Quantifying Surface Energy Values on Polyolefin Packaging Materials
Polyolefin surface energy quantification relies on standardized liquid titration or goniometry to secure ink adhesion and lamination bond strength across runs.
Oleamide Blooming
Slip Agent
Progressive accumulation of slip additives on the surface of a polypropylene film reduces drag during high-speed packaging and converting operations. This specific behavior, known as oleamide blooming, involves the migration of a fatty acid amide from the interior of the plastic to the exterior interface. Oleamide is chosen for its ability to reach the surface quickly after extrusion, providing an almost immediate reduction in friction.
This is essential for films that are converted shortly after manufacture. Once the molecules reach the surface, they form a thin, lubricating layer that allows the film to slide over metal parts without sticking. This prevents the build-up of static and reduces the risk of the film tearing or jamming in the machine.
Friction Control
Managing the amount of additive that reaches the surface is a delicate balance for film producers. During oleamide blooming, the concentration of the chemical increases until it covers the entire surface of the material. This layer is what determines the coefficient of friction, which is a measure of how easily the film slides against itself or other surfaces.
If the bloom is too heavy, the film may become too slippery to be wound properly on a core. This can lead to rolls that are telescoping or unstable during shipping. Conversely, if the migration is too slow, the film will be tacky and difficult to process.
The speed of the blooming depends on the temperature of the storage environment and the thickness of the film. Higher temperatures accelerate the movement of the molecules through the polymer matrix. This means that a film produced in the winter may behave differently than one produced in the summer.
Engineers must adjust the formulation to ensure that the friction levels remain consistent throughout the year. Testing the coefficient of friction at different stages of storage helps to map the blooming curve for each specific product.
Coating Interaction
Interaction between the slip layer and subsequent coatings is the most common source of trouble for converters. While oleamide blooming is beneficial for handling, the resulting wax-like surface can be very difficult to print on or laminate. The amide molecules can block the reactive sites created by corona treatment, leading to poor ink adhesion or low lamination bond strength.
This is particularly problematic if the film is stored for a long time, as the layer continues to thicken. In some cases, the ink may seem to bond initially but will then fail a tape test after a few days as more amide migrates under the ink layer. Selection of the correct ink system or the use of a primer can help to overcome these issues.
Some converters prefer erucamide for its slower blooming characteristics, which allows more time for the printing process to take place. Monitoring the surface energy and performing regular adhesion tests are the only ways to ensure that the bloom does not compromise the final product. The presence of the additive must be accounted for in every step of the design and production process.
Thermodynamic Wetting and Surface Free Energy in Polyolefin Lamination
Thermodynamic wetting in polyolefin lamination demands substrate polar surface energy above 6.0 mN/m to achieve complete adhesive spreading and bond durability.