KR20040056019A - Back light unit of liquid crystal display device - Google Patents

Abstract

PURPOSE: A back light unit of an LCD device is provided to apply an embossing process to a semi-light receiving portion of a sub light guide plate, and to condense light to minimize light loss while reflecting the light, thereby improving brightness. CONSTITUTION: A main light guide plate(71) is configured on a rear side of an LCD panel. A sub light guide plate(72) configures a semi-light receiving portion in embossing type on an incident surface of the main light guide plate(71). A light source portion(73) is formed on one side of the sub light guide plate(72), first-dimensionally arrays RGB LEDs, and emits light. A housing(74) fixes the light source portion(73), and condenses the light emitted from the light source portion(73) in one direction. The first and second reflecting plates(75,76) are configured in a lower section of the main light guide plate(71), and reflect light leaking from an opposite side to an LCD panel.

Description

Back light unit of liquid crystal display device

The present invention relates to a liquid crystal display (LCD), and more particularly to a backlight unit of a liquid crystal display device suitable for improving the brightness.

CRT (Cathode Ray Tube), one of the commonly used display devices, is mainly used for monitors such as TVs, measuring devices, information terminal devices, etc., but the miniaturization of electronic products due to the weight and size of CRT itself It was unable to actively respond to the demand for weight reduction.

Therefore, in the trend of miniaturization and light weight of various electronic products, CRT has a certain limit in weight and size, and is expected to be replaced. Liquid crystal display (LCD) and gas discharge using electro-optic effects Plasma Display Panel (PDP) and Electro Luminescence Display (ELD) using the electroluminescent effect, among others, are being actively studied for the liquid crystal display device.

In order to replace the CRT, a liquid crystal display device having advantages such as small size, light weight, and low power consumption has recently been developed to be able to perform a sufficient role as a flat panel display device. As used in monitors and large information display devices, the demand for liquid crystal display devices continues to increase.

The liquid crystal display may be classified into a liquid crystal panel displaying an image and a driving unit for applying a driving signal to the liquid crystal panel. The liquid crystal panel may include first and second glass substrates bonded to each other with a predetermined space, and It consists of the liquid crystal layer injected between the 1st, 2nd glass substrate.

The first glass substrate (TFT array substrate) may include a plurality of gate lines arranged in one direction at a predetermined interval, a plurality of data lines arranged at regular intervals in a direction perpendicular to the gate lines, A plurality of pixel electrodes formed in a matrix form in each pixel region defined by crossing a gate line and a data line, and a plurality of thin films which are switched by signals of the gate line to transfer the signal of the data line to each pixel electrode Transistors are formed.

The second glass substrate (color filter substrate) includes a black matrix layer for blocking light in portions other than the pixel region, an R, G and B color filter layer for expressing color colors, and a common electrode for implementing an image. Is formed.

The first and second glass substrates are bonded to each other by a seal material having a predetermined space by a spacer and having a liquid crystal injection hole, so that the liquid crystal is injected between the two substrates.

On the other hand, since most of the liquid crystal display devices are light-receiving elements that display an image by controlling the amount of light source coming from the outside, a separate light source, that is, a backlight, is required for irradiating light to the liquid crystal panel. It is divided into edge type and direct type according to the location where the lamp unit is installed.

The light source includes EL (Electro Luminescence), LED (Light Emitting Diode), CCFL (Cold Cathode Fluorescent Lamp), HCFL (Hot Cathode Fluorescent Lamp), etc., especially long life, low power consumption and thin can be formed. CCFL is widely used in large color TFT LCDs.

The CCFL method uses a fluorescent discharge tube in which mercury gas containing argon, neon, or the like is sealed at a low pressure in order to use a penning effect. Electrodes are formed at both ends of the tube, and the cathode is formed in a wide plate shape.When voltage is applied, as in the sputtering phenomenon, charged particles in the discharge tube collide with the plate-shaped cathode to generate secondary electrons, which excite surrounding elements to excite the plasma. To form.

These elements emit strong ultraviolet light, which in turn excites the phosphor, causing the phosphor to emit visible light.

In the double-edge method, the lamp unit is installed on the side of the light guide plate for guiding the light, and the lamp unit covers a lamp emitting light, a lamp holder inserted at both ends of the lamp to protect the lamp, and an outer circumferential surface of the lamp, and one side It is provided with a lamp reflector plate fitted to the side of the light guide plate to reflect the light emitted from the lamp toward the light guide plate.

The edge method in which the lamp unit is installed on the side of the light guide plate is applied to a relatively small liquid crystal display device such as a monitor of a laptop computer and a desktop computer, and has good uniformity of light and a long service life. It is advantageous to thin the liquid crystal display device.

On the other hand, the direct method began to develop mainly as the size of the liquid crystal display device became larger than 20 inches, and arranged a plurality of lamps in a row on the lower surface of the diffusion plate to direct light directly to the front of the liquid crystal panel. will be.

The direct method is mainly used for a large screen liquid crystal display device requiring high luminance because the light utilization efficiency is higher than that of the edge method.

However, the liquid crystal display device adopting the direct method is used as a large monitor or a television, which takes longer to use than a laptop computer, and because the number of lamps is larger, the failure and life of the lamp in the direct method than the edge method. It is more likely that a lamp that will not turn on appears.

In the direct method, because a plurality of lamps are installed on the bottom of the screen, for example, due to the life and failure of the lamp, if one lamp does not light up, the part where the lamp does not light up becomes significantly darker than the other part. The part will appear immediately on the screen.

For this reason, since the lamp is frequently replaced in the direct method, the lamp unit should be easily disassembled and assembled.

As described above, the liquid crystal display device uses a liquid crystal to control the amount of light transmitted through the screen, and uses the light to determine the contrast and the color of the screen.

For example, the viewing angle of which the image quality varies greatly depending on the viewing angle, the transmittance according to the projection light emitting display, and the transmitted light pass through the color filter to display the red (R), green (G), and blue (B) colors. These include color reproducibility depending on how much they are reproduced, luminance representing the contrast of the image, and afterimages in which the traces of the image remain long when the same image is continued for a long time.

Currently, liquid crystal displays are expanding beyond the displays of portable products to desktop PC monitors and home TVs. Although the liquid crystal display has the physical advantages of light and thin, the color reproducibility and luminance, among the above characteristics, are particularly weak compared to the CRT.

Conventional LCD monitors have 40-50% color reproducibility compared to the NTSC system adopted by the National Television System Committee for color television broadcasting. Could meet.

However, in the case of a TV which is attracting attention as a market for a new liquid crystal display device, it is required to develop a liquid crystal display device capable of realizing color reproducibility of CRT level or higher.

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

The color of the light source is determined by chromaticitycordinates determined 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 using the transformation matrix. Subsequently, when the x, y values of red, green, and blue are expressed in 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.

In this case, a triangular area formed by each color coordinate of red, green, and blue becomes a color reproduction area, and as the triangle area becomes larger, color reproducibility is increased. Color reproducibility depends on color purity and luminance, and color reproducibility increases as color purity and luminance increase.

Here, the tristimulus values X, Y, and Z represent weights of individual color-matching functions close to a spectrum, and particularly Y represents a stimulus value for brightness.

On the other hand, the color temperature of the white color based on the color change of the light emitted according to the temperature of the heat source is called the color temperature, the color temperature on the monitor is represented by three, that is, 9300K, 6500K and 5000K.

The closer the color temperature is to 9000K, the more white is added to the blue color. If the color temperature is 6500K, the red color is added to the white. If the color temperature is 5000K, the color becomes neutral. The color temperature is obtained from the color coordinates (x, y) of white. As the color temperature is around 9000K, the European broadcasting union (EBU) standard can be satisfied.

In the case of the liquid crystal display device described above, the emission spectrum of the backlight is combined with the transmission spectrum of the color function and the color filter to determine tristimulus values for each wavelength of the visible light region. Correlation between extremes should be adjusted accordingly. That is, in order to optimize color reproducibility and color temperature, the emission spectrum of the backlight should be changed, and the transmission spectrum of the color filter should be adjusted to maximize the emission efficiency.

If a white, blue, green, and red LEDs must be used at the same time, many application problems occur. In particular, when using blue, green, and red LEDs at the same time, it is difficult to apply realistically because of a technical problem of gathering different colors coming out according to the position of each LED to make white.

Therefore, in order to realize white light, it is required that all three wavelengths of one LED emit light with a predetermined intensity or more.

As such, there is an urgent need for the development of a backlight capable of utilizing the advantages of the backlight of the SMD (Surface Mounting Device) LED of the mobile phone, which is not only small and cold, but also has a small power consumption.

Meanwhile, the configuration of a general backlight assembly is as follows.

1 is a view for explaining the structure of a general backlight assembly.

As shown in FIG. 1, the fluorescent lamp 1, the light guide plate 2, the diffusion material 3, the reflection plate 4, the diffusion plate 5, the prism sheet 6, and the like are constituted.

First, when the voltage is applied to the fluorescent lamp 1, residual electrons present in the fluorescent lamp 1 move to the anode, and the moving residual electrons collide with argon (Ar) to excite argon to proliferate cations, The multiplying cations collide with the cathode to release secondary electrons.

When the emitted secondary electrons flow through the tube to initiate discharge, the flow of electrons by the discharge collides with, and ionizes, the mercury vapor to emit ultraviolet rays and visible light, and the emitted ultraviolet rays excite the phosphor coated on the inner wall of the lamp to display visible light. It emits light and emits light.

Subsequently, the light guide plate 2 is a wave guide for injecting the light emitted from the fluorescent lamp 1 into the surface to emit an upper surface light source. The light guide plate 2 has excellent light transmittance, PMMA (Poly Methyl Meth Acrylate). ) Resin is used.

Factors related to light incidence efficiency of the light guide plate 2 include light guide plate thickness versus lamp diameter, the distance between the light guide plate and the lamp, the shape of the lamp reflector, and the like. In general, the fluorescent lamp 1 is thicker than the center of the light guide plate 2. By inclining in the direction, the light incidence efficiency is increased.

The light guide plate 2 of the backlight unit for an LCD includes a printing light guide plate, a V-cut light guide plate, and a scattering light guide plate.

Subsequently, the diffusion material 3 is composed of Si0 ₂ , particles, PMMA, solvent, and the like. At this time, the Si0 ₂ particles described above are used for light diffusion and have a porous particle structure. PMMA is also used to attach Si0 ₂ particles to the lower surface of the light guide plate 2.

The diffusion material 3 is applied to the lower surface of the light guide plate in the form of a dot, and the area of the dot is gradually increased in order to obtain a uniform surface light source on the light guide plate 2. That is, the area ratio occupied by the dot per unit area is smaller in the one closer to the fluorescent lamp 1, and the area ratio occupied by the dot per unit area is larger in the far side from the fluorescent lamp 1.

In this case, the shape of the dot may have various shapes. If the area ratio of the dots per unit area is the same, the same brightness effect may be obtained on the light guide plate regardless of the shape of the dot.

Subsequently, the reflector 4 is installed at the rear end of the light guide plate 2 so that the light emitted from the fluorescent lamp 1 is incident into the light guide plate 2.

The diffusion plate 5 is installed on the light guide plate 2 to which the dot pattern is applied to obtain uniform luminance according to a viewing angle. As the material of the diffusion plate 5, PET or PC (Poly) is used. Carbonate) resin is used, and the upper part of the diffusion plate 5 has a particle coating layer that serves as a diffusion.

Subsequently, the prism sheet 6 is to increase the front luminance of the light that is transmitted through the diffusion plate 5 and reflected. The prism sheet 6 allows only the light of a specific angle to pass therethrough and the light incident at the remaining angle. Total internal reflection occurs and returns back to the bottom of the prism sheet 6. As described above, the returning light is reflected by the reflecting plate 4 attached to the lower part of the light guide plate 2.

The backlight assembly configured as described above is fixed to the mold frame, and the display unit disposed on the upper surface of the backlight assembly is protected by the top chassis, and the top chassis and the mold frame are coupled while receiving the backlight assembly and the display unit therebetween.

Hereinafter, a backlight unit of a conventional liquid crystal display device will be described with reference to the accompanying drawings.

2 is a perspective view illustrating a backlight unit using a conventional fluorescent lamp.

As shown in FIG. 2, the fluorescent lamp 11 is coated on the inner surface to emit light, and the fluorescent lamp 11 is fixed, and the light emitted from the fluorescent lamp 11 is in one direction. A lamp housing 12 for condensing, a light guide plate 13 for supplying the light emitted from the fluorescent lamp 11 to the liquid crystal panel side of the backlight, and light leaking to the opposite side of the liquid crystal panel attached to the lower part of the light guide plate 13 Reflector 14 reflecting light to the light guide plate 13, a diffuser plate 15 positioned above the light guide plate 13 to uniformly diffuse the light emitted from the light guide plate 13, and the diffuser plate 15 A prism sheet 16 positioned above and condensing light diffused from the diffusion plate 15 to a liquid crystal panel, and a protective sheet positioned above the prism sheet 16 to protect the prism sheet 16. 17, storing the components It consists of a main support (18) that secure.

In the backlight unit configured as described above, the light emitted from the fluorescent lamp 11 is focused on the light incident surface of the light guide plate 13, and then passes through the light guide plate 13 through the diffuser plate 15 and the prism sheet 16 to the liquid crystal panel. Delivered.

However, as described above, the backlight unit using the conventional fluorescent lamp has low color reproducibility due to the light emission characteristics of the light source itself. In addition, it is difficult to obtain a high brightness backlight unit due to constraints of the size and capacity of the fluorescent lamp.

On the other hand, in recent years, the backlight unit has been used as a function for reading information displayed on the screen of a liquid crystal display in a dark place, but recently, the light guide plate has been formed thinner due to various requirements such as design, low power, and thinning. In addition to the ability to express various colors, technologies for reducing power consumption using LEDs (Light Emitting Diodes) are being made.

3 is a perspective view illustrating a backlight unit using a conventional LED.

As shown in FIG. 3, the LED light sources 22 are disposed on both sides of the light guide plate 21 formed on the rear side of the liquid crystal panel, and the LED light source 22 illuminates the liquid crystal panel so that the screen can be displayed even in a dark place. Can be.

Here, the LED light source 22 is composed of LED lamps 23 arranged one-dimensionally, the LED lamp 23 is a red LED, green LED, blue LED is disposed on the PCB substrate, respectively.

The backlight unit configured as described above turns on the LED lamp 23 of the LED light source 22 when an image is realized on the liquid crystal panel. Voltage is applied to the red, green, and blue LEDs of the three colors of the LED lamp 23, and the red, green, and blue light emitted are color-mixed by scattering in the light guide plate 21 to produce white light. Is illuminated on the back of the liquid crystal panel.

4 is a plan view of a backlight unit using a conventional LED.

As shown in FIG. 4, the LED lamp 23 including the red LED 23a, the green LED 23b, and the blue LED 23c and the light emitted from the LED lamp 23 are evenly distributed on the liquid crystal panel. It consists of the light guide plate 21 for making it.

In this way, the monochromatic light of R, G, and B is emitted from the LED lamp 23 from the LED light source (22 in FIG. 3) to emit white light by using the LED lamp 23 as a light source. In the region "a" of 21, a portion 20 in which the light emitted by each LED lamp 23 does not overlap occurs to produce uniform white light, and in the region "b" of the light guide plate 21, The monochromatic light emitted from R, G, and B can be mixed from the LED lamp 23 to produce uniform white light.

Thus, the backlight unit uses only half of the light guide plate 21 far from the LED light source 22 by forming a light spot on the light guide plate 21 so that only the “b” region of the light guide plate 21 can be effectively used.

By using a light emitting diode (LED) as a light source for illuminating the liquid crystal panel as described above, it is possible to easily reduce the power consumption and miniaturization of electronic devices such as notebook PCs.

On the other hand, LED is a solid element using the photoelectric conversion effect of the semiconductor. In order to emit LED, a DC voltage of about 1.5V needs to be applied, thus eliminating the need for a DA-AC converter, thereby significantly reducing power consumption.

In addition, since LEDs are semiconductor devices, they are more reliable than cathode ray tubes, and are small in size and long in life.

The backlight unit of the conventional liquid crystal display device configured as described above illuminates the liquid crystal panel by mixing white light emitted from red, green, and blue LEDs emitting three primary colors of additive mixed color.

However, in the backlight unit of the conventional liquid crystal display device as described above, there are the following problems.

That is, the loss is increased in the process of reflecting light to the light guide plate has a disadvantage that the brightness is lowered.

The present invention has been made to solve the conventional problems as described above by embossing the light incident portion of the sub light guide plate to condense the light to minimize the loss in the process of reflecting light to improve the brightness It is an object of the present invention to provide a backlight unit of a liquid crystal display device.

1 is a view for explaining the structure of a typical backlight assembly

2 is a cross-sectional view showing a backlight unit using a conventional fluorescent lamp

3 is a cross-sectional view showing a backlight unit using a conventional LED.

4 is a plan view of a backlight unit using a conventional LED

5 is a perspective view showing the overall configuration of a liquid crystal display device in the present invention;

6 is a cross-sectional view showing a backlight unit of a liquid crystal display according to the present invention.

FIG. 7 is an enlarged view of the sub light guide plate of FIG. 6. FIG.

Explanation of symbols for the main parts of the drawings

71: main light guide plate 72: sub light guide plate

73: light source portion 74: housing

75: first reflector 76: second reflector

77: PCB Board

The backlight unit of the liquid crystal display device according to the present invention for achieving the above object is a main light guide plate configured on the back of the liquid crystal panel, the sub light guide plate having an embossed form on the incident surface of one side of the main light guide plate; And a light source unit configured to emit light at one side of the sub light guide plate, a housing configured to fix the light source unit and to condense the light emitted from the light source unit in one direction, and to a lower end of the main light guide plate, to the opposite side of the liquid crystal panel. It characterized in that it comprises a first, second reflector for reflecting the light leaking.

Here, the second reflecting plate is made of Al coated with Ag, and the light source unit is composed of a red LED, a blue LED, and a green LED arranged one-dimensionally on a PCB substrate.

Hereinafter, the backlight unit of the liquid crystal display according to the present invention will be described in detail with reference to the accompanying drawings.

5 is a perspective view showing the overall configuration of a liquid crystal display device in the present invention.

As shown in Fig. 5, a shield case 31 made of metal for forming the upper frame and a display window 32 for determining an effective screen of the liquid crystal display module are formed.

The liquid crystal panel 33 formed below the shield case 31 and the display window 32 is a TFT or color filter made of a thin layer such as a source / drain electrode, a gate electrode or an amorphous silicon layer between two glass substrates. Etc. are laminated.

A drain circuit board 34, a gate circuit board 35, and an interface circuit board 36 are formed on the liquid crystal panel 33, and joiners 37 and 38 for connecting the circuit boards are provided. 39). These circuit boards 34, 35, 36 are fixed to the shield case 31 via the insulating sheet 40.

On the other hand, the light shielding space 51 is provided below the liquid crystal panel 33 through the rubber cushion 50, and the diffusion plate 52 and the prism sheet 53 are provided. The diffuser plate 52 has a function of diffusing light generated from a light guide plate described later to obtain uniform planar light, and the prism sheet 53 is used to increase the luminance in the front direction.

The light guide plate 54 is provided below the prism sheet 53, and the fluorescent tube unit 55 is provided on two sides of the light guide plate 54.

In addition, a reflecting plate 56 is provided below the light guide plate 54 to reflect light incident from the fluorescent tube unit 55 into the light guide plate 54 in the direction of the liquid crystal panel 33. have.

In addition, a lower case 57 having an opening 58 is provided below the reflecting plate 56.

Although not shown in the drawing, the fluorescent tube unit 55 is configured with a fluorescent lamp and a lamp housing for condensing the light emitted from the fluorescent lamp in one direction.

6 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to the present invention.

As shown in FIG. 6, the main light guide plate 71 formed on the rear surface of the liquid crystal panel 33 (in FIG. 5) and the sub-incoming part formed on the incident surface of the main light guide plate 71 are embossed. A light guide plate 72 and a light source unit 73 configured to be disposed at one side of the sub light guide plate 72 to arrange light in a plurality of green, blue, and red light emitting diodes in one dimension, and to fix the light source unit 73. And a housing 74 for condensing the light emitted from the light source unit 73 in one direction and a lower end of the main light guide plate 71 to reflect the light leaking out to the opposite side of the liquid crystal panel. 2 reflectors 75 and 76 are comprised.

Here, the second reflector 76 has a reflective effect by using a material coated with Ag in Al.

In the light source unit 73, a red LED, a green LED, and a blue LED are arranged in one dimension on the PCB substrate 77.

The housing 74 is made of Al.

The embossed shape of the sub-light guide part 72, that is, the exit surface of the sub LGP 72 may be formed by forming a plurality of grooves through a stamper or punching.

The backlight unit of the liquid crystal display according to the present invention configured as described above receives R, G, and B colors from the light source unit 73 primarily through the sub light guide plate 72 in which the incoming light incident portion is embossed to condense white light. In this case, the color mixture of the white light finally emitted through the main light guide plate 71 may be maximized, thereby maximizing color separation and luminance of the light incident part.

That is, FIG. 7 is an enlarged view of the sub light guide plate of FIG. 6.

As shown in FIG. 7, the surface of the sub light guide plate 72 carrying light incident portion is configured in an embossed form.

Therefore, by making the light incident portion of the sub light guide plate 72 into the embossed form, the radiation angle can be significantly reduced because the light is collected by the same principle as the light condensing effect of the convex lens as well as the refraction caused by the difference of the medium ( The location of incidence is the same, but the radial shape is different).

As a result, not only the amount of white light incident on the main light guide plate 71 can be increased, but also some direction can be given to the incident light, so that light control in the main light guide plate 71 is facilitated.

Due to these various factors, the LED backlight system using the sub light guide plate 72 having an embossed shape in the incoming light receiving unit can significantly increase the brightness of the module than the conventional LED backlight system.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

As described above, the backlight unit of the liquid crystal display according to the present invention has the following effects.

That is, by configuring the sub-light guide plate having the embossed portion on the incident surface of the main light guide plate, the light collection efficiency can be improved not only by refraction caused by the difference of the medium but also by the light condensing effect of the convex lens.

Claims (3)

A main light guide plate configured on the back of the liquid crystal panel, A sub light guide plate having an incident light portion having an embossed shape on an incident surface of one side of the main light guide plate; A light source unit configured at one side of the sub light guide plate to emit light; A housing for fixing the light source and condensing the light emitted from the light source in one direction; And a first reflector and a second reflector configured to reflect light leaking out to the opposite side of the liquid crystal panel, the lower end of the main light guide plate. The backlight unit of claim 1, wherein the second reflector is formed of Al coated with Ag. The backlight unit of claim 1, wherein the light source unit comprises one-dimensionally arranged red, blue, and green LEDs on a PCB substrate.