JPH0411277B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a paint booth circulating water system that separates unpainted paint dust washing water from a painting line for automobiles or home appliances into solid-liquid into paint slag and treated water, and repeatedly uses the treated water as circulating water. Regarding processing method. In order to separate the paint in solid-liquid cleaning water for unpainted paint dust, various inorganic flocculants are used, or a polymer flocculant is used in combination with the inorganic flocculant.
A method is used to separate solid-liquid paint dust into large flocs that tend to settle or float, and the resulting treated water is used again as circulating water in the paint booth. As an inorganic flocculant, an acidic flocculant (for example, aluminum sulfate, aluminum chloride, polyaluminum chloride, ferric chloride, zinc chloride, zinc sulfate, etc.) is generally used, but if such a flocculant is used, the coating Since the pH of wastewater is in the acidic range,
In order to return this to a neutral range and to bring it into the optimum pH range for floc formation, an alkaline agent such as caustic alkali is added as a pH adjuster. However, when a PH adjuster is used, chlorides and sulfates such as sodium chloride and sodium sulfate are formed due to the presence of chloride ions or sulfate ions in the painting wastewater. Since these salts are partially dissolved, they also exist in the treated water after separating the paint slag. Therefore, if the circulating water is not blowed down or the amount of blowdown is extremely small, the salt concentration in the circulating water will gradually increase, which may lead to corrosion of the upper part of the booth, such as the paint booth duct, which is in contact with the mist.
In addition, the separated paint slag also contains high concentrations of chlorides and sulfates, and when this is incinerated, hydrogen chloride gas and sulfurous acid gas are generated, causing serious problems that pollute the atmosphere. However, there is a problem in that the lifespan of the incinerator is extremely shortened. In order to prevent problems such as air pollution caused by such harmful gases, a huge amount of capital investment has been required. Furthermore, zinc chloride and zinc sulfate, which are said to be preferable among the flocculants mentioned above, are added to the optimal pH using an alkaline agent.
When adjusting the paint slag to the area, it is generated.
Although the particles of Zn(OH) ₂ floc are coarse and have a high settling rate, they have a small specific surface area, so they are not sufficient to hide paint scum and make it tack-free, resulting in uncoated areas such as hydrospin ducts and piping. Blocks the paint processing equipment. Therefore, the present invention aims to solve the above-mentioned problems.The present invention aims to solve the above-mentioned problems by producing flocs of Zn(OH) ₂ and related complexes by hydrolysis in a pH range of 10 to more than 7. Alkali metal zincate (Na, K, Li as alkali metals)
It has been discovered that uncoated paint dust can be easily flocculated or floated by adding it to painting wastewater, and the present invention has been achieved based on this discovery.
That is, the present invention provides an aqueous alkali metal zincate solution (here, the alkali metals include Na, K, and Li).
Alternatively, when this and a linear strong cationic polyamine containing an amino group or a quaternized amino group as a cationic group and an average molecular weight of 500 to 100,000 carbon atoms are added to paint wastewater, carbon dioxide gas in the air is generated during a long circulation process. In addition, the organic components in the paint are decomposed by aerobic bacteria to produce organic acids, and by reacting with these organic acids, the pH gradually decreases and becomes slightly alkaline. Then,
The present invention relates to a method for treating circulating water in a paint booth, which generates a floc of Zn(OH) ₂ or a complex related thereto, and easily floats or coagulates unapplied paint dust. Here, weak alkalinity means a pH range of 10 or less to greater than 7. The flocculant used in the present invention does not generate chlorides or sulfates during pH adjustment like known acidic flocculants, so it does not cause pollution problems due to harmful corrosive gases, corrosion of paint booth ducts, and paint sludge incinerators. All of the problems that were caused by negative effects were resolved. Furthermore, although the particles of flocs such as Zn(OH) ₂ produced by the present invention are fine and have a slow sedimentation rate,
Since it has a property of having a large specific surface area, it sufficiently hides the surface of the paint slag and makes it non-adhesive, and the problem of clogging of uncoated paint processing equipment such as hydrospin ducts and piping is also substantially eliminated. Furthermore, a feature of the present invention that should be emphasized is that the flocculant used in the present invention does not have a pH
Since chlorides and sulfates are not produced during adjustment, a portion of the circulating water after paint sludge has been removed can be introduced into activated sludge treatment without any problems. Paints applicable to the treatment method of the present invention include oil-based and water-soluble paints such as epoxy, melanin, acrylic, alkyd, polyester, and urethane resins. Painting booths to which the flocculant used in the present invention is applied include all wet-type booths such as water curtains, ventilates, and no-pump type booths. When using the treatment agent used in the present invention, about 0.1 to 50 parts by weight of an alkali metal zincate is usually added to 100 parts by weight of unapplied paint in the circulating water. If the amount added is too small than this range, good results will not be obtained, and if it is larger than this range, the pH of the circulating water will become too high, which is also undesirable. The addition method is to inject it into a place where the chemical can be easily dispersed, such as the discharge port of a circulation pump. In this case, when a cationic polyamine-type polymer is added, the ability to remove the stickiness of the paint is further enhanced, and, for example, it is possible to more efficiently prevent paint from adhering to the walls, ceiling, and floor of the painting booth. . The aqueous alkali metal zincate solution (here, the alkali metals include Na, K, and Li) has the general formula, M
It has the structure of an aqueous MOH (M=Li, Na, K) solution of [Zn(OH) ₃ ], M[Zn(OH) ₄ ], and complexes mainly composed of these, but the pH is greater than 10 to 7. It may be any material that produces a floc of Zn(OH) ₂ or a complex mainly composed of Zn(OH) 2 by hydrolysis within a certain range, and the above general formula is an example thereof. Strong cationic polyamines, which are recognized to have an increased treatment effect when used in combination with aqueous alkali metal zincate solutions, are linear strong cationic polyamines that have amino groups or quaternized amino groups as cationic groups and contain carbon atoms with an average molecular weight of 500 to 100,000. Examples of polyamines include polycondensates of polyethylene glycol and hexamethylene diamine, or polycondensates of ethylene diamine and ethylene dichloride, and ammonia or ethylene dichloride. If the average molecular weight is less than 500, sufficient aggregation effect cannot be obtained;
Up to 100,000 is preferable for the effectiveness of the present invention. but,
If it exceeds 100,000, it may be difficult to use in terms of effectiveness and operation, but it can be used. The ratio of strong cationic polyamine used is 1 part by weight of zinc dissolved in alkali metal hydroxide.
It is desirable to add each to the painting booth circulating water in a range of 0.2 to 5 parts by weight, and it is not preferable to deviate from this range because the effect will be poor. Regarding the strong cationic polyamines, US Pat.
It is described in detail in the specifications of No. 3372129 and No. 3468818, which are cited as reference materials. Also, if a paint booth is operated for a long time without the addition of strong cationic polyamines, for example, partial blowdown will not prevent water spoilage caused by aerobic bacteria; When used together, it is advantageous because it can also prevent bad odors caused by rotting water. The treatment agent used in the present invention can also be used in combination with a commonly used alkaline flocculant such as sodium aluminate or calcium hydroxide. The present invention will be explained in detail below using examples. Example 1 A test painting booth (PH approx. 9.8
~10 water capacity 100, pH approx. 9.8~10 circulating water volume 10
/min), preliminarily add 7.1% by weight of zinc to a sodium zincate aqueous solution (30% by weight of caustic soda aqueous solution).
) is dissolved in water at 0.05% (50g), and then a 1:1 mixture of melamine alkyd resin type solid color and acrylic melanin resin type metallic color, which are top coats for automobiles, is dissolved at 0.35% (50g) in water. g/min, and the aforementioned sodium zincate aqueous solution at 0.07 g/min were continuously injected into the circulating water using a spray gun and a metering pump, respectively. The operating time of the test painting booth is 1 hour. As a result of the test, it was observed that the paint was completely modified to a non-tacky state and floated. The paint recovery rate was 75%. The quality of the treated water after removing paint slag is PH9.8-10, electrical conductivity 460μV/cm,
The visibility was good at 30cm. Example 2 In Example 1, a strong cationic polyamine type polymer was separately added in an amount of 39% by weight corresponding to the amount of zinc in the sodium zincate aqueous solution that was added in advance to the retained water and continuously injected into the circulating water. It has also been found that this results in a paint sludge that is easier to process. As the strong cationic polyamine, a polycondensate of polyethylene glycol and hexamethylene diamine (average molecular weight of about 3000) was used. The paint recovery rate was 90%. The quality of the treated water was good, with a pH of 9.6 to 10, electrical conductivity of 560 μV/cm, and visibility of 30 cm. The combined use of cationic polyamine not only improves the recovery rate of the paint but also completely eliminates its tackiness. Next, the results of Examples 1 and 2 are summarized in Table 1. However, for things that are sensual and difficult to quantify, such as the stickiness of paint slag, the order of treatment is ◎,
It was expressed in four stages: ○, △, and ×. In addition, mild steel (SS-41) and commercially available galvanized iron plates were used for the corrosion test.
Add the test piece and 40ml of the test solution to the shear dish, and
The sample was placed in a blow dryer at a temperature of 0.degree. C., and when the liquid had dried, another test solution was added and the sample was left to stand for 4 days, after which the weight loss due to corrosion was measured.

[Table] As is clear from Table 1 above, Examples 1 to 2
has fully achieved its intended purpose and will make a great contribution to industry. The above-mentioned known flocculants; ZnCl ₂ , FeCl ₃ , AlCl ₃
Table ₂ summarizes the results of comparative examples in which the same methods as in Example 1 were used for NaAlO 2 and NaAlO 2 , except that metals with an equivalent weight corresponding to 7.1% by weight of zinc were used.

【table】

[Table] The evaluation method is the same as in Table 1. As is clear from Table 2 above, it is recognized that the objective of the present invention cannot be achieved with known flocculants.

[Brief explanation of drawings]

The attached figure shows a treatment flow sheet for circulating water in a test painting booth according to the method of the present invention. 1...Compressor, 2...Valve, 3...
Spray gun, 4... Paint tank, 5... Circulating water tank, 6... Strainer or slag remover, 7...
Valve, 8... Centrifugal pump, 9...
...Valve, 10...Condenser water bath, 11...Sample collection port, 12...Painting booth.

Claims (1)

[Scope of Claims] 1. A treatment method for suppressing contamination in a wet painting booth, which cleans the air in the wet painting booth with water, removes unapplied paint dust, and circulates and reuses the water, which substantially comprises: Alkali metal zincate (as an alkali metal) that does not contain chloride or sulfate ions.
Add an aqueous solution (containing Na, K or Li) to the circulating water at a ratio of 0.1 to 50 parts by weight (as alkali metal zincate) per 100 parts by weight of unpainted paint dust to absorb carbon dioxide gas from the air. By this and/or by decomposition of organic substances in unapplied paint, the pH of the circulating water is gradually lowered to weak alkalinity.
A method for treating circulating water in a wet painting booth, characterized by solid-liquid separation of unpainted paint dust cleaning water into paint slag and treated water. 2. A treatment method for suppressing contamination in a wet painting booth in which the air in the wet painting booth is washed with water, unpainted paint dust is removed, and the water is recycled and reused. Alkali metal zincate (as an alkali metal) that does not contain ions
An aqueous solution (containing Na, K or Li) and a linear strong cationic polyamine containing an amino group or a quaternized amino group as a cationic group and having an average molecular weight of 500 to 100,000 carbon atoms are added to the unpainted paint dust 100. The above-mentioned strong cationic polyamine is added to circulating water at a ratio of 0.1 to 50 parts by weight of alkali metal zincate and 0.2 to 5 parts by weight of the strong cationic polyamine to 1 part by weight of zinc, and carbonic acid is extracted from the air. By absorbing gas and/or decomposing organic substances in unpainted paint, the pH of the circulating water is gradually lowered to weak alkalinity, and the unpainted paint dust cleaning water is converted into solid-liquid paint slag and treated water. A method for treating circulating water in a wet painting booth, characterized by separating the water.