For Additive Manufacturing, i.e. the application of two- or three-dimensional functional structures (e.g., for electronic or medical applications), state-of-the-art printing technologies play a key role.
Depending on the particular application several printing technologies are utilized at the MATERIALS institute:
- maskless non-contact digital technologies like inkjet printing or aerosol jet printing are taking advantage of their variability of the patterns to be printed.
- contact printing technologies like screen printing or flexography where the functional inks or pastes are applied onto the substrate via prefabricated screens (screen printing) or clichés (flexography).
In inkjet printing (non-contact technique), single droplets (drop-on-demand) of low viscosity inks are printed on the substrate. Thereby the droplets are ejected from nozzles located in the printing head by means of piezo technology. Industrial inkjet printing headscontain up to 2048 nozzles, allowing for a high degree of parallelization. At the MATERIALS institute three state-of-the-art inkjet printers are available, a Dimatix DMP 2800 and two PIXDRO LP50 systems, allowing for the integration of different industrial printing heads.
For this technology of the US based company Optomec the inks are nebulized by pneumatic or ultrasonic means and the resulting aerosol is continuously transported to the printing head via a system of tubes. Using a shielding gas the aerosol jet is focused onto the substrate surface. As the nozzle is typically located 1-5mm above the surface of the substrate, this technology is a contactless direct structuring method with high resolution (down to 10µm). It allows printing on non-planar substrates and the realization of 2.5D-structures.
In screen printing, a highly viscous paste is applied via a pre-structured screen using a doctor blade. Parameters like blade velocity, mesh size or thread thickness influence the printing quality. Amongst other applications, at MATERIALS screen printing is done with the help of a semiautomated Thieme LAB 1000 and used a.o. for the PyzoFlex® technology.
In flexography (instrument…), a doctor blade is used to distribute the high viscosity ink onto the anilox role, which subsequently wets the pre-fabricated cliché bearing the pattern to be transferred. Afterwards, and in a role-based-process, the ink is being transferred from the cliché to the substrate. Parameters like anilox volume (which defines the amount of ink to be transferred), printing speed or role-to-role distance affect the printing quality.
From Materials over processes to devices
Depending on the particular printing technology the first step is formulating a printable ink or paste with the desired functionality (e.g., metal nano-particle-based inks for conductive structures). The printing process is thereby optimized for each application: for successful printing process development a deep understanding of the components ink or pastes, substrate and printing strategy as well as the interdependencies (e.g., of wetting and adhesion) is necessary.
Equally essential are post processing steps like drying or thermal or photonic curing of the printed structures (via UV, laser or flash light), in order to transform the applied nano-particles into a conductive structure, for example.
For the fabrication of three-dimensional printed plastic objects, two technologies are available at MATERIALS: In “Fused Filament Fabrication” melted plastic is applied layer by layer using a heated nozzle. As an alternative to this technology, MATERIALS offers an inkjet based 3D printer (Stratasys Objet Pro 30) to apply polymer building blocks and support structures (which are removed afterwards) on complex structures (e.g. moveable objects), in thin layers and subsequently UV cured.