engleski

Interpretation of Ink Tack Stability Testing Results for Improved Offset Printability

One of the key requirements for offset ink is for it to remain fluid while in the offset machine, whilst it must also dry sufficiently once on the printing substrate. Too fast or too slow drying of ink on a substrate can cause its own variety of printing problems such as mottle, set-off failure, gloss reduction. Thus, the appropriate ink transfer through the rollers as well as to the printing substrate is of great importance. Ink tack is considered responsible for ink transfer, insufficient ink tack results in poor ink transport, high tack may influence the surface causing damage to the printing paper. Ink tack should not be considered as a static value due to the numerous factors influencing it ; in addition, these factors are not constant during the printing process. The presented study aims to observe the dynamic ink tack readings from the printers’ perspective. As a function of distribution and splitting time, readings serve to determine the ink stability on the printing press. The impact that prolonged film splitting has on the printability is evaluated in the laboratory conditions. The ink tack results are taken as an ink tack curve, formed from readings taken as a function of time and should be explained as such. The experiment was performed on an IGT Tackoscope, a tack measuring device, IGT inking unit and IGT Amsterdam, a printability tester. The IGT Tackoscope operates by sensors to define and calculate the force required to separate the ink layers in the contact zone between two rollers fed initially by a distribution system. Two different inks were tested, one ink being a faster drying ink than the other. By setting different distribution times on the high-speed inking unit, the strips of a laboratory reference paper were subsequently printed under laboratory conditions. The evaluation of the laboratory prints showed a good correlation between the ink tack readings and printability results. The presented method of evaluating dynamic tack test results can help in preventing a variety of printing problems by providing a more precise prediction of offset ink stability during the printing process.

tack stability test, printability, ink splitting, tack curve

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