Meaning
Migration of slip additive molecules from the polymer matrix to the surface of a moulded part or film to reduce friction. Polymer processors use these additives to prevent films from sticking together and to assist part ejection. This surface modification is dynamic and time-dependent.
Coefficient Reduction
This process occurs because the additive is partially incompatible with the host polymer, causing it to diffuse out of the bulk material. Once on the surface, the molecules form a microscopic lubrication layer that lowers the coefficient of friction. Moulders can control this by adjusting the concentration of erucamide blooming in the formulation.
Adhesion Interference
Excessive migration can cause issues during downstream processes like printing, painting, or adhesive bonding. If the surface layer of slip additive is too thick, inks and glues cannot adhere to the plastic part. Engineers must carefully time these finishing processes to occur before the migration has run to completion.
Thermal Stability
Processing temperatures play a critical role in the rate and extent of this migration. High temperatures accelerate the diffusion of slip molecules, while cold storage conditions slow the process. Sourcing and moulding teams must select the appropriate slip grade depending on the expected storage and transport temperatures.
This choice helps prevent issues like film blocking or adhesion failure.
