Slot-die coating is a method of coating a wide layer of thin film on a substrate. It has the advantages of large-area coating with high reproducibility and uniform thickness. For this reason, it has been widely applied in various industrial manufacturing fields. To secure higher coating uniformity under various coating conditions, estimating and controlling the flow rate of the coating solution discharged to the substrate is crucial. In this study, a practical gravimetric flow rate measurement method for slot-die coating uniformity evaluation has been introduced. The gravimetric method is a technique for accurately and quickly estimating the flow rate through the mass change over time using a precision weighing balance. We analyzed the measurement principle and errors caused by fluid mechanics such as hydrodynamic force or capillary force. The dynamic properties based on fluid viscosity were also evaluated for flow rates from 5 to 50 μL/s. The repeatability of the fabricated measurement system was ~1.5 μL/s. Finally, it was confirmed that the settling time for high-viscosity fluid could be advanced by 56.4% through multi-step feedforward control.

Slot-die coating technique has become a subject of interest owing to its mass and large area production characteristics. To date, numerous research on the fluid dynamics of coated solution and experimental decision of the coating conditions to improve quality of coated layer have been conducted. However, few studies have been done on the optimization of slot-die coater geometry owing to the high cost associated with its fabrication. In this study, we optimize the geometry of the slotdie coater using computational fluid dynamics. We used a statistical optimization technique (Box-Behnken design). In the optimization process, we determined the significant factors that affect the velocity variation of coated fluid in the transverse direction. An optimal geometry was derived using a desirability test which is generally used to evaluate the suitability of a selected geometry value based on the maximization of the velocity uniformity. Experimental results presenting the uniformity of the coated layer in the transverse direction improved from 4.7% to 1.4%.

Recent manufacturing methods for fabricating flexible devices have attracted a keen interest, with a strong demand by industrial manufactures. For thin film application on flexible devices, slot-die coating was found to be the most suitable method having excellent uniformity. Optimization of the reservoir of slot-die coater should be prioritized, since it is an important parameter affecting the uniformity of the final outcome of the coated layer. However, the numerous designs of reservoir makes prototyping difficult, and also results in high manufacturing cost. This study analyzed the velocity deviation of the slot-die coater outlet using CFD analysis, and shape optimization was performed by contour map. We introduce a facile and low-cost fabrication method for a slot-die coater, using polydimethylsiloxane materials and three-dimensional printing technique. The fabricated polymer slot-die coater was further evaluated by the leakage test of solution.