JPS5934239B2 - How to recycle electrocoated paint liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recycling an electrodeposition paint liquid in an electrodeposition coating process, and in particular, the present invention relates to a method for recycling an electrodeposition paint liquid during the operation of an electrodeposition coating process. The present invention relates to a method for regenerating an electrodeposition coating solution that has deteriorated due to harmful ions by removing the harmful ions contained therein.

Generally, in the electrodeposition coating process, the electrodeposition paint liquid system contains impure ions derived from the manufacturing process of the paint, impurity ions brought in from the softening water used for dilution, and miscellaneous ions brought in from the pretreatment process of the material to be coated. Inherent impurity components such as, as well as decomposition products from paint resin that are generated due to the operation of the electrodeposition coating process - anions, electrolytic products, liberated sulfur, etc., gradually accumulate. As a result, the electrodeposition paint liquid deteriorates, and this paint liquid 5
The condition of the coating film of articles processed and manufactured using this method deteriorates.

In order to eliminate such deterioration of the paint liquid, various methods have been used to regenerate the paint liquid.
As one method for this purpose, there has been a conventional method of using an ion exchange resin, and by this method, it is possible to regenerate the electrodeposition coating liquid.

For example, this method has been commonly used for electrodeposition coating of aluminum materials. In this case, impurity ions contained in the paint solution are adsorbed and removed by the ion exchange resin, but in the case of method 5, it is necessary to regenerate the ion/exchange resin. However, in this ion exchange resin regeneration process, the ion exchange resin whose adsorption capacity has deteriorated due to backwash water is washed with water in a backwash method.
Next, it is regenerated by recycling chemical solution treatment, and this chemical solution water is washed with water, and then this water is extruded with paint solution to make it useful for the next application, but these washing water systems have a high COD value. Substances with chemical properties are involved, and the amount of water used to wash them is large. Furthermore, since the electrodeposition coating liquid used in this electrodeposition coating process is frequently subjected to ion exchange treatment, its regeneration 5 must be carried out frequently. Therefore, a large amount of wash water with a high COD value must be frequently discharged. If this water is discharged as is, it will pose serious pollution problems. Therefore, various countermeasures against this problem have been taken in the past, but no countermeasure that is industrially satisfactory has yet been found. The present invention overcomes the drawbacks of the above-mentioned conventional methods, and relates to a method whose one purpose is to produce a lower COD value and a smaller amount of waste water (and less frequently).5 The present invention ι In the process, the electrodeposition coating liquid is over-treated, separated into a concentrated liquid and a permeation-treated liquid, the former is returned to the electrodeposition tank as it is, and part or all of the latter permeation-treated liquid is subjected to anion exchange. The present invention relates to a method of performing dialysis using an electrodialysis device equipped with a membrane and a cation exchange membrane, removing inherent ions, and returning the deionized dialyzed solution to the electrodeposition tank.

By this method, it is possible to smoothly regenerate the electrodeposition coating liquid during the electrodeposition coating process without frequently discharging a large amount of wastewater containing components with a high COD value. Originally, superpermeable membranes allow small molecules to permeate along with water. Therefore, when this superfiltration treatment is carried out by the method of the present invention, most of the paint resin components are contained in the concentrated liquid, low molecular electrolytes, amines, etc. are mainly absorbed in the permeate liquid, and some of the resin components permeate. The low molecular weight components are also mainly non-electrolytes. Therefore, electrodialysis of this permeate causes less contamination of the dialysis membrane than the conventional method of directly electrodialyzing the paint liquid, allows long-term operation of the equipment, and reduces the pH of the paint liquid during operation. Regeneration treatment is possible under favorable conditions without causing extreme changes in concentration. According to the present invention, the electrodialysis method uses an anion exchange membrane and a cation exchange membrane alternately,
A device in which a superfiltered permeate of the paint solution is supplied to a compartment of a divided chamber, a dialysis concentration chamber is filled with a dilute inorganic electrolyte solution, and the cathode and anode chambers at both ends are filled with an electrolyte solution. Can be done. On the other hand, a dialysis device consisting only of anion exchange membranes and a dialysis device consisting only of cation exchange membranes are connected in series or in parallel, and anion exchange membranes and cation exchange membranes are installed alternately. It is also possible to obtain the same effect as a dialysis machine. As described above, the method of the present invention does not require operations such as recycling used ion exchange resin, which was essential in the conventional electrocoating paint recycling process, and therefore eliminates the problems that occur during ion exchange resin recycling. A large amount of C such as
It is also extremely useful in terms of pollution control, since a large amount of wastewater containing OD components can be eliminated.

Furthermore, since such complicated operations can be omitted, the operation process is also simplified. Recycling of the paint does not cause a sudden change in the composition of the electrodeposition bath and does not adversely affect the thickness or properties of the electrodeposition film. Therefore, smooth electrodeposition operation can be performed. One embodiment of the present invention will be explained below with reference to the drawings.

In FIG. 1, the paint liquid drawn out from the electrodeposition tank 1 into the sub-tank 2 is sent to the super-filtration device 4 by the pump 3, and the obtained concentrated liquid is sent to the sub-tank 8, while the obtained permeated liquid is sent to the sub-tank 8. The liquid is controlled to open and close by the bypass valve 11.
An appropriate amount of the liquid is sent to the sub-tank 5, and from there to the electrodialyzer 7 for dialysis, and the deionized liquid is sent to the sub-tank 8. The paint liquid in the sub-tank 8 is returned to the electrodeposition tank 1. The dialysis concentrate leaving the electrodialysis device 7 is sent to a tank 10, from where it is sent to the electrodialysis device 7 via a pump 9 for circulation.
When the concentrated liquid in the tank 10 reaches a certain concentration, it is replaced with fresh liquid. The present invention will be explained below with reference to Examples.

Example 1 Electrodeposition paint liquid (solid content concentration 8.0%, pH 9.17, specific resistance 1800Ω (V7
Acrylic melamine resin paint liquid (l/20℃) 100e
was taken out from the electrodeposition tank and fed to an ultraf filtration device equipped with an AbcOrHFM ultrafiltration membrane at a liquid pressure of 3.6 kg/CTIL2, and the obtained concentrate was returned to the electrodeposition tank via a subtank, while the obtained concentrate was Of the collected permeate, 22 e/h was supplied to the electrodialyzer.

The electrodialysis device consists of 10 pairs of cation exchange membranes (Neocepta C66-5T1 manufactured by Tokuyama Soda Co., Ltd.) and anion exchange membranes (
NeoSepta ACH-45T (manufactured by Tokuyama Soda Co., Ltd.) was used as the second
It was arranged in the manner shown in the figure and had an effective area of 40 dm2. 6 in this compartment? The liquid was passed at a flow rate of /Sec. The electrode chamber was divided by a cation exchange membrane, 1 (fl) of mirabilite solution was circulated, and 0.002N mirabilite solution was circulated in the dialysis ion concentration side chamber, and continuous treatment was performed at a current density of 30 mA/Dm2. The dialyzed solution was sufficiently deionized. Also, at this time, CO to the concentration side circulating fluid
The permeation of a certain component D was extremely small. The electrodialyzed solution was sent to a sub-tank where it was mixed with the concentrated solution, and then returned to the electrodeposition bath.

After continuing this process for 5 hours, the paint liquid in the electrodeposition tank had a pH of 8.
．． 9. Specific resistance 2050ΩCTIL. /20°C, the film thickness decreased, and the gloss recovered to the same level as before the electrodeposition paint liquid deteriorated. Table 1 shows a comparison between each liquid after each step and the paint liquid after regeneration.

As is clear from the above explanation, according to the method of the present invention, impurity ions and impurity substances that are generated in the electrocoating liquid and are undesirable for electrocoating are removed from the electrocoating liquid during the electrocoating process. , the painting process can be operated pollution-free and simply without emitting large amounts of substances with high COD values that are unavoidably generated in the recycling process to the outside as in conventional methods, Moreover, the resulting electrocoated finished product has the advantage that the coating film has excellent physical properties as described above.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram of an electrodeposition coating liquid regeneration process showing one embodiment of the present invention.

Claims (1)

[Claims] 1 Electrodeposition coating liquid in the electrodeposition coating process is separated into a concentrated treatment liquid and a permeation treatment liquid by filtration treatment, the concentration treatment liquid is returned to the electrodeposition tank, and the permeation treatment liquid is passed through an anion exchange membrane and a cation exchange 1. A method for regenerating an electrodeposition coating solution, which comprises introducing the solution into an electrodialysis device comprising a membrane for dialysis treatment, and returning the deionized solution to an electrodeposition tank.