Shock absorption of semi-interpenetrating network acrylic pressure-sensitive adhesive for mobile display impact resistance

Abstract

With the development of mobile display shapes from flat to flexible, the conventional glass cover window must be replaced by a film-type window. However, film-type cover windows have low impact resistance owing to their poor shock absorption. Therefore, to realize their application to flexible displays, it is essential to characterize and improve the shock-absorbing characteristics of the display film. In this study, a semi-interpenetrating network (semi-IPN) acrylic pressure-sensitive adhesive (PSA) consisting of a crosslinked network structure with a linear acrylic polymer chain was developed. The influence of the multi-functional monomer content and UV dose on the properties of the semi-IPN PSA was studied. The peel strength of the semi-IPN PSA was higher than 10 N/25 mm, which is generally considered as the PSA standard for mobile displays. With an increase in crosslink density, the storage modulus increased, but the damping factor decreased. To evaluate shock absorption, a falling ball impact tester was used to estimate the shock absorption ratio (ΔF) of the film. The semi-IPN PSA incorporating 30 phr of the multi-functional monomer exhibited higher ΔF (31.2%) than that of a conventional UV-curable PSA film (24.6%). This shows that even with the relatively low damping factor of the semi-IPN PSA, its structure could improve shock absorption. Moreover, we suggested two mechanisms for shock absorption of the semi-IPN PSA, energy dissipation into the PSA layer and extended contact time.