JP7633083B2 - How to apply paint - Google Patents

Description

The present invention relates to a method for applying paint.

Conventional methods for applying paint to the surface of an article include spray painting and brush painting.

Spray painting is a method of applying paint by spraying a mist of paint onto the surface to be painted using a sprayer. The viscosity of the paint needs to be kept low to ensure a uniform diameter for the mist to be sprayed, so a thinner is added to the paint. A film of paint (coating film) is formed in the desired area of the surface by moving the sprayer manually or automatically. Because the viscosity of the paint is kept low, the 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 intermediate drying to harden the coating film formed in one spraying process after that process, and then performing the next spraying process.

Brush painting is a method in which paint attached to a brush is applied directly to the surface to be painted. By manually moving the brush, a coating is formed in the desired area of the surface. To obtain a coating of the desired thickness, a procedure is usually repeated in which, after one coating step, intermediate drying is performed to harden the coating formed in the previous step, and then the next coating step is performed.

In the above-mentioned spray painting, the mist-like paint spreads over a wide area, so in order to form a coating only on the desired area of the painted surface, it is necessary to mask the areas other than the desired area and remove the masking after painting 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 spread into the air, which also increases costs. Furthermore, when the painted surface has a complex shape, it is difficult to achieve a uniform coating thickness.

In addition, the above-mentioned brush painting method has the disadvantage that it is difficult to achieve a uniform film thickness, and the quality of the paint depends on the skill of the worker. In addition, if the surface to be painted is inclined relative to the horizontal plane, the applied paint is likely to flow downward (sag). Therefore, in order to obtain a coating 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.

The present invention was made in consideration of the above problems, and aims to provide a paint application method that can form a coating film of uniform thickness without dripping, even on a surface that is inclined relative to the horizontal plane.

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 passes each extending in the second direction and arranged at intervals from each other in the first direction, and at least one second pass arranged at an interval from each of the first passes between two adjacent first passes in the first direction, the method including the following steps:
(1) a first application 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 of drying the first layer of the coating film; and (3) a second application step of forming a second layer of a coating film on the coated surface in such a manner that the second layer of the coating film is in close contact with the first layers of the two adjacent coating films by moving the inkjet print head along the second path.

The method of the second aspect of the present invention further includes a third application step, after completion of the second application step, of forming a further layer of coating film in a direction perpendicular to the painted surface, overlying the first layer of coating film and the second layer of coating film, the third application step forming the further layer of coating film by moving the inkjet printhead along a plurality of third passes, each of which extends in the second direction and is arranged at a distance from one another in the first direction.

In the method of the third aspect of the present invention, the third application step is carried out immediately after the second application step is completed.

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

In the method of the fifth aspect of the present invention, the first applying step comprises:
(1) a first underlayer application step of forming a first underlayer of a coating film on the painted surface by moving the inkjet print head along the first path; and (2) a first upper layer application step of forming a first upper layer of a coating film on the first underlayer of the coating film by moving the inkjet print head along the first path.
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 a coating on the painted surface by moving the inkjet printhead along the second path; and (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.

In the method of the sixth aspect of the present invention, the paint is any of two-component paints consisting of a base agent and a hardener, time-curing paints, heat-curing paints, light-curing paints, and hot-melt paints, or paints to which a diluent has been added.

In the method of the seventh aspect of the present invention, the coating surface is a plane inclined relative to the horizontal plane.

In the method of the eighth aspect of the present invention, the coating surface is a convex surface whose intersection with a plane perpendicular to the second direction is an upwardly convex curve, or a concave surface whose intersection with a plane perpendicular to the second direction is a downwardly convex curve.

The present invention has the excellent effect of forming a coating film of uniform thickness without dripping, even on a coating surface that is inclined relative to the horizontal plane.

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. 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. 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. 1 is a schematic explanatory diagram showing variations in the cross-sectional appearance 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. FIG. 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.

The following describes an embodiment of the present invention in detail with reference to the drawings.

Figure 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 an Cartesian robot to which an inkjet printhead is attached. Note that the coating apparatus may also be configured as an articulated robot instead of a Cartesian robot.

In FIG. 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 direction and the Y direction are mutually perpendicular directions in a horizontal plane, and the Z direction is a vertical direction.

The first slide shaft 10 extends in the X direction and is fixed to the base plate B.

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

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

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

The inkjet print head 40 includes a syringe (not shown), a paint flow path that connects the syringe and the discharge port, and a valve that opens and closes the discharge port. The syringe is pressurized by compressed air, and is filled with paint. The valve body of the valve that opens and closes 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 moves back and forth 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. It should be noted that the direction in which droplets are discharged from the discharge port can be changed to a direction other than vertically downward (-Z direction) by changing the mounting angle of the inkjet print head 40 with respect to the slider that slides along the third slide shaft 30.

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 increases/decreases, 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 increases/decreases, 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.

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

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 relative 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.

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 of the inclined coating surface F2 with respect to the horizontal plane is greatest is the direction obtained by rotating the Y axis 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 may be a convex surface (see F2 CVX in FIG. 4A) in which the intersection line with a plane perpendicular to the X direction is a curved line that is convex upward (i.e., in the +Z' direction, when the direction perpendicular to the inclined coating surface F2 is the Z' direction), or a concave surface (see F2 _CCV in FIG. 4A) in which the intersection line with a _plane perpendicular to the X direction is a curved line that is convex downward (i.e., in the -Z' direction).

Below, we will explain the method of applying paint to each of the horizontal painting surface F1 and the inclined painting surface F2, with reference to Figures 2 to 4. Here, Figure 2 is a schematic explanatory diagram showing the application path on the painting surface when applying paint using the method of an embodiment of the present invention, and Figures 3 and 4 are schematic explanatory diagrams showing variations in the cross-sectional form of the paint film formed on each painting surface when applying paint to a horizontal painting surface and an inclined painting surface, respectively, using the method of an embodiment of the present invention.

First, we will explain how to apply paint to the horizontal painting surface F1.

When applying paint to the horizontal coating surface F1, 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 coating surface F1 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 coating surface F1. Then, independently of the position control of the inkjet print head 40 described above, the 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, and coating is performed along the coating path P1.

2, coating path P1 on horizontal coating surface F1 is composed of n paths P1x ₁ to P1x _n (where n is a natural number equal to or greater than 2) each extending in the X direction and arranged in the Y direction at intervals D ₁ to D _n-1 . The inkjet print head 40 then applies paint along coating path P1 through the following steps <1> to <2n-1> (where i is a natural number satisfying 2≦i≦n-1).
<1> Coating is performed while moving in the +X direction or −X direction along the path _P1x1 .
<2> Move in the +Y direction _by a distance D1.
...
<2i-1> Coating is performed while moving in the +X direction or −X direction along the path P1x _i .
Move in the <2i>+Y direction by a distance D _i .
<2i+1> Coating is performed while moving in the +X direction or −X direction along the path P1x _i+1 .
...
<2n-1> Coating is performed while moving in the +X direction or −X direction along path P1x _n .
Here, when the movement directions in two successive coating steps (e.g., step <2i-1> and step <2i+1>) are the same, in the movement step between the two steps (e.g., step <2i>), the inkjet print head 40 not only moves in the +Y direction, but also moves in the +X direction or -X direction from the end point of the pass of the previous coating step (e.g., P1x _i ) to the start point of the pass of the subsequent coating step (e.g., P1x _i+1 ). Conversely, when the movement directions in the two successive coating steps are different, in the movement step between the two steps, the inkjet print head 40 only moves in the +Y direction.

The above-mentioned distances D ₁ to D _n-1 (the intervals between adjacent passes) are set arbitrarily according to the thickness of the coating film to be formed on the coating surface, and may all be the same or may be different from each other, provided that the distances D ₁ to D _n-1 are selected so that the two linear or curved coating films formed in the two successive coating processes are in close contact with each other.

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 can be such that movement in the +Y or -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 can be interrupted while the inkjet print head 40 moving along the coating path P1 is in that area to maintain the outlet closed.

In the paint application method according to an embodiment of the present invention, in order to form a coating film of the desired thickness on the painted 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 application process without an intermediate drying process. On the other hand, multiple layers refers to layers formed by multiple application processes each having an intermediate drying process interposed therebetween.

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

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

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 immediately returned to the start point of the application pass P1, and then, by the second movement along the application pass P1, the second layer L2 of the coating film is formed 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. With this coating method, the first and second coatings are essentially a single coating process with no intermediate drying process between them, so 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.

As shown in FIG. 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 and the possibility of peeling at the interface between the two layers can be further reduced compared to the case shown in FIG. 3(B).

Figure 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 piezo element. However, if the required coating thickness cannot be obtained even with the maximum amount of paint that can be achieved by this adjustment, the coating film can be realized as one consisting of multiple (two in the illustrated example) layers S1 and S2 as shown in Figure 3(D). In this case, the first layer S1 is formed by the first coating process in which the inkjet print head 40 is moved along the coating path P1 shown in Figure 2, and then intermediate drying is performed, and then the second layer S2 is formed on the first layer S1 by the second coating process 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 Figure 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 process, becomes very large, and there is a high possibility that wrinkles and cracks will occur during drying. In contrast, the coating method shown in Figure 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 when drying.

As shown in FIG. 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 FIG. 3(D), and the possibility of peeling at the interface between the two layers can be reduced.

The method of applying paint to the horizontal coating surface F1 is not limited to the above. For example, the above-mentioned embodiments can 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 each layer and in the application that forms each layer does not necessarily have to be the same, and may be different from each other.

Next, we will explain how to apply paint to the inclined painting surface F2.

When applying paint to an inclined coating surface F2, similar to the case of a horizontal coating surface F1, the inkjet print head 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 coating path on the inclined coating surface F2. Then, independently of the position control of the inkjet print head 40 described above, the voltage applied to the piezoelectric element of the inkjet print head 40 is controlled to eject a predetermined amount of paint with a predetermined droplet diameter at each position on the coating path, thereby performing coating along the coating path.

Below, a method of applying paint to an inclined painted surface F2 will be described with reference to Figures 2 and 4. Here, Figure 4 is a schematic explanatory diagram showing variations in the cross-sectional form of a coating film formed on an inclined painted surface F2 when paint is applied to the inclined painted 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 Figure 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 Figure 4). Note that, below, a case in which a linear coating film is formed on an inclined painted surface F2 along a linear path as shown in Figure 2 will be described, but it is also possible to form a curved coating film along a curved path.

When paint is applied to the inclined painted surface F2, the coating film formed on the inclined painted surface F2 consists of two or more layers including the first layer S1 in all of the embodiments described below. Therefore, first, the simplest embodiment in which the coating film consists 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).

Figure 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 the first layer coating path P21 shown in Figure 2, and then forming the second layer S2 in a second coating step in which the inkjet print head 40 is moved along the second layer coating path P22 shown in Figure 2 after an intermediate drying step.

2, the first layer coating pass P21 is configured by arranging passes P21x 1 to P21x n (first passes) each extending in the X direction (a direction perpendicular to the Y'direction; a second direction) at intervals _{D 1} to D _{n-1 in} the Y' direction (first direction) where the gradient of the inclined coating surface F2 with respect to the horizontal plane is greatest. The inkjet print head 40 then executes the first coating step through the following 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 in the +Y' direction _by a distance D1.
...
<2i-1> Coating is performed while moving in the +X direction or −X direction along the path P21x _i .
Move in the <2i>+Y' direction by a distance D _i .
<2i+1> Coating is performed while moving in the +X direction or −X direction along the path P21x _i+1 .
...
<2n-1> Path P21x Coating is performed while moving in the +X direction or the -X direction along _n .
Here, when the movement directions in two successive coating steps (e.g., step <2i-1> and step <2i+1>) are the same, in the movement step between the two steps (e.g., step <2i>), the inkjet print head 40 not only moves in the +Y' direction, but also moves in the +X or -X direction from the end point of the pass of the previous coating step (e.g., P21x _i ) to the start point of the pass of the subsequent coating step (e.g., P21x _i+1 ). Conversely, when the movement directions in the two successive coating steps are different, in the movement step between the two steps, the inkjet print head 40 only moves in the +Y' direction.
In addition, the above-mentioned distances D ₁ to D _n-1 (the distances between adjacent passes) are selected so that in the second coating process described below, a coating film formed between two coating films formed along adjacent passes (e.g., passes P21x _i and P21x _i+1 ) (e.g., along pass P22x ₁ ) adheres closely to the above-mentioned two coating films.

In this first coating step, a plurality of sets of coating films are formed along each of the paths P21x ₁ to P21x _n , each set being spaced apart by a distance D ₁ to D _n-1 , 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)).

Note that since the position in the Z direction (vertical direction) (or Z' direction) differs in each of the above-mentioned application steps (<1>, ... <2i-1>, ... <2n-1>), the inkjet print head 40 may be repositioned in the Z direction (vertical direction) (or Z' direction) as necessary in each of the above-mentioned movement steps (<2>, ... <2i>, ...).

At the end of the first coating step, there remain areas on the inclined coating surface F2 where no coating film is formed between the coating films formed along each of the paths P21x ₁ to P21x _n . In order to apply paint to these areas, a second coating step is performed in which the inkjet print head 40 is moved along the second layer coating path P22.

2, the second layer coating path P22 is configured by arranging paths P22x ₁ to P22x _n-1 (second paths) each extending in the X direction with a gap in the Y' direction where the gradient of the inclined coating surface F2 with respect to the horizontal plane is greatest, so that a coating film that adheres closely to two coating films formed along adjacent paths (e.g., paths P21x _i and P21x _i+1 ) is formed between these two coating films, as shown in FIG. 2. The inkjet print head 40 then performs the second coating step by moving in the +X direction or -X direction along each of the paths P22x ₁ to P22x _n-1 while moving in the +Y' direction each time.

In this second coating step, along each of the paths P22x ₁ to P22x _n-1 , a coating film is formed in close contact with the coating film already formed along the adjacent path, and these films constitute the second layer S2 (only one of the coating films constituting the second layer S2 is shown in FIG. 4(A)).

Note that while FIG. 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, 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, each of the first layer S1 and the second layer S2 will be composed of multiple layers that overlap 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.

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 (first layer S1) already formed along the paths P21x ₁ to P21x _n in the preceding first coating step acts as a bank, so to speak, to prevent the coating film formed between the banks in the second coating step from sagging. More specifically, the coating film located on the upper side of the inclined coating surface F2 (for example, the coating film formed along the path P21x _i ) prevents the latter coating film from sagging through the adhesive force acting between the latter coating film and the coating film formed in the second coating step, and the coating film located on the lower side (the coating film formed along the path P21x _i+1 ) prevents the latter coating film from sagging by blocking the downward flow of the coating film formed in the second coating step.

As described above, the method of applying paint to the inclined coating surface F2 according to an 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. Below, a modified version of this method will be described, mainly with reference to FIG. 4.

Figure 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 Figure 4 (A) (more precisely, overlapping them in the Z' direction (third direction) perpendicular to the inclined coating surface F2) to cover them. In this case, the third layer S3 is formed in the third coating process after the intermediate drying process following the first and second coating processes. Note that the third coating process may be performed immediately after the second coating process is completed, that is, without the intermediate drying process. In the third coating process, the inkjet print head 40 moves along a coating path (not shown) (third path) configured similarly to the coating path P1 (see Figure 2) for the horizontal coating surface F1, which is alternately arranged in the Y' direction at a predetermined interval.

In the coating film formed in this manner, 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 each 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.

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.

Even with the coating film formed in this way, the surface of the uppermost layer (the second layer L2 of the second layer S2) has a smooth appearance, achieving higher coating quality.

Figure 4(D) shows a modified version of the coating of Figure 4(C), in which the second layer S2 in Figure 4(C) is made up of multiple layers (three in the illustrated example) including a first layer L1 that is attached to the coating of the first layer S1 rather than to the inclined coating surface F2.

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.

In the coating film formed in this manner, the coating film of each layer constituting the second layer S2 does not sag because it adheres firmly to the coating film formed earlier. In addition, the surface of the uppermost layer (the third layer L3 of the second layer S2) has a smooth appearance, so high coating quality can be achieved, as in the cases of Figures 4(B) and 4(C).

Figure 4 (E) is a modified version of the coating film in Figure 4 (A), in which the first lower layer S1L formed in the first lower layer coating process and the first upper layer S1U formed on top of the first lower layer S1L (more precisely, overlapping in the Z' direction) in the first upper layer coating process after the intermediate drying process are intended to act as banks. Note that the first upper layer coating process may be performed immediately after the first lower layer coating process is completed, i.e., without going through the intermediate drying process.

In each of the first lower layer coating process and the first upper layer coating process, the inkjet print head 40 moves along the first layer coating path P21 shown in FIG. 2, similar to the first coating process in the coating film of FIG. 4(A), to form the first lower layer S1L and the first upper layer S1U. Then, after the first lower layer coating process and the first upper layer coating process are completed, the second coating process is performed following the intermediate drying process. In the second coating process, 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 starting 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 process of forming the second layer L2 is performed immediately after the process of forming the first layer L1 is completed, that is, without going through the intermediate drying process. 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.

This type of application method is advantageous when the thickness of the coating to be formed on the inclined coating surface F2 is large.

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

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 that forms a large angle θ with 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 used instead of the Cartesian robot as the robot constituting the above-mentioned coating device.

In addition, as shown in Figure 5, when paint is applied to a workpiece W' having three coating surfaces F1, F2, F3, where coating surface F1 is horizontal (see Figure 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 Figure 5 (A). In such a case, paint can be applied to all of the coating surfaces by adopting the following method.
(1) In the state shown in Fig. 5(A), the inkjet print head 40 is moved along coating paths similar to the 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. 5B), 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 the coating 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 is applied to the surface F3 to be coated that is inclined relative to the horizontal plane.)

In this way, when applying paint to a workpiece having multiple coating surfaces that are at an angle to one another, 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 relative to the horizontal plane. Therefore, for coating surfaces that will be inclined relative to the horizontal plane in the subsequent coating process, applying the coating method for inclined coating surfaces can prevent the paint film from dripping during the subsequent coating process, even if the coating is performed while the coating surface is horizontal.

The method of the embodiment of the present invention can be applied to apply any paint. For example, the method of the embodiment of the present invention can be applied to apply two-component paints consisting of a base agent and a hardener, time-curing paints, heat-curing paints, light-curing paints, hot melt paints, and other paints. It can also be applied to apply the above-mentioned paints by adding a diluent.

40 Inkjet print head F2 Inclined painted surface (painted surface)
X Second direction Y' First direction P21 (P21x ₁ to P21x _n ) First pass P22 (P22x ₁ to P22x _n-1 ) Second pass S1 First layer of coating S2 Second layer of coating

Claims (8)

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 application 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 of drying the first layer of the coating film; and (3) a second application step of forming a second layer of a coating film on the coated surface in such a manner that the second layer of the coating film is in close contact with the first layers of the two adjacent coating films by moving the inkjet print head along the second path. 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. The method of claim 2, wherein the third application step is performed immediately after the second application step is completed. The method according to claim 2, wherein the third coating step is performed after the second coating step and after an intermediate drying step for drying the second layer of the coating film. The first coating step includes:
(1) a first underlayer application step of forming a first underlayer of a coating film on the painted surface by moving the inkjet print head along the first path; and (2) a first upper layer application step of forming a first upper layer of a coating film on the first underlayer of the coating film by moving the inkjet print head along the first path.
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:
10. The method of claim 1, further comprising: (1) forming a first layer of a second layer of coating on the painted surface by moving the inkjet printhead along the second path; and (2) immediately after completing the step of forming the first layer of the second layer of coating, forming a second layer of the second layer of coating overlying the first layer of the second layer of coating by moving the inkjet printhead along the second path. The method according to any one of claims 1 to 5, characterized in that the paint is one of two-component paints consisting of a base agent and a hardener, time-curing paints, heat-curing paints, light-curing paints, and hot-melt paints, or paints to which a diluent has been added. The method according to any one of claims 1 to 6, characterized in that the coating surface is a plane inclined relative to a horizontal plane. The method according to any one of claims 1 to 6, characterized in that the coating surface is a convex surface whose intersection with a plane perpendicular to the second direction is an upwardly convex curve, or a concave surface whose intersection with a plane perpendicular to the second direction is a downwardly convex curve.

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