表面自由エネルギーとインキ転移率

抄録

There still exist ambiguous problems to be solved in the mechanism of ink transference to solid surfaces during printing process. The objective of this study is to clarify the fundamental relationship between surface free energy and ink transfer. Model ink droplets (0.1-0.2μl) of aqueous and non-aqueous types were placed by a micro-syringe on one substrate surface and attached to another surface parallel to the deposited one with the gap of 150μm. Droplets were elongated perpendicularly toward separation by adjusting computer control at constant velocities (10-70μm/sec). Cross-sectional views of liquid during the deformation process were recorded by means of video systems and analyzed to determine the transfer ratio. As the aqueous type, water and polyethylene glycol based inks were employed, and dibutyl phthalate based ink was employed as the non-aqueous type, respectively. Four types of substrates having different surface free energies were examined, namely, Al foil and three polymers, such as polyethylene terephthalate (PET), polytetrafluorethylene (Teflon) and silicone rubber. The following conclusions are obtained for the model inks combined with couples of the substrates: (1) As for the ink based on water with high polar component of surface tension, the transfer to the substrates with high surface free energy is generally unstable. In the combination of the same surfaces with very low surface free energy, the transfer seems to suffer gravitational effect, because the mostly remaining liquid on the substrates positioned low after the transfer. Also compared with the water based ink, the transfer ratio of the polyethylene glycol based ink is more stable because of the lower surface tension, and the deviation of the transfer ratio is smaller. (2) In the case where combination of the substrates is different and the difference of surface free energy is high, the water based ink transfers almost to the substrates having the higher surface free energy. As for the polyethylene glycol based ink, the transfer ratio to the polymer surfaces with the lower free energy reaches 10-20%. (3) As for the non-aqueous ink based on dibutyl phthalate with high dispersion component of surface tension, in the case where combination of substrate surfaces is the same, the transfer is mostly stable and the ratio reaches about 50%. Also in the case where each couple of the substrates is different, the transfer of 10-20% to the substrate with lower surface free energy takes place, as is different from the water based ink. (4) The effect of elongation velocity on the transfer ratio is almost negligible in the range of 10-70μm/sec. (5) The cross-sectional profiles of liquids viewed during slow deformation process are deeply related to interactive forces between liquid and substrate that are mutually due to their surface free energies. Also some findings in the viewed profiles obtained through the elongation indicate that it would be difficult for those profiles to be approximated by circular locus, as assumed by Yakhnin et al.