1, Fraunhofer IGB, Stuttgart, , Germany
3, Karlsruhe Institute of Technology KIT, Karlsruhe, , Germany
Polyurethanes (PU) are versatile materials that are used in a variety of applications. They can be found in the fields of insulation, cushioning and light-weight materials. Recently, PU materials gained entry into the field of inkjet printable materials. It has successfully been shown that PU materials can be fabricated using reactive inkjet printing. Further on, porous PU materials are of specific interest in the fields of adsorber materials or as scaffolds in tissue engineering. Due to the versatility of PU materials, it is possible to formulate numerous inks, yielding diverse material properties. The combination of printing technology and porous structures has previously been shown using a DLP printer in combination with a UV-curable O/W-emulsion, yielding conductive porous objects. Thus, a combination of polyurethane foam chemistry and ink formulation is the goal. We investigated inks that can be used to obtain polyurethane foams via reactive inkjet printing. Generally, two inks are necessary to produce polyurethane foam via reactive inkjet printing. The first ink containing an isocyanate reactive component often called polyol and the second ink containing the isocyanate component. As inkjet printing is limiting the selection of materials, mostly due to the materials viscosity, low viscous isocyanate monomers were chosen. Furthermore, the polyol ink consists of a variety of components such as main polymer, a crosslinker, a blowing agent and catalysts.
We tested selected materials for their general usage as PU reactants with caution to inkjet printing. Therefore, low viscous materials such as poly(ethylene glycol) as the linear bulk polymer and 1,6-hexamethylene diisocyanate (HDI) as the reactive isocyanate component were chosen. The materials were characterized by means of rheology and tensiometry to assure the usability in an inkjet printhead. We will show the influence of the concentration of dibutyltin dilaurate (DBTL) and iron(III) chloride as the main gelling catalyst by means of creamtime measurements. Selected materials were printed using a Fujifilm Dimatix DMP-3000. The printed structures were characterized by FT-IR spectroscopy as well as light- and scanning electron microscopy.