JPH11293496A - Electrodeposition coating method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the coating defect without enlarging the distance between materials to be coated by cutting the energization to the electrode successively from an electrode at the position, where the material is passed, in accordance with the movement of the material to be coated till the start of the energization to the succeeding material to be coated, thereby hardly causing abnormal current between the preceding and the succeeding materials to be coated. SOLUTION: A plurality of electrodes positioned at the inlet side of the material to be coated is divided into blocks of the adequate number of the electrodes and current is preferably supplied and cut from block to block. A switch S closed when the whole preceding material to be coated (automobile body B1 ) is sunk in a coating material is opened to synchronize with the passage of the body B1 to lower the potential of both side electrodes of the succeeding B0 and the potential difference between B0 and B1 is decreased to almost prevent the generation of the abnormal current. The switch S is closed when the whole body B0 is sunk in the coating material and connected to a cathode and then, the bodies B0 and B1 have the same potential and the electrodeposition coating of the body B0 is started without causing the abnormal current between the B0 and the B1 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electrodeposition coating method and an electrodeposition coating apparatus applied to, for example, undercoating of a car body.

[0002]

2. Description of the Related Art In an electrodeposition coating line for an automobile as described above, for example, using an overhead conveyor,
Continuously immersing the car body in the coating solution in the electrodeposition tank,
For example, after the electrode arranged in the electrodeposition tank is used as an anode, the body is used as a cathode, and a DC voltage is applied, the inside of the tank is moved by a predetermined distance (a predetermined time), and then the coating is pulled up from the coating liquid to perform continuous coating. The resin component of the paint precipitates on the body while moving through the paint liquid, and a coating film is formed.

[0003]

However, in such an electrodeposition coating line, since the body of the automobile is continuously immersed in the electrodeposition tank, the current flowing through the electrodeposition tank at the entrance side of the electrodeposition tank precedes. There is a problem that a potential difference is generated between the body and a subsequent non-energized body that is being immersed in the tank, and an abnormal current is generated between the bodies.

That is, as shown in FIG. 8, a preceding body B1 is connected to a cathode of a power supply device, while
The rod-shaped electrodes P disposed on both sides thereof along the movement path of the body are respectively connected to the anode, so that the tip of the succeeding body B0 immediately after entering the tank not yet connected to the cathode has a positive pole. Therefore, the generation of oxygen gas based on the electrolysis of water, which is a coating liquid component, causes a striped coating defect on the subsequent body B0.

Table 1 shows the time-dependent change in the resistance value of the film formed on the tip of the succeeding body B0 when the potential difference between the preceding body B1 and the anode P is 250 V as described above. And the preceding body B1 and the succeeding body B0
The current flowing between the two bodies B1 and B0 is calculated by setting the potential difference between the two bodies to 125 V (intermediate value of the potential difference between the anode P and the body B1).

[0006]

[Table 1]

As shown in this table, the entire body B0 is completely immersed (completely immersed) after the tip of the succeeding body B0 begins to be immersed in the coating liquid, and is connected until the body B0 is connected to the cathode. In 50 seconds, the resistance Rf of the film becomes 0.47-
As a result of changing to 2.8Ω, 37 to between body B1 and B0
It is calculated that a current of 22 A (average current value: 29.5 A), that is, an electric quantity of 1,475 coulombs (29.5 A × 50 sec) flows, and oxygen gas corresponding to this electric quantity is generated. In addition, both bodies B1-B0
The distance d between them is 700 mm, and the resistance R
d was calculated as 2.9Ω.

In order to avoid coating defects due to such abnormal currents, it is necessary to increase the spacing between the bodies in continuous coating, thereby increasing the total length of the electrodeposition tank and increasing the conveyor speed. There is a problem that the equipment length of the coating line is increased, the equipment cost is increased, and the layout of the line is restricted, and solving such a problem has been a problem of the conventional electrodeposition coating.

In the above, the problem of the prior art has been described by taking as an example the case of cationic electrodeposition coating (the object to be coated is a cathode) which is excellent in corrosion resistance and is the mainstream of electrodeposition coating. There is a similar problem based on the abnormal current also in the anion electrodeposition coating connected to the above (in this case, hydrogen gas is generated since the tip of the subsequent body B0 is a negative electrode), and the same problem as described above. have.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the conventional electrodeposition coating, and a coating film is applied to the object while the object is continuously moved in a coating liquid. In continuous electrodeposition coating to be electrodeposited, there is almost no abnormal current between the preceding and subsequent workpieces, preventing coating defects without increasing the gap between workpieces in continuous electrodeposition coating It is an object of the present invention to provide an electrodeposition coating method capable of reducing the length of electrodeposition coating equipment and an electrodeposition coating apparatus used for such electrodeposition coating.

[0011]

According to a first aspect of the present invention, there is provided an electrodeposition coating method in which an object to be coated is continuously immersed in a coating liquid in the electrodeposition tank and disposed in the electrodeposition tank. In the electrodeposition coating in which a coating film is electrodeposited on the object to be coated while moving in the tank along the plurality of electrodes, the energization of the electrodes is performed according to the movement of the object, and the subsequent object to be coated is applied. Until the energization of the electrode is started, the electrode is sequentially cut off from the electrode at the position where the object has passed, and the electrodeposition coating method according to the present invention is characterized in that In the coating method described in the above, among the electrodes, a plurality of electrodes positioned on the entrance side of the object to be coated is divided into an appropriate number of blocks, and the configuration is such that the block is energized or disconnected. As described above, such a configuration in the electrodeposition coating method It is a means for solving the problems of come.

According to a third aspect of the present invention, there is provided an electrodeposition coating apparatus including a plurality of electrodes arranged along a moving direction of an object to be coated in an electrodeposition tank, and an inlet of the object to be coated among the electrodes. The electrodeposition coating apparatus according to claim 4 of the present invention is arranged along the moving direction of the object to be coated, wherein a plurality of electrodes located on the side are connected to a power source via independent switch means. A plurality of electrodes are provided in the electrodeposition tank, and a plurality of electrodes located on the entrance side of the object to be coated among these electrodes are divided into an appropriate number of blocks, and independent switch means are provided for each block. The present invention is characterized in that it is connected to a power supply via a power source, and the configuration of such an electrodeposition coating apparatus is a means for solving the above-mentioned conventional problems.

[0013]

In the electrodeposition coating method according to the first aspect of the present invention, energization of a plurality of electrodes arranged in the electrodeposition tank along the moving direction of the object to be coated is performed to advance the object to be coated. It is intermittent (on-off) accordingly. That is, the energization to the electrode disposed on the entrance side of the object to be coated of the electrodeposition tank is sequentially cut off from the electrode at the position where the object to be coated passes, and until the energization to the subsequent object to be coated is started. During this time, the following non-energized object is prevented from passing through the vicinity of the energized electrode because the non-energized object is kept in the cutoff state. The potential difference becomes extremely small, so that an abnormal current is hardly generated between the objects to be coated, and the occurrence of defective coating is eliminated without increasing the distance between the objects to be coated.

That is, as shown in FIG. 1, the switch S, which is closed when the preceding object to be coated, that is, the vehicle body B1 is completely immersed in the coating liquid, is opened in synchronization with the passage of the body B1, so that the subsequent object is opened. Since the potential of the electrodes P on both sides of the body B0, which is the object to be coated, becomes lower, the body B1 -B0
The potential difference between them becomes very small, so that an abnormal current hardly occurs. The potential difference at this time is estimated to be about one-fifth of the conventional method, and the amount of electricity flowing between the bodies B1 and B0 is reduced to one-fifth by the potential difference.
95 coulombs. This amount of electricity is only 0.4% or less of the amount of electricity required for electrodeposition coating.

The switch S opened in response to the passage of the body B1 is closed again when the subsequent body B0 is completely immersed in the coating liquid and connected to the cathode, but is closed again by the connection of the body B0 to the cathode. Since the electric potential is the same as that of the body B1, no abnormal current is generated between the bodies B1 and B0.
Electrodeposition coating is started.

According to a second aspect of the present invention, there is provided an electrodeposition method in which a plurality of electrodes disposed in an electrodeposition tank and located on the inlet side of an object to be coated. Since the electrodes are appropriately divided into blocks and energization to these electrodes is intermittently intermittently performed for each block, compared to a case where the individual electrodes are independently turned on and off, the connection between the power supply device and the electrodes is reduced. In addition to simplifying the wiring between them, the number of switches and the like as means for turning on and off the electric current and limit switches and photocouplers as means for detecting the position of the object to be coated are reduced, and equipment costs are reduced. It will be.

According to a third aspect of the present invention, there is provided an electrodeposition coating apparatus including a plurality of electrodes disposed in an electrodeposition tank along a moving direction of the object to be coated. Are connected to a power supply via independent switch means, respectively, and thus have a structure suitable for carrying out the electrodeposition coating method according to the present invention.

According to a fourth aspect of the present invention, there is provided an electrodeposition coating apparatus including a plurality of electrodes disposed in an electrodeposition tank along a moving direction of the object to be coated. Are divided into an appropriate number of blocks, and each block is connected to a power supply via an independent switch means. Therefore, compared to a device connected to each individual electrode, In addition, the wiring becomes simpler, the number of switches and position detectors are reduced, and the cost of the apparatus is reduced.

[0019]

According to the electrodeposition coating method according to the first aspect of the present invention, the object to be coated has passed according to the movement of the object until the energization of the subsequent object to be coated is started. Since the energization to the electrode at the position is sequentially cut off, the potential difference between the preceding and following objects to be coated becomes extremely small, and an abnormal current between the objects to be coated can be almost prevented. Since the occurrence of defective coating is eliminated without increasing the distance between the coated objects, an extremely excellent effect that the conveyor speed can be reduced and the length of the electrodeposition coating equipment can be reduced can be obtained.

[0020] As an embodiment of the electrodeposition coating method according to the present invention, in the coating method according to the second aspect, a plurality of electrodes located on the entrance side of the object to be coated are divided into blocks, and energization to these electrodes is blocked. Since the intermittent operation is performed every time, the wiring can be simplified, and the number of components such as switches and photocouplers can be greatly reduced. Brought.

According to a third aspect of the present invention, there is provided an electrodeposition coating apparatus in which the plurality of electrodes located on the inlet side of the object to be coated in the electrodeposition tank are connected to a power source via independent switch means. With the configuration described above, the energization to the electrodes can be sequentially cut off according to the movement of the object to be coated, and the electrodeposition coating method according to the present invention can be smoothly carried out. The electrodeposition coating apparatus according to claim 4, wherein the electrodes are divided into blocks of an appropriate number and connected to a power supply for each block via independent switch means. In comparison with the above device connected to the switch means and the power supply,
Since the wiring becomes simple and the number of components of the switch means and the position detection means is reduced, an even more excellent effect that the cost of the apparatus can be greatly reduced is brought about.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings.

FIGS. 2 to 7 are cross-sectional explanatory views of an electrodeposition coating apparatus sequentially showing steps in a case where the electrodeposition coating method is applied to an undercoat of an automobile body as an embodiment of the electrodeposition coating method according to the present invention. It is.

The electrodeposition coating apparatus 1 shown in FIG. 1 comprises an electrodeposition tank T filled with a coating liquid L and an overhead head disposed on the electrodeposition tank T for continuously transporting an automobile body to be coated. It is mainly composed of a conveyor C and a plurality of rod-shaped electrodes P arranged on both sides of the electrodeposition tank T along the moving path of the automobile body.

The electrode P is an automobile body (object to be coated)
Are divided into three blocks every four, and each block is connected to the anode A of the power supply via switches S1, S2 and S3, respectively. All the remaining electrodes P are directly connected to the anode A without passing through a switch.

On the other hand, an automobile body as a workpiece is
It is designed to be continuously carried into the electrodeposition coating apparatus 1 in a state of being suspended by a hanger (not shown) on the over-head conveyor C, and is lowered at a predetermined position to reach the electrodeposition tank T.
Starts to be immersed in the coating liquid L, and when it is completely immersed in the coating liquid L, it is connected to a cathode of a power supply device (not shown) via a bus bar disposed along the overhead head conveyor C. I have.

FIG. 2 shows a body B which is a preceding object to be coated.
1 is completely immersed in the coating liquid L and shows a state immediately after being connected to the cathode. At this time, the switches S1, S2 and S3 are closed, all the electrodes P become positive potential, and the power of the body B1 is changed. Coating is started.

FIG. 3 shows a point in time when about 10 seconds have elapsed from the state shown in FIG. 2. As the body B1 advances to the left in the figure, the tip of the succeeding body B0 is immersed in the coating liquid L. However, since the rear part of the body of the preceding body B1 is located in front of the electrode P at the right end in the figure, and the tip of the succeeding body B0 is located away from the electrode P, energization to all the electrodes P is continued. ing.

FIG. 4 shows the state shown in FIG.
This indicates the state at the time when 0 seconds have elapsed, and the subsequent body B0
Since the front end of the vehicle body approaches the rightmost electrode P in the figure, and the rear body of the preceding body B1 has almost passed the electrode P belonging to the first block connected to the first switch S1. The switch S1 is opened, and the power supply to the four electrodes P (eight on both sides) belonging to the first block is cut off. The switches S1, S2, S3 are automatically opened and closed by output signals from limit switches, proximity switches, photocouplers and the like used as position detecting means for the bodies B1, B0.

FIG. 5 shows the state shown in FIG.
It shows the positional relationship between the bodies B1 and B0 at the time when 0 seconds have passed (30 seconds after the total immersion).
Is passing through the electrode P belonging to the second block connected to the second switch S2 and the rear body B0
Is close to the electrode P of the second block, the second switch S2 is opened, and the current supply to the four electrodes P (eight on both sides) newly belonging to the second block is cut off.

FIG. 6 shows the state shown in FIG.
In this state, the rear part of the body of the body B1 passes through the electrode P belonging to the third block connected to the third switch S3, and the front end of the body of the subsequent body B0 is connected to the electrode of the third block. Since P is approaching, the third switch S3 is opened, and the power supply to the four electrodes P (eight on both sides) belonging to the third block is further interrupted, and the twelve electrodes on the entrance side (24 on both sides) are turned off. The potential of the electrode P of the book becomes zero.
During this time, the electrodeposition coating is continued on the preceding body B1 with the remaining electrodes P.

FIG. 7 shows the state shown in FIG.
0 seconds, that is, when about 50 seconds have elapsed after the body B1 has completely submerged in the coating liquid L, indicating a state immediately before the subsequent body B0 has completely submerged. When submerged and connected to the cathode, switches S1, S
2 and S3 are all closed, and the electrodeposition coating on the subsequent body B0 is started.

As described above, in the electrodeposition coating method according to the present invention, the period from when the body B0 starts to be immersed in the coating liquid L to when it is completely immersed in the coating liquid L and connected to the cathode.
Since the power supply to the electrode P close to the body B0 is cut off, the potential difference between the preceding body B1 and the preceding body B1 is reduced, and an abnormal current hardly occurs between the two. Coating defects can be prevented without increasing the distance between B0, the length of the electrodeposition tank T can be shortened, and equipment costs and layout restrictions can be avoided.

In the above embodiment, an example is shown in which rod-shaped electrodes are used and the electrodes are divided into four blocks.
The present invention is not limited by the shape of the electrodes and the number thereof, and more precise control is possible by increasing the number of blocks. In addition, the connection between the electrodes can be simplified by replacing the block of the rod-shaped electrodes of several pieces with a plate-shaped integrated electrode having the same width.

In the above-described embodiment, the cation electrodeposition in which the object to be coated is connected to the cathode and the electrode is connected to the anode has been described. Needless to say, current can be prevented, and the same effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of an electrodeposition tank for explaining the operation of an electrodeposition coating method according to the present invention.

FIG. 2 is a process diagram showing a procedure of an electrodeposition coating method according to an embodiment of the present invention, and is a longitudinal sectional view of the electrodeposition coating apparatus showing a state immediately after the object to be coated is completely immersed.

FIG. 3 is a longitudinal sectional view of the electrodeposition coating apparatus showing a state after about 10 seconds have passed since the article to be completely immersed.

FIG. 4 is a vertical cross-sectional view of the electrodeposition coating apparatus, showing a state after about 20 seconds have passed from the complete immersion of the object to be coated.

FIG. 5 is a longitudinal sectional view of the electrodeposition coating apparatus showing a state after about 30 seconds have passed since the article to be completely immersed.

FIG. 6 is a longitudinal sectional view of the electrodeposition coating apparatus showing a state after about 40 seconds have passed since the article to be completely immersed.

FIG. 7 is a vertical cross-sectional view of the electrodeposition coating apparatus showing a state after about 50 seconds have passed from the complete immersion of the object to be coated.

FIG. 8 is a schematic plan view of an electrodeposition tank for explaining a conventional electrodeposition coating method.

[Explanation of symbols]

 1 Electrodeposition equipment T Electrodeposition tank L Coating liquid B1 Body (object to be coated) B0 Body (subsequent object to be coated) P electrode S, S1, S2, S3 Switch (switch means) A Anode (power supply)

Claims (4)

[Claims] An object to be coated is continuously immersed in a coating liquid in an electrodeposition tank, and the object to be coated is moved along a plurality of electrodes provided in the electrodeposition tank. In the electrodeposition coating for electrodepositing a coating film, the energization of the electrode is performed according to the movement of the object, and the position at which the object to be coated has passed until the energization of the subsequent object is started. An electrodeposition coating method characterized by sequentially cutting off from the electrodes. 2. The electrode according to claim 1, wherein a plurality of electrodes located on the entrance side of the object to be coated are divided into an appropriate number of blocks, and power is supplied or cut off for each block. Electrodeposition method. 3. An electrodeposition tank having a plurality of electrodes arranged along the moving direction of the object to be coated, wherein a plurality of electrodes located on the inlet side of the object to be coated among the electrodes are independent switches. An electrodeposition coating apparatus, wherein the apparatus is connected to a power source via a means. 4. An electrodeposition tank provided with a plurality of electrodes arranged along the moving direction of the object to be coated, and a plurality of electrodes located on the inlet side of the object to be coated among the electrodes have an appropriate number. An electrodeposition coating apparatus, wherein the apparatus is divided into blocks, and each block is connected to a power source via independent switch means.