Ultraviolet-patterned acrylic pressure-sensitive adhesives for flexible displays

Abstract

Acrylic pressure-sensitive adhesives (PSAs) are extensively used to fasten display layers. Although PSAs must show sufficient adhesion for application to existing displays, PSAs must utilize stretching and recovery to mitigate the effects of deformation for application to flexible displays. Therefore, in this study, an ultraviolet (UV)-patterned acrylic PSA was prepared by incorporating a region showing variable degrees of crosslinking achieved using a contrasting UV-patterned film. The gel fraction was measured to confirm the degree of crosslinking, and the adhesion was measured by peel strength, pull-off, and lap shear tests. Dynamic mechanical analysis (DMA) stress relaxation was used to measure the recovery. The highest gel fraction was obtained at a crosslinker content of 1 part per hundred resin (phr) and a UV dose of 1600 mJ/cm2. The low-crosslink-density area was optimized using the 50% gray patterned film. The acrylic PSA prepared with 0.001 phr of 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBT), a light-emitting compound used to visualize the pattern formation, showed the clearest pattern. Although the adhesion of the UV-patterned acrylic PSA initially decreased, it gradually increased for the 2 mm pattern. However, the shear adhesion was maintained without appreciably changing. Although the acrylic PSA could not withstand certain deformation conditions during UV patterning, it was stretchable at a pattern size of 4 mm, and the recovery increased to approximately 60% at a pattern size of 2 mm. The results confirmed that the UV-patterned PSA is suitable for application to flexible displays.