Note! Observation of ink penetration into coated paper by confocal laser scanning microscope
In this work, ink penetration into coated grades is reported using a confocal laser scanning microscope (CLSM). With this technique, the penetration of ink could be observed with three-dimensional images. Offset inks, pigment and dye type ink jet inks are used to print on various grades of coated paper. The penetration of magenta ink jet pigments and dyes in ink jet grade papers could be characterized by CLSM because magenta pigments and magenta dye have fluorescence on the excitation wavelength of 514nm. The difference between the two inks was dramatic: the pigment stayed on the surface of the paper while the dye penetrated into the coating layer. The dye was found to even penetrate through the coating layer into the paper for the commercially coated grade. According to the experiment of the chromatographic effect, Rhodamine B separated from the ink vehicle into the coated layer. However, the distribution of ink vehicle on the surface side of coated layer can be observed by this stain technique because fluorescence dye would be also penetrated to the half depth of ink vehicle. In order to discriminate between coating and ink vehicle, a double staining technique was applied. Rhodamine B was used to stain the ink vehicle. Acridine Yellow was used to stain the coated paper. While Rhodamine B emits fluorescence by the argon laser beam of the wavelength of 514nm, Acridine Yellow emits fluorescence by the argon laser beam of the wavelength of 453nm. The ink vehicle and coated paper could be simultaneously observed by the alternate detection of Rhodamine B and Acridine Yellow. It was observed that ink vehicle spreads along the surface of clays. Certain regions of the coating layer, potentially clay or latex clusters, contained no ink vehicle inside them. In addition, it was confirmed that ink vehicle concentrates into small bubbles in the coated layer. The CLSM stain technique was found to be a powerful technique to understand the position of ink vehicle, pigments or dyes after printing on coated grades. The technique is of high value because sample preparation is minimal, detailed information can be obtained, and wide area can be observed nondestructively.
Ozaki Y, Bousfield DW, Shaler SM 2006. “Observation of ink penetration into coated paper by confocal laser scanning microscope”, Journal of Graphic Technology, 3(1): 50-58.