (Alodine 1225 manufactured by Nippon Paint Co., Ltd.) as a pre-painting treatment so that the dry film thickness was 5μ. Each material is coated with a natural roll coater to reach a maximum temperature of 200℃.
Bake for 60 seconds. Next, as a top coat paint, outer diameter 10
Oil-free polyester paint (Super Rack DIF F manufactured by Nippon Paint Co., Ltd.) containing 20wt% of glass fibers with a diameter of ~13μ and a length of 5~60μ based on the raw paint.
-60 matte 5 colors) was applied using a reverse roll coater to a dry film thickness of 13 to 15 μm, and baked at the maximum temperature the material reached at 200°C for 60 seconds.
13). On the other hand, test primer 1 was used on a galvanized steel plate (thickness: 0.4 mm) that had been pre-painted with a zinc phosphate treatment agent (Granozin 46 manufactured by Nippon Paint Co., Ltd.) and treated in the same manner as in the previous example. Painting was performed to obtain sample coated board 14. The performance of the aluminum-zinc alloy coated steel sheet prepared based on the above examples and the galvanized coated steel sheet was compared, and the results are shown in Attached Table 3.

【table】

【table】

【table】

[Table] Evaluation method Γ Boiling water test...Immersed in boiling water for 8 hours, left at room temperature for 16 hours, and evaluated with gloss retention 4TT folded tape (○: Good, △: Slightly weak ×: Poor) Γ Edge creep resistance ...A painted board whose three sides and back were sealed with polyester tape was exposed to a salt spray tester (JIS-K-5400.7.8.).
Blistering and blistering of the paint film from unsealed edges (hereinafter referred to as edge creep)
Evaluate. Edge creep was evaluated in two ways: maximum blister length (mm) and edge creep index.
Edge creep index = (10 - blister width evaluation) x (maximum blister length: mm) Blister width evaluation: 10-point rating (10: no defects, 1: blisters on all edges) (the larger the edge creep index is) , indicating a significant tendency for corrosion under the paint film.)

[Brief explanation of drawings]

Figures 1 to 4 are cross-sections of a coating film formed on an aluminum-zinc alloy plated steel plate.
Characteristic X-ray photographs of EPMA (Electron Probe Micro Analysis). Figure 1 is a photograph of the end face at a magnification of 1000 times, and Figure 2 is a magnification showing the presence of Al in the aluminum-zinc alloy plating layer. Figure 3 is a 1000x photograph showing the presence of Zn, and Figure 4 is a 1000x photograph showing the presence of Si.
Figures 5 to 8 show the characteristics of EPMA (electron probe micro analysis) on the end face showing the results of salt spray tests on the same as above.
Figure 5 is a photograph of the end face at a magnification of 1000 times; Figure 6 is a photograph taken at a magnification of 1000 times showing the presence of Al in the aluminum-zinc alloy plating layer;
FIG. 7 shows a photograph with a magnification of 1000 times, which also shows the presence of Zn, and FIG. 8 shows a photograph with a magnification of 1000 times, which also shows the presence of Si. 1 shows an aluminum-zinc alloy plated steel plate.

Claims (1)

[Claims] 1 Aluminum treated with chromate chemical conversion treatment
An undercoat paint containing a mixture of a paint film-forming resin, a substance, calcium chromate, and strontium chromate is applied to a zinc alloy plated steel plate, and a top coat is applied on top of this undercoat paint. A painted steel sheet with a characteristic aluminum-zinc alloy plated steel sheet as a substrate.