Induction Lithography (Continuous Mold Rolling)
Roll-to-roll (R2R) lithography is a continuous manufacturing process used to create patterns on a polymer substrate. Thermally curing of R2R embossed features is time consuming, and is commonly replaced with faster UV or chemical curing. A technique termed induction lithography has been conceived as a R2R process for heating, forming and cooling along the perimeter of the roll. The patterned polymer surface needs no additional curing steps, which increases efficiency of the R2R lithography process. The results of initial investigation prove the feasibility of said conceptual process, and initial experiments confirm heating of the lithography roll by induction heating. The implemented device is shown in the figure at right. While the materials and dimensions of the patterned center roll may vary according to the application requirements, the steel shell has thicknesses on the order of one millimeter. Internally, the roll is comprised of a thermally and electrically insulating material such as Teflon with a radius on the order of 0.5 centimeters above an aluminum core for structural support. Coolant is circulated internal to the patterned roll.
The temperature of the shell as a function of the roller position is of particular interest and importance to the induction lithography process. Consider a process beginning at a cooling temperature of 20°C, a shell thickness of 1 mm and a roller speed of 20 RPM. The lower right figure plots the transient temperature of a point on the shell beginning from an angular position equal to zero. During the first few rotations, the induction heating of the shell causes the shell temperature to rise as indicated by the continuously increasing (spiral) temperature. After a couple of rotations, the shell has nearly reached a steady state in which the total heat flux from heating and cooling are equal. The peak temperature of the shell is approximately 280°C, which can be adjusted by changing the heating power and/or coolant temperature. With this transient temperature profile around the roller, the patterned center roller acts as a continuous mold rolling system, similar to the filling, cooling, and resetting stages of injection molding.