JPS5839239B2 - How to prepare electrodeposition paint liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing an electrodeposition coating liquid containing an ionically dissolved synthetic resin, and is intended to facilitate electrodeposition coating operations.

Electrodeposition coating is widely used as a coating technique.

However, the following two points are still raised as problems regarding the coating technology.

The first problem relates to the collection of adhering paint liquid by taking it out.

In order to remove the adhering paint liquid remaining on the object to be treated, the object to be treated is transported from the electrodeposition process to the washing step, and washing water is sprayed onto the object, or the object is placed in a washing tank filled with washing water. It is common practice to soak and wash.

The paint liquid washed out from the object to be treated is dissolved in the washing water, but this is, in other words, a loss of the paint carried out from the electrodeposition bath, and if this continues for a long period of time, the amount of loss becomes enormous.

Therefore, some measure is desired to collect the washed out paint and return it to the electrodeposition bath for recycling.

The second problem concerns the removal of miscellaneous ions that cause various adverse effects.

During electrodeposition coating, the polycarboxylic acids, pigments, organic solvents, and other additives in the electrodeposition paint form a coating film on the object to be coated, which is the anode, and are removed from the electrodeposition bath, but some of the amines or Most of the sulfate ions, phosphate ions, zinc ions, and various substances present in the pigments are generally accumulated in the electrodeposition bath, while the processing liquid from the conversion coating process of the cane treatment body is carried into the paint. Some or most of the contaminant low-molecular-weight ions, such as water-soluble ions, accumulate in the paint, so the resistivity of the paint liquid gradually decreases and deteriorates.

When an object to be treated is electrodeposited using such a deteriorated paint liquid, pinholes are formed in the electrodeposited film during baking, resulting in a decrease in corrosion resistance and appearance.

Further, positively charged amines, ammonia, etc. are liberated from the paint over time, and the pH of the paint increases.

If electrodeposition is performed using an electrodeposition solution with such an elevated pH, the thickness of the finished coating film will become extremely thick, which will not only result in a decrease in performance, but also cause problems such as a marked decrease in the gloss of the coating film. There is a problem.

Therefore, some measure is desired to prevent the accumulation of various inorganic ions, including amines, which are free in the electrodeposition bath.

The present invention has been made in view of the above-mentioned problems, and provides a method for preparing an electrodeposition paint that simultaneously solves both of the above-mentioned problems in a continuous electrodeposition process.

Conventionally, as a technique to deal with the above-mentioned problems,
496 are known.

This technology removes low molecular weight substances and excess counterions from the bath composition by subjecting the electrodeposition composition to an ultrafiltration process, and removes the concentrated liquid (paint solids) and permeate liquid (containing miscellaneous ions and low molecular weight substances). ), the concentrated liquid is returned to the electrodeposition bath, and the permeated liquid is subjected to reverse osmosis treatment to obtain a second concentrated liquid and a second permeated liquid, and at least a part of the second permeated liquid is transferred to the object to be treated. In this method, the second concentrated liquid is used as washing water and the second concentrated liquid is discharged.

In this technique, the second concentrated liquid is discharged, but since this liquid contains a small amount of effective low-molecular coating material, it would be very effective if it could be recycled.

On the other hand, this second concentrated liquid contains miscellaneous ions that have a serious effect on the object to be processed, and these must be removed.

The inventor has discovered that both of these problems can be solved at once by the method of the present invention described in the claims.

In the present invention, at least a part of an electrodeposition bath liquid containing an ionically dissolved synthetic resin is subjected to ultrafiltration treatment to be separated into a concentrated liquid and a permeated liquid, and the concentrated liquid is returned to the electrodeposition bath, while the permeated liquid is is subjected to reverse osmosis treatment to separate it into a second permeated liquid and a second concentrated liquid, and the permeated liquid is supplied to a washing tank or a liquid draining tank, and the second concentrated liquid is subjected to an ion exchange treatment to obtain a third permeated liquid. , a method for preparing an electrodeposition coating liquid, characterized in that the third permeate liquid is supplied to a washing tank or a drain tank of the object to be treated in the same manner as the second permeate liquid.

The electrodeposition bath liquid used in the present invention may be any known electrodeposition coating liquid in which a synthetic resin vehicle is ionically dissolved, and which has been conventionally used for electrodeposition coating.

There are also particular restrictions on equipment for ultrafiltration, reverse osmosis, and ion exchange.

The method of the present invention will be explained below with reference to the drawings. In Fig. 1, 1 is an electrodeposition coating tank containing an electrodeposition bath liquid, 2 is a washing tank, and the object to be treated (not shown) is placed in the electrodeposition bath. After being electrodeposited, it is pulled out and transported to the washing tank 2.

This washing tank has 2 tanks or 3 inspection levels.

The electrodeposition coating tank 1 is connected to a sub-tank 3, a part of the electrodeposition bath liquid is sent to the sub-tank 3, and at least a part of the electrodeposition paint liquid in the sub-tank 3 is sent to an ultrafiltration treatment 4.

The concentrated liquid is separated into a concentrated liquid and a permeated liquid by the ultrafiltration process, and the concentrated liquid containing substantially a polymer resin and a pigment is returned to the sub-tank 3, and the permeated liquid is sent to the reverse osmosis device 5.

A second permeated liquid and a second concentrated liquid are obtained by the reverse osmosis treatment. Since the second permeated liquid is an aqueous medium that is substantially purer than the electrodeposition bath, it is sent to the washing tank as washing water for the object to be treated.

The second concentrated liquid is sent to the ion exchange device 6.

A third permeate from which miscellaneous ions have been substantially removed by the ion exchange treatment is obtained, a part of which is sent to the washing tank 2 as washing water for the object to be treated, and the other part is sent to the sub-tank 3.

The washing water overflows from the washing tank to the electrodeposition coating tank 1, and the electrodeposition coating liquid is replenished from the sub-tank 3 to the electrodeposition bath.

In this case, comparing the purity of the second permeate with the second a condensate and the third permeate (pH value and electrical conductivity are factors), the second permeate is the purest, followed by the third permeate. liquid,
This is followed by the second concentrated liquid.

Therefore, when cleaning the object to be treated, it is preferable to send the second permeate to the rear washing tank and the third permeate to the previous wash tank (see FIG. 1).

Figure 2 shows an example of the case where the object to be treated is electrocoated using a vertical hanging method. is the first
A draining tank 2' is provided in place of the washing tank 2 higher than in the case shown in the figure.

This method is currently being widely adopted because it has advantages such as saving the area of the electrodeposition bath and improving drainage compared to the horizontal hanging method, and it prevents the adhering paint from staying on the surface of the aluminum shape. This is convenient because the liquid drains naturally.

By the way, the adhering paint in the first drain tank 2' is
Compared to the adhering paint in the final draining tank, the solvent,
The paint itself is stable due to its high water content, and can be sent to the electrodeposition bath again for reuse.

However, the adhering paint that remains in the final draining tank 2' tends to gel, become a gel substance, and easily become dirty.

Therefore, in this system, the pure second permeate is continuously or intermittently supplied to the final drain tank 2', and the third permeate is supplied as required.

This prevents the formation of gel substances and makes it possible to effectively recover the paint.

EXAMPLE 8% (by weight) of an electrodeposition paint having the following composition in which a vehicle resin (thermosetting acrylic paint) was ionically dissolved was placed in an electrodeposition coating tank (capacity: 77 I'') to form an electrodeposition bath. The A-6063 extruded material to be treated was electrocoated in the bath by the method shown in FIG. 1 (the amount of amine in the bath was 40±31n9/I).

○ Composition of electrodeposition paint A thermosetting acrylic resin Aqueous solution organic solvent containing amine compound A-... 150 d of coating was applied per day with a film thickness of 10 to 12 μm.

Electrodeposition bath 19.631 A was applied to an ultrafiltration device (UP) using a membrane (cellulose acetate type), concentrated liquid 18.41 A, and permeated liquid 1.23 A! was separated.

1.231 A of this permeated liquid was subjected to reverse osmosis (RO) (permeable membrane polyamide resin system) to separate 0.03 A of the second permeated liquid and 1.27 A of the second concentrated liquid.

The third permeated liquid obtained by treating the second concentrated liquid 1.21 with an anion type and cation type ion exchange resin is transferred to the previous washing tank.
The permeate was supplied to the subsequent washing tank as washing water, and the overflow was returned to the electrodeposition bath.

The results in this step were as follows.

○UF: Inlet pressure 4 to 9/cI7L, outlet pressure 3.
7 to 9/cal, inlet temperature 23°C ○RO: Inlet pressure 20 kg/cir, inlet pressure
18yu/CTL Inlet temperature 23℃ ○ Electrodeposition bath liquid: pH 8,26 Electrical conductivity 600μ0/c
IIL ○UF, the state after RO treatment The pH of the RO permeate is 9.80, but the liquid volume is l
/40, and the pH value is 6.4 to 7 due to ion exchange treatment.
, 2, so it is not a problem when considered as a whole.

Electrical conductivity after ion exchange is 170-220μO/CIr
It became L.

The pH value is preferably a low value between 8 and 8.5, and the lower the electrical conductivity, the purer it is, so the above results are preferable.

In the above example, the method of separating the second permeated liquid and the second concentrated liquid, using the second permeated liquid as washing water, and discharging the second concentrated liquid is a conventional method. pH and pH of the bath when subjected to ion exchange treatment by the method of the present invention
Figure 3 shows the comparison of changes in .

As is clear from this graph, according to the conventional method, it is necessary to perform ion exchange treatment periodically, and ion exchange treatment (K
(A is a cation exchange treatment, A is an anion exchange treatment), a temporary decrease in pH is observed, but an overall decrease in pH is observed, but the overall pH value tends to be high, so bath management is required. It's not easy.

On the other hand, according to the present invention, since the pH value is continuously kept constant, electrodeposition coating can be performed smoothly.

As mentioned above, the present invention utilizes a combination of an ultrafiltration device, a reverse osmosis device, and an ion exchange device to improve
-1496), it is possible to completely recover the low-molecular resin paint components present in the second concentrated liquid that has passed through the reverse osmosis device, and the third permeated liquid that has passed through the ion exchange device contains miscellaneous ions and low-molecular-weight resins. Since it is substantially pure and does not contain any paint components, it can be reused as washing water in a washing bath and/or an electrodeposition bath, and a series of continuous operations can be performed. Effective recovery of paint by carry-out and substantially pure wash water are obtained, facilitating the electrocoating operation.

[Brief explanation of the drawing]

Figure 1 is a flow sheet showing an example of the method of the present invention;
Figure 3 is a flow sheet showing another embodiment of the method of the present invention.
The figure is a curve diagram showing the change over time in the pH value of the electrodeposition bath solution. 1... Electrodeposition coating tank, 2... Washing tank, 3
...Subtank, 4...Ultrafiltration device, 5...Reverse osmosis device, 6...Ion exchange device, 2'... Liquid drain tank.

Claims (1)

[Scope of Claims] 1. At least a part of the electrodeposition bath liquid containing the ionically dissolved synthetic resin is subjected to ultraviolet overtreatment to be separated into a concentrated liquid and a permeated liquid, and the concentrated liquid is returned to the electrodeposition bath. On the other hand, the permeated liquid is subjected to reverse osmosis treatment to be separated into a second permeated liquid and a second concentrated liquid, and the permeated liquid is supplied to a washing tank or a liquid draining tank, and the second concentrated liquid is subjected to an ion exchange treatment and a third concentrated liquid is obtained. A method for preparing an electrodeposition coating liquid, which comprises obtaining a permeated liquid and supplying the third permeated liquid to a washing tank or a liquid draining tank of the object to be treated in the same manner as the second permeated liquid. 2. A method for preparing an electrodeposition coating liquid according to claim 1, characterized in that the second permeate liquid and the third permeate liquid are used as washing water for a vertically suspended object to be treated.