Underfilm

Underfilm refers to a foundational or sublayer film applied to a substrate beneath a visible or top decorative or functional film in a multilayer structure. It is used to alter surface properties, enhance adhesion, provide barrier performance, or modify optical or mechanical characteristics. The term is used across industries and can denote different implementations depending on context.

Materials and structure: Underfilms are typically polymeric films such as PET, polyethylene (PE), polypropylene (PP), or polyimide, often combined with an adhesive or tie layer. They may also be functional layers with barrier properties (oxygen/moisture), dielectric properties, or thermal stability. The specific formulation depends on the required interface with the substrate and the top film.

Applications: In packaging, underfilms serve as sealant layers, adhesion promoters, or barrier layers between the substrate and top film. In electronics and photovoltaics, underfilms act as dielectric or protective layers beneath printed or deposited films. In architectural and automotive films, they can provide surface energy modification, adhesion promotion, and mechanical durability.

Manufacturing and processing: Underfilms are applied by extrusion coating, laminating, or coating processes, sometimes in combination with vacuum deposition for barrier or dielectric functions. The interface quality—adhesion, moisture resistance, and thermal compatibility—determines overall performance.

Quality and challenges: Common issues include delamination at the underfilm/top-film interface, moisture ingress, differential thermal expansion, and compatibility with inks or coatings applied to the top film. Proper material selection, surface treatment, and testing (peel strength, barrier performance) are essential.