Formulation of drop on demand soy inkjet inks

Abstract

Soy protein has a complex 3-D shape and contains 19 different amino acids, which are held together in a coiled structure by peptide bonds. The basic application of industrial-grade soy protein is for a use as a binder in paper coatings. In this work, soy polymer Pro-Cote 4610E was used for formulation of drop on demand piezoelectric inkjet inks. Soy drop on demand inks performance was compared to ones of inks formulated with acrylic polymer Joncryl 678 and commercial inkjet ink. During formulation, sodium hydroxide was more successful in solubilizing of soy polymer than ammonium hydroxide. Preliminary soy ink formulations were made, and based on these results, a design of experiments (DOE) was carried out to optimize ink formulations. The DOE was executed with another aim to compare soy and acrylic based chemistry performance. A combination measure of ink density, surface tension and viscosity was used to assess inkjet printability. Drop behavior was controlled by Reynolds, Weber and Ohnesorge numbers. Reciprocal value of Ohnesorge number (Z number) was calculated, and used for prediction of soy protein inks and acrylic inks jettability. The print design for Dimatix Material Printer DMP-2800 consisted of solid patches and lines of varied width and orientation. At first, even inks with proper Z number were creating satellite drops and were puddling, which was removed by increasing the drop velocity from 0.2 m ∙ s⁻¹ to around 4 m ∙ s⁻¹. Thus, it was found that higher voltage is crucial for proper drop formation. The quality of printed lines was evaluated by measuring their width and raggedness using image analysis. Print mottle was evaluated on solid patches. All inks, soy, acrylic and commercial, exhibited printed line widths greater than their nominal widths, which was expected, due to printing on plain inkjet paper. There were no significant differences in quality of print lines between soy and acrylic inks and commercial ink. Soy ink achieved the best print uniformity of solids, when compared to formulated acrylic or commercial inkjet ink.