DE4420585A1 - Electro-optical system - Google Patents

Abstract

A process is disclosed for producing multidirectional orientation layers. A photo-curable precursor of the orientation layer that contains one or several substantially linear photopolymers and/or photo-oligomers is applied on a substrate then exposed to linearly polarised light under 2 or more different azimuth angles O. Also disclosed are multidirectional orientation layers produced by this process.

Description

The invention relates to an electro-optical system containing one Liquid crystal layer between two substrates, which with electrode and orientation layers arranged above are provided.

Electro-optical liquid crystal systems usually require an edge orientation of the molecules. For this, the electrode layers and if necessary, further layers such. B. color filter layers, insulating layers, off substrates provide an orientation layer applied, which is in direct contact with the liquid crystal layer and the liquid crystal molecules prefer their molecular orientation direction imposes.

One can differentiate between planar (also called homogeneous neter) and homeotropic orientation, the preferred direction by one Angle of attack or tilt against the substrate level or against the normal the substrate level can be tilted; speaks in the former case one of tilted-planar orientation, while the latter case as called tilted-homeotropic. Depending on the size of the tilt angle one further distinguishes between low-tilt and high-tilt orientation.

To generate the orientation layers, both inorganic and organic materials have also been proposed.

So it is z. B. possible, tilted-planar orientation layers Evaporation of the substrate with SiO in a vacuum chamber. A planar orientation is obtained when the evaporation source forms an angle of approximately 30 ° with the substrate plane; if the SiO evaporation source, however, at a grazing angle Lich arranged the substrate level, however, there is training a high-tilt orientation layer.  

The in the industrial manufacture of electro-optic liquid crystal displays currently The most common method is that on the substrate a thin polymer layer is applied, which is then under Pressure application z. B. with a cloth stretched on a roller or similar materials is rubbed, making the preferred direction fixed and a tilt angle is induced. It can be different Polymer materials such as B. polyvinyl alcohol (PVA) or polyimides ver be used, the latter because of their good chemical and thermal stability are very common.

In a typical process, a polyimide film is coated on the Elek Trode layers and possibly further layers provided substrate z. B. by spin-going in a thin layer of e.g. B. 30-100 nm brought and hardened at 150-250 ° C. Then the layer is Repeatedly in the same direction with a cotton cloth or similar on one Proof of z. B. 5-25 kg / cm² grated.

With polyimide orientation films tilted planar orientation received films, the tilt angle is typically 1-8 ° or more.

Homeotropic surface orientations can e.g. B. by coating with polyimides, lecithin or quaternary ammonium compounds be preserved; chromium complexes or silane are also present connections have been proposed. A tilted-homeotropic orien can z. B. can be obtained by rubbing a homeotropic Orientation layer or by applying surface-active sub punch on a planar tilted orientation layer.

Schadt et al. beat in Jpn. J. Appl. Phys, 31 (1992) 2155, orien tated photopolymer coatings as orientation layers turn, these generally a planar or low-tilt orientation indu adorn. For the production of oriented photopolymer coatings are photopolymers such. B. Poly (vinyl 4-methoxycinnamate) on a with an electrode provided substrate and then with linearly polarized light.  

As an application of oriented photopolymer coatings from Schadt et al. u. a. proposed a hybrid liquid crystal display, which pixel with has different twist values of the liquid crystal. These Hybrid displays are made using a mask technique Change in the direction of polarization to harden the photopolymeri obtainable material used linearly polarized light obtained.

The orientation layers described so far in the literature fulfill the very different requirements when using them in electro-optic liquid crystal displays are not always put in satisfactory scope.

The present invention was therefore based on the object of new orias Specification layers and thus the range of the specialist to enlarge available orientation layers. Furthermore, the present invention the task of new electro-optical Liquid crystal systems indicate which such orientation layers included. Other objects of the present invention the person skilled in the art takes from the following detailed description.

It has been found that these tasks are accomplished by providing the Orientation layers according to the invention and the invention according electro-optic liquid crystal systems, which such Contain orientation layers, be solved.

The invention relates to a method for producing multidirec national, d. H. two or more preferred directions of orias coating layers, which is characterized in that a photo curable precursor of the orientation layer applied to a substrate and then shift below 2 or more with linearly polarized light to which azimuth angles Φ are applied. The exposure alternating at the corresponding azimuth angles or at the same time when irradiating light with two or more preferred directions linear polarization. The invention further relates  multidirectional orientation layers as well as electro-optic liquid crystal systems containing a liquid crystal layer between 2 sub straten, which with electrodes and arranged above orientation layers are provided, at least one of the orientation layers is multi-directional.

To create the multidirectional orientation layer, the Precursor of the photocurable orientation layer on a substrate upset.

The substrate preferably has a flat surface and can be made of various materials such as B. metal, glass, quartz glass or art consist of material, with transparent substrates being preferred. Especially substrates coated with electrodes are preferred, the Electrode coatings e.g. B. from structured or unstructured Tin oxide or indium tin oxide (ITO) can exist and in particular also active switching elements such. B. TFT's (thin film transistor) or MIM's (metal-insulator-metal) can have. The coated with electrodes and then use multidirectional orientation layers substrates can be used to manufacture electro-optic liquid crystal elements are used, which are static, passive, active or after the so-called in-plane switching method (DE 40 00 451) can be controlled.

The substrates can be used in addition to the multidirectional orientation layer and the electrode layer also other coatings such. B. Color filter coatings, separator acting as diffusion barriers layers etc., the order of these coatings can be chosen largely freely. Only the multidirectional Orientation layer usually forms the outermost layer, which then in to orient the electro-optic liquid crystal display directly with the the liquid crystal is in contact.  

The precursor of the photocurable orientation layer contains one or several photopolymers or oligomers, which are essentially linear are and their degree of polymerization is preferably at least 5, ins particularly at least 10 and very particularly at least 20. The term photopolymers or oligomers denotes photoreactive Compounds, the photoreactive group itself contain or with photoreactive additives such. B. photoreactive Networkers react.

The requirement that the photopolymerizable oligomers or polymers should have an essentially linear structure is due to the fact that dim the multidirectional orientation layers 2 or more have preferential directions that the rod-shaped liquid force a preferential direction on crystal molecules. When using the later linear is essentially linear photo oligomers or polymers Structure of the multidirectional orientation layer in the precursor already preformed. By irradiation with linearly polarized light, a directed large-linking reaction induced, causing the photooligomers or polymers under a substantially parallel orientation be linked together. This creates a microscopic array of one-dimensional, parallel preferred directions, which for Edge orientation of the liquid crystal molecules is used.

The crosslinking reaction can be carried out in various ways become. So it is z. B. possible that the precursor of the orientation layer in addition to essentially linear photo oligomers and / or polymers bifunctional, photoreactive additives such as B. contains bisazides. An example is the reaction of polydienes with 4-alkyl-2,5-bis (p-azido benzal) called cyclohexanone, which has a maximum absorption 365 nm.

The crosslinking reaction can continue on the photopoly linkage merizable groups based on the essentially linear Photooligomers and / or polymers of the orientation precursor layer are included. The photopolymerizable groups can both in the substantially linear photo oligomers or polymers  of the precursor of the orientation layer (main chains connections) or are also in page groups, which laterally to the essentially linear photo oligomers or polymers are attached (side chain connections). Besides that, of course photopolymerizable compounds are also used, which photopolymerizable groups in the main and side chain linkage contain.

Side chain connections in which adj bearded photopolymers and / or oligomers over in the side groups located photopolymerizable groups are linked.

The polymer backbone of the photopolymerizable side chain compounds gene is preferably based on C-C main chains, with poly- or oligovinyls and poly- or oligoacrylates and their derivatives can be placed. Polymers or Oligomers with heteroatoms in the main chain, for example poly or Oligoethers, esters, amides, imides, urethanes and siloxanes.

On the polymer backbone - (P) - are photopolymerizable groups PPG attached directly or via a spacer Sp. Schematic:

Examples of preferred PPG's are in the following overview 1 guided.  

Overview 1

In the following overview 2 are preferred examples of polymer backbone - (P) - or groupings - (P) -Sp- specified, where for PPG in particular the structures specified above are to be used.  

Overview 2

Overview 2 above is also a few examples of suitable ones To take spacer groups Sp.

Through the spacer groups Sp and the photopolymerizable groups PPG can be the distance between neighboring preferred lines in the hardened orientation layer can be influenced. At the above given linkage of adjacent oligomer or polymer compounds by adding bifunctional agents (crosslinkers) the distance can be increased neighboring preferred lines through the structure of the crosslinker molecule to be influenced.

The structures given are to be understood as examples only and are intended to be merely illustrate the invention without limiting it. The expert can easily generate more linear, at a convenient distance Specify suitable connections in the preferred directions.

The photooligomer and / or polymer of the precursor of the orientation Layer are preferably in a solvent such as. B. methylene chloride, chlorobenzene, toluene or other solvents, where optionally a crosslinker component and / or also others Additives such as B. Adhesion promoter can be added. It is also possible the components of the precursor without adding a solution by mixing, if necessary with gentle heating.

The precursor is then pre-coated on the optionally Substrate z. B. by knife coating and in particular by spin coating brings. Then the solvent component is preferred by heating to temperatures of e.g. B. 50-100 ° C removed. The fat the precursor layer is between 20 and 300 and preferably between 40 and 100 nm.

Then the precursor layer is irradiated with linearly polarized light, preferably monochromatic light is used which is on the maximum absorption wavelength of the photopolymerizable group or connection is adapted.  

To create the multidirectional structure of the orientation layer the precursor is used with linearly polarized light under different Azimuth angles Φ irradiated. The angle Φ is a second irradiation direction in relation to a first irradiation direction of the angle in the substrate level, which results when the radiation sources in each case be connected to the medium normal of the substrate. The radiation with linearly polarized light at different angles Φ can at the same time as well as successively, but preferably simultaneously By the method according to the invention, several are continuous preferential lines that can be created without further structuring entire display, while that of Schadt et al. in Jpn. J. Appl. Phys. 31 (1992) 2155 proposed mask technique for generating Pixel with different twist led.

The radiation assigned to the individual radiation directions performance can be selected both simultaneously and differently, whereby the relative share of the different preferred directions in the Orientation layer can be varied. The radiation power is typically between 5 and 50 mW / cm², but also Deviations from these values are possible. The radiation duration is usually between 1 min or less and 60 min, in particular between 1-5 min, but here too deviations from these Values are possible.

It was found that the arrangement of the linearly polarized light swell with respect to the substrate plane, which is determined by the height angle Θ is specified (angle between substrate plane and connecting line Light source and intersection of the means normal with the substrate plane), is not very critical and in another area z. B. between 10 and 90 ° (0 ° corresponds to grazing light). Also the Pretilt angle of the orientation layers according to the invention, the typi between 0 ° and 5 ° can be achieved by varying the height angle Θ can only be influenced insignificantly.  

It was further found that the stability of the hardened orientation layers can usually be improved if the on the substrate applied precursor of the orientation layer before loading with linearly polarized light and / or after exposure to linear polarized light, with unpolarized light (power e.g. 500-5000 mW / cm²) is irradiated. A final heat treatment of the Orientation layer at temperatures between 50 and 120 ° C and one Treatment duration between 15 and a few hours is generally advantageous.

The multidirectional orientation layers according to the invention point preferably 2-15, in particular 2-8, particularly preferably at least 2 and especially at least 3 preferred directions.

The orientation layers according to the invention are preferred for Manufacture of liquid crystal displays used. Applications are however also in micro-optics, integrated optics, related to optical sensors and elsewhere possible.

The orientation according to the invention can be particularly preferred layers for the production of ferroelectric liquid crystal displays the SSFLG principle specified by Lagerwall. The Liquid crystal layer has an SmC * phase, which makes the liquid crystal molecules on the substrate surfaces have a tilt angle of +0 or Have -0. This surface-induced orientation of the liquid crystal Molecules settles because of the very thin thickness of the liquid crystal layer of typically less than 3 µm through the entire liquid crystal layer away, and you can liquid crystal between 2 bistable Switch states with + Θ and -Θ ("bookshelf geometry"). It was found that the stability of the two switching states are increased can, if the substrates have bidirectional orientation layers, the two preferred directions of which are linearly polarized by irradiation with 2 th light sources were obtained, which were opposed by one Azimuth angles of Φ = 2Θ are rotated. It has been found that such ferroelectric displays compared to a significantly increased stability  have mechanical loads (shock resistance) as corresponding Displays without bidirectional orientation layers, whereby only one slight and in any case acceptable increase in switching voltage was observed.

Also preferred are liquid crystal displays with inventive Orientation layers, which are nematic or cholesteric liquid contain crystals.

For example, a twisted nematic cell is particularly preferred contains doped liquid crystal, the pitch length of the liquid crystal can be strongly temperature-dependent. The substrate plates have a multidirectional orientation and force the liquid crystal a certain temperature depending on the doping determined twist value. When the temperature changes, the temperature changes Pitch length of the liquid crystal and the twist jumps discretely if for that changed pitch length p (T) due to the orientation layers a narrow table preferred twist state is defined. The change in the twist causes a transmission change, so that the arrangement as a discrete Thermometer works. It represents one without the inventive for the expert Routine task to be solved represents the preferred directions of the multi directional orientation layers, the total concentration of the The dopant and its temperature dependency fit that a desired temperature display such. B. the ad of 10 K jumps results.

The orientation layers according to the invention are preferably used for Manufacture of liquid crystal displays used, being the improvement conventional displays and also the implementation of completely new ones Enable displays. The orientation layers according to the invention is therefore of considerable economic importance.

Claims (4)

1. A method for producing multidirectional orientation layers, characterized in that a photocurable precursor of the orientation layer, which contains one or more, essentially linear photopolymers and / or oligomers, is applied to a substrate and subsequently with linearly polarized light at 2 or more different azimuth angles Φ is applied. 2. Multi-directional orientation layer, available according to the The method of claim 1. 3. Using the multidirectional orientation layer after Claim 2 for the production of electro-optical liquid crystal systems. 4. Electro-optical liquid crystal system containing a liquid crystal layer between substrates, which with electrode and orientation layers arranged above are provided, wherein at least one of the orientation layers multidirectional is oriented.