CA1321944C - Cationic coagulants plus colloidall silica for use in paint detackification - Google Patents

Abstract

ABSTRACT
Water soluble low molecular weight cationic polymeric coagulants in combination with colloidal silica are excellent paint detackification agents for treating paint spray booth waters which are contaminated with paint particles.

Description

~321944 Introduction -This invention relates to a wet spray booth treating agent and to a method for the treatment of a wet spray booth by the use of the agent. Wet spray booths are used, for instance, in the automotive industry for painting automobile bodies. More particularly the invention relates to a wet spray booth treating agent for diminishing the tackiness of coating material entrained in circulating water that is sprayed for collecting surplus paint and precluding the coating material from adhering fast to the interior of the circulating water sy~tem and to a method for the treatment of the circulating water by the use of the treating agent.
Generally in the automotive industry, the amount of paint applied to an automobile body ranges from 50 to 80% of the amount of paintsupplied and the remaining 50 to 20% of the supplied paint constitutes an excess that is removed in a subsequent process. For the collection of the surplus paint, the automobile body is treated in a wet spray booth adapted to give a wash with water and the water so used for the washing is circulated for re-use.
The surplus paint which is collected in the washing water in the wet spray booth has high tackiness. Consequently, it adheres to the water-film panel, the piping system, the spray nozzle, etc. of the spray booth, it clogs the piping system and the nozzle, and seriously degrades the efficiency of water washing. Further, if the surplus paint clogs the waste gas discharge system and interferes with the flow air in the spray :
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booth the vapor of the solvent of the paint fills up the interior of the booth to produce a state dangerous to safety and hygiene and seriously degrade the shop environment. More-over, the greater part of the surplus paint settles to the bottom of the booth and the bottom of the circulation pit in the spray booth system. The sediment of paint so formed hardens into a rubbery mass with elapse of time. The removal of this hardened mass and the cleaning of the bottoms take up much time and labor.
The paint collected in the washing water not merely causes adhesion or sedimentation within the system but also components of the paint may dissolve or may disperse into fine particles. An increase in total dissolved solvant (TDS) accelerates the progress of corrosion inside the system.
Further, the solvent in the paint not merely increases the hydrocarbon (HC) content of the waste gas from the booth but also dissolves into the cleaning water and increases the chemical oxygen demand (COD) of the water being circulated. The solvent of the paint, depending on the solvent used, may acidify the circulating water and consequently accelerate the corrosion of the system.
Prior Art United States Patent 4,564,464 ~ The compositions are pumpable, hectorite clay containing slurries. In addition to hectorite, which has been proven as a most effective detackify-ing agent, the slurries include thinning agents such as water-soluble aliphatic and/or alicyclic amines. Water conditioning : :- ,: . . . : .

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agents, such as water-soluble polyphosphates are also made part of the slurry formulation.
United States Patent 4,629,572 - Paintspray booth wastes from clear oil-based coating compositions, such as lacquers, which have been collected in a water wash are easily aetackified and removed from the wash water by contacting the wastes in the wash water with (1) a water-dispersible polymeric condensation reaction product of a urea or an amino triazine and an aldehyde and l2) a water-swellable clay.
United States Patent 4,504,395 - The compositions comprise a hectorite clay, an anti-foaming agent and, optionally, an aluminum oxide material and a montmorillonite clay. These compositions are introduced into a paint spray booth water wash system so as to detackify oversprayed paint.
United States Patent 4,153,548 - An acidic silica sol and coagulating polymer are used to reduce the tackiness of paint solids of electrodeposition paints and to condition such solids so that they can be separated and removed from the drippings and wash water obtained as a result of the application of electrodeposition paints to various types of products. The polymers used in the practice of this invention are usually acrylamide polymers or anionic acrylamide polymers.
United States Patent 3,515,575 - An improvement in the process of deactivating and collecting paints ~ith a water curtain in a water wash booth comprises maintaining in the water at least 0.5 ppm of a water~soluble polymer having an average molecular weight of from 1,000 to 15,000,000 and having repeating 132~

groups with the formula r I 1 tc--CH2~
R' wherein R is a hydrogen atom or methyl group and R' is an amide or carboxyl group.
A number of polymers are suggested in column 4 of the specification. Mentioned in passing is that the polymers may be used in conjunction with absorbents. A wide variety of absorbents are mentioned, one of which is colloidal silica. No other reference to colloidal silica is made.
United States Patent 3,738,945 discloses preferred polymers used in the invention, e.g.epichlorohydrin dimethylamine ammonia polymers. The patent does not teach or suggest treating paint spray booth waters.
The Drawing The drawing is of a laboratory scale paint spray recirculation tester.
The Invention In one aspect, the invention provides a method for the treatment of circulating water which collects surplus paint in a paint spray booth, which method comprises treating this water with a paint detackifying amount of a paint detackification agent comprising (A) a water soluble cationic polymeric coagulant having a molecular weight less than 500,000; and (B) an aqueous colloidal silica sol having an average particle size between about 1-150 nm, the ratio of A to B being from 1/50 to 50/1.

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(The ratio of A to B iS expressed on an actives basis, i.e. the amounts expressed are based on the amounts of solid active ingredients, so that degrees of dilution with solvent do not affect the ratio.) The invention also provides a novel detackifying agent which comprises components (A) and (B) as defined above, in the above-defined ratio.
The Paints The invention can be used to detackify a wide range of paint products including water-based paints, oil-based paints, lacquers, enamels, and the newer high~solid paints. The invention is particularly adapted to detackifying high-solid paints and clear coats which are applied in the form of organic solvent suspensions. A particularly noteworthy advantage of the invention is that it is capable of coagulating pigmented base coat and clear overcoats when such contaminations are present together in the circulating waters of paint spray booths.
The Water-Soluble Low Molecular Weight Cationic Polymeric Coaqulants These cationic polymeric coagulants have molecular weights less than 500,000, preferably less than 100,000, and usually within the range of 10-200,000.
A preferred water-soluble cationic polymeric coagulant is the subject of United States Patent 3,738,945. A preferred coagulant of this type is the reaction product of epichlorohydrin, dimethylamine and ammonia in accordance with the teachings of United States Patent 3,738,945, which product has a molecular ~.

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weight of about 50,000 and is available under the trade-mark Nalco 8100. This particular polymer is used in the form of a 48~ by weight aqueous solution and such a solution is referred to hereafter as Polymer l.
Another useful polymer is polydiallyldimethyl ammonium chloride (DADMAC) having a molecular weight of about 100,000, which can be used as a 20% by weight a~ueous solution. Such a solution of this polymer is referred to hereater as Polymer 2.
Other cationic polymeric coagulants include such low molecular weight polymers as melamine formaldehyde resins of the type described in United States Patent 4,656,05g. Similarly, water-soluble urea formaldehyde resins may be used. Also useful are the polvethylene imines or any of the water-soluble polymers described in Canadian Patent 731,212.
The polymers are preferably employed as dilute aqueous solutions, e.g. 5-15% weight. Commercially, they are usually supplied as concentrates and can be diluted on-site. The amounts of polymer used in the practice of the invention vary between l and l,000 ppm by weight of the circulating water in the paint spray booth. Routine experimentation will determine the optimum dosage.
The A~ueous Colloidal Silica Sols These products are well known and are produced by the neutralization of sodium silicate with sulphuric acid followed by demetalization or deionization to remove sodium sulphate and subsequent concentration. Typical commercial silica sols are those set forth below in Table I. The products listed below are .- , .
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all commercially available from Nalco Chemical Company, One Nalco Center, Naperville, Illinois 60566-1024, United States of America.
Table I
~ Specific Particle Product Silica GravitySize (nm) Nalcoag 1115 15 1.100 4 10.
Nalcoag 1130 30 1.21 8 10.0 Nalcoag 1030 30 1.20 13 10.2 Nalcoag 1140 40 1.30 15 9.7 Nalcoag 1050 50 1.39 20 9.0 Nalcoag 1060 50 1.3g 60 8.5 Nalcoag 2329 40 1.30 80 8.4 Nalcoag 2326 14.5 1.10 5 9.0 Nalcoag 2327 40 1.29 20 9.3 Nalcoag 1034A 34 1.23 20 3.0 The preferred particle size range used in this invention is between 1-20 nm, although larger particle sizes up to about 150 nm may be used. The amount of colloidal silica used in the compositions of the invention vary between 1 to 5,000 ppm.

Registered Trade-mark of Nalco Chemical Company ~ : :

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Ratio of the Water-Soluble Cationic Polymeric Coagulants to Colloidal Silica The ratio of the water-soluble polymeric coagulants to colloidal silica is generally within the range of 1/50 to 50/1;
preferably it is 1/5 to 5/1 (actives basis).
Example 1 In this test (see the drawing), desired amounts of detackifying agent are added to the water manually or using a chemical pump to monitor the chemical demand. The detackifying agent is allowed to mix in the tank through water recirculation for 5 minutes. The paint being tested is then sprayed into the chamber at a rate of 2 ml/min. through an air atomized spray gun located 12 inches above the center of the scrubbing section.
The test paint is sprayed for 5 minutes, then the paint kill is tested for tackiness or stickiness. The testor wets his hand with the water solution in the test tank, then takes a sample of the floating paint sludge from the water tank, squeezes, and rubs tightly between his fingers. Any tackiness ox stickiness present is a poor paint kill. A chart for degree of paint kill is provided here to assure consistent description. A miniumum degree of kill of 6 is required to assure booth cleanliness.
When good paint kill is achieved, paint is continuously sprayed, and the paint sludge conditions tested every few minutes.
At any given time, if any trace of tackiness of sludge is present, paint spray should be discontinued and the program re-examined.
The amount of paint sprayed should be recorded, the dosage of the detackifying agent and the condition of sludge.

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'' ' ` , Additional detackifying agent and other chemicals such as anti-foam agents, flocculents and the like can be added and paint spray resumed. This process should be repeated at least four times to be confident of obtaining consistentresults.
Chart for Degree of Paint Kill Perfect Complete kill, sludge is soupy 9 Excellent Paint sludge is non-tacky, non-gritty 8 Very Good Paint sludge is not tacky or gritty, but slightly plastic, may roll 7 Good Not tacky, plastic consistency, sludge rolls and can easily reroll 6 OK Minimum performance, very slightly tacky. It rolls with water and reroll.
Can wash off without rubbing.

Borderline May stick slightly to glove, but falls off with rubbing.

4 Unacceptable Slightly tacky, sticks to glove with pressure, does not rub off, may roll.
3 Moderate failure Does not roll, stick to glove, smears 2 Severe failure Tacky, smears 1 Very sticky Smears 0 Like raw paint The detackification effects were tested against high solids enamels. The results are set forth below in Tables II
and III. Table II compares a composition of the invention with a detackifying composition in accordance with United States Patent 4,792,364 that is composed of Nalco 8000 and Nalco 8001 .

Table III shows the effectiveness of the composition of the invention in detackifying three different paints.

Nalco 8000 is a Trade-mark for a melamine formaldehyde/poly-vinyl alcohol polymer mixture.
Nalco 8001 is a Trade-mark for a polystyrene/acrylate copolymer.

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Table II

Initial Amount Clear Coat Program Ratio Charge Added Sprayed Polymer No. 1/ 9.5 mls 17.1 mls Nalcoag 11151/2 (500 ppm)(900 ppm) 161 mls (Actives basis) 8000/8001 4/1 8.08 mls12. 35 mls 124 mls (425 ppm)(650 ppm) The new system has been checked several times and gave reproducible results. Other paint samples were also checked.

Table III

Initial Amount System Ratio Charge Added Total MLS

Polymer No. 1/ 1:2 9.5 mls 13.3 mls Inmont Nalcoag 1115(actives basis~~500 ppm) (700 ppm) Garnet Red enamel Sprayed 67.0 1:2 9.5 mls 13.3 mls DCT 3000 (500 ppm) (700 ppm) PPG
Clear coat 92.0 " 1:2 9.5 mls 13.3 mls PPG #99 (500 ppm) (700 ppm) Black Cherry enamel 98.0 Example 2 All systems were charged initially with 9.5 mls (500 ppm) of chemical and maintained with 1.9 mls (100 ppm) increments to 17.1 mls (900 ppm) total of chemical added. This equals the type of charge necessary for 8000/8001 to detackify DCT 3000 PPG
clear coat.
The following results were yielded when using synthetic .' ~
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Chicago tap water:
Table IV
Total mls PPG DCT 3000 Quality of System Clear Coat Sprayed Initial Kill Polymer No. 1/ 52.0 mls Kill 7 Nalcoag 1115 Somewhat Very foamy 1:15 (actives basis) dispersed Polymer No. 1/ 42.0 mls Kill 7 Nalcoag 1115 Somewhat 1:30 ratio dispèrsed Polymer No. 1/ 66.0 mls Kill 7-8 Nalcoag 1115 Floating 1:3 ratio Polymer No. 1/ 24.0 mls Kill 7 Nalcoag 1115 2:1 ratio Polymer No. 1/ 18.0 mls Kill 6 Nalcoag 1115 3:1 ratio Recheck of 89.0 Kill 8 Polymer No. 1/ Floating Nalcoag 1115 1:3 ratio Polymer No. 1/ 180. Kill 8-9 Nalcoag 1115 Floating 1:2 ratio Polymer No. 1/ 81.0 Kill 8 Nalcoag 1115 Floating 1:1.5 ratio - ~
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Claims (6)

1. A method for the treatment of the circulating water which collects surplus paint in a paint spray booth which comprises treating this water with a paint detackifying amount of a paint detackification agent comprising (A) a water soluble cationic polymeric coagulant having a molecular weight less than 100,000; and (B) a aqueous colloidal silica sol having an average particle size between about 1-150 nm, the ratio of A to B being from 1/50 to 50/1 (actives basis).

2. A method according to claim 1 wherein the ratio of (A) to (B) is within the range 1/5 to 5/1.

3. The method of claim 1 or 2 wherein the water soluble cationic polymer coagulant is a water-soluble polymer formed by the reaction of epichlorohydrin dimethylamine and ammonia and has a molecular weight of 50,000 and the colloidal silica sol has an average particle size between 1-20 nm.

4. A detackifying agent for detackifying paint contained in circulating waters which collect surplus paint from a paint spray booth, which detackifying agent comprises (A) a water soluble cationic polymeric coagulant having a molecular weight less than 100,000; and (B) a aqueous colloidal silica sol having an average particle size between about 1-150 nm, with the ratio of A to B being from 1/50 to 50/1 (actives basis).

5. An agent according to claim 4 wherein the ratio of (A) to (B) is within the range 1/5 to 5/1.

6. An agent according to claim 4 or 5 wherein the water soluble cationic polymeric coagulant is a water-soluble polymer formed by the reaction of epichlorohydrin dimethylamine and ammonia and has a molecular weight of 50,000 and the colloidal silica sol has an average particle size between 1-20 nm.