JP2909564B2 - Film treatment method in cationic electrodeposition coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a membrane separation method in cationic electrodeposition coating.

[0002]

2. Description of the Related Art In the case of cationic electrodeposition coating, in an electrodeposition tank, an object to be electrodeposited is used as a negative electrode, and a cationic paint having a positive charge is deposited on the surface of the electrodeposited object to perform coating.
The paint from the electrodeposition tank is partially supplied to the ultrafiltration device by a pump and separated into a paint concentrate and a filtrate, and the concentrate is returned to the electrodeposition tank, while the filtrate is pumped to the washing tank. Here, the excess paint adhered to the surface of the electrodeposit is washed and removed by the filtrate, and the paint is returned to the electrodeposition tank by overflow. Further, a method is also known in which the filtrate from the ultrafiltration is subjected to reverse osmosis filtration treatment, and the filtrate is used as washing water.

In such an electrodeposition coating system, it is important to maintain the filtrate flow rate of the ultrafiltration device or the reverse osmosis filtration device at a high level in order to increase the paint recovery and the quality of the filtrate. However, conventionally, in an electrodeposition coating system equipped with such a film processing apparatus, during operation of the film processing apparatus, a resin or pigment as a paint component, or phosphoric acid, carbonic acid, and pigment mixed in the paint with time. It has been known that inorganic salts and the like resulting from the reaction with the catalyst adhere to the membrane surface of the membrane treatment apparatus, and the flow rate of the filtrate in the membrane treatment apparatus decreases.

Therefore, conventionally, there have been proposed some measures for washing and removing such deposits on the film surface or preventing the formation of carbonate. For example, see JP-A-59-8499.
No. 7 proposes a method for preventing the generation of carbonates by temporarily and continuously filling an aqueous acetic acid solution on the filtrate side of an ultrafiltration device. However, according to this method, it is only possible to prevent the generation of carbonate on the filtrate side, and it is not possible to prevent the generation of carbonate on the paint side or the adhesion of dirt on the membrane surface.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional electrodeposition coating, and is intended for use in an electrodeposition coating system including an ultrafiltration device and a reverse osmosis filtration device. It is another object of the present invention to provide a membrane processing method capable of maintaining the filtrate flow rate of these membrane processing devices high over time.

[0006]

The first aspect of the film processing method in the cationic electrodeposition coating according to the present invention is an electrodeposition step of adhering a cationic electrodeposition paint to an object to be electrodeposited and excessive electrodeposition attached to the object to be electrodeposited. Including a water washing step of washing and removing the paint, supplying the cationic electrodeposition paint as an undiluted solution to an ultrafiltration or reverse osmosis filtration device, performing a filtration treatment, returning the obtained paint concentrate to the electrodeposition step, and washing the filtrate with water In the cationic electrodeposition coating which is sent to the washing step as water, the filtration device is temporarily stopped, and an aqueous solution of an organic carboxylic acid is sealed in the undiluted solution side of the filtration device.

The second of the film treatment methods in the cationic electrodeposition coating according to the present invention is an electrodeposition step of attaching a cationic electrodeposition coating to an object to be electrodeposited, and a water washing for washing away excess electrodeposition paint adhering to the object to be electrodeposited. The process comprises the steps of supplying a cationic electrodeposition paint as a stock solution to an ultrafiltration device, performing a filtration treatment, returning the obtained paint concentrate to the electrodeposition step, sending the filtrate as washing water to the washing step, and The filtrate from the outer filtration device is supplied as a stock solution to a reverse osmosis filtration device, filtered, and the obtained concentrated solution is returned to the filtrate storage tank, and the filtrate is sent to the washing step as washing water. The osmosis filtration device is temporarily stopped, and an aqueous solution of an organic carboxylic acid is pressurized and sealed in the undiluted solution side of the reverse osmosis filtration device.

The method of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the first embodiment of the method according to the present invention.
And 14 are supplied to the ultrafiltration device 4 to be separated into a filtrate and a paint concentrate, and the filtrate is stored in the filtrate storage tank 5, and this filtrate is intermittently washed by the pump 9 through the pipe 16 through the washing tank 3.
Sent as a washing liquid. On the other hand, the paint concentrate is returned to the electrodeposition tank 1 via the pipe 15 by the pump 12.

In such an electrodeposition coating method, usually,
The ultrafiltration device 4 is used for energy saving and management inspection.
Paused regularly or irregularly. When the undiluted solution stays in the ultrafiltration device or its piping system, paint is deposited on the ultrafiltration membrane or the piping system, especially on the undiluted solution side. Pause after replacement.

Therefore, according to the method of the present invention, when the ultrafiltration apparatus is temporarily stopped, the valve 11 is closed and the valve 10 is closed.
To replace the ultrafiltration device and the piping system with the filtrate in the filtrate storage tank, the organic carboxylic acid aqueous solution tank 6 to the pump 8
Then, the acid aqueous solution is pressurized and sealed in the tube 17 on the stock solution side of the ultrafiltration device. After the replacement of the ultrafiltration apparatus and the piping system with the filtrate in the filtrate storage tank is completed, the valves 10 and 12 are closed, and the pump 8 is stopped at the same time.

As the organic carboxylic acid, an acid used as a neutralizing agent in a paint, such as formic acid, acetic acid, glycolic acid, malic acid, lactic acid, etc., is preferable because it does not have a harmful effect on the paint. The encapsulation amount of these acids is 5% in the filtrate.
A range of 00 to 20000 mg / liter is preferred. When the amount of the acid is less than 500 mg / liter in the filtrate, the effect of washing the paint components and inorganic salts is poor, and it is difficult to achieve the intended purpose. On the other hand, when the amount exceeds 20,000 mg / liter, the concentration of the acid component in the cationic paint becomes excessively high, which adversely affects the coating quality.

As described above, according to the method of the present invention, when the ultrafiltration device is temporarily stopped and the ultrafiltration device or the piping system is replaced with the filtrate in the filtrate storage tank, the ultrafiltration device is placed on the stock solution side. By sealing the aqueous acid solution under pressure, a part of the acid permeates through the membrane and moves to the filtrate side, and the generation of inorganic salts can be prevented also on the filtrate side. FIG. 2 is an apparatus configuration diagram showing a second method of the present invention. In this electrodeposition coating method, in addition to the device configuration shown in FIG. 1, the filtrate from the filtrate storage tank 5 is further processed by the reverse osmosis filtration device 21 by the pump 24, and the concentrated solution is filtrated by the pipe 27. The filtrate is returned to the storage tank 5 and the filtrate is sent to the washing tank 22 via the pipe 28.

In the second method, since the reverse osmosis filtration device and its piping system hardly contain paint components, the device may be stopped as it is, and at this time, the second organic carboxylic acid By pressurizing and enclosing the acid solution from the aqueous solution tank 23 to the undiluted solution side in the pipe 29 by the pump 25, not only the undiluted solution side but also the filtrate side can be washed in the same manner as described above.

[0014]

Examples of the method of the present invention will be described below. Example 1 In an electrodeposition coating method having the apparatus configuration shown in FIG.
As an ultrafiltration device, NTU-212 manufactured by Nitto Denko Corporation
Using 0-S6E, this ultrafiltration apparatus was stopped every 24 hours, and an acetic acid aqueous solution was pressurized and sealed on the undiluted solution side so that the concentration in the filtrate was 5000 mg / liter, and electrodeposition coating was performed. Was.

As Comparative Example 1, electrodeposition coating was performed in the same manner as described above, except that the aqueous acetic acid solution was not sealed in the stock solution when the ultrafiltration apparatus was stopped. Table 1 shows the transition of the filtrate flow rate in the ultrafiltration device.

[0016]

[Table 1]

Example 2 In an electrodeposition coating method having the apparatus configuration shown in FIG.
As an ultrafiltration device, NTU-212 manufactured by Nitto Denko Corporation
Using 0-S6E, this ultrafiltration apparatus was stopped every 24 hours, and an acetic acid aqueous solution was pressurized and sealed on the undiluted solution side so that the concentration in the filtrate was 5000 mg / liter, and at the same time, a reverse osmosis filtration apparatus was used. Also, an acetic acid aqueous solution was pressure-filled on the undiluted solution side so that the concentration in the filtrate was 5000 mg / liter, and electrodeposition coating was performed.

As Comparative Example 2, electrodeposition coating was performed in the same manner as described above, except that the aqueous solution of acetic acid was not sealed in the ultrafiltration device and the reverse osmosis filtration device on the stock solution side. Table 2 shows the transition of the filtrate flow rate in the reverse osmosis filtration device.

[0019]

[Table 2]

[0020]

As described above, according to the method of the present invention,
When the membrane treatment apparatus is temporarily stopped, the flow rate of the filtrate of the membrane treatment apparatus can be kept high over a long period of time by filling the undiluted solution with an aqueous solution of an organic carboxylic acid under pressure.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing a first method of the present invention.

FIG. 2 is an apparatus configuration diagram showing a second method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electrodeposition tank, 2 and 3 ... Rinse tank, 4 ... Ultrafiltration apparatus, 5
... filtrate storage tank, 6 ... organic carboxylic acid aqueous solution tank, 21 ... reverse osmosis filtration device, 22 ... water washing tank, 23 ... second organic carboxylic acid aqueous solution tank.

Claims (2)

(57) [Claims] 1. An ultrafiltration process comprising the steps of: an electrodeposition step of depositing a cationic electrodeposition paint on an object to be electrodeposited; and a water washing step of washing and removing excess electrodeposition paint adhered to the object to be electrodeposited. The ultrafiltration apparatus is supplied to the apparatus, filtered, and the obtained concentrate is returned to the electrodeposition step. In the cationic electrodeposition coating in which the filtrate is sent to the washing step as washing water, the ultrafiltration apparatus is temporarily stopped, and the ultrafiltration is stopped. A membrane treatment method for cationic electrodeposition coating, wherein an aqueous solution of an organic carboxylic acid is pressurized and sealed in a stock solution side of a filtration device. 2. An ultrafiltration method comprising the steps of: an electrodeposition step of attaching a cationic electrodeposition paint to an object to be electrodeposited; and a water washing step of washing and removing excess electrodeposition paint adhered to the object to be electrodeposited. It is supplied to the device, filtered, and the obtained paint concentrate is returned to the electrodeposition step.The filtrate is sent to the washing step as washing water, and the filtrate from the ultrafiltration apparatus is sent to the reverse osmosis filtration apparatus as a stock solution. Supply, filtration treatment, return the resulting concentrated solution to the filtrate storage tank, temporarily suspend the reverse osmosis filtration device in the cationic electrodeposition coating to send the filtrate to the washing step as washing water, the undiluted solution of the reverse osmosis filtration device A film treatment method in cationic electrodeposition coating, wherein an aqueous solution of an organic carboxylic acid is pressure-filled on the side.