JP2001329383A - Coated metallic sheet having excellent corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated metallic sheet which has both of excellent corrosion resistance in flat parts, flawed parts of coating films, etc., and excellent corrosion resistance at cut end faces and the flawed parts of the coating films in combination. SOLUTION: The metallic sheet possessing a plating layer having a metallic structure which consists of 4 to 10 mass% Al, 1 to 4 mass% Mg, and if necessary, 0.002 to 0.1 mass% Ti, 0.001 to 0.45% B and the balance Zn and inevitable impurities and has a [primary crystal Al phase] or [primary crystal Al phase) and (Zn single phase) co-existing in the base of [the ternary eutectic structure of Al/Zn/Zn2Mg) is provided with a chemical conversion treated film formed on the surface of the plating layer, a primer coating film formed on the surface of this chemical conversion treated film and a finish coating film formed on the primer coating film.

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 having excellent corrosion resistance. More specifically, a Zn—Al—Mg-based plating layer or A consisting of 4 to 10% by mass of Al, 1 to 4% by mass of Mg, and the balance of Zn and unavoidable impurities.
l: 4 to 10% by mass, Mg: 1 to 4% by mass, Ti: 0.
002 to 0.1% by mass, B: 0.001 to 0.45% by mass, and the balance being Zn and Zn-A consisting of unavoidable impurities
The present invention relates to a coated metal plate having an l-Mg (-Ti-B) -based plating layer and having excellent corrosion resistance.

[0002]

2. Description of the Related Art Painted hot-dip galvanized steel sheets and the like have conventionally been used as metal sheets for building materials inside and outside of buildings. In recent years, air pollution has progressed and the atmosphere and rainwater have been acidified by sulfur oxides and nitrogen oxides. Therefore, flat parts, cut end faces, and coatings of such metal plates for interior and exterior building materials The corrosion rate of the galvanized layer increases under the coating such as a damaged portion, and the durability is concerned. For example,
Corrosion of the flat portion is caused by corrosive ions such as Cl ^- ions permeating the coating film, causing corrosion of the galvanized layer and pushing up the coating film by the volume-expanded Zn-based corrosive material. Confirmed as coating blister.

[0003] Thus, the ratio of using a hot-dip galvanized steel sheet having more excellent corrosion resistance as a coating base sheet in place of the conventional hot-dip galvanized steel sheet having a problem in terms of corrosion resistance tends to increase. is there. That is, Zn-
When the content of Al in the Al-based plating layer is increased,
Corrosion resistance such as flat portions and scratched portions of the coating film can be improved. However, by increasing the Al content of the coated hot-dip Zn-Al-plated steel sheet, it is possible to improve the corrosion resistance of the flat portion or the scratched portion of the coating film, but the corrosion resistance of the cut end face is not always satisfactory. Absent.
For example, at the cut end surface of a painted hot-dip Zn-55% Al-plated steel sheet, the Zn-rich
The phase is selectively corroded to form a corrosion product, and the corrosion product raises the coating film, causing coating blistering or peeling of the coating film, which is called edge creep, which causes a problem that the corrosion resistance is reduced.

[0004] On the other hand, painted molten Zn-55% Al
As a method of improving the corrosion resistance of the cut end face of the plated steel sheet, for example, a method of improving the end face corrosion resistance by using a paint in which strontium chromate or calcium chromate is blended in an amount of 30 to 70% by mass with respect to the nonvolatile content of the undercoat paint. (Japanese Patent Publication No. 2-36384) is known.

However, in the evaluation of the salt spray test, the coated hot-dip Zn-55% Al-plated steel sheet treated by this method has a certain degree of end face corrosion resistance as compared with the coated steel sheet using a conventionally used undercoat paint. Has been found, but the effect of the improvement is not remarkable under the atmospheric environment of the actual use environment. Further, the coated hot-dip Zn-55% Al-plated steel sheet treated by this method does not show sufficient moisture resistance in a high-temperature and high-humidity environment, and may cause blistering of the coating film even in a flat portion. In addition to steel plates for building interior and exterior building materials, the same applies to metal plates used in home appliances such as refrigerators, washing machines, microwave ovens, vending machines, office equipment, automobiles, and air conditioner outdoor units. Therefore, high corrosion resistance is desired.

[0006]

That is, the coating molten Zn-
In the case of the Al-based plated steel sheet, the corrosion resistance of the flat portion and the damaged portion of the coating film was improved as compared with the conventional painted hot-dip galvanized steel sheet, but the corrosion resistance of the cut end face was not always satisfactory. Therefore, the object of the present invention is to
An object of the present invention is to provide a coated metal plate that solves such a problem and has both excellent corrosion resistance in a flat portion and a damaged portion of a coating film and excellent corrosion resistance in a cut end surface portion and a damaged portion of a coating film.

[0007]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a specific Zn-Al-Mg-based plating layer or Zn-Al-Mg
Using a metal plate having a (-Ti-B) -based plating layer,
When a chemical conversion coating, an undercoat and an overcoat are provided thereon, the corrosion resistance at the cut end and the corrosion resistance at the scratched part of the coating are well-balanced in the prior art, which has a good balance of the two properties. The inventors have found that a coated metal plate can be obtained, and have completed the present invention.

That is, the coated metal sheet having excellent corrosion resistance according to the first aspect of the present invention comprises Al: 4 to 10% by mass, Mg:
1 to 4% by mass and the balance consisting of Zn and unavoidable impurities, and [primary Al phase] or [primary Al phase] and [primary Al phase] in a [Al / Zn / Zn ₂ Mg ternary eutectic structure] substrate. Zn single phase]
A metal plate having a plating layer having a mixed metal structure, a chemical conversion treatment film formed on the surface of the plating layer,
An undercoat formed on the surface of the chemical conversion coating and an overcoat formed on the undercoat are provided.

The coated metal sheet having excellent corrosion resistance according to the second aspect of the present invention comprises 4 to 10% by mass of Al, 1 to 4% by mass of Mg, 0.002 to 0.1% by mass of Ti, B consists of 0.001 to 0.45 mass%, the balance being Zn and unavoidable impurities, and a [primary Al phase] or [primary Al phase] in the [Al / Zn / Zn ₂ Mg ternary eutectic structure] matrix. Crystal Al phase)
And a metal plate having a plating layer having a mixed metal structure of [Zn single phase] as a base material, a chemical conversion coating formed on the surface of the plating layer, and formed on the surface of the chemical conversion coating. An undercoat film and an overcoat film formed on the undercoat film are provided.

The coated metal sheet having excellent corrosion resistance according to the first and second aspects of the present invention has A
Al and Mg in the plating layer are dense and hardly soluble under the coating near the scratched portion of the coated metal plate and near the cut end surface, in addition to the corrosion resistance of the flat portion of the metal plate because it contains l and Mg. The corrosion product has a function of forming corrosion products, and the stable corrosion product has a function of shielding corrosive ions entering from the outside. Blisters and rust are not easily generated in the vicinity.

In the coated metal sheet having excellent corrosion resistance according to the first and second aspects, the chemical conversion coating may be a conventional chromium-based chemical conversion coating or a non-chromium-based chemical conversion coating. Chromium compounds are increasingly being included in steel materials that are preferably not contained in consideration of the environment. Therefore, when the chemical conversion treatment film is a non-chromium-based chemical conversion treatment film, it is possible to provide an environmentally conscious and highly durable steel sheet.

Further, in the coated metal sheet having excellent corrosion resistance according to the first and second aspects, the surface of the chemical conversion coating is coated with strontium chromate as a rust inhibitor in an amount of 10 to 60% by mass based on the nonvolatile component. An undercoat film having a film formed thereon and an overcoat film formed on the undercoat film are provided. Strontium chromate is a compound that exhibits a very excellent rust prevention effect. In the coated metal sheet according to the first and second aspects of the present invention, by using strontium chromate as a rust preventive on the surface of the chemical conversion coating, the coating film is particularly suitable for a damaged part, a cut end face and its vicinity. Demonstrates excellent rust prevention effect.

Further, in the coated metal sheet having excellent corrosion resistance according to the first and second aspects, the surface of the chemical conversion treatment film is coated with a non-chromium-based rust preventive, for example, a silica-calcium-based rust preventive against a non-volatile component. An undercoat film formed with a coating film containing 2 to 50% by mass and an overcoat film formed on the undercoat film are provided. Chromium compounds are increasingly being included in steel materials that are preferably not contained in consideration of the environment. Therefore, when the chemical conversion treatment film is a non-chromium-based chemical conversion treatment film, it is possible to provide an environmentally conscious and highly durable steel sheet. Further, in the coated metal sheet having excellent corrosion resistance according to the first and second aspects, an undercoating film containing no rust inhibitor is provided on the surface of the chemical conversion treatment film. In the present invention, a metal plate having high durability can be obtained even if the undercoating film does not contain a rust-preventive pigment.

Further, in the coated metal sheet having excellent corrosion resistance according to the first and second aspects, the coated metal sheet may be:
Steel plates for interior and exterior building materials for construction, home appliances, vending machines,
It is a metal plate for office equipment, automobiles or outdoor units of air conditioners. 2. Description of the Related Art Steel plates for building interior / exterior building materials, home appliances, vending machines, office equipment, metal plates for automobiles or air conditioner outdoor units, particularly steel plates, are required to have high durability. By using the coated metal plate of the present invention, it is possible to manufacture a product in which coating film swelling and rust hardly occur on the damaged portion of the coating film, the cut end face, and the vicinity thereof.

[0015]

Embodiments of the present invention will be described below in detail. The metal plate used in the present invention is Zn
-Al-Mg-based plated steel sheet, the molten Zn-Al disclosed in Japanese Patent Application Laid-Open No. Hei 10-226865 of the present applicant.
Mg-plated metal plate (first embodiment) or hot-dip Zn disclosed in Japanese Patent Application Laid-Open No. 10-306357 of the present applicant.
-Al-Mg-based plated metal plate (second embodiment). The molten Zn—Al—Mg-based plated metal sheet according to the first aspect of the present invention is a molten Zn comprising Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance being Zn and unavoidable impurities.
-A hot-dip coated metal plate having excellent corrosion resistance in which an Al-Mg plated layer is formed on the surface of the metal plate, wherein the plated layer is [Al / Z
n / Zn ₂ Mg ternary eutectic structure]
Phase) or [primary crystal Al phase] and [Zn single phase] are mixed.

Further, in the second embodiment of the present invention, the molten Z
n-Al-Mg (-Ti-B-)-based plated metal plate
l: 4 to 10% by mass, Mg: 1 to 4% by mass, Ti: 0.
002-0.1% by mass, B: 0.001-0.045% by mass, the balance being Zn and molten Zn composed of unavoidable impurities
-A hot-dip coated metal plate having excellent corrosion resistance in which an Al-Mg plated layer is formed on the surface of the metal plate, wherein the plated layer is [Al / Z
n / Zn ₂ Mg ternary eutectic structure]
Phase) or [primary crystal Al phase] and [Zn single phase] are mixed.

The difference between the metal plates in the first embodiment and the second embodiment lies in whether or not a predetermined amount of Ti and B is contained in the plating layer, and they exhibit the same operation and effect. It is. Al in the plating layer of the metal plate in the first and second embodiments has an effect of improving the corrosion resistance of the plating layer and suppressing dross generation in the plating bath during the production of the metal plate. . The Al content was specified in the range of 4 to 10% by mass for the following reason. That is, when the Al content is less than 4% by mass, the effect of improving the corrosion resistance is not sufficient, and the effect of suppressing the generation of the top dross of the Mg oxide is low, and the surface smoothness after plating is poor, and the appearance of the coating is impaired. Becomes Conversely, if the Al content exceeds 10% by mass, Fe-A at the interface between the plating layer and the base steel sheet.
The growth of the l-based alloy layer becomes remarkable, the workability of the plated layer and the adhesion of the plated layer are reduced, and when a coated steel sheet is processed, it causes large cracks and peeling of the paint film. The most preferable Al content is 5.0 to 7.0% by mass.

Mg in the plating layer of the metal plate has a function of generating a uniform, dense and stable corrosion product on the surface of the plating layer, thereby significantly improving the corrosion resistance of the plating layer. The reason for specifying the Mg content in the range of 1 to 4% by mass is as follows. That is, if the Mg content is less than 1% by mass, the effect of uniformly generating corrosion products is not sufficient, and if it exceeds 4% by mass, the effect of improving the corrosion resistance by Mg is saturated, and conversely, the top of the Mg oxide system Dross is likely to occur, causing a deterioration in the appearance after painting. On the other hand, if the Mg content exceeds 4% by mass, the workability of the plating layer is reduced, which causes large cracks in the coating film when the coated steel sheet is processed. The most preferred Mg content is 2.5-3.5% by mass.

In the ternary composition of Zn—Al—Mg containing Al and Mg in Zn in such amounts, the molten Zn—A
When the Zn ₁₁ Mg ₂ phase is crystallized in the 1-Mg plating layer, the Zn ₁₁ Mg ₂ phase has a high gloss, has a conspicuous pattern, deteriorates the surface appearance, and deteriorates the corrosion resistance (see Japanese Patent Laid-Open No. 226865 and JP-A-10-30
No. 6357). This Zn ₁₁ Mg ₂ phase becomes a noticeable pattern even after painting, and deteriorates the surface appearance and corrosion resistance. Therefore, as a result of intensive studies by the present applicant, it has been found that the size of the Zn ₁₁ Mg ₂ phase depends on the temperature of the hot-dip bath and the speed of the hot-dip layer (see Japanese Patent Application Laid-Open No. Hei 10-226865). . Therefore, the molten Zn-A used in the first aspect of the present invention
In the production of an l-Mg plated metal sheet, for example, a hot-dip Zn-Al-Mg plated steel sheet, for example, when the bath temperature of a hot-dip bath is set to a melting point or higher and 450 ° C. or lower, and a cooling rate after plating is controlled to 10 ° C./sec or higher. The Zn ₁₁ Mg ₂ phase does not appear, and a metal structure free from surface defects can be obtained.

Further, in the second aspect of the present invention, Ti and B in the plating layer of the metal plate are the same as those of the molten Zn—Al—
It has the effect of suppressing the formation and growth of the Zn ₁₁ Mg ₂ phase in the Mg plating layer (see Japanese Patent Application Laid-Open No. 10-306357). Zn ₁₁ Mg ₂ phase, corrosion resistance deteriorates as well as poor appearance after painting becomes conspicuous pattern for high gloss. In this case, if the Ti content is less than 0.002% by mass, Z
The effect of suppressing the formation and growth of the n ₁₁ Mg ₂ phase is not sufficient.
If the content exceeds 1% by mass, a Ti-Al-based precipitate grows in the plating layer, which causes irregularities on the plating layer surface and impairs the appearance after coating.
It must be within the range of mass%. B content is 0.00
If it is less than 1% by mass, the effect of suppressing the formation and growth of the Zn ₁₁ Mg ₂ phase is not sufficient, and if it exceeds 0.045% by mass, a Ti-B or Al-B-based precipitate grows in the plating layer, and the plating layer Since the surface has irregularities, which causes the appearance after coating to be impaired, the B content needs to be in the range of 0.001 to 0.045% by mass.

When the metal plate having the hot-dip Zn—Al—Mg plating layer according to the first and second embodiments of the present invention as described above is used, since the plating contains 4% by mass or more of Al, The corrosion rate of the plating layer is suppressed and the addition of Mg further suppresses the corrosion rate of the plating layer. Under the coating film near the end face, Al and Mg in the plating layer exhibit a function of forming a dense and hardly soluble corrosion product, and furthermore, this stable corrosion product prevents corrosive ions invading from the outside. Since it has an effect of shielding, it has a remarkable feature that coating film swelling and rust hardly occur at a portion where the coating film is damaged, at the cut end face, or in the vicinity thereof.

The coated metal sheet of the present invention is manufactured using a continuous coating line in the same manner as a conventional coated metal sheet. First, the surface of the metal having the specific plating layer is subjected to a chemical conversion treatment. The chemical conversion coating at this time is not particularly limited, and may be a chromate coating or a non-chromate coating. For example, in the case of a chromate coating, corrosion resistance,
In order to ensure coating film adhesion, the total amount of chromium
The amount of r is preferably 5 to 100 mg / m ² . Further, in the case of a non-chromate-based film, the amount of the film is preferably 10 to 100 mg / m ² in order to secure corrosion resistance and film adhesion.

In the first and second aspects of the present invention, the Zn-Al-Mg
An undercoating film is further formed on the surface of the metal plate having a (Ti-B) -based plating layer, and the undercoating film at this time is the same as a conventional hot-dip galvanized steel sheet or hot-dip Zn-Al-plated steel sheet. It can be formed by a similar method using a coating film thickness or a coating resin. The coating thickness is in the range of 3 to 7 μm, which is the same as that of a conventional hot-dip galvanized steel sheet or hot-dip Zn-Al coated steel sheet. Similarly, an epoxy resin, an epoxy-urethane resin, an acrylic resin, a polyester resin, a phenoxy resin, or the like can be used as the coating resin. Further, as a rust-preventive pigment in the undercoat paint, chromic acid-based rust-preventive pigments such as strontium chromate, calcium chromate, barium chromate, zinc chromate, aluminum phosphate, zinc phosphate, calcium phosphate, calcium carbonate, silica −
An undercoating film can be formed by adding a non-chromate type rust preventive pigment such as a calcium type alone or by adding two or more kinds to a coating resin.

For example, in the case of strontium chromate, which is typically used as a chromic acid-based rust-preventive pigment, the content of strontium chromate is preferably in the range of 10 to 60% by mass, more preferably 25 to 30% by mass, based on the nonvolatile content. %. In general, when the amount of strontium chromate is less than 10% by mass, the steel sheet has better corrosion resistance than conventional hot-dip galvanized steel sheet or hot-dip Zn-Al coated steel sheet. %, The effect of improving the corrosion resistance is saturated, the workability of the coating film and the adhesion of the coating film are reduced, and when a coated metal plate is processed, large coating film cracking or coating film peeling is caused.

Further, as a non-chromate type rust preventive pigment, for example, in the case of an anticorrosion inhibitor (hereinafter referred to as silica-calcium type) in which calcium ions are bonded to porous silica particles by ion exchange, a silica-calcium type anticorrosion pigment is used. The rust pigment is preferably added in the range of 2 to 50% by mass, more preferably 5 to 25% by mass, based on the nonvolatile content. In another embodiment of the present invention, it may not be necessary to add a rust inhibitor. In the configuration of the present invention,
In some cases, sufficient durability can be obtained even without the addition of a rust preventive agent. In particular, when a non-chromate chemical conversion film is used, a chromium-free coated metal plate is obtained.

In the present invention, an overcoat film is further formed on the undercoat film, and the overcoat film at this time has the same thickness as that of a conventional hot-dip galvanized steel sheet or hot-dip Zn-Al coated steel sheet. It can be formed by a similar method using a coating resin. That is, the resin of the overcoat film is not particularly limited, and for example, heat-sensitive resins such as polyester-based, urethane-based, acrylic-based, silicone-modified polyester-based, silicone acrylic-based, polyvinyl chloride-based, and vinylidene fluoride-based fluororesins. Either a curing type or a thermoplastic type coating resin may be used. Also, it may be a color coating coated with pigments or a transparent clear coating, and if necessary, an inorganic or organic resin aggregate or powder may be added to these resins. can do. Further, these coating films can be formed by applying a paint with a roll coater or the like or by laminating resin films.

In this manner, a metal plate having a specific Zn—Al—Mg based plating layer (first embodiment) or a Zn—Al—Mg (—Ti—B) based plating layer according to the present invention is used as the metal plate. When a chemical conversion treatment film, an undercoating film, and an overcoating film are provided thereon, since the plating layer contains Al and Mg, not only the excellent corrosion resistance of the flat portion of the metal plate but also the conventional technology cannot be used. It was possible to obtain a coated metal sheet having excellent corrosion resistance at the end of the plated metal sheet and excellent corrosion resistance at the part where the coating film was damaged, and the coated metal sheet thus obtained was used for building purposes.・ Metal plates for exterior building materials, refrigerators, washing machines, household appliances such as microwave ovens, vending machines, office equipment,
It can be suitably used as a member requiring corrosion resistance, such as an automobile and an air conditioner outdoor unit.

[0028]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. (Examples 1 to 18 and Comparative Examples 1 to 8) Zn shown in Table 1,
Fused Zn-Al with Al, Mg, Ti and B content
-Mg-based plated steel sheet and Zn-Al-Mg- (Ti-
B) -based plated steel sheet (sheet thickness: 0.4 mm, coating weight on one side: 120 g / m ² ) was manufactured on a Sendzimir continuous hot-dip plating line (business production machine). These plated steel sheets were subjected to a surface conditioning treatment, washed with hot water and water, and dried. Thereafter, a coating type chromate treatment liquid [trade name, manufactured by Nippon Paint Co., Ltd .; Surfcoat NRC3]
[00NS] with a roll coater and dried at 100 ° C. without washing with water to form a chromate film having a total Cr content of 40 mg / m ² .

Then, on the chromate film thus formed, strontium chromate was blended in an amount of 25% by mass with respect to the non-volatile content, and an undercoat of epoxy resin was further blended with titanium oxide and silica powder as extenders. The paint was applied to a dry film thickness of 5 μm, and 200
It dried at ° C and formed the undercoat film. On the undercoat film thus formed, a top coat of vinylidene fluoride-based fluororesin is applied so as to have a dry film thickness of 22 μm, and similarly dried at 250 ° C. to form an overcoat film. Then, coated metal plates 1 to 9 of the present invention having a fluororesin-based coating film as a top coating film were prepared (Examples 1 to 9). Further, on the chromate film, an undercoat paint of epoxy resin containing 25% by mass of strontium chromate with respect to the non-volatile content and titanium oxide powder and silica as extender pigments to a dry film thickness of 5 μm. After coating and drying at 215 ° C to form an undercoat film,
13μm dry coating thickness of polyester resin top coat
And dried in the same manner at 215 ° C. to form a top coat, thereby preparing coated metal plates 10 to 18 of the present invention having a polyester resin coat as the top coat. 18).

For comparison, molten zinc (0.2%
Al) A comparative coated steel sheet 1 having a fluororesin-based coating film by applying a similar coating using a coated steel sheet, a hot-dip Zn-5% Al-plated steel sheet and a hot-dip Zn-55% Al-plated steel sheet
To 3 (Comparative Examples 1 to 3) and Comparative Painted Metal Plates 5 to 7 having a polyester-based resin were prepared (Comparative Examples 5 to 7).
Further, using a hot-dip Zn-55% Al-plated steel sheet, an undercoat paint containing 50% by mass of strontium chromate with respect to the non-volatile content is applied to form a fluororesin topcoat film and a polyester-base topcoat film, respectively. Comparative coated steel sheets 4 and 8 were prepared (Comparative Examples 4 and 8).

The coated steel sheet according to the present invention and the comparative coated steel sheet thus prepared were subjected to the following corrosion resistance test. (1) Accelerated corrosion resistance test A test specimen in which the upper and lower cut end surfaces and the back surface of a coated steel plate were repaired with paint, and the coating film on the flat portion was scratched with a cutter knife, was subjected to acid rain combined corrosion test for 600 cycles. [One cycle: 0.1% NaCl corrosion liquid spray (temperature: 35 ° C. ×
1 hour, pH: 4, adjusted with sulfuric acid) → drying (temperature: 50)
℃ × 4 hours) → wetting (temperature: 50 ° C. × 3 hours, relative humidity: 98%)], and the coating film bulging (edge creep) generated from the unrepaired cut end face and the cut end of the cut end face. The occurrence rate of red rust was measured. In addition, the rate of rusting from the scratched portion of the coating film was measured. The symbol ◎ indicates that the coating blister width from the cut end face not repaired is 0.5 mm or less, the symbol ○ indicates that the coating blister width is 0.6 to 1.0 mm, and the coating blister width is 1.1 to 1.1. Those having a thickness of 2.0 mm were evaluated with the symbol △, and those having a coating blister width of more than 2.0 mm were evaluated with the symbol x. Next, the rate of occurrence of red rust was determined as the rate of occurrence of red rust in this area in the corrosion resistance test for the area 100 of the test target portion of the cut surface cut, and no occurrence of red rust was observed in the cut of the cut end face. Those were evaluated with the symbol ◎, those with 5% or less were evaluated with the symbol ○, those with 6 to 20% were evaluated with the symbol △, and those with more than 20% were evaluated with the symbol ×. Further, similarly, ◎ indicates no occurrence of rust from the scratched portion of the coating film, 記号 indicates 25% or less, △ indicates 26-50%, and × indicates more than 50%. did.

(2) Outdoor Exposure Corrosion Resistance Test Specimens in which the upper and lower cut end surfaces and the back surface of a coated steel plate were repaired with paint were exposed outdoors for 3 years and 3 months at an inland test site 800 m inland from Tokyo Bay shore in Ichikawa City, Chiba Prefecture. After the test, the width of the coating blister generated from the unrepaired cut end face and the occurrence rate of red rust at the cut end of the cut end face were measured. The symbol ◎ indicates that the coating blister width from the unrepaired cut end face was 0.5 mm or less, and the symbol 、 indicates that the coating bulge width was 0.6 to 1.0 mm.
〜2.0 mm were evaluated with the symbol △, and those exceeding 2.0 mm were evaluated with the symbol x. In addition, the symbol ◎ indicates that no red rust was observed at the cut edge of the cut end face, and the symbol △ indicates a symbol of 5% or less and the symbol を indicates a symbol of 0.6 to 20% or less, and the symbol X indicates a symbol of more than 20%. . Tables 1 and 2 show these results.

[0033]

[Table 1]

[0034]

[Table 2]

From the above results, the coated steel sheet of the present invention is excellent in both accelerated corrosion resistance and exposure corrosion resistance. In particular, it should be noted that the coated steel sheet of the present invention is excellent in both corrosion resistance of the cut end surface and the coating scratched portion in a well-balanced manner. In addition, Examples (Examples 1 to 3 and Example 7) using a hot-dip Zn-Al-Mg-based plated steel sheet as a base material
To 9) and Zn-Al-Mg- (Ti-B) -based plated steel sheets as base materials (Examples 4 to 6 and Example 1).
0-12), it was found that excellent effects were exhibited.

(Examples 19 and 20, Reference Examples and Comparative Examples 1 to 11) A Zn-Al-Mg (Ti-B) -based plated steel sheet containing Zn, Al, Mg, Ti and B shown in Table 3 Zn-Al-M containing Zn, Al and Mg
A g-plated steel sheet (sheet thickness: 0.4 mm, coating weight on one side: 120 g / m ² ) was produced by a continuous hot-dip galvanizing line of Sendzimir system (business production machine). These plated steel sheets are subjected to surface conditioning treatment, washed with hot water and water,
Dried. Thereafter, the molten Z thus produced is
One of the n-Al-Mg-based plated steel sheets is subjected to (a) a coating type titanium-based non-chromium treatment on both sides, and is dried at the reached sheet temperature of 100 ° C. without washing with water, and the total coating amount is 75 mg /
A titanium-based coating type pretreatment film of cm ² was formed. Also,
The other of the hot-dip Zn—Al—Mg-based plated steel sheets produced in this manner was subjected to a coating-type chromate treatment on both sides in the same manner as in (b) to form a chromate film having a total Cr content of 40 mg / m ² .

Next, an undercoat paint of epoxy resin containing titanium oxide and silica powder as an extender pigment and having no rust-preventive pigment was formed on the pre-coating film thus formed to a dry film thickness of 5 μm. Painted on, reaching plate temperature 21
Dry baking at 5 ° C. to form an undercoat film. On top of the undercoat film thus formed, a polyester resin topcoat paint is applied to a dry film thickness of 13 μm, and dried and baked at an ultimate plate temperature of 215 ° C. to form an overcoat film. Metal plates were produced (Examples 19 to 22).

On the other hand, for comparison, a hot-dip galvanized steel sheet (0.2% Al) and a hot-dip Zn-5% Al-plated steel sheet were used as substrates, and the same treatment and coating as in the example were performed to obtain a coated steel sheet. (Comparative Examples 9, 11, 12, 14, and 1)
5). In addition, non-chromic rust preventive pigments (silica-
(Calcium-based) was blended at 25% by mass with respect to the non-volatile component, and coated, and the coated steel sheet was produced in the same process as above except for the other conditions (Comparative Examples 10, 13 and 16). Further, each substrate was coated with 25% by mass of strontium chromate as an undercoating film based on the non-volatile component and applied, and the other conditions were the same as in the above to produce a coated steel sheet (Reference Example and Comparative Example). 17-19).

The coated steel sheets thus manufactured were subjected to a corrosion resistance test in the same manner as in Examples 1 to 18 and Comparative Examples 1 to 8 described above. Table 3 shows the results.

[0040]

[Table 3]

From the results shown in Table 3, it can be seen that the coated steel sheet of the present invention has excellent corrosion resistance even if the undercoat does not contain a rust-preventive pigment, and particularly has excellent corrosion resistance at the cut end face and the damaged portion of the coating film.
In particular, Examples 19 and 2 in which no chromate film was applied
It is noteworthy that the same effect is obtained at 0.

[0042]

As described above, in a coated metal plate in which an undercoating film is formed on the surface of a metal plate on which a chemical conversion coating film is formed, and an overcoating film is formed thereon,
Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance being Zn and unavoidable impurities.
-10% by mass, Mg: 1-4% by mass, Ti: 0.002
0.1% by mass, B: 0.001 to 0.045% by mass,
When a metal plate having a plating layer composed of Zn and unavoidable impurities is used, the plating layer contains Al and Mg, so not only the corrosion resistance of the flat portion of the metal plate but also the coating of the painted metal plate is damaged. Al and Mg in the plating layer show the action of forming a dense and hardly soluble corrosion product under the coating film near the part and the cut end face, and furthermore, this stable corrosion product invades from the outside. Since it has an action of shielding ionic ions, coating film swelling and rust hardly occur at the damaged portion of the coating film, at the cut end face, and in the vicinity thereof.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C23C 2/26 C23C 2/26 // C23F 11/00 C23F 11/00 F (72) Inventor Hiroshi Kanaya Ichikawa-shi, Chiba 7-in-1 Nisshin Steel Co., Ltd., Technical Research Laboratory at Takatani Shinmachi (72) Inventor Kazuyoshi Sugawara 7-in-1 Nisshin Steel Co., Ltd., Technical Research Laboratory, Takatani Shinmachi, Ichikawa-shi, Chiba F-term (reference) 4D075 AE03 BB73X CA33 DA06 DB01 DB05 DB07 DC02 DC12 DC18 EB15 EB17 EB22 EB33 EB35 EB38 EB42 EC13 4F100 AA02H AA22C AB01A AB09B AB10B AB18B AK19E AK41E AK53D BA05 BA07 BA10A BA10E CA14D CC00D EH66B02A02 J02B02 J02 GB02 J02A AB02 BA10 BA14 BA15 BA17 BA21 BB05 BC02 CA11 CA16 CA22 CA27 CA53 4K062 AA01 BA08 BA10 BA14 CA05 FA12 FA16

Claims (7)

[Claims] 1. Al: 4 to 10% by mass, Mg: 1 to 4% by mass, and the balance consisting of Zn and unavoidable impurities.
[Primary crystal Al phase] or a plating layer having a metal structure in which [Primary crystal Al phase] and [Zn single phase] are mixed in a substrate of l / Zn / Zn ₂ Mg ternary eutectic structure. To have a metal plate,
A chemical conversion coating formed on the surface of the plating layer, an undercoat formed on the surface of the chemical conversion coating, and a coated metal having excellent corrosion resistance formed by providing an overcoat formed on the undercoat. Board. 2. Al is 4 to 10% by mass, Mg is 1 to 4% by mass, Ti is 0.002 to 0.1% by mass, and B is 0.00% by mass.
1 to 0.45 mass% and the balance consisting of Zn and inevitable impurities, [ternary eutectic structure of Al / Zn / Zn ₂ Mg]
[Primary Al phase] or [Primary Al phase] and [Z
n single phase] as a substrate, a metal plate having a plated layer having a mixed metal structure, a chemical conversion coating formed on the surface of the plating layer, an undercoat formed on the surface of the chemical conversion coating A coated metal plate having excellent corrosion resistance, comprising a film and an overcoat formed on the undercoat. 3. The chemical conversion film according to claim 1, wherein the chemical conversion film is a non-chromium chemical conversion film.
A coated metal sheet having excellent corrosion resistance described in 1. 4. An undercoat film formed on the surface of the chemical conversion coating film, wherein strontium chromate is incorporated as a rust inhibitor in an amount of 10 to 60% by mass based on a nonvolatile component, and an undercoat film formed on the undercoat film. 4. A method according to claim 1, wherein a top coat is provided.
A coated metal plate with excellent corrosion resistance as described in the item. 5. An undercoating film formed on the surface of a chemical conversion coating film in which a chromium-free rust inhibitor is blended in an amount of 2 to 50% by mass with respect to a nonvolatile component, and an undercoating film formed on the undercoating film. The coated metal sheet having excellent corrosion resistance according to any one of claims 1 to 3, further comprising a top coat. 6. The corrosion resistance according to claim 1, wherein the undercoat formed on the surface of the chemical conversion coating contains no rust inhibitor other than the extender pigment. Excellent painted metal plate. 7. The coated metal sheet according to claim 1, wherein the metal sheet is a steel sheet for building interior / exterior building materials, a home appliance, a vending machine, an office machine, a car or an outdoor unit of an air conditioner. A coated metal steel sheet excellent in corrosion resistance according to any one of claims 6 to 6.