Three Dimensional Observation of Coated Paper by Confocal Laser Scanning Microscopy, 2005 TAPPI Coating Conference

The depth of coating penetration into paper and the distribution of coating components are important attributes in determining final product quality. Many techniques have been proposed to characterize the coating layer, but most are limited in some way or have difficult sample preparation steps.

A new method is described here to image the coating layer using confocal laser scanning microscope (CLSM). The new method uses similar fluorescent staining methods used in the field of biology. Coated papers are stained by a fluorescent dye and rinsed. Rhodamine B is used as the fluorescent dye due it part to its fluorescence at the excitation wavelength of 514 nm. Control studies show that latex binder is preferentially stained with Rhodamine B, but cellulose in the base paper, kaolin clay and calcium carbonate are only minimally stained.

The three dimensional (3D) structure of a paper coating layer was observed by CLSM with a developed fluorescence stain technique. Information about the coating layer over a wide area could be obtained nondestructively. The results are used to characterize the depth of penetration of the coating layer into the paper, the occurrence of bubbles, and the possible distribution of latex and optical brighteners. The structure of double coated papers was also discernible. The technique potentially could be used to identify the location of other components if they can be tagged with a fluorescent dye.