HK1007196B - Optical device - Google Patents

Description

The invention relates to an optical component with an anisotropic film of interlaced liquid crystal monomers with locally different orientation of the liquid crystal molecules.

Anisotropic transparent or coloured polymer network layers with a spatial orientation of the optical axis that can be specified at a point are of great interest in the field of display technology and integrated optics.

For some years now, substances that have this property in principle have been known, namely certain interconnectable liquid crystalline diacrylates and diepoxides, which can be oriented in the LC phase as monomers, i.e. before interconnection, in cells by conventional orientation layers or by external fields, e.g. magnetic or electric fields, and then in a second step by photoresonance without losing the orientation of the monomer state.

The structure of the layer is known from EP-A 331 233 for example. It is produced by orientating a monomer layer in the outer field and then irradiating a part of the layer through a mask. The networking is triggered only in the irradiated area. The direction of the outer field is then changed and the unlinked monomer areas are reoriented in relation to the new field direction.

Orientation layers play a crucial role in the construction of liquid crystal display cells. They determine the orientation of the liquid crystal material in the cell, i.e. the position of the optical axis and thus the feasibility of liquid crystal display cells, e.g. so-called TN or STN cells.

In recent times, methods have been developed to produce orientation layers with locally variable orientation properties, e.g. in US-A 4.974.941 the orientation of dichroic dye molecules in polymer is described by photolithography, which produces a thermally unstable orientation of the chromophores and is therefore not applicable to the orientation of the interlaced liquid crystals used here.

The purpose of the invention is to provide improved layer structures of the above-mentioned type for optical and electro-optical components.

According to the invention, this is solved by an orientation layer in contact with the liquid crystal layer from a photooriented polymer net (PPN).

The orientation layers consist of photo-oriented polymer network layers (PPNs) which induce high-resolution orientation patterns on LC layers by selective irradiation with polarized UV light. These are e.g. cinnamic acid derivatives as described in Swiss patent applications Nos. 2244/91 and 2246/91 and in the article by M. Schadt et al., Jpn. J. Appl. Phys., Vol. 31 (1992), pp. 2155-2164. The orientation process is based on photo-induced orientation and dimerization of the polymer side chains.

The fact that these PPN polymers were able to orient certain interconnectable LC monomer layers in a structured way and to interconnect them in a way that maintained their orientation was surprising. 1) Ro 47 to 7269 Tg = 156°C The temperature of the water is approximately The Commission has not yet adopted a decision on the application of the scheme. Tg = 105°C and LC monomer layers of diacrylate components, such as and their mixtures.

The combination of PPN and interconnectable LC monomers, as described in the present invention, is hereinafter also called a hybrid layer. It enables for the first time to transfer the optically recorded high-resolution orientation structure of a thin polymer layer into a double-breaking densely interconnected polymer layer of any thickness. Some useful properties of such hybrid layers are listed. They are insoluble in many solvents, especially for low-molecular LC, they are thermally stable, their optical anotropy is almost temperature-independent, the optical anisotropy can be large by Δn.2 The local resolution of the orientation structure is determined by the PPN, so they are in the submicron range.

The combination of photolithographically structured PPN coatings and highly anisotropic, sharply oriented liquid crystal network layers will make it possible to realize a large number of well-known optical components in a new way.

For example, it is possible to create strip waveguide structures in cells, to create structured retarder plates, polarizing beam splinters, etc. by using double refraction. Another possibility is to fix TN structures by networking and thus to create polarization rotors. These can extend over the entire cell surface, but they can also be limited to the smallest areas.

Another application is 3D slides for line graphics. In this case, the two substrates coated with PPN are first irradiated with linearly polarized UV light and then, in a second exposure step, the two sub-images for the right and left eye with linearly polarized UV light, whose polarization direction is rotated +45 and -45 degrees respectively to the first irradiation, are inscribed in one of the PPN layers. With these substrates, a liquid crystal cell is constructed and filled with interconnectable LC monomers of this invention. The structure induced by the PPN orientation layers is fixed by interconnection. A linear optical structure is obtained, which separates the portion of the polarised light that is distorted or transmitted parallel to the polarisation direction of the first degree of the polarisation, while the other portion is perceived by a 3D contrast lens and is transmitted through the left and right polarity of the first degree of the polarisation.

As described in the examples, the structured lattice layer can be realized as a coating of a substrate by spincoating the latticeable LC monomers on substrates coated with PPN or by preparing the lattice layer in a cell and then separating a substrate.

This coating can now, for example, be used as an orientation layer for LCDs, combining the properties of orientation and double refraction in a confined space.

Either the oriented anisotropic lattice coating itself induces an orientation to the adjacent LC layer, in which case the orientation pattern of the LC layer and the double refraction pattern of the lattice layer are correlated, or the oriented lattice coating is rubbed to form an orientation independent of the structure of the lattice layer, as in a conventional orientation layer.

In addition, an additional layer can be applied to the oriented network coating. For example, it is possible to sputter a transparent conductive layer (ITO) without damaging the network coating. These possibilities are of great importance for display technology. In particular, retarder layers, as required for STN displays, can be integrated into the display.

Another aspect of the invention is to mix dichroic dyes that are aligned parallel to the oriented monomers into the interlaced monomers. This makes it possible to create locally structured dichroic filters and dichroic polarizers. A special application is structured dichroic beam splitters.

It is also possible to mix chiral molecules with the networkable monomers or to incorporate functionalized chiral molecules into the network.

Another aspect of the invention is to mix the interconnectable LC monomers with functionalised LC molecules with a strong permanent axial or lateral dipole moment, which can enhance or otherwise influence the orientation of the PPN layer by an external electric field, which, among other things, allows the LC layer to be oriented from a homogeneous orientation at one boundary layer to a homotropic orientation at the other boundary layer, using the layer thickness.

A particularly important application is to produce orientation layers with a given tilt angle, as required in LC displays, by appropriate choice of layer thickness and/or direction and strength of the external magnetic or electric field.

Example 1

A 1% solution of PPN1 in NMP is sprayed on two ITO-coated glass plates, spinning parameters: 4000 UpM, pre-dried for 2 hours at 130°C on the heat bank, then vacuum-dried for another 4 hours at 180°C.

The two coated plates are irradiated with linearly polarized light by a 400 W Hg high pressure lamp for 1/2 hour at 25°C. Then a 10 mu thick LC cell is made from these substrates, the plates being arranged so that they are perpendicular to each other with respect to the direction of polarization of the irradiation.

The cell is filled at 140 °C with interconnectable LC1 and cooled to 95 °C in the nematic phase.

The nematic layer is oriented in the cell and takes the TN configuration as prescribed by the preparation of the orientation layers.

The oriented cell is exposed to the unpolarized light of a 100 W Hg high pressure lamp for several minutes at 90°C. The LC layer is interlaced while maintaining the TN configuration, thus fixing the cell structure and maintaining it unchanged when cooled to RT.

Example 2

As in example 1, an LC cell is constructed, but in this example only one of the substrates is coated with PPN. The second substrate has a conventional orientation layer of rubbed polyimide. Again, a TN cell is formed when the direction of friction of the polyimide layer is oriented parallel to the direction of polarization of the UV light used to irradiate the PPN substrate.

Example 3

As in example 1, glass plates coated with PPN1 are irradiated with linearly polarized UV light. Then one of the plates is irradiated a second time by a chrome mask with linearly polarized UV light but rotated 90 degrees in the direction of polarization. From the plates an LC cell is built and filled with networkable LC1 and networked.

Example 4 The three-dimensional slide:

As in example 2, the two substrates coated with PPN1 are irradiated with linearly polarized light and then in a second and third exposure step the two sub-images of the 3d line object containing the information for the right and left eye respectively are inscribed on one of the two substrates. This is done by in the second exposure step the one sub-image with UV light whose direction of polarization is rotated by +45 degrees with respect to the first irradiation is irradiated through a mask, and in the third exposure step the second sub-image with -45 degrees of polarization is inscribed by another mask with the contour of the second part.

As in example 2, the second unstructured substrate may be equipped with a conventional orientation layer.

Example 5

A PPN1 coating is sprayed on a substrate plate, as in example 1, and dried and irradiated with linearly polarized UV light. Then a mixture of NMP-soluble LC monomers and photoinitiator is sprayed on this coating and dried in the dark at 140°C on the heat bank. The temperature is lowered to 90°C, so that the LC layer is in the nematic phase.

The following illustrations illustrate further examples of the invention. Fig. 1a schematic section through a so-called retarder cellFig. 2a section and a view of a structured so-called retarder cellFig. 3a schematic representation of a colour compensated so-called STN liquid crystal displayFig. 4a schematic representation of a liquid crystal cell for colour displayFig. 5a colour grid of the cell as shown in Fig. 4Fig. 6a section through a structured so-called polarization cellFig. 7a schematic representation of a slide projection for three-dimensional projectionFig. 8a schematic representation of a projection device for stereoscopic image reflectionFig.9a schematic representation of a projection device for stereoscopic image reflection

The photoinduced orientation and interconnection of the LC monomers allows the production of transparent anisotropic polymer coatings with defined optical diffraction δ = Δn·d, where Δn = ((ne-no) means the anisotropy of the layer (ne = exceptional refractive index, no = ordinary refractive index), and d means the thickness of the layer. The optical diffraction is determined by the layer thickness and can be in the range of 0 < d < 400 nm.

The retarder cell shown in Figure 1 is a diagram of two substrates 1,5 spaced apart, e.g. glass plates with PPN layer 2,4 facing each other, and an LC network 3 between them.

The structured retarder cell shown in Figure 2 is similar in structure and has two substrates 1,5, but their interfaced surfaces are structured with PPN layers 2,4, and between them is an LC network 3.

The structuring is apparent from the supervision b.

The stripes indicate the direction of the optical axis of the retarder layer.

The ability to form patterns or large-scale optical retarder layers with the methods and materials described above opens up a variety of possibilities for producing novel liquid crystal displays. The new liquid crystal displays can be operated in both transmission and reflection. As electro-optical effects, all known field effects are basically available, namely the Twisted Nematic Effect (TN-LCDs), Supertwisted Nematic Effects (STN-LCDs), Deformation Uprighted Phases (DAP-LCDs), as well as the following ferroelectric field effects: Stabilized Ferroelectric Surface (SSF) effect, Heated Ferroelectric (DHF) effect, Short Pitch and Pitch-Sustainable Ferroelectric (SBF).

The so-called STN cell shown in Fig. 3 is composed of two glass plates 1.5 which are coated with control electrodes 2.6. The electrodes are usually segmented, i.e. if it is an indicator cell, the electrode layer 2 on the plate 1 shown in the figure to the left is covered as usual with an orientation layer 3 which aligns the adjacent molecules of the liquid crystal 10 between the plates in a preferential direction.

The right plate 5 also has such an orientation layer 7 on the surface facing the liquid crystal, but between it and the electrode layer 6 there is an intermediate layer 9 in the form of a hybrid layer consisting of a combination of a PPN layer oriented and, if necessary, structured by irradiation with linearly polarized light and a photovoltaic LC layer applied to it, oriented in the uninterconnected state by contact with the PPN layer.

It is anisotropic and is therefore well known in itself as a retarder layer for colour compensation of STN cells. However, the particular advantage of the present hybrid layer is that its anisotropic properties can be affected to a large extent by the manufacturing conditions of UV light irradiation. The optical gauge difference of layer 9 and the direction of the main axis of the double refractive ellipsoid Δn can be precisely formed in this way so that optimal colour compensation occurs.

The layer 9 can also be structured, i.e. its optical properties can be different in different areas, instead of being uniform.

Instead of a hybrid layer 9 on one of the two plates, it is also possible to provide such retarder layers on both plates.

The hybrid retarder layer 9 can also be placed between the glass plate 1 and the electrode layer 2. This is of particular interest if the layer thickness of the retarder layer 9 does not have an electrical effect, i.e. when applying a voltage to the electrodes no voltage drop is to be generated over layer 9.

The hybrid retarder layer 9 may also be applied to the outer surface of the substrate 1,5.

The orientation layers 3,7 can be maintained by steam or rubbing, but it is also possible to use PPN layers for the orientation layers.

The liquid crystal display cell shown in Fig. 3 is completed by a linear input polarizer 4 and a linear output polarizer 8 cross-arranged to the first.

Unpolarized light 12 from a light source 11 is linearly polarized by the polarizer 4 in the direction perpendicular to the plane of the character and is converted into elliptically polarized light when passing through the liquid crystal in its shown off state by decomposition and partial rotation. Without layer 9, this light would be colored due to the wavelength-dependent different duration in the liquid crystal 10. Layer 9 in itself is known to cause color compensation, so that a black-and-white contrast between a turned off state results. The linearly polarized polarizer 8 allows the part of the light 13 that vibrates parallel to its polarization direction to pass through 14 beams.

Instead of choosing the optical gear difference and the position of the double refractive ellipsoid of the optical retarder layer in such a way as to compensate for the inherent colour of STN display cells, these values can be selected in conjunction with the polarizer settings to produce colours from the cell as shown in Figure 3.

It is known that both in optically bistable field effects and in those with grayscale, which are the underlying properties of the effects (wave guiding, double refraction) with appropriate polarizer positions can be used to generate colors. These interference colors can be affected by additional retarder layer. The aforementioned possibility of structuring the retarder layer in terms of its optical properties, i.e. patterns with different gear differences and location of the double refractive ellipsoid in different areas, makes different adjacent color surfaces possible.

An example of a colour display with different coloured dots arranged side by side in a regular grid is shown in Figures 4 and 5.

The display cell shown in Fig. 4 is largely the same as the cell shown in Fig. 3. In contrast to Fig. 3, the retarder layer 9 and the electrode layer 6 are interchanged. In addition, these two layers are divided into individual areas according to a grid.

For colour rendering, for example, the retarder layer is trained to turn red in the area of the upper left image point 15, green in the area of the adjacent right image point 16, yellow in the area of the next image point 17 of the row and then red again.

The different optical gauges of the optical retarder layer in the different areas can be produced by different durations (exposure times) of light radiation during polymerisation or by different intensities of the polymerising light.

In addition, as already mentioned, sequential irradiation can also produce the wall orientation layers in grid form with different orientation directions, which can also vary the relative position of the nematic directors with respect to the polarizers for each image point.

The optical retarder layers may also be applied between electrode layers and wall orientation layers or on the outer sides of the glass panes, as shown in Figure 4.

The structured polarization rotor shown in Figure 6 consists of two spaced substrates 1.5 with facing surfaces of structured PPN layers 2.4 and a structured LC network layer 3 between them, consisting of a grid of TN and parallel cells.

The three-dimensional slide shown in Figure 7 is a linear polarizer 11 and a cell of two parallel substrates 12, 16 with a uniformly oriented PPN layer (unstructured) on one substrate 12 and a structured PPN layer on the other substrate 16.

The two screens show the orientations of the input orientation layer 13 and the output orientation layer 15.

The rear projection device as shown in Figure 8 contains a linear polarizer 38 in the path of light coming from a light source 36 37 which first polarizes the light parallel to the character plane. Behind it is a TN-LCD 40 to 47, which is equipped with a variety of controllable pixels (e.g. in the form of a matrix of square segments). Each adjacent pixel contains the image information for the right or left eye. When the light is turned off, the light leaves the cell with a 90° rotation of the polarization direction. The light now reaches a focusing optical structure 48 and a mirror 49. The mirror directs the light to a projection screen in which the image is located.

The stereo forward projection device shown in Figure 9 can be implemented in an analogue manner: in this case, the structured polarization rotary viewfinder 52 located in the image plane of the first figure is placed on a transparent substrate 54 and a second optical lens 55 projects this plane onto a polarization-preserving projection wall.

Claims (19)

1. An optical component comprising an anisotropic layer (9) of cross-linked liquid-crystalline monomers with locally varying orientation of the liquid crystal molecules, characterised by an orientation layer in contact with the liquid crystal layer and consisting of a photo-orientable polymer network (PPN).
2. An optical component according to claim 1, characterised in that the orientation layer has an orientation of the polymer molecules which differs in locally limited regions.
3. An optical component according to claim 2, characterised in that the direction of the optical axis of the anisotropic layer varies according to the orientation of the polymer molecules of the orientation layer.
4. A process for the production of an optical component according to claim 1, characterised in that the liquid-crystalline monomers are oriented by interaction with the PPN layer and the orientations are fixed in a subsequent cross-linking step.
5. A process according to claim 4, characterised in that the cross-linking is effected by irradiation with light.
6. A process according to claim 4, characterised in that the cross-linkable monomers are diacrylates and the orientation layer material is cinnamate derivatives.
7. A process according to claim 4, characterised in that the cross-linking is effected in a cell consisting of two parallel orientation layers.
8. A process according to claim 7, characterised in that one of the two orientation layers is removed after cross-linking.
9. A process according to claim 4, characterised in that a substrate coated with PPN is selectively structured by repeated illumination with linear-polarised UV light of varying polarisation direction, and then the cross-linkable LC material is oriented and cross-linked by spin-coating or immersion processes.
10. A process according to any one of claims 4 to 9, characterised in that the cross-linkable LC material used consists of mixtures of multi-functionalised LC monomers and functionalised dichroic chromophores.
11. A process according to any one of claims 4 to 9, characterised in that the cross-linkable LC material used consists of mixtures of multi-functionalised LC monomers and chiral molecules.
12. A process according to any one of claims 4 to 9, characterised in that the cross-linkable LC material used comprises mixtures of multi-functionalised LC monomers and functionalised LC monomers with an axial or lateral permanent dipole moment such that said mixtures have a positive or negative dielectric anisotropy.
13. Use of an optical component according to any one of claims 1 to 3 as a retarded layer.
14. Use of an optical component according to any one of claims 1 to 3 as a cholesteric filter.
15. Use of an optical component according to any one of claims 1 to 3 as a dichroic filter.
16. Use of an optical component according to any one of claims 1 to 3 as a dichroic polariser.
17. Use of an optical component according to any one of claims 1 to 3 as a polarisation rotator.
18. Use of an optical component according to any one of claims 1 to 3 as an image carrier cell in which the image information is stored by cell segments of different orientation.
19. Use of an optical component according to any one of claims 1 to 3 in a three-dimensional projection system.