JP4147776B2 - Backlight for LCD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back light for a liquid crystal display with which a bright display screen can efficiently be obtained. <P>SOLUTION: A back light body 10 for the liquid crystal display is composed of first fluorescent tubes 13 arranged side by side, a housing 12 housing the fluorescent tubes, a light guide plate 11 arranged so as to cover the opening of the housing, second fluorescent tubes 14 arranged on both side faces of the light guide plate, a light diffusing resin plate 17 arranged on the back surface of the light guide plate, and lamp reflectors 15. The housing is formed into a roughly U-shaped cross section by bending a metal sheet, and a reflection sheet is stuck to its inner surface. The lamp reflectors are respectively attached to both side end parts of the light guide plate so as to surround the peripheral surface of the fluorescent tube 14. <P>COPYRIGHT: (C)2003,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a backlight for a liquid crystal display configured by arranging a plurality of fluorescent tubes behind a display screen.
[0002]
[Prior art]
In general, liquid crystal displays are widely used as display devices such as personal computers and television monitors. Recently, in order to obtain a bright display screen, a backlight is often installed on the back of a transmissive liquid crystal display for display. In particular, in the case of color display, since a color filter is used for the liquid crystal panel, use of a backlight is indispensable because the light transmittance is reduced by using many filters. In recent years, demands for improvement in lightness, thinness, and the like for liquid crystal displays have led to demands for backlights that are thinner, more compact, brighter, and have uniform and uniform illumination.
[0003]
Conventionally, the structure of the backlight is roughly classified into two types, one of which is a direct type in which a plurality of fluorescent tubes are arranged on the back of the display screen, and the other is on the side of the light guide plate. This is an edge light type with a fluorescent tube. FIG. 4 is a cross-sectional view showing an outline of the basic configuration of such a conventional backlight for a liquid crystal display. FIG. 4 (a) is a direct type backlight, and FIG. 4 (b) is an edge light type backlight. .
[0004]
The direct type backlight shown in FIG. 4A is installed behind the liquid crystal panel unit 1, a plurality of juxtaposed fluorescent tubes 4, a housing 3 for housing these fluorescent tubes 4, and a housing 3. The diffusion plate 2 is disposed so as to cover the entire opening. The housing 3 is formed by bending a plate-like metal (SUS, Al, etc.), and has a substantially U-shaped cross section. A reflective sheet that reflects light from the fluorescent tube 4 is attached to the inner surface of the housing 3. The diffusing plate 2 contains fine particles such as titanium dioxide and calcium carbonate in a translucent resin (acrylic, polycarbonate, etc.), has a plate thickness of about 2 to 3 mm, and direct light generated from the fluorescent tube 4 It has a function of diffusing light by scattering the reflected light reflected by the reflection sheet by the contained fine particles. Due to this light diffusing function of the diffusing plate 2, illumination that is uniform and free from unevenness in brightness and darkness can be obtained. In addition, in order to achieve illumination without bright and dark unevenness, the distance W between the fluorescent tubes 4 is preferably set to about 25 to 30 mm.
[0005]
The edge light type backlight shown in FIG. 4B is formed by arranging one (or several) fluorescent tubes 6 along one side surface of one side of a rectangular light guide plate 5. A lamp reflector 7 is attached to the side end of the light guide plate 5 so as to surround the peripheral surface of the fluorescent tube 6 disposed on the side surface, and a reflection sheet is attached to the back surface of the light guide plate 5. On the other hand, sheets such as a prism lens and a diffusion sheet are attached to the front surface of the light guide plate 5. In this figure, the liquid crystal panel portion is omitted. The light guide plate 5 is made of a light-transmitting resin such as acrylic, and a large number of traps 8 made of unevenness are provided on the inner surface. When direct light from the fluorescent tube 6 and reflected light from the lamp reflector 7 enter the light guide plate from the side surface of the light guide plate 5, the incident light is repeatedly reflected in the light guide plate, and the light spreads throughout the light guide plate. At the same time, the light is irregularly reflected (or refracted) by the trap 8 so that the light is extracted forward from the front surface of the light guide plate 5. The light leaking to the back side of the light guide plate 5 is reflected by the reflection sheet and returned to the light guide plate. The light extracted from the front surface of the light guide plate 5 by this function is diffused by the diffusion sheet and then radiated by the prism lens toward the front of the light guide plate 5. As a result, uniform and uniform illumination can be obtained.
[0006]
[Problems to be solved by the invention]
However, such a conventional backlight for a liquid crystal display has a problem that it is difficult to obtain a brighter display screen. In the case of the direct type backlight as described above, for example, in order to obtain a brighter display screen, it is conceivable to increase the number of fluorescent tubes juxtaposed, but for that purpose, the distance between the fluorescent tubes is shortened. Then, the temperature in the housing increases due to heat generated together with light from each fluorescent tube, which causes a problem in that the energy conversion efficiency of the fluorescent tube decreases, and the luminance of the fluorescent tube decreases.
[0007]
In the case of an edge light type backlight, since the number of fluorescent tubes arranged on the side surface of the light guide plate is limited regardless of the size of the display screen, the brightness of the display screen is originally not high and brighter. If the number of fluorescent tubes is increased to obtain a display screen, the thickness of the backlight portion increases, and the efficiency decreases due to the temperature rise due to heat radiation of each fluorescent tube, as in the case of the direct type described above. There was a problem such as.
[0008]
Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a backlight for a liquid crystal display capable of obtaining a brighter display screen with high efficiency.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a backlight for a liquid crystal display according to the present invention includes a plurality of juxtaposed first fluorescent tubes, a housing for housing the plurality of first fluorescent tubes, and an opening of the housing. A light guide plate disposed so as to cover the light guide plate, a second fluorescent tube disposed on a side surface of the light guide plate, and a light diffusing resin plate disposed on the back surface of the light guide plate , The light from the fluorescent tube and the second fluorescent tube is simultaneously supplied to the front side of the light guide plate, and the light diffusing resin plate has a pattern that reflects light in parallel with the first fluorescent tube. The pattern is characterized in that it is located approximately in the middle of the first fluorescent tubes adjacent to each other when the resin plate is viewed from the front side .
[0010]
And it is characterized by arrange | positioning the resin plate which has a light diffusibility in the back surface of the said light-guide plate, and arrange | positioning a semi-permeable film in the back surface of the said light-guide plate.
[0011]
According to such a configuration, since the light from both the plurality of fluorescent tubes juxtaposed on the back surface of the light guide plate and the fluorescent tubes disposed on the side surfaces are used, it is possible to obtain equivalent light using only the back fluorescent tube. The distance between the fluorescent tubes is longer than that in the case, and the luminance unevenness can be suppressed by combining the first and second fluorescent tubes, so the distance between the fluorescent tubes can be increased. As a result, temperature rise due to heat dissipation can be suppressed. For this reason, since the efficiency of the fluorescent tube is improved and good luminance is obtained, brighter illumination can be obtained.
[0012]
A pattern for reflecting light is provided on the resin plate in parallel with the first fluorescent tube, and when the resin plate is viewed from the front side, the pattern is positioned approximately in the middle of the adjacent first fluorescent tubes. Or a first region that transmits light and a second region that attenuates or blocks light, and the second region is arranged at a position facing the first fluorescent tube. Then, it is effective in eliminating illumination unevenness. Moreover, it is preferable that a trap made of unevenness is provided on the back surface of the light guide plate.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a backlight for a liquid crystal display according to the first embodiment of the present invention. As shown in FIG. 1, in this embodiment, the backlight main body 10 includes a plurality of juxtaposed first fluorescent tubes 13, a housing 12 that houses these fluorescent tubes 13, and the entire opening of the housing 12. The light guide plate 11 is disposed so as to cover the light guide plate, and each of the second fluorescent tubes 14 is disposed on both side surfaces of the light guide plate 11 along the side surface, and the lamp reflector 15.
[0014]
The housing 12 is formed by bending a plate-like metal (SUS, Al, etc.), has a substantially U-shaped cross-section, and reflects light from the fluorescent tube 13 on the inner surface of the housing 12. A reflective sheet is attached. The lamp reflectors 15 are attached to both end portions of the light guide plate 11 so as to surround the peripheral surface of the fluorescent tube 14 disposed on the side surface of the light guide plate 11. The light guide plate 11 is made of a light-transmitting resin such as acrylic, and a large number of traps 16 made of unevenness are provided on the inner surface on the back side. Sheets such as a prism lens and a diffusion sheet are attached to the front surface of the light guide plate 11, and the fluorescent tube 14 is parallel to the fluorescent tube 13.
[0015]
In this backlight, light from both the fluorescent tubes 13 juxtaposed on the back surface of the light guide plate 11 and the fluorescent tubes 14 arranged on both side surfaces of the light guide plate 11 are used, so that only one of them is used. And brighter illumination.
[0016]
Further, in the present embodiment, a light-diffusing resin plate (made of acrylic, polycarbonate, or the like, containing fine particles such as titanium dioxide or calcium carbonate) 17 is disposed in contact with the light guide plate 11 on the back surface of the light guide plate 11. A lamp reflector 15 is attached so as to sandwich the resin plate 17 and the light guide plate 11.
[0017]
At this time, the light generated radially from the peripheral surface of each fluorescent tube 13 juxtaposed on the back surface of the light guide plate 11 is reflected by a reflection sheet affixed to the inner surface of the housing 12, and is emitted from each fluorescent tube 13. When direct light and reflected light from the reflection sheet enter the resin plate 17 from the opening of the housing 12, the direct light and the reflected light are scattered by the fine particles contained in the resin plate. Due to the light diffusibility of the resin plate 17, the light is sufficiently diffused in the resin plate and then emitted forward. On the other hand, the light radially generated from the peripheral surface of the fluorescent tube 14 disposed on the side surface of the light guide plate 11 is caused by the lamp reflector 15 attached to the side end of the light guide plate 11 so that a part of the light surrounds the peripheral surface. The reflected direct light from the fluorescent tube 14 and the reflected light from the lamp reflector 15 enter the light guide plate from the side of the light guide plate 11 facing the fluorescent tube 14 and are repeatedly reflected in the light guide plate. The entire surface is diffused by the trap 16 provided on the back surface of the light guide plate 11 so that light is extracted from the front surface of the light guide plate 11 and emitted forward. The light refracted by the trap 16 and leaked from the back side of the light guide plate 11 is reflected by the reflection sheet on the inner surface of the housing 12 and returned to the light guide plate. These lights are diffused by the diffusion sheet and then aligned forward by the prism lens.
[0018]
In this way, the light from both the fluorescent tubes 13 juxtaposed on the back surface of the light guide plate 11 and the fluorescent tubes 14 disposed on both side surfaces of the light guide plate 11 is used, so that only the fluorescent tubes on the back surface of the light guide plate 11 are used. The distance W ′ between the fluorescent tubes 13 is longer than the distance W (see FIG. 4A) between the fluorescent tubes when the equivalent light is to be obtained. Further, in the conventional direct type, the distance W could not be increased in order to prevent luminance unevenness such as the presence of the fluorescent tube behind, but in this embodiment, the edge light type Since the luminance unevenness is difficult to occur when combined, the distance W ′ can be increased. That is, the fluorescent tubes 13 can be arranged at a distance of about 30 mm or more. For this reason, the heat dissipation in the housing 12 is improved, and the temperature rise due to the heat generated from each fluorescent tube can be suppressed. Thereby, the fluorescent tube can emit light with good energy conversion efficiency and good luminance can be obtained, so that brighter illumination can be obtained, and illumination with uniform brightness and darkness can be obtained.
[0019]
In addition, providing the trap only on the back side of the light guide plate is easier to design for the arrangement of the trap for efficiently extracting light from the entire front surface of the light guide plate than providing it on the front side, Light and dark unevenness need not be noticeable.
[0020]
Next, another embodiment of the present invention will be described. FIG. 2 is a cross-sectional view of a main part of a backlight for a liquid crystal display according to the second embodiment. In the second embodiment shown in this figure, a translucent film 37 is disposed in contact with the light guide plate 31 on the back surface of the light guide plate 31 of the backlight body 30 instead of the resin plate having light diffusibility. The lamp reflector 35 is attached so as to sandwich the semi-transmissive film 37 and the light guide plate 31. Further, on the surface of the semi-transmissive film 37 facing the juxtaposed fluorescent tubes 33, a second region for dimming or blocking light passing along the fluorescent tubes 33 at a position X facing each fluorescent tube 33. A pattern 38 corresponding to the above is printed and provided, and a portion without the pattern 38 becomes a first region through which light passes. These points are different from the first embodiment of FIG. In addition, about another structure and an effect, it is the same as that of 1st Embodiment mentioned above.
[0021]
The semi-transmissive film 37 is formed by thinly depositing silver or the like on a resin film, and transmits light from each fluorescent tube 33 on the back side toward the front, and reflects part of the light to the back side. Has a half-mirror function. Further, the pattern 38 has a function of diffusing light from each fluorescent tube 33 by scattering light by fine particles contained in the printing material.
[0022]
At this time, on the front surface of the backlight main body 30, the portion located directly above each fluorescent tube 33 becomes bright because the distance from the fluorescent tube 33 is short, and the portion located between each fluorescent tube 33 has a distance. It ’s so far away that it ’s dark. For this reason, the brightness unevenness of light and dark becomes conspicuous. By providing the pattern 38 at the position X directly above the fluorescent tube 33, the transmitted light traveling directly above the fluorescent tube 33 is reduced by diffusion. The light and the light diffused by the pattern 38 are directed to the dark portion between the fluorescent tubes 33, so that the brightness unevenness of light and darkness is effectively eliminated. As a result, uniform, non-uniformity and brighter illumination can be obtained.
[0023]
FIG. 3 is a cross-sectional view of a main part of the third embodiment. In the third embodiment shown in this figure, a pattern 48 made of unevenness for reflecting light is formed on the fluorescent tube 43 on the back surface of the light guide plate 41 on the front surface of the resin plate 47 having light diffusibility of the backlight body 40. It differs from the first embodiment in that it is provided in parallel and the pattern 48 is located at a position Y approximately in the middle of the fluorescent tubes 43 adjacent to each other. In addition, about another structure and an effect, it is the same as that of 1st Embodiment.
[0024]
When the distance W ′ between the fluorescent tubes 43 becomes longer and the interval becomes wider, the luminance of the portion between the fluorescent tubes 43 decreases and the luminance unevenness becomes conspicuous. By providing the pattern 48 at the position Y of the portion, the light leaked to the back side of the light guide plate 41 by the trap 46 on the back surface of the light guide plate out of the light from the fluorescent tube 44 on the side surface of the light guide plate 41 is caused by the pattern 48. Since the light is diffusely reflected and radiated forward, the luminance of this portion is improved, the luminance is uniform on the front surface of the backlight body 40, and unevenness in brightness is eliminated. Further, by reflecting the light from each fluorescent tube 43 by the pattern 48, this light can be directed to a portion without the pattern 48, and the light from the fluorescent tube 43 can be effectively utilized.
[0025]
Heretofore, with respect to the fluorescent tubes arranged on the side surfaces of the light guide plate, an example in which one fluorescent tube is arranged on each side surface of the light guide plate has been taken up. However, the fluorescent tubes are arranged only on one side surface of the rectangular light guide plate. A tube may be disposed, a tube may be disposed on two to four side surfaces, or a plurality of fluorescent tubes may be disposed on one side surface.
[0026]
【The invention's effect】
As described above, the backlight for a liquid crystal display according to the present invention has fluorescent tubes arranged on the back and side surfaces of the light guide plate, and a resin plate having light diffusibility is arranged on the back surface of the light guide plate. Since the distance between each fluorescent tube on the back side can be increased and heat dissipation is improved and the temperature rise of the fluorescent tube can be suppressed, the efficiency of the fluorescent tube is improved. As a result, it was possible to obtain a brighter display screen.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a backlight for a liquid crystal display according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of main parts of a second embodiment of the present invention.
FIG. 3 is an essential part cross-sectional view of a third embodiment of the present invention.
FIG. 4 is a cross-sectional view of a conventional backlight for a liquid crystal display.
[Explanation of symbols]
10, 30, 40 Backlight 11, 31, 41 Light guide plate 12, 32, 42 Housing 13, 33, 43 First fluorescent tube 14, 34, 44 Second fluorescent tube 16, 36, 46 Trap 37 Semi-transmissive Film 38, 48 Pattern 47 Resin plate

Claims (5)

A plurality of juxtaposed first fluorescent tubes, a housing for housing the plurality of first fluorescent tubes, a light guide plate arranged to cover the opening of the housing, and a side surface of the light guide plate It is composed of a second fluorescent tube arranged and a resin plate having light diffusibility arranged on the back surface of the light guide plate, and simultaneously transmits the light from the first fluorescent tube and the second fluorescent tube to the front surface of the light guide plate. The resin plate having light diffusibility is provided with a pattern that reflects light in parallel with the first fluorescent tube, and this pattern is obtained when the resin plate is viewed from the front side. A backlight for a liquid crystal display, which is located approximately in the middle of the first fluorescent tubes adjacent to each other . The backlight for a liquid crystal display according to claim 1 , wherein a translucent film is disposed on the back surface of the light guide plate. The translucent film has a first region that transmits light and a second region that attenuates or blocks light, and the second region is disposed at a position facing the first fluorescent tube. The backlight for a liquid crystal display according to claim 2 . The backlight for a liquid crystal display according to any one of claims 1 to 3 , wherein a trap made of irregularities is provided on a back surface of the light guide plate. The backlight for a liquid crystal display according to any one of claims 1 to 4 , wherein the interval between the first fluorescent tubes is about 30 mm or more.

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