微型凹版胶印中液体转移过程的仿真研究

Simulation of Liquid Transfer between Separating Walls for Modeling Micro-gravure-offset Printing

本文通过数字建模方式对凹版胶印过程中的液体转移过程进行研究。具体方法是,用两个相互平行的印版间液体的转移过程模拟在硅橡胶辊或软垫的作用下油墨转移到承印物上的过程;用梯形网穴与其上方运动的印版间的液体转移过程模拟油墨从凹版网穴拉出并转移到硅橡胶辊或软垫上的过程。阐释在两平行印版间的液体转移过程中,液体的拉伸、分裂,以及反冲过程,同时观察卫星式液滴的产生,评估分离速度、液体黏度、表面张力、重力以及接触角对液体转移过程的影响。研究液体从梯形网穴转移到其上方运动的印版中的3个阶段:1)整体拉伸阶段;2)中央拉伸、分裂、以及反冲阶段;3)平衡阶段。找出转移液体的最终幅宽与上部印版的接触角的关系,分析剪切高度的影响因素。本文还对初始距离和网穴形状对液体转移的影响进行了探讨。

A numerical study of the liquid transfer processes that occur during micro-gravure-offset printing is carried out. Specifically, liquid transfer between two parallel separating plates and between a trapezoidal cavity and an upward moving plate＇are simulated, as models of the printing of ink from the offset pad onto the substrate and the picking up of ink from the gravure plate by the offset pad, respectively. During the liquid transfer between two parallel plates, the stretching, breaking and recoil of the liquid are illustrated, and the generation of a satellite droplet is observed. The influences of the separation velocity, liquid viscosity, surface tension, gravity force, and contact angles on the liquid transfer are estimated. For the transfer of liquid from the cavity to the upward moving plate, the findings indicate that the process can be divided into three stages： （1） a whole stretching stage; （2） a central stretching, breakup and recoil stage; and （3） an equilibrium stage. The final width of transferred liquid is closely related to the contact angle at the upper plate, while the cut height is mainly affected by the contact angle at the cavity side wall. The effects of the initial distance and cavity shape are also discussed.