Optically clear pressure-sensitive adhesive with flexible crosslinking agent for high recovery efficiency, low energy storage modulus, and excellent folding resistance

Optically clear pressure-sensitive adhesive (OCA) possesses exceptional optical properties and exhibits pressure-sensitive adhesion, making it widely utilized in the adhesive layers of various electronic display devices. However, the increasing popularity of foldable mobile phones in recent years has imposed new requirements on the overall performance of OCA. Conventional pressure-sensitive adhesives can enhance recoverability through cross-linking but often demonstrate inadequate adhesive strength. In this study, three long-chain crosslinking agents (CL) were synthesized using hydroxyethyl acrylate (HEA), dicyclohexylmethane diisocyanate (HMDI), polypropylene glycol (PPG), polyether amine (PEA), and hydroxyl-terminated polybutadiene (R45V). The long-chain CL agent contains numerous flexible segments that improve the recovery capability of the OCA while maintaining a certain level of adhesion. The optical clear pressure-sensitive adhesive, crosslinked by three flexible crosslinkers, exhibits a low glass transition temperature (−60 to −40°C) and a low storage modulus (<0.1 MPa), along with an appropriate 180° stripping force (6–8 N/25 mm). Optically transparent pressure-sensitive adhesives demonstrate excellent recovery properties (>85%), high light transmittance (>92%), and exceptional flexibility. Moreover, compared to market products, the optically transparent pressure-sensitive adhesive shows superior folding resistance (>100,000 times). This indicates its suitability for applications in flexible optical displays such as foldable mobile phones and wearable electronics.