JP3303893B2 - Control of acid backwashing time of cationic electrodeposition coating liquid and new acid backwashing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a module of a selectively permeable filtration membrane, such as an ultrafiltration membrane, to recover a paint by washing an object to be coated with water with a filtrate and to use a used cationic electrodeposition. The present invention relates to a novel acid backwashing method for a cationic electrodeposition coating solution, which can keep a filtrate amount of a membrane module high when separating unnecessary components such as inorganic salts from a paint. Furthermore, the present invention provides a novel acid backwash under specific conditions of the membrane module, which is not only a crystal of inorganic salts such as mainly lead carbonate deposited on the outside of the membrane surface of the membrane module under normal operation, but also an inner salt. A new acid backwashing method for cationic electrodeposition coating liquid that elutes mainly the crystals of inorganic salts such as lead phosphate deposited on the cross section and prevents the formation of gel layers such as electrodeposition paints and pigments deposited on the inside It is about. Further, the present invention relates to a novel method for backwashing a cationic electrodeposition coating solution, wherein the position of an acid backwash hole provided in a membrane module is improved.

[0002] The present invention also relates to a novel management method for determining the start time of acid backwashing. More specifically,
The present invention, the factors that determine the Sangyakuarai start timing (b) Chemical treatment
Specific electric conductivity of the water adhered management of an object to be coated after final wash, (ii) phosphorus in the coating stock solution acid radical, the filtrate volume leaving the (c) membrane module Nitsu
In addition, the present invention relates to a novel management method in which a specific element alone or a combination thereof is out of an allowable limit value. In addition, the present invention, in the acid backwash, all specific conditions
Contact the acid solution to the membrane cross section of the membrane module as long as the conditions are satisfied.
Der relates acid backwash method of cationic electrodeposition coating liquid for
You. More specifically, the present invention provides a specific range of (a) acid concentration,
(b) Sangyakuarai time, (c) Sangyakuarai speed and (d) Sangyakuarai amount of all
The present invention relates to a novel acid backwashing method for a cationic electrodeposition coating liquid, in which an acid backwash in a range satisfying the condition (1) is applied to a membrane module.

[0003]

2. Description of the Related Art With the development of electrodeposition technology, management of a cationic electrodeposition coating liquid has become an important problem. In other words, the cationic electrodeposition coating liquid is contained in an aqueous medium in a state where the basic resin is solubilized by an acid, and as the basic resin is used, the basic resin is electrodeposited as a coating film on the substrate. The acid used for the solubilization remains in the solution. In addition, unnecessary components such as carbon dioxide from the atmosphere, organic solvents from supplements, various salts from pretreatment (chemical conversion treatment), and decomposition products from resins, etc. accumulate in the electrodeposition coating liquid during use. become. As a result, various drawbacks such as deterioration of the electrodeposition coating film and deterioration of electric efficiency occur. Therefore, it is a major challenge in electrodeposition coating to remove the above-mentioned unnecessary components from the electrodeposition coating solution while collecting the paint, and to maintain the composition always in a state not much different from the initial use. In fact, many processing methods have been proposed. Among them, the most efficient one is a membrane treatment method using an ultrafiltration membrane that collects and regenerates the active ingredient and stably circulates the filtrate obtained by separating the unnecessary ingredient. is there.

In this film processing method, the stability of the electrodeposition paint is
There is a need for a method that can stabilize the amount of filtrate at a high level because of changes in paint concentration and contamination with impurities. The solution to this problem was to increase the pressure of the electrodeposition paint.However, the more pressure applied, the more clogging of the membrane module became, and the performance of the membrane became stable and high level in the long term. Had a problem.

[0005]

As a basic means for solving clogging of a membrane module, a method of backwashing a membrane module with an acid has also been developed (Japanese Patent Publication No. 59-52240). FIG. 2 is a schematic diagram showing a state where crystals are deposited on a cross section of the membrane module when the membrane module is continuously operated. In this case, although crystal precipitation on the outside (filtrate side) of the membrane module as shown in FIG. 2- (A) can be prevented, if the long-term operation is performed, the membrane module as shown in FIG. 2- (B) There is a problem that a coating is gradually formed on the inner cross section and the inner side, and clogging of the membrane module newly occurs, and a fundamental solution thereof is demanded. In addition, even if an attempt is made to prevent clogging of the membrane module by the above-described acid backwashing, the time for starting the acid backwashing may be a time when the operation is temporarily or irregularly temporarily stopped, or Taking advantage of the experience of crystal precipitation and coating formation on the membrane module, the company has been forced to take temporary measures such as temporarily performing acid backwashing, and is far from a systematic solution. Was desired.

[0006]

As a result of various studies on the above-mentioned problems, the present inventors have found that the crystal coating deposited on the inner cross section of the above-mentioned membrane module does not elute by ordinary acid backwashing.
The cause is that the phosphoric acid used in the chemical conversion treatment process remains in the adhesion water of the object to be coated, and the phosphate ions combine with the lead ions in the paint to become lead phosphate, which precipitates as lead phosphate crystals. discovered that due to the deposited film module section, the start timing of Sangyakuarai to the membrane module membrane surface
Determined by management based on specific detection items , and
By performing the acid backwash in a range that satisfies all conditions found to be able to fully prevent the clogging of the membrane module, thereby completing the present invention.

More specifically, the inventor of the present invention has empirically determined that the acid backwashing start time is determined by: (a) the specific conductivity of the water adhering to the object to be processed (work) after the final water washing of the chemical conversion treatment ; (B) Phosphate groups in the undiluted paint solution , (c) The present invention is completed by experimentally confirming a close relationship with the permissible limit of the amount of filtrate, and finding a combination of permissible limits. Reached. Furthermore,
Specifically, the inventor of the present invention has found that acid backwashing is performed when (a) acid concentration, (b) acid
Backwash time, (c) acid backwash rate (acid backwash flow rate), (d) acid backwash
Experimentally confirm that all elements of quantity are closely related
As a result, the present invention has been completed .

That is, the present invention provides:
In the process of recovering the cationic electrodeposition coating solution,
Of the aliphatic or aromatic monovalent or intermittent
Starts acid backwashing when backwashing a polyacid-containing solution.
following( I ), ( B ) Or ( I ) + ( B ) Combination,
( I ) + ( C ) Combination, ( B ) + ( C ) Or ( I ) + ( B ) + ( C ) Combination
Limit of detection items in the electrodeposition coating process consisting of
Pickling time of the cationic electrodeposition coating liquid to be carried out when it comes off
To provide a management method. (B) Specific conductivity of the water adhering to the substrate after the final rinsing of the chemical conversion treatment
(B) Phosphate groups in the stock solution of electrodeposition paint, (c) The amount of filtrate leaving the membrane module.  By membrane treatment method
In the process of recovering the cationic electrodeposition coating solution,
Of the aliphatic or aromatic monovalent or intermittent
In the acid backwashing of the polyacid containing solution,(a) to (d)
All ofThe acid is added to the membrane section of the membrane module within the range that satisfies the conditions.
A method of backwashing the cationic electrodeposition coating solution by contacting the solution.
Offer. (a) Acid concentration: 600 ppm or more, (b) Acid backwashing time: 60 seconds or more / between 30 minutes and 24 hours
(C) Acid backwashing rate (acid backwashing flow rate): 5 L / min / module
(D) Acid backwashing amount: 5 L / module or more.  Or, in the backwash, the drainage distribution of the membrane module
Acid provided at the opposite end, opposite to the end with the tube
Bring the acid solution into contact with the membrane section of the membrane module through the backwash hole
Another feature is that it is a method.  Or smell
And acid backwashing at the upper and lower ends or in the middle of the membrane module
The acid backwash hole provided on the membrane section of the membrane module
Another feature is that it is a method of contacting a liquid.

Hereinafter, the present invention will be described in detail with reference to the drawings and the like. FIG. 3 is a schematic diagram showing a flowchart for performing cationic electrodeposition coating according to the method of the present invention. The cationic electrodeposition coating step basically includes five steps: a degreasing step, a chemical conversion step, an electrodeposition (coating) step, a washing step, and a baking step. In this step, the membrane module 1 is used in a step that connects the electrodeposition step and the washing step.

That is, typically, the membrane module 1 is used in an electrodeposition bath 15 to extract water and other low-molecular components from the contaminated electrodeposition paint (stock solution) 2 to form a concentrated paint. The filtrate 3 containing the water and other low-molecular components is returned to the electrodeposition tank 15 as 2 ′, and is returned to the water washing step including a plurality of water washing tanks 16 as a water washing liquid.

The membrane module referred to in the present invention is basically any membrane module which can separate an effective component such as a resin and a pigment in an electrodeposition coating material from unnecessary components such as water, impurity ions and other low molecular components. , And a film having an average pore diameter of 1 μm or less. If the pore diameter is larger than this, a coating component, a resin, a pigment, and the like effective for electrodeposition will be transmitted. Preferably, the average pore size is 0.5 μm or less or the molecular weight cut off is 50.
Ultrafiltration membranes (UF), reverse osmosis membranes (RO), microfilters (MF) and the like having a molecular weight of 100,000 or less may be mentioned, and these may be used alone or in combination. Particularly, an ultrafiltration membrane (UF) is preferable.

In addition, there are pores having a skin layer on the surface and having selective permeation ability for blocking large molecules and permeating only small molecules, and a supporting layer below which pores are continuously increased. So-called asymmetric membranes can also be used. In addition, a pre-filter such as a bag filter is provided before the stock solution 2 is put into the membrane module of the present invention to separate aggregates and the like.
It may be removed. Further details will be described.

In the degreasing step, oil stains adhering to the surface of the object 9 such as a metal steel plate are washed in a degreasing bath 10 using an alkaline solution and the like, and then washed in a washing bath 11 to remove electricity. This is a step in which the electrodeposition paint can be efficiently electrodeposited on the surface of the article 9 in the application step. The chemical conversion treatment step is performed as a pretreatment for electrodeposition coating in order to improve coating adhesion and corrosion resistance. In the chemical conversion bath 12, the surface of the article 9 is usually subjected to a phosphoric acid coating treatment, In this step, the phosphoric acid remaining on the surface of the article 9 by washing with the washing bath 13 is washed away. The cation electrodeposition step is a step of using the object 9 as a negative electrode and depositing an electrodeposition paint having a positive charge on the surface of the object 9. The washing process is a process in which a plurality of washing tanks 1
This is a step of washing the excess paint components adhered to the surface of the article 9 with a washing liquid (filtrate) and overflowing the components effective for electrodeposition into the electrodeposition tank 15.

By controlling the amount of the electrodeposition solution overflowed from the washing step and the amount of the electrodeposition solution separated and concentrated in the membrane module 1 or the like, the concentration of the electrodeposition solution in the electrodeposition tank 15 can be kept constant. You can keep it. However, when the filtration of the electrodeposition paint by the membrane module 1 is continuously performed for a long period of time, when the membrane module 1 is backwashed with an acid according to the conventional method, lead carbonate is mainly contained outside the membrane module as shown in FIG. The deposition of crystals of the inorganic carbonate is no longer observed, but as shown in FIG. 2- (b), the deposition of crystals is gradually formed on the inner cross section of the membrane module.
A gel layer made of a resin and a pigment is also formed inside the membrane module, and the membrane module is newly clogged.

[0015] However, the present invention is from reaching the inner cross-section and inner clogging of the membrane modules is eliminated by acid backwash in the range that meet certain all <br/> conditions below. FIG. 1 is a schematic diagram showing the positions of acid backwash holes provided in a membrane module for performing acid backwash according to the method of the present invention. That is, as shown in FIG. 1, an aliphatic and aromatic monovalent or polyvalent acid-containing solution is supplied from the acid backwash (hole) 4 of the membrane module 1 within a range satisfying all of the following specific conditions. by acid backwash the membrane cross-section, outer membrane module, the inner cross-section, the inner clogging does not occur. (a) Acid concentration: 600 ppm or more, (b) Acid backwashing time: 60 seconds or more / intermittent continuous at intervals of 30 minutes to 24 hours (c) Acid backwashing speed (acid backwashing flow rate): 5 L / min / (D) Acid backwash: 5 L / module or more.

The acid solution used in the present invention refers to an acid solution of an acid such as an aliphatic or aromatic monohydric or polyhydric acid such as acetic acid, formic acid, hydroxyacetic acid, glycolic acid, lactic acid alone or a combination thereof. . The use of acetic acid is preferred. Here, the acid backwash refers to backwashing the filtrate containing the acid solution at a predetermined concentration on the membrane cross section of the membrane module. Thus, for example, Figure 1 -
As in the conventional example shown in (a), the filtrate discharge hole of the membrane module 1 is used as it is, and the specific amount of (a) to (d) is added to the filtrate.
Not only conditions the case of feeding on the injection of the acid solution in a range satisfying the Te, 1 - as shown in (b), towards providing separate and filtrate holes and Sangyaku washing hole is preferred. That is, acid reverse
The location of the washing hole is the end of the membrane module where the drainage pipe is located.
Is a case where it is provided at the opposite end located oppositely . Further, as shown in FIG. 1- (C), it is preferable to provide a plurality of places such as two places because the supply of the acid solution to the membrane module becomes uniform. In addition, the upper and lower ends of the membrane module are more efficient as the location of the acid backwashing hole. It may be provided in the middle of the membrane module. That is, the acid backwash hole is placed above the membrane module.
This is a case where a plurality is provided at the lower end or at the middle .

According to the above method of the present invention, in particular, a crystal of inorganic carbonate mainly composed of lead phosphate deposited on the inner cross section of the membrane module can be positively dissolved, which is a preferable method. In the present invention, it is necessary to carry out the acid backwash in a range that meet certain all <br/> conditions. That is, (a) the acid concentration is 500 ppm or more, preferably 50 ppm
0 to 5,000 ppm, more preferably 700 to 20,000 ppm
00 ppm. (b) Acid backwashing time of 60 seconds or more / 30 minutes to 24 hours, preferably 60 to 600 seconds / 30 minutes to 24 hours, more preferably 60 to 240 seconds / 30 minutes to 24 hours. It is. (c) The acid supply rate is 5 L / min / module or more, preferably 6 to 10 L / min / module, more preferably 6 to 8 L / min / module.
L / min / module. (d) The acid backwashing amount is 5 L / min / module or more, preferably 6-15 L / min / module, more preferably 6-12.
L / min / module.

In the present invention, when the acid concentration (a) is extremely high, the pH in the electrodeposition solution is greatly reduced, which has an adverse effect. If the acid concentration (a) is less than 500 ppm, lead carbonate and lead phosphate deposited on the film surface cannot be sufficiently dissolved. The acid backwashing time (b) is 60 seconds / 30.
If the interval is less than minutes to 24 hours, lead carbonate and lead phosphate deposited on the film surface cannot be sufficiently dissolved. If the acid backwashing time (b) is extremely long, the filtration efficiency will be reduced. When the acid supply rate (c) is less than 5 L / min / module, the effect of backwashing is reduced. On the other hand, if the speed is extremely high, the backwash pressure increases and the film is damaged. If the acid backwashing amount (d) is less than 5 L / min / module, the amount of acid passing through the inner cross section of the membrane decreases, and the effect of acid backwashing decreases. On the other hand, if the acid backwashing amount (d) is extremely large, it exceeds the upper limit of the amount of neutralizing agent (MEQ; acid amount) in the paint control, which adversely affects the coating.

In the present invention, it is preferable to discard the filtrate when the value of the neutralizing agent of the paint becomes high. In particular, it is effective to drain the filtrate immediately after the acid backwash. The start time of the specific acid backwashing in the present invention is desirably determined by the method of starting the specific acid backwashing start time according to the present invention, but is not limited thereto, and for example, unnecessary components such as inorganic salts may be contained in the membrane module. It may be carried out in batches at a certain amount of deposition time, or it may be carried out periodically by using a specific acid backwashing operation at a predetermined time, taking advantage of the experience in the operation up to now. good.

Next, the start time of the acid backwashing has been conventionally determined on a batch basis empirically, but according to the control method of the present invention,
The following specific elements (a) to (c) below alone or
Union of the combination [(a), (b) any one of, or (a) + (b)
So, the combination of (a) + (c), a set of (b) + (c) or (b) + (b) + (c)
It carried out when an off-allowable limit value of the detection item in comprising electrodeposition coating process from combined], it is the efficiency desirable to employ management methods acid backwash time of cationic electrodeposition coating solution. (B) Specific conductivity of water adhering to the substrate after the final washing of the chemical conversion treatment; (b) Phosphate groups in the stock solution of electrodeposition paint; and (c) the amount of filtrate leaving the membrane module. More specifically, the present invention is preferably carried out under the following conditions for controlling the timing of acid backwashing.

(A) When the specific conductivity of the water adhering to the object after the final washing of the chemical conversion treatment exceeds 30 to 60 S / cm, (b) the phosphate group in the undiluted solution of the electrodeposition paint is 10 to 10 S / cm. If the concentration exceeds 30 ppm, (c) the amount of filtrate exiting the membrane module is 80 to 95% of the set value.
If it falls below. In implementing the above management method,
The acid backwashing start signal issued from the inspection points (a) to (c) above is transmitted to the acid backwash pump located at the position connected to the membrane module, and the pump is operated to start the acid backwash. It is desirable to adopt a method of doing so. Of course, when the acid backwash time has arrived by the implementation of the management method of the present invention, the acid backwash pump may be manually operated.

The permissible limit value in the method of controlling the timing of the acid backwash is determined by (c): the type and concentration of the cationic electrodeposition paint, the neutralizing agent (acid) to be incorporated, and additives such as pigment. Is a value determined by the amount of filtrate in which the stock solution of the paint determined by the type of the liquid exits the membrane module. The acid backwashing time of the present invention is controlled so as not to deviate from the permissible limit value, so that unnecessary components such as inorganic salts are not always deposited on the membrane module, and a stable cationic electrodeposition coating is performed. Is important.

The allowable limit value is as follows: (a) The specific conductivity is 30 to 60.
When it exceeds μS / cm, preferably 30 to 50 μS / cm, more preferably 30 to 40 μS / cm, (b) the phosphate group is 10 to 30 ppm, preferably 10 to 20 pp
m, more preferably more than 10-15 ppm,
(C) The amount of the filtrate is 80 to 95% of the set value, preferably 85 to 95%.
95%, more preferably below 90-95%. When the permissible limit value is in the above range, the desired effect can be obtained.

Hereinafter, a specific description will be given with reference to the drawings.
In FIG. 3, the object 9 having left the chemical conversion bath 12 is washed with a washing bath 13.
The specific conductivity in the attached water 14 after washing with water is automatically measured by a specific conductivity meter, and (a) the specific conductivity is 30 to 60 μm.
If the signal exceeds S / cm, the signal is sent to the acid backwash pump 21.
To start the acid backwash. At that time, the acid is pumped up from the acid tank 18 by an acid injection pump (not shown) which operates simultaneously with the acid backwash pump 21, while the filtrate is injected from the filtrate tank 17 to obtain an acid solution having a predetermined concentration and the acid backwash pump. By operating 21, a predetermined amount of backwash flows through the acid backwash hole for a predetermined time and at a backwash speed, and is brought into contact with the membrane surface of the membrane module 1. In addition, a phosphate measuring device for paint is put in the electrodeposition tank 15 and automatically measured. (B) When the phosphate exceeds 10 to 30 ppm, the signal is transmitted to the acid backwashing pump 21, Activate and start pickling. Further, the value of the filtrate flow meter 23 is (c) the set value of the filtrate amount of 80 to 80%.
When the signal falls below 95%, the signal is sent to the acid backwash pump 21.
To start the acid backwash. In the present case, the combination of (a), (b) either, or (b) + (B),
The combination of (a) + (c), the combination of (b) + (c) or (b) + (b) + (c)
Limited to As measuring instruments for detecting the allowable values of (a) to (c), for example, (a) is a specific conductivity meter, (b) is an ion meter,
For (c), a filtrate flow meter can be used.

[0025]

The present invention is illustrated by the following examples, which do not limit the scope of the invention. (Example 1) According to the electrodeposition coating process of FIG.
Using the UF-1000 electrodeposition paint of Asahi Kasei Kogyo Co., Ltd., UF module KCV-3010, as the (b) time of the method of controlling the acid backwashing time of the present invention, the phosphoric acid root in the stock solution of the electrodeposition paint was 45 ppm. Ultrafiltration was sometimes performed, and acetic acid was used as an acid backwashing solution, and the results of acid backwashing under the following conditions were summarized in the following table. NV (non-volatile content) 20 ± 1% pH 6.3 ± 0.2 MEQ (amount of acetic acid neutralizer) 27 ± 2 Specific conductivity (μS / cm) 1550 ± 100 Pb 1500 ppm PO ₄ 45 ppm UF Operating conditions Inlet / Exit 2.8 / 0.8 (kg /
cm ² ) Acid backwash conditions (table below) Backwash / filtration Continuous operation at a filtration interval of 60 seconds / 60 minutes

[0026]

[Table 1]

[0027]

[Table 2] <Change in filtrate volume>

[0028]

[Table 3] <Results of membrane module analysis: after 2 years>

(Comparative Example A) Further, acid backwashing is carried out under the same conditions as in Example 1;
When the concentration of the phosphate group in the stock solution of the electrodeposition paint is 7 ppm, smooth cationic electrodeposition cannot be performed. Also, when the acid backwashing time management method (A) and (C) of the present invention also deviate from the allowable values, a smooth cationic electrodeposition coating cannot be performed.

Example 2 According to the electrodeposition coating process of FIG. 3, E manufactured by Kansai Paint Co., Ltd.
The electrodeposition paint of L-0400 was subjected to ultrafiltration using UF module KCV-3010 manufactured by Asahi Kasei Kogyo Co., Ltd., and acid backwashing was performed under the following conditions using acetic acid as an acid backwashing solution. 4 to 5.

Paint NV (non-volatile) 10 ± 1% pH 6.5 ± 0.2 MEQ (amount of acetic acid neutralizer) 30 ± 2 Specific conductivity (μS / cm) 1600 ± 100 Conductivity (μS / cm) 90 UF Operating conditions Inlet / outlet 2.5 / 0.5 (kg /
cm ² ) Acid backwashing conditions 600 ppm Backwash pressure excess 2.0 (kg / cm ² )

[0032]

[Table 4] In Table 5, as for the form of the acid backwashing hole in the membrane module, FIG. 1- (a) was used for Comparative Example 3, and FIG. 1- (B) was used for Example 2.

[0033]

[Table 5] <Change in filtrate volume / Results of membrane analysis>

[0034]

According to the novel acid backwashing method of the cationic electrodeposition coating solution according to the present invention, the filtrate amount of the membrane module can be kept high, and lead carbonate deposited on the outside, inside section and inside of the membrane surface of the membrane module. And the formation of gel layers of lead phosphate crystals, electrodeposition paints, and pigments, thereby preventing clogging of the membrane module. Further, the acid backwashing start time can be rationally determined by the specific method of controlling the acid backwash according to the present invention.
Also, smooth acid backwashing within the range that satisfies all specific conditions
Can be done .

[Brief description of the drawings]

FIG. 1 is a schematic view showing the positions of acid backwash holes provided in a membrane module for performing acid backwash according to the method of the present invention.

FIG. 2 is a schematic diagram showing a state where crystals are deposited on a cross section of the membrane module when the membrane module is operated continuously.

FIG. 3 is a schematic diagram showing a flowchart for performing cationic electrodeposition coating according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Membrane module 2 Electrocoat (paint undiluted solution) 2 'Concentrated paint 3 Filtrate (hole) 4 Acid backwash (hole) 9 Coating object 10 Degreasing bath 11, 13 Rinse bath 12 Chemical bath 14 Adhered water 15 Electroplating tank 16 , 16 'Rinse tank 17 Filtrate tank 18 Acid tank 19 Signal 20 Circulation pump 21 Acid backwash pump 22 Filtrate pump 23 Filtrate flow meter 24 Filtrate discharge flow meter A Specific conductivity B Paint phosphate root C Filtrate amount

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C25D 13/24 301 B01D 61/22 B01D 65/06

Claims (6)

(57) [Claims] In the step of recovering a cationic electrodeposition coating solution by a membrane treatment method, an acid or aromatic monovalent or polyvalent acid-containing solution is intermittently and continuously backwashed on a cross section of a membrane of a membrane module. , Start of acid backwashing in any of the following ( a ) and ( b )
Or ( a ) + ( b ) combination, ( b ) + ( c ) combination, ( b ) +
( C ) or ( b ) + ( b ) + ( c ), the acid reversal of the cation electrodeposition coating liquid, which is carried out when the detection limit in the electrodeposition coating process is out of the permissible limit value of the combination. How to manage the washing time. (B) Specific conductivity of water adhering to the object after the final washing in the chemical conversion treatment; (b) Phosphate groups in the stock solution of electrodeposition paint; and (c) the amount of filtrate leaving the membrane module. 2. An acid backwash is provided with a drainage pipe of the membrane module.
Acid backwash holes provided at the opposite end opposite to the end
A method for bringing the acid solution into contact with the membrane cross section of the membrane module.
The cationic electrodeposition coating according to claim 1, characterized in that:
How to control the timing of acid backwashing of liquid . 3. The method according to claim 3, wherein the acid backwash is performed at the upper and lower ends of the membrane module or
From the acid backwash holes provided in the middle, the membrane of the membrane module
Characterized in that it is a method of bringing the acid solution into contact with a cross section.
The acid backwashing time of the cationic electrodeposition coating solution according to claim 1
Management method . 4. In the step of recovering a cationic electrodeposition coating solution by a membrane treatment method, an acid and / or aromatic monovalent or polyvalent acid-containing solution is intermittently and continuously backwashed on a membrane section of the membrane module. An acid backwashing method for a cationic electrodeposition coating solution, wherein the acid solution is brought into contact with the membrane section of the membrane module within a range satisfying all of the following conditions (a) to (d) . (a) Acid concentration: 600 ppm or more, (b) Acid backwashing time: 60 seconds or more / intermittent continuous at intervals of 30 minutes to 24 hours (c) Acid backwashing speed (acid backwashing flow rate): 5 L / min / (D) Acid backwash: 5 L / module or more. 5. An acid backwash is provided with a drainage pipe of the membrane module.
Acid or backwash holes provided on the opposite end you located opposite to the end portion
A method for bringing the acid solution into contact with the membrane cross section of the membrane module.
The cationic electrodeposition coating according to claim 4, characterized in that:
Acid backwashing method of liquid . 6. An acid backwash is performed at the upper and lower ends of the membrane module or
From the acid backwash holes provided in the middle, the membrane of the membrane module
Characterized in that it is a method of bringing the acid solution into contact with a cross section.
The method for backwashing a cationic electrodeposition coating solution according to claim 4 .