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

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 (Delta F) of the film. The semi-IPN PSA incorporating 30 phr of the multi-functional monomer exhibited higher Delta F (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 semiIPN 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.