KR100674234B1 - Optically compensated bend mode lcd - Google Patents

Abstract

The present invention discloses an optically compensated band mode liquid crystal display device. The disclosed invention includes an optically compensated band mode liquid crystal display device comprising a first phase compensation film disposed outside the lower substrate and a second phase compensation film disposed outside the upper substrate, wherein the first and second phase compensation films Silver is composed of disk-type liquid crystal molecules, the liquid crystal molecules of the first phase compensation film is a twist tilt arrangement having a symmetrical distribution about the interface with the liquid crystal molecules of the lower region centered on the middle layer of the liquid crystal layer, The liquid crystal molecules of the second phase compensation film are arranged in a twist tilt having a symmetrical distribution around the interface with the liquid crystal molecules in the upper region about the middle layer of the liquid crystal layer, and the phases of the first and second phase compensation films The delay is characterized in that the phase delay of the liquid crystal layer is equal to the absolute value thereof, and the sign is opposite.

Description

Optically compensated band mode liquid crystal display {OPTICALLY COMPENSATED BEND MODE LCD}

1A and 1B are cross-sectional views of a conventional OCB mode liquid crystal display device.

2A and 2B are cross-sectional views showing phase compensation films of a conventional OCB mode liquid crystal display.

3A and 3B are cross-sectional views of an OCB mode liquid crystal display device according to the present invention.

4 is a cross-sectional view schematically showing an arrangement of liquid crystal molecules of the liquid crystal layer and the phase compensation films according to the present invention.

(Explanation of symbols for the main parts of the drawing)

50-lower substrate 52-pixel electrode

54-first horizontal alignment layer 56-first polarizing plate

58-First Phase Compensation Film 70-Upper Substrate

72-counter electrode 74-second horizontal alignment layer

76-second polarizer 78-second phase compensation film

60-liquid crystal layer

The present invention relates to an optically compensated band mode liquid crystal display device, and more particularly, to an optically compensated band mode liquid crystal display device to which a dopant is added.

In general, an optically compensated band mode liquid crystal display (OCB-LCD) is a liquid crystal molecules arranged in a splay state before applying an electric field, and arranged in a band state after applying an electric field. The light is adjusted according to the change of the voltage of the state. The OCB-LCD has a fast response speed while obtaining even viewing angle characteristics in all directions without multiple rubbing processes.

However, such an OCB-LCD requires a driving difficulty in applying a high voltage at a moment to bring it into a band state.

Therefore, conventionally, a twisted OCB-LCD that can stably operate without requiring a high driving voltage has been proposed.

1A and 1B are cross-sectional views for explaining the operation of a conventional twisted OCB-LCD.

First, referring to FIG. 1A, the lower substrate 21 and the upper substrate 31 are disposed to face each other at a predetermined distance (hereinafter, referred to as a cell gap). A driving electrode, for example, a pixel electrode 23 is formed on an inner surface of the lower substrate 21, and a first horizontal alignment layer 25 is formed on one surface of the pixel electrode 23. A driving electrode, for example, a counter electrode 33 is formed on the inner surface of the upper substrate 31, and a second horizontal alignment layer 35 is formed on the surface of the counter electrode 33. In addition, the first and second horizontal alignment layers 25 and 35 have rubbing axes parallel to each other.

The first polarizing plate 29 having a predetermined polarization axis is disposed on the outer surface of the lower substrate 21. In addition, a second polarizing plate 39 having a predetermined polarization axis is disposed on the outer surface of the upper substrate 31. Here, the polarization axes of the first and second polarizing plates 29 and 39 are arranged to cross each other, and any one of these polarization axes is a rubbing axis and a predetermined angle, for example, an angle of 25 to 50 degrees or 110 to 140 degrees, More preferably, it is arranged to achieve 45 ° or 135 °.

The liquid crystal layer 40 including the plurality of liquid crystal molecules 40a is interposed in the space between the lower substrate 21 and the upper substrate 31. The dopant is added to the liquid crystal layer 40 to be in a twisted state before voltage application, and the twisted state is the same as or similar to the band state when the voltage is applied. The liquid crystal can be driven without applying a high voltage. In addition, by setting the ratio of the cell gap and the pitch value of the liquid crystal to about 0.25 to 0.36, it is possible to have a high transmittance and a low driving voltage, and the unevenness of the state which may occur during manufacturing can be solved by applying one high voltage to the manufacturing. One such dopant is a chiral dopant.

On the other hand, in order to improve the contrast, a first phase compensation film 27 is interposed between the lower substrate 21 and the first polarizing plate 29, and a second between the upper substrate 31 and the second polarizing plate 39. The phase compensation film 37 is interposed. Here, as shown in FIG. 2A, the first phase compensating film 27 has liquid crystal molecules arranged to form a symmetrical distribution with respect to an interface with the lower portion X1 of the middle layer ML of the liquid crystal layer 40. It consists of 27a. As shown in FIG. 2B, the second phase compensation film 37 has liquid crystal molecules 37a arranged to form a symmetrical distribution with respect to the interface X and the upper portion X2 of the middle layer ML of the liquid crystal layer 40. It is composed of The refractive index anisotropy of the liquid crystal molecules is compensated by the phase compensation films 27 and 37.

The OCB mode liquid crystal display device having such a configuration is operated as follows.

First, even after a dopant is added to the liquid crystal layer immediately after fabricating the liquid crystal display, the liquid crystal molecules 40a may be arranged in a splay state under the influence of the first and second horizontal alignment layers 25 and 35 in some or all of the pixels. Can be. However, when a sufficiently large starting voltage is initially applied, the liquid crystal molecules 40a are arranged in a twisted state of 180 ° as shown in FIG. 1A under the influence of the added dopant, and are returned to the splay state even when the voltage application is stopped. It does not return. After this initial process, the OCB mode liquid crystal display of the present invention arranges the liquid crystal molecules in a twisted state of 180 ° before applying voltage.

This mode is driven in a specific voltage range. When the voltage is applied, the twist state starts to become sufficiently similar to the band state, and the light is at a 45 degree angle with the rubbing direction of the love layer. In this case, when a further voltage is applied, the liquid crystals stand in the vertical direction, and the light transmitted through the polarizing plate becomes dark under the influence of the liquid crystal layer. By adjusting the refractive index anisotropy at the front side of the phase compensation film, a perfect dark state at a desired voltage can be achieved, thereby reducing the driving voltage.

However, in the conventional twisted OCB-LCD, even if the first and second phase compensation films 27 and 37 are disposed outside the upper and lower substrates 21 and 31, the inside of the first and second phase compensation films 27 and 37 can be obtained. Since the liquid crystal molecules are arranged in a symmetrical distribution with respect to the liquid crystal molecules 40a in the liquid crystal layer 40 only around the interface, the viewing angle compensation is not perfectly achieved.

Accordingly, it is an object of the present invention to provide an OCB-LCD capable of compensating the viewing angle perfectly in any direction of the screen.

In order to achieve the above object of the present invention, a predetermined distance of the present invention is opposed to each other, each inner surface of the upper substrate and the lower substrate formed with a drive electrode; A liquid crystal layer interposed between the upper and lower substrates, composed of several liquid crystal molecules, and to which a twisted dopant (having a pitch as a spiral structure with a chiral dopant as a liquid crystal material) is added; A first horizontal alignment layer disposed on an inner surface of the lower substrate and having a predetermined rubbing axis; A second horizontal alignment layer disposed on an inner surface of the upper substrate and having a rubbing axis parallel to a rubbing axis of the first horizontal alignment layer; A first polarizer disposed outside the lower substrate and having a predetermined polarization axis; A second polarizing plate perpendicular to the polarization axis of the first polarizing plate disposed outside the upper substrate; A first phase compensation film interposed between the lower substrate and the first polarizing plate; And a second phase compensation film interposed between the upper substrate and the second polarizing plate, wherein the first and second phase compensation films are composed of disk-type liquid crystal molecules, and the liquid crystal molecules of the first phase compensation film are Twist tilt is arranged to form a symmetrical distribution around the interface and the liquid crystal molecules of the lower region centered on the middle layer of the liquid crystal layer, the liquid crystal molecules of the second phase compensation film is the upper region centered on the middle layer of the liquid crystal layer Twist tilt is arranged to form a symmetrical distribution around the interface with the liquid crystal molecules of the phase delay of the first and second phase compensation film, the absolute value of the phase delay of the liquid crystal layer is the same, the phase is opposite It features. Alternatively, the driving voltage is controlled by creating a desired dark state at a specific voltage by having a value slightly larger or smaller than the absolute value of the retardation of the liquid crystal layer when viewed from the front (± 0.2 of the retardation value of the liquid crystal layer). It is done.

(Example)

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

3A and 3B are cross-sectional views of an OCB-LCD according to the present invention, and FIG. 4 is a cross-sectional view briefly showing an arrangement of liquid crystal molecules of a liquid crystal layer and phase compensation films according to the present invention.

First, referring to FIG. 3A, the lower substrate 50 and the upper substrate 70 are disposed to face each other at a predetermined distance (hereinafter, referred to as a cell gap). The pixel electrode 52 which is a driving electrode is formed on the inner surface of the lower substrate 50, and the first horizontal alignment layer 54 is formed on one surface of the pixel electrode 52. The counter electrode 72 is formed on the inner surface of the upper substrate 70, and the second horizontal alignment layer 74 is formed on the surface of the counter electrode 72. Here, the pixel electrode 52 and the counter electrode 72 may be formed of a transparent conductor in the case of a transmissive type and an opaque conductor in the case of a reflective type. In addition, the first and second horizontal alignment layers 54 and 74 have a pretilt angle of 40 degrees or less, and have parallel rubbing axes. Here, the arrow in the figure indicates the rubbing direction.

The liquid crystal layer 60 including the plurality of liquid crystal molecules 60a is interposed in the space between the lower substrate 50 and the upper substrate 70. Here, it is preferable that the liquid crystal molecules 60a have a positive dielectric anisotropy. In addition, the dopant is added to the liquid crystal layer 60 so that the liquid crystal layer 60 rapidly changes to a state similar to or similar to a band state when a voltage is applied. In this case, the dopant serves to twist the liquid crystal molecules 40a between the upper and lower substrates by 180 °, and the dopant includes a chiral dopant. In addition, the dopant is added at a 0.26 to 0.36 d / p ratio (d: cell gap, p: pitch) so that the twisted state is stably maintained after the starting voltage is applied.

The first polarizing plate 56 having a predetermined polarization axis is disposed on the outer surface of the lower substrate 50. In addition, a second polarizing plate 76 having a predetermined polarization axis is disposed on the outer surface of the upper substrate 70. Here, the polarization axes of the first and second polarizing plates 56 and 76 are arranged to intersect with each other, and any one of these polarization axes is a rubbing axis of the first and second horizontal alignment layers 54 and 74 and a predetermined angle example. For example, it is preferably arranged to form an angle of 25-50 degrees or 110-140 degrees, more preferably 45 degrees or 135 degrees.

Meanwhile, in order to improve contrast, a first phase compensation film 5 8 is interposed between the lower substrate 50 and the first polarizing plate 5 6 , and between the upper substrate 70 and the second polarizing plate 7 6 . The second phase compensation film 7 8 is interposed. 4 is a diagram illustrating the structures of the liquid crystal layer 60 and the first and second phase compensation films 58 and 78. As shown in FIG. 4, the first phase compensation film 58 and the second phase compensation film 78 are composed of a disk type, that is, liquid crystal molecules 58a and 78 a having a height smaller than a radius. . In addition, the liquid crystal molecules 58a of the first phase compensation film 58 are symmetric about an interface with the liquid crystal molecules 60a arranged at the lower portion X1 of the middle layer ML of the liquid crystal layer 60. Twist-tilt arranged to make a distribution. In addition, the liquid crystal molecules 78a of the second phase compensation film 78 are symmetric about an interface with the liquid crystal molecules 60a arranged at the upper portion X2 of the middle layer ML of the liquid crystal layer 60. Twist-tilt arranged to make a distribution. At this time, in order to completely compensate for the viewing angle, phase retardation (thickness of the phase compensation film × refractive index anisotropy of the disk type liquid crystal molecules) of the liquid crystal molecules 58a and 78a constituting the first and second phase compensation films 58 and 78. ) Is the same as the absolute value of the phase delay of the liquid crystal layer 60 in the desired voltage band, the phase has the opposite value or the difference between the absolute value of the phase delay value of the liquid crystal layer is 0.2um or less, the desired degree at the desired voltage It is characterized by adjusting the driving voltage by making the dark state of. The use of such phase compensation films 58 and 78 can more fully compensate for the viewing angle.

The OCB mode liquid crystal display device having such a configuration is operated as follows.

First, even after a dopant is added into the liquid crystal layer 60 immediately after fabrication of the liquid crystal display, the liquid crystal molecules 60a are splayed in whole or in part by the influence of the first and second horizontal alignment layers 54 and 74. Arranged in a state. However, when the d / p value is 0.25 to 0.36, when the starting voltage is initially applied, the liquid crystal molecules 60a are arranged in a twisted state in the entire pixel region as shown in FIG. 3A by the influence of the added dopant. If the voltage application is interrupted, it does not return to the splay state again. After this initial process, the OCB mode liquid crystal display of the present invention arranges the liquid crystal molecules in a twisted state of 180 ° before applying voltage.

Meanwhile, when a predetermined voltage is applied to the pixel electrode 23, the liquid crystal molecules 40a arranged in a twisted state by an electric field generated between the pixel electrode 23 and the counter electrode 33 are similar to or in a band state. Rearranged to state. At this time, since the twist state to which the voltage is applied is similar to or the same as the band state, a sudden phase change such as a transition from the splay to the band state does not occur. Therefore, there is no unnecessary process such as application of a high voltage required when changing from splay to a band state, and since the liquid crystal molecules 40a arranged in the band state are arranged up and down symmetrically with respect to the middle layer ML, the phase is naturally Is compensated. Accordingly, the viewing angle is greatly compensated.

At this time, the phase delays of the first and second phase compensation films 58 and 78 may be adjusted according to voltages, thereby realizing both normal white or normal black modes.

As described in detail above, according to the present invention, in an OCB-LCD driving a twist-band state by adding a predetermined dopant in the liquid crystal layer, the phase compensation film is composed of disk-type liquid crystal molecules, and this disk type The liquid crystal molecules of are arranged to be twisted so as to be symmetrical 90 degrees with the arrangement of the liquid crystal molecules of the corresponding liquid crystal layer. In addition, the phase delay of the phase compensation film is equal to the absolute value of the phase delay of the liquid crystal layer, and the phase is reversed. Accordingly, the viewing angle is greatly compensated.

In addition, various changes can be made in the range which does not deviate from the summary of this invention.

Claims (7)

Opposed to each other at a predetermined distance, and each inner side thereof includes an upper substrate and a lower substrate on which driving electrodes are formed; A liquid crystal layer interposed between the upper and lower substrates and composed of several liquid crystal molecules, wherein the dopant is added and twisted ; A first horizontal alignment layer disposed on an inner surface of the lower substrate and having a predetermined rubbing axis; A second horizontal alignment layer disposed on an inner surface of the upper substrate and having a rubbing axis parallel to a rubbing axis of the first horizontal alignment layer; A first polarizer disposed outside the lower substrate and having a predetermined polarization axis; A second polarizing plate perpendicular to the polarization axis of the first polarizing plate disposed outside the upper substrate; A first phase compensation film interposed between the lower substrate and the first polarizing plate; And A second phase compensation film interposed between the upper substrate and the second polarizing plate, The first and second phase compensation film is composed of disk-type liquid crystal molecules, The liquid crystal molecules of the first phase compensation film are arranged in a twist tilt so as to form a symmetrical distribution around the interface with the liquid crystal molecules in the lower region with respect to the middle layer of the liquid crystal layer, The liquid crystal molecules of the second phase compensation film are arranged in a twist tilt so as to have a symmetrical distribution around the interface with the liquid crystal molecules in the upper region with respect to the middle layer of the liquid crystal layer, The phase retardation of the first and second phase compensation films is equal to the phase retardation of the liquid crystal layer and its absolute value is the same, and the phase is opposite, or the phase retardation value at the front is greater than the phase retardation value of the liquid crystal layer. Optically compensated band mode liquid crystal display device having a difference of 0.2 or less. The optically compensated band mode liquid crystal display of claim 1, wherein the dopant is added to the extent that liquid crystal molecules can be twisted by 180 ° before application of a driving voltage. The method of claim 2, wherein the dopant is added in a 0.26 to 0.36 dip ratio (d / p) characterized in that the entire pixel is stabilized by applying a voltage above a predetermined voltage at the time of manufacture even if some or all of the pixels are in the splay state An optically compensated band mode liquid crystal display, characterized by being in a twisted state. The optical axis of claim 1, wherein the rubbing axes of the first and second horizontal alignment layers form an angle with any one of the polarization axes of the first and second polarizing plates, preferably at an angle of 45 degrees or 135 degrees. Band mode liquid crystal display device compensated with. The optically compensated band mode liquid crystal display device according to claim 1, wherein the liquid crystal molecules in the liquid crystal layer have a positive dielectric anisotropy and a value of 3 to 15. The optically compensated band mode liquid crystal display device wherein the product of the cell gap and refractive index anisotropy of the liquid crystal used in claim 1 has a value between 0.5 um and 1.2 um. According to claim 1, a value of 0.2 or less is added to the absolute value of the phase delay value of the liquid crystal layer to make a dark at a specific voltage, thereby creating a normally white state, or having a value of 0.3 to 0.5. Nomally Black) optically compensated band mode liquid crystal display.

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