KR100829696B1 - Back light unit and liquid crystal display having the same - Google Patents

Abstract

A backlight unit having a structure capable of improving luminance uniformity and a liquid crystal display using the same are disclosed. The backlight unit according to the present invention includes a light guide plate including a light source unit providing light, a light incident surface on which light provided from the light source unit is incident, and a light exit surface on which light input through the light incident surface is converted into surface light and output. The light incidence surface is curved and is disposed to form a predetermined angle with a surface perpendicular to the light emission surface.

Light guide plate, backlight unit, liquid crystal display device

Description

BACK LIGHT UNIT AND LIQUID CRYSTAL DISPLAY HAVING THE SAME}

1 is a cross-sectional view showing a conventional edge-light type backlight unit.

2A is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2B is a cross-sectional view illustrating an embodiment of the liquid crystal panel of FIG. 2A.

FIG. 2C is an enlarged partial cross-sectional view of a portion of the backlight unit of FIG. 2A.

3 is a partial cross-sectional view of a portion of a backlight unit according to another embodiment of the present invention.

4 is a partial cross-sectional view of a portion of a backlight unit according to another embodiment of the present invention.

5 is a partial cross-sectional view of a portion of a backlight unit according to another embodiment of the present invention.

6 is a graph showing experimental data of measuring luminance characteristics of the backlight unit according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a backlight unit and a liquid crystal display using the same, and more particularly, to a backlight unit having a structure capable of improving luminance uniformity and a liquid crystal display using the same.

In general, a liquid crystal display is an electronic device that transmits electrical information generated by various devices to visual information by using a change in liquid crystal transmittance according to an applied voltage.

The liquid crystal display device is thus a display element for various information and does not have its own light source. Therefore, a separate device for uniformly illuminating the entire screen of the liquid crystal panel outside the liquid crystal panel is required. As a device that satisfies such a condition, a back light unit that provides light to the screen of the liquid crystal display device is used.

Cold Cathode Fluorescent Lamps are widely used as the light source in the backlight unit. Depending on the location of the light source, the direct type of the light source is located below the liquid crystal panel, and the light source is disposed on the side of the light guide plate. It is divided into edge-light type.

1 is a cross-sectional view showing a conventional edge-light type backlight unit.

The conventional backlight unit 100 includes a light source unit 110, a light guide plate 120, a reflective sheet 130, and an optical film 140.

The light source unit 110 includes one or more cold cathode fluorescent lamps 112 and a light source reflector plate 114 for generating light of a predetermined wavelength. The light generated from the cold cathode fluorescent lamp 112 is uniformly mixed in the light guide plate 120 and output through the upper surface thereof.

In this case, the light source reflector 114 and the reflector sheet 130 formed of a reflector reflect light to the light guide plate 120 to improve light efficiency.

Optical film 140 generally includes a diffusion sheet 142, a prism sheet 144, and a protective sheet 146. The function of each component constituting the optical film 140 will be described briefly as follows.

Light uniformly mixed and output in the light guide plate 120 passes through the diffusion sheet 142, and the diffusion sheet 142 diffuses or condenses the light output from the light guide plate 120 to make the luminance uniform and to change the viewing angle. Widen.

The light passing through the diffusion sheet 142 is rapidly lowered in brightness, the prism sheet 144 is used to prevent this. The prism sheet 144 refracts the light emitted from the diffusion sheet 142 so that the light incident at a low angle is concentrated toward the front, thereby increasing the luminance in the effective viewing angle range.

The protective sheet 146 is positioned on the prism sheet 144 to prevent scratches of the prism sheet 144 and to widen the viewing angle narrowed by the prism sheet 144.

The prism sheet 144 used in the conventional backlight unit 100 has a prism array structure composed of a plurality of fine prisms on any one surface of the base film as known in the art. At this time, the prism array may be disposed on the light guide plate 120 (so-called "pre-prism sheet") or on the opposite side of the light guide plate 120 (so-called "reverse prism sheet").

In general, the reverse prism sheet is known to be advantageous in terms of light efficiency relative to the prismatic sheet, and a planar light source unit to which the reverse prism sheet is applied is disclosed in US Patent No. 5,126,882. The contents of this document are hereby incorporated by reference in their entirety.

By the way, in the planar light source unit of the structure disclosed in the above document, the light incidence plane of the light guide plate to which the light output from the light source unit is input and the light exit plane to which the input light is output are arranged to be orthogonal, and in such a structure, the luminance uniformity decreases. There is a problem.

Accordingly, there is a need for development of a backlight unit and a liquid crystal display device having a structure capable of improving the uniformity of luminance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight unit having an improved structure, and a liquid crystal display device using the same, in which luminance uniformity is improved as compared with the conventional art.

In order to achieve the above object, the present invention provides a light source unit for providing light, a light incident surface to which light provided from the light source unit is incident, and a light output surface in which light input through the light incident surface is converted into surface light and output. It includes a light guide plate, wherein the light incident surface is a curved surface, and provides a backlight unit disposed to form a constant angle with a surface perpendicular to the light exit surface.

In the backlight unit according to the exemplary embodiment, an angle formed between the light incident surface and the light exit surface of the light guide plate is smaller than 90 °. At this time, preferably, the angle formed between the light incident surface and the light exit surface of the light guide plate is greater than 85 ° and smaller than 90 °.

In addition, in the backlight unit according to another embodiment of the present invention, an angle formed between the light incident surface and the light exit surface of the light guide plate is greater than 90 °. At this time, preferably, the angle formed between the light incident surface and the light exit surface of the light guide plate is greater than 90 ° and smaller than 95 °.

Meanwhile, the backlight unit of the present invention may further include a prism sheet including a prism array including a plurality of micro prisms disposed side by side in one direction. In this case, preferably, the prism sheet has a surface on which the prism array is disposed on the light guide plate side.

In order to achieve the above object, the present invention also controls the orientation of the liquid crystal layer according to the electrical signal applied from the outside and the liquid crystal panel for displaying the image using the light provided from the outside, and disposed adjacent to the liquid crystal panel To provide a liquid crystal display device including a backlight unit for providing light. The backlight unit may include a light guide plate including a light source unit providing light, a light incident surface on which light provided from the light source unit is incident, and a light exit surface on which light input through the light incident surface is converted into surface light and output. It includes, wherein the light incident surface is a curved surface and is arranged to have a constant angle with the surface perpendicular to the light output surface.

In the liquid crystal display according to the exemplary embodiment of the present invention, an angle formed between the light incident surface and the light exit surface of the light guide plate is smaller than 90 °. At this time, preferably, the angle formed between the light incident surface and the light exit surface of the light guide plate is larger than 85 ° and smaller than 90 °.

In addition, in the liquid crystal display device according to another embodiment of the present invention, the angle between the light incident surface and the light exit surface of the light guide plate is greater than 90 °. In this case, preferably, the light incident surface and the light exit surface of the light guide plate are The angle formed by the plane is greater than 90 ° and less than 95 °.

Meanwhile, the liquid crystal display of the present invention may further include a prism sheet including a prism array including a plurality of micro prisms disposed side by side in one direction. In this case, preferably, the prism sheet has a surface on which the prism array is disposed on the light guide plate side.

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

2A is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention. FIG. 2B is a cross-sectional view illustrating an embodiment of the liquid crystal panel of FIG. 2A. 2C is an enlarged partial cross-sectional view of a part of the backlight unit of FIG. 2A, and illustrates a light source unit 222 and a part of the light guide plate 224 adjacent to the light source unit.

2A to 2C, the liquid crystal display 200 may display the liquid crystal panel 210 and the liquid crystal panel 210 to display an image according to a driving signal and a data signal applied from the outside. It includes a backlight unit 220 disposed on the back.

In understanding and implementing the present invention, the precise structural characteristics of the liquid crystal panel 210 are not important, and the spirit of the present invention may be widely applied to any structure of the liquid crystal panel commonly used in the liquid crystal display device. Therefore, the structure of the liquid crystal panel 210 described below is merely provided as an example for understanding the present invention.

The liquid crystal panel 210 includes a lower substrate 212a and an upper substrate 212b, a color filter 213, a black matrix 214, a pixel electrode 215, a common electrode 216, a liquid crystal layer 217, and a TFT array. 218 and a pair of polarizing films 118a and 118b disposed on outer surfaces of the lower and upper substrates 212a and 212b, respectively.

The color filter 213 includes color filters corresponding to red (R), green (G), and blue (B), and when light is applied, generates the image corresponding to the color of red, green, or blue.

The TFT array 218 switches the pixel electrode 215 as a switching element.

The common electrode 216 and the pixel electrode 215 convert the arrangement of the molecules of the liquid crystal layer 217 according to a predetermined voltage applied from the outside.

The liquid crystal layer 217 is composed of a plurality of liquid crystal molecules, and the liquid crystal molecules change an arrangement in accordance with a voltage difference generated between the pixel electrode 215 and the common electrode 216, whereby the backlight unit ( Light provided from 220 is incident on the color filter 213 in response to a change in the molecular arrangement of the liquid crystal layer 217.

The backlight unit 220 is positioned at the rear of the liquid crystal panel 210 and provides light, for example, white light, to the liquid crystal panel 210.

The backlight unit 220 includes a light source unit 222, a light guide plate 224, and an optical sheet 228, and the light source unit 222 is driven in an edge-light manner in which both side surfaces of the light guide plate 224 are disposed.

The light source unit 222 includes a light source 222a and a light source reflecting plate 222b disposed outside the light source, and light provided from the light source unit 222 is input to the light guide plate 224.

In the present embodiment, the light source 222a includes a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) that generates light having a predetermined wavelength, for example, white light. Linear light sources can be used. However, the above linear light source is not used for the light source 222a.

In another embodiment of the present invention, the light source 222a may use a point light source such as a light emitting diode (LED). In this case, the number of light emitting diodes used as the light source 222a may be appropriately selected according to the size of the liquid crystal panel 210 to be illuminated. In addition, there is no limitation to the light emitting diode used as the light source 222a, and one white light emitting diode is used or a combination of three light emitting diodes generating colors of red (R), green (G), and blue (B). It is also possible to use.

The light source reflecting plate 222b is disposed outside the light source 222a. The light source reflector 222b may be made of metal or plastic, and the inner wall may be coated with a material capable of reflecting light to reflect light emitted from the light source 222a to the side of the light guide plate 224. have.

The light generated from the light source 222a is incident on the light guide plate 224 through the side of the light guide plate 224, that is, the light incident surface 224a, and the light source reflector 222b receives the light generated from the light source 222a. Reflecting toward the 224 side improves the efficiency of light incident on the light guide plate 224.

The light guide plate 224 is substantially parallel to the viewing plane of the liquid crystal panel 210 disposed above the light incident through the light incident surface 224a disposed on the side thereof, using the principle of total internal reflection. It is uniformly mixed while transmitting in the direction, and is output in the form of surface light through the light exit surface 224b.

The light guide plate 224 according to the exemplary embodiment has a structure in which the light incident surface 224a is inclined toward the inside of the light guide plate 224 without being perpendicular to the light exit surface 224b.

Specifically, as shown in FIG. 2C, the angle α formed between the light incident surface 224a and the light emitting surface 224b is smaller than 90 °, and the light incident surface 224a of this structure is formed of a light guide plate ( The luminance uniformity of the light output through the light exit surface 224b of 224 is improved. Therefore, luminance uniformity of the backlight unit 220 and the liquid crystal display 220 having the light guide plate 224 having the above structure may be improved as compared with the related art.

On the other hand, in order for the light incident on the light guide plate 224 to be emitted in the direction of the liquid crystal panel 210, total reflection must be diffused inside the light guide plate 224. To this end, a light scattering pattern 225 as shown by dot-printing for printing white ink may be formed on the rear surface of the light guide plate 224 opposite to the light exit surface 224b.

On the other hand, a non-printing light guide plate that does not go through the printing process may be used. U. S. Patent No. 6,123, 431 discloses a non-printing light guide plate in which a light scattering pattern is formed by forming grooves on the surface of the light guide plate. Disclosed is a non-printing light guide plate which also serves as a diffuser plate function by having a scattering function due to a refractive index difference within. The contents of these documents are incorporated herein by reference.

Further, in another embodiment of the present invention, the light guide plate 224 may use a so-called prism light guide plate having a prism array composed of a plurality of linear prisms on the rear surface of the light guide plate 224 opposite to the light exit surface 224b. U.S. Patent Nos. 6,502,947 and 6,874,902 disclose the structure of such prism light guide plates, the contents of which are incorporated herein by reference.

The light guide plate 224 may be made of a transparent acrylic resin such as poly methyl methacrylate (PMMA).

The reflective sheet 226 is disposed on the bottom surface of the light guide plate 224 and serves to reflect the light exiting to the bottom surface of the light guide plate 224 to re-inject into the light guide plate 224.

The reflective sheet 226 may be manufactured by coating silver (Ag) on a sheet made of SUS, brass, aluminum, PET, and the like, and titanium coating to prevent deformation due to endotherm for a long time even if heat is generated minutely.

In addition, the reflective sheet 226 may be manufactured by dispersing bubbles for scattering light in a sheet made of synthetic resin such as PET.

The backlight unit 220 may include at least one optical sheet 228 disposed between the light guide plate 224 and the liquid crystal panel 210. The optical sheet 228 improves luminance by effectively injecting light emitted from the light guide plate 224 into the visible surface of the liquid crystal panel 210, and uniformizes light incident on the liquid crystal panel 210, thereby providing a front surface of the visible surface. This uniform luminance distribution is achieved.

In one embodiment of the present invention, the optical sheet 228 includes three optical sheets consisting of a diffusion sheet 228a, a prism sheet 228b, and a protective sheet 228c.

The diffusion sheet 228a is disposed in parallel with the light exit surface 224b at the upper portion of the light guide plate 224, and scatters the light emitted from the light guide plate 224 to uniform luminance throughout the visible surface of the liquid crystal panel 210. Let's do it. The diffusion sheet 228a is irregularly distributed with a plurality of beads capable of scattering light, and includes a protective layer having a high haze effect and a high transmittance, and the light guide plate 224. Diffuses and condenses the light emitted from In addition, the light is transmitted in the direction of the prism sheet 228b to be described later disposed on the upper portion, thereby widening the viewing angle and hiding the pattern formed on the light guide plate 224.

In understanding and practicing the present invention, the precise structural and material properties of the diffusion sheet 228a are not critical, and the idea of the present invention may be applied to the diffusion sheet 228a using any structure and material conventionally used for the backlight unit. It can be widely applied.

A prism sheet 228b may be disposed on the diffusion sheet 228a to improve light efficiency and brightness, and the prism sheet serves to compensate for the reduced luminance in the diffusion sheet 228a. Since the prism sheet 228b refracts the light emitted from the diffusion sheet 228a and concentrates the light incident at a low angle toward the front side, the luminance increases in the effective viewing angle range.

In understanding and practicing the present invention, the exact structural and material properties of the prism sheet 228b are not critical, and the idea of the present invention may be applied to the prism sheet 228b using any structure and material conventionally used for the backlight unit. It can be widely applied.

A protective sheet 228c may be disposed on an upper portion of the prism sheet 228b, which may prevent scratches of the prism sheet 228b, and may reduce the viewing angle reduced by the prism sheet 228b within a predetermined range. Function to re-expand at.

In understanding and practicing the present invention, the precise structural and material properties of the protective sheet 228c are not critical, and the idea of the present invention may be applied to the protective sheet 228c using any structure and material conventionally used for the backlight unit. It can be widely applied.

Hereinafter, other embodiments of the present invention will be described with reference to the drawings. However, the same reference numerals are used for the same parts as the above-described embodiment, and they will not be repeated.

3 to 5 are partial cross-sectional views illustrating some embodiments of the backlight unit of the present invention, and illustrate a relationship between the light source unit 222 and the light guide plates 324, 424, and 524. Other configurations, not shown, follow the configuration of the foregoing embodiment.

Referring to FIG. 3, in another embodiment of the present invention, the light guide plate 324 has a curved surface of the light incident surface 324a, and an angle formed by the tangent to the light incident surface 324a and the light exit surface 324b. It can be configured to be smaller than 90 °. The light incident surface 324a having such a structure improves luminance uniformity of light output through the light emitting surface 324b of the light guide plate 324.

Referring to FIG. 4, in another embodiment of the present invention, the light guide plate 424 has a structure in which the light incident surface 424a is inclined to the outside of the light guide plate 424 without being orthogonal to the light exit surface 424b. have.

That is, the angle β formed between the light incident surface 424a and the light emitting surface 424b is greater than 90 °, and the light incident surface 424b of this structure also passes through the light emitting surface 424b of the light guide plate 424. Improves brightness uniformity of output light.

Referring to FIG. 5, in another embodiment of the present invention, the light guide plate 524 has a light incident surface 524a of which is curved, and a tangent to the light incident surface 524a and the light emitting surface 524b are formed. The angle can be configured to be greater than 90 °. Similarly, the light incident surface 524a having such a structure improves the luminance uniformity of light output through the light exit surface 524b of the light guide plate 524.

6 is a graph showing experimental data of measuring luminance characteristics of the backlight unit according to the present invention.

In this experiment, the luminance and luminance uniformity of the following four samples were measured according to the angle between the light exit surface and the light incident surface of the light guide plate.

Sample No. Angle (°) material size One 85 PMMA 14.1 in 2 95 PMMA 14.1 in 3 93 PMMA 14.1 in 4 90 PMMA 14.1 in

 On the other hand, in this experiment, the light guide plate used the prism light guide plate in which the prism array was formed in the back surface of the light emission surface. At this time, the pitch of each prism was 50 micrometers, and the prism light guide plate whose curvature radius is about 25 micrometers was used.

Type of optical sheet model name Remarks Prism sheet Inverse prism sheet Pitch 50㎛, Bead Layer Reflective sheet RP 17N (SKC) Protection sheet 125TL2 (Kimoto)

In addition, in this experiment, the optical sheet of Table 2 was used. SKC's RP 17N and Kimoto's 125TL2 were used for the reflective sheet and the protective sheet, respectively. On the other hand, as a prism sheet, the prism sheet had a pitch of 50 µm and a height of 40 µm. In addition, on the rear surface of the prism sheet, fine beads having a diameter of about 8 μm were mixed with a binder made of urethane acrylate to form an application layer.

Referring to FIG. 6, as in the prior art, when the light emitting surface and the light incident surface are orthogonal (sample 4), it can be seen that the luminance represents the maximum value. On the other hand, it can be seen that the uniformity of the luminance obtained by measuring the ratio of the luminance value of the brightest part and the luminance value of the darkest part is also the greatest when the light exit plane and the light entrance plane form an angle of 90 ° (sample 4). . In other words, when the light emitting surface and the light incident surface are orthogonal, the luminance rises but the luminance uniformity decreases.

In contrast, as the angle between the light exit surface and the light incident surface becomes an acute or obtuse angle, the luminance gradually decreases within 6%, but the uniformity of the luminance is rapidly improved. For example, when the light emitting surface and the light incident surface form an angle of 85 degrees (sample 1), the luminance decreases by about 5%, but the uniformity of the luminance is improved by 20% or more.

Therefore, according to the present invention, it is possible to implement a backlight unit and a liquid crystal display device in which the luminance uniformity can be further improved while maintaining the luminance at a level comparable to the prior art.

In the backlight unit according to the present invention as described above, the light incidence surface of the light guide plate is configured to be inclined or curved surface with respect to the light exit surface to improve the uniformity of light output through the light exit surface to improve the brightness uniformity of the display device It can greatly improve.

Preferred embodiments of the invention described above have been disclosed for purposes of illustration. Therefore, those skilled in the art having ordinary knowledge of the present invention will be capable of various modifications, changes, and additions within the spirit and scope of the present invention, and such modifications, changes and additions should be regarded as belonging to the following claims.

Claims (12)

A light source unit providing light; And And a light guide plate including a light incident surface to which light provided from the light source unit is incident, and a light emitting surface to which light input through the light incident surface is converted into surface light and output. The light incident surface is a curved surface, the backlight unit, characterized in that disposed to form a constant angle with the surface perpendicular to the light exit surface. The backlight unit of claim 1, wherein an angle formed between the light incident surface and the light emitting surface of the light guide plate is smaller than 90 °. delete The backlight unit of claim 1, wherein an angle formed between the light incident surface and the light emitting surface of the light guide plate is greater than 90 °. delete The method according to any one of claims 1, 2, or 4, Further comprising a prism sheet comprising a prism array consisting of a plurality of micro-prism arranged side by side in any one direction, And the prism sheet has a surface on which the prism array is disposed on the light guide plate side. A liquid crystal panel for controlling the alignment of the liquid crystal layer according to an electrical signal applied from the outside and expressing an image using light provided from the outside; And A backlight unit disposed adjacent to the liquid crystal panel to provide light; The backlight unit, A light source unit providing light; And And a light guide plate including a light incident surface to which light provided from the light source unit is incident, and a light emitting surface to which light input through the light incident surface is converted into surface light and output. And the light incidence surface is a curved surface and is disposed to form a predetermined angle with a surface perpendicular to the light emission surface. The liquid crystal display of claim 7, wherein an angle formed between the light incident surface and the light emitting surface of the light guide plate is smaller than 90 degrees. delete The liquid crystal display of claim 7, wherein an angle formed between the light incident surface and the light emitting surface of the light guide plate is greater than 90 degrees. delete The method according to any one of claims 7, 8 or 10, Further comprising a prism sheet comprising a prism array consisting of a plurality of micro-prism arranged side by side in any one direction, And the surface of the prism array on the side of the light guide plate.

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