JP6642624B2 - Chemical injection control method and control device for circulating water treatment chemical in wet coating booth - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method and an apparatus for properly controlling a chemical for treating a circulating water treatment chemical in a wet coating booth.

  2. Description of the Related Art In a coating process in the automobile industry, home appliances, metal products manufacturing industry, and the like, various paints are spray-painted. Paints used industrially are roughly classified into solvent-based paints and water-based paints, and each paint is used alone or in combination.

  Aqueous paints are broadly classified into three types: water-soluble, dispersion-type, and emulsion-type. However, since all use water as a solvent (some solvents may be used in combination), there is no flammability. In recent years, in particular, the range of application has been expanding because of its advantages such as safety and hygiene and no risk of pollution caused by solvents.

  In the coating process in various industries, the yield of the paint sprayed on the object to be coated is not necessarily 100%. For example, in the automobile industry, it is about 60 to 80%, and 40 to 20% of the paint used is in the next step. Is the surplus paint to be removed. In order to collect the excess paint sprayed excessively, water is washed in a wet coating booth, and the washing water is circulated.

In this case, the water-based paint is soluble or dispersed in water, and solid-liquid separation is difficult. Therefore, the water-based paint remains in the circulating water of the wet coating booth and accumulates, causing the following problem.
(A) The circulating water becomes highly viscous and highly viscous, increasing the load of the circulating pump.
(B) Precipitated and insolubilized paint, dust other than paint, and SS components cause blockage failure of nozzles and piping systems and adhesion failure to water film plates and the like.
(C) Foaming disorder occurs.
(D) The circulating water has a high COD and a high BOD, so that it rots, and the working environment is deteriorated due to odor.
(E) Due to high COD and high BOD, wastewater treatment becomes difficult and the load on the treatment equipment increases.

In order to solve such a problem, conventionally, a treatment agent has been added to circulating water to coagulate and separate excess paint in the circulating water.
Patent Document 1 describes that a phenolic resin and a cationic polymer are used in combination as a treatment agent for efficiently coagulating a paint in a circulating water of a wet coating booth containing an aqueous paint and / or a solvent-based paint. Have been. By using a phenolic resin and a cationic polymer together, an effective treatment can be performed by the following mechanism.

  That is, when a phenolic resin is dissolved in an alkaline aqueous solution or the like and injected into circulating water of a wet coating booth, the phenolic resin is dispersed in a dissolved state or in a colloidal state. At this time, if a cationic polymer is present, the phenolic resin is charge-neutralized and coagulates and becomes insoluble. On the other hand, the paint dissolved or colloidally dispersed in the circulating water is also charged and neutralized by the cationic polymer to be coagulated and insolubilized, but when the phenolic resin is insolubilized by the cationic polymer, the coagulated paint is involved. It flocks in the form of an ellipse and aggregates. The floc of phenolic resin aggregated in a form involving paint becomes particles of a certain size, so it is easy to separate and remove from circulating water, and it is easy to separate and remove by flotation, centrifugation, filtration, etc. Can be.

In the treatment of the circulating water in the wet coating booth, it is important to add the treatment chemical in an appropriate amount for the paint contained in the circulating water. Therefore, conventionally,
(1) During the painting time, dosing only while the conveyor carrying the product is moving (2) Doing the dosing according to the quantity while counting the number of production (3) Time to discard paint Therefore, in addition to (1) and (2), a method of injecting medicine during this time period is performed. These are methods of injecting medicine based on information that can be predicted in advance, and can be said to be feedforward control.
In addition, information on whether the medicine is actually being ejected and whether there is a remaining amount in the tank is also important for ensuring proper medicine injection.It is important to record the ejection amount and remaining amount of the medicine with a sensor. It is said that it is desirable to carry out the control in combination with the above-described feedforward control.

On the other hand, there are condition fluctuations that are difficult to predict in advance, such as changing the type of paint and discarding or throwing away paint or thinner, and feed forward control cannot perform appropriate chemical injection control for these changes. .
From such a situation, if the quality of the circulating water in the wet coating booth is constantly measured, and if the fluctuation can be implemented together with the chemical injection control (feedback control) of the circulating water treatment chemical, more stable chemical injection control can be achieved. It is thought that stable treatment of circulating water is possible.

JP-A-2004-337671

In a wet coating booth circulating water system using a water-based paint or a water-based paint and a solvent paint mixed paint, the amount of paint in the circulating water may suddenly increase unexpectedly.In this case, in the conventional feed forward control, this sharp Unable to cope with an increase in the amount of paint, the circulating water foams, or the flocculation treatment with the high-molecular flocculant of the water taken from the circulating water and sent to the sludge collecting device becomes defective, and the sludge recovery amount decreases.
The turbidity or suspended solids concentration of the water fed from the circulating water tank to the sludge collecting device and the water returned from the sludge collecting device to the circulating water tank were measured. Note that control has been performed in the past. However, in this method, appropriate treatment of paint (non-adhesion, aggregation (primary aggregation), Cannot be performed, and this is not a fundamental countermeasure against the shortage of the circulating water treatment chemical when the paint load is increased.
On the other hand, it is not preferable to constantly add a circulating water treatment chemical in anticipation of an increase in paint load, because the chemical cost increases.

  The present invention solves the above-mentioned problems of the prior art, and provides a method and an apparatus capable of appropriately coping with an unexpected increase in paint load in the circulating water of a wet-type painting booth and performing appropriate chemical injection control of a treatment chemical. The purpose is to do.

The present inventors have conducted intensive studies to solve the above problems, and as a result, detected an increase in paint load in the circulating water of the wet coating booth by detecting an increase in the turbidity or the concentration of suspended solids in the circulating water. It has been found that by controlling the chemical injection of the circulating water treatment chemical in accordance with the increase in the concentration of the suspended solids, it is possible to carry out the proper treatment of the paint.
That is, the present invention provides the following.

[1] A wet coating booth is a method for controlling the injection of a treatment agent for preventing tackiness, agglomeration or floating of paint in circulating water into the circulating water, based on the turbidity of the circulating water or the concentration of suspended solids. Controlling the addition of the treatment agent to the circulating water by a wet coating booth.

[2] The turbidity or suspended substance concentration of the circulating water is measured, and the addition of the treatment agent is started when the measured value of the turbidity or suspended substance concentration becomes equal to or more than a predetermined value A set in advance. Alternatively, the method according to [1], wherein the amount of the treatment chemical added is increased.

[3] When the measured value of the turbidity or the suspended substance concentration becomes equal to or less than a predetermined value B set in advance, the addition of the processing agent is stopped or the amount of the processing agent added is reduced. The method for controlling chemical injection of a chemical for treating circulating water in a wet coating booth according to [2].

[4] The wet method according to any one of [1] to [3], wherein the treatment agent is a phenolic resin and an organic coagulant, or a phenolic resin, an organic coagulant and a polymer flocculant. Chemical injection control method for paint booth circulating water treatment chemicals.

[5] A wet coating booth is a device for controlling the injection of a treatment agent for preventing tackiness, agglomeration or floating of the paint in the circulating water into the circulating water, wherein the turbidity meter measures the turbidity of the circulating water or It has an SS meter for measuring the concentration of suspended solids, and control means for inputting the measured value of the turbidity meter or the SS meter and controlling the addition of the treatment agent to the circulating water based on the measured value. A chemical injection control device for a wet coating booth circulating water treatment chemical, characterized in that:

[6] When the measured value of the turbidity meter or the SS meter becomes equal to or more than a predetermined value A set in advance, the control means starts the addition of the processing agent or increases the amount of the processing agent added. The chemical injection control device for a wet coating booth circulating water treatment chemical according to [5], which outputs a signal indicating that the chemical is to be processed.

[7] The control means stops the addition of the processing agent or reduces the amount of the processing agent when the measured value of the turbidity meter or the SS meter becomes equal to or less than a predetermined value B set in advance. The chemical injection control device for a wet coating booth circulating water treatment chemical according to [6], which outputs a signal.

[8] The wet method according to any one of [5] to [7], wherein the treatment agent is a phenolic resin and an organic coagulant, or a phenolic resin, an organic coagulant and a polymer flocculant. Injection booth circulating water treatment chemical injection control device.

  ADVANTAGE OF THE INVENTION According to this invention, since it can respond | correspond to the unexpected increase of the paint load of the circulating water of a wet-type coating booth appropriately, and can perform appropriate chemical | medical-agent injection | pouring control of a processing chemical | chemical, stabilization of a process can be achieved.

FIG. 3 is a system diagram showing a chemical injection control device for a wet coating booth circulating water treatment chemical used in Example 1. 4 is a graph showing the change over time in the concentration of suspended solids in circulating water in Example 1.

  Hereinafter, embodiments of the present invention will be described in detail.

The method for controlling chemical injection of a wet coating booth circulating water treatment chemical according to the present invention is a method for controlling the chemical injection into the circulating water of a processing chemical for making the paint in the wet coating booth circulating water non-adhesive, coagulating or floating. The addition of the treatment agent to the circulating water is controlled based on the turbidity of the circulating water or the concentration of suspended substances (hereinafter, may be simply referred to as “turbidity etc.”).
The chemical spraying control device for a wet coating booth circulating water treatment chemical of the present invention is a chemical spraying control device for treating a chemical in a wet coating booth circulating water to prevent the paint from sticking, coagulating or floating into the circulating water. A turbidity meter for measuring the turbidity of the circulating water or an SS meter for measuring the concentration of suspended solids (hereinafter, both measurement sensors may be simply referred to as “turbidity meter or the like” in some cases); And a control means for inputting a measured value from a degree meter or the like and controlling the addition of the treatment agent to the circulating water based on the measured value.

  The chemical injection control of the circulating water treatment chemical in the present invention is, specifically, measuring the turbidity of the circulating water, and measuring the turbidity and the like to a predetermined value A (hereinafter referred to as “upper limit A”). When the amount becomes equal to or more than the above, the addition of the treatment agent is started or the amount of the treatment agent is increased, and the measurement value such as turbidity is set to a predetermined value B (hereinafter referred to as “lower limit value B”). It is preferable to stop the addition of the processing chemicals or reduce the amount of the processing chemicals when the following conditions are satisfied.

Here, the predetermined values A and B are not particularly limited, and are appropriately determined according to the quality of the circulating water, the fluctuation range of the paint load, and the like. Although not particularly limited, for example, in the case of turbidity, the predetermined value A is set in a range of 100 to 1000, and the predetermined value B is set in a range of 10 to 200. In the case of the suspended substance concentration, the predetermined value A is set in a range of 50 to 500, and the predetermined value B is set in a range of 5 to 200.
As the turbidity meter, a general laser turbidity sensor or the like can be used. The unit of turbidity is NTU.
Further, as the SS meter, a transmission type or scatterer type optical SS meter or the like can be used. Specifically, an SS checker manufactured by Optex can be used. The unit of the suspended substance concentration is mg / L.

  The measurement of the turbidity of the circulating water by a turbidity meter or the like may be performed at any point in the circulating water system.For example, the circulating water returned to the circulating water tank from the wet coating booth or the circulating water in the circulating water tank Although the turbidity and the like can be measured, it is preferable to measure the turbidity and the like of the circulating water in the circulating water tank since the effect of injecting the circulating water treatment chemical can be quickly grasped. In this case, it is preferable that the sensor such as the turbidity meter is provided at a position where the water depth is about half of the water depth in the circulating water tank, in order to reduce the influence of water level fluctuation and sediment sludge.

  The turbidity of the circulating water, etc., decreases when the paint in the circulating water rises or sinks due to the treatment with the treatment agent.However, since it is not preferable that the paint sediments, the circulating water treatment agent used in the present invention is used for treating the paint. It is preferable to use a floating agent, and it is preferable to use a phenolic resin described below in combination with an organic coagulant such as a cationic polymer. It is preferable to further use a polymer coagulant in combination with these, because the stability of the treatment can be further improved.

  Hereinafter, preferred embodiments of the present invention will be described in more detail.

<Phenolic resin>
The phenolic resin used in the present invention is a condensate of a phenol such as a monohydric phenol such as phenol, cresol or xylenol and an aldehyde such as formaldehyde or a modified product thereof, and the phenolic resin before crosslinking and curing. Resins. Specific examples include the following.

[1] Condensate of phenol and formaldehyde [2] Condensate of cresol and formaldehyde [3] Condensate of xylenol and formaldehyde [4] Obtained by alkylating the phenolic resin of the above [1] to [3]. Alkyl-modified phenolic resin [5] polyvinyl phenol

  These phenolic resins may be of novolak type or resol type. In addition, a phenolic resin having a weight average molecular weight of about 1,000 to 10,000 can be suitably used.

  One of these phenolic resins may be used alone, or two or more of them may be used in combination.

  Since such a phenolic resin is hardly soluble in water, it is preferably used as a solution or an emulsion by dissolving or dispersing in a water-soluble solvent. Examples of the solvent used include ketones such as acetone, esters such as methyl acetate and the like, water-soluble organic solvents such as alcohols such as methanol, alkaline aqueous solutions, amines, etc., and preferably caustic soda (NaOH) and caustic potash (KOH). Dissolved in an alkaline agent such as

  When the phenolic resin is used as an alkaline aqueous solution, the alkaline aqueous solution preferably has an alkaline agent concentration of 1 to 25% by mass and a phenolic resin concentration of 1 to 50% by mass. When the phenolic resin concentration is high, the phenolic resin may be dissolved by heating to about 70 to 80 ° C.

  In the present invention, when the chemical injection control of the phenolic resin is performed according to the turbidity of the circulating water, the measured value of the phenolic resin is controlled by ON / OFF control according to the turbidity of the circulating water. The addition of the phenolic resin may be started when the upper limit A or more is reached, and the addition of the phenolic resin may be stopped when the lower limit B or less is reached. The addition amount of the phenolic resin may be increased when the measured value such as the degree becomes equal to or more than the upper limit value A, and the added amount of the phenolic resin may be decreased when the measured value becomes equal to or less than the lower limit value B.

The amount of the phenolic resin added to the circulating water varies depending on the control method and the quality of the circulating water (the type of paint in the circulating water, the content of the paint, etc.). When the measured value is equal to or higher than the upper limit A, the addition of 1 to 100 mg / L to the circulating water as an active ingredient amount (solid content of the phenolic resin) is started. Preferably, the addition of the phenolic resin is stopped.
When the amount of the phenolic resin to be added is increased or decreased, if the measured value of the turbidity or the like exceeds the upper limit A in the range of 1 to 100 mg / L with respect to the circulating water as the amount of the active ingredient, it is added. It is preferable to increase the amount, and when the amount falls below the lower limit value B, the amount to be added is reduced.

<Organic coagulant>
As the organic coagulant, a cationic coagulant is preferable. Examples thereof include cationic polymers such as (dimethylaminoethyl methacrylate) and DADMAC (diallyldimethylammonium chloride), but are not limited thereto.

  One of these organic coagulants may be used alone, or two or more thereof may be used in combination.

  In the present invention, when the chemical control of the organic coagulant is performed in accordance with the turbidity of the circulating water, the measured value of the turbidity and the like of the organic coagulant is controlled by ON / OFF control in accordance with the turbidity of the circulating water. The addition of the organic coagulant may be started when the upper limit value A or more is reached, and the addition of the organic coagulant may be stopped when the lower limit value B or less is reached. The addition amount of the organic coagulant may be increased when the measured value such as the degree becomes equal to or more than the upper limit value A, and may be decreased when the measured value becomes equal to or less than the lower limit value B.

The amount of the organic coagulant added to the circulating water varies depending on the control method and the quality of the circulating water (such as the type of paint in the circulating water and the content of the paint). When the measured value is equal to or higher than the upper limit A, the organic coagulant starts adding 0.2 to 20 mg / L to the circulating water as an active ingredient amount, and when the measured value is equal to or lower than the lower limit B, It is preferred to stop adding the organic coagulant.
When the amount of the organic coagulant added is increased or decreased, when the measured value of turbidity or the like exceeds the upper limit A in the range of 0.2 to 20 mg / L with respect to the circulating water as the amount of the active ingredient. It is preferable to increase the amount of addition, and to decrease the amount of addition when the amount becomes equal to or less than the lower limit B.

<Polymer flocculant>
In the present invention, a phenolic resin and an organic coagulant are added together with a polymer coagulant comprising a water-soluble polymer having a weight average molecular weight of usually more than 1,000,000, preferably 5,000,000 or more. It is preferable that the flocculated floc of the paint by the coagulant is further coarsened by the polymer flocculant.
In this case, as the polymer flocculant, one or more known anionic polymer flocculants, cationic polymer flocculants, amphoteric polymer flocculants and the like can be used.

When a polymer coagulant is used, a good coagulation effect is obtained in an amount of 0.1 to 10% by mass, preferably 0.5 to 2% by mass, based on the amount of the surplus paint, as an active ingredient. May be determined as appropriate.
In addition, the polymer coagulant may be controlled by chemical injection according to the turbidity of the circulating water, as in the case of the phenolic resin and the organic coagulant. The effect can be obtained.

<Drug injection point>
There is no particular limitation on the phenolic resin and organic coagulant injection point, and it may be added to any part of the circulating water system, but in the normal case, the return water from the circulating water tank or wet painting booth to the circulating water tank It is added to piping or both. Further, the phenolic resin and the organic coagulant may be added to the same place or may be added to separate places.

  The polymer flocculant is usually added to a sludge collecting device or a piping for supplying circulating water from a circulating water tank to the sludge collecting device. As shown in the section of the embodiment described later, it may be injected into a water intake pump to a sludge collecting device.

  The pH of the coagulation treatment system is preferably from about 6.0 to 8.5 from the viewpoint of preventing corrosion of the equipment and the effect characteristics relating to the pH of the cationic polymer added as the organic coagulant. Therefore, when the pH falls outside this range and becomes low, it is preferable to adjust the pH by adding an alkali agent. Normally, in actual machines, the range does not deviate to the high pH side, but if it deviates extremely, the pH may need to be adjusted.

<Recovery of flocculated floc>
By the addition of the phenolic resin and the organic coagulant, and further the addition of the polymer flocculant, the paint in the circulating water quickly becomes tack-free, flocculates and floats to generate flocs. For separation and recovery of flocs generated by aggregation, a method using flotation, wedge wire, rotary screen, bar screen, cyclone, centrifugal separator, filtration device, or the like can be employed.

  The sludge separated and recovered by such a method is subjected to incineration and landfill after gravity dehydration or after dehydration by an ordinary method.

<Applicable circulating water>
The present invention is directed to the treatment of circulating water, such as wet coating booth circulating water containing a water-based paint, or wet coating booth circulating water containing a water-based paint and a solvent-based paint, in which turbidity and the like greatly increase due to a sharp increase in paint load. Can be applied effectively.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

  In the following, the following circulating water treatment chemicals were used.

Alkaline solution of phenolic resin: NaOH aqueous solution of phenol / formaldehyde polycondensate (weight average molecular weight 8,000) (phenolic resin concentration: 30% by mass, NaOH concentration: 10% by mass, pH: 12 to 13) (hereinafter referred to as " Phenolic resin solution ").
Cationic polymer: aqueous solution of alkylamine-epichlorohydrin condensate (weight average molecular weight: 100,000) (cationic polymer concentration: 50% by mass)
Polymer flocculant: W / O emulsion of acrylamide / 2 (acryloyloxy) ethyltrimethylammonium chloride copolymer (weight average molecular weight 7,000,000) (active ingredient concentration 40% by mass)

[Example 1]
In the wet coating booth circulating water treatment apparatus shown in FIG. 1, the chemical injection control of the treatment chemical based on the suspended solid concentration of the circulating water was performed according to the present invention.
This wet coating booth circulating water treatment chemical dispensing control apparatus uses a water-based paint and a solvent paint, and treats the wet-painting booth circulating water with an average circulating water paint concentration of 100 mg / L using a circulating water amount of 10 m ³ / min. It is a device, and the paint load may rise suddenly and irregularly due to the abandoned spraying or disposal of paint.

In FIG. 1, reference numeral 1 denotes a circulating water tank in which water that has collected excess paint from a wet coating booth is returned via a pipe 11.
The circulating water in the circulating water tank 1 is treated to be tack-free, coagulated, and floated by adding a processing chemical, and the coagulated water transmitted through the screen 2 is sent to the wet coating booth via the pipe 12 by the pump 12P.

  Further, water containing floating and flocculated flocs in the circulating water tank 1 is taken in by the water intake pump 3 and sent to the sludge collection device 4 via the pipe 13. The sludge of the flocculated floc is separated into solid and liquid by the sludge collecting device 4, and the collected sludge is stored in the collected sludge storage tank 5. On the other hand, the separated treated water is returned to the circulating water tank 1 via the pipe 14.

  In this processing apparatus, a phenolic resin solution is added to the circulating water in the circulating water tank 1 from a pipe 15 having a chemical injection pump 15P. Then, the cationic polymer is added to the circulating water in the circulating water tank 1 from the pipe 17 having the chemical injection pump 17P. The polymer flocculant is injected from the pipe 16 through the chemical inlet of the water intake pump 3.

  In the circulating water tank 1, an SS meter 6 for measuring the concentration of suspended solids in the circulating water in the tank is provided at a position slightly above the middle of the water depth, and the measured value of the SS meter 6 is input to the control panel 7. Is done. The control panel 7 controls ON / OFF signals of the chemical injection pumps 15P and 17P based on the input measurement values of the SS meter 6.

In this example, the polymer coagulant was added in an amount of 0.5% by mass as an active ingredient in a surplus paint, and the addition of the alkaline solution of the phenolic resin and the cationic polymer was ON / OFF controlled according to the following control criteria. .
When the SS total 6 is 200mg / L or more: ON
When the measured value of SS meter 6 is 100 mg / L or less: OFF
That is, when the concentration of the suspended substance in the circulating water tank 1 rises and the concentration of the suspended substance becomes 200 mg / L or more, the chemical injection pumps 15P and 17P are turned ON to start the chemical injection, and the suspension of the circulating water is started by the chemical injection. When the concentration of the suspended solids drops and becomes 100 mg / L or less, the chemical injection pumps 15P and 17P are turned off to stop the chemical injection.
At the time of chemical injection ON, the phenolic resin solution was added as an active ingredient in an amount of 10 mg / L, and the cationic polymer was added as an active ingredient in an amount of 2.0 mg / L.

  First, at the start of the operation, the chemical injection control was not performed for the phenol-based resin solution and the cationic polymer, and the phenol-based resin solution was 5.0 mg / L as the active ingredient and the cationic polymer was 1.0 mg / L as the active ingredient. L, and the polymer coagulant was added in an amount of 0.5% by mass as an active ingredient with a surplus paint. At this time, as shown by the broken line in FIG. 2, the paint load of the circulating water suddenly rises irregularly due to the spraying and discarding of the paint. With the addition, the concentration of the suspended substance gradually decreases. However, this drop in suspended solids concentration is very gentle.

After the treatment without the chemical injection control, the chemical injection of the phenolic resin solution and the cationic polymer was started by the above ON / OFF for the phenolic resin solution and the cationic polymer while the chemical injection of the polymer flocculant was left as shown in the solid line of FIG. In addition, by turning the chemical injection ON when the concentration of the suspended substance in the circulating water is increased, and by turning OFF the chemical injection when the concentration of the suspended substance is decreased, the increased concentration of the suspended substance in the circulated water is immediately reduced.
That is, when the concentration of the suspended substance becomes 200 mg / L or more, chemical injection of the phenolic resin solution and the cationic polymer is started, and these chemicals react with the paint in the circulating water to float up. The concentration of suspended solids in the circulating water drops quickly. When the suspended substance concentration becomes 100 mg / L or less, the chemical injection is stopped, so that waste of the chemical can be omitted.
As described above, according to the present invention, it can be seen that effective processing can be performed with the minimum necessary chemical injection amount. Note that the circulating water treatment chemical cost per unit time could be reduced to about 0.8 times by performing ON / OFF control as compared with the case where control was not performed.

DESCRIPTION OF SYMBOLS 1 Circulating water tank 2 Screen 3 Intake pump 4 Sludge collection device 5 Collection tank for collected sludge 6 SS meter 7 Control panel

Claims (2)

A wet coating booth is a method for controlling the chemical injection into the circulating water of a treatment agent for preventing tackiness, agglomeration or floating of the paint in the circulating water,
The treatment agent is a phenolic resin and an organic coagulant, or a phenolic resin, an organic coagulant and a polymer flocculant,
The turbidity of the circulating water is measured, and when the measured value of the turbidity is equal to or greater than a predetermined value A, the addition of the treatment agent is started, and the measured value of the turbidity is a predetermined value. B. A method for controlling chemical injection of a treatment agent for circulating water in a wet coating booth , wherein the addition of the treatment agent is stopped when the value becomes B or less . A wet coating booth is a device for controlling the injection of a treatment agent for preventing tackiness, agglomeration or floating of paint in circulating water into the circulating water, wherein the turbidity meter measures turbidity of the circulating water; is inputted measured values in degrees meter, have a control means on the basis of the measured value to control the addition of the treatment agent to the circulating water,
The treatment agent is a phenolic resin and an organic coagulant, or a phenolic resin, an organic coagulant and a polymer flocculant,
The control means outputs a signal for starting the addition of the treatment agent when the measured value of the turbidity meter is equal to or more than a predetermined value A set in advance, and the measured value of the turbidity meter is set in advance. A chemical injection control device for a wet coating booth circulating water treatment chemical, which outputs a signal for stopping the addition of the treatment chemical when the value falls below a predetermined value B.

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