Powder coating method of coated object

Abstract

To provide a powder coating method of a coated object, that is not only capable of easily removing surplus powder coating, but also in no need of repairing through re-coating.SOLUTION: A powder coating method of a coated object comprises the steps of: causing a powder coating material to adhere to a coated object to form a coating material layer; heating the coated object formed with the coating material layer to melt the powder coating material included in a lower layer portion in contact with the coated object, of the coating material layer; after melting of the powder coating material included in the lower layer portion, removing an upper layer portion where the powder coating material remains as powder without being molten, of the coating material layer; and, after removing the upper layer portion, heating the coated object to form a coating film.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for powder coating an article. [Background technology]

[0002] In some powder coating methods for coating an object, after a powder coating has been applied to form a coating layer, excess powder coating from the coating layer is removed mechanically.

[0003] For example, Patent Document 1 discloses a method for powder coating a metal plate used in assembling an assembly, in which the powder paint of the paint layer formed on the part of the metal plate that will be processed during assembly is removed with a vacuum nozzle or scraper. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-269730 Summary of the Invention [Problem to be solved by the invention]

[0005] In the powder coating method described in Patent Document 1, the powder coating is removed from the coating layer in the portion of the metal plate to be processed to form a rectangular shape in cross section. However, it is difficult to remove the powder coating and form the coating layer into a uniform and accurate rectangular shape in cross section. For this reason, in the powder coating method described in Patent Document 1, the coating layer is repaired by repainting it.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a powder coating method for an object that allows excess powder paint to be easily removed and does not require repair by repainting. [Means for solving the problem]

[0007] In order to achieve the above object, the powder coating method for a substrate according to the present disclosure includes the steps of forming a paint layer, melting the powder paint, removing an upper layer portion, and forming a coating film. The step of forming a paint layer comprises adhering powder paint to the substrate to form a paint layer. The step of melting the powder paint comprises heating the substrate on which the paint layer has been formed to melt the powder paint contained in the lower layer portion of the paint layer that contacts the substrate. The step of removing the upper layer portion comprises melting the powder paint contained in the lower layer portion, and then removing the upper layer portion of the paint layer where the powder paint does not melt and remains in powder form. The step of forming a coating film comprises heating the substrate to form a coating film after removing the upper layer portion. Effect of the Invention

[0008] According to the configuration of the present disclosure, in the step of melting the powder paint, the object on which the paint layer is formed is heated to melt the powder paint contained in the lower layer portion of the paint layer that contacts the object. In addition, in the step of removing the upper layer portion, after the powder paint contained in the lower layer portion is melted, the upper layer portion of the paint layer in which the powder paint does not melt and remains in powder form is removed. Therefore, only the upper layer portion is removed from the paint layer, and only the lower layer portion remains, so that the excess powder paint can be easily removed. In addition, since the lower layer portion remains, repair by repainting is not necessary. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a housing that is an object to be coated in a powder coating method according to a first embodiment of the present disclosure. [Diagram 2] 1 is a flowchart showing a powder coating method according to a first embodiment of the present disclosure. [Diagram 3] FIG. 1 is a conceptual diagram of a housing when powder paint is applied in a paint layer forming process of a powder coating method according to a first embodiment of the present disclosure. [Figure 4] A conceptual diagram of an induction heating device that preheats a housing in a preheating process of a paint layer provided in a powder coating method according to embodiment 1 of the present disclosure. [Diagram 5]A graph showing the relationship between the thickness of a paint layer and the temperature of the paint layer in a preheating process of the paint layer provided in the powder coating method according to the first embodiment of the present disclosure. [Figure 6] A conceptual diagram of a suction nozzle for removing the upper layer of a paint layer in a removal step of the upper layer of the paint layer, which is provided in the powder coating method according to the first embodiment of the present disclosure. [Figure 7] FIG. 11 is a perspective view of a housing that is an object to be coated in a powder coating method according to a second embodiment of the present disclosure. [Figure 8] FIG. 11 is a cross-sectional view of an induction heating device that preheats a housing in a preheating step of a paint layer provided in a powder coating method according to a second embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a powder coating method for a substrate according to an embodiment of the present disclosure will be described in detail with reference to the drawings, in which the same or equivalent parts are designated by the same reference numerals.

[0011] (Embodiment 1) In the powder coating method for a coating object according to the first embodiment, in order to increase efficiency, the metal plates are assembled and then the entire assembly is coated with powder paint, rather than being assembled after painting the metal plates. In this powder coating method, the assembly is preheated after the powder paint is applied in order to make it easier to remove excess powder paint. The powder coating method will be described below using an example in which the assembly is a housing. First, the object to be powder coated, i.e., the housing which is the coating object, will be described with reference to FIG. 1.

[0012] FIG. 1 is a perspective view of a housing 1A which is an object to be coated in the powder coating method according to the first embodiment.

[0013] As shown in FIG. 1, the housing 1A has a rectangular box shape to house parts and machines. Although not shown, the housing 1A is installed on a ship's hull or a structure on the ship's hull. As a result, the housing 1A is likely to come into contact with seawater and is easily corroded by chloride ions contained in seawater. Therefore, a coating is formed on the outer and inner surfaces of the housing 1A to prevent corrosion. That is, the housing 1A is painted.

[0014] When painting the housing 1A, it is desirable to form a thick coating. If the coating on the housing 1A is thin, moisture and chloride ions can easily reach the metal plate that forms the housing 1A, which can result in corrosion. Therefore, in order to form a thick coating, the housing 1A is powder coated. This is because, in the case of powder coating, the diameter of the powder paint is larger than in solvent coating and electrocoating, and a thick coating can be formed in one coat.

[0015] On the other hand, the housing 1A is produced by combining metal plates formed into the respective shapes of the top, bottom, front, back, right side, and left side of the housing 1A. In general, assemblies assembled from such metal plates are produced by painting the metal plates of the respective shapes described above and then combining the metal plates. In contrast, the housing 1A is produced by combining the metal plates of the respective shapes described above and then painting them in order to simplify the process and increase the production efficiency.

[0016] In detail, the housing 1A has an opening 11 formed in the front portion. When painting the housing 1A, not only the outer surface portion of the housing 1A is painted, but also the inside of the housing 1A, i.e., the inner surface portion, is painted using the opening 11. Specifically, when painting the housing 1A, powder paint is sprayed from the opening 11 toward the inside of the housing 1A, thereby powder coating the inner surface portion of the housing 1A.

[0017] However, in this powder coating, the sprayed powder paint that does not adhere to the inner surfaces of the top, front, back, right side, and left side of the housing 1A falls onto and accumulates on the inner surface of the bottom of the housing 1A. As a result, excess powder paint adheres to the inner surface of the bottom of the housing 1A, and the coating film formed on the inner surface of the bottom becomes thick.

[0018] In such cases, mechanical removal of the top layer of the coating is considered in order to achieve the appropriate coating thickness. However, it is difficult to remove only the excess powder coating from the coating. As a result, more powder coating than the excess powder coating may be removed from the coating. In such cases, repairs by repainting are required.

[0019] Therefore, in the method of powder coating the housing 1A, in order to make it easier to remove only the excess powder paint, the powder paint is applied to the assembled housing 1A, and then the housing 1A is preheated. The excess powder paint is then removed from the housing 1A. Next, the configuration of the powder coating method according to the first embodiment will be described in detail with reference to Figures 2 to 6.

[0020] FIG. 2 is a flowchart showing the powder coating method according to the first embodiment.

[0021] As shown in FIG. 2, in the powder coating method according to the first embodiment, that is, the powder coating method for a housing 1A, first, the housing 1A, which is the object to be coated, is assembled (step S1).

[0022] In detail, a metal plate, for example a steel plate, is cut into a rectangular shape to form the top, bottom, front, back, right side, and left side portions. In addition, bending and punching processes are performed using a press or press brake as necessary. Then, pretreatment is performed, for example, in the following order: degreasing, water washing, surface conditioning, chemical conversion treatment, water washing, post-treatment, and pure water washing.

[0023] Here, the surface conditioning may be performed by a chemical treatment such as zinc phosphate conversion treatment, iron phosphate conversion treatment, zirconium conversion treatment, etc., which dissolves oxides on the surface. Alternatively, the surface conditioning may be performed by a blasting treatment, which physically processes the surface.

[0024] After pre-processing the metal plates that will make up the top, bottom, front, back, right side, and left side sections, these metal plates are combined and then joined using techniques such as rivets, screws, welding, and adhesives to assemble the housing 1A.

[0025] Next, a paint layer is formed on the housing 1A (step S2). That is, a paint layer made of powder paint is formed on the housing 1A. Here, the paint layer refers to a layer formed by piling up powder paint, and refers to a layer before the powder paint described below completely melts to form a coating film. Figure 3 shows how the powder paint is applied to the housing 1A to form the paint layer.

[0026] FIG. 3 is a conceptual diagram of the housing 1A when the powder paint is applied in the paint layer forming process.

[0027] As shown in Fig. 3, in forming a paint layer, first, the housing 1A is hung from a metal hanger 2. In detail, hanging holes 13, 14 are formed in a top surface 12 of the housing 1A. Meanwhile, the hanger 2 has a horizontal bar 21 extending linearly, and hooks 22, 23 extending from the vicinity of both ends of the horizontal bar 21. The housing 1A is hung from the hanger 2 by engaging the hooks 22, 23 of the hanger 2 with the hanging holes 13, 14.

[0028] On the other hand, the hanger 2 is made of a conductive material and is suspended from a grounded rail 24. The hanger 2 is suspended from such a rail 24, and thereby is grounded.

[0029] In this state, the powder paint is applied to the housing 1A using the hand gun 3. In detail, the powder paint that has been charged by a corona charging method or a tribocharging method is sprayed onto the housing 1A, and the powder paint is adhered to the housing 1A by electrostatic force.

[0030] At this time, in the case of the corona charging method, a negative potential is applied to the handgun 3, and the powder paint becomes negatively charged by corona discharge. In application using the corona charging method, the negatively charged powder paint is sprayed onto the housing 1A. In the case of the tribocharging method, the powder paint becomes positively charged inside the handgun 3 due to friction between the powder paint and the inner wall of the handgun 3. In application using the tribocharging method, the positively charged powder paint is sprayed onto the housing 1A.

[0031] The powder paint sprayed onto the housing 1A is made of a thermosetting resin, such as an epoxy-based, epoxy-polyester-based, polyester-based, or fluororesin-based material.

[0032] Furthermore, not only is the powder paint sprayed onto the outer surface of the housing 1A by the hand gun 3, but the powder paint is also sprayed onto the inside of the housing 1A through the opening 11 of the housing 1A, thereby forming a paint layer made of the powder paint on the outer and inner surfaces of the housing 1A.

[0033] In forming this paint layer, by adjusting the amount and time of powder paint sprayed, a paint layer having a thickness of several tens of μm to several hundreds of μm is formed on the outer and inner surfaces of each of the top, front, back, right side, and left side of the housing 1A.

[0034] For example, if the housing 1A is used in an environment where it may be splashed with seawater, a paint layer with a thickness of 150 to 300 μm is formed. If the housing 1A is used in an area where seawater will not splash on it but it is within 300 m from the coast, a paint layer with a thickness of 100 to 150 μm is formed. If the housing 1A is used in an area 300 m to 10 km from the coast, a paint layer with a thickness of 60 to 150 μm is formed. Furthermore, if the housing 1A is used in an area where the distance to the coast is more than 10 km, a paint layer with a thickness of 40 to 150 μm is formed.

[0035] On the other hand, a paint layer thicker than the above-mentioned thickness is formed on the bottom surface of the housing 1A. When the paint layer is formed, the powder paint is attached to the housing 1A by electrostatic force, so that 50-70% of the powder paint adheres to the housing 1A, but 30-50% of the powder paint scatters into the air and falls downward due to gravity. As a result, not only the sprayed powder paint but also the powder paint that has scattered into the air and fallen adheres to the upper surface of the bottom surface of the housing 1A. As a result, when the powder paint is sprayed on the outer and inner surfaces of the top surface, front surface, back surface, right side surface, and left side surface of the housing 1A to form a paint layer of the above-mentioned thickness, a paint layer thicker than that is formed on the upper surface of the bottom surface. For this reason, a paint layer thicker than the above-mentioned thickness is formed on the bottom surface of the housing 1A.

[0036] Returning to Fig. 2, after the paint layer is formed on the housing 1A, the housing 1A is preheated (step S3). In this specification, preheating refers to heating the housing 1A in advance as a pretreatment for baking to form a coating film. An apparatus for performing the preheating is shown in Fig. 4.

[0037] FIG. 4 is a conceptual diagram of an induction heating device 4A that preheats the housing 1A in the paint layer preheating process.

[0038] As shown in FIG. 4, the induction heating device 4A includes a coil 41. The induction heating device 4A is disposed under the rail 24. In the preheating process of the paint layer shown in step S3, the hanger 2 that suspends the housing 1A shown in FIG. 3 is moved along the rail 24. Then, as shown in FIG. 4, the housing 1A is disposed on the induction heating device 4A. As a result, the induction heating device 4A faces the bottom surface of the housing 1A. Then, in this state, a current is passed through the coil 41, so that a current is passed through the bottom surface of the housing 1A by electromagnetic induction, generating Joule heat. As a result, the bottom surface of the housing 1A is heated. That is, the bottom surface of the housing 1A is preheated.

[0039] In preheating the housing 1A, the paint layer formed on the bottom surface of the housing 1A is heated until only the lower layer portion having the target thickness melts. Figure 5 shows the relationship between the thickness of the paint layer and the temperature of the paint layer.

[0040] Fig. 5 is a graph showing the relationship between the thickness of the paint layer and the temperature of the paint layer in the preheating process of the paint layer. Fig. 5 shows the temperature of the paint layer when a specific time has elapsed since the start of preheating the paint layer. The horizontal axis of the graph shows the thickness of the paint layer in μm. The vertical axis shows the temperature in °C. Furthermore, the temperature T0 shown in the graph shows the temperature at which the powder paint forming the paint layer completely melts, and the temperature T1 shows a temperature about 20 °C lower than that temperature T0.

[0041] As shown in FIG. 5, when the paint layer is preheated, the paint layer is less likely to be preheated and the temperature tends to be lower as the thickness increases. As a result, assuming that the target thickness is t1, the paint layer having the thickness t1 reaches a temperature T1 that is about 20° C. lower than the temperature T0 at which the powder paint completely melts, for example, when a certain time has elapsed since the start of preheating the paint layer. Since the powder paint contains a mixture of multiple types of polymers with different molecular chains, it does not completely melt at a certain temperature, but the polymers with short chain lengths contained in the powder paint melt first at a low temperature. Then, at a higher temperature, for example, at temperature T1, the polymers with long chain lengths contained in the powder paint begin to melt. As a result, at temperature T1, the part of the paint layer that contacts the bottom surface of the heated housing 1A melts, and the powder paint becomes a highly viscous liquid or is in a blocking state.

[0042] On the other hand, when the paint layer has a thickness t2 that is thicker than the thickness t1, the temperature of the paint layer only reaches a temperature T2 that is lower than the temperature T1. As a result, the polymer contained in the powder paint does not melt, and the powder paint remains in powder form.

[0043] From these facts, it can be seen that when a paint layer with thickness t2 is heated to temperature T1, in the lower part of the paint layer with thickness t1 that is in contact with the bottom surface of housing 1A, the powder paint melts and becomes a highly viscous liquid state or in a blocking state, and in the upper part of the paint layer above the lower part, the powder paint remains in powder form. It can also be seen that by heating the paint layer with thickness t2 to temperature T1 and blowing off or sucking up the upper part of the paint layer in that state, only the upper part can be removed.

[0044] In preheating the housing 1A in step S3 shown in FIG. 2, the above-mentioned phenomenon is utilized to heat the housing 1A until the paint layer reaches a temperature T1.

[0045] It should be noted that the temperature T1 is described as being about 20°C lower than the temperature T0 at which the powder paint completely melts, but this temperature T1 is merely an example. In preheating the housing 1A, it is sufficient to heat the housing 1A to a temperature at which the lower layer of the paint layer, which is in contact with the bottom surface of the housing 1A and has a target thickness, becomes a highly viscous liquid or in a blocking state, depending on the type of powder paint.

[0046] Following preheating of the housing 1A, the upper layer of the paint layer is removed (step S4). An apparatus for removing the upper layer is shown in FIG.

[0047] FIG. 6 is a conceptual diagram of a suction nozzle 5 for removing the upper layer portion of a paint layer in the process of removing the upper layer portion.

[0048] The suction nozzle 5 has an outer diameter that allows it to be inserted into the opening 11 of the housing 1A. Although not shown, the suction nozzle 5 is connected to a suction device that sucks in air inside the suction nozzle 5. In removing the upper layer portion of the paint layer shown in step S4, the suction nozzle 5 is inserted into the opening 11 of the housing 1A and the paint layer on the inner surface of the bottom part of the housing 1A is sucked up. In the upper layer portion of the paint layer, as described above, the powder paint remains in powder form. The suction nozzle 5 is used to suck up the powder paint that remains in powder form. This removes the upper layer portion from the paint layer.

[0049] Returning to FIG. 2, next, a coating film is formed (step S5). In detail, the housing 1A is placed in an oven heated to a temperature equal to or higher than the above-mentioned temperature T0, and the remaining lower layer portion of the paint layer formed on the bottom surface of the housing 1A is baked. Also, the paint layer formed on each surface portion other than the bottom surface of the housing 1A is baked. This hardens the powder paint formed from a thermosetting resin in the paint layer. Although some of the powder paint has hardened due to the preheating in step S3, the entire powder paint is completely hardened by the process of placing it in the oven. As a result, a coating film is formed on each surface portion of the housing 1A.

[0050] In step S2 described above, a paint layer of the desired thickness, i.e., the target thickness, is formed on each of the top, front, back, right side, and left side of the housing 1A. In step S4, the upper layer is removed from the paint layer on the bottom of the housing 1A, leaving only the lower layer of the target thickness. In step S5, the paint layer of this thickness is baked to form a coating. As a result, a coating of uniform thickness can be formed on each surface of the housing 1A. This makes it possible to form a coating that does not require repair by repainting.

[0051] The above-mentioned step S2 of forming a paint layer on the housing 1A is an example of a step of forming a paint layer as defined in the present disclosure. The step S3 of preheating the housing 1A is an example of a step of melting the powder paint contained in the lower layer portion as defined in the present disclosure. The step S4 of removing the upper layer portion of the paint layer is an example of a step of removing the upper layer portion as defined in the present disclosure. Furthermore, the housing 1A is an example of a coated object as defined in the present disclosure.

[0052] As described above, in the powder coating method according to the first embodiment, in the step of preheating the housing 1A, the bottom surface of the housing 1A on which the paint layer is formed is heated to melt the powder paint contained in the lower layer portion of the paint layer that contacts the bottom surface. In addition, in the step of removing the upper layer portion of the paint layer, the upper layer portion of the paint layer in which the powder paint does not melt and remains in powder form is removed. In the powder coating method according to the first embodiment, only the upper layer portion is removed from the paint layer, leaving only the lower layer portion, so that the excess powder paint can be easily removed. In addition, as a result of removing the excess powder paint, the thickness of the coating film becomes appropriate and the coating film is less likely to crack.

[0053] In the process of preheating the housing 1A, the thickness of the upper layer to be removed and the lower layer to be left in the final product can be determined simply by adjusting the temperature, making it easy to adjust the thickness of the coating film.

[0054] In the process of preheating the housing 1A, the housing 1A is heated using a non-contact induction heating device 4A. Therefore, the paint layer does not come into contact with the heating device and is not deformed. According to the powder coating method of the first embodiment, a coating film without damage can be formed.

[0055] In addition, in the process of preheating the housing 1A, the induction heating device 4A can be used to heat a localized portion, i.e., the bottom surface of the housing 1A. According to the powder coating method of the first embodiment, the thickness of the coating film can be adjusted only in the localized portion.

[0056] Furthermore, in the process of removing the upper layer of the paint layer, only the lower layer of the target thickness remains, and the paint film is formed by this lower layer, so repairs by repainting are not necessary.

[0057] In the powder coating method of embodiment 1, the housing 1A is painted after it is assembled, which results in higher manufacturing efficiency than a method in which the housing 1A is assembled after painting the top, bottom, front, back, right side, and left side components of the housing 1A.

[0058] (Embodiment 2) In the first embodiment, the bottom surface of the housing 1A is heated to melt the powder paint contained in the lower layer of the paint layer on the bottom surface of the housing 1A that is in contact with the bottom surface. Then, the upper layer above the lower layer is removed. However, the location to be heated and the location to remove the upper layer are not limited to this.

[0059] The powder coating method may be any method that heats the substrate to melt the powder coating contained in the lower layer of the coating layer formed on the substrate, the lower layer being in contact with the substrate. Also, it may be any method that removes the upper layer of the coating layer, in which the powder coating is not melted and remains in powder form, after the lower layer of the coating layer is melted. Therefore, as long as these conditions are met, the location to be heated and the location to remove the upper layer are optional.

[0060] In the second embodiment, a corner inside the housing 1A is heated to melt the powder paint contained in the lower layer of the paint layer at that corner.

[0061] A powder coating method according to the second embodiment will be described below with reference to Figures 7 and 8. In the second embodiment, the configuration different from the first embodiment will be mainly described.

[0062] FIG. 7 is a perspective view of a housing 1B which is an object to be coated in the powder coating method according to the second embodiment.

[0063] First, the locations of the housing 1B where the powder paint is likely to adhere in excess will be described with reference to Fig. 7. In Fig. 7, for ease of understanding, only the corners on the front side, left side side, and bottom side of the housing 1B are enlarged.

[0064] When powder paint is sprayed onto the inner surfaces of the front, back, right side, and left side of the housing 1B, powder paint that has scattered and fallen from these inner surfaces accumulates on the four corners of the rectangular inner bottom surface of the housing 1B. As a result, as shown in Fig. 7, the thickness of the paint layer 6 is thick at the four corners of the bottom surface. In the powder coating method according to the second embodiment, therefore, in order to remove the excess powder paint from the four corners, the four corners of the bottom surface of the housing 1B are preheated in the process of preheating the housing 1B described in Fig. 2. An induction heating device 4B for preheating the four corners is shown in Fig. 8.

[0065] Fig. 8 is a cross-sectional view of an induction heating device 4B that preheats the housing in the preheating step of the paint layer 6 provided in the powder coating method according to the second embodiment. For ease of understanding, Fig. 8 shows an enlarged view of only the induction heating device 4B that preheats the corner on the front and left side of the bottom surface of the housing 1B, out of the induction heating devices 4B that preheat the four corners of the bottom surface of the housing 1B. The cross section shown is a cross-section of the corner and the induction heating device 4B cut along a plane parallel to the front surface of the housing 1B.

[0066] As shown in Fig. 8, induction heating device 4B has flat plate portions 42 and 43 that are perpendicular to each other. In addition, although not shown, induction heating device 4B has another flat plate portion that is perpendicular to flat plate portions 42 and 43. Coils 44 and 45 and another coil (not shown) are provided on flat plate portions 42 and 43 and the other flat plate portion (not shown). Furthermore, although not shown, induction heating device 4B is disposed under rail 24 described in the first embodiment, and has a movement mechanism that moves induction heating device 4B itself up and down.

[0067] In the powder coating method of embodiment 2, in the process of preheating the housing 1B described in Figure 2, an induction heating device 4B shown in Figure 8 is brought close to a corner on the front side and left side of the bottom portion of the housing 1B.

[0068] In detail, although not shown, the hanger 2 described in the first embodiment is moved along the rail 24 to position the housing 1B above the induction heating device 4B. Furthermore, in this state, the movement mechanism moves the induction heating device 4B upward. As a result, the left side surface portion of the corner on the front side and left side of the bottom surface portion of the housing 1B faces the flat plate portion 42 of the induction heating device 4B. Also, the bottom surface portion of the corner faces the flat plate portion 43 of the induction heating device 4B. Furthermore, the front surface portion of the corner faces the flat plate portion (not shown) of the induction heating device 4B. Then, in this state, a current is passed through the coils 44 and 45 and a coil (not shown) provided in the induction heating device 4B. As a result, a current is passed through the corner to generate Joule heat. As a result, the corner is preheated.

[0069] The induction heating device 4B is also placed close to other corners of the bottom surface of the housing 1B (not shown). Then, current is passed through the coils 44 and 45 of the induction heating device 4B and a coil (not shown) to pass current through those corners and generate Joule heat. As a result, those corners are also preheated.

[0070] After the four corners of the bottom surface of the housing 1B are preheated, excess powder coating is then removed from the four corners of the bottom surface of the housing 1B. For example, the suction nozzle 5 described in the first embodiment is inserted into the opening 11, and the four corners of the bottom surface inside the housing 1B are sucked by the suction nozzle 5. This causes the excess powder coating at those four corners to be sucked. This removes the excess powder coating from those four corners.

[0071] The powder coating method according to the second embodiment is similar to that of the first embodiment except for the above-mentioned step of preheating the casing 1B and the step of removing the upper part of the paint layer 6. Therefore, a description of the steps before the step of preheating the casing 1B will be omitted. Also, a description of the steps after the step of removing the upper part of the paint layer 6 will be omitted.

[0072] As described above, in the powder coating method according to the second embodiment, in the step of preheating the housing 1B, each of the four corners of the bottom surface of the housing 1B on which the paint layer 6 is formed is heated to melt the powder paint contained in the lower layer portion of the paint layer 6 formed on those four corners. In addition, in the step of removing the upper layer portion of the paint layer 6, the upper layer portion of the paint layer 6 formed on the four corners where the powder paint does not melt and remains in powder form is removed. In the powder coating method according to the second embodiment, as in the case of the first embodiment, only the upper layer portion is removed from the paint layer 6, and only the lower layer portion remains. As a result, the excess powder paint can be easily removed.

[0073] In addition, in the step of preheating the housing 1B, only the four corners of the bottom surface of the housing 1B, where excess powder paint is likely to accumulate, are preheated. Therefore, in the powder coating method according to the second embodiment, the step of preheating the housing 1B can be easily performed.

[0074] Although the methods for powder coating an object to be coated according to the first and second embodiments of the present disclosure have been described above, the method for powder coating an object to be coated is not limited thereto.

[0075] For example, in the first and second embodiments, examples are described in which the object to be coated is housings 1A, 1B. However, the object to be coated is not limited to this. The object to be coated may be any object that is to be powder coated. Therefore, the object to be coated may be something other than housings 1A, 1B, for example, the object to be coated may be equipment for fixing equipment to a hull. Also, in the first and second embodiments, housings 1A, 1B are installed on the hull or a structure on the hull, but the object to be coated may be something other than the hull, such as factory equipment, a vehicle, etc.

[0076] In the first embodiment, only the bottom surface of the housing 1A, which is the object to be coated, is preheated. Then, the upper layer portion of the paint layer 6 on the bottom surface, where the powder paint is not melted and remains as powder, is removed. In the second embodiment, only the four corners of the bottom surface of the housing 1B, which is the object to be coated, are preheated. Then, the upper layer portion of the paint layer 6 on those four corners is removed. However, the preheating step included in the powder coating method is not limited to this. The preheating step may be any step that heats the object to be coated on which the paint layer 6 is formed, and melts the powder paint contained in the lower layer portion of the paint layer 6 that contacts the object to be coated. Then, the step of removing the upper layer portion may be any step that melts the powder paint contained in the lower layer portion, and then removes the upper layer portion of the paint layer 6, where the powder paint is not melted and remains as powder. In this specification, melting includes bringing the powder paint forming the paint layer 6 into a blocking state. For this reason, the bottom surface or parts other than the four corners of the bottom surface of the housings 1A, 1B may be preheated, or the upper layer portion may be removed from the paint layer 6 on the bottom surface or parts other than the four corners of the bottom surface of the housing.

[0077] For example, the top surface of the housings 1A and 1B may be preheated to melt the powder paint in the lower layer of the paint layer 6 formed by accumulating the powder paint on the outer surface of the top surface. Then, the upper layer of the top surface may be removed to remove the excess powder paint. In addition, when a recess is formed in at least one of the top surface, bottom surface, front surface, back surface, right side surface, and left side surface of the housings 1A and 1B, the recess may be preheated to melt the powder paint in the lower layer of the paint layer 6 in the recess. Then, the upper layer of the paint layer 6 in the recess may be removed to remove the excess powder paint.

[0078] In the first and second embodiments, the step of assembling the housings 1A, 1B is performed by a powder coating method. However, the powder coating method is not limited to this. The powder coating method may start with a step of applying powder paint to an object to be coated to form a paint layer 6. Therefore, the powder coating method may be performed using the housings 1A, 1B that have been assembled in advance.

[0079] Further, while it has been described that the housings 1A, 1B may be any object to be powder coated, the object may be an assembled product or a processed product formed by pressing.

[0080] In the first and second embodiments, the powder paint is made of a thermosetting resin, but the powder paint may be made of a thermoplastic resin.

[0081] As described above, the method for powder coating an object to be coated is not limited to the above-described embodiment, and various modifications and substitutions can be made thereto. Various aspects of the present disclosure are described below as appendices.

[0082] (Appendix 1) A step of depositing a powder coating material on an object to be coated to form a coating layer; a step of heating the substrate on which the paint layer is formed to melt the powder paint contained in a lower layer portion of the paint layer that is in contact with the substrate; a step of melting the powder coating material contained in the lower layer portion, and then removing an upper layer portion of the coating layer in which the powder coating material is not melted and remains in powder form; After removing the upper layer portion, the substrate is heated to form a coating film; Equipped with A method for powder coating an object. (Appendix 2) The substrate is made of a metal material, In the step of melting the powder coating material, the object to be coated is heated by induction heating. 2. A method for powder coating an object as described in appendix 1. (Appendix 3) In the step of melting the powder coating material, a portion of the workpiece where the coating layer is formed thicker than other portions is heated to melt the powder coating material contained in the lower layer portion of the portion where the coating layer is formed thicker, In the step of removing the upper layer portion, the upper layer portion in the portion where the paint layer is formed thick is removed. 3. A method for powder coating an object as described in claim 1 or 2. (Appendix 4) The object to be coated has a box shape and has a corner formed on the inside of the box, In the step of melting the powder coating material, the corner portion is heated, In the step of removing the upper layer portion, the upper layer portion of the paint layer formed in the corner portion is removed. 4. A method for powder coating an object as described in appendix 3. (Appendix 5) In the step of forming the paint layer, the powder paint is sprayed onto the substrate to form the paint layer, In the step of melting the powder paint, the part where the powder paint is sprayed and deposited thicker than the other parts due to being located below the other parts in the step of forming the paint layer is heated. A method for powder coating an object according to claim 3. (Appendix 6) In the step of removing the upper layer portion, the powder paint contained in the upper layer portion is sucked. 6. A method for powder coating an object according to any one of claims 1 to 5. (Appendix 7) The method further includes a step of forming a metal plate into a three-dimensional shape or assembling the metal plate into a three-dimensional shape to produce the object to be coated; The step of forming the paint layer is carried out after the step of preparing the substrate. 7. A method for powder coating an object according to any one of claims 1 to 6. [Explanation of symbols]

[0083] 1A, 1B housing, 2 hanger, 3 hand gun, 4A, 4B induction heating device, 5 suction nozzle, 6 paint layer, 11 opening, 12 top surface portion, 13, 14 hanging holes, 21 horizontal rod, 22, 23 hooks, 24 rail, 41 coil, 42, 43 flat plate portion, 44, 45 coil.

Claims

1. A step of depositing a powder coating material on an object to be coated to form a coating layer; a step of heating the substrate on which the paint layer is formed to melt the powder paint contained in a lower layer portion of the paint layer that is in contact with the substrate; a step of melting the powder coating material contained in the lower layer portion, and then removing an upper layer portion of the coating layer in which the powder coating material is not melted and remains in powder form; After removing the upper layer portion, the substrate is heated to form a coating film; Equipped with A method for powder coating an object.

2. The substrate is made of a metal material, In the step of melting the powder coating material, the object to be coated is heated by induction heating. A method for powder coating an object according to claim 1.

3. In the step of melting the powder coating material, a portion of the workpiece where the coating layer is formed thicker than other portions is heated to melt the powder coating material contained in the lower layer portion of the portion where the coating layer is formed thicker, In the step of removing the upper layer portion, the upper layer portion in the portion where the paint layer is formed thick is removed.

3. A method for powder coating an object according to claim 1 or 2.

4. The object to be coated has a box shape and has a corner formed on the inside of the box, In the step of melting the powder coating material, the corner portion is heated, In the step of removing the upper layer portion, the upper layer portion of the paint layer formed in the corner portion is removed. A method for powder coating an object according to claim 3.

5. In the step of forming the paint layer, the powder paint is sprayed onto the substrate to form the paint layer, In the step of melting the powder paint, the part where the powder paint is sprayed and deposited thicker than the other parts due to being located below the other parts in the step of forming the paint layer is heated. A method for powder coating an object according to claim 3.

6. In the step of removing the upper layer portion, the powder paint contained in the upper layer portion is sucked.

3. A method for powder coating an object according to claim 1 or 2.

7. The method further includes a step of forming a metal plate into a three-dimensional shape or assembling the metal plate into a three-dimensional shape to produce the object to be coated; The step of forming the paint layer is carried out after the step of preparing the substrate.

3. A method for powder coating an object according to claim 1 or 2.

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