Generally, a conventional liquid crystal display (LCD) comprises two substrates having electrodes facing each other and liquid crystal material disposed therebetween. In manufacturing the liquid crystal display, the two substrates are combined to define a vacant liquid crystal cell therebetween. The liquid crystal material is thereafter injected into the vacant cell.
Conventionally, the liquid crystal material is prepared and injected into the vacant cells in the following manner. First, the liquid crystal material is placed in a container. Next, the container and vacant liquid crystal cells are placed in a vacuum chamber. The pressure of the chamber is maintained in a high vacuum state of 10.sup.-4 torr to 10.sup.-5 torr, whereby air bubbles formed within the liquid crystal material or inside the container are removed.
A liquid crystal injection hole of the vacant crystal cell is dipped into or touched with the liquid crystal material disposed in the container while keeping the pressure of the chamber in a high vacuum state of 10.sup.-4 torr to 10.sup.-5 torr. By raising the pressure in the chamber from the vacuum state to normal atmospheric pressure, the liquid crystal material is injected through the liquid crystal injection hole by the pressure differential between the vacant liquid crystal cell and the chamber.
There are two well-known methods for injecting the liquid crystal material into the vacant liquid crystal cell: a dipping method and a touch method. Hereinafter, the two methods are explained with reference to FIGS. 1 and 2, respectively.
With reference to FIG. 1, in practicing the dipping method, a substantial quantity of liquid crystal material 4 is present in the container 1. The injection hole 3 of the vacant liquid crystal cell 2 is deeply dipped in the liquid crystal material 4. The amount of the liquid crystal material used for one dipping process is about 100 cc, substantially more than is necessary to fill the vacant cell. The remaining liquid crystal material cannot be used for another dipping process because the remaining liquid crystal material may be contaminated.
As described above, the dipping method can be disadvantageous in that a substantial amount of liquid crystal material is wasted because the liquid crystal material is easily polluted. Also, an alignment film doped at the injection hole 3 of the liquid crystal cell 2 may be damaged by overly rapid injection of the liquid crystal material into the liquid crystal cell.
With reference to FIG. 2, in practicing the touch method, the liquid crystal material 4 is injected into the liquid crystal cell 2 by placing a relatively small amount of liquid crystal material 4 in a slightly protruded border 5 formed on the container 1. The surface of the liquid crystal material 4 protrudes or bulges upwardly due to surface tension. The injection hole 3 of the vacant liquid crystal cell 2 is placed in contact with or touched to the protruded surface of the liquid crystal material, whereby the liquid crystal material 4 is injected into the injection hole 3.
The conventional touch method can be advantageous as compared to the dipping method in that the liquid crystal material is not overly wasted because a relatively small amount of liquid crystal material is put in the container 1 for injection. However, the conventional touch method can have disadvantages. Because the surface tension of the liquid crystal material to be injected differs according to, inter alia, the kind of liquid crystal material being injected and the vacuum state, the structure of the container 1, the amount of the liquid crystal material 4 to be placed in the container, and the vacuum state must be carefully controlled. In addition, the amount of the liquid crystal material should be controlled according to the number of liquid crystal cells to be injected at a time.
A further problem experienced in practicing the aforedescribed methods is that a number of air bubbles are produced during the high vacuum state of the air removal step. Often several of these air bubbles reach the surface of the liquid crystal material and combine to make a larger air bubble. The larger air bubble tends to burst, displacing the liquid crystal material beyond the container 1 and thereby resulting in waste of the liquid crystal material.
To overcome the above-mentioned disadvantages, a method for gradually raising the vacuum has been suggested. However, this method has a disadvantage in that it substantially increases the amount of time required to perform the method.