Polyurethane compositions with a low content of diisocyanate monomer(s)

Abstract

At least one isocyanate-reactive monomer is reacted with an excess of molten monomeric diisocynate to produce at least one reaction product and a maximum of 0.5 wt % of free isocyanate groups. The reaction product is then mixed with at least 20 wt. %, based on the total weight of reaction product, of at least one isocyanate-terminated prepolymer which is essentially free of diisocyanate monomers and has a viscosity at 20° C. of at least 1.500 mPa·s, the isocyanate-terminated prepolymer having a content of free NCO groups of up to 25 wt % and containing a maximum of 0.1 wt. % of diisocyanate monomer(s) based on the weight of the isocyanate-terminated prepolymer. A polyurethane composition containing less than 0.1 wt. % of monomeric diisocyanate, based on the total weight of the resulting polyurethane composition, is produced.

1 . A process for producing a polyurethane composition with a content of diisocyanate monomer(s) of less than 0.1 wt. %, based on the total weight of the resulting polyurethane composition, said process comprising: 
 a step of reacting at least one isocyanate-reactive polymer with at least one isocyanate-terminated prepolymer that is essentially free of diisocyanate monomers and has a viscosity at 20° C. of at least 1,500 mPa·s, the isocyanate-terminated prepolymer having a content of free NCO groups of up to 25 wt. % and containing a maximum of 0.1 wt. % of diisocyanate monomer(s) based on the weight of the isocyanate-terminated prepolymer, wherein the reaction of the isocyanate-reactive polymer with the isocyanate-terminated prepolymer is carried out in the molten state and in the presence of an excess of NCO groups made available by the isocyanate-terminated prepolymer, to thereby produce a polyurethane composition containing less than 0.1 wt. % of monomeric diisocyanate and containing at least 0.5 wt. % of free NCO groups, based on the total weight of the resulting polyurethane composition,    wherein following said reacting step, said process is free of a distillation step and free of any other removal step to reduce the content of diisocyanate monomer(s) from above 0.1 wt. % to less than 0.1 wt. % based on the total weight of the resulting polyurethane composition.