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W. F. SCHEUFELE and N. G. TOMPKINS Dewey and Almy Division, W. R. Grace & Co., Cambridge 40, Mass.
Formulation of Water-Thinnable Paints from EmulsifierF k e Vinyl Acetate Copolymer Dispersions
ALL water-thinnable paints yield films containing appreciable amounts of watersoluble, extractable material which give them a tendency to water-spot excessively, or to show poor wet pigment ruboff behavior, poor wet adhesion to sealed surfaces, or even poor scrubbability in highly pigmented films. In paints based on poly(viny1 acetate) and vinyl acetate copolymer emulsions of the conventional type, the greater part of this water-soluble material has its source in the basic resin emulsion vehicle. Films of some such vehicles contain around 5% of readily extractable water-soluble substances and this represents a considerable handicap to the paint industry formulator in his attempts to overcome the above-mentioned defects. Techniques for making emulsifier-free dispersions of some types of polymer have been described by Whitby ( 3 ) , Willis ( 4 ) , and Stannett ( 2 ) . Modifications of their methods have been found effective for copolymers of 7 5 parts of vinyl acetate with 25 parts of dibutyl maleate, and several dispersions of this material have been made which contain virtually no water-extractable substances.
Films from these emulsifier-free latices have been prepared and their behavior has been compared with that of similar films from conventional vinyl acetatedibutyl maleate copolymer emulsions when immersed in water at room temperature. They have been found to whiten and absorb water more slowly than similar films from conventional emulsions, although the ultimate quantity absorbed is greater. Apparently. in vinyl acetate copolymer systems, the rate of film whitening or water absorption is a function of the emulsification system, while the maximum quantity of water absorbed follows more closely the molecular weight of the resin, which is somewhat lower in the case of the emulsifier-free latices than in the conventional emulsions used in this work. To compare the behavior of an emulsifier-free product with conventional materials of the same type in actual paint formulations, three series of white paints were made, one from an emulsifier-free vinyl acetate copolymer emulsion and one from each of two otherwise similar conventional materials. I n each series, consisting of four paints, the
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C o p o l y m e r A ( Hydroxyethyl C e l l u l o s e E m u l s l f l e C o p o l y m e r B ( Polyvinyl A l c o h o l E m u l s i f i e d ) 1 .oo 17 0
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The emulsifier-free product gives superior performance when exposure to water is o f short duration
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pigment volume concentration was varied from soy0 to 80% in steps of 10%~. The scrubbability of these paints was then determined (7) with the results given in the figure. I t j s evident that the emulsifier-free product gives superior performance where, as in interior painting, exposure to water is likely to be of relatively short duration. Experiments conducted by tinting the 607, pigment volume concentration paints and qualitatively evaluating them for resistance to water spotting and to wet pigment ruboff, also showed clearly the superior water resistance of the paint film containing the emulsifier-free material. In formulating paints from emulsifier-free latices, the choice of wetting agents and stabilizers proved to be critical for adequate stability. Ethylene oxide adducts of nonylphenol having 30 to 40 moles of ethylene oxide gave best results. In contrast to conventional copolymer emulsion, the emulsifier-free products did not require added solvent for good film consolidation when dried a t 40' F. or for good pigment binding in highly pigmented films. Their smaller particle size made the use of coarse inerts advisable to maintain flatness. Coarse calcium carbonate serves the double purpose of providing a satisfactory inert pigment and at the same time maintaining the pH value in the range of maximum stability. I t appears that emulsifier-free vinyl acetate copolymer emulsions represent a promising approach where the application of conventional emulsions of this type are limited by the high rate of water absorption of their films. Many such uses exist in the paint, paper, leather, and woven ' and nonwoven textile fields.
INDUSTRIAL AND ENOINEERINO CHEMISTRY
(1) Federal Specification TT-P-29-Paint Latex Base, Interior, Flat White and Tints, Revision 2, Dec. 22, 1955. (2) Stannett, V., J. Polymer Sci. 21, 343 (1956). (3) Whitby, G. S., Gross, M. D., Miller, J. R., Costanza, A. J., Ibid., 16, 549 (1955). (4) Willis, J. M., IND. END. CHEM.41, 2272 (1949).
