JPH0990352A - Liquid crystal display element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display element which can give bright display with high contrast without using a polarizing plate by interposing a scattering type liquid crystal between a pair of substrates, forming reflection planes on the surface of the back substrate of the substrate pair where the polymer liquid crystal is in contact with, in such a manner that he plural reflecting planes making an angle >=42 deg. to <=70 deg. to the substrate plane are arranged with a pitch >=2μm to <=50μm. SOLUTION: Transparent electrodes 4, 5 such as ITO are formed on the back glass substrate 2, on which an acryl resin film is formed by printing under pressure and hardened while the film is pressed with a die which is subjected to ultra-precision processing by ion beam etching. Thus, projections like triangular prisms shown as electrodes 6 in the figure are formed and vapor deposition of aluminum is applied from the upper right side of the projection to deposit an aluminum reflecting film 7 on only the right slope of the projection. Then a liquid crystal panel is produced by an usual method. The obtd. liquid crystal display element has about 65% reflectance compared to about 25% reflectance of an element produced by a conventional method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element, and more particularly to a bright liquid crystal display element using liquid crystal and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, liquid crystal has been widely used as a medium whose refractive index is variable by voltage. The refractive index of the liquid crystal is different between the refractive index in the uniaxial direction of the molecule (ordinary light refractive index: n _o ) and the refractive index in the long axis direction of the molecule (extraordinary light refractive index: n _e ), and n _e is larger. The refractive index of the liquid crystal with respect to the incident light liquid crystal stand perpendicularly to the panel by the electric field applied to n _o, and the case where the liquid crystal is oriented in one horizontal direction to the substrate, polarization and the molecular long axis to polarization parallel N _e and n for the other polarization
will be _o .

The most widely used liquid crystal elements are the twisted nematic (TN) mode and the electric field controlled birefringence (ECB) mode. However, these modes require a polarizing plate and thus the transmittance (reflection) The rate is low and the display is dark.

Dynamic scattering mode (DSM) and polymer dispersed liquid crystal are available as modes without using a polarizing plate. In both cases, the DSM mode is transparent in the no-voltage state, and scattering occurs when a voltage is applied, and the polymer-dispersed liquid crystal, on the contrary, enters the scattering state in the no-voltage state.

In the polymer-dispersed liquid crystal, a low-molecular nematic liquid crystal is wrapped in a polymer matrix (microcapsule or porous material), and when no voltage is applied, incident light is scattered due to the mismatch of the refractive index between the polymer and the liquid crystal. Then, when a voltage is applied and the liquid crystal molecules stand up, the refractive indices for incident light match and the liquid crystal molecules become transparent. JP-A-5-34669 discloses a proposal for applying a polymer-dispersed liquid crystal to a direct-view display.

In the polymer microcapsules, since the liquid crystals are arranged along the spherical capsule wall surface, the refractive index thereof is close to the average value of the refractive index n _e in the major axis direction and the refractive index n _{o in} the minor axis direction, It becomes n _o when a voltage is applied. Refractive index anisotropy Δn
Is less than 0.3, there is no difference in refractive index between the polymer and the liquid crystal in the scattered state of 0.15. When the difference in refractive index between air and polymer (cellulose) is large like paper, backscattering occurs and the surface of the paper becomes bright white due to reflected light. However, when the difference in refractive index is small, scattering is mainly forward scattering and the reflecting surface is dark.

For this reason, in the polymer dispersed liquid crystal, a projection type display using a Schlieren optical system capable of obtaining a contrast between a forward scattering state and a transparent state has been announced.

There are several types of polymer-dispersed liquid crystals depending on the method of preparation, but the type that promotes polymerization by irradiation with ultraviolet rays has the best scattering performance. This type of polymer-dispersed liquid crystal is prepared by injecting a mixed solution in which a nematic liquid crystal, a monomer and an oligomer, which are polymer precursors, and a small amount of a polymerization initiator are compatibilized into an empty cell, and then irradiating with ultraviolet rays to The molecular precursor is polymerized to produce microcapsules.

[0009]

However, in the mode using the conventional polarizing plate, there is a problem that the display becomes dark when the reflective display is performed. A polymer-dispersed liquid crystal does not require a polarizing plate, but its backscattering is insufficient, so brightness and contrast are insufficient. Further, in the case of color display, a color filter is usually used, but the color filter reduces the amount of incident light, resulting in a dark display.

Further, since the polymer-dispersed liquid crystal mixed solution before polymerization contains a highly volatile monomer, when the vacuum injection method which is usually used is used, the monomer is volatilized and a desired microscopic amount is obtained. I can't make capsules. On the other hand, in order to prevent volatilization, it is unavoidable that air bubbles are mixed in when injection is performed in the atmosphere. There is a problem that the bubbles in the panel become white bright spots in the projection type display device and become black defects in the direct view type display.

In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide a liquid crystal display device which enables bright and high-contrast display without using a polarizing plate, and a manufacturing method thereof.

[0012]

In order to achieve the above object, the liquid crystal display device of the present invention has a scattering type liquid crystal sandwiched between a pair of substrates and is adjacent to a polymer liquid crystal of a back side substrate of the pair of substrates. On the substrate surface, 42 degrees or more with respect to the horizontal surface of the substrate 70
It has a structure in which a plurality of reflecting surfaces having an inclination angle of not more than 2 degrees are provided at a pitch of 2 μm or more and 50 μm or less. In the above description, the term "plurality" is a concept including many. The reflecting surface is preferably flat.

In the above structure, it is preferable that the width of the reflecting surface is 20% or more and 70% or less of the pitch, and the light absorbing surface is arranged behind the pair of substrates. Further, in the above-mentioned configuration, it is preferable that the inclined surface faces upward when viewed from the viewing direction of the display in order to improve the contrast.

Next, in the first method of manufacturing a liquid crystal element of the present invention, a pair of substrates is sandwiched by spacers having a predetermined particle size, and the periphery of the substrates is sealed except for two or more openings. After adhering the cells to form a cell, the cell is exposed to a depressurized chamber and the air inside the cell is evacuated, and is not compatible with the pre-polymerization liquid crystal of the polymer dispersed liquid crystal and the polymer precursor. A solvent that does not react is brought into contact with the two or more openings, and then the chamber is returned to atmospheric pressure to fill the inside of the cell with the solvent, and then at least one opening is filled with high pressure at atmospheric pressure. In the state where the liquid crystal before the polymerization of the molecular dispersed liquid crystal and the mixed solution of the polymer precursor are in contact with each other,
The solvent is discharged from an opening other than the at least one opening, the solvent inside the cell is replaced with the mixed solution, and then the mixed solution is polymerized.

In the above structure, the solvent is preferably ultrapure water from the viewpoint of cost. Here, ultrapure water refers to water obtained by reverse osmosis membrane treatment which is usually used in the semiconductor industry or the like, and water having an electric resistivity of 16 megaΩ · cm or more and having very few impurities. Freon or the like can be used as the other solvent.

Further, in the above construction, it is preferable that the solvent is discharged by heating the vicinity of the opening other than at least one opening in contact with the mixed solution to a temperature not lower than the boiling point of the solvent.

Next, in the second method of manufacturing a liquid crystal element of the present invention, a pair of substrates are sandwiched by spacers having a predetermined particle size, and the periphery of the substrates is sealed except at least one opening. To create a cell by bonding, the cell is composed of a display panel portion and a preliminary space provided in the farthest portion from the opening, in a state in which the cell is exposed to a depressurized chamber and air inside the cell is exhausted, A solvent that does not chemically react with the liquid crystal before polymerization of the polymer-dispersed liquid crystal and the polymer precursor is brought into contact with the opening, and then the chamber is returned to atmospheric pressure, and the solvent having a volume smaller than that of the preliminary space is opened. Part of the polymer precursor, and then, at a pressure higher than the saturated vapor pressure of the polymer precursor, a liquid to be brought into contact with the opening is mixed with the liquid crystal before polymerization of the polymer dispersed liquid crystal and the polymer precursor. Melting And left switch to, and satisfies the mixed solution inside the display panel.

In the above-mentioned constitution, it is preferable that the solvent is incompatible with the mixed solution of the liquid crystal before polymerization of the polymer dispersed liquid crystal and the polymer precursor, since the dissolution of impurities can be avoided.

Light entering the liquid crystal panel from the air is
Refracts according to Snell's law. Since the refractive index of glass is about 1.5, light incident on the glass substrate of the liquid crystal panel at an incident angle of 90 degrees enters the liquid crystal layer at a refraction angle of 41.8 degrees. Since the light incident from the front of the panel is not refracted, the incident light distributed at the incident angle of 0 to 90 degrees becomes the refracted light distributed at 0 to 42 degrees. When a voltage is applied to a scattering type liquid crystal such as a polymer-dispersed liquid crystal and it is in a transparent state, the refracted light travels straight as it is and is reflected by a reflecting surface having an inclination angle of 42 degrees. The light is incident on the glass / air interface at an angle of, and is totally reflected and cannot be emitted from the panel, resulting in a black display. On the other hand, when the liquid crystal is in the scattering state,
The light reflected by the reflecting surface is scattered to obtain a bright white display.

In the first to second manufacturing methods of the liquid crystal element of the present invention, the inside of the cell is evacuated in the decompression chamber,
Since the opening of the seal is closed with a solvent, air can be prevented from entering the cell. Next, to prevent the monomer from volatilizing,
After the mixed solution containing the monomer is brought into contact with the solvent under atmospheric pressure or a pressure higher than the saturated vapor pressure of the monomer, the solvent is expelled from the outside of the cell or the inside of the display panel to the preliminary space, and the mixed solution is used instead. By introducing into the inside, the mixed solution can be injected without the inclusion of bubbles.

[0021]

EXAMPLES Specific examples will be described in detail below. (Embodiment 1) FIG. 1 is a sectional view of a liquid crystal display device of the present invention. Glass substrate (5 cm) on the back side (as seen by the observer)
Corners 2 have transparent electrodes 4 and 5 made of, for example, indium-tin oxide alloy (ITO) formed thereon, and acrylic resin is pressure-film printed on the transparent electrodes 4 and 5 and then ultra-precision processed by ion beam etching. By pressing with a metal mold and curing in a state where it was molded, a protrusion having a shape in which a triangular prism like the electrode 6 was turned down was provided. The height of the protrusion is 5 μm, the right inclined surface is 45 degrees with respect to the horizontal plane of the substrate, and the left inclined surface is about 8
It was molded at 0 degrees so that a plurality of protrusions were arranged in parallel at a pitch of 10 μm. Upper right of this board (60 degrees from horizontal)
Aluminum was vapor-deposited to a thickness of 200 nm to deposit the aluminum reflection film 7 only on the right inclined surface of the protrusion.

This substrate 2 and the counter glass substrate 1 on which the transparent electrode 3 is formed are dispersed with 12 μm spherical spacers and then bonded with a sealing resin 9 to form an empty cell, and a polymer dispersion before polymerization is carried out by an injection method described later. Polymer liquid crystal 8 was prepared by injecting mold liquid crystal and polymerizing it by irradiation with ultraviolet rays. The composition of the mixed solution before polymerization is as follows: Nematic liquid crystal E-8 (80% by weight) manufactured by BDH, UV-curable acrylic resin monomer 2 ethylhexyl acrylate and oligomer, and a polymerization initiator (Irgacure 651) 0.1% by weight.
It is possible to mix. The particle size of liquid crystal microcapsules is 1
The liquid crystal is in a scattering state of 8a when no voltage is applied, and when a voltage is applied, liquid crystal molecules are vertically aligned as in 8b to be in a transparent state. However, the scattering when no voltage is applied is almost forward scattering.

A black light-absorbing plate 10 is placed behind this panel so that the inclined reflecting surface 7 faces obliquely upward, that is, the right side of the paper faces upward from the observer, and the fluorescent light obliquely upward. The liquid crystal display panel was observed almost from the front under the lamp illumination. The light absorbing plate 10 is formed by printing black paint on the glass surface, for example.

When the incident light ray is incident on the liquid crystal layer 8a in the scattered state on the electrode 5 as shown by the solid line 11, the light reflected by the reflection film 7 is scattered again and returns to the observation direction in many cases. Therefore, the reflectance is 25% when the substrate 2 has only transparent electrodes.
On the other hand, the structure of the liquid crystal display device of the present invention was improved to 65%, while it was about the same. If the interval between the plurality of inclined reflective films 7 is further narrowed, the probability that light will hit the reflective surface increases, but it becomes difficult for light to return to the liquid crystal layer. Therefore, it is better to leave the interval between adjacent reflective films as in this embodiment. good. In this embodiment, the pitch of the reflecting surface is 10 μm and the width of the reflecting surface is 5 μm, but if the width of the reflecting surface is 20% or more and 70% or less of the pitch, the effect of improving the reflectance is high. Further, the pitch at which the reflecting surface is provided is preferably 2 μm or more, which does not increase diffraction. Also,
The height of the protrusion is at most 10 μm because the thickness of the liquid crystal layer is 10 μm or less (the width is 1 when the tilt angle is 45 °).
0 μm), the maximum pitch is preferably 50 μm or less.

On the other hand, an incident light beam 12 having a small incident angle (an angle formed with the interface normal) is incident on the liquid crystal layer 8b which is transparent by applying a voltage from the electrode 6, and the light reflected by the inclined reflection film 7 is , Is reflected from the substrate in a slightly downward direction from the horizontal direction, hits the back surface of the adjacent reflection film, is emitted from the panel, and is absorbed by the light absorption surface behind. As the angle of incidence increases, the light reflected by the reflective film re-enters the liquid crystal layer and strikes the interface between the upper substrate and the air, but it is always totally reflected. For example, when an incident ray 13 having an incident angle of 85 degrees is reflected by the reflection film 7 at a refraction angle of 42 degrees,
Since it is incident on the interface between the upper substrate and the air at 48 degrees, it is totally reflected and cannot be emitted to the observer side. Light that does not strike the inclined reflecting surface is absorbed by the light absorbing surface 10. Therefore, when the liquid crystal was in a transparent state, almost no reflected light was observed and a black display with a reflectance of 5% was obtained.

The angle of the inclined surface may be 42 degrees or more, but if it is too vertical, the white display in the scattering state becomes dark, so it is preferably about 70 degrees or less. Further, in the case of the reflective display element, most of the incident light is incident from above the panel, so that the inclined surface can be made brighter when it is directed upward as seen from the observer as in this embodiment.

As a result, the contrast of the liquid crystal display device of the present invention was about 13: 1, and it was possible to achieve a high contrast display which is more than twice as high as that of the conventional example using only transparent electrodes. As described above, the display element of the present invention realizes a display with a wide viewing angle, which is a reflective bright color display. Although the polymer dispersion type liquid crystal is used as the scattering / transmission variable medium in the present embodiment, the present invention is not necessarily limited to this, and the mode for switching between the focal conic state and the transparent state of the cholesteric-nematic phase transition type liquid crystal or the dynamic scattering mode is also used. Good.

Next, a method of manufacturing the liquid crystal element of the present invention will be described with reference to the conceptual diagram of FIG. After spraying spacers on one glass substrate, a sealing resin is printed by screen printing on a counter substrate of approximately the same size to form a seal 21, and then both substrates are bonded to form a cell 20. In FIG. 2, the cell 20 is shown in plan view. Of these, the portion below the dashed-dotted line of the cell 20 is the display panel portion 24 in which the pixel electrode is formed, and the portion surrounded by the seal 21 above the dashed-dotted line is the preliminary space 23. First, the cell 20 is put in the chamber 18, the exhaust valve 26 is opened, and the air in the chamber and the internal space of the cell 20 is exhausted to 0.1 torr. In this state, as shown in the figure, the opening 19 of the seal is brought into contact with the nematic liquid crystal 22 contained in the container so that the liquid crystal completely closes the opening, and then nitrogen gas is introduced from the exhaust valve 26 into the chamber. When the pressure is returned to atmospheric pressure, the nematic liquid crystal 22 gradually enters the cell. And if the chamber lid opens,
Immediately, when the opening 19 of the cell 20 is brought into contact with the mixed solution 25 of the polymer-dispersed liquid crystal before polymerization, which has been facilitated in advance, the nematic liquid crystal 22 and the mixed solution 25 are brought into contact with each other by the surface tension, and the nematic liquid crystal is brought into contact. The mixed solution 25 is injected into the cell as 22 goes into the back, and finally the nematic liquid crystal 22 enters the preliminary space 23, and the display panel section 24 is entirely occupied by the mixed solution. Then, the cell 20 was cut along the one-dot chain line, and the display panel 24 was irradiated with ultraviolet rays to complete the polymer dispersed liquid crystal element.

As described above, by using the method for manufacturing a liquid crystal element according to the present invention, it is possible to inject a mixed solution without volatilizing a monomer and mixing bubbles. Since the monomer used in this example volatilizes at about 0.5 atm,
Although the mixed solution was injected at atmospheric pressure, the mixed solution may be injected at a pressure at which the saturated vapor pressure at which the volatilization of the monomer starts is higher, and the injection may not be at atmospheric pressure. The nematic liquid crystal was used in the first injection in the chamber, but the present invention is not limited to this, and a solvent that does not chemically react with the mixed solution, does not pollute the inside of the cell, and does not volatilize during depressurization is used. If so, it is not limited to this. However, in the case of nematic liquid crystal, since it is one component of the mixture, it may be compatible, but in the case of other solvents, a solvent that is not compatible with the mixed solution is more preferable.

Example 2 A method of manufacturing a second liquid crystal element of the present invention will be described with reference to the conceptual diagram of FIG. Cell 2
No. 0 has two openings, one at the top and one at the bottom, and like the first embodiment, after exhausting the inside of the cell in the chamber, the specific resistance stored in the funnel 33 equipped with the dispenser valve and the receiving tray 32 was 16 megaΩ.・ The ultrapure water 29 of cm or more, the opening 3
When injected from 0 and 31, the inside of the cell was occupied by ultrapure water without bubbles. And immediately after taking it out of the chamber,
The opening 30 was brought into contact with the mixed solution 25 of polymer-dispersed liquid crystal before polymerization, and in that state, the glass near the other opening 31 was heated to 102 ° C. by the heater 34. Then, as the ultrapure water was evaporated and discharged from the opening 31, the mixture 25 was injected, and the mixed solution 25 was injected into the cell without bubbles. The protrusions (reflection surfaces) are preferably formed in a stripe shape inside the seal 21 in the direction of the solution flow, that is, in the direction of the vertical stripes in FIGS.

In the present embodiment, ultrapure water was first injected, but it is not limited to this as long as it is a solvent that does not chemically react with the mixed solution and is incompatible.

[0032]

According to the present invention, a scattering type liquid crystal is sandwiched between a pair of substrates, and the substrate surface adjacent to the polymer liquid crystal on the back side substrate of the pair of substrates is 42 degrees or more and 70 degrees or less with respect to the horizontal plane of the board. By providing a plurality of reflecting surfaces having an inclination angle of 2 μm or more and 50 μm or less, it is possible to realize a liquid crystal display element that enables bright and high-contrast display without using a polarizing plate. That is, the liquid crystal display device of the present invention can realize a bright reflective display that does not require a polarizing plate by providing an inclined reflective surface behind a scattering liquid crystal such as a polymer dispersed liquid crystal. Further, the method for producing a liquid crystal element of the present invention, by injecting a solvent that does not volatilize in vacuum and then substituting it with a mixed solution of a polymer-dispersed liquid crystal before polymerization at atmospheric pressure, to prevent volatilization of the monomer, Can be injected without

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display device of the present invention.

FIG. 2 is a conceptual diagram of a method for manufacturing a liquid crystal element of the present invention.

FIG. 3 is a conceptual diagram of a second liquid crystal element manufacturing method of the present invention.

[Explanation of symbols]

 1, 2 Glass substrate 3, 4, 5 Transparent electrode 6 Electrode 7 Aluminum reflective film 8 Polymer dispersed liquid crystal 8a, 8b Liquid crystal 9 Seal resin 10 Light absorbing plate 11 Incident light beam 12 Incident light beam 13 Incident light beam 18 Chamber 19 Seal opening 20 cell 21 seal 22 nematic liquid crystal 23 preliminary space 24 display panel 25 mixed solution of polymer dispersed liquid crystal before polymerization 26 exhaust valve 29 ultrapure water 30, 31 opening 32 saucer 33 funnel 34 heater

Claims (8)

[Claims] 1. A scattering type liquid crystal is sandwiched between a pair of substrates, and an inclination angle of 42 degrees or more and 70 degrees or less with respect to a horizontal plane of the substrate is provided on a substrate surface of the back side substrate of the pair of substrates adjacent to the polymer liquid crystal. A liquid crystal display element in which a plurality of reflective surfaces are provided at a pitch of 2 μm or more and 50 μm or less. 2. The width of the reflecting surface is 20% or more and 70% of the pitch.
The liquid crystal display element according to claim 1, wherein the light absorption surface is arranged behind the pair of substrates. 3. The liquid crystal display element according to claim 2, wherein the inclined surface faces upward when viewed from the viewing direction of the display. 4. A pair of substrates are adhered to each other by sandwiching a spacer having a predetermined particle size and sealing the periphery of the substrates except for two or more openings to form a cell, and then depressurizing the cell. In a state in which the air inside the cell is exhausted by exposing it to the above chamber, a solvent that is not compatible with the pre-polymerization liquid crystal of the polymer dispersed liquid crystal and the polymer precursor and does not cause a chemical reaction is introduced into the two or more openings. After contacting, the chamber is returned to atmospheric pressure, the inside of the cell is filled with the solvent, and then at least one opening at atmospheric pressure is filled with the liquid crystal before polymerization of the polymer dispersed liquid crystal and the polymer precursor. In a state where the mixed solution is in contact, the solvent is discharged from an opening other than the at least one opening, the solvent inside the cell is replaced with the mixed solution, and then the mixed solution is polymerized. Manufacture of liquid crystal elements Method. 5. The method for producing a liquid crystal element according to claim 4, wherein the solvent is ultrapure water. 6. The method for producing a liquid crystal device according to claim 4, wherein the solvent is discharged by heating the vicinity of the opening other than at least one opening in contact with the mixed solution to a temperature equal to or higher than the boiling point of the solvent. 7. A cell is produced by adhering a pair of substrates by sandwiching a spacer having a predetermined particle size and sealing the periphery of the substrate except at least one opening, and the cell is a display panel section. Liquid crystal and polymer precursor before polymerization of polymer-dispersed liquid crystal in a state in which the cell is exposed to a depressurized chamber and air inside the cell is exhausted, and a preliminary space provided farthest from the opening. After contacting a solvent that does not chemically react with the opening with the chamber, the chamber is returned to atmospheric pressure, and the solvent having a volume smaller than the preliminary space is introduced into the cell through the opening, and then the polymer precursor is added. In a pressure higher than the saturated vapor pressure of the body, the liquid to be brought into contact with the opening is switched to a mixed solution of the polymer liquid crystal before polymerization of the polymer dispersed liquid crystal and the polymer precursor and left to stand, and the mixed solution is displayed as described above. A method for manufacturing a liquid crystal element, characterized by filling the inside of a panel. 8. The method for producing a liquid crystal device according to claim 7, wherein the solvent is incompatible with the mixed solution of the liquid crystal before polymerization of the polymer-dispersed liquid crystal and the polymer precursor.