JPH10104620A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is increased in the light incidence surface area of a photoconductor and equipped with a back light whose luminance uniformity is adjustable. SOLUTION: This liquid crystal display device is equipped with the back light consisting of the photoconductor 5 made of a transparent body, a reflecting plate 4 which is installed on the reverse surface of the photoconductor, a diffusion plate 6 which is installed on the top surface of the photoconductor, and a linear light source which supplies illumination light to a liquid crystal display element 8 laminated on the diffusion plate 6 through the photoconductor 5. In this case, at least one groove 50 where the linear light source 1 is stored is provided at part of the reverse surface of the photoconductor 5 while a thin part 5' is left in the center of the top surface side of the photoconductor 5, a light transmission adjusting film 13 which cuts off part of the light from the linear light source 1 and reflects the rest to make the surface luminance of the photoconductor 5 uniform is installed on the bottom surface of the groove 50, and a reflecting plate 3 is installed on the reverse surface of the linear light source 1.

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 provided with a thin, high-luminance backlighting light source (a so-called backlight).

[0002]

2. Description of the Related Art A conventional liquid crystal display device uses a nematic liquid crystal having a positive dielectric anisotropy between two electrode substrates.
It has a helical structure that is twisted to a degree, and a polarizing plate is arranged outside both electrode substrates so that its polarization axis (or absorption axis) is orthogonal or parallel to the liquid crystal molecules adjacent to the electrode substrate. An image is displayed by controlling the transmission of light from the backlight by changing the alignment direction of the liquid crystal molecules by applying a potential difference to the electrodes and providing a potential difference to the electrodes (for example, See Japanese Patent Publication No. 51-13666).

[0003] Such a liquid crystal display element having a twist angle (α) of 90 degrees has problems in the steepness (γ) of the change in the transmittance of the liquid crystal layer with respect to the voltage applied to the liquid crystal layer and the viewing angle characteristics. ,
The number of time divisions (corresponding to the number of scanning electrodes) was 64, which was a practical limit.

However, in order to cope with recent demands for improving image quality and increasing the amount of display information for a liquid crystal display device, the twist angle α of liquid crystal molecules is set to more than 180 degrees, and the time-division driving characteristic is increased by utilizing the birefringence effect. Applied Physics Letter 45, N
o.10,1021 1984 (Applied Physics Letter, TJScheffe
r, J.Nehring: "A new, highly multiplexable liquidcrys
tal display "), and a super twisted birefringence (SBE) liquid crystal display has been proposed.

FIG. 6 is an exploded perspective view for explaining an example of the overall configuration of a liquid crystal display device to which the present invention is applied, wherein 1 is a cold cathode fluorescent lamp (CFL) as a linear light source, and 2 is a cold cathode fluorescent lamp. Power supply cable, 3 is a reflection sheet, 4 is a reflection plate, 5 is a light guide, 6 is a diffusion plate, 7 is a prism sheet, 8 is a liquid crystal display element, 9 is a lower frame, 10 is an upper frame, 11 is a printed circuit board, 12 is a drive IC mounted on a printed circuit board, 14
Is a spacer, 15 is a light shielding frame, 16 is a lamp cover, and 17 is an intermediate frame.

In FIG. 1, the structure of the backlight comprises a cold cathode fluorescent lamp 1, a reflection sheet 3, a reflection plate 4, a light guide 5, a diffusion plate 6, and a prism sheet 7.

A printed circuit board 1 is provided above the backlight.
The liquid crystal display element 8 integrated with the liquid crystal display element 1 is laminated, and the backlight and the liquid crystal display element 8 are held by the intermediate frame 17, which is sandwiched between the lower frame 9 and the upper frame 10, and together with the spacer 14 and the light shielding frame 15. The liquid crystal display device is fixed.

As described above, the backlight used in this type of liquid crystal display device includes a light guide 5 made of a transparent plate,
At least one of the reflection plate 4, the diffusion plate 6, and the light guide
A surface light source is constituted by a linear light source composed of cold cathode fluorescent lamps 1 arranged along the vicinity of one side, and the liquid crystal display element 8 is illuminated from the back.

The light guide 5 is formed of a transparent resin plate or the like, and propagates light from the cold cathode fluorescent lamp 1 from one end to the other end of the light guide 5 to form a lower surface (back surface) of the light guide. The surface is directly subjected to a rough surface or a printing process, and the reflecting plate 4 provided thereunder, the diffusing plate 6 provided on the upper surface of the light guide, and the prism sheet 7 provided as necessary provide a uniform surface light source. It illuminates the liquid crystal display element 8 stacked above the diffusion plate 6.

[0010] A reflection sheet 3 is provided around the cold cathode fluorescent lamp 1 except for a region facing the light guide 5, and the light of the cold cathode fluorescent lamp 1 is efficiently introduced into the light guide 5. It has a configuration.

FIG. 7 is a cross-sectional view of a main part for explaining in more detail the structure of a backlight part constituting a liquid crystal display device according to the prior art. Reference numeral 12 denotes a drive IC mounted on a printed circuit board. Corresponds to the same part. In addition, 2
Is a power supply cable for a cold cathode fluorescent lamp.

In FIG. 1, a cold cathode fluorescent lamp 1, a power supply cable 2, a reflection sheet 3, a reflection plate 4, a light guide 5, and a diffusion plate 6 are provided.
The backlight (light source unit) is configured by the prism sheet 7.

A liquid crystal display element 8 is stacked above the backlight, which is a light source section, and is integrated with a lower frame 9 and an upper frame 10 together with a printed circuit board 11 on which a driving IC 12 is mounted to constitute a liquid crystal display device.

The light from the cold cathode fluorescent lamp 1 propagates through the light guide 5 to uniformly illuminate the back surface of the liquid crystal display element 8 with the diffusion plate 6 and the prism sheet 7 as indicated by arrows.

[0015]

The above-mentioned conventional backlight is a so-called side-edge light source system in which a linear cold cathode fluorescent lamp 1 is installed at one end of a light guide 5, so that the liquid crystal display device has When the thickness of the light guide 5 is reduced with the increase in size and thickness, naturally, the edge area of the light guide facing the cold cathode fluorescent lamp is reduced, and the light incident area is reduced. This causes a reduction in the efficiency of use of the light emitted from the cold cathode fluorescent lamp 1 and uneven brightness.

In addition, in this side edge method, there is a limit in the reflection efficiency of the reflection sheet 3, and it is difficult to obtain a backlight having high brightness without uneven brightness over the entire area of the screen, especially in a large size.

As a measure for improving the brightness of the backlight, backlights having various structures have been conventionally proposed.

FIG. 8 is a sectional view for explaining an example of a conventional backlight, wherein 1a and 1b are first and second cold cathode fluorescent lamps, 3a and 3b are first and second reflection sheets, 5
Reference numerals a, 5b, and 5c denote first, second, and third light guide elements, and the same reference numerals correspond to the same parts.

This backlight divides the light guide into first, second and third light guide elements 5a, 5b and 5c, and interposes the first and second cold cathode fluorescent lamps 1a and 1a. 1b and the first and second reflection sheets 3a and 3b, respectively, and the light from the first and second cold-cathode fluorescent lamps 1a and 1b is introduced into the light guide elements on both sides to thereby provide the cooling. This is to improve the use efficiency of light from the cathode fluorescent lamp.

However, in this configuration, the cold cathode fluorescent lamp 1
In order to prevent the light from a and 1b from directly irradiating the liquid crystal display element, the reflection sheets 3a and 3b are provided above the cold cathode fluorescent lamp.
However, since the light guide is discontinuous, it is difficult to make the brightness uniform and obtain illumination without uneven brightness.

FIG. 9 is a sectional view for explaining another example of the conventional backlight, and the same reference numerals as those in FIG. 8 correspond to the same functional parts.

In this configuration, the first and second light guides 5a and 5b, which are divided into two, are abutted to each other, and the cold cathode fluorescent lamp 1 is stored in the abutted portion, and the cold cathode fluorescent lamp 1 is directly above the abutted portion. By forming an inclined surface in the region, uniformity of luminance is obtained.

However, in this configuration, it is difficult to control the brightness uniformity only on the inclined surface, and the manufacturing accuracy and the inclined surface of the butted portion of the first and second light guide elements 5a and 5b divided into two parts. Therefore, it is difficult to obtain a uniform brightness with good yield.

FIG. 10 is a sectional view of a principal part for explaining still another example of the conventional backlight.
The recessed portion 13 'is formed on the inner surface of the concave portion 50, and the diffusion / light transmitting / reflecting portion 13 is formed on the lower surface of the recessed portion 50.

In this configuration, the diffusion / light transmission / reflection unit 13 '
The light-shielding effect is insufficient and the luminance uniformity is insufficient, and the use of a light source having a special shape different from the above examples as the cold cathode fluorescent lamp 1 has disadvantages in terms of versatility. .

As described above, in the prior art, it has been difficult to improve the light use efficiency of the cold cathode fluorescent lamp and the uniformity of the irradiation light of the liquid crystal display element as the light guide is made thinner. .

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a liquid crystal display device having a backlight capable of increasing the light incident area of a light guide and adjusting the uniformity of luminance. It is in.

[0028]

The configuration for achieving the above object is described below with reference to the reference numerals of the embodiments.

That is, a first aspect of the present invention provides a light guide made of a transparent plate, a reflector provided on the back surface of the light guide, and a diffuser provided on the surface of the light guide. In a liquid crystal display device provided with a backlight comprising a linear light source for providing illumination light to the liquid crystal display element laminated on the diffusion plate through the light guide, a part of the back surface of the light guide 5 is provided with the light guide. At least one groove 50 for accommodating the linear light source 1 is provided in the center of the front surface side of the light body leaving a thin portion 5 ', and a part of light from the linear light source 1 is shielded on the bottom surface of the groove 50. A light-transmitting adjustment film 13 for reflecting a part of the light-guiding member 5 to make the surface brightness uniform, and a reflecting plate 3 on the lower surface of the linear light source 1. .

In this configuration, the light from the linear light source 1 directly enters the light guide 5 on both sides in the longitudinal direction, so that the light use efficiency is improved.

Then, uniform brightness can be obtained in the entire area of the light guide on the liquid crystal display element side by the action of adjusting the uneven brightness by the light shielding / reflecting portion 13 provided above the linear light source 1.

In a second aspect of the present invention, there is provided a light guide made of a transparent plate, a reflection plate provided on a back surface of the light guide, and a diffusion plate provided on a surface of the light guide. In a liquid crystal display device provided with a backlight comprising a linear light source for providing illumination light via the light guide to a liquid crystal display element laminated on a diffusion plate, the light guide 5 is replaced by at least two light guide elements 5.
a, 5b, and 5c, the linear light sources 1a and 1b are respectively accommodated between the divided light guide elements, and a transparent body 5 is provided above the linear light sources 1a and 1b on the liquid crystal display element side.
e, 5d, respectively, and the transparent bodies 5e, 5d
On the lower surfaces of the linear light sources 1a and 1b on the side of d, a part of the light from the linear light source 1 is shielded, and a part of the light is reflected to reflect light to adjust the surface luminance of the light guide 5 to be uniform. It is characterized in that the films 13a and 13b are provided, respectively, and the reflector 3 is provided on the lower surface of each of the linear light sources 1a and 1b.

The above-mentioned transparent members 5e and 5d correspond to the light guide element 5
Although it is preferable to use the same material as the a, 5b, and 5c, it may be formed of another material as long as the material is the same.

Also in this configuration, each linear light source 1a, 1
b from the light guide element 5 on both sides in the longitudinal direction.
Since the light is incident on a, 5b and 5b, 5c, the light use efficiency is improved.

The uniform brightness is obtained over the entire area of the light guide on the liquid crystal display element side by the action of adjusting the uneven brightness by the light transmission adjusting films 13a and 13b provided above the linear light sources 1a and 1b.

Further, the third invention according to claim 3 is as follows.
In the first or second invention, the light-transmitting adjustment film 13 (1
3a, 13b), the thin portion 5 '(5'a, 5'b) or the transparent body 5 in the density distribution of a thin film of silver, aluminum or white paint or a halftone dot pattern or a fine line pattern.
e and 5d are formed so that the luminance of the surface of the liquid crystal display element side is uniform with the entire surface of the light guide.

The bottom surface of the groove 50 in the first invention may be a flat surface or a concave surface curved in a direction perpendicular to the longitudinal direction of the linear light source, or a cross section having an angle at the longitudinal center of the bottom surface. Can have a pentagonal shape,
The light transmission adjusting film 13 may be provided so as to follow each of the bottom surfaces.

Further, the above-mentioned light transmission adjusting film may be such that a film-like member in which a thin film of aluminum or silver or a halftone dot pattern or a thin line pattern of a white paint is formed on a transparent thin plate is provided above the linear light source. is there.

As the linear light source, a so-called cold-cathode fluorescent lamp is generally used. However, any other light source that irradiates the light guide along the side edge of the light guide may be used. It is also possible to use a type of light source.

As described above, according to the present invention, it is possible to improve the brightness of the backlight and to eliminate the uneven brightness which is a problem due to the thinning / large size of the light guide accompanying the thinning and size increase of the liquid crystal display device. Thus, a liquid crystal display device capable of displaying a high quality image can be obtained.

[0041]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1A and 1B are cross-sectional views of a main part of a liquid crystal display device according to a first embodiment of the present invention, in which FIG. 1A is a perspective view, and FIG. It is sectional drawing along.

In the figure, 1 is a cold cathode fluorescent lamp as a linear light source, 3 is a reflection sheet, 4, 4, and 4b are reflection plates, 5
Is a light guide made of an acrylic plate, 5 'is a thin portion, 6 is a diffusion plate, 8 is a liquid crystal display element, 13 is a light transmission adjusting film, and 50 is a groove. On the lower surface of the light guide 5 excluding the groove 50, a rough surface or a printed dot 5 ″ is provided directly for reflecting light to the upper surface of the light guide.

A groove 50 is formed in the lower part of the center of the light guide 5 in a direction parallel to the side of the light guide, and the cold cathode fluorescent lamp 1 is accommodated in the groove 50.

The groove 50 has a rectangular cross section with an open lower portion, and the inner wall in a direction perpendicular to the surface of the light guide 5 is substantially 90 degrees with respect to the surface of the light guide 5. The bottom surface of the groove 50 is formed leaving a thin portion 5 ′ on the liquid crystal display element side of the light guide 5, and the bottom surface is formed of any one of a halftone dot pattern or a fine line pattern by vapor deposition of aluminum or application of a white paint. Is formed.

The cold cathode fluorescent lamp 1 using the light transmission adjusting film 13
The amount of light transmitted from the thin film, the halftone dot pattern or the fine line pattern is controlled such that the luminance distribution over the entire surface of the light guide 5 on the liquid crystal display element side is uniform and no luminance unevenness occurs. It is set by adjusting the amount of reflection.

A reflector 4 is provided on the entire lower surface of the light guide 5, and a silver reflective sheet 3 for reflecting light of the cold cathode fluorescent lamp 1 is provided below the cold cathode fluorescent lamp 1. However, in order to improve workability, a slight decrease in reflectance is recognized, and the reflection plate 4 can be used instead.

Further, reflectors 4a and 4b are provided at the longitudinal and lateral edges of the cold cathode fluorescent lamp 1 of the light guide 5, respectively.

According to this embodiment, it is possible to obtain a high-brightness liquid crystal display device in which the brightness is uniform over the entire surface and the light use efficiency of the cold cathode fluorescent lamp is improved.

FIG. 2 is a sectional view of a main portion of a backlight portion for explaining the structure of a liquid crystal display device according to a second embodiment of the present invention, wherein 1a and 1b are cold cathode fluorescent lamps, 3a and 3b are reflection sheets, 5'a and 5'b are thin portions, 13a and 13b are light transmission adjusting portions, 50a and 50b are grooves, and the same reference numerals as those in FIG. 1 correspond to the same portions.

In this embodiment, except that the grooves formed in the light guide 5 are two parallel grooves 50a and 50b.
This is the same as the embodiment.

The use of a plurality of cold cathode fluorescent lamps as in this embodiment is particularly effective when the size of the liquid crystal display device is increased. In the figure, two cold cathode fluorescent lamps are used. Can also be increased.

According to this embodiment as well, a high-brightness liquid crystal display device having uniform brightness over the entire surface and improved light use efficiency of the cold cathode fluorescent lamp can be obtained.

FIG. 3 is a sectional view of a principal part for explaining the structure of a liquid crystal display device according to a third embodiment of the present invention.
c is a groove, and the same reference numerals as those in FIGS. 1 and 2 correspond to the same functional parts. This embodiment has the same configuration as that of the above embodiment except that the shape of the groove in each of the above embodiments is a cross section whose bottom has a concave shape on the cold cathode fluorescent lamp 1 side.

The amount of light transmitted from the cold cathode fluorescent lamp 1 toward the liquid crystal display element by the light transmission adjusting film 13 is such that the luminance distribution over the entire surface of the light guide 5 on the liquid crystal display element side is uniform and luminance unevenness does not occur. The adjustment of the amount of light shielding or the amount of reflection of the thin film, halftone dot pattern or fine line pattern is the same as in the above embodiments.

According to this embodiment as well, a high-brightness liquid crystal display device having uniform brightness over the entire surface and improved light use efficiency of the cold cathode fluorescent lamp can be obtained.

FIG. 4 is a sectional view of a principal part for explaining the structure of a fourth embodiment of the liquid crystal display device according to the present invention. Reference numeral 50c denotes a groove, and the same reference numerals as those in FIGS.

This embodiment has the same configuration as the above embodiment except that the cross section of the groove in each of the above embodiments is a pentagon.

The amount of light transmitted from the cold cathode fluorescent lamp 1 toward the liquid crystal display element by the light transmission adjusting film 13 is such that the luminance distribution over the entire surface of the light guide 5 on the liquid crystal display element side is uniform and luminance unevenness does not occur. The adjustment of the amount of light shielding or the amount of reflection of the thin film, halftone dot pattern or fine line pattern is the same as in the above embodiments.

According to this embodiment, a high-brightness liquid crystal display device having uniform brightness over the entire surface and improved light use efficiency of the cold cathode fluorescent lamp can be obtained.

FIG. 5 is a sectional view of a principal part for explaining the structure of a liquid crystal display device according to a fifth embodiment of the present invention. In FIG. 5, reference numerals 5a, 5b and 5c denote light guides. Elements 5d and 5e are transparent plates.

In FIG. 10, only the backlight portion is shown, and the reflection plate, the diffusion plate, and the liquid crystal display device are not shown.

In this embodiment, the light guide itself is replaced by the light guide elements 5a, 5a instead of the grooves in the above embodiments.
b, 5c, and has the same function as the thin portion in the above-described embodiment, with transparent bodies 5d and 5e having the same thickness as the thin portion in the above-described embodiment interposed between the light guide elements. It is.

Note that the transparent members 5d and 5e are
It is preferable to use the same transparent material as a, 5b, and 5c.

The cold cathode fluorescent lamp 1 is placed in a recess formed by the light guide elements 5a, 5b, 5c and the transparent bodies 5d, 5e.
a, 1b, and the same translucent adjusting films 13a, 13b as those in the above embodiment are provided on the lower surfaces of the transparent bodies 5d, 5e, that is, on the cold cathode fluorescent lamps 1a, 1b side.

According to the present embodiment, a high-brightness liquid crystal display device having uniform brightness over the entire surface and improved light use efficiency of the cold cathode fluorescent lamp can be obtained.

As described above, according to the configuration of the liquid crystal display device of each of the above-described embodiments, the efficiency of using the light emitted from the cold cathode fluorescent lamp constituting the backlight is improved, and the liquid crystal display device is reduced in thickness and size. The present invention is particularly effective when applied to a display device, and a so-called frame can be narrowed to enlarge a display screen area.

[0068]

As described above, according to the present invention,
Provided is a liquid crystal display device capable of efficiently introducing light emitted from a cold cathode fluorescent lamp constituting a backlight into a light guide, and obtaining a high-quality image display that is bright over the entire screen and has no uneven brightness. Can be.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a principal part explaining a structure of a first embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a main part plan view for explaining the structure of a second embodiment of the liquid crystal display device according to the present invention.

FIG. 3 is a main part plan view for explaining the structure of a third embodiment of the liquid crystal display device according to the present invention.

FIG. 4 is a main part plan view for explaining the structure of a fourth embodiment of the liquid crystal display device according to the present invention.

FIG. 5 is a main part plan view for explaining the structure of a fourth embodiment of the liquid crystal display device according to the present invention.

FIG. 6 is a developed perspective view illustrating an example of the overall configuration of a liquid crystal display device to which the present invention is applied.

FIG. 7 is a cross-sectional view of a principal part for further describing in detail the structure of a backlight portion constituting a liquid crystal display device according to the related art.

FIG. 8 is a cross-sectional view illustrating an example of a conventional backlight.

FIG. 9 is a cross-sectional view illustrating another example of a conventional backlight.

FIG. 10 is a cross-sectional view of a main part illustrating still another example of a conventional backlight.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cold cathode fluorescent lamp (CFL) 3, 3a, 3b Reflective sheet 4, 4a, 4b Reflector 5 Light guide 5 'Thin part 5 "Print dot 5a, 5b, 5c Light guide element 5d, 5e Transparent 6 Diffusion Plate 8 Liquid crystal display element 13, 13a, 13b Light transmission adjusting film 50, 50a, 50b Groove.

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[Procedure amendment]

[Submission date] September 17, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

[0041]

Embodiments of the present invention will be described below.
This will be described with reference to an example.

【Example】

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction contents]

In the figure, 1 is a cold cathode fluorescent lamp as a linear light source, 3 is a reflection sheet, 4, 4a and 4b are reflection plates,
5 is a light guide made of an acrylic plate, 5 'is a thin portion, 6 is a diffusion plate, 8 is a liquid crystal display element, 13 is a light transmission adjusting film, and 50 is a groove. On the lower surface side of the light guide 5 excluding the groove 50, a rough surface or a printed dot 5 ″ is provided directly for reflecting light to the upper surface of the light guide.

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (3)

[Claims] A light guide made of a transparent plate, a reflection plate provided on a back surface of the light guide, and a diffusion plate provided on a surface of the light guide.
In a liquid crystal display device provided with a backlight comprising a linear light source for providing illumination light to the liquid crystal display element laminated on the diffusion plate via the light guide, a part of the back surface of the light guide includes the light guide. At least one groove for accommodating the linear light source is provided in the center of the front side of the body while leaving a thin portion, and a part of light from the linear light source is shielded and a part is reflected on a bottom surface of the groove. A liquid crystal display device provided with a light transmission adjusting film for equalizing the surface luminance of the light guide. 2. A light guide comprising a transparent plate, a reflector provided on a back surface of the light guide, and a diffuser provided on a surface of the light guide.
In a liquid crystal display device provided with a backlight comprising a linear light source that provides illumination light via the light guide to a liquid crystal display element stacked on a diffusion plate, the light guide is divided into at least two light guide elements. The linear light source is accommodated between the divided light guide elements, and a transparent body is disposed above the liquid crystal display element side of each linear light source. On the lower surface of the light guide, there is provided a light transmission adjusting film for blocking a part of the light from the linear light source and reflecting a part thereof to equalize the surface luminance of the light guide. Liquid crystal display. 3. The liquid crystal display element according to claim 1, wherein the light-transmissive adjusting film is a thin film of silver, aluminum, or white paint, or the thin portion in a halftone pattern or a fine line pattern density distribution, or the transparent body. A liquid crystal display device formed so that the brightness of the side surface is uniform with the entire surface of the light guide.