JP4201267B2 - Liquid crystal display with reflective polarizing plate - Google Patents

Description

  The present invention relates generally to devices for displaying information, and more particularly to liquid crystal displays (LCDs).

  Displays incorporated in flat cuvettes are known. The cuvette is an electrode made of an alignment film made of an optically transparent conductive material, and is usually formed by two parallel glass plates. After assembly of the cuvette, the cuvette is filled with a liquid crystal material that forms a film having a thickness in the range of 5-12 μm. A liquid crystal material is an active medium that changes its optical properties, such as the angle of rotation of the plane of polarization under the influence of an electric field. Changes in optical properties are seen with crossed polarizers that are usually bonded to the outer surface of the cuvette. Areas of the display where the electrodes are not electrically charged transmit light and appear bright, and areas under voltage appear dark (l. K. Vistin, JVHO, 1983, vol. XXVII, ed. 2, pp. 141. -148).

  In a reflective display, a mirror (mirror) or reflector (reflector) is provided behind the LC cuvette so that incident light passes twice through the cuvette. Image formation is performed analogously to a transmission display (Pochi Yeh, Claire Gu, Optics of liquid Crystal Displays, N.Y., 1999, p.p. 233 237).

  The main drawback of conventional displays is the small viewing angle because light propagates towards the front of the multilayer LC display only within a narrow cone angle range. Such displays typically use an absorbing polarizer based on a polymer such as polyvinyl alcohol having optical anisotropy, which is the polymer as described in US Pat. No. 5,007,942. Can be obtained through uniaxial stretching of the film and subsequent dyeing of the film with iodine fume or organic dyes. Therefore, the angle-dependent ellipsoid of the real and imaginary parts of the refractive index of the polarizing plate has a stretched shape (like a needle).

Also, a normal display has a relatively low brightness, a low contrast and a high power consumption due to a large number of absorbing films.
Color displays usually have the same design where color filters are used. Each pixel of the color image is formed through mixing (mixing) of three colors (red, blue and green) in the proper ratio (Nikkei Electronics, 1983, 5-23, pp 102-103). Using an absorption filter can result in additional light loss in the device and consequently increase energy consumption.

  LC displays are known in which the polarizing film is obtained from aligned supramolecular complexes of dichroic dyes. Such polarizing plates have high optical properties and a small thickness, allowing their placement inside the display. This simplifies the design and increases the durability of the display. Furthermore, the fabrication techniques of such films allow several functions to be combined into one film (eg, polarization and LC orientation) (RU2120651, 15.04.96).

  WO 99/31535 describes an LC display element that incorporates a polarizing plate that includes a birefringent anisotropic absorption film having a refractive index that increases with increasing wavelength of incident light. In particular, such a polarizing plate can be obtained from an LLC dichroic dye and can have a constant thickness in order to set an interference extreme on at least one side of the polarizing plate. The patent application also describes a reflective polarizer.

  One drawback of using such polarizers for color displays is that they reflect light in a wide spectral range that leads to the smeared colors (smeared colors). Furthermore, further development of display technology requires a better optical identification of the polarizing element, especially an increased viewing angle where there is efficient light conversion.

  Accordingly, one object of the present invention is to have increased display brightness, spectrally clean color images, and white, black and color construction in the image to increase image contrast and richness. The object is to provide a display configured to be able to produce components and having an increased viewing angle of the display.

These and other objects are achieved by a liquid crystal display comprising a front panel and a rear panel, electrodes, a polarizing plate, and a liquid crystal film between the front panel and the rear panel. The polarizing plate on the rear panel preferably includes at least one element that reflects in at least one region of the spectrum and has a multilayer structure. The multilayer structure includes at least two anisotropic films separated by at least one intermediate film that is optically transparent in the spectral region. The refractive index and thickness of the anisotropic film in the multilayer film structure, supplies an extreme value with respect to the ratio of the polarized light reflected polarized light transmitted in the region of the spectrum. The invention will be better understood by reading the following description with reference to the accompanying drawings, in which:

  The LC display of the present invention shown in FIG. 1 includes a front panel 1 and a rear panel 2 each having a functional film such as an electrode, a polarizing film, an adhesive film, and a liquid crystal film 3 disposed between the front panel and the rear panel. Inside the front panel 1 is a thin crystal film 4 that functions as a dichroic polarizing plate. The crystal film 4 is dye (Vat Blue 4); bis-benzimidazole- [2,1-a; 1'2'b '] anthra [2,1,9-def; 6,5,10 -d'e'f '] diisoquinoline-6,9-dion; method described below from LLC containing 12.5% blend of Vat Red 15 (vat red 15) in a ratio of 5.2: 2: 1 Can be formed. LLC is transformed into an insoluble form after treatment with barium ions. The thickness of the crystal film 4 is about 100 nm. Since the crystalline film 4 is a high order (high order) anisotropic film, it can simultaneously operate as an alignment layer for the LC display.

  A reflective polarizing plate 5 having a multilayer film structure is provided on the inner surface of the rear panel 2. Further, the rear panel 2 is provided with an absorption film 6 on the outer surface of the rear panel 2.

  The reflective polarizer 5 is composed of three films as shown in FIG. 2: starting from the rear panel 2 of the display, obtained from the LLC of the dye Vat Red 15 (construction red 15), which is approximately 60 nm thick. Crystal film 7, approximately 100 nm thick, isotropic transparent film 8 of polyvinyl acetate, and approximately 60 nm thick crystal film obtained from LLC of dye Vat Red 15 9. Crystal films 7 and 9 are distinguished by their high anisotropy: it reaches 0.8 at a wavelength interval of 570-600 nm. The films 7, 8, and 9 are sequentially formed on the rear panel 2 by the method described below. The reflective polarizer 5 has a total reflectivity of about 44% of polarized light with respect to the extraordinary direction and about 1% with respect to the normal direction. FIG. 3 shows the corresponding spectral characteristics of the reflected light for different directions of polarization.

The display is characterized by a bright image, rich colors (green), high contrast and a wide viewing angle. Preferably, at least one anisotropic film of the multilayer structure 5 is optically transparent in the above-mentioned region of the spectrum for both components (components) of polarized light. The at least one anisotropic film preferably has an anisotropic magnitude of 0.4 or more in a desired spectral region. Preferably, at least one anisotropic film of the multilayer structure 5 is an E-type polarizing plate in at least one region of the spectrum.
Anisotropic films are usually obtained from at least one organic dye and / or derivative thereof that is configured to be able to form a lyotropic liquid crystal (LLC). At least one of the polarizing plates is preferably disposed between the front panel and the rear panel of the display. Preferably, the absorption film 6 that absorbs at least the entire desired spectral region or visible wavelength region is provided on the outer surface of the rear panel 2 along the direction of incident light. It is preferred that at least one anisotropic film of the display is at least partially crystalline.

In a color display, the polarizing plate 5 of the rear panel 2 is preferably composed of a matrix of color reflecting elements, each reflecting in at least one region of the spectrum. The choice of matrix element is governed by the conditions for supplying a set of basic colors. Usually, the basic colors are blue with a wavelength in the range 400-500 nm, green with a wavelength in the range 500-600 nm and red with a wavelength in the range 600-700 nm.
Preferably, the absorption film 6 disposed on the rear panel 2 and composed of a matrix of colored reflective elements absorbs in the entire visible wavelength region.
The display includes white, black and colored components in the color image.

  The LC display according to the present invention includes a front panel and a rear panel, electrodes, a polarizing plate, and other functional films, and a liquid crystal film between the front panel and the rear panel. The polarizing plate of the front panel is neutral and transmits one polarization component of light and efficiently absorbs the other components.

  The polarizing plate of the rear panel of the monochrome display represents a multilayer structure including at least two optically anisotropic films separated by an optically transparent intermediate film. The thickness and refractive index of all films are chosen so that the polarizer transmits orthogonally polarized radiation that efficiently reflects one polarized radiation in a certain region of the spectrum and is later absorbed by the filter. Is done.

  In a color display, the rear panel polarizers represent a matrix of color reflective elements, each implemented in the same manner as the reflective polarizer described above for a monochromatic display. The choice of matrix element is governed by the conditions for supplying a set of basic colors in the image. In order to obtain a spectrally clear and high contrast color image, it is preferred that each matrix element reflects in a narrow spectral range.

In the production of the multilayer structure 5, it is preferable to obtain a thin homogeneous film having a high degree of anisotropy and one refractive index and preferably (compared to the wavelength). Optiva Technology (Lazarev P., Paukshto M. , Proceeding of the 7 th International Display Workshops, Materials and Components, Kobe, Japan, November 29 December 1 (2000), pp 1159-1160) crystal thin film or obtained by the method of the The membrane can be used in the production of the multilayer structure 5.

  The first choice of materials for producing such multilayer structures is the appropriate spectral properties and molecules, such as amines, phenols, ketones and others that are in the plane of the molecule and part of the aromatic bond system. Based on the existence of developed systems of aromatic conjugated cycles and π-conjugated bonds in groups. The molecules themselves or their fragments have a flat structure. Suitable organic materials are indanthrone (Vat Blue 4), dibenzoimidazole 1,4,5,8-naphthalenetetracarboxilic acid (Vat Red 14), dibenzoimidazole 3,4,9,10-perylentatracorboxilic acid, quinacridone (Pigment Violet 19), derivatives thereof, and combinations thereof.

  Dissolving such organic compounds in a suitable solvent produces a colloidal system (liquid crystal solution) in which the molecules bind to the supramolecular complex and function as the kinetic unit of the system. LC is a pre-ordered state of the system in which an anisotropic crystalline thin film (or crystalline thin film in other terms) is then dipped during supramolecular complex orientation and subsequent removal of solvent.

The method of preparing a thin anisotropic crystalline thin film from a colloidal system having a supramolecular complex includes the following steps:
Depositing (growing) the colloidal system on a substrate (or wear, or one of the films of a multilayer structure); The colloidal system has thixotropic properties such that the colloidal system must be at a constant temperature and have a constant dispersion phase concentration;
-Increase the flow rate of the grown colloidal system through an external impact (which can be strain due to heating, shearing, etc.) appropriate to supply the reduced viscosity of the system. The stage to convert to a state. The external impact may continue during all subsequent processing of the orientation or may have a required duration (lifetime) so that the system does not return to a state with increased viscosity during orientation;
Applying an orienting force to the system, which can be performed mechanically as well as otherwise; Forces form colloidal kinetic units (kinetic units) undergo the necessary orientation and form structures that can be the basis for future crystal lattices in the resulting film. Must be sufficient;
Transforming the resulting oriented region of the thin film from the reduced viscosity state achieved by the main external influence into the initial or higher viscosity state of the system. This is performed in such a way that there is no disorientation of the structure in the resulting thin film so as to avoid appearance defects on the surface of the film;
-Removing the solvent from the resulting thin film while the crystal structure is formed.

  Within the resulting film, the molecular planes are parallel to each other and form a three-dimensional crystal on at least a portion of the film. By optimizing this method of thin film production, a single crystal film can be obtained. The optical axis of such a crystal is perpendicular to the molecular plane. Such a film has a high degree of anisotropy and a high refractive index in at least one direction. The thickness of the membrane usually does not exceed 1 μm.

  The resulting film thickness can be controlled through the initial LC solid phase content and the LLC grown film thickness. Furthermore, colloidal mixtures can be used to obtain films with intermediate optical properties (in this case, supramolecular complexes formed in solution are combined). Absorption and refraction can have various values within a range determined by the initial components of the film obtained from the mixture of colloidal solutions. Mixing various colloidal systems and obtaining a combined supramolecular complex is a matter of the flatness of the molecules (or their fragments) and the dimensions of the molecules from the above organic compounds (3.4Å). ) Is possible with one match.

In a wet layer, the molecules have a good order along one direction due to the orientation of the supramolecular complex of the substrate. Forming a three-dimensional crystal structure during the evaporation of the solvent seems more energetically favorable to the molecule.
The multilayer film structure includes at least two anisotropic films obtained by the above-described method. Here, the optical axes of the individual anisotropic films are usually in the same direction. Reflection of light in a certain spectral range by the polarizing plate can occur due to interference effects in the thin film. The thickness of the film and the refractive index for each direction of polarization are selected so that one of the light is efficiently reflected by this structure while the other polarization component passes unreflected. In order to absorb the light transmitted through the multilayer structure, a film of total absorbing material is provided on the outer surface of the rear panel along the direction of radiation propagation. This removes glare from the rear panel of the display and improves image contrast. Furthermore, such a design allows to obtain a black color in the image.

Since the resulting film is thin (less than 100 nm) and has a high degree of anisotropy, the number of films is minimal (eg 3), so that a multilayer structure can be placed inside the LC display.
A polarizing plate for the front panel can also be obtained by the techniques described above with a corresponding selection of organic materials or mixtures of materials having an appropriate absorption spectrum that form the LLC. Furthermore, this polarizing plate can also be arranged inside the display.

  The internal arrangement of all the functional films of the display reduces the size and improves the durability of the display device, and simplifies the device manufacturing process.

  Furthermore, the method of manufacturing an anisotropic film according to the present invention is based on the fact that the angle-dependent ellipsoids of the real part and the imaginary part of the refractive index have a disk-like shape. Changing the ellipsoid shape of the imaginary part of the refractive index significantly improves the parameters of the polarizer and its angular characteristics. Using such a polarizer in the display can actually increase the viewing angle up to 180 °.

  Further, the polarizing plate of the rear panel of the color display, which represents a matrix of color reflecting elements, can be obtained by the above-described technique using a mask for forming a local coating, for example. Here, the film of anisotropic material is grown continuously instead of by the technique described above. In areas where it is desirable for the coating to be preserved to form a locally reflective polarizing element, the coating material is converted to an insoluble form. The remaining area is cleaned through a water wash. Another film of anisotropic material is grown on top of the resulting film and the procedure is repeated. If necessary, an additional polarizing film can be used. Therefore, a multilayer film structure of polarizing plates, which is a matrix of individual elements, is formed. Each element of the matrix reflects a certain spectrum of light and one polarization.

  A liquid crystal display was provided. The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or are not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible with respect to the above teachings. Embodiments have been selected and described in order to best explain the principles of the invention and its practical application, thereby providing a variety of embodiments having the invention and various modifications to suit the actual use anticipated by those skilled in the art. Embodiment is best utilized. It is intended that the scope of the invention be defined by the claims and their equivalents.

1 is a schematic partial view of a liquid crystal display having an internal polarizing plate according to an embodiment of the present invention. FIG. 2 is a partial view of the influence display of FIG. 1 showing details of a multilayer reflective polarizer. 4 is a graph showing spectral characteristics of a liquid crystal display according to an embodiment of the present invention.

Claims (14)

A front panel and a rear panel, an electrode, a polarizing plate, and a liquid crystal film between the front panel and the rear panel;
Polarizing plate on the rear panel is at least one region of the spectrum, a polarizing plate of the multilayer film structure that efficiently reflected the one polarization component, the multilayer film structure is at least one region of the spectrum Including at least two anisotropic films separated by at least one optically transparent intermediate film, wherein the refractive index and thickness of the anisotropic film in the multilayer structure are transmitted in the region of the spectrum A liquid crystal display, characterized in that it is selected to provide an extreme value for the ratio of polarized light and reflected polarized light. The display according to claim 1, wherein at least one of the anisotropic films of the multilayer structure is optically transparent in the region of the spectrum for both components of polarized light. The display according to claim 1, wherein at least one of the anisotropic films has an anisotropic magnitude of 0.4 or more in the spectrum region. The display according to claim 1, wherein at least one of the anisotropic films is an E-type polarizing plate in at least one region of the spectrum. The anisotropic film is obtained from at least one organic dye and / or a derivative thereof, a display according to any one of claims 1 or 4 are those which are capable of forming a lyotropic liquid crystal. The display according to claim 1, wherein at least one of the polarizing plates is disposed between the front panel and the rear panel of the display. 7. The method according to claim 1, further comprising an absorption film provided on an outer surface of the rear panel along a direction of propagation of incident radiation in at least one region of the spectrum. display. The display according to claim 7, wherein the absorption film absorbs all wavelengths in the visible range. The display according to claim 1, wherein at least one of the anisotropic films is at least partially crystalline. The display according to any one of claims 1 to 9, wherein the polarizing plate of the rear panel includes a matrix of color reflecting elements each reflecting in at least one region of the spectrum. 11. A display according to claim 10, wherein the elements of the matrix are selected to provide a set of basic colors. 12. The display of claim 11, wherein the basic colors include blue having a wavelength in the range of 400 to 500 nm, green having a wavelength in the range of 500 to 600 nm, and red having a wavelength in the range of 600 to 700 nm. Further comprising an absorption film provided on the outer surface of the rear panel along the direction of propagation of incident radiation, the polarizing plate of the rear panel includes a matrix of color reflective elements, each reflecting in at least one region of the spectrum The display according to claim 10, wherein the absorption film absorbs all wavelengths in the visible range. 14. A display according to any one of the preceding claims, characterized in that the display is characterized by the presence of white, black and color components of a color image.

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