JPH05281538A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce reflection light on the surface and the back face of a protective plate and the surface of a liquid crystal panel and the like without decreasing the display light of the liquid crystal panel. CONSTITUTION:A 1/4 phase plate 4 is provided on the surface of a liquid crystal panel 7 having a linear polarizing plate 5 on a display light side, and a linear polarizing plate 2 and a 1/4 phase plate 3 are provided on the back face of a transparent protective plate 1 for protecting the surface of the liquid crystal panel 7. Thereby unnecessary reflected light, generated by the reflection of extraneous light on the linear polarizing plate 5, is shut off by the linear polarizing plate 2, and the display light from the liquid crystal panel 7 passes through the linear polarizing plate 2 after the polarizing plane thereof is rotated by 1/2 phase through 1/4 phase difference plates 4, and 3.

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,
More specifically, LCD TVs, laptops,
The present invention relates to a liquid crystal display device such as a digital timepiece that reduces reflection of external light from a liquid crystal panel and a protective plate.

[0002]

2. Description of the Related Art A display device using a liquid crystal can be driven at low voltage and low power consumption, has good compatibility with an integrated circuit, can be displayed in a lightweight and thin shape, and can be freely selected in size, and can be displayed in full color. Since there are features such as display,
Recently, it has been used for displaying LCD TVs, laptop computers, digital clocks, etc. The liquid crystal uses an electro-optical effect, but as a liquid crystal display device, a field effect type, in particular, a field effect type that uses a Twisted Nematic Field Effect is widely used. ..

FIGS. 3A and 3B are diagrams for explaining the operation principle of a conventional liquid crystal display device. FIG. 3A shows the case where the voltage is off, and FIG. 3B shows the case where the voltage is ON. In the figure, 10 and 11 are linear polarizing plates (hereinafter simply referred to as polarizing plates), 12 is a liquid crystal, 13 is a liquid crystal cell, and 14 is a liquid crystal panel.

The liquid crystal panel 14 is provided with polarizing plates 10 and 11 on both end faces of a liquid crystal cell 13, and transmits incident light L from the polarizing plate 10 side according to a voltage applied to the liquid crystal 12. It is cut off and output as light and darkness to the polarizing plate 11 side. The liquid crystal cell 13, for example, encloses a nematic liquid crystal 12 having a positive dielectric anisotropy between two glass substrates (not shown) that have been subjected to a homogeneous (parallel) alignment treatment, and the long axis direction of liquid crystal molecules is 90 between two glass substrates
° Treated to twist. A transparent electrode plate (not shown) is provided inside the two glass substrates, and a voltage applied between the transparent electrode plates is turned on or off. Polarizing plates 10 and 11
Have polarization directions P and A, respectively, and P and A form orthogonal Nicols arranged at right angles to each other.

FIG. 3A shows the case where the voltage applied to the liquid crystal cell 13 is off, and the major axis of the liquid crystal molecules of the liquid crystal 12 is twisted by 90 ° in the glass substrate. The incident light L is linearly polarized by the polarizing plate 10 and rotates the plane of polarization by 90 ° according to the twist of the molecules of the liquid crystal 12. The incident light L whose polarization plane is rotated by 90 ° coincides with the polarization direction of the polarizing plate 11, and therefore is transmitted,
A bright screen can be obtained on the liquid crystal panel 14. Next, FIG.
When a voltage equal to or higher than the threshold voltage is applied to the liquid crystal cell 13 as in (b), the liquid crystal molecules are aligned in parallel with the direction of the electric field, which is the direction in which the overall energy decreases. Therefore, the polarizing plate 1
The incident light L passing through 0 maintains the plane of polarization and is orthogonal to the polarization direction of the polarizing plate 11, the light is blocked, and the liquid crystal panel 14 becomes a dark screen. As described above, the surface of the liquid crystal panel 14 is the polarizing plate 11, but in order to protect the polarizing plate 11, it is usually
As shown in FIG. 4, a transparent protective plate 1 is provided on the front surface of the polarizing plate 11.
5 is placed.

FIG. 4 is a diagram for explaining reflection of external light from the conventional liquid crystal panel 14 and the protective plate 15. The protective plate 15 is made of a transparent acrylic plate or the like and is slightly parallel to the polarizing plate 11. Are spaced apart from each other. However, since the light is reflected at the interface having different refractive index, the protective plate 1 of the external light L ₀ is applied to the image transmitted from the liquid crystal panel 14 through the protective plate 15.
5 reflected light La on the front surface, reflected light Lb on the back surface of the protective plate 15, reflected light Lc from the polarizing plate 11 on the liquid crystal panel surface, and
Reflected light Ld from the inside of the liquid crystal panel 14 is added, and reflection of these external lights makes the image display from the liquid crystal panel 14 very difficult to see.

Regarding the antireflection filter for preventing the reflection of extraneous light in order to make the displayed image easy to see, for example, "Antireflection filter for display device" in Japanese Utility Model Laid-Open No. 63-24581 and Japanese Utility Model Laid-Open No. 2-102502. The "antireflection light transmitting plate" in the publication is disclosed. Both of them use a CRT (cathode ray tube) as a display device, and the former "antireflection filter for display device" has a light control film for limiting the direction of incident light and adjusting the light amount, and a polarizing film. ,
A 1/4 wavelength plate (1/4 phase difference plate) is laminated, and this is sandwiched between a glass plate and a glass plate etched on the surface on the side of external light to diffusely reflect reflected light.
A circularly polarizing plate is composed of a polarizing film and a quarter-wave plate to block the reflected light of the external light reflected on the display surface. Furthermore, the light control film limits the incident angle of the display image so that the image is external. It is an antireflection plate that prevents it from entering the eyes of the observer through the reflector. The latter "anti-reflective light transmission plate" is a circularly polarizing plate made by bonding a polarizing film and a quarter-wave plate on the opposite side of a transparent substrate with a matte finish on one side is doing.

[0008]

As described above, in the case of a liquid crystal display device, if the protective plate 15 is simply placed in parallel with the polarizing plate 11 on the surface of the liquid crystal panel, the external light is reflected on the display of the liquid crystal panel 14. Although it is difficult to see, the antireflection plate for the CRT display device described above uses a circularly polarizing plate, which is one of the methods having a relatively high effect of reducing reflection.

FIG. 5 is a sectional view for explaining a conventional circularly polarizing plate, in which 16 is a circularly polarizing plate, 17 is a polarizing plate, and 18 is a polarizing plate.
Is a quarter wave plate. The circular polarization plate 16 is a polarization plate 17
And a quarter wave plate 18 are combined, and the circularly polarizing plate 16 is bonded or laminated so that the quarter wave plate 18 is on the display panel (not shown) surface side.

FIG. 6 is a diagram for explaining a model of a light wave after passing through each element of a circularly polarizing plate when the conventional polarizing plate 17 is used with the external light (natural light) side used. External light is shown in Figure 6.
Assuming that the three-dimensional coordinates X, Y, and Z shown in (1) advance in the X-axis direction, the polarizing plate 17 causes the vibration plane of the passing light to be 45 ° with respect to the Y-axis, a quarter phase difference. Board 16 is Y
The angle is such that the phase of the light wave in the Z-axis direction is delayed by ¼ wavelength with respect to the light wave in the axial direction.

Now, when external light passes through the polarizing plate 17,
The vibrating surface of the light wave a is inclined by 45 ° with respect to the Y axis (Fig. 6).
(2)). Further, when passing through the quarter-wave plate 16, the Z-axis direction of the light wave b oscillates in the right turn with a quarter-phase delay (FIG. 6 (3)). When such an oscillating light wave is reflected on the back surface of the 1/4 phase plate 18 or the display panel surface,
The light wave c turns left with an inverted phase (Fig. 6).
(4)). When this reflected light again passes through the 1/4 retardation plate 18, the vibration of the light wave d in the Z-axis direction is further delayed by 1/4 phase and is delayed by a total of 1/2 phase with respect to the Y-axis vibration (Fig. 6 (5)). Since the vibrating surface of the light wave d is orthogonal to the pass axis of the polarizing plate 17, it cannot pass through the polarizing plate 17. That is, the reflected light from the surface of the display panel is not absorbed by the polarizing plate 17 and does not go out, and the reflection of the external light is greatly reduced.

However, the display panel is the liquid crystal panel 1.
In the case of 4, the light emitted from the surface of the liquid crystal panel 14 is
After being linearly polarized by the polarizing plate 17 on the surface of the liquid crystal panel 14, it passes through the quarter-wave plate 16 so that the liquid crystal panel 1
Except when the polarizing plate 17 on the 4th surface is parallel to the y axis or the z axis, the light passing through the 1/4 phase difference plate 16 has a vibration in the y axis direction of 1 / The light becomes circularly polarized light or elliptically polarized light that is shifted by four wavelengths. On the other hand, the polarizing plate 1
As shown in FIG. 6 (2), in No. 7, the transmittance of light other than the light whose vibration surface is inclined by 45 ° with respect to the y-axis is usually as low as 45%. Therefore, the light emitted from the surface of the liquid crystal panel 14 is
The display light becomes very dark because it is largely attenuated by the polarizing plate 17. For example, the method of reducing the reflection by the circularly polarizing plate 16 in which the polarizing plate and the 1/4 retardation plate shown in FIG. 5 are combined one by one has a drawback that the display light is blocked by about 60%. In addition, the production process becomes complicated and expensive by etching or multi-coating the surface of the glass substrate adhered on the circularly polarizing plate as in the prior art and further adhering the light control film. There was a problem, it was easy to produce, and there was no way to reduce reflection without attenuating the display light of the liquid crystal panel.

[0013]

In order to solve the above-mentioned problems, the present invention provides a liquid crystal display device having an optically transparent protective plate which is arranged so as to face the surface of a liquid crystal panel. A linear polarizing plate and a 1/4 phase plate are sequentially provided on the surface of the plate facing the liquid crystal panel, and a 1/4 phase plate is provided on the surface of the liquid crystal panel.

[0014]

In the liquid crystal display device configured as described above, the reflection of light on the back surface of the protective plate and the liquid crystal panel surface is reduced by the circular polarizing plate on the back surface of the protective plate. .. On the other hand, the display light from the liquid crystal panel is circularly polarized by the circularly polarizing plate formed on the surface of the liquid crystal panel, and the plane of polarization of the circularly polarizing plate on the protective plate side is aligned with the axis of the polarizing plate, so it passes without attenuation. ..

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display device of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view for explaining the configuration of an embodiment of the liquid crystal display device according to the present invention.
Reference numeral 1 is a protective plate, 2 and 5 are linear polarizing plates, 3 and 4 are quarter-wave plates, 6 is a liquid crystal cell, and 7 is a liquid crystal panel.

In FIG. 1, a liquid crystal cell 6 is, for example, a twisted nematic liquid crystal cell in which twisted nematic liquid crystal is sealed between glass substrates having transparent electrodes, and light polarized by a linear polarizing plate (not shown) is used as an electrode (see FIG. It is blocked or shielded by the linear polarizing plate 5 in accordance with a voltage applied to (not shown). The linear polarizing plates 2 and 5 are plate-shaped bodies in which a polyvinylalmar film is heated and elongated to arrange chain molecules in a certain direction to uniformly adsorb iodine, and the iodine film is sandwiched between cellulosic films. As the retardation plate, a polymer resin such as polycarbonate stretched uniaxially or biaxially is used. A transparent acrylic plate or the like is used as the protective plate 1.

The above-mentioned linear polarizing plate 2 is made up of a quarter phase plate 3
Forming a circularly polarizing plate, and the linearly polarizing plate 2 is bonded to the protective plate 1. On the other hand, the quarter retardation plate 4 is bonded to the upper surface of the linearly polarizing plate 5 on the light exit side of the liquid crystal panel 7. Operations of reflected light of external light and display light with respect to the liquid crystal display panel 7 configured as described above will be described with reference to FIG.

FIG. 2 shows a liquid crystal display device of the present invention.
It is a figure for demonstrating the model of the light wave after passing through each element, when external light injects from the protective plate side. In FIG. 2, a waveform is drawn assuming that light travels in the x-axis direction on three-dimensional coordinate axes xyz that are orthogonal to each other. Polarizing plate 2
Is the polarization plane of the polarizing plate
Is tilted 135 ° with respect to the y-axis. That is, the absorption axes of the polarizing plate 2 and the polarizing plate 5 are orthogonal to each other. 1/4 phase plate 3,
In No. 4, the angle of the light wave in the z-axis direction is delayed by 1/4 with respect to the light wave in the y-axis direction.

First, the reflected light of external light will be described.
Now, when external light passes through the polarizing plate 2, its light wave a becomes vibration of the plane of polarization inclined by 45 ° with respect to the y axis (FIG. 2 (2)).
When it further passes through the phase difference plate 3, its light wave b is 1 in the z-axis direction.
It becomes a circularly polarized vibration that rotates to the right with a phase delay of / 4 (Fig. 2
(3)). When the circularly polarized light wave of such vibration is reflected by the back surface of the retardation plate 4 or the surface of the polarizing plate 5, the waveform of the light wave c becomes a left-handed circularly polarized light having an inverted phase (FIG. 2 (4)). ). When this reflected light passes through the 1/4 phase difference plate 4 again, the waveform of the light wave d shows that the vibration in the z-axis direction is 1 /
There is a total delay of 1/2 phase with respect to the vibration of 4 phases and the y-axis (FIG. 2 (5)). Since this light wave is linearly polarized and the vibrating surface is orthogonal to the pass axis of the polarizing plate 2, it cannot pass through the polarizing plate 2. That is, the reflected light is absorbed by the polarizing plate 2 and does not go out.

Next, the display light of the liquid crystal panel will be described. Further, the display light of the liquid crystal panel, that is, the light wave e that has passed through the polarizing plate 5 becomes the vibration of the vibrating surface inclined by 135 ° with respect to the y axis (FIG. 2 (6)). When a light wave of such a vibration passes through the phase difference plates 3 and 4, the vibration in the z-axis direction is shifted by 1/4 phase from the vibration in the y-axis direction, and the phase difference plates 3 and 4 make a total of 1 phase difference.
/ 2 phase delay. The vibrating surface of this light becomes circularly polarized light that rotates rightward as shown in FIG. 2 (8) (FIG. 2 (7)). Further, when passing through the phase difference plate 4, the phase shifts by 1/4 and the passing axis of the polarizing plate of 2 coincides with the phase difference plate 4, so that it goes out without being attenuated.

[0021]

As described above, according to the liquid crystal display device of the present invention, display light from the liquid crystal panel can be efficiently displayed without being attenuated, and external light is reflected from the back side of the protective plate and the liquid crystal panel surface. Since it is possible to eliminate the external reflection that occurs, it is possible to reduce the total amount of reflected light, and to make the display screen bright and easy to see with less external light reflection (reflection) even when the external light is strong. Moreover, 1/4
Since it can be composed of a retardation plate and a linear polarizing plate, it is easy to produce and inexpensive.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining a configuration of an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a diagram for explaining a model of a light wave after passing through each element when external light is incident from the protective plate side in the liquid crystal display device of the present invention.

FIG. 3 is a diagram for explaining the operation principle of a conventional liquid crystal display device.

FIG. 4 is a diagram for explaining reflected light of external light from a protective plate of a conventional liquid crystal panel.

FIG. 5 is a cross-sectional view for explaining a conventional circularly polarizing plate.

FIG. 6 is a diagram for explaining a model of a light source after passing through each element when external light is incident on a circularly polarizing plate in the conventional circularly polarized light.

[Explanation of symbols]

1 ... Protective plate, 2, 5 ... Linearly polarizing plate, 3, 4 ... 1/4 phase difference plate, 6 ... Liquid crystal cell, 7 ... Liquid crystal panel.

Claims (1)

[Claims] 1. A liquid crystal display device having an optically transparent protective plate arranged so as to face the surface of a liquid crystal panel,
A liquid crystal display device characterized in that a linear polarizing plate and a 1/4 phase plate are sequentially provided on the surface of the protective plate facing the liquid crystal panel, and a 1/4 phase plate is provided on the surface of the liquid crystal panel. ..