Low free formaldehyde melamine-formaldehyde detackifier and method of using

Abstract

A melamine-formaldehyde detackifer having a less than 0.15% free formaldehyde which comprises a melamine-formaldehyde polymer detackifier to which has been added a formaldehyde scavenging agent selected from an effective amount of urea, acetylacetone, and a combination of urea with an enhancer selected from glyoxal and acetylacetone. The use of the low free formaldehyde detackifier is also described.

Description

BACKGROUND OF THE INVENTION

Automobile parts, bicycles, toys, appliances and other industrial and consumer articles are conventionally spray painted in areas called spray booths wherein water curtains are employed to wash the air and to remove over-sprayed paint, lacquer or enamel solids. The wash water is then treated to remove paint solids, and the treated water is recirculated.

A water curtain is typically created by pumping water into a trough above the overspray area. The overflow from the trough is then controlled so that a uniform sheet of water falls along the length of the trough and down the booth's wall. Spray nozzles are also commonly used. Droplets of oversprayed paint, emitted by a spray gun, contact and are captured by the water curtain.

A major problem associated with spraying operations concerns the tacky or adhesive nature of the over-sprayed coating materials. Solids tend to agglomerate and accumulate on the walls, ceiling and floor of spray areas and to clog water spray equipment, recirculating pumps and the like. Thus, the overspray, or paint mist, captured in the water system of a spray booth must be detackified, or "killed", before it adheres to the walls, piping, etc. of the spray booth. Paint that sticks to spray booth surfaces usually cannot be easily removed from the equipment and tends to build up overtime, which hampers spray booth efficacy.

One solution, which has been found to have practical application to the overspray problem, involves the use of chemicals which, when added to spray booth water, detackify paint solids. A wide variety of chemical formulations have been proposed for this purpose, and have been described in coassigned U.S. Patent Application Ser. No. 185,720 C-1453IA dated Apr. 25, 1988 of Faust et al, the pertinent portions of which are incorporated by reference. The above enumerated Faust et al application relates to the use of melamine-aldehyde-type polymers, more specifically melamine-formaldehyde polymers, to kill over-sprayed paint. The polymer is used preferably in combination with at least one polymeric coagulant.

DETAILED DESCRIPTION OF THE INVENTION

The Faust et al formulation for example has the disadvantage that it contains excessive free formaldehyde. Since formaldehyde is a potential carcinogenic material its level should be reduced to less than about 0.15%, and preferably to less than 0.1%. A search of pertinent U.S. patent literature produced the following references: Patent No. 2,345,543 of Wohnsiedler et al, which describes cationic melamine-formaldehyde resin solutions; No. 3,723,058 of Reinhard et al, which describes removal of free formaldehyde from solutions of methylolated carbamate finishing agents and textiles treated therewith; No. 3,957,431 of Pal et al, which describes a process for easy care finishing cellulosics having low formaldehyde release; No. 4,120,840 of Hurlock et al, which describes the use of phosphorous acid to stabilize quaternized polyacrylamide and No. 4,127,382 of Perry, which describes a process for the reduction of free formaldehyde in textile fabrics. The latter patent uses a formaldehyde scavenger, which comprises a heterocyclic compound free of carbonyl groups and containing a NH group. Patent No. 4,612,556 of Moira, to a self-contained pressure sensitive copying material, describes the removal of free formaldehyde from a formaldehyde containing suspension of microcapsules by the addition of a compound having a beta dicarbonyl group or a cyclic ketone. Patent No. 4,686,047 of Arots describes a process for the detackification of paint spray operations.

None of the above art describes a melamineformaldehyde detackifier having less than 0.15% free formaldehyde using a formaldehyde scavenging agent selected from the group consisting of urea, acetylacetone, a combination of urea with an enhancer of glyoxal or acetylacetone. Although the inventor has ascertained that the above enumerated compounds provide the desired results, other materials have been tested and found wanting. These materials include, inter alia, phthalimide, dihydroxyacetone, hydrazine, melamine, phosphorous acid, ethylene glycol, baker's yeast, Candida boidini yeast cake, Pseudomonas putida cake, and cyanamid. Only urea, acetylacetone, mixtures thereof and mixtures of urea with glyoxal provide satisfactory results.

As can be seen from the tests, urea and acetylacetone can reduce the level of free formaldehyde down to below 0.15%. The use of glyoxal, however, does not so do. In some cases the urea resulted in the formation of a precipitate. This precipitate is believed to be primarily melamine formaldehyde with some urea formaldehyde. The addition of acetylacetone to urea at levels, where neither alone scavanged enough formaldehyde, greatly prevents precipitate formation and thus results in an effect greater than that of either product alone. This combination, however, is relatively touchy in that a precipitate may form. The use, however, of urea and glyoxal is relatively stable and yields clear solutions without precipitation or cloudiness.

The following examples demostrate the instant invention in greater detail. They are not intended to limit the scope of the invention in any way.

EXAMPLES 1-8

In these examples, one starts with a fine colloidal suspension of melamine-formaldehyde polymer such as Calgon Corporation's CA-289, which has a molecular weight of about 2,200, a pH of about 1.6 to about 2.1 and contains about 8% active melamine-formaldehyde as is further defined in the aforementioned Faust et al Application Ser. No. 185,720. To a 50 g aliquot of the resin suspension one adds the amount of scavenger specified in Table I below while stirring at room temperature. The starting urea-formaldehyde suspension had a free formaldehyde content of greater than 0.3% formaldehyde. The times at which the formaldehyde content of the treated material was evaluated are also set forth in the table. The effectiveness of the detackifier was evaluated as follows: For each product 200 mls of cold tap water was added to an open mouth one pint glass jar equipped with a magnetic stir bar. While stirring the jar at high speed, a carbonate ion source was added so as to provide an alkalinity of 1000 ppm (calcium carbonate basis), 0.5 ml of test product was then added to the jar. As stirring continued, 6 drops of a commmercially available white, paint as defined in Table I, were added to the jar. After 30 seconds, 2.0 ml of Calgon polymer 9230 (high molecular weight (5-6,000,000) copolymer of acrylamide and dimethyldiallyl ammonium chloride) was added to the jar. After 30 more seconds, the samples were evaluated. The results are given in Table I.

TABLE I__________________________________________________________________________% H.sub.2 COEx.No.Remarks Treatment Time Found Scavenged__________________________________________________________________________1 3.0 g acetylacetone; orange; 3 hrs. 0.16 47* sl. haze; phenol type odor 1 day 0.073 79 2 days 0.059 832 1.0 g urea; turns from 3 hrs. 0.063 79* opalescent to cloudy 24 hrs. 0.027 92 48 hrs. 0.030 913 1.0 g urea; hvy cloud 24 hrs. 0.036 89*4 2 g urea; opalescent @ 24 hrs. 0.035 90* 23 days, found hvy cloud5 0.5 g urea; hvy. cloud 24 hrs. 0.058 83* 23 days 0.02 946 0.25 g urea; opalescent 24 hrs. 0.13 62* 17 days 0.17 507 0.10 g urea; opalescent 24 hrs. 0.21 38* 17 days 0.26 528 0.05 g urea; opalescent 24 hrs. 0.27 21* 17 days 0.29 15__________________________________________________________________________ *PAINT KILL: good paint kill, dispersion and flocculation with PPG WHITE and PPG high solids clear coat.

EXAMPLES 9-12

In these examples, one starts with the same colloidal suspension as in Examples 1-8, but to the 50 melamine-formaldehyde dispersion one adds acetylacetone as specified in each example. The paint kill jar test was also carried out as in Examples 1-8.

Table II A shows the results of the jar test of Examples 1-8 but using the materials of Example 9-12. The results are reported as 9A-12A corresponding respectively to 9-12, Table II and Table II A.

TABLE II__________________________________________________________________________ Time toEx. Develop % H.sub.2 CONo. Treatment Cloud Days Found Scavenged__________________________________________________________________________ 9 3.0 Acetylacetone; orange; >110 days 3 hrs. 0.16 47 sl. haze, phenol type odor 1 0.073 79 2 0.059 8310 3.0 g Acetylacetone; orange; >104 days 1 0.07 79 sl. haze 21 0.05 85 51 0.05 8511 2.0 g Acetylacetone; orange; >104 days 1 0.1 71 slight haze 21 0.09 74 51 0.11 6812 1.0 g Acetylacetone; orange; >104 days 1 0.18 47__________________________________________________________________________ TABLE II A______________________________________PAINT KILL JAR TESTEx Floc Final WtrNo Tack Smear % Float Description Clarity______________________________________ 9A -- No 100 Excellent Clear10A -- No 100 Excellent Clear11A -- No 100 Excellent Clear12A -- No 100 Excellent Clear______________________________________

EXAMPLES 13-20

In these examples, one starts with the same colloidal suspension as in Examples 1-8, but to the 50 g xelamine-formaldehyde dispersion one adds acetylacetone and urea as specified in each example. The paint kill jar test was also carried out as in Examples 1-8 where indicated. In Example 20, 550 g of the urea-formaldehyde dispersion was used. This would be equivalent to 0.38 g acetylacetone and 0.25 g urea had the same 50 gram aliquot been used. The purpose of Example 20 is to show that scaling up 11 fold still provides adequate formadehyde scavenging. As can be seen from Tables III, and III A, less urea and acetylacetone were used than when the individual components were used in Examples 1-8 and 9-12 respectively. Superior results are obtained. Table III A corresponds to Table III in the same manner as Table II A corresponds to Table II.

TABLE III__________________________________________________________________________ Time toEx. Develop % H.sub.2 CONo. Treatment Cloud Days Found Scavenged__________________________________________________________________________13 1.0 g Acetylacetone; stir; >88 days 12 0.047 86 add 0.25 g urea 26 0.066 81 52 0.066 8114 0.5 g Acetylacetone; stir; add 24 hrs. 2 0.09 74 0.25 g urea 13 0.059 83 38 0.09 7415 0.25 g Acetylacetone; stir; >77 days 2 0.12 65 0.25 g urea 13 0.1 71 38 0.11 6816 0.13 g Acetylacetone; stir; >77 days 2 0.14 59 0.25 g urea 13 0.12 38 38 0.14 5917 1.0 g Acetylacetone; stir; 5 days add 2.0 g urea18 0.75 g Acetylacetone; stir; >32 days 7 0.05 74 0.25 g urea 14 0.04 7819 0.38 g Acetylacetone; stir; >32 days 7 0.06 68 0.25 g urea 14 0.05 7420 4.18 g Acetylacetone; stir; >11 days 10 min. 0.26 41 2.75 g urea 30 min. 0.23 43 50 min. 0.18 55 90 min. 0.19 53 150 min. 0.18 55 270 min. 0.16 60 420 min. 0.14 65 4 days 0.1 75__________________________________________________________________________ TABLE III A______________________________________PAINT KILL JAR TESTEx. Floc Final WtrNo. Tack Smear % Float Description Clarity______________________________________13A -- No 95 Good Clear18A No No 90% Light & Clear 10% sus- frothy pended19A No No 95% Light & Clear 5% sus- frothy pended______________________________________

EXAMPLE 21-31

In Examples 21-23 one again starts with the same colloidal suspensions as in Examples 1-8 but to the 50 g aliquot adds glyoxal as specified. As can been seen no formaldehyde was scavenged. However, when urea was first added stirred for one hour followed by glyoxal additions and again stirred for a quarter hour the amount of urea scavenged was greatly increased. The results are reported in Table IV below. In Table IV A the Paint Kill Jar Test was carried out, again showing the results wherein No. 24A corresponds to No. 24, etc. There is no Paint Kill Jar Test results for Examples 21-31 as glyoxal, per se, scavenged no formaldehyde.

TABLE IV__________________________________________________________________________ Time toEx. Develop % H.sub.2 CONo. Treatment Cloud Days Found Scavenged__________________________________________________________________________21 1.2 ml glyoxal, 40% aq. >59 days 5 0.24 0 17 0.24 022 0.6 ml glyoxal, 40% aq. >59 days 5 0.24 0 17 0.24 023 0.3 ml glyoxal, 40% aq. >59 days 5 0.21 024 0.2 g urea; stir 1 hr; >62 days 7 0.031 91 add 0.88 ml 40% glyoxal 23 0.02 .vertline.9025 1.0 g urea; 0.88 ml 40% >59 days 1 0.02 .vertline.90 glyoxal26 0.5 g urea; 0.88 ml 40% >59 days 1 0.38 80 glyoxal27 1.0 g urea; 0.44 ml 40% >59 days 1 0.02 .vertline.90 glyoxal 21 0.02 .vertline.9028 0.5 g urea; 0.44 ml 40% >59 days 1 0.025 87 glyoxal 21 0.02 .vertline.9029 0.2 g urea, but 1.76 ml >62 days 7 0.034 90 40% aq. glyoxal 23 0.02 .vertline.9030 1.0 g urea; 1.76 ml >59 days 1 0.025 87 40% glyoxal 21 0.02 .vertline.9031 0.5 g urea; 1.76 ml >59 days 1 0.064 66 40% glyoxal 21 0.03 90__________________________________________________________________________ TABLE IV A______________________________________PAINT KILL JAR TESTEx. Floc Final WtrNo. Tack Smear % Float Description Clarity______________________________________24A No Some 90 Light Clear25A Yes Yes 95 Tight pack; Clear light; frothy Encapsulated live paint26A Yes Yes 97 Light; frothy Clear (live paint)27A No Lgt Smear 97 Tight pack; Clear light; frothy28A No No 90 Light; frothy Clear29A No Some 85 Light Clear30A No Lgt Smear 85 Bubbles; no Clear floc31A No Some 70 Very loose, Clear tiny floc______________________________________

Although the definitions of the "paint kill jar test" are fully described in the Faust et al application, which was incorporated by reference, for the sake of completeness, the definitions are briefly described here. After adding the coagulant and stirring, a froth or "floc" appears on the top of the jar. This floc is coagulated particles of "detackified paint". "Tack" is the tackiness of the paint and is inversely proportional to the effectiness of the treatment, e.g. no tack means good killing of the paint. The "smear" is readily obtained by smearing the floc between ones thumb and forefinger. Other equivalent tests can be made. The "% float" is the percentage of the floating floculated material. The "final wtr clarity" is the clarity of the water beneath the floc.

Although specific melamine-formaldehyde dispersions are used in the specific examples, the formaldehyde scavenging properties of my invention are equally applicable to other formaldehyde resin detackifiers. A desirable formulation is a blend of about 98% melamine formaldehyde dispersion, about 1.5% acetylacetone and about 0.5% urea. The presently most preferred formulation is a blend of about 98.5% melamine-formaldehyde dispersions, of about 0.5% glyoxal 40% aqueous and about 1.0% urea; all percentages being by weight.

Claims

1. In a method of detackifying over-sprayed, water-insoluble paint in a spray booth operation, which comprises contacting over-sprayed, water-insoluble paint with paint spray booth water containing a melamine-formaldehyde polymer detackifier, the improvement comprising adding to said paint spray booth water a malamine-formaldehyde polymer detackifier containing a formaldehyde scavenging agent comprising urea and glyoxal in an amount sufficient to reduce the amount of free formaldehyde in the polymer to less than 0.15%.

2. The method of claim 1, wherein a polymeric coagulant is also added to the paint spray booth water in an amount sufficient to flocculate detackifier paint.

3. In a method of detackifying over-sprayed, water-insoluble paint in a spray booth operation, which comprises contacting over-sprayed, water-insoluble paint with paint spray booth water containing a malamine-formaldehyde polymer detackifier, the improvement comprising adding to said paint spray booth water a melamine-formaldehyde polymer detackifier containing a formaldehyde scavenging agent comprising urea and acetylacetone in an amount sufficient to reduce the amount of free formaldehyde in the polymer to less than 0.15%.

4. The method of claim 3, wherein a polymeric coagulant is also added to the paint spray booth water in an amount sufficient to flocculate detackified paint.