JP6624346B2 - Painted metal plate and method for manufacturing coated metal plate - Google Patents

Description

The present invention relates to a coated metal plate and a method for manufacturing a coated metal plate.
Priority is claimed on Japanese Patent Application No. 2017-209460 filed on October 30, 2017, the content of which is incorporated herein by reference.

  Instead of conventional painted products that are painted after processing, painted metal plates coated with coatings are used for automobiles, home appliances, building materials, civil engineering, machinery, furniture, containers, etc. It is becoming. In general, such a coated metal plate is cut and press-molded after coating a metal plate with a paint.

  Since the coated metal plate is mainly used as an exterior material and is exposed to various solvents and chemicals, it often has solvent resistance and chemical resistance. Since it is an exterior material, there are usually many painted metal plates that are colored, and the film thickness of such a coating film is relatively thick because of concealment for color tone. On the other hand, in the case of a metal-coated metal plate in which the appearance of the metal plate as the base material is designed as it is, it is necessary to apply a clear coating containing no coloring pigment. In such a case, by reducing the thickness of the clear coating film, the coated metal plate becomes excellent in metal appearance. Also, from the viewpoints of productivity and commerciality, the thinner the film thickness of the clear coating film, the better.

  Generally, it is required that the coating film does not deteriorate or discolor due to chemicals as chemical resistance. However, when the thickness of the coating film is small, there is a problem that the chemicals penetrate to the plating interface and dissolve the plating, rather than the coating film is deteriorated by the chemicals. In the case of colored coating, even if the metal is discolored by chemicals, the appearance does not become abnormal, the metal dissolves and corrosion products are generated, and the generated corrosion products cause the coating to swell. Abnormal appearance. On the other hand, in the case of the clear coating, the appearance is regarded as abnormal when the metal changes color. That is, in the clear coating, it is necessary that the chemical components do not reach the metal. Such a property is called chemical penetration resistance.

Conventionally, several examples of a coated metal plate having excellent chemical resistance have been reported.
For example, Patent Literature 1 below discloses a technique for coating a metal plate by applying a paint containing a solvent-soluble fluororesin as a main component.

  In addition, Patent Document 2 below discloses a process using a polyester resin having a high glass transition temperature, a polyester resin having a low glass transition temperature, and a coating film using an aminoformaldehyde resin to provide processability, stain resistance, and scratch resistance. A technique of a coated metal plate having excellent resistance and chemical resistance is disclosed.

  Patent Document 3 below discloses a technique of a pre-coated metal having excellent stain resistance, chemical resistance, weather resistance and workability by coating a polyacryl resin on an upper layer and a polyester resin on a lower layer. Have been.

  In addition, Patent Document 4 below discloses a technique of a coated metal plate having excellent workability, corrosion resistance (particularly, end face corrosion resistance), chemical resistance, and the like by using a coating film in which a specific polyurethane resin and a polyester resin are mixed. Have been.

  Patent Document 5 below discloses a technique of a metal plate having excellent bending workability by using a coating film in which melamine resin particles having a particle size of 50 nm or less are dispersed.

  Patent Document 6 below discloses a technique of thickening an aminoblast resin in a surface layer of a coating film using an aminoblast resin such as a melamine resin.

Japanese Patent Application Laid-Open No. 5-111675 Japanese Patent Laid-Open No. Hei 7-331167 Japanese Patent Application Laid-Open No. 7-313929 JP 2013-213281 A JP 2005-53002 A Japanese Patent Application Laid-Open No. 2006-175815

  However, the fluororesin used in the technique of Patent Document 1 is expensive and is not industrially preferable.

  As described in Patent Document 2, there is suggested that a self-condensation reaction of a melamine resin as a cross-linking agent is used in forming a coating film using a solvent-based paint. However, what is disclosed therein does not consider the conditions for surface concentration necessary for forming the barrier layer. It is also disclosed that an amine compound is added for surface concentration, but the effect is such that it affects the distribution density of the melamine self-condensed particles formed. Therefore, the structure of the coating film obtained from these conditions is such that particles of coarse self-condensate of about 50 to 100 μm are dispersed in the coating film, and surface concentration as distribution density of the particles is recognized. The effect of improving the chemical penetration resistance of the coating film was limited.

  The polyacrylic resin used in the technique of Patent Document 3 is inferior in workability, and when the coating film disclosed in Patent Document 3 is a clear coating film, the barrier property is not sufficient. And furthermore, poor in chemical penetration resistance.

  The coating film disclosed in Patent Document 4 does not have sufficient barrier properties, and further has poor chemical penetration resistance.

  When the melamine resin particles are dispersed in a coating film as in the technique of Patent Document 5, the coating film has poor solvent resistance.

  In the technique disclosed in Patent Document 6, the melamine resin particles in the coating film have a large particle size, do not have sufficient barrier properties, and have poor chemical penetration resistance.

  As described above, Patent Documents 1 to 6 do not disclose a technique for obtaining a coated metal plate having excellent metal appearance, chemical penetration resistance, and solvent resistance while suppressing manufacturing costs.

  Therefore, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a coated metal plate having excellent metal appearance, chemical permeation resistance, and solvent resistance, in which production costs are suppressed. And a method for manufacturing such a coated metal sheet.

The present inventors have conducted intensive studies on the above problems, and as a result, formed a resin coating containing at least one surface of a metal plate having a first site having a urethane bond skeleton and a second site having a triazine ring skeleton. , By appropriately controlling the glass transition temperature of such a resin coating and the state of the second portion in the resin coating, the metal appearance, chemical permeation resistance and solvent resistance can be reduced while suppressing production costs. We arrived at the ability to produce excellent coated metal sheets.
The gist of the present invention completed on the basis of such knowledge is as follows.

(1) A coated metal plate according to one embodiment of the present invention includes a metal plate, and a first coating film that is located on at least one surface of the metal plate and contains a resin. It has a first site having a urethane bond skeleton and a second site having a triazine ring skeleton. The first coating has a glass transition temperature of 85 ° C or more and 170 ° C or less. When the second portion is stained with osmium oxide and observed at a magnification of 100,000 times using a transmission electron microscope, a dispersed second portion in which particles having a number average particle size of 5 to 20 nm are dispersed, A concentrated second portion, which is present at a position from the surface of one coating film to a depth of 15 nm and in which particles having a number average particle size of 5 nm or more are not observed, is observed.
(2) The coated metal plate according to the above (1), wherein the N concentration N1 at a depth of 0.2 μm from the surface of the first coating film is from the interface between the first coating film and the metal plate. N1 / N2, which is the ratio to the N concentration N2 at a depth of 0.2 μm on the first coating film side, may be 1.2 or more.
(3) In the coated metal plate according to the above (1) or (2), the first coating may have a plurality of the concentrated second portions.
(4) The coated metal plate according to any one of the above (1) to (3) further includes a second coating between the first coating and the metal plate; The glass transition temperature may be equal to or lower than the glass transition temperature of the first coating film.
(5) In the coated metal plate according to the above (4), the second coating film may contain a resin and have a urethane bond skeleton.
(6) In the coated metal plate according to the above (4) or (5), the second coating film may contain a resin and have an epoxy group.
(7) In the coated metal plate according to any one of the above (4) to (6), the second coating film may contain a resin and have a siloxane bond.
(8) In the coated metal sheet according to any one of the above aspects (4) to (7), the second coating film is any one selected from the group consisting of P, V, Ti, Si, and Zr. The above elements may be included.
(9) In the coated metal plate according to any one of the above (4) to (8), the glass transition temperature of the first coating is higher than the glass transition temperature of the second coating by 5 ° C. or more. Is also good.
(10) In the coated metal sheet according to any one of the above (4) to (9), the thickness of the second coating film may be 0.5 μm or more and 15 μm or less.
(11) In the coated metal plate according to any one of the above (1) to (10), the thickness of the first coating film may be 0.5 μm or more and 15 μm or less.
(12) In the coated metal plate according to any one of the above aspects (4) to (11), at least one of the first coating film and the second coating film may contain a coloring agent.
(13) In the coated metal plate according to any one of the above (4) to (12), the second coating film may contain a black pigment as a coloring agent.
(14) In the coated metal plate according to any one of the above (1) to (13), a texture may be formed on at least one surface of the metal plate.

(15) A method for manufacturing a coated metal plate according to another aspect of the present invention is a method for manufacturing a coated metal plate having a predetermined first coating film on at least one surface of the metal plate, wherein at least one of the metal plates is provided. A first resin containing, on one surface, a polyurethane resin (a) containing an anionic functional group and having a glass transition temperature of 75 ° C. or more and 160 ° C. or less, a triazine ring-containing water-soluble curing agent (b), and an aqueous solvent; Applying a paint, forming the first coating by heating the metal plate coated with the first coating, when forming the first coating, the first coating applied the first coating The metal plate coated with the first paint is heated so that the heating time from the start of heating the metal plate to the maximum temperature is 1 second or more and 30 seconds or less, and cooling from the maximum temperature to 30 ° C. So that the time is between 0.1 and 5 seconds The applied the metal plate of the first coating to cool.
(16) In the method for producing a coated metal sheet according to (15), the triazine ring-containing water-soluble curing agent (b) may be a melamine resin containing an imino group.
(17) In the method for producing a coated metal plate according to the above (15) or (16), the first coating composition contains the content (Wa) of the polyurethane resin (a) based on the total solid content and the content based on the total solid content. The total content (Wa) + (Wb) of the content (Wb) of the triazine ring-containing water-soluble curing agent (b) satisfies the following formula (I), and The ratio (Wb) / (Wa) of the content (Wa) of the polyurethane resin (a) and the content (Wb) of the triazine ring-containing water-soluble curing agent (b) with respect to the total solid content is as follows: Formula (II) may be satisfied.
90% by mass ≦ (Wa) + (Wb) ≦ 100% by mass Formula (I)
0 <(Wb) / (Wa) ≦ 1 Expression (II)
(18) The method for producing a coated metal plate according to any one of the above (15) to (17), wherein the coated metal further has a predetermined second coating film between the metal plate and the first coating film. A method for manufacturing a board, comprising: a polyurethane resin (c) having a glass transition temperature equal to or lower than a glass transition temperature of the polyurethane resin (a), an epoxy resin (d), and a silane coupling prior to the application of the first paint. An agent (e) and at least one of a rust preventive (f) containing at least one element selected from the group consisting of P, V, Ti, Si and Zr, and an aqueous solvent. The second paint may be applied on at least one surface of the metal plate, and the second paint film may be formed by heating the metal plate to which the second paint is applied.
(19) In the method for producing a coated metal sheet according to the above (18), the glass transition temperature of the polyurethane resin (c) may be 5 ° C. or lower than the glass transition temperature of the polyurethane resin (a) .
(20) In the method for producing a coated metal sheet according to any one of the above aspects (15) to (19) , the heating is performed at a temperature of 40 to 100 ° C. for 1 to 20 seconds, and then for 1 to 10 seconds. The heating may be performed up to over 200 ° C. during the heating time.

  As described above, according to the present invention, it is possible to obtain a coated metal sheet which is excellent in metal appearance, chemical penetration resistance, and solvent resistance, in which the production cost is suppressed.

It is explanatory drawing which showed typically an example of the structure of the coating metal plate which concerns on embodiment of this invention. It is explanatory drawing which showed typically an example of the structure of the coating metal plate concerning the embodiment. It is explanatory drawing which showed typically another example of the structure of the coating metal plate concerning the embodiment. It is explanatory drawing which showed typically another example of the structure of the coating metal plate concerning the embodiment. It is explanatory drawing for demonstrating the upper layer coating film of the coating metal plate which concerns on the same embodiment. It is a flowchart for demonstrating an example of the flow of the manufacturing method of the coating metal plate concerning the embodiment. 9 is a microscope image when the upper layer coating film of Test Example 3 is observed with a transmission electron microscope. 10 is an element mapping image of osmium when the upper coating film of Test Example 3 is observed with a transmission electron microscope. 9 is a microscope image when the upper layer coating film of Test Example 3 is observed with a transmission electron microscope. 9 is a microscope image when the upper layer coating film of Test Example 3 is observed with a transmission electron microscope. It is explanatory drawing for demonstrating the upper layer coating film in case a several thickening part is formed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(Overall configuration of painted metal sheet and its outline)
First, an overall configuration of a coated metal plate according to an embodiment of the present invention will be described with reference to FIGS. 1A to 3. 1A and 1B are explanatory views schematically showing an example of the structure of the coated metal plate according to the present embodiment. FIGS. 2A and 2B are other diagrams of the structure of the coated metal plate according to the present embodiment. It is explanatory drawing which showed an example typically. FIG. 3 is an explanatory diagram for describing the upper coating film of the coated metal plate according to the present embodiment.

  As schematically shown in FIG. 1A, the coated metal plate 1 according to the present embodiment has an upper coating film 13 as a first coating film on one surface of a metal plate 11 serving as a base material. Further, as schematically shown in FIG. 1B, a lower coating film 15 may be provided between the metal plate 11 and the upper coating film 13 as a second coating film.

  Further, as schematically shown in FIGS. 2A and 2B, in the coated metal plate 1 according to the present embodiment, the upper coating film 13 may be provided on both surfaces of the metal plate 11, or the upper coating film may be provided. 13 and the lower coating film 15 may be provided on both surfaces of the metal plate 11.

  Note that the configuration of the coated metal plate 1 according to the present embodiment is not limited to the configuration illustrated in FIGS. 1A to 2B. For example, the upper coating film 13 and the lower coating film are formed on one surface of the metal plate 11. A configuration in which the upper coating film 13 or the lower coating film 15 is provided on the other surface of the metal plate 11 is also feasible.

The upper coating film 13 which is an example of the first coating film has a first portion having a urethane bonding skeleton (hereinafter also referred to as “urethane portion”) and a second portion having a triazine ring skeleton (hereinafter also referred to as “triazine portion”). .)). The glass transition temperature of the upper layer coating film 13 is 80 ° C. or more and 170 ° C. or less.
Further, as schematically shown in FIG. 3, the second portion having a triazine ring skeleton was stained with osmium oxide and observed at a magnification of 100,000 times using a transmission electron microscope. The particles are present at the dispersed second site (the reference numeral 101 in FIG. 3) in which the above particles are dispersed and at a position from the surface of the upper layer coating film 13 to a depth of 15 nm, and particles having a number average particle diameter of 5 nm or more are not observed. Both the concentrated second portion (reference numeral 103 in FIG. 3) is present.

  The coated metal sheet 1 according to the present embodiment is a coated metal sheet excellent in metal appearance, chemical penetration resistance, and solvent resistance without using an expensive resin such as a fluororesin, by the above configuration. . The reason is presumed as follows.

  First, in order for the glass transition temperature of the upper layer coating film 13 to be 80 ° C. or more and 170 ° C. or less, it is necessary that the urethane portion has a considerably high glass transition temperature. Since the urethane portion has a high glass transition temperature, a high cohesive force is generated in the urethane portion when the upper coating film 13 is formed. As a result, the triazine moiety is not condensed alone, the triazine moiety is dispersed in the urethane moiety, and the urethane moiety and the triazine moiety are likely to be preferentially bonded. When the triazine moiety having high solvent resistance is bonded to the urethane moiety, a three-dimensional network structure is formed. As a result, the upper coating film 13 has improved barrier properties (that is, resistance to chemical penetration). In order to obtain such characteristics, in the present embodiment, the glass transition temperature of the upper layer coating film 13 is set to 80 ° C. or more and 170 ° C. or less.

  In addition, the triazine portion forms a domain in the upper coating film 13 and is dispersed in a granular form (reference numeral 101 in FIG. 3), and is concentrated on the surface layer of the upper coating film 13 to form a concentrated portion 103. The triazine moiety having high solvent resistance increases the solvent resistance of the upper coating film 13. Moreover, as described above, when a high cohesive force is generated in the urethane site when forming the upper layer coating film 13, the urethane site and the triazine site are likely to be preferentially bonded, and as shown schematically in FIG. Then, the finely divided granular triazine portion (hereinafter, also referred to as “triazine granular material 101”) is in a state of being concentrated on the surface layer of the upper coating film 13. From this point, the solvent resistance of the upper layer coating film 13 is further improved.

  When the finely divided triazine sites (triazine granules 101) are concentrated on the surface layer of the upper coating film 13, light scattering by the triazine sites is suppressed, and the transparency of the upper coating film 13 is improved. In addition, the glossiness of the underlying metal plate 11 is easily recognized from the outside. Thereby, in the coated metal plate 1 according to the present embodiment, the metal appearance is also improved.

  As described briefly above, the coated metal plate 1 according to the present embodiment has the above-described configuration, without using an expensive resin such as a fluororesin, and has a metal appearance, chemical penetration resistance, and solvent resistance. It is presumed to have excellent properties.

  Hereinafter, each configuration of the coated metal plate 1 according to the present embodiment will be described in detail.

<About the metal plate 11>
In the coated metal plate 1 according to the present embodiment, various commonly known metal plates can be used as the metal plate 11. Specifically, examples of the metal plate 11 include various metal plates and alloy plates such as a steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a titanium plate, and a copper plate. In the coated metal plate 1 according to the present embodiment, various types of plating (not shown) may be applied to the surface of the metal plate 11. The type of plating is not particularly limited, and examples thereof include zinc plating, aluminum plating, copper plating, nickel plating, and alloy plating thereof.

  In particular, when the metal plate 11 is a plated steel sheet, the chemical permeation resistance tends to be inferior. Therefore, the effect of improving the chemical permeation resistance by providing the upper coating film 13 is more effective.

  The galvanized steel sheet used as the metal sheet 11 is not particularly limited, and is a galvanized steel sheet, an electrogalvanized steel sheet, a zinc-nickel alloy-coated steel sheet, a galvannealed galvanized steel sheet, an aluminized steel sheet, an aluminum-zinc steel sheet. Various generally known plated steel sheets such as an alloyed plated steel sheet and a stainless steel sheet can be applied. In particular, the use of a galvanized steel sheet as the metal plate 11 is more preferable because the corrosion resistance is further improved. Here, the zinc-based plated steel sheet refers to a zinc-coated zinc-plated steel sheet, a zinc-nickel alloy-plated steel sheet, a hot-dip galvanized steel sheet, an aluminum-zinc alloy-plated steel sheet, or the like. It refers to a plated steel sheet in which an alloy with a metal is plated on the surface of the steel sheet. The galvanized steel sheet may be any of a hot-dip galvanized steel sheet, an electrogalvanized steel sheet, and the like.

  In addition, on the surface of the metal plate 11, in order to further improve the design of the coated metal plate 1 according to the present embodiment, a satin finish, a rough surface, a streak (hairline), a cloth (satin), a hammer (hammer), and the like are provided. Various textures may be formed. In the coated metal plate 1 according to the present embodiment, since the transparency of the upper layer coating film 13 is improved by the above-described configuration, the above-described texture is formed on the surface of the metal plate 11. In addition, the metallic feeling recalled by the texture is easily recognized from the outside.

<About upper layer coating film 13>
As described above, the upper coating film 13 of the coated metal plate 1 according to the present embodiment includes a urethane site (a first site having a urethane bond skeleton), a triazine site (a second site having a triazine ring skeleton), and And a resin coating containing:

Hereinafter, each part included in the upper layer coating film 13 will be described.
The urethane bond skeleton of the urethane site in the upper coating film 13 can be confirmed by analyzing the upper coating film 13 by Fourier transform infrared spectroscopy and detecting a vibration peak attributed to the urethane bond. .

  The triazine ring skeleton of the triazine moiety is a skeleton derived from a triazine ring contained in the melamine resin. That is, the triazine site is a site derived from the triazine ring contained in the melamine resin.

  As described earlier with reference to FIG. 3, the triazine site was stained with osmium oxide and observed with a transmission electron microscope at a magnification of 100,000 to find that the particle had a number average particle size of 5 to 20 nm. And a concentrated second portion in which particles having a number average particle size of 5 nm or more are present at a position from the surface of the upper layer coating film 13 to a depth of 15 nm and particles having a number average particle size of 5 nm or more are not observed. Is done.

Here, as schematically shown in FIG. 3, the enriched portion 103 according to the present embodiment has a range of a position from the surface layer of the upper coating film 13 toward the metal plate 11 to a depth d (15 nm). Exists within.
Note that “the triazine portion is concentrated in the surface layer of the upper coating film 13” means that a granular triazine portion (that is, a triazine granular material) is provided on the surface side of the upper coating film 13 opposite to the interface with the metal plate 11. Object 101) is unevenly distributed in layers. In other words, it indicates that the region of the granular triazine site unevenly distributed in a layer shape constitutes the surface layer of the upper coating film 13.
Here, “the triazine portion is unevenly distributed in a layer to form the enriched portion 103” means that the average concentration (average content) of the triazine portion in the region where the triazine portion is unevenly distributed is other than the unevenly distributed portion. This means that the average concentration of the triazine moiety in the region is 1.2 times or more.

  Here, the triazine portion according to the present embodiment is dispersed in the upper coating film 13 as particles having a number average particle size of 5 nm or more and 20 nm (in other words, the number average particle size of the triazine particulate 101 is 5 nm or more and 20 nm or less). ) And is concentrated in the surface layer within a depth of 15 nm from the surface of the upper coating film 13 (in other words, the depth d in FIG. 3 is 15 nm or less).

  Here, that the triazine portion is concentrated in the surface layer within a depth of 15 nm from the surface of the upper coating film 13 is unevenly distributed in a layer on the surface side of the upper coating film 13 opposite to the interface with the metal plate 11. This indicates that the region of the granular triazine portion exists within a depth of 15 nm from the surface of the upper coating film 13. In other words, it indicates that the region of the granular triazine site unevenly distributed in the layer structure constitutes the surface layer of the upper coating film 13 and has a thickness of 15 nm or less.

  When the number average particle size of the granular triazine moiety (that is, the triazine particulate 101) is less than 5 nm, the chemical permeation resistance may decrease. On the other hand, when the number average particle size of the triazine portions dispersed in a particle form exceeds 20 nm, the metal appearance and chemical permeation resistance of the coated metal plate 1 are reduced, or the metal appearance, chemical permeation resistance and workability are reduced. Sometimes. Here, when the workability of the coated metal plate 1 is reduced, cracks and the like occur in the upper layer coating film 13, and the chemical permeation resistance and the solvent resistance are also reduced. The number average particle size of the triazine sites (triazine granules 101) dispersed in a granular form is more preferably 5 nm or more and 15 nm or less from the viewpoint of metal appearance, chemical permeation resistance and solvent resistance.

  When the granular triazine portion is not concentrated in the surface layer of the upper coating film 13 (that is, when the concentrated portion 103 does not exist), the metal appearance and the solvent resistance may be reduced. Further, when the granular triazine portion is concentrated beyond the depth of 15 nm from the surface of the upper coating film 13 (that is, the depth where the concentrated portion 103 exists is more than 15 nm from the surface of the upper coating film 13). ), The workability may be reduced. When the workability of the coated metal plate 1 is reduced, cracks and the like occur in the upper layer coating film 13, and the chemical permeation resistance and the solvent resistance are also reduced.

  As shown in FIG. 6, it is preferable that a plurality of concentrated portions 103 are formed in the upper layer coating film 13. By forming a plurality of concentrated portions 103, the barrier properties are further improved, and suitable chemical resistance can be obtained. In order to form the thickened portion 103, a heating method in an upper layer coating film forming step described below is important. This will be described later.

Here, in the upper coating film 13 according to the present embodiment, the N concentration N1 at a depth of 0.2 μm from the surface of the upper coating film 13 and the upper coating film 13 from the interface between the upper coating film 13 and the metal plate 11 N1 / N2, which is the ratio to the N concentration N2 at a depth position of 0.2 μm on the side, is 1.2 or more.
By setting N1 / N2 to 1.2 or more, it is possible to more reliably improve the metal appearance and the solvent resistance. N1 / N2 is more preferably 1.5 or more and 10 or less.

Next, various analysis methods for the triazine site in the upper coating film 13 will be described.
First, the upper coating film 13 to be analyzed is dyed with osmium oxide. Thereby, the triazine site in the upper coating film 13 is selectively dyed. Next, using a microtome, a focused ion beam processing device, or the like, the coating film dyed with osmium oxide is cut along the film thickness direction to prepare a coating film sample whose cross section can be observed. Subsequently, the thin film sample is observed at a magnification of 100,000 times using a transmission electron microscope. In this observation, the triazine site in the thin film sample is observed black in the STEM-BF (bright field) image and white in the STEM-HAADF (dark field) image.

  The triazine site in the upper layer coating film 13 can be confirmed by the above-described analysis method. In addition, the triazine part in the upper layer coating film 13 analyzes the coating film by energy dispersive X-ray spectroscopy or Fourier transform infrared spectroscopy, detects nitrogen and osmium, and is attributed to a triazine ring. It can also be confirmed by detecting a vibration peak.

  The thickness of the region where the granular triazine portion is concentrated (that is, the thickness of the concentrated portion (concentrated second portion) 103 which is the region of the granular triazine portion unevenly distributed in a layer shape) is measured by the following method. Value. As described above, the thin film sample is observed with a transmission electron microscope at a magnification of 100,000 to obtain a STEM-BF (bright field) image. The obtained STEM-BF (bright field) image is binarized by, for example, a threshold value 120. Then, in the obtained binarized image, the thickness of the layered region observed black from the surface of the upper layer coating film 13 is measured at any 20 places, and the average value is calculated for the region where the granular triazine portion is concentrated. Calculate as thickness. In addition, the position where the thickening portion 103 exists is to be focused on the position of the lower end (the interface on the metal plate 11 side) of the thickness of the thickening portion 103 obtained as described above in the binary image. Can be specified. In addition, when a region which is observed as a layered black from the surface of the upper coating film 13 is confirmed, it is considered that the granular triazine portion is concentrated in the surface layer of the upper coating film 13.

  The number average particle size of the granular triazine portion (the number average particle size of the triazine granules 101) is a value measured by the following method. As described above, the thin film sample is observed at a magnification of 500,000 by a transmission electron microscope to obtain a STEM-BF (bright field) image. The obtained STEM-BF (bright field) image is binarized by, for example, a threshold value 120. Then, in the obtained binarized image, the equivalent circle diameter of the granular region observed as black is calculated by the formula: equivalent circle diameter = 2 (area / π) 0.5. The “area” in the above equation indicates the area of a granular region observed as black. The calculation of the equivalent circle diameter is performed at 20 arbitrarily selected granular regions, and the average value is determined as the number average particle size of the granular triazine sites.

The average concentration of the triazine portion concentrated on the surface layer side of the upper coating film 13 can be measured as follows. That is, the distribution of the N element concentration in the depth direction from the surface layer side of the upper layer coating film 13 to the metal plate was measured, and the N element concentration N1 at a distance of 0.2 μm from the outermost layer and the metal plate or lower layer were measured. N1 / N2, which is the ratio between the N element concentration and N2 at a position of 0.2 μm on the surface side from the boundary with the coating film, is determined.
The elemental analysis in the depth direction can be performed by a known method. For example, high-frequency glow discharge spectroscopy (GD-OES: Glow Discharge Optical Emission Spectroscopy), Auger electron spectroscopy (AES: AugerElectron Spectroscopy, etc.) are used. It is feasible.

Next, the glass transition temperature (Tg) of the upper layer coating film 13 will be described.
The glass transition temperature of the upper coating film 13 is 85 ° C. or more and 170 or less. When the glass transition point temperature of the upper coating film 13 is lower than 85 ° C., the chemical penetration resistance of the coated metal plate 1 is reduced. On the other hand, when the glass transition point temperature of the upper layer coating film 13 exceeds 170 ° C., the workability of the coated metal sheet 1 decreases. When the workability of the coated metal sheet 1 is reduced, cracks and the like occur in the upper coating film 13 and the chemical permeation resistance and the solvent resistance are also reduced. The glass transition temperature of the upper layer coating film 13 is preferably 100 ° C. or more and 170 ° C. or less, more preferably 110 ° C. or more, from the viewpoint of chemical permeation resistance and solvent resistance (particularly, chemical permeation resistance). 165 ° C or lower.

  When the coated metal sheet 1 according to the present embodiment has the lower coating film 15, the glass transition temperature of the upper coating film 13 is preferably equal to or higher than the glass transition temperature of the lower coating film 15. When the glass transition temperature of the upper coating film 13 is lower than the glass transition temperature of the lower coating film 15, the adhesion between the upper coating film 13 and the lower coating film 15 is reduced, and the chemical penetration resistance is reduced. There is.

  On the other hand, it is preferable that the glass transition temperature of the upper coating film 13 is higher than the glass transition temperature of the lower coating film 5 by 5 ° C. or more. When the difference between the glass transition temperature of the upper coating film 13 and the glass transition temperature of the lower coating film 15 is 5 ° C. or more, the adhesion between the upper coating film 13 and the lower coating film 15 is further improved, and the chemical permeation resistance is improved. Properties are further improved.

  Further, the glass transition temperature of the upper layer coating film 13 is more preferably higher than the glass transition temperature of the lower layer coating film 15 in the range of 10 ° C. or more and 50 ° C. or less. When the glass transition temperature of the upper layer coating film 13 is higher than the glass transition temperature of the lower layer coating film 15 by 10 ° C. or more, the chemical permeation resistance is easily increased. On the other hand, when the glass transition temperature of the upper coating film 13 is higher than the glass transition temperature of the lower coating film 15 by 50 ° C. or less, a decrease in the hardness of the coating film is easily suppressed.

  Here, the glass transition temperature (Tg) is a value measured by the following method. First, a coating film to be measured is peeled off or scraped off to prepare a measurement sample. Then, using the measurement sample, the glass transition point temperature is determined according to the differential scanning calorimetry (DSC method) of the plastic transition temperature measuring method (JIS K7121 1987).

The upper layer coating film 13 preferably has no silica. This is because when the upper coating film 13 contains silica, the chemical resistance of the upper coating film 13 is deteriorated.
For the same reason, it is preferable that the upper coating film 13 does not have at least one metal complex compound selected from zinc, aluminum, and titanium. Here, examples of the at least one metal complex compound selected from zinc, aluminum and titanium include zinc stearate, zinc gluconate, zinc picolinate, zinc citrate, zinc acetylacetonate, aluminum acetate, and aluminum stearate. , Aluminum ethylate, aluminum isopropylate, aluminum triisopropylate, aluminum ethyl acetoacetate di-diisopropylate, aluminum trisethyl acetoacetate, aluminum tris (acetyl acetate), aluminum oxide isopropoxide trimer, titanium tetraisopropoxide, Titanium tetranormal butoxide, titanium butoxide dimer, titanium tetra-2-ethylhexoxide, titanium diisopropoxybis (acetyl Cetonate), titanium tetraacetylacetonate, titanium dioctyloxybis (octylene glycolate), titanium diisopropoxybis (ethylacetoacetate), titanium diisopropoxybis (triethanolaminate), titanium lactate ammonium salt, titanium Lactate, polyhydroxytitanium stearate and the like can be mentioned.

<About the lower layer coating film 15>
In the coated metal plate 1 according to the present embodiment, the lower coating film 15 is not particularly limited, and may be a polyurethane resin, an epoxy resin, an acrylic resin, a polyester resin, a phenol resin, a polyolefin resin, an alkyd resin, A well-known resin coating such as a melamine resin and a silicone resin can be applied. Further, when forming such a resin coating film, a known additive such as a silane coupling agent can be used.

  Among these resin coating films, from the viewpoint of metal appearance, chemical permeation resistance, and solvent resistance, the lower coating film 15 has at least a first site having a urethane bonding skeleton (hereinafter, also referred to as “urethane site”). And a site having at least one of an epoxy group and a siloxane bonding skeleton (hereinafter, a site having an epoxy group is also referred to as an “epoxy site” and a site having a siloxane bonding skeleton is also preferably referred to as a “siloxane site”). It is preferable to use a resin coating film. Further, it is preferable that the lower layer coating film 15 contains a compound having at least one element selected from the group consisting of P, V, Ti, Si and Zr, in addition to the urethane site as described above. .

  Here, when the urethane portion further has an anionic functional group, the dispersibility of the urethane portion in an aqueous medium (aqueous paint) is improved, and the film forming property of the lower layer coating film 15 is enhanced, so that the lower layer coating film 15 is formed. Adhesion with the metal plate 11 is improved, and the barrier property (that is, chemical permeation resistance) of the lower coating film 15 is enhanced.

  Also, by including a urethane site and at least one of an epoxy group and a siloxane bonding skeleton, the chemical permeation resistance of the lower coating film 15 is improved. Further, by making the lower coating film 15 a resin coating film having at least a urethane portion, the transparency of the lower coating film 15 is improved, and the metal appearance is also improved.

  In addition, compounds having at least one element selected from the group consisting of P, V, Ti, Si and Zr generally often function as a rust inhibitor, Such a compound may be contained. By including the compound in the lower layer coating film 15, the corrosion resistance of the coated metal plate 1 can be further improved.

Next, each part included in the lower layer coating film 15 will be described.
Examples of an anionic functional group that is preferably contained in the urethane moiety include a carboxylic acid group (carboxy group) and a sulfonic acid group (sulfo group). On the other hand, the urethane-bonded skeleton of the urethane site is a skeleton derived from a polyurethane resin. That is, the urethane site is a site derived from the polyurethane resin, and can be said to be a site that may further have an anionic functional group.

  An epoxy site having an epoxy group is a site derived from an epoxy resin. That is, the epoxy group of the epoxy moiety is an epoxy group residue that did not react with the urethane moiety derived from the polyurethane resin. Further, the siloxane bond skeleton of the siloxane moiety is a skeleton derived from a silicone resin having a siloxane bond or a silane coupling agent capable of forming a siloxane bond.

  The urethane-bonded skeleton of the urethane portion, the epoxy group of the epoxy portion, and the siloxane-bonded skeleton of the siloxane portion in the lower coating film 15 are formed by energy dispersive X-ray spectroscopy or Fourier transform infrared spectroscopy. This can be confirmed by analyzing the film 15 and detecting an element constituting the corresponding bond or functional group, or detecting a vibration peak attributed to the corresponding bond or functional group. In addition, the presence of a compound having at least one element selected from the group consisting of P, V, Ti, Si and Zr in the lower coating film 15 indicates that such a compound is detected by energy dispersive X-ray spectroscopy. It is possible to confirm whether or not the contained element is detected.

Next, the glass transition temperature of the lower coating film 15 will be described.
The glass transition temperature of the lower coating film 15 is preferably equal to or lower than the glass transition temperature of the upper coating film 13. The glass transition temperature of the lower coating film 15 is more preferably in the range of 80 ° C. or more and 170 or less, and the glass transition temperature of the upper coating film 13 or less. When the glass transition point temperature of the lower layer coating film 15 is lower than 80 ° C., the chemical permeation resistance may decrease. On the other hand, when the glass transition point temperature of the lower coating film 15 exceeds 170 ° C., workability may be reduced. When the processability decreases, cracks and the like may occur in the lower layer coating film 15, and the chemical permeation resistance and the solvent resistance may also decrease. The glass transition temperature of the lower coating film 15 is more preferably equal to or lower than the glass transition temperature of the upper coating film 13 from the viewpoint of chemical permeation resistance and solvent resistance (particularly, chemical permeation resistance). It is in the range of not less than 170 ° C.

<Thickness of upper coating film 13 and lower coating film 15>
In the coated metal plate 1 according to the present embodiment, the thickness of the upper layer coating film 13 as described above is preferably 0.5 μm or more and 15 μm or less. When the thickness of the upper layer coating film 13 is less than 0.5 μm, the chemical permeation resistance of the coated metal plate 1 may be reduced. On the other hand, when the thickness of the upper layer coating film 13 exceeds 15 μm, the transparency of the upper layer coating film 13 is reduced, and the metal appearance may be reduced. The film thickness of the upper layer coating film 13 is more preferably 1 μm or more and 10 μm or less from the viewpoint of metal appearance and chemical permeation resistance.

  Further, in the coated metal plate 1 according to the present embodiment, when the lower coating film 15 is provided in addition to the upper coating film 13, the thickness of the lower coating film 15 is preferably 0.5 μm or more and 15 μm or less. . By setting the film thickness of the lower layer coating film 15 to 0.5 μm or more and 15 μm or less, it becomes possible to further improve the chemical permeation resistance while maintaining the metal appearance. The film thickness of the lower layer coating film 15 is more preferably more than 1.0 μm and 15 μm or less from the viewpoint of chemical permeation resistance.

<About the coloring agent in the upper coating film 13 and / or the lower coating film 15>
In the coated metal plate 1 according to the present embodiment, the upper coating film 13 and / or the lower coating film 15 as described above may contain a coloring agent. By including a coloring agent in the upper layer coating film 13 and / or the lower layer coating film 15, the color tone of the product can be adjusted, and it can be applied to various uses.

  Here, when the coloring pigment is a black pigment, it is preferable to disperse it in the lower layer coating film 15. This is because, when the black pigment is dispersed in the upper coating film 13, the chemical resistance may be reduced. It is considered that such a decrease in chemical resistance is because the black pigment in the upper layer coating film 13 easily penetrates the chemical. The black pigment concentration in the lower coating film 15 is not particularly limited, but is preferably, for example, 0.5% by mass or more and 20% by mass or less based on the total solid content of the lower layer coating film 15. . If the black pigment concentration in the lower layer coating film 15 is less than 0.5% by mass, coloring may be insufficient. On the other hand, when the black pigment concentration in the lower layer coating film 15 exceeds 20% by mass, the chemical resistance and the corrosion resistance may decrease.

<Specific configuration of upper layer coating film 13 and lower layer coating film 15>
In the coated metal plate 1 according to the present embodiment, the upper coating film 13 is, specifically, a polyurethane resin (a) having a glass transition temperature of 75 ° C. or more and 160 ° C. or less, and a triazine ring-containing water-soluble curing agent. A resin coating film obtained by curing an upper layer paint containing the water-soluble melamine resin (b) and an aqueous solvent (for example, a resin coating film containing a crosslinked product of a polyurethane resin and a water-soluble melamine resin) is preferable. The resin coating film formed from such an upper layer paint has a glass transition temperature of 85 ° C. or more and 170 ° C. or less as a whole. At this time, there are a water-soluble melamine resin (b) dispersed in the upper coating film 13 in a granular form and a water-soluble melamine resin (b) concentrated on the surface side of the upper coating film 13. When the lower coating film 15 is further provided between the upper coating film 13 and the metal plate 11, the glass transition temperature of the polyurethane resin (a) is as follows. It is preferably at least the glass transition temperature of (c).

  When a polyester resin is used in place of the polyurethane resin, the polyester resin has lower chemical resistance than the polyurethane resin, and therefore, it is necessary to increase the thickness of the upper coating film in order to obtain the same chemical resistance. . If the thickness of the upper layer coating film is too large, it is not preferable because a desired metal appearance cannot be obtained when a clear coating film is formed.

  When the lower coating film 15 is provided on the coated metal plate 1 according to the present embodiment, the lower coating film 15 has a glass transition temperature of the polyurethane resin (a) of the upper coating film 13 specifically. A polyurethane resin (c) having a temperature of not more than a temperature, an epoxy resin (d), a silane coupling agent (e), and at least one element selected from the group consisting of P, V, Ti, Si and Zr A resin coating film obtained by curing a lower layer coating material containing at least one of a rust preventive agent (f) and an aqueous solvent (for example, a resin coating film containing a crosslinked product of a polyurethane resin (c) and an epoxy resin (d)) A resin coating film containing a crosslinked product of a polyurethane resin (c), an epoxy resin (d), and a silane coupling agent (e); a polyurethane resin (c), an epoxy resin (d), a silane coupling agent (e); Frame Coating film containing a product and a rust inhibitor (f), resin coating film containing a crosslinked product of a polyurethane resin (c) and a silane coupling agent (e), polyurethane resin (c) and a silane coupling agent (e) , A resin coating containing a crosslinked product of the above and a rust inhibitor (f), a resin coating containing a polyurethane resin (c) and a rust inhibitor (f), etc.).

As above, the coated metal plate 1 according to the present embodiment has been described in detail.
As described above, the coated metal sheet 1 according to the embodiment can be used for automobiles, home appliances, building materials, civil engineering, machinery, furniture, containers, and the like.

(About the manufacturing method of painted metal sheet)
Subsequently, a method for manufacturing a coated metal plate according to the present embodiment will be described in detail with reference to FIG. FIG. 4 is a flowchart showing an example of the flow of the method for manufacturing a coated metal plate according to the present embodiment.

The method for manufacturing a coated metal plate according to the present embodiment includes, on at least one surface of the predetermined metal plate 11,
This is a method for manufacturing a coated metal sheet 1 having at least an upper coating film 13. As shown in an example in FIG. 4, the manufacturing method of the painted metal plate includes a texture forming step (step S101) of forming a predetermined texture on the surface of the metal plate 11 as necessary, and a metal plate as necessary. A lower-layer coating film forming step of forming the lower-layer coating film 15 on the metal plate 11 or a lower-layer coating film forming step of forming the upper-layer coating film 13 on the metal plate 11 or the lower-layer coating film 15 (step S105). Have.

  Here, the texture forming step and the lower layer coating film forming step may be performed as needed. For example, the coated metal plate 1 in which the upper layer coating film 13 is formed on the metal plate 11 having no texture or the like may be used. In manufacturing, only step S105 of the three steps shown in FIG. 4 is performed.

  The most important step in the method for manufacturing a coated metal plate shown in FIG. 4 is an upper layer coating film forming step (step S105). In the upper layer coating film forming step, a polyurethane resin (a) containing an anionic functional group and having a glass transition temperature of 75 ° C. or more and 160 ° C. or less, and a water-soluble melamine resin (b) as a water-soluble curing agent containing a triazine ring are used. And an aqueous solvent (an upper layer paint is an example of a first paint) on the metal plate 11 (when the lower layer coating film 15 is formed on the metal plate 11). , On the lower coating film 15), and heating and cooling the metal plate coated with the upper coating material to form the upper coating film 13.

  The method for manufacturing a coated metal sheet according to the present embodiment is performed by the above-described method using the coated metal sheet according to the present embodiment (that is, a coated metal sheet having excellent metal appearance, chemical penetration resistance, and solvent resistance). Can be manufactured while suppressing costs. The reason is presumed as follows.

  First, in general, when a coating film is formed with a paint containing a polyurethane resin and a water-soluble melamine resin, the melamine resin is inferior in compatibility with the polyurethane resin and thus hardly coexists with the polyurethane resin. As the self-condensed grains increase, a phenomenon occurs in which the melamine resin concentrates on the surface layer of the coating film.

  On the other hand, in the method for manufacturing a coated metal sheet according to the present embodiment, the polyurethane resin (a) containing an anionic functional group is employed, so that the polyurethane resin (a) and the triazine ring-containing The water-soluble melamine resin (b), which is a water-soluble curing agent, is uniformly mixed and coexists. When the upper layer paint in this state is formed on the metal plate 11 (or on the lower layer coating film 15) and heated, the self-shrinkage of the water-soluble melamine resin (b) is suppressed, and the water-soluble melamine resin (b) The reaction with the polyurethane resin (a) occurs preferentially. Further, when the evaporation (drying) of the aqueous solvent proceeds by heating, the polyurethane resin (a) is in a molten state. When the polyurethane resin (a) is in a molten state, the glass transition temperature is as high as 75 ° C. or higher and 160 ° C. or lower, so that the viscosity increases. As a result, a high cohesive force is generated and the diffusion rate of the melamine resin (b) decreases. Thereby, the self-shrinkage of the water-soluble melamine resin (b) is suppressed, and the reaction between the water-soluble melamine resin (b) and the polyurethane resin (a) occurs preferentially.

  As described above, while the melamine resin (b) having low compatibility with the polyurethane resin (a) is concentrated on the surface layer of the coating film, the self-shrinkage of the water-soluble melamine resin (b) is suppressed, and the polyurethane resin (a) ). However, since the self-shrinkage of the water-soluble melamine resin (b) is not completely suppressed, the reaction product of the water-soluble melamine resin (b) reacted with the polyurethane resin (a) is contained in the upper layer coating film 13. And a reaction product resulting from self-shrinkage of the water-soluble melamine resin (b) coexist. As a result, the portions derived from the water-soluble melamine resin (b) include those dispersed in the upper coating film 13 in a granular form and those concentrated in the surface layer of the upper coating film 13. Moreover, as described above, when the upper layer coating film 13 is formed, a high cohesive force is generated in the polyurethane resin (a), so that the reaction between the water-soluble melamine resin (b) and the polyurethane resin (a) occurs. It occurs preferentially. Therefore, the micronized granular water-soluble melamine resin (b) concentrates on the surface layer of the upper coating film 13 to form a concentrated portion 103 as shown in FIG. The non-concentrated, micronized water-soluble melamine resin (b) forms triazine particles 101 as shown in FIG.

  When the lower coating film 15 is provided, the lower coating film is formed using a polyurethane resin (c) having a glass transition temperature of 80 ° C. or higher and 160 ° C. or lower and having a lower glass transition temperature than the polyurethane resin (a). By forming the layer 15, high adhesion between the upper layer coating film 13 and the lower layer coating film 15 can be realized. Further, by employing the polyurethane resin (a) containing an anionic functional group, the dispersibility of the urethane portion in the aqueous medium (aqueous paint) is improved, so that the film forming property of the upper layer coating film 13 is enhanced, and High adhesion between the coating film 13 and the lower coating film 15 is realized.

  As described above, the method for manufacturing a coated metal sheet according to the present embodiment is applied to the coated metal sheet according to the present embodiment (that is, a coated metal sheet having excellent metal appearance, chemical penetration resistance, and solvent resistance). Is estimated to be able to be manufactured while suppressing costs.

  Hereinafter, the method for manufacturing a coated metal sheet according to the present embodiment will be described in detail.

<About upper layer coating film formation process>
Although the flow is opposite to that shown in FIG. 4, the upper layer coating film forming step will be described in detail below.
In the upper coating film forming step, first, an upper coating material, which is an example of the first coating material, is prepared. The upper layer paint contains a polyurethane resin (a), a water-soluble melamine resin (b) which is a water-soluble curing agent containing a triazine ring, and an aqueous solvent.

[About polyurethane resin (a)]
The polyurethane resin (a) is a polyurethane resin containing an anionic functional group and having a glass transition temperature of 75 ° C. or more and 160 ° C. or less. In the case of forming the lower coating film 15 as well as the upper coating film 13 in the coated metal plate according to the present embodiment, the glass transition temperature of the polyurethane resin (a) is determined by the polyurethane resin used for the lower coating film 15. It is preferably at least the glass transition temperature of (c).

  In order to obtain a high glass transition point temperature (85 ° C. or more and 170 ° C. or less) in the upper coating film 13 as mentioned above, it is suitable to use a polyurethane resin having a urethane bond. Point temperature polyester resins are difficult to manufacture. Further, since a polyurethane resin having a high glass transition temperature has a very high melt viscosity, it is difficult to apply (form a coating film) unless a coating material dispersed in an aqueous medium is used. For this reason, by imparting an anionic functional group to the polyurethane resin, the polyurethane resin can be dispersed in an aqueous medium together with the water-soluble melamine resin.

  The polyurethane resin (a) is, for example, a polyvalent resin such as ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bisphenol hydroxypropyl ether, glycerin, trimethylolethane, and trimethylolpropane. It is obtained by reacting an alcohol with a diisocyanate compound such as hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and further extending the chain with a diamine or the like, dispersing in water, and the like. Can be.

  Examples of the polyurethane resin (a) include polyether polyurethane resin (polyurethane resin having a polyether skeleton), polyester polyurethane resin (polyurethane resin having a polyester skeleton), and polyether polyester polyurethane resin (polyether skeleton and polyester skeleton). Is preferred. Coatings using these polyurethane resins are likely to have improved chemical penetration resistance and solvent resistance.

A polyether polyurethane resin, a polyester polyurethane resin, and a polyether polyester polyurethane resin can be obtained by using at least one of a polyether polyol and a polyester polyol as polyhydric alcohols.
Examples of the polyether polyol include polyethylene glycol, polyoxyethylene glycol, polyoxypropylene glycol, polytetramethylene glycol, and a copolymer thereof.
Further, polyester polyols, for example, terephthalic acid, isophthalic acid, adipic acid, azelaic acid, dibasic acid dialkyl esters such as sebacic acid and ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol Glycols such as 1,6-hexane glycol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, polyoxyethylene glycol, polyoxypropylene glycol, and polytetramethylene ether glycol. It can be obtained by reacting.
The polyester polyol can be obtained by, for example, ring-opening polymerization of lactones such as polycaprolactone, polyvalerolactone, and poly (β-methyl-γ-valerolactone).

  The glass transition temperature of the polyurethane resin (a) is from 75 ° C to 160 ° C. When the glass transition temperature of the polyurethane resin (a) is less than 75 ° C., the resistance to chemical penetration decreases. On the other hand, when the glass transition temperature of the polyurethane resin (a) exceeds 160 ° C., the processability decreases. When the processability decreases, cracks and the like occur in the upper layer coating 13, and the chemical permeation resistance and the solvent resistance also decrease. The glass transition temperature of the polyurethane resin (a) is preferably 100 ° C. or more and 160 ° C. or less from the viewpoint of chemical permeation resistance and solvent resistance (particularly, chemical permeation resistance).

  Here, the glass transition temperature of various resins including the polyester resin can be measured according to the differential scanning calorimetry (DSC method) of the method for measuring the transition temperature of plastic (JIS K7121 1987).

[About water-soluble melamine resin (b)]
As the water-soluble melamine resin (b) which is a water-soluble curing agent containing a triazine ring, generally known water-soluble melamine resins (such as imino-type melamine resins, methylol-type melamine resins, and fully alkyl-etherified melamine resins) can be used. it can. Commercially available water-soluble melamine resins include, for example, water-soluble melamine resins manufactured by Nippon Carbide, Ornex, and DIC.

  As the water-soluble melamine resin (b) as described above, it is particularly preferable to use a melamine resin containing an imino group (imino-type melamine resin). By using a melamine resin containing an imino group, the granular water-soluble melamine resin is easily concentrated on the surface layer of the upper coating film 13, so that the solvent resistance is further improved.

  In addition, "water-soluble" indicates that the amount of the target substance dissolved in 100 parts by mass of water at 25 ° C is 5 parts by mass or more (preferably 10 parts by mass or more).

[About colorant]
The colorant dispersed in the upper layer paint containing the above components is not particularly limited, and a known colorant can be appropriately used. Examples of such coloring agents include various inorganic pigments such as titanium oxide, zinc oxide, calcium carbonate, aluminum oxide, barium sulfate, aluminum, iron oxide, copper / chromium composite oxide, carbon black, cyanine, quinacridone, and the like. Various organic pigments, various dyes, and the like can be used.

  If the colorant used is a black pigment such as carbon black or a metal oxide exhibiting black, the chemical resistance may be reduced, so the concentration in the upper layer paint is limited or dispersed in the lower layer paint. It is preferable to disperse it in the lower layer paint.

  The type of carbon black to be dispersed in the upper layer paint is not particularly limited. For example, known carbon blacks such as furnace black, Ketjen black, acetylene black, and channel black can be used.

  The particle size of the carbon black to be used is not particularly limited as long as there is no problem in the dispersibility and coating film quality in the paint and the paintability, but those having a primary particle size of about 10 to 120 nm are used. Cheap. In particular, when chemical resistance or corrosion resistance is required, it is preferable to use one having a primary particle diameter of 10 to 50 nm. These carbon blacks are generally difficult to disperse while maintaining the primary particle diameter because agglomeration occurs in the process of dispersing in the paint. That is, actually, secondary particles having a particle diameter larger than the primary particle diameter are present in the paint. In such an upper layer paint, it exists in a similar form.

  Although there is no particular limitation on the type of the metal oxide that exhibits black, a known black pigment such as, for example, triiron tetroxide or a copper / chromium composite oxide can be used.

[Aqueous solvent]
Examples of the aqueous solvent include water and a mixed solution of water and a lower alcohol. Such an aqueous solvent preferably contains 50% by mass or more (preferably 80% by mass or more) of water.
It is not preferable to use a solvent typified by an organic solvent as the solvent, because the melamine particles only exist in a dispersed state in the coating film and do not concentrate on the surface. As described above, in order to concentrate melamine on the surface of the coating film formed using the solvent-based paint, it is necessary that the solvent-based paint contains an amine compound. Thus, melamine particles can be concentrated on the surface without using an amine compound.

  Examples of the water include distilled water, ion-exchanged water, ultrapure water, and ultrafiltration water. Examples of the lower alcohol include alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, butanol, and isopropyl alcohol.

[Content]
In the upper layer paint containing the above components, the content of the polyurethane resin (a) with respect to the total solid content (Wa, unit: mass%) and the content of the water-soluble melamine resin (b) with respect to the total solid content (Wb) , Unit: mass%), the total content (Wa) + (Wb) satisfies the following formula (11), and the content (Wa) of the polyurethane resin (a) and the water solubility It is preferable that the ratio (Wb) / (Wa) of the content (Wb) of the melamine resin (b) satisfies the following expression (13).
90% by mass ≦ (Wa) + (Wb) ≦ 100% by mass Expression (11)
0 <(Wb) / (Wa) ≦ 1 Expression (13)

  Here, in the above formula (11), when the total content (Wa) + (Wb) is less than 90% by mass, the metal appearance, chemical permeation resistance and solvent resistance of the coated metal plate 1 are reduced. Sometimes. Further, in the above formula (13), when the ratio (Wb) / (Wa) exceeds 1, the water-soluble melamine resin (b) becomes excessive, and the workability of the coated metal plate 1 may be reduced. When the processability decreases, cracks and the like occur in the upper layer coating 13, and the chemical permeation resistance and the solvent resistance also decrease.

From the viewpoint of metal appearance, chemical permeation resistance and solvent resistance, the total content (Wa) + (Wb) satisfies the following expression (15), and the ratio (Wb) / (Wa) is It is more preferable to satisfy the expression (17).
95% by mass ≦ (Wa) + (Wb) ≦ 100% by mass Expression (15)
0.1 ≦ (Wb) / (Wa) ≦ 0.3 Expression (17)

It is preferable that the upper layer paint has no silica. If the upper layer paint contains silica, the upper layer coat 13 contains silica, and as a result, the chemical resistance of the upper layer coat 13 deteriorates.
For the same reason, it is preferable that the upper layer coating does not have at least one metal complex compound selected from zinc, aluminum and titanium. Here, examples of the at least one metal complex compound selected from zinc, aluminum and titanium include zinc stearate, zinc gluconate, zinc picolinate, zinc citrate, zinc acetylacetonate, aluminum acetate, and aluminum stearate. , Aluminum ethylate, aluminum isopropylate, aluminum triisopropylate, aluminum ethyl acetoacetate di-diisopropylate, aluminum trisethyl acetoacetate, aluminum tris (acetyl acetate), aluminum oxide isopropoxide trimer, titanium tetraisopropoxide, Titanium tetranormal butoxide, titanium butoxide dimer, titanium tetra-2-ethylhexoxide, titanium diisopropoxybis (acetyl Cetonate), titanium tetraacetylacetonate, titanium dioctyloxybis (octylene glycolate), titanium diisopropoxybis (ethylacetoacetate), titanium diisopropoxybis (triethanolaminate), titanium lactate ammonium salt, titanium Lactate, polyhydroxytitanium stearate and the like can be mentioned.

[About film forming method (coating method)]
In the upper coating film forming step, a method of forming (applying) the upper coating material on the metal plate 11 or the lower coating film 15 is not particularly limited, and examples thereof include a roll coating method, a ringer roll coating method, and an air spray method. Well-known film forming methods (coating methods) such as an airless spray method and an immersion method can be used. In addition, when a film is formed on a continuous coating line called a coil coating line or a sheet coating line, which is fully equipped with a film forming apparatus (coating apparatus) for performing these well-known film forming methods (coating methods), the coating work efficiency is high and a large amount is obtained. It is more suitable because production is possible.

[About heating method (baking method) and cooling method]
In the upper coating film forming step, the method of heating the upper coating film after forming (applying) the upper coating film on the metal plate 11 or the lower coating film 15 is not particularly limited. A generally known device such as an oven, a direct-fired oven, a far-infrared oven, and an induction heating oven can be used. By heating the film of the upper layer paint, the aqueous solvent present in the film of the upper layer paint is dried, and thereafter, the polyurethane resin (a) and the water-soluble melamine resin (b) react to form the upper layer coating film 13. It is formed.

  On the other hand, the method of cooling the upper layer coating film 13 after heating is not particularly limited, and for example, a known method such as water cooling (spraying, submerging, etc.) or air cooling (spraying with nitrogen gas, etc.) is used. can do.

  In the upper layer coating film forming step, in particular, after forming the upper layer coating, heating under conditions such that the heating time from the start of heating to the maximum attainment temperature is 1 second or more and 30 seconds or less, It is preferable to form the upper coating film 13 by cooling under conditions such that the cooling time is 0.1 seconds or more and 5 seconds or less. Here, the heating time and the cooling time are measured by detecting the temperature of the metal plate with a thermocouple.

  When heating is performed in a short time of 1 second or more and 30 seconds or less as described above after the formation of the upper layer coating material, the self-shrinkage of the water-soluble melamine resin (b) is further suppressed, and the above-mentioned 0.1 mm or less is used. When cooling is performed in a short time of not less than 2 seconds and not more than 5 seconds, diffusion of the water-soluble melamine resin (b) is suppressed. As a result, the water-soluble melamine resin (b) reacted with the polyurethane resin (a) forms a domain and is dispersed in the upper coating film 13 in the form of particles having a number average particle size of 5 nm or more and 20 nm. Tends to be concentrated in the surface layer within a depth of 15 nm from the surface. For this reason, in the manufactured painted metal sheet 1, the metal appearance, chemical permeation resistance and solvent resistance are further easily improved.

  Here, when the heating time is less than 1 second, the reaction between the polyurethane resin (a) and the water-soluble melamine resin (b) becomes insufficient, and the chemical penetration resistance and the solvent resistance may decrease. . On the other hand, when the heating time exceeds 30 seconds, the water-soluble melamine resin (b) is liable to self-condensate, the self-condensed particles become large, and a phenomenon occurs in which the water-soluble melamine resin (b) is concentrated on the surface layer of the coating film. In the coated metal plate 1, the metal appearance and chemical resistance may be reduced.

  When the cooling time is shorter than 0.1 second, the cooling is rapidly performed, and the upper coating film 13 may be cracked. On the other hand, when the cooling time exceeds 5 seconds, diffusion of the water-soluble melamine resin (b) occurs, and the metal appearance and chemical permeation resistance of the manufactured coated metal plate 1 may be reduced.

  From the viewpoint of metal appearance, chemical penetration resistance and solvent resistance, the heating time is preferably 1 second or more and 20 seconds or less. In addition, from the same viewpoint, the cooling time is preferably 0.1 seconds or more and 2 seconds or less.

  The maximum temperature and the holding time are not particularly limited. Depending on the aqueous solvent used, the maximum temperature, which is equal to or higher than the boiling point of the aqueous solvent, is appropriately set. What is necessary is just to set a holding time of not less than seconds and not more than 5 seconds.

  In the case where a plurality of concentrated portions 103 are formed by the upper layer coating film 13, first, heating is performed to a temperature of 40 to 100 ° C. for 1 to 20 seconds. Next, it heats to more than 200 degreeC in 1 to 10 seconds. Then, it cools. By forming the upper layer coating film 13 in this manner, in addition to the concentrated portion 103 of the surface layer, the concentrated portion 103 is formed at a depth position other than the surface layer.

  As above, the upper layer coating film forming step according to the present embodiment has been described in detail.

<About lower layer coating film formation process>
Subsequently, the lower layer coating film forming step in the method for manufacturing a coated metal sheet according to the present embodiment will be described.
In the method for manufacturing a coated metal sheet according to the present embodiment, the lower coating film forming step is not particularly limited, and the lower coating film 15 is formed by a known method using a known lower coating material as an example of the second coating material. Can be formed.

  Among the well-known methods, from the viewpoints of metal appearance, chemical permeation resistance and solvent resistance, the lower layer coating film forming step includes an anionic functional group and has a glass transition temperature of not more than the glass transition temperature of the polyurethane resin (a). It contains a certain polyurethane resin (c), an epoxy resin (d), a silane coupling agent (e), and at least one element selected from the group consisting of P, V, Ti, Si and Zr. A step of forming a lower layer coating film 15 by forming a lower layer coating material containing at least one of the rust preventive agent (f) and the aqueous solvent on at least one surface of the metal plate 11, heating and cooling, and then cooling. Preferably, there is.

[About polyurethane resin (c)]
As mentioned earlier, the glass transition temperature of the polyurethane resin (c) is preferably equal to or lower than the glass transition temperature of the polyurethane resin (a). When the glass transition temperature of the polyurethane resin (c) is equal to or lower than the glass transition temperature of the polyurethane resin (a), the adhesion between the lower coating film 15 and the upper coating film 13 is improved, and the chemical permeation resistance is further improved. It will be easier.

  The glass transition temperature of the polyurethane resin (c) is in the range of 80 ° C. or more and 160 ° C. or less, and the glass transition temperature of the polyurethane resin (a) or less (preferably, the glass transition temperature of the polyurethane resin (a)). 5 ° C. or more). When the glass transition temperature of the polyurethane resin (c) is less than 80 ° C., the resistance to chemical penetration may decrease. On the other hand, when the glass transition temperature of the polyurethane resin (c) exceeds 160 ° C., workability may be reduced. When the workability is reduced, cracks and the like occur in the lower layer coating film 15, and the chemical permeation resistance and the solvent resistance are also reduced. The glass transition temperature of the polyurethane resin (c) is preferably in the range of 100 ° C. or more and 160 ° C. or less from the viewpoint of chemical permeation resistance and solvent resistance (particularly, chemical permeation resistance).

  The polyurethane resin (c) may be a polyurethane resin containing a polyurethane resin having a glass transition temperature of 80 ° C. or more and 160 ° C. or less, and a polyurethane resin having a glass transition temperature of 20 ° C. or more and 60 ° C. or less. By using polyurethane resins having different glass transition temperatures and adjusting the glass transition temperature of the polyurethane resin (c), chemical permeation resistance can be further improved.

  As specific types of the polyurethane resin (c), various polyurethane resins exemplified as the polyurethane resin (a) can be mentioned.

[About epoxy resin (d)]
Examples of the epoxy resin (d) include a bisphenol A epoxy resin, a bisphenol F epoxy resin, a novolak epoxy resin, and an aliphatic epoxy resin. Among these resins, it is particularly preferable to use the epoxy resin as the epoxy resin (d) because the aliphatic epoxy resin hardly discolors by baking.

  Specific types of these epoxy resins (d) are not particularly limited, and various commercially available epoxy resins (d) can be used, and the glass transition temperature is within the above range. Such a compound can be synthesized on its own and used as appropriate.

[About silane coupling agent (e)]
The silane coupling agent (e) is not particularly limited, and various known silane coupling agents can be used. Examples of such a silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, and N-2- (amino Ethyl) -3-aminopropyltriethoxysilane, N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane, bis (trimethoxysilylpropyl) amine, 3-glycidoxypropyltrimethoxysilane, 3-glycol Sidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane and the like can be mentioned. By including such a silane coupling agent in the lower layer paint, the chemical permeation resistance of the lower layer coating film 15 can be further improved.

[About rust inhibitor (f)]
In the lower coating film forming step according to the present embodiment, as the rust preventive (f), a rust preventive containing at least one element selected from the group consisting of P, V, Ti, Si and Zr is used. It is possible to use. By including such a rust preventive (f) in the lower layer paint, the corrosion resistance of the lower layer coating film 15 can be improved.

  Examples of the compound containing P that functions as the rust inhibitor (f) include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, and tetraphosphoric acid, and salts thereof, and aminotri (methylenephosphonic acid). ), 1-hydroxyethylidene-1,1-diphosphonic acid, phosphonic acids such as ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic acid) and salts thereof, and organic phosphoric acids such as phytic acid and salts thereof And the like.

  Examples of the compound containing V that functions as a rust inhibitor (f) include, for example, vanadium pentoxide, metavanadate, ammonium metavanadate, sodium metavanadate, vanadium oxytrichloride, vanadium trioxide, vanadium dioxide, vanadium oxysulfate, Vanadium oxyacetylacetonate, vanadium acetylacetonate, vanadium trichloride, phosphorus vanadomolybdic acid and the like can be mentioned. Further, the pentavalent vanadium compound is an organic compound having at least one functional group selected from the group consisting of a hydroxyl group, a carbonyl group, a carboxyl group, a primary to tertiary amino group, an amide group, a phosphoric acid group and a phosphonic acid group. Oxovanadium cation and a salt of an inorganic acid anion such as hydrochloric acid, nitric acid, phosphoric acid or sulfuric acid or an organic acid anion such as formic acid, acetic acid, propionic acid, butyric acid or oxalic acid Alternatively, a chelate of an organic acid and a vanadyl compound, such as vanadyl glycolate and vanadyl dehydroascorbate, can be used.

  Examples of the compound containing Ti that functions as the rust preventive (f) include, for example, titanium potassium oxalate, titanyl sulfate, titanium chloride, titanium lactate, titanium isopropoxide, isopropyl titanate, titanium ethoxide, and titanium 2-ethyl. Examples thereof include -1-hexanolate, tetraisopropyl titanate, tetra-n-butyl titanate, titania sol, titanium hydrofluoric acid, and salts thereof.

  Examples of the compound containing Si that functions as the rust inhibitor (f) include, for example, Snowtex C, Snowtex O, Snowtex N, Snowtex S, Snowtex UP, Snowtex PS-M, and Snowtex PS-L. Colloidal silica such as, Snowtex 20, Snowtex 30, Snowtex 40 (all manufactured by Nissan Chemical Industries, Ltd.), Adelite AT-20N, Adelite AT-20A, Adelite AT-20Q (all manufactured by Asahi Denka Kogyo) and the like. Aerosil 50, Aerosil 130, Aerosil 200, Aerosil 300, Aerosil 380, Aerosil TT600, Aerosil MOX80, Aerosil MOX170 (all manufactured by Nippon Aerosil Co., Ltd.) and the like.

  Examples of the compound containing Zr that functions as a rust preventive (f) include, for example, zirconyl nitrate, zirconyl acetate, zirconyl sulfate, zirconium ammonium carbonate, potassium zirconium carbonate, sodium zirconium carbonate, zirconium acetate, zirconium hydrofluoric acid or the like. Salts and the like can be mentioned.

[About colorant]
The colorant dispersed in the lower layer paint containing the above components is not particularly limited, as in the upper layer paint, and a known one can be appropriately used. As such a coloring agent, for example, various inorganic pigments such as titanium oxide, zinc oxide, calcium carbonate, aluminum oxide, barium sulfate, aluminum, iron oxide, carbon black, and various organic pigments such as cyanine and quinacridone, Various dyes and the like can be used.

[Aqueous solvent]
As the aqueous solvent, water or a mixture of water and a lower alcohol can be used as in the case of the upper layer paint. Such an aqueous solvent preferably contains 50% by mass or more (preferably 80% by mass or more) of water.

  Examples of the water include distilled water, ion-exchanged water, ultrapure water, and ultrafiltration water. Examples of the lower alcohol include alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, butanol, and isopropyl alcohol.

[Content]
As described above, the contents of the polyurethane resin (c), the epoxy resin (d), the silane coupling agent (e), and the rust inhibitor (f) are not particularly limited. The content of each component may be appropriately determined in accordance with the characteristics required in (1). For example, the content of the polyurethane resin (c) can be in the range of 30 to 95% by mass, and the content of the epoxy resin (d) can be in the range of 1 to 5% by mass. It is possible. The content of the silane coupling agent (e) can be, for example, in the range of 10 to 40% by mass, and the content of the rust preventive (f) is, for example, in the range of 1 to 15% by mass. Within. The content of each component is adjusted from the above range so that the total content of the polyurethane resin (c), the epoxy resin (d), the silane coupling agent (e), and the rust inhibitor (f) becomes 100% by mass. It may be determined appropriately.

[About film forming method (coating method), heating method (baking method) and cooling method]
In the lower coating film forming step, there is no particular limitation on the method of forming the lower coating material on at least one side of the metal plate 11 and cooling after heating, and for example, various methods as described in the upper coating film forming step are used. A film forming method (coating method), a heating method, and a cooling method can be used. The maximum temperature, the heating time, the holding time, and the cooling time of the metal plate 11 coated with the lower layer paint are not particularly limited, and may be set as appropriate.

<Other components>
In the method for manufacturing a coated metal sheet according to the present embodiment, both the upper layer paint and the lower layer paint may contain well-known additives such as a wax, a leveling agent, an antifoaming agent, a thickener, and a dispersant. Good. That is, in the coated metal plate according to the present embodiment, both the upper coating film 11 and the lower coating film 15 may contain these well-known additives.

<About the texture forming process>
In the method for manufacturing a coated metal plate according to the present embodiment, the surface of the metal plate 11 to which the above-mentioned upper layer paint is applied is provided with a satin finish, a rough surface, a streak (hairline), a cloth (satin), a hammer, as necessary. Various textures such as (hammers) may be formed. By forming the above-described texture on the surface of the metal plate 11 in advance, it is possible to further improve the design of the painted metal plate according to the present embodiment.

  Here, the method and the apparatus used for forming the various textures as described above are not particularly limited, and various known materials can be appropriately used.

  As above, the method for manufacturing a coated metal plate according to the present embodiment has been described in detail.

  Hereinafter, the coated metal plate and the method for manufacturing the coated metal plate according to the present invention will be described more specifically with reference to Examples and Comparative Examples. The following examples are merely examples of the coated metal sheet and the method for manufacturing the coated metal sheet according to the present invention, and the method for manufacturing the coated metal sheet and the coated metal sheet according to the present invention is limited to the following examples. It is not done.

(Test Example 1) <Metal plate (original plate)>
Nippon Steel & Sumitomo Metal Corporation's hot-dip galvanized steel sheet “NS Silver Zinc (registered trademark)” (hereinafter referred to as “GI”) and Nippon Steel & Sumitomo Metal Corporation's galvanized steel sheet “NS Zinc Coat (registered trademark)” ) "(Hereinafter referred to as" EG "), Nippon Steel & Sumitomo Metal Corporation's zinc-nickel alloy plated steel sheet" NS Zinclite (registered trademark) "(hereinafter referred to as" ZL "), zinc-iron. Alloy plating “NS Silver Alloy (registered trademark)” (hereinafter referred to as “GA”), aluminum plate “JIS3004” (hereinafter referred to as “Al”), stainless steel plate “SUS430” (hereinafter referred to as “SUS”) ), Nippon Steel & Sumitomo Metal Corporation's zinc-aluminum-magnesium-silicon alloy plated steel sheet "Super Dima (registered trademark)" (hereinafter referred to as "SD"), Nissin Steel Zinc made Formula Company - aluminum - magnesium alloy plated steel sheet "ZAM (registered trademark)" (. Hereinafter referred to as "ZAM") was used as the metal plate (original plate). The thickness of each of the metal plates was 0.6 mm.

The plating adhesion amount of ZL was 20 g / m ² per one side, and the nickel amount in the plating layer was 12% by mass. Further, GI, SD, GL, coating weight of ZAM was per side 60 g / ^{m 2,} respectively. The coating weight of GA was 45 g / m ² per side. The amount of EG plated was 20 g / m ² per side.

<Paint>
In this test example, a single-layer structure as shown in FIG. 1A having only an upper layer coating film on one side of a metal plate (original plate) as described above, or FIG. 1B having a lower layer coating film and an upper layer coating film as shown in FIG. A coated metal plate having a two-layer structure as shown was produced. Here, the polyurethane resin used for adjusting the upper layer paint and the lower layer paint is shown in Table 1 below. Similarly, the polyester resin, the water-soluble melamine resin, the silane coupling agent, the rust inhibitor, and the colorant used for preparing the lower layer paint are shown in Tables 2 to 7 below, respectively.

[Homemade polyurethane resin A]
145 g of 1,3-bis (isocyanatomethyl) cyclohexane, 20 g of dimethylolpropionic acid, 15 g of neopentyl glycol, 75 g of a polycarbonate diol having a molecular weight of 1,000, and 64 g of acetonitrile as a solvent were added. Stirred for hours. After confirming that the amine equivalent reached a predetermined value, the reaction solution was cooled to 40 ° C., and 30 g of triethylamine (boiling point: 89 ° C.) was added to obtain an acetonitrile solution of a polyurethane prepolymer. 300 g of this solution was dispersed in 700 g of water using a homodisper to form an emulsion. The solution was kept at 40 ° C., and 35.6 g of ethylenediaminehydrazine monohydrate was added as a chain extender to cause a chain extension reaction. Subsequently, acetonitrile used in the synthesis of the polyurethane prepolymer was distilled off at 50 ° C. under a reduced pressure of 150 mmHg to obtain a self-made polyurethane resin A.
Note that triethylamine used as a raw material has been removed in a resin purification step.

[Homemade polyurethane resin B]
145 g of 1,3-bis (isocyanatomethyl) cyclohexane, 20 g of dimethylolpropionic acid, 15 g of neopentyl glycol, 75 g of a polycarbonate diol having a molecular weight of 1,000, and 64 g of acetonitrile as a solvent were added. Stirred for hours. After confirming that a predetermined amine equivalent was reached, the temperature of the reaction solution was lowered to 40 ° C., and 20.00 g of triethylamine (boiling point: 89 ° C.) was added to obtain an acetonitrile solution of a polyurethane prepolymer. 300 g of this solution was dispersed in 700.00 g of water using a homodisper to form an emulsion, the solution was kept at 40 ° C., 21 g of γ- (2-aminoethyl) aminopropyltrimethoxysilane as a chain extender, and ethylenediamine hydrazine A chain extension reaction was performed by adding 18 g of monohydrate. Subsequently, acetonitrile used in the synthesis of the polyurethane prepolymer was distilled off at 50 ° C. under a reduced pressure of 150 mmHg to obtain a self-made polyurethane resin B.
Note that triethylamine used as a raw material has been removed in a resin purification step.

  Using the raw materials shown in Tables 1 to 7 and mixing each raw material in a predetermined amount in water according to the descriptions in Tables 8 and 9, an upper layer paint and a lower layer paint were produced, respectively.

  In Table 9, in the lower coatings 9, 10, and 11, the main resin-2 was blended at a ratio of 15 parts by mass with respect to 100 parts by mass of the main resin-1.

<Manufacture of painted metal sheets>
Various metal plates were degreased by immersion in an aqueous solution containing 2% by mass of FC-4336 (manufactured by Nippon Parkerizing Co., Ltd.) at a temperature of 60 ° C. for 10 seconds, washed with water, and dried.

  Next, each of the lower layer paints manufactured as described above was applied by a roll coater so as to have a predetermined dry film thickness. In an induction heating furnace into which hot air is blown, the lower coating film is heated (dried) under the condition that the maximum temperature of the metal plate reaches 150 ° C. and the heating time from the start of heating to the maximum temperature reaches 10 seconds. Cured). One second after reaching the maximum temperature, water was wiped on the coated metal plate by spraying, and water-cooled under the condition that the cooling time from the maximum temperature to 30 ° C. was 1 second. In addition, the holding time of the maximum attainment temperature during heating was set to 1 second.

  Next, each of the upper layer paints produced as described above was applied by a roll coater so as to have a predetermined dry film thickness. In an induction heating furnace into which hot air is blown, the upper coating film is heated (dry curing) under the condition that the maximum temperature of the metal plate reaches 230 ° C. and the heating time from the start of heating to the maximum temperature reaches 10 seconds. did. One second after reaching the maximum temperature, spray water on the painted metal plate, and after one second from reaching the maximum temperature, spray water on the painted metal plate, Water cooling was performed under the condition that the cooling time from the highest temperature to 30 ° C. was 1 second. In addition, the holding time of the maximum attainment temperature during heating was 1 second.

<Level>
The structure of the upper layer coating film and the lower layer coating film was analyzed for each of the manufactured coated metal plate samples.
Specifically, the constituent parts of the upper layer coating film and the lower layer coating film (urethane bond skeleton (UB), triazine ring skeleton (TR), epoxy group (EP), presence or absence of siloxane bond (silane) derived from a silane coupling agent) Is determined by analyzing the coating film using a Fourier transform infrared spectrophotometer (FT-IR, Frontier manufactured by PerkinElmer) and determining whether or not the following vibration peaks are observed. In the case where it was performed, "Yes" was described in the table.
Urethane bond backbone (UB): 1540cm ^-1 are observed in the vicinity of the N-H vibrational peak of bending vibration, and the vibration peak triazine ring skeleton of C = O stretching vibration is observed near 1730cm ^-1 (TR): 1550,1450,815Cm ^-1 vibrational peak epoxy group derived from triazine ring observed in the vicinity (EP): 910cm ^-1 from epoxy groups observed in the vicinity of the vibration peak siloxane bond: 1050 cm ^-1 Si observed in the vicinity -O-Si stretching vibration vibration peak

Further, according to the method described above, in the upper layer coating film, the thickness of the concentrated portion existing in the surface layer (concentration depth), and the number average particle size (particle size) of granular triazine sites (water-soluble melamine resin) ) Were measured respectively. The N concentration N1 at a depth of 0.2 μm from the surface of the first coating and the N concentration N2 at a depth of 0.2 μm from the interface between the first coating and the metal plate toward the first coating. And N1 / N2 (concentration ratio), which was the ratio to the above, was measured according to the method described above. Further, the glass transition temperature (Tg) of each coating film was measured for each of the manufactured coated metal sheet samples according to the method described above.
In addition, the surface layer enriched portion was stained with osmium oxide, and when observed at a magnification of 100,000 times using a transmission electron microscope, whether or not melamine particles of 5 nm or more were observed, and a plurality of enriched portions were formed. Was determined according to the method described above.

<Evaluation method>
Each of the manufactured painted metal plates was evaluated according to the following criteria.

[Metal appearance]
For each manufactured coated metal plate, the L *, a *, b * color system of CIELAB (JISZ8729) was measured with a Konica Minolta CR-400 spectrophotometer (light source 10 ° D65, SCI method), (Excellent) A, B, C, and D (poor) were evaluated in four grades.
A: L * is 60 or more and | a * | ≦ 1
B: L * is less than 60 and | a * | ≦ 1
C: L * is less than 60 and | a * | ≧ 1
D: L * is less than 60, | a * | ≧ 1, and | b * | ≧ 6

[Chemical penetration resistance test]
Each coated metal plate manufactured was cut to a width of 5 cm, and the samples whose end faces were all protected with Nitoflon (registered trademark) tape were immersed in 5% sulfuric acid solution and 5% sodium hydroxide solution at 20 ° C. for 24 hours to change color. Was evaluated in four grades of (excellent) A, B, C, and D (poor).
A: No discoloration AB: Very slight discoloration B: Slight discoloration C: Many discoloration D: Many discoloration and coating peeling

[Workability test]
Each of the manufactured coated metal plates was cut into a width of 5 cm, and subjected to 2T bending in a 20 ° C. atmosphere by a test method according to JIS G3312. Specifically, two coated plates identical to the test piece were sandwiched inward, and 180 ° close bending was performed with the surface on which the upper layer coating film and the lower layer coating film were formed facing outward. The cracks of the coating film were evaluated on four scales of (excellent) A, B, C, D (poor).
A: No cracks B: Slight cracks C: Many cracks D: Many cracks and peeling of coating film

[Stain resistance test]
Magic ink (Terani Chemical Co., Ltd.) red was applied to each of the manufactured coated metal plates, and after 24 hours, wiped off with ethanol, and the traces of the ink were removed (excellent), A, B, C, D (poor). Was evaluated in four steps. In the case of a marked trace, an a * value indicating redness of CIELAB (JISZ8729) was measured before and after the test using a commercially available spectrophotometer (light source: 10 ° D65, SCI method), and the difference was determined. (Δa *) was evaluated as follows.
A: No trace B: Slight trace C: Δa * ≦ 3
D: Δa *> 3

Table 10 shows the levels and evaluation results of the manufactured coated metal plates. The abbreviations in Table 10 are as follows. The same applies to other tables for abbreviations and the like.
UB: Urethane bond skeleton TR: Triazine ring skeleton EP: Epoxy group Silane: Siloxane bond Rust inhibitor: Rust inhibitor (f)
Concentration depth: the thickness of the condensed portion formed on the surface layer (sometimes referred to as the surface condensed portion) Particle size: Number average particle size of triazine granules (water-soluble melamine resin) Tg: Each coating Glass transition temperature of film Tg difference: Difference in glass transition temperature between upper and lower coating films (glass transition temperature of upper coating film−glass transition temperature of lower coating film)

  As is clear from Tables 10-1 and 10-2, the coated metal plate corresponding to the examples of the present invention has excellent metal appearance, chemical penetration resistance, solvent resistance, and workability. .

  On the other hand, as is clear from Table 10-2 above, when a concentrated layer is not formed on the surface of the upper coating film 13 (when the surface layer is observed at a magnification of 100,000, melamine particles having a number-average particle diameter of 5 nm or more are not found). In the case of (observed) (Comparative Example 105), it can be seen that the chemical penetration resistance is clearly inferior to that of the example. When the urethane-bonded skeleton is not present in the upper coating film 13 (Comparative Example 104), it can be seen that the chemical permeation resistance is clearly inferior to the examples. When there is no triazine ring skeleton and no granular triazine moiety is concentrated in the surface layer of the upper coating film (Comparative Example 103), it is apparent that the chemical resistance permeability and the solvent resistance are clearly inferior to those of the examples. . When the glass transition point temperature of the upper layer coating film 13 is lower than 80 ° C. (Comparative Example 101), it can be seen that the chemical resistance permeability is clearly inferior to the examples. When the glass transition temperature of the upper layer coating film 13 is higher than 170 ° C. (Comparative Example 102), the processability is clearly inferior, and it is found that the chemical resistance and the solvent resistance are reduced when processed. .

Further, as is clear from Table 10-2, when the upper layer coating material contained silica (Comparative Example 106), the chemical permeation resistance and the stain resistance were inferior to those of the examples.
When the upper layer coating material contained a metal complex compound (Comparative Examples 107, 108, and 109), the chemical penetration resistance was inferior to that of the examples.

  Further, in the case where the granular triazine portion in the upper layer coating film 13 is concentrated at a position exceeding 15 nm from the surface layer (Example 143), the workability is reduced as compared with the other examples, and processing is performed. It can be seen that when this is done, the chemical resistance and the solvent resistance decrease. In addition, when the glass transition temperature of the lower layer coating film 15 is higher than the glass transition temperature of the upper layer coating film 13 (Example 146), it can be seen that the chemical permeation resistance is inferior to those of the other examples.

(Test Example 2) <Metal plate (original plate)>
An electrogalvanized steel sheet “NS ZINKOTE (registered trademark)” (hereinafter referred to as “EG”) manufactured by Nippon Steel & Sumitomo Metal Corporation was used as a metal sheet (original sheet). The amount of EG plated was 20 g / m ² per side.

<Paint>
In this test example, a single-layer structure as shown in FIG. 1A having only an upper layer coating film on one side of a metal plate (original plate) as described above, or FIG. 1B having a lower layer coating film and an upper layer coating film as shown in FIG. A coated metal plate having a two-layer structure as shown was produced.

Commercially available resins, silane coupling agents, and rust inhibitors used for forming the upper layer coating film and the lower layer coating film are as follows.
Polyurethane resin for upper layer coating: polyurethane resin 4 in Test Example 1
Polyurethane resin for lower layer coating: polyurethane resin 3 in Test Example 1
Water-soluble melamine resin: Melamine resin 2 in Test Example 1
Epoxy resin: Epoxy resin 1 in Test Example 1
Silane coupling agent: Silane coupling agent 1 in Test Example 1
Rust inhibitor: Rust inhibitor 2 in Test Example 1
Wax: Chemipearl S100 (Mitsui Chemicals)

  The upper layer paint was prepared by mixing the polyurethane resin, the melamine resin, and the wax in predetermined amounts, respectively, in a composition according to Table 11. Similarly, a lower layer paint was prepared by mixing the polyurethane resin, epoxy resin, silane coupling agent, rust inhibitor, and colorant in predetermined amounts, respectively, in a composition according to Table 11.

<Manufacture of painted metal sheets>
Various metal plates were degreased by immersion in an aqueous solution containing 2% by mass of FC-4336 (manufactured by Nippon Parkerizing Co., Ltd.) at a temperature of 60 ° C. for 10 seconds, washed with water, and dried.

  Next, each of the lower layer paints produced as described above was applied by a roll coater so as to have a dry film thickness of 0.5 μm. Heating (drying) the lower coating film in an induction heating furnace into which hot air is blown under the condition that the maximum temperature of the metal plate reaches 150 ° C and the heating time from the start of heating to the maximum temperature reaches 5 seconds. Cured). One second after reaching the maximum temperature, the painted metal plate was sprayed with water by spraying, and water-cooled under the condition that the cooling time from the maximum temperature to 30 ° C. was 1 second. In addition, the holding time of the maximum attainment temperature during heating was 1 second.

  Next, each of the upper layer paints produced as described above was applied by a roll coater to a dry film thickness of 10 μm. In an induction heating furnace into which hot air is blown, the upper coating film is heated (dry curing) under the condition that the maximum temperature of the metal plate reaches 230 ° C. and the heating time from the start of heating to the maximum temperature reaches 10 seconds. did. One second after reaching the maximum temperature, spray water on the painted metal plate, and after one second from reaching the maximum temperature, spray water on the painted metal plate, Water cooling was performed under the condition that the cooling time from the highest temperature to 30 ° C. was 1 second. In addition, the holding time of the maximum attainment temperature during heating was 1 second.

<Level>
For each of the manufactured coated metal sheet samples, the position (concentration depth) of the region where the granular triazine site (water-soluble melamine resin) is concentrated, and the granular The number average particle size (particle size) of the triazine moiety (water-soluble melamine resin) was measured. In addition, the concentration of the triazine moiety present in the area where the granular triazine moiety (water-soluble melamine resin) was concentrated was measured according to the method described above. Further, the glass transition temperature (Tg) of each coating film was measured for each of the manufactured coated metal sheet samples according to the method described above.
In addition, the surface layer enriched portion was stained with osmium oxide, and when observed at a magnification of 100,000 times using a transmission electron microscope, whether or not melamine particles of 5 nm or more were observed, and a plurality of enriched portions were formed. Was determined according to the method described above.

<Evaluation method>
The metal appearance, chemical permeation resistance test, and stain resistance test of each of the manufactured coated metal plates were evaluated in the same manner as in Test Example 1. The workability test and the corrosion resistance of the worked part were evaluated as follows.

[Workability test]
Each of the manufactured coated metal plates was cut into a width of 5 cm, and subjected to a 6T bending in a 20 ° C. atmosphere by a test method according to JIS G3312. Specifically, the same coated plate as the test piece was sandwiched between six inner sides, and the surface on which the upper layer coating film and the lower layer coating film were formed was outwardly bent by 180 degrees. The cracks of the coating film were evaluated on four scales of (excellent) A, B, C, D (poor).
A: No cracks B: Slight cracks C: Many cracks D: Many cracks and peeling of coating film

[Corrosion resistance test of processed part]
Each of the manufactured painted metal plates was cut into a width of 5 cm and extruded. The extrusion height was 7 mm. Thereafter, a salt spray test according to JIS Z 2371 was performed for 240 hours. After the test, the white rust generation area ratio in the entire area of the processed portion was determined by visual observation and evaluated as follows. In addition, the white rust occurrence area ratio is a percentage of the area of the white rust occurrence site with respect to the area of the observation site.
A: White rust occurrence area rate less than 10%
B: White rust generation area rate 10% or more and less than 25% C: White rust generation area rate 25% or more and less than 50% D: White rust generation area rate 50% or more and less than 75% E: White rust generation area rate 75% or more

Table 11 shows the levels and evaluation results of the manufactured coated metal plates. The abbreviations and the like in Table 11 are the same as in Table 10.
However, (Wa) + (Wb) and (Wb) / (Wa) are as follows.
(Wa) + (Wb): Content of polyurethane resin (a) with respect to total solid content (Wa: unit, mass%) and content of water-soluble melamine resin (b) with respect to total solid content (Wb: unit, mass) %) And the total content of (Wb) / (Wa): the content (Wa) of the polyurethane resin (a) based on the total solid content, and the content (Wb) of the water-soluble melamine resin (b) based on the total solid content. And the ratio of

  As is clear from Table 11, the total content (Wa) + (Wb) of the polyurethane resin (a) and the water-soluble melamine resin (b) used in the upper coating film 13 is 90% by mass or more and 100% by mass. % And the ratio (Wb) / (Wa) is more than 0 and 1 or less, it can be seen that the chemical penetration resistance of the manufactured coated metal plate is further improved.

(Test Example 3) <Metal plate (original plate)>
An electrogalvanized steel sheet “NS ZINKOTE (registered trademark)” (hereinafter referred to as “EG”) manufactured by Nippon Steel & Sumitomo Metal Corporation was used as a metal sheet (original sheet). The amount of EG plated was 20 g / m ² per side.

<Paint>
In this test example, a single-layer structure as shown in FIG. 1A having only an upper layer coating film on one side of a metal plate (original plate) as described above, or FIG. 1B having a lower layer coating film and an upper layer coating film as shown in FIG. A coated metal plate having a two-layer structure as shown was produced.

  The upper layer paint-3 in Test Example 1 was used as the upper layer paint, and the lower layer paint-8 in Test Example 1 was used as the lower layer paint.

<Manufacture of painted metal sheets>
Various metal plates were degreased by immersion in an aqueous solution containing 2% by mass of FC-4336 (manufactured by Nippon Parkerizing Co., Ltd.) at a temperature of 60 ° C. for 10 seconds, washed with water, and dried.

  Next, each of the lower layer paints produced as described above was applied by a roll coater so as to have a dry film thickness of 1.0 μm. Heating (drying) the lower coating film in an induction heating furnace into which hot air is blown under the condition that the maximum temperature of the metal plate reaches 150 ° C and the heating time from the start of heating to the maximum temperature reaches 5 seconds. Cured). One second after reaching the maximum temperature, water was wiped on the coated metal plate by spraying, and water-cooled under the condition that the cooling time from the maximum temperature to 30 ° C. was 1 second. In addition, the holding time of the maximum attainment temperature during heating was set to 1 second.

  Next, each of the upper layer paints produced as described above was applied by a roll coater so as to have a dry film thickness of 8 μm. In an induction heating furnace into which hot air has been blown, the upper layer temperature is set so that the maximum sheet temperature of the metal plate, the heating time from the start of heating to the maximum temperature, and the holding time at 40 to 100 ° C. are as shown in Table 12. The coating film was heated (dried and cured). One second after the temperature reached the maximum temperature, the coated metal plate was sprayed with water by spraying, and water-cooled under the condition that the cooling time from the maximum temperature to 30 ° C. was the time shown in Table 12. In addition, the holding time of the maximum attainment temperature during heating was set to 1 second.

<Level>
For each of the manufactured painted metal sheet samples, the thickness of the surface concentrated portion (concentration depth) and the number of granular triazine sites (water-soluble melamine resin) in the upper layer coating film according to the method described above. The average particle size (particle size) was measured. The N concentration N1 at a depth of 0.2 μm from the surface of the first coating and the N concentration N2 at a depth of 0.2 μm from the interface between the first coating and the metal plate toward the first coating. Was measured in accordance with the method described above. Further, the glass transition temperature (Tg) of each coating film was measured for each of the manufactured coated metal sheet samples according to the method described above.
In addition, the surface layer enriched portion was stained with osmium oxide, and when observed at a magnification of 100,000 times using a transmission electron microscope, whether or not melamine particles of 5 nm or more were observed, and a plurality of enriched portions were formed. Was determined according to the method described above.

<Evaluation method>
The same evaluation as in Test Example 1 was performed on each of the manufactured painted metal plates.

  Table 12 shows the levels and evaluation results of the manufactured coated metal plates. The abbreviations in Table 12 are the same as in Table 10.

As is clear from the above Table 12, after forming the upper layer paint, the heating time from the start of heating to the highest temperature is heated for 1 second to 30 seconds, and the cooling time from the highest temperature to 30 ° C. When the upper coating film 13 is formed by cooling under the condition of 0.1 second or more and 5 seconds or less, the obtained coated metal plate has excellent metal appearance, chemical penetration resistance, workability, and solvent resistance. Excellent chemical penetration resistance.
In addition, the first coating film manufactured by the method of holding at a temperature of 40 to 100 ° C. for 1 to 20 seconds, and then heating to over 200 ° C. for 1 to 10 seconds, and then cooling, has a plurality of concentrated layers It was formed (Examples 315, 316, 317). When a plurality of concentrated layers were formed on the first coating film, all of the metal appearance, chemical penetration resistance, workability and solvent resistance were excellent.

  When the maximum plate temperature was 160 ° C. (Comparative Example 301), the chemical permeation resistance and the solvent resistance were poor.

  Here, the cross section of the upper coating film 13 of Example 303 was dyed with osmium oxide, and then observed with a transmission electron microscope (TEM), and the distribution of osmium was observed with TEM-EDX. Various obtained microscope images were shown in FIGS. 5A to 5D. 5A, 5C, and 5D show cross-sectional TEM images of the upper coating film 13 of Example 303, and FIG. 5B shows the TEM-image of the upper coating film 13 of Example 303 dyed with osmium oxide. FIG. 4 shows an element mapping image of osmium when observed by EDX.

  As is clear from FIG. 5A, in the upper layer coating film 13 of Example 303, a black line-shaped region is reflected on the surface layer side in the cross-sectional TEM image. Looking at the osmium element mapping image shown in FIG. 5B, the osmium element that selectively stains the triazine site is linearly distributed in a portion corresponding to the black linear region in FIG. 5A. From this result, it can be seen that the black linear region in FIG.

  FIG. 5C is an enlarged view of the central portion of the upper coating film 13 in the cross-sectional TEM image in FIG. 5A. Referring to FIG. 5C, it can be seen that a black granular material is reflected in the cross-sectional TEM image. FIG. 5D is an enlarged view of one of the black particles. When a region corresponding to FIGS. 5C and 5D is confirmed in FIG. 5B, it is found that an osmium element is dispersed in such a region. Therefore, it can be seen that these dispersed osmium portions correspond to the triazine granules 101. That is, it can be seen that the black granules in FIGS. 5C and 5D are the triazine granules 101.

  As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is apparent that those skilled in the art to which the present invention pertains can conceive various changes or modifications within the scope of the technical idea described in the appended claims. It is understood that these also belong to the technical scope of the present invention.

1 painted metal plate 11 metal plate 13 upper layer coating film (first coating film)
15 Lower layer coating (second coating)
101 Triazine granules (dispersed second part)
103 Concentrated part (concentrated second part)

Claims (20)

A metal plate;
A first coating film containing a resin, which is located on at least one surface of the metal plate;
With
The first coating is:
A first site having a urethane binding skeleton;
A second moiety having a triazine ring skeleton;
Has,
The glass transition temperature of the first coating is 85 ° C or more and 170 ° C or less,
The second site is stained with osmium oxide and observed with a transmission electron microscope at a magnification of 100,000:
A dispersed second site in which particles having a number average particle size of 5 to 20 nm are dispersed;
A concentrated second portion that is present at a position from the surface of the first coating film to a depth of 15 nm and in which particles having a number average particle size of 5 nm or more are not observed:
A coated metal plate, characterized in that: N concentration N1 at a depth of 0.2 μm from the surface of the first coating, N at a depth of 0.2 μm on the first coating from the interface between the first coating and the metal plate. The coated metal sheet according to claim 1, wherein a ratio of N1 / N2 to the concentration N2 is 1.2 or more. The coated metal sheet according to claim 1, wherein the first coating has a plurality of the concentrated second portions. Further comprising a second coating between the first coating and the metal plate,
The coated metal plate according to any one of claims 1 to 3, wherein a glass transition temperature of the second coating film is equal to or lower than a glass transition temperature of the first coating film. The said 2nd coating film contains resin, and has a urethane bond skeleton, The coated metal plate of Claim 4 characterized by the above-mentioned. The coated metal sheet according to claim 4, wherein the second coating film contains a resin and has an epoxy group. The coated metal sheet according to any one of claims 4 to 6, wherein the second coating film contains a resin and has a siloxane bond. The second coating film contains at least one element selected from the group consisting of P, V, Ti, Si, and Zr. A coated metal plate as described in. The coated metal sheet according to any one of claims 4 to 8, wherein the glass transition temperature of the first coating is higher than the glass transition temperature of the second coating by 5 ° C or more. The coated metal plate according to any one of claims 4 to 9, wherein the thickness of the second coating film is 0.5 m or more and 15 m or less. The coated metal sheet according to any one of claims 1 to 10, wherein the first coating has a thickness of 0.5 m or more and 15 m or less. The coated metal sheet according to any one of claims 4 to 11, wherein at least one of the first coating film and the second coating film contains a coloring agent. The said 2nd coating film contains a black pigment as a coloring agent, The coated metal plate of any one of Claims 4-12 characterized by the above-mentioned. The coated metal plate according to any one of claims 1 to 13, wherein a texture is formed on at least one surface of the metal plate. A method for producing a coated metal plate having a predetermined first coating film on at least one surface of the metal plate,
A polyurethane resin (a) containing an anionic functional group and having a glass transition temperature of 75 ° C. or more and 160 ° C. or less, a triazine ring-containing water-soluble curing agent (b), and an aqueous solvent on at least one surface of the metal plate; Applying a first paint containing, forming the first coating by heating the metal plate coated with the first paint ,
When forming the first coating film,
Heating the metal plate coated with the first paint, so that the heating time from the start of heating of the metal plate coated with the first paint to the maximum attainment temperature is 1 second or more and 30 seconds or less,
Cooling the metal plate coated with the first paint so that the cooling time from the highest temperature to 30 ° C. is 0.1 second or more and 5 seconds or less. Manufacturing method of metal plate. The method for producing a coated metal sheet according to claim 15, wherein the triazine ring-containing water-soluble curing agent (b) is a melamine resin containing an imino group. The first paint,
The total content (Wa) of the content (Wa) of the polyurethane resin (a) with respect to the total solid content and the content (Wb) of the triazine ring-containing water-soluble curing agent (b) with respect to the total solid content (Wa) + ( Wb) satisfies the following formula (I), and
The ratio (Wb) / () of the content (Wa) of the polyurethane resin (a) to the total solid content and the content (Wb) of the triazine ring-containing water-soluble curing agent (b) to the total solid content. The method for producing a coated metal sheet according to claim 15, wherein Wa) satisfies the following expression (II).
90% by mass ≦ (Wa) + (Wb) ≦ 100% by mass Formula (I)
0 <(Wb) / (Wa) ≦ 1 Expression (II) A method for producing a coated metal plate further having a predetermined second coating between the metal plate and the first coating,
Prior to the application of the first paint, a polyurethane resin (c) having a glass transition temperature equal to or lower than the glass transition temperature of the polyurethane resin (a), an epoxy resin (d), a silane coupling agent (e), and P A second paint containing at least one of the rust preventives (f) containing at least one element selected from the group consisting of V, Ti, Si and Zr, and an aqueous solvent, The method according to any one of claims 15 to 17, wherein the second coating film is formed by coating on at least one side of a plate and heating the metal plate coated with the second paint. The method for producing the coated metal sheet described in the above. The method according to claim 18, wherein the glass transition temperature of the polyurethane resin (c) is lower than the glass transition temperature of the polyurethane resin (a) by 5C or more. 20. The heating method according to claim 15, wherein the heating is performed at a temperature of 40 to 100 [deg.] C. for 1 to 20 seconds, and then heating is performed to a temperature of more than 200 [deg.] C. with the heating time of 1 to 10 seconds. 3. The method for producing a coated metal sheet according to item 1.