JPS5941498A - Treatment of electrodeposition paint bath - Google Patents

Abstract

PURPOSE:To prevent the org. solvent of an electrodeposition paint bath from being exhausted out of a system and to eliminate the accumulation of impurity ions, by a method wherein the paint in an electrodeposition paint bath is subjected to ultrafiltration treatment and the conc. liquid is returned to the above mentioned bath while the filtrate is subjected to reverse osmosis treatment to be converted to washing water which is, in turn, used in the deionizing treatment of the conc. liquid. CONSTITUTION:After an object to be coated is painted by an electrodeposition paint bath 1, the coated one is washed by washing baths 2, 3. On the other hand, the paint in the bath 1 is guided to an ultrafiltration apparatus 4 and the obtained conc. liquid 5 is directly returned to the bath 1 while the filtrate 6 is sent to a storage tank 7. In this case, the part of the filtrate is treated by a reverse osmosis apparatus 8 and the filtrate 9 from which an org. solvent and impurity ions are removed by reverse osmosis treatment is sent to the washing bath 3 to be used by washing the object to be coated. On the other hand, the conc. liquid 10 by the apparatus 8 is returned to the storage tank 7 and the part thereof is returned to the bath 1 by a pipeline 11. At this time, impurity ions are removed by an anion exchange resin tower 12 and a cation exchange resin tower 13 provided to the bypass 14 of the pipeline 11.

Description

[Detailed description of the invention] The present invention relates to a method of treating an electrocoating paint bath.

The paint in the electrodeposition paint bath is subjected to ultrafiltration treatment, and the liquid is used to wash the excess paint that has adhered to the coated object with water, collect it, and then return it to the electrodeposition paint bath. The so-called closed-circuit electrodeposition coating method, in which paint components are returned to the electrodeposition paint bath as a concentrated liquid, is used to save paint and prevent pollution.
It has already been put into practical use for car body painting, etc. However, according to such a conventional ultrafiltration treatment method for an electrodeposition paint bath, as is well known, the electrodeposition paint bath contains about 2 to 5% by volume of a ta-containing solvent. ,
This organic solvent will be contained in the filtrate of ultrafiltration treatment, so if this filtrate is used for washing the object to be coated,
Since it is discharged as wastewater from the coating system after washing together with the washing water supplied from outside the system, it increases the COD and BOD loads of the wastewater. In addition, in the electrocoating paint bath, for example, when painting the body of an automobile, miscellaneous ions such as phosphate ions from the pre-treatment stage of painting such as surface treatment are gradually accumulated, resulting in the gloss of the painted surface. Conventionally, the filtrate of ultrafiltration was partially discharged into the system to control the concentration of miscellaneous ions in the electrodeposition bath. Discharge of such filtrate not only unnecessarily discards the solvent, which is a valuable component, but also increases the COD and T30D loads of the wastewater, as described above.

The present invention was made in order to solve the above-mentioned problems in electrodeposition coating, and it does not discharge the organic solvent from the electrodeposition paint bath to the outside of the system, and also prevents the accumulation of miscellaneous ions in the electrodeposition paint bath. It is an object of the present invention to provide a method for treating an electrodeposition paint bath that can avoid such problems.

The method for treating an electrodeposition bath according to the present invention involves ultrafiltrating at least a portion of the paint in the electrodeposition paint bath, returning the resulting concentrate to the electrodeposition paint bath, and subjecting the filtrate to reverse osmosis treatment. It is characterized in that at least 1 B of the filtrate from the osmosis treatment is used as water for washing the object to be coated, and at least a part of the concentrated liquid from the reverse osmosis treatment is returned to the electrodeposition paint bath after being treated with an ion exchange resin. .

Preferred embodiments of the present invention will be described below based on the drawings.

After the object to be coated (not shown) is coated with electrodeposition paint bath 1,
Excess paint adhered is washed off in water wash baths 2 and 3. On the other hand, the paint in the electrodeposition paint bath is led to an ultrafiltration device 4, and the concentrated liquid 5 obtained here is returned to the electrodeposition paint bath as it is, while the filtrate 6 is sent to a storage tank 7. Here, a part of the filtrate is treated by the reverse osmosis device 8, and the reverse osmosis treated filtrate 9 from which organic solvents and miscellaneous ions have been removed is sent to the water washing bath 3 and used for washing the object to be coated. Ru.

On the other hand, the concentrated liquid 1o obtained by reverse osmosis treatment is returned to the storage tank 7,
Some parts are electrodeposited using pipe 11! 1′, :I bath. In the present invention 1, the anion exchange phase JJ is added to this conduit.
T? A bypass 14 comprising a column 1.2 and a cation exchange resin column 13 is provided, and by operating a valve, a part or the entire amount is returned to the electrodeposition paint bath after removal of miscellaneous ions by ion exchange treatment. Of course, if necessary, ion exchange treatment may be performed using only either an anion exchange resin or a cation exchange resin.

In the above, the filtrate 6 from ultrafiltration is introduced into the storage tank 7, and the filtrate is introduced from there to the reverse osmosis device.
The concentrated liquid obtained by reverse osmosis treatment is returned to this storage tank 7. Therefore, the filtrate from the ultrafiltration and the concentrate from the reverse osmosis treatment are mixed in the storage tank 7, and a portion of these is returned to the electrodeposition paint bath via the pipe 11 (and bypass 14). In this case, the filtrate obtained by ultrafiltration can be immediately led to the reverse osmosis device, and the obtained concentrated liquid can be sent to the pipe line 11 without providing the storage tank 7.

In addition, in the present invention, since the object to be coated is washed with water using a reverse osmosis filtrate that does not contain a solvent, the concentration of the solvent in the washing bath becomes very small, and it is not washed away during the washing bath. In order to avoid agglomeration of the paint, the reverse osmosis treatment is applied: l! A part of the contracted flow 10 can also be returned to the washing bath 2 and/or 3 through a pipe (not shown).

As described above, according to the present invention, the paint from the electroattractive paint bath is subjected to ultrafiltration treatment, the filtrate containing organic solvent thus obtained is then subjected to reverse osmosis treatment, and the filtrate free of organic solvent and miscellaneous ions is obtained. This concentrated liquid is ion-exchanged and returned to the electrocoating paint bath, so that no harmful ions are accumulated in the electrocoating paint bath and do not have a harmful effect on the coating. ,
Moreover, the organic solvent is directly returned to the electrodeposition paint bath. Therefore, the organic solvent is not discharged to the outside of the system, contributing to its saving. In other words, the filtrate obtained by reverse osmosis treatment does not contain any organic solvent, and therefore, the object to be coated that has been washed with this filtrate is finally washed in the third water washing bath 15 with washing water supplied from the system. Even when cleaning is done, the washing wastewater generated here does not contain organic solvents, which contributes to the prevention of pollution.

[Brief explanation of drawings]

The drawing is a flowchart 1 showing a preferred embodiment of the method of the invention. 1... Electrodeposition paint bath, 4... Ultrafiltration device, 5...
Filtrate by ultrafiltration treatment, 6... Filtrate by ultrafiltration treatment, 8... Reverse osmosis device, 9... Filtrate by reverse osmosis treatment, 10... Concentrate liquid by reverse osmosis treatment, 12...・
Anion resin exchange tower, 13...Cation resin exchange tower.

Claims (1)

[Claims] (1) Part of the paint in the electrocoating paint bath is subjected to ultrafiltration treatment, the resulting concentrated liquid is returned to the electrocoat paint bath, and the filtrate is subjected to reverse osmosis treatment. Electrodeposition bath treatment characterized in that a part of the water is used as washing water for the object to be coated, and at least a part of the concentrated liquid obtained by reverse osmosis treatment is treated with an ion exchange resin and then returned to the electrodeposition paint bath. Method.