Analytic Study of Non-Newtonian Double Layer Coating Liquid Flows in Optical Fiber Manufacturing

In mass manufacturing of optical fibers, the wet-on-wet polymer resin coating is an efficient process for applying double layer coatings on the glass fiber. This paper presents an analytic study on the behavior of non-Newtonian polymer resins in the double layer coating liquid flow inside a secondary coating die of the optical fiber coating applicator. Based the approximations of fully developed laminar flow and the power law model of non-Newtonian fluid, the coating liquid flow of two immiscible resin layers is modeled for the simplified geometry of capillary annulus, where the surface of glass fiber moves at high fiber drawing speed. The effects of important parameters such as non-Newtonian fluid properties, the coating die size, and fiber drawing speed are investigated on the resin velocity profiles and secondary coating layer thickness.