MANUFACTURE OF POLYMER COATING-FINELY SOLID POLYISOCYANATE SHOWING DELAY REACTIVITY AND USE

This invention relates to the production of polymer-coated, finely divided polyisocyanates by mixing (A) solid, finely divided polyisocyanates (preferably dimeric diisocyanates or urea diisocyanates) with (B) polyisocyanates differing in composition from those mentioned under (A) (preferably (cyclo) aliphatic polyisocyanates, such as biuretized diisocyanates or trimers or NCO-prepolymers), in quantities of from 0.05 to 50 parts by weight, and preferably in quantities of from 0.2 to 25 parts by weight, of (B) per 100 parts by weight of (A). The solid polyisocyanate particles surface-modified by covering with polyisocyanates (B) and then reacted with (D) isocyanate-reactive compounds containing reactive hydrogen atoms or with compounds free from active hydrogen atoms which form polymers with isocyanates in sub-equivalent to substantially equivalent quantities (preferably 0.5 to 1.0 equivalent per NCO-equivalent), in the presence of (C) inert, weakly polar organic solvents, (for example aliphatic hydrocarbons or relatively long chain dialkyl ethers), plasticizers, polyols or aromatic polyamines. A polymer coating is formed by the reaction of (B) and (D) around the solid polyisocyanate cores (A). The present invention also relates to the polyisocyanate particles covered with polyisocyanates (B) on the surface of the solid polyisocyanates (A) and, in particular, to the foreign-polymer coated, finely particulate polyisocyanates of retarded reactivity obtained by reaction with (D). The present invention also relates to the use of the polyisocyanate-covered and, more particularly, polymer-coated polyisocyanates, optionally in suspension in polyols and/or plasticizers, for the production of polyurethanes, more particularly in one-component polyurethane reactive systems having a long shelf life and a high thickening point.