Predicting inkjet dot spreading and print through from liquid penetration- and picoliter contact angle measurement

Abstract

Abstract In this study we have evaluated the suitability of laboratory testing methods to predict inkjet printing results. We have developed and used testing liquids that are spanning the operational window of industrial High Speed Inkjet (HSI) printers while still covering the maximum possible range of viscosity and surface tension. First we correlated liquid penetration measured with ultrasound (ULP) and direct absorption (ASA) to print through from HSI prints. The best correlation ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msup><m:mrow><m:mi mathvariant="italic">R</m:mi></m:mrow><m:mrow><m:mn>2</m:mn></m:mrow></m:msup><m:mo stretchy="false">≈</m:mo><m:mn>0.7</m:mn></m:math> {R^{2}}\approx 0.7 ) was found for the sized paper. For papers with increasing liquid penetration speed we found a decreasing ability of both testing methods to predict print through, for the strong absorbing paper the correlation drops to <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:msup><m:mrow><m:mi mathvariant="italic">R</m:mi></m:mrow><m:mrow><m:mn>2</m:mn></m:mrow></m:msup><m:mo stretchy="false">≈</m:mo><m:mn>0.2</m:mn></m:math> {R^{2}}\approx 0.2 . Second we correlated contact angle and drop diameter to the dot area from HSI prints. Contact angle turned out to be a better predictor for printed dot area than drop diameter. Evaluating the change in contact angle over time we found the highest correlation to the dot area in the print when measuring the contact angle as soon as possible, in our case 1 ms after deposition of the drop on the paper. We also compared contact angle with microliter drops to picoliter drops, which are in the size scale of the actual inkjet droplet. To our great surprise correlations for microliter drops were equal or better than for picoliter drops, particularly for highly absorbing papers. Thus in order to predict dot spreading on paper our results suggest to measure the contact angle with microliter drops. Overall we found that, using laboratory testing methods, print through and dot spreading for HSI printing can be quite well predicted for slow absorbing papers but not very well for fast absorbing papers.