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The vibration frequency of the coating machine is monitored and adjusted to improve the surface properties of the coated paper. The doctor blade coating process has seen significant advancements in recent years, and it has attracted widespread interest among many researchers. They have sought to develop mathematical models to explain phenomena occurring at the blade tip and beneath it during the coating process, and have studied the combined effects of factors such as coating blade pressure, blade angle, and coating concentration in extensive practical applications of coating machines. Here, a direct link is established between the K&N printability of the coated bleached paperboard and the influence of blade tip vibration.
For doctor blade coating of low-grade paper with poor formation, it is assumed that when a straight scraping force is applied to the paper surface, fibers on high-density flocculated clumps are either lifted or scraped off by direct friction with the blade’s inclined surface. When the blade undergoes natural vibration due to the roughness of the base paper surface, its frequency is independent of the paper machine speed; this frequency is the superposition of multiple component frequencies. The results of these studies on blade tip vibration indicate:
① Installing an infrared dryer after the first coater to improve the curing performance of the primer coating, and effectively reducing the vibration of the straight blade on the second coater, both improve the surface properties of the coated board.
② Installing a backing plate on the coating blade of the second coater to shorten the free overhang of the straight blade can increase the vibration frequency from 1200 Hz to 3100 Hz and reduce the amplitude from 0.293 mm to 0.0082 mm (peak-to-peak displacement). This also improves the surface properties of the coated board and its K&N printability. Coater suppliers should comprehensively consider the impact of blade tip vibration on the board surface during design and improve or develop new beveled blade coaters. Based on the results of these studies, we recommend that reducing amplitude or increasing frequency will improve the surface properties of coated board and enhance its printability.