Park Jong-Han, Park Keun
Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea.
R&D Department, Rastech Co. Ltd., Daejeon 34037, Korea.
Micromachines (Basel). 2019 Sep 28;10(10):654. doi: 10.3390/mi10100654.
Nanoimprint lithography (NIL) is a micro/nanoscale patterning technology on thermoplastic polymer films, and has been widely used to fabricate functional micro/nanoscale patterns. NIL was also used to develop micro/nanoscale patterns on curved surfaces by employing flexible polymer stamps or micropatterned metal molds with macroscopic curvatures. In this study, two-step ultrasonic forming was used to develop micropatterns on a curved surface out of a flat metal stamp, by connecting ultrasonic imprinting and stretching processes. Ultrasonic imprinting was used to replicate functional micropatterns on a flat polymer film, using a flat ultrasonic horn and micropatterned metal stamps with prism and dot micropatterns. An ultrasonic stretching process was then used to form a curvature on the patterned film using a curved ultrasonic horn and a soft mold insert, to avoid damage to the pre-developed micropatterns. The ultrasonic horn was designed to have three different tip radii, and the resulting forming depth and curvature formation were investigated experimentally. As a result, three different curved surfaces containing two different micropatterns were obtained. The developed curved films containing micropatterns were then evaluated optically, and showed different optical diffusion and illumination characteristics according to the film curvature and micropattern type. These results indicate that the proposed technology can extend the functionality of conventional micropatterned products by imposing appropriate curvatures.
纳米压印光刻技术（NIL）是一种用于热塑性聚合物薄膜的微/纳米级图案化技术，已被广泛用于制造功能性微/纳米级图案。通过使用具有宏观曲率的柔性聚合物印章或微图案化金属模具，NIL还被用于在曲面上开发微/纳米级图案。在本研究中，通过连接超声压印和拉伸工艺，采用两步超声成型法在平面金属印章的曲面上制作微图案。超声压印用于在平面聚合物薄膜上复制功能性微图案，使用平面超声变幅杆和带有棱镜和点状微图案的微图案化金属印章。然后使用弯曲超声变幅杆和软模芯在图案化薄膜上进行超声拉伸工艺以形成曲率，以避免损坏预先制作的微图案。超声变幅杆设计有三种不同的尖端半径，并通过实验研究了由此产生的成型深度和曲率形成情况。结果，获得了包含两种不同微图案的三种不同曲面。然后对含有微图案的已开发曲面薄膜进行光学评估，结果表明，根据薄膜曲率和微图案类型，薄膜具有不同的光扩散和照明特性。这些结果表明，所提出的技术可以通过施加适当的曲率来扩展传统微图案产品的功能。
