Recently, mechanical engineering is showing a high interest in biomimetics to solve technical problems. Particularly, there have been some attempts to apply characteristics of a lotus surface which maintains its clean surface without being wet to products that require a clean surface. Researching the studies of past 10 years, outstanding examples of producing a superhydrophobic surface whose contact angle is higher than 150° have been reported by using photolithography, laser, E-beam, and metal anodizing. However, in order to apply these kinds of methods in real life and to the industrial environment, there are many problems to be solved in terms of structural robustness and durability by surface friction and vibration of external environments.
Therefore, this study is to suggest a method to simply create products with superhydrophobic feature. Also it is to suggest a process and mold technology based on mass production of superhydrophobic surfaces considering mass production and commercialization. To achieve this level, chemical maleficence of final products, durability, productivity, and geometric shapes of application products have to be considered.
To create superhydrophobic fine patterns, this study has applied electric discharge machining(EDM). EDM is categorized into die sinking electric discharge machining(DS-EDM) and wire cutting electric discharge machining(WC-EDM). Also this technology can process a wide range of surface roughness of metal by controling process conditions such as current and frequency. An electric discharge machined surface can be easily replicated by liquid silicone rubber(LSR). And we replicated metal surfaces of wide range surface roughness processed by the two types of EDM. We analyzed the hydrophobic characteristics of the replicated silicone surface, and as a result, the replicated silicone surface which is made by replicating wire cutting electric discharge machined surface of high surface roughness showed a contact angle of higher than 150.1°, which implied the possibility of producing superhydrophobic surfaces.
In order to assess the possibility of manufacturing superhydrophobic silicone-based products, we produced a curve silicone surface of large area. We applied injection molding technology as a typical molding technology. To perform injection molding, we designed and produced a metal mold core, and processed fine patterns by using WC-EDM based on assessed results of hydrophobic characteristics. By performing injection molding, curve silicone surface was created within a short cycle time. Also, as a result of evaluating hydrophobic surface, we have created a superhydrophobic surface with 150.3° of contact angle, and the result showed 3.8° of low contact angle hysteresis, an excellent dynamic property.
This study applied electric discharge machining and injection molding technology, and has developed a production technology system that can mass produce superhydrophobic silicone surfaces.