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To reduce its environmental impact, the printing industry is transitioning towards using water-based inks. The liquid vehicle typically contains, besides water, cosolvents and surfactants to modify the physical properties of the ink [1]. Pigments and polymeric particles are added to create the print itself. To optimize the print quality, a thorough understanding of the transport processes of these complex liquids in paper substrates is necessary. Most conducted research focuses on the uptake of liquid in uncoated cellulose sheets [2], [3], [4]. However, the effect of a coating layer, consisting of CaCO3 and some polymeric binders, on top remains to be investigated.
Performing in-situ dynamic measurements of the imbibition process is challenging because the paper is only about 125 μm thin and the initial liquid uptake can be within 1 s [2]. Hence, large spatial and temporal resolutions are required. An ultra-fast NMR-based imaging technique [5], as schematically shown in figure 1, was developed for this purpose.
The transport mechanism is studied by following the obtained spatially dependent liquid distributions over time. An example of these liquid profiles obtained for the imbibition of a water-glycerol mixture, containing 20 wt% glycerol, can be seen in figure 2.
The results show that liquid imbibes without a clearly defined fluid front. Moreover, it is found that the short-term liquid uptake consists of three distinct phases which are different from the uptake in uncoated paper [3]. It is suggested that the coating acts as a resistance layer and slows down the imbibition such that imbibition and swelling happen at similar timescales.
| References | [1] A. Kamyshny and S. Magdassi, “Inkjet ink formulations,” Inkjet-based Micromanufacturing, pp. 173–189, May 2012, doi: 10.1002/9783527647101.CH12. [2] K. Sarah and H. Ulrich, “Short timescale wetting and penetration on porous sheets measured with ultrasound, direct absorption and contact angle †,” 2018, doi: 10.1039/c8ra01434e. [3] R. J. K. Nicasy, C. Waldner, S. J. F. Erich, O. C. G. Adan, U. Hirn, and H. P. Huinink, “Liquid uptake in porous cellulose sheets studied with UFI-NMR: Penetration, swelling and air displacement,” Carbohydr Polym, vol. 326, p. 121615, Feb. 2024, doi: 10.1016/J.CARBPOL.2023.121615. [4] T. Karppinen, I. Kassamakov, J. Aaltonen, H. Pajari, and E. Hæggström, “Measuring liquid penetration in the thickness direction of paper,” The European Physical Journal - Applied Physics, vol. 32, no. 1, pp. 65–71, Oct. 2005, doi: 10.1051/EPJAP:2005071. [5] R. J. K. Nicasy, H. P. Huinink, S. J. F. Erich, O. C. G. Adan, and N. Tomozeiu, “Ultra Fast Imaging NMR method for measuring fast transport processes in thin porous media,” Magn Reson Imaging, vol. 103, pp. 61–74, Nov. 2023, doi: 10.1016/J.MRI.2023.06.009. |
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| Country | the Netherlands |
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