Method and apparatus for filling liquid crystal cells with a medium comprising at least one liquid crystalline material

Abstract

A method for filling liquid crystal cells (40) with a medium (30) comprising at least one liquid crystalline material. In the method at least one liquid crystal cell (40) is placed inside a vacuum chamber (12), the vacuum chamber is evacuated, at least one fill opening (46) of the at least one liquid crystal cell (40) is contacted with the medium, and the pressure in the vacuum chamber is raised causing the medium to fill the cavity inside the liquid crystal cell. A signal indicating the amount of oxygen remaining inside the vacuum chamber is provided by an oxygen sensor (20) mounted inside the vacuum chamber and completion of the evacuation of the vacuum chamber is determined based on said signal. Further disclosed is an apparatus for carrying out the process.

Claims

1. Method for filling liquid crystal cells (40) with a medium (30) comprising at least one liquid crystalline material, the liquid crystal cells (40) comprising two substrates (42) joined together with a peripheral seal (44) so that a cavity is formed, wherein the liquid crystal cells (40) comprise at least one fill opening (46), the method comprising the steps of a) placing at least one liquid crystal cell (40) inside a vacuum chamber (12), b) evacuating the vacuum chamber (12), c) contacting the at least one fill opening (46) with the medium (30) comprising at least one liquid crystalline material after evacuation of the vacuum chamber (12) has been completed, and d) raising the pressure in the vacuum chamber (12), wherein the rising pressure in the vacuum chamber (12) causes the medium (30) to fill the cavity inside the at least one liquid crystal cell (40), characterized in that a signal indicating the amount of oxygen remaining inside the vacuum chamber (12) is provided by means of an oxygen sensor (20) mounted inside the vacuum chamber (12) and completion of the evacuation of the vacuum chamber (12) is determined based on said signal.

2. Method according to claim 1, wherein the evacuation of the vacuum chamber (12) is considered to be completed if the signal indicating the amount of oxygen inside the vacuum chamber (12) is below a predetermined threshold.

3. Method according to claim 2, wherein the threshold is determined by comparing the signal indicating the amount of oxygen inside the vacuum chamber (12) to a signal of a pressure sensor mounted inside the vacuum chamber (12).

4. Method according to claim 1, wherein a primary evacuation is performed in a pressure range of ambient pressure to an intermediate pressure in the range of from 10 mbar to 50 mbar and a secondary evacuation is performed after completion of the primary evacuation, wherein a vacuum pump (18) is operated at reduced capacity during the primary evacuation and the vacuum pump (18) is operated at full capacity during secondary evacuation.

5. Method according to claim 1, wherein the pressure inside the vacuum chamber (12) after the evacuation is considered to be completed is greater than or equal to 1.0*10.sup.−4 mbar.

6. Method according to claim 1, wherein the medium (30) is provided in a tray (16) located inside the vacuum chamber (12), the at least one liquid crystal cell (40) being arranged such that the fill opening (46) is at the bottom, the fill opening (46) being contacted with the medium (30) by submerging the fill opening (46) in the medium (30) by lowering the liquid crystal cell (40) or raising the tray (16).

7. Method according to claim 1, wherein after the medium (30) has filled the liquid crystal cell (40), the at least one fill opening (46) is sealed.

8. Method according to claim 1, wherein two or more liquid crystal cells (40) are processed simultaneously in the same vacuum chamber (12).

9. Method according to claim 1, wherein nitrogen gas or ultra clean compressed air is introduced into the vacuum chamber (12) for raising the pressure inside the vacuum chamber (12).

10. Apparatus (10) for filling liquid crystal cells (40) with a medium (30) comprising at least one liquid crystalline material, the apparatus (10) comprising: a vacuum chamber (12), a tray (16) for holding the medium (30), the tray (16) being located inside the vacuum chamber (12), means for submerging a fill opening (46) of at least one liquid crystal cell (40) in the medium (30), a vacuum pump (18), an oxygen sensor (20), a control unit (22), wherein the control unit (22) is adapted to carry out the steps of a method according to claim 1.

11. Apparatus (10) according to claim 10, wherein the oxygen sensor (20) is based on a potentiometric zirconia solid electrolyte cell.

12. Apparatus (10) according to claim 10, wherein the means for submerging a fill opening (46) are constructed as a mount which holds the at least one liquid crystal cell (40) such that the fill opening (46) is located inside the tray (16) and means for controlling a fill level of the medium (30) inside the tray (16).

13. Apparatus (10) according to claim 10, wherein the means for submerging a fill opening (46) are constructed as a lift which is configured to lower the at least one liquid crystal cell (40) into the tray (16).

14. Apparatus (10) according to claim 10, wherein the means for submerging a fill opening (46) are constructed as a lift which is configured to raise the tray (16) such that the fill opening (46) is located inside the tray (16).

15. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The drawings show:

[0052] FIG. 1a a first embodiment of the apparatus for filing liquid crystal cells prior to submerging a fill opening in a medium comprising at least one liquid crystalline material,

[0053] FIG. 1b the first embodiment of the apparatus after submerging the fill opening in the medium,

[0054] FIG. 2a a second embodiment of the apparatus prior to submerging the fill opening in the medium,

[0055] FIG. 2b the second embodiment of the apparatus after submerging the fill opening in the medium,

[0056] FIG. 3 a diagram illustrating a controlled two-stage evacuation,

[0057] FIG. 4 a diagram showing pressure and oxygen signals for a filling process using the first embodiment of the apparatus,

[0058] FIG. 5 a diagram showing pressure and oxygen signals for a filling process using the second embodiment of the apparatus,

[0059] FIG. 6a a diagram showing the pressure for different cells, and

[0060] FIG. 6b a diagram showing the oxygen level for different cells.

[0061] FIGS. 1a and 1b schematically show a first embodiment of an apparatus 10 for filling liquid crystal cells 40 with a medium 30. The apparatus 10 comprises a vacuum chamber 12 and a tray 16 for providing the medium 30 is located inside the vacuum chamber 12.

[0062] The tray 16 is connected to a reservoir which in the depicted example is a medium storage 32. A medium valve 34 is used to control supply of the medium 30 from the medium storage 32 to the tray 16.

[0063] The vacuum chamber 12 is connected to a vacuum pump 18 for evacuation the vacuum chamber 12. Both the vacuum pump 18 as well as the medium valve 34 are controlled by a control unit 22.

[0064] Preferably, evacuation of the vacuum chamber 12 is performed in two stages. In a primary evacuation stage, the vacuum pump 18 is operated at reduced power, for example by partially closing a valve for regulating pumping power (a regulating valve is not displayed in the drawings). After an ambient pressure inside vacuum chamber 12 has been reduced to below about 50 mbar, the vacuum pump 18 is operated at full power for the second evacuation stage.

[0065] An oxygen sensor 20 is arranged within the vacuum chamber 12 and is also connected to the control unit 22. Further, it is possible to arrange a pressure sensor, which is not displayed in the drawings, within the vacuum chamber 12 and this pressure sensor may also be connected to the control unit 22. A vent 24 with a vent valve 26, which is connected to the control unit 22, may be used to raise the pressure inside the vacuum chamber 12 in a controlled manner.

[0066] In the situation depicted in FIG. 1a, an empty liquid crystal cell 40 which is formed by two substrates 42 and a seal 44 is located in the vacuum chamber 12. A fill opening 46 is located at the bottom of the liquid crystal cell 40. The liquid crystal cell 40 is arranged such that the fill opening 46 is located below a maximum fill level of the tray 16.

[0067] In FIG. 1a, the vent valve 26 is closed and the vacuum pump 18 is used to evacuate the vacuum chamber 12. The completion of the evacuation is indicated by a signal provided by the oxygen sensor 20. Upon completion of the evacuation, the control unit 22 stops the vacuum pump 18 and begins the filling process by opening the medium valve 34 so that the medium 30 flows from the medium storage 32 into the tray 16. By filling the tray 16, the fill opening 46 is submerged into the medium 30 as depicted in FIG. 1b.

[0068] After submerging the fill opening 46 into the medium 30, the control unit 22 opens the vent valve 26 so that, for example, nitrogen may enter the vacuum chamber 12 so that the pressure inside the vacuum chamber 12 rises.

[0069] As illustrated in FIG. 1b, the rising pressure inside the vacuum chamber 12 pushes the medium 30 into the liquid crystal cell 40. After filling of the liquid crystal cell 40 is complete, the fill opening 46 is sealed in a subsequent process step and the liquid crystal cell 40 is completed.

[0070] FIGS. 2a and 2b schematically depict a second embodiment of the apparatus 10 for filling liquid crystal cells 40 with a medium 30.

[0071] The vacuum chamber 12 of the apparatus 10 of the second embodiment is divided into an upper chamber 13 and a lower chamber 14 by means of a gate 28. Each of the two chambers 13, 14 is connected to a vacuum pump 18. Both vacuum pumps 18 are connected to the control unit 22. The oxygen sensor 20 which is used to monitor evacuation of the liquid crystal cell 40 is located in the upper chamber 13.

[0072] In the situation depicted in FIG. 2a, the empty liquid crystal cell 40 is located in the upper chamber 13. The tray 16 which is already filled with the medium 30 is located in the lower chamber 14 and both chambers 13 and 14 are being evacuated.

[0073] The gate 28 may be opened in order to connect the upper chamber 13 and the lower chamber 14 and to allow the fill opening 46 of the liquid crystal cell 40. By means of the division of the vacuum chamber 12, the volume surrounding the liquid crystal cell 40 is reduced which facilities evacuation of the residual air which may be trapped inside the cavity of the liquid crystal cell 40.

[0074] The gate 28 is opened when the oxygen sensor 20 indicates that the evacuation of the upper chamber 13 is complete. Preferably, a two stage evacuation is performed in the upper chamber 13 as described with respect to the first embodiment of FIGS. 1a and 1b.

[0075] In order to contact the fill opening 46 of the liquid crystal cell 40, which is located at the bottom, with the medium 30, the tray 16 holding the medium 30 is raised by means of a lifting mechanism. Reference numeral 36 indicates the upward movement of the tray 16.

[0076] After the fill opening 46 has been contacted with the medium 30, the control unit 22 opens the vent valve 26 so that, for example, nitrogen may enter the vacuum chamber 12 so that the pressure inside the vacuum chamber 12 rises.

[0077] As illustrated in FIG. 2b, the rising pressure inside the vacuum chamber 12 pushes the medium 30 into the liquid crystal cell 40. After filling of the liquid crystal cell 40 is complete, the fill opening 46 is sealed in a subsequent process step and the liquid crystal cell 40 is completed.

[0078] The diagram of FIG. 3 shows the pressure inside the upper chamber 13 and the lower chamber 14 of the second embodiment of the apparatus 10 as described with respect to FIGS. 2a and 2b. In order to observe the pressure, further pressure sensors are arranged in the upper chamber 13 and the lower chamber 14. The x-axis of the diagram indicates the elapsed time in minutes and the y-axis indicates the measured pressure in mbar.

[0079] As described above, evacuation of the upper vacuum chamber 13 which holds the liquid crystal cell 40 is preferably performed in two stages. In the primary evacuation stage, the vacuum pump 18 is operated at reduced power. After an ambient pressure inside vacuum chamber 12 has been reduced to below about 50 mbar, the vacuum pump 18 is operated at full power for the second evacuation stage. The change from the primary evacuation stage to the secondary evacuation stage is visible in the diagram of FIG. 3 where at point 50 the slope of the pressure curve becomes steeper.

[0080] At point 52 as indicated in FIG. 3, the gate 28 is opened and thus the upper chamber 13 and the lower chamber 14 become connected. This causes pressure equalization between the two chambers 13 and 14.

[0081] At point 54, the vent valve 26 is opened and the pressure in the connected chambers 13 and 14 rises.

[0082] The diagram of FIG. 4 shows recorded signals of the oxygen sensor 20 and of an additional pressure sensor which are arranged in the vacuum chamber 12 of the apparatus 10 of the first embodiment as shown in FIGS. 1a and 1b. The x-axis of the diagram indicates the elapsed time in minutes. The left y-axis indicates the measured pressure in mbar and the right y-axis indicates the oxygen level in arbitrary units.

[0083] During the evacuation of the vacuum chamber 12, the pressure drops rapidly at first and then begins to converge towards the final pressure of the vacuum pump 18. Even so the chamber 12 itself is evacuated rapidly, the air trapped inside the liquid crystal cell 40 only slowly leaks out through the fill opening 46. The completion of the evacuation, wherein essentially all air is evacuated from the cavity of the liquid crystal cell 40 cannot safely be determined from the signal of the pressure sensor as only small and gradual changes are observed.

[0084] The oxygen level indicated by the oxygen sensor 20, however, experiences a rapid drop which may by easily identified and indicates completion of the evacuation process. At point 53, the evacuation is considered to be complete. The vacuum pump 18 is switched off and the fill opening 46 of the liquid crystal cell 40 is submerged in the medium 30. In order to ensure that the liquid crystal cell 40 is submerged in a calm and stable medium 30, a waiting time is added before the vent step is started. At point 54, the vent valve 26 is opened and the filling process is started.

[0085] The diagram of FIG. 5 shows recorded signals of the oxygen sensor 20 and of additional pressure sensors which are arranged in the upper vacuum chamber 13 and the lower vacuum chamber 14 of the apparatus 10 of the second embodiment as shown in FIGS. 2a and 2b. The x-axis of the diagram indicates the elapsed time in minutes. The left y-axis indicates the measured pressure in mbar and the right y-axis indicates the oxygen level in arbitrary units.

[0086] During the evacuation of the vacuum chambers 13 and 14, the pressure drops rapidly at first and then begins to converge towards the final pressure of the vacuum pump 18. Because the air which is trapped inside the cavity of the liquid crystal cell 40 only slowly leaks out through the fill opening 46, the pressure of the upper chamber drops slower than the pressure of the lower chamber 14. The completion of evacuation, wherein essentially all air is evacuated from the cavity of the liquid crystal cell 40 cannot safely be determined from the signal of the pressure sensor as only small and gradual changes are observed.

[0087] The oxygen level indicated by the oxygen sensor 20, however, experiences a rapid drop which may by easily identified and indicates completion of the evacuation process. At point 52, the gate 28 is opened so that the upper chamber 13 and the lower chamber 14 become connected. At point 54, the vacuum pump 18 is switched off, the vent valve 26 is opened and the filling process is started.

[0088] FIG. 6a shows a diagram wherein the pressure during evacuation of the vacuum chamber 12 of the apparatus 10 of the first embodiment has been recorded for different types and numbers of liquid crystal cells 40. FIG. 6b shows a diagram with the corresponding oxygen levels which have been recorded by the oxygen sensor 20. The x-axis of the diagrams of FIGS. 6a and 6b indicates the elapsed time in minutes. The y-axis of FIG. 6a indicates the measured pressure in mbar and the y-axis of FIG. 6b indicates the oxygen level in arbitrary units.

[0089] A first curve, which is shown as dotted line, indicates the data recorded for one cell with substrate sizes of 300 mm×300 mm and a cell gap of 35 μm. A second curve, which is shown as dashed line, indicates the data recorded for one cell with substrate sizes of 1200 mm×1200 mm and a cell gap of 35 μm. A solid third curve indicates the data recorded for four cells with substrate sizes of 1200 mm×1500 mm and a cell gap of 35 μm.

[0090] The completion of the evacuation process is indicated by the rapid drop of the oxygen level indicated by the oxygen sensor 20. As shown by the three points 61, 62 and 63, the corresponding recorded pressure levels are slowly changing and do not provide a clear indication which may be used to determine when evacuation has been completed.

[0091] In a conventional process for filling of a single cell of size 300 mm×300 mm, the evacuation of the vacuum chamber 12 is continued until about 130 minutes have lapsed in order to ensure complete evacuation of the cavities of the cells. With the inventive process evacuation is considered to be complete after about 114 minutes as indicated by a rapid drop of the oxygen level indicated by the oxygen sensor 20 at the first point 61.

[0092] In a conventional process for filling of a single cell of size 1200 mm×1200 mm, the evacuation of the vacuum chamber 12 is continued until about 140 minutes have lapsed in order to ensure complete evacuation of the cavities of the cells. With the inventive process evacuation is considered to be complete after about 125 minutes as indicated by a rapid drop of the oxygen level indicated by the oxygen sensor 20 at the second point 62.

[0093] In a conventional process for filling of four cells of size 1200 mm×1500 mm, the evacuation of the vacuum chamber 12 is continued until about 400 minutes have lapsed in order to ensure complete evacuation of the cavities of the cells. With the inventive process evacuation is considered to be complete after about 140 minutes as indicated by a rapid drop of the oxygen level indicated by the oxygen sensor 20 at the third point 63.

[0094] Thus, the inventive method provides a safe way to determine completion of evacuation without having to rely on safety margins and experience of the operator. By reducing unnecessary time delays the required time for a complete process cycle is advantageously reduced.

LIST OF REFERENCE NUMERALS

[0095] 10 apparatus [0096] 12 vacuum chamber [0097] 13 upper chamber [0098] 14 lower chamber [0099] 16 tray [0100] 18 vacuum pump [0101] 20 oxygen sensor [0102] 22 control unit [0103] 24 vent [0104] 26 vent valve [0105] 28 gate [0106] 30 medium [0107] 32 medium storage tank [0108] 34 medium valve [0109] 36 lifting motion [0110] 40 liquid crystal cell [0111] 42 substrate [0112] 44 seal [0113] 46 fill opening [0114] 50 point (activation of turbo pump) [0115] 52 point (opening of gate) [0116] 53 point (waiting) [0117] 54 point begin filling [0118] 61 point (pressure ok) [0119] 62 point (pressure ok) [0120] 63 point (pressure ok)