JP3429616B2 - Liquid crystal display device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light-scattering type liquid crystal cell in which the magnitude of the light-scattering property of a liquid crystal layer is controlled by the magnitude of a voltage applied to the liquid crystal layer, and in particular, it is formed from a three-dimensional fine structure made of a polymer and a liquid crystal. The present invention relates to a reflection type liquid crystal display device using a so-called polymer dispersion type liquid crystal cell having a liquid crystal dispersion film.

[0002]

2. Description of the Related Art A liquid crystal display device has a display system that utilizes birefringence and optical rotatory power of a liquid crystal by using a deflection plate typified by a twisted nematic mode and a super twisted nematic mode. There is a system that utilizes light scattering by liquid crystals without using a polarizing plate as represented by a phase transition mode. Among them, the light-scattering method does not require a polarizing plate, and therefore has a feature that brighter display is possible without loss (absorption) of light by the deflecting plate. One of the light scattering methods is a polymer-dispersed liquid crystal display element, which has been actively developed in recent years. This has a structure in which a liquid crystal is dispersed in a droplet form by a support such as a resin, or a liquid crystal dispersion film in which a resin network structure is formed in the liquid crystal is sandwiched between substrates with electrodes. In this method, generally, when no voltage is applied, the orientation of the liquid crystal is disturbed by the support, and light is scattered due to minute fluctuations in the refractive index. When a voltage is applied to this element, when the liquid crystal has a positive dielectric anisotropy, the liquid crystal molecules are aligned in the direction of the electric field and the fluctuation of the refractive index is reduced, so that the liquid crystal layer becomes transparent. This method, in addition to the brightness of the display,
It also has the advantage of fast response speed. When such a light-scattering liquid crystal display device is used as a reflection type direct-view display device, in general, a black background is provided behind the device to provide a black display when the device is in a transparent state and the device is in a scattering state. In that case, the method of displaying white by back light scattering by the device is simple. However, since the backscattered light intensity of such a light-scattering liquid crystal display element is small,
In order to obtain sufficient whiteness, it is necessary to take measures such as increasing the thickness of the liquid crystal layer. However, such a measure has a problem that the driving voltage of the element is increased. Also,
As another method, a mirror surface is provided on the back side of the liquid layer cell, and further,
There is known a system in which an external light blocking means provided with a black surface is provided on the upper surface of the element so that the regularly reflected light of the external light is not directly visible (Japanese Patent Publication No. 45-21729). In this case, when the pixel is in the scattering state, white display is obtained by visually recognizing scattered light of light having an incident angle from a direction other than the direction of specular reflection, and when the pixel is in the transparent state, it is observed by the observer's eyes. Since no light reaches, a black display is obtained. However, this method has problems that the display device does not have a flat plate shape and the brightness of the white portion is insufficient. In view of such a problem, the present inventors have shown that the light absorption layer and the reflection characteristics only for an incident angle in a specific range, and an angle-selective light reflection plate and a scattering layer that transmit light in other incident angle ranges. A reflective liquid crystal display device having a bright white background is devised by a structure in which liquid crystal display devices of the same type are sequentially stacked (Japanese Patent Laid-Open No. 6-258638).
issue). In this configuration, light with a large incident angle that is not directly related to display and the optical path is bent by the liquid crystal layer, and light that has entered the reflecting plate at a large acquisition angle is reflected by the reflecting plate and then enters the liquid crystal cell again. The whiteness of the cloudy part is increased. This device is a liquid crystal display device that is extremely excellent in that it is extremely bright and provides high contrast, but when the pixel electrode is fine and it is incident from a specific diagonal direction due to external light, the image of the transparent pixel is scattered. There is a problem in that it is reflected in pixels and causes a ghost phenomenon.

[0003]

The present invention has been made in view of the above problems of the prior art, and an object thereof is to improve a ghost phenomenon in a reflection type liquid crystal display device using a scattering type liquid crystal cell and an angle selective reflector. To provide a liquid crystal display device having high display performance.

[0004]

A liquid crystal display device according to the present invention comprises a pair of transparent substrates having transparent pixel electrodes on the inner surface thereof and spaced and opposed to each other, and a liquid crystal which is sandwiched between the substrates and whose light scattering property is changed by application of an electric field. A liquid crystal cell having a light control layer, a light diffusing means having a characteristic of transmitting light having an incident angle in a specific range including the viewing direction and scattering light having an incident angle other than that, and a specific light diffusing means including the viewing direction. It has a structure in which a light-absorbing layer and a light-reflecting means having an angle selectivity for transmitting light having an incident angle in the range and reflecting light in the other incident angle range in a direction other than the viewing direction are laminated. It is a feature. The liquid crystal dimming layer of the liquid crystal display device of the present invention can be used as long as it is a system capable of switching between a scattering state and a transparent period by an electric field, and among them, an electric field controlled dynamic scattering system (DSM), a phase transition system ( PC) and polymer dispersion method (PDLC) are typical. this house,
The DSM method is a method in which a liquid crystal layer having a negative dielectric anisotropy and an ionic dopant is used as a liquid crystal layer, and a scattering state is caused by turbulence due to an electric current. The phase transition method has a positive dielectric anisotropy. A cholesteric liquid crystal is used as a liquid crystal layer, and a phase change from a focal conic structure of a cholesteric phase to a homeotropic alignment of a nematic phase by applying a voltage is used. PDLC has a structure in which liquid crystals are dispersed in a fine shape as an independent phase or a continuous phase in a porous film made of a polymer. The present invention can use any method in principle as long as it is a scattering mode, but it can be driven at a relatively low voltage and has a high response speed.
The polymer dispersion type liquid crystal display mode is particularly preferably used because a high retention rate can be obtained when active driving is performed. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1. The structure and operation of the liquid crystal display device of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an example of the structure of a reflective liquid crystal display device using a conventional angle-selective reflector. The liquid crystal light control layer 13 capable of switching between a transparent state and a scattering state by applying a voltage has a transparent substrate 11 having transparent electrodes 12a and 12b on its inner surface.
The liquid crystal cell 10 is formed by being sandwiched between a and 11b.
Reference numeral 20 is a light absorbing means such as a black film. An angle selective reflector 3 is provided between the light absorbing means 20 and the liquid crystal cell 10.
0 is placed. 2. FIG. 2 is a cross-sectional view of a specific example of the conventional angle-selective reflector 30 and its function, in which a fine prism structure is formed on the surface of a translucent resin such as acrylic resin or polycarbonate. θi is the incident angle of light. θ
i ^c is an incident angle corresponding to the total reflection angle α on the lower surface of the angle-selective reflector. Incident light 5 with incident angle θi smaller than θi ^c
01 is refracted in the reflection plate and has a curved optical path, but transmits through the reflection plate. On the other hand, the incident light 502 having an incident angle θi larger than θi ^c is totally reflected by the bottom surface of the reflector, and the total reflected light 5
It is reflected as 03. As described above, the angle-selective reflector has different transmission / reflection properties depending on the incident angle of light. 3. FIG. 3 schematically shows the operation of a reflective liquid crystal display device using the conventional angle-selective reflector 30.
In this figure, the substrate and electrodes of the liquid crystal cell are omitted and shown schematically. 101 corresponds to a scattering pixel and 102 corresponds to a transparent pixel. The incident light 504 is scattered by the liquid crystal light control layer, and a part 505 of the backscattered light reaches the observer. Of the forward scattered light, the light 506 whose incident angle with respect to the reflector is larger than θi ^c
Is reflected by the reflection plate, is incident on the liquid crystal light control layer again, is scattered again, and a part 507 of the forward scattered light reaches the observer. As described above, in this method, in addition to the backscattered light, the reflected light of the component having a large incident angle is also used, so that bright white can be obtained. The optical path connecting the observer and the transparent pixel is 50
The color of the light absorbing layer is observed because it reaches the light absorbing layer as in 8. When the light absorption layer is black, black and white are displayed naturally. 4. FIG. 4 illustrates a problem of a conventional reflective liquid crystal display device using a conventional angle selective reflector. 6
Reference numeral 0 denotes a light source, which is arranged at a position that obliquely illuminates the display element. This corresponds to, for example, the case where the display element is illuminated from an oblique direction with a table lamp or the like. If the incident angle .theta.i at this time the light incident on the transparent pixel 102 is larger than .theta.i ^c, 517 is reflected at an angle-selective reflection plate 30 is incident on the scattering pixel 101. The light is further scattered, some of which 510 reaches the observer. In FIG. 3, the light scattered by the reflector is a part of the light previously scattered, whereas in FIG. 4, all the reflected light of the unscattered light is incident on the scattering pixel, and thus the element is transparent. A ghost phenomenon occurs in which a portion adjacent to a pixel becomes bright. This phenomenon is hardly a problem under diffuse illumination or when the pixel is large, but it is a problem when the pixel is made fine and illumination is performed only from an oblique direction. 5. The liquid crystal display element of FIG. 5 is the liquid crystal display element according to the present invention, and in addition to the configuration shown in FIG. 1, transmits light of an incident angle in a specific range including the viewing direction and transmits light of other incident angles. A light diffusing means (hereinafter referred to as an angle selective diffusing plate) 40 having a property of scattering light is provided. 6. FIG. 6 shows the operation of the angle-selective diffusion plate 40. Here, δi is the incident angle, and δi ^c is the switching angle of transmission / diffusion of the diffusion plate. Incident light 511 having an incident angle smaller than δi ^c passes through the diffuser plate, whereas large incident light 512 is scattered by the diffuser plate. As the angle-selective diffusing plate exhibiting such characteristics, a visibility control plate commercialized by Sumitomo Chemical under the trade name of Lumisty, or a field-selecting glass marketed by Nippon Sheet Glass under the trade name of ANGLE21. And the like are preferably used, but any one having a similar function can be used. 7. FIG. 7 shows the liquid crystal display device of FIG. 5 (however, the substrate is omitted).
It shows the action of. Consider the light 513 obliquely incident on the transparent pixel as described in FIG. This light passes through the transparent pixels but is scattered by the angle-selective diffusion plate 40, and the component 514 having a small incident angle also passes through the angle-selective reflection plate 30 and is absorbed by the light absorption layer. Of the scattered light, light 5 with an angle of incidence or more reflected by the angle-selective reflector 40
15 is reflected by the reflection plate and again enters the angle-selective reflection plate 30. At this time, if the angle-selective reflection plate 30 has an incident angle equal to or larger than the scattering angle, it is further scattered, and a part thereof. Will reach the scattering pixel 101. In this way, the intensity of the obliquely incident light transmitted through the transparent pixel 102 due to scattering is reduced, so that the ghost phenomenon as in the conventional art is hardly observed. On the other hand, for the optical path connecting the observer 70 and the transparent pixel 102, the angle selective reflector 3
By configuring both 0 and the angle-selective diffusion plate 40 to transmit light, the color of the light absorption layer, for example, black is recognized by the transparent pixel.

As described above, the incident angle range for transmitting light of the angle-selective reflector and the angle-selective diffuser must both include the direction of the observer. If this condition is not satisfied, the contrast is Will fall. Generally, when the observation direction is the front direction, δi ^c and θi ^c are 30 °
It is preferably at least 70 °. If this angle is too small, there is a problem that the viewing angle becomes narrow, and if it is too large, the whiteness of the scattering portion is insufficient. δi ^c and θ
and i ^c is preferably approximately equal, but alternatively the .delta.i ^c may be smaller than .theta.i ^c. However, even in this case, it is preferable that the ranges of δi ^c and θi ^c are both within the above range.

[0007]

EXAMPLES The present invention will be described more specifically with reference to Examples.

Example 1 A pair of vertically oriented glass substrates 11a and 11b having transparent electrodes 12a and 12b were superposed on each other with a spacer of 8 μm therebetween so that their surfaces to be oriented were opposed to each other, and a space was manufactured by Merck. Liquid crystal of the nematic liquid crystal BL002 and the chiral nematic liquid crystal S811 (S811 concentration: 4.
4% by weight) 13 was injected between the glass plate polarizing plates to prepare a phase transition type liquid crystal cell. The pixel electrodes were matrix electrodes with a pitch of 300 μm. The bottom of the cell is transparent to vertically incident light and has an incident angle of 27 ° in the front-back direction.
An angle-selective diffusion plate 30 having a characteristic of scattering the above light is superposed, and an angle-selection made of a polycarbonate micro-prism sheet having a 90 ° prism as shown in FIG. The liquid crystal display element was manufactured by stacking the reflective sheet 20 so that the apex angle was in the direction of the diffusion plate, and further providing a black light absorbing layer under the layer. The ridges of the microprism sheet were arranged so as to be in the left-right direction with respect to the element (that is, so as to be orthogonal to the direction in which the diffuser plate has angle selectivity). In such an arrangement, the microprism sheet reflects light having an incident angle of about 36 ° or more from the normal to the display surface and transmits light of less than that in the front-back direction of the element. When a part of the pixels of this device were operated under diffuse illumination, a good black and white display was obtained at a voltage of 10 V in the range of ± 27 ° in the front-rear direction. In addition, even when the device was illuminated obliquely from above, the ghost phenomenon was hardly observed.

Comparative Example 1 In Example 1, a liquid crystal display device was manufactured without using the angle selective diffusion plate. When this device was operated under diffuse illumination, good black and white display was obtained in the range of ± 36 ° in the front-rear direction, but when illuminated from oblique information, the ghost phenomenon in which the area adjacent to the display pixel became bright. Was observed.

Example 2 A pair of vertically aligned glass substrates having transparent electrodes were stacked with a 7 μm spacer so that the pixel electrodes face each other, and monoacrylate and diacrylate were filled in the space between the substrates. A polymer-dispersed liquid crystal cell was produced by injecting a mixed composition of a prepolymer composition containing the mixed acrylate composition and a photopolymerization initiator and a nematic liquid crystal BL036 manufactured by Merck Ltd., and irradiating with ultraviolet rays. . Thereafter, a liquid crystal display element was produced in the same manner as in Example 1. When a part of the pixels of this device were operated under diffused illumination, good black and white display was obtained in the range of ± 27 ° in the front-back direction, the operating voltage was as low as 5V, and the response speed was extremely fast at about 40 msec. . Further, even when the device was illuminated from diagonally above, the ghost phenomenon was hardly observed.

Example 3 A liquid crystal display device was manufactured in the same manner as in Example 2 except that the angle selective diffuser plate having an angle of 35 ° at which the transmission / diffusion optical characteristics were switched was used. No ghost phenomenon is seen in this one, and in addition, it is ± 35
Good contrast was obtained at 0 °, which was superior to that of Example 1.

The embodiments of the present invention will be described below. 1. A pair of transparent substrates, which have transparent pixel electrodes on the inner surface and are arranged to face each other with a space between them, and a liquid crystal cell having a liquid crystal light control layer sandwiched between the substrates, the light scattering property of which is changed by application of an electric field, and a viewing direction. Transmits light in a specific range of incident angles, including
Light diffusing means having a characteristic of scattering light of other incident angles, and transmitting light of an incident angle of a specific range including the viewing direction, and transmitting light of other incident angle range in a direction other than the viewing direction. A liquid crystal display device having a structure in which a light-reflecting means having an angle selectivity to reflect light and a light-absorbing layer are laminated. 2. When the incident angle is taken with respect to the normal line of the display surface of the device, the angle-selective reflector and the angle-selective diffuser transmit light with an incident angle of 0 °, and the respective optical characteristics change from transmission to reflection. and, the angle of incidence (θi ^c, δi ^c) switching from transmission to diffusion or less 70 ° 30 ° or more, the liquid crystal display device of the 1 observation direction is the front direction. 3. 2. The liquid crystal display device according to the above 2, wherein θ i ^c and δ i ^c are substantially the same. 4. The liquid crystal display element of 1, 2, or 3 wherein the selective light reflecting means is composed of a prism group formed on a plate-shaped transparent substrate with the apex angle facing the liquid crystal cell side. 5. The liquid crystal display device according to 1, 2, 3 or 4, wherein the liquid crystal light control layer has a structure in which liquid crystal is dispersed in a porous film made of a polymer. 6. The liquid crystal display device according to any one of 1, 2, 3 or 4, wherein the liquid crystal light control layer is a negative liquid crystal to which an ionic dopant is added. 7. The liquid crystal display element of 1, 2, 3 or 4 wherein the liquid crystal light control layer is a positive cholesteric liquid crystal.

[0013]

[Effects] The liquid crystal display device of the present invention transmits a scattering type liquid crystal cell and light having an incident angle within a specific range including the viewing direction,
Incident in a specific range including the viewing direction to a reflective liquid crystal display element including a light reflecting means having an angle selectivity for reflecting light in an incident angle range other than the above to a direction other than the viewing direction and a light absorbing layer. Since it is equipped with a light diffusing means that has the property of transmitting light at an angle and scattering light at other incident angles, a bright white display is possible, and a ghost phenomenon does not occur under any illumination. It has extremely excellent display performance that hardly occurs. Also, by setting the transmission angle range of the angle-selective reflector and the angle-selective diffuser to a specific range,
It is possible to achieve both a sufficient viewing angle and contrast. Furthermore, by using the polymer dispersed liquid crystal as the liquid crystal light control layer, it is possible to provide a liquid crystal display device which operates at a low voltage and has a high response speed, as well as a bright display as described above.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a cross-sectional structure of an example of a reflection type liquid crystal display element using a conventional angle selective reflection plate.

FIG. 2 is a diagram schematically showing a cross-sectional structure of an example of an angle-selective reflector used in the present invention and an action of the element.

FIG. 3 is a diagram schematically showing a cross-sectional structure of an example of a reflection-type liquid crystal display element using a conventional angle-selective reflection plate and an operation of the element.

FIG. 4 is a diagram schematically showing a cross-sectional structure of an example of a reflective liquid crystal display device using a conventional angle-selective reflector and an operation of the device.

5 is a diagram schematically showing a cross-sectional configuration of a liquid crystal display element using an angle selective diffusion plate in the liquid crystal display element of FIG.

FIG. 6 is a diagram illustrating the operation of the angle-selective reflector used in the present invention.

FIG. 7 is a diagram illustrating the operation of the liquid crystal display element of FIG. 5 (however, the substrate and electrodes are not shown).

[Explanation of symbols]

10 liquid crystal cell 11a translucent substrate 11b translucent substrate 12a transparent electrode 12b transparent electrode 20 light absorbing means (black film) 30 angle selective reflection plate α total reflection light θi incident angle θi ^c angle selective reflection plate bottom surface incident angle .delta.i incident angle .delta.i ^c diffusion switched transmittance / diffusion plate angle 40 angle selectivity diffuser 60 light source 501 incident angle .theta.i is .theta.i ^c smaller incident light 502 incident angle .theta.i corresponding to the total reflection angle α is from .theta.i ^c Incident light 503 Total reflection light 504 Incident light 101 Scattering pixel 102 Transparent pixel 505 Part of backscattered light (light reaching the observer side) 506 Total reflection Forward scattered light 507 506 Front scattered light is angularly scattered Part of light (light reaching the observer side) 508 Optical path 509 connecting observer and transparent pixel Part of forward scattered light 511 Incident light 512 Incident light 513 Incident light 514 Angle selection Light component 515 scattered by the diffuser plate and having a smaller incident angle Light component 516 or more incident angle reflected by the angle-selective reflection plate Incident light 517 Incident light

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-270768 (JP, A) JP-A-6-258638 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/1335 G02F 1/1334

Claims (4)

(57) [Claims] 1. A liquid crystal having a pair of transparent substrates which have transparent pixel electrodes on the inner surface and are arranged to face each other at a distance, and a liquid crystal light control layer which is sandwiched between the substrates and whose light scattering property is changed by application of an electric field. Cell, light diffusing means having characteristics of transmitting light of an incident angle in a specific range including the viewing direction and scattering light of an incident angle other than that, and light of an incident angle in a specific range including the viewing direction A liquid crystal display device having a structure in which a light-reflecting means having an angle selectivity for transmitting light in an incident angle range other than that and reflecting in a direction other than the viewing direction and a light-absorbing layer are laminated. . 2. When the incident angle is taken with respect to the normal line of the display surface of the device, the angle-selective reflector and the angle-selective diffuser transmit light with an incident angle of 0 ° and their respective optical characteristics. 2. The liquid crystal display element according to claim 1, wherein the incident angle at which transmission is switched from transmission to reflection and from transmission to diffusion is 30 ° or more and 70 ° or less, and the observation direction is the front direction. 3. The liquid crystal display device according to claim 1, wherein the selective light reflecting means is composed of a prism group formed on the plate-shaped transparent substrate with the apex angle facing the liquid crystal cell side. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal light control layer has a structure in which liquid crystal is dispersed in a porous film made of a polymer.