JPH02119975A - Treatment of water circulating through coating booth - Google Patents

Abstract

PURPOSE:To reduce the stickiness of paint captured in water circulating through a coating booth and to facilitate the removal of the paint by adding a maleic acid polymer to the water contg. hardness components by >=30ppm (expressed in terms of CaCO3). CONSTITUTION:A proper amt. of a maleic acid polymer is added to water contg. hardness components by >=30ppm (expressed in terms of CaCO3) and used under circulation as washing water in a wet spray booth in the coating stage of an automobile plant, etc., to make excess paint captured in the water nonsticky. The nonsticky paint particles are separated with a physical solid-liq. separating means such as a wedge wire and the resulting paint-free water can be used again as washing water. The maleic acid polymer may be a homo- or copolymer of maleic acid and the amt. of the polymer added to the circulating water is >=0.01ppm, preferably 0.1-1,000ppm.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for treating circulating water in a paint booth, and in particular, in a wet spray painting booth, the present invention relates to a method for treating circulating water in a paint booth, and in particular, in a wet spray painting booth, the present invention relates to a method for treating circulating water in a paint booth. This invention relates to a method for treating circulating water in a paint booth that reduces stickiness and prevents paint from sticking and solidifying inside the system.

[Prior Art] In a painting process in the automobile industry, the yield of paint sprayed onto a car body is generally 60-80%, and 40-20% of the paint used is excess paint that must be removed in the next step. In order to collect this excessively sprayed excess paint, it is usually treated in a wet spray booth by washing with water, and the washing water is recycled.

In such wet spray booths, the excess paint collected in the flushing water is highly adhesive, so it adheres to the spray booth's water curtain plate, piping system, spray nozzles, etc., causing clogging of the piping and nozzles. This will significantly reduce the water washing efficiency. In addition, if the exhaust system of the spray booth is clogged due to excess paint adhesion and air circulation is obstructed, paint solvent will fill the booth, creating a health and safety hazard and significantly deteriorating the work environment. let Furthermore, most of the surplus paint is deposited at the bottom of the booth pit and circulation bit of the spray booth, and the deposited paint solidifies into a rubbery state over time, requiring a great deal of time and effort to clean and remove.

Furthermore, the paint collected in the washing water not only adheres or settles within the system, but also dissolves paint components or disperses as fine particles. Particularly in the case of water-based paints, they are easily dispersed and increase suspended solids (SS) and dissolved solids (TDS) in water. An increase in TDS promotes corrosion in the system. Furthermore, the solvent in the paint not only increases the hydrocarbons (I(C)) in the booth exhaust, but also dissolves in the wash water and increases the COD of the circulating water. acidify water,
As a result, corrosion of the system is accelerated.

In order to solve these problems, spray booth treatment agents that are mixed into circulating water have been developed, including: ■ Alkali such as NaOH and KOH ■ Amphoteric metals such as Zn salt ■ Cationic polymer ■ Surface activity A method is known in which a single agent or a combination of two or more agents is added to the cleaning water.

[Problems to be Solved by the Invention] However, the above-mentioned conventional treatment agents have the following problems: ■ They are not sufficiently effective. ■ The applicable pH range is narrow, making it difficult to perform stable treatment, and requiring a large amount of pH adjuster. ■ There are limited types of paints that can be applied, including acrylic paints,
Less effective against phthalate paints.

It had the following problems and could not be said to be industrially advantageous.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and provide a method for treating circulating water in a painting booth that can efficiently treat all types of paint.

[Means for Solving the Problems] The method for treating circulating water in a painting booth of the present invention reduces the hardness component to 3
It is characterized in that a maleic acid-based polymer is added to painting booth circulating water containing 0 ppm (calculated as CaCO3) or more.

That is, the present inventors have developed a wet painting booth treatment agent with a molecular weight of over 1000 and a molecular weight of 500.
We have developed a processing agent containing an anionic or nonionic water-soluble polymer of 0.000 or less and a coagulant that has the effect of coagulating the water-soluble polymer, and the applicant has previously filed a patent application for this treatment agent (
Patent application No. 1983-323620. (hereinafter referred to as "first application")
. According to the wet-type paint booth treatment agent of the prior application, it is possible to solve the conventional problems and efficiently treat paint booth circulating water.

As a result of intensive research into a more efficient treatment method for painting booth circulating water, the present inventors found that the addition of maleic acid-based polymers to painting booth circulating water containing a specific hardness component was extremely difficult. They found that it is effective and completed the present invention.

The present invention will be explained in detail below.

The paint booth circulating water to be treated in the present invention is paint booth circulating water that is recycled as washing water for wet spray booths in the painting process of automobile factories, etc., and contains hardness components of 30 ppm or more in terms of CaCO5. .

The maleic acid-based polymer added to such paint booth circulating water may be a homopolymer of maleic acid or a copolymer consisting of a polymer unit copolymerizable with maleic acid. Compounds that can be copolymerized with maleic acid include:
Examples include acrylamide, acrylic acid, acrylic ester, and styrene. Further, the molecular weight of the maleic acid-based polymer is preferably about 400 to 500,000 from the viewpoint of anti-tackiness of the paint. In other words, a maleic acid polymer with a molecular weight of less than 400 cannot sufficiently provide this anti-tackifying effect, whereas a maleic acid polymer with a molecular weight of more than 500,000 has a strong effect of aggregating paint particles, and the maleic acid polymer itself It is unsuitable because the stickiness becomes strong.

In the present invention, the maleic acid-based polymer is used if! j may be used alone or in combination of two or more.

In the present invention, an appropriate amount of the maleic acid-based polymer is injected into the wet booth circulating water to make the excess paint collected in the water tack-free. The amount of maleic acid polymer added is not particularly limited, and is appropriately determined depending on the type of paint, the concentration of collected surplus paint, the concentration of hardness components, etc. in the circulating water of the painting booth to be treated. Generally, it is 0.01 ppm or more, preferably 0.1 to 11 ppm to the circulating water.
Approximately 000pp, 0 for the amount of excess paint in circulating water
．． 0.01 to 300% by weight, preferably 0.05 to 10% by weight, and is appropriately determined by a jar test.

There are no particular restrictions on the injection method, and maleic acid-based polymer solutions, semi-dissolved suspensions or emulsified liquids, or
The maleic acid polymer powder may be continuously or intermittently injected into the circulating water at an appropriate injection position.

In this way, by adding the maleic acid-based polymer, excess paint in the circulating water becomes tack-free. Since the paint particles that have become tack-free can be easily separated into solid and liquid, by separating them, the separated water can be reused as rinsing water.

Although there are no particular limitations on the means for separating paint particles in the used wash water discharged from the booth, flotation separation or physical solid-liquid separation means may be employed. Specific examples of the physical solid-liquid separation means include wedge wires, rotary screens, bar screens, and cyclones.

The sludge recovered by the solid-liquid treatment can be dehydrated by gravity or by a conventional dehydrator, and then disposed of by incineration, landfill, or the like.

In addition, according to the method of the present invention, the stickiness of excess paint etc. collected in the washing water is sufficiently improved, so that the effect can be achieved without using any other flocculants etc. during solid-liquid separation. Although it is possible to perform solid-liquid separation, in order to perform the separation more reliably and efficiently, it is preferable to use an organic polymer flocculant to coarsen the flocs. Particularly when flotation separation means is employed as the separation means, it is advantageous to use a flocculant.

Examples of polymer flocculants include nonionic polymer flocculants such as polyethylene oxide, polyacrylamide, methylcellulose, urea-formalin resin, poly(meth)acrylates, partial hydrolysates of poly(meth)acrylamide, and polystyrene sulfonic acid. Anionic polymer flocculants such as salts, polydiallyl quaternary ammonium salts, poly(meth)acrylic acid amino esters, polyethylene imine, polyamide polyamines, dihaloalkane polyamine polycondensates,
Mannich modified polyacrylamide, Hofmann decomposition product of polyacrylamide, polyaminoalkyl (meth)
Acrylate, polyvinylpyridium halide, poly(
Examples include cationic polymer flocculants such as meth)acrylate polyalkylene polyamines, cationized starches, chitosan, polyvinylimidacin, and water-soluble copolymers thereof.

These flocculants can be used alone or in combination of two or more.

These flocculants are preferably added immediately before the separation means, and in this case, it is advantageous to provide a suitable reaction tank because flocculation can proceed more easily. Also,
The amount added is 0.001 by weight relative to excess paint.
~100%, usually in the range of 0.01 to 50%, and when injected into circulating water, it varies depending on the amount of excess paint in the water, but 0.01 to 11000pp, usually 0.05
The range is preferably from 1,100 pp to 1,100 pp, and the optimum amount to be added is generally determined as appropriate by a jar test.

In addition, in the present invention, an alkaline agent, a surfactant, etc. may also be used in combination.

The alkaline agent further reduces the tackiness of the paint and is also effective in preventing corrosion of the equipment.

Surfactants are effective in improving the dispersibility and emulsification of paints. As the surfactant, any anionic surfactant, nonionic surfactant, zwitterionic surfactant or cationic surfactant known per se may be used. One or a combination of two or more can be used. Specifically, sodium alkylbenzene sulfonate, sodium higher alcohol sulfate, sodium alkyl sulfate,
Sodium alkyl sulfonate, sodium alkyl sulfosuccinate, sodium dialkyl sulfosuccinate,
Anionic surfactants such as sodium alkylnaphthalene sulfonate-formalin condensate, sodium alkylnaphthalene sulfonate, sulfonated heterocyclic compounds, fatty acid-amino acid condensate; polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether,
Nonionic surfactants such as polyethylene glycol fatty acid ester, polyoxyethylene fatty acid amide ether, polyethylene glycol alkylamine ether, polyhydric alcohol fatty acid ester, polyoxyethylene polyhydric alcohol fatty acid ester, alkylolamide; betaine type, imidacillin type, Sulfonic acid type or alanine type amphoteric surfactants: Cationic surfactants such as alkylviridinium hydrochloride, alkyltrimethylammonium halide, polyoxyethylene alkylamine, polyoxyethylene dodecylamine, etc. can be mentioned. In the present invention, among these surfactants, it is preferable to use nonionic surfactants.

[Function] By adding maleic acid-based polymer to paint booth circulating water of a specific hardness, maleic acid-based polymer molecules that have become insolubilized in the wash water are adsorbed to excess paint. The paint is made tack-free by being coated with a film of maleic acid-based polymer molecules.

The paint that has become tack-free coagulates and is more likely to undergo solid-liquid separation.

Therefore, according to the method of the present invention, extremely excellent processing effects can be achieved.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 According to the method of the present invention, circulating water in a wet spray painting booth at an automobile factory was treated. The outline of the wet spray painting booth targeted for treatment is as follows.

Wet spray painting booth ■ Painting item: Car body ■ Paint type Acrylic resin paint Phthalate paint Melamine paint ■ Paint booth type: Venturi set Water capacity: 350rr? Circulating water amount: 1000rn'/Hr Blow water amount: 30rr1''/day■ Circulating water quality pH Near, 5 Electrical conductivity: 600 ps/cm Turbidity: 25
0 (degrees) Calcium hardness: 55 ppm (as CaC05) In this painting booth, excessive paint adhered to the water curtain board and exhaust duct, causing problems with poor exhaust, so cleaning and removal was carried out once a week. .

However, since the deposits have a very strong adhesive force and harden into asphalt, cleaning and removing them is extremely difficult and requires a great deal of effort.

A maleic acid-based polymer was added to the circulating water of such a wet spray coating booth according to the following specifications.

(Molecular weight: aOO) ■ Injection amount: 0.5% by weight based on excess paint ■ Injection method: Continuous injection using chemical injection pump O Injection location: IFi
As a result, the following effects were observed on the ring pump suction side.

(i) The adhesion of excess paint to the water curtain plate and exhaust duct has been drastically reduced to about 1/3 to 115 times the conventional level.

(ii) There was no solidification of adhering paint or sediment, and most of the material was sand-like or mud-like, making cleaning work easier.

(iii) Previously, cleaning work was required once a week, but the cleaning work has been significantly reduced to once a month.

In addition, in the above treatment, by injecting 0.5% by weight of Ca(OH)2 into the surplus paint together with the maleic acid polymer, the tackiness of the paint was further reduced to 1/10 or less of the conventional one.

[Effects of the Invention] As detailed above, according to the painting booth circulating water treatment method of the present invention, the stickiness of the collected paint can be effectively reduced, and the paint can be turned into free-flowing particles and easily removed. It can be made possible. Moreover, it is effective for almost all paints, and has a high anti-tack effect even for acrylic paints, phthalic acid paints, and high solid paints, which were conventionally considered difficult to make adhesive-free.

Therefore, according to the method of the present invention, (1) clogging of nozzles due to adhesion of paint to piping etc. is prevented, water washing efficiency is maintained at a good level, and maintenance is reduced.

■ Deterioration of the working environment due to blockage of the exhaust system is prevented.

■ Paint sludge deposited or floating in booth pits etc. becomes difficult to solidify and can be easily removed. Therefore, the removal work is reduced.

■ Washing waste liquid becomes easier to separate into solid and liquid, making wastewater treatment easier.

■ Solids in used washing water can be separated and removed with high separation efficiency, and the clarity of circulating washing water can be maintained at a high level.

This effect is also achieved, making it possible to carry out painting booth treatment industrially very advantageously.

Claims (1)

[Claims] (1) A method for treating circulating paint booth water, which comprises adding a maleic acid-based polymer to circulating paint booth water containing hardness components of 30 ppm (calculated as CaCO_3) or more.