JP2006247456A - Method for treating water circulating through wet coating booth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for surely flocculating/surfacing produced sludge by covering the surface of produced sludge with a phenolic resin. <P>SOLUTION: Paint in circulating water which circulates through a wet coating booth and contains water paint and/or solvent-based paint is surfaced and separated by adding a melamine-aldehyde acid colloidal solution and an aluminum compound or an iron compound to the circulating water to make paint un-tacky and then adding the phenolic resin to the resulting circulating water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a wet paint booth circulating water treatment method capable of efficiently aggregating a paint in a wet paint booth circulating water containing a water-based paint and / or a solvent-type paint.

Various paints are spray-painted in the painting process of the automobile industry, home appliances, metal product manufacturing industries, and the like.
Industrially used paints are roughly classified into solvent-based paints and water-based paints, and each paint is used alone or in combination.
Of these, water-based paints are roughly classified into water-soluble, dispersion-type, and emulsion-types, but all use water as a solvent (some solvents may be used in combination), and are therefore flammable. In recent years, its application range is being expanded in particular because it has advantages such as being safe and hygienic and having no fear of pollution caused by solvents.
By the way, in the painting process in various industries, the yield of the paint sprayed on the object is generally not 100%, for example, in the automobile industry, it is about 60 to 80%.
40-20% of the paint used is excess paint that should be removed in the next step.
In order to collect the excessively sprayed excess paint, it is usually treated in a wet painting booth by washing with water, and the washing water is recycled.
In this case, since the water-based paint is soluble or dispersed in water and solid-liquid separation is difficult, the water-based paint remains and accumulates in the circulating water of this wet paint booth, causing the following problems.
(A) Circulating water becomes highly viscous and highly viscous, increasing the load on the circulation pump.
(B) Deposited and insolubilized paint, dust other than paint, and SS components cause clogging troubles in nozzles and piping systems, and troubles in adhesion to water film plates.
(C) It causes foaming failure.
(D) Since the circulating water becomes high COD and high BOD, it rots and the working environment deteriorates due to the odor of rot.
(E) Because of high COD and high BOD, wastewater treatment becomes difficult, and the load on the treatment apparatus increases.
In order to solve such a problem, conventionally, surplus paint in the circulating water has been aggregated and separated. In this aggregation separation, after adding the melamine / aldehyde acid colloid solution,
A method of floating and separating has been proposed.
Japanese Patent Publication No. 6-2259

However, in the above conventional method, after adding a melamine / aldehyde acid colloid solution or the like to the wet paint booth circulating water containing a water-based paint and / or a solvent-type paint, the paint is made non-tacky to generate sludge, When the levitation treatment is attempted, there is a problem that the sludge becomes finer and hardly floats, and the sludge tends to accumulate in the booth and the circulating water tank.
The present invention solves the above-mentioned conventional problems, and provides a method of reliably agglomerating and floating by covering the surface of the generated sludge with a phenol resin.

The present invention adds a melamine / aldehyde acid colloid solution, an aluminum compound or an iron compound to a wet paint booth circulating water containing a water-based paint and / or a solvent-type paint to detackify the paint, and then add a phenolic resin. Thus, the paint in the circulating water is floated and separated.
The details of the coagulation mechanism of the paint according to the present invention are not clear, but are estimated as follows.
That is, when a melamine / aldehyde acid colloidal solution, an aluminum compound or an iron compound is added to the wet painting booth circulating water containing water-based paint and / or solvent-type paint, the paint becomes non-tacky, and then the phenolic resin is converted into an alkaline aqueous solution, etc. The phenolic resin promotes the precipitation of tack-free paint (sludge) and forms a strong and hydrophobic resin film on the sludge surface. It is thought that it will rise easily.
In the present invention, the aluminum compound is preferably water-soluble, and specifically, polyaluminum chloride, sulfuric acid band, or alumina sol is preferable.
As the iron compound, water-soluble compounds are suitable, and specifically, ferric chloride or polyiron sulfate is preferable.
The phenolic resin is preferably a condensate of monohydric phenols and aldehydes or a modified product thereof.
Furthermore, the phenolic resin has an alkali agent concentration of 1 to 25% by weight and a phenolic resin concentration of 1
It is preferable to add as a 50% by weight alkaline aqueous solution.

As described above in detail, according to the processing method for circulating water in a wet coating booth according to the present invention, the paint in the circulating water in the wet coating booth can be efficiently agglomerated and floated and separated and removed.

Hereinafter, an embodiment of a method for treating circulating water in a wet paint booth according to the present invention will be described in detail.
The melamine / aldehyde acid colloid solution used in the present invention is produced by further adding an acid to methylolmelamine obtained by reacting melamine and aldehyde. If necessary, it may be produced by adding an acid to a methylol melamine further alkyl etherified. Examples of the aldehyde used here include formaldehyde, paraformaldehyde, acetaldehyde, paraacetaldehyde and the like, and formaldehyde and paraformaldehyde are particularly preferable from the viewpoint of handling and reaction efficiency.
The charging ratio of melamine and aldehyde is preferably 1 to 6 mol of aldehyde with respect to 1 mol of melamine. However, if the amount of aldehyde exceeds 2.5 mol, the amount of free aldehyde increases when the acid colloid solution is prepared. Therefore, the amount of aldehyde is preferably 2.5 mol or less.
The methylol melamine thus obtained does not dissolve in water, but dissolves in a colloidal form in the acid solution. The alkylated methylol melamine obtained by further alkylating methylol melamine is water-soluble and becomes colloidal when an acid is added.
A monobasic acid is suitable as the acid used here. Specific examples include organic acids such as formic acid, acetic acid, lactic acid, and propionic acid in addition to mineral acids such as hydrochloric acid and nitric acid. Hydrochloric acid is particularly preferable because a stable colloidal solution can be obtained.
The amount of the monobasic acid, particularly hydrochloric acid, is about 0.5 to 1.5 mol, preferably 0.7 to 1.3 mol, per 1 mol of melamine.
In the initial stage of preparing the colloidal solution, there are a lot of free aldehydes. However, after the preparation, the free aldehydes are reduced when left standing at room temperature for aging. The aging time is 5 days to 3 at room temperature.
In the case of heating for a month, it is appropriate that the temperature is about 50 ° C. for about 2 to 3 hours.
The amount of melamine / aldehyde acid colloid solution added varies depending on the amount of paint applied, the method of painting, etc., but the concentration of melamine / aldehyde acid colloid solution in the washing water is 1 to 5000 mg.
/ L, usually about 5 to 500 mg / l. It is preferable to make it into the range of 0.1-300% by the weight of a melamine aldehyde acid colloid solution with respect to the excess paint amount.
In the present invention, after adding the melamine / aldehyde acid colloid solution to the washing water,
It is preferable to adjust the pH of the washing water to 4 to 10, particularly 5 to 9. When the pH deviates from this range, the effect of reducing the tackiness of the paint is not sufficiently exhibited.
As the acid or alkali used for pH adjustment, a known pH adjuster such as hydrochloric acid, nitric acid, sodium hydroxide, or ammonia can be used.
In place of the melamine / aldehyde acid colloid solution, a water-soluble inorganic compound having a paint non-adhesive effect can also be used. Examples of such an inorganic compound include an aluminum compound and an iron compound.
In particular, examples of the aluminum compound include polyaluminum chloride, sulfuric acid band, and alumina sol. On the other hand, ferric chloride or poly iron sulfate is mentioned as an iron compound.
The amount of these inorganic compounds added is preferably in the range of 0.1 to 300%.
As a method for adding such a melamine / aldehyde acid colloidal solution or an inorganic compound to the booth, it is usually preferable to add by continuous injection according to the amount of washing water spray to the coating booth, but it may be intermittent injection. There are no particular restrictions on the location where the melamine / aldehyde acid colloidal solution or inorganic compound is added, but it should be added to the paint booth supply side of the flush water, particularly to the piping system immediately before the flush water and paint come into contact. It is the most efficient.
In the present invention, first, such a coating is made tack-free, and then a phenol resin is added.
The phenolic resin used in the present invention is a condensate of phenols such as phenol, cresol, xylenol, etc., such as monohydric phenols, and aldehydes such as formaldehyde, or a modified product thereof, and is a phenolic resin before crosslinking and curing. Resin.
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 [1] to [3] above Alkyl-modified phenolic resin [5] Polyvinylphenol These phenolic resins may be novolak type or resol type.
Since such a phenolic resin is hardly soluble in water, it is preferably used as a solution or emulsion by dissolving or dispersing it in a solvent that can be dissolved in water.
Solvents used include ketones such as acetone, esters such as methyl acetate, water-soluble organic solvents such as alcohols such as methanol, alkaline aqueous solutions, amines, etc., preferably caustic soda (NaOH) and caustic potash (KOH). It is used by dissolving in an alkaline agent such as
When the phenolic resin is used as an alkaline aqueous solution, the alkaline aqueous solution is preferably in the range of an alkali agent concentration of 1 to 25% by weight and a phenolic resin concentration of 1 to 50% by weight.
When the phenolic resin concentration is high, the phenolic resin may be dissolved by heating to about 70 to 80 ° C.
A phenol resin may be used individually by 1 type, and 2 or more types may be mixed and used for it.
The amount of phenolic resin added is 1 mg / L or more, preferably 5 mg / L or more as an active ingredient amount (resin solid content) with respect to the wet paint booth circulating water, and the paint (solid content) in the circulating water is added. On the other hand, the amount of the active ingredient is 0.1% by weight or more, preferably 0.5% by weight or more.
If the amount of phenolic resin added is less than this ratio, a sufficient aggregation effect cannot be obtained.
However, even if the phenolic resin addition amount is excessively large, the effect of improving the coagulation effect commensurate with the addition amount may not be obtained, and foaming may occur. Is added in an amount of 1000 mg / L or less, especially 5
It is preferable that the amount is 200 mg / L, and the amount of the active ingredient is 100% by weight or less, particularly 0.5 to 10% by weight with respect to the paint in the circulating water.
The more preferable range of the addition amount of the phenolic resin varies depending on the content of the coating amount in the circulating water and the type of the coating, but in the present invention, in the above-described addition amount range of the phenolic resin,
Colloidal solution equivalent value of circulating water after adding phenolic resin is +0.001 meq / L
Above, especially +0.005 meq / L or more and +1 meq / L or less, especially +0.5 meq / L
It is preferable to add a phenolic resin so that it may become + 0.005- + 0.05 meq / L especially so that it may become L or less.
Even when the colloid solution equivalent value is higher or lower than the above range, a good aggregation effect cannot be obtained.
Therefore, the equivalent value of the colloidal solution is measured using the supernatant water obtained by adding the phenolic resin to the circulating water and agglomeration treatment as test water, and based on this result, the addition amount of the phenolic resin is determined, or It is an effective method to extract treated water from the circulating water system, measure the colloidal solution equivalent value, and perform chemical injection control based on this result.
The method for adding the phenolic resin to the circulating water is not particularly limited, and may be intermittently added to the circulating water system once or twice a day, or may be continuously added.
Desirably, it is preferable to continuously inject a fixed amount by a pump.
There is no restriction | limiting in particular as an addition location of a phenol-type resin, Although you may add in any location of circulating water, Usually, adding to the separation tank inlet side of the return of circulating water is preferable.
The pH of the coagulation treatment system is preferably about 6.0 to 8.5 from the viewpoint of preventing corrosion of the equipment and the effect characteristics regarding the pH of the cationic polymer, and therefore the pH falls within this range. When it comes off, it is preferable to adjust the pH by adding an alkali or an acid.
Normally, the range does not deviate to the high pH side in an actual machine, but pH adjustment may be necessary if the range deviates extremely.
By adding the phenolic resin, a resin film is formed on the surface of the non-tackifying sludge of the paint, which makes it easy to float. Next, the aggregated sludge is separated using a floating separator.
As the levitation separation apparatus used here, a pressure levitation apparatus that is normally used can be employed.
The sludge separated and recovered by such a method is subjected to gravity dewatering or after dewatering by a normal method,
Incinerated and landfilled.
The wet paint booth circulating water treatment method of the present invention is applicable to wet paint booth circulating water containing water-based paint, wet coating booth circulating water containing solvent-based paint, and wet coating booth circulating water containing water-based paint and solvent-based paint. Can be applied effectively.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.
In the following, the melamine / aldehyde acid colloid solution and the phenol resin used in the following manner were used.
[Preparation of melamine / aldehyde acid colloid solution]
A product prepared by aging by adding 0.05 mol of methylolated melamine obtained by reacting 2 mol of formaldehyde to 1 mol of melamine to 100 ml of 1.35 wt% aqueous hydrochloric acid (
Hereinafter abbreviated as “M / F”).
[Preparation of phenolic resin solution]
10 g of caustic soda and 150 g of pure water were placed in a beaker, heated to 70 ° C., and then dissolved by adding 40 g of the following phenolic resin and stirring.

Gunei Chemical Co., Ltd. novolak-type phenolic resin “Resist Top PSM 4324”
The agglomeration test was performed on the following two types of water-based paints and solvent-clear paints.
[Water-based paint]
Intermediate coating: “GWP-600” manufactured by Nippon Paint
Metallic base: Nippon Paint "AR-2300"
[Solvent paint]
Top clear paint: Nippon Paint "OG173"

Examples 1-10, Comparative Examples 1-5
Using a test apparatus with a retained water volume of 50 L, the test was conducted with a circulating water volume of 100 L / min. The spray condition of the paint was sprayed for 20 minutes at a speed of 15 g / min. As a medicine, a predetermined amount of a melamine / aldehyde acid colloid solution or an inorganic compound was continuously added to a test water tank, and then a predetermined amount of a phenolic resin was continuously added. Then, it supplied to the pressure levitation apparatus. In the examples of the present invention, in order to see the floating performance, the floating amount of paint sludge in the circulating water tank (the ratio of the floating paint sludge to the total amount of paint sludge in the circulating water tank) and the floating speed were measured.
Table 1 shows addition amounts of melamine / aldehyde acid colloidal solution, inorganic compound and phenolic resin, and test results.

From Table 1, it can be seen that the sludge flying height and the flying speed are remarkably improved only by adding a small amount of a phenolic resin to a melamine / aldehyde acid colloidal solution or an inorganic compound which is a conventional paint detackifying agent.

In the wet painting booth that uses water-based paint and / or solvent-type paint, the present invention has made it possible to easily process surplus paint sludge from the circulating water so that it can be treated. It can be used for booth wastewater treatment.

Claims (6)

Add melamine / aldehyde acid colloidal solution, aluminum compound or iron compound to wet paint booth circulating water containing water-based paint and / or solvent-type paint to detackify the paint, and then add phenolic resin, A method for treating circulating water in a wet paint booth characterized by floating and separating paint in circulating water. 2. The method of treating wet paint booth circulating water according to claim 1, wherein the aluminum compound is polyaluminum chloride, sulfuric acid band, or alumina sol. The method of treating wet paint booth circulating water according to claim 1, wherein the iron compound is ferric chloride or polyiron sulfate. The method of treating wet paint booth circulating water according to claim 1, wherein the phenolic resin is a condensate of monohydric phenols and aldehydes or a modified product thereof. 5. The method of treating wet paint booth circulating water according to claim 4, wherein the phenolic resin is added as an alkaline aqueous solution having an alkali agent concentration of 1 to 25% by weight and a phenolic resin concentration of 1 to 50% by weight. 6. The wet paint booth treatment method according to claim 1, wherein the paint in the circulating water is an aqueous paint.