JPH05232439A - Phase difference plate type liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the white display of the STN type liquid crystal display device of a phase difference plate system. CONSTITUTION:A phase compensating member 10 consisting of a 1st phase difference plate 2, a 2nd phase difference plate 3, a 1st polarizing plate 5, a 3rd phase difference plate 4 and a 3rd polarizing plate 6 is provided on the upper side of the STN type liquid crystal display element 1. The light absorption axis 9 of the 3rd phase difference plate 4 is installed in a + or -10 deg. range with respect to the light absorption axis of the 1st polarizing plate 5. As a result, the liquid crystal display device with which the coloration of transmitted light is completely removed and which enables the ideal white display is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using a super twisted nematic (STN) liquid crystal, and in particular, a retardation plate capable of excellent black and white display, that is, paper white display regardless of the viewing angle. System liquid crystal display device.

[0002]

2. Description of the Related Art A conventional liquid crystal device of this type performs a black and white display by a structure in which a polarizing plate and a retardation plate are superposed on a liquid crystal element and an illumination light source (backlight light source) including a cold cathode tube is arranged. ing. That is, the conventional liquid crystal device is
A liquid crystal display device having a twisted spiral structure made of nematic liquid crystal having positive dielectric anisotropy is formed between two electrode plates, and a light absorption axis is orthogonal to liquid crystal molecules adjacent to the electrode plates. Polarizing plates are arranged above and below both electrode plates so as to be parallel to each other, and two retardation plates are arranged between the upper polarizing plate and the liquid crystal display element (for example, Japanese Patent Publication No.
-13666 publication). Then, cold cathode fluorescent lamps and the like are arranged on the upper and lower sides or the left and right sides of the back side of the liquid crystal display element to serve as a backlight light source for black and white display.

[0003]

In the conventional retardation plate type liquid crystal display device, as described above, two retardation plates are provided between the liquid crystal display element and the upper polarizing plate to reduce coloring of display light. However, there is a problem that the coloring of the display light cannot be completely removed.

An object of the present invention is to provide a transmissive liquid crystal display device capable of eliminating the above-mentioned problems of the prior art and removing display light to perform complete black and white display (white display: paper white display). To do.

[0005]

In order to achieve the above object, the present invention provides a super twist nematic liquid crystal layer having a positive dielectric anisotropy to which an optically active substance is added, and a twisted liquid crystal layer. A liquid crystal display element 1 comprising a pair of electrode plates sandwiching the liquid crystal layer, the liquid crystal display element having an alignment film imparting a spiral structure.
A first retardation plate 2, a second retardation plate 3, a first polarizing plate 5 constituting an upper polarizing plate on the upper surface side of the liquid crystal display element, and a first retardation plate provided on the lower surface side of the liquid crystal display element. In a retardation plate type liquid crystal display device having two polarizing plates 7, a phase compensating member composed of a third retardation plate 4 and a third polarizing plate 6 is provided on the first polarizing plate 5. The third retardation film 4 is installed so as to be in contact with the third retardation film 4.

In the present invention, the absorption axis angle of the third polarizing plate 6 is ± 10 with respect to the absorption axis angle of the first polarizing plate 5.
It is characterized in that it is set within the range of degrees. Furthermore, the present invention includes an alignment film that imparts a twisted spiral structure of approximately 240 ° to a reference line to a super twist nematic liquid crystal layer having a positive dielectric anisotropy and added with an optical rotatory substance. A liquid crystal display device 1 comprising a pair of electrode plates sandwiching the liquid crystal layer, and a first liquid crystal display device provided on the upper surface side of the liquid crystal display device.
A retardation plate 2, a second retardation plate 3, a first polarizing plate 5, a third retardation plate 4, a third polarizing plate 6, and a second polarizing plate 7 installed on the lower surface side of the liquid crystal element. The light absorption axes of the first retardation plate, the second retardation plate, the first polarizing plate, the second polarizing plate, the third retardation plate, and the third polarizing plate are approximately the same with respect to the reference line. 68 °, 36.5 °, 87 °, 165 °, 4
The feature is that it is set to 5 ° and 90 °.

The refractive index anisotropy Δn · d of the first retardation plate 2, the second retardation plate 3 and the third retardation plate 4 is 35.
It is characterized in that it is set to 0 nm.

[0008]

The unidirectionally polarized illumination light entering the liquid crystal display element 1 from the second polarizing plate 7, which is the lower polarizing plate, has different polarization axes depending on the light wavelength when passing through the liquid crystal display element 1. Will be transmitted light. This transmitted light passes through the first retardation plate 2, the second retardation plate 3 and the first polarizing plate 5 and is corrected so that the polarization axis corresponding to the light wavelength has a polarization axis in substantially one direction. However, the display light at this time is still accompanied by a slight difference in the polarization axes.

In the present invention, the display light transmitted through the first polarizing plate 5 is passed through the phase compensating member 11 including the third retardation plate 4 and the third polarizing plate 6, so that the polarization axes are perfectly aligned. Display light is obtained.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1A and 1B are (a) a schematic sectional view and (b) a schematic front view illustrating an embodiment of a retardation plate type liquid crystal display device according to the present invention, in which 1 is a liquid crystal display element and 2 is a first retardation plate. 3 is a second retardation plate, 4 is a third retardation plate, 5 is a first polarizing plate, 6 is a third polarizing plate, 7 is a second polarizing plate, 8 is a light absorption axis of the first polarizing plate, 9 Is a light absorption axis of the third polarizing plate, and 10 is a phase compensation member.

As shown in FIG. 1A, the first retardation plate 2 is superposed on the upper surface side (front surface) of the liquid crystal display element 1, and the second retardation plate 3 and the first polarizing plate 5 are placed on the first retardation plate 2. The phase compensating member 10 including the third retardation plate 4 and the third polarizing plate 6 is laminated. The second polarizing plate 7 is installed on the lower surface side of the liquid crystal display element 1, and a backlight light source (not shown) is installed below the second polarizing plate 7 if necessary.

The light absorption axis 8 of the first polarizing plate 5 constituting the phase compensating member 11 has a reference line X as shown in (b).
The light absorption axis 9 of the third polarizing plate 6 constituting the phase compensation 10 is substantially 90 ° with respect to the −X-ray (parallel to the YY line), and the light absorption axis 8 of the first polarizing plate 5 is the same. On the other hand, it is set within a range of ± 10 °. FIG. 2 is an explanatory view of a twist angle of a liquid crystal display element used in an STN liquid crystal display device according to the present invention, in which the rubbing direction of a rubbing film that gives a twist angle to a nematic liquid crystal layer of the liquid crystal display element 1 is set to the upper side. 1a for the rubbing axis and 1 for the lower rubbing film
By forming it in the direction of b, a twist angle of 240 ° is given counterclockwise in the thickness direction of the liquid crystal layer. This twist angle is set to be line-symmetric with respect to the reference line XX.

FIG. 3 is an explanatory view of the angles of the light absorption axes of the respective polarizing plates and the retardation plate which are set for the liquid crystal element having the twist angle set as described above, as shown in FIG. Is counterclockwise with respect to the reference line XX line, a is the light absorption axis angle of the third polarizing plate 6, b is the light absorption axis angle of the third retardation plate 4, and c is the light of the second retardation plate 3. Absorption axis angle, d is the light absorption axis angle of the first retardation plate 2, e is the light absorption axis angle of the first polarizing plate 5, and f is the light absorption axis angle of the second retardation plate 3.

As a concrete numerical example of the angle of the light absorption axis of each polarizing plate and the retardation plate, as shown in (b),
= 90 °, b = 45 °, c = 36.5 °, d = 68 °,
e = 87 ° and f = 165 ° are adopted. The refractive index anisotropy Δn · d of the first retardation plate 2, the second retardation plate 3, and the third retardation plate 4 is 350 nm.

FIG. 4A is a schematic view of a light transmitting action in one embodiment of the retardation plate type liquid crystal display device according to the present invention,
(B) is an explanatory view showing the polarization state at each point of (a), the same reference numerals as in FIG. 1 correspond to the same parts, and 11 is the incident light to the liquid crystal display device. In the figure, incident light 1
The first polarizing plate 7 receives polarized light in the direction a in FIG. 3 and enters the liquid crystal display element 1. As for the polarization state of the light at this time, each color component RGB is polarized in the same direction as shown in A of (b).

The light incident on the liquid crystal display element 1 has a large difference in the polarization axes of the respective color components RGB as shown in B of (b) due to the difference in the twisting action with respect to the refractive index anisotropy which varies depending on the wavelength. Is emitted. The light emitted from the liquid crystal display element 1 has its polarization axis regulated by the first polarizing plate 2.
It becomes as shown in C of (b). Then, the light emitted from the first retardation plate 2 passes through the second retardation plate 3 and the first polarizing plate 5, and each color component RGB has substantially the same polarization axis as shown in D of (b). However, it still involves some polarization axis differences.

The light emitted from the first polarizing plate 5 passes through the phase compensating member 10 composed of the third retardation plate 4 and the third polarizing plate 6 to produce the polarized light of each color component as shown in E of (b). It is emitted to the observation side as light whose axes are completely matched. As a result, the coloring of the display light is completely removed. FIG. 5 is an explanatory diagram of the relationship between the absorption axis angle of the third polarizing plate with respect to the first polarizing plate and the display contrast in the retardation plate type liquid crystal display device according to the present invention, and as shown in FIG. First polarizing plate 5 having a light absorption axis of 90 ° with respect to the line XX
When the light absorption axis of the third polarizing plate 7 is at the same angle (that is, 90 ° with respect to the reference line XX) with respect to the light absorption axis 8 of No. Drops sharply.

If the angle of deviation exceeds ± 10 °, the practical limit of 10K (K is the contrast ratio) or less is obtained. FIG. 6 is an explanatory diagram of the relationship between the absorption axis angle of the third polarizing plate with respect to the first polarizing plate and the chromaticity of white display in the retardation plate type liquid crystal display device according to the present invention.
As described in FIG. 1, with respect to the light absorption axis 8 of the first polarizing plate 5 whose light absorption axis is 90 ° with respect to the reference line XX,
When the light absorption axis of the third polarizing plate 7 is at the same angle (that is, 90 ° with respect to the reference line XX), the x value and the y value in the CIE chromaticity are approximately 0.315, which are in agreement. The x value and the y value increase as they deviate from the same angle.

From the above facts, the range of deviation of the light absorption axes of the first polarizing plate 5 and the third polarizing plate 7 is preferably within ± 10 °. FIG. 7 is an exploded perspective view for explaining an example of a mounting structure of the retardation plate type liquid crystal display device according to the present invention, which is characterized by a structure in which a driving circuit and a backlight light source are integrated.
An IC 21 that drives the liquid crystal display device 20 is mounted on a frame-shaped printed circuit board 22 having a window for fitting the liquid crystal display device 20 in the center.

The printed circuit board 22 in which the liquid crystal display device 20 is fitted is a frame-like body 23 formed by plastic molding.
Of the metal frame 24, and the claw 25 of the metal frame 24 is overlapped with the window 2
The frame 24 and the frame-shaped body 2 by being bent into 6
3 is fixed. Then, the cold cathode fluorescent lamps 2 which are the light sources of the backlights arranged at the upper and lower ends of the liquid crystal display element 20.
7, 27 ', a light guide 28 made of an acrylic plate or the like for uniformly irradiating the liquid crystal display device 20 with light from the cold cathode fluorescent lamps 27, 27', white metal coating on a metal plate, etc. The reflected plate 29 and the milky white diffuser plate 30 that diffuses the light from the light guide plate 28 are fitted into the window portion from the back side of the frame body 23 in the order shown.

A power supply circuit (not shown) for lighting the cold cathode fluorescent lamps 27, 27 'is provided on the back side of the frame-like body 23 (reflecting plate 29).
It is stored in a recess (not shown) provided at a position facing the recess 31). The diffuser plate 30, the light guide 28, the cold cathode fluorescent lamps 27 and 27 ', and the reflector plate 29 are fixed by bending a tongue piece 32 provided on the reflector plate 29 into the fore edge 33 of the frame-shaped body 23. ..

In this way, a liquid crystal display device which is thin, lightweight, and capable of displaying white completely without coloring the display due to a change in viewing angle is constructed. FIG. 8 is a partially broken perspective view illustrating a configuration example around a liquid crystal display element when the retardation plate type liquid crystal display device according to the present invention is used as a color liquid crystal display device. Color filters 45R, 45G, 45B and a light shielding film 45D between the color filters 45R, 45G, 45B.
A smoothing layer 43 made of an insulating material is provided to reduce irregularities on the surface due to the provision of 45B and the light shielding film 45D. Then, the upper alignment film 22 is formed on the smooth layer 43 to give a light absorption axis (optically anisotropic axis) to the liquid crystal layer.

The structure of the polarizing plate and the retardation plate of the liquid crystal display device using the liquid crystal display element shown in FIG. 8 is the same as that shown in FIG. 1, and the mounting structure thereof is a drive circuit including a drive IC. Other than that, it is the same as that shown in FIG. Figure 9
FIG. 3 is an external view showing an example of an electronic apparatus using the retardation plate type liquid crystal display device according to the present invention, showing a so-called laptop personal computer.

In the figure, 50 is a liquid crystal display device according to the present invention, 51 is a mounting part, 52, 53 and 54 are brightness, contrast and other display state adjusting parts, 55 is a main body part, 5
Reference numeral 6 is an operation unit. 10 is a block diagram showing the system configuration of the laptop personal computer shown in FIG. 9, and the liquid crystal display device 20 constituting the liquid crystal display unit 60 is driven by the drive IC 21. The drive IC 21 is a control LS managed by the microprocessor unit 61.
Under the control of I62, the liquid crystal display device 20 displays characters, figures, and other data stored in the ROM and RAM or input from the operation unit such as a keyboard.

According to the embodiments and concrete examples described above, a large capacity information display performance is achieved which can achieve a wide viewing angle, a high contrast and bright complete white display (paper white display) regardless of the viewing angle. A liquid crystal display device can be realized. Further, by combination with a color filter, a color liquid crystal display device having high definition and good color purity can be provided.

[0026]

As described above, according to the present invention,
Illumination light that is incident on the liquid crystal display element from the second polarizing plate, which is the lower polarizing plate, and is polarized in a single direction becomes transmitted light having different polarization axes depending on the light wavelength when passing through the liquid crystal display element. However, this transmitted light is corrected by passing through the first retardation plate, the second retardation plate and the first polarizing plate 5 so that the polarization axis corresponding to the light wavelength has a polarization axis in substantially one direction. At the same time, the coloring due to the slight difference in the polarization axes still contained in the display light at this time is passed through the phase compensating member including the third retardation plate and the third polarizing plate, whereby the display light with the polarization axes perfectly aligned. Is obtained on the observation side.

As a result, the problems in the prior art described above can be solved and a retardation plate type liquid crystal display device having an excellent function can be provided.

[Brief description of drawings]

1A and 1B are schematic cross-sectional views and schematic front views illustrating an embodiment of a retardation plate type liquid crystal display device according to the present invention.

FIG. 2 is an explanatory diagram of a twist angle of a liquid crystal display element used in an STN liquid crystal display device according to the present invention.

FIG. 3 is an explanatory diagram of an angle of a light absorption axis of each polarizing plate and a retardation plate which is set for a liquid crystal element in which a twist angle is set.

FIG. 4A is a schematic diagram of a light transmitting action in an embodiment of the retardation plate type liquid crystal display device according to the present invention, and FIG. 4B is an explanatory diagram showing a polarization state at each point in FIG. 4A.

FIG. 5 is an explanatory diagram of a relationship between an absorption axis angle of a third polarizing plate with respect to a first polarizing plate and display contrast in a retardation plate type liquid crystal display device according to the present invention.

FIG. 6 is an explanatory diagram of a relationship between an absorption axis angle of a third polarizing plate with respect to a first polarizing plate and a chromaticity of white display in the retardation plate type liquid crystal display device according to the present invention.

FIG. 7 is an exploded perspective view illustrating an example of a mounting structure of a retardation plate type liquid crystal display device according to the present invention.

FIG. 8 is a partially broken perspective view illustrating a configuration example around a liquid crystal display element when the retardation plate type liquid crystal display device according to the present invention is used as a color liquid crystal display device.

FIG. 9 is an external view showing an example of an electronic apparatus using the retardation plate type liquid crystal display device according to the present invention.

10 is a block diagram showing a system configuration of the laptop personal computer shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display element 2 1st retardation plate 3 2nd retardation plate 4 3rd retardation plate 5 1st polarizing plate 6 3rd polarizing plate 7 2nd polarizing plate 8 Light absorption axis of 1st polarizing plate 9 3rd polarization Light absorption axis of plate 10 Phase compensation member

Claims (4)

[Claims] 1. A liquid crystal layer is sandwiched by a super twist nematic liquid crystal layer having a positive dielectric anisotropy and added with an optical rotatory substance, and an alignment film for imparting a twisted spiral structure to the liquid crystal layer. Liquid crystal display element composed of a pair of electrode plates, first phase plate, second phase plate provided on upper surface side of the liquid crystal display element, first polarizing plate constituting upper polarizing plate, and lower surface of the liquid crystal display element In a retardation plate type liquid crystal display device having a second polarizing plate provided on a side thereof, a phase compensating member including a third retardation film and a third polarizing plate is provided on the first polarizing plate. A retardation plate type liquid crystal display device, wherein the third retardation plate is installed so as to be in contact with the third retardation plate. 2. The absorption axis angle of the third polarizing plate constituting the phase compensating member according to claim 1, set within a range of ± 10 degrees with respect to the absorption axis angle of the first polarizing plate. And a retardation plate type liquid crystal display device. 3. An alignment film for imparting a twisted spiral structure of about 240 ° with respect to a reference line to a super twist nematic liquid crystal layer having a positive dielectric anisotropy and added with an optical rotatory substance, A liquid crystal element including a pair of electrode plates sandwiching a liquid crystal layer, and a first liquid crystal display element disposed on the upper surface side of the liquid crystal display element.
A retardation plate, a second retardation plate, a first polarizing plate, a phase compensating member including a third retardation plate and a third polarizing plate, and a second polarizing plate installed on the lower surface side of the liquid crystal element. And the light absorption axes of the first retardation plate, the second retardation plate, the first polarizing plate, the second polarizing plate, the third retardation plate, and the third polarizing plate are approximately the same with respect to the reference line. 68 °, 36.5 °, 87
A retardation plate type liquid crystal display device characterized by being set to °, 165 °, 45 ° and 90 °. 4. The first retardation plate according to claim 3,
Refractive index anisotropy Δn · d of the second retardation plate and the third retardation plate
Is 350 nm, a retardation plate type liquid crystal display device.