Investigation On Colloidal Properties And Inkjet Performance Of Waterbased Pigment Red 122 Dispersion

Inkjet printing using pigment ink was used widely in digital textile printing due to its simple process, flexibility and environment-friendly. Water based pigment ink is a mixture based on ultrafine pigment dispersion. The study for the colloidal dispersion is obviously important in application of this technology.First of all, the influence of pH, electrolytes, organic solvents and surfactants on the interface structure of ultrafine pigment red 122 dispersant stabilized by polymer of PSMA was investigated using electrophoresis, particle size analysis and stability tests. The mechanisms of these factors on the shear rheological properties and wetting ability of dispersion were discussed from the point of view of solid-liquid interface. Finally, high-speed CCD technology was used to examine the effects of viscosity, surface tension and solids particles on the drop formation under the conditions of low Reynolds number, and inkjet performance at different pulse frequencies.The results are listed as follows:(1) The electrophoresis mobility and zeta potential increased with increasing pH of dispersion, but decreased when pH of dispersion was greater than 10.45. When pH of dispersion is less than 3, the dispersion appeared precipitation at room temperature. In the range of 3.39 10.45, the dispersions keep stable at room temperature and 60 degree after 24 hours placement. When pH is 7, the zeta potential decreased with increasing electrolyte concentration, caused the deteriorated stability of dispersion.(2) In the selected solvent, ethanol has the worst effect on particle size distribution. The electrophoretic mobility decreased with increasing the number of hydroxyl and length of hydrophobic chain. The analysis by the solubility parameter theory showed the change of hydrogen bond force is the main factor leading to the decline in stability of dispersion.(3) The thickness of adsorbed polymer layer decreased with the increase of the ethanol concentration, and then the pigment particles aggregated when the concentration of ethanol is higher than 40%. The zeta potentials became more negative with the increasing of the ethanol concentration, and then changed reversely when the ethanol concentration was higher than 16%. The thickness and structure of adsorbed polymer layer on the particle determined the stability of pigment dispersion.(4) When the concentration was low, the anionic surfactant was adsorbed onto pigment with the polymer of PSMA to increase the negative charge, which resulted in greater zeta potential. While the concentration of anionic surfactant was high enough to form micelles, a larger peak appear in the zeta potential distribution curve. Non-ionic surfactant S465 reduces the electrophoretic mobility of particles. (5) The dispersion take on shear thickening under high-shear rate region, that is, shear viscosity increase with increasing shear rate. In the region of Newtonian fluid, the relationship between shear viscosity and solids concentration of dispersion accord with the function ofη= 0.19exp (17.02φ), which showed that the attraction between particles increased when the solid concentration increased. The max packing solids concentration calculated by Dabak model is 0.38 rather than 0.625 by Brown hard-sphere model.(6) The viscosity of dispersion decreased as pH of dispersion increased. pH of dispersion have an obvious effects under low shear rate while little effect took place under low shear viscosity. With increasing electrolyte concentration, the shear viscosity under low shear rate (0 10 s^-1) increased. With the temperature increasing, the viscosity decreased in a linear relation. Temperature had a great impact under low shear rate than higher shear rate. The critical shear rate for set of thickening was related to the viscosity in the Newtonian region, and increased linearly with increasing Newtonian viscosity.(7) Diethylene glycol ether with the group of -C4H9 had the strongest ability to reduce surface tension of the dispersion. The aqueous solution can spray out completely on the glass and stainless steel sheets. Diethylene glycol ether had good cooperating effect with the surfactants on wetting the surface of solid.(8) Drop formation can be divided into two stages, the largest drop formation and the drop breakup. The first stage affected mainly by surface tension and inertial force while the viscosity had a greater influence on the drop breakup process. The viscosity of fluid had a negative side effect on the constriction of neck, caused shorter time of drop breakup and satellite droplets. The solid particles shorten the times of drop formation and drop breakup.(9)The inkjet performance affected by surface tension, viscosity solvent and pigment particles under high jet frequency (2¹5 KHz) was investigated using high speed CCD. Experimental results showed that the droplet velocity were stable in 2¹0 KHz frequency region, and fluctuated in 10¹5 KHz frequency region. The fluctuations were affected by the solvent. The particles (pigment and latex particles) will cause reduced droplet velocity.The main contribution of the paper is in investigation on mechanism of solvent interacting with the adsorbed polymer on pigment and the influnce of solvent on the inkjet behavior of fluid. The velocity of droplet at different frequencies and stability of inkjet is strongly affected by the components of solvent.