KR20130011457A - Method of forming alignment layer for liquid crystal display device - Google Patents

Abstract

PURPOSE: A method for forming an alignment layer for a liquid crystal display device is provided to minimize DC afterimage and AC afterimage. CONSTITUTION: A photo-alignment material is coated on a substrate to form an alignment material layer(ST110). A first curing process for imide reaction is performed on the alignment material layer(ST120). UV is irradiated on the alignment material layer(ST130). Microwave is irradiated on the alignment material layer(ST140). [Reference numerals] (ST110) An alignment material layer forming process; (ST120) First plasticity process; (ST130) Light alignment process; (ST140) Second plasticity process(microwave)

Description

Method of forming alignment layer for liquid crystal display device {Method of forming alignment layer for liquid crystal display device}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a method of forming an alignment film capable of improving the imidation ratio and preventing a problem of afterimages.

In recent years, as the society enters the information age, the display field that processes and displays a large amount of information has developed rapidly. Is replacing the existing Cathode Ray Tube (CRT).

Generally, the driving principle of a liquid crystal display device utilizes the optical anisotropy and polarization properties of a liquid crystal. Since the liquid crystal has a long structure, it has a directionality in the arrangement of molecules, and the direction of the molecular arrangement can be controlled by artificially applying an electric field to the liquid crystal.

Therefore, when the molecular alignment direction of the liquid crystal is arbitrarily adjusted, the molecular arrangement of the liquid crystal is changed, and light is refracted in the molecular alignment direction of the liquid crystal by optical anisotropy, so that image information can be expressed.

In order to drive the liquid crystal as described above, an alignment layer for arranging the initial liquid crystal is required. In general, the alignment film is a polymer resin, which is a means for aligning a liquid crystal in a predetermined direction, and is positioned in contact with the liquid crystal as an uppermost layer of the array substrate and the color filter substrate constituting the liquid crystal display device.

Hereinafter, the configuration of the liquid crystal display device will be described with reference to FIGS. 1 and 2.

1 is a perspective view illustrating a general liquid crystal display device, and FIG. 2 is a cross-sectional view of the liquid crystal display device.

As shown, the liquid crystal display device includes a color filter substrate B2 and an array substrate B1, and a liquid crystal layer 14 filled between the two substrates B1 and B2.

In detail, the array substrate B1 includes a gate wiring 12 and a data wiring 24 formed on the transparent first substrate 22 so as to intersect with each other. The thin film transistor T, which is a switching element, is formed at the intersection.

The region defined by the intersection of the gate wiring 12 and the data wiring 24 is a pixel region P, which is the smallest unit in which an image is displayed. In the pixel region P, a pixel voltage is applied from the thin film transistor T. The transparent pixel electrode 17 to be applied is constituted.

The first alignment layer 32 formed of polyimide is formed on the entire surface of the substrate 22 on which the pixel electrode 17 is formed.

The color filter substrate B2 includes a black matrix 6 that is a light blocking means corresponding to a boundary of the pixel region P on a transparent second substrate 5 facing the first substrate 22. The color filters 7a, 7b, and 7c are formed corresponding to the pixel region P. As shown in FIG. The color filters 7a, 7b, and 7c have red, green, and blue colors.

A planarization film (not shown) is formed on an entire surface of the second substrate 5 including the color filters 7a, 7b, and 7c and the black matrix 6, and a common electrode is formed on the entire surface of the planarization film (not shown). (18) and the second alignment film 34 are formed.

However, an alignment process is performed on the first alignment layer 32 and the second alignment layer 34 for arranging the liquid crystal layer 14 in a predetermined direction. This alignment process is classified into a contact method using a rubbing cloth or a non-contact method using light (ultraviolet rays).

The above-described contact method forms a fine groove on the surface through physical friction using a rubbing cloth, and the non-contact method irradiates the surface of the alignment layer with light such as UV.

However, the contact alignment process using the rubbing cloth has various disadvantages in view of the size of the rubbing device and the cost of replacing the rubbing cloth.

Therefore, a non-contact method in which an alignment process can be completed by only a process of irradiating light is preferred, and in particular, in an alignment process for forming a plurality of regions having different alignment directions of liquid crystals in a single pixel, alignment using light as described above. The process is useful.

In general, in the alignment process using a non-contact method, an optical alignment material made of a polymer material such as a polyimide resin including a photoreactor is used.

For example, a non-contact orientation process using Cyclobutan dianhydride (hereinafter referred to as "CBDA") has been disclosed in Patent Publication No. 10-2008-90680.

The above-mentioned non-contact type orientation is performed by the orientation film application | coating process, the 1st baking process by heating, a UV orientation process, and the 2nd baking process by heating.

For example, as shown in FIG. 3, an alignment agent made of polyamic acid obtained from CBDA is coated and formed into a polyimide by a first firing process at about 230 ° C. for about 1 hour. Thereafter, UV is irradiated to cleave the ring of cyclobutane to impart anisotropy. Thereafter, the second firing process is performed under the condition of about 200 to 230 ° C.

However, according to the first firing process by heating as described above, since there are many carboxylic acid sites acting as charge sites under high temperature conditions, DC afterimage problems occur. In addition, since the above first firing step has a limitation in the imidization ratio, the problem of AC afterimage also occurs due to the low crystallinity of the alignment film. In addition, since the first and second firing processes have to proceed for about 1 hour, there is a problem of low process yield.

On the other hand, rearrangement of monomers generated by the ring of cyclobutane due to photo-alignment plays a very important role in anisotropic properties. However, fluidity is not sufficient because the solvents have been evaporated by the first and second firing processes in the above-described alignment process, and thus, anisotropic properties arise because no rearrangement of the monomers occurs.

The present invention seeks to solve the problem of residual image and anisotropy in the conventional non-contact alignment process.

That is, in the conventional non-contact type alignment process using CBDA, according to the first and second firing processes before and after the UV alignment process, problems of DC afterimage and AC afterimage occur due to a large number of carboxylic acid sites and low imidization ratio. In addition, since there is no solvent in the alignment film by the firing step, there is a limit in rearrangement of the monomers, whereby the anisotropic characteristic is lowered.

Accordingly, the present invention is to provide a method of forming an alignment film that can prevent the problem of residual image and the problem of deterioration of anisotropic properties in place of the firing step.

In order to solve the above problems, the present invention comprises the steps of forming an alignment material layer by applying a photo alignment material on the substrate; A first firing step of causing an imide reaction in the alignment material layer; A photo alignment step of irradiating UV on the alignment material layer after the first firing process; After the optical alignment step, there is provided a method of forming an alignment layer for a liquid crystal display device comprising a second firing step of irradiating microwaves to the alignment material layer.

The wavelength of the microwave used in the second firing step is characterized in that 10 ~ 15cm.

In the first firing step, the microwave is irradiated to the alignment material layer.

The wavelength of the microwave used in the first firing step is characterized in that 10 ~ 15cm.

The first firing step of irradiating microwaves to the alignment material layer is characterized by using a catalyst and a dehydrating agent.

The dehydrating agent is characterized in that any one of acetic anhydride, propionic anhydride, trifluoroacetic anhydride.

The catalyst is characterized in that any one of pyridine, collidine, lutidine, triethylamine.

The first firing step is characterized in that to heat the alignment material layer for 1 hour under the conditions of 200 ~ 230 ℃.

The UV is characterized by having a wavelength of 230 ~ 270nm and irradiated for 5-15 minutes.

The photo-alignment material is characterized in that the polyamic acid.

In the present invention has the effect of minimizing the afterimage problem in the non-contact type alignment process and improve the anisotropic properties.

In other words, by rearranging the monomer generated in the UV alignment process using a microwave (microwave), the anisotropic characteristic is improved.

In addition, it is possible to increase the imidation rate by the microwave irradiation process made before the UV alignment process, thereby minimizing the problem of DC afterimage and AC afterimage.

Therefore, the liquid crystal display device including the alignment film manufactured by the alignment process of the present invention can provide a high quality image.

1 is a perspective view illustrating a general liquid crystal display device.
2 is a cross-sectional view of a liquid crystal display device.
3 is a view for explaining a conventional alignment process.
4 is a flowchart illustrating a method of forming an alignment film according to the present invention.
5a to 5c show the change of the alignment material according to the alignment film forming process according to the present invention.
6A through 6E are cross-sectional views illustrating an alignment film forming process according to an exemplary embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.

4 is a flowchart illustrating a method of forming an alignment layer according to the present invention, and FIG. 5 illustrates a change of the alignment material according to the alignment layer forming process according to the present invention.

As shown, a photo-alignment material is applied on top of the substrate to form an alignment material layer. (ST110) The photo-alignment material may be a polyimide polymer represented by the following formula.

Here, M may be cyclobutane. For example, the polyimide polymer represented by the above formula can be obtained from CBDA represented by the following formula.

After the alignment material layer forming process ST110, the first firing process ST120 is performed to cure the alignment material layer. For example, the first firing process ST120 may be performed by irradiation of microwaves. Alternatively, the first firing process (ST120) may be performed under conditions of about 200 ~ 250 ℃ in the oven.

For example, when the microwave is irradiated in the first firing process ST120, the time of the first firing process ST120 may be reduced. That is, in the case of the firing process by the conventional heating, about 1 hour in the condition of about 200 ~ 230 ℃ proceeds, while in the first firing process (ST120) using a microwave as in the present invention, a much shorter time than this Since the process time is shortened, process efficiency can be improved. For example, a microwave having a wavelength of about 10 to 15 cm can be irradiated for about 3 to 7 minutes.

Microwaves act on the reaction with thermal and non-thermal effects, thereby accelerating the reaction by the microwaves. Due to the non-thermal effects of microwaves, the reaction rate increases due to the increase of entropy or decrease of activation energy due to the increase in the number of atoms and molecules by the polarization effect and the number of collisions. . Referring to FIG. 5A, irradiating microwaves to polyamic acid obtained from CBDA accelerates the imide reaction, thereby increasing the imidization rate in a short process time.

Therefore, when using the microwave in the first firing process (ST120) as in the present invention, it is possible to minimize the AC afterimage problem by the high imidization rate, and consequently to minimize the carboxylic acid site to prevent the DC afterimage problem. have.

On the other hand, in order to increase the imidation ratio in the first firing step (ST110), a catalyst and a dehydrating agent may be used. For example, in the imide reaction, water is generated. By using a dehydrating agent, water can be removed to promote the imide reaction. For example, the dehydrating agent may be any one of acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, and may be added in an amount of about 0.01 to 20 moles based on 1 mole of polyamic acid. In addition, the catalyst may be any one of pyridine, collidine, lutidine, triethylamine, and may be added in a ratio of 0.01 to 10 moles based on 1 mole of polyamic acid.

Next, after the first firing step ST120, a light alignment step ST130 for imparting anisotropy is performed. Polarized UV may be used in the photo alignment process ST130. As shown in FIG. 5B, the cyclobutane ring is selectively destroyed by UV irradiation to impart anisotropy to the alignment layer.

The UV has a wavelength of about 230 ~ 270nm and may be irradiated for about 5-15 minutes. The photo alignment process (ST130) may be carried out at room temperature (25 ℃) or may be carried out under the conditions of about 170 ~ 230 ℃. In addition, the photo alignment process ST130 may be performed in an inert gas, for example, a nitrogen atmosphere. Under inert gas, side reaction oxidation can be minimized, and deterioration of alignment film properties due to oxidation can be prevented.

Next, the second firing process ST140 is performed after the photo alignment process ST130. The second firing process ST140 uses microwaves, thereby rearranging monomers generated in the photo alignment process ST130. The wavelength of the microwave may be about 10 to 15 cm, it is irradiated for about 3 to 7 minutes.

Microwaves affect the movement of molecules, especially monomers. Referring to FIG. 5C, the irradiated microwaves move the monomer generated in the photo alignment process (ST130) to rearrange the monomers.

That is, when the baking process by heating is performed after the photo alignment process as in the related art, the movement of molecules is very limited because there is no solvent in the alignment film. Therefore, rearrangement of the monomers generated in the photo-alignment process does not occur, and the orientation characteristic (anisotropic characteristic) is lowered.

However, in the present invention, by irradiating the microwaves affecting the movement of the molecules after the photo alignment process (ST130), it is possible to rearrange the monomers generated in the photo alignment process (ST130), thereby improving the orientation characteristics. This can minimize the problem of AC afterimage.

6A through 6E are cross-sectional views illustrating an alignment film manufacturing process according to an exemplary embodiment of the present invention.

6A to 6E illustrate the color filter substrate of the liquid crystal display as an example, but it may be applied to the case where the alignment layer is formed on the array substrate. In addition, the process of forming a color filter, a common electrode, etc. on the color filter substrate is shown, but is not limited thereto, and may be applied to the process of forming the alignment layer for the initial alignment of the liquid crystal.

First, as shown in FIG. 6A, a black matrix 102 as a light blocking means is formed on one surface of the substrate 100 in which a plurality of pixel regions P1, P2, and P3 are defined.

The black matrix 102 is for blocking light leakage regions, and is configured to correspond to gate wirings, data wirings, thin film transistors, and the like, and has a portion corresponding to the pixel regions P1, P2, and P3 open. It has a shape.

Next, the first color filter 104a is formed in the first pixel region P1 by coating and patterning any one of red, green, and blue color resins on the substrate 100 on which the black matrix 102 is formed. .

Next, as shown in FIG. 6B, the second color filter 104b is formed in the second pixel region P2 by coating and patterning any other color resin among red, green, and blue, and successively red, The third color filter 104c is formed in the third pixel region P3 by coating and patterning any one of green and blue color resins.

Thereafter, a transparent conductive material is deposited on the black matrix 102 and the first to third color filters 104a, 104b and 104c to form a common electrode 106. Although the common electrode 106 is formed on the first to third color filters 104a, 104b, and 104c in the drawing, the planarization layer (not shown) is formed on the first to third color filters 104a, 104b, It is formed covering the 104c, the common electrode 106 may be formed on the planarization layer.

Next, an alignment material layer 108 is formed by applying an optical alignment material such as polyamic acid on the common electrode 106.

As shown in FIG. 6C, a first firing process of irradiating or heating microwaves is performed on the alignment material layer 108. As shown in FIG. 5A, the imide reaction proceeds by the first firing process to obtain a polyimide.

For example, when irradiating microwaves in the first firing process, the imide reaction may be accelerated by the thermal and non-thermal effects of the microwaves. The high imidation rate can be obtained by irradiation of microwaves to minimize the problem of AC afterimage, and consequently to minimize the carboxylic acid site to prevent DC afterimage. In addition, it is possible to increase the process efficiency by reducing the process time.

As described above, a catalyst and a dehydrating agent may be used to increase the imidation ratio in the first firing step.

Next, as shown in FIG. 6D, a photo alignment process of irradiating UV is performed on the alignment material layer 108 having undergone the first firing process.

For example, the UV has a wavelength of about 230 ~ 270nm and can be irradiated for about 10 minutes. The UV irradiation process may be carried out at room temperature (25 ℃) or may be carried out under the conditions of about 170 ~ 230 ℃. In addition, the UV irradiation process may be performed in an inert gas, for example nitrogen atmosphere.

Next, as shown in FIG. 6E, a second firing process of irradiating microwaves to the substrate 100 having undergone the photo alignment process by UV irradiation is performed.

As described above, the cyclobutane ring of the polyimide is broken by the UV irradiation process to generate monomers. Such monomers lower the anisotropic properties of the alignment layer.

In the conventional alignment process, a post-baking process, which is a heating process, is performed after the UV irradiation process, and rearrangement of monomers does not occur even if heat is applied in the alignment film without the solvent. Therefore, the monomers arranged perpendicularly to the rubbing direction lower the anisotropy characteristic of the alignment layer, and the image quality of the liquid crystal display device also decreases due to the unwanted liquid crystal arrangement.

In the present invention, however, the rearrangement of monomers is caused by irradiating microwaves that affect the movement of molecules after the UV irradiation process. Therefore, it has the effect that the anisotropic characteristic of an oriented film improves. Therefore, in the case of the liquid crystal display including the alignment layer manufactured by the alignment layer manufacturing method according to the embodiment of the present invention, the afterimage is minimized to provide a high quality image.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be appreciated.

100: substrate
102: Black Matrix
104a: first color filter
104b: second color filter
104c: third color filter
106: common electrode
108: alignment material layer
110: alignment film

Claims (10)

Applying an optical alignment material on the substrate to form an alignment material layer;
A first firing step of causing an imide reaction in the alignment material layer;
A photo alignment step of irradiating UV on the alignment material layer after the first firing process;
A second firing step of irradiating microwaves to the alignment material layer after the photo alignment step
Method of forming an alignment film for a liquid crystal display device comprising a.
The method of claim 1,
The wavelength of the microwave used in the second firing step is a method of forming an alignment film for a liquid crystal display device, characterized in that 10 ~ 15cm.
The method of claim 1,
And the first firing step comprises irradiating microwaves to the alignment material layer.
The method of claim 3, wherein
The wavelength of the microwave used in the first firing step is a method of forming an alignment film for a liquid crystal display device, characterized in that 10 ~ 15cm.
The method of claim 3, wherein
And the first firing step of irradiating the layer of the alignment material with microwaves uses a catalyst and a dehydrating agent.
The method of claim 5, wherein
And said dehydrating agent is any one of acetic anhydride, propionic anhydride and trifluoroacetic anhydride.
The method of claim 5, wherein
The catalyst is a method of forming an alignment film for a liquid crystal display device, characterized in that any one of pyridine, collidine, lutidine, triethylamine.
The method of claim 1,
The first firing step is a method of forming an alignment layer for a liquid crystal display device, characterized in that the alignment material layer is heated for 1 hour under the conditions of 200 ~ 230 ℃.
The method of claim 1,
The UV has a wavelength of 230 ~ 270nm and the method of forming an alignment layer for a liquid crystal display device characterized in that for 5 to 15 minutes irradiation.
The method of claim 1,
And the photo-alignment material is a polyamic acid.

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