Physical Transport
Mass transfer processes in polymer and paper substrates involve the spontaneous movement of internal functional agents to the surface of a material. Additive migration describes this movement of low molecular weight substances like plasticizers, slip aids, or stabilizers from the interior bulk phase to the outer boundary of a packaging substrate. This redistribution alters the surface properties and can affect both printing and adhesion.
Driving Force
Concentration gradients and chemical incompatibilities within the polymer matrix propel these molecules outward over time. This process accelerates when storage temperatures rise, as thermal energy increases molecular motion and allows the mobile components to slip between polymer chains more easily. If the additive has limited solubility in the base resin, it naturally seeks a lower-energy state by accumulating at the boundary layer.
Performance Consequence
Surface contamination from these traveling molecules often prevents adhesives from wetting the substrate or disrupts ink adhesion. In flexible packaging applications, such chemical shifts can result in delamination or failed heat seals during high-speed filling operations. Selecting polymer grades with higher molecular weight additives or utilizing barrier coatings reduces this risk by physically blocking the molecular pathway.
The rate of this accumulation determines the shelf life of the untreated substrate before converting.
