Cold-curing polyurethane-based binder for moulding sand

摘要

The invention relates to a cold-curing polyurethane-based binder for moulding sand mixtures for the production of casting cores and moulds. It is formed by reacting a solution of a monomeric polycyclic phenol containing one OH group per ring with a polyisocyanate containing at least two NCO groups per molecule, the molar ratio between the OH groups and the NCO groups being in the range from 1 : 1.0 to 1.5. The novel feature here is that the solvent for the phenol is a mixture of a carboxylic acid ester, an acid amide containing tertiary amide groups and a ketone, each of these constituents having a boiling point of above 130 DEG C, and that one or more acetylenically unsaturated compounds of the formula where R<1> and R<2> are hydrogen atoms or hydrocarbon radicals having up to 8 carbon atoms or form a 5- to 8-membered cycloaliphatic radical, in each case with inclusion of the carbon atom which is adjacent to both of them, are added to the solvent. Casting cores and moulds produced using the novel binder have superior initial strengths in addition to good decomposition properties.