Low viscosity polyurethane acrylate dispersions

摘要

Radiation curable polyurethane dispersions (UV-PUDs) suffer from viscosity problems in manufacture. Regardless of the process used, it is often found that UV-PUDs hydrolysed via hydroxycarboxylic acids, that are potentially ionic groups, exhibit an increase in viscosity immediately after synthesis. The higher is the initial viscosity of the dispersion, the greater is the fall in viscosity over the following few weeks. It has been found that UV-PUDs hydrolysed in this patent have a lower initial viscosity, if a large part of the urethanisation initially takes place in the absence of acid-carrying compounds. These acid-carrying compounds can be added at a later stage in the reaction process.