High Electrical Resistivity Inkjet Ink Composition

When printing in the drop-on-demand mode employing certain inkjet ink compositions on substrates which retain high static electric charges, such as in poly(ethylene) and poly(vinyl chloride) shrink wrap packaging materials, the printer nozzle tends to clog up more frequently than normal (52). 

Namely, poly(ethylene) and poly(vinyl chloride) films tend to hold high static electrical charge. This static charge is generated when the substrates unwind from the spool or are transported via a conveyor system under the printer nozzle. The static charge can be up to 40 kV. This charge tends to distort the ink droplets, causing the droplets to break up more easily and form microsatellites. These microsateUites then accumulate on the printer nozzle. 

Then the ink builds up around the nozzle on the nozzle plate, which leads to poor quality images. Thus, the printer nozzle requires periodic cleaning, which leads to more frequent printer downtime. 

This drawback can be minimized by using compositions with a high electrical resistivity. Such an inkjet ink composition comprises a nonconductive solvent, binder resins that are soluble in this nonconductive solvent, and a colorant that is also soluble in the nonconductive solvent (52). Compositions with high electrical resistivity are shown in Table 5.17. 

In Table 5.17 the rosin ester resin promotes film formation on the printed image, the vinyl resin is a vinyl chloride/vinyl acetate resin containing acrylic acid monomer units for improving adhesion to substrates. 

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