JP2007176060A - Coated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel sheet having excellent designing properties without deteriorating spangle patterns characteristic of an Al-Zn alloy plated steel sheet largely containing an Al component in the plating layer and inherent metal feeling associated therewith and also excellent in corrosion resistance and machinability. <P>SOLUTION: This coated steel sheet is produced by forming a chemical conversion film on the surface of an Al-Zn alloy plated steel sheet, forming a clear primer layer with film thickness of 2 to 10 μm containing a chromate based rust-preventing pigment on the upper layer of the same, and further forming a clear coating film with film thickness of 5 to 15 μm on the upper layer of the same. The content of the chromate based rust-preventing pigment in the clear primer layer is 5 to 40 mg/m<SP>2</SP>in terms of metallic chrome. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coated steel sheet having characteristic design properties and excellent corrosion resistance, and suitable for applications such as exterior and interior materials for buildings such as panels and siding, or exterior materials for home appliances. Moreover, this coated steel plate can also be used as a steel plate for kitchens or the like as a substitute for a stainless steel plate having high design properties.

  A chemically treated steel sheet in which an organic thin film having a film thickness of about 1 μm containing chromic acid and an acrylic resin is formed on the surface of an aluminum-zinc alloy plated steel sheet containing a large amount of an aluminum component in the plating layer exhibits good corrosion resistance as a non-coating material. Therefore, it is mainly used for building materials. Moreover, this chemical conversion treated steel sheet is well received in the market for a spangle pattern peculiar to aluminum-zinc alloy plating containing a large amount of aluminum in the plating layer and a design feeling (brightness) due to a metallic feeling associated therewith. However, it is difficult to say that the chemical resistance of the chemical conversion treated steel sheet is sufficient compared to the coating material.

As a means for improving the corrosion resistance without impairing the spangle pattern of the aluminum-zinc alloy plated steel sheet, it is conceivable to apply a clear coating.
Patent Document 1 proposes a coated steel sheet coated with a colored resin having a predetermined concealment ratio as a colored coated steel sheet utilizing the spangle pattern of an aluminum-zinc alloy plated steel sheet. However, this colored coated steel sheet is intended to suppress the brightness produced by the spangle pattern by coloring it, and has a drawback that the design properties of the spangle pattern are impaired.

  In order to remedy this drawback, Patent Document 2 and Patent Document 3 propose a colored coated steel sheet having a spangle pattern and a metallic appearance that is formed with a resin layer containing aluminum powder or a pearl pigment. However, these coated steel sheets are composed of a single layer of resin, so that the durability in outdoor use such as roofs is inferior to that of ordinary coated steel sheets, and coating film damage is likely to occur when subjected to severe processing. Therefore, the application is limited.

On the other hand, although ordinary coated steel sheets are excellent in corrosion resistance, the spangle pattern peculiar to aluminum-zinc alloy-plated steel sheets is not visible due to the highly concealed coating film, and even when the skin pass treatment is applied, the glossiness is particularly high. In the coating film, irregularities derived from spangle patterns are raised on the surface of the coating film, and the appearance is impaired.
Japanese Unexamined Patent Publication No. 63-7937 JP 2001-212507 A JP 2001-348676 A

  Therefore, an object of the present invention is to have excellent design without sacrificing the spangle pattern peculiar to an aluminum-zinc alloy-plated steel sheet containing a large amount of aluminum components in the plating layer and the unique metallic feeling associated therewith, and to have corrosion resistance and The object is to provide a coated steel sheet with excellent workability.

  The inventors of the present invention have made extensive studies to solve the above problems, and as a result, a clear primer layer having a rust preventive property mainly composed of a clear resin on an aluminum-zinc alloy plated steel sheet on which a chemical conversion treatment film is formed ( By forming an overcoat layer (upper layer clear coating film) consisting of a lower layer clear coating film) and a clear coating film containing a small amount of coloring pigments as necessary, it has excellent design characteristics unique to aluminum-zinc alloy plated steel sheets. The present inventors have found that a coated steel sheet that can be utilized and also excellent in corrosion resistance and workability can be obtained, and the present invention has been completed.

That is, the gist of the present invention is as follows.
[1] A chemical conversion coating is formed on the surface of an aluminum-zinc alloy-plated steel sheet having an aluminum-zinc alloy plating layer having an aluminum content of 40 to 70% by mass, and a chromate-based rust preventive pigment is formed thereon. A coated steel sheet in which a clear primer layer having a film thickness of 2 to 10 μm is formed, and further a clear coating film having a film thickness of 5 to 15 μm is formed thereon, and the chromate-based rust preventive in the clear primer layer A coated steel sheet having a pigment content of 5 to 40 mg / m ² in terms of chromium metal.

[2] The coated steel sheet according to the above [1], wherein the clear coating film contains a color pigment having a content of 2% by mass or less in the coating film.
[3] In the coated steel sheet according to [1] or [2], the chemical conversion treatment film includes an organic resin, phosphoric acid or / and a phosphoric acid compound, and chromic acid or / and partially reduced chromic acid. The coated steel sheet, wherein the adhesion amount is 5 to 40 mg / m ² in terms of metallic chromium.

  The coated steel sheet of the present invention has a unique design that clearly shows a spangle pattern, a beautiful and stable color appearance, and excellent performance in corrosion resistance and adhesion.

The details of the present invention and the reasons for limitation will be described below.
The coated steel sheet of the present invention is a coated steel sheet in which a chemical conversion treatment film is formed on the surface of an aluminum-zinc alloy-plated steel sheet, and two layers of a clear primer layer containing a specific component and a clear coating film are formed on the surface. It is.

  The aluminum-zinc alloy plated steel sheet to be the base steel sheet is a plated steel sheet having an aluminum-zinc alloy plated layer containing 40 to 70% by mass of aluminum. Here, if the aluminum content in the plating layer is less than 40% by mass or more than 70% by mass, a beautiful spangle on the plating surface cannot be obtained. That is, when the aluminum content in the plating layer is less than 40% by mass, a uniform grayish black appearance like a hot dip galvanized steel sheet is obtained, whereas when the aluminum content exceeds 70% by mass, a uniform silver white appearance is obtained. End up. In view of corrosion resistance, the aluminum content is preferably in the range of 40 to 70% by mass. In addition, an aluminum-zinc alloy plated steel sheet in which the plating layer is composed of 40 to 70% by mass of aluminum and the balance is substantially only zinc, the Fe and Al of the base material steel sheet cause an excessive alloying reaction and Adhesiveness tends to be lowered, and therefore, in order to suppress alloying, the plating layer usually contains about 3% by mass or less of Si.

  Since the spangle on the plating surface cannot be sufficiently recognized as a spangle when the average diameter is less than 0.01 mm, the average diameter is preferably 0.01 mm or more. In order to make the spangle look clearer, the average diameter is preferably 0.3 mm or more. Further, it is desirable in terms of spangle sharpness that the skin pass treatment after plating is not performed or is performed very lightly. The average diameter of the spangle is arbitrarily selected from 10 steel plate samples of 10 cm × 10 cm, and when the number of spangles crossing the length of 1 cm is counted, [average diameter of spangle] (unit: mm) = 100 / [total of 10 count values].

  There are no particular restrictions on the chemical conversion treatment film formed on the surface of the aluminum-zinc alloy-plated steel sheet. For example, a phosphate treatment film, a chromate treatment film, a silica-containing chromate treatment film, or an organic resin thin film should be applied. However, from the viewpoint of forming a film having excellent adhesion and excellent appearance uniformity, it contains an organic resin, phosphoric acid or / and a phosphoric acid compound and chromic acid or / and partially reduced chromic acid ( Preferably, a chemical conversion treatment film (having them as the main component) is preferred. In this case, as the organic resin, a water-dispersible resin that can be stably dispersed in the chromic acid solution, for example, an acrylic resin or a urethane resin dispersed with an emulsifier can be used.

Among the components of such a chemical conversion treatment film, chromium acts as a binder for obtaining adhesion with the plating layer, and the organic resin effectively acts on adhesion with the upper layer film. However, the upper layer film (clear primer layer, clear coating film) has low concealability and the plating surface appearance can be seen through. Therefore, in order to make the appearance beautiful, the phosphoric acid component (phosphoric acid or / and phosphorus) Acid compound) is required. That is, the addition of the phosphoric acid component suppresses coloring due to chromium or the like, so that good adhesion can be obtained without impairing the appearance. In this case, in view of the clear properties, chromium deposition amount of the chemical conversion coating is preferably 40 mg / ^{m 2} or less reckoned as metal chromium, 25 mg / ^{m 2} or less is particularly preferred. On the other hand, from the viewpoint of adhesion and corrosion resistance, the chromium adhesion amount is preferably 5 mg / m ² or more in terms of metal chromium.

Next, the clear primer layer formed in the upper layer of the said chemical conversion treatment film is demonstrated.
The clear primer layer (lower clear coating film) is formed for imparting adhesion between the upper clear coating film and the substrate and imparting corrosion resistance. The film thickness of the clear primer layer is preferably in the range of 2 to 10 μm. When the film thickness is less than 2 μm, sufficient rust prevention and adhesion when subjected to severe processing may not be obtained. On the other hand, when the film thickness exceeds 10 μm, scratch resistance decreases and production costs also increase. Therefore, it is not preferable.

In the clear primer layer, a chromate-based anticorrosive pigment is blended for imparting antirust properties. Examples of chromate-based rust preventive pigments include strontium chromate, potassium chromate, zinc chromate, calcium chromate, and barium chromate, and one or more of these can be used. Strontium is most preferred.
The content of the chromate rust preventive pigment in the clear primer layer is 5 to 40 mg / m ^{2 in} terms of metal chromium. If the content of chromate-based anticorrosive pigment exceeds 40 mg / m ² , it will be colored yellowish, making it impossible to provide a colorless coated steel sheet and reducing the clearness (transparency). Therefore, it is not preferable. In order to give a particularly high colorless clear feeling, the content is desirably 20 mg / m ² or less. On the other hand, if the content is less than 5 mg / m ² , sufficient corrosion resistance cannot be obtained.

  The type of organic resin that is the main component of the clear primer layer is not particularly limited and may be a known one. It is particularly preferable to use it. Moreover, even when using resin with inferior weather resistance like the epoxy resin generally used with the general coated steel plate, the modified resin containing an epoxy resin component, etc., it can apply as an interior use.

  The organic resin is composed of a main resin and a curing agent. When a polyester resin is used as the main resin, the polyester resin has a number average molecular weight of 1000 to 30000, preferably 3000 to 20000. When the number average molecular weight is less than 1000, the coating film has low elongation, so that sufficient processability cannot be obtained, and a desirable coating film performance cannot be obtained. On the other hand, if the number average molecular weight exceeds 30000, the resin becomes highly viscous, so that an excessive dilution solvent is required, and the ratio of the resin in the paint is reduced, making it impossible to obtain an appropriate coating film.

  The polyester resin is a copolymer obtained by heat-reacting a polybasic acid component and a polyhydric alcohol by a known method. As the polybasic acid component, for example, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, tetrahydrophthalic anhydride, trimellitic anhydride, maleic acid, adipic acid, fumaric acid and the like can be used. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, Glycerin, pentaerythritol, trimethylolpropane, trimethylolethane and the like can be used.

  Moreover, a polyisocyanate compound and / or an amino resin can be used as a curing agent when a polyester resin is used as a main resin. As the polyisocyanate compound, an isocyanate compound obtained by a general production method can be used. Among them, phenol, cresol, aromatic secondary amine, third, which can be used as a one-component paint, among others, can be used. A polyisocyanate compound blocked with a blocking agent such as a secondary alcohol, lactam or oxime is preferred. By using this blocked polyisocyanate compound, it is possible to store in one liquid, and the use as a paint becomes easy.

  More preferable polyisocyanate compounds include non-yellowing hexamethylene diisocyanate (hereinafter abbreviated as HDI) and derivatives thereof, tolylene diisocyanate (hereinafter abbreviated as TDI) and derivatives thereof, 4,4′-diphenylmethane diisocyanate ( Hereinafter, abbreviated as MDI) and derivatives thereof, xylylene diisocyanate (hereinafter abbreviated as XDI) and derivatives thereof, isophorone diisocyanate (hereinafter abbreviated as IPDI) and derivatives thereof, trimethylhexamethylene diisocyanate (hereinafter abbreviated as TMDI) and its Derivatives, hydrogenated TDI and its derivatives, hydrogenated MDI and its derivatives, hydrogenated XDI and its derivatives, and the like.

  When a polyisocyanate compound is used as the curing agent, the compounding ratio [NCO / OH] of the isocyanate group of the polyisocyanate compound to the hydroxyl group in the main resin is 0.8 to 1.2, more preferably 0.90 to molar ratio. It is desirable that the range is 1.10. When the [NCO / OH] molar ratio is less than 0.8, the coating film is not sufficiently cured, and the desired coating film hardness and strength cannot be obtained. On the other hand, when the molar ratio of [NCO / OH] exceeds 1.2, side reactions between excess isocyanate groups or between isocyanate groups and urethane blends occur, and the processability of the coating film is lowered.

  As the amino resin that is a curing agent, resins obtained by reaction of urea, benzoguanamine, melamine, and the like with formaldehyde, and those obtained by alkyl etherification with alcohols such as methanol and butanol can be used. Specific examples include a methylated urea resin, an n-butylated benzoguanamine resin, a methylated melamine resin, an n-butylated melamine resin, and an iso-butylated melamine resin.

When an amino resin is used as the curing agent, the blending ratio (weight ratio of solid content) of the amino resin and the main resin is [main resin] / [amino resin]: 95/5 to 65/35, preferably 90/10. The ratio is preferably 75/25. When the blending ratio of the amino resin is less than 95/5, the coating film hardness is insufficient. On the other hand, when it exceeds 65/35, the processability is insufficient.
In addition to the chromate-based anticorrosive pigments described above, silica-based pigments, phosphate-based pigments, phosphite-based pigments, etc., should be blended in the clear primer layer (primer coating composition). Can do. A curing catalyst such as p-toluenesulfonic acid, tin octoate or dibutyltin dilaurate can be used depending on the purpose and application. Furthermore, a small amount of various additives such as an antifoaming agent, a leveling agent, and an ultraviolet absorber can be added.
The clear primer layer in the present invention is basically one that does not contain a color pigment (color pigment content: 0% by mass), but if necessary, a small amount of color pigment is added within a range that does not reduce the clear feeling. You can also

Next, the clear coating film (upper clear coating film) formed in the upper layer of the said clear primer layer is demonstrated.
The film thickness of the clear coating film is 5 to 15 μm. If the film thickness is less than 5 μm, sufficient corrosion resistance and processed part corrosion resistance cannot be obtained, and the color appearance is not stable when colored. On the other hand, if the film thickness exceeds 15 μm, the processability deteriorates and coating defects such as cracks occur. Is likely to occur, and the manufacturing cost increases, which is not preferable.
The clear coating film in the present invention is basically one that does not contain a color pigment (content of color pigment: 0% by mass), but a color pigment can also be added if necessary. However, when a coloring pigment is blended, the blending amount needs to be 2% by mass or less as a ratio in the coating film. When the blending amount of the color pigment exceeds 2% by mass, the clearness of the color drops, so the beautiful spangle of the base becomes unclear, and the unique metallic feeling is lost. Furthermore, the color tone changes due to film thickness fluctuations during production. Becomes noticeable and is not preferable. Although there is no particular lower limit on the amount of the coloring pigment, it is generally added in an amount of 0.1% by mass or more from the viewpoint of the coloring effect.

  As the color pigment to be blended in the clear coating film, usual pigments used in exterior and interior paints can be used. Examples include phthalocyanine, quinacridone, indigo, perylene, quinophthalone, azo, and isoindoline pigments, carbon black, yellow iron oxide, bengara, etc., one or more of these Can be used.

The type of the organic resin that is the main component of the clear coating film is not particularly limited as long as it can be formed by a coated steel sheet manufacturing facility. This organic resin is composed of a main resin and a curing agent. As the main resin, an acrylic resin and / or a polyester resin are particularly preferable from the viewpoints of weather resistance, hardness, workability, and adhesion.
The acrylic resin used as the main resin is not particularly limited as long as it is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of 1500 to 12000, but a preferred range of the number average molecular weight. Is 1700-10000. The hydroxyl groups in the molecule of the acrylic resin are randomly arranged in the main chain of the acrylic resin, and if the number average molecular weight is less than 1500, the workability is remarkably lowered. On the other hand, if the number average molecular weight exceeds 12000, the viscosity becomes high, so that an excessive dilution solvent is required, and the proportion of the resin in the paint decreases, so that an appropriate coating film cannot be obtained. Furthermore, the compatibility with other compounding components is significantly reduced. The number average molecular weight of the acrylic resin is a polyester-converted molecular weight measured by gel permeation chromatography (hereinafter referred to as GPC).

  The acrylic resin is a copolymer obtained by subjecting an acrylic monomer or methacrylic monomer having a hydroxyl group and an acrylic ester or methacrylic ester to a heat reaction by a known method. As the acrylic monomer having a hydroxyl group and the methacrylic monomer, for example, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, and the like can be used. Examples of acrylic esters and methacrylic esters include methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylic acid-n-butyl, acrylic acid-2-ethylhexyl, methyl methacrylate, ethyl methacrylate, and methacrylic acid. Isopropyl, n-butyl methacrylate, 2-ethylhexyl methacrylate and the like can be used.

  The polyester resin used as the main resin is not particularly limited as long as it is a compound having at least two hydroxyl groups in one molecule and having a number average molecular weight of 1000 to 8000, but a preferable range of the number average molecular weight thereof. Is 1200 to 7000, more preferably 1500 to 6000. The hydroxyl group in the molecule of the polyester resin may be at either the end or the side chain in the molecule. If the number average molecular weight of the polyester resin is less than 1000, the processability is remarkably lowered. On the other hand, if the number average molecular weight exceeds 8000, the viscosity becomes high, so that an excessive dilution solvent is required, and the proportion of the resin in the paint decreases, so that an appropriate coating film cannot be obtained. Furthermore, the compatibility with other compounding components is significantly reduced. In addition, the number average molecular weight of a polyester resin is a polystyrene conversion molecular weight measured by GPC.

  The acrylic resin or / and polyester resin which is the main resin is used in combination with a curing agent. As the curing agent, a polyisocyanate compound and / or an amino resin can be used.

  Examples of the polyisocyanate compound include HDI and derivatives thereof obtained by a general production method, TDI and derivatives thereof, MDI and derivatives thereof, XDI and derivatives thereof, IPDI and derivatives thereof, TMDI and derivatives thereof, hydrogenated TDI and derivatives thereof, water Examples thereof include hydrogenated MDI and derivatives thereof, hydrogenated XDI and derivatives thereof, and in particular, phenols, cresols, aromatic secondary amines, tertiary alcohols, lactams, which can be used as one-pack type paints, A polyisocyanate compound blocked with a blocking agent such as oxime is preferred. By using this blocked polyisocyanate compound, it can be stored in a single liquid and can be easily used as a coating material.

  As the amino resin, resins obtained by reaction of urea, benzoguanamine, melamine and the like with formaldehyde, and those obtained by alkyl etherification with alcohols such as methanol and butanol can be used. Specific examples include a methylated urea resin, an n-butylated benzoguanamine resin, a methylated melamine resin, an n-butylated melamine resin, and an iso-butylated melamine resin.

It is preferable that the compounding quantity of the hardening | curing agent in a clear coating film (coating composition for clear coating films) shall be 9-50 mass% in the ratio in resin solid content. When the blending amount of the curing agent is less than 9% by mass, the coating film hardness is not sufficient, while when it exceeds 50% by mass, the workability becomes insufficient.
For clear coatings (coating compositions for clear coatings), colorless and transparent particulate additives composed of silica, nylon, acrylic resin, etc., p-toluenesulfonic acid, tin octoate, depending on the purpose and application An appropriate amount of a curing catalyst such as dibutyltin dilaurate and other additives can be blended.

  There are no particular restrictions on the coating method of the coating composition for forming the clear primer layer and the clear coating described above, but it is preferable to apply the coating composition by a method such as roll coater coating or curtain flow coating. . After the coating composition is applied, the coating film is baked by heating means such as hot air heating, infrared heating, induction heating, etc., and the resin is crosslinked to obtain a resin layer. The baking treatment for heat-curing the coating film is usually performed at a maximum plate temperature of about 180 to 260 ° C., and baking is performed for about 30 seconds to 3 minutes in this temperature range.

After applying the chemical conversion treatment liquid with a roll coater to a 55% by mass aluminum-zinc alloy plated steel sheet (indicated as “GL” in Table 1) with a plate thickness of 0.35 mm and a coating weight of 80 g / m ² per side, Drying was performed at a reaching plate temperature of 80 ° C. using a hot air drying furnace to form a chemical conversion film of any one of the following AC.
A: Chemical conversion coating consisting of acrylic resin, chromic acid and phosphoric acid compound B: Chemical conversion coating consisting of acrylic resin and chromic acid C: Chemical conversion coating consisting of silica fine particles and chromic acid

  Next, a primer coating composition containing the chromate-based rust preventive pigment shown in Table 1 was applied with a bar coater so as to have a predetermined dry film thickness, and baked at an ultimate temperature of 210 ° C. for a baking time of 35 seconds. A clear primer layer was formed. Further, a clear coating composition containing no colorant or having the colorant shown in Table 1 was applied to the upper layer with a bar coater so as to have a predetermined dry film thickness, reaching a temperature of 230 ° C., and baking time. A clear coating film was formed by baking in 40 seconds, and the coated steel sheets of the present invention and comparative examples were obtained.

  In the primer coating composition, an isocyanate curable polyester resin in which 25 parts by mass of an isocyanate compound was blended with 100 parts by mass of a polyester resin having a number average molecular weight of 12,000 as a base resin was mixed. The coating composition was prepared by stirring for a period of time. In the coating composition for clear coating, a melamine curable polyester resin in which 20 parts by mass of a melamine resin is blended with 100 parts by mass of a polyester resin having a number average molecular weight of 3000 is used as a base resin, and a color pigment is mixed as necessary. After that, the coating composition was prepared by stirring with a ball mill for about 30 minutes.

Moreover, as a comparative example, a coated steel sheet without a clear primer layer and a coated steel sheet without a chemical conversion treatment film were produced by methods according to the above-described conditions. Similarly, as a comparative example, a coated steel plate using a SUS304 stainless steel plate (indicated as “SUS304” in Table 1) as a coating original plate was manufactured by a method according to the above-described conditions.
About each coated steel plate obtained as mentioned above, the designability (visibility of spangle), appearance, appearance stability, corrosion resistance, and coating film adhesion were evaluated by the following evaluation methods. The results are shown in Tables 1 and 2 together with the coating composition of each coated steel sheet.

(1) Designability The sample surface was visually observed and evaluated according to the following criteria.
(Double-circle): Spangle can be confirmed clearly.
○: Although it is slightly blurred, a spangle pattern can be confirmed.
(Triangle | delta): A spangle pattern can hardly be confirmed.
X: Spangle cannot be confirmed at all.
(2) Appearance (evaluated only when no color pigment is added to the clear coating)
The sample surface was visually observed and evaluated according to the following criteria.
A: A colorless and transparent color appearance was obtained.
○: The whiteness slightly decreased.
Δ: Slightly colored appearance.
X: The appearance became intensely colored.
(3) Appearance stability (evaluated only when a color pigment is added to the clear coating)
The surface of three samples coated under the same conditions was visually observed and evaluated according to the following criteria.
○: No difference in color appearance in all three sheets.
X: A difference in color appearance is recognized among the three sheets.

(4) Corrosion resistance JIS for the test material (sample)
In accordance with the bending test method described in G 3322, a 4T bending process was performed in which the bending angle was 180 ° and the inner distance between the bendings was 4 plates of the test material (0.35 mm), and then the salt spray test SST (JIS
After performing Z 2371) for 1000 hours, the surface of the bent portion was observed and evaluated according to the following criteria.
○: No swelling or rusting of the coating film is observed.
Δ: Slight swelling or rusting is observed.
X: The occurrence of swelling or rust of the coating film is clearly recognized.
(5) Coating film adhesion After immersing the test material (sample) in boiling water for 2 hours and drying, JIS
G cross-cut according to the method of cross-cut test described in G 3322, a transparent adhesive tape (trade name: “Cello Tape” manufactured by Nichiban Co., Ltd.) is applied after the cross cut, and then this tape is peeled off A cross-cut tape peeling test for testing the adhesion of the coating film was conducted and evaluated according to the following criteria.
○: No peeling of coating film ×: Peeling of coating film

  In Tables 1 and 2, No. in which the blending amount of the color pigment in the clear coating film is excessive. The comparative example of No. 6 is inferior in appearance stability, and the film thickness of the clear primer layer is too small, the chromate-based anticorrosive pigment is not added, or the blending amount thereof is too small. The comparative examples of 11, 17, and 18 are inferior in corrosion resistance or adhesion. In addition, No. which does not form a clear primer layer. No. 19 comparative example, No. which does not form a chemical conversion film. In the comparative example of 25, either or both of corrosion resistance and adhesion are inferior. In addition, No. using SUS304 as the original plate. Since the comparative example of 26 has no spangle pattern, the designability is inferior. On the other hand, in the examples of the present invention, excellent performance is obtained in all cases.

Claims (3)

The film | membrane which forms a chemical conversion treatment film on the surface of the aluminum-zinc alloy plating steel plate which has an aluminum-zinc alloy plating layer whose aluminum content is 40-70 mass%, and contains the chromate-type antirust pigment in the upper layer A coated steel sheet in which a clear primer layer having a thickness of 2 to 10 μm is formed, and further a clear coating film having a thickness of 5 to 15 μm is formed on the upper layer, and the inclusion of a chromate-based anticorrosive pigment in the clear primer layer A coated steel sheet characterized in that the amount is 5 to 40 mg / m ² in terms of metallic chromium.   2. The coated steel sheet according to claim 1, wherein the clear coating film contains a color pigment having a content of 2% by mass or less in the coating film. The chemical conversion treatment film includes an organic resin, phosphoric acid or / and a phosphoric acid compound, and chromic acid or / and partially reduced chromic acid, and the film adhesion amount is 5 to 40 mg / m ² in terms of metal chromium. The coated steel sheet according to claim 1 or 2, wherein