Determination of Surface Properties of Films for Packaging

The article presents a comprehensive study of the surface properties of polymer films used in flexible packaging, with emphasis on their suitability for forming stable ink layers under flexographic printing conditions. The growing use of polymer substrates with insufficient surface energy makes the topic highly relevant, as achieving reliable adhesion between the ink and film surface remains a technological challenge. The aim of the research was to assess the wettability and adhesion potential of commercial polypropylene (PP) and polyethylene terephthalate (PET) films with different surface characteristics by evaluating the kinetics and equilibrium values of the contact angle. The methodology was based on image analysis of droplets of distilled water, ethylene glycol, and UV­flexographic ink with automated calculation of contact angle parameters to obtain quantitative indicators of interfacial interactions.
The results demonstrate a clear differentiation of the examined materials according to their surface energy and ability to interact with liquid systems. Glossy PP and PET films (20 μm) showed the lowest equilibrium contact angles and rapid stabilization of the three­phase boundary, indicating favorable conditions for uniform ink transfer and reliable formation of printing elements. Glossy PP (35 μm) exhibited intermediate behavior, allowing its effective use in production if surface activation parameters are properly controlled. Matte PP (40 μm) demonstrated high equilibrium contact angles and pronounced hysteresis, confirming the presence of energetically heterogeneous surface areas and the need for prior corona or plasma treatment to ensure adequate adhesion.
The practical value of the study lies in providing scientifically justified criteria for selecting polymer substrates for high­quality flexible packaging. The findings contribute to a more rational choice of materials and improved process stability in modern flexographic printing systems.