mist

In printing, to mist means to atomize ink into fine droplets during high-speed operation, usually as an unintended consequence rather than a desired outcome. This occurs when ink encounters air resistance as it travels from the supply system toward the press rollers or substrate. At speeds above roughly 300 metres per minute on web presses, the shear forces become strong enough to break ink into a visible haze or fog that coats nearby press components and the surrounding air.

Misting happens most readily with inks that have lower viscosity or poor adhesion properties. Thin, runny inks and those formulated for fast drying are particularly prone to atomization. The phenomenon is worse on presses with high line speeds, wide web widths, and in conditions where humidity is low, because dry air provides less resistance to droplet formation. Offset lithography and flexographic printing see more misting than gravure, where the ink transfer mechanism is more controlled.

Misting creates several practical headaches. Ink fog settles on impression cylinders, guide rollers, and drive components, building up as a sticky residue that attracts dust and can eventually affect print quality or cause slippage. The dispersed ink also represents material loss and creates air quality concerns in the pressroom. Beyond the equipment, mist deposits on printed sheets and finished rolls, contaminating edges and causing page adhesion problems in bound work.

Pressrooms reduce misting through several routes: increasing ink viscosity (within the limits of print quality), reducing line speed when possible, improving ventilation to break up atomized particles, and using mist suppressants or anti-misting sprays applied to the ink film. Some newer presses include dedicated mist management systems with extraction ports positioned near high-risk zones. Ink suppliers have developed formulations with better cohesion to resist atomization at high speeds.

The term itself is descriptive, drawn directly from the visible fog that forms. Unlike technical jargon that abstracts the phenomenon, mist is what operators actually see and complain about. It remains a practical constraint on press productivity and a reason why ink properties must be matched carefully to specific press speeds and substrate types.