Development of a software for predicting injection flow of liquid crystal for the purpose of reducing the cost of liquid crystal display

注入工艺是制造液晶显示器的重要工艺之一。本研究的目的是开发一个广泛应用的软件，可以数值预测注射过程。该软件可大大缩短任意尺寸和形状液晶显示器的注射时间，提高生产率，降低成本。选择Leslie-Ericksen方程作为液晶流动的本构方程，并对运动方程和本构方程进行Hele-Shaw近似。采用有限差分法对控制微分方程进行离散。在这项研究中，我们考虑了液晶的表面张力的影响，并在注射过程中的细胞间隙的变化。关于表面张力，假设弯月面的形状在整个自由表面上是均匀的，并且接触角很小，我们可以将其设置为零。结果表明，表面张力的影响可以用附加压差Δ p=2γ/h（γ：表面张力，h：泡孔间隙）表示，它是注射过程的驱动力。针对泡孔间隙的变化，利用材料力学中的Hertz公式，结合泡孔内的压力分布和隔片的弹性，计算了每一时间步的局部泡孔间隙，并在开发软件的同时，进行了注射过程的实验。采用75 mm × 100 mm ×4.5μm的液晶盒，拍摄了注射过程中自由面位置的动态照片。用所开发的计算软件对实验数据进行了计算，结果令人满意。

Injection process is one of the most important processes for manufacturing liquid crystal displays (LCD). The purpose of this research project is to develop a widely used software which can predict numerically the injection process. Such the software makes possible to reduce greatly the injection time for LCD with arbitrary size and shape, leading to high productivity and to a decrease in cost.The Leslie-Ericksen equation was selected as a constitutive equation for liquid crystalline flow, and the Hele-Shaw approximation was made for both the equation of motion and the constitutive equation. Finite difference method was employed to discretize the governing differential equations. In this study, we have taken into account the effects of surface tension of liquid crystals and variation in cell gap during injection process. Concerning the surface tension, it was assumed that the shape of a meniscus was uniform throughout the free surface and that a contact angle was so small that we could put it to be zero. As a result, it is concluded that the effect of the surface tension can be expressed as an additional pressure difference Δ p=2γ/h (γ : surface tension, h : cell gap), which is the driving force of the injection process. Concerning the variation in cell gap, we computed the local cell gap at every time step by using both the pressure distribution in the cell and the elasticity of spacers with resort to the Hertz formula in the field of mechanics of materials.In parallel with developing the software, we made an experiment for injection process. Using a liquid crystal cell with 75mm×100mm×4.5μm in size, we took photographs of the positions of a free face at every moment during the injection process. The agreement of the experimental data with the computational results obtained with using the software developed was satisfactory.