Substrate Protection
Chemical formulations applied to paperboard or paper substrates restrict the migration of moisture, grease, oxygen, or mineral oil hydrocarbons through the packaging wall. Mill operations apply barrier coatings during wet-end converting or off-line dispersion processes to create continuous films over cellulose fibres. Measurement relies on water vapour transmission rates measured under ISO 15106 standard conditions and oil resistance evaluations.
Functional limits exist where microscopic pinholes or flex cracking during die-cutting disrupt layer continuity.
Application Mechanism
Blade coaters and rod coaters distribute aqueous polymer dispersions or bio-based wax emulsions onto the raw paper stock. Film formation depends on water evaporation and heat-induced polymer particle coalescence within drying tunnels. Standard base papers require uniform surface smoothness and controlled porosity to prevent excessive strike-through into the fibre network.
When coat weights fall below prescribed dry targets, pinhole defects open channels for gas transfer. Higher coat weights increase resistance but risk surface cracking during fold scoring. Substrate stiffness and moisture content influence coating adhesion during high-speed converting runs.
Performance Limit
Recyclability assessments under Cepi guidelines restrict synthetic polymer additions to defined mass percentages. Substrates treated with high-density polyolefin emulsions require modified repulping protocols to separate synthetic fragments from reusable wood pulp. Plasticizer migration into dry food products remains zero under standardized food contact migration testing.
