A process for the preparation of hard polyurethane foams

摘要

A process for the production of rigid polyurethane foam with improved thermodimensional stability and reduced thermal conductivity comprises reacting (a) polyisocyanates with (b) compounds with isocyanate-reactive hydrogen atoms in presence of (c) water and optionally (d) physical blowing agents and (e) catalysts and other additives etc. 60-100 wt% of component (b) consists of a polyol mixture containing (b1) a polyol obtained by addition of ethylene oxide (EO) and/or propylene oxide (PO) to a hexitol or hexitol mixture and (b2) a polyol obtained by addition of EO and/or PO to one or more aromatic amines, such that the total hexitol content and the total amine content of the polyol mixture is 15-30 wt% and 1-10 wt% respectively.