JPH1184380A - Liquid crystal display device and its liquid crystal panel lighting device - Google Patents

Abstract

(57) [Summary] A high-quality image display is obtained by uniformly illuminating the entire effective display area by a front illumination method. The liquid crystal panel includes a reflection type liquid crystal panel, and a liquid crystal panel lighting device that is stacked on the front surface of the liquid crystal panel and illuminates the liquid crystal panel from the front surface. Many light diffusion / reflection areas 1
The light guide plate 11 includes a substantially rectangular light guide plate 11 made of a transparent plate having a light source 5 and a light source 12 installed along at least one edge of the light guide plate 11. Reflective liquid crystal panel 16 installed on the back side
Is illuminated, the reflected light from the liquid crystal panel passes through the light guide plate 11 and is emitted to the front surface side, whereby an image formed on the liquid crystal panel 16 is displayed.

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 more particularly to a liquid crystal display device using a reflection type liquid crystal panel which modulates light incident from a display surface side and emits the light to the display surface side, and its illumination. Related to the device.

[0002]

2. Description of the Related Art In recent years, a so-called liquid crystal display device using a liquid crystal panel has been frequently used as a display device as a monitor of an image reproducing device or various information terminals.

In this liquid crystal display device, a simple matrix type known as an STN type and a T
An active matrix type using a non-linear element such as FT is generally used.

Since these liquid crystal panels are not of a self-luminous type, a separate illumination light source is required to visualize an image formed on the liquid crystal panel. There are two types of liquid crystal panels: transmissive and reflective. In monitors for information terminals, etc., transmissive liquid crystal panels are often used for high brightness and high contrast display. A visible image is formed by modulating light from the backlight with an image formed on the liquid crystal panel.

FIG. 7 is a cross-sectional view for explaining a conventional configuration example of a liquid crystal display device having a transmission type liquid crystal panel and a backlight device, that is, a so-called backlight. It is configured such that illumination light from a backlight transmitted through the liquid crystal panel is modulated by an image formed on the liquid crystal panel, and emitted to the surface side of the liquid crystal panel to visualize the image.

That is, this type of liquid crystal display device has a liquid crystal panel sandwiching a liquid crystal layer between two transparent substrates and having an upper polarizing plate 7a on the surface side and a lower polarizing plate 7b on the back side.
A backlight having a substantially rectangular transparent light guide plate 1 and a light source (here, a cold cathode fluorescent lamp) 2 including a cold cathode fluorescent lamp or a light emitting diode installed along one edge of the light guide plate 1 10 'is provided, and the backlight 10' illuminates the liquid crystal panel 6 from the back.

[0007] The light source 2 is provided with a light source reflector 3 for improving the utilization efficiency of light emitted from the light source.
A light guide plate 11 is provided on the edge of the light guide plate 1 opposite to the light source 2.
An end face reflection film 4 for further utilizing the light propagating through the surface for illumination is provided. Then, the light guide plate 1
Is provided with a light diffusion region 5 formed by dot printing or the like.

Further, on the back side of the light guide plate 1 constituting the backlight 10 ′, there is provided a reflection plate 8 that totally reflects light emitted from the light guide plate 1 to the back surface and returns the light to the liquid crystal panel 6 side. .

[0009] Such a backlight 10 'is laminated on the liquid crystal panel 6 via a light amount distribution correcting member such as a diffusion film 9 or a prism plate (not shown) to constitute a transmissive liquid crystal display device. .

Since a transmissive liquid crystal display device equipped with a backlight of this type is known, no particular reference is given.

[0011]

The above-described illumination device for a liquid crystal panel has an optimum configuration for illuminating a transmission type liquid crystal panel from behind. However, it does not make sense to apply a liquid crystal display device to a liquid crystal display device using a reflection type liquid crystal panel that actively uses external light, in addition to such a transmission type.

In a reflection type liquid crystal display device, a reflection plate is provided on the back surface in order to totally reflect light incident from the front surface side and emit the light again from the front surface side, or two substrates constituting a liquid crystal panel. The reflective layer is formed on the inner surface on the lower substrate side.

On the other hand, in a reflection type liquid crystal display device using external light as illumination light, it is difficult to read a display in a dark environment with little external light.

Conventionally, a front illuminating means (a front illuminating means) such as a light emitting diode or a lamp for illuminating the front side of a reflective liquid crystal display device for displaying a simple pattern such as a character, a symbol or a figure is used. A device provided outside a display area is known. However, the illumination by such front illumination means cannot uniformly illuminate the entire effective display area of the liquid crystal panel. Therefore, the illumination using the small-sized liquid crystal panel is effective. In a panel, it is difficult to uniformly illuminate the entire effective display area, and it is particularly difficult to apply the present invention to a liquid crystal display device that displays a moving image or the like.

Further, it is conceivable to stack a backlight having the above-mentioned structure on the surface side of the reflective liquid crystal panel with the light diffusion region 5 facing the surface. As a result, the intensity (luminance) of the display light modulated and emitted by the liquid crystal panel is suppressed, and the visibility of the displayed image is significantly reduced, so that the function of the lighting device cannot be performed. In the above backlight,
Since the area of the light diffusion region is large, the amount of reflected light modulated by the liquid crystal panel that passes through the light guide plate is limited, and visibility is further reduced.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to uniformly illuminate the entire effective display area by a front illumination method to obtain a high-quality image display, and its illumination. It is to provide a device.

[0017]

The object of the present invention is to provide a lighting device comprising a light guide plate and a light source on the surface side of a reflection type liquid crystal panel, and to form the lighting device on the surface side of the light guide plate so that the light source can be used. This is achieved by providing a configuration that prevents light from being emitted toward the front side in a light diffusion region for directing the light toward the liquid crystal panel, and reducing the area of the light diffusion region.

That is, the liquid crystal display device of the present invention is characterized by having the following configurations (1) and (2), and the liquid crystal panel lighting device of the present invention has the following configuration (3). It is characterized by points.

(1) A liquid crystal display device comprising: a reflection type liquid crystal panel; and a liquid crystal panel lighting device which is laminated on the surface side of the liquid crystal panel and illuminates the liquid crystal panel from the front side. The apparatus comprises a substantially rectangular light guide plate made of a transparent plate having a large number of light diffusion / reflection regions of a relatively small area on the surface side thereof, and a light source installed along at least one edge thereof. The light emitted from the light guide plate is emitted to the back side of the light guide plate to illuminate a reflective liquid crystal panel installed on the back side, so that the reflected light from the liquid crystal panel passes through the light guide plate and the front surface side The image formed on the liquid crystal panel is displayed by emitting the light to the liquid crystal panel.

(2) A substantially rectangular light guide plate made of a transparent plate having a large number of light diffusion / reflection regions with a relatively small area on the surface side, and a light source installed along at least one edge of the light guide plate A liquid crystal panel illuminating device, wherein light emitted from the light source is emitted to the back side of the light guide plate to illuminate a reflective liquid crystal panel laminated on the back side, and an image formed on the liquid crystal panel is used. The modulated illumination light passes through the light guide plate and is emitted to the surface side of the light guide plate.

(3) The light diffusion / reflection region in (2) comprises a light diffusion layer formed on the back side of the light guide plate and a light absorption layer formed on the back surface of the light diffusion layer. I do.

The area of the light diffusion / reflection region in each of the above structures is formed smaller than that formed in the backlight used in the above-mentioned conventional liquid crystal display device.
The degree may be set to a size having no practical problem in consideration of the reflection performance of the liquid crystal panel and the luminance of the light source. Further, the distribution can be changed according to the luminance distribution of the light emitted from the light guide plate.

The above-described liquid crystal display device and the liquid crystal panel lighting device according to the present invention can be applied irrespective of the type of liquid crystal panel (simple matrix type, active matrix type, and other types of liquid crystal panels) and the screen size.
Even in an environment where external light is insufficient, it is possible to obtain a uniform, high-brightness image with good visibility over the entire effective display area.

It is not necessary to always light the light source of the above illuminating device. The light source is turned off when the luminance of the external light is large, and is turned on when necessary when the external light has a low luminance. Can be.

[0025]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1A and 1B are explanatory views of a liquid crystal display device according to a first embodiment of the present invention, wherein FIG. 1A is a cross-sectional view, FIG. 1B is a cross-sectional view of a main part of a lighting device, 10 is a liquid crystal panel lighting device, 11 is a transparent light guide plate made of a substantially rectangular acrylic resin or the like, 12 is a light source, 1
3 is a light source reflector, 14 is an end face reflector, 15 is a light diffusion / reflection region, 15a is a light diffusion layer, 15b is a light absorption layer, 16 is a reflection type liquid crystal panel, 17 is a polarizing plate, and 18 is a reflection plate. is there.

As shown in FIG. 1A, this liquid crystal display device has a light guide plate 11 on the surface side (display surface side) of a reflection type liquid crystal panel 16 and a light source 12 installed along one edge thereof. A liquid crystal panel illuminating device 10 including a cold cathode fluorescent lamp is laminated.

The illustrated liquid crystal panel 16 has basically the same structure as a transmissive liquid crystal panel, and has a reflection plate 18 for totally reflecting light laminated on the back surface thereof. The same applies to the type in which a total reflection member for light is provided on the inner surface of the substrate described above, in which case the above-mentioned reflection plate 18 becomes unnecessary.

The light diffusion / reflection region 15 formed on the front surface side of the light guide plate 11 is, as shown in FIG.
5a and a light absorbing layer 15b laminated on the back surface.

The light diffusion layer 15a is provided between the light source 12 and the light guide plate 11.
Is diffused and reflected in the direction of the liquid crystal panel 16 as indicated by an arrow L in FIG. 5A, and the modulated light reflected by the liquid crystal panel 16 is reflected by the light diffusion / reflection region 15. The light is emitted to the front side through the gap. At this time, the light absorption layer 15b prevents the light incident on the light diffusion layer 15a from being emitted to the front side and becoming a bright spot on the observation side.

FIG. 2 is a plan view of the liquid crystal display device shown in FIG. 1 as viewed from the front side, and shows one shape of a light diffusion / reflection region 15 formed on the light guide plate 11 constituting the liquid crystal panel lighting device 10. Here is an example. In this figure, in order to facilitate understanding, the size and arrangement interval of the light diffusion / reflection regions 15 are enlarged so as to be different from actual ones.

The light diffusion / reflection area 15 shown in FIG.
Fine particles of silicon oxide or the like regularly arranged and formed by screen printing or the like on the surface side of the light guide plate 11 of 0.3 mm
A light-diffusing layer 15a is formed by forming dots at a density of 15 to 20 / cm to form a light-diffusing layer 15a, and a light-absorbing material such as graphite particles is formed thereon by screen printing or the like to form a light-absorbing layer 15b.
The configuration is as shown in FIG.

Although the illustrated light diffusion / reflection regions 15 have been described as being formed on the surface of the light guide 11 at the same size and at the same interval, the shape, optical characteristics, or According to the light emission characteristics of the light source, the size or interval of the light diffusion / reflection region 15 is changed as shown in FIG.
The brightness on the screen can be made uniform by increasing or decreasing the distance from 2.

Light incident on the side edge of the light guide plate 11 from the light source 12 is diffused downward by the light diffusion / reflection region 15, that is, in the direction of the liquid crystal panel, and illuminates the liquid crystal panel from the surface. The light that has entered the liquid crystal panel is reflected by the liquid crystal panel and enters the light guide plate 11 again, and most of the light passes through the gap between the light diffusion / reflection regions 15 and exits to the front side.
The emitted light becomes image display light modulated by an image formed on the liquid crystal panel.

The light diffusion / reflection region 15 is not limited to the dot shape, but may be a thin line shape parallel to the longitudinal direction of the light source 12.

According to the configuration of this embodiment, regardless of the effective display area (screen size) of the liquid crystal panel, even in an environment where external light is insufficient, the effective display area is uniform over the entire area.
In addition, an image with high luminance and good visibility can be obtained.

In the above embodiment, the light diffusion / reflection region 15 is formed of the light diffusion layer 15a and the light absorption layer 1
5b, the inner surface of the light guide plate 11 without the light absorbing layer 15b may be provided with the function of a light diffusing layer only as the light absorbing layer 15b.

Here, various light compensating members are not shown.

FIG. 4 is a sectional view showing another example of the shape of the light diffusion / reflection region for explaining the second embodiment of the liquid crystal display device according to the present invention.

The light diffusion / reflection region 15 is
When injection molding is used, a minute concave portion 19 is formed on the surface side, and a light absorbing material such as graphite particles is filled in the concave portion 19 to form a light absorbing layer, and the light guide plate 11 without the concave portion 19 is formed. The inner surface on the front side has the same function as the light diffusion layer.

It is to be noted that a light diffusion layer similar to that of the above embodiment may be provided below the light absorbing material.

According to the structure of this embodiment, even in an environment where external light is insufficient, uniform and high-luminance visibility is obtained over the entire effective display area regardless of the effective display area (screen size) of the liquid crystal panel. Good image can be obtained.

FIG. 5 is a sectional view showing another example of the shape of the light diffusion / reflection region for explaining the third embodiment of the liquid crystal display device according to the present invention.

In this embodiment, the light guide plate 11 is formed in a wedge shape in which the thickness of the light guide plate 11 is gradually reduced from the side of the linear light source, and a function of correcting a light quantity shortage due to a distance from the light source is added.

The same effect can be obtained by forming the same light diffusion / reflection region 15 in the light guide plate 11 having this shape as in the first and second embodiments.

FIG. 6 is a plan view of a liquid crystal display device according to a fourth embodiment of the present invention, as viewed from the front side of the liquid crystal display device.
1 shows an example of the shape of the light diffusion / reflection region 15 formed in FIG.
In this figure, as in FIG. 2, the size and arrangement interval of the light diffusion / reflection regions 15 are different from actual ones for easy understanding.

In the above embodiment, a cold cathode fluorescent lamp is used as a light source for illuminating the liquid crystal panel of the liquid crystal display device. In this embodiment, the light emitting diode array 20 is provided at one edge of the light guide plate 11. It is. The color tone of the light emitting diode 20 is desirably white based on visibility. Other configurations are equivalent to any of the above-described embodiments.

According to this embodiment, in addition to the effects of the above embodiments, by using a light emitting diode as an illumination light source,
Power consumption can be greatly reduced.

[0048]

As described above, according to the liquid crystal panel illuminating device of the present invention, it is possible to uniformly illuminate the liquid crystal panel from the surface side for observing an image. An optimal lighting device is realized, and a liquid crystal display device using the lighting device can clearly recognize the displayed image even in a dark environment where the amount of external light is insufficient. Can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a plan view of the liquid crystal display device shown in FIG. 1 as viewed from the front side.

FIG. 3 is an explanatory view of another example of the light diffusion / reflection region in the first embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a cross-sectional view showing another example of the shape of the light diffusion / reflection region for explaining the second embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a cross-sectional view showing another example of the shape of the light diffusion / reflection region for explaining the third embodiment of the liquid crystal display device according to the present invention.

FIG. 6 is a plan view of a liquid crystal display device according to a fourth embodiment of the present invention, as viewed from the front side of the liquid crystal display device.

FIG. 7 is a cross-sectional view illustrating a conventional configuration example of a liquid crystal display device including a transmissive liquid crystal panel and a backlight device, a so-called backlight.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Liquid crystal panel illuminating device 11 Light guide plate 12 Light source 13 Light source reflector 14 End face reflector 15 Light diffusion / reflection area 15a Light diffusion layer 15b Light absorption layer 16 Liquid crystal panel 17 Polarizer 18 Reflector.

Claims (3)

[Claims] 1. A liquid crystal panel, comprising: a reflection type liquid crystal panel; and a liquid crystal panel illuminating device which is laminated on the surface side of the liquid crystal panel and illuminates the liquid crystal panel from the surface side. It is composed of a substantially rectangular light guide plate made of a transparent plate having a large number of light diffusion / reflection regions, and a light source installed along at least one edge thereof, and emits light emitted from the light source on the back side of the light guide plate. The image formed on the liquid crystal panel by emitting and illuminating the reflective liquid crystal panel installed on the back side, passing the reflected light from the liquid crystal panel through the light guide plate and emitting to the surface side. A liquid crystal display device characterized by displaying. 2. A substantially rectangular light guide plate made of a transparent plate having a large number of light diffusion / reflection regions on the surface side, and a light source provided along at least one edge of the light guide plate, and emitted from the light source. And illuminating the reflective liquid crystal panel stacked on the back side by emitting light to the back side of the light guide plate,
A lighting device for a liquid crystal panel, wherein illumination light modulated by an image formed on the liquid crystal panel passes through the light guide plate and is emitted to the surface side of the light guide plate. 3. The liquid crystal panel illumination according to claim 2, wherein said light diffusion / reflection region comprises a light diffusion layer formed on the back side of said light guide plate and a light absorption layer formed on the back surface of said light diffusion layer. apparatus.