Backlight unit and liquid crystal display device having the same

A backlight unit comprising: a quadrilateral light guide plate 4; and a substrate 3 comprises a plurality of light-emitting diodes 2; and an inner frame 8 which surround the light guide plate 4; and an outer frame 7 which surround the inner frame 8 and the substrate 3; a plurality of rubber members 9; wherein a side of the inner frame 8 is opposite to the light-emitting diodes 2, and two corners are formed edges of the side; and the rubber member 9 is placed the each corners; and wherein the rubber member 9 comprises a cylindrical part; and wherein the cylindrical part is projected inside of the inner frame 8.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit as surface light source function and particularly improvement of support structure for light guide plate, and further the present invention relates to a crystal display device having the same.

2. Description of the Prior Art

In recent years, as the display devices of such information machines as laptop personal computers and word processors and the display devices of such image machines as portable television sets, video movies, and car navigation systems, the liquid crystal display (LCD) devices have come to be used in more cases than not with a view to utilizing such features as lightness, thinness, and low power consumption. For the most part, these liquid crystal display devices having a backlight unit such as a lighting unit throw a light on a liquid crystal display panel from behind.

Lighting method of backlight unit is classified an edge light method and a direct under light method. An edge light method which comprises placing a light guide plate behind a display element, and output a point light using as a LED (light-emitting diode) or a linear light using as a fluorescent discharge tube, for example. A direct under light method which comprises placing a light diffuser plate behind a display element, and output plural linear light using as plural fluorescent discharge tubes, for example. Generally, an edge light method is better than a direct under light method, concerning thin thickness body. Thus, an edge light method is suitable for personal digital assistance (PDA), and laptop personal computer.

A backlight unit used an edge light method that needs holding a light guide plate and a light part by a frame belongs to the backlight unit. For example, a light guide plate sandwiched between the frame and a back cover belongs to the backlight unit is proposed. For example, a light guide plate fixed to the frame by double-sided adhesive tape is proposed. The light guide plate sandwiched structure is preferable, because it doesn't use additional double-sided adhesive tape and easy to assemble.

As above structure that needs setting the light guide plate near the light part. The light guide plate approximate to the light part, it can be inducing a light of the light part to the light guide plate high efficiency, and prevent to uneven luminance occurs.

Therefore, prior art proposed that the frame having a press-supporting part (See JP2003-215546A). Prior art JP2003-215546A is disclosed a LCD device having a plastic frame which enclosed a light guide plate and a LED; wherein the plastic frame comprises a elastic press-supporting part such as a plastic spring; wherein the press-supporting part is formed on a edge of the frame and the edge is opposite to the LED, and the press-supporting part press the light guide plate to the LED.

However, in the above method by using the prior art JP2003-215546A, it is easy to occur pressing defective at the press-supporting part under wide temperature range of external environment. The plastic frame comprises the plastic spring part is sensitive temperature changes. The plastic frame is easy to stretch and deform by temperature changes. Function of the press-supporting part is damaged by the plastic frame stretched or the plastic frame deformed. That is, the light guide plate is pressed by the press-supporting part under the room temperature, but the press-supporting part is deformed by temperature raised and the press-supporting part couldn't press to the light guide plate, then the light guide plate is easy to move inside of the plastic frame. Backlash of the light guide plate is significantly impairing the commercial value and image disqualify such as uneven luminance occurs. For example, the LCD device having the prior art structure and installed a car navigation system, backlash of the light guide plate occurs and image disqualify such as uneven luminance occurs. Because, the room temperature of the car sometimes rising high temperature.

As structure of prior art JP2003-215546A which comprises a frame having a press-supporting part such as a plastic spring and press and support to the light guide plate. It is necessary to set the plastic springs on each side of the plastic frame for pressing as horizontally and vertically if keep stable supporting condition. But, it is difficult to assemble the light guide plate into the plastic frame when the plastic springs are set on each side of the plastic frame. In case of the plastic springs are set on horizontally sides or the plastic springs are set on vertically sides, the position of the light guide plate is unsettled. Therefore, the LCD device having the prior art structure occurs image disqualify.

The present invention has been proposed in view of the conventional actual situation, and the object thereof is to provide a backlight unit which structure is certain pressing the light guide plate to the light part such as LED without being influenced by external environment, and prevent to occurs image disqualify such as uneven luminance and easy to assemble the light guide plate. In addition, the object thereof is to provide a liquid crystal display (LCD) device having the backlight unit.

SUMMARY OF THE INVENTION

To accomplish the above object, the present invention provides a backlight unit comprising: a quadrilateral light guide plate and a plane light output from a light-output surface of the light guide plate; and a substrate comprises a plurality of light-emitting diodes which output a light to an edge of the light guide plate; and an inner frame which surround the light guide plate; and an outer frame which surround the inner frame and the substrate; a plurality of rubber members which press the light guide plate to the light-emitting diodes; wherein a side of the inner frame is opposite to the light-emitting diodes, and two corners are formed edges of the side; and the rubber member is placed the each corners; and wherein the rubber member comprises a cylindrical part; and wherein the cylindrical part is projected inside of the inner frame. And the present invention provides a liquid crystal display device having the backlight unit as above described.

According to the present invention, the plurality of rubber members press the light guide plate to the light-emitting diodes. For room temperature, the light guide plate is pressed by the plurality of rubber members, and the light guide plate is certain pressed to the light-emitting diodes, and the light guide plate is supported by the plurality of rubber members constantly. When the room temperature rose to high temperature, the plurality of rubber members absorbed for the inner frame expansions by high temperature. Thus, the light guide plate is supported by the plurality of rubber members constantly. In case of the rubber member is deformed by high temperature, the rubber member is quickly returned with temperature dropped. More over, it is easy to assemble the light guide plate. That is, set the plurality of rubber members into the given places of the plastic frame, and then push the light guide plate into the inner frame. Also built in performance is well.

According to the present invention of the backlight unit, the plurality of rubber members press the light guide plate to the light-emitting diodes. Thus, the light guide plate is supported constantly. Therefore, the backlight unit is certain pressing the light guide plate to the light-emitting diodes without being influenced by external environment, and prevent to occurs image disqualify such as uneven luminance and easy to assemble the light guide plate. More over, it is easy to assemble the light guide plate. In addition, the liquid crystal display (LCD) device having the same invention of the backlight unit, the LCD device is excellent image view and getting high reliability.

The above and other objects, characteristic features and advantages of the present invention will become apparent to those skilled in the art from the description to be given herein below with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of a backlight unit as surface light source function and the crystal display device having the backlight unit according to the present invention will be described hereinafter with reference to the drawings.

FIG. 1is shown an exploded perspective view of a backlight unit1according to the present invention. A backlight unit1as an embodiment comprises a flexible circuit board3which having a plurality of light-emitting diodes (LEDs)2, a light guide plate4as flat board shape, a reflection sheet5, and an optical sheet6(SeeFIG. 1). A plurality of light-emitting diodes (LEDs)2output a light to an edge of the light guide plate4, and the plane light output from a light-output surface of the light guide plate4.

The plural light-emitting diodes (LEDs)2are mounted on a flexible circuit board3. The flexible circuit board3is set along to a line as a long side of the light guide plate4(FIG. 1). Then, the LEDs2are set along to a line of the light guide plate4. The light guide plate4is piled on a reflection sheet5. An optical sheet6is piled on the light guide plate4. A light output from LEDs2is input to the edge of the light guide plate4directly, and/or, a light output from LEDs2is reflected by a reflection sheet5and then input to the edge of the light guide plate4. The light through the light guide plate4and an optical sheet6, and the light is output to a liquid crystal display panel21. Thus, the embodiment backlight unit1is used an edge light method.

Embodiment backlight unit1is consisted combination of an outer frame7and an inner frame8. Around of the light guide plate4, a reflection sheet5, and an optical sheet6is supported the combination of the outer frame7and the inner frame8, and those parts are installed (refer toFIG. 1).

According to embodiment, the outer frame7is made of metal such a stainless steel or titanium alloy. The inner frame8is made of plastic such as polymer plastic. The outer frame7comprises an outline wall71and a base place72. The outer frame7is rectangular shape and formed a window at the base place72. The outline wall71is stand vertically to surface of the base place72. Then, the outline wall71is stand vertically to the light-output surface of the light guide plate4.

FIG. 2is shown a schematic perspective view of an inner frame8belongs to the backlight unit1according to the embodiment. The inner frame8comprises an outline wall81which support to three sides of the light guide plate4. The inner frame8is rectangular shape but cut off a part of side. The flexible circuit board3is set at the cut part of the inner frame8. The inner frame8comprises an outline wall81and the outline wall81is into the outer frame7. The outline wall81consists of a long side wall81aand two short side wall81band81c. An end of the short side wall81bis connected a left end of the long side wall81aas right angle (SeeFIG. 2). The other end of the short side wall81bconsists with a very short wall81das right angle towards a short side wall81c. An end of the short side wall81cis connected a right end of the long side wall81aas right angle (SeeFIG. 2). The other end of the short side wall81cconsists with a very short wall81eas right angle towards a short side wall81b.

FIG. 3is shown an expanded perspective view of a support pin82formed on the inner frame8according to the embodiment. A side of the inner frame8is opposite to the light-emitting diodes2, and two corners are formed edges of the side, and the support pin82is placed the each corners. Plural support pins82are projected toward to bottom of the inner frame8(SeeFIG. 3). An end of the long side wall81ais connected to an end of the short side wall81c, right angle and makes a corner. For the corner, surround of the support pin82that is cut a part of side wall81a,81c. Thickness of the support pin82is shorter than the thickness of the inner frame8. Height of a surface step83is lower than the top of the inner frame8, and height of the back of the support pin82is within a space that is the cut part of side wall81a,81c. Thus, the support pin82is formed on a surface step83of the inner frame8. Then, the end of the long side wall81ais connected with the end of the short side wall81b,81cby through the surface step83.

FIG. 4is shown a perspective view of a rubber member9belongs to the backlight unit1according to the embodiment.FIG. 5is shown a bottom side perspective view of a rubber member9attached conditions belongs to the backlight unit1according to the embodiment. The backlight unit1comprising a plurality of rubber members9which press the light guide plate4to the light-emitting diodes2. The rubber member9is made of rubber materials such a silicone rubber. The rubber member9functions as a rubber spring. The rubber member9comprises a press part9aas cylindrical shape and a projection part9bthat is formed on the press part9a(SeeFIG. 4). Outer diameter of the press part9ais larger than width between inside of the81a,81b, or81cand outside of the81a,81b, or81c(SeeFIG. 5). The press part9ais cut a part of the rubber member9, and the press part9ais set the space that is the cut part of side wall81aand81b, or the cut part of side wall81aand81c(SeeFIG. 5).

The cylindrical press part9ais formed a through-hole9cat the center. The support pin82is inserted to the through-hole9cand the rubber member9is set to the inner frame8(SeeFIG. 5). Outside of the press part9ais projected from inside of the81a,81b, or81c. Thus, Outside of the press part9ais attached side of the light guide plate4. Therefore, the light guide plate4is pressing to the LED2by the plural rubber members.

As above described is basic structure of the backlight unit1. The structure of the backlight unit1that is prefer to set the light guide plate4near the light-emitting diodes2. Therefore, embodiment backlight unit1comprises a plurality of rubber members9which press the light guide plate4to the light-emitting diodes2.

A hook9dis formed on top of the projection part9b. The hook9dis projected to inside of the rubber member9, and bottom side9eof the hook9dis hook side (SeeFIG. 4). The hook9dis hooked surface step83of the inner frame8when the cylindrical press part9ais inserted the support pin82. Thus, the hook9dprevents to drop the rubber member9from the support pin82. Further, combination of the projection part9band the hook9dprevent to turn the rubber member9around of the support pin82. The cylindrical press part9ais made of a silicone rubber. Thus, the cylindrical press part9aprevents to drop itself by frictional force between the silicone rubber and the support pin82. Moreover, the hook9dprevents to drop the rubber member9certainly.

FIG. 5is shown a bottom side perspective view of attached conditions for the inserted rubber member9and the support pin82.FIG. 6is shown a plane view of attached conditions for the outer frame7and the inner frame8.FIG. 7is shown an expanded perspective section view of a rubber member9attached conditions.FIG. 8is shown an expanded perspective view of a rubber member9attached conditions.

According to shape of the support pin82is combination full cylindrical shape and half cylindrical shape. That is, the support pin82is the full cylindrical shape at side of the surface step83, and the support pin82is half cylindrical shape at side of tip (SeeFIG. 5,FIG. 7). Then, when the rubber member9inserted the support pin82, a space100is formed between the support pin82and the cylindrical press part9a(SeeFIG. 5). The space100is adjusting for elastic force of the cylindrical press part9a. That is, the shape of the support pin82confront to the cylindrical press part9ais formed the half cylindrical shape, and then, the half cylindrical shape of the support pin82adjust to the elastic force of the cylindrical press part9aproper range. When needed large elastic force, formed the support pin82full cylindrical shape, for example.

The cylindrical rubber member9is a fine small part. If the rubber member9is dropped after assembles, difficult to find and re-assemble the dropped rubber member9. The hook9dis hooked surface step83of the inner frame8when the cylindrical press part9ais inserted the support pin82. Thus, the hook9dprevents to drop the rubber member9from the support pin82. Further, combination of the projection part9band the hook9dprevent to turn the rubber member9around of the support pin82. Then, the rubber member9attaches the light guide plate4certainly. Therefore, the light guide plate4is supported constantly by the cylindrical rubber member s9.

Regarding assemble method of the cylindrical rubber member9to the inner frame8that is following steps. First, set the rubber member9to the support pin82. When the center through-hole9cis inserted the support pin82, the projection part9bis bent toward the outside. The support pin82is inserted the center through-hole9c, and the projection part9breturn original positions by elastic restoring force of it. Then, the rubber members9are hooked to the inner frame8. Next, set the inner frame8into the outer frame7. Head of the inner frame8is a side of the rubber members9settled, preferably. Next, set the light guide plate4into the inner frame8. It is easy to set the light guide plate4what means attach a side of the light guide plate4to the outside of the rubber members9, and then, push and insert the light guide plate4. Then, the light guide plate4is supported constantly by the cylindrical rubber members9, and the light guide plate4is assembled into the inner frame8.

The cylindrical rubber members9are attached corners of the light guide plate4one-to-one correspond. Then, the light guide plate4is pushed the arrow direction inFIG. 6by the rubber member9. As the result, structure of the backlight unit is certain pressing the light guide plate4to the LED2. And the corners of the light guide plate4are chamfered at the top side, preferably. Then, attach area between the light guide plate4and the cylindrical press part9ais enlarged, and the cylindrical press part9apressing the light guide plate4, constantly. And the corners of the light guide plate4are rounded is acceptable to use.

Also the cylindrical rubber members9are attached an inside of the outer frame7. That is, a side of the cylindrical rubber member9is attached corners of the light guide plate4, and opposite side of the cylindrical rubber member9is attached an inside of the outer frame7, at once. Then, the plural cylindrical rubber members9are sandwiched between the inner frame8and the outer frame7. Therefore, the plural cylindrical rubber members9prevent to shaky between the inner frame8and the outer frame7.

As above embodiment, the cylindrical rubber member9is set to the each end of the long side wall81a, and the plural cylindrical rubber members9presses the light guide plate4to the light-emitting diodes2, and positioning the light guide plate4to given position in the inner frame8. It is possible to set the rubber springs on the middle area between the light-emitting diodes2and a side of the long side wall81athat means the middle positions of the side wall81aand81c. It is possible to set the additional rubber members on the middle positions of the side wall81aand81c, additions to above embodiment. Those layouts of the rubber members9perform as pressing work and positioning work as well.

The present invention provides a liquid crystal display device comprises the backlight unit1as above described embodiment. And the backlight unit1is a lighting unit throws a light on a liquid crystal display panel from behind. According to the present invention will be described hereinafter with reference to the drawings.

FIG. 9is shown an exploded perspective view of a liquid crystal display device according to the embodiment. According to the present invention, embodiment liquid crystal display (LCD) device comprises the backlight unit1as above described. That is, embodiment liquid crystal display device comprising; a liquid crystal display panel21; and the backlight unit1under the liquid crystal display panel21; and a outside frame22which is made of metal, polymer plastic, or composite of metal and polymer plastic, and wherein the frame22holding the liquid crystal display panel21and the backlight unit1.

The liquid crystal display panel21comprises an array substrate, an opposed substrate and a liquid crystal material inserted between the two substrates. The array substrate is formed with pixel electrodes corresponding to display pixels and a switching device (thin-film transistor) in matrix form. Also, on the liquid crystal display panel21, signal lines for transmitting signals to the pixel electrodes and gate lines for transmitting switching signals to the thin-film transistor that is the switching device are wired to be orthogonal to each other. On the other hand, the opposed substrate is provided substantially over the entire surface thereof with opposed electrodes formed of a transparent electrode material (ITO, for example) and with color filter layers corresponding to pixels. Furthermore, polarization plates are bonded to the outer surfaces of the array and opposed substrates, respectively, so that their polarization axes may be perpendicular to each other.

To the liquid crystal display panel21is having the configuration described above, a circuit board for supplying operation signals to the liquid crystal display panel21is electrically connected. The switching device is operated based on the operation signals transmitted from the circuit board to display images. The region in which the images are displayed is a display region and, therefore, the liquid crystal display panel21has a display region in which plural display pixels are arrayed.

The backlight unit1as above described is incorporated of the liquid crystal display panel21into the liquid crystal display device. The plane light output from a light-output surface of the light guide plate4. That is, a light output from a plurality of light-emitting diodes2is input to the edge of the light guide plate4and input to the edge of the light guide plate4, and the light through the light guide plate4and an optical sheet6, and the light output to a liquid crystal display panel21. To the liquid crystal display panel21, passed through the light guide plate4and thereafter irradiated onto the liquid crystal display panel21. The irradiated light is transmitted to the light guide plate4to display images, such as letters, pictures, etc., on the liquid crystal display panel21with predetermined brightness. According to the embodiment backlight unit1, certain pressing the light guide plate4to the light-emitting diodes2, and prevent to occurs image disqualify such as uneven luminance.

FIG. 10AandFIG. 10Bare shown a side section views of a prior art liquid crystal display device and as shown relations between a light output condition and a distance that the distance is between a light guide plate and a plurality of light-emitting diodes2, whereinFIG. 10Ais shown in case of the distance L1is large, and whereinFIG. 10Bis shown in case of the distance L2is small. In case of the distance L1is large that cause of the light guide plate4is not pressed enough, an optical sheet6is easy to input a light directory and the light is reflected far to the light-emitting diodes2. Then, occurs image disqualify such as uneven luminance. Meanwhile, in case of the distance L2is large that cause of the light guide plate4is pressed enough, most of the light input to the light guide plate4directories and the other light which in the optical sheet6is reflected near to the light-emitting diodes2. Then, image disqualify such as uneven luminance doesn't occurs. According to the embodiment backlight unit1, certain pressing the light guide plate4to the light-emitting diodes2, and prevent to occurs image disqualify such as uneven luminance such asFIG. 10Bas described.