JP2000010095A - Backlight unit and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a bending phenomenon of a prism sheet and a diffusion sheet linked with surrounding environment such as temp., humidity which causes luminance unevenness, deterioration of display quality or the like of a backlight unit or a liquid crystal display and to drastically improve luminance unevenness and display quality by locating a diffusion sheet (or a diffusion plate) or a transparent plate which is thicker than other sheets on the uppermost part of each of backlight units consisting of an edge light mode or a direct mode. SOLUTION: A dot pattern for uniformizing light is formed on a rear side of a light guide plate 1 and a reflection sheet 2 is located on the plane. A diffusion sheet 3 and one or more prism sheets 4 are successively laminatingly located on a surface side (a light-emitting surface side) of the light guide plate 1 besides a diffusion sheet (a diffusion plate) 5 with >=0.2 mm thickness is located on the prism sheets 4 covering their full surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit used for a transmission type display device and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Conventionally, in a display device for information equipment such as a laptop type or notebook type word processor or a personal computer, a lightweight and lightweight device has been used.
Liquid crystal display devices are frequently used by taking advantage of features such as thinness and low power consumption.

In recent years, with the colorization of such a liquid crystal display device, a backlight unit for illuminating a display area of a liquid crystal panel from the back thereof has been almost built in.

[0004] The backlight units are roughly classified into a direct type using a uniformizing means such as a lighting curtain and an edge light type using a light guide plate. 2. Description of the Related Art With the spread of word processors and personal computers of the type, most of illumination units used for them are of edge light type.

FIG. 4 shows a sectional view of a conventional edge light type lighting unit. In this edge light type illumination unit, in order to effectively use the light emitted from the fluorescent lamp, the reflection sheet (or the reflection plate) is formed on the back surface of the light guide plate 21 having a uniform shape and the same shape as the outer shape of the light guide plate. ) 22
Is disposed, and at least one or more diffusion sheets 23 and at least one or more prism sheets are provided on the front side emission light surface of the light guide plate 21 to increase the brightness. Further, a diffusion sheet 25 is disposed on the upper part. A fluorescent lamp 26 is wrapped and held by a lamp reflector 27 on the side surface of the light guide plate 21. The above members are configured to be incorporated and held in a resin frame (housing) 28.

[0006]

Recently, there has been a growing demand from personal computer users for a liquid crystal display device, and a demand for higher brightness as well as higher density and larger display screens has been increasing. That is, a liquid crystal monitor which has a display area of 13 inches or more, which can replace a CRT monitor conventionally used in a desktop personal computer, and which can obtain the same brightness as a CRT has been demanded. However, when trying to obtain high brightness equivalent to a CRT with such a large-screen liquid crystal display device,
In addition to increasing the number of fluorescent lamps used for the backlight unit, it is essential to use a prism sheet or a polarization separation sheet.

However, a film sheet such as a prism sheet, a modified separation sheet or a diffusion sheet has a thickness of 0.1 m.
The sheet has a thickness of m to 0.2 mm. As the screen size increases, the sheet is likely to be distorted or deformed. Furthermore,
As the number of lamps increases for higher brightness, heat generation also increases, and a bending phenomenon due to heat is observed even in a normal use state. The present invention solves the above-described problems, and can solve problems such as uneven brightness or reduced display quality due to the above-described phenomenon that is likely to occur with a larger screen and higher brightness of a liquid crystal display device. It is an object to provide a backlight unit and a liquid crystal display device using the same.

[0008]

In order to achieve the above object, a first backlight unit according to the present invention is an edge light having a means for equalizing light so as to illuminate a liquid crystal panel from a back surface thereof. Or a direct-type backlight, in which at least one or more prism sheets are disposed on a first diffusion sheet or a diffusion plate from a side closer to the light source, and a second diffusion sheet having a thickness of 0.2 mm or more is disposed thereon. 2
Is disposed so as to cover the entire surface of the prism sheet.

Next, a second backlight unit of the present invention is an edgelight type or direct type backlight having a means for equalizing light so as to illuminate a liquid crystal panel from its back surface, First from the side closer to the light source
Diffusion sheet or diffusion plate, at least one or more prism sheets thereon, a second diffusion sheet or diffusion plate thereon, and a transparent plate having a thickness of 0.2 mm or more and a light transmittance of 90% or more thereon. Are disposed so as to cover the entire surface of the prism sheet.

Next, a liquid crystal display device according to the present invention is characterized in that a liquid crystal panel is mounted on an emission light surface of the first or second backlight unit of the present invention and held by a frame.

In the liquid crystal display device, it is preferable that the backlight unit is held on a liquid crystal panel by using a frame. According to the present invention, in the edge light type or the direct type, etc., a diffusion sheet (or a diffusion plate) or a transparent plate thicker than other sheets is arranged at the top of each backlight unit configuration, so that the backlight is provided. It is possible to suppress the bending phenomenon of the prism sheet or the diffusion sheet due to the ambient environment such as temperature and humidity, which causes the luminance unevenness of the light unit or the liquid crystal display device and the deterioration of the display quality. It can be improved significantly.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first backlight unit of the present invention is an edgelight type or direct type backlight having a means for equalizing light so as to illuminate a liquid crystal panel from the back. A first diffusion sheet or a diffusion plate from a side closer to the light source, at least one or more prism sheets are disposed thereon, and a second diffusion plate having a thickness of 0.2 mm or more is provided on the first diffusion sheet or the diffusion plate. It is a configuration arranged to cover.

The second backlight unit is a similar edge-light type or direct-type backlight, and includes a first diffusion sheet or a diffusion plate from a side closer to the light source, and at least one or more prisms thereon. A sheet, a second diffusion sheet (or diffusion plate) on the sheet, and a transparent plate having a thickness of 0.2 mm or more and a light transmittance of 90% or more are disposed on the prism sheet so as to cover the entire surface of the prism sheet. is there.

Next, a liquid crystal display device according to the present invention has a configuration in which a liquid crystal panel is mounted on an emission light surface of the first or second backlight unit and held by a frame.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a backlight unit and a liquid crystal display device using the same according to an embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a backlight unit according to the present invention. In FIG. 1, a dot pattern for light equalization is formed on the back surface of a light guide plate 1, and a reflection sheet 2 is disposed on the surface. On the surface side (outgoing light surface side) of the light guide plate 1, a diffusion sheet 3 and one or more prism sheets 4 are arranged in a state of being sequentially stacked. Further, the prism sheet 4
A diffusion sheet (diffusion plate) 5 having a thickness of 0.2 mm or more is disposed over the entire surface of the prism sheet 4. A fluorescent lamp 6 is disposed on a side surface of the light guide plate 1 in a state where the fluorescent lamp 6 is covered by a lamp reflector 7 except for a light incident side of the light guide plate 1. The above members are configured to be mounted and held on a frame (housing) 8.

The uppermost diffusion sheet (diffusion plate) 5 used in this configuration has the effect of reducing the dark reversal phenomenon of narrowing the viewing angle by the prism sheet and the effect of preventing the prism sheet from being damaged. In order to prevent the occurrence of uneven brightness due to deformation due to humidity, a base material having a base thickness larger than a normal thickness of 0.2 mm or more is employed.

FIG. 2 shows a second embodiment of the present invention, which has substantially the same structure as that of the above embodiment, but has a diffusion layer having a normal thickness of 0.2 mm or less on the prism sheet 4. A sheet 9 is disposed thereon, and a transparent plate 10 having a thickness of 0.2 mm or more and a light transmittance of 90% or more is disposed thereon so as to cover the entire surface of the diffusion sheet 9. In this configuration, a thick transparent plate 1 is provided on a backlight configuration similar to the conventional one.
0 is placed.

As the transparent plate used at this time, a substrate made of polycarbonate (PC) or acrylic (PMMA) having a high light transmittance was used. Further, a black frame printing 11 is provided around the substrate.
By doing so, a clear backlight without unnecessary light leakage from around the emission light surface can be obtained.

FIG. 3 is a cross-sectional view of a liquid crystal display device using the illumination unit of the present invention. The liquid crystal panel 11 is mounted on a housing 8, and a backlight unit is formed by a metal frame or the like having an open display unit. And the liquid crystal panel 11 are fixed.

With the above configuration, it is possible to suppress the bending phenomenon of the prism sheet or the diffusion sheet due to the surrounding environment such as temperature or humidity, which is likely to occur when increasing the screen size and the brightness of the liquid crystal display device. Thus, the display quality of a backlight unit having both a large screen and high luminance and a liquid crystal display device using the same can be greatly improved.

Although the present embodiment has been described with reference to an edge light type backlight unit as an example, the same sheet configuration can be applied to other backlight configurations such as a direct type or a hollow light guide type. The same effect can be obtained.

As described above, according to the present invention, a problem arises when an attempt is made to achieve a high luminance of 200 to 300 cd / m ² or more, which is required for a large-screen monitor for a CRT having a display screen of more than 13 inches. It is possible to suppress the bending phenomenon of the prism sheet and the diffusion sheet due to the heat generated from the fluorescent lamp and the influence of the temperature or humidity of the surrounding environment, and the brightness of the backlight unit and the liquid crystal display device using the same. Problems such as unevenness and deterioration of display quality can be greatly improved.

[0024]

As described above, according to the present invention, it is possible to suppress the bending phenomenon of the prism sheet and the diffusion sheet due to the heat generated from the fluorescent lamp and the influence of the temperature or humidity of the surrounding environment. Problems such as uneven brightness and reduced display quality of the light unit and the liquid crystal display device using the same can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a backlight unit according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration of a backlight unit according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration of a liquid crystal display device using the backlight unit according to the embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a configuration of a conventional backlight unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light guide plate 2 reflection sheet 3 diffusion sheet 4 prism sheet 5 diffusion sheet (diffusion plate) 6 fluorescent lamp 7 lamp reflector 8 frame (housing) 9 diffusion sheet 10 transparent plate 11 black frame printing 12 liquid crystal panel

Claims (4)

[Claims] 1. An edge light type or direct type backlight having a means for equalizing light to illuminate a liquid crystal panel from a back surface thereof, wherein the first diffusion sheet or the diffusion sheet is provided from a side closer to the light source. A back, wherein at least one or more prism sheets are disposed thereon, and a second diffusion plate having a thickness of 0.2 mm or more is disposed over the prism sheet so as to cover the entire surface of the prism sheet. Light unit. 2. An edge light type or direct type backlight having a means for equalizing light to illuminate a liquid crystal panel from a back surface thereof, wherein the first diffusion sheet or the diffusion sheet is provided from a side closer to the light source. Plate, on which at least one or more prism sheets, a second diffusion sheet or a diffusion plate thereon, and a transparent plate having a thickness of 0.2 mm or more and a light transmittance of 90% or more are further provided thereon. A backlight unit, which is arranged so as to cover the entire surface. 3. A liquid crystal display device comprising a backlight unit according to claim 1, wherein a liquid crystal panel is mounted on a light emitting surface of the backlight unit. 4. The liquid crystal display device according to claim 3, wherein the backlight unit is held on a liquid crystal panel using a frame.