Fabrication of Rubbing Cloths with Various Pile Densities for the LCD Process and Their Effects on Rubbing of Polyimide Alignment Layers

Abstract: The mechanical rubbing of a polyimide (PI) layer with a velvet cloth has been dominantly used to induce auniform alignment of liquid crystal molecules in the manufacturing process of liquid crystal displays (LCDs). The rub-bing process is affected by its process parameters and also by the nature and properties of the rubbing cloth used. Wefabricated the rubbing cloths with various pile densities and different weaving structures and then investigated how theparameters were related to the effect of the cloth on the rubbing process and the properties of rubbed PI alignment lay-ers (ALs). As the pile density increases at same rubbing process parameters, the degree of molecular orientation of therubbed AL and its surface roughness increase with an increase of the contact area between the rubbing cloth and theAL surface. Furthermore, a more uniform rubbing is also achieved. The results in this work showed that higher piledensity of the rubbing cloth induces a better rubbing effect, which is indeed more favorable to the LCD process. It wasalso observed that the weaving can exert some influence on the rubbing process.Keywords: rubbing cloth, pile density, rubbing process, polyimide, liquid crystal display