KR20070059282A - Backlight unit using light emitting diode - Google Patents

Abstract

A backlight unit is provided to prevent red mura and color defect from being generated, thereby improving the color uniformity, by forming a diffusing plate to include a long wavelength blocking agent instead of a UV(Ultra Violet) blocking agent. An LED(Light Emitting Diode)(10) has a plurality of red, green, and blue light sources(10R,10G,10B) disposed regularly. A reflecting plate(20) is disposed below the LED part, wherein the reflecting plate reflects the lights emitted from the LED part to the front. A diffusing plate(30) is disposed above the LED part, wherein the diffusing plate diffuses the emitted lights uniformly. The diffusing plate contains a long wavelength blocking agent.

Description

Backlight unit using LED

 1 is a graph showing the transmittance of each wavelength of the diffusion plate of the backlight unit using the LED according to the prior art.

Figure 2 is a planar photograph showing a state in which the red mura and color phenomena occurred in the diffusion plate of the backlight unit using the LED according to the prior art.

3 is a cross-sectional view showing a backlight unit using an LED according to an embodiment of the present invention.

4 is a graph showing the transmittance of each wavelength of the diffusion plate of the backlight unit using the LED according to an embodiment of the present invention.

5 is a view showing a comparison of the color coordinates of the diffusion plate according to the prior art and the diffusion plate according to the embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

10: light source 20: reflector

30: diffusion plate 40: prism sheet

50: protective sheet

The present invention relates to a backlight unit using an LED, and more particularly, by adding a long wavelength blocking agent to a diffusion plate instead of a UV blocking agent, to prevent occurrence of red mura or color splashing, and to improve color uniformity. It relates to a backlight unit using the LED.

With the development of the electronic device industry, various display devices having small size and low energy consumption are being developed, and image devices, computers, mobile communication terminals, etc. using the same are being developed. Liquid crystal displays (LCDs), which reflect this trend, have been in the spotlight as display devices such as monitors and mobile communication terminals.

Since the LCD does not spontaneously generate light, it is usually common to have a backlight unit for irradiating light onto the LCD panel from the back of the LCD panel. In this case, the backlight unit generates white light so that the color of the image implemented by the LCD panel can be reproduced close to the actual color.

As the backlight unit of the LCD as described above, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or the like is conventionally used as a light source. Among them, the conventional LCD backlight unit using the CCFL is arranged on a side of the light guide plate by using a light source means using the CCFL, and supplies the light generated from the CCFL to a predetermined region of the LCD panel through the light guide plate, diffuser plate and prism It is configured to. In this case, the conventional backlight light sources such as CCFL are mostly light sources using the plasma principle, and implement white.

However, the above-described conventional light sources have the following problems. That is, as the plasma gas pressure changes, the lifetime is shortened, and an inverter for obtaining a high operating voltage of several hundred volts required for plasma discharge is required. In addition, when applied to a portable product, most of the power is consumed by the backlight, the conventional light source such as CCFL or EEFL has a problem that the power consumption is not good, so that excessive power is consumed.

In order to solve the above problems, a backlight unit using an LED (Light Emitting Diode) has been proposed. An LED is a light emitting device that generates light by using a light emitting phenomenon generated when a voltage is applied to a semiconductor. As the material of the LED, materials that satisfy the conditions such that the emission wavelength is present in the visible or near infrared region, the light emission efficiency is high, and the p-n junction can be manufactured are suitable.

Such LEDs have advantages in that they are smaller in size, longer in life, and have higher energy efficiency and lower operating voltages compared to conventional CCFLs. In addition, the response speed is fast, the pulse operation can be modulated by high frequency, and the light output can be easily changed by current control.

Here, the backlight unit using the LED according to the prior art, the LED unit in which a plurality of red, green and blue monochromatic light sources are regularly arranged, and provided below the LED unit Reflecting plate for reflecting the light emitted from the LED unit to the front and a diffusion plate provided on the upper portion of the LED unit to reduce the non-uniformity of the emitted light. On the diffusion plate, a prism sheet for collecting light to increase brightness is provided. On the prism sheet, a protection sheet for protecting the prism sheet and increasing the viewing angle is provided.

However, the diffusion plate used in the backlight unit using the LED according to the prior art as described above, as the diffusion plate used in the backlight unit using the conventional CCFL as it is, in order to block the UV short wavelength emitted from the CCFL, It is made by melting the UV blocker in powder form together with other raw materials.

Here, Figure 1 is a graph showing the transmittance of each wavelength of the diffusion plate of the backlight unit using the LED according to the prior art, Figure 2 is a mura and color phenomena of red on the diffusion plate of the backlight unit using the LED according to the prior art It is a plane photograph showing the generated state.

The diffusion plate of the backlight unit using the LED according to the prior art formed by the addition of the UV blocking agent is, as shown in Figure 1, the blue wavelength corresponding to the short wavelength region (see reference numeral "A") by the UV blocking agent The transmittance is reduced and, conversely, the transmittance of red corresponding to the long wavelength region (see reference numeral “B”) is increased, so that the entire diffuser plate is shown as a red line rather than white as shown in FIG. 2. The mura of the red and the color swept phenomenon occurs, which caused a problem that the overall color uniformity is lowered.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to prevent the occurrence of red mura or color bleeding on the diffusion plate, and thus to improve the overall color uniformity. To provide a unit.

The backlight unit using the LED according to the present invention for achieving the above object,

An LED unit in which a plurality of red, green, and blue monochromatic light sources are regularly arranged;

A reflection plate provided below the LED unit to reflect the light emitted from the LED unit to the front; And

And a diffuser plate provided at the upper portion of the LED unit to uniformly diffuse the emitted light and include a long wavelength blocker.

Here, the diffusion plate is characterized in that consisting of a long wavelength blocking agent, a base resin, a diffusion agent, an antistatic agent and a heat dissipating agent.

The base resin may be polymethylmethacrylate (PMMA), polystyrene (PS), polymethyl methacrylate (PMMA) and polystyrene (PS) mixed with polymethacrylstyrene (MS), And cyclo-olefin polymer (cyclo-olefin polymer: COP) is characterized in that it consists of any one selected from the group consisting of.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

3 is a cross-sectional view illustrating a backlight unit using an LED according to an exemplary embodiment of the present invention.

In the backlight unit using the LED according to the embodiment of the present invention, as shown in FIG. 3, the LED unit 10 in which monochromatic light sources of a plurality of red 10R, green 10G, and blue 10B are regularly arranged is provided. ), A reflector 20 provided below the LED unit 10 to reflect the light emitted from the LED unit 10 to the front, and the light emitted from the upper part of the LED unit 10. It includes a diffusion plate 30 to uniformly diffuse.

Typically, a prism sheet 40 is provided on the diffusion plate 30 to increase light by collecting light, and a protective sheet 50 that protects the prism sheet 40 and secures a viewing angle on the prism sheet 40. ) Is provided. The configuration of the sheets may vary depending on the overall configuration.

Here, the diffusion plate 30 according to the present embodiment is made by melting the long wavelength blocker in the form of powder together with other raw materials. That is, the diffusion plate 30 used in the present invention is not applied to the diffusion plate used in the backlight unit using the conventional CCFL as it is, and added to the existing diffusion plate to block the UV short wavelength emitted by the CCFL. Instead of the UV blocking agent, the above-mentioned long wavelength blocking agent was added and produced.

In detail, the diffusion plate 30 is made by melting together a long wavelength blocker, a base resin, a diffuser material, an antistatic agent, and a heat dissipating agent. Among these, the base resin may generally be made of polymethylmethacrylate (PMMA). However, when a resin having a high absorption rate, such as polymethyl methacrylate (PMMA), is applied to the diffusion plate 30, when the backlight is turned on, the light source surface side of the diffusion plate 30 starts to dry, and for a predetermined period of time. While there is a large difference in absorption amount between the inner surface and the outer surface of the diffusion plate 30, there is a risk that the diffusion plate 30 is wheeled toward the liquid crystal panel.

Therefore, in order to prevent such warpage of the diffusion plate 30 in advance, instead of the polymethyl methacrylate (PMMA), polystyrene (PS), or the polymethyl methacrylate (PMMA) and polystyrene Resin having lower absorbency than polymethyl methacrylate (PMMA), such as polymethacrylstyrene (MS) mixed with (PS), or cyclo-olefin polymer (COP), can be used. .

4 is a graph showing the transmittance of each wavelength of the diffusion plate of the backlight unit using the LED according to an embodiment of the present invention.

As described above, the diffusion plate 30 of the backlight unit using the LED according to the embodiment of the present invention, which is formed by adding the long wavelength blocking agent, is formed by the long wavelength blocking agent, as shown in FIG. Since the transmittance of red corresponding to "C" may be reduced, it is possible to reduce the occurrence of red mura and color drift, which are seen as red lines in the diffusion plate 30.

On the other hand, the LED unit 10, as described above is composed of a single color light source of a plurality of red (10R), green (10G) and blue (10B) is arranged regularly, as described above, the LED unit 10 is red The reason for the configuration of a plurality of LEDs emitting monochromatic light of 10R, green 10G, and blue 10B is as follows.

A typical multi-color liquid crystal display device further includes a color filter in addition to the liquid crystal display panel and the backlight. That is, by using a backlight composed of a three-wavelength fluorescent lamp as a light source, the white light emitted here is separated into three colors of red, green, and blue in the color filter, and then additively mixed to realize various colors.

In general, as a determinant of the image quality of a liquid crystal display device, a viewing angle, which is an angle to view a screen, color reproducibility of how red, green, and blue colors are transmitted through a color filter to reproduce colors, and contrast of an image Luminance, indicating a residual image after long traces of the image when the same image is maintained for a long time. In the case of using LED as a light source, in order to realize accurate color reproduction by passing white light through a color filter, mixing using LEDs emitting red, green, and blue colors rather than LED elements emitting white light is performed. It is technically easy to realize the white light in a way to make it possible, and a realistic implementation is possible.

In relation to the color reproducibility described above, the color of the light source is generally determined by chromaticity coordinates defined by the International Lighting Commission. That is, after calculating tristimulus values X, Y and Z from the spectra of an arbitrary light source, color coordinates x, y and z of red, green and blue are obtained from the tristimulus values by the transformation matrix. Subsequently, if the x, y values of red, green, and blue are represented by Cartesian coordinates, a horn-shaped spectral trajectory is drawn, which is called a CIE chromaticity diagram. All common light sources have their color coordinates inside these horseshoe shapes.

5 is a view showing a comparison of the color coordinates of the diffusion plate according to the prior art and the diffusion plate according to the embodiment of the present invention, Figure 5 (a) shows the color coordinates of the diffusion plate according to the prior art, (b) shows the color coordinates of the diffusion plate according to the embodiment of the present invention.

Referring to FIGS. 5A and 5B, first, a diffusion plate of a backlight unit using an LED according to the related art formed by adding a UV blocking agent decreases transmittance of blue corresponding to a short wavelength region, and corresponds to a long wavelength region. Whereas the transmittance of the red was increased, and the red mura and color phenomena occurred, the diffusion plate 30 of the backlight unit using the LED according to the embodiment of the present invention formed with the addition of the long wavelength blocking agent was formed in the long wavelength region. Due to the decrease in transmittance of the corresponding red, the color coordinates are shifted to the short wavelength band. That is, according to the embodiment of the present invention, it can be seen that the long wavelength blocking agent reduces red light as a whole of the diffusion plate, thereby reducing mura and color drift of red and changing the color to purple. Therefore, the present invention can improve the overall color uniformity.

Although the preferred embodiments of the present invention have been described in detail above, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

As described above, according to the backlight unit using the LED according to the present invention, by adding a long wavelength blocker to the diffuser instead of a UV blocker, the transmittance of red corresponding to the long wavelength region is reduced, so that a red line is seen in the diffuser plate. It can prevent the red mura and color shading from occurring. Therefore, there is an effect that can improve the overall color uniformity.

Claims (3)

An LED unit in which a plurality of red, green, and blue monochromatic light sources are regularly arranged; A reflection plate provided below the LED unit to reflect the light emitted from the LED unit to the front; And And a diffuser plate provided at the upper portion of the LED unit to uniformly diffuse the emitted light and include a long wavelength blocker. The method of claim 1, The diffusion plate is a backlight unit using an LED, characterized in that consisting of a long wavelength blocking agent, a base resin, a diffusion agent, an antistatic agent and a heat dissipating agent. The method of claim 2, The base resin is polymethylmethacrylate (PMMA), polystyrene (PS), polymethylmethacrylate (PMMA) and polystyrene (PS) mixed with polymethacrylstyrene (MS), and cyclo Backlight unit using an LED, characterized in that made of any one selected from the group consisting of olefin polymer (cyclo-olefin polymer: COP).

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