Backlight device comprising a reflector comprising a protruding part provided in a portion where a holding member is attached and liquid crystal display device having the same

A backlight device is incorporated into a liquid crystal display device so as to illuminate a liquid crystal panel from a backside. The backlight device includes a light-guiding plate emitting a light, which is incident on a side surface thereof, from a front surface, and a reflector arranged along the side surface of the light-guiding plate so as to reflect a light from a light source accommodated inside thereof and guide the light to the side surface of the light-guiding plate through an opening part. A least one minute protruding part, which protrudes in a direction parallel to the side surface of said light-guiding plate, is formed on an edge part of the opening part of the reflector facing the light-guiding plate. The side surface of the light-guiding plate is brought into contact with the protruding part of the reflector when the light-guiding plate moves toward the reflector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to backlight devices for backside illumination of liquid crystal display device and, more specifically, to an edge-light type backlight device which introduces a light from a side surface of a light-guiding plate made of a transparent plate.

2. Description of the Related Art

A liquid crystal panel of a liquid crystal display device performs a screen display by not emitting a light by itself but transmitting and interrupting a light by a polarization action. Therefore, generally, a backlight device, which illuminates a liquid crystal panel from a backside, is incorporated in a liquid crystal display device.

FIG. 1is an exploded perspective view of a conventional backlight device. The conventional backlight device shown inFIG. 1comprises reflectors12, in which fluorescent tubes11or the like as a light source are accommodated and held, and a light-guiding plate13made of a transparent plate. The reflector12are located along side surfaces of the light-guiding plate13so as to reflect a light emitted from the fluorescent tubes11and introduce the light to the light-guiding plate13. Each reflector12is generally formed of a metal plate in a channel shape, and arranged so that an opening part faces the side surface of the light-guiding plate13. The light-guiding plate13is formed of, for example, a highly transparent PMMA resin, and has a thickness of about 10 mm.

A diffusion plate14is arranged on a light-emitting surface (a surface on a side where the liquid crystal panel is arranged) of the light-guiding plate13. The diffusion plate14is formed, for example, of a polyester base resin, and a thickness thereof is about 0.1 mm. A reflection plate15is arranged on a backside opposite to the light-emitting surface of the light-guiding plate13. The reflection plate15is formed of, for example, a polyester base resin.

The reflectors12, the light-guiding plate13, the diffusion plate14, and the reflection plate15are accommodated in a backside cover16, which is formed of, for example, an aluminum plate having a thickness of 0.8 mm. A frame17formed of an aluminum plate is provided over the diffusion plate14. It should be noted that the fluorescent tubes11as a light source are held in the reflectors12by holding members18made of a silicon rubber having a thickness of 1.0 mm.

FIG. 2is a plan view of the backlight device shown inFIG. 1. The periphery of the backlight device is covered by the frame17, and the diffusion plate14is exposed inside the frame17. A light introduced from the fluorescent tubes11into the light-guiding plate13is emitted from the diffusion plate14at a uniform illumination intensity. The liquid crystal panel is illuminated from the backside by this light.

FIG. 3is an enlarged cross-sectional view taken along a line III-III inFIG. 2. As shown inFIG. 3, the light-guiding plate13is accommodated in the backside cover16. The reflector12is arranged along and near the side surface of the light-guiding plate13. The light-guiding plate13and the reflectors12are held in a state where they are sandwiched between the frame17and the backside cover16.

According to the above-mentioned arrangement structure, if an air gap between the light-guiding plate and each reflector12is reduced due to a thermal expansion of the light-guiding plate13and when a shock is applied to the backlight device, it is possible that the light-guiding plate13contacts with the fluorescent tubes11in the reflectors12. In a worst case, the fluorescent tubes11, which are made of glass tubes, may be damaged due to the contact with the light-guiding plate13.

In order to prevent such a problem, it is considered to form a structure in which an opening part of each reflector12facing the light-guiding plate13is made smaller than the side surface of the light-guiding plate13. That is, a size of the opening part of the reflector12is set so that the light-guiding plate13does not contact with the fluorescent tubes11by bringing the light-guiding plate13into contact with a rim of the reflector12.

Thus, there is suggested a structure to fix the reflector itself relative to the light-guiding plate. That is, a groove is formed on a surface of the light-guiding plate near the side surface thereof so as to couple the light-guiding plate and the reflector by bringing the rim of the reflector into engagement with the groove so as to maintain the positional relationship between the light-guiding plate and the reflector always constant (for example, refer to Patent Document 1). Alternatively, a step is made on an end part of the reflector facing the light-guiding plate so as to form a structure in which the reflector covers the light-guiding plate over the portion of the step.

As mentioned above, according to the structure which maintains a distance between the reflector and the light-guiding plate constant by bringing the reflector and the light-guiding plate into engagement with each other, there is no possibility that the light-guiding plate contacts with the fluorescent tubes in the reflector, which can prevent the fluorescent tubes from damaging.

However, if such a structure is made, an area of the opening part, through which the light introduced from the reflector into the light-guiding plate passes, is reduced, which may generate a problem that a luminance is greatly reduced. That is, in the structure disclosed in Patent Document 1, since the groove is formed on the light-guiding plate so as to insert a rim of the reflector into the groove, an area of the light-guiding plate through which a light passes is reduced due to the groove, which results in a reduction in the luminance. Additionally, also in the structure disclosed in Patent Document D2, the area of the opening part is reduced by an area corresponding to the steps provided on the end part of the reflector, which results in a reduction in the luminance.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improved and useful backlight device in which the above-mentioned problems are eliminated.

A more specific object of the present invention is to provide a backlight device having a structure in which a light-guiding plate cannot enter inside a reflector while acquiring an opening area sufficient to the light-guiding plate.

In order to achieve the above-mentioned object, there is provided according to one aspect of the present invention a backlight device configured to be incorporated into a liquid crystal display device, comprising: a light-guiding plate emitting a light, which is incident on a side surface thereof, from a front surface; and a reflector arranged along the side surface of the light-guiding plate so as to reflect a light from a light source accommodated inside thereof and guide the light to the side surface of the light-guiding plate through an opening part, wherein at least one minute protruding part, which protrudes in a direction parallel to the side surface of said light-guiding plate, is formed on an edge part of the opening part of the reflector facing the light-guiding plate; and the side surface of the light-guiding plate is brought into contact with the protruding part of the reflector when the light-guiding plate moves toward the reflector.

In the above-mentioned backlight device, the reflector is preferably formed of a metal plate, and the protruding part is preferably formed by deforming the metal plate. Additionally, the reflector may have a holding member for fixing the light source, and the protruding member may be provided in a portion where the holding member is attached and the protruding member may be in contact with the holding member. Further, a coat may be applied on a surface of said protruding part facing said light-guiding plate, the coat having a coefficient of friction smaller than that of the reflector.

Additionally, there is provided according to another aspect of the present invention a liquid crystal display device comprising the above-mentioned backlight device and a liquid crystal panel arranged on the backlight device.

According to the above-mentioned present invention, the protruding part formed on the reflector serves as a stopper so that the side surface of the light-guiding plate contacts with the protruding part and cannot enter further inside the reflector when the light-guiding plate moves toward the reflector. Therefore, the light-guiding plate never contact with the light source retained inside the reflector, thereby preventing the light source from being damaged.

Moreover, a contact area between the reflector and the retaining member is increased by forming the protruding part at a position where the light source is brought into contact with the retaining member of the light source, and, thus, heat is released through the reflector and a cooling effect to cool the light source can be raised.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, a description will be given, with reference to the drawings, of embodiments of the present invention.

FIG. 4is a plan view of a backlight device according to a first embodiment of the present invention.FIG. 5is an enlarged cross-sectional view taken along a line V-V inFIG. 4. Since the backlight device according to the first embodiment of the present invention has the same fundamental structure as the backlight device shown inFIG. 1, parts that are the same as the parts shown inFIG. 1are given the same reference numerals, and descriptions thereof will be omitted.

The backlight device according to the first embodiment of the present invention shown inFIG. 4differs from the backlight device shown inFIG. 1in that a reflector12A is processed. Light is uniformly emitted from the surface of the diffusion plate14shown inFIG. 4so as to illuminate a liquid crystal panel (not shown in the figure) arranged on the frame17.

In the present embodiment, as shown inFIG. 5andFIG. 6, minute protruding parts20are formed in parts of the rim of the opening part of the reflector12A. It should be noted thatFIG. 6is a perspective view of the reflector12A according to the first embodiment of the present invention, in which an enlarged view of the part forming the protruding parts20is shown together.

The protruding parts20are formed to protrude inward at the edge of the opening part in portions near both ends of the reflector12A in a longitudinal direction. The protruding direction of the protruding parts20is a direction parallel to the side surface of the light-guiding plate13. The reflector12A is formed of a metal plate such as an aluminum plate which can be formed by sheet-metal processing. A small protruding shape such as the protruding part20can be formed easily by driving a wedge-shaped jig from outside.

As shown inFIG. 5, a distance D between the side walls of the reflector12A is equal to or greater than a thickness T of the light-guiding plate13so that an opening area through which light from the fluorescent tubes11passes is acquired sufficiently. However, in such as structure, there is a possibility of the light-guiding plate13entering from the opening part of the reflector12A and contacting with the fluorescent tubes11. Thus, according to the present embodiment, by providing the protruding parts20, the distance D1between the protruding parts20in the portion where the protruding pats20are provided is made smaller than the thickness T of the light-guiding plate13. Thereby, the light-guiding plate13is in a state where it is in contact with the protruding parts20, and cannot enter inside the reflector12A, and the light-guiding plate13is prevented from being brought into contact with the fluorescent tubes11.

The protruding parts20protrude inside the opening part of the reflector12A. Thereby the opening area of the opening part is reduced, but the area occupied by the protruding parts20is an extremely small area which can be neglected with respect to the opening area. Thus, a reduction in luminance due to the protruding parts20is as small as it can be disregarded.

Although the protruding parts20are provided opposite with each other at the same position on both side walls of the reflector12A in the present embodiment, it is not always necessary to provide two pieces of protruding parts20opposite to each other. The protruding parts20may be provided at different positions in the longitudinal direction of the reflector12A. Additionally, at least one protruding part20may be provided on one of the sidewalls of the reflector12A. Further, the protruding parts20may be provided at arbitrary positions in the longitudinal direction of the reflector12A if they are positions opposite to the side surface of the light-guiding plate13.

Next, a description will be given, with reference toFIG. 7, of a second embodiment of the present invention.FIG. 7is a perspective view of a reflector12B provided in a backlight device according to the second embodiment of the present invention. InFIG. 7, an enlarged view of a portion (encircled by a dashed line) provided with the holding members18is shown together.

As shown inFIG. 7, in the present embodiment, the protruding parts20are provided at positions where the holding members18are attached. The holding members18are members located between the reflector12B and the fluorescent tubes11so as to hold the fluorescent tubes11so that the fluorescent tubes11do not move in the reflector12B. The holding members18are formed of silicon rubber having a thickness of, for example, 1.0 mm.

The holding members18are parts attached to the reflector12B originally, and they interrupt light. Thus, the area occupied by the holding members18is not included in the opening area of the reflector12B. Accordingly, by providing the protruding parts20in the portions where the holding members18are provided, the influence given from the protruding parts20to the opening area can be completely eliminated.

Additionally, the contact area is increased by the contact between the protruding parts20and the holding members18, which can cause an increase in an amount of heat transmitted from the fluorescent tubes11to the reflector12B through the holding members18. Thereby, a cooling effect of the fluorescent tubes11by the reflector12B can be increased.

As mentioned above, according to the present embodiment, by providing the protruding parts20, the distance between the protruding parts20is made smaller than the thickness of the light-guiding plate13in the portions where the protruding parts20are provided. Thereby, the light-guiding plate13is in the state where it is brought into contact with the protruding parts20, and cannot enter inside the reflector further, and the light-guiding plate13is prevented from contacting with the fluorescent tubes11. Additionally, by providing the protruding parts20in the portions where the holding members18are attached, heat from the fluorescent tubes11can be efficiently transmitted to the reflector12B, which can increase the cooling effect.

Here, when incorporating the reflector12B into the backside cover16, normally, the reflector12B is inserted between the sidewall of the backside cover16and the light-guiding plate13from one end side thereof. Accordingly, the protruding parts20formed on the opening edge portion of the reflector12B slide on the side surface of the frame17or the light-guiding plate13. Accordingly, it is preferable to apply a coating process to the protruding parts20to reduce a friction resistance.

FIG. 8is a plan view of the reflector12B to which a coating process is applied, a portion (a portion encircled by a dashed line) being shown in enlargement. The reflector12B shown inFIG. 8is applied with a coating to reduce a friction on not only the protruding parts20but also an entire outer surface thereof. The coating is hatched portions in the enlarged view inFIG. 8. As for the coating, it is preferable to use a fluorocarbon resin (μ=0.05) or a Teflon (registered trademark) resin (μ=0.04-0.05) having a coefficient of friction much smaller than the coefficient of friction μ=0.3-0.5 of the material of the reflector12B such as, for example, an aluminum plate.

The above-mentioned coating process is not limited to the present embodiment, and applicable to the reflector12A according to the above-mentioned first embodiment.

The present application is based on Japanese priority application No. 2005-157582 filed May 30, 2005, the entire contents of which are hereby incorporated herein by reference.