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Summary:
Conventional test methods for determining drying time of printing inks are subjective. The comment methods involve finger swiping and visual assessment or accompanied complicated procedures by rubbing tester with destruction of samples. These methods encounter difficulties in qualifying the extent of drying, thus, seem to be restricted to obtain comparative data of drying property. In this paper, the methodology of determining the drying time of inks on substrate by monitoring reflected speckle patterns arisen from ink surface by laser illumination was discussed. The dynamic alteration of speckle patterns corresponds to the fluctuation of microscopic structure of the ink surface with penetration and evaporation of dispersion elements. The methodology assumed when the correlation coefficient of successive speckle patterns captured by CMOS camera at a certain time interval is in a stationary state, the ink film is considered as dried. The method is objective, noncontact, and inexpensive. The experimental data of inks drying measured by the speckle method were compared with the result byASTM F2498 for inkjet print and JIS K5701 for drawndown offset ink. The comparison results showed that the speckle method has good correlation for different media with ASTM F2498, however no significant relation with JIS K 5701 which leads to transference of the undried inner ink rather than surface. The reflective speckle is limited to observe the surface area of ink films. Transmitted speckle patterns of samples should be investigated to improve conformity test purpose as a future work.