Enhancement of flexographic print quality on bleached kraft liner using nano-silica from rice husk

Nano-silica from rice husk (nano-RHS) was synthesized and used in a coating agent to enhance the flexographic print quality of bleached kraft liner. The rice husk was refluxed with a 2 M HCl solution and calcined in a muffle furnace at 650 °C for 4 h. The particle size of the resultant rice husk ash was reduced to a very fine nano-RHS by hexadecyl trimethyl ammonium bromide. The synthesized nano-RHS in different proportions - 1%, 2%, 3%, 4% and 5% (w/wresin) - was added to a water-based coating agent consisting of acrylic resin. The coating agent with nano-RHS additive was applied by gravure rolling onto the surface of a 170 g/m2 bleached kraft liner 3-4 μm in thickness. The flexographic print quality was determined with printing details of 31.5 lpc using water-based process colors. The results indicated that the coating agent with 1% nano-RHS was the most promising for improving the flexographic print quality on the bleached kraft liner. At this fraction, the best print quality in terms of high sharpness of fonts and texts, line art, realistic image, and TVI curve (under the requirements of ISO 12647-6) were achieved. In addition, low tone-value and ΔE*abwith a large, three-dimensional color profile and the widest color gamut were obtained.