Manufacturing method of painted metal sheet

Abstract

To provide a method for manufacturing a coated metal plate which easily bakes a coated film onto a metal substrate.SOLUTION: A method for manufacturing a coated metal plate includes a coating step, a first heating step, and a second heating step. The coating step is a step of coating a coating material 2 containing a resin, a pigment and a solvent onto a surface of a metal substrate 1. The first heating step is a step of heating the metal substrate 1 by heat conduction after the coating step. The second heating step is a step of blowing hot air to the coating material coated onto the surface of the metal substrate 1, and heating the coating material, after the first heating step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a coated metal sheet that can be used as a building material or the like. [Background technology]

[0002] Conventionally, a method for manufacturing a flow-pattern coated metal plate is known (see, for example, Patent Document 1). This method for manufacturing a flow-pattern coated metal plate involves rotating the applicator roll of a roll coater in the forward direction relative to the conveyance direction of a metal substrate, applying a high-viscosity vinyl chloride resin coating composition, and then baking the composition. The metal substrate to which the coating composition has been transferred by the applicator roll is continuously conveyed and undergoes the steps of drying, baking, and cooling to become a coated metal plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-245519 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional methods for producing coated metal sheets, the metal substrate onto which the coating composition has been transferred by a coating roll is generally transported into a furnace where the surface is heated by hot air to dry and bake the substrate.

[0005] However, when the coating composition is heated from the surface, the surface of the coating composition hardens first, making it difficult for the solvent inside the coating composition to evaporate, and making it difficult to bake the coating composition.

[0006] The present disclosure has been made in consideration of the above-mentioned problems in the conventional art, and an object of the present disclosure is to provide a method for producing a coated metal sheet that facilitates baking of a coating film onto a metal substrate. [Means for solving the problem]

[0007] In order to solve the above problems, a method for producing a painted metal plate according to one embodiment of the present disclosure includes a painting step, a first heating step, and a second heating step. The painting step is a step of applying a paint containing a resin, a pigment, and a solvent to a surface of a metal substrate. The first heating step is a step of heating the metal substrate by thermal conduction after the painting step. The second heating step is a step of blowing hot air onto the paint applied to the surface of the metal substrate to heat the paint after the first heating step. Effect of the Invention

[0008] In one embodiment of the method for producing a painted metal plate according to the present disclosure, the metal substrate is heated by thermal conduction in the first heating step before the surface of the paint begins to harden in the second heating step, so that the solvent located deeper than the surface of the paint is more likely to evaporate, making it easier to bake the coating onto the metal substrate. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an apparatus used in a method for producing a coated metal sheet according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of an apparatus used in the method for producing a coated metal sheet according to the second embodiment. [Diagram 3] FIG. 3 is a schematic diagram of an apparatus used in a method for producing a coated metal sheet according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present disclosure relates to a method for producing a painted metal sheet that can be used as a building material, etc., and more specifically, to a method for producing a painted metal sheet that is formed by applying a paint containing a resin, a pigment, and a solvent to the surface of a metal substrate, and then evaporating the solvent to bake the pigment onto the metal substrate.

[0011] Hereinafter, the method for producing a coated metal sheet according to the present disclosure will be described based on an embodiment. Note that the embodiment of the method for producing a coated metal sheet according to the present disclosure is not limited to the following embodiment, and various modifications are possible within the scope of the technical idea of ​​the present disclosure.

[0012] A method for producing a coated metal sheet according to a first embodiment will be described with reference to FIG.

[0013] The method for producing a coated metal sheet includes a coating step, a first heating step, and a second heating step. The coating step includes a step of applying a paint 2 containing a resin, a pigment, and a solvent to the surface of a metal substrate 1.

[0014] The metal substrate 1 used in the present embodiment is not particularly limited, but examples thereof include an aluminum-plated steel plate, a zinc-plated steel plate, an aluminum-zinc-plated steel plate, a stainless steel plate, etc. In addition, a long metal substrate can be used as the metal substrate 1.

[0015] When painting the metal substrate 1, the metal substrate 1 is unwound from a pay-off reel (not shown) in which the long metal substrate 1 is wound into a coil shape and continuously transported while undergoing various treatments, and the metal substrate 1 after the painting process is cut to the desired dimensions or wound up again into a coil shape without cutting, in a continuous processing process.

[0016] Prior to the painting process for such a metal substrate 1, if necessary, pretreatment such as chemical conversion treatment such as chromate treatment or zinc phosphate treatment, or removal of dirt such as oil, grease, and dust from the surface of the metal substrate 1 may be performed, and then the painting process may be performed.

[0017] In addition, prior to carrying out an outer layer coating in which paint 2 (topcoat paint) is applied to form a topcoat coating film on the surface of the metal substrate 1, an appropriate undercoat coating film may be formed on the metal substrate 1 as necessary, and / or an appropriate intermediate coating film may further be formed.

[0018] When forming an undercoat coating film, the paint (undercoat paint) can be, for example, an epoxy resin-based paint in which extender pigments such as titanium oxide, fine clay powder, calcium carbonate, and anti-rust pigments are dispersed in a thermosetting resin such as epoxy resin, epoxy urethane resin, or polyester resin. Anti-rust pigments can be, for example, those mainly composed of chromates such as strontium chromate or calcium chromate. In undercoating, an undercoat paint having such a composition is applied to one side of the metal substrate 1, and in some cases, an undercoat paint is also applied to the other side of the metal substrate 1. In addition, a backcoat paint having a different composition from the undercoat paint may be applied to the other side of the metal substrate 1. The undercoat paint and backcoat paint can be applied by an appropriate application device consisting of immersion, spray, brush application, roll coater, air knife, electrostatic application, etc.

[0019] After the undercoat paint is applied, the undercoat paint can be cured by baking or the like onto the metal substrate 1 to form an undercoat paint film.

[0020] The thickness of the undercoat film is not particularly limited and may be appropriately set, but is preferably in the range of 3 to 25 μm.

[0021] In addition, when forming the intermediate coating film, a suitable liquid coating material for precoat use can be used as the coating material (intermediate coating material), and for example, a polyester-based, urethane-based, alkyd-based, fluorine-based, acrylic-based, vinyl chloride-based, or other coating material can be used. The intermediate coating material can be applied by a suitable coating device consisting of immersion, spraying, brush coating, roll coater, curtain coater, air knife, electrostatic coating, or the like, and after the intermediate coating material is applied, the undercoat coating material can be cured by baking or the like on the metal substrate 1 to form the intermediate coating film. The thickness of the intermediate coating film at this time is appropriately adjusted, but it is preferable that the dry coating film thickness is 5 to 40 μm, particularly 10 to 30 μm. When such an intermediate coating film is formed, the coating film performance such as corrosion resistance, weather resistance, chemical resistance, and hiding power of the coated metal plate can be improved within the range of the coating film thickness that can be applied by the coating material, and is particularly suitable when the coated metal plate is used as an exterior building material.

[0022] When applying an outer layer coating to the metal substrate 1, the paint 2 can be an appropriate liquid paint for precoat purposes, similar to the above-mentioned intermediate paint, and for example, polyester-based, urethane-based, alkyd-based paint, fluorine-based, acrylic-based, vinyl chloride-based paint, etc. can be used.

[0023] In addition, a suitable pigment is contained in a solvent as the paint 2. Examples of such pigments include titanium oxide, carbon black, iron oxide yellow, iron oxide red (red oxide), aluminum flakes, mica flakes, colored glass flakes, and organic blue (phthalocyanine blue). The blending ratio of such pigments in the paint 2 can be set within an appropriate range, but is usually preferably 0.1 to 80% by weight, and particularly preferably 0.5 to 50% by weight.

[0024] In particular, a metallic appearance can be imparted to the coating film by including metal powder such as aluminum powder, nickel powder, copper powder, etc. as a pigment in the paint 2. This metal powder also includes powders of composites of metal and inorganic substances, such as metal-coated glass powder.

[0025] The average particle size of the metal powder is preferably in the range of 5 to 80 μm, particularly 10 to 30 μm. If the particle size is too large, the coating properties of the coating material 2 deteriorate, and it becomes difficult to apply the coating uniformly when applying with a roll coater. If the particle size is too small, a sufficient metallic feel cannot be imparted to the outer coating film made of the pigment baked onto the metal substrate 1, and when using flaky metal powder, the change in light reflectivity due to the disturbance of the arrangement may not be fully exhibited.

[0026] When such metal powder is used, the amount of the powder in the coating material 2 is preferably in the range of 1 to 15% by weight.

[0027] When applying the coating material 2, the coating material 2 is supplied to the peripheral surface of the coating roll 3 while rotating, and then the coating material 2 on the peripheral surface of the coating roll 3 is brought into contact with the surface of the metal substrate 1 to apply the coating material 2, and then the metal substrate 1 is transported toward the heating roll 71.

[0028] In the example shown in FIG. 1, a pickup roll 5 is disposed above a paint pan 4 in which a paint 2 is stored. The pickup roll 5 is disposed so that its lower portion is immersed in the paint 2 in the paint pan 4. The pickup roll 5 is disposed so that the peripheral surface of the applicator roll 3 contacts the peripheral surface of the pickup roll 5. A long metal substrate 1 is transported between the applicator roll 3 and a backup roll 6 disposed opposite the applicator roll 3. At this time, the pickup roll 5 is driven to rotate, so that the paint 2 is supplied to the peripheral surface of the pickup roll 5, and the paint 2 supplied to the peripheral surface of the pickup roll 5 is supplied to the peripheral surface of the applicator roll 3. Furthermore, the applicator roll 3 rotates, so that the paint 2 is supplied to the surface of the metal substrate 1 and applied thereto. The metal substrate 1 to which the paint 2 has been applied is transported toward a heating roll 71. Here, the rotation direction of the applicator roll 3 may be forward or reverse to the conveying direction of the metal substrate 1, but in the example shown in FIG. 1, the applicator roll 3 is rotated in the reverse direction to the conveying direction of the metal substrate 1.

[0029] The first heating step is a step of heating the metal substrate 1 by thermal conduction after the painting step. The heating of the metal substrate 1 in the first heating step is performed without the intervention of the paint 2 applied to the surface of the metal substrate 1. The heating of the metal substrate 1 in the first heating step is performed by a metal substrate heating device 7.

[0030] The metal substrate heating device 7 does not indirectly heat the metal substrate 1 via the coating material 2, but directly heats the metal substrate 1 without the coating material 2. The metal substrate heating device 7 of this embodiment has a heating roll 71 with which the metal substrate 1 comes into contact. The heating roll 71 is made of metal and has an internal heater 70, and the heating roll 71 itself is heated by the internal heater 70. The heated heating roll 71 heats the metal substrate 1 that it comes into contact with by thermal conduction. The coating material 2 is not directly heated by the heating roll 71, but is heated by thermal conduction from the metal substrate 1.

[0031] The heating roll 71 does not have to be made of metal, and may be made of a material having a predetermined thermal conductivity. As the heater 70 for heating the heating roll 71 itself, various heaters, including an electric heater, may be appropriately used. The heating roll 71 does not have to have the heater 70 inside, and may be heated by an external heat source.

[0032] In the first heating step, the coating material 2 applied to the surface of the metal substrate 1 is not directly heated by the heating roll 71. For this reason, the surface of the coating material 2 applied to the surface of the metal substrate 1 (i.e. the surface opposite to the side in contact with the surface of the metal substrate 1) is not easily heated, and hardening of the surface of the coating material 2 is not easily promoted.

[0033] The paint 2 is heated from the side in contact with the surface of the metal substrate 1 by heat conduction from the metal substrate 1. For this reason, the solvent inside the heated paint 2 is likely to escape into the atmosphere from the surface of the paint 2 where curing has not progressed, and evaporation from the paint 2 is likely to progress.

[0034] After the first heating step as described above, a second heating step is carried out. The second heating step is a step of blowing hot air onto the paint 2 applied to the surface of the metal substrate 1 to heat the paint 2. In this embodiment, the paint 2 is heated in the second heating step by a heating furnace 8. The heating of the paint 2 in this second heating step is widely and generally carried out as disclosed in Patent Document 1, and a detailed description thereof will be omitted.

[0035] In the second heating step, the surface of the paint 2 applied to the surface of the metal substrate 1 is directly heated. In the second heating step, the surface of the paint 2 is heated, and hardening of the surface of the paint 2 progresses. As hardening of the surface of the paint 2 progresses, the solvent inside the paint 2 becomes less likely to escape from the surface of the paint 2 and to evaporate from the paint 2, but because evaporation of the solvent inside the paint 2 progresses in the first heating step, only a small amount of solvent remains inside the paint 2 in the second heating step, and no problems occur.

[0036] Through the first and second heating steps, the solvent contained in the paint 2 is evaporated from the paint 2, and the pigment is baked onto the metal substrate 1, forming an outer coating film on the metal substrate 1. The outer coating film formed on the metal substrate 1 has a lower content of residual solvent than in the conventional example, and is in a good dry state.

[0037] Next, a method for producing a coated metal sheet according to a second embodiment will be described with reference to Fig. 2. The method for producing a coated metal sheet according to the second embodiment is mostly the same as the method for producing a coated metal sheet according to the first embodiment. Therefore, explanations that overlap with the first embodiment will be omitted, and differences will be mainly described.

[0038] In the method for producing a coated metal sheet of the first embodiment, the metal substrate heating device 7 has a heating roll 71. In contrast to this, in the method for producing a coated metal sheet of the second embodiment, the backup roll 6 also serves as the metal substrate heating device 7. The backup roll 6 is made of metal and has an internal heater 70, and the backup roll 6 itself is heated by the internal heater 70. The heated backup roll 6 heats the metal substrate 1 that it comes into contact with by thermal conduction. The coating material 2 is not directly heated by the backup roll 6, but is heated by thermal conduction from the metal substrate 1.

[0039] The backup roll 6 does not have to be made of metal, but may be made of a material having a predetermined thermal conductivity. As the heater 70 for heating the backup roll 6 itself, various heaters, including an electric heater, may be appropriately used. The backup roll 6 does not have to have the heater 70 inside, but may be heated by an external heat source.

[0040] In the second embodiment, in the first heating step, the paint 2 applied to the surface of the metal substrate 1 is not directly heated, and therefore the surface of the paint 2 is not easily heated and hardening of the surface of the paint 2 is not easily promoted. As a result, the solvent inside the heated paint 2 is easily released into the atmosphere from the surface of the paint 2 where hardening has not progressed, and evaporation from the paint 2 is easily promoted.

[0041] The outer coating film formed through the first and second heating steps has a lower content of residual solvent than in the conventional example and is in a good dry state.

[0042] In the second embodiment, the backup roll 6 also serves as the metal substrate heating device 7, so that there is no need to provide a separate large-scale device as the metal substrate heating device 7.

[0043] Next, a method for producing a coated metal sheet according to a third embodiment will be described. The method for producing a coated metal sheet according to the third embodiment is mostly the same as the methods for producing coated metal sheets according to the first and second embodiments. Therefore, explanations that overlap with the first and second embodiments will be omitted, and differences will be mainly described.

[0044] The methods for producing a coated metal sheet according to the first and second embodiments do not include a step of heating the metal substrate 1 before the coating step. In contrast, the method for producing a coated metal sheet according to the third embodiment further includes a pre-coating heating step of heating the metal substrate 1 by thermal conduction before the coating step.

[0045] In the third embodiment, the metal substrate heating device 7 has a heating roll (not shown) with which the metal substrate 1 comes into contact, located upstream of the backup roll 6. This heating roll is made of metal and has an internal heater, similar to the heating roll 71, and the heating roll itself is heated by the internal heater. The heated heating roll heats the metal substrate 1 in contact with it by thermal conduction.

[0046] In this way, by providing a pre-painting heating step in which the metal substrate 1 is heated by heat conduction before the painting step, it becomes easier to apply a highly viscous paint 2 in the painting step, and it becomes easier to shorten the heating time (drying time) in the first heating step and the second heating step. Furthermore, when the temperature of the metal substrate 1 before painting is set to 140°C or lower, it is possible to make the paint 2 low in viscosity without increasing the amount of solvent contained in the paint 2.

[0047] Next, a modified method for producing a coated metal sheet will be described with reference to Fig. 3. The modified method for producing a coated metal sheet is mostly the same as the method for producing a coated metal sheet of the first embodiment. Therefore, explanations that overlap with the first embodiment will be omitted, and differences will be mainly described.

[0048] In the method for producing a coated metal sheet according to the first embodiment, the metal substrate heating device 7 includes a heating roll 71. In contrast to this, in the method for producing a coated metal sheet according to the modified example, the metal substrate heating device 7 is configured with an electromagnetic induction heating device 72. The electromagnetic induction heating device 72 heats the metal substrate 1 by electromagnetic induction heating (Induction Heating). In the modified example, the heating roll 71 is not provided, and therefore the metal substrate 1 is transported from the backup roll 6 toward the heating furnace 8. The electromagnetic induction heating device 72 is provided between the backup roll 6 and the heating furnace 8, and heats the metal substrate 1 transported from the backup roll 6 toward the heating furnace 8 by electromagnetic induction heating.

[0049] In the modified example, in the first heating step, the paint 2 applied to the surface of the metal substrate 1 is not directly heated, and therefore the surface of the paint 2 is not easily heated and hardening of the surface of the paint 2 is not easily promoted. As a result, the solvent inside the heated paint 2 is easily released into the atmosphere from the surface of the paint 2 where hardening has not progressed, and evaporation from the paint 2 is easily promoted.

[0050] The outer coating film formed through the first and second heating steps has a lower content of residual solvent than in the conventional example and is in a good dry state.

[0051] Furthermore, in the modified example, since the metal substrate heating device 7 is composed of an electromagnetic induction heating device 72, there is no need to place a device such as a roll on the transport path of the metal substrate 1, and there is no need to significantly change the transport path of the metal substrate 1 compared to the conventional example.

[0052] A demonstration experiment was conducted on the manufacturing method of the coated metal sheet of the present disclosure, and will be described below.

[0053] <Steel plate> A 0.35 mm thick hot-dip 55% aluminum-zinc-magnesium alloy-plated steel sheet (Nippon Steel & Co., Ltd., SGL) was coated with 50 g / m of paint-type chromate (Nihon Parkerizing Co., Ltd., model number: ZM1300) as a base treatment. 2 Apply at a basis weight of

[0054] <Undercoat> Primer (Nippon Paint Industrial Coatings Co., Ltd., model number: P667S) was applied at 4.8 g / m. 2 The coating is applied at a basis weight of 100g and baked at 200°C for 30 seconds to form a primer coating.

[0055] <Outer layer paint> Two types of paint 2 (manufactured by Kansai Paint Co., Ltd., model number: GHK01) were applied to the metal substrate 1: a low-viscosity paint with a paint viscosity of 60 sec (Ford cup, 20°C) and a high-viscosity paint with a paint viscosity of 180 sec (Ford cup, 20°C).

[0056] <Production of evaluation test pieces> First, a plated steel sheet coated with paint-on chromate is prepared.

[0057] Next, a primer is applied to the prepared plated steel sheet and dried to form the metal substrate 1.

[0058] Next, paint 2 is applied as a topcoat to metal substrate 1. When the topcoat is to be a multi-layered film having two or more layers, the topcoat painting process of applying paint 2 to metal substrate 1 is repeated.

[0059] <Examples and Comparative Examples> There are a total of 10 Examples, numbered 1 to 5 and 11 to 15, and a total of 6 Comparative Examples, numbered 6 to 10 and 16, which are hereinafter referred to as Examples 1 to 5, Examples 11 to 15, Comparative Examples 6 to 10, and 16, respectively.

[0060] Examples 1 to 5 and Comparative Examples 6 to 9 are examples that do not include a pre-painting heating step as in the first and second embodiments, and Comparative Example 10, Examples 11 to 15, and Comparative Example 16 are examples that include a pre-painting heating step as in the third embodiment.

[0061] Furthermore, Examples 1 to 5 and Comparative Examples 6 to 9 are examples in which a low-viscosity paint with a paint viscosity of 60 sec (Ford cup, 20°C) was used as paint 2, while Comparative Example 10, Examples 11 to 15, and Comparative Example 16 are examples in which a high-viscosity paint with a paint viscosity of 180 sec (Ford cup, 20°C) was used.

[0062] Moreover, Comparative Examples 6 to 9 are examples that do not include the first heating step.

[0063] Other test conditions and evaluation results are shown in [Table 1].

[0064] [Table 1]

[0065] <Evaluation Results> Appearance was evaluated for the presence or absence of "popping." "Popping" is a coating defect that occurs when the solvent contained in Paint 2 evaporates and escapes into the atmosphere as Paint 2 dries. Popping is likely to occur when the surface layer of the topcoat coating film formed by drying Paint 2 hardens faster than the interior of the topcoat coating. Cases where no "popping" was found with the naked eye on the surface of the topcoat coating film were rated "○ (good)," and cases where "popping" was found were rated "× (bad)."

[0066] Appearance was also evaluated for the presence or absence of a "rough" feeling. "Rough" feeling refers to the sensation when the surface of the topcoat film is palpated. Macroscopically, this cannot be recognized as "cracks", but microscopically, like "cracks", it is one of the coating film defects formed when the solvent evaporates from Paint 2 and escapes into the atmosphere. The less "rough" feeling there is, the more beautiful the appearance of the topcoat film. When the surface of the topcoat film was directly palpated with a finger, if no "rough" feeling was detected, it was rated as "○ (good)", and if a "rough" feeling was detected, it was rated as "× (bad)".

[0067] Appearance was also evaluated for the presence or absence of "roping." "Roping" is a phenomenon in which the thickness of the topcoat coating changes in the shape of a sine curve in the width direction of the strip (metal substrate 1). It looks like there are "streaks" in the direction of the strip's travel. In the metal coating industry, this defect is called roping, ribbing, or roll marks. The evaluation of roping was performed using a high-viscosity paint 2 that is prone to roping.

[0068] The appearance of the surface of the topcoat coating film in Examples 1 to 5 is superior to that in Comparative Examples 6 to 9. In addition, the total heating time after coating of paint 2 is the same for Examples 5 and 6 at 20 (sec), but the resistance of the topcoat coating film to processing and boiling water as well as the appearance is superior in Example 5 compared to Comparative Example 6. The reason for this is presumed to be that the first heating step by heat conduction promotes the removal of the solvent in paint 2, which has some effect on the formation of the topcoat coating film that is more than just an improvement in appearance. The workability is a method for measuring the limit at which a steel plate coated with a topcoat coating film can be bent 180° (JIS K 3312, room temperature 20°C), and is evaluated by whether up to T (T = 1, 2, 3, ...) spacers of the same thickness as the test specimen can be sandwiched when bending. The number of spacers that can be sandwiched is smaller for 6T (6 sheets) than for 8T (8 sheets), and this indicates that the bending R is smaller and even severe processing is possible. Boiling water resistance was evaluated by scratching the topcoat film with a cutter, immersing it in boiling water for 5 hours, removing it, and using cellophane tape to evaluate the adhesion of the topcoat film. If the topcoat film peeled off with the cellophane tape, it was rated as "× (poor)" and if no peeling occurred, it was rated as "○ (good)".

[0069] Examples 11 to 15 and Comparative Example 16 are all examples that include a pre-painting heating process, and the plate temperature (temperature of metal substrate 1) conditions in the pre-painting heating process were changed to evaluate the presence or absence of "popping" and the feeling of "roughness" as well as the presence or absence of "roping."

[0070] If the heating conditions in the pre-painting heating step were appropriate, no roping occurred and a good surface appearance was obtained, as shown in Examples 11 to 15. On the other hand, if the heating temperature in the pre-painting heating step was low, as in Comparative Example 10, roping occurred with the highly viscous paint 2. Conversely, if the heating temperature in the pre-painting heating step was too high, as in Comparative Example 16, numerous defects occurred in the topcoat coating film, and the surface of the topcoat coating film did not have a good appearance.

[0071] In the above-described first embodiment, second embodiment, and modified example, the hot air is blown onto the paint 2 in the second heating step, but the hot air does not have to be blown onto the paint 2 in the second heating step. That is, in the above-described embodiments and modified examples, an undercoat coating film and an intermediate coating film are formed prior to applying the paint 2 to the surface of the metal substrate 1, but it is not necessary to form an undercoat coating film and an intermediate coating film on the surface of the metal substrate 1. In this case, the hot air is blown onto the same paint as the paint 2 in the first embodiment, second embodiment, and modified example, which is applied to the surface of the metal substrate 1.

[0072] As is clear from the first embodiment, second embodiment, and modified example described above, the manufacturing method of the first aspect of the coated metal sheet includes a coating step, a first heating step, and a second heating step. The coating step is a step of coating the surface of the metal substrate 1 with a paint 2 containing a resin, a pigment, and a solvent. The first heating step is a step of heating the metal substrate 1 by thermal conduction after the coating step. The second heating step is a step of blowing hot air onto the paint 2 applied to the surface of the metal substrate 1 to heat the paint 2 after the first heating step.

[0073] According to the first embodiment, in the first heating step, the paint 2 applied to the surface of the metal substrate 1 is not directly heated, so the surface of the paint 2 applied to the surface of the metal substrate 1 is not easily heated, and hardening of the surface of the paint 2 is not easily promoted. In addition, since the paint 2 is heated from the side in contact with the surface of the metal substrate 1, the solvent inside the heated paint 2 is likely to escape into the atmosphere from the surface of the paint 2 where hardening has not progressed, and evaporation from the paint 2 is likely to progress. Through the first heating step and the second heating step, the solvent contained in the paint 2 is evaporated from the paint 2, and the outer coating film is baked onto the metal substrate 1. The coating film formed on the metal substrate 1 has a low content of residual solvent and is in a good dry state.

[0074] The second embodiment can be realized by combining with the first embodiment. In the second embodiment, in the first heating step, the metal substrate 1 is heated by thermal conduction through the heating roll 71 with which the metal substrate 1 is in contact.

[0075] According to the second embodiment, the metal substrate 1 can be heated by a roll (heating roll 71) that is generally installed on the transport path of the metal substrate 1.

[0076] The third aspect can be realized by combining with the first or second aspect. The third aspect further comprises a pre-painting heating step of heating the metal substrate 1 by thermal conduction before the painting step.

[0077] According to the third aspect, the heating time (drying time) in the first heating step and the second heating step can be easily shortened. [Explanation of symbols]

[0078] 1 Metal substrate 2 Paint 3 Coating roll 4 Paint Pan 5 Pickup Roll 6 Backup Role 7 Metal substrate heating device 70 Heater 71 Heating Roll 72 Electromagnetic induction heating device 8 Heating furnace

Claims

1. A coating process of coating a surface of the metal substrate with a paint containing a resin, a pigment, and a solvent; a first heating step of heating the metal substrate without using the paint applied to the surface of the metal substrate after the painting step; A second heating step of blowing hot air onto the paint applied to the surface of the metal substrate after the first heating step to heat the paint, The method does not include a step of heating the metal substrate before the painting step. A method for manufacturing painted metal sheets.

2. The method for producing a coated metal sheet according to claim 1 , wherein in the first heating step, the metal substrate is heated by thermal conduction through a heating roll with which the metal substrate is in contact.

3. A coating process for coating a surface of a metal substrate with a paint containing a resin, a pigment and a solvent; a first heating step of heating the metal substrate without using the paint applied to the surface of the metal substrate after the painting step; a second heating step of blowing hot air onto the paint applied to the surface of the metal substrate to heat the paint after the first heating step; A pre-painting heating process for heating the metal substrate by thermal conduction before the painting process, The method for producing a coated metal sheet, wherein the temperature of the metal substrate is 35°C or higher and 140°C or lower in the pre-painting heating step.

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