Coating material and method for producing coated metal sheets using said coating material

Abstract

[Problem] Coated metal sheets are mainly used in the exterior of buildings or the like. Since the coated metal sheets are thin, room temperature easily rises due to sunlight. For that reason, forming coating films on the back surfaces (sides not receiving solar radiation) of metal boards is known to reduce thermal radiation. However, practical application thereof has not been realized because the coating films cannot bear machining such as bending of the coated metal sheets and said machining results in detachment or cracks of the coating films. The problem to be addressed is to provide: a coating material which enables formation of a coating film exhibiting a high thermal-radiation-reduction effect and excellent flexibility; and a coated metal sheet using said coating material. [Solution] This coating material is for performing coating on metal boards, is characterized by including a vehicle, an aluminum powder, a solvent, and a suspending agent, and is characterized in that the vehicle is included in an amount of 100 mass parts, the aluminum powder is included in an amount of 45-65 mass parts, and a volatile component is included in an amount of 70-90% based on the mass in said coating material. This method for producing coated metal sheets uses said coating material.

Description

Paint and method for manufacturing painted metal plate using said paint

[0001] The present invention relates to a paint, and more particularly to a paint that reduces heat radiation when applied to a metal plate used for the exterior of a building or the like, and a method for producing a painted metal plate by applying the paint.

[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 building when exposed to solar heat. For this reason, paint with a heat-shielding effect is applied to the metal substrate to impart heat-shielding properties. By imparting heat-shielding properties, the rise in the temperature inside the building 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 heat-shielding properties to a metal substrate, for example, a coated metal sheet in which a coating film containing aluminum powder is formed on the back surface (the side not exposed to solar radiation) of the metal substrate is known. By forming a coating film containing aluminum powder on the back surface of the metal substrate, it is possible to reduce heat radiation into the room. However, unless the content of aluminum powder in the coating film is increased, it is not possible to sufficiently reduce heat radiation. However, when the content of aluminum powder is increased, there is a problem that when the coated metal sheet is processed, such as by bending, the coating film cannot withstand the processing, resulting in peeling or cracking of the coating film, and this has not been put into practical use.

[0004] For this reason, a coated metal plate is known in which the content of aluminum powder in the coating film on the back surface of the metal substrate is reduced, flexibility is improved to prevent peeling or cracking of the coating film, and a solar radiation reflective coating film is formed on the front surface of the metal substrate (the side that receives solar radiation) (see Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2001-89871

[0006] However, the coating film provided on the back surface of the metal substrate in Patent Document 1 does not have sufficient ability to reduce heat radiation, and therefore merely forms a solar radiation reflective coating film on the front surface (the side that receives solar radiation) of the metal substrate, and the effect of reducing heat radiation from the back surface of the metal substrate cannot be said to be sufficient.

[0007] Furthermore, when forming a solar reflective coating on the surface of a metal substrate (the surface exposed to solar radiation), the need to include a solar reflective pigment limits the design possibilities, such as color tone. On the other hand, if the radiant heat reduction effect can be increased simply by applying it to the back surface, it is possible to sufficiently reduce heat penetration by protecting the surface with a general weather-resistant coating that is not solar reflective, and this allows for freedom in design possibilities, such as color tone.

[0008] The present invention has been made in consideration of the problems with the conventional inventions, and an object of the present invention is to provide a coating material that has a high thermal radiation reduction effect and is capable of forming a coating film with excellent flexibility.

[0009] In order to achieve the above object, the present invention has at least the following configuration or executes the following procedure.

[0010] One aspect of the present invention is a paint for coating a metal substrate, comprising a vehicle, aluminum powder, a solvent, and an anti-settling agent, the vehicle being 100 parts by mass, the aluminum powder being 45 to 65 parts by mass, and the paint containing 70 to 90% by mass of volatile components. This configuration enables the formation of a coating film that is highly effective in reducing thermal radiation and has excellent flexibility.

[0011] One aspect of the present invention is a method for producing a coated metal plate by applying a paint containing a vehicle, aluminum powder, a solvent, and an anti-settling agent, the vehicle being 100 parts by mass, the aluminum powder being 45 to 65 parts by mass, and a volatile component being 70% to 90% by mass, the method comprising the steps of: applying the paint to the back surface of a metal substrate, which is the side that is not exposed to solar radiation; and drying the paint on the coated metal substrate to form a coating film with a thickness of 1.0 to 3.0 μm and an emissivity of 0.45 or less. This configuration makes it possible to produce a coated metal plate that is highly effective in reducing thermal radiation and has excellent flexibility.

[0012] As described above, according to the present invention, a painted metal sheet can be provided that has a high thermal radiation reduction effect and excellent flexibility, and by using the painted 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.

[0013] FIG. 2 is a cross-sectional view of an apparatus used in an experiment to evaluate the heat-shielding effect of the present invention.

[0014] 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 intended to limit the present invention.

[0015] <Paint> The paint according to the present invention is a paint for coating a metal substrate and contains a vehicle, aluminum powder, a solvent, and an anti-settling agent. The ratio of each sample in the paint is 45 to 65 parts by mass of aluminum powder per 100 parts by mass of vehicle, and volatile components account for 70% to 90% by mass in the paint according to the present invention. Here, the vehicle refers to a resin component that does not contain solvents or the like. Volatile components refer to solvents and the like, and more specifically, components that evaporate when the paint is heated at 200°C. Components that do not evaporate when the paint is heated at 200°C are referred to as solid components. In other words, paint can be divided into solid components and volatile components.

[0016] Furthermore, the paint of the present invention contains a large amount of aluminum powder, 45 to 65 parts by mass, per 100 parts by mass of vehicle, which allows for a high content of aluminum powder on the coating film surface, thereby enhancing the heat radiation reduction effect. Furthermore, the paint of the present invention contains a large amount of volatile components, 70 to 90% by mass, which allows for a low proportion of vehicle and aluminum powder in the paint, allowing for a coating amount of 10.0 to 20.0 g / m. ２When the vehicle is 100 parts by mass, the aluminum powder is 45 to 65 parts by mass, and the volatile components are 70 to 90% by mass, so that the aluminum powder and volatile components are high relative to the vehicle. This makes it possible to control the film thickness to 1.0 to 3.0 μm, and the absolute amount of aluminum powder can be reduced. This allows the formation of a coating film with excellent flexibility. In other words, the coating material according to the present invention has a vehicle content of 100 parts by mass, an aluminum powder content of 45 to 65 parts by mass, and a volatile component content of 70 to 90% by mass, so that the coating material has a high thermal radiation reduction effect and is capable of forming a coating film with excellent flexibility.

[0017] Thermosetting resins such as polyester resin, acrylic resin, vinyl acetate resin, phthalate ester resin, epoxy resin, and urethane resin can be used as the vehicle. Low-molecular-weight polyester resins are particularly preferred, such as Beckolite 46-118. These resins are preferred because of their excellent hardness, flexibility, water resistance, chemical resistance, and adhesive properties. The solids content of Beckolite 46-118 is 59.0% to 61.0% by mass at 107.5°C, according to the manufacturer's values. Furthermore, the value measured when heated at 200°C is 57.6% by mass. Therefore, Beckolite 46-118 contains 42.4% volatile components by mass. Alternatively, alkoxysiloxanes, which have excellent heat resistance, may be used as the resin.

[0018] It is preferable to use commercially available aluminum pigments as the aluminum powder. For example, Toyo Aluminum Co., Ltd.'s Aluminum Paste 0810M can be used. Aluminum Paste 0810M has an aluminum concentration of 66-69% by mass, 3% or less of stearic acid, and 28-33% of mineral spirits. In other words, 100 g of Aluminum Paste 0810M contains 66-69 g of aluminum powder. Furthermore, the measured value when heated at 200°C was 69.3% by mass. Therefore, this value was used as the aluminum content. However, because Aluminum Paste D462GR, a colored aluminum pigment, contains colored pigments and methacrylic resin, the aluminum content was set to 32.0%, as stated in the SDS.

[0019] The solvent may be a commercially available solvent, such as ST3000FX, ST1000, or Anon, manufactured by Chugai Shoko Co., Ltd.

[0020] If necessary, additives may be mixed in. Examples of additives that may be used include anti-settling agents such as Floon SH-290 and Disparlon A603-20X, and anti-foaming agents such as Floren AC-303HF.

[0021] <Painted Metal Sheet> Next, a painted metal sheet produced by applying the paint of the present invention to a metal substrate will be described. Applying the paint of the present invention to the back surface of a metal substrate can form a painted metal sheet with a high thermal radiation reduction effect and excellent flexibility. Here, the front surface of the painted metal sheet refers to the side that receives solar radiation when the painted metal sheet is used for the exterior of a building, and the back surface of the painted metal sheet refers to the side opposite the side that receives solar radiation. The front surface of the metal substrate (the side that receives solar radiation) is affected by rainwater and ultraviolet rays, so it is desirable to apply a weather-resistant paint to it. To further enhance the heat-shielding effect, a solar radiation-reflecting coating film may be formed on the surface of the painted metal sheet. The coating film formed on the front surface of the painted metal sheet is referred to as a weather-resistant coating film, and the coating film formed on the back surface of the painted metal sheet is referred to as an aluminum-containing coating film. An important aspect of the present invention is that the coating film (aluminum-containing coating film) formed by applying the paint of the present invention to the back surface reduces heat radiation to the indoor side.

[0022] The metal substrate can be made of a metal required for the application, and specific examples include aluminum-zinc alloy plated steel sheet (Galvalume Steel Sheet (registered trademark)), iron sheet, copper sheet, steel sheet, aluminum sheet, etc.

[0023] When forming a coating film on the surface of a coated metal sheet, it is preferable to use a paint containing a mixture of resin and pigment as the weather-resistant coating film. Additives may be added as needed. When forming a weather-resistant coating film, the thickness of the coating film is in the range of 10 μm to 60 μm. The thickness may be changed as needed.

[0024] Resins that can be used for weather-resistant coating films include polyester resins, acrylic resins, vinyl acetate resins, phthalate ester resins, epoxy resins, and urethane resins. Polyester resins are particularly preferred. The reason for their preference is that polyester resins are excellent in terms of hardness, weather resistance, flexibility, water resistance, chemical resistance, and adhesiveness.

[0025] The aluminum-containing coating film formed on the back surface of the coated metal sheet of the present invention is formed by applying the coating material of the present invention at a rate of 10.0 to 20.0 g / m. When the applied coating material is dried, the film thickness is in the range of 1.0 to 3.0 μm.

[0026] The thickness of the aluminum-containing coating film is in the range of 1.0 to 3.0 μm. Within this range, the aluminum-containing coating film has excellent flexibility, and is unlikely to be damaged even when the coated metal sheet is subjected to bending or other processing. Furthermore, when a coating film of this thickness is formed by applying the paint according to the present invention, the coating film has an emissivity of 0.45 or less and exhibits excellent radiant heat reduction effects.

[0027] Next, a method for producing a coated metal plate by applying the coating material according to the present invention to a metal substrate will be described. To form an aluminum-containing coating film, the method includes a coating step of applying the coating material according to the present invention to the back surface of the metal substrate, which is the side not exposed to solar radiation, at a rate of 10.0 to 20.0 g / m2, and a coating film formation step of drying the coating material on the coated metal substrate to a film thickness of 1.0 to 3.0 μm or less. This allows for the formation of a coating film with an emissivity of 0.45 or less. Specifically, the coating is performed using a roll coater, but this is not limiting and application can also be done with a brush, roller, or the like. Application can also be done by spraying.

[0028] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0029] Experiments were conducted using a prototype heating box 1 made of a 30 cm wooden plywood board 2 and a painted metal plate 3, as shown in Figure 1. To ensure steady-state operation, the outer sides of the box were covered with aluminum laminate sheets. A 25 mm thick expanded polystyrene insulation was placed on the bottom, and heat dissipation from the bottom was ignored and considered to be from the sides only. Since the amount of heat entering and radiated was equal in steady-state operation, the amount of heat radiated from the sides was considered to be the amount of heat entering. Heat was radiated from a heat lamp 4 placed above the painted metal plate 3, and each parameter was measured. Two 270 W heating lamps 4 were used, with lamp irradiation distances of 116 mm and 154 mm, respectively. This simulated solar radiation on a midsummer day (temperature 30°C). After confirming steady-state operation, the entire side surface, excluding the top and bottom, was evaluated. The side emissivity of the heating box was determined to be ε = 0.02 based on actual measurements. The total side area was 0.33 m2. For temperature and WBGT (heat index) evaluations, steady-state conditions were confirmed, and the average values ​​for one hour between 3 and 4 hours after the start of lamp irradiation were used. A thermocouple sensor and a Memory HiLogger LR8400 (manufactured by Hioki E.E. Corporation) were used for temperature measurement, and a FUSO-87595SD (manufactured by FUSO Corporation) was used for WBGT measurement. The metal plate 3 had a white front surface and a beige back surface. The metal plates with the back surfaces coated with the paints of Examples 1 and 10 and Comparative Example 6 (blank) were used to confirm the difference in heat penetration (Table 1). Furthermore, to confirm the effect of the color tone of the metal substrate surface, the surface of the metal plate 3 was painted black, and similar tests were conducted. A single 270W lamp 4 was used, and the lamp irradiation distance was 220 mm (Table 2). The measurement results are shown in Tables 1 and 2. The average temperature on the back surface of the top plate is the surface temperature inside the top plate. The WBGT and average space temperature were measured at position A, 10 cm from the bottom, at the center of the prototype heating box 1. In Example 1, the temperature of the underside of the top plate was higher than that of the uncoated Comparative Example 6 (blank). However, when actually air-conditioning the interior, the space temperature is important, and the WBGT becomes important when people are working there. In particular, the electricity cost of air-conditioning is a major expense, so reducing this cost is the primary objective.In addition, the reduction rate of heat penetration was about the same regardless of the surface color of the solar reflective coating, etc., indicating that there was no effect on the surface color.

[0030]

[0031]

[0032] The painted metal sheets used were metal substrates coated with the paints of Examples 1 to 12 on the back side. Furthermore, as comparative examples, metal substrates coated with the paints of Comparative Examples 1 to 5 were used. Furthermore, as comparative example 6, a commercially available color steel sheet was used for reference. This color steel sheet had a white front surface and a cream-colored back surface. An aluminum-zinc alloy-plated steel sheet (Galvalume Steel Sheet (registered trademark)) with a thickness of 0.27 mm was used as the metal substrate. Furthermore, the painted metal sheets of the examples were manufactured using the method for manufacturing a painted metal sheet according to the present invention.

[0033] Examples 1, 3 to 10, and 12: Vehicles used were Beckolite 46-118, Beckolite 46-119, Acrydic 56-728, and EPICLON H-360 manufactured by DIC Corporation; aluminum pigments used were Aluminum Paste 0810M, Aluminum Paste 4640NS, Aluminum Paste 5660NS, Aluminum Paste Z460, and Aluminum Paste D462GR manufactured by Toyo Aluminum K.K.; solvents used were ST-3000FX, ST-1000, and Anon manufactured by Chugai Shoko Co., Ltd.; anti-settling agents used were Floon SH-290 and Disparlon A603-20X; and anti-foaming agent used was Floren AC-303HF. Coated metal plates were prepared by baking the paint at 200°C for 60 seconds.

[0034] Example 2 A coated metal plate was prepared in the same manner as in Example 1, except that the surface was painted with a matte black spray.

[0035] Example 11 A coated metal plate was prepared in the same manner as in Example 10, except that the surface was painted with a matte black spray.

[0036] Comparative Examples 1 to 5: Beckolite 46-118 manufactured by DIC Corporation was used as the vehicle, Aluminum Paste 0810M manufactured by Toyo Aluminum K.K. was used as the aluminum pigment, ST3000FX and Anon manufactured by Chugai Shoko Co., Ltd. were used as the solvent, Flownon SH-290 was used as the anti-settling agent, and Flowlen AC-303HF was used as the defoaming agent. Coated metal plates were prepared by baking the paint at 200°C for 60 seconds.

[0037] Comparative Example 6 A commercially available color steel plate was used, which was not coated with the paint according to the present invention.

[0038] Comparative Example 7 A commercially available color steel plate was used, the front surface of which was painted with a matte black spray paint, and the back surface of which was not coated with the paint according to the present invention.

[0039] These paints were applied to color steel plates (150 x 150 x 0.5 mm) and placed on a heater. The surface temperature of the heater was measured using a thermocouple attached to the heater, and the thermal emissivity reduction effect was estimated by comparing the results with the radiation temperature measured using a non-contact thermometer. The principle of this measurement will be explained below.

[0040] Radiant heat can basically be thought of as the amount of infrared radiation emitted from a surface. A thermometer measures this amount of infrared radiation and then calculates the surface temperature. However, because the amount of emitted heat is a function of the surface temperature and emissivity, the thermometer cannot calculate the surface temperature unless the emissivity is known. This is why thermometers are calibrated using a pseudo-blackbody. Because they are calibrated using a blackbody, if a surface with a lower emissivity is measured, the measured temperature will naturally be lower than the actual temperature. For example, even if the actual surface temperature is 200°C, if the emissivity is 0.64, the thermometer will display 160°C.

[0041] Normally, when measuring a person's body temperature with a thermometer, the surface to be measured (such as human skin) is first measured with a thermocouple and then corrected. In this case, since correction is being made using a blackbody, the thermometer measures a lower temperature. The ratio of the surface temperature measured by the thermometer to the contact surface temperature measured by the thermocouple is the emissivity of the surface.

[0042] The room temperature was set to 23°C, the heater was set to 100°C, and the surface temperature of the metal plates prepared in the Examples and Comparative Examples was measured using a contact thermocouple and compared with measurements using a non-contact blackbody-corrected thermometer to determine the emissivity. The amount of radiant heat was also calculated using the Stefan-Boltzmann equation. The prepared metal plates were then bent to check for cracks, peeling, or the like in the coating film, thereby evaluating their flexibility.

[0043] Table 3 shows the results for metal plates coated with the paints of Examples 1 to 12 and Comparative Examples 1 to 7. Table 3 shows that the paints according to the present invention have excellent emissivity and flexibility. Note that, for the formulations in Table 3, unless otherwise specified, the units are given in parts by mass. Table 3 lists the mass ratio of aluminum powder to 100 parts by mass of vehicle, and also lists the mass ratios of solids and volatile components. These ratios enable the paints according to the present application to form coating films that have a high thermal radiation reduction effect and excellent flexibility.

[0044]

[0045] The coating material according to the present invention is useful because it can more reliably suppress the amount of heat that penetrates into the room. In addition, the coating material according to the present invention has excellent flexibility, making it useful because it can be used to produce coated metal sheets that are easy to process.

[0046] 1. Prototype heating box 2. Wooden plywood 3. Painted metal plate 4. Heat lamp

Claims

1. A paint for coating metal substrates, comprising a vehicle, aluminum powder, a solvent, and an anti-settling agent, wherein the vehicle is 100 parts by mass and the aluminum powder is 45 to 65 parts by mass, and the volatile components of the paint are 70% to 90% by mass.

2. A method for manufacturing a coated metal plate by applying the paint described in claim 1, comprising: a coating step of applying the paint to the back surface of the metal substrate, which is the side that is not exposed to solar radiation; and a coating film formation step of drying the paint on the coated metal substrate to form a coating film with a thickness of 1.0 to 3.0 μm and an emissivity of 0.45 or less.

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