Dual cure polyurethane formulations for 3D printing applications

A method for additive manufacturing a three-dimensional part in a layer-by-layer manner, the method comprising:

• (i) providing a carrier substrate to support the three-dimensional part and a print head connected to a reservoir of a reactive curable printable composition;
• (ii) printing the reactive curable printable composition with the print head as extrudate strands onto the carrier substrate to form a first layer;
• (iii) printing the reactive curable printable composition with the print head as extrudate strands onto the first layer to form a second layer;
• (iv) optionally repeating step (iii) one or more times to form a third layer or the third layer and subsequent layer(s);
• (v) exposing the formed layers to radiation directly after forming each layer and/or after forming all of the layers;
• and
• (vi) curing the formed layers of the reactive curable printable composition to obtain the three-dimensional part,
• wherein the reactive curable printable composition is a pasty polyurethane composition comprising:
• at least one polyisocyanate resin;
• at least one monomer and/or prepolymer that is polymerizable by exposure to radiation;
• and
• at least one photoinitiator, wherein:
• the pasty polyurethane composition has a first viscosity factor (1.5/15) of at least 2 and a second viscosity factor (5/50) at an application temperature,
• the first viscosity factor (1.5/15) is the viscosity of the pasty polyurethane composition at a shear rate of 1.5/s divided by the viscosity of the pasty polyurethane composition at a shear rate of 15/s and the second viscosity factor (5/50) is the viscosity of the pasty polyurethane composition at a shear rate of 5/s divided by the viscosity of the pasty polyurethane composition at a shear rate of 50/s,
• the pasty polyurethane composition has a viscosity at a shear rate of 1.5/s of at least 10 Pas, and
• the first viscosity factor (1.5/15) is greater than the second viscosity factor (5/50).