Most flexible packaging manufactured today is made of multilayer films that are composed of 3-12 layers. Each of these layers is typically bonded to the adjacent layer with a laminating adhesive or heat seal coating. Often times the films that make up these layers are made of low surface energy materials like polyolefins and polyesters. While these films offer many performance benefits that are critical for packaging films they can be notoriously difficult to adhere to. When film to film adhesion becomes a challenge, pre-treatment is necessary to ensure sufficient bonding.
Film Pretreatment
Plastic films like polyethylene, polypropylene, and PET often undergo oxidative pretreatment such as the corona plasma process during manufacturing. These oxidative processes do initially improve surface energy and make the film more accepting of coatings and adhesives, but this increase in surface energy declines significantly after only a short time during storage. To ensure materials used in multilayer packaging films remain accepting of adhesives and coatings during storage a primer can be applied to the film.
Lupasol® P - The Ideal Primer for Packaging Films
Lupasol® P is a cationic polyethyleneimine with a branched polymer structure.
It is an incredibly effective adhesion promoter for multilayer packaging films manufactured by coating, laminating, extrusion coating, or coextrusion. The use of Lupasol® P in multilayer films allows for the combination of materials that improve the physical, chemical, and mechanical properties of the laminate.
Lupasol® P Properties
Property
Value
Avg. Molecular Weight
750,000
Brookfield Viscosity
25,000 cps
Solids
50%
pH
11
Charge Density
17
Pour Point
-3°C
Usage Recommendations
Lupasol® P should be diluted to 0.5-1.0% in water prior to use. Up to 30 wt% of an alcohol such as methanol, ethanol, or IPA can be added to reduce drying time and improve wettability. Addition of a nonionic surfactant at 0.5% is also recommended to improve wetting onto low surface energy materials. Lupasol® P primer solutions can be applied at a rate of 1-5 g per square meter using traditional coating methods including dip coating, or transfer roll. Once applied to the substrate, the Lupasol® P primer coating must be throughly dried prior to combination with other films. A warm stream of air can be used to accelerate drying time. Once dried the coated film can be rewound for storage or immediately combined with other films. Combination of the Lupasol® coated film with a topcoat should be carried out under heat (50-100°C) and pressure.
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