KR100268031B1 - Fabrication method for photosensitive alignment layer of lcd - Google Patents

Abstract

PURPOSE: A method for manufacturing a photo-alignment film is provided to be capable of forming a thermally stable film so that an initial alignment is maintained during an annealing process. CONSTITUTION: A thin film is formed by coating a photo-alignment material on a glass substrate, on which a transparent electrode is formed, and annealing a solvent used at the coating process at a predetermined temperature. An ultraviolet ray or a laser is irradiated on the thin film. The photo-aligned thin film is annealed at a predetermined temperature so that a polyamic acid is transformed into a polyimide. The solvent is annealed in a temperature range of 70 to 90. The step of annealing the photo-aligned film is carried out in a temperature range of 200 to 300.

Description

Method of forming an optical alignment film of a liquid crystal display device

The present invention relates to a liquid crystal display device, and more particularly, to a method of forming a thermally stable optical alignment film.

Information display devices, which are used to convert electrical signals into visual images using electro-optical devices and can be directly decoded by humans, are used in home TVs, scientific instruments, oscilloscopes, and radars. It is widely applied to indicators, numbers, letters, and graph display terminals, CAD terminals, industrial equipment indicators, and indicators for transportation, transportation, aerospace, military and aerospace.

In particular, flat, lightweight, and low power consumption flat panel displays have large radial display devices that convert electrical energy into light as a function of image signals, and diffuse, absorb, birefringence, and reflection. It is classified into a non-emissive type display device that obtains a desired color and luminance by controlling ambient light, back light or side light by using an optical effect that can cause an electrical change such as refraction.

In the non-emissive display device, a liquid crystal display (LCD) using liquid crystal is most commonly applied.

LCDs are suitable for electronic devices using integrated circuits and have the most suitable characteristics for the display of portable miniature electronic devices to operate at low voltage and low power consumption.

The LCD is composed of a liquid crystal display panel, a driving circuit and a lighting device as required.

1 illustrates a general liquid crystal display panel.

As the liquid crystal 5 material, nematic liquid crystals, cholesteric liquid crystals, smectic liquid crystals and mixed liquid crystals thereof are used.

The transparent electrode 3 forms tin oxide, indium oxide or a mixture thereof on the glass substrate 2 by spraying, vapor deposition or sputtering.

The spacer 6 is for keeping the thickness of the liquid crystal layer 5 constant and uses a mylar film or a Teflon film.

An inorganic adhesive and an organic adhesive are used as the sealant (sealer) 7, and airtightness must be maintained to prevent deterioration of the liquid crystal 5 due to moisture intrusion.

The alignment film 4 is for uniformizing the liquid crystal molecules, and performs a parallel alignment treatment, a vertical alignment treatment, or a combination thereof in accordance with the display method.

The polarizing plate 1 is attached to the upper and lower portions of the glass substrate so that the polarization directions are orthogonal to each other for linear light of the light passing through the liquid crystal layer.

In the LCD formed as described above, when a voltage is applied to the liquid crystal, the direction of light passing is changed. That is, when the array of liquid crystal molecules is a twisted nematic (TN) type LCD, when light is projected onto the liquid crystal 5 without a voltage applied, the light is twisted along the groove in which the liquid crystal molecules are arranged. When passing through and applying a voltage, the light goes straight without twisting the light so that the light does not pass and is displayed black on the screen.

Meanwhile, a manufacturing process of the liquid crystal display panel of the LCD will be described below.

An ITO thin film is formed on the glass substrate 2 and selectively etched to form the transparent electrode group 3. When the transparent electrode group 3 is formed, a solution in which the alignment layer 4 material is dissolved is applied thereon by using a spin coating method, then dried, and the solvent is volatilized to form the alignment layer 4. With the pair of glass substrates 2 formed in this manner, the alignment layers 4 face each other, a spacer gap 6 is formed at the edge thereof so that a cell gap through which the liquid crystal 5 can be injected is formed through a subsequent process. ) And the sealing agent 7 is applied to the edge of the glass substrate 2 so as to maintain the airtightness inside the cell and then pressurized to form a liquid crystal cell. In this case, since a plurality of liquid crystal cells are formed on the glass substrate 2, the glass substrate 2 is cut using silicon carbide or a diamond cutter to divide each liquid crystal cell. Subsequently, the unit liquid crystal cell and the liquid crystal are placed in a vacuum chamber, the liquid crystal 5 is injected into the liquid crystal cell in a vacuum state, and then an injection hole (not shown) is sealed to complete the manufacturing process of the liquid crystal display panel.

In particular, the liquid crystal alignment process related to this invention is demonstrated in detail.

As is well known, the liquid crystal molecules injected into the cell are organic compounds having a long, narrow nematic shape, and in the natural state, the liquid crystal molecules are gently and regularly arranged so that the grooves are brought into contact with an alignment film having a groove in a predetermined direction. The arrangement will change accordingly.

Conventionally, rubbing to form a viewing angle by forming an orientation force in a specific direction by rubbing a surface of a substrate coated with an alignment film while rotating a cylindrical roll of metal on a surface of a fabric in which cotton or nylon fibers are implanted. The method is used, but there are problems such as random phase distortion and light scattering due to the inherent electrical and mechanical defects caused by friction.

Recently, new methods for liquid crystal molecular alignment have been proposed. That is, the pretilt angle of the liquid crystal is very important for increasing the contrast ratio as well as the switching time of the LCD, and a technique for achieving the pretilt angle by using a non-rubbing technique is proposed. have.

In particular, as an example of the prior art, a polyvinyl-4-me-thoxy cinnamic acid (PVCN) derivative produced by the reaction of polyvinyl alcohol and 4-methoxy cinnamic acid on a glass substrate. When applied and irradiated with linearly polarized ultraviolet rays, an optical alignment layer (4) cross-linked by an optical reaction is formed, and the optical alignment layer (4) has liquid crystal molecules in a planar structure in a desired direction. Can be oriented.

Method to use as an alignment layer after photoalignment using azo (azo) single molecule in place of the PVCN, azo side-chain polyamic acid (azo side-chain polyamic acid) or polyimide (polyimide) coated on a glass substrate to photoalignment A method of coating a glass substrate by coating azo main-chain polyamic acid on a glass substrate without heat treatment has been used or attempted.

However, the conventional optical alignment methods exhibit excellent liquid crystal alignment, but are heat treated at a temperature of about 200 ° C. to 300 ° C. during the sealing process of the liquid crystal cell, which is essential for LCD manufacturing. This deterioration has made it difficult to manufacture LCD.

Accordingly, an object of the present invention is to provide a method for forming a photo-alignment layer of a thermally stable liquid crystal display device in which the initial alignment is maintained even during the heat treatment process, which is essential in the manufacturing process of the liquid crystal display device. have.

In order to achieve the above object, the present invention provides a method for forming an optical alignment film of an LCD, by applying a polymer material having azo molecules bonded to a main chain structure of a polyamic acid to a glass substrate on which a transparent electrode is formed, and applying a solvent used in the application. Heat treating at a predetermined temperature to form a thin film; Photo-alignment by irradiating the thin film with UV or laser; And converting the polyamine acid into polyimide by heat-treating the photo-oriented thin film at a predetermined temperature.

The optical orientation of the liquid crystal display device formed in this way has low flexibility of the azo polyimide converted from polyamine acid, so that the optical orientation does not break down even when heat-treated at a temperature of about 200 ° C. to 300 ° C. during the liquid crystal cell sealing process of the LCD. Since the thermally stable state can be maintained, a large area liquid crystal display device can be manufactured, and an effect of manufacturing a high quality liquid crystal display device can be obtained.

1 is a cross-sectional view showing a cross-sectional structure of a general liquid crystal display device;

2 is a manufacturing process diagram of an optical alignment film of a liquid crystal display device according to the present invention;

3 is a polarization micrograph of a nematic liquid crystal cell to which a P1 photoalignment material treated in the process of Example 1) is applied;

4 is a polarization micrograph of a nematic liquid crystal cell to which a P1 photoalignment material treated by the process of Example 2) is applied;

5 is a polarization micrograph of a nematic liquid crystal cell to which a P1 photoalignment material treated by the process of Example 3) is applied;

6 is a polarization micrograph of a nematic liquid crystal cell to which a P2 photoalignment material treated in the process of Example 1) is applied;

7 is a polarization micrograph of a nematic liquid crystal cell to which a P2 photoalignment material treated in the process of Example 2) is applied;

8 is a polarization micrograph of a nematic liquid crystal cell to which a P2 photoalignment material treated by the process of Example 3) is applied;

9 is a polarization micrograph of the nematic liquid crystal cell to which the P3 photoalignment material treated in the process of Example 1) is applied;

10 is a polarization micrograph of a nematic liquid crystal cell to which a P3 photoalignment material treated by the process of Example 2) is applied;

FIG. 11 is a polarization micrograph of a nematic liquid crystal cell to which a P3 photoalignment material treated by the process of Example 3) is applied;

12 is a polarization micrograph of a nematic liquid crystal cell to which a P3 photoalignment material treated in the process of Example 4) is applied.

〈Explanation of the Signs of Major Parts of Drawings〉

One ; Polarizing plate 2; Glass substrate

3; Transparent electrode 4; (Optical) alignment film

5; Liquid crystal 6; Spacer

7; Sealer

Hereinafter, a preferred embodiment of a method of forming an optical alignment film of an LCD according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a process block diagram sequentially showing a process of forming an optical alignment film of an LCD according to the present invention.

As shown, the present invention consists of azo-main chain polyamic acid thin film formation step, photo-alignment step, and imidization step.

First, in the thin film formation step, an ad molecular material in which azo molecules are bonded to the main chain structure of polyamic acid is applied to a glass substrate on which a transparent electrode is formed, and the solvent used for application is heat-treated at a temperature range of about 70 to 90 ° C. A main chain polyamine acid thin film is formed.

In the photoalignment step, when the UV light or laser light is irradiated to the azo-chain polyamine acid thin film, the photoalignment layer is oriented by a photoreaction. At this time, the azo-chain polyamine acid has high flexibility.

In the imidization step, the photo-aligned photoalignment film 4 is heat-treated at a temperature in the range of 200 to 300 ° C. to convert azo-chain polyamine acid to azo-chain polyimide. In this case, the converted azo-chain polyimide has low flexibility, and since it is converted to polyimide in the photo-oriented state, the photo-aligned state is not destroyed even when heated to a similar temperature. That is, even when heat-treated at a temperature of about 200 ℃ to 300 ℃ during the sealing process during the LCD manufacturing process, the photo-alignment state is not destroyed, thereby maintaining a thermally stable state.

Hereinafter, the working effect of the present invention through the examples.

In the embodiment, the photo-alignment material is photo-aligned by applying azo monomolecule (P1) or polyimide to the substrate, and the photo-alignment by applying azo-chain polyamic acid (P2) to the substrate and azo-chain polya The conventional liquid crystal display panel was constructed by dividing the mixed acid (P3) onto the substrate and photoalignment.

Chemical structure of the photo-alignment material is as follows.

Formula 1 is a chemical formula of azo monomolecule, Formula 2 is a chemical formula of azo-branched polyamine acid, and Formula 3 is a chemical formula of azo-chain polyamine acid.

Such photo-alignment materials were photo-aligned by the following steps, respectively.

Example 1) Predrying => Photoalignment

Example 2) Predrying => Imidization => Photoalignment

Example 3) Predrying => Photoalignment => Imidization

Example 4) Predrying => Photoalignment => Imidization => Heat Treatment

The soft curing step was carried out for 30 minutes at 80 ° C. as a process for evaporating the solvent contained in each photo-alignment material applied on the substrate.

In the photo alignment step, 350 nm UV was irradiated to each photo alignment material for 10 minutes.

In the imidization step, the pre-dried photo-alignment material was hard cured at 250 ° C. for 60 minutes to form a polyimide film.

In the thermal aging step, a temperature (for 300 minutes at 300 ° C.) applied during the sealing process, which is normally performed in the LCD manufacturing step, is arbitrarily set and heated.

3 to 5 are attached to the polarization microscope picture of the nematic liquid crystal cell to which the P1 photo-alignment material is applied between the polarizing plates crossed at right angles, FIG. 3 is a photo-alignment by the process of Example 1, Figure 4 Is photo-aligned by the process of Example 2), Figure 5 is photo-aligned by the process of Example 3).

In the exemplary drawings, the upper left (arm) is a texture when the optical axis of the liquid crystal 5 and the direction of the polarizer 1 are 0 °, and the upper right (name) is the optical axis and the polarizer 1 of the liquid crystal 5. ) Is the texture when the direction of 45 °, the lower left (arm) is the texture when the optical axis of the liquid crystal 5 and the direction of the polarizing plate 1 is 90 °, the lower right (light) is the optical axis of the liquid crystal 5 And the texture when the direction of the polarizing plate 1 is 135 degrees.

That is, as shown in FIG. 3, in the case of photoalignment after predrying according to Example 1), alignment characteristics are excellent depending on the optical axis of the liquid crystal and the azimuth angle of the polarizing plate, as shown in FIG. 4. Preliminary drying => imidization => according to Example 2) it can be seen that the photo-alignment characteristics are almost lost. This can be seen that since the imidization process of the photo-alignment material proceeds first, the flexibility of the photo-alignment material is reduced and thus the photo-alignment is not smoothly performed during the photo-alignment process.

FIG. 5 shows that the alignment characteristics are excellent according to the optical axis of the liquid crystal and the azimuth angle of the polarizing plate when pre-dried => photo alignment => imidization according to Example 3). That is, when the photoalignment is performed by irradiating UV before the photoalignment material is imidated, the photoalignment is performed in a state where the flexibility of the photoalignment material is high, and is converted to polyimide by a subsequent imidization process to have thermal stability.

6 to 8 are attached to the polarization micrographs of the nematic liquid crystal cell to which the P2 photo-alignment material is applied between the polarizing plates crossed at right angles, FIG. 6 is a photo-alignment by the process of Example 1), FIG. Is photo-aligned by the process of Example 2), and FIG. 8 is photo-aligned by the process of Example 3).

In the exemplary drawings, the upper left (arm) is a texture when the optical axis of the liquid crystal 5 and the direction of the polarizer 1 are 0 °, and the upper right (name) is the optical axis and the polarizer 1 of the liquid crystal 5. ) Is the texture when the direction of 45 °, the lower left (arm) is the texture when the optical axis of the liquid crystal 5 and the direction of the polarizing plate 1 is 90 °, the lower right (light) is the optical axis of the liquid crystal 5 And the texture when the direction of the polarizing plate 1 is 135 degrees.

That is, as shown in FIG. 6, in the case of photoalignment after pre-drying according to Example 1), alignment characteristics are excellent according to the optical axis of the liquid crystal and the azimuth angle of the polarizing plate, as shown in FIG. 7. Preliminary drying => imidization => according to Example 2) it can be seen that the photo-alignment characteristics are almost lost. This can be seen that since the imidization process of the photo-alignment material proceeds first, the flexibility of the photo-alignment material is reduced, so that the photo-alignment is not smoothly performed during the photo-alignment process.

FIG. 8 shows that the alignment characteristics are excellent according to the optical axis of the liquid crystal and the azimuth angle of the polarizing plate when pre-dried => photo-alignment => imidization according to Example 3). That is, when the photoalignment is performed by irradiating UV before the photoalignment material is imidated, the photoalignment is performed in a state where the flexibility of the photoalignment material is high, and is converted to polyimide by a subsequent imidization process to have thermal stability.

9 to 12 are attached to the polarized light micrograph of the nematic liquid crystal cell to which the P3 photo-alignment material is applied between the polarizing plate crossed at right angles, Figure 9 is a photo-alignment by the process of Example 1, Figure 10 Is photo-aligned by the process of Example 2), FIG. 11 is photo-aligned by the process of Example 3), and FIG. 12 is photo-aligned by the process of Example 4).

In the exemplary drawings, the upper left (arm) is a texture when the optical axis of the liquid crystal 5 and the direction of the polarizer 1 are 0 °, and the upper right (name) is the optical axis and the polarizer 1 of the liquid crystal 5. ) Is the texture when the direction of 45 °, the lower left (arm) is the texture when the optical axis of the liquid crystal 5 and the direction of the polarizing plate 1 is 90 °, the lower right (light) is the optical axis of the liquid crystal 5 And the texture when the direction of the polarizing plate 1 is 135 degrees.

That is, as shown in FIG. 9, in the case of photoalignment after pre-drying according to Example 1), alignment characteristics are excellent depending on the optical axis of the liquid crystal and the azimuth angle of the polarizing plate, as shown in FIG. 10. Preliminary drying => imidization => according to Example 2) it can be seen that the photo-alignment characteristics are almost lost. This can be seen that since the imidization process of the photo-alignment material proceeds first, the flexibility of the photo-alignment material is reduced and thus the photo-alignment is not smoothly performed during the photo-alignment process.

FIG. 11 shows that the alignment characteristics are excellent according to the optical axis of the liquid crystal and the azimuth angle of the polarizing plate when pre-dried => photo-alignment => imidization according to Example 3). That is, when the photoalignment is performed by irradiating UV before the photoalignment material is imidated, the photoalignment is performed in a state where the flexibility of the photoalignment material is high, and is converted to polyimide by a subsequent imidization process to have thermal stability.

FIG. 12 shows that the alignment characteristics are excellent according to the optical axis of the liquid crystal and the azimuth angle of the polarizing plate when pre-drying => photoalignment => imidization => heat treatment according to Example 4). That is, even when heat-treated at a temperature of about 200 ℃ to 300 ℃ during the sealing process of the liquid crystal cell, which is essential in the LCD manufacturing process, it can be seen that the alignment ability is not lost or the alignment ability is not lowered. As mentioned above, photo-alignment by UV irradiation prior to imidization of the photo-alignment material results in photo-alignment in a highly flexible state of the photo-alignment material, which is converted into polyimide by a subsequent imidization process and thermally stable. Because you have.

The foregoing is merely illustrative of the preferred embodiment of the present invention and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without changing the subject matter of the present invention.

Therefore, according to the present invention, by applying a process step of fabricating a photo-alignment material into a thin film and then photo-aligning and converting to polyimide, an optical alignment film having a thermal stability can be obtained, and further, an alignment film of a large-area liquid crystal display device. It can produce the effect or to produce an alignment film of a high-quality liquid crystal display device.

Claims (6)

In the method of forming an optical alignment film of LCD, Forming a thin film by coating a photo-alignment material on a glass substrate on which a transparent electrode is formed and heat-treating the solvent used for coating at a predetermined temperature; Photo-alignment by irradiating the thin film with UV or laser; And converting the polyamic acid into polyimide by heat-treating the photo-aligned thin film at a predetermined temperature. The method of claim 1, wherein the optical alignment material is an azo-chain polyamine acid (P3) material. The method of claim 1, wherein the photoalignment material is an azo single molecule (P1) or a polyimide material. The method of claim 1, wherein the photoalignment material is an azo-subchain polyamic acid (P2) material. The method of claim 1, further comprising heat-treating the solvent used for coating in the step of applying the thin film of the advertising molecular material at a temperature range of 70 to 90 ° C. 7. The method of claim 1, wherein the heat treatment of the optical alignment layer is performed at a temperature in a range of 200 to 300 ° C. 7.

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