Using a rotational viscosimeter, the flow curve of offset printing inks is recorded. The viscosity is tested as a function of the shear rate. The ink is temperature-controlled during this test because the viscosity of offset inks also depends on the temperature.
The sliding friction coefficient of the ink surface can be used to estimate the drying behaviour or the degree of curing of printing inks. The surface becomes smoother the drier/more cured the ink is. This relationship is well-known with UV inks and varnishes and is used by the UV Cure Check measuring device which is offered by PITSID GmbH to determine the degree of curing.
However, this method can also be used for other ink systems, e.g. for oxidative drying inks or for dispersion varnishes. As these inks take a relatively long time to completely dry, the coefficient of sliding friction is measured at fixed intervals and the time at which no change occurs is recorded. This final value can be used to calculate the drying progression over time.
The degree of curing can also be determined with an FTIR spectrometer. The conversion of the acrylate double bonds is measured using a band in the IR spectrum. In addition, the interaction of the UV lamp and printing ink can be evaluated with regard to curing. The efficiency of the curing process can be determined over the complete printing format and the necessary radiation dosage for a speed-dependent power control of the lamp can be ascertained.
By equipping the institut’s own printing press with state-of-the-art drying technology, the institut’s researchers are able to conduct practical tests, e. g. during the development of new offset printing inks. In addition to LED-UV-technology, the press is equipped with conventional and iron-doped mercury-vapour lamps, an infrared dryer and a hot and cold air system as well.