KR20060028883A - Liquid crystal display device - Google Patents

Abstract

First and second substrates opposed to each other at a predetermined interval of the present invention; A liquid crystal layer squeezed at a predetermined angle on the first and second substrate opposing surfaces; A first polarizing plate having a first polarization axis disposed under the liquid crystal layer; And a second polarizing plate having a second polarizing axis that is displaced at a predetermined angle, not perpendicular to the first polarizing axis, disposed on the liquid crystal layer.

By changing the angle between the polarization axes of the upper and lower polarizers with the liquid crystal display device as described above, phase delays are generated in the compensation film in the polarizers and are offset from the phase delays in the liquid crystal panel, without additional process or cost increase. It is possible to reduce the black luminance and ultimately improve the contrast ratio.

Polarizer, polarization axis, luminance, contrast ratio, twisted nematic liquid crystal

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

1 is an exploded perspective view of a liquid crystal panel of a conventional TN mode.

Figure 2 is a perspective view of the polarizer of the conventional TN mode liquid crystal panel viewed from the upper top.

3 is a cross-sectional view of a liquid crystal panel when an electric field is applied in a conventional TN mode liquid crystal display.

4 is an enlarged cross-sectional view of region A shown in FIG. 3.

5 is a perspective view of a liquid crystal panel according to an embodiment of the present invention.

6 is a view showing the relationship between the angle and transmittance between the polarization axis and the horizontal axis according to an embodiment of the present invention.

7 is a plan view as seen from the upper top of the polarizing plate in the liquid crystal display according to the embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

100 lower substrate 110 lower alignment layer

110a: lower alignment layer rubbing axis direction 150: lower polarizing plate

150a: polarization axis of lower polarizer 200: upper substrate

210: upper alignment layer 210a: upper alignment layer rubbing axis direction

250: upper polarizing plate 250a: polarizing axis of upper polarizing plate

300: liquid crystal layer 300a: liquid crystal molecules

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having an improved contrast ratio.

Recently, liquid crystal display devices, which are one of the flat panel display devices that are continuously attracting attention, are liquid.

A device that changes the optical anisotropy by applying an electric field to a liquid crystal that combines the liquidity and optical properties of the crystal.It has a low power consumption, a small volume, a large size, and a high definition compared to a conventional cathode ray tube. have.

In general, a liquid crystal display device is arranged by interposing liquid crystal molecules between a pair of light-transmissive substrates, and light is emitted or blocked according to the alignment state of the liquid crystal molecules to perform image display.

In general, the alignment mode of various liquid crystal display devices may be made using properties and alignment patterns of liquid crystals, and a representative example thereof is a twisted nematic (TN) mode liquid crystal display device.

1 is an exploded perspective view of a liquid crystal panel of a conventional TN mode, and FIG. 2 is a perspective view of a polarizer of a conventional TN mode liquid crystal panel viewed from an upper upper end thereof.

As shown in FIGS. 1 and 2, the liquid crystal display of the TN mode includes opposing upper and lower substrates 10 and 20, pixel electrodes 11 disposed on an inner surface of the lower substrate 10, and an upper portion thereof. On the common electrode 21 disposed on the inner surface of the substrate 10, the alignment film (not shown) disposed on the surface of the upper / lower substrate opposing surface, respectively, and the outer surface of the opposing surface of the upper / lower substrate 10, 20, respectively. The liquid crystal layer 30 may be interposed between the polarizing plates 15 and 25 and the upper and lower substrates 10 and 20, and may include liquid crystal molecules.

The alignment film (not shown) is a horizontal alignment film, is oriented perpendicular to the rubbing axes 12a and 12b, and the angle θ ₁ between the polarization axes 15a and 25a of the upper and lower polarizing plates 15 and 25 is 90 degrees. The polarization axes 15a and 25a of the upper and lower polarizing plates 15 and 25 are attached to each other in a direction perpendicular to each other.

That is, the rubbing axis 12a of the lower alignment layer and the polarization axis 15a of the lower polarizing plate 15 are attached in the same direction, and the rubbing axis 12b of the upper alignment layer 21 and the polarization axis 25a of the upper polarizing plate 25 are attached. Are attached in the same direction.

In addition, the pixel electrode 11 and the common electrode 21 have a plate shape and are interposed between a thin film transistor (not shown) and a color filter (not shown), respectively.

Before the electric field is applied between the pixel electrode 11 and the common electrode 21, the liquid crystal molecules 30a are formed by the influence of the upper and lower alignment layers 11 and 21 as shown in FIGS. 1 and 2. ° is arranged twist.

Accordingly, before the electric field is applied, light passing through the lower polarizer 15 passes through the twisted liquid crystal molecules 30a and passes through the upper polarizer 25. Accordingly, the screen is in a white state, which is called normally white mode.                         

In addition, although not shown, when an electric field is applied, the liquid crystal molecules are gradually oriented parallel to the electric field direction, and when a predetermined voltage or more is applied between the substrates, the liquid crystal molecules are rearranged in the direction of the electric field, so that the upper and lower substrates are Perpendicular to each other.

Therefore, the light passing through the lower polarizer passes through the twisted liquid crystal molecules and becomes perpendicular to the upper polarizer so that the light is blocked by the polarizer.

Accordingly, the screen is black.

3 is a cross-sectional view of a liquid crystal panel when an electric field is applied in a conventional TN mode liquid crystal display, and FIG. 4 is an enlarged cross-sectional view of region A shown in FIG.

As shown in FIG. 3, the arrangement state of the liquid crystal molecules in the black mode applies an electric field to a pixel electrode (not shown) and a common electrode (not shown) of the upper and lower substrates 60 and 50. When the liquid crystal molecules 30a are rearranged in the direction of the electric field, the liquid crystal molecules 30a are oriented vertically between the two substrates 60 and 50.

In this case, as shown in FIG. 4, the axis of the liquid crystal molecules 30a inside the liquid crystal panel is not vertically aligned by the electric field, but rather tilts toward the lower substrate due to the influence of the surface energy and the rubbing direction of the alignment layer.

As a result, in the conventional TN mode liquid crystal display, phase delay occurs in the black mode, resulting in an increase in luminance, thereby reducing a contrast ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device in which the brightness ratio is increased and the contrast ratio is reduced due to the structural problem of the liquid crystal in the black mode of the conventional TN mode liquid crystal display device.

The liquid crystal display of the present invention comprises: first and second substrates disposed to face each other at predetermined intervals; A liquid crystal layer squeezed at a predetermined angle on the first and second substrate opposing surfaces; A first polarizing plate having a first polarization axis disposed under the liquid crystal layer; And a second polarizing plate having a second polarizing axis that is displaced at a predetermined angle, not perpendicular to the first polarizing axis, disposed on the liquid crystal layer.

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

<Example>

5 is a perspective view of a liquid crystal panel according to an embodiment of the present invention.

As shown in FIG. 5, the TN mode liquid crystal display according to the present invention includes a first substrate 100 including a pixel electrode (not shown) and a second substrate 200 including a common electrode (not shown). ) Are opposed to each other by a predetermined distance.

In this case, the distance between the first and second substrates 100 and 200 is referred to as a cell gap d.

In addition, alignment layers 110 and 210 are formed on the surface of the first substrate 100 and the surface of the second substrate 200 to determine an arrangement state of initial liquid crystal molecules.

The alignment layers 110 and 210 are horizontal alignment layers having a pretilt angle of 5 ° or less, and the two alignment layers 110 and 210 are rubbed in a direction perpendicular to each other.                     

Here, reference numeral 110a illustrated in the drawing denotes the rubbing axis direction of the first alignment layer 110, and reference numeral 210a denotes the rubbing axis direction of the second alignment layer 210.

The liquid crystal layer 300 is sandwiched between the alignment layers 110 and 210 of the first and second substrates 100 and 200. Here, the liquid crystal layer 300 includes several liquid crystal molecules 300a, and a material having a positive dielectric anisotropy (Δε) is used.

In addition, the first polarizing plate 150 and the second polarizing plate 250 are disposed on the first substrate 100 and the second substrate 200. These first and second polarizing plates 150 and 250 have first and second polarization axes 150a and 250a for transmitting only light in a predetermined direction.

The polarization axis 150a of the first polarizing plate 150 and the polarization axis 250a of the second polarizing plate 250 are disposed substantially perpendicular to each other, but the angles between the polarization axes 150a and 250a are not set to 90.00 °. do.

The liquid crystal display device having such a configuration is arranged in a rubbing state of the horizontal alignment layer of the liquid crystal molecules 300a when no electric field is formed between the pixel electrode and the common electrode.

That is, since the alignment layers 110 and 210 are vertically aligned with each other, the major axes of the liquid crystal molecules 300a are arranged in a 90 ° twist while being parallel to the substrate surface.

At this time, the angle between the polarization axes 150a and 250a of the first and second polarizing plates 150 and 250 is not substantially 90 °, but is almost vertically oriented. Therefore, when the electric field is applied, light applied from the bottom surface of the first substrate 100 is Although the first polarizer 150 and the liquid crystal layer 300 pass, the second polarizer 250 does not pass, and thus light is blocked to form a black mode.                     

In this case, since the long axis of the liquid crystal molecules 300a slightly lies in the direction of the first substrate 100 due to the influence of the surface energy and the rubbing direction of the horizontal alignment layers 110 and 210 (see FIG. 4), In consideration of such an effect, the contrast ratio may be improved by finely adjusting the angles between the polarization axes 150a and 250a of the polarizing plates 150 and 250.

FIG. 6 is a view illustrating angles and transmittances between a polarization axis and a horizontal axis according to an embodiment of the present invention, and FIG. 7 is a plan view seen from the upper top of the polarizer in the liquid crystal display according to the embodiment of the present invention.

As shown in FIGS. 6 and 7, in the case of the WV-SA TN mode currently produced as a prototype, an angle θ ₂ between the polarization axes 150a and 250a and the horizontal line 310 is 45.00 on the simulation. It can be seen that the transmittance is lowest when the temperature is 45.04 ° instead of °.

That is, when the angle between the polarization axis and the horizontal axis is 45.04 ° instead of 45.00 °, the transmittance is lowest, and only the direction of the polarization axis is slightly changed without adding a process or raising the production cost, thereby lowering the brightness in black to increase the contrast ratio. You can.

Accordingly, as illustrated in FIG. 7, the polarizing plate is manufactured by manufacturing the polarizing plate at an angle θ ₂ between the polarizing axes 150a and 250a of the upper and lower polarizing plates 150 and 250 and the horizontal line 310 at 45.04 °. The phase delay is generated in the compensation film therein, and the phase delay in the liquid crystal panel (not shown) cancels each other, thereby reducing the black luminance and eventually improving the contrast ratio.

In addition, although not covered in the embodiment of the present invention, the predetermined angle between the horizontal axis and the polarization axis may be 40.01 ° to 99.99 °.

In the liquid crystal display of the present invention, the phase delay is generated in the compensation film in the polarizer by changing the angle between the respective polarization axes of the upper and lower polarizers, and the phase delay in the liquid crystal panel is offset from each other. It is possible to reduce the black luminance without improving the contrast ratio.

In addition, the present invention is not limited to the embodiments, and various changes can be made by those skilled in the art without departing from the gist of the present invention as claimed in the following claims.

Claims (3)

First and second substrates opposed to each other at a predetermined interval; A liquid crystal layer squeezed at a predetermined angle on the first and second substrate opposing surfaces; A first polarizing plate having a first polarization axis disposed under the liquid crystal layer; And a second polarizing plate having a second polarizing axis that is displaced at a predetermined angle not perpendicular to the first polarizing axis disposed on the liquid crystal layer. The method of claim 1, And a predetermined angle between the polarization axis and the horizontal axis is 40.01 ° to 99.99 °. The method of claim 1, And the liquid crystal layer is a material having a positive dielectric anisotropy (Δε).

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