Optical Properties of Colorless Polymer Coatings on the Mirrored Surface of Containers

The optical characteristics of light-reflecting surfaces, birefringence, and pleochroism effects in multilayer coatings of metal, glass, and plastic packaging made from biaxially oriented isotactic polypropylene (BOPP) were investigated. Birefringence induces bright coloration in transparent, colorless BOPP films under polarized light, leading to the manifestation of pleochroism. Polarized light arises from the reflection of natural or artificial illumination on mirrored surfaces, with the proportion of polarized radiation in the reflected light flux depending on the angle of incidence and the properties of the dielectric mirror surface. The study proposes utilizing the color effects observed in polymer films to enhance the visual appeal of packaging and to provide protective marking. The protection of product packaging against counterfeiting represents a significant social and economic challenge in modern society. Protective marking, when combined with information encoding, ensures consumer safety—particularly for pharmaceuticals and corrosive household chemicals. The reliable encoding and recognition of hidden security information on transparent polymer packaging depend on the contrast and color differentiation of structural elements, such as barcodes or trademarks, which become visible only under polarized light. This article presents the results of instrumental measurements and quantitative assessments of colored radiation reflected from colorless mirrored surfaces of metal, glass, and polymer containers. The optimal number of transparent polymer film layers required to achieve vivid coloration of labels or packaging visible in polarized light, as well as the contrast necessary for effective protective marking, has been determined.