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Fig. 4. The effect of basis weight on the ink mark length As shown in Fig. 4, the ink absorptions of the softwood and hardwood papers slightly decreased with increasing basis weight, as revealed by the increasing ink marks length. When the basis weight varied from 60 g/m 2 to 100 g/m 2 , the corresponding ink mark lengths for the softwood and hardwood papers changed, respectively, from 4.7 cm and 4.4 cm to 5.1 cm and 4.8 cm. Because the increased basis weight only facilitated the deposition of pulp fibers in the Z-direction of the paper, which has no effect on the fibers and internal structure of the paper, only a slight increase in ink mark length was detected. Meanwhile, the longer fibers tend to sink first and crosslink to form the lower layer of paper on the molded net during paper formation and dewatering. The fine fibers fall into the gaps on the surface of the wet web of paper due to their minimal size. The size of the void structure was effectively reduced, which thus resulted in the low ink absorption of the paper. Effect of Different Basis Weights on the Accuracy of Overprinting The surface compressibility of paper, one of the important factors affecting the clarity of the printing patterns and the accuracy of overprinting, determines the contact degree between the paper surface and the inking rubber at the moment of embossing. The basis weight significantly affects its surface compressibility, which in turn determines the accuracy of overprinting and finally reflects the quality of printing products. The basis weight of a paper can directly reflect its compressibility, which is responsible for the printing smoothness of a paper under the action of printing pressure. Especially during the first printing, the thickness of the paper was compressed by the printing pressure and partially rebounded after the cessation of the pressure. Therefore, the registration deviation always appeared during the subsequent overprinting because of the contact difference between two printings. When the basis weight of the paper was relatively low, the printing pressure caused a low compression deformation of the paper, due to the strong resilience of thin paper. As a result, the overprint had a relatively small error.
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Dong et al . (2020 ). “Ink absorption and overprint,” B io R esources 15(1), 1397-1406.
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