KR20070003534A - In-plane switching mode liquid crystal display device including optical retardation film and manufacturing method of the same - Google Patents

Abstract

An IPS(In-Plane Switching) mode LCD and a method for manufacturing the same are provided to improve the leakage of light in a dark state, prevent the reduction of contrast ratio, and improve the conversion of color according to viewing angle. An LCD panel(410) includes first and second substrates. A first polarizing plate(420) is positioned on a first surface of the LCD panel, and includes a first supporter(424a), a first polarizing element(422), and a second supporter(424b). A second polarizing plate(430) is positioned on a second surface of the LCD panel, and includes a third supporter(434a), a second polarizing element(432), and a fourth supporter(434b). A first optical compensation film(440) is positioned between the first polarizing plate and the LCD panel.

Description

FIELD OF THE INVENTION A horizontal field type liquid crystal display device including an optical compensation film and a method of manufacturing the same {in-plane switching mode liquid crystal display device including optical retardation film and manufacturing method of the same}

1 is a cross-sectional view showing a conventional horizontal electric field type liquid crystal display device.

2 is a view showing a simulation result of contrast characteristics of a dark state in a conventional horizontal electric field type liquid crystal display device.

3 is a cross-sectional view schematically showing a conventional polarizing plate.

4 shows the xyz polar coordinate system;

FIG. 5 is a diagram showing the transmittance of the orthogonal state polarizer according to polar and azimuth angles.

FIG. 6 is a diagram showing results of simulation of contrast characteristics in a dark state with respect to a conventional polarizing plate in an orthogonal state. FIG.

7 is a schematic cross-sectional view of a horizontal field type liquid crystal display device according to a first embodiment of the present invention;

FIG. 8 is a view showing a simulation result of contrast characteristics of a dark state in a horizontal field type liquid crystal display device according to a first embodiment of the present invention; FIG.

9 is a schematic cross-sectional view of a horizontal field type liquid crystal display device according to a second embodiment of the present invention;

FIG. 10 is a view showing a simulation result of contrast characteristics of a dark state in a horizontal field type liquid crystal display device according to a second embodiment of the present invention; FIG.

11 is a schematic cross-sectional view of a horizontal field type liquid crystal display device according to a third embodiment of the present invention.

12 is a view showing a Poincare sphere showing a polarization state of light passing through each optical element in a horizontal field type liquid crystal display device according to a third embodiment of the present invention.

13 is a schematic cross-sectional view of a horizontal field type liquid crystal display device according to a fourth embodiment of the present invention;

FIG. 14 is a view showing a pore curry sphere showing a polarization state of light passing through each optical element in a horizontal field type liquid crystal display device according to a fourth embodiment of the present invention; FIG.

<Description of Symbols for Main Parts of Drawings>

410 liquid crystal display panel 420 first polarizing plate

422: first polarizer 424a, 424b: first and second supports

430: second polarizer 432: second polarizer

434a, 434b: third and fourth supports

440: first optical compensation film 450: second optical compensation film

460: third optical compensation film

The present invention relates to a liquid crystal display device, and more particularly, to a horizontal field type liquid crystal display device including an optical compensation film.

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

Among various types of liquid crystal displays, twisted nematic (TN) liquid crystal displays are widely used. In these TN liquid crystal displays, liquid crystal molecules are arranged to be parallel to two substrates and to be misaligned between two substrates. The liquid crystal molecules adjacent to make 90 degrees. The liquid crystal molecules of the TN liquid crystal display are driven by an electric field in a direction perpendicular to the substrate between the pixel electrode of the lower substrate and the common electrode of the upper substrate. Thus, when no electric field is generated, the liquid crystal molecules are arranged parallel to the substrate, and when the electric field is generated by applying a voltage to the two electrodes, the liquid crystal molecules are arranged parallel to the electric field to be perpendicular to the substrate.

However, the TN liquid crystal display has a disadvantage that the viewing angle characteristics are not excellent. Various methods have been proposed to overcome the shortcomings of a narrow viewing angle, and one example is a horizontal electric field method, that is, an LCD in an in-plane switching (IPS) mode.

Hereinafter, a horizontal field type liquid crystal display device will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a conventional horizontal electric field type liquid crystal display device.

As shown in FIG. 1, the lower substrate 10 and the upper substrate 20 are arranged at a predetermined interval. On the inner surface of the lower substrate 10, a thin film transistor T including a gate electrode, a semiconductor layer, a source electrode, and a drain electrode is formed. In addition, the common electrode 12 and the pixel electrode 14 are formed in the pixel region on the inner surface of the lower substrate 10 with a predetermined interval. Although not shown, the common electrode 12 and the pixel electrode 14 are formed parallel to each other, the pixel electrode 14 is electrically connected to the drain electrode of the thin film transistor (T). Next, the protective layer 16 covers the thin film transistor T, the common electrode 12, and the pixel electrode 14. The common electrode 12 and the pixel electrode 14 are formed on different layers, but may be formed on the same layer. In addition, as illustrated in FIG. 1, the pixel electrode 14 may be formed on the same layer as the source and drain electrodes of the thin film transistor T, or may be formed of a separate material on the protective layer 16.

On the inner surface of the upper substrate 20, a black matrix 22 having an opening corresponding to the pixel region is formed, and a color filter layer 24 is formed corresponding to the opening of the black matrix 22. The black matrix 22 prevents light leakage current in the thin film transistor T and blocks light in portions except the pixel region in correspondence with the thin film transistor T. The color filter layer 24 includes red, green, and blue color filters, and one color filter corresponds to one pixel area. In addition, the color filter layer 24 partially covers the black matrix 22, so that a boundary between the color filters is formed on the black matrix 22. An overcoat layer 26 is formed on the color filter layer 24. The overcoat layer 26 protects the color filter layer 24, prevents the material of the color filter layer 24 from eluting, and flattens the surface of the substrate 20 including the color filter layer 24.

The liquid crystal layer 30 is positioned between the two substrates 10 and 20, and the liquid crystal molecules of the liquid crystal layer 30 are arranged parallel to the two substrates 10 and 20. Although not illustrated, an alignment layer is formed on each of the two substrates 10 and 20 adjacent to the liquid crystal layer 30, and the alignment layer is aligned by a method such as rubbing to determine the initial arrangement of the liquid crystal molecules.

Lower and upper polarizers 40 and 50 are disposed on outer surfaces of the two substrates 10 and 20, respectively, and light transmission axes of the lower and upper polarizers 40 and 50 are disposed to be perpendicular to each other.

In such a horizontal field type liquid crystal display, when a voltage is applied to the common electrode 12 and the pixel electrode 14, an electric field parallel to the substrate is formed on the two electrodes 12 and 14, and the liquid crystal of the liquid crystal layer 30 is formed. The molecules are arranged side by side in this electric field, ie perpendicular to the two electrodes 12, 14.

As described above, in the horizontal field type liquid crystal display device, a pixel electrode and a common electrode are formed on the same plane, and a horizontal electric field is generated between the two electrodes so that the liquid crystal molecules are arranged in parallel with a horizontal electric field parallel to the substrate. The viewing angle of the device can be widened.

However, such a horizontal field type liquid crystal display has a problem in that light leakage occurs when displaying a black state, thereby showing a low contrast ratio value.

FIG. 2 is a diagram illustrating a simulation result of contrast characteristics of a dark state in a conventional horizontal field type liquid crystal display device. Here, the light transmission axis of the lower polarizing plate corresponds to the x axis of FIG. 2 in parallel with the horizontal direction of the panel, and the light transmission axis of the upper polarizing plate corresponds to the y axis of FIG. 2 in parallel to the longitudinal direction of the panel. In addition, the optical axis of the liquid crystal layer is parallel to the light transmission axis of the upper polarizing plate. As shown in FIG. 2, in the dark state, large light leakage occurs at 45 degrees, 135 degrees, 225 degrees, and 315 degrees corresponding to the diagonal directions of the liquid crystal display panel, thereby increasing luminance. The contrast ratio is lowered.

However, this problem is not a problem of the horizontal electric field itself, but a problem appearing in the polarizers currently used.

3 is a cross-sectional view schematically showing a conventional polarizing plate. As shown in FIG. 3, the conventional polarizing plate 70 includes a polarizing element 72 positioned between the first and second supports 74a and 74b and the first and second supports 74a and 74b. . Polyvinyl alcohol is widely used as the polarizer 72, and triacetylcellulose is widely used as the first and second supports 74a and 74b.

A polarizing plate 70 having the structure of FIG. 3 is attached to upper and lower liquid crystal panels using an adhesive layer or the like. In this case, the support adjacent to the liquid crystal display panel may be formed to have a phase delay, and generally, a negative C plate having n _x = n _y > n _z is used.

Types of polarizing plates include O type polarizers and E type polarizers. Among them, O type polarizers are widely used because they have better dark state characteristics.

When the two conventional O-type polarizing plates are arranged such that the light transmission axes are perpendicular to each other, the transmittance of light may be expressed as follows.

과

는 각 편광판의 편광 방향을 나타내는 벡터이고, φ와 θ는 시야각 방향을 나타낸 것으로, 도 4에 도시한 바와 같이, xyz 극좌표계(polar coordinate)에서 방위각(azimuthal angle)과 극각(polar angle)으로 각각 정의된다. here,

and

Is a vector representing the polarization direction of each polarizer, and φ and θ represent the viewing angle directions. As shown in FIG. 4, the azimuthal angle and the polar angle in the xyz polar coordinate system are respectively shown. Is defined.

The transmittance | permeability of the orthogonal state polarizing plate according to polar angle (theta) and azimuth angle (phi) obtained from the above transmittance | permeability formula was shown in FIG. As shown in FIG. 5, light leakage occurs when the polar angle θ is near 70 degrees, and the light leakage is large when the azimuth angle φ is near 45 degrees.

Using these results, the result of simulating the contrast characteristic in the dark state with respect to the orthogonal polarizing plate is shown in FIG. As shown in FIG. 6, it can be seen that light leakage appears at 45 degrees, 135 degrees, 225 degrees, and 315 degrees corresponding to the diagonal direction of the liquid crystal display panel. This is because the orthogonality of the two polarizing plates is broken depending on the viewing angle direction even if the polarizing plate is perpendicular to the light transmission axis.

As mentioned above, such light leakage increases the dark state luminance of the liquid crystal display, causing a problem of lowering the contrast ratio.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a horizontal field type liquid crystal display device which can prevent a decrease in contrast ratio by improving light leakage in a dark state.

Another object of the present invention is to provide a horizontal field type liquid crystal display device which can improve color inversion according to a viewing angle.

According to an aspect of the present invention, there is provided a horizontal field type liquid crystal display device including a liquid crystal display panel including first and second substrates, a first surface of the liquid crystal display panel, a first support, and a first support. A first polarizing plate comprising a polarizing element and a second support, a second polarizing plate positioned on a second surface of the liquid crystal display panel, and including a third support, a second polarizing element and a fourth support, and the first polarizing plate And a first optical compensation film positioned between the liquid crystal display panel and the third support, which is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first, second, third and fourth supports are formed of triacetylcellulose.

The first optical compensation film is a + C plate of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). The + C plate has a phase delay value less than or equal to λ / 2 (λ is a wavelength of visible light).

The first support is a -C plate of n _x = n _y > n _z .

A second optical compensation film is further included between the second polarizing plate and the liquid crystal display panel.

The first and second optical compensation films are + C plates of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The + C plate has a phase delay less than or equal to λ / 4 (λ is the wavelength of visible light).

The first polarizer is positioned between the first and second supports, and the second polarizer is located between the third and fourth supports.

Another horizontal field type liquid crystal display device according to the present invention comprises a liquid crystal display panel including first and second substrates and a liquid crystal layer, a first support, a first polarizing element and a first support on a first surface of the liquid crystal display panel. A second polarizing plate comprising a second support, a second polarizing plate positioned on a second surface of the liquid crystal display panel, and including a third support, a second polarizing element and a fourth support, the liquid crystal display panel and the second A first optical compensation film positioned between the polarizing plates, a second optical compensation film positioned between the first optical compensation film and the second polarizing plate, wherein the third support is adjacent to the liquid crystal display panel; It has a phase delay value of 10 nm to +10 nm.

The first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first to fourth supports are formed of triacetyl cellulose.

The first optical compensation film is a + C plate of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The second optical compensation film is an A plate of n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The optical axis of the A plate is parallel or perpendicular to the optical axis of the liquid crystal layer.

The + C plate has a phase delay value less than or equal to λ / 4 (λ is a wavelength of visible light).

The A plate has a phase delay greater than or equal to λ / 4 (λ is the wavelength of visible light) and less than λ.

The liquid crystal layer has a phase delay value greater than or equal to λ / 4 (λ is a wavelength of visible light) and smaller than λ.

A third optical compensation film is further included between the liquid crystal display panel and the first polarizing plate.

The first optical compensation film is an A plate of n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, n _z is a refractive index in the z direction). The 3 optical compensation film is a + C plate of n _x = n _y <n _z .

The optical axis of the A plate is perpendicular to the optical axis of the liquid crystal layer.

The + C plate has a phase delay less than or equal to λ / 4 (λ is a wavelength of visible light), and the liquid crystal layer and the A plate have a phase delay greater than or equal to λ / 4 and less than λ.

The first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The first polarizer is positioned between the first and second supports, and the second polarizer is located between the third and fourth supports.

A method of manufacturing a horizontal field type liquid crystal display device according to the present invention comprises the steps of forming a liquid crystal display panel including first and second substrates, a first support and a first polarizing element on a first surface of the liquid crystal display panel. And forming a first polarizing plate including a second support, and forming a second polarizing plate including a third support, a second polarizing element, and a fourth support on a second surface of the liquid crystal display panel. And forming a first optical compensation film between the first polarizing plate and the liquid crystal display panel, wherein the third support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first, second, third and fourth supports are formed of triacetylcellulose.

The first optical compensation film is a + C plate of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The + C plate has a phase delay value less than or equal to λ / 2 (λ is a wavelength of visible light).

The first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

A second optical compensation film is further included between the second polarizing plate and the liquid crystal display panel.

The first and second optical compensation films are + C plates of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The + C plate has a phase delay less than or equal to λ / 4 (λ is the wavelength of visible light).

The first polarizer is positioned between the first and second supports, and the second polarizer is located between the third and fourth supports.

According to another aspect of the present invention, there is provided a method of manufacturing a horizontal liquid crystal display device, the method including: forming a liquid crystal display panel including first and second substrates and a liquid crystal layer; Forming a first polarizing plate including a first polarizing element and a second support, and forming a second polarizing plate including a third support, a second polarizing element, and a fourth support on a second surface of the liquid crystal display panel. Forming a first optical compensation film between the liquid crystal display panel and the second polarizing plate, and forming a second optical compensation film between the first optical compensation film and the second polarizing plate. And the third support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm.

The first to fourth supports are formed of triacetyl cellulose.

The first optical compensation film is a + C plate of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The second optical compensation film is an A plate of n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The optical axis of the A plate is parallel or perpendicular to the optical axis of the liquid crystal layer.

The + C plate has a phase delay value less than or equal to λ / 4 (λ is a wavelength of visible light).

The A plate has a phase delay greater than or equal to λ / 4 (λ is the wavelength of visible light) and less than λ.

The liquid crystal layer has a phase delay value greater than or equal to λ / 4 (λ is a wavelength of visible light) and smaller than λ.

A third optical compensation film is further included between the liquid crystal display panel and the first polarizing plate.

The first optical compensation film is an A plate of n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, n _z is a refractive index in the z direction). The 3 optical compensation film is a + C plate of n _x = n _y <n _z .

The optical axis of the A plate is perpendicular to the optical axis of the liquid crystal layer.

The + C plate has a phase delay less than or equal to λ / 4 (λ is a wavelength of visible light), and the liquid crystal layer and the A plate have a phase delay greater than or equal to λ / 4 and less than λ.

The first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction).

The first polarizer is positioned between the first and second supports, and the second polarizer is located between the third and fourth supports.

Hereinafter, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

7 is a schematic cross-sectional view of a horizontal field type liquid crystal display including a polarizing plate and an optical compensation film according to a first embodiment of the present invention.

As illustrated in FIG. 7, the first polarizer 120 is positioned below the liquid crystal display panel 110, and the second polarizer 130 is positioned above the liquid crystal display panel 110. An optical compensation film 140 is positioned between the first polarizer 120 and the liquid crystal display panel 110.

Although not shown, the liquid crystal display panel 110 includes a lower first substrate, an upper second substrate, and a liquid crystal layer positioned between the first and second substrates. The liquid crystal display panel 110 has a horizontal electric field method. A thin film transistor, a common electrode, and a pixel electrode are formed on an inner surface of the first substrate, and a black matrix and a color filter layer are formed on an inner surface of the second substrate. In addition, an overcoat layer covering the black matrix and the color filter layer may be further formed on the inner surface of the second substrate.

The first polarizer 120 includes a first polarizer 122 between the first and second supports 124a and 124b and the first and second supports 124a and 124b, and the second polarizer 130 includes And a second polarizer 132 between the third and fourth supports 134a and 134b and the third and fourth supports 134a and 134b. Here, the first and second polarizers 122 and 132 are made of polyvinyl alcohol (PVA), and the first to fourth supports 124a, 124b, 134a, and 134b are triacetylcellulose: TAC). In this case, the first and third supports 124a and 134a adjacent to the liquid crystal display panel 110 may be formed of a material having no phase delay, that is, having a retardation value of −10 nm to +10 nm. Do.

The optical compensation film 140 is preferably a positive C plate where n _x = n _y <n _z , and may have a phase delay value less than or equal to λ / 2. Such a + C plate can be formed by coating or stretching.

Meanwhile, in the first embodiment of the present invention, the first support 124a may have a phase delay. In this case, -C plate may be used as in the prior art. When the first support 124a has a phase delay, the phase delay value of the + C plate which is the optical compensation film 140 may vary according to the phase delay value of the first support 124a.

In the horizontal field type liquid crystal display device according to the first embodiment of the present invention having such a structure, a result of simulating a contrast characteristic of a dark state is shown in FIG. 8. Here, the light transmission axis of the lower first polarizing plate corresponds to the x axis of FIG. 8 in parallel with the transverse direction of the panel, and the light transmission axis of the upper second polarizing plate corresponds to the y axis of FIG. 8 in parallel with the longitudinal direction of the panel. do. In addition, the optical axis of the liquid crystal layer is parallel to the light transmission axis of the upper first polarizing plate.

As shown in FIG. 8, it can be seen that the diagonal light leakage of the panel is significantly reduced in the dark state. Therefore, the fall of contrast ratio can be prevented.

The second embodiment of the present invention proposes a structure which can prevent the lowering of the contrast ratio more than the first embodiment.

9 is a schematic cross-sectional view of a horizontal field type liquid crystal display including a polarizing plate and an optical compensation film according to a second embodiment.

As illustrated in FIG. 9, the first polarizer 220 is positioned under the liquid crystal display panel 210, and the second polarizer 230 is positioned above the liquid crystal display panel 210. The first optical compensation film 240 is positioned between the first polarizing plate 220 and the liquid crystal display panel 210, and the second optical compensation film 250 is disposed between the second polarizing plate 230 and the liquid crystal display panel 210. Located.

As in the first embodiment, the liquid crystal display panel 210 includes a lower first substrate, an upper second substrate, and a liquid crystal layer positioned between the first and second substrates. The liquid crystal display panel 210 has a horizontal electric field method. A thin film transistor, a common electrode, and a pixel electrode are formed on an inner surface of a first substrate, and a black matrix and a color filter layer are formed on an inner surface of a second substrate. In addition, an overcoat layer covering the black matrix and the color filter layer may be further formed on the inner surface of the second substrate.

The first polarizer 220 includes a first polarizer 222 between the first and second supports 224a and 224b and the first and second supports 224a and 224b, and the second polarizer 230 is And a second polarizer 232 between the third and fourth supports 234a and 234b and the third and fourth supports 234a and 234b. Here, the first and second polarizers 222 and 232 are made of polyvinyl alcohol (PVA), and the first to fourth supports 224a, 224b, 234a, and 234b are triacetylcellulose: TAC). In this case, the first and third supports 224a and 234a adjacent to the liquid crystal display panel 210 may be formed of a material having no phase delay, that is, a phase delay value of −10 nm to +10 nm.

Preferably, the first and second optical compensation films 240 and 250 are + C plates where n _x = n _y <n _z , and may have a phase delay value less than or equal to λ / 4. . Such a + C plate can be formed by coating or stretching.

Meanwhile, in the second embodiment of the present invention, the first support 224a may also have a phase delay, and a -C plate may be used. When the first support 224a has a phase delay, by adjusting the phase delay value of the + C plate, which is the first optical compensation film 240 directly above the first support 224a, the first support 224a is phased. The same effect can be obtained when there is no delay, that is, when the phase delay value is -10 nm to +10 nm.

In the horizontal field type liquid crystal display device according to the second embodiment of the present invention, a result of simulating the contrast characteristic of a dark state is shown in FIG. 10.

As shown in FIG. 10, it can be seen that the diagonal light leakage of the panel in the dark state is smaller than in the first embodiment. Therefore, lowering of the contrast ratio can be prevented more than in the first embodiment.

FIG. 11 is a schematic cross-sectional view of a horizontal field type liquid crystal display device including a polarizing plate and an optical compensation film according to a third embodiment of the present invention.

As illustrated in FIG. 11, the first polarizing plate 320 is positioned below the liquid crystal display panel 310, and the second polarizing plate 330 is positioned above the liquid crystal display panel 310. First and second optical compensation films 340 and 350 are formed between the liquid crystal display panel 310 and the second polarizing plate 330.

Although not shown, the liquid crystal display panel 310 includes a lower first substrate, an upper second substrate, and a liquid crystal layer positioned between the first and second substrates. The liquid crystal display panel 310 has a horizontal electric field method. A thin film transistor, a common electrode, and a pixel electrode are formed on an inner surface of the first substrate, and a black matrix and a color filter layer are formed on an inner surface of the second substrate. In addition, an overcoat layer covering the black matrix and the color filter layer may be further formed on the inner surface of the second substrate.

The first polarizer 320 includes a first polarizer 322 between the first and second supports 324a and 324b and the first and second supports 324a and 324b, and the second polarizer 330 And a second polarizer 332 between the third and fourth supports 334a and 334b and the third and fourth supports 334a and 334b. Here, the first and second polarizers 322 and 332 are made of polyvinyl alcohol (PVA), and the first to fourth supports 324a, 324b, 334a, and 334b are triacetylcellulose (triacetylcellulose: TAC). In this case, the first and third supports 124a and 134a adjacent to the liquid crystal display panel 310 may be formed of a material having no phase delay, that is, a phase delay value of −10 nm to +10 nm.

It is preferable that the first optical compensation film 340 is a positive C plate where n _x = n _y <n _z , and the + C plate may be formed by coating or stretching.

On the other hand, it is preferable that the second optical compensation film 350 is an A plate in which n _x ≠ n _y = n _z . In this case, the optical axis direction of the A plate may be parallel or perpendicular to the rubbing direction of the liquid crystal layer of the liquid crystal display panel 310, that is, the optical axis direction of the liquid crystal layer. Here, the optical axis direction of the liquid crystal layer is parallel to the light transmission axis direction of the second polarizing plate 330, and is perpendicular to the light transmission axis direction of the first polarizing plate 320. The light transmission axis of the first polarizing plate 320 may be parallel to the horizontal direction of the liquid crystal display panel 310, and the light transmission axis of the second polarizing plate 330 may be parallel to the longitudinal direction of the liquid crystal display panel 310.

In the third embodiment of the present invention, in order to prevent light leakage according to the viewing angle, the first optical compensation film 340, which is a + C plate, may have a phase delay value less than or equal to λ / 4, and the liquid crystal display panel 310 ) May have a phase delay value greater than or equal to λ / 4 and smaller than λ, and the second optical compensation film 350, which is an A plate, may have a phase delay value greater than or equal to λ / 4 and smaller than λ. Can be.

Meanwhile, in the third embodiment of the present invention, the first support 324a may have a phase delay, and in this case, a -C plate may be used as in the prior art. When the first support 324a has a phase delay, the same effects as the present invention may be obtained by adjusting the phase delay values of the first and second optical compensation films 340 and 350.

FIG. 12 is a view illustrating a Poincare sphere showing a polarization state of light passing through each optical element in the horizontal field type liquid crystal display according to the third exemplary embodiment having the structure of FIG. 11. The poincaré sphere expresses all polarization states of light on the sphere, and the polarization state can be easily predicted using the poincaré sphere when the optical axis and the phase delay value of the optical element are known. In this Poincare sphere, the equator represents linear polarization, the point at pole S ₃ represents left handed circular polarization, the point at-S ₃ represents right handed circular polarization, and the upper half of the remaining region Left handed elliptical polarization, and the lower hemisphere represents right handed elliptical polarization.

In Figure 12, S ₁ point when looking for a liquid crystal display of the present invention from the front side indicates the state of polarization of the first polarizing plate, _one of -S point represents the state of polarization of the second polarizing plate. The polarization states of the first and second polarizers are symmetrical with respect to the center O of the Poincare sphere, and thus are perpendicular to each other, thereby displaying an excellent dark state.

By the way, when looking at the liquid crystal display at an angle, the polarization state of the first polarizing plate moves to the point A, and the polarization state of the second polarizing plate moves to the F point. Since the points A and F are not symmetrical with respect to the center O, the polarization states of the first and second polarizing plates are not perpendicular to each other. Therefore, it is preferable to make the polarization state of the light which reaches the 2nd polarizing plate perpendicular to the polarization state of a 2nd polarizing plate using an optical compensation film.

As shown in FIG. 12, when the horizontal electric field liquid crystal display according to the fourth embodiment of the present invention is viewed obliquely, the polarization state of light passing through each optical element is a + C plate, the first optical compensation. It moves from point A to point B by the film (340 of FIG. 11), and moves from point B to point C by the second optical compensation film (350 of FIG. 11) which is A plate. In this case, since the + C plate and the A plate have different phase delays according to wavelength bands, the degree of rotation is different so that there is a slight difference in reaching the end point C. Point C by this compensation film is symmetrical with point F with respect to the center O. Therefore, the polarization state (point C) of the light reaching the second polarizing plate is perpendicular to the polarization state of the second polarizing plate, and blocks the light to display an excellent dark state.

As described above, in the third embodiment of the present invention, by controlling the polarization state using the + C plate and the A plate, light leakage can be prevented and the contrast ratio can be prevented from being lowered.

On the other hand, in the case of the horizontal field type liquid crystal display, color shift occurs according to the viewing angle due to dispersion characteristics of the liquid crystal.

A fourth embodiment of the present invention proposes a structure capable of improving color inversion while preventing a decrease in contrast ratio. 13 is a schematic cross-sectional view of a horizontal field type liquid crystal display including a polarizing plate and an optical compensation film according to a fourth embodiment of the present invention.

As illustrated in FIG. 13, the first polarizing plate 420 is positioned below the liquid crystal display panel 410, and the second polarizing plate 430 is positioned above the liquid crystal display panel 410. First and second optical compensation films 440 and 450 are sequentially positioned between the liquid crystal display panel 410 and the second polarizing plate 430, and a third is disposed between the liquid crystal display panel 410 and the first polarizing plate 420. The optical compensation film 460 is located.

As in the third embodiment, the liquid crystal display panel 410 includes a lower first substrate, an upper second substrate, and a liquid crystal layer positioned between the first and second substrates. The liquid crystal display panel 410 has a horizontal electric field method. A thin film transistor, a common electrode, and a pixel electrode are formed on an inner surface of the first substrate, and a black matrix and a color filter layer are formed on an inner surface of the second substrate. In addition, an overcoat layer covering the black matrix and the color filter layer may be further formed on the inner surface of the second substrate.

The first polarizer 420 includes a first polarizer 422 between the first and second supports 424a and 424b and the first and second supports 424a and 424b, and the second polarizer 430 And a second polarizer 432 between the third and fourth supports 434a and 434b and the third and fourth supports 434a and 434b. Here, the first and second polarizers 422 and 432 are made of polyvinyl alcohol (PVA), and the first to fourth supports 424a, 424b, 434a, and 434b are triacetylcellulose: TAC). In this case, the first and third supports 424a and 434a adjacent to the liquid crystal display panel 410 may be formed of a material having no phase delay, that is, a phase delay value of −10 nm to +10 nm.

It is preferable that the first optical compensation film 440 is an A plate in which n _x ≠ n _y = n _z . In this case, the optical axis direction of the A plate is perpendicular to the rubbing direction of the liquid crystal layer of the liquid crystal display panel 410, that is, the optical axis direction of the liquid crystal layer. Here, the optical axis direction of the liquid crystal layer is parallel to the light transmission axis direction of the second polarizing plate 430, and is perpendicular to the light transmission axis direction of the first polarizing plate 420. The light transmission axis of the first polarizing plate 420 may be parallel to the horizontal direction of the liquid crystal display panel 410, and the light transmission axis of the second polarizing plate 430 may be parallel to the vertical direction of the liquid crystal display panel 410.

The second and third optical compensation films 450 and 460 are preferably + C plates where n _x = n _y <n _z , and the + C plates may be formed by coating or stretching. .

In the fourth embodiment of the present invention, the second and third optical compensation films 450 and 460, which are + C plates, may have a phase delay value less than or equal to λ / 4 to prevent light leakage according to the viewing angle. The liquid crystal layer of the liquid crystal display panel 410 may have a phase delay value greater than or equal to λ / 4 and smaller than λ, and the first optical compensation film 440, which is an A plate, is larger than or equal to λ / 4 and smaller than λ. It may have a phase delay value.

FIG. 14 is a view showing a Poincare sphere showing a polarization state of light passing through each optical element in the horizontal field type liquid crystal display device according to the fourth embodiment of the present invention having the structure of FIG. 13.

As shown in FIG. 14, when the horizontal field type liquid crystal display according to the fourth exemplary embodiment of the present invention is viewed obliquely, the polarization state of light passing through each optical element is a lower third of + C plate. The first optical compensation film (Fig. 13) moves from point A to point B by the optical compensation film (460 in Fig. 13) and from point B to point C by the liquid crystal display panel (410 in Fig. 13). 440 of 13 moves from point C to point D. At this time, it is compensated that the position is shifted for each wavelength, it is collected at almost one point at the point D, and moved from the point D to the point E by the second optical compensation film (450 in Fig. 13) + plate. The point E by the compensation film is symmetrical with the point F with respect to the center O, and almost all wavelength bands are located at one point. Accordingly, the polarization state (point E) of the light reaching the second polarizing plate is perpendicular to the polarization state of the second polarizing plate, blocks the light to display an excellent dark state, and improves color inversion according to the viewing angle.

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

The horizontal field type liquid crystal display device including the polarizing plate and the optical compensation film according to the present invention has the following effects.

The support adjacent to the liquid crystal display panel is formed of a material having no phase delay, and by using the compensation films of the + C plate and the A plate, it is possible to reduce the diagonal light leakage of the panel in the dark state. Therefore, the fall of contrast ratio can be prevented and color inversion according to a viewing angle can be improved.

Claims (56)

A liquid crystal display panel comprising first and second substrates; A first polarizing plate disposed on a first surface of the liquid crystal display panel and including a first support, a first polarizing element, and a second support; A second polarizing plate disposed on a second surface of the liquid crystal display panel and including a third support, a second polarizing element, and a fourth support; A first optical compensation film positioned between the first polarizing plate and the liquid crystal display panel Including; And the third support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method according to claim 1, And the first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method according to claim 1, And wherein the first, second, third and fourth supports are formed of triacetyl cellulose. The method according to claim 1, The first optical compensation film is a horizontal field type liquid crystal display in which n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Device. The method according to claim 4, And the + C plate has a phase delay value less than or equal to λ / 2 (λ is a wavelength of visible light). The method according to claim 5, And the first support is a -C plate of n _x = n _y > n _z . The method according to claim 1, And a second optical compensation film between the second polarizing plate and the liquid crystal display panel. The method according to claim 7, The first and second optical compensation films are horizontal electric fields in which + C plates of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction and n _z is a refractive index in the z direction). Type liquid crystal display device. The method according to claim 8, The + C plate has a phase delay of less than or equal to λ / 4 (λ is a wavelength of visible light). The method according to claim 9, Wherein the first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). The method according to claim 1, And the first polarizing element is positioned between the first and second supports. The method according to claim 1, And wherein the second polarizer is positioned between the third and fourth supports. A liquid crystal display panel comprising first and second substrates and a liquid crystal layer; A first polarizing plate disposed on a first surface of the liquid crystal display panel and including a first support, a first polarizing element, and a second support; A second polarizing plate disposed on a second surface of the liquid crystal display panel and including a third support, a second polarizing element, and a fourth support; A first optical compensation film positioned between the liquid crystal display panel and the second polarizing plate; A second optical compensation film positioned between the first optical compensation film and the second polarizing plate Including; And the third support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method according to claim 13, And the first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method according to claim 13, And the first to fourth supports are formed of triacetyl cellulose. The method according to claim 13, The first optical compensation film is a horizontal field type liquid crystal display in which n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Device. The method according to claim 13, The second optical compensation film is a horizontal field type liquid crystal display device wherein n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). . The method according to claim 17, And the optical axis of the A plate is parallel or perpendicular to the optical axis of the liquid crystal layer. The method according to claim 16, And the + C plate has a phase delay value less than or equal to λ / 4 (λ is a wavelength of visible light). The method according to claim 17, Wherein the A plate has a phase delay value greater than or equal to λ / 4 (λ is a wavelength of visible light) and smaller than λ. The method according to claim 13, Wherein the liquid crystal layer has a phase delay value greater than or equal to λ / 4 (λ is a wavelength of visible light) and smaller than λ. The method according to claim 13, And a third optical compensation film between the liquid crystal display panel and the first polarizing plate. The method according to claim 22, The first optical compensation film is an A plate of n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, n _z is a refractive index in the z direction). 3 The optical compensation film is a horizontal field type liquid crystal display device of n ₊ = n _y <n _z + C plate. The method according to claim 23, And the optical axis of the A plate is perpendicular to the optical axis of the liquid crystal layer. The method according to claim 23, The + C plate has a phase delay less than or equal to λ / 4 (λ is a wavelength of visible light), and the liquid crystal layer and the A plate have a phase delay greater than or equal to λ / 4 and smaller than λ. LCD display device. The method according to claim 13, Wherein the first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). The method according to claim 13, And the first polarizing element is positioned between the first and second supports. The method according to claim 13, And wherein the second polarizer is positioned between the third and fourth supports. Forming a liquid crystal display panel comprising first and second substrates; Forming a first polarizing plate on a first surface of the liquid crystal display panel, the first polarizing plate including a first support, a first polarizing element, and a second support; Forming a second polarizing plate including a third support, a second polarizing element, and a fourth support on the second surface of the liquid crystal display panel; Forming a first optical compensation film between the first polarizing plate and the liquid crystal display panel Including; And the third support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method of claim 29, And the first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method of claim 29, And the first, second, third and fourth supports are formed of triacetyl cellulose. The method of claim 29, The first optical compensation film is a horizontal field type liquid crystal display in which n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Method of manufacturing the device. The method according to claim 32, And the + C plate has a phase delay value less than or equal to λ / 2 (λ is a wavelength of visible light). The method according to claim 33, Wherein the first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Manufacturing method. The method of claim 29, And a second optical compensation film between the second polarizing plate and the liquid crystal display panel. The method of claim 35, wherein The first and second optical compensation films are horizontal electric fields in which + C plates of n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction and n _z is a refractive index in the z direction). Method of manufacturing a liquid crystal display device. The method of claim 36, The + C plate has a phase delay of less than or equal to λ / 4 (λ is a wavelength of visible light). The method of claim 29, Wherein the first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Manufacturing method. The method of claim 29, And the first polarizing element is positioned between the first and second supports. The method of claim 29, And the second polarizing element is positioned between the third and fourth supports. Forming a liquid crystal display panel comprising first and second substrates and a liquid crystal layer; Forming a first polarizing plate on a first surface of the liquid crystal display panel, the first polarizing plate including a first support, a first polarizing element, and a second support; Forming a second polarizing plate including a third support, a second polarizing element, and a fourth support on the second surface of the liquid crystal display panel; Forming a first optical compensation film between the liquid crystal display panel and the second polarizing plate; Forming a second optical compensation film between the first optical compensation film and the second polarizing plate Including; And the third support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method of claim 41, And the first support is adjacent to the liquid crystal display panel and has a phase delay value of -10 nm to +10 nm. The method of claim 41, Wherein the first to fourth supports are formed of triacetyl cellulose. The method of claim 41, The first optical compensation film is a horizontal field type liquid crystal display in which n _x = n _y <n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Method of manufacturing the device. The method of claim 41, The second optical compensation film is a horizontal field type liquid crystal display device wherein n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Method of preparation. The method of claim 45, And the optical axis of the A plate is parallel or perpendicular to the optical axis of the liquid crystal layer. The method of claim 44, The + C plate has a phase delay value less than or equal to λ / 4 (λ is a wavelength of visible light). The method of claim 45, And A plate has a phase delay value greater than or equal to λ / 4 (λ is a wavelength of visible light) and smaller than λ. The method of claim 41, The liquid crystal layer has a phase delay value greater than or equal to λ / 4 (λ is a wavelength of visible light) and smaller than λ. The method of claim 41, And a third optical compensation film between the liquid crystal display panel and the first polarizing plate. The method of claim 50, The first optical compensation film is an A plate of n _x ≠ n _y = n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, n _z is a refractive index in the z direction). 3 The optical compensation film is a manufacturing method of a horizontal field type liquid crystal display device of the + C plate of n _x = n _y <n _z . The method of claim 51, And the optical axis of the A plate is perpendicular to the optical axis of the liquid crystal layer. The method of claim 51, The + C plate has a phase delay less than or equal to λ / 4 (λ is a wavelength of visible light), and the liquid crystal layer and the A plate have a phase delay greater than or equal to λ / 4 and smaller than λ. Method of manufacturing a liquid crystal display device. The method of claim 41, Wherein the first support is a -C plate of n _x = n _y > n _z (n _x is a refractive index in the x direction, n _y is a refractive index in the y direction, and n _z is a refractive index in the z direction). Manufacturing method. The method of claim 41, And the first polarizing element is positioned between the first and second supports. The method of claim 41, And the second polarizing element is positioned between the third and fourth supports.

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