What is the composition of printing ink?

Printing is widely used in our society for transmitting and presenting information. This has resulted in printing being used on many different surfaces ranging from aluminium can and plastic bottles through to paper. Special inks have been developed for use in these different situations.

Printing inks are made of four basic components:

• Pigments - to colour the ink and make it opaque

• Resins - which bind the ink together into a film and bind it to the printed surface

• Solvents - to make the ink flow so that it can be transferred to the printing surface

• Additives - which alter the physical properties of the ink to suit different situation.

These are formulated into ink in a two steps process.

Step 1 - Varnish manufacture

Varnish is the clear liquid that is the base of any ink. Different varnishes are made for different inks, but they are all made by mixing the resins, solvents and additives (often at high temperatures) to form a homogeneous mixture. The resins react together to some extent to make larger molecules, making the varnish more viscous the longer these reactions are allowed to occur.

Step 2 - Pigment dispersal

The pigment is mixed into the varnish and then ground to break up clumps of pigment and to spread the pigment evenly through the ink.