造纸涂层材料动态选择性渗吸机制及渗吸模型的研究

The transport of fluid in the coating of paper is directly dependent on the structural imbibition performance of coating material. And the imbibtion characteristic is further stressed due to the wide application of environmentally friendly water-based ink and digital ink jet printing. However we often don’t consider this important factor previously when designing and developing the novel coating materials of paper in our domestic research because of the complicated and disordered porous structure of coating. For some quality problems arising from penetrating, we only have to resort to some compensating technologies like surface finishing and modification to correct or decrease these. The solution for problem above is not reasonable and leads to pretty bad imbibitions performance of paper coating in contrast to some high quality products imported. Previous experimental studies show that the competitive regime of absorption quite often occurred in the process of imbibtion, which could not be explained by some classic spontaneous imbibtion theories. Therefore what reason generates this kind of interested behavior of imbibition? Moreover, how does the interparticle pores and intrapaticle pores of irregular structure chose the preferential way to penetrate in the porous media and what force system to drive this wetting and wicking ways. In this research, we set to find out the intrinsic scientific problems in the behavior mechanism of imbibition, the process of wicking and wetting, and the characterized disorderedly stochastic porous structure. Considering these, we attempt to disclose the essence mechanism of dynamic competitive imbibition. The fruits obtained in this project will supply an efficient method and theoretical basis to control and design the imbibition performance before manufacturing the coating material. And some theories and methods for the industry of papermaking are formed eventually.

流体在纸张涂层中的传输直接由涂层本身的渗吸性能决定。同时，随着环保型水基油墨和数字喷墨印刷技术的广泛应用，又对涂层渗吸控制能力提出了更高的要求。由于涂层复杂无序的多孔网络结构，国内对涂层材料的设计和开发，并没有预先考虑材料的渗吸特性，常常通过涂层成型后的表面整饰和改性来弥补渗吸性能的不足，这也是我国高品质纸张涂层材料依赖进口的主要原因。前期实验研究表明，涂层渗吸存在选择性的竞争机制，经典渗吸理论仍无法解释这些渗吸行为，那么产生这种机制的机理何在？面对小孔和大孔的随机结构，渗吸、润湿行为又如何驱动？本课题结合现代分析测量技术，通过对涂层渗吸行为机制、多孔介质的渗吸润湿过程，复杂网络结构的表征等方面进行探讨，揭示动态选择性渗吸机制形成的内在机理。研究成果能预先从材料结构上对渗吸特性进行设计和控制，为高性能涂层材料的生产提供科学的理论依据，并形成我国造纸涂层材料渗吸的基础理论。

印刷流体在纸张涂层中的传输直接由涂层本身的渗吸性能决定，很多印刷质量问题都与纸张涂层材料的渗吸特性有密切关系。由于涂层材料是一种典型的无规、无序多孔结构，给渗吸性能的研究和表征带来了很多技术难题。本课题针对造纸涂层材料的渗吸特性，对涂层材料的渗吸行为进行了全面的研究，主要体现以下几个方面：. （1）从理论推导和实验仿真分别考察了经典渗吸模型的内在关系，在渗吸初期惯性力渗吸和Bosanquet渗吸是一致的。在渗吸过程的中后期，涉及惯性力的Bosanquet渗吸会转化成Lucas-Washburn渗吸。因此在描述纸张涂层材料渗吸时，Bosanquet渗吸模型能够较为全面的表征材料渗吸特性。. （2）在渗吸实验及根时间标度下，发现了有悖经典理论的渗吸分区现象。提出了形成渗吸分区的毛细凝聚润湿模式：粗糙表面的毛细凝聚作用形成了液膜，液膜的平滑效应降低了后续的润湿能力，导致渗吸性能的下降。. （3）从纸张涂层材料结构上，给出了形成渗吸分区的结构性证据。基于粗糙表面的润湿模式和润湿接触线长度变化，建立了基于润湿接触线的毛细管渗吸模型，实施了根时间机制下的实验与模型的匹配，取得良好的效果。. （4）基于FHH分形方法，证明了造纸涂层材料在纳米孔/介孔范围内存在的分形特征。依据涂层材料分形的特征，对润湿接触线进行了线形分形建模，提出了基于分形结构的渗吸模型，探讨了根时间机制下和时间机制下渗吸模型与实验渗吸的匹配。证明了惯性力累积效应在渗吸初期形成的积极作用。. （5）研究了纸张的Y向渗吸，对于未加填的纸张，纸张的Y向渗吸不服从经典的渗吸模型。但是随着填料的增加，加填会形成一些新的孔隙结构，纸张的Y向渗吸将服从Bosanquet渗吸模型。因此对于加填的文化用纸，纸张的Y向渗吸均服从Bosanquet渗吸模型。. 本课题所建立的渗吸模型、渗吸行为、材料分形结构及相关的研究结论，能够对涂层材料渗吸进行较为全面的解释，对涂层材料渗吸创新设计及结构改进、新型涂层材料的研发有重要的意义。