Preparation of pigmented inkjet ink for six-color printing on silk fabric

This research prepared five sets of pigmented inkjet inks and pretreated the silk fabric with chitosan, glycine and N-[(2-hydroxyl-3-trimethylammonium) propyl] chitosan chloride (HTACC) to enhance print quality. The six pigmented inkjet inks comprising black (Bk), cyan (C), magenta (M), yellow (Y), light cyan (LtC) and light magenta (LtM) colors were prepared with surface-modified pigments and a pigment-to-binder ratio of 1:2. The binder was the copolymer of styrene-acrylic acid emulsion. Different ratios of diethylene glycol and glycerol for verifying the ink viscosity, surface tension with jettability were investigated. The prepared inks had pH in the range of 6.7-8.8, zeta-potential in the range from (-35) to (-50) mV, the pigment particle sizes in the range of 100-300 nm, surface tension in the range of 39 – 46 mN m-1. The black inks prepared by the pigment-to-binder ratios of 1:0, 1:0.5, 1:1, 1:1.5 and 1:2 exhibited both the Newtonian flow at low shear rates (21-142 s-1) and non-Newtonian flow at high shear rates (180-741 s-1). The ink formulation 5 with a pigment-to-binder ratio of 1:2 which was in the jettable range on a viscosity-surface tension criteria map had the viscosity in a range of 2.78 – 3.44 mPa s which jetted the printing pattern completely. The ink formulation 5 was thus best suited for printing with an Epson piezoelectric type inkjet printer. The silk fabric pretreated with chitosan, HTACC, and mixed chitosan and glycine was then each printed with the ink formulation 5. The printed silk fabrics were analyzed for color gamut and color saturation, stiffness, light and wash fastnesses. The printed silk fabrics exhibited that the color gamut and color saturation of the pretreated fabrics provided a wider color gamut than the printed colors on the untreated fabrics. The mixed chitosan and glycine, and HTACC pretreatments enhanced markedly the chroma while the color strength of the fabrics with HTACC pretreatments increased most. The pretreated silk fabrics by chitosan or HTACC did not increase the fabrics stiffness. The light fastness of the pretreated fabrics did not change from the untreated ones, although the wash fastness increased from 4 to 4-5. The extent of coagulation efficiency between the pretreatment reagents and inks was investigated by UV-visible spectroscopy from which HTACC can exhibit strong interaction with the pigments in the inks.