KR20090059458A - Alignment layer, forming method of the same, and liquid crystal display device including the same - Google Patents

Abstract

An alignment layer, a formation method thereof and a liquid crystal display including the same for improving the orientation force are provided to improve black brightness and reduce still-image. A polymer film(114) including a photo-induced material is coated on the top of a substrate. By using the stamp including a plurality of patterns in single-side, a plurality of grooves is formed on the membranous polymers film surface. The membranous polymers film including groove is plasticized. The polarized ultraviolet ray is irradiated in the plasticized polymer film. Groove has the depth of 10 nanometer to 1 micrometer and the width of 10 nanometer to 1 micrometer.

Description

An alignment layer, a method of forming the same, and a liquid crystal display including the same {alignment layer, forming method of the same, and liquid crystal display device including the same}

The present invention relates to a liquid crystal display device, and more particularly, to an alignment layer, a method of forming the same, and a liquid crystal display device including the same.

In general, a liquid crystal display device is disposed by facing two substrates on which the field generating electrodes are formed, injecting a liquid crystal material between the two substrates, and then moving the liquid crystal molecules by an electric field generated by applying a voltage to the field generating electrodes. Therefore, the device expresses an image by the transmittance of light which varies accordingly.

Hereinafter, a liquid crystal display according to the related art will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view showing a conventional liquid crystal display device.

As shown in FIG. 1, the liquid crystal display includes a lower substrate 10 and an upper substrate 30 arranged at a predetermined interval, and the liquid crystal layer 50 is positioned between the two substrates 10 and 30. do.

The gate electrode 12 is formed on the inner surface of the lower substrate 10, and the gate insulating layer 14 covers the gate electrode 12. The active layer 16 and the ohmic contact layer 18 are sequentially formed on the gate insulating layer 14 on the gate electrode 12, and the source and drain electrodes 20 and 22 are formed thereon. The source and drain electrodes 20 and 22 are spaced apart from the gate electrode 12, and the ohmic contact layer 18 is divided into two parts by removing corresponding regions between the source and drain electrodes 20 and 22. Lose. The active layer 16 is exposed between the source and drain electrodes 20, 22. The gate electrode 12, the active layer 16, the ohmic contact layer 18, and the source and drain electrodes 20 and 22 form a thin film transistor T and are exposed between the source and drain electrodes 20 and 22. The portion of the active layer 16 thus formed becomes a channel of the thin film transistor T. Although not illustrated, a gate wiring connected to the gate electrode 12 is formed on the same layer as the gate electrode 12, and the data wiring connected to the source electrode 20 on the same layer as the source and drain electrodes 20 and 22. Are formed, and the gate wiring and the data wiring intersect to define the pixel region.

A passivation layer 24 is formed on the thin film transistor T, and the passivation layer 24 has a contact hole 24a partially exposing the drain electrode 22. The pixel electrode 26 is formed in the pixel area above the passivation layer 24, and the pixel electrode 26 contacts the drain electrode 22 through the contact hole 24a.

On the inner surface of the upper substrate 30, a black matrix 32 having an opening corresponding to the pixel region is formed, and a color filter layer 34 is formed corresponding to the opening of the black matrix 32. The black matrix 32 prevents the light leakage current generated in the thin film transistor T in correspondence with the thin film transistor T, and blocks light in portions other than the pixel region in correspondence with the gate wiring and the data wiring. The color filter layer 34 includes red, green, and blue color filters, and one color filter corresponds to one pixel area. In addition, the color filter layer 34 partially overlaps the black matrix 32 to form a boundary between the color filters on the black matrix 32. The transparent common electrode 36 is formed on the entire surface of the upper substrate 30 on the color filter layer 34.

In order to protect the color filter layer 34 and to flatten the surface of the upper substrate 30 including the color filter layer 34, an overcoat layer (not shown) is further provided between the color filter layer 34 and the common electrode 36. It may be formed.

Liquid crystal molecules of the liquid crystal layer 50 positioned between the two substrates 10 and 30 are arranged parallel to the two substrates 10 and 30.

The lower alignment layer 42 and the upper alignment layer 44 are formed on the two substrates 10 and 30 adjacent to the liquid crystal layer 50, respectively, and the surfaces of the lower and upper alignment layers 42 and 44 are aligned in a predetermined direction to form a liquid crystal. Determine the initial arrangement of the molecules.

In this case, the alignment direction of the lower alignment layer 42 and the alignment direction of the upper alignment layer 44 may be vertical. In this case, the liquid crystal molecules of the liquid crystal layer 50 have a 90 degree twisted arrangement from the liquid crystal molecules adjacent to the lower substrate 10 to the liquid crystal molecules adjacent to the upper substrate 30, and the twisted nematic ( It is called twisted nematic mode.

The rubbing orientation method is a typical method for making the surfaces of the alignment films 42 and 44 have a constant orientation.

The rubbing orientation method is a method of aligning an organic polymer in a predetermined direction by coating the organic polymer on a substrate in the form of a thin film and then rotating the rubbing roll wound with a rubbing cloth to rub the organic polymer. As the material of the rubbing orientation method, a polyimide polymer compound having low dielectric constant, high thermal stability, and excellent mechanical strength is mainly used. This rubbing orientation method has been widely used because it can process a large area at high speed.

However, the rubbing orientation method may cause contamination and may cause peripheral element destruction. In more detail, in the rubbing orientation method, since the orientation is induced by the contact of the rubbing cloth and the polymer film, unwanted scratches or foreign matter from the rubbing cloth remain on the alignment film. Thus, problems such as spots on the screen may be caused. In addition, static electricity may be generated during the rubbing process, and the peripheral device may be destroyed by the static electricity.

On the other hand, as mentioned above, a plurality of patterned layers are formed on the substrate of the liquid crystal display device. That is, the thin film transistor, the gate and the data wiring, and the pixel electrode are formed on the lower substrate, and the color filter layer and the common electrode are formed on the upper substrate. Therefore, these layers produce a step on the substrate, and the step results in a region in which the rubbing cloth cannot come into contact with the alignment film. In this case, the alignment of the liquid crystal is not uniform in the region, the light leakage phenomenon occurs.

In particular, as a method for overcoming the narrow viewing angle of the TN mode liquid crystal display, a transverse field type liquid crystal display has been developed. In the transverse field type liquid crystal display, since the patterned common electrode and the pixel electrode are repeated on the lower substrate, There are many areas that occur. Therefore, the area where the orientation is not uniform is increased and the possibility of light leakage phenomenon is high.

In the transverse electric field type liquid crystal display device, since the common electrode is formed on the lower substrate, an alignment film is formed on the color filter layer or the overcoat layer of the upper substrate. If the alignment layer is formed directly on the color filter layer and the rubbing process is performed, the color filter layer may be damaged. If the alignment layer is formed on the overcoat layer and the rubbing process is performed, the overcoat layer may be somewhat soft. Linear staining occurs, which causes a defect of the liquid crystal display device.

As such, the problem of the rubbing orientation method is caused by the physical contact between the rubbing roll and the substrate.

Therefore, in order to solve the problem of the rubbing orientation method, a method of forming an alignment layer that does not require physical contact has been widely studied. Among them, a photo-alignment method has been proposed in which an alignment film has structural anisotropy by irradiating polarized light (UV) to the polymer film.

However, the photo-alignment method can solve the problem of the rubbing alignment method by physical contact, but has the disadvantage of low anchoring energy.

More specifically, in the rubbing orientation method, since the side chains of the organic polymer are aligned in a certain direction, the alignment of the liquid crystal is controlled not only by the chemical interaction between the side chains and the liquid crystal molecules, but also by rubbing on the surface of the alignment layer. Since a plurality of regular grooves are generated, the orientation of the liquid crystal molecules is also controlled by the mechanical interaction between the grooves and the liquid crystal molecules. In contrast, in the photoalignment method, no groove is formed on the surface of the alignment layer, and the alignment of the liquid crystal molecules is controlled only by chemical interaction between the polymer film and the liquid crystal molecules by photoreaction. Therefore, the photo-alignment method has a lower anchoring energy than the rubbing alignment method, which causes afterimages.

2 is a graph showing the azimuth anchoring energy of the alignment layer formed by the conventional rubbing and photoalignment methods. Here, P1 and P2 on the graph represent the alignment film formed by the photoalignment method, and R1 and R2 represent the alignment film formed by the rubbing orientation method.

As shown in FIG. 2, the azimuthal anchoring energy of the alignment films R1 and R2 formed by the rubbing orientation method and the alignment films P1 and P2 formed by the photoalignment method was measured, and thus formed by the rubbing orientation method. It can be seen that the anchoring energy of the alignment layers R1 and R2 has a value that is about 10 times larger than the anchoring energy of the alignment layers P1 and P2 formed by the photoalignment method.

The weak alignment force of the alignment film by the photo-alignment method appears as a problem such as an afterimage or an increase in black luminance.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an alignment film and a method of forming the same by the photo-alignment method which can improve the orientation force.

Another object of the present invention is to provide an alignment layer, a method for forming the same, and a liquid crystal display including the same, capable of reducing afterimages and improving black luminance.

In order to achieve the above object, the alignment layer forming method of the present invention comprises applying a polymer film including a photo-alignment material on a substrate, and using a stamp including a plurality of patterns on one surface to form a plurality of grooves on the surface of the polymer film. Forming, firing the polymer film including the grooves, and irradiating polarized ultraviolet rays to the fired polymer film. Here, the groove preferably has a width of 10 nanometers to 1 micrometer and a depth of 10 nanometers to 1 micrometer.

Firing the polymer film is performed for 30 minutes to 4 hours at a temperature of 200 to 350 degrees.

The photo-alignment material includes a photoreactor selected from cinnamoyl and azo materials. Alternatively, the photo-alignment material may include a cyclobutane dianhydride (CBDA) as a photoreactor, wherein the polarization direction of the polarized ultraviolet light is perpendicular to the longitudinal direction of the groove.

According to an exemplary embodiment of the present invention, a liquid crystal display device includes a first and a second substrate disposed opposite to each other, a first and a second alignment layer formed on inner surfaces of the first and second substrates, and the first and second alignment layers, respectively. Wherein the first and second alignment layers are formed of a photo-alignment material, and include grooves having a width of 10 nanometers to 1 micrometer and a depth of 10 nanometers to 1 micrometer on the surface.

On the other hand, the liquid crystal display of the present invention further comprises a pixel electrode and a common electrode formed on the first substrate, the reflecting portion and the transmissive portion is defined on the first and the second substrate, the first portion located in the reflecting portion An orientation direction of the first and second alignment layers is different from an orientation direction of the first and second alignment layers positioned in the transmission part.

According to the present invention, in forming an alignment layer by photo-alignment method to prevent staining due to contamination or element destruction by static electricity, a plurality of grooves are formed on the surface of the alignment layer to provide not only chemical interaction between the alignment layer and the liquid crystal molecules, The orientation of the liquid crystal molecules is also controlled by the mechanical interaction between and the liquid crystal molecules. Accordingly, the alignment force of the liquid crystal molecules may be improved to reduce afterimages and to improve black brightness.

In addition, by applying the alignment layer according to the present invention to the transmissive transverse electric field type liquid crystal display device, a separate retardation layer may be omitted, thereby reducing costs and processes.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention.

3 is a perspective view showing an alignment film formed according to an embodiment of the present invention.

As illustrated, the alignment layer 110 of the present invention includes a plurality of grooves 114 formed along one direction on the surface of the polymer layer 112. Each groove 114 has a width w of about 10 nanometers to 1 micrometer and a depth d of about 10 nanometers to 1 micrometer.

Although not shown, a side chain of the polymer is arranged on the surface of the polymer film 112 in parallel with the longitudinal direction of the groove 114.

The alignment layer 110 according to the present invention is formed using a photoalignment material. Such a photo-orientation material includes a polymer having a photoreactor, and induces a photoreaction by irradiating polarized ultraviolet rays to the polymer film, thereby making the polymer film anisotropic. The photo-alignment material used in the present invention is divided into polymers that undergo photo-dimerization, photo-decomposition, and photo-isomerization reactions according to the reaction to ultraviolet rays.

The photopolymerization reaction induces anisotropy by irradiating linearly polarized ultraviolet rays to the polymer membrane and reacting only molecules in a specific direction. The photo-alignment material that undergoes the photopolymerization reaction is a photoreactor with a cinnamoyl type in the polymer side chain. Polymers containing materials may be used. When irradiating linearly polarized ultraviolet rays, a polymerization reaction occurs selectively when the direction of the carbon double bond in the cinnamoyl-based material included in the polymer side chain coincides with the polarization direction of the ultraviolet ray. Therefore, linear photopolymerization of a polymer containing cinnamoyl based material using such a property may impart anisotropic properties to the polymer film.

The photolysis reaction is to selectively cleave molecular bonds in a specific direction by irradiating linearly polarized ultraviolet rays onto the polymer membrane. As the photo-alignment material for the photolysis reaction, a CBDA-based polymer including cyclobutane dianhydride (CBDA) may be used as the photoreactor. CBDA-based polymer has the following structure.

When ultraviolet rays linearly polarized on the CBDA-based polymer are irradiated, the CBDA ring of the side chain located in the polarization direction is decomposed and only the side chain in the direction perpendicular to the polarization direction remains, so that the liquid crystal molecules are aligned in the direction perpendicular to the polarization direction. do.

The photoisomerization reaction converts cis-state polymer materials into trans-state polymer materials by irradiating polarized light or converts trans-type polymer materials into cis-type liquid crystal molecules. It is to determine the orientation direction of. In the case of the cis type, the side chains are arranged parallel to the substrate so that the liquid crystal molecules are arranged homogeneously in the substrate. In the case of the trans type, the side chains are arranged perpendicular to the substrate and the liquid crystal molecules are arranged perpendicular to the substrate. alignment).

As the photo-alignment material for the photoisomerization reaction, a polymer including an azo-based material may be used as the photoreactor.

Hereinafter, an alignment film forming method according to an embodiment of the present invention will be described in detail with reference to FIGS. 4A to 4F.

4A to 4F are perspective views illustrating an alignment film forming process according to an exemplary embodiment of the present invention. Here, the material of the alignment layer is a material causing a photolysis reaction, and will be described taking as an example a CBDA-based polymer material including a cyclobutane dianhydride (CBDA) as an optical reactor.

As shown in FIG. 4A, the polymer film 112 is formed on the substrate 100. The polymer film 112 may be formed by dissolving a CBDA-based polymer in an organic solvent and then applying it onto the substrate 100. In this case, a coating method such as spin coating, roll coating, or bar coating may be used as the coating method, or a printing method may be used.

Here, various layers may be formed on the substrate 100 under the polymer film 112. For example, layers such as a gate line, a data line, a thin film transistor, and a pixel electrode may be formed on the substrate 100, or layers such as a black matrix, a color filter layer, and a common electrode may be formed. In the case of a transverse electric field type liquid crystal display, the pixel electrode and the common electrode may be formed together on the substrate 100, and only the black matrix and the color filter layer may be formed.

Subsequently, as shown in FIG. 4B, a stamp 120 is disposed on the polymer film 112. The stamp 120 includes a plurality of patterns engraved or embossed on one surface. For example, the stamp 120 may include a plurality of convex patterns 122 formed along one direction. Here, the stamp 120 is arranged so that the convex pattern 122 faces the polymer film 112.

As shown in FIG. 4C, the stamp 120 is contacted with the polymer film 112 and pressure is applied to the stamp 120 so that the material of the polymer film 112 is filled in the space between the convex patterns 122. Therefore, a pattern corresponding to the convex pattern 122 of the stamp 120 is formed on the surface of the polymer film 112. Subsequently, the polymer membrane 112 is fired by heating at a temperature of about 200 to 350 degrees for about 30 minutes to 4 hours.

Here, the space between the convex pattern 122 may be filled by capillary phenomenon by using the surface energy difference between the stamp 120 and the polymer film 112.

As shown in FIG. 4D, when the stamp 120 is separated from the fired polymer film 112, the surface of the polymer film 112 corresponds to the convex pattern 122 of the stamp 120 in the longitudinal direction along the first direction. A plurality of grooves 114 are formed. In addition, the CBDA-based polymer 116 having an irregular arrangement is located on the surface of the polymer film 112.

Next, as illustrated in FIG. 4E, ultraviolet rays linearly polarized on the alignment layer 110 are irradiated. At this time, the polarization direction of the ultraviolet ray is a second direction perpendicular to the first direction, and thus the polarization direction of the ultraviolet ray is perpendicular to the longitudinal direction of the groove 114. As such, when irradiated with ultraviolet rays, the side chain 116a of the polymer having a direction perpendicular to the polarization direction is decomposed and the side chain 116a of the polymer remains in the side chain 116a of the first direction. 114) are arranged side by side. Therefore, the alignment layer 110 according to the present invention can be formed.

Subsequently, as shown in FIG. 4F, when the liquid crystal molecules 130 are disposed on the alignment layer 110, the liquid crystal molecules 130 are arranged in parallel with the grooves 114 and the side chains 116a.

As such, when using the alignment layer 110 of the present invention having a groove 114 on the surface and formed of a photo-alignment material, in addition to the mechanical interaction between the groove 114 and the liquid crystal molecules 130, the side chain 116a and the liquid crystal molecules Since the orientation is controlled by the chemical interaction between the 130, it is possible to increase the anchoring energy. Therefore, it is possible to reduce the occurrence of afterimages and to improve the black luminance. In addition, when the alignment film according to the present invention is used, problems such as scratches or foreign matter due to rubbing do not occur through non-contact orientation.

Here, the width and depth of the groove 114 may be formed smaller than the groove generated by the rubbing orientation by adjusting the pattern size of the stamp. As mentioned above, the width of the groove 114 may be smaller than about 10 nanometers. It is preferred that it is larger and smaller than 1 micrometer, and the depth is larger than 10 nanometers and smaller than 1 micrometer.

On the other hand, the photo-alignment method is easy to form regions having different alignment directions in one alignment film, so that the multi-domain can be formed in the pixel region by the photo-alignment method, thereby ensuring a wide viewing angle. Accordingly, by applying the method of manufacturing the alignment film according to the present invention, it is possible to provide a liquid crystal display device having a wide viewing angle and having no afterimage and having black bend due to strong alignment force.

In addition, the divisional orientation may be applied to the reflective transmissive liquid crystal display, which will be described in detail with reference to FIG. 5.

5 is a cross-sectional view schematically showing a reflective liquid crystal display device according to the present invention. The reflective transmissive liquid crystal display is a transverse electric field mode in which a pixel electrode and a common electrode are formed on the same substrate to induce a horizontal electric field.

As illustrated, the first substrate 210 and the second substrate 220 are disposed to be spaced apart at regular intervals, and the reflecting portion R and the transmitting portion T are disposed on the first substrate 210 and the second substrate 220. ) Is defined. The liquid crystal layer 230 is positioned between the first and second substrates 210 and 220.

On the inner surfaces of the first substrate 210 and the second substrate 220 adjacent to the liquid crystal layer 230, first and second alignment layers 214 and 222 for initial arrangement of liquid crystal molecules of the liquid crystal layer 230 are respectively formed. Is formed. The reflecting plate 212 is formed in the reflecting portion R of the first substrate 210, and the first alignment layer 214 covers the reflecting plate 212. In addition, first and second polarizing plates 242 and 244 are attached to outer surfaces of the first and second substrates 210 and 220, respectively. The light transmission axis of the first polarizing plate 242 has a direction perpendicular to the light transmission axis of the second polarizing plate 244.

Although not shown, a common electrode and a pixel electrode are formed between the first substrate 210 and the first alignment layer 214. When voltage is applied to the two electrodes, the first and second substrates 210 are disposed between the two electrodes. , A horizontal electric field parallel to 220 is formed.

Here, the first and second alignment layers 214 and 222 are made of a photoalignment material, and are formed according to the process illustrated in FIGS. 4A to 4E, and have grooves (not shown) in a predetermined direction on the surface.

In the reflective part R of the transflective liquid crystal display, light from the outside passes through the second polarizing plate 244, and then sequentially turns the second substrate 220, the second alignment layer 222, and the liquid crystal layer 230. After passing, the light is reflected by the reflector 212, and then passes through the liquid crystal layer 230, the second alignment layer 222, and the second substrate 220 in order to reach the second polarizer 244.

On the other hand, in the transmission part T, light from a backlight (not shown) under the first polarizing plate 242 passes through the first polarizing plate 242, and the first substrate 210, the first alignment layer 214, and the liquid crystal. The second polarizer 244 is sequentially passed through the layer 230, the second alignment layer 222, and the second substrate 220.

In this case, when the light reaching the second polarizing plate 244 coincides with the light transmission axis of the second polarizing plate 244, the white image is displayed and coincides with the light transmission axis of the second polarizing plate 244. If not, it is blocked and a black image is displayed.

However, in the transmission part T, light passes through the liquid crystal layer 230 only once, whereas in the reflection part R, the light passes through the liquid crystal layer 230 twice, so that the reflection part R and the transmission part T ), There is a path difference between the lights, and the output light is not the same. Therefore, in order to make the state of light output from the transmission part T and the reflection part R equal, the thickness of the liquid crystal layer 230 of the transmission part T is equal to 2 of the thickness of the liquid crystal layer 230 of the reflection part R. It is desirable to double.

Meanwhile, a retardation plate may be further provided between the second substrate 222 and the second polarizing plate 244. In this case, the polarization state of the light is changed in the transmission part T by the birefringence of the liquid crystal layer 230 and the retardation plate. Light in an undesired direction such as elliptical polarization is generated, which lowers the brightness of the black state. Therefore, a method of forming a separate phase difference layer only in the reflecting portion R has been required.

However, in the present invention, the orientation directions of the first and second alignment layers 214 and 222 are different in the reflecting portion R and the transmitting portion T. Therefore, the light output from the reflecting portion R and the transmitting portion T is controlled by adjusting the alignment directions in the reflecting portion R and the transmitting portion T, even if a separate phase difference layer is not formed in the reflecting portion R. The state of can be made the same, and the brightness of the black state can be improved. In addition, since it is not necessary to form a separate retardation layer, the manufacturing process and cost can be reduced.

The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit of the present invention.

1 is a cross-sectional view showing a conventional liquid crystal display device.

2 is a graph showing the azimuth anchoring energy of the alignment layer formed by the conventional rubbing and photoalignment methods.

3 is a perspective view showing an alignment film formed according to an embodiment of the present invention.

4A to 4F are perspective views illustrating an alignment film forming process according to an exemplary embodiment of the present invention.

5 is a cross-sectional view schematically showing a reflective liquid crystal display device according to the present invention.

Claims (9)

Coating a polymer film including a photo-alignment material on a substrate; Forming a plurality of grooves on the surface of the polymer film by using a stamp including a plurality of patterns on one surface; Firing the polymer film including the grooves; Irradiating polarized ultraviolet rays to the fired polymer film An alignment film forming method comprising a. The method according to claim 1, The groove has a width of 10 nanometers to 1 micrometer and a depth of 10 nanometers to 1 micrometer. The method according to claim 1, The firing of the polymer film is carried out for 30 minutes to 4 hours at a temperature of 200 to 350 degrees. The method according to claim 1, The photo-alignment material is an alignment film forming method comprising a photoreactor selected from cinnamoyl (a) and azo (azo) based materials. The method according to claim 1, The photo-alignment material comprises a cyclobutane dianhydride (CBDA) as a photoreactor, wherein the polarization direction of the polarized ultraviolet light is perpendicular to the longitudinal direction of the groove. An alignment layer formed of a photo-alignment material, the groove includes a groove having a width of 10 nanometers to 1 micrometer and a depth of 10 nanometers to 1 micrometer. The method according to claim 6, The photo-alignment material is an alignment layer comprising a photoreactor selected from cinnamoyl-based, azo-based and cyclobutane dianhydride (CBDA) -based material. First and second substrates facing each other; First and second alignment layers formed on inner surfaces of the first and second substrates, respectively; A liquid crystal layer positioned between the first and second alignment layers Including, The first and second alignment layers are formed of an optical alignment material, and include a groove having a width of 10 nanometers to 1 micrometer and a depth of 10 nanometers to 1 micrometer on the surface. The method according to claim 8, Further comprising a pixel electrode and a common electrode formed on the first substrate, the reflecting portion and the transmission portion is defined on the first and second substrate, the alignment direction of the first and second alignment layer positioned in the reflecting portion is And a direction different from that of the first and second alignment layers positioned in the transmissive part.

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