JP2003172931A - Liquid crystal display device and electronic appliance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which can provides a bright transmissive display and can secure a certain degree of visibility even under a bright operating environment by increasing use efficiency of illumination light. <P>SOLUTION: The liquid crystal display device has a liquid crystal cell 15 holding a liquid crystal layer 27 between a counter substrate 3 and an element substrate 2, and a backlight 18 arranged at the outer surface side of the liquid crystal cell 15. An upper polarizing plate 20 is provided at the outer surface side of the counter substrate 3, and a lower polarizing plate 23, a reflective polarizing plate 24, a diffusion adhesive 25 and a quarter-wave plate 26 are provided between the element substrate 2 and the backlight 18 in this order from the substrate side. A reflector plate 29 is provided at the outer surface side of a light transmission plate 16 of the backlight 18, and a scattering sheet 30 and two prism sheets 31 and 32 are sequentially provided at the inner surface side of the light transmission plate 16. <P>COPYRIGHT: (C)2003,JPO

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 and an electronic apparatus, and more particularly to the structure of a liquid crystal display device mainly including a transmissive display, which includes an illumination device.

[0002]

2. Description of the Related Art As a liquid crystal display device capable of displaying even in a dark place, an illuminating device (hereinafter also referred to as a backlight) is provided on the back side of a liquid crystal cell, and display is performed by utilizing light emitted from the illuminating device. There is a transmissive liquid crystal display device. The illuminator used here is generally a cold cathode fluorescent lamp (C
CFL), a light emitting diode (LED), and the like, and a light guide plate having a structure for emitting the light incident from the light source to the liquid crystal cell side while propagating inside.

An active matrix type liquid crystal display device is known as a liquid crystal display device having high definition and excellent display quality. As a display method of an active matrix type liquid crystal device, Twisted Nema
The tic (hereinafter abbreviated as TN) mode display method is currently the mainstream. The reason is that the TN mode liquid crystal device balances various characteristics basically required for a display, such as bright, high contrast, relatively fast response speed, low drive voltage, and easy gradation display. This is because they are well equipped. In the case of a TN mode liquid crystal cell, a structure is adopted in which the major axis direction of liquid crystal molecules is twisted by 90 ° between the element substrate and the counter substrate, and polarizing plates are respectively provided on the outer surfaces of these substrates so that their transmission axes are orthogonal to each other. It is arranged.

However, in the liquid crystal display device of this type, in view of the display principle, only the polarized light having a vibration direction in one direction is extracted from the light emitted from the backlight by the polarizing plate and used for display. There is. In the case of the conventional liquid crystal display device, since the polarizing plates disposed above and below the liquid crystal cell are absorption type polarizing plates, the polarized light which is not used for display is absorbed by the polarizing plates. That is, in the conventional liquid crystal display device, of the light emitted from the backlight,
Only about half the light contributes to the display, and there is a problem that the light utilization efficiency of the backlight is low.

In order to deal with this problem, a liquid crystal display device provided with a reflective polarizing plate has been proposed. In the case of this liquid crystal display device, polarized light not used for display is reflected by the reflective polarizing plate, and the polarized light is reflected by a reflective plate or the like installed on the outer surface of the light guide plate of the backlight and returns to the reflective polarizing plate again. It will be. Even if some depolarization occurs during that time, the light returns almost in the polarization state that was reflected by the reflective polarizing plate at the beginning, so it is transmitted through the reflective polarizing plate and used for display. The light was very little, and it was not possible to sufficiently improve the light utilization efficiency of the backlight. Generally speaking, in the conventional transmissive liquid crystal display device, the display is dark for the brightness of the backlight,
It has been required to realize brighter transmissive display by increasing the utilization efficiency of the light of the backlight.

Further, as a method for improving the light utilization efficiency of the backlight, there has been proposed a liquid crystal display device having a quarter wavelength plate on the outer surface side of a reflective polarizing plate. When a quarter-wave plate is arranged on the outer surface side of the reflective polarizing plate, linearly polarized light in one polarization direction reflected by the reflective polarizing plate is transmitted through the quarter-wave plate and converted into, for example, clockwise circular polarized light. To be done. When this right-handed circularly polarized light is reflected by a reflector installed on the outer surface of the light guide plate of the backlight, this time it returns as left-handed (reverse) circularly polarized light and passes through the quarter-wave plate. /
After passing through the four-wave plate, it is converted into linearly polarized light whose polarization axis is orthogonal to that before transmission. Then, this linearly polarized light is transmitted through the reflective polarizing plate this time, and can be used for display. As described above, when the quarter-wave plate is used, a large amount of light emitted from the backlight and reflected by the reflective polarizing plate can be reused, and thus bright transmissive display can be obtained. This technique is disclosed in, for example, Japanese Patent Laid-Open No. 10-
It is disclosed in Japanese Patent No. 162619, Japanese Patent Laid-Open No. 2000-98372, and the like.

[0007]

By the way, in recent years, this type of transmissive liquid crystal display device has been adopted for an image display section of a mobile phone, an image display section of a digital camera, etc., and has the advantages of small size and light weight. It is widely used mainly for various portable electronic devices. Since the utilization efficiency of the light of the backlight is improved by the above technique, the brightness of the transmissive display is also improved year by year. However, the transmissive liquid crystal display device has the following major drawbacks when applied to portable electronic devices. That is, depending on the environment in which the portable electronic device is used, the brightness of the backlight is much weaker than sunlight, for example, in the outdoors where the sunlight is strong, so the image displayed on the liquid crystal screen is very dark and very difficult to see. There was a problem.

As a method of solving this problem, for example, increasing the output of a backlight that illuminates the liquid crystal panel can be considered. However, when the output of the backlight is increased, the power consumption of the backlight is increased, so that a large capacity power supply device is required. This is not practical for electronic devices where portability is important.

The present invention has been made in order to solve the above-mentioned problems, and a bright transmissive display can be obtained by increasing the utilization efficiency of the light of the backlight, and the visibility is also to some extent in a bright environment of use. It is an object of the present invention to provide a liquid crystal display device capable of ensuring the above.

[0010]

In order to achieve the above object, a liquid crystal display device of the present invention comprises a liquid crystal cell in which a liquid crystal is sandwiched between a first substrate and a second substrate which are arranged to face each other. ,
A liquid crystal display device comprising a light source and a light guide plate, and an illuminating device arranged on the outer surface side of the second substrate of the liquid crystal cell, wherein the first surface is provided on the outer surface side of the first substrate. A polarizing plate is provided, and a second polarizing plate, a light diffusing layer, a reflective polarizing plate are provided between the second substrate and the lighting device from the side of the second substrate.
A first retardation plate is provided in this order, and a reflection plate is provided on a surface of the light guide plate opposite to a side where the liquid crystal cell is arranged.

Alternatively, in the liquid crystal display device of the present invention, a first polarizing plate is provided on the outer surface side of the first substrate, and the second substrate side is provided between the second substrate and the lighting device. To the second polarizing plate, the reflective polarizing plate, the light diffusing layer, and the first retardation plate in this order, and the reflecting plate is provided on the surface of the light guide plate opposite to the side where the liquid crystal cell is arranged. It is characterized by that. That is, in the liquid crystal display device of the present invention,
With respect to the positional relationship between the reflective polarizing plate and the light diffusing layer, whichever is closer to the second substrate side, the same action and effect can be obtained.

The present inventor reuses the reflected light from the reflective polarizing plate for transmissive display by combining the reflective polarizing plate and the quarter-wave plate, and also adds a light diffusion layer. By scattering even a small amount of light incident from various directions in a bright environment and emitting it to the front side (observer side) of the liquid crystal cell for reflective display, It was found that at the same time as improving the utilization efficiency, it is possible to secure a certain degree of visibility even in a bright environment.

The display principle of the liquid crystal display device of the present invention will be described below with reference to FIG.

In the liquid crystal display device shown in FIG.
A first polarizing plate 51 (upper polarizing plate) arranged on the upper surface of the upper substrate 50 has a transmission axis in a direction parallel to the paper surface, and a second polarizing plate 53 (lower polarizing plate) arranged on the lower surface of the lower substrate 52. And the transmission axis of the reflective polarizing plate 55 is perpendicular to the paper surface. In addition, the case where the quarter-wave plate 56 is used as the first retardation plate will be described. In addition to the basic structure of the liquid crystal display device of the present invention, FIG. 10 shows two prism sheets 58 and 59, a scattering sheet 60 and the like.

Of the light L1 emitted from the illuminating device 62 (backlight) below the liquid crystal cell 61, the linearly polarized light L2 having a vibration direction perpendicular to the paper surface is the reflection polarizing plate 55, the second.
Of the TN liquid crystal layer 57 and the TN liquid crystal layer 57. In the state in which no voltage is applied, the light transmitted through the TN liquid crystal layer 57 has its polarization direction rotated by 90 °, is converted into linearly polarized light L2 ′ having a vibration direction parallel to the paper surface, and is transmitted through the first polarizing plate 51 to display white. (That is, the normally white mode in this case). On the other hand, in the voltage applied state, T
Even if the polarized light is transmitted through the N liquid crystal layer 57, the polarization direction is still perpendicular to the paper surface, so that this polarized light cannot be transmitted through the first polarizing plate 51, resulting in black display.

Next, paying attention to the linearly polarized light L3 having a vibration direction parallel to the paper surface reflected by the reflection polarizing plate 55,
By passing through the / 4 wavelength plate 56, for example, it is converted into clockwise circularly polarized light. When this right-handed circularly polarized light is reflected by a reflection plate 64 or the like installed on the outer surface of the light guide plate 63 of the illuminating device 62, this time it returns as left-handed (reverse) circularly polarized light to the ¼ wavelength plate 56. Since it is transmitted, it is converted to linearly polarized light L3 ′ having a vibration direction perpendicular to the paper surface after passing through the quarter-wave plate 56. Then, this linearly polarized light L3 '
Since it can pass through the reflective polarizing plate 55 and the second polarizing plate 53, it can be used for display. In this way, by reusing the reflected light from the reflective polarizing plate 55, the transmissive display can be made brighter.

Focusing on the incident light L4 from the upper side of the liquid crystal cell 61 assuming use in a brighter place, the linearly polarized light L of the incident light L4 having a vibration direction parallel to the plane of the paper.
5 passes through the first polarizing plate 51 and enters the TN liquid crystal layer 57. In the state where no voltage is applied, the light transmitted through the TN liquid crystal layer 57 has its polarization direction rotated by 90 °, is converted into linearly polarized light L5 having a vibration direction perpendicular to the paper surface, and is transmitted through the second polarizing plate 53 to be a light diffusion layer. Reach 54. At this time, the light diffusion layer 54
The light is scattered by the action of, and is emitted to at least the upper side (viewer side) of the liquid crystal cell 61 even at a slight amount. Therefore, the light L5 ′ is oscillated again by the TN liquid crystal layer 57 in parallel with the paper surface. The light is converted into linearly polarized light having a direction and passes through the first polarizing plate 51. This light enables reflective display. Also, this action does not have any adverse effect on the transmissive display. Although the case where the light diffusing layer 54 is provided between the second polarizing plate 53 and the reflective polarizing plate 55 has been described here, even if the light diffusing layer is provided between the reflective polarizing plate and the first retardation plate, the function thereof is achieved. Is exactly the same.

As described above, the liquid crystal display device of the present invention has a transmissive structure when viewed as a whole, and is also capable of reflective display. As described above, it is possible to realize a liquid crystal display device that can obtain bright transmissive display and can secure a certain degree of visibility even in a bright environment of use.

In the above description of the display principle, it was explained that the first retardation plate was a quarter-wave plate, but the first retardation plate may be, for example, a 3 / 4-wave plate. /
Various retardation plates other than the two-wave plate can be used.
However, it is desirable to include at least a quarter wave plate.

That is, the first retardation plate is not necessarily 1 /
Even if it is not a four-wave plate, when the polarized light that is once reflected on the lower surface of the reflective polarization plate is reflected by the reflective plate on the outer surface of the lighting device and then returns, polarization conversion occurs at the first retardation plate and the reflected polarized light is generated. Since some component that can be transmitted through the plate is generated, the effect of reusing the reflected light is inevitably produced as compared with the case where the first retardation plate is not provided, regardless of the magnitude of the effect. However, as described above, when the first retardation plate is a quarter-wave plate, when the polarized light that was once reflected on the lower surface of the reflective polarizing plate is reflected again and then returned, theoretically, Since 100% of polarized light can pass through the reflective polarizing plate, all can contribute to display. Therefore, the reuse efficiency can be maximized, and brighter transmissive display can be obtained as compared with the case where another retardation plate is used.

Further, it is desirable that the first retardation plate includes a quarter wave plate and a half wave plate. However, in this case, it is necessary to dispose a half-wave plate on the reflective polarizing plate side.

A wave plate in which a quarter wave plate and a half wave plate are combined is known as a wide band quarter wave plate. According to this structure, the illumination light can be reused in a wide wavelength band. Can be planned.

Further, it is preferable that the retardation value of the first retardation plate is in the range of 100 nm to 180 nm.

According to this structure, the wavelength is 380 to 780.
Most of the visible light band of nm can be covered, and the function as the first retardation plate in the liquid crystal display device of the present invention can be fulfilled with respect to visible light.

The wavelength dispersion of the first retardation plate is 1
The following values are desirable.

For example, when the wavelength dispersion is represented by the ratio of the retardation value at the wavelength of 450 nm and the retardation value at the wavelength of 590 nm, the retardation plate which has been commercially available in the past has usually the wavelength dispersion exceeding 1. On the other hand, in recent years, a retardation plate having a wavelength dispersion of 1 or less has been provided. When this retardation plate is used, the fact that the chromatic dispersion takes a value of 1 or less means that the retardation value becomes larger as the wavelength becomes longer. Even if the wavelength of is changed, it will function as a quarter-wave plate. Therefore, according to this configuration, it is possible to fulfill the function as the first retardation plate of the present invention with respect to light of different wavelengths.

It is desirable that the light diffusion layer has an adhesive and particles mixed in the adhesive and having a refractive index different from that of the adhesive.

According to this structure, the adhesive serves as an adhesive layer for adhering the second polarizing plate and the reflective polarizing plate or an adhesive layer for adhering the reflective polarizing plate and the first retardation plate, and at the same time, Since the adhesive layer itself has a function of scattering light, the device configuration can be simplified.

The light diffusion layer preferably has a backscattering property.

When the liquid crystal display device is used in a sufficiently bright place, light is incident from a considerably wide angle side. Therefore, when the incident light is specularly reflected, the eyes of the user who see it from almost the front of the panel. I can't enter. On the other hand, when the light diffusion layer is inserted in the structure of the panel, the light incident from the wide-angle side is also scattered on the front side of the panel, so that the light enters the eyes of the user and reflection display is possible. That is, in the present invention, the reflective display becomes visible as long as the light diffusion layer has forward scattering. However, if the light diffusion layer further has backscattering, the amount of light reflected is increased as compared with the case of only forward scattering, so that the reflective display can be made brighter.

When the degree of the scattering function of the light diffusion layer is expressed by haze, the haze value is preferably 60% or more.

The "haze" used herein is a measure of transmittance generally called "haze" in the field of optics, and is a value expressed in% by dividing diffuse transmittance by total light transmittance. . A larger haze value means more scattered light, and a smaller haze value means less scattered light. As the function of the light-scattering layer of the present invention, the larger the haze, the higher the reflectance, which is desirable in that the reflective display becomes brighter, but on the other hand, for transmissive display, the light emitted from the illumination device is scattered. Therefore, the transmissive display becomes darker. Therefore, it is necessary to optimize the balance. The reason why the haze value is preferably 60% or more will be described in detail later.

On the other hand, as a structure on the illuminating device side, it is desirable to provide a prism sheet between the first retardation plate and the light guide plate.

According to this structure, the light emitted from the illuminating device can be efficiently condensed in the viewing direction of the user.

Particularly, by using the prism sheet composed of two prism sheets whose light collecting directions are substantially orthogonal to each other, the light emitted from the illuminating device can be condensed almost in the front direction of the liquid crystal cell. .

Further, it is desirable to provide a scattering sheet between the prism sheet and the light guide plate.

According to this structure, the light emitted from the illuminating device can be scattered in advance before entering the prism sheet, and the light emitted from the illuminating device can be uniformly introduced into the prism sheet.

With respect to the reflection plate arranged on the outer surface side of the light guide plate of the illumination device, it is desirable that the reflection surface be a mirror surface.

The reflecting plate in the present invention functions not only to guide the light emitted from the illuminating device to the liquid crystal cell side first, but also to reuse the reflected light from the reflecting polarizing plate in the transmissive display. In addition, in the reflective display, a function of reflecting external light that has passed through the light diffusion layer is fulfilled. Therefore, it is required to reflect more light, and in that sense, it is desirable to make the reflecting surface a mirror surface.

Further, it is desirable to provide a second retardation plate between the first polarizing plate and the first substrate or between the second polarizing plate and the second substrate. .

According to this structure, for example, STN (Super
Twisted Nematic) Even if the display is colored, such as when a liquid crystal is used, the coloring can be compensated.

Regarding the relationship between the transmission axis of the second polarizing plate and the transmission axis of the reflecting polarizing plate, the following two types can be considered.

First, the transmission axis of the second polarizing plate and the transmission axis of the reflecting polarizing plate are parallel to each other. According to this structure, all the light transmitted through the reflective polarizing plate in the transmissive display can be transmitted through the transmission axis of the second polarizing plate, so that the light use efficiency in the transmissive display can be maximized.

On the other hand, the transmission axis of the second polarizing plate and the transmission axis of the reflecting polarizing plate are made to intersect each other in a plane, and they are arranged so that the angle φ formed between them is in the range of 0 ° <φ ≦ 10 °. You can also In the case of this configuration, contrary to the above configuration, part of the light transmitted through the reflective polarizing plate in the transmissive display cannot pass through the transmission axis of the second polarizing plate, so that the light utilization efficiency in the transmissive display is high. It is slightly lower than the configuration. On the other hand, in the reflective display, a part of the light transmitted through the transmission axis of the second polarizing plate is reflected by the reflective polarizing plate, so that the reflective display can be slightly brightened. The reason why the angle φ formed by the transmission axis of the second polarizing plate and the transmission axis of the reflecting polarizing plate is preferably in the range of 0 ° <φ ≦ 10 ° will be described later.

The display mode of the liquid crystal display device of the present invention is preferably a normally white mode.

According to this structure, it is possible to realize a black display screen on a white background with low power consumption.

Another liquid crystal display device of the present invention has a liquid crystal cell in which a liquid crystal is sandwiched between a first substrate and a second substrate which are arranged opposite to each other, a light source and a light guide plate, and the liquid crystal cell Second
And a lighting device arranged on the outer surface side of the substrate, wherein a first polarizing plate is provided on the outer surface side of the first substrate, and the second substrate and the lighting device are provided. And a second polarizing plate, a hologram sheet, a reflective polarizing plate, and a first retardation plate are provided in this order from the side of the second substrate, which is opposite to the side of the light guide plate on which the liquid crystal cell is arranged. It is characterized in that a reflecting plate is provided on the side surface.

Alternatively, another liquid crystal display device of the present invention is
A first polarizing plate is provided on the outer surface side of the first substrate, and a second polarizing plate, a reflective polarizing plate, and a hologram sheet are provided between the second substrate and the lighting device from the second substrate side. The first retardation plate is provided in this order, and the reflection plate is provided on the surface of the light guide plate opposite to the side where the liquid crystal cell is arranged. That is, in this liquid crystal display device, the same action and effect can be obtained regardless of which of the positional relationship between the reflective polarizing plate and the hologram sheet is on the second substrate side.

In another liquid crystal display device of the present invention, a hologram sheet is arranged instead of the light diffusion layer in the liquid crystal display device of the present invention. The hologram sheet has a function of transmitting only light incident from a predetermined direction and reflecting light incident from a different direction. By using this hologram sheet and properly arranging the direction of the interference fringes, light emitted from the illumination device can be transmitted without any hindrance in transmissive display, and external light can be reflected to the upper surface side of the liquid crystal cell in reflective display. Therefore, also with this configuration, it is possible to realize the liquid crystal display device which is an object of the present invention and which can obtain a bright transmissive display and can secure a certain degree of visibility even in a bright environment of use.

It is desirable to use absorption type polarizing plates as the first polarizing plate and the second polarizing plate.

According to this structure, a high contrast display can be obtained.

The electronic equipment of the present invention is characterized by including the liquid crystal display device of the present invention.

According to this structure, by providing the liquid crystal display device of the present invention, it is possible to realize a portable electronic device having a bright display screen suitable for use outdoors, for example, in strong sunlight. it can.

[0054]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment] A first embodiment of the present invention will be described below with reference to FIGS.

The liquid crystal display device of this embodiment is an example of an active matrix type transmissive liquid crystal display device using a thin film transistor (hereinafter abbreviated as TFT) as a switching element, and FIG. 1 is a perspective view showing the overall configuration of the liquid crystal display device, and FIG.
2A is an enlarged view of one pixel in FIG. 2A, FIG. 2 is a sectional view of the liquid crystal display device, FIG. 3 is a diagram showing spectral characteristics of a color filter used in the liquid crystal display device, and FIG. FIG. 6 is a diagram showing the effect of a scattering sheet and a prism sheet used in FIG. In all of the following drawings, in order to make the drawings easy to see, the film thicknesses, the dimensional ratios, and the like of the respective constituent elements are appropriately changed. In addition, in FIG. 2, wiring on the inner surface side of each substrate, switching elements, electrodes,
Illustration of the alignment film and the like is omitted.

The liquid crystal display device 1 according to the present embodiment is shown in FIG.
As shown in (a), it is roughly composed of a liquid crystal cell 15, a light guide plate 16 arranged on the outer surface side thereof, and a backlight 18 (illumination device) having an LED 17 (light source). In the liquid crystal cell 15, the element substrate 2 (second substrate) on the side where the TFT is formed and the counter substrate 3 (first substrate) are arranged to face each other, and a liquid crystal layer (not shown) is provided between these substrates 2 and 3. Is enclosed. On the inner surface side of the element substrate 2, a large number of source lines 4 and a large number of gate lines 5 are provided in a grid pattern so as to intersect each other. TFTs 6 are formed near the intersections of the source lines 4 and the gate lines 5, and the pixel electrodes 7 are connected via the TFTs 6, respectively. That is,
One TFT 6 and one pixel electrode 7 are provided for each pixel arranged in a matrix. On the other hand, one common electrode 8 is formed on the entire inner surface of the counter substrate 3 over the entire display area in which a large number of pixels are arranged in a matrix. In this specification, the surface of each substrate constituting the liquid crystal cell 15 on the liquid crystal layer side is referred to as an “inner surface”, and the opposite surface is referred to as an “outer surface”.

As shown in FIG. 1B, the TFT 6 includes a gate electrode 10 extending from the gate line 5 and a gate electrode 10.
An insulating film (not shown) covering the semiconductor layer, a semiconductor layer 11 formed on the insulating film and made of polycrystalline silicon, amorphous silicon, or the like, and a source line 4 electrically connected to a source region in the semiconductor layer 11. It has a source electrode 12 and a drain electrode 13 electrically connected to a drain region in the semiconductor layer 11. The drain electrode 13 of the TFT 6 is electrically connected to the pixel electrode 7. The pixel electrode 7 is formed of a transparent conductive film such as ITO, and the common electrode 8 on the counter substrate 3 side is also formed of a transparent conductive film such as ITO.

Looking at the sectional structure of the liquid crystal display device 1, FIG.
As shown in, the upper glass substrate 19 constituting the counter substrate 3
An upper polarizing plate 20 (first polarizing plate) is provided on the outer surface of the above, and a color filter 21 having R (red), G (green), and B (blue) color material layers is provided on the inner surface side. Although not shown, a common electrode and an alignment film are formed on the color filter 21. A color filter having a spectral characteristic as shown in FIG. 3 is used as the color filter 21. Particularly, the G spectral characteristic has a minimum transmittance of 10% in the visible light region.
As described above, those having an average transmittance of 40% or more for the three colors of R, G and B are used.

On the other hand, on the outer surface of the lower glass substrate 22 constituting the element substrate 2, the lower polarizing plate 23 is provided from the lower glass substrate 22 side.
(Second Polarizing Plate), Reflecting Polarizing Plate 24, Diffusing Adhesive 25
A (light diffusion layer) and a quarter-wave plate 26 (first retardation plate) are provided in this order. Further, although not shown, the above-mentioned gate line 5, source line 4, TFT 6, pixel electrode 7 are formed on the inner surface side of the lower glass substrate 22, and an alignment film is formed. A liquid crystal layer 27 made of TN liquid crystal having a positive dielectric anisotropy is enclosed between the substrates 2 and 3.

Specifically, the upper polarizing plate 20 and the lower polarizing plate 23
Both are composed of absorption type polarizing plates. For the reflective polarizing plate 24, for example, DBEF (trade name: manufactured by 3M)
What is called PCF (a combination of a cholesteric liquid crystal film and a quarter-wave plate, trade name: manufactured by Nitto Denko Corporation) is used. The diffusion pressure-sensitive adhesive 25 has a particle size of 2 to 2 having a refractive index different from that of the pressure-sensitive adhesive in the acrylic resin-based pressure-sensitive adhesive.
A mixture of 3 μm beads is used. The layer thickness of the diffusion adhesive 25 is, for example, about 10 to 50 μm.
As the quarter-wave plate 26, a normal one made of polycarbonate or the like may be used, but if possible, it is preferable to use one having a wavelength dispersion of 1 or less. Alternatively, a ½ wavelength plate may be further inserted on the inner surface side of the ¼ wavelength plate 26.
The retardation value of the quarter-wave plate 26 is 100 nm to
It is preferably in the range of 180 nm. In that case, it can function as a quarter-wave plate for all visible light.

The backlight 18 has the light guide plate 16 and the LEDs 17 arranged on the incident end face thereof, and the outer surface of the light guide plate 16 is a reflection plate 29 having a mirror-finished surface.
Is provided. The light guide plate 1 is provided on the inner surface side of the light guide plate 16, that is, between the light guide plate 16 and the element substrate 2 of the liquid crystal cell 15.
From the 6 side, the scattering sheet 30, the two prism sheets 31,
32 are sequentially provided. Each prism sheet 31, 3
The reference numeral 2 is an array of a plurality of convex shapes each having a triangular cross section extending in one direction, and has a function of condensing light in a direction (cross-sectional direction) orthogonal to the extending direction of the convex shapes. . The two prism sheets 31 and 32 are arranged so that the light collecting directions are orthogonal to each other.

Regarding the axial arrangement of the respective polarizing plates, the upper polarizing plate 20 and the lower polarizing plate 23 are arranged so that their transmission axes are orthogonal to each other, and the lower polarizing plate 23 and the reflective polarizing plate 24 have their transmission axes parallel to each other. Are arranged as follows. On the element substrate 2, the counter substrate 3
The alignment film formed above is subjected to rubbing treatment in a direction orthogonal to each other, and the liquid crystal layer 27 sandwiched between these alignment films is in a state of being twisted by 90 ° with no voltage applied.

The liquid crystal display device 1 of the present embodiment is shown in FIG.
Although the position of the light diffusion layer (diffusion pressure sensitive adhesive 25) is different from that shown in FIG. 10, the display principle is exactly the same as that described in the section [Means for solving the problem] with reference to FIG.

That is, of the light emitted from the backlight 18, for example, linearly polarized light having a vibration direction perpendicular to the paper surface passes through both the reflective polarizing plate 24 and the lower polarizing plate 23,
It is incident on the liquid crystal layer 27. Liquid crystal layer 2 when no voltage is applied
The light transmitted through 7 has its polarization direction rotated by 90 ° and is converted into linearly polarized light having a vibration direction parallel to the paper surface, and is then converted into upper polarization plate 20.
To be displayed in white (normally white mode). On the other hand, when a voltage is applied, the polarization direction remains perpendicular to the plane of the paper even though it passes through the liquid crystal layer 27, so that this polarization cannot pass through the upper polarizing plate 20, resulting in black display. In the present embodiment, by adopting the normally white mode, a black display screen on a white background can be realized with low power consumption.

Next, the linearly polarized light having the vibration direction parallel to the paper surface reflected by the reflection polarizing plate 24 is converted into the quarter wavelength plate 26.
Is converted into, for example, right-handed circularly polarized light. This right-handed circularly polarized light is reflected by the reflection plate 29 or the like and then returns as left-handed circularly polarized light to pass through the quarter-wave plate 26. Therefore, after passing through the quarter-wave plate 26, it is perpendicular to the paper surface. It is converted into linearly polarized light having a vibration direction. Since this linearly polarized light can pass through the reflective polarizing plate 24 and the lower polarizing plate 23, it can be used for display. Thus, by reusing the reflected light from the reflective polarizing plate 24, the transmissive display can be made brighter. Particularly in the case of the present embodiment, since the transmission axis of the lower polarizing plate 23 and the transmission axis of the reflective polarizing plate 24 are parallel to each other, all the light transmitted through the reflective polarizing plate 24 in the transmissive display can pass through the lower polarizing plate 23. It is possible to maximize the light use efficiency in the transmissive display.

On the other hand, when the liquid crystal display device 1 is used in a bright place, external light enters from above the liquid crystal cell 15. Of the incident light, linearly polarized light having a vibration direction parallel to the paper surface passes through the upper polarizing plate 20 and enters the liquid crystal layer 27. When no voltage is applied, the light transmitted through the liquid crystal layer 27 has its polarization direction rotated by 90 °, is converted into linearly polarized light having a vibration direction perpendicular to the paper surface, and is sequentially transmitted through the lower polarization plate 23 and the reflection polarization plate 24 to be diffused. Reach the adhesive 25. When light is scattered here and scattered light is emitted toward the counter substrate 3 side (viewer side), this light is converted again by the liquid crystal layer 27 into linearly polarized light having a vibration direction parallel to the paper surface, and It passes through the polarizing plate 20. This light enables reflective display.

As described above, according to the liquid crystal display device 1 of the present embodiment, a bright liquid crystal display is obtained, and a color liquid crystal display device capable of ensuring a certain degree of visibility even in a bright environment of use is realized. be able to.

Further, as the color filter 21, the spectral characteristic of G, which has the highest visibility to the human eye, has a minimum transmittance of 10% or more in the visible light region, and an average transmittance of R, G, and B colors of 40% or more. As described above, since the color filter having a relatively high transmittance and a light color is used, bright transmissive display and reflective display can be realized.

Especially for the transparent display, the backlight 1
Since the scattering sheet 30 and the two prism sheets 31 and 32 are provided on the inner surface side of the light guide plate 16 of No. 8, the front brightness of the liquid crystal cell 15 is improved and a bright transmissive display can be obtained. As an example, FIG. 4 is a diagram showing a measurement result performed by the present inventor to verify the effect of the scattering sheet and the two prism sheets. This is a measurement of the luminance while moving the luminance meter in the polar angle direction with respect to the normal direction of the light guide plate of the backlight. In FIG. 4, the horizontal axis represents the angle [°] with respect to the normal direction, and the vertical axis represents the brightness [cd / m ² ]. In FIG. 4, a curved line shown by a broken line is nothing installed on the light guide plate, a curved line shown by a two-dot chain line is only a scattering sheet is installed on the light guide plate, and a curved line shown by a one-dot chain line is a light guide plate. The scattering sheet and one prism sheet are installed on the upper side, and the curve shown by the solid line shows the scattering sheet and the two prism sheets installed on the light guide plate, respectively.

As is apparent from FIG. 4, as the scattering sheet, the first prism sheet and the second prism sheet are added from the state where nothing is installed on the light guide plate, the light is emitted from the wide angle side. It can be seen that the emitted light is condensed in the direction of the angle of 0 °, and the front luminance is greatly improved.
In the case of the present embodiment, the light condensed on the front surface is slightly scattered to the surroundings because of the action of the diffusion pressure-sensitive adhesive, but the provision of the scattering sheet and the two prism sheets makes it possible to obtain sufficient front luminance. It is possible to improve and obtain a bright transmissive display.

In the case of the present embodiment, the diffusion adhesive 25 is used as the light diffusion layer, and this diffusion adhesive 25 functions as an adhesive layer for adhering the reflection polarizing plate 24 and the quarter-wave plate 26. At the same time, since the adhesive layer itself has a function of scattering light, the device structure can be simplified. Further, if the diffusion adhesive 25 has backscattering in particular, the reflective display can be made brighter.

Although the transmission axis of the lower polarization plate 23 and the transmission axis of the reflection polarization plate 24 are parallel to each other in the present embodiment, the transmission axis of the lower polarization plate and the transmission axis of the reflection polarization plate intersect in a plane. It may be arranged such that the angle φ formed is in the range of 0 ° <φ ≦ 10 °. In the case of this configuration, a part of the light transmitted through the reflective polarizing plate in the transmissive display cannot be transmitted through the transmission axis of the lower polarizing plate, and the light utilization efficiency in the transmissive display is slightly reduced, but in the reflective display, Since a part of the light transmitted through the transmission axis of the plate is reflected by the reflective polarizing plate, it is possible to slightly brighten the reflective display.

[Second Embodiment] The second embodiment of the present invention will be described below.
The embodiment will be described with reference to FIG.

The liquid crystal display device of this embodiment is also an example of a transmissive liquid crystal display device of the active matrix system, and its basic configuration is exactly the same as that of the first embodiment. FIG. 5 is a cross-sectional view showing the liquid crystal display device of the present embodiment, but the difference from the first embodiment is only the position of the diffusion adhesive. Therefore, in FIG. 5, the same components as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the first embodiment, the diffusing adhesive 25 is arranged between the reflective polarizing plate 24 and the quarter-wave plate 26, whereas in the present embodiment, the lower polarizing plate 23 and the reflective polarizing plate 23 are reflected. A diffusion adhesive 25 is arranged between the polarizing plate 24 and the polarizing plate 24. The only difference is this point, and the rest of the configuration is exactly the same as in the first embodiment.

Also in the liquid crystal display device 35 of the present embodiment, it is possible to realize a color liquid crystal display device which can obtain a bright transmissive display and can secure a certain degree of visibility even in a bright use environment. The same effect as that of the embodiment can be obtained.

[Electronic Equipment] Examples of electronic equipment equipped with the liquid crystal display device of the above-described embodiment will be described.

FIG. 7 is a perspective view showing an example of a mobile phone. In FIG. 7, reference numeral 1000 indicates a mobile phone main body, and reference numeral 1001 indicates a display unit using the above liquid crystal display device.

FIG. 8 is a perspective view showing an example of a wrist watch type electronic device. In FIG. 8, reference numeral 1100 indicates a watch body, and reference numeral 1101 indicates a display section using the above liquid crystal display device.

FIG. 9 is a perspective view showing an example of a portable information processing device such as a word processor and a personal computer. In FIG. 9, reference numeral 1200 is an information processing apparatus, reference numeral 1202 is an input unit such as a keyboard, reference numeral 1204 is the information processing apparatus main body, and reference numeral 1206 is a display unit using the above liquid crystal display device.

Since the electronic apparatus shown in FIGS. 7 to 9 is equipped with the liquid crystal display device of the above embodiment, it is a portable device equipped with a bright color liquid crystal display unit suitable for use outdoors, for example, in strong sunlight. Type electronic equipment can be realized.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, a retardation plate (second retardation plate) may be provided between the upper polarizing plate and the upper glass substrate or between the lower polarizing plate and the lower glass substrate. Although the TN liquid crystal is used in the above-described embodiment, even when the display is colored, especially when the STN liquid crystal is used, the color difference can be compensated by providing the retardation plate.

Further, a hologram sheet may be arranged instead of the diffusion adhesive in the above embodiment. Also in this case, it is possible to realize a liquid crystal display device that can obtain a bright transmissive display and can secure a certain degree of visibility even in a bright environment of use. Further, although an example of the active matrix type liquid crystal display device using the TFT has been described in the above-mentioned embodiment, an active matrix type liquid crystal display device using a thin film diode (TFD) as a pixel switching element, or The present invention can be applied to a passive matrix type liquid crystal display device.

[0084]

EXAMPLES Example 1 The present inventor actually prototyped a liquid crystal display device having the basic configuration of the first embodiment, and in order to demonstrate the effects of the present invention, optical characteristics such as reflectance and transmitted luminance were obtained. Was evaluated. The results will be reported below.

Samples in which the haze of the diffusion adhesive was varied to 8 types from 0% to 95% with respect to the liquid crystal display device of the first embodiment shown in FIG. Of 0% is a sample in which a diffusion adhesive is not used), and the reflectance and the transmission brightness of each sample were measured. The reflectance was measured by irradiating the liquid crystal panel with light from a light source installed at a position inclined by 30 ° in the polar direction from the normal direction of the liquid crystal panel, and measuring the intensity of the reflected light in the normal direction with a luminance meter. . As the reference value of reflectance, the reflected light intensity of a standard white plate made of barium sulfate was set to 100%. The transmitted brightness was obtained by measuring the intensity of transmitted light in the normal direction of the liquid crystal panel with a brightness meter. The transmitted luminance was measured both with and without the quarter wave plate installed. further,
The visibility in bright outdoors was evaluated. This is a sensitive evaluation by humans. The evaluation results are shown in [Table 1] below. Further, FIG. 6 shows a graph of [Table 1].

[0086]

[Table 1] As shown in Table 1 and FIG. 6, the haze of the diffusion adhesive is 0.
%, The transmission brightness without the ¼ wavelength plate was 200 cd / m ² , whereas the transmission brightness with the ¼ wavelength plate was 280 cd / m ² , Brightness is about 4
It has improved by about 0%. From this, it was verified that the illumination light reflected by the reflective polarizing plate was reused by using the ¼ wavelength plate, and the transmitted brightness was certainly improved.
In addition, looking at the points where the haze of the diffusion adhesive is 0% and 80%, the reflectance is increased from 5.0% to 8.0%, and the reflectance is increased by using the diffusion adhesive having the haze of 80%. About 60%
It was proved to improve.

Further, focusing on the haze of the diffusion adhesive,
As the haze value increases, the reflectance increases and the transmitted luminance tends to decrease. Therefore, it is necessary to consider the balance between the two in order to optimize the haze value. First, regarding the reflectance, the visibility in the bright outdoors cannot be improved unless the reflectance is increased by at least about 50% as compared with the conventional case (reflectance: 5.0%) in which a diffusion adhesive is not used. Therefore, in order for the reflectance to be 7.5% or more, the haze needs to be 60% or more.
On the other hand, regarding the transmission brightness, when the haze is 60% or more, it is considerably lower than the transmission brightness in the region where the haze is small, but still the transmission brightness at the maximum haze of 95% is 199 cd / m ^2. As a result, a value equivalent to the conventional transmission brightness of 200 cd / m ² which does not use a quarter-wave plate can be obtained. Therefore, by setting the haze of the diffusion adhesive to 60% or more, at least the brightness equal to or higher than the conventional one can be obtained in the transmissive display, and at the same time, the visibility in the bright outdoor by the reflective display can be compared with the conventional one. Can be improved.

Example 2 Next, in the liquid crystal display device of the first embodiment, the angle φ formed by the transmission axis of the lower polarization plate and the transmission axis of the reflection polarization plate was evaluated.

A sample in which φ was shaken in 8 types between 0 ° and 60 ° (however, φ = 0 ° means that both transmission axes are parallel) was made as a prototype, and the transmittance was measured for each. did. The measurement results are shown in [Table 2] below.

[0090]

[Table 2] As is clear from Table 2, the transmittance tends to decrease as φ increases. This is because as φ increases, the rate at which light that has passed through the reflective polarizing plate cannot pass through the lower polarizing plate increases. On the other hand, although the measurement was not performed here, the brightness of the reflective display should have increased.
If the value of φ is specified by the degree of decrease in transmittance,
In the range of 0 ° <φ ≦ 10 °, there is almost no decrease in the transmittance (2% or less), so that it is not visually recognized that the transmissive display is dark for the one in which both transmission axes are parallel,
The reflective display can be brightened. From this viewpoint, when the transmission axis of the lower polarization plate and the transmission axis of the reflection polarization plate are not parallel, the angle φ formed by these transmission axes is 0 ° <φ ≦ 10 °.
It is desirable to set the range to.

[0091]

As described above in detail, according to the present invention, a bright transmission display can be obtained by using a phase difference plate represented by a quarter-wave plate and a light diffusion layer.
For example, it is possible to realize a liquid crystal display device capable of ensuring a certain degree of visibility even in a bright environment such as outdoors where the sun is strong.

[Brief description of drawings]

FIG. 1 is a diagram showing a liquid crystal display device according to a first embodiment of the present invention, FIG. 1 (a) is a perspective view showing the entire configuration of the liquid crystal display device, and FIG. It is an enlarged view of one pixel in a).

FIG. 2 is a sectional view showing the same liquid crystal display device.

FIG. 3 is a diagram showing spectral characteristics of a color filter used in the liquid crystal display device.

FIG. 4 is a diagram showing an effect of a scattering sheet and a prism sheet used in the liquid crystal display device.

FIG. 5 is a sectional view showing a liquid crystal display device according to a second embodiment of the present invention.

FIG. 6 is a graph showing an example of the present invention, and is a graph showing a relationship between haze, reflectance, and transmitted brightness of a diffusion adhesive.

FIG. 7 is a perspective view showing an example of an electronic apparatus using the liquid crystal display device of the present invention.

FIG. 8 is a perspective view showing another example of the electronic device of the same.

FIG. 9 is a perspective view showing still another example of the electronic device.

FIG. 10 is a diagram for explaining the display principle of the liquid crystal display device of the present invention.

[Explanation of symbols]

1,35 Liquid crystal display device 2 element substrate (second substrate) 3 Counter substrate 15 Liquid crystal cell 16 Light guide plate 17 LED (light source) 18 Backlight (illuminator) 20 Upper polarizing plate (first polarizing plate) 21 color filter 23 Lower polarizing plate (second polarizing plate) 24 reflective polarizing plate 25 diffusion adhesive 26 1/4 wave plate (first retardation plate) 27 Liquid crystal layer 29 Reflector 30 scattering sheet 31, 32 Prism sheet

Claims (21)

[Claims] 1. A liquid crystal cell in which liquid crystal is sandwiched between a first substrate and a second substrate which are arranged opposite to each other, a light source and a light guide plate, and an outer surface side of the second substrate of the liquid crystal cell. A liquid crystal display device provided with an illuminating device disposed on the first substrate, wherein a first polarizing plate is provided on an outer surface side of the first substrate, and the first polarizing plate is provided between the second substrate and the illuminating device. A second polarizing plate, a light diffusing layer, a reflective polarizing plate, and a first retardation plate are provided in this order from the second substrate side, and on the surface of the light guide plate opposite to the side where the liquid crystal cell is arranged. A liquid crystal display device comprising a reflection plate. 2. An outer surface side of the second substrate of the liquid crystal cell, the liquid crystal cell having a liquid crystal sandwiched between a first substrate and a second substrate which are arranged opposite to each other, a light source and a light guide plate. A liquid crystal display device provided with an illuminating device disposed on the first substrate, wherein a first polarizing plate is provided on an outer surface side of the first substrate, and the first polarizing plate is provided between the second substrate and the illuminating device. A second polarizing plate, a reflective polarizing plate, a light diffusing layer, and a first retardation plate are provided in this order from the second substrate side, and on the surface of the light guide plate opposite to the side where the liquid crystal cell is arranged. A liquid crystal display device comprising a reflection plate. 3. The liquid crystal display device according to claim 1, wherein the first retardation plate includes at least a quarter-wave plate. 4. The liquid crystal display device according to claim 3, wherein the first retardation plate includes a quarter-wave plate and a half-wave plate. 5. The liquid crystal display device according to claim 1, wherein the retardation value of the first retardation plate is in the range of 100 nm to 180 nm. 6. The liquid crystal display device according to claim 3, wherein the wavelength dispersion of the first retardation plate has a value of 1 or less. 7. The light diffusion layer comprises a pressure sensitive adhesive, and particles mixed in the pressure sensitive adhesive and having a refractive index different from that of the pressure sensitive adhesive, and the light diffusing layer according to claim 1. The liquid crystal display device according to item 1. 8. The liquid crystal display device according to claim 1, wherein the light diffusion layer has backscattering. 9. The liquid crystal display device according to claim 1, wherein a haze of the light diffusion layer is 60% or more. 10. The liquid crystal display device according to claim 1, further comprising a prism sheet provided between the first retardation plate and the light guide plate. 11. The liquid crystal display device according to claim 10, wherein the prism sheet is composed of two prism sheets whose light collecting directions are substantially orthogonal to each other. 12. A scattering sheet is provided between the prism sheet and the light guide plate.
0. The liquid crystal display device according to 0 or 11. 13. The liquid crystal display device according to claim 1, wherein the reflection surface of the reflection plate is in a mirror surface state. 14. A second retardation plate is provided between the first polarizing plate and the first substrate or between the second polarizing plate and the second substrate. 14. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. 15. The transmission axis of the second polarizing plate and the transmission axis of the reflective polarizing plate are parallel to each other.
15. The liquid crystal display device according to any one of items 1 to 14. 16. The transmission axis of the second polarization plate and the transmission axis of the reflection polarization plate intersect each other in a plane, and an angle φ formed by the transmission axis is in a range of 0 ° <φ ≦ 10 °. 15. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a liquid crystal display device. 17. The liquid crystal display device according to claim 1, wherein the display mode is a normally white mode. 18. An outer surface side of the second substrate of the liquid crystal cell, the liquid crystal cell having a liquid crystal sandwiched between a first substrate and a second substrate opposite to each other, a light source and a light guide plate. A liquid crystal display device provided with an illuminating device disposed on the first substrate, wherein a first polarizing plate is provided on an outer surface side of the first substrate, and the first polarizing plate is provided between the second substrate and the illuminating device. A second polarizing plate, a hologram sheet, a reflective polarizing plate, and a first retardation plate are provided in this order from the second substrate side, and reflected on the surface of the light guide plate opposite to the side where the liquid crystal cell is arranged. A liquid crystal display device comprising a plate. 19. A liquid crystal cell having a liquid crystal sandwiched between a first substrate and a second substrate which are arranged to face each other, a light source and a light guide plate, and the outer surface side of the second substrate of the liquid crystal cell. A liquid crystal display device provided with an illuminating device disposed on the first substrate, wherein a first polarizing plate is provided on an outer surface side of the first substrate, and the first polarizing plate is provided between the second substrate and the illuminating device. A second polarizing plate, a reflective polarizing plate, a hologram sheet, and a first retardation plate are provided in this order from the second substrate side, and are reflected on the surface of the light guide plate opposite to the side where the liquid crystal cell is arranged. A liquid crystal display device comprising a plate. 20. The first polarizing plate and the second polarizing plate are absorption type polarizing plates.
20. The liquid crystal display device according to any one of items 1 to 19. 21. An electronic device comprising the liquid crystal display device according to claim 1. Description: