Evaluation of Physical Properties and Drying Efficiency of the Pulps Used in Thin Paper Production

In this study, we evaluated the physical properties and drying efficiency of the virgin pulps and recycled fibers, which were the main raw materials for the manufacture of thin paper grades. We selected hardwood bleached kraft pulp (HwBKP), softwood bleached kraft pulp (SwBKP), recycled liquid crystal display interleaf (LCD interleaf), and recycled steel interleaf (steel interleaf) according to the annual usage, and determined the fiber characteristics and drying efficiency after the stock preparation of the pulps using a laboratory disintegrator or a valley beater. And then the handsheets were made of those pulps to determine their strengths and optical properties. The LCD interleaf showed higher freeness and lower water retention value (WRV) than the steel interleaf because the fibers from the LCD interleaf were longer, wider, and less fibrillated than those from steel interleaf. The fiber length and fines content of SwBKP were higher than those of HwBKP at the same freeness after beating, which was consistent with fiber image observation. The drying efficiency of LCD interleaf was higher than steel interleaf, but the handsheets made of steel interleaf showed higher tensile strength, and lower opacity and light scattering coefficient than those made of LCD interleaf. Considering the lower freeness and higher WRV of steel interleaf, it was thought that the fibers from steel interleaf were more fibrillated than those from LCD interleaf. The drying efficiency was higher for HwBKP than for SwBKP. The handsheets made from SwBKP exhibited higher tensile strength and lower opacity and light scattering coefficient than those made from HwBKP. Therefore, we concluded that if LCD interleaf and HwBKP with excellent drying efficiency are used or steel interleaf and SwBKP with high strength are less refined and used for manufacturing thin papers, drying energy can be reduced effectively in a papermaking process.