Composition and system for treating paint spray booth water

Abstract

Disclosed are combinations of one or more cationic starch(es) and aluminum salts to produce a composition for detackifying paint at lower doses than those required using conventional treatments while providing improved handling and a more green environmental profile. The compositions may be utilized in methods of detackifying and dispersing solvent borne paints and/or coagulating/flocculating and dispersing waterborne paints during the treatment of paint spray booth water.

Claims

1. A detackifying composition consisting essentially of: an acidic aqueous solution of a cationic starch; and a water soluble, inorganic metal salt selected from the group consisting of iron halogen salts, alum, aluminum chloride, and ferric sulfate.

2. The detackifying composition according to claim 1, wherein: the composition comprises a solution in which the metal salt comprises from 50% to 85% of the dry weight and the cationic starch comprises from 15% to 50% of the dry weight.

Description

DETAILED DESCRIPTION

(1) The current invention is a composition and method to treat solids in a water system. Specifically, the water system could be a paint booth recirculation system, where paint solids are treated and separated from the booth water. The composition consists of a metal salt and cationic starch.

(2) The purpose of this invention is to develop a more environmentally friendly paint treatment product to detackify and coagulate water-borne and solvent-borne paints. Over the years, products that have been used to detackify and coagulate paints included caustic, metal salts, silicates, quaternary ammonium salts, starch, tannin, melamine formaldehyde and combinations of the above. Over the last 20-25 years, the melamine chemistry has been proven the preferred chemistry in performance and overall operating cost, however, the stigma of the formaldehyde in the product provided a negative connotation. A few years ago, a more environmentally friendly or greener technology has been developed utilizing metal salts and a chitin based polymer.

(3) The present disclosure is directed to a composition comprising both a cationic starch and a metal salt that satisfactorily detackifies a wide range of solvent-borne paints and coagulates water-borne and solvent-borne paints. The composition includes (a) a 1-50% solution of cationic starch and (b) a 50-99% solution of at least one metal salt, preferably aluminum chlorohydrate and/or ferric chloride. Other metal salts including, for example, alum, aluminum chloride, polyaluminum chloride and ferric sulfate could also be used. These materials would provide 0.3-18% of cationic starch solids and 25-40% metal salt solids. The preferred composition contains 15-50% of the cationic starch component and 50-85% of the metal salt component.

(4) A range of starches that would be suitable for inclusion in this composition may be found in U.S. Pub. Pat. Appl. No. 2010/0326923, the contents of which are hereby incorporated, in their entirety, by reference. The preparation of cationic starch quarternary ammonium ethers is well known in the art. They may be synthesized by reacting starch and, e.g., a quarternary halohydrin salt with an alkali. The procedure used to synthesize a quarternary starch combination is disclosed in Starch: Chemistry and Technology, Whistler, R. L. and Paschall, E. F. eds., Chapter 16, Production and Uses of Cationic Starches, by Paschall E. F. (1967). This prior art reference is hereby incorporated by reference, in its entirety and for all purposes.

(5) Applicable starches disclosed therein include corn, potato, bean, tapioca, sago, rice, wheat, waxy maize, grain sorghum, grain starches in raw or modified forms, e.g., modified with acid, oxidizing agent and the like; to amylose and amylopectin; and to the linear and branched components respectively, of corn starch; and also to dextrin.

(6) The quarternary ammonium starches consist of a starch group and a quarternary ammonium group. The degree of substitution of these products is within the range of about 0.01 to 1.00 quarternary units per anhydroglucose unit in the starch group, more preferably, 0.1 to 0.75. A range of such starches is available commercially from Dober (previously Dober Chemical) of 11230 Katherine's Crossing, Suite 100, Woodridge, Ill.

(7) The composition of the present invention is typically prepared by first adding acid to the starch polymer solution to reduce the pH to 2-5 and achieve an intermediate solution comprising 1-35% solids. Once this is accomplished, the metal salt(s) is/are blended into the starch polymer solution with the pH of the resulting treatment solution being adjusted to provide for an acidic solution, preferably having a pH of 4-6. The specific target pH range for the treatment solution is determined, at least in part, by the solubility of the particular metal salt(s) used in combination with the starch polymer(s).

(8) The composition of the present invention is intended to be added to the paint spray booth water system, specifically, to be added to the recirculating water entering the paint spray booth area. When used in this manner, the composition dosage is dependent on, for example, the amount of paint entering the water and the composition of the paint. Typically, for every gallon of solvent-borne paint in the water, 0.1-0.2 gallons of the disclosed detackification composition would be added. Furthermore, for each gallon of water-borne paint in the water, 0.01-0.02 gallons of disclosed detackification composition is added. Although the necessary dosing requirements can be determined through limited experimentation, the disclosed dosage ranges should generally be sufficient to achieve acceptable detackification and coagulation of solvent-borne paints and/or acceptable coagulation of water-borne paints.

(9) The paint booth water system is maintained at a pH of 7.5-9.5. The total alkalinity is operated between 250-800 ppm. An operating target is determined by the type of paint sprayed. The elevated pH and alkalinity in the booth water, disperses the paint droplet. Paint dispersion provides more paint droplet surface area, which is needed for the present invention to coat and detackify. The pH and alkalinity can then be adjusted by using, for example, dense soda ash, sodium metasilicate and/or caustic soda.

(10) The recirculating water utilized in scrubbing water-borne paint particles has a preferred alkalinity operating range is 250-500 ppm with a preferred pH range of 7.5-8.5. The lower alkalinity is considered suitable because water-borne paints are not typically hydrophobic and can achieve sufficient dispersion without help from additional water chemistry tweaks apart from the pH and alkalinity to achieve sufficient coagulation of the paint from the recirculating

(11) In contrast to the water-borne paint particles, the recirculating water utilized in scrubbing solvent-borne paint particles has a preferred alkalinity operating range of 400-1000 ppm with a preferred pH range of 8.2-9.5. Solvent-borne paints tend to be more sticky and hydrophobic than water-borne paints. Accordingly, increases in both the alkalinity and pH relative to the water-borne paint particles are useful for improving the dispersal of the paint droplets. As will be appreciated by those skilled in the art, however, attention must be directed to controlling the conditions of and additives in the recirculating water to avoid excessive dispersal that will tend to suppress the desired coagulation and increase the likelihood of undesirable foaming within the aqueous system will occur.

(12) As will be appreciated by those skilled in the art, during paint spray booth operation objects are sprayed with paint. Some, and typically most, of the paint or other coating emitting from the paint spray nozzles or other application devices, will be reach and attach to a surface of the target object with an overspray portion of the paint or other coating remains in the paint spray booth air. The paint spray booth air, laden with paint overspray particles, can be exhausted from the spray paint chamber through a water scrubber. As the contaminated air passes through the scrubber, a portion of the overspayed paint particles is transferred into the recirculation water, where the paint particles come into contact with the disclosed composition and is, consequently, detackified and induced to coagulate with other similarly converted paint particles.

(13) The detackifier composition need only be added to the paint spray booth water during the paint operation and at a feed rate sufficient to maintain a treatment effective concentration within the recirculating water in the paint spray booth. The treatment composition feed can be accomplished by, for example, activating the treatment feed pumps in concert with the paint spray flow switches. The paint spray booth operation can be controlled and/or monitored to determine the application rate of primer, basecoat, clearcoat or other coating composition is being applied in each paint spray unit and how much of that material is expected to end up as overspray and be captured within the aqueous system. This data can then be used for adjusting the dosage of the treatment composition as a ratio of the coating materials being captured. Alternatively, if more precise application data is not available, a target feed rate can be used to ensure that sufficient quantities of the treatment composition are available within the recirculating system to address a worst case paint particle capture. Depending on the materials utilized and the control system(s) available, a wide range of dosages can be utilized with acceptable results. For example: an example dosage ratio could be 20:1 whereby for every 20 gallons of paint over spray captured within the recirculating water, 1 gallon of the treatment composition would be introduced to detackify solvent-borne paint. Depending on the particular operating characteristics, other dosage ratios of 15:1 or 25:1 ratio could be utilized as well.

(14) The detackified paint particles will separate from the paint booth system water by coagulating with other paint particles and then sinking or floating, depending on the amount of air entrained in the water through the scrubbing process or other processes and accumulate within specific regions of the system configured for removing the separated and collected paint particles.

(15) The utilizing the disclosed compositions in the operation of a paint spray booth can provide a number of advantages relative to conventional detackification compositions and methods including, for example: 1) reducing the dosage necessary to achieve acceptable paint detackification when compared with the dosage required using a conventional melamine chemistry; 2) reducing the associated waste solids; 3) reducing the dissolved solids in the recirculating paint spray booth water; 4) reduces cost of treating/maintaining a paint spray booth system; 5) reducing the moisture retention within the captured paint sludge cake dryness; and 6) improving paint solids separation from the paint spray booth water.

(16) While the present invention has been described with references to preferred embodiments, various changes or substitutions may be made on these embodiments by those ordinarily skilled in the art without departing from the scope of the present invention. Therefore, the scope of the present invention encompasses not only those embodiments described above, but all those that fall within the scope of the claims provided below.