KR20070073505A - Backlight unit and liquid crystal display having the same - Google Patents

Abstract

A backlight unit and an LCD(Liquid Crystal Display) including the same are provided to form a slanted sidewall of a reflection plate, thereby improving the brightness property of an edge portion. A reflection plate(20) includes a sidewall slantly formed with a predetermined angle such as 23 to 30 degrees and extended from a base. Plural light sources(10) are arranged at the reflection plate. A light guide panel(30) is formed at the upper portion of the reflection plate and the light source. The light guide panel is separated from the sidewall of the reflection plate with a predetermined distance such as 6 to 8mm horizontally. The light source is red, green and blue light emitting diodes. The light emitting diode is a side surface light emitting diode. The reflection plate includes an opening so that the light source is exposed through the opening. A diffusion sheet is arranged at the upper portion of the light guide panel. A prism sheet is arranged at the upper portion of the diffusion sheet. A protection sheet is arranged at the upper portion of the prism sheet.

Description

Backlight unit and liquid crystal display including the same {Backlight Unit and Liquid Crystal Display having the same}

1 is an exploded perspective view schematically showing the structure of a backlight unit using a conventional light emitting diode as a light source.

2 is a cross-sectional view showing a partial cross section of a conventional backlight unit.

Figure 3 is an exploded perspective view schematically showing the structure of the backlight unit according to the present invention.

4 is a perspective view showing a reflecting plate according to the present invention.

5 is a cross-sectional view showing a part of a light source, a reflector and a light guide plate according to the present invention;

6 is a graph showing luminance uniformity according to a separation distance between a reflector and a light guide plate;

7A to 7C are distribution charts measuring luminance uniformity according to a separation distance between a reflecting plate and a light guide plate.

8A to 8C are distribution charts of measuring color uniformity according to a separation distance between a reflecting plate and a light guide plate.

9 is an exploded perspective view showing a liquid crystal display device according to the present invention;

<Explanation of symbols for the main parts of the drawings>

10, 100: light source 20, 200: reflector

30, 300: Light guide plate 40, 400: Diffusion sheet

50, 500: prism sheet 60, 600: protective sheet

70, 700: lower chassis 800: backlight unit

1000: liquid crystal display panel

The present invention relates to a backlight unit and a liquid crystal display including the same. More particularly, in a backlight unit using a light emitting diode (LED) as a light source, a backlight unit capable of improving luminance and color uniformity and a liquid crystal including the same It relates to a display device.

In general, the liquid crystal display (LCD) is expanding its application range due to features such as lightweight, thin, low-power drive, full-color, high-resolution implementation. Currently, liquid crystal displays are used in computers, notebooks, PDAs, telephones, TVs, and audio / video devices. In the liquid crystal display, a light transmittance is adjusted according to an image signal applied to a plurality of control switches arranged in a matrix to display a desired image on a panel of the liquid crystal display.

Since the liquid crystal display does not emit light by itself, a light source such as a backlight unit is required. The backlight unit is divided into a direct method of dimming the front surface of the panel by arranging a light source on one side of the panel, and an edge method of reflecting and diffusing light on a light guide plate and a reflective sheet by disposing a light source on one side or a plurality of side surfaces of the panel. Lose. Among these, the direct type backlight unit is generally used in large liquid crystal display devices because of high light utilization efficiency, simple configuration, and no limitation on the size of the display surface.

As the backlight light source, an electroluminescent lamp (EL), a light emitting diode (LED), a cold cathode fluorescent lamp (CCFL), or the like is used. As demand for products that emphasize high color reproducibility and eco-friendliness is increasing, research and development on a backlight unit using a light emitting diode (LED) is being actively performed as an optimal solution.

1 is an exploded perspective view schematically illustrating a structure of a backlight unit using a conventional light emitting diode (LED) as a light source, and FIG. 2 is a cross-sectional view showing a partial cross section thereof.

Referring to FIG. 1, the backlight unit includes a plurality of light sources 1, a reflector 2 reflecting light emitted from the light source 1, and an upper portion of the light source 1 and the reflector 2. It includes a light guide plate 3 disposed. A diffusion sheet 4, a prism sheet 5, and a protective sheet 6 are disposed on the light guide plate 3, and the light source 1, the reflecting plate 2, the light guide plate 3, and the diffusion sheet 4 are provided. , A lower chassis 7 for receiving the prism sheet 5 and the protective sheet 6.

Referring to FIG. 2, which shows a partial cross section of the light source 1, the reflecting plate 2, and the light guide plate 3, the light source 1 used above is a light emitting diode (LED), and a plurality of light emitting diodes are aligned. And mounted on the substrate 8. In general, the light emitting diode used in the direct type backlight unit is a side-emitting type. The side light emitting diode has a directivity angle characteristic in which light is emitted in a vertical direction and light is spread in a horizontal direction as much as possible.

As described above, even if the path of the emitted light is increased by using the side-emitting light emitting diode, there is a limit in the area where the light emitted from each light emitting diode reaches and thus the luminance uniformity characteristics are deteriorated.

The present invention is to solve the above problems, by forming a light guide plate to be spaced apart a predetermined distance in the horizontal direction from the inclined side wall of the reflecting plate, a backlight unit and a liquid crystal display including the same to improve the brightness uniformity and color uniformity It aims to provide.

The present invention includes a reflecting plate including a base and a side wall extending from the base to be inclined at a predetermined angle to achieve the above object, a plurality of light sources provided on the reflecting plate and a light guide plate formed on the reflecting plate and the light source, The light guide plate is provided to be spaced apart from the side wall of the reflective plate in a horizontal direction by a predetermined distance.

Preferably, the light guide plate is formed to be spaced apart from the side wall of the reflecting plate by 6 to 8 mm in a horizontal direction, and the side wall of the reflecting plate is formed to be inclined at an angle of 23 to 30 degrees with respect to the base.

The light source may be a light emitting diode (LED), and the light emitting diode may be a side light emitting diode. In addition, the light emitting diodes may include red (R), green (G), and blue (B) light emitting diodes.

The reflecting plate may include an opening so that the light source is exposed through the opening of the reflecting plate.

The backlight unit of the present invention is disposed on an upper portion of the light guide plate to spread light incident from the light source, a prism sheet disposed on an upper portion of the diffusion sheet to diffuse and collect light, and an upper portion of the prism sheet. It may further include a protective sheet disposed to protect the prism sheet.

The present invention provides a liquid crystal display device comprising the above-described backlight unit.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

3 is an exploded perspective view schematically illustrating a structure of a backlight unit according to the present invention.

Referring to FIG. 3, the backlight unit includes a plurality of light sources 10, a reflector 20 reflecting light emitted from the light source 10, and an upper portion of the light source 10 and the reflector 20. It includes a light guide plate 30 disposed. The light guide plate 30 includes a diffusion sheet 40, a prism sheet 50, and a protective sheet 60 on the light guide plate 30, and includes the light source 10, the reflector plate 20, the light guide plate 30, and the diffusion sheet 40. The lower chassis 70 may accommodate the prism sheet 50 and the protective sheet 60.

The light source 10 is a light emitting diode (LED), it is preferable to use a side light emitting diode. This minimizes the distribution of light emitted in the vertical direction and has a directivity angle characteristic in which the light spreads in the horizontal direction as much as possible.

The reflection plate 20 reflects the light incident from the light source 10 to the light emitting surface of the backlight to increase the light utilization efficiency. In addition, the reflection amount of the entire incident light is adjusted so that the entire outgoing surface of the backlight has a uniform luminance distribution.

The reflector 20 is generally made of a metal material, for example, aluminum (Al), or a base of a reflector plate made of a metal such as stainless steel (SUS), copper, aluminum, or resin such as PET. The material can be manufactured by coating a material having a high reflectance such as silver (Ag) on the material, and can prevent the incident light from leaking out and improve the luminance characteristic with a high reflectance layer structure having excellent concealability.

The reflective plate 20 may be attached to the lower chassis 70 by an adhesive, a double-sided adhesive tape, or the like. Furthermore, the reflector plate 20 may be integrally formed with the lower chassis 70.

The light guide plate 30 spreads the path of the light emitted from the light source 10 as long and wide as possible, so that the light of each of the red (R), green (G), and blue (B) light emitting diodes is well mixed to uniform the color. Serves to improve That is, in order to provide a white light source to the liquid crystal display panel, the light source 10 is composed of red, green, and blue light emitting diodes. Each light color is uniformly mixed by the light guide plate 30 so that the luminance and color uniformity are excellent. Can provide light. The light guide plate 260 is generally made of a transparent material having a constant refractive index, such as polyolefin or polycarbonate, which is an acrylic resin, poly methacrylate (PMMA).

The diffusion sheet 40 disperses the light incident from the light guide plate 30 to prevent the light from being partially concentrated and to have a uniform distribution.

The prism sheet 50 is provided on the diffusion sheet 40 to collect light diffused from the diffusion sheet 40 in a direction perpendicular to the liquid crystal panel plane.

The protective sheet 60 is provided on the prism sheet 50 to protect the prism sheet 50 and increase a viewing angle.

4 is a perspective view showing a reflector according to the present invention, Figure 5 is a cross-sectional view showing a part of a light source, a reflector and a light guide plate according to the present invention.

Referring to the drawings, the light source 10 is a light emitting diode (LED), and a plurality of light emitting diodes are aligned and mounted on the substrate 80. A circuit pattern is formed on the substrate 80 so that external power can be transferred to the light emitting diode through the circuit pattern.

At this time, the light emitting diodes are arranged to be adjacent to the red (R), green (G) and blue (B) light emitting diodes in order to provide white light. The present invention is not limited thereto, and a white light emitting diode using a blue light emitting chip and a yellow phosphor may be disposed, and blue light emitted from a blue light emitting diode may be disposed by aligning a plurality of blue light emitting diodes and then disposing a separate phosphor layer. It may be converted to white light and then provided as white light.

As shown in the drawing, the reflector 20 may include an opening in a portion where the light emitting diode is formed, so that the light emitting diode may be exposed through the opening.

Reflector 20 according to the present invention is formed to be inclined to one side wall and the other side wall facing the rectangular box-shaped reflecting plate 20 of which the top is open. That is, the reflective plate 20 includes a base 20a which is a flat area, and a sidewall 20b extending from the base and inclined at a predetermined angle θ, that is, one sidewall and the other sidewall.

The light emitted from the light emitting diode provided in the base 20a of the reflector 20 is reflected on one sidewall and the other sidewall formed to be inclined with the base 20a by a predetermined angle θ so that the light is emitted upward. Therefore, it is possible to prevent the occurrence of the dark portion of the outer portion, and improve the luminance uniformity.

In addition, the sidewall 20b formed to be inclined at a predetermined angle θ with the base 20a of the reflector 20 includes only one sidewall and the other sidewall, but is not limited thereto. All side walls may be formed to be inclined at a predetermined angle θ with the base 20a.

As described above, the reflecting plate of the present invention can form an inclination of a predetermined angle on the sidewall of the reflecting plate, thereby preventing the occurrence of the dark portion of the outer portion and improving luminance uniformity. Here, as a result of measuring the luminance uniformity according to the angle θ formed between the base 20a and the side wall 20b of the reflecting plate, the angle θ formed between the base 20a and the side wall 20b of the reflecting plate is about 23 to about. The luminance uniformity was high at 30 degrees, and no dark portion was formed at the outer edge at this angle.

In addition, the present invention provides a light guide plate 30 on the light source 10 and the reflective plate 20 for uniform mixing of colors. The light guide plate 30 may be provided to be spaced apart from the side wall 20b of the reflecting plate by a predetermined distance in the horizontal direction. When the light guide plate 30 is formed on the outermost upper sidewall 20b of the reflecting plate, it is not effective to remove the dark portion of the outer portion, and color uniformity may not be improved. In addition, when the light guide plate 30 is formed to be in contact with a predetermined position of the side wall 20b of the reflecting plate, light diffusion due to the light guide plate 30 is limited, so that a dark region of the outer portion may be severely generated.

Referring to FIG. 5, the reflector 20 includes a base 20a and sidewalls 20b extending from the base 20a and inclined at a predetermined angle θ, and provided with a light source provided in the reflector 20. 10, a light guide plate 30 is formed. As mentioned above, the side wall 20b of the reflecting plate is preferably formed to be inclined at an angle of 23 to 30 degrees with respect to the base 20a. In addition, the light guide plate 30 is formed to be spaced apart from the side wall 20b of the reflecting plate by a predetermined distance d in the horizontal direction from the side wall 20b of the reflecting plate.

This structure allows the light from the light source 10 to the outer portion to be reflected by the side wall 20b of the reflecting plate, so as to upwardly exit between the reflecting plate 20 and the light guide plate 30. Thus, by improving the luminance characteristic of the outer portion, it is possible to prevent the dark portion from occurring and improve the luminance uniformity. In addition, the light guide plate 30 formed on the light source 10 and the reflector 20 may be uniformly mixed to improve color uniformity.

Hereinafter, a preferable value of a predetermined distance d between the reflective plate 20 and the light guide plate 40 will be described with reference to the drawings.

FIG. 6 is a graph showing luminance uniformity according to the separation distance d between the reflecting plate 20 and the light guide plate 30 when the side wall 20b of the reflecting plate is inclined with respect to the base 20a at 23.6 degrees. . That is, the X value represents the distance (mm) formed by the light guide plate 30 spaced apart from the side wall 20b of the reflecting plate in the horizontal direction, and the Y value represents the luminance uniformity (%).

Referring to the drawings, it can be seen that the luminance uniformity is the highest when the distance between the reflecting plate 20 and the light guide plate 30 is about 6 to 8 mm (②). When the separation distance is 0 mm (1), that is, when the light guide plate 30 is formed in contact with the side wall 20b of the reflecting plate, a dark portion is generated in the outer part, thereby showing low luminance uniformity. In addition, when the separation distance is 20 mm (③), that is, when the light guide plate 30 is formed 20 mm apart in the horizontal direction from the side wall (20b) of the reflecting plate, the light diffusion of the outer portion is not achieved, resulting in uneven luminance characteristics. .

7A to 7C are distribution charts in which luminance uniformity is measured according to the separation distance d between the reflecting plate 20 and the light guide plate 30, and FIGS. 8A to 8C are the separation distances between the reflecting plate 20 and the light guide plate 30. It is a distribution chart which measured the color uniformity according to d). 7A and 8A show that the distance d between the reflecting plate 20 and the light guide plate 30 is 0 mm (①), and FIGS. 7B and 8B show the separation between the reflecting plate 20 and the light guide plate 30. 7C and 8C show the case where the distance d between the reflecting plate 20 and the light guide plate 30 is 20 mm (3).

In FIGS. 7A to 7C, luminance refers to a luminance value according to color, and is bright as red. When the distance d between the reflecting plate 20 and the light guide plate 30 is 0 mm (①), the luminance uniformity is 70%. When the distance d is 7 mm (②), the luminance uniformity is 75%. When the separation distance d is 20 mm (③), it shows a luminance uniformity of 72%. Therefore, when the light guide plate 30 is formed 7 mm apart in the horizontal direction from the side wall 20b of the reflecting plate, it can be seen that the luminance uniformity is relatively excellent.

8A to 8C, the color difference is a color difference value according to a difference from the color value when the color value at the coordinate values x = 0 and y = 0 is 0. FIG. In this case, the closer the color difference value is to 0, the more uniform the color is. When the distance d between the reflecting plate 20 and the light guide plate 30 is 0 mm (①), the color uniformity is about 85%, and when the distance d is 7 mm (②), about 90% of the color is obtained. Uniformity is shown, and color separation of about 80% is shown when the separation distance d is 20 mm (③). Therefore, when the light guide plate 30 is formed 7 mm apart in the horizontal direction from the side wall 20b of the reflecting plate, it can be seen that the color uniformity is relatively excellent. Referring to FIG. 8B, when the separation distance d is 7 mm (②), the greenish green region having a high color non-uniformity in the lower portion of the backlight unit is relatively reduced, so that the color of the entire backlight unit is almost uniform, and color uniformity is shown. It can be seen that the characteristics are improved.

Accordingly, in the present invention, the light guide plate is formed on the reflector and the light source including the inclined sidewall, and the light guide plate is preferably spaced 6 to 8 mm in a horizontal direction from the side wall of the reflector. In addition, the side wall of the reflective plate preferably extends from the base has a slope of 23 to 30 degrees.

The backlight unit having such a structure has an effect of improving luminance uniformity by improving luminance characteristics of the outer portion due to sidewalls of the reflecting plate and improving color uniformity due to the light guide plate. Particularly, in the present invention, the light guide plate is formed to be spaced apart from the side wall of the reflective plate by a predetermined interval, thereby further improving luminance uniformity and color uniformity characteristics.

9 is an exploded perspective view illustrating a liquid crystal display including a backlight unit according to the present invention.

Referring to FIG. 9, the liquid crystal display includes a backlight unit 800 including a light source 100, a reflector 200, and a light guide plate 300, and a liquid crystal display panel 1000 formed on the backlight unit 800. Include. In addition, the backlight unit 800 may further include an upper chassis (not shown) to surround a predetermined region and a side of the liquid crystal display panel 1000. This is an example including the backlight unit of the present invention described above, a detailed description thereof will be omitted.

The backlight unit 800 includes a reflector 200, a light source 1000 provided on the reflector 200 to generate light, a light guide plate 300 disposed on the light source 100, a diffusion sheet 400, and a prism. A lower portion for accommodating the sheet 500 and the protective sheet 600, the reflecting plate 200, the light source 100, the light guide plate 300, the diffusion sheet 400, the prism sheet 500 and the protective sheet 600. The chassis 700.

The reflector 200 includes a base 200a and sidewalls 200b extending from the base 200a and inclined at a predetermined angle, and the light guide plate 300 is disposed on the light source 100 provided in the reflector 200. ) Is formed. The side wall 200b of the reflector may be inclined at an angle of 23 to 30 degrees with respect to the base 200a. In addition, the light guide plate 300 may be formed to be spaced apart from the side wall 200b of the reflecting plate by 6 to 8 mm without being in contact with the reflecting plate 200.

The liquid crystal display panel 1000 includes an upper substrate provided with a plurality of color filters, a lower substrate provided with a plurality of thin film transistors and coupled to the upper substrate, and encapsulated between the upper substrate and the lower substrate coupled through a sealant. Containing liquid crystals.

The upper substrate includes a black matrix and a red, green, and blue color filter on the bottom surface of the insulating substrate made of a transparent insulating material such as glass, and a color filter of red, green, and blue to prevent light interference between cell regions. An overcoat film, and a common electrode made of a transparent conductive material such as ITO or IZO on the overcoat film.

In addition, the lower substrate may include a plurality of gate lines arranged in one direction at regular intervals, a plurality of source lines arranged at regular intervals in a direction perpendicular to the gate line, and the gate line and the source line may be defined to cross each other. A plurality of pixel electrodes formed in a matrix form in a pixel area and a plurality of thin film transistors switched by the gate line signal to transfer a source line signal to each pixel electrode. The thin film transistor includes a gate electrode, a gate insulating film, an active layer and an ohmic contact layer, a source electrode and a drain electrode. And a protective layer for insulating the thin film transistor from the pixel electrode.

By applying a gate voltage to the gate electrode of the thin film transistor, an operating voltage applied through the data line is applied to the pixel electrode, and the direction of the liquid crystal is changed by a voltage difference with the transparent electrode of the upper substrate. The degree of light transmission of is determined. Accordingly, the transmitted light is represented by the color represented by each of the color filters.

Such a liquid crystal display device of the present invention can prevent the dark portion of the outer portion, and can obtain display screen characteristics excellent in luminance uniformity and color uniformity.

The technical gist of the present invention is not limited to the above-described embodiment, and various modifications and variations are possible, and the present invention may be applied to backlight units having various structures. For example, the backlight unit of the present embodiment has been described in the example using a plurality of light emitting diodes (LEDs) as a light source for supplying light, but is not limited thereto, and is applied to a backlight unit using a cold cathode fluorescent lamp (CCFL). Of course, the effect according to the invention can be obtained.

As mentioned above, although this invention was demonstrated in detail using the preferable Example, the scope of the present invention is not limited to a specific Example and should be interpreted by the attached Claim. In addition, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

According to the present invention, in a backlight unit using a plurality of light emitting diodes (LEDs) as light sources, the inclined sidewalls of the reflecting plate may be formed to improve luminance characteristics of the outer portion and prevent occurrence of dark portions, thereby improving luminance uniformity. In addition, a light guide plate may be formed on the reflective plate and the light source to improve color uniformity. In particular, the present invention has the effect of obtaining a further improved brightness uniformity and color uniformity by forming the light guide plate spaced apart from the side wall of the reflector by a predetermined interval.

Claims (9)

A reflection plate including a base and sidewalls extending from the base and inclined at a predetermined angle; A plurality of light sources provided in the reflector; And A light guide plate formed on the reflection plate and the light source; The light guide plate is a backlight unit, characterized in that formed spaced apart from the side wall of the reflecting plate in a horizontal direction. The method according to claim 1, The light guide plate may be formed to be spaced apart from the side wall of the reflective plate 6 to 8mm in a horizontal direction. The method according to claim 1 or 2, The side wall of the reflector is a backlight unit, characterized in that formed inclined at an angle of 23 to 30 degrees with respect to the base. The method according to claim 1 or 2, The light source is a backlight unit, characterized in that the light emitting diode (LED). The method according to claim 4, And the light emitting diode is a side light emitting diode. The method according to claim 4, The light emitting diode includes a red (R), green (G) and blue (B) light emitting diode. The method according to claim 1 or 2, The reflector includes an opening, the backlight unit, characterized in that provided so that the light source is exposed through the opening of the reflecting plate. The method according to claim 1 or 2, A diffusion sheet disposed on the light guide plate to disperse light incident from the light source; A prism sheet disposed on the diffusion sheet to diffuse and focus light; And And a protective sheet disposed on the prism sheet to protect the prism sheet. A liquid crystal display device comprising the backlight unit according to claim 1.

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