Adherable polyester film

Claim 1

A process for preparing an aqueous, film-forming coating emulsion of a carboxyl group-containing polyurethane composition consisting essentially of a polymer of at least one diol, the total amount of the diol component being 50 mole %, and 50 mole % of at least one diisocyanate, the polymer being modified by esterifying the terminal hydroxyl groups and amidizing any terminal amine groups of the polymer by treatment with the anhydride of a dicarboxylic acid, thus providing carboxyl groups, the acid number of the carboxyl group-containing polyurethane being about 3-20; said process comprising the following sequential steps: (a) dissolving the carboxyl group-containing polyurethane in an organic solvent selected from the group consisting of tetrahydrofuran and mixtures of tetrahydrofuran with at least one other organic cosolvent selected from the group consisting of methanol, acetone, dioxane, dimethoxyethane, and methyl ethyl ketone, the amount of cosolvent other than methyl ethyl ketone or total amount of such cosolvents being at most about 25 weight % of the solvent mixture, and the amount of methyl ethyl ketone being at most about 75 weight % of the solvent mixture, the balance in each case being tetrahydrofuran; (b) neutralizing the carboxylic groups with an inorganic base, ammonia, or an organic amine; (c) adding a sufficient amount of water with good agitation to cause emulsification; and (d) evaporating the organic solvent.