抄録
Ink trapping was studied by observing the printed surface immediately after trapping using cast-coated papers and black offset proofing ink. There are many ink peaks on the surface. As there is same number of ink peaks on the ink roller after trapping, the ink transfer progressed via cavitation theory. The number of the ink peaks increased as the amount of trapped ink (y) decreased. We studied ink trapping by effects of ink variation (three black inks for offset proofing, synthetic paper and web offset) and printing substrate variation (coated papers, cast-coated papers, and plastic sheets). In each substrate with each ink, the number of the ink peaks increased with decreasing the y value. In the variation of the ink, the number of the ink peaks increased as following, synthetic paper ink ‹ offset proofing ink ‹ web-offset ink. At y = ca. 1.0 g m-2 using the cast-coated paper with the offset proofing ink, because the number of the ink peaks agreed well with the number of pinholes on the paper surface, the most of cavities in the ink trapping seemed to form by air supply from the paper surface. We also observed many ink peaks in ink trapping using the plastic sheets, air unsuppliable substrates. At small y value (y = ca. 1.0 g m-2), the number of the ink peaks is one fourth smaller than the number of the ink peaks on the cast-coated paper.
