Clarification of Ink Mottle.

The relationship of coating micropore, optical properties and print mottle were studied. Coated papers with various micropore size distribution were prepared on a pilot SDTA coater and were printed on a 4 color sheet-fed offset press. The print mottle was evaluated both visually and with an image analyzer. The micropore of the coating, unevenness of the coating and optical properties of the coated paper such as whiteness were measured. Then the relationship between print mottle and these measured factors was studied.The results are summarized as follows ;(1) There is no mutal relationship between print mottle and micropore of coating.(2) Uneven whiteness of non-printed areas affects the print mottle. Sometimes it increases print mottle and sometimes it decreases print mottle.(3) Such uneven whiteness is caused by uneven opacity of the paper.