JPS61272399A - Apparatus for coating by electrodeposition - Google Patents

Abstract

PURPOSE:To save pure water for neutralization and to prevent the sticking of sludge to a diaphragm by placing a diaphragm electrode mechanism surrounding a counter electrode which confronts a body to be coated and a means of setting the electric conductivity of an electrolytic soln. in the mechanism at a certain value or above. CONSTITUTION:Water paint 3 is filled into a tank 2 for coating by electrodeposition, and an electrode 4 as a body to be coated and a counter electrode 5 which confronts the electrode 4 are arranged in the tank 2 so that the electrode 5 is put in a diaphragm electrode mechanism 10 having a diaphragm 8. An electrolytic soln. is circulated between the mechanism 10 and an electrolytic soln, tank 16. An electric conductivity sensor 26 is laced above the tank 16 to measure the concn. of acetic acid. A rise in the concn. of acetic acid is inputted in a control circuit 27 as a change in electric conductivity, and a solenoid valve 28 is operated so that the electric conductivity of the electrolytic soln, in the mechanism 10 is kept at >=1,000 microsiemens/cm by feeding pure water or suspending the feed. By this structure, the electric resistance of the diaphragm is increased with the lapse of time, so satisfactory coating by electrodeposition is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrodeposition coating apparatus, and particularly to an electrodeposition coating apparatus using a diaphragm for adjusting the concentration of a neutralizing agent.

[Conventional technology]

Electrodeposition coating has a uniform coating film with excellent adhesion, is easy to automate and save labor, and generates little pollution, so it is suitable for undercoating metal coatings, one-coat finishing, etc. For example, it is used for coating automobile bodies. It is widely used for film processing, etc.The paint used for electrodeposition coating has a basic composition of resin that contains acid groups (e.g.
There are two main types of paints: anionic paints with carboxyl groups) and cationic paints with bases (e.g. amine groups), but both have extremely low solubility in water when used alone. For example, in the case of cationic paints, an alkaline neutralizer such as triethylamine is mixed in, and in the case of cationic paints, an acidic neutralizer such as acetic acid is mixed in to neutralize them into salts, thereby increasing their solubility in water. is used.

In this way, a neutralizing agent is mixed in depending on the nature of the resin component of the paint, but as the electrodeposition process of the object to be coated 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 acetic acid as a neutralizing agent is continuously accumulated in the above-mentioned aqueous paint solution, and the pH gradually changes, causing phenomena such as re-dissolution of the painted surface or generation of pinholes. For this reason, in recent years, one electrode is separated from the other electrode by a diaphragm, and the amine or acetic acid is electrically extracted from the aqueous solution to increase the neutralizing agent in the aqueous solution. So-called PH management has been implemented to prevent this, and efforts are being made to make it effective.

[Problem that the invention seeks to solve]

Conventionally, neutral membranes and ion exchange membranes have been used as the diaphragm. In this case, for example, the concentration of the electrode was kept to about 300 to 600 [micro-Siemens/C11] in terms of conductivity, since the higher the acid concentration in the electrode, the greater the wear on the electrode. . For this reason, in the conventional example, the concentration of the polar solution must always be maintained at a relatively low value, which has the disadvantage of requiring a large amount of pure water to take the acid out of the polar solution tank. On the other hand, heavy metals, other inorganic substances, and organic sludge tend to adhere to the diaphragm, and this sludge grows over time and increases the electrical resistance of the diaphragm, which reduces the current flow. This has caused the inconvenience that a predetermined coating film thickness cannot be obtained.

[Purpose of the invention]

The present invention improves the disadvantages of the conventional example, and in particular eliminates the increase in electrical resistance of the diaphragm portion, thereby providing an electrodeposition coating apparatus that can always obtain a coating film with a preset uniform thickness. Its purpose is to provide.

[Means for solving problems]

Therefore, in the present invention, the other electrode is immersed in an aqueous paint solution in an electrodeposition coating tank corresponding to the object to be coated, and a neutralizer is provided surrounding the other electrode. It is equipped with a diaphragm for removing the agent, and the conductivity of the polar liquid in this diaphragm is 10
00 (Micro Siemens/C11) or higher at all times, and thereby attempts to achieve the above objective.

[Embodiments of the invention]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings, taking as an example a case in which a cationic paint is used.

In this attached drawing, ■ indicates the entire electrocoating device;
2 shows an electrodeposition coating tank, and 16 shows an electrolyte tank.

In the electrodeposition coating tank (hereinafter simply referred to as rED tank) 2, in addition to the aqueous paint solution 3, there are one electrode 4, which is the object to be coated, and the other electrode 5, which is provided correspondingly. They are arranged and equipped at predetermined intervals. Of these, the other electrode 5 is housed in a diaphragm electrode mechanism 10 formed in a cylindrical shape in this embodiment.

This diaphragm electrode mechanism 10 includes a cylindrical diaphragm 8 and diaphragm support members 7A attached to the upper and lower ends of the diaphragm 8 in the figure.
, 7B, and the other electrode 5 disposed inside. In this embodiment, the diaphragm 8 is a polyethylene film (with an average hole diameter of 0.001 to 0.01μ)
Although a neutral membrane (neutral membrane) is used, other common neutral membranes such as a polyethylene membrane, an acrylic membrane, or an ion exchange membrane may also be used.

An electrodeposition pipe 13 installed outside the electrodeposition coating tank 2 is connected to the diaphragm electrode mechanism 10 .

On the other hand, a circulation pump 17 is provided in the inflow line 15 from the polar liquid tank 16 to the diaphragm electrode mechanism 10, and this inflow line 15 and the circulation pump 17 constitute a polar liquid re-introduction means. . Then, from the polar liquid tank 16 to the valve 25
The polar liquid 11 is pushed by the liquid flowing into the diaphragm electrode mechanism 10 through the outflow line 14 and flows out into the polar liquid tank 16, so that a predetermined circulation is performed.

The polar liquid tank 16 is provided with a conductivity sensor 26, and when a predetermined conductivity is reached, the sensor 26 detects this and sends it to the control circuit 27. On the other hand, in order to introduce pure water from the outside to dilute the polar liquid in the polar liquid tank 16 and maintain the electrical conductivity of the polar liquid within a predetermined range, a bypass line 29 leading to the polar liquid tank 16 via a solenoid valve 28 is installed. It is provided. When the control circuit 27 receives a detection signal from the sensor 26, it sends a valve opening signal to the electromagnetic valve 28 to open the electromagnetic valve 28.

When the electromagnetic valve 28 is opened, pure water is allowed to flow into the polar liquid tank 16 from the outside. 29 indicates a pure water introduction pipe in this case.

Next, the overall operation of the above embodiment will be explained.

First, an object to be coated 4 and a diaphragm electrode mechanism 10 are placed in an ED tank 2 filled with an aqueous solution 3 of a cationic paint neutralized with acetic acid as a neutralizing agent. the other electrode 5
When the electrode is connected to the DC power source 6 as the positive electrode and a DC voltage is applied, electrodeposition coating starts immediately, and the colloidal molecules of the resin component and pigment, which are positively charged in the aqueous solution, move toward the object to be coated 4 at the negative electrode. After adhering to the surface of the coating material 4 and discharging, the solid matter of the coating material aggregates to form a coating film.On the other hand, the negatively charged acetic acid in the aqueous solution moves toward the other electrode 5, and at this time It is extracted from the aqueous solution by the diaphragm 8 and discharged at the other electrode 5 to generate acid. Then, the acetic acid accumulated in the polar liquid of the diaphragm electrode mechanism 10 is taken out to the polar liquid tank 16 by the action of the circulation pump 17. Therefore, the electrical conductivity of the polar liquid tank 16 gradually increases as the acetic acid concentration increases, but the sensor 26 constantly measures this concentration and inputs it as an electrical signal to the control circuit 27 as a change in electrical conductivity. are doing. Then, the conductivity is set in advance in the control circuit 27 to a certain value (2000 micro-Siemens/cm
), a signal is sent to the electromagnetic valve 28 to open it and introduce pure water into the polar liquid tank 16 from the outside. The polar liquid in the polar liquid tank 16 is diluted and discharged to the outside through the overflow pipe 13.

The polar fluid in the polar fluid tank 16 is diluted and its conductivity decreases, but when this value reaches a value preset in the control circuit 27 (1500 micro-Siemens/ω), the electromagnetic valve 28 is closed and the electrical conductivity is reduced. Stop the water supply. Conventionally, the upper and lower limits were set at 300 to 600 (Micro Siemens/
c111], but in this example, this is managed by 1
500~2000 (Micro Siemens/cff
i) (in some cases 1000 to 2000 microSiemens/am), so the concentration of neutralizing agent in the polar solution is more than 5 times that of the conventional method (Note: The relationship between conductivity and concentration The relationship is not linear, so even if the conductivity is about 3 times higher, the concentration will be more than 5 times higher.) On the other hand, since the acid concentration of the polar liquid discharged from the polar liquid discharge pipe 13 is five times higher, the required amount of pure water is reduced to 115.

In this way, the acetic acid extracted into the diaphragm electrode mechanism 10 is discharged to the outside through the electrolyte discharge pipe 13, so that even if paint is replenished into the ED tank 2 as the electrodeposition work progresses, the acetic acid extracted into the diaphragm electrode mechanism 10 is
The concentration of the neutralizing agent in tank D is kept constant, so a good coating film can be formed, and at the same time, the concentration of the polar solution is relatively high (as it is set, The dissolving action eliminates the adhesion of heavy metals, other inorganic and organic sludge to the diaphragm, and this makes it possible to increase the electrical resistance by replacing the (other) electrode as necessary. This has the advantage that it can be kept to a minimum.

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.

In addition, in the above example, the acid concentration of the polar liquid was set to 20,000
Although the example is exemplified where the setting is around 1,000 micro Siemens/cm), the present invention is not necessarily limited to this.
Micro Siemens/Country] or above is sufficient.

〔Effect of the invention〕

Since the present invention is configured and functions as described above, the amount of pure water that was conventionally required to dilute the acid concentration of the polar liquid can be significantly saved (approximately 1/4 to 115 times less than the conventional amount). Since the liquid concentration is set to a relatively high value, it is possible to eliminate the adhesion of heavy metals, other inorganic substances, and organic sludge to the diaphragm, which conventionally occurs, and therefore the electrical resistance of the diaphragm decreases over time. It is possible to provide an unprecedented and excellent electrodeposition coating apparatus that can almost completely eliminate the disadvantages of the conventional example in that the applied current decreases and a predetermined coating thickness cannot be obtained.

[Brief explanation of the drawing]

The accompanying drawing is a system diagram showing one embodiment of the present invention. 2-...-electrodeposition coating tank, 4---=-one electrode, 5
−・−・・−・Other electrode, 8・・−−−One diaphragm.

Claims (1)

[Claims] (1) The other electrode is immersed and arranged in the paint aqueous solution in the electrocoating tank corresponding to the object to be coated, which forms one electrode, and the neutralizing agent installed surrounding the other electrode is removed. 1. An electrodeposition coating apparatus comprising a diaphragm for use in the diaphragm, and the electrical conductivity of the polar liquid within the diaphragm is always set to 1000 [micro-Siemens/cm] or more.