JPH11125818A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device with a back light structure capable of increasing the luminance of a large-sized liquid crystal display device and capable of reducing the weight of the display device. SOLUTION: The device is provided with a liquid crystal panel 30 which is constituted by holding liquid crystal layer 2 between a pair of transparent substrates 3a and 3b which are arranged opposite to each other and at least one of which is provided with a pixel selecting electrode, a pair of polarizing plates 1a and 1b arranged on the front and rear sides of the interposed liquid crystal panel 30, a driving means for impressing a voltage corresponding to a display signal on the aforesaid electrode, and the back light 10 installed on the rear side of the liquid crystal panel, and the back light 10 is constituted of a nultilayered structure where plural light guide plates 20, 21a, 21b and 22 are laminated in the thickness direction, and the uppermost-layered light guide plate 20 positioned on the panel 30 side is a signal plate, and at least one light transmission plate positioned under the uppermost plate 20 is a composite light transmission plate with is constituted by joining plural light guide plates 21a and 21b together in a plane direction so as to form one layer, and the back light 10 is provided with linear light sources 8a, 8b, 8c and 8d along the opposed side edges of the multilayered light guide plate.

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 having a backlight that uniformly illuminates the entire display area of a large-screen-size liquid crystal panel and reduces the weight of the device. .

[0002]

2. Description of the Related Art A high-definition and color display liquid crystal display device for a notebook computer or a computer monitor is provided with a light source (so-called backlight) for illuminating a liquid crystal panel from behind. As the backlight, there are known a side edge type in which a linear lamp is arranged on a side surface of a transparent plate formed of an acrylic resin or the like called a light guide plate, and a direct type in which a lamp is arranged just below the back of a liquid crystal panel. I have.

In particular, a notebook-type computer which requires a thinner type employs a side-edge method, and a liquid crystal display device for a monitor also uses a side-edge method to reduce the depth.

This type of liquid crystal display device basically forms a so-called liquid crystal panel in which a liquid crystal layer is sandwiched between two substrates at least one of which is made of transparent glass or the like, and is formed on the liquid crystal panel substrate. A method of selectively applying a voltage to the various electrodes for forming a pixel to turn on and off a predetermined pixel, forming the various electrodes and an active element for pixel selection, and selecting the active element to form a predetermined pixel. Are turned on and off.

[0005] The latter type of liquid crystal display device is called an active matrix type, and is the mainstream of the liquid crystal display device because of its contrast performance, high-speed display performance and the like. A conventional active matrix type liquid crystal display device employs a so-called vertical electric field method in which an electric field for changing the orientation direction of a liquid crystal layer is applied between an electrode formed on one substrate and an electrode formed on the other substrate. I was

In recent years, a so-called lateral electric field method (I
A liquid crystal display device of the PS type is also realized. As this in-plane switching mode liquid crystal display device, a device in which a very wide viewing angle is obtained by using a comb electrode on one of two substrates is known (Japanese Patent Publication No. 63-21907,
U.S. Pat. No. 4,345,249).

[0007]

The size of a liquid crystal display device for a computer monitor of various information processing apparatuses is increasing year by year, not limited to a notebook type computer, and the size of a backlight is also increasing accordingly. Also,
There is also a strong demand for higher brightness, and a brighter (stronger) backlight is needed.

Further, the side edge method requires a light guide plate formed of a relatively thick transparent plate such as an acrylic plate, so that the weight increases as the size increases, and it is difficult to reduce the weight. there were.

Further, it is necessary to increase the number of lamps in order to cope with higher brightness of the liquid crystal panel.

In the case of the side-edge type, the thickness and weight of the light guide plate for introducing the increased light emitted from the lamp (linear light source) are increased. In the case of the direct type backlight, the thickness of the entire liquid crystal display device is increased. Is a problem.

FIG. 9 is a schematic view for explaining a schematic configuration of a conventional high-luminance side-edge type backlight, and includes a light guide plate 23 and a linear light source (cold cathode fluorescent lamp) 8a installed along two sides thereof. , 8b, reflectors 7a, 7b for increasing the efficiency of light emission of the linear light sources 8a, 8b, the diffusion film 4 installed on the upper surface (the liquid crystal panel side) of the light guide plate 23, and the reflector 9 installed on the lower surface. Be composed. Although a prism sheet and the like are arranged on the diffusion film, illustration is omitted.

In this configuration, since the linear light sources 8a and 8b are arranged on the two sides of the light guide plate 23, brighter illumination light can be obtained as compared with the case where only one linear light source is used. But,
As described above, merely increasing the number of light sources has a limit in improving luminance.

FIG. 10 is a schematic diagram for explaining another schematic configuration of a conventional high brightness side edge type backlight.

In this configuration, the backlight described with reference to FIG. 9 is double-hung. With this configuration, high brightness can be achieved, but since another light guide plate 24 is used in addition to the light guide plate 23, the weight and thickness are considerably increased.

FIG. 11 is a schematic diagram for explaining still another schematic configuration of a conventional high brightness side edge type backlight.

In this configuration, in order to reduce the weight of the light guide plate, the two light guide plates 21a and 21b are joined together on the same plane, and the cross sections of the respective light guide plates 21a and 21b are joined to form a wedge shape toward the center. As shown in FIG.

The diffusion film 4 is disposed on the upper layer (the liquid crystal panel side) of the light guide plates 21a and 21b.
Although the light reflection patterns 21aA and 21bA are formed on the lower surface of 1b, it is difficult to sufficiently reduce the luminance drop at the joint, and it is difficult to make the distribution of the illumination light uniform.

An object of the present invention is to provide a liquid crystal display device having a backlight structure capable of increasing the brightness and reducing the weight of a large size liquid crystal display device.

[0019]

In order to achieve the above object, the present invention is characterized by the following constitution.

(1) A liquid crystal panel having a liquid crystal layer sandwiched between a pair of transparent substrates having a pixel selection electrode on at least one of them opposed to each other, and a pair of liquid crystal panels arranged on both sides of the liquid crystal panel. A polarizing plate, driving means for applying a voltage corresponding to a display signal to the electrodes, and a backlight installed on the back surface of the liquid crystal panel, wherein the backlight has a plurality of light guides in a thickness direction. The uppermost light guide plate located on the side of the liquid crystal panel is a single plate, and at least one lower light guide plate is connected to a plurality of light guide plates in a plane direction to form a single layer. And a linear light source disposed along opposing side edges of the light guide plate.

(2) The cross section of the composite light guide plate in (1) has a substantially wedge shape whose thickness gradually decreases toward the center.

(3) A light reflection pattern is provided on at least one back surface of the plurality of light guide plates in (1) or (2).

The side edge type backlight of a large-sized liquid crystal display device requires a thick light guide plate to obtain high luminance. The light guide plate is generally made of a highly transparent acrylic resin, and the weight increases due to the increase in area and thickness in accordance with the size of the liquid crystal panel.

According to the present invention, as described above, a plurality of light guide plates are stacked, a plurality of intermediate light guide plates are connected, and a space (hollow portion) is formed with a wedge-shaped cross section. To reduce weight. In addition, discontinuity of illumination distribution due to multiple joints is eliminated by using a single light guide plate on the upper layer and by providing a light reflection pattern on the back surface of the light guide plate and uniforming over the entire screen. A backlight having an optimal distribution can be configured.

In the liquid crystal display device, the transmission / non-transmission of the illumination light from the backlight is controlled by the change in the voltage applied to the liquid crystal layer to change from white display to black display or from black display to white display. . The present invention relates to a twisted nematic (TN type) liquid crystal having a twist angle of about 90 degrees, and a twist angle of 20 degrees.
Super twisted nematic of 0 to 260 degrees (S
(TN type) Liquid crystal display device using liquid crystal, vertical alignment type (vertical electric field type) TFT, horizontal electric field type liquid crystal display device operated by electric field parallel to substrate surface, and other types of liquid crystal display devices Can also be applied.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples.

[Embodiment 1] FIG. 1 is a schematic sectional view for explaining a first embodiment of a liquid crystal display device according to the present invention.
Is a lower polarizing plate, 1b is an upper polarizing plate, 2 is a liquid crystal layer, 3a is a lower substrate, 3b is an upper substrate, 4 is a light diffusion film, 5 is a prism sheet, 6 is a light diffusion film, 7a and 7b are reflectors, 8
Reference numerals a, 8b, 8c, and 8d denote linear light sources (lamp: cold cathode fluorescent lamp), 9 is a reflector, 10 is a backlight, 11 is a hollow portion, 20 is a first layer light guide plate, and 21a and 21b are intermediate layer guides. A light plate, 22 is a lower light guide plate, 20A and 22A are light reflection patterns, and 30 is a liquid crystal panel.

When the liquid crystal display device is of the TN type or vertical alignment type vertical electric field type, the product Δn · d of the refractive index anisotropy Δn of the liquid crystal layer 2 and the cell gap (gap between the upper and lower substrates) is 0. The range of 0.2 to 0.6 μm is preferable in order to achieve both the contrast ratio and the brightness.
A range of 5 to 1.2 μm is preferable, and a range of 0.2 to 0.5 μm is preferable in the horizontal electric field method.

Here, as the upper and lower substrates 3b and 3a,
Two glass substrates each having a thickness of 0.7 mm, a surface polished, and a transparent electrode of ITO (indium tin oxide) formed by a sputtering method are used. The dielectric anisotropy Δnε between these upper and lower substrates 3b and 3a is positive, the value is 4.5, and the birefringence Δn is 0.19 (589 nm, 20 ° C.).
And a cell gap of 6 μm
Therefore, Δn · d was 1.41 μm.

Then, the polyimide-based orientation control film applied to the substrate surface was applied by a spinner, baked at 250 ° C. for 30 minutes, and rubbed to form a pretilt angle of 3.5 degrees. The pretilt angle was measured by a rotating crystal method. The rubbing directions of the upper and lower substrates were set such that the twist angle (twist angle) of the liquid crystal molecules was 240 degrees in order to perform time-division driving. Here, the twist angle is defined by the rubbing direction and the type and amount of the optical rotatory substance added to the nematic liquid crystal.

The maximum value of the torsion angle is limited because the lighting state near the threshold value is an orientation that scatters light, the upper limit is 260 degrees, the lower limit is limited by contrast, and the lower limit is 200 degrees.

The purpose of this embodiment is to provide a liquid crystal display device capable of displaying black and white with sufficient contrast even when the number of scanning lines is 200 or more. Further, the lower substrate 3a, the upper substrate 3b, and the polarizing plates 1a and 1
Δn · d = 0.4 made of polycarbonate during b
One μm retardation film was disposed on each sheet (not shown).

The backlight 10 of this embodiment has a multilayer structure in which a first-layer light guide plate 20, intermediate-layer light guide plates 21a and 21b, and a lower-layer light guide plate 22 are laminated.

A linear light source (cold cathode fluorescent lamp) 8 is provided on two opposite sides of the multi-layered light guide plate of the backlight 10.
a, 8c and 8b, 8d, and reflectors 7a, 7b. Further, a reflection plate 9 is provided at the lowermost portion to improve light use efficiency.

Illumination light from the backlight 10 passes through the diffusion film 6 → the prism sheet 5 → the diffusion film 4 to illuminate the back of the liquid crystal panel 30. The illumination light is modulated and emitted so as to form an image on the upper surface of the liquid crystal panel according to the lighting and non-lighting of the pixels constituting the liquid crystal panel.

FIG. 2 is a perspective view illustrating the structure of the light guide plate portion of the backlight in FIG.

As shown, the multi-layer light guide plate constituting the backlight comprises a first layer light guide plate 20 and two intermediate layer light guide plates 2.
1a, 21b and the lower light guide plate 22. The first layer light guide plate 20 is a single plate having a uniform thickness, the lower intermediate light guide plates 21a and 21b are connected in a plane direction to form a single layer, and the lower light guide plate 22 is formed of the first layer light guide plate 20. It is the same veneer. Each of the intermediate-layer light guide plates 21a and 21b has a wedge-shaped cross section whose thickness gradually decreases toward the joint portion (center portion).

Therefore, as shown in FIG. 1, the multilayer light guide plate is composed of the intermediate light guide plates 21a and 21b and the lower light guide plate 2a.
2 has a hollow portion 11, and the weight is reduced accordingly.

The discontinuity of the illumination light distribution due to the joint of the intermediate light guide plates 21a and 21b can be reduced by using a single light guide plate for the upper layer and by using the first light guide plate 20 and the lower light guide plate. 22 can be eliminated by providing a light reflection pattern formed by wedge shape processing, ink printing, or the like on at least the back surface of the first layer light guide plate 20, and illumination light having a uniform distribution over the entire screen can be given to the liquid crystal panel. . Also, a light reflection pattern may be provided on the back surfaces of the second-layer light guide plates 21a and 21b.

According to the present embodiment, the discontinuity of the illumination light distribution at the joint between the intermediate layer light guide plates 21a and 21b is eliminated, and the back of the large-sized liquid crystal display device can achieve high luminance and light weight. A liquid crystal display device having a light structure can be provided.

[Embodiment 2] FIG. 3 is a perspective view for explaining a structure of a light guide plate portion of a backlight for explaining a second embodiment of the liquid crystal display device according to the present invention.

In this embodiment, the intermediate light guide plates 21a and 21a
2 is the same as that of the first embodiment except that the wedge shape b is formed on the surface opposite to that of FIG. 2, that is, on the surface facing the first layer light guide plate 20.

Similarly, in this embodiment, the discontinuity of the illumination light distribution at the joint between the intermediate light guide plates 21a and 21b can be eliminated, so that a large-sized liquid crystal display device can have high luminance and light weight. A liquid crystal display device having a backlight structure can be provided.

[Embodiment 3] FIG. 4 is a perspective view for explaining a structure of a light guide plate portion of a backlight for explaining a third embodiment of the liquid crystal display device according to the present invention.

In this embodiment, four intermediate light guide plates 21
a, 21b, 21c, and 21d are connected to the same plane, and their wedge shapes are the same as those in FIG. However, in this case, the joint is vertical and horizontal cross-shaped.

The intermediate layer light guide plates 21a, 21b, 21
The discontinuity of the illumination distribution due to the joint between c and 21d can also be reduced by using a single plate as the upper layer light guide plate and at least the first layer light guide plate 20 of the first layer light guide plate 20 and the lower layer light guide plate 22.
Can be resolved by providing a light reflection pattern on the back of
Illumination light having a uniform distribution over the entire screen can be given to the liquid crystal panel.

Similarly, in this embodiment, the discontinuity of the illumination light distribution at the joint between the intermediate layer light guide plates 21a and 21b, 24c and 24d is eliminated, so that a large-sized liquid crystal display device has high luminance and weight. A liquid crystal display device having a backlight structure that can be reduced can be provided.

[Embodiment 4] The embodiment 4 is similar to the embodiment 4 shown in FIG.
Same as the third embodiment except that the wedge-shaped surfaces of the intermediate light guide plates 21a, 21b, 21c, and 21d are surfaces in the same direction as the first embodiment (the surface opposite to the liquid crystal panel). It is.

Similarly, in this embodiment, the discontinuity of the illumination light distribution at the joint of the intermediate light guide plates 21a, 21b, 24c and 24d is eliminated, and the brightness and weight of a large-sized liquid crystal display device are increased. A liquid crystal display device having a backlight structure that can be reduced can be provided.

[Embodiment 5] FIG. 5 is a perspective view illustrating the structure of a light guide plate portion of a backlight for explaining a fourth embodiment of the liquid crystal display device according to the present invention.

In this embodiment, two lower light guide plates 25a and 25b connected to the same plane as the upper light guide plate 24 of the single plate are used.
And a lower light guide plate 25a, 25
The lower surfaces of the lower light guide plate 2 and the lower light guide plate 2a are linear light sources 8a arranged along two sides.
Those that are incident on 5a and 25b were used. Further, a light reflection pattern is formed on a surface on the lower light guide plate side of the upper light guide plate 24.

With this configuration, the intermediate layer light guide plate 25
It is possible to provide a liquid crystal display device having a backlight structure in which discontinuity of the illumination light distribution at the joint between a and 25b is eliminated, and high-luminance and weight reduction of a large-sized liquid crystal display device can be achieved.

[Embodiment 6] FIG. 6 is a perspective view for explaining the structure of a light guide plate portion of a backlight for explaining a liquid crystal display device according to a fifth embodiment of the present invention.

In this embodiment, the light guide plates 25a, 25
The fourth embodiment is the same as the fourth embodiment except that the wedge-shaped surface b is directed toward the liquid crystal panel (upper light guide plate) and the light reflection pattern is formed on the back surface of the intermediate light guide plates 25a and 25b.

With this configuration, the intermediate layer light guide plate 25
It is possible to provide a liquid crystal display device having a backlight structure in which discontinuity of the illumination light distribution at the joint between a and 25b is eliminated, and high-luminance and weight reduction of a large-sized liquid crystal display device can be achieved.

The light reflection pattern in each of the above embodiments can be formed by dot printing, depressions, slit-like grooves, wedge-shaped grooves, or any other shape having a light reflection function.

In each of the above embodiments, a plurality of light guide plates are connected to form an intermediate layer or a lower layer light guide plate. However, a light guide plate which is continuous and integrated at the joint may be used.

FIG. 7 is an exploded perspective view for explaining a schematic overall structure of a liquid crystal display device constituting the liquid crystal display device of the present invention.

The liquid crystal display element is a so-called module in which a backlight, a drive circuit, other mechanical parts and the like are incorporated in a liquid crystal panel.

Reference numeral 30 denotes a liquid crystal panel, 31 denotes an upper frame (shield case), 32, 33, and 34 denote substrates for mounting a driving IC, 35 denotes an inverter substrate for driving a light source (cold cathode fluorescent lamp), and 40 denotes a lower frame (lower side). Case), the same reference numerals as in FIG. 1 indicate the same functional parts.

That is, the driving IC mounting substrates 32, 33,
The backlight 10 is disposed on the back surface of the liquid crystal panel 30 in which the LCD panel 34 is integrated, and is sandwiched and fixed between the upper frame 31 and the lower frame 30.

FIG. 8 is an external view of a desktop monitor using the liquid crystal display device of the present invention. The monitor has a structure in which a main body 50 is supported by a stand 60, and has a thin, lightweight monitor having a large-screen liquid crystal panel 30. It is.

It is needless to say that the liquid crystal display device according to the present invention can be used not only for the above-mentioned desktop monitor but also for a display device of a portable personal computer such as a notebook type.

[0064]

As described above, according to the present invention,
By forming a side edge type backlight with a multilayer structure and forming a hollow portion in the light guide plate, a large-sized, high-brightness, and lightweight liquid crystal display device can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a perspective view illustrating a configuration of a light guide plate portion of the backlight in FIG.

FIG. 3 is a perspective view illustrating a configuration of a light guide plate portion of a backlight explaining a second embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a perspective view illustrating a configuration of a light guide plate portion of a backlight for explaining a third embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a perspective view illustrating a configuration of a light guide plate portion of a backlight for explaining a fourth embodiment of the liquid crystal display device according to the present invention.

FIG. 6 is a perspective view illustrating a configuration of a light guide plate portion of a backlight explaining a fifth embodiment of the liquid crystal display device according to the present invention.

FIG. 7 is an exploded perspective view illustrating a schematic overall structure of a liquid crystal display element constituting the liquid crystal display device of the present invention.

FIG. 8 is an external view of a desktop monitor using the liquid crystal display device of the present invention.

FIG. 9 is a schematic diagram illustrating a schematic configuration of a conventional high-luminance side-edge type backlight.

FIG. 10 is a schematic diagram illustrating another schematic configuration of a conventional high-luminance side-edge type backlight.

FIG. 11 is a schematic diagram illustrating still another schematic configuration of a conventional high-luminance side edge type backlight.

[Explanation of symbols]

1a Lower polarizing plate 1b Upper polarizing plate 2 Liquid crystal layer 3a Lower substrate 3b Upper substrate 4 Light diffusion film 5 Prism sheet 6 Light diffusion film 7a, 7b Reflector 8a, 8b, 8c, 8d Linear light source (lamp: cold cathode fluorescent lamp) 9) Reflector 10 Backlight 11 Hollow 20 First layer light guide 21a, 21b Intermediate light guide 22 Lower light guide 20A, 22A Light reflection pattern 30 Liquid crystal panel.

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[Procedure amendment]

[Submission date] September 21, 1998

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (3)

[Claims] 1. A liquid crystal panel having a liquid crystal layer sandwiched between a pair of transparent substrates having a pixel selection electrode on at least one of them opposed to each other, and a pair of liquid crystal panels arranged on both sides of the liquid crystal panel. In a liquid crystal display device comprising: a polarizing plate; a driving unit for applying a voltage according to a display signal to the electrode; and a backlight installed on a back surface of the liquid crystal panel, wherein the backlight is arranged in a thickness direction. It has a multilayer structure in which a plurality of light guide plates are stacked, and the uppermost light guide plate located on the side of the liquid crystal panel is a single plate, and at least one lower light guide plate is connected to the plurality of light guide plates in a plane direction. A liquid crystal display device, comprising: a composite light guide plate having a single layer, and a linear light source disposed along opposing side edges of the light guide plate. 2. The composite light guide plate according to claim 1, wherein a cross section of the composite light guide plate has a substantially wedge shape whose thickness gradually decreases toward the center.
3. The liquid crystal display device according to 1. 3. The liquid crystal display device according to claim 1, wherein a light reflection pattern is provided on at least one back surface of the plurality of light guide plates.