Painted metal sheets and paints

Abstract

To provide a coated metal plate obtained by subjecting a metal substrate to coating, mainly used for the exterior coating, etc., of a building, but capable of easily increasing the temperature of a room when shone by sunlight since the coated metal plate is relatively thin to more surely suppress an amount of heat entered into a room.SOLUTION: A coated metal plate obtained by subjecting a metal substrate to coating includes an aluminum containing coating film formed on a rear surface opposite to a surface receiving solar radiation. The aluminum containing coating film includes an organic resin and aluminum pigment including aluminum particles having a particle size of 10-25 μm and a kurtosis of 0.025-0.175.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a coated metal sheet, and more particularly to a coated metal sheet for use on the exterior of buildings, etc. [Background technology]

[0002] Painted metal sheets are metal substrates coated with paint, and are mainly used for the exterior of buildings. However, because painted metal sheets are relatively thin, they have the problem of easily raising the temperature inside the room when exposed to sunlight. For this reason, paint with a heat-shielding effect is applied to the metal substrate to impart a heat-shielding function. By imparting a heat-shielding function, the rise in the temperature inside the room can be suppressed, which leads to a reduction in the use of air conditioning equipment, and ultimately contributes to the prevention of global warming.

[0003] As a method for imparting a heat shielding function to a metal substrate, for example, a coated metal plate is known in which a solar heat reflective coating film is formed on the front side (the side exposed to solar radiation) of a metal substrate and a coating film containing an aluminum pigment is formed on the back side (the side not exposed to solar radiation) of the metal substrate (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2001-89871 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the coated metal sheet of Patent Document 1 has a problem in that it does not have a sufficient heat shielding effect. This is because the coating film containing an aluminum pigment provided on the back surface of the coated metal sheet does not have a sufficient heat shielding effect, and therefore cannot sufficiently reduce heat radiation into the room.

[0006] The present invention has been made in view of the problems associated with the conventional inventions, and one of the objects of the present invention is to provide a coated metal sheet having a high heat shielding effect. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention has at least the following configuration or executes the following procedures.

[0008] A coated metal sheet according to one aspect of the present invention is a coated metal sheet in which a coating is applied to a metal substrate, and an aluminum-containing coating film is formed on the back surface opposite the surface exposed to solar radiation, and the aluminum-containing coating film is characterized in that it contains an organic resin and an aluminum pigment containing aluminum particles having a particle size of 10 μm to 25 μm and a kurtosis in the range of 0.025 to 0.175. With this structure, the amount of heat entering the room can be more reliably suppressed. This is because an aluminum-containing coating film is formed on the back surface.

[0009] Preferably, a solar radiation reflective coating film is formed on the surface that receives solar radiation. This configuration can more reliably reduce the amount of heat entering the room.

[0010] Preferably, the aluminum-containing coating film is characterized in that the aluminum pigment is 15 to 25 parts by volume relative to 100 parts by volume of the organic resin. With this configuration, the thermal emissivity from the rear surface of the coated metal sheet can be reduced more reliably.

[0011] Preferably, the aluminum-containing coating has a thickness of 1.8 μm to 4.1 μm. With this configuration, a coated metal sheet having excellent flexibility can be obtained.

[0012] A coating material according to one aspect of the present invention is a coating material for coating a metal substrate, and is characterized in that it contains an organic resin and an aluminum pigment containing aluminum particles having a particle size of 10 μm to 25 μm and a kurtosis in the range of 0.025 to 0.175. With this configuration, a coated metal plate with a high heat insulating effect can be formed. Effect of the Invention

[0013] As described above, according to the present invention, a coated metal sheet with a high heat-shielding effect can be provided. Therefore, by using the coated metal sheet of the present invention for the exterior of a building, particularly on the roof, the amount of heat entering the room can be more reliably suppressed. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a cross-sectional view of an apparatus used in an experiment to evaluate the heat-shielding effect of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described. Note that the embodiment described below is merely a specific example for carrying out the present invention, and is not to be construed as limiting the present invention.

[0016] The coated metal plate according to the present invention has a coating film formed on the front surface and the back surface of the metal substrate. The coating film formed on the front surface of the metal substrate is formed of a solar radiation reflective paint that easily reflects sunlight, and the coating film formed on the back surface of the metal substrate is formed of a paint containing an aluminum pigment that easily reduces heat radiation from the back surface. The front surface of the coated metal plate refers to the side that receives solar radiation when the coated metal plate is used for the exterior of a building, and the back surface of the coated metal plate refers to the surface opposite to the side that receives solar radiation. The coating film formed on the front surface of the coated metal plate is called a solar radiation reflective coating film, and the coating film formed on the back surface of the coated metal plate is called an aluminum-containing coating film. A coating film that easily reflects solar radiation is formed on the front surface of the coated metal plate, and a coating film that suppresses heat radiation is formed on the back surface of the coated metal plate, thereby achieving higher heat insulation. An important point in the present invention is that the coating film formed on the back surface reduces heat radiation to the indoor side. In other words, the aluminum-containing coating film formed on the back surface is the main feature of the present invention.

[0017] The metal substrate may be made of a metal required for the application. Specific examples include aluminum-zinc alloy plated steel sheet (Galvalume Steel Sheet (registered trademark)), iron sheet, copper sheet, steel sheet, aluminum sheet, etc.

[0018] The solar radiation reflective coating film formed on the surface of the coated metal sheet of the present invention is formed from a paint in which a resin and a pigment are mixed. If necessary, additives and the like may be mixed in. The additives and the like may include thickeners such as synthetic fine silica, organic bentonite, carboxymethyl cellulose, and polyvinyl alcohol, crosslinking agents such as melamine-based, benzoguanamine-based, and isocyanate-based crosslinking agents, and dispersants such as polyacrylic acid and polyacrylates.

[0019] The thickness of the solar reflective coating film is in the range of 10 μm to 60 μm, and the thickness may be changed as necessary.

[0020] Resins that can be used for the solar radiation reflective coating film include polyester resins, acrylic resins, vinyl acetate resins, phthalate ester resins, epoxy resins, urethane resins, etc. In particular, polyester resins are preferred. The reason why polyester resins are preferred is that they are excellent in terms of high hardness, weather resistance, flexibility, water resistance, chemical resistance, adhesiveness, etc.

[0021] The pigments used in the solar radiation reflective coating film are pigments that have excellent reflectivity to sunlight. Specific examples include metal compounds such as metal oxides, sulfides, and chromates, insoluble dyes (color pigments), and lake pigments. The above-mentioned pigments may be used alone or in combination of two or more.

[0022] It is preferable to use a solar reflective coating film having a solar reflectance of 40% or more. Note that the solar reflectance may be selected based on the requirements of the time.

[0023] The aluminum-containing coating film formed on the back surface of the coated metal sheet of the present invention is formed from a paint in which a resin and an aluminum pigment are mixed. If necessary, additives may be mixed in. The additives may include thickeners such as synthetic fine silica, organic bentonite, carboxymethyl cellulose, and polyvinyl alcohol, crosslinkers such as melamine, benzoguanamine, and isocyanate, and dispersants such as polyacrylic acid and polyacrylates.

[0024] The thickness of the aluminum-containing coating film is 1.2 μm to 5.9 μm, and preferably in the range of 1.8 μm to 4.1 μm. If the thickness is 1.8 μm or less, the thermal emissivity becomes high and sufficient heat shielding effect cannot be obtained. If the thickness is 4.1 μm or more, problems arise in bending, and the aluminum-containing coating film is likely to be damaged when the coated metal sheet is bent.

[0025] Resins used for the aluminum-containing coating film include polyester resins, acrylic resins, vinyl acetate resins, phthalate ester resins, epoxy resins, urethane resins, etc. In particular, polyester resins are preferred. The reason why polyester resins are preferred is that they are excellent in hardness, flexibility, water resistance, chemical resistance, adhesiveness, etc. In addition, alkoxysiloxanes, which have excellent heat resistance, may be used as the resin.

[0026] The aluminum pigment used in the aluminum-containing coating uses aluminum particles produced by crushing aluminum, etc. The aluminum particles used are scaly. A scaly shape refers to a shape such as a flat or curved plate, in which the area when observed from a certain direction (area in plan view) is larger than the area when observed from an angle perpendicular to the observation direction. Therefore, the thickness is extremely small (thin) compared to the particle size.

[0027] The aluminum particles used have a particle size of 10 μm to 25 μm and a kurtosis in the range of 0.03 to 0.175. That is, aluminum particles with a relatively large particle size and uniform particle size are used. By using an aluminum pigment using aluminum particles in this range, it is possible to more reliably reduce heat radiation from the back side of the coated metal plate. This is thought to be because the use of aluminum particles with a relatively large particle size and uniform particle size results in a coating film in a state in which the particles are uniformly and thinly dispersed on the metal substrate. Furthermore, since the coating film is formed in a state in which the particles are uniformly and thinly dispersed on the metal substrate, the flexibility is also improved. In general, aluminum pigments with a wide average particle size distribution, that is, those with a low kurtosis value or a negative value, are used in order to improve hiding power. Note that kurtosis represents the sharpness of the particle size distribution.

[0028] The amount of the pigment used in the aluminum-containing coating film is in the range of 5 to 40 parts by volume of the aluminum pigment per 100 parts by volume of the resin, and preferably 15 to 25 parts by volume. When the amount of the aluminum pigment is in the range of 15 to 25 parts by volume, the coating film has a better heat-shielding effect. If the amount is less than 15 parts by volume, the thermal emissivity becomes high and sufficient heat-shielding effect cannot be obtained. If the amount is more than 25 parts by volume, problems occur in bending, and there is a possibility that the aluminum-containing coating film may be damaged when the coated metal sheet is bent.

[0029] To form an aluminum-containing coating film, a paint is applied to a metal substrate. Specifically, the paint is applied using a roll coater, but the method is not limited thereto, and the paint may be applied using a brush, roller, or the like. The paint may also be applied using a spray method. In other words, the paint may be applied by any method as necessary. EXAMPLES

[0030] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0031] The experiment was carried out using a prototype heating box 1 made of a wooden plywood 2 with sides of 40 cm and a painted metal plate 3 as shown in Figure 1. The sides and bottom were covered on the outside with an aluminum laminate sheet, and a 30 mm thick foamed polystyrene was placed on the bottom. The experiment was carried out by radiating heat from a heating lamp 4 placed above the painted metal plate 3. Two heating lamps 4 with a specification of 270 W were used, and the lamp irradiation distance was set to 7 cm. This is based on the assumed amount of solar radiation on a midsummer day (temperature 30°C). The amount of radiant heat was evaluated by measuring the temperature at position A (temperature A), 20 cm from the bottom at the center of the prototype heating box 1.

[0032] The coated metal sheet according to the present invention was a metal substrate coated on both the front and back sides. The metal substrate was an aluminum-zinc alloy plated steel sheet (Galvalume Steel Sheet (registered trademark)) with a thickness of 0.27 mm. A paint containing polyester resin as a solar reflective paint was applied to the front side of the metal substrate to form a coating film with a thickness of 50 μm (solar reflectance 86%). The aluminum-containing coating film formed on the back side of the metal substrate was formed by applying a paint prepared by stirring and mixing the materials of the following Examples and Comparative Examples. The coating amount was 10 g / m unless otherwise specified. 2 The coating was carried out to form an aluminum-containing coating having a thickness of about 2.5 μm.

[0033] <Examples 1 to 5> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 22.5 parts by volume The aluminum pigment used had an average particle size of 9.8 μm to 25.8 μm and a kurtosis of 0.025 to 0.175.

[0034] <Example 6> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 22.5 parts by volume The aluminum pigment used had an average particle size of 18.7 μm and a kurtosis of 0.087. In Example 6, the aluminum-containing coating film was formed only on the back surface, and the front surface was uncoated.

[0035] <Comparative Examples 1 to 6> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 22.5 parts by volume The aluminum pigment used had an average particle size of 6.8 to 37.5 μm and a kurtosis of −0.078 to 0.201.

[0036] <Comparative Examples 7 and 8> In Comparative Example 7, the solar reflective paint was applied only to the front surface, and the back surface was left unpainted, while in Comparative Example 8, the metal substrate was used, that is, both surfaces were left unpainted.

[0037] Table 1 shows the results of the coated metal sheets using Examples 1 to 6, and Table 2 shows the results of the coated metal sheets using Comparative Examples 1 to 8. From Tables 1 and 2, it can be seen that the thermal emissivity from the backside of the coated metal sheet is affected by the average particle size and kurtosis of the aluminum pigment used. It was also found that this affects the A temperature. Specifically, it was found that a coated metal sheet with a high heat shielding effect can be obtained by using an aluminum pigment with an average particle size of 9.8 μm to 25.8 μm and a kurtosis of 0.025 to 0.175. Also, as can be seen by comparing Example 6 with Comparative Example 8, it can be seen that the thermal emissivity is significantly reduced by forming an aluminum-containing coating film on the backside.

[0038] TIFF0007603317000001.tif28159

[0039] TIFF0007603317000002.tif27159

[0040] Next, an experiment was conducted to see how the blending ratio of organic resin and aluminum pigment affects thermal emissivity and flexibility. Flexibility was evaluated with a grade of ◯ or ×. ◯ means that no problems occurred when bending, and × means that problems such as cracking of the coating occurred when bending.

[0041] <Examples 7 to 11> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 14.9 parts by volume to 25.3 parts by volume The aluminum pigment used had an average particle size of 18.7 μm and a kurtosis of 0.083.

[0042] <Comparative Examples 9 and 10> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 13.4 parts by volume, 30.3 parts by volume The aluminum pigment used had an average particle size of 18.7 μm and a kurtosis of 0.083.

[0043] Table 3 shows the results for coated metal sheets using Examples 7 to 11 and Comparative Examples 9 and 10. It can be seen from Table 3 that the blending ratio of organic resin and aluminum pigment affects the thermal emissivity and flexibility from the back side of the coated metal sheet. Specifically, if the ratio of aluminum pigment is too high, problems arise in flexibility, and if the ratio of aluminum pigment is too low, problems arise in thermal emissivity. Therefore, the aluminum pigment is preferably in the range of 14.9 to 25.3 parts by volume per 100 parts by volume of organic resin.

[0044] TIFF0007603317000003.tif34159

[0045] Next, an experiment was conducted to examine the effect of the thickness of the aluminum-containing coating film formed on the back side of the metal substrate. The aluminum-containing coating film formed on the back side of the metal substrate was made by mixing 22.5 parts by volume of aluminum pigment with 100 parts by volume of organic resin. The kurtosis of the aluminum pigment used was 0.083.

[0046] <Examples 12 to 16> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 22.5 parts by volume The aluminum pigment used had an average particle size of 18.7 μm and a kurtosis of 0.083, and was applied to a film thickness of 1.8 μm to 4.1 μm.

[0047] <Comparative Examples 11 and 12> Polyester resin and melamine crosslinking agent 100 parts by volume Aluminum pigment 22.5 parts by volume The aluminum pigment used had an average particle size of 18.7 μm and a kurtosis of 0.083.

[0048] Table 4 shows the results for the coated metal sheets using Examples 12 to 16 and Comparative Examples 11 and 12. It can be seen from Table 4 that the thermal emissivity and flexibility of the rear surface of the coated metal sheet are affected by the film thickness. Specifically, it can be seen that if the film thickness is less than 1.8 μm, there is a problem with the thermal emissivity, and if the film thickness exceeds 4.1 μm, there is a problem with the flexibility.

[0049] TIFF0007603317000004.tif39159 [Industrial Applicability]

[0050] INDUSTRIAL APPLICABILITY The coated metal sheet according to the present invention is useful for the exterior of a building, particularly for the roof, since it can more reliably suppress the amount of heat entering the room. [Explanation of symbols]

[0051] 1. Prototype heating box 2. Wooden plywood 3. Painted metal plate 4 Heat Lamps

Claims

1. A coated metal plate in which a coating is applied to a metal substrate, An aluminum-containing coating is formed on the back side opposite the surface exposed to sunlight. The aluminum-containing coating film includes an organic resin and an aluminum pigment including aluminum particles having a particle size of 10 μm to 25 μm and a kurtosis in the range of 0.025 to 0.175; The aluminum-containing coating film contains 14.9 to 25.3 parts by volume of the aluminum pigment per 100 parts by volume of the organic resin, The coated metal sheet has a thickness of 1.8 μm to 4.1 μm.

2. 2. The coated metal sheet according to claim 1, further comprising a solar reflective coating film formed on the surface that receives solar radiation.

3. A method for producing a coated metal plate by applying a coating to a metal substrate, comprising: forming an aluminum-containing coating film having a thickness of 1.8 μm to 4.1 μm on a back surface opposite to the surface receiving solar radiation; The aluminum-containing coating film includes an organic resin and an aluminum pigment including aluminum particles having a particle size of 10 μm to 25 μm and a kurtosis in the range of 0.025 to 0.175; The aluminum-containing coating film contains 14.9 to 25.3 parts by volume of the aluminum pigment per 100 parts by volume of the organic resin.

4. A method for manufacturing a painted metal plate as described in claim 3, characterized in that a solar reflective coating film is formed on the surface receiving solar radiation.

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