Optical Alignment
Optical techniques that minimize light scattering at material interfaces are critical for enhancing the transparency and efficiency of composite materials. By applying refractive index matching, developers can align the refractive indices of coatings and paper fibres with their surrounding matrices. This reduction in index mismatch prevents light from refracting or reflecting at the borders between different components, allowing the light to pass through the material with minimal distortion.
This technique is commonly applied in liquid-crystal displays, optical sensors, and specialized packaging laminations.
Coating Formulation
In the paper and packaging industry, this technique is utilized to create highly transparent barriers or gloss coatings on paperboards. The mineral pigments used in typical coatings have a refractive index close to one point five, which matches the index of the binder and cellulose fibres when wet. When the coating dries, air voids can form, causing a large refractive index difference that scatters light and makes the paper opaque.
Applying a specific resin that fills these voids and achieves refractive index matching restores the transparency of the paper substrate, enabling clear viewing of underlying print.
Performance Limit
Temperature variations can disrupt the index match because different materials do not expand or contract at the same rate. This differential thermal expansion shifts the refractive indices of the materials unevenly, which introduces scattering and haze in the finished product.
