CA1207217A - Paint detackification using oil-in-water emulsions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for the detackification of oversprayed paint solids which comprises contacting the oversprayed paint solids with an oil-in-water emulsion. In the case of certain paints, the emulsion will also trap or capture the volatile organic paint solvents in the oversprayed paint or lacquer solids. After separation the paint material containing solvents can be used as a fuel, the emulsion can be reused.

Description

;~07~7 Great quantities of paints, lacquers, varnishes, base coats and clear coats are used in the automobile, appliance, and allied industries to coat finished products. These paints, lacquers, varnishes, base coats and clear coats hereinafter referred to as paints, are generally solvent-based. In the use of these materials, generally in enclosed areas called paint spray booths, substantial quantities of solvent and oversprayed paint solids are discharged into the booth atmosphere. These materials represent environmental hazards which have to be controlled. Current paint spray booths comprise a chamber, a duct system for passing air down through such chamber to remove volatile organic paint carriers and oversprayed paint particles present in the chamber into a sump containing a cir-culating hydr~philic liquid located at the bottom of the cham-ber which has been adapted to remove volatile organic paint carriers and paint particles from the air containing them.
This system has generally been satisfactory for removing paint particles but has not been effective for removing the volatile organic components present as paint carriers.
Paint spray booths generally represent major items of capital expense and, as such, replacing paint spray booths with more effective systems which would enable removal of volatile organic carriers would be prohibitively expensive. Consequent-ly, it is important to find a method for modifying existing equipment so that this existing equipment can recover volatile organic paint carriers rather than discharge these volatile organic paint carriers into the atmosphere.
The prior art shows the use of various materials to be employed as fluids in the sump of paint spray booths which will trap paint particles and which act as solvents for vola-.

.~" 1 ~7~7 tile organic carriers. References employing oil-in water emul-sions for this purpose include Japanese Kokai 52990, United States patent No. 4,265,642, and ~,378,235, and commonly assigned United States Patent No. 4,378,235.
In the Japanese reference,an oil-in-water emulsion of a purified white oil mixed with a detergent such as alkyl ben-zene sulphonic acid is used to scrub volatile organic carriers from contaminated air. The emulsion is used in an absorption tower to trap volatile organic carriers. While systems of this type could be effective, no mention is made of reusing this emulsion Since materials of this type, which include petrol leum products, are expensive without reuse of this emulsion, procedures of this type tend to be impractical.
n United States patent No. 4,265,542 there is disclosed a method for the removal of volatile organic carriers from the air in paint spray booths using an oil-in-water emulsion. While the oil-in-water emulsion is reusable, ultrafiltration is used to separate the components of the emulsion to allow recovery of a solvent or oil phase from which volatile organic carriers can be distilled. Ultrafiltration techniques for handling large volumes of continuously recirculated liquid present in paint spray booths are impractical. Large paint spray booths of this type generally employ circulation of up to 10,000 gallons per minute of liquid and the ultra-filtration of even a small fraction of this amount is economically impractical.
United States Patent No. 4,396,405 discloses a pH
sensitive oil-in-water emulsion which may be used in a process to recover volatile organic materials from paint spray booths.
The paint solids in this case are filtered off and discarded.

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rrhe emphasis in this reEerence is to recover volatile organic materials from the oil-in-water emulsion by wreaking the oil-in-water emulsion and then distilling the volatile organic materials from the oil phase of the emulsion. This oil phase may then be recombined with the aqueous phase to reform the emulsion.
United States patent 4,378,235 discloses a process for the removal of volatile organic paint carriers from paint spray booth sumps using an oil-f 2a -2~

in-water emulsion. In this case paint solids are filtered, and the volatile organic material is recovered as in the previously mentioned application by distillation from the oil phase of the oil-in-water emulsion.
While the above two references provide an advance in the art, a continuous process of this type requires expensive equipment such as distillation units and oil-in-water separators, and while recovering volatile organic materials, are not as efficient as desired.
The subject invention seeks to provide a process for the recovery of oversprayed paint solids from paint spray booth systems and secondarily, and to provide for the recovery of volatile organic carriers assoc-~ated with the paint from paint spray booth systems. The process of thus invention calls fox the use of an oil-in-water emulsion which will detackify the paint solids so as to allow for their ready separation from the oil-in-water emulsion, but which will also, in the case of certain types of paints, trap or capture the volatile organic paint carrier in the oversprayed paint particles. By the use of this invention detackified oversprayed paint or lacquer solids carryingthe volatile organic carrier are easily separated from the oil-in-water emulsion. The detackified paint material containing the solvent may then.be used as a fuel, or further treated to recover the volatile organic material. The oil-in-water emulsion may be reused.
Accordingly, this invention seeks to provide to the art a method for the detackification of oversprayed paint and/or lacquer solids.
Further, this invention seeks to provide to the art a method for the detackification of oversprayed paint solids and the recovery of volatile organic paint carriers.
Still further, this invention seeks to provide a method for the recovery of volatile organic paint carriers from paint spray booths by 7~7 removing from the oil-in-water emulsion used as the hydrophilic liquid in the base or sump of the paint spray booth detackified oversprayed paint solids having entrained therein the volatile organic paint carriers.
Thus in its broadest aspect this invention provides a method for the detackification of oversprayed paint solids which comprises con-tacting the oversprayed paint solids with an oil-in-water emulsion.
This invention is directed to a method for the detackification of paint solids and the recovery o-f volatile organic paint carriers from paint spray booth systems. The paint spray booths of the type for which this invention is designed may be of a wet wall, center draft, or other canstruction. Paint spray booths of these types operate, in a sense, as large gas scrubbers with air passing through the booth picking up substan-tial quantities of volatile organic carriers, and paint particles that do not meet the object being painted. The air, after picking up the materials, passes inta a sump or the like where it isintimately contacted with the hydrophilic fluid which is generally recirculated throughout the paint spray booth. The hydrophilic fluid serves to trap oversprayed paint particles to prevent their release into the atmosphere and, also, has served to some extent, to trap the organic vapors collected from the booth.
The organic vapors that are generally encountered inpaint spray booths of the type described are those commonly used ?7 2 as organic carriers in industrial finishes such as paints and lacquers and may consist of aromatic materials such as benzene, xylene, toluene, low-boiling ethers, esters, ketones such as methyl isobutyl ketone, methyl amyl ketone, and mixtures thereof. Accordingly, the hydrophilic liquid scrubblng medium which is employed must act as a solvent for these types of volatile organic paint carriers. It is also important in the us of this invention that the oversprayed paint solids be detackified. This means essentially that the individual particles must not stick to the sides of the booth, process equipment, or agglomerate with themselves to form materials which cannot be easily handledO Ideally, the oversprayed paint solids !
should be detackified to the point where they can be readily separated from the hydrophilic liquid being employed. This separatlon step may be done by filtration, flotation, coagulation, or the like.
We have found that when certain oil-in-water emulsions are employed, suitable paint detackification is obtained. In addition, the detackified paint solids often contain substant1al quantities of the oversprayed volatile organic paint carriers.
These solids may be readily removed by separating the oversprayec paint solids from the hydrophilic liquid.
The hydrophilic liquid chosen for use in this invention is an oil-in-water emulsion system which comprises an organic liquid having a boiling point of at least 150 C., an oil-in-water emulsifier, and water.
efore briefly describing the process in which the oil-in-water emulsions of this invention are utililzed, the following explanation is presented for each of the components of¦
the oil-in-water emulsions of this invention.

7~7 The Organic Liquid The organic liquid component of the oil-in-water emulsions of this invention should be a non-volatile, water-immiscible, hydrocarbon material which has the further characteristic of acting as a solvent for volatile organic paint carrier used in the paint or lacquer being employed in paint spray booth. Organic liquids employed may be primarily aliphatic, paraffinic, aromatic or mixtures thereof. The organic liquids may either be halogenated or non-halogenated and should generally having a boiling point greater than lS0F. and, preferably 200F., and most preferably, above 300F. Viscosities of materials used may range from that of a 100 SEC primarily aliphatic petroleum process oil tothat of a highly chlorinated paraffinic material having a viscosity in excess of 20,000 cps. Thus, the only criteria for materials of this type are those stated above.
Typical materials which can be employed include Telura 323, a process oil manufactured by Exxon Company, United States of America, which is categorized as having a boiling point of from 545-88~E., negligible solubility in water, a specific gravity of.~O3 at 60F., a Cleveland open cup flash point of 330 F. and a viscosity at 100 F, of 105-115. This oil is believed to be a complex mixture of aliphatic and aromatic petroleum hydrocarbons. Also useful are various chlorinated paraffinic materials such as those designated Kloro 6000, Kloro 7000, CW 52, CW 170, CW 8560 Erom the Keil Chemical Division of the Ferro Corporation; as well as Isopar M , a branched paraffinic material available from the Humble Oil Refinery Company; LOPS , a low odor paraffinic solvent purchased from the Exxon Company, United States of America; and Marcol* 82, a highly aliphatic viscous white oil available from Exxon Company, United States of America.

* Trade Marks %~7 For safety purposes, the organic liquid employed in the oil-in-water emulsion of this invention should be substanti-ally non-toxic and have a flash point greater than 250 F. A
preferred organic liquid for use in this invention is Telura 323 described above.
It will be seen however, that substantial variations in organic liquids can be accomplished without varying from the spirit and intent of this invention. As an example, 10 weight motor oil has been satisfactorily employed in laboratory experi-ments as the oil phase of the oil-in-water emulsion.
The Oil-In-Water Emulsifiers The oil-in-water emulsifiers useful in this invention are those capable of forming a relatively stable oil-in-water emulsion with the organic liquid selected Generally these mate-rials will have an HLB value ranging from about 6 to about 40 and most preferably from about 10 to 30. The HLB system is de-fined in the Atlas HLB Surfactant Selector. Since the oil-in-water emulsions of this invention do not have to be broken, ease of breakability is not an important criteria. The emulsifier may be any water-soluble anionic, cationic, nonionic, or mixture o emulsifiers falling within the above criteria. Preferred emulsifiers for use in this invention are saturated and unsatu-rated fatty acids and alkali metal salts thereof containing 12-30 and, preferably, 16-24 carbon atoms. Other oil-in-water emulsifiers such as the condensation proauct of cocoamine reacted with 2 moles of ethylene oxide may be used. The prefer-red emulsifiers of the invention form emulsions which break when made acidic. It is expected, however, that oil-in-water emulsi-fiers other than those specifically enumerated herein may be employed. An especially preferred emulsifier for use in this invention is oleic acid.

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Water The water used to form the oil-in-water emulsions of this invention should preferably not contain more than 150 ppm hardness as Ca 2 or Mg +2. It has been found that excessive hardness in water being used creates soap scum with the prefer-red fatty acid emulsifiers. If hard water is encountered, how-ever, chelating agents such as NTA and/or EDTA may be added to the water on a 1:1 molar basis to combat hardness.
Formation of the_Emulsion The components of the emulsion used in this invention are used in the following weight percentages:
A. Hydrocarbon Oil Generally 1-250,000 ppm by weight of the emulsion Preferably 2-125,000 ppm by weight of the emulsion Most Preferably 10-75,000 ppm by weight of the emulsion B. Emulsifier Generally .1-30~ by weight of the hydrocarbon oil Preferably 1-20% by weight of the hydrocarbon oil Most Preferably 1.5-10~ by weight of the hydrocarbon oil C. Water balance The emulsion is formed by simply mixing the above-mentioned ingredients together. In formulating the emulsions of the subject invention we have generally found that emulsions having an alkaline aqueous phase of from pH 7.5-12 and prefer-ably a pH 8-11 are preferred due to their greater ability to detackify the paint materials used. pH adjustment of the emul-sion can be accomplished by merely adding a small quantity of an 07~

alkaline metal hydroxide, preferably sodium or potassium hydroxide to water prior to mixing to form the emulsion.
Once the emulsion has been formed, it may be used in the spray booth as the hydrophilic liquid to capture the vola-tile organic paint carrier materials and oversprayed paints pre-sent in the paint spray booth. We have found that at the levels mentioned above the oversprayed paint and/or lacquer particles are detackified. These detackified materials, which we have found to additionally contain the bulk of the volatile organic paint carrier present in the spray booth, are then separated from the oil-in-water emulsion. Due to the fact that the paint carrier will also carry with it some of the oil-in-water emul-sion, it has been found generally that additional quantities of the hydrocarbon oil and emulsiier may optionally be added to maintain the composition of the oil-in-water emulsion.
The oil-in~water emulsion may be reused indefinitely and continuously recirculated in the paint spray booth so long as additional quantities of materials are added to replace what is lost with the oversprayed paint particles.
The detackified oversprayed paint particles are re-moved from the oil-in-water emulsion by flotation, skimming, or the like. We have found that when the subject invention is operating properly the detackified paint or carrier overspray generally floats on the surface of the emulsion allowing for ready removal. This removal is accomplished by skimming using known means. Saturation is, of course, also allowable, and may be employed. The method of separation employed is not critical to ,~ .

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this invention and other means known to those skilled in the art may be employed.
As stated above J the separation of the detackified paint particles from the oil-in-water emulsions can be accomplished by a variety of means. When the process of this inventionis employed on enamel and/or base coat/clear coat materials, oily sludges are produced which disperse in the emulsion. These sludges tend to sink to the bottom of the sludge removal system. Accordingly, when employing this invention in a spray booth utilizing these particular types of paints, or similar materials, means for removing sludge from the bottom of the sludge removal system should be provided.
The recovered detackiEied oversprayed paint particles in this invention may be further treated to recover the volatile organic component, pigment and other paint components, or may simply be used as a high B.T.U.
fuel. Due to the fact that only minor amounts of the hydrocarbon oil are employed in forming the oil-in-water emulsion of this invention, the process is economical, and hydrocarbon oil losses are kept at a minimum level. The emulsion employed need not be breakable, and does not have to be subjected to complicated processing steps to recover the volatile 2~ organic material or the oversprayed paint solids.
While substantial amounts generally 6-9%) of volatile organic paint carrier may be recovered in the detackified paint sludge by the method of this invention when certain types of paints are being treated, sludges from certain paint types, notably enamels and/or base and clear coats, will generally contain less than one percent by weight volatile organic carrier.
In order to further illustrate the use and practice of this invention the following examplesarepresented:

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Example 1 In order to determine the effectiveness of the oil-in-water emulsions of the subject invention, a system containing a Binks spray booth, emulsion feed system, and Nordsor airless paint spray system was assembled.
About 3-5 gallons of premixed paint is placed in a stainless steel paint pot sitting on a weighing scale. The suction line for the Nor~son spray system is placed in the pot.
The paint pot is well covered with aluminum foil during the tests. The paint spray rate during the test can be obtained by observing the loss of weight in the pot per unit time. The air pressure to the Nordson unit is maintained at 14-16 psi.
A paint filter ~4 and paint tip tO16-~02) was used. the spray gun was positioned in the front of the spray booth and was aimed toward the water curtain. Air flow over the spray gun is approximately 100-150 ft/min. The air flow through the booth is about 3000-3300 CFM.
The paint spray booth is a Binks Dynaprecipitor model with a water capacity of 350 gallons. Air movement in the booth is directed toward the water curtain and enters the Dynaprecipitor unit through an opening at the top of the water curtain where it passes through the first of four washes. The recirculation rate to the header is about 150 gal/min.
The spray booth has a beach and a trough in the front to allow for the skimming and recovery of floating paint solids.
There is no mechanism provided to recover sinking paint sludge.
The paint spray booth is equipped with a level control so that makeup water is added automatically.

1~l~72~L7 A metering pump and mixing device is used to feed the oil-in-water emulsion. A lQ gpm centrifugal pump is used to feed¦
booth water to the pump of the metering pump and mixing device.
A 0-3 gpm gear pump supplies oil to the mixing chamber of the metering pump and mixing device. It is in the special mixing chamber that the oil is emulsified in the booth water.
Oil-in-water emulsion made in the metering pump and mixing device passes through a static mixer for additional mixing prior to entering the header in the spray booth.
A pH controller connected to a tank probe controls additions of caustic in the booth. Additions of acid are rarely ¦
requiced and are made with graduated cylinders as required.
Experimental Procedure The sequence of events for running the detackification tests done in this study is outlined below.
1. The paint to be used is well mixed with an air operated mixer.
2. The booth is filled with water and the pH is then adjusted The oil is charged via a metering pump and mixing device. The pH is optimized with respect to foam and emulsion stability. The emulsions used tended to foam more at higher pH
values.

3. Begin spraying paint at 40-70 grams/minute.

4. Observe the condition of the paint sludge in the spray booth. The oversprayed paint sludge is consideced tacky if it adheres to metal surfaces orl sticks to the skin when rolled between the fingers.

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S. No adjustments to the system are made as long as the paint sludge is detackified.
6. If the paint sludge floats it ls removed periodically by skimming the sludge onto the beach and into the trough and collected in a 5-gallon pail. Free water is allowed to separate and is drained before the paint sludge is weighed.
7. When tacky sludge is observed, additional soluble oil is charged to the spray booth. Normally, the booth i5 initially charged at a low concentration which means that additions of soluble oil may be required a short time after painting begins.
Additions of oil are made until the paint sludge formed becomes detackified.

When additions of oil are made and the paint sludge becomes detackified, then spraying should continue until the tackiness is again obtained. In this manner, paint overspray to detackifier ratios are obtained. These ratios are equivalent to the maintanance dosages required to keep the detackified program working properly. The run times for these tests vary between 1-5 hours.
8. Foaming with the oil-in-watec emulsion programs can be controlled by lowering the pH of the system or by using Nalco 71-D5 Antifoam or Nalco 2WP-546, available from Nalco Chemical Company, Oak Brook, Illinois.

lZ~i7217 9. Sludge samples are taken and analyzed for BTU and I¦
oil, % water, and % solids. A determination on the condition of sinking paint sludge is made at the time the booth is dtai,ned. Observations are made as to whether or not sludge sticks to the bottom pan or if it can be easily hosed with water.
10. Samples of the emulsion are taken at regular intervals and are analyzed for total volatile organic carrier, oil, BOD, COD, TOC and hardness.

The following compositions were tested:
Composition I
93.3% Telura 323 7% Oleic Acid Composition II
70.0% Oil, Napthenic 100 sec neutral 3~7~ Tall oil, fatty acid, 26% rosin 1.3~ Chlorinated paraffin wax 10.7~ Sodium petroleum sulfonate 4.7~ Sulfonated castor oil 3.7~ Fatty acid (waste stream) -3.3~ Isopropanol amine (mixed) 1.4% Biocide .001~ Anti-foam Based on the above examples, the oil-in-water emulsions used in this invention satisfactorily detackify paint and organic solids and also allow removal of the volatile organic carrier - l4 -72~7 associated with the paint or carrier. The removed sversprayed solids or sludge is readily disposable and may be employed as a . high BTU fuel.
: The compositions were tested according to the procedure outlined above, results are found in Tables I - V. Data found i : Tables VI-VIII was obtained using a pilot center draft spray : booth designed by the Flakt Company having similar capacities anc air flow to the Binks booth used in Table I-IV.
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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for the detackification of oversprayed paint solids which comprises contacting the oversprayed paint solids with an oil-in-water emulsion.

2. The method of Claim 1 wherein the oil-in-water emulsion contains 1 - 250,000 ppm by weight hydrocarbon oil.

3. The method of Claim 1 wherein the oil-in-water emulsion contains 2 - 125,000 ppm by weight hydrocarbon oil.

4. The method of Claim 1 wherein the oil-in-water emulsion contains 10 - 75,000 ppm by weight hydrocarbon oil.

5. The method of Claim 2 wherein the oil-in-water emulsion contains 0.1 - 30% by weight ox the hydrocarbon oil of a oil-in-water emulsifying agent.

6. A method for the continuous detackification and re-covery of oversprayed paint solids from paint spray booths of the type having a bottom sump and a recirculating hydrophilic liquid employed in said sump, the method comprising the steps of:
(a) employing as the hydrophilic liquid in the sump, an oil-in-water emulsion;
(b) contacting the oil-in-water emulsion with the over-sprayed paint, lacquer or enamel solids from the paint spray booth;
(c) separating a detackified paint, lacquer, or enamel solid from said oil-in-water emulsion; and, (d) recovering the oversprayed paint, lacquer, or enamel solids.

7. The method of Claim 6 wherein the oil-in-water emul-sion comprises:
(a) 1 - 250,000 ppm by weight of the emulsion of a hydro-carbon oil;
(b) .1 - 30% by weight of the hydrocarbon oil of an oil-in-water emulsifying agent; and, (c) balance water.

8. The method of Claim 6 wherein the oil-in-water emulsion comprises:
(a) 2 - 125,000 ppm by weight of the emulsion of a hydrocarbon oil;
(b) 1 - 20% by weight of the hydrocarbon oil of an oil-in-water emulsifying agent; and, (c) balance water.

The method of Claim 6 wherein the oil-in-water -emulsion comprises:
(a) 10 - 75,000 ppm by weight of the emulsion of a hydrocarbon oil;
(b) 1.5 - 10% by weight of the hydrocarbon oil of an oil-in-water emulsifying agent; and, (c) balance water.

10. A method for the continuous detackification and re-covery of oversprayed paint solids from paint spray booths of the type having a bottom sump and a recirculating hydrophilic liquid employed in said sump, the method comprising the steps of:
(a) employing as the hydrophilic liquid in the sump, an oil-in-water emulsion;
(b) contacting the oil-in-water emulsion with the over-sprayed paint, solids from the paint spray booth;
(c) separating a detackified paint solid from said oil-in-water emulsion;
(d) recovering the oversprayed paint solids;
(e) adding additional oil and oil-in-water emulsifier to maintain the composition of the emulsion; and (f) continuing steps (b) - (e) above.