JPS6096794A - Method and apparatus for electrodeposition coating - Google Patents

Abstract

PURPOSE:To perform electrodeposition coating to an article to be coated having a different area in a constant film thickness, by detecting the coating area of the article to be coated and changing the effective area of an opposed electrode plate corresponding to the detection value while supplying a current between the article to be coated immersed in an electrodeposition paint and said electrode plate. CONSTITUTION:In an apparatus wherein an article 1 conveyed through a hanger 2 by an overhead conveyor 3 is immersed in the electrodeposition paint 7 in an electrodeposition tank 7 and a current is supplied between the article 1 to be coated, contacted with buss bars 4, 11 electrically through a collector 5 and the hanger, and first and second opposed electrode plates 15, 28 arranged in the electrodeposition paint 7 to apply electrodeposition coating to the article 1 to be coated, the surface area of the article 1 to be coated is detected at a position B before immersion into the electrodeposition paint 7 by an area detector 23 such as a photoelectric tube. On the basis of this detection value, a contactor 27 is turned ON or OFF by a control means 25 and the supply of a current to the above mentioned second opposed electrode 28 is turned ON or OFF corresponding to the area of the above mentioned article 1 to be coated and the entire effective areas of the opposed electrodes 15, 28 are changed to constantly control the film thickness of an electrodeposition film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrodeposition coating method and an apparatus therefor, and more particularly to an electrodeposition coating method and an apparatus therefor in which the counter electrode area is made variable according to the electrodeposition area of an object to be coated.

Prior art electrodeposition coating is a coating in which when a water-based paint is dispersed or dissolved in water, the paint particles are electrophoresed using the fact that they are positively or negatively charged, and the paint is deposited on the object to be coated. This method is widely used for coating various industrial products such as automobile bodies, electric refrigerators, and electric washing machines because the resulting coating film has excellent corrosion resistance.

There are two types of electrodeposition coatings: anionic and cationic. Conventionally, anionic electrodeposition has been mainly used because the paint is inexpensive and has relatively good coverage. However, the anionic electrodeposition coating method has the problem of leaching of the metal or chemical coating from the object to be coated.
Recently, cationic electrodeposition coating methods have come into use. That is, this method has the advantage that the adhesion of the coating film to the object to be coated is good, and the corrosion resistance of the resulting coating film is superior to that of anionic electrodeposition coatings.

Conventionally, electrodeposition coating, for example, cationic electrodeposition coating, has been carried out using an apparatus as shown in FIGS. 1 and 2. That is, in the same figure, when a hanger 2 carrying an object 1 to be coated, such as an automobile interior, on which a chemical conversion film has been formed, is conveyed by an overhead conveyor 3, first
At the rear end position A of the busper 4 (the position where it is carried into the electrocoating line), the current collectors 5a and 5b of the current collector 5 provided on the hanger 2 are connected to the negative electrocoating voltage from the first DC power supply 6. is applied to the first bus spar 4.

However, at this position, the object 1 to be coated is still in the electrodeposition bath 1f! 1
Since it is not immersed in the cationic electrodeposition coating bath 7 contained in the cationic electrodeposition coating bath 9, no current flows therein.

In this way, the hanger 2 is connected to the overhead conveyor 3.
When the first limit switch 8 is activated and the activation signal is sent via the wiring 9 to the control unit 6a of the DC power supply 6, for example, the input to the SCR and sent to the contactor 1 via a relay circuit (not shown) provided in the control section 6a.
Turn off 0. Therefore, no voltage is applied to the object to be coated 1 from the time the object to be coated 1 starts to be immersed in the electrocoating paint bath 7 until the object to be coated 1 is half immersed in the C position as described later. Not done.

On the other hand, even if the signal is input to the control section, the predetermined negative voltage is maintained applied to the second bus spar 11, so that the second bus spar 11 is engaged and completely collapsed. Another object 1 to be coated continues to be electrocoated. When the hanger 2 reaches position C along the overhead conveyor 3, the object 1 to be coated is in a half-submerged state. At this C position, the second
The limit switch 12 is activated, and the activation signal is sent to the control section 6a of the DC power supply 6 via the wiring 13, and a relay circuit (not shown) provided in the control section 6a.
Contactor 1o is turned on via A.

Therefore, a regular electrodeposition voltage is applied to the part of the object 1 immersed in the bath via the first busper 4, the current collector 5, and the hanger 2.

As the hanger 2 further travels on the overhead conveyor 3, the object 1 to be coated is further immersed in the bath and is completely immersed. During this time, the current collectors 5a151) are both engaged with the first busper 3, and a negative voltage is applied to the object 1 to be coated, which forms a cathode, and an anode connected to the DC power supply device 6 via a conductive wire 14. Electricity is applied between the plate 15 and the cationic electrodeposition paint to perform electrodeposition coating. When the zero position is reached, the current collector 5a engages with the first busper 3 and the current collector 5b engages with the insulator 16, and then the current collector 5a engages with the insulator 16 and the current collector 5b engages with the second busper 3. When the hanger further travels, the current collectors 5a and 5b
Both engage the second hanger 11. Furthermore, since the first buspar 3 and the second buspar 11 are both at the same potential, the transfer is smoothly performed while the coating voltage is applied to the object 1 to be coated. Next, another new object 1 to be coated is carried into the electrodeposition coating line and the same cycle as described above is repeated. In addition, in FIG. 2, the reference numeral 17 is a bottom anode. Also, during this period, the electrodeposition paint is applied to conduit 1.
8, pump P and filter F
The electrolyte is circulated through the conduit 2o to the electrodeposition bath 19.

However, in such conventional electrodeposition coating methods, an electrodeposition coating device in which the area of the anode plate remains constant is used, so when coating objects with different surface areas,
When electrocoating a workpiece with a large surface area, the film thickness becomes thin, while when electrocoating a workpiece with a small surface area, the film thickness becomes thick, making it extremely difficult to form a desired film thickness using the same equipment. There was a problem that.

OBJECTS OF THE INVENTION The present invention has been made in view of these conventional problems.Firstly, an object to be coated is immersed in an electrodeposition paint bath, and a gap between the object to be coated and a counter electrode plate is formed. The above-mentioned problems can be solved by an electrodeposition coating method characterized in that the effective area of the counter electrode plate is changed depending on the coating area of the object to be coated, in which the object is electrodeposited by applying electricity. The purpose is to resolve the issue.

Second, an electrocoating tank containing an electrocoating paint, an object conveying device, a first return electrode installed in the electrocoating tank, and a first
In an electrodeposition coating apparatus comprising a power supply connected to a return electrode and a workpiece, the workpiece conveying device has an area detection means for the workpiece and a cough area detection means connected to the inlet side of the workpiece conveyance device. It is an object of the present invention to solve the above-mentioned problems by an electrodeposition coating apparatus characterized in that a control means and a second counter electrode plate whose energization is controlled by the control means are provided in the electrodeposition bath. It is said that

Structure and Function of the Invention The method of the present invention using the electrodeposition coating JA apparatus according to the present invention will be explained below with reference to the drawings. FIGS. 3 and 4 are diagrams showing one embodiment of the present invention, and based on the figures, the method and apparatus thereof according to the present invention will be simultaneously explained using the case of cationic electrodeposition paint as an example.

That is, in the figure, an object to be coated 1, such as an automobile body, on which a chemical conversion film has been formed by treatment with a chemical conversion treatment liquid such as a phosphate, is conveyed by an object conveying device comprising a hanger 2 and an overhead conveyor 3. When it comes to
The current collector 5a of the current collector 5 provided on the hanger 2 is located at the rear end position ffA of the bus spar 4 (the position where it is carried into the electrodeposition coating line).

5b is the conductor 21 and branch conductor 2 from the DC power supply device 6
2 to which a negative electrodeposition coating voltage is applied.
comes into contact with buspar 4. However, at this position, the object 1 to be coated is not yet immersed in the cationic electrodeposition coating bath 7 used in the electrodeposition bath 19, so no current flows.

In this way, the hanger 2 is connected to the overhead conveyor 3.
When it reaches position B (the position just before the start of immersion), the first limit switch 8 is activated, and the activation signal is transmitted via wiring 9 to the control unit 6a of the DC power supply 6, such as a Zyristor SCR. is input to the contactor 1 via a relay circuit (not shown) provided in the control section 6a.
Turn off 0. Therefore, no voltage is applied to the object 1 from the time the object 1 starts to be immersed in the electric paint bath 7 until the object 1 is half immersed in the C position as described later. Not done. At this position B, the area of the object to be coated 1 is detected by the object area detection means 23. As the object area detecting means 23, for example, there is a method of detecting the type of the vehicle body, which is the object to be painted, using a phototube, and detecting the area to be coated, which is stored in advance for each vehicle type in a control direction.

On the other hand, even when the signal is input to the control section 6a, a predetermined negative voltage is maintained applied to the second buspar 11, and the second buspar 11 is engaged for this purpose. Another object 1 to be coated, which is completely immersed, continues to be electrodeposited. When the hanger 2 reaches position C along the overhead conveyor 3, the object 1 to be coated is in a half-submerged state. In this C position, the second limit switch 12 is activated, and the activation signal is transmitted to the control unit 6 of the DC power supply device 6 via the wiring 13.
a and turns on the first contactor 10 via a relay circuit (not shown) connected to the control section 6a. A regular electrodeposition coating voltage is applied via the first busper 4, current collector 5, and hanger 2.

When the hanger 2 further travels on the overhead conveyor 3, the object 1 to be coated is further immersed in the bath and is completely immersed in the bath. During this time, the current collectors 5a and 5b are both engaged with the first busper 3, and are connected to the object 1 to be coated, which forms a cathode by applying a negative voltage, to the DC power supply device 6 via the conductor 14. Electricity is applied through a cationic electrodeposition paint between the first anode plate 15 and the RI electrodeposition coating. When reaching position D, the collector 5a engages with the first busbar 3 and the collector 5b engages with the insulator 16. When the hanger 2 further travels, both collectors 5a and 5b engage with the second busbar. 11. However, since both the first busper 3 and the second busper 11 have the same potential, the object to be coated 1
The transfer is carried out smoothly while the coating voltage remains applied.

Next, when the object to be coated reaches point E, if the area of the object to be coated 1 is small, for example, if the area of the object to be coated is 50 m2, then the first
The area of the anode, which is the return electrode plate 15 and the polarization plate 17, is 12.
The area was 5 m2, and the ratio of the area of the object to be coated to the area of the anode was 4=1. In this case, the area is detected by the object area detection means 23 and input to the control device 25 via the operating line 24, and in the case of a small area as described above, the object 1 reaches point E. Even if it passes, the third limit switch 2
6 is not activated and the second contactor 27 is kept off. Therefore, the anode, which is the second counter electrode plate 28, is not energized.

On the other hand, when the area of the object to be coated 1 is large, the area is detected by the object to be coated @ area detection means 23 and inputted to the control device 25 via the actuation line 24, Since the limit switch 26 is activated,
When the object 1 to be coated reaches the E position, the third limit switch 26 is activated, and as a result, the contactor 2a of the box 2 is turned on, and the anode, which is the second return electrode plate 28, is energized. .

For this reason, for example, the return electrode 15 of the box 1 initially has 12.5
The anode area was increased from m2 to 17.5 m2 by energizing the second counter electrode plate 28 and the polarization plate 29. Therefore, the polarity ratio is 4 to 1 for the surface area of the object 1 to be coated, which has a large surface area of 70 m2, and the same polarity ratio as in the case of a small surface area of the object to be coated can be obtained.

Next, another new object 1 to be coated is carried into the electrodeposition coating line, and the operation is repeated in the same cycle as described above. The object 1 to be coated after electrodeposition coating is lifted out of the bath, and then, at the end point of the second busper 11, the current collector 5b and then the current collector 5a are separated from the second hasper 11, and then A-
It is conveyed to the next process by the par head conveyor 3. During this time, the electrodeposition paint is partially extracted from the conduit 18 and circulated through the conduit 10 to the electrodeposition bath 19 via the pump P and filter F.

The above has described an electrodeposition coating method in which the area of the return electrode plate is changed in two stages, but it is of course possible to change the area in more stages.

Moreover, although the above description has been made regarding cationic electrodeposition coating, it goes without saying that anionic electrodeposition coating can also be carried out in the same manner.

Effects of the Invention As described above, the first invention of the present application immerses an object to be coated in an electrodeposition paint, and applies electricity between the object to be coated and a return electrode to electrolyte the object. In the method of electrodeposition coating, the effective area of the counter electrode plate is changed according to the coating area of the object to be coated. Even when coating is applied, the effective area for electrodeposition coating on the return electrode plate can be changed according to changes in the coating area, so the electrode ratio can be kept constant, and therefore the coating thickness is always constant. Electrodeposition coating can be performed.

In addition, when painting objects with a large area to be coated, if you use conditions that increase the film thickness, such as increasing the voltage or increasing the solid content, in order to obtain a specified amount of film thickness, In the conventional method, a coated object with a small coating area has a film thickness exceeding the specified value, whereas the method of the present invention allows the specified film thickness to be maintained.

Further, the second invention of the present application provides an electrodeposition tank containing an electrodeposition paint, a coating object conveying device, a first counter electrode plate provided in the electrodeposition tank, and a first counter electrode plate. In the electrodeposition coating apparatus, the electrodeposition coating apparatus includes a power supply connected to the object to be coated and a power source respectively connected to the object to be coated. , the electrodeposition coating apparatus is characterized in that the electrodeposition tank is provided with a second counter electrode whose energization is controlled by the control means, so that the area of the object to be coated installed on the delivery side is Since the detection means can detect the coating area of the object to be coated, and the control device can control the energization to the second return electrode according to the coating area, the polarity ratio can be kept constant. Electrodeposition coating can be performed with a film thickness of . In addition, the area facing the tooth can be changed by controlling the energization to the second return electrode using the control device without changing various electrodeposition conditions within the same device, making work management extremely easy. Moreover, the equipment cost is low.

[Brief explanation of drawings]

Figure 1 shows a conventional electrodeposition coating device.
3 is a schematic plan view of the apparatus, FIG. 3 is a schematic sectional view without showing the electrodeposition coating apparatus according to the present invention, and FIG. 4 is a schematic plan view of the N coating apparatus according to the present invention. DESCRIPTION OF SYMBOLS 1...Object to be coated, 2...Hanger, 3...Overhead competition A7, 6...Power source, 7...Electrodeposition paint, 15.17...First counter electrode plate, 19. . . . Electrodeposition tank, 23 . . . Area detection means for the object to be coated, 25 . . . Control means, 28. 29 . . . Second return electrode plate. Patent applicant Nissan Motor Co., Ltd.

Claims (2)

[Claims] (1) In a method of electrocoating the object by immersing the object in electrodeposition paint and applying electricity between the object and the return electrode,
An electric @ coating method characterized in that coating is performed by changing the effective area of the return electrode according to the coating area of the object. (2) An electrodeposition tank containing electrodeposition paint, a coating object conveyance device, a first return electrode provided in the electrodeposition tank, and a respective one between the first return electrode plate and the object to be coated. In an electrodeposition coating apparatus comprising a connected power supply, an area detecting means for the object to be coated is provided on the inlet side of the object conveying device, a control means connected to the area detecting means, and an area detecting means for detecting the area of the object to be coated, and a control means connected to the area detecting means; a second whose energization is controlled by the control means;