Flexographic Inks

Flexography uses low viscosity liquid inks which dry by evaporation. Although the original aniline inks were dye based, most flexographic inks are pigment based.

The viscosity of flexo ink must be low enough to transfer properly to the inking system.

However, if the viscosity is too low the ink will run off of the plate and the ink will not have adequate print density.

In addition it may run down the sides of images, fill in reverses and halftones and even build a halo around characters.

There are additional viscosity concerns with water based flexo inks. These contain a binder that is soluble in a base such as ammonia or morpholine.

If insufficient base is present, the binder will precipitate before the ink is printed. The pH decreases and the viscosity of the system increases, causing the ink to coagulate.

Some amines are volatile and will evaporate while the ink is on press. This causes a decrease in pH and coagulation.