Based on the variational methods, design equations for coating dies that are widely used in the photographic emulsion coating industries have been obtained in analytical forms, and the key dimensionless parameters that affect the coating weight uniformity have been identified. The effects on coating weight uniformity of a tapered angle in the die distribution chamber have been investigated and its performance is compared with nontapered dies. The coating weight uniformity index has been defined in terms of the pressure ratio in the distribution chamber and sample calculations have been made for each die to show the effects of die internal dimensions on coating weight uniformity indexes. Other factors that could also affect the coating weight uniformity, such as the precision of machining of the die slot opening, a distorted wetting line on the lower pressure side coating bead meniscus, and turbulent eddies in the vacuum box, have been discussed briefly.
John Chong, "Coating Weight Uniformity and Die Internal Design" in Journal of Imaging Science and Technology, 1997, pp 41 - 47, https://doi.org/10.2352/J.ImagingSci.Technol.1997.41.1.art00007