In-Mold Roller (IMR) injection molding is the most commonly used In-Mold Decoration technology for ink transfer. IMR is easily automated. It not only decorates but can govern surface feel and wear-resistance characteristics which add product value. The trouble with the IMR process is ink washout, that is when the polymer melt flow distorts the printed pattern. Mold design and molding process parameters govern ink wash out. However, there is no academic research on ink wash out.
Here, we used a 0.05mm thick membrane for IMR ink transfer. We varied the injection rate (90, 100 and 110 ccm/s), and the mold (50, 60 and 70℃) and melt (240, 250 and 260 ℃) temperature, to mold and decorate 100mm square plates, each 2.5mm thick. Than measured the ink wash out displacements and adhesion. We also used microcellular foaming to suppress ink wash out and to improve adhesion.
We found that ink wash out displacement increases with injection rate, mold temperature and melt temperature. Near the gate, we find the most displacement. We also found that adhesion decreases with the injection rate, but improves with mold and melt temperatures. We quantified this using fall off area measurements. We find that microcellular foaming significantly suppresses wash out.
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