engleski

THE CONTACT ANGLE OF REFERENCE LIQUIDS ON FLEXOGRAPHIC PRINTING PLATES AS A FUNCTION OF TIME

Wetting and spreading of a liquid on a solid surface are two surface phenomena which highly influence many processes in various industrial fields. The wetting properties of the printing areas on a printing plate have an important role in gaining high quality imprints since they influence ink transfer from a printing plate onto the printing substrate. In flexography are that properties even more important as the printing inks are of lower viscosity and the pressures in the printing process are lower in comparison to the other printing techniques. Although wetting properties could be observed by measuring static contact angle, the time dependant contact angle is of high importance as time for the ink transfer from the anilox roller onto the printing plate and finally to the printing substrate is very short. This paper shows results of determining wetting characteristics of two flexographic printing plates by measuring the dynamic contact angle of reference liquids and its influence on the surface free energy calculation. The obtained results have shown that contact angle values of two reference liquids are slightly influenced by the time of measurement, meaning they reach equilibrium state very fast. Furthermore, it could be seen that printing plate type also influences the dynamic contact angle values. Surface free energy of printing areas at investigated printing plates has not been significantly changed. This research proved that time of the measurement has slight influence on the value of the contact angle which means that reference liquids reach equilibrium state quickly and therefore surface characterization of the flexographic printing plates could be made by observing only static contact angle. On the other hand, when the most viscous liquid of the ones used (glycerol) was applied on the surface, contact angle changed in time so further research should be directed to determining the dynamic contact angle of the printing ink on the printing plate’s printing areas.

contact angle; wetting; surface free energy; flexographic printing plate

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