The metal pigments have special characteristics. In case of
bronze colours and with only few exceptions, therefore,
pigment and binder are delivered separately and mixed to
homogenous inks according to the prescribed mixture ratio
only before use. Without such separate delivery the metal
pigment may trigger polymerisation of the UV binder.
In general, there are two types of metal pigments: leafing
and non-leafing pigments.
The leafing pigments have a flat structure which favours a
very good metal effect. However, wetting of the pigment
surface by binders is difficult which results in insufficient
embedding of the pigment particles in the ink film which in
turn leads to lacking split resistance and to abrasion of the
inks.
The non-leafing metal pigment types have a rather spherical
structure which results in a less intensive metal gloss.
On the other hand, these pigments can be wetted easily
and therefore exhibit a considerably higher split resistance
and better wiping stability