JPS6037200B2 - Electrodeposition coating method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a lightning coating method.

In the lightning coating line for car bodies, etc., the so-called lightning tank method is often used, in which the lightning coating voltage is applied to the object to be coated and the coating begins to soak into the coating. This method has the disadvantage that steps are likely to occur on the vertical surface of the coated object as an initial problem during bonding, and this disadvantage is particularly noticeable when cationic electrodeposition paint is used. The drawback is that it requires a large amount of correction and sharpening man-hours.

In addition, as a two-stage voltage method, a voltage slightly lower than the second stage voltage is applied from the start of immersion to the complete immersion of the object to be coated, and then the second stage voltage is applied after the object is fully immersed to complete the tortoise coating. A method is also known in which the first stage voltage is set to a current that is considerably higher than the paint deposition starting current value (the current value per unit area of the object to be coated for the electrodeposition paint to start depositing on the object). Since it was set so that it would flow onto the coating, there was a problem in that the drawbacks of the energized tank method described above could not be completely overcome.

On the other hand, in the method of applying electricity after the object to be coated is completely immersed, it is generally said that the surface of the paint film is good, but even if the application of voltage is started with ramp control that gradually increases to the coating voltage. Even so, the peak of the initial current is still high, so gas pinholes are likely to occur as an initial problem. Furthermore, it is necessary to set the output current value of the DC power supply to a high value, and when the collector on the vehicle body that is fully submerged comes into contact with the bus bar to which voltage is applied, an overcurrent flows and sparks are generated. Due to the ease of production, etc., there is a drawback that equipment costs and maintenance costs are relatively high compared to the number of units produced. The present invention has been made in view of the above-mentioned points, and its purpose is to eliminate the above-mentioned drawbacks and difficulties. Before dipping, the object to be coated is connected to a power source for electrodeposition, and at least immediately before dipping, the voltage applied from the power source for electrodeposition is controlled to the atmosphere, and after the object to be coated starts dipping, The object is to apply a voltage so as to have a value lower than the lower limit of the paint deposition current density so that the object to be coated is half submerged, and then to perform coating by changing the voltage to a coating voltage.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the invention. In the figure, when a hanger 2 carrying an object 1 to be coated, such as an automobile body, which has been treated with a chemical conversion treatment liquid such as phosphate to form a chemical conversion film, is conveyed by an overhead conveyor 3, a first At the rear end position A of the bus bar 4 (the position where the bus bar 4 is carried into the coating line), the current collectors 5a and 5b of the current collector 5 provided on the hanger 2 connect the conductor 7 and the branch conductor 8 from the DC power supply device 6. and contacts the first bus bar 4 to which a negative electrodeposition coating voltage is applied. but,
In this position, the coating material 1 is still in the electrocoating bath 10', the inner surface of which is lined 9.
1 is not submerged at all, so no current flows. Therefore, no spark is generated even in a partially engaged state. When the hanger 2 travels along the overhead conveyor 3 and reaches the B position (the position just before the start of bonding) as described above, the first limit switch 12 is activated, and the activation signal is transmitted through the wiring 13 to direct current. The signal is input to the control section 6a of the power supply device 6, and turns off the contact 14 via a relay circuit (not shown) provided in the control section 6a.

Therefore, no voltage is applied to the object to be coated 1 from the time the object to be coated 1 starts to immerse into the electrodeposited paint layer 11 until the object to be coated 1 is half submerged at position C 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 bar 16, and therefore the second bus bar 16 is engaged and fully submerged. Another piece of paint 1 continues to be electroplated.

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 limit switch 17 is activated, and its activation signal is input to the control section 6a of the DC power supply 6 via the wiring 18, and is connected to the control section 6a or via the relay circuit. Turn on 14. Therefore, a regular electrodeposition voltage is applied to the portion of the object 1 immersed in the margin through the first bus bar 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 eventually completely submerged.

During this time, the conductors 5a and 5b are both engaged with the first bus bar 3, and are connected to the object 1 to be coated, which forms a cathode by applying a negative voltage, and the DC power supply device 6 via a conductive wire 19. Electricity is applied between the anode plate 21 housed in the diaphragm chamber 201 and the anode plate 21 housed in the diaphragm chamber 201 through a cationic electrodeposition paint layer to perform electrodeposition coating. When the hanger 2 reaches the D position, the conductor 5a is connected to the first bus bar 3 and the conductor 5b is connected to the insulator 1.
5, then the conductor 5a engages with the insulator 15, the conductor 5b engages with the second bus bar 16, and when the hanger 2 further travels, both the conductors 5a and 5b engage with the second bus bar 16. engage with. Furthermore, since the first bus bar 3 and the second bus bar 16 are both at the same potential, the coating voltage is applied to the object 1 and the coating is smoothly carried out. Next, another new coated material 1 is carried into the Kameka coating line and the same cycle as described above is repeated.

The object 1 to be coated, which has been coated with glaze coating, is lifted out of the bath, and then placed at the terminal point of the second bus bar 16 by the current collector 5b.
However, after the current collector 5a is separated from the second bus bar 16, it is transported to the next process by the overhead conveyor 3. In addition, in the figure, 22 is a ground wire. Second
The figure shows a second embodiment of the invention.

In the same figure, a hanger 102 on which an object 101 to be coated, such as an automobile body, which has been treated with a chemical conversion treatment liquid such as phosphate to form a chemical conversion film, is transferred to an overhead conveyor 103.
When the rear end F of the bus bar 104 is conveyed by
At this position, first, the current collector 105 provided on the hanger 102 engages with the bus bar 104 to which a conductive wire 107 is connected from the DC power supply 106 and a negative box coating voltage is applied. However, at this position, the object 101 to be coated is still
Since the electrodeposition bath 110' whose inner surface is lined 109 is not immersed in the cationic electrodeposition paint 111 contained therein, no current flows. Therefore, the current collector 105
Even if the current collector 105 is only partially engaged with the bus bar 104, no spark is generated when the current collector 105 starts to engage with the bus bar 104, for example. As described above, when the hanger 102 reaches the G position (position just before the start of bonding) on the overhead conveyor 03, it comes into contact with the first limit switch 112 and activates the switch, and the activation signal is transmitted via the wiring 113. The control unit 10 of the DC power supply device 106
6a, which causes the control circuit of the control unit 106a to operate, and the silicon-controlled rectifier path (
By controlling the voltage applied to the gate of the SCR, the voltage applied from the SCR to the bus bar 104 is, for example, 15 V, so that a current considerably smaller than the paint deposition current density flows through the object to be coated.

That is, the object to be coated further advances from position G and begins to immerse into the electrodeposited paint layer 111, and a voltage of -5V is applied to the object to be coated 101 until just before it is half immersed. When the hanger 102 travels along the overhead conveyor 103 and reaches the H position, the object 101 to be coated is in a half-submerged state.

The position of the object to be coated 101 at this time is indicated by a two-dot chain line in FIG. The second limit switch 117 is activated at this H position, and the activation signal is input to the control unit 106a of the DC power supply 106 via the wiring 118,
The third limit switch 124 is actuated by the preceding removal of the object to be coated 101 from the tank, and this actuation signal is input to the control section 106a via the wiring 123.
The control circuit 06a operates and the SC of the DC power supply 106
By controlling the pulse signal applied to the gate of R, the voltage applied from the SCR to the bus bar 104 via the conductive wire 107 is controlled to rise to a regular electrodeposition coating voltage. That is, when the object to be coated 101 is half-submerged, a negative voltage whose rise is controlled is applied to the object to be coated, and another object to be coated 101 in front has just appeared or retracted (position K). Therefore, in this embodiment, only one object to be coated 101 can be placed in the tank 110 at a time. In this way, the object to be coated 101 is completely immersed from the semi-immersed state, and the anode is connected to the object to be coated 101 and the DC power supply device 106 via the conductor 119 through the conductor 119 and stored in the diaphragm chamber 120' until it is time to take a bath. Board 12
1 and 1 through the cationic electrodeposition paint layer while applying a regular coating voltage to complete the electrodeposition coating. ·next,
Table 1 shows the test conditions and test results of a test example conducted using the method of the second example and a comparative example conducted using the same method as the test example but with different conditions.

The test objects to be coated were automobile bodies (5 test examples and 5 comparative examples, total 1 car body) on which a phosphate conversion film was formed as a pretreatment.
0 units), and La.0 units on the actual line. There are intral results. In addition, the applied voltage 1 in the same table is the low voltage applied from just before the car body starts immersing in the bath until it is half immersed, and the applied voltage 2 is the low voltage applied to the car body from the time it is half immersed until it is qualified. Electrodeposition coating voltage. Note that the electrodeposition characteristics in Table 1 are under the condition of an applied voltage of 0.
Table 1 In the above example, in the section where a minute voltage of -5V is applied, the current density on the car body surface in contact with the electrodeposited paint layer is much lower than the lower limit of the paint deposition current density. Therefore, it is estimated that the current density is considerably lower than the current density at which the paint is abnormally deposited.

{b) The surface of this car body is simply coated with lightning paint bath, and {c) The surface area of the car body is increasing at a rate corresponding to the conveyance speed of the conveyor. Next, in the rising section of the dew coating voltage, the above {a}, {b}
Since the voltage is increased to the normal coating voltage under the conditions of {c' and {c', the time that the car body surface exists under the current density at which paint is abnormally deposited is short, and the lightning electrophoresis phenomenon occurs on the car body surface and in the vicinity of the surface. Since the electroosmotic phenomenon, the electrodeposition phenomenon, and the electrolysis phenomenon proceed in a mutually stable state, no stepping occurs. Furthermore, in the haze coating voltage application section, the peak of the current value disappears due to the reasons {b} and [c} above, and as a result, rapid gas generation on the surface of the coating is suppressed, so that the coating film It is considered that no gas pinhole remained inside. On the other hand, in the above comparative example,
- In the voltage application section, the current density on the surface of the car body that is in contact with the rigid electric paint is estimated to be close to the lower limit of the paint deposition current density or slightly exceed the lower limit.

(e} Therefore, in addition to mere adhesion of paint grade, it is determined that a slight electrodeposited coating film is formed on the surface of the vehicle body. Also, {f} a value close to the lower limit value or the lower limit value It is thought that there is a region in which electrical paint is abnormally deposited in a region slightly exceeding is looser than in the above test example, and the time the car body surface is kept under {f} conditions is longer. As a result, horizontal stripes, which are considered to be a step phenomenon in the early stage, occur on the flower surface, and Therefore, if the applied voltage 1 is further increased, it is estimated that the same vertical steps as in the case of a condensation tank will be reproduced. As described above, in the decoating coating method according to the present invention, before the object to be coated or being immersed in the haze paint bath, the object to be coated is connected to the haze deposition power source, and
At least immediately before immersion, the voltage applied from the dewing power source is controlled to a mist, and after the object to be coated starts immersion, the voltage is applied so that the current density of paint deposition becomes a value lower than the lower limit value. After the object to be coated is partially immersed, the voltage is applied to the dew coating voltage to perform the coating, so that the step on the vertical surface of the object to be coated, which occurs when using the conventional method, does not occur. Furthermore, the occurrence of gas pinholes is completely eliminated.

In addition to the above-mentioned effects, in the method of the first embodiment, the bus bar is arranged in two stages, and the object to be coated is always immersed in the latter stage and is being electrocoated, so that it can be used in a mass production line. It is suitable for
Compared to the stage energization method, the equipment costs for the power supply device and related control system are lower.

In addition, in the method of the second embodiment, the voltage applied to the object from the start of immersion to half-immersion is applied at a minute voltage, for example, 15
Since the bolts are used, a minute current lower than the paint deposition current density is applied to the surface of the bonded part, and as a result, the above-mentioned four glaze coating phenomena are promoted more stably than in the case of the first embodiment. .

The example shown in FIG. 2 has a configuration suitable for a small to medium-sized electrodeposition line, but if this equipment is installed in multiple rows, it can be applied to a mass production line that can form a high-quality haze coating.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the military uniform coating method according to the present invention, and FIG. 2 is a schematic diagram showing a second embodiment. 1,101...Object to be coated, 2,102...
・Hanger, 3,103...Overhead conveyor,
4, 16, 104... bus bar, 5...
・Current collector, 5a, 5b, 105... Current collector, 6
, 106... DC power supply magic, 6a, 106a...
...control unit, lo, 110...electrodeposition bathtub, 1
1,111...Cationic electrodeposition paint grade, 12,1
7,112,117'124...Limit switch, 1
4...Contact, 15...Insulator, 21,1
21...Anode plate. Figure 1 Figure 2

Claims (1)

[Claims] 1. Before the object to be coated is immersed in the electrodeposition paint bath, the object to be coated is connected to a power supply for electrodeposition, and at least immediately before immersion, the voltage applied from the power supply for electrodeposition is controlled to the atmosphere. After the object to be coated starts to be immersed, a voltage is applied so that the current density for coating is lower than the lower limit of the paint deposition current density, and after the object to be coated is half immersed, the voltage is changed to the electrodeposition voltage and the coating is started. An electrodeposition coating method characterized by: