Printing Qualities on Inkjet-Printed Paper from Varnish Coating Agent with Rice Husk Silica Particles

To enhance printing qualities, this study used refluxed silica (SiO₂) from rice husk by hydrochloric acid (HCl) at different molarities and reaction times as coating agent for printed paper. Characterization of the refluxed silica from 2M HCl 120 min elucidated the purity of 98.7% and amorphous structure. Particle size of the silica exhibited uniform size of 3 μm and the color measurement (CIE L*a*b*) indicated 94.79+0.48+1.24, whiteness and color difference (E) were 84.85, 3.28, respectively. The coating agent was prepared by water-based varnish of acrylic resin mixed with the synthesized silica at different proportions: 0.0, 0.5, 1.0, and 1.5 (%wt), and later was applied on 170 g/m²-white kraft papers. The results showed that the water-based coating varnish with silica exhibited an increase of viscosity as increasing the amount of the silica. Printing qualities indicated that the vanished printed paper with 1.0% silica elucidated the highest details in shadow tone and text (font) sharpness. The color gamut yielded a wider scope than the printed papers which were varnished with the silica at 0.0%, 0.5% and 1.5%. Nonetheless, the color density showed insignificant difference to 1.5% silica varnished paper.