Effect of silane acrylate on the surface properties, adhesive performance, and rheological behavior of acrylic pressure sensitive adhesives for flexible displays

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In this study, novel silane acrylates, urethane silane acrylate (USA) and urethane silane linear acrylate (USLA), comprised of urethane and silane groups were designed and synthesized, and their effect on the surface properties, adhesion, and rheological behavior of acrylic PSA was evaluated. The introduction of the synthesized USA and USLA affected the chain arrangement, and at least 3 wt% of the silane acrylates was required to alter the surface properties (roughness and wettability). Compared to a commercial silane acrylate (SA), USA and USLA showed improved cohesion of the acrylic PSA aided by the urethane bond; however, the length of the terminal silane groups produced some variations. USA improved the cohesive properties of acrylic PSA due to its short chain, which further increased the peel strength of the acrylic PSA as compared to USLA (USA: 1363 ± 173 gf/25 mm, USLA: 1258 ± 132 gf//25 mm, based on 1 wt% content). However, at 3 wt% or more, excessive cohesion led to a decrease in the interaction with the substrate, thereby decreasing the peel strength. On the other hand, SA gradually increased the peel strength of the acrylic PSA, but cohesive failure occurred due to the insufficient increase in the cohesion. With respect to the flexibility of the acrylic PSAs, SA slightly improved the modulus of the high-temperature region aided by the silane group, and the recovery properties were increased from 10.8% to a maximum of 31% at 100% strain. In addition, the low cohesive properties resulted in very high stress relaxation properties (>99%). The effects of USA and USLA on flexibility were similar, but the high cohesive force further improved the elastic properties, resulting in better recovery than those imparted by SA (USA: 87 ∼ 89.4%, USLA: 56.6 ∼ 91.7%). Comparing the two urethane-based silane acrylates, the stress relaxation property of USA was lower than that of USLA, which is related to the cohesive property of the acrylic PSA. In addition, all of the synthesized acrylic PSAs showed excellent optical properties with transmittance >98.1% and haze <2.23%, indicating their potential for application in flexible displays.