Fabrication of seamless roller molds using step-and-rotate curved surface photolithography and application on micro-lens array optic film

Abstract

This paper describes an innovative approach for fabricating seamless roller molds based on conventional photolithography. The fabricated seamless roller molds are then applied in a UV-curing roller imprinting process to replicate ball-lens-array microstructures on a polymer substrate, which finally forms a light-converging optical film to be used in back-light units of flat panel displays. The roller imprinting process has the advances such as quickly, low cost and large area. First of all, a method for spread coating of a thin photo-resist (PR) layer on a cylindrical surface of a metal roller is developed. This spread coating system relies on pneumatically driven air flow which squeezes through a narrow gap between a roller and an outer ring, and results in a uniformly coated thin PR layer on the cylindrical surface. Secondly, a step-and-rotate UV-exposure system is constructed for transforming patterns defined by a photo-mask to the coated PR layer. Continuous and seamless patterning on the whole cylindrical surface of the roller is achieved through accurate mechanical alignment and precision rotation control of the roller as well as a parallel UV light source. Finally, using the patterned and developed PR structures as a mask, a variety of microstructures with complicated and seamless patterns can be directly fabricated on the metal roller surface by either chemical etching or electroforming process, which complete the fabrication of seamless roller molds. Through UV-curable roller-imprinting, an optical film with ball-lens-array micro-structures have been fabricated and experiment results show a gain value of luminous of 1.2 has been accomplished.