## 2 Fabrication of Cliche and Reverse Offset Printing
### Fabrication of Cliche Using Various Resins  
To increase the durability of the mold during repeated ultraviolet nanoimprint lithography (UV-NIL) processes and to separate the cliche smoothly, a surface treatment process to lower the surface energy was conducted. The coating process consisted of forming a self-assembled monolayer (SAM) on the surface of the master mold and reducing the surface temperature. The material used for this process was octadecyltrichlorosilane (OTS). The OTS coating process was carried out by vapor deposition in which the wafer was placed in a beaker, and OTS solution was vaporized using a hot plate kept at a temperature of 120 \({}^{\circ}\)C for one hour [20]. The entire process was carried out in an N\({}_{2}\) atmosphere and the vaporized OTS was deposited on the master mold patterns.  
After the releasing layer was coated on the surface of the master mold, the cliche was fabricated from UV curable resins using the NIL process. As the role of the cliche is to facilitate detachment of the ink from the blanket, it may be intuitively considered advantageous to make the adhesive force between the cliche and the ink larger than that between the blanket and the ink. In addition, the force with which the cliche pulls the ink must be greater than the cohesion force of the ink [17]. Considering the relationship between these adhesion and cohesion forces, it can be deduced that the ink tends to move away from the blanket toward the cliche as the surface tension of the cliche significantly differs from that of the blanket. To verify this assumption, various resins with different surface energies were selected and the surface energies of each cliche were calculated by contact angle measurements [21; 22]. In detail, the ASTM D5946, water droplet transfer technique, was applied to measure the contact angle and the surface energy can be determined from the experimental contact angle and liquid surface tension based on [PERSON]'s rule [23]. Table 1 lists the type of resins used in the experiment and the contact angle and the surface energy of the cliches made from each resin. The resins used in the experiments are all UV-curable poly-urethanacrylate (PUA) types and have different viscosities and surface energies by controlling other additional components. For comparison, the surface energies of glass, the Si wafer, PET film, and blanket used in our experiment are also given.  
The NIL process used for cliche fabrication is as follows. The resin is dispensed on the coated master mold, a substrate is applied on it, and then the rolling process is performed for pressing, while maintaining a conformal contact. As a next step, when the pattern of the master is filled with resin, UV rays with a 365-nm wavelength are incident on it to harden it. The released substrate has the reversed pattern of the master mold. Figure 2 shows the fabricated flexible cliche. The pattern was not broken but remained stable even when the substrate was properly bent.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **PUA1** & **PUA2** & **PUA3** & **PUA4** & **PUA5** & **Glass** & **PET** & **Blanket** \\ \hline C.A. (\({}^{\circ}\)) & 101.5 & 90.3 & 85.76 & 85.3 & 23.64 & 52.7 & 43 & 109.5 \\ S.E. (mN/m) & 21.51 & 25.63 & 30.8 & 30.5 & 79.11 & 53.63 & 59.8 & 19.6 \\ \hline \end{tabular}
\end{table}
Table 1: Contact angles and surface energies of various resins used to fabricate cliche and other materials for comparison.  
Figure 1: Silicon master mold with a line and space pattern for the UV-NIL process to fabricate the cliché.