From Color to Chemometrics: Strategies to Determine Coating Thickness and Quality

Within the glass processing industry a well-known method to perform in-situ process control is the determination of color. Therefore, most coating plants for glass or foils are equipped with visible wavelength range spectrometersfor two purposes: (1) Monitoring the appearance and the intended final color / quality (2) Color values and their variation as very sensitive indicators for applied layer thicknesses.

However, for more complex layer designs, e.g. triple silver coatings, color variation might be misleading layer thickness indicators. In these cases physical method based calculation processes must be used to determine the layer thickness from the measured spectral data.

Another field of application is the wet coating on diffuse materials like paper. A demand for process control and thus process capable metrology arises out of this. Neither color measurement nor thickness determination based upon interference are sufficient to provide stable process metrology results. Therefore, a method based on chemometric models was introduced to provide the machine operator with reliable process information. The talk will show how a combination of different process capable methods – color, physical, and chemometric models – helps the operator to stabilize coating processes and control the final product quality with a single equipment.