Originally Posted by Terence
The blades are drawn over the support.
In the case of the paper blade, the open well is filled with emulsion and the leading edge keeps the paper flat. In the case of the film blade, there cannot be a leading edge, as it would scratch the film, so it is open and the emulsion is poured ahead of the blade.
An adjustable doctor blade is the trailing edge in each case and it 'scrapes' off the emulsion to the fixed height that the coater sets the blade for.
This gap is typically 5 mils, but the range is from 2 mils to 20 mils. Often, viscosity must be adjusted for the gap width, and if the gap is large, a dam must be used to prevent premature leaking and side flow.
A chill set block is used often for heavy film coatings, but for FB paper, the paper support will absorb most of the excess moisture and set up nicely.