Pigment inks have the potential to have a big future in digital textile printing, especially when it comes to environmental aspects and process simplification. One major key difference between dye and pigment ink is that the pigment is insoluble to water while dye is soluble. Another benefit of using pigment inks in digital textile printing is the ease and has a quick time process. Pigment inks for digital textile printing have a great chance to prevail in the market for special material applications but also for the commonly used textile fibers when needing to save energy and water consumption.
2.2 Pigment versus reactive printing
Fig. 2 schematically shows the process of printing with pigment inks compared to reactive inks. Due to their chemical characteristics, reactive dyes have to be bonded to the textile fibre after printing. Therefore, a steaming process of 8-12 minutes at 102°C (saturated steam) is necessary. Subsequently, the unbound dye has to be removed in a complex washing process (after treatment) at different temperatures ranging from about 50°C to 98°C, with soaping agent to 60°C, and finally 30°C (slightly acid). Then the printed textile has to be dried.
In comparison, the pigment printing process does not need the complex steaming and washing steps. Since the pigment dye is printed only on the top layer of the fabric without any chemical bonding, the textile fabric has to be condensed at 150-170°C for a few minutes to fix the pigments. Consequently, the pigment printing process requires significantly less water due to the omitted washing step. This may be a crucial deciding factor when deciding on whether to use digital pigment printing in the future.
Nevertheless, an additional point has to be mentioned regarding the printing process with pigment inks.
Due to the insolubility of the pigment particles, the sedimentation of them could result in problems of nozzle clogging in the fine nozzles of inkjet printing machines. Therefore, to overcome this, two things should be noted: firstly, all the inks have to be well stirred before using and secondly, the necessity of a print head with a circulating system becomes more and more important. The circulation provides a kind of continuous flow that avoids sedimentation and thus clogging the nozzles. In particular, the white pigment inks mostly based on the inorganic compound titanium dioxide need those circulating systems.
