Dispersions that are substantially free of volatile organic compounds and that have a high solids content

A process for the preparation of a polyurethane dispersion substantially free from volatile organic compounds and maintaining a total VOC content of less than 1000 ppm, said dispersion not containing amines or other volatile compounds that have a boiling point of below 250° C., the process comprising the steps of:

• (i) synthesizing, in the absence of acetone or methyl acetate or any other volatile solvent, a polyurethane prepolymer from isocyanates, polyols selected from polycarbonate polyols and polycarbonate-polyether polyol mixtures, and a component A present in an amount below 2 weight percent based on the total weight of the prepolymer, wherein said component A is a carboxyl containing diol, and
• (ii) dispersing the obtained prepolymer into a water phase optionally comprising other non-volatile additives,
• (iii) adding one or more non-volatile neutralizing agents prior to, simultaneously with or after dispersing the prepolymer in water and,
• (iv) forming, simultaneously with or subsequent to the dispersing, polyurethane by reacting with one or more extension agents comprising a component B, said component B having x hydroxyl groups and y amine groups, wherein x can be 0 or more than 0 and x+y≥2, and wherein component B contains one or multiple amino groups and one or multiple sulfonate groups capable of forming a salt, such that the dispersion of the polyurethane has a solids content of at least 50 weight percent and a viscosity lower than 250 mPa·s as measured at 25° C. using a Brookfield LVF viscometer, and wherein the amount of component B is such that between 0.02 and 0.70 equivalent of isocyanate reactive groups is added with respect to the isocyanate functions that are present in the prepolymer, and the remaining isocyanate functions are extended by other extension agents, wherein the total amount of extension agent employed is such that the ratio of isocyanate reactive groups in the total amount of extension agent to the isocyanate groups in the prepolymer is in the range from about 0.7:1 to about 2.0:1.