JPH08182901A - Treating agent for circulating water of wet coating booth - Google Patents

Abstract

PURPOSE: To produce a treating agent for a circulating water of a wet coating booth preventing an equipment relating to a wet coating booth from being clogged by paint residues, improving booth efficiency, contributing to easy equipment maintenance, and being easy for handling and not harmful by making unhardend paint captured in water non-tacky in a wet coating booth for an automobile or various house appliances. CONSTITUTION: The unhardend paint captured in water is efficiently made non-tacky, and separation of paint residues from treated water becomes easy by using a treating agent containing an alumina sol and a water soluble high- molecular compd. forming a flock with the alumina sol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in a wet coating booth for automobiles or household electric appliances, makes non-adhered paint collected in water tack-free, and fixes it to paint dregs and treated water. The present invention relates to a treatment agent for circulating water in a wet coating booth used for liquid separation.

[0002]

2. Description of the Related Art In the painting process of automobiles or household electric appliances, paint is generally sprayed and painted in a painting booth. However, surplus paint that does not adhere to the object is collected in water and treated. Has been done. The excess paint collected in the rinsing water is highly adhesive, so the booth wall, pump, piping,
It adheres to the shower nozzle, the water film swirl part, etc., which may impair the circulation of water and further significantly reduce the efficiency of collecting paint mist. This causes problems such as reduced work efficiency, shortened device life, discharge of paint mist to the outdoors, and generation of odor.

In order to solve these problems, an alkaline agent such as caustic soda (USP-4678586) as a treating agent for circulating water in a wet coating booth, a combination of an amphoteric metal salt and a cationic polymer (JP-A-59-155481). ),
Melamine-aldehyde resin acid colloid (Japanese Patent Publication 4-23
17), a urea-melamine-aldehyde resin acid colloid (JP-A-63-241089), a water-soluble protein (JP-A-63-260970), a combination of a water-soluble polymer and a coagulant (JP-A-1-260). No. 281,172) has been proposed. However, although each of these conventional methods has its own characteristics, the coating is not sufficiently tack-free and
There is a problem that the workability is not good such that the applied pH range is narrow and the pH needs to be adjusted.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve various problems associated with the treatment of such circulating water in a wet coating booth. The present invention improves the tack-free effect of the paint and wet coating. It is an object of the present invention to provide a treatment agent for circulating water in a wet coating booth, which prevents clogging of booth-related equipment due to paint slag, improves booth efficiency, contributes to equipment maintenance, is easy to handle, and is not dangerous.

[0005]

SUMMARY OF THE INVENTION The present invention has conducted systematic research on the treatment of such circulating water in a wet coating booth, particularly in relation to detackification of a coating, and as a result, it has been confirmed that alumina sol,
The present invention has been completed based on the finding that a floc formed from a specific water-soluble polymer compound is effective for making a coating tack-free.

That is, the present invention relates to a treating agent for circulating water in a wet coating booth, which contains an alumina sol and a water-soluble polymer compound which forms flocs with the alumina sol.

The alumina sol in the present invention generally has a solid content of 1 to 30% by weight, preferably 5 to 20% by weight, has a pH of 1.5 to 7, preferably 2 to 6, and has an average particle diameter. Is 1 mμ to 500 mμ, preferably 5 m
It is a colloidal alumina hydrate having a size of μ to 200 mμ.
In the colloidal solution, the polymerized alumina particles are positively charged, and the anions in the water act as a stabilizer and are dispersed therein. Alumina having a particle size smaller than 1 mμ is likely to be gelled, and alumina having a particle size larger than 500 mμ is not practically preferable because the stability of the particles is poor and the particles easily precipitate. Alumina sol is produced by reacting an alkaline aluminate aqueous solution and a water-soluble aluminum salt solution at a pH of 9 to 10 for a short time to produce and age an alumina gel, and then the alumina gel is mixed with a monovalent inorganic acid or organic acid. A method to generate a uniform sol by acting acid (Japanese Patent Publication No. 4)
No. 0-8409), a method of hydrothermally treating a dispersion of an alumina gel in the presence of an acid to form an alumina sol (Japanese Patent Publication No. 40/40).
No. 14292), or a method of dispersing a pseudo-boehmite alumina slurry produced by blowing carbon dioxide gas into a sodium aluminate solution while stirring it in a monovalent inorganic acid (British Patent No. 1440194). Can be manufactured. In addition, a commercially available alumina sol (eg, Nissan Chemical Co., Ltd., alumina sol series) can also be used.

The water-soluble polymer compound which forms flocs with the alumina sol in the present invention is a water-soluble polymer which is condensed in an aqueous solution due to the presence of the alumina sol.
Examples of such water-soluble polymers include casein sodium salt, ovalbumin, lactalbumin, glue, gelatin, soybean protein, water-soluble proteins such as histones, tannin, carboxymethyl cellulose (CM).
C), polyvinyl alcohol and derivatives thereof, polymers containing homopolymers or copolymers of sodium alginate, acrylic acid, methacrylic acid, maleic acid, acrylamide and the like, or salts thereof. In particular, water-soluble proteins represented by sodium caseinate, and polyvinyl alcohol having a molecular weight of 1,000 to 500,000 are preferable because the flocs formed when they are used in combination with alumina sol have a strong cationic property and are excellent in adhesion to a paint slag.

The treatment agent of the present invention contains, as an active ingredient, an alumina sol and a water-soluble polymer compound which forms flocs when used in combination with the alumina sol. The alumina sol and the water-soluble polymer compound show a slight effect of detackifying the paint slag even when used individually, but when they are used in combination, they show a marked detackification effect. The combination ratio of both is not limited and varies depending on the properties of the alumina sol used and the type of the water-soluble polymer compound, but when both are used in combination, the flocs formed are generally set to be cationic. Good. For determining the ionicity of flocs, for example, a known colloid titration test method (Ryoichi Sente, colloid titration method, pages 3 to 6, published by Nankodo 1969) can be used. In this method, for example, toluidine blue is added as an indicator and then titrated with potassium polyvinyl alcohol sulfate. When the flock formed is cationic, the blue color of toluidine blue does not change because potassium polyvinyl alcohol sulphate reacts preferentially with flock, which has a much higher molecular weight than toluidine blue. However, when the equivalence point is reached, all the flocs react with the polyvinyl alcohol potassium sulfate, and the subsequently dropped polyvinyl alcohol potassium sulfate reacts with toluidine blue to change to reddish purple. On the other hand, when the floc is anionic, this color change occurs immediately.
This can be used to determine whether the floc is cationic. As a concrete combination ratio, for example, when the water-soluble polymer compound is sodium casein, the weight ratio of alumina sol (calculated as solid content) to sodium casein is 1: 100 to 100: 1, preferably 1:20 to 20. The pH of the solution is 4.5 to 9.
5, preferably 5.5 to 8.5.

The application of the treatment agent of the present invention to the circulating water of a wet coating booth can be carried out at an appropriate point in the circulating water system, for example, where the treating agent on the suction side or the discharge side of the circulating water pump is well dispersed in the water system. It is better to inject continuously. In some cases, intermittent injection is also possible. The amount to be added is not uniformly determined depending on the water quality of the target circulating water, the type of paint, the amount of paint in water, the type of this treatment agent, the structure of the booth, etc. Alumina sol is 0.01 to 100 in terms of solid content.
%, Preferably 0.05 to 20% by weight, and the water-soluble polymer compound is 0.01 to 100% by weight, preferably 0.05 to 20% by weight in terms of solid content. Both are usually separately injected into the circulating water of the wet spray booth, but they may be mixed in advance and then injected.

By thus injecting the treating agent of the present invention into the circulating water of the wet spray booth, the overspray paint in water becomes tack-free. For solid-liquid separation of the debris-free paint slag, flotation separation, centrifugation with a cyclone, etc. facilitate solid-liquid separation, and the separated water can be circulated for reuse.

[0012]

[Function] The surface of the paint slag in the circulating water has an anionic charge in the water. When the treating agent of the present invention is added to the circulating water of the wet coating booth, it is adsorbed on the surface of the paint slag, and the flocs surround the paint slag. Alumina sol itself is cationic and binds with paint dregs in a neutral manner to form flocs, which shows a non-adhesive effect.However, since the amount of flocs formed is small, it is effective unless a large amount of alumina sol is added. Not enough. In the present invention, when a water-soluble polymer compound is used in combination therewith, the formation of flocs is significantly increased, and the synergistic effect thereof makes it possible to exert a great effect even when added in a small amount.

[0013]

The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Production of Alumina Sol] To an autoclave equipped with a stirrer and having a capacity of 1 liter, 50 g of dried aluminum hydroxide gel (Kyoward S-200S, manufactured by Kyowa Chemical Industry Co., Ltd.), 445 g of water and 5 g of acetic acid were added and sealed. The temperature was raised to 130 ° C. with stirring and maintained at this temperature for 2 hours. After cooling, this was used as an alumina sol. The cation strength of this alumina sol is 0.04 meq / g
The (sol) and the solid content were 7.3% by weight.

[Measurement of Cation Strength] Alumina sol 0.2
g was added to 100 mL of ion-exchanged water, and hydrochloric acid was added to adjust the pH to 4. 3 drops of 0.1 wt% toluidine blue indicator was added, and 1/400 N (per sulfate group) aqueous solution of potassium polyvinylsulfate (manufactured by Wako Pure Chemical Industries, reagent) was added dropwise to change the color of the solution from blue to magenta. The end point was when the change occurred. [Drop volume 3.35 mL]

Separately, hydrochloric acid was added to 100 mL of ion-exchanged water to adjust the pH to 4, and a polyvinyl alcohol potassium sulfate aqueous solution was dropped to give a blank. [Drop amount 0.15 mL] (Sample drop amount-blank drop amount) x 1/400 x 1 / 0.2 = (3.35-0.15) x 1/400 x 1 / 0.2 = 0 .04 (meq / g)

[Water-Soluble Polymer] Casein sodium salt: Casein sodium spray (manufactured by Sanki Co., Ltd.) is used. Polyvinyl alcohol (PVA): molecular weight of about 50,000, Goshenol NH-20 (trade name; manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) is used. Sodium alginate: Kergin MV (trade name; manufactured by Sansho Co., Ltd.) is used. Carboxymethyl cellulose (CMC): Serogen 7A
(Manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[Floc Cation Confirmation Test] The produced flocs are placed in ion-exchanged water, and hydrochloric acid is added to adjust the pH to 4
When toluidine blue indicator was dropped after adjusting to
If the liquid is blue, the flocs are cationic.

[Test Apparatus and Test Method] A test was performed using the test apparatus shown in FIG. In FIG. 1, a circulating water pit, a circulating water line connected to a circulating water pump, a paint collecting portion, and a spray gun for spraying paint. This test device has 10 liters of water,
The circulating water flow rate is 20 liters / minute. To the circulating water, the treatment agent of the present invention or a comparative treatment agent is added to adjust the pH to 6 to
Adjusted to 8. The test was conducted by spraying 300 g of each of the aminoalkyd resin-based paint (Organo Select 120; manufactured by Nippon Paint Co., Ltd.) and the paint for automobile intermediate coating (L-53; manufactured by Dainippon Paint Co., Ltd.) at a rate of 10 g / min. After spraying, the mixture was transferred to another container, stirred for 30 minutes to make uniform, and allowed to stand for 1 day, and the weight of the paint residue adhering to the bottom of the container was measured, and the tackiness of the paint residue was observed. The weight of the paint slag adhering to the container was weighed after the sample was dehydrated and dried in a dryer at 110 ° C.

[Results] The results are shown in Tables 1 and 2. The addition amount in the examples and comparative examples is in terms of solid content. From these results, it can be seen that the treatment agent of the present invention is very effective in making the coating tack-free.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

By adding the treatment agent of the present invention to the wet booth, the paint collected in the circulating water is made non-tacky, and the sticking and clogging of the paint to the booth-related equipment are prevented.
It greatly contributes to equipment maintenance and operability improvement. Further, the water after solid-liquid separation from the paint slag is clean, and can be easily recirculated and the water can be saved.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the configuration of a test apparatus used in an example of the present invention.

Claims (2)

[Claims] 1. A treatment agent for circulating water in a wet coating booth, comprising an alumina sol and a water-soluble polymer compound that forms flocs with the alumina sol. 2. The treating agent for circulating water in a wet coating booth according to claim 1, wherein the flocs formed by the alumina sol and the water-soluble polymer compound have a cationic property.