KR20070002656A - Liquid crystal display device with photo-alignment layer - Google Patents

Abstract

An LCD including a photo alignment layer is provided to improve a reaction rate of (2+2) cyclo reaction, improve anisotropy, and stably maintain the anisotropy even against thermal, optical and physical impact by employing a molecular structure that can make a chemical bond with a cinnamoyl group and thus maintaining a predetermined distance between cinnamoyl groups. A first substrate(10) includes a thin film transistor in each of pixel regions defined by gate lines and data lines that vertically intersect each other. A second substrate(2) faces the first substrate and is bonded with the first substrate. A liquid crystal layer(3) is formed between the first and second substrates. Alignment layers(4a,4b) are formed at an inner surface of the first or second substrate, and include a cinnamide group obtained by amidating a cinnamoyl group to allow a hydrogen bond.

Description

Liquid crystal display device with a photoalignment layer {Liquid Crystal Display Device With Photo-alignment Layer}

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a photon isomerization reaction for explaining problems in the prior art.

2 is a view showing a hydrogen bond structure for improving the photoreaction of the alignment film according to the present invention.

3A to 3C are structural diagrams of cinnamid according to the present invention.

4 is a cross-sectional view showing a general liquid crystal display device.

* Explanation of symbols on the main parts of the drawings

1: first substrate 2: second substrate

3: liquid crystal layer 4a, 4b: first and second alignment films

8 pixel electrode 11 gate electrode

12 gate insulating film 13 semiconductor layer

14a: source electrode 14b: drain electrode

15: shield 16: black matrix

17: color filter layer 18: overcoat layer

19: common electrode 20: spacer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device (LCD), and more particularly, to a liquid crystal display device having an optical alignment film having a newly designed structure of cinnamoyl group to impart stable anisotropy.

Recently, the liquid crystal display of the flat panel display has been gradually used as an alternative means of overcoming the shortcomings of the cathode ray tube (CRT) due to the advantages of miniaturization, light weight, low power consumption, and full color. It is expanding.

The liquid crystal display device is formed by injecting liquid crystals between the two substrates after the two substrates are opposed to each other to be spaced apart from each other by a predetermined interval. Function as an element is required.

Since the function is determined according to the arrangement characteristics of the liquid crystal molecules of the liquid crystal display device, a technique of uniformly controlling the alignment of the liquid crystal molecules is very important.

The uniform alignment state of the liquid crystal is difficult to obtain simply by interposing the liquid crystal between two substrates, and it is common to form an alignment film capable of aligning the liquid crystal.

An organic polymer material such as polyimide is mainly used as the alignment layer, and is mainly based on a rubbing method of forming the alignment layer by rubbing the surface with a special type of cloth after forming the polymer material.

The rubbing method is widely used in the manufacture of liquid crystal display devices because of easy implementation and simple process.

However, the alignment film may be contaminated by dust adhered to a special type of cloth used during rubbing, and the alignment may not be easy depending on the alignment film material. In addition, the thin film transistor may be damaged by static electricity generated during rubbing.

In order to solve the problem of the rubbing method, the research and development of the rubbing free treatment without mechanical rubbing is active.

Currently, the photo-alignment method has attracted attention among various non-rubbing treatment methods. The photo-alignment method includes a photolysis method, a photopolymerization method, a photoisomerization method, and the like.

The photo-decomposition is a method of arranging liquid crystals by generating optical anisotropy by using a photolysis reaction that selectively cuts partial bonds of molecules in a specific direction by irradiating linearly polarized ultraviolet rays onto a polymer film which is a photo-alignment material. .

The photo-polymerization is a method of arranging liquid crystals by irradiating linearly polarized light on a polymer film exhibiting a photopolymerization reaction and polymerizing only molecules in a specific direction.

In addition, the photo-isomerization is a method of controlling the direction of the liquid crystal molecules by irradiating polarized light by forming a photo alignment layer by mixing the molecules that react with the polymer.

Meanwhile, cinnamate-based polymers such as polyvinyl cinnamate (PVCN) and polyvinyl methoxy cinnamate (PVMC) are mainly used as the photo-alignment alignment layer material.

In addition, the chemical structure of the photo-alignment alignment layer material can be divided into two parts, forming and improving a main chain and a pretilt angle, which serve to arrange liquid crystal molecules in one direction by polymer photoreaction. It is divided into side chains. At this time, the side chain is used that includes a photosensitive group, such as cinnamoyl (alkyl) group, alkyl (alkyl) group, ethenyl group.

For example, when photoalignment is performed using a cinnamoyl group represented by Formula 1, a cyclobutane ([2 + 2] cycloaddition) reaction is performed by light (UV) or heat. cyclobutane) is formed, which causes anisotropy to align the liquid crystal molecules in one direction.

However, the liquid crystal display device with the conventional optical alignment film as described above has the following problems.

However, in the case of photoalignment using cinnamoyl, the distance between the double bonds of the cinnamoyl group is far due to steric hindrance in addition to the [2 + 2] cycle addition reaction, as shown in FIG. The problem is that cis-trans photoisomerization may also occur. Moreover, photoisomerization may occur predominantly depending on the linked bonds.

  In this case, since the photoisomerization reaction can be easily changed by heat or light as a reversible reaction, the possibility of a problem in orientation reliability becomes very high.

The present invention has been made to solve the above problems, by using a material having a hydrogen bond, such as cinnamid as a photo-alignment material, the hydrogen bond cancels the effect of the steric hindrance of the cinnamoyl group It is an object of the present invention to provide a liquid crystal display device having an optical alignment film for improving the effect of optical alignment by approaching the position of the double bond and increasing the yield of the addition reaction in a [2 + 2] cycle.

According to an exemplary embodiment of the present invention, a liquid crystal display device having an optical alignment layer includes a first substrate including a thin film transistor in each pixel region defined by vertically crossing gate lines and data lines, and the first substrate. Amide cinnamoyl group is formed on the inner surface of the first substrate or the second substrate and the liquid crystal layer formed between the second substrate and the second substrate bonded to the substrate, and the hydrogen bonding between the first substrate and the second substrate It is characterized in that it comprises an alignment film having a cinnamide group (cinnamide group).

Specifically, when the photo-alignment material according to the present invention is designed in a structure capable of having hydrogen bonds, the Cinnamoly group group, it maintains a constant distance between each other by UV or heat during photo-alignment so that photoisomerization does not occur. It is characterized by.

At this time, in order to design the cinnamoyl group into a structure capable of having a hydrogen bond, it is possible by amidating a chemical having a cinnamoyl group with an amine. As a result, the hydrogen atom of the cinnamoyl group is substituted with an amino group, and as shown in the following formula (2), a cinnamid structure is produced. As shown in FIG. 2, the cinnamide structure may form a hydrogen bond by light or heat to maintain a constant distance therebetween.

Referring to FIGS. 3A to 3C, when looking at the Cinnamide structure in three dimensions, the angles of oxygen (O) and hydrogen (H) of the amide group are not located on the horizontal line, so cinnamid When forming hydrogen bonds (HO) with each other, since the hydrogen bonds are formed in a twisted form, the probability that the double bonds are closely located increases.

This close double bond increases the cyclobutane production through the addition reaction by [2 + 2] cycle by light (UV) or heat, thereby increasing anisotropy. Here, the [2 + 2] cyclo addition reaction is a reaction in which a ring is formed by a double bond reaction, also referred to as a Diels-Alder reaction.

As such, the anisotropy formed by the structural change through the chemical reaction can increase the stability of the orientation from heat, electrical or physical impact compared to the reversible intramolecular structural change caused by the physical energy state.

Therefore, in the case of forming anisotropy through polarized light or non-polarized UV irradiation using a cinnamoyl group to align a compound such as a liquid crystal, the structure is designed to enable a chemical reaction such as hydrogen bonding. That is, it is important to increase the probability of the addition reaction in the [2 + 2] cycle by allowing the photosensitive functional groups to be positioned at each other, such as hydrogen bonds.

In addition, in the cinnamide structure, anisotropy formation can be expected through fries photo-rearrangement, and thus anisotropy formation larger than the cinnamate structure can be expected. The magnitude of anisotropy can be explained by the density of factors that can contribute to the anisotropy at the surface of the material. The cinnamid structure of the present invention can cause photodimerization reaction and pride slag rearrangement in one light unit, so that the density of the factor that can contribute to anisotropy can be increased up to about twice, thereby increasing the anisotropy. The cinnamate structure was used as a conventional photoalignment film photosensitive group, and is an esterification reaction of a cinnamoyl group.

Hereinafter, referring to FIG. 4, a liquid crystal display device having an optical alignment layer having a cinnamic group as a photosensitive functional group will be described.

The liquid crystal display device according to the present invention includes a liquid crystal layer 3 formed between the first substrate 1 and the second substrate 2, the first and second substrates 1 and 2, and the first and second agents. A spacer 20 formed between the two substrates 1 and 2 to maintain a constant gap between the two substrates, and a photo-alignment material having a cinnamic group as a side chain on the first substrate or the second substrate; It consists of the photo-alignment films 4a and 4b.

Among the substrates, the first substrate 1 is a thin film transistor (TFT) array substrate, and a switching element, that is, a thin film transistor (TFT), is formed to selectively turn on / off a data signal according to a gate voltage. The second substrate 2 is a color filter array substrate, on which a color filter layer 17 for color representation is formed.

Specifically, the gate electrode 11 formed on the first substrate 1 in parallel and arranged in parallel, the gate electrode 11 formed at a predetermined thin film transistor position, and the gate insulating layer 12 formed on the entire surface including the gate electrode 11. And a semiconductor layer 13 formed on the gate electrode 11, a data line 14 formed to intersect with the gate wiring, and a source / drain electrode 14a / 14b formed on the semiconductor layer 13. And a first passivation layer 15 formed on the entire surface including the source / drain electrodes 14a and 14b, a pixel electrode 8 connected to the drain electrode 14b and formed in a majority of the pixel region, and the pixel. There is a first alignment film 4a formed on the entire surface including the electrode 8.

In addition, a black matrix 16 formed on the second substrate 2 to prevent light leakage, a color filter layer 17 formed between the black matrix 16, and a color filter layer 17 are formed on the entire surface of the second substrate 2. The second passivation layer 18 that protects the color filter layer 17, the common electrode 19 formed on the second passivation layer 18, and the second alignment layer 4b formed on the entire surface including the common electrode 19. There is). The second passivation layer 18 may not be formed. In addition, although a ball spacer is shown in the drawing, it is also possible to use a column spacer formed by patterning an organic material on a first substrate or a second substrate as a cell gap forming material.

In this case, at least one of the first and second alignment films 4a and 4b is an optical alignment film having a cinnamic group as a photosensitive functional group. That is, at least one may use the rubbing alignment film instead of the photo-alignment film. The optical alignment layer may be applied to any device such as an IPS mode, a VA mode, a display device using a polysilicon liquid crystal, in addition to the TN mode illustrated in FIG. 4.

Hereinafter, a method of manufacturing a liquid crystal alignment layer using a photoalignable material having a cinnamic group as a side chain will be described in detail.

The photo-alignment material having the cinnamid group of the present invention as a side chain is dissolved in an organic solvent at a viscosity of 1 to 20% by weight and 1 to 100 cps, and coated on a substrate with a thickness of 10 to 500 nm to form an alignment film.

Here, the organic solvent is chlorobenzene, N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N, N-dimethylimidazolidinone (DMI), N, N- Dipropylimidazolidinone (DPI), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), cyclopentanone, cyclohexanone, dichloroethane, butylcellulsolve, gamma butyrolactone And tetrahydrofuran (THF).

The liquid crystal aligning agent dissolved in the organic solvent is coated on a substrate to a predetermined thickness in a range of 10 to 500 nm to form a film. In this case, all possible conventional methods such as spin coating and roll printing may be used.

Thereafter, ultraviolet rays are irradiated onto the surface of the alignment film coated with the liquid crystal aligning agent obtained in the above step to prepare a photosensitive polymer liquid crystal alignment film. In this case, the ultraviolet rays are inclined or vertically irradiated with ultraviolet rays linearly polarized using a polarizer or unpolarized ultraviolet rays not using a polarizer to produce a liquid crystal alignment layer.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

That is, the photo-alignment material according to the present invention may be a photo-alignment material having a side chain in which a cinnamoyle group is designed to enable chemical bonding between the photo-alignment material and the cinnamide group. It is characterized by improving the anisotropy by designing cinnamoyl group to improve the reaction rate of the addition reaction in the [2 + 2] cycle by chemical bonding between each other.

The liquid crystal display device having the optical alignment layer according to the present invention as described above has the following effects.

By introducing a molecular structure capable of chemical bonding such as hydrogen bonding to cinnamoyl group, and designing the structure so that cinnamoyl groups can maintain a certain distance from each other, it improves the reaction rate of addition reaction in [2 + 2] cycle, Through the arrangement, the anisotropy is improved and the formed anisotropy can be maintained stably against heat, light, and physical impact.

As a result, the reliability and the image quality of the liquid crystal display device having the same as well as the reliability of the alignment material are improved.

Claims (3)

A first substrate having a thin film transistor in each pixel region defined by vertically crossing gate wiring and data wiring; A second substrate opposed to the first substrate, A liquid crystal layer formed between the first and second substrates; The optical alignment layer is formed on the inner surface of the first substrate or the second substrate and comprises an alignment layer having a cinnamid group (cinnamide group) amidated cinnamoyl group to enable hydrogen bonding with each other Liquid crystal display device provided. The method of claim 1, And the alignment layer is provided with anisotropy by light or heat. The method of claim 1, The alignment layer is provided with an optical alignment layer, characterized in that the anisotropy is imparted by polarized light or non-polarized UV irradiation.

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