Water‐based inks and coatings require alcohols and surfactants to lower their surface tensions to acceptable levels, but have inherent problems of surface wetting, foaming, flow and levelling common to water‐based systems. They are formulated quite differently from solvent‐based systems, which wet readily and transfer well on to most ink train materials. Surfactants used in water‐based systems tend to be highly surface‐active and can vary significantly with concentration and speed of diffusion depending on the surfactant type and molecular weight and structure compared with inherently low surface tension alcohols. A coating process is dynamic and, because active surfactants are utilized, surface tension will vary as application and press speed vary. It is the resulting variation in the speed of diffusion of the surfactant molecules that directly impacts on the quality of spreading and adhesion. Ink and coatings formulators must have knowledge of the principles of dynamic surface tension, and have instruments that can measure surface tension characteristics. Instruments must be simple to use, accurate, and as automatic as possible, to allow formulators to spend a minimum amount of time gathering necessary data.
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