Each of these processes require different performance attributes.
• Offset printing requires high color strength with high pigment loadings, good flow, and workable viscosity. Offset ink must be immiscible with water. If high gloss is essential, lower oil absorption pigments are needed.
• Flexography ink is liquid and must be very fluid, with almost instantaneous drying properties. Rheology is critical, and low oil adsorption pigments are advantageous. If used for food packaging, different components must be suitable for food contact.
• Gravure ink must be low in viscosity and very fluid. Pigment loadings are relatively low.
• Letterpress ink must be fairly viscous, with a fairly high tack. The ink must have very good flow and the rheology must work at fairly high pigment loading. If high gloss is required, lower oil adsorption pigments are desirable.
• Screen Printing: The most critical performance requirement is rheology. The viscosity must be low, but prevent blurry printing. This is achieved with higher structure pigment blacks and by the adding fumed silica as a thixotrope or thickener. Optical density can be achieved with relatively low pigment black loadings. The choice of pigment carbon black depends on the undertone, jetness, and gloss required.