The quality of lithographic printing depends on a satisfactory ink/water emulsion being formed on the plate cylinder of the press as lithography relies on a physical distinction between the hydrophobic image and hydrophilic non-image areas of the lithographic plate.
With the exception of waterless plate printing all other types of lithographic plate require the application of a fountain solution to wet the non-image plate areas. However at the hydrophobic image surface the remaining fountain solution isunable to form a continuous film because of the higher surface tension and forms globules which should be picked-up by the ink.
This fragile equilibrium, also called ink/water balance is necessary to guarantee the optimum print quality. A certain degree of ink/water emulsification (emulsion capacity) is needed to remove the unwanted ink from the non-image area of the plate but excess would destroy the difference in surface energies of the emulsion and the pure fount solution leading to a severe loss in printing quality.
With labscale water balance tests on open systems realness conditions couldn’t be simulated because important parameters like, water content and nip forces profiles, have not been quantified or controlled sufficiently. With the modern measuring system from Novomatics new methods for roller based ink/water balance tests are introduced that cannot only determine rheological properties like vertical tack and ink elasticity but also quantifies accurately the relevant water balance parameters like:
- minimal emulsified water content for correct plate cleaning
- maximal emulsified water content for stable emulsion (for example, sufficient tack)
- dynamics of water pickup and release
- amount of free surface water
- effects of different ink residual times
- and much more
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