JP2004089861A - Top clear coating method for automobile body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a top clear coating method for an automobile body capable of efficiently forming a top clear layer excellent in flatness. <P>SOLUTION: A control circuit 15 controls a flow rate Qfm of suction air by adjusting a pressure regulator 12 for suction air such that a feed amount Qp of a fine particle coating material F measured by a powder flow rate measurement device 7 becomes a set feed amount Qm and adjusts a pressure regulator 13 for dilution air such that a flow rate Qt of conveying air i.e., a sum of the flow rate Qfm and a flow rate Qfs of the dilution air becomes constant. The fine particle coating material F having an average particle diameter of 10-25 μm fed to a coating gun 5 is pulse-charged by a corona discharge generated by applying a pulse-like high voltage from a pulse voltage generation device 6 to a corona electrode of the coating gun 5 and is coated on a surface of the automobile body. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a top clear coating method for an automobile body, and more particularly to an electrostatic powder coating method using a fine particle paint.
[0002]
[Prior art]
Various coating methods have been adopted for painting automotive bodies.However, from the viewpoint of environmental protection, electrostatic powder coating has attracted attention as an environmentally friendly and pollution-free coating method that does not use solvents. I have. In this electrostatic powder coating, powder paint is supplied from a paint tank to a paint gun via an injector, and is conveyed from a nozzle opening formed at the tip of the paint gun to an automobile body, which is an object to be coated, along with a conveying air flow. Injected toward. At this time, a high voltage is applied to the pin-type electrode provided at the tip of the coating gun and the vehicle body is grounded, and corona discharge is generated from the electrode of the coating gun toward the vehicle body. Therefore, when the powder paint sprayed from the nozzle opening passes near the electrode, the powder paint collides with ions generated by corona discharge and is charged. The powder paint charged in this way is applied on the surface of the automobile body under the influence of the conveying air flow and the electric force along the electric force line.
[0003]
[Problems to be solved by the invention]
In this way, powder coating is performed on an automobile body. Particularly, since the top clear layer is required to have excellent smoothness, use of a fine particle coating having a small particle diameter has been proposed. However, when the particle diameter of the powder coating material is reduced, the coating efficiency is reduced and the surface potential of the powder coating material is liable to increase. As a result, there is a possibility that electrostatic repulsion is caused and a skin roughness phenomenon occurs.
[0004]
The present invention has been made to solve such a problem, and an object of the present invention is to provide a top clear coating method for an automobile body, which can efficiently form a top clear layer having excellent smoothness.
[0005]
[Means for Solving the Problems]
The top clear coating method for an automobile body according to the present invention is characterized in that a suction air is blown from a compressed air source into a main nozzle of an injector connected to a paint tank containing a fine particle paint having an average particle diameter of 10 to 25 μm. The fine particle paint is sucked and supplied to the gun body, the flow rate of the fine particle paint is measured, the flow rate of the suction air is controlled so that the flow rate becomes the set supply amount, and the sum with the flow rate of the suction air is constant. A small flow of dilution air is blown into the sub-nozzle of the injector from the compressed air source, and the fine particles of paint are sprayed from the gun body toward the surface of the automobile body, and pulse-shaped to a plurality of corona electrodes provided at the tip of the gun body. This is a method of charging the ejected fine particle paint by generating a corona discharge by applying a high voltage.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a configuration of an apparatus for carrying out a method of top clear coating an automobile body according to an embodiment of the present invention. A paint tank 1 containing a particulate paint F having an average particle size of 10 to 25 μm is a so-called fluidized bed tank provided with a perforated plate 2, and a paint gun 5 is connected to the paint tank 1 via a paint supply device. . One end of the transport pipe 3 is inserted into the paint tank 1, an injector 4 is connected to the other end of the transport pipe 3, and a paint gun 5 is connected to the injector 4. A pulse voltage generator 6 is connected to the coating gun 5.
[0007]
A powder flow measuring device 7 for measuring the flow rate of the powder coating material F from the change in capacitance in the conduit is attached to the transport pipe 3, and an amplification circuit 8 is connected to the powder flow measuring device 7 to further amplify. The correction circuit 9 is connected to the circuit 8. An output signal from the correction circuit 9 is input to the controller 10, and the controller 10 supplies suction air and dilution air to the main nozzle 4a and the sub-nozzle 4b of the injector 4, respectively.
[0008]
The controller 10 includes a valve 11 connected to a compressed air source (not shown) and opened / closed based on an operation signal of the coating gun 5, and a suction air pressure regulator 12 connected to the valve 11 via a branch point A. And a pressure regulator 13 for dilution air. These regulators 12 and 13 are connected to the main nozzle 4a and the sub-nozzle 4b of the injector 4, respectively. Further, the controller 10 has a control panel 14 and a control circuit 15 connected to the control panel 14, the regulators 12 and 13, and the correction circuit 9.
It is assumed that the set supply amount Qm of the powder paint F and the flow rate Qt of the transport air for transporting the powder paint F to the coating gun 5 have been input from the control panel 14 in advance.
[0009]
As shown in FIG. 2, the coating gun 5 has a substantially cylindrical gun body 16, and a powder flow path 17 is formed on the central axis of the gun body 16. The diameter of the powder passage 17 is gradually increased toward the front end of the gun body 16, and an electrode holding member 18 is suspended inside the powder passage 17 and on the central axis of the gun body 16. The electrode holding member 18 has a streamlined cross-sectional shape, and its front end projects slightly forward from the front end of the gun body 16. Due to the presence of the electrode holding member 18, an annular nozzle is formed at the front end of the powder passage 17. An opening 19 is formed. Four corona electrodes 20 are radially held by the electrode holding member 18 such that the tip ends project into the powder flow path 17. Each corona electrode 20 is electrically connected to each other, and is connected to the pulse voltage generator 6.
[0010]
Next, the method of this embodiment will be described. First, flowing air is blown into the paint tank 1 to keep the particulate paint F in a fluid state in the paint tank 1. When the coating gun 5 is operated, a valve 11 in the controller 10 is opened according to the operation signal, and compressed air from a compressed air source (not shown) passes through the valve 11 and is diverted at a branch point A to be used for suction air. The suction air is blown into the main nozzle 4a of the injector 4 via the pressure regulator 12, and the dilution air is blown into the sub nozzle 4b of the injector 4 via the pressure regulator 13 for dilution air. By the suction air blown into the main nozzle 4a, the fine particle paint F is sucked from the paint tank 1 into the transport pipe 3, and further the fine particle paint F is supplied to the coating gun 5 by the suction air and the dilution air. It is squirted toward a certain car body.
[0011]
The powder flow rate measuring device 7 measures the flow rate of the fine particle paint F based on the density in the transport pipe 3 measured as a change in capacitance and the flow rate Qf of the measurement air introduced into the transport pipe 3. The output signal from the powder flow rate measuring device 7 is amplified by an amplifier circuit 8 and subjected to, for example, a zero-point correction by a correction circuit 9 and then controlled by a controller 10 as a signal representing the supply amount Qp of the fine particle paint F. Input to the circuit 15. Here, the zero-point correction is to reduce the influence of powder adhering to the inner wall of the transport pipe 3 during the supply of the fine particle paint to a level that does not adversely affect practical use. The measured value during operation is corrected using (a measured value corresponding to the amount of adhered powder) as a correction reference value.
[0012]
The control circuit 15, which has received the signal representing the supply amount Qp from the correction circuit 9, compares the supply amount Qp represented by this signal with the set supply amount Qm of the fine particle paint F previously input from the control panel 14, and performs the set supply. The suction air pressure regulator 12 is adjusted according to the excess or deficiency with respect to the amount Qm to control the flow rate Qfm of the suction air blown into the main nozzle 4a of the injector 4. Thereby, the fine particle paint F having the set supply amount Qm is always supplied to the coating gun 5. At the same time, the control circuit 15 calculates a difference Qt-Qfm between the transport air flow rate Qt and the suction air flow rate Qfm input in advance from the control panel 14 so that the dilution air flow rate Qfs matches this difference. The pressure regulator 13 for dilution air is adjusted. That is, the dilution air is controlled such that the flow rate Qt of the transport air, which is the sum of the flow rate Qfm of the suction air and the flow rate Qfs of the dilution air, is constant.
[0013]
In the coating gun 5 to which the particulate paint F of the set supply amount Qm is supplied in this manner, first, the pulse voltage generator 6 generates a pulse-like high voltage as shown in FIG. To generate a corona discharge from the corona electrode 20 toward the automobile body as the object to be coated. At this time, it is preferable that the peak value of the pulse-like high voltage is set in the range of 50 to 150 KV, the pulse width t1 is set in the range of 50 μs to several hundred ms, and the pulse interval t2 / pulse width t1 is set in the range of 1 to 50.
[0014]
In this state, the fine particle paint F is supplied to the powder flow path 17 together with the conveying air, and is ejected forward from the annular nozzle opening 19. The ejected powder paint is charged by negative ions generated by corona discharge generated from the corona electrode 20 toward the vehicle body, then travels toward the vehicle body and is applied to the surface of the vehicle body.
[0015]
Here, since a pulsed high voltage is applied to each corona electrode 20, negative ions due to corona discharge do not fill the space between the gun and the car body, and fine particles having an average particle size of 10 to 25 μm. Even when the paint F is used, the rise in the surface potential of the paint is suppressed, and the occurrence of electrostatic repulsion is suppressed. In addition, the corona discharge suppressing action due to the space charge of the negative ions is reduced, and a uniform corona discharge is generated from the whole of the plurality of corona electrodes 20 during application of the pulse voltage. improves.
Further, since the pulse-like high voltage is applied, the corona current can be reduced without lowering the applied voltage by adjusting the pulse width and the pulse interval.
[0016]
Further, as described above, by controlling the supply amount Qm of the fine particle paint F and the flow amount Qt of the conveying air independently of each other, the fluctuation of the suction air flow rate Qfm accompanying the control of the paint discharge amount from the coating gun 5 can be reduced. And the flow rate Qt of the conveying air can be kept constant. Therefore, the coating pattern from the coating gun 5 is stable, and a coating film having a stable film thickness distribution can be formed.
[0017]
As shown in FIG. 4, a pulse-like high voltage having a constant base voltage Vb can be applied from the pulse voltage generator 6 to the plurality of corona electrodes 20 of the coating gun 5, and the same effect is obtained. be able to. The base voltage Vb is preferably about 0 to 50 KV.
[0018]
The measuring air introduced into the conveying pipe 3 in the powder flow measuring device 7 in the paint supply device also becomes a part of the conveying air for conveying the powder coating material F to the coating gun 5. Since the air flow rate Qf is extremely smaller than the suction air flow rate Qfm and the dilution air flow rate Qfs, it is not included in the transport air flow rate Qt. However, taking into account the flow rate Qf of the measurement air, the sum of the flow rate Qfm of the suction air, the flow rate Qfs of the dilution air, and the flow rate Qf of the measurement air may be used as the flow rate Qt of the transport air.
[0019]
The control circuit 15 in the controller 10 can be configured by a computer. Alternatively, as shown in FIG. 5, it may be configured using a subtractor 21, a PID (proportional-integral-derivative) controller 22 and a comparator 23. The difference Qm−Qp between the set supply amount Qm input from the control panel 14 and the supply amount Qp input from the correction circuit 9 is calculated by the subtractor 21, and based on the difference, the PID controller 22 controls the suction air pressure. While the voltage command Vm to the regulator 12 is created, the difference Vt−Vm between the voltage command Vt indicating the flow rate Qt of the carrier air input from the control panel 14 and the voltage command Vm to the suction air pressure regulator 12 described above. Is calculated by the comparator 23 as a voltage command Vs to the pressure regulator 13 for dilution air. Then, the suction air pressure regulator 12 and the dilution air pressure regulator 13 are controlled by the voltage commands Vm and Vs, respectively.
[0020]
A control valve may be used instead of the suction air pressure regulator 12 and the dilution air pressure regulator 13.
[0021]
【The invention's effect】
As described above, according to the present invention, the fine particle paint having an average particle diameter of 10 to 25 μm is stably supplied to the gun body so as to have a set supply amount, and a plurality of corona electrodes provided at the tip of the gun body. Since the fine particle paint is pulse-charged, it is possible to efficiently form a top clear layer having excellent smoothness while suppressing the occurrence of electrostatic repulsion.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an apparatus for carrying out a method of top clear coating an automobile body according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration of a coating gun used in the embodiment.
FIG. 3 is a diagram showing a pulse-like high voltage waveform applied to a plurality of corona electrodes in the embodiment.
FIG. 4 is a diagram showing a pulse-like high voltage waveform applied to a plurality of corona electrodes in another embodiment.
FIG. 5 is a block diagram showing a configuration of an apparatus for performing a top clear coating method for an automobile body according to still another embodiment.
[Explanation of symbols]
Reference Signs List 1 paint tank, 3 transfer pipe, 4 injector, 4a main nozzle, 4b sub nozzle, 5 painting gun, 6 pulse voltage generator, 7 powder flow measuring device, 8 amplifier circuit, 9 correction circuit, 10 controller, 11 valve, 12 Pressure regulator for suction air, 13 Pressure regulator for dilution air, 14 Control panel, 15 Control circuit, 16 Gun body, 17 Powder flow path, 18 Electrode holding member, 19 Nozzle opening, 20 Corona electrode, 21 Subtractor, 22 PID Controller, 23 comparator.

Claims (1)

In a method of forming a top clear layer by electrostatically applying a charged powder coating on a surface of an electrically grounded automobile body,
By blowing suction air from a compressed air source into a main nozzle of an injector connected to a paint tank containing a fine particle paint having an average particle diameter of 10 to 25 μm, the fine particle paint is sucked from the paint tank and supplied to the gun body,
The flow rate of the fine particle paint is measured, and the flow rate of the suction air is controlled so that the flow rate becomes the set supply amount. At the same time, the dilution air is supplied from the compressed air source to the injector so that the sum of the suction air flow rate and the suction air flow rate becomes constant. Blow it into the sub nozzle,
Spray fine particle paint from the gun body toward the surface of the car body,
A top clear coating method for an automobile body, which comprises charging a fine particle paint ejected by applying a pulsed high voltage to a plurality of corona electrodes provided at a tip end portion of a gun body to generate a corona discharge. .

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