Ultraviolet Light Blocking Optically Clear Adhesives for Foldable Displays via Highly Efficient Visible-Light Curing

Abstract

Abstract The design of a new foldable smartphone's organic light-emitting diode (OLED) panel, developed to reduce power consumption, necessitates the utilization of an advanced optically clear adhesive (OCA) capable of blocking UV light, in addition to its conventional functions of adhesion and strain relief. However, a challenge arises due to the presence of a UV blocking agent within the OCA. This presents a technical limitation, preventing the application of UV curing technology widely utilized in the OCA manufacturing process. Recently, a method for producing UV-blocking OCA through visible-light curing has been proposed, utilizing a new photo-initiating system (PIS). Nevertheless, the curing speed remains significantly slow, which hinders its commercialization. In this study, we have developed a highly efficient photo-initiating system (PIS) that enables the rapid production of UV-blocking OCAs suitable for commercialization under visible-light irradiation. Through a mechanistic analysis of existing PIS, we suggested that the photocatalysts (PCs) in the excited state dissipates upon the occurrence of the triplet-triplet energy transfer (EnT) or energy transfer (ET) with UV blocking agents, thereby impeding the curing rate. To address this, we employed a newly designed PC to reduce both EnT and ET rates when combined with UV absorbers, in comparison to a previously reported PC. Combining the PC with carefully chosen co-initiators, we created a new PIS that generates radicals rapidly through electron transfer. Under 452 nm visible light, we achieved UV-blocking OCAs at a rate approximately 10 times faster than before, while maintaining excellent UV-blocking ability, optical transparency, and viscoelastic properties. In UV-blocking tests, covered OLED device covered with the UV-blocking OCA demonstrated superior UV-blocking performance, indicating broad applications in protecting diverse smart devices with various form factors from UV irradiation.