Enhancing the peel strength between PET and UV-curable layer with highly transparent waterborne polyurethane interlayer

The performance of brightness enhancement films in liquid crystal displays is fundamentally governed by the interfacial adhesion and light transmittance between the Polyethylene terephthalate (PET) base layer and UV-curable layer. In this study, a series of waterborne polyurethane (WPU) were synthesized to serve as interfacial adhesion layer to achieve robust adhesion while maintaining the transparency of the BEFs. By adjusting the molar ratio between polyester diol and isosorbide, the structural proportion of soft and hard segments were changed and modified. The effects of the hard segment content on the surface energy, thermal stability, peel strength, and mechanical properties of the WPU were investigated. The results indicated that the incorporation of WPU with the isosorbide structure enhanced the peel strength between PET and UV-curable layer, while the transparency of PET was maintained. Compared to untreated PET, the introduction of WPU interlayer increased the peel strength between the PET and the UV-curable layer to 1.36 N/mm, representing a 91% improvement. This work provides an effective strategy for design and synthesis of WPU interlayer with strong adhesion and high transparency of PET and UV-curable layer.