KR101159326B1 - Liquid crystal display device - Google Patents

Abstract

The present invention provides a liquid crystal display device using a light emitting diode as a light source, to improve a hot spot problem due to point emission by forming an optical sheet for condensing light having a predetermined distance from the light emitting diode. Display panel; A light guide plate disposed under the liquid crystal display panel; At least one light emitting diode formed on a side surface of the light guide plate and emitting light; a light emitting diode printed circuit board having the light emitting diode and the light guide plate bent and mounted thereon and mounted with driving elements for driving the light emitting diode; An upper portion of the light guide plate and formed at a predetermined distance away from an end of the light emitting diode to prevent light from being focused on a liquid crystal display panel positioned around a light source of the light emitting diode. An optical sheet for maintaining a predetermined distance from the optical sheet; And a light blocking film formed on the light emitting diode printed circuit board so as to overlap with the light guide plate and the optical sheet to block unnecessary light.

Light Emitting Diode, Hot Spot, Optical Sheet, Prism Sheet, Liquid Crystal Display

Description

[0001] LIQUID CRYSTAL DISPLAY DEVICE [0002]

1 is a perspective view schematically showing a side type backlight device.

2 is a perspective view schematically showing a direct type backlight device;

3 is an exploded perspective view schematically illustrating a structure of a liquid crystal display according to an exemplary embodiment of the present invention.

4A is an exemplary diagram schematically illustrating the progression of light in a single medium of light emitting diodes.

4B is an exemplary view schematically showing a process in the case where light emitted from a light emitting diode is incident into another medium.

FIG. 5 is a cross-sectional view of the liquid crystal display shown in FIG. 3 with the backlight unit in the center; FIG.

FIG. 6 is an enlarged cross-sectional view illustrating an incident part of a light guide plate of the liquid crystal display illustrated in FIG. 5.

DESCRIPTION OF REFERENCE NUMERALS

100: liquid crystal display panel 141: reflector

142: light guide plate 143: optical sheet

147: light emitting diode 148: light emitting diode printed circuit board

150: mold frame 160: polarizing plate

170: light shielding film

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device using a light emitting diode (LED) as a light source.

BACKGROUND ART In general, a liquid crystal display device is a display device in which data signals according to image information are individually supplied to pixels arranged in a matrix, and a desired image is displayed by adjusting light transmittance of the pixels.

Accordingly, the liquid crystal display includes a liquid crystal display panel in which pixels are arranged in a matrix and a driving unit for driving the pixels.

The liquid crystal display panel includes a thin film transistor array substrate, a color filter substrate, and a liquid crystal layer formed at a spaced interval between the array substrate and the color filter substrate, which are bonded to face each other to maintain a uniform cell gap. It consists of.

A common electrode and a pixel electrode are formed on the liquid crystal display panel where the array substrate and the color filter substrate are bonded to apply an electric field to the liquid crystal layer.

Therefore, when the voltage of the data signal applied to the pixel electrode is controlled while the voltage is applied to the common electrode, the liquid crystal of the liquid crystal layer is rotated by dielectric anisotropy according to the electric field between the common electrode and the pixel electrode. Characters or images are displayed by transmitting or blocking light for each pixel.

In this case, since the liquid crystal display does not emit light by itself and displays an image by adjusting light transmittance, a separate device, ie, a backlight device, for irradiating light to the liquid crystal display panel is required.

In the backlight device, a lamp is disposed on one side or both sides of the liquid crystal display panel so that light is reflected, diffused, and collected by the light guide plate, the reflector plate, and the optical sheets to be disposed on the front surface of the liquid crystal display panel. A side type for transmitting light and a lamp are disposed on a rear surface of the liquid crystal display panel so that light is directly transmitted to the front surface of the liquid crystal display panel.

1 is a perspective view schematically illustrating the side type backlight device.

Referring to FIG. 1, a side type backlight device includes a light guide plate 10 disposed on a rear surface of a liquid crystal display panel (not shown), a lamp 20 disposed on a side surface of the light guide plate 10, and a rear surface of the light guide plate 10. A lamp holder (not shown) that fixes the lamp 20 to the side surface of the light guide plate 10 and a lamp reflector 25 and wiring for applying power to the lamp 20. 26).

The light generated by the lamp 20 is incident on the side of the light guide plate 10 of a transparent material, and the reflector 30 disposed on the rear surface of the light guide plate 10 receives light transmitted through the rear surface of the light guide plate 10. Reflected to the upper surface of 10) to reduce the loss of light and improve the uniformity.

Therefore, the light guide plate 10 transmits the light generated by the lamp 20 together with the reflecting plate 30 to the upper surface.

2 is a perspective view schematically illustrating the direct type backlight device.

Referring to FIG. 2, a direct type backlight device includes a reflector 30 disposed on a rear surface of a liquid crystal display panel (not shown) and a plurality of light incident light incident on the entire rear surface of the liquid crystal display panel. Lamps 20, covers the lamps 20, a diffuser plate 40 for diffusing light generated from the lamps 20, and a power source for applying the lamps 20 to the lamps 20. The wirings 26 are comprised.

Generally, the lamp 20 applied to the side type backlight device or the direct type backlight device includes a tube-type cold cathode fluorescent lamp having a length corresponding to a long side distance or a short side distance of a liquid crystal display panel. Cathode Fluorescence Lamp (CCFL) is applied, and the cold cathode fluorescent lamp generates white light by the power supplied through the wiring 26 at both ends.

Since the liquid crystal display device configured as described above mainly uses a cold cathode fluorescent lamp for the backlight device, power consumption by the light source is severe and high heat is generated while generating light.

In addition, mercury applied as a fluorescent material to the cold cathode fluorescent lamp is harmful to the human body, and thus, there is a problem in that it cannot cope with the stricter environmental regulations.

In addition, in recent years, in order to improve the transmittance and color reproducibility of a liquid crystal display, one frame of an image is time-divided into a plurality of subframes, and red, green, and blue light are sequentially sequentially generated according to the plurality of subframes. Although the time-division type liquid crystal display device for supplying is actively developed, the backlight device using the cold cathode fluorescent lamp has a problem that the range applicable to the time-division type liquid crystal display device is limited.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and there is no problem caused by environmental regulation of cold cathode fluorescent lamps, and an object of the present invention is to provide a liquid crystal display device applicable to a time-division type liquid crystal display device.

In addition, another object of the present invention to provide a liquid crystal display device having a light source having a low power consumption.

In addition, another object of the present invention to provide a liquid crystal display device that can improve the hot spot problem that occurs when using a light emitting diode as a light source.

Further objects and features of the present invention will be described in the configuration and claims of the invention which will be described later.

In order to achieve the above object, the liquid crystal display device of the present invention comprises a liquid crystal display panel; A light guide plate disposed under the liquid crystal display panel; At least one light emitting diode formed on a side surface of the light guide plate and emitting light; a light emitting diode printed circuit board having the light emitting diode and the light guide plate bent and mounted thereon and mounted with driving elements for driving the light emitting diode; An upper portion of the light guide plate and formed at a predetermined distance away from an end of the light emitting diode to prevent light from being focused on a liquid crystal display panel positioned around a light source of the light emitting diode. An optical sheet for maintaining a predetermined distance from the optical sheet; And a light blocking film formed on the light emitting diode printed circuit board so as to overlap with the light guide plate and the optical sheet to block unnecessary light.

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

3 is an exploded perspective view schematically illustrating a structure of a liquid crystal display according to an exemplary embodiment of the present invention, and shows a liquid crystal display employing a light emitting diode as a light source.

The light emitting diode used as a backlight of the liquid crystal display device has a longer lifespan than a cold cathode fluorescent lamp and has an advantage of not requiring a separate inverter because it operates at 5V DC.

In other words, high-brightness LEDs have a longer lifespan than conventional cold-cathode fluorescent lamps and consume only 20% of the power of existing products, and do not require additional equipment such as inverters, which is advantageous for thinning products and improving internal area efficiency. In addition, the color implementation ability is evaluated to be superior to the cold cathode fluorescent lamps, and since 2006, mercury regulations are being promoted worldwide.

As such, the next-generation light source light emitting diode, which is energy efficient and almost semi-permanent, can be used as the main light source of mobile devices such as mobile phones, digital cameras, and personal digital assistants (PDAs). It is up to expectations.

As shown in the drawing, the liquid crystal display device according to the present embodiment using the light emitting diode as a light source includes a liquid crystal display panel 100 in which pixels (not shown) are arranged in a matrix form, and a driving circuit unit for driving the pixels. 120, 130).

In this case, although not shown in the drawing, the liquid crystal display panel 100 includes an array substrate and a color filter substrate bonded together to maintain a uniform cell gap facing each other, and a liquid crystal layer formed between the array substrate and the color filter substrate. It consists of.

In addition, the driving circuits 120 and 130 may include various elements such as a timing controller for driving the liquid crystal display panel 100 and a tape carrier package (TCP) 122 and 132. A printed circuit board (PCB) 121 and 131 attached thereto.

In this case, a common electrode (not shown) and a pixel electrode (not shown) are formed on the liquid crystal display panel 100 where the array substrate and the color filter substrate are bonded to apply an electric field to the liquid crystal layer.

Therefore, when the voltage of the data signal applied to the pixel electrode is controlled while the voltage is applied to the common electrode, the liquid crystal of the liquid crystal layer rotates by dielectric anisotropy according to the electric field between the common electrode and the pixel electrode. For example, characters or images are displayed by transmitting or blocking light for each pixel.

In this case, as described above, since the LCD does not emit light by itself and has a characteristic of displaying an image by adjusting light transmittance, a separate device, ie, a backlight unit, for irradiating light to the liquid crystal display panel 100 ( backlight unit 140 is required.

The backlight unit 140 includes a light emitting diode assembly (145) including a light emitting diode (not shown) for emitting light, a reflection sheet (141) for reflecting the light emitted from the light emitting diode, A light guide plate 142 for guiding light and a plurality of optical sheets 143 installed on an upper surface of the light guide plate 142 to diffuse and collect light transmitted from the light guide plate 142. And the like.

As described above, the liquid crystal display device includes a liquid crystal display panel 100, driving circuit parts 120 and 130, and a backlight unit 140. In this case, the liquid crystal display panel 100, driving circuit parts 120 and 130, and a backlight unit are used. Various types of components are used to support and engage 140.

That is, the liquid crystal display panel 100 and the backlight unit 140 are stacked on the mold frame 150, and the side surfaces of the stacked liquid crystal display panel 100 and the backlight unit 140 are formed on the mold frame ( 150 to be supported by the mold frame 150 is coupled to the upper case 151 and the lower cover 152 by using a screw.

On the other hand, although not shown in detail in the drawing, the light emitting diode assembly 145 formed on the edge of the light guide plate 142 is a printed circuit in which unit light emitting diodes arranged at regular intervals and a driving circuit for driving the unit light emitting diodes are mounted. A substrate is provided.

The LED backlight as described above can be effectively applied to supply the light to the flat panel display as well as the liquid crystal display by replacing the cold cathode fluorescent lamp which is harmful to the human body and cannot respond to environmental regulations.

In addition, the LED backlight time-divides one frame of an image into a plurality of subframes in order to improve transmittance and color reproducibility, and sequentially supplies red, green, and blue light according to the plurality of subframes. Can be applied very effectively to a time-division liquid crystal display device for displaying an image.

On the other hand, when the light emitting diode is used as a light source, a hot spot phenomenon occurs in which a light pattern and a dark pattern are alternately generated according to the point light source characteristics of the light emitting diode. That is, the light generated from the light emitting diode as the point light source is transmitted to the light guide plate 142 having a constant emission angle, and the light guide plate 142 serves to uniformly distribute the incident light emitting diode light as an overall light guide plate ( 142), the hot spot phenomenon appears relatively bright near the light emitting diode light source.

4A is an exemplary diagram schematically illustrating a process of a light emitted from a light emitting diode in a single medium, and FIG. 4B is an exemplary diagram schematically illustrating a process of a case where light emitted from a light emitting diode is incident into another medium.

4A and 4B illustrate radiation angles of light emitting diodes as point light sources when viewed from the top of the liquid crystal display panel.

As shown in FIG. 4A, the light of the light emitting diode 147 in a single medium, such as air, maintains an emission angle α of about 110 degrees. However, as shown in FIG. 4B, the light emitting diode 147 is shown. The light emitted from) decreases its radiation angle (α ') as it passes through the light guide plate. This is because light is transmitted from the small medium (I) to the light guide plate, which is the dense medium (II), which causes the hot spot phenomenon to deepen in the light guide plate.

In order to improve the hot spot phenomenon, there is a method of reducing the pitch of the light emitting diodes by increasing the number of the light emitting diodes or increasing the distance between the light emitting diodes and the light guide plate. However, if the distance between the light emitting diode and the light guide plate is increased as described above, the image display area of the liquid crystal display panel is reduced, and the cost is increased because the number of the light emitting diodes needs to be increased to reduce the pitch of the light emitting diode.

In another embodiment, the prism sheet may be formed to have a predetermined distance from the light source of the light emitting diode to prevent light collection at the incident part of the light guide plate in which the hot spot is a problem, which will be described in detail with reference to the accompanying drawings. Explain.

FIG. 5 is a cross-sectional view of the liquid crystal display illustrated in FIG. 3 based on the backlight unit, and FIG. 6 is an enlarged cross-sectional view illustrating an incident part of the light guide plate of the liquid crystal display illustrated in FIG. 5.

As shown in the drawing, the liquid crystal display includes a liquid crystal display panel 100 and a separate device for irradiating light to the liquid crystal display panel 100, that is, the backlight unit 140.

The liquid crystal display panel 100 is a liquid crystal formed between the array substrate 110 and the color filter substrate 105 and the array substrate 110 and the color filter substrate 105 which are bonded to face each other to maintain a uniform cell gap. It consists of layers (not shown). Here, reference numeral 125 denotes an image display area in which an image is displayed on the liquid crystal display panel 100.

In this case, a common electrode (not shown) and a pixel electrode (not shown) are formed on the liquid crystal display panel 100 where the array substrate 110 and the color filter substrate 105 are bonded to apply an electric field to the liquid crystal layer. . In addition, polarizers 160 are provided outside the array substrate 110 and the color filter substrate 105, respectively.

Therefore, when the voltage of the data signal applied to the pixel electrode is controlled while the voltage is applied to the common electrode, the liquid crystal of the liquid crystal layer rotates by dielectric anisotropy according to the electric field between the common electrode and the pixel electrode. For example, characters or images are displayed by transmitting or blocking light for each pixel.

In this case, the backlight unit 140 may include a light emitting diode 147 emitting light, a reflecting plate 141 reflecting light emitted from the light emitting diode 147, a light guide plate 142 guiding light, and the light guide plate ( It is installed on the upper surface of the 142 is composed of a plurality of optical sheets 143 and the like to diffuse and collect the light transmitted from the light guide plate 142.

In this case, although not shown in detail in the drawings, each of the light emitting diodes 147, which implements the red, green, and blue elements, includes a lead electrically connected to each other, and a mold for protecting the light emitting diodes 147. And a lens that uniformly emits light emitted from each light emitting diode 147 element. In addition, the light emitting diode 147 is connected to a light emitting diode printed circuit board 148 on which a plurality of driving elements for driving the light emitting diode 147 are mounted, and is electrically connected to the light emitting diode 147. The printed circuit board 148 is bent and mounted on the light guide plate 142 in the form of a flexible printed circuit (FPC).

In the present exemplary embodiment, a case is described in which one light emitting diode 147 element implementing red, green, and blue colors is embedded in one light emitting diode lamp (or chip), but the present invention is limited thereto. The light emitting diode 147 may be applied to a lamp in which all the light emitting diodes 147, which implement the colors of red, green, and blue, are incorporated. There is an advantage that can be improved.

In addition, in the present embodiment, for example, a light emitting diode 147 element that implements the colors of red, green, and blue are shown as an example, but the light emitting diode 147 may be formed of white or various colors other than the red, green, and blue depending on the purpose of use. It can generate light of color. In addition, the light emitting diodes) may generate light of different colors according to the purpose of use, or may be divided into a predetermined number of groups to generate light of different colors for each group.

Light generated by the light emitting diode 147 is incident to the side surface of the light guide plate 142 formed of a transparent material.

In this case, the reflective plate 141 disposed on the rear surface of the light guide plate 142 reflects the light transmitted through the rear surface of the light guide plate 142 to the top surface of the light guide plate 142 to reduce the loss of light and to the top surface of the light guide plate 142. It serves to improve the uniformity of transmitted light.

Accordingly, the light guide plate 142 transmits the light generated from the light emitting diode assembly 145 together with the reflecting plate 141 to the upper surface.

For the optical sheet 143 disposed between the liquid crystal display panel 100 and the light guide plate 142, a diffusion sheet and a prism sheet may be applied, and a protective sheet may be added.

The diffusion sheet disperses the light incident from the light guide plate 142 to prevent the light from being partially concentrated to prevent staining in the image displayed on the liquid crystal display panel 100, and to prevent the light incident from the light guide plate 142. It serves to deflect the angle vertically.

The prism sheet collects light incident from the diffusion sheet to be uniformly distributed on the entire surface of the liquid crystal display panel 100.

In addition, the protective sheet protects the optical sheets 143 which are sensitive to dust and scratches, prevents the flow of the optical sheets 143 when the backlight unit 140 is transported, and diffuses the light incident from the prism sheet. It can have a function to make the light more uniformly distributed.

At this time, in the present embodiment, the optical sheet 143 including a prism sheet for condensing the light of the light emitting diode is formed by a predetermined distance (W) away from the end of the light emitting diode 147 to surround the light source of the light emitting diode 147. It is possible to reduce the hot spots that occur. In this case, although it depends on the size and design criteria of the panel, the end of the optical sheet 143 is to maintain a distance (W ') of about 1.5 ~ 2mm with the image display area (125).

That is, referring to FIG. 6, light emitted from the light emitting diode 147 in the direction of the arrow is incident on the upper liquid crystal display panel 100 through the light guide plate 142. As shown in this embodiment, the optical sheet 143 Since the light emitting diode 147 is positioned at the end of the light emitting diode 147 by a predetermined distance (W), it is possible to prevent condensing of light at the incident part of the light guide plate 142 where a hot spot is a problem. The incident part of the light guide plate 142 means a front end portion of the light guide plate on which the light emitting diode light source is incident. Here, the small arrow shown in the drawing shows that the light can not be collected because the prism sheet is removed by way of example.

Meanwhile, a light blocking film 170 for blocking unnecessary light is overlapped with a part of the light guide plate 142 and the optical sheet 143 on the light emitting diode 147 and the light guide plate 142 configured as described above. The light shielding tape of the tape type may be used as the light shielding film 170. In this case, the light blocking film 170 may overlap about 0.5 mm with the optical sheet 143.

Here, reference numeral 150 denotes a mold frame in which the liquid crystal display panel 100 and the backlight unit 140 are stacked and bonded.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

As described above, the liquid crystal display device according to the present invention can improve the life of the liquid crystal display device by maximizing energy efficiency by providing a light emitting diode assembly capable of realizing low heat generation and low consumption instead of the conventional cold cathode fluorescent lamp. can do.

In addition, the liquid crystal display according to the present invention can reduce the hot spot phenomenon occurring around the light source by forming the optical sheet away from the light emitting diode light source by a predetermined distance.

Claims (8)

A liquid crystal display panel; A light guide plate disposed under the liquid crystal display panel; At least one light emitting diode formed on a side of the light guide plate and emitting light; A light emitting diode printed circuit board which is bent and mounted above the light emitting diode and the light guide plate and mounted with driving elements for driving the light emitting diode; An upper portion of the light guide plate and formed at a predetermined distance away from an end of the light emitting diode to prevent light from being focused on a liquid crystal display panel positioned around a light source of the light emitting diode. An optical sheet for maintaining a predetermined distance from the optical sheet; And And a light shielding film formed on an upper portion of the light emitting diode printed circuit board so as to overlap the light guide plate and the optical sheet. The liquid crystal display of claim 1, wherein the light emitting diodes realize colors of red, green, and blue. The liquid crystal display of claim 1, wherein the light emitting diode is white. The liquid crystal display of claim 1, wherein the optical sheet comprises a diffusion sheet for diffusing light. The liquid crystal display of claim 1, wherein the optical sheet comprises a prism sheet for condensing light. The liquid crystal display of claim 1, wherein the light blocking film comprises a tape type light blocking tape and overlaps the light guide plate and the optical sheet with a width of 0.5 mm. delete The liquid crystal display of claim 1, wherein an end of the optical sheet maintains a distance of 1.5 mm to 2 mm from the image display area.

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