JPH07148461A - Coated metal panel - Google Patents

Abstract

PURPOSE:To provide a coated metal panel excellent in the corrosion resistance of the edge face and processed part thereof and generating no red rust by using an aluminum-zinc alloy plated steel panel as a material. CONSTITUTION:A chemical forming treatment layer is applied to the surface of an aluminum-zinc alloy plated steel panel and undercoat and topcoat coatings are subsequently applied to the treatment layer to produce a coated metal panel. In this case, the undercoat coating contains a linear polyester resin with a wt. average mol.wt. of 5,000-20,000 and glass transition temp. of 40 deg.C or less as a main component of a color developing agent and also contains strontium chromate or a mixture of strontium chromate and aluminum phosphomolibdate as anti-corrosive pigment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal sheet which uses an aluminum-zinc alloy-plated steel sheet as a raw material and which is particularly excellent in corrosion resistance at a cut end face and a bent portion.

[0002]

2. Description of the Related Art In recent years, market demand for coated metal sheets used for roofs and building exteriors and requiring long-term durability has been further increased. Therefore, not only in the paint used, but also in metal materials, aluminum zinc alloy plated steel sheets and aluminum plated steel sheets, which are materials for improving durability, have been developed in place of the conventional hot-dip galvanized steel sheets, improving durability. Has been planned. The following techniques have been disclosed as paints to be used for these improved metal materials. First, for aluminum-zinc alloy-plated steel sheets, in Japanese Patent Publication No. 2-32355 and Japanese Patent Publication No. 2-36384, strontium chromate, calcium chromate, or both are used in combination as an anticorrosive pigment for the undercoat paint. Discloses a method for improving the corrosion resistance of the end face, which has been a problem in the past. For aluminum plated steel sheets,
JP-A-14866 and JP-A-59-159334 disclose a method of improving corrosion resistance by using strontium chromate and calcium carbonate in combination as a rust preventive pigment for an undercoat paint, or by compounding a Zn-Mg alloy powder. Has been done.

[0003]

In general, aluminum-zinc alloy-plated steel sheets and aluminum-plated steel sheets are improved in corrosion resistance of the material itself, as compared with the conventionally used hot-dip galvanized steel sheets. Is recognized. Nevertheless, when used as a coated metal plate, there is a drawback that the corrosion resistance of the cut end face and the processed portion is inferior, and in any of the above-mentioned conventional techniques, similar disadvantages remain as a problem. Is the current situation. There are many unclear points about the above reason, but it is presumed as follows. In the plating layer of the aluminum-zinc alloy-plated steel sheet material, aluminum and zinc are not necessarily uniformly dispersed, and the surface of the aluminum-zinc alloy-plated steel sheet material is
There is a lot of aluminum (aluminum rich layer),
Since it is mostly covered with an aluminum oxide film, it has better corrosion resistance than hot-dip galvanized steel sheets, but both are coated metal sheets (in most cases, epoxy resin-based undercoat paint is applied). When compared as, against corrosion from the exposed cut end face and processed part, the coating metal plate of aluminum zinc alloy plated steel plate material is hard and brittle because the epoxy resin-based undercoat coating film is It is also unlikely that it will form, and that the corrosion from the side surface (cut end surface) will progress rapidly. The object of the present invention is to use an aluminum zinc alloy-plated steel sheet as a material,
Another object of the present invention is to provide a coated metal plate which is excellent in corrosion resistance of the processed part and does not cause red rust.

[0004]

As a result of various studies to solve the above problems, the present inventors have found that a combination of a specific color-developing agent and a specific rust-preventive pigment as an undercoat paint for a coated metal plate. It has been found that a coated metal plate without the above-mentioned defects can be produced by using the same, and based on this finding, the present invention has been completed. That is, the present invention is a coated metal plate prepared by applying a chemical conversion treatment layer on the surface of an aluminum-zinc alloy-plated steel sheet, and then applying a primer coating composition and a top coating composition, wherein the primer composition has a weight average molecular weight of 5,000.
A linear polyester resin having a glass transition temperature of 0 to 20,000 and a glass transition temperature of 40 ° C. or lower was used as a main component of the color-developing agent, and strontium chromate alone or a mixture of strontium chromate and aluminum phosphomolybdate was used as an anticorrosion pigment. The present invention provides a coated metal plate characterized by being a paint. In the present invention, the linear polyester resin (hereinafter referred to as LP resin) used as a color-developing agent for the undercoat paint contains a dihydric alcohol and a dibasic acid in OH / C.
It is obtained by condensation polymerization of OOH in an equivalence ratio of 1.0 to 1.2, and has a linear structure. Therefore, the glass transition temperature can be controlled by selecting the type of monomer compound with a flexible resin. It can be designed as low as desired. Examples of the dihydric alcohol as the LP resin raw material of the color developing agent of the present invention include
Use of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, butanediol, pentanediol, hexanediol, neopentyl glycol, hexylene glycol, saturated dihydric alcohol such as polyethylene glycol or polypropylene glycol having a degree of polymerization of 10 or less. Can
If desired, a small amount of a dihydric alcohol having a phenyl group, such as bisphenol A, an ethylene oxide adduct of bisphenol A, or a propylene oxide adduct of bisphenol A, can be used in combination therewith.

As the dibasic acid used as the LP resin raw material for the color developing agent of the present invention, saturated dibasic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and tetrahydrophthalic acid are mainly used, and if necessary, A small amount of dibasic acid having a phenyl group such as terephthalic acid can be used together.
The weight average molecular weight of the LP resin used in the present invention is 5,000.
It is necessary that it is in the range of 0 to 20,000 and the glass transition temperature is 40 ° C. or lower. L in the present invention
When the weight average molecular weight of the P resin is less than 5,000, it is difficult to obtain the original tough coating film, and when it exceeds 20,000,
The viscosity of the resin is high, making it difficult to form a coating material, which is not preferable. Further, the glass transition temperature of the LP resin used in the color developing agent of the present invention needs to be 40 ° C. or lower, and when the glass transition temperature exceeds 40 ° C., the coating film becomes hard and brittle,
The corrosion resistance of the end face and the processed portion, which is the object of the present invention, is reduced. In the present invention, an LP resin satisfying the above conditions can be appropriately selected and used, and for example, an LP resin composed of ethylene glycol and adipic acid, ethylene glycol, an LP resin composed of bisphenol A and adipic acid, sebacic acid, and diethylene glycol. An LP resin composed of hexanediol, adipic acid, and terephthalic acid can be preferably used. For example, commercially available bisphenol A diglycidyl ether and adipic acid as the main components of Byron GK590, GK130, and GK780 [all trade names of Toyobo Co., Ltd.] can be preferably used. When the LP resin of the present invention is used in an undercoat paint, a melamine resin (abbreviated as M in the table), a urea resin (abbreviated as U in the table), or a polyfunctional isocyanate compound (abbreviated in the table as a crosslinking agent) is used. It is desirable to use (hereinafter abbreviated as N) mixed with the LP resin. In the present invention, strontium chromate (S in the table is used as an anticorrosive pigment for the undercoat paint.
Abbreviated as C) is 5 to 30% by weight in the solid content of the undercoat paint,
Preferably, a blending amount of 10 to 25% by weight can be used.

If the amount of strontium chromate added to the undercoat paint of the present invention is less than 5% by weight, the anticorrosion effect will be reduced,
Further, even if it is used in an amount exceeding 30% by weight, the effect of the present invention is not hindered, but from the viewpoint of efficiency, the improvement of the anticorrosion effect commensurate with the added amount cannot be obtained. In the epoxy resin-based undercoating composition that has been generally used conventionally, a compounding amount of more than 30% by weight was usually required in the solid content of the undercoating composition, but in the undercoating composition of the present invention, the addition amount of strontium chromate is 30% by weight. It is also characterized in that even with the following blending amounts, excellent end face corrosion resistance is exhibited. Further, aluminum phosphomolybdate (abbreviated as PMA in the table) used together with strontium chromate as a rust preventive pigment in the undercoat paint of the present invention is 0 to 5 times, preferably 0 to 3 times the strontium chromate. The double can be mixed and used. By using strontium chromate and aluminum phosphomolybdate together as the rust preventive pigment of the present invention, the compounding amount of strontium chromate can be reduced without lowering the corrosion resistance of the undercoat paint. As for the addition method, both can be mixed and then dispersed separately in the undercoat paint. Further, other extender pigment components can be appropriately mixed and dispersed in the undercoat paint of the present invention, if desired. The coated metal sheet made of the aluminum-zinc alloy-plated steel sheet of the present invention is characterized in that the undercoat paint specified in the present invention is used, and the chemical conversion treatment or the undercoat of the surface to be coated in the method for preparing the coated metal sheet of the present invention is performed. As a method such as coating or top coating, a known method that is generally used in the past can be applied. Further, as the top coat paint used for the coated metal plate of the present invention,
For example, polyurethane resin paints, acrylic resin paints, alkyd resin paints, silicone polyester resin paints, and fluorine resin paints can be appropriately selected and used.

[0007]

The linear polyester resin used in the undercoating paint in the present invention has a glass transition temperature of 40 ° C. or lower as compared with the epoxy resin (glass transition temperature, 60 ° C. or higher) used in general undercoating paint. The coating film is flexible and has high permeability to water and oxygen. Therefore, against the end surface corrosion of the coated metal plate of the aluminum-zinc alloy-plated steel sheet, the formation of an oxide film of aluminum is assisted, and the end surface is significantly stabilized even in the alkaline atmosphere generated by the cathode reaction.

[0008]

EXAMPLES The present invention will be described in detail with reference to Examples and Comparative Examples. Examples 1 to 8 and Comparative Examples 1 to 6 In a suitable amount of a mixed solvent (methyl isobutyl ketone / xylene = 1/1 weight ratio), according to the solid content composition of the undercoat paint shown in Table 1, a color developing agent was used. And pigment were mixed, and the particle size was dispersed to 15 μm or less with an attritor. After further mixing the remaining components, a mixed solvent was added to adjust the viscosity of the paint to 100 ± 10 seconds (20 ° C.) with Ford Cup No. 4 to prepare a total of 14 kinds of undercoat paint. The LP resin Byron used here is a linear polyester resin manufactured by Toyobo Co., Ltd., and is synthesized using bisphenol A diglycidyl ether and adipic acid as main raw materials.
Silicon dioxide is mixed as an extender pigment to give a blending composition of 5
Weight percent dispersion aids and crosslinking catalysts were added as additives.
Next, chromic acid-based chemical conversion treatment liquid, ZN-R1415A
[Nihon Parker Rising Co., Ltd.] coating amount is 20-8
Roll coating to 0 mg / m ² (dry state),
The undercoat paint prepared above is applied to the surface of an aluminum-zinc alloy-plated steel sheet (unit weight: AZ-150) having a thickness of 0.6 mm dried at 90 ° C. by a roll coater so that the dry film thickness becomes 5 μm. Then, baking was performed at a plate temperature of 200 ° C. for 60 seconds. Furthermore, a polyvinylidene fluoride resin-based top coating [Pre-color No. manufactured by NOF CORPORATION]. 800
0 blue, registered trademark] was applied by a roll coater to a dry film thickness of 20 to 25 μm, and the plate temperature was 240 ° C.
Baking was performed for 0 seconds to obtain a total of 14 kinds of test pieces.

[0009]

[Table 1]

Note 1) Byron GK590 [trade name of Toyobo Co., Ltd.] weight average molecular weight 8000, glass transition temperature 15 ° C., hydroxyl value 20
-30 mg KOH / g 2) Byron GK130 [trade name of Toyobo Co., Ltd.] Weight average molecular weight 7,000, glass transition temperature 10 ° C, hydroxyl value 30
-40mgKOH / g 3) Byron GK780 [trade name of Toyobo Co., Ltd.] Weight average molecular weight 11,000, glass transition temperature 30 ° C, hydroxyl value 1
0-13 mg KOH / g 4) Byron GK770 [trade name of Toyobo Co., Ltd.] Weight average molecular weight 13,000, glass transition temperature 50 ° C., hydroxyl value 1
0-13 mg KOH / g 5) Byron GK290 [trade name of Toyobo Co., Ltd.] Weight average molecular weight 20000, glass transition temperature 70 ° C, hydroxyl value 4
-6 mg KOH / g 6) Epokey 834 [trade name of Mitsui Toatsu Chemicals, Inc.] glass transition temperature 60 ° C 7) Melamine resin solution; Sumimar M40S [trade name of Sumitomo Chemical Co., Ltd.] 8) Polyfunctional isocyanate compound; Coronate 2507
[Product name of Nippon Polyurethane Co., Ltd.] 9) Strontium chromate 10) Aluminum phosphomolybdate The test pieces prepared as described above were tested by the following test method, and the results are shown in Table 2.

[Test Method and Evaluation Method] 1. Adhesion (after 10 Hrs of boiling water) A test piece cut into 7 × 25 cm was immersed in boiling water for 10 hours, left at room temperature for 1 hour, and then tested for adhesion (10 Hrs of boiling water) by the following two methods. (1) With a cutter knife on the coated surface, it is eye-catching (1 mm: 10 ×
10 cross cuts) were cut, and this part was extruded from the back by an Erichsen tester by 6.5 mm. (2) A 4T bending process (four sheets to be coated, which are the same as the test pieces, are sandwiched inside and bent 180 degrees in close contact). After that, all attempted peeling of cellophane tape to the test site. The following 5 point method was used for evaluation, and 5 points were evaluated as having no peeling at all,
A score of 4 or less was rejected. 5 points; 0 peeling, 4 points; 1 to 1
0% peeling, 3 points; 11-30% peeling, 2 points; 31-50
% Peeling, 1 point; 51% or more peeling 2. Edge creep resistance: A salt spray test machine [J
IS K-5400 (1990) 9.1], and the state of swelling of the coating film from the unsealed end face was observed.
The maximum corrosion length (mm) of blistering from the end face to the center of the test piece was evaluated. 1000 hours, 2000 hours and 3
The results at a salt spray test time of 000 hours are shown in Table 2. 3. Corrosion resistance of processed part A salt spray tester [JIS
K-5400 (1990) 9.1] was tested for 2000 hours, and swelling and rusting of the processed part were observed. Evaluation was made by a 5-point method, and if there was no abnormality, 5 points were passed and 4 points or less were rejected. 5 points; no abnormality at all; 4 points; minute swelling; 3 points; obvious swelling; 2 points; swelling and rusting occurred; 1 point; partial peeling occurred. The results are shown in Table 2.

[0012]

[Table 2]

The results of the above examples show that, in the compounding ratios shown in Table 1, Comparative Examples 1 to 4 out of the range of the present invention.
Has extremely poor corrosion resistance of the processed part and edge creep resistance of the end face. On the other hand, Examples 1 to 8 of the present invention show excellent results on both the end face and the processed part, and the obvious problem is that the disadvantage of the coated metal sheet that the corrosion resistance of the end face and the processed part, which has been a problem in the past, is poor. It has been shown to be a good, painted metal sheet.

[0014]

EFFECTS OF THE INVENTION The coated metal sheet of the present invention, which is made of aluminum zinc alloy plated steel sheet and uses the undercoating paint in which the specified linear polyester resin and the specified rust preventive pigment are combined, is cut not only on the painted surface but also on the cut surface. It has the effect of significantly improving the corrosion resistance of the end face and the bent processed portion.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09D 167/02 PKW C09K 13/00

Claims (1)

[Claims] 1. A coated metal plate prepared by applying a chemical conversion treatment layer to the surface of an aluminum-zinc alloy-plated steel sheet and then applying an undercoat paint and a topcoat paint, wherein the undercoat paint has a weight average molecular weight of 5,000 to 20. It is a coating material containing a linear polyester resin having a glass transition temperature of 40 ° C. or less as the main component of the color-developing agent and strontium chromate alone or a mixture of strontium chromate and aluminum phosphomolybdate as an anticorrosive pigment. A painted metal plate characterized by that.