JPH0210239B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in electrodeposition coating equipment.

Conventionally, one electrode is provided in an electrodeposition tank filled with water-dispersible or water-soluble electrodeposition paint, and the object to be coated that is transported in the electrodeposition tank is used as the other electrode, and the coating is applied between the two electrodes. A method is known in which electrocoating paint is deposited on the object to be coated by applying a constant direct current using a so-called energization tank method in which electricity is applied before the object is immersed in the electrodeposition tank. According to this electrodeposition coating,
It is possible to paint automobile bodies, etc. fairly well, but as mentioned above, the energizing tank method is used to pass a constant DC current between the electrode and the object to be coated, so when the object to be coated enters the tank, A drawback is that a large current flows through the object partially immersed in the electrodeposition bath, resulting in the formation of hatch marks, or undulations, on the surface of the coating.

In order to prevent hatch marks from forming on the coating surface, in Japanese Patent Publication No. 54-41617,
The electric current flowing between the object to be coated and the electrode is changed in the direction of conveyance of the object to be coated, and increases as it progresses in the direction of conveyance, that is, electrodeposition coating is performed with the current value at the bath entry section being reduced. We are proposing an electrodeposition coating method.

According to this electrodeposition coating method, it is possible to obtain an electrodeposition coating film with a better appearance without hatch marks, but in this method, the change in the current transport direction is It is generated by changing the distance from the object to be coated or the voltage value applied between this electrode and the object to be coated in the transport direction, so when changing the size of the electrode, it is necessary to change the size of the electrode. Prepare electrodes or
Alternatively, a specially shaped electrode must be prepared, and if the distance between the electrode and the object to be coated is changed, the distance from the electrode to the object to be coated must be increased toward the tank side. The electrodes have to be arranged diagonally, which requires a large space, which makes the electrodeposition bath quite large.Furthermore, when changing the voltage value applied between the electrode and the object to be coated, There are many drawbacks, such as the need for a device to change the voltage applied to the electrodes.

On the other hand, as the coating progresses on the object in the electrodeposition tank,
As the paint components in the paint adhere to the object to be coated, the concentration of the neutralizing agent in the paint increases, and the Coulombic efficiency of the paint decreases, resulting in a decrease in the film thickness of the paint film. . For this reason, in order to maintain a constant concentration of the neutralizing agent in the paint, a diaphragm chamber is installed in the electrodeposition tank along the conveyance path of the object to be coated. Electrodeposition coating equipment of a type that maintains a constant concentration of neutralizing agent in the paint by removing an amount of neutralizing agent commensurate with the film-forming component in the membrane chamber is increasingly used. In this type of electrodeposition coating apparatus, a paint whose neutralizing agent concentration is the same as that of the paint in the tank can be used as a replenishing paint, and the electrodeposition tank can be easily managed. In this type of electrodeposition coating equipment equipped with a diaphragm chamber, the diaphragm chamber (electrode plate) is not installed near the tank entry area in order to prevent the generation of hatch marks. Since the coating cannot be applied effectively to the object to be coated, in order to obtain the desired coating film, a predetermined number of diaphragm chambers must be shifted toward the exit tank, which results in a longer electrodeposition tank. There's a problem.

In addition to the above-mentioned Japanese Patent Publication No. 54-41617, in order to solve the problem when entering the tank, a variable resistor is installed on each electrode to lower the current value when entering the tank (see
56-7761) and the concentration of the ion diaphragm is variable.
A device that lowers the current value when entering the tank (Utility Model No. 55-96166)
No.).

However, in the former case, it is necessary to install a variable resistor, which complicates control, and as painting progresses, the coulomb efficiency of the paint decreases.
Like No. 41617, there is a problem of deterioration.
In the latter case, it is necessary to make the concentration of the ion diaphragm variable, which makes concentration management difficult, and requires ionized water with different ion concentrations, which complicates the equipment.

The present invention provides an electrodeposition coating apparatus of the type equipped with the above-mentioned diaphragm chamber, which is free from the above-described drawbacks of the conventional structure and which prevents the formation of hatch marks on the surface of the coated film formed. The purpose is to

The present invention provides a plurality of diaphragm chambers along the conveyance path of the object to be coated in an electrodeposition tank filled with an electrodeposition paint, and arranges an electrode plate in each of the diaphragm chambers. Electrodeposition coating in which the electrodeposition paint is applied to the surface of the object by electrodeposition by applying a DC voltage between the object to be coated and the object immersed in the coating material using an energizing tank method. In the apparatus, in order to circulately supply diaphragm water whose conductivity is lower than the conductivity of diaphragm water supplied to other diaphragm chambers to the diaphragm chamber on the entrance side of the electrodeposition bath, cooling is performed to cool the diaphragm water. It is characterized by having a diaphragm water circulation circuit equipped with a container.

That is, in the electrodeposition coating apparatus of the present invention,
The diaphragm water circulation circuit equipped with the above-mentioned cooler allows diaphragm water in the diaphragm chamber on the entrance side of the electrodeposition tank among the plurality of diaphragm chambers arranged along the transport direction of the object to be coated in the electrodeposition tank. By cooling the diaphragm water, its conductivity is lowered than that of the diaphragm water in other diaphragm chambers, and the current flowing between the object to be coated and the electrode in the bath entry section is reduced. This prevents a large amount of current from flowing when the coating material is placed in the bath, thereby preventing hatch marks from forming on the coating surface. As described above, according to the present invention, the structure is simple enough to reduce the water conductivity of the diaphragm in the diaphragm chamber on the tank entrance side compared to other diaphragms, and the coating film can be effectively removed without requiring extra space. It is possible to prevent hatch marks from forming on the surface, and to form a coating film effectively immediately after entering the electrodeposition tank without increasing the length of the electrodeposition tank.

Next, an electrodeposition coating apparatus according to a preferred embodiment of the present invention will be described.

The present invention can be applied to both anionic and cationic electrodeposition coating methods, and FIG. 1 shows a cationic electrodeposition coating apparatus.

The cationic electrodeposition coating device shown in Figure 1 is
It has an electrodeposition tank 1, in which a diaphragm device 2 is arranged along both side walls 1a. This diaphragm device 2 has a plurality of diaphragm chambers 3, and inside each of the diaphragm chambers 3, electrode plates 4 connected to the anode side of a DC power source V are arranged. The cathode side of the DC power supply V is immersed in the coating liquid 5 in the electrodeposition tank 1, and the object 6 to be coated is conveyed along the diaphragm device 2 by the conveyor C shown in FIG. It is connected to the. The electrode plate 4 and the object to be coated 6 are energized by a so-called energization bath method in which the electrode plate 4 and the object to be coated 6 are energized before the object to be coated 6 is immersed in the electrodeposition tank 1. The anionic electrodeposition coating device has the same structure as the cationic electrodeposition coating device shown in FIG. 1, but the diaphragm chamber 3
The inner electrode plate 4 is connected to the anode of the DC power supply V, while the object 6 to be coated is connected to the cathode of the DC power supply V. Diaphragm water is supplied into the diaphragm chamber 3 from a supply pipe 7 that extends from the top of the diaphragm chamber to near the bottom, and a discharge pipe that extends outward from the upper side of the diaphragm chamber and penetrates the side wall of the electrodeposition tank 1. 8 to the outside of the electrodeposition tank 1.

A plurality of diaphragm chambers 3 arranged along the side wall of the electrodeposition bath 1 are divided into an entry side diaphragm chamber 3a and a remaining diaphragm chamber 3b, as shown in FIG.
In the diaphragm chamber 3b, diaphragm water with a conductivity (400 to 500 μ/cm) used for ordinary electrodeposition coating is filled in the diaphragm chamber 3a.
is filled with diaphragm water having a lower conductivity (50 to 100 μ/cm) than the conductivity of the diaphragm water in the diaphragm chamber 3b. The diaphragm chamber 3a on the tank entry side includes the diaphragm chamber 3a.
The first part that circulates and supplies the diaphragm water with low conductivity to a.
A diaphragm water circulation circuit 9 is connected to the remaining diaphragm chamber 3b, and a second diaphragm water circulation circuit 10 is connected to the remaining diaphragm chamber 3b for circulating and supplying diaphragm water having the above-mentioned normal conductivity to the diaphragm chamber 3b.

As shown in FIG. 3, the conductivity-temperature characteristics of the diaphragm water are almost proportional, and by utilizing this, the first diaphragm water circulation circuit 9 is
A cooler C _p is provided for cooling the diaphragm water flowing therein and lowering its conductivity to the predetermined low conductivity. Characteristic lines a and b shown in Figure 3 show changes in conductivity when the temperature of diaphragm water is changed, which has conductivities of 160 μ/cm and 400 μ/cm at the standard temperature (20°C). In the examples described later, the diaphragm water with an electrical conductivity of 100μ/cm is of characteristic line a.
The diaphragm water with an electrical conductivity of 400 to 500 μ/cm is of characteristic line b. This has the advantage that the temperature of each diaphragm water can be lowered. However, it is not necessary to use diaphragm water having different characteristic lines a, , b, and only diaphragm water exhibiting characteristic line a may be used.

The first and second diaphragm water circulation circuits 9 and 1
0 have first and second diaphragm water storage tanks 11, respectively.
and 12 are provided, and inside these first and second diaphragm water storage tanks 11 and 12, a diaphragm chamber 3 is provided.
The diaphragm water discharged from a and 3b is accommodated. Therefore, the first diaphragm water storage tank 11
The conductivity of the diaphragm water in the diaphragm chamber 3a is the same as that of the diaphragm water in the diaphragm chamber 3a, and the conductivity of the diaphragm water in the second diaphragm water storage tank 12 is the same as that of the diaphragm chamber 3b.

As the coating of the object 6 in the electrodeposition bath 1 progresses, the diaphragm chamber 3 contains neutralized paint components corresponding to the solid matter electrodeposited on the object 6 in the coating liquid 5. agent is absorbed. The electrical conductivity of the diaphragm water in the diaphragm chamber 3 increases by the amount of the absorbed neutralizing agent. Therefore, the first
The second diaphragm water storage tanks 11 and 12 are respectively provided with conductivity adjusting devices 13 and 14 for maintaining the conductivity of the diaphragm water within a predetermined range. The conductivity adjustment devices 13 and 14 are connected to a pure water supply pipe 1 for supplying pure water to the diaphragm water storage tanks 11 and 12.
5,16. This pure water supply pipe 15,
16 is provided with automatic on-off valves 17 and 18, and these automatic on-off valves 17 and 18 are connected to the valve driving device 1.
Its opening and closing are controlled by 9 and 20. The valve driving devices 19, 20 detect the conductivity of the diaphragm water in the first and second diaphragm water storage tanks 11, 12, and output a signal S when the conductivity becomes higher than the value in the predetermined range. The electrical conductivity detection devices 21 and 22 are connected to the electrical conductivity detection devices 21 and 22. When the valve drive devices 19 and 20 receive the signal S from the conductivity detection devices 21 and 22, they open the on-off valves 17 and 18, supply pure water to the diaphragm water storage tanks 11 and 12, and
The conductivity of the diaphragm water in the diaphragm water storage tanks 11 and 12 is maintained at a predetermined value.

A pump P is interposed in the pipelines on the supply side of the first and second diaphragm water circulation circuits 9 and 10, and this pump P supplies diaphragm water whose conductivity is kept constant to the diaphragm water storage tanks 11 and 12. from the diaphragm chamber 3.
Therefore, the conductivity of the diaphragm water in the diaphragm chamber 3b is maintained at the normal conductivity within the above-mentioned predetermined range, and the conductivity of the diaphragm water in the diaphragm chamber 3a
The conductivity of the diaphragm water within the diaphragm is maintained within a predetermined range lower than the above-mentioned normal conductivity.

In addition, in order to gradually increase the conductivity of the diaphragm water in the plurality of diaphragm chambers 3 from the tank entry side, the diaphragm chamber 3b near the diaphragm chamber 3a on the tank entry side is also shown by imaginary lines in FIG. The first diaphragm water circulation circuit 9 is extended as shown in FIG. The conductivity may be intermediate between the conductivities of the diaphragm water in the storage tanks 11 and 12.

Examples of the present invention will be described below in which electrodeposition coating is performed using the cationic electrodeposition coating apparatus having the structure described above and under the following electrodeposition conditions, and in which the cationic electrodeposition coating apparatus is similarly used. Comparative Examples 1 and 2 in which electrodeposition was performed under the following electrodeposition conditions are shown in FIG. Fourth
The figure shows the relationship between the elapsed time and the change in the current flowing between the object to be coated and the electrode plate when the object to be coated is immersed in the electrodeposition bath while being conveyed.

(1) Electrodeposition conditions in the example Electrodeposition tank: 35 m long, 2.5 m wide, 2 m deep Diaphragm chamber: 2 m high, 0.1 m thick, 1 m wide (the first diaphragm from the tank entry side) The height of the room is
1.5m) Number of pieces placed on one side: 17 Object to be coated: Car body Total surface area: 60m ² Paint: OTO-U-52 (manufactured by Nippon Paint Co., Ltd.) Electrical conductivity: 1400μ/cm Temperature: 27℃ Concentration: 21% Coulombs Efficiency 33mg/c Applied voltage: 330V (cation type) Conductivity of diaphragm water in the diaphragm chamber on the entry side (temperature of diaphragm water at this time: 10℃, characteristic line a shown in Figure 3)
100μ/cm Electrical conductivity of diaphragm water in other diaphragm chambers (temperature of diaphragm water at this time: 20 to 40℃, characteristic line b shown in Figure 3)
400 to 500 μ/cm Total immersion time of the object to be coated in the electrodeposition bath 2.5 minutes (2) Electrodeposition conditions for Comparative Example 1 The conductivity of all the membrane chambers in the above example was set to 400 to 400 μ/cm.
500μ/cm.

Other electrodeposition conditions were the same as in the above example.

(3) Electrodeposition conditions for Comparative Example 2 Three of the diaphragm chambers in the entrance part on both sides of the electrodeposition tank were removed, and the conductivity of the remaining diaphragms (14 on each side) was set to 400 to 500 μ/cm. What I did.

Other electrodeposition conditions were the same as in the above example.

As shown by the characteristic line b in FIG. 4, in Comparative Example 1, a large current flowed when the object to be coated entered the bath, resulting in hash marks. Comparative example 2 shown in characteristic line c in Fig. 4
Although no hash mark appeared when entering the tank,
Since the current that flows when the object to be coated enters the tank is extremely small, a coating film cannot be effectively formed when the object enters the tank. Therefore, in order to obtain the desired coating film, a predetermined number of diaphragm chambers are shifted toward the exit side of the tank. There is a problem in that the electrodeposition tank must be arranged in such a way that the electrodeposition bath becomes long.

On the other hand, in the embodiment of the present invention shown in characteristic line a in Fig. 3, when the object to be coated, which is a car body, was electrocoated, a good painted surface without any hash marks was obtained without a large current flowing when entering the tank. I was able to get it.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a cationic electrodeposition coating apparatus to which the present invention can be applied, and FIG. 2 is a schematic diagram showing an electrodeposition coating apparatus according to an embodiment of the present invention.
Figure 3 is a graph showing the conductivity temperature characteristics of diaphragm water, and Figure 4 is the elapsed time when the object to be coated is immersed in the electrodeposition tank under the electrodeposition conditions of the example of the present invention and the comparative example. 2 is a graph showing the relationship between changes in the current flowing between the object to be coated and the electrode plate. DESCRIPTION OF SYMBOLS 1...electrodeposition tank, 3...diaphragm chamber, 3a...diaphragm chamber on tank entry side, 3b...other diaphragm chamber, 9...first diaphragm water circulation circuit, 10...second diaphragm water circulation circuit, 11
...first diaphragm water storage tank, 12...second diaphragm water storage tank,
C _p ...Cooler.

Claims (1)

[Claims] 1. A plurality of diaphragm chambers are provided along the conveyance path of the object to be coated in an electrodeposition bath filled with the electrodeposition paint, and an electrode plate is arranged in each of the diaphragm chambers. In an electrodeposition coating device that performs painting by electrodepositing the electrodeposition paint on the surface of the object to be coated by applying a DC voltage between the object to be coated and the object to be immersed in the bath, In order to circulately supply diaphragm water having a conductivity lower than that of diaphragm water supplied to other diaphragm chambers to the diaphragm chamber on the bath entrance side of the electrodeposition tank, a cooler is provided to cool the diaphragm water. An electrodeposition coating device characterized by being provided with a diaphragm water circulation circuit.