## 3 Results and Discussion
### Printing Properties of Coated Paper
This uniform performance underscores the robustness of the coating formulations in maintaining dry pick resistance, irrespective of the specific crosslinker used. It suggests that while zirconium content and crosslinker type are critical factors for other properties, such as wet rub and wet pick resistance, they have a negligible impact on dry pick resistance. This insight is valuable for formulating coating colors that require consistent dry pick resistance, offering flexibility in crosslinkers' choice without compromising this property. This consistency in dry pick resistance across different crosslinkers and zirconium contents ensures that manufacturers can achieve reliable performance in their coated paper products. Figure 9 presents images of the ink set-off test of coated paper treated with coating colors containing crosslinkers with different zirconium contents and a polyamine-based crosslinker, highlighting the effects of zirconium content on ink set-off properties. Ink set-off is a crucial parameter measured to ensure that excessive amounts of ink do not transfer from the printed packaging surface to the unprinted surfaces, which can affect the quality and appearance of printed materials [40; 41]. At a concentration of 0.5 parts, all crosslinkers, including the potassium zirconium carbonate (KZC) series and the polyamine-based PBC, exhibited excellent ink set-off properties. This suggests that at lower concentrations, the crosslinkers effectively contribute to minimizing ink transfer, ensuring high-quality print results. Figure 8: Images demonstrating similar dry pick resistance after dry pick test of the coated paper: (**a**) dry pick images at 0.5 part (indicating lower crosslinker concentration); (**b**) dry pick images at 0.9 part (indicating higher crosslinker concentration). Figure 9: Images demonstrating similar ink set-off properties after ink set-off test of the coated paper: (**a**) ink set-off images at 0.5 part (indicating lower crosslinker concentration); (**b**) ink set-off images at 0.9 part (indicating higher crosslinker concentration). However, at an increased concentration of 0.9 parts, the KZC series demonstrated worse ink set-off properties compared to PBC. This indicates that the KZC series is more effective in lower concentrations and that increasing the zirconium content beyond a certain threshold may negatively impact ink set-off performance. The deterioration in ink set-off properties at higher concentrations for the KZC series could be due to over-crosslinking or changes in the coating layer's surface characteristics, which may lead to increased ink transfer. This analysis underscores the importance of optimizing crosslinker concentration in coating formulations. While the KZC series is effective at lower concentrations, careful consideration must be given to its concentration to avoid compromising ink set-off properties. Conversely, PBC appears to perform better at higher concentrations, offering more flexibility in formulation adjustments. Understanding these relationships is essential for selecting the appropriate crosslinker type and concentration to achieve desired ink set-off properties and ensure the quality of printed packaging materials. Figure 10 presents images of the print mottle test of coated paper treated with coating colors containing crosslinkers with different zirconium contents and a polyamine-based crosslinker. Print mottle is tested for coated paper to evaluate the uniformity and quality of the printed surface [42; 43]. The results indicate that the types of crosslinkers, whether zirconium-based or polyamine-based, and their concentration in the coating colors did not significantly affect the printing quality of the coated paper. All printed images were well-defined on the coated paper without noticeable mottle. This uniform performance across different crosslinkers suggests that both zirconium-based and polyamine-based crosslinkers are effective in producing a smooth and uniform coating layer that supports high-quality printing.