Wet paint booth circulating water treatment agent

Abstract

A method for treating a circulating water in a wet paint booth, the method including adding a treatment agent including an aqueous solution including a tannin and an alkali metal hydroxide and/or an alkali metal carbonate to the circulating water in any of passages for the circulating water in the wet paint booth, wherein the passages include for supplying the circulating water from a water tank to a paint booth, for collecting an uncoated paint in the circulating water, and for returning the circulating water to the water tank; to detackify the uncoated paint collected in the circulating water.

Claims

1. A method for treating a circulating water in a wet paint booth, the method comprising: adding a treatment agent to the circulating water somewhere along a passage for the circulating water, wherein, the circulating water is supplied from a water tank to a paint booth for collecting an uncoated paint and is returned to the water tank in the passage, the treatment agent consists essentially of an aqueous solution comprising an alkali metal hydroxide and/or an alkali metal carbonate, a tannin and water, the aqueous solution has a pH of 10 to 13, a tannin concentration in the aqueous solution is 10 to 30% by mass, and the tannin has a solubility in water such that as a pH in water becomes higher, the solubility of the tannin in water becomes higher, whereby a part of the tannin in a mixture of the circulating water and the treatment agent obtained by the adding the treatment agent to the circulating water is precipitated due to decreased pH of the aqueous solution by dilution of the treatment agent with the circulating water, and the obtained precipitate of the tannin detackifies the uncoated paint collected in the circulating water.

2. The method according to claim 1, further comprising adding a coagulant to the circulating water.

3. The method according to claim 1, further comprising adding a polymer flocculant to the circulating water.

4. The method according to claim 2, further comprising adding a polymer flocculant to the circulating water.

5. The method according to claim 1, wherein the tannin is mimosa tannin and/or quebracho tannin.

6. The method according to claim 1, wherein the passage includes the water tank, the paint booth, a path from the water tank to the paint booth, and a path from the paint booth to the water tank.

7. The method according to claim 1, wherein the tannin is a condensed tannin and/or a hydrolyzable tannin obtained from wood and/or vegetation materials.

8. The method according to claim 2, wherein the coagulant has behavior of neutralizing electric charge of fine particles in water to coagulate the fine particles.

9. The method according to claim 3, wherein the polymer flocculant comprises an anionic polymer, a cationic polymer, or an amphoteric polymer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a conceptual diagram showing one configuration example of a wet paint booth.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(2) A wet paint booth circulating water treatment agent according to the present invention comprises an aqueous solution comprising a tannin, and an alkali metal hydroxide and/or an alkali metal carbonate.

(3) The tannin to be used in the present invention is a water-soluble compound derived from plant, in which the tannin reacts with protein, alkaloid or metal ion, and is bonded therewith to form a poorly soluble salt. The tannin is broadly classified into condensed tannin (catechol tannin) and hydrolyzable tannin (pyrogallol tannin).

(4) In the condensed tannin, a main component is a polymer of a compound having a phenol skeleton. The condensed tannin is extracted from needle leaf trees/broad leaf trees, such as mimosa, acacia, larch, quebracho, gambier, persimmon or the like. The condensed tannin shows pH of 4.2 to 4.5.

(5) On the other hand, in the hydrolyzable tannin, a main component is an ester of aromatic carboxylic acid. The hydrolyzable tannin is extracted from a dicotyledon such as chestnut, oak, tara, tea, terminalia chebula, rhus chinensis, gallnut or the like. The hydrolyzable tannin shows pH of 2.3 to 4.5. As the tannin to be used in the present invention, condensed tannin is preferred, and mimosa tannin and/or quebracho tannin is further preferred.

(6) The wet paint booth circulating water treatment agent of the present invention is the aqueous solution having a tannin concentration of preferably 10 to 30% by mass, and further preferably 20 to 30% by mass. If the tannin concentration is excessively low, the tannin concentration is low in the form of a finished product and logistic cost is high.

(7) As the alkali metal hydroxide and/or the alkali metal carbonate to be used in the present invention, mentioned can be sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate or the like. A content of the alkali metal hydroxide and/or the alkali metal carbonate in the aqueous solution is in the range in which pH of the aqueous solution is preferably 10 to 13, and further preferably 10.5 to 11.5. If the content of the alkali metal hydroxide and/or the alkali metal carbonate is excessively low, a treatment effect tends to be reduced.

(8) A wet paint booth to which the wet paint booth circulating water treatment agent of the present invention can be applied is not particularly restricted in the type, and may be of a dispersion type or a floating type.

(9) The wet paint booth circulating water treatment agent according to the present invention is added to the circulating water in any of passages for the circulating water in the wet paint booth. The passages include for supplying the circulating water from a water tank to a paint booth, for collecting an uncoated paint in the circulating water, and for returning the circulating water to the water tank. The additive amount of the wet paint booth circulating water treatment agent according to the present invention can be appropriately adjusted according to a state of detackifying of the uncoated paint.

(10) Moreover, the wet paint booth circulating water treatment agent according to the present invention is adhered onto the uncoated paint to cause the detackifying of the uncoated paint, and is discharged outside a system together with paint sludge in a sludge separation process, and therefore is preferably replenished appropriately in the amount corresponding thereto.

(11) It is preferable to add a coagulant to the circulating water together with the wet paint booth circulating water treatment agent according to the present invention. The coagulant has behavior of neutralizing electric charge of fine particles in water to coagulate the fine particles. The coagulant is broadly classified into an organic coagulant and an inorganic coagulant.

(12) Examples of the organic coagulant include sodium alginate; a chitin-chitosan coagulant; a biocoagulant such as TKF04 strain, BF04 strain or the like; a cationic polymer coagulant such as polyethyleneimine, cation-modified polyacrylamide, polyamine, polyamine sulfone, polyamide, polyalkylene-polyamine, an amine-crosslinked polycondensate, polydimethylaminoethylacrylate, dimethyldiallylammonium chloride, a condensation product of alkylamine and epichlorohydrin, a condensation product of alkylene dichloride and polyalkylene polyamine, a condensation product of dicyandiamide and formalin, DAM (homopolymer or copolymer comprising dimethylaminoethyl methacrylate), and the like. The cationic polymer coagulant is composed of a cationic polymer having a weight average molecular weight of preferably not less than one thousand and not more than one million, and further preferably not less than five thousand and not more than 0.3 million, for example.

(13) Examples of the inorganic coagulant include an aluminum coagulant such as aluminum sulfate (alum), polyaluminum chloride (PAC), polyaluminum hydroxychloride, a quasi boehmite alumina sol (AlO(OH)) or the like; an iron salt coagulant such as ferrous hydroxide, ferrous sulfate, ferric chloride, polyferric sulfate, an iron-silica inorganic-polymer coagulant or the like; a zinc coagulant such as zinc chloride or the like; active silica, a polysilica-iron coagulant, and the like.

(14) The amount of the coagulant to be added to the circulating water can be appropriately adjusted according to a formation state of aggregated flocs of the uncoated paint. The amount of the coagulant to be added to the circulating water is preferably 0.01 to 30 parts by mass, and further preferably 0.5 to 20 parts by mass, based on 100 parts by mass of the tannin.

(15) When the cationic polymer coagulant is used, the additive amount thereof is preferably 0.01 to 20 parts by mass, and further preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of the tannin. Moreover, the additive amount of the cationic polymer coagulant is preferably 0.001 to 1 meq/L, and further preferably 0.002 to 0.5 meq/L in terms of a colloid equivalent amount relative to the circulating water, for example.

(16) When the inorganic coagulant is used, the additive amount thereof is preferably 0.01 to 100 parts by mass, and further preferably 1 to 50 parts by mass in terms of a metal oxide relative to 100 parts by mass of the tannin.

(17) It is preferable to flocculate the aggregated flocs of the uncoated paint obtained by the behavior of the coagulant from a viewpoint of facilitating precipitation and centrifugation so as to form coarse flocs.

(18) In the present invention, a polymer flocculant can be further added to the circulating water in order to form the coarse flocs. The polymer flocculant comprises an anionic polymer, a cationic polymer or an amphoteric polymer. Such a polymer has a weight average molecular weight of usually more than one million, and preferably not less than five million.

(19) Examples of the polymer flocculant comprising an anionic polymer include sodium polyacrylate, a sodium polyacrylate-amide derivative, a partially hydrolyzed polyacrylamide, partially sulfomethylated polyacrylamide, poly(2-acrylamide)-2-methylpropane sulfate and the like.

(20) Examples of the polymer flocculant comprising a cationic polymer include polyaminoalkylacrylate, polyaminoalkylmethacrylate, polyethyleneimine, halogenated polydiallyl ammonium, chitosan, a urea-formalin resin and the like.

(21) Examples of the polymer flocculant comprising an amphoteric polymer include a copolymer of acrylamide, aminoalkyl methacrylate and sodium acrylate and the like.

(22) The additive amount of the polymer flocculant can be appropriately adjusted according to a formation state of the coarse flocs. The additive amount of the polymer flocculant is preferably 0.01 to 20 parts by mass, and further preferably 0.5 to 10% by weight, relative to 100 parts by mass of the tannin, for example. Moreover, the additive amount of the polymer flocculant is preferably 0.001 to 1 meq/L, and further preferably 0.002 to 0.5 meq/L in terms of the colloid equivalent amount relative to the circulating water, for example.

(23) Supplementary abhesives can be added to the circulating water together with the wet paint booth circulating water treatment agent according to the present invention. Examples of the supplementary abhesives include an alumina sol, sepiolite, a melamine-formaldehyde resin, a phenol-formaldehyde resin, bentonite, hectorite, linear cationic polyamine, sodium plumbite and the like.

(24) The aggregated flocs or the coarse flocs formed by the above-described method are separated and removed from the circulating water by a publicly known method. Thus, clarification of water that circulates in the wet paint booth can be achieved.

EXAMPLES

(25) Next, the present invention is more specifically described by giving Examples and Comparative Examples. However, the following Examples only state one embodiment according to the present invention, and the present invention is not limited to the following Examples.

(26) [Detackifying of Water Base Paint]

Example 1

(27) A water treatment agent A composed of an aqueous solution comprising 10% of mimosa tannin and 1.6% of NaOH was prepared. The water treatment agent A had very little odor and had pH of 10.4.

(28) In a 500 mL bottle, 0.03 mL of 50% solution of an alkylamine-epichlorohydrin condensation product (hereafter, written as a coagulant A), 300 mL of tap water, 1 mL of water base silver paint for automotive body and 0.3 mL of the water treatment agent A were fed, and a lid was put on, and the bottle was shaken 60 times per 30 seconds.

(29) The resulting treated water had pH of 7.9, and an electric charge of 0.020 meq/L.

(30) Foamabilities

(31) All of the treated water was put in a 1 L measuring cylinder, and an aeration ball was placed on a bottom in the measuring cylinder, and air was supplied at 1.5 L/min to allow bubbling. A foam volume at 2 minutes from the start of the bubbling, or the time in seconds that elapsed before the foam volume reaches 700 mL was measured.

(32) The bubbling was stopped when the foam volume reached 700 mL or when 2 minutes elapsed from the bubbling start. The foam volume at 2 minutes from the stop of the bubbling and the time in minutes that elapsed before the foam completely disappeared were measured.

(33) Turbidity

(34) The treated water was subjected to filtration using a Whatman No. 41 filter paper (particle retention capability: 20 to 25 microns). Turbidity of the obtained colature was measured.

(35) Secondary Flocculability

(36) To the treated water, 1 mL of 1% diluted solution of an emulsion polymer flocculant (containing acrylamide-2-(acryloyloxy)ethyltrimethyl ammonium chloride copolymer) was added. A secondary flocculation state was observed. A case where floc diameter was not less than 1 mm was evaluated as good, and a case where floc diameter was less than 1 mm was evaluated as poor.

(37) The test results are shown in Table 1. In addition, in treatment of water containing a water base paint, it is preferable to be low turbidity and low foamability.

Comparative Example 1

(38) A treatment agent E composed of an aqueous solution comprising 10% of mimosa tannin was prepared. The treatment agent E had pH of 4.8.

(39) A treated water was obtained in the same manner as in Example 1 except that the treatment agent A was changed to the treatment agent E, and the amount of the coagulant A was changed to 0.02 mL. The treated water was evaluated for pH, electric charge, foamabilities, turbidity and secondary flocculability. The results are shown in Table 1. Meanwhile, the volume reduction of the coagulant A was for keeping the electric charge conditions in line with Example 1.

Comparative Example 2

(40) A treated water was obtained in the same manner as in Example 1 except that the treatment agent A was changed to the treatment agent E, and 0.1 mL of 2.5% NaOH aqueous solution was further added. The treated water was evaluated for pH, electric charge, foamabilities, turbidity and secondary flocculability. The results are shown in Table 1. Meanwhile, the addition of 2.5% NaOH aqueous solution was for keeping the pH and the electric charge conditions in line with Example 1.

Comparative Example 3

(41) A treated water was obtained in the same manner as in Example 1 except that the amount of the treatment agent A was changed to zero, and the amount of the coagulant A was changed to zero. The treated water was evaluated for pH, electric charge, foamabilities, turbidity and secondary flocculability. The results are shown in Table 1.

(42) TABLE-US-00001 TABLE 1 foam foam volume volume at 2 min. at 2 min. from Time before from Time before electric bubbling 700 ml-foam bubbling foam treatment charge start appearance stop disappearance turbidity floccu- agent pH [meq/l] [ml] [sec] [ml] [min] [deg] lability Ex.1 A 7.9 0.020 500 100 30 8 Good Comp. Ex. 1 E 7.2 0.035 400 80 30 33 Good Comp. Ex. 2 E + NaOH 7.9 0.014 700 55 100 30 26 Good Comp. Ex. 3 7.4 0.100 700 55 200 30 100 Poor

(43) The results described above indicate the following. That is, the treatment agent (Example 1) according to the present invention can effectively achieve clarification of water. Moreover, the resulting treated water has low foamability and fast defoaming.

(44) In contrast, the tannin aqueous solution (Comparative Example 1 or 2) being the conventional technique cannot achieve sufficient clarification of water. Moreover, the resulting treated water has slow defoaming.

Example 2

(45) A treatment agent B composed of an aqueous solution comprising 22% of quebracho tannin and 4.8% of NaOH was prepared. The treatment agent B has pH of 10.8.

(46) A treatment agent B composed of an aqueous solution comprising 10% of quebracho tannin and 1.6% of NaOH was prepared. The treatment agent B had very little odor. The treatment agent B or B is considered to be comparable to the treatment agent A in a detackifying effect.

Example 3

(47) A treatment agent C composed of an aqueous solution comprising 10% of acacia tannin and 1.6% of NaOH was prepared. The treatment agent C had a strong ammonia-like odor. The treatment agent C is considered to be comparable to the treatment agent A in a detackifying effect, but to be lower than the treatment agent A in operability because of the odor.

(48) [Detackifying of Solvent Base Paint]

(49) (Wet Paint Booth)

(50) An outline of a wet paint booth is described with reference to FIG. 1. The wet paint booth shown in FIG. 1 had a paint spray gun S installed in an upper portion, and was configured so as to spray a paint at 5 g/min. A circulating water was stored in a pit 5 (water tank: the total volume of the circulating water was 50 L). The circulating water can be pumped up at 100 L/min by a pump P, and the circulating water can be flowed on a water screen panel 4 in a curtain form, and can be returned to the pit. In a treating agent supply portion 6, a treatment agent, a coagulant or a polymer flocculant can be added to the circulating water. Moreover, a volatile matter such as a solvent vapor can be sucked out of the booth by an exhaust fan F.

Example 4

(51) Operations were carried out in the wet paint booth shown in FIG. 1. First, 10 mL of the treatment agent A and 0.6 mL of the coagulant A were added to a circulating water from a treating agent supply portion 6, and the circulating water was circulated by a pump so as to uniformly distribute the treatment agent A and the coagulant A in the circulating water. A solvent base middle coat gray paint for automotive body was sprayed from a paint spray gun S at 5 g/min. Spraying was stopped when 4 minutes elapsed.

(52) After stopping the spraying, pH and electric charge of the circulating water were measured. Moreover, tackiness of sludge floated on a surface of the circulating water accumulated in a pit was evaluated by the following criteria by finger touch.

(53) A: No tackiness

(54) B: No tackiness, but easily solidified if kneaded

(55) C: Slightly tacky

(56) D: Significantly tacky

(57) The results are shown in Table 2.

Comparative Example 4

(58) Spraying was performed in the same manner as in Example 4 except that the treatment agent A was changed to the treatment agent E, and 3 mL of a 2.5% NaOH aqueous solution was further added.

(59) After stopping the spraying, pH and electric charge of the circulating water were measured. Moreover, tackiness of sludge floated on a surface of the circulating water accumulated in a pit was evaluated by criteria same with the criteria in Example 4 by finger touch. The results are shown in Table 2.

Comparative Example 5

(60) Spraying was performed in the same manner as in Example 4 except that the amount of the treatment agent A was changed to zero, and the amount of the coagulant A was changed to zero. After stopping the spraying, pH and electric charge of the circulating water were measured. Moreover, tackiness of sludge floated on a surface of the circulating water accumulated in a pit was evaluated by criteria same with the criteria in Example 4 by finger touch. The results are shown in Table 2.

Example 5

(61) Operations were carried out in the wet paint booth shown in FIG. 1. First, 4.8 mL of the treatment agent B was added from a treating agent supply portion 6, and circulating water was circulated by a pump so as to uniformly distribute the treatment agent B in the circulating water. A solvent base white paint for automotive body was sprayed from a paint spray gun S at 5 g/min. Then, spraying was stopped when 4 minutes elapsed.

(62) After stopping the spraying, pH and electric charge of the circulating water were measured. Moreover, tackiness of sludge floated on a surface of the circulating water accumulated in a pit was evaluated by criteria same with the criteria in Example 4 by finger touch. The results are shown in Table 2.

Comparative Example 6

(63) Spraying was performed in the same manner as in Example 5 except that the amount of the treatment agent B was changed to zero.

(64) After stopping the spraying, pH and electric charge of the circulating water were measured. Moreover, tackiness of sludge floated on a surface of the circulating water accumulated in a pit was evaluated by criteria same with the criteria in Example 4 by finger touch. The results are shown in Table 2.

(65) TABLE-US-00002 TABLE 2 electric Treatment charge Paint agent pH [meq/l] Tackiness Ex. 4 Gray A 7.41 0.005 B Comp. Ex. 4 Gray E + NaOH 7.44 0.005 C Comp. Ex. 5 Gray 7.40 0~0.005 D Ex. 5 White B 7.80 0.08 A Comp. Ex. 6 White 7.70 0.005 D

(66) The results described above indicate that an alkali solution of tannin (Examples 4 and 5) have a higher effect on suppressing the tackiness in comparison with the tannin aqueous solution (Comparative Example 4) in detackifying treatment of the solvent paint.

EXPLANATION OF SYMBOLS

(67) S: Paint spray F: Exhaust fan P: Circulating water pump 4: Water screen panel 5: Water tank 6: Treating agent supply portion