DE2159165A1 - Liquid crystal cell and process for their manufacture - Google Patents

Description

Patent attorneys Dipi.-ing. Linen weaver

DipL-ing. Carpenter ~ 1; March 1872

DipL-lng. v. Wengwsky 21 5 9 1 5 5- ■

8München2, Rosental7 "'t

«Tel. 2603989:

E L "BCTROVAC Manufacture of electrotechnical Spezialartikel Gesellschaft m.b.H. Rampengasse 5, A-H94 Vienna XIX.

Liquid crystals and processes for their manufacture

The invention relates to a liquid crystal cell in which the crystalline liquid is between plates made of inorganic material, in particular glass, is embedded, at least one of which is transparent and those-optionally with transparent or reflective Thin-film electrodes are covered, as well as processes for their manufacture.

A liquid crystal cell is a controllable light barrier or a controllable reflector, in which the special properties occurring between the melting point and clearing point are more crystalline, i.e. anisotropic, liquids are exploited. In the case of the light barrier version, all plates and Thin-film electrodes must be transparent, when designed as a reflector you need transparent plates as well and thin-film electrodes, at least one reflective thin-film electrode, the carrier plate of which is opaque can be.

For liquid crystal cells, mainly nematic crystalline liquids and are used in precision Electric fields are preferred as controlling influencing variables. For practical use it is necessary to use relatively thin layers of the crystalline liquid

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ability to form whose thickness is of the order of 10

2
to 10 jam, in particular from 5 to 30 yum. So far the procedure has been that between plates made of transparent material, especially made of glass, which were covered with transparent or reflective thin-film electrodes depending on requirements ■, strips or a partially interrupted frame made of a film has been arranged on the edge of the plate Thickness corresponded to the clear distance. The main film material used was polyhexafluoroethylene. After the crystalline liquid had been filled in, the cell was sealed with an epoxy resin. In this embodiment, the constancy of the distance at some distance from the edge leaves something to be desired, especially in the case of pressure loads. This makes the production of large-area positive crystal cells more difficult, if not impossible. Furthermore, the service life of about 10 hours is still modest, for which the not completely hermetic seal, which does not sufficiently prevent the diffusion of solvent vapors and atmospheric substances, is named as the cause.

A comprehensive overview of the properties of crystalline liquids can be found e.g. at: A.Saupe "Recent results in the field of liquid Kristalle ", Journal for Applied Chemistry, 80th year (1968), pages 99 Ms 115, or in: H.Sackmann and D.Demus "Properties and structures of thermotropic crystalline liquid states", advances in chemical research, 12th year (1969), pages 349 Ms 386. Practical application "". " fertilizers are e.g. in US Pat. No. 2,400,877, No. 2 524 286, No. 2 544 659, ITr. 3 135 207 and ITr. 3 322 485, or in the magazine Electronics from 6/7/1970, pages 64 to 70, and in the magazine Electronic Design from. September 13, 1970, pages 76 to 81. ·

By the Austrian patent specification

No. 284 361 is a method for producing multiple glazing units became known, with the panels

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fused to form a ridge at the edge and a drainage hole in at least one corner of the unit is provided in one plate, which is finally sealed. For liquid crystal cells are Multiple glazing units manufactured in this way cannot be used because "the one necessary for their manufacture Fusion process the thin-film electrodes would be destroyed and the required narrow clearance would not or cannot be produced with the required tolerance ..

The Austrian patent specifications No. 261 015 and No. 261 016 make it practical to use a grain of thick grain layers to produce a "

Electrode system has become known, but are used there Grains not for the purpose of closely spacing plates.

The invention aims to improve rough practical conditions while avoiding the disadvantages mentioned to create corresponding liquid crystal cells.

According to the invention, a single layer of grains is arranged between them to distance the plates, by which the clear distance between the plates is determined, whereby the mean distance between the grains is essential, For example, at least ten times larger than the mean grain size, and furthermore the plates are at their Edge zones, preferably by hot pressure welding or with- " by means of glass solder hermetically connected to one another, whereby for the purpose of filling the crystalline liquid initially filling and ventilation openings that remain free are hermetically sealed.

Apart from the fact that the intended goal is achieved hereby, much thinner plates can now be used can be used than in the known designs, which in addition to material and space savings is still an option offers to advantageous developments of the invention, which are described below. Also the production of large areas

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Liquid crystal cells are essential to the invention relieved.

If plates covered with thin-film electrodes are used, the grains must of course be made of insulating material.

Although in practice mainly nematic crystalline liquids or mixtures with a nematic uses crystalline liquid as the main component for liquid crystal cells, the invention is not limited to these, but to all types and mixtures

A gen, as long as they only show anisotropic behavior, can be used.

With regard to the narrowness of the grain spectrum, no extreme requirements need to be made. It has been found to be sufficient in practice, grain fractions to use whose boundaries do not fm over 25 i ° upper grain boundary and an upper grain limit of less than or equal to 25 at an upper grain limit of more than 25 / im. do not differ from each other by more than 6 pm. Such grain fractions can be obtained, for example, by sieving out with sieve fabrics in accordance with DIN 4188, whereby one step can be skipped, for example "" grains of 25 μm to 32 μm clear mesh size or of

W 28 jum to 36 / um clear width. Comminution processes are also known in which a narrow grain spectrum is obtained without sieves, for example by means of a jet mill, which is used with advantage in particular for grain sizes below 25 μm. A usefully narrow range of grains can also be achieved by means of air separators.

The large tolerance with respect to the grain size can be allowed because when connecting the edge zones by means of hot pressure welding, the grains that in the edge zones, if there are any, are pressed into the plates, in the rest of the plate area partly into the

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Plates penetrate, sometimes being pressed flat a little, which means that the clear distance is much closer to the tolerance adjusts. It is also possible, through a suitable choice of material, to deliberately aim only for penetration or only for flat pressure. If the panels are connected without heating, the close tolerance of the clearance is achieved by that at first only that. at the upper grain boundary lying grains are clamped and it is thus possible that the the rest, for example by vibration, to remove.

• ^ The number of pull or vents may be up to a single opening per g liquid crystal layer are reduced when the air is evacuated between the distanced plates prior to filling of the crystalline liquid, use being made expediently of a three-way use. The closure of the filling or ventilation openings can be done in a known manner without disadvantages by means of an epoxy resin, since the area that comes into contact with the crystalline liquid is much smaller than in the conventional designs and this contact also on one "dead. arm" occurs. The closure can also be done by welding or melting, the "dead arm" again protecting the bulk of the crystalline liquid.

Since the grains cover a maximum of about one percent in area, it plays a role for many purposes, for example for neon letters, it doesn't matter if the Granules consist of opaque material. However, if necessary, the grains can be visually sufficient for the Disappear if they are made of a transparent material that is at least approximately the same Refractive index, like the crystalline liquid. It is also possible without significant loss of strength to keep individual, not too large areas of the liquid crystal cell free of grains. In the recess of this Areas are expediently used with the help of masks, screen printing stencils or the like.

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The fact that now much thinner plates are used without impairing the stability can, it is more easily possible to form positive crystal cells in multiple layers, that is, several one stack forming plates are provided, with crystalline liquid being arranged in the spaces between the plates is. These separate layers of crystalline liquid can advantageously consist of different crystalline Liquids or crystalline liquids doped with various foreign substances exist. the Configuration of the thin-film electrodes can be of Be different from layer to layer. The production of curved liquid crystal cells is also part of the invention Execution possible in a simple manner. Because the plate stack over its surface by means of the grains is distant, it can after connecting the plates by heating and then allowing them to cool in a suitable shape can be curved without losing the exact spacing.

According to a development, the liquid crystal cell according to the invention is used as a screen, for example for a Oscillator or a television receiver formed, wherein a known device for generating the Image grid is provided. For training as a screen of a color television receiver are expedient as many layers of crystalline liquid doped with the appropriate dyes are provided as primary colors are used to build up the color image.

To produce a liquid crystal cell according to the invention, it is expedient to proceed in such a way that the first Plate is covered with grains of a grain fraction, the limits of which at an upper grain limit of less or equal 25 jum not more than 6 ^ um and with an upper grain limit " of more than 25 pm not more than 25 # of the upper grain boundary differ from each other, the grains by means of sieving

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or sprinkling on a portioned amount, screen printing stencils, vibration distribution or the like. single layer at intervals be arranged, which in the average the grain size considerably, exceed that of the grains covered plate the second plate is placed, these process steps continue until the desired number of panels is reached, whereupon the entire stack heated under the application of pressure, hermetically at the edge zones with the recess of flushing or ventilation openings connected and finally brought to cool, whereupon the crystalline liquid is poured in and the Füllbzw. Vent openings are hermetically sealed.

If there is a 15-hour relaxation temperature that is lower than that of the panel material (Strain point) of the grain material, the entire stack is advantageously heated to a temperature that the 15 hour relaxation temperature (strain point) of the Grain material and exceeds the 15 hour relaxation temperature of the panel material is not achieved, whereby the grains on the clear distance to be produced are pressed together and adhere to the plates or foreign layers in a flat manner.

If the 15 hour relaxation temperature is the same or higher than that of the panel material (Strain-Point) of the grain material, the entire stack is expediently heated to a temperature which exceeds the 15 hour relaxation temperature (strain point) of the panel material. The Plates are pressed more strongly against one another and connected to one another over parts of their edges when heated (Hot pressure welding).

The manufacturing method according to the invention above all offer the advantage that they can be rationalized with relatively little effort.

Further details of the invention result

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on the basis of the drawing, in the three exemplary embodiments are shown.

The .Figuren 1 to 5 show an inventive Liquid crystal cell with thin-film electrodes practically completely covering the plates, u.zw.

1 shows a section along the line I-I of FIG. 2, Fig. 2 is a plan view,

3 shows an enlarged oblique view through a partially broken part of the liquid crystal cell,

4 a - ^ etail on a further enlarged scale and

5 shows another possible embodiment of this detail. the ™ Fig. 6 to

9 show various training options, for example for thin-film electrodes.

10 shows a section through a multilayer liquid crystal cell and

11 shows a section through a curved liquid crystal cell.

The liquid crystal cell shown in FIGS. 1 to 5 represents the basic principle of the invention. It consists of two glass plates 1, 2 practically completely covered on the inside with thin-film electrodes 11, 12, between which a single layer of grains 3 of P insulating Material is arranged by which the clear distance between the plates is determined. The grains 3 are drawn exaggerated for the sake of clarity and better representation. At their edge zones 4, 5, 6, 7, the glass plates are hermetically connected to one another by hot pressure welding, which means the application of heat and pressure. In this case, filling or venting openings 8.9 are recessed at two corners by, for example, during hot pressure welding at the location of the openings 8.9, wires made of a material with a greater thermal expansion coefficient than the glass plate material, such as copper, are inserted the he-

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cold pull out easily, creating the desired Openings 8,9 arise. Through one of these openings

8 becomes nematic crystalline liquid 10 or a mixture with a nematic crystalline liquid filled in as the main component, through the other opening

9 the air can escape. The openings 8, 9 are closed by means of epoxy resins 13, 14, with only very small areas of contact between the epoxy resin 13, 14 and the crystalline liquid 10, also on a "dead arm". The number of openings 8, 9 is of course neither limited to two, nor do they have to be arranged diagonally opposite one another in the corners, but the illustrated embodiment has proven to be particularly practical. The openings 8, 9 can also be closed by welding or melting. When a voltage is applied to the thin-film electrodes 11, 12, the previously translucent nematic crystalline liquid 10 becomes opaque in a known manner, the degree of shadowing depending on the field strength. That is why it is so important to keep the distance between the plates 1, 2 exactly over the entire surface, for which purpose the grains 3 are used according to the invention. The control can also take place by means of a magnetic field, in which case the thin-film electrodes 11, 12 can be dispensed with. Ä

: ■ - If you choose a transparent one for the grains 3 Material that has at least approximately the same refractive index as the crystalline liquid 10, the grains 3 thus become practically invisible, which is why they cannot be seen in FIG. 2 either.

In order to clearly show the principle of the invention, a section from the liquid crystal cell is shown enlarged in an oblique view in FIG. Here, a "-L'eil the glass plate 1 and the thin-film electrode, the distance between the plates 1,2 has been broken away. Is in reality 10 ^ö 10 bia ² pm, at a realized execution

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Example 20 μm, the thickness of the thin-film electrodes 11, 12 is in the order of magnitude of 0.5 (μm. It can be seen that the mean distance between the grains 3 exceeds the grain size substantially, approximately at least ten times, whereby the space occupied by the grains 3 is a maximum of about one percent of that of the crystalline liquid 10 Space. Although the grains 3 therefore only take up little space and are also visually made to disappear they bring about a decisive improvement in the strength of the cell and that which is uniform over the surface Distancing the glass plates 1,2. The thickness of the glass plates 1, 2 can be compared to the known designs can be reduced, which extends the application of liquid crystal cells.

Another advantage of the invention is that the surface quality of the glass plates 1, 2 is no longer so high demands must be made, as with the previous versions.

4 and 5 show a greatly enlarged detail from Figure 1 two possible ways of performing the spacing the glass plates 1,2 through the grains 3. In the embodiment according to Figure 4, the grain material softens before Panel material, in the version according to Fig. 5, the panel material softens before the grain material. These two Execution options are to be understood as extremes between which there are flowing transitions. Exist, for example Glass plates 1, 2 and grains 3 from the same glass, the result is something similar to FIG. 5, if not so strong penetration of the grains 3 into the glass plates 1, 2, because the temperature of the grains 3 remains behind the glass plates 1, 2 during the heating process. The latter Execution offers the best strength results. The grains 3 can here on the thin-film electrodes 11, 12 rest, as shown in Fig. 4 and 5 in each case for plate 2 (thin-film electrode 12), whereby they the thin-film

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Electrode 12 can also be pushed into the plate a little (Pig. 5). But you can also use the thin-film electrodes Cut through 11, 12 as shown in each case for plate 1 (thin-film electrode 11).

Since the liquid crystal cell according to the invention is made from a material that is chemically and thermally stable is robustly designed and hermetically sealed, it is suitable for crystalline materials without further protective measures Liquids of various kinds, so in addition to those with the anisotropy range at room temperature, also for those with higher and lower anisotropy ranges.

As mentioned, this is the case with the electric field controllable version of a liquid crystal cell necessary to attach the glass plates 1,2 in a known manner to cover their inside with thin-film electrodes 11,12. Such transparent thin-film electrodes 11, 12 is made from tin oxide or indium oxide, for example, reflective ones from aluminum, for example. If you cover them entire plate surface with thin-film electrodes 11, 12, an electrically controllable light barrier or an electrically controllable reflector is obtained in the simplest way Art. Only one thin-layer electrode 11, 12 is led to the outside at the edge zones 4, 6, as for example Fig. 3 for shows the thin-film electrode 12 at the edge zone 6. At Small thin-film electrodes 11, 12 are applied to the edge zones 5, 7.

It is known by designing the thin-film electrodes 11, 12 in the most varied of configurations possible to display different characters such as numbers and letters in a controlled manner.

FIGS. 6 to 9 show known exemplary embodiments for this purpose. The glass plate 15 shown in top view in Figure 6 carries, for example, a thin

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light electrode configuration 1 6,17,18,19,20,21, 22, as is usual for a seven-segment digit display is. The glass plate 23 shown in Figure 7 is also covered with a thin-film electrode 24, which serve as a counter electrode for the one shown in Fig.6 can.

Figures 8 and 9 show further examples of thin-film electrode configurations frequently used in practice. The glass plate 25 shown in Figure 8 has vertically running tracks of thin-film electrodes 26a to g, the glass plate 27 shown in FIG. 9 horizontally running tracks of thin-film electrodes 28a to g. One forms from the with the tracks of thin-film electrodes 26,28 covered glass plates a liquid crystal cell according to FIGS. 1 and 2, one obtains the known grid, whereby only that small area - "point" - comes to light whose horizontal and vertical electrodes 26, 28 are connected to voltage.

10 shows a section through a multi-layer, in particular a three-layer, according to the invention Liquid crystal cell. Four glass plates 29,30,31,32 are separated by a single layer of grains 3 each and connected to one another at the edge zones 33, 34 by means of glass solder 35. For the purpose of filling crystalline Liquid in the spaces are expediently similar to Figure 2 at two opposite corners per layer 36,37,38 two filling or venting openings 8,9 are provided, whereby the openings 8,9 of the middle layer advantageous over those of the first and third layers offset diagonally. The openings can through Leaving a gap free when applying the amount of solder glass, which is expediently carried out by means of screen printing will. Each layer 36,37,38 crystalline liquid is spatially completely separated from the rest.

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It is also possible to use transparent thin-film electrodes to be attached to the top and bottom of the glass plates 30,31 isolated from one another, - the glass plates 29,32 need thin-film electrodes only on their respective inside, so that also with regard to the electrical control complete separation is possible. Thus, each layer 36 »37.38 of crystalline liquid can be seen completely independent of the rest and can therefore also consist of different or with different foreign substances, for example Dyes, doped crystalline liquids are made. The practical application of a multilayer Liquid crystal cell is made by the possibility of following the invention, the glass plates 29, 30, 31, 32 without loss To be made thin in terms of robustness is much easier, if not made possible in the first place.

For the purpose of forming the liquid crystal cell according to the invention As a screen, the glass plates have in a known manner similar to the glass plates 25, 27 in FIG. 8 and 9 thin-film electrodes 26, 28. A screen for a color television receiving set is functionally similar 10, the thin-film electrodes also being arranged similarly to FIGS. 8 and 9.

According to the invention, it is now without size. g ren expense possible curved manufacturing liquid crystal cells, see. Fig. 11 shows a section through a curved liquid crystal cell. It is initially constructed exactly like that shown in FIGS. After or at the same time as the hot pressure welding, the glass plates 39-40, which have already been distanced from the grains 3, are placed in a mold made of a material that is not wetted by glass, for example graphite or boron nitride, whereupon by heating in the transformation area for the glass plates 39,40 glass used, the glass plates 39,40 deform in the desired way, which shape is retained after cooling. Only then is the crystalline liquid 10 poured in.

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Claims (14)

Claims 1. Liquid crystal cell, in which the crystalline liquid between plates made of inorganic material, in particular glass, of which at least one is transparent and optionally with transparent or reflective thin-film electrodes are covered, characterized in that for distancing the Plates (1,2,15,23,25,27,29,30,31,32,39,4O) between these a single layer of grains (3) is arranged, through which the clear distance between the plates is determined, the mean distance between the grains (3) is substantially, for example ■ at least ten times greater than the mean grain size, furthermore the plates at their edge zones (4,5,6,7,33,34), preferably by hot pressure welding or by means of glass solder, are hermetically connected to each other, for the purpose of filling the crystalline liquid (10,36,37,38) initially remaining free filling or ventilation openings (8,9) hermetically Are completed. 2. Liquid crystal cell according to claim 1, characterized in that the grains (3) consist of a transparent one Material that has at least approximately the same refractive index as the crystalline liquid (10,36, 37.38). . 3. Liquid crystal cell according to claim 1 or 2, characterized in that several forming a stack Plates (29,30,31,32) are provided, with crystalline liquid (36,37, 38) is arranged (Fig. 10). 4. Liquid crystal cell according to claim 3, characterized in that the separate layers (36,37,38) crystalline liquid made from various crystalline IT particles 209829/0428 liquids or doped with various foreign substances crystalline liquids. 5. Liquid crystal cell according to one of claims 1 to 4, characterized in that the plates (39,40) are curved (Fig. 11). 6. Liquid crystal cell according to one of the following. Proverbs 1 to 5, characterized in that they are used as a screen, For example, for an oscillator or a television receiver, is formed, one known per se Device for generating the image grid is provided. 7. Liquid crystal cell according to claim 6, characterized in that it is used as a screen of a color television receiver is formed, with as many layers more crystalline, with the appropriate dyes doped liquid (10) are provided, are used as primary colors to build up the color image. 8 .. A method for producing a liquid crystal cell according to any one of claims 1 to 7, characterized in that characterized in that the first plate (2,32) is covered with grains (3) of a grain fraction, the limits of which at a upper grain limit of less than or equal to 25 / im no more than 6 μm and with an upper grain limit of more than 25 μm do not deviate from one another by more than 25 $ of the upper grain limit, the grains (3) by means of sieving or scattering a portioned amount, screen printing stencils, vibration distribution or the like. arranged in a single layer at intervals which on average considerably exceed the grain size on which the grains (3) are covered Plate (2,32) the second plate (1,31) is placed, these process steps are continued until the desired number of plates (32,39,29) is reached, whereupon the 209829/0428 entire stack is heated under pressure, at the edge zones (4,5,6,7,33,34) with the recess of filling or Vent openings (8,9) are hermetically connected and finally brought to cool, whereupon the crystalline liquid (10, -36,37) are filled and the filling or ventilation openings (8,9) are hermetically sealed. 9. A method for producing a liquid crystal cell according to claim 8, characterized in that if there is a 15-hour relaxation temperature (strain point) of the lower than that of the panel material Grain material, the entire stack is heated to a temperature which is the 15 hour relaxation temperature (Strain-Point) of the grain material and the 15 hour relaxation temperature of the panel material not reached, with the grains (3) on the to be produced clear distance are pressed together and adhere to the plates or foreign layers in a flat manner. 10. The method according to claim 8 or 9 »characterized in that the plates (29,30,31 , 32) at least over parts of their edge zones (33» 34) are hermetically connected by means of glass solder (35) (Fig.10). 11. The method according to claim 10, characterized in that the amount of glass solder is applied by means of screen printing will. . '"■■ .- 12. The method according to claim 8, characterized in that that when there is a 15-hour relaxation temperature that is the same or higher than that of the panel material (Strain-Point) of the grain material, the entire stack is heated to a temperature that corresponds to the 15-hour relaxation temperature (Strain-Point) of the panel material exceeds. 13. The method according to claim 12, characterized in that the plates (1, 2, "5 ° i , 40) 'over parts of their loading 209829/0428 border printed more strongly on top of each other when heated and be connected to each other. 14. The method according to any one of claims 8 to 13, characterized in that the plates (39,40) when heated be curved. 209829/0 42 8