Introduction

Printing inks are complicated mixtures of chemical compounds. The composition varies by printing process, by whether printing is sheetfed or web, and by substrate.

The composition varies by the solvent base, be it oil based or water based. It varies by drying mechanism and by whether the drying is by primarily chemical or by primarily physical processes.

Inks are divided into liquid and paste inks.

Gravure, flexo, ink jet, electrographic and some electrophotographic inks (or toners) are liquid inks. Lithographic and letterpress inks are paste inks.

The distinction between liquid and paste inks can be an arbitrary one, since it is based on apparent viscosity. A printing ink consists of vehicle and pigment.

Vehicle is all in the ink except the pigment.

“Varnish” is often used interchangeably with vehicle, but actually vehicle consists of varnish plus performance additives and solvent/diluent. As suggested by the name, the vehicle transports the pigment from the ink fountain to the substrate.

Varnishes must be chosen to wet the pigment. It it doesn't wet the pigment, suspension is virtually impossible and the ink will not have the desired rheological properties.