JPS6033915B2 - Electrodeposition coating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lightning coating apparatus, and more particularly to a haze coating apparatus using a diaphragm electrode for adjusting the concentration of a neutralizing agent.

Haze coating has a uniform coating film with excellent adhesion, is easy to automate and save labor, and generates little pollution. Therefore, it is suitable for undercoating metal coatings, one-coat finishing, etc., and is used for example on automobile bodies. Widely used for coating film processing, etc.

The basic composition of the paint used for flea coating is acidic groups (
There are two main categories: anionic paints with bases (e.g., carboxyl groups) and cationic paints with bases (e.g., amine groups), but both have extremely low solubility in water when used alone. For anionic paints, for example, an alkaline neutralizer such as triethylamine is mixed in, and for cationic paints, an acidic neutralizer such as lactic acid is mixed in to neutralize the paint and turn it into a salt in order to increase its solubility in water. things are used. In this way, a neutralizing agent is mixed in depending on the nature of the resin component of the paint, but as the haze treatment of the object progresses, the resin component in the aqueous solution decreases, so the paint must be replenished from the outside. Must be. At this time, amine or lactic acid as a neutralizing agent is continuously accumulated in the above-mentioned aqueous paint solution, and the pH changes with time, causing phenomena such as re-dissolution of the painted surface or generation of pinholes. For this reason, these days,
One electrode is separated from the other electrode by a diaphragm, and amine or lactic acid is permeated and extracted from the aqueous solution to prevent an increase in the neutralizing agent in the aqueous solution.
It is managed and effective. To explain this in detail using a cationic paint as an example, as shown in FIG. A DC power source 6 is used with the crushed object 4 as one electrode and the counter electrode 5 as the other electrode.
The opposite electrode 5 is connected to the opposite electrode 5, and one electrode is connected to the object 4 to be coated, and when the aqueous paint solution 3 is energized, the positively charged cationic resin and pigment move toward the object 4 by electric forces and form a coating film. Arrive at Ryukyu.

On the other hand, the neutralizing agent component, for example, lactic acid ion, in the solution moves toward the counter electrode 5. The counter electrode 5 is surrounded by a cornice 8 supported by a diaphragm support member 7, forming a so-called diaphragm electrode 10. The diaphragm 8 is an ion exchange membrane (anion membrane) or a neutral membrane that allows the lactic acid ions to pass through easily, and the lactic acid ions that have passed through the corner 8 reach the opposite electrode and are discharged. Therefore, lactic acid accumulates in the polar liquid 11 between the counter electrode 5 and the B high film 8. The corneal membrane electrode 101 is connected to the polar fluid circulation and discharge device 1.
3 is connected. This polar liquid circulation and discharge device 13 includes a polar liquid tank 16 connected to the diaphragm electrode 10 by outflow and inflow lines 14 and 15, a circulation pump 17 provided in the middle of the inflow line 15, and a polar liquid tank 16 connected to the polar liquid tank 16. It consists of a water supply line 18 that supplies water. The polar liquid 11 in which the neutralizing agent has accumulated in the corneal membrane electrode 10 is transferred to the polar liquid tank 16 by the action of the circulation pump 17.
It is designed to be taken out. The polar liquid tank 16 is equipped with a concentration detection electrode 19, and when the conductivity in the polar liquid tank 16 reaches a predetermined value as the lightning coating progresses, the detector 200 detects this and controls the detection signal. The signal is sent to the circuit 21. Immediately upon receiving the detection signal, the control circuit 21 sends a valve opening signal to the solenoid valve 22 provided in the water supply line 18 to cause the solenoid valve 22 to engage. The solenoid valve 22
Water is supplied to the polar liquid tank 16 via a water supply line 18 at a check valve, and a portion of the neutralizing agent is discharged to the outside by an overflow 23. Therefore, the ED tank 2
Even if paint is continuously supplied from the outside to the diaphragm electrode 10
Since the neutralizing agent is accumulated inside the ED tank 2 and the neutralizing agent is discharged to the outside by the polar liquid circulation/discharging device 13, the p inside the ED tank 2 is
The H value is kept constant. By the way, when an ion exchange membrane is used as the diaphragm in the above-mentioned conventional electrodeposition coating equipment, the selectivity of the neutralizing agent is good, and the removal (loss) of the solvent that is mixed in for the purpose of achieving chemical balance of the paint. On the other hand, the film has a low tensile strength and is difficult to handle in the ED tank, making it expensive. Since the neutralizing agent is removed at a high rate from both of them, the neutralizing agent becomes insufficient from the aqueous paint solution. Therefore, pH adjustment must be performed by using one of the counter electrodes as a bare electrode that is not surrounded by a diaphragm. However, even if the neutralizing agent concentration in the polar solution (for example, acid concentration) increases, the acid removal efficiency will not decrease, but since the current density at the counter electrode is high, increasing the acid concentration in the polar solution will cause the electrode to wear out rapidly, making it difficult to put into practical use. This has the disadvantage that a large amount of pure water is required to remove a certain amount of acid from the system.

On the other hand, when a neutral membrane is used as a diaphragm, the membrane has a large tensile strength and is easy and inexpensive to handle in the ED tank, and the neutralizing agent can be removed by changing the concentration of the neutralizing agent in the polar solution. While it has the advantage of low cloning efficiency and easy control of neutralizing agent removal, the film lacks selectivity and solvent loss is large, making it difficult to obtain the desired coating thickness and requiring solvent replenishment. When the concentration of the neutralizing agent in the polar solution increases, for example, the acid concentration, the acid removal efficiency decreases, so it has to be taken out of the system at a low concentration, resulting in a disadvantage that a large amount of pure water is consumed.

The present invention has been developed in view of the above-mentioned drawbacks of the prior art, and has a simple structure that makes use of the above-mentioned advantages of a neutral membrane, reduces solvent loss, and makes it possible to easily control neutralizing agent removal, making it practical. The purpose is to provide a coating device.

The present invention comprises a counter electrode that is immersed in an aqueous paint solution in a coating tank corresponding to the object to be coated, which forms one electrode, and a counter electrode that is immersed in the paint aqueous solution in the coating tank, and a counter electrode that is provided surrounding the counter electrode for removing a neutralizing agent. A neutral membrane, an electrodialysis means for sequentially taking out the polar liquid that permeates the neutral membrane and flows into the counter electrode side, and appropriately extracting the neutralizing agent component from the polar liquid, and neutralization by the electrodialysis means. The present invention aims to achieve the above object by exploring a configuration including a means for reintroducing the polar liquid from which a part of the agent has been removed into the aqueous paint solution outside the neutral membrane. .

An embodiment of the present invention will be described below with reference to FIG.

Let's take a cationic paint as an example. FIG. 2 is a schematic diagram showing the lightning coating apparatus IA according to the present invention.

In the figure, a diaphragm 8A made of a neutral film is used as a diaphragm electrode 10A provided corresponding to the post-coating material 4 in the ED tank 2. In this case, as the neutral membrane, a polyethylene membrane with an average pore diameter of 0.01 to 0.1 mm is used in this example, but a polysulfon membrane (with an average pore diameter of Alternatively, an acrylic film (average pore diameter of 0.01 to 0.1 mm) may be used.

Neutral membranes tend to allow water to enter and be extracted with the acid in the paint aqueous solution 3, and therefore, regardless of acid accumulation, the polar solution 1
Since the acid concentration of No. 1 is kept relatively low, the Coulombic efficiency of the membrane can be increased. A circulation discharge device 13A is connected to the diaphragm electrode 10A. The main components of this circulating discharge device 13A are a polar liquid tank 16 connected to the diaphragm electrode 10A via outflow and inflow lines 14 and 15A, and an outflow and inflow line 30 and 31 connected to the polar liquid tank 16. It consists of an electrodialysis tank 32, which is the main part of the electrodialysis means, and a neutralizing agent discharge tank 42, which is connected to the electrodialysis tank 32 through outflow and inflow lines 40 and 41. The polar liquid tank 16 is interposed between the diaphragm electrode 10A and the electrodialysis tank 32, and controls the flow rate of outflow and inflow of the electrodialysis tank 32 to the diaphragm electrode 1.
This allows for independent adjustment of the polar liquid circulation flow rate of 0A. Inflow line 15A from polar fluid tank 16 to porcine membrane electrode 10A
is provided with a circulation pump 17, and this inflow line 15A and the circulation pump 17 constitute an electrolyte re-introduction means. Pushed by the liquid flowing from the polar liquid tank 16 to the electrode 10A via the valve 25, the polar liquid 11 flows out through the outflow line 14 to the polar liquid tank 16, and a predetermined circulation is performed. There is. A liquid level gauge 2 is installed in the polar liquid tank 16.
is provided, and when a predetermined liquid level is reached, the liquid level gauge 26
detects this and sends it to the control circuit 27. The outlet side inflow line 15A of the circulation pump 17 is provided with a side line 29 leading to the ED tank 2 via a solenoid valve 28. When the control circuit 27 receives a detection signal from the liquid level gauge 26, it sends a valve signal to the solenoid valve 28 to close the solenoid valve 28. The electrolytic valve 28 allows the polar liquid in the polar liquid tank 16 to flow out into the ED tank 2. As mentioned above, the water that has entered through the bran film 8A increases the amount of polar liquid, so it is returned to the ED tank 2, and at this time, the solvent accumulated in the polar liquid tank 16 is returned and the polar liquid is Liquid tank 16
This is to periodically update the polar liquid inside the tank to improve the quality of management. The electrodialysis tank 32 uses an ion exchange membrane 33 having a large ion exchange capacity. The electrodialysis tank 32 is supplied with polar fluid by a pump 34 provided in the outflow line 301 of the polar fluid tank 16. Then, by applying a DC voltage to both sides of the ion exchange membrane 33, the acid in the polar liquid is removed to one compartment 35. The solvent in the polar solution remains in compartment 36 without being removed. The acid removal efficiency by the ion exchange membrane 33 having a large ion exchange capacity is determined by the buccal membrane 8 of the corneal electrode 10A.
Compared to A, it has the ability to exhibit a high efficiency of approximately 30 to 5 tones. Therefore, the area of the ion exchange membrane 33 used in the electrodialysis tank 32 is 1/30 to 1/5 of the area of the diaphragm 8A.
0 and can be made small. Furthermore, the voltage required for electrodialysis is as low as several tens of volts, and the energy burden is also small. Furthermore, the amount of acid removed to the compartment 35 side can be easily controlled by changing the current applied to the electrodialysis chamber 32. The compartment 36 is connected to the polar fluid tank 16 via an inflow line 31, so that the solvent remaining in the compartment 36 is returned to the polar fluid tank 16. On the other hand, the compartment 35 is connected to a neutralizing agent discharge tank 42 by the outflow and inflow lines 40 and 41. A circulation pump 43 is provided in the inflow line 41 so that the neutralizing agent extract in the compartment 35 is taken out to a neutralizing agent discharge tank 42 . This neutralizing agent discharge tank 42 includes a concentration detection electrode 44.
is provided, and when the acid concentration in the inner side increases and reaches a predetermined conductivity, a detector 45 detects this and sends a detection signal to a control circuit 46. This control circuit 4
6 outputs a valve opening signal to the solenoid valve 48 of the water supply line 47 immediately upon inputting the detection signal to open the solenoid valve 48. As a result, a predetermined amount of water is supplied to the neutralizing agent discharge tank 42, and the neutralizing agent is discharged to the outside along with an overflow 49. Next, the overall operation of the above embodiment will be explained.

First, an object to be coated 4 and a diaphragm electrode 10A are placed in an ED tank 2 filled with an aqueous solution 3 of a cationic paint neutralized with lactic acid as a neutralizing agent. When the counter electrode 5 is connected to the DC power supply 6 with ten poles and a DC voltage is applied, lightning coating starts immediately, and the positively charged resin components and pigment colloid molecules in the aqueous solution move towards the object 4 to be coated at one pole. move,
After adhering to the surface of the object to be coated 4 and generating electric discharge, the solid matter of the paint aggregates to form a coating film.

On the other hand, negatively charged lactic acid in the aqueous solution moves toward the counter electrode 5, and at this time is extracted from the aqueous solution by the diaphragm 8A and discharged at the counter electrode 5, producing acid. Therefore, the acid concentration in the polar liquid increases, but when lactic acid is extracted by the diaphragm 8A, water is also extracted together with the solvent in the aqueous solution, so the increase in the acid concentration in the polar liquid is relatively small, and the Coulombic efficiency of removing lactic acid in the diaphragm 8A is small. does not decrease. The lactic acid accumulated in the polar liquid of the separator mine electrode 10 is pumped into the polar liquid tank 1 along with the solvent and water by the action of the circulation pump 17.
It is taken out to 6. The polar liquid in the polar liquid tank 16 is pumped 3
4, it is further sent to the electrodialysis tank 32.

This electrodialysis chamber 32 removes acid with high efficiency using an ion exchange membrane 33 having a large ion exchange capacity, and at the same time returns the polar liquid containing the solvent to the polar liquid tank 16. Polar liquid tank 1
6, since the amount of polar liquid gradually increases due to the water extraction action of the diaphragm 8A, this is monitored by the liquid level gauge 26,
When a predetermined liquid level is reached, the electromagnetic valve 38 is opened under the control of the control circuit 37 that has received the detection signal, and a predetermined amount of polar liquid is returned into the ED tank 2 . As a result, the solvent remaining in the polar solution without being removed in the electrodialysis tank 32 returns to the aqueous solution in the ED tank 2, eliminating loss of solvent, and the water extracted by the diaphragm 8A is returned. Compared to the case where a large amount of pure water or the like is supplied from the outside to take out the lactic acid in the diaphragm electrode 10A, the amount of pure water consumed can be extremely reduced, and furthermore, the polar liquid in the polar liquid tank 16 is constantly and regularly refreshed. Therefore, smooth pHH management can be performed. The acid removed in the electrodialysis tank 32 is taken out to a neutralizing agent discharge tank 42 by the action of a circulation pump 43. When a certain concentration is reached, the detector 45 detects this and the solenoid valve 48 is opened and closed under the control of the control circuit 46. The acid is discharged to the outside together with the overflow 49 caused by the water supply. Since the electrodialysis tank 32 uses an ion exchange membrane 33, it is possible to remove acid even at high concentrations, and
Since the electrodialysis tank 32 is small and the electrode surface is small, replacing the electrodes due to wear and tear is not economical, and the amount of electricity flowing to remove the acid is 1/30 compared to the ED tank 2.
Since it is small at ~1/50, the consumption of the electrode itself is small, and from the above, acid removal can be performed at a high concentration without impairing practicality. need to be extremely small. The amount of neutralizing agent taken out from the polar liquid tank 16 to the neutralizing agent discharge tank 42 can be easily controlled by adjusting the current of the electrodialysis tank 32. In this way,
The lactic acid extracted into the diaphragm electrode 10A is discharged to the outside by the polar liquid circulation and discharge device 13A, so even if the paint is replenished into the ED tank 2 as the electrodeposition process progresses, the concentration of the neutralizing agent in the ED tank remains unchanged. That is, the pHH is kept constant and a good coating film can be formed.

Although the above embodiments have been explained using cationic paints as electrodeposition paints, the present invention is not limited to this in any way, and is equally applicable to cases where anionic paints are used. be able to.

Alternatively, the diaphragm electrode and the electrodialysis tank may be directly connected without intervening a polar liquid tank. As described above, according to the present invention, it is possible to use a neutral membrane that is easy to handle and inexpensive in the ED tank as the diaphragm of the diaphragm electrode, and it is also possible to extremely reduce solvent loss and to use a large amount of pure water. It is possible to obtain a simple and highly practical desorption coating device that can easily control the removal of the neutralizing agent without the need for it.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional lightning coating device, and FIG. 2 is a schematic diagram showing a lightning coating device according to an embodiment of the present invention. 3...Aqueous paint solution, 4...Object to be coated, 5...
...Opposite pole, 8A...corneal membrane "10A...
・Diaphragm electrode, 11... Electrolyte, 15A...
・Inflow line as means for re-introducing polar liquid, 32...
・Electrodialysis tank is the main part of electrodialysis means. Figure 7 Figure 2

Claims (1)

[Claims] 1. A counter electrode that is immersed and disposed in an aqueous paint solution in an electrodeposition coating tank corresponding to the object to be coated that forms one electrode, and a neutral membrane for removing a neutralizing agent that is provided surrounding this counter electrode. Electrodialysis means for sequentially extracting the polar liquid that permeates the neutral membrane and flows into the counter electrode side and appropriately extracts the neutralizing agent component from the polar liquid; An electrodeposition coating apparatus comprising: a means for reintroducing the polar liquid from which the polar liquid has been removed into the paint aqueous solution outside the neutral film.