Study on Print Mottle Effect of Binder Migration and Latex Film Formability During Consolidation Process, 1993 Coating Conference Proceedings

Effects of binder migration and latex film formability on print mottle were studied.

In the first stage, binder migration was mainly in lab scale experiments. Clay/calcium carbonate coating colors were prepared with starch/latex binder system and were coated by specially designed lab-coater, MLC-70, which was able to control the interval period between coating and drying.

Surface starch and latex contents of coated samples prepared in several interval periods were measured directly from scraped powder by an absorptiometric procedure and pyrolysis gas chromatography, respectively.

Difference of migration behaviors between starch and latex was discussed. Influence of latex Tg level on migration behavior was also discussed.

Coated samples were printed by lab scale printer, RI print tester, and print mottle was evaluated. Relationships between print mottle and the surface binder contents were discussed.

In the second stage, the pilot scale coating was carried out to confirm the results obtained by lab experiments. Coating colors prepared with latexes of three different Tg levels were coated by a SDTA pilot coater.

Coated samples were printed by RI print tester and commercial sheet-fed offset press.

Though the migration behaviors of starch and latex in pilot coating were almost the same as those in lab coating, some differences were found in print mottle tendency between both coatings.

Besides binder migration, other factors which seemed to affect print mottle were found, i.e. latex film formability.

Temperature at the coated surface during drying process was measured and the influence of film formability on print mottle was discussed.