JP5801691B2 - Coated metal plate - Google Patents

Description

  The present invention relates to a coated metal plate.

  Conventionally, a coated metal plate (pre-coated metal plate) obtained by previously coating a metal plate such as a plated steel plate has been widely used for building materials.

  In order to improve the corrosion resistance of the coated metal plate, a primer containing a chromate-based anticorrosive agent is applied and formed on the metal plate (primer treatment) prior to the coating of the metal plate.

  For example, in Patent Document 1, at least one surface of a zinc-based or aluminum-based plated steel sheet that has been subjected to a coating pretreatment is coated with about 5 to 50 wt% chromate-based antibacterial agent in a urea resin composed of a reaction product of polyamine and polyisocyanate. A coated steel sheet comprising a first coating layer having a thickness of 10 to 80 μm containing a rusting agent and a second coating layer having a thickness of 15 to 30 μm mainly composed of a fluororesin formed thereon. Is disclosed.

JP 2000-185259 A

  However, according to the study by the present inventors, it has become clear that the corrosion resistance of the coated metal sheet is not improved as much as expected even when the primer treatment using the chromate-based rust inhibitor is performed. It was. In particular, the metal plate is exposed to the outside at the end face of the coated metal plate, but it is difficult to improve the corrosion resistance at this end face.

  On the other hand, demands for improving the corrosion resistance of coated metal plates have been increasing in recent years. For example, there is a need for coated metal plates that exhibit high corrosion resistance even under the eaves where corrosion is most likely to occur in buildings in coastal areas. ing.

  This invention is made | formed in view of said point, and it aims at providing the covering metal plate with high corrosion resistance especially in an end surface.

The coated metal plate according to the present invention includes a metal plate, a first coating layer that covers the first surface in the thickness direction of the metal plate, and a second coating layer that covers the first coating layer. Because
The first coating layer contains a chromate-based anticorrosive, and the elution rate of chromate ions per length of the end surface from the first coating layer to the water at the end surface of the coated metal plate is 15 to 100 μg / m · h.

In the present invention, further comprising a third coating layer covering a second surface opposite to the first surface of the metal plate, and a fourth coating layer covering the third coating layer,
The third coating layer contains a chromate-based rust inhibitor, and the elution rate of chromate ions per length of the end surface from the third coating layer to the water at the end surface of the coated metal plate is , area by der of 0.1~5μg / m · h.

In this invention, it is preferable that content of the chromate-type rust preventive agent per area in said 3rd coating layer is the range of 1-10 g / m < ² >.

  In the present invention, the third coating layer is at least one resin selected from a urea resin composed of a reaction product of a polyamine and a polyisocyanate, a high molecular weight saturated polyester resin crosslinked with a melamine resin, an epoxy resin, and an aqueous polymer. It is preferable to contain.

  In the present invention, it is preferable that the fourth coating layer is formed of at least one of a polyurethane resin paint and a polyester resin paint.

  In this invention, it is preferable that the thickness of said 1st coating layer is the range of 5-30 micrometers.

  In this invention, it is preferable that the thickness of said 1st coating layer is the range of 5-30 micrometers, and the thickness of said 3rd coating layer is the range of 2-10 micrometers.

In this invention, it is preferable that content of the chromate-type rust preventive agent per area in said 1st coating layer is the range of 5-15 g / m < ² >.

  In the present invention, the first coating layer comprises at least one resin selected from a urea resin made of a reaction product of a polyamine and a polyisocyanate, a polyester resin crosslinked with a melamine resin, an epoxy resin, and an aqueous polymer. It is preferable to include.

  In the present invention, the second coating layer is preferably formed of at least one of a polyurethane resin paint and a polyester resin paint.

  According to the present invention, it is possible to obtain a coated metal plate that has particularly high corrosion resistance at the end face and exhibits high corrosion resistance from the beginning of exposure to the outdoors.

1 is a schematic cross-sectional view showing an embodiment of the present invention.

  Hereinafter, an embodiment of the present invention will be described.

  In the present embodiment, as shown in FIG. 1, the coated metal plate 1 includes a metal plate 2, a first coating layer 3 that covers a first surface in the thickness direction of the metal plate 2, and the first coating. A second covering layer 4 covering the layer 3 is provided. The first coating layer 3 contains a chromate rust inhibitor, and the second coating layer 4 does not contain a chromate rust inhibitor.

  In the present embodiment, the coated metal plate 1 includes a third coating layer 5 that covers the second surface opposite to the first surface of the metal plate 2, and a fourth coating layer that covers the third coating layer 5. The coating layer 6 is further provided. The third coating layer 5 contains a chromate rust inhibitor, and the fourth coating layer 6 does not contain a chromate rust inhibitor. In the present invention, the coated metal plate 1 may not include the third coating layer 5 and the fourth coating layer 6, but the third coating layer 5 and the fourth coating as in the present embodiment. It is preferable to provide the layer 6.

  Although the material in particular is not restrict | limited as the metal plate 2, The steel plate which consists of appropriate steel materials, such as stainless steel, is mentioned. It is also preferable that the metal plate 2 is a steel plate on which plating treatment has been performed, such as a hot-dip galvanized steel plate or a hot-dip aluminum-galvanized steel plate.

  It is also preferable that a chemical conversion treatment layer (not shown) is formed on the metal plate 2 on at least one of the first surface and the second surface as a pretreatment for coating. The chemical conversion treatment layer is a layer formed by a known chemical conversion treatment. Examples of the treatment agent (chemical conversion treatment agent) for forming the chemical conversion treatment layer include chromium such as a chromate treatment agent, a trivalent chromic acid treatment agent, a chromate treatment agent containing a resin, and a trivalent chromic acid treatment agent. Treatment agents; Phosphate treatment agents such as zinc phosphate treatment agents and iron phosphate treatment agents; Oxide treatment agents containing metal oxides such as cobalt, nickel, tungsten, zirconium alone or in combination; Corrosion Treatment agent containing an inhibitor component for preventing oxidization; treatment agent in which a binder component (organic, inorganic, organic-inorganic composite, etc.) and inhibitor component are combined; treatment agent in which an inhibitor component and metal oxide are combined; binder component and silica And a treatment agent in which a sol such as titania or zirconia is combined; a treatment agent in which the components of the exemplified treatment agents are further combined.

As an example of a chromium-containing treatment agent, prepared by blending water and water-dispersible acrylic resin, a silane coupling agent having an amino group, and a source of chromium ions such as ammonium chromate and ammonium dichromate Treatment agents to be used. The water-dispersible acrylic resin is obtained, for example, by copolymerizing a carboxyl group-containing monomer such as acrylic acid and a glycidyl group-containing monomer such as glycidyl acrylate. The chemical conversion treatment layer formed from this chemical conversion treatment agent has high water resistance, corrosion resistance, and alkali resistance, and this chemical conversion treatment layer suppresses the occurrence of white rust and black rust on the metal plate, thereby improving the corrosion resistance. In order to improve corrosion resistance and prevent coloration of the chemical conversion treatment layer, the chromium content in this chemical conversion treatment layer is preferably in the range of 5 to 50 mg / m ² .

  Examples of oxide treating agents containing zirconium oxide include water and water-dispersible polyester urethane resins, water-dispersible acrylic resins, zirconium compounds such as sodium zirconium carbonate, and hindered amines. And a treatment agent prepared in this manner. The water-dispersible polyester-based urethane resin is synthesized, for example, by reacting a polyester polyol with hydrogenated isocyanate and self-emulsifying by copolymerizing dimethylol alkyl acid. Such a water-dispersible polyester-based urethane resin imparts high water resistance to the chemical conversion treatment layer without using an emulsifier, leading to improvement in corrosion resistance and alkali resistance of the metal plate 2.

  Under the chemical conversion treatment layer or instead of the chemical conversion treatment, nickel plating treatment, cobalt plating treatment, or the like may be performed.

  The chemical conversion treatment layer may be formed by a known method such as a roll coating method, a spray method, a dipping method, an electrolytic treatment method, or an air knife method using a chemical conversion treatment agent. After application of the chemical conversion treatment agent, a step such as standing at room temperature or drying or baking with a heating device such as a hot air furnace, an electric furnace, or an induction heating furnace may be added as necessary. A curing method using energy rays such as infrared rays, ultraviolet rays and electron beams may be applied. The temperature and drying time during drying are appropriately determined according to the type of chemical conversion treatment agent used and the required productivity. The chemical conversion treatment layer thus formed becomes a continuous or discontinuous film on the plating layer. The thickness of the chemical conversion treatment layer is appropriately determined according to the type of treatment, required performance, and the like.

  As described above, the first coating layer 3 is formed so as to cover the first surface of the metal plate 2, and the third coating layer 5 is formed so as to cover the second surface of the metal plate 2. When the chemical conversion treatment layer is formed on the metal plate 2, the first coating layer 3 and the third coating layer 5 are formed so as to cover the chemical conversion treatment layer.

  The first coating layer 3 and the third coating layer 5 contain a chromate rust inhibitor. Each of the 1st coating layer 3 and the 3rd coating layer 5 is formed from the coating material (henceforth a primer coating) containing a chromate-type antirust agent. The undercoat paint is preferably not a thermoplastic resin paint such as polyvinyl chloride, but a paint that is cured by heating (baked cross-linking paint).

  The undercoat paint contains a chromate rust inhibitor. An example of a preferable undercoat paint is a urea resin-based paint containing a blocked isocyanate and a polyamine. Urea resin-based paints can be easily thickened, and a thick paint film can be formed with this paint without generating bubbles (bubbles). The blocked isocyanate is a compound obtained by reacting an isocyanate group of polyisocyanate with a blocking agent to block. By using a blocked isocyanate, it becomes possible to make the paint one component.

When a urea resin-based undercoating material is used, when this undercoating material is heated, the blocking agent is dissociated from the blocked isocyanate and the isocyanate group (—NCO) is regenerated. Polymerization occurs when this isocyanate group reacts with an amino group (—NH ₂ ) in the polyamine to form a urea bond (—NHCONH—). Therefore, each of the first coating layer 3 and the third coating layer 5 formed from a urea resin-based undercoat paint contains a urea resin made of a reaction product of polyamine and polyisocyanate.

  In particular, the undercoat paint for forming the first coating layer 3 preferably contains a urea resin and a polyester resin crosslinked with a melamine resin. In this case, chromate ions are particularly easily eluted from the first coating layer 3, and thus the elution rate of chromate ions from the first coating layer 3 can be improved. The undercoat paint for forming the third coating layer 5 preferably contains an epoxy resin. In this case, chromate ions can be eluted from the third coating layer 5 over a long period of time while suppressing the initial chromate ion elution from the third coating layer 5.

  The blocked isocyanate is produced by reacting the polyisocyanate with a suitable blocking agent. Polyisocyanates are roughly classified into aromatic polyisocyanates and aliphatic polyisocyanates. Aromatic polyisocyanates are excellent in reactivity. Aliphatic polyisocyanates are excellent in weather resistance and hardly yellow. Therefore, in general, polyurethane-based paints are used mainly for aliphatic polyisocyanates including alicyclic compounds, which can form coatings with excellent weather resistance. Even in the case of one-component paints, aliphatic polyisocyanates are blocked. The blocked isocyanate obtained by reacting with the agent is the mainstream.

  In this embodiment, since the weather resistance is not necessarily required for the first coating layer 3 and the third coating layer 5, an aliphatic polyisocyanate may be used. However, the aromatic polyisocyanate having excellent reactivity is more preferable because the adhesion between the first coating layer 3 and the third coating layer 5 is improved. Examples of the polyisocyanate suitable for use in the present embodiment include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, naphthalene diisocyanate, and tolidine diisocyanate. Of these, tolylene diisocyanate is preferred from the viewpoint of performance and economy.

  The polyisocyanate may not be a monomer but may be a derivative such as a prepolymer, an adduct (adduct such as trimethylolpropane), an isocyanurate body, and a biuret body. Moreover, you may use combining 2 or more types of polyisocyanate or its derivative (s).

  As the polyisocyanate blocking agent, the dissociation temperature, which is the temperature at which the blocking agent is dissociated from the blocked isocyanate, is 150 ° C. in order to increase the thickness of the first coating layer 3 and the third coating layer 5. What becomes the above is preferable. When a blocking agent having a dissociation temperature lower than 150 ° C. (for example, cresol having a dissociation temperature of 120 ° C. or methyl ethyl ketone oxime having a dissociation temperature of 140 ° C.), a bubble (bubbles) is likely to be generated during baking after coating. Film coating may be difficult. On the other hand, if the dissociation temperature is too high, it is necessary to increase the baking temperature or to increase the baking time. Therefore, the dissociation temperature is preferably 200 ° C. or lower, particularly 180 ° C. or lower. In particular, the dissociation temperature of the blocking agent is preferably 150 to 200 ° C, more preferably 160 to 180 ° C. An example of a particularly preferable blocking agent is ε-caprolactam having a dissociation temperature of 170 ° C.

  The polyisocyanate and the blocking agent can be reacted by a known method. In general, a polyisocyanate in a solvent and a stoichiometric amount or a slightly excess amount of a blocking agent can be reacted under heating. The number average molecular weight of the blocked isocyanate is preferably in the range of 1000 to 4000. Since various products are commercially available as the blocked isocyanate, an appropriate one can be selected from commercially available products.

  The polyamine blended in the undercoat paint may be either an aliphatic (including alicyclic) polyamine or an aromatic polyamine, but is preferably an alicyclic polyamine. As the alicyclic polyamine, for example, an alicyclic polyamine used as a curing agent for an epoxy resin can be used. Specific examples of the alicyclic polyamine include 1-cyclohexylamino-3-aminopropane, diaminocyclohexanes, bis (4-aminocyclohexyl) methane, bis (4-aminocyclohexyl) sulfone, and 3,3′-dimethyl-4. , 4'-diaminodicyclohexylmethane, isophoronediamine and the like. Most preferred is 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane. One or more polyamines can also be used.

  The blending ratio of the blocked isocyanate and the polyamine in the undercoat paint is preferably such that the isocyanate group / amino group molar ratio is in the range of 0.6 to 2.0. This molar ratio is more preferably 0.8 to 1.2.

  As the rust inhibitor, a chromate-based rust inhibitor having excellent rust prevention properties is used. Specific examples of the chromate rust preventive include zinc chromate, strontium chromate, barium chromate, calcium chromate and the like. Among these, only one kind may be used, or two or more kinds may be used in combination.

  Ratio of chromate-based rust preventive to total amount of non-volatile content in undercoat paint (blocking agent portion of blocked isocyanate is not included in non-volatile content) (that is, each of first coating layer 3 and third coating layer 5 The ratio of the chromate-based rust preventive agent is set according to the elution rate of desired chromate ions from each of the first coating layer 3 and the third coating layer 5. The elution rate of chromate ions increases as the proportion of chromate-based anticorrosive increases, and the elution rate of chromate ions decreases as the proportion of chromate-based anticorrosive decreases. The ratio of the chromate rust inhibitor is preferably adjusted within a range of 5 to 50% by mass. Good corrosion resistance of the end face of the coated metal plate 1 is ensured by the proportion of the chromate-based rust inhibitor being 5% by mass or more, and the first coating layer 3 is obtained by this proportion being 50% by mass or less. And the favorable workability and long-term adhesiveness of the 3rd coating layer 5 are ensured. More preferably, the ratio of the chromate rust inhibitor is 20 to 40% by mass.

  When an undercoat paint is prepared, for example, a chromate rust inhibitor is added to a resin solution obtained by dissolving blocked isocyanate and polyamine in an appropriate solvent. An undercoat paint is obtained by uniformly dispersing the agent in the resin liquid. As the solvent, generally an organic solvent can be used. Specific examples of the solvent include hydrocarbon solvents such as toluene and xylene, ester solvents such as ethyl acetate and butyl acetate, ether solvents such as cellosolves, and ketone solvents such as methyl isobutyl ketone, methyl ethyl ketone, isophorone and cyclohexanone. Etc.

  In order to increase the thickness of the first coating layer 3 and the third coating layer 5, it is particularly preferable to use the urea resin-based coating as described above as the undercoat coating. In this case, when forming the undercoat paint, the blocking agent is dissociated from the blocked isocyanate in the undercoat paint, and the generated free polyisocyanate reacts with the polyamine to form a urea resin. Therefore, the 1st coating layer 3 and the 3rd coating layer 5 come to have the structure where the chromate-type rust preventive agent was disperse | distributed in the urea resin produced | generated by reaction of polyisocyanate and polyamine.

  A baked cross-linking type paint other than the urea resin-based paint as described above may be used as the undercoat paint. For example, as the undercoat paint, an epoxy resin paint, a polyester resin paint containing a crosslinking agent, or the like may be used. Also in this case, the first coating layer 3 and the third coating layer 5 having a structure in which the chromate rust inhibitor is dispersed in the cross-linked and cured resin are formed. In this case, the ratio of the chromate-based rust preventive agent to the total amount of nonvolatile components in the undercoat paint (that is, the ratio of the chromate-based rust preventive agent in each of the first coating layer 3 and the third coating layer 5) Is also set according to the desired elution rate of chromate ions from each of the first coating layer 3 and the third coating layer 5. The ratio of the chromate rust inhibitor is preferably adjusted within a range of 1 to 50% by mass.

  As the polyester resin-based paint, the same paint as the polyester resin-based paint used as a top coat described later can be used except that a chromate-based rust inhibitor is added. As an epoxy resin-type coating material, the appropriate thing currently used for the conventional coated steel plate can be used.

  An aqueous polymer paint may be used as the undercoat paint. Examples of the aqueous polymer contained in the aqueous polymer coating include acrylic resin, urethane resin, and polyester resin. Examples of the water-based polymer paint containing an acrylic resin include Ode Color 610 manufactured by Nippon Fine Coatings Co., Ltd. and Almatex manufactured by Mitsui Chemicals. As a water-based polymer paint containing a urethane resin, trade name Superflex manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and the like can be mentioned. As a water-based polymer paint containing a polyester resin, trade name “Hardlen” manufactured by Toyobo Co., Ltd. may be mentioned.

  When such an aqueous polymer paint contains a chromate rust inhibitor, at least a part of the chromate rust inhibitor is dissolved in water in the aqueous polymer paint. A part of the rust preventive pigment is dissolved in water in the state of the paint before drying from this water-based polymer paint, and the chromate-based rust preventive is water-soluble even in the dry paint film formed from this water-based polymer paint. Therefore, the elution rate of chromate ions can be improved.

  When an undercoat paint other than a urea resin paint, such as an epoxy resin paint or a polyester resin paint, is used, the thickness of the coating film that can be formed without generating a crack by one coating is about 20 μm. Compared to the case of resin-based paint, the thickness of the coating film is reduced. Therefore, in order to adjust the amount of chromate-based anticorrosive paint in the first coating layer 3 and the third coating layer 5 to a desired amount, the undercoat paint is applied twice or more as necessary. Also good. Moreover, in order to adjust the amount of chromate-based anticorrosive paint in the first coating layer 3 and the third coating layer 5 to a desired amount, for example, inclusion of a chromate-based anticorrosive agent in the undercoat paint The amount may be adjusted in the range of 25 to 50% by mass, or 30 to 50% by mass.

  The undercoat paint may further contain appropriate components as necessary. Examples of such components include extender pigments (eg, silica, alumina, talc, calcium carbonate, titania, etc.) added for the purpose of adjusting the physical properties of the coating film and reducing costs. When the extender pigment is used, the content of the extender pigment in the undercoat paint is preferably within a range of 20% by mass or less, particularly 10% by mass or less, with respect to the total nonvolatile content in the undercoat paint.

  Undercoat paint contains a small amount of various additives such as antifoaming agents, pigment dispersants, anti-sagging agents, leveling agents, silane coupling agents, catalysts for the reaction of polyisocyanates and polyamides (eg organotin compounds), etc. May be.

  When the undercoat paint is applied onto the metal plate 2, an appropriate application method such as roll coating, curtain flow coating, spray coating, or the like can be employed. When continuous coating is applied to the coiled metal plate 2, a roll coat is generally employed. If the thickness of the coating film does not reach the required thickness after one application, the undercoat may be applied twice or more. When the undercoat paint is applied twice or more, two or more undercoat paints having different compositions may be used.

  After the undercoat paint is applied on the metal plate 2, when the undercoat paint film is heated as necessary, the first coating layer 3 or the third coating layer 5 is formed. The heating temperature of the coating film is preferably in the range where the maximum temperature reaches 180 to 240 ° C., and the heating time of the coating film is preferably in the range of 30 to 70 seconds. If the heating temperature is too low, the resin in the undercoat paint may not be sufficiently cured, and if the heating temperature is too high, the resin in the undercoat paint may be decomposed to deteriorate film properties such as workability. A particularly preferable range of the maximum temperature achieved during heating is 200 to 220 ° C.

  The thickness of each of the first coating layer 3 and the third coating layer 5 is set in accordance with the desired elution rate of chromate ions from each of the first coating layer 3 and the third coating layer 5. . As the thickness of these coating layers increases, the elution rate of chromate ions increases, and as the thickness decreases, the elution rate of chromate ions decreases. The thickness of the first coating layer 3 is preferably set in the range of 5 to 30 μm, and the thickness of the third coating layer 5 is preferably set in the range of 2 to 10 μm.

  In addition, the content of the chromate rust preventive agent per area inside each of the first coating layer 3 and the third coating layer 5 is also the same as that of each of the first coating layer 3 and the third coating layer 5. Is set according to the elution rate of the desired chromate ion from.

In particular, the content of chromate-based corrosion inhibitor per area of the first cover layer 3 is preferably in the range of 5 to 15 g / m ^2, be in the range of 5 to 10 g / m ² Further preferred. In this case, the elution rate of chromate ions from the first coating layer 3 is appropriately controlled. Furthermore, the coated metal plate is prevented from becoming yellowish over time due to the chromate-based rust preventive agent in the first coating layer 3, and the good appearance of the coated metal plate is prolonged. Maintained over time.

The content of the third chromate corrosion inhibitor per area of the covering layer 5 is preferably in the range of 1 to 10 g / m ^2, be in the range of 1 to 5 g / m ² Further preferred. In this case, the elution rate of chromate ions from the third coating layer 5 is appropriately controlled. Furthermore, the coated metal plate is prevented from becoming yellowish over time due to the chromate-based rust inhibitor in the third coating layer 5, and the good appearance of the coated metal plate is prolonged. Maintained over time.

  As described above, the second film is formed on the first film, and the fourth film is formed on the third film. As a coating for forming each of the second coating and the fourth coating (hereinafter referred to as top coating), for example, at least one of a polyurethane coating and a polyester coating not containing a chromic acid rust preventive agent is used. Is done. In this case, even when the first coating and the second coating contain a large amount of chromate-based rust inhibitor, the coated metal plate 1 having excellent workability can be obtained.

  The polyurethane-based paint is a paint containing a polyisocyanate and a polyol, and may be a commercially available product or may be prepared by a known method. The polyurethane-based paint used as the top coat is also preferably a one-component paint in which polyisocyanate is reacted with a blocking agent and contained in the form of blocked isocyanate.

  As the polyisocyanate used in the top coating material, an aliphatic polyisocyanate including an alicyclic type, which is excellent in weather resistance and can form a coating film which hardly causes yellowing, is preferable. Examples of such aliphatic polyisocyanates include hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and the like. The polyisocyanate may be a prepolymer, an adduct, an isocyanurate body, a biuret body, or the like.

  A particularly preferred polyisocyanate is hydrogenated diphenylmethane diisocyanate capable of forming a coating film excellent in processability. However, since this polyisocyanate is quite expensive, other polyisocyanates may be used in combination. In that case, when at least 20% by mass of the total polyisocyanate is hydrogenated diphenylmethane diisocyanate, a coating film excellent in processability can be obtained.

  Polyol components and polyethers (eg, those obtained by ring-opening polymerization of ethylene oxide or propylene oxide using a polyhydric alcohol as an initiator) are generally used as polyol components used in polyurethane-based paints. 1 type (s) or 2 or more types can be used.

  A preferred polyol component is polyester. As this polyester, it is preferable to use a high molecular weight saturated polyester resin. The polyester resin may be a linear polyester obtained by polycondensation of one or two or more saturated aliphatic (including alicyclic) or aromatic dicarboxylic acids and glycols. Examples of suitable dicarboxylic acids are succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid Examples of glycols are ethylene glycol, propylene glycol, butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol , Hydroquinone and the like. In addition to the above reaction components, the saturated polyester resin may also be a trivalent or higher carboxylic acid (eg, trimellitic acid) and / or a trivalent or higher alcohol (eg, glycerin, trimethylolpropane, pentaerythritol, sorbitol, etc.). A branched polyester obtained by copolymerization of

  The polyester resin used as the polyol component of the polyurethane paint preferably has a weight average molecular weight of 5000 to 20000, more preferably 8000 to 15000, and a hydroxyl group content of 1.0 to 4.0% by mass, more preferably 2.0. -3.0 mass% and a glass transition temperature are -30 degreeC-0 degreeC. Thereby, a top-coated polyurethane coating film excellent in both weather resistance and processability is formed.

  A preferred polyurethane paint is a blocked isocyanate containing at least 20% by mass or more of a blocked isocyanate obtained by blocking hydrogenated diphenylmethane diisocyanate with a suitable blocking agent, and a polyester having the above preferred molecular weight, hydroxyl group content and glass transition temperature as a polyol component. And a resin. The molar ratio of isocyanate group / hydroxyl group in the polyurethane-based paint is preferably in the range of 0.6 to 2.0, particularly 0.8 to 1.2.

  A polyester-based paint suitable for use in the top coating contains, for example, a polyester resin as described as a polyol component in the description of the polyurethane-based paint and a melamine resin as a crosslinking agent. The melamine resin is particularly preferably alcohol-modified. Polyester paints are slightly more workable than polyurethane paints, but are economically more advantageous than polyurethane paints.

  The top coating material has 10 masses of inorganic filler such as glass fiber, alumina fiber, boron nitride, and organic filler such as thermoplastic resin beads (eg, acrylic resin or nylon beads, average particle diameter is preferably 1 to 50 μm). You may make it contain in the quantity below%. Thereby, unevenness is formed on the surface of the coating film, the wear resistance of the coating film is improved, and it becomes difficult to be damaged. In particular, in the case of resin beads, the appearance is reduced in gloss and design is imparted.

  It is also preferred that the top coat further contains a color pigment. Similarly to the case of the undercoat paint, the top coat paint may further contain appropriate components (for example, extender pigments, other resins, various additives, and the like) as necessary.

  After the top coating is applied on the first coating layer 3, the coating film of the top coating is heated as necessary to form the second coating layer 4, and the third coating layer 5 is formed on the third coating layer 5. After the top coating is applied, the fourth coating layer 6 is formed by heating the coating film of the top coating as necessary. The heating temperature of the coating film is preferably in the range where the maximum temperature reaches 200 to 240 ° C., and the heating time of the coating film is preferably in the range of 40 to 90 seconds. If the heating temperature is too low, the resin in the top coating material may not be sufficiently cured, and if the heating temperature is too high, the resin in the top coating material may be decomposed to deteriorate film properties such as workability. A particularly preferable range of the maximum temperature achieved during heating is 200 to 220 ° C.

  The top coat can also be applied in the same manner as the undercoat. The thicknesses of the second coating layer 4 and the fourth coating layer 6 are preferably 15 to 40 μm, and more preferably 20 to 25 μm. If the thickness of the second coating layer 4 and the fourth coating layer 6 is too small, the hues of the second coating layer 4 and the fourth coating layer 6 may become unstable, and the corrosion resistance and weather resistance may be insufficient. There are things to do. On the other hand, when the thickness of the 2nd coating layer 4 and the 4th coating layer 6 is too large, workability will fall.

  The coated metal plate 1 may further include a coating layer other than the first to fourth coating layers 6 described above. For example, a fifth coating layer (not shown) may be formed between the first coating layer 3 and the metal plate 2. A sixth coating layer (not shown) may be formed between the first coating layer 3 and the second third coating layer 5. A seventh coating layer (not shown) may be formed between the third coating layer 5 and the metal plate 2. An eighth covering layer (not shown) may be formed between the third covering layer 5 and the fourth covering layer 6. However, the second coating layer 4 and the fourth coating layer 6 are disposed on the outermost layer of the coated metal plate 1. The coating layers other than the first to fourth coating layers 6 (the fifth to eighth coating layers and the like) can be formed from an appropriate resin paint such as an epoxy resin paint.

  In the present embodiment, as described above, the elution rate of chromate ions per length of the end surface from the first coating layer 3 on the end surface of the coated metal plate 1 into the water is in the range of 5 to 100 μg / m · h. It is. The end surface of the coated metal plate 1 is a surface in a direction orthogonal to the thickness direction of the coated metal plate 1, and this end surface includes a cut surface when the coated metal plate 1 is cut. The length of the end surface is the length of the end surface along the direction orthogonal to the thickness direction of the coated metal plate 1.

The elution rate of the chromate ion is a value measured for the coated metal plate 1 before being installed in a building or the like. In measuring the elution rate of chromate ions, for example, a strip-shaped sample cut into a size of 50 mm × 5 mm in plan view is cut out from the coated metal plate 1. When the coated metal plate 1 includes the third coating layer 5, the third coating layer 5 exposed on the end face of the sample is sealed, or a measurement sample without the third coating layer 5 is prepared. Thus, elution of chromate ions from the third coating layer 5 is prevented. Fifteen samples are immersed in ion-exchanged water having a temperature of 25 ° C. and a volume of 70 cm ³ for 24 hours. As a result, chromate ions are eluted from the first coating layer 3 into the water at the end face of the sample to obtain extracted water containing chromate ions. Subsequently, a sample is taken out from the extracted water, and the chromate ion concentration in the extracted water is further measured. The chromate ion concentration is measured using a spectrophotometer. In this case, a strontium chromate aqueous solution having a known concentration (for example, strontium chromate aqueous solutions having concentrations of 1.5 ppm, 10 ppm, and 50 ppm) is measured in advance by a spectrophotometer, and a calibration curve is created based on the result. Using this calibration curve as a reference, the chromate ion concentration in the extracted water can be derived from the measurement result of the extracted water by a spectrophotometer. From the chromate ion concentration in the extracted water, the elution rate of chromate ions per length of the end surface from the first coating layer 3 on the end surface of the coated metal plate 1 into the water is calculated.

  When the elution rate of chromate ions from the first coating layer 3 into the water at the end face of the coated metal plate 1 is 5 μg / m · h or more as described above, the coated building board is installed in a building or the like The chromate ions are quickly eluted from the end face of the coated metal plate 1. For this reason, immediately after the covering metal plate 1 is installed in a building or the like, the end surface of the covering metal plate 1 exhibits high corrosion resistance, and therefore the covering metal plate 1 is hardly corroded. Furthermore, when the elution rate of chromate ions is 100 μg / m · h or less, deterioration of workability due to excess of the chromate-based rust inhibitor in the first coating layer 3 is suppressed. . The elution rate of the chromate ions is preferably in the range of 15 to 90 μg / m · h.

In the present embodiment, as described above, the elution rate of chromate ions per length of the end surface from the third coating layer 5 to the water on the end surface of the coated metal plate 1 is 0.1 to 5 μg / m · The range of h is preferable. This elution rate of chromate ions is also a value measured for the coated metal plate 1 before being installed in a building or the like. In measuring the elution rate of chromate ions, for example, a strip-shaped sample cut into a size of 50 mm × 5 mm in plan view is cut out from the coated metal plate 1. When the covering metal plate 1 includes the first covering layer 3, the first covering layer 3 exposed on the end face of the sample is sealed, or a measurement sample without the first covering layer 3 is prepared. Thus, elution of chromate ions from the first coating layer 3 is prevented from occurring. Fifteen samples are immersed in ion-exchanged water having a temperature of 25 ° C. and a volume of 70 cm ³ for 24 hours. Thereby, chromate ions are eluted from the third coating layer 5 into the water at the end face of the sample to obtain extracted water containing chromate ions. Subsequently, a sample is taken out from the extracted water, and the chromate ion concentration in the extracted water is further measured. The chromate ion concentration is measured using a spectrophotometer. In this case, a strontium chromate aqueous solution having a known concentration (for example, strontium chromate aqueous solutions having concentrations of 1.5 ppm, 10 ppm, and 50 ppm) is measured in advance by a spectrophotometer, and a calibration curve is created based on the result. Using this calibration curve as a reference, the chromate ion concentration in the extracted water can be derived from the measurement result of the extracted water by a spectrophotometer. From the chromate ion concentration in the extracted water, the elution rate of chromate ions per length of the end surface from the third coating layer 5 on the end surface of the coated metal plate 1 into the water is calculated.

  When the coated architectural board is installed in a building or the like when the elution rate of chromate ions from the third coating layer 5 into the water at the end face of the coated metal sheet 1 is 5 μg / m · h or less as described above The chromate ions are slowly eluted from the third layer on the end face of the coated metal plate 1. Therefore, even when the coated metal plate 1 is installed in a building or the like for a long time, chromate ions are supplied to the end surface of the coated metal plate 1 from the third layer, and the end surface of the coated metal plate 1 Exhibits high corrosion resistance, and therefore the coated metal plate 1 is less likely to corrode over a long period of time. That is, the chromate ions are rapidly eluted from the first covering layer 3 so that the coated metal plate 1 is exposed to the outdoors such as being installed on the building, and the corrosion resistance is high at the end face of the covered building plate. In addition, chromate ions are slowly eluted from the third coating layer 5, so that high corrosion resistance is obtained for a long time after the coated metal plate 1 is exposed to the outdoors such as being installed in a building. It will last. Furthermore, when the elution rate of chromate ions is 0.1 μg / m · h or more, a sufficient amount of chromate ions can be supplied to the end face of the coated metal plate 1 to improve corrosion resistance. . The elution rate of this chromate ion is preferably in the range of 2 to 5 μg / m · h.

  The elution rate of chromate ions from each of the first coating layer 3 and the third coating layer 5 depends on the composition of these coating layers, the thickness of these coating layers, and the chromate system in these coating layers. It can be appropriately adjusted depending on the content of the rust inhibitor. For example, as described above, the elution rate of chromate ions increases as the ratio of the chromate rust preventive agent in each of the first coating layer 3 and the third coating layer 5 increases, and the chromate salt anticorrosive agent increases. As the proportion of rusting agent decreases, the elution rate of chromate ions decreases. The elution rate of chromate ions increases as the thickness of each of the first coating layer 3 and the third coating layer 5 increases, and the elution rate of chromate ions decreases as the thickness decreases.

  Further, when the coated metal plate 1 is subjected to 0T folding so that the first coating layer 3 is disposed outside the metal plate 2, the length of the folded portion from the folded portion into the water is reduced. It is preferable that the elution rate of chromate ions per unit is in the range of 0.6 to 11.0 mg / m · h. In this case, the elution rate of chromate ions at the portion of the coated metal plate 1 that has been subjected to the bending process is increased, and therefore, the portion of the coated metal plate 1 that has been subjected to the bending process exhibits high corrosion resistance from the initial stage of installation. Is done. The length of the bent portion is the length of the bent portion along the direction orthogonal to the thickness direction of the coated metal plate 1.

The elution rate of chromate ions at the bent portion is a value measured for the coated metal plate 1 before being installed in a building or the like. In measuring the elution rate of chromate ions, for example, a test sample having a width of 50 mm is subjected to 0T bending, and further, sealing is performed on the end face of the sample to suppress elution of chromate ions. This sample is immersed in ion-exchanged water having a temperature of 25 ° C. and a volume of 70 cm ³ for 24 hours. Thereby, chromate ions are eluted into the water from the part where the coating film cracking of the processed part of the sample occurs, and the extracted water containing chromate ions is obtained. Subsequently, after removing a sample from the extracted water, the chromate ion concentration in the extracted water is measured. The chromate ion concentration is measured using a spectrophotometer. From this measurement result, the amount of chromate ions in the extracted water can be derived, and based on the result, the elution rate of chromate ions per unit length of the bent portion can be calculated.

  The elution rate of chromate ions from the bent portion depends on the composition of the first coating layer 3, the physical properties of the second coating layer 4, etc., the thickness of the first coating layer 3, the first coating layer 3 may be appropriately adjusted depending on the content of the chromate-based rust inhibitor in No. 3. For example, as described above, the elution rate of chromate ions increases as the ratio of the chromate-based rust inhibitor in the first coating layer 3 increases, and chromium decreases as the ratio of the chromate-based rust inhibitor decreases. The elution rate of acid ions is reduced. Further, as the thickness of the first coating layer 3 increases, the elution rate of chromate ions increases, and as the thickness decreases, the elution rate of chromate ions decreases.

[Example 1]
As a metal plate, a 55% aluminum / zinc alloy plated steel plate (thickness 0.8 mm, plating adhesion amount 75 g / m ² per side) was prepared. A chromate treatment agent (product number NRC300, manufactured by Nippon Paint Co., Ltd.) is applied to both sides of this metal plate by bar coating so that the amount of chromium deposited is 30 mg / m ^2, and the maximum plate temperature is 100 ° C. Heated for about 10 seconds.

  By adding strontium chromate and silica to a paint containing a urea resin and a melamine-crosslinked polyester resin (trade name Cenocoil # 2362 manufactured by Cashew Co., Ltd.), an undercoat paint for forming a first coating layer is obtained. Prepared. The ratio of strontium chromate to 20.8% by mass and the ratio of silica to 5% by mass with respect to the total nonvolatile content in the undercoat paint. This undercoat paint was applied to one side of a metal plate by a bar coater, and further heated for 60 seconds so that the maximum plate temperature reached 216 ° C., thereby forming a first coating layer having a thickness of 25 μm.

  An undercoat paint for forming a third coating layer was prepared by adding strontium chromate and silica to an epoxy resin paint (trade name Nippe Super Coat 661, manufactured by Nippon Fine Coatings Co., Ltd.). The ratio of strontium chromate to 33% by mass and the ratio of silica to 5% by mass with respect to the total nonvolatile content in the undercoat paint. This undercoat paint is applied on the surface of the metal plate opposite to the first coating layer side by a bar coater, and further heated for 60 seconds so that the maximum reached plate temperature is 216 ° C. A coating layer was formed.

  A polyester resin coating (manufactured by Nippon Fine Coatings Co., Ltd., product number NSC3800) was prepared as the top coating. This top coat was applied on the first coating layer and the third coating layer by a bar coater, and further heated for 60 seconds so that the maximum plate temperature reached 224 ° C. As a result, a second coating layer having a thickness of 15 μm was formed on the first coating layer, and a fourth coating layer having a thickness of 7 μm was formed on the third coating layer. As a result, a coated metal plate was obtained.

[Examples 2 to 4]
In Example 1, the thicknesses of the first coating layer and the third coating layer were changed as shown in the following table. Other than that was the same method and conditions as Example 1, and obtained the covering metal plate.

[Example 5]
As a metal plate, a 55% aluminum / zinc alloy plated steel plate (thickness 0.8 mm, plating adhesion amount 75 g / m ² per side) was prepared. A chromate treatment agent (product number NRC300, manufactured by Nippon Paint Co., Ltd.) is applied to both sides of this metal plate by bar coating so that the amount of chromium deposited is 30 mg / m ^2, and the maximum plate temperature is 100 ° C. Heated for about 10 seconds.

  An undercoat paint for forming the first coating layer was prepared by adding strontium chromate and silica to an aqueous acrylic resin paint (trade name Odecolor # 610, manufactured by Nippon Fine Coatings Co., Ltd.). The ratio of strontium chromate to 23% by mass and the ratio of silica to 5% by mass with respect to the total nonvolatile content in the undercoat paint. This undercoat paint was applied onto one surface of a metal plate by a bar coater, and further heated for 60 seconds so that the maximum temperature reached 200 ° C., thereby forming a first coating layer having a thickness of 5 μm.

  An undercoat paint for forming a third coating layer was prepared by adding strontium chromate and silica to an epoxy resin paint (trade name Nippe Super Coat 661, manufactured by Nippon Fine Coatings Co., Ltd.). The ratio of strontium chromate to 33% by mass and the ratio of silica to 5% by mass with respect to the total nonvolatile content in the undercoat paint. This undercoat paint is applied to the surface of the metal plate opposite to the first coating layer side by a bar coater, and further heated for 60 seconds so that the maximum plate temperature is 200 ° C. A coating layer was formed.

  A polyester resin coating (manufactured by Nippon Fine Coatings Co., Ltd., product number NSC3800) was prepared as the top coating. This top coat was applied on the first coating layer and the third coating layer by a bar coater, and further heated for 60 seconds so that the maximum plate temperature reached 224 ° C. As a result, a second coating layer having a thickness of 15 μm was formed on the first coating layer, and a fourth coating layer having a thickness of 7 μm was formed on the third coating layer. As a result, a coated metal plate was obtained.

[Examples 6 to 8]
In Example 5, the thicknesses of the first coating layer and the third coating layer were changed as shown in the following table. Other than that was the same method and conditions as Example 5, and obtained the covering metal plate.

[Example 9]
The first coating layer and the third coating layer were formed on the metal plate by the same method and conditions as in Example 1.

  A polyurethane-based resin paint (manufactured by BASF, product number POLYCERAM U HD6000HR) was prepared as the top coat. This top coating was applied to the first coating layer and the third coating layer by a bar coater, and further heated for 60 seconds so that the maximum plate temperature reached 232 ° C. As a result, a second coating layer having a thickness of 15 μm was formed on the first coating layer, and a fourth coating layer having a thickness of 7 μm was formed on the third coating layer. As a result, a coated metal plate was obtained.

[Example 10]
As a metal plate, a 55% aluminum / zinc alloy plated steel plate (thickness 0.8 mm, plating adhesion amount 75 g / m ² per side) was prepared. A chromate treatment agent (product number NRC300, manufactured by Nippon Paint Co., Ltd.) is applied to both sides of this metal plate by bar coating so that the amount of chromium deposited is 30 mg / m ^2, and the maximum plate temperature is 100 ° C. Heated for about 10 seconds.

  First coating layer and third coating layer are formed by adding strontium chromate and silica to paint (trade name Cenocoil # 2362 manufactured by Cashew Co., Ltd.) containing urea resin and melamine-crosslinked polyester resin An undercoat paint was prepared. The ratio of strontium chromate to 20.8% by mass and the ratio of silica to 5% by mass with respect to the total nonvolatile content in the undercoat paint. This undercoat paint is applied on both surfaces of the metal plate by a bar coater, and further heated for 60 seconds so that the maximum plate temperature is 216 ° C., thereby forming a first coating layer having a thickness of 25 μm and a third coating layer having a thickness of 15 μm. A coating layer was formed.

  A polyester resin coating (manufactured by Nippon Fine Coatings Co., Ltd., product number NSC3800) was prepared as the top coating. This top coat was applied on the first coating layer and the third coating layer by a bar coater, and further heated for 60 seconds so that the maximum plate temperature reached 224 ° C. As a result, a second coating layer having a thickness of 15 μm was formed on the first coating layer, and a fourth coating layer having a thickness of 7 μm was formed on the third coating layer. As a result, a coated metal plate was obtained.

[Comparative example]
As a metal plate, a 55% aluminum / zinc alloy plated steel plate (thickness 0.8 mm, plating adhesion amount 75 g / m ² per side) was prepared. A chromate treatment agent (product number NRC300, manufactured by Nippon Paint Co., Ltd.) is applied to both sides of this metal plate by bar coating so that the amount of chromium deposited is 30 mg / m ^2, and the maximum plate temperature is 100 ° C. Heated for about 10 seconds.

  An undercoat paint for forming a first coating layer and a third coating layer is prepared by adding strontium chromate and silica to an epoxy resin paint (trade name Nippe Super Coat 661, manufactured by Nippon Fine Coatings Co., Ltd.). did. The ratio of strontium chromate to 33% by mass and the ratio of silica to 5% by mass with respect to the total nonvolatile content in the undercoat paint. This undercoat paint is applied on both surfaces of the metal plate by a bar coater, and further heated for 60 seconds so that the maximum plate temperature is 200 ° C. Three coating layers were formed.

  A polyester resin coating (manufactured by Nippon Fine Coatings Co., Ltd., product number NSC3800) was prepared as the top coating. This top coat was applied on the first coating layer and the third coating layer by a bar coater, and further heated for 60 seconds so that the maximum plate temperature reached 224 ° C. As a result, a second coating layer having a thickness of 15 μm was formed on the first coating layer, and a fourth coating layer having a thickness of 7 μm was formed on the third coating layer. As a result, a coated metal plate was obtained.

[Evaluation test]
(Evaluation of chromate ion elution rate from the first coating layer)
A strip-shaped sample cut into a size of 50 mm × 5 mm in plan view was cut out from the coated metal plate obtained in each of the examples and comparative examples. The third coating layer exposed on the end face of this sample was sealed. Fifteen samples were immersed in ion-exchanged water having a temperature of 25 ° C. and a volume of 70 cm ³ for 24 hours to obtain extracted water containing chromate ions. Subsequently, a sample was taken out from the extracted water, and the chromate ion concentration in the extracted water was further measured with a spectrophotometer. This chromate ion concentration was derived on the basis of a calibration curve obtained from the results of measuring strontium chromate aqueous solutions having a concentration of 1.5 ppm, 10 ppm, and 50 ppm with a spectrophotometer in advance. From the chromate ion concentration in the extracted water, the elution rate of chromate ions per length of the end surface from the first coating layer on the end surface of the coated metal plate into the water was calculated.

(Evaluation of chromate ion elution rate from the third coating layer)
In the chromate ion elution rate evaluation from the first coating layer, the first coating layer was sealed without sealing the third coating layer exposed on the end face of the sample. Otherwise, the chromic acid per unit length of the end surface from the third coating layer to the water at the end surface of the coated metal plate in the same method and conditions as the evaluation of the elution rate of chromate ions from the first coating layer. The elution rate of ions was calculated.

(Corrosion resistance evaluation)
A sample having a size of 100 mm × 300 mm in plan view was cut out by cutting the coated metal plate obtained in each example and comparative example. The sample for end face part evaluation was obtained by sealing the end face in each short side (side with a length of 100 mm) of this sample.

  Moreover, the sample of the dimension of 50 mm x 100 mm of planar view was cut out by cut | disconnecting the covering metal plate obtained by each Example and the comparative example. This sample was subjected to 2T bending or 4T bending so that the first coating layer was disposed outside the metal plate. Further, the end face of this sample was sealed. As a result, a sample for evaluating the 2T bent portion and a sample for evaluating the 4T bent portion were obtained.

  Each sample for end face part evaluation, 2T bending process part evaluation, and 4T bending process part evaluation was exposed outdoors in Nago City, Okinawa Prefecture and Noto City, Ishikawa Prefecture under the following conditions.

  Eaves condition: Place the sample so that the part where the corrosion is evaluated faces downward, and surround the part where the sample is evaluated for corrosion with a wall of about 300mm, so that the influence of wind, temperature, etc. The raindrops were not directly applied to the sample.

  Normal conditions: The sample was placed so that the site where its corrosion is evaluated faces south at an angle of 30 ° to the ground.

The degree of corrosion of each sample was confirmed when 1 year passed (short term) from the start of exposure and when 10 years passed (long term). As a result, the degree of corrosion of the end face of the sample for end face evaluation was evaluated according to the following criteria.
A: The swollen width is 0 mm or more and less than 1 mm.
○: The swelling width is 1 mm or more and less than 2 mm.
Δ: The swelling width is 2 mm or more and less than 3 mm.
X: The swollen width is 3 mm or more.

Moreover, about each sample for 2T bending process part evaluation and 4T bending process part evaluation, the degree of corrosion of a bending part was evaluated by the following references | standards.
A: The swelling rate is less than 5%.
○: The swelling rate is 5% or more and less than 15%.
Δ: The swelling rate is 15% or more and less than 30%.
X: The swelling rate is 30% or more.

  The swelling rate is the ratio of the product of the density and area of swelling in this processed part to the area of the processed part to be evaluated.

  In addition, each example and comparative example were evaluated with two or more samples, and when there was a difference in evaluation for each sample, two types of evaluations were listed in the table.

DESCRIPTION OF SYMBOLS 1 Coated metal plate 2 Metal plate 3 1st coating layer 4 2nd coating layer 5 3rd coating layer 6 4th coating layer

Claims (9)

A metal plate, a first coating layer covering a first surface in the thickness direction of the metal plate, and a second coating layer covering the first coating layer, the first surface of the metal plate a third coating layer covering the second surface opposite to a the third fourth further coated metal sheet Ru and a coating layer which covers the covering layer,
The first coating layer contains a chromate-based anticorrosive, and the elution rate of chromate ions per length of the end surface from the first coating layer to the water at the end surface of the coated metal plate is , 15 ~100μg / m · Ri range der of h, the third coating layer contains a chromate-based anticorrosive agent, in water from the third coating layer at the end face of the coated metal plate, coated metal sheet elution rate of chromate ions per length of the end face, characterized in range der Rukoto of 0.1~5μg / m · h. The third content of the chromate-based anticorrosive agent per area of the coating layer is coated metal plate according to claim 1 in the range of 1 to 10 g / m ^2. The third coating layer contains at least one resin selected from a urea resin made of a reaction product of a polyamine and a polyisocyanate, a high molecular weight saturated polyester resin crosslinked with a melamine resin, an epoxy resin, and an aqueous polymer. 3. The coated metal plate according to 1 or 2 . The fourth coating layer, coated metal plate according to any one of claims 1 to 3 is formed from at least one of a polyurethane resin paint and polyester resin paint. The coated metal plate according to any one of claims 1 to 4 , wherein the thickness of the first coating layer is in the range of 5 to 30 µm. The range of the first thickness of the coating layer is 5 to 30 [mu] m, coated metal sheet according to any one of the third coating thickness of layer is in the range of 2~10μm claims 1 to 4. The first content of the chromate-based anticorrosive agent per area of the coating layer is coated metal plate according to any one of claims 1 to 6 in the range of 5 to 15 g / m ^2. The said 1st coating layer contains at least 1 type of resin chosen from the urea resin which consists of the reaction product of a polyamine and polyisocyanate, the polyester resin bridge | crosslinked with the melamine resin, an epoxy resin, and an aqueous polymer. The covering metal plate as described in any one of thru | or 7 . The coated metal plate according to any one of claims 1 to 8 , wherein the second coating layer is formed of at least one of a polyurethane resin paint and a polyester resin paint.

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