Enhanced interfacial bonding properties of flexible PET-AR&AF optical films by Si transition layer in roll-to-roll manufacture

Driven by the ever-increasing demand for curved, rollable, foldable, and stretchable displays, flexible and transparent cover window films using in curvature design have become an urgent need. Besides, the integration of other composite functional films (e.g., anti-reflective and anti-fingerprint) on the cover window film can be further realized through the development of commercial roll-to-roll (R2R) coating process. However, the widespread implementation of these optical films on a large scale is impeded by the challenges of poor durability. Here, we prepared anti-reflection & anti-fingerprint (AR&AF) cover window optical films on flexible polyethylene terephthalate with hard coating (PET-HC) substrates by introducing Si transition layers using high vacuum roll-to-roll sputtering with organic evaporation module. Compared to the original PET-HC-AR&AF films, the introduction of the Si transition layer can effectively improve the bonding properties of the film-substrate interface, while the optical properties are changed massively as the Si transition layer thickness increases. The balanced optical and mechanical properties are obtained via depositing ultra-thin 1 nm Si transition layer. Average reflectance and transmittance of 0.28 % and 95.1 % are observed in the wavelength of 420–680 nm. The vertical tensile testing shows that the film-substrate bonding strength increases by more than 29 % compared to PET-HC-AR&AF without Si transition layer pretreatment. Meanwhile, the number of surface scratches is sharply reduced after 3000 cycles of the steel-wool abrasion test and the water contact angle (WCA) is still over 90°. Due to the enhanced bonding strength between the organic substrate and the inorganic film material, roll-to-roll commercial-scale manufacturing process is available, which is essential for achieving cover window films for the next generation of flexible or foldable displays with high-performance and good mechanical properties.