Curtain coating-a new coating process for specialty papers-is emerging as a potential method for coating printing paper grades as well.In Part 1,we discussed the operational principles of the process.In Part 2,we present results from pilot-coater trials that demonstrate:(a)the operational window of the process and potential defects,and(b)a value proposition for coating lightweight coated(LWC)papers.By removing the air layer traveling with the web(moving faster than 400 m/min),we have been able to coat LWC at web speeds as high as 1500 m/min.Coating at high speeds requires low air void volume in the coating color and viscosity control.The most challenging issue has been removal of air bubbles from the coating color that might break up the curtain at the slot die exit or create coating layer defects.Macrovoids created from large air bubbles are easily managed.Microvoids of a few 10ths of a millimeter,however,are more difficult to remove and can induce fine coating layer defects.Careful choice of coating formulations and deaeration has made high-speed curtain coating possible.We show that curtain coating can achieve low coat weights(5.8 g/m~2)on LWC,with high coverage(85%),even at low coating solids(54%)to avoid detrimental bubbles in the coating.At a constant coat weight of 5-6 g/m~2,we saw nearly a 40% advantage in coating coverage using the curtain coating process instead of a metered size press.
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机译：幕涂-一种用于特种纸的新涂布工艺-也正在成为涂布印刷纸等级的一种潜在方法。在第1部分中，我们讨论了该过程的操作原理。在第2部分中，我们介绍了中试涂布机试验的结果证明：（a）工艺的操作窗口和潜在缺陷，（b）涂布轻质涂层（LWC）纸的价值主张。通过去除与纸幅一起移动的空气层（移动速度超过400 m / min） ，我们已经能够以高达1500 m / min的网速涂布LWC。高速涂布需要在涂料颜色和粘度控制方面降低空气空隙量。最具挑战性的问题是从涂料中去除气泡可能会破坏缝口模具出口处的帘幕或造成涂层缺陷。易于处理由大气泡产生的微孔。微孔只有十分之几毫米，因此更难以清除，并可能导致细微的涂层缺陷。小心c涂料配方和脱气的选择使高速幕涂成为可能。我们证明，即使在涂料固含量低的情况下，幕涂也可以在LWC上实现低涂层重量（5.8 g / m〜2），高覆盖率（85％）。 54％）以避免涂层中有害的气泡。在5-6 g / m〜2的恒定涂层重量下，我们发现采用幕涂工艺而非定量施胶机可将涂层覆盖率提高近40％。
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