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The dimensional stability of paper during printing is crucial for ensuring production quality and runnability. However, inkjet printing faces inherent challenges due to the hygroscopic nature of paper and the use of water-based inks. Despite freshly printed sheets are flat, a considerable development of paper curl is often observed during storage. In this study, we establish the link between the migration of ink co-solvents and the long-term curl development of printed paper. A4 paper sheets were sprayed with a water-glycerol model ink and changes in the sheet's curvature were monitored using a 2D-laser sensor. We also investigated glycerol migration by splitting the sheets into layers and determining the glycerol distribution using high-performance liquid chromatography. Our results demonstrate the development of curl during storage as well as glycerol migration in thickness direction of the sheet, both on a comparable timescale. We thus propose that long term curl in inkjet printing can be caused by z-directional migration of the co-solvent (glycerol) over time. This study enhances understanding of the physical mechanisms that drive the long-term curl phenomenon in inkjet-printed sheets. The results can be used to optimize printing processes, allowing for the production of higher quality printed products with greater dimensional stability.

Paper derived from lignocellulose has great advantages over plastics as packaging material, nevertheless, the poor water- and oil-resistances of paper-derived products limited their application in high-end field. Herein, novel dimer acid-based waterborne polyurethanes (DWPUs) with different content of dimer acid-based polyester polyol (DG) were prepared and used as water- and oil-resistant coating for paper substrate. The effects of DG contents on water- and oil-resistances, mechanical properties and thermal stability of DWPUs coated papers were systematically investigated. When the content of DG reached up to 7 wt% (based on polyester glycol), the paper coated by DWPU exhibited 88.06% decrease in Cobb 60 value, 8.7 times increase in kit rating compared with uncoated paper. Meanwhile, DWPUs coated papers showed good mechanical properties and thermal stability. These improvements are attributed to the flexible long-alkyl chain, and six-ring structure of DWPUs as well as the continuous and homogeneous DWPU-derived membrane on the surface of paper. This study provides a new framework for the preparation of high quality, multifunctional, environmentally friendly water- and oil-resistant coatings for paper substrates.

[Display omitted] • For the first time the root cause for paper curl developing over days and weeks is described. • The curl of the paper sheets is caused by migration of co-solvents (e.g., glycerol) from the inkjet ink. • A 2D-laser scanner is utilized to investigate short- and long-term paper curl. • Glycerol migration in paper sheets is monitored using a combination of sheet splitting and subsequent HPLC analysis. The dimensional stability of paper during printing is crucial for ensuring production quality and runnability. However, inkjet printing faces inherent challenges due to the hygroscopic nature of paper and the use of water-based inks. Despite freshly printed sheets are flat, a considerable development of paper curl is often observed during storage. In this study, we establish the link between the migration of ink co-solvents and the long-term curl development of printed paper. A4 paper sheets were sprayed with a water-glycerol model ink and changes in the sheet's curvature were monitored using a 2D-laser sensor. We also investigated glycerol migration by splitting the sheets into layers and determining the glycerol distribution using high-performance liquid chromatography. Our results demonstrate the development of curl during storage as well as glycerol migration in thickness direction of the sheet, both on a comparable timescale. We thus propose that long term curl in inkjet printing can be caused by z-directional migration of the co-solvent (glycerol) over time. This study enhances understanding of the physical mechanisms that drive the long-term curl phenomenon in inkjet-printed sheets. The results can be used to optimize printing processes, allowing for the production of higher quality printed products with greater dimensional stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel dimer acid-based waterborne polyurethanes (DWPUs) were designed and prepared. • DWPUs were first used as multifunctional coatings for paper substrates. • Papers coated by DWPUs exhibited excellent water- and oil-resistances. • Alkyl and uniform membrane of DWPUs are critical to improve papers' properties. Paper derived from lignocellulose has great advantages over plastics as packaging material, nevertheless, the poor water- and oil-resistances of paper-derived products limited their application in high-end field. Herein, novel dimer acid-based waterborne polyurethanes (DWPUs) with different content of dimer acid-based polyester polyol (DG) were prepared and used as water- and oil-resistant coating for paper substrate. The effects of DG contents on water- and oil-resistances, mechanical properties and thermal stability of DWPUs coated papers were systematically investigated. When the content of DG reached up to 7 wt% (based on polyester glycol), the paper coated by DWPU exhibited 88.06% decrease in Cobb 60 value, 8.7 times increase in kit rating compared with uncoated paper. Meanwhile, DWPUs coated papers showed good mechanical properties and thermal stability. These improvements are attributed to the flexible long-alkyl chain, and six-ring structure of DWPUs as well as the continuous and homogeneous DWPU-derived membrane on the surface of paper. This study provides a new framework for the preparation of high quality, multifunctional, environmentally friendly water- and oil-resistant coatings for paper substrates. [ABSTRACT FROM AUTHOR]