JPH06258624A - Reflection type display element - Google Patents

Abstract

PURPOSE:To provide the bright reflection type display element having a wide visual angle and to realize the bright reflection type display having a large capacity and wide visual angle by using substrates having a high refractive index as substrates for holding a liquid crystal/high-polymer layer. CONSTITUTION:This display element is so formed that the refractive index near the surface of the front side substrate 1 in contact with the liquid crystal 3/high-polymer 4 layer is >=1, more preferably >=1.5. Since the refractive index of the substrate 1 is much higher than the refractive index of air and, if the light is made incident in a diagonal direction, the light is made incident at a nearly perpendicular angle on the liquid crystal 3/high-polymer 4 layer. The light exclusive of the light penetrating from the front surface, is consequently made incident eventually at the nearly perpendicular angle on the surface of the display element and, therefore, the scattering efficiency is improved. The light emitted to be scattered in the direction to the front surface is emitted in a diagonal direction at the boundary between the substrate 1 and the air and, therefore, the visual angle is eventually widened. The effect is higher if the display element is applied particularly to a display element having scattering with large dependency on the visual angles, among the display elements of the light scattering type.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a reflection type display element used for a display of an office automation equipment or a small information equipment, or an outdoor display device.

[0002]

2. Description of the Related Art In recent years, with downsizing of office automation equipment, development for thinning and lightweighting computer displays has been in progress. In particular, development of polymer dispersed liquid crystal display devices that have the possibility of realizing bright paper white display without a backlight is active. For example, as shown in JP-B-3-52843, a microcapsule type in which a liquid crystal is enclosed in a polymer capsule and fixed with a binder, or JP-B-61-50212.
Of the Swiss cheese structure in which liquid crystal droplets are dispersed in a polymer as shown in 8 or Japanese Patent Publication No.
There are many displays such as those in which liquid crystals are dispersed in a sponge-like network as shown in 126915, or those in which polymer particles are dispersed in an aligned state in the liquid crystals shown in European Patent Publication EP0488116A2. The device is being developed.

[0003]

However, in the conventional polymer-dispersed liquid crystal display element, the brightness and contrast greatly depend on the viewing angle when the reflection type is used, and it is bright when viewed from the front but becomes dark when deviated from the front. Therefore, there is a problem that the display becomes difficult to see.

Therefore, the present invention is to solve such a problem, and an object thereof is to provide a bright reflective display element having a wide viewing angle.

[0005]

In a reflective display device in which a liquid crystal and a polymer are dispersed in each other, the refractive index of at least the surface of the front substrate near the surface in contact with the liquid crystal / polymer layer is 1 or more,
More preferably, it is 1.5 or more.
Further, the substrate is made of one kind of material, or the substrate has a refractive index distribution in the thickness direction of the substrate. Hereinafter, details of the present invention will be shown by examples.

[0006]

【Example】

(Embodiment 1) This embodiment shows an example in which the present invention is applied to a display device in which a liquid crystal and a polymer are oriented and dispersed. FIG. 1 shows a simple cross-sectional view of the display device of this example. A simple principle will be described with reference to FIG. When light is incident on the display element from the outside, the light is refracted at the interface between the air and the substrate 1 as shown in FIG. 1, and when the light is incident from an oblique direction, the refractive index of the substrate 1 is sufficiently higher than that of air. Since it is large (1 or more, preferably 1.5 or more), light is incident on the liquid crystal 3 / polymer 4 layer at an angle close to vertical. Therefore, light other than light incident from the front also enters the surface of the display element at an angle close to vertical, so that the scattering efficiency is improved. Further, since the light that is going to be scattered in the front direction is emitted obliquely at the interface between the substrate 1 and the air, the viewing angle is widened. The present invention is particularly effective when applied to a display element having a large viewing angle dependency of scattering among the light scattering type display elements.

Next, a method of manufacturing the display element will be described. First, for the substrate, TaF3 manufactured by HOYA is used as the front substrate 1.
(Refractive index 1.8) was used, and after the transparent electrode 2 was formed thereon, the electrode surface was subjected to orientation treatment. Ordinary borosilicate glass was used as the counter substrate 7, and aluminum was deposited as the reflective electrode 6. The surface of this electrode was subjected to orientation treatment.
After that, the two substrates were fixed with a gap of 5 μm (not necessarily 5 μm, optimized depending on the application). The composition sealed in this gap will be described. Liquid crystal 3 (liquid crystal TL202 manufactured by Merck and chiral component CB1 manufactured by Merck)
5 and a mixture of dichroic dye S-344 manufactured by Mitsui Toatsu Dyes Co., Ltd. shown as 5 in FIG. 1 at 95: 2.5: 2.5) and biphenyl methacrylate as a polymer precursor 90: The mixture was mixed in No. 10 and sealed in the above-mentioned empty panel, and ultraviolet rays were irradiated in the liquid crystal phase to polymerize the polymer precursor to precipitate polymer particles 4 from the liquid crystal 3.

Next, the electro-optical characteristics of the display device thus manufactured were measured. In order to investigate the difference from the electro-optical characteristics when a conventional glass substrate having a normal refractive index (about 1.5) is used, light is projected from a direction inclined by 45 degrees from the normal line of the display element surface to display. The intensity of light reflected in the normal direction of the device was measured. According to this, assuming that the reflectance when white paper is arranged is 100%, the reflectance of the display element of the present invention is about 80% when an electric field is applied, which is a conventional example (reflectance of 50%).
You can see that it is considerably improved compared to.

The liquid crystal, polymer, chiral component and dichroic dye used here are not limited to those shown here, and any material that functions as a display element may be used. Further, the mixing ratio of these is not limited to the ratio shown here. The chiral component and the dichroic dye may not be blended. For polymers, UV curable or electron beam curable resin precursors such as acrylic resin precursors, methacrylic resin precursors, crotonates, cinnamates, and epoxy resin precursors having shorter molecular lengths can also be used in the same manner. . A thermosetting resin such as an epoxy resin can also be used. Further, a thermoplastic resin such as ethyl cellulose may be used to be heated to make it compatible with the liquid crystal, to be enclosed in the gap between the substrates and to be slowly cooled slowly for phase separation.

The front substrate 1 used here may be any one having a refractive index of 1.6 or more.

The substrate 7 used for the back side may be made of any material (resin or the like).

Regarding the electrode formed on the substrate, the electrode 2 needs to be transparent, but the electrode 7 may be a transparent, reflective or light absorbing electrode, but a reflective electrode is preferable. . In order to use the reflective mode without using the reflective electrode, a reflective layer may be arranged on the back side of the substrate 7.

The rubbing treatment was performed as the orientation treatment applied to the electrodes, but the present invention is not limited to this, and vertical orientation treatment may be performed. In this case, it is necessary to use a liquid crystal having a negative dielectric anisotropy. An alignment film may be formed during the alignment treatment. It also functions without the alignment treatment.

(Embodiment 2) This embodiment shows an example in which the present invention is applied to a display device having a structure in which microcapsules containing liquid crystal as a liquid crystal / polymer material are dispersed in a polymer binder. A method of manufacturing the device will be described. Reflective electrode 6
On the borosilicate glass substrate 7 on which was formed the high refractive index glass 1 on which the electrode 2 was formed by spreading a suspension of liquid crystal, PVA and water and evaporating the water, was laminated. At this time, 2 in the liquid crystal
If no chromatic dye is added, it becomes milky white when no electric field is applied, and it becomes a mirror when an electric field is applied. When a dichroic dye is mixed in the liquid crystal and an omnidirectional reflective electrode is used as the reflective electrode, the dye color is displayed when no electric field is applied, and the color of the omnidirectional reflector is displayed when an electric field is applied. . In any case, the brightness was improved by 1.3 times as compared with the conventional one.

The liquid crystal used is PN001 manufactured by Rodick,
Although PVA was used as the polymer, it is not limited to these. The liquid crystal preferably has a large birefringence when a dichroic dye is not used. When a dichroic dye is used, the birefringence may be controlled according to the application. The dichroic dye may not be used, but when it is used, a compound having a large dichroic ratio is preferable. The polymer may be any material that can immobilize liquid crystals as microcapsules.

The materials and conditions shown in the first embodiment can be used for the substrate 1, the substrate 7, and other conditions, but it is not necessary to subject the substrates to the alignment treatment.

(Embodiment 3) This embodiment shows an example in which the present invention is applied to a display device having a Swiss cheese structure.
The conditions of the substrate and electrodes used are the same as in Example 1. However, it is not necessary to perform the alignment treatment on the substrate electrode. The substrate 1 and the substrate 7 were fixed with a gap of 10 μm (not necessarily 10 μm, optimized depending on the application), and a mixture of liquid crystal and polymer precursor was enclosed in this gap. This was cured at 82 ° C. for 10 minutes to phase-separate the liquid crystal and the polymer. At this time, if no dichroic dye is added to the liquid crystal, it becomes a milky white when no electric field is applied, and a mirror when an electric field is applied. When a dichroic dye is mixed in the liquid crystal and an omnidirectional reflective electrode is used as the reflective electrode, the dye color is displayed when no electric field is applied, and the color of the omnidirectional reflector is displayed when an electric field is applied. . In each case, the brightness is improved by about 1.5 times as compared with the conventional one.

E7 (manufactured by Merck) as a liquid crystal and an epoxy resin precursor (EPON828, Mi as a polymer precursor)
ller Stephenson) and hexylamine as a curing agent, but as the polymer precursor, in addition to such a thermosetting resin, an acrylic resin precursor such as bisphenol acrylate, a methacrylic resin precursor, crotonate, cinnamate, An ultraviolet curable or electron beam curable resin precursor such as an epoxy resin precursor can be similarly used. Further, a thermoplastic resin such as ethyl cellulose may be used to be heated to be compatible with the liquid crystal, sealed in the gap between the substrates, and gradually cooled to be phase-separated.

(Embodiment 4) In this embodiment, an example in which this embodiment is applied to a display element in which liquid crystals are oriented and dispersed in an oriented gel network is shown. The conditions of the substrate and electrodes used are the same as in Example 1. The alignment treatment on the substrate electrode may be similarly performed. Board 1 and board 7 are separated by a gap 5
μm (not necessarily 5 μm, optimized depending on the application)
The liquid crystal and the polymer precursor were sealed in this gap. In addition, ultraviolet rays (intensity 3mW) in the liquid crystal phase
/ Cm2, wavelength 300 nm-400 nm) was irradiated for 10 minutes, and the liquid crystal and the polymer were phase-separated. At this time, the intensity of ultraviolet rays may be stronger or weaker than this, and even if the wavelength is shorter than this, it is cured. Moreover, you may irradiate an electron beam. At this time, if no dichroic dye is added to the liquid crystal, a mirror is formed without applying an electric field, and a milky white is formed by applying an electric field. When a dichroic dye is mixed in the liquid crystal, the dye color is displayed when no electric field is applied, and a milky white color appears when an electric field is applied, as in Example 1. In each case, the brightness is improved by about 1.5 times as compared with the conventional one.

E7 (manufactured by Merck & Co., Inc.) was used as the liquid crystal, and an acrylic resin precursor in which a long chain spacer such as an alkyl chain was inserted between bisphenol and acrylate was used as the polymer precursor. An ultraviolet curable or electron beam curable resin precursor such as an acrylic resin precursor, a methacrylic resin precursor, a crotonate, a cinnamate, or an epoxy resin precursor can be similarly used. A thermosetting resin such as an epoxy resin can also be used. Further, a thermoplastic resin such as ethyl cellulose may be used to be heated to be compatible with the liquid crystal, sealed in the gap between the substrates, and gradually cooled to be phase-separated.

(Embodiment 5) In this embodiment, a case in which a plurality of substrates having different refractive indexes are laminated together is used as the high refractive index substrate. As the substrate 1 used in the previous example, borosilicate glass, TaF3 (refractive index of about 1.8) and FDS1 (manufactured by HOYA, refractive index of about 2) were laminated in this order. When such a substrate was used in place of the substrate 1 of Examples 1 to 4, the brightness was 1.
I was able to improve it about twice.

As for the glass used, it is very effective to combine the glass so that the refractive index at the surface close to the liquid crystal layer becomes high. Any number of laminated glass may be used.

In this embodiment, an example in which the refractive index changes stepwise in the thickness direction of the substrate has been described, but a substrate having a continuous refractive index distribution in the thickness direction of the substrate as a high refractive index substrate is also the same. Can be used. For example, if a glass substrate is formed by a sol-gel method, a substrate having a refractive index distribution can be easily manufactured by impregnating a high-refractive material from one surface of the substrate and baking it. When a resin is used, the resin precursor may be gelated in the same manner, and the resin precursor having a different refractive index may be impregnated therein to complete the polymerization.

(Embodiment 6) In this embodiment, an example in which a two-terminal element or a three-terminal element is formed on one of the substrates sandwiching the liquid crystal / polymer layer is shown. FIG. 2 shows a simple cross-sectional view of the display device of this example. The same as Example 1 except that the two-terminal element was formed on the substrate 7. FIG. 3 shows an example in which a three-terminal element is formed. Even if the two-terminal element and the three-terminal element do not have the configurations shown in the drawings, they can be similarly used as long as they can drive the liquid crystal. In either case, a high refractive index substrate (TaF3, manufactured by HOYA) is used as the front substrate 1. Of course, the substrate as shown in Example 5 can be used as well. As the liquid crystal / polymer filled between these substrates, the materials of Examples 1 to 4 can be used. Any of the above-mentioned configurations is capable of performing large-capacity display which is 1.2 to 1.4 times brighter than a conventional liquid crystal / polymer dispersed large-capacity reflective display element using a two-terminal element or a three-terminal element. It has become possible. In this embodiment, the example in which the two-terminal element or the three-terminal element is formed on the back substrate is shown.
Of course, these can be formed on the front substrate. However, at this time, it is necessary to use a substrate having good heat resistance.

If a color filter is provided in this embodiment,
A large-capacity reflective color display can be realized.

Although the embodiments have been described above, the contrast can be remarkably improved by applying non-glare treatment, anti-reflection treatment, or both treatments to the surface of the display element in all the embodiments.

[0027]

As described above, according to the present invention, it is possible to provide a bright reflective display device having a wide viewing angle by using a substrate having a high refractive index as a substrate sandwiching a liquid crystal / polymer layer. Further, by combining with a two-terminal element or a three-terminal element substrate, a large-capacity bright reflective display element having a wide viewing angle can be realized.

[Brief description of drawings]

FIG. 1 is a simple cross-sectional view of a display element of Example 1.

FIG. 2 is a sectional view of a display element when a two-terminal element of Example 6 is used.

FIG. 3 is a sectional view of a display element when a three-terminal element of Example 6 is used.

[Explanation of symbols]

 1 high refractive index substrate 2 transparent electrode 3 liquid crystal 4 polymer 5 dichroic dye 6 electrode 7 substrate 8 protective layer 9 insulating layer 10 scan electrode 14 source electrode 15 gate electrode 16 semiconductor layer 17 drain electrode 18 gate insulating layer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hidehito Iizaka 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (5)

[Claims] 1. A reflective display device in which a liquid crystal and a polymer are dispersed in each other, wherein the refractive index of at least the surface of the front substrate near the surface in contact with the liquid crystal / polymer layer is 1 or more. element. 2. The reflective display element according to claim 1, wherein the refractive index is 1.5 or more. 3. The reflective display element according to claim 1, wherein the substrate is made of one kind of material. 4. The reflective display element according to claim 1, wherein the substrate has a refractive index distribution in the thickness direction of the substrate. 5. The reflective display element according to claim 1, wherein a two-terminal element or a three-terminal element is formed on at least one of the substrates sandwiching the liquid crystal / polymer.