“At the heart of the inkjet printer is the print head – it determines whether printing is a success or a failure. Keeping it working for as long as possible is the topmost priority,” explains Dr. Ulrich Lauter, co-developer of the new polymeric binder VINNOL® E 18/38 and a technical service manager at WACKER. The print head, together with the printing ink, determines the quality of the print.
For the highest resolution, the print head must be designed in such a way that the smallest-possible ink droplets form and strike the printing surface. However, the smaller the droplets, the lower the viscosity of the ink has to be. The ink also determines the degree of color saturation. Particularly brilliant color prints are obtained with pigments that are dispersed very finely and homogeneously in the liquid printing ink – the tiny pigment particles must not form large agglomerates and should remain in suspension for long periods of time.
“These requirements – low viscosity and no settling – pose a dilemma for ink makers,” says Dr Lauter. “The thinner the fluid ink, the more readily the pigment particles will settle.” Settling not only impairs color brilliance, but also shortens the service life of the print head. If individual nozzles in the print head become clogged with pigment particles, the inkjet printer will stop working. A key role regarding viscosity and dispersibility is played by the polymeric binder employed. “As inkjet printing technology advances, it is essential that the binders in particular be optimized,” stresses Dr. Lauter. The binder is the film-forming component of a printing ink – it envelops the pigment particles, binding them together and fixing them on the substrate.
WACKER has been offering binders under the brand name VINNOL® E for many years. These enable ink makers to keep settling to a minimum, explains the WACKER expert: “The binders are vinyl chloride–vinyl acetate copolymers, which we produce by emulsion polymerization. These polymers are recognized for their ability to interact with the pigment surface, stabilizing the finely ground particles and keeping them in suspension.” That is why VINNOL® E represents a good compromise between the two conflicting goals of low viscosity and little or no settling.