Effect of photo-initiators on the crosslinking behavior of organic thin films and their applicability to flexible display encapsulation layer

In this work, we examined photocurable materials for organic layers that can be used as an encapsulation layer in flexible displays. Photo-initiators, which are essential for UV-crosslinking, can be classified into two categories: Type-1 initiators that produce free radicals through the cleavage reaction caused by UV irradiation and Type-2 initiators that generate free radicals without the cleavage reaction. Type-2 initiators are more desirable for the encapsulation organic layer of the flexible display due to the low outgassing of unreacted components. To optimize the curing properties of organic coatings, the effect of initiator type on the real-time crosslinking behaviors were mainly scrutinized. The flow properties of pre-cured coatings such as shear viscosity and surface tension were also measured to evaluate the applicability in the inkjet coating process, and transmittance and refractive index were analyzed for the optical properties of cured thin films. As a result, it was found that Type-2 initiators, exerting the intrinsic low outgassing performance, are more advantageous in developing the display encapsulation technology as a key component in the organic layer.