KR100269353B1 - An airogel liquid crystal display and a method for manufacturing thereof - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to remove a polarizer and a polymide and to control the size and density of a liquid crystal pore. CONSTITUTION: Neighboring pores(13') are connected through an interconnection path(13"). A liquid crystal layer(13) formed in the pores(13') and the interconnection path(13") can be controlled by the dimension and density of the pores(13') At an OFF state where a voltage is not applied, an incident light is scattered by a difference between a reflective factor of the liquid crystal layer(13) molecular and a reflective factor of an air gel(14) molecular. If an external voltage is applied, the liquid crystal molecular of each liquid crystal layer(13) is uniformly arranged in one direction where an electric field is formed. Thus no scattering is caused at a surface(13a) between the liquid crystal layer(13) and the air gel layer(14).

Description

Liquid crystal display using porous airgel and manufacturing process thereof {AN AIROGEL LIQUID CRYSTAL DISPLAY AND A METHOD FOR MANUFACTURING THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a manufacturing process thereof, in which a liquid crystal layer is formed in a pore of an aerogel so that an alignment layer is not required and a polarizer is not required.

TN (twisted nematic) liquid crystal displays (TNs), which are generally used, have recently been used in notebook computers and the like due to their stable display performance and their applicability to be used in either active or passive matrix. It has been applied to products requiring low power consumption, and it has become a mainstream liquid crystal display device.

However, since the polarizing plate must be used, 70-80% of the light incident on the display element is actually lost, and there is a problem in luminance, and many problems such as light scattering phenomenon and phase distortion due to the alignment process are generated. In particular, the former problem is that since the power consumption of the TN display element itself is low, it is necessary to increase the power of the backlight and the like, which is a great obstacle.

In order to solve the above problems, there is a polymer dispersed liquid crystal (PDLC) display device that is proposed. This is a liquid crystal in which a liquid crystal is dispersed as a fine particle in a polymer, in combination with a technique of dispersing a liquid crystal and a material other than the liquid crystal and operating it by using the difference in refractive index of the two materials, and then encapsulating the liquid crystal. It is a display device. In this device, an alignment film and a polarizing plate are not necessary.

1 is a cross-sectional view of the above-described PDLC device. Reference numeral 2 denotes electrodes attached to two substrates 1, and the light transmittance of the liquid crystal 3 dispersed in the polymer 4 can be changed. have. The liquid crystal 3 dispersed in the above-described polymer 4 is sealed by the actual material 5. The liquid crystal is dispersed in a polymer in a capsule form to form liquid crystal fine particles (3) and the molecular arrangement is changed according to the voltage applied by the electrode.

The above structure utilizes the phenomenon that, when the structure itself is transparent but does not dissolve with each other, and when two kinds of liquids having different refractive indices are forcibly mixed, the entirety becomes a white opaque cream. This phenomenon occurs not only because each liquid in the mixed state becomes opaque, but also because light is scattered at the interface when light passes through the interface due to different refractive indices of the two liquids.

When the liquid crystal is formed into a small capsule in the polymer and dispersed, as shown in FIG. 2 (a), the light incident due to the difference in refractive index between the liquid crystal particles 3 and the polymer 4 in a state where no voltage is applied. Are all scattered and become milky opaque. From the outside, the liquid crystal fine particles 3 having a refractive index distribution in the range of n ₀ to n _e are retained in the polymer having a refractive index n _p , so that the liquid crystal particles become opaque, which results in scattering light. However, when a voltage is applied from the outside, as shown in FIG. 2 (b), the liquid crystals of the liquid crystal particles 3 are aligned in the electric field direction, and thus the refractive index n ₀ seen in the arrow direction is constant for all particles. If a liquid crystal in which n ₀ is matched with the refractive index n _p of the polymer 4 as the dispersion catalyst is selected, scattering does not occur at the interface between the two and appears coarse.

Therefore, the polymer dispersed liquid crystal display device can be applied to a display element in which the amount of light transmittance changes according to the ON / OFF voltage.

However, the polymer dispersed liquid crystal display device cannot control the size and density of the liquid crystal fine particles, and it is difficult to freely control the scattering of light generated at the interface, so that it is not reproducible to secure an opaque screen in the OFF state. Hysteresis occurs due to difficulty in physicochemical control of the interface, and thus there is a limit in gray level when applied to a display.

Accordingly, the present invention was devised to solve the above problems, and it is possible to remove the polarizing plate and the alignment layer, and to provide an airgel liquid crystal display device and a method of manufacturing the same, which can freely control the size and density of the liquid crystal layer pores. It aims to provide.

In order to achieve the above object, the liquid crystal display device of the present invention, a porous airgel layer having a plurality of pores; A liquid crystal formed in the pore; And a switching element for controlling the light transmittance of the liquid crystal. The airgel is preferably a transparent silica airgel, and it is preferable to add a dye in order to improve the contrast ratio and the light scattering state. Further, in addition to the above-described configuration, it is possible to further configure the color filter and the TFT, and it is also possible to further configure the reflecting plate for application to the reflective liquid crystal display device.

In addition, the manufacturing process for obtaining the liquid crystal display device comprises the steps of: forming a wet gel layer on a substrate on which an electrode is formed; Drying the wet gel by supercritical drying to form a porous airgel having a plurality of pores; And injecting liquid crystal into the pores of the porous airgel. In addition to this method, the mixture of the airgel and the liquid crystal is mixed by a homogenizer; And forming an airgel-liquid crystal layer on the substrate on which the electrode is formed.

1 is a diagram showing a cross section of a conventional polymer dispersed liquid crystal (PDLC).

2 is a view showing the operation principle of the PDLC of FIG.

3 is a cross-sectional view of an airgel liquid crystal display device according to the present invention;

4 is a view showing an application example of the airgel liquid crystal cell of the present invention.

5 is a view showing a pattern of the pore of the airgel liquid crystal device of the present invention.

6 is a view showing an embodiment of a manufacturing process of a liquid crystal display of the present invention.

7 is a view showing another embodiment of the manufacturing process of the liquid crystal display device of the present invention.

Low density silica airgel, one of the new transparent porous materials, was developed in the 1930s by producing microporous airgel by removing liquid components without destroying the microstructure of water glass through supercritical drying. General silica aerogels are used in all fields that require ultra-insulation, from transparent insulating glass to insulating refrigerators.

The silica aerogel is composed mainly of silica having abundant chemical properties in the earth's crust. Eggplants are made using supercritical liquids.

This airgel is manufactured by a sol-gel process and a supercritical fluid drying process, and can produce an airgel having various characteristics according to operating parameters (starting material, temperature, pH, catalyst, etc.). In general, the airgel manufacturing process uses a sol-gel process to prepare a wet gel, which is then subjected to two separate processes of drying the wet gel using a supercritical fluid process to obtain an airgel. In the sol-gel process, it is possible to form pores of a desired size and density depending on the gelation time, the amount of starting material, and the conditions of the supercritical drying process.

In order to apply the airgel to the liquid crystal display device, the airgel layer of the present invention forms a pore 13 ', as shown in FIG. 3, and the pore 13' is formed with a neighboring pore 13 '. It is connected by a connection passage 13 ". Therefore, the liquid crystal layer 13 formed in this pore 13 'and the connection passage 13" can be controlled according to the size and density of the pore mentioned above. . In general, since the liquid crystal is an anisotropic material having different refractive indices of light depending on the direction, as shown in FIG. 3 (a) in the OFF state, the refractive index of the molecules of the liquid crystal layer 13 and the molecules of the aerogel 14 are different. All of the incident light is scattered by the difference with the refractive index and becomes opaque. Looking at this state from the outside, since the liquid crystal layer 13 having the refractive index distribution with the refractive index of the molecules of the liquid crystal layer 13 is n _{o to} n _e is dispersed in the airgel layer 14 having the refractive index n _a , It becomes opaque by scattering. That is, the combination of the liquid crystal layer and the airgel layer 14 described above can be used as an element for scattering light.

However, if the external voltage is applied, Fig. 3 (b) and the like, so that the liquid crystal molecules of the liquid crystal layer 13 is uniformly aligned in the direction in which the electric field is formed, the normal refractive index of the liquid crystal molecules (n _o) is in all of the particles It becomes constant. Therefore, since the liquid crystal is selected such that the refractive index n _a of the airgel is equal to the normal refractive index n _o of the liquid crystal molecules, scattering does not occur at the interface 13a between the liquid crystal layer 13 and the airgel layer 14. Without transparency.

The fabricated airgel liquid crystal cell and a voltage applied thereto are shown in FIG. 4. 4 (a) is opaque because the liquid crystal molecules of the liquid crystal cell are irregularly dispersed before voltage application, and when voltage is applied, the liquid crystal molecules become transparent as shown in FIG. 4 (b) to read characters under the liquid crystal cell. It becomes possible.

In the above-described airgel liquid crystal display device, the size and density of the pore 13 'on which the liquid crystal layer 13 is formed can be freely controlled according to the composition ratio and process conditions of the starting material in the manufacture of the airgel. In addition, the surface treatment of the interface 13a between the liquid crystal layer 13 and the airgel layer 14 also makes the hydrogel hydrophobic by the esterification reaction on the surface, so that an airgel strong in moisture can be obtained without shrinkage in the air.

In addition, in order to increase the contrast in the liquid crystal display device and to improve the opacity caused by light scattering in the OFF state of the liquid crystal, it is preferable to add a dye to the airgel layer, and to add a blue or black dye. More preferred.

In addition to the structure shown in FIG. 3, the airgel liquid crystal display device may be a solid that can maintain a shape of the airgel layer. Thus, the existing substrate may be removed, and a lightweight material such as a plastic substrate may be used. In addition, a TFT layer and a color filter may be additionally formed on the substrate to be applied as a general color display, and a reflection plate may be further configured to be applied to a reflective LCD which increases the scattering phenomenon.

In addition, the above-described pore 13 'can be applied in various forms as necessary. For example, various types of pores as shown in FIG. 5 are possible.

The airgel liquid crystal display of the present invention uses airgel as a matrix for dispersing liquid crystal molecules, and unlike PDLC, the pore size can be controlled from several nm to several tens of micrometers, and the refractive index ranges from 1.06 to 1.65. Because of the large range of the liquid crystal applicable. In addition, since the transmittance of light in the airgel is constant in the visible region, it is possible to obtain a liquid crystal display device having high reliability in maintaining a stable scattering state.

The manufacturing process for obtaining the airgel liquid crystal display device described above is as follows. First of all, the sol-gel process for obtaining the aerogel may be performed by using a catalyst such as metal alkoxide such as tetra-ethylorthosilicate (TEOS) or tetra-methylorthosilicate (TMOS), water and hydrochloric acid (HC1), and ammonium hydroxide (NH ₄ OH). Used. That is, the alkoxide solution, water, and hydrochloric acid (HC1) were optimized in a mixed molar ratio to make a mixed solution. At this time, the alcohol was not added, and the alkoxide and water were present in one phase by the alcohol (alcohol) produced by the reaction. The hydrolysis reaction of the reactants described above was simply stirred and reacted for about 10 hours. The alcohol produced in the hydrolyzed silica mixture solution was not removed, and water and NH ₄ OH were mixed at an optimized molar ratio, and a calculated amount of nonalcoholic solvent was mixed for density control. It was mixed using. The mixed solution was poured into a test tube or various types of molds and sealed, followed by polymerization in a constant temperature bath at a constant temperature to maintain gelation. The gelation time was set to the time until the interface of the sole was not moved by tilting the test tube containing the sol solution by 90 °.

Subsequently, in the supercritical process, the wet gel obtained in the sol-gel reaction was used as carbon dioxide as a supercritical solvent. The wet gel is placed in an autoclave and sealed to supply carbon dioxide to completely fill the reactor with liquid carbon dioxide. Liquid carbon dioxide is pumped to remove the mixed solution in the wet gel. Supercritical is maintained by raising temperature and pressure above the critical point of carbon dioxide. After maintaining a certain time, slowly release carbon dioxide and decompression to atmospheric pressure to open the reactor and take out the aerogel.

The aerogels prepared by the above-described process have hydroxy groups on the surface thereof, thereby making them hydrophilic, thus condensation occurs and moisture in the air is very well absorbed. Therefore, in order to make the surface of the airgel hydrophobic, a methoxylation reaction is carried out for at least 4 hours at a temperature of 150 ° C. or higher.

6 and 7 show an embodiment of a process for applying the airgel layer obtained by the above process to a liquid crystal display device.

6 (a) is placed in a container of the aerogel and the liquid crystal obtained by the above method, and mixed by the homogenizer 21 to form a liquid crystal-airgel mixture. Thereafter, as shown in FIG. 6A, the liquid crystal-airgel layer 16 is formed on the substrate 11 on which the electrode 12 is formed. On the substrate 11 on which the liquid crystal-airgel layer 16 is formed, another substrate 11 having the electrode 12 formed by the real material 15 is sealed and bonded.

FIG. 7A shows a process of forming the airgel layer 14 on the substrate 11. The wet gel 17 for obtaining the airgel is formed on the substrate 11 on which the electrode 12 is formed, placed in the high pressure reactor 22, and sealed to supply carbon dioxide. The temperature and pressure of the high-pressure reactor 22 is raised above the critical point of carbon dioxide to maintain a supercritical state. After a certain time, the carbon dioxide is slowly released and reduced to normal pressure to obtain a substrate having a porous airgel layer as shown in FIG. By injecting liquid crystal into the pore 13 'formed on the airgel 14 as shown in FIG. 7 (c), an airgel liquid crystal display device is obtained.

Unlike the conventional manufacturing method, the papermaking method for obtaining the liquid crystal display of the present embodiment does not require an alignment process such as rubbing for the arrangement of liquid crystal molecules, and thus the alignment film coating process and the alignment process are excluded. Simplification is possible. In addition, since a device such as a spacer for maintaining a gap of the liquid crystal substrate, a polarizer and an analyzer for polarizing light, and a device such as a compensation film are not required to compensate for light, each forming process is eliminated, thereby simplifying manufacturing costs. Savings.

The present invention may of course be applied to a reflective liquid crystal display device in which an aluminum (Al) layer and a reflective layer are formed on a substrate to increase scattering effect in addition to the above-described method.

According to the present invention, it is possible to remove a polarizing plate and an alignment layer in manufacturing a liquid crystal cell. Therefore, not only the cost of the polarizing plate can be reduced and the alignment process can be simplified, but also there is no loss of light due to the polarizing plate, so that it is possible to reduce the waste of power caused by light generation. In addition, since the manufacturing process of the airgel is stabilized, it is possible to form a liquid crystal pore having a desired density and size, thereby providing a liquid crystal display device having high reliability of image quality.

Claims (12)

Board; A transparent electrode formed on the substrate; A porous airgel layer having a plurality of pores formed on the projection electrode; A liquid crystal formed in the pore; And An airgel liquid crystal display device comprising a switching device for controlling the light transmittance of the liquid crystal. The aerogel liquid crystal display device according to claim 1, wherein the airgel layer contains a transparent silica airgel. The airgel liquid crystal display device according to claim 1, wherein a dye is added to the airgel layer. The aerogel liquid crystal display device according to claim 1, wherein the pores are connected to neighboring pores by a connection passage. The aerogel liquid crystal display device according to claim 1, wherein the substrate is made of plastic or glass. The aerogel liquid crystal display device according to claim 1, wherein a reflection plate is further formed inside the substrate. The airgel liquid crystal display device according to claim 1, wherein the starting bill forming the airgel layer is a metal alkoxide or a silica alkoxide. Forming a wet gel layer on the substrate on which the electrode is formed; Drying the wet gel layer by supercritical drying to form a porous airgel having a plurality of pores; And Airgel liquid crystal cell manufacturing process comprising the step of injecting a liquid crystal into the pore of the porous airgel. The airgel liquid crystal cell manufacturing process according to claim 8, wherein the supercritical solvent for supercritical drying is carbon dioxide. The airgel liquid crystal cell manufacturing process according to claim 8, wherein after the supercritical drying in the airgel layer forming step, a methoxylation step is further configured on the surface of the airgel. Forming a wet gel; Drying the wet gel by supercritical drying to form an airgel; Mixing the airgel-liquid crystals described above to form an airgel-liquid crystal mixture; The airgel liquid crystal cell manufacturing process comprising the step of forming the airgel-liquid crystal layer by laminating the airgel-liquid crystal mixture on the substrate on which the electrode is formed. 12. The process of claim 11, further comprising laminating a separate substrate on which the separate electrode is formed on the airgel-liquid crystal layer formed on the substrate.

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