Meaning
Chemical compounding agents incorporated into polymer resins migrate to the surface to reduce the coefficient of friction of the finished plastic. Plastic film extruders and injection moulders use slip additives to prevent polyethylene or polypropylene products from sticking to each other or to the metal surfaces of processing machinery. This surface modification occurs as the fatty acid amides crystallize and bloom to the exterior of the cooled part.
Migration Mechanism
Internal additives like erucamide or oleamide dissolve in the hot polymer melt during extrusion or moulding. As the plastic cools and solidifies, these molecules become incompatible with the polymer matrix and slowly migrate to the surface. This blooming process creates a microscopic lubricating layer that lowers the friction of the part.
The speed of this migration depends on the temperature of the polymer and the specific crystal structure of the base polyolefin.
Processing Benefit
Low surface friction prevents thin plastic films from sticking together when wound onto large rolls. In injection moulding, these additives assist in ejecting deep-draw parts from the steel core of the tool without causing surface scratches. This smooth release reduces cycle times and prevents part deformation during the ejection phase.
Secondary Consequence
Excess concentration of these lubricating agents can interfere with secondary operations such as printing, adhesive bonding or metallization. The oily surface layer prevents inks and coatings from adhering properly to the plastic. Careful monitoring of additive levels is necessary to avoid these downstream assembly failures.
