Development and scale‐up of thermoplastic poly(ether‐ester) glycol polyurethanes for flexography

This study presents an experimental essay on the production of thermoplastic polyurethanes for flexographic printing ink applications. Four formulations were obtained by step‐growth polymerization reactions having the pre‐polymer 4,4′‐diphenylmethylene diisocyanate and Voranol 2120 L® catalyzed by dibutyltin dilaurate as common ground. In the chain extension step, ethanol or ethyl acetate was used as solvent, and the use or not of castor oil as a chain extender in addition to hexanedioic acid and 2,2′‐oxydi(ethan‐1‐ol) was evaluated. The chemical structures of the synthesized thermoplastic polyurethanes (TPUs) were evaluated by Fourier transform infrared spectroscopy, 1H NMR, gel permeation chromatography, differential scanning calorimetry, and rheological features were assessed by density and viscosity analysis. The TPU resins were used to produce flexographic printing inks and further tested by friction, adhesion, gloss, and Gardner viscosity essays. It was found that the castor oil presence enhanced ink viscosity in 66% (from 26,790 to 44,440 Pa s) as well as improved strength. Formulations using ethanol as solvent showed the best results. The experiments were carried in a 250 ml reactor and then, scaled up to 2000 ml, keeping the power transfer per unit of volume constant at around 0.8 W/L. The analytical results from the larger scale were as good as the obtained in scale one, showing promising application. Four thermoplastic polyurethane resins were synthesized by step‐growth polymerization. The influence of different chain extenders was evaluated, of which, castor oil was successfully incorporated without promoting crosslinking reactions. The resins were produced with two solvents for comparison in terms of physical‐chemical interactions with raw materials. An increase of 8 times of the reacting volume was mathematically designed and ran. The formulated resins were used in the production of flexographic printing ink for packaging applications.