University of Minho,
Keywords: hybrid nanopigments, ink-jet, digital printing textiles
Summary:Ink-jet printing on textiles can be done of two forms, either with pigments or with dyes. Pigments are of universal application to all fibers. Dyes are specific to each different fiber. In the case of cotton and other cellulosic fibres, the dyes used are reactive dyes and in the case of polyamide, for example they are acid dyes. Polyester is printed with disperse dyes. The nanopigments we developed t at the university together with Ecofoot, a spin-off company founded in 2012 with the present researchers the University, are hybrid nanopigments, made up of an inorganic particle, amourphous silica, and a reactive dye. The combined properties of both of these elements give it unique properties. After a one and a half year project of development for a machine manufacturer of the 4 CMYK colors , cyan, magenta, yellow and black, they tested in their digital printing machine for garments, DGT, and the results show that these pigments can replace present used pigments to obtain fast and bright colors. The initial usual problems of blocking were overtaken and the fixation was improved throughout the project so as to obtain equivalent results in terms of fastness as the best commercial pigments in the market The fastness to multiple washing is even better. For fixation binders were introduced into the printing ink, and the formulation include the products used in such formulations, to ensure a smooth run in the machine, so that the ink does not dry quickly on the printing head but dries on the textile. This last point is relevant so that the ink does not spread and has well marked boundaries. The ink with hybrid nanopigments can also be used as a reactive dye on cellulosic fibres, only needing to change the process. Instead of a binder, the usual continuous washing-off procedure of the excess dye is applied after the printing The advantage is that with the hybrid nanopigments, the washing-off is easier and instead of the temperature at 100ºC a lower temperature of 60ºC can be used to extract the dye in the soaping stage of the process. This will economize energy and emissions of CO2. The hybrid pigments have proven in an industrial environment to be equivalent in quality to the best commercial pigments, and other attributes can be appreciated such as brighter colors than pigments and better handle than most pigments in the market.