Preparation, characterization, and monitoring of an aqueous graphite ink for use in binder jetting

Abstract

The use of particle loaded inks in binder jetting offers several advantages, such as the improved sintering ability or the adaption of material properties in a printed part. Various aspects have to be considered for the preparation and the printability. A high stability is necessary, therefore agglomeration and sedimentation of the particles must be avoided. It is also important that long filaments and thus satellite droplets are not formed during printing. In this study, inks loaded with graphite nanoparticles were investigated regarding their stability and drop formation behavior to qualify them for reliable processing in binder jetting. Polyvinylpyrrolidone (PVP) was used as a binder for the binder jetting process and simultaneously as a dispersing agent for the nanoparticles. The PVP mass fraction was investigated for its dispersion effect. To meet the print head requirements, the particle size distribution had to be below 1 μm. To destroy agglomerates with a diameter above this limit, ultrasonic treatment was used. The duration of the ultrasonic treatment was examined to identify the minimum time required to obtain a well dispersed ink. Particle loaded inks were then prepared and the fluid mechanical properties were determined for inks with different particle mass fractions. Monitoring of the drop formation provided information about a stable drop generation, the filament lengths, and the velocity of the drops. It was possible to qualify inks with a maximum particle mass fraction of 10 m% for the binder jetting process.