JPS5914942A - Coated steel plate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coated steel sheet using an aluminum-zinc alloy plated steel sheet as a substrate.

BACKGROUND ART Conventionally, so-called painted steel plates, which are steel plates or galvanized steel plates coated with paint, have been provided as steel plates with improved corrosion resistance. For galvanized steel sheets that have been painted, the surface of the galvanized copper sheet is chemically treated with zinc ricinate or chromic acid, and then an undercoat is applied to the surface of the chemical conversion treatment layer, and then this undercoat is applied. It is formed by applying a top coat to the surface of the paint film, and the corrosion resistance and weather resistance are improved by the galvanizing chemical conversion treatment and the paint layer on the surface. In addition, as the undercoat paint that forms the undercoat film, strontium chromate%'y
[]0-mate rust preventive pigments with chromic acid ions such as calcium chromate, barium chromate, zinc chromate,
Calcium tridate, calcium phosphate, aluminum phosphate 1 titanium phosphate \ lead cyanamide , calcium lead oxide 1 Rust preventive pigments such as basic chromic acid are applied to the non-volatile portion of the primer paint ($R sum of fat solids and total pigments). ), the corrosion resistance of galvanized steel sheets is further improved by using 5 to 30% by weight of the same.

By the way, it is known that an aluminum-zinc alloy coated steel sheet, in which an aluminum-zinc alloy plating layer is formed on the surface of the steel sheet, has better corrosion resistance than the above-mentioned galvanized steel sheet. Zinc aluminum removal machine product disclosed in 1986-2
Corrosion-resistant aluminum-zinc coated material and its manufacturing method disclosed in Japanese Patent Publication No. 2528, Corrosion-resistant zinc alloy coated iron metal article and its manufacturing method disclosed in Japanese Patent Publication No. 54-8335, and disclosed in Japanese Patent Publication No. 56-44143-Q Iron substrate product having a fixed material and method for manufacturing the same, Special Publication No. 1987-11
According to the improved treatment method for iron strands by hot-dip treatment disclosed in Publication No. 390-1'+, aluminum-zinc alloy coated steel sheets have a surface area of 2 to 6 times that of galvanized steel sheets. It is said to be monophagous. However, when a coated steel plate is formed by the above method using this aluminum-zinc alloy plated steel plate as a substrate,
When used in a corrosive atmosphere, the paint film applied to the surface may blister or peel off from the edge of the coated steel plate (cut edges of the coated steel plate). It was significantly inferior compared to The reason why such blistering and peeling tends to occur on coated steel sheets using aluminum-zinc alloy plated steel sheets as a substrate is that aluminum and zinc are not evenly distributed in the aluminum-zinc alloy plating layer, and there is more aluminum than zinc. The zinc-rich phase is unevenly distributed in the aluminum-rich phase (aluminum-rich phase) and the aluminum-rich phase (zinc-rich phase), and the zinc-rich phase is shaped like an ant's fruit, forming a three-dimensional relationship with the aluminum-rich phase. It has an entangled structure, and it is thought that under a corrosive atmosphere, the zinc-rich phase corrodes and disappears in preference to the aluminum-rich phase, and the resulting hydrogen gas and corrosion products push up the coating film.

In other words, on the end face of an aluminum-zinc alloy plated steel sheet, batteries are formed by the aluminum-rich phase and the iron on the end face, and the zinc-rich phase and the iron on the end face, respectively.Because the potentials of each metal are different, one zinc-rich phase forms a battery. corrodes first.

The present invention has been made in view of the above points, and provides corrosion resistance that prevents the coating film applied to the surface from peeling off or blistering even when an aluminum-zinc alloy plated steel plate is formed as a substrate. The purpose is to provide an excellent coated steel plate.

That is, the present invention applies chemical conversion treatment to form an aluminum-zinc alloy plating layer (1) on the surface of an aluminum-zinc alloy-plated steel sheet (2) on which an ILI trinium-zinc alloy plating layer (1) has been formed on the surface by a hot-dip plating method. Chemical conversion treatment layer (3)
On the surface of this chemical conversion treatment layer (3), an undercoat containing 30 to 70% of strontium chromate or calcium chromate (1%) based on the non-volatile content of the undercoat is applied. The present invention will be described in detail below, in which the above-mentioned objects have been achieved by a coated steel plate characterized by coating a top coat on top of the paint.As shown in the attached figure, the surface of the steel plate (8) An aluminum-zinc alloy plating layer (1) is formed by a hot-dip plating method.As mentioned above, this aluminum-zinc alloy plating layer f1) is an aluminum-rich phase in which aluminum contains a large amount of zinc as well as aluminum. (6) and a zinc-rich phase (7) containing more zinc than aluminum, and the zinc-rich phase (7) is intertwined with the aluminum-rich phase (6) like an ant's nest. Aluminum zinc alloy plating phase (1
The + component is not limited in any way, but for example, M is 4 to 75% by weight, the remainder is mostly zinc, and Si,
Those containing a trace amount of a third component such as Mg and Ce%Sn can be used, such as All-Zn-St alloy, Al-Zn-Mg alloy, A11. - It is used as a plating for Zn-Ce alloy, M-Zn-Sn alloy, etc., especially when M is 55% by weight and Zn is 434
It is preferable to use one containing 1.6% by weight.

A chemical conversion treatment layer (3) is formed on the surface of this aluminum-zinc alloy plating layer (it) by subjecting it to a chromic acid-based or zinc ricinate-based chemical conversion treatment. Chemical conversion treatment can be done by spraying, dipping or 1do.
- This can be done by a paint coating method, etc. Next, the surface of the chemical conversion treatment layer (3) is coated with D sterium or calcium chromate at a ratio of 18
Baking dries at a temperature of 0 to 220°C to form an undercoat film (4)
After forming, and. Here, as the undercoat paint, epoxy-based, epoxy-uretashi-based, polyester-based, and polymer epoxy-based undercoat paints can be used. In addition to blending calcium chromate, extender pigments such as titanium oxide and various antirust pigments shown in the conventional examples may also be blended as appropriate. If the amount of strontium chromate or calcium chromate is less than 30% by weight based on the non-volatile content of the undercoat, the effect of reducing blistering of the topcoat (6) will be small;
If it exceeds % by weight, the adhesion to the top coat (5) will be poor. Further, as the top coating paint, polyester resin paint, acrylic resin paint, acrylic resin paint, tan resin paint, silicone polyester resin paint, silicone acrylic resin paint, fluororesin paint, etc. can be used. These top coat paints and the above-mentioned undercoat paints are used in correspondence with each other in order to improve adhesion.For example, the earth coat paints are polyester-based, acrylic-based, aluminum-based, silicone polyester-based, and silico-diacryl-based. For fluorine-based top coats, it is preferable to use epoxy-based, epoxy-uretashi-based, or polyester-based undercoat paints, and for fluorine-based top coats, it is preferable to use polymeric epoxy-based undercoat paints. In this way, a top coat (5) is formed over the entire surface of the base coat (4) to obtain a coated steel sheet as shown in the attached drawings.

Therefore, by using the Kuma aluminum-zinc alloy plated steel plate (2) as the substrate for this painted steel plate, the aluminum-zinc alloy plated layer (+l) on the surface has a higher corrosion resistance than that of a conventional galvanized steel plate used as the substrate. It is a material that can increase the
) can prevent the penetration of water etc. and improve corrosion resistance, weather resistance and water resistance. Furthermore, the undercoat film (4) formed between the aluminum-zinc alloy plated steel sheet (2) and the topcoat film (5) is coated with 30 to 70% by weight of chromic acid based on the non-volatile content of the undercoat paint. By applying an undercoat containing 0% calcium or 0% calcium oxide, a soil coating film (
5) can prevent corrosion of the aluminum-zinc alloy plating layer (1) without reducing the adhesion with the aluminum-zinc alloy plating layer f11, and can suppress corrosion of the zinc-rich phase (7) of the aluminum-zinc alloy plating layer f11. .

As described above, in the present invention, strontium chromate or calcium chromate is added to the surface of the chemical conversion treatment layer of an aluminum-zinc alloy plated steel sheet at a ratio of 3% to the non-volatile content of the undercoat.
Corrosion resistance can be increased by using a plate containing 0 to 70% by weight as a substrate, and the zinc-rich phase of the aluminum-zinc alloy plating layer will corrode with an undercoat film containing a large amount of strontium chromate or calcium chromate. It is possible to prevent the surface coating film from blistering or peeling even in a corrosive atmosphere.

The present invention will be explained in detail below with reference to Examples.

<Examples 1 to 4, Comparative Examples 1 to 4> A155% by weight, Zn 48.4% by weight, plate thickness 0.4 sheets,
St 1.6% by weight aluminum-zinc alloy plated steel sheet (plating area 150 y/m" (both sides)', plating thickness 20 microns on one side) was roll coated with a chromic acid chemical conversion treatment solution and heated at 40 to 50℃. Next, the surface of the formed chemical conversion treatment layer was coated with 60% of the non-volatile content of the Epo + diurethane undercoating paint at a board temperature of 200°C as shown in the table below.
Baked for a second, then coated with oil-free polyester 1 (Super Lac DIF F- manufactured by Nippon Peisito Co., Ltd.).
80 Sorairo) was applied using a D-ru coater to a dry film thickness of 10 μm, and baked at a plate temperature of 200° C. for 60 seconds to obtain a coated steel plate.

<Example 5.6> A coated steel plate was prepared in the same manner as in Example 1, except that an undercoat in which the amount of calcium chromate shown in the following table was blended with the nonvolatile content of the Epo+Shiureta Y-based undercoat was used. Obtained.

<Conventional example> Strontium chromate was applied to the surface of a galvanized iron plate (Z-25) with a thickness of 0.4 am at a ratio of 1 to the non-volatile content of the undercoat.
A coated steel plate was obtained in the same manner as in Example 1, except that an epoxy resin-based undercoat containing 0% by weight was applied.

Next, the adhesion of the coated steel plates obtained in Examples 1 to 6, Comparative Examples 1 to 4, and the conventional example and the coating film blistering on the end surface were measured. In addition, evaluation of adhesion and coating film blistering at the end surface was performed as follows.

Adhesion: The adhesion of the coating film was evaluated by forcibly peeling off the bent portion with a septum after 4T close bending, and evaluating the peeled state of the coating film. The results are then judged using a 5-point scale [5 points (excellent) → 1 point (poor)]: ◎...5 points, ○...4 points, △・
・, 2 to 3 points, ×...1 point, were displayed.

Blistering of the paint film on the end surface: A painted steel sheet whose three sides and back surface were sealed with polyester tape was exposed to a salt spray tester (JIS K-54007, 8).
This test evaluates the blistering condition of the paint film from the edge of the seal (hereinafter referred to as etch-clean).
The maximum length of the hanging star is indicated by ■). The results are shown in the table below.

From the results in the table above, it is clear that the edge creep of the coating film changes greatly depending on the content of strontium oxide or calcium chromate in the undercoat paint, and Comparative Example 1.
It can be seen that in the case of Example 2.3, the adhesion was long lasting and the edge creep was large, and in the case of Comparative Example 4, the adhesion was decreased. On the other hand, in the examples, both adhesion and etch creep resistance were satisfactory.

[Brief explanation of drawings]

The attached drawing is a partially cutaway enlarged sectional view of one embodiment of the present invention,
(1) is an aluminum zinc alloy plating layer, (2) is an aluminum zinc alloy plated steel sheet, (3) is a chemical conversion treatment layer, (
4) is the undercoat film, f5) Vi±coat film, +611
”t Al tririch phase, (7) Fi zinc rich phase, (8)
It is a U steel plate. Agent Patent Attorney Ishi 1) Choshichi

Claims (1)

[Claims] fl A chemical conversion treatment layer is formed by chemical conversion treatment of an aluminum zinc alloy plating layer on the surface of an aluminum zinc alloy plated copper plate on which an aluminum zinc alloy plating layer is formed by hot dipping, and this chemical conversion treatment layer 0 chromic acid strips on the surface of
It is characterized by applying a "F coating paint containing 30 to 70% by weight of calcium chromate or calcium chromate based on the non-volatile content of the undercoat, and then applying a topcoat on top of this undercoat." Painted steel plate. (2) The polymer for the top coat is polyester resin,
Acrylic resin, acrylic resin, urethane resin, silicon]:
The coated steel sheet according to claim 1, wherein the coated steel sheet is at least one kind of polymer selected from , I polyester resin, silicone acrylic resin, fluororesin, etc.