KR19990009548A - LCD and its manufacturing method - Google Patents

Abstract

The present invention discloses a liquid crystal display device using the vertical alignment of liquid crystal molecules and a method of manufacturing the same. The liquid crystal display device may include a first substrate; A second substrate provided to face the first substrate; A transparent electrode layer formed on each of the first and second substrates; an alignment layer formed on each of the transparent electrode layers; Polarizing plates provided on outer surfaces of the first substrate and the second substrate, respectively; And a polymer network liquid crystal layer made of a nematic liquid crystal and a polymer having negative dielectric anisotropy on the first substrate and the second substrate. The liquid crystal display device of the present invention can freely adjust the pretilt angle of the liquid crystal molecules to increase the response time of the cell and to secure the viewing angles of 140 degrees at the left and right and 120 degrees at the top and the bottom. In addition, since there is no refractive index anisotropy in the long axis direction of the liquid crystal molecules in the state where no voltage is applied, contrast is 200: 1 or more.

Description

LCD and its manufacturing method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a method of manufacturing the same. Unlike the horizontal alignment in conventional twisted nematic (TN) and super twisted nematic (STN) liquid crystal display devices, a liquid crystal material having negative dielectric anisotropy as a liquid crystal material (-) A liquid crystal display device using a material and a method of manufacturing the same.

Currently, the mainstream liquid crystal display devices are twisted nematic (TN) and super twisted nematic (STN) active matrix thin film transistor liquid crystal display devices. However, since the liquid crystal display elements have a narrow viewing angle, a method of vertically aligning the liquid crystal material using negative liquid crystal dielectric anisotropy has been proposed to solve this problem.

1 is a view showing the operation principle of a conventional liquid crystal display device using the horizontal alignment of liquid crystal molecules.

Referring to this, the transparent electrode layers 13 and 14 and the alignment layers 15 and 16 are sequentially disposed on the first substrate 11 and the second substrate 12 provided to face the substrate. Formed. The liquid crystal layer 18 is formed between the first substrate 11 and the second substrate 12. This liquid crystal layer 18 is composed of a nematic liquid crystal 17 having a negative dielectric anisotropy.

In the liquid crystal display device having such a structure, when no voltage is applied (OFF), the liquid crystal molecules are arranged so as to be perpendicular to the substrate. When a voltage is applied (ON), the liquid crystal molecules are rearranged in a direction parallel to the substrate based on negative dielectric anisotropy.

Generally, the pretilt angle depends on the surface alignment treatment of the liquid crystal material or the liquid crystal display panel substrate. Therefore, by the rubbing treatment of the alignment films 15 and 16, the tilt direction of the liquid crystal molecule array in a voltage application state can be appropriately controlled.

In the liquid crystal display device as described above, compared to the conventional TN and STN methods, the viewing angle is wider and the foreground decline generated when displaying halftones can be suppressed. However, there is a problem that the response speed of the liquid crystal molecules according to the application of voltage is slow.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a liquid crystal display device capable of solving the above problems and increasing the response speed and freely adjusting the pretilt angle according to the magnitude of the applied voltage.

Another object of the present invention is to provide a method of manufacturing the liquid crystal display device.

1 is a view showing the operation principle of a conventional liquid crystal display device,

2 is a view showing the operating principle of the liquid crystal display device according to the present invention.

Explanation of symbols for the main parts of the drawings

11, 21 ... 1st board 12, 22 ... 2nd board

13, 14, 23, 24 ... transparent electrode layer 15, 16, 25, 26 ... alignment layer

17, 27 ... nematic liquid crystal 18, 29 ... liquid crystal layer

19, 20, 30, 31 ... Polarizer 28 ... Polymer

In order to achieve the first object of the present invention, in the present invention, the first substrate; A second substrate provided to face the first substrate; A transparent electrode layer formed on the first substrate and the second substrate, respectively; Alignment layers formed on the transparent electrode layers, respectively; Polarizing plates provided on outer surfaces of the first substrate and the second substrate, respectively; And a polymer network liquid crystal layer formed between the first substrate and the second substrate and having a negative dielectric anisotropy and a polymer network liquid crystal layer. .

The second object of the present invention is to (a) coating the vertical alignment agent on the upper and lower substrates on which the transparent electrode layer is formed, followed by heat treatment to form an alignment layer, respectively; (b) rubbing the alignment layer; (c) bonding the upper and lower substrates to form an empty cell; (d) injecting a liquid crystal composition comprising a nematic liquid crystal having a negative dielectric anisotropy, a photopolymerizable monomer, and a photopolymerization initiator into the empty cell; (e) irradiating light while applying a voltage to the resultant; And (f) arranging polarizing plates on the outer side surfaces of the upper and lower substrates, respectively.

The amount of the photopolymerizable monomer is preferably 0.5 to 2% by weight based on the total weight of the liquid crystal composition. Here, when the content of the photopolymerizable monomer is less than 0.5% by weight, the network is not formed well, and when the content of the photopolymerizable monomer is more than 2% by weight, the polymer and the liquid crystal are so formed that light scattering occurs at the interface between the polymer and the nematic liquid crystal. Large phase separation is undesirable.

In the liquid crystal display device of the present invention, the liquid crystal layer comprises a liquid crystal having a negative dielectric anisotropy containing a chiral agent having a pitch of rotating the liquid crystal molecules by 90 degrees and a polymer network liquid crystal made of a polymer.

Hereinafter, a manufacturing method of the liquid crystal display device of the present invention will be described with reference to FIG. 2.

First, the transparent electrode layers 23 and 24 are formed on the first substrate 21 and the second substrate 22, respectively. Subsequently, the alignment layers 25 and 26 are formed by coating and heat treating a vertical alignment agent on the substrate. Herein, the vertical alignment agent is not particularly limited, and polyimide or the like is used.

Subsequently, the photo alignment layers 25 and 26 are subjected to a rubbing treatment, and then the two substrates are bonded to form a blank cell. At this time, the rubbing directions of the alignment layers formed on the two substrates are perpendicular to each other.

As a liquid crystal composition, a mixture of a liquid crystal having a negative dielectric anisotropy, a photopolymerizable monomer, and a polymerization initiator is injected into the completed empty cell. Specific examples of nematic liquid crystals having negative dielectric anisotropy here include N- (p-methoxybenzylidene) -p- (n-butyl) aniline [N- (p-methoxybenzylidene) -p- (n-butyl) aniline: MBBA].

The photopolymerizable monomers include styrene and its derivatives: methyl, ethyl, propyl, butyl, pentyl, hexyl, amyl, 2-ethylhexyl, octyl, nonyl, dodecyl, isodecyl, lauryl, hexadecyl, cyclohexyl, benzyl , Methoxyethyl, ethoxyethyl, butoxyethyl, phenoxyethyl, allyl, metaallyl, glycidyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-chloro-2-hydroxypropyl, dimethylamino Acrylates or methacrylates having substituents such as hexyl, diethylaminohexyl, isobornyl, and the like: ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tripropylene glycol, butylene glycol, tetramethylene glycol, hexamethylene glycol And polyfunctional acrylates and methacrylates such as neopentyl glycol, butanediol, hexanediol, trimethylolpropane, pentaerythritol and dipentaerythritol, and derivatives thereof.

Examples of the photopolymerization initiator include 2-hydroxy-2-methyl-1-phenylpropan-1-one (Merck, Darocure 1173), 1-hydroxycyclohexylphenyl ketone (Ciba-Geigy Corporation, Igacure 184), 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one (Merck, Darocure 1116), benzyldimethyl ketal (Ciba-Geigy Corporation, Igacure 651) and the like can be used. .

When the process of injecting the liquid crystal composition into the empty cell is completed, the liquid crystal layer 29 is formed by curing ultraviolet light by irradiating ultraviolet rays with a voltage near a threshold voltage applied thereto. As a result, the liquid crystal layer 28 is composed of a polymer network liquid crystal composed of a nematic liquid crystal 27 and a polymer 28. Here, the arrangement of the polymers may be slightly inclined in the direction perpendicular to the substrate. However, as shown in FIG. 2, it is most preferable that the polymers are arranged in a line perpendicular to the substrate because it is very free to control the pretilt angle of the liquid crystal molecules.

Thereafter, polarizing plates 30 and 31 are provided on the outer surfaces of the first and second substrates 21 and 22, respectively. At this time, the direction of the polarization plane of each polarizing plate is arranged to match the rubbing direction of the alignment layer.

Looking at the operation principle of the liquid crystal display device according to the present invention, as follows.

In the state where no voltage is applied, the liquid crystal is vertically aligned, and light is blocked in the cell having the cross nicol polarizing plate to show a black state. When a voltage is applied to the cell, the liquid crystal molecules are rearranged in a direction inclined slightly in a direction parallel to the substrate on which the electrode is formed, and exhibit light refractive anisotropy effect on incident light, thereby passing light. As a result, a white state is shown.

As mentioned above, the pretilt angle of a liquid crystal can be adjusted freely by performing the hardening process of a liquid crystal composition in the state which applied the voltage. Therefore, the rise time at the time of voltage application and the decay time due to the liquid crystal side chain of the polymer network formed in the cell can be shortened. In addition, when the gray scale is displayed by applying a voltage to the cell, the long axis of the liquid crystal molecules is inclined by 90 degrees to have a wider viewing angle than the horizontally aligned TN type liquid crystal display device.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

Example 1

ITO electrode layers were formed on the two substrates, respectively, and a vertical alignment agent was spin-coated on the ITO electrode layers. Here, JALS-204-R48 (Japanese synthetic rubber) which is a polyimide compound was used as a vertical alignment agent.

The substrate coated with the vertical alignment agent was baked at about 90 ° C. to form an alignment layer. This alignment film was then rubbed and refired at about 180 ° C., and the vertical alignment agent was again coated.

A blank cell was prepared by bonding two substrates on which a rubbed alignment film was formed. At this time, the rubbing directions in the alignment films formed on the substrates were perpendicular to each other.

The liquid crystal composition was injected into the empty cell. The liquid crystal composition was prepared by mixing 98.97% by weight of MJ96723 (Merck), 1% by weight of mesogen 257 (Mesogen 257, Merck) as a photocurable liquid crystalline diacrylate, and 0.03% by weight of photocuring agent Darocure 1173. .

Subsequently, 10 mW of UV was irradiated while applying a voltage (1.7 V) while the liquid crystal was injected into the empty cell to complete the cell. Finally, a polarizing plate is attached to the outer surface of the upper substrate and the lower substrate of the cell, thereby completing the liquid crystal display device.

Example 2

The same procedure as in Example 1 was carried out except that phenoxymethacrylate, which was a monoacrylate instead of mesogen 257, was used.

Electro-optical properties of the liquid crystal display devices manufactured according to Examples 1 and 2 were measured.

As a result of the measurement, the response time of the cell prepared according to Example 1 was about 30 ms, the viewing angle was 130 degrees above, below, left and right, and the contrast was 200: 1 or more. The response time of the cell manufactured according to Example 2 was about 25 ms, and the viewing angle was 130 degrees above, below, left, and right, and the contrast was 200: 1 or more.

In summary, it can be seen that the response time is faster and the viewing angle is wider than the conventional TN cell (response time: 50 ms, viewing angle: 120 degrees left and right, 90 degrees up and down).

Comparative Example 1

The same procedure as in Example 1 was carried out except that only MJ96723 (Merck) was used as the liquid crystal composition.

Comparative Example 2

Except that the content of mesogen 257 of Example 1 is 3% by weight, it was carried out in the same manner as in Example 1.

Comparative Example 3

Except for the content of mesogen 257 of Example 1 was 5% by weight, it was carried out in the same manner as in Example 1.

Comparative Example 4

Except that the content of mesogen 257 of Example 1 is 10% by weight, it was carried out in the same manner as in Example 1.

In the case of the cell prepared according to Comparative Example 1, a phase similar to that of the polymer dispersed cell appeared. In other words, the polymer and the liquid crystal phases were largely separated so that the polymer cured in the cell causes the liquid crystal and the optical scattering.

In the case of the cell manufactured according to Comparative Example 2, the viewing angle was excellent in the upper, lower, left, and right directions of 130 degrees or more as in the case of Example 1, but the response time was long as about 70 ms.

In the case of the cells prepared according to Comparative Examples 3 and 4, light scattering occurred due to the difference in refractive index at the interface between the liquid crystal and the polymer, and the contrast was greatly reduced to about 100: 1.

The liquid crystal display device of the present invention can freely adjust the pretilt angle of the liquid crystal molecules to increase the response time of the cell and to secure a viewing angle of 140 degrees at the left and right and 120 degrees at the top and the bottom. In addition, since there is no refractive index anisotropy in the long axis direction of the liquid crystal molecules in the state where no voltage is applied, contrast is 200: 1 or more.

Claims (7)

First substrate; A second substrate provided to face the first substrate; A transparent electrode layer formed on the first substrate and the second substrate, respectively; Alignment layers formed on the transparent electrode layers, respectively; Polarizing plates provided on outer surfaces of the first substrate and the second substrate, respectively; And And a polymer network type liquid crystal layer comprising a nematic liquid crystal having a negative dielectric anisotropy and a polymer between the first substrate and the second substrate. The liquid crystal display device according to claim 1, wherein the rubbing direction of the alignment film formed on the first substrate is perpendicular to the rubbing direction of the alignment film formed on the second substrate. The liquid crystal display device according to claim 1, wherein the polarization plane of the polarizer provided on the first substrate is perpendicular to the polarization plane of the polarizer provided on the second substrate. (a) coating a vertical alignment agent on the upper and lower substrates on which the transparent electrode layers are formed, and then performing heat treatment to form alignment layers, respectively; (b) rubbing the alignment layer; (c) bonding the upper and lower substrates to form an empty cell; (d) injecting a liquid crystal composition comprising a nematic liquid crystal having a negative dielectric anisotropy, a photopolymerizable monomer, and a photopolymerization initiator into the empty cell; (e) irradiating light while applying a voltage to the resultant; And (f) a method of manufacturing a liquid crystal display device, comprising the steps of providing polarizing plates on the upper and lower substrate outer surfaces, respectively. The method of claim 4, wherein the amount of the photopolymerizable monomer is 0.5 to 2 wt% based on the total weight of the liquid crystal composition. The method of claim 4, wherein in the step (b), the rubbing direction of the alignment layer formed on the upper substrate is adjusted to be perpendicular to the rubbing direction of the alignment layer formed on the lower substrate. The method of claim 4, wherein in step (f), the polarization plane of the polarizer of the upper substrate is adjusted to be perpendicular to the polarization plane of the polarizer of the lower substrate.