Comparative study of the relationship between structure and rheology properties of UV-curable reactive diluent monomers

The rheological properties of several diluent monomer acrylates such as viscosity and thixotropy have been measured and related to their chemical structure and functionality. These are, in turn, related to their misting characteristics in a reference offset lithographic ink. Thixotropic measurements showed that higher tetrafunctional acrylates DITMPTA and PPTTA have lower thixotropy than the other acrylates examined. On the other hand, low functionality acrylates such as DPGDA, TPGDA and Actilane 421 showed higher thixotropy than the higher functionality acrylates such as GPTA and OTA 480. These results indicate that there is a direct relationship between thixotropy and molecular weight, functionality and branching of the molecules. Highly branched molecules may interact physically by intermolecular interpenetration. These interpenetrating structures may maintain their interaction even at high shear conditions. The difunctional acrylates exhibit higher thixotropy due to their lower intermolecular interaction resulting from their linear structure. These processes have important implications when preparing and formulating UV-curable lithographic inks.