JP5845126B2 - Painted metal plate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a coated metal plate having a self-repairing coating film and a method for producing the same.

  As a means for improving the scratch resistance of a coated metal plate, it is well known to increase the hardness of the coated film (so-called hard coat). However, although the hard coat film is difficult to be scratched, it cannot be repaired once it is scratched. Moreover, since the hard coat film is inferior in workability, it is difficult to apply it to a pre-coated metal plate.

  As a means for solving such a problem, it has been proposed to increase the resilience of the coating film to give the coating film self-healing properties (see, for example, Patent Document 1). A coating film excellent in rebound resilience can be repaired even if it is damaged, and is excellent in workability because it is soft. Thus, the precoat metal plate which is excellent in both scratch resistance and workability can be manufactured by forming the coating film which is excellent in impact resilience.

  Patent Document 1 describes that a urethane (meth) acrylate obtained by reacting a hydroxy group-containing (meth) acrylate, polycaprolactone polyol and polyisocyanate is used to form a coating film having excellent scratch resistance. Yes.

Japanese Patent Laid-Open No. 2004-35599

  When it is desired to color the coating film of a coated metal plate having a self-healing coating film, it is conceivable to add a coloring pigment to the self-healing coating film. However, according to preliminary experiments by the present inventors, when a color pigment is blended with a self-healing coating film containing urethane (meth) acrylate, depending on the type of the color pigment, the self-healing property is remarkably lowered and gloss is increased. And so on.

  As a means of coloring the coating of the coated metal plate without impairing the self-healing property, a clear coating (self-healing coating) containing urethane (meth) acrylate is formed on it by forming an undercoat coating containing a coloring pigment. ). In this way, it is expected that a coating film having a high gloss and self-repairing property, which is colored in an arbitrary color, can be formed by adopting a two-coat configuration. However, according to the preliminary experiments by the present inventors, a clear coating film (self-repairing coating film) containing a urethane (meth) acrylate formed on a colored coating film (undercoating film) by a general method. As a result, the self-healing property of the top coating film was significantly reduced against the initial expectation.

  As described above, when a coated metal plate having a conventional self-healing coating film has a two-coat structure in order to improve design properties, the self-healing property of the coating film may be deteriorated.

  The present invention has been made in view of the above points, and is a coated metal plate having a self-repairing coating film having a two-coat configuration, which is excellent in both self-repairing property and coating film adhesion of the coating film. It aims at providing a board and its manufacturing method.

  The present inventor has found that the above problem can be solved by adjusting the number of hydroxy groups in the undercoat coating film, and has further studied and completed the present invention.

That is, this invention relates to the following coated metal plates.
[1] A metal plate, an undercoat film formed on the metal plate and containing a resin having a hydroxy group, an overcoat film formed on the undercoat film and containing urethane (meth) acrylate, A coated metal sheet having a hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film, which is calculated by the following method, in the range of 0.2 to 0.8.
[Measurement Method of Hydroxy Group / Methylene Group Absorbance Ratio of Resin Constructing Undercoat Film]
Measure the infrared absorption spectrum of the resin constituting the undercoat film by infrared spectroscopy,
From the value of the peak height of the hydroxy group of 3300 ± 100 cm ⁻¹ and the value of the peak height of the methylene group of 725 ± 10 cm ^{−1 in} the obtained infrared absorption spectrum, “peak height of hydroxy group / methylene The value calculated as “group peak height” is the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film. Here, the peak height of the hydroxy group and the peak height of the methylene group are the height to the top in the wave number range of each peak from the baseline.
[2] The coated steel sheet according to [1], wherein the undercoat coating film includes a color pigment.

Moreover, this invention relates to the manufacturing method of the following coated metal plates.
[3] A step of preparing a metal plate, and an undercoat containing a hydroxyl group and a resin having a hydroxyl value of 5 to 45 mgKOH / g is applied on the metal plate, and a final plate temperature of 180 to 250 ° C. The step of forming an undercoating film on the metal plate by baking, and applying an overcoating paint comprising a composition containing a hydroxy group-containing (meth) acrylate, a polyol and a polyisocyanate on the undercoating film, Forming a top coat film on the undercoat film by curing the composition; and a method for producing a coated metal sheet.
[4] The method for producing a coated metal plate according to [3], wherein the undercoat paint includes a color pigment.

  ADVANTAGE OF THE INVENTION According to this invention, the coating metal plate which is excellent in the self-restoration property of a coating film, coating-film adhesiveness, and design property can be provided.

  The coated metal plate of this invention has a metal plate (coating original plate), the undercoat coating film formed on the said metal plate, and the top coat film formed on the said undercoat coating film. As will be described later, a chemical conversion film or the like may be formed between the metal plate and the undercoat film.

  Hereinafter, each component of the coated metal plate of this invention is demonstrated.

(1) Coating original plate The kind of metal plate used as the coating original plate is not particularly limited. Examples of coated raw sheets include cold-rolled steel sheets, galvanized steel sheets, Zn-Al alloy-plated steel sheets, Zn-Al-Mg alloy-plated steel sheets, aluminum-plated steel sheets, stainless steel sheets (austenite, martensite, ferrite, Martensite two-phase system), aluminum plates, aluminum alloy plates, copper plates and the like. The metal plate may be subjected to known coating pretreatments such as degreasing and pickling.

  The plate | board thickness of a metal plate is not specifically limited, According to the use of a coating metal plate, it can set suitably. For example, the plate thickness of the metal plate is about 0.1 to 2 mm.

(2) Chemical conversion treatment film From the viewpoint of improving the coating film adhesion and the corrosion resistance of the coated metal plate, the chemical conversion treatment film may be formed on the surface of the plating layer.

The type of chemical conversion treatment is not particularly limited. Examples of the chemical conversion treatment include chromate treatment, chromium-free treatment, phosphate treatment and the like. The adhesion amount of the chemical conversion coating is not particularly limited as long as it is within a range effective for improving coating film adhesion and suppressing corrosion. For example, in the case of a chromate film, the adhesion amount may be adjusted so that the total Cr conversion adhesion amount is 5 to 100 mg / m ² . Further, in the case of a chromium-free coating, the Ti-Mo composite coating has a range of 10 to 500 mg / m ² , and the fluoroacid-based coating has a fluorine equivalent or total metal element equivalent deposit of 3 to 100 mg / m ^2. The adhesion amount may be adjusted. Moreover, what is necessary is just to adjust the adhesion amount so that it may become 5-500 mg / m < ² > in the case of a phosphate membrane | film | coat.

  The chemical conversion film can be formed by a known method. For example, the chemical conversion solution may be applied to the surface of the metal plate by a roll coating method, a spin coating method, a spray method, or the like, and dried without being washed with water. The drying temperature and drying time are not particularly limited as long as moisture can be evaporated. From the viewpoint of productivity, the drying temperature is preferably in the range of 60 to 150 ° C. as the ultimate plate temperature, and the drying time is preferably in the range of 2 to 10 seconds.

(3) Undercoat coating The undercoat coating is formed on the surface of the metal plate (or the surface of the chemical conversion coating when a chemical conversion coating is formed). The undercoat coating improves the coating adhesion and corrosion resistance of the coated metal plate. Moreover, the undercoat coating film can also improve the design property of a coating metal plate by mix | blending various pigments.

  The kind of resin (base resin) constituting the undercoat coating is not particularly limited as long as it has a hydroxy group. Examples of the resin constituting the undercoat coating include polyester, epoxy resin, acrylic resin, and the like. The number average molecular weight of these resins is not particularly limited, but is preferably about 2000 to 30000 from the viewpoint of productivity. When the number average molecular weight is less than 2,000, it may be difficult to form an undercoat coating film. On the other hand, when the number average molecular weight exceeds 30000, the stability of the undercoat paint may be deteriorated.

  The undercoat coating film may be transparent, but may be colored by blending an arbitrary coloring pigment. Examples of the color pigment include titanium oxide, carbon black, chromium oxide, iron oxide, bengara, titanium yellow, cobalt blue, cobalt green, aniline black, phthalocyanine blue and the like.

  Moreover, you may mix | blend an antirust pigment with a base coat from a viewpoint of improving corrosion resistance. Examples of rust preventive pigments include zinc phosphate, zinc phosphite, magnesium magnesium phosphate, magnesium phosphate, magnesium phosphite, silica, calcium ion exchanged silica, zirconium phosphate, aluminum trihydrogen phosphate, zinc oxide Zinc phosphomolybdate, barium metaborate, strontium chromate and the like. Further, an extender pigment may be blended in the undercoat coating film. Examples of extender pigments include barium sulfate, titanium oxide, silica, calcium carbonate and the like.

One feature of the coated metal sheet of the present invention is that the resin constituting the undercoat film has a predetermined amount of hydroxy groups. More specifically, in the coated metal sheet of the present invention, the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat film obtained by the following measurement method is in the range of 0.2 to 0.8. Is a feature. When the absorbance ratio is less than 0.2, the adhesion between the metal plate (or chemical conversion film) and the undercoat film, and the adhesion between the undercoat film and the topcoat film are insufficient. On the other hand, when the absorbance ratio is more than 0.8, the self-healing property of the top coat film is insufficient.
[Measurement method of absorbance ratio of hydroxy group / methylene group]
1) First, the infrared absorption spectrum of the resin constituting the undercoat coating film is measured by infrared spectroscopy.
2) Then, from the value of the peak height of the hydroxy group of 3300 ± 100 cm ⁻¹ and the value of the peak height of the methylene group of 725 ± 10 cm ^{−1 in} the obtained infrared absorption spectrum, The value calculated as “height / peak height of methylene group” is the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film. Here, the peak heights of the hydroxy group and the methylene group are obtained as the height to the top of the wave number range of each peak from the baseline. It is preferable that the base line for obtaining the peak height of each peak is a line connecting the lowest portions on both sides of each peak. This is because even if adjacent peaks partially overlap, the influence of adjacent peaks can be eliminated.

  In the coated metal sheet of the present invention, the reason why the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat film is in the range of 0.2 to 0.8 will be described again after explaining the structure of the topcoat film. explain.

  The thickness of the undercoat coating film is not particularly limited, but is preferably in the range of 3 to 15 μm. When the film thickness is less than 3 μm, the coating film adhesion and the corrosion resistance may not be sufficiently improved. Further, when the undercoat coating film is a colored coating film, there is a possibility that the coating original plate (metal plate) cannot be sufficiently concealed. On the other hand, when the film thickness is more than 15 μm, it becomes easy to generate a crack when baking.

  The undercoat coating film can be formed by a known method. For example, an undercoating paint containing a resin having a hydroxyl group, a coloring pigment, or the like may be applied to the surface of a coating original plate (metal plate) and baked. At this time, in order to make the hydroxyl group / methylene group absorbance ratio of the resin constituting the undercoat coating film within the range of 0.2 to 0.8, the hydroxyl value is 5 to 45 mgKOH as the resin to be blended in the undercoat paint. It is preferable to use a resin within the range of / g (preferably 10 to 35 mgKOH / g). By baking such an undercoating paint containing a resin at an ultimate plate temperature of 180 to 250 ° C. for 20 to 60 seconds, an undercoating film having the absorbance ratio in the range of 0.2 to 0.8 can be formed. (See Examples). When the baking temperature is less than 180 ° C., the paint cannot be sufficiently baked, and the function of the undercoat film may not be sufficiently exhibited. On the other hand, when the baking temperature is higher than 250 ° C., the adhesion between the undercoat film and the topcoat film may be reduced due to excessive baking. The method for applying the undercoat paint is not particularly limited, and may be appropriately selected from methods used for producing precoated steel sheets. Examples of such a coating method include a roll coating method, a flow coating method, a curtain flow method, a spray method, and the like.

(4) Top coating film The top coating film is a coating film having a self-repairing property, which is formed on the under coating film.

  As the resin (base resin) constituting the top coat film, urethane (meth) acrylate capable of imparting self-healing properties to the paint film is used. Urethane (meth) acrylate is obtained by reacting hydroxy group-containing (meth) acrylate, polyol and polyisocyanate.

  The hydroxy group-containing (meth) acrylate is obtained by replacing the hydrogen atom of the carboxyl group of (meth) acrylic acid with an atomic group having a hydroxyl group. Examples of hydroxy group-containing (meth) acrylates include polycaprolactone-modified alkyl (meth) acrylate, hydroxyalkyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloyloxyethyl 2-hydroxyethyl-phthalic acid, 2-hydroxy-3-acryloyloxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, glycerol mono (meth) acrylate, pentaerythritol tri (Meth) acrylate is included.

  A polyol is an organic compound having two or more hydroxy groups in one molecule. Examples of the polyol include polyester polyol, polyether polyol, and polycaprolactone polyol.

  The polyisocyanate is an organic compound having two or more (preferably three or more) isocyanate groups in one molecule. Examples of polyisocyanates having two isocyanate groups in one molecule include tolylene diisocyanate, naphthalene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, 2,2,4-trimethylhexa Diisocyanate monomers such as methylene diisocyanate, methyl-2,6-diisocyanate hexanoate, norbornane diisocyanate are included. Examples of polyisocyanates having three or more isocyanate groups in one molecule include compounds obtained by isocyanurate modification of a diisocyanate monomer, compounds obtained by adduct modification of a diisocyanate monomer, compounds obtained by biuret modification of a diisocyanate monomer, 2-isocyanate Isocyanate prepolymers such as ethyl-2,6-diisocyanate caproate, triaminononane triisocyanate are included.

  As urethane (meth) acrylate which can give self-restoring property, a well-known thing can be used suitably. For example, urethane (meth) acrylate obtained by reacting hydroxy group-containing (meth) acrylate, polycaprolactone polyol and polyisocyanate described in Patent Document 1 can be used.

  In such urethane (meth) acrylate, the portion corresponding to hydroxy group-containing (meth) acrylate and polyisocyanate functions as a hard segment that resists external force, and the portion corresponding to polyol as a soft segment that relaxes external force. Function. In addition, hydrogen bonds formed between polar groups (for example, —NH and —CO in urethane bonds) contained in urethane (meth) acrylate function as pseudo-crosslinks that dissociate and recombine according to external forces. The coating film containing urethane (meth) acrylate is considered to exhibit self-healing ability by the following mechanism. When an external force is applied to the coating film containing urethane (meth) acrylate, hydrogen bonds between polar groups (for example, -NH and -CO in the urethane bond) are dissociated, and the soft segment with high mechanical freedom moves. Absorb external force. Thereafter, when the external force disappears, the soft segment having a high degree of mechanical freedom returns to the original position, and the hydrogen bonds between the dissociated urethane bonds are recombined.

  Although the film thickness of a top coat film is not specifically limited, The inside of the range of 5-30 micrometers is preferable, and the inside of the range of 8-20 micrometers is more preferable. When the film thickness is less than 5 μm, the self-repairing property may not be sufficiently exhibited. On the other hand, when the film thickness is more than 30 μm, it becomes easy to generate a crack when baking.

  The top coat film can be formed by a known method. For example, a top coating composition containing a hydroxy group-containing (meth) acrylate, polyol and polyisocyanate may be applied to the surface of the undercoat coating and baked to be cured. The method for applying the top coat is not particularly limited, and may be appropriately selected from methods used for producing precoated steel sheets. Examples of such a coating method include a roll coating method, a flow coating method, a curtain flow method, a spray method, and the like. The baking temperature is preferably in the range of 180 ° C. to 280 ° C. at the ultimate plate temperature, and the baking time is preferably in the range of 20 to 100 seconds. When baked under these conditions, a top coat film having excellent self-repairing properties can be formed.

(5) Back surface coating film The coating metal plate of this invention may have the coating film formed also in the surface on the opposite side to the surface in which the said undercoat coating film and top coating film were formed. The back coating film may have a one-coat configuration or a two-coat configuration. Moreover, the kind of resin which comprises a back surface coating film, and the kind of pigment are not specifically limited. For example, a back coating film can be formed by applying a known paint by a known method.

(6) Effect of the present invention As described above, the coated metal plate of the present invention has a hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film within the range of 0.2 to 0.8. With one feature.

  The hydroxy group contained in the resin constituting the undercoat film is bonded to polar groups contained in the coating original plate, the chemical conversion film, and the topcoat film, thereby improving the adhesion of the undercoat film to these. Accordingly, the resin constituting the undercoat coating film preferably has a predetermined amount or more of hydroxy groups, and more specifically, the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film is 0.2 or more. It is preferable. When the absorbance ratio is less than 0.2, the adhesion of the undercoat film to the coating original plate (or chemical conversion film) and the adhesion of the topcoat film to the undercoat film are reduced, and the coated metal plate is processed. Delamination occurs.

  On the other hand, the hydroxyl group of the resin constituting the undercoat film is a polar group that contributes to the self-healing property of the urethane (meth) acrylate constituting the topcoat film (for example, —NH or —CO in the urethane bond). Also bind to. Thus, if the polar group that should contribute to self-healing properties is oriented to the undercoat coating film side and consumed in bonds that do not contribute to self-healing properties, the self-healing properties of the topcoat film will deteriorate. Accordingly, the resin constituting the undercoat coating film preferably has a predetermined amount or less of hydroxy groups, and more specifically, the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film is 0.8 or less. It is preferable. When the absorbance ratio is more than 0.8, the self-healing property of the top coat film is lowered and the scratch resistance is lowered.

  In the coated metal plate of the present invention, the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film is in the range of 0.2 to 0.8. For this reason, the coated metal plate of this invention has ensured coating-film adhesiveness, without impairing the self-restoration property of top coat film.

  As described above, the coated metal plate of the present invention is excellent in both the self-repairing property and the coating film adhesion property of the coating film while being a coated metal plate having a two-coat configuration. Moreover, since the coating metal plate of this invention can mix | blend arbitrary coloring pigments etc. with an undercoat, it is excellent also in design property.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

1. Preparation of coated steel sheet A ferritic stainless steel sheet (SUS430, BA material) having a thickness of 0.4 mm was prepared as a coating original sheet. After degreasing the surface of the coating original plate, a chromium-free chemical conversion treatment solution (titanium hydrofluoric acid (H ₂ TiF ₆ ): 0.1 mol / L, zircon hydrofluoric acid (H ₂ ZrF ₆ ): 0.1 mol / L) It was coated with a bar coater so that the total metal element equivalent adhesion amount of Ti and Zr was 3.5 mg / m ² . The steel sheet coated with the chemical conversion solution was heated at a final plate temperature of 100 ° C. for 10 seconds to form a chemical conversion film.

  An undercoat paint was applied to the surface of the chemical-treated coating original plate, and baked at an ultimate plate temperature of 200 to 260 ° C. for 50 seconds to form an undercoat coating film having a dry film thickness of 5 μm. The undercoat paint was prepared by the following procedure. First, 100 parts by mass of a polyester resin (Byron 822, Byron 560, Byron 226, Byron 802, Byron KS-1520V or Byron 220; both Toyobo Co., Ltd.) and 10 parts by mass of a melamine resin (Cymel 303; Mitsui Cytec Co., Ltd.) Was added to a solvent so that the solid content was 40% by mass to prepare a resin solution. An acidic catalyst (Catalyst 600; Mitsui Cytec Co., Ltd.) was added to this resin solution so that the final concentration was 0.5% by mass to prepare a clear paint. Furthermore, 5 parts by mass of carbon black (MA-100; Mitsubishi Chemical Corporation) was added to 100 parts by mass of the resin solid content to the clear paint to prepare an undercoat paint. Table 1 shows the hydroxyl value and molecular weight of the polyester resin used.

After forming the undercoat coating film, the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film was measured. Hydroxy group / methylene group absorbance ratio of the resin constituting the undercoating film, an infrared spectrophotometer; in the measured infrared absorption spectra using (AVATAR 320 FT-IR Nicolet Co.), 3300 ± 100 (cm ^{- 1} ) The peak height of the hydroxy group and the peak height of the methylene group of 725 ± 10 cm ⁻¹ were obtained as “peak height of hydroxy group / peak height of methylene group”. The peak height of the hydroxy group and the methylene group was determined as the height from the base line to the uppermost part in the wave number range of each peak from the line connecting the lowest parts on both sides of each peak.

Next, the top coat was applied to the surface of the undercoat film, and baked at an ultimate plate temperature of 220 ° C. for 50 seconds to form a top coat film having a dry film thickness of 12 μm made of urethane methacrylate. The top coating material was prepared by mixing 250 parts by mass of the main agent and 125 parts by mass of the curing agent prepared by the following procedure.
(Main agent)
A mixture of 40 parts by mass of a polyester polyol (Flexorez 188; King Industries) and 30 parts by mass of a hydroxy group-containing methacrylate (Cotax LH601; Toray Fine Chemical Co., Ltd.) is dissolved in 180 parts by mass of methyl isobutyl ketone and solid. A main agent having a content of 28% by mass was prepared.
(Curing agent)
Hexamethylene diisocyanate (Duranate 24A-100; Asahi Kasei Corporation) 86.3 parts by mass was dissolved in 38.7 parts by mass of ethyl acetate to prepare a curing agent having a solid content of 69% by mass.

  Table 2 shows the composition of the prepared coated steel sheet (the hydroxyl value of the polyester resin blended in the undercoat paint, the baking temperature of the undercoat paint, and the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat paint). As shown in Table 2, the coated steel sheets of Examples 1 to 6 in which an undercoat containing a polyester resin having a hydroxyl value of 5 to 45 mg KOH / g was baked at an ultimate plate temperature of 180 to 250 ° C. constitute an undercoat film. The hydroxy group / methylene group absorbance ratio of the resin was in the range of 0.2 to 0.8. On the other hand, in the coated steel sheets of Comparative Examples 1 to 3, the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film was outside the range of 0.2 to 0.8.

2. Evaluation test (1) Self-healing property The self-healing property of the coating film was evaluated about each coated steel plate. In accordance with JIS K 5600-5-4 (scratch hardness (pencil method)), the coating film surface of each coated steel sheet was scratched with a pencil having a hardness of H or 2H. After standing at room temperature for 10 minutes, the state of scratches on the coating film was visually observed to evaluate the self-healing property of the coating film. If the scratches made using a pencil with a hardness of 2H were repaired, it was evaluated as “◎”, and the scratches made with a pencil with a hardness of 2H were not repaired. When the scratches used were repaired, they were evaluated as “◯”, and when the scratches applied using a pencil with a hardness of H were not repaired, they were evaluated as “x”.

(2) Coating film adhesion The coating film adhesion was evaluated for each coated steel sheet. Each coated steel plate was bent 180 ° so that the coating film was on the outside (0t bending or 1t bending). Next, a cellophane tape was applied to the bending ridge line, the cellophane tape was peeled off in a direction perpendicular to the bending ridge line, the peeled state of the coating film was visually observed, and the coating film adhesion was evaluated. When the coating film was not peeled even at 0t bending, it was evaluated as “」 ”. When the coating film was peeled off at 0t bending, it was evaluated as“ ◯ ”when the coating film was not peeled off at 1t bending. However, when a coating film peeled, it evaluated as "x".

(3) Results Table 3 shows the hydroxy group / methylene group absorbance ratio of the undercoat film, the self-healing evaluation results of the coating film, and the evaluation results of the coating film adhesion for each coated steel sheet.

  As shown in Table 3, the coated steel sheet of Comparative Example 1 had an insufficient number of hydroxy groups on the surface of the undercoat coating film, so that the self-healing property of the coating film was insufficient. In addition, the coated steel sheets of Comparative Examples 2 and 3 had insufficient coating film adhesion because the number of hydroxy groups on the surface of the undercoat coating film was too small. On the other hand, the coated steel sheets of Examples 1 to 6 were excellent in both self-healing properties and coating film adhesion of the coating film because the number of hydroxy groups on the surface of the undercoat coating film was appropriate.

  From the above results, it can be seen that the coated steel sheet of the present invention is excellent in both the self-repairing property and the coating film adhesion of the coating film even in the case of the two-coat configuration.

  The coated metal plate of the present invention is excellent in self-restoration of the coating film, adhesion of the coating film, and design properties. For example, a pre-coated metal plate used for home appliances, building materials, civil engineering, machinery, automobiles, furniture, containers, etc. Useful as.

Claims (4)

A metal plate,
An undercoating film formed on the metal plate without any other coating film and containing a resin having a hydroxy group,
A top coat film formed on the surface of the undercoat film and having self-healing properties including urethane (meth) acrylate,
The hydroxy group / methylene group absorbance ratio on the surface of the topcoat film side of the resin constituting the undercoat film calculated by the following method is in the range of 0.2 to 0.8.
Painted metal plate with 2 coats .
[Measurement method of absorbance ratio of hydroxy group / methylene group on the surface of the topcoat film side of the resin constituting the undercoat film]
The infrared absorption spectrum on the surface of the top coat film side of the resin constituting the undercoat film formed on the metal plate is measured by a reflection method of infrared spectroscopy,
From the value of the peak height of the hydroxy group of 3300 ± 100 cm ⁻¹ and the value of the peak height of the methylene group of 725 ± 10 cm ^{−1 in} the obtained infrared absorption spectrum, “peak height of hydroxy group / methylene The value calculated as “group peak height” is the hydroxy group / methylene group absorbance ratio of the resin constituting the undercoat coating film. Here, the peak height of the hydroxy group and the peak height of the methylene group are the height to the top in the wave number range of each peak from the baseline.   The coated metal sheet according to claim 1, wherein the undercoat coating film includes a color pigment. Preparing a metal plate;
By applying an undercoat paint containing a hydroxyl group-containing resin having a hydroxyl value of 5 to 45 mg KOH / g on the metal plate without any other coating film, and baking at a final plate temperature of 180 to 250 ° C. Forming an undercoat on the metal plate;
Self-healing property on the undercoat coating is obtained by applying a topcoat containing a composition containing a hydroxy group-containing (meth) acrylate, polyol and polyisocyanate to the surface of the undercoat and curing the composition . Forming a topcoat film having :
The manufacturing method of the coating metal plate of 2 coat structure containing.   The said undercoat paint is a manufacturing method of the coating metal plate of Claim 3 containing a coloring pigment.