Presently we run two Heidelberg printing presses – a single colour with numbering & perforation, used mostly for NCR books and our new four colour Heidelberg VP print press. The alcohol dampening system in our multicolour press provides excellent colour calibration, smooth and even coverage through the entire press run. The alcohol used almost universally in the printing industry is called isopropanol, or IPA. It is completely soluble in water, and doesn’t have an unpleasant odour or any side effects.
IPA reduces surface tension of the dampening solution. Surface tension is the microscopic attractive force between liquid molecules that makes water form a droplet. When this force is reduced by alcohol, the droplet "relaxes", and the same volume of water will spread thinner to cover a greater area of the plate. This spreading is sometimes referred to, quite correctly, as wetting.
Because IPA evaporates so readily, it reduces the amount of fountain solution carried across to the stock and also to the ink, evaporating swiftly because of the mechanical heat generated during printing. IPA has a high affinity for water, and takes some of the water along with it when evaporating. Consequently, there is less water in the ink and less water in the printed stock.
IPA also takes away heat when it evaporates. This feature of isopropanol, called latent heat of evaporation, cools the press right where it is needed, in the printing nip, and so aids the printer by stabilising temperatures which can affect ink viscosity and transfer.
IPA slightly increases the fountain solution viscosity (or body), which gives a thinner, more uniform film allowing the press operator better control over the colour and drying of jobs.