Printing Inks

Process cyan is almost always Pigment Blue 15:3, the beta form of copper phthalocyanine blue, and process magenta is usually Pigment Red 57:1, sold as rubine toner. Process yellow is typically a diarylide yellow such as Pigment Yellow 12 or 13, and black is carbon black, often toned with a blue such as Prussian blue for a deeper, more neutral black. The ink system and substrate decide the exact grade.

Mainly alcohols and esters. Ethanol, isopropanol and n-propanol dissolve the binder and evaporate quickly, while ethyl acetate and n-propyl acetate are used with nitrocellulose and polyurethane resins, especially in gravure. Small amounts of slower solvents stop ink drying on the anilox roll or cylinder. In India, food-packaging inks must follow IS 15495, which the FSSAI packaging regulations refer to and which excludes toluene, so food-pack converters ask for toluene-free inks.

Sheetfed offset inks dry in two steps: the thin oil fraction sets into the paper by absorption, then the drying oils and alkyds in the vehicle cross-link with oxygen from the air. Cobalt octoate is a strong surface drier and manganese octoate is also active, and the two are often used together at low doses. Too much drier shortens shelf life and can dry ink on the rollers, so the dose comes from the ink maker's trials.

Waxes give printed work rub, scuff and scratch resistance and add slip. Fine micronised polyethylene wax moves to the surface as the ink film forms and leaves a low-friction layer, so cartons, labels and magazines survive stacking, transport and handling without marking. Polyethylene gives hardness and rub resistance, and PTFE blends add extra slip. Choose the grade by particle size, melting point and ink type: offset, flexo or gravure, water- or solvent-based.