Meaning
Time-dependent diffusion of a fatty acid amide slip agent from the bulk polymer to the surface of a moulded part or film reduces the coefficient of friction. This physical process, known as erucamide migration, occurs because the additive is partially incompatible with the polyolefin matrix at room temperature. As the slip agent accumulates at the polymer-air interface, it forms a thin microscopic layer that facilitates sliding and prevents blockiness.
However, this surface layer can interfere with subsequent processing steps such as printing, adhesive bonding, or metallization, which can cause laminates to delaminate under stress.
Diffusion Rate
Concentration gradient and ambient temperature govern the speed at which the additive moves through the solid polymer. In polypropylene or polyethylene films, erucamide migration proceeds over several days before reaching a stable equilibrium. Higher temperatures accelerate this diffusion, meaning that rolls stored in warm warehouses may develop high surface concentrations much faster than those stored in cool conditions.
Surface Effects
Excess accumulation of the slip agent can lead to cosmetic issues or adhesion failures on the final product. When the migrated layer becomes too thick, it appears as a hazy residue or bloom on the polymer surface. This deposit impairs the adhesion of printing inks and laminated layers, requiring the converter to corona-treat the surface or source a resin with a lower slip agent content.
Friction Reduction
Moulded components require a controlled coefficient of friction to function correctly in automated assembly lines. While erucamide migration ensures smooth part ejection and low sliding resistance, the level of slip must be balanced to avoid part slippage in conveyor belts. The moulder must monitor the surface friction over time to confirm that the additive does not exceed the allowed limits.
