Application of Confocal Laser Scanning Microscopy To the Study of Backtrap Mottle

Backtrap mottle is a common printing defect that is difficult to correct. A good understanding of the mechanisms that leads to backtrap mottle is still lacking in the literature. A confocal laser scanning microscopy (CLSM) is used to evaluate samples that had different tendencies towards backtrap mottle. The coating structure is observed by staining the coating with a fluorescence dye. The final location of ink vehicle was observed by staining the resin with a fluorescent dye. Final prints that had backtrap mottle could be directly observed from the fluorescence of the magenta ink pigment. The distribution of magenta ink tends to be obscure on backtrap prints. Samples with uneven coated layer distributions correlated to the occurrence of backtrap mottle even though the coat weight is uniform. In addition, the contrast of fluorescence intensity was strong at portions of the thin coated layer: pore volume may decrease at region with thin coated layer. Samples with uneven ink resin distribution, tend to have backtrap mottle. Moreover, the resin hardly penetrates in regions with thin coated layers.