GB1076688A - Polyurethane resins - Google Patents

Abstract

Polyurethanes are prepared by reacting a predominantly linear compound having reactive hydrogen atoms and at least one OH group and a M.W. of 300 to 20,000, a polyisocyanate and if desired a chain lengthening agent and a compound having at least one hydrogen atom reactive with isocyanate groups and at least one anionic salt-type group or group capable of salt-formation, the ratio of isocyanate groups to hydrogen atoms reactive with isocyanate groups in the compounds capable of salt formation being such that the groups capable of salt formation present do not undergo reaction with the isocyanate groups, and the resulting polyurethane is subsequently converted at least partly to the salt form by reaction with an organic or inorganic base in the case where groups capable of salt formation are present, the proportion by weight of the salt type groups contained in the polyurethane being more than 1% and not more than 15% and, when the groups capable of salt formation are carboxyl groups, not more than 8%. The compounds of M.W. 300 to 20,000 are preferably polyesters, polyesteramides, polyethers, polyacetals or polythioethers and the polyisocyanates are suitably aliphatic, cycloaliphatic or aromatic and may be masked or partially reacted. Suitable chain lengthening agents are glycols, diamines, hydrazines, ammonia, aminoalcohols, mono- and diamino-carboxylic acids and water. The compounds containing at least one reactive hydrogen atom and at least one salt-type group or group capable of salt formation may be a hydroxy- or mercaptoacid, a mono- or diamino-carboxylic acid, dicarboxylic acids, hydroxy- and carboxy-sulphonic acids, aminosulphonic acids, organic phosphorus compounds, addition products of unsaturated acids, unsaturated nitriles, dicarboxylic acid anhydrides, sulphocarboxylic acid anhydrides, lactones, reaction products of olefins with sulphur trioxide, epoxycarboxylic and epoxysulphonic acids, sultones, and disulphonic acid anhydrides with amines, hydrazines, ammonia aminoalcohols and alcohols and hydrazinocarboxylic acids. It is preferred to first form a prepolymer containing excess NCO groups, with or without a solvent and then to react this prepolymer with chain lengthening agents and salt compounds if desired in an organic solvent and/or water. The anionic polyurethane may be converted into the aqueous phase by partially or completely replacing the organic solvent after termination of the reaction and, if desired, salt formation. Emulsifiers, dispersing agents, fillers, plasticizers and pigments may be added to the aqueous dispersions.