Method for producing polyurethane hard foam composite elements using Mannich polyols

A method for producing rigid polyurethane foam composite elements comprising at least one outer layer and a rigid polyurethane foam layer, the method comprising

• forming a reaction mixture by mixing
• (a) polyisocyanates with
• (b) compounds having at least two hydrogen atoms reactive with isocyanate groups,
• (c) optionally flame retardant(s),
• (d) blowing agent, comprising at least one aliphatic or cycloaliphatic hydrocarbon having 4 to 8 carbon atoms,
• (e) catalyst, and
• (f) optionally auxiliaries and adjuvants,
• applying the reaction mixture to the at least one outer layer, and
• curing the reaction mixture to form the rigid polyurethane foam layer, wherein
• component (b) comprises at least one polyether alcohol (b1), prepared by alkoxylation of a starter or of a starter mixture, wherein the at least one polyether alcohol (b1) has an average functionality of 4 to 8 and a hydroxyl number of 300 to 600 mg KOH/g, at least one aromatic Mannich condensate (b2), which may have been alkoxylated, preparable by reaction of an aromatic compound which on an aromatic ring carries at least one hydroxyl group and/or at least one group —NHR, where R is any organic radical or is hydrogen, one or more aldehydes and/or ketones, and one or more primary or secondary amines, at least one aromatic polyester polyol (b3), and optionally chain extenders and/or crosslinking agents,
• wherein a fraction of aromatic Mannich condensate is greater than 5 wt % to less than 20 wt %, based on a total weight of component (b),
• wherein an isocyanate index on mixing of components a) to f) is 160 to 230;
• and
• wherein the blowing agent (d) comprises physical blowing agents and optionally chemical blowing agents and wherein the physical blowing agent comprises exclusively hydrocarbons as physical blowing agent.