Surfactant Migration Impact on Dynamic Surface Tension in Hardwood Stock
Residual surfactant migration in hardwood stock depresses dynamic surface tension below forty millinewtons per meter, triggering jetting print defects.
Flexographic Ink Coalescence
Film Instability
Ink film instabilities on non-porous surfaces lead to the formation of clusters or beads before the drying process is complete. This flexographic ink coalescence creates a blotchy or mottled appearance in solid print areas as the liquid pulls away from the substrate. It typically occurs when the surface energy of the film or foil is too low to support a continuous layer of the applied ink.
Liquid Dynamics
High surface tension in water based inks often drives the fluid to minimize its surface area by forming droplets rather than a smooth film. When flexographic ink coalescence happens, the individual dots or lines of the image merge into irregular patches. This effect is exacerbated by slow drying conditions or an excessive volume of ink delivered by the anilox roller.
Surface Treatment
Treatment of the substrate surface through corona discharge or chemical primers helps to increase its receptivity and prevent the beads from forming. Printers also modify the ink chemistry by adding alcohols or specialized surfactants to promote better wetting and faster evaporation. Maintaining the correct balance between the drying speed and the fluid flow is necessary to eliminate flexographic ink coalescence in high quality packaging graphics.
Precise control of the surface tension differential between the ink and the substrate ensures a uniform print.