Dynamic Surface Tension Measurement in Liquid Curtain Coating Systems
Dynamic surface tension at millisecond surface ages dictates liquid curtain stability and dynamic wetting limits in paperboard coating operations.
Surface Age
Interface Evolution
Time-dependent states of a freshly created or treated surface describe how its energy and chemical composition change before it is further processed. The surface age is the interval between the moment a substrate is extruded or treated and the moment a coating or ink is applied. During this period, surfactant molecules migrate from the bulk of the material to the surface, which can significantly alter its bonding characteristics.
Surfactant Migration
Additives within a polymer film or a coating slip move toward the air-interface to reach a state of lower energy. This process is not instantaneous and can take anywhere from a few milliseconds to several days to reach equilibrium. If a surface is too young, it may have a high energy that promotes wetting, but this energy can drop as more surfactants accumulate.
Understanding this timing is necessary for optimizing the adhesion of laminated structures.
Bonding Capability
Variations in the age of the substrate at the point of application lead to inconsistent print quality and bond strength. Production lines are designed to minimize the delay between corona treatment and coating to capture the surface in its most active state. In some cases, a surface must be allowed to age to a specific point to ensure that the chemical reactions are complete.
Monitoring the history of a roll of material is a standard part of the converting process.