FR2487841A1 - Water-miscible diluent for coating compsns. esp. for automobiles - contg. glycol cpds., alkanol(s) and ketone(s) used to reduce pollution - Google Patents

Abstract

Diluent comprises a water-miscible organic solvent capable of dissolving the organic solvent based coating compsns. It is formed of (a) a satd. aliphatic glycol or glycol ether contg. >=3C atoms and a cpd. of formula (I) RO-(CH2(R1)-O)n-R2 where R is H, 1-4C alkyl or acetyl; R1 is -CH2, -CH2CH2-, -CH2-CH(CH3)-, or -CH(CH2OH)-; R2 is 1-4C alkyl or hydroxyalkyl or acetyl and n = 1-4 and mixts. of these cpds., (b) 10-60 pts. of a 1-8C monoalkanol; and (c) 10-50 pts. of a =12C satd. aliphatic ketone and the sum of (a), (b) and (c) being 100 pts. by wt. Atmospheric pollution is reduced when coating compsns. are applied by applying an organic solvent based compsn. to a water miscible organic diluent to a substrate and passing the gaseous effluent into water. Diluent is used for paints etc. esp. in the automobile industry.

Description

 The present invention provides a means for reducing pollution by gases from the application of coating compositions. The invention therefore relates to improvements to avoid pollution by gases, such as air pollution, and more particularly the invention relates to the use of a diluent based on organic compounds miscible with water. More particularly, the diluent serves to dilute or reduce the concentration and the viscosity of the composition used as a coating composition during the application of this composition to a substrate.

 The coating industry, particularly the paint industry, has gone through a revolution in the field of compositions that can be used to apply coating compositions to various substrates, due to air pollution. Many techniques such as the use of a powder coating technique, coating compositions with a high dry matter content, coating compositions with a lower organic content, etc., constitute various means for solving the problem. air pollution problem. All of these techniques require entirely new technology to completely satisfy the authorities responsible for preventing air pollution. The advantage of the present invention is the possibility of using known technology concerning the application of currently known coating compositions, such as liquid paints used as primer layers and top coating or finishing compositions in industry. transportation vehicles, such as the automotive industry. It has been found that by using a completely water-miscible thinner for painting, the technique currently known for liquid paints based on thinners or organic materials can be used.

The present invention relates to a method for reducing air pollution resulting from the application of a coating composition. The method comprises the steps according to which
1. a coating composition based on organic solvent, containing a diluent composition based on organic solvent entirely miscible with water, is applied to a substrate or substrate, so as to form a gaseous effluent containing an air mixture, gaseous organic solvent and gaseous diluent; and,
2. gaseous effluent is passed through a gas absorption device containing a non-reactive liquid solvent capable of absorbing the gaseous organic solvent of the coating composition and the gaseous diluent composition.

/dans laquelle R est un atome d'hydrogène, un groupe alkyle ayant 1 à 4 atomes de carbone ou -(0)-C-CH3;
R1 est, indépendamment, choisi parmi -CH2, -CH2-CH2-; -CH2 -CH (CH3)-; et CH(CH2OH)-;
R2 est choisi, indépendamment, parmi un groupe alkyle ayant 1 ou 4 atomes de carbone et comportant éventuellement un substituant hydroxyle, et -(0)-C-CH3;; et
n est un nombre valant 1 à 4 7 et leurs mélanges, en une quantité comprise entre environ 10 et environ 60 parties en poids;
b. un monoalcanol miscible à l'eau, comportant environ 1 à environ 8 atomes de carbone, présent en une quantité comprise entre environ 10 et environ 60 parties en poids; et
c. une cétone aliphatique saturée, miscible à l'eau, contenant jusqu'à 12 atomes de carbone et présente en une quantité comprise entre environ 10 et environ SO parties en poids, la somme (a + b + c) valant au total 100 parties en poids.The diluent usable in the present invention can be any fully water-miscible organic-based diluent composition. However, it is preferred that the diluent is a composition comprising:
at. a water-miscible compound chosen from a saturated aliphatic glycol or a saturated aliphatic glycol ether oxide, each containing at least 3 carbon atoms, and a compound of formula (I)

/ in which R is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or - (0) -C-CH3;
R1 is, independently, chosen from -CH2, -CH2-CH2-; -CH2 -CH (CH3) -; and CH (CH2OH) -;
R2 is chosen, independently, from an alkyl group having 1 or 4 carbon atoms and optionally comprising a hydroxyl substituent, and - (O) -C-CH3; and
n is a number from 1 to 4 7 and their mixtures, in an amount between about 10 and about 60 parts by weight;
b. a water-miscible monoalkanol, having about 1 to about 8 carbon atoms, present in an amount between about 10 and about 60 parts by weight; and
vs. a saturated aliphatic ketone, miscible with water, containing up to 12 carbon atoms and present in an amount of between approximately 10 and approximately SO parts by weight, the sum (a + b + c) being worth in total 100 parts weight.

 Optionally, other water-soluble organic acids, aldehydes or esters can be used.

The invention will now be described in more detail, by way of non-limiting examples, with reference to the appended drawings in which
Figure 1 is a schematic diagram of the process of the present invention comprising the use of the solvent by-products; and
Figure 2 is a schematic view of a washer with spray projection in a cyclone. This scrubber is a device for absorbing gaseous effluent by a liquid.

 In carrying out the process of the present invention, any coating composition based on an organic solvent can be used, in particular primer compositions and finishing coating compositions, based on organic, which the 'is used in the transport vehicle industry, particularly in the automotive industry. The materials generally used by the automotive industry are liquid paints, such as varnishes, which are oil-based paints which form a film by evaporation of the solvent or by freezing from a molten state. In addition, enamels are used which are oil-based paint compositions containing binders which form a film by oxidation or polymerization on exposure to air.

Well-known and very diverse coating compositions can be used, such as epoxy resins, vinyl resins, phenolic, acrylic resins, urethane-type coatings, silicone resins, amino resins, alkyd resins, etc. It is known that the current state of technology knows very diverse types of coating compositions of this type. The most preferred coating composition is an acrylic-based finishing composition commonly used in the automotive industry. A second preferred coating composition is a composition of urethane type with a high dry matter content, described more fully in the US patent.
United States of America NO 4,070,509. For a list of suitable epoxy resins, see "Federation Series on Coatings
Technology "(Federal Series on Coatings Technology), n020, July 1972; for a list of suitable vinyl resins, see n019, April 1972 of this series; for a list of suitable phenolic resins, see n018,
March 1971, of this series; for a list of suitable acrylic resins, see no. 17, March 1971 of this series; for a list of suitable urethane coatings, see no. 15, July 1970, of this series; for suitable lessons on silicone resins, see n014,
July 1970 of this series; for suitable teachings on amino resins, see n013, December 1969 of this series; for suitable teaching on alkyd resins, see n05, March 1967, of this series.

Other coatings can also be used, such as polyesters, polyamides, silicones, polybenzimi dazole, etc. Among the coatings listed above, the most preferred are acrylic resins.

 In the current coating industry, in particular the paint industry, the organic solvents used are those containing various organic materials normally comprising hydrocarbons in the liquid state at ambient temperatures and pressures, such as hexane, cyclohexane, heptane, etc. In addition, organic solvents can also contain aromatic solvents, such as benzene-based and naphthalene-based materials, and their alkyl and hydroxyl derivatives, such as toluene, xylene, etc .; phenol; naphthalene, tetrahydronaphthalene, butylphenol, bisphenol A or F, ethylbenzene, cumene, acetophenone, methylphenyl-carbinol, etc.

 The present invention relates to the use of a paint thinner, which is applied at the same time as the paint based on organic solvent. By "at the same time" is meant to indicate that the diluent and the coating composition are mixed beforehand and applied as if it were a coating composition or a paint. By "diluent" is meant a composition which decreases the concentration of the coating composition or desired paint or dilutes it or facilitates its application, since this diluent can dissolve or disperse the coating composition based on organic solvent. This solvent or diluent is used in an amount of approximately 10 to approximately 95 parts by weight relative to the total composition applied, the rest of this composition being the coating composition based on organic solvent that is applied.

dans laquelle R est un atome d'hydrogène, un groupe alkyle ayant 1 à 4 atomes de carbone ou -(O)C-CH3;
R1 est choisi, indépendamment, parmi -CH2, -CH2-CH2-; -CH2-CH (CH3)-; et -CH(CH2OH)-;
R2 est choisi, indépendamment, parmi un groupe alkyle ayant 1 à 4 atomes de carbone et éventuellement substitué par un groupe hydroxyle, et -(O)-C-CH3; et
n vaut 1 à 4.The diluent contains an organic solvent composition fully miscible with water. By a "composition of organic solvent entirely miscible with water" is meant a composition entirely composed of an organic material, preferably containing just carbon, hydrogen and oxygen atoms, which is a solvent of the coating composition based on organic matter and is entirely soluble in batten, even if part of the constituents may not be entirely water-soluble. Suitable diluents from group (a) are a monoalkyl or dialkyl ether oxide of ethylene glycol or diethylene glycol, or a monoalkyl, dialkyl or trialkyl ether oxide of triethylene glycol and their acetic derivatives. The alkyl group has 1 to 4 carbon atoms. Suitable examples are saturated glycols containing at least 4 carbon atoms. Or the diluent is a compound of formula (I)

wherein R is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or - (O) C-CH3;
R1 is independently selected from -CH2, -CH2-CH2-; -CH2-CH (CH3) -; and -CH (CH2OH) -;
R2 is independently chosen from an alkyl group having 1 to 4 carbon atoms and optionally substituted by a hydroxyl group, and - (O) -C-CH3; and
n is 1 to 4.

dans laquelle R, R2 et n ont le sens décrit ci-dessus; et
R4 est un groupe alkylène saturé ayant 2 à 4 atomes de carbone.A preferred diluent corresponds to the formula (II)

in which R, R2 and n have the meaning described above; and
R4 is a saturated alkylene group having 2 to 4 carbon atoms.

 Examples of materials from group (a) are "Cellosolve" (trademark of Union Carbide designating a monoethyl ether of ethylene glycol), methyl "Cellosolve", butyl- "Ceilosolve", ltisobutyl- "Cellosolve ", hexyl-" Cellosolve "," Carbitol "(trademark of Union Carbide designating a monoethyl ether of diethylene glycol), butyl-" Carbitol ", hexyl-" Carbitol ", propylene glycol monobutyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, butoxy - triglycol C4H90 (C2H4-O) 3H, methoxy -triglycol CH3O (C2H4-0-) 3H, ethoxy-triglycol C2H50 (C2H40) 3, l-butoxyethoxy-2-propanol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene -glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, whose molecular weight can go up to a maximum of around 2000, lthexylene glycol, 2-ethy l-1,3-hexanediol, 1,5-pentane-dioî, "ester-dioî 204" (2,2-dimethyl-3-hydroxypropyl 2,2-dimethyl3-hydroxy-propionate), etc.

 The water-miscible alcohols which can be used in the present invention have 1 to 8 carbon atoms, such as methanol, ethanol, propanol, butanol, isobutanol, pentanol, hexanol, heptanol ## octanol, methylamyl alcohol, etc.

 The aliphatic ketones miscible with a strip which can be used in the present invention are acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl # ketone, methoxy acetone, cyclohexanone, methyl-n-amyl ketone, methyl isoamyl ketone, ethyl butyl ketone, diisobutyl ketone, isophorone, acetyl acetone (2,4-pentane-dione), diaceton alcohol (CH3) 2C (OH) CH2C (O) CH3.

 It should be understood that other organic materials can be added to the diluent in order to give it additional dissolving properties. The main requirement for these possible additional materials is that they are miscible with water. These are generally acids and esters, the acid containing from 1 to 6 carbon atoms such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, etc.

 Suitable esters which can be used are methyl acetate, ethyl acetate, hexylene glycol diacetate, dimethyl ester of succinic acid, glutaric acid, acid adipic, etc., the number of carbon atoms of the usable compounds being up to approximately 10.

 The gaseous effluent from the application of the paint includes not only that which comes from the application of the paint itself, but also from the volatilization of the solvent of the liquid paint during the drying thereof. By "gas" is meant to include not only a gaseous effluent, but also a cloud of atomized paint formed during the application of the paint to a substrate.

 The most preferred gaseous effluent is an effluent containing, in the gas phase, solvents for liquid paint, which are a mixture of substances, in particular a hydrocarbon substance and an oxygenated substance.

 By "oxygenated" is meant substances which are organic solvents such as paint solvents containing oxygen in the molecule of the solvent, as in the case of an alcohol, part of an acid, a ester or ether.

 When applying a liquid paint to a substrate, this paint is atomized, without using air or by pneumatic or electrostatic means. The cloud of paint from the spray booth of this paint is collected in a water washing area by a curtain of water. The paint applied to the substrate is then dried by passing this substrate through a heated chamber in which the solvent is volatilized. During the application and drying of the paint, gaseous effluent is formed.

 Before passing this gaseous effluent to the atmosphere, it is treated according to one aspect of the process of the present invention which consists in diffusing, bubbling or passing the gaseous effluent in an absorption device by a liquid, such as a liquid absorber , which is a gaseous effluent solvent.

 The liquid absorber containing the gaseous effluent can be retained in a suitable tank and then be collected and regenerated as desired. The advantage of using a liquid for absorption is that this liquid is easy to handle, pump, store and regenerate.

 By using the absorbent liquid according to the present invention, it is possible to simplify the control of the total pollution due to an industrial installation. In this way, it is not necessary to modify the equipment currently used to manufacture and use organic paints because the present invention does not concern the modification of the paint or its application equipment, but rather the absorption. gaseous effluent and the most efficient and economical regeneration of the absorption liquid, as well as organic based solvents.

 When a water wash zone normally operates near a paint spray booth, there is a curtain of water that washes the walls of a paint spray box or spray booth. Water can be sprayed on the walls or in some other way collect the cloud of paint.

 The absorption liquid according to the present invention is a liquid which does not react with gaseous effluent.

In addition, this liquid can be a liquid material and which, if necessary, is essentially non-volatile at ambient temperatures and pressures, as well as at temperatures and pressures at which the industrial process and the regeneration of the organic solvent can be carried out. Very advantageously, the absorption liquid is water. It should be understood that a little hydrolysis will occur when the organic ester is part of the diluent and that the strip constitutes the absorption liquid.

dans laquelle R3 contient de 3 à 4 atomes de carbone et m se situe entre 2 et 2000, comme du polyoxyéthylène-glycol, du polyoxypropylène-glycol, du polyoxybutylène-glycol; des polyols aliphatiques saturés ayant 2 à 12 atomes de carbone comme le glycérol, des esters dibasiques comme les esters dialkyliques (ayant jusqutà 8 atomes de carbone par groupe) d'acides polycarboxyliques aliphatiques saturés (jusqutà 10 atomes de carbone par groupe acide) comme un oxalate de dialkyle, un malonate de dialkyle, un succinate de dialkyle, un glutarate de dialkyle, un adipate de dialkyle, un pimélate de dialkyle, un subérate de dialkyle, un azélate de dialkyle, un sébacate de dialkyle, etc.; des cétones aliphatiques saturées comme le diacétonealcool, la méthyl-heptyl-cétone; des esters d'acides dicarboxyliques aromatiques comme du phtalate de dialkyle comportant 4 à 13 atomes de carbone par groupe alkyle, comme le phtalate de didécyle ou de dioctyle, etc.; des esters organiques de l'acide phosphorique comme le phosphate de tricrésyle, des huiles de silicone comme des silanes ou des polysiloxanes, comme des polymères de diméthylsiloxane et leurs mélanges non réactifs. On entend inclure dans le terme "polyoxyalky 1 ne", des composés préparés par réaction de l'oxyde d'éthylène, de l'oxyde de propylène et/ou de l'oxyde de butylène ensemble avec ou sans d'autres corps pouvant réagir avec eux comme des alcools, tant qu'il existe au moins plusieurs chaînons répétés

Other liquids suitable for absorption are those whose vapor pressure is less than a value corresponding to 1 mm of mercury (133.3 Pa) at 20 C, even better, less than 0.01 mm of mercury (1 , 33 Pa). Examples of these absorption liquids are polyoxyalkylene glycol, preferably corresponding to the structural formula

in which R3 contains from 3 to 4 carbon atoms and m is between 2 and 2000, such as polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol; saturated aliphatic polyols having 2 to 12 carbon atoms such as glycerol, dibasic esters such as dialkyl esters (having up to 8 carbon atoms per group) of saturated aliphatic polycarboxylic acids (up to 10 carbon atoms per acid group) as a dialkyl oxalate, dialkyl malonate, dialkyl succinate, dialkyl glutarate, dialkyl adipate, dialkyl pimelate, dialkyl suberate, dialkyl azelate, dialkyl sebacate, etc .; saturated aliphatic ketones such as diacetonalcohol, methyl heptyl ketone; esters of aromatic dicarboxylic acids such as dialkyl phthalate having 4 to 13 carbon atoms per alkyl group, such as didecyl or dioctyl phthalate, etc .; organic esters of phosphoric acid such as tricresyl phosphate, silicone oils such as silanes or polysiloxanes, such as dimethylsiloxane polymers and their non-reactive mixtures. The term “polyoxyalky 1 ne” is intended to include compounds prepared by the reaction of ethylene oxide, propylene oxide and / or butylene oxide together with or without other reactive substances with them like alcohols, as long as there are at least several repeat links

 It should be understood that other non-reactive substances may be added as diluents or agents for controlling the viscosity in order to contribute to the fluidity of the liquid. Another absorption liquid is a 50/50 mixture by volume of didecyl phthalate and a polyoxyalkylene glycol ("Ucon LB-65", trademark of Union Carbide) having a vapor pressure below 1.33 Pa at 20 C.

 When using an absorption liquid, it is preferred that this liquid has as low a vapor pressure as possible. This allows for as little volatilization of the liquid as possible during absorption of the effluent from the spraying of paint.

 On the other hand, when water is used as absorption liquid, the handling of the composition is improved due to the affinity of water for all the constituents of the composition, that is to say that the composition of coating dissolves in water-miscible thinner.

 The overall process according to the present invention is represented by the diagram in FIG. 1. It shows the formation of the gaseous effluent at 10. This effluent passes through an absorption device through a liquid containing an absorption liquid 12. The outlet of this absorption liquid allows the absorbed gaseous effluent to pass to a regeneration zone 14. In this zone 14, the liquid absorption agent is separated from the gaseous effluent.

The liquid absorption agent is then recycled through a conduit 16 to return to the liquid absorption device and still serve there. The gaseous effluent is mainly a solvent in the gaseous phase from liquid paint. It can be reprocessed during the manufacture of liquid paint in 18.

 A type of apparatus that can be used for absorption by a liquid in the present invention is shown in Figure 2 showing a diagram of a spray washer 20 in a cyclone having an inlet 22 of air or gas. The gas arriving through the inlet 22 tangentially enters the chamber 24 of the cyclone, which has an inlet 26 and an outlet 27 for liquid. The inlet 26 allows the absorption liquid to pass through a conduit 28 to be sprayed by several nozzles forming spray distribution groups. The top of this spray distributor is a central disc 32 projecting widely into the chamber 24.

 The gaseous effluent from the industrial process enters through the inlet 22 and circulates in a circular or helical path around the chamber 24, coming into direct contact with the absorption liquid 34 sprayed in the form of a fine division of this liquid, this which ensures a large contact surface of the liquid with the air. A very high efficiency is obtained because almost all of the gaseous effluent containing undesirable pollutants is absorbed in the liquid phase, while the remaining gas leaves passing between fins 36 intended to avoid swirling. The absorption liquid is then collected at the outlet 27 to be then treated in the regeneration zone 14. The chamber 24 can be made of any stable metal in the presence of the gaseous effluent, for example stainless steel, glass coated metal, etc.

A series of chambers 24 forming cyclones can be used to purify gaseous effluent gradually by passing effluent from each of the chambers into the next.

 Spray washers in a cyclone chamber are described more fully in the manual "Chemical Engineers Handbook", 4th edition, pages 18-33 et seq.

 The regeneration zone is above all a means of separating the absorption liquid from the gaseous effluent which is absorbed there. Any device can be used to perform the separation. Two main techniques are preferred. One consists in vacuum distillation and the second in the use of micro-filtration. In vacuum distillation, it is highly preferred that there is a large difference between the boiling point of the absorption liquid and the gaseous effluent absorbed therein. If the difference is at least 1100C, a very effective separation can be obtained.

 The most preferred gas washer is that described in United States Patent No. 3,971,461.

 When a solvent completely miscible with water and comprising the constituents indicated in formula A is introduced into the gas washer described in the aforementioned United States patent No. 3,971,641, the gas is better washed .

FORMULA A (Liquid at ambient temperatures and pressures)
Constituent parts by weight
Methanol 10
Isopropyl alcohol 30
Acetone 20
"Cellosolve" acetate 30
DBE (mixture of dimethyl esters of acid
succinic, glutaric acid and
11 adipic acid) 10
it has been found that when using the gas washer described in the aforementioned patent NO 3 971 641, that the absorption liquid is water and that the diluent is a composition of formula A with an acrylic paint, the linear speed of the effluent gas should be about 1.52 m / sec, preferably about 0.31 to 1.22 m / sec. If the speed of the gaseous effluent is greatly increased, there may not be enough absorption of the fluid by the aqueous absorption liquid. Slowing the movement of the effluent markedly increases the effectiveness or efficiency of the contact between the spraying of the absorption liquid and the gaseous effluent.

 A more efficient technique for separating the absorption liquid from the gaseous effluent which is absorbed therein may involve the use of membranes facilitating an operation of the micro-filtration type. In other words, membranes are inserted into a conduit through which the liquid passes.

 A low molecular weight substance will pass through the membrane while a higher molecular weight substance will not be able to cross it. This regenerates the absorption liquid and allows it to be reprocessed for use again in all operations.

 It goes without saying that, without departing from the scope of the invention, numerous modifications can be made to the organic thinner miscible with water and to its application with a view to reducing the air pollution due to the application of a coating composition, in particular of a paint.

Claims (8)

 1. Thinner for coating compositions, comprising an organic base solvent entirely miscible with water and capable of dissolving coating compositions based on organic solvents, this diluent being characterized in that it comprises  (a) a water-miscible compound chosen from a saturated aliphatic glycol or a saturated aliphatic glycol ether oxide, each containing at least 3 carbon atoms, and a compound of formula (I):

 / in which R is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms or - (O) C-CH3;  R1 is independently selected from -CH2, -CH2-CH2-; -CH2-CH (CH3) -; and -CH (CH2OH) -;  R2 is independently selected from an alkyl group having 1 to 4 carbon atoms and which is optionally substituted by a hydroxyl group, and - (O) C-CH3; and  n is a number are 1 to 4 / and their mixtures, this compound or mixture being present in an amount ranging from about 10 to about 60 parts by weight;  (b) a water-miscible monoalcohol having 1 to about 8 carbon atoms and which is present in an amount of from about 10 to about 60 parts by weight; and  (c) a saturated, water-miscible aliphatic ketone having up to 12 carbon atoms and which is present in an amount of from about 10 to about 50 parts by weight, the sum (a + b + c) being in total 100 parts by weight.  2. Thinner according to claim 1, characterized in that it also comprises, in an amount of about 10 to about 50 parts by weight, water-soluble organic acids or their esters. R4 is a saturated alkylene group having 2 to 4 carbon atoms.  in which R, R2 and n have the meaning defined above; and

 3 Thinner according to claim 1, characterized in that the constituent (a) is a compound corresponding to the formula (II)  4. Method for reducing air pollution resulting from the application of coating compositions, this method being characterized in that it comprises the steps according to which  A) A coating composition based on at least one organic solvent and which contains a fully water-miscible diluent, formed of at least one organic based solvent, is applied to a substrate, thereby forming a gaseous effluent containing a mixture of air, gaseous organic solvent and gaseous diluent, and  B) passing this gaseous effluent into water which absorbs the organic solvent, which has become gaseous, of the coating composition, as well as the diluent, which has become gaseous.  5. Method for reducing air pollution resulting from the application of coating compositions, this method being characterized in that it comprises the steps according to which  A) A coating composition based on at least one organic solvent, containing a completely water-miscible diluent and formed of at least one organic based solvent, is applied to a substrate, forming a gaseous effluent containing a mixture air, gaseous organic solvent and gaseous diluent, the water-miscible diluent formed by at least one organic-based solvent consisting of  a) a water-miscible compound, chosen from a saturated aliphatic glycol or a saturated aliphatic glycol ether oxide, each containing at least 3 carbon atoms, and a compound of formula (I)

 / in which R is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms or - (0) -C-CH3;  R1 is independently selected from -CH2; -CH2-CH2-; -CH2-CH (CH3) -; and -CH (CH2OH) -;  R2 is independently selected from an alkyl group having 1 to 4 carbon atoms and optionally having a hydroxyl substituent, and - (O) C-CH3; and  n is a number from 1 to 4 / or mixtures thereof, in an amount between about 10 and about 60 parts by weight;  b) a water-miscible monoalcohol, having 1 to about 8 carbon atoms, present in an amount of from about 10 to about 60 parts by weight; and  c) a saturated aliphatic ketone, miscible with water, having up to 12 carbon atoms and present in an amount of about 10 to about 50 parts by weight, the sum (a + b + c) being total 100 parts by weight; and  B) passing this gaseous effluent through a gas absorption device containing a non-reactive liquid solvent capable of absorbing the organic solvent, passed to the gaseous state, of the coating composition as well as the diluent, passed to the state gaseous.  6. Method according to claim 5, characterized in that the liquid intended to absorb the gas is water.  7. Method according to claim 5, characterized in that the diluent also comprises, in an amount of about 10 to about 50 parts by weight, at least one water-soluble organic acid or its ester.  8. Method according to claim 5, characterized in that the constituent (a) is a compound of formula (II)

  in which R, R2 and n have the meaning defined above; and R4 is a saturated alkylene group having 2 to 4 carbon atoms.