DE2916670A1 - Liq. crystal display cell prodn. - by coating monomolecular hydrated silica film on electrode with oriented PVA film contg. tri:ethoxy vinyl silane - Google Patents

Abstract

Twisted nematic liq. crystal (LC) display cell prodn. with the required orienting film for the LC mols. involves evaporating conductive transparent electrodes onto the cell plates, applying a monomol. adhesive layer of SiO2.xH2O to these, then a well-anchored layer of triethoxy vinyl silane and PVA and providing the loose ends of these mols. with a pref. direction, which is transferred to the LC mols., by directed polishing with cotton. Effective orientation is obtd. and the layers are stable after heating to 200 degrees C, allowing the cells to be heat sealed. Surface energy is relatively high (steeper angle of wetting than usual).

Description

Process for the production of liquid crystal displays

The present invention relates to a new, simple and inexpensive one Process for the production of liquid crystal displays according to the twisted nematic Principle, especially of multi-element displays for alphanumeric or image reproduction purposes.

Such displays generally consist of two parallel flat glass plates, each provided with a conductive, transparent electrode pattern, which are spaced of about 10 µm from each other and their space with the liquid crystal mixture is filled out. This cell is sealed at the edges. This cell is in front and pasted with polarization foils on the back. When applying voltage to selected, opposite front and rear electrodes changes the one in between Liquid crystal layer with regard to their optical activity, see above that the plane of polarization of the transmitted light is rotated, whereby, depending on Arrangement of the polarization films with the preferred axis parallel or perpendicular to one another, the addressed pattern appears light on a dark background or dark on a light background.

An essential part of any twisted nematic liquid crystal display is the superficial molecular orientation layer on each of the two plates. It is very thin and has the purpose of making the elongated liquid crystal molecules that touch this layer to orientate directionally planar by hetero-epitaxy, whereby the direction of orientation of the upper plate perpendicular to that of the lower plate stands so that the planar layers of the molecules between the two electrodes with its preferred directions a spiral staircase-like, a quarter turn in total adopt twisted structure. Several methods have heretofore been used to make these surface molecular alignment layers to produce: 1) The method of Jannings, described in Appl. Phys. Lett.

, 21, 173 (1972). Here a thin layer of Si0 is vapor-deposited at an angle, i.e. at an angle of incidence of approx. 60 °.

As a result, it takes on a scale-like structure, with the alignment the furrows between the scales perpendicular to the direction of impact of the steam jet. This method has the disadvantage that it requires extensive equipment. aside from that is the thus achievable optical contrast of the liquid crystal cell between applied and the lack of voltage when the cell is backlit is only about 30: 1. 2) Organic "Surfactant" layers. These are monomolecular layers created by immersion of the plates made in solutions and subsequent rubbing in one direction will. A method practiced so far is, for example, that of Kahn (Appl. Phys. Lett., 22, 386 (1973)) in which the plates are immersed in a solution be what molecules of amino-vinylsilane contains. However, this is a complicated, expensive, and not overly permanent connection. In particular, suffers this orientation layer during heating, that during cell sealing is required.

Also all other known methods, this molecule-orienting surface layer produce poor results: this is how the glass plates were made with lecithin rubbed in the preferred direction (J.F. Dryer, in Liquid Crystals 3, Gordon & Breach, London 1973, p. 1113). Or the surfaces of the plates were chemically etched (M.F. Schiekel, K. Fahrenschon, Appl. Phys. Letters, 19, 391 (1971)). Or an organic one Molecular layer (such as polyamide resin) was physically absorbed and directed rubbed (W. Haas, J. Adams, J. Flannery, Phys. Rev. Letters 25, 1326 (1970)). Man can also get partial orientation by rubbing the surface of the glass with paper, cellulose or cotton wool (H. Zocker, Z. Phys. Chem. 132, 285 (1928)).

A popular method is the precipitation of quaternary ammonium salts from aqueous solution (I. Halber, H.A. Huggins, U.S. Patent 3,656,834). The deliver less densely packed monomolecular layers parallel alignment, the Direction obtained by slowly pulling back the glass plates in the preferred direction (J.E. Proust, L. Ter-Minassian-Saraga, E. Guyon, Solid State Comm. 11, 1227 (1972)). Finally, Kahn (Appl. Phys. Lett., 22. 386 (1973)) used organosilane agents. With N, NDimenthyl-N-octadecyl-3-aminopropyl-trimethoxy-silyichloride (DMOAP) coatings perpendicular alignment was achieved while N-methyl-3-aminopropyl-trimethoxysilane (MAP) showed parallel (lying) alignment of the molecules.

The invention described below solves the problem of a surfactant layer with improved directional-planar orientability for liquid crystals to specify.

First, on the electrode plate by dipping it in a colloidal Silicon dioxide solution deposited a firmly adhering anchoring layer made of Si02. A monomolecular layer of triethoxyvinylsilane and polyvinyl alcohol is then placed on top of this absorbed by immersion. The organic, elongated molecules "bite" each other with their hydrophilic ends stuck in the Si02.x H20 layer, while their loose lyophilic Ends in any direction. After the solvent has evaporated, it will Surface film then "brushed" with a rotating cotton roller, whereby the loose ends of the molecules all lay in one direction, the brushing direction. By The layer is then polymerized by heating.

The LC molecules take over the orientation through Van der Waals forces the surfactant layer, i.e. they are oriented in a direction-planar manner. The orientations The upper and lower plates of the FK cell are crossed by 90 ". Further details are communicated below.

In addition, another anchoring layer was found, which has certain advantages over that described above.

These are the strongly surface-active inorganic ones Carboxylato-chromium complex of perfluorononaoic acid (available from 3M Co, St. Paul, Minnesota, USA, under the trade name F.C.-805 as a 33% solution). This Chromium complex is already used as a surface orientation agent, which is homeotropic Liquid crystal orientation results (so the molecules are perpendicular to the electrode plates stand), used (Z. Blank, W.B. Hatfield and D. Johnston, Conference Record of 1978 Biennial Display Research Conference, Cherry Hill N.J., USA, Oct. 15, 1975, p. 44).

However, the invention requires a directional planar LC molecule orientation. For this purpose, the commercially available isopropanol solution of the complex mentioned is made up 0.01% concentration diluted with demineralized water. Polyvinyl alcohol is then used in it resolved to 0.02%. The method of surface treatment by dipping, drying and polishing is the same as described above. This results in a homogeneous, i.e. parallel, directional alignment of the positive-anisotropic liquid crystal (Rotating cell) without the occurrence of undesirable false inclinations.

The layers are stable after heating to 200C. These treated like that FK cells can be heat sealed.

They are also characterized by a higher surface energy than those previously described, which is indicated by a steeper wetting angle power.

The procedure is described again in detail below: The glass plates used are float glass plates, so they were made as large as possible in order to preserve them Flatness is made by solidifying the liquid glass on a bath of liquid tin. For cells measuring 9 x 12 cm, plates 4 mm thick are used. First the glass plates are cleaned, which is done with ultrasound in a bath of methanol-acetone-trichlorethylene happens. Then they are vaporized with transparent electrodes. this happens in a high vacuum through suitable masks. First a film 100 Å thick made of bismuth oxide, Bi203, vapor-deposited. Its purpose is to fix the subsequent thin layer of gold to bind so that no island formation occurs. The gold film is 25 2 thick.

To prevent islanding, he is again thick with a 100 R Bi203 layer covered. The transparent electrodes produced in this way have the Advantage of being on float glass plates without heating, warping or warping the same can lead, can be applied in any pattern. As a transparent one However, electrodes can also have layers of In203 or Sn02, which are exposed to heat must be applied.

The LC molecule-orienting surfactant layer is now placed on these plates upset. The nematic mixtures were successfully used as liquid crystals positive dielectric anisotropy E7, E18, ZLI 1132, ZLI 1083, ZLI 1085, ZLI 1237, NM 8243, etc., which are commercially available.

The following materials produce molecule-oriented surface layers, which are applied by dipping on the plates and rubbed directed after drying are: 1) triethoxyvinylsilane, hydrolyzed at different pH values; 2) Merck Silicon dioxide immersion bath diluted with ethyl acetate and aqueous polyvinyl alcohol solution; 3) Colloidal silica solution mixed with aqueous polyvinyl alcohol solution; 4) Triethoxyvinylsilane mixed with silicon dioxide immersion bath and with aqueous Polyvinyl alcohol.

This last mix gave the best results. They were like this manufactured: For a 3 liter solution a) 0.6 g Polyvinyl alcohol added to 300 ml of boiling water, with constant stirring. Then is cooled and filtered.

b) Then 2.5 ml silicon dioxide immersion bath from Merck with 20 ml Thinner, Merck ZLI 903, diluted.

c) 0.5 ml of triethoxyvinylsilane (Merck) are pipetted.

Solution a) is diluted to 3 liters with demineralized water. 0.5 ml b) and 0.5 ml c) are added to this while stirring. The pH of the Solution is adjusted to 4-5 with hydrochloric acid. The solution is stirred for 1 minute and kept hot overnight. It can then be stored in plastic bottles. Most of the ionic contamination from the HC1 occurs during the polymerization stage of the cell at 1800 C and thus has on the liquid crystal display no harmful influence.

The solution can be kept for months.

The pre-cleaned substrates are then immersed in the orientation solution for 1 hour immersed. Then they are slowly pulled out and dried at room temperature, followed by a temperature treatment of 15 minutes at 125 ° C.

Then these substrates are covered with cotton velvet by means of a Roller rotating at 700 rpm, rubbed, the direction of rubbing at one of the Substrate runs away from the operator, when the other runs towards the operator. Any rubbing treatment is repeated, shifting the roller sideways by 2 cm. With those of this type produced liquid crystal cells will have excellent directional parallel output direction Achieved in the rubbing direction, with the extremely small angle of inclination of about 2 "of the LC molecules against the base plate (so-called pre-tilt). Layer the liquid crystal thus obtained do not contain any visible incorrect inclination or direction reversal zones.

The method according to the invention is intended to be repeated with the aid of the drawing explained.

The figures show: FIG. 1 the production of the surfactant layers using of triethoxyvinylsilane.

Step 1 shows the chemisorption of Si02.x H20, also being random SiOH and Si-O-Si groups can be present.

It can be seen that oxygen is a bond between silicon ions the applied layer and metal ions in the glass surfaces.

Step 2 shows the absorption of polyvinyl alcohol.

Step 3 shows the hydrogen bonding during evaporation of the solvent.

Step 4 shows the polymerization of Si02.

x H20 while drying at 1200 C, with the polyvinyl chains were oriented by directional rubbing.

Step 5 finally shows the condensation during the curing process 1800 to 200 ° C.

Fig. 2 shows the process when using the inorganic carpoxylato-chromium complex the perfluoronanonoic acid.

Step 1 shows the chemisorption of the complex, again with the Oxygen is a bond between the chromium ions of the complex and metal ions manufacture in the surface of the glass.

Step 2 shows the absorption of polyvinyl alcohol on the chromium complex and the orientation of the molecules by directional rubbing.

Step 3 shows the condensation during curing at '80 ° C.

Claims (3)

Claims 0 A method for producing liquid crystal display cells according to the twisted nematic principle, especially for the production of the necessary Surface alignment layer for the liquid crystal molecules, characterized in that that conductive, transparent Bi203-Au-Bi203 electrodes are placed on the plates of the cell are vapor-deposited that a monomolecular adhesive layer made of SiO2. x H 20 is applied that thereon a well anchored layer of triethoxyvinylsilane and polyvinyl alcohol, and that the loose ends of these molecules then be provided with a preferred direction by means of directional polishing with cotton, which is transferred to the liquid crystal molecules. 2. The method according to claim 1, characterized in that a layer from a carboxylato-chromium complex and polyvinyl alcohol is applied. 3. The method according to claim 1 or 2, characterized in that the orientation layer is polymerized at 180 to 200 ° C.