Coating method and coating device for insulators

Abstract

To provide a coating method and a coating apparatus of an insulator which can improve coating quality when coating a surface to be coated of the insulator.SOLUTION: Discharging coating mist from a spray gun 61 toward a surface W1 to be coated while a charged conductor 2 is in contact with an opposite side of the surface W1 to be coated of a resin bumper W, coating the surface W1 to be coated is performed. Therefore, compared with a case where the surface W1 to be coated is directly charged, a charging state of the surface W1 to be coated can be made a desired state. The coating mist is not charged, or the coating mist is charged with a reverse polarity to that of the conductor 2 and to a lower potential in absolute value than the conductor 2. Electric charges of the coating mist coated on the surface W1 to be coated are hardly left on the bumper W and thereby prevented from electrically repelling the coating mist discharged toward the surface W1 to be coated. Therefore, excellent coating quality is obtained.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a coating method and coating apparatus for insulating materials, and more particularly to an improvement for improving coating quality. [Background technology]

[0002] Plastic molded products such as plastic bumpers for automobiles are so-called insulators (non-conductors) with high surface electrical resistance. For this reason, when electrostatic painting is performed to improve the coating efficiency when painting the surface (surface to be painted) of this type of insulator, a conductive material is painted on the insulator to make it a conductor, and while the insulator is earthed, a charged paint mist is sprayed toward the surface of the insulator to be painted. However, in this case, a dedicated material and a dedicated process are required to paint the conductive material, which leads to high costs, etc.

[0003] Patent Document 1 discloses a technique for charging a surface to be coated without the need for a process of painting an insulator with a conductive material. Patent Document 1 discloses that, when electrostatically painting the surface of an insulator to be coated by applying a negative charge (charging) to the paint, the surface of the insulator to be coated is positively charged before painting. Specifically, the positive electrode of a high-voltage generator is placed opposite the surface to be coated, the positive electrode is applied with a positive voltage to positively ionize the air by corona discharge, and the positively ionized air positively charges the surface to be coated. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-76218 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the technology disclosed in Patent Document 1, the surface of the insulating material to be coated is directly charged by a high-voltage generator, which may cause variations in the distribution of charges on the surface to be coated, making it difficult to obtain a desired charged state on the surface to be coated. For example, it is difficult to uniformly charge a desired area of ​​the surface to be coated or to uniformly charge the entire surface to be coated, making it difficult to obtain a desired coating state by electrostatic coating, and there are limitations to improving the coating quality.

[0006] Furthermore, as disclosed in Patent Document 1, in electrostatic painting, the paint mist is charged (negatively) with a relatively high voltage, and when painting an insulator, the charge of the paint mist applied to the surface to be painted tends to remain on the insulator, causing electrical repulsion between the paint mist and the paint mist that is subsequently sprayed toward the surface to be painted, making it difficult to obtain a sufficient paint film thickness, which is also one of the factors that limit the improvement of painting quality.

[0007] The present invention has been made in consideration of the above-mentioned points, and an object of the present invention is to provide a method and apparatus for painting an insulator that can improve the painting quality when painting the surface of an insulator to be painted. [Means for solving the problem]

[0008] The solution of the present invention for achieving the above object is based on a method for painting an insulator, which comprises the steps of: bringing a charged conductor into contact with or close to the opposite side of the insulator surface to be painted; and applying a non-charged paint mist toward the insulator surface to be painted. To The method includes a coating process for coating the surface of the insulator by discharging the coating material. The coating process is carried out in a state where the conductor is electrified and a discharge device for discharging the paint mist is grounded, and after the coating process is completed, the application of electricity to the conductor is stopped and the conductor is grounded, thereby removing electricity from the conductor and the insulator. It is characterized by:

[0009] Due to this specific feature, in the painting process, the electrically charged conductor is in contact with or in close proximity to the insulator, so that the paint mist discharged toward the surface of the insulator to be painted is attracted to the surface, and the surface is painted. In such a charging form of the insulator (a form in which the insulator is charged by contacting or bringing the electrically charged conductor into close proximity), the variation in the distribution of charges on the surface to be painted can be alleviated compared to the case in which the surface of the insulator to be painted is directly charged (conventional technology), and it is possible to obtain a desired charged state for the surface to be painted. For example, it is possible to uniformly charge a desired area of ​​the surface to be painted, or to uniformly charge the entire surface to be painted. Since the charged state of the surface to be painted has a large effect on the finish of the painting in electrostatic painting, it is possible to obtain a high painting quality by making it possible to obtain a desired charged state for the surface to be painted. In addition, the paint mist is not charged, Potato This makes it possible to prevent the paint mist from electrically repelling each other due to the electric charge of the paint mist remaining on the insulator, making it possible to obtain a sufficient thickness of the paint film, which also results in high paint quality. The coating process is a coating process using non-charged paint mist. In this case, the charging state can be controlled by controlling only the current flow through the conductor for charging the insulator, and there is no need to control the current flow for charging the discharge device. This makes it possible to obtain a desired charging state for the surface of the insulator to be coated with relatively simple control, and high coating quality can be obtained. Furthermore, compared to the case where a charged insulator is grounded to remove static electricity, grounding the conductor enables quick and reliable removal of static electricity from the conductor and insulator, thereby shortening the tact time of processes including the painting process and static removal process, and realizing an efficient painting method.

[0012] As another means for solving the above-mentioned problem, the present invention is based on a method for painting an insulator, and includes a coating step in which a charged conductor is brought into contact with or close to the opposite side of the insulator surface to be coated, and a paint mist is sprayed toward the insulator surface to be coated, the paint mist being charged with a charge of the opposite polarity to the conductor and with a potential with a lower absolute value than the conductor, thereby coating the insulator surface to be coated, The coating process is carried out in a state where electricity is passed through the conductor to charge it, and where a discharge device for discharging the paint mist is charged with a charge of the opposite polarity to the conductor and with a potential with a lower absolute value than the conductor. The method further comprises a static elimination step of, after the painting step is completed, stopping the current flow to the conductor and earthing the conductor, thereby eliminating static electricity from the conductor and the insulator.

[0013] This coating process uses a paint mist that is charged with a charge of the opposite polarity to the conductor and with a potential lower in absolute value than the conductor. This makes it possible to increase the potential difference between the insulator charged by the conductor and the paint mist discharged from the discharge device (the potential difference can be increased compared to when uncharged paint mist is used), and the attractive force acting on the paint mist toward the surface to be coated can be increased. As a result, the paint mist can be effectively applied to the surface of the insulator to be coated, and wasted paint (paint that has not been applied to the surface of the insulator to be coated; overspray mist) can be reduced.

[0016] In addition, the earth path that earths the conductor includes a space surrounded by a non-conductive member, and the neutralization process is carried out by reducing the air pressure in the space and generating a vacuum discharge in the space.

[0017] According to this, the air pressure in the space is adjusted to adjust the electrical resistance of the earth path, and thus the timing for generating a vacuum discharge can be adjusted, making it possible to easily adjust the timing for performing the static elimination process.

[0020] The coating step is performed in a state in which the conductor is supported by a non-conductive member.

[0021] According to this, in the painting process, the conductor is not grounded (insulated), so the surface of the insulator to be painted can be painted while maintaining a high charge on the conductor. In other words, a large potential difference between the insulator and the paint mist can be maintained, and the attractive force acting on the paint mist toward the surface to be painted can be increased, reducing wasted paint.

[0022] A coating device for carrying out the above-mentioned coating method is also included in the scope of the technical idea of ​​the present invention. In other words, the coating device is based on the premise of an insulator coating device, and includes a conductor that is in contact with or in close proximity to the surface of the insulator opposite to the surface to be coated, a charging unit for charging the conductor, and a non-charged paint mist that is directed toward the surface of the insulator. To and a discharge device for discharging the liquid. The charging unit is configured to continuously energize the conductor during a coating process in which a paint mist is discharged toward a surface of the insulating material to be coated, while the discharge device is grounded. The charging unit is configured to stop energizing the conductor after the coating process is completed, and includes a static elimination unit capable of switching the conductor between an earthed state and an insulated state. It is characterized by:

[0023] In the painting operation performed by this painting device, the charging unit charges a conductor, and the conductor comes into contact with or close to the surface of the insulator opposite the surface to be painted, thereby charging the insulator. In this state, paint mist is sprayed from the spraying device towards the surface to be painted of the insulator, and the paint mist is attracted to the surface to be painted of the insulator, thereby painting the surface to be painted. As mentioned above, in this type of charging of the insulator, the variation in the distribution of charges on the surface to be painted can be reduced compared to when the surface to be painted of the insulator is directly charged, and the charged state of the surface to be painted can be obtained as desired, thereby obtaining high painting quality. Furthermore, the paint mist sprayed from the spraying device is not charged. Potato This makes it possible to prevent the paint mist from electrically repelling each other due to the electric charge of the paint mist remaining on the insulator, making it possible to obtain a sufficient thickness of the paint film, which also results in high paint quality. The coating process is also performed with a discharge device that discharges non-charged paint mist. In this case, the charging state can be controlled by controlling only the current flow through the conductor for charging the insulator, and the charging state of the coated surface of the insulator can be set to a desired state with relatively simple control, resulting in high coating quality. After the painting process is completed, the conductor and the insulator are neutralized by switching the conductor to an earthed state using the neutralization unit, which enables quicker and more reliable neutralization of the conductor and the insulator compared to neutralizing the charged insulator by earthing it, thereby shortening the tact time of the process including the painting process and the neutralization process.

[0026] As another means for solving the above-mentioned problem, the present invention provides a coating device for an insulator, the coating device comprising a conductor in contact with or in close proximity to a surface of the insulator opposite to a surface to be coated, a charging unit for charging the conductor, and a discharge device for discharging a paint mist toward the surface to be coated of the insulator, the paint mist being charged to a potential with a polarity opposite to that of the conductor and with a lower absolute value than that of the conductor, The charging unit is configured to continuously energize the conductor in a coating process in which a paint mist is sprayed toward the surface of the insulator to be coated, while the spray device is configured to be charged with a charge of opposite polarity to the conductor and with a potential with a lower absolute value than the conductor. The charging unit is configured to stop the passage of electricity to the conductor after the coating process is completed, and is characterized by having a static elimination unit that can switch the conductor between an earthed state and an insulated state.

[0027] This is the case when a discharge device is provided that discharges paint mist that is charged with a charge of the opposite polarity to the conductor and with a potential lower in absolute value than the conductor. This makes it possible to increase the potential difference between the insulator charged by the conductor and the paint mist discharged from the discharge device, thereby making it possible to obtain a large attractive force acting on the paint mist toward the surface to be coated. As a result, the paint mist can be effectively applied to the surface to be coated of the insulator, and the amount of paint wasted can be reduced.

[0030] The static elimination unit further includes a static elimination tube that is disposed between the conductor and the earth and is made of a non-conductive material, and an air pressure adjustment unit that adjusts the air pressure inside the static elimination tube.

[0031] According to this, by adjusting the air pressure inside the static elimination tube, the electrical resistance of the earth path between the conductor and the earth can be adjusted, and the timing for generating a vacuum discharge can be adjusted, which makes it possible to easily adjust the timing for static elimination.

[0034] The conductor is supported by a non-conductive support member.

[0035] According to this, in the painting process, the conductor is not grounded (insulated), so the surface of the insulator to be painted can be painted while maintaining a high charge on the conductor. In other words, a large potential difference between the insulator and the paint mist can be maintained, and the attractive force acting on the paint mist toward the surface to be painted can be increased, reducing wasted paint.

[0036] The conductor is a jig that supports the insulator.

[0037] Since the conductor for charging the insulator also functions as a jig for supporting the insulator, there is no need to provide a separate jig, which simplifies the configuration of the coating device. Effect of the Invention

[0038] In the present invention, the surface of the insulator to be coated is painted by ejecting a paint mist toward the surface of the insulator to be coated while bringing a charged conductor into contact with or close to the opposite side of the surface to be coated. This makes it possible to obtain a desired charged state of the surface to be coated compared to when the surface of the insulator to be coated is directly charged. In addition, in the coating process, uncharged paint mist or paint mist charged to a potential with a polarity opposite to that of the conductor and with a lower absolute value than the conductor is ejected toward the surface of the insulator to be coated. This makes it possible to prevent the paint mist from electrically repelling each other due to the charge of the paint mist remaining on the insulator, and makes it possible to obtain a sufficient thickness of the coating film. These actions make it possible to obtain high coating quality. [Brief description of the drawings]

[0039] [Figure 1] 1 is a diagram showing a schematic configuration of a coating device according to an embodiment; [Diagram 2] FIG. 2 is a sequence diagram for explaining the procedure of the painting method according to the embodiment. [Diagram 3] FIG. 13 is a diagram for explaining a painting preparation process. [Figure 4] FIG. 1 is a diagram for explaining a painting process. [Diagram 5] FIG. 13 is a diagram for explaining a static elimination process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example will be described in which a plastic bumper (e.g., a front bumper, which is an insulator in the present invention) of an automobile is painted by electrostatic painting. The plastic bumper is, for example, an injection-molded product of polypropylene, and the outer surface visible from the outside when the bumper is attached to the automobile is the surface to be painted, and the surface to be painted is electrostatically painted.

[0041] -Outline of the coating equipment- Fig. 1 is a diagram showing a schematic configuration of a coating apparatus 1 according to this embodiment. As shown in Fig. 1, the coating apparatus 1 includes a conductor 2, a support member 3, a charging unit 4, a static electricity removing unit 5, and a coater (discharge device; see Fig. 4) 6. Each of these will be described in detail below.

[0042] (conductor) The conductor 2 is a conductive metal member that supports the bumper W (see Figure 3) and negatively charges the bumper W by contacting the back surface of the bumper W (the surface opposite the surface W1 to be painted) (by imparting the negative charge received from the charging unit 4 to the bumper W, thereby negatively charging it).

[0043] Specifically, the conductor 2 comprises a base portion 21 extending horizontally, a cylindrical or rectangular pillar portion 22 extending downward from the center of the underside of the base portion 21, a plurality of contact bodies 23, 23, ... erected on the upper surface of the base portion 21, and a power receiving portion 24 extending downward from a predetermined position on the underside of the base portion 21 (in Figure 1, the position to the left of the pillar portion 22).

[0044] The configuration of the contact bodies 23 is not particularly limited, but the height dimension of each contact body 23, 23, ... is set so that when the bumper W is supported by the conductor 2 (see the state shown in FIG. 3), the upper end of each contact body 23, 23, ... contacts the back surface of the bumper W. In this embodiment, the bumper W to be electrostatically painted is curved so that the central portion of its longitudinal direction (the vehicle width direction when mounted on the vehicle body) slightly bulges toward the front of the vehicle. In addition, when the bumper W is supported by the conductor 2, as shown in FIG. 3, the front of the bumper W (the front when mounted on the vehicle body) is placed on the conductor 2 so that it faces upward. For this reason, the height dimension of each contact body 23, 23, ... is set longer toward the center of the contact body 23, and the position of the upper end is set at a higher position, and when the bumper W is supported by the conductor 2, the upper end of each contact body 23, 23, ... contacts the back surface of the bumper W. Note that each contact body 23, 23, ... may be an independent columnar shape, or may be a frame shape in which the upper ends of each contact body are connected to each other. 1, a plurality of the contact bodies 23, 23, . . . are disposed in a direction perpendicular to the plane of FIG. 1 in order to stably support the bumper W.

[0045] Furthermore, the support state of the bumper W by this conductor 2 may be such that the bumper W is fixed to the conductor 2 (fixed by a fastener or the like not shown), or it may be such that the bumper W is supported without being fixed (simply placed on top).

[0046] In this manner, the conductor 2 according to this embodiment has both a function of negatively charging the bumper W and a function as a jig for supporting the bumper W.

[0047] (Support member) The support member 3 is a member for supporting the conductor 2, and is connected to the lower end of the support portion 22 of the conductor 2. The support member 3 includes a resin non-conductive support portion (non-conductive member) 31 connected to the lower end of the support portion 22 of the conductor 2, and a metal base support portion 32 connected to the lower end of the non-conductive support portion 31. The base support portion 32 is erected on a floor surface (floor surface of a paint booth not shown) F, and the conductor 2 is supported on the floor surface F by the support member 3. In other words, since the support member 3 includes the non-conductive support portion 31, the conductor 2 is supported in a state insulated (electrically insulated) from the floor surface F. The configuration for insulating the conductor 2 from the floor surface F is not limited to this.

[0048] (Charging unit) The charging unit 4 is a unit for passing a current through the conductor 2 to negatively charge the conductor 2.

[0049] The charging unit 4 includes a cascade 41 as a high voltage generator, and a high voltage controller 42 that controls the cascade 41 .

[0050] The cascade 41 is connected to the power receiving portion 24 of the conductor 2 via a power line 43, and applies a negative electrostatic high voltage to the conductor 2 via the power line 43 and the power receiving portion 24, thereby negatively charging the entire conductor 2.

[0051] The high voltage controller 42 is connected to the cascade 41 and controls the start and stop of output of the voltage (negative electrostatic high voltage) output from the cascade 41, and can set this voltage to any value. The voltage (electric potential for negatively charging the conductor 2) output from the cascade 41 is not particularly limited, but is set experimentally or empirically as a value that ensures a large electric potential difference with the paint mist discharged from the coater 6 in electrostatic painting, which will be described later, and can sufficiently reduce wasted paint (overspray mist).

[0052] (Static charge removal unit) The static elimination unit 5 includes a static elimination tube 51 , an air pressure adjustment unit 52 , and a static elimination controller 53 .

[0053] The static elimination tube 51 is made of a resin pipe (non-conductive member). The upper end of the static elimination tube 51 is closed by a metal upper conductor 51a. The upper conductor 51a is connected to the support portion 22 of the conductor 2 and is electrically connected to the support portion 22.

[0054] Further, a metal earth pipe 51b is attached to the lower part of the static eliminator 51, and an earth wire 51c is connected to the earth pipe 51b. The earth wire 51c is earthed (grounded).

[0055] The air pressure adjustment unit 52 includes an air pipe 52a extending horizontally. The lower end of the static elimination tube 51 is connected to the air pipe 52a, and the internal space of the air pipe 52a and the internal space of the static elimination tube 51 are in communication with each other.

[0056] A vacuum pump 52b is connected to one end (the right end in FIG. 1) of the air pipe 52a. A vacuum regulator 52c is attached to the air pipe 52a, and when the vacuum pump 52b operates to evacuate the internal space of the air pipe 52a and the internal space of the static electricity removal tube 51, the internal pressures can be adjusted by the vacuum regulator 52c.

[0057] The static elimination controller 53 is connected to the vacuum pump 52b and the vacuum regulator 52c, and performs ON / OFF control of the vacuum pump 52b and control of the vacuum regulator 52c (control for adjusting the pressure in the internal space of the static elimination tube 51). In other words, when the conductor 2 is charged, the vacuum pump 52b is operated by a control signal from the static elimination controller 53, the pressure in the internal space of the static elimination tube 51 is adjusted by control of the vacuum regulator 52c, and when this pressure reaches a predetermined level or lower (when the amount of air in the internal space of the static elimination tube 51 falls to a predetermined level or lower), a vacuum discharge occurs inside the static elimination tube 51, electricity can flow through the earth path from the conductor 2 to the earth wire 51c, and the charge of the conductor 2 is earthed via the earth wire 51c.

[0058] (painting machine) As shown in FIG. 4, the paint sprayer 6 is equipped with a spray gun 61 that atomizes (atoms) paint to generate paint mist and sprays this paint mist toward the surface W1 of the bumper W to be painted, a multi-joint robot (not shown) that moves the spray gun 61, and a paint sprayer controller 62 that controls the operation of the spray gun 61 and the multi-joint robot.

[0059] Methods for atomizing paint in the spray gun 61 include an air atomization method (air spray gun method) that uses air to atomize the paint, a hydraulic atomization method (airless spray gun method) that uses paint hydraulic pressure to atomize the paint, and a rotary atomization method that uses a rotating atomizing head to atomize the paint. The air atomization method is adopted for the spray gun 61 of the paint sprayer 6 according to this embodiment, but other methods may be adopted, or a combination of two or more of these methods may be used.

[0060] The sprayer 6 is earthed so that the paint mist discharged from the spray gun 61 toward the surface W1 of the bumper W is not electrically charged. The sprayer 6 may be earthed via an earth wire (not shown) or via an articulated robot.

[0061] In this embodiment, a water-based paint is used as the paint discharged from the coater 6. There is no particular restriction on the type of paint, and a solvent-based paint can also be used.

[0062] The sprayer controller 62 controls the operation of the spray gun 61 and the articulated robot in electrostatic painting, which will be described later, and controls the discharge of paint mist from the spray gun 61 and the operation of the articulated robot so that the discharge direction of the paint mist is toward the surface W1 of the bumper W to be painted. Specifically, the sprayer controller 62 stores information (information such as the amount of rotation angle of each joint of the articulated robot) for moving the spray gun 61 toward the surface W1 of the bumper W to be painted, which is the target of painting, by offline teaching in advance. During electrostatic painting, the articulated robot operates according to a control signal from the sprayer controller 62 and based on the information, so that the spray gun 61 faces the area to be painted, and the surface W1 of the bumper W is painted by the paint mist being discharged from the spray gun 61.

[0063] The aforementioned controllers (high-pressure controller 42, static electricity removal controller 53, and sprayer controller 62) are connected by signal lines and are capable of sending and receiving information to each other. In accordance with this signal transmission and reception, command signals are sent to instruct the start and end of control of each device (cascade 41, vacuum pump 52b, vacuum regulator 52c, spray gun 61, and articulated robot).

[0064] -Painting method steps- Next, a description will be given of the procedure of the coating method using the coating apparatus 1 configured as described above. Fig. 2 is a sequence diagram for explaining the procedure of this coating method.

[0065] The procedure of this painting method is, in order, a ground-off step as a painting preparation step, a high-voltage application step, a painting step, a high-voltage removal step, and a static electricity removal step, as shown in Fig. 2. The details will be explained below.

[0066] As pretreatment for electrostatic painting, similar to the conventional electrostatic painting, a degreasing process is performed to break down the grease adhering to the surface W1 of the bumper W to be painted, a cleaning process is performed to wash away the broken down grease and the degreasing liquid, and a drying process is performed to evaporate the cleaning water.

[0067] FIG. 3 is a diagram for explaining the painting preparation process (earth-off process and high-voltage application process).

[0068] In the earth-off process, the static electricity removal controller 53 of the static electricity removal unit 5 outputs a pump stop command signal to the vacuum pump 52b and also outputs a pressure adjustment stop command signal to the vacuum regulator 52c, whereby the internal space of the air pipe 52a and the internal space of the static electricity removal tube 51 are opened to the atmosphere, etc., and set to a pressure equal to or higher than a predetermined value (a pressure at which vacuum discharge does not occur). This earth-off process may be performed with a bumper (unpainted bumper) W placed on the conductor 2, or may be performed before the bumper W is placed on the conductor 2.

[0069] When this earth-off process is completed, an earth-off completion signal is output from the static electricity removal controller 53 to the high-voltage controller 42. When the high-voltage controller 42 receives the earth-off completion signal, the high-voltage application process is started. In this high-voltage application process, a high-voltage application command signal is output from the high-voltage controller 42 to the cascade 41, which causes the cascade 41 to apply a negative electrostatic high voltage to the conductor 2 via the power line 43 and the power receiving unit 24, so that the entire conductor 2 is negatively charged. The application of the negative electrostatic high voltage to the conductor 2 continues (continues during the painting process) until a painting completion signal (painting completion signal from the paint sprayer controller 62), which will be described later, is received.

[0070] When the entire conductor 2 is charged to a predetermined potential (negative potential) by this high voltage application process, the high voltage controller 42 outputs a high voltage application completion signal to the sprayer controller 62. When the sprayer controller 62 receives the high voltage application completion signal, the painting process starts. In this painting process, a painting command signal is output from the sprayer controller 62 to the spray gun 61 and the articulated robot, and this controls the discharge of paint mist from the spray gun 61 and the operation of the articulated robot so that the discharge direction of the paint mist is toward the bumper W. FIG. 4 is a diagram for explaining this painting process. In FIG. 4, the spray gun 61 shown by a solid line shows a state in which it is painting the front surface of the bumper W (the front surface when mounted on the vehicle body), and the spray gun 61 shown by a two-dot chain line shows a state in which it is painting the side surface of the bumper W (the side surface when mounted on the vehicle body).

[0071] In this painting process, the paint mist discharged from the spray gun 61 toward the surface W1 of the bumper W to be coated is attracted to the surface W1 of the bumper W, and the surface W1 is coated. At this time, the paint mist discharged from the spray gun 61 becomes statically charged as it approaches the electrically charged surface W1 of the bumper W to be coated, and so flies toward the conductor 2 and the surface W1 to be coated along the electrostatic force of attraction, and is applied to the surface W1 to be coated. In addition, since the paint mist has a larger mass than the dust floating in the air, the electrostatic force of attraction acts more strongly on the paint mist than on the floating dust, and so the paint mist flies toward the surface W1 to be coated in preference to the floating dust, and is applied to the surface W1 to be coated.

[0072] This painting process is carried out for a predetermined time, and when the painting process is completed, a painting completion signal is output from the sprayer controller 62 to the high-voltage controller 42. When the high-voltage controller 42 receives the painting completion signal, a high-voltage release process is started. In this high-voltage release process, a high-voltage application release command signal is output from the high-voltage controller 42 to the cascade 41, which causes the cascade 41 to release the negative electrostatic high voltage that was being applied to the conductor 2 via the power line 43 and the power receiving unit 24 (release the supply of charge). As a result, a negative charge is no longer supplied to the conductor 2, but since the conductor 2 is supported insulated from the floor surface F as described above, a negative charge remains in the conductor 2.

[0073] When the supply of charge to the conductor 2 is terminated by the high voltage termination step, the high voltage controller 42 outputs a high voltage termination completion signal to the charge removal controller 53. When the charge removal controller 53 receives the high voltage termination completion signal, the charge removal step is started. In this charge removal step, the charge removal controller 53 outputs a pump operation command signal to the vacuum pump 52b and a pressure adjustment command signal to the vacuum regulator 52c, which operates the vacuum pump 52b and adjusts the pressure in the internal space of the charge removal tube 51 under the control of the vacuum regulator 52c. When this pressure reaches a predetermined level or lower (when the amount of air in the internal space of the charge removal tube 51 falls to a predetermined level or lower), a vacuum discharge is performed inside the charge removal tube 51, and electricity can be passed through the earth path from the conductor 2 to the earth wire 51c, so that the charge of the conductor 2 is earthed via the earth wire 51c. FIG. 5 is a diagram for explaining this charge removal step. As indicated by the dashed arrow in Figure 5, electricity can flow through the earth path from the conductor 2 to the earth wire 51c (the conductor 2, the upper conductor 51a, the internal space of the static elimination tube 51, the earth pipe 51b, and the earth wire 51c), and the conductor 2 is earthed.

[0074] By this static elimination process, the electric charges remaining in the conductor 2 and the bumper W are discharged, and the conductor 2 and the bumper W are neutralized. By carrying out the static elimination process using vacuum discharge inside the static elimination tube 51 in this manner, the conductor 2 and the bumper W are instantly neutralized.

[0075] Through the above operations, the formation of one paint film on the bumper W is completed.

[0076] The paint film of the bumper W is configured as a multi-layer film. For example, a base paint film is formed on the surface of the surface W1 to be painted, a color paint film is formed on the surface of this base paint film, and a clear paint film is formed on the surface of this color paint film, forming a three-layer film. The painting method using the painting device 1 described above can be applied to the production of any paint film. When the above-mentioned painting method is applied to the production of all paint films, one paint film is produced, and then after a paint drying process, the next paint film production operation is started. In other words, when a three-layer film is produced, the procedure of the above-mentioned painting method is repeated three times.

[0077] When the above painting operations are completed, the bumper W is detached from the conductor 2 (by a transfer robot or a worker), and the bumper W is transported to a vehicle assembly line and attached to the vehicle body.

[0078] -Effects of the embodiment- As described above, in this embodiment, the surface W1 of the bumper W to be coated is painted by discharging paint mist from the spray gun 61 of the paint applicator 6 toward the surface W1 of the bumper W to be coated while contacting the charged conductor 2 with the opposite side of the surface W1 of the bumper W to be coated (the back surface of the bumper W), which is an insulator. Therefore, compared with the case where the surface W1 of the bumper W to be coated is directly charged (the technology of the above-mentioned Patent Document 1), it is possible to reduce the variation in the distribution of charges on the surface W1 to be coated, and it is possible to obtain a desired charged state of the surface W1 to be coated. For example, it is possible to uniformly charge the entire bumper W. Since the charged state of the surface W1 to be coated has a large effect on the finish of the electrostatic coating, it is possible to obtain a high coating quality by making it possible to obtain a desired charged state of the surface W1 to be coated.

[0079] In addition, in general electrostatic painting, the paint mist is negatively charged, and when painting an insulator, the charge of the paint mist applied to the surface to be painted remains on the insulator and is electrically repelled by the paint mist that is then sprayed toward the surface to be painted, making it difficult to obtain a sufficient paint film thickness and high painting quality. However, in this embodiment, the paint sprayer 6 is earthed and the paint mist is not charged, so this prevents the paint mists from electrically repelling each other, making it possible to obtain a sufficient paint film thickness, which also makes it possible to obtain high painting quality.

[0080] In addition, while the above-mentioned Patent Document 1 is directed to positively charging an insulator, it is difficult to positively charge a resin material such as polypropylene. In this embodiment, since the insulator (bumper W) is negatively charged, a wide variety of materials can be used as the insulator, making the present invention highly versatile.

[0081] In addition, in this embodiment, there is no need for a process of painting a conductive material on the bumper W, which is an insulator. Therefore, a dedicated material or process is not required when painting a conductive material, and costs can be reduced. In addition, when painting this conductive material, since the conductive material contains a conductive pigment such as carbon, there are cases where the desired color development cannot be obtained by electrostatic painting. However, in this embodiment, since there is no need for a process of painting a conductive material, the desired color development can be obtained, and this also allows for high painting quality to be obtained.

[0082] In addition, in this embodiment, the painting process is performed with the conductor 2 energized by the charging unit 4 and the coater 6 grounded, so that it is only necessary to control the energization of the conductor 2 for charging the bumper W (only the control by the high voltage controller 42 is required), and there is no need to control the energization for charging the coater 6. Therefore, with relatively simple control, it is possible to obtain a desired charged state for the coated surface W1 of the bumper W, and high painting quality can be obtained.

[0083] Furthermore, in this embodiment, after the painting process is completed, the current to the conductor 2 is stopped, and the conductor 2 is grounded by operating the static elimination unit 5, thereby eliminating static electricity from the conductor 2 and the bumper W. Therefore, compared to the case where the charged bumper itself is grounded to eliminate static electricity, it is possible to quickly and reliably eliminate static electricity from the conductor 2 and the bumper W by grounding the conductor 2, thereby shortening the tact time of the painting work including the above-mentioned processes, and realizing an efficient painting method.

[0084] In this embodiment, the conductor 2 is supported by a support member 3 having a non-conductive support portion 31. Therefore, in the painting process, the conductor 2 is not grounded (insulated), so that the surface W1 of the bumper W to be painted can be painted while maintaining the charge of the conductor 2 high. In other words, the potential difference between the bumper W and the paint mist can be maintained large, and the attractive force (electrostatic attractive force) acting on the paint mist toward the surface W1 to be painted can be large, reducing the amount of paint wasted. For this reason, the amount of air sprayed from the spray gun 61 of the painter 6 toward the bumper W can be set to a relatively small amount, for example, 400 NL / min (the general amount of air sprayed is about 1000 NL / min). In addition, when the painting operation is controlled by the air pressure of the spray gun 61, the air pressure can be set to a relatively small value, for example, 0.02 MPa (the general air pressure is about 0.15 MPa). In other words, even if the amount of sprayed air or the air pressure is reduced, most of the paint mist discharged from the spray gun 61 can be applied to the bumper W, thereby reducing the amount of paint wasted.

[0085] -Other embodiments- The present invention is not limited to the above-described embodiment, and all modifications and applications encompassed within the scope of the claims and equivalents thereto are possible.

[0086] For example, in the above embodiment, the case where a plastic bumper W of an automobile is painted by electrostatic painting has been described as an example. The present invention is not limited to this, and can also be applied to the case where other insulators are painted by electrostatic painting. In addition, the size of the insulator applicable to the present invention is not particularly limited, and the present invention can be applied to the case where an insulator larger than the above-mentioned bumper W is painted by electrostatic painting, or the case where an insulator smaller than the bumper W is painted by electrostatic painting. In addition, by improving the shape of the conductor 2, it is also possible to charge only a part of the insulator (a desired part to be electrostatically painted). In this case, the part of the insulator can be uniformly charged, and high painting quality can be obtained.

[0087] In the above embodiment, the conductor 2 is provided with a plurality of contact bodies 23, 23, ..., and the bumper W is charged by contacting these contact bodies 23, 23, ... with the bumper W. The present invention is not limited to this, and the bumper W may be charged by arranging the conductor 2 close to the bumper W. In this case, the voltage output from the cascade 41 (the potential that negatively charges the conductor 2) and the proximity distance of the conductor 2 to the bumper W are appropriately set so that a sufficient potential is obtained at the bumper W. In this case, a jig for supporting the bumper W is provided separately. The jig in this case may be conductive or non-conductive.

[0088] In the above embodiment, the coater 6 is grounded to prevent the paint mist from being charged. In the present invention, the coater 6 may be positively charged and the paint mist may be positively charged (charged with a charge of the opposite polarity to that of the conductor 2). This makes it possible to increase the potential difference between the bumper W and the paint mist (the potential difference can be increased compared to when non-charged paint mist is used), and the attractive force acting on the paint mist toward the surface W1 to be coated can be increased. As a result, the paint mist can be effectively applied to the surface W1 to be coated of the bumper W, and the amount of paint wasted can be reduced. In addition, the electrostatic atomization effect of charging the paint mist makes it possible to reduce the particle size of the paint mist, and high painting quality can be obtained. In addition, in the present invention, the potential to which the paint mist is charged in this case is a charge of the opposite polarity to that of the conductor 2 and a potential with a lower absolute value than that of the conductor 2. According to this, the electric charge of the paint mist applied to the surface W1 of the bumper W to be coated is unlikely to remain on the surface W1 to be coated (most of the electric charge of the paint mist is neutralized by some of the electric charges on the surface W1 of the bumper W, so that the electric charge of the paint mist is unlikely to remain on the surface W1 to be coated), and it is possible to suppress electrical repulsion with the paint mist discharged toward the surface W1 to be coated, and it is possible to obtain a sufficient thickness of the coating film, which also results in high coating quality. One example is setting the charged potential of the conductor 2 to -20 kV and the charged potential of the paint mist to +2 kV. Although these values ​​are not limited to these, the absolute value of the electric potential to charge the paint mist is sufficiently smaller than the absolute value of the electric potential to charge the conductor 2, so that the electric charge of the paint mist applied to the surface W1 of the bumper W is unlikely to remain on the surface W1 to be coated.

[0089] In the above-described embodiment, the static elimination unit 5 uses vacuum discharge to reduce the electrical resistance of the earth path that earths the conductor 2. There are no particular limitations on the configuration for static elimination in the present invention, and a well-known variable electrical resistor may be used, or an earth wire may be connected to the conductor 2 with a switch that can be opened and closed provided on the earth wire, and the switch may be closed in the static elimination process to discharge the charge remaining in the conductor 2 and the bumper W.

[0091] Furthermore, in the embodiment described above, the conductor 2 and the bumper W are instantly neutralized by a neutralization process that utilizes vacuum discharge inside the neutralization tube 51. However, the present invention is not limited to this, and in the neutralization process, the electrical resistance of the earth path that earths the conductor 2 may be gradually lowered to slow down the movement of charges, thereby stably neutralizing the electricity. [Industrial Applicability]

[0092] INDUSTRIAL APPLICABILITY The present invention is applicable to a coating method and coating apparatus for electrostatically coating the surface of a resin molded product, such as a resin bumper for an automobile. [Explanation of symbols]

[0093] 1. Painting equipment 2 Conductors 23 Contact body 3 Supporting member 31 Non-conductive support part (non-conductive member) 4 Charging unit 5. Static electricity removal unit 51 Static eliminator tube 52 Pressure Adjustment Unit 6. Painting machine (discharge device) W Bumper (insulator) W1 Surface to be painted

Claims

1. A method for coating an insulator, comprising the steps of: The method includes a coating process for coating the surface of the insulator by discharging a non-charged paint mist toward the surface of the insulator while bringing a charged conductor into contact with or in close proximity to the opposite side of the surface of the insulator, The coating process is carried out in a state where the conductor is electrified and the spraying device that sprays the paint mist is grounded, a discharge step of removing electricity from the conductor and the insulator by stopping the current flow to the conductor and earthing the conductor after the coating step is completed,

2. A method for coating an insulator, comprising the steps of: The method includes a coating process in which a paint mist is sprayed onto the surface of the insulator to be coated, the paint mist being charged to a potential with a polarity opposite to that of the conductor and with a lower absolute value than that of the conductor, while a charged conductor is brought into contact with or close to the opposite side of the surface of the insulator to be coated, thereby coating the surface of the insulator to be coated; the coating step is carried out in a state where electricity is passed through the conductor to charge it, and a discharge device for discharging the paint mist is charged with a charge of opposite polarity to the conductor and with a potential having a lower absolute value than the conductor; a discharge step of removing electricity from the conductor and the insulator by stopping the current flow to the conductor and earthing the conductor after the coating step is completed,

3. A method for coating an insulator according to claim 1 or 2, a discharge path for grounding the conductor includes a space surrounded by a non-conductive member, and the discharge step is carried out by reducing the air pressure in the space and generating a vacuum discharge in the space.

4. A method for coating an insulator according to claim 1, 2 or 3, 13. A method for painting an insulator, comprising the steps of: applying paint to the insulator; ... and applying paint to the conductor while the conductor is supported by a non-conductive member.

5. An apparatus for coating an insulator, comprising: a conductor in contact with or adjacent to a surface of the insulator opposite the surface to be coated; a charging unit for charging the conductor; and a discharge device that discharges a non-charged paint mist toward the surface of the insulator to be coated. The charging unit is configured to continuously supply electricity to charge the conductor during a coating process in which a paint mist is sprayed toward a surface of the insulator to be coated, while the spray device is grounded; The charging unit is configured to stop energizing the conductor after the coating process is completed, 13. A coating device for insulating materials, comprising: a static elimination unit capable of switching the conductor between an earthed state and an insulated state.

6. An apparatus for coating an insulator, comprising: a conductor in contact with or adjacent to a surface of the insulator opposite the surface to be coated; a charging unit for charging the conductor; a discharge device that discharges a paint mist that is charged to a potential having a polarity opposite to that of the conductor and a lower absolute value than that of the conductor toward the surface to be coated of the insulator, the charging unit is configured to continuously energize the conductor in a coating process in which a paint mist is discharged toward a surface of the insulator to be coated, while the discharge device is configured to be charged with a charge of opposite polarity to the conductor and to a potential with a lower absolute value than the conductor; The charging unit is configured to stop energizing the conductor after the coating process is completed, 13. A coating device for insulating materials, comprising: a static elimination unit capable of switching the conductor between an earthed state and an insulated state.

7. In the coating apparatus for insulating materials according to claim 5 or 6, The static electricity removal unit is characterized in that it comprises an electrostatic removal tube arranged between the conductor and the earth and made of a non-conductive material, and an air pressure adjustment unit that adjusts the air pressure inside the electrostatic removal tube.

8. In the coating apparatus for insulating materials according to claim 5, 6 or 7, 13. An apparatus for coating an insulator, comprising: a support member supporting said conductor; and a non-conductive support member supporting said conductor.

9. In the coating apparatus for insulating materials according to any one of claims 5 to 8, 13. An apparatus for coating an insulator, comprising: a conductor that is a jig for supporting the insulator.

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