WO2024028287A1

WO2024028287A1 - Method and apparatus for filling liquid crystal cells with a medium comprising at least one liquid crystalline material

Info

Publication number: WO2024028287A1
Application number: PCT/EP2023/071220
Authority: WO
Inventors: Ronald VAN DEN HEUVEL; Wil BOONEN
Original assignee: Merck Patent Gmbh
Priority date: 2022-08-03
Filing date: 2023-08-01
Publication date: 2024-02-08

Abstract

The invention relates to a method (100) for filling liquid crystal cells (40) with a medium (30) comprising at least one liquid crystalline material. The liquid crystal cells (40) comprise two substrates (42) joined together with a peripheral seal (44) so that a cavity (43) is formed, wherein the liquid crystal cells (40) comprise at least one fill opening (46). In a first step a) of the method (100) at least one liquid crystal cell (40) is placed (A) inside a vacuum chamber (12). In a subsequent step b) the vacuum chamber (12) is evacuated (B). After evacuation has been completed, the at least one fill opening (46) of the at least one liquid crystal cell (40) is contacted (C) with the medium (30) in a step c). In a subsequent step (D) the pressure in the vacuum chamber (12) is raised to an overpressure, wherein the rising pressure in the vacuum chamber (12) causes the medium (30) to fill (E) the cavity inside the at least one liquid crystal cell (40). Further aspects of the invention relate to an apparatus (10) for filling a liquid crystal cell (40) with a medium (30) comprising at least one liquid crystalline material, and to a computer readable medium (23) comprising a computer executable routine configured to perform at least one step of a method (100) according to the invention. The invention further relates to liquid crystal cells (40) obtainable by the method (100), in particular window elements for applications in buildings and vehicles with energy savings and improved comfort.

Description

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

The invention relates to a method for filling liquid crystal cells with a medium comprising at least one liquid crystalline material, the liquid crystal cells comprising two substrates joined together with a peripheral seal so that a cavity is formed, wherein the liquid crystal cells comprise at least one fill opening. Further aspects of the invention relate to an apparatus for filling a liquid crystal cell with a medium comprising at least one liquid crystalline material and to the use of overpressure in a process for filling liquid crystal cells with a medium comprising at least one liquid crystalline material. The invention relates further to a computer storage medium comprising a computer executable routine (program I code) configured such that at least one step of a method according to the invention can be executed. The invention further relates to liquid crystal cells obtainable by the method, in particular window elements for applications in buildings and vehicles with energy savings and improved comfort.

The review article by R. Baetens et al. “Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of- the-art review”, Solar Energy Materials & Solar Cells 94 (2010) pages 87-105 describes tintable smart windows. Smart windows can make use of several technologies for modulating the transmittance of light such as devices based on electrochromism, liquid crystal devices and electrophoretic or suspended-particle devices. Liquid crystal-based devices employ a change in the orientation of liquid crystal molecules between two conductive electrodes by applying an electric field which results in a change of their transmittance.

Known liquid crystal devices such as LCD display devices and liquid crystal based smart windows comprise two substrates with a liquid crystal layer sandwiched between the two substrates. In order to form a liquid crystal cell, the two substrates are arranged parallel to each other, and the two substrates are joined by a peripheral seal such that a cavity between the two substrates is formed. At least one fill opening is arranged in the peripheral seal to allow filling of the cavity with a medium comprising at least one liquid crystalline material. After filling of the cavity, the at least one fill opening (or fill port) is sealed.

US 4,099,550 discloses an apparatus for filling a liquid crystal cell of a liquid crystal display device. The liquid crystal cell is provided with a filling port and the apparatus comprises a vacuum tank and a holder for supporting a plurality of cells. The apparatus further comprises a holder for the liquid crystal which includes capillary passages for the liquid crystal. The vacuum tank is evacuated, and the capillary passages are brought in contact with the filling ports of the cells. Subsequently, an inert gas is introduced into the vacuum tank thereby filling the liquid crystal into the cells through the filling ports.

US 5,725,032 describes a method for filling a liquid crystal cell with liquid crystal. The method comprises the step of placing the cell having a cavity and inlet openings in its top and bottom edges in a vacuum chamber which encloses upper and lower liquid crystal supply members each having a liquid crystal impregnated yarn exposed through a slot therein. The vacuum chamber is evacuated, the liquid crystal supply members are brought into contact with the top and bottom inlet openings and the chamber is returned to an atmospheric pressure. Returning the chamber to atmospheric pressure causes liquid crystal to be sucked into the cavity through the inlet openings.

US 2002/0039168 A1 describes an apparatus for injecting liquid crystal materials and methods for manufacturing liquid crystal panels by using the same. The method comprises the steps of forming a liquid crystal cell having two substrates and a sealant deposited on the inner surface near the edge of the liquid crystal cell and having an injection hole, putting the liquid crystal cell in a vacuum chamber having a tray containing liquid crystal material and an ultrasonic wave generator, evacuating air from the vacuum chamber to keep the liquid crystal cell under high vacuum, completely immersing the injection hole of the liquid crystal cell in the liquid crystal material under high vacuum, and injecting the liquid crystal material into the cell gap between the two substrates through the injection hole while irradiating ultrasonic waves to the liquid crystal material.

US 2004/0141144 A1 describes a method for the production of a liquid crystal display apparatus. The liquid crystal display apparatus is produced by the steps of arranging pixel electrodes, TFT devices and signal wiring on one surface of one substrate, arranging a transparent layer on a portion of one surface of a transparent substrate which portion is to be a display portion, bonding the one substrate and the transparent substrate to each other while the one surface having the pixel electrodes formed thereon faces the one surface having the transparent layer formed thereon, and injecting a liquid crystal between the substrates to form a liquid crystal layer. Liquid crystal devices intended to be used as smart windows are large devices and thus the volume of the cavity formed by the two substrates is large compared to the size of the fill openings. The gap size of the cavity of usually about 10 pm to 50 pm is small compared to the size of the fill openings which usually have a width of about 25 mm to 40 mm. When the liquid crystal cell is placed into a vacuum chamber and the vacuum chamber is evacuated, air trapped inside the cavity may only be released through the fill openings. While the vacuum chamber may be evacuated quickly, the speed of evacuation of the cavities is limited. There may be a significant amount of air remaining inside the cells even though the pressure in the vacuum chamber outside of the cavities would indicate sufficient evacuation. If filling of the cells is started too early, trapped air inside the cells may cause visible defects in the liquid crystal device.

In order to avoid such defects, it is common to continue evacuation for a certain amount of time even though a pressure sensor would indicate a sufficiently low pressure and thus completion of evacuation. This so-called waiting time slows down the filling process. Furthermore, the filling process of the evacuated cavity is slowed down due to capillary filling effects dominating the process and medium viscosity impacting the filling process negatively. Furthermore, the filling process itself takes a certain amount of time, the so-called filling time. The filling time starts upon full evacuation of the cell and takes until the cell is filled completely with the respective fill material, in particular the respective liquid-crystalline material. Generally, there are two ways to improve and speed up the overall filling process, reducing the waiting time and/or to reducing the filling time. The devices and methods described in the prior art do not provide satisfactory solutions to these problems and are also often quite complex.

It is an object of the invention to provide a method for filling liquid crystal cells with a medium comprising at least one liquid crystalline material wherein filling speed can be increased and thus unnecessary process times may be avoided. Another object of the invention is to provide a method with reduced complexity when compared to the methods as described in the prior art. The filling speed may thus be increased, preferably based on a robust process that may also allow to fill large cells, e.g. facade windows.

A further object of the invention may be seen in providing a method for filling liquid crystal cells with a medium comprising at least one liquid crystalline material wherein the pressure inside the cavities is controlled. A method for filling liquid crystal cells with a medium comprising at least one liquid crystalline material is proposed. The liquid crystal cells comprise two substrates joined together with a peripheral seal so that a cavity is formed, wherein the liquid crystal cells comprise at least one fill opening.

In a first step a) of the method at least one liquid crystal cell is placed inside a vacuum chamber. In a subsequent step b) the vacuum chamber is evacuated. After evacuation has been completed, the at least one fill opening of the at least one liquid crystal cell is contacted with the medium comprising at least one liquid crystalline material in a step c). In a subsequent step d) the pressure in the vacuum chamber is raised to an overpressure, wherein the rising pressure in the vacuum chamber causes the medium to fill the cavity inside the at least one liquid crystal cell.

The medium comprising at least one liquid crystalline material is preferably in a liquid state. The medium may comprise a single liquid crystalline material or a mixture of two or more liquid crystalline materials.

The liquid crystal cell is, for example, a liquid crystal cell device suitable for a switchable window. Further, the liquid crystal cell may be a cell suitable for a liquid crystal display (LCD). The substrates are preferably of rectangular shape wherein the length of the sides of the rectangle may be in the range of from 200 mm to 5000 mm, especially preferred in the range of from 500 mm to 4000 mm and most preferred in the range of from 1000 mm to 2500 mm. Substrates can be of arbitrary shape, wherein rectangular shape is the most common shape. In more demanding embodiments, the length of the sides (of the rectangle or the longest side of the arbitrary shape) may be in the range of from 600 mm to 2000 mm or from 800 mm to 1800 mm or from 1000 mm to 1600 mm or from 1300 to 1500 mm. Therein, the length of the sides is preferably defined as the longest side of the particular shape. The respective method allows for the filling of bigger panels (assembly) of liquid crystal cells or for the filling of bigger individual liquid crystal cells in faster time frames. The method is thus preferably used for producing liquid crystal windows, in particular larger liquid crystal windows suitable for use in facades. The facade windows may be of at least one meter or up to several meters in height and/or diagonal diameter and/or length. Several meters may be any of 1 m to 5 m or 1.5 m to 4.5 m or 2 m to 4 m Particularly, in case of a rectangular shaped cell, the dimensions may be between 50 mm x 50mm up to 1600 mm x 3500 mm. Alternatively, the provided shapes may be any of triangular shaped, trapezoid shaped and/or polygonal shaped substrates. Particularly, the respective area covered by the respective shape corresponds to the area spanned by the given dimensions of the rectangular shape stated above.

The liquid crystal windows can be used in sustainable glazing applications in buildings and vehicles, in particular by giving energy savings with respect to lighting, cooling and/or heating and by positively impacting the lifecycle e.g. in terms of maintenance, while in addition providing improved thermal and visual comfort.

The substrates are preferably optically transparent. The two substrates may be independently selected from a polymer or a glass. Suitable glass substrates include, for example, float glass, downdraw glass, chemically or heat-treated toughened glass, borosilicate glass and aluminosilicate glass.

Suitable polymer substrates include, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinylbutyral (PVB), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide (PI), COP (cyclic olefin polymers) and cellulose triacetate (TAC).

The two substrates are arranged as a cell wherein a gap is formed by the two substrates. The size of the gap is preferably from 1 pm to 300 pm, preferably from 3 pm to 100 pm and more preferably from 5 pm to 100 pm, and most preferably from 10 pm to 50 pm. The cell is usually sealed by means of glue lines located at or near the edges.

A pressure sensor may be used to determine the pressure inside the vacuum chamber. The pressure inside the cell may be determined indirectly via the pressure of the vacuum chamber (in cases where no oxygen sensor is used, the oxygen sensor, particularly in combination with the pressure sensor, is described in greater detail below). The pressure sensor allows to determine the pressure in the vacuum chamber and evacuation may be completed upon using the respective waiting time for completion of evacuating the cell. Nevertheless, the pressure sensor may allow to determine the respective pressure increase and thus to determine the pressure inside the vacuum chamber and/or the cell. The setup can be configured such that it starts a repressurization (to initiate the filling of the cell) once the respective setup has reached a determined pressure minimum and once the at least one fill opening or respective multiple fill openings (of multiple cells) has/have been brought in contact with the fill material. This allows the determination of the timepoint for initiating to bring the fill material, in particular the liquid-crystalline material, in contact (submerge) with the fill opening I fill openings (of a single or of multiple cells) and to monitor the pressure increase that results in filling the cell(s). Furthermore, the pressure sensor allows to determine the time point of reaching atmospheric pressure level and/or to determine the time point of reaching overpressure level. Furthermore, the pressure sensor allows to determine the pressure increase behavior up to the respective time points of reaching atmospheric and/or overpressure level. The pressure level may be monitored such that the setup is configured to increase the pressure with a different time constant after the atmospheric pressure level has been reached, up to the preferably predetermined overpressure level. This allows to further modulate the filling speed and to optimize the filling behavior based on the filling level and the applied (over)pressure. The pressure signal may thus be used to control the respective pressure pumps e.g., their respective pumping speed. The pressure sensor may thus provide the signal to optimize (reduce) the filling time.

Evacuation is preferably performed in a controlled manner. In a preferred embodiment of the method a signal indicating an amount of oxygen remaining inside the vacuum chamber may be provided by means of an oxygen sensor (in addition to the pressure sensor) mounted inside the vacuum chamber and completion of the evacuation of the vacuum chamber may be determined based on said signal. The oxygen sensor may be used to reduce the waiting time.

Preferably, the evacuation of the vacuum chamber is considered to be completed if the signal indicating the amount of oxygen inside the vacuum chamber is below a predetermined threshold.

In order to determine the threshold, empirical studies may be conducted. For example, several test runs may be performed wherein the signal of the oxygen sensor is recorded and the time used for evacuating the vacuum chamber is reduced for each subsequent run. The threshold is then set to the recorded sensor value measured after completion of the evacuation for the test run which produced a correctly filled liquid crystal cell in the least amount of time. Also, the threshold may be determined by comparing the signal indicating the amount of oxygen inside the vacuum chamber to a signal of a pressure sensor mounted inside the vacuum chamber. Alternatively or additionally, to providing a predetermined threshold, the derivative of the signal may be determined and the derivative may be compared to a predetermined threshold. The derivative of the signal indicates a slope or speed of change of the signal. Preferably, the evacuation of the vacuum chamber is considered to be completed when a steep slope is detected.

If a pressure sensor is used (in addition to an oxygen sensor) to observe the evacuation of the vacuum chamber, the signal of the pressure sensor drops rapidly at the beginning of the evacuation process and then converges slowly towards an end pressure of the vacuum pump. Air trapped inside the cavity of the liquid crystal cells will only slowly leak out of the cavities. Completion of the evacuation process wherein essentially all air has been removed from the cavities is hardly visible in a signal of a pressure sensor.

When the vacuum chamber and thus the liquid crystal cells are evacuated, there are two gas flow regimes to be recognized. The first flow regime is a laminar flow regime. After a cross over pressure has been reached, a molecular flow regime is entered.

In the first flow regime, it is difficult to establish large pressure differences inside the cell: the pump down mechanism via the fill openings is a gradual one. A careful balance must be maintained between the pressure inside the cell and the vacuum chamber. As it is not possible to directly control the pressure inside the cell, the pressure of the vacuum chamber must be controlled such that a force exerted onto the substrate caused by a pressure difference between the chamber pressure and the cell pressure is not exceeding maximum load or maximum allowed stress level inside the substrate material.

The conductance in laminar flow region is characterized by the average pressure difference over the filling ports. As the absolute pressure inside the vacuum chamber is lowered, the pressure difference between the cell and the vacuum chamber is also lowered, hence the conductance becomes smaller and smaller.

Once the pressure (or rather the molecular mean free path) is in the order of the spacing of the cell, a cross over point is reached from laminar flow to the molecular flow region. The conductance in the molecular flow region is pressure independent. Since the physical first part of the cell which enters into the molecular flow region, are the filling ports, a pressure difference now can be generated between the top part of the cell and the filling ports. The pressure difference between the chamber and cell is now always lower than the maximum allowed stress level inside the substrate material. Pumping the vacuum chamber can now be done at maximum speed/capacity of the vacuum pump.

In other words, the residual air between the filling ports and the other parts inside the cell may progressively flow out of the cell, until a level is reached wherein essentially all air is removed by pumping through the filling ports. On that moment, the oxygen signal which is measured in the vacuum chamber (and which was determined by the residual gas flow from the air inside the cell) is seen to be dropping steeply. This steep drop is an indication that the cell is pumped down to an acceptable level to start the filling process with the medium.

In order to avoid a large pressure difference between the inside of a liquid crystal cell and the vacuum chamber during evacuation, it is preferred to perform a primary evacuation in a pressure range of ambient pressure to an intermediate pressure in the range of from 10 mbar to 50 mbar. After completion of the primary evacuation, it is preferred to perform a secondary evacuation. During primary evacuation, a vacuum pump is operated at reduced capacity and during secondary evacuation the vacuum pump is operated at full capacity.

By performing such a controlled evacuation, the maximum stress exerted onto the substrates is limited to a safe value. Optical distortions of the final liquid crystal cell due to stress in the substrates is advantageously avoided.

Preferably, after the evacuation has been completed, wherein the completion can be defined as stated above, the evacuated liquid crystal cell can be brought into contact with a medium comprising at least one liquid crystal material.

In other words, combining a pressure sensor and an oxygen sensor may be used to optimize (reduce) both the waiting time and the filling time. Furthermore, their combination may allow to optimize the respective transitions from different flow regimes to optimize the respective pump performance to further optimize (reduce) the respective time of running the process. The setup can be configured such that it brings the at least one fill opening or respective multiple fill openings (of multiple cells) in contact with the fill material and starts a repressurization (to initiate the filling of the cell) determined by a pressure and/or oxygen minimum.

For successful filling of the liquid crystal cells the pressure inside the vacuum chamber should not be too low in order to avoid degradation of the liquid crystals in the medium. Preferably, the pressure is greater or equal to 1.0*1 O'⁴ mbar. Thus, it is preferred that the thresholds used in conjunction with the signal of the oxygen sensor is chosen such that after the evacuation is considered to be completed, the pressure in the vacuum chamber is greater than or equal to 1.0*10^(-4) mbar.

The medium for filling the at least one liquid crystal cell is preferably provided in a tray which is connected to a reservoir. The tray is preferably located inside the vacuum chamber and the at least one liquid crystal cell is arranged such that the fill opening is located at the bottom so that the fill opening may be contacted with the medium inside the tray by submerging the fill opening into the medium by lowering the liquid crystal cell, by raising the tray and/or by adjusting the fill level of the medium in the tray. The medium on the tray may comprise a surface exposed towards the cavity of the vacuum chamber (such that the surface may be brought in contact with the inner surface of the cavity) and wherein that surface can be moved towards the fill opening by adjusting the fill level of the medium on the tray such that the fill opening submerges into the medium. The adjustment of the medium height inside the tray is a simple and straight forwards implementation. The height adjustment of the liquid crystal cell and/or of the tray allows greater freedom in setup design and implementation schemes.

After the at least one fill opening of the at least one liquid crystal cell has been contacted with the medium, the pressure inside the chamber is raised. In embodiments, where several fill openings and/or several cells are to be filled, all fill openings of all cells must be in contact with the medium (submerged) before the pressure inside the chamber is raised. The rising pressure pushes the medium into the cavity between the substrates and the cells are filled.

Overpressure is preferably to be understood as a pressure above atmospheric pressure level (atmospheric pressure not included in the range). More precisely, the overpressure can be in a range from 1.1 bar to 6 bar or from 1.3 bar to 5 bar or in a range from 1.5 bar to 3 bar or in a range from 1.8 bar to 2.5 bar or in a range from 1.9 bar to 2.1 bar. Alternatively, the overpressure can be preset to 2 bar. Overpressure can be understood as a pressure in addition (on top) of the atmospheric pressure level. Alternatively or additionally, an overpressure level can be chosen defined such that the overpressure level itself is set to a maximum pressure (level) being in a range from 1.1 bar to 6 bar or from 1.3 bar to 5 bar or in a range from 1.5 bar to 3 bar or in a range from 1.8 bar to 2.5 bar or in a range from 1.9 bar to 2.1 bar. Alternatively, the overpressure level can be preset to 2 bar. Operating at overpressure levels of smaller or equal to 2 bar allows to use standard pressure equipment for the vacuum chamber. In alternative embodiments, the overpressure (level) exceeds 2 bar, e.g. ranging between 2.5 bar to 5 bar or ranging from 2.8 bar to 4.5 bar or being preset to exactly 3 bar or being set to exactly 4 bar. In these embodiments the pressure (level) can promote the filling of the respective liquid crystal cell even further, but the demand with respect to the pressure safety precautions is also increasing. In these cases, vacuum chambers with particularly thick chamber walls and pressure distributing geometries have to be used. Additionally or alternatively, overpressure designed equipment components may be used, e.g. viewing windows, (safety) valves, high pressure seals, etc.

Using an overpressure level of 2 bar in comparison to atmospheric pressure level of 1 bar is shown as matter of example in the following Table 1. The column "cell height" represents the filling along the axis of the filling direction starting from the inlet of the liquid crystal cell and preferably parallel to the side of the cell e.g., the longer side of a rectangle. In an alternative implementation, the shorter side can be the side parallel to the filling direction e.g., in case of a rectangular shape of the liquid crystal cell. In such a case more than one inlet (fill opening) for the medium comprising at least one liquid crystalline material may be provided configured to be in contact with the medium in the vacuum chamber simultaneously.

Table 1: Cell height (level of filling) vs. filling time in a comparison at ambient (atmospheric = atm) pressure in the vacuum chamber at 1 bar vs. overpressure level at 2 bar and respective time gain.

In this exemplary comparison experiment, there is initially no advantage observed at 2.0 bar in filling the cell from a 0.0 m to a 0.6 m range. This is due to the liquid crystalline material filling being initially delayed by the fact that the installed safety overpressure relief valve has a specific flow (not pressure) limitation, therefore the intake of pressure is limited. Pressurizing the chamber takes time, therefore in the beginning of the venting cycle the contribution of overpressure is not visible in the results (but noticeable from 0.6 m upwards). Exchanging the safety overpressure relief valve may further accelerate venting. In the present example, the pressure (level) is ramped up to 2 bar over a course of 30 min, e.g. mainly limited by the equipment's flow capacity of the safety overpressure relief valve not allowing to exceed above 2 bar. Furthermore, the pressure increase from vacuum (1.0*1 O'⁵ mbar) to overpressure (level) (2.0*10³ mbar) is executed slowly (ca. 30 min) to avoid any deformation and stress induced damages to the cells. The time for increasing the pressure to the overpressure level may be the time filling takes to reach any particular cell height that is indicated in table 1 from 0.0 m to any of these respective values. The respective timing is shown with respect to the applied pressure (level). In particular, the time is set such that 1 bar is reached, even in case of an overpressure (level) of 2 bar is to be reached.

Particularly, the pressure increase from vacuum to overpressure or overpressure level can take place in the time of filling the liquid crystal cell from a 0.0 m to a 2.5 m range or from a 0.0 m to a 1.6 m range or from a 0.0 m to a 1 m range or from a 0.0 m to a 0.8 m range or from 0.0 m to bigger than 1.6 m. The method allows for a respectively large liquid crystal cell to be filled. In a respective pressure increasing scheme the ramping up of the pressure inside the vacuum cell can be performed in a single increase. In other words, only a single time constant may be used to describe the respective increase of the pressure inside the vacuum cell up to the pressure (level) to be reached. In particular, the filling of the liquid crystal cell may overlap with the respective increase of pressure, wherein the filling speed of the liquid crystal cell may increase with increasing pressure, particularly after the overpressure regime has been reached inside the vacuum cell.

Additionally or alternatively, the pressure increase from vacuum to atmospheric pressure level can take place in the time of filling the liquid crystal cell from a 0.0 m to a 1 m range or from a 0.0 m to a 0.8 m range or from a 0.0 m to a 0.6 m range. The pressure increase from atmospheric pressure level to a preset and/or a final overpressure level can take place in a time thereafter. Overpressure (level) can set in at a cell height of filling at any of 1 m, 0.8 m, 0.6 m and/or 0.4 m. Further preferably, the overpressure (level) can set in at any range combination of the respective single values provided here e.g., between 0.4 m and 1 m or between 0.6 m and 0.8 m. Furthermore, additionally or alternatively the pressure increases from vacuum to atmospheric pressure level and the increase from atmospheric pressure level to the preset and/or the final overpressure level can exhibit different time constants, in particular at least two time constants. Also, the respective filling speed of filling the liquid crystal cell can exhibit different time constants, potentially reducing the stress on the respective liquid crystal cell under filling conditions.

The overpressure (level) can be kept constant from the time of reaching a preset overpressure level until filling of the liquid crystal cell is completed to at least 70 % or to at least 80 % or to at least 90 % or to 100 % (complete filling, filled cell). Additionally or alternatively, the overpressure (level) can be kept constant by the opening threshold of an overpressure safety valve. The safety valve can protect the equipment. Additionally, it may be an easy way to keep the pressure at a preset level by applying pressure to the vacuum chamber (now under pressure, particularly overpressure) slightly above the opening threshold of the pressure safety valve. Thus, the pressure is kept at the level of the threshold of the safety valve. Varying the overpressure with respect to the filling level of the liquid crystal cell may allow to adapt the respective filling conditions to the cell inherent pressure conditions to reduce stress onto the cell and/or to improve the filling speed.

Preferably, nitrogen gas or ultra clean compressed air is introduced into the vacuum chamber for raising the pressure inside the vacuum chamber to the overpressure or overpressure level.

The vacuum chamber can be filled with another gaseous medium comparable to nitrogen gas or dry, purified and/or clean air. Clean air refers to the absence of dust particles e.g., due to filtering as well as absence of any microbial cells and/or other biological material such as human (skin) cells.

If ultra clean compressed air is used as gaseous filling medium for the vacuum chamber, a combination of the oxygen sensor with the provided overpressure (level) scheme provides the advantage that the oxygen levels can be monitored during evacuation to determine the exact time point of evacuation. Thus, the stress induced to the apparatus as well as the stress induced to the liquid crystal cell can be minimized as described above. This is because in the transition from a laminar flow regime to a molecular flow regime a cross over takes place. Using the oxygen sensor may provide the means to monitor that transition. This allows to reduce the waiting time (potentially eliminating it completely).

It can be preferred to perform a primary pressure increase in a pressure range of an intermediate pressure (level) in the range of from 10 mbar to 50 mbar to ambient pressure (level). After completion of the primary pressure increase, it can be preferred to perform a secondary pressure increase. During primary pressure increase, a pressure pump is operated at reduced capacity and during secondary pressure increase the pressure pump is operated at full capacity.

Alternatively, the pressure increase can also be provided by using evaporated liquid nitrogen. A pressure sensor may be used to control the pressure (level) inside the vacuum chamber and to track a respective pressure increase with different time constants resulting in different time constants with respect to the filling of the liquid crystal cell with liquid crystal medium. Furthermore, a trace oxygen level can be provided to allow a combined scheme with the oxygen sensor even in cases where evaporated liquid nitrogen is provided. This keeps up the flexibility of the gaseous medium used with setup layout.

The method may further comprise the step of releasing the overpressure (level) in the inner vacuum chamber to atmospheric pressure level for taking out the liquid crystal cell from the vacuum chamber by a pressure release valve controlled by an electronic control unit. Reaching equilibrium chamber pressure (using an over pressure release valve) and thus reaching ambient pressure (atmospheric pressure level)This allows to take out the respective (completely) filled liquid crystal cell from the vacuum chamber. The atmospheric pressure (level) is defined for matter of the respective method and any respective embodiment of such a respective method as the pressure at room temperature (22 °C) on sea level. Alternatively or additionally, the respective ambient pressure (level) at the respective manufacturing site is to be defined as atmospheric and/or ambient pressure (level). Ambient pressure (level) and atmospheric pressure (level) can be used synonymously.

After the cavity has been filled with the medium and after the liquid crystal cell has been taken out from the vacuum chamber, the at least one fill opening (or fill port or inlet) is sealed and the liquid crystal cell is completed.

Sealing the cavity after it has been filled with the (liquid crystalline material comprising) medium, the at least one fill opening (or fill port or inlet) may be sealed for completion of the liquid crystal cell. Sealing the at least one fill opening allows to finish the liquid crystal cell to hold the liquid crystalline material in the cavity of the liquid crystal cell for taking out the liquid crystal cell from the vacuum chamber.

Preferably, two or more liquid crystal cells are processed simultaneously in the same vacuum chamber. Preferably, between 2 and 200 liquid crystal cells and more preferably, between 10 and 120 liquid crystal cells may be processed simultaneously. For example, four liquid crystal cells are processed at the same time. The optimum number of liquid crystal cells which are processed simultaneously in the same vacuum chamber may depend on the size of the liquid crystal cells.

The described method and the described respective apparatus (see below) may not be limited to the filling of a single liquid crystal cell at a time. It is possible to process only a single cell at one time, though. Providing the holders and/or the lifts for processing multiple liquid crystal cells at a time allows to further speed up the manufacturing process of the respective liquid crystal cells. Furthermore, bigger charges of liquid crystal cells can be manufactured, where e.g., a charge comprises the amount of liquid crystal cells manufactured in a single run. A single run may be a single run through of all method steps described above. In case the method is repeated with newly provided empty cells, a new charge of cells will be provided.

A further aspect of the invention is providing an apparatus for filling liquid crystal cells with a medium. The apparatus preferably comprises a vacuum chamber, a tray, means for submerging a fill opening of at least one liquid crystal cell in the medium, a vacuum pump, a pressure pump, and a control unit. The tray can be located inside the vacuum chamber and be adapted to hold the medium. The vacuum pump can be configured to evacuate the vacuum chamber.

Vacuum pumps such as rotary vane pumps, cryopumps or scroll pumps may be used with and without combination with turbomolecular pumps. For successful filling of the liquid crystal cell(s) the pressure inside the vacuum chamber should not be too low in order to avoid degradation of the liquid crystals in the medium. Preferably, the pressure is greater or equal to 1.0*1 O'⁴ mbar. Thus, it is preferred that a pressure threshold, potentially used in conjunction with the signal of the oxygen sensor, is chosen such that after the evacuation is considered to be completed, the pressure in the vacuum chamber is greater than or equal to 1.0*1 O'⁴ mbar.

The control unit is preferably adapted and configured to carry out the steps of one of the described methods for filling liquid crystal cells with a medium. Thus, features described with respect to the method apply to the apparatus and vice versa features described with respect to the apparatus apply to the methods.

The vacuum chamber may be divided into an upper chamber and a lower chamber which may be separated by means of a gate. In such a setup, the liquid crystal cells to be filled are arranged in the upper chamber and the tray comprising the medium is arranged in the lower chamber. The upper chamber has a smaller volume than the total combined volume of the vacuum chamber which makes it easier to perform a controlled evacuation of the upper chamber and thus to evacuate the cavities inside the liquid crystal cells. After evacuation of both the upper chamber and the lower chamber is complete, the gate is opened.

The apparatus may make use of one or more vacuum pumps such as rotary vane pumps, cryopumps or scroll pumps which may be used with and without combination with one or more turbomolecular pumps.

The apparatus may make use of one or more pressure pumps such as compressor pumps, compressors and/or a cryo-liquified gas evaporator e.g. for evaporation of liquid nitrogen, which may be used with and without combination with one or more filters and/or diffusors. Diffusors allow a steady influx of gaseous medium into the vacuum chamber. This allows to reduce turbulences and thus may reduce negative impacts upon manufacturing caused by vibrations migrating in the medium flowing in the liquid crystal cell. Preferably, the means for submerging a fill opening are constructed as a mount which holds the at least one liquid crystal cell such that the fill opening is located inside the tray (for filling) and means for controlling a fill level of the medium inside the tray.

Mounting the liquid crystal cell can be provided for by mechanical constructions that clamp the respective liquid crystal cells individually and/or collectively. The mounts may have clamping structures that contact at least a single liquid crystal cell.

"Locating inside the tray" is particularly to be understood such that the tray and the liquid crystal cell with its fill openings are oriented and arranged relative to each other such that the liquid crystal medium may contact the fill openings upon the liquid crystal medium being released (or dispensed) onto the tray to a certain level. The level can be preset and/or can be defined by the respective orientation and arrangement of the liquid crystal cell, its holder, and the tray accordingly.

Submerging is preferably executed in one of three manners. The apparatus preferably comprises a tray configured to contain a (liquid crystalline) medium and the apparatus further comprising a lifting mechanism, configured such that the tray is to be lifted to the at least one fill opening, after evacuation, until the at least one fill opening is dipped into the (liquid crystalline) medium. Alternatively, the apparatus comprises a lifting mechanism configured such that the liquid crystal cell is lowered towards the (liquid crystalline) medium, after evacuation, until the at least one fill opening is dipped into the (liquid crystalline) medium. Further alternatively, the apparatus comprises at least one fill opening positioned in an empty tray and a valve configured to be opened, after evacuation, such that (liquid crystalline) medium is dispensed into the tray until the at least one fill opening is submerged.

Preferably, the means for submerging a fill opening of a liquid crystal cell are constructed as a lifting mechanism which is configured to lower the at least one liquid crystal cell into the tray (for filling).

A lift described here and elsewhere may be a structure that allows to perform the respective task of moving the respective holder of the liquid crystal cell up and down. Alternatively or additionally, the means for submerging a fill opening of a liquid crystal cell are constructed as a lifting mechanism which is configured to raise the tray such that the fill opening is located inside the tray (for filling).

The respective lift construction may be any of a robotic arm, a moving chain conveyor where the holder and/or the tray is/are placed on and/or a respective moving plate, the holder and/or the tray is/are placed on. The tray may have the same lift structure as the lift for raising/lowering the holder of the liquid crystal cell. Alternatively, the lift for these two structures may be different.

The apparatus may further comprise a reservoir for supplying the medium to the tray. A valve may be used to control the supply of the medium. The reservoir may be connected to a valve and a respective dispending device (nozzle, diffusor, filter system) that allows to dispense the liquid crystal medium from the reservoir onto the tray. It is particularly possible to lower and raise the level of the medium in order to submerge the fill openings into the medium. Upon raising the level of the medium, the surface of the medium upon the tray moves upwards, particularly until a part of the volume of the medium encloses a part of at least one liquid crystal cell. This way, the medium can be brought in contact to the fill opening even in cases where the tray and/or the holder of the liquid crystal cell a provided as stationary units (no lift implemented or not activated).

Preferably, the apparatus comprises a vent valve which is configured to introduce air, nitrogen and/or ultraclean compressed air in a controlled manner into the vacuum chamber in order to raise the pressure. Preferably, an inert gas such as nitrogen is used. The vent valve may be connected to a supply for pure nitrogen or ultraclean compressed air. Passive influx can be provided until an ambient or atmospheric pressure level is reached in case the vacuum chamber is purged with air.

Nevertheless, to achieve overpressure, either a respective pressure pump, a compressor or a respective liquid gas evaporator has to be provided as described elsewhere in the description.

Preferably, the apparatus (further) comprises an overpressure safety valve and/or a pressure release valve controlled by the control unit for releasing the overpressure down to atmospheric pressure level for taking out the liquid crystal cell from the vacuum chamber. Pressure release can also take place in a controlled manner to avoid any abrupt pressure changes in the cavity potentially damaging the liquid crystal cell. Particularly, the pressure release takes place before the liquid crystal cell is removed from the medium and/or before the liquid crystal cell is sealed. Pressure release of the vacuum chamber is to be executed before the cells are removed from the liquid crystal medium (draining liquid crystal medium from the tray when chamber pressure equals ambient pressure). Liquid crystal cells are sealed after the filling process i.e. in a subsequent (other) process step.

The apparatus may comprise a pressure sensor for measuring the pressure inside the vacuum chamber. The pressure sensor may be used for controlling the rate at which the vacuum chamber is evacuated by the vacuum pump and/or the pressure sensor may be used for controlling the rate at which the vacuum chamber is repressurized by a pressure pump for filling the liquid crystal cell with the medium comprising at least one liquid crystalline material.

An oxygen sensor can be provided inside the vacuum chamber. The oxygen sensor is preferably based on a potentiometric zirconia solid electrolyte cell. Preferably, the oxygen sensor produces a signal which indicates the partial pressure of oxygen. The oxygen sensor can be connected to the control unit which controls the evacuation of the vacuum chamber in response to the signal provided by the oxygen sensor.

Using an oxygen sensor (additionally to a pressure sensor) in a method or an apparatus where an overpressure can be applied to the vacuum chamber may have the advantage that not only the evacuation can be speeded up, but also the pressure increase can be controlled in the step, where the evacuated vacuum chamber is refilled with gaseous medium for filling the liquid crystal cell with the medium comprising at least one liquid crystalline material. The oxygen sensor may serve as a purity detector in case liquid nitrogen, or a comparable oxygen-free gas, is provided. In such a case, appearance of oxygen can serve as a direct hint for leakage into the apparatus and may point to potential compromising impurities in the gaseous medium lowering the cleanliness of the liquid crystal cells. The liquid crystal cells may be compromised by particles being incorporated into the medium comprising at least one liquid crystalline material. Therefore, charges of potentially flawed liquid crystal cells can be easily identified and discarded. Alternatively or additionally, the oxygen sensor may serve to monitor the respective transition from the molecular flow regime to the laminar flow regime. Therefore, the pressure applied to the vacuum cell can be increased slowly in a low-pressure regime as described elsewhere. After the pressure crossover point (where the molecular flow regime transitions to a laminar flow regime) is reached the pressure increase can be performed at full capacity e.g., of the pressure pumps until the respective overpressure is reached. The respective combination of the oxygen sensor and the overpressure regime allows to implement an improved setup safety scheme and extends the observed setup parameters.

According to another aspect, a computer readable medium may be provided, the computer readable medium comprising a computer executable routine configured to perform at least one step of a method according to the invention. This allows the implementation of the routines to the control unit to control a respective method.

Particularly, the computer readable medium may be any of a flash drive, an SSD, a hard drive, an HDD, a USB-stick, a compact disk, a magnetic storage disc. The control unit may be any of a processor, a computer processor, or comparable. The computer readable routine may be a program or computer code that when executed by the control unit implements the method steps as described above. Additionally, the computer readable routine allows an apparatus as described above to execute the necessary steps to implement a method as described above. Therefore, all features and their respective advantages apply to the described invention as a whole, independent of their respective category (device, system, method, use).

Particularly, the computer readable routine may comprise the timing for opening the respective valves and the timing for starting the respective vacuum pumps and/or pressure pumps to allow for evacuating the vacuum chamber in a controlled but automated fashion and/or to allow the repressurization (= putting the chamber back under pressure after it has been evacuated) of the vacuum chamber, particularly up to the overpressure, in a controlled and automated fashion. Furthermore, the computer readable routine may provide the timing for lowering and/or raising either of the tray and/or the liquid crystal cell (holder) and or the fill level of the medium comprising the at least one liquid crystalline material in the tray. Particularly, the method as described above can be performed in a fully automated fashion, particularly after the (empty) liquid crystal cells are placed inside the respective vacuum chamber (in their respective holder and/or lift) up until particularly the take out of the (filled; sealed) liquid crystal flow cells.

According to another aspect a liquid crystal cell comprises a medium which comprises at least one liquid crystalline material. The liquid crystalline material is filled into the liquid crystal cell with a method according to the method described elsewhere throughout the description. Filling a liquid crystal cell with a respective method allows to manufacture liquid crystal cells of bigger dimensions.

The liquid crystal cell may be a cell suitable for a liquid crystal display (LCD). The substrates are preferably of rectangular shape wherein the length of the sides of the rectangle may be in the range of from 200 mm to 5000 mm, especially preferred in the range of from 500 mm to 4000 mm and most preferred in the range of from 1000 mm to 2500 mm. Substrates can be of arbitrary shape, wherein rectangular shape is the most common shape. In more demanding embodiments, the length of the sides (of the rectangle or the longest side of the arbitrary shape) may be in the range of from 600 mm to 2000 mm or from 800 mm to 1800 mm or from 1000 mm to 1600 mm or from 1300 to 1500 mm. Therein, the length of the sides is preferably defined as the longest side of the particular shape. The respective method allows for the filling of bigger panels (assembly) of liquid crystal cells or for the filling of bigger individual liquid crystal cells in faster time frames. The method is thus preferably used for producing liquid crystal windows, in particular larger liquid crystal windows suitable for use in facades. The facade windows may be of at least one meter or up to several meters in height and/or diagonal diameter and/or length. Several meters may be any of 1 m to 5 m or 1.5 m to 4.5 m or 2 m to 4 m Particularly, in case of a rectangular shaped cell, the dimensions may be between 50 mm x 50mm up to 1600 mm x 3500 mm. Alternatively, the provided shapes may be any of triangular shaped, trapezoid shaped and/or polygonal shaped substrates. Particularly, the respective area covered by the respective shape corresponds to the area spanned by the given dimensions of the rectangular shape stated above.

Furthermore, the method avoids or minimizes the effect of "ballooning" when compared to alternative methods. This effect causes a liquid crystal cell to be bigger in the middle of the cell (from each side, in the center of mass e.g., of the substrates). Using the method may result in particularly flat windows, where the deviation of diameter from the edge towards the middle differs only by 0.1 % to 5 %, further in particular from 0.2 % to 3 %, further in particular from 0.4 % to 1 %.

Further, for example, the liquid crystal cell is a liquid crystal cell device suitable for a switchable window.

According to another aspect, a switchable window comprises two substrates joined together with a peripheral seal so that a cavity is formed, filled with a medium comprising at least one liquid crystalline material, the liquid crystal cells, wherein the liquid crystalline material configured to be switched between at least two states further comprises the dimensions of the window with a length of the sides of the window being in the range of from 200 mm to 5000 mm or in the range of from 500 mm to 4000 mm or in the range of from 1000 mm to 2500 mm.

Generally speaking, the term "vacuum pumps" may refer to any pump suitable for the task. Rotary vane pumps, cryopumps or scroll pumps may be used with and without combination with turbomolecular pumps.

The term "pressure pump" may refer to any suitable pressure providing mean for the task to provide a respective overpressure. Compressors (with respective filtering and pressure safety valves) as well as liquid nitrogen evaporation tanks may be provided to provide the respective gaseous medium for filling the respective vacuum chamber up to the respective overpressure.

Further generally speaking, the respective features and advantages linked to certain features are not limited to the method, the apparatus and/or the computer readable medium comprising a computer executable routine. Furthermore, all features can be used to specify all other respective categories and the respective advantages apply accordingly.

The nomenclature "feature A and/or feature B" is used throughout the description. It can be transferred to "feature A, feature B, or feature A and feature B". As the full listing would lead to a respective long and repetitive recasting of big portions of the description this nomenclature is used as a short abbreviate sentence construction.

The nomenclature with brackets such as "(feature)" is to be understood that the respective feature is optional and/or preferably implemented.

Certain embodiments shall be used to explain the respective general aspects described above with respect to the figures in the following.

Brief description of the drawings

The drawings show in: Figure 1 a first embodiment of the apparatus for filling liquid crystal cells prior to submerging a fill opening in a medium comprising at least one liquid crystalline material,

Figure 2 the first embodiment of the apparatus after submerging the fill opening in the medium,

Figure 3 a schematic diagram of a first embodiment of a method for filling liquid crystal cells with a medium,

Figure 4 a diagram showing a comparison of filling speed at 1 bar (= ambient I atmospheric) pressure vs. 2 bar (= overpressure), and

Figure 5 a diagram showing cell filling time with a default (= at 1 bar ambient I atmospheric pressure) and using an accelerated processing (at 2 bar overpressure.

Like-functioning and corresponding means and like-functioning and corresponding structures, as well as corresponding method steps, are numbered using the same reference signs throughout the description of the drawings. The reference signs shall not be interpreted as limiting the scope of protection. The scope of protection is derived from the wording of the claims (alone). The wording "embodiment", "example" and "part of the invention" may be used throughout the following description also as matter of example for explanatory reasons. Nevertheless, the wording of the claims will give the respective feature combinations protection is sought for and/or protection is claimed (after grant). The respective features, as described here throughout the description, alone or in any of their possible combinations, are claimed to be eligible subject matter to limit the respective scope of protection throughout any proceedings at any respective patenting institution and/or patent office and/or patenting agency, in any jurisdiction. Furthermore, "any type of proceedings" refers to any proceedings up to grant or thereafter.

Figures 1 and 2 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. The tray 16 is located inside the vacuum chamber 12.

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. A dispenser 33 is provided to avoid turbulences and vibrations in the flowing medium 30 provided to the tray 16. The vacuum chamber 12 is connected to a vacuum pump 18 for evacuation of the vacuum chamber 12. Evacuation takes place along an evacuation suction direction 59 in which (ambient) atmosphere is evacuated from the vacuum chamber 12. Both the vacuum pump 18 as well as the medium valve 34 are controlled by a control unit 22. The control unit comprises a computer storage medium 23. Thereon, a computer routine is stored that allows to run the respective controls of the respective valves, their timing of opening, as well as the opening time. The computer routine on the computer storage medium 23 is thus adapted to implement a respective method 100 as described with respect to figure 3. Additionally, the vacuum chamber 12 is connected to a pressure pump 50. The vacuum chamber 12 further comprises an overpressure safety valve 51 to limit the maximum pressure inside the vacuum chamber 12 upon applying overpressure to the vacuum chamber 12. The overpressure relief valve 51 is a mechanical valve, i.e. it is not controlled by a control unit 22. This is to prevent safety loss when a control unit is non-functional. Furthermore, there is a pressure release valve 52, to release overpressure from the process chamber controlled by the control unit 22 based on the computer executable routine stored on a computer readable storage medium 23. Furthermore, there is a safety overpressure relief valve (not controlled) to prevent over pressure of the process chamber to avoid any damage to the setup.

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 the 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.

An oxygen sensor 20 can be arranged such that it is connected with the vacuum chamber 12 and can be 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 up to atmospheric pressure. The vent valve 26 with vent 24 may be used for emergency pressure increase and/or for emergency depressurization (leveling out the overpressure with the ambient atmosphere). In the situation depicted in figure 1, an empty liquid crystal cell 40 which is formed by two substrates 42 and a seal 44, forming a cavity 43, 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 it can be lowered by a lift (not shown) such that it can be lowered along a cell lowering motion until the fill opening 46 is located below a maximum fill level of the tray 16.

In figure 2, the vent valve 26 is closed and the vacuum pump 18 is used to evacuate the vacuum chamber 12. The pressure valve 53 and overpressure relief valve 51 are closed as well. No gaseous medium can pass pressure release vent 56 and overpressure safety vent 55. 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 figure 2, by lowering the liquid crystal cell 40 with lift 47.

After submerging the fill opening 46 into the medium 30, the control unit 22 may open the vent valve 26 by assistance of the computer routine on the computer storage medium 23 so that, for example, nitrogen may enter the vacuum chamber 12 so that the pressure inside the vacuum chamber 12 rises. The pressure can be increased up to the atmospheric ambient pressure level in a passive fashion as the ambient pressure is higher than the vacuum level in cases where (filtered) ambient and atmospheric air is used to purge the cell. Nevertheless, to increase the pressure above atmospheric pressure level, a pressure pump 50 is used. The pressure increases until reaching the threshold for opening the overpressure relief valve 51. Upon reaching the threshold level of the overpressure relief valve 51, the overpressure relief valve 51 opens to avoid overpressure potentially damaging the setup, the process chamber in general and/or the liquid crystal cell 40. For operating the pressure pump 50, a respective pressure valve 53 is opened to link the pressure pump 50 to the inner parts of the vacuum chamber 12 via a pressure pump valve 53 with pressure vent. The cavity 43 of the liquid crystal cell 40 is linked to the inner part of the vacuum chamber 12 by fill openings 46. Upon reaching the desired overpressure (level), the pressure pump 50 can be kept running at an overpressure level slightly above the opening threshold of the overpressure relief valve 51. This guarantees that the threshold pressure level is set to be the respective pressure level inside the inner part of the vacuum chamber 12. Alternatively, the pressure pump 50 can be turned off, after the pressure valve 53 has been closed. The pressure level is kept constant over the filling operation.

The valves and pumps are linked via (electronic) links 54 (may be implemented as computer I control terminals) to the control unit 22 wherein the computer storage medium 23 hosts a computer routine that is configured to control the valves and pumps. Therefore, a distributed control network can be enabled.

As illustrated in figure 2, 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 and the filled liquid crystal cell 40 is removed from vacuum chamber 12, the fill opening 46 is sealed in a subsequent process step and the liquid crystal cell 40 is completed (= filling operation E).

Thereafter, the pressure can be released using a pressure release valve 52. Upon opening the respective pressure release valve 52, the pressure balances with the ambient pressure level reaching ambient pressure level. An influx of ambient atmosphere is prevented through the efflux of gas medium through the pressure release valve 52 via pressure release vent 56. Any pollution of the inner part of the vacuum chamber 12 is avoided that way.

The apparatus 10 is configured to allow the respective ranges from vacuum levels e.g. down to below about 50 mbar, preferably down to vacuum levels of 1.0*1 O'⁴ and up to at least 2 bar (2.0*10³ mbar) of overpressure. This can be achieved by respective structural stability promoting structures e.g., partial or complete thickenings of the walls and/or structure enhancing geometries e.g., polygonal (octagonal) shapes. Up to 2 bar, a standard vacuum technology chamber can be used.

Figure 3 shows a schematic diagram of a first embodiment of a method for filling liquid crystal cells 40 with a medium. In a first step A, a liquid crystal cell 40 is placed inside a vacuum chamber 12, followed by an evacuation step B in which the vacuum chamber 12 is evacuated. Evacuation is achieved as described with respect to the embodiments shown in figures 1 and 2. Upon reaching the evacuation state of the vacuum chamber 12 with the liquid crystal cell 40, a step C of contacting a fill opening 46 with a liquid crystal medium follows. The contacting may be promoted either by lowering the liquid crystal 40 with lift 47 and/or by raising the tray 16 by lift 48 and/or adjusting the height of the medium 30 by supplying more medium 30 through the dispenser 33 from the reservoir 32 to the tray 16. After the fill opening 46 is in contact with the liquid crystal medium, a step D follows. In step D, the pressure is risen in the vacuum chamber 12 until an overpressure level is reached as described with respect to the embodiments in the figures 1 and 2, as well as shown in greater detail in figures 3 and 4. The rising pressure forces the liquid crystal medium 30 to fill the liquid crystal cell 40. This process can be summarized as a filling operation E. It comprises substeps E1, where the pressure rises from vacuum pressure level to ambient pressure. This can take place by either passively purging the cell by a respective inert or ultraclean gas or by already using a respective pressure pump 50. In substep E1, the filling operation E starts and is running. Upon reaching the atmospheric pressure level, overpressure is applied raising the pressure in the vacuum chamber 12 to pressure levels exceeding the ambient pressure level. Even though the term ambient pressure level and/or atmospheric pressure level is used throughout the description the respective gas does not have to be provided from the atmosphere. This definition applies to the embodiments shown in the figures, but also to the more general aspects of the description. To do that, the pressure pump 50 is activated and the pressure valve 53 is opened to allow passage of pressurized gas (above ambient pressure) to purge into the inner part of the vacuum cell 12. This substep E2 can be described as the acceleration stage of applying the overpressure. In this step the filling operation E speeds up compared to the filling operation E at ambient pressure level. In alternative embodiments, the substep E2 can be performed upon reaching the overpressure level. The respective embodiment chosen depends highly on the liquid crystal medium 30 to be filled into the liquid crystal cell 40 and e.g., its viscosity level. After the filling operation E is completed, in step F the pressure is released from the vacuum chamber 12. This can be done by opening the pressure release valve 52 as described previously. The filling step E is frequently performed in parallel or temporally overlapping to the step D, the pressure increase. The pressure increase step D is furthermore the driving step for the filling step E. The pressure release step F is followed by a step G of taking out the now filled liquid crystal cell 40 from the inside of the vacuum chamber 12. Step G is done by first bringing fill opening 46 of the liquid crystal cell 40 out of contact with the liquid crystal medium 30. Thereafter, the liquid crystal cell 40 can be withdrawn from vacuum chamber 12. The liquid crystal cell 40 is to brought out of contact from the medium 30 and sealed. Raising the liquid crystal cell 40 with lift 47 and/or lowering the tray 16 by lift 48 and/or releasing medium 30 to lower the height of the medium 30 on the tray 16 may be implemented and used to bring the liquid crystal cell 40 and the medium 30 out of contact. Figure 4 shows a diagram comparing the filling speed at 1 bar (= ambient / atmospheric) pressure vs. 2 bar (= overpressure). The left axis represents the fill time in minutes, the right axis represents gain at increased fill pressure in minutes. The x- axis represents the filled cell height in meter. As matter of example a method 100 for filling liquid crystal cells 40 with a medium 30 comprising at least one liquid crystalline material is performed at 1 bar filling pressure. This pressure corresponds to atmospheric or ambient pressures. For reasons of comparison and as a proof of principle, a method 100 for filling liquid crystal cells 40 with a medium 30 comprising at least one liquid crystalline material is performed at 2 bar filling pressure. Graph 101 shows the fill level increase at 1 bar (= atmospheric I ambient) pressure as dotted line. The fill level is given in height of the liquid crystal cell 40 (x-axis). The height can be measured in a perpendicular direction of the ground level and/or in the direction 45 of the filling of the cell 40 e.g., from the inlet / fill opening 46. Graph 102 shows the fill level increase at 2 bar overpressure as straight line. For better comparison of the early stage, before the overpressure gain take over point 104, graph 102 (fill level increase at 2 bar overpressure) is set off with respect to graph 101 (fill level increase at 1 bar). Furthermore, the data points that resulted in graph 102 are subtracted from the data points that resulted in graph 101. The respective resulting data points are shown in graph 103 showing the fill time gain at direct comparison of fill level increase at 1 bar vs. at 2 bar. Graph 101 and graph 102 move parallel to each other and also mainly parallel to the x-axis at first. In the 0.0 to 0.6 m range there is initially no advantage observed at 2.0 bar the processing and liquid crystalline material filling is dominated by capillary filling. A pressure increase from vacuum (1.0*1 O'⁵ mbar) to overpressure (2.0*10³ mbar) is executed slowly (ca. 30 min). The pressure is limited with respect to the equipment construction. Higher pressures further increase acceleration. Flow rate is limited with respect to the equipment related safety features of the over pressure safety vent valve. The equipment in the current examples is with a construction of the chamber is designed (and certified) to handle a pressure range 1.0*10^(-5) mbar (vacuum) to 2.0*10³ mbar (overpressure). At filling heights of 0.6 m the overpressure gain take over point is reached. At filling heights bigger than 0.6 m the cells are filled faster what can be seen in the comparison graph 103. With an increasing height the filling time gain increases. In some embodiments the pressure is increased in a respective 2 level increase E1, E2. Up to the 0.6 m height the pressure level is increased up to atmospheric levels or to the overpressure. This allows to concatenate the time of filling with the time of pressure increase, optimizing the filling scheme. Figure 5 shows a diagram showing cell filling time at default (1 bar) and at accelerated processing (2 bar) fitted by second-order polynomials. The diagram's y-axis represents the filling time from start of venting at 1 bar in the first experiment and in venting up to overpressure of 2 bar in minutes. The x-axis gives the filled cell height in meters as already explained with respect to figure 4. Graph 105 shows the polynomial fit for the 1 bar experiment data shown in graph 101 in figure 4. The polynomial fit is based on the formula y = 119,94x2 + 11 , 5x with standard deviation R² = 0,9906. Graph 106 shows the polynomial fit for the 2 bar experiment data shown in graph 102 in figure 4. The polynomial fit is based on the formula y = -0,5448x² + 92,067x with standard deviation R² = 0,9902. In the respective embodiment, there are not only are there two distinct sub-steps, filling initiation E1 , and acceleration stage E2. Furthermore, the acceleration stage E2 further comprises a more complex timing pattern that can be fitted with the respective second order polynomial. Therein, the second order contributes with a negative constant multiplicator.

List of Reference Numerals

10 apparatus

12 vacuum chamber

16 tray

18 vacuum pump

20 oxygen sensor

22 control unit

23 computer storage medium

24 vent

26 vent valve

30 medium

32 medium storage tank

33 medium dispenser

34 medium valve

36 cell lowering motion

40 liquid crystal cell

42 substrate

43 cavity

44 seal

45 filling direction 46 fill opening

47 lift for lowering the liquid crystal cell

48 lift for raising the tray

50 pressure pump

51 overpressure relief valve

52 pressure release valve

53 pressure pump valve

54 link

55 overpressure safety vent

56 pressure release vent

57 atmospheric pressure dry air influx

58 pressurized dry air influx I (typically) nitrogen gas

59 evacuation suction direction

60 pressure sensor

100 method for filling liquid crystal cells with a medium comprising at least one liquid crystalline material

101 fill level increase at 1 bar (= atmospheric I ambient) pressure

102 fill level increase at 2 bar overpressure

103 fill time gain at direct comparison of fill level increase at 1 bar vs. at 2 bar

104 overpressure gain take over point

105 second order polynomial fit on fill level increase at 1 bar pressure data

106 second order polynomial fit on fill level increase at 2 bar pressure data

A placing a liquid crystal cell inside a vacuum chamber

B evacuating the vacuum chamber

C contacting a fill opening with a liquid crystal medium

D raising the pressure in the vacuum chamber

E filling of the liquid crystal cell

E1 substep of E where pressure rises from vacuum pressure level to ambient pressure

E2 substep of E where pressure rises from ambient pressure level to overpressure

F releasing the pressure in the vacuum chamber

G taking out the liquid crystal cell from the inside of the vacuum chamber

Claims

Patent Claims

1 . Method (100) for filling at least one liquid crystal cell (40) with a medium (30) comprising at least one liquid crystalline material, the at least one liquid crystal cell (40) comprising two substrates (42) joined together with a peripheral seal (44) so that a cavity (43) is formed, wherein the liquid crystal cells (40) comprise at least one fill opening (46), the method comprising the steps of a) placing (A) at least one liquid crystal cell (40) inside a vacuum chamber (12), b) evacuating (B) the vacuum chamber (12), c) contacting (C) 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 characterized by d) raising (D) the pressure in the vacuum chamber (12) to an overpressure, wherein the rising pressure in the vacuum chamber (12) causes the medium (30) to fill the cavity (43) inside the at least one liquid crystal cell (40).

2. Method (100) 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 by raising the tray (16), and/or wherein the medium (30) on the tray comprises a surface exposed towards the cavity (43) of the vacuum chamber (12) and wherein that surface is moved towards the fill opening (46) by adjusting the fill level of the medium (30) on the tray such that the fill opening (46) submerges into the medium (30).

3. Method (100) according to claim 1 or 2, wherein the overpressure or overpressure level is above atmospheric pressure level, wherein atmospheric pressure is not included in the range, or wherein the overpressure or overpressure level is in a range from 1.1 bar to 6 bar or from 1 .3 bar to 5 bar or in a range from 1.5 bar to 3 bar or in a range from 1.8 bar to 2.5 bar or in a range from 1.9 bar to 2.1 bar or at 2 bar.

4. Method (100) according to any one of claims 1 to 3, wherein the pressure increase from vacuum to overpressure or overpressure level takes place in the time of filling the liquid crystal cell from a 0.0 m to a 2.5 m range or from a 0.0 m to a 1.6 m range or from a 0.0 m to a 1 m range or from a 0.0 m to a 0.8 m range or from 0.0 m to larger than 1.6 m. Method (100) according to any one of claims 1 to 4, wherein the pressure increase from vacuum to atmospheric pressure level takes place in the time of filling the liquid crystal cell (40) from a 0.0 m to a 1 m range or from a 0.0 m to a 0.8 m range or from a 0.0 m to a 0.6 m range and wherein the pressure increase from atmospheric pressure level to a preset and/or a final overpressure or overpressure level takes place in a time thereafter; and/or wherein the pressure increase from vacuum to atmospheric pressure level and the increase from atmospheric pressure level to the preset and/or the final overpressure or overpressure level exhibit different time constants. Method (100) according to any one of claims 1 to 5, wherein the overpressure or overpressure level is kept constant from the time of reaching a preset overpressure level until filling of the liquid crystal cell is completed to at least 70 % or to at least 80 % or to at least 90 % or to 100 %, wherein 100 % designates complete filling or respectively a completely filled liquid crystal cell (40), and/or wherein the overpressure or overpressure level is kept constant by the opening threshold of an overpressure relief valve (51). Method (100) according to any one of claims 1 to 6, wherein nitrogen gas or ultra clean compressed air is pumped into the vacuum chamber (12) for raising the pressure inside the vacuum chamber (12) to the overpressure or overpressure level. Method (100) according to any one of the claims 1 to 7, wherein the method (100) further comprises the step of e) releasing (F) the overpressure in the inner vacuum chamber (12) to atmospheric pressure level, for taking out (G) the liquid crystal cell (40) from the vacuum chamber (12), by a pressure release valve (52) controlled by an electronic control unit (22). Method (100) according to claim 8, wherein after the medium (30) has filled the liquid crystal cell (40) and the liquid crystal cell (40) has been taken out (G) of the vacuum chamber (12), the at least one fill opening (46) is sealed. 10. Method (100) according to any one of claims 1 to 9, wherein two or more liquid crystal cells (40) are processed simultaneously in the same vacuum chamber (12).

11 . 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), a pressure pump (50), and a control unit (22), wherein the control unit (22) is adapted to carry out at least one step of a method according to any one of claims 1 to 10.

12. Apparatus (10) according to claim 11 , 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) are provided.

13. Apparatus (10) according to either claim 11 or 12, comprising a tray (16), the tray (16) being configured to contain a medium (30), the apparatus (10) further comprising a lifting mechanism (47) configured such that the tray (16) is to be lifted to the at least one fill opening (46), after evacuation, until the at least one fill opening (46) is dipped into the medium (30); or comprising a lifting mechanism (47) configured such that the liquid crystal cell (40) is lowered towards the medium (30), after evacuation, until the at least one fill opening (46) is dipped into the medium (30); or comprising at least one fill opening (46) configured to be positioned in an empty tray (16) and a valve configured to be opened, after evacuation, such that the medium (30) is dispensed into the tray (16) until the at least one fill opening (46) is submerged. Apparatus (10) according to any one of the claims 11 to 13, wherein the apparatus (10) further comprises an overpressure relief valve (51) and/or a pressure release valve (52) controlled by the control unit (22) for releasing (F) the overpressure down to atmospheric pressure level for taking out (G) the liquid crystal cell (40) from the vacuum chamber (12). Computer readable medium (23) comprising a computer executable routine configured to perform at least one step of a method according to any one of the claims 1 to 10. A liquid crystal cell (40) with a medium (30) comprising at least one liquid crystalline material filled into the liquid crystal cell (40) using the method according to any of the claims 1 to 10. Switchable window comprising two substrates (42) joined together with a peripheral seal (44) so that a cavity (43) is formed filled with a medium (30) comprising at least one liquid crystalline material, wherein the window is configured to be switched between at least two optical states and has dimensions with a length of the sides of the window being in the range of from 200 mm to 5000 mm or in the range of from 500 mm to 4000 mm or in the range of from 1000 mm to 2500 mm.