Inkjet painting method

Abstract

To provide an ink jet nozzle head and a coating applicator which can obtain, when coating a workpiece with wide pattern of a prescribed color, desired pattern width and pattern thickness through small number of scans without interfering with the workpiece.SOLUTION: An ink-jet coating method discharging coating material supplied to an ink-jet nozzle at prescribed pressure to a work surface by use of the ink-jet nozzle capable of opening / closing a nozzle hole N through movement of a needle valve 22 comprises the steps of: forming a first coating film by discharging the coating material with a first valve opening amount of the needle valve; and forming a second coating film by discharging the coating material with a second opening amount of the needle valve which is smaller than the first opening amount at a terminal part of the first coating.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an inkjet coating method, and more particularly to an inkjet coating method used for painting boundary areas in, for example, two-tone painting. [Background technology]

[0002] In the automobile manufacturing process, for example, when applying two-tone paint (called two-tone painting) to the surface of a car body (work surface), since painting with a spray gun sprays the paint in a mist, the car body is masked and then painted with a spray gun to create a boundary line.

[0003] However, there is a problem in that the masking process for the vehicle body and the subsequent removal of the masking process after painting are troublesome and reduce work efficiency. To address this issue, a method has been attracting attention in which a boundary line is created without masking by using an inkjet nozzle with a narrow spray width (high droplet straightness) (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-195936 Summary of the Invention [Problem to be solved by the invention]

[0005] It is known that inkjet painting takes longer to paint the same area than airbrush painting or bell painting. Therefore, as shown in Figure 9, in two-tone painting of a workpiece W, in order to shorten the cycle time, in one color painting area Ar, the boundary area Ar1 with the other color is painted by inkjet painting, the adjacent painting area Ar2 is painted by, for example, airbrush painting, and the painting area Ar3 adjacent to the painted area Ar2 is painted by, for example, bell painting.

[0006] However, as shown in Figure 10, the ink particles k1 in the coating film M1 formed by inkjet coating are arranged in a regular, granular pattern, while the ink particles k2 in the coating film M2 formed by airbrush coating are arranged in an irregular pattern. As a result, there was a problem that the color of the inkjet-coated and airbrush-coated adjacent areas M3 looked different even though they were made of the same ink color. Furthermore, even if the thickness of the inkjet coating M1 is gradually reduced as shown in Figure 11 and an airbrush coating M2 is formed on top of it, there is a problem that the step-like difference in the adjacent part M3 appears as streaks, which makes the appearance unattractive.

[0007] The present invention has been made with attention to the above points, and aims to provide an inkjet coating method that can improve the appearance when inkjet coating is performed on a work surface by eliminating changes in the appearance of the coating in areas adjacent to coating films of the same color produced by other coating methods. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the inkjet coating method of the present invention uses an inkjet nozzle whose nozzle hole can be opened and closed by moving a needle valve, and ejects paint supplied to the inkjet nozzle at a predetermined pressure onto a work surface, the method comprising the steps of: ejecting paint by setting the valve opening of the needle valve to a first valve opening to form a first coating film; and ejecting paint in a mist form at a terminal end of the first coating film by setting the valve opening of the needle valve to a second valve opening smaller than the first valve opening to form a second coating film. In the step of forming the second coating film, the distance between the nozzle hole and the work surface is set to be longer than the distance between the nozzle hole and the work surface when the first coating film is formed. It is characterized by: Here, in the step of forming the second coating film, it is desirable to gradually reduce the opening time of the needle valve from the opening time of the needle valve when forming the first coating film, thereby gradually reducing the film thickness of the second coating film.

[0009] In order to solve the above-mentioned problems, the inkjet coating method of the present invention uses an inkjet nozzle whose nozzle hole can be opened and closed by moving a needle valve, and ejects paint supplied to the inkjet nozzle at a predetermined pressure onto a work surface, the method comprising the steps of: ejecting paint by setting the needle valve to a first valve opening amount to form a first coating film; and ejecting paint in a mist form at a terminal end of the first coating film by setting the needle valve to a second valve opening amount smaller than the first valve opening amount to form a second coating film, wherein in the step of forming the second coating film, the needle valve opening time is gradually reduced from the needle valve opening time when forming the first coating film, thereby gradually reducing the film thickness of the second coating film.

[0010] With this configuration, at the end of the first coating film, the needle valve is opened to a second valve opening shorter than the first valve opening to eject paint and form a second coating film, which results in the paint droplets being misted in the same way as in airbrush coating or bell coating, thereby eliminating the droplets that become chunky in conventional inkjet coating. Furthermore, in forming the second coating film, increasing the distance from the nozzle hole to the coating surface reduces the tendency for droplets to travel in a straight line, and as with airbrush coating and bell coating, the paint particles are arranged irregularly, eliminating the regularity of particle arrangement seen in conventional inkjet coating. Furthermore, if the film thickness at the end of the inkjet coating is gradually reduced in forming the second coating film, the change in appearance of the adjacent area between the inkjet-coated coating film and the coating film formed by another coating method such as airbrush coating can be made smooth. As a result, in the adjoining area between a coating film produced by inkjet coating and a coating film produced by another coating method such as airbrush coating, there is no change in the appearance of the coating, and the appearance can be improved. [Effects of the Invention]

[0011] According to the present invention, an inkjet coating method can be provided that, when inkjet coating is performed on a work surface, can eliminate changes in the appearance of the coating in areas adjacent to coating films of the same color produced by other coating methods, thereby improving the appearance. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram showing an example of the overall configuration of a coating device to which an inkjet coating method according to this embodiment is applied. [Figure 2] FIG. 2 is a perspective view of the inkjet nozzle head. [Figure 3] FIG. 3 is a schematic diagram showing the arrangement of ejection ports formed on the front surface of the head array provided in the inkjet nozzle head of FIG. [Figure 4]4(a) and (b) are cross-sectional views of the nozzle body provided in the inkjet nozzle head of FIG. [Figure 5] FIG. 5 is a plan view schematically showing the coating state when the inkjet nozzle head makes one scan. [Figure 6] FIG. 6 is a plan view showing the trajectory of the inkjet nozzle head when it is reciprocated to perform multiple scans. [Figure 7] FIG. 7 is a cross-sectional view showing the positional relationship between the work surface and the nozzle. [Figure 8] FIG. 8 is a cross-sectional view showing the distance between the work surface and the nozzle. [Figure 9] FIG. 9 is a perspective view showing a coating area on a work surface. [Figure 10] FIG. 10 is a side view showing an image of paint particles in the adjoining area between a conventional inkjet coating film and an airbrush coating film. [Figure 11] FIG. 11 is a cross-sectional view showing the adjoining portion of a conventional inkjet-coated film and an airbrush-coated film. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of an inkjet coating method according to the present invention will be described below with reference to the drawings. The inkjet coating method according to this embodiment is applied to a coating device in, for example, an automobile production line, and ejects paint for, for example, two-tone coating (having a boundary line with a paint of another color). More specifically, it applies coating to a boundary portion Ar1 of a workpiece W shown in FIG. 9.

[0014] FIG. 1 is a block diagram showing an example of the overall configuration of a coating device to which an inkjet coating method according to this embodiment is applied. The coating device 1 shown in Figure 1 comprises an inkjet nozzle head 10, a robot arm 2 to which the inkjet nozzle head is attached at its tip, and a robot controller 3 that drives and controls the robot arm 2. The robot arm 2 is a six-axis articulated robot that is capable of positioning the inkjet nozzle head 10 at a predetermined distance from the workpiece, even if the workpiece has a curved surface. Furthermore, the inkjet nozzle head 10 can be moved by the robot arm 2 in a direction parallel to the workpiece while coating (scanning).

[0015] A plurality of hoses 11 (11a to 11d) branched by a manifold 4 are connected to the inkjet nozzle head 10. Of these, hoses 11a to 11c serve as paint supply paths to the inkjet nozzle head 10, and hose 11d serves as a paint recovery path from the inkjet nozzle head 10. One end of a hose 12 is connected to the branching point side of the manifold 4, and the other end of the hose 12 is connected to a color change valve 5 that switches between paints.

[0016] The color change valve 5 is connected to the paint circulation supply device 6 by a plurality of hoses 13 and one hose 14. The plurality of hoses 13 are used as paint supply paths from the paint circulation supply device 6 to the color change valve 5 for each paint color, and the hose 14 is used as a paint recovery path from the color change valve 5 to the paint circulation supply device 6. Further, the paint circulation supply device 6 is configured so that pressure applied to the valve is controlled by an air panel 7 .

[0017] The inkjet nozzle head 10 also includes a plurality of nozzle bodies 17, which will be described later, and the inkjet controller 8 controls the opening and closing of the valves of these nozzle bodies 17. The inkjet controller 8 and the robot controller 3 are configured so that their operations are controlled by a program executed on a PC (personal computer) 9 in which coating conditions are set.

[0018] FIG. 2 is a perspective view of the inkjet nozzle head 10. As shown in FIG. As shown in FIG. 2, the inkjet nozzle head 10 comprises a rectangular parallelepiped head array 15 having a plurality of ejection ports 20 (20a to 20m) formed on the front surface thereof, a plurality (13) of nozzle bodies 17 (17a to 17m) attached to the rear side of the head array 15, and a U-shaped nozzle stopper 18 for pressing and fixing the nozzle bodies 17 to the head array 15 from behind.

[0019] Three hose joints 16a to 16c are provided on the upper surface of the head array 15, and the hoses 11a to 11c can be connected to them, respectively. Further, a discharge joint 19 is provided on the underside of the head array 15, to which a hose 11d can be connected.

[0020] That is, the paint supplied from the paint circulation supply device 6 is sent to the manifold 4 after the desired color is selected by the color change valve 5, and is then supplied to the inkjet nozzle head 10 and ejected, and the recovered paint that is not ejected is circulated from the manifold 4 through the color change valve 5 to the paint circulation supply device 6. Furthermore, when changing the paint color, cleaning liquid (thinner) can be supplied from the discharge joint 19 to clean the head array 15, manifold 4, color change valve 5, and the inside of the hoses connecting them.

[0021] 3 shows the arrangement of the ejection ports 20a to 20m formed on the front surface of the head array 15. As shown in the figure, nozzle holes N1 to N13 are arranged at the center positions of the ejection ports 20a to 20m, respectively. Of these, nozzle holes N12 and N13 are arranged on a straight line L1 that is parallel to the scanning direction, but the positions of nozzle holes N1 to N11 are arranged along a straight line that is inclined at a predetermined angle (linearly) with respect to the scanning direction.

[0022] 3, the position of the lowest nozzle hole N1 is located on a line L2 that is parallel to the scanning direction and a predetermined distance (for example, 2.75 mm) below the line L1. By arranging the nozzle holes N1 to N13 in this manner, the pattern width per scan is increased.

[0023] Furthermore, the configuration of the nozzle body 17 (17a to 17m) is not particularly limited, but for example, a known configuration (for example, the configuration disclosed in Japanese Patent No. 4123897) as shown in Figures 4(a) and (b) can be adopted. The nozzle body 17 includes a nozzle hole N provided on the front surface, a paint chamber 21 for supplying paint to the nozzle hole N, a needle valve 22 at the tip of the paint chamber 21 for closing or opening the nozzle hole N, and a movable iron core 23 arranged behind the needle valve 22. The nozzle body 17 further includes a fixed core 24 that faces the movable core 23 via a spring material 26, and an electromagnetic solenoid 25 that moves the movable core 23 along the nozzle axial direction by magnetic force.

[0024] That is, the closing and opening operation of the needle valve 22 relative to the nozzle hole N is driven by a drive mechanism consisting of a movable iron core 23, a spring material 26, a fixed iron core 24, and an electromagnetic solenoid 25. This drive mechanism is housed in an accommodation space 27, and an elastic diaphragm 28 is provided to surround the needle valve 22 to prevent the paint in the paint chamber 21 from leaking out, and pressure P is applied to the paint in the paint chamber 21 via a paint supply port 30.

[0025] In addition, to prevent the pressurized paint from leaking out from between the elastic diaphragm 28 and the needle valve 22, a pressure P equivalent to the pressure applied to the paint is applied to the gas or liquid in the storage space 27 through the pressurizing passage 31.

[0026] With this nozzle body 17, when no current is applied to the electromagnetic solenoid 25, the movable iron core 23 and needle valve 22 are pushed forward by the biasing force of the spring material 26, and the nozzle hole N is closed as shown in Figure 4(a). At this time, the paint supplied from the paint supply port 30 is not ejected from the nozzle hole N, but is discharged from the paint discharge port 32. On the other hand, when current is passed through the electromagnetic solenoid 25, the movable iron core 23 is attracted to the fixed iron core 24 as shown in Figure 4(b), which causes the needle valve 22 to move backward, opening the nozzle hole N and causing paint to be discharged by pressure P. The amount of opening of the needle valve 22 is adjusted by the time that current is passed through the electromagnetic solenoid 25. The discharge speed of paint droplets from the nozzle hole N is 7000 to 12000 mm / s.

[0027] Next, the coating operation using the inkjet nozzle head 10 in the coating device 1 will be described. When the drive control of the robot arm 2 by the robot controller 3 and the drive control of the nozzle body 17 by the inkjet controller 8 are synchronized and the inkjet nozzle head 10 is scanned in the direction of the arrow shown in Figure 5, coating is performed from the nozzle hole N1 to the nozzle hole N13 with a predetermined line width (0.5 mm in this embodiment), and the formation of the first coating film M1 (see Figure 7) begins.

[0028] At this time, to form a target film thickness (e.g., 15 μm), the valve opening (first valve opening) of the needle valve 22 is set to, e.g., 30 μm, thereby setting the diameter of the paint droplets to, e.g., 500 μm. The valve opening is the axial distance between the needle valve 22 and the nozzle hole N. The discharge speed of the paint droplets from the nozzle hole N is set to 12,000 mm / s, and the distance d from the nozzle hole N to the coating surface shown in FIG. 8 is set to, e.g., 20 mm, to maintain the droplets' ability to travel straight.

[0029] Paint is ejected from all nozzle holes N at the same time, but the ejection time from nozzle holes N1 to N6 in the first scan is, for example, 8 μm / scan, the ejection time from nozzle holes N7 to N12 is twice that, 16 μm / scan, and the ejection time from nozzle hole N13 is 8 μm / scan.

[0030] Nozzle holes N12 and N13 are positioned at the same position in the pattern width direction (no offset), and the other nozzle holes N1 to N12 are formed with an offset dimension in the pattern width direction of, for example, 0.25 mm. Therefore, as shown in the figure, nozzle holes N1 to N12 are coated with adjacent nozzle holes overlapping by 0.25 mm in the pattern width direction. As a result, the pattern width after one scan by ejection from nozzle holes N1 to N13 is 3.0 mm. Here, because nozzle hole N12 and nozzle hole N13 are not offset in the direction perpendicular to the scanning direction (because they are arranged along a straight line parallel to the scanning direction), no steps are formed at the edge of the coated film after one scan, and the boundary line after coating can be clearly defined.

[0031] Furthermore, in the coating device 1, the pattern width achieved by one scan of the inkjet nozzle head 10 is 3 mm. Therefore, if a larger pattern width is desired, multiple scans can be performed by moving the inkjet nozzle head 10 back and forth as shown by the arrows in Figure 6. At this time, scanning is performed above the coated surface from the previous scan with a predetermined offset dimension (1.5 mm in this embodiment) in a direction perpendicular to the scanning direction (pattern width direction), and by varying the ejection time of nozzle holes N1 to N12 based on the offset dimension, a wide pattern with a uniform film thickness can be formed (ejection from nozzle hole N13 is not necessary for the second or subsequent scans).

[0032] From the second scan onwards, ejection is performed only from nozzle holes N1 to N12, and all of these ejection volumes are set to 8 μm per scan. An offset of 1.5 mm is then applied in the direction perpendicular to the scanning direction (pattern width direction), allowing for overcoating on top of the film coated by nozzle holes N1 to N6 in the previous scan. As a result, the overcoated portion meets the target thickness (15 μm) of the coated film.

[0033] Furthermore, as the inkjet nozzle head 10 repeatedly scans and approaches the end of the inkjet coating (for example, when it reaches a position 15 mm before the end), the valve opening amount (second valve opening amount) of the needle valve 22 is reduced, for example to 24 μm or less, thereby reducing the diameter of the paint droplets to, for example, 300 μm or less, and turning them into a mist, similar to airbrush coating or bell coating.

[0034] In addition, as shown in Figure 7, the distance d from the nozzle hole N to the coating surface is set to a longer distance, for example, between 68 mm and 80 mm, to reduce the straightness of the droplets. This results in the paint particles being irregularly arranged, similar to airbrush painting and bell painting.

[0035] Furthermore, the opening time of the needle valve 22 is gradually reduced to, for example, 35 μs, gradually reducing the amount of ink ejected per spray. As a result, the coating thickness is gradually reduced to 1 μm toward the end of the inkjet coating (for example, a tapered portion (second coating) M4 with a width of 15 mm is formed) as shown in FIG. After inkjet coating is completed in this manner (boundary portion Ar1 in FIG. 9), a coating film M2 is formed in the coating area Ar2 in FIG. 9 by, for example, airbrush coating from above the gradually tapering portion M4 of the coating film shown in FIG.

[0036] As described above, according to this embodiment, in the gradually decreasing portion M4, the terminal portion of the inkjet coating is formed with a gradual decrease in film thickness, so that the change in appearance between the coating film M1 formed by inkjet coating and the adjacent portion M3 of the coating film M2 formed by another coating method such as airbrush coating can be made smooth. In particular, the diameter of the paint droplets is made into a mist, similar to airbrush painting and bell painting, so the droplets that form as particles in conventional inkjet painting can be eliminated. Furthermore, by increasing the distance d from the nozzle hole N to the coating surface, the droplets are less likely to travel in a straight line, and the paint particles are arranged irregularly, similar to airbrush painting and bell painting, eliminating the regularity of particle arrangement seen in conventional inkjet painting. As a result, in the adjacent area M3 between the coating film M1 formed by inkjet coating and the coating film M2 formed by another coating method such as airbrush coating, the appearance of the coating is prevented from changing, and the appearance can be improved.

[0037] In the above-described embodiment, the inkjet nozzle head 10 is configured to have 13 nozzle holes N, but the present invention does not limit the number. Furthermore, in the above embodiment, of the multiple nozzle holes N arranged in a row, the two nozzle holes N at one end are arranged along a straight line parallel to the scanning direction, but the present invention is not limited to this example, and three or more nozzle holes may be arranged along a straight line parallel to the scanning direction at one end of the multiple nozzle holes arranged. [Explanation of symbols]

[0038] 1 Coating device 2. Robotic Arm 3 Robot controller (robot control unit) 4 Manifold (paint supply means) 5 Color change valve (paint supply means) 6 Paint circulation supply device (paint supply means) 7 Air panel (paint supply means) 8 Inkjet controller (nozzle control unit) 9 PC 10 Inkjet nozzle head 11 Hose 12 hose 13 Hose 14 Hose 17 Nozzle body 22 Needle valve 20 outlet N Nozzle hole

Claims

1. An inkjet coating method using an inkjet nozzle capable of opening and closing a nozzle hole by moving a needle valve, the ink being supplied to the inkjet nozzle at a predetermined pressure and ejected onto a work surface, comprising: a step of discharging paint by setting the valve opening amount of the needle valve to a first valve opening amount to form a first coating film; a step of discharging a mist of paint at a terminal end of the first coating film by setting the valve opening amount of the needle valve to a second valve opening amount that is smaller than the first valve opening amount, thereby forming a second coating film; Equipped with In the step of forming the second coating film, An inkjet coating method characterized in that the distance between the nozzle hole and the work surface is longer than the distance between the nozzle hole and the work surface when forming the first coating film.

2. An inkjet coating method using an inkjet nozzle whose nozzle hole can be opened and closed by moving a needle valve, in which paint supplied to the inkjet nozzle at a predetermined pressure is ejected onto a work surface, a step of discharging paint by setting the valve opening amount of the needle valve to a first valve opening amount to form a first coating film; a step of discharging a mist of paint at a terminal end of the first coating film by setting the valve opening amount of the needle valve to a second valve opening amount that is smaller than the first valve opening amount, thereby forming a second coating film; Equipped with In the step of forming the second coating film, an inkjet coating method, characterized in that the open time of the needle valve is gradually reduced from the open time of the needle valve when forming the first coating film, thereby gradually reducing the film thickness of the second coating film.

3. In the step of forming the second coating film, 2. The inkjet coating method according to claim 1, wherein the opening time of the needle valve is gradually reduced from the opening time of the needle valve when forming the first coating film, thereby gradually reducing the film thickness of the second coating film.

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