Micro mechanical studies of urethane-linked siloxane hybrid materials for flexible display

Abstract

Flexible display occupies the largest portion of the upcoming display market. One of the main challenge to commercialize the flexible display is fabrication of flexible cover window while maintaining its protective properties from the external environment. Therefore, it should be sufficiently hard enough to protect the inner part and flexible enough to give a device flexibility. In other words, the cover window must be sufficiently rigid and flexible at the same time. Additionally, as it is used to optical devices, it should be highly transparent. Previously, transparent urethane-siloxane hybrid materials for flexible display are reported in our laboratory. These urethane-siloxane materials are formed by cross-linking between urethane monomer and oligo-siloxane resin by radical polymerization. Since urethane monomer is in the solid phase at room temperature it should be agitated over 60℃. Due to the solid phase of urethane monomer, additional agitation process to make a homogenous resin is necessary. Herein, we use the silane which already contains urethane bond and hydroxyl group as an end group in organic chain to make a double urethane bonds. Since urethane bonds are formed in the organic chain of silane, additional urethane monomer does not need, rather double urethane bonds are formed in the precursor state. Then, we fabricate double urethane-methacrylate oligo-siloxane (DUMOS) resin by sol-gel reaction with methacrylate silane. DUMOS resin are analyzed by FT-IR and 29Si-NMR analysis. Furthermore, double urethane contained siloxane hybrid films (DUMSH) are fabricated through UV radical polymerization process. It is analyzed by tensile test and 3-point bending test to confirm the improved elastic and flexural properties. Its elastic modulus is 1.35 GPa, and it is similar to methacrylate oligo-siloxane hybrid materials (MSH) without urethane bond. However, it has a strain about 2.6%, which is four times higher than that of the conventional MSH. And it exhibits 2 GPa of flexural modulus and it is comparable to MSH which has 2.9 GPa. However, DUMSH shows 3.1 % of flexural strain that is 4 times larger than that of MSH.