Polyurethaner-based binder for producing cores and casting molds using isocyanates containing a uretonimine and/or carbodiimide group, a mold material mixture containing said binder, and a method using said binder

A mold material mixture, comprising as the binder:

• (A) one or more polyol compounds comprising at least 2 hydroxy groups per molecule;
• (B) one or more isocyanate compounds comprising at least 2 isocyanate groups per molecule, containing at least one isocyanate compound having at least 2 isocyanate groups per molecule, further comprising per molecule at least one uretonimine group and/or carbodiimide group;
• and
• (C) refractory mold base materials.

A method for producing a shaped body as a casting mold or as a core, comprising:

• (i) mixing refractory mold base materials with a binder, comprising:
• (A) one or more polyol compounds comprising at least 2 hydroxy groups per molecule;
• and
• (B) one or more isocyanate compounds comprising at least 2 isocyanate groups per molecule, containing at least one isocyanate compound with at least 2 isocyanate groups per molecule, further comprising at least one uretonimine group and/or carbodiimide group per molecule, in a binding quantity of 0.2 to 5% by weight, preferably 0.3 to 4% by weight, particularly preferably 0.4 to 3% by weight, relative to the amount of refractory mold base material, so as to obtain a mold material mixture;
• (ii) introducing the mold material mixture or the ingredients thereof into a shaping tool;
• (iii) curing the mold material mixture in the shaping tool so as to obtain an integral mold;
• and
• (iv) subsequently separating the cured mold from the tool and optionally curing the same further, whereby a cured shaped body is obtained.