Textile substrates present considerable challenges for the printing of functional devices, because of their considerable roughness and intrinsic porosity, not present on conventional polymer film flexible substrates. Initial ink behaviour after printing is governed by two processes, the spreading of ink across and the infiltration of ink into the fibrous substrate. The presence of ink deposits on the substrate enables better electrical conductivity and finer feature resolution, however, infiltration within the textile promotes durability and resistance to degradation through wash cycles. Most existing studies of fluid infiltration into textile substrates have investigated large scale fluid infiltration, e.g. water wicking in garments or polymer infiltration during composite fabrication. Consequently, most modelling approaches are based on homogenised approximations to the real pore structure in textiles, typically using Darcy’s law or the Washburn equation, which cannot capture the complex fibre architecture in a typical textile. This is of particular concern with inkjet printing where a typical drop has a length scale comparable with the warp and weft of a fabric.
The behaviour of drops of a nanoparticle silver ink deposited by inkjet printing on woven textile has been observed using 2- 3-dimensional imaging techniques. Computed X-ray microtomography has been used to characterise ink transport through the fabric fibre architecture illustrating the influence of the warp and weft. Detailed surface structure of the fabric and the distribution of nanoparticles on the textile surface after printing and heat treatment has been studied by SEM including 3-D reconstructions from sequential sliced images. The porosity within a tow of fibres (yarn) plays an important role in controlling ink spreading and penetration. This is shown to be more important than the larger scale inter-tow porosity governed by the weave. The importance of the fibre surface properties in controlling ink behaviour is further demonstrated through ae comparative study of the interaction of a nanoparticle silver ink with cotton and polyester textile surfaces. The more hydrophilic cotton fabric shows greater spreading and infiltration of the ink than is observed with the polyester materials. Further hydrophobic chemical treatment of the fabrics using commercial water repellent finishes reduces the fabric surface tension, leading to reduced ink spreading and smoother ink deposition on the surface with higher areal ink concentration and improved electrical conductivity. Fibre architecture is shown to influence ink penetration and spreading in the longitudinal and transverse directions of a fibre tow with tighter fibre structures inducing lower levels of spreading.