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Fig. 1. (A) The capillary structure sizes of the paper surfaces; (B) the ink mark lengths of different papers A two-step process was employed in printing, involving pressing the ink into the voids on the surface of the paper and the subsequent penetration of the ink into the voids by capillary absorption. As shown in Fig. 1B, beating remarkably reduced the ink absorption of both softwood paper and hardwood paper. The ink absorption performance of the hardwood paper was better than that of the softwood paper, which was mainly attributed to the short and narrow fibers of hardwood pulp. Many capillary structures and high surface smoothness resulted from the paper preparation to improve the spreading, adhesion, and penetration of ink. Furthermore, the ink absorption of the paper was closely related to the gap size between fibers. The gap sizes of papers with different beating speeds were measured with a polarizing microscope, as shown in Fig. 1A. The prepared paper with a beating revolution value of 5000 revs showed a void distribution of 120 μm to 165 μm between fibers. These large voids allowed the ink to penetrate into the papers and caused a short ink mark length of 3.5 cm, indicating excellent ink absorption. With increased beating speed, the space between the fibers decreased to a range from 50 μm to
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Dong et al . (2020 ). “Ink absorption and overprint,” B io R esources 15(1), 1397-1406.
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