DE19832812A1 - Process for the production of smectic type of liquid crystal display using substrates printed with smectic layer and then bonded together - Google Patents

Abstract

The active matrix LCD is formed with a smectic liquid crystal layer between a pair of substrates. The smectic layer can be of a ferroelectric or antiferroelectrical form or a mixture containing smectic liquid crystal. The structure is formed by printing a thin film of crystal onto the substrate with a temperature in excess of 30 Degrees being applied. The substrates are then bonded together.

Description

In addition to nematic and cholesteric liquid crystals, more recently also smectic (e.g. ferroelectric, antiferroelectric or so-called DHF) Liquid crystals used in commercial display devices, such as. B. in Information Display (SID), Vol. 14 (2), February 1998, pages 20 to 27 described.

A smectic liquid crystal display (LCD) consists of polarizers, with Electrodes, e.g. B. of indium tin oxide, coated substrates made of plastic or glass, with orientation layers and possibly other layers (Passivation, diffusion barrier, insulation, anti-reflective layers, etc.) and Color filter layers are provided, a liquid crystal layer and possibly active thin-film elements.

In general, smectic LCDs can be used as both passive matrix and Manufacture and use active matrix displays.

In the case of a passive matrix, the individual picture elements (pixels) of one are created Liquid crystal displays by crossing a series of electrodes (Conductor tracks), which as rows and columns on the bottom or top of the Displays is formed. The crossing points of the horizontal and vertical Electrodes form addressable pixels. Various were used for addressing Multiplex schemes developed.  

Among other things, because of the advantageous high switching speeds Liquid crystal displays suggested based on the combination ferroelectric or also from antiferroelectric liquid crystal materials and active matrix elements, cf. WO 97/12355 or Ferroelectrics 1996, 179, 141-152, or Information Display (SID), Vol. 14 (2), February 1998, Pages 20-27.

With active matrix technology (AMLCD), a substrate is usually used a non-structured electrode combined with an active matrix substrate. There is an electrical on each pixel of the active matrix substrate nonlinear element, for example a thin film transistor z. B. of the type amorphous silicon or polycrystalline silicon. For the nonlinear element can also be diodes, metal insulator metal and the like. act elements, which are advantageously produced using known thin-film processes.

Regardless of the question of whether it is an active matrix or a Passive matrix display is involved in the manufacture of such displays take into account that the layer thickness of such smectic displays is very small and in the range from 0.5 to 3 µm, in particular in the range 1 and 2 µm, especially between 1, 1 and 1.7 µm. It is also about smectic liquid crystals around materials with higher flow viscosity, in Difference to the nematic liquid crystals widely used today, see e.g. B. H. Kneppe, F. Schneider in D. Demus et. al. (Ed.) Handbook of Liquid Crystals, 1998, Vol. 2A, pages 142ff.

The combination of these two properties, namely high viscosity and low layer thicknesses, associated with the requirement for LCDs with large Surfaces, now leads to a significant practical problem with the  efficient filling of such displays with the smectic liquid crystal.

The filling process has so far been carried out in such a way that a finished but empty display, in which the two substrate plates apart from one another with a filling opening are glued, is filled in that the liquid crystal mass in the isotropic or liquid crystalline phase through capillary forces through the filling opening in the display is pulled. To support this process, a Overpressure can be used. Still, even at a high temperature due to the high smectic flow viscosities and the very low Plate spacing makes this process so inefficient that it often takes many hours very large areas even days are needed to make large area displays, d. H. fill those with a screen size larger than 10 inches (25 cm). In addition, there is the possibility of filling in the isotropic phase Evaporation and the thermal decomposition of individual mixture components.

The object of the present invention is to provide a method for Manufacture of smectic liquid crystal displays, the two substrates and one Intermediate smectic liquid crystal layer have the disadvantages avoids the known processes and smectic production Liquid crystal displays allowed on a technical scale.

The object is achieved by a method in which the smectic liquid crystal layer or a mixture containing the smectic Contains liquid crystal in a printing process on at least one of the two Substrates is applied and the substrates are then smectic Liquid crystal display can be put together.  

The invention relates to a manufacturing process for smectic Liquid crystal displays in which the smectic liquid crystal layer in the form a thin film is printed on at least one of the two carrier substrates is and the two substrates glued together only after this printing process become. This printing process can be screen printing, offset printing, or flexo printing be another common printing process.

The method according to the invention avoids the lengthy and therefore disadvantageous Filled by capillary forces and thus enables factory-made Mass production of smectic LCDs.

There are several variants. According to a variant, a Adhesive frame on one, and the smectic liquid crystal layer on the other substrate printed. Then the adhesive frame in a suitable manner be pre-dried or hardened to avoid undesired mixing of adhesive frame and liquid crystal to prevent.

The smectic liquid crystal print layer can be attached to the inner structure of a smectic LCD, e.g. B. spacers, active matrix, color filter, black grid etc. can be adjusted. This happens because the smectic layer in a print pattern is adapted to the LCD architecture. This allows the smectic liquid crystal can be printed to fit on the pixels, while e.g. B. the spacers are not printed.

It is also advantageous to heat and cool after the adhesive has been glued Substrates, whereby the liquid crystal undergoes various phase transitions and is thus reoriented. At the same time, the adhesive frame can be used be fully hardened.  

Suitable components for liquid crystal displays are described, for example, in C. Prince, Seminar Lecture Notes, Volume I, p. M-3/3-M-3/22, SID International Symposium 1997, Boston, USA; BB Bahadur, Liquid Crystals Application and Uses, Vol. 1, pp. 410, World Scientific Publishing, 1990; E. Lüder, Recent Progress of AMLCD's, Proceedings of the 15 ^th international display research conference, 1995, p.9-p.12, Displays 1993, Vol. 14, No. 2, pp. 86-93 and contacts 1993 (2nd ), Pp. 3-14, T. Tsukuda, TFT / LCD: Liquid Crystal Displays Addressed by Thin-Film Transistors, Gordon and Breach 1996, ISBN 2-919875-01-9 or C. Prince, Seminar Lecture Notes, Volume I , p. M-3/3-M-3/22, SID International Symposium 1997, Boston, USA and literature cited therein.

It has been found that the viscosity of the liquid crystal to be printed at the application is preferably in a certain range. Here we understand the average viscosity, e.g. B. in a Bohlin viscometer (Manufacturer Bohlin Instruments Ltd., Cirencester, UK) is determined. It is the Medium viscosity is relevant because the coating process has a clear one Preferred direction of the liquid crystal is not defined.

In order to determine a preferred viscosity range for the printing process, the viscosity as a function of the shear rate and the temperature is determined for the liquid crystal. The range of the shear rate relevant for the coating process is then determined or the information provided by the device manufacturer is used and the measured viscosity is averaged over this range. This range of the shear rate is 0.1-10 ⁵ 1 / s, preferably 1-10 ⁴ 1 / s, preferably 10-1000 1 / s, particularly preferably 20-500 1 / s.

The printing temperature is preferably chosen so that that described above average viscosity is less than 20 Pas (Pascal seconds), preferably less than 10 Pas, preferably less than 4 Pas, particularly preferably less than 2.5 Pas, most preferably less than 1.5 Pas.

It should be noted that the average viscosity determined in this way does not is directly related to the electro-optical rotational viscosity, which is usually between 0.1-2 Pas (s, e.g. C. Escher et. al., Liquid Crystals 1988, Vol. 3, No. 4, pages 469-484).

The invention is further illustrated by the following examples.

example 1

An active matrix LCD with a smectic liquid crystal layer is produced, by separating two glass substrates A and B after thorough cleaning like treated as follows:

Substrate A

• - Application of red-green-blue color filter dots by photolithography
• - Applying a leveling layer
• - Application of an all-over transparent electrode made of indium tin Sputtering oxide
• - Applying a thin insulating layer of silicon dioxide by sputtering or steaming
• - Applying an auxiliary layer for the adhesive frame by photolithography
• - Application of an orientation layer wet film by spin coating or Spray coating or roller coating or printing
• - Drying and curing of the wet film  
• - Detachment of the auxiliary layer and thus release of the surface for the Adhesive frame
• - Rub the orientation layer for orientation
• - Printing on the adhesive frame, e.g. B. by screen printing on the released surface
• - Predrying the adhesive in the adhesive frame

Substrate B

• - Application of an active matrix made of thin-film transistors (TFT) including supply lines according to relevant thin-film processes Technology (see above quote from Tsukuba 1996)
• - Applying a thin insulating layer of silicon dioxide by sputtering or steaming
• - Application of an auxiliary layer for the adhesive frame by photolithography
• - Application of an orientation layer wet film by spin coating or Spray coating or roller coating or printing
• - Drying and curing of the wet film
• - Detachment of the auxiliary layer and thus release of the surface for the Adhesive frame
• - Rub the orientation layer for orientation
• - Print the previously degassed and filtered commercially available smectic liquid crystal mixture ®FELIX-015-000 (manufacturer Hoechst / Frank ford) with the help of a commercially available offset printing machine, that the raised TFT elements as well as the exposed adhesive frame be spared.

Following the separate production of both display halves, the substrate B submitted and the substrate A placed in a positioning device, and  the two substrates are pressed together. Through short-term local Heating the adhesive frame z. B. with a masked infrared lamp or through The cell is glued together with UV light or high-energy radiation.

Then the cell is above the clearing point temperature, i.e. to about 90 ° C, heated and cooled again, whereby the smectic liquid crystal oriented according to the rubbing direction. The cell is made with polarizers provided and contacted with the control electronics.

Example 2

A passive matrix LCD with smectic liquid crystal layer is produced, by separating two glass substrates A and B after thorough cleaning like treated as follows:

Substrate A

• - Application of red-green-blue color filter dots by photolithography
• - Applying a leveling layer
• - Application of an all-over transparent electrode made of indium tin Sputtering oxide (ITO layer)
• - Structuring this ITO layer into conductor tracks (lines)
• - Applying an insulation layer by vapor deposition
• - Applying an auxiliary layer for the adhesive frame by photolithography
• - Applying a wet film of polyimide precursor solution by spin Coating
• - Evaporation of the solvent and curing of the polyimide film Formation of an orientation layer
• - Detachment of the auxiliary layer and thus release of the surface for the Adhesive frame  
• - Rub the orientation layer for orientation
• - Printing on the adhesive frame, e.g. B. by screen printing on the released surface
• - Predrying the adhesive

Substrate B

• - Application of an all-over transparent electrode made of indium tin Sputtering oxide (ITO layer)
• - Structuring this ITO layer into conductor tracks (columns)
• - Applying an insulation layer by vapor deposition
• - Application of an auxiliary layer for the adhesive frame by photolithography
• - Applying a wet film of polyimide precursor solution by spin Coating
• - Evaporation of the solvent and curing of the polyimide film Formation of an orientation layer
• - Detachment of the auxiliary layer and thus release of the surface for the Adhesive frame
• - Rub the orientation layer for orientation
• - Print the previously degassed and filtered, then smectic liquid crystal mixture mixed with spacer particles ®FELIX-015-100 (manufacturer: Hoechst / Frankfurt) with the help of the Offset printing in such a way that the exposed adhesive frame is left out.

Following the separate production of both display halves, the substrate B submitted and the substrate A in an evacuated positioning device imposed that the desired crossing of rows and columns arises, and the two substrates are pressed together. Through short-term local Heating the adhesive frame z. B. with a masked infrared lamp or through  The cell is glued together with UV light or high-energy radiation. The cell is then removed from the evacuated positioning and gluing device away. By suspending the glued display on the outer Atmospheric pressure, the two substrate glasses are placed on the spacers pressed, and this results in a stable, uniform cell spacing.

The cell is then heated above the clearing point temperature and again cooled, whereby the smectic liquid crystal corresponding to the Direction of rubbing oriented. The cell is provided with polarizers and with the Control electronics contacted.

Example 3

The process described in Examples 1 and 2 is modified by that the smectic liquid crystal layer to be printed to reduce the Flow viscosity with a lower boiling solvent or additive, e.g. B. toluene, Methylene chloride, ethanol or the like is provided and thus better in thin Layers becomes printable.

Before the two cells stick together, the coated substrate is added Vacuum or heated in an air stream and the solvent evaporates.

Example 4

The method described in Examples 1 and 2 is thereby modified that the application of the smectic to be printed Liquid crystal layer at a slightly elevated temperature of 50 ° C and the liquid crystal mixture is therefore more fluid and therefore better in thin layers becomes printable.  

Example 5

The method described in Examples 1 and 2 is thereby modified that the application of the smectic to be printed Liquid crystal layer at a slightly elevated temperature of greater or is equal to x ° C and the liquid crystal mixture is therefore more fluid and therefore becomes better printable in thin layers. The value x results from this a measurement of the average shear viscosity of the smectic to be printed Liquid crystal mixture or the mixture of liquid crystal to be printed and eluent. The value x is the temperature at which the viscosity is smaller than 20 Pas (Pascal second). Experiments have shown that below this Viscosity good printability with a commercially available flexographic printing machine (Manufacturer Nissha Printing, Japan) results.

Example 6

A smectic test mix is made

• - 2- (4-hexyloxyphenyl) -5-octylpyrimidine (60% by weight)
• - 2- (4-decyloxyphenyl) -5-octylpyrimidine (40% by weight)

manufactured.

For this mixture, the viscosity is a function of the temperature and the Shear rate determined.  

The following results are obtained:

Claims (8)

1. A method for producing smectic liquid crystal displays which have two substrates and an intermediate smectic liquid crystal layer, characterized in that the smectic liquid crystal layer or a mixture which contains the smectic liquid crystal is applied in a printing process to at least one of the two substrates and the substrates subsequently can be put together to form a smectic liquid crystal display. 2. The method according to claim 1, characterized in that the Printing process takes place at a temperature of more than 30 ° C. 3. The method according to claim 1 or 2, characterized in that the average shear viscosity of the printing mass at the temperature of the Printing process is less than 20 Pas. 4. The method according to any one of claims 1 to 3, characterized in that the liquid crystal display has an image diagonal of more than 25 cm (10 Inches). 5. The method according to any one of claims 1 to 4, characterized in that the smectic liquid crystal layer only on one of the substrates is printed.   6. The method according to claim 5, characterized in that a Adhesive frame for connecting the two substrates to the other substrate is applied, and the substrates pre-dried and then be put together. 7. The method according to claim 6, characterized in that the adhesive when assembling the substrates by local heating of the Adhesive frame is done. 8. Smectic liquid crystal display, obtainable by a process according to one of claims 1 to 7.