JP2007276187A - Coated steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel plate having excellent design properties, corrosion resistance and repeated slide characteristics and especially suitable as a shutter material without losing a spangle pattern peculiar to an Al-Zn alloy plated steel plate much in the content of Al in its plating layer and the brightness and the hue accompanied thereby. <P>SOLUTION: Chemical treatment films are formed on both sides of the Al-Zn alloy plated steel plate, clear primer layers with a film thickness of 2-10 μm containing a rustproof pigment are formed on the surfaces of the chemical treatment films and upper clear coating films with a film thickness of 5-15 μm containing 1-10 mass% of fluoroplastic fine particles are further formed on the surfaces of the clear primer layers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a coated steel sheet having a characteristic design property, excellent repeated sliding characteristics and corrosion resistance, and particularly suitable for various shutter materials. Moreover, since this coated steel plate has high design properties, it is also suitable as a peripheral member of a shutter.

  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, although this chemical conversion treated steel sheet has workability in roll forming or the like, it is difficult to say that the repeated sliding characteristics and corrosion resistance are sufficient as compared with a normal coated steel sheet used for a shutter.

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 limited in application because they are inferior in durability to ordinary coated steel sheets due to a single layer of resin, and are liable to damage the coating film when subjected to severe processing. Is done. Furthermore, when these coated steel sheets are applied to applications that require repeated sliding characteristics such as shutters, there is a problem that coating film scratches are likely to occur, resulting in performance degradation such as a decrease in durability and noise generation.

On the other hand, ordinary coated steel sheets used for shutters are formed by forming a highly concealable coating film containing a large amount of color pigments and other additives on a colored primer. Although this steel sheet is excellent in various performances such as corrosion resistance, the addition of a metallic pigment causes a significant decrease in repeated sliding characteristics, so there is a limit to the provision of design properties by imparting a glitter feeling. Further, even when a skin pass treatment is performed on the plating surface, there is a problem that unevenness derived from the spangle pattern is raised on the surface of the coating film and the appearance is impaired particularly when a coating film with high glossiness is formed.
Japanese Unexamined Patent Publication No. 63-7937 JP 2001-212507 A JP 2001-348676 A

  Accordingly, an object of the present invention is to have an excellent design without sacrificing the spangle pattern unique to an aluminum-zinc alloy-plated steel sheet containing a large amount of an aluminum component in the plating layer and its associated glitter, as well as corrosion resistance and repeated sliding. The object is to provide a coated steel sheet having excellent dynamic characteristics.

  The present inventors have repeated intensive studies to solve the above problems, and as a result, on both surfaces of the aluminum-zinc alloy plated steel sheet on which the chemical conversion treatment film has been formed, a clear primer layer having adhesion and rust prevention properties, and repetition. Utilizing the excellent design characteristics unique to aluminum-zinc alloy-plated steel sheets by forming an upper clear coating film that has sliding characteristics and blends a small amount of color pigment as required, especially suitable for shutter materials The present inventors have found that a coated steel sheet can be obtained and have completed the present invention.

That is, the gist of the present invention is as follows.
[1] A film thickness in which a chemical conversion film is formed on both surfaces 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 rust preventive pigment is contained in the upper layer. A clear primer layer having a thickness of 2 to 10 μm was formed, and an upper clear coating film having a thickness of 5 to 15 μm and containing 1 to 10 mass% of fluororesin-based fine particles in the coating film was formed thereon. Painted steel sheet.

[2] The coated steel sheet according to [1], wherein the upper clear coating film contains a color pigment having a content of 2% by mass or less in the coating film.
[3] The coated steel sheet according to the above [1] or [2], wherein the content of the chromium compound in the chemical conversion coating is 40 mg / m ² or less in terms of metallic chromium.
[4] The coated steel sheet according to any one of the above [1] to [3], wherein the content of the chromium compound in the clear primer layer is 40 mg / m ² or less 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 terms of continuous slidability, corrosion resistance, and adhesion required as a shutter material. Have.

The details of the present invention and the reasons for limitation will be described below.
The coated steel sheet of the present invention formed a chemical conversion film on both surfaces of an aluminum-zinc alloy plated steel sheet, and formed two layers of a clear primer layer containing a specific component and an upper clear film on the upper layer. Painted steel sheet. In general, when a shutter is wound or unwound on a drum during ascent and descent, a phenomenon occurs in which the front surface and the back surface come into contact with each other and rub against each other, which causes a scratch on the coating film. It may cause winding failure and noise generation. The coated steel sheet of the present invention has a coating film / coating film that provides excellent design, corrosion resistance, and adhesion as a shutter material, and has a specific coating film that has extremely excellent repeated sliding characteristics on both sides. Also, a high degree of scratch resistance can be obtained against a phenomenon peculiar to a shutter in which the front surface and the back surface rub against each other.

  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 Adhesion tends to be lowered, and therefore, usually, in order to suppress alloying, the plating layer 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 that the skin pass treatment after plating is not carried out or carried out very lightly in order to ensure the sharpness of spangles. 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 coating formed on the surface of the aluminum-zinc alloy plated steel sheet, such as phosphate processing coating, chromate coating, silica-containing chromate coating, various metal oxides, organic resins, etc. From the viewpoint of forming a film having excellent adhesion and excellent appearance uniformity, an organic resin and chromic acid can be used as the chemical conversion film. It is preferable to form a thin film containing (preferably containing them as a main component). 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 coating, chromium acts as a binder for obtaining adhesion with the plating layer, and the organic resin effectively acts on adhesion with the upper coating film. However, since the upper coating film has low concealability and the plating surface appearance can be seen through, the chromium compound content in the chemical conversion coating is 40 mg / m in terms of metallic chromium, in particular, in order to make the appearance beautiful. It is preferably ² or less, more preferably 25 mg / m ² or less.
In addition, as the chemical conversion treatment film not containing chromic acid, silicic acid, silicic acid compound, calcium, calcium compound, zirconic acid, zirconic acid compound, vanadic acid, vanadic acid compound, molybdic acid compound, phosphoric acid, phosphoric acid compound It is preferable that 1 or more types of these are included and the adhesion amount is 0.3-3 g / m < ² >. In this case, an organic resin such as a water-dispersible acrylic resin or urethane resin may be used as the binder.

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 to provide adhesion between the upper coating film and the substrate and to provide corrosion resistance. The film thickness of the clear primer layer is 2 to 10 μm. If 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, if it exceeds 10 μm, the feeling of clearness and scratch resistance will deteriorate, and the production cost will also be reduced. Since it rises, it is not preferable.

  In the clear primer layer, an antirust pigment is added to impart antirust properties. Examples of the rust preventive pigment include chromate, silica pigment, phosphate pigment, phosphite pigment, calcium compound, aluminum oxide, zirconic acid, zirconic acid compound, vanadic acid, vanadic acid compound , One or more of molybdic acid compounds, phosphoric acid, phosphoric acid compounds and the like can be used. Among these, chromate is most preferable from the viewpoint of corrosion resistance. Examples of the chromate include strontium chromate, potassium chromate, zinc chromate, calcium chromate, barium chromate and the like, and strontium chromate is most preferable.

However, since the chromate has a yellow or yellow-green color tone, the content of the chromate in the clear primer layer needs to be in a range that is colorless and does not deteriorate the clear feeling. That is, the content of the chromium compound in the clear primer layer is preferably 40 mg / m ² or less in terms of metallic chromium. If the content exceeds 40 mg / m ² , it is unfavorably colored in a yellowish color, making it impossible to obtain a colorless coated steel sheet and reducing the clear feeling. In order to obtain a particularly colorless and clear feeling, the content of the chromium compound is desirably 20 mg / m ² or less in terms of metallic chromium.

  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. Even when using resins with poor weather resistance, such as epoxy resins and modified resins containing epoxy resin components, which are commonly used in general coated steel sheets, the interior side of the shutter or the shutter for indoor use If so, it can be applied.

  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 and the hydroxyl group in the main resin is 0.8 to 1.2, more preferably 0.9 to A range of 1.1 is desirable. 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, if the molar ratio of [NCO / OH] exceeds 1.2, side reactions between excess isocyanate groups or between isocyanate groups and urethane bonds occur, and the processability of the coating film decreases.

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 compounding ratio (mass ratio of the 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.

  For the clear primer layer (primer coating composition), a curing catalyst such as p-toluenesulfonic acid, tin octoate, and dibutyltin dilaurate can be used in addition to the above-described rust preventive pigment, 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. In addition, the clear primer layer in the present invention basically contains no 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 upper clear coating film formed on the clear primer layer will be described.
The film thickness of the upper clear coating film is 5 to 15 μm. When the film thickness is less than 5 μm, sufficient repeated sliding characteristics cannot be obtained, and when it is colored, the color appearance is not stable. On the other hand, when the film thickness exceeds 15 μm, the workability is deteriorated and coating defects such as cracks occur. This is not preferable because it tends to occur and the manufacturing cost increases.

  Fluororesin fine particles are blended in the upper clear coating film. The shutter has a structure in which a belt-shaped steel plate (generally referred to as “slat material”) is connected by caulking to dozens of dozens. A phenomenon occurs in which the surface and the back surface come into contact and rub. This phenomenon is repeated each time the shutter is moved up and down, causing scratches on the surface of the paint film, but if scratches occur on the paint film surface, it may cause winding failure and noise, so there is no scratch as much as possible. It is necessary to do so. Therefore, repeated sliding characteristics are required, but the fluororesin-based fine particles blended in the upper clear coating film have the effect of greatly suppressing the generation of scratches on the coating film under such conditions. Examples of the fluororesin-based fine particles having such an action include fine particles such as tetrafluoroethylene, a copolymer of tetrafluoroethylene and hexafluoropropylene, and a copolymer of tetrafluoroethylene and ethylene. One or more of these can be used. These fluororesin-based fine particles exhibit a stable lubricating action over a wide temperature range, and remarkably improve the repeated sliding characteristics of the coating film. The coated steel sheet according to the present invention has an upper clear coating film that has excellent repetitive sliding characteristics on both sides, so that it is highly resistant to a phenomenon peculiar to a shutter in which the front surface and the back surface are rubbed against each other. The scratch resistance of the coating film can be obtained.

The addition amount of the fluororesin-based fine particles in the coating film is 1 to 10% by mass. If the amount added is less than 1% by mass, the lubricity to prevent scratches is insufficient, while if added in excess of 10% by mass, an effect commensurate with the amount added cannot be obtained, and on the contrary, the clearness decreases. And the manufacturing cost is increased, which is not preferable. A more preferable addition amount of the fluororesin-based fine particles is 2 to 7% by mass. The particle diameter of the fluororesin-based fine particles added to the coating film is not particularly limited, but generally those having an average particle diameter of about 1 to 30 μm can be applied.
In the upper clear coating film, a lubricant other than the fluororesin fine particles, for example, polyolefin fine particles such as polyethylene may be further added.

The upper clear coating film in the present invention is basically one containing no color pigment (content of color pigment: 0% by mass), but may contain a color pigment as required. 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. If the blending amount of the color pigment exceeds 2% by mass, the clearness will be lowered, and the beautiful spangles of the base will become unclear, and the unique metallic feeling will be lost. 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 a coloring pigment blended in the upper clear coating film, a normal pigment used for exterior / interior coating 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 upper 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 an upper layer clear coating film (coating composition for upper layer 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.
In addition, the upper clear coating film (coating composition for upper clear coating film) is a colorless and transparent particulate additive consisting of silica, nylon, acrylic resin, silica, glass fiber, acrylic beads, depending on the purpose and application. It is also possible to adjust the gloss by adding a colorless and transparent matting agent such as. Furthermore, a suitable amount of a curing catalyst such as p-toluenesulfonic acid, tin octoate, 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 upper clear coating described above, but preferably the coating composition is applied by a method such as roll coater coating or curtain flow coating. Good. 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 a chemical conversion treatment solution with a roll coater to a 55% by mass aluminum-zinc alloy plated steel plate (indicated as “GL” in Table 1) with a plate thickness of 0.3 mm and a coating weight of 65 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 and chromic acid B: Chemical conversion coating consisting of 20 parts by mass of calcium ion exchanged silica + 20 parts by mass of phosphoric acid + 60 parts by mass of water-dispersed urethane resin C: consisting of silica fine particles and chromic acid, Chemical conversion coating with a SiO ₂ / Cr mass ratio of 2.5

Then, a primer coating composition appropriately blended with the following antirust pigments a and b is applied with a bar coater so as to have a predetermined dry film thickness, and is baked at an ultimate temperature of 210 ° C. for a baking time of 35 seconds. Formed.
a: strintium chromate (added amount is adjusted according to Cr adhesion amount)
b: Calcium ion exchanged silica fine particles (addition amount: 10 mass% in solid content ratio)
Furthermore, a coating composition for an upper clear coating film in which an upper layer is appropriately blended with tetrafluoroethylene fine particles having an average particle size of about 4 μm as fluororesin fine particles and a colorant shown in Table 1 has a predetermined dry film thickness. As described above, coating was performed with a bar coater, and an upper clear coating film was formed by baking at an ultimate temperature of 230 ° C. and a baking time of 40 seconds, thereby obtaining the coated steel sheets of the present invention example and the comparative example.

In the primer coating composition, an isocyanate curable polyester resin in which 25 parts by mass of an isocyanate compound is blended with 100 parts by mass of a polyester resin having a number average molecular weight of 12,000 as a base resin is used. The coating composition was prepared by stirring for about 1 hour.
In the coating composition for the upper clear coating film, 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 coloring agent were appropriately blended, and then stirred for about 30 minutes with a ball mill to prepare a coating composition.

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, color stability, continuous slidability, corrosion resistance, and 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 upper clear coating)
The sample surface was visually observed and evaluated according to the following criteria.
○: A colorless and transparent color appearance was obtained.
Δ: Very slightly colored appearance.
X: Appearance was clearly colored.
(3) Color tone stability (evaluated only when a color pigment is added to the upper 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) Continuous slidability A rubbed tester (trade name: product name: ½ inch (1.27 cm) in diameter and 2 mm in height so that the front surface of the sample is convex is used as an indenter. Ohira Rika Kogyo Co., Ltd. “RUBBING TESTER”), put a flat plate sample of the same coating on the table, and continuously reciprocate over a length of about 100mm under a load of 2kg, 10,000 reciprocations The subsequent surface condition was evaluated according to the following criteria.
A: Scratches are not noticeable.
○: Slight scratches are noticeable.
(Triangle | delta): Coating-film peeling (exposure of the plating surface) generate | occur | produced partially.
X: Coating film peeling (exposed plating surface) occurred over the entire length.

(5) Corrosion resistance In accordance with the bending test method described in JIS G 3322, the test material was subjected to 4T bending processing with a bending angle of 180 °, an inner interval of bending: 4 sheets of the test material thickness, and then JIS
After conducting a combined cycle corrosion test (CCT) based on K 5621 for 250 cycles (1500 hours), the surface was observed and evaluated according to the following criteria.
A: No blistering or rusting is observed.
○: Swelling of the coating film or generation of rust is observed at an area ratio of 10% or less.
(Triangle | delta): Generation | occurrence | production of the swelling of a coating film or rust is recognized by the area ratio of more than 10% and 50% or less.
X: Swelling of the coating film or generation of rust is observed at an area ratio of more than 50%.
(6) Adhesion After immersing the test material in boiling water for 2 hours and drying, put a grid according to the grid pattern test method described in JIS G 3322, and then apply a transparent adhesive tape (trade name: Nichiban ( “Cero tape”) was applied, and then this tape was peeled off to perform a cross-cut tape peeling test to test the coating film adhesion, and evaluation was performed according to the following criteria.
○: There is peeling of the coating film ×: There is no peeling of the coating film

In Tables 1 and 2, No. 14 in which the film thickness of the upper clear coating is less than the range of the present invention, No. 15 in which the addition amount of the fluororesin-based fine particles in the upper clear coating is less than the range of the present invention, No. 16 to which polyethylene fine particles are added instead of fluororesin fine particles is inferior in either or both of continuous slidability and color tone stability. In addition, the film thickness of the clear primer layer is less than the scope of the present invention, No. 12, no chemical conversion treatment film is formed, No. 19, no rust preventive pigment is added in the clear primer layer, clear primer No. 20 that does not form a layer is inferior in either or both of corrosion resistance and adhesion. In addition, the clear primer layer thickness exceeds the range of the present invention, No. 9, the addition amount of the coloring pigment in the upper clear coating film is excessive, the addition amount of the fluororesin fine particles in the upper clear coating film No. 17 exceeding the scope of the present invention is inferior in design. Moreover, since the thing using SUS304 as an original plate does not have a spangle pattern, the design property is inferior.
On the other hand, the coated steel sheets of the examples of the present invention all have excellent performance.

Claims (4)

  A chemical conversion film is formed on both surfaces 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 the film thickness containing the anticorrosive pigment is 2 to 2 A coating characterized by forming a clear primer layer of 10 μm, and further forming an upper clear coating film having a thickness of 5 to 15 μm containing 1 to 10 mass% of fluororesin-based fine particles in the coating film. steel sheet.   The coated steel sheet according to claim 1, wherein the upper clear coating film contains a color pigment having a content of 2% by mass or less in the coating film. Content of the chromium compound in a chemical conversion treatment film is 40 mg / m < ² > or less in conversion of metal chromium, The coated steel plate of Claim 1 or 2 characterized by the above-mentioned. Coated steel sheet according to the content of chromium compound in the clear primer layer is, any one of the preceding claims, characterized in that it is 40 mg / m ² or less reckoned as metal chromium.