JP2004117594A - Backlight structure of liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight structure of a liquid crystal display device which is inexpensive, generates no uneven brightness and increases illumination color variation. <P>SOLUTION: A color converting sheet 40 is provided between a light emitting element 27 and a light guide plate 28. The color converting sheet 40 is composed of a resin sheet containing one or both of a fluorescent material and a pigment. The fluorescent material absorbs light of a specified wavelength and emits light of a different wavelength, and the pigment absorbs or reflects light of a specified wavelength. Thereby, the color of light emitted from the light emitting device 27 is converted into white or yellow. The light of the converted color is emitted in the direction of a liquid crystal display panel 25 via the light guide plate 28. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a backlight used in a liquid crystal display device, and more particularly to a structure capable of effectively converting a color of illumination into a desired color.
[0002]
[Prior art]
As shown in FIG. 7, the conventional backlight structure of this type of liquid crystal display device includes a light guide plate 8 placed on the bottom surface 10 of the frame 4, and LEDs installed on the side surfaces of the light guide plate 8. A circuit board 6 including a light emitting element 7 is disposed. On the light guide plate 8, a diffusion sheet 9 and a liquid crystal display panel 5 are arranged in this order, and the liquid crystal display device 1 is formed. The light guide plate 8 is fixed to the first housing portion 4 a of the frame body 4, and the circuit board 6 is incorporated in a state of being stood in the second housing portion 4 b of the frame body 4. At this time, the circuit board 6 is positioned and sandwiched between the light guide plate 8 and the frame body 4 and fixed so that the light emitting element 7 faces the light receiving portion 13 provided in the light guide plate 8. The light guide plate 8 is fixed by fitting a hook 14 provided on a side surface thereof into a groove 15 provided in the frame body 4. A light shielding plate 19 is provided on the circuit board 6 to prevent light leakage. The conventional backlight structure is configured in this way (for example, FIG. 7 of Japanese Patent Application No. 2002-78828).
[0003]
[Problems to be solved by the invention]
In the backlight structure of a liquid crystal display device, the color of illumination is usually determined by the color of light emitted from the light-emitting element 7, but in order to increase product variations or provide unique products, various illumination colors are required. It has been. For this reason, the color which illuminates the liquid crystal display panel 5 by changing the color of the light irradiated from the light-guide plate 8 may be changed using the diffusion sheet 9 which apply | coated the color conversion agent to the base material sheet.
[0004]
However, in the case of the diffusion sheet 9 having the color conversion function as described above, an area equivalent to that of the liquid crystal display panel 5 is necessary, so that the area is wide and the price is high. Therefore, it has been a problem to change the illumination color at a lower cost.
[0005]
Further, by applying the color conversion agent to the diffusion sheet 9, the light diffusion action of the diffusion sheet 9 is lowered and insufficient, and luminance unevenness may occur. For this reason, it has been a problem to change the illumination color without causing luminance unevenness.
[0006]
The present invention has been made in view of the above-described problems of the prior art, and provides a backlight structure of a liquid crystal display device that can increase variations in illumination colors without causing uneven luminance.
[0007]
[Means for Solving the Problems]
According to the backlight structure of the liquid crystal display device of the present invention, as shown in claim 1, in the backlight structure of the liquid crystal display device that illuminates by irradiating the liquid crystal display panel with light from the light emitting element through the light guide plate, A color conversion sheet for converting the color of light emitted from the light emitting element is interposed between the light emitting element and the light guide plate. As shown in claim 2, the color conversion sheet in the backlight structure of the liquid crystal display device is made of a resin sheet containing one or both of a phosphor and a pigment. As shown in claim 3, the resin sheet in the backlight structure of the liquid crystal display device contains a diffusing member. According to a fourth aspect of the present invention, the color conversion sheet in the backlight structure of the liquid crystal display device covers at least the light emitting surface of the light emitting element. According to a fifth aspect of the present invention, the color conversion sheet in the backlight structure of the liquid crystal display device covers the light emitting surface of the light emitting element and is fixed to a circuit board on which the light emitting element is mounted. The distance between the light emitting element and the light receiving portion of the light guide plate in the backlight structure of the liquid crystal display device is set to a size that is equal to or slightly larger than the thickness of the color conversion sheet, as shown in claim 6. Yes.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the backlight structure of the liquid crystal display device of the present invention, a color conversion sheet is interposed between the light emitting element and the light guide plate. This color conversion sheet is composed of a resin sheet containing one or both of a phosphor and a pigment. The phosphor absorbs light of a specific wavelength and emits light of a different wavelength, and the pigment absorbs or reflects light of a specific wavelength. Thereby, the color of the light emitted from the light emitting element is changed to the color of the light beam that passes through the color conversion sheet as it is (for example, blue, red, etc.), or the color of the light beam that has changed due to absorption or reflection (for example, blue, red, etc.). Yellow, etc.) are mixed and converted to white or yellow. The light beam whose color has been converted in this way is irradiated in the direction of the liquid crystal display panel through the light guide plate.
[0009]
As described above, in the present invention, since the color of light emitted from the light emitting element to the light guide plate is converted by the color conversion sheet, only a small area portion such as the light emitting surface of the light emitting element is covered with the color conversion sheet. It will be good. Further, since the diffusion sheet or other structure is not touched, there is no influence on diffusion, light guide and the like, and luminance unevenness does not occur.
[0010]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view showing a backlight structure of a liquid crystal display device according to an embodiment of the present invention, and FIG. Also in this backlight structure, the basic structure is the same as that of a normal one. The light guide plate 28 is housed in the first housing portion 24a of the frame body 24, and the hook 34 is fitted in the groove 35 of the frame body 24. The circuit board 26 on which the light emitting element 27 is mounted is housed in the second housing portion 24b of the body 24, and the diffusion sheet 29, the liquid crystal display panel 25, and the light shielding plate 39 are stacked on top of each other.
[0011]
In this structure, a color conversion sheet 40 is provided between the light emitting element 27 and the light guide plate 28. The color conversion sheet 40 is based on a resin sheet 41 such as a silicone rubber sheet having a thickness of about 0.1 to 0.5 mm as shown in FIGS. One or both of a phosphor 42 such as a body and a pigment 43, and a diffusion member 44 made of a glass ball, silica or the like having a diameter of about 1 to 10 μm are mixed.
[0012]
The color conversion sheet 40 has a belt shape that covers the light emitting surface 31 of the light emitting element 27 and is in close contact with the surface of the circuit board 26. In this embodiment, the portion of the color conversion sheet 40 that is in close contact with the circuit board 26 is fixed to the surface of the circuit board 26 by fixing means such as double-sided tape. The color conversion sheet 40 is firmly fixed by sandwiching the color conversion sheet 40 between the edges 33a and 33b of the light receiving section 33 having the concave shape of the light guide plate 28 and the surface of the circuit board 26. . In addition, the space | interval between the light-receiving part 33 of the light-guide plate 28 and the light emitting element 27 is set to the dimension equal to or slightly larger than the thickness of the color conversion sheet 40. FIG. Thereby, it can prevent that the light emitting element 27 is pressed and damaged by interposing the color conversion sheet 40. Further, the color conversion sheet 40 may be of a size that can cover at least the light emitting surface 31 of the light emitting element 27, and may be directly fixed to the light emitting surface 31.
[0013]
In the backlight structure having the above configuration, as shown in FIG. 3, when the light beam B1 from the light emitting element 27 made of, for example, a blue LED hits the phosphor 42, in the case of the YAG phosphor, the blue light beam around 460 nm is absorbed. The yellow light beam b1 near 550 nm is emitted. The yellow light beam b1 is mixed with the blue light beam B2 that passes through the resin sheet 41 as it is without hitting the phosphor 42, and is irradiated to the light guide plate 28 as a light beam B3. In the case of a YAG phosphor, when the amount is increased, the color tone of the emitted light beam b1 becomes stronger in yellow, and when mixed with the blue light beam B2, the light beam B3 appears white or yellow. In this way, the blue light emission color is changed to a brighter white color or a unique yellow color, and the liquid crystal display panel 25 is illuminated via the light guide plate 28 and the diffusion sheet 29.
[0014]
As shown in FIG. 4, when the pigment 43 is mixed in the color conversion sheet 40, the light beam B <b> 1 from the light emitting element 27 strikes the pigment 43 and absorbs or reflects light of some wavelengths according to the color of the pigment 43. As a result, the light beam bb1 of the same color as the pigment 43 is formed, and the light guide plate 28 is irradiated with the light beam B3 mixed with the light beam B2 passing through the resin sheet 41 as it is. The color conversion sheet 40 mixed with the pigment 43 is not only capable of color conversion as described above, but also when a color conversion sheet mixed with a pigment of the same color as the emission color of the light emitting element 27 is used. Color tone and brightness can be stabilized by eliminating the intensity of light emission and uneven brightness.
[0015]
As shown in FIG. 5, when the diffusion member 44 is mixed with the phosphor 42 and the pigment 43 in the color conversion sheet 40, when the light beam B <b> 1 emitted from the light emitting element 27 strikes the diffusion member 44, the light beam B <b> 1 is The diffused light diffuses and hits the surrounding phosphor 42 and the pigment 43 or passes through as it is. In this way, the light beam B1 applied to the color conversion sheet 40 is diffused and is applied to the light guide plate 28 as a light beam with less occurrence of color unevenness and luminance unevenness.
[0016]
On the other hand, the backlight structure has a structure in which the light emitting element 27 is disposed so as to face the side surface of the light guide plate 28 and irradiates light from the side of the light guide plate 28. As shown in FIG. The light emitting element 27 is disposed so as to face the lower surface 28b of the light receiving portion 28a extended to the side of the light guide plate 28, and the light is irradiated toward the reflecting surface 28c obtained by obliquely cutting the upper surface of the light receiving portion 28a. A structure using the color conversion sheet 40 can be applied.
[0017]
【The invention's effect】
According to the present invention, by arranging the color conversion sheet between the light emitting element and the light guide plate, it is possible to change the emission color of the light emitting element and increase the variation of illumination. In particular, since the emission color can be changed simply by providing a color conversion sheet so as to cover the light emitting surface of the light emitting element, the area of the color conversion sheet can be kept small, and the emission color can be changed at low cost.
[0018]
In addition, since the color conversion sheet is merely interposed between the light emitting element and the light guide plate, the diffusion sheet and the light guide plate are not touched. It is possible to prevent the occurrence of luminance unevenness due to a decrease in function and light guiding function.
[0019]
Furthermore, since a very thin color conversion sheet is only interposed between the light emitting element and the light guide plate, the thickness of the backlight structure can be kept thin.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing a backlight structure of a liquid crystal display device according to an embodiment of the present invention.
2 is a cross-sectional view of a main part of the backlight structure shown in FIG.
FIG. 3 is an enlarged cross-sectional view of the color conversion sheet shown in FIG.
4 is another enlarged cross-sectional view of the color conversion sheet shown in FIG. 1. FIG.
FIG. 5 is another enlarged cross-sectional view of the color conversion sheet shown in FIG.
6 is a cross-sectional view showing a partial modification when the structure shown in FIG. 1 is applied to a structure in which a light emitting element is disposed below a light guide plate.
FIG. 7 is an exploded perspective view showing a backlight structure of a conventional liquid crystal display device.
[Explanation of symbols]
4,24 Frames 5, 25 Liquid crystal display panels 6, 26 Circuit boards 7, 27 Light emitting elements 8, 28 Light guide plates 9, 29 Diffusion sheet 40 Color conversion sheet 41 Resin sheet 42 Phosphor 43 Pigment 44 Diffusion member

Claims (6)

In the backlight structure of a liquid crystal display device that illuminates by irradiating the liquid crystal display panel with light from the light emitting element via the light guide plate,
A backlight structure of a liquid crystal display device, wherein a color conversion sheet for converting a color of light emitted from the light emitting element is interposed between the light emitting element and the light guide plate. 2. The backlight structure of a liquid crystal display device according to claim 1, wherein the color conversion sheet is made of a resin sheet containing one or both of a phosphor and a pigment. The backlight structure of a liquid crystal display device according to claim 2, wherein the resin sheet contains a diffusion member. The backlight structure of a liquid crystal display device according to claim 1, wherein the color conversion sheet covers at least a light emitting surface of the light emitting element. The back of the liquid crystal display device according to claim 1, wherein the color conversion sheet covers a light emitting surface of the light emitting element and is fixed to a circuit board on which the light emitting element is mounted. Light structure. 2. The backlight of a liquid crystal display device according to claim 1, wherein the distance between the light emitting element and the light receiving portion of the light guide plate is set to a size equal to or slightly larger than the thickness of the color conversion sheet. Construction.

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