A non-contact and online ink thickness sensor for printing machines using the photoacoustic effect

Abstract

We have developed an ink thickness sensor by employing a photoacoustic technique in order to enable the online measurement of ink thickness for printing machines such as a sheet-fed press. This sensor enables the online measurement of black ink thickness, which was impossible using the conventional methods. In order to detect the photoacoustic signals from the ink on a rotating ink roller using a non-contact technique, the halogen light chopping frequency was made to coincide with the pipe acoustical resonance frequency of the photoacoustic cell. With this method, even though the photoacoustic cell is an open cell, the sensitivity of the photoacoustic cell could be improved as compared to the conventional non-resonant closed cell. Further, it was clarified both experimentally and theoretically that the photoacoustic signal strength of black ink corresponds to an ink film thickness when the optimum halogen light chopping frequency is selected. In addition, a study is made on the characteristics of the photoacoustic signal strength variation for the clearance between the resonance tube and the ink roller.

Use of Total Internal Reflection Raman (TIR) and Attenuated Total Reflection Infrared (ATR-IR) Spectroscopy to Analyze Component Separation in Thin Offset Ink Films after Setting on Coated Paper Surfaces

“…5 The spectroscopic methods, such as confocal Raman, UV resonance Raman, Fourier Transform Infrared (FT-IR) spectroscopy, photoacoustic (PAS) spectroscopy, and transmission spectroscopy can provide information of ink behavior and paper-ink interactions nondestructively with minimal demands for sample preparation, on measuring environments, and time. 6 For instance, the PAS technique is successfully applied for on-line ink penetration measurement on a rotating ink roller, 7 and FT-IR transmission spectroscopy may be applied for separation and absorption studies of offset ink oils into different mineral coatings. 8 More surface-sensitive attenuated total reflection infrared (ATR-IR) FT-IR spectroscopy is shown to be suitable for light and water fastness studies of ink jet prints, 9 tint strength analysis of ink pigments, 10 ink-substrate adhesion studies, and for the analysis of the effects of pigments in offset printed papers.…”