GB1090387A - Aqueous cellulose derivative emulsion coating compositions - Google Patents

Abstract

An aqueous emulsion coating composition contains, as the essential film-forming constituent, a plasticized organic-soluble, water-insoluble cellulosic polymer in the form of spherical particles having a diameter of 0.1 to 0.8 microns, and an emulsifier. The composition may comprise 10 to 40% of a cellulose ester or ether soluble in one or more volatile organic solvents but insoluble in water, 10 to 30% of a plasticizer therefor, the proportion of the plasticizer being between one-fifth and one-half that of the cellulose ester or ether, 40 to 80% of water, the proportion of water being at least one-half of the combined proportions of the cellulose ester or ether, and 1/2 to 10% of an emulsifier, part or all of the emulsifier being an anionic emulsifier, the percentages being calculated on the total weight of the above ingredients only. The cellulose derivative may be in the form of spherical particles of average diameter 0.3 to 0.6 micron. The cellulose derivative may be a nitrocellulose, or a cellulose acetate, acetate butyrate or propionate. It may be an ethyl cellulose. The composition may contain also 2 to 20% of a coalescing agent calculated on the combined weight of only the agent and the ingredients already specified, there being more than one part of agent plus plasticizer for every three parts by weight of cellulose derivative. The coalescing agent is defined as a liquid solvent for the cellulose derivative having a boiling-point of 120 DEG to 230 DEG C., preferably at least 130 DEG C., and a relative rate of evaporation of 0.01 to 0.5, preferably up to 0.3, butyl acetate being 1.0, as determined with a Shell Thin Film Evaporator at 0% relative humidity and 25 DEG C. The coating composition may be prepared by forming an initial emulsion of the oil-in-water type from the cellulose derivative, the plasticizer, the emulsifier, water and a volatile organic solvent, distilling off the solvent, if necessary adding further proportions of any of the ingredients (other than the solvent), so as to maintain the proportions of the ingredients within the ranges specified. The oil-in-water type emulsion may be formed without the cellulose derivative, the latter then mixed into the emulsion, either alone or in the form of a solution in some or all of the organic solvent. The ingredients of the composition may all be mixed together in a high-shear mixer or a solution of the cellulose derivative in a volatile organic solvent treated in such a mixer before the other ingredients are added. The object of this treatment with a high shear mixer is to reduce the particle size of the cellulose derivative.