KR20050067310A - Back-light unit of liquid crystal display - Google Patents

Abstract

The present invention relates to a backlight unit of a liquid crystal display device, the backlight unit of the liquid crystal display device of the present invention includes a lamp for emitting light; A first light guide plate provided on a side of the lamp and configured to irradiate the light supplied from the lamp upward; A second light guide plate provided on an upper portion of the lamp to transmit and reflect the light supplied from the lamp; A reflector for reflecting light from the lamp and incident on the light guide plate; It is provided at regular intervals on the first light guide plate and the second light guide plate, and diffuses the light incident from the first light guide plate and the second light guide plate to irradiate the upper portion and the light transmittance of the light incident from the diffuser plate It comprises a liquid crystal panel which adjusts and displays an image.

Description

BACK-LIGHT UNIT OF LIQUID CRYSTAL DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit of a liquid crystal display device, and more particularly, to a backlight unit capable of obtaining sufficient luminance with a smaller number of lamps than a conventional direct type method and making the liquid crystal display device thin.

Recently, with the development of various portable electronic devices such as mobile phones, PDAs, and notebook computers, there is an increasing demand for flat and thin flat panel display devices that can be applied thereto.

Such flat panel displays include Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Field Emission Display (FED), Vacuum Fluorescent Display (VFD). Although research has been actively conducted, liquid crystal displays (LCDs) are currently in the spotlight due to mass production technology, ease of driving means, and high quality.

In general, a liquid crystal display device is a liquid crystal in which a thin film transistor array substrate and a color filter substrate facing each other are bonded to maintain a constant cell gap, and a liquid crystal layer is formed in the constant cell gap. A panel includes a liquid crystal display, a driving unit for driving the liquid crystal panel to display an image, and a backlight unit positioned at a rear surface of the liquid crystal panel to supply light to the liquid crystal panel.

The liquid crystal display device is a transmissive display device, and a desired image is displayed on a screen by adjusting the amount of light passing through the liquid crystal layer by refractive index anisotropy of liquid crystal molecules. Therefore, in the liquid crystal display device, a back light, which is a light source passing through the liquid crystal layer, is provided for displaying an image. In general, the backlight can be classified into two types.

The first is an edge-type backlight, in which a lamp is provided on the side of the liquid crystal panel to provide light to the liquid crystal layer, and the second is directly underneath the lamp, which is provided on the back of the liquid crystal panel to provide light directly to the front of the liquid crystal panel. Type backlight.

The side backlight may be installed on the side of the liquid crystal panel to supply light to the liquid crystal layer through the reflector and the light guide plate. Therefore, since the thickness can be made thin, it is mainly used for the notebook etc. which are manufactured with thin thickness. However, in the side type backlight, since a lamp emitting light is located on the side of the liquid crystal panel, it is difficult to apply to a large area liquid crystal panel, and it is difficult to obtain high luminance because light loss occurs through the light guide plate. Therefore, there has been a problem that it is not suitable for the large-area liquid crystal panel for LCD TVs, which has been in the spotlight recently.

In the direct backlight, since the light emitted from the lamp is directly supplied to the liquid crystal layer and there is no loss of light due to the light guide plate, sufficient brightness can be provided to a large area liquid crystal panel. It is mainly used to

 1 is a view showing a backlight unit including a conventional direct type backlight.

As shown in the figure, the liquid crystal display device 1 includes a liquid crystal panel 3 and a backlight unit 10 provided on the rear surface of the liquid crystal panel 3. The liquid crystal panel 3 is a place where an actual image is realized and includes a transparent first substrate 3a and a second substrate 3b such as glass and a liquid crystal layer (not shown) formed therebetween.

Although not shown in the drawing, a plurality of gate lines arranged to be uniformly spaced apart laterally and a plurality of data lines arranged to be uniformly spaced apart vertically intersect each other on the first substrate 3a. Pixels are provided in these intersecting regions. The pixels are individually provided with a switching element such as a thin film transistor and a pixel electrode.

In addition, a color filter layer of red, green, and blue is formed on the second substrate 3b to display various color images by mixing red, green, and blue light that have passed through the red, green, and blue color filter layers. Done. In addition, the outer surface of the color filter layer, the black matrix for preventing light leakage is formed densely in a net form. The second substrate 3b is provided with a common electrode to form an electric field in the liquid crystal layer together with the pixel electrode of the first substrate 3a to change the light transmittance of the liquid crystal layer, thereby supplying it from the backlight unit 10. Display the light as an image.

The backlight unit 10 emits light and supplies a plurality of lamps 11 to supply the front surface of the liquid crystal panel 3, and a reflector reflecting light emitted from the lamps 11 to improve light efficiency. , 17), a diffusion plate 15 for diffusing the light emitted from the lamp 11 and incident on the liquid crystal panel 3, and re-diffusing light diffused by the diffusion plate 15. And an optical sheet 16 which focuses and enters the liquid crystal panel 3.

The reflective plate 17 provided on the rear surface of the lamp 11 reflects the light emitted from the rear surface of the lamp 11 toward the diffuser plate 15 to reduce the loss of light and to the diffuser plate 15. Improve the uniformity of the incident light.

A diffusion sheet and a prism sheet may be applied to the optical sheet 16 disposed between the liquid crystal panel 3 and the diffusion plate 15, and a protective sheet may be added.

The diffusion sheet disperses the light incident from the lamp 11 to prevent the light from being partially concentrated to cause stains in the image displayed on the liquid crystal panel 3, and the prism sheet is incident from the diffusion sheet. By condensing the angle of light vertically, the light is uniformly distributed on the entire surface of the liquid crystal panel 3.

As described above, the direct type backlight unit is mainly used in large-area liquid crystal panels, which are being produced in recent years, and are used to obtain brighter brightness even in small and medium-area liquid crystal panels. The direct type backlight unit has a merit of providing clear image quality through high brightness by directly supplying the light of the lamp to the front of the liquid crystal panel, but as the number of lamps is increased to obtain high brightness, There is a problem that the production cost is increased, and also because the light is supplied directly, the amount of light incident on each area of the liquid crystal panel may vary according to the distance to the lamp. That is, the light uniformity of the image displayed on the liquid crystal panel may decrease.

In addition, since a separate space for providing a plurality of lamps must be secured on the rear surface of the liquid crystal panel, the liquid crystal display device is limited in thickness.

In addition, since the heat emitted from the lamp is conducted to the liquid crystal panel via the upper diffusion plate and the optical sheet, the deterioration of the liquid crystal due to heat can reduce the image quality of the liquid crystal display device.

Therefore, the present invention has been devised to solve the above-mentioned conventional problems, and an object of the present invention is to provide a lamp and a light guide plate in an overlapping area, and to secure a constant space between the light guide plate and the diffuser plate on the light guide plate, An object of the present invention is to provide a backlight unit of a liquid crystal display device which improves light uniformity of light of a lamp supplied to a liquid crystal panel to improve image quality.

The backlight unit of the liquid crystal display device for achieving the object of the present invention as described above includes a lamp for emitting light; A first light guide plate provided on a side of the lamp and configured to irradiate the light supplied from the lamp upward; A second light guide plate provided on an upper portion of the lamp to transmit and reflect the light supplied from the lamp; A reflector for reflecting light from the lamp and incident on the light guide plate; It is provided at regular intervals on the first light guide plate and the second light guide plate, and diffuses the light incident from the first light guide plate and the second light guide plate to irradiate the upper portion and the light transmittance of the light incident from the diffuser plate It comprises a liquid crystal panel which adjusts and displays an image.

Referring to the backlight unit of the present invention as described above in detail with reference to the accompanying drawings as follows.

2 is a simplified cross-sectional view of the backlight unit according to the present invention.

Referring to FIG. 2, the backlight unit includes a lamp 111 that emits light, a first light guide plate 120 that is provided on both sides of the lamp 111, and radiates light supplied from the lamp 111 to an upper portion thereof. A second light guide plate 125 disposed above the lamp 111 to transmit and reflect the light supplied from the lamp 111, and a reflecting plate 122 to reflect the light of the lamp 111 and enter the upper portion of the lamp 111; And a diffusion plate 115 that is uniformly spaced apart on the first light guide plate 120 and diffuses the light supplied from the first light guide plate 120 and the second light guide plate 125 to be irradiated upwardly. An optical sheet 116 for re-diffusing and condensing the light incident from the diffuser plate 115 and supplying the light to the upper part, and a liquid crystal panel for controlling the light transmittance of the light incident from the optical sheet 116 to display an image ( 103).

The backlight unit is provided on one side of the light guide plate 120 as in the related art, and is not a side type method of supplying light to the side surface of the light guide plate 120. In addition, the light guide plate 120 is removed and provided on the rear surface of the liquid crystal panel 103. It is not a direct type method of directly supplying light to the entire liquid crystal panel 103. The backlight unit illustrated in FIG. 3 is a mixture of a conventional side type method and a direct type method. The backlight unit is surrounded by the first LGP 120, the second LGP 125, and the reflector 122. It is a backlight unit having a form.

The backlight unit further forms the first light guide plate 120 and the second light guide plate 125 which were not included in the conventional direct type backlight unit.

When the lamp 111 is seen, the first light guide plate 120 is formed on both sides, the second light guide plate 125 is formed on the upper side, and the reflector plate 122 is formed on the lower side thereof. It is provided in an enclosed space. That is, the light of the lamp 111 is incident toward the liquid crystal panel 103 through any one of the first LGP 120, the second LGP 125, and the reflecting plate 122.

Looking at the first light guide plate 120, the second light guide plate 125 and the reflecting plate 122 surrounding the lamp 111 in order, first, the first light guide plate 120 is the same material as the conventional light guide plate, It is made of a transparent plastic resin, and uniformly distributes the light of the lamp 111 incident from both sides of the first light guide plate 120 to irradiate upwards. At this time, by additionally forming a diffusion pattern such as light diffusion printing, fine shape, corrosion, etc. in the first light guide plate 120, the light proceeding in the first light guide plate 120 can be emitted evenly over the entire surface. have.

As described above, since the light of the lamp 111 is uniformly distributed through the first light guide plate 120 and the second light guide plate 125 surrounding the outside of the lamp 111, the conventional direct type Without using a large number of lamps as described above, even a small number of lamps can be used to sufficiently and evenly emit the light of the lamps over the entire liquid crystal panel. In addition, the liquid crystal display device may be manufactured to be thinly formed by overlapping an area where the first LGP 220 and the second LGP 225 are provided without securing a space for forming the lamp 111. .

Meanwhile, the second light guide plate 125 may be made of the same transparent plastic resin as the first light guide plate 120, and may be made opaque than the first light guide plate 120. When the first LGP 120 and the second LGP 125 have the same light transmittance, they pass through the second LGP 125 located closest to the lamp 111 as in the conventional direct type. Since light has the highest luminance, bright lines having high luminance are displayed in the region of the liquid crystal panel 103 corresponding to the position of the lamp 111. That is, unevenness in brightness may be caused.

Therefore, the second light guide plate 125 is less opaque than the first light guide plate 120, thereby lowering the light transmittance. The second LGP 125 may pass a portion of the light of the lamp 111 directly to the upper portion, and partially reflect the light of the lamp 111 to be incident toward the liquid crystal panel 103 through the first LGP 120 and the reflective plate 122. do. At this time, the second light guide plate 125 is made of a reflective material, or by applying a reflective material on the lower surface of the second light guide plate 125 to which the light of the lamp 111 is incident, all of the light of the lamp 111 is first The light guide plate 120 may be incident.

On the other hand, the light emitted through the first light guide plate 120 and the second light guide plate 125 is incident to the diffusion plate 115, the first light guide plate 120 and the second light guide plate 125 and the diffusion plate ( It is naturally diffused in a predetermined space provided between the 115 and then incident to the diffusion plate 115. Therefore, light passing through the first LGP 120 and the second LGP 125 may be higher than the light diffusing plate 115.

In this case, when the diffusion plate 115 is directly stacked on the first light guide plate 120 and the second light guide plate 125, the diffusion plate 115 may be made of an opaque material to increase the light diffusion effect. In this case, as the diffusion plate 115 becomes opaque, light transmittance decreases and luminance decreases, but light diffusion effect increases. Therefore, the light transmittance and light diffusion rate should be properly considered.

On the other hand, the diffuser plate 115 evenly diffuses the incident light so that the light amount can be evenly emitted without dense to any one place. Light emitted from the diffuser plate 115 is incident on the optical sheet 116.

The optical sheet 116 is usually composed of a diffusion sheet for diffusing the incident light, and a prism sheet for condensing the light diffused widely to emit vertically. The diffusion sheet re-diffuses the light diffused by the diffusion plate 115 to uniformly diffuse the light that is not sufficiently diffused by the diffusion plate 115. In addition, the prism sheet refracts uniformly diffused light upward so that the prism sheet is accurately incident on the entire surface of the liquid crystal panel 103.

The movement path of light as described above will be described in detail with reference to FIG. 3.

3 is a view illustrating a movement path of light emitted from a lamp in the backlight unit of the present invention.

As shown in the figure, the light emitted from the lamp 211 is incident on the first LGP 220, the second LGP 225, and the reflecting plate 222. The first LGP 220 uniformly propagates incident light and irradiates the light upwardly, and the second LGP 225 directly passes some of the incident light and reflects some of the incident light to the first LGP 220. To be incident on. The reflective plate 222 reflects the light traveling to the rear surface of the first light guide plate 220 and emits the light to the upper portion of the first light guide plate 220.

As such, the light emitted through the first LGP 220 and the second LGP 225 may have a predetermined distance between the first LGP 220 and the second LGP 225 and the diffuser plate 215. It diffuses naturally in the excitation space and is incident on the diffusion plate 215.

The light incident on the diffusion plate 215 is uniformly diffused and incident on the diffusion sheet 216a, and the light further diffused by the diffusion sheet 216a is refracted upward by the prism sheet 216b to form a liquid crystal. It is incident on the front of the panel.

In FIG. 3, the diffusion plate, the diffusion sheet, and the prism sheet are arranged at regular intervals to accurately represent the path of light, and are actually stacked on each other.

As described above, as the first light guide plate 220 is formed on both sides of the lamp 211, the light of the lamp 211 is uniformly passed through the first light guide plate 220 and the second light guide plate 225. Can be emitted to the top. Therefore, the first light guide plate 220 and the second light guide plate 225 can irradiate light to the front of the liquid crystal panel without using many lamps as in the conventional direct type method, and the first light guide plate 220 and An additional diffusion effect may be obtained by the spaced space between the second LGP 225 and the diffusion plate 215.

In addition, since the lamp 211 is surrounded by the first light guide plate 220 and the second light guide plate 225, the heat emitted from the lamp 211 is the first light guide plate 220 and the second light guide plate 225. Part is dispersed, and part is dispersed by natural convection in the spaced space between the first and second light guide plates 220 and 225 and the diffusion plate 215, and thus, to the liquid crystal panel via the diffusion plate 215. It can reduce the heat conducted. Therefore, it is possible to prevent the deterioration of the image quality of the liquid crystal display due to the deterioration of the liquid crystal due to the heat emitted from the lamp 211.

On the other hand, the lamp used as a light source in the backlight unit includes a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL) and an external electrode. Fluorescent lamp (External Electrode Fluorescent Lamp).

The cold cathode fluorescent lamp and the external electrode fluorescent lamp are lamps in which the emitted light is evenly radiated in all directions, and when applied to the backlight unit of the present invention, the second light guide plate 225 is opaque and the second light guide plate 225 ), The light transmittance should be lowered. That is, when the light transmittance of the second light guide plate 225 is made to be the same as the light transmittance of the first light guide plate 220, the light of the lamp emitted in all directions passes through the second light guide plate 225 and the liquid crystal panel. This is because bright lines with high luminance can be displayed.

The light emitting device includes a side emitting light emitting device and a front emitting light emitting device. The side emitting light emitting device is a light emitting device in which most light is emitted to the side of the light emitting device, and the front emitting light emitting device is a light emitting device in which most light is emitted to the front of the light emitting device. The application of such a light emitting device to the backlight unit will be described with reference to the accompanying drawings.

FIG. 4A is a view showing a side emitting light emitting device applied to a backlight unit, and FIG. 4B is a view showing a front emitting light emitting device applied to the backlight unit.

As shown in the figure, the first LGP 320 is formed on both sides of the side emission light emitting device 350. Since the side emission light emitting device 350 emits light toward the side in the normal driving, the side light emitting device 350 supplies most of the light to the first light guide plate 320 disposed on both sides of the side light emitting device 350 even when disposed.

When the front emission light emitting device 352 is generally disposed, light is emitted upward, and most of the light is incident on the second LGP 325. Therefore, the front emission light emitting device 352 is laid on its side so that most of the light is incident on the first LGP 320.

As described above, the backlight unit of the liquid crystal display of the present invention forms a plurality of lamps and the first and second light guide plates in an overlapping area, and has a predetermined spaced space between the first and second light guide plates and the diffuser plate, Since light can be uniformly irradiated onto the entire liquid crystal panel, sufficient luminance can be obtained even if the number of lamps is reduced compared to the conventional art, resulting in a reduction in production cost and a thin liquid crystal display device.

In addition, since the first and second light guide plates and the reflecting plate surround the lamp, and a predetermined space is provided between the first and second light guide plates and the diffuser plate, the light emitted from the lamp can be dispersed as much as possible, Deterioration of the liquid crystal and deterioration of the image quality of the liquid crystal display due to the deterioration of the liquid crystal can be prevented.

1 is a view showing a backlight unit including a conventional direct type backlight.

2 is a simplified cross-sectional view of the backlight unit according to the present invention;

3 is a view showing a movement path of light emitted from a lamp in the backlight unit of the present invention.

Figure 4a is a view showing that the side emitting light emitting device is applied to the backlight unit.

Figure 4b is a view showing a front emission light emitting device applied to the backlight unit.

** Description of the symbols for the main parts of the drawings **

103: liquid crystal panel 111: lamp

115: diffuser plate 116: optical sheet

120: first light guide plate 122: reflecting plate

125: second light guide plate

Claims (9)

Lamps emitting light; A first light guide plate provided on a side of the lamp and configured to irradiate the light supplied from the lamp to the top; A second light guide plate provided on an upper portion of the lamp to transmit and reflect light supplied from the lamp; A reflection plate reflecting light of the lamp and incident on the light guide plate; A diffusion plate provided on the first light guide plate and the second light guide plate at regular intervals to diffuse light incident from the first light guide plate and the second light guide plate and to irradiate the light upwardly; And And a liquid crystal panel configured to display light incident from the diffusion plate as an image by adjusting light transmittance. The backlight unit of claim 1, wherein the first light guide plate and the second light guide plate are integrated. The backlight unit of claim 1, wherein the first light guide plate and the second light guide plate have different light transmittances. The backlight unit of claim 1, wherein the first light guide plate and the second light guide plate have the same light transmittance. The backlight unit of claim 1, wherein the lamp is a side emitting light emitting device. The backlight unit of claim 1, wherein the lamp is a front emission light emitting device. The backlight unit of claim 1, wherein a space is provided between the first light guide plate, the second light guide plate, and the diffusion plate. The backlight unit of claim 1, wherein the diffusion plate is disposed to be in close contact with upper surfaces of the first and second light guide plates. The backlight unit of claim 1, further comprising a diffusion sheet between the diffusion plate and the liquid crystal panel to re-diffuse light incident from the diffusion plate.