Manufacturing plastic films and sheets requires precise control of opacity. This is done by measuring reflectance for opaque films and transmission for transparent films. To ensure quality, a custom cross beam is placed on the production machine to hold an in-line spectrophotometer. This instrument takes measurements on the left, center and right side of the film.
Additionally, film processors can orient the crystallites in a plane to reduce dispersion and increase optical homogeneity. For example, biaxially oriented polypropylene film (BOPP) is stretched in two directions as it cools to provide high transparency. To prevent wasting an entire print run, plastic manufacturers extract a sample for laboratory measurement. The opacity values of Oppalyte films range from 60 to 95%.
ExxonMobil measures the opacity of some white films to replace paper in certain applications. X-Rite's online plastic color measurement and control system includes a non-contact spectrophotometer, a customized transverse beam, and quality control software to monitor color throughout the run. ESwin closed-loop color control software is used in combination with an X-Rite online color measurement instrument to manage color quality on continuous process manufacturing lines, display results, and execute automatic closed-circuit in-line color control on plastic machinery. By using these methods, plastic manufacturers can ensure color harmony from raw material inspection and color matching in the laboratory to production quality control and final inspection.
This helps them keep color, brightness, transparency and haze in harmony so that the line can keep moving.