Development of an inkjet ink to produce touch sensing surfaces

A touch sensing material called QTC is currently produced by Peratech Ltd. The material is a composite with conducting particles in a polymer matrix. When a pressure is applied to the composite the conductivity rises sharply. By using this property, the QTC surface can tell where and how much pressure is applied onto a surface. QTC can be used as a 3D touch screens, sensing robot hand and so on. Currently QTC surfaces are produced by screen printing which is a costly technique due to the batch wise, slow and non automated process and also due to its high waste of ink. Another method of printing conductive surfaces or pattern is inkjet printing. It is a digitally controlled deposition of ink droplets and the jetted pattern can be easily controlled by the printer software. Inkjet printing gives no or low waste and can print several inks simultaneously. The inkjet ink, compared to the screen printing paste, has to be low viscous and has to contain small particle sizes and no aggregates to avoid blocking the print head. The dispersion of particles in the inkjet ink is therefore of great importance. In this work two types of conductive particles were used, so called K2 and K1. K2 is currently used in the QTC screen printing paste. K1 particles are slightly smaller but of the same type. The particle size of K2 had to be reduced to be inkjet printable and it was done with a bead mill. The products, though, did not meet the requirements for inkjet printing. The smaller K1 particles were mixed with binder, dispersing agents and additives and were then bead milled. Before printing, the inks were filtered and characterized, to make sure that they met the requirements for viscosity, surface tension and particles sizes. The printing was done with two printers, HP Deskjet 5650 and Printos P16 Digital Textile Printer and the experiments showed that the Printos printer was suited to print this ink. The touch sensing property of the printed surfaces was investigated by measuring the conductivity of the surfaces when different pressures were applied. Experiments showed that the touch sensing property could be controlled by changing the amount of binder in the ink. The developed ink could be successfully inkjet printed and was highly touch sensing.Validerat; 20101217 (root