Coating method

Abstract

[Problem] To provide a coating method capable of high-quality coating by suppressing dripping in the direction of gravity when coating a coating surface that intersects a horizontal plane. [Solution] This coating method is a method for forming a multilayer coating film by discharging droplets 51 from a nozzle toward a coating surface 50 that intersects a horizontal plane, by means of an inkjet coating method. In the coating method, first, a coating film is formed by discharging droplets so as to provide a gap at least in the direction of gravity between the droplets on the coating surface. Next, formation of a coating film 70 on the upper layer side is repeated by discharging droplets so as to fill the gap in the coating film 60 on the lower layer side and to provide a gap at least in the direction of gravity between the droplets thereby forming a laminated coating film. Then, the laminated coating film is cured.

Description

Painting method

[0001] The present invention relates to a coating method.

[0002] 2. Description of the Related Art A known coating method uses an inkjet coating system to form a coating film by ejecting droplets from a nozzle onto a coating surface (see Patent Document 1).

[0003] JP 2009-154062 A

[0004] The coating surface is produced by an inkjet coating method, ejecting droplets in an arrangement in which some of the droplets overlap in both the main scanning direction and the sub-scanning direction (for convenience of explanation, this is called a permuted arrangement). When the coating surface intersects a horizontal plane, for example, when the coating surface is a vertical plane, dripping occurs in the direction of gravity, resulting in uneven film thickness. As a result, the coating quality deteriorates.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a coating method that can suppress dripping in the direction of gravity when coating a surface that intersects a horizontal plane, thereby enabling high-quality coating.

[0006] The coating method of the present invention, which achieves the above object, is a coating method that uses an inkjet coating system to eject droplets from a nozzle toward a coating surface that intersects a horizontal plane to form a multilayer coating film. In this coating method, droplets are first ejected onto the coating surface so as to leave gaps between the droplets at least in the direction of gravity, thereby forming a coating film. Next, droplets are ejected so as to fill the gaps in the lower coating film and leave gaps between the droplets at least in the direction of gravity, thereby repeatedly forming an upper coating film, thereby forming a laminated coating film. The laminated coating films are then cured.

[0007] According to the coating method of the present invention, when a coating film is formed on a coating surface, the drying of the droplets is promoted and the flow of the droplets among themselves is suppressed. As a result, the liquid is not scattered and wasted, and dripping is suppressed. Therefore, when coating a coating surface that intersects a horizontal plane, dripping in the direction of gravity is suppressed, enabling high-quality coating.

[0008] FIG. 1 is a cross-sectional view of a main portion showing an example of a coating apparatus using an inkjet coating method. FIG. 2 is a schematic diagram showing the steps of a coating method according to an embodiment. FIG. 3 is a schematic diagram showing the steps of a coating method following FIG. 2A. FIG. 2 is a schematic diagram showing the steps of a coating method following FIG. 2B. FIG. 3 is a schematic diagram showing the steps of a coating method following FIG. 2C. FIG. 4 is a schematic diagram used to explain the operation of a coating method according to an embodiment together with FIG. 3A. FIG. 4 is a schematic diagram used to explain the operation of a coating method according to an embodiment together with FIG. 4B. FIG. 4 is a schematic diagram used to explain the operation of a coating method according to an embodiment, where dripping occurs on a coating surface in a comparative coating method. FIG. 4 is a schematic diagram used to explain the operation of a coating method according to an embodiment, where dripping occurs on a coating surface in a comparative coating method. FIG. 5 is a schematic diagram used to explain the operation of an improved coating speed by a coating method according to an embodiment. FIG. 6 is a schematic diagram showing the steps of a coating method according to a first modification. FIG. 6 is a schematic diagram showing the steps of a coating method following FIG. 6B. FIG. 7 is a schematic diagram showing the steps of a coating method according to a second modification. FIG. 7 is a schematic diagram showing the steps of a coating method following FIG. 7B. FIG. 8A is a schematic diagram showing the procedure of the coating method following FIG. 7C. FIG. 8B is a schematic diagram showing the procedure of the coating method following FIG. 7D. FIG. 8C is a schematic diagram showing the procedure of the coating method according to Modification 3. FIG. 8A is a schematic diagram showing the procedure of the coating method following FIG. 8A. FIG. 8B is a diagram showing how droplets that form a coating film on the lower layer side are hardened by heating in the coating method according to Modification 4. FIG. 8C is a schematic diagram used to explain the coating method according to Modification 5.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments shown here are merely examples for embodying the technical concept of the present invention and are not intended to limit the present invention. Therefore, all other embodiments, examples, and operational techniques that can be conceived by those skilled in the art without departing from the spirit of the present invention are included in the scope and spirit of the present invention, as well as in the scope of the inventions set forth in the claims and their equivalents.

[0010] In addition, for the convenience of illustration and ease of understanding, the drawings attached to this specification may be represented schematically with the scale, aspect ratio, shape, etc. appropriately changed from the actual product, but these are merely examples and do not limit the interpretation of the present invention.

[0011] In this specification, ordinal numbers such as "first," "second," etc. may be used. However, unless otherwise specified, these ordinal numbers are used to identify components for the sake of convenience, and do not specify the number or order.

[0012] <Embodiments> The coating device of the embodiments can be incorporated into a coating device that paints automotive parts such as outer panels, interior panels, and bumpers of an automobile body. The coating device can have a multi-nozzle configuration by incorporating multiple coating devices. The paint is not particularly limited, but is automotive paint. Automotive paint is a thermosetting paint with an acrylic resin, alkyd resin, polyester resin, or the like as a base resin. The automotive paint can be a water-based paint or an organic solvent-based paint. The automotive paint can contain color pigments and luster pigments as needed. When painting automotive parts, the surface to be coated may be nearly vertical, so a relatively high-viscosity paint is used.

[0013] As shown in FIG. 1, the coating device 10 has a nozzle 20 that ejects droplets of paint, and an acoustic tube 30 in which the nozzle 20 is disposed.

[0014] The nozzle 20 has a hollow housing 21 and a piezoelectric element 22 arranged within the housing 21. The nozzle 20 is arranged within the acoustic tube 30 so that its position relative to the acoustic tube 30 can be freely changed. A small gap is formed between the outer periphery of the nozzle 20 and the acoustic tube 30. The housing 21 has a paint discharge portion 23 at its tip (lower end in FIG. 1 ). A paint chamber 24 is formed between the housing 21 and the piezoelectric element 22. Paint is supplied to the paint chamber 24 from a paint supply source (not shown). The piezoelectric element 22 deforms when a voltage is applied. The paint in the paint chamber 24 is discharged from the discharge portion 23 by the mechanical movement of the piezoelectric element 22.

[0015] The acoustic tube 30 has an inlet 31 through which sound waves are introduced and an outlet 32 ​​through which droplets ejected from the nozzle 20 are directed toward the coating surface. The sound source 40 is arranged toward the inlet 31 of the acoustic tube 30. The sound source 40 is composed of a sound wave generator that generates sound waves having a predetermined wavelength and a predetermined amplitude. The sound source 40 irradiates the generated sound waves toward the inlet 31 of the acoustic tube 30. The acoustic tube 30 has a propagation path 33 between the inlet 31 and the outlet 32 ​​through which sound waves propagate. The propagation path 33 has a bend 34 along the path. The tip of the nozzle 20 is arranged at the bend 34 of the propagation path 33 of the acoustic tube 30. The sound waves within the acoustic tube 30 are irradiated toward the tip of the nozzle 20 from a direction oblique to the droplet ejection direction from the nozzle 20. As a result, the droplets ejected from the nozzle 20 are atomized by the application of sound pressure.

[0016] The coating device 10 has a detour propagation path 35 located upstream of the discharge surface of the nozzle 20 in the sound wave propagation direction, which causes the sound waves in the acoustic tube 30 to detour to the side opposite the sound wave irradiation side of the nozzle 20. The detour propagation path 35 is formed by a gap between the outer periphery of the nozzle 20 and the acoustic tube 30. The sound waves in the acoustic tube 30 travel from the gap located on the inlet portion 31 side to the detour propagation path 35, and then travel in a detour toward the gap located on the opposite side of the nozzle 20.

[0017] The coating device 10 has a structure in which sound waves that have been deflected by the detour propagation path 35 are irradiated onto droplets ejected from the nozzle 20. The sound waves that have traveled inside the detour propagation path 35 are irradiated onto droplets ejected from the nozzle 20 along a guide surface 37 formed on the inner wall of the acoustic tube 30. The droplets ejected from the nozzle 20 are also irradiated with sound waves that have traveled along a propagation path 33 from the inlet 31 to the outlet 32.

[0018] Next, the coating method will be described.

[0019] 2A, 2B, 2C, and 2D are schematic diagrams illustrating the steps of a coating method according to an embodiment. FIG. 2A shows a coating film formed on a coating surface 50, FIG. 2B shows an upper coating film 70 formed on a lower coating film 60, FIG. 2C shows a layered coating film 80 formed by repeatedly forming coating films, and FIG. 2D shows the layered coating film 80 cured. The X-axis in FIGS. 2A and 2B indicates the main scanning direction in which the coating head with the nozzle 20 moves to paint one line, and the Y-axis indicates the sub-scanning direction in which the coating head moves to paint the next line. The arrows indicate the flow of the coating head movement. For ease of understanding, in FIGS. 2C and 2D, the coating films of each layer are shown shifted in the sub-scanning direction.

[0020] 2A, 2B, 2C, and 2D, an example of a procedure for forming a multilayer coating film by an inkjet coating method by ejecting droplets 51 from a nozzle 20 toward a coating surface 50 that intersects with a horizontal plane will be described. The coating film formed by ejecting droplets 51 has a dot shape in which droplets 51 are intermittently arranged. The angle at which the coating surface 50 intersects with the horizontal plane is not particularly limited, but for ease of understanding, the coating surface 50 is assumed to be a vertical plane that extends including the direction of gravity. The direction of gravity is downward in the figures.

[0021] First, as shown in FIG. 2A, droplets 51 are ejected onto a coating surface 50 so as to provide gaps between the droplets 51 at least in the direction of gravity, thereby forming a coating film.

[0022] In this specification, "providing gaps in the direction of gravity" means that the droplets 51 are applied so that adjacent droplets 51 in the sub-scanning direction do not overlap each other. From the viewpoint of making the thickness of the coating film that is finally formed uniform, the droplets 51 adjacent in the sub-scanning direction are not aligned in a line in the direction of gravity. It is preferable that the applied droplets 51 are arranged in a close-packed state in a planar quadrangle while providing gaps at least in the direction of gravity.

[0023] 2B, an upper coating film 70 (shown by hatched circles) is applied over the lower coating film 60 (shown by open circles). At this time, droplets 51 are ejected so as to fill gaps in the lower coating film 60 and to provide gaps between droplets 51 at least in the direction of gravity.

[0024] Next, as shown in FIG. 2C, the upper coating film 70 is repeatedly formed on the lower coating film 60 to form a laminated coating film 80.

[0025] Then, as shown in FIG. 2D, the laminated coating film 80 is cured.

[0026] 3A and 3B are schematic diagrams used to explain the operation of the coating method of this embodiment, and Fig. 4A and 4B are schematic diagrams used to explain the occurrence of dripping 102 on a coating surface 100 (e.g., a vertical surface) in a comparative coating method.

[0027] As shown in FIG. 4A, in the comparative coating method, droplets 101 are ejected by an inkjet coating method so that the droplets 101 are arranged in a manner that they partially overlap each other in both the main scanning direction and the sub-scanning direction (permuted arrangement).

[0028] As shown in FIG. 4B, gravity acting on the impacted droplet 101 itself causes dripping 102 on the coating surface 100 (for example, a vertical surface), resulting in an uneven film thickness.

[0029] On the other hand, as shown in FIG. 3A , according to the coating method of this embodiment, gaps are formed between the droplets 51 that have landed on the coating surface 50 (e.g., a vertical surface). This increases the contact area between the droplets 51 and the air, accelerating drying, compared to when the droplets 51 are in contact with each other and adjacent to each other.

[0030] 3B, the droplets 52 on the upper layer are then arranged to fill the gaps in the coating film 60 on the lower layer, so that the previously arranged and dried droplets 51 serve as a foothold and the flow of the droplets 52 ejected on the upper layer is suppressed. As a result, dripping in the direction of gravity is suppressed. The arrow indicated by the dashed line with an "x" symbol in FIG. 3B shows a state in which the flow of the droplets 52 ejected on the upper layer is suppressed.

[0031] Therefore, according to the coating method of this embodiment, when a coating film is formed on a coating surface 50 (e.g., a vertical surface), the drying of the droplets 51 is promoted and the flow of the droplets 51 among themselves is suppressed. As a result, the liquid is not scattered and wasted, and dripping can be suppressed. Therefore, when coating a coating surface 50 that intersects with a horizontal plane, dripping in the direction of gravity is suppressed, enabling high-quality coating.

[0032] FIG. 5 is a schematic diagram used to explain the effect of improving the coating speed by the coating method of this embodiment.

[0033] Dripping on a coating surface 50 (e.g., a vertical surface) is caused by gravity acting on the paint itself. One way to suppress dripping is to reduce the coating weight of each layer. To achieve this, one method is to eject minute droplets 53 from a nozzle with a relatively small diameter (e.g., φ50 μm).

[0034] In the coating method of the embodiment, by providing gaps between the landed droplets 51, dripping of each droplet 51 can be suppressed. Therefore, the ejected droplets 51 can be made larger than the microdroplets 53. For example, when ejecting droplets 51 whose diameter (2d) upon impact is twice the diameter (d) of the ejected microdroplets 53, the coating speed is doubled.

[0035] (Variation 1) Figures 6A, 6B, and 6C are schematic diagrams showing the steps of a coating method according to Variation 1. Figure 6A shows the state in which a coating film has been formed on a coating surface 50, and corresponds to Figure 2A. Figure 6B shows the state in which droplets 51 forming a lower coating film 60 are cured before an upper coating film 70 is formed. Figure 6C shows the state in which an upper coating film 70 has been formed on a lower coating film 60, and corresponds to Figure 2B.

[0036] First, as shown in FIG. 6A, droplets 51 are ejected onto a coating surface 50 so as to provide gaps between the droplets 51 at least in the direction of gravity, thereby forming a coating film.

[0037] Next, as shown in FIG. 6B, before forming the upper coating film 70, the droplets 51 that form the lower coating film 60 are cured (primary curing).

[0038] 6C, an upper coating film 70 (indicated by hatched circles) is applied over the lower coating film 60 (indicated by light gray circles). At this time, droplets 51 are ejected so as to fill gaps in the lower coating film 60 and to provide gaps between droplets 51 at least in the direction of gravity.

[0039] Thereafter, similarly to the case shown in Fig. 2C, the formation of the upper coating film 70 on the lower coating film 60 is repeated to form a laminated coating film 80. Then, similarly to the case shown in Fig. 2D, the laminated coating film 80 is cured (secondary curing).

[0040] With the configuration of Modification 1, by hardening the droplets 51 that form the coating film 60 on the lower layer, the droplets 51 that have been placed and primarily hardened first serve as a foothold, further suppressing the flow of the droplets 51 ejected on the upper layer. As a result, dripping in the direction of gravity is further suppressed. Therefore, when coating a coating surface 50 that intersects with a horizontal plane, dripping in the direction of gravity is further suppressed, enabling higher quality coating.

[0041] (Variation 2) FIGS. 7A, 7B, 7C, 7D, and 7E are schematic diagrams illustrating the steps of a coating method according to Variation 2. FIG. 7A illustrates the formation of a coating film on a coating surface 50 and corresponds to FIG. 2A. FIG. 7B illustrates the curing (primary curing) of droplets 51 forming a lower coating film 60 before the formation of an upper coating film 70 and corresponds to FIG. 6B. FIG. 7C illustrates the formation of an upper coating film 70 on a lower coating film 60 and corresponds to FIG. 2B. FIG. 7D illustrates the formation of a layered coating film 80 by repeated coating film formation and corresponds to FIG. 2C. FIG. 7E illustrates the curing (secondary curing) of the layered coating film 80 and corresponds to FIG. 2D. For ease of understanding, in FIGS. 7D and 7E, the coating films of each layer are shifted in the sub-scanning direction.

[0042] In Modification 2, the coating film formed by ejecting droplets 51 has a linear shape in which the droplets 51 are continuously arranged. In this respect, Modification 2 differs from the embodiment and Comparative Example 1 in which the droplets 51 are arranged intermittently in a dot shape.

[0043] The coating film formed by discharging the droplets 51 in this manner can be in the form of dots or lines, and an appropriate coating film shape can be selected depending on the shape of the coating surface 50, etc.

[0044] First, as shown in FIG. 7A, droplets 51 are ejected onto a coating surface 50 so as to provide gaps between the droplets 51 at least in the direction of gravity, thereby forming a coating film.

[0045] Next, as shown in FIG. 7B, before forming the upper coating film 70, the droplets 51 that form the lower coating film 60 are cured (primary curing).

[0046] 7C , an upper coating film 70 (indicated by a hatched circle) is formed on a lower coating film 60 (indicated by a light gray circle). At this time, droplets 51 are ejected so as to fill gaps in the lower coating film 60 and to provide gaps between droplets 51 at least in the direction of gravity.

[0047] Next, as shown in FIG. 7D, the upper layer coating film 70 is repeatedly formed on the lower layer coating film 60 to form a laminated coating film 80.

[0048] Then, as shown in FIG. 7E, the laminated coating film 80 is cured.

[0049] The configuration of Modification 2 promotes leveling between droplets 51 in the direction perpendicular to gravity, improving the surface roughness of the coating surface. Therefore, when coating a coating surface 50 that intersects with a horizontal plane, dripping in the direction of gravity is further suppressed, enabling higher quality coating.

[0050] (Variation 3) Figures 8A and 8 are schematic diagrams showing the procedure of a coating method according to Variation 3. Figure 8A shows a state in which a coating film has been formed on a coating surface 50, and corresponds to Figure 2A. Figure 8B shows a state in which an upper coating film 70 has been formed on a lower coating film 60, and corresponds to Figure 2B.

[0051] In Modification 3, the droplets 54 that form the upper coating film 70 are larger than the droplets 51 that form the lower coating film 60. In this respect, Modification 3 differs from the embodiment and Comparative Example 1, in which the droplets 51 that form the upper coating film 70 are the same size as the droplets 51 that form the lower coating film 60. Note that the coating film formed by ejecting the droplets 51, 54 has a dot shape in which the droplets 51, 54 are arranged intermittently, similar to the embodiment and Comparative Example 1.

[0052] First, as shown in FIG. 8A, droplets 51 are ejected onto a coating surface 50 so as to provide gaps between the droplets 51 at least in the direction of gravity, thereby forming a coating film.

[0053] 8B, an upper coating film 70 (shown by hatched circles) is applied over the lower coating film 60 (shown by open circles). At this time, droplets 54 are ejected so as to fill gaps in the lower coating film 60 and to provide gaps between droplets 54 at least in the direction of gravity.

[0054] Thereafter, similarly to the case shown in Fig. 2C, the formation of the upper layer coating film 70 on the lower layer coating film 60 is repeated to form a laminated coating film 80. Then, similarly to the case shown in Fig. 2D, the laminated coating film 80 is cured.

[0055] The configuration of Modification 3 allows for better leveling between droplets 51, improving the surface roughness of the coating surface. Therefore, when coating a coating surface 50 that intersects with a horizontal plane, dripping in the direction of gravity is further suppressed, enabling higher quality coating.

[0056] (Modification 4) FIG. 9 is a diagram showing how droplets 51 forming a lower coating film 60 are heated and cured in a coating method according to Modification 4.

[0057] In Modification 1, as shown in Fig. 6B, the droplets 51 forming the lower coating film 60 are cured (primary curing) before the formation of the upper coating film 70. At this time, as shown in Fig. 9, the droplets 51 forming the lower coating film 60 can be heated by a heater 90 or the like.

[0058] With the configuration of Variation 4, even when a paint type that does not dry naturally is used, the droplets 51 that form the lower coating film 60 can be cured (primary curing) by heating. Therefore, even when a paint type that does not dry naturally is used, dripping can be suppressed. Therefore, when coating a coating surface 50 that intersects a horizontal plane, dripping in the direction of gravity can be suppressed, enabling high-quality coating.

[0059] (Modification 5) Fig. 10 is a schematic diagram used to explain a coating method according to Modification 5. For ease of understanding, the coating films of the individual layers are shown shifted in the sub-scanning direction.

[0060] In the fifth modification, the coating film formed by ejecting the droplets 51 has a dot shape in which the droplets 51 are arranged intermittently, as in the embodiment and the first comparative example.

[0061] As shown in Figure 10, an upper coating film 70 (indicated by a hatched circle) is formed by overcoating a lower coating film 60 (indicated by a hollow circle). At this time, droplets 51 are ejected so as to fill gaps in the lower coating film 60 and to provide gaps between the droplets 51 at least in the direction of gravity. Furthermore, the position where the upper coating film 70 is formed is shifted in the coating progress direction (main scanning direction) by half a droplet (r) of the droplets 51 that form the lower coating film 60 relative to the position where the lower coating film 60 was formed.

[0062] If the configuration is as in Modification 5, the coating speed can be increased.

[0063] The above describes embodiments and modifications of the coating method of the present invention, but the present invention is not limited to the configurations described in the above embodiments and modifications, and can be modified as appropriate based on the claims.

[0064] The following embodiments are also included within the scope of the present invention: a coating method according to claim 2 or claim 3 having the features of claim 4; a coating method according to any one of claims 2 to 4 having the features of claim 5; and a coating method according to any one of claims 2, 3, or 5 having the features of claim 6.

[0065] REFERENCE SIGNS LIST 10 Coating device 20 Nozzle 30 Acoustic tube 40 Sound source 50 Coating surface 51, 52, 54 Droplets 53 Microdroplets 60 Lower coating film 70 Upper coating film 80 Layered coating films 90 Heater

Claims

1. A coating method using an inkjet coating system to form multi-layer coating films by ejecting droplets from a nozzle onto a coating surface that intersects a horizontal plane, comprising the steps of: ejecting droplets onto the coating surface so as to leave gaps between the droplets at least in the direction of gravity to form a coating film; ejecting droplets so as to fill the gaps in the lower coating film and leave gaps between the droplets at least in the direction of gravity to repeatedly form an upper coating film, thereby forming layered coating films; and curing the layered coating films.

2. The coating method according to claim 1, wherein the droplets forming the lower coating film are cured before the upper coating film is formed.

3. The coating method according to claim 2, wherein the droplets forming the lower coating film are cured by heating.

4. The coating method according to claim 1, wherein the coating film formed by ejecting droplets has a dot shape in which the droplets are arranged intermittently, or a linear shape in which the droplets are arranged continuously.

5. The coating method according to claim 1, wherein the droplets forming the upper coating film are larger than the droplets forming the lower coating film.

6. A coating method according to claim 1, wherein the coating film formed by ejecting droplets has a dot shape in which the droplets are arranged intermittently, and the position where the upper layer coating film is formed is shifted in the coating progress direction from the position where the lower layer coating film is formed by half a droplet of the droplets that form the lower layer coating film.

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