Slot-Die Coating of an On-the-Shelf Polymer with Increased Dielectric Permittivity for Stack Actuators

Nitrile–butadiene rubbers (NBR) have been extensively used as dielectric materials due to their commercial availability, excellent mechanical properties, glass transition temperature below 0 °C, and increased dielectric permittivity owing to the presence of polar nitrile groups. Despite these advantages, their processability is poor and cross-linking into thin films is a challenge. Cross-linking requires long times, temperatures exceeding 160 °C, and an inert atmosphere. Such cross-linking conditions are incompatible with the continuous manufacturing process of stack actuators. Here, we developed an NBR that can be easily processed into thin films, cross-linked fast, and on-demand by UV-induced thiol-ene reaction in the presence of a dimethoxy-2-phenylacetophenone initiator and 2,2′-(ethylenedioxy)diethanethiol cross-linker. The mechanical properties of the NBR can be easily tuned by the amount of cross-linker used. Additionally, a semi-automated manufacturing process for stack actuators is presented. Here, we slot-die coat the dielectric and spray-coat the electrode through a mask. Because of the commercial availability of the starting materials, an easy and robust protocol for cross-linking, and reproducible manufacturing, it can be envisioned that this material has the potential to replace the well-known acrylate film, VHB, which engineers often use to construct dielectric elastomer actuators in different prototype devices.