Roll coating processes are common to a range of industries including those dealing with textiles, adhesives, and sealants. FLOW-3D gives process engineers and scientists the ability to assess various material properties and coating regimes to identify sources of defects and optimize roll coating process parameters.
Forward, Reverse and Meniscus Roll Coating
In the examples to the right, velocity streamlines are plotted for the forward (top), reverse (middle), and starved (bottom) operating regimes common in roll coating processes. FLOW-3D gives researchers the ability to analyze factors such as roll speeds and material properties and their effect on the stability of the dynamic contact line as well as contributions to defects such as air entrainment, ribbing, and non-uniform edge profiles.
In the forward roll coating simulation shown below, FLOW-3D accurately captures the onset of a ribbing instability as it relates to increased roll speeds, as described in Lee, et al . The model implements one-fluid VOF, surface tension and viscosity to capture the complex nature of such instabilities which can be seen in production.
In the simulation below, FLOW-3D captures a cascade defect in a forward roll coating process. Due to increased roll speed of the web roller on the top, the dynamic contact line becomes unstable, allowing air to be entrained into the coating fluid.
Gravure coating transfers fluid from an engraved cylinder, called a gravure roll, onto a moving substrate. The gravure roll is patterned with small wells or cells that have been engraved into its surface. The engraved cylinder rotates through a well of fluid. The thickness of the fluid application to the gravure roll is controlled by a doctor blade. The cup-like shape of each cell captures and holds the fluid in place as the cylinder turns past the doctor blade. The pattern, depth, and shape of the cells determine the weight and appearance of the coating on the substrate.
The FLOW-3D simulation shown below looks at the effect of cell depth on deposition. The model compares two cell depths: 30 microns and 53.3 microns. The 30-micron cell depth allows for a much more uniform deposition, which will transfer to the resultant coating.