Optimization of water-based ink formulation based on different NCO : OH ratios of polyurethane dispersion

Due to environmental concerns presently water-based inks are in demand in packaging and label printing, when the application is on paper and paperboard. But these inks are found to be incompatible while printing on a non-porous substrate like the films of polyethylene and polypropylene which are majorly used in the packaging industry for printing. Adhesion as well as optical properties (gloss) of water-based ink deposited onto the polymer film substrate are critical in flexible packaging. Hence the objective is to optimize water-based ink formulation for specific type of binder, its percentage, and percentage of other ingredients such as surfactant and polymer emulsion to achieve the complete adhesion and maximum gloss, which is utmost important for the growth of the water-based ink market in flexible packaging. The design of experiments (mixture model) was conducted to formulate water-based inks by varying the percentages of pigment-binder ratio (resin percentage), surface wetting agent, and polyethylene-based polymer emulsion. Scotch tape qualitative test method was used to measure the adhesion of ink. Adhesion percentage was calculated by analysing the area of ink which remained intact on the substrate. Data was analysed by using the multivariate data analysis method. This model was used to optimize the formulation for complete adhesion of water-based ink on the film substrate. The model explains that complete adhesion of water-based ink on polyethylene substrate takes place at 35.24 % of resin (1:1.5 pigment-binder ratio), 1 % of polymer emulsion, and 0.3 % of surfactant. Complete adhesion is observed for 1.35 and 1.4 NCO : OH ratios of polyurethane dispersion. Response surface design was used to find out the effect of binder and surfactant on the gloss of ink. The response surface model explains that surface tension is the dominant parameter for improving the gloss of ink on the substrate. Maximum 80.5 % gloss was observed for higher means at 1.4 NCO : OH ratio of binder and when 0.3 % of substrate wetting agent was used.