基于格子Boltzmann的喷印OLED散点墨滴沉积仿真分析

LBM Based Simulation Analyses of the Scattered Droplet Deposition in Printed OLEDs

为解决喷印OLED发光层制备中基板污点、涂布不均等问题引起的Mura缺陷,建立基于单松弛格子玻尔兹曼方法(BGK-LBM)的3维数值模型,对喷印OLED像素槽附近墨滴落点偏差引起的散点沉积缺陷进行仿真分析。先研究不同墨滴尺寸以不同撞击速度撞击不同接触角平板后的最大铺展半径,再以最大铺展半径为参考研究不同润湿性梯度下的像素槽外墨滴的铺展回流,最后得出接触角变化时的墨演有效落点偏差的相图。结果表明:对于微米级直径的OLED喷印墨滴,尺寸越大、墨滴撞击速度越大、像素槽内接触角越小其最大铺展半径越大;而针对存在落点偏差的散点,当最大铺展半径大于或等于散点的落点偏差时,将在足够的像素槽基板内外接触角差值引起的润湿性梯度牵引下重新进入像素槽内;撞击速度还影响其回缩阶段的回缩速度,撞击速度越小回缩越慢,因此墨滴会受到润湿性梯度的影响而被牵引向润湿度高的一侧;只有当像素槽内外接触角造成的润湿性梯度足够时,在撞击铺展后边缘进入像素槽边界处的墨滴才能被牵引重新流入像素槽内,散点沉积缺陷即得到抑制。本文提出的最大铺展半径可以用来拓宽像素槽外墨滴的有效落点范围,作为喷印OLED制备中打印精度控制的参考,用于指导生产。

In order to solve the Mura defects caused by substrate blemishes and uneven coating during the inkjet printing of OLED emissive layer,a 3D numerical simulation model based on Bhatnagar-Gross-Krook-lattice Boltzmann method(BGK-LBM)was established to simulate and analyze the scattered deposition defects caused by the deviation of inkjet drop points near the pixel pits.Firstly,the maximum spreading radius of the inkjet droplets after impacting with different size,contact angles and different impact speeds was studied.Then,the spreading and rebounding of the inkjet droplet outside the pixel pits under different wettability gradients were studied using the maximum spreading radius as a reference.Finally,the phase diagrams of effective droplet deviations of different contact angles were obtained.The results showed that for the micron OLED inkjet droplets,the maximum spreading radius is proportional to the size and the impact velocity of the inkjet droplets,and inversely proportional to contact angle inside the pixel pits.For scattered inkjet droplet with deviation,when the maximum spreading radius is greater than or equal to the deviation of the inkjet droplet,it is re-entered the pixel slot under the traction of wettability gradient caused by the difference between the inner and outer contact angles of the pixel substrate.Also,the retraction of spreading droplet is proportional to the impact velocity.Therefore,the droplet is pulled to the more hydrophilic side with the influence of wettability gradient.And the inkjet droplet is pulled back into the pixel pitsonly if the edge of the droplets after impacting and spreading is entered into the pixel pit with wettability gradient.Finally,the defects of scatter deposition is inhibited.The proposed maximum spreading radius widens the effective range of the inkjet droplet outside the pixel pits,which can be used as a reference for production of OLED emissive layer.