Slot Die Coating

FLOW-3D is used in industry research and design of slot die coating processes. In slot die coating, fluid is forced out of a slot onto a rapidly moving substrate which is positioned very close to the slot. Sometimes multiple slots are used to create layered coatings of several materials. Many industries employ slot die coating machines because of their relative simplicity. Another benefit of slot die coating is a high rate of coating uniformity, even in coating thicknesses measured in nanometers.

In the example below, one slot is applying a 120-micron thick layer of a non-Newtonian material onto a substrate that is moving from right to left.

Slot coating simulation
Time series of a slot die coating simulation

In FLOW-3D, fluid-solid contact lines and contact angles are automatically computed as part of the overall dynamics of the flow. This is well illustrated in this example, where three separate contact lines develop in the region between the slot and the web.

Case Study

This image from an industry case study, presented by Roche Diagnostics GmbH at the 2014 FLOW-3D European User’s Conference, shows a 3D model of slot die coating without vacuum assist. There is an excellent agreement between the experiment pictured on the top left, and the simulation done in FLOW-3D.

Simulation of a slot die coating without vacuum assist, courtesy Roche Diagnostics GmbH

Slot Die Design

The FLOW-3D simulation shown below, courtesy of 3M, shows the fluid residence time inside the internal cavity of a slot die. The design of the slot die is very important to the success of the coating process, and is specific to the rheology of the coating fluid.

Simulation courtesy of 3M