Technical Field

This invention is related to the field of optics, particularly to the process of making liquid crystal (LC) optical devices, and can be used to fill the space between the two substrates of the LC device with liquid crystal substance and to polymerize LC polymer by UV radiation.

Background Art

The cells of the LC devices includes two substrates (usually glass) joined together with a special adhesive. The inner surface of the substrates a layer ensurring the LC molecules orientation is deposited. Then the space between substrates is filled with LC. One of the important technological processes in the fabrication of these devices is the filling of liquid crystal substance into the cell.

Currently, various types of equipment and methods for filling LC device with LC substance exist. They may include a vacuum chamber with valves to connect to a vacuum pump and for inlet of the inert gas. Inside the chamber, a container with the LC material and a system to inject LC and the LC device to be filled is installed.

A conventional device for liquid crystal vacuum filling into one and more cells [1] contains a container for LC substance that includesthree parallel longitudinal grooves. In the central groove, there is a spiral ankle made of an inert material, the adjacent grooves of which form capillary holes. The edge grooves are used to receive the extruded LC substance. Upon turning on vacuum in the chamber, the filling hole of the cell is brought into contact with the LC substance using a special mechanism. LC is filled into the cell by the capillary effect, assisted by the supply of inert gas into the chamber. Due to the capillary hole, the contact area of the LC substance and the cell may be decreased to a smallest possible size.

In conventional methods based on capillary effect, the LC substance is not fully used, which leads to an increase in the cost of the prepared LC device, as modern liquid crystals are expensive materials with special characteristics. In addition, during evacuation of the chamber, the unwanted evaporation of some components of LC substance is possible, which becomes essential in the case of using LC substance with easily volatile components.

To address the above issues, a device and method of its fabrication have been proposed, allowing to reduce the filling time and the consumption of LC substance [2] . The referenced patent [2] proposed to fill LC cells in an evacuated environment by using a capillary-type liquid crystal dispenser. The LC cell is installed with the filling hole up and LC substance is supplied drop by drop into the LC cell in the required quantity. The size of the drop is determined by choosing the diameter of the dispenser's capillary. Counting the number of drops allowed a precise control of the amount of filled substance.

In the device shown in [3], the vacuum chamber is divided into two sections by a flexible sheet, and each section is coupled to its own evacuation device. In the first section, a heater is placed to heat the substrates. The second second section is hermetically sealed to the first one and can be removed from it only together with the flexible sheet. Prior to joining of two substrates, the liquid crystal is dropped on one substrate and then the other substrate is attached to the first substrate under pressure. Sandwiched between the two substrates, the liquid crystal spreads at high temperature.

In another case, the LC filling device is placed in a vacuum chamber between two parallel holding plates, which are used to apply pressure to the LC cell substrates preventing expansion of the LC substance during pressure increase and to ensure a uniform thickness of the LC layer. A retort-type tube is used as a container for LC substance. lin order to ensure the isotropic conditions of filling of the LC substance, both the lower substrate and the LC substance are heated [4], For the same purpose, several ways to heat the LC cell and the LC substance during filling are suggested in [5],

In the LC filling process, it is also very important to control the amount of the filling substance, since in case of insufficient quantity the bubbles in the LC layer may be formed, and in case of excess quantity the orientation of the LC molecules may be disturbed.

One of the closest prior arts for the apparatus of the current invention is the device for vacuum injecting liquid crystal, which is a chamber with vacuum and gas inlet valves, on the top of which the LC device is placed, and a heated unit at the bottom, consisting of a LC substance bearing container and an applicator to deliver the LC substance to the injection port of LC device, designed with the possibility of control the heating temperature [6], The surface of the applicator is arch-grooves shaped to supply the optimal amount of LC material to the LC device. The applicator operation is controlled by a special controller, allowing the applicator motions up and down and rotates over 180°.

However, in the process of making modern LC devices, it is very important to precisely define and strictly control all technological parameters: not only the vacuum level in the chamber, the temperatures of the LC substance and the filling device, but also the flow of injected gases and the amount of the LC substance filled into the LC device. In addition, it is necessary to exclude the evaporation of some volatile components of LC substance during the evacuation of the chamber, and to ensure the lossless consumption of an expensive LC substance and visual control of the filling process. Taking into account that in modern LC technologies new LC polymers are widely used, it is also advantageous to provide the possibility of LC polymerization under UV radiation.

Summary of Invention

The principal objective/embodiment of the present invention includes an apparatus for filling liquid crystal device with liquid crystal substance, which ensures precise definition and strict control of all parameters of the technological process, lossless of liquid crystal substance, visual control of filling process and polymerization of the LC polymer with UV radiation.

The other embodiment of the present invention includes the apparatus for filling a liquid crystal device with liquid crystal substance in which:

- The unit, containing the LC material holding container and the applicator providing LC material to the filling hole of the LC device, is designed in the form of a heated quartz vial, the temperature of which is precisely set and controlled. One end of the quartz vial is equipped with a hollow needle and the other with a piston system controlled by a step motor; - The possibility to inject a precise amount of LC substance into the LC device at a manageable and controlled speed is provided by setting and precise control of the rotation speed of a step motor that controls the piston motion;

- The semitransparent heating stage with the possibility to set and control the heating temperature, consisting of two glued quartz plates with mounted between heating element in the form of Ni-Cr thin wire meander is provided for placing the device to be filled with liquid crystal

- In another embodiment, the heating stage is two glued glass plates, one of which has a surface covered with ITO (Indium Tin Oxide) layer, which ensures uniform heating of the stage.

- A system of precise mechanical manipulators is provided to precisely align of a quartz tube needle and a liquid crystal cell inlet port;

- The injected gases flow controlling system is provided;

- UV LEDs with a controllable irradiation intensity are placed next to the stage, e.g. above the stage;

- Light source is located below the stage in the lower part of the chamber, and above the light source, above and below the stage the crossing polarizers are located for visual control of filling process.

The essence of the invention is that, unlike similar ones related to the same topic, is that the device of this invention enables filling of the LC device with LC substance in high vacuum and it has a semitransparent heating stage for placing the device to be filled with liquid crystal substance, the temperature of which is set and controlled; a heated quartz vial for placing LC substance, the temperature of which is set and controlled, and one end of which has a hollow needle and the other is equipped with a step motor driven system to inject the precise amount of LC substance into the LC device at a manageable speed; a system of precise mechanical manipulators for combining a quartz tube needle with a liquid crystal cell inlet port; a system for determining the flow of injected gases; a system of light emitting diodes to ensure the polymerization of LC polymer with a controllable intensity of UV radiation; a light source and a system of crossed polarizers for visual monitoring of the filling process.

Brief Description of the Drawings

The device of the current invention showing main embodiments of the invention is shown schematically in Eigure 1.

The unit containing heating quartz vial for placing and LC substance and supplying it to the injection port of liquid crystal device is shown schematically in Eigure 2.

Modes for Carrying out the Invention

The device of the current invention combines components necessary for implementation and control of all technological process steps of liquid crystal substance filling into the liquid crystal device.

In the vacuum chamber (1) a semi-transparent heating stage (2) is installed, which is moved left and right by the manipulator (3). The filling LC device (4) is placed on the stage and heated by contact heat transduction method. The LC substance (7) is filled into a heated quartz vial (5), one end of which has a special thin hollow needle (6) and the other end has a piston (8) controlled by a step motor (15). The connection of piston to the step motor is provided by means of micrometric screw (16) and adapting pipe (17). The quartz vial is placed in thermo-insulated case (12) heated electrically by means of coil (13) and the temperature is controlled by thermo-couple (14). The connection of the tube needle to the inlet port of the LC device is provided by means of longitudinal and rotating manipulators (not shown in Figures). Visual control of the filling process is provided by illuminating the device with white light (9) coupled to crossed polarizers (10). Polymerization of the LC polymer is carried out by irradiating LC cells with UV light emitting diodes (11).

The apparatus works as follows:

The LC device to be filled is placed on a heating stage. To carry out the filling of the LC device with LC substance in isotropic phase, the filling LC device and the LC substance are heated; moreover, the temperature of both the LC device and LC substance is precisely controlled. The stage is heated electrically, and the LC device installed on it is heated by contact method. The liquid crystal substance is poured into a heated quartz vial, one end of which has a special thin needle. LC substance temperature is controlled. LC substance is injected from the vial into the LC device by means of a piston system controlled by a step motor. The quartz vial needle is connected to the inlet port of the LC device allowing rightleft, up-down and rotary motion provided by manipulators.

Both thermal and optical polymerization of LC polymer is envisaged, which can be carried out homogeneously on a 4” surface as an example. The thermal polymerization is carried out by heating the stage, and the opticaly induced polymerization is realized using a system of UV LEDs with controlled intensity.

The rotary polarizers mounted on the top and bottom walls of the apparatus and the transparency of the cell mounting stage allow to monitor the filling process by crossed polarizers.

The system is designed to operate in either high vacuum or using a gas flow. The degree of vacuum and gas flow can be set and controlled using dedicated sensors, and the data can be monitored and visualized.

References

1. Hideo Matsuzaki, Keiji Yajima. Apparatus for filling liquid crystal into the cells of liquid crystal display devices. US patent US4099550A, 1975.

2. Taizo Abe. Method and despenser for flilng liquid crystal into LCD cell. US patent US005511591, 1996.

3. Yamazaki et al. Liquid crystal filling device. US patent US004691995C1, 2004.

4. Watanabeetal.Methodof filling aliquid crystal device with liquid crystal. US patenUS4922974, 1990.

5. Choi Yoo Jin, Kim Jin Yun. dispositif et procede d'injection de cristal liquided ans un panneau a crystal liquid. Patent de Republic Francaise FR 2752954 - Al, 1997.

6. Masayuki Shimamune, Takashi Enomoto, Tatsuo Murata, Mutsuo Mitsui. Apparatus for vacuum injecting liquid crystal. US patent US005546998A, 1996.