JPH0125396B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for cleaning a permeable membrane such as an excess membrane or a reverse osmosis membrane used in a cationic electrodeposition coating process to remove a coating solution or a cleaning solution containing excess coating material.

Prior Art Generally, in electrodeposition coating, an article to be coated made of a conductive substrate is immersed in a paint liquid in a paint liquid tank, a diaphragm electrode is provided in the paint liquid tank, and the electrode is used as an anode and the article as a cathode. The article is coated by applying a voltage between the diaphragm electrode and the article. A so-called cationic electrodeposition coating method is known.

In this type of electrodeposition coating method, resin decomposition products, neutralizing agents, and other unnecessary substances accumulate during coating, so the coating liquid and washing waste liquid are subjected to excessive operations such as overflow or reverse osmosis to separate unnecessary substances. The concentrated paint liquid obtained upon removal is reused.

However, in membrane separation using permeable membranes such as overflow or reverse osmosis, the membranes themselves become clogged as over-operation progresses, so it is necessary to clean the membranes.

This clogging of the membrane is generally understood to be caused by metal carbonate salts formed when carbon dioxide gas in the air is absorbed into the paint liquid. An aqueous solution was supplied to the permeable membrane and the membrane was cleaned (Special Publication Publication No. 1983-
(Refer to Publication No. 52240).

However, in such conventional cleaning methods, since the acetic acid solution is prepared and supplied separately, it takes time and effort to control the concentration, etc., and it is inevitably disadvantageous in that it is costly.

OBJECT OF THE INVENTION That is, an object of the present invention is to provide a method for cleaning a permeable membrane by an extremely easy and inexpensive means without requiring special concentration control or the like.

Another object of the present invention is to provide a cleaning method in which the polar liquid of the diaphragm electrode is used as a cleaning solution for the permeable membrane.

Structure of the Invention According to the present invention, (A) an electrically conductive article to be coated is immersed in a paint liquid tank, a voltage is applied between the diaphragm electrode provided in the paint liquid tank and the article, and (B) A process for circulating and supplying the polar liquid in the diaphragm electrode; (C) A cleaning process for removing excess paint adhering to the coating surface formed in the coating process; (D) ) At least a part of the paint liquid in the painting process or the cleaning liquid containing surplus paint recovered in the washing process is introduced into a permeable membrane such as an excess membrane or a reverse osmosis membrane to form a filtrate and a concentrated paint liquid. Overprocessing to separate into
A cationic electrodeposition coating method comprising: supplying a part of the polar liquid that is circulated into the diaphragm electrode to the permeable membrane to clean the permeable membrane; A cleaning method is provided.

Preferred Embodiments of the Invention The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 showing an example of an apparatus for suitably performing cationic electrodeposition coating, a coating area generally indicated by A along a conveyance path 2 of an article to be coated 1;
A cleaning area, generally designated B, is provided.

The article 1 to be coated is an electrically conductive article, and any article mainly made of metal can be used. For example, continuous strip-shaped metal plates, metal wires or strands, molded products such as rods, plates, pipes, etc., parts and assemblies of vehicles, electrical equipment, building materials, furniture, etc. can be used.

The coating area A includes a paint liquid tank 3 equipped with a diaphragm electrode 70 and an article 1 to be coated in the paint liquid 4 in the paint liquid tank 3.
It consists of an article support and conveyance mechanism C for immersing and conveying the article, and a power supply mechanism D for applying a voltage between the article and the electrode.

The article to be coated 1 is transferred to the insulating member 5 by the conveyance mechanism C.
The hanger 6 is suspended on the power supply rail 8 connected to the negative side of the power supply 7 through the hanger 6.
A current collector (not shown) attached to the slider slides to apply a negative voltage. A positive terminal of the power source 7 is connected to an electrode 71 inside the diaphragm electrode 70.

The coating liquid 4 includes, for example, a resin having a cation-forming group such as a quaternary ammonium group, a neutralizing agent or stabilizer such as acetic acid, lactic acid, and glycolic acid;
It also contains various other solvents, pigments, surfactants, electrolyte salts, etc., and is used as a so-called cationic paint.

That is, according to the present invention, a voltage is applied using the diaphragm electrode 70 provided in the paint liquid tank 3 as an anode and the conductive object to be coated 1 immersed in the paint liquid 4 as a cathode, thereby performing cationic electrodeposition coating. It will be done.

In this case, current is applied between the two electrodes while the paint liquid in the liquid tank is circulated or stirred by the pump 9 via the riser 10.

The applied voltage is generally between 50 and 300 volts and the current is on the order of 1 to 15 amperes per dm ² of article area. The article may be immersed, energized, and transported by either the so-called slipper-dip method or the tact method.In the case of continuous articles, a continuous metal plate or metal wire may be continuously immersed in the paint liquid tank 3. Any method of supplying this information may be adopted. Paint liquid 4 stored in paint liquid tank 3
Although the concentration varies depending on the purpose of coating, generally speaking, it is preferably 10 to 30%. In this way, an electrodeposited coating film with a thickness of 5 to 100 μm can be formed on the surface of the article.

A diaphragm electrode 70 provided in the paint liquid tank 3 includes an electrode 71 made of stainless steel, ferrite carbon, etc., and an electrode 72 provided around the electrode 71, as shown in FIG. an electrically insulating diaphragm box 73 containing the diaphragm box 7;
It consists of a diaphragm 74, such as an ion exchange membrane, which is stretched over an opening facing the article 3 to be coated and partitions the paint liquid 4 and the electrode 71.

As this diaphragm, a known ion exchange membrane is used, such as an ion exchange membrane formed by hot-pressing a cationic resin such as polystyrene divinyl onto fibers such as polypropylene.

As electrodeposition coating progresses, the electrode 71 dissolves in the polar liquid (the electrode liquid in the area divided by the diaphragm box 73 and the diaphragm 74) and cations are generated. 72 and paint liquid 4
Since the cations are separated from each other, it is effectively prevented that the cations enter the paint liquid and adversely affect the coating. As the polar liquid 72, a solution of acetic acid, formic acid, lactic acid, gelicolic acid, etc. is generally used.

In the present invention, the polar liquid 72 is supplied in circulation. That is, the polar liquid 72 is circulated through the circulation pump 75, and the degree of ionization, that is, the electrical conductivity, of the polar liquid 72 is measured by the ionization meter 76, and if the acid concentration in the polar liquid 72 increases, By supplying pure water from the pipe 77 into the polar liquid tank 78 to dilute the polar liquid 72, the concentration of acid such as acetic acid in the polar liquid 72 is controlled.

As mentioned above, the paint liquid 4 contains acid components such as acetic acid, lactic acid, and glycolic acid that are used as neutralizing agents or stabilizers, but as the electrodeposition progresses, the paint It adheres to the article to be coated 1 and is taken out from the coating liquid 4. As a result, the acid concentration in the paint liquid 4 increases, and the balance between the neutralizer or stabilizer in the paint liquid 4 and the paint is lost, leading to poor painting work.

Since acetate ions and the like pass through the diaphragm 74, the acid concentration in the polar solution increases as cationic electrodeposition coating progresses.

Therefore, in the present invention, as described above, the polar liquid 72
The concentration of acids such as acetic acid is controlled by circulating the water and replenishing pure water as needed to keep its electrical conductivity constant, thereby maintaining the balance between the neutralizer or stabilizer in the paint solution 4 and the paint. It is.

The acid concentration in this polar liquid is generally controlled to be on the order of 1000 to 2500 ppm.

If the concentration of an acid such as acetic acid exceeds the above range, water or the like is appropriately replenished, and the increased amount of polar liquid is discharged from the system. Discharging is normally carried out after a neutralizing treatment is carried out by supplying and mixing a neutralizing agent through piping 79.

An auxiliary tank 11 is provided adjacent to the paint liquid tank 3. That is, the paint liquid 4 in the paint liquid tank 3
The paint liquid overflows into the auxiliary tank 11 from above the partition wall 12 of both tanks, and bubbles and debris on the paint liquid are removed in the auxiliary tank 11.

The paint liquid overflowing into the auxiliary tank 11 is circulated into the paint liquid tank 3 via a paint liquid circulation path 13. Although only one such circulation path is shown in the embodiment shown in the accompanying drawings, more than one circulation path will generally be employed.

In the specific example shown in FIG. 1, in order to make the composition of the paint inside the paint liquid tank 3 uniform and to perform uniform stirring, the paint liquid from the auxiliary tank 11 is transferred to the paint liquid tank 3.
A circulation path 13 is provided for circulating the paint liquid, and a pump 9 and a riser 10 for circulating and stirring the paint liquid are provided in this circulation path 13.

In the middle of the circulation path 13, the path can be branched to provide a replenishment tank 14 and a replenishment paint agitation pump 14' for replenishing the paint liquid. Instead of adding the auxiliary tank 11 to the paint liquid tank 3, the paint liquid may of course be taken out from the top of the paint liquid tank 3 and circulated to the bottom.

The electrodeposition coating film formed in this way is insoluble in water, but when the article to be coated comes out of the paint liquid tank 3 after finishing the electrodeposition coating, the surface of the electrodeposition coating film is The paint in the paint tank inevitably physically adheres to the paint. If the paint physically adhered to the surface of the electrodeposited coating is heated as it is, defects such as uneven color and non-uniform gloss will occur.

Therefore, the article to be coated 1 on which the electrodeposition coating film is formed
After being lifted from the coating liquid 4, in the cleaning area B, the excess coating liquid physically attached to the electrodeposited coating film and carried out is removed by washing.

The cleaning area B is provided close to the unloading side of the coating area A and along the conveyance path 2. This cleaning area B is
In the case of this embodiment, it consists of a first cleaning area E and a second cleaning area F that are arranged in series in the conveying direction of the coated article. In this case, the first cleaning area E consists of a liquid tank 16 containing a cleaning liquid 15 containing excess paint, and the electrodeposition-coated articles from the electrodeposition coating area A are supported and conveyed by a hanger 6 and immersed in the cleaning liquid 15. and then undergoes primary cleaning. The coated article is then lifted out of the cleaning liquid 15 and exposed to a spray shower from nozzles 17, 18 in a second cleaning zone F to complete the cleaning operation. The excess paint-containing liquid 15 in the liquid tank 16 is transferred from the bottom to the pipe 19.
The liquid is extracted from the spray tube 21 by the pump 20 and is sprayed for preliminary cleaning of the article 1 to be coated, and then circulated to the auxiliary tank 11.

Further, an excess device or reverse osmosis device 22 is provided in series with the paint liquid tank 3 or the auxiliary tank 11, and an excess device or reverse osmosis device 23 is provided in series with the surplus paint-containing cleaning liquid recovery tank 16.

That is, as the electrodeposition coating progresses, the paint liquid tank 3
The solid content of the paint liquid 4 in the cleaning area B has been diluted, and the cleaning liquid containing excess paint recovered in the cleaning area B contains paint components in a diluted form.

Therefore, in the present invention, at least a part of the paint solution 4 region or the surplus paint-containing cleaning solution 15 is led to an excess device or a reverse osmosis device to separate and recover the concentrated paint solution, and this is provided for reuse. It is.

In the embodiment shown in FIG. 1, a pipe 24 is provided to draw out the paint liquid 4 from the bottom of the auxiliary tank 11 and lead it to an excess device or a reverse osmosis device 22. The coating liquid is supplied to the high pressure side of the excess device 22, etc. The filtrate 25 separated by the excess device 22 is stored in a reservoir 26, while the concentrated paint liquid is stored in the piping 22.
7 and then circulated to the paint liquid tank 3. The excess liquid 25 in the liquid reservoir 26 is sent to the spray nozzle 17 of the second cleaning liquid F through the piping 28 and the excess liquid sending pump 29, and is used for the secondary cleaning of the coated article. It is used as a sealing liquid for the sealing parts of pumps 24' and 29.

Further, a pipe 31 is provided for extracting the excess paint-containing cleaning liquid 15 from the bottom of the cleaning liquid recovery tank 16 and leading it to the excess equipment 23. Supplied to the paint passage side (high pressure side). In this way, the water contained in the cleaning liquid and the low molecular weight components in the paint pass through the excess membrane, etc., and enter the liquid 33.
The liquid is discharged to the liquid reservoir 34 as a liquid.

On the other hand, the liquid in which the paint solids in the cleaning liquid are concentrated can be reused if mixed with the paint liquid.
It is circulated in concentrated form to the auxiliary tank 11 through the pipe 35. The collected filtrate 33 passes through the piping 36 and the filtrate feed pump 37 to the second cleaning area F.
is sent to the spray nozzle 18 of.

In the present invention, the excess device includes salts,
A specific permeable membrane capable of permeating low-molecular substances such as solvents or decomposed resin molecules, i.e., a relatively dense cellulose-based, polyamide-based, or polysulfonate-based permeable membrane layer with a thickness of 0.1 to 10 microns, and a supporting layer. Spongy thickness 20 to 1000 with permeability
A tubular type that uses an excess permeable membrane consisting of a micron auxiliary tank, a spiral type that uses a permeable membrane and a support layer (porous sheet) wound in a spiral, or a hollow fiber type that uses a permeable membrane that is processed into a hollow fiber shape. Any excess device such as may be used. For example, such an excess permeable membrane may be formed into an open tube or assembled into a flat plate, and paint liquid or cleaning liquid may be applied under pressure to the passage surrounded by the permeable membrane at a rate of, for example, 0.5 to 5 kg/kg. It is passed under a pressure of cm ² gauge and is separated into a filtrate containing the aforementioned low molecular weight solutes and a paint liquid with concentrated paint solids.

Further, as the reverse osmosis device, any reverse osmosis device equipped with a selectively permeable membrane that allows only water in the paint solution to pass through is used, and the liquid containing the paint is passed through the passage surrounded by this selectively permeable membrane. Under high pressure, e.g.
By passing it under a pressure of 100 kg/cm ² , it is separated into a filtrate consisting of water that does not contain low-molecular soluble components such as salts and a liquid in which the paint content is concentrated.

An important feature of the present invention is that a part of the polar liquid 72 that is circulated and supplied into the diaphragm electrode 70 is used as a cleaning liquid for the permeable membrane.

That is, from the circulation process of the polar liquid 72, a part of the polar liquid 72 is supplied to the excess device or the permeation membrane of the reverse osmosis device 22 and/or 23 via the pump 38 and the piping 39.

The permeable membranes used in these overflow devices become clogged due to precipitation of carbonates such as lead carbonate during long-term electrodeposition coating.

Therefore, the polar liquid 72 contains 1000% of acid such as acetic acid.
Since it is contained on the order of ~2500ppm, as mentioned above, by using a part of the polar liquid to clean the permeable membrane, lead carbonate, etc. deposited on the permeable membrane can be effectively cleaned and removed. be.

Moreover, the concentration of acid such as acetic acid in this polar liquid 72 is
Since it is controlled to maintain the balance with the paint, even if it is mixed into the paint liquid, the composition of the paint liquid will not substantially change or deteriorate.

In addition, there is no need to install a special control mechanism to control the acid concentration of the cleaning liquid or a new cleaning liquid supply mechanism, and it can be easily implemented by making a simple design change to the conventional coating equipment. The advantages are achieved, which are both cost-effective and cost-effective.

The supply of the polar liquid 72 during cleaning is preferably carried out by supplying it to the permeable side of the permeable membrane and bringing it into contact with the permeable membrane, or by backwashing. Generally, on the flow side of the membrane, metal acetates, etc. are ionized around the cationic resin and stabilized by dissociation, so metal carbonates do not precipitate, and on the liquid side of the membrane, the metal salts become cationic. This is because it is considered that metal carbonate is precipitated because it separates from the resin and becomes unstable.

Therefore, it is preferable to supply the polar liquid 72 to the liquid side.

The contact between the polar liquid 72 and the permeable membrane during cleaning is as follows:
Although it varies depending on the state of clogging of the permeable membrane, it generally takes about 30 minutes to 3 hours. Backwash is 30~
After 60 minutes of continuous spinning, it is sufficient to continue spinning for about 0.5 to 1 minute.

In addition, the polar liquid 72 is supplied as a cleaning liquid by itself, but as long as the concentration of acid such as acetic acid is 200 ppm or more, it is diluted and used by replenishing pure water or excess liquid from the pipe 80 or excess liquid from the reverse osmosis device. It is also possible.

In the present invention, during normal painting work without cleaning, a portion of the polar liquid is pumped into various pumps 9, 15, 2 used in each process.
It can also be used as a sealing liquid for flushing seal parts such as 0, 24', 29, 32, 37, 38, 75, etc.

That is, since the polar liquid 72 contains an acid such as acetic acid, it has the effect of dissolving and removing the rotary part of the paint and precipitated salts adhering to the rotating shaft of the pump, the seal surface, etc. By using such a polar liquid as a sealing liquid, deterioration of the coating liquid and substantial variation in the coating composition can be effectively prevented, and electrodeposition coating using a closed circuit becomes possible.

Thus, it will be understood that according to the present invention, a permeable membrane can be cleaned by extremely easy and inexpensive means without requiring special concentration control or a special acid supply tank.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a specific example for suitably carrying out the method of the present invention, and FIG. 2 is a diagram showing an example of the polar liquid circulation process. A is the paint area, B is the cleaning area, C is the transport mechanism, D is the power supply mechanism, E is the primary cleaning area, F is the secondary cleaning area, 1
1 is an article to be painted, 3 is a paint liquid tank, 4 is a paint liquid, 11
is an auxiliary tank, 15 is a cleaning liquid containing surplus paint, 16 is a cleaning liquid tank, 22 and 23 are excess equipment or reverse osmosis equipment, 38 is a polar liquid supply pump, 39 is a polar liquid supply pipe, 70 is a diaphragm electrode, and 72 is a polar liquid , 75 is a polar liquid circulation supply pump, and 76 is an ionization meter.

Claims (1)

[Scope of Claims] 1 (A) A conductive article to be coated is immersed in a paint liquid tank, and a voltage is applied between the diaphragm electrode provided in the paint liquid tank and the article to (B) A process for circulating and supplying the polar liquid inside the diaphragm electrode. (C) A cleaning process for removing excess paint adhering to the coating surface formed in the painting process. (D) In the above painting process. A passing process in which at least a part of the paint liquid or the cleaning liquid containing excess paint recovered in the washing process is introduced into a permeable membrane such as an excess membrane or a reverse osmosis membrane to separate it into a filtrate and a concentrated paint liquid. A cationic electrodeposition coating method comprising: supplying a part of the polar liquid that is circulated into the diaphragm electrode to the permeable membrane to clean the permeable membrane. Cleaning method.