JP2000147487A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the disadvantages of conventional semi-transmission type liquid crystal display devices and to obtain a liquid crystal display device giving a bright high-contrast display both in transmission and reflection modes. SOLUTION: The liquid crystal display device has at least a liquid crystal cell 2, a polarizing plate 3 disposed on the cell 2, a polarized light reflecting plate 1 disposed under the cell 2 and having a property of reflecting or transmitting incident light in accordance with the polarization direction and a light source disposed in the lowest layer, and can be converted to a transmission type or reflection type. A means for shading light which passes the polarized light reflecting plate 1 and has a specified incident angle is provided between the liquid crystal cell 2 and the light source. The lightproof means is preferably a microlouver, which shades light regularly reflected to the direction of an observer.

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 capable of switching between a transmission type and a reflection type.

[0002]

2. Description of the Related Art In recent years, many portable information devices equipped with a liquid crystal display device have been put on the market. These portable devices are used in various lighting environments unlike office use. Although the reflection type liquid crystal display device has low power consumption, it has a problem that it cannot be visually recognized under dark external light. On the other hand, in the transmission type liquid crystal display device, there is a problem that power consumption is increased, a battery life is shortened, and visibility is deteriorated in a very bright environment such as under sunlight.

In order to cope with the above-mentioned problems, transflective liquid crystal display devices have been put to practical use. This uses a material that transmits a part of light, such as thin aluminum, as the reflector, and transmits light from a light source provided below the liquid crystal cell so that it can be used as a transmission type.
However, the transflective liquid crystal display device has a problem that the display surface becomes dark when used as a reflective type or when used as a transmissive type because the reflectance of the reflector is low.

[0004]

SUMMARY OF THE INVENTION The present invention improves the drawbacks of the conventional transflective liquid crystal display device and provides a liquid crystal display device capable of obtaining a bright and high-contrast display during transmission and reflection. The purpose is to:

[0005]

A first feature of the present invention is that:
A liquid crystal cell and a polarizing plate arranged above the liquid crystal cell, a polarizing reflector arranged below the liquid crystal cell and having a characteristic of reflecting or transmitting incident light depending on the polarization direction, and a light source arranged at the lowermost layer In a liquid crystal display device which is configured to have at least and can be switched to a transmission type or a reflection type, a means for blocking light at a specific incident angle transmitted through a polarizing reflector is provided between a liquid crystal cell and a light source. Another object of the present invention is to provide a liquid crystal display device.

FIG. 1 is an explanatory diagram of the function of the polarizing reflector used in the present invention. The light Ll incident on the polarizing reflector 1 is transmitted (L2 light) or reflected (L3 light) depending on its polarization direction. In the figure, ○ indicates light polarized in the direction perpendicular to the paper. Such a polarizing reflector is available from Sumitomo 3M Limited by RDF (Re
It is commercialized under the trade name of Flexible Display Film.

FIG. 2 shows a configuration example of a reflection type liquid crystal display device using a polarizing reflection plate. A polarizing plate 3 is arranged on the viewer side of the liquid crystal cell 2. For ease of explanation, 90
A case where a twisted nematic mode liquid crystal having a twist is used will be described.

It is assumed that the polarization reflector 1 has the same reflection characteristics as those of FIG. The light polarized by the polarizing plate 3 (the transmission direction of the polarized light is represented by 31) is in the off state when the liquid crystal 22 is twisted (a), and in this case, when the liquid crystal 22 reaches the polarizing reflector, the polarization plane is 90 °. ° rotated and reflected by the polarizing reflector. This light is further rotated by 90 ° in the plane of polarization, and is incident on the polarizing plate 3 again. At this time, since the transmission axis of the polarizing plate coincides with the polarization plane, light can pass through the polarizing plate and reach the observer 9. On the other hand, when the liquid crystal is not twisted (b), the liquid crystal is in the on state. In this case, the rotation of the polarization plane by the liquid crystal does not occur, and the light reaching the reflection plate is transmitted through the polarization reflection plate 1 and arranged on the lower surface. The light is absorbed by the provided light absorption layer 5. Therefore, in this case, no light reaches the observer, and a black display is obtained.

FIG. 3 shows an example in which a transflective device using a polarizing reflector is used as a reflective device. When the liquid crystal 22 is twisted (a), the liquid crystal 22 is in the off state. In this case, when the liquid crystal 22 reaches the polarizing reflector, the polarization plane is rotated by 90 ° and reflected by the polarizing reflector. This light is further rotated by 90 ° in the plane of polarization, and is incident on the polarizing plate 3 again. At this time, since the transmission axis of the polarizing plate coincides with the polarization plane, light can pass through the polarizing plate and reach the observer. On the other hand, when the liquid crystal is not twisted (b), the liquid crystal is in the on state. In this case, the rotation of the polarization plane by the liquid crystal does not occur, and the light reaching the reflection plate is transmitted through the polarization reflection plate 1 and disposed on the lower surface. Light source.

In a fluorescent lamp or the like generally used as a light source, a reflecting plate is provided on the back surface, and a part of the light is reflected by the light source and emitted as shown in FIG. Also use EL for the light source
In the case of using a light source or the like, or in a sidelight type light source using a light guide plate, there is also reflected light, which lowers the black sensitivity and the contrast.

FIG. 4 shows a configuration example of a liquid crystal display device according to the present invention. In this configuration, a light-shielding layer 7 is provided between the light source and the polarizing reflector in addition to the configuration of FIG. The light absorbing layer needs to have a function of blocking incident light to the light source or reflected light from the light source during reflection and transmitting light when transmitted.

FIG. 5 shows an example of the configuration of a light-shielding layer preferable for the liquid crystal display device of the present invention. In the case of this drawing, a member that blocks light in the direction of regular reflection with respect to the direction of the observer is used. As such a member, a member called a microlouver is already commercially available. The drawing shows a film in which a light shielding layer is disposed obliquely inside. In this case, most of the light from the same direction as the inclination of the louver is transmitted as indicated by L5, but light at an incident angle in the opposite direction is blocked.

When such a light-shielding layer is used for the light-shielding layer 1 shown in FIG.
6 is reflected in the off state in the same manner as in the conventional example (L6 ').
Reach the observer. Therefore, a white state is observed. Next, in the ON state, the light transmitted through the polarizing reflector is absorbed by the backlight layer 7 as indicated by L7, so that the contrast does not decrease as in the conventional example. Next, a case where this apparatus is used in a transmission type will be described with reference to FIG.

Lights L8 and L9 emitted from the light source 6 are incident on the louver, and light (L) having a direction parallel to the inclination of the louver as a main component.
8) is incident on the polarizing reflector. The light which has passed through the polarizing reflector and has become linearly polarized light has a polarization plane of 9 by the cell as shown in this figure.
The display is black when rotated by 0 ° and white when not rotated. When the observer 9 is in the louver inclination direction, good contrast can be realized in this manner.

As described above, by inserting an element having an angle dependence in transmission characteristics, such as a microlouver, between the polarizing reflector and the light source, a high contrast can be obtained both during transmission and reflection. be able to. In addition, when viewed from the direction opposite to the inclination of the louver, brightness is insufficient at the time of transmission, but generally in a display device such as a portable device,
In many cases, the louver is viewed from a direction inclined by about 10 ° to 30 ° forward from the normal direction, and if this direction is made coincident with the direction of the inclination of the louver, the louver can be used without any practical problem. Louver tilt angle is 0 ° to 45 ° from normal
Is preferable, and the range of 10 ° to 30 ° is more preferable.

Next, a second configuration example of the liquid crystal display device of the present invention will be described with reference to FIG. In this configuration example, a phase difference plate 72 is used as a light shielding layer. In the figure, reference numeral 6 denotes a quarter-wave plate whose polarization plane is 90 ° like a TN off state in a liquid crystal layer.
In the case of rotation (c), white display is performed in the same manner as described above. In the case where the liquid crystal is not twisted as in the ON state of TN (d), the linearly polarized light transmitted through the polarizing reflection plate becomes circularly polarized light by the phase difference plate and enters the light source. The reflected light (mainly circular knitted light) from the light source is converted into linearly polarized light by the retardation plate, but the polarization plane is rotated by 90 °, so that it cannot be transmitted through the polarizing reflection plate. Therefore, also in this configuration, good contrast can be obtained at the time of reflection.

Next, the case of transmission is shown in FIG. In this case, when the light from the light source is not polarized, the phase plate does not substantially act, and is similar to FIG. However, in FIG. 6, the directivity was at an angle, but in this example, there is substantially no directivity. By arranging the retardation plate between the polarizing reflector and the light source in this way, it can be made to function substantially as a light shielding layer against the reflected light from the light source, and a high contrast can be obtained at the time of reflection. .

The display mode has been described above for the sake of simplicity. However, if the display mode is such that the polarization state of light incident on the reflective polarizer can be modulated by applying a voltage, the display mode is TN.
The present invention is not limited to the type, and for example, an STN mode optically compensated by a phase difference plate, a bend mode, an electric field control birefringence mode, or the like can be used.

In the above description, the present invention shows the case where the negative / positive display is inverted at the time of transmission and at the time of reflection. However, such an operation may not be preferable in practical application. This can be solved by inverting the driving data signal by an inverter or the like. The inversion of the data signal may be performed by a circuit inside the display device or an external circuit. In particular, if a circuit is configured to be inverted at the same time when the light source is turned on, the display can be used without discomfort. In the above description, the case of monochrome display has been described. However, color display can be performed by providing a color filter.
In this case, the color filter can be provided on the inner surface of the substrate or between the polarizing reflector and the lower substrate. In this case, if the thickness of the substrate is large, color mixing with other pixels occurs when viewed obliquely. In order to reduce this problem, the thickness of the substrate needs to be １ ／ or less of the pixel pitch. With such a configuration, it is possible to obtain an apparatus having a wide viewing angle and a high contrast with less color mixing due to parallax.

Specifically, at a pixel pitch of about 300 μm, it is preferable to use a substrate of 150 μm or less. This substrate thickness is difficult to realize on a glass substrate in manufacturing,
It can be realized only in the resin substrate. As such a resin substrate, a smooth, optically isotropic substrate such as polycarbonate, polyolefin, acrylic, or polyarylate can be used. These substrates may be further subjected to a surface treatment such as coating.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

Example 1 A liquid crystal display device as shown in FIG. 4 was constructed. RDF-C manufactured by Sumitomo 3M Ltd. was used as the polarizing reflector 1, and a TN type cell having a 90 ° twist was used as the liquid crystal cell 2. As the light shielding layer 7, a microlouver film manufactured by Sumitomo 3M was used. The inclination of the louver was opposite to the clear viewing direction, and the inclination angle was 20 °. The backlight unit 6 was disposed below the light shielding layer 7. When the device of the present example and the device without the light-shielding layer 7 were observed at an inclination angle of 20 ° from the clear viewing direction, respectively, in a reflection mode in which the backlight was not turned on,
The device of the present invention could display clear black, while the device without the light-shielding layer turned black to gray, and the device of the present invention was superior in contrast.

Example 2 In Example 1, a display device shown in FIG. 7 was constructed using a quarter-wave plate instead of the microlouver film of the light shielding layer 7. When the apparatus of this example and the apparatus without a quarter-wave plate were observed at an inclination angle of 20 ° from the clear viewing direction, the contrast and the brightness were the same in the transmission mode, but the reflection without turning on the backlight was performed. In the mode of the present invention, clear black was displayed in the mode, whereas black was gray without the light-shielding layer, and the apparatus of the present example was superior in contrast as compared with the other. In addition, this device provided good contrast even in the observation direction opposite to the clear viewing direction.

Embodiments 3 and 4 In Embodiments 1 and 2, when the signal data was inverted and displayed when the backlight was lit, no negative / positive inversion was observed even when the display was switched, and good display was achieved. I did it.

Embodiment 5 In Embodiment 1, striped color filters 24 of red, green and blue are formed between the transparent electrode 232 and the lower substrate 212 as shown in FIG. In this embodiment, the substrate is a 100 μm thick polyethersulfone-based film, and the width and pitch of the electrodes are 300 μm each.
And 330 μm. In the same manner, another device was prepared using a glass substrate having a thickness of 0.5 mm.
The color change depending on the viewing angle and the color purity were superior to the apparatus using the polyether sulfone having a thickness of 0 μm or the apparatus using glass having a thickness of 0.5 mm. Similarly, an apparatus was prepared using a resin substrate having a thickness of 200 μm. This device was less dependent on viewing angle than when using 0.5 mm thick glass,
It was inferior to a 100 μm thick substrate.

[0026]

[Effect] 1. Claims 1 and 3 The effect of reflected light from the backlight during reflection can be reduced, and high contrast can be obtained. 2. The brightness at the time of transmission and the contrast at the time of reflection can both be maximized. 3. (4) The reflected light from the light source can be shielded by the polarizing reflector. Therefore, a high contrast can be obtained at the time of reflection, and there is almost no loss of light at the time of transmission, so that a bright display is possible. In addition, when the luminance of the apparatus is constant, a darker light source is sufficient, so that the power consumption of the apparatus can be reduced. 4. According to a fifth aspect of the present invention, it is possible to prevent image reversal at the time of switching between reflection and transmission, which occurs when a polarization reflection plate is used, and to provide a natural display. 5. According to a sixth aspect of the present invention, when the thickness of the substrate is equal to or less than の of the pixel pitch, it is possible to improve a color change and a color purity depending on a viewing angle when the color is formed. 6. Claim 7 It is possible to provide a device in which the color change and the degree of color paper according to the viewing angle in the case of colorization are improved even in high definition display with a small pixel pitch.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a function of a polarizing reflector used in the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of a reflection type liquid crystal display device using a polarization reflection plate.

FIG. 3 is a schematic cross-sectional view showing a configuration when a transflective device using a polarizing reflector is used as a reflective device.

FIG. 4 is a schematic cross-sectional view showing the configuration of a liquid crystal display device (the liquid crystal display device of Example 1) in which a light shielding layer 7 is provided between a light source and a polarizing reflector in addition to the configuration of FIG.

FIG. 5 is a diagram showing an example of a preferred configuration of a light-shielding layer for the liquid crystal display device of the present invention.

6 is a schematic cross-sectional view showing a configuration of a liquid crystal display device using the light shielding layer shown in FIG. 5 for the light shielding layer 1 in FIG.

FIG. 7 is a schematic cross-sectional view illustrating a configuration of a liquid crystal display device having a 波長 wavelength plate (Example 2).

FIG. 8 is a schematic cross-sectional view showing a configuration when a polarizing reflection plate is used as a transmission type.

FIG. 9 is a schematic sectional view illustrating a configuration of a liquid crystal display device according to a fifth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Polarization reflection plate 2 Liquid crystal cell 22 Liquid crystal 211 Upper substrate 212 Lower substrate 231 Upper electrode 232 Lower electrode 24 Color filter 3 Polarizer 31 Transmission direction of polarizer 5 Light absorption layer 6 1/4 wavelength plate 7 Shielding layer L1 Incident light L2 Transmitted light L3 Reflected light L6 Incident light from the specular reflection direction with the largest amount of reflected light L6 'L6 Reflected light in the off state L7 Light transmitted through the polarizing reflector in the L6 on state L8 Light exiting the light source 6 L9 Exiting the light source 6 Light ○ Light polarized in the direction perpendicular to the paper plane a When the liquid crystal is twisted (when the polarization plane rotates 90 °) b When the liquid crystal is not twisted c When the polarization plane rotates 90 ° like the TN off state d When there is no twist in the liquid crystal layer as in the ON state of TN

Claims (7)

[Claims] 1. A liquid crystal cell, a polarizing plate disposed above the liquid crystal cell, a polarizing reflector disposed below the liquid crystal cell and having a characteristic of reflecting or transmitting incident light depending on a polarization direction, and a lowermost layer. In a liquid crystal display device that is configured to include at least a light source and that can be switched to a transmission type or a reflection type, light of a specific incident angle transmitted through a polarizing reflector between a liquid crystal cell and a light source is blocked. A liquid crystal display device comprising means for performing the following. 2. The liquid crystal display device according to claim 1, wherein light in a specular reflection direction is shielded for an observer. 3. The liquid crystal display device according to claim 1, wherein the light shielding means is a microlouver. 4. A liquid crystal cell, a polarizing plate disposed above the liquid crystal cell, a polarizing reflector disposed below the liquid crystal cell and having a characteristic of reflecting or transmitting incident light depending on a polarization direction, and disposed on a lowermost layer. Comprising a light source and
In a liquid crystal display device capable of switching between a transmission type and a reflection type, a means for changing a phase difference between ordinary light and extraordinary light of light transmitted through a polarizing reflector between a liquid crystal cell and a light source by a multiple of 1/4 cycle. A liquid crystal display device, comprising: 5. The liquid crystal display device according to claim 1, further comprising means for inverting and driving display data. 6. The liquid crystal cell according to claim 1, wherein a color filter is provided inside the liquid crystal cell or between the reflective polarizer and the lower substrate, and the thickness of the substrate is set to １ ／ or less of the pixel pitch. Liquid crystal display. 7. The substrate according to claim 1, wherein the substrate is a resin film.
The liquid crystal display device according to any one of the above.