Several intermittent coating technology developments have been commercialized. Therefore; number of commercial products produced are increasing. Among the many products that are patch-coated using this technology are transdermal and mucosal medical patches, lithium-ion batteries. organic light emitting diodes, labels and the organic photovoltaics used in thin-film solar cells.
The initial patch-coating process was roll coating to create a series of continuous separated lanes on the substrate, The separate strips were obtained by taping the coating roll into segmented discrete lanes of the desired width. The area between the tape contained the coating solution that was transferred to the substrate as the discrete lanes. This process could not coat discrete shapes such as rectangles and squares.
Slot-die coating can also be used to create machine direction lanes and discrete patches. The machine direction lanes are prepared by using internal inserts in the distribution cavity that restrict flow to the desired lanes that are then transferred to the substrate in the coating bead.
The initial technology to continuously coat discreet patches was initiated by two patents issued in the 1990s. Choinski patented a process  that created patches by flow control and mechanical movement of the extrusion die coater to break the bead and create the discrete areas. The withdrawal time and return determined the size of the patch. Milbourn and Barth  patented a sophisticated process using a slot-die coater in which the patch size was determined by precisely withdrawing the slot die to break the bead and returning to create patches.
Subsequently, there has been a consistent development of methods are commercially available technology to develop a cost efficient process that can meet the tight specification. This is primarily based on the slot die coater A significant factor in the expanded use of the discontinuous process has been the development of laboratory discontinuous coaters that can produce coated patches with the tolerance required and allow for efficient optimization of the coting solution, can apply multiple llayers and product is commercial quality for accurate evaluation and customer evaluation. Figures 1 & 2 are examples of laboratory patch coaters.
A paper on intermittent slot-die coating was presented at the 2015 AIMCAL Web Coating & Handling Conference USA in which the functioning and interactions of the hardware components and rheology of coating solutions were discussed.
1. Choinski, E.J., 1990, Method And Apparatus For Patch Coating Printed Circuit Boards, U.S. Patent 4,938,994.
2. Milbourn, T.M. and J.J. Barth, 1994, Method Of Applying Discrete Coating Patches To A Moving Web, U.S. Patent 5,360,6293
3. Miller, Mark. Intermittent Coating, AIMCAL Web Coating & Handling Conference USA, October 2015