JP2003311877A - Highly durable coated steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly durable coated steel plate suppressed in the rise in temperature due to solar rays and excellent in coating film deterioration resistance and corrosion resistance. <P>SOLUTION: As a substrate plating steel plate, a Zn alloy plated steel plate containing 1-10 mass% Mg, 2-19 mass% Al, and 0.01-2 mass% Si is used, and characterized in that Mg and Al satisfy Mg (mass%)+Al (mass%)≤20 mass% and the remainder comprises Zn and inevitable impurities. A topcoating layer containing 2-60 mass% of an infrared-resistant pigment and having not less than 4.0% of solar radiation reflectivity at a wavelength of 780-2,100 nm is provided to the uppermost layer of at least the single surface of the Zn alloy plated steel plate to obtain the highly durable coated steel plate. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel sheet having excellent durability. More specifically, the present invention relates to the field of outdoor building materials such as roofs and walls, the field of outdoor home appliances such as air conditioner outdoor units and vending machines, and automobiles. It is suitable for outer plates such as.

[0002]

2. Description of the Prior Art Painted steel sheets used outdoors are usually coated steel sheets for corrosion resistance, chemical conversion treatment for corrosion resistance and paint adhesion, undercoat coating for corrosion resistance (primer coating),
It consists of a top coating that is designed and has weather resistance.

Conventionally, in the case of a coated steel sheet that is used outdoors for a long time, deterioration of the coating film and corrosion of the plated steel sheet occur due to sunlight, acid rain, flying sea salt, etc. Therefore, various improvement methods have been studied. .

For example, fluororesin resins are well known as those having excellent resistance to deterioration of coating film. This is to suppress the reaction of the resin constituting the coating film to be decomposed by the light energy of the sun by utilizing the large binding energy of C—F. Further, a fluororesin compound containing an ultraviolet absorber or a hindered amine light stabilizer is also used.
UV absorbers and hindered amine-based light stabilizers have lower weather resistance than fluororesin-based resins, but are cheaper and more versatile than polyester-based, urethane-based, silicon polyester-based, acrylic-based, and polyvinyl chloride-based resins. It is also widely used as an additive to improve.

On the other hand, hot-dip galvanized steel sheet is widely used as the base steel sheet, and when corrosion resistance is required, hot-dip galvanized-5% aluminum alloy-plated steel sheet or 55% is used.
Aluminum-zinc alloy plated steel sheet is used.

In particular, for applications requiring long-term durability, a combination of 55% aluminum-zinc alloy plated steel sheet with a fluorine resin coating is used, and this combination has been commercialized by many coated steel sheet manufacturers. Many studies have been conducted on the undercoating for preventing the corrosion of the base steel sheet, and in applications requiring high corrosion resistance, rust preventive pigments added to the maximum extent possible are used.

As an example to which the above-mentioned technique is applied, there is Japanese Patent Laid-Open No. 10-264305. In this technology, an adhesive layer containing a UV absorber and a hindered amine light stabilizer is applied on a polyvinyl chloride resin film, and then a fluororesin film containing the UV absorber is adhered onto it to form a laminated laminate film. It is to be made. By treating this laminated laminate film on a plated steel sheet, the corrosion resistance and weather resistance are improved.

Although it is possible to impart excellent weather resistance and corrosion resistance by treating this laminated laminate film on a plated steel sheet, it is possible to obtain a coating due to a temperature rise of the coated steel sheet when used outdoors for a long time. Since it is not possible to suppress the increase in the deterioration rate of the film and the corrosion rate of plating,
In many years of use, deterioration and corrosion of the coating film become a problem.

Although this case is only one example, the conventional high-durability coated steel sheet was developed such that the weather resistance is maintained by the resin of the top coating and the UV absorber or the hindered amine light stabilizer, and the corrosion resistance of the under coating is maintained. It was based on the design concept of holding it with an anticorrosive pigment and plating. Certainly, although excellent coated steel sheets have been developed based on this design concept, it has not been taken into consideration that the temperature rise during outdoor use accelerates the deterioration of the coating film and the corrosion of the plated steel sheet. The fact that temperature accelerates the deterioration of coated steel sheets is also evident from the fact that the deterioration in the subtropical regions is greater than that in the boreal regions.

By the way, the temperature rise due to sunlight is greatly affected by color. Since white coated steel plates reflect infrared rays contained in sunlight efficiently, by changing the color of the top coating of the coated steel plate to white, deterioration of the coating film due to temperature rise even when used outdoors The increase in the speed and the corrosion rate of the plating can be suppressed to some extent. However, the white coating film is rarely used outdoors because it is contaminated by rain and other stains. The colors that are used outdoors are blackish, blue, green, and brown, which usually absorb infrared light contained in the sunlight, so the temperature of the coated steel plate rises, There is a problem of increasing the deterioration rate of the coating film and the corrosion rate of the plated steel sheet.

[0011]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned problems. Specifically, the temperature rise of a coated steel sheet is suppressed, and the deterioration rate of the coating film and the corrosion rate of the plating are suppressed to improve durability. It provides a coated steel sheet having excellent properties.

[0012]

Means for Solving the Problems The present inventors have studied in detail the deterioration behavior of a top coating film constituting a coated steel sheet and the corrosion behavior of a plated steel sheet. As a result, the temperature of the coated steel sheet was increased by adding a pigment that efficiently reflects infrared rays caused by sunlight into the top coating film and using the Zn-Al-Mg-Si alloy-plated steel sheet as the undercoat steel sheet. The present invention has been found to suppress the deterioration rate of the coating film and the corrosion rate of the plating.

The gist of the present invention is as follows. (1) As a coating lower layer of a coated steel sheet, Mg: 1 to 10 mass%, Al: 2 to 19 mass%, Si: 0.01 to 2 mass% are contained, and Mg and Al are represented by the following formula Mg. (Mass%) + Al (mass%) ≦ 20 mass%, with the balance Zn and unavoidable impurities
An infrared resistant pigment having an n-alloy plating layer and having a solar reflectance of 4.0% or more at a wavelength of 780 nm to 2100 nm is at least 2 on the uppermost layer of at least one surface of the coated steel sheet.
Characterized by having a topcoat coating containing 60% by weight,
Highly durable coated steel sheet. (2) Between the Zn alloy plating layer and the top coating,
The highly durable coated steel sheet according to (1) above, which has a chemical conversion treatment layer and an undercoat coating containing a rust preventive pigment. (3) The highly durable coated steel sheet according to the above (1) or (2), wherein the infrared resistant pigment contains a black pigment. (4) The infrared resistant pigment contains a complex oxide pigment having one or more structures selected from the group consisting of an ilmenite structure, a forsterite structure, a spinel structure, an inverse spinel structure, a friderite structure and a rutile structure. The highly durable coated steel sheet according to any one of (1) to (3) above, which is characterized. (5) Any one of (1) to (4) above, wherein the infrared resistant pigment contains an oxide of one or more of zirconium oxide, yttrium oxide, and indium oxide. Highly durable coated steel sheet described in. (6) The infrared resistant pigment is Si, Al, Fe, Mg,
Any one selected from Ni, Ti, Cr and Ca
High-durability coated steel sheet according to any one of (1) to (5) above, characterized in that it contains one or two or more of two kinds of metals or alloys with two or more kinds of metals. .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

The base plated steel sheet used in the present invention is M
g: 1 to 10% by mass, Al: 2 to 19% by mass, Si:
0.01 to 2 mass% and Mg and Al are Mg
Zn-Al-M satisfying (mass%) + Al (mass%) ≤ 20 mass%, and the balance Zn and unavoidable impurities
It is a g-Si alloy plated steel sheet.

Mg is added to improve the corrosion resistance of the plating layer. The reason why the addition amount is limited to 1% by mass to 10% by mass is that if the amount is less than 1% by mass, the effect of addition cannot be obtained.
This is because if the amount exceeds 0% by mass, the plating layer becomes fragile and the plating may peel during processing.

Al is added for the purpose of improving the workability of the plating layer and improving the corrosion resistance. The reason why the addition amount is limited to 2% by mass to 19% by mass is that the effect of improving the corrosion resistance and workability cannot be obtained at 2% by mass, and the effect of improving the corrosion resistance is saturated when the amount exceeds 19% by mass.

Si is added for the purpose of improving the adhesion between plating and base iron. The reason why the addition amount is limited to 0.01% by mass to 2% by mass is that when the amount is less than 0.01% by mass, the effect of improving the adhesiveness does not appear, and when the amount exceeds 2% by mass, the plating layer itself becomes brittle during processing. This is because plating peeling may occur.

The relationship between the amounts of Mg and Al added is such that Mg (mass%) + Al (mass%) ≦ 20 mass%. The reason why the total of the mass% of both is limited to 20 mass% or less is that the coated steel sheet itself has high corrosion resistance after coating, and the plating layer can efficiently release heat to the outside, resulting in a temperature rise. Because it can be suppressed. Mg and Al
The lower limit of the sum of the addition amounts of is not particularly limited, but is preferably 3 mass% or more.

For coating the uppermost layer of the underplated steel sheet of the present invention, 2% by mass to 60% of an infrared resistant pigment having a solar reflectance of 4.0% or more at a wavelength of 780 nm to 2100 nm.
It is included in the range of mass%. 7 as an infrared resistant pigment
This is because when the solar reflectance at a wavelength of 80 nm to 2100 nm is 4.0% or more, infrared light from sunlight can be efficiently reflected and the temperature rise of the coated steel sheet can be suppressed. If it is less than 2% by mass, the effect of addition does not appear. On the other hand, if it exceeds 60 mass%, the effect of suppressing the temperature rise of the coated steel sheet is improved, but on the other hand, the workability is lowered, which is not preferable. This infrared resistant pigment is preferably 10 to 55
It is contained in an amount of 30% by mass, more preferably 30 to 50% by mass. The reflectance of the infrared resistant pigment is 6.0% or more, and further 8.
0% or more is more preferable.

When adjusting tones such as dark blue and green, black pigments are suitable as the infrared resistant pigment of the present invention. This is because the use of a black pigment makes it easy to produce a deep color that is widely used in the field of outdoor building materials. Ordinary black color tends to absorb infrared light and causes a temperature rise. However, in the present invention, the temperature rise can be suppressed by selecting a solar radiation reflectance of 4.0% or more at a wavelength of 780 nm to 2100 nm. It is possible. The type of pigment is not particularly limited, but as the organic black pigment, an azo organic pigment having a residue having an azomethine group is suitable.

As the infrared resistant pigment of the present invention, a composite oxide pigment is suitable. The complex oxide pigment is a solid solution of a compound of two or more metals and oxygen, or a compound of two or more metals and oxygen and one or more compounds containing one or more metals and oxygen compounds. It is a thing. As such a complex oxide pigment, those having a structure such as an ilmenite structure, a forsterite structure, a spinel structure, an inverse spinel structure, a friderite structure, a rutile structure, etc. are preferable, and particularly an ilmenite structure, a spinel structure, an inverse spinel structure. , Rutile structure is preferred. Since these complex oxide pigments reflect infrared light contained in sunlight well,
The temperature of the coated steel sheet is less likely to rise, which contributes to suppressing the deterioration rate of the coating film and the corrosion rate of the plating. Since the complex oxide-based pigment has various colors depending on the type of metal contained, it is possible to easily carry out color matching. For example, as the yellow pigment, a pigment having a rutile structure or the like in which CrSbO ₄ and TiO ₂ are solid-solved can be used, and as the blue pigment, a pigment having a spinel structure or the like having a composition of CoAl ₂ O ₄ can be used, and a brown pigment the available pigment a spinel structure such as having a composition of ZnFe ₂ O _4, as a black pigment may be used pigments having a spinel structure such as having a composition of CuCr ₂ O _4. Fe, Cr, and
A composite oxide pigment containing at least one of Co, Mn, Cu, and Zn is suitable. The complex oxide pigments containing these metals are characterized by having a high reflectance in the near infrared region.

The infrared resistant pigment of the present invention is preferably an oxide of at least one selected from zirconium oxide, yttrium oxide and indium oxide. Since these oxides well reflect infrared light contained in sunlight, the temperature of the coated steel sheet is less likely to rise, which contributes to the suppression of the deterioration rate of the coating film and the corrosion rate of the plating. You may coat and use these oxides on the surface of other pigments, such as titanium oxide and mica.

As the infrared resistant pigment, Si, Al, Fe,
A material containing one or two or more of any one metal selected from Mg, Ni, Ti, Cr and Ca or an alloy with two or more metals is suitable. These infrared resistant pigments not only reflect infrared rays caused by sunlight well, but also have excellent water resistance, which is an important factor when used outdoors, and to manufacture coated steel sheets with excellent durability. You can The reason why each of the above metals and the various alloys of the above metals exhibit excellent performance has not been clarified, but it is presumed that the reason is that a dense and stable oxide film is formed on the surface.

Each of the infrared resistant pigments of the present invention may be used alone or as a mixture of plural kinds.

Since the amount of pigment added to the uppermost coating film should be determined in consideration of the color of the coated steel sheet as well as the durability, it is natural that the infrared resistant pigment of the present invention and other pigments are not used. There is no problem even if a color pigment is mixed and toned. Coloring is based on general pigments and dyes. As the pigment, known pigments can be used regardless of whether they are inorganic, organic, or a composite of the two. Titanium white, zinc yellow, alumina white, cyanine blue, and other cyanine pigments, carbon black, and pyrazolone orange. , Azo pigments, dark blue, condensed polycyclic pigments, and the like. In addition to these, bright pigments such as metal flakes / powder, pearl pigments, mica pigments, indigoid dyes, sulfur dyes, phthalocyanine dyes, diphenylmethane dyes, nitro dyes, acridine dyes and the like can be mentioned. The pigment concentration is not particularly limited and may be determined depending on the required color and hiding power. Further, in addition to the color pigments, any of those usually added to paints can be added without any problem. For example, extender pigments such as calcium carbonate, talc, gypsum and clay, and other organic crosslinked fine particles and / or inorganic fine particles. Further, if necessary, a surface smoothing agent, an ultraviolet absorber, a hindered amine light stabilizer, a viscosity adjusting agent, a curing catalyst, a pigment dispersant, a pigment settling inhibitor, a color separation preventing agent and the like can be used.

The resin used in the coating film of the present invention is preferably one having excellent weather resistance, discoloration resistance, gloss retention and water resistance, such as polyolefin resin, acrylic resin,
Examples thereof include urethane resin, epoxy resin, polyester resin, silicon polyester resin, vinyl chloride resin, fluorine resin, butyral resin, polycarbonate resin, and phenol resin. Mixtures or copolymers of these can also be used. In addition to these, isocyanate resin, amino resin,
A silane coupling agent or a titanium coupling agent can be used together as an auxiliary component. Since the precoated metal sheet according to the present invention is often used as it is without being repaired after processing, in applications where severe processing is applied, a resin system in which a polyester resin is crosslinked with melamine,
Resin system that cross-links polyester resin with isocyanate,
Vinyl chloride resin type and fluorine resin type (solvent-soluble type, dispersion mixed type with acrylic resin) are desirable.

In order to further improve the weather resistance of the top coat of the present invention, a hindered amine-based UV stabilizer having a HALS structure, and a benzophenone-based, benzotriazole-based, oxalic acid anilide-based, cyanoacrylate-based, and triazine-based UV-absorbing agent are used. The agent may be added or chemically bonded to the resin forming the coating film. One of these may be added, but it is preferable to use a plurality of ultraviolet stabilizers and ultraviolet absorbers in combination in order to efficiently improve the weather resistance.

By coating the coating film of the present invention to a thickness of 1 μm or more, preferably 5 μm or more, excellent performance can be obtained. If it is less than 1 μm, the effect of suppressing the temperature rise due to the pigment does not appear, and the deterioration rate of the coating film and the corrosion rate of plating are not reduced. Examples of the coating method include a brush, a roll coater, a curtain flow coater, a roller curtain coater, electrostatic coating, spray coating, a blade coater, a die coater, and dip coating. After that, hot air, induction heating,
It is dried and cured by heating in the near infrared and far infrared.
If the resin of the organic coating layer is curable by electron beams or ultraviolet rays, it is cured by these irradiations. These may be used in combination.

If necessary, a chemical conversion treatment may be applied on the undercoated steel sheet of the present invention. It is treated for the purpose of strengthening the adhesion between the coating and the base steel sheet, and for the purpose of improving corrosion resistance. As the chemical conversion treatment, known techniques can be used, and examples thereof include zinc phosphate treatment, chromate treatment, silane coupling treatment, complex oxide film treatment, tannic acid treatment, and a mixture treatment thereof. Further, for the purpose of further improving the corrosion resistance, an undercoat coating may be provided between the chemical conversion treatment layer and the top coating of the present invention. Anticorrosion pigments can be added to the undercoat to further improve the corrosion resistance. As the rust preventive pigment, known rust preventive pigments can be applied, for example, zinc phosphate, iron phosphate, aluminum phosphate, zinc phosphite, and other phosphate-based rust preventive pigments, calcium molybdate, aluminum molybdate, Barium molybdate, etc. molybdate anticorrosion pigments, vanadium oxide, etc. vanadium anticorrosion pigments, calcium silicates, etc. silicate pigments, strontium chromate,
Chromate-based rust preventive pigments such as zinc chromate, calcium chromate, potassium chromate and barium chromate, finely divided silica such as water-dispersed silica and fumed silica, and ferroalloy such as ferrosilicon can be used. These may be used alone or in combination of two or more.

As the resin used for the undercoat paint of the present invention, generally known resins can be applied depending on the application. That is, it is a polyolefin resin, an acrylic resin, a urethane resin, an epoxy resin, a polyester resin, a silicone polyester resin, a vinyl chloride resin, a fluorine resin, a butyral resin, a polycarbonate resin, a phenol resin, or the like. Mixtures or copolymers of these can also be used. Further, an isocyanate resin, an amino resin, a silane coupling agent, a titanium coupling agent, or the like can be used in combination therewith as an auxiliary component. The form of the paint is not particularly limited, and examples thereof include organic solvent-based paints, water-based paints, colloidal dispersion-based paints, powder paints, and electrodeposition paints.

The thickness of the undercoat coating is not particularly limited, but is preferably 1 μm or more and less than 100 μm. If it is less than 1 μm, the effect of improving corrosion resistance is unclear,
If it exceeds 100 μm, the workability is deteriorated, cracking of the coating film occurs in severe processing, and as a result, the corrosion resistance is deteriorated.

As the coating method, for example, brush, roll coater, curtain flow coater, roller curtain coater, electrostatic coating, spray coating, blade coater,
There are die coaters, dip coating, etc. After that, it is dried and cured by heating with hot air, induction heating, near infrared, far infrared, or the like. If the resin of the organic coating layer is curable by electron beams or ultraviolet rays, it is cured by these irradiations. These may be used in combination.

An intermediate coating may be provided between the top coating of the present invention and the base coating having a rust preventive pigment. The intermediate coating is not particularly limited, and the intermediate coating used for ordinary three-coat coating can be applied as it is. Further, for the purpose of further suppressing a temperature rise, a spherical hollow body having heat insulating properties may be added as an intermediate coating. As the spherical hollow body, a ceramic hollow body such as a glass balloon or a resin hollow body such as polystyrene can be applied. When an undercoat layer having an anticorrosive pigment is used, the coating using the spherical hollow body is treated as an intermediate coat layer between the overcoat layer and the undercoat layer of the present invention.

[0035]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these. A cold-rolled steel sheet having a thickness of 0.8 mm was used as a plating original plate. The Zn alloy plating was produced by the hot dipping method. That is, Zn-Al-Mg-Si alloy plating baths having various compositions are adjusted at 400 ° C to 500 ° C, and a cold-rolled steel sheet is immersed in this plating bath for 3 seconds to perform Zn-Al-Mg-Si alloy plating. A steel plate was manufactured. The coating weight was adjusted to 135 g / m ² on one side by nitrogen wiping. Table 1 shows the elemental composition of the obtained plating layer. Coating type chromate treatment (Cr adhesion amount 5
0 mg / m ² ) and then an epoxy base coat containing a Cr-based anticorrosive pigment was applied to a thickness of 5 μm.
Various infrared resistant pigments of the present invention and comparative pigments were added to the top coat.

[0036]

[Table 1]

The following were added as the infrared resistant pigment of the present invention. All the pigments examined this time are 780 nm to 2
The solar reflectance at a wavelength of 100 nm is 4.0% or more. Pigment A: Complex oxide calcined pigment of Fe, Cr, Co Pigment B: Complex oxide calcined pigment of Cu, Cr, Mn Pigment C: Complex oxide calcined pigment of Zn, Fe, Cr Pigment D: Cr, Sb, Ti complex oxide calcined pigment pigment E: Co, Zn, Al complex oxide calcined pigment pigment F: Co, Ti, Ni, Zn complex oxide calcined pigment pigment G: Zirconium oxide pigment pigment H: Yttrium oxide pigment pigment I: Ferrosilicon pigment pigment J: Azomethine azo pigment pigment K: 1: 1 mixture of Fe, Cr, Co composite oxide fired pigment and zirconium oxide pigment (weight ratio) Comparative pigment Was used as carbon black. Carbon black has a characteristic of absorbing infrared light from sunlight well. Pigment X: Polyester resin was used as the resin for the top coating of carbon black.
The composition of the dry coating film is 40% by mass of the pigment of the present invention, 10% by mass of the coloring pigment (titanium oxide), and 5% of the resin.
It was adjusted to be 0% by mass. Further, a small amount of carbon black was added so that the hue was Munsell symbol N9.5 to N6. In the table of conditions and test results, the mass% is calculated excluding the addition amount of carbon black used for toning. Cyclohexanone was added as a solvent to prepare a paint. The topcoat paint prepared in this manner was applied to the above-mentioned undercoated undercoated steel sheet so that the dry film thickness was 15 μm. The backside was treated with the same undercoating on the surface to a thickness of 3 μm, and the same as the topcoating with a thickness of 7 μm. All coating was done by bar coating. The details of the conditions are shown in Table 2.

The durability of the coated steel sheet was investigated by conducting an outdoor exposure test for one year in Gushizu Village, Okinawa Prefecture. 100m for each coated steel plate
It was cut into a size of m × 50 mm, and the swelling width from the upper flash portion of the cut end face portion was measured. Using a hot-dip galvanized steel sheet as the base-plated steel sheet and using carbon black as the pigment of the overcoat paint as a reference, one with a swelling width smaller than the reference sample is 1, an equivalent is 2 and a large one is 3, 1 was passed.

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

From Table 2, it can be seen that when a base-plated steel sheet within the scope of the present invention is used and a top coat containing the pigment of the present invention is applied, the corrosion resistance in an outdoor environment is improved. This tendency is not reproduced in an environment where sunlight is hard to hit such as a salt spray test, and the highly durable coated steel sheet of the present invention efficiently reflects infrared rays of sunlight to suppress a temperature rise. Therefore, it can be seen that the deterioration rate of the coating film and the corrosion rate of the plating are slowed.

[0043]

EFFECTS OF THE INVENTION The highly durable coated steel sheet of the present invention is excellent in weather resistance and corrosion resistance in an outdoor environment exposed to sunlight, and is used as a roofing material and a wall material for outdoor building materials, an air conditioner outdoor unit for outdoor home appliances, and the like. It is suitable.

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) B32B 27/20 B32B 27/20 A C09D 5/00 C09D 5/00 Z 5/33 5/33 7/12 7/12 201/00 201/00 C23C 28/00 C23C 28/00 AF term (reference) 4D075 AE03 CA13 CA32 CA33 CA38 DA06 DB02 DB05 DC02 DC10 DC18 EA05 EB13 EB15 EB16 EB19 EB22 EB32 EB33 EB35 EB38 EB42 EC11 EC54 4F100 AB AB09B AB10B AB11B AB18B AB31B AK53 AT00A CA13C CC01C CC03 EH46 EH66B EJ69 YY00C 4J038 CB001 CD021 CD091 CE061 CG001 DA041 DB001 DD001 DE001 DG001 DL031 HA066 HA02 KA04 HABHABA06 A02 BA05 A02 BA05 A02 BA02 A05A02 BA02 ABA4A02

Claims (6)

[Claims] 1. As a lower layer for coating a coated steel sheet, Mg: 1 to 10% by mass Al: 2 to 19% by mass Si: 0.01 to 2% by mass, and Mg and Al are represented by the following formula Mg ( Mass%) + Al (mass%) ≦ 20 mass%, with the balance Zn and unavoidable impurities
An infrared resistant pigment having an n-alloy plating layer and having a solar reflectance of 4.0% or more at a wavelength of 780 nm to 2100 nm is at least 2 on the uppermost layer of at least one surface of the coated steel sheet.
Characterized by having a topcoat coating containing 60% by weight,
Highly durable coated steel sheet. 2. The highly durable coated steel sheet according to claim 1, further comprising a chemical conversion treatment layer and an undercoat containing a rust preventive pigment between the Zn alloy plating layer and the overcoat. 3. The high durability coated steel sheet according to claim 1, wherein the infrared resistant pigment contains a black pigment. 4. The infrared resistant pigment includes a complex oxide pigment having one or more structures selected from the group consisting of an ilmenite structure, a forsterite structure, a spinel structure, an inverse spinel structure, a friderite structure and a rutile structure. The highly durable coated steel sheet according to any one of claims 1 to 3, which is characterized by the above. 5. The infrared resistant pigment contains any one kind or two or more kinds of oxides of zirconium oxide, yttrium oxide, and indium oxide, and any one of claims 1 to 4. Highly durable coated steel sheet according to item. 6. The infrared resistant pigment is Si, Al, F
e, Mg, Ni, Ti, Cr, and any one kind of metal selected from the group consisting of two or more kinds of metal, or one or more kinds of alloys with metal. The highly durable coated steel sheet according to any one of claims 1 to 5.