Special offset inks: Metallic / Pearlescent
A special position among the printing inks has been earned by those printing inks manufactured using metal pigments, iridescent pearl effect pigments, or interference pigments.
These printing inks are also called gold and silver printing inks, or inks that demonstrate a metal-like character.
Gold bronze pigments are obtained from ground brass alloys with a varying proportion of copper and zinc. The higher the copper content in the alloy, the redder the gold bronze. The technology used in the manufacture of bronzes enables the particle sizes of the metal pigments to be adapted to the respective printing technology.
For offset printing this is 3.5 μm; for gravure and flexographic printing 8–9 μm (the ink film thickness is therefore considerably higher than is usual with conventional inks/pigments (0.1–3 μm).
For the manufacture of silver pigments, aluminum with a purity of 99.5% is assumed. After melting in induction furnaces, the liquid molten mass is lacerated by a compressed air stream. The end product is a metal granulate with a metallically polished surface. These inks dry like a normal offset printing ink by absorption and oxidation.
The latest developments are gold and silver printing inks which are built up on water-dilatable dispersion varnishes and are transferred via coating units with a chambered blade system . These inks dry by absorption into the substrate and evaporation of the water contained in the ink. They have a clearly higher brilliance than the normal gold and silver printing inks which are based on varnish.
Inks with pearlescent effect pigments enable a characteristic gloss of the printed image comparable to the iridescent gloss of pearls. These pigments possess a mica core which is encased by one or more metal oxide layers.
Printing inks with metal pigments are also used in gravure and flexographic printing. The structure of these inks is identical to that of organic or inorganic color pigments.
Silver-metallic printing inks which are mixed with colored inks in any proportion are classified as satin inks.