JPH10109054A - Electrostatic coating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent electrified coating particles from being stuck to a coating device itself or its supporting mechanism and from contaminating them by providing an electrode disposed at the position opposite to the object to be coated and away from the tip of an object side of a high voltage impressing electrode and detecting current value flowing through the electrode thereby controlling a coating state. SOLUTION: In this electrostatic coating device 10, a reference electrode 20 disposed at the position opposite to the object 30 to be coated and away from the tip of the object 30 side of the high voltage impressing electrode is provided. The current value flowing through the reference electrode 20 is monitored at the time of coating, and when the current value flowing through the reference electrode 20 rises above a normal value, the contamination of the coating device itself, etc., is minimized by controlling the coating state by a suitable method. The current value flowing through the reference electrode 20 is directly monitored by a monitor by monitoring a display value of an ammeter 21 for monitoring the current value electrically connected to the reference electrode 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic coating apparatus, and more particularly to an improvement in an electrostatic coating apparatus for preventing charged paint particles from adhering to and contaminating the coating apparatus itself or its supporting mechanism.

[0002]

2. Description of the Related Art An electrostatic coating apparatus has a mechanism for atomizing paint, a mechanism for charging the atomized paint, and a mechanism for imparting a momentum for transporting the charged paint particles to the vicinity of an object to be coated. Device, especially a rotating cup ("bell")
Sometimes referred to as. ), The atomization of paint by the centrifugal force of a spray head such as a disc, and the application of a high voltage for forming the electrostatic charge and the electrostatic field of the paint to such a spray head is generally performed by rotary atomization. The coating apparatus can provide an excellent coating method with high coating efficiency.

[0003]

As described above, the rotary atomizing coating apparatus has the effect of increasing the coating efficiency on the object by charging the paint particles. Is not in a predetermined position, that is, almost in front of the coating apparatus, the charged paint particles adhere to the nearby ground position, that is, in many cases, the coating apparatus itself or the support mechanism of the coating apparatus, and contaminate them. There was a problem. This contamination not only causes high voltage leakage, but also makes it impossible to apply voltage,
In extreme cases, there is a risk of heat generation and ignition. Further, there is also a problem that when a certain amount of dirt accumulates, it peels off and adheres to an object to be coated, thereby deteriorating the finish of coating. For this reason, it is necessary for an operator to frequently wipe off the dirt on the coating machine, and the operation is complicated, and there is a problem that productivity is reduced.

[0004] Such a problem can be solved by providing a means for confirming that the object to be coated is located in front of the coating machine. The use of a processing device or the like increases the cost, which is a problem.

[0005] By installing a high-voltage electrode having the same polarity as the spray head in the main body of the coating apparatus, it is conceivable to prevent the charged paint particles from adhering to the main body of the coating apparatus. It is dangerous because it was done.

Accordingly, an object of the present invention is to provide an improved electrostatic coating apparatus which can solve the above-mentioned problems in the prior art. A further object of the present invention is to provide an electrostatic coating apparatus capable of preventing charged paint particles from adhering to and contaminating the coating apparatus itself or its support mechanism.

[0007]

Means for Solving the Problems In the electrostatic coating using the electrostatic coating apparatus, the present inventors have found that the actual arrangement position of the object to be coated is located at a position farther from the set position or the object to be coated. As a result of diligent research on the generation of dirt due to the adhesion of charged paint particles to the coating apparatus main body etc. that occurs due to the absence of for some reason, the coating apparatus main body was provided with an almost grounded electrode, When the value of the current flowing into the coating is measured, there is a correlation between the increase in the current value and the increase in the amount of dirt due to the adhesion of the charged paint particles to the coating apparatus body and the like. The inventors have found that there is a time delay from the start of rising to the start of rising of the amount of dirt, and have reached the present invention.

That is, the present invention for solving the above-mentioned objects provides an electrostatic coating apparatus having a mechanism for atomizing a paint and an electrode mechanism for applying a high voltage to the paint. And an approximately grounded electrode at a position opposite to an object to be coated, and detects a current value flowing into the electrode to control a coating state.

In the present invention, the control of the coating state may further include:
An electrostatic coating apparatus comprising at least one control selected from the group consisting of control of a paint discharge amount, a state of application of a high voltage, a state of transport of an object to be coated, and a warning to an operator. It shows. According to the present invention, the distance between the roughly grounded electrode and the object-side tip of the high-voltage application electrode is greater than the distance between the assumed position of the object and the object-side tip of the high-voltage application electrode. 1 shows an electrostatic coating apparatus which is also large.

[0010] The present invention further provides an electrostatic coating apparatus in which the outer peripheral portion is substantially covered with an insulator except for the above-mentioned roughly grounded electrode and a portion which emits paint particles to an object to be coated. FIG.

The present invention also provides an electrostatic coating device which is a rotary atomizing electrostatic coating device having the above-described configuration.

[0012]

As described above, according to the present invention, charged paint particles are monitored by monitoring the value of current flowing into a substantially grounded electrode (hereinafter referred to as a reference electrode) provided in a direction opposite to the object to be coated. Predicts whether or not the paint adheres to the coating device body.Based on the prediction, control the paint discharge amount, stop applying high voltage, stop transporting the workpiece, and warn the operator. Thus, a simple index for controlling the so-called coating state can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments. FIG. 1 is a perspective view schematically showing the appearance of the tip portion of an embodiment of the electrostatic coating apparatus according to the present invention. FIG. 2 is a graph showing the change over time in the current value flowing through the reference electrode and the amount of dirt in the coating apparatus. FIG. 3 is a perspective view schematically showing the outer appearance of the tip portion of another embodiment of the electrostatic coating apparatus according to the present invention.

As shown in FIG. 1, an electrostatic coating apparatus 10 according to the present invention comprises a high-voltage applying electrode (a cup 1 in FIG. 1).
The reference electrode 20 that is substantially grounded is provided at a position opposite to the object 30 from the object-side tip of 2).

In the electrostatic coating method, most of the atomized paint particles adhere to an object to be coated, since the coating efficiency is enhanced by electrostatic force. For example, in a rotary atomizing electrostatic coating apparatus having a spray head such as a cup, the paint supplied to the front central portion of the high-speed rotating spray head is thinly stretched by centrifugal force and atomized from the tip of the outer peripheral edge of the cup. The spray head is conveyed to the front of the cup by the shaping air blown from the periphery of the spray head, but since a high voltage is applied to the spray head and corona discharge is generated from the tip of the outer peripheral edge of the spray head, the grounded coating is applied. An electrostatic field is formed on the object, and the paint particles emitted from the tip of the outer peripheral edge of the spray head are charged as described above. The coating particles charged in this manner are more likely to adhere to the object to be coated due to the clonal force, so that the coating efficiency is increased.

In such an electrostatic coating, in order to perform good coating by forming an electrostatic field, a distance A (hereinafter referred to as a distance) from the tip of the high-voltage applying electrode (cup 12) to an assumed position of the object 30 to be coated. , The average distance). In this case, when the object to be coated is disposed within the average distance A and good coating is performed, in the opposite direction to the object to be coated, the object to be coated and the tip of the outer peripheral edge of the voltage application electrode are connected. Normally, almost no current due to corona discharge flows through the reference electrode provided at a position at a distance B longer than the average distance A.

However, depending on the shape of the object to be coated, it may partially have a shape longer than the average distance A,
In an extreme case, when there is an unexpected defect such as a partial loss of the object to be coated, there is a possibility that an attempt is made to paint even though the object to be coated does not exist. In such a case, since the paint particles are charged, the paint particles are applied to the nearest grounding body against the shaping air, that is, the coating device body, or the support device that supports the coating device. The drawbacks due to electrostatic painting will occur.

In such a case, as a precursor, the ion current flowing into the reference electrode 20 increases as shown in FIG. That is, the contamination due to the application of the paint particles to the coating device occurs after the rise of the increase in the current value of the reference electrode.

Therefore, the value of the current flowing into the reference electrode 20 at the time of painting is monitored, and when the value of the current flowing through the reference electrode 20 exceeds a specified value, the painting state is controlled by an appropriate method, whereby And the like can be minimized.

The value of the current flowing through the reference electrode 20 can be directly monitored by a monitor by a monitor person, and the display value of a current value monitoring ammeter 21 electrically connected to the reference electrode 20 can be directly monitored. The measured value from the total 21 is sent as an electric signal to an arithmetic device (not shown) such as a microcomputer at all times or at regular intervals, and the arithmetic device determines whether the measured value is within a specified value. What is necessary is just to comprise so that the program which controls a coating condition will be started when it exceeds a prescribed value.

The control of the paint state can be performed by controlling the paint discharge amount, for example, by squeezing or stopping the discharge of the paint. Depending on the magnitude of the current value, a sound generating means such as a bell or a buzzer or a lamp may be used. It is also possible to take actions such as issuing a warning to the worker by means of light emitting means such as, stopping the transfer of the object to be coated, and stopping the application of a high voltage. It is also possible to do it.

The reference electrode 20 does not necessarily need to be completely grounded, and can be configured to conduct a current to a safe position sufficiently farther than the electrostatic coating apparatus by a certain length of ground wire or the like. It should be done.

In the electrostatic coating apparatus of the present invention, in order to stably obtain an effect of preventing an abnormal coating state by monitoring the value of the current flowing to the reference electrode, the object to be coated between the reference electrode and the high-voltage application electrode is required. It is desirable that the distance B from the side tip is larger than the average distance A (A <B). The distance B is not particularly limited because it is influenced by the shape and size of the coating apparatus. For example, the distance B is 1 to 3 times, more preferably 1.2 to 1.5 times the distance A. Degree. Further, a grounded conductor should not be provided between such a reference electrode and a high-voltage application electrode (spray head), and it is desired that the outer surface of the coating apparatus main body be covered with an electrical insulator. . In addition, the fact that there is a grounded body other than the reference electrode at a site further away from the object to be coated than the arrangement position of the reference electrode does not necessarily impair the effect of the present invention, but in order to stabilize the detection performance of the reference electrode. It is desirable that these portions, especially the portions near the reference electrode, are also covered with an insulator. In many cases, painting is sufficient for such an electrically insulating coating. However, if necessary, the outer surface of the coating apparatus may be surrounded by an electrically insulating cover 22 as shown in FIG. It is also possible to take the form. Further, for the same reason, it is desirable to provide such an electrically insulating coating on the surface of the support mechanism of the coating apparatus.

When an electrode applied to the same polarity as the high voltage application electrode, such as a repulsion electrode, is present between the high voltage application electrode and the reference electrode, the current of the coating apparatus is monitored by monitoring the current. There is little effect of preventing contamination, and even when the object to be coated is located at a position distant from the average distance, almost no current flows through the reference electrode, and an operation of controlling the coating state by changing the current value. Becomes difficult. Although the coating device itself can be prevented from being stained to some extent by grounding the repelling electrode, the use of the repelling electrode is not so desirable because the support device of the coating device located at a position farther than the installation position of the repelling electrode tends to become dirty.

The constituent material of the reference electrode is not particularly limited as long as it is an electric conductor. For example, stainless steel, brass,
It is possible to use a metal material such as aluminum or an aluminum alloy, a conductive metal oxide, a conductive paint or a conductive resin. In the conductive paint or the conductive resin composition, as the conductive filler, existing ones such as carbon particles and silver particles may be used, and as the resin component, for example, epoxy-based, fluorine-based, etc., having excellent solvent resistance. Although it is desirable that they are, it is not particularly limited to these.

The reference electrode is formed by directly processing a thin plate of a metal material or the like, or by coating a suitable base material surface with a conductive paint coating, metal deposition, electroless plating, sputtering, CVD or the like. Can be obtained by forming In particular, in a mode in which the outer periphery of the coating apparatus main body is surrounded by the electrically insulating cover as described above, the use of a conductive paint makes it possible to form an electrode of a predetermined shape at low cost and with ease of workability. Desirable for.

Further, the size of the electrode surface of the reference electrode is not particularly limited. For example, a width of 10 to 30 may be used so that the fluctuation of the current value can be detected satisfactorily and reliably.
mm. Also, the electrode surface does not necessarily need to be present all around the coating device body,
If only a part of the peripheral surface is provided extremely, even if a phenomenon occurs where an electric field is likely to be formed in a local area having another direction, such a change cannot be captured. It is desirable that the current value be present over substantially the entire circumference so that a change in the current value can be detected.

Further, as in the embodiment shown in FIG. 3, the reference electrode 20 may be arranged so as to float from the main body of the coating apparatus or the synthetic resin cover 22 surrounding the main body. In this case, the detection performance is improved, but on the other hand, there is a disadvantage that dirt is difficult to clean.

As described above, the electrostatic coating apparatus according to the present invention has been described taking the case of a rotary atomizing electrostatic coating apparatus as an example. In the present invention, however, by providing a reference electrode on the side opposite to the object to be coated, It is possible to obtain the function of preventing contamination of the coating apparatus itself, and this provides a common advantage to an apparatus for automatically coating, particularly to those having a mechanism for applying static electricity, The present invention is not limited to the above-described rotary atomizing electrostatic coating apparatus, but can be applied to various electrostatic coating apparatuses. However,
In the case of a device that is used by an operator to directly perform painting, for example, in the case of an electrostatic handgun, the distance between the object to be painted and the painting device is adjusted, and the state of paint adhesion to the painting device is determined. Since it is possible for an operator to directly perform such a process, it is considered that formation of such a reference electrode and monitoring of a current value flowing to the reference electrode are not so necessary. Further, from the viewpoint of obtaining the effective operation of the present invention, an apparatus having a large corona discharge amount is desirable. In such a case as charging only by contact charging, for example, in the case of a triboelectric powder coating apparatus, the detection ability is reduced. Such a problem also arises. However, even with such a device, the advantage of minimizing contamination of the coating device is obtained.

Further, in the electrostatic coating apparatus according to the present invention, the components other than the external components of the electrostatic coating apparatus in which the above-described reference electrode is provided are the same as those of the conventional electrostatic coating apparatus. Any of the embodiments can be used.

For example, taking the case of the above-mentioned rotary atomizing electrostatic coating apparatus as an example, the spray head is not limited to a cup-shaped one as illustrated in FIG. Can also be employed. In the above description, the spray head is made of a metal and used as a high-voltage application electrode. However, the spray head may be made of an insulating material such as resin, and a high-voltage application electrode may be separately provided.
The structure of the spray head, in which the spray head body is made of an insulating material and has a high voltage application electrode on the rear surface, is described in detail in Japanese Patent Application No. 7-291394 filed earlier by the present inventors. However, a brief description is given below.

The insulating material constituting the spray head is not particularly limited as long as it has sufficient resistance to the coating composition to be used, in particular, a solvent and the like and is insulating. Although it depends on the type of the coating composition to be formed, for example, various synthetic resins such as polyetheretherketone can be preferably used.

The high voltage application electrode provided on the rear surface of the spray head may be formed by directly contacting the rear surface of the spray head, or may be formed at a predetermined distance from the rear surface of the spray head, for example, about 1 to 10 mm. Although it is possible to form them separately at a distance, it is desirable to form them by directly contacting the rear surface of the spray head. In special cases, such as when using a water-based paint, it may be desirable to provide an external discharge electrode. For example, it is possible to form a discharge electrode directly on the rear surface of the spray head by using a conductive paint, a metal deposited film, a conductive metal oxide deposited film, an electroless plated film, a sputtered film, a CVD film, or the like. Of course, a mode in which a thin metal plate is attached can also be adopted. Such a high voltage applying electrode may be formed entirely on the rear surface of the spray head, but is preferably in a plurality of specific directions from the center of the spray head, for example, 2 to 12 electrodes. A form that is locally extended outward only in the direction of the degree,
A substantially star-shaped configuration is effective for increasing the corona discharge amount, and is desirable. Further, when a plurality of high voltage application electrodes are formed in this manner, 10 KΩ to 50
It is desirable for the stabilization of discharge to be connected to a common high-voltage generator via a resistance of 0 MΩ.

As the motor for rotating the spray head and the high voltage application electrode, any of an electric motor using electric power and an air motor using air pressure can be used. Any device that can generate an appropriate voltage according to the condition can be used. Also, as a paint supply system, water-based, organic solvent-based,
A drive that uses a pump having an appropriate capacity and discharge amount, such as a gear pump, depending on the type of paint to be applied, such as a high solid type, a two-part high solid type, and the like, and further appropriately controls the pump rotation speed remotely. It is possible to use a mixing device such as a device or a static mixer. In addition, safety devices such as a spark guard system, a constant voltage device, a fire extinguishing system, and other various types of conventionally known various aspects can also be used as various insulating and explosion-proof components. In addition to the monitoring of the current amount of the reference electrode according to the present invention and the control device related thereto, it is also possible to provide another known control device that monitors the device and performs an abrupt stop when an abnormality occurs.

[0035]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

FIG. 4 is a sectional view schematically showing the structure of the tip of a rotary atomizing electrostatic coating apparatus as one embodiment of the electrostatic coating apparatus according to the present invention. In the apparatus of this embodiment, a metal cup 12 as a spray head is fixed to the tip of a hollow shaft 11 of a motor incorporated in the apparatus, while a paint pump (not shown) is mounted inside the hollow shaft 11. Is disposed inside the metal cup 12, and a paint outlet hole 14 (a large number of fine holes are annularly arranged) is opened at a central portion on the front side of the cup 12. ). An air ring 15 that surrounds the outer periphery of the hollow shaft 11 at regular intervals is attached to the rear surface of the cup 12. Inside the air ring 15, an opening is formed at a front end surface facing the rear surface of the cup 12. Many air outlet holes 16
And a ring-shaped manifold connecting the air inlet 17 opening to the side surface, and the air inlet 17 communicates with an air supply pump (not shown). The hollow shaft 11 is electrically connected to a high-voltage generator (not shown) by a cable or the like, so that a predetermined applied voltage can be applied to the cup 12 that is in communication with the hollow shaft 11.

In the apparatus of this embodiment, the paint passes through the paint nozzle 13 located at the center of the rotation axis of the cup, and from the paint outlet hole 14 to the front surface of the cup 12 (cup inner surface).
Supplied to Since the cup 12 is rotated at a high speed by the motor, the paint supplied to the front of the cup is thinly stretched along the front of the cup by centrifugal force, and directed toward the outer peripheral edge of the cup. Will be released. The discharged paint particles are controlled in a desired pattern by a pattern adjusting air called a shaping air ejected from an air outlet hole 16 of an air ring 15 and are carried toward the object to be coated. On the other hand, since a high voltage is applied to the metal cup, corona discharge is performed from the tip of the cup toward the object to be coated. The paint particles are further charged by corona discharge in addition to the charge obtained by contacting the cup, and the thus-painted paint particles are separated by a predetermined average distance A (in the case of the present embodiment) When it is within about 250 mm), it adheres to the substrate efficiently due to the cloning force.

The outer surface of the coating apparatus of this embodiment is covered with a synthetic resin cover 22, and is spaced from the tip of the outer peripheral edge of the cup 12 by a distance B (about 30 in the present embodiment).
0 mm), a stainless steel strip having a width of about 30 mm is attached to the outer surface of the cover 22 over the entire circumference to form a reference electrode 20.
Are grounded by a ground wire 23. A current meter 21 for monitoring a current value is provided in the middle of the ground wire 23, and a microcomputer (not shown) is electrically connected to the current meter 21. Is always input to the microcomputer as an electric signal. In this microcomputer,
It is determined whether or not the input current value is within a set value, for example, 20 μA. If the current value is exceeded, it is determined that the set value exceeds the set value for 0.3 seconds and that the current value tends to increase. In such a case, a program is installed which issues a stop signal to the mechanism for controlling the paint pump and issues an operation signal to the audio warning device.
Therefore, when the object to be coated does not exist within the average distance A in front of the coating apparatus for some reason, the discharge of the coating is stopped and a warning is issued at the same time. In addition, the paint particles adhere to the support mechanism, and the contamination is minimized, and the operator can be made aware of this condition.

[0039]

As described above, according to the present invention, a substantially grounded reference electrode is provided in the electrostatic coating apparatus in a direction opposite to the object to be coated, and a current value flowing into the reference electrode is monitored. By predicting whether the charged paint particles are in a state of adhering to the coating apparatus main body, based on such prediction, control of the paint discharge amount, stop of the application of high voltage, stop of the transport of the workpiece, Since it is possible to obtain a simple index for controlling a so-called coating state such as a warning to an operator, the coating particles may be removed from the coating apparatus when the object to be coated is not arranged at a predetermined position for some reason. It is possible to minimize the generation of dirt attached to the main body, etc., which makes it impossible to apply voltage due to high voltage leakage, and furthermore the danger of ignition due to heat generation. Defects such as deterioration of coating finish due to the dirt deposited on the surface and adhesion to the object to be coated, and a decrease in productivity due to frequent removal of dirt from the coating machine by an operator are reduced in a simple and compact manner. This can be prevented beforehand by the configuration.

Further, in the present invention, the distance between the above-mentioned roughly grounded electrode and the tip of the high-voltage applying electrode on the object side is determined by the assumed position of the article and the tip of the high-voltage applying electrode on the object side. And the outer peripheral portion of the electrostatic coating device is substantially covered with an insulator except for the above-mentioned roughly grounded electrode and a portion that emits paint particles to the object to be coated. In this case, the change in the current value detected at the reference electrode due to the abnormal arrangement of the object to be coated occurs more remarkably and reliably, and it is possible to more stably detect such an abnormal state. Becomes

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an outer shape of a tip portion of an embodiment of an electrostatic coating device according to the present invention;

FIG. 2 is a graph showing a time-dependent change in a current value flowing through a reference electrode and a stain amount of a coating apparatus,

FIG. 3 is a perspective view schematically showing the outer appearance of a tip portion of another embodiment of the electrostatic coating apparatus according to the present invention;

FIG. 4 is a cross-sectional view schematically showing a tip structure of a rotary atomizing electrostatic coating apparatus as one embodiment of the electrostatic coating apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Electrostatic coating device, 11 ... Hollow shaft, 12 ... Cup (high voltage application electrode), 13 ... Paint supply nozzle, 14 ... Paint supply port, 15 ... Air ring, 16 ... Air outlet hole, 17 ... Air inlet Reference numeral 20: Reference electrode 21: Ammeter for monitoring the current value 22: Cover made of synthetic resin 23: Ground wire 30: Coating object A: Coating object from the tip of the high voltage applying electrode (cup 12) Distance to the assumed position of the location. B: Distance from the tip of the high voltage application electrode to the reference electrode.

Claims (5)

[Claims] In an electrostatic coating apparatus having a mechanism for atomizing a paint and an electrode mechanism for applying a high voltage to the paint, a position of the high-voltage applying electrode opposite to the workpiece from a tip of the workpiece on the workpiece side. An electrostatic coating apparatus comprising: a substantially grounded electrode; and detecting a current value flowing into the electrode to control a coating state. 2. The method according to claim 1, wherein the control of the coating state is at least one selected from the group consisting of a control of a paint discharge amount, a high voltage application state, a conveyance state of an object to be coated, and a warning to an operator. The electrostatic coating device according to claim 1, wherein the electrostatic coating device is a control. 3. The distance between the generally grounded electrode and the tip of the high voltage application electrode on the object side is greater than the distance between the assumed position of the object and the tip of the high voltage application electrode on the object side. The electrostatic coating device according to claim 1, wherein the value is also large. 4. An outer peripheral portion of the electrostatic coating apparatus is substantially covered with an insulating material except for the above-mentioned substantially grounded electrode and a portion for discharging paint particles to an object to be coated. Item 4. The electrostatic coating device according to any one of Items 1 to 3. 5. The electrostatic coating device according to claim 1, wherein the electrostatic coating device is a rotary atomizing electrostatic coating device.