Relationship between coating structure and print mottle.

Print mottle, as a printing defect, is becoming a serious concern for papermakers and printers, due to the increasing demand for high quality printing, to the increase of coating and printing speeds, and to the decrease of coating weight. The intention of this study is to evaluate quantitatively the relationship between print mottle and chemical distribution in the coated paper by the use of image analysis and ESCA analysis. The results are summarized as follows : 1. A method of obtaining the surface profile of the binder distribution was developed using ESCA with an analyzer slit of 2 mm diameter of effective area.2. A quantitative evaluation method for print mottle by image analysis was developed.3. Print mottle caused by non-uniform absorption of dampening solution corresponds directly with the non-uniformity of the surface distribution of binders and pigments. And both print mottle and non-uniformity of binder distribution at the coated surface have a scale of 1-3 mm diameter.4. Depth profiles of the coated layer show uneven distribution not only of the binder but also the pigments. Also, starch and latex show different distributions in the coated layer.5. No clear relationship between z-direction distribution of chemical components and print mottle was detected, and thus, print mottle seems to be independent of the z-directional coating composition.