Reduction of pitch error of the micro-prism array in brightness enhancement film by compensating z-axis positioning accuracy

Brightness enhancement film (BEF), as a polyethylene terephthalate (PET) film with the micro-prism array on the surface, is an indispensable core optical component for a back light unit (BLU) in liquid crystal display. Roll-to-roll (RTR) imprinting approach is the most mature and reliable technology to produce the BEF in the industry. Of course, the machining accuracy of the micro-prism array on the roller mold will directly determine the optical performance of BEF manufactured by RTR. The objective of this paper is to reduce pitch error of the machined micro-prism array on the roller mold based on geometric error viewpoint. First, geometric error of the ultra-precision horizontal drum roll lathe that has the main influence on the pitch accuracy of the machined micro-prism array is identified through volumetric error model and sensitivity analysis. Then, the compensation operation is performed for the dominant geometric error component according to the theoretical analysis results. Finally, a verification experiment after compensation is conducted to fabricate the micro-prism array on the roller mold using plunge cutting method. The measurement result shows the micro-prism array with a less than 25 nm pitch error, while a 6.018 nm area roughness is obtained, which validates the effectiveness of the geometric error analysis and compensation to reduce the pitch error of the machined micro-prism array on the roller mold.