Analysis and Design of Internal Coating Die Cavities

The purpose of the internal cavities of coating dies of all types is to distribute the coating liquid in a manner which in conjunction with the rest of the coating process produces a liquid film with uniform dimensions and properties. Whereas the constancy of feed rate and take-away speed play the biggest role in the down-web uniformity of the final film, the liquid passages internal and external to the coating die have the biggest impact on the cross-web uniformity of the coated liquid. Although cross-web nonuniformities in the liquid passages external to the coating die can drastically affect the final coating uniformity, the focus of this chapter is the influence on the cross-web uniformity of the passages internal to the coating die.