JP2001318371A - Liquid crystal display - Google Patents

Abstract

(57) Abstract: To prevent a decrease in maximum light transmittance which occurs when an alignment direction of liquid crystal molecules does not coincide with an optical axis of a polarizing section. A liquid crystal display device includes a liquid crystal display panel (3) having a liquid crystal layer (LQ) sandwiched between transparent insulating substrates (G1) and (G2), and an incident and outgoing light disposed on the substrates (G1, G2) on the side opposite to the liquid crystal layer (LQ). Polarizing parts PL1 and PL2 and polarizing part P
And a backlight 1 disposed behind the L1. The substrates G1 and G2 include a plurality of transparent electrodes forming a matrix array of a plurality of display pixels together with the liquid crystal layer LQ, and first and second alignment films covering the transparent electrodes and contacting the liquid crystal layer LQ. In particular, the polarizing section PL1 includes a circular polarizer 2 that circularly polarizes light incident on the liquid crystal panel 3 from the backlight 1, and the polarizing section PL2 converts a light emitted from the liquid crystal panel 3 into linearly polarized light. 4, and quarter-wave plate 4
And a linear polarizer 5 that linearly polarizes the output light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device for displaying an image by selectively transmitting light from a backlight.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have become lighter and thinner.
Because of its characteristic of low power consumption, it is widely used as a monitor display for notebook personal computers, portable information devices, small TVs, and the like. Particularly, an active matrix type liquid crystal display device in which a thin film transistor is added as a switching element of a pixel is rapidly developing. Although the screen size of the liquid crystal display device is relatively small and is about 20 inches diagonally at the maximum, a large screen up to about 100 inches diagonal is obtained by using a projection display device that projects an image using the liquid crystal display device as a light source. be able to. For this reason, projection type display devices are also becoming increasingly popular.

A typical liquid crystal display (LCD) has a liquid crystal panel in which a liquid crystal layer is sandwiched between two glass substrates. On these substrates, a plurality of transparent electrodes are formed facing each other so as to form a matrix array of display pixels together with a liquid crystal layer. The liquid crystal layer is obtained by injecting and sealing a liquid crystal composition into a cell in which the gap between these glass substrates is surrounded by a sealing material, and has a light transmittance corresponding to a pixel voltage applied between transparent electrodes of each display pixel. Is set. If the liquid crystal panel is for color display, a colored layer of three primary colors (RGB) is formed as a color filter on one of these glass substrates. As a display method of the liquid crystal layer, for example, a twist nematic (TN) type, a super twist (ST) type, a guest host (GH) type, a birefringence control (ECB) type, a ferroelectric (FLC) type, or the like is used. .

[0004] Such a liquid crystal display device generally has a disadvantage that the viewing angle is narrow. As a measure for widening the viewing angle, for example, in-plane switching (1P
S), addition of an optical compensator, division of a region in an orientation direction, amorphous orientation, or a combination thereof are known. In the region division in the orientation direction, the liquid crystal molecules are oriented in different directions for each divided region of the display pixel. It is desirable that the alignment direction of the liquid crystal molecules coincides with the optical axes of the polarizing parts attached to these glass substrates on the side opposite to the liquid crystal layer. When the alignment direction of the liquid crystal molecules is shifted from this optical axis, the maximum light transmittance is reduced.

[0005]

However, when the number of divided regions in the alignment direction is large or when the alignment direction is not constant in each divided region, the alignment direction of the liquid crystal molecules cannot be made coincident with the optical axis of the polarizing section. In addition, amorphous orientation and A
Also in the case of the SM mode, it cannot be essentially made to coincide with the optical axis of the polarizing section.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a liquid crystal display device which can prevent a decrease in maximum light transmittance which occurs when the alignment direction of liquid crystal molecules does not coincide with the optical axis of a polarizing section. To provide.

[0007]

According to a first aspect of the present invention, a liquid crystal display panel in which a liquid crystal layer is sandwiched between first and second transparent insulating substrates, and a first liquid crystal layer on a side opposite to the liquid crystal layer. And a polarizing part for incidence and a light emitting part respectively arranged on the second transparent insulating substrate, and a backlight arranged behind the polarizing part for incident light, wherein the first and second transparent insulating substrates have a plurality of display pixels. A plurality of transparent electrodes facing each other via the liquid crystal layer so as to form a matrix array with the liquid crystal layer,
And a first and a second alignment film that respectively cover the plurality of transparent electrodes and are in contact with the liquid crystal layer. The incident polarization unit includes a circular polarizer that circularly polarizes light incident on the liquid crystal panel from the backlight. A polarizing plate for converting a light emitted from the liquid crystal panel into linearly polarized light;
There is provided a liquid crystal display device including a linear polarizer that linearly polarizes output light of a / 4 wavelength plate. According to a second aspect of the present invention, the liquid crystal display device according to the first aspect, further comprising a plurality of switching elements connected to the transparent electrodes of the plurality of display pixels on one of the first and second transparent insulating substrates. Is provided. According to a third aspect of the present invention, the circular polarizer includes a linear polarizer that linearly polarizes incident light and a quarter-wave plate that converts output light of the linear polarizer into variable polarization. Is provided.

According to a fourth aspect of the present invention, there is provided the liquid crystal according to the third aspect, wherein the optical axis of the quarter-wave plate of the incident-side polarization section is orthogonal to the optical axis of the quarter-wave plate of the emission-side polarization section. Display device.

According to a fifth aspect of the present invention, there is provided the liquid crystal display device according to the fourth aspect, wherein the liquid crystal layer includes liquid crystal molecules which are vertically aligned in the absence of a voltage.

In these liquid crystal display devices, the circular polarizer polarizes light incident on the liquid crystal layer from the backlight via the first transparent insulating substrate. For this reason, even when the liquid crystal molecules have various azimuths in the liquid crystal layer, the circularly polarized light similarly propagates in the liquid crystal layer. Light transmitted through the liquid crystal layer is converted from circularly polarized light into linearly polarized light by a quarter wavelength plate. Therefore, the linear polarizer can polarize the light transmitted through the liquid crystal layer in the same state as when linearly polarized light is incident on the liquid crystal layer. Here, since the circularly polarized light passes through the liquid crystal layer without being affected by the shift of the orientation direction of the liquid crystal molecules with respect to the optical axes of the first and second polarizing portions, a decrease in the maximum light transmittance can be prevented. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid crystal display according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows the component arrangement of the liquid crystal display device. This liquid crystal display device includes a backlight 1, a circular polarizer 2, a liquid crystal panel 3, a quarter-wave plate 4, and a linear polarizer 5 as components. The liquid crystal panel 3 includes two transparent insulating substrates G1 and G2 made of a glass plate or the like, and a liquid crystal layer LQ sandwiched between the transparent insulating substrates G1 and G2. The transparent insulating substrates G1 and G2 include a plurality of transparent electrodes facing each other via the liquid crystal layer LQ so as to form a matrix array of a plurality of display pixels together with the liquid crystal layer LQ, and cover the plurality of transparent electrodes with the liquid crystal layer LQ. First and second alignment films in contact with each other are included. The liquid crystal layer LQ is obtained by injecting and sealing a liquid crystal composition into a cell in which the gap between the transparent insulating substrates G1 and G2 is surrounded by a sealing material, and according to the pixel voltage applied between the transparent electrodes of each display pixel. Light transmittance is set. The backlight 1 is arranged behind the circular polarizer 2 in the incident polarizer. The circular polarizer 2 is an incident polarizer PL1 disposed on the transparent insulating substrate G1 on the side opposite to the liquid crystal layer LQ, and the quarter-wave plate 4 and the linear polarizer 5 are opposite to the liquid crystal layer LQ. The output polarizing part PL2 disposed on the transparent insulating substrate G2 on the side. 1/4
The optical axis of the wave plate 4 and the optical axis of the polarizer 5 are set to form an angle of 45 degrees. The circular polarizer 2 circularly polarizes light incident on the liquid crystal panel 3 from the backlight 1, the quarter-wave plate 4 converts light emitted from the liquid crystal panel 3 into linearly polarized light,
The linear polarizer 5 linearly polarizes the output light of the quarter-wave plate 4. Here, the liquid crystal panel 3 is used as an optical shutter for modulating light from the backlight 1. If the liquid crystal panel 3 is for color display, a color layer of three primary colors (RGB) is further formed as a color filter on one of the transparent insulating substrates G1 and G2. When the driving method of the liquid crystal panel 3 is a simple matrix type, for example, a plurality of Y electrodes are formed on the transparent insulating substrate G1 as band-shaped transparent electrodes along a row of display pixels, and a plurality of X electrodes are formed.
The electrode is formed on the transparent insulating substrate G2 as a strip-shaped transparent electrode along the column of the display pixels. The RGB color layers are arranged below these X electrodes. When the driving method of the liquid crystal panel 3 is an active matrix type, for example, a plurality of pixel electrodes are formed on the transparent insulating substrate G1 as transparent electrodes arranged in a matrix corresponding to a plurality of display pixels. A counter electrode is formed on the transparent insulating substrate G2 as a transparent electrode facing the plurality of pixel electrodes, a plurality of scanning lines are formed on the transparent insulating substrate G1 along rows of the plurality of pixel electrodes, and a plurality of signal lines are formed on the transparent insulating substrate G1. A plurality of thin film transistors are formed on the transparent insulating substrate G1 along the columns of the pixel electrodes, and a plurality of thin film transistors are formed as switching elements in the transparent insulating substrate G1 near intersections of these scanning lines and signal lines. Each thin film transistor is formed using a semiconductor thin film of, for example, amorphous silicon (a-Si), and is driven via a corresponding scanning line and connected so as to apply a potential of a corresponding signal line to a corresponding pixel electrode. RG
The B colored layer is formed on the transparent insulating substrate G2 side. The transparent insulating substrates G1 and G2 are further electrically connected to each other via an electrode transfer material (transfer) such as a silver paste disposed at the periphery of the screen in order to supply a voltage from one to the other. In the liquid crystal display device shown in FIG. 1, light emitted from a backlight 1 passes through a circular polarizer 2 to become a circularly polarized light and is incident on a liquid crystal panel 3, from which a quarter-wave plate 4 and a polarizer are formed. Come out through 5. As the display mode of the liquid crystal layer LQ, TN, π cell, HAN (Hybrid Aligned Nematic), homogeneous or ASM can be used. Here, it is assumed that the TN mode is amorphous alignment. Since the incident light of the liquid crystal layer LQ is circularly polarized light, the incident light propagates in the liquid crystal layer LQ similarly in any direction with respect to liquid crystal molecules having various azimuth angles depending on locations. When the light transmitted through the liquid crystal layer LQ passes through the 波長 wavelength plate 4, the same polarization state as when linearly polarized light enters the normal TN arrangement is obtained, and the light passes through the linear polarizer 5. . In such a liquid crystal display device, a loss in transmittance is smaller than when light from the backlight 1 enters the liquid crystal layer LQ without being circularly polarized, and a good display image can be obtained. In addition, an effect of reducing the Fresnel reflection at each interface of the liquid crystal layer LQ due to ambient light incident from the exit polarizing part PL2 side is obtained, and the image quality is improved. FIG. 2 shows a component arrangement of a liquid crystal display device according to a second embodiment of the present invention. In FIG. 2, the same parts as those in the first embodiment are denoted by the same reference numerals, and differences will be described in detail. In this embodiment, a vertical alignment ECB mode is used as the display mode of the liquid crystal layer LQ by alignment division.
The incident-side polarizing section PL1 includes a linear polarizer 6 and a quarter-wave plate 7 arranged between the backlight 1 and the liquid crystal panel 3. The optical axis of the quarter-wave plate 7 is shifted from the optical axis of the linear polarizer 6 by 45 degrees. The light exiting the backlight 1 passes through the linear polarizer 6 and becomes linearly polarized light. The light is further converted into circularly polarized light by the 板 wavelength plate 7 and enters the liquid crystal spring 3. The liquid crystal layer LQ is in a state where liquid crystal molecules are aligned substantially perpendicular to the substrates G1 and G2 when no voltage is applied, and does not have optical anisotropy when the liquid crystal layer LQ is viewed from the front. Therefore, when no voltage is applied, the circularly polarized light incident on the liquid crystal layer remains in the same polarization state as the liquid crystal layer L.
The light passes through Q and enters the quarter-wave plate 4. The circularly polarized light passes through the 波長 wavelength plate 4 to become linearly polarized light at an angle of 45 ° with respect to the optical axis of the 波長 wavelength plate 4, and
Incident on. The optical axis of the quarter-wave plate 7 is parallel to the optical axis of the quarter-wave plate 4, and the optical axis of the linear polarizer 5 is at an angle of 45 degrees with respect to the optical axis of the quarter-wave plate 4. Make
In this case, when the oscillation direction of the linearly polarized light emitted from the quarter-wave plate 4 and the absorption axis of the linear polarizer 5 are matched, a normally black display is obtained. When the oscillation direction of the linearly polarized light coming out of the quarter-wave plate 4 and the transmission axis of the linear polarizer 5 are matched, a normally white display is obtained. Next, when a voltage is applied to the liquid crystal layer LQ, the liquid crystal molecules fall in several directions, but the light incident as circularly polarized light does not depend on the azimuth of the liquid crystal molecules, and in any direction. The polarization state of the molecule changes to elliptically polarized light having the same ellipticity. In such a liquid crystal display device, a loss in transmittance is smaller than in a case where only a normal linear polarizer is used, and a good display image can be obtained. FIG. 3 shows a component arrangement of a liquid crystal display device according to a third embodiment of the present invention. In FIG. 3, parts similar to those of the second embodiment are denoted by the same reference numerals, and differences will be described in detail. The emission-side polarization section PL2 has a negative optical compensator 8 disposed between the liquid crystal panel 3 and the quarter-wave plate 4 in order to improve viewing angle characteristics. It is preferable that the retardation of the negative optical compensator 8 be substantially equal to the retardation of the liquid crystal layer LQ. In such a liquid crystal display device, the effect that the loss of transmittance is small as compared with the case where only a normal linear polarizer is used is maintained, and the viewing angle characteristics can be further improved. FIG. 4 shows a component arrangement of a liquid crystal display device according to a fourth embodiment of the present invention. In FIG. 4, the same parts as those in the second embodiment are denoted by the same reference numerals, and differences will be described in detail. In this embodiment, the entrance-side polarization section PL1 and the exit-side polarization section PL2 include quarter-wave plates 7 'and 4' having optical axes orthogonal to each other. In such a liquid crystal display device, when the two quarter-wave plates 7 'and 4' are viewed together, a negative optical anisotropy is obtained. As a result, the viewing angle characteristics can be improved on the same principle as in the third embodiment without the necessity of the negative optical compensator as shown in FIG. In this case, the relationship between the optical axis of the linear polarizer 6 and the optical axis of the linear polarizer 5 is normally black when the relationship is cross Nicol, and normally white when the relationship is parallel nicol.

FIG. 5 shows the structure of a three-panel projection system according to a fifth embodiment of the present invention. This projection system includes a liquid crystal display device for red, green and blue having a structure substantially as shown in FIG. However,
The backlight 1 and the linear polarizer 6 are commonly used in these liquid crystal display devices, and the red, green, and blue incident mirrors 10 (R), 10 (G), 10 (B) and red,
Exit mirrors 11 (R), 11 for green and blue
(G) and 11 (B) are added. Light emitted from the backlight 1 serving as a light source passes through the straight-line changing plate 6 and enters the incident mirror 10.
(R), 10 (G) and 10 (B) are reflected. The reflected light from the incident mirror 10 (R) passes through the quarter-wave plate 7 (R), the liquid crystal panel 3 (R), the quarter-wave plate 4 (R), and the linear polarizer 5 (R) and exits. The light is reflected by the mirror 11 (R). The reflected light of the incident mirror 10 (G) is a 波長 wavelength plate 7
(G), liquid crystal panel 3 (G), quarter-wave plate 4 (G),
And the output mirror 11 passing through the linear polarizer 5 (G).
(G) is reflected. The reflected light from the incident mirror 10 (B) is reflected by the incident mirror 10 (B) and
(B), liquid crystal panel 3 (B), quarter-wave plate 4 (B),
And the exit mirror 11 passing through the linear polarizer 5 (B).
It is reflected at (B). The reflected light from the output mirror 11 (R) is projected onto an external screen via the output mirrors 11 (G) and 11 (B), and the reflected light from the output mirror 11 (G) is externally output via the output mirror 11 (B). The light is projected on the screen, and the reflected light from the emission mirror 11 (B) is directly projected on the external screen. In the projection system having such a configuration, in addition to the transmittance improving effect of the liquid crystal display device shown in FIG. 2, the incidence mirrors 10 (R), 10 (G),
(B) and output mirrors 11 (R), 11 (G), 11
The linear polarizers 6 and 5 (R), 5 are set in the polarization direction in which the reflection efficiency of the linearly polarized light when the light is reflected in (B) is the best.
Since the transmission axes of (G) and 5 (B) can be matched, the light use efficiency can be further improved.

[0013]

As described above, according to the present invention, the circular polarizer polarizes the light incident on the liquid crystal layer from the backlight via the first transparent insulating substrate. For this reason, even when the liquid crystal molecules have various azimuths in the liquid crystal layer, the circularly polarized light similarly propagates in the liquid crystal layer. Light transmitted through the liquid crystal layer is converted from circularly polarized light into linearly polarized light by a quarter wavelength plate. Therefore, the linear polarizer can polarize the light transmitted through the liquid crystal layer in the same state as when linearly polarized light is incident on the liquid crystal layer. here,
Since the circularly polarized light passes through the liquid crystal layer without being affected by the shift in the orientation direction of the liquid crystal molecules with respect to the optical axes of the first and second polarizing portions, it is possible to prevent a decrease in the maximum light transmittance.
Therefore, it is possible to provide a liquid crystal display device that can prevent a decrease in the maximum light transmittance that occurs when the orientation direction of the liquid crystal molecules does not coincide with the optical axis of the polarizing section.

[Brief description of the drawings]

FIG. 1 is a diagram showing a component arrangement of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a component arrangement of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a component arrangement of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a component arrangement of a liquid crystal display device according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a structure of a three-panel projection system according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Back light 2 ... Circular polarizer 3 ... Liquid crystal panel 4 ... 1/4 wavelength plate 5 ... Linear polarizer 6 ... Linear polarizer 7 ... 1/4 wavelength plate 8 ... Negative optical compensator PL1 ... Polarization part for incidence PL2: emission changing portion G1, G2: transparent insulating substrate LQ: liquid crystal layer

Claims (5)

[Claims] 1. A liquid crystal display panel having a liquid crystal layer sandwiched between first and second transparent insulating substrates, and disposed on the first and second transparent insulating substrates on opposite sides of the liquid crystal layer, respectively. An input / output polarization section; and a backlight disposed behind the input polarization section. The first and second transparent insulating substrates form a matrix array of a plurality of display pixels together with the liquid crystal layer. A plurality of transparent electrodes facing each other with the liquid crystal layer interposed therebetween, and a first electrode which covers the plurality of transparent electrodes and contacts the liquid crystal layer.
And the second alignment film, wherein the incident polarizer includes a circular polarizer that circularly polarizes light incident on the liquid crystal panel from the backlight, and the output polarizer linearly converts light emitted from the liquid crystal panel. A liquid crystal display device, comprising: a quarter-wave plate for converting to polarized light; and a linear polarizer for linearly polarizing output light of the quarter-wave plate. 2. The liquid crystal display according to claim 1, further comprising a plurality of switching elements respectively connected to the transparent electrodes of the plurality of display pixels on one of the first and second transparent insulating substrates. apparatus. 3. The method according to claim 1, wherein the circular polarizer comprises a linear polarizer for linearly polarizing incident light and a quarter-wave plate for converting output light of the linear polarizer to circularly polarized light. The liquid crystal display device as described in the above. 4. The liquid crystal display according to claim 3, wherein the optical axis of the quarter-wave plate of the incident-side polarization section is orthogonal to the optical axis of the quarter-wave plate of the emission-side polarization section. apparatus. 5. The liquid crystal display device according to claim 4, wherein the liquid crystal layer includes liquid crystal molecules that are vertically aligned without applying a voltage.