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.
Surface Energy Heterogeneity
Energetic Variation
Spatial variation in the attractive forces of a solid surface defines the uneven distribution of energy across a substrate. This surface energy heterogeneity appears as inconsistent wetting behavior where liquids spread easily in some zones while beading in others. It is a primary factor in the bonding of adhesives and the adhesion of printing inks to polymers and treated boards.
Chemical Origin
Contamination from process chemicals or variations in the crystalline structure of a coating can create these energetic differences. When a material exhibits surface energy heterogeneity, the contact angle of a liquid droplet will change depending on its location on the sheet. This lack of uniformity often stems from incomplete corona treatment or the migration of slip agents to the surface of a plastic film.
Diagnostic Procedure
Testing for this condition involves the use of dyne pens or contact angle goniometry across multiple points on the material. A high degree of surface energy heterogeneity leads to unpredictable results in the laminating station and may cause the finished product to delaminate under stress. Manufacturers must ensure that the cleaning and treatment processes are uniform to maintain a consistent surface for subsequent converting steps.
Consistent energy levels across the web prevent localized adhesion failure in the final package.