No abstract

Hot stamping foils are used in the printing mdustiy to achieve metallic effects on packaging, pseudo-holographic images for security applications, and other products. The performance of the foil in the stamping process is in part determined by the thickness of the release coating on the carrier foil. This coating is too thin (approximately lOnm) for successful application of conventional measurement methods. We describe a fluorescence-based optical technique to measure the thickness of this release coating on-line. A fluorescent rhodaniine dye added to the release coating allows excitation and detection in the visible part of the spectrum. Multimode optical fibre is used for excitation beam delivery and signal collection from a probe head situated on the coating machine. We outhne the system calibration and show some representative results from industrial trials.