Curved liquid crystal display

A curved liquid crystal display is provided. The curved liquid crystal display (LCD) comprises a first curved substrate; a second curved substrate; a first curved liquid crystal alignment layer disposed between the first curved substrate and the second curved substrate; a second curved liquid crystal alignment layer disposed between the first curved liquid crystal alignment layer and the second curved substrate; and a liquid crystal layer including first and second liquid crystal molecules with negative dielectric anisotropy and disposed between the first curved liquid crystal alignment layer and the second curved liquid crystal alignment layer, the first liquid crystal molecules are aligned at a surface of the first curved liquid crystal alignment layer, and the second liquid crystal molecules are aligned at a surface of the second curved liquid crystal alignment layer, wherein, in an initial state when no electric field is applied, the first liquid crystal molecules are relatively vertically aligned as compared with the second liquid crystal molecules with respect to the first curved substrate and the second liquid crystal molecules are relatively tilt-aligned as compared with the first liquid crystal molecules with respect to the first curved substrate.

CLAIM OF PRIORITY

This application claims the priority of and all the benefits accruing under 35 U.S.C. §119 to Korean Patent Application No. 10-2014-0155383 filed on Nov. 10, 2014, Korean Patent Application No. 10-2015-0041474 filed on Mar. 25, 2015 and Korean Patent Application No. 10-2015-0122352 filed on Aug. 31, 2015 in the Korean Intellectual Property Office (KIPO), the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Disclosure

The invention relates to a curved liquid crystal display (LCD).

2. Description of the Related Art

Liquid crystal displays (LCDs) are one of the most widely used types of flat panel displays. Generally, an LCD includes a pair of display panels having electric field generating electrodes such as pixel electrodes and a common electrode and a liquid crystal layer interposed between the display panels.

The LCD generates an electric field in the liquid crystal layer by applying voltages to the electric field generating electrodes. Accordingly, the alignment of liquid crystals of the liquid crystal layer is determined, and polarization of incident light is controlled. As a result, an image is displayed on the LCD.

As LCDs are used as displays of television receivers, their screen is becoming larger in size. As the size of the LCDs increases, a viewing angle may greatly differ depending on whether a viewer watches a central part of the screen or both ends of the screen.

To compensate for this difference in viewing angle, LCDs may be curved (concave or convex). From the perspective of a viewer, LCDs may be classified into portrait-type LCDs whose vertical length is greater than their horizontal length and are curved in a vertical direction and landscape-type LCDs whose vertical length is smaller than their horizontal length and are curved in a horizontal direction.

SUMMARY OF THE INVENTION

Exemplary embodiments of the invention provide a curved liquid crystal display (LCD) with improved light transmittance.

However, exemplary embodiments of the invention are not restricted to those set forth herein. The above and other exemplary embodiments of the invention will become more apparent to one of ordinary skill in the art to which the invention pertains by referencing the detailed description of the invention given below.

According to an exemplary embodiment of the invention, a curved liquid crystal display (LCD), comprises a first curved substrate; a second curved substrate; a first curved liquid crystal alignment layer disposed between the first curved substrate and the second curved substrate; a second curved liquid crystal alignment layer disposed between the first curved liquid crystal alignment layer and the second curved substrate; and a liquid crystal layer including first and second liquid crystal molecules with negative dielectric anisotropy and disposed between the first curved liquid crystal alignment layer and the second curved liquid crystal alignment layer, the first liquid crystal molecules are aligned at a surface of the first curved liquid crystal alignment layer, and the second liquid crystal molecules are aligned at a surface of the second curved liquid crystal alignment layer, wherein, in an initial state when no electric field is applied, the first liquid crystal molecules are relatively vertically aligned as compared with the second liquid crystal molecules with respect to the first curved substrate and the second liquid crystal molecules are relatively tilt-aligned as compared with the first liquid crystal molecules with respect to the first curved substrate.

The curved LCD according to the exemplary embodiment of the invention, may further comprise a patternless electrode disposed between the first curved substrate and the first curved liquid crystal alignment layer and having no slit pattern; and a pattern electrode disposed between the second curved liquid crystal alignment layer and the second curved substrate and having a slit pattern.

In the curved LCD according to the exemplary embodiment of the invention, the second curved liquid crystal alignment layer may have a higher content of polymerized reactive mesogens per unit area than the first curved liquid crystal alignment layer.

In the curved LCD according to the exemplary embodiment of the invention, the first curved liquid crystal alignment layer may have a lower content of a polymerization initiator than the second curved liquid crystal alignment layer.

In the curved LCD according to the exemplary embodiment of the invention, the second curved liquid crystal alignment layer may include a “2-1” curved liquid crystal alignment layer and a “2-2” curved liquid crystal alignment layer having a lower content of an imide group (—CONHCO—) than the “2-1” curved liquid crystal alignment layer and having a higher content of polymerized reactive mesogens than the “2-1” curved liquid crystal alignment layer.

In the curved LCD according to the exemplary embodiment of the invention, a side of the first curved substrate facing a user viewing an image displayed by the LCD may be concave.

According to another exemplary embodiment of the invention, a curved liquid crystal display (LCD), comprises a first curved substrate; a second curved substrate; a liquid crystal layer disposed between the first curved substrate and the second curved substrate, the liquid crystal layer including liquid crystal molecules with negative dielectric anisotropy; a first curved liquid crystal alignment layer disposed between the liquid crystal layer and the first curved substrate; and a second curved liquid crystal alignment layer disposed between the liquid crystal layer and the second curved substrate, the second curved liquid crystal alignment layer having a higher content of a polymerization initiator than the first curved liquid crystal alignment layer.

The curved LCD according to the another exemplary embodiment of the invention, may further comprise a patternless electrode disposed between the first curved substrate and the first curved liquid crystal alignment layer and having no slit pattern; and a pattern electrode disposed between the second curved liquid crystal alignment layer and the second curved substrate and having a slit pattern.

In the curved LCD according to the another exemplary embodiment of the invention, the liquid crystal molecules may include first liquid crystal molecules aligned at a surface of the first curved liquid crystal alignment layer and second liquid crystal molecules aligned at a surface of the second curved liquid crystal alignment layer, in an initial state when no electric field is applied, the first liquid crystal molecules may be relatively vertically aligned as compared with the second liquid crystal molecules with respect to the first curved substrate and the second liquid crystal molecules may be relatively tilt-aligned as compared with the first liquid crystal molecules with respect to the first curved substrate.

In the curved LCD according to the another exemplary embodiment of the invention, the second curved liquid crystal alignment layer may include a “2-1” curved liquid crystal alignment layer and a “2-2” curved liquid crystal alignment layer having a lower content of an imide group (—CONHCO—) than the “2-1” curved liquid crystal alignment layer and having a higher content of polymerized reactive mesogens than the “2-1” curved liquid crystal alignment layer.

In the curved LCD according to the another exemplary embodiment of the invention, a side of the first curved substrate facing a user viewing an image displayed by the LCD may be concave.

According to the exemplary embodiments, it is possible to provide a curved LCD with improved light transmittance.

Other features and exemplary embodiments will be apparent from the following detailed description, the drawings, and the claims.

DETAILED DESCRIPTION OF THE INVENTION

Spatially related terms, such as “below”, “lower”, “under”, “above”, “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially related terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” relative to other elements or features would then be oriented “above” relative to the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially related descriptors used herein interpreted accordingly.

Exemplary embodiments of the invention will hereinafter be described with reference to the accompanying drawings.

FIG. 1is a schematic exploded oblique view of a curved liquid crystal display (LCD) according to an exemplary embodiment of the invention.FIG. 2is a schematic enlarged view of area II ofFIG. 1.

Referring toFIGS. 1 and 2, a curved LCD500C includes a first curved substrate100C, a second curved substrate200C spaced apart from and facing the first curved substrate100C, and a liquid crystal layer300C disposed between the first curved substrate100C and the second curved substrate200C.

Each of the first and second curved substrates100C and200C includes a display area DAC and a non-display area NDAC. The display area DAC is a region where an image can be viewed, and the non-display area NDAC is a region where no image is viewed. The display area DAC is surrounded by the non-display area NDAC.

A common electrode110C may be disposed between the first curved substrate100C and the second curved substrate200C, and may be a “patternless” electrode with no slit pattern. Pixel electrodes291C may be disposed between the second curved substrate200C and the common electrode110C, and may be patterned electrodes with slit patterns.

The liquid crystal layer300C may be disposed between the common electrode110C and the pixel electrodes291C. The liquid crystal layer300C may include liquid crystal molecules LC with negative dielectric anisotropy. A first curved liquid crystal alignment layer AL1C may be disposed between the common electrode110C and the liquid crystal layer300C. A second curved liquid crystal alignment layer AL2C may be disposed between the liquid crystal layer300C and the pixel electrodes291C.

The second curved substrate200C may be a thin-film transistor (TFT) substrate. In the display area DAC of the second curved substrate200C, a plurality of gate lines GLC, which extend in a first direction, and a plurality of data lines DLC, which extend in a second direction that is perpendicular to the first direction, may be formed. The pixel electrodes291C may be disposed in pixels PXC, respectively, which are defined by the gate lines GLC and the data lines DLC.

Each of the pixel electrodes291C may include sub-pixel electrodes291-1C and291-2C, which are spaced apart from each other. For example, the sub-pixel electrodes291-1C and291-2C may be generally rectangular. Each of the sub-pixel electrodes291-1C and291-2C may be pattern electrodes with slit patterns. More specifically, each of the sub-pixel electrodes291-1C and291-2C may have slit patterns including a stem SC, branches BC extended from the stem SC and incisions DC disposed among the stem SC and the branches BC. The stem SC may be formed in a cross shape, and the branches BC may be radially branched off from the stem SC at an angle of about 45° relative to the stem SC.

Each of the gate lines GLC may include gate electrodes224-1C and224-2C, which protrude from the gate lines GLC toward the pixel electrodes291C along the second direction. Each of the data lines DLC may include source electrodes273-1C and273-2C and drain electrodes275-1C and275-2C. The source electrodes273-1C and273-2C may protrude from the data lines DLC and may be formed in a U shape. The drain electrodes275-1C and275-2C may be spaced apart from the source electrodes273-1C and273-2C.

The pixel electrodes291C may be provided with a data voltage via switching elements TFTs. The gate electrodes224-1C and224-2C, which correspond to the control terminals of the TFTs, may be electrically connected to one of the gate lines GLC, and the source electrodes273-1C and273-2C, which correspond to the input terminals of the TFTs, may be electrically connected to one of the data lines DLC via contact holes285-1C,285-2C,285-3C and285-4C, and the drain electrodes275-1C and275-2C, which correspond to the output terminals of the TFTs, may be electrically connected to one of the pixel electrodes291C.

The pixel electrodes291C may generate an electric field together with the common electrode110C and may thus control the alignment direction of the liquid crystal molecules LC of the liquid crystal layer300C, which is disposed between the common electrode110C and the pixel electrodes291C. The pixel electrodes291C may distort the electric field and may thus control the alignment direction of first liquid crystal molecules LC1and the alignment direction of second liquid crystal molecules LC2.

The TFT substrate may have a structure in which a base substrate (not illustrated) formed of glass or a polymer, the gate electrodes224-1C and224-2C, a gate insulating layer (not illustrated), a semiconductor layer (not illustrated), an ohmic contact layer (not illustrated), the source electrodes273-1C and273-2C, the drain electrodes275-1C and275-2C, a passivation layer (not illustrated) and an organic layer (not illustrated) are stacked.

The channel of the TFTs may be formed by the semiconductor layer. The semiconductor layer may be disposed to overlap the gate electrodes224-1C and224-2C. The source electrodes273-1C and273-2C may be spaced apart from the drain electrodes275-1C and275-2C, respectively, relative to the semiconductor layer.

A sustain electrode line SLC may include a stem line231C, which extends substantially in parallel to the gate lines GLC, and a plurality of branch lines235C, which are branched off from the stem line231C. The sustain electrode line SLC may be optional, and the shape and arrangement of the sustain electrode line SLC may be varied.

The non-display area NDAC, which is the periphery of the display area DAC, may be a light-shielding region surrounding the display area DAC. In the non-display area NDAC of the second curved substrate200C, one or more driving units (not illustrated) providing a gate driving signal and a data driving signal to each of the pixels PXC in the display area DAC may be provided. The gate lines GLC and the data lines DLC may extend from the display area DAC through to the non-display area NDAC, and may be connected to the driving units.

The first curved substrate100C may be a substrate opposite to the second curved substrate200C. The common electrode110C may be disposed on the first curved substrate100C.

A color filter layer (not illustrated) may be formed in part of the display area DAC corresponding to each of the pixels PXC, and may include red (R), green (G) and blue (B) color filters. The color filter layer may be included in one of the first and second curved substrates100C and200C. For example, in response to the color filter layer being included in the first curved substrate100C, the first curved substrate100C may have a structure in which a base substrate (not illustrated) formed of glass or a polymer, the color filter layer and an overcoat layer (not illustrated) are stacked. The overcoat layer may be a planarization layer covering the color filter layer. In this example, the common electrode110C may be disposed on the overcoat layer.

Alternatively, in response to the color filter layer being included in the second curved substrate200C, the second curved substrate200C may have a color-filter-on-array (COA) structure in which the color filter layer is formed on a transparent insulating substrate where the TFTs are provided. For example, the color filter layer may be disposed between an organic layer and a passivation layer that covers the source electrodes273-1C and273-2C and the drain electrodes275-1C and275-2C.

A light-shielding pattern layer (not illustrated) may be disposed along the boundaries among the R, G and B color filters of the color filter layer. The light-shielding pattern layer may be included in one of the first and second curved substrates100C and200C. For example, the light-shielding pattern layer may be a black matrix.

During the fabrication of the curved LCD500C by bending a flat-panel LCD, a misalignment may occur between the first curved substrate100C and the second curved substrate200C due to the stress applied to the first and second curved substrates100C and200C. For example, during the bending of the flat-panel LCD, the first curved substrate100C may be shifted leftward or rightward relative to the second curved substrate200C, and as a result, the state of the alignment of the first and second curved substrates100C and200C may become different from the state of the alignment of the first and second flat substrates of the flat-panel LCD. Such misalignment between the first curved substrate100C and the second curved substrate200C may degrade the display quality of the curved LCD500C.

For example, when each of the first and second curved liquid crystal alignment layers AL1C and AL2C includes multiple domains that differ from each other in the alignment direction of the directors of liquid crystal molecules therein, any misalignment between the domains of the first curved liquid crystal alignment layer AL1C and the domains of the second curved liquid crystal alignment layer AL2C may cause interference or a conflict in an alignment direction between the first liquid crystal molecules LC1, which are aligned at an inclination at the surface of the first curved liquid crystal alignment layer AL1C, and the second liquid crystal molecules LC2, which are aligned at an inclination at the surface of the second curved liquid crystal alignment layer AL2C along a different direction from the first liquid crystal molecules LC1. As a result, the liquid crystal molecules between the first liquid crystal molecules LC1and the second liquid crystal molecules LC2may be vertically aligned, thereby forming texture. The texture, however, may be viewed within the display area DAC as a smudge or dark area and may lower the light transmittance of the curved LCD500C.

The curved LCD500C will hereinafter be described in further detail with reference toFIG. 3.FIG. 3is a cross-sectional view taken along line III-III′ ofFIG. 1. More specifically,FIG. 3illustrates an initial state of alignment of liquid crystal molecules in the curved LCD500C when an electric field is yet to be applied.

Referring toFIG. 3, the first liquid crystal molecules LC1may be liquid crystal molecules aligned at the surface of the first curved liquid crystal alignment layer AL1C. The second liquid crystal molecules LC2, i.e., “2-1” liquid crystal molecules LC2-1and “2-2” liquid crystal molecules LC2-2, may be liquid crystal molecules aligned at the surface of the second curved liquid crystal alignment layer AL2C. The first liquid crystal molecules LC1are relatively vertically aligned as compared to the second liquid crystal molecules LC2. The second liquid crystal molecules LC2are relatively tilt-aligned or obliquely aligned as compared to the first liquid crystal molecules LC1. In other words, the first liquid crystal molecules LC1have a pre-tilt angle larger than that of the second liquid crystal molecules LC2-1and LC2-2, and the second liquid crystal molecules LC2-1and LC2-2have a pre-tilt angle smaller than that of the first liquid crystal molecules LC1.

The pre-tilt angle is an angle between the directors of the curved substrates100C and200C and a director of the liquid crystal molecules LC1, LC2-1and LC2-2. The pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2at the apex of the curved substrates100C and200C is substantially the same as the pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2in the flat substrates. For example, a radius R of curvature of the curved LCD500C may be equal to or greater than 2000 mm and equal to or less than 5000 mm. In this case, the pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2at the apex of the curved substrates100C and200C is substantially the same as the pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2in the flat substrates. The term “apex”, as used herein, denotes an arbitrary point on a curve where the slope of a tangent at the point is substantially zero.

The pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2may be adjusted by controlling the concentration of the reactive mesogens, the concentration of the polymerization initiator, the voltage and the amount of irradiation. As more polymers of reactive mesogens are formed, the liquid crystal molecules LC1, LC2-1and LC2-2can be aligned at an inclination. As the concentration of the polymerization initiator is higher, more polymers of reactive mesogens can be formed.

A difference in the pre-tilt angle between the first liquid crystal molecules LC1aligned on the surface of the first curved liquid crystal alignment layer AL1C and the second liquid crystal molecules LC2-1and LC2-2aligned on the surface of the second curved liquid crystal alignment layer AL2C is due to a difference in the content of the polymers of reactive mesogens.

The first curved liquid crystal alignment layer AL1C has a relatively low content of the polymers of reactive mesogens as compared to the second curved liquid crystal alignment layer AL2C. In other words, the second curved liquid crystal alignment layer AL2C has a relatively high content of the polymers of reactive mesogens as compared to the first curved liquid crystal alignment layer AL1C.

The reactive mesogens are compounds having a polymerizable end group for polymerization and a mesogenic structure to develop the liquid crystallinity and, for example, may be represented by Formula (1):
P1-SP1-MG-SP2-P2  (Formula 1)

In Formula (1), each of P1and P2is a polymerizable end group, for example, a (meth)acrylate group, a vinyl group, a vinyloxy group, an epoxy group, or the like. SP1is a spacer group linking P1to MG, for example, an alkyl group having a carbon number of 1 to 12, an alkoxy group having a carbon number of 1 to 12, or the like. SP2is a spacer group linking P2to MG, for example, an alkyl group having a carbon number of 1 to 12, an alkoxy group having a carbon number of 1 to 12, or the like. MG is a mesogenic structure, for example, cyclohexyl group, biphenyl group, terphenyl group, naphthalene or the like.

Meanwhile, the polymerization initiator serves to initiate the polymerization of the reactive mesogens. As the concentration of the polymerization initiator is higher, more polymers of reactive mesogens can be formed. The second curved liquid crystal alignment layer AL2C may have a relatively high content of the polymerization initiator as compared to the first curved liquid crystal alignment layer AL1C. In other words, the first curved liquid crystal alignment layer AL1C may have a relatively low content of the polymerization initiator as compared to the second curved liquid crystal alignment layer AL2C.

Therefore, the second liquid crystal molecules LC2-1and LC2-2aligned on the surface of the second curved liquid crystal alignment layer AL2C may be aligned relatively at an inclination as compared to the first liquid crystal molecules LC1aligned on the surface of the first curved liquid crystal alignment layer AL1C. The first liquid crystal molecules LC1aligned on the surface of the first curved liquid crystal alignment layer AL1C may be aligned relatively vertically as compared to the second liquid crystal molecules LC2-1and LC2-2aligned on the surface of the second curved liquid crystal alignment layer AL2C.

The curved LCD500C may suppress the occurrence of a smudge or a dark portion caused due to a collision of the alignment directions of the first liquid crystal molecules LC1and the second liquid crystal molecules LC2-1and LC2-2by making different the pre-tilt angles of the first liquid crystal molecules LC1and the second liquid crystal molecules LC2-1and LC2-2.

For example, the first liquid crystal alignment layer surface AL1C may be a vertical alignment (VA)-type liquid crystal alignment layer comprising a polyimide with at least one VA group bonded thereto, selected from among a hydrocarbon derivative having an imide group (—CONHCO—) in the repeating unit of the main chain thereof, having an alkyl group in the side chain thereof, and having the terminal thereof substituted with an alkyl group, a hydrocarbon derivative having the terminal thereof substituted with a cycloalkyl group, and a hydrocarbon derivative having the terminal thereof substituted with aromatic hydrocarbon.

For example, the second curved liquid crystal alignment layer AL2C may have a multilayer structure consisting of a “2-1” curved liquid crystal alignment layer AL2-1C and a “2-2” curved liquid crystal alignment layer AL2-2C. The second curved liquid crystal alignment layer AL2C may include a polymerization initiator contrary to the first curved liquid crystal alignment layer AL1C.

For example, the “2-1” curved liquid crystal alignment layer AL2-1C may be a VA-type liquid crystal alignment layer comprising a polyimide having an imide group (—CONHCO— in the repeating unit of the main chain thereof and having the VA group and the polymerization initiator bonded to the side chain thereof. The “2-2” curved liquid crystal alignment layer AL2-2C may comprise polymers of reactive mesogens. The polymers of reactive mesogens may be spaced apart from each other on the surface of the “2-1” curved liquid crystal alignment layer AL2-1C.

Referring further toFIG. 3, in an initial state when no electric field is applied to the curved LCD500C, the second curved liquid crystal alignment layer AL2C may form at least two domains that differ from each other in the alignment direction of liquid crystal molecules therein in each of first and second regions R1and R2, but the first curved liquid crystal alignment layer AL1C may form only one domain where the alignment direction of liquid crystal molecules is substantially uniform throughout the first and second regions R1and R2. The first and second regions R1and R2denote left and right sides, respectively, of an imaginary straight line C-C′ that passes through the apex of the first curved substrate100C and the apex of the second curved substrate200C.

In the first region R1and the second region R2of the second curved liquid crystal alignment layer AL2C, the “2-1” liquid crystal molecules LC2-1may be aligned in a first oblique direction, and the “2-2” liquid crystal molecules LC2-2may be aligned in a second oblique direction. The second curved liquid crystal alignment layer AL2C may form at least two domains in which the alignment direction of the “2-1” liquid crystal molecules LC2-1and the alignment direction of the “2-2” liquid crystal molecules LC2-2are different from each other in the first region R1. The second curved liquid crystal alignment layer AL2C may form at least two domains in which the alignment direction of the “2-1” liquid crystal molecules LC2-1and the alignment direction of the “2-2” liquid crystal molecules LC2-2are different from each other in the second region R2. The first oblique direction may be the direction of an angle of about −α° (where α is a positive real number) with respect to the imaginary straight line C-C′, and the second oblique direction may be the direction of an angle of about +α° with respect to the imaginary straight line C-C′.

On the other hand, in the first region R1of the first curved liquid crystal alignment layer AL1C, the first liquid crystal molecules LC1may all be aligned in a third oblique direction and may thus form a single domain. In the second region R2of the first liquid crystal alignment layer AL1C, the first liquid crystal molecules LC1may all be aligned in a fourth oblique direction and may thus form a single domain. For example, the third oblique direction may be the direction of an angle of about −β° (where β is a positive real number) with respect to the imaginary straight line C-C′, and the fourth oblique direction may be the direction of an angle of about +β° with respect to the imaginary straight line C-C′.

As described above, multiple domains in which the alignment directions of the liquid crystal molecules are different from each other are formed selectively only in the second curved liquid crystal alignment layer AL2C from among the first curved liquid crystal alignment layer AL1C and the second curved liquid crystal alignment layer AL2C in each of the first region R1and the second region R2, thereby suppressing the occurrence of a spot defect or a dark portion caused due to a collision of the alignment directions of the first liquid crystal molecules LC1and the second liquid crystal molecules LC2-1and LC2-2.

A method of fabricating the curved LCD500C will hereinafter be described with reference toFIGS. 4 to 9.FIGS. 4 to 9are cross-sectional views illustrating a method of fabricating the curved LCD500C.

Referring toFIG. 4, a first flat substrate100is disposed to face a second flat substrate200while maintaining a predetermined cell gap with the second flat substrate200. For example, the second flat substrate200may be a TFT substrate, and the first flat substrate100may be a color filter substrate opposite to the second flat substrate200.

A common electrode110may be disposed on the first flat substrate100, and a first flat liquid crystal alignment layer AL1may be disposed on the common electrode110. The common electrode110may be formed of indium tin oxide (ITO), indium zinc oxide (IZO), indium zinc oxide, indium oxide, zinc oxide, tin oxide, gallium oxide, titanium oxide, aluminum (Al), silver (Ag), platinum (Pt), chromium (Cr), molybdenum (Mo), tantalum (Ta), niobium (Nb), zinc (Zn), magnesium (Mg), or an alloy or a deposition layer thereof. As mentioned above with regard to common electrode110C, the common electrode110may be a “patternless” electrode with no slit patterns.

For example, the first flat liquid crystal alignment layer AL1may be formed by applying a first VA polyimide with the VA group bonded to the side chain thereof onto the common electrode110and drying the polyimide. The first VA polyimide may have an imide group (—CONHCO—) in the repeating unit of the main chain thereof and have a VA group only in the side chain thereof. The VA group has already been described above, and thus, a detailed description thereof will be omitted.

For example, the first VA polyimide may comprise, but is not limited to, a polymer compound represented by Formula (2):

where a, b and c are natural numbers.

Pixel electrodes291may be disposed on the second flat substrate200, and a “2-1” flat liquid crystal alignment layer AL2-1may be disposed on the pixel electrodes291.

The pixel electrodes291may be formed of ITO, IZO, indium zinc oxide, indium oxide, zinc oxide, tin oxide, gallium oxide, titanium oxide, Al, Ag, Pt, Cr, Mo, Ta, Nb, Zn, Mg, or an alloy or a deposition layer thereof. As mentioned above with the pixel electrodes291C, the pixel electrodes291may be pattern electrodes with slit patterns. The second flat substrate200may be partially exposed through the slit patterns of the pixel electrodes291.

For example, the “2-1” flat liquid crystal alignment layer AL2-1may be formed by applying a composite liquid crystal aligning agent, comprising a second VA polyimide with the VA group and a polymerization initiator in the side chain thereof and reactive mesogens RM, onto the pixel electrodes291and drying the composite liquid crystal aligning agent. The second VA polyimide, unlike the first VA polyimide, may include the polymerization initiator. The VA group and the polymerization initiator have already been described above, and thus, detailed descriptions thereof will be omitted.

The “2-1” flat liquid crystal alignment layer AL2-1may comprise, but is not limited to, a polymer compound represented by Formula (3):

where a, b and c are natural numbers.

The polymerization initiator absorbs ultraviolet (UV) light and is thus easily decomposed into radicals, thereby facilitating the photo-polymerization of the reactive mesogens RM. For example, the polymerization initiator may absorb UV light within a long wavelength range of about 300 nm to about 400 nm, and may thus be decomposed into radicals, thereby facilitating the photo-polymerization of the reactive mesogens RM.

Referring toFIG. 5, the liquid crystal layer300is disposed between the first flat substrate100and the second flat substrate200. The liquid crystal layer300may be formed by injecting or dropping a liquid crystal composition comprising liquid crystal molecules (LC1and LC2) between the first flat substrate100and the second flat substrate200.

Each of the liquid crystal molecules have negative dielectric anisotropy. In an initial state when no electric field is applied to a flat LCD500, the liquid crystal molecules may be substantially vertically aligned with respect to the first and second flat substrates100and200. That is, during the initial state, the VA group of the first flat liquid crystal alignment layer AL1and the VA group of the “2-1” flat liquid crystal alignment layer AL2-1may align the liquid crystal molecules substantially vertically with respect to the first and second flat substrates100and200. The expression “liquid crystal molecules substantially vertically with respect to the first and second flat substrates100and200”, as used herein, means that the liquid crystal molecules are aligned at an angle of about 88° to 90° with respect to the first and second flat substrates100and200.

After the formation of the liquid crystal layer300, a thermal treatment process H may be performed by applying heat from below the first flat substrate100.

Referring toFIG. 6, as a result of the thermal treatment process H, the reactive mesogens RM contained in the “2-1” flat liquid crystal alignment layer AL2-1may be eluted into the liquid crystal layer300. As a result, the “2-1” flat liquid crystal alignment layer AL2-1ofFIG. 6has a lower content of the reactive mesogens RM than the “2-1” flat liquid crystal alignment layer AL2-1ofFIG. 5, and the liquid crystal layer300ofFIG. 6, unlike the liquid crystal layer300ofFIG. 5, may contain the reactive mesogens RM.

In response to an electric field being generated between the common electrode110and the pixel electrodes291and being applied to the flat LCD500, the liquid crystal molecules may be obliquely aligned in a direction perpendicular to the electric field. More specifically, “1-1” liquid crystal molecules LC1-1and “2-1” liquid crystal molecules LC2-1may be aligned in a first oblique direction, and “1-2” liquid crystal molecules LC1-2and “2-2” liquid crystal molecules LC2-2may be aligned in a second oblique direction. Thereafter, in response to UV light being applied onto the flat LCD500, the polymerization initiator included in the “2-1” flat liquid crystal alignment layer AL2-1may initiate the photo-polymerization of the reactive mesogens RM, thereby forming a “2-2” flat liquid crystal alignment layer AL2-2.

More specifically, referring toFIG. 7, the reactive mesogens RM may move to the “2-1” flat liquid crystal alignment layer AL2-1including the polymerization initiator and may thus form the “2-2” flat liquid crystal alignment layer AL2-2on the “2-1” flat liquid crystal alignment layer AL2-1. As the “2-2” flat liquid crystal alignment layer AL2-2is formed, the content of the reactive mesogens RM in the liquid crystal layer300may gradually decrease. It may be understood that the reactive mesogens RM lost from the liquid crystal layer300are used to form the “2-2” flat liquid crystal alignment layer AL2-2.

The “2-2” flat liquid crystal alignment layer AL2-2may comprise polymers of reactive mesogens partially disposed on the surface of the “2-1” flat liquid crystal alignment layer AL2-1. The polymers of reactive mesogens may be spaced apart from each other at a predetermined distance on the surface of the “2-1” flat liquid crystal alignment layer AL2-1.

As more polymers of reactive mesogens are formed, the liquid crystal molecules can be aligned at an inclination. The “2-2” flat liquid crystal alignment layer AL2-2may fix or stabilize the alignment direction of the “2-1” liquid crystal molecules LC2-1and the “2-2” liquid crystal molecules LC2-2. Accordingly, the2-1″ liquid crystal molecules LC2-1and the “2-2” liquid crystal molecules LC2-2may continue to be obliquely aligned even after the electric field applied to the flat LCD500ceases. On the other hand, the first liquid crystal molecules LC1may return to their original state of alignment of being vertically aligned upon the cessation of the electric field applied to the flat LCD500. The first liquid crystal molecules may be relatively vertically aligned as compared with the second liquid crystal molecules and the second liquid crystal molecules are relatively tilt-aligned as compared with the first liquid crystal molecules.

Referring toFIGS. 8 and 9, the residual reactive mesogens RM in the liquid crystal layer300may be removed by applying fluorescent UV light onto the flat LCD500with no electric field applied to the flat LCD500. Thereafter, a bending process B for bending the flat LCD500may be performed, thereby obtaining a curved LCD (for example, the curved LCD500C ofFIG. 3).

FIG. 10is an analytical graphical representation of a pre-tilt angle with respect to a flat liquid crystal display device500ofFIG. 9.

Table 1 shows the measurement results of a pre-tilt angle P1of liquid crystal molecules LC1(seeFIG. 9) aligned on the surface of a first flat liquid crystal alignment layer AL1(seeFIG. 9) and a pre-tilt angle P2of second liquid crystal molecules LC2-1and LC2-2(seeFIG. 9) aligned on the surface of a second flat liquid crystal alignment layer AL2-1and AL2-2(seeFIG. 9). The pre-tilt angle is an angle between of the first and second flat substrates100and200and directors the liquid crystal molecules LC1, LC2-1and LC2-2. For example, if the pre-tilt angle is 90°, the liquid crystal molecules LC1, LC2-1and LC2-2may be aligned substantially vertically with respect to the first and second flat substrates100and200(seeFIG. 5), and if the pre-tilt angle is 0°, the liquid crystal molecules LC1, LC2-1and LC2-2may be aligned horizontally with respect to the first and second flat substrates100and200.

TABLE 1Pre-tilt angle P1 of the liquidPre-tilt angle P2 of the liquidNumber ofcrystal molecules aligned oncrystal molecules aligned onsamplesthe surface of the first flatthe surface of the second flat(S/S) = 6liquid crystal alignment layerliquid crystal alignment layerMaximum89.52°88.88°value(Max)Minimum88.69°87.82°value(Min)Average89.10°88.31°value(Avg)Standard0.3130.439deviation(Std)

Referring toFIG. 10and Table 1, the pre-tilt angle P1of the liquid crystal molecules LC1(seeFIG. 9) aligned on the surface of the first flat liquid crystal alignment layer AL1(seeFIG. 9) has a relatively greater value than the pre-tilt angle P2of the second liquid crystal molecules LC2-1and LC2-2(seeFIG. 9) aligned on the surface of the second flat liquid crystal alignment layer AL2-1and AL2-2(seeFIG. 9).

A difference between the pre-tilt angle P1of the liquid crystal molecules LC1(seeFIG. 9) aligned on the surface of the first flat liquid crystal alignment layer AL1(seeFIG. 9) and the pre-tilt angle P2of the second liquid crystal molecules LC2-1and LC2-2(seeFIG. 9) aligned on the surface of the second flat liquid crystal alignment layer AL2-1and AL2-2(seeFIG. 9) may prevent texture from being generated due to misalignment between the first curved substrate100C (seeFIG. 3) and the second curved substrate200C (seeFIG. 3) that may occur during the bending process B (seeFIG. 9).

Meanwhile, referring toFIG. 3, the pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2at the apex of the curved substrates100C and200C is substantially the same as the pre-tilt angle of the liquid crystal molecules LC1, LC2-1and LC2-2in the flat substrates100and200. Thus, the pre-tilt angle of the first liquid crystal molecules LC1aligned on the surface of the first curved liquid crystal alignment layer AL1C may be larger than the pre-tilt angle of the second liquid crystal molecules LC2-1and LC2-2aligned on the surface of the second curved liquid crystal alignment layer AL2C. The imaginary straight line C-C′ is an imaginary straight line that passes through the apex of the first curved substrate100C and the apex of the second curved substrate200C.

For example, a radius R of curvature of the curved LCD500C may be equal to or greater than 2000 mm and equal to or less than 5000 mm. In this case, the pre-tilt angle of the liquid crystal molecules LC1aligned on the surface of the first curved liquid crystal alignment layer AL1C at the apex of the curved substrates100C and200C may be larger than the pre-tilt angle of the liquid crystal molecules LC2-1and LC2-2aligned on the surface of the second curved liquid crystal alignment layer AL2C.

FIG. 11is an image showing the light transmittance distribution of the curved LCD500C.FIG. 12is an image showing the light transmittance distribution of a curved LCD according to a first comparative example.

The curved LCD500C ofFIG. 11was fabricated by forming the first flat liquid crystal alignment layer AL1on the common electrode110using the first VA polyimide and forming the “2-1” flat liquid crystal alignment layer AL2-1on the pixel electrodes291using a composite liquid crystal aligning agent comprising the second VA polyimide and the reactive mesogens RM, as illustrated inFIG. 4; and forming the liquid crystal layer300through the injection of a liquid crystal composition comprising the liquid crystal molecules LC, performing the thermal treatment process H, applying UV light and performing the bending process B, as illustrated inFIGS. 5 to 9.

The curved LCD according to the first comparative example was fabricated by forming both the first flat liquid crystal alignment layer AL1and the “2-1” flat liquid crystal alignment layer AL2-1using the composite liquid crystal aligning agent during the step ofFIG. 4; forming the liquid crystal layer300through the injection of a liquid crystal composition comprising the liquid crystal molecules LC and performing the thermal treatment process H during the step ofFIG. 5; applying UV light; and performing the bending process B.

Referring toFIGS. 11 and 12, texture that may be generated due to a conflict between the alignment direction of first liquid crystal molecules and the alignment direction of second liquid crystal molecules is viewed from the curved LCD according to the first comparative example as dark areas, as indicated by dotted lines, but no such texture is detected in the curved LCD500C.

FIG. 13is an image showing the light transmittance distribution of a curved LCD according to a second comparative example. The curved LCD according to the second comparative example was fabricated by forming both the first flat liquid crystal alignment layer AL1and the “2-1” flat liquid crystal alignment layer AL2-1using the first VA polyimide during the step ofFIG. 4; forming the liquid crystal layer300through the injection of a liquid crystal composition comprising both the reactive mesogens RM and the liquid crystal molecules LC during the step ofFIG. 5; applying UV light; and performing the bending process B.

Referring toFIG. 13, texture that may be generated due to a conflict between the alignment direction of first liquid crystal molecules and the alignment direction of second liquid crystal molecules is viewed from the curved LCD according to the second comparative example as dark areas.