Ultrasonic Systems for Liquid Absorption Measurement: Part. 2. Validation of Ultrasonic Testing for Liquid Absorption Uniformity, 2005 Papermaking Conference

Experiments were carried out on coated paper with simulation of surface non-uniformity by the printed pattern with difference in ink density. The printed areas of different ink density were in the form of 3 mm stripes. Simulated difference in ink coverage ranged from 100% to zero in the amount of ink coverage (with 80, 60, 40, 20, 10, 4, 2 and 1% in between) and was printed with laser ink. Printed areas represented at the same time the different surface structure and chemistry. The surface difference was tested with liquid on dynamic penetration tester with ultrasonic sensor consisted with 32 micro sensors (1 mm2 each). The results obtained for Non-uniformity Index by ultrasonic method showed very good correlation with the difference in ink density measured by image analysis. Ultrasonic sensor was able to recognize the difference in non-uniformity of liquid penetration into coated and printed paper surface down to very small ink density difference which equals “1” on visual rating scale (no mottle). Application: This study shows that Penetration Evenness Analyzer is a reliable tester which can be used for QC as well as for troubleshooting and new product development. Non – uniformity of liquid phase penetration into paper from coating color may results in streaks and form the ink into coated or uncoated paper may cause the print mottle.