Laser-induced plasma emission spectroscopy (LIPS): A useful analytical tool for the surface chemical characterization of coated paper materials

A new method for the chemical analysis of the coating in light weight coated (LWC) grade paper is described. A method has recently been developed that employs laser-induced plasma emission spectrometry (LIPS) to produce rapid and relatively inexpensive, three-dimensional profiles of paper coatings and fillers. The technique involves ablating the paper coating from the top of the coating down to the paper base with a focused laser beam. It is able to provide definitive spatial resolution and characterization of the chemical homogeneity of the paper coating and thus relate that information to the efficiency of the coating method. It can also provide information on binder migration, a serious hindrance for the improvement of stable coatings. Herein, several LWC paper grades and their base papers were analyzed using LIPS. It was found that pigment identification of light weight paper coatings is possible as well as coat weight distribution maps and profiles. Blade and film coating generate noticeably different coating distribution profiles that can be detected by LIPS. The phenomenon of binder migration was demonstrated by observing its masking effects on Si spectra. An investigation of filler content in base papers involved analysis of base paper used in LWC grades. The papers represented two different types of formers, but because of the proprietary nature of part of the research, little else was revealed. A significantly greater amount of surface filler was noted in Former A than in Former B, as indicated from Mg spectra of the filler.