Observation of the Ink Vehicle Penetration into Coated Paper by Confocal Laser Scanning Microscope

A good understanding of the final location of ink pigments and oils is important to improve print quality and to understand the mechanisms of ink setting. A new method to characterize the location of ink pigments and ink vehicle after printing is developed using a confocal laser scanning microscope (CLSM). Magenta dyes and pigments are natural to detect and characterize. Offset ink oils and coating layers are stained with distinct fluorescent dyes before imaging. Simultaneous observation of the coating and the ink vehicle is possible. Inkjet dyes are found to penetrate through the coating layer into the fiber network for standard coating layers. Even for grades developed for inkjet printing, the dyes are found to penetrate over ten ?m into the coating in high density ink areas, but pigmented inkjet inks show little penetration of pigments into the coating layers. The dye used to tag ink oils is found to separate from the oil as the oil moves through the coating layer. However, correction to the results is possible. In offset inks, the ink oils are found to accumulate around kaolin pigments and in bubbles inside the coating layer.