impressão offset e solução de molha

What is a fountain solution in offset printing?

Although digital printing has been gaining ground, offset printing remains the most suitable solution for many large-volume situations. The offset printing process, more artisanal and often regarded as an art, results from the direct contact between the paper and the plate containing the image you want to print. In this activity we frequently hear about the “fountain solution”, but what is it anyway?

The fountain solution

The fountain solution is a liquid that serves to keep the areas of the plate that do not have printing graphics, clean and ink-free.

The basic composition of the fountain solution comprises water, a buffer salt that keeps the pH between 4.8 and 5.5 and isopropyl alcohol in the proportion of 6% to 8%. The most important feature of the fountain solution is the amount or concentration of each ingredient present.

In order to evaluate whether the proportion of each ingredient is correct, the pH value is measured as this value varies proportionally with the concentration of acids in the solution. However, in the case of buffered solutions, the pH remains constant within a wide range of concentrations. That is why it becomes necessary to measure the conductivity, which, on the contrary, varies linearly with concentration, and is, therefore, the value that best expresses the quantity of ingredients in the solution. The conductivity of the fountain solution is evaluated using equipment that express the values in µS (micro Siemens).

Ink and fountain solution

Each work has its own point of equilibrium between the amount of ink and the amount of fountain solution needed.

There is a narrow range inside which the ink and the solution interact in a stable way. The lack of water is easily perceived, since it causes the clogging of points in shady (dry) areas; on the other hand, excess solution is not always easily perceived, unless it is really excessive. A small excess causes emulsification, slows down the ink drying process, reduces the gloss and the printout’s resistance to abrasion.

In conclusion, only the absolutely necessary amount of ink should be used to obtain the desired saturation, and only the absolutely necessary amount of fountain solution to keep the counter-graphic areas of the plate clean. The effective control of these processes significantly improves the print quality and the final result of the work.