During combustion, solvent based inks release strong odours which are perceptible by people.
Water based inks have now been developed which do not release perceptible combustion odours.
What are the differences between the two types of ink that make them behave so differently?

Let’s start by looking at their different formulations:
A drop of solvent based ink is composed of 35% pigment and 65% apolar solvent.
A drop of water based ink is composed of 33% pigment, 33% water soluble non-toxic polar solvent and 33% water.

The problem arises during firing.
In a drop of solvent based ink, the solvent is burnt and broken up into compounds which are very strong smelling, while the pigment is fixed to the surface of the substrate.
In a drop of water based ink, the non-toxic polar solvent is burnt and broken up into odourless compounds, while the ink fixes to the substrate, as in the case of solvent based ink.

Why do people not smell any odour?

The polar solvents used in solvent based inks are primarily composed of long carbon chains with a variable number of branches. Combustion breaks these chains (cracking) into smaller chains which are responsible for the strong odour.
Water based inks, on the other hand, contain specific water soluble polar solvents whose molecules are degraded during combustion in such a way as not to generate strong smelling emissions.

Using water based inks thus does not require the printing system to be modified with post-combustion systems to burn the products of primary combustion to reduce the odour.