A paint spray booth detackifying composition which includes mixtures of styrene-acrylate polymer and a melamine-formaldehyde polymer and the method of using same.
It is an object of this invention to provide a composition that will provide a detackified paint sludge having minimum volume and high dewaterability.
It is an object of the invention to provide a detackifier that will have low toxicity.
SUMMARY OF THE INVENTION
The invention includes a paint detackifying composition and the method of using it. In broadest terms, the paint detackifying composition includes a melamine-formaldehyde resin styrene-acrylate resin mixture with a mole ratio within the range of 2:1 to 4:1, respectively. This mixture preferably is provided in an aqueous system at a dosage of at least 25 ppm and at most 800 ppm.
THE DISCUSSION OF THE INVENTION
In practice, a suitable melamine-formaldehyde resin is provided under the trademark MAGNIFLOC 515C, a trademark of the American Cyanamid Company. Generally, suitable melamine formaldehyde resins should have a weight average molecular weight of at least 2,000 and be soluble in water at pH below 2.5. Preferably, the molecular weight will be in the range of 2,500-4,000.
A suitable styrene-acrylate resin is provided under the trademark ESICRYL R-11, a trademark of the Emulsion System Company or OPACIFIER 11, a trademark of the Essential Chemical Company. Styrene-acrylate resins generally can be used. However, the most preferred will have a molecular weight within the range of 50,000-100,000.
Generally, the styrene-acrylate polymer is prepared separately and packaged separately from the melamine-formaldehyde polymer. The two are then charged into the system. The styrene-acrylate can be used as purchased. Melamine-formaldehyde can also be used as purchased.
LABORATORY TEST
Laboratory tests were conducted using a clay/amine product which is a standard in the industry today, representing over 60% of the U.S. detackifying market for high density paint systems.
Desired amounts of detackifiers were added to the water manually or using a chemical pump to monitor the chemical demand. These detackifiers were allowed to mix in the tank through water circulation for 5 minutes. The paint being tested was 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. An exhaust fan pulling air from the lower section of the scrubbing chamber helped the air flow through the water and increased scrubbing efficiency. This exhaust fan also aided in eliminating paint mist during the test and made the whole unit operable in that atmosphere. The test paint was sprayed for 10 minuts and the paint kill then tested for tackiness or stickiness. Tackiness or stickiness was determined by wetting the test runner's hand by the water solution in the test tank and taking a sample of the floating paint sludge from the water tank and squeezing and rubbing it slightly between his fingers until a degree tackiness is determined. The test is somewhat subjective. However, that is the best method that is currently available.
In general, at the conclusion of a good paint kill, paint is continuously sprayed, and the paint sludge conditions tested every 10 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, the chemical dosage, and condition of sludge should be recorded.
Additional chemicals should be added and paint spray resumed. Repeat this process at least four times.
Let's take a hypothetical example of the test in order to see how the product maintenance ratio is calculated:
______________________________________
mls of mls of
paint sprayed
chemicals added
Comments
______________________________________
0 57 ml Start spraying
(or 3,000 ppm)
initial kill #8
120 19 Final kill #6
recharge chemicals
60 19 Recharge chemicals
55 19 Recharge chemicals
67 Finish sprayed
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In this case, the initial charge of chemicals is 19 mls or 1,000 ppm (based on 5 gallons of water) and the product maintenance ratio is 3:1 paint/product.
In the following tests, the maintenance ratio represents the ratio of paint to product requred to maintain acceptable levels of tackiness or stickiness for the paint kill.
Test 1
Paint: DuPont 706-AC 301 white base coat
Wt. % solids: 59%
Spray Rate: 2.0 ml/min
Water recirculation rate: 2 GPM
Product use: polyamine and bentonite clay slurry at 1:3 ratio on active basis
Initial Charge: 300 ppm
Maintenance Charge: 3:1 paint:product
Test 2
Paint: DuPont 706-AC 301 white base coat
Wt. % solids: 59%
Spray Rate: 2.0 ml/min
Water recirculation rate: 2 GPM
Product use: melamine formaldehyde/styrene-acrylate at 2.4:1 ratio
Initial Charge: 820 ppm
Maintenance Charge: 15:1 paint:product
Test 3
Paint: DuPont clear coat RK-3840
Wt. % solids: 60.0%
Spray Rate: 2.0 ml/min
Water recirculation rate: 2 GPM
Product use: melamine formaldehyde/styrene-acrylate at 4:1 ratio
Initial Charge: 900 ppm
Maintenance Charge: 10:1 paint:product
Test 4
Paint: In Mont E12 CK002
Wt. % solids: 35%
Spray Rate: 2.0 ml/min
Water recirculation rate: 2 GPM
Product use: melamine formaldehyde polymer/styrene-acrylate at 3:1 ratio
Initial Charge: 70 ppm
Maintenance Charge: 35:1 paint:product
DISCUSSION OF TEST RESULTS
Generally, we have found that the laboratory test results have higher detackifier requirements than are actually needed in the field. A discrepancy occurs primarily due to difference in spray rate vs. water flow rate under laboratory and field conditions.
In practice, the polymer works best when dosed in a system having a pH within the range of 7.5 to 9.5.
Generally, the system should be dosed prior to the detackification process. Pre-dosing appears to allow the formation of floc and adequate dispersion of the detackifier throughout the system.
Preferably, floc within the range of 0.1 to .about.1.mu. micron will be formed. Generaly floc with the range of 0.5-0.75 microns is found to be most desirable.
The detackifying systems are generally water containing the detackifier compositions.
The detackifier of this invention is a floating/sinking depending on the ratio of the two components, A/B.
The detackifier bonds with paint and removes the stickiness of the paint. Generally, when the invention is working and is appropriately dosed there will be no stickiness to the feel and no paint adhering to any surfaces that come in contact with water and filtration commonly used in paint detackification removal systems.
