Reduced migration of multi-arm structured plasticizer from pressure-sensitive adhesive films

Abstract

Temporary protective film (TPF) is used as a surface protection for the encapsulation layer during cell cutting and laser lift-off in the manufacturing process of an organic light-emitting diode. TPFs should satisfy the following requirements: good wettability on the surface during the protection step, low peel strength, and clear debonding properties during the removal step. Herein, we used multi-arm-structured trimethylolpropane ethoxylate (TPEG) and linear-structured poly(ethylene glycol) 200 (PEG200) plasticizers to attain these requirements for a polyurethane-based a pressure-sensitive adhesive (PSA). The PSA films with TPEG successfully satisfied the aforementioned requirements. The PSA films with plasticizers exhibited similar wettability and polar surface energy with those of the substrate, thereby demonstrating an interface energy with the substrate of approximately zero. Additionally, the 180 degrees peel strength test showed that the peel strength of the PSA with TPEG was lower than that with PEG200. The observation coincides with small-amplitude oscillatory shear test results obtained via rotational rheology measurements. Furthermore, debonding properties were characterized using time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the adherend surfaces after peeling off the TPFs. The structural properties of TPEG affected migration to a lesser extent than those of PEG200. This is in good agreement with the surface free energies of the adherend surfaces after removing the TPFs. The proposed design strategy can be applied in electronic industry where surface protection using ultra-peelable adhesive films is required.Graphical abstractA schematic diagram of a thermally crosslinked urethane PSA with two plasticizer additives: multi-arm TPEG and linear PEG200. The addition of plasticizers forms hydrogen bonds with the polyurethane main chain