How to apply paint

Abstract

To provide a coating material applying method that can form a coated film having an even thickness without causing leakage on a slope coated surface as well.SOLUTION: A coating material applying method forms a coated film on a coated surface by discharging droplets of coating materials while moving an inkjet print head along application paths. The application paths include a plurality of first paths respectively extended in a second direction and arranged with an interval from each other in a first direction and at least one second path arranged between the two first paths made adjacent to each other in the first direction with an interval from the first paths, where a direction in which an inclination gradient on the coated surface is maximum is defined as the first direction and a direction perpendicular to the first direction is defined as the second direction. The method includes the following steps: (1) a first application step of forming a first layer of the coated film along the first path; (2) an intermediate drying step of drying the first layer of the coated film; and (3) a second application step of forming a second layer of the coated film in a mode in which the layer adheres tightly to the first layers of the adjacent two coated films, along the second path.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method for applying paint. [Background technology]

[0002] Conventionally, methods for applying paint to a surface of an article include spray painting, brush painting, and the like.

[0003] Spray painting is a method of applying paint by spraying a mist of paint onto a surface using a sprayer. Since it is necessary to keep the viscosity of the paint low in order to make the diameter of the sprayed mist uniform, a diluent is added to the paint. By moving the sprayer manually or automatically, a film of paint (coating film) is formed on the desired area of ​​the surface to be painted. Since the viscosity of the paint is kept low, the thickness (film thickness) of the coating film formed by one spraying is small. Therefore, in order to obtain the desired film thickness, it is necessary to repeat the procedure of performing intermediate drying to harden the coating film formed in one spraying process after the previous process, and then performing the next spraying process.

[0004] Brush painting is a method of applying paint directly to a surface by moving the brush. A coating is formed on the desired area of ​​the surface by manually moving the brush. To obtain a coating of the desired thickness, a procedure is usually repeated in which, after each coating step, intermediate drying is performed to harden the coating formed in the previous step, and then the next coating step is performed. Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned spray painting, the mist-like paint is diffused over a wide area, so in order to form a coating film only on the desired area of ​​the coating surface, it is necessary to mask the areas other than the desired area and remove the masking after the coating is completed, which requires a lot of time and cost. In addition, large-scale equipment is required to collect the mist-like paint that has diffused into the air, which also increases costs. Furthermore, when the coating surface has a complex shape, it is difficult to make the coating thickness uniform.

[0006] In addition, the above-mentioned brush painting has the disadvantage that it is difficult to make the film thickness uniform, and the quality of the painting depends on the skill of the worker. In addition, when the surface to be painted is inclined with respect to the horizontal plane, the applied paint is likely to flow downward (sagging), so in order to obtain a coating film of the desired thickness, it is necessary to repeat the application process with a small film thickness and the intermediate drying process many times, which takes a lot of time.

[0007] The present invention has been made in consideration of the above-mentioned problems, and has as its object to provide a method of applying paint which is capable of forming a coating film of uniform thickness without dripping, even on a coating surface which is inclined relative to the horizontal plane. [Means for solving the problem]

[0008] In order to achieve the above object, a first aspect of the present invention provides a method for applying paint to a surface inclined with respect to a horizontal plane using an inkjet printhead, the inkjet printhead being configured to eject droplets of the paint while moving along an application path on the surface to be coated, thereby forming a coating film on the surface to be coated, the application paths including a plurality of first paths each extending in the second direction and arranged at intervals from each other in the first direction, and at least one second path arranged at an interval from each of the first paths between two adjacent first paths in the first direction, the method including the following steps: (1) a first coating step of forming a first layer of a coating film on the coated surface by moving the inkjet print head along the first path; (2) an intermediate drying step for drying the first layer of the coating film; (3) a second coating step of forming a second layer of the coating film on the coated surface in such a manner that the second layer is in close contact with the two adjacent first layers of the coating film by moving the inkjet print head along the second path.

[0009] The method of the second aspect of the present invention further includes a third application step of forming a further layer of coating film on top of the first layer of coating film and the second layer of coating film in a direction perpendicular to the coating surface after the second application step is completed, and the third application step forms the further layer of coating film by moving the inkjet printhead along a plurality of third passes each extending in the second direction and arranged at intervals from each other in the first direction.

[0010] In the method of the third aspect of the present invention, the third coating step is carried out immediately after completion of the second coating step.

[0011] In the method of the fourth aspect of the present invention, the third coating step is carried out after the second coating step and after an intermediate drying step for drying the second layer of the coating film.

[0012] In the method of the fifth aspect of the present invention, the first coating step comprises: (1) a first underlayer coating step of forming a first underlayer of a coating film on the coated surface by moving the inkjet print head along the first path; (2) a first upper layer application step of forming a first upper layer of the coating film overlying the first lower layer of the coating film by moving the inkjet print head along the first path; Including, The first upper layer coating step is performed immediately after the first lower layer coating step is completed, or after the intermediate drying step of drying the first lower layer of the coating film is completed; The second coating step includes: (1) forming a first layer of a second layer of coating on the painted surface by moving the inkjet printhead along the second path; (2) immediately after completing the step of forming the first layer of the second layer of the coating, forming a second layer of the second layer of the coating over the first layer of the second layer of the coating by moving the inkjet printhead along the second path; Includes.

[0013] In the method of the sixth aspect of the present invention, the paint is any one of a two-component paint consisting of a base agent and a curing agent, a time-curing paint, a heat-curing paint, a light-curing paint, and a hot-melt paint, or a paint having a diluent added thereto.

[0014] In the method of the seventh aspect of the present invention, the surface to be coated is a plane inclined relative to a horizontal plane.

[0015] In the method of the eighth aspect of the present invention, the coated surface is a convex surface whose intersection with a plane perpendicular to the second direction is an upward convex curve, or a concave surface whose intersection with a plane perpendicular to the second direction is a downward convex curve. Effect of the Invention

[0016] According to the present invention, it is possible to obtain the excellent effect of forming a coating film of uniform thickness without sagging even on a coating surface that is inclined with respect to the horizontal plane. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a coating apparatus used to apply paint using a method according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating a coating path on a surface when coating a paint using a method according to an embodiment of the present invention. [Diagram 3] 1A to 1C are schematic explanatory diagrams showing variations in the cross-sectional aspects of a coating film formed on a horizontal coating surface when a coating material is applied to the horizontal coating surface using a method according to an embodiment of the present invention. [Figure 4] 1A to 1C are schematic explanatory diagrams showing variations in the cross-sectional aspects of a coating film formed on an inclined painted surface when a paint is applied to the inclined painted surface using a method according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram illustrating a process for applying paint to an article having multiple painted surfaces that are angled relative to one another using a method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0019] 1 is a schematic diagram of a coating apparatus used to apply paint using a method according to an embodiment of the present invention. In the illustrated embodiment, the coating apparatus is configured as a Cartesian robot to which an inkjet printhead is attached. Note that the coating apparatus may be configured as an articulated robot instead of a Cartesian robot.

[0020] 1, B is a base plate, 10 is a first slide shaft extending in the X direction, 20 is a second slide shaft extending in the Y direction, 30 is a third slide shaft extending in the Z direction, and 40 is an inkjet print head. Note that the X and Y directions are mutually perpendicular directions within a horizontal plane, and the Z direction is a vertical direction.

[0021] The first slide shaft 10 extends in the X direction and is fixed to a base B.

[0022] The second slide shaft 20 extends in the Y direction and is attached to the first slide shaft 10 via a slider (not shown). The slider slides along the first slide shaft 10, allowing the second slide shaft 20 to move back and forth in the +X direction and -X direction (see arrow Mx ​​in the figure).

[0023] The third slide shaft 30 extends in the Z direction and is attached to the second slide shaft 20 via a slider (not shown). The slider slides along the second slide shaft 20, allowing the third slide shaft 30 to move back and forth in the +Y direction and -Y direction (see the arrow My in the figure).

[0024] The inkjet print head 40 is attached to the third slide shaft 30 via a slider (not shown). As the slider slides along the third slide shaft 30, the inkjet print head 40 can move back and forth in the +Z direction / -Z direction (up and down) (see arrow Mz in the figure).

[0025] The inkjet print head 40 includes a syringe (not shown), a paint flow path connecting the syringe and a discharge port, and a valve for opening and closing the discharge port. The syringe is pressurized by compressed air, and is filled with paint. The valve body of the valve for opening and closing the discharge port is attached to one end of a rod, and the other end of the rod is connected to a piezoelectric element. When a pulsed voltage is applied to the piezoelectric element, the rod reciprocates in its longitudinal direction, and the discharge port is opened and closed by the valve body of the valve attached to the end of the rod. As a result, the paint supplied from the syringe through the paint flow path is discharged as minute droplets from the discharge port. In the illustrated embodiment, the paint droplets are discharged vertically downward (-Z direction) from the discharge port. By changing the mounting angle of the inkjet print head 40 with respect to the slider that slides along the third slide shaft 30, the direction in which the droplets are discharged from the discharge port can be made to be a direction other than vertically downward (-Z direction).

[0026] At this time, by lengthening / shortening the duration of the pulsed voltage applied to the piezoelectric element, the amount of paint heading toward the nozzle can be increased / decreased, making it possible to increase / decrease the diameter of the droplets of the paint ejected. Also, by increasing / decreasing the voltage applied to the piezoelectric element, the amount of movement (stroke) in the longitudinal direction of the rod can be increased / decreased, making it possible to increase / decrease the amount of paint heading toward the nozzle, making it possible to increase / decrease the diameter of the droplets of the paint ejected. If the paint filled in the syringe is a two-component paint in which the base agent and hardener are mixed, the viscosity of the paint increases over time, but by increasing the voltage applied to the piezoelectric element and increasing the stroke in accordance with the increase in viscosity, the amount of paint ejected can be kept constant.

[0027] When applying paint using the coating device configured as described above, a workpiece (item) W having a coating surface F is fixed to a base plate B by an appropriate method, and the above-mentioned Cartesian robot is operated in the manner described in detail below.

[0028] In the illustrated embodiment, the coating surface F includes a horizontal coating surface F1, which is a horizontal plane, and an inclined coating surface F2, which is a plane inclined with respect to the horizontal plane. Below, a method of applying paint to each of the horizontal coating surface F1 and the inclined coating surface F2 will be described.

[0029] For ease of explanation, the horizontal coating surface F1 is assumed to be a rectangular plane having a long side extending in the X direction and a short side extending in the Y direction. The inclined coating surface F2 is assumed to be a plane that intersects with the horizontal plane at an angle θ, and the direction in which the gradient with respect to the horizontal plane is greatest is the direction in which the Y axis is rotated around the X axis by the angle θ, i.e., the Y' direction (see FIG. 2). The inclined coating surface F2 is assumed to be a rectangular plane having a long side extending in the X direction and a short side extending in the Y' direction. The inclined coating surface F2 is assumed to be a convex surface (F2 in FIG. 4(A)) whose intersection with a plane perpendicular to the X direction is a convex curve upward (i.e., in the +Z' direction, when the direction perpendicular to the inclined coating surface F2 is the Z' direction). CVX ) or a concave surface whose intersection with a plane perpendicular to the X direction is a downward (i.e., -Z' direction) convex curve (F2 in Fig. 4(A) CCV (see reference).

[0030] Hereinafter, a method for applying paint to each of a horizontal surface F1 and an inclined surface F2 will be described with reference to Figures 2 to 4. Here, Figure 2 is a schematic explanatory diagram showing a coating path on a coating surface when paint is applied using the method according to an embodiment of the present invention, and Figures 3 and 4 are schematic explanatory diagrams showing variations in the cross-sectional aspects of the coating film formed on each coating surface when paint is applied to a horizontal surface and an inclined surface, respectively, using the method according to an embodiment of the present invention.

[0031] First, a method for applying paint to the horizontal coating surface F1 will be described.

[0032] When applying paint to the horizontal surface F1 to be coated, the inkjet print head 40 is moved in the Z direction (vertical direction) along the third slide shaft 30 so that the distance to the horizontal surface F1 to be coated is a distance suitable for discharging paint droplets, and fixed at an appropriate position. In this state, the position of the inkjet print head 40 in the X and Y directions is controlled by controlling the movement of the third slide shaft 30 in the Y direction along the second slide shaft 20 (see arrow My in FIG. 1) and the movement of the second slide shaft 20 in the X direction along the first slide shaft 10 (see arrow Mx ​​in FIG. 1), and the inkjet print head 40 is moved along a predetermined coating path P1 (see FIG. 2) on the horizontal surface F1 to be coated. Then, independently of the position control of the inkjet print head 40 described above, a voltage applied to the piezoelectric element of the inkjet print head 40 is controlled to discharge a predetermined amount of paint with a predetermined droplet diameter at each position on the coating path P1, thereby performing coating along the coating path P1.

[0033] In the embodiment shown in FIG. 2, the coating path P1 on the horizontal coating surface F1 is defined by P1x1 to P1x n (where n is a natural number greater than or equal to 2) n paths are spaced apart from each other by D1 to D n-1 The inkjet print head 40 is configured by being arranged in the Y direction with a gap therebetween. <1> The paint is applied along the application path P1 through steps ~<2n-1> (where i is a natural number satisfying 2≦i≦n-1). <1> Coating is performed while moving in the +X or -X direction along the path P1x1. <2> Move a distance D1 in the +Y direction. ... <2i-1> Path P1x i Coating is performed by moving in the +X or -X direction along the axis. <2i> + Distance D in the Y direction i Move only. <2i+1> Path P1x i+1 Coating is performed by moving in the +X or -X direction along the axis. ... <2n-1> Path P1x n Coating is performed by moving in the +X or -X direction along the axis. Here, when the movement directions in two successive coating steps (for example, step <2i-1> and step <2i+1>) are the same, in the movement step between the two steps (for example, step <2i>), the inkjet print head 40 not only moves in the +Y direction but also moves in the same direction as the pass of the previous coating step (for example, P1x i ) from the end point of the coating process pass (e.g., P1x i+1 In contrast, when the movement directions in two successive coating steps are different, the inkjet print head 40 only moves in the +Y direction in the movement step between the two steps.

[0034] In addition, the above-mentioned distances D1 to D n-1 The distances (between adjacent passes) are set arbitrarily according to the thickness of the coating film to be formed on the coating surface, and may be the same or different from each other. However, the distances D1 to D n-1 is selected so that two linear or curved coating films formed in two successive coating steps are in close contact with each other.

[0035] The shape of the coating path P1 is not limited to the one described above. For example, the movement of the inkjet print head 40 along the coating path P1 may be such that movement in the +Y direction or the -Y direction is repeated with movement in the +X direction sandwiched between. In addition, if the horizontal coating surface F1 includes an area where paint should not be applied, the application of voltage to the piezoelectric element may be interrupted while the inkjet print head 40 moving along the coating path P1 is in that area, thereby maintaining the discharge port in a closed state.

[0036] In the coating method according to the embodiment of the present invention, in order to form a coating film of a desired thickness on a coating surface, the coating film is made up of a single layer or multiple layers. This will be described in detail below. Note that a single layer refers to a layer formed by a single coating step without an intermediate drying step. On the other hand, multiple layers refers to layers formed by multiple coating steps each having an intermediate drying step interposed therebetween.

[0037] A method for applying paint to a horizontal surface F1 to be coated will be described below with reference to Figures 2 and 3. Figure 3 is a schematic explanatory diagram showing variations in the cross-sectional appearance of a coating film formed on a horizontal surface F1 to be coated when paint is applied to the horizontal surface F1 to be coated using a method according to an embodiment of the present invention. This figure is a cross-sectional view taken along the direction of the arrow X in Figure 2, and each circle in the figure shows a schematic cross-section of a linear or curved coating film formed along a path extending in the X direction (the direction perpendicular to the paper surface of Figure 3).

[0038] FIG. 3(A) shows a coating film consisting of a single layer formed by a single coating pass. As described above, the amount of paint discharged from the inkjet print head 40 can be adjusted by the duration of the pulse voltage applied to the piezoelectric element. Therefore, if the required thickness of the coating film can be achieved by such adjustment, the coating film can be realized as consisting of a single layer S1 formed by a single coating pass P1, as shown in FIG. 3(A). In this case, the coating of the paint on the horizontal coating surface F1 is completed by moving the inkjet print head 40 only once along the coating pass P1 shown in FIG. 2.

[0039] FIG. 3B shows a coating film consisting of a single layer formed by multiple application passes. As described above, the amount of paint discharged from the inkjet print head 40 can be adjusted by the duration of the pulse voltage applied to the piezoelectric element. However, if the required thickness of the coating film cannot be obtained even with the maximum amount of paint that can be achieved by this adjustment, the coating film can be realized as a single layer S1 formed by multiple (two in the illustrated example) application passes P1 as shown in FIG. 3B. In this case, after the inkjet print head 40 forms the first layer L1 of the coating film by the first movement along the application pass P1 shown in FIG. 2, it is returned to the start point of the application pass P1 immediately, and then, by the second movement along the application pass P1, it forms the second layer L2 of the coating film on the first layer L1 of the coating film. Note that, before starting the second movement along the application pass P1, the inkjet print head 40 may be moved in the +Z direction (vertically upward) as necessary. According to this coating method, the first and second coatings are essentially a single coating process with no intermediate drying process between them, so that the first layer L1 and the second layer L2 adhere firmly to each other, reducing the possibility of peeling at the interface between the two layers.

[0040] As shown in Figure 3(C), by shifting the coating path P1 when forming the first layer L1 and the coating path P1 when forming the second layer L2 in the Y direction by 1 / 2 the diameter of the paint droplet, the adhesion between the first layer L1 and the second layer L2 can be improved compared to the case shown in Figure 3(B), and the possibility of peeling at the interface between the two layers can be further reduced.

[0041] FIG. 3(D) shows a coating film consisting of multiple layers. As mentioned above, the amount of paint discharged from the inkjet print head 40 can be adjusted by the duration of the pulse voltage applied to the piezoelectric element. However, if the required thickness of the coating film cannot be obtained even with the maximum amount of paint that can be achieved by this adjustment, the coating film can be realized as a coating film consisting of multiple layers S1, S2 (two in the illustrated example) as shown in FIG. 3(D). In this case, the first layer S1 is formed by a first coating step in which the inkjet print head 40 is moved along the coating path P1 shown in FIG. 2, and then intermediate drying is performed, and then a second layer S2 is formed on the first layer S1 by a second coating step in which the inkjet print head 40 is moved along the coating path P1. Such a coating method is advantageous when the amount of paint is large. In such a case, in the coating method shown in FIG. 3(B), the thickness of the coating film consisting of a single layer formed by the first and second coatings, which are essentially considered to be a single coating step, becomes very large, and there is a high possibility that wrinkles and cracks will occur during drying. In contrast, the coating method shown in FIG. 3(D) prevents the layer (coating film) formed by one coating from becoming excessively thick, even when a large amount of paint is used, and reduces the possibility of wrinkles or cracks occurring during drying.

[0042] As shown in Figure 3(E), by shifting the coating path P1 when forming the first layer S1 and the coating path P1 when forming the second layer S2 in the Y direction by 1 / 2 the diameter of the paint droplet, the adhesion between the first layer S1 and the second layer S2 can be improved compared to the case shown in Figure 3(D), and the possibility of peeling at the interface between the two layers can be reduced.

[0043] The method of applying paint to the horizontal coating surface F1 is not limited to the above. For example, the above-mentioned embodiments may be combined as appropriate. In addition, when the coating film is made up of multiple layers, the number of layers may be three or more. Similarly, when the layer is made up of multiple layers, the number of layers may be three or more. Furthermore, the amount of paint ejected from the inkjet print head 40 in the application to form each layer and each layer does not necessarily have to be the same, and may be different from each other.

[0044] Next, a method for applying paint to the inclined coating surface F2 will be described.

[0045] When applying paint to the inclined surface F2, similarly to the case of the horizontal surface F1, the inkjet printhead 40 is appropriately positioned in the Z direction (vertical direction) (or Z' direction), and its position in the X and Y' directions is controlled to move it along a predetermined application path on the inclined surface F2. Then, independently of the position control of the inkjet printhead 40 described above, the voltage applied to the piezoelectric element of the inkjet printhead 40 is controlled to eject a predetermined amount of paint with a predetermined droplet diameter at each position on the application path, thereby performing application along the application path.

[0046] Hereinafter, a method for applying paint to an inclined coated surface F2 will be described with reference to Fig. 2 and Fig. 4. Fig. 4 is a schematic explanatory diagram showing variations in the cross-sectional aspects of a coating film formed on an inclined coated surface F2 when paint is applied to the inclined coated surface F2 using a method according to an embodiment of the present invention. This figure is a cross-sectional view taken along the X direction in Fig. 2, and each circle in the figure shows a schematic cross-section of a coating film formed along a path extending in the X direction (a direction perpendicular to the paper surface of Fig. 4). In the following, a case in which a linear coating film is formed on an inclined coated surface F2 along a linear path as shown in Fig. 2 will be described, but it is also possible to form a curved coating film along a curved path.

[0047] When a paint is applied to the inclined coating surface F2, the coating film formed on the inclined coating surface F2 is composed of two or more layers including the first layer S1 in any of the embodiments described below. First, the simplest embodiment in which the coating film is composed of only two layers, the first layer S1 and the second layer S2, will be described below with reference to Figures 2 and 4(A).

[0048] 4(A) shows a coating film consisting of only two layers, a first layer S1 and a second layer S2. This coating film is realized by forming the first layer S1 in a first coating step in which the inkjet print head 40 is moved along a first-layer coating path P21 shown in FIG. 2, and then forming the second layer S2 in a second coating step in which the inkjet print head 40 is moved along a second-layer coating path P22 shown in FIG. 2 after an intermediate drying step.

[0049] As shown in FIG. 2, the first layer coating pass P21 is arranged at intervals D1 to D2 in the Y' direction (first direction) where the gradient of the inclined coating surface F2 with respect to the horizontal plane is the largest. n-1 With the gap between the paths P21x1 and P21x2, the paths P21x1 to P21x2 extend in the X direction (the direction perpendicular to the Y direction; the second direction). n The inkjet print head 40 is configured by arranging the following: <1> The first coating step is carried out through steps 1 to <2n-1>. <1> Coating is performed while moving in the +X direction or the -X direction along the path P21x1. <2> Move a distance D1 in the +Y' direction. ... <2i-1> Path P21x i Coating is performed by moving in the +X or -X direction along the axis. <2i> +Y' direction with distance D i Move only. <2i+1> Pass P21x i+1 Coating is performed by moving in the +X or -X direction along the axis. ... <2n-1> Path P21x n Coating is performed by moving in the +X or -X direction along the axis. Here, when the movement directions in two successive coating steps (for example, step <2i-1> and step <2i+1>) are the same, in the movement step between the two steps (for example, step <2i>), the inkjet print head 40 not only moves in the +Y' direction but also moves in the same direction as the pass of the previous coating step (for example, P21x i ) from the end point of the subsequent coating process pass (e.g., P21x i+1 In contrast, when the movement directions in two successive coating steps are different, the inkjet print head 40 only moves in the +Y' direction in the movement step between the two steps. In addition, the above-mentioned distances D1 to D n-1 (the interval between adjacent passes) is the interval between adjacent passes (for example, passes P21x i and pass P21x i+1 ) (eg, along path P22x1) is selected so that the coating film formed between the two coating films formed along path P22x2 is in close contact with the two coating films described above.

[0050] In this first coating process, passes P21x1 to P21x n are formed along the distances D1 to D n-1 A plurality of sets of coating films separated by a distance of 0.05 mm are formed, which constitute the first layer S1 (only one of the sets of coating films that constitute the first layer S1 is shown in FIG. 4(A)).

[0051] In addition, each of the above-mentioned coating steps ( <1> , ...<2i-1>, ...<2n-1>), the positions in the Z direction (vertical direction) (or Z' direction) are different, so <2> , ...<2i>, ...), the inkjet print head 40 may be repositioned in the Z direction (vertical direction) (or Z' direction) if necessary.

[0052] At the end of the first coating step, the inclined coating surface F2 is provided with paths P21x1 to P21x nBetween the coatings formed along each of the first and second layers, there remains an area where no coating is formed. In order to apply paint to this area, a second coating step is performed in which the inkjet print head 40 is moved along the second layer coating path P22.

[0053] The second layer application pass P22 is a pass that is adjacent to the pass P21x as shown in FIG. i and pass P21x i+1 ) along the Y' direction, where the gradient of the inclined coating surface F2 with respect to the horizontal plane is the largest, so that a coating film that adheres to the two coating films is formed between the two coating films formed along the Y' direction, and the paths P22x1 to P22x2 extending in the X direction are spaced apart from each other. n―1 The inkjet print head 40 moves in the +Y' direction each time, and passes through passes P22x1 to P22x n―1 The second coating step is performed by performing coating while moving in the +X direction or the -X direction along each of the axes.

[0054] In this second coating process, passes P22x1 to P22x n―1 Along each of these paths, a coating is formed that adheres closely to the coating already formed along the adjacent path, forming a second layer S2 (only one of the coatings that form the second layer S2 is shown in FIG. 4(A)).

[0055] 4(A) shows a case where the first layer S1 and the second layer S2 are formed by a single first-layer application pass P21 and a single second-layer application pass P22, respectively, but the first layer S1 and the second layer S2 may be formed by multiple first-layer application passes P21 and multiple second-layer application passes P22, respectively. In this case, the first layer S1 and the second layer S2 each consist of multiple layers overlapping each other vertically (more precisely, in the Z' direction (third direction) perpendicular to the inclined coating surface F2). This allows a thicker coating film to be formed on the inclined coating surface F2.

[0056] The coating film (second layer S2) formed in the above-mentioned second coating step does not sag even though the inclined coating surface F2 is inclined with respect to the horizontal plane. This is because the coating film (second layer S2) formed in the above-mentioned second coating step does not sag even though the inclined coating surface F2 is inclined with respect to the horizontal plane. n This is because the coating film (first layer S1) already formed along the inclined coating surface F2 acts as a bank, so to speak, and prevents the coating film formed between the banks from dripping in the second coating step. More specifically, the coating film (for example, the first layer S2) located on the upper side of the inclined coating surface F2 (for example, the first layer S3) acts as a bank, so to speak, and prevents the coating film formed between the banks from dripping in the second coating step. i The coating film formed along the path P21x) prevents the latter coating film from dripping through the adhesive force acting between it and the coating film formed in the second coating process, and the coating film located below (path P21x i+1 The coating film formed along the first coating step blocks the downward flow of the coating film formed in the second coating step, thereby preventing the latter coating film from sagging.

[0057] As described above, the method of applying paint to an inclined coating surface F2 according to the embodiment of the present invention is characterized in that the coating film formed in the preceding coating step acts as a bank to prevent the coating film applied in the subsequent coating step from dripping. In the following, a modified version of the method will be described mainly with reference to FIG. 4.

[0058] FIG. 4(B) shows a coating film including a third layer S3 (further layer) formed on top of the first layer S1 and second layer S2 constituting the coating film of FIG. 4(A) (more precisely, overlapping them in the Z' direction (third direction) perpendicular to the inclined coating surface F2) so as to cover them. In this case, the third layer S3 is formed in the third coating step after the intermediate drying step following the first and second coating steps. Note that the third coating step may be performed immediately after the second coating step is completed, that is, without the intermediate drying step. In the third coating step, the inkjet print head 40 moves along a coating path (not shown) (third pass) configured similarly to the coating path P1 (see FIG. 2) for the horizontal coating surface F1, which is alternately arranged in the Y' direction at a predetermined interval.

[0059] In the coating film thus formed, the uppermost layer (third layer S3) is formed in a single coating step (third coating step). Therefore, compared to the coating film in Fig. 4(A) in which the uppermost layers (first layer S1 and second layer S2) are formed in separate coating steps (first coating step and second coating step), the boundary between the coating films arranged in the Y' direction is less noticeable. Therefore, in the coating film in Fig. 4(B), the surface of the uppermost layer (third layer S3) has a smooth appearance, and higher coating quality can be achieved.

[0060] The same advantages as those described above can also be obtained by the coating film shown in FIG. 4(C). The coating film in FIG. 4(C) is formed by forming the third layer S3 in FIG. 4(B) as the second layer L2 of the second layer S2. That is, in FIG. 4(C), the second layer S2 is composed of the first layer L1 and the second layer L2 formed between the adjacent coating films of the first layer S1, and the second layer L2 of the second layer S2 is formed so as to cover the first layer S1 and the first layer L1 of the second layer S2. In this case, the inkjet print head 40 forms the first layer L1 of the second layer S2 by a first movement along the second layer coating path P22 shown in FIG. 2, and then moves along a coating path configured by alternately arranging coating paths (not shown) (third paths) in the same manner as the coating path P1 (see FIG. 2) for the horizontal coating surface F1 at a predetermined interval in the Y' direction, thereby forming the second layer L2 (further layer) of the second layer S2.

[0061] Even in the coating film thus formed, the surface of the uppermost layer (the second layer L2 of the second layer S2) has a smooth appearance, and higher coating quality can be achieved.

[0062] Figure 4(D) is a modified example of the coating film of Figure 4(C), in which the second layer S2 in Figure 4(C) is composed of multiple layers (three in the illustrated example) including a first layer L1 which is attached to the coating film of the first layer S1 rather than to the inclined coating surface F2.

[0063] Here, the first layer L1 is made of a coating film formed from paint droplets having a smaller diameter than the coating film of the first layer S1, and each coating film is attached to each of the coating films of the first layer S1 on both sides in the Y' direction. The second layer L2 is made of a coating film formed from paint droplets having substantially the same diameter as the first layer L1, and each coating film is attached to each of the two coating films of the first layer L1 formed between the coating films of the adjacent first layer S1. Furthermore, the third layer L3 is made of a coating film formed from paint droplets having substantially the same diameter as the first layer L1 and the second layer L2, and is attached to the first layer L1 and the second layer L2 so as to cover them, and is formed parallel to the inclined coating surface F2.

[0064] In the coating film thus formed, the coating film of each layer constituting the second layer S2 is firmly attached to the coating film formed earlier, so that sagging does not occur. In addition, the surface of the topmost layer (the third layer L3 of the second layer S2) has a smooth appearance, so that high coating quality can be achieved, as in the cases of Figures 4(B) and 4(C).

[0065] Fig. 4(E) is a modified example of the coating film in Fig. 4(A), which is intended to have the first lower layer S1L formed in the first lower layer coating step and the first upper layer S1U formed on the first lower layer S1L (more precisely, overlapping in the Z' direction) in the first upper layer coating step after the intermediate drying step function as a bank. Note that the first upper layer coating step may be performed immediately after the first lower layer coating step is completed, i.e., without the intermediate drying step.

[0066] In each of the first lower layer coating step and the first upper layer coating step, the inkjet print head 40 moves along the first layer coating path P21 shown in FIG. 2, similar to the first coating step for the coating film in FIG. 4(A), to form the first lower layer S1L and the first upper layer S1U. After the first lower layer coating step and the first upper layer coating step are completed, the second coating step is performed following the intermediate drying step. In the second coating step, the inkjet print head 40 forms the first layer L1 of the coating film by the first movement along the coating path P22 shown in FIG. 2, and then immediately returns to the start point of the coating path P22, and subsequently forms the second layer L2 of the coating film on the first layer L1 of the coating film by the second movement along the coating path P22, thereby forming the second layer S2 consisting of the first layer L1 and the second layer L2. In other words, the step of forming the second layer L2 is performed immediately after the step of forming the first layer L1 is completed, that is, without the intermediate drying step. In this way, the second layer S2 consisting of the first layer L1 and the second layer L2 is formed between the coating consisting of the first lower layer S1L and the first upper layer S1U which act as banks.

[0067] Such a coating method is advantageous when the coating film to be formed on the inclined coating surface F2 is thick.

[0068] The method of applying paint to the inclined coating surface F2 is not limited to the above. For example, the above-mentioned embodiments may be combined as appropriate. In addition, when the coating film is made up of multiple layers, the number of layers may be three or more. Similarly, when the coating film is made up of multiple layers, the number of layers may be set arbitrarily.

[0069] In the above, the direction in which the paint droplets are discharged from the nozzle of the inkjet print head in the coating device used to apply paint using the method of the embodiment of the present invention has been described as being vertically downward (-Z direction). However, when coating paint on an inclined coating surface F2 having a large angle θ with respect to the horizontal plane, for example, in the coating film of FIG. 4(A), the distance between the two adjacent coating films of the first layer S1 formed first when viewed in the -Z direction becomes significantly smaller than the diameter of the paint droplets forming the coating film of the second layer S2. In such a situation, it is difficult for the paint droplets discharged from the nozzle of the inkjet print head to pass between the two adjacent coating films of the first layer S1 and reach the inclined coating surface F2. Therefore, in such a case, a function of rotating the inkjet print head may be added to the Cartesian robot constituting the above-mentioned coating device so that the paint droplets are discharged from the nozzle perpendicular to the inclined coating surface F2. Furthermore, in order to realize such a function, an articulated robot may be adopted instead of the Cartesian robot as the robot constituting the above-mentioned coating device.

[0070] As shown in Fig. 5, for example, in the case of applying paint to a workpiece W' having three coating surfaces F1, F2, and F3, where coating surface F1 is horizontal (see Fig. 5(A)) and coating surfaces F2 and F3 are inclined at different angles to the horizontal plane, if it is not possible to use an orthogonal robot or an articulated robot with the function of rotating the inkjet print head as described above, it is not possible to apply paint to coating surface F3, which forms a large angle with the horizontal plane, in the state shown in Fig. 5(A). In such a case, the following method can be adopted to apply paint to all of the coating surfaces. (1) In the state shown in Fig. 5(A), the inkjet print head 40 is moved along coating paths similar to coating paths P21 and P22 (see Fig. 2) relative to the surface F1 to be coated, thereby forming a coating film having a cross section as shown in Fig. 4. (In other words, the coating method for an inclined surface to be coated is applied to the surface F1 to be coated in a horizontal state.) (2) In a state where the workpiece W' is rotated so that the surface F2 to be coated is horizontal (see FIG. 5(B)), the inkjet print head 40 is moved along the coating path P1 (see FIG. 2) relative to the surface F2 to be coated, thereby forming a coating film having a cross section as shown in FIG. 3. (In other words, the coating method for horizontal surfaces is applied to the surface F2 to be coated that has been made horizontal by rotating the workpiece W'.) (3) In the state shown in Fig. 5(B), the inkjet print head 40 is moved along application paths P21 and P22 (see Fig. 2) relative to the surface F3 to be coated, thereby forming a coating film having a cross section as shown in Fig. 4. (In other words, the coating method for an inclined surface to be coated is applied to the surface F3 to be coated that is inclined relative to the horizontal plane.)

[0071] In this way, when applying paint to a workpiece having multiple coating surfaces that are at an angle to each other, it is possible to apply the coating method for horizontal coating surfaces to all of the coating surfaces by rotating the workpiece each time so that each coating surface is horizontal. However, when coating the second or subsequent coating surfaces, the coating surface that has been previously coated will be inclined with respect to the horizontal plane. Therefore, for coating surfaces that will be inclined with respect to the horizontal plane in the subsequent coating process, even if the coating is performed while the coating surface is horizontal, applying the coating method for inclined coating surfaces can prevent the coating film from dripping during the subsequent coating process.

[0072] The method according to the embodiment of the present invention can be applied to apply any type of paint. For example, the method according to the embodiment of the present invention can be applied to apply two-component paints consisting of a base agent and a curing agent, time-curing paints, heat-curing paints, light-curing paints, hot melt paints, etc. The method can also be applied to apply the above-mentioned paints by adding a diluent thereto. [Explanation of symbols]

[0073] 40 Inkjet Printhead F2 Inclined painted surface (painted surface) X 2nd direction Y' 1st direction P21(P21x1~P21x n ) 1st pass P22(P22x1~P22x n―1 ) 2nd pass S1 First layer of coating S2 Second layer of coating

Claims

1. 1. A method for applying paint to a surface inclined relative to a horizontal plane using an inkjet printhead, comprising: the inkjet printhead is configured to eject droplets of the paint while moving along a coating path on the surface to be coated, thereby forming a coating film on the surface to be coated; On the coated surface, a direction in which the gradient of the inclination of the coated surface with respect to the horizontal plane is the largest is defined as a first direction, and a direction perpendicular to the first direction is defined as a second direction. The coating pass is a plurality of first paths each extending in the second direction and arranged at intervals in the first direction; at least one second path arranged between two adjacent first paths in the first direction and spaced apart from each of the first paths; Including, The method includes the following steps. (1) a first coating step of forming a first layer of a coating film on the surface by moving the inkjet print head along the first path; (2) an intermediate drying step for drying the first layer of the coating film; (3) a second coating step of forming a second layer of the coating film on the coated surface in such a manner that the second layer is in close contact with the first layers of the coating film adjacent to each other by moving the inkjet print head along the second path;

2. After the second coating step, a third coating step is performed to form a further layer of coating film on the first layer of coating film and the second layer of coating film in a direction perpendicular to the painted surface; 2. The method of claim 1, wherein the third applying step forms additional layers of the coating by moving the inkjet printhead along a plurality of third passes, each of which extends in the second direction and is spaced apart from one another in the first direction.

3. The method of claim 2 , wherein the third coating step occurs immediately after the second coating step.

4. 3. The method of claim 2, wherein the third coating step is performed after the second coating step and after an intermediate drying step for drying a second layer of the coating.

5. The first coating step includes: (1) a first underlayer application step of forming a first underlayer of a coating film on the coated surface by moving the inkjet print head along the first path; (2) forming a first upper layer of the coating film over the first lower layer of the coating film by moving the inkjet printhead along the first path; Including, The first upper layer coating step is performed immediately after the first lower layer coating step is completed, or after the intermediate drying step of drying the first lower layer of the coating film is completed; The second coating step includes: (1) forming a first layer of a second layer of coating on the painted surface by moving the inkjet printhead along the second path; (2) immediately after completing the step of forming the first layer of the second layer of the coating, moving the inkjet printhead along the second path to form a second layer of the second layer of the coating over the first layer of the second layer of the coating. The method of claim 1 , comprising:

6. The method according to any one of claims 1 to 5, characterized in that the paint is any one of a two-component paint consisting of a base agent and a curing agent, a time-curing paint, a heat-curing paint, a light-curing paint, and a hot-melt paint, or a paint having a diluent added thereto.

7. The method according to any one of claims 1 to 6, characterized in that the surface to be coated is a plane inclined relative to a horizontal plane.

8. The method according to any one of claims 1 to 6, characterized in that the coating surface is a convex surface whose intersection line with a plane perpendicular to the second direction is an upward convex curve, or a concave surface whose intersection line with a plane perpendicular to the second direction is a downward convex curve.

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