Contact pressure analysis in roll to roll process for super-hydrophobic surface fabrication

Y.G Kang, C. Jung, Y. Jeon, M.G. Lee
Ajou University,

Keywords: pressure deviation, Roll to roll process, super-hydrophobic surface


Recently, super-hydrophobic surfaces have played an important role in reducing friction, preventing fouling & icing, and enhancing self-cleaning. Mobile, home appliance, construction and transportation industries can adopt the hydrophobic surfaces if they are able to present the roles. Conventional process to manufacture the super-hydrophobic surfaces is typically with deposition processes in vacuum environment, which make the productivity limited. It is inadequate to mass production because it needs long lead time and expensive facility. The vacuum environment also gives a barrier to fabricate the surface on a large areas. To overcome the limitations, roll to roll process has been applied to pattern nano-micro scale structure on a large area in an ambient environment. This work shows a basic study of the roll to roll system’s perspective based on a finite element analysis (FEA). This forecasts whether the super-hydrophobic characteristics can be achievable or not, especially is focused on the uniformity of contact pressure on the large area. A FEA is applied to anticipate the perspective. To realizing the super-hydrophobicity on a large area film in an ambient environment, uniformly patterned nano-micro scale structures need to be formed, by pressing the photo- or thermo- sensitive film using the roll to roll processes. To analyze the pressure distribution over the roller contact, a FE model was established. A commercial numerical tool, ANSYS 18.0 was adapted for the modeling. The model has two rollers with length of 350 mm and diameter of 60 mm. The roller also has a central shaft with diameter of 10 mm to apply boundary conditions. The upper roller’s core material is an aluminum alloy and the roller has a thin skin of a typical silicone rubber with thickness of 3 mm, whereas the lower rollers is a pure aluminum alloy with the same properties with the upper one’s core. The center axis of the lower roller is constrained to have no motion is all directions, and the upper roller is under the constraints of no degrees of freedom except for the vertical displacement. And then a displacement of 5 μm is applied to the upper roller’s central shaft. From the study, the pressure in the middle area of the roller has relatively lower distribution compared to the value at the both end of the roller. This is because of the deflection of the rollers when contacting. After analyzing the FEA model, it was found that the pressure distribution on the contact surfaces of rollers has the minimum stress of 0.11 MPa in the middle and the maximum stress of 0.37 MPa at both the end. The resulting pressure deviation is about 70 %. This non-uniform pressure may give an adverse effect on the pattern uniformity. This may result in failure fabricating the super-hydrophobic surface. Therefore, an innovative uniform pressurized roller system will be presented in the conference by the authors. The system has a special shaped roller which gives good uniformity of contact pressure. This will be also verified by analyzing similar FEA model except the special roller.