JP2007055137A - Coated metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated metal sheet having excellent weatherability without using a fluorocarbon resin coating. <P>SOLUTION: A hue paint film 3 is set on a metal sheet 2. A clear paint film 4 containing a polyester resin which is prepared from a cyclic aliphatic polybasic acid and an aliphatic polyhydric alcohol and contains no aromatic component and at least one of an ultraviolet absorber and a light stabilizer is set on the outer layer of the hue paint film 3. The coated metal sheet 1 is excellent in adhesion between the clear paint film 4 and the hue paint film 3. Even when the coated metal sheet 1 is exposed to an outdoor atmosphere for a long time, the occurrence of the breakage, peeling, discoloration, gloss degradation etc. , of the paint films can be prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a coated metal plate that has good weather resistance and can be suitably used for building materials and the like.

  Steel sheets such as cold-rolled steel sheets and hot-rolled steel sheets, and pre-coated steel sheets (painted steel sheets) coated with a hue coating on the surface of plated steel sheets that are formed with a plating coating such as an aluminum-zinc alloy plating coating are suitable for exterior building materials. Widely used (see Patent Document 1). Since these coated steel sheets are used in an environment where they are exposed outdoors for a long period of time, high weather resistance is required so that the coating film will not crack or peel off, or cause significant discoloration or chalking. It has been.

  Therefore, components such as pigments, resins, curing agents, etc. of hue coatings on coated steel sheets have been studied, and the weather resistance has been improved by the surface treatment of pigments, optimization of resin monomer components, introduction of urethane crosslinking with isocyanate, etc. As shown in the figure, it was difficult to maintain high weather resistance over a long period of time, although a good weather resistance was obtained in a short period of time.

  In addition, attempts have been made to improve the weather resistance by providing a clear coating on the outer layer of the hue coating, but peeling may occur due to deterioration of the underlying hue coating due to light transmitted through the clear coating, It was difficult to maintain and ensure sufficient weather resistance over a long period of time, such as cracks occurring in itself and significant discoloration and choking.

  In addition, attempts have been made to improve the weather resistance by providing a clear coating film on the outer layer of the hue coating film, but the adhesion between such a clear coating film and the hue coating film deteriorates over time, Peeling occurs due to long-term use, or cracking or peeling is likely to occur when performing mechanical processing after a long time after painting, so that deterioration in processing over time occurs, and sufficient weather resistance cannot be obtained. there were.

On the other hand, as a coated steel sheet having weather resistance that has been conventionally used, there is one that uses a fluororesin paint mainly composed of a fluororesin. The fluorine-containing resin exhibits its function due to the stability resulting from the fact that the bond energy between fluorine atoms and carbon atoms is larger than the bond energy between hydrogen atoms and carbon atoms.
JP 2001-29883 A

  However, fluororesin paints are paints with excellent weather resistance, but the fluoropolymers and calcined pigments that are raw materials are expensive and are used only for limited applications. If scratches occur when mechanical processing is performed, cracks will occur over time starting from the scratches, and the coating will easily peel off. When sticking occurs, it is necessary to repair, and it takes troublesome work. For this reason, it is required to improve the weather resistance of the coated metal plate without using a fluororesin paint as compared with the conventional polyester resin-based coated metal plate.

  This invention is made | formed in view of said point, and it aims at providing the coating metal plate which has the weather resistance superior to the conventional polyester resin-type coating steel plate, without using a fluorine-containing resin. Is.

  The present inventors have obtained the knowledge that a certain degree of weather resistance can be improved by forming a clear coating film on the uppermost layer of the coated metal plate. Although it is considered that the resin coating in the coating due to photoactivity is prevented from being decomposed by the clear coating, the clear coating made of a polyester resin containing an aromatic component generally used conventionally has long-term weather resistance. Therefore, it was difficult to maintain the film, and it was inevitable that fine cracks or peeling occurred in the coating film.

  As a result of intensive studies, the present inventors have attempted to further improve the weather resistance by improving the composition of the clear coating film, and have completed the present invention.

  That is, the coated metal plate 1 according to the present invention is provided with a hue coating 3 on the metal plate 2, and an outer layer of the hue coating 3 is composed of a cyclic aliphatic polybasic acid and an aliphatic polyhydric alcohol, and has an aromatic A clear coating film 4 containing a polyester resin not containing a group component and at least one of an ultraviolet absorber and a light stabilizer is provided. For this reason, the clear coating film 4 has excellent adhesion to the hue coating film 3, and also when the coated metal plate 1 is exposed to the outdoors for a long time, the coating film is cracked or peeled off. In addition, it is possible to prevent discoloration of the coating film and deterioration of gloss. This is because even if a resin degradation reaction occurs due to light irradiation or the like, the chain reaction of degradation as described above is blocked by the action of the UV absorber or light stabilizer in the clear coating film, and is also generated by degradation. It is presumed that the physical properties of the resulting product are also less brittle, and these synergistic effects work to provide good weather resistance.

  In the painted metal plate 1, the cycloaliphatic polybasic acid is hexahydrophthalic anhydride, and the aliphatic polyhydric alcohol is at least selected from 1,6-hexanediol, neopentyl glycol and hydrogenated bisphenol A. It is preferable that it contains 1 type, In this case, the weather resistance of the coating metal plate 1 can further be improved.

  The polyester resin preferably has a number average molecular weight of 1000 to 10,000, a hydroxyl value of 20 to 150 mgKOH / g, and a glass transition point of -10 to 60 ° C. In this case, the coating film processability, handling property, solvent resistance, and coating film hardness of the clear coating can be improved with a good balance.

  Moreover, it is preferable that the said ultraviolet absorber is at least 1 type selected from a benzotriazole type ultraviolet absorber and a hydroxyphenyl triazine type ultraviolet absorber, In this case, the weather resistance of the coating metal plate 1 is further improved. Can do.

  The light stabilizer is preferably a hindered amine light stabilizer. In this case, the weather resistance of the coated metal plate 1 can be further improved.

  The coated metal plate 1 is coated with a liquid clear paint on the surface of the uncured hue paint applied to the metal plate 2, and the hue paint and the clear paint are simultaneously formed in this state to form the hue paint. The film 3 and the clear coating film 4 are preferably formed. If it does in this way, the adhesiveness between the hue coating film 3 and the clear coating film 4 can further be improved.

  According to the present invention, excellent weather resistance can be imparted to the coating film of the coated metal sheet without applying fluorine coating, thereby reducing the cost of the coated metal sheet, relaxing restrictions on use, and disposal. It is possible to obtain a coated metal plate having excellent weather resistance while preventing adverse effects on the environment and preventing complicated processes during mechanical processing.

  Hereinafter, the best mode for carrying out the present invention will be described.

  Although the appropriate steel plate etc. can be used as the metal plate 2 used by this invention, For example, plated steel plates, such as a hot-dip aluminum-zinc alloy plating steel plate and a hot dip galvanization steel plate, a stainless steel plate etc. can be mentioned.

  A chemical conversion treatment layer can be formed on the metal plate 2 prior to the formation of the coating film. Examples of the chemical conversion treatment layer include a chromate (chromate) treatment layer, a phosphate treatment layer, and a composite oxide film formation.

  In forming the chromate (chromate) treatment layer, the surface of the metal plate 2 can be treated with an aqueous solution containing hexavalent chromium and an inorganic acid such as sulfuric acid. A layer made of a hydrated oxide containing valent chromium is formed. Moreover, a phosphate process layer is a layer which consists of a 3rd phosphate formed by processing the metal plate 2 surface using the aqueous solution containing a 1st phosphate and phosphoric acid. Examples of the type of phosphate include zinc phosphate, manganese phosphate, and iron phosphate. In addition, the thickness of the chemical conversion treatment layer is generally in the range of 1 to 2 μm in the case of the phosphate treatment layer.

  The hue coating film 3 formed on the surface of the metal plate 2 is a hue paint colored by containing an appropriate resin such as polyester, epoxy, acrylic or urethane and a colorant such as a pigment or dye. It can be formed by coating and film formation.

  As the colorant contained in such a hue coating film 3, appropriate ones can be used. Specific examples thereof include, as pigments, titanium oxide, carbon black, iron oxide yellow, iron oxide red ( Bengala), aluminum flakes, mica flakes, colored glass flakes, organic blue (phthalocyanine blue) and the like. Examples of the dye include “AIZEN SPILON dye series” manufactured by Hodogaya Chemical Co., Ltd. The blending ratio of such a colorant in the hue paint is usually preferably 0.1 to 40% by weight, particularly preferably 0.5 to 35% by weight.

  In particular, by adding aluminum powder as a pigment in the hue paint, a metallic appearance can be imparted to the coating film. At this time, it is preferable to mix | blend aluminum powder in a hue coating material so that content in the hue coating film 3 may become the range of 10-25 weight%. .

  In the application and film formation of the hue paint, apply by an appropriate method such as spray coating, bar coater coating, roller curtain coater, curtain flow coater, roll coater, etc., then pass through a hot air drying furnace or dielectric heating device etc. A film can be formed by heating and drying. The coating amount and film thickness of the hue coating film 3 are adjusted as appropriate, but it is preferable that the film thickness be in the range of 10 to 20 μm.

  In addition, the lower layer of the hue coating film 3 is used for the purpose of reducing the influence of the metal plate 2 on the coating material to improve the adhesion of the coating film or to provide rust prevention. 5 may be provided. As the undercoat paint (primer) for forming the undercoat paint film 5, an appropriate one such as an epoxy paint or a polyurethane resin paint can be used. Rust preventive pigments and the like can be included. In forming the undercoat film 5, the undercoat paint is applied onto the metal plate 2 by an appropriate method such as spray coating, bar coater coating, roller curtain coater, curtain flow coater, roll coater, etc., and then dried with hot air The undercoat film 5 can be formed by forming a film by heating and drying through a furnace, a dielectric heating device, or the like. The undercoat coating 5 can be formed so as to be in close contact with the chemical conversion treatment layer when a chemical conversion treatment layer is provided, and can be formed so as to be in direct contact with the metal plate 2 when no chemical conversion treatment layer is provided. it can. At this time, two or more types of undercoat films 5 having different compositions may be sequentially provided to form a multi-layer undercoat film 5 having two or more layers. The coating amount and film thickness of the undercoat coating film 5 are appropriately adjusted, but it is preferable that the film thickness be in the range of 1 to 10 μm.

  In the present invention, a clear paint containing a polyester resin and at least one of an ultraviolet absorber and a light stabilizer is applied to the outer layer of the hue coating film 3 formed on the metal plate 2 as described above, and the film is formed. A clear coating film 4 is formed.

  As said polyester resin, what has the structure which ester-polymerized the monomer component which contains a cyclic aliphatic polybasic acid and aliphatic polyhydric alcohol and does not contain an aromatic component is used. If the monomer component contains a chain acid monomer or an aromatic monomer, the clear coating film 4 may not be sufficiently adhered to the hue coating film 3, and cracks or peels off when exposed outdoors for a long time. , Discoloration and gloss deterioration may occur, and sufficient weather resistance cannot be obtained.

  An example of the cycloaliphatic polybasic acid is hexahydrophthalic anhydride. Examples of the aliphatic polyhydric alcohol include 1,6-hexanediol, neopentyl glycol, hydrogenated bisphenol A, and the like.

  Such a polyester resin can be produced using a known method.

  The polyester resin preferably has a number average molecular weight of 1,000 to 10,000. When the number average molecular weight is less than 1000, the crosslink density becomes too high when the clear coating film 4 is formed with this clear paint, so that the flexibility is lowered and there is a possibility of causing a problem in workability. On the other hand, when the number average molecular weight exceeds 10,000, the viscosity of the solution becomes high, handling becomes difficult, and there is a possibility of causing a problem in the coating workability when a clear paint is used. Further, the hydroxyl value (OH value) of the polyester resin is preferably in the range of 20 to 150 mgKOH / g. If the hydroxyl value is less than 20 mgKOH / g, the clear coating has low curability and the resulting clear coating film 4 Sufficient film hardness may not be obtained, solvent resistance may be reduced, and if the hydroxyl value exceeds 150 mg KOH / g, the coating processability of the resulting clear coating film 4 may be decreased. Absent. Moreover, the acid value of this polyester resin has the preferable range of 1-25 mgKOH / g. The glass transition temperature of the polyester resin is preferably −10 to 60 ° C. If the glass transition temperature is less than −10 ° C., the hardness of the clear coating film 4 to be obtained may be lowered. If the temperature exceeds 60 ° C., the processability of the resulting clear coating film 4 may be lowered, which is not preferable.

  Moreover, it is preferable to contain the hardening | curing agent of a polyester resin in a clear coating material. Examples of such curing agents include polyisocyanate compounds containing at least two thermally dissociable blocked isocyanate groups in one molecule, melamine, and the like.

  Examples of such polyisocyanate compounds include compounds called isocyanate monomers such as hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, and the like. Examples include those prepared by blocking a part or all of isocyanate groups of a polyisocyanate compound with a blocking agent, such as polyisocyanate derivatives such as biuret bodies, isocyanurate bodies, and adduct bodies of trimethylolpropane. Examples of this blocking agent include, for example, ketoxime blocking agents such as ε-caprolactam, methyl ethyl ketoxime, methyl isoamyl ketoxime, methyl isobutyl ketoxime, and phenol blocking agents such as phenol, cresol, catechol and nitrophenol. And alcohol blocking agents such as isopropanol and trimethylolpropane, and active methylene blocking agents such as malonic acid esters and acetoacetic acid esters. These polyisocyanate compounds may be used alone or in combination of two or more.

  Although the content of the curing agent is appropriately adjusted, in order to give the clear coating film 4 particularly excellent weather resistance, the hydroxyl group in the polyester resin and the reactive functional group (polyisocyanate in the curing agent). In the case of a compound, the molar ratio with the thermally dissociable blocked isocyanate group) is such that the reactive functional group in the curing agent is in the range of 0.8 to 1.5 mol with respect to 1 mol of hydroxyl group in the polyester resin. Is preferred. Moreover, when it contains melamine, it is preferable to make it be the range of 10-50 weight part of melamine with respect to 100 weight part of polyester resins.

  Further, a curing reaction catalyst may be contained in the clear paint. Examples of the curing reaction catalyst include tin compounds and zinc compounds. Examples of tin compounds include tin halides such as tin chloride and tin bromide, and organic tin compounds such as dibutyltin diacetate and dibutyltin dilaurate. Examples of zinc compounds include zinc halides such as zinc chloride and zinc bromide. And zinc salts of organic acids such as zinc octylate and zinc laurate. One kind of tin compound or zinc compound as a curing reaction catalyst may be used, or two or more kinds may be used in combination, or may be used in combination with another curing reaction catalyst. The curing reaction catalyst is preferably used in a proportion of 0.01 to 5% by weight with respect to the total heating residue in the clear paint. If this amount is less than 0.01% by weight, the effect of promoting the curing reaction may not be sufficiently exerted, and if it exceeds 5% by weight, the water resistance and moisture resistance of the clear coating film 4 are reduced. As a result, the stain resistance, decontamination property, weather resistance and the like of the clear coating film 4 may be reduced. From the viewpoint of the balance between the curing speed and the physical properties of the clear coating film 4, a more preferable blending amount of this curing reaction catalyst is in the range of 0.01 to 2% by weight with respect to the total heating residue in the composition.

  Further, as the ultraviolet absorber (UVA), a benzotriazole ultraviolet absorber as shown in the following formula (1), a hydroxyphenyl triazine ultraviolet absorber as shown in the following formulas (2) to (7), and the like are used. These can be used alone or in combination of two or more. Examples of such UV absorbers include product numbers “TINIVIN 384-2”, “TINIVIN 400”, “TINIVIN 411L”, “TINIVIN 900”, “TINIVIN 928” and the like provided by Ciba Specialty Chemicals Co., Ltd. Can be used.

  Further, as the light stabilizer (HALS), high molecular weight type hindered amine light stabilizers as shown in the following formulas (8) and (9), and hindered amine light stabilizers as shown in the following formulas (10) to (13). These can be used alone or in combination of two or more. Examples of such light stabilizers include product numbers “TINUVIN 111 FDL”, “TINUVIN 123”, “TINUVIN 144”, and “TINUVIN 292” provided by Ciba Specialty Chemicals.

  Only one of these ultraviolet absorbers and light stabilizers may be included in the clear paint, but it is more preferable to include both of them. At this time, the contents of the ultraviolet absorber and the light stabilizer are appropriately adjusted. However, if these contents are excessive, the clear coating film 4 may be markedly yellowed, and the clear paint is preserved. Sometimes, in a low temperature environment, the ultraviolet absorber or the light stabilizer is likely to crystallize and aggregate, and it may be difficult to regenerate it. Therefore, when the clear paint contains only the UV absorber, the content is preferably in the range of 1 to 3% by weight with respect to the total amount of the resin components in the clear paint, and contains only the light stabilizer. When making it, it is preferable to make the content into the range of 1-3 weight% with respect to the resin component whole quantity. When the ultraviolet absorber and the light stabilizer are used in combination, the content of the ultraviolet absorber is in the range of 0.5 to 3% by weight relative to the total amount of the resin component, and the content of the light stabilizer is the total amount of the resin component. On the other hand, it is preferable that the range is 0.5 to 3% by weight, and the total amount of both is preferably 1 to 5% by weight with respect to the total amount of the resin components.

  When applying clear paint and forming a film, the metal plate 2 to which the hue paint is applied is applied by an appropriate method such as spray coating, bar coater coating, roller curtain coater, curtain flow coater, roll coater, etc. Then, the film can be formed by curing and drying by heating through a hot air drying furnace or a dielectric heating device.

  The clear paint may be applied and formed after the hue paint is formed, but after the clear paint is applied on the wet film of the hue paint by a spray or a curtain coater, the hue paint and the clear paint are applied. The film may be formed by so-called wet-on-wet coating and baking, in which film formation is performed by baking and drying simultaneously. In this case, the adhesion between the formed hue coating 3 and the clear coating 4 is further improved.

  The temperature and time required for curing the clear paint depend on the type of each component and the reaction catalyst used, but are generally in the range of 180 to 250 ° C. and about 10 seconds to several minutes. The amount of coating and the film thickness when forming this clear paint are not particularly limited, but if it is too thick, there is a risk of occurrence of wrinkles during film formation, and the film thickness is usually in the range of 3 to 20 μm. It is preferable.

  The glass transition temperature of the clear coating film 4 thus formed is preferably 10 to 80 ° C. If the glass transition temperature is less than 10 ° C., the coating film hardness may be lowered. If the glass transition temperature exceeds 80 ° C., the workability may decrease, which is not preferable.

  In the coated metal plate 1 such as a coated steel plate configured as described above, the clear coating film 4 has excellent adhesion to the hue coating film 3, and the coated metal plate 1 is exposed to the outdoors for a long time. Even in this case, it is possible to prevent the coating film from being cracked, peeled off, and the like, and to prevent the coating film from being discolored or glossy. This is because even if a resin degradation reaction occurs due to light irradiation or the like, the chain reaction of degradation as described above is blocked by the action of the UV absorber or light stabilizer in the clear coating film, and is also generated by degradation. The physical properties of the resulting product are also less brittle, and it is assumed that these synergistic effects work to exhibit good weather resistance.

  For this reason, the weather resistance excellent in the coating film of the coating metal plate 1 can be provided, without giving a fluororesin coating, and, thereby, the cost reduction of the coating metal plate 1, relaxation of restrictions regarding use, and the time of disposal It is possible to obtain a coated metal plate 1 having excellent weather resistance while preventing adverse effects on the environment and preventing complication of processes during mechanical processing.

(Examples 1-4, Comparative Examples 1-4)
The surface of a molten aluminum-galvanized steel sheet having a thickness of 0.35 mm and an aluminum content of 55% by weight was subjected to a coating-type chromate treatment so as to be 40 mg / m ^{2 in} terms of Cr amount.

  Next, an undercoat paint (“NSC667 Primer” manufactured by Nippon Fine Coatings Co., Ltd.) was applied and baked and cured by heating at a final ultimate plate temperature of 200 ° C. for 30 seconds to form an undercoat film 5 having a film thickness of 4 μm. .

  Next, a hue paint ("NSC300HQ brown color" manufactured by Nippon Fine Coatings Co., Ltd .; polyester type; containing carbon black, titanium oxide, iron oxide yellow and iron oxide red) is applied, and the final reached plate temperature is 220 ° C. Baking and hardening by heating for 2 seconds, film thickness 15μm, carbon black content 0.5% by weight, titanium oxide content 3% by weight, iron oxide yellow content 6% by weight, iron oxide red content 6% by weight A hue coating 3 was formed.

  A clear coating film 4 was formed on the surface of the hue coating film 3 to obtain a coated steel sheet.

  As the clear paint for forming the clear coating film 4, for Examples 1, 3, and 4 and Comparative Examples 1 and 2, a block that is a crosslinking agent for each polyester resin varnish shown in Tables 1 and 2 Isocyanate (“Desmodur VPLS2253” manufactured by Sumika Bayer Urethane Co., Ltd.) was blended so that the equivalent ratio of hydroxyl group to isocyanate group was 1: 1.2, and further as a curing catalyst for 100 parts by weight of the polyester resin. 0.5 parts by weight of an organotin catalyst (“SCAT-24” manufactured by Sansha Co., Ltd.), 0.5 parts by weight of an acrylic resin-based surface conditioner, and 0.2 parts by weight of wax (active ingredient amount) Added.

  Moreover, about Example 2 and Comparative Examples 3 and 4, with respect to each polyester resin varnish shown in Tables 1 and 2, melamine resin varnish which is a crosslinking agent (Dainippon Ink Chemical Co., Ltd. “Super Becamine J” -820-60 ") is blended in an amount of 20 parts by weight with respect to 100 parts by weight of the polyester resin, 0.5 parts by weight of the acrylic resin-based surface conditioner, and 0.2 parts by weight of the wax. (Amount of active ingredient) was added.

  In addition, when a UV absorber ("TINUVIN400" manufactured by Ciba Specialty Chemicals Co., Ltd.) and a light stabilizer ("TINUVIN 144" manufactured by Ciba Specialty Chemicals Co., Ltd.) are blended in the clear paint, the required amount of xylol is previously added. It was mixed after dissolving in

  Then, this clear paint was applied to the surface of the hue paint with a bar coater, and was baked and cured by heating at a final plate temperature of 230 ° C. for 40 seconds to form a clear coating film 4 having the thickness shown in Tables 1 and 2. Formed to obtain a coated steel sheet.

(Example 5)
The hue paint is diluted with paint thinner ("N Thinner 600 (NFC)" manufactured by Nihon Fine Coatings) and adjusted so that the viscosity measured with a No4 Ford cup at room temperature is 20 seconds. Apply and then apply the clear paint immediately with an air spray gun coater with the hue paint wet, and then bake and cure the hue paint and clear paint simultaneously by heating at a final plate temperature of 230 ° C for 40 seconds. I let you. Other than that was carried out similarly to Example 4, and obtained the coated steel plate.

(Comparative Example 5)
A coated steel sheet was obtained in the same manner as in Example 1 except that the clear coating film 4 was not formed.

(Comparative Example 6)
As the coated steel sheet, a fluororesin coated steel sheet ("Everflon" manufactured by Nippon Steel & Steel Co., Ltd.) was used.

<< Accelerated weathering test 1 >>
About the coated steel plate of each Example and a comparative example, the test based on JISK5400 (1990) 9.8 was performed in the state which adhered and covered the polyester tape to the edge part, and the glossiness by a sunshine carbon arc lamp type | formula at this time The retention rate and hue change were measured. At this time, the continuous irradiation test was performed at a black panel temperature of 83 ° C., and the evaluation after 4000 hours was performed according to the following criteria.
Gloss retention ◎… 70% or more.
○: 50% or more and less than 70%.
Δ: 30% or more and less than 50%.
X: Less than 30% hue change A: 3.0 or less.
○: More than 3.0 and 6.0 or less.
Δ: More than 6.0 and 9.0 or less.
X: Over 9.0.

<< Accelerated weather resistance test 2 >>
For the coated steel sheets of each Example and Comparative Example, polyester tape is attached to the edge portion to cover, and an ultra accelerated weathering tester (“SUV-F2” manufactured by Iwasaki Electric Co., Ltd.) and a moisture resistance tester (“CT manufactured by Suga Tester”) -3 type "), a UV irradiation test under conditions of an irradiation time of 24 hours, a black panel temperature of 63 ° C. and an ultraviolet intensity of 100 mW / cm ² , a test time of 24 hours, a bath temperature of 50 ° C., and a bath humidity of 98%. The gloss retention and hue change were measured after repeating the test cycle of 10 cycles of the wet test under the above conditions, and evaluation was performed according to the following criteria.
Gloss retention ◎… 70% or more.
○: 50% or more and less than 70%.
Δ: 30% or more and less than 50%.
X: Less than 30% hue change A: 3.0 or less.
○: More than 3.0 and 6.0 or less.
Δ: More than 6.0 and 9.0 or less.
X: Over 9.0.

《Bending adhesion test》
For the coated steel sheets of each Example and Comparative Example, after bending 180 ° with the coated surface outside at a room temperature of 20 ° C., cellophane adhesive tape was applied to the surface of the bent portion, and was thoroughly rubbed with a finger and adhered. I immediately pulled it off. This test was performed by changing the T number at the time of bending, and the place where the cellophane adhesive tape was peeled off at the bent portion was visually observed and evaluated as follows. The T number is the number of plates having the same thickness as the coated steel plate sandwiched inside the bent portion during bending.
◎… No peeling of coating film by 0T folding.
○: Peeling of the coating occurs at 2T or less.
X: Peeling of the coating occurs at 3T or less.

<Coating hardness>
The hardness of the top coat film of the coated aluminum-zinc alloy plated steel sheet of each example and comparative example was determined in accordance with JIS K5400 (1990) 8.4.2.
○: Cracks in the coating leading to the substrate occur at 3H or higher.
Δ: Cracks in the coating film leading to the substrate occur at H or higher.
X: Cracks in the coating leading to the substrate occur at F or higher.

<Adhesion test>
For each example and comparative example, after the coated steel sheet was immersed in boiling ion exchange water at 98 ° C. or higher for 6 hours and then immersed in ion exchange water at 23 ° C. for 18 hours, this was subjected to 5 cycles. Then, it was dried at room temperature for 2 hours, and then 10 × 10 = 100 film cut grids were made at 1 mm intervals. This coated steel sheet was extruded 6 mm with Erichsen to allow the cellophane adhesive tape to adhere to the coating film, which was immediately peeled off and evaluated according to the following evaluation criteria.
◎… No peeling of clear film.
○: Less than 5% peeling of clear coating film.
X: Peeling of the coating film of 5% or more of the clear coating film or less than the hue coating film occurs.

However, Comparative Example 5 in which no clear coating film was formed was evaluated according to the following criteria.
○: No peeling of coating film.
X: Peeling of the coating film occurred.

《Salt spray test》
For each of the examples and comparative examples, the edge of the coated steel sheet cut to dimensions of 7 cm wide and 15 cm long is sealed with polyester tape, and further, the lower region divided into the upper and lower parts of the coated steel sheet is cut with a cutter knife. Two cut flaws intersecting the cross were formed and used as test samples. This test sample is subjected to a salt spray test for 3000 hours by the test method defined in JIS K 5400 9.1, and the occurrence of white rust and blister is observed on the coating film and the cut part of the flat part, and the following evaluation criteria are used. evaluated.
◎… No abnormalities in the upper area, and rust blisters in the cut area in the lower area are 5 mm or less on one side ○… No abnormalities in the upper area, and rust blisters in the cut area in the lower area are 10 mm or less on one side × Rust blisters in the upper area

It is a schematic sectional drawing which shows an example of the coating metal plate which concerns on this invention.

Explanation of symbols

1 Painted metal plate 2 Metal plate 3 Hue coating 4 Clear coating

Claims (6)

  A polyester film comprising a hue coating (3) on a metal plate (2), and an outer layer of the hue coating (3) comprising a cyclic aliphatic polybasic acid and an aliphatic polyhydric alcohol and containing no aromatic component. A coated metal plate provided with a clear coating film (4) containing a resin and at least one of an ultraviolet absorber and a light stabilizer.   The cycloaliphatic polybasic acid is hexahydrophthalic anhydride, and the aliphatic polyhydric alcohol contains at least one selected from 1,6-hexanediol, neopentyl glycol and hydrogenated bisphenol A. The painted metal plate 1 according to claim 1.   The number average molecular weight of the said polyester resin is 1000-10000, the hydroxyl value is 20-150 mgKOH / g, and the glass transition point is the range of -10-60 degreeC, The coated metal plate of Claim 1 or 2 characterized by the above-mentioned. .   4. The coated metal plate according to claim 1, wherein the ultraviolet absorber is at least one selected from a benzotriazole-based ultraviolet absorber and a hydroxyphenyltriazine-based ultraviolet absorber.   The coated metal plate according to any one of claims 1 to 4, wherein the light stabilizer is a hindered amine light stabilizer. A liquid clear coating is applied to the surface of the uncured hue coating applied to the metal plate (2), and the hue coating and the clear coating are simultaneously formed in this state to form the hue coating (3) and the clear coating. The coated metal plate according to any one of claims 1 to 5, wherein a film (4) is formed.

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