GB2400052A

GB2400052A - Method for reusing over-sprayed aqueous paint

Info

Publication number: GB2400052A
Application number: GB0407319A
Authority: GB
Inventors: Susumu Hibi; Hiroki Narahashi
Original assignee: Nippon Paint Co Ltd
Current assignee: Nippon Paint Co Ltd
Priority date: 2003-03-31
Filing date: 2004-03-31
Publication date: 2004-10-06
Also published as: JP2004298747A; GB0407319D0

Abstract

A method of reusing an over-sprayed aqueous paint 20 comprising ``````a step of spray-coating an article 50 to be coated with an aqueous paint 20 comprising a binder component containing a melamine resin as a curing agent; ```a step of collecting a dust 4 of the over-sprayed aqueous paint together with booth circulation water; ```a step of separating a diluted paint solution 6 containing the collected aqueous paint and booth circulation water into a concentrated solution 8 and a filtrate 11 using an ultrafiltration membrane 9; ```a step of determining an amount of effluent components passing through the ultrafiltration membrane 9 together with booth circulation water, based on an effluent rate of the effluent components relative to initial booth circulation water, and then replenishing the amount to the concentrated solution; and ```a step of using the filtrate as booth circulation water, and the concentrated solution as an aqueous paint.

Description

METHOD FOR REUSING OVER-SPRAYED AQUEOUS PAINT

FIELD OF THE INVENTION

10001] The present invention relates to a method for collecting and reusing an aqueous paint which is not coated on an article to be coated in a spray coating method, and more particularly, to a method for collecting and reusing an aqueous paint which is not coated on an automobile body and the like upon spray coating.

BACKGROUND OF THE INVENTION

[00023 When a paint is spray-coated on an article to be coated such as an automobile body and the like in a coating booth, a large amount of a dust of a paint which is not coated on an article to be coated is generated, and the paint dust is collected by dissolving or dispersing in washing water in a coating booth.

Since a large amount of a paint is collected in washing water, the large amount of paint is lost when the paintontaining water is wasted as it is, and leads to a problem of environmental pollution.

100031 Then, it has previously been studied to collect and reuse a paint collected in washing water and a collecting method has been proposed in JP-A No. 49-51324. The proposed method comprises to collect a sprayed aqueous paint composition in water and remove water by filtering the resulting paint diluting water through a reverse osmosis filter or an ultrafiltration membrane, to return the concentration to the same as that of the original aqueous paint composition. In this method, a concentration of a nonvolatile material, such as 2 5 water-soluble resin (such as, water-soluble alkyd resin and water- soluble acrylic resin), a pigment and the like for forming a coated film is approximated to that of the original aqueous paint composition, for the reuse.

[00041 However, the aqueous paint using the melamine-curing type generally contains highly water-soluble components, such as a melamine resin and a surface adjusting agent, and when water is removed by filtration for collection, the components and water are both removed, and a content of the components in the collected aqueous paint becomes small. As a result, the curability or We like of a paint to be reused is reduced, and the film properties such as hardness, water resistance, weather resistance and the like of a cured coated film are 1 o deteriorated.

[00051 JP-A No. 5-214292 describes a method for solving this problem by controlling a SP value of a resin which is a binder component. However, in the method, a component of an aqueous paint is limited to a non-emuent material, and there is a design limit for improving the performance of a coated film.

OBJECT OF THE INVENTION

t000 The present invention is to solve the previous problems, and an object of the present invention is to provide a method of reusing a melamine resin curing type aqueous paint by which, even in aqueous paint containing highly water 2 0 soluble and effluent components, curability does not change during a process of collection and concentration, and film properties, such as hardness, water resistance, weather resistance and the like of a cured coated film are not deteriorated.

SUMMARY OF THE INVENTION

[00071 The present invention provides a method of reusing an over-sprayed aqueous paint, which comprises: a step of spray-coating an article to be coated with an aqueous paint comprising a binder component containing a melamine resin as a curing agent; a step of collecting a dust of the oversprayed aqueous paint together with booth circulation water; a step of separating a diluted paint solution containing the collected aqueous paint and booth circulation water into a concentrated solution and a filtrate using an ultrafiltration membrane; a step of determining an amount of effluent components passing through the ultrafiltration membrane together with booth circulation water, based on an effluent rate of the effluent components relative to initial booth circulation water, and then replenishing the amount to the concentrated solution; and a step of using the filtrate as booth circulation water, and the concentrated solution as an aqueous paint.

BRIEF DESCRIPTION OF THE DRAWING

[00081 Fig. 1 is a view schematically showing a construction of a recycle system 2 o for a single color aqueous paint which can be utilized in the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[00091 In the method of the present invention, a melamine resin curing type aqueous paint is used. The melamine resin curing type aqueous paint refers to a paint containing a binder component of a combination of a base resin and a melamine resin, and a pigment and an additive which are usually used in an aqueous paint for coating an automobile body, in the state where they are dissolved or dispersed in an aqueous medium. A preferable base resin is an s aqueous polyester resin.

[00101 A polyester resin is prepared by condensing a polyvalent carboxylic acid component and a polyvalent alcohol component, provided that a small proportion a'monocarboxylic acid, hydroxycarboxylic acid, lactone' an alkyd resin and the like may be incorporated therein.

lO01 1l The polyvalent carboxylic component includes aromatic polyvalent carboxylic acid, such as phthalic anhydride, isophthalic add, terephthalic acid, trimellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride, and pyromellitic anhydride; hexahydrophthalic anhydride, tetrahydrophthalic anhydride, 1,4- and 1, 3<yclohexanedicarboxylic acid, maleic anhydride, succinic anhydride, adipic acid, sebacic acid, azelaic acid; hydroxylcarboxylic acid, such as hydroxybenzoic acid, hydroxypivalic acid, and 12ydroxystearic acid; and monocarboxylic, acid such as benzoic aid and t-butylbenzoic acid.

100121 The polyvalent alcohol component may indude diols and tri- or more valent polyols. Preferable are hydroxyl group-terminal polyalkadienediol derivatized from a conjugated alkadiene oligomer or polymer having a polymerization degree of 5 to 50 (molecular weight in a range of 1,000 to 4,000, particularly 1,500 to 3,000), 1,4-polyisoprenediol, 1,4- and 1,2polybutadienediol, and a hydrogenated denvative thereof.

2s 100131 A polyester resin may be one obtained by further reacting with a monoepoxide compound such as Carjula E (trade name, manufactured by Shell Chemical Co.,Ltd.), and lactones (,B-propiolactone, dimethylpropiolactone, butyrolactone, y-valerolactone, ú caprolactone, y- caprolactone, yaprylolactone, crotolactone, o-valerolactone, o- caprolactone etc.). In particular, lactones are useful for forming a polyester chain by itself by ring opening-addition to a polyester chain of polyvalent carboxylic acid and polyvalent alcohol, and further improving the antihipping of an aqueous paint. These may be contained in an amount of 3 to 30% by weight, preferably 5 to 20% by weight, particularly 7 to 15% by weight of a polyester resin.

4] A polyester resin may be an alkyd resin containing a drying oil or a semidrying oil and fatty acid thereof. A drying oil or a semidrying oil and fatty acid thereof may be fatty acid having a carbon number of 6 or more or a fat or oil containing the same, and may be contained in an amount of up to 30% by weight, preferably up to 25% by weight, particularly 10 to 20% by weight of a polyester resin Examples of the fatty oil or components are castor oil, linseed oil, dehydrated castor oil, tung oil, safflower oil, soybean oil, tall oil, palm oil, palm kernel oil and fatty acid thereof. Palm oil and palm kernel oil are preferable.

l001q A polyester resin can be synthesized, for example, by condensing a 2 o polyvalent carboxylic acid component, a polyvalent alcohol component and the reaction components by heating at 150 to 250 C for 4 to 10 hours in a nitrogen stream by the conventional method. Thereupon, a catalyst which is usually used in a condensing reaction may be used.

100161 The condition of a condensing reaction should be regulated such that an 2 5 acid value of the resulting polyester resin reaches 5 to 150 mgKOH/g (solid material), preferably 10 to 100 mgKOH/g (solid material), a hydroxy group value reaches 30 to 250 mgKOH/g (solid material), preferably 50 to 150 mgKOH/g (solid material), and a weight average molecualr weight reaches 10,000 to 200,00O, preferably 25,000 to 16O,000.

[00171 An aqueous paint may further contain a fine powder of a resin containing a carboxyl group, for example, an acrylic resin or a polyester resin containing a carboxyl group in addition to the polyester resin. As a fine powder of such the resin, a fine powder having a particle diameter of 3 to 60 m, particularly 5 to 25 m, and an acid value of 15 to 300 mgKOH/g (solid material), particularly 30 to 100 mgKOH/g (solid material) can be preferably used. By dispersing such the resin fine particle, not only an aqueous paint can be made to be high solid, but also a sagging limit thickness can be improved due to the structural viscosity effect.

100181 An amount of the resin fine powder to be added is an amount such that a weight ratio of a resin fine powder and a polyester resin is 2/98 to 40/60, preferably 5i95 to 30/70, particularly 10/90 to 25/75.

100191 The melamine resin is a cross-linking agent and, when heated, the resin reacts with a hydroxy group or the like contained in a base resin such as a polyester resin and the like to cure. It is preferable that the melamine resin also 2 0 reacts with a fine powder of a resin which is optionally added. Examples of the melamine resin include di-, trim, tetra-, penta-, hexa- methylolmelamine and alkyl ether thereof (the alkyl is methyl' ethyl, propyl, isopropyl, butyl, isobutyl etc.), and the like. A preferable number average molecular weight Mn of the melamine resin is 300 to 3,000. When a number average molecular weight Mn is smaller than 300, there is a possibility that the curability of a coated film becomes insufficient and, when a number average molecular weight exceeds 3,000, there is a possibility that a resin insufficiently becomes aqueous. More preferable number average molecular weight is 300 to 2,000.

tW2oq Examples of a commercially available product of the melamine resin include hydrophilic melamine and/or hydrophobic melamine resins such as UMicoat (trade name) 506, UMicoat 21 Z. "Micoat 723, Hymen (trade name) 238", Camel 202., Camel 254, UCymel 211., "Cymel 303, Camel 370, Camel 325" and Cymel 1156. manufactured by Mitsui Cytec, MU ban (trade name) 20Nn, MU ban 20 SBU and MU ban 128 manufactured by Mitsui Chemical 1 o Co., Ltd., and USumimar (trade name) M-50W, USumimar M NONE and Sumimar M-30W manufactured by Sumitomo Chemical Co., Ad l0021l A content of the melamine resin in an aqueous paint is an amount such that a solid material weight ratio of a polyester resin and a melamine resin is 50/50 to 95/5, preferably 60/40 to 90/10. When the weight ratio is smaller than 50/50, antihipping property of a coated film is reduced. When the weight ratio exceeds 95/5, curability of a paint is reduced, and film properties of a cured coated film is deteriorated.

[00221 An aqueous medium for dissolving or dispersing a polyester resin is usually deionized water. The aqueous medium may contain a small amount of a water-miscible organic solvent, such as diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, methanol, ethanol, isopropyl alcohol, nbutyl alcohol, sec-butyl-alcohol, t-butyl alcohol, dimethylforrnamide and N-methylpyrrolidone, as necessary.

tO023] Examples of a base to be used include inorganic bases such as alkali metal hydroxide and aqueous ammonia, and amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, isopropylamine, diisopropylamine, diethylenetriamine, triethylenetetramine, monoethanolamine, diethanolamine, 2-amino-2methylpropanol, morpholine, N methylmorpholine, N-ethylmorpholine, pipeline, dimethylethanolamine, diethylethanolamine and dimethyidodecylamine. Triethylamine, dimethylethanolamine and diethylethanolamine are preferable.

100241 An aqueous paint which is suitably used in the present invention can contain conventional pigment, for example, titanium dioxide, white lead, zinc white, zinc sulfide' graphite, carbon black, rust preventing pigment and' optionally, filler pigment such as calcium carbonate, barium sulfate, silicic acid series, silicate series and aluminum hydrate series. In the present invention, an aqueous paint which is most preferably used is a mixture of titanium dioxide as l 5 a white pigment and carbon black as a black pigment.

[o02q A content of a pigment in a paint composition is expressed as a weight ratio in a resin solid material in a pigmenVpaint composition, and is in a range of usually 0.01/1 to 1/1, preferably 0.03/1 to 0.9/1.

100261 The method of the present invention can be performed, for example, in a recycle system for an aqueous paint as shown in Fig.1. Fig.1 represents a recycle system for a single color aqueous paint. First, an aqueous intermediate coating paint 20 is ejected through a coating gun 2 in a coating booth 1 to spray-coat an article to be coated (in the present case, an automobile body) 50.

Thereupon, an over-sprayed paint 4 which is not attached to an article to be coated 50 is collected in a booth circulation water tank 6 by an air stream 70 from a ceiling and transferred to a booth circulation water tank 5. The booth circulation water 6 is utilized repeatedly.

[00271 After a certain coating term, all or a part (preferably all) of the content in a booth circulation water tank 5 is transferred to a concentration tank 7. The content 8 in a concentration tank 7 is usually separated by an ultrafiltration device 9 into a filtrate 11 and a concentrated paint. The separated filtrate 11 is transferred to a filtrate tank 10 and is stored there. On the other hand' the concentrating paint is returned again to a concentration tank 7, further separated and concentrated by an ultrafiltration device 9, and a concentrated 1 o paint 13 having the concentration finally reaching the desired concentration is transferred to a collected paint tank 12 and stored there.

[00281 The concentrated paint 13 is taken out as necessary, and a reduced amount of a paint is replenished with a fresh aqueous paint, and is transferred to a coating gun 2 and is reused at coating On the other hand, the filtrate 11 is transferred to a booth circulation water tank 5, reutilized for washing a booth 1 or in booth circulation water 6, or is transferred to a washing tank 30, and is used as washing water 31 for washing an ultrafiltration device 9 after concentration and separation.

[00291 In the method of the present invention, it is preferable that booth circulation water 6 contains a water-miscible organic solvent in an amount of 1 to 10% by weight, particularly 2 to 8% by weight. This is for improving paint stability in booth circulation water (diluted paint solution). As the water-miscible organic solvent, in particular, butyl diglycol, ethylene glycol monobutyl ether and the like are preferable. When a content of the water-miscible organic solvent is 2 5 smaller than 1% by weight, paint is aggregated after concentration, and stability of a diluted paint solution is reduced. When the content exceeds 10% by weight, stability of a concentrated paint is reduced, and filtering efficacy at ultrafiltration concentration is reduced.

100301 In addition, it is preferable that a pH of booth circulation water 6 is adjusted to 8.0 to 9.0, particularly 8.2 to B.8. This is for maintaining the dilution stability of an amine neutralization-type paint. When a pH of booth circulating water is lower than 8.0, stability of a diluted paint solution is reduced, and a diluted paint solution is aggregated at concentration. When a pH exceeds 9.0, resistance to hydrolysis of a resin is remarkably reduced, stability of a paint is l o reduced, and qualities of a coated film are reduced.

tO031l A pH of booth circulation water is adjusted by inclusion of a base. As the base, the bases as mentioned above can be used. Inter alla, a particularly preferable base is dimethylethanolamine, triethylamine and the.like.

[00321 Since a concentrated paint 13 is concentrated, a part of a highly water soluble melamine resin and an additive is flown-out into booth circulation water, and curability and flowability are reduced. Therefore, when this is reused as it is in coating, there is a high possibility that a cured coated film inferior in film properties such as hardness, water resistance, weather resistance and the like, and appearance is formed.

100331 In the present specification, a component of an aqueous paint which is particularly highly water-soluble and effluent, is passed through an ultrafiltration membrane together with booth circulation water and is flown out at a substantial ratio during a process of collection and concentration of an aqueous paint is called effluent components. The "substantial ratio" refers to such a ratio that 2 5 influences on film properties of a coated film which is formed of the collected and membrane-concentrated paint.

4] In addition, among the effluent components, a component which is actually carried with booth circulation water, that is, a component having a smaller dimension than a size of a hole of an ultrafiltration membrane is called "effluent component". That is, Effluent component amount" means an amount of a solid material in an effluent component.

100351 An amount of an effluent component which is flown-out during a process of collection and concentration of an aqueous paint can be calculated by multiplying both of an amount of an effluent component contained in an 1 o aqueous paint and an effluent rate of an effluent component relative to booth circulation water. Herein, an effluent component is hydrophilic or hydrophobic, and it is difficult to determine to what extent an effluent component is flown-out under the specified condition for collecting and concentrating an excessive paint, from the properties of an effluent component alone. However, an effluent rate of an effluent component relative to booth circulation water can be determined, for example, by devising the following method.

100361 First, a polyester resin varrish having the concentration lower than that of an aqueous paint (e.g. nonvolatile matter 40%) is prepared. An aqueous solution obtained by adding a water-miscible organic solvent to water or pure 2 o water is added to a polyester resin vamish, to dilute the solid content to 10% by weight. Using an ultrafiltration membrane, a diluted polyester resin varnish is concentrated until a filtrate is obtained at the same amount as that added. The solid content of the resulting filtrate is measured. An effluent rate (%) of a polyester resin relative to booth circulation water is calculated by an equation: solid matter concentrat ion of filtrate (%) x filtrate amount (9) polyester resin content (9) A kind of a polyester resin used is not particularly limited as far as it is aqueous, but it is preferable that an effluent rate is 10% or smaller.

[00371 Then, a mixed resin varnish containing the polyester resin and a melamine resin at the same amount ratio as that of an aqueous paint is prepared. An aqueous solution obtained by adding a water-miscible organic solvent to water or pure water is added to a mixed resin varnish to dilute the solid content to 10% by weight. Using an ultrafiltration membrane, a diluted mixed resin varnish is concentrated until a filtrate is obtained at the same amount as that added. A solid material of the resulting filtrate is measured. An effluent rate (%) of an effluent component relative to booth circulation water is calculated by an equation: (Solid content of filtrate (%) x filtrate amount (g) - polyester resin content (9) x polyester resin effluent rate(%)) / (effluent component content (a)).

Procedure from a step of preparing the mixed resin varnish to a step of calculating an effluent rate is repeated every kind of an effluent component.

100381 When an effluent rate of an effluent component is used, an amount of an effluent component which is lost during a process of collecting and concentrating an excessive paint can be calculated. Herein, regarding one kind 2 0 of an effluent component A, values which are determined by actual measurement are represented by the following symbols.

[00391 Table 1

Initial paint charging amount(part by weight) a Booth circulation water charging amount (part by weight) b Solid content of initial coating (% by weight) c Solid material rate of flow-out component A relative to total paint solid d material (% by weight) Effluent rate of effluent component A (% by weight) Y Solid content of first filtrate (%) n1 100401 An amount (part by weight) of an effluent component in an initial coating is represented by an equation: nil x (a+b).

An amount of a component which is flown-out into booth circulation water at first concentration is represented by an equation: In, x b.

An effluent component amount of an effluent component A relative to a paint solid material 100 is represented by: n'.bxaCdY X100 =100dY.

nob ac When an effluent component A at the same amount as the calculated effluent component amount is replenished into a concentrated paint 13, regarding the effluent component A, the same component amount as that of an initial paint is reproduced. When the calculation and replenishing are repeated also on the remaining effluent component, the same component composition as that of an initial paint is reproduced, and the same quality can be maintained.

100411 A cycle of collection and concentration is usually repeated plural times or several times. At a second cycle or later, booth circulation water has already contained a certain amount of an effluent component unlike initial booth 2 o circulation water. Therefore, an amount of an effluent component which is flown-out from an aqueous paint at a second cycle or later is different from that at a first cycle. However, an effluent rate of an effluent component has already been determined and, when the value is used, an amount of an effluent component which is flown-out at a second cycle or later can be theoretically calculated. A calculation equation is shown in Table 2.

00421 Table 2

Cycle No. Replenishing amount relative to paint solid material 100 part by weight (part by weight) 1 (a + b) ( b) x100dY 3 (a + b)

N

10043] At each cycle of collection and concentration at second or later cycle, regarding the effluent component A and other effluent component, when the same amount as that calculated according to the equation of an effluent component is replenished into a concentrated paint 13, the same component composition as that of an initial paint is reproduced, and the same quality can be maintained.

[ 441 As the number of cycle is increased, the concentration of an effluent component in booth circulation water is increased, and gradually reaches the saturated concentration. Accompanied with this, an effluent amount of an effluent component is gradually decreased and, at a time point when the concentration reaches the saturated concentration, a component is no longer flown-out. Thereupon, an effluent component is not flown-out, and a change in a composition of a concentrated paint 13 is not caused. That is, theoretically, aner the concentration of an effluent component in boom circulation water reaches the saturated concentration, a Imposition of a concentrated paint is equivalent to that of an initial paint, and it becomes possible to reuse a concentrated paint as it is without correcting an amount of an effluent component.

100451 The concentration of an effluent component in booth Circulation water after N cycle is represented by an equation: nN = n, + b b x nix, Then, the saturated concentration of a effluent component in booth circulation water is represented by an equation: limnN =n, x a+b Actually, when a solid material content in booth circulation water reaches 70% or more of the theoretical saturated concentration, an amount of an effluent component can be neglected' and a concentrated paint can be reused without correcting a composition.

E)(AMPLES 100461Then, the present invention will be explained specifically by way of Examples, but the present invention is not limited to them. In Examples, Upartn, 2 o Aim and Grater are based on weight unless otherwise indicated.

1004 Preparation Example 1 Synthesis of polyester resin

Table 3

Component Charging amount (part) Phthalic anhydride 19.16 Adipic acid 18. 93 Triymethylolpropane 14.67 Neopentyl glycol 15.14 Glycidyl alcohol ("Carjula E" manufactured by Shell 10.88 Chemical Co., Ltd.) -CaDrolactone 1 5 77 Trimellitic add 5.44 Dibutyltin oxide 0.1 100481 Components shown in Table 3 were placed into a reaction vessel equipped with a stirrer, a temperature regulator and a cooling tube, and a temperature was risen. Water produced by the reaction was azeotropically removed with xylene.

10049] Temperature was adjusted at 1 90 C for about 2 hours from refluxing initiation, stirring and dehydration continued until an acid value corresponding to carboxylic acid was 40 and a hydroxy value was 99, and the reaction was completed. Further, 6 parts of dimethylethanolamine was added, and 113 parts 10of deionized water was then added. A number average molecular weight of the resulting polyester resin was 3,000' and a solid content of an aqueous solution was 44%.

00501 Preparation Example 2 Preparation of aqueous paint 1520.4 Parts of the polyester resin varnish obtained in Preparation Example 1, 10 parts of deionized water, 32.4 parts of titanium dioxide ("CR-97 (trade name)" manufactured by Ishihara Sangyo Kaisha, Ltd.), 17.1 parts of precipitated barium sulfate (B-34 (trade name) manufactured by Sakai Chemical Industry Co., Ltd.) and 0.5 part of carbon black ("MA-100 (trade named manufactured by Mitsubishi Chemical Co., Ltd.) were placed into a paint conditioner, to which 80 parts of glass beads having a particle diameter of 1.4 to 2.0 mm were added, followed by dispersing the materials a mill at room temperature for 1 hour. The dispersion was passed through a wire net to remove the glass beads, to obtain a pigment paste. A particle size of a pigment contained in the pigment paste was 10 him or smaller.

10051] 80.4 Parts of the resulting pigment paste, 59.3 parts of the polyester resin varnish obtained in Preparation Example 1, 15 parts of a melamine resin (Micoat 723 (trade name)" manufactured by Mitsui Cytec, solid content 100%), 1.0 part of a surface adjusting agent 1 (Surfinol 1 04E (trade name) manufactured by Air Products Japan, solid content 0%), 0.8 part of a surface adjusting agent 2 (Polyflow KL-245 (trade name)" manufactured by Kyoeisha Chemical Co., Ad., solid content 100%), 2.2 parts of a surface adjusting agent 3 (UBYK-381 (trade mane)" manufactured by Bic Chemie, solid content 52%) and 8 parts of deionized water were placed into a disperser, followed by stirring for 10 minutes to obtain an aqueous paint.

100521 A solid material ratio of a polyester resin and a melamine resin was 7/3, and the solid content of a paint was 59.7%. In addition, a particle size of a pigment was measured by a particle gauge method (JIS K 5400A method) and 2 o was found to be 10,um or smaller.

0531 Reference ExamDIe A cationic electrodeposition paint (UPower Top U50(trade name) manufactured by Nippon Paint Co., Ltd.) was electrocoated on a zinc phosphate-treated melt zinc-plated steel plate having a length of 150 mm, a width of 70 mm and a thickness of 0.7 mm at a dry thickness of 20,um, followed by baking and curing at 160 C for 30 minutes.

100541 Then, the aqueous paint obtained in Preparation Example 2 was coated on the electrodeposited film with air spray at a dry thickness of 25,um, followed by baking and curing at 150 C for 30 minutes. Appearance of the resulting coated film was good. Gloss (20 gloss) of the surface was measured using a gloss-meter "digital gonioloss-meter manufactured bySuga Test Instrument Co., Ad. and found to be 68. In addition, a pencil hardness was H. 1005!0 An aqueous base paint ("AR-2000 (trade name)" manufactured by Nippon Paint Co., Ltd.) was spray-coated on the coated film by 2 stage at a dry thickness of 15 Em. It was pre-heated at 80 C for 5 minutes and, thereafter, cooled to room temperature. Thereon, a solvent-type dear paint (UMack Flow 0-1801w (trade name)" manufactured by Nippon Paint Co., Ltd.) was spray coated at a dry thickness of 35,um. It was baked and cured at 1 40 C for 30 minutes.

[00561 Water resistance adhesion test The resulting coated plate was immersed in warm water at 40 C for 10 days. A coated film was dried, and cross-cut to a steel plate in a gridiron layout manner at intervals of 2 mm to form 100 independent squares (length 2 mm, width 2 mm). A pressuresensitive adhesive tape (Cellophane tape.

2 0 manufactured by Nichiban Co., Ltd.) was applied on 100 squares with a finger, and it was rapidly peeled from a coated surface in an about 45 direction. The adhesion was assessed by number of squares peeled among 100. The results of assessment was 0. An assessment value indicates that O is most excellent in adhesion, and 100 is most poor.

|005n Anti chipping property test Another coated plate prepared as described above was cooled to ARC, and set on a sample holder of a flying stone testing machine (manufactured by Suga Test Instrument Co., Ltd.). 100 9 of No.7 ground stones was charged into a testing machine, and was ejected at an air pressure of 3 kg/cm2 to collide with a surface of a coated film. An angle of a coated plate was arranged as an entrance angle of stones being 30 . An extent of a peeling damage of a coated film was assessed by the following criteria. The result of assessment was 4.

1005 Table 4

No destruction 4 Slight peeling damage 3 An area of peeling damage is half or less an entire surface area 2 An area of peeling damage is half or more an entire surface area 1 Entire surface peeling 100591 Comparative Example 1 A test was performed by diluting and membraneoncentrating the aqueous paint obtained in Preparation Example 2. First, 1,500 9 of a 5% aqueous solution of butyl diglycol was added to 500 9 of the aqueous paint to dilute the paint to a solid content of 15%. Thereafter, dimethylethanolamine was added thereto, and a pH was adjusted to 8.5. Then, the diluted paint was circulated into a pencil type UP module equipped with a liquid supplying pump (manufactured by Asahi Chemical Industry Co., Ad.), and concentrated until the same amount (1,500 9) as that of the diluted solution of a filtrate was produced.

The solid content of the filtrate (filtrate NV) was 2.6%.

l0060l An electrodeposited film was formed on a melt zinc-plated steel plate as 2 o in Reference Example, the resulting concentrating paint was spray- coated thereon, which was baked and cured. Appearance, luster and pencil hardness of the resulting coated film were measured. The results are shown in Table 7.

[00611 Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film. Water resistance adhesion and anti chipping property of the resulting coated film were tested and assessed. The results of assessment are shown in Table 7.

00671 Example 1

Measurement of effluent rate (1) Polyester resin 1,700 g of a 5% aqueous solution of butyl diglycol was added to 500 9 of the polyester resin varnish (solid content 44%) obtained in Preparation Example 1 to dilute to a solid content of 10%. Dimethylethanolamine was added thereto, and a pH was adjusted to 8.0. The solution was circulated into a pencil-type OF module equipped with a liquid supplying pump (manufactured by Asahi Chemical Industry Co., Ltd. ) to concentrate, to obtain 1,700 g of a filtrate. The solid content of the filtrate was 0.86%. A polyester resin effluent rate was calculated from the value, and found to be 6.6%.

00631 (2) Melamine resin The polyester resin varnish obtained in Preparation Example 1 and UMicoat 723 (trade name)" manufactured by Mitsui Cytec which was a melamine 2 o resin (solid material 100 ) were mixed so that a solid material ratio of a polyester resin and a melamine resin was 7/3, and diluted with pure water to a solid content of 40%.

100641 1,500 9 of a 5% aqueous solution of butyl diglycol was added to 500 9 of the resulting mixed varnish to dilute to a solid content of 10%.

Dimethylethanolamine was added thereto, and a pH was adjusted to 8.0. The solution was circulated into a penal-type OF module equipped with a liquid supplying pump (manufactured by Asahi Chemical Industry Co., Ltd.) to concentrate, to obtain 1,500 9 of a filtrate. a solid content of the filtrate was 3.26%. A melamine resin effluent rate was calculated from the value and the polyester resin effluent rate, and found to be 66%.

[006q (3) Additive The polyester resin varnish obtained in Preparation Example 1 and UPdy Flow KL-245 (trade name)n (solid content 100%) manufactured by Kyoeisha Chemical Co., Ltd. which was a surface adjusting agent 2 were mixed so that a 1 o solid ratio of a polyester resin and a surface of adjusting agent was 95/5, and diluted with pure water to a solid content of 40%.

[00661 1500 g of a 5% aqueous solution of butyl diglycol was added to 500 9 of the resulting mixed varnish to dilute to a solid content of 10%.

Dimethylethanolamine was added thereto, and a pH was adjusted to 8.0. The solution was circulated into a pencil type UF-module equipped with a liquid supplying pump (manufactured by Asahi Chemical Industry Co., Ltd.) to concentrate, to obtain 1,500 9 of a filtrate. A solid content of the filtrate was 1.24%. An effluent rate of a surface adjusting agent 2 was calculated from the value and the polyester resin effluent rate, and found to be 60%.

2 o 100671 According to the same manner as that described above, effluent rates of USurfinol 1 04E (trade name)" manufactured by Air Products Japan which was a surface adjusting agent 1 and UBYK-381 (trade name) manufactured by Bic Chemie which was a surface adjusting agent 3 were also calculated. The results were 0% and 25%, respectively.

2 5 [00681 In the following Examples 2 to 5, regarding the concentrated paint obtained in Comparative Example 1, a method of correcting amounts of all effluent components will be explained.

0069l Example 2

The concentrated paint obtained in Comparative Example 1 underwent dilution and membrane-concentration one time, and corresponds to a concentrated paint obtained by performing one cycle of collection and concentration in a method of reusing an over-sprayed aqueous paint. Then, by substituting the effluent rate obtained in Example 1 for an equation in which the cycle number shown in Table 2 was 1, effluent amounts of respective effluent components were calculated, provided that, regarding surface adjusting agents 1, 2 and 3, since a constituent ratio was very small, they were added up as an additive. The results of calculation are shown in Table 5

100701 Table 5

Effluent Solid rate d (%) Effluent rate Y Effluent components (56) component amount (g) Polyester resin 34.3 6.6 2.3 Melamine resin 14. 7 66 9.7 Additive 1.9 42 0.8 100711 Thereafter, an amount corresponding to the effluent components amount was added to the concentrated paint obtained in Comparative Example 1 to obtain a reuse paint.

1007Z] As in Reference Example, an electrodeposited film was formed on a melt zinc-plated steel plate, the resulting reuse paint was spray-coated thereon, which was baked and cured. Appearance, luster and pencil hardness of the resulting coated film were measured. The results are shown in Table 7.

100731 Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film. Water resistance adhesion and anti chipping property of the resulting coated film were tested and assessed. The results of assessment are shown in Table 7.

100741 Examole 3 s As in Example 2, 5 cycles of dilution and membraneconcentration were performed while correcting a composition of a concentrated paint, to obtain a concentrated paint. The solid content of booth circulation water (corresponding to a filtrate produced at a 4 cycle) used in dilution was measured, and found to be 7.4%. In the aqueous paint system, the theoretical saturated concentration of an effluent components relative to booth circulation water was calculated to be 10.4%, and the solid content was 71% of the theoretical saturated concentration.

1 751 As in Reference Example, an electrodeposited film was formed on a melt zinplated steel plate, the resulting concentrated paint was spraycoated thereon as it was, which was baked and cured. Appearance, luster and pencil hardness of the resulting coated film were measured. The results are shown in

Table 7

100761 Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film. Water resistance adhesion and anti 2 o chipping property of the resulting coated film were tested and assessed. The results of assessment is shown in Table 7.

00771 ExamoIe 4 As in Example 2, a solid content of effluent amount of respective effluent components in the case of the cycle number of 5 were calculated. The results 2 5 of calculation are shown in Table 6.

[007 Table 6

Flow-out components Effluent component amount (9) Polvester resin 0.72 Melamine resin 3.1 Additive 0.25 10079] Thereafter, an amount corresponding to an effluent amount of the effluent components was added to the concentrated paint obtained in Example 3 to obtain a reuse paint.

100801 As in Reference Example, an electrodeposited film was formed on a melt zinclated steel plate, the resulting reuse paint was spray-coated thereon, which was baked and cured. Appearance, luster and penal hardness of the resulting coated film were measured. The results are shown in Table 7.

l0081l Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film. Water resistance adhesion and anti chipping property of the resulting coated film were tested and assessed. The results of assessment are shown in Table 7.

00821 Example 5

As in Example 2, 8 cycles of dilution and membranconcentration were performed while correcting a composition of the concentrated paint, to obtain a concentrated paint. The solid content of booth circulation water (corresponding to a filtrate produced at a 7 cycle) used in dilution was measured to be 9. 1%.

In the aqueous paint system, the theoretical saturated concentration of an effluent component relative to booth circulation water was calculated to be 2 o 10.4%, and the solid content was 88% of the theoretical saturated concentration.

l0083l As in Reference Example, an electrodeposited film was formed on a melt zinc-plated steel plate, and the resulting concentrating paint was spray-coated thereon as it was, which was baked and cured. Appearance, luster and penal hardness of the resulting coated film were measured. The results are shown in

Table 7.

[00841 Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film Water resistance adhesion and anti chipping properb/ of the resulting. coated film were tested and assessed. The results of assessment are shown in Table 7.

100851 Table 7

Example No. Cycle Presence or Appear- Luster Hardness Water Ante number absence of ance resistance chippin correction adhesion 9 _ property Reference O Absence Good 68 4 Comparative 1 Absence Good 66 B 0 3 Exampe 1 Example 2 1 Presence Good 66 H O 4 Example 3 5 Absence' Good 68 H O 4 Example 4 5 Presence Good 68 4 Example 5 8 Absenceb Good 66 H O 4 a) In cycles 1 to 4, a composition of the concentrated paint was corrected.

b) In cycles 1 to 7, a composition of the concentrated paint was corrected.

[00861 In the following Examples 6 to 9, regarding the concentrated paint obtained in Comparative Example 1, a method of correcting amounts of effluent lo polyester resin and melamine resin will be explained.

0087l Example 6

A polyester resin and a melamine resin were added to the concentrated paint obtained in Comparative Example 1 at an amount corresponding to an effluent component amount calculated in Example 2, to obtain a reuse paint.

According to the same manner as that of Example 2 except the above, an electrodeposited film was formed on a melt zinc-plated steel plate, and the resulting reuse paint was spray-coated thereon, which was baked and cured.

Appearance, luster and pencil hardness of the resulting coated film were F measured. The results are shown in Table 8.

100881 Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film. Water resistance adhesion and anti chipping property of the resulting coated film were tested and assessed. The results of assessment are shown in Table 8.

00891 Examole 7 According to the same procedure as that of Example 3 except that only effluent component amounts of a polyester resin and a melamine resin were corrected, a 5 concentrated paint was obtained. The resulting concentrated paint formed a coated film without correcting a composition, followed by assessing. The results of assessment are shown in Table 8.

1009Gl Example 8

A polyester resin and a melamine resin were added to the 5 concentrated paint obtained in Example 7 at an amount corresponding to a effluent component amount calculated in Example 4, to obtain a reuse paint. A coated film was formed of the resulting reuse paint, followed by assessing. The results of assessment are shown in Table 8.

100911 Example 9

According to the same procedure as that of Example 5 except that only effluent component amounts of a polyester resin and a melamine resin were corrected, a 8th concentrated paint was obtained. The resulting concentrated paint formed a coated film without correcting a concentration, followed by assessing. The results of assessment are shown in Table 8.

[00921 Table 8

Example No. Cycle Presence or Appearance Luster Hardness Water Ante number absence of resistance chipping correction adhesion property: Reference O Absence Good 68 H 4

Example

Comparative 1 Absence Good B 3

Example 1 _

Example 6 1 Presence Good H 0 4 Example 7 5 Absence' Good 68 H 0 4 l Example 8 5 Presence Good 68 H 0 4 Example 9 8 Absenceb Good -H 0 4 a) In cycles 1 to 4, a composition of the concentrated paint was corrected.

b) In cycles 1 to 7, a correction of the concentrated paint was corrected.

100931 In the following Examples 10 to 13, regarding the concentrated paint obtained in Comparative Example 1, a method of correcting an amount of a effluent melamine resin will be explained.

00941 Example 10

A melamine resin was added to the concentrated paint obtained in Comparative Example 1 at an amount corresponding to an effluent component I amount calculated in Example 2, to obtain a reuse paint. According to the same I manner as that of Example 2 except the above, an electrodeposited film was formed on a melt zinclated steel plate, and the resulting reuse paint was spray-ooated thereon, which was baked and cured. Appearance, luster and pencil hardness of the resulting coated him were measured. The results are

shown in Table 9.

100951 Further, as in Reference Example, a base coated film and a clear coated film were formed on the coated film. The water resistance adhesion and the anti-chipping of the resulting coated film were tested, and assessed. The I results of assessment are shown in Table 9.

[00961 ExamoIe 1 1 The same procedure as that of Example 3 except that an effluent component amount of a melamine resin was replenished, a 5 concentrated paint was obtained. The resulting concentrated paint formed a coated.film without correcting a composition, followed by assessing. The results of assessment are shown in Table 9.

971 Example 12

A melamine resin was added to the 5th concentrated paint obtained in Example 11 at an amount corresponding to Me effluent component amount 1 o calculated in Example 4, to obtain a reuse paint. A coated film was formed of the resulting reuse paint, followed by assessing. The results of assessment are

shown in Table 9

9 Example 13

According to the same procedure as that of Example 5 except that an effluent component amount of a melamine resin was replenished to obtain an 8 concentrated paint. A coated paint was formed of the resulting concentrated paint without correcting a composition, followed by assessment. The results of assessment are shown in Table 9. !

Table 9

Example No. Cycle Presence or Appearance Luster Hardness Water Anti- I number absence of resistance chipping correction adhesion property I Reference O Absence Good 68 H 4

Example

Comparative 1 Absence Good 66 3

Example 1 _ _

Example 10 1 Presence Good 66 H O 4 Example 11 5 Absences Good 68 H 4 I

_

Example 12 5 Presence Good 68 H O 4 Example13 8 Absenceb Good -H O 4 -- a) In cycles 1 to 4, a composition of the concentrated paint was corrected.

b) In cycles 1 to 7, a composition of the concentrated paint was corrected.

101001 According to the method of reusing a melamine resin curing type aqueous paint of the present invention, in even an aqueous paint which is highly water-soluble and contains an effluent component, curability does not change during a process of collection and concentration, and film properties, such as hardness, water resistance, weather resistance and the like of a cured coated film are not deteriorated.

Claims

WHAT IS CLAIMED IS: 1. A method of reusing an over-sprayed aqueous paint,

which comprises: a step of spray coating an article to be coated with an aqueous paint comprising a binder component containing a melamine resin as a curing agent; a step of collecting a dust of the over-sprayed aqueous paint together with booth circulation water; a step of separating a diluted paint solution containing the collected aqueous paint and booth circulation water into a concentrated solution and a filtrate using an ultrafiltration membrane; a step of determining an amount of effluent components passing through the ultrafiltration membrane together with booth circulation water, based on an effluent rate of the effluent components relative to initial booth circulation water, and then replenishing the amount to the concentrated solution; and a step of using the filtrate as booth circulation water, and the concentrated solution as an aqueous paint.
2. The method according to claim 1, wherein the effluent 2 o component which is replenished to the concentrated solution is a melamine resin in the binder component.
3. The method according to claim 1, wherein the effluent components to be replenished to the concentrated solution are a base resin and a melamine resin in the binder component.

2 5
4. The method according to anyone claims 1 to 3 wherein, in case where cycles are repeated more than several times, the reduced amount of the effluent components is replenished to the concentrated solution, when the effluent components in the booth circulation water have a concentration of 70 % by weight or less, and if the concentration of the effluent components reaches to more than 70 % by weight, then the replenishing step is not conducted and the concentrated solution is recycled as it is.
5. The method of reusing an aqueous paint according to any one of claims 1 to 4, wherein the booth circulation water contains a water-miscible organic solvent in an amount of 1 to 10% by weight, and controls a pH within the range of 8.0 to 9.0.