Process for the production of polyurethane particles

A process for the production of particles from a solution or melt of a heat-activatable polyurethane which comprises the reaction product of:

• a) a crystallizing oligomeric dihydroxy compound,
• b) optionally an amorphous oligomeric dihydroxy compound in an amount by weight which is less than the amount of component a),
• c) an aromatic and/or aliphatic diisocyanate and
• d) optionally a low molecular weight difunctional chain extender, optionally in admixture with
• e) a light stabilizer, antioxidant, powdering agent or a polyfunctional cross-linking compound,
• which comprises:
• i) dissolving a compressible auxiliary agent at a pressure of between 50 and 1000 bar into a conveyable solution or melt of a heat-activatable polyurethane having a polyurethane content of between 40 and 100 wt. % and a solvent content of 0 to 60 wt. % to obtain a mixture of polyurethane, compressible auxiliary agent and optionally solvent,
• ii) optionally adjusting of the temperature of the resulting mixture to a temperature of from 40° K below to 150° K above the crystallite melting point of the polyurethane,
• iii) expanding the mixture by means of an expansion device into a container, while adjusting the temperature in the container to at least 5° K below the softening temperature of the polyurethane to maintain the open jet particles in a form in which they do not agglomerate, and
• iv) separating the formed particles from the stream of decompressed compressible auxiliary agent and optionally solvent.