Ink used for lithographic offset presses is a paste, rather than a fluid. That means it is thick and tacky.It is typically delivered in canisters. The image below shows Quattro offset printing inks from 4S Graphics.
Like all printing inks, offset lithography ink consists of three substances:
- The ink vehicle is the fluid part of the ink that transports the pigment onto the substrate. This is typically an oil based material.
- The pigment is the part of the ink that imparts gloss, color, texture, and other characteristics to the printed image. Pigments can be black, white (either opaque or transparent), and colored. The colored pigments are usually produced from either mineral sources or from derivatives of organic coal tar. Other materials such as metallic powders are used for specialty inks.
- Various additives influence the characteristics of the ink. Driers speed up the drying of inks. Bodying agents increase the viscosity. Waxes help prevent printing defects like ink setoff and blocking and they increase the scuff resistance of the ink. Other materials are added to reduce the ink’s tack, improve its distribution on the printing plate, prevent oxidizing and enhance other properties of the ink.
Web offset inks tend to be more fluid and have less tack than sheetfed lithographic inks. Most offset inks dry rapidly without the need for additional equipment, but there are also inks optimized for infrared, ultraviolet or electron beam curing. All offset inks contains water-repellent materials, needed because offset lithography is based on the fact that oil and water do not mix.
Since offset presses can print on a wide variety of surfaces, a large number of inks are available for the process. This YouTube movie shows how it’s manufactured.
More information on inks is available on this page.