KR20160020192A - Liquid crystal display device having reflective polarizer - Google Patents

Abstract

A liquid crystal display device implements a reflection-type polarizing plate by coating a coating-type polarizing device between a liquid crystal panel and a brightness improving film to be perpendicular to a polarization axis of the brightness improving film, thereby replacing a conventional PVA elongation-type polarizing plate due to improved brightness and enhanced polarization degree and contrast range. The liquid crystal display device includes the liquid crystal panel; a first polarizing plate which is located in a lower part of the liquid crystal panel, and comprises the coating-type polarizing device and the brightness improving film; and a second polarizing plate which is located in an upper part of the liquid crystal panel. An optical axis of the coating-type polarizing device is orthogonal to an optical axis of the brightness improving film.

Description

TECHNICAL FIELD [0001] The present invention relates to a liquid crystal display device having a reflective polarizer,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device provided with a reflection type polarizing plate.

Recently, interest in information display has increased, and a demand for using portable information media has increased, and a light-weight flat panel display (FPD) that replaces a cathode ray tube (CRT) And research and commercialization are being carried out. Particularly, among such flat panel display devices, a liquid crystal display (LCD) is an apparatus for displaying an image using the optical anisotropy of a liquid crystal, and is excellent in resolution, color display and picture quality and is actively applied to a notebook or a desktop monitor have.

Such a liquid crystal display device is driven by two opposing electrodes and a liquid crystal layer formed therebetween. The liquid crystal molecules of the liquid crystal layer are driven by an electric field generated by applying a voltage to the two electrodes.

The liquid crystal molecules have a polarization property and an optical anisotropy. The polarization property means that when the liquid crystal molecules are placed in the electric field, the charges in the liquid crystal molecules collide with both sides of the liquid crystal molecules, and the molecular alignment direction changes according to the electric field. Refers to changing the path of the emitted light and the polarization state differently depending on the incident direction or polarization state of the incident light due to the elongated structure of the liquid crystal molecules and the aforementioned molecular arrangement direction.

Accordingly, the liquid crystal display device has a liquid crystal panel composed of a pair of transparent insulating substrates, each of which has electric field generating electrodes formed on the surfaces facing each other with a liquid crystal layer interposed therebetween, as an essential component, and the electric field change between the electric field generating electrodes The alignment direction of the liquid crystal molecules is artificially adjusted, and various images are displayed by using the transmittance of the changed light.

At this time, the polarizing plates are respectively disposed on the upper and lower sides of the liquid crystal panel. The polarizing plate transmits the light having the polarization component coinciding with the transmission axis, determines the degree of transmission of light by the arrangement of the transmission axes of the two polarizing plates and the arrangement characteristics of the liquid crystal .

FIGS. 1A and 1B are diagrams illustrating characteristics of light transmitted through a liquid crystal panel.

Referring to the drawings, a typical liquid crystal display device includes a liquid crystal panel P and a backlight unit (not shown) for supplying light from the back of the liquid crystal panel P. The liquid crystal panel P includes a liquid crystal layer 30, The first and second substrates 10 and 5 and the first and second polarizers 50a and 50b attached to the outer surfaces of the first and second substrates 10 and 5, respectively.

Although not shown, a plurality of pixels having transparent pixel electrodes formed on the inner surface of the first substrate 10 and a thin film transistor for on / off controlling the liquid crystal driving voltage transmitted to the pixel electrodes are provided, On the inner surface of the second substrate 5, a color filter and a common electrode for color implementation are provided.

The liquid crystal layer 30 interposed between the first and second substrates 10 and 5 is a twisted nematic (TN) mode. In the OFF state of the voltage, The first and second polarizers 50a and 50b are parallel to each other and are twisted at an azimuth angle of 90 degrees from the first substrate 10 to the second substrate 5, Are orthogonal to each other.

Since the liquid crystal panel P does not emit light itself, the backlight unit for supplying light to the liquid crystal panel P is positioned on the back surface of the liquid crystal panel P.

When light is emitted from the backlight unit when the voltage is off in the liquid crystal panel P, only the linearly polarized light parallel to the polarization axis thereof is transmitted by the first polarizer 50a as shown in Fig. 1A, And is rotated 90 degrees along the azimuth angle of the liquid crystal layer 30 while passing through the liquid crystal layer 30 to transmit white light through the second polarizer plate 50b.

Next, when the voltage is on, the liquid crystal molecules of the liquid crystal panel P are aligned perpendicular to the first and second polarizers 50a and 50b as shown in FIG. 1B, and the linearly polarized light transmitted through the first polarizing plate 50a is blocked by the second polarizing plate 50b to display black.

The conventional liquid crystal display device having such a structure has a polarizing plate of a PVA elongation type in which iodide ions are stretched into water soluble polyvinyl alcohol (PVA) and aligned by the first and second polarizing plates 50a and 50b I am using it.

The PVA stretched polarizer absorbs light components in the direction in which the iodine ions are aligned, thereby achieving a transmittance of about 43% and a polarization degree of 99.99% or more.

There is a reflection type polarizing plate in which a new polarizing plate develops polarized light due to a refractive index difference in a specific direction. However, since the contrast ratio is lowered due to leakage of light in the black state, the polarizing plate can not be used alone, and is used like the polarizing plate of the PVA type.

It is an object of the present invention to provide a liquid crystal display device having a reflective polarizing plate for improving polarizability and contrast ratio to replace a conventional PVA stretched polarizer.

Other objects and features of the present invention will be described in the following description of the invention and the claims.

According to an aspect of the present invention, there is provided a liquid crystal display device including a reflective polarizer, including: a liquid crystal panel; A first polarizer positioned below the liquid crystal panel and comprising a coating type polarizing element and a brightness enhancement film; And a second polarizer disposed on the upper side of the liquid crystal panel, wherein the coating type polarizing element and the brightness enhancement film have optical axes perpendicular to each other.

At this time, the coating type polarizing element includes an orientation layer; And a polarizing layer arranged on the alignment layer, and may block only a part of the P-polarized light incident from the brightness enhancement film.

At this time, the coating type polarizing element may have a transmittance of 10% to 50%.

The second polarizer may be a coating type polarizing element.

As described above, the liquid crystal display device provided with the reflective polarizer according to the present invention realizes a reflective polarizer by coating the coating type polarizing element between the liquid crystal panel and the brightness enhancement film so as to be perpendicular to the polarization axis of the brightness enhancement film, And at the same time, the polarization and the contrast ratio are improved.

FIGS. 1A and 1B are diagrams illustrating characteristics of light transmitted through a liquid crystal panel. FIG.
2 is a cross-sectional view schematically showing a part of a structure of a liquid crystal display device according to a first embodiment of the present invention.
3 is a cross-sectional view schematically showing the structure of a lower polarizer plate according to the first embodiment of the present invention.
Fig. 4 is an exemplary view schematically showing a principle of improving luminance in a liquid crystal display device to which a brightness enhancement film is applied. Fig.
5 is an illustration showing, by way of example, the arrangement of a host material and a guest material in a coated polarizing element;
6 is a sectional view schematically showing a structure of a lower polarizer plate according to a second embodiment of the present invention.
7 is a cross-sectional view schematically showing the structure of a lower polarizer plate according to a third embodiment of the present invention.
FIG. 8 is a table showing the transmittance, the degree of polarization, the brightness, and the contrast ratio of the reflective polarizer according to the first to third embodiments of the present invention, in comparison with the polarizer of the comparative example of the PVA type.
FIG. 9 is a table comparing the transmittance, the degree of polarization, the brightness, and the contrast ratio of the reflective polarizer according to the first embodiment of the present invention in accordance with the transmittance of the coated polarizer.
10 is a cross-sectional view schematically showing a part of a structure of a liquid crystal display device according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification. The dimensions and relative sizes of the layers and regions in the figures may be exaggerated for clarity of illustration.

It will be understood that when an element or layer is referred to as being another element or "on" or "on ", it includes both intervening layers or other elements in the middle, do. On the other hand, when a device is referred to as "directly on" or "directly above ", it does not intervene another device or layer in the middle.

The terms spatially relative, "below," "lower," "above," "upper," and the like, And may be used to easily describe the correlation with other elements or components. Spatially relative terms should be understood to include, in addition to the orientation shown in the drawings, terms that include different orientations of the device during use or operation. For example, when inverting an element shown in the figures, an element described as "below" or "beneath" of another element may be placed "above" another element. Thus, the exemplary term "below" can include both downward and upward directions.

The terminology used herein is for the purpose of describing embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. &Quot; comprise "and / or" comprising ", as used in the specification, means that the presence of stated elements, Or additions.

2 is a cross-sectional view schematically showing a part of a structure of a liquid crystal display device according to a first embodiment of the present invention.

In this case, the liquid crystal display according to the first embodiment of the present invention shown in FIG. 2 shows the case of using the TN mode, but the present invention is not limited thereto. The present invention can be applied regardless of a liquid crystal mode such as an in-plane switching (IPS) mode or a fringe field switching (FFS) mode as well as a VA (vertical alignment) mode.

Referring to the drawings, a liquid crystal display according to a first embodiment of the present invention roughly comprises a color filter substrate 105, a color filter substrate (not shown), a color filter substrate 105 and a liquid crystal layer 130 formed between the array substrate 110 and the liquid crystal layer 130.

The color filter substrate 105 separates the sub-color filter from the color filter 107 constituted by a plurality of sub-color filters that realize the colors of red, green and blue and blocks light transmitted through the liquid crystal layer 130 A black matrix (BM) 106, and a transparent common electrode 108 for applying a voltage to the liquid crystal layer 130.

The array substrate 110 includes a plurality of gate lines (not shown) and data lines (not shown) arranged vertically and horizontally to define a plurality of pixel regions, a thin film transistor as a switching element formed in a crossing region between gate lines and data lines, And a pixel electrode 118 formed in the region.

The thin film transistor includes a gate electrode 121 connected to a gate line, a source electrode 122 connected to a data line, and a drain electrode 123 electrically connected to the pixel electrode 118 through a contact hole formed in the protective film 115b . The thin film transistor is connected to the source electrode 122 and the drain electrode by a gate voltage supplied to the gate insulating film 115a and the gate electrode 121 for insulation between the gate electrode 121 and the source / And an active layer 124 that forms a conductive channel between the electrodes 123.

When the amorphous silicon thin film is used as the active layer 124, the source / drain regions of the active layer 124 are connected to the source / drain electrodes 122 and 123 through the ohmic-contact layer 125 made of the n + amorphous silicon thin film. Thereby forming an ohmic contact.

However, the present invention is not limited thereto. The active layer 124 may be formed of a polycrystalline silicon thin film, an oxide semiconductor, or another semiconductor material.

The color filter substrate 105 and the array substrate 110 constructed as described above are adhered to each other by a sealant 140 formed on the periphery of the image display area to constitute a liquid crystal panel, The adhesion of the substrate 110 is achieved through a cementing key (not shown) formed on the color filter substrate 105 or the array substrate 110.

Such a liquid crystal panel is provided with a backlight unit on its back surface to supply light. This is because the liquid crystal display itself is a device that does not have a light emitting element, and thus requires a separate light source. The light source may be a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), a fluorescent lamp of a hot cold fluorescent lamp (HCFL), or a light emitting diode (LED).

At this time, an upper polarizer 150b and a lower polarizer 150a are attached to the outer surfaces of the color filter substrate 105 and the array substrate 110 so as to selectively transmit only specific polarized light.

These polarizing plates 105a and 105b transmit only the light vibrating in the same direction as the polarization axis from the light provided from the backlight unit and the light vibrating in the other direction absorbs or reflects by using a proper medium, .

Between the liquid crystal layer 130 and the common electrode 108 and between the liquid crystal layer 130 and the pixel electrode 118 is formed an upper alignment film 109 and a lower alignment film 109 which are rubbed in a predetermined direction, 119 are interposed between the liquid crystal and the alignment direction of the liquid crystal.

 Accordingly, the linearly polarized light passing through the lower polarizer 150a is changed in polarization state due to the anisotropy of the liquid crystal, passes through the upper polarizer 150b, and the liquid crystal layer 130 realizes a gray scale according to the voltage intensity do.

At this time, the present invention is characterized in that the lower polarizing plate 150a is formed as a reflective polarizing plate using the coating type polarizing element 155 and the brightness enhancement film 160, thereby improving the brightness and improving the polarization and contrast ratio. However, the first embodiment of the present invention is an example of applying a general PVA stretching type polarizing plate as the upper polarizing plate 150b, but the present invention is not limited thereto. Instead of the PVA stretching type polarizing plate, May be used to constitute the upper polarizer 150b.

When the upper polarizer 150a is constituted by a typical PVA stretching type polarizing plate, for example, a PVA film treated with iodine is used as a polarizing substrate, and excellent transparency, ultraviolet absorbing property and durability Can be used as a protective layer for protecting the PVA film. The triacetate cellulose (TAC) film can be used as a protective layer for protecting the PVA film.

Further, a protective film and a release film may be further attached to protect the polarizing substrate and the protective layer adhered to each other.

At this time, the protective film is attached to the outside of the first protective layer to prevent scratches on the surface of the upper polarizer 150a until the upper polarizer 150a is attached to the final product, and the upper polarizer 150a is attached to the final product It can be attached to the outside of the second protective layer until it is attached.

The release film and the second protective layer are adhered to each other by an adhesive, and the final product is adhered to the release surface of the release film. On the other hand, a pressure-sensitive adhesive may not be formed on the first protective layer to which the protective film is attached.

The upper polarizer 150a having such a configuration is attached to the upper surface of the liquid crystal panel, and the release surface of the release film is attached.

At this time, the upper polarizer 150 attached to the upper surface of the liquid crystal panel may further include a reinforcing substrate for protecting the liquid crystal panel from external impact.

Here, the reinforced substrate may be made of, for example, a tempered glass having a thickness of about 3 mm to protect the liquid crystal panel inside from external impact. Such a tempered glass is a glass reinforced by heating a molded plate glass at a temperature of 500 to 600 ° C. which is close to a softening temperature, compressing and deforming the glass surface portion by quenching by compressed cooling air, Compared to ordinary glass, it has a bending strength of 3 to 5 times, an impact resistance of 3 to 8 times, and excellent heat resistance.

The lower polarizer 150a is a reflection-type polarizer and includes a coating-type polarizer 155 and a brightness enhancement film 160, which will be described in detail with reference to the drawings.

3 is a cross-sectional view schematically showing the structure of a lower polarizer plate according to the first embodiment of the present invention.

4 is an exemplary view schematically showing a principle of improving brightness in a liquid crystal display device to which a brightness enhancement film is applied.

5 is an illustration showing, by way of example, the arrangement of a host material and a guest material in a coated polarizing element.

Referring to the drawings, a lower polarizer 150a according to a first embodiment of the present invention may be composed of a substrate (not shown), a coating type polarizing element 155 formed on a substrate, and a brightness enhancement film 160.

At this time, the present invention is characterized in that a low polarization degree of the brightness enhancement film 160 is improved by adding a coating type polarizing element 155 whose optical axes are orthogonal to each other. That is, by adding the coating type polarizing element 155 so that the optical axis is orthogonal to the brightness enhancement film 160, the polarizing plate can be applied as a polarizing plate similar to a conventional PVA stretching type polarizing plate. Rather, So that the luminance is improved.

At this time, when the lower polarizer 150a is manufactured in an in-cell form on the array substrate 110, that is, the outer surface of the array substrate 110, the array substrate 110 may be substituted for the substrate.

Alternatively, the transparent substrate may be formed on a transparent substrate and attached to the array substrate 110. The transparent substrate may be an isotropic film such as TAC, PMMA, COP, PET, or PP.

Here, the stacking order of the coating type polarizing element 155 and the brightness enhancement film 160 may be changed, but it is preferable that the brightness enhancing film is located at a position close to the backlight unit.

First, the brightness enhancement film 160 may be provided on the lower side of the liquid crystal panel 100 where the backlight unit 170 is located, as shown in FIG.

Like the upper polarizer 150b, the lower polarizer 150a including the brightness enhancement film 160 separates light incident as optical means for converting natural light or polarized light into linearly polarized light into two polarized light components orthogonal to each other, Reflection, and / or scattering of the other polarized light component.

In the present specification, the brightness enhancement film 160 separates incident light into two polarized light components orthogonal to each other, transmits one polarized light component, reflects the other polarized light component, and recycles light, And has the function of improving the efficiency of light emitted from the light source.

In the case of a general polarizer, the P-polarized light is transmitted through the liquid crystal panel, but the S-polarized light is absorbed. However, when the luminance enhancement film 160 is used, the P-polarized light is transmitted to the liquid crystal panel 100, and the S-polarized light is reflected toward the backlight unit 170 and is non-polarized by diffusing or scattering, do.

The brightness enhancement film 160 may have a multi-layer structure in which the first thermoplastic resin 160a and the second thermoplastic resin 160b are alternately laminated. The brightness enhancement film 160 having such a structure can be produced, for example, by extruding two kinds of resins together and stretching the extruded film.

The total thickness of the brightness enhancement film 160 is preferably 20 to 800 占 퐉.

The first thermoplastic resin 160a exhibits optically anisotropic properties.

As the resin for forming the first thermoplastic resin 160a, any suitable resin can be selected. For example, the first thermoplastic resin 160a may be a polyethylene terephthalate resin, a polytrimethylene terephthalate resin, a polybutylene terephthalate resin, a polyethylene naphthalate resin, a polybutylene naphthalate resin, Or mixtures thereof. These resins exhibit excellent birefringence developability by stretching and excellent stability of birefringence after stretching.

As the second thermoplastic resin 160b, any suitable one can be selected. For example, the second thermoplastic resin 160b may include a polystyrene resin, a polymethyl methacrylate resin, a polystyrene glycidyl methacrylate resin, or a mixture thereof. The resin may have a halogen group such as chlorine, bromine and iodine introduced therein to increase the refractive index. Alternatively, the resin may contain any additive for adjusting the refractive index.

The brightness enhancement film 160 may be a commercially available one such as DBEF (Double Brightness Enhancement Film).

The brightness enhancement film is used to improve the brightness (white brightness) when a white image is displayed on a liquid crystal display device. However, in the conventional liquid crystal display device, it is possible to increase the white luminance by using the luminance enhancement film, but at the same time, the luminance (black luminance) in the case of displaying a black image is increased and consequently the contrast ratio contrast ratio can not be obtained.

Further, the brightness enhancement film itself can not replace the polarizing plate because of low polarization, and is merely an optical film used for the purpose of improving brightness.

However, when the coating type polarizing element 155 is interposed between the liquid crystal panel 100 and the brightness enhancement film 160 so as to be orthogonal to the polarization axis of the brightness enhancement film 160 as in the present invention, the white brightness is increased, It is possible to suppress the increase of the black luminance to a minimum and realize a reflective bottom polarizer 150a which can achieve a high contrast ratio in the frontal direction.

In other words, since the coating type polarizing element 155 is configured such that the optical axes thereof are orthogonal to the brightness enhancement film 160, an increase in black brightness in the case of displaying a black image can be minimized. Accordingly, the polarization and the contrast ratio can be improved, and it becomes possible to replace the conventional PVA stretched polarizer.

At this time, it is necessary to control the thickness or the dye concentration, that is, the transmittance so that the coating type polarizing element 155 functions to partially block the P-polarized light incident from the lower brightness enhancement film 160 . In other words, the brightness enhancement film 160 serves as the main polarizer, while the coating type polarizing element 155 suppresses the increase of the black brightness by the brightness enhancement film 160 to the minimum so that the polarization and contrast ratio of the reflective polarizer .

Such a coated polarizing element 155 is formed on the same substrate as the array substrate 110. The polarizing element 155 is formed on the alignment layer 155a and the alignment layer 155a formed on the array substrate 110, Layer 155b.

The orientation layer 155a may be formed of polyimide or polyamide.

As the alignment layer 155a is subjected to an alignment treatment such as rubbing or a light distribution, numerous micro grooves may be formed along the entire orientation layer 155a along a certain direction.

The polarizing layer 155b may be made of a host material and a guest material.

As the host material, a liquid crystalline polymer or a reactive liquid crystal monomer exhibiting liquid crystal properties may be used. At this time, the reactive liquid crystal monomer is a liquid crystal substance including a terminal group capable of polymerization, and is a monomer molecule having a liquid crystal phase including a terminal capable of polymerization with a mesogen that exhibits liquid crystallinity.

As the polarizing layer 155b is coated or coated on the orientation layer 155a, the host material interacts with the fine grooves formed in the orientation layer 155a to arrange along the orientation direction.

The guest material may be composed of a dichroic dye. A dichroic dye absorbs one of the two polarization components of light and transmits the other. As the dichroic dyes, iodine-based, anthraquinone-based propyrin azo, biazo, triazo etc. may be used.

The dichroic dye absorbs or transmits light in a specific wavelength range. In the present invention, visible light can be polarized by absorbing and transmitting light in a wavelength range corresponding to R, G, and B colors. Further, the dichroic dye may not be an R, G, or B dye but may be a cyan, magenta, or yellow dye.

However, the present invention is not limited thereto, and two or more dyes can be used, and a combination of such dyes can be designed to have a desired transmission color.

As described above, various kinds of dichroic dyes can be used in the present invention. For convenience of explanation, only dichroic dyes corresponding to R, G, and B colors will be described below.

Dichroic dyes of the R, G, and B colors are mixed into the host material and arranged along the host material when the host material is arranged. That is, the arrangement direction of the R, G, and B dyes is arranged along the direction of the fine grooves of the orientation layer 155a, that is, along the rubbing direction performed on the orientation layer 155a.

As the R, G, and B dyes are arranged in a certain direction, the polarizing component parallel to the arrangement direction of the R, G, and B dyes is absorbed and the polarizing component perpendicular to the absorption direction is transmitted Thereby polarizing incident light into light having a specific polarization direction.

A polarizing layer 155b in which a liquid crystalline polymer or a reactive liquid crystal monomer 153 as a host material and a guest material R, G, and B dyes 154 are mixed is disposed on the alignment layer 155a rubbed in the Y- The reactive liquid crystal monomer 153 is arranged along the Y axis direction and the R, G, and B dyes 154 are also aligned with the reactive liquid crystal monomer 153, And the alignment direction is maintained as the polymerization proceeds.

The total thickness of the coated polarizing element 155 thus configured is preferably 10 μm or less, more preferably 5 μm or less.

At this time, the brightness enhancement film 160 may be attached to the coating type polarizing element 155 through an adhesive (not shown).

As described above, the present invention realizes a reflective polarizing plate by interposing the coating type polarizing element 155 between the liquid crystal panel 100 and the brightness enhancement film 160 so as to be perpendicular to the polarization axis of the brightness enhancement film 160, And at the same time, the polarization and the contrast ratio are improved.

However, the present invention is not limited thereto, and the coating type polarizing element 155 may be interposed within the brightness enhancement film 160 or between the liquid crystal panel 100 and the brightness enhancement film 160, And the lower side of the brightness enhancement film 160, which will be described with reference to the drawings.

FIG. 6 is a cross-sectional view schematically showing a structure of a lower polarizer plate according to a second embodiment of the present invention, and FIG. 7 is a sectional view schematically showing the structure of a lower polarizer plate according to the third embodiment of the present invention.

6 and 7 illustrate the structure of the lower polarizer plate when the lower polarizer plate is manufactured in an in-cell form on the outer surface of the array substrate.

However, the present invention is not limited thereto. Alternatively, the transparent substrate may be formed of a transparent substrate and attached to the array substrate. The transparent substrate may be an isotropic film such as TAC, PMMA, COP, PET, or PP.

6, a lower polarizer 250a according to the second embodiment of the present invention includes a first brightness enhancement film 260a, a coating type polarizing element 255, 2 brightness enhancement film 260b.

The optical axes of the first brightness enhancement film 260a and the second brightness enhancement film 260b are aligned with each other while the optical axis of the coating type polarizing element 255 is aligned with the first and second brightness enhancement films 260a and 260b. Are orthogonal to each other.

Although not shown in detail, the first and second brightness enhancement films 260a and 260b may have a multi-layer structure in which a first thermoplastic resin and a second thermoplastic resin are alternately laminated. The first and second brightness enhancement films 260a and 260b having such a structure can be produced, for example, by extruding two kinds of resins together and stretching the extruded film.

As described above, since the coating type polarizing element 255 is configured such that the optical axes of the first and second brightness enhancement films 260a and 260b are orthogonal to each other, the increase of the black brightness in the case of displaying a black image is minimized The road can be suppressed. Accordingly, the polarization and the contrast ratio can be improved, and it becomes possible to replace the conventional PVA stretched polarizer.

The coating type polarizing element 255 needs to be adjusted in its thickness and dye concentration, that is, transmittance so as to serve only to block a part of the P-polarized light incident from the second brightness enhancement film 260b therebelow.

The coating type polarizing element 255 may be composed of an orientation layer 255a formed on the first brightness enhancement film 260a and a polarizing layer 255b formed on the orientation layer 255a.

At this time, a predetermined adhesive may be interposed between the array substrate 210 and the first brightness enhancement film 260a and between the coating type polarizing element 255 and the second brightness enhancement film 260b.

7, the lower polarizer 350a according to the third exemplary embodiment of the present invention includes a first coating type polarizing element 355 ', a brightness enhancement film 360, And a second coated polarizing element 355 ".

At this time, the optical axes of the first coating type polarizing element 355 'and the second coating type polarizing element 355' coincide with each other, while the brightness enhancing film 360 is orthogonal to each other.

Although not shown in detail, the brightness enhancement film 360 may have a multi-layer structure in which the first thermoplastic resin and the second thermoplastic resin are alternately laminated. The brightness enhancement film 360 having such a structure can be produced, for example, by extruding two kinds of resins together and stretching the extruded film.

As described above, since the first and second coated polarizing elements 355 'and 355 " are configured such that the optical axes of the first and second coated polarizing elements 355' and 355 "are orthogonal to the brightness enhancement film 360, The polarization and the contrast ratio can be improved, and it becomes possible to replace the conventional polarizing plate of the PVA elongation type.

The thickness of the first and second coating type polarizing elements 355 'and 355' is controlled so as to block only a part of the P-polarized light incident from the backlight unit or the brightness enhancement film 360, In other words, it is necessary to adjust the transmittance.

The first and second coating type polarizing elements 355 'and 355' 'are formed of polarizing layers 355b' and 355b '' formed on the orientation layers 355a 'and 355a' and the orientation layers 355a 'and 355a' Lt; / RTI >

At this time, a predetermined pressure-sensitive adhesive may be interposed between the first coating type polarizing element 355 'and the brightness enhancement film 360.

Hereinafter, the optical characteristics of the reflective polarizer according to the first to third embodiments of the present invention will be described in detail with reference to conventional PVA stretched polarizers.

FIG. 8 is a graph showing the transmittance, the degree of polarization, the brightness, and the contrast ratio of the reflection type polarizing plate according to the first to third embodiments of the present invention in comparison with the PVA stretching type polarizing plate of the comparative example.

Shows the transmittance, the polarization degree, the brightness, and the contrast ratio of the conventional PVA stretched polarizing plate and DBEF film and the reflective polarizing plate according to the first to third embodiments of the present invention, respectively.

In this case, the first embodiment and the second embodiment are cases where the transmittance of the coating type polarizing element is 30%, and the third embodiment is an example of the case where the transmittance of the coating type polarizing element is 50%.

Referring to the table, the transmittances of the conventional PVA stretched polarizer and DBEF film and the reflection polarizer according to the first through third embodiments of the present invention were 43%, 46.3%, 28%, 26%, and 18%, respectively. %, And the degree of polarization is 99.996%, 97.5%, 99.993%, 99.995%, and 99.997%.

The brightnesses of the conventional PVA stretched polarizer and DBEF film and the reflective polarizer according to the first through third embodiments of the present invention are 450nit, 510nit, 475nit, 465nit, and 385nit, and the contrast ratios are 1300, 28, 1359, 1311, and 1920, respectively.

As described above, the reflection type polarizing plate according to the first to third embodiments of the present invention shows much higher contrast ratio than the DBEF film, and shows the same degree of polarization as that of the conventional PVA stretched type polarizing plate.

In particular, the reflection type polarizing plate according to the first embodiment of the present invention shows a higher luminance than the conventional PVA-type polarizing plate, while the decrease in transmittance is not greater than that of the second and third embodiments .

9 is a graph showing the transmittance, the degree of polarization, the brightness, and the contrast ratio of the reflective polarizer according to the first embodiment of the present invention compared with the transmittance of the coated polarizer.

The case 1, the case 2, the case 3, the case 4, and the case 5 each have a case where the transmittance of the coating type polarizing element is 10%, 20%, 30%, 40%, and 50%, respectively.

Referring to the table, the transmittances of the case 1, the case 2, the case 3, the case 4, and the case 5 were 8%, 17%, 28%, 35%, and 45%, and the degrees of polarization were 99.997%, 99.995%, 99.993% , 99.98%, and 99.95%, respectively.

It can be seen that the luminance for the case 1, the case 2, the case 3, the case 4 and the case 5 is 341nit, 422nit, 475nit, 488nit and 506nit, and the contrast ratios are 1982, 1885, 1359, 852 and 687.

As described above, as the transmittance of the coating type polarizing element increases, the transmittance of the reflection type polarizing plate increases, while the polarization degree and the contrast ratio decrease. In the present invention, Case 3 is a preferred embodiment.

Meanwhile, as described above, the upper polarizer may be formed using a coating type polarizing element instead of the PVA stretched polarizer, which will be described in detail in the following fourth embodiment of the present invention.

10 is a cross-sectional view schematically showing a part of a structure of a liquid crystal display device according to a fourth embodiment of the present invention.

In this case, the liquid crystal display according to the fourth embodiment of the present invention shown in FIG. 10 can be applied to the first to third embodiments of the present invention, except that the upper polarizer plate is formed using the coating type polarizing element. The liquid crystal display device according to the present invention is substantially the same as the liquid crystal display device according to the first embodiment.

As described above, the liquid crystal display according to the fourth embodiment of the present invention shown in FIG. 10 shows the case of using the TN mode, but the present invention is not limited thereto. The present invention is applicable regardless of the liquid crystal mode such as the VA mode as well as the IPS mode or the FFS mode.

Referring to the drawings, a liquid crystal display according to a fourth embodiment of the present invention roughly includes a color filter substrate (not shown) while maintaining a cell gap by a color filter substrate 405, an array substrate 410 and a column spacer 405 and a liquid crystal layer 430 formed between the array substrate 410 and the liquid crystal layer 430.

The color filter substrate 405 separates the sub-color filter from the color filter 407 constituted by a plurality of sub-color filters implementing the colors of red, green and blue and blocks light transmitted through the liquid crystal layer 430 A black matrix 406, and a transparent common electrode 408 for applying a voltage to the liquid crystal layer 430.

The array substrate 410 includes a plurality of gate lines (not shown) and data lines (not shown) arranged vertically and horizontally to define a plurality of pixel regions, thin film transistors which are switching elements formed in the intersections of the gate lines and the data lines, And a pixel electrode 418 formed in the region.

The thin film transistor includes a gate electrode 421 connected to a gate line, a source electrode 422 connected to a data line, and a drain electrode 423 electrically connected to the pixel electrode 418 through a contact hole formed in the protective film 415b . The thin film transistor is connected to the source electrode 422 and the drain electrode 422 by a gate voltage supplied to the gate insulating film 415a and the gate electrode 421 for insulation between the gate electrode 421 and the source / And an active layer 424 that forms a conduction channel between the electrodes 423.

When the amorphous silicon thin film is used as the active layer 424, the source / drain regions of the active layer 424 are connected to the source / drain electrodes 422 and 423 through the ohmic-contact layer 425 formed of the n + amorphous silicon thin film Thereby forming an ohmic contact.

However, the present invention is not limited thereto. The active layer 424 may be formed of another semiconductor material such as a polycrystalline silicon thin film or an oxide semiconductor.

The color filter substrate 405 and the array substrate 410 are adhered to each other by a sealant 440 formed on the outer periphery of the image display area to constitute a liquid crystal panel and the color filter substrate 405 and the array substrate 410 (Not shown) formed on the color filter substrate 405 or the array substrate 410. As shown in FIG.

Such a liquid crystal panel is provided with a backlight unit on its back surface to supply light. This is because the liquid crystal display itself is a device that does not have a light emitting element, and thus requires a separate light source.

At this time, an upper polarizer 450b and a lower polarizer 450a are attached to the outer surfaces of the color filter substrate 405 and the array substrate 410 to selectively transmit only specific polarized light.

Between the liquid crystal layer 430 and the common electrode 408 and between the liquid crystal layer 430 and the pixel electrode 418 is formed an upper alignment film 409 and a lower alignment film 419, So that the initial alignment state of the liquid crystal and the alignment direction are uniformly aligned.

At this time, the present invention is characterized in that the lower polarizer 450a is made of a reflection type polarizing plate by using the coating type polarizing element 455 and the brightness enhancement film 460, thereby improving the brightness and improving the polarization and contrast ratio.

Particularly, the fourth embodiment of the present invention is characterized in that an upper polarizer 450b is formed by using a coating type polarizing element instead of a conventional PVA stretched polarizer. In this case, the entire thickness of the liquid crystal display device can be reduced, which makes it possible to cope with the slimming down of the product, while providing an effect of simplifying the process when the device is manufactured in the in-cell form.

At this time, the upper polarizer 150 attached to the upper surface of the liquid crystal panel may further include a reinforcing substrate for protecting the liquid crystal panel from external impact.

The lower polarizer 450a is a reflection type polarizer and includes a coating type polarizing element 455 and a brightness enhancement film 460, which will be described with reference to the above description.

That is, the lower polarizer 450a according to the fourth embodiment of the present invention may be composed of a coating type polarizing element 455 and a brightness enhancement film 460 sequentially formed on the outer surface of the array substrate 410.

At this time, the present invention is characterized in that the low polarization degree of the brightness enhancement film 460 is improved by adding a coating type polarizing element 455 whose optical axes are mutually orthogonal. That is, by adding the coating type polarizing element 455 so that the optical axis is orthogonal to the brightness enhancement film 460, the polarizing plate can be applied as a polarizing plate like the conventional PVA stretching type polarizing plate. Rather, So that the luminance is improved.

The brightness enhancement film 460 may have a multi-layer structure in which the first thermoplastic resin and the second thermoplastic resin are alternately laminated. The brightness enhancement film 460 having such a structure can be produced, for example, by extruding two types of resins together and stretching the extruded film.

When the coating type polarizing element 455 is interposed between the liquid crystal panel and the brightness enhancement film 460 so as to be orthogonal to the polarization axis of the brightness enhancement film 460 as described above, the white brightness is increased, It is possible to realize a reflective bottom polarizer 450a which can achieve a high contrast ratio in the frontal direction.

In other words, since the coating type polarizing element 455 is configured such that the optical axes thereof are orthogonal to the brightness enhancement film 460, it is possible to minimize the increase of the black brightness in the case of displaying a black image. Accordingly, the polarization and the contrast ratio can be improved, and it becomes possible to replace the conventional PVA stretched polarizer.

At this time, it is necessary to control the thickness and the dye concentration, that is, the transmittance so that the coating type polarizing element 455 functions to partially block the P-polarized light incident from the lower brightness enhancement film 460 .

Such a coated polarizing element 455 may be composed of an orientation layer 455a formed on the array substrate 410 and a polarization layer 455b formed on the orientation layer 455a.

The orientation layer 455a may be formed of polyimide or polyamide.

The polarizing layer 455b may be made of a host material and a guest material.

As the host material, a liquid crystal polymer or a reactive liquid crystal monomer showing mainly liquid crystal properties can be used. Here, the reactive liquid crystal monomer is a liquid crystal substance including a terminal group capable of polymerization, and is a monomer molecule having a liquid crystal phase including a terminal capable of polymerization with a mesogen that exhibits liquid crystallinity.

As the polarizing layer 455b is coated or coated on the orientation layer 455a, the host material interacts with the fine grooves formed in the orientation layer 455a to arrange along the orientation direction.

The guest material may be composed of a dichroic dye. A dichroic dye absorbs one of the two polarization components of light and transmits the other. As the dichroic dye, an iodine-based dye, an anthraquinone-based propyline azo dye, a biazo dye, and a triazo dye may be used.

Two or more dyes can be used to absorb or transmit light in a specific wavelength range, and a combination of these dyes can be designed to have the desired transmission hue.

The total thickness of the coated polarizing element 455 thus configured is suitably 10 μm or less, more preferably 5 μm or less.

At this time, the brightness enhancement film 460 may be attached to the coated polarizing element 455 through an adhesive (not shown).

As described above, the present invention realizes the reflection type polarizing plate by interposing the coating type polarizing element 455 between the liquid crystal panel and the brightness enhancement film 460 so as to be orthogonal to the polarization axis of the brightness enhancement film 460, The polarization and the contrast ratio are improved.

However, the present invention is not limited to this, and the coating type polarizing element 455 may be interposed within the brightness enhancement film 460 or between the liquid crystal panel and the brightness enhancement film 460, The present invention can be applied to the lower side of the brightness enhancement film 460 as well.

While a great many are described in the foregoing description, it should be construed as an example of preferred embodiments rather than limiting the scope of the invention. Therefore, the invention should not be construed as limited to the embodiments described, but should be determined by equivalents to the appended claims and the claims.

150a, 150b, 250a, 350a, 450a, 450b:
155, 255, 355, 355, 455: Coated polarizing element
155a, 255a, 355a ', 355a ": orientation layer
155b, 255b, 355b ', and 355b "
160, 260a, 260b, 360, and 460:

Claims (4)

A liquid crystal panel;
A first polarizer positioned below the liquid crystal panel and comprising a coating type polarizing element and a brightness enhancement film; And
And a second polarizer positioned above the liquid crystal panel,
Wherein the coating type polarizing element and the brightness enhancement film have optical axes perpendicular to each other. The liquid crystal display device according to claim 1, wherein the coating type polarizing element
An orientation layer; And
And a polarizing layer arranged on the alignment layer,
Polarized light incident from the brightness enhancement film. The liquid crystal display of claim 2, wherein the coating type polarizing element has a transmittance of 10% to 50%. The liquid crystal display of claim 1, wherein the second polarizer is a coating type polarizing element.

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