Recent experimental advances in characterising inks and substrates optimising inkjet processes and ink adhesion
Inkjet printing processes are governed by the solid-liquid interactions between ink and nozzle and ink and substrate. In particular, due to the large range of very different substrates, a proper adjustment of the ink to the substrate properties is important to ensure a proper print image preventing e.g. fuzzy images due to excessive drop spreading or Marangoni-effect driven coffee stain effects. We will explain and illustrate on customer examples, how state-of-the-art dynamic surface tension and picoliter sessile drop contact angle measurements help to adjust inks to certain printing processes. In addition, we provide ideas how interfacial rheology measurements can be useful to gain insight into Marangoni flows during evaporation. Also, considering the polar and disperse parts of the inks’ surface tension and the substrates’ surface free energy can help significantly optimising not only the print image, but also the durability, i.e. long term stability of a particular ink-substrate pairing, as will be illustrated in this presentation. Further, we will demonstrate on the example of polyethylene and polypropylene when and why test-inks (i.e. dyne pens) fail to monitor the efficiency of plasma and/or corona pre-treatments and how modern contact angle measurements can prevent substrate overtreatment and thus assuring best durability of a coating. In this context, we will also illustrate how the recently patented liquid needle dosing technique facilitates high speed contact angle measurements, in that possible error sources still present in traditional contact angle techniques are intrinsically excluded and thereby provide substrate’s surface free energy data of highest reproducibility and best comparability combined with greatest ease-of use.