KR20060112141A - Backlight unit and liquid crystal display device having the same - Google Patents

Abstract

A backlight unit and an LCD comprising the same are provided to improve the efficiency for cooling LEDs(Light Emitting Diodes) even without a radiator or a cooling fan, by interposing a heat conducting sheet between an LED circuit board and a reflective sheet. An LED circuit board(41) has a plurality of LEDs(42) which are protrusively mounted on a surface thereof. A reflective plate(51) is disposed on the LED circuit board, and reflects the lights emitted from the LEDs. A heat conducting sheet(71) is interposed between the LED circuit board and the reflective plate. The heat conducting sheet comprises a polyacrylic rubber. The heat conducting sheet further comprises aluminum.

Description

BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE HAVING THE SAME}

1 is an exploded perspective view of a liquid crystal display according to a first embodiment of the present invention;

2 is a cross-sectional view of the assembled state of FIG.

   3 is an enlarged cross-sectional view of the LED light source region of FIG. 1, and

4 is a cross-sectional view illustrating an assembled state of a liquid crystal display according to a second exemplary embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

10: upper chassis 20: liquid crystal display panel

25 drive unit 30 light control member

40: LED light source portion 41: LED circuit board

42: LED 51: reflector

52: LED receiver 61: gap pad

71: heat conductive sheet 72: adhesive

80: lower chassis

The present invention relates to a backlight unit and a liquid crystal display including the same, and more particularly, to a backlight unit using an LED as a light source and a liquid crystal display including the same.

The LCD includes a thin film transistor substrate, a color filter substrate, and a liquid crystal display panel in which liquid crystal is injected between both substrates. Since the liquid crystal display panel is a non-light emitting device, a backlight unit for supplying light is disposed on the rear surface of the thin film transistor substrate. Light transmitted from the backlight unit is adjusted according to the arrangement of liquid crystals. The liquid crystal display panel and the backlight unit are housed in the chassis.

The backlight unit is divided into an edge type and a direct type according to the position of the light source. The edge type is a structure in which a light source is installed on the side of the light guide plate, and is mainly applied to a relatively small liquid crystal display device such as a laptop type and a desktop computer. Such an edge type backlight unit has a good light uniformity, a long service life, and is advantageous for thinning a liquid crystal display device.

The direct type is a structure mainly developed as the size of the liquid crystal display device is enlarged. The direct type is a structure in which at least one light source is disposed on the rear surface of the liquid crystal display panel to supply light to the liquid crystal display panel. Such a direct type backlight unit may use a large number of light sources as compared to an edge type backlight unit to secure a high luminance, but has a disadvantage that luminance is not uniform.

On the other hand, as a light source of the backlight unit, LEDs having high luminance and excellent color reproducibility are used. LEDs generate more heat than other light sources such as cold cathode fluorescent lamps (CCFLs) and external electrode fluorescent lamps (EEFLs) .If the heat is not properly dissipated, luminance decreases and color shift occurs. do.

Heat dissipation fins, heat pipes, cooling fans, etc. are used to remove heat generated from the LEDs, but there is a problem in that the liquid crystal display becomes heavy and thick.

Accordingly, an object of the present invention is to provide a backlight unit having a thin thickness and excellent LED cooling efficiency and a liquid crystal display including the same.

The object is, according to the present invention, an LED circuit board having a plurality of LEDs mounted to protrude from the substrate surface; A reflection plate disposed on the LED circuit board and reflecting light from the LED; It can be achieved by a backlight unit comprising a heat conducting sheet interposed between the LED circuit board and the reflecting plate.

The thermally conductive sheet preferably includes polyacryl rubber, which is a material having high thermal conductivity.

It is preferable that the said heat conductive sheet further contains aluminum which is excellent in thermal conductivity.

It is preferable that the thermal conductivity of the said heat conductive sheet in the plate surface direction is larger than 15 W / mK.

It is preferable that the thermal conductivity of the said heat conductive sheet in the thickness direction is larger than 1.4 W / mK.

It is preferable that the thermal conductivity in the plate direction of the thermally conductive sheet is 10 W / mK or more larger than the thermal conductivity in the thickness direction.

On the other hand, an object of the present invention and the liquid crystal display panel; The liquid crystal display device may also be achieved by a liquid crystal display device positioned on a rear surface of the liquid crystal display panel and including the backlight unit.

It is preferable that the LED is scattered over the entire plate surface of the reflecting plate.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

In various embodiments, like reference numerals refer to like elements, and like reference numerals refer to like elements in the first embodiment and may be omitted in other embodiments.

A liquid crystal display according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 2 as follows.

1 and 2 are exploded perspective and assembled cross-sectional views of a liquid crystal display according to a first embodiment of the present invention, respectively.

The liquid crystal display device 1 includes a liquid crystal display panel 20, a light adjusting member 30 disposed on the rear surface of the liquid crystal display panel 20, a reflecting plate 51 positioned on the rear surface of the light adjusting member 30, and a reflecting plate 51. It includes the LED circuit board 41, which is located on the back of the) and the LED 42 is mounted, the heat conductive sheet 71 in close contact between the reflecting plate 51 and the LED circuit board 41.

The liquid crystal display panel 20, the light adjusting member 30, the reflecting plate 51, the thermal conductive sheet 71, and the LED circuit board 41 are accommodated in the upper chassis 10 and the lower chassis 80.

The liquid crystal display panel 20 bonds the thin film transistor substrate 21 on which the thin film transistor is formed, the color filter substrate 22 facing the thin film transistor substrate 21, and the two substrates 21 and 22 to each other, thereby bonding a cell gap. a sealant 23 forming a gap), and a liquid crystal layer 24 positioned between both substrates 21 and 22 and the sealant 23. The LCD panel 20 adjusts the arrangement of the liquid crystal layer 24 to form a screen, but because it is a non-light emitting device, light must be supplied from the LED light source unit 40 located on the rear surface.

One side of the thin film transistor substrate 21 is provided with a driver 25 for applying a drive signal. The driver 25 includes a flexible printed circuit board (FPC. 26), a driving chip (27) mounted on the flexible printed circuit board (26), and a circuit board (PCB) connected to the other side of the flexible printed circuit board (26). 28). The driver 25 illustrated represents a chip on film (COF) method, and other known methods such as a tape carrier package (TCP) and a chip on glass (COG) may be used. In addition, the driver 25 may be formed on the thin film transistor substrate 21 during the wiring formation process.

The light adjusting member 30 disposed on the rear surface of the liquid crystal display panel 20 may include a diffusion plate 31, a prism film 32, and a protective film 33.

The diffusion plate 31 is composed of a coating layer including a base plate and beads of beads formed on the base plate. Since the LED 42 is not a surface light source but a point light source, the arrangement of the LEDs 42 may be recognized by the user and the luminance may be uneven. The diffusion plate 31 diffuses the light supplied from the LED 42 to make the luminance uniform. In order to prevent the arrangement of the LEDs 42, a light blocking pattern made of a material having a low transmittance may be formed at a portion of the diffusion plate 31 through which the light of the LEDs 42 is most strongly supplied. In some cases, a light guide plate and a diffusion film may be used instead of the diffusion plate 31.

The prism film 32 is formed with a triangular prism-shaped prism on the upper surface. The prism film 32 collects the light diffused from the diffusion plate 31 in a direction perpendicular to the plane of the upper liquid crystal display panel 20. Two prism films 32 are usually used, and the micro prisms formed on each prism film 32 form a predetermined angle. The light passing through the prism film 32 is almost vertically progressed to provide a uniform luminance distribution. If necessary, a reflective polarizing film may be used together with the prism film 32, and only the reflective polarizing film may be used without the prism film 32.

The protection film 33 positioned at the top protects the prism film 32 that is weak to scratches.

The LED circuit board 41 is positioned over the entire rear surface of the liquid crystal display panel 20. The LED circuit board 41 may be made of a main material of a metal such as aluminum to facilitate heat transfer.

The LED 42 is mounted on the LED circuit board 41, and the LED 42 is also disposed on the entire rear surface of the LCD panel 20. The LEDs 42 include LEDs 42 emitting red, blue, and green colors, respectively, and light of each color is mixed to supply white light to the liquid crystal display panel 20. The method of arranging the LEDs 42 of each color is not limited.

The reflecting plate 51 is provided on the LED circuit board 41. The reflector 51 is provided with an LED receiver 52 corresponding to the arrangement of the LED 42, and the LED 42 is accommodated in the LED receiver 52. The reflector 51 serves to reflect the light incident to the lower part and to supply the diffuser 31. The reflecting plate 51 may be made of polyethylene terephthalate (PET) or polycarbonate (PC). In addition, the reflecting plate 51 may be provided to be thicker so that um is not generated by the strong heat generated from the LED 42.

The thermal conductive sheet 71 is interposed between the LED circuit board 41 and the reflecting plate 51. The thermally conductive sheet 71 is a thin plate containing polyacryl rubber, which is a material having excellent thermal conductivity, and further includes aluminum to further improve thermal conductivity. The thickness of the thermal conductive sheet 71 is not limited, but may be 0.08 to 1.5 mm.

 The thermal conductive sheet 71 is in close contact with the LED circuit board 41 and the reflecting plate 51 between the LED circuit board 41 and the reflecting plate 51 to transfer heat generated in the reflecting plate 51 by the LED 42. Received and transmitted to the LED circuit board (41). The thermal conductive sheet 71 has a different thermal conductivity in the plate direction and a thermal conductivity in the thickness direction, and the thermal conductivity in the plate direction is larger than 10 W / mK in comparison with the thermal conductivity in the thickness direction. The thermal conductivity in the plate direction is preferably 15 W / mK or more and the thermal conductivity in the thickness direction is 1.4 W / mK or more.

Similar to the reflecting plate 51, the thermal conductive sheet 71 is provided with an LED receiving port 52 corresponding to the arrangement of the LED 42, and the LED 42 is accommodated in the LED receiving port 52.

A gap pad 61 is provided between the LED circuit board 41 and the lower chassis 80. The gap pad 61 is a thin plate made of a material having excellent thermal conductivity, and may have a thickness of about 0.5 mm. The LED pad 41 and the lower chassis 70, which are made of metal, are brought into close contact with each other by the gap pad 61, and the heat transferred from the thermal conductive sheet 71 to the LED circuit board 41 is transferred to the lower chassis 70. The light is transmitted to the outside of the liquid crystal display 1.

The reason why the LED cooling efficiency of the liquid crystal display according to the first embodiment is excellent will be described with reference to FIG. 3. 3 is an enlarged cross-sectional view of the LED light source region of FIG. 1.

As described above, when the LED 42 is driven, heat is generated in the reflector 51. Since the reflecting plate 51, the heat conducting sheet 71, the LED circuit board 41, the gap pad 61, and the lower chassis 80 are in close contact with each other, most of the heat generated in the reflecting plate 51 is caused by continuous conduction. Delivered to the lower chassis 80. At this time, since the LED 42 is a point light source, heat is intensively generated in a portion close to the LED 42 of the reflecting plate 51.

Heat generated in a portion close to the LED 42 of the reflecting plate 51 is transferred to the heat conductive sheet 71 in close contact with the rear surface of the reflecting plate 51. Since the thermal conductive sheet 71 has a larger thermal conductivity in the plate direction than in the thickness direction, most of the heat moves along the plate surface of the thermal conductive sheet 71. As a result, the heat in the heat conductive sheet 71 is not distributed in the form of dots, but is uniformly distributed over the entire surface of the heat conductive sheet 71. As such, the heat dispersed on the front surface of the heat conductive sheet 71 is transferred to the LED circuit board 41 in close contact with the heat conductive sheet 71. The heat transferred to the LED circuit board 41 is transferred to the gap pad 61 in close contact with the LED circuit board 41 and finally transferred to the lower chassis 80 in close contact with the gap pad 61.

When there is no heat conduction sheet 71 in close contact between the reflecting plate 51 and the LED circuit board 41, the heat generated in the reflecting plate 51 is not reflected because the reflecting plate 51 and the LED circuit board 41 are not in close contact with each other. It cannot be easily conducted to the outside of the liquid crystal display device 1. On the other hand, when the thermally conductive sheet 71 is interposed, the thermally conductive sheet 71 evenly disperses the heat generated in the reflective plate 51, and then easily heats the heat through the LED circuit board 41 in close contact with the thermally conductive sheet 71. In this way, the LED 42 is cooled efficiently.

On the other hand, when the thermal conductivity of the thermal conductive sheet 71 is not significantly different in the thickness direction and the plate surface direction, the heat transferred from the reflecting plate 51 to the thermal conductive sheet 71 is located at the lower part of the LED 42 of the thermal conductive sheet 71. Concentrate on what you do. At this time, since the portion where heat is concentrated is a part of the thermal conductive sheet 71, the thermal conductive contact area with the LED circuit board 41 is limited and cooling is not performed efficiently. Heat sink fins and / or cooling fans are needed to dissipate the concentrated heat.

On the other hand, in the first embodiment, since the heat generated from the reflecting plate 51 mainly moves along the plate surface direction of the heat conductive sheet 71, the contact area with the LED circuit board 41 is widened, and a separate heat sink fin or cooling fan is used. The LED 42 can be cooled effectively without using it. Therefore, it is possible to reduce the weight, thickness and noise of the liquid crystal display device 1.

Hereinafter, the liquid crystal display device 1 according to the second embodiment of the present invention will be described. 4 is a cross-sectional view illustrating an assembled state of a liquid crystal display according to a second exemplary embodiment of the present invention.

Adhesives 72 are applied to both surfaces of the heat conductive sheet 71 of the liquid crystal display device 1. The heat conductive sheet 71 is firmly adhered to each of the reflecting plate 51 and the LED circuit board 41 by the applied adhesive 72 to facilitate heat conduction from the reflecting plate 51 to the LED circuit board 41. The adhesive 72 uses resin excellent in adhesiveness and thermal conductivity. Each of the reflective plate 51 and the LED circuit board 41, which are made of metal, is difficult to adhere to each other by the adhesive 72 applied to both surfaces of the thermal conductive sheet 71, thereby increasing the adhesion and improving the thermal conductivity.

The above embodiments can be variously modified. The LED 42 is not interspersed with the entire plate surface of the reflecting plate 51, but the 'c' or 'ㅁ' letter arrangement is possible. In addition, to improve the cooling efficiency of the LED 42, the thermal conductive sheet 71 according to the present invention may be used as a heat sink fin, a heat pipe, or a cooling fan.

Thus, although some embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that the embodiments may be modified without departing from the spirit or spirit of the invention. There will be. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

As described above, according to the present invention, there is provided a backlight unit having a thin thickness and excellent in LED cooling efficiency and a liquid crystal display including the same.

Claims (8)

An LED circuit board having a plurality of LEDs mounted to protrude from the substrate surface; A reflection plate disposed on the LED circuit board and reflecting light from the LED; And a heat conducting sheet interposed between the LED circuit board and the reflecting plate. The method of claim 1, The thermally conductive sheet is a backlight unit, characterized in that it comprises a poly acrylic rubber. The method of claim 2 The heat conducting sheet further comprises a backlight unit, characterized in that aluminum The method of claim 1, And a thermal conductivity in the plate direction of the thermally conductive sheet is greater than 15 W / mK. The method of claim 1, And a thermal conductivity in the thickness direction of the thermal conductive sheet is larger than 1.4 W / mK. The method of claim 1, And a thermal conductivity in the plate direction of the thermal conductive sheet is 10 W / mK or more than the thermal conductivity in the thickness direction. A liquid crystal display panel; A liquid crystal display device, comprising: a backlight unit positioned on a rear surface of the liquid crystal display panel, and comprising a backlight unit according to any one of claims 1 to 6. The method of claim 7, wherein And the LEDs are scattered over the entire surface of the reflecting plate.

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