Polyurethane foam and process for producing same

A process for producing rigid PUR/PIR foams having an apparent density of 30-90 kg/m3 according to ISO 845:2006, an open-cell content of >90% according to ISO 4590:2002, and having an average cell diameter of <50 μm according to optical microscopy evaluation, comprising the steps of

• i) producing reaction mixture R) comprising
• a polyol formulation P) comprising
• an isocyanate-reactive component A) comprising at least one polyol component A1) having a functionality of >2.5 comprising at least one of polyether polyols, polyester polyols, polycarbonate polyols, polyether polycarbonate polyols and polyether ester polyols,
• a catalyst component D) comprising a catalytically active compound D1) having Zerewitinoff-active hydrogens,
• an assistant or additive substance E) comprising a cell-opening compound,
• wherein a proportion of all primary OH functions present in the isocyanate-reactive component A) based on a total number of terminal OH functions in the component A) is at least 30%,
• a polyisocyanate component B) and
• CO2 in the supercritical state as blowing agent component C),
• ii) introducing the reaction mixture R) into a mold,
• iii) foaming the reaction mixture R) and
• iv) demolding a rigid PUR/PIR foam formed from the reaction mixture R).