Rapid prototyping of electrically conductive components using 3D printing technology

A method of rapid prototyping of electrically conductive components is described. The method is based on 3 D printing technology. The prototyped model is made of plaster-based powder bound layer-by-layer by an inkjet printing of a liquid binder. The resulting model is highly porous and can be impregnated by various liquids. In a standard prototyping process, the model is impregnated by epoxy or polyurethane resin, wax solution, etc. In the test described in this paper, to obtain the electric conductivity, the model has been impregnated by a dispersion of carbon nanofibers (CNF) in epoxy resin. Surface resistivity of the model below 800 Omega/sq has been obtained when impregnated by a mixture containing less than 4 wt.% CNF. Volume resistivity of the molded and hardened CNF dispersion used for model impregnation have also been measured and a value less than 200 Omega cm has been obtained at 3 wt.% CNF content. Unexpectedly, the onset of electric conductivity (percolation threshold) occurred at lower mass fraction of CNF for a dispersion containing CNF agglomerates, when compared to the mixture with well uniformly dispersed fibers. This happened both for the impregnated model and for the molded CNF dispersion itself. An explanation of this phenomenon, based on percolation theory is given. (C) 2009 Elsevier B.V. All rights reserved.