Web Coating

A coating line is comprised of many basic process elements and subsystems--all of which must perform as specified to obtain a high-quality, low-cost product. The important components of the coating line include the solution mixing process, the coating applicator and ancillary hardware, the dryer and the heating and ventilating hardware to move the air to the drying web and remove the solvent, process control and measurement instruments, web transport system, and the environmental control systems.  All of these can contribute to the formation of defects in the coating.

All of these can contribute to the formation of defects. Often variability in one system can lead to defects in another part of the process. For example, the viscosity of a coating solution is determined by the mixing process and if out of limits can cause defects in the coating application and in the drying of a coating. Tension variation in the web moving through the coater/dryer can result in scratches and rub defects.

To insure optimum performance there are two types of measurements that need to be made. The first is the measurement and control of major process variables such as dryer inlet air conditions, dryer sir solvent levels. Line speed, substrate tension levels etc. flow rate to the pumps etc.  The second measurements needed are variables which impact the performance of the coating line and coated product, film temperature in the dryer, dryer slot velocity, dryer return air solvent concentration, ambient air conditions in the coating facility, etc.

All of these measurements should be stored in a computer for subsequent analysis and troubleshooting. Table 1 (click on image below) is a list of suggested process measurements.