KR20020014130A - Backlight Unit with Blue LED and Green and Red Emitting Fluorescent Sheet and Producing White Light by Using the Same - Google Patents

Abstract

PURPOSE: A backlight unit having a blue light-emitting-diode(LED) and green/red fluorescent plates is provided to extend the lifetime by ten times as compared with a conventional cold cathode fluorescent lamp, by having a thickness of 2 millimeter or smaller while the thickness of the cold cathode fluorescent lamp is 4 millimeter. CONSTITUTION: The back light unit includes a blue LED kit(14), a green/red fluorescent plates(15), a light guide plate(B), a reflection plate(10), a diffusion plate(9) and a solder frame(7). After blue light emitting from the blue LED kit passes through the green/red fluorescent plates attached to a side surface or upper surface of the light guide plate, white light is emitted.

Description

Backlight Unit with Blue LED and Green and Red Emitting Fluorescent Sheet and Producing White Light by Using the Same}

The present invention relates to a backlight unit using a blue light emitting diode, a fluorescent plate and a light guide plate coated with green and red light emitting phosphors, and a method of obtaining white light using the same.

Backlights are widely used as light sources in displays. Notebook computers use cold cathode fluorescent lamps as backlight sources. Cold cathode fluorescent lamps used in notebook computers are available in all colors and have a good color gamut.

However, since an inverter must be used to drive the cold cathode fluorescent lamp, not only the space occupied by the inverter is large, but also a booster circuit required for the cold cathode fluorescent lamp is required. In addition, since the cold cathode fluorescent lamp used in notebook computers consumes a lot of energy, the ultra-low power and ultra-slim backlights are possible by replacing the backlight with a light emitting diode that operates with only 10% of the power consumption of the existing lamp.

Mobile phones, which are widely used for small displays, are also mainly used with surface-mounted light emitting diodes (surface mounting device LEDs). SMD LEDs are widely used in keeping with the trend of miniaturization of information and communication devices. SMD LEDs are not only small but also very low in power, making them ideal for backlighting small displays such as cell phones.

However, currently used SMD LEDs use monochrome SMD LEDs, so there is no problem in displaying characters or simple monochrome images, but it is not applicable to places where various color reproduction is required, such as notebooks. If a variety of colors are to be implemented, it is required that all of the blue, green, and red colors of one LED emit more than a certain intensity.

As such, the backlight using a white light emitting diode is able to take advantage of the backlight of the SMD LED of the mobile phone, which is not only small and cold but also has a small power consumption. In the method of generating white light, the blue light emitting diode chip 2 is attached to the reflection cup 1, and then the green light emitting phosphor 4 and the red light emitting phosphor 5 are mixed with the transparent resin. It is coated on the chip 2 and the blue light emitting diode is operated.

However, this method has a lot of difficulties in the process of making white light emitting diodes. In particular, not only the concentration of the green light emitting phosphor and the red light emitting phosphor coated on the blue light emitting diode chip 2 but also the shape of the coating greatly changes the white light emitting form. Therefore, the most important core technology in the process of making a white light emitting diode is a technique of coating a phosphor under the same conditions on a blue light emitting diode chip at all times.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an ultra low-power type and ultra-small backlight unit comprising a fluorescent plate coated with a blue light emitting diode, a green light emitting diode and a red light emitting phosphor, a light guide plate, and a diffusion plate. It is done.

The present invention is to solve many difficulties in the manufacturing process of the white light emitting diode used in the conventional backlight using a blue light emitting diode and a fluorescent plate coated with green light emitting and red light emitting phosphor.

1 is a cross-sectional view of a conventional white light emitting diode.

2 is an external perspective view of a backlight unit used in the related art.

FIG. 3 is an exploded perspective view of each part of the backlight including the light emitting diode, the diffusion plate, and the light guide plate of FIG. 2.

4 is a blue light emitting diode kit 14 in which a plurality of light emitting diodes A are connected in parallel.

5 is a schematic view showing that light is refracted by the light guide plate B. FIG.

6 is an exploded perspective view of each part of the backlight unit used in the present invention.

Figure 7 is an exploded perspective view of each part of the backlight unit of another structure used in the present invention.

8 is an emission spectrum of light emitted from a backlight used in the present invention.

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

A: white light emitting diode B: light guide plate

DESCRIPTION OF SYMBOLS 1 Reflection cup 2 Blue light emitting diode chip 3 Connecting line 4 Green light emitting phosphor

5: red light emitting phosphor 6: epoxy lens

7: lead frame 8: white light emitting diode kit

9 diffuser 10 reflector

11: refraction hemisphere 12: transparent plastic

13: Refraction direction of light 14: Blue light emitting diode kit

15: green red light emitting fluorescent plate

The backlight unit of the present invention is composed of a blue light emitting diode, a fluorescent plate coated with a green light emitting diode and a red light emitting phosphor, a light guide plate, a reflecting plate, and a diffusion plate.

According to the present invention, the blue light emitted from the blue light emitting diode is mixed with the green light emitting phosphor and the red light emitting phosphor, and then passes through the coated fluorescent plate. A method of emitting white light is used.

The conventional method is to produce a white light emitting diode by doping a green light emitting diode and a red light emitting phosphor mixed with a transparent resin on a blue light emitting diode chip. However, this method has a lot of problems in developing a technology for coating green light emitting diodes and red light emitting phosphors on the blue light emitting diode chip under the same conditions.

The defect rate is very high in the process of making a white light emitting diode. In particular, when manufacturing white light emitting diodes, the price of the blue light emitting diode is about 1000 times higher than the price of the used phosphor, and the defective product formed by doping the phosphor once cannot be reused. Considering this, the defects in the process of doping the phosphors lead to enormous economic losses in discarding expensive blue light emitting diodes.

In the present invention, white light is produced using a blue light emitting diode and a fluorescent plate coated with green light emitting and red light emitting phosphors. This method has an advantage in that the white light emitting method is very simple. In addition, if a problem occurs with a fluorescent plate made by mixing green and red light-emitting phosphors, it can be reused by simply replacing it with a new fluorescent plate. Therefore, it is possible to easily improve the economic problems due to the technical problems and defective rate that occurs when making the existing white light emitting diodes yourself.

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

1 is a cross-sectional view of a conventional white light emitting diode, in which a blue light emitting diode chip 2 is attached to an upper portion of a reflecting cup 1, and a top of the blue light emitting diode chip 2 is a green light emitting phosphor 4 and a red color. It was coated with a transparent resin doped with the luminescent phosphor 5. The connection line 3 connects the blue light emitting diode chip 2 and the lead frame 7, and electricity is supplied thereto. Reference numeral 6 is an epoxy lens.

FIG. 2 is an external perspective view of a conventionally used backlight unit, and includes a light guide plate B, a white light emitting diode kit 8, a diffuser plate 9, a reflector plate 10, and a lead frame 7, and a light guide plate B. FIG. ) And the white light emitting diode kit 8 are formed vertically.

3 is an exploded perspective view of FIG. 2, in which a plurality of hemispheres having different sizes are formed at a predetermined angle with the ground of the light guide plate.

4 is a white light emitting diode kit 8 in which a plurality of white light emitting diodes A are connected in parallel.

5 is a schematic view showing that light is refracted by the light guide plate B used, and shows that the refracting direction 13 of the light is directed toward the diffuser plate by the formed hemispheres 11. Reference numeral 12 is a transparent plastic.

FIG. 6 is an internal perspective view of the backlight unit used in the present invention, in which a light guide plate B and a green / red light emitting fluorescent plate 15 coated with green and red light emitting phosphors are attached to the light guide plate side. The blue light emitting diode kit 14, the reflecting plate 10, the diffusion plate 9, and the lead frame 7 may be formed, and the light guide plate B and the blue light emitting diode kit 14 may be vertically formed.

7 is almost the same as in FIG. 6, but a fluorescent plate 15 having green light emitting and red light emitting phosphors is attached to the upper surface of the light guide plate unlike FIG. 6.

8 is an emission spectrum of light emitted from a backlight used in the method of FIG. 6 or 7.

Green light emitting phosphor refers to all phosphors that absorb blue and emit green. Preferred examples of the phosphors corresponding to this group are SrGa ₂ S ₄ : Eu, ZnS: CuAl, ZnS: CuAuAl, SrGa ₂ S ₄ : Eu, ZnGa ₂ S ₄ : Eu, SrS: Ce and the like. Red luminescent phosphors refer to all phosphors that absorb blue and emit red. Preferred examples of phosphors of this group include (ZnCd) S: AgCl, (ZnCd) S: AgAuCl, (ZnCd) S: AgAuAl, ZnGa ₂ S ₄ : Mn, SrY ₂ S ₄ : Mn, SrS: Eu and the like.

As confirmed by the emission spectrum of FIG. 8, the light emitted from the backlight has a similar intensity in the blue region, the green region, and the red region. As a result, various colors can be reproduced, and color video can be easily implemented.

In order to emit light with uniform brightness, the area closer to the light emitting diode has higher illuminance than the part far away, so that the size of the refractive hemisphere 11 is smaller to the part closer to the light emitting diode, and gradually larger to the far side, or for refraction. In the case where the size of the hemisphere 11 is the same, the density of the hemisphere 11 (the number of the hemispheres for refraction per unit area) is small and the far part is made large.

The bottom plate on which the refractive hemispheres 11 are formed may be used to incline upward from the light emitting diode, or to be inclined downwardly or to have no inclination, but in each case, to make uniform brightness on all sides of the backlight. In order to properly change the shape of the refractive hemispheres (11). In addition, when the size of the display is large, the light emitting diodes may be formed on both sides corresponding to each other, so that the intensity of light directed toward the diffuser plate 9 is uniformly adjusted as a whole.

The phosphor for emitting white light is a mixture of phosphors which absorb blue and emit green and red in an appropriate molar ratio of 30:70 to 70:30. A preferred example of the phosphor that absorbs blue to emit green is SrGa ₂ S ₄ : Eu, and a preferred example of the phosphor that absorbs blue to emit red is (Zn Cd) S: AgCl.

The use ratio of the two phosphors is the sum of the intensity of light in the green region (510 to 550 nm) (M in FIG. 8) when the sum of the intensity of light in the blue region (430 to 480 nm) is 1.0. It is preferable to adjust so that the sum of the intensities (N in FIG. 8) of the light in the red regions 610-680 nm is in the range of 0.7 to 1.3, respectively. As a result, not only the white light can be emitted, but also the loss of the three primary colors of light due to the color filter in the TFT-LCD used in the implementation of color video can be minimized.

Phosphors coated with green and red phosphors have a suitable thickness of 5-20 m. When the phosphor is coated on the fluorescent plate, an acrylic resin, a silicone resin, an epoxy resin, or the like may be used as the transparent resin, but an acrylic resin is most preferably used.

An embodiment of the present invention is as follows.

<Example>

A phosphor obtained by mixing SrGa ₂ S ₄ : Eu and (Zn Cd) S: AgCl in a molar ratio of 40:60 was mixed with acrylic resin (Joncryl 2630, Johnson Polymers) dissolved in 20% by volume of solvent. The solvent used here is methoxyethanol. The amount of the phosphor was 0.5 weight ratio with respect to 100 weight ratio of acrylic resin. The green and red luminescent phosphors are mixed with acrylic resin and applied to a transparent film to form a fluorescent plate. 8 is an emission spectrum of light emitted from the backlight unit having the configuration of FIG. 6 or 7. In this case, light emission peaks occur in the blue, green, and red regions, and the sums of the light intensities (L, M, and N) of the regions are similar.

The thickness of the SMD type blue light emitting diode according to the present invention is within 1 mm. Therefore, the thickness of the backlight unit of the present invention can be produced within 2mm. The unit thickness of the cooling cathode fluorescent lamp is 4 mm. Compared to the cooling cathode fluorescent lamp, the backlight unit of the present invention can reduce the thickness by about 1/2 and minimize the power consumption to about 10 to 20%. In addition, the lifespan of the light emitting diode is about 10 times that of the existing cooling cathode fluorescent lamp and can be used semi-permanently.

In the white light emitting method of the present invention, the purity of white light generated by combining blue, green, and red in an appropriate ratio is increased. As a result, the backlight unit using white generated as a light source enables high definition color video.

In the present invention, since a green light emitting diode coated with a blue light emitting diode, a green light emitting phosphor, and a red light emitting phosphor is separately used, the white light emitting process is very simple. Therefore, the technical problem and the economic loss caused by the defective rate when the backlight is made using the white light emitting diode can be easily improved by using the method of the present invention.

Claims (5)

A backlight unit comprising a blue light emitting diode kit (14) and a green / red light emitting fluorescent plate (15), a light guide plate (B), a reflecting plate (10), a diffusion plate (9), and a lead frame (7). 2. The backlight unit according to claim 1, wherein blue light emitted from the blue light emitting diode kit (14) passes through the green / red light emitting fluorescent plate (15) attached to the side or top surface of the light guide plate and emits white light. The phosphor according to claim 1, wherein the green / red light-emitting phosphor is a phosphor in which a phosphor that absorbs blue to emit green light and a phosphor that absorbs blue to emit red light are mixed in a molar ratio of 30:70 to 70:30. Backlight unit, characterized in that the coating. The light intensity of the green / red light emitting phosphor according to claim 1 or 3, wherein the intensity of light in the blue (430-480 nm): green (510-550 nm): red (610-680 nm) region is 1: 1: (0.7-1.3): ( 0.7-1.3) to emit light so as to have a ratio. The light source was a blue light emitting diode, and the transparent film was passed through a green and red light emitting fluorescent plate 15 coated with green light emission and a red light emitting phosphor, and the passed light was blue (430-480 nm): green (510-550 nm). : White light generation method, characterized in that the intensity of light in the red (610-680nm) region is 1: 1: (0.7-1.3): (0.7-1.3) ratio.