JPH11290620A - Filtration device and treatment liquid circulation device for coating process using the same - Google Patents

Abstract

(57) [Summary] [Problem] A filtered device which is not concentrated in one place, has excellent cleaning properties and replacement workability, and has a long service life and a circulating flow rate of a processing solution can be automatically and constantly maintained. Provided is a treatment liquid circulation device for a coating process. A filtering device (24a) provided in a circulation system of an electrodeposition coating device or a degreasing device, and a housing (241).
a, a liquid inlet 243a formed in the housing, a filter medium holding tube 244a having a plurality of through holes 245a, one end of which is provided through one main surface of the housing, and a plurality of through holes. 247a attached to the filter medium holding tube
And a liquid outlet 251a provided outside the housing and at the other end of the filter medium holding tube. Liquid inlet 243a
Is provided on the bottom surface of the housing or a surface having substantially the same height as the housing, and the liquid outlet 251a is provided vertically below the liquid inlet 243a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtering device used in an electrodeposition coating device or a degreasing device for an automobile body or an automobile part, and a processing liquid circulation device using the same. The present invention relates to a filtration device which is not concentrated, has good cleaning properties and replacement workability, and has a long service life, and a treatment liquid circulation device for a coating process using the same.

[0002]

2. Description of the Related Art Undercoating is used for painting an automobile body.
A three-coat coating system consisting of an intermediate coating and a top coating is employed. Among these, the undercoating process comprises various processes such as water washing, degreasing, surface conditioning, chemical conversion, and electrodeposition.

[0003] These coating processes include working water or pure water for a washing process, a degreasing solution for a degreasing process, a surface conditioning solution for a surface conditioning process, and a chemical conversion solution for a chemical conversion process. In the case of the electrodeposition coating process, various types of liquids (hereinafter simply referred to as processing liquids) for performing processing, such as an electrodeposition coating liquid, pure water, and working water, are sprayed on the body, or a tank filled with the processing liquid. A processing liquid circulation device for returning the processing liquid to the inside is provided.

[0004] A conventional processing liquid circulating apparatus mainly comprises a circulating pipe constituting a system, a pump, and a filter for removing foreign matter in the processing liquid. A heat exchanger is provided for the processing liquid that needs to be maintained at the temperature.

[0005] Above all, in the degreasing step and the electrodeposition coating step, a large amount of dust is brought into the tank by the body, and it is important to periodically clean and replace the filter. FIG. 9 shows a filter 24 conventionally used in the electrodeposition coating process. The filter 24 has a filter cartridge 247 mounted on a partition plate 252 formed in the housing 241 and is formed above the housing 241. Liquid inlet 2
The coating liquid is introduced from 43, and the filtrate is drawn out from a liquid outlet 251 formed downstream of the partition plate 252. Housing 2
The coating liquid introduced into the filter cartridge 41
47 through the through hole of the internal conduit 244 and the partition plate 2
After passing through the filter cartridge 247, dust passes through the filter cartridge 247 and is filtered, and the filtered dust is deposited upstream of the partition plate 252. The accumulated dust is periodically cleaned, and the filter cartridge 247 is replaced at regular intervals.

[0006]

However, in such a conventional filter 24, dust tends to accumulate on the upstream side of the partition plate 252 when the operation is continued for a long time (shown by oblique lines in FIG. 9). Filter cartridge 247
Is substantially reduced. Further, dust deposited on the filter 24 is difficult to remove and cleaning workability is extremely poor. Further, when the filter cartridge 247 is replaced, solidified deposits hinder the replacement workability.

In the conventional filter 24, the pressure gauges 23 are attached to the upstream and downstream sides of the partition plate 252, and the pressure difference between these pressure gauges is periodically checked to determine the timing for cleaning or replacing the filter. However, the degree of clogging of the filter does not simply correlate with the operating time of the processing liquid circulation device, and it may be clogged in a short time depending on the environment, such as after a holiday or after settling. Not a few. If the amount of dust contained in the coating liquid is larger than usual, the circulator will continue to operate with the filter clogged unless the frequency of filter differential pressure management is increased, and the required discharge rate will be insufficient. As a result, the processing quality is reduced.

[0008] Conversely, clogging may be difficult if the coating liquid itself is kept clean even if it is operated for a long time, but this is the case when the cleanliness of the coating liquid is maintained at a high level. However, the frequency of differential pressure management cannot be reduced because sudden garbage can be generated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and the filtered dust is not concentrated at one place, and has excellent cleaning properties and replacement workability, and has a long service life. An object of the present invention is to provide an apparatus and a processing liquid circulation apparatus for a coating process that can automatically and constantly maintain a circulation flow rate of the processing liquid.

[0010]

According to a first aspect of the present invention, there is provided a filtration apparatus provided in a circulation system of an electrodeposition coating apparatus or a degreasing apparatus, comprising: a housing; A formed liquid inlet, a filter medium holding tube having a plurality of through holes, one end of which is provided through one main surface of the housing; and the filter medium holding tube covering the plurality of through holes. And a liquid outlet provided outside the housing and at the other end of the filter medium holding tube, wherein the liquid inlet is at the bottom of the housing or at substantially the same height as the same. And the liquid outlet is provided below the liquid inlet in the vertical direction.

In the filter device according to the present invention, the liquid to be filtered is introduced into the housing through the liquid inlet, and the liquid inlet is provided on the bottom surface of the housing or a surface having substantially the same height as the housing. Therefore, after ascending in the housing, it passes through the filter medium, reaches the filter medium holding pipe through the through hole of the filter medium holding pipe, and further flows down the filter medium holding pipe to reach the liquid outlet.

That is, in the filtration device of the present invention, the liquid is introduced from below the housing, so that the liquid flow in the housing is directed upward from below, and the liquid flow direction is changed when passing through the filter medium. Since the filtrate is discharged from under the housing, the filtered dust does not accumulate in the housing. That is, dust adheres only to the surface of the filter medium, so that it is sufficient to clean or replace only the filter medium when cleaning. In addition, since such dust adheres almost uniformly to the surface of the filter medium, it is possible to prevent the effective area of the filter medium from decreasing.

[0013] In the filtration device of the present invention, the housing includes a detachably provided lid, and the filter medium is attached to and detached from the filter material holding tube. More preferably, it is provided as possible. Cleaning and replacement of the housing or the filter medium can be performed by removing the filter body while removing the lid, so that the workability is significantly improved.

In the filtering device of the present invention, although not particularly limited, the filtering device according to the third aspect is characterized in that the dust-absorbing material having a permanent magnet part at least partially replaces the part of the filtering material with the filter material holding tube. It is characterized by being provided in.

In the filter device according to the third aspect, since the dust-absorbing material having the permanent magnet portion is provided, dust such as iron powder circulating in the housing can be adsorbed.
As compared with the above-described invention, the dust collecting effect is greater, and large dust such as iron powder can be adsorbed. Therefore, clogging of the filter medium can be prevented, and the life of the filter medium can be extended.

The filtering device according to claim 3 is not limited to the filtering device according to claim 1 or 2, but has a permanent magnet portion instead of a part of the filter medium in a general filtering device. A filtering device provided with a dust absorbing material may be used.

In order to achieve the above object, the treatment liquid circulating apparatus for a coating step according to the fourth aspect is used in an electrodeposition coating apparatus or a degreasing apparatus, and the filtration apparatus according to any one of the first to third aspects. And a pump for sucking the processing liquid, wherein the processing liquid circulating apparatus for the coating process is provided in the circulation pipe, wherein the liquid for directly or indirectly detecting the differential pressure of the processing liquid at the liquid inlet and the liquid outlet of the filtration device. And a power converter for controlling power supplied to the pump based on a differential pressure of the processing liquid detected by the hydraulic pressure detector.

According to the fourth aspect of the present invention, the output of the pump is controlled by using the differential pressure of the processing liquid at the liquid inlet and the liquid outlet of the filtration device as a control factor. That is, when the differential pressure of the processing liquid at the liquid inlet and outlet of the filtration device is equal to or higher than a predetermined value,
This is nothing more than an increase in flow resistance due to dust trapped in the filtration device, so that the output of the pump is increased, and conversely, the output of the pump is reduced when the pressure difference becomes less than a predetermined value. Thereby, the discharge amount of the filtrate at the liquid outlet of the filtration device is maintained at a constant amount.

In this case, there is no particular limitation, but more specifically, there is a control method that refers to a look-up table.
6. The treatment liquid circulation device for a coating process according to claim 5, wherein the power conversion unit supplies electric power to the pump with respect to a differential pressure of the filtration device at which a flow rate of the treatment liquid discharged from a tip of the circulation pipe becomes constant. And a power supply to the pump is selected with reference to the look-up table based on the differential pressure detected by the hydraulic pressure detecting means.

Since the discharge amount of the circulating device is maintained constant by such a control method, the processing quality of the object to be processed can be maintained. In particular, in a circulation device such as an electrodeposition coating device or a degreasing device via a heat exchanger, the flow rate is directly affected by the amount of heat to be exchanged, so that the effect on temperature control is great. Also, when the present invention is applied to a spray-type cleaning device, the discharge amount is directly connected to the quality, so that the effect is large.

In the treatment liquid circulating apparatus for a coating process of the present invention, although not particularly limited, in a preferred embodiment, in the treatment liquid circulating apparatus for a coating process according to the present invention, the electric power conversion means is an electric motor of the pump. And an inverter for converting the frequency of the power supplied to the inverter.

On the other hand, the treatment liquid circulating apparatus for a coating process according to a seventh aspect of the present invention is characterized in that, when the value of the electric power supplied to the pump by the electric power conversion means becomes equal to or more than a predetermined value, an activating means for raising the effect is provided. It is further characterized by being provided.

In the present invention, there is no particular problem when the value of the electric power supplied to the pump is within the range of the electric power supplied to the pump, but when the clogging of the filtration device becomes remarkable. If the power supplied to the pump cannot cope with the problem, such as when an abnormality occurs in the circulating pipe itself or the like, it is necessary to alert the user to that effect and immediately perform cleaning, replacement, or abnormal inspection of the filtration device. I do. In this way, it is sufficient to carry out the inspection only when necessary, and the number of maintenance steps can be significantly reduced.

The filtration device and the treatment liquid circulation device for the coating process of the present invention are not particularly limited, but are applied to a degreasing process of an undercoating process, an electrodeposition coating process (including a UF water washing process and a water washing process) and the like. Preferably, the present invention can be applied to both a stirring circulation system and a spray circulation system.

[0025]

According to the first and second aspects of the present invention,
Filtered debris will not accumulate in the housing and will only adhere to the surface of the filter media.
When cleaning, it is enough to clean or replace only the filter media. In addition, since such dust adheres almost uniformly to the surface of the filter medium, it is possible to prevent the effective area of the filter medium from decreasing. Further, the cleaning and replacement workability is good.

In addition, according to the third aspect of the present invention, since relatively large dust such as iron powder circulating in the housing can be adsorbed, the dust collecting effect can be further increased and the filter medium can be adsorbed. Can be prevented from clogging, which contributes to extending the life of the filter medium.

According to the invention of claims 4 to 7,
Since the circulation flow rate of the processing solution can be automatically and constantly maintained,
The number of maintenance steps can be remarkably reduced, and the processing quality of the object to be processed can be greatly improved.

In addition to the above, according to the invention of claim 7, it is sufficient to carry out inspection only when necessary, so that the number of maintenance steps can be significantly reduced.

[0029]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a block diagram showing an embodiment of a treatment liquid circulation device for a coating process of the present invention, FIG. 2 is a sectional view showing an embodiment of a filtration device of the present invention, and FIG. 3 is an enlarged view of the filter medium of FIG. Sectional view shown as
FIG. 4 is a graph illustrating the operation of the treatment liquid circulating apparatus for a coating process of the present invention, and FIG. 5 is a graph illustrating the operation of a conventional treatment liquid circulating device for a coating process.

FIG. 1 shows an example in which the treatment liquid circulating apparatus of the present invention is applied to an agitating circulation system in an electrodeposition tank 1 of an electrodeposition coating apparatus. That is, the first circulation device 2a is an embodiment of the present invention. In addition, as the spray circulation system of the UF water washing process, the second
And third circulation devices 2b and 2c.

The electrodeposition tank 1 is filled with the electrodeposition coating liquid L, and a voltage of about 300 V is applied to an electrode (not shown).
When a direct current is applied between this and the body B on the ground side, electrophoresis of the paint particles occurs, and an electrodeposition coating film is formed on the inner and outer plates of the body B and the inner surface of the bag structure. The body B is grounded by an overhead conveyor C via a coating hanger H.

"1a" is an overflow tank of the electrodeposition tank 1, and the electrodeposition coating liquid L overflowing from the electrodeposition tank 1 is collected in the overflow tank 1a, and is again returned to the electrodeposition tank 1 by the first circulation device 2a. Returned to

First circulation device 2 according to an embodiment of the present invention
a has a circulation pipe 21a having one end connected to the overflow tank 1a and the other end connected to a nozzle 25a provided in the electrodeposition tank 1, and a pump 2 connected to the circulation pipe 21a.
2a, two pressure gauges 23a, 23a, and a filter 24a are provided. This filter 24a is a filtration device according to the present invention.

As shown in FIGS. 2 and 3, the filter 24a has a housing 241a in which a lid 242a is detachably provided.
43a is formed, and the flange of the liquid inlet 243a is connected to the flange of the circulation pipe 21a.

A plurality of through holes 2 are provided in the housing 241a.
A plurality of filter material holding tubes 244a having 45a (only three tubes are shown in FIG. 2) are provided, and a lower end portion of the filter material holding tube 244a is provided to penetrate the bottom surface of the housing 241a. As shown in FIG.
The upper end of 44a is closed, but a plurality of through holes 245a are formed in the middle, and the lower end is further connected to a liquid outlet tube 2 described later.
The liquid in the housing 241a flows into the filter medium holding tube 244a through the through hole 245a because it is communicated with the tube 46a, and reaches the liquid outlet tube 246a.

The filter medium holding pipe 244a is provided with a filter medium 247a so as to cover the plurality of through holes 245a. As shown in FIG. 3, the filter medium 247a is inserted from above using a flange 248a fixed to the filter medium holding tube 244a as a stopper, and is fixed with screws 249a. Further, a packing 250a is interposed at each of the upper and lower ends to prevent liquid from entering through the gap.

As described above, each filter medium holding tube 244a
Is connected to the liquid outlet pipe 246a at a position vertically lower than the liquid inlet 243a, and one end of the liquid outlet pipe 246a serves as a liquid outlet 251a. Is the circulation pipe 21
a.

The liquid inlet 243a and the liquid outlet 251
Pressure gauges 23a, 23a are provided in a circulation pipe 21a near a. The output signals of the two pressure gauges 23a, 23a are sent to an inverter control circuit 26a, where they are processed, and then power of a predetermined frequency is output to an electric motor (not shown) for driving the pump 22a. . Also,
The output signal from the inverter control circuit 26a is also sent to the alarm 27a.

In the latter part of the electrodeposition tank 1, UF (Ultra Filte
(r, ultrafiltration) A water washing step is provided, and the excess paint is collected from the paint adhered to the body surface in the electrodeposition tank 1 by washing the body B with pure water. The UF rinsing process of FIG. 1 comprises two stages of spray rinsing,
Each stage is provided with a collection tank 1b, 1c, respectively.

A second circulation device 2b is provided between the former recovery tank 1b and the spray nozzle 25b. One end of the second circulation device 2b is connected to the collection tank 1b.
And a circulation pipe 21b having the other end connected to a spray nozzle 25b provided in the washing chamber. The circulation pipe 21b is provided with a pump 22b and a filter 24b.

On the other hand, a third circulation device 2c is provided between the recovery tank 1c and the spray nozzle 25c at the subsequent stage.
Is provided. The third circulation device 2c has a circulation pipe 2 having one end connected to the collection tank 1c and the other end connected to a spray nozzle 25c provided in the washing chamber.
1c, and a pump 22c and a filter 24c are provided in the circulation pipe 21c.

It should be noted that a rinsing step is further provided after the UF rinsing step, and the excess paint that could not be washed in the UF rinsing step is further washed away to prevent the occurrence of secondary deposition on the electrodeposition. In addition, although the UF rinsing step in FIG. 1 is constituted by a two-stage spray rinsing step, such a specific configuration is not limited to the present invention, and a full dip rinsing step may be added.

Next, the operation will be described. First, the filter 24
For a, the liquid inlet 243a is connected to the housing 241a.
The paint liquid (containing dust) introduced into the inside rises inside the housing 241a and is filtered when the dust passes through the filter medium 247a. The filtrate that has passed through the filter medium 247a enters the filter medium holding pipe 244a from the through hole 245a of the filter medium holding pipe 244a, is collected by the liquid outlet pipe 246a, and is then led out of the liquid outlet 251a. Filter media 24
The garbage filtered in 7a remains in the housing,
Since the liquid inlet 243a is provided near the bottom surface of the housing 241a, it adheres only to the surface of the filter medium 247a without depositing on the bottom surface of the housing. Therefore, it is sufficient to clean or replace only the filter medium when cleaning. In addition, such garbage is collected by the filter medium 247a.
Will adhere almost uniformly to the surface of the filter medium 24.
The effective area of 7a can be prevented from being reduced.

By the way, to clean or replace the filter medium 247a, the operation can be easily performed only by removing the lid 242a from the housing 241a and removing the screw 249a.

On the other hand, the inverter control circuit 26a according to the present embodiment controls the frequency of the electric power supplied to the electric motor for driving the pump 22a. This control is based on output signals from the two pressure gauges 23a, 23a, based on the liquid inlet 243a and the liquid outlet 25 of the filter 24a.
1a, and the inverter output is selected based on the calculated differential pressure, as shown in the upper and middle stages of FIG. By doing so, in the first circulation device 2a, the discharge amount from the nozzle 25a becomes a constant amount.

In the conventional circulating apparatus, when the filter is clogged, a pressure difference occurs before and after the filter, thereby decreasing the discharge amount from the nozzle 25a as shown in FIG. In 2a, the output frequency from the inverter control circuit 26a is determined in accordance with the magnitude of the differential pressure across the filter 24a as shown in the upper and middle stages of FIG. The discharge amount can be maintained.

The relationship between the actual differential pressure detected by the pressure gauges 23a, 23a and the frequency output from the inverter control circuit 26a is experimentally obtained in advance and stored in a memory as a look-up table. At the time of actual operation, the determination may be made with reference to the lookup table.

The inverter control circuit 26a
Then, when the frequency of the electric power output to the pump 22a becomes equal to or higher than a predetermined value, a signal is sent to the alarm device 27a to issue an alarm. As a result, clogging and abnormalities that cannot be dealt with by increasing the capacity of the pump can be automatically alerted to the maintenance inspector.

According to the circulating apparatus 2a of this embodiment, even if the filter 24a is clogged and the discharge amount is reduced, the output of the pump 22a is increased to automatically recover the discharge amount. The simplification and the stable discharge amount make it possible to maintain and improve the stirring capacity. In addition, the alarm device 27a
Therefore, the maintenance and inspection person can appropriately and promptly perform inspection and replacement of the filter and other abnormal measures based on the notification.

Second Embodiment FIG. 6 is a sectional view showing another embodiment of the filtration device of the present invention.
FIG. 7 is an enlarged sectional view showing the dust-absorbing material of FIG.

In the present embodiment, as shown in FIG. 6, some of the plurality of filter media 247a provided in the filter device 24a are replaced with permanent magnet portions 253a made of permanent magnets.
Is attached to the filter medium holding tube 244a.

As shown in FIG. 7, the dust-absorbing material 252a has a permanent magnet portion 253a made of a permanent magnet provided at the center.
And stainless steel portions 254a made of stainless steel provided at both ends thereof, and are formed in a hollow shape so as to be inserted into the filter medium holding tube 244a. This dust absorbing material 25
2a has basically the same shape as the filter medium 247a, and can be inserted not only into the filter medium holding tube 244a but also the packing 250a and the screw 249a can be used as they are. Further, the permanent magnet portion 253a is provided at a vertically symmetric position so that it can be mounted from either side when mounted on the filter medium holding tube 244a.

The number of such dust-absorbing materials 252a to be installed is appropriately determined based on various conditions such as the concentration of dust such as iron powder contained in the liquid to be filtered, the required quality of the filtrate, and the capacity of the housing. 247a instead of dust absorbing material 252
By providing a, magnetic dust such as iron powder introduced into the housing is adsorbed by the permanent magnet portion 253a. Therefore, not only the dust removal rate is further improved, but also the clogging of the filter medium 247a is reduced by that much, so that the life of the filter medium 247a can be extended.

Also, by having the same shape and structure as the filter medium 247a, compatibility is improved, and any filter medium holding tube 24
4a can also be attached. Further, since the entire structure is formed by permanent magnets only at necessary positions instead of being formed by permanent magnets, the cost can be reduced, and by employing a vertically symmetric structure, the workability of mounting the filter medium holding tube 244a can be improved. Is improved. Except for cost, the whole may be constituted by permanent magnets.

FIG. 8 is a cross-sectional view showing still another embodiment of the filtering device of the present invention. In this example, in a filtering device having a general structure, a dust absorbing material 2 is used instead of some of the filtering media 247a.
52a are provided. In this type of filtering device 24a, as described above, if the operation is continued for a long time, dust tends to accumulate on the upstream side of the partition plate 252.
Both ends (at least the lower end) of 52 a
By setting the range in which the effective adsorption effect is achieved above the deposits, it is possible to provide an efficient adsorption effect in addition to cost reduction.

The embodiments described above are described for the purpose of facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

For example, the filter 24a shown in FIG.
The invention is not limited to the circulation system in the tank of the electrodeposition coating apparatus shown in FIG. 1, but can be applied to the stirring system in the tank of the degreasing apparatus.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a treatment liquid circulation device for a coating process of the present invention.

FIG. 2 is a cross-sectional view showing an embodiment of the filtration device of the present invention.

FIG. 3 is an enlarged sectional view showing the filter medium of FIG. 2;

FIG. 4 is a graph illustrating the operation of the treatment liquid circulation device for a coating process according to the present invention.

FIG. 5 is a graph illustrating the operation of a conventional treatment liquid circulation device for a coating process.

FIG. 6 is a sectional view showing another embodiment of the filtration device of the present invention.

FIG. 7 is an enlarged sectional view showing the dust-absorbing material of FIG. 6;

FIG. 8 is a sectional view showing still another embodiment of the filtration device of the present invention.

FIG. 9 is a sectional view showing a conventional filtration device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrodeposition tank 2a, 2b, 2c ... Circulation device 21a, 21b, 21c ... Circulation piping 22a, 22b, 22c ... Pump 23a ... Pressure gauge (flow rate detection means) 24a ... Filter (filtration device) 241a ... Housing 242a ... Lid Body 243a ... Liquid inlet 244a ... Filter medium holding tube 245a ... Through hole 246a ... Liquid outlet tube 247a ... Filter material 251a ... Liquid outlet 252a ... Dust absorbing material 253a ... Permanent magnet part 254a ... Stainless steel part 24b, 24c ... Filter 25a ... Nozzle, 25b , 25c ... Spray nozzle 26a ... Inverter control circuit (power conversion means) 27a ... Alarm (alert means) C ... Conveyor B ... Body (object to be coated) H ... Painting hanger

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B05C 11/10 B01D 29/42 501C C23G 3/00 510 C25D 13/24 301 35/02 Z

Claims (7)

[Claims] 1. A filtration device provided in a circulation system of an electrodeposition coating device or a degreasing treatment device, comprising: a housing; a liquid inlet formed in the housing;
A filter medium holding tube having a plurality of through holes and one end portion provided through one main surface of the housing, and a filter medium attached to the filter medium holding tube so as to cover the plurality of through holes; A liquid outlet provided outside the housing and at the other end of the filter medium holding tube, wherein the liquid inlet is provided on a bottom surface of the housing or a surface having substantially the same height as the housing, A liquid outlet provided below the liquid inlet in the vertical direction. 2. The filtering device according to claim 1, wherein the housing includes a detachably provided lid, and the filter medium is detachably provided on the filter medium holding tube. 3. The filtering device according to claim 1, wherein a dust-absorbing material having a permanent magnet part at least in part is provided in the filter material holding tube in place of the part of the filter material. . 4. A treatment liquid for a coating step, which is used in an electrodeposition coating apparatus or a degreasing treatment apparatus, wherein the filtration apparatus according to claim 1 and a pump for sucking the treatment liquid are provided in a circulation pipe. In the circulation device, a liquid pressure detection unit that directly or indirectly detects a differential pressure of the processing liquid at a liquid inlet and a liquid outlet of the filtration device, and a differential pressure of the processing liquid detected by the liquid pressure detecting unit. And a power converting means for controlling power supplied to the pump based on the processing liquid. 5. A look-up table in which a relationship between a pressure difference of the filtration device and a power supply to the pump, wherein the flow rate of the processing liquid discharged from the end of the circulation pipe is constant, is stored in the power conversion means. 5. The treatment liquid circulating apparatus for a coating process according to claim 4, further comprising: selecting power to be supplied to said pump by referring to said look-up table based on the differential pressure detected by said liquid pressure detecting means. . 6. The treatment liquid circulating apparatus according to claim 5, wherein said electric power conversion means is an inverter for converting the frequency of electric power supplied to an electric motor of said pump. 7. The apparatus according to claim 5, further comprising a stimulating means for stimulating the fact that the value of the electric power supplied to said pump by said electric power converting means becomes equal to or more than a predetermined value. Processing liquid circulation device for coating process.